Active Automotive Suspensions

Abstract

The analysis of passive automotive suspensions in the last chapter showed that there are significant trade-offs in performance between the ride quality, rattle space and tire deflection transfer functions. Improvements in any one of the three transfer functions in the case of passive suspensions is often obtained at the expense of deterioration in the other two transfer functions. In this chapter, we look at the use of active suspensions in which electronically controlled actuators placed in the suspension are used to provide significantly superior performance. Alternate control laws are analyzed and the performance that active suspensions can provide is studied and compared with that of passive suspensions. The factors that limit the performance of active suspensions are studied. The analysis of ``invariant points'' is used to understand these performance limitations. A simple control law called sky-hook damping which needs only a few sensor measurements and can provide most of the benefits of full state feedback control laws is discussed. Finally, the chapter looks at actual experimental implementation issues, including the dynamics of hydraulic actuators used to provide the active force.