Apparatus for restricting the velocity of a hydraulic piston in its end positions

Claim 1

In a hydraulic excavator, an apparatus for restricting the movement of a piston of an operating hydraulic unit, when said piston approaches at least its one end position in a cylinder, comprising: the operating hydraulic unit coupled between two excavator parts which are movable with respect to each other by means of the operating hydraulic unit; a main valve which is coupled to the operating hydraulic unit in orner to be actuated by a first pressure medium supplied thereto; a servo-circuit for regulating the main valve having an associated servo-pressure therein; a hydraulic piston-cylinder sensor is secured to one of the excavator parts and has a freely projecting piston rod directed towards the second of the excavator parts; and a pressure difference sensing valve which is coupled between said hydraulic piston-cylinder sensor and main valve; a pressure provided in said hydraulic piston-cylinder sensor when the piston of the operating hydraulic unit approaches its end position, in that said piston rod of said hydraulic piston-cylinder sensor mounted on the one excavator part is actuated by the second excavator part, said pressure exceeds the servo-pressure, and said pressure difference sensing valve sensing the pressure difference between said pressure in said piston-cylinder sensor and the servo-pressure and, in accordance therewith, throttle valve means between said pressure difference sensing valve and main valve for throttling said first pressure medium supplied to the main valve such that a second pressure medium supplied the main valve to the operating hydraulic unit is throttled.