Shock absorber damping force control system for vehicle

Claim 1

A damping force control system for a shock absorber for use in a vehicle, comprising: an actuator for varying a damping force of the shock absorber provided between a sprung mass and an unsprung mass; first means for detecting at least one of a sprung mass vertical vibration of the sprung mass and a relative vibration between the sprung mass and the unsprung mass; second means for deriving a sprung mass velocity based on the detection result of the first means, producing a first signal indicative of the derived sprung mass velocity, and defining a sign of the sprung mass velocity based on whether the sprung mass velocity is in an upward direction or a downward direction; third means for deriving a relative velocity between the sprung mass and the unsprung mass based on the detection result by the first means, producing a second signal indicative of the derived relative velocity, and defining a sign of the relative velocity based on whether the relative velocity is in an expansion direction or a compression direction, wherein the sign of the relative velocity in the expansion direction and the compression direction correspond to the sign of the sprung mass velocity in the upward direction and downward direction, respectively; fourth means for extracting at least a high-frequency component within a predetermined frequency band from the at least one of the sprung mass vertical vibration and the relative vibration and producing a third signal indicative of the extracted high-frequency component; and fifth means, responsive to the first signal, second signal and third signal, for controlling an operation of the actuator to provide a lower damping force of the shock absorber when the sign of the sprung mass velocity and the sign of the relative velocity are different from each other, to provide a higher damping force of the shock absorber when the sign of the sprung mass velocity and the sign of the relative velocity are the same, and to reduce a degree of the higher damping force in accordance with a magnitude of the high-frequency component when the sign of the sprung mass velocity and the sign of the relative velocity are the same.