The Relative Performance Capabilities of Passive, Active and Semi-Active Car Suspension Systems

Performance and Design Considerations for Dissipative Semi-Active Suspension Systems for Automobiles

Following previous work aimed at determining the relative performances of automobile suspension systems of passive, active and semi-active types by calculation, similar theoretical methods are applied here to evaluate a class of semi-active system that contains a passive spring of fixed stifness in parallel with the active damper. The static attitude control of the vehicle derives from the springs and in the cases considered the spring stiffness is adequate from this point of view. Systems based on two alternative forms of control law are studied. Results which show the best systems to offer particularly good performance for rough road conditions are presented. By adaptation of the damper control law using continuously updated information some capacity to obtain good performance under moderate conditions is shown to exist, but performance comparable with that obtainable from a purpose designed or fully adaptive system on average main road and motorway conditions is not possible.

Performance Predictions for a Pneumatic Active Car Suspension System

A mathematical model of a pneumatic active car suspension system in a single wheel station form excited by realistic road roughness input is set up. The active control is exerted through a d.c. motor-driven air-pump.

The model is used to show that essentially all the advantages of active control, within the terms of reference, are obtained by employing the control only at low frequencies and having the suspension parameters adapt to the running conditions as they vary.

Control laws are derived using limited state feedback, linear stochastic optimal control theory and power consumption, and space requirements are evaluated. System performance is shown to be good in comparison with other known arrangements and encouragement for further work to extend the results is given.