Patent GB-845238-A (GB)
Title: Improvements relating to agricultural tractors
IPC: A01B63/112
Filed: 1957-11-26
Abstract: 845,238. Tractor power-lift mechanisms. SMIRTHWAITE, T. Nov. 26, 1958 [Nov. 26, 1957], No. 36842/57. Class 79(1). Mechanism for regulating the depth of working of agricultural implements towed by a tractor 1, Fig. 1, by means of an upper link 6 and two lower links 4, 5 comprises a lever 34 which has the drafting force from the links 4, 5 applied below its fulcrum which is constituted by a shaft extending through the tractor body while its upper end is loaded by a spring 36 and controls a semi-rotary valve 45 for adjusting the supply of hydraulic fluid to a ram 46 to raise or lower the implement. The valve has a central fixed portion 60 having a passage 61, Figs. 9 and 12, to which fluid is supplied by a pump 76, a sleeve 62 having three ports 93 and connected for manual operation by a linkage to a handle 63 adjusted to correspond to the required depth of the implement, and a sleeve 72 having three ports 94 and connected by a link 39 to the lever 34. When the implement is at the required depth, fluid from the pump passes through the central ports 93, 94 to an outlet 78 connected to the reservoir 75. If the depth of the implement increases the sleeve 72 is turned to move the central ports 93, 94 out of register and to bring into register the ports for supplying fluid to the ram 46 through an outlet 77 until equilibrium is restored. If the depth decreases, ports are brought into register to allow fluid from the ram to pass through an outlet 79 to the reservoir, the central ports 93, 94 also being brought into register so that the pump output is again by-passed to the reservoir. To raise the implement for transport, the lever 63 is raised and fluid supplied to the ram through the outlet 77. As the drafting force decreases the sleeve 72 is turned by the lever 34 until the latter engages a stop 42 when the port 93 supplying the outlet 77 is at the edge of the port 94 so that lifting continues until the lever 63 is released when it is pulled downwardly through an angle of 5 degrees by a spring 122 to cut off the supply to the ram and to by-pass the output from the pump. The lever 63 normally rotates a friction disc which has its motion arrested by a stop 107, Fig. 3, 5 degrees before the lever reaches its fully raised position. This relative movement stresses the spring 122 and also causes pins 108 on the friction disc to move in relation to arcuate slots in a disc 101 secured to the lever so that the angular movement of the lever under the action of the spring is limited. An arm 68 secured by a wing nut 70 provides a stop for the lever 63 and adjusts the height of a pivot 112 in a linkage 110, 113 whereby the lever 34 may be caused to release the tractor clutch if the drafting force suddenly increases. The pivot 112 is connected to a link 120 connected to I the arm 68 and is guided by a slotted member 115 pivoted at 116. Reducing the height of the arm 68 increases the travel of the lever 34 which is necessary to release the clutch. The lever 34 is secured to a shaft 32 having two sets of lugs and pivot pins each of which is designed for engagement by light and heavy links 4, 5 while the lugs for engagement with the link 6, which may also be of light or heavy construction, have a narrower gap between them at the top than at the bottom to accommodate two different sizes of pivot pin. The shaft 32 may also have lugs for engagement by stabilizing lugs.