GB1483065A - Control device for agricultural tractor implement couplings - Google Patents

Abstract

1483065 Tractor power lift control FIAT SpA 27 July 1974 [27 July 1973] 29302/74 Heading A1P A hydraulic control device for a tractor three point linkage comprises two, serially connected, double acting hydraulic rams, one for each of the lower draft links with the upper chamber of ram 10 being connected to the lower chamber of ram 11 by an intermediate conduit 40, 40a such that fluid acting on one ram also acts upon the other. The volume of fluid transferred between the rams is variable by means of a slidable and rotatable control valve 32 to vary the inclination of the links when so desired. During working when it is not desired to allow variation in the inclination a transverse stabiliser device 41 is made operable to maintain the trim of the rams 10, 11. The stabiliser device 41 includes a spring biassed slide) valve 68 which moves in dependence on the pressure in the intermediate conduit 40, 40a from a first postion (shown) in which fluid flows in ram lines 37, 38 to an upper position in which flow is prevented. When it is desired to override the stabilizer devices 41, e.g. during link movement to and from a working position or during operation of valve 32, the device 41 is manually locked in a third position by operation of a lost motion drag link 84 whereby the ram line 37 is kept open to flow and the ram line 38 is closed to flow. To lower the implement when in its working position as control lever 66 is moved to its lower shown position so that an increased diameter part 57 (see also Fig. 4) of piston 56 in pilot valve 46 cuts off communication between conduits 55, 55a and so that end 62a of piston 62 in discharge valve 47 does not close transverse bores 60b (only one shown) in a piston 60 of valve 47. In this way fluid from pump 42 passes along flow path 48, 50 to act upon piston valve 52 and fluid above piston valve 53 drains via conduit 55, milling 58 in part 57, discharge chamber 59 line 65 piston 60 and continuation, of line 65 to a sump. Assuming that there is pressure in intermediate conduit 40, 40a ram 10 extends to discharge fluid via path 37, 72, 71, 37, 63, 60a, 60b, 59, 65, 60, 65 to the sump. Similarly the transfer of fluid between the rams causes ram 11 to extend and discharge via line 40, 92. The upper chamber 36 of ram 11 is filled via line 50, 50a, 138, 38 during this stage since valve piston, 52 opens line 50a. To raise the implement during work the lever 66 is moved upwardly to connect conduits 55, 55a via milling 58 and close bores 60b with piston end 62a. Piston 53 is thus pressurized to close line 50a and fluid flows to extend the jacks via check valve 67. If the rams do not move together during raising or lowering the difference causes the pressure in line 40, 40a and hence in stabilizer device chamber 70 to fall to zero. The valve slide 68 thus moves up to block direct communication between chambers 73 and 74, and 72, 71 (upper or second position) until the rams are again in unison. The control valve 32 includes a rotatable piston 93 (see also Fig. 2) whose longitudinal setting determines the position of valves 102, 103 and thus whether fluid from pump 98 is transferred to or from the upper draft link ram 22 or to the sump. Its) rotational position controls the position of valve 109 in line 92 and whether fluid is transferred to or from the rams 10, 11 to change their inclination. When the rams 10, 11 are to be kept in a floating state a control lever 61, which controls the relative position of pistons 60, 62 and hence the sensitivity of the control device, is moved to open valve 124 so that the pressure in lines 50, 50a is transmitted to chamber 70 to keep slide valve 68 in its lower position.