The Steering Control Method Of4WIS Electric Vehicle

Four wheels of4WIS can be independently controlled.4WIS have the advantage that at low speed, it reduces the turning radius to improve the flexibility and at high speed, it increases the turning radius to enhance the stability. Along with the progress of science and technology, using the control technology to improve handing stability and safety of vehicle become a hot research topic in the field of automobile.In this paper, based on the front wheel steering vehicles, reference vehicle model is established. Reference vehicle model is based on the pilot output angle and the speed of the car as the input, with ideal sideslip angle and yaw rate as the output. According to the parameters of the experimental prototype, vehicle mode is established. This paper designed a feed-forward controller and feed-back controller. Driver-vehicle-road closed loop system is established. The control effect was verified.The minimum absolute value of the sum of four tire sideslip angle is the performance index of the system. With ideal sideslip angle, yaw rate and the tire side slip angle’s scope in linear area, feed-forward controller is designed as constraint conditions. Thus ensure the system the characteristics of low energy consumption and high accuracy. It validate that, according to the road adhesion coefficient, feed-forward controller may distribute four wheels steering angles, to make full use of adhesion. there is insufficient in the feed-forward controller. Under the effect of feed-forward controller, the time required for system to reach steady state is longer than ideal time; the system has overshoot; perturbations system exist static error.In the design method of feed-back controller, the tire sideslip angle and yaw torque are as the input of linear system. According to the theory of regional pole assignment, pole position was calculated. Simulation verified that the two change curves of the pole position in this model and in the ideal model are the same. The values of the elements in the feedback gain matrix are solved. Based on the compare and analysis, the values of the parameters are detemined.Based on establishing the coordinate transformation equation, road function and the driver model, Driver-vehicle-road closed loop system is established. According to the result of the double line road simulation test, the vehicle has good tracking ability and handing stability. Through the above proves that the controller designed in this paper has good control effect.