Patent GB-816475-A (GB)
Title: Improvements in or relating to control means for tractors
IPC: A01B61/02
Filed: 1955-06-24
Abstract: 816,475. Tractor power-lift mechanisms. MASSEY-HARRIS-FERGUSON Inc. June 24,1955 [June 29, 1954], No. 18311/55. Class 79(1) In a tractor having an implement attaching hitch movable between working and transport positions by a power unit and having overload release means adapted to cause the power unit to withdraw its support from the hitch, means are provided to initiate the operation of the overload release means only when the deceleration rate of the tractor exceeds a predetermined value. The invention is applied in the preferred embodiment to a tractor having a pair of lower links connected to a hydraulically operated rock shaft and an upper link connected to the hydraulic system to vary the position of the linkage in response to draft load. The rock shaft is connected to a piston 15a in a cylinder 15 to which is pivoted at 21 an arm 20 oarrying a weight, the weight tending to pivot the arm on tractor deceleration, and such pivoting being resisted by a spring 25. Such pivoting of the arm 20 releases a lever 52 from a recess 54 in the arm 20, the lever 52 being then permitted to move into the dotted line position in Fig. 2. The lever 52 is connected by a pin 49 and toggle levers 43, 44 to a plunger 42 in casing 29 of a valve 28. The valve 28 has ducts 31, 33 leading respectively to the cylinder 15 and a reservoir for power-lift fluid. A bore 30 in the valve houses the plunger 42, a ball 34, a tubular element 35 and a spring 37. Movement of the lever 52 into its dotted line position causes the toggle levers 43, 44 to collapse, whereon pressure in the cylinder 15 and in the spring 37 causes the element 35 and ball 34 to move to the right in Fig. 7 enabling the cylinder 15 to be connected by the ducts 31, 33 and bore 30 to the reservoir. Such "dumping" action of the valve 28 causes the tractor to be relieved of the weight of the implement, and hence the tractor to lose traction until the driver can disengage the tractor clutch. The valve 28 is reset by a manual lever 60 carried by a shaft 61 mounted in a cover plate 63, the shaft 61 carrying an arm 64 on which is mounted a resilient roller 56 defining the released position of the lever 52. In order that the tension of the spring 25, and hence the deceleration initiating the overload release, can be varied, the spring 25 is anchored to an arm 26 of a bell crank lever, the other arm 76 of which is engaged by an arm 78 on a sleeve 79 concentric with the shaft 61. The sleeve 79 also carries a hand lever 80 which has a pin 82 engageable with a notched, eccentrically mounted plate 84, the notches corresponding to decelerations of ¢g, ¥g, 1g, 1“g and 1¢g. To determine the lowest permissible deceleration at which the lever 52 is released, an adjustable stop for the arm 26 is provided comprising a lockable screw 72 on the lever 52. In order to increase the resistance to pivotal movement of the arm 20 when the lift linkage is in its raised position and therefore the effective deceleration, a spring assembly 100 is provided between the arm 20 and an arm 95 rotatably mounted on a shaft 49 carrying the bell crank lever 26, 76. The assembly 100 comprises a spring 110 arranged between projections 108, 109 on telescopic links within the spring, one link being pivoted at 103 to the arm 20 and having a slotted connection 106 with the arm 95 and the other link being pivoted to the arm 95 and having a slotted connection 104 with the arm 20. The arm 95 carries a projection 98 engageable with the piston 15a so that the arm 95 is moved to position C, Fig. 2, when the piston is moved to the raised position of the linkage. In position C the projections 108, 109 co-operate with the spring 110 to resist pivotal movement of the arm 20.