Designing a fuzzy logic controller to adjust the angle of tires in four wheel steering vehicles

In this paper, a 4 wheel steering vehicle (4WS) was used as a template and a vehicle was modeled (experimental) by using 2 degree of freedom system. The dynamics governing the Yaw behavior of a vehicle has been simulated with MATLAB/SIMULINK software. A controller, working by fuzzy logic was then designed. A relationship between front and rear angle of tires in different speeds and different front steering angle was found after running simulation for over 600 times. This controller increases the directional stability property of experimental vehicle when this vehicle is turning or maneuvering. The relationship was then used to make rules for the fuzzy logic controller. Subsequently, the experimental vehicle was compared with an uncontrolled vehicle and a vehicle with a very high lateral stiffness which there is infinitesimal slipped on turning or maneuvering (reference). This allows us to correctly identify the amount of slipping in our experimental vehicle. Our results show significant improvement of directional stability property of experimental vehicle in comparison with uncontrolled vehicle in different speed and different steering angles. Also the gotten results show that the side slip angle and the yaw rate of experimental vehicle were enhanced significantly.