When driving downhill, downhill safety assistance control can ensure a safe speed. A downhill safety assistance system was developed by our research group to help hybrid electric vehicles to maintain a stable speed when driving downhill. For hybrid electric buses, in addition to the pneumatic braking system, the motor can quickly provide an electrical braking torque, and the engine can be considered a mechanical brake. The downhill safety assistance system for hybrid electric buses maintains the desired downhill speed on different road slopes. However, when and how to activate or deactivate the downhill safety assistance system because of the driver’s operation or the road conditions was not discussed in combination with the energy management strategy for the vehicle. Additionally, there is currently no dynamic control strategy for the transition process when the braking modes of the downhill safety assistance system change, which can lead to instability. To address the limitations of previous studies, a dynamic coordinated control strategy of the downhill safety assistance system is proposed considering practical application, which focuses on the above two aspects to keep the entire system stable. To improve the ride comfort and the vehicle safety when the downhill safety assistance system works in conjunction with the energy management strategy for the vehicle, the proposed control strategy is developed to activate or deactivate the downhill safety assistance system based on the driver’s driving habits and operation and the road conditions in order to reduce the workload and to improve the driveability of the buses. To maintain the ride comfort during the transient process of shift in the braking mode and to maintain a stable speed over the overall course, the mode-shift coordinated control strategy of the downhill safety assistance system is presented, which combines the braking modes to ensure that the braking torque changes steadily without saltation. The experimental results validate the performance of the entire dynamic coordinated control strategy of the downhill safety assistance system with a high stability, and the statistics demonstrate that the downhill safety assistance system obviously improves the fuel economy and reduces the driver workload.
This paper presents an investigation into the road-holding ability of a vehicle equipped with a roll-plane hydraulically interconnected suspension system. Ideally, the roll-plane hydraulically interconnected suspension system has the capability to decouple the roll mode from all the other vehicle suspension modes. However, anti-roll bars are unable to decouple the warp mode from the other modes, and therefore they limit the travel of the wheels and weaken the road-holding ability of a vehicle on uneven road surfaces. In this paper, vehicle dynamic analysis is carried out with three different configurations: a vehicle with only a spring–damper as a benchmark vehicle; a vehicle with a spring–damper in conjunction with anti-roll bars; a vehicle with a spring–damper in conjunction with a roll-plane hydraulically interconnected suspension. Simulations and corresponding experimental verification with different road excitations are then implemented. The experimental results agree well with the simulations under low-frequency road excitations. The results demonstrate that, when the vehicle undergoes off-road driving, the anti-roll bars weaken the road-holding ability of the vehicle while the hydraulically interconnected suspension system has a negligible effect.
In this study, the mechanisms that cause bush loosening and rotation failure were studied on the connecting-rod small end of a high-power-density engine. Using the thermoelastic plasticity model and the thermomechanical coupling method, the stress field and the assembly contact force of the connecting-rod small end were predicted by considering four different loading conditions: first, the initial loading condition; second, the thermal loading condition; third, the mechanical loading condition; fourth, the unloading condition. This process showed the effects of the initial interference fit, the operating temperature and the wall thickness of the bush on the assembly contact force. It was found that, first, a large interference leads to a small assembly contact force after unloading, second, a higher operating temperature significantly reduces the assembly contact force and, third, the wall thickness of the bush has little influence on the assembly contact force. In conclusion, a high operating temperature is the main cause of bush loosening and rotation. This conclusion was validated by the experimental results. On the basis of this study, it is suggested that the operating temperature is limited in order to maintain the reliability of the connecting-rod small end.
The effect of the addition of ethanol on the combustion and emission characteristics of dimethyl ether combustion were investigated in this study using an electronically controlled common-rail dimethyl ether engine. The ignition delay, the crank angle for 50% mass fraction burned, the combustion duration, the nitrogen oxide emissions, the hydrocarbon emissions and the carbon monoxide emissions of the fuel blends with the addition of different percentages of ethanol were analysed for different loads and for different injection timings separately. The results suggest that the effect of ethanol on the dimethyl ether combustion mainly prolongs the ignition delay and inhibits the combustion rate. The ignition delay is prolonged significantly with increasing percentage of ethanol added for low loads or retarded injection timings. A reduction in the combustion rate and an increase in the combustion duration are associated with a higher percentage of ethanol added for high loads or advanced injection timings, leading to lower nitrogen oxide emissions. On the addition of 15% ethanol, the nitrogen oxide emissions are reduced by about 17% for a brake mean effective pressure of 1.2 MPa, and by 32% when the start of injection is at –7° crank angle after top dead centre. Premixed combustion with a sharply prolonged ignition delay and a shortened combustion duration can be achieved by the addition of 15% ethanol when the start of injection is at 5° crank angle after top dead centre. The carbon monoxide emissions show a tendency to increase with increasing amount of ethanol added, whereas the hydrocarbon emissions remain nearly the same until the percentage of ethanol reaches 15%.
This paper presents a unified approach to the problem of dimensional synthesis of the five-link, four-link, and three-link (double-wishbone) suspension mechanisms with a rack-and-pinion steering input. In a simplified approach, the guiding links are assumed to be removed from their joints, allowing the wheel to be exactly driven through a number of prescribed jounce–rebound and steering positions during the kinematic synthesis process. Alternatively, the tie rod is maintained in place, and the rack length and the lengths of the remaining four guiding links are allowed to vary. An optimization problem based on the aggregated change in distance between the released ball joints evaluated in the aforementioned positions is then defined. By prescribing to the wheel a jounce–rebound motion only, rear-suspension mechanisms of the five-link, four-link, and three-link types can be conveniently synthesized by following the same procedure. Several solutions obtained through synthesis are then analyzed for their changes in steering error, recessional wheel motion, wheel track, toe angle and camber angle, showing very promising results. Additionally, a comprehensive review of nearly 150 publications relevant to the suspension design of automobiles is provided in the paper.
The evaporative cooling system concepts proposed over the past century for engine thermal management in automotive applications are examined and critically reviewed. The purposes of this review are to establish the evident system shortcomings and to identify the remaining research questions that need to be addressed to enable this important technology to be adopted by vehicle manufacturers. Initially, the benefits of the evaporative cooling systems are restated in terms of the improved engine efficiency, the reduced carbon dioxide emissions and the improved fuel economy. This is followed by a historical coverage of the proposed concepts dating back to 1918. Possible evaporative cooling concepts are then classified into four distinct classes and critically reviewed. This culminates in an assessment of the available evidence to establish the reasons why no system has yet been approved for serial production commercially. Then, by systematic examination of the critical areas in evaporative cooling systems for application to automotive engine cooling, the remaining research challenges are identified.
The diesel and natural gas dual-fuel engine has gained increasing interest in recent years because of its excellent power and economy. However, the diesel substitution rate cannot be controlled optimally, owing to the lack of a feedback indicator reflecting the cylinder combustion process, which easily leads to a serious thermal load problem. This paper presents a closed-loop control with feedback from a piston maximum temperature (PMT) pattern to regulate the diesel substitution rate in real time. A v-support vector machine (v-SVM) is proposed to train classifiers for online recognition of the PMT pattern. Nitrogen oxide (NOx) emission levels, excess air coefficient, engine speed and inlet pressure are chosen as feature variables. The PMTs, calculated by finite element analysis in ANSYS, are utilized to determine the labels of feature data. Moreover, 10-fold cross-validation is employed to choose the optimal kernel function, kernel parameters and penalty factor. A synthetic minority oversampling technique (SMOTE) is introduced to remedy the class imbalance problem in training classifiers. Furthermore, a timer-based debouncing mechanism is employed to alleviate the dynamic process influence on the PMT pattern recognition. Experiment revealed that the classifiers yield desirable predictions, with classification accuracies higher than 90%. Meanwhile, the diesel substitution rates are regulated to appropriate values through the closed-loop control algorithm, which guarantees that the dual-fuel engine runs in its safe region and maintains its excellent economy.
Turbulent jet ignition combustion is a promising concept for achieving high thermal efficiency and low NOx (nitrogen oxides) emissions. A control-oriented turbulent jet ignition combustion model with satisfactory accuracy and low computational effort is usually a necessity for optimizing the turbulent jet ignition combustion system and developing the associated model-based turbulent jet ignition control strategies. This article presents a control-oriented turbulent jet ignition combustion model developed for a rapid compression machine configured for turbulent jet ignition combustion. A one-zone gas exchange model is developed to simulate the gas exchange process in both pre- and main-combustion chambers. The combustion process is modeled by a two-zone combustion model, where the ratio of the burned and unburned gases flowing between the two combustion chambers is variable. To simulate the influence of the turbulent jets on the rate of combustion in the main-combustion chamber, a new parameter-varying Wiebe function is proposed and used for the mass fraction burned calculation in the main-combustion chamber. The developed model is calibrated using the least-squares fitting and optimization procedures. Experimental data sets with different air-to-fuel ratios in both combustion chambers and different pre-combustion chamber orifice areas are used to calibrate and validate the model. The simulation results show good agreement with the experimental data for all the experimental data sets. This indicates that the developed combustion model is accurate for developing and validating turbulent jet ignition combustion control strategies. Future work will extend the rapid compression machine combustion model to engine applications.
A constant demand in engineering design is to couple aesthetics and functionality of design. In this paper, a method is proposed to rapidly update the structural analysis models given the modifications made in the styling/packaging designs, forming a concurrent mechanism for developing the automotive styling and body structure. The seemingly disparate domains are represented by and thus coupled through a pair of wireframes. A joint mapping based on the hard points in packaging and a part mapping encoding local influences between wireframes are established. The deformation transfer from one of the wireframes to the other is solved as an optimization with constraints obtained from the two mappings. Finally, the finite element mesh model is adapted in accordance with the deformed structural wireframe, using a mesh morphing method based on the free-form deformation technique. Numerical results validate the proposed method and demonstrate its effectiveness.
An innovative non-pneumatic tyre called the mechanical elastic wheel is introduced; significant challenges exist in the prediction of the dynamic interaction between this mechanical elastic wheel and soil containing an obstacle owing to its highly non-linear properties. To explore the mechanical properties of the mechanical elastic wheel and the soil, the finite element method is used, and a non-linear three-dimensional finite element wheel–soil interaction model is also established. Hyperelastic incompressible rubber, which is one of the main materials of the mechanical elastic wheel, is analysed using the Mooney–Rivlin model. The modified Drucker–Prager cap plasticity constitutive law is utilized to describe the behaviour of the soil, and the obstacle is represented as an elastic body. Simulations with different rotational speeds of the mechanical elastic wheel were conducted. The stress distribution and the displacement of the mechanical elastic wheel and the soil were obtained, and the effects of different rotational speeds on the displacement, the velocity and the acceleration of the hub centre are presented and discussed in detail. These results can provide useful information for optimization of the mechanical elastic wheel.
This paper presents a new approach to the design, testing and analysis of a magnetorheological brake which uses a multi-path magnetic circuit to satisfy the braking demand of vehicles. In contrast with a general braking system, an automotive brake exhibits an outstanding performance for high torques and long reaction times. We use a proposed power-law model and finite element analysis to obtain the magnetorheological braking performance for a high shear rate and a high-intensity magnetic field. Finite element analysis with different structures is adopted to determine the parameters of the magnetorheological braking and the layout of the magnetic circuits. An integrated prototype is also fabricated and tested. The test results show that the brake torque is relatively high, and the torque can be accurately controlled by the input current. The reaction time is less than 100 ms. We also analyse the experimental results and use these as the basis for fabricating a full-sized prototype. The full-sized prototype generally exhibits a high torque capacity and a fast dynamic response, thereby validating the feasible application of magnetorheological fluids in automotive braking.
In this paper a novel regenerative dual-braking strategy is proposed for utility and goods delivery unmanned vehicles on public roads, which improves their ability to recover regenerative energy and consequently improves the fuel use of parallel hybrid powertrain configurations for land unmanned vehicles where the priority is not comfort but extension of their range. Furthermore, the analysis takes into account the power-handling ability of the electric motor and the power converters. In previous research, a plethora of regenerative braking strategies have been reported; in this paper, the key contribution is that the vehicle electric regeneration is related to a fixed braking distance in relation to the energy storage capabilities specifically for unmanned utility-type land vehicles where passenger comfort is not a concern but pedestrian safety is of critical importance. Furthermore, the power converter capabilities of the vehicle facilitate the process of extending the braking time by introducing a variable-deceleration profile. The proposed approach has therefore resulted in a regenerative algorithm which improves the energy storage capability of the vehicle without considering the comfort since this analysis is applicable to unmanned vehicles. The algorithm considers the distance as the key parameter, which is associated with safety; therefore, it allows the braking time period to be extended, thus favouring the electric motor generation process while maintaining safety. This method allows the vehicle to brake for longer periods rather than for short bursts, hence resulting in more effective regeneration with reduced use of the dual system (i.e. the caliper–stepper motor brake system). The regeneration method and analysis are addressed in this paper. The simulation results show that the proposed regenerative braking strategy improved the ability of the hybrid powertrain configuration to recover energy significantly. The paper is also supported by experimental data that verify the theoretical development and the simulation results. The two strategies developed and implemented utilize a constant braking torque and a constant braking power. Both methods were limited to a fixed safety-based distance. Overall, the results demonstrate that the constant-braking-torque method results in better energy-based savings.
In order to improve the shielding performance of the underbody protective structure of military vehicles when subjected to explosive events, a multi-layer honeycomb sandwich structure is proposed. Full consideration of the computing response of the underbody protective structure under blast loading is a large-scale and strongly non-linear problem; a reasonably simplified finite element model is constructed in this paper. LS-DYNA software was employed to simulate blast loading by using the *LOAD_BLAST equation and to compute the dynamic responses of the vehicle; then, full-scale experiments were performed to validate the accuracy of the numerical simulation. The geometric dimensions and the shape parameters of the multi-layer honeycomb sandwich structure are selected as the design variables, thereby establishing a response surface and a mathematical optimization model by employing the design-of-experiments method. A Pareto spatial optimal set is obtained by applying a multi-objective genetic algorithm. Eventually, using the normal-boundary intersection algorithm an optimum design was obtained, which can apparently enhance the shielding performance of the underbody protective structure of military vehicles without increasing the mass.
The pressure in the wheel cylinder plays an important role in the anti-lock braking system, but direct measurement usually needs expensive sensors. Therefore, estimation of the pressure in the wheel cylinder is of great significance to optimize the algorithm of the anti-lock braking system. There are two commonly used estimation methods: one is based on the hydraulic model, and the other is based on the equation for the tyre dynamics. Both of these, however, suffer from inadequacies. The former method is sensitive to the accuracy of the model in practical applications, and an accumulated error appears if some parameters of the process are not sufficiently accurate. In the latter method the pressure in the wheel cylinder is calculated for each cycle but, when the vehicle is running, the fluctuations in the deceleration are relatively large. To estimate the pressure more accurately, a novel method is proposed in this paper, which combines these two methods on the basis of the extended Kalman filter. The method can compensate for the inadequacies of the two methods mentioned above by using the variation in the wheel speed as the observation variable to modify the hydraulic model. It can decrease its sensitivity to the accuracy of the hydraulic model and improve the accuracy of the estimated magnitude of the pressure. The estimated results are compared with the real values which are obtained by using a pressure sensor on a typical low-friction road and on an asphalt road; in addition, the effectiveness of the novel method is validated by hardware-in-the-loop tests and vehicle tests. The results show that the proposed method can provide an accurate estimation of the pressure in the wheel cylinder during hydraulic control of the anti-lock braking system or any other brake control system.
This paper presents a design synthesis framework for directional performance optimization of multi-trailer articulated heavy vehicles with trailer lateral dynamic control systems, e.g. active trailer steering, trailer differential braking, active roll control or the coordination of the three systems. In order to demonstrate the effectiveness of the proposed framework, it was applied to the design optimization of a multi-trailer articulated heavy vehicle with an active trailer steering controller. In the design, a set of lateral stability measures is originally defined, and the design problem under simulated test manoeuvres is implemented using a parallel computing technique. It is illustrated that the proposed framework and the performance measures can be used to identify effectively the desired variables and to predict reliably the performance envelopes of multi-trailer articulated heavy vehicles with active safety systems by considering the concept of driver-adaptive-vehicle design.
Accurate air–fuel ratio control is a key affecting factor for improving fuel economy and reducing exhaust emissions for internal combustion engines. Challenging issues in air–fuel control are the accurate estimation of cylinder air charge for achieving the stoichiometric in-cylinder air–fuel ratio and the disposition of measurement time delay from the oxygen sensor for removing its limits on the achievable feedback performance. In this article, based on hybrid discrete–continuous-time descriptions for the cylinder air charge dynamics and air–fuel feedback regulation controlled plant, a novel fuel injection controller with adaptive feedback and predictive feedforward is designed to ensure accurate air–fuel control of a gasoline direct injection engine. The feedforward fuel injection is determined based on the cylinder air charge prediction using unscented Kalman filter for the compensation of the injection delay and modelling error and the attenuation of the measurement noise. The feedback fuel compensation is designed as a proportional-integral structure with adaptive gains by means of an adaptive stabilization method of uncertain input delayed systems for the management of the transport delay and parameter uncertainty. The effectiveness of the proposed fuelling control against time delay, modelling error, measurement noise and parameter uncertainty is demonstrated by the simulation utilizing experimental data from a real V6 GDI engine.
This paper focuses on invetigating the relationship between the contact features of the tyres and the tyre wear in a quantitative sense as a function of the tyre structure and the manoeuvre parameters by utilizing a modified theoretical tyre wear model. The modified tyre wear model was developed by combining a modified ring model for the tyres and a modified brush model and was validated. The model parameters were also identified by physical experiments. Moreover, the contact features were characterized as the contact length, the asymmetry factor and the rolling resistance shift in order to investigate the influence of the contact features on the tyre wear. The amount of wear versus the three key variables of the contact features with variations in the tyre parameters was plotted and analysed. The results show that the maximum normal contact pressure does not play the most important role in the tyre wear. An increase in the damping coefficient can lead to an increase in the tyre wear, whereas increases in the effective elastic constant, the effective bending density and the effective bending stiffness result in a decrease in wear. The three key variables of the contact features increase with increasing vertical load, increasing rolling velocity and increasing damping coefficient and with decreasing inflation pressure and decreasing effective bending stiffness. The tyre wear follows the same trend when the three key variables increase or decrease synchronously. This analysis provides a quantitative indication of the relationship between the contact features and the tyre wear in order to obtain guidelines for tyre manufacturers on how to achieve less tyre wear.
This paper presents a new approach for the reliability analysis of vehicle systems by considering typical characteristics based on goal-oriented methodology. First, solutions are proposed for vehicle systems with multiple fault modes, a standby structure at any position, a multiple-input closed-loop feedback link, multiple functions, and multiple conditions for the goal-oriented method. Then, a two-level goal-oriented model and the new rules of goal-oriented operation for such vehicle systems are proposed. Furthermore, the quantitative method and the qualitative method are improved. In addition, the analysis process for these vehicle systems based on the new goal-oriented method is formulated. Finally, this new goal-oriented methodology is applied in the dynamic availability analysis and qualitative analysis of the power-shift steering transmission for a heavy military vehicle. In order to verify the feasibility, the advantages, and the correctness of the new goal-oriented methodology, the results are compared with those from fault tree analysis and Monte Carlo simulations. In general, this study not only improves the theory of the goal-oriented method and widens the application of the goal-oriented method but also provides a new reliability analysis method for such vehicle systems. In addition, the analysis process of the new goal-oriented method shows that the goal-oriented method has advantages in system reliability modeling and system reliability analysis for vehicle systems.
Electric vehicles are becoming more popular in the market. To be competitive, manufacturers need to produce vehicles with a low energy consumption, a good range and an acceptable driving performance. These are dependent on the choice of components and the topology in which they are used. In a conventional gasoline vehicle, the powertrain topology is constrained to a few well-understood layouts; these typically consist of a single engine driving one axle or both axles through a multi-ratio gearbox. With electric vehicles, there is more flexibility, and the design space is relatively unexplored. In this paper, we evaluate several different topologies as follows: a traditional topology using a single electric motor driving a single axle with a fixed gear ratio; a topology using separate motors for the front axle and the rear axle, each with its own fixed gear ratio; a topology using in-wheel motors on a single axle; a four-wheel-drive topology using in-wheel motors on both axes. Multi-objective optimisation techniques are used to find the optimal component sizing for a given requirement set and to investigate the trade-offs between the energy consumption, the powertrain cost and the acceleration performance. The paper concludes with a discussion of the relative merits of the different topologies and their applicability to real-world passenger cars.
Although the traditional energy regeneration system which uses electric or hydraulic energy recovery to regenerate part of the overflow energy loss during the acceleration and braking stages of the swing process of a hydraulic excavator, the modification cost is high and the control system is complex. To reduce the overflow energy loss of the swing process of the hydraulic excavator and to simplify the control system, a novel swing driving system based on a hydraulic accumulator to regenerate and utilize the energy automatically during the acceleration process is presented. The working mode and the assessment criteria of the swing system are analysed. The characteristics of the traditional swing system and the proposed swing system are compared. The relationships between the pressures of the two motor chambers, the pressures of the hydraulic accumulator and the motor speed of the proposed swing system in one working cycle are studied. The experimental results showed that the energy recovery efficiency of the proposed swing driving system, which can regenerate the energy automatically based on the hydraulic accumulator, was up to 80% during the acceleration stage of the swing process, and the energy consumption of the power system in one working cycle was reduced by 16.5% in comparaison with that of the traditional driving system.
An index which links the fuel composition to particulate matter emissions (the PN index) was developed and is here evaluated with model fuels in a single-cylinder optical-access spray-guided direct-injection engine; the model fuels have independent control of the double-bond content and volatility, as used in the index. This index is investigated in three different engines: a single-cylinder research engine, a V8 engine recently available in the market and a current-production supercharged V6 engine. A number of market gasolines were tested in all three engines, and the results follow the trends predicted by the particle number index. Imaging of the in-cylinder sprays shows that the composition of the model fuels affects the mixture homogeneity and their particulate matter emissions; in particular, the lack of a light end in the model fuel composition can lead to misleadingly low particle number emissions owing to improved mixture preparation which is unrepresentative of market fuels. The PN index was investigated in a Jaguar Land Rover V6 engine with five different fuels over a simulated New European Driving Cycle, and the results show that the index trends are followed. The emissions were evaluated from two fuels representing the EU5 reference-fuel specifications that has been developed using the particle number index to give a difference in particulate matter emissions. The results from these fuels show that a difference in the particle number emissions of a factor of about 2 can be seen at both stoichiometric conditions and rich conditions, for two fuels representative of the EU5 reference-fuel specifications. This follows trends predicted by the particle number index. This has important implications for policy makers and European Union legislation, where particle number emissions from gasoline vehicles are now regulated for the first time, as batch-to-batch variations in the fuel composition would result in different test results under the current legislation.
Homogeneous charge compression ignition engines require a smart control system to regulate the input quantities of the engine in various operational conditions. Achieving an optimum combustion needs an appropriate system response for different engine loads and speeds according to the power acquired from the engine, as well as the amounts of emissions present in the exhaust. Therefore, performing a set of experimental tests together with numerical simulations in a wide range of conditions facilitates calibration of the input parameters of the engine. In this study, the effects of the thermodynamic parameters and the thermokinetic parameters on the engine output in the preliminary design stage were obtained at different speeds to determine the optimum exhaust emissions, the optimum combustion timing and the ranges of misfiring and knock, using multiple-zone thermodynamic modelling. On the assumption that the simulation cycle is closed, the probability density function was used to determine the initial conditions for the temperature and the residual gas from the previous cycle mass distribution in each area inside the cylinder. The results obtained proved that the kinetic properties of the mixture due to the effects of the the air-to-fuel ratio, the percentage of exhaust gas recirculation and the percentage of reformer gas have dominant effects on the output in comparison with the thermodynamic parameters such as the intake pressure and the intake temperature. At low speeds, exhaust gas recirculation retards combustion and delays engine knock. At higher engine speeds, the reformer gas advances combustion and improves misfiring.
This paper shows development challenges for 11-liter heavy-duty off-highway diesel engines to meet Tier 3 emission regulations with a base diesel engine compliant with Tier 2 emission regulations. In the case of the installation of an exhaust gas recirculation (EGR) system for reduction of NOx emissions, there exists a risk of increased particulate matters (PM) emissions. An in-cylinder PM reduction is still necessary since a diesel particulate filter (DPF) after-treatment system is not under the consideration. The objective of this research is to see whether the base engine has a potential to meet Tier 3 emission regulations by changing in-cylinder configuration parameters including the bowl shape, injector position, the number of intake and exhaust valves, injector tip protrusion, and injector tip specifications such as nozzle spray angle and nozzle flow rate. These parameters are very important parts which enhance the air and fuel mixing process that helps the combustion process. Thus, the optimization of these design variables is essential to improve combustion efficiency and emissions reduction. In this study, the multi-dimensional computational fluid dynamics (CFD) code KIVA-3V is used to perform combustion simulations. The Kelvin–Helmholtz/Rayleigh–Taylor (KH-RT) model is employed for spray breakup and a reduced chemical mechanism for n-heptane is employed to simulate ignition delay and combustion of diesel fuel. To verify the simulation results, engine bench tests were performed with installations of the final version of in-cylinder geometry in C1-8 mode which is one of main test cycles to meet Tier 3 emission regulations. Finally, Tier 3 emission regulations have been met with the currently optimized in-cylinder configuration parameters.
In this study, the transient nitrogen oxide reduction performance of a urea selective catalytic reduction system installed on a non-road diesel engine was tested on an engine dynamometer bench over a scheduled non-road transient cycle mode. Based on the measurement results, the characteristics of the transient selective catalytic reduction behaviours of nitrogen oxide reduction were evaluated. Also, in this study, the effects of several thermal management strategies for improving the selective catalytic reduction efficiency was investigated by transient selective catalytic reduction simulations. The kinetic parameters of the current simulation code for selective catalytic reduction were calibrated and validated by comparison with the measurement data. As a result of this study, it was found that a thermal management strategy utilizing a partial temperature rise in the transient time domain can be an efficient approach for improving the transient selective catalytic reduction efficiency, in comparison with the temperature rise over the entire cycle period. Furthermore, this study can provide some guideline data for the magnitude and the duration of the temperature rise required to obtain the target selective catalytic reduction efficiency over the non-road transient cycle mode. In the last part of this study, the impact of the variation in the space velocity on the transient selective catalytic reduction efficiency was assessed using transient selective catalytic reduction simulations.
For a vehicle equipped with an automatic transmission, the shift control strategy should reflect the driver’s intention in the dynamic performance and the economy performance of the vehicle. However, the driver’s intention is difficult to identify and involve in the shift strategy because of the complexity of driving environments, the diversity of powertrain parameters and the randomness of the driver’s behaviour. Therefore, in this paper, by considering a vehicle equipped with an automated manual transmission as the study object, a novel multi-parameter coordinated shift control strategy is proposed on the basis of identification of the driver’s intention. First, in order to predict the intention of the driver more effectively, the relative opening degree of the accelerator is defined on the basis of the dynamic analysis. Then, the characteristics of the driver’s expected acceleration, which involve the influence of the driving environment, are proposed. They can be classified into five categories, namely stop, deceleration, keep, acceleration and urgent acceleration. Next, a fuzzy control system is designed to identify the driver’s acceleration characteristics in real time. This considers the vehicle speed, the rate of change in the opening degree of the accelerator and the relative opening degree of the accelerator as the inputs and the quantitative intention of the driver as the output. Finally, the novel multi-parameter coordinated shift control strategy is formulated on the basis of the vehicle speed, the opening degree of the accelerator and the quantitative intention of the driver. The designed shift strategy is compared with conventional methods using simulations and is verified by road tests. The results show that the shift control strategy can make the vehicle shift much more effective.
The series hybrid electric vehicle makes it easier to have fully independent controls for the engine–generator unit and for the traction motors; this is not feasible in parallel hybrid electric vehicles or series–parallel hybrid electric vehicles. The existing research does not consider this feature. Therefore, a novel control method called engine torque command handling is developed in this study and is added to the optimal energy management strategy, namely dynamic programming; this makes the most of the inertia of the engine–generator unit. The hidden fuel economy improvement factor, as demonstrated by the the difference between the command and the behaviour, can then be found. As a result, a considerable improvement in the fuel economy with straightforward but powerful concepts, such as modification of the engine operating points and the on–off period, is developed in the series hybrid electric bus. The simulation is evaluated by AMEsim–Simulink co-simulation with the well-known urban bus test profiles: the Manhattan cycle, the Braunschweig cycle and the Orange County cycle. The results show the significant potential for reduction in the energy consumption without changing the components or the structure of the vehicle system. This method can be applied to any type of vehicle that allows independent engine power generation without interruption.
Improved fuel efficiency in hybrid electric vehicles requires a delicate balance between the internal combustion engine usage and battery energy, using a carefully designed energy management control algorithm. Numerous energy management strategies for hybrid electric vehicles have been proposed in literature, with many of these centered on the equivalent consumption minimisation strategy (ECMS) owing to its potential for online implementation. The key challenge with the equivalent consumption minimisation strategy lies in estimating or adapting the equivalence factor in real-time so that reasonable fuel savings are achieved without over-depleting the battery state of charge at the end of the defined driving cycle. To address the challenge, this paper proposes a novel state of charge feedback ECMS controller which simultaneously optimises and selects the adaption factors (proportional controller gain and initial equivalence factor) as single parameters which can be applied in real time, over any driving cycle. Unlike other existing state of charge feedback methods, this approach solves a conflicting multiple-objective optimisation control problem, thus ensuring that the obtained adaptation factors are optimised for robustness, charge sustenance and fuel reduction. The potential of the proposed approach was thoroughly explored over a number of legislative and real-world driving cycles with varying vehicle power requirements. The results showed that, whilst achieving fuel savings in the range of 8.40 –19.68% depending on the cycle, final battery state of charge can be optimally controlled to within ±5% of the target battery state of charge.
In this paper, the development of a Miller cycle gasoline engine which has a high compression ratio from 11.5:1 to 12.5:1, single-stage turbocharging and external cooled exhaust gas recirculation is described. The improvement in the fuel economy by adding external cooled exhaust gas recirculation to the Miller cycle engine at different geometric compression ratios were experimentally evaluated in part-load operating conditions. The potential of adding external cooled exhaust gas recirculation in full-load conditions to mitigate pre-ignition in order to allow higher geometric compression ratios to be utilized was also assessed. An average of 3.2% additional improvement in the fuel economy was achieved by adding external cooled exhaust gas recirculation to the Miller cycle engine at a geometric compression ratio of 11.5:1. It was also demonstrated that the fuel consumption of the engine with external cooled exhaust gas recirculation was reduced by 3–7% in a wide range of part-load operating conditions and that the engine output of the Miller cycle engine at a geometric compression ratio of 12.5:1 increased at 2000 r/min in the full-load condition. The Miller cycle engine with external cooled exhaust gas recirculation at a geometric compression ratio of 12.5:1 achieved a broad brake specific fuel consumption range of 220 g/kW h or lower, with the lowest brake specific fuel consumption of 215 g/kW h. While there are still challenges in implementing external cooled exhaust gas recirculation, the Miller cycle engine with single-stage turbocharging and external cooled exhaust gas recirculation showed its potential for substantial improvement in the fuel economy as one of the technical pathways to meet future requirements in reducing carbon dioxide emissions.
Airborne particulate matter emitted from motor vehicle brakes is a contributor to urban air quality. Therefore, a method to rank brake pairs (pads and rotors) with respect to their particle emission factors in a reliable way is needed to develop a low-emission disc brake. A novel inertial disc brake dynamometer designed for brake particle emission studies, a modified SAE J 2707 cycle, an electrical low-pressure cascade impactor and a filter are used to test five different pad materials against cast-iron rotors. By changing only the pad materials, it is shown that the differences between the mass emission factor and the number emission factor of the the worst brake pair and those of the best brake pair decreases by more than four times and 19 times respectively. Furthermore, the results show that the material combination ranked the best in terms of the mass emission factor is ranked the worst in terms of the number emission factor. The results reveal that this combination of a test stand, a test cycle and particle instruments can discriminate between different brake pair materials in a reliable way in the case of the mass emission factors while more research has to be carried out in the case of the number emission factors.
This work presents a turbulent premixed combustion modeling approach which is based on chemical kinetics. In this approach, the smallest length scales are of the order of 0.1–1.0 mm for typical engine simulations with a Reynolds-averaged Navier–Stokes turbulence model and, after adaptive mesh refinement technology is used to consider the magnitude of the subgrid field, the Reynolds-averaged Navier–Stokes turbulent flow field can be well resolved. For solution of the flame front, an artificially thickened laminar flame concept is introduced to balance the computational accuracy and the computational cost. Around the artificially thickened laminar flame front, a special grid resolution strategy is designed, i.e. using much finer resolution in the normal direction of the flame front and typical adaptive mesh refinement resolution in the other two perpendicular directions. Then, chemical kinetics can be applied to the chemistry process which occurs in the flame front. To use this chemical-kinetics-based turbulent premixed combustion modeling approach better, a good chemical kinetics mechanism is very important. For this reason a practical primary-reference-fuel chemical kinetics mechanism is improved and validated in present work. The newly improved mechanism resolves several issues in the existing mechanisms, including unrealistically fast autoignition reactions and limited laminar flame speed validation. After reoptimization of those laminar-flame-speed-related reactions, the new mechanism can correctly compute the laminar flame speeds for a wide range of Ford spark ignition engines and for various operating conditions. Using this combustion modeling approach together with the new mechanism, simulations of the combustion and the emissions of several spark ignition engines for typical operating conditions were carried out. The simulated in-cylinder pressures, the simulated burn rates, and the simulated emissions including the brake specific carbon monoxide emissions, the nitrogen oxide emissions, and the unburned hydrocarbon emissions are compared with the experimental data, and very good agreement is found without tuning any model constants.
Turbocharging plays a significant role in internal-combustion engines. For engines in the future or for engines operating at a high altitude, compressors which are able to deliver a high pressure ratio are preferable. However, the poor low-end torque characteristics of turbocharged engines, which are often restricted by the narrow operating range of compressors at a high pressure ratio, result in a severe problem for turbocharging. The use of variable diffuser vanes is an effective method to increase the operating range, but the potential of an extended operating range at a high pressure ratio and improvement in the torque performance of engines is unclear. Nowadays, the pressure ratio of a turbocharger compressor may be only 1–4. Because of the increase in the pressure ratio, estimating the potential is ultimately worthwhile. In this paper the performances of a centrifugal compressor with different diffuser vane angles are investigated, the range extension and the improvement in the torque performance which benefited from variable diffuser vanes are estimated and the mechanisms for range extension are revealed. The approach includes steady three-dimensional Reynolds-averaged Navier–Stokes simulations and theoretical analysis. Adjusting the vane angle from –10° to 10° improves the operating range of a compressor by 23.5% (with fixed vanes) to 54.9% at a pressure ratio of 4.8. The range extension is otained by utilizing the shifts in the choke line and the surge line. A method of assessing the choking component based on the simulation results is proposed. The diffuser, the flow stability of which was enhanced comparatively by closing it (pivoting the vanes by –10° and –5°), contributes mainly to reducing the surge flow. With this range extension, the improvement in the maximum torque is estimated to be 78%.
Fully three-dimensional computational fluid dynamic simulations with detailed combustion chemistry of a turbulent jet ignition system installed in a rapid compression machine are presented. The turbulent jet ignition system is a prechamber-initiated combustion system intended to allow lean-burn combustion in spark ignition internal-combustion engines. In the presented configuration, the turbulent jet ignition prechamber has a volume that is 2% of the volume of the main combustion chamber in the rapid compression machine and is separated from the main chamber by a nozzle containing a single orifice. Four simulations with orifice diameters of 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm respectively are presented in order to demonstrate the effect of the orifice diameter on the combustion behavior of the turbulent jet ignition process. Data generated by the simulations is shown including combustion chamber pressures, temperature fields, jet velocities and mass fraction burn durations. From the combustion pressure trace, the jet velocity, and other field data, five distinct phases of the turbulent jet ignition process are identified. These phases are called the compression phase, the prechamber combustion initiation phase, the cold jet phase, the hot jet phase, and the flow reversal phase. The four simulations show that the orifice diameter of 1.5 mm provides the fastest ignition and the fastest overall combustion as reflected in the 0–10% and 10–90% mass fraction burn duration data generated. Meanwhile, the simulation for the orifice diameter of 1.0 mm produces the highest jet velocity and has the shortest delay between the spark and the exit of a jet of hot gases into the main chamber but produces a slower burn duration than the simulation for the larger orifice diameter of 1.5 mm. The simulations for orifice diameters of 2.0 mm and 3.0 mm demonstrate that the combustion speed is reduced as the orifice diameter increases above 1.5 mm. Finally, a discussion is given which examines the implications that the results generated have in regard to implementation of the turbulent jet ignition system in an internal-combustion engine.
Digitally controlled electromechanical actuators with d.c. motors have been installed on a growing number of luxury vehicles, improving the vehicle performance significantly. However, the installation space and the cost issues of speed sensors in d.c. motors have limited the application of electromechanical actuators on medium-size and compact vehicles. In this paper, a novel adaptive high-order sliding-mode observer, which is based on the hybrid sliding-mode method and adaptive theory, is proposed. By integration of two adaptive gains with a high-order sliding-mode observer, the proposed observer facilitates application without the use of a filter, reduces the estimation oscillations and strengthens the system’s robustness. The effectiveness of the proposed adaptive observer was validated by simulations and experimental data.
The steering performance is one of the major concerns in special engineering vehicle fields. This study aims to investigate the steering performance of an articulated tracked vehicle. An improved dynamic steering model for an articulated tracked vehicle is proposed when considering the shear stress–shear displacement relation of the soil at the track–ground interface. In this model, the mechanical, kinematic and dynamic models of the articulated unit are constructed to evaluate the movement performance of the articulated unit, and the kinematic and dynamic models of the front vehicle and the rear vehicle are developed to evaluate the steering performance. The created dynamic model is then applied to analyse the steering performance of a specific articulated tracked vehicle. A mechanically controlled united simulation model and actual tests of an articulated tracked vehicle are utilized to verify the established steering model. The results of the comparisons show the effectiveness of the proposed dynamic steering model.
Earthmoving equipment in motor graders, which can be considered to be complex multibody systems (MBSs), are critical components for earthwork, compaction and re-handling. They have not yet received much attention due to their unusual applications and complicated structures. In this paper, a comprehensive study of an earthmoving MBS, from the mechanism identification and sensitivity analysis to the multi-objective optimization, is presented. First, the earthmoving MBS is identified to be a six degrees-of-freedom spatial hybrid mechanism, where a three revolute-revolute-prismatic-spherical (RRPS) and one spherical subchain (so, RRPS-S) spatial parallel mechanism is the key subsystem, through the mechanism analysis and synthesis. An earthmoving virtual prototyping model is built according to the system topology and connectivity. The kinematic simulations are carried out by imposing corresponding driving functions. Afterwards, the sensitivity analysis is introduced to extract several most relevant design variables from the global ones. A multi-objective optimization process is carried out to improve working performance, where fuzzy sets are used to define different objectives. Results show that the optimal earthmoving mechanism provides better lifting and parallel lifting capabilities.
This study aims to investigate the switching model predictive control strategy for a heavy-vehicle system in order to coordinate the actuator between active rear steering and differential braking control manoeuvres for emergency threat avoidance in difficult environments. We present the controller performances for the lateral dynamic behaviour, the yaw stability and the manoeuvrability of a vehicle when subjected to a sudden threat or disturbance such as a gust of wind, a road bank angle or a split-μ road surface in order to enable a fast safe lane-change trajectory to be followed. The vehicle was driven at a medium forward speed and a high forward speed in order to investigate the effectiveness of the proposed approach in avoiding the threat, maintaining the stability and enablinge a fast safe lane-change trajectory to be followed. We compared two different controllers (a model predictive controller and a switching model predictive controller) for two different control manoeuvres (active rear steering with differential braking control and active rear steering with direct yaw moment control). The simulation results demonstrate that the proposed switching model predictive control method provides an improved fast safe lane-change manoeuvre in a threat avoidance scenario for both control manoeuvres. It also demonstrated that the proposed active rear steering with differential braking control is more useful for maintaining the stability of the vehicle in a threat avoidance scenario with disturbance effects than is active rear steering with direct yaw moment control.
The direct-start method without requiring a starter is a viable and cost-effective solution for generating a frequent and efficient restarting process when start–stop technology is used on a gasoline direct-injection engine. During the direct-start process, the first-cycle combustion characteristics play a key role in determining whether the start mode is successful or not, because the start energy is wholly derived from the in-cylinder combustion without the support of a starter motor on the gasoline direct-injection engine. However, the first-cycle fuel–air mixing and combustion characteristics during the direct-start process of a gasoline direct-injection engine are not fully understood. In this work, the influences of the injection parameters, including the delay between the injection and ignition, the excess air ratio for the single-injection strategy, the delay between the first injection and the second injection for the dual-injection strategy and the ratio of the fuel mass in the first injection to the fuel mass in the second injection for the dual-injection strategy, on the combustion pressure, the heat release rate, the accumulated heat release and the indicated work were investigated experimentally by cycle-by-cycle analysis. The results show that the optimal delay between the injection and ignition of the single-injection strategy was 200 ms as a longer delay or a shorter delay can result in a reduction in the heat released rate, the indicated work and the firing boundary. A shorter delay with the optimal injected fuel mass tended to be more beneficial to the accumulated heat released, the indicated work and the crankshaft speed. Furthermore, with increasing delay and increasing fuel ratio of the fuel mass in the first injection to the fuel mass in the second injection for the dual-injection strategy, the heat release rate, the accumulated heat release and the indicated work first increased and then decreased. The optimum delay was 10 ms and the ratios of the fuel mass in the first injection to the fuel mass in the second injection were 4/1 and 5/1 respectively under the test conditions. Additionally, the dual-injection strategy with an optimized control parameter produced a higher heat release and higher indicated work than the single-injection strategy did.
An automotive junction box distributes electric power to electric systems installed in a vehicle with overcurrent protection. As a larger number of electric systems are installed, the junction box is equipped with more components, functionalities and connections. However, owing to the fuse accessibility, its installation space is so restricted that a downsized design is required for the junction box. The junction box is composed of small signal circuitry for control and monitoring, and large current-carrying circuitry for power distribution which includes many parallel traces. Because of these unique features, widely used techniques for downsizing printed-circuit boards are not applicable. Also, there is no rule for designing large current-carrying parallel traces, and it is difficult to optimize the size of the printed-circuit board for the automotive junction box. This paper presents the design rules for a printed-circuit board when downsizing a junction box. First, the layout strategy for the power distribution components is presented, which is determined by the sum of the squares of the currents flowing through connector pairs. Then, the thermal effects of parallel traces are simulated for different conditions by using thermal analysis software. Based on the results, an analytical estimation of the additional temperature rises due to parallel traces and rules for a thermally effective arrangement of the parallel traces are presented.
Vehicle crash optimization is a representative non-linear dynamic response structural optimization that utilizes highly non-linear vehicle crash analysis in the time domain. In the automobile industries, crash optimization is employed to enhance the crashworthiness characteristics. The equivalent-static-loads method has been developed for such non-linear dynamic response structural optimization. The equivalent static loads are the static loads that generate the same displacement field in linear static analysis as those of non-linear dynamic analysis at a certain time step, and the equivalent static loads are imposed as external loads in linear static structural optimization. In this research, the conventional equivalent-static-loads method is expanded to the crash management system with regard to the frontal-impact test and a full-scale vehicle for a side-impact crash test. Crash analysis frequently considers unsupported systems which do not have boundary conditions and where adjacent structures do not penetrate owing to contact. Since the equivalent-static-loads method uses linear static response structural optimization, boundary conditions are required, and the impenetrability condition cannot be directly considered. To overcome the difficulties, a problem without boundary conditions is solved by using the inertia relief method. Thus, relative displacements with respect to a certain reference point are used in linear static response optimization. The impenetrability condition in non-linear analysis is transformed to the impenetrability constraints in linear static response optimization.
The occurrence of surge or stall in a centrifugal compressor and the role of the tip clearance flow in the instability in the centrifugal compressor are investigated in this study. A computational method is used to study the flow field in the centrifugal compressor in order to gain a better understanding of the surge or stall mechanism. It is found that, near surge or stall conditions, the tip leakage flow at the leading edge deflects more upstream; as the deflection increases, a more severe spillage occurs which finally leads to instability of the compressor. A ring air jet injection is used to eliminate the instabilities and to extend the stable flow range of the compressor. Using an air jet injection, the stable flow range of the compressor was successfully increased with minimal decrease in the efficiency of the compressor. The effects of different injection parameters such as the mass flow, the yaw angle, the injection angle, the slot width and the slot distance on the compressor flow field are studied, and an optimum design for the air jet injection is developed. Further investigation of the compressor with the optimum injection configuration shows that, near surge or stall conditions, the tip leakage at the leading edge is still under control, manifesting a much smaller spillage than does the Dresser–Rand Datum compressor without an air injection. The dominant factor for the instability of the compressor with an injection is found to be the leading-edge separation rather than the tip leakage.
In this work the dynamic substructuring approach was applied to a noise, vibration and harshness problem within the automotive engineering field. In particular, a noise, vibration and harshness analysis was carried out on the body-in-white structure of a passenger car. The work focuses on the theory of component mode synthesis. Two component mode synthesis reduction methods, namely the Craig–Bampton method and the Craig–Chang method, were applied to the body-in-white structure of the Volvo V40. The influences of various parameters were investigated. In particular, the effect of the reduction basis on the response accuracy and on the reduction time was studied. Moreover, the effects of the connection properties between different parts of the model were examined. The simulation times of the reduced models and of the full finite element model were compared. The results showed that the Craig–Chang method performs better when the modes are retained for up to one and a half times the maximum frequency response studied. Additionally, the Craig–Chang method gives a very accurate representation of the system dynamics even when connections with a low stiffness are used. Finally, it is possible to reduce the simulation time by up to 90% if component mode synthesis methods are used instead of the full finite element model.
The coupled vibro-acoustic response of a sedan is analysed, and the effect of the folding rear-seat aperture is studied. First, a simplified model of an acoustic cavity that consists of two adjacent boxes connected by an aperture is modelled. An analytical solution is proposed to calculate the acoustic eigenfrequencies of the simplified model. Then, the uncoupled acoustic eigenfrequencies of the actual cavity (where the trunk cavity and the cabin cavity are connected through an aperture) are computed. It is shown that the planar acoustic eigenfrequencies of the sedan can be calculated approximately using the analytical solution proposed. To clarify the effect of the folding rear-seat aperture further, the coupled vibro-acoustic response of the sedan is analysed using different case studies. It is observed that the booming noise is highly correlated with the calculated uncoupled planar acoustic eigenfrequencies.
The time and effort required for maintenance of an automobile system are highly dependent on its disassemblability, which is one of the most important attributes of its maintainability. To evaluate the disassemblability index, i.e. to measure the ease of disassembly, the disassemblability factors (both the design factors and the contextual factors) of an automobile system are identified. These and their interrelations are modelled by considering their structure using the graph theory. The directed graph (digraph) of the disassemblability of the automobile system is defined; the nodes of this represent its disassemblability factors, while the edges represent their degrees of influence. An equivalent matrix of the digraph establishes the system’s disassemblability function which characterizes the disassemblability of the system, leading to development of the disassemblability index. A high value of the disassemblability index indicates that it is very easy to remove or replace parts. The disassemblability index ratio is used to compare the actual conditions of disassembly with the ideal conditions of disassembly. A case study of an automobile gearbox is illustrated using the step-by-step procedure of the proposed methodology of disassemblability. The proposed methodology is helpful to evaluate and compare various alternative designs of the automobile system and, therefore, can aid the design and development of automobile systems from the disassembly viewpoint.
Nonpneumatic tires made from materials with a low viscoelastic energy loss can be an option for developing tires with a low rolling resistance. For better fuel-efficient design of nonpneumatic tires, the rolling energy loss of the nonpneumatic tires may need to be analyzed at a component level. The objective of this study is to develop a numerical tool that can quantify the rolling energy loss and the corresponding internal heat generation of a nonpneumatic tire. We construct a thermomechanical model that covers the interaction between the deformation and the related heat generation in an elastomer material. We suggest, for various vehicle loads and various rolling speeds, a coupled thermoviscoelastic material model for a nonpneumatic tire with a hexagonal cellular spoke in order to investigate the temperature distribution of the nopneumatic tire generated by hysteresis and convection loss to the air. Using a hyperviscoelastic material model developed from uniaxial (tension and compression) tests and dynamic mechanical analysis, a thermomechanical model is constructed by combining a shear-deformation-induced hysteresis and a cooling procedure when exposed to the air. The model of the temperature rise of the nonpneumatic tire is validated using temperature measurement with a thermal imaging camera during rolling of the nonpneumatic tire. The developed tool combining the viscoelastic material model with the aerodynamic heat loss quantifies well the hysteretic energy loss and the temperature distribution at each component of the nonpneumatic tire.
Control of diesel oxidation catalyst (DOC) outlet temperature is critical for downstream diesel particulate filter regeneration, but is challenging to control due to the non-minimum phase behavior and varying time delay. To effectively address this issue, a novel and time-efficient composite controller based on modified active disturbance rejection control (mADRC) is proposed for DOC-out temperature control in this paper. The proposed mADRC-based composite controller is a new combination of a model-based feedforward controller and a mADRC with time delay compensation through the mass flow rate of exhaust gas. The model-based feedforward controller is designed to partially compensate the variations of DOC inlet temperature and mass flow rate, while the mADRC is proposed to address the remain disturbances and model uncertainties including time delay uncertainties. Simulation and test results through a high-fidelity Gamma Technologies-Power model demonstrate the effectiveness and robustness of the proposed composite controller in the DOC-out temperature control under steady state and a highly transient new European dynamic cycle (NEDC).
The pivotal steering ability of a skid-steered vehicle is an important advantage compared with the steering ability of an Ackermann steered vehicle. In the pivotal steering condition, the strong non-linearity of the properties of the tyres makes prediction of the dynamic modelling and the performance difficult. For this purpose, this paper proposes an experimentally validated dynamic model to describe the motion of a skid-steered vehicle in the pivotal steering condition. The mechanical analytical model of the tyres was constructed on the assumption of an ‘elliptical parabolic’ contact pressure distribution. The dynamic model has nine degrees of freedom, including the longitudinal motion, the lateral motion and the yaw motion of the body and also the rotation of the wheels; the motor saturation is also considered. The analysis and experiments were based on a specific 6 x 6 unmanned skid-steered vehicle which is driven by six independent in-wheel motors, and the driving control algorithm of the vehicle was also described. By comparing the results of experiments and simulations, it was shown that the dynamic model provided an accurate prediction of the performance.
Multi-hole nozzles have a wide range of application in the fuel supply system of modern diesel engines, although single-hole nozzles dominate basic internal flow and spray research. The parameters of the nozzle geometry are crucial factors that can alter the internal flow dynamics of the nozzle and the consequent spray behaviours. The novelty of this study lies in implementing the application of practical prototype mini-sac multi-hole diesel nozzles to experimental and numerical studies. The internal flow and spray characteristics generated by practical multi-hole (10-hole) nozzles with different sac wall thicknesses (0.4 mm, 0.6 mm and 0.8 mm) were investigated in conjunction with a series of experimental and computational methods using a constant injection quantity (2 mm3/hole). Globally, the analysis mainly concentrated on different nozzle flow dynamics, different injection processes and different spray morphologies. Specifically, the high-speed video observation method was applied to visualize the injection processes and the spray evolution of different nozzles inside a high-pressure vessel. Furthermore, numerical simulations were conducted to reveal the three-dimensional nature of the internal flow inside different configurations; this was instructive in helping us to understand better the mechanism behind the spray behaviours. The results indicate that intense cavitating, turbulent and spiral rotating flow patterns occur inside practical multi-hole nozzles, and the consequent sprays emerging from the nozzles are perturbed, asymmetrical and unstable in both the near field and the far field. Moreover, a decrease in the nozzle hole length can increase the effects of cavitation, turbulence, the void fraction and the axial and radial injection velocity components on the nozzle hole exit; this is accompanied by an intriguing longer injection duration, wider near-field and far-field spray widths, a lower injection rate, and overlapping or even shorter spray propagation. However, these changes are not linear, and different parameters have different sensitivities to the variation in the nozzle hole length.
When a charge is ignited at the bottom of a vehicle, the underbody and the occupants are the most vulnerable. The protection of the vehicle underbody is still a significant problem in the environment of a buried-mine blast impulse. The first part of this study presents an algorithm that can be used to simulate a shallow-buried-mine blast. Models using the multiple-material arbitrary Lagrangian–Eulerian algorithm and the initial-impulse mine algorithm respectively were constructed on the basis of experiments carried out by Anderson et al. The accuracy and superiority of the initial-impulse mine algorithm were proved by comparing the results for the jump velocity and the computation time. The second part introduces a blast experiment on a full-scale armoured vehicle. The occupant was represented by a Hybrid III 50th-percentile adult-male dummy. A numerical model was established using the initial-impulse mine method; the seat position represented the worst-case situation, which was same as for the experiments. A comparison of the experimental data and the simulation results, which include the peak acceleration of the floor and the force to which the dummy’s tibia is subjected, showed good agreement.
Estimation of the air charge and the volumetric efficiency is one of the most challenging tasks in the control of internal-combustion engines owing to the intrinsic complexity and the non-linearity of the gas flow phenomena. In particular, with emerging new technologies such as systems with variable valve timing and variable valve lift, the number of effective parameters increases greatly, making the estimation task more complicated. On the other hand, using a three-way catalyst converter needs strict control of the air-to-fuel ratio to around the stoichiometric ratio, and hence more accurate models are required for estimation of the air charge. Therefore, various models have been proposed in the literature for estimation of the volumetric efficiency and the air charge. However, they are either strictly based on physical first principles, making them impractical for conventional applications, or nearly fully empirical and need many experimental data for calibration. In this paper, using a novel approach, a new semiempirical model is proposed for estimation of the volumetric efficiency, which is calibrated with very few experimental data and can be used easily for real-time applications. In addition to the valve timings, the engine speed and the intake manifold pressure, the inlet valve lift is also considered as the model input. The generalizability of the model is proved by applying it to estimate the volumetric efficiency of six different engines. Furthermore, a systematic approach is taken to simplify the proposed model and to strengthen its prediction capability. The result is a simple, practical and generalizable model which can be used for various spark ignition engines, can be trained with very few data and can be utilized for estimating accurately the volumetric efficiency in real-time applications.
To address the abnormal noise problem of single-cylinder gasoline engines in the idle condition, acoustic spectral and intensity analysis was carried out. Then the noises were identified as valve impact noises caused by the anomalous dynamic performance of the engine valve mechanism. To improve further the dynamic performance of the mechanism by optimization of the valve spring, a multi-body dynamic model of the valve mechanism was developed on the basis of the key performance and the structure parameters of the valve spring. By using the optimization strategy, the oscillation amplitude of the valve spring and the valve impact force can be reduced by about 62.5% and 27% respectively. Finally, optimized sample pieces were produced for acoustic verification tests. The obtained results showed that the engine’s overall working noise was reduced by about 2.0 dB(A), and the sound quality of the engine was determined using both objective measurements and subjective evaluation of the noise, vibration and harshness performance. It can be concluded that the valve impact noise can be reduced by optimization of the valve springs.
As is known, estimation of the dynamic states of a vehicle plays an important role in safety control, but it is difficult to obtain the vehicle states accurately without expensive measurement instruments because of the non-linear and huge hysteretic characteristics. Nowadays, many methods have been adopted to solve this problem, the results of which are not ideal because it is assumed that the key parameters are constant, in particular in severe manoeuvres. This paper develops a novel estimation method for the vehicle states using the extended Kalman filter with a fusion algorithm. First, the optimal key parameters (the equivalent roll stiffness and the equivalent roll damping) are identified by genetic algorithms using the data from the relationship between the key parameters and the vehicle real-time states. Then, a novel non-linear observer for the side-slip angle and the roll angle is established on the basis of a four-degree-of-freedom vehicle model by utilizing the identified key parameters and the sensors mounted on normal vehicles. The performance of the observer is investigated using both simulations and real-vehicle experiments. The results demonstrate the reasonable accuracy of the estimation method proposed in this paper.
The adhesion coefficients of a bisectional road have significant coupled influences on the shimmy characteristics of the front wheels of a vehicle. A four-degree-of-freedom model for a representative sport utility vehicle was established. This model considered the adhesion coefficients of a bisectional road and the friction of the steering system of the suspension. The existence and stability of the system’s limit cycles were qualitatively determined using the Hopf bifurcation theorem and the centre manifold theory based on the model. The influences of the adhesion coefficients on the Hopf bifurcation characteristics of the system were calculated using a numerical method. The results showed that the road adhesion coefficient μ1 of the left front wheel and the road coefficient μ2 of the right front wheel significantly affected the vehicle shimmy and coupling relationship when different. Keeping μ1 at a certain value, the swing angles and the angular velocities of the two front wheels consistently decreased when μ2 decreased. The phenomenon repeatedly occurred when the difference μ between the adhesion coefficients increased. Moreover, the discrepancy between the amplitude of the left front wheel and the amplitude of the right front wheel is much more apparent when both the adhesion coefficients are larger. Good agreement between the shimmy characteristics of the two wheels was also found when comparing the results using the centre manifold reduced-dimensions method with the numerical method. Furthermore, a higher reduced order caused the reduced system to be closer to the original system.
Conventional vehicle electronic stability control requires one steering-wheel angle sensor, one lateral acceleration sensor and one yaw rate sensor to obtain a good control performance. The control system stops working when a sensor fault is detected, which means that the vehicle runs in an unprotected state. Thus, various sensor fault diagnosis algorithms have been designed to detect and isolate the faulty sensor, but these algorithms also can be used for fault-tolerant control to preserve the safety of the vehicle. However, determining which of the different sensors is faulty is very difficult as the conventional residual comparison algorithm can only find the existence of a sensor fault but cannot locate the faulty sensor, and very few research studies have focused on this problem. In this paper, an ingenious sensor fault diagnosis algorithm is proposed. The sensor fault is detected, located and isolated by cross-checking with three different yaw rate estimates. The steering-wheel angle observer and the lateral acceleration observer are designed to provide corresponding estimated sensor signals which are employed to estimate the different yaw rates by using an extended Kalman filter. A novel decision-making process is carefully designed to locate the faulty sensor based on the different yaw rate residuals. Electronic stability control is not interrupted as the faulty sensor signal is reconfigured by the estimated signal. Experimental tests on a real car show that the proposed algorithm is efficient for detecting the sensor fault and identifying which sensor is faulty. Simulations show that the vehicle stability control strategy based on the proposed sensor fault-tolerant control algorithm has a better performance than the traditional control strategy does.
A gyroscopic system is designed and utilized as an actuator for the prevention of vehicle rollover. The vehicle motion before rollover and during rollover is considered in two phases: before lift-off of the wheels and after lift-off of the wheels. The lateral load transfer ratio is used to identify the time when the wheels lift off the ground. Based on the equations of motion for the vehicle on two wheels, an imminent rollover algorithm is designed to specify the rollover risk. A fuzzy controller that determines the required roll moment to stabilize the vehicle is designed. A gyroscopic package is designed to apply the corrective roll torque directly on the rolling mass of the vehicle in the opposite direction to the rollover moments. The performance of the proposed system is investigated by simulating some severe manoeuvres, and the results show that the system is able to stabilize the vehicle successfully.
In this paper, in order to improve the roll stability of an articulated vehicle carrying a liquid, an active roll control system is utilized by employing two different control methods. First, a 16-degree-of-freedom non-linear dynamic model of an articulated vehicle is developed. Next, the dynamic interaction of the liquid cargo with the vehicle is investigated by integrating a quasi-dynamic liquid sloshing model with a tractor–semitrailer model. Initially, to improve the lateral dynamic stability of the vehicle, an active roll control system is developed using classical integral sliding-mode control. The active anti-roll bar is employed as an actuator to generate the roll moment. Next, in order to verify the classical sliding-mode control performance and to eliminate its chattering, the backstepping method and the sliding-mode control method are combined. Subsequently, backstepping sliding-mode control as a new robust control is implemented. Moreover, in order to prevent both yaw instability and jackknifing, an active steering control system is designed on the basis of a simplified three-degree-of-freedom dynamic model of an articulated vehicle carrying a liquid. In the introduced system, the yaw rate of the tractor, the lateral velocity of the tractor and the articulation angle are considered as the three state variables which are targeted in order to track their desired values. The simulation results show that the combined proposed roll control system is more successful in achieving target control and reducing the lateral load transfer ratio than is classical sliding-mode control. A more detailed investigation confirms that the designed active steering system improves both the lateral stability of the vehicle and its handling, in particular during a severe lane-change manoeuvre in which considerable instability occurs.
Among all the ancillary loads of a vehicle, the air-conditioning system accounts for the majority of fuel consumption, and its performance significantly affects the fuel economy of the vehicle. Topological similarities between the electrical system and the air-conditioning system can be utilized to formulate a new mild hybrid technique in which the compressor is treated as an energy conversion device and the evaporator as an energy storage device. Thus, the free kinetic energy during vehicle deceleration is harvestable by the air-conditioning system, provided that the on–off sequence of the clutch command is synchronized to the occurrence times of deceleration events. Motivated by this conceptualization, we are interested in three problems: first, the way in which the specific energy and the specific power of the evaporator can be measured; second, the types of new feature that the formulated optimization problem has; third, the method that is an appropriate mathematical tool for solving the problem. In order to solve these problems, energy-based models developed for air-conditioning systems with conventional evaporators and storage evaporators using a phase-change material are utilized, because they are physics based and have been validated against experimental data in previous work. A framework similar to that used in the energy management of a hybrid electric vehicle is established, and its unique characteristics are identified. The low-cost method using the air-conditioning system as an energy buffer, which is a very promising mild hybrid technique that has been demonstrated in conventional vehicles, is also applicable to hybrid electric vehicles.
In this paper, a high-resolution visualization technique was used in combination with an extensively validated zero-dimensional model in order to relate the external structure of a diesel spray to the internal properties in the vicinity of the nozzle. For this purpose, three single-hole convergent nozzles with different diameters were tested for several pressure conditions. The analysis of the obtained images shows that the spray width significantly changes along the first few millimetres of the spray. From the high-resolution images obtained, two parameters were evaluated. The first is the external non-perturbed length, where droplet detachment was not observed. The second is a transitional length, which is defined as the axial position where the spray width increases linearly after transient behaviour, making it possible to establish a spray cone angle definition. Furthermore, the internal liquid core length was estimated for these nozzles using an extensively validated zero-dimensional model. The liquid core length proved to be correlated with both the transitional length and the non-perturbed length with a very high degree of reliability. In the case of the transitional length, a quadratic correlation was observed, whereas a linear relationship was confirmed between the liquid core length and the non-perturbed length. The results presented here may help to shed light on better understanding of such a complex process as atomization.
A road grade estimation model which uses the curvature to express the rate of change in the grade is proposed in this paper. The assumption that the rate of change in the road grade equals zero is widely accepted in the field of online road grade estimation. This assumption is reasonable to some extent, but it results in an inevitable time lag in the rolling-hills situation. This paper offers a road curvature estimation method which can be used to express the rate of change in the road grade. The recursive least-squares algorithm is used to the estimate the curvature, and then the Kalman filter is employed to estimate the road grade from the other vehicle states. Field tests are performed on a highway in a mountainous area. The offline road grade is used to analyse the instantaneous error and the time lag. The field test results show that the model performs well in reducing the time lag, especially in periods where the gradient changes rapidly.
Abnormal operating conditions for the timing belt can lead to cracks, fatigue, sudden rupture and damage to engines. In this study, an intelligent system was developed to detect and classify high-load operating conditions and high-temperature operating conditions for timing belts. To achieve this, vibration signals in normal operating conditions, high-load operating conditions and high-temperature operating conditions were collected. Time-domain signals were transformed to the frequency domain and the time–frequency domain using the fast Fourier transform method and the wavelet transform method respectively. In the data-mining stage, 25 statistical features were extracted from different signal domains. The improved distance evaluation method was adopted to select the best features and to reduce the input space for the classifier. Then, the signal features from the time domain, the frequency domain and the time-frequency domain were fed into an artificial neural network to evaluate the accuracy of this designed procedure for detecting inappropriate operating conditions for the timing belt. Based on all these features extracted from the signals in the time, frequency and time–frequency domains, the artificial neural network classifier detected and classified normal operating conditions, high-load operating conditions and high-temperature operating conditions with accuracies of 73.3%, 85% and 89.2% respectively. The classification accuracies using features selected by improved distance evaluation in the signals from the time, frequency and time–frequency domains were found to be 85%, 95.8% and 95% respectively. The results showed that the developed system was capable of detecting and classifying both the normal operating conditions and abnormal operating conditions for the timing belt. The results also suggested that a combination of signal processing and feature selection can significantly enhance the classification accuracy.
Measurements and optimal control are used to study whether the fuel economy of a diesel engine can be improved through periodic control of the wastegate, illustrating how modern optimal control tools can be used to identify non-trivial solutions that can improve performance. The measurements show that the pumping torque of the engine is changed when the wastegate is controlled in a periodic manner versus stationary even if the mean position is the same. If this decreases the fuel consumption or not is seen to be frequency and operating point dependent. The measurements indicate that the phenomenon occurs in the time scales capturable by mean value engine models (MVEM). The operating points are further analyzed using a MVEM and optimal control. It is shown that whether the optimal solution exhibits periodic oscillations or not is operating point dependent, but is not due to the instantaneous nature of the controls. Even if an actuator model is added the oscillations persist for reasonable time constants, the frequency of the oscillations is however affected. Further it is shown that the periodic control can be predicted by optimal periodic control theory and that the frequency of the control affects the resulting efficiency.
This study investigates the limited-slip and steering characteristics of a dual continuously variable transmission system. The dual continuously variable transmission is a unique final drive system composed of two continuously variable transmissions, with one continuously variable transmission connected to each rear wheel. In this study, a dynamic model of the dual continuously variable transmission system is derived, and models of the conventional final drive systems, i.e. the solid axle and the open differential, are used as benchmarks. In the simulations, the dual continuously variable transmission model, the solid axle model and the open differential model are applied to a vehicle dynamic model for split-μ road tests and a series of steering tests. According to the results of the split-μ road tests, the limited-slip function of a dual continuously variable transmission system is verified. The results of the steering tests show that different torque distributions for the inside wheels and the outside wheels while cornering can be controlled with different gain values of the continuously variable transmissions; for this reason, the application of the dual continuously variable transmission system as a torque-vectoring device is proposed, and a basic setting principle is presented. The results of this study establish a fundamental knowledge for developing the dual continuously variable transmission as an advanced final system for improving the vehicle dynamics.
Driving electric vehicles by electric motors can result in many unique advantages for dynamic control of electric vehicles. With the superior fast and accurate torque control performance of electric motors, electric vehicles, in particular, can achieve higher levels of safety and handling performance. A simple, effective and efficient anti-skid control method specified for electric vehicles is proposed in this paper by considering the real-world resistance factors. This method is developed on the basis of sensing and regulating a newly defined parameter, namely the ratio of the drive motor torque to the angular acceleration of the wheels, both of which can be easily obtained for electric motors. The monotonic relationship between the slip ratio and the ratio of the drive motor torque to the angular acceleration of the wheels is proved under both acceleration conditions and deceleration conditions, by considering the real-world resistance factors. The simulations and the experimental results show that the ratio of the drive motor torque to the angular acceleration of the wheels can be efficiently used, instead of the slip ratio, in anti-skid control. The results indicate that electric vehicles can achieve high-performance vehicle motion control with more flexible and simplified configurations by using in-wheel electric motors.
Cast iron brake discs are commonly used in the automotive industry, and efforts are being made to gain a better understanding of the thermal and mechanical phenomena occurring at braking. The high thermomechanical loading at braking arises from interaction between the brake disc and the brake pads. Frictional heating generates elevated temperatures with a non-uniform spatial distribution often in the form of banding or hot spotting. These phenomena contribute to material fatigue and wear and possibly also to cracking. The use of advanced calibrated material models is one important step towards a reliable analysis of the mechanical behaviour and the life of brake discs. In the present study, a material model of the Gurson–Tvergaard–Needleman type is adopted, which accounts for asymmetric yielding in tension and compression, kinematic hardening effects, viscoplastic response and temperature dependence. The material model is calibrated using specimens tested in uniaxial cyclic loading for six different temperatures ranging from room temperature to 650 °C. A special testing protocol is followed which is intended to activate the different features of the material model. Validation of the model is performed by using tensile tests and thermomechanical experiments. An application example is given where a 10° sector of a brake disc is analysed using the commercial finitie element code Abaqus under a uniformly applied heat flux on the two friction surfaces. The results indicate that the friction surface of the hat side and the neck can be critical areas with respect to fatigue for the uniform heating studied.
Two control strategies for power flow control in hybrid electric vehicles (HEVs) with parallel configuration and a planetary gear system as a power coupling device between the internal combustion engine and the electric machine are proposed in this paper. The aim of both strategies is to determine, for a given driving cycle, an appropriate mixture of the power provided by the two engines. Performance is measured not only in terms of fuel consumption; driving cycle tracking and preservation of energy in the bank of batteries are also considered. The first strategy, named the PGS strategy as it is designed around the planetary gear system, is heuristic, inspired by bang–bang optimal control formulations and has low computational load, while the second is an optimal one derived from Pontryagin’s minimum principle (PMP). It is shown that, under appropriate choice of the weighting parameters in the Hamiltonian of the PMP, both strategies give very similar results and, therefore, that the PGS strategy corresponds to a feasible solution to an optimization problem. Both strategies can be implemented in real time, however, the PGS strategy is easier to tune. Tuning of the strategies’ parameters is independent of the driving cycle. The power flow control laws are continuous and enforce the use of the internal combustion engine with the maximum possible efficiency. The strategies are tested with simulations of a power train of a hybrid diesel–electric bus subjected to the demands of four representative urban area driving cycles. Although optimization solutions are based on simplified dynamic models, simulation results are verified with more detailed dynamic models of the HEV main subsystems. This allows us to evaluate the accuracy of the results and to verify the hypothesis established in the optimization formulation. Simulation results indicate that both strategies attain good fuel consumption reduction levels.
Engine downsizing is a proven approach for achieving a superior fuel efficiency. It is conventionally achieved by reducing the swept volume of the engine and by employing some means of increasing the specific output to achieve the desired installed engine power, usually in the form of an exhaust-driven turbocharger. However, because of the perceptible time needed for the turbocharger system to generate the required boost pressure, a characteristic of turbocharged engines is their degraded driveability in comparison with those of their naturally aspirated counterparts. Mechanical supercharging refers to the technology that compresses the intake air using the energy taken directly from the engine crankshaft. It is anticipated that engine downsizing which is realised either solely by a supercharger or by a combination of a supercharger and a turbocharger will enhance a vehicle’s driveability without significantly compromising the fuel consumption at an engine level compared with the downsizing by turbocharging. The capability of the supercharger system to eliminate the high exhaust back pressure, to reduce the pulsation interference and to mitigate the surge issue of a turbocharged engine in a compound-charging system offsets some of the fuel consumption penalty incurred in driving the supercharger. This, combined with an optimised down-speeding strategy, can further improve the fuel efficiency performance of a downsized engine while still enhancing its driveability and performance at a vehicle level. This paper first reviews the fundamentals and the types of supercharger that are currently used, or have been used, in passenger car engines. Next, the relationships between the downsizing, the driveability and the down-speeding are introduced to identify the improved synergies between the engine and the boosting machine. Then, mass production and prototype downsized supercharged passenger car engines are briefly described, followed by a detailed review of the current state-of-the-art supercharging technologies that are in production as opposed to the approaches that are currently only being investigated at a research level. Finally, the trends for mechanically supercharging a passenger car engine are discussed, with the aim of identifying potential development directions for the future. Enhancement of the low-end torque, improvement in the transient driveability and reduction in low-load parasitic losses are the three main development directions for a supercharger system, among which the adoption of a continuously variable transmission to decouple the supercharger speed from the engine speed, improvement of the compressor isentropic and volumetric efficiency and innovation of the supercharger mechanism seem to be the potential trend for mechanically supercharging a passenger car engine.
Conventional vehicle suspensions suppress vehicle vibrations by dissipating the vibration energy into unrecyclable heat with hydraulic dampers. This can be a considerable amount of energy which is worthy of attention for energy recovery. Electromagnetic regenerative dampers, or shock absorbers, are proposed to harvest this dissipated energy and to improve the fuel efficiency. The suspension dynamics with these regenerative dampers can be significantly different from the suspension dynamics with conventional dampers. First, different from conventional hydraulic dampers, the electromagnetic regenerative dampers have a significantly higher inertia, which is introduced by the electromagnetic generator. This has an important impact on the suspension dynamics. Second, the damping coefficient of electromagnetic dampers is related to the electric load connected to the output of the generator and can be controllable. Although various concepts have been proposed, the influences of these types of regenerative damper on the vehicle dynamics have not yet been thoroughly investigated. This paper models two types of rotational electromagnetic regenerative damper, with and without a mechanical motion rectifier, and analyzes their influences on the vehicle suspension performance in comparison with those of the conventional damper. The modeling in this paper also considers the case when the tires lose contact with the ground. Simulations were carried out with step road profile excitations and road profile excitations defined by the International Standardization Organization in order to evaluate the influences of the equivalent inertia mass and the equivalent damping coefficient. The results showed that, with an optimized equivalent inertia mass, both types of electromagnetic damper can achieve better ride comfort performances than a constant damper does. In addition, the mechanical motion rectifier mechanism can significantly improve the ride comfort and the road-handling performance of electromagnetic regenerative dampers by reducing the negative effect of the amplified generator inertia. In addition, the energy-harvesting potential of the presented dampers under road profile excitations defined by the International Standardization Organization was evaluated.
This paper presents a model-based approach for continuously adapting an engine calibration to the traffic and changing pollutant emission limits. The proposed strategy does not need additional experimental tests beyond those required by the traditional calibration approach. The method utilises information currently available in the engine control unit to adapt the engine control to the particular driving patterns of a given driver. Additional information about the emissions limits should be provided by an external structure if an adaptation to the pollutant immission is required. The proposed strategy has been implemented in a light-duty diesel engine, and showed a good potential to keep NO x emissions around a defined limit.
An important method for saving energy and reducing the emissions from hybrid electric vehicles is to shorten the working time of the engine, which results in frequent engine starts and stops. The accompanying vibration and noise problems cause the driveability and the ride comfort to deteriorate significantly. In this study, experiments on the vibrations of the driver’s seat track are performed and analysed to evaluate quantitatively the vibrations during the engine start. The measurement results show that vibrations in the longitudinal direction are the most severe, whereas vibrations in the lateral direction are the weakest. Based on the test results, a full-vehicle multi-body dynamics model, including the driveline, the powertrain mounts and the suspensions, is developed and verified. Some countermeasures are researched using numerical simulations to reduce the uncomfortable longitudinal vibrations. Optimization analysis demonstrates that the effects of the reduction in the vibrations are limited even by the optimal initial crank angle, the start-up time and the stiffnesses of the torsional damper and the half-shafts. Hence, parameter optimizations cannot completely eliminate the uncomfortable vibrations. Fortunately, as compensation control benefits from the fast response of electric motors in hybrid vehicles, it can play an active role in reducing the longitudinal seat track vibrations and in improving the ride comfort. However, the effect of the compensation controller greatly depends on the accuracy of the torque estimator.
Since improving the energy efficiency and reducing the air pollution are two of the largest issues in the automobile industry, many researchers have developed various combustion and emission technologies to solve these challenges. Among these various technologies, the gasoline–diesel dual-fuel method is of interest to improve the thermal efficiency and to reduce the emissions in diesel engines. The gasoline allows formation of a premixed fuel–air mixture without early ignition owing to its high evaporation rate and low reactivity. In order to investigate the effect of gasoline on the dual-fuel combustion and emission characteristics, combustion of gasoline–diesel blend fuels was simulated in a compression ignition engine by using the KIVA-3V code. For the multi-fuel simulations, a modified KIVA-3V code with a discrete multi-component model was used to represent the multi-fuel evaporation processes. This study showed that the gasoline in the dual-fuel blend improved the fuel–air mixing process to form homogeneous mixtures for the two different injection strategies: port fuel injection and direct injection of gasoline. In addition, the combustion characteristics of gasoline–diesel blend fuel were discussed by comparing them with those of the conventional diesel fuel. The gasoline in the dual-fuel blend increases the indicated power because of the release of high fuel energy and decreases the soot emissions. In this study, various gasoline-to-diesel ratios and various injection timings were used in order to enhance the understanding of the dual-fuel engine. The present study showed that low emissions and a high indicated power were achieved as the gasoline content is increased up to a certain value. However, an increase in the gasoline content in the dual fuel caused the autoignition and the combustion performance to deteriorate.
Air-conditioning and refrigeration systems are extensively adopted in homes, industry and vehicles. An important step in achieving a better performance and a higher energy efficiency for air-conditioning and refrigeration systems is a control-based model and a suitable control strategy. As a result, a dynamic model based on the moving-boundary and lumped-parameter method is developed in this paper. Unlike existing models, the proposed model lumps the effects of the fins into two equivalent parameters without adding any complexity and considers the effect produced by the superheated section of the condenser, resulting in a model that is not only simpler but also more accurate than the existing models. In addition, a model predictive controller is designed on the basis of the proposed model to enhance the energy efficiency of the air-conditioning and refrigeration systems. Simulations and experimental results are presented to demonstrate the accuracy of the model. The experiments show that an energy saving of about 8% can be achieved by using the proposed model predictive controller compared with the conventional on–off controller under the examined scenario. The better performance of the proposed controller requires electrification of the automotive air-conditioning and refrigeration systems so as to eliminate the idling caused by running the air-conditioning and refrigeration systems when a vehicle stops.
Numerical investigations are carried out to investigate the reduction in the aerodynamic drag of a vehicle by employing a dimpled non-smooth surface. The computational scheme was validated by the experimental data reported in literature. The mechanism and the effect of the dimpled non-smooth surface on the drag reduction were revealed by analysing the flow field structure of the wake. In order to maximize the drag reduction performance of the dimpled non-smooth surface, an aerodynamic optimization method based on a Kriging surrogate model was employed to design the dimpled non-smooth surface. Four structure parameters were selected as the design variables, and a 16-level design-of-experiments method based on orthogonal arrays was used to analyse the sensitivities and the influences of the variables on the drag coefficient; a surrogate model was constructed from these. Then a multi-island genetic algorithm was employed to obtain the optimal solution for the surrogate model. Finally, the surrogate model and the simulation results showed that the optimal combination of design variables can reduce the aerodynamic drag coefficient by 5.20%.
Energy security concerns and an abundant supply of natural gas in the USA provide the impetus for engine designers to consider alternative gaseous fuels in the existing engines. The dual-fuel natural-gas diesel engine concept is attractive because of the minimal design changes, the ability to preserve a high compression ratio of the baseline diesel, and the lack of range anxiety. However, the increased complexity of a dual-fuel engine poses challenges, including the knock limit at a high load, the combustion instability at a low load, and the transient response of an engine with directly injected diesel fuel and port fuel injection of compressed natural gas upstream of the intake manifold. Predictive simulations of the complete engine system are an invaluable tool for investigations of these conditions and development of dual-fuel control strategies. This paper presents the development of a phenomenological combustion model of a heavy-duty dual-fuel engine, aided by insights from experimental data. Heat release analysis is carried out first, using the cylinder pressure data acquired with both diesel-only and dual-fuel (diesel and natural gas) combustion over a wide operating range. A diesel injection timing correlation based on the injector solenoid valve pulse widths is developed, enabling the diesel fuel start of injection to be detected without extra sensors on the fuel injection cam. The experimental heat release trends are obtained with a hybrid triple-Wiebe function for both diesel-only operation and dual-fuel operation. The ignition delay period of dual-fuel operation is examined and estimated with a predictive correlation using the concept of a pseudo-diesel equivalence ratio. A four-stage combustion mechanism is discussed, and it is shown that a triple-Wiebe function has the ability to represent all stages of dual-fuel combustion. This creates a critical building block for modeling a heavy-duty dual-fuel turbocharged engine system.
Recently, an active safety system based on vehicle-to-vehicle communication was introduced to minimize the threat of car accidents on the road and to overcome the limitations of the current sensor-based advanced driver assist system. In order to implement the system based on vehicle-to-vehicle communication, target classification is the key layer to be developed. In this study, based on the transmitted path history of the remote vehicles, the road geometry around the host vehicle is reconstructed without in-vehicle sensors such as vision cameras. A tracking algorithm for the remote vehicle is formulated in order to predict its position continuously by using an extended Kalman filter. A local map is obtained with an outlier filter, and the target classification algorithm is designed from vehicle-to-vehicle communication data. The proposed algorithms are validated by simulations and experiments carried out using test vehicles.
A multi-chamber perforated resonator is a type of silencer which can attenuate broadband noise. In order to address the noise issues originating from the intake system of a turbocharged engine, measurement tests are carried out to characterize the range and the amplitudes of the noise frequencies. A transfer matrix method and a non-linear least-squares optimization algorithm are combined in order to design the multi-chamber perforated resonator. A transmission loss test facility is designed on the basis of the two-load method so as to validate the acoustic performance of the resonator. Despite the difference between the amplitude of the transmission loss from the tests and the amplitude of the transmission loss obtained by the transfer matrix method, the shapes of the two curves have the same trend, and the measured transmission loss can meet the design target in the frequency range of interest. From the comparison between the intake noise spectrum with the resonator and the intake noise spectrum without the resonator, it can be seen that this resonator can efficiently attenuate the broadband intake noise of the engine. Also, a computational fluid dynamics flow simulation analysis of the intake system with the resonator is made so that its flow characteristics can be studied. The simulation results show that the air pressure drop of this resonator is slightly higher than that of the straight pipes but is still relatively low. It is also noted that the diameter and the curvature of the pipes have a great influence on the air velocity as well as on the pressure drop.
Engine tests were conducted to investigate the efficiency and the peak pressure rise rate performance of different fuel injection strategies for the direct injection of neat n-butanol in a compression ignition engine. Three different strategies were tested: a single-shot injection; a pilot injection; a post-injection. A single-shot injection timing sweep revealed that early injections had the highest indicated efficiency while late injections reduced the peak pressure rise rate at the cost of a slightly reduced thermal efficiency. Delayed single-shot injections also had increased emissions of nitrogen oxides, total hydrocarbon and carbon monoxide. Addition of a pilot injection had a negative effect on the peak pressure rise rate. Because of the low cetane number of butanol and the relatively lean and well-premixed air–fuel mixture, the pilot injection failed to autoignite and instead ignited simultaneously with the main injection. This resulted in slightly increased peak pressure rise rates and significantly increased unburned butanol hydrocarbon emissions. Conversely, the use of an early post-injection produced a noticeable engine power output and allowed the main injection to be shortened and the peak pressure rise rate to be substantially reduced. However, relatively early post-injections slightly reduced the indicated efficiency and increased the nitrogen oxide emissions and the carbon monoxide emissions compared with the single-shot injection strategy. These results recommended the use of a single-shot injection for low loads and medium loads owing to a superior thermal efficiency and suggested that the application of a post-injection may be more suited to high-load conditions because of the substantially reduced peak pressure rise rates.
The airbag is an occupant protection device widely used in the automotive industry. Federal Motor Vehicle Safety Standard 208 requires the low-risk deployment airbag system to be utilized in vehicles to protect out-of-position occupants. This paper presents a design-for-six-sigma low-risk deployment passenger airbag optimized by adding a passenger protection wrap. The passenger protection wrap reduces the cushion impact force on the passenger by ensuring pressure dispersion. A series of static tests were conducted to demonstrate the proposed system using Federal Motor Vehicle Safety Standard 208 test procedures. The test results shows that the proposed passenger airbag satisfies the criteria established by Federal Motor Vehicle Safety Standard 208 and also presents a significant improvement over conventional airbag systems.
A two-dimensional analytical approach is developed to study the acoustic behaviour of a multi-chamber reactive muffler. The value of the transmission loss is obtained by matching the acoustic pressure and the particle velocity across the interfaces between different domains in the muffler. The analytical approach is validated by experimental results. Unlike the transfer matrix method, with this approach the acoustic behaviours can be studied above the first cut-off frequency of the muffler. Next, the effects of several structural parameters on the transmission loss value are invetigated, including the radii of the baffle holes, the inlet and the outlet, as well as the lengths and the radii of the expansion chambers. The variations in these parameters lead to quite large changes in the value of the transmission loss of the multi-chamber reactive muffler. Then, these parameters are chosen as the variables for the optimal design of the muffler, where the objective is the average transmission loss value between 1000 Hz and 3000 Hz. The results show that the objective value increases from 23.3 dB to 54.9 dB during optimization. The analytical approach in this paper can be used for analysis and optimization of the multi-chamber reactive muffler to reduce the noise effectively and efficiently in various applications.
In this paper, fatigue damage analysis and structural improvement of a commercial vehicle cab were carried out, in which a simulation technique and durability road tests were combined. A full-scale finite element model of the cab was established and then validated by means of physical testing and analysis of its stiffness and its modal performance. The loading spectra, in accordance with the durability road test, were obtained by adopting the virtual iteration method. With the established finite element model, the stress distributions in the cab under unit excitation were determined. The obtained stress distributions were then used to assess the total fatigue life of the cab by employing the strain–life (–N) method; thus, the critical regions were determined. The results showed that some components near the pillars and mounts are easy to damage because of the stress concentrations. It was also demonstrated that the predicted regions are reliable, which was verified by comparison with the physical durability road tests. Finally, structural improvements in the critical structures were made; the fatigue life assessment of the improved cab showed an obvious improvement in its durability performance.
A power management strategy is a key necessity for power-split electromechanical transmission systems. A model predictive control strategy which is based on finite-horizon optimization and can combine the advantages of instantaneous optimization and global optimization is a good solution for online optimization of the power management. Therefore, a model-predictive-control-based power management strategy is proposed for a two-mode electromechanical transmission. A model predictive control strategy consists of two parts: a predictive model and a receding-horizon optimization algorithm. A predictive model is used for predicting future information on the electromechanical transmission states, and real-time receding-horizon optimization with a finite horizon is adopted for optimal decision making. First, the predictive model, including the battery state and the transmission output torque, which provides a priori knowledge for optimal calculation, is proposed. Then, to ensure optimal operating areas of the engine and the motors, a novel overall efficiency calculation method for the whole powertrain including the engine, the motors, the power-split coupled machine and the battery is proposed and regarded as the optimization objective. The overall efficiency not only is focused on the engine fuel economy but also determines the power loss of the motors, the battery and the planetary gears together, which enhances the fuel economy and the transmission efficiency significantly. Based on the predictive model and receding-horizon optimization, the MPC strategy is established and tested by hardware-in-the-loop simulations under Urban Dynamometer Driving Schedule and New European Driving Cycle conditions. The test results showed that the power management strategy can enhance the fuel economy and proved to be a potential real-time optimization method for power distribution in the electromechanical transmission system; this strategy can provide theoretical support for actual application of electromechanical transmission systems.
The Sunswift project of the University of New South Wales, Australia, exists to provide university students with a multi-disciplinary engineering challenge, enhancing the true educational value of their degree with a unique hands-on real-world experience of creating solar–electric hybrid vehicles. The design and development of the low-drag ‘solar supercar’ Sunswift eVe car are described here, detailing the student-led process from initial concept sketches to the completed performance vehicle. eVe was designed to demonstrate the potential of effective solar integration into a practical passenger-carrying vehicle. It is a two-seater vehicle with an on-body solar array area of 4 m2 and a battery capacity of 16 kW h, which is capable of sustained speeds over 130 km/h and a single-charge range of over 800 km. Carbon fiber was used extensively, and the components were almost all designed, built, and tested by students with industry and academic mentorship. The eVe project was initiated in mid-2012, and the car competed in the 2013 World Solar Challenge, taking class line honours. It subsequently set a Fédération Internationale de l’Automobile land speed record in 2014 for the fastest average speed of an electric vehicle over 500 km; it is now the team’s intent to develop the car to road-legal status.
Water medium retarders are auxiliary braking devices which can reduce the vehicle speed by converting the mechanical energy of a driving vehicle to the total energy of the working fluid. These retarders can replace service brakes in non-emergency braking conditions. This study analysed the dynamic and thermodynamic characteristics of water medium retarders. An observer was designed to identify the optimal braking power of the water medium retarder under different braking conditions. The braking process involving the retarder can be divided into three stages. The controller was designed separately at each stage to control the braking torque of the water medium retarder according to braking requirements. A combined dynamic and thermodynamic vehicle model was also constructed with MATLAB/Simulink. The effects of the controller on the vehicle feedback control system were analysed. The results show that the controller equipped with the observer can effectively control the water medium retarder to satisfy the braking requirements of vehicles on the assumption that the coolant circulation is sufficiently radiated. Finally, an experiment was conducted to determine the performance of the controller and to validate the simulation results.
This paper presents a method of identifying the dynamic characteristics of tyres for non-steady-state conditions on the basis of road measurements on a vehicle. The side force acting on the tyre is presented as a function of not only the slip angle but also the slip angle derivative (i.e. the velocity of the change in the slip angle). Hence, the influence of the manoeuvre dynamics on the tyre characteristics and the difference between the characteristics obtained for steady-state conditions and the characteristics for non-steady-state conditions are shown. Also the results of computer simulations prepared for different types of tyre characteristics are presented in this paper. It is evident from the presented graphs that applying dynamic non-linear tyre characteristics for computer simulations instead of steady-state characteristics enables us to describe the real motion of a vehicle better.
This paper proposes a modified bilinear tyre force model for simulations of the vehicle dynamics, which is the core part in reconstruction analysis of vehicle collision accidents. The physical parameters involved were estimated using a statistical method based on experimental test results of the tyre forces. With an appropriate setting of the input data related to a tyre blowout, a simulation analysis of the dynamics of the vehicle which had suffered the tyre blowout was performed. The developed simulation analysis results for the dynamic behaviour of a vehicle with normal tyres with total locks or with a one-wheel lock and for vehicles with tyre blowouts when driving straight or turning corresponded well to the results of other commercial programs. The reliability of these results was proved by comparing them with the corresponding data for many vehicles involved in blowout-related accidents and in particular the path travelled by those vehicles as recorded on black-box footages.
In this paper, the effects of the injection timing, the injection pressure and the engine load on the combustion noise of a pilot-ignited direct-injection natural-gas engine were explored by analysing the separate components of the in-cylinder pressure. The results suggested that retarding the injection timing and reducing the injection pressure are effective ways of controlling the combustion noise. This can be attributed to the promoted burning rate at advanced injection timings and to the increased injection pressure. However, the effect of the engine load seems to be less obvious, although the resonance pressure level appears to increase with increasing engine load; the estimated combustion noise shows a decreasing tendency.
The rectilinear rear independent suspension investigated in this paper benefits from its excellent kinematic characteristics. Because of the over-constraints of the rectilinear rear independent suspension as a rigid-flexible coupled multi-body system, its elastokinematics are heavily dependent on the compliance characteristics. This paper proposes an efficient approach to establish its elastokinematic model based on the transfer matrix method. First, the overall system transfer equation of the rectilinear rear independent suspension is established. Then, the statics equation is obtained by introducing external loads and expanding the overall system transfer equation. Different configurations of rubber bushings are discussed with respectg to the natural frequency and the static deflections. Comparisons between numerical simulations and kinematic and compliance tests not only verified the approach but also demonstrated the excellent wheel alignment capacity of the rectilinear rear independent suspension.
Because of various environmental factors (e.g. road type and traffic congestion) and the involvement of human action (e.g. drowsiness and consciousness level), the time-variant nature of the car-following process necessitates the use of adaptive modelling approaches. In contrast with the existing car-following models with a fixed structure, this paper proposes an adaptive framework based on an online local linear neuro-fuzzy model, supported by a recursive singular spectrum analysis signal-processing technique, to model the time-variant car-following behaviour in a microscopic traffic flow. The online local linear neuro-fuzzy model is initially trained by a set of offline data and then is adapted to the car-following data by means of an adaptive weighted least-squares technique. Furthermore, the recursive singular spectrum analysis technique is employed to decompose the traffic data in an online manner and then to remove useless components (e.g. the measurement noise) to produce well-behaved data. The proposed synergistic approach is applied to real-world car-following data, collected at the Hollywood freeway section of the US 101 Highway. The empirical results demonstrate that the developed approach successfully describes the car-following behaviour while conventional offline models fail in the case of large variations in the traffic data or congestion in the traffic flow.
The performance of an internal-combustion engine is directly related to the fuel quantity that can react with the oxygen in the air during the exothermic oxidation step, also called combustion. Thus, the amount of fuel introduced is intrinsically linked to the air volume that can be admitted into the cylinder (air filling of the cylinder). Hence keeping the air in the cylinder is one of the most important concepts to predict in simulations. Nevertheless, the phenomenon of air filling depends on many parameters. Also, the discharge coefficients, and the impact of the piston presence near the valves on the flow, during valve overlap are investigated. For this, a digital flow bench is constructed to reproduce a series of tests carried out on a flow test bench functioning as a result of the reduction in the pressure. In this paper, the engine studied is a 125 cm3 single-cylinder four-stroke atmospheric type with two valves. Thus, the idea of this paper is to treat the case of engines with large valve overlaps as small engines or engines with variable valve timing. First, traditional tests through a single valve are performed. The forward and reverse directions are systematically tested to ensure proper operation of the digital testing, and to determine the differences between tests and simulations in the case of conventional configurations. Then, the flow through the entire cylinder head, i.e. the intake valve–cylinder with piston–exhaust valve system, is tested and studied. The aim is to compare the results obtained by the tests and the simulations during the valve overlap period. Significant differences were highlighted between the rates measured in one-dimensional simulations and in the tests. It was noteworthy that the one-dimensional code overestimated the mass passing through the system during valve overlap by about one fifth of the estimated mass passing through the system from the results obtained with the test rig.
In this study, a two-stroke outboard engine was modified to accommodate two direct fuel injectors for reactivity-controlled compression ignition combustion in one cylinder, while the production direct-injection spark ignition combustion system was maintained in the other cylinder. This setup enabled direct comparisons of the performances at equivalent operating conditions. The engine’s octane requirement for homogeneous charge compression ignition combustion was studied with primary reference fuels for ranges of engine speed, load, and delivery ratio. The resulting primary reference fuel requirement was used to determine the baseline ratio of low-reactivity fuel to high-reactivity fuel. Experiments using gasoline and diesel fuel were unsuccessful as they resulted in unstable combustion and rapid accumulation of particulate matter in the emissions-sampling equipment. Reactivity-controlled compression ignition experiments with gasoline and n-heptane (higher volatility) proved to be successful. The low-reactivity fuel fraction and the high-reactivity start-of-injection timing were found to be independent combustion-control levers. At 1500 r/min, an indicated mean effective pressure of 2.5 bar and nitrogen oxides emissions of 1.25 g/kW h, reactivity-controlled compression ignition resulted in a lower coefficient of variation in the indicated mean effective pressure, lower carbon monoxide emissions and a significantly higher gross indicated efficiency than those for the direct-injection spark ignition homogeneous mode and the direct-injection spark ignition stratified mode (36.3% versus 27.0% and 25.7% respectively); at 1200 r/min, an indicated mean effective pressure of 2.0 bar and hydrocarbon + nitrogen oxide emissions of about 16.5 g/kW h, the reactivity-controlled compression ignition efficiency was still significantly better than those for the direct-injection spark ignition homogeneous mode and the direct-injection spark ignition stratified mode (32.9% versus 25.2% and 26.6% respectively). Overall, the viability of reactivity-controlled compression ignition combustion in a two-stroke engine was demonstrated; with further design optimization, it will probably be possible to use a standard diesel fuel instead of n-heptane.
By optimizing the aerodynamic shape parameters, the aerodynamic performance of the vehicle becomes better as the aerodynamic drag decreases. The driving stability also becomes better as the aerodynamic lift decreases. This research presents aerodynamic shape optimization which employs the multi-variable parametric model and the iterative optimal approach to reduce the aerodynamic drag and the aerodynamic lift. For aerodynamic studies with computational fluid dynamics simulations, a parametric surface grid model was used to morph and enhance the mesh quality by linear deformation of the exterior surfaces. This method employed the radial basis function model, and integrated optimization with multi-software provides excellent morphing ability and reasonable optimal designs. In this paper, the process of aerodynamic optimization for a vehicle body is divided into two phases. The first phase is two-dimensional body optimization aimed at a global search, and the second phase aims at a local approximation by running three-dimensional body optimization. The iterative optimal approach can optimize efficiently the aerodynamic characteristics with a reduction in the aerodynamic drag of 13.23% and a marked improvement in the aerodynamic lift. Sensitivity analysis of the design parameters demonstrated that the hood angle is the major factor in the aerodynamic drag coefficient CD. For the aerodynamic lift coefficient CL, the trunk lid angle is the major factor. In addition, the angle of the windshield and the angle of the side window have small influences on CL. The results obtained are accurate reference values for application in automotive engineering.
This paper describes an advanced braking algorithm for robust longitudinal risk management to prevent or mitigate rear-end collisions. Since the proposed safety system works in conjunction with a human driver, the longitudinal safety system must be acceptable to the driver. The key to achieving this is to ensure that control signals are given at the appropriate time. In order to construct an suitable control system, a new longitudinal safety index was developed by using the time to collision and the warning index, which are well-known safety parameters in longitudinal safety control. The clearance and the relative velocity constitute essential signals for safety monitoring in longitudinal safety control. These measured sensor signals include the uncertainty in the measurement noise. To design a robust safety monitoring and control mode decision, information consisting of fusion of the measurement signals was obtained. In addition, an expected error range of the proposed safety index from the measurement noise can be defined from the covariance matrix of the Kalman filter and the deviation of the function of the new longitudinal safety index. The control performance of the proposed algorithm was evaluated by analysis of the simulation results. From this analysis, it can be concluded that the proposed advanced braking algorithm can substantially enhance the longitudinal safety and can guarantee a robust performance with respect to the sensor uncertainty.
This paper presents a thermodynamics-based mean-value engine model that predicts the temperature and pressure at the end of each discrete combustion phase, the peak temperature and pressure, and the indicated mean effective pressure. The model has sensitivities to the engine speed, the main and pilot injection quantities and timings, and the temperature and pressure conditions in the intake and exhaust manifolds. Mathematical relationships are established between the input variables and the output variables through the thermodynamic principles of the modified ideal-gas-limited pressure cycle. Modifications to the ideal-gas cycle include the pilot combustion stage, the effective compression ratio based on the fuel injection timing and start of combustion, the effect of the constant-volume burn ratio on combustion, and the exhaust valve opening timing. The model is also augmented with empirical correlations for the ignition delay, the constant-volume burn ratio, and the heat transfer in order to improve the fidelity of the model. It is validated using test data from a Ford 6.7 l diesel engine. Unlike most data-regression-based mean-value engine models, the model presented in this paper does not sacrifice essential details of the underlying physics while providing a computationally efficient simulation tool.
The objective of the article is to develop an analytical model to investigate the dynamic behaviour of an automotive powertrain during gearshifts. First, an integral model is proposed by incorporating lumped-mass component models, and its compatibility with previous control-oriented models is experimentally validated. Second, gearshifts that induce dynamic behaviour including clonk, contact loss and clutch stick–slip are numerically simulated. The mechanism and impact source of the dynamic behaviour and also the coupling characteristic between different dynamic behaviours are studied. The dynamic characteristics of the behaviour are studied by obtaining the wavelet transform of the output torque. Finally, the impacts of the system parameters on the dynamic behaviour are examined by using the proposed model.
The development of advanced riding assistance systems requires the analysis of user reactions in emergency situations. Motorcycle riding simulators are an alternative to ‘on-road’ testing so that virtual environment dangerous scenarios can be investigated without risks for the participants. In this paper, we propose a process for validation of a low-cost motorcycle simulator characterized by, first, an elastic resistance on the steering input and, second, a counter-steering strategy. For this, 16 riders tested the simulator in different manoeuvres, including a cornering manouvre in a non-urban environment, a slalom manoeuvre and a lane-change manoeuvre. Objective evaluations and subjective evaluations showed that the simulator was realistic, in particular for investigating lateral avoidance scenarios. The development of suitable motorcycle simulators will significantly advance the field of motorcycle safety research.
To solve the oil shortage and emission problems resulting from millions of conventional vehicles driven by engines, vehicle electrification has become one of the possible solutions recognized worldwide. A model-predictive-control-based anti-skid method for electric vehicles is presented in this paper. In this control strategy, a novel single parameter, denoted Rat, is regulated to constrain the skid of the vehicle. Rat is the ratio of the wheel acceleration to the drive motor torque, both of which are easy to obtain for electric motors. It is proved in this paper that, for electric vehicles, the wheel slip can be detected using the new parameter Rat. Model predictive control is employed in this research to restrict Rat within its safety region. Both the simulation results and the experimental results show that the model predictive control Rat method introduced in this paper can detect and prevent the potential skid of the electric vehicles.
The hydraulic power-split architecture, or the hydromechanical transmission, can exist in over 1000 configurations. Since a specific hydromechanical transmission configuration has a unique kinematic characteristic, the optimal hydromechanical transmission configuration for one application is different from the optimal hydromechanical transmission configurations for other applications. This study finds the optimal hydromechanical transmission configuration for a hybrid hydraulic city bus. Since a hydromechanical transmission uses at least one planetary gear set, the process of finding a suitable hydromechanical transmission configuration for a hybrid hydraulic city bus is very time consuming, but this study simplifies the procedure by utilizing the critical speed ratio crit, where crit is the missing link between the planetary gear set configuration, its gear ratio and its kinematic characteristic. This simplification also allows complex dual-stage hydromechanical transmission architecture configurations to be considered as candidates for the optimal drivetrain of the hybrid hydraulic city bus. The hydromechanical transmission configuration candidates are simulated over three city bus driving cycles and, to ensure that they operate at the optimal conditions for each driving cycle, dynamic programming is used. This study also establishes two power recirculation modes, one of which is useful because of its high efficiency. A single-stage power-split architecture configuration candidate is found to be the optimal drivetrain for a hydromechanical transmission bus.
The prediction of the wet-clutch service life still remains a challenge for scientists and engineers. Previous research has shown the significance of the wet-clutch friction characteristics on the driveline dynamics. To avoid driveline vibrations an increasing friction coefficient with increasing sliding speed is desirable. Consequently, prediction of the occurrence of driveline vibrations relies on a detailed knowledge of how the friction characteristics are affected by wet-clutch degradation, as well as an understanding of the driveline dynamics. Wet clutches are used in both automatic transmissions and all-wheel-drive systems in cars, where they are referred to as limited slip couplings by manufacturers. Wet clutches used in automatic transmissions are subjected to high slip levels, but for very limited time periods. In all-wheel-drive systems, where the limited slip coupling can be used to control the torque transfer to, for example, the rear wheels, the slip levels are low but continuous. Most wet-clutch research has been performed for clutches in automatic transmissions and not for clutches used in all-wheel-drive systems. Thus, a simulation model was developed to evaluate how different operating conditions of the limited slip coupling influence degradation of the friction characteristics and the tendencies towards driveline vibrations. First, the changes in the friction characteristics with the time of ageing are simulated. The friction characteristics after ageing are used as the input to a simplified driveline model, which is used to evaluate the occurrence of vibrations. It is shown how the developed simulation model can be used as an efficient tool for engineers. The developed simulation model can be used to predict how the operating conditions for the limited slip coupling influence degradation of the friction characteristics.
For diesel homogeneous charge compression ignition engines, combustion is unstable during the mode-switching process because of an unfavourable evaporation environment, especially at low speeds. Unusual fluctuations in the net indicated mean effective pressure and a spike in the transient emissions occur in the transitional cycles between modes. In this study, first, experiments were performed to characterize the hydrocarbon emissions during the combustion mode-switching process between homogeneous charge compression ignition and conventional diesel compression ignition. The results showed that the hydrocarbon emissions decreased as the speed increased at a constant load. When the load increased at a constant speed, the hydrocarbon emissions decreased. A spike in the hydrocarbon emissions during the transitional cycles was observed at 1000 r/min when mode switching from homogeneous charge compression ignition to compression ignition. Second, based on the spike phenomenon, a method of fuel adjustment was proposed to eliminate the fluctuations in the net indicated mean effective pressure and the spike in the hydrocarbon emissions in the five transitional cycles. Finally, by regulating the fuel adjustment coefficient in the five transitional cycles, the spike phenomenon of the transient hydrocarbon emissions was eliminated, and the fluctuations in the net indicated mean effective pressure decreased. The coefficient of variation in the net indicated mean effective pressure decreased to 2%.
The motion trajectory optimization method for an intelligent vehicle in the planning and control of the trajectory of an intelligent vehicle under high-speed driving working conditions is difficult to research. In order to ensure that the intelligent vehicle runs steadily under high-speed driving working conditions, an improved-genetic-algorithm-based motion trajectory-planning method was introduced to optimize the generated trajectory. The trajectory optimization method considers the influence of the dynamic constraints to ensure that the vehicle runs steadily under high-speed driving working conditions. First, a B-spline curve is used to parameterize the generated trajectory. Then, the improved genetic algorithm is used to optimize the parameters of the B-spline curve so that the parameterized trajectory satisfies the dynamic constraints and so that the optimized trajectory is feasible. The simulation results showed that the optimized trajectory satisfies the dynamic constraints better, that the optimized effect is effective and that the vehicle steers steadily under high-speed driving working conditions.
In order to improve the thermal efficiency of engines, it is essential to increase their geometric compression ratio or the expansion ratio. This research explores the technology options to enable a higher expansion ratio in future boosted spark-ignition direct-injection engines, with the aim of significantly reducing the fuel consumption while achieving the same torque and combustion performances as those of baseline turbocharged engines. Variable-valve-actuation technologies such as the late-intake-valve-closing cam strategy and the early-intake-valve-closing cam strategy were considered, and their effectiveness in reducing the effective compression and preventing knock in high-compression-ratio engines was assessed. To compensate for the torque loss due to late intake valve closing or early intake valve closing, multi-stage boosting systems including the turbocharger–supercharger combination and the two-stage turbocharger were implemented and compared. In this study, a Miller cycle engine concept with a high expansion ratio of 12.0:1 was developed with variable valve actuation and multi-stage boosting. On the basis of this new concept, an engine was built and extensively tested on an engine dynamometer to assess its part-load fuel consumption and full-load performance. The experimental results indicated that this engine concept can improve the fuel economy of the vehicle by 3–4% at typical city and highway driving conditions while maintaining the same performance.
A semiempirical reciprocating compressor model was developed to characterize the time response of the pressure within a compressed-natural-gas storage tank. The model assumes isentropic compression in the single-stage compressor that feeds into an isothermal reservoir, i.e. compression heat was assumed to dissipate between the cylinder and the tank. This low-order model utilizes a few key variables such as the compression ratio, the cylinder volume, the tank volume, and the engine speed and yields a reasonable approximation for the pressure inside a tank over time. The natural-gas compressor used to validate the model is a unique automotive internal-combustion engine that was heavily modified to have two distinct modes. In one mode, all engine cylinders fire normally providing locomotion for a natural-gas vehicle. In the other mode, one cylinder of the engine is used to compress low-pressure residential natural gas, in multiple stages, to a standard US compressed-natural-gas vehicle storage tank pressure of 248 bar (3600 lb/in2 gauge). It was found that the first-order response model closely matches the trend in the tank pressure over time seen in laboratory experiments, with a typical error of less than 5%.
A shaft-clinching process aimed at developing a lightweight, integrated and highly reliable assembly is a very effective technique for the assembly of hub-bearing units. In this study, a reliable elastic–plastic finite element model of the shaft-clinching assembly process was developed by using the Abaqus platform and was applied to simulate the shaft-clinching assembly process of automobile wheel-hub-bearing units. To ensure the precision of the developed finite element model, the motion equations of the rivet head during the shaft-clinching process were obtained on the basis of theoretical derivation, on-site testing and the structural parameters of the equipment. Further, a series of experiments was performed for identifying the mechanical properties of the investigated material and the realistic friction conditions existing at the rivet head–workpiece interface. Based on the obtained reliable preprocessing data, the developed finite element model was used to simulate the shaft-clinching assembly process. Subsequently, the finite element model was validated using experiments on the shaft clinching of a wheel-hub-bearing unit. Comparison between the simulation results and the experimental results in terms of the axial clinching force–time curve and the ultimate deformed shape of the hub shaft showed good agreement, thereby validating the developed model. Finally, the influences of the axial distance between the upper surface of the inner ring and the forming surface of the rivet head, the friction factor, the radius ratio of the internal gear to the external gear and the maximum inclination angle of the rivet head on the clinching process were studied. The results of this study are expected to aid optimization of the shaft-clinching assembly process.
The matching problem becomes much more difficult between a regulated two-stage turbocharging system and a diesel engine when they are required to work at different altitudes. This is mainly because there are three or even four main variables to be determined for a regulated two-stage turbocharging system, and the change in the operating altitude also extends the matching problem from a two-dimensional problem of the speed and the load to a three-dimensional problem of the speed, the load and the operating altitude. An optimal scheme for a regulated two-stage turbocharging system should be determined to optimize the plateau adaptability based on the relationship between the matching point, the desirable pressure ratio distribution and the operating altitude. Therefore, a theoretical study on matching a regulated two-stage turbocharging system to a diesel engine at different altitudes is conducted in this paper. The turbine equivalent area of a regulated two-stage turbocharging system is derived on the basis of the turbine flow characteristic model with the thermodynamics equations and the mass and energy conservation of the turbocharging system. The speed and altitude ranges are discussed with the results calculated by the proposed matching model in MATLAB software. Then the simulations with GT-Power software are carried out to validate the application of the equivalent matching model. The calculated results show that the problem of the speed range of the regulated two-stage turbocharging system at different altitudes can be converted to the speed range of a matching scheme based on different pressure ratio distributions at a constant altitude. The altitude range of the regulated two-stage turbocharging system is mainly affected by the matching speed and the bypass flow rate ratio. The validation results of the GT-Power model show that the plateau adaptability of the matched regulated two-stage turbocharging system can be investigated effectively using the equivalent matching model. Therefore, the equivalent matching model can be utilized to achieve a reasonable selection of the matching speed and it can simplify the matching problem of the regulated two-stage turbocharging system at different altitudes.
Traction control, which can be performed by different types of chassis control system, plays an important role in vehicle motion control. Since the propulsive force is actually produced by the friction between the tyre and road, information on the tyre–road friction is crucial for traction control. In this paper, a robust and effective tyre–road friction coefficient identification algorithm for straight acceleration is proposed, and a coordinative traction control method is designed by integrated usage of gear shifting control, engine control and braking control. For different driving conditions, the tyre forces were observed by a sliding-mode observer or calculated from the states of the vehicle directly, and the tyre–road friction coefficients were estimated by the recursive least-squares method or calculated from the linear characteristics between the friction coefficient and the slip ratio consequently. Based on the estimated tyre–road information, a practical and systematic coordinative traction control algorithm was designed to integrate shifting control, engine torque control and braking pressure control. Finally, the proposed methods are verified by both simulations and road tests. The results show that the estimation algorithms can identify the variation in the road conditions with considerable accuracy and response speed, and the controller successfully adjusted the slip ratios of the driving wheels in the stable region with good performances on different types of road.
In this paper, a method to set the target on-centre steering force characteristic is described. First, both the linear correlations and the non-linear correlations between subjective evaluations and objective metrics were established. During this process, subjective and objective evaluation tests regarding the on-centre steering force characteristic were conducted on a moving-base driving simulator by 15 experienced drivers. To ensure the reliability of the subjective ratings, a method to evaluate the ratings was introduced. Then the linear correlations and the non-linear correlations were analysed using multiple linear regression analysis and a neural network respectively. Second, by setting the desired subjective ratings as an optimization goal, target objective metrics were obtained on the basis of either the linear correlations or the non-linear correlations by means of non-linear programming. The target on-centre steering force characteristic was therefore designed on the basis of the target objective metrics. The results showed that the target on-centre steering force characteristic obtained from the linear correlations was quite similar to that obtained from the non-linear correlations. Also, it was verified that the target on-centre steering force characteristic matched the drivers’ preferences. From the correlations and the target on-centre steering force characteristic, engineers can establish the ratings of subjective evaluations and determine how to design the system to meet the target during the virtual design process. It shows a great potential in assisting the engineers to design a good steering feel at the early stages of the development process. Furthermore, the feasibility of this proposed method to allow customers to customize the on-centre steering force characteristic was explored. During this process, a fixed-base driving simulator was used instead of a moving-base driving simulator for cost reasons.
For the existing electric parking brake system which is used as a secondary brake system, accurate rear-wheel slip control has not been realized. In addition, the time spent to produce the required braking force after the electric parking brake button is pressed is too long, which reduces the system’s response speed. All the above means that the vehicle risks a loss in stability and a braking distance that is too large. To solve these problems, the clamping force should be controlled, and the velocity of the clamping mechanism should be increased in the idle stroke. In this paper, on the assumptions that the motor speed is limited and that the length of the idle stroke is hard to identify because of abrasion of the friction pads, a variable transmission and a novel electric parking brake actuator are designed to reduce the clamping time. In the novel electric parking brake system, the belt reducer of the existing electric parking brake is replaced by a load-sensing, continuously variable transmission, in which the reduction ratio changes with the load torque. Additionally, a reduced-order observer is presented to estimate the motor speed, and a sliding-mode controller is designed to control the clamping force. The controller is robust against uncertainties and disturbance of the parameters. The mathematical model of the system is initially constructed using MATLAB/Simulink to simulate the behaviours of the novel actuator. Then the designed control system for various adhesion coefficient conditions involving an abrupt change in the road friction is investigated. As a result, the effectiveness of the sliding-mode controller is validated by simulations, and the comprehensive performance of the actuator is significantly improved.
Autonomous vehicle technology is greatly valued nowadays, and an active collision avoidance system is one of the key parts for autonomous driving. This study presents a comprehensive architecture of an active collision avoidance system for an autonomous vehicle, which is integrated with a decision-making module, a path-planning module, a lateral-path-following module and a fuzzy adaptive following module (longitudinal motion) to deal with potential hazards on a straight road or a curved road. In order to make the planned path for overtaking manoeuvres safer, an improved harmonic velocity potential approach for path planning is presented, which innovatively enhances the effect of an obstacle potential on a road by adding a scale term, so that it can generate a smooth path for a vehicle-overtaking manoeuvre. All the potentials which are used for vehicle lane keeping or lane changing are well designed. The lateral-path-following module is based on the constrained linear model predictive control approach, which ensures that the host vehicle can follow the planned path precisely. Furthermore, when the overtaking manoeuvre is not suitable, the fuzzy adaptive following module is utilized to ensure that the host vehicle can adaptively keep a safe distance from the preceding vehicle. Tactical decisions, such as overtaking, accelerating or decelerating, are determined by the decision-making module. Finally, several typical scenarios with low traffic on a straight road or a curved road are simulated to verify the effectiveness and the feasibility of the active collision avoidance system. The simulation results show that the host vehicle can make a successful collision avoidance manoeuvre without the intervention of a human driver in different situations.
In general, hydroforming optimization aims to make a desired shape of a plastically deformed structure under dynamic forces. The automotive industry has shown great interest in tube hydroforming, which is a metal-forming process. The forces from the hydraulic fluid are utilized to deform a tube. The internal pressures and the axial feedings (of the axial forces) determine the quality of the deformed product. In this research, an optimization process is employed to evaluate the appropriate external forces but defects are prevented. The equivalent static loads method for non-linear static response structural optimization is used for the optimization process because the tube-hydroforming process is analysed by non-linear dynamic response analysis. The equivalent static loads are the static loads that generate the same response field as that of non-linear dynamic analysis and are utilized as the loading conditions in linear static response optimization. A novel process is added to the original equivalent static loads method for non-linear static response structural optimization to address the objective function and the design variables for tube-hydroforming optimization. A new technique is proposed to use the external forces as the design variables in linear static response optimization. A few hydroforming examples are solved by using the newly proposed techniques.
Finite element simulations of a rollover protective structure are an important aspect in its design, as it provides a means of structural integrity qualification prior to the required destructive testing. A good understanding of the rollover protective structure behaviour under simulated loading offers engineering practitioners the opportunity to optimize the design. The testing conditions, which are outlined in the applicable standards, result in plastic deformation of the rollover protective structure, associated with material hardening of various areas of the structure. An accurate description of the material behaviour is important for finite element simulations of the structural response. This research examines some of the hardening models commonly used in simulations of rollover protective structures, which are available in most finite element commercial software, including linear and multi-linear isotropic and kinematic hardening models and non-linear kinematic hardening models. The numerical performance of the plasticity models in representing the material behaviour was compared with the experimental data for commonly used rollover protective structure material. Analysis revealed the potential benefits and drawbacks of the various models. Moreover, a damage-induced softening model was implemented at the structure joints in conjunction with the non-linear hardening models. Enhanced computational results were obtained through this modelling variation, highlighting the importance of material modelling at the primary structure and the joints of a rollover protective structure.
The fuel savings of plug-in hybrid electric vehicles strongly rely on the energy management strategy deployed onboard. For the current mass-produced plug-in hybrid electric vehicles, notably the Toyota Prius, the energy management strategy is a rule-based type, which is configured to optimize instantly the fuel consumption without taking into consideration the upcoming driving patterns of the given route schedule. Hence, it operates the vehicle first in the electric mode over a predefined all-electric range and then in the charge-sustaining mode. The energy consumption results are seen to be far from optimal when compared with global optimization strategies with prior knowledge of the scheduled route, such as dynamic programming. Hence, this study presents the methodology to optimize the rule-based energy management strategy for real-time implementation in the Prius plug-in hybrid electric vehicle, using dynamic programming as the global optimization routine. The optimization process takes into account the desired trip profile selected by the driver on the vehicle’s onboard Global Positioning System and linked to a traffic management system. A basic rule-based energy management strategy, which emulates the vehicle performance and the energy consumption, has been set first using on-road measurement data logging. As a second step, the dynamic programming optimization routine was applied to the model, assuming a repeated New European Driving Cycle as the scheduled route. The results obtained for the behaviours of the powertrain components under optimal control are evaluated and used to update the operating energy management rules of the basic controller. Finally, an optimized rule-based controller is proposed by coupling between the dynamic programming and the basic rule-based controller, followed by an evaluation of the energy consumption and the powertrain efficiency of the three investigated control strategies.
Brake-related particulate matter contributes considerably to the non-exhaust emissions of the transport sector in urban areas of the world. The airborne particle emissions from automotive brakes currently lack any proper regulations. Future regulations require test stands, test cycles and particle instruments to be suitable for measuring the brake emissions. This present work focuses on the design of a novel test stand for reliable measurements of the brake emissions with a high sampling efficiency. A test stand in the form of an inertial disc brake dynamometer was redesigned to allow control of the cleanness of the incoming air and to assure isokinetic sampling. The cleanness of the incoming air, together with an over-pressurized chamber around the brake assembly, ensures that all the particles measured originate from the brake materials. In order to evaluate the novel design, the number and size distributions of the brake emissions are measured online with and without control of the cleanness of the intake air. The results reveal that this test stand can be proposed as a standard test stand to assess objectively the emissions of airborne brake particles in future regulations.
The optimal design of driveline components in passenger vehicles requires detailed knowledge of the effects that load case scenarios introduce into the system. In many cases the latter are difficult to obtain, since a large number of tested cases are required experimentally. Excessive torque loading often occurs during driveline ‘clutch abuse’ events, where the clutch is suddenly engaged and a transient power wave is transmitted across the driveline. This work details the development and validation of a numerical tool, which can be used to simulate such abuse scenarios. The scenario examined consists of a sudden clutch engagement in first gear in a stationary vehicle. The numerical model is validated against experimentally measured torque data, showing fairly good agreement. A set of parametric studies is also carried out using a numerical tool in order to determine the driveline parameters of interest, which affect the generated torque amplitudes.
The vehicle height adjustment system of an electronically controlled air suspension poses challenging hybrid control problems, since it can operate in several distinct discrete modes (the gas-charging mode, the gas-discharging mode and the no-action) by switching the on–off solenoid valves. This paper describes the development and experimental validation of a new vehicle height adjustment controller for an electronically controlled air suspension based on the theory of hybrid systems. The mixed logical dynamic modelling approach, which is an effective model structure for hybrid systems, is chosen to obtain the hybrid dynamic behaviours of the vehicle height adjustment system. On the basis of some reasonable assumptions and a linear approximation for the non-linearities of the components, the mixed logical dynamic model of the system is constructed by using the hybrid systems description language, which is a high-level hybrid modelling language. Using this model, a constrained optimal control problem is formulated and solved by tuning a hybrid model predictive controller, which can track the desired vehicle height through controlling the on–off statuses of the solenoid valves directly. Simulations and experimental results are presented finally to show how the hybrid framework and the optimization-based control strategy can be successfully applied to solve the vehicle height control problem of an electronically controlled air suspension in a systematic way.
In this study, a gear fork control algorithm for a dual-clutch transmission is proposed to improve the shift quality for the downshift from second gear to first gear during coast-down. First, to investigate the shift characteristics, a dual-clutch transmission shift performance simulator was developed including the gear fork system. Using the dual-clutch transmission simulator, the shift characteristics for the downshift from second gear to first gear were investigated during coast-down. From the simulations and the test results, it was found that vibrations occur in the speed of the output shaft owing the large change in the speed gradient of the input shaft at the moment of synchronization, resulting in a change in the longitudinal acceleration of the vehicle, which causes the shift quality to deteriorate. Based on the dynamic models of the gear fork system and the test results, a gear fork control algorithm is proposed which generates a constant cone torque to reduce the speed gradient of the input shaft. It was found from the simulations and the vehicle test results that the amplitudes of the vibrations in the speed of the output shaft and the peak-to-peak acceleration of the vehicle were reduced by the gear fork control algorithm proposed in this study, which improved the shift quality by as much as 50%.
The present paper identifies single-input single-output linear minimum-order models for the hydraulic unit of an anti-lock brake system in the increase mode and the decrease mode. The input variable and the output variable in the models for the increase mode and the decrease mode are the pressure of master cylinder and the pressure of the brake caliper respectively. In the process of model identification, excitation signals are designed by introducing a novel method to change the states of the solenoid supply valve and the solenoid discharge valve and to generate different operating modes. It is shown that the excitation signals are persistently exciting of a certain order and cover the bandwidth of the system. In this study, the structure models (the output error model, the autoregressive with exogenous input model, the autoregressive moving-average with exogenous input model and the box Jenkins model) are identified for the increase mode and the decrease mode by employing the experimental data of a test automobile and using the ordinary least-squares method and the prediction error method. After validation of the model outcome by comparison with the experimental results, the best models are presented for the increase mode and the decrease mode of the hydraulic unit in a test automobile.
Regenerative braking significantly improves the energy efficiency in electric vehicles. Cooperative control between regenerative braking and friction braking during anti-lock braking control is a critical issue in brake system coupling. For safety concerns, regenerative braking is often terminated at the beginning of anti-lock braking control. Oscillations between activation of an anti-lock braking system and exit from anti-lock braking system control may occur under poorly matched control parameters. To solve these problems, we propose an index that indicates the possibility of activation of an anti-lock braking system. It is derived by a fuzzy logic algorithm which is based on the estimated regenerative braking torque, the estimated friction braking torque and other vehicle state variables. Regenerative braking can be adjusted on the basis of the index to ensure that such braking is of a low level when an anti-lock braking system is activated. Simulations and experiments are carried out to evaluate the effectiveness of the index. The results show that regenerative braking decreases as the index increases, thereby improving the braking safety and the driving comfort during the transient process of activation of an anti-lock braking system.
The conventional approach in vehicle suspension optimization based on the ride comfort and the handling performance requires decomposition of the multi-performance targets, followed by lengthy iteration processes. Suspension tuning is a time-consuming process, which often requires the benchmarking of competitors’ vehicles to define the performance targets of the desired vehicle by experimental techniques. Optimum targets are difficult to derive from benchmark vehicles as each vehicle has its own unique vehicle set-up. A new method is proposed to simplify this process and to reduce significantly the development process. These design objectives are formulated into a multi-objective optimization problem together with the suspension packaging dimensions as the design constraints. This is in order to produce a Pareto front of an optimized vehicle at the early stages of design. These objectives are minimized using a multi-objective optimization workflow, which involves a sampling technique, and a regularity-model-based multi-objective estimation of the distribution algorithm to solve greater than 100-dimensional spaces of the design parameters by the software-in-the-loop optimization process. The methodology showed promising results in optimizing a full-vehicle suspension design based on the ride comfort and the handling performance, in comparison with the conventional approach.
The driver’s starting intention, which coordinates the engine output torque and the engagement speed of clutch for a vehicle equipped with an automated manual transmission, may be the key state for automated manual transmission clutch control. Fast and accurate identification of the starting intention can ensure a smooth clutch engagement and a smooth start of a vehicle. In this paper, a novel method based on an artificial error back-propagation neural network is proposed to identify the driver’s starting intention. By analysis of the experimental data, the driver’s starting intention can be defined strictly and divided into three modes: a slow start, a medium start and a fast start. The statistical regularity of the acceleration pedal opening is obtained on the basis of a novel method for processing the experimental data. Because in the first period of time in a starting process, the time proportion of the acceleration pedal opening over a certain value is closely related to the driver’s starting intention, therefore, this statistical regularity of the acceleration pedal opening is regarded as the input of the neural network, and the Broyden–Fletcher–Goldfarb–Shanno algorithm is applied to train the neural network. The real-vehicle test results with different drivers show that the identification accuracy of the driver’s starting intention is greater than 95% during the first 600 ms with the proposed artificial error back-propagation neural network. This can provide a reasonable quantization method of the driver’s starting intention for smooth automated manual transmission clutch control.
In the UK, the number of fatal accidents on rural roads is approximately double that on urban roads. Statistics have also shown that accidents on rural roads decreased less than on other road types. The narrow width and complex geometry are less forgiving to drivers’ mistakes. A potential remedy for this problem is automated driving in which the ability to plan -in real time- safe and feasible paths is essential. The literature review of recently proposed path planning methods has revealed that most of them utilise either forward simulations of a vehicle dynamics model or describe a priori mathematically a reference path. In this paper, the weaknesses of the reviewed methods are discussed and a new path planning method that belongs to the latter category is presented. The method is based on a direct element concept and as shown and discussed is extremely versatile. It is unique in the sense that for the first time it facilitates the prediction of the maximum vehicle slip angle and the definition of a reference path that minimises it. Contrary to other methods it is very flexible in defining arbitrary boundary and intermediate conditions. The overall computational cost as analysed is very small. Simulations illustrate its performance and comparisons with other methods highlight its strengths.
The study presented in this paper discusses developments in the area of anti-lock braking control for full electric vehicles. The main contributions of the paper are the development and experimental validation of the combined electric and hydraulic brake system with application of a continuous anti-lock braking system, which is expected to be more effective than the existing industrial solutions. It covers the topic of high-performance braking and driving comfort under a direct slip control function. The research is related to the full electric sport utility vehicle equipped with four individual on-board motors and a decoupled electrohydraulic brake system. The brake controller architecture includes functions of the continuous anti-lock braking system strategy, a brake blending algorithm aimed at minimization of the friction brake torque and operational limitations of the electric brakes. The developed brake controller was subjected to different validation procedures but, within the framework of this paper, emergency braking tests on a wet surface with a low coefficient of friction are considered. The results obtained demonstrate significant improvements in the braking performance, the driving comfort and the control performance for continuous anti-lock braking control of the electric vehicle compared with those of diverse vehicle configurations and, in particular, with those of a sport utility vehicle of the same type equipped with an internal-combustion engine and a conventional hydraulic brake system.
Many studies using a laser scanner have been conducted in order to study the environment of vehicles in real time. The method to find the driving area using a two-dimensional lidar sensor is divided into a forward-looking lidar sensor and a downward-looking lidar sensor based on the installation method. A downward-looking lidar sensor looks at the ground, enabling it to recognize kerbs and ditches which are lower than the installation position of the sensor. However, a downward-looking lidar sensor requires pre-processing to find the road boundary. The existing sensor models cannot generate an occupancy grid map without support, as the driving area recognized through a downward-looking lidar sensor forms a circular sector shape from the sensor installation position to the road boundary. This paper proposes a road sensor model that is capable of modelling an occupancy grid. We also propose a method to generate an occupancy grid map more suitable for autonomous vehicles by presenting the occupancy grid map in curvilinear space. The proposed method was validated by an experiment at Hanyang University campus and the quantitative results obtained from that experiment. We also compared this method with three conventional sensor model methods. The experimental results show that our method performs better than the conventional methods do in terms of both visual qualities and metric qualities.
This paper investigates the fuel consumption of an articulated vehicle with a hydraulic regenerative braking system. The vehicle is a four-axle tractor–semitrailer with a volume-limited payload. It is equipped with hub-mounted hydraulic pump–motor units that pump fluid from a low-pressure reservoir to a high-pressure reservoir during braking events and generate a propulsive torque when high-pressure fluid flows through them to the low-pressure reservoir during acceleration. Several possible control strategies are proposed and simulated using a validated mathematical model of the fuel consumption of the vehicle. A global optimisation calculation indicates that the maximum possible reduction in fuel consumption due to the regenerative braking system is 11–22%, depending on the driving cycle. The simulations indicate that the simple ‘greedy’ algorithm decreases the fuel consumption by 9–17% for the same conditions. Two heuristic algorithms and a model predictive control approach were also investigated. Although these more sophisticated controllers were able to improve on the greedy controller slightly for some conditions, they may not be implementable in practice.
Recent progress made in making clutches lightweight and in reducing torsional vibrations has led to the emergence of new vibroacoustic phenomena due to the out-of-plane vibrations of the clutch. These vibrations are generated along the axial direction of the clutch system. Contrary to torsional vibrations that can be simulated by unidirectional lumped-mass models, axial vibrations require a three-dimensional approach to describe the dynamics of the components. Finite element models are widely used to design or optimize the components of the clutch. However, no finite element model of a complete clutch has been developed for analysis of axial vibrations. The main difficulties are the complexity of the system, the great number of non-linearities, the difficulties of instrumentation for validation and the variation in the behaviour along the engagement stroke. This paper provides a validated three-dimensional finite element model of the dynamic behaviour of the clutch for studying axial vibrations. The model simulates the axial static and dynamic characteristics of the clutch. Model accuracy and validation are achieved by comparing the numerical results with the experimental data. The results show the crucial parameters to consider in order to reproduce correctly the non-linear axial behaviour and the dynamic characteristics of the clutch system, namely the orthotropic behaviour of the friction material and the geometrical parameters of some components that should be detailed. Validation is carried out on each component and for the system assembly by dedicated experiments and instrumentation.
Reliability-based design optimization is an optimization technique based on the stochastic approach. Many studies using this approach assume the uncertainty in the design variable to be constant. However, when the uncertainty depends on the values of the design variable, this assumption results in the wrong conclusions. Therefore, the uncertainty should be considered as a variable in reliability-based design optimization. The uncertainty in the thickness during optimization, such as the tolerance, had been assumed to be a constant in automotive structures. However, in practice, the tolerance of the thickness depends on the nominal thickness. Hence, in this paper, reliability-based design optimization of an automotive structure such as an engine cradle and a body-in-white with a variable uncertainty is carried out. General Motors Korea provides the tolerance guide which defines the dependence between the nominal thickness and the tolerance. The information is adopted to define the variable uncertainty. Thus, the variable uncertainty can modify the uncertainty with respect to the design point, resulting in an accurate reliability estimation. Finally, reliability-based design optimization with a variable uncertainty is performed using the Akaike information criterion method which determines the fittest distribution of the performance based on the maximum likelihood estimation of the candidate distributions. Consequently, the automotive structures are optimized to reduce the mass while still satisfying the target reliabilities of the performances when considering a variable uncertainty.
This paper presents the application of adaptive algorithms to integrated chassis control. Integrated chassis control uses electronic stability control and active front steering as actuators. In order to generate the control yaw moment using electronic stability control and active front steering, and to coordinate the relative magnitude of the tyre force generated by active front steering with that generated by electronic stability control, a fast and simple yaw moment distribution procedure is needed. For this purpose, adaptive methods, namely the least-mean-square algorithm, the sign–sign least-mean-squares algorithm and the leaky least-mean-square algorithm, are applied. To coordinate active front steering and electronic stability control in the leaky least-mean-square algorithm, a particular weight set is selected. To check the effectiveness of the adaptive algorithms in integrated chassis control, simulations using the vehicle simulation package CarSim® were carried out.
A model-based indicated torque estimation method for a turbocharged diesel engine is presented in this study. The proposed model consists of two submodels: a steady-state indicated torque model; a transient torque coefficient model using the Elman neural network. Experiments are designed to acquire the database for the model. The optimal parameters of the Elman neural network are determined; the results show that the mean absolute percentage error of the transient torque coefficient for the estimated values using the Elman neural network and the experimental values is within 2% and the maximum error is about 7%. A comparison of the usability of the back-propagation network and that of the Elman neural network for transient estimation problems is studied; the results show that the Elman neural network is more applicable in terms of the transient accuracy and the convergence time. To validate the accuracy of the model, the experimental results for a new engine speed with two new processes are employed as test data; it is shown that the mean absolute percentage error of the indicated torque is within 2% and the maximum error is about 6%. Furthermore, explicit formulation of the Elman neural network model is acquired and rewritten as C code. Then, online validation is conducted and the results show that the mean absolute percentage error of the indicated torque is within 6%, with a maximum error of 15%.
This paper presents a new model predictive control system for hybrid electric vehicle platooning using route information to improve fuel economy. The new features of this study are as follows. First, a system for hybrid electric vehicle platooning has been developed considering varying the desired vehicle speed. Second, a general model of road slope in a vehicle platoon is developed. Third, the effect of prediction horizon and sampling interval on battery efficiency is analyzed. The model predictive control problem is solved using a discrete numerical computation method, the continuation and generalized minimum residual method. Computer simulation results reveal improvements in fuel economy using the proposed control method.
This paper investigates the effect of a dimethyl ether–soybean oil methyl ester blend as an alternative fuel on the combustion and the spatial distributions of nitrogen oxide emissions and soot emissions in a diesel engine using experimental and numerical approaches. The results obtained from the combustion and the emission characteristics (such as the heat release, the nitrogen oxide emissions, the soot emissions, the carbon monoxide emissions and the hydrocarbon emissions) of a dimethyl ether–soybean oil methyl ester blend are compared with the results from a conventional diesel fuel. The test fuels used in this investigation were dimethyl ether–soybean oil methyl ester blend, dimethyl ether and a conventional diesel fuel. The dimethyl ether–soybean oil methyl ester blend is a mixture of 80 wt % dimethyl ether and 20 wt % biodiesel fuel. A numerical calculation was conducted to analyse the combustion characteristics, the spray behaviours, the mixture formation, the emissions characteristics and the spatial distributios of nitrogen oxides and soot for the dimethyl ether–soybean oil methyl ester blend in a cylinder by using the AVL FIRE program. The numerical results showed that the combustion characteristics of the dimethyl ether–soybean oil methyl ester blend and diesel fuel were in good agreement with the experimental results, such as the combustion pressure and the rate of heat release. It was found that the effect of the dimethyl ether–soybean oil methyl ester blend on the combustion characteristics in an engine resulted in a shorter ignition delay and advanced ignition compared with those using conventional diesel fuel. In addition, the combustion duration of the dimethyl ether–soybean oil methyl ester blend was shorter than that of diesel fuel. The combustion effect of the dimethyl ether–soybean oil methyl ester blend on the concentration of the exhaust emissions indicated that the carbon monoxide emissions and the hydrocarbon emissions were lower than those from diesel fuel. On the other hand, the nitrogen oxide emissions of the dimethyl ether–soybean oil methyl ester blend slightly increased in comparison with those from diesel fuel. The soot emission concentration was nearly zero for the entire test range.
This paper summarises the measured emergency braking performance of a tri-axle heavy goods vehicle semitrailer fitted with a novel pneumatic slip control braking system developed by the Cambridge Vehicle Dynamics Consortium. Straight-line braking tests were carried out from 40 km/h in order to compare a commercially electro-pneumatic available anti-lock braking system and the Cambridge Vehicle Dynamics Consortium system, which has bi-stable valves coupled with a sliding-mode slip controller. On average, the Cambridge Vehicle Dynamics Consortium system reduced the stopping distance and the air use by 15% and 22% respectively compared with those for the conventional anti-lock braking system. The most significant improvements were seen on a wet basalt-tile surface (with similar friction properties to ice) where the stopping distance and the air use were improved by 17% and 30% respectively. A third performance metric, namely the mean absolute slip error, is introduced to quantify the ability of each braking system to track a wheel slip demand. Using this metric, the bi-stable valve system is shown to improve the wheel slip demand tracking by 62% compared with that of the conventional anti-lock braking system. This improvement potentially allows more accurate control of the wheel forces during extreme manoeuvres, providing scope for the future development of advanced stability control systems.
Vehicle rollovers are a serious safety issue for drivers and passengers and have led to many fatal accidents on the road. This paper describes a system and a method of enhancing vehicular stability to reduce the likelihood of rollover for motor vehicles, and in particular for sport utility vehicles. Under the concept of pulsed active steering, one control strategy called pulsed active rear steering was investigated and is discussed in detail. To verify this system, the yaw and roll model was derived and the pulse signal parameters (the frequency and the amplitude) were evaluated to determine their optimum values. A full-vehicle model was built in CarSim and co-simulated with MATLAB/Simulink as the control module. Moreover, we designed and prototyped the proposed system for a sport utility vehicle and then conducted road tests with different manoeuvres. The results from simulations and experiments confirmed that the proposed pulsed active rear-steering system is promising for rollover prevention of sport utility vehicles.
Variations in the parameters affect the injection characteristics of a common-rail injection system and leads to fluctuation in the fuel injection quantity. This paper is aimed at combining the numerical modelling and design of experiments to investigate the significant effects of the interactions between the common-rail injector parameters on the fluctuation in the fuel injection quantity using response surface methodology. A numerical model of a common-rail injector was developed. The model was validated by comparing simulation results with experimental measurements, which showed that it can accurately predict the fuel injection quantity of the system. The design of experiments was performed using a two-level five-factor D-optimal design. The factors studied were the pre-tension of the control valve spring, the diameter of the outlet orifice, the diameter of the inlet orifice, the needle lift and the diameter of the nozzle holes. A quadratic response surface model was suggested by means of partial least-squares regression analysis. The distribution of the standardized residuals, the relation between the predicted fluctuation and the observed fluctuation in the fuel injection quantity, the coefficient R2 of determination and the adjusted coefficient
More accurate information about the basic vehicle parameters can improve the dynamic control functions of a vehicle. Methods for online estimation of the mass, the rolling resistance, the aerodynamic drag coefficient, the yaw inertia and the longitudinal position of the centre of gravity of an electric hybrid vehicle is therefore proposed. The estimators use the standard vehicle sensor set and the estimate of the electric motor torque. No additional sensors are hence required and no assumptions are made regarding the tyre or the vehicle characteristics. Consequently, all information about the vehicle is available to the estimator. The estimators are evaluated using both simulations and experiments. Estimations of the mass, the rolling resistance and the aerodynamic drag coefficient are based on a recursive least-squares method with multiple forgetting factors. The mass estimate converged to within 3% of the measured vehicle mass for the test cases with sufficient excitation that were evaluated. Two methods to estimate the longitudinal position of the centre of gravity and the yaw inertia are also proposed. The first method is based on the equations of motion and was found to be sensitive to the measurement and parameter errors. The second method is based on the estimated mass and seat-belt indicators. This estimator is more robust and reduces the estimation error in comparison with that obtained by assuming static parameters. The results show that the proposed method improves the estimations of the inertial parameters. Hence, it enables online non-linear tyre force estimators and tyre-model-based tyre–road friction estimators to be used in production vehicles.
The safety of vehicles has been studied in the past on the basis of the safety of passengers. Recently, pedestrian safety has also attracted attention. The pedestrian protection performance of vehicles has gradually improved but is still not sufficiently good. Devices such as the pop-up hood and the pedestrian protection airbag system are generally used to protect pedestrians. Since these devices are relatively newer than other parts of an automobile, a standard design process has not yet been rigorously established. There have been studies that demonstrated how to determine the design parameters of the devices using computer simulations. In this research, a novel design process for a pedestrian protection airbag is proposed, which utilizes the results of the experiments. Some parameters of the pedestrian protection airbag system, which cannot be determined by simulations, are selected and obtained using experiments. They are the folding method of the airbag, the height type of the airbag and the inflator type. The design results using simulations are incorporated in the initial design of the proposed process. The experimental facilities are prepared on the basis of a mid-sized passenger vehicle, and the headform tests are performed according to the protocol of the European New Car Assessment Programme test. The proposed design process selects the rolling and folding method, the small height type and the bottom spurt inflator type. The resultant design is evaluated and analysed using experiments, and it is found to be satisfactory.
Wireless power transfer is a promising method to address the concerns over charging an electric vehicle. Since wireless charging stations operate without large cables or above-ground stations, they can be conveniently installed in public locations without the risk of vandalism or weather-inflicted damage, improving the lifespan of the electric vehicle charging station. In order for wireless charging stations to become widespread, possible health effects regarding exposure to the strong electromagnetic fields present during wireless power transfer must be investigated. This work examines, first, the potential human safety hazards, second, the electronic device interference, and, third, the thermal heating effects of wireless charging systems. A 3.3 kW wireless power transfer prototype was built in order to examine these effects. Changes in the wireless power transfer efficiency due to the coil misalignment were also investigated using an automated three-axis platform. Design considerations for electric vehicle wireless charging systems and safety recommendations are presented.
A control variable method was used to study experimentally the properties of automatic mechanical transmission actuators under cryogenic running conditions. Only one temperature variable was changed during the experiment so as to facilitate the comparison between the impacts of the temperature on the execution characteristics of actuators. From a series of cryogenic experiments and data analysis, the cryogenic characteristic curves (e.g. for the clutch, for the throttle, for gear selection and for putting the automatic mechanical transmission into gear) were drawn, providing guidance for subsequent temperature compensation control methods. In addition, given that the phenomenon in which the clutch and the shift gear in the automatic mechanical transmission control system seized up at –40 °C, a cryogenic thawing strategy was then added to the automatic mechanical transmission control system. The results show that this cryogenic thawing strategy can effectively reduce the starting and running resistances of the automatic mechanical transmission at low temperatures, enabling vehicles equipped with the automatic mechanical transmission control system to operate normally at –40 °C and thus enhancing the reliability of these vehicles in low-temperature operation. The present temperature compensation control method and the cryogenic thawing strategy are of great significance for improving the reliability and security of automatic mechanical transmission control at low temperatures.
Apart from improving the fuel economy, a reduction in the variability of the fuel economy is also of significant importance for hybrid electric vehicles. Previously, research on how to optimise the sizes of the powertrain components of hybrid electric vehicles has generally focused on improving the fuel economy over a given driving pattern. The variability of the fuel economy over a realistic range of driving patterns has generally been overlooked, and this can mean that the fuel economy benefits of hybrid electric vehicles are not consistently realised in real-world usage. In a recent study, a new methodology for design optimisation of the powertrain components of hybrid electric vehicles was proposed for the reduction in the variability of the fuel economy due to variation in the driving patterns, but the methodology needs to be validated in real-world usage for practical applicability. In this paper, the methodology is validated in real-world driving conditions. This paper investigated the methodology for 10 real-world driving patterns generated by 10 different drivers over a predefined route consisting of urban and highway driving. The study was carried out using a simulation model of a Toyota Prius hybrid electric vehicle which was considered as the benchmark vehicle. The design produced by the methodology reduced the variability of the fuel economy by 5.3% without reducing the average fuel economy compared with the Toyota Prius over the 10 real-world driving patterns. This demonstrates that the methodology described is applicable to real-world usage.
Analysing the dynamic behaviour of a suspension is essential to achieve the best relationship possible between the ride comfort and the handling. In the past, much effort was spent in investigating the dynamic transmission behaviour of a suspension on a test rig. The majority of these test rigs allow only a vertical deflection. However, the longitudinal direction becomes increasingly important when optimizing the ride comfort on uneven roads. This study investigates the various possibilities for identifying the longitudinal dynamic behaviour and the bump sensitivity of a suspension, by means of a completely rigid clamp acting on a motionless tyre or a stiff dummy wheel. Furthermore, excitations superimposed on the suspension are investigated in detail followed by a parameter study to discover their influence on the longitudinal transmission behaviour of the suspension. Additionally, the results of multi-body simulations are compared with the real measurements. The adopted approach enables the influences of different suspension parameters to be analysed and evaluated on a real suspension test rig and a virtual suspension test rig, in connection with a tyre or for a stand-alone axle.
The automobile seat is an important and unique device in the automobile system, which directly contacts the human body. The dynamic characteristics of the automobile seat are the key parameters for its vibration security and dynamic performance. Both experiments and finite element simulations are conducted to analyse the fore-and-aft operating modes of a new type of automobile seat system in this paper. The results and their correlation analysis between the experimental data and the computational models are given. By using finite element simulations, the computational results of the modes with the first 12 orders for the automobile seat are in the range 0–100 Hz, including the integral modes and the local modes of the automobile seat. An experimental method was designed to measure the seat frame mode using an impact hammer, a triaxial accelerometer, uniaxial accelerometers and a 24-channel LMS vibration test system. The experimental data were analysed by estimating the frequency response function and the modal parameters and validated using LMS Test.Lab software. The experimental results for five integral modal parameters of the automobile seat between 0 Hz and 100 Hz are given. The orthogonal experimental method is used to design nine different working states of the automobile seat with variations in the positions of different adjustable devices (the headrest, the height adjuster, the recliner and the track slide). Finally, the influences of the above-mentioned adjustable devices on the fore-and-aft operating mode are analysed by the single-factor analysis method using finite element simulations.
Energy management strategies for a power-split hydraulic hybrid wheel loader are studied in this paper. The differences between the powertrain and the energy management system for on-road vehicles and the powertrain and the energy management system for off-road vehicles are first identified. Unlike on-road vehicles where the engine powers only the drivetrain, the engine in a wheel loader powers both the drivetrain and the working hydraulic system. In a non-hybrid wheel loader, the two subsystems interfere with each other since they share the same engine shaft. By using a power-split powertrain, this not only allows for optimal engine operation and regenerative braking but also greatly reduces the interference between the drivetrain and the working functions. An energy management strategy based on dynamic programming is developed to give full system optimization including both the drivetrain and the working functions. Both a long loading cycle and a short loading cycle are studied in this paper. The dynamic-programming-based strategy is compared with a rule-based strategy using simulation studies.
This paper describes motorized active suspension damper control with dynamic friction and actuator delay compensation for an enhanced ride quality. The control algorithm consists of a supervisory controller, an upper-level controller and a lower-level controller. The supervisory controller determines the control modes, such as the passive control modes and the active control mode. The upper-level controller, which incorporates the existing actuator delay, computes the damping force using linear quadratic control theory. The actuator input is determined by the lower-level controller by compensating the dynamic friction torque. To estimate the sprung-mass displacement, the sprung-mass velocity, the unsprung-mass displacement and the unsprung-mass velocity, two state estimators are proposed. An adaptive observer is developed for the non-linear dry friction to estimate the ball-screw dynamic friction caused by the axial movement of the actuator and the viscosity. The performance of the proposed control algorithm was evaluated from simulations. It was shown from simulations that the proposed motorized active suspension damper control with a friction and delay compensation algorithm can improve the ride quality.
Modification of the fuel–air charge properties has the potential to improve the load range of low-temperature combustion with ultra-low nitrogen oxide emissions (less than 0.2 g/kW h) and ultra-low smoke emissions (less than 0.01 g/kW h). The ignition characteristics of the cylinder charge are altered by injecting the highly reactive diesel fuel into a homogeneous lean air–fuel mixture of low-reactivity fuel. The ethanol–diesel combination has been of particular recent interest since ethanol is a renewable biofuel. The additional advantages of ethanol include excellent anti-knock properties, high volatility and reduction in the compression work through charge cooling. In this work, a detailed investigation using diesel-ignited ethanol experiments was conducted on a high-compression-ratio (18.2:1) diesel engine. The emissions, the combustion performance and the thermal efficiency characteristics are analysed at different values of the exhaust gas recirculation, the intake boost pressure, the ethanol fraction and the diesel injection timing. The empirical investigations supported by detailed zero-dimensional engine cycle simulations indicate that a diesel injection timing close to top dead centre provides direct control over the ignition timing across the engine load range. The nitrogen oxide–soot trade-off of conventional diesel combustion, which is affected by exhaust gas recirculation, is minimized to achieve clean combustion over a wide load range (indicated mean effective pressure, 4–17 bar) with increased ethanol fraction and moderate intake dilution through a combination of modulation of the exhaust gas recirculation level and an increase in the intake boost pressure. The operation at low loads is constrained by the minimum diesel amount necessary for stable and efficient combustion while progressively retarded combustion phasing is necessary at higher loads to satisfy the physical engine constraints (peak cylinder pressure, less than 170 bar; peak pressure rise rate, less than 15 bar/deg crank angle). The improved understanding of this combustion strategy through experimental and theoretical research provides the necessary guidance for obtaining clean efficient full-load operation (demonstrated at an indicated mean effective pressure of 19.2 bar).
Noise and vibration refinement and energy efficiency are the key drivers in powertrain development. The final drive (the differential) is a source of vibration concern and also contributes to the powertrain inefficiency. To optimise differential characteristics for the key objectives of refinement and efficiency, detailed models of the gear interactions as well as the support bearing dynamics are required. This study reports the integrated lubricated bearing and gear contacts with an eight-degree-of-freedom dynamic analysis (a tribo-dynamic model). Non-Newtonian shear behaviour of thin lubricant-film conjunctions is taken into account in the integrated tribo-dynamic analysis, which has not hitherto been reported in the literature. The results show that the transmitted vibration spectra from the system onto the differential casing are dominated by the bearing frequencies rather than by those due to the meshing of gears. It is also shown that a sufficiently high bearing preload improves the vibration refinement but can lead to a marginally reduced transmission efficiency.
This paper presents a warm-forging process for the manufacture of an aluminium alloy differential case in an automobile, which has usually been produced from ductile cast iron. In order to replace the conventional ductile cast iron with a lightweight material in the differential case, aluminium alloy 6082 is utilized in the proposed warm-forging process, which is then analysed by numerical simulations using DEFORM-3D. Experimental warm forging using aluminium alloy 6082 was conducted in a 1600 tonf press shop to evaluate the proposed design in the die and the punch as well as the forgeability of the aluminium alloy differential case. The as-forged aluminium alloy differential case not only provides a net shape but also has a crack-free volume internally, while reducing the total weight by about 40% based on the proposed design.
In this paper, a dynamic mathematical model of an autonomous ground vehicle was used to analyse its transient response and to design a heading-angle controller for the vehicle. A suitable ‘control-oriented model’ that could accurately characterize the phenomenon of interest was used to design the controller. The efficacy of this model was evaluated by corroborating its results with experimental data. This model included the cornering stiffness of the tyres as an unknown parameter, and two approaches were attempted to estimate its value. The dynamics of the actuator were included in the analysis since the response time to steer the front wheel is of the same order as that of the heading-angle dynamics of the vehicle. The performance of two controllers (namely a classical transfer-function-based controller and an optimal linear quadratic regulator) were evaluated using the IPG: CarMaker® simulation platform over a range of speeds. The transfer-function-based controller was also implemented on the experimental test vehicle at low speeds (high-speed experimental implementation was not possible because of safety concerns). It was found that control gain scheduling helped to track the desired heading angles of the vehicle at various speeds. Subsequently, a lane-change manoeuvre using the test vehicle was performed to evaluate the controller further. It was found that the transfer-function-based heading-angle controller could provide a comparable performance with that of the linear quadratic regulator, while keeping the sensing requirements to a minimum; thus, it was suitable for real-time implementation in an autonomous ground vehicle.
This paper proposes a coordinated control algorithm of the differential braking, the front and rear traction torques and the active roll moment to enhance the limit-handling performance. The coordinated algorithm is designed to maximize the driving velocity while keeping the vehicle in a lane. First, the analysis of the cornering dynamics is described to consider the non-linear characteristics of the tyres during acceleration or deceleration. The target vehicle motions are determined on the basis of the driver’s intention and the current states of the vehicle. An optimization-based control allocation strategy is utilized to distribute the actuator control inputs optimally by considering the tyre and vehicle limitations. Closed-loop simulations of a driver–vehicle–controller system were conducted to investigate the performance of the proposed control algorithm. The performance of the coordinated algorithm was compared with those of the individual coordination algorithms. The simulation results show that the proposed integrated chassis controller improves the performance in high-speed cornering with respect to the driving speed without losing stability compared with simple coordination chassis control systems.
Adaptive feedforward control is a common approach for handling uncertainties and time-varying effects in automotive control applications. The adaptation of the feedforward controller, usually formed by a lookup table, is often combined with a linear feedback controller. The feedforward controller is used to overcome the nonlinearities that are due to variations of the operating point. The feedback controller is used to deal with fast disturbances. If the system behavior is changing, for example due to varying fuel qualities or aging effects, the feedforward controller has to be adapted. A common problem is the fact that the bandwidths of the feedback controller and the adaptation of the feedforward controller have to be separated, i.e. the adaptation of the feedforward controller has to be slower than the feedback controller. Otherwise, the coupling effects lead to an unexpected behavior of the control system, which may also lead to instability. This paper presents an analysis of this effect using a linear representation of the adaptation of the feedforward controller. Based on the results of this analysis, the paper presents a method to decouple the feedback controller and the adaptation of the feedforward controller, which allows a fast adaptation of the feedforward controller. Ideally, the adaptation is as fast as the feedback controller. The system is then able to adapt during operating point transients without the need to stay at some operating points for longer periods. The proposed method does not depend on the structure of the feedforward controller, nor does it depend on the method of the adaptation. Experiments on a natural gas–diesel dual-fuel engine are used to validate the proposed method.
This paper deals with a powershift automated manual transmission, i.e. an automated manual transmission with a torque gap filler, which essentially integrates, in a typical manual transmission layout, a torque gap filler assembly with the aim of reducing the torque gap that occurs during gearshifts. The torque gap filler consists of an additional mechanical link between the engine and the transmission output shaft, thus enabling the engine power to flow through this parallel path also when the launch clutch is disengaged, with clear benefits in terms of both sportiness and passenger comfort. This paper is the first part of a two-part study which, after a general description of the transmission architecture and its working principle, examines a practical implementation of the torque gap filler concept; the additional mechanical components and their integration into a traditional automated manual transmission are presented. Then, kinematic analysis and dynamic analysis of the transmission are proposed. The evolution of the transmission speeds are studied in the whole working range of the vehicle; the equations of motion are derived and used to show the effect of the torque gap filler on the torque transmitted to the wheels and consequently on the vehicle acceleration during gearshifts. The companion paper (Part 2) covers control issues and provides experimental validation.
This paper presents an observer-based fault detection and isolation strategy to detect and isolate an air leakage in the compressor–throttle path and a fault in the boost pressure sensor in a turbocharged gasoline engine. The strategy is applicable to engines not equipped with a hot-film air mass flow meter sensor. A novel combination of a turbocharger model and a control volume model for the pressure dynamics of the intercooler is used to design an asymptotically stable non-linear observer which estimates the unmeasured turbocharger variables. The turbocharger observer’s estimation error is used as a residual in the fault detection and isolation process where the effects of the measurement noise and the model simplifications are cancelled using the maximum-likelihood ratio as the test statistic. An engine charge estimation observer is added to the turbocharger observer for detection and isolation of the air leakage from the sensor fault. Validation of all models and the fault detection and isolation strategy is carried out for a modern gasoline turbocharged engine. The experimental results reveal the ability of the control-oriented strategy to perform online detection and isolation of air leakage through a hole with a diameter of 5 mm or larger.
A pinless friction stir spot welding tool with a scrolled convex shoulder is used to create spot welds on aluminum alloy plates. The effects that the rotation rate, the dwell time, the plunge depth, and the plunge rate have on the spot welding process are investigated. A strong correlation was found to exist between the joint strength versus the tool rotation rate and the joint strength versus the dwell time. Low rotation rates and short dwell times resulted in significantly stronger welds and, conversely, higher rotation rates and longer dwell times resulted in spot welds with hooking defects and lower joint strengths. Using shear tests and macrosection analysis on the spot welds, the dependences of the joint strength, the spindle torque, the temperature and the axial force on the identified process parameters are discussed. A computational fluid dynamics model is created to simulate the effect that the tool rotation rate has on the heat generated and the material flow during spot welding.
Low-temperature combustion in diesel engines offers attractive benefits through simultaneous reduction in the nitrogen oxide emissions and the soot emissions. However, it is known that the in-cylinder conditions typical of low-temperature combustion operation tend to produce high emissions of unburned hydrocarbons and carbon monoxide, reducing the combustion efficiency. The present study develops from the hypothesis that this characteristic poor combustion efficiency is due to the in-cylinder mixture preparation strategies which are non-optimally matched to the requirements of the low-temperature combustion mode. In this work, the effects of three key fuel path parameters, namely the injection fuel quantity ratio, the dwell and the injection timing, on the carbon monoxide and hydrocarbon emissions were examined using a central-composite-design design-of-experiments method. The experiments were performed on a single-cylinder diesel research engine operating in a mixing-controlled low-temperature combustion mode at high and moderate exhaust gas recirculation rates with a split fuel injection for all conditions. The experiments identified the potential of fuel metering control for optimising the hydrocarbon emissions in low-temperature combustion by showing the effects of the fuel control parameters on the fuel mixing quality and the emission formation mechanisms. The response surfaces created from the detailed statistical analysis give a potent visualisation of the constraints on low-temperature combustion operation. This in turn allowed improved prescription of combustion modifications with the potential to moderate the negative effects observed.
The number of engine control actuators and potential fuel sources are constantly increasing to meet fuel economy targets and global energy demand. The increased engine control complexity resulting from new actuators and fuels motivates the use of model-based control methodologies over map-based empirical approaches. Purely physics-based control techniques have the potential to decrease calibration burdens but must be complex to represent nonlinear engine behavior with low computational requirements. Artificial neural networks are recognized as powerful tools for modeling systems which exhibit nonlinear relationships, but they lack physical significance. Combining these two techniques to produce semiphysical artificial neural network models which provide acceptable accuracy while minimizing the artificial neural network size, the calibration effort and the computational intensity is the focus of this research. To minimize the size of the neural network, sensitivity analyses are carried out on the critical inputs and the minimum number of required neurons. The most critical physical parameters are selected as follows: the laminar flame speed; the turbulence intensity; the total in-cylinder mass. The control algorithm derivation is described, and the process validated in real time using an engine dynamometer. The real-time experimental results demonstrate that the semiphysical artificial neural network approach can produce accurate ignition timing control for both gasoline and E85. Robustness of the semiphysical neural network approach is also discussed on the basis of the real-time experimental results.
One of the major shortcomings to be addressed in the widespread applications of biodiesel fuel for compression ignition engines is the formation of higher nitric oxide emissions. It is well established in the literature that thermal nitric oxide is a dominant source for nitric oxide formation in engines. Thermal nitric oxide formation increases by any in-cylinder combustion strategy that alters the in-cylinder temperatures, the oxygen fraction or the residence time of high-temperature post-flame burned gases. The differences between the properties of biodiesel in terms of a higher bulk modulus, a higher cetane number and the presence of a fuel-bound oxygen fraction and the properties of diesel are found to affect the in-cylinder charge conditions and thus the nitric oxide formation. The present work aims to understand the major contributor to the higher nitric oxide formation with biodiesel based on experimental investigations in two different engine configurations: one with a conventional mechanical-type injection system and the other with a modern common-rail direct-injection system. The experimental results highlight that the dynamic injection timing advanced up to a maximum of 2.6° crank angle owing to the higher bulk modulus of biodiesel. This factor contributes to specific nitric oxide emissions which are 7.5% higher in an engine having a mechanical-type injection system. The increase in the nitric oxide is neutralized on restoring the injection timing to that of the diesel injection time setting. In the case of an engine with a modern common-rail direct-injection system, the injection timings remain unaltered, and the nitric oxide concentrations for diesel and for biodiesel–diesel blends also remains the same.
This paper presents a control algorithm for the motorized active suspension damper. The control algorithm consists of supervisory, upper-level and lower-level controllers. The supervisory controller determines the control modes, such as the passive mode, the roll mode and the body acceleration mode. The upper-level controller computes the damping force using linear quadratic control theory. The actuator input is determined by the lower-level controller. Three state estimators, namely the vehicle body's velocity estimator, the suspension state estimator and the friction estimator, are proposed to estimate the sprung-mass and unsprung-mass velocities, the tyre deflection, the roll angle, the roll rate and the friction. The performance of the proposed control algorithm was evaluated via simulations and vehicle tests. It was shown from both simulations and vehicle tests that the proposed control algorithm can improve the ride quality using a motorized active suspension damper.
In this paper an analysis method for a collision between a motorcycle and a car is presented, with the limitation that the frontal part of the motorcycle is involved, with wheelbase shortening. The velocities of the vehicles before the collision are usually the most important information for analysis of an accident and its causes, and therefore the methods to succeed in estimating these velocities are of great importance. The work focuses on finding an empirical formulation for the relative velocity between the motorcycle and the other vehicle, starting from the kinetic energy loss due to the collision and allowing for the mass of the motorcycle’s rider at the moment of collision. The equation was found by numerically simulating seven different impact configurations between a car and a motorcycle, with various impact velocities and masses in predefined ranges. Experimental crash tests conducted between a car and a motorcycle and the use of a high-speed video camera allowed the motion of the two-wheeler and its driver to be studied during the impact. A series of tests on crashes between a motorcycle with a rider and a vehicle was carried out, which also allowed validation of the formulation found.
In order to approach properly a wide variety of issues concerning urban large passenger transport vehicles, such as the design of the bus structure, the comfort of passengers, the non-collision injury risk and the operating characteristics of the bus, detailed knowledge of the loads that the buses support when operating is required. These loads depend on numerous factors such as the geographic and urban features of the city where they operate, the type of route and the driver. All these factors provide the nature of these loads with a wide variability, and so studies based on experimentally obtained data during representative periods of operation must be developed. The main objective of the present paper is to carry out a representative characterization of the operating loads supported by large passenger transport vehicles during normal operation. It is with this aim that a study of the longitudinal accelerations and lateral accelerations to which large passenger transport vehicles are subjected was conducted over urban routes by using the data collected by the Global Positioning System. An extensive assessment of recorded data was carried out to evaluate whether the precision and the sample rate of the Global Positioning System were sufficient to characterize these accelerations accurately. To ensure that the sample was representative, data for an operation time of more than 600 h were recorded using 10 different models of large passenger transport vehicles operating over 13 different urban routes. From all the position data recorded, the instant longitudinal accelerations were calculated using second-order central differentiation, and the lateral accelerations were obtained using first-order central differentiation and the curvature radius. All the calculated accelerations were then subjected to data processing developed on an ad-hoc basis to filter the information that did not refer to accelerating manoeuvres. After this data-processing procedure, it was verified that both the lateral accelerations and the longitudinal accelerations fit normal probability distributions with a minimum margin of error (maximum differences of 0.165 m/s2 for lateral accelerations and 0.038 m/s2 for longitudinal accelerations).
This paper presents the background rationale and key findings for a model-based study of supercritical waste heat recovery organic Rankine cycles. The paper’s objective is to cover the necessary groundwork to facilitate the future operation of a thermodynamic organic Rankine cycle model under realistic thermodynamic boundary conditions for performance optimisation of organic Rankine cycles. This involves determining the type of power cycle for organic Rankine cycles, the circuit configuration and suitable boundary conditions. The study focuses on multiple heat sources from vehicles but the findings are generally applicable, with careful consideration, to any waste heat recovery system. This paper introduces waste heat recovery and discusses the general merits of organic fluids versus water and supercritical operation versus subcritical operation from a theoretical perspective and, where possible, from a practical perspective. The benefits of regeneration are investigated from an efficiency perspective for selected subcritical and supercritical conditions. A simulation model is described with an introduction to some general Rankine cycle boundary conditions. The paper describes the analysis of real hybrid vehicle data from several driving cycles and its manipulation to represent the thermal inertia for model heat input boundary conditions. Basic theory suggests that selecting the operating pressures and temperatures to maximise the Rankine cycle performance is relatively straightforward. However, it was found that this may not be the case for an organic Rankine cycle operating in a vehicle. When operating in a driving cycle, the available heat and its quality can vary with the power output and between heat sources. For example, the available coolant heat does not vary much with the load, whereas the quantity and quality of the exhaust heat varies considerably. The key objective for operation in the vehicle is optimum utilisation of the available heat by delivering the maximum work out. The fluid selection process and the presentation and analysis of the final results of the simulation work on organic Rankine cycles are the subjects of two future publications.
One of the most important tasks in designing an automatic transmission system is to find the gear ratios and the corresponding number of gear teeth. In this paper, an artificial neural network and a genetic algorithm are used for this optimization with regard to an epicyclic gear train. First, MATLAB and an artificial neural network are employed to model the system, and the results depict the accuracy of the artificial neural network calculations. Then, using the same software and with the aid of a genetic algorithm, the optimized speed ratios and gear ratios are obtained. It can be seen that a series of gear ratios is produced. Another genetic algorithm was used to calculate the optimized gear ratio and the corresponding number of gear teeth. A Simpson gear train is used to demonstrate the methodology. The proposed model is very accurate and efficient, such that the resulting numbers of optimized gears have an error of less than ±0.3%. This method is much easier and has a lower computation cost than solving the related equations.
The effects of a split injection were investigated in a spray-guided direct-injection spark ignition engine under lean stratified operation. In-cylinder pressure analysis, exhaust emissions measurement and visualization of the spray and combustion were applied. From the results using a single-injection strategy, stratified combustion showed advanced and rapid combustion characteristics. However, the low work conversion efficiency and the high nitrogen oxide emissions were obstacles to stratified combustion. Furthermore, the smoke emissions were high as a result of the dominant mixing-controlled combustion. A dual-injection strategy was applied to control the level of stratified combustion by modifying the dwell time and the split ratio. With a split injection, the nitrogen oxide emissions and the smoke emissions were reduced because of the moderated combustion speed and the enhanced local homogeneity. The liquid phase of the stratified mixture and the luminous sooting flame were reduced significantly as well. However, a low combustion efficiency and a low indicated mean effective pressure resulted owing to the over-mixing effect when the portion of lean premixed combustion was increased. Via moderately controlled stratified combustion, a split injection could be an effective way to reduce the nitrogen oxide emissions and the smoke emissions with a reasonable indicated mean effective pressure and a reasonable combustion efficiency.
This paper describes the application of a parallel finite-volume compressible Navier–Stokes computational fluid dynamics solver to the complex aerodynamic problem of a land-based supersonic vehicle, BLOODHOUND SSC. This is a complex aerodynamic problem because of the supersonic rolling ground, the rotating wheels and the shock waves in close proximity to the ground. The computational fluid dynamics system is used to develop a mature vehicle design from the initial concept stage, and the major aerodynamic design changes are identified. The paper’s focus, however, is on the predicted aerodynamic behaviour of the finalised (frozen) design which is currently being manufactured. The paper presents a summary of the data bank of predicted aerodynamic behaviours that will be used as the benchmark for vehicle testing and computational fluid dynamics validation throughout 2015 and 2016 in an attempt to achieve a Land Speed Record of 1000 mile/h (approximately Mach 1.3). The computational fluid dynamics predictions indicate that the current design has a benign lift distribution across the whole Mach range of interest and a sufficiently low drag coefficient to achieve this objective. It also indicates that the fin is sized appropriately to achieve the static margin requirements for directional stability. The paper concludes by presenting the impact of feeding the detailed computational fluid dynamics predictions into the overall vehicle performance model together with recommendations for further computational fluid dynamics study.
The methodology for studying a tyre blow-out process using both experiments and simulations is presented in this paper. To achieve this, a tyre blow-out generator and an experimental device for tyre blow-out are developed. Moreover, tyre blow-out experiments in the static state are implemented. Then, the finite element tyre model corresponding to the experiments is established. The experimental results show that the tyre blow-out generator developed can effectively replicate the sudden inflation pressure loss without inflicting permanent damage on the tyre structure. The comparison between the simulations and the experiments shows that the finite element tyre model developed can simulate the tyre blow-out phenomenon and that the simulation analysis method is correct and effective. The tyre blow-out generator developed and the finite element tyre model established therefore provide the basis for further simulations and investigations of tyre blow-out during the normal motion of a vehicle and its effect on the handling stability.
An estimation of the realistic permeability of a soot deposit layer accumulated in a wall-flow diesel particulate filter was performed in this study. A unique contribution of this work is that the current methodology is highly applicable to the real-world design and development processes of diesel particulate filters. To conduct baseline simulation, a one-dimensional numerical model describing the behaviours of the exhaust gas and soot within a diesel particulate filter was constructed, employing the well-known single-channel approach. On the basis of this in-house model, the microstructural properties of a soot deposit layer were calibrated by finding the best fit to the measurement data adopted from the open literature. For the optimal applicability of the proposed methodology, the permeability of the deposit is modelled as a variable which depends on the temperature and the average wall velocity, while the porosity is constant. The current model and methodology were validated by comparison with the measurement data for pressure drops through diesel particulate filters. In particular, to boost the practical implementation of the current methodology, a map of the permeability of the soot deposit was created as a function of the operating conditions. In the last part of this study, the pressure drop characteristics through a diesel particulate filter under various operating conditions were examined using an analysis of the breakdown of the individual pressure drop mechanisms.
This paper is concerned with developing a new method for measuring a driver’s steering efficiency during a steering manoeuvre, for investigating the driver’s steering performance and for evaluating the steering comfort. Electromyography was successfully used to measure the driver's muscle activity and to reveal the function of the driver's key muscles in the steering manoeuvre. A measurement of the driver's steering efficiency during a dynamic steering manoeuvre with two hands is presented on the basis of a regression analysis of the electromyography and steering-force data. The proposed measurement procedure consists of two parts. First, a multiple-regression analysis of the steering-force and electromyography data is conducted, and the steering forces in the steering wheel plane are predicted using the electromyography data of the key muscles producing the steering torque. Second, by predicting the steering force, the force capacity of the driver in the steering manoeuvre is estimated, and then the steering efficiency of the driver is measured. The steering efficiency of the driver, which characterizes the inefficiency, is thought to be a significant movement control strategy employed by driver, and its application in investigating the driver's steering strategy is the subject of further study.
This paper focuses on the safety and stability of a four-wheel independent driving electric vehicle under various braking failure conditions. The power of this four-wheel independent driving electric vehicle is generated from four in-wheel motors using by-wire technology. A dynamic coupling vehicle model with the function of four-wheel driving and four-wheel steering, which includes a flexible suspension system, is established. Subsequently, by combining the change in the non-linear tyre forces at each corner, a quantitative analysis of the transient dynamic behaviours is conducted for different braking failure cases. The control authorities for front steering and rear steering are presented for the special electric vehicle model. Based on functional redundancy of corrective yaw moment generation, three steering control strategies are proposed for fault tolerance in braking failure cases, which include control of the front steering, control of the rear steering and control of the integrated front and rear steering. The controllers of the steering system are designed on the basis of the integral sliding-mode method and a simplified reference model with four-wheel steering. Finally, the effect of the steering control strategies for different braking failure cases are compared with numerical simulations. The result suggests that braking failure could be effectively controlled by using the functional redundancy of the steering system. However, not all steering corrective techniques are available; some even cause performance deterioration for the special condition, and an appropriate control strategy is recommended for different failure cases.
An improvement in the fuel economy of nontactical vehicles has and continues to be a significant initiative for US military ground vehicles. This paper investigates the potential improvement in the fuel economy of a prototype-built nontactical series hybrid cargo van. A baseline conventional vehicle is first modeled and validated. The current series hybrid van equipped with a lead–acid battery pack and an a.c. induction traction motor is then modeled and simulated in two driving cycles. A vehicle equipped with a nickel–metal hydride battery pack and a vehicle with a lithium-ion battery pack, together with an optimal hybrid powertrain control strategy, are simulated for further improvement in the fuel economy. The simulation results indicate improvements in the fuel economy of 39.6% and 43.6% for the vehicle with a nickel–metal hydride battery pack and the vehicle with a lithium-ion battery pack respectively. A hardware-in-the-loop application for motor-in-the-loop testing is also conducted to evaluate a permanent-magnet traction motor which is designed to replace the current induction motor. This study provides a design guideline and battery pack sizing for series hybrid powertrains in light-duty nontactical vehicles.
Lap time simulation is one of the most powerful tools for evaluating design proposals in motorsport engineering. In particular, transient simulations play an important role as the ultimate and more accurate approach than other static or quasi-steady-state methodologies. In this paper, first, the method to transform the differential equations of a system into a formally linear continuous and then discrete state-space representation, particularised for a seven-degree-of-freedom suspension and a transient cornering model, is proposed. The use of time-variant coefficients in the matrices of the model will allow the non-linear and time-variant characteristics of these systems to be described. Second, in the case of the transient cornering model, this representation is translated into a transfer function in order to apply a discrete control strategy such as a finite-time strategy or a predictive strategy for an adaptive ideal driver. It was found that the calculation methodology described above can be successfully applied with a more than acceptable degree of accuracy according to comparison with the results using other mechanical or numerical software (ADAMS or Simulink). It was also observed that the use of the curvature of the track as a reference in the control closed loop is sufficiently accurate to force the car to follow the target path closely. Furthermore, both predictive control and finite-time control (including integration) provide excellent results with a smooth response of the steering input. Many lap time simulators are language specific; however, the methodology proposed in this paper will run in most programming languages.
Lap-time simulation is an important computational tool for many motor racing teams, but the assumption of ideal operating conditions and a ‘perfect’ racing driver is usually made. The aim of this paper is to extend lap-time simulation to include robustness to disturbances on the vehicle and robustness to mistakes by the driver. A previously developed receding-horizon model predictive control with a convex optimisation method for lap-time simulation is extended with a tube-based technique for robust model predictive control. A linear quadratic regulator compensatory controller maintains the vehicle close to the nominal vehicle path and speed trajectories in the presence of disturbances to the vehicle. An ensemble of disturbed trajectories defines a tube of trajectories, which is then used to modify the nominal vehicle path so that the track boundary constraints are satisfied in the presence of the disturbances. The lap time versus r.m.s. steering velocity curves for two different vehicle models demonstrate the expected trade-off: a decrease in the activity of the compensatory steering control increases the tube width, which leads to a longer lap time. The technique has application to designing and setting up cars to perform well in the presence of disturbances.
In this paper an alternative method is proposed for defining the suspension performance targets through the use of full-vehicle modelling consisting of a ride model and a handling model. These models are derived with the use of a non-linear damper, suspension kinematic characteristics and basic vehicle dimensions. The vehicle performances can be explored using the design-of-experiments method. The non-sorting method is then employed to sort for non-dominated solutions, where these samples represent the Pareto front of the vehicle performances in ride comfort and handling. The k-means clustering method is used to classify further the solution into different unique optimum characteristics. The expectation–maximization algorithm is developed to compute the allowable variance of design parameters required to achieve the specific optimum design targets. This method can be a very useful tool in the earliest design stages where vehicle data are inadequate. This methodology potentially reduces the uncertainty in the achievable vehicle performance targets by allowing engineers to compare the optimum limit of the suspension with those of benchmark vehicles in the early suspension design and development process
A perforated resonator can attenuate the broadband noise generated by the air intake system of a turbocharged engine. This paper mainly focuses on the sound transmission theory of a perforated resonator with a multi-chamber. The numerical decoupling method for a perforated resonator with a single chamber is extended to a perforated resonator with a multi-chamber in order to calculate the transmission loss. To verify the modified algorithm, a two-microphone method is adopted to measure the transmission loss of the resonator. The measurement uncertainty of the experiment is discussed further. The experimental and analytical results on the resonator are presented, and good agreement is found. To determine the optimal structural parameters of the resonator in order to match the given target, a modified algorithm obtained by using the non-linear least-squares method is proposed for the resonator, and a detailed analysis of the selection of the design variables and optimization modes with different design variables is carried out. The optimized results show that all optimization modes can meet the target curve. Therefore, it provides multiple solutions for researchers to determine flexibly the best solution. Finally, a robustness analysis is carried out to show that the variations in the structural parameters have little effect on the transmission loss. It is expected that the research methods and conclusions of the study can provide theoretical support and application guidance for the sound design of a turbocharged engine air intake system.
Skid steering has been applied to various electric vehicles and unmanned vehicles because of its advantages in mobility and layout flexibility. This paper proposes an analytical lateral dynamic model of skid steering for a wheeled vehicle that could be applied to its design and control. The model is described by second-order ordinary differential equations in an explicit form. The steady-state characteristics of skid steering for wheeled vehicles are analysed on the basis of differential equations. The results of the steady-state analysis show that the steady-state response of the skid-steered wheeled vehicle is determined by the stability factor. When the vehicle has a neutral steer property, the neutral yaw rate gain is positively related to the velocity difference, and the neutral turning radius is inversely related to the velocity difference rate.
This paper focuses on the design of the power management strategy as the key factor in improving the performance in terms of the efficiency, the range and the fuel consumption for a small-scale series hybrid electric vehicle. A complex hybrid vehicle system is considered, and a practically realisable and traceable neurofuzzy strategy for improving the vehicle efficiency is introduced. The method results in extending the vehicle’s range while deciding when to switch the internal-combustion engine on or off as a function of the state of charge of the battery and the electrical power produced from the generator. Consequently, the speed of the internal-combustion engine (i.e. the current produced) is determined as a function of the driving conditions. Suitable tests were performed in order to verify the effectiveness of the proposed strategy; the verification tests were carried out using a consolidated model which also includes real-world experimental vehicle data. The results show that, by using the proposed power management strategy, a good compromise between the efficiency, the range and the fuel consumption can be obtained in many practically useful driving conditions.
Because of the storage and safety of hydrogen on board vehicles, there still exist many problems; this paper introduces a system of hydrogen-rich gases and its application to an electronically controlled spark ignition engine. The hydrogen-rich gases from the designed reformer are produced by methanol dissociated by the heat recycled from the exhaust emissions of an engine. The effects of the hydrogen-rich gases on the performances of the engine were investigated for lean-burning operations. The test results indicate that the engine can operate using a very lean fuel mixture owing to the wide ignition limits of the hydrogen-rich gases. When the excessive air-to-fuel ratio is higher than 1.4, the nitrogen oxide emissions are reduced by 90%, the carbon monoxide emissions are ultra-low, and the hydrocarbon emissions are at nearly the same level as those produced from a gasoline engine. In addition, while maintaining the power output of the engine, lean burning of the hydrogen-rich gases and partial recycling of the exhaust heat significantly improve the brake thermal efficiency of methanol.
With a combination of dual-fuel injection and exhaust gas recirculation or intake air temperature control to retard the homogeneous charge compression ignition combustion phase, the potential of expanding the homogeneous charge compression ignition load range was investigated. The experimental work was carried out on a real-time control dual-fuel homogeneous charge compression ignition operation test bench, which was based on a four-cylinder optimized kinetic process engine. It was observed that, with gasoline and n-heptane injection, the acceptable ranges of the exhaust gas recirculation rate and the intake air temperature were enlarged, and the load range of the homogeneous charge compression ignition engine was expanded. The intake air flow quantity can be raised by reducing the intake air temperature, and the indicated thermal efficiency of homogeneous charge compression ignition can be increased by utilizing sufficient n-heptane in the fuel. Compared with exhaust gas recirculation, intake air temperature control might be a better method to improve the indicated thermal efficiency of homogeneous charge compression ignition combustion. Also, from the viewpoint of deterioration in the emissions, exhaust gas recirculation is a better strategy for load expansion in homogeneous charge compression ignition with a high ratio of gasoline to fuel.
Narrow tilting vehicles offer an opportunity to reduce both traffic congestion and carbon emissions by having a small road footprint, a low weight and a small frontal area. Their narrow track requires that they tilt into corners to maintain stability; this may be achieved by means of an automated tilt control system. Automated tilt control systems can be classed as steering tilt control in which active control of the front-wheel steering angle is used to maintain stability, direct tilt control in which some form of actuator is used to exert a moment between the tilting part(s) of the vehicle and non-tilting part(s), or a combination of the two, namely steering–direct tilt control. Combined steering–direct tilt control systems have the potential to offer improved performance as, unlike steering tilt control systems, they are effective at low speeds while offering superior transient roll stability to direct tilt control systems. This paper details the implementation of a steering direct tilt control system on a prototype narrow tilting vehicle and presents experimental results which demonstrate a 36% reduction in load transfer from the inside wheel to the outside wheel during a ramp-steering manoeuvre when compared with a direct tilt control system.
Recovering the kinetic energy of a vehicle is one inherent advantage of an electric vehicle. A permanent-magnet synchronous motor is widely adopted for the traction motor in an electric vehicle with the advantage of a high efficiency and a high torque density. The principle for electric braking control of the permanent-magnet synchronous motor under field-oriented control is studied. The efficiency model of the electric drive system, which is different from that of the internal-combustion engine drive system, can be exactly described by analytical equations. On this basis, the battery power can be expressed as a function of the angular velocity and the electromagnetic torque of the motor. By solving the partial differential equation for the battery power, the instantaneous optimal regenerative braking torque of the permanent-magnet synchronous motor is simply calculated according to the vehicle braking torque demand and the motor speed. Compared with the existing efficiency map method, the analytical technology is easily implemented. Then a four-wheel-drive electric vehicle is investigated to achieve optimal regenerative braking control. The dynamic behaviour of braking in the four-wheel-drive electric vehicle is also considered. The parallel braking pattern and the series braking pattern are investigated in order to evaluate the availability of braking energy recovery. The instantaneous optimal regeneration energy can be recovered for the series braking system, and a significant amount of energy can be recovered for the parallel braking system by adjusting the free travel of the brake pedal.
This paper presents a path-planning strategy for autonomous vehicles which aims to provide safe and feasible manoeuvres in various driving environments. Our strategy uses a hierarchical architecture which consists of three components: a behaviour planner, a map and path selector and a local-path planner. The behaviour planner performs the rule-based decision process which determines the overall vehicle manoeuvres. The map and path selector preprocesses perception data and chooses a local-path-planning algorithm using the results of the behaviour planner. From this selection, the local-path planner generates a driveable and collision-free path. For reliable path generation under various driving conditions, the proposed local path planner employs two algorithms: a road-model-based path planning algorithm and a graph-structure-based path-planning algorithm. The former is used for structured road driving, such as lane keeping or changing, and the latter is used for unstructured road driving. The proposed hierarchical path-planning algorithm was implemented in the autonomous vehicle called A1, which was applied with an in-vehicle-network-based distributed system architecture. A1 won the 2012 Autonomous Vehicle Competition organized by the Hyundai Motor Group in Korea.
An electronic brake safety evaluation index is proposed as a quantitative analysis metric for evaluating the fail-safe control strategies of brake-by-wire systems for improvement in the straight braking stability. The proposed electronic brake safety evaluation index is developed with the combination of a longitudinal deceleration deviation term and a lateral deviation term of a vehicle in straight braking situations. A fuel cell electric vehicle with a brake-by-wire system model is used to simulate the effectiveness of the electronic brake safety evaluation index in various failure modes. Brake safety evaluation scenarios are proposed to find effective fail-safe control strategies for the brake-by-wire systems. The simulation results for the fail-safe control strategies of a brake-by-wire system in various failure modes show that the proposed electronic brake safety evaluation index can be a useful and effective quantitative metric for evaluating fail-safe control strategies in the development, verification and validation stages of brake-by-wire systems.
The vibration signal measured from the cylinder head contains much effective information about the combustion process. The vibration signal can be measured with a vibration displacement sensor, a vibration velocity sensor or a vibration acceleration sensor. In this study the signals measured with the three sensors were compared. The comparison results showed that the vibration displacement measured from the cylinder head is mainly caused by the fixed bracket of the diesel engine, and it is difficult to extract combustion information from the vibration displacement. The vibration velocity signal was compared with the pressure increase rate. The comparison results showed that the two signals have similar trends in the main combustion process. The vibration velocity signal contains much information about combustion. The vibration acceleration signal is hardly influenced by the fixed bracket but contains the vibration response excited by the impact of the opening and closing of the valves and other impact-exciting sources. Based on the results of analyses, it can be concluded that the vibration velocity sensor is the best sensor to estimate the combustion process. The vibration velocity signal was used to estimate the timing of the start of combustion for a two-cylinder homogeneous charge compression ignition engine. The results demonstrated that the accuracy of estimation fulfils the requirement of the application.
In this paper, a macroslip detection method is proposed for a metal V-belt continuously variable transmission, and a clamping force control strategy is suggested on the basis of a macroslip detection method. Using the rotational accelerations of the primary and secondary pulleys, the velocity of the secondary pulley and the speed ratio of the continuously variable transmission variator, observation signals are defined. The characteristics of the observation signals are investigated by simulations in a vehicle-driving environment. It is found that two observation signals became unsynchronized when macroslip occurs. Considering the oscillations of the acceleration signal and the noise from the sensors or the differentiating process, a signal-processing method for the observation signals is suggested. Based on the signal-processing results, a variable called the ‘amplitude difference rate’ is introduced for slip evaluation. A macroslip detection method that uses the amplitude difference rate is proposed. The effectiveness of the macroslip detection method is validated by experiments. It is found from the experiments that the proposed method can effectively detect macroslip with an acceptable time delay. In addition, a clamping force control strategy based on the macroslip detection method is developed. In this strategy, the clamping force is maintained at a minimum value with a safety factor of 1 in normal driving conditions but an additional clamping force is applied when macroslip is detected. It is found from the simulation results that macroslip is eliminated by clamping force control. It is expected that the efficiency of the continuously variable transmission system can be improved by reducing the marginal clamping force using the proposed macroslip detection method and the clamping force control strategy.
Dual-fuel technology has the potential to offer significant improvements in the emissions of carbon dioxide from light-duty compression ignition engines. In these smaller-capacity high-speed engines, where the combustion event can be temporally shorter, the injection timing can have an important effect on the performance and emissions characteristics of the engine. This paper discusses the use of a 0.51 l single-cylinder high-speed direct-injection diesel engine modified to achieve port directed gas injection. The effect of the pilot diesel injection timing on the dual-fuel engine performance and emissions was investigated at engine speeds of 1500 r/min and 2500 r/min and loads equivalent to gross indicated mean effective pressures of 0.15 MPa, 0.3 MPa, 0.45 MPa and 0.6 MPa, for a fixed gas substitution ratio (on an energy basis) of 50%. Furthermore, the effect of the pilot injection quantity was investigated at a constant engine speed of 1500 r/min by completing a gaseous substitution sweep at the optimised injection timing for each load condition. The results identify the limits of single-injection timing during dual-fuel combustion and the gains in the engine performance and stability that can be achieved through optimisation of the pilot injection timing. Furthermore, the pilot injection timing and quantity were shown to have fundamental effects on the formation and emissions of carbon monoxide, nitrogen oxide and total hydrocarbon. The potential for dual-fuel combustion to achieve significant reductions in the specific carbon dioxide was also highlighted, with reductions of up to 30% being achieved at full load compared with the baseline diesel case.
One of the major challenges in the control of advanced combustion modes, such as premixed charge compression ignition, is controlling the timing of the combustion event. A nonlinear model-based controller is outlined and experimentally shown to be capable of controlling the engine combustion timing during diesel premixed charge compression ignition operation on a modern diesel engine with variable valve actuation by targeting the desired values of the in-cylinder oxygen mass fraction and the start of injection. Specifically, the experimental results show that the strategy is capable of controlling the start of combustion and the intake oxygen mass fraction to within 1° crank angle and 1% respectively. A stability analysis also demonstrates that this control strategy ensures asymptotically stable error dynamics.
This paper deals with the frictional behaviour of a tyre tread elementary volume in sliding contact with road asperities. Friction is assumed to be composed of two main components: adhesion and deforming hysteresis. The target, which was fixed in collaboration with a motorsport racing team and with a tyre-manufacturing company, is to provide an estimation of local grip for online analyses and real-time simulations and to evaluate and predict adhesive and hysteretic frictional contributions arising at the interface between the tyre tread and the road. A way to approximate the asperities, based on rugosimetric analyses on a macroscale and a microscale, was introduced. The adhesive component of friction was estimated by means of a new approach based on two different models found in the literature, whose parameters were identified thanks to a wide experimental investigation previously carried out. The hysteretic component of friction was estimated by means of an energy balance taking into account the viscoelastic behaviour of rubber (which was characterized by means of appropriate dynamic mechanical analysis tests) and the internal stress–strain distribution (which was due to indentations of the road). The model results are finally shown and discussed, and the validation experimental procedure is described. The correct reproduction of the friction phenomenology and the model prediction capabilities are highlighted, making particular reference to the grip variability due to changes in the working conditions.
Fault monitoring in internal-combustion engines is crucial for keeping the vehicle performance within the acceptable standards of emission levels and drivers’ demands. This paper analyses how a vehicle’s performance and engine variables are affected by a leakage fault in the exhaust manifold. The threshold leakage that causes the vehicle to exceed the emission standards is determined for a class M1 vehicle tested on a chassis dynamometer over the New European Driving Cycle. It is shown that, when a leakage of 6 mm diameter on the exhaust manifold is introduced, the vehicle emissions exceed those specified in the European 2013 on-board diagnostics standard. In addition, the effects of the said leakage fault on the performance of a 1.7 l turbocharged gasoline engine are analysed at different speed–torque operating points by running the engine in a test cell. The results show that, for this 6 mm leakage, at most operating points the driver cannot notice any reduction in the engine torque. Using the engine performance analysis, a fault effect map for the turbocharged gasoline engine is obtained. This helps to design monitoring algorithms for detection of the exhaust manifold leakage fault. As an application of the map, a strategy is presented on the basis of a comparison between the measured and the estimated pressures downstream of the turbine for the purpose of detecting the exhaust manifold leakage.
This paper presents a mode shift control algorithm for reducing the variation in the driveshaft torque for a dual-mode power-split-type hybrid electric vehicle. To evaluate the shift characteristics of this hybrid electric vehicle, dynamic models for the hybrid electric vehicle powertrain were developed. Using the dynamic models, a mode shift performance simulator was developed, and simulations were performed. To analyse the shift characteristics during the mode shift, bond-graph models for the transient state were constructed, and state equations were derived. From the bond-graph models and state equations, it was found that the transient torque occurs because of the inertia torques of the first motor–generator and the second motor–generator. Based on the transient torque, a mode shift control algorithm was proposed, which compensates for the transient torque. To evaluate the performance of the proposed control algorithm, a test bench for the dual-mode power-split-type hybrid electric vehicle was developed. From the simulations and test results, it was found that the variation in the driveshaft torque was reduced by the proposed control algorithm, which provides improved shift quality.
Individually controlled electric motors provide opportunities for enhancing the handling characteristics and the energy efficiency of fully electric vehicles. Online power loss minimisation schemes based on the electric motor efficiency data may, however, be impractical for real-time implementation owing to the heavy computational demand. In this paper, the optimal wheel torque distribution for minimal power losses from the electric motor drives is evaluated in an offline optimisation procedure and then approximated using a simple function for online control allocation. The wheel torque allocation scheme is evaluated via a simulation approach incorporating straight-ahead driving at a constant speed, a ramp manoeuvre and a sequence of step steer manoeuvres. The energy-efficient wheel torque allocation scheme provides motor power loss reductions and yields savings in the total power utilisation compared with a simpler method in which the torques are evenly distributed across the four wheels. The method does not rely on complex online optimisation and can be applied on real electric vehicles in order to improve the efficiency and thus to reduce power consumption during different manoeuvres.
In this work, a short preview of traffic provided by on-board sensors is used to minimize fuel consumption in a parallel hybrid vehicle capable of controlling both the vehicle velocity and the torque-split ratio. A two-stage version of Pontryagin’s minimum principle was used, but some of the standard simplifying assumptions in reduced-order modelling of hybrid vehicles were avoided to ensure that the fuel economy is not unduly compromised. The proposed controller is implemented in a receding-horizon fashion to incorporate updated telemetry information at each sampling instant. The effectiveness of the proposed method is demonstrated by simulations on two hybrid vehicle models containing higher-order dynamics and non-linearities. It is shown that the controller maintains the engine operation within the high-engine-efficiency region, and successive improvements in the fuel economy are achieved as the traffic preview length is increased.
The nitrogen oxide emissions characteristics of biodiesel–diesel blends in a light-duty diesel engine operating at a moderate load are investigated using KIVA coupled with chemical kinetics. Pure diesel, 20 vol % biodiesel–80 vol % diesel and 50 vol % biodiesel–50 vol % diesel are investigated. A reduced mechanism concerning methyl butanoate and n-heptane is applied in the combustion model. The characteristics of the combustion and nitrogen oxide emissions for different fuels are compared. The effects of the injection timing and the exhaust gas recirculation rate on the nitrogen oxide emissions are of particular interest. The results show that 50 vol % biodiesel–50 vol % diesel has the shortest ignition delay, the longest spray penetration and the lowest fuel-to-oxygen equivalence ratio at the spray tip under the same initial conditions, which results in the highest nitrogen oxide emissions. As the injection timing is retarded, the nitrogen oxide emissions of blended fuels gradually decrease. The nitrogen oxide emissions of 50 vol % biodiesel–50 vol % diesel are close to those of the diesel case with increasing exhaust gas recirculation rate from 19.6% to 25%. By further increasing the exhaust gas recirculation rate to 28%, the nitrogen oxide emissions can be reduced further. It is thus suggested that increasing the exhaust gas recirculation rate by a small amount is more effective in controlling the formation of nitrogen oxides for blends with a high biodiesel content than injection timing retardation is at a moderate engine load.
This paper presents a numerical model for evaluating fugitive dust emissions and transport in a near field induced by a moving vehicle. The dust emission model describes the quantity and location of emitted dust. The transport of the dust is recorded by the Lagrangian particle-tracking method, and the turbulence dispersion of particles is modeled stochastically. The presented model is validated numerically for the prediction of dust concentration in a region near the vehicles through a careful comparison with the available experimental data. The simulation results compare reasonably well with the experimental data. This model provides, for the first time, a validated dust emission and transport model suitable for the near field of moving vehicles.
Partially premixed compression ignition in a diesel engine is a combustion mode between diffusion combustion and homogeneous charge compression ignition combustion, the combustion controllability and the emission performances of which are close to those of a homogeneous charge compression ignition combustion engine; the mixing period plays a key role in realizing partially premixed compression ignition, and a long premixed process before combustion is necessary to make the fuel and air mix well. Partially premixed compression ignition combustion in a boosted six-cylinder heavy-duty diesel engine is realized by adjusting the injection timing and the rate of exhaust gas recirculation based on a single injection. The effects of the injection timing, the exhaust gas recirculation rate and the load rate on the combustion and the heat release pattern are studied. The factors which influence the mixing period and the ignition delay and its regularity are researched. Endoscope technology and the two-colour method are also used to gain an insight into partially premixed compression ignition combustion. The results show that both early injection and late injection have a long mixing period, which helps to form a more homogeneous mixture, and no diffusion combustion is found in the heat release rate curves. Premixed combustion and low-temperature combustion are the key factors in reducing the particulate matter emissions and nitrogen oxide emissions simultaneously. However, the low-temperature combustion and the dilute mixture may lead to incomplete combustion; consequently, for relatively late-injection conditions, the hydrocarbon and carbon monoxide emissions increase dramatically and the fuel consumption becomes worse. In these partially premixed combustion patterns, the effect of the injection pressure on the particulate matter and nitrogen oxide emissions is not clearly observable. At lower load rates, partially premixed compression ignition combustion displays a low-temperature and a high-temperature two-stage heat release. When the engine load rate is increased to 50%, diffusion combustion appears in the early-injection modes, which leads to higher nitrogen oxide and particulate matter emissions.
Experiments were carried out on the exhaust of an engine on a test bed with a selective catalytic reduction catalyst. The reductant could be introduced either as 5% ammonia in nitrogen gas or as a spray of aqueous urea droplets. Conversion of nitrogen oxides was investigated at temperatures near 488 K (215 °C) and 533 K (260 °C), which are typical of a diesel passenger car exhaust system. The experiments with a urea spray were carried out for three reductant levels, i.e. for two reductant levels that were deficient and for one reductant level that was approximately stoichiometric. The experiments were run to steady state conditions. The spray was introduced into the system in two different ways, sprayed either into a mixing can and nozzle arrangement or into the system via an oblique pipe; in the latter case the spray impinged on an angled plate mixer. A transient case was also investigated where the engine load was ramped up from a brake mean effective pressure of 6 bar to 10 bar over 20 s and, after reaching the steady state, was ramped back down to a brake mean effective pressure of 6 bar over 20 s and allowed to reach a steady state. The nitrogen oxide supplied was 100% nitric oxide in all these experiments. This was achieved by using a palladium diesel oxidation catalyst to remove hydrocarbons and carbon monoxide from the exhaust stream but without oxidising the nitric oxide. Measurements were made with a Fourier transform infrared gas analyser. The steady-state results showed that the percentage nitric oxide conversion observed using a urea spray had a value that was about 10% below the percentage conversion observed with ammonia gas when using either spray configuration. There was evidence that urea droplets were being transported unconverted through the selective catalytic reduction catalyst in both steady-state engine-load tests and transient engine-load tests. The ammonia deficit was 20% or more of the potential amount of ammonia injected by the aqueous urea spray.
This paper describes a dynamic model with four degrees of freedom for simulating the rollover stability performances of articulated loaders. The dynamic model considers three translational degrees of freedom and a rotational degree of freedom about the tilting axis and was verified by field experiments and virtual prototype experiments. The field experiments using a scaled articulated loader are detailed, and the experimental data of the lateral load transfer ratio, the lateral acceleration and the roll angle of the vehicle are provided for classification at different speeds and different turning radii. The virtual prototype experiments are modelled on the experimental model as well as the simulation conditions. Comparing the experimental data with the theoretical data shows that the dynamics model is reasonable and that the virtual prototype simulation can be used instead of the field experiments to improve the security of active safety technology development.
In order to comply with increasingly stringent diesel-engine emission legislation, fast and precise control of the turbochargers and exhaust-gas recirculation are necessary. The difficulties lie in certain disadvantageous plant properties such as cross-couplings and non-linearities, the disturbance of the air path by fast operating-point changes and the multitude of air-path configurations that are available. In this paper, a novel model-based approach for air-path control based on cascaded control is proposed. The resulting multi-variable controller has a low sensitivity to the non-linearity of the plant and the disturbances caused by sudden changes in the operating point. Furthermore, the controller is applicable to various types of air-path configuration. This flexibility is demonstrated by a system analysis of the models of two engines which span a broad range of air-path configurations. The performance of the proposed controller is compared experimentally with that of a conventional model-based multi-variable controller, by implementing both on an engine test bench. This comparison confirms that the cascaded controller presented herein can handle the cross-couplings of the system and that it exhibits a lower sensitivity to the non-linearity and the disturbances than the conventional controller does.
This paper deals with driving simulation and in particular with the important issue of motion sickness. The paper proposes a methodology to evaluate the objective illness rating metrics deduced from the motion sickness dose value and questionnaires for both a static simulator and a dynamic simulator. Accelerations of the vestibular cues (head movements) of the subjects were recorded with and without motion platform activation. In order to compare user experiences in both cases, the head-dynamics-related illness ratings were computed from the obtained accelerations and the motion sickness dose values. For the subjective analysis, the principal component analysis method was used to determine the conflict between the subjective assessment in the static condition and that in the dynamic condition. The principal component analysis method used for the subjective evaluation showed a consistent difference between the answers given in the sickness questionnaire for the static platform case from those for the dynamic platform case. The two-tailed Mann–Whitney U test shows the significance in the differences between the self-reports to the individual questions. According to the two-tailed Mann–Whitney U test, experiencing nausea (p = 0.019 < 0.05) and dizziness (p = 0.018 < 0.05) decreased significantly from the static case to the dynamic case. Also, eye strain (p = 0.047 < 0.05) and tiredness (p = 0.047 < 0.05) were reduced significantly from the static case to the dynamic case. For the perception fidelity analysis, the Pearson correlation with a confidence interval of 95% was used to study the correlations of each question with the x illness rating component IR x , the y illness rating component IR y , the z illness rating component IR z and the compound illness rating IR tot . The results showed that the longitudinal head dynamics were the main element that induced discomfort for the static platform, whereas vertical head movements were the main factor to provoke discomfort for the dynamic platform case. Also, for the dynamic platform, lateral vestibular-level dynamics were the major element which caused a feeling of fear.
The characterization of knock intensity distributions can provide useful insights into the process and help to improve knock control system designs. In this paper, an extensive statistical analysis is performed on knock intensity data recorded under a broad range of operating conditions. First, the critical issue of whether the data exhibit any cycle-to-cycle correlations is investigated, and it is shown that knock intensity closely approximates a cyclically independent random process. The study then focuses on the variation of knock intensity distributions with operating condition, and on the quantification of these distributions using simple scalar measures. The relationship between knock event distributions and knock intensity distributions is also investigated, and it is shown that knock event data are binomially distributed regardless of the underlying knock intensity distribution. This supports ongoing efforts to exploit binomial probability theory in knock event simulation and controller design.
In this paper the systematic development of an integrated braking controller for a vehicle driven by an electric motor on the front axle is presented. The objective is to engage the electric motor only during braking, up to the point at which the vehicle reaches its manoeuvrability and stability limit. The control challenges are to distribute the braking effort correctly between the hydraulic brakes at the four tyres and the electric motor, to handle the tyre saturation and motor constraints effectively and to adapt the control allocation based on the vehicle’s states. The controller is designed using the state-dependent Riccati equation control technique, the vehicle state estimation and the ‘magic formula’ tyre model. The state-dependent Riccati equation control technique is a suboptimal control design technique for non-linear systems. A novel method for constructing the state-dependent coefficient formulation of the system dynamics is proposed. Soft constraints in the state dynamics are described, while an augmented penalty approach is suggested for handling the system’s hard constraints. The performance of the controller was evaluated for different braking scenarios using simulations in a MATLAB/Simulink environment. An eight-degree-of-freedom non-linear vehicle model was utilized. The numerical results show that the controller suboptimizes the regenerative braking effort while considering the tyre force saturation, the motor torque limits, the vehicle yaw rate and the slip angle error. A comparison with a constrained linear quadratic regulator shows the advantages of the proposed controller.
The continuous drive for increased fuel efficiency and sustained innovation in the automobile industry requires the adoption of radically new technological advances. Road vehicle aerodynamic design is primarily concerned with reduction in the drag and generation of a downforce. Current trends in both aircraft and wind turbine blade design show significant interest in shape-adaptive (morphing) advanced structural concepts for improved aerodynamic performance or the realization of new functionality. Morphing structures are also of interest because they have the potential to create designs of simple construction and reduced mass. However, there is an inherent contradiction between the need to create compliant structures to keep actuator demands low and the requirement for designing stiff load-carrying structures. This highlights the key design challenge for morphing structures. Ways of addressing these conflicting demands include the use of advanced composite materials which have extremely anisotropic stiffness properties or multistable behaviour. This review provides a perspective on recent developments in research on morphing structures and the potential applications for these emerging technologies in automobile aerodynamic design.
Three-dimensional models of detailed wheel assemblies which have different spoke types are established. The effects of the number of spokes and the twist angle of the spokes on the air-flow field and the convective heat transfer of an automobile brake disc are investigated using the computational fluid dynamics method. To validate the numerical approach employed in this paper, two reference experiments were simulated and the calculation results agree with the experimental data well. It can be concluded from this study that the spoke type has a significant influence on the wheel flow field and the convective heat dissipation of the disc. When the twist angle of the spokes is kept at 0°, the convective cooling performance of the disc of a five-spoke wheel is better than that of the baseline and modified designs. When there is a constant number of spokes equal to six, the convective heat dissipation capacity of the disc improves as the twist angle of the spokes increases. An optimized spoke configuration is proposed and it has the best convective cooling performance of all the cases simulated in the present work.
In this study, a new controllable engine mounting system for vibration control of passenger vehicles is proposed. The proposed mounting system consists of two smart material actuators: a piezostack actuator and a magnetorheological-fluid actuator. First, the dynamic responses of an in-line four-cylinder engine supported by three rubber mounts are mathematically analysed by considering the six-degree-of-freedom motion of the engine body, whose excitation is generated by the inner forces during the engine combustion process. Second, the proper positions of the two actuators are determined. Two magnetorheological mounts are used as roll mounts, and one piezostack mount is used as the right-hand mount, in order to reduce the unwanted engine vibration in a broadband frequency range. Third, the piezostack mount and the magnetorheological mount are designed and manufactured, followed by installation in the engine mounting system. Subsequently, for effective vibration isolation, a sliding-mode controller, which is robust to disturbances and system uncertainties, is designed. Finally, in order to demonstrate the effectiveness of the proposed new engine mounting system, vibration control performances are evaluated by adopting the hardware-in-the-loop simulation test method associated with the sliding-mode controller. The vibration control responses are presented at various engine operating speeds in the time domain and the frequency domain. It was found that the vibration control performance is improved by 30% at an engine speed of 750 r/min and by 17% at an engine speed of 2000 r/min using the proposed engine mounting system associated with the controllers.
Previous methods for the evaluation of the sound quality in vehicle interiors focused on the linear regression analysis of subjective sound quality metrics using statistics and estimations of subjective sound quality values by neural networks. Recently, sound quality evaluation using subjective measures has focused on identifying sound quality metrics which can predict subjective responses. It has been used to study a variety of subjective measures such as the four parameters used by Zwicker, but it is difficult to identify highly correlated sound quality metrics with the jury test. The Mahalanobis distance is a useful method to reduce the number of dimensions and to develop measures based on the correlation between the various variables. In particular, the Mahalanobis distance can be used as a new sound quality metric because it can convert the sound quality that is represented by several measures to a single value. In this study, a new sound quality metric is suggested which employs the four parameters used by Zwicker and is based on the Mahalanobis distance in order to predict subjective responses in sound quality evaluation. In addition, in order to calculate the Mahalanobis distance more accurately, after using data from a number of vehicles, sound quality metrics were reselected to remove those that do not require correlation analyses between each metric. Finally, we verified that the logarithmic Mahalanobis distance can be used not only as a new sound quality metric through correlation analysis with a jury test but also as a criterion to determine the vehicle quality. In order to verify the reliability of the regression equation, arbitrary vehicle data are applied to the regression equation. The regression equation using the logarithmic Mahalanobis distance is validated by the listening results, and the regression results after applying arbitrary data are similar.
Piston rings play an important role in the lubricant system of reciprocating engines with consequences for engine wear, power losses and oil consumption. The computational solution of piston ring dynamics is a very complex problem which requires multiple numerical approaches supplemented by suitable inputs. This paper demonstrates the principles of the numerical solution of piston ring dynamics in mixed-lubrication conditions incorporating a virtual engine and experimental inputs. A simulation algorithm is integrated into the user-guided interface and it is available for industry usage. The solution results are presented for a passenger car petrol engine with a three-piston-ring configuration.
It is well known that the inflation pressure affects the tyre properties, which in turn influence the stability and safety of a vehicle. Single-track vehicles are characterized by some weakly damped vibration modes and are particularly sensitive to such variations. This work analyses the characteristics of a high-performance tyre set as a function of the inflation pressure through experimental characterization. The effect on the stability of a racing motorcycle is investigated at different speeds using an advanced motorcycle multi-body code.
Variable-displacement vane-type oil pumps represent one of the most innovative pump types for industrial applications, especially for engine lubrication systems. The aim of this paper is to develop a complete and accurate mathematical model for a typical variable-displacement vane-type oil pump to investigate its working performance. First, the detailed theoretical model was built on the basis of pump geometric design and dynamic analyses. Next, numerical simulations with the constructed model and experiments on the actual pump system were carried out to analyse the main power loss factors in order to develop the complete model for high modelling accuracy. The estimated pump performance using the complete pump model was finally verified by numerical simulations in comparison with practical tests.
Engine downsizing is an important route to meeting tightening emission regulations and improving engine efficiency. However, when a new air charging system such as a turbocharger is selected to enable downsizing of an internal-combustion engine for increased specific power and efficiency, extensive resource-intensive optimization procedures are currently required. In this paper, a method of emulating an engine charge system is developed on the basis of a charge air-handling unit and a real-time turbocharger model comprising map based compressor and turbine models with improved data density and range via numerical and analytical approaches. Variables such as the boost pressure, back pressure, turbocharger speed and the mass flow rate of air are used to compare the response of the charge system emulation with the real turbocharger. The emulation method achieves considerable accuracy when compared with the real turbocharger hardware. This approach will enable future engine developments to be assessed prior to the prototype hardware phase, resulting in significantly lower costs and shorter time frames for the development process.
Rubber-like materials are widely used in many fields and are often installed in various mechanical systems. These materials are used as dampers, oil sealing gaskets and other important automotive parts. In the design of rubber-like materials, engineers consider the lifetime, the durability and the reliability. The lifetime prediction of rubber material is very important in the design process; however, it is difficult to predict the lifetime of rubber materials because of changing properties under complex operational environments such as the temperature, the humidity and the vibration and because of long-time consumption. The highly accelerated life test is generally used to predict the long-term lifetime of rubber materials. We conducted compression set tests with polyacrylate (ACM) rubber gasket material and regressed the experimental data with several models using a successive zooming genetic algorithm. We compared the regressed recovery curves of the single-parameter model, the two-parameter model and the four-parameter model in terms of the mean squared error. Finally, using the Arrhenius equation, we predicted the quantitative long-term lives for a rubber gasket made of polyacrylate (ACM) rubber with chlorine cure sites at lower temperatures.
This paper aims at designing optimal gear shift strategies for conventional passenger vehicles equipped with discrete ratio transmissions. In order to study quantitatively an optimal trade-off between the fuel economy and the driveability, the vehicle driveability is addressed in a fuel-optimal gear shift algorithm based on dynamic programming by three methods: method 1, weighted inverse of power reserve; method 2, constant power reserve; method 3, variable power reserve. Furthermore, another method based on stochastic dynamic programming is proposed to derive an optimal gear shift strategy over a number of driving cycles in an average sense, hence taking into account the vehicle driveability. In contrast with the dynamic-programming-based strategy, the obtained gear shift strategy based on stochastic dynamic programming is real time implementable. A comparative analysis of all proposed gear shift methods is given in terms of the improvements in the fuel economy and the driveability. The variable-power-reserve method achieves the highest fuel economy without sacrificing the driveability.
Highly pressurized direct injection applied to automotive vehicles was developed for better power and fuel efficiency, but it causes fuel impingement, which generates more soot emissions. In the present study, analyses of the combustion characteristics and fuel impingement were conducted with a direct-injection spark ignition engine using split-injection strategies. Full three-dimensional unsteady Eulerian–Lagrangian two-phase numerical simulations were carried out to predict the flow field and the combustion characteristics as functions of the injection duration ratio and the weight of the second pulse injection. Experimental data were coupled for verification, providing the boundary and initial conditions for the benchmark case. The results showed that the weight of injection became maximally 35% less as the weight of the second pulse injection decreased. The amount of liquid fuel film, which was influenced by the injection duration ratio, had a varying range from approximately 1% to 4%. When a greater amount of the liquid fuel film impinged on the piston surface, this induced more soot formation. However, the fuel–air mixture was the most prominent factor for determining the overall combustion characteristics. A split injection can increase the thermal efficiency and the fuel consumption rate; however, without optimization, poor combustion characteristics such as knocking, incomplete combustion and soot emissions can result.
Results are presented following a series of experimental measurements on a submerged NACA-type intake oriented between – 30° and + 30° yaw to the free stream in an atmospheric boundary layer wind tunnel at a unit Reynolds number of nominally 1 x 106. The intake was subjected to a range of upstream wall boundary layer conditions, and the mass flow into the intake (as measured by an orifice plate) was monitored to assess the aerodynamic performance. The mass flow data are supported by qualitative flow visualisation within the duct, using a smoke filament illuminated in a laser light sheet in order to gain insight into the flow physics. The intake performance, expressed in terms of a non-dimensional flow momentum coefficient, is seen to degrade both with increasing intake orientation to the free stream (changes of nominally 40% are seen for the angle range tested) and with increasing upstream boundary layer displacement thickness (changes of nominally 30% are seen for the range tested). These data are presented as a graphical carpet plot; it is intended that this is used as a guide to performance prediction in non-aeronautical applications where there are often significant changes in both the local flow direction and the boundary layer thickness. Flow visualisation studies show that the degradation in the intake performance with increasing yaw angle can be attributed to a progressive change in the vortex-pair structure within the intake as the local flow angle is increased. Both an increase in the lateral separation and an increase in the size of the respective vortex cores are considered to act so as to reduce the magnitude of the induced inflow into the intake.
A lightweight electric vehicle equipped with an automatic–manual transmission offers many advantages in terms of the transmission efficiency, the improvement in driveability, and the shift quality. A conventional automatic–manual transmission for a vehicle powered by an internal-combustion engine requires an electronically controlled clutch to isolate and engage the engine power for smooth gear changes, because of the high inertia of the internal-combustion engine. This makes the system complicated and, therefore, more expensive. Hence, a clutchless automatic–manual transmission with the advantages of a high efficiency, a low cost and a simple structure was adopted and developed in this paper. This study is focused on exploring the feasibility of a clutchless automatic–manual transmission adopted in an electric vehicle and proposes a gear-change control technique for a clutchless automatic–manual transmission, which includes identification of the model parameters, control of the synchronization speed during gear engagement, and motion control of the gear-change actuator mechanism. Theoretical analysis, simulation and experiment confirm that the designed control technique is able to achieve smooth gear shifting. Therefore, the feasibility of a clutchless automatic–manual transmission is verified.
The yaw rate is a key state for vehicle dynamics stability control. However, the time delay from the steering input to the yaw rate measured by the yaw rate sensor changes with the frequency of the steering input and can also be affected by the road friction and the vehicle speed. In order to reduce the time delay effect on the vehicle dynamics stability controller, a new comprehensive yaw rate prediction method is proposed. A seven-degree-of-freedom non-linear vehicle model is adopted as the prediction model. A quadratic polynomial extrapolation method is used to compute the future steering-wheel input in the prediction horizon. A model-based yaw rate prediction algorithm is combined with a feedback compensator to guarantee the robustness of the algorithm. Meanwhile, a linear extrapolation method is utilized to minimize the defects of model-based prediction since the simplified vehicle model cannot fully model the hysteresis or other non-linearities of the vehicle systems. Experimental tests on the vehicle show that the combined algorithm is able to predict the yaw rate about 100 ms earlier than the sensor measurement is. Simulations show that the vehicle stability control strategy based on the proposed comprehensive prediction method has a better performance than the traditional control strategy does.
This work investigates the potential of in-cylinder exhaust gas recirculation stratification for reducing the rate of pressure rise in dimethyl ether homogeneous charge compression ignition engines and its coupling with both thermal stratification and fuel stratification. Numerical analyses were performed using a five-zone version of the CHEMKIN-II kinetics rate code and the kinetic mechanics of dimethyl ether. The effects of inert components were used to represent the presence of exhaust gas recirculation in calculations. Three cases of exhaust gas recirculation stratification were tested in terms of both thermal stratification and fuel stratification at a fixed initial temperature, fixed initial pressure and fixed fuelling rate at bottom dead centre. In order to explore the appropriate stratification of exhaust gas recirculation, the exhaust gas recirculation width (defined as the difference between the exhaust gas recirculation ratios in zone 1 and zone 5 in the five-zone model) which we employed was from 0% to 30%. The case of exhaust gas recirculation homogeneity (called case 1), in which the exhaust gas recirculation width is 0%, was examined. In case 2, exhaust gas recirculation is located densely in a hot zone for combination with thermal stratification or in a fuel-rich zone for combination with fuel stratification. The last case (case 3) was the inverse of case 2. Ringing was reduced to an acceptable level in the case of fuel stratification with an appropriate exhaust gas recirculation distribution, which slowed the rapid burning during the compression stroke.