Two Contrasting Versions of the Optimal Active Vehicle Suspension

Abstract

It is generally agreed that vehicle suspensions should isolate the body from roadway unevenness inputs but it is less clear on which other functions are most important. Some studies focus on keeping the wheel-road contact force excursions as small as possible for safety reasons and others focus on limiting the main suspension deflection for good rigid body motion control. In this paper, two performance indices are used which lead to optimal state variable feedback laws for the suspension force. Body isolation is traded off in one case against contact force variation and in the other against suspension deflection. The use of symmetric root locus sketches shows the types of system that result in both cases. It is shown that optimal active suspensions designed according to different criteria are not necessarily comparable and it may not be fair to compare an optimal suspension with a conventional one, unless all aspects of suspension performance are considered simultaneously.