Dynamics And Hybrid Control Of Vehicle 4WS System

4WS (four wheel steering) is a new technology in vehicle systems. Compared with the current 2WS (two wheel steering) , 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 improves the operation stability.This thesis has the research contents as following:1) The research on the tyre nonlinearity The tyre nonlinear model affects the steering characteristics and stability of the vehicle. Based on neural network, the identification is made for a Magic Formula tyre model. Furthermore, the simulation is done to validate the accuracy of the identification. A tyre cube nonlinear model is used in robust control of 4WS system. The nonlinear controller is gained2) The analysis of 4WS system by nonlinear dynamics Combined the nonlinear tyre model with a driver model, a nonlinear 4WS model is put forward. Its stability is analyzed and the result is verified by simulation.3) The stochastic vibration analysis of 4WS system.As 4WS system is a typical system with stochastic perturbations, which are from the road surface unevenness and side wind and can't be described by deterministic function, the probability and statistics theory must be used in such research. The random analysis of 4WS is focused on stochastic stability, especially in stochastic bifurcation. The results have both theoretical and application significance.4) The hybrid control of 4WS systemBased on the switched system theory, the original system is divided into two subsystems: the low-speed system and the high-speed system. In the first step, by H2/H∞ mixed design method, the respective robust controller is designed for the two subsystems. The method is based on LMI ( linear matrix inequality).In the second step, by changing the coefficients of H2/H∞ mixed design method, the two Lyapunov matrix is found to guarantee the stability. When the system model is changed and the robust controller can't stabilize the whole system, a switchedlaw is designed to guarantee the stability the global switched system.5) The control system implementation of 4WS systemBased on the hybrid controller of 4WS system, an implementation scheme is put forward. The mechanical structure and electrical solutions are provided respectively. The SoC design and RTOS technology are integrated into the electrical part. The embedded system software structure is described in details.