More on a Decoupled Control Model of a Vehicle Suspension System

Abstract

In a recent paper (1) we proposed a new control model for a passenger car suspension system. It consists of a partial decoupling of the full car 3D motion into quarter car suspension models whose number is 3 instead of 4. These 3 decoupled sub-dynamics are supplemented by a single second order one which carries the coupling content of the original full model. The decoupled subsystems thus are not the ubiquitous integrals as in classical noninteracting control but the more realistic physical subsystems (the quarter car suspensions) which make up the full coupled system. The special decoupling feedback which leads to this structural result is found to depend on a vector of 4 real valued control design parameters. The latter, in turn, reveal to be crucial to two main issues in suspension control: first, distribute the 3 controls designed for the decoupled subsystems over the 4 actuators, next, further shape the uncontrolled part of the dynamics of the sprung and/or unsprung masses. One potential use of this new model is to reconcile the many control laws (so-called skyhook, local control, etc.) which are designed for quarter car suspensions with their basic application which remains the control of the full car suspension system. This new model evacuates the necessity of assuming the chassis mass as equally distributed over the 4 wheels or over the front and rear wheels. The results of the so-called skyhook and local control strategies may thus be substantially improved simply by applying these control design methods to the 3D chassis variables (the heave, roll and pitch) instead of the 4 chassis deflections.