GB832516A - Improvements relating to hydraulic servo-motor systems - Google Patents

Abstract

832,516. Fluid-pressure servomotor-control systems. SOC. INDUSTRIELLE GENERALE DE MECANIQUE APPLIQUEE S.I.G.M.A. June 18, 1956 [June 18, 1955], No. 18813/56. Class 135. An hydraulic servomotor system comprises a continuous delivery pump 1, an hydraulic jack 12, a selector valve 7 therefor movable in opposite directions from a neutral position in which the opposed pressure chambers 10, 11 of the jack are shut off from the pump delivery conduit 5, and a by-pass valve 30 which is interposed between the conduit 5 and a return conduit 9, the valve 30 being urged in the opening direction by the pressure in the conduit 5 and in the closing direction by the pressure in a chamber 35 communicating with conduit 5 through a restricted orifice 36 and with the return line through an orifice or channel 38 which is blocked by the selector valve 7 except when the latter is in its neutral position. The pump is thus unloaded in the neutral position of the selector valve. The system is particularly applicable to the control of the lifting beam 16 of an agricultural or earth-digging tractor, the beam being connected through a lever 15 to the piston-rod 14. The valve 7 is operated by a hand lever 8 connected to one end of a floating lever 28, the other end of which is connected to the piston-rod 14 so that the valve 7 is returned to its neutral position when the beam is moved to the position corresponding to the hand lever. The outflow of liquid from the chamber 11 during the descent of the beam is limited by a spring-loaded valve 11a having a calibrated orifice therein. Except in the neutral position of the valve 7, the channel 38 is blocked by one of the lands 40. If the pressure rises unduly in the conduit 5, the pilot relief valve 41 opens to relieve pressure in the chamber 35 and hence allow the by-pass valve to open against a light spring 37. Liquid is locked in the chambers 10, 11 when the valve 7 is in the neutral position by spring-closed valves 24, 25 either of which is opened directly by the supply pressure and the other by the supply pressure acting on a plunger 26. Exhaust fluid enters a bore 21 in the valve 7 and returns to the sump 2 via a chamber 22 and a channel 23. Lateral slots 33 in the valve 30 enable it to close progressively. In a modification, the valve 30 has a skirt with staggered ports for the same purpose. The valves 7, 30, 24, and 25 are arranged in a control block 6 connected to the jack by flexible pipes 18, 19. If desired, the pump, jack, and valves may be grouped together as a single unit or all mounted separately. The calibrated orifice 36 may be arranged in a channel in the block 6.