Patent GB-1398782-A (GB)
Title: Hydraulic system
IPC: F15B11/02
Filed: 1972-07-26
Abstract: 1398782 Driving auxiliary apparatus; power steering mechanism INTERNATIONAL HARVESTER CO 26 July 1972 [16 Aug 1971] 34943/72 Heading B7H [Also in Division F2] In a tractor hydraulic system comprising a single variable-output pump 10 feeding both a first hydraulic circuit 80 for supplying a power steering unit 84, a brake unit and/or a power-lift linkage and a second hydraulic circuit 70 for supplying an auxiliary drive motor 124 on an implement, a priority valve 50 establishes priority flow to the first circuit 80 when the steering unit is operated, a regulator valve 35 varies the pump output to maintain a set operating pressure in the first circuit when the second circuit is isolated by the priority valve, and a pressure compensating valve 149 and a flow compensating valve 140A are connected to the second circuit 70 for setting and controlling the pressure and flow rate in the second circuit and varying the pump output in accordance with such setting. The pump 10 is driven by an engine through a shaft 26 and includes a swash plate 18 which is displaceable by a de-stroking cylinder 22 acting in opposition to a spring 20 in the direction of reduced output. The priority valve 50 comprises a spool 54 which is displaceable against a spring 58 to uncover a port 59 leading to the second circuit 70 by a pressure drop developed across the spool by fluid flowing through a restriction 57 in the spool and through a line 110 and a non-return valve 190 to the second circuit 70. When the steering unit 84 is operated to pressurize one of lines 82C, 82D connected to a steering cylinder 83, the spool 104, 104<SP>1</SP> of one of demand valves 102, 102<SP>1</SP> is depressed against a spring 105, 105<SP>1</SP> to block the line 110 so that there is no flow through or pressure drop across the spool 54 and the spool blocks the port 57 to make all of the fluid delivered by the pump available for steering purposes. A relief valve 60 is connected to the line 110 downstream of the priority valve 50. The regulator valve 35 includes a spool 37 which is displaced against a spring 40 if the pressure in the first circuit exceeds the set value so that a port 39 is uncovered and fluid pressure is directed to the de-stroking cylinder 22 to reduce the output of the pump 10. The auxiliary drive motor 124 is supplied from the second circuit 70 through a directional control valve 125 and an adjustable orifice 126 having a control lever 127, the valves 140A and 149 varying the displacement of the pump 10 so that the pressure drop across the orifice is held constant for rotating each orifice setting to a specific flow rate and so that the pressure in the circuit 70 upstream of the orifice can be maintained at a set value. The flow compensating valve 140A comprises a spool 136 which is subjected at opposite ends to the pressures upstream and downstream of the orifice 126 and is displaceable against a spring 134 to direct fluid pressure through a line 180 and an internal passage 41 in the regulating valve 35 to the de-stroking cylinder 22. The pressure compensating valve 149 has a spool 154 which is displaceable to direct fluid pressure through the valve 140A to the de-stroking cylinder against a spring 152 the force of which can be adjusted by means of a threaded member 156.