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.

Abstract: An active suspension system isolates a first member from vibration in a second member. A hydraulic actuator is connected between the first and second members and includes a cylinder having a second chamber and a first chamber defined on opposite sides of a piston in the cylinder. A rod is attached to the piston with a first end extending out of the cylinder and a second end within the third chamber. A valve arrangement controlling flow of fluid between the first and second chambers and a source of pressurized hydraulic fluid and a tank which control applies force to the piston that counteracts the transmission of vibration between the first and second members. A load leveling valve assembly connects the third cylinder chamber selectively to the source or the tank to maintain the piston centered in the cylinder under static load conditions.

Abstract: A suspension system has a pair of cylinders connected between the cab or axle and a chassis of a vehicle to isolate the driver from vibrations. A pair of hydraulic cylinders is coupled to opposite sides of the cab or axle and to the vehicle chassis. A separate accumulator is coupled each hydraulic cylinder to act as a hydraulic spring that attenuates side to side motion. A leveling valve selectively control the flow of fluid to or from both hydraulic cylinders to level the cab or seat in response to load changes.