A conditional-proportional damper schedule for semi-active suspension of ground vehicles

Abstract

The suspension system of a ground vehicle is responsible for ride comfort and for isolation of the chassis from the road disturbances. The performance of a suspension system can be quantitatively expressed by the root-meansquare acceleration experienced by the chassis under given terrain conditions. The suspension performance is crucial for ride comfort as well as the health of equipment and personnel on-board the chassis. Typically some variant of springdamper system is used for ground vehicle suspension. The spring deforms to the road undulations and the role of the damper is to attenuate the oscillations induced by the spring and suspended mass. Extremely low level of damping makes the suspension system prone to resonance phenomenon which can be hazardous to the chassis. On the other hand, an extremely high level of damping substantially reduces the effectiveness of the spring, thereby drastically reducing the performance of the suspension system. Adaptively varying the damping coefficient based on certain kinematic conditions has been a subject matter of interest because of the performance improvement that can be achieved with inexpensive hardware. Such suspension systems are said to be Semi-active. Several strategies for adjusting the damper for improving the isolation performance are available in literature. Model reference skyhook strategy is one of the most popular techniques for scheduling the damping co-efficient. Unfortunately, it requires the absolute positions and velocities which are not easily measurable. An alternative strategy is available in literature which is based on easily measurable relative kinematics. In this paper, we show that this alternative strategy leads to performance degradation against the sky-hook strategy. Further, this paper proposes a novel strategy for scheduling the damper which is based on easily measurable quantities and at the same time achieves an isolation performance close to benchmark Sky-hook damper.