Torque Distribution Strategy Of Wheel Driven Electric Vehicle Based On Road Condition Recognition

Wheel driven electric vehicle drived by four motor directly,the four wheels can be controlled independently,so it can be controlled more flexibly and accurately.In view of the yawing,sideslipping or steering excessively or insufficiently of the vehicle running on extreme road conditions,the torque distribution strategy based on road identification can improve maneuverability and stability of the vehicle.Firstly,a seven-degree freedom nonlinear and a two-degree freedom linear dynamic models of electric vehicle have been built based on massive structure and dynamic characteristics of the wheel driven electric vehicle,nonlinear and linear simulation platform of the vehicle is established and the PID controller is used to run electric vehicle.Secondly,according to the vehicle dynamics model,a differential controller based on Ackermann steering model is designed to correct the vehicle trajectory in real time.Aiming at the problem of vehicle trajectory deviation under the condition of low road adhesion coefficient in differential control,the torque allocation strategy based on the stability target optimization is studied further,the longitudinal force of the tires are distributed with the different road adhesion coefficient to improve the stability of vehicle under complex conditions.On low road adhesion coefficient and more complex road,multi-objective optimization torque allocation strategy which combined stability objectives with maneuverability objectives has be used to improve the yaw response speed and the grasp the ground performance of the vehicle.Under different working conditions,according to adjust the weights of stability and maneuverability,takes the center of mass side-slip angle as the important parameters which influence the stability of vehicle control,uses fuzzy control selectively to adjust the proportion of two kinds of objective function,adjust the distribution of the weight coefficient of two kinds of objective functions dynamically.The simulation results show that,compared with the stability target's torque assignment strategy,multi-objective optimization torque allocation strategy which combined stability objectives with maneuverability objectives has faster dynamic response speed and better dynamic tracking and control precision.Finally,in order to obtain road condition information in real time,the nonlinear observer is designed,according to lateral dynamic characteristics based on two-degree freedom vehicle model,takes the deviation between sensor and vehicle model as the correction terms to determine the feedback gain of the nonlinear observer,and the road friction coefficient can be estimated,then the longitudinal force of tire can be distributed reasonably according to the dynamically estimating road information.The simulation results show that the accuracy of the estimation of road friction coefficient can meet the requirements of control system,adjusting longitudinal force based on road friction coefficient in real time can improve the vehicle handling and stability performance effectively.