Patent GB-896462-A (GB)
Title: Improvements in hydraulic power lift systems for agricultural tractors
IPC: A01B63/114
Filed: 1960-03-16
Abstract: 896,462. Fluid-pressure servomotor-control systems. SOC. INDUSTRIELLE GENERALE DE MECANIQUE APPLIQUEE. March 16, 1960 [March 20, 1959], No. 9333/60. Class 135. [Also in Group XXXI] A tractor power-lift hydraulic system comprises a continuously driven pump 4 supplying fluid from a reservoir 5 through a filter 6 and a valve system to a one-way ram 2 which operates a lift arm 36 through a roller 39 and crank 37. The valve system comprises a distributing valve 7, a discharge valve 9 controlling discharge passages 13 and a holding valve 10 controlling return of fluid from the ram. The valve 7, which has a portion of narrower diameter between its end portions 7a and 7b, operates in a bore having portions 21 and 22 of greater diameter. The pump supply conduit 12, which includes an overload valve 26, leads to the portion 21 and to a chamber at the upper part of valve 10, which is also connected to the bore of valve 7 by the conduit 13. The conduit 13 also leads from the bore of valve 7 to the valve 9 the chamber of which is connected by a conduit 18 to the enlargement 22. The valve 9 is urged to the left by a spring 20 and opposite sides of the valve are connected by a small bore 19. The valve 10 is upwardly urged by a spring 16 and is connected by a passage 11 to the ram cylinder 13. The valve 7 is controlled by a lever 32 which is connected by a follow-up linkage 33, 35 to the lift arm 36. With the lever in the left-hand position, the valve slide 7 is in the right-hand position, Fig. 1, the end portion 7a closing the enlargement 22. The pressures on each side of valve 19 become equal and due to the spring bias, discharge passage 13 is shut off by movement of the valve to the left. Due to pressure in the conduit 12 and passage 14 the valve 10 is moved downwardly and pressure fluid is supplied to the ram cylinder. As the lift arms are raised, the valve 7 is moved by the links 33, 34 to the left and the enlargement 22 is freed, valve 9 moves to the right and the discharge passage 13 opens. With diminished pressure in the space 14, the valve 10 moves upwardly to close the conduit 11 and maintain the ram in a " hold " position. Downward movement of the lift arms is prevented, but upward movement is allowed. Similarly, the lever 32 may be put in an intermediate position, at which the " holding conditions apply (Fig. 2). Above the position corresponding to the set position of lever 32, the conditions of Fig. 1 would apply until the position of Fig. 2 is restored. A valve 27, having tapered slotted portions 27a, allows pressure fluid to be delivered through conduit 11 to the ram cylinder but impedes the flow in the return direction to an extent adjustable by a screw 30. To lower the implement, the lever 32 is put in the extreme right-hand position, Fig. 3, drawing the valve 7 to the left, closing enlargement 21 and opening 22. A low pressure is obtained in conduits 12 and 13, determined by the springs 16 and 20, sufficient to open valve 10 and allow return flow from the ram cylinder. A cock 23 having a large passage 23a and small passage 23b is biased by spring 25 to the positions shown in Figs. 1, 2 and 3. To obtain " weight transfer," the cock 23 is put in the position of Fig. 4, or in a throttled intermediate position, whereby the pressure in conduits 11 and 12 is raised, the valve 10 is opened and pressure in the ram cylinder is increased. An implement may be allowed to " float " freely with the conditions of Fig. 3. The conduit 11 may be provided with a three-way cock 31 to enable an auxiliary ram to be supplied.