Novel constrained control of active suspension system integrated with anti-lock braking system based on 14-degree of freedom vehicle model

Abstract

This paper deals with a novel method for integration of the active suspension system and the anti-lock braking system. In the proposed method, a new nonlinear controller with state constraints is developed for the active suspension system based on the response prediction of 14-degree of freedom vehicle model. The proposed controller isolates the vehicle from road roughness in normal conditions and assists the anti-lock braking system by ensuring a good contact between the tyre and road during hard braking. In addition, the tyre deflection is limited to prevent the threat of tyre bursting. To develop the active suspension system controller, at first, a performance index consisting of a weighted combination of predicted responses of suspension system is expanded as a function of current control input. At the same time, the state constraints of tyre normal force and tyre deflection are transformed to the equivalent constraints of control input by the same prediction approach. Then, the control law is found by minimizing the expanded performance index in the presence of input constraints. The Karush–Kuhn–Tucker theorem is employed to solve the performed constrained optimization problem analytically. The performance of the proposed active suspension system controller integrated with the designed nonlinear anti-lock braking system controller is evaluated for a full vehicle model including roll and pitch motions during braking on irregular random roads. The results show that both the body acceleration and the vehicle stopping distance are decreased for the proposed integrated strategy compared with other conventional strategies.