Patent GB-797904-A (GB)
Title: Improvements in or relating to tractor hydraulic systems
IPC: A01B63/10
Filed: 1956-01-03
Abstract: 797,904. Tractor hydraulic systems. FORD MOTOR CO., Ltd. Jan. 3, 1956 [Jan. 3, 1955], No. 207/56. Class 79(1) A tractor hydraulic system of the type employing a constantly operating pump 37, Fig. 1, wherein pump output liquid is either by-passed to a sump 38 or directed a work-producing mechanism (e.g. lifting ram cylinder 42) and wherein liquid from the mechanism 42 is discharged to the sump 38, comprises a valve housing 29, Fig. 6, having connections 40, 41, 43 to the pump 37, sump 38 and the mechanism 42, a valve 59 reciprocably mounted in the housing 29 and movable in one direction to a closed position closing communication between the pump 37 and the sump 38 to build up pressure in the mechanism 42, valve positioning means 61 independently reciprocable between two predetermined positions, the valve 59 being movable in the opposite direction to one of the two positions determined by the means 61, the valve 59 in one of the two last mentioned positions opening communication between the pump and the sump and in the other of the two last mentioned positions opening communication between the mechanism 42 and the sump 38. As shown in Fig. 1, the vanetype pump 37 draws liquid through a conduit 39 from the sump 38 and delivers it by a conduit 40 to the valve housing 29, from whence it is either delivered by a conduit 43 to the lifting cylinder 42 or returned by a conduit 41 to the sump, according to the position of the control valve 28. A piston 44 is connected by a rod 46, crank arm 47 (pivoted at 48 on the tractor), lift arms 49 and lift rods 51 to lower links 16, pivoted at 17 on the tractor, and connected to a plough 11. An A-frame 14 on the plough beam 13 is connected to an upper link 18 connected at 19 to a rod 21, carried by the tractor. The rod 21 is surrounded by a draft-resisting spring 22 between the tractor and the link 18, and is pivotally connected at 24 to a lever 23 the upper end of which is pivotally connected at 33 to a manual quadrant lever 31, pivoted at 32 on the tractor, and the lower end of which is pivoted at 26 to a rod 27 connected at 109 to the control valve 28. The lever 31 is movable from a neutral position in the directions of the arrows 34 and 36 to the lifting and lowering positions, respectively. A connection 30 is provided between the piston 44 and the lever 23, so that at the completion of the lifting stroke the piston causes the control valve to move into the neutral position. An increase of draft on the plough 11 will cause the rod 21 to move to the right and pivot the lever 23 about the point 33 and cause the valve 28 to move to the lifting position and likewise a decrease in draft will cause the valve 28 to move to the lowering position. When the manual lever 31 is operated, the lever 23 pivots about the connection 24. If the plough drifts due to leakage of liquid from the cylinder 42, the connection 30 will cause the valve 28 to move to the lifting position. Referring to Fig. 6, the valve housing 29 is provided with bores 52, 53, 54, 55 and 56 for a check valve 57, under the urge of a spring 69; a split-flow valve 58; the control valve 28 which is under the urge of a spring 116; the valve 59; and the means 61 in the form of a piston, respectively. The check valve 57 has an axial bore 72 connecting the right-hand side of the bore 52 with a valve seat 73, for a ball valve 74 under the urge of a spring 76, the ball controlling flow of liquid from the bore 72 to the ram supply conduit 43. The bore 52 also intersects the pump output conduit 40 which is connected to the bores 54 and 55. A passageway 86 connected through a low pressure relief valve 62 with the sump, is connected to the bore 55 and the latter is connected through a valve seat 83 with the conduit 40. The bore 55 is also connected by a passageway 84 with the conduit 43. Slidable in the bore 55 is the valve 59 having a body portion 91 provided with a peripheral groove 96 connected to an axial bore 98, and an enlarged head 92 carrying a valve to engage the seat 83 and a diametral groove 101 in its end free open to the bore 98 and the bore 56. The piston 61 is movable between a shoulder 77 and a fixed stop 78. A chamber 102 at the left of the piston 61 is connected by passageways 123, 107 with the bore 54, whilst a chamber 129 at the right of the piston 61 is connected by a passageway 128 with a passageway 108 connected to the bore 54. The valve 59 is movable to three positions, one as shown in Fig. 6, a second position in which the valve head 92 engages the seat 83 and closes communication between the passageways 40 and 86 and a third position in which the piston is abutting the stop 78 and the valve head is in engagement with the piston so that the groove 96 is aligned with the passageway 84. The control valve 28 has two spaced lands 112, 113 forming therebetween a chamber 114 in constant connection with the passage 40, the bore 54 to the right of the land 113 being connected to the sump at 118. The bore 53 for the split flow valve 58 is formed at opposite ends of the valve 58 with chambers 132 and 141. The chamber 132 is connected by a restricted passage 134 with the bore 54 and the left-hand end of the valve 58 co-operates with a passage 138 connected by a passage S to the sump. The chamber 141 is connected by a passage 148 with the bore 52 to the right of the check valve 57 and also to the passage 128. The passage 107, 108 in the bore 54 are slightly displaced axially so that the land 113 controls those passages in sequence. In the neutral position of the control valve shown in Fig. 6, liquid is neither supplied to nor withdrawn from the cylinder 42, the land 113 is positioned so that the left-hand end of the passageway 108 is opened and liquid is passed through the passage 128 to the chamber 129 to move the piston 61 against the shoulder 77, the liquid in the chamber 102 passing through the then opened righthand end of the passage 107 to the sump via the hole 118. The valve 59 is urged to the right to abut the piston 61 by pressure of liquid on the area formed between the head 92 and body 91. When it is desired to lift the plough the valve 28 is moved to the right so that the land 113 then opens the left-hand end of the passageway 107 to supply pressure liquid to the chamber 102 and thus cause the valve head 92 to engage the valve seat 83 and close-off the passageway 86 to the sump. During this operation the piston 61 is retained against the shoulder 77 by liquid from passages 108 and 128. The passageway 128 also allows liquid to pass to the chamber 141, passage 148, bore 52, axial passage 72 and through valve seat 73 to open the valve 74 and supply liquid to the passage 43. During the initial stages of the lift the split-flow valve 58 is caused to rapidly move to-and-fro to alternately by-pass some of the liquid through the passage 134, which is still uncovered and passage 139 to the sump. These movements of the valve 58 are caused by pressure differences at the opposite ends of the valve due to the restricted passageway 134. Finally the passage 134 is covered by the land 112. The split-flow valve prevents excessive pressure build-up in the cylinder 42. When the lift is complete the valve 28 is moved to the left which causes the ram to slow down. Continued movement causes the land 113 to close the passage 107 and cut off the supply of liquid to the chamber 102 and thereafter open the passage and chamber 102 to the sump through the hole 118. During this time the chamber 129 is still supplied with liquid from the passage 108 which is still slightly open at its left-hand edge. Near the end of the movement of the valve 28 the passage 134 is opened by the land 112 to allow the splitflow valve to function again and cushion the implement against a sudden stop or rebound. When the valve 28 is moved to the left from neutral both chambers 102, 129 are connected by the passages 107, 108 to the sump and the valve 59 is moved fully over to the right against the piston 61 which then abuts the stop 78. At this time the passage 84 is connected to the groove 97 in the valve 59 and thus to the axial passage 98 which communicates via the chamber 102, and groove 101 in the head 92 with the sump. Liquid therefore passes from the cylinder 42 to the sump. Moreover pressure liquid moves the valve 58 to the extreme right and allows liquid to flow to the sump via the passageway 134 and thus by-pass the ball valve 62. If the tractor engine driving the pump 37 is stopped the implement may be lowered by moving the lever 31 which then causes a flange 111 on the valve 28 to rock a lever 151 pivoted to the housing 29 which lever in turn moves the valve 59 to align the groove 96 with the pump 84. Specification 790,158 is referred to.