Analysis And Experimental Study On Vehicle Stability Control Of The New Four Wheel Steering

As the major transportation in modern society,the vehicle industry promotes people's living standard rapidly and socio-economic development.Vehicle safety running,fast driving,manipulation convenient and ride comfort are the pursuit target of modern automobile,however,the frequent occurrence of traffic accidents and the resulting vehicle manipulation stability problem have become a serious social issue and a hot topic of today's automotive industry.The four wheel steering(4WS)system is an effective active control technology for improving vehicle safety and maneuverability.The 4WS system for improving the vehicle stability gets great development aboard,and it is gradually equipped to the moderate and top class cars,In recent years,the rapid development of China's economy and the enhancement of the road condition have promoted the increasing amount of car ownership and the constant pursuit of the vehicle speed.However,the research on this field is just in the initial stage in China.On this account,research on the wheel steering technology to enhance the vehicle security has practical significance and broad prospects.This thesis is based on the cooperative research project of Hunan University and University of Waterloo "The stability analysis and experimental study of the new 4WS vehicle".Based on the 4WS technology from some related domestic and international research results,the thesis has taken full advantage of the impact of 4WS technology on the vehicle steering stability.The characteristics of vehicle lateral dynamics and the control strategies are regarded as the research subject based on the development of steer-by-wire(SBW)technology.The influence of nonlinear and uncertainty on vehicle dynamics are fully considered by this thesis.A systematic research on control strategies for active 4WS vehicle is carried and a novel active steering technique named Pulsed Active Rear Steering System(PARS)for enhancing vehicular stability is proposed.What's more,the design and experimental research of the test platform are carried out.The thesis research results present that:1)For controller design and the visualization of the simulation verification,the vehicle numerical model and virtual prototype model are built based on mechanism parameters and characteristic attributes of the Lexus test vehicle.The models provide a fast and accurate simulation platform of chassis control system which can verify different control strategies and control effects for 4WS vehicle.Furthermore,a virtual prototype of 4WS vehicle is established by ADAMS software for the demand of the simulation visual.The ADAMS/Car virtual prototype and Matlab/Simulink controller are used to realize the "mechanical-control system" joint simulation by ADAMS/Controls module.Through experimental verification,the error can be controlled within 10%,the model can reflect the dynamic characteristics of the vehicle,and it can be used to study the vehicle dynamic stability.2)The relationship between vehicle active steering angle and vehicle stability is researched.The causes of vehicle instability and the relationship between vehicle dynamics parameters and vehicle stability are studied from two aspects of driver and road environment.The 4WS control mechanism and the dynamic relationship between the steering wheel angle and vehicle yaw rate and sideslip angle are studied based on a linear vehicle model.The qualitative analysis of active steering form,frequency and amplitude of the angle on the effects of stable performance are demonstrated:The control parameters have a great influence on the vehicle stability.All of these provide a reference for design of the active steering controller.3)The model tracking control strategy based on the tire lateral stiffness weight function and the optimal control principle of the 4WS vehicle is studied considering the nonlinear characteristics of tire's lateral stiffness.The active 4WS optimal controller algorithm of front and rear angle is deduced and designed to achieve the tradeoff between vehileyaw rate and sideslip angle control based on vehicle weight model and SBW technology.The effect of the controller is verified by simulation.To further improve the vehicle handling stability under influence of uncertainty factors,the control strategy of a sliding mode variable structure(SMC)of the 4WS vehicle is studied.The SMC controller is designed by treating the cornering stiffness of the vehicle tires and outer disturbance as uncertain parameters.It is used to overcome the disturbance of unknown parameters and the influence of external disturbance.The robustness of the control effect is verified by simulation.The 4WS SMC controller can guarantee the quality of steering response under the influence of uncertain factors,and meet the requirements of robustness.4)A novel active rear wheel pulse steering control strategy is proposed based on the concept of active pulse control proposed by Professor Khajepour Amir of University of Waterloo.The optimal feedback controller is designed by using the methods of frequency analysis and optimal control theory.The simulation analysis ofthe ARPS on vehicle yaw and roll performance is demonstrated.A feedback controller is design to achieve the tradeoff between yaw rate and sideslop angle control.To take full advantage of the vehicle outer wheel lateral forces and reduce the inside wheel prematurely reach saturation occurs,the concept of rear wheel independent steering pulse is proposed.The control strageties based on the pulse angle control algorithm and the optimal allocation algorithm distribution control are studied.To realize the optimal distribution of the left and right rear wheel steering angle,the control distribution algorithm of the rear wheel is studied by using the theory of control distribution.5)In order to further verify the effectiveness of the active pulse steering system,the HIL test bed of active front wheel pulse steering control system based on LabVIEW is established,and the feasibility of active front wheel steering control is verified by HIL simulation.The front wheel active steering control system is designed and manufactured.A real time control platform based on NI PXI system and sbRIO embedded system are built.The dynamic simulation model program and the active pulse steering controller program are established.The experimental results show that the controller can real-time control the front wheel pulse steering,and can quickly control vehicle rollover index within the range of stability.To verify the control effect of the active pulse steering signal on the rear wheel,a complete hydraulic pulse steering device was designed and installed on the test Lexus vehicle to carry out the vehicle test study.The validity and economy of the active pulse steering system were verified from the vehicle test and operability.The Lexus vehicle with multi-link rear suspension is choosed as the experimental vehicle.A hydraulic pulse steering system is designed and the experimental vehicle is reformed.The pulse steering system is installed in the experimental vehicle for the road test.The experimental results show that the performance of the pulse frequency on the vehicle stability is basically consistent between the theoretical calculation and simulation results.Different pulse signals have different influence on the stability of the vehicle,which can be chosen according to the actual motion state of the vehicle to improve the yaw and lateral stability.The rear wheel drive pulse steering system can effectively reduce the yaw rate and lateral acceleration of the vehicle,and improve the yaw and lateral stability of the vehicle.These provide a new research space and experimental basis for improving the performance of 4WS technology.