GB1433024A - Variable displacement pump having pressure compensator control means - Google Patents

Abstract

1433024 Reciprocating pumps CATERPILLAR TRACTOR CO 8 June 1973 27481/73 Heading F1A In a swash-plate pump, e.g. for supplying hydraulic implement circuits on tractors, cartridge assemblies 98 and 122 incorporate deliverypressure responsive means 104 and resilient means 44, respectively, for biasing the swash-plate 30 into its minimum and maximum stroke positions, respectively, the cartridge assemblies being interchangeable for reversing the flow of the pump. An adjustable, minimum stroke stop 108, and a maximum stroke stop 40 are also interchanged for flow reversal. The cartridge assemblies are secured by flanges 50 and 100 located between head member 16 and housing 18, and by nut 52 and plug 138. Duplicate cartridge connections 62, 74 and 90, 124 are provided. In operation, with the implement circuit control valves in their neutral position whereby a pilot line 38 is connected to tank, on starting the pump, with the swash-plate 30 biased to its maximum stroke position by spring 44, delivery pressure in outlet port 36 is directed via passages 56, 62 and 64 to chamber 58 beneath spool valve 60. Flow takes place through the spool valve passage 66 and restriction 68 to tank via-passage 72 and pilot line 38, resulting in a differential pressure across the spool valve causing it to move upwardly against spring 76 until spool groove 78 connects vent port 88 to port 80 which communicates via passage 84 with cylinder 82 of piston 42, thereby venting cylinder 82. Since the delivery pressure acts on piston 104 via passages 92 and 94, venting of cylinder 82 will permit movement of the swash-plate 30 by piston 104 into its minimum stroke position. When the implement circuit control valves are opened, pilot line 38 is closed, so that pressure equalization takes place above and below spool valve 60, permitting its downward movement by spring 76 to connect cylinder 82 to delivery pressure via the spool valve passages. As piston 42 is of greater cross-section than piston 104, the swash-plate is moved to its maximum stroke position. When the delivery pressure exceeds a predetermined level, a pressurerelief valve 114 opens and vents the upper end of spool valve 60 which moves to vent cylinder 82, thereby causing movement of the swash-plate into its minimum stroke position.