Abstract: An active suspension system for supporting a mass, such as a seat on a base of a vehicle, includes a hydraulic actuator coupled between the seat and the base, an pneumatic off-load device between the seat and the base, and a control system which actively controls the hydraulic actuator and which controls the off-load member. The control system actively controls the hydraulic actuator as a function of a seat position error signal. A flow control valve controls the extension and retraction of the actuator. A proportional pressure control valve is connected between a primary pressure reducing valve and an inlet of the flow control valve. During start up, the pressure control valve prevents the supply of pressurized fluid to the flow control valve until the flow control valve is driven to its center or null position. During an electrical power failure, the solenoid operated pressure control valve is spring driven to a shut off position preventing communication of pressure to the flow control valve.

Abstract: An active suspension system for supporting a mass, such as a seat on a base of a vehicle includes a hydraulic actuator coupled between the seat and the base, an pneumatic off-load device between the seat and the base, and a control system which actively controls the hydraulic actuator and which controls the off-load member. The control system actively controls the hydraulic actuator as a function of a seat position error signal. The control system also controls the off-load member as a function of a signal used in the active control of the actuator. A compressor and a vent are coupled to the pneumatic device for controlling pressurization thereof. The control system comprises an electronic control unit which repeatedly executes a control algorithm at a predetermined rate, and which controls the operational status of the compressor and the vent as a function of the position error signal and the predetermined rate.