Patent GB-644121-A (GB)
Title: Improvements in or relating to aircraft propeller variable speed drives
IPC: B64D27/00
Filed: 1946-04-18
Abstract: 644,121. Change-speed gear; clutches, positive and ratchet. UNITED AIRCRAFT CORPORATION. April 18, 1946; No. 12056. Convention date, Dec. 14. 1944. [Class 80(ii) ] [Also in Groups XXIX and XXXIII] Hydraulic actuating-means for a baulked synchronized toothed clutch-member 44 selecting two rations in a countershaft-gear arranged between a driving shaft 18, carrying an aircraft propeller 14, acts on the clutch-member in both directions through springs 90, which permit the clutchmember 44 to lag behind its actuating collar 58, as for torque-unloading and synchronizing, and produce a snap-action final engagement of the clutch. The propeller-governor, (not shown) is automatically, reset conjointly with the ratio-shift operation. The clutch member 44 slides axially on a splined sleeve 26 fast with the engine-shaft 12, and has external clutch-teeth meshing selectively with internal teeth in freelymounted low-and high-ratio wheels 40, 42, which constantly mesh groups of stepped pinions 36, 38, fast on circumferentiallydistributed countershafts 34, carrying also fast pinions 32 driving a common wheel 30 secured to the driven propeller-shaft 18. The toothed clutch member 44 is operated by supplying pressure-oil to the appropriating sides of a pair of double-acting pistons 48, Fig. 2, having rack-teeth 50, meshing pinions 54, Fig. 1, cranks 56 on which engage an axially slidable grooved collar 58, through which pass freely bolts 80 telescoping inside outer sleeves 81, which carry the snap-action springs 90 between abutments 84, 86 Fig. 14, on the bolts and sleeves respectively. At the beginning of a shift, the clutch-member 44 resists movement, due to torque-loading, so that the springs 90 are 'compressed' by the appropriate abutments 84 or 86, until their coils' close up, whereupon the clutch-member 44 is positively withdrawn to a central baulked position. Fig. 14, in which baulk-pins 78, projecting axially from opposite sides of the clutch-member 44, abut against axiallyfixed side plates 66 or 68, preventing further movement until the parts are synchronized, whereupon the clutchmember 44 turns relatively to the side-plates 66, 68, to an extent limited by engagement of a slot with a spacer bolt 70 connecting the side-plates, thus allowing their baulk-pins 78 to enter holes in the side-plates 66 or 68, whereupon the compressed springs 90 complete a snap engagement of the clutchmember with the wheel 40 or 42. Torque unloading may be effected by closing the enginethrottle. Upshift synchronizing is accelerated by the fricton drag caused by the rightward thrust of the side-plate 68 on a flange on the wheel 42. Downshift synchronizing, produced by opening the engine-throttle, is accelerated, and overspeeding of the engine prevented, by a one-way friction clutch comprising segmental friction-blocks 74 which jam between recesses in a support-member 61, secured to the driving-shaft 12 and a surrounding cylindrical clutch-surface formed on the wheel 40, whenever the driving- shaft 12 tends to rotate more rapidly than the wheel 40. Pressure-supply to the conduits 97, 102 of the double-acting shiftpistons 48 is controlled by a two-position rotary-valve 62, Fig. 10, operated manually through a lever 100, to connect the delivery conduits 97,102 alternately to pressure and exhaust conduits 67, 103, the former through a pair of axial grooves 101 in the side of the valve-plug, the latter through a similar pair of grooves leading through the hollow interior of the plug. To prevent operation of the valve in the absence of oil-pressure, a spring-loaded piston 105 thrusts a peg into one of the plug-grooves to lock the plug, release being effected by oil-pressure reaching the piston 105 through a duct 107. Alteration of the setting of the propeller-governor (not shown) for upshift is effected by the baulk-pins 78, Fig. 14, which, in their final rightward movement press on pins 65 carried by a disc 63 which moves to the right and operates a piston-valve 94, Fig. 1, directing pressureoil from a duct 92, through a duct 96 to the governor, to vary the setting of the propeller governor to suit the new speed-ratio. During downshift, a spring returns the valve 94 to vent the governor-line 96 to make the suitable downshift setting adjustment. During the upshift the line 92 receives its pressure from ports 92 uncovered by the ratio-shift pistons 48 at a suitable point in their stroke. Specification 590,607 is referred to.