GB977515A - Improvements in or relating to hydraulic pumps - Google Patents

Abstract

977,515. Hydraulic pumps. WEATHERHEAD CO. Nov. 20, 1961 [Feb. 9, 1961], No. 41493/61. Heading F1A. A swash plate pump has an axially movable cylinder block 20 which is adjusted in accordance with outlet pressure to vary the pump output. The block 20 slides along cylindrical surfaces 21, 32, in the pump casing and has piston controlled inlet ports 29, 30, to each cylinder and stationary cylinder extensions 24 leading to outlet ports 25b which connect through passages 26 to the pump outlet 63. The outlet pressure in passage 63 is transmitted through a sliding tube 83 to the base of a plunger valve 70 controlling the transmission of pressure through passage 72 to a cylinder 76 or the release of pressure therefrom through passage 88. The cylinder block 20 is urged to the right to its maximum output position, shown in Fig. 1, by a spring 60 assisted by the force of the outlet pressure on the tube 83. At a predetermined pressure the valve 70 is moved by the outlet pressure against its loading spring 78 to admit pressure to cylinder 76, which pressure reacts on plunger 69 carried by the cylinder block 20 to force the block to the left whereby the spill through the inlet ports 29, 30, on each stroke is increased and the pump output reduced. If the pump output pressure decreases, valve 70 is moved to the left by spring 78 to permit the pressure in chamber 76 to be reduced through exhaust port 88 whereby the block moves to the right to increase output. The opposite sides of the block 20 are interconnected through a passage 20a which, due to the hydraulic fluid which enters through a port 38 and fills the pump casing, acts to damp the motion of the block. In a modification, Fig. 4, the opposite sides of the block are connected through a passage 115 containing an adjustable plug 116 which controls the amount of damping of the block movement. In Fig. 8 the sliding tube 154 transmitting the outlet pressure to the base of the control plunger 70, Fig. 1, is in contact with the outlet 156 of the plunger base during normal running but when the pump is stopped is moved away therefrom by spring washers 165 to open a gap 160 through which the high pressure in the outlet 153 is exhausted to the low pressure reservoir 157, whereby when the pump is restarted the plungers are not under load for a few revolutions and wear on the swash plate is reduced. Specifications 952,203 and 958,973 are referred to.