GB1001889A - Improvements in or relating to hydraulic pumps and motors - Google Patents

Abstract

1,001,889. Reciprocating pumps and motors. CATERPILLAR TRACTOR CO. April 30, 1962, No. 16350/62. Heading F1A. In a pump or motor having cylinders alternately communicating with an inlet port and an outlet port, said ports being disposed asymmetrically with respect to the line passing through the cylinder positions at which the piston is at its top and bottom dead centres, a bleed passage communicates between the outlet port and a point between the inlet and outlet ports for registration with the cylinders prior to their registration with the outlet port, a check valve being provided in the passage to permit flow from the cylinders into the outlet port. In the embodiment shown the pump or motor comprises a rotatable cylinder block 13 coupled to a drive shaft 18 and urged against a valve face by a spring 32, the housing and block being tiltable to vary the output and reverse the flow. For a reversible flow pump, a bleed passage 49, Fig. 5, is provided for the inlet port and the outlet port. The check valve 44 controlling the bleed passage of the acting inlet port 34 is held closed by a piston 51 actuated by the outlet port pressure. When the port functions are reversed, piston 51 is moved back by a spring 50 to permit operation of the check valve. Cylinders 37 simultaneously overlap the bleed port and the acting outlet port before losing communication with the bleed port. For a reversible motor, Fig. 11, bleed passages 54a are provided for the inlet port and the exhaust port, only that associated with the acting exhaust port being effective. Check valves 44 are held in bores in the cylinder head, Fig. 1, by threaded plugs.