GB1332798A - Hydraulic system - Google Patents

Abstract

1332798 Hydrostatic transmission control BORG-WARNER CORP 6 Oct 1970 [16 Oct 1969] 47424/70 Heading F2D [Also in Division G3] A variable displacement pump 10 supplying motor 45 is controlled by a flow compensator valve 29 which responds to the pressure drop across restrictor 40 to establish a control pressure in servomotor 19 by connecting the latter to supply and exhaust ports 53, 52 via line 30 and normally-connected ports 31, 48 in pressure compensator valve 20. Auxiliary piston 17 responds to pump output pressure to provide a bias opposing servomotor 19. The valve 20 has a spool 21 moved leftwards by excess output pressure to connect servomotor 19 to sump 34, the spool also responding via cam 27 and spring 26 to swashplate displacement so as to maintain torque input constant up to a datum pressure above which the swashplate angle is reduced more rapidly to provide a sharp cut-off. With a restrictor located at 62, pilot valve 61 opens at a set pressure to open by-pass valve 63 and simultaneously causes valve 29 to reduce pump displacement. When restrictor 62 is shifted to 72, the pilot valve no longer controls valve 29. In modifications of this system, the swashplate angle might be reversed and the flow compensator spool can have differential area end leads, in which latter case spring 46 can be omitted. In an alternative system (Fig. 2, not shown), the pressure compensator spool is embodied in the main servo-piston (78) and acts at a preset pressure to admit fluid from the output line via (90, 91, 87, 88) to the servomotor to reduce pump displacement. In a further system (Fig. 3, not shown), the restrictor 40 is in the return line downstream of motor 45 and the pilot valve 68 acts to admit fluid to chamber 38 of the flow compensator valve to cause the latter to reduce pump displacement. The pressure compensator spool (120) is operated in this case by a floating lever connected at one end to a pressure sensor (95) and at the other end to the swashplate. Piston 17 is omitted although its bias spring (94) as used in Fig. 2, is retained. In Fig. 4, (not shown), the flow compensating and by-pass functions are provided by a single valve.