GB614904A - Improvements in or relating to variable-speed mechanical power transmission devices - Google Patents

Abstract

614,904. Change-speed gear; friction and ratchet clutches. LAMMEREN, W. P. VAN. July 12, 1939, No. 20274/36. [Class 80 (ii)] Contracting coilspring clutches, e.g. 17-20, Fig. 1, serving to introduce one or more alternative ratios in a change-speed gear of the countershaft type, Fig. 1, or planetary type, Fig. 8, are operated automatically in accordance with load-torque which acts on the free ends of the coil-springs to expand them selectively out of engagement with their corresponding driven (or driving) members, the other ends of the coil-springs being secured to the corresponding driving (or driven) members. In both constructions, the torqueresponsive member is a coil spring 40, Figs. 1 and 4, arranged between the final driven member 2 and a freely-mounted planet-carrier 37, wheels 35 on which mesh a ring-gear 38, fast with the final driven member 2, and a sun 34 on an intermediate driven shaft 1b. As the torque-spring 40 yields under varying load, an inner extension 2b of the final driven shaft 2 turns inside the shaft 1b and controls the clutches through cams 3 ... 6 as described below. In the three-speed countershaft gear, Fig. 1, three clutch-springs 18, 19, 20 each have one end secured to the intermediate driven shaft. 1b and their other end free on driving wheels 14, 12, 13 respectively, meshing wheels on a countershaft 16 which is driven only when a freely-mounted wheel 11 is clutched to a driving shaft 1a by a fourth clutch-spring 17 which has a reversed arrangement, i.e. one end is secured to the driving shaft 1a whilst its other end is free on the driven wheel 11. The clutch-springs 18, 19, 20 are operated by turning movement of the cams 5, 4 and 3, which turn bell-crank levers, e.g. 21, Fig. 5, the free end 21b of each of which presses tangentially on the free end 20b of the corresponding clutchspring to expand it out of engagement. The countershaft-driving clutch-spring 17 is operated by a similar lever, but this is actuated by axial movement of the cone 6 which, for this purpose, has a helical pin-and-slot connection (Fig. 7, not shown) with the selector shaft 2b. All the clutches may have this reversed arrangement and be operated by cones, the selectorshaft 2b being then arranged to move axially instead of turning in response to torque. Under top-speed light-load conditions, the cam arrangement is such that the intermediate driven shaft 1b is directly connected to the aligned driving shaft 1a by the direct-drive clutch-spring 18, all the other clutches being disengaged. Increased load turns the selector shaft 2b so that the cam 5 disengages the directdrive clutch-spring 18 ; the cone 6 moves axially to the left to allow the countershaft-driving clutch-spring 17 to engage and at the same time the cam 4 allows the second-speed clutchspring 19 to engage and provide a drive through the wheel 12. Further load increase causes the cam 4 to disengage the second-speed clutchspring 19 and the cam 3 to engage the low-speed clutch - spring 20, the countershaft - driving clutch-spring 17 remaining in and the directdrive clutch-spring 18 out, drive being through the wheel 13. Reverse is by sliding a dog clutch-sleeve 28, normally connecting the driving shaft 1a directly with an aligned input shaft 1 through toothed clutch-wheels 32, 31, the sleeve being slid to the right until it declutches the wheel 32 and gear-teeth on its periphery drive through an idler, a wheel 26 on a shaft carrying a further pinion 25, meshing directly with a wheel 14 fast on the intermediate driven shaft 1b which is thus driven reversely and imparts a rigid drive to the final driven shaft 2 by abutting projections 41, 42, Fig. 4, which cut out the torque-spring 40 in this direction. In the two-speed airscrew drive shown in Fig. 8, the intermediate driven shaft 42, which carries a driven sun 52 of the two-speed planetary gear, is connected to the driven propeller 45 by a planet-gear 60 and torque-spring 62 similar to that in Figs. 1 and 4. Yielding of the torque-spring 62 under load causes a cam 58 on the driven propeller-sleeve to turn on the shaft 42 and rock the spindle 56 of a bellcrank lever which, as before, expands a coil clutch-spring 54, secured at one end to the intermediate driven shaft 42, out of engagement with a stepped planet carrier 41, whereupon the carrier is prevented from backward rotation by a roller detent 53 and the driven sun 52 picks up a reduced drive from the driving sun 48, superseding the previous solid high-speed drive.