Control of Suspensions for Vehicles With Flexible Bodies—Part II: Semi-Active Suspensions

Two methods of control of semi-active suspensions that specifically address the problem of structural vibrations of the vehicle body are considered. These control strategies are based on those developed for active suspension systems in Part I of this study and rely on either modifications of suspension control forces that account for body compliance or on the addition of a proof-mass actuator to reduce structural vibrations. A half-car model that includes body compliance is used to evaluate the effects of these control strategies on the performance of the suspensions with two-state and continuously modulated dampers. The performances of the systems are evaluated in both the time and frequency domains. The effect of time delays in the process of actuating the adjustable dampers is investigated. Significant reductions of structural vibrations are observed when the nodes of body beaming modes are a sufficient distance away from the suspension mounting points, and the time delays in the control system are negligible. The results deteriorate markedly when two-state dampers are used instead of continuously variable dampers or when a time delay in excess of 5 ms is present in the control loop. When the preference in suspension design shifts toward road holding it becomes increasingly difficult to improve the vehicle structural response without sacrificing other aspects of performance.