Patent GB-1243380-A (GB)
Title: Hydraulic flow amplifier valve assembly
IPC: F15B13/02
Filed: 1968-12-31
Abstract: 1,243,380. Power steering mechanism. CATERPILLAR TRACTOR CO. 31 Dec., 1968 [13 March, 1968], No. 61894/68. Heading B7H. In vehicle steering mechanism including an amplifier valve assembly 26 for regulating flow of pressure fluid from a pump 18 to hydraulic steering rams 16, 17 in response to operation of a metering unit 21 by a steering wheel to transfer fluid across the metering unit at a rate proportional to the desired rate of operation of the steering rams, the amplifier valve assembly 26 comprises a steering control valve 29 operated by fluid flow from the metering unit 21 to direct fluid from the pump 18 to the rams 16, 17 at an amplified rate proportional to the flow from the metering unit, and a compensating valve 33 bleeds fluid from an inlet passage 61 fed by the pump 18 to regulate the pressure therein. The control valve 29 includes a spool 42 centralized in a bore 44 by springs 51, 52 and having at its ends chambers 48, 49 which communicate through conduits 53, 54, a lock valve 37 and conduits 23, 24 with the metering unit 21. Each end of the spool 42 has a slot 73 which is just out of communication with a respective recess 57, 59 connected by a passage 56, 58 with the opposite chamber 48, 49. A central land 66 on the spool 42 prevents communication between the inlet passage 61 and two chambers 67, 68 connected to the rams 16, 17 through a blocker valve 36, outlet passages 76, 77 and conduits 31, 32. Two further lands 69, 71 on the spool 42 control communication between the chambers 67, 68 and drain passages 62, 63 connected through a conduit 64 to a drain tank 27. When the metering unit 21 is operated by rotation of the steering wheel fluid is delivered to one of the chambers 48, 49 so that increased pressure therein displaces the spool 42 to such an extent that the corresponding groove 73 communicates sufficiently with the respective recess 57, 59 to relieve the pressure. Such movement of the spool 42 results in the land 66 opening communication between the inlet passage 61 and the appropriate chamber 67, 68 by the necessary amount for fluid from the pump 18 to flow to the rams 16, 17 at an amplified rate proportional to the rate of flow through the groove 73. The compensating valve 33 regulates the pressure in the inlet passage 61 in such a way that the pressure drop across the land 66 varies according to the resistance encountered by the rams 16, 17 and is loaded by a spring 92 and subjected to the pressure in the chamber 67 or 68 through a shuttle valve 94 and a passage 93. The blocker valve 36 includes a spool 43 which prevents communication between the chamber 67, 68 and outlet passages 76, 77 to fix the position of the rams 16, 17 unless the control valve 29 is operated. Should external forces create excessive pressure in the rams 16, 17 the blocker valve 36 opens to vent fluid from the rams through the shuttle valve 94 and passage 93 to a relief valve 41. The lock valve 37 includes a spool 98 which is normally moved against spring loading 104 by pump output pressure acting thereon through a conduit 102 and a slug 103 into a position wherein the conduits 23, 24 and 53, 54 are in respective communication. The spool 98 is further moved against additional spring loading 106 in the event of excessive pressure to isolate the conduits 23, 24, and when the pump 18 is not operating the spring loading 104 moves the spool 98 into a position wherein the conduits 23, 24 are connected to the conduits 31, 32 through conduits 38, 39 so that the rams 16, 17 can be manually operated from the metering unit 21. The rams 16, 17 are connected between the frame sections 12, 13 of an articulated vehicle wherein limiting valves 112, 113 connected in the conduits 23, 24 cooperate with stops 116, 117 to limit relative turning of the frame sections. Each limiting valve 112, 113 includes a spool, Fig. 2 (not shown), displaceable upon engagement with the respective stop 116, 117 to vent the conduit 23 or 24 and halt the turning movement. The amplification ratio of the control valve may be made variable by providing solenoid-controlled means, Fig. 3 (not shown), for varying the spring loading acting on the compensating valve. In another embodiment, Fig. 4 (not shown), the control valve includes a pair of spools each having therein a first orifice through which the metering unit communicates with the steering rams and a second orifice through which fluid from the pump flows to the rams, flow through the first orifice creating a pressure drop which shifts the spool so that fluid flows across the second orifice with an equivalent pressure drop. In a further embodiment, Fig. 5 (not shown), the control valve and blocker valve comprise a single spool which moves in response to fluid flow from the metering unit to maintain equal pressure drops across first and second fixed orifices through which the metering unit and the pump respectively communicate with the steering rams.