Patent GB-889893-A (GB)
Title: Improvements in or relating to hydraulic systems
Inventor: HERSHMAN GORDON LEITH
IPC: E02F3/43
Filed: 1960-09-02
Abstract: 889,893. Hydraulic apparatus; valves. INTERNATIONAL HARVESTER CO. Sept. 2, 1960, No. 30322/60. Classes 69 (2) and 135. An hydraulic system for the earth-working implement on a tractor comprises a valve 14 which is operable to control the flow of fluid to and from a ram 10 and embodies automatically-operative means for returning the valve from a ram-operative position to a neutral position in response to a predetermined increase in pressure resulting from a restriction in the hydraulic circuit, a restrictor valve 12 which is between the control valve and the ram and has a plunger 65 displaceable to restrict the flow of pressure fluid therethrough for moving the control valve to the neutral position, and adjustable means 84 operable by a moving element of the ram to displace the plunger to the flow-restricting position when the movable element reaches a predetermined position in its travel corresponding to the setting of the adjustable means. The ram, which is connected to the earth-moving implement on the tractor, has a piston 24 in a cylinder 21, the ends of which are joined by conduits 11, 13, 15 to the control valve 14 which, in turn, is connected by conduits 16, 18 to a pump 19 and reservoir 17. The restrictor valve 12 is interposed between the conduits 11, 15 and has a through bore 74, 75 controlled by an annular groove in the plunger which is urged by a spring 68 to a downward, unrestricting position and carries the adjustable stop 84. The plunger is formed with a slot 78 receiving a member 80 to which is secured an indicator 79 and which is connected by a flexible cable 87 in a sheath 89 to a rod 94 secured to the eye 26a of the rod of the piston 24. The control valve, which may be of the type described in Specification 688,023, and U.S.A. Specification 2,836,195, consists of a spool 35 urged to a central position by a spring 51 and movable in one direction or the other by a lever 28 to connect either line 13 or 15, connected to ports 31, 32 respectively, to a port 29 joined by the conduit 18 to the pump 19, the fluid passing through radial and axial passages 36, 37, 38 in the spool. The passage 37 is closed at its right-hand end by the spring-pressed spool 39 of a relief valve controlling a passage 59 leading to a port 30 connected to the conduit 16 and sump 17. The spool 39 carries a pin 40 abutting a sleeve 41 slidable on a tubular extension 35d of the spool 35 of the control valve. In the position shown, the sleeve 41 is axially spaced by a gap 46 from a sleeve 45 secured to the extension 35d by a pin 44, the gap receiving one or other of garter springs 47, 60 when the spool 35 is moved to one or other of its operative positions. In operation, when it is desired to lower the piston 24 and implement, the lever 28 is moved to displace the spool 35 of the control valve to the right to a position in which the pump 19 is connected to the conduit 15 and upper end of the cylinder 21, the garter spring 47 engaging the gap 46 to retain the spool in the selected position. The flow through the valve 12 to the ram is unrestricted until the member 80 attached to the eye 26a of the ram by the cable 87 abuts the stop 84, which has been adjusted to a position corresponding to the desired depth of operation of the implement, and moves the plunger 65 upwardly against the pressure of the spring 68, the movement of the plunger gradually restricting the flow and increasing the pressure in the conduits 15, 18 and passages 36, 37, 38 in the valve spool. The increase in pressure in the passage 37 displaces the spool 39 of the relief valve which, by means of the pin 40, moves the sleeve 41 to close the gap 46 so that the garter spring is no longer able to retain the spool in the selected position and the centring spring returns the spool to its neutral position to disconnect the pump from the ram.