Patent GB-1235355-A (GB)
Title: An improved tractor power lift mechanism
Inventor: ASHFIELD HERBERT EDWARD
IPC: A01B63/10
Filed: 1968-02-09
Abstract: 1,235,355. Power lift device. DAVID BROWN TRACTORS Ltd. 30 Jan., 1969 [9 Feb., 1968], No. 6448/68. Heading A1P. A hydraulic power lift mechanism comprises two pumps 10 and 77 (high and low output respectively), at least one ram assembly 41 and means for automatically hydraulically connecting the output of either of the pumps to the ram comprising a manually operated spool valve 16 and an automatic shuttle valve 49. The manually operated spool valve has four positions. The "hold position" (as shown in Fig. 2) connects the high output pump 10 via conduits 14 and 35 to the sump 12. Similarly the low output pump 77 is connected via conduits 78, 82 and 35 to the sump, as there is no draught force signal sent via Bowden cable 87 to the control device 80. Thus the oil pressure in the lower half of the shuttle valve 49 is zero and the piston 95, Fig. 3 (not shown), drops thus connecting the lower part of the ram 41 via conduits 100 and 47 to the spool valve 16 where the flow line is closed. Thus the ram remains in any position it has attained. Movement of the operating handle to the "vent position" causes the spool 21 to move into the bore 20 against the spring 76 until the balls 67 are opposite the holes 72. The left to right movement of the spring biased member 64 urges the balls into the said holes and holds the spool in the "vent position". The output of the pump 10 is as it was in the "hold position" but the lower part of the ram 41 is now connected to the sump 12 via conduits 100, 47 and 35. The ram piston and thus the link arms 102, 103 and 104 drop under gravity and the pressure in the upper part of the shuttle valve 49 falls to zero. To further lower the aforesaid links the operating handle is moved against the spring bias 76 to the "lower position". In this position the pump 10 is connected via conduits 14 and 39 to the upper part of the ram which forceably lowers the links 102-4. If the pressure becomes too large the spring-closed relief valve 40 opens and bleeds off oil to the sump. When the handle is released it automatically returns to the "vent position". Draught controlling signals are now received via the Bowden cable 87 and the valve device 80 controls the depth of operation (in known manner) according to the setting of the handle 84. The oil from the pump 77 for draught control is delivered via conduits 78 and 81 to the shuttle valve 49 causing the piston 95, Fig. 3 (not shown), to rise and thence via conduit 100 to the lower part of the ram 41. In the "lift position" the spool 21 is moved out of the bore 20 against the restoring force of spring 76 until the balls 67 are urged by the spring biased member 64 into the holes 71 whereupon the spool is locked. The upper part of the ram 41 is now connected via conduits 39 and 35 to the sump 12. The high output pump is connected to the lower half of the ram 41 via conduits 14 and 47, the shuttle valve 49, and conduit 100. When the ram is fully raised the pressure in the lower half will rise and oil flows through the radial passage 51 and the bore 50, acts upon the central projection 59, causing the piston 57 to move against the action of spring 60, and allows oil into the bore 52 from where a small quantity escapes via opening 53. The majority flows through opening 61 and acts on plunger 63 moving the piston 64 away from spool 21 against spring 68 allowing the balls 67 to come out of the holes 71 and the spool to return to the hold position under the action of the spring 76. The excess oil then flows away through the opening 53.