Adaptive Nonlinear Control in Active Suspensions 1

We study the sensitivity of a recently developed nonlinear control scheme with respect to variations in the parameters of the active suspension. Based on comparative simulation results, we conclude that the parameters of the hydraulic actuator dynamics are the ones to which closed-loop system performance is most sensitive. In fact, it is enough to estimate only one parameter in order to guarantee good performance , while variations in the remaining parameters can be dealt with through judicious choice of the controller parameters. We use tuning functions for our adap-tive backstepping scheme, and provide guidelines for the choice of the xed controller parameters. performance, sensitivity analysis. 1. INTRODUCTION Active suspension designs aspire to improve the inherent tradeoo between passenger comfort and road handling. However, they introduce the additional considerations of suspension travel and power consumption, which must be factored into the overall design goals. In our recent papers (Lin and Kanellakopoulos, 1995, 1996) we exploited the exibility of backstepping (Krsti c et al., 1995) to improve the tradeoo between ride quality and suspension travel. Our resulting nonlinear controller does not only handle the inherent nonlinear nature of the hydraulic dynamics, but also introduces additional nonlinearities to make the suspension stiier near its travel limits. This intentional infusion of nonlinear-ity represents a departure from previous designs which attempt to produce linear closed-loop systems (Thomp-In this paper we are concerned with the sensitivity of the aforementioned nonlinear scheme with respect to variations in the parameters of the active suspension plant.