Control of a shimmy vibration in vehicle steering system using a magneto-rheological damper

Vehicle stability largely depends on the vibration of the steering system. A four degrees of freedom dynamic model of an automotive steering system with a magneto-rheological damper is presented in this study. Firstly, an equivalent mathematical model of the steering system is developed. The nonlinear equation of motion obtained from the dynamic model is then linearized around its equilibrium point to make it suitable for the design of an appropriate controller for vibration suppression. In this work, a new type of adaptive sliding mode controller is designed for control of the magneto-rheological damper and hence to control unwanted vibration. It is shown that the proposed control logic is very effective for settling steering motion near the equilibrium position. The shimmy vibrations of the wheels are reduced by a considerable amount and the steering system becomes stable. In addition, a comparative work is undertaken between the proposed controller and an ordinary sliding mode controller to demonstrate the advantage of the proposed methodology.