Patent GB-1239281-A (GB)
IPC: A01B63/111
Filed: 1968-07-29
Abstract: 1,239,281. Tractor power-lift mechanisms. COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH. 29 July, 1968, No. 36051/68. Heading A1P. In mechanism for automatic draft and position control of an implement 8 towed from the three-point hitch-linkage 6, 7, of a tractor, draft working and position working of the implements is selected and controlled by a single operating lever 30. The mechanism includes a control valve 13 totally immersed in oil provided on the suction side of a pump 11 to control the lift shaft 3 via hydraulic ram 2, and a device 41, 44, 48 responsive to signals from the implement 8 via draft sensing spring-assembly 9 or positive sensing cam 10 provided on lift shaft 3, the device 41, 44, 48 also being responsive to movement of the operating lever 30. The control valve 13 includes a slide valve 19 slidable in casing 18 and spool valve 20 slidable in valve 19, the slide valve 19 being actuated through lever 36 by operating lever 30, the spool valve 20 being actuated through lever 61 by the responsive device 41, 44, 48, and both valves being spring-urged towards their respective actuating levers. The responsive device comprises a "draft" radial arm 41 and a "position" radial arm 44, mounted on a spindle 47 one on each side of a central cam 48, the cam 48 being spring urged towards and into engagement (e.g. by a pin) with "draft" radial arm 41. Automatic Draft Control Operating lever 30 is moved to the required draft setting in its "draft control range", in which case the "draft" radial arm 41 is rigid with cam 48. This actuates, via cam 34 and lever 36, sleeve valve 19 in direction S2 thus connecting hydraulic cylinder 1 and oil-sump 12 through conduit 16, passage 22 in casing 18, and port 24 in sleeve valve 19, to exhaust cylinder oil and lower the implement into the ground. As the tractor moves forward, draft forces increase which actuate draft sensing assembly 9 which in turn actuates "draft" radial arm 41 in a clockwise direction, and thus cam 48 clockwise. Cam 48 then actuates spool valve 20 in direction S2 gradually closing exhaust port 24 which is fully closed when draft forces exerted by the implement balance the setting on the operating lever 30. Any increase in soil draft forces causes cam 48 to actuate valve 20 in direction S2 and the pump suction is opened to the sump 12 through a port 23 in valve 20, passage 21 in casing 18, and conduit 14. High pressure oil then enters hydraulic cylinder 1 causing the implement to lift. As the implement is lifted, draft forces decrease and spool valve 20 is actuated in direction S1 until the preset draft value is reached when all ports are closed and the valves are in their neutral position. If draft forces decrease, spool valve 20 is actuated in direction S1, opening cylinder 1 to sump 12 through conduit 16, passage 22 and port 24 to cause the implement to lower into the ground, until a state of balance is achieved. Position Control Operating lever 30 is moved to the required position setting in which case the "position" radial arm 44 is rigid with cam 48. Movement of lever 30 from its "implement transport" position to the required setting actuates sleeve valve 19 in direction S2 thus lowering the implement, due to discharge from the cylinder 1, drawing-in of the piston 2, and anticlockwise rotation of lift shaft 3. As cam 10 on lift shaft 3 rotates, "position" radial arm 44 and thus cam 48 rotates clockwise causing spool valve 20 to move in direction S2 progressively closing port 24 which is fully closed when the implement has moved to the position corresponding to the setting on lever 30. For raising the implement, reverse action takes place. The mechanism is also provided with an overload release should the implement strike an obstruction causing the draft forces to increase abnormally. The operating lever may also have a range to control single-acting external rams, or double acting external rams, and the mechanism may also be provided with a response control 17, 72 to control the speed of response when the implement has to be lowered into the soil.