Performance limitations for active and passive suspensions

This paper investigates a systems approach to suspension design for passive and active suspensions. We seek to understand the set of dynamic responses which are achievable for both passive and active systems. To this end. we view a suspension system as a mechanical multi-port network and draw on concepts from electrical circuits such as passivity and reciprocity. We give an example of a suspension which is stiff to loads on the sprung mass, is soft to road disturbances, which can be realised actively but not passively. Degrees of freedom and constraints on various transfer functions are examined for quarter- and half-car models.