HYDRAULIC SYSTEM COMPRISING A LOCKING DEVICE FOR MAINTAINING A CONTROL VALVE IN ITS WORKING POSITION

摘要

A hydraulic system includes a selective control valve and a cam member movable to selected positions for controlling a hydraulic cylinder powered by a pump. A follower is urged to a locking relationship with the cam by a hydromechanical mechanism to releasably hold the control valve in the selected positions. The hydromechanical mechanism includes a bore exposed to sump pressure and to pressure upstream and downstream from a metering valve in a passage interconnecting the pump and the control valve. A hollow apertured sleeve is movably mounted in the bore. An apertured piston is slidably received by the sleeve. A rod, engageable with the follower, extends through the piston and sleeve apertures. A first spring interconnects the rod and the piston and a second spring interconnects the piston and the sleeve. The sleeve moves to a preload position in response to a no-flow differential pressure between the sump and the passage to urge the follower via the rod towards its locking position. The piston moves in response to fluid flow through the passage to bias the follower toward its locking position. The piston and the rod move to automatically allow the follower to release from the cam when the function of the hydraulic cylinder is completed. Also, the sleeve and rod move to automatically allow the follower to release from the cam when system pressure in the passage is lost.