Patent GB-1372892-A (GB)
Title: Hydraulic lifting system
IPC: A01D34/24
Filed: 1971-11-01
Abstract: 1372892 Hydraulic lifting system for combine harvester ROBERT BOSCH G.m.b.H. 1 Nov 1971 [2 Nov 1970] 50722/71 Heading A1F A hydraulic lifting system for the cuttertable 35 of a combine harvester comprises a lifting cylinder 30 pivotally connected between the cutter-table 35 and the chassis 32 of the harvester and pressurised by an oil pump 1 via a system of valves contained in a casing 5 of a control apparatus 6. A control linkage is disposed in an adjacent second casing 55 bolted to the casing 5, and is influenced by the position of the cutter-table 35 via arms 96 and 96' and by the pressure in the working line 31 to the lifting cylinder 30 by means of a piston 101 which slides in a bore 107 in the second casing, being acted upon by the pressure in the end portion of the bore which forms a pressure chamber 109 connected via a duct 115 to the working line 31. A hydraulic accumulator 37 is provided on the chassis 32 of the harvester as a resilient element for the cutter-table 35. A hand lever 78 acts on the control linkage, and can be set either to lift the cutter-table 35 to a particular height, or to allow it to slide on the ground with a certain proportion of its weight taken by the lifting cylinder 30. In the latter case that proportion is kept constant, despite undulations in the ground. Valve system. The valve system is identical to that described in Specification 1196210; movement of the valve slide 13 to the left (Fig. 1) causes oil to be delivered to the lifting cylinder, movement to the right causes oil to be removed from it. In either case the return of the valve slide 13 to its original position causes the oil flow to be cut off again. Control linkage. The valve slide 13, forced by a spring 26, projects into the second casing 55 where it bears via a stop 54 against a curved sector of an actuating lever 57 of the control linkage which is pivoted to the casing 55 at 56. The actuating lever 57 is pivotally connected at 59 to a summing lever 60, which is pivotally connected to an intermediate link 62 at 61 and, as shown in Fig. 2, moveably connected to a lever 65 rigid with the hand lever 78. The intermediate link 62 is pivotally connected at 79 to a control member 80, one end 99 of which is forked and guided in an annular recess 100 of the piston 101, the other end being pivotally connected to a lever 82; the lever 82 is rigidly connected to the arm 96' at a pivot 89 fixed to the casing 55. Operation. In operation, if the cutter-table 35 is sliding over the ground with the pressure in the lifting cylinder 30 supporting a proportion of its weight, then that pressure remains constant. For if the pressure in the cylinder 30 is varied by the cutter-table passing over an undulation in the ground, then that variation is communicated to the pressure chamber 109, upsetting the balance of forces on the piston 101; its resulting movement is then communicated to the actuating lever 57 via the control linkage, and the valve slide 13 is moved to permit the necessary flow of oil. As the pressures in the lifting cylinder 30 and in the pressure chamber 109 are restored to their original values, so the piston 101 and the actuating lever 57 are restored to their original positions and the oil flow is cut off. The proportion of the weight of the cuttertable 35 taken by the lifting cylinder 30 may be set using the hand lever 78, movement of which pivots the actuating lever 57 and thus causes a flow of oil to or from the lifting cylinder 30, the flow being cut-off again as above by the compensating motion of the piston 101. Thus to each position of the hand lever 78 there corresponds a particular pressure in the lifting cylinder 30. In the above regime, where the cutter-table is sliding on the ground, the lever 80 rests against a stop 98 on the casing 55, which thus creates a further fixed pivot for the control linkage, a lost-motion connection between arms 96 and 96' taking up any motion of the cutter table. If the hand lever 78 is moved to increase the pressure in the lifting cylinder 30 then the system is so arranged that at the point when the whole weight of the cuttertable 35 is borne by the lifting cylinder 30 then the piston 101 comes up against a stop in the form of the end face 133 of a tongue 126. At this point the end 99 of the lever 80 becomes in effect a fixed pivot for the control linkage, and the stop 98 is thereafter irrelevant. In order that this arrangement can be maintained for different cutter-tables the prestressing of the spring 122 against which the piston 101 acts can be adjusted by means of a screwed adjusting ring 123, and in order that a wide range of weights of cutter table can be accommodated the spring 122 has a curved characteristic. If the hand lever 78 is now moved so. as further to increase the. pressure so that the cutter-table 35 is lifted off the ground then the compensating motion of the control linkage which restores the position of the actuating lever 57 and hence of the slide valve 13 and thus cuts off the oil flow, is caused by the motion of the cutter-table 35 about its pivot 97 on the chassis 32, which motion pivots the arm 96' and hence the lever 82 about the point 89, the piston 101 now being immobile.