Patent GB-790542-A (GB)
Title: Improvements in or relating to differential gears
Inventor: FERGUSON HENRY GEORGE
IPC: F15B21/00
Filed: 1953-06-01
Abstract: 790,542. Controlling differential gearing. MASSEY - HARRIS - FERGUSON (GREAT BRITAIN), Ltd., [formerly MASSEY-HARRIS - FERGUSON (MANUFACTURING, Ltd.]. June 1, 1954 [June 1, 1953], No. 15136/53. Class 80 (2). In an agricultural tractor with an hydraulic power lift for a hitched implement controlled by a hand lever and a differential transmission gear lockable by a friction clutch engaged by an hydraulic servomotor controlled by a valve, an operative connection between the valve and the power lift is such that when the hand lever is positioned to lift the implement the valve is operated to disengage the clutch and the valve is also operated automatically, to disengage the clutch in the event of certain eventualities during the operation of the tractor. Manual means may also be provided for varying the clutch pressure. In Fig. 1, the power lift servomotor is controlled by the hand lever 12 and an overload-release device includes a rod 20 loaded by a reaction spring 21. The pressure in the clutch servo 3 is controlled by a relief valve 5, the loading spring 7A of which is controlled by an adjustable lever 8. The lever 12 has a one-way connection 11 with the stem 10 of valve 5 so that, when lever 12 is moved into vertical position to energize the lifting servo, valve 5 is opened to cause disengagement of the clutch. Similarly, on the occurrence of a predetermined overload, rod 20 acts on stem 10 through linkage 13, 14, 15, 28 to open valve 5. The latter may also be opened upon a predetermined steering movement in either direction or by application of a brake to either driving-wheel, or by movement of the hitch links. In the constructional form shown in Fig. 3, the lever 8, normally retained in adjusted position by a spring-loaded detent 46, acts on valve 5 through a torsion-spring 7A and a lever 44, lever 12 co-operates with collar 11 on stem 10 through linkage 51, 52, while rods 49, 50, actuated by the over-load-release device and by either brake pedal, act on the other arm 44A of lever 44. In modifications, a separate exhaust valve is arranged in the hydraulic circuit for operation mechanically, electrically or hydraulically by the overload-release device or by steering or braking. In the arrangement shown in Fig. 8, a single pump 100 supplies both the lift servo 104 and, through piping 107 controlled by two piston valves 109, 110 in series and operated by a manual lever 112, the clutch servo 3. With lever 112 in vertical position, both valves 109, 110 are open. The clutch is therefore engaged, so long as pump 100 is delivering or so long as there is sufficient pressure in the system due to the weight of the implement. If lever 112 is moved anticlockwise, valve 110 is not moved but valve 109 is lowered to shut off supply to servo 3 and relieve the latter through a discharge passage 111, so disengaging the clutch. Valve 109 is also shut off when the ram of servo 104 moves to lift the implement. Anti-clockwise movement of lever 112 from the vertical position has no effect on valve 109 but lowers valve 110 first to bring into circuit a spring-loaded relief valve 121 and then to open a discharge passage 122. A rod 123, operated by the overload-release device or by steering or braking, also serves to lower valve 110. Specification 687,341 is referred to.