This patent discloses a hydraulic cylinder for use in exercise machines to deliver a controllable fast acting force. The invention uses a hydraulic cylinder with features that allow high acceleration rates, rapid changes of force level and direction, and positive force limitation.

Abstract: This invention is a hydraulic cylinder for use in exercise machines to deliver a controllable fast acting force. The invention uses a hydraulic cylinder with features that allow high acceleration rates, rapid changes of force level and direction, and positive force limitation. In the preferred embodiment, the hydraulic cylinder is composed of a rodless hydraulic cylinder coupled to a cable pulley system. A water source delivers water to generate a force against an inner bi-directionally moving piston to generate a regulated movement and force.

The ends of the rodless hydraulic cylinder are sealed by both a water control spool valve and a controllable poppet style pressure relief valve. The water control spool valves adjustably permits water to enter and exit the hydraulic cylinder to regulate the direction and speed of movement of the piston. The pressure relief valve controls the desired maximum pressure and corresponding forces exerted on cylinder. Thus, both the internal speed and force of movement of the piston can be controlled. THe invention can deliver high acceleration/speed, high force resistance; high acceleration/speed, low force resistance; low acceleration/speed, high force resistance; or low acceleration/speed, low force resistance exercise forces and movements depending on the water flow, internal pressure, and resulting generated forces.