A theoretical justification of the sine with dwell manoeuvre

The sine with dwell (SWD) manoeuvre has received much attention within the context of vehicle stability testing. This manoeuvre is used in a test developed by the NHTSA, designed to certificate electronic stability control systems in light vehicles. The test is used in legislations as well as in consumer tests all over the globe. The SWD manoeuvre was designed using test vehicles on a test track and experimentally validated. The paper at hand uses optimal control theory to theoretically justify the use of the SWD manoeuvre to produce a severe lateral motion and over-steering based on steering input. It is shown that a manoeuvre similar to the SWD manoeuvre can be obtained from an optimal control problem using simple vehicle dynamics models. The optimal control method is further used to analyse the manoeuvre's robustness with respect to vehicle dimensions and tyre properties. It is shown that the manoeuvre is robust in dimensions, which theoretically motivates its application for various sizes of vehicles.     

Critical review of handling diagram and understeer gradient for vehicles with locked differential

The steady-state cornering behaviour of rear-wheel drive vehicles fitted with locked differential is critically analysed by means of simple, albeit carefully formulated, vehicle models, which allow for a rigorous theoretical analysis. Results obtained for some classical manoeuvres, with either constant forward speed, steer angle or turning radius, clearly show that, in the case of locked differential, the vehicle cornering behaviour is strongly affected by the manoeuvre. As an important consequence, the handling diagram is not unique and the understeer gradient is no longer dependent only upon the lateral acceleration, as in vehicles equipped with an open differential. Accordingly, this study shows that some typical tools and concepts of vehicle dynamics are indeed inadequate in the case of locked differential.     

转矩式限滑差速器对后轮驱动汽车操纵稳定性影响的研究

采用7自由度车辆动力学模型,对装用JA1020LSD型转矩式限滑差速器的后轮驱动汽车进行了操纵稳定性研究。通过仿真分析和道路试验研究表明:装用限滑差速器后增加了后轮驱动车辆的不足转向趋势,即改善了操纵稳定性,但转向力矩略有增加。     

Effect of handling characteristics on minimum time cornering with torque vectoring

In this paper, the effect of both passive and actively-modified vehicle handling characteristics on minimum time manoeuvring for vehicles with 4-wheel torque vectoring (TV) capability is studied. First, a baseline optimal TV strategy is sought, independent of any causal control law. An optimal control problem (OCP) is initially formulated considering 4 independent wheel torque inputs, together with the steering angle rate, as the control variables. Using this formulation, the performance benefit using TV against an electric drive train with a fixed torque distribution, is demonstrated. The sensitivity of TV-controlled manoeuvre time to the passive understeer gradient of the vehicle is then studied. A second formulation of the OCP is introduced where a closed-loop TV controller is incorporated into the system dynamics of the OCP. This formulation allows the effect of actively modifying a vehicle's handling characteristic via TV on its minimum time cornering performance of the vehicle to be assessed. In particular, the effect of the target understeer gradient as the key tuning parameter of the literature-standard steady-state linear single-track model yaw rate reference is analysed.     

Optimisation of handling and traction in a rear wheel drive vehicle by means of magneto-rheological semi-active differential

This paper presents a semi-active differential, magneto-rheological fluid limited slip differential, which allows us to bias the torque between the driving wheels. It is based on the magneto-rheological fluid employment, by which it is possible to change, in a controlled manner, the internal friction torque and, consequently, the torque bias ratio. This device is an adaptive one and allows us to obtain an asymmetric torque distribution in order to improve vehicle handling. The device modelling and the control algorithm, realised for this activity, are described. The illustrated results highlight the advantages that are attainable regarding directional behaviour, stability, and traction.     

Quasi-steady-state linearisation of the racing vehicle acceleration envelope: a limited slip differential example

In the motorsport environment, passive limited slip differentials are a well-established means of improving the traction limitation imposed by the open differential. Torque sensing types are highly adjustable, and can alter both the stability and agility of the vehicle in the various cornering phases of a typical manoeuvre. In this paper, an adjustable clutch plate or ‘Salisbury’ differential model is presented, which can significantly alter its torque bias characteristics through adjustments in the drive/coast ramp angle, the number of friction faces and preload. To allow robust evaluation of differential parameter changes on ultimate vehicle performance and handling balance, a unified acceleration or ‘GG’ diagram framework is then described. This builds on traditional GG diagram approaches, by using nonlinear constrained optimisation to define both the vehicle acceleration limits and a ‘feasibility’ region within the performance envelope. By linearising a seven degrees of freedom vehicle model at multiple operating points, eigenvalue and yaw rate response analysis is then used to establish contours of stability and agility throughout the GG envelope. This brings new insights into the way in which handling balance changes below and up to the vehicle's acceleration limits.     

Development of evolutionary cone type LSD for SUV/RV utilizing the axiomatic approach and the ultrasonic nano crystal surface modification technology

Surface topology, cone angle and the forces acting on the cone of the clutch type limited slip differential (LSD) are major design parameters for the bias ratio and the noise condition. Therefore much research has been dedicated to these developments but the results have been used to submit patents. A new cone type limited slip differential for sport utility vehicles and recreational vehicles, which has a very simple structure and easy compliance with the vehicle performance, has been developed by the axiomatic approach and the ultrasonic nano crystal surface modification (UNSM) technology. The design criteria and optimal value of the design parameters are determined by the axiomatic approach utilizing CAE tools. Test methodologies in a test rig and in a vehicle were also developed. Test results showed good performance of bias ratio and noise level but durability is still under testing. This study is an extension of F2006P266, FISITA 2006.     

基于功能安全的分布式驱动电动汽车前轮失效补偿控制

分布式驱动电动汽车可以实现四轮转矩分配和差动转向,提升整车的动力学控制性能和经济性,但是四轮转矩独立可控的特点也对功能安全提出挑战。当前轮单侧电机出现执行器故障失效情况时,不仅会产生附加横摆力矩降低车辆安全性,差动转向功能的存在还会使车辆严重偏航。基于此,在设计分布式驱动-线控转向一体化底盘的基础上,基于功能安全提出一种分布式驱动电动汽车前轮失效补偿控制策略。首先建立分布式驱动失效动力学模型,分析前轮失效对车辆状态的影响机理,发现单一的驱动转矩截断控制无法满足车辆状态修正需求;其次设计一套备用的线控转向结构,通过变截距滑模控制算法提高切换状态下线控转向系统的转角跟踪性能,并用台架试验验证跟踪的准确性;然后设计自适应失效诊断观测器实时诊断驱动系统的电机故障,在将对应轮进行驱动转矩截断后,通过模型预测控制算法对车轮转矩重新分配实现纵向和侧向的状态跟踪;最后通过仿真和实车试验验证所提失效补偿控制策略的有效性和可用性。研究结果表明：分布式驱动电动汽车前轮单侧电机失效后,备用的线控转向系统能及时矫正前轮转角,所提出的失效补偿控制策略能够快速恢复车辆的稳定性和路径跟踪能力。     

An adaptive integrated algorithm for active front steering and direct yaw moment control based on direct Lyapunov method

In this article, an adaptive integrated control algorithm based on active front steering and direct yaw moment control using direct Lyapunov method is proposed. Variation of cornering stiffness is considered through adaptation laws in the algorithm to ensure robustness of the integrated controller. A simple two degrees of freedom (DOF) vehicle model is used to develop the control algorithm. To evaluate the control algorithm developed here, a nonlinear eight-DOF vehicle model along with a combined-slip tyre model and a single-point preview driver model are used. Control commands are executed through correction steering angle on front wheels and braking torque applied on one of the four wheels. Simulation of a double lane change manoeuvre using Matlab^®/Simulink is used for evaluation of the control algorithm. Simulation results show that the integrated control algorithm can significantly enhance vehicle stability during emergency evasive manoeuvres on various road conditions ranging from dry asphalt to very slippery packed snow road surfaces.     

Driver steering and muscle activity during a lane-change manoeuvre

The article reports an experimental study of driver steering control behaviour in a lane-change manoeuvre. Eight test subjects were instrumented with electromyography to measure muscle activation and co-contraction. Each subject completed 30 lane-change manoeuvres with one vehicle on a fixed-base driving simulator. For each driver, the steering torque feedback characteristic was changed after every ten manoeuvres; the response of the vehicle to steering angle inputs was not changed. Drivers' control strategies were found to be robust to changes in steering torque feedback. Path-following errors, muscle activity and muscle co-contraction all reduce with the number of lane-changes performed by the driver, suggesting the existence of a learning process. Comparing the test subjects, there was some evidence that high levels of co-contraction were used to allow high-frequency steering inputs to be generated. The results contribute to the understanding of vehicle–driver (and more generally, human–machine) dynamic interaction.     

电动汽车转矩定向分配差速器建模与动态仿真

本文中提出一种新型具备转矩定向分配功能差速器的集中式电驱动桥系统。该集中驱动系统可以在不改变总驱动转矩的条件下,类似分布式驱动方式实现驱动转矩在左右轮间的任意分配,从而产生改变车辆横摆动力学的直接横摆力偶矩。首先,分析了转矩定向分配差速器结构特点及其工作原理;其次,利用键合图理论建立了其动力学模型,并仿真分析了其动态响应特性;然后,设计了转矩响应控制系统以改善该差速器的动态性能;最后,嵌入整车模型进行了联合仿真。结果表明,装备该差速器的车辆可任意分配左右轮驱动转矩,并有效改善车辆操控特性。     

Vehicle dynamics control of an electric-all-wheel-drive hybrid electric vehicle using tyre force optimisation and allocation

ABSTRACT

Hybrid Electric Vehicles (HEV) offer improved fuel efficiency compared to conventional vehicles at the expense of adding complexity and at times, reduced total power. As a result, HEV generally lack the dynamic performance that customers enjoy. To address this issue, the paper presents a HEV with electric All-Wheel-Drive capabilities via the use of torque vectoring electric rear axle drive (TVeRAD) to power the rear axle. The addition of TVeRAD to a front wheel drive HEV improves the total power output. To improve the handling characteristics of the vehicle, the TVeRAD provides torque vectoring at the rear axle. A bond graph model of the drivetrain is developed and used in co-simulation with CarSim. The paper proposes a control system which utilises control allocation to optimise tyre forces. The proposed control system is tested in the simulation environment with a high fidelity CarSim vehicle model. Simulation results show the control system is able to maximise vehicle longitudinal performance while avoiding tyre saturation on low mu surfaces. More importantly, the control system is able to track the desired yaw moment request on a high speed double lane change manoeuvre through the use of the TVeRAD to improve the handling characteristic of the vehicle.     

Driver steering and muscle activity during a lane-change manoeuvre

The article reports an experimental study of driver steering control behaviour in a lane-change manoeuvre. Eight test subjects were instrumented with electromyography to measure muscle activation and co-contraction. Each subject completed 30 lane-change manoeuvres with one vehicle on a fixed-base driving simulator. For each driver, the steering torque feedback characteristic was changed after every ten manoeuvres; the response of the vehicle to steering angle inputs was not changed. Drivers' control strategies were found to be robust to changes in steering torque feedback. Path-following errors, muscle activity and muscle co-contraction all reduce with the number of lane-changes performed by the driver, suggesting the existence of a learning process. Comparing the test subjects, there was some evidence that high levels of co-contraction were used to allow high-frequency steering inputs to be generated. The results contribute to the understanding of vehicle-driver (and more generally, human-machine) dynamic interaction.     

并联式混合动力汽车模式切换控制策略研究

并联式混合动力汽车模式切换时离合器会介入传动系统，容易引起较明显的冲击感，是影响整车驾驶舒适性的主要因素。为此，提出了基于离合器双模糊和电机转矩协调的模式切换控制策略。首先建立混合动力汽车模式切换过程的动力学模型，以减小离合器滑磨功为目标，对模式切换时的离合器接合过程进行划分；其次，结合混合动力汽车模式切换的基本要求和驾驶意图，制定离合器双模糊控制策略，分别对滑摩阶段的接合时长和转矩同步阶段的压力变化率进行控制；然后以离合器滑磨功和整车冲击度为优化目标，采用二次型最优控制算法对滑摩阶段的接合压力进行优化，从而获取模式切换过程中离合器的最优接合压力轨迹；在此基础上，通过实时计算离合器传递转矩，根据电机转矩响应快的特点，制定电机转矩协调控制策略；最后，基于某混合动力试验样车，在底盘测功机上分别进行缓加速、中等加速和急加速下的模式切换试验，对所提出的控制策略进行验证。试验结果表明：该策略能较好地反映驾驶人驾驶意图，保证离合器的使用寿命，所产生的整车冲击度均处于合理范围之内，改善了整车模式切换过程中的驾驶舒适性。     

Judder analysis of electronically controlled limited slip differential

The electronically controlled limited slip differential system used on the new Skyline contributes to improvements in vehicle dynamics. One important performance parameter that is improved is the start-off acceleration when one drive wheel is on an ultra-low friction surface. There was concern, however, that larger LSD torque might cause drivetrain judder due to the negative μ-v slope of the wet multiplate clutch used in the system. An analysis based on natural mode calculations clarified the mechanism generating judder, and the results of stability calculations revealed measures for improvements. As a result, the problem of self-excited vibration was resolved.     

Optimal preview game theory approach to vehicle stability controller design

Dynamic game theory brings together different features that are keys to many situations in control design: optimisation behaviour, the presence of multiple agents/players, enduring consequences of decisions and robustness with respect to variability in the environment, etc. In the presented methodology, vehicle stability is represented by a cooperative dynamic/difference game such that its two agents (players), namely the driver and the direct yaw controller (DYC), are working together to provide more stability to the vehicle system. While the driver provides the steering wheel control, the DYC control algorithm is obtained by the Nash game theory to ensure optimal performance as well as robustness to disturbances. The common two-degrees-of-freedom vehicle-handling performance model is put into discrete form to develop the game equations of motion. To evaluate the developed control algorithm, CarSim with its built-in nonlinear vehicle model along with the Pacejka tire model is used. The control algorithm is evaluated for a lane change manoeuvre, and the optimal set of steering angle and corrective yaw moment is calculated and fed to the test vehicle. Simulation results show that the optimal preview control algorithm can significantly reduce lateral velocity, yaw rate, and roll angle, which all contribute to enhancing vehicle stability.     

A General Method for the Evaluation of Vehicle Manoeuvrability with Special Emphasis on Motorcycles

This paper presents a novel approach to the assessment of the manoeuvrability of vehicles which is not based on the simulation of open-loop manoeuvres, nor does it rely on the modelling of the driver as a control system. Instead, the essence of the method is the solution of a two-point optimal control boundary value problem, in which a vehicle, subject to physical constraints like tyre adherence and road borders, among others, is required to go between given initial and final positions as fast as possible. The control inputs - i.e., the driver's actions - that make the vehicle move between the two states in the most efficient way are found as a part of the solution procedure and represent the actions of a sort of ideal, perfect driver . The resulting motion is called the optimal manoeuvre and, besides being the most efficient way that the given vehicle has for travelling between the two points according to the chosen optimal criterion, may be taken as a reference for meaningful comparisons with other vehicles. The value of the penalty function, used to define the optimal condition occurring at the optimal manoeuvre, may be taken as a measure of manoeuvrability or handling. With this approach the manoeuvrability properties are established as intrinsic to the vehicle, being defined with respect to an ideal perfect driver. Some possible forms of the penalty function, which means slightly different concepts of manoeuvrability and handling, are discussed. In the end, the case of motorcycles and some examples of optimal manoeuvres are given.     

Additional 4WS and Driver Interaction

This investigation is based on a complex 4-wheel vehicle model of a passenger car that includes steering system and drive train. The tyre properties are described for all possible combined longitudinal and lateral slip values and for arbitrary friction conditions. The active part is an additional steering system of all 4 wheels, additionally to the driver's steering wheel angle input. Three control levels are used for the driver model that thereby can follow a given trajectory or avoid an obstacle.

The feedback control of the additional 4 wheel steering is based on an observer which can also have adaptive characteristics. Moreover a virtual vehicle model in a feedforward scheme can provide desired steering characteristics.

To get information for critical situations a cornering manoeuvre with sudden u-split conditions is simulated. Further a similar manoeuvre is used to evaluate the reentry in a high friction area from low friction conditions. And finally the performance of the controller is shown in a severe lane change manoeuvre.     

Coordinated control strategies for active steering,differential braking and active suspension for vehicle stability,handling and safety improvement

ABSTRACT

In this paper, a coordinated control strategy is proposed to provide an effective improvement in handling stability of the vehicle, safety, and comfortable ride for passengers. This control strategy is based on the coordination among active steering, differential braking, and active suspension systems. Two families of controllers are used for this purpose, which are the high order sliding mode and the backstepping controllers. The control strategy was tested on a full nonlinear vehicle model in the environment of MATLAB/Simulink. Rollover avoidance and yaw stability control constraints have been considered. The control system mainly focuses on yaw stability control. When rollover risk is detected, the proposed strategy controls the roll dynamics to decrease rollover propensity. Simulation results for two different critical driving scenarios, the first one is a double lane change and the other one is a J-turn manoeuvre, show the effectiveness of the coordination strategy in stabilising the vehicle, enhancing handling and reducing rollover propensity.     

A General Method for the Evaluation of Vehicle Manoeuvrability with Special Emphasis on Motorcycles

This paper presents a novel approach to the assessment of the manoeuvrability of vehicles which is not based on the simulation of open-loop manoeuvres, nor does it rely on the modelling of the driver as a control system. Instead, the essence of the method is the solution of a two-point optimal control boundary value problem, in which a vehicle, subject to physical constraints like tyre adherence and road borders, among others, is required to go between given initial and final positions as fast as possible. The control inputs - i.e., the driver's actions - that make the vehicle move between the two states in the most efficient way are found as a part of the solution procedure and represent the actions of a sort of ideal, perfect driver. The resulting motion is called the optimal manoeuvre and, besides being the most efficient way that the given vehicle has for travelling between the two points according to the chosen optimal criterion, may be taken as a reference for meaningful comparisons with other vehicles. The value of the penalty function, used to define the optimal condition occurring at the optimal manoeuvre, may be taken as a measure of manoeuvrability or handling. With this approach the manoeuvrability properties are established as intrinsic to the vehicle, being defined with respect to an ideal perfect driver. Some possible forms of the penalty function, which means slightly different concepts of manoeuvrability and handling, are discussed. In the end, the case of motorcycles and some examples of optimal manoeuvres are given.