GB871053A - New or improved hydraulic power lift mechanism for tractors - Google Patents

Abstract

871,053. Tractor power-lift mechanisms. DAVID BROWN INDUSTRIES Ltd Feb. 24, 1960 [Feb. 27, 1959; July 23, 1959], Nos. 6921/59 and 25255/59. Class 79(1). Means are provided to maintain a predetermined minimum pressure in the hydraulic system of a tractor power-lift mechanism with automatic depth control. A pump 10 supplies a ram 12 in which the pressure is controlled by a depth control valve 35 and a valve 36 which maintains a predetermined pressure in the system. The valve 35 is operated through a cable 44 and a lever 45 by a spring-loaded telescopic link 30 and is set by a hand lever 49 through a bell-crank lever 47. If the lever 49 is moved to position 84 the valve 35 is closed by a spring 52 to raise the pressure in the ram and lift the implement by a linkage including a shaft 26 which operates an overcentre device 60 during its last few degrees of movement. The device 60 contains a spring 90 which acts through an arm 58, rod 57, arm 56, shaft 23, arm 22, rod 21, bell crank lever 20, rod 19 and a plate 18 to open a valve 16 between'the pump 10 and its sump 11. A valve 17 having greater resistance to operation than the valve 16 remains closed together with a non-return valve 15 to trap the fluid in the ram. If leakage of fluid occurs the over-centre device 60 re-closes the valve 16 until the ram is fully recharged. To obtain quick penetration with a light implement on hard soil, the lever 49 is moved to the position 85 causing a rod 72 to rotate the arm 56 to open both valves 16, 17 and reduce. the pressure to zero. With the hand lever 49 in the position 83, the valve 35 is fully open and the automatic variations in its movement are insufficient to cause throttling of the flow from the pump so that if the implement is provided with a depth-regulating wheel or skid load transfer occurs due to the action of the valve 36. The latter consists of a spring-closed member 37 having a bleed hole 38 communicating with an adjustably spring-loaded ball 39. A screwed member 40 having axial grooves engaged by a spring-loaded ball 78 enables the operator to adjust the load on the ball 39. When the latter is lifted the member 37 becomes unbalanced and opens until the pressure in the hydraulic system again falls to the predetermined minimum. The cable 44 may be disconnected from the link 30 and a coupling 71 from the shaft 26 so that apparatus such as a loading shovel, bulldozer, tipping trailer or a push-off stacker may be operated, the lever 49 controlling the valves 16, 17 so that the linkage may be raised, locked or lowered. The first Provisional Specification describes a modification in which a separate manual control combined with an over-centre device is provided for the valves 16, 17.