Performance limitations and constraints for active and passive suspensions: a mechanical multi-port approach

This paper develops a framework using mechanical multi-port networks to stu dy the performance capabilities and constraints in vehicle suspensions. We seek to understand the set of dynamic responses which are achievable for bo th passive and active systems. To this end, we view a suspension system as a mechanical multi-port network and draw on concepts from electrical circui ts such as passivity and reciprocity. We identify necessary conditions on t he external behaviour of a quarter-car model for the suspension to be capab le of passive realisation, and thereby establish that several behaviours or force laws cannot be implemented without an internal power source. We stud y the number of available degrees of freedom (i.e., independently specifiab le impedances in the quarter-, half- and full-car cases.