LIMITATIONS TO SUSPENSION PERFORMANCE IN A TWO-DEGREE-OF-FREEDOM CAR ACTIVE SUSPENSION

Abstract

It is often assumed that if practical difficulties are neglected, active systems could produce in principle arbitrary ideal behavior. This paper presents the factorization approach that is taken to derive limitations of achievable frequency responses for active vehicle suspension systems in terms of invariant frequency points and restricted rate of decay at high frequencies. The factorization approach enables us to determine complete sets of such constraints on various transfer functions from the load and road disturbance inputs for typical choices of measured outputs and then choose the “most advantageous” vector of the measurements from the point of view of the widest class of the achievable frequency responses. Using a simple linear two degree-of-freedom car suspension system model it will be shown that even using complete state feedback and in the case of in which the system is controllable in the control theory sense, there still are limitations to suspension performance in the fully active state.