A semi-active control policy to reduce the occurrence and severity of end-stop impacts in a suspension seat with an electrorheological fluid damper

A semi-active on-off control policy has been developed to reduce the severity of suspension seat end-stop impacts caused by shocks or high magnitude vibration. An electrorheological fluid damper was used to realize the required two-state damping. The effects of the free travel (i.e., the relative displacement within which the suspension damper has low damping) and the on-state damping on end-stop impacts were investigated with a sinusoidal input motion. It was found that both a shorter free travel and higher on-state damping reduced both the occurrence of end-stop impacts and their severity. The control policy was also tested with a random signal at different input magnitudes. The on-off control policy improved the performance of the seat suspension when end-stop impacts would otherwise occur with high magnitude inputs, without causing poor vibration isolation with low magnitude inputs. It is concluded that a successful compromise can be achieved between steady vibration isolation and end-stop impact reduction. (C) 1997 Academic Press Limited.