GB992322A - Improvements in hydraulic pumps - Google Patents

Abstract

992,322. Reciprocating pumps. INTEGRAL Ltd., and T. E. BEACHAM. April 26, 1963 [Jan. 26, 1962], No. 3139/62. Heading F1A. [Also in Division G3] In an hydraulic pump having a shaft carrying a rotary cylinder block with pistons coacting with a swash plate and with cylinders communicating in succession with inlet and discharge ports in a stationary valve plate, the casing is of unequal wall thickness such that the longitudinal stress in the casing is substantially constant throughout its circumference. The thickness of the wall of casing 10, Figs. 2 and 3, is such that the centroid of the casing cross-section coincides with the mean position of the resultant thrust of the pistons 21. This substantially prevents unequal longitudinal stresses in the casing 10 and thereby maintains parallel the mating faces between the cylinder block 16 and the valve plate 28 provided with inlet and discharge ports 29, 30. In order to avoid stresses due to unequal thermal expansion, the valve plate 28 is supported on pins 33, 35 screwed into the casing 10 to project into a closely fitting hole and a slot 36 respectively, in the valve plate. Ports 37 and grooves 38, 39 maintain hydrostatic balance across the valve plate 28. The swash plate 23 is held in its load position by a piston 26, Figs. 3 and 6, subjected to the pump delivery pressure through a conduit 42. At a predetermined pump delivery pressure a piston 43, biased by a control spring 44, is forced to the left and, due to the travel x to close a drain passage 46 being greater than the dimension y, a gradual build up of pressure below a piston 47 results, and the latter is eventually raised causing a rod 53 and a piston 49 to close a drain passage 50 and open a passage 54 respectively. This communicates the pump delivery pressure to a piston 60 of larger area than the piston 26 so that the swash plate 23 is rotated about a pair of rockers 24 to its off-load position. A gear pump 31 driven by the pump shaft circulates oil through the casing for cooling the pump, reducing the pressure in the casing to below the inlet pressure to ensure that slippers 22 are not disengaged from the swash plate 23, and for lubricating shaft bearings 17, 18.