Patent GB-738561-A (GB)
Title: Power operating system for tractor hitch linkage
IPC: A01B63/111
Filed: 1949-03-25
Abstract: 738,561. Agricultural implements. FERGUSON, Inc., H. March 25,1949 [March 25, 1948], No. 8262/49. Class 6 (1). [Also in Group XXIX] A tractor hydraulic-lift system comprises, in combination, automatic control mechanism responsive to draught-load on the lifting links, an alternative position-control mechanism adapted to maintain the links in a constant position independently of the load, and a safety-release device which operates, on overload, irrespective of the particular mechanism in use at the moment. The system is of the general type disclosed in Specification 470,069, comprising a hydraulic ram 36 operating lift-arms 41 through a piston-rod 38 and an arm 39 on a rock-shaft 40. Oil is supplied to the ram, from a sump 50, by a pump 43 and valve 46. Movement of the valve-plunger 46 to uncover a port 48 permits escape of fluid from the ram with a lowering of the arms 41 while a reverse movement uncovers a port 47 allowing fluid to be pumped into the ram. The plunger is moved by a system of three levers 86, 87, 88, pivoted together at 89 in Y-formation, the lever 88 being loaded by a spring 90. At its upper end, the lever 86 carries a spindle 82 received in slots 83 in members 84 secured to the rear-axle housing 35. The spindle carries rollers 81 engageable by cams 78 mounted on the rockshaft 40. Integral with the lever is a curved tongue 99 which can be engaged by a crank 57. The lever 87 terminates in a similar tongue 97 which can also engage the crank. A yoke 94 is pivoted at 95 to the lever 87 and to a plunger 63 secured to a rocker 26 connected to the upper hitch-link 21. The crank 57 is carried on a shaft 56 (Fig. 7) passing coaxially through the boss 55 of a hand lever 52. The shaft 56 terminates outwardly in a bar 53 so that it can be latched to the lever 52 in either of two diametrically-opposed positions wherein the crank co-operates with one of the tongues 97 or 99. Automatic draught-control.-The bar 53 is latched to the lever 52 so that the crank 57 may coact with the tongue 97 on lowering of the lever 52 from the position shown in Fig. 2. This causes the lever 87 to tilt about the pivot 95, thereby forcing the lever 88 rearwardly against the action of the spring 90 to open the port 48 and allow fluid to escape from the ram, the implement being thereby lowered. Equilibrium is attained by the rearward movement of the pivot 95 due to compression in the top link 21 upon the implement's reaching its working depth. The tongue 97 then becomes the fulcrum of the lever-system which moves to and fro under the action of the yoke 94 and plunger 63 to maintain the implement at a constant working draught-load. Automatic position-control.-In this condition, the crank 57 presses on the tongue 99 when the lever 52 is in the position shown in Fig. 2. Lowering of the lever 52 therefore tilts the lever 86 rearwardly about the spindle 82. The lever 86 carries a hook-like abutment 92 which contacts-the spring-loaded upper end of the lever 88, thereby pulling it rearwardly to uncover the port 48 so that the arms 41 are lowered as fluid escapes from the ram. Equilibrium is re-established by the movement of the rollers 81 and spindle 82 along the slot 83 due to the withdrawal of the cam-surface 78, the leversystem 86-88 then re-setting itself about the fulcrum 99. In this arrangement, the lever 87 is completely floating and plays no part unless overload occurs. Overload release.-In the event of excessive upward movement of the hitch-link 21, due to overload, the plunger 63 is thrust forwardly and forces the lever 87 against an abutment 101 fixed to the ram 36. The lever-system 86-88 then tilts about this point to uncover the port 48. The lever-system, in this case, has a spring- loaded toggle-action about the pivot 89 irrespective of whether the system is conditioned for draught or position control. Raising for transport.-A cut-off mechanism, independent of the overload-release, is also provided for immobilizing the ram-piston when it reaches its outermost position. The pistonskirt engages the upper end of the hook-like abutment 92 thereby tilting the lever 86, 88 about the pivot 82 to close the plunger valve. During this action, the lever 87 becomes free and inoperative. This feature forms the subject of Specification 738,593. Specifications 470,068, 470,087, 510,352, 617,166, 684,150 and 738,603 also are referred to.