Patent GB-1420054-A (GB)
Title: Modulating control valve
IPC: B66D1/44
Filed: 1974-02-21
Abstract: 1420054 Valves CATERPILLAR TRACTOR CO 21 Feb 1974 [21 Feb 1973] 7983/74 Heading F2V An operating mechanism for a winch drum 41, Fig. 2, includes a control valve 51, Fig. 3, for selectively releasing a normally engaged brake 32 while simultaneously engaging a normally disengaged clutch 26, and selectively releasing brake 32 without simultaneously engaging clutch 26, brake 32 and clutch 26 being provided in the input gearing of drum 41. Control valve 51 comprises a spool 52 axially slidable in a bore 53 to control fluid communication between an inlet chamber 54 and actuating chambers 26<SP>1</SP>, 32<SP>1</SP>, 44<SP>1</SP> respectively for clutch 26, brake 32 and a normally engaged clutch 44. Fluid pressure within inlet chamber 54 is controlled by a relief valve assembly 56 which is variably loaded in response to the position of spool 52 to control flow to a lubrication line 86. In the neutral or "hold" position, shown, fluid is supplied by pump 73 and line 76 to inlet chamber 54 but spool 52 prevents flow from the latter via non-return valve 77 to branched port 81, connected to brake actuating chamber 32<SP>1</SP> and to drain 71 via spool slots 188. Brake 32 thus remains engaged. Clutch actuating chambers 26<SP>1</SP>, 44<SP>1</SP> both communicate with drain 71 so that clutches 26, 44 respectively remain disengaged and engaged. Winch drum 41 is thus locked and input shaft 21 free to rotate. Relief valve spool 66 produces a pressure of 50 p.s.i. in chamber 54, the latter also communicating via restriction 93 with a chamber 92 containing a loading piston 64 acting via springs 67, 68 on relief spool 66. However in the neutral position, chamber 92 is vented to drain 71 via passage 94 and aligned groove 96 in spool 52. When the latter is moved manually leftwards against the bias of centering spring 58 to a second position (Fig. 5, not shown) groove 96 moves out of register with passage 94 causing pressure to increase in chamber 92, thus forcing piston 64 rightwards to increase the loading on relief spool 66. Pressure in chamber 54 thus increases to about 350 p.s.i. In the second position of spool 52, brake port 81 is connected with inlet chamber 54 via metering slots 79 in the spool, thus causing release of brake 32. Simultaneously a band cuts-off connection between clutch actuating chamber 26<SP>1</SP> and drain 71 causing engagement of clutch 26. Clutch 44 remains engaged. Thus input shaft 21 can now drive drum 41 to reel in cable 46. When spool 52 is moved rightwards from the neutral to a third position, brake port 81 is again connected via metering slots 79 with inlet chamber 54, causing release of brake 32. However clutch 26 is maintained disengaged since actuating chamber 26<SP>1</SP> still communicates with drain 71. Thus a load supported by cable 46 is released. When spool 52 is moved further rightwards to a fourth position (Fig. 4, not shown), groove 103 connects inlet chamber 54 with actuating chamber 44<SP>1</SP>, thus disengaging clutch 44 to permit free wheeling rotation of drum 41. Should pump 73 fail, emergency release of brake 32 can be effected since in the fourth position of spool 52 an accumulator 99 supplies fluid pressure to actuating chamber 32<SP>1</SP> via slots 101 in spool 52. Rightwards movement of relief valve spool 66 is damped by the restricted escape of fluid from chamber 84 via orifice 88.