Abstract: A hydraulic actuator for an active of semi-active vehicle suspension system has a cylinder with a piston therein. A piston rod is attached to the piston and extends out of the cylinder. First and second chambers are formed on opposites sides of the piston enabling the piston to be driven in a manner that counteracts vibrations in the vehicle, A third chamber is provided in the cylinder for connection to a load leveling apparatus. A novel structure reduces the overall length of the hydraulic actuator. A displacement sensor is incorporated into the hydraulic actuator to provide an electrical signal that indicated how far the piston rod extends from the cylinder.

Abstract: A suspension system, connected between two members of a vehicle, includes a cylinder having first and second chambers separated by a moveable piston. The piston has a larger surface area in the first chamber than in the second chamber. A first proportional valve connects the first chamber selectively to a source of pressurized fluid or a tank, and a second proportional valve connects the second chamber selectively to the source or the tank. A controller electrically operates the first and second proportional valves. A pilot-operated valve opens when pressure in the second chamber exceeds a predefined level, thereby providing a path through which fluid flows from the first chamber to the tank. Thus when fluid from the source is applied to the second chamber, both the second proportional valve and the pilot-operated valve open to convey a greater amount of fluid from the first chamber to the tank.