Yaw Stability Control With Suspension K&C Characteristics For In-wheel-motor Electric Vehicle

In recent years,the research of in-wheel-motor electric vehicles has become more popular in the field of electric vehicles with advantages of wheel-torque-drive independence and compact structure etc.The characteristic of wheel-torque-drive independence changes traditional control methods of vehicle yaw stability,which drives this control technology to be shifted.So the work in this thesis has great theoretical and practical significance with research on yaw stability control of in-wheel-motor electric vehicles.At present,research on yaw stability control mainly pays attention to lateral dynamics of in-wheel-motor electric vehicles.However,the coupling relationship between the lateral motion of the vehicle and the vertical and vertical movement was ignored,which will affect the performance of vehicle lateral dynamic controls under extreme conditions.Unlike the existing commonly-used methods,this paper considers the coupling effect of vertical dynamics on lateral ones,and investigates coupling relationship among lateral,vertical and vertical motions as well as control theories of yaw stability with considering suspension K&C characteristics,which can improve performances of lateral control.The influence of suspension K & C characteristic on lateral dynamics is analyzed and comes down to changes of tire sideslip angle caused by wheel alignment parameters toe and camber as well as additional camber angle torque.To reduce the cost of calculating parameters of suspension K&C characteristics,we determine factors which have a major effect on the lateral dynamics of the vehicle.and then a lateral dynamic model is proposed with suspension K & C characteristics.The simulation results carried out in ve DYNA,a high-precision vehicle dynamic software,indicate that this model has greater accuracy.For the yaw stability control under the condition of under-steering,it is pointed out in the thesis that under-steering is due to the saturation of tire lateral force,which leads to insufficient lateral force and then the desired control of yaw rate tracking is out of hand.Therefore,based on the proposed lateral dynamic model,a new method of coupling longitudinal and lateral dynamics integrative control is presented according to characteristics of the coupling dynamics.As a result,the single control of lateral motion is extended to a coupling control of longitudinal and lateral dynamics with suspension K & C characteristics,and to solve the problem of under-steering we give a method of yaw stability control based on sliding mode control theory.And the controller is verified to be feasible and effective by the simulation results.In view of the problem that the strong nonlinearity and the difficulty of online computing for parameters of suspension K & C characteristics,a data modeling method is employed to improve the expression of suspension K&C characteristics.Then we establish a Physics/ MAP mixed dynamic model of the longitudinal,lateral and vertical coupling motion using the data MAP model to represent the changes of toe and the camber angle.On this basis,a nonlinear control method is designed to realize the control of yaw stability,which consists of steady-state control,reference dynamic feedforward control and feedback control.The simulation results show that the controller can remarkably improve the steering performance of vehicles running on the low adhesion-coefficient road.