Motion Simulation And Research On Four-Wheel Steering Electric Vehicle

With energy and environmental increasing crisis, and the portability of in-wheel motor, the electric car gradually into the spotlight of public. This article studies the control strategies of four-wheel steering vehicle based on electric vehicles combining with four-wheel steering technology and direct yaw control technology, aimed as lateral dynamics of the vehicle characteristics in linear and nonlinear condition to vehicle handling and stability control.Firstly, based on the SAE standards, the paper established a vehicle model with ten degrees of freedom and tire model for analysis vehicle dynamics and simulating for controller. Meanwhile, a two degrees of freedom linear vehicle model was established for desired model. Rear steering controller were designed for four-wheel steering vehicle based on PID control and fuzzy control aimed as side-slip angle to zero for control point. By analyzing dynamic properties of vehicle in three speed of low, medium, high, it proofs that the vehicle of fuzzy controller can take advantage of rear wheel steering, decreasing turning radius at low speed and increasing stability at high speed.The four-wheel steering controller includes direct yaw control by fully using in-wheel motor to adjust longitudinal force of tire and increasing yaw rate which reduced by rear wheel steering. Then the paper studied the desired side slip angle and desired yaw rate desired. Vehicle model to output the ideal model to follow, while ensuring compliance with the traditional front-wheel longitudinal force of front wheel steering vehicle. The paper designed controller using four-wheel steering and direct yaw control integrated control strategy based on fuzzy control-wheel, considering the output of vehicle model following desired model and ensuring longitudinal force of front tire equal with front wheel steering vehicle’s. Compared to only four-wheel steering control, integrated control can make side slip angle and yaw rate being close to desired value, not only to further improve the stability of the vehicle, but also avoiding the problem that too small yaw rate at high-speed steering.