Research On Control Strategy Of Differential Assist Steering System Based On Electric Vehicle With In-Wheel Motors

The electric vehicle with in-wheel motors has good application prospect and technical development potential with the advantages of high transmission efficiency,space layout flexibility and electronic and active chassis system realization convenience.Changing the torques of in-wheel motors,the Differential Assist Steering System(DASS)can be realized.To offer good road feeling and to improve the vehicle handling performance and stability as well,this thesis research on the control strategy of road feeling and handling stability for the DASS based on electric vehicle with in-wheel motors.Firstly,dynamic model of DASS,model of in-wheel motors,model of 3-DOF vehicle with tire force and wheel dynamics considered and driver model with preview are established.Secondly,considering the nonlinear characteristics of models and external disturbance,the DASS road feeling control strategy is proposed based on the designed DASS assist characteristic and the H∞ robust control theory.At last,the negative influence on handling stability from differential assistance is analyzed and vehicle stability control strategy which takes yaw rate as control variable is designed based on fuzzy-sliding mode theory.With the consideration of the buffeting problem caused by sliding mode control,fuzzy logic theory is used to compute parameters of sliding mode reaching law according to the corresponding condition,so that a proper reaching speed is fulfilled and high frequency buffeting is weakened.The simulation results show that the controller proposed not only offers a good road feeling,but also improves the vehicle handling performance and stability.The thesis provides a promising research value on DASS.