Patent GB-1402804-A (GB)
Title: Tractor hitch
IPC: B60D1/04
Filed: 1973-02-01
Abstract: 1402804 Tractor hitches DEERE & CO 1 Feb 1973 [1 Feb 1972] 5143/73 Heading A1P Each lower connecting pin (not shown) of an implement is received in a pivoted hook 40 co-operating with latch part 44 of lower lift link 18 (or in a fixed hook (not shown) cooperating with a movable latch member (not shown)), an actuator 46 being pivoted to the hook 40 and to the link 18 for effecting latching and unlatching of the connecting pins, the draft load of the implement being kept constant by adjustment of the working depth in response to the draft load which tends to move the hook 40 to its unlatching position (dished line in Fig. 2) clear of latch part 44. The lower links 18 are connected together by an arch pivoted to them (Fig. 1, not shown), and the upper central link comprises a hydraulic actuator suspended at its coupling end from the arch by tension springs. Springs 54 fluid is supplied to the chamber 51 to maintain the hook 40 in its latching position (full line in Fig. 2). The pressure in each chamber 51 is transmitted via port 58 and lines 102, 103, 107, 108, 109 to an adjustable control valve 116 which when deflected from its neutral position by an over pressure or under pressure in the chamber 51 supplies pressure fluid to a hydraulic cylinder 30 so as to raise or lower the links 18. Pressure fluid is supplied from pump 92 via an unlatching valve 100, lines 104. 105, 106 and non-return valves 112 to ports 70 in the actuators 46. From each port 70 the fluid flows into a groove 72 in the piston 52 and through a port 76 into the chamber 51. The port 76 is normally partly obstructed by the head 82 of a valve member 80 acted on by a spring 86 and bearing by its rod 84 against the end of the cylinder 48, so that as the draft load on the hook 40 causes the hook 40 to pivot rearwardly about 38, the port 76 becomes less obstructed,- the pressure in the chamber 51 rises and is transmitted to control valve 116 which raises the implement. If the draft load on the hook 40 should cause the pressure in the chamber to fall, the valve 116 lowers the implement. In a modification (not shown), the valve bore 78 is located in a rearward extension of the cylinder 48, the valve member 80 having its rod 84 urged against the rear face of the piston 52. To ensure that the hooks 40 remain latched if the pump 92 or lines 96 or 104 should fail, a check valve 111 is held open by pump pressure, and the valves 112 prevent back-flow. Flow restrictor 110 maintains pressure in the chambers 51 greater than the force of springs 54, 56. Coupling: The hooks 40 are pivoted to the unlatching position by manual movement of the valve 100 to vent the chambers 51 to the reservoir 94, the operator manipulates the tractor and the control valve 116 to dispose the connecting pins of the implement in the hooks 40, and the hooks 40 are latched by operation of the valve 100. The implement may be lowered (if necessary) by venting the cylinder 30 to the reservoir 94, by means of the control valve 16. In a further embodiment (Fig. 4, not shown) the control valve is responsive to the sum of the draft loads on the two hooks 40, instead of by the larger of the loads as in Figs. 2 and 3. The pressure fluid in the chambers 51 is transmitted by separate lines to separate concentric equal areas at the right-hand end of control valve 116. The control valves 120, 122 are moved in the lines 102, 103 to isolate lines 107 and 108 from each other.