Research On Modeling And Simulating Of Four Wheel Steering For Vehicle

4WS (four wheel steering) is a new technology in vehicle field. Compared with the current 2WS (two wheel steering), 4WS has such advantages: when the vehicle turns at low speed, it provides more smaller steering radius and improves the flexibility; when the vehicle turns at high speed, it changes roadway rapidly and improves the vehicle stability.This thesis studies on 4WS and dynamics characteristic of 4WS system, it includes the research contents as follows:The structure of 4WS system is introduced by the numbers, and then the steering characteristics of 4WS at different speed are analyzed. Compared with 2WS, the different and advantage of 4WS are indicated. On the basis of studying the 4WS, 2DOF linear model with 2WS, 2DOF linear model with 4WS and 3DOF linear model with 4WS are modeled mathematically.The nonlinear factors are analyzed on mathematics model of 4WS, especially the tyre nonlinear model affects the steering characteristics and stability of the vehicle. After familiar tyre model are introduced, the"magic"formula is chosen to express the relationship between the lateral force and lateral angle. On the basis of a lot of testing and studying on the tyre, the relationship curve of the lateral force and lateral angle with the tyre is plotted, and the parameters of the"magic"formula are ascertained. After 2DOF nonlinear model with 4WS are established.Controler of 4WS system is designed based on 2DOF linear model, and the simulations based on Matlab software, which includes sideslip angle response, yaw rate response, are done to validate the accuracy of the dynamics model, comes to the conclusion that 4WS can improve the response characteristic much. The rationalization mind of controller design based on the above-mentioned simulations.The last chapter summarizes the research work and its deficiency in this thesis, and lists the future works in the area.