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

Abstract

Based on the well-known quarter car representation of the automobile suspension design problem, pdomnce parameters relating to passenger discomfort, working space and tyre load variability are generated for passive, active and semi-active suspension systems. Active systems of two types having different hardware implications are considered, and linear optimal control theory is used in each case to derive a good set o control law parameters. The semi-active systems studied have control laws based on the fully active systems, but are capable only of dissipating energy, so that where the corresponding active system would be acting as an energy supply, the semi-active system switches off Practically realizable switching dynamics are assumed in the calculations. Results for all the systems, for one road surface roughness and vehicle speed, are generated in a form which allows comparison between systems of diffient types which have equal suspension working space requirements. The wider implications of the results are discussed, and far-reaching conclusions about the relative capabilities and design features of passive, active and semi-active systems are drawn.