| Because of the mobility and flexibility at low speed and the better lateral stability at high speed of a four-wheel-steering (4WS) vehicle, the paper researches the four-wheel-steering system on the project of"the modes and the intelligence control technique researching of four-wheel-steering Vehicle"of Chongqing education committee. Firstly, the methods of establishing 4WS model and the models which have been established up to now are analyzed, simulated and compared. According to the better method of mathematical modeling, the paper establishes a four-free-degree (the lateral movement, the yawing movement, the rolling movement and the pitching movement) nonlinear dynamic mathematical model of 4WS vehicle. And the equations are resolved; the model is simulated in MATLAB. Because of the heavy-nonlinear factors, the model is hard to be simulated visually. It is instead by the neural network with feed-back loops, which is trained in MATLAB, is turned into a SIMULINK form with not only the multi-input ports and multi-output ports but also the dynamic motion. Then, paper analyzes the steering modes at all kinds of control conditions, establishes the control model of 4WS vehicle. The writer makes use of the fuzzy controller to predicate the steering modes. At last, paper derives the steering angle of back wheels at a certain steering mode based on the relationship of mechanics and geometric when vehicle steering.Furthermore, the paper analyzes the tire dynamic models which have been established as yet and researches the transient response of the tire. The writer makes use of the"Uni-tire"model as the dynamic model of the tire at the process of establishing the mathematical model of the vehicle 4WS system.Finally, the paper imitates the control process of the 4WS system with the calculator simulative technology, analyzes the control effectiveness, and compares with the front-wheel-steering mode's, verifies the validity and the possibility of the result from the theories research.
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