Design of fuzzy logic controller for four wheel steering system

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Design of fuzzy logic controller for four wheel steering system

Ozatay, Evren / Unlusoy, Samim Y. / Yildirim, Murat A.

In this study, the FLC (Fuzzy Logic Control) is proposed for the design of a four-wheel steering control system for a standard, understeered, medium size passenger car. Here, an approach to the control of the rear wheel steering angle based on fuzzy theory has been implemented. It has been emphasized that to analyze the lateral dynamics, it is necessary to include the roll motion of the 4WS vehicle model. The influence of the suspension roll dynamics in steering control becomes dominant especially for vehicles with soft suspension systems. Therefore, a nonlinear 3-dof vehicle model was used, with the nonlinearity being introduced from the tire model. The fuzzy PID controller is able to tolerate poor selections or inadequate implementations of the controller gains, which would make most conventional controllers unstable. Since nonlinear effects will be encountered in many complicated systems, the ability of the fuzzy PID controller to tolerate these unmodeled nonlinear and gain-value variation factors is a substantial advantage over conventional linear PID controllers in real-world applications. Both steady state and lane change maneuvers are employed, to compare the performances of the control strategies previously introduced in the literature for four wheel steering with the fuzzy controlled vehicle. The results from the simulations given in the previous section show that the sideslip angle can be significantly reduced. It means that vehicle stability and controllability can be improved, and driving performance become better. Further, simulation results show that the FLC type four wheel steering system improves the response time of yaw rate, and hence the cornering ability.