Patent ID: 6701823
Filing Date: 2004-03-09
Classification: F15B

Abstract:
A method for controlling a lift cylinder (2) of working machines such as excavators, wheeled loaders or the like, wherein the lift cylinder (2) can be pressurized in vertical direction by an external force (external load P), wherein the pressure cylinder space (12) and the suction cylinder space (11) of the lift cylinder (2) are pressurized with pressurized fluid via a line connecting these two spaces (11, 12) to one another and containing a control element (3), wherein the control element (3) controls the flows to and from the cylinder spaces (12, 11) and the overflow into a tank (25) for the working medium via a hydraulic pump (7), characterized in thata distribution channel (5) in the control element (3) is pressurized by the hydraulic pump (7), whereupon the pressure cylinder space (12) or the suction cylinder space (11) is connected via a control piston (4), in that, at a predetermined pressure produced in the cylinder space (12) by the external force/load (P), the cylinder space is connected via a check valve (15) to this distribution channel (5) and the feed flow from the pump (7) to the distribution channel (5) is stopped by a stop valve (8) that can be influenced by a pressure sensor (20), whereupon the suction cylinder space (11) is connected to the channel (5), and in that, when another predetermined pressure is reached, the check valve (15) closes and the stop valve (8) is opened, thus allowing feed flow from the hydraulic pump (7) to the distribution channel (5) for application of an additional force in the suction cylinder space (11).