Patent GB-856789-A (GB)
Title: Control mechanism for tractor hydraulic system
IPC: A01B63/114
Filed: 1959-03-02
Abstract: 856,789. Tractor power lift mechanisms. ALLIS - CHALMERS MANUFACTURING CO. March 2 1959 [March 3, 1958], No. 7236/59. Class 79(1). A tractor power lift system comprises a power lift arm 29 actuated by a ram 32 from a valve controlled fluid pressure motor 34 and a weight transfer arm 17 connected through linkage 36 to the valve control mechanism. A plough is connected to the links 17 in a manner which permits free anti-clockwise movement and is shown in the limiting position of clockwise movement in Fig. 1. The clockwise limit position may be varied by an adjustment member 18. The valve control mechanism may also be controlled manually by levers 37 and 38, the former governing operations of "lift" and "lower", the latter providing adjustment of the weight transfer mechanism 36. The pump and valve mechanism, 34, comprises three large pistons 40 and one small piston 41, operated by cams 42 and supplied with fluid from a reservoir 44. The pistons deliver to a valve 47, the pistons 40 communicating through grooves 76 and non-return valves 53 with a pressure manifold 51 and the small piston 41 through a groove 76 and a non-return valve 59 to a conduit 54 leading to a valve B and connected to the manifold 51 by a non-return valve 56. In the right hand position of the valve spool 87 all the pistons are shortcircuited through conduits 49 and a pipe 83 to the reservoir 44. As the valve spool 87 is moved to the left, the pistons, starting with 41, are brought into operation successively. The valve B connects with the hydraulic ram 32 through the conduit 33 and the manifold 51 also connects with a valve 61 which requires a large pressure to unseat it and a smaller pressure to retain it open. A pressure relief valve 66 connects the piston 41 to the reservoir 44. The valve spool 86 has a head 86 operated upon by one or other of links 89 and 92. Link 89 is connected to the hand lever 37 and also operates a plunger 96 in valve B. By operation of lever 37, the valve spool 86 can be moved to the left or "lift" position, and when the implement is raised, pressure may be relieved through valves 61 and 66. The valve spool may be returned to the right e.g. in the "hold" position of lever 37 and the implement remains raised by virtue of the arrangement of non-return valves 53, 59, 97. The lever 37 may then be actuated to depress the plunger 96 and so lower the implement, the fluid returning through pipes 54 and 83 and valve 47. The valve spool 86 is also acted upon by the link 92 which is spring urged in an anti clockwise direction by the spring 100 which also urges a link 101 into contact with a link 102 connected through the linkage 36 to the implement 14. Sudden shocks upon the implement are partly absorbed by the spring 27 and cause separation of the members 101 and 102. If the implement remains at a greater depth, the power lift mechanism is caused to operate by the spring 100. The depth at which the implement works is adjusted by use of the hand lever 28 which adjusts the position of the pivot 93 relative to the valve 47 between the positions shown in Figs. 2 and 4 wherein one or other of stop members 103 or 104 cooperate with a member 72 upon the valve. The implement may be raised by operation of lever 37 without altering the position of lever 38 which may be set for a particular depth of working and may be fully lowered or lowered to the position wherein the depth control linkage again becomes effective.