Variable displacement pump having pressure compensation control means

Claim 1

A variable displacement axial piston pump of the type having a housing means containing an inlet port and a discharge port, a plurality of piston means and an angularly adjustable swash plate means for determining piston displacement and thereby the amount of fluid discharged from the pump, resilient means in a first cartridge assembly means biasing the swash plate means to its maximum discharge position whereby a maximum of fluid is displaced by the pump, and pressure responsive means in a second cartridge assembly means for shifting said swash plate means to its minimum discharge position in response to a pressure such as from a hydraUlic system, reversing means whereby interchanging said first cartridge assembly means with said second cartridge assembly means causes the pump flow direction to be reversed, said reversing means comprising a pair of stop means, one of which is associated with the swash plate adjacent said first cartridge assembly means and the other of which is associated with the other of said cartridge assembly means, said stop means being interchangeable, one with the other, said first cartridge assembly means comprising a first generally cylindrical cartridge member in a first bore in said housing means, said second cartridge assembly means comprising a second cartridge member in a seond bore in said housing, and wherein said first and second cartridge members are dimensioned so as to permit interchanging of said cartridge members in said bores, said second cartridge member comprising a generally elongated member and said pressureresponsive means comprising a first reciprocable piston extending from a bore in one end of said cartridge member and thereby defining a first chamber therein, said first cartridge member being a generally elongated member and wherein said resilient means in said first cartridge member comprises a second reciprocable piston extending from a reciprocable bore in one end of said cartridge member and thereby defining a second chamber therein, and further including spring means in said second chamber biasing said piston outwardly from said bore, and further including a pilot line in said housing adapted to sense pressure from a hydraulic system and wherein said means for suddenly shifting said swash plate to its minimum discharge position compriss spool means responsive to line pressure for directing pressure fluid to said first chamber so as to cause said first reciprocable piston to tilt said swash plate means to the minimum discharge position, and wherein said spool means compriss a spool contained in a bore and defining a third chamber at one end of said bore, and further including poppet valve means for relieving excessive pressure occurring in said third chamber.