Research On Motion Control Strategy Of Four-wheel Electric Vehicle Under Uneven Road Surface

With the development of science and technology,the shortage of global resources and environmental pollution,clean and efficient automobile energy has become the pursuit of all countries.Under this background,electric vehicles have achieved unprecedented development.In the past,most electric vehicles used a single motor to provide power,which had problems such as insufficient power,slow response speed and low flexibility.The four wheels can be controlled independently and the comprehensive performance of the vehicle can be improved by loading the hub motor on the wheels of the vehicle.However,when the electric vehicle driven by four-wheel-hub motor turns to drive,it is difficult to guarantee its stability and safety performance because of its high systematicness.Therefore,this paper takes the four-wheel electric vehicle as the research object,and studies the steering stability control strategy of the vehicle under the condition of simulated road slope.Firstly,considering the actual road surface of vehicles,the road surface is detected by lidar,and the road slope is set and converted into the offset of vehicle centroid;According to the dynamic characteristics of the vehicle,the characteristics of vehicle movement in longitudinal direction,lateral direction,vehicle yaw movement and rolling movement of four wheels are studied,and a seven-degree-of-freedom vehicle dynamic model is established.At the same time,considering the influence of wheel state on vehicle running state,Dugoff tire model is chosen to characterize the influence of wheel force on vehicle stability.The simulation vehicle model is built in Carsim software,and the parameters of the vehicle model are compared and set according to the actual situation.Secondly,the steering stability control strategy takes the vehicle speed and steering angle as input variables,and the slip ratio,yaw rate and centroid deflection angle as output variables to establish an electronic differential system.The theoretical speed is obtained by Ackerman steering geometric model,and the wheel speed is monitored at the same time.The motor is controlled to track the wheel reference speed by the way of logic threshold,that is,the outer wheel decelerates and the inner wheel accelerates,ensuring that the slip rate is within the driving stability range of the vehicle and realizing the coordinated control of the wheel slip rate.The additional yaw moment is calculated by sliding mode control,and the buffeting is suppressed by combining dynamic sliding mode with exponential reaching law Then,according to the principle of minimum coefficient of road adhesion,the required additional yaw moment is distributed to each wheel,thus changing the yaw rate and centroid deflection angle of the vehicle.At last,the model is simulated in Matlab/Carsim.The steering conditions of vehicles under different steering speeds and steering angles are verified respectively,and the simulation data of dual-hub and four-hub electric vehicles are output.The simulation results show that the slip rate of vehicles can be controlled in a stable range under different road slopes and vehicle driving conditions,and the yaw rate and centroid deflection angle can improve the large deviation without control,and basically track its ideal value.It is verified that the control strategy proposed in this paper can ensure the steering stability of the four-wheel vehicle.