Active Suspension: Future Lessons from The Past 10-02-02-0010

Active suspension was a topic of great research interest near the end of last century. Ultimately broad bandwidth active systems were found to be too expensive in terms of both energy and financial cost. This past work, developing the ultimate vehicle suspension, has relevance for today’s vehicle designers working on more efficient and effective suspension systems for practical vehicles. From a control theorist’s perspective, it provides an interesting case study in the use of “practical” knowledge to allow “better” performance than predicted by theoretically optimal linear controllers.

A brief history of active suspension will be introduced. Peter Wright, David Williams, and others at Lotus developed their Lotus modal control concept. In a parallel effort, Dean Karnopp presented the notion of inertial (Skyhook) damping. These concepts will be compared, the combination of these two distinctly different efforts will be discussed, and eventual vehicle results presented.

Most of the contemporary literature treated active suspension as a theoretical vibration isolation problem, but handling improvements from active suspension were even more impressive. Handling and actual hardware considerations motivated a confluence of both primary approaches. This innovative implementation of a control algorithm preserving features of both Lotus modal control and inertial damping is discussed, and compared with theoretical optimal controllers. Finally, a surprising fundamental performance limit of the modal inertial damping algorithm is discussed, and a solution presented.