GB741804A - Improvements relating to hydraulic power lift systems for tractors - Google Patents

Abstract

741,804. Hydraulic machines. FERGUSON, Inc., H. Feb. 26, 1951 [March 15, 1950], No. 4576/51. Class 69 (2). In a tractor hydraulic system comprising a main actuator 18, a pump 20 for supplying pressure fluid to said actuator, a hand lever 30 for controlling the delivery of pressure fluid from the pump, and a control device connected by a conduit 55 to the pump and by a conduit 62 to an auxiliary actuator 40, the device is responsive to a predetermined pressure developed in the auxiliary actuator so as to actuate the hand lever to interrupt the delivery of pressure fluid from the pump to the auxiliary actuator. The operation of the hand lever 30, main actuating mechanism 18, 14, load responsive means 31 and valve plunger 23 are generally as disclosed in Specification 470,069, [Group XXXI], when the lever 30 is moved to the substantially upright position, the plunger 23 is depressed to uncover a passage 25 leading from the reservoir or sump 22 to the pump 20 and pressure fluid is supplied through conduit 55 to the chamber 51 of a valve member, where it flows past a spring-loaded valve 57 into a chamber 52, and thence past a spring-loaded checkvalve 60 into conduit 62 and the cylinder 41 of the auxiliary actuator 40. Pressure fluid in chamber 52 also flows into a conduit 72 to act upon the plunger 70 of the control device. The plunger 70 has a head 73 engaging an end portion 67 of the lever 30, and is held in its retracted position against the action of the pressure fluid by two links 80, 81 of a toggle mechanism which are held in an open, i.e. approximately straight line, position by a spring 90, the angle between the links being governed by an adjustable stop member 92. When the pressure on the plunger 70 increases sufficiently to initiate closing movement of the links they will " snap over " to a folded position in which the head 73 of the plunger 70 moves the lever 30 to raise the plunger 23 to block the supply line 25 and the exhaust conduit 27 with the result that the auxiliary actuator 40 is hydraulically locked. Subsequent movement of the lever 30 to raise the plunger 23 to uncover the conduit 27 will also, via a mechanical connection between the lever 30 and the valve stem 56, open the valve 57, an extension 68 thereon depressing the valve 60 so that pressure fluid in the cylinder 41 has passage to the sump 22.