Dynamics Simulation And Robust Control Research Of 4WS Vehicle

Four Wheel Steering(4WS) is an advanced vehicle control technique which can improve steering characteristics.Compared with the traditional Front Wheel Steering (FWS),4WS has such advantages:when the vehicle turns at low velocity,it provides more smaller steering radius and improves the flexibility;when the vehicle turns at high speed,it can quickly change lanes to reduce the possibility of facing the trail, while the body need not have a big swing.Therefore,4WS can enhance the handling stability and improve the active safety for vehicles.Based on the theory of vehicle dynamics and control technology,this paper investigates the following issues:(1) The steering characteristics of 4WS is detailed.The 2DOF FWS vehicle model is built up,2DOF and 3DOF 4WS vehicle model also are built up.(2) Based on the 4WS vehicle model with linear tire lateral force characteristics,the control algorithm is designed to use feed-forward plus feed-back control framework by following the reference model.And the simulation is processed in MATLAB/Simulink to compare traditional FWS vehicle with 4WS vehicle,and 4WS vehicle open-loop control with closed-loop robust control of the state of responses of Yaw Velocity and Sideslip Angle.(3) For the nonlinear tire lateral force characteristics,considering the change of tire vertical load caused by roll motion,the 4WS control algorithm is investigated.The 4WS vehicle model containing both nonlinear tires module and vehicle module is built up in MATLAB/Simulink.The effect of nonlinear tire characteristics on 4WS dynamics is analyzed thoughtfully.By comparison and analysis of the simulation results,the following conclusions can be drawn:the designed control algorithms can keep the Sideslip Angle of the vehicle approaching to zero.By following the reference model,the performances of the Yaw Velocity responses is improved.Consequently,the handling stability is enhanced.