The Study On Control Algorithm And Handling Dynamic Simulation Of Four Wheel Steering Vehicles

Four Wheel Steering (4WS) is an advanced vehicle control technique which can improve steering characteristics. Compared with traditional front wheel steering vehicles, 4WS vehicles can steer the front wheels and the rear wheels individually for cornering, according to the vehicle motion states such as the information of vehicle speed, yaw velocity and lateral acceleration. 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:Firstly, a 3DOF 4WS vehicle model is built up by using the Lagrange equations, containing lateral, yaw and roll motions.Secondly, 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 verify the control algorithm.Thirdly, for the nonlinear tire lateral force characteristics, considering the change of tire vertical load caused by roll motion, the four wheel steering 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 and lateral acceleration responses are improved. Consequently, the handling stability is enhanced.