Patent GB-770157-A (GB)
Title: Improvements in tractor power-lift mechanisms
IPC: A01B63/114
Filed: 1952-10-14
Abstract: 770,157. Tractor power-lift mechanisms. FITZPATRICK, H. J. (Ferguson, Inc., H.) Oct. 14, 1952, No. 25693/52. Class 79(1). In a tractor power-lift mechanism comprising a rear-mounted hitch linkage raised and lowered by a hydraulic piston and cylinder actuator 27 supplied from an engine-driven pump 35 through a valve mechanism 38 having a neutral position locking the actuator 27, a unit 24 is provided responsive to the pressure in the actuator 27 and comprising an element 48 moved by pressure variation which operates a floating lever 43 controlling the valve mechanism 38 whereby the pressure is maintained in the actuator 27 at a value determined by a manual lever 25 which can vary the effective length of the lever 43 and whereby the implement load transferred by the linkage to the tractor is maintained corresponding constant. As shown, the linkage comprises draft links 20 connected by members 34 to arms 33 on a shaft 31 which is connected by an arm 30 to the piston rod 29, the cylinder 27 supplied through a pipe 36. The valve mechanism 38 comprises a spindle 39 and a sleeve 40 having ports 41, 42 uncovering of the ports 41 by movement of the spindle 39 causing delivery of liquid under pressure to the pipe 36, uncovering of the ports 42 by movement of the spindle 39 causing the pipe 36 to be connected to a sump 37, and with the spindle 39 in the position shown in Fig. 2 the liquid in the pipe 36 being trapped. The lever 43 is acted on by a spring 46, an eccentric 45 on the lever 25 and the element 48 connected to the device 24. A branch 50 from the pipe 36 leads to a passage 70 in the device 24, the passage 70 being connected to chambers 69 containing plungers 68 bearings on a crosspiece 67 secured to a rod 56. A helical spring 58 surrounds the rod 56 in a chamber 55 of the device 24 and acts on a shoulder 59 of the casing 38 of the device and on a washer 60 held on the rod 56 by a head 66, which rod is secured to the element 48. The device 24 is mounted on the tractor by bolts 63, the washer 60 abutting under the action of the spring 58 a part 62 of the tractor. In operation the requisite pressure is set in the hydraulic portion of the power lift mechanism by movement of the lever 25, the pressure in the portion being fed to the chambers 69 through the pipe 50 and acting on the rod 56 through the plungers 68 and crosspiece 67 to cause movement of the element 48 and hence through corresponding movement of the lever 43 adjustment of the valve mechanism 38. Accordingly the portion of the implement load transferred to the tractor driving wheels 23 can be increased by upward movement of the lever 25. The range of hydraulic pressure can be changed by substituting springs 58 of different strengths, such pressure being below that at which a spring loaded safety valve 72 is operative. The pipe 36 may be provided with a further branch 36A leading to auxiliaries (not shown). To establish hydraulic pressures sufficient to operate the auxiliaries means, such as a strut (not shown) connected between the lift links 20 and a pin 50a on the tractor, are provided to prevent the links being raised. The top position of the links 20 is fixed by projections 51 on the lever 43 engaging the piston 28, hence causing counterclockwise movement of the lever 43 about its pivot 46 with the element 48 and consequent movement of the valve 38. Specification 470,069 is referred to.