Drive by wire control of an electro-hydraulic active suspension a backstepping approach

Passengers' comfort in long road trips is of crucial importance; as a result, active suspension control became a vital subject in recent researches. This paper studies the control of an electro-hydraulic active suspension, based on the backstepping control strategy. Our goal is to control the car vertical motion and keep it to zero, in order to ensure passengers' comfort. The active suspension model is highly non-linear and non-differentiable due to the hydraulic components, especially the servo-valve. Moreover, in most studies, it was always assumed that the chamber volume of the hydraulic actuator is constant, while in fact the volume varies with the piston motion. This induces an additional non-linear term to the classic model. Therefore, a powerful control strategy is needed, and the backstepping is used here for being a powerful non-linear approach able to overwhelm all these facets. However, choosing the car vertical motion as the control variable results in an unstable zero dynamics; hence, it is often combined with another variable such as the suspension travel or the vertical acceleration. To remedy this problem, we introduced a damping term in the mathematical model to ensure that zero dynamics will remain stable regardless of the control variable choice. As it will be demonstrated, the backstepping used with the model we established is an ideal drive by wire control to compensate road fluctuations.