Patent GB-1349834-A (GB)
Title: Tractor hydraulic lift system
IPC: A01B63/111
Filed: 1972-04-25
Abstract: 1349834 Tractor hydraulic lift system FORD MOTOR CO Ltd 25 April 1972 [11 June 1971] 19038/72 Heading A1P A hydraulic lift system for a tractor provides for regulation of the height of an implement responsive to implement draft, to drive line torque and to height of the hitch above the ground. A hydraulic lift cylinder 20 with piston 22 operates ram arm 25 to rotate rock shaft 26 and lift arms 27 which are connected to the lift links of the tractor. Hydraulic spool-type valve 30 regulates flow into and out of the cylinder, and this valve is operated by control rod 34 connected to servo lever 32. The upper end of lever 32 is mounted on crank 36 and control lever 37 serves to rotate this crank. Selector rod 56 is mounted on lever 32 by block 67 slidingly receiving the rod and pivotally mounted on the lever. Snap ring 69 and spring 70 hold the rod in position. The free end of selector rod 56 has a bifurcated end 57 supporting roller 59 adapted to move along rails 50 and 64. The position of the selector rod is adjusted by hand lever 63 via pivot 61, lever 60 and link 62 which supports the end of the rod. The selector rod may be moved along upper rail 64 from the top where it is actuated solely responsive to draft, to the upper end of rail 50 where it is actuated solely responsive to position of the hitch and to the lower end of rail 50 where it is actuated primarily responsive to drive torque. In the intermediate positions, the selector rod is actuated by combinations of torque and positional control or draft and position control. Position control. The action of lever 37 causes spool valve 35 to be opened or closed so that rock shaft 26 rotates. Cam 41, which is attached to the ram arm 25, is also rotated and cam follower 44 mounted on lever 45 follows cam surface 42. The upper end of lever 45 is mounted on fixed pivot 46 mounted in housing cover 21 and the other end of the lever supports pivot 51 to which are connected to the rails 50 and 64. A spring 52 biases the upper end of rail 50 rearwardly (to the right in Fig. 2) to hold cam follower 44 against cam surface 42. This lever 45 therefore moves pivot 51 forwardly or backwardly and with it selector rod 56 which is positioned as in Fig. 2. The action of selector rod 56 on servo lever 32 causes the latter to rotate so as to operate valve 30 and thereby put the hydraulic cylinder into a neutral or "hold" position. Draft control: The top link of the tractor is attached to draft plunger 39 which is mounted for fore-and-aft reciprocation. Draft spring 40 biases plunger 39 towards a fixed control position. When selector rod 56 is positioned along rail 64 then movement of plunger 39 is transmitted to the plunger via link 66 which is pivotally connected to offset portion 65. Rail 64 can pivot about 51 and selector rod 56 is thereby moved to operate spool valve 30. When the selector rod is positioned at the top of rail 64 follow-up movement of lever 45 will not move the rod, as in position control. Torque control: A torque sensing device interposed between the tractor transmsision and rear wheels of the tractor is connected via rod 49 to rail 50. In a manner similar to that described above but with the selector rod engaging rail 50, a movement of rod 49 is transmitted to spool valve 30. Overcorrecting and hunting can be prevented by feeding in some position control and not allowing the rod to move to the lower end of the rail. Snap ring 69 and spring 70 act as an override. construction to protect the linkage against damage if the draft or torque changes rapidly so as to tend to move the valve spool 35 beyond its range of movement and also permits the piston 20 to engage servo lever 32 at top of lift and force, it rearwardly a small amount to restore valve 30 to neutral position and cut off flow of hydraulic fluid to lift cylinder 20.