Patent GB-876258-A (GB)
Title: Improvements in or relating to tractors
Inventor: MARINDIN ROBERT
IPC: E02F9/24
Filed: 1957-04-15
Abstract: 876,258. Tractor power-lift mechanisms; controlling vehicles. INTERNATIONAL HARVESTER CO. OF GREAT BRITAIN Ltd. Feb. 6, 1958 [April 15, 1957], No. 12217/57. Classes 79(1) and 79(5). In a tractor power-lift system a draftresponsive control valve 16 Figs. 1, 4 is adapted to establish a connection to a by-pass valve 25 so that the pump output through a supply line 23a is by-passed at low pressure when the power-lift is not in operation and excessive heating &c. of the fluid is avoided. The valve 16 may be actuated manually by a lever 45a for raising and lowering, passages 17, 18, 19 leading to the lift ram 6 Fig. 2 being brought into communication with exhaust ports 21 for lowering, whilst the bypass valve 25 is maintained open by a piston 29 under pressure of trapped fluid in a cylinder 33. For raising, the valve 16 is moved so that the fluid in cylinder 33 exhausts through passages 34-36 allowing the by-pass valve 25 to close under pressure of its spring 25a whereby the pump supply pressure builds up and passes to the passages 17, 18 through a non-return valve 38 (not shown) Fig. 6. On return of the valve 16 to neutral, pressure is built up in the cylinder 33 through an adjustable restriction. The valve 16 is used for automatic draft control and is operable by movement of a draft-responsive bell-crank 9 connected at 12 to the top link of an implement three-point attachment and rotatable against a draft reaction spring 11. Movement of the crank 9 is transmitted to the valve 16 through a push rod 47 including a lost motion connection 47a biased by a spring 50, which permits manual control of the valve 16 independently of the draft control. A followup linkage 61 is also provided between the lifting cranks 3 and the lever 45a so that it is automatically returned to neutral when the lift system is in the fully raised position. A spring loaded lost-motion connection 66 provides for manual movement of the lever 45a to the lift-position when the system is fully raised so that pressure fluid can be made available at an auxiliary tapping for operation of auxiliary apparatus. Overload release is provided by a piston valve 55 actuated by a plunger 54 on the valve 16 when excessive movement takes place due to an implement meeting an obstruction. The valve 55 permits escape of pressure fluid 'in the ram passage 17, 18 through passages 59, 60, the valve automatically remain. ing open under pressure of escaping fluid so that the lifting force cannot be re-applied by recoil action. In a modification the valve 55 may be connected to operate clutch disengaging means on overload. In further examples alternative selectable depth control is provided, the valve 16 Fig. 9 being alternatively operable by a cam 81 on the cross-shaft 2 through a roller 78 and link 77 which may be swung in and out of operative position by a lever 82 which selects the required working depth. Alternatively the cam 81 may actuate a second valve (not shown) through the linkage 43 and the levers 45a, 82 may be set to provide for the automatic draft control mechanism to over-ride the depth control when predetermined draft loads are exceeded. Specifications 829,346 and 876,260 are referred to.