Patent GB-610097-A (GB)
Title: Improvements in or relating to variable-speed power-transmission systems
IPC: F16H47/06
Filed: 1946-03-22
Abstract: 610,097. Variable-speed gear; friction clutches. SINCLAIR, H. March 22, 1946, No. 8981. [Class 80 (ii)] Relates to means for obtaining neutral and permitting operation of a reverse-gear 17, a range-changing gear, or a selective gear having two or more output members, whilst the gear-wheels are stationary and the transmission is subject to the idle-drag of a hydrokinetic transmitter 12 which drives the reverse &c. gear through a stepwise changespeed gear 16 in which at least some of the ratios are selected by positive synchro-couplings 69-72, e.g. of the Legge type (described in the Specifications enumerated below), which cannot conveniently be employed to give neutral, and a slippable clutch 23, provided between input and output shafts 13, 29 of the change-speed gear, is momentarily engaged during an upshift to maintain drive-torque and also to unload the positive shift-elements, as described in Specifications 376,468 and 534,470. According to this invention, the slippable clutch 23 connects the input and output shafts 13, 29 of the changespeed gear 16 at a ratio higher than any of those introduced by the positive synchrocouplings, and the change-speed gear is also provided with a positive clutch 59 for interrupting the transmission path of at least one of the synchro-coupled ratios, whereby a definite neutral can be obtained. In the three-speed gear shown, an input pinion 52, connected to the driving shaft 13 through the clutch-drum 23, drives a countershaft 24 from which two reduced ratios are picked up through a pair of stepped wheels 54, 55, normally clutched to the countershaft by the neutralizing clutch 59, and constantly meshing freely-mounted wheels 66, 67, which have clutch-teeth 70, 71 for selective engagement with teeth 72 on a synchro-coupling nut 73 helically splined on the driven shaft 29. Take-up pawls 77, 78 on each side of the nut 73 traverse the nut along the spline under relative speed differences, the nut being locked in either of the two gear-positions, in the inner neutral position shown, or in an outer idle position, by a four-position lock-sleeve 79 all operating as described below. Top speed is by engaging the slippable clutch 23 to provide a direct connection between driving and driven shafts 13, 29, the synchro-coupling nut 73 being at that time locked in an idle position at the right of the clutch-teeth 71. The self-contained reversegear comprises a driving sun 86, and a planetcarrier 88, with clutch-teeth 91, which is slid axially by a lever 96 to engage fixed teeth 92 for reverse or the teeth of a final output ring- gear 89 for solid forward drive. Shift-rails 63, 84, which operate the neutralizing clutch 59 and the synchro-coupling locksleeve 79 preselectively through resilient links 62, 83, as described in Specification 513,974, are mounted side-by-side and controlled by a ball-mounted shift-lever 98 guided in a slotted gate, Fig. 3 (not shown), having two longitudinal slots and a cross-slot joining the midpoint of one to the end of the other. The lever engages either shift-rail at the cross-slot when the shift-rail 63 is in position 64F to engage the neutralizing clutch 59, and the shift-rail 84 is in position N to move the synchro-coupling lock-sleeve 79 to the neutral position shown. In operation, if a vehicle embodying this transmission is brought to rest with a synchrocoupled ratio still effective, and it is desired to engage reverse, the synchro-coupling lock-sleeve 79 and positive clutch 59 are first preselectively biassed to neutral by moving the shift-lever 98 to the end of the corresponding gate-slot, and then the slippable clutch 23 is momentarily engaged by depressing a pedal 51. Idle-drag, of the fluid transmitter 12, operating through the clutch 23, turns the final output member 18 slightly forward sufficient to unload the synchrocoupled ratio, permitting both the synchrocoupling lock-sleeve 79 and neutralizing clutch 59 to disengage, thus neutralizing the changespeed gear and allowing free engagement of the reverse-gear, after which the neutralizing clutch 59 and first-speed synchro-coupling can be engaged by the preselector-lever 98. If it is inconvenient for forward movement of the vehicle to accompany the slight forward rotation of the output member 18, the latter may be connected to the output member 89 of the reverse gear by a torsionally resilient coupling comprising segmental rubber blocks 106, Fig. 6, between alternating radial webs 107, 108 on the coupled members 89, 18, the member 18 being journalled on two rows of needle rollers 104 on the member 89. The slippable clutch 23 is a friction clutch with a single driven plate 35 disengaged by pull-off springs 9 and engaged through radial levers 41 and a thrust-collar 49 by depression of the pedal 51, engagement pressure being augmented by the drive-torque acting through rollers 39 on cam-inclines 38 on the presserplate 36. The synchro-coupling is generally similar to those described in Specifications 354,711, 410,083, 486,589, 513,974 and 534,470, but its lock-sleeve 79 has at one end alternate long and short splines 80A, 80B, Fig. 8, which co-operate with shaft-splines 81 to produce a balking effect. The coupling comprises a nut 73 threaded on a helical spline 74 on the driven shaft 29 and having external straight splines 73<1> permanently engaged by splines 79<1> in the external locksleeve 79 so as always to rotate therewith. Clutch-teeth 72 on the nut engage selectively with the first and second speed clutch-teeth 71, 70 and the nut carries the usual pawls 77, 78 to be picked up by the clutch teeth 71, 70 for winding the nut in the appropriate direction. In the first-speed position the nut-teeth 72 clutch the low-speed teeth 71 (as in Fig. 8) and forward torque urges the nut 73 to its rearmost position (right of Fig. 8) against a stop-collar 76 fixed on the shaft 29, whilst overrun torque is taken through the forward splines 79<1> of the lock-sleeve 79, which is also in its rearmost position (one step to the right of that in Fig. 8) with its splines 79<1> bridging the nut- and shaftsplines 73<1>, 81. For upshift to second-speed the shift-lever 98 is operated preselectively to move the shiftrail 84 to the extreme left (notch 2, Fig. 2, engaging the detent 85), loading the spring-link 83 for leftward bias on the lock-sleeve 79. The latter immediately moves out of engagement with the shaft splines 81, which it is able to do since it is not transmitting forward torque in first-speed, and assumes a balked position shown in Fig. 8 in which further leftward movement is obstructed by abutment of the long internal splines 80A in the lock-sleeve with the ends of the shaft-teeth 81. This releases the nut 73 so that when the pedal 51 is subsequently depressed to execute the upshift, the overrun torque applied by slipping engagement of the direct-drive clutch 23 causes the nut 73 to screw leftwards, disengaging the low-speed clutch-teeth 71, and also slowing down the engine until one of the second-speed clutch teeth 70 pick up the nut-pawl 77, causing the nut 73 to resume its leftward movement, which is still further continued by subsequent engagement and disengagement with the second-speed clutch-teeth 70 of the nut-teeth 72, until the nut is arrested at its extreme forward position by a front stop-collar 75 on the shaft 29. The turning movement of the nut 73 also turns the lock-sleeve 79, causing its long splines 80A to ride off the shaft-splines 81, and permitting its shift-bias spring-link 83, Fig. 1, to move it further to the left until its short splines 80B align with the shaft-splines 81, in which position it is again arrested. The direct-drive frictionclutch 23 is now disengaged by releasing the pedal 51, permitting the engine to accelerate so that the second-speed clutch-teeth 70 pick up the opposite nut-pawl 78 and screw the nut to the right until its clutch-teeth 72 engage the second speed clutch-teeth 70, at which time the corresponding turning movement of the lock-sleeve 79 moves its short splines 80B out of alignment with shaft-splines 81 and permits the shift-bias spring 83 to move the 'lock-sleeve fully to the extreme left, with a long and short spline lying closely on each side of a shaft spline and serving to transmit both forward and overrun torque in the locked secondspeed. To introduce high-speed, direct-drive through the friction clutch 23, the shift-rail 84 is moved one step to the right (notch 3 engaging detent 85, Fig. 2). Engagement of the friction clutch 23 applies overrun torque, the intervening torque-reversal freeing the lock-sleeve 79 and permitting its shift-bias spring 83 to move it to the right until its short splines 80B disengage the shaft splines 81, whereupon overrun torque turns the nut 73 to its extreme left position in which it remains idle. For the downshift to second speed the shiftrail 84 is moved to the extreme left and, when the direct drive friction-clutch 23 is disengaged, the consequent engine acceleration screws the nut 73 to the right to clutch the second-speed teeth 72, at the same time freeing the locksleeve for travel to the extreme left, by its bias-spring 83 as before. For downshift to first-speed the shift-rail 84 is moved to the extreme right (notch 1 engaging detent 85, Fig. 2), whereafter momentary slipping engagement of the direct-drive clutch 23 or interruption of engine power unloads the lock-sleeve 79, permitting its shift-bias spring 83 to move to the right until its splines 79<1> are obstructed by the left faces of the shaft-splines 81. Subsequent disengagement of the clutch 23 or restoration of engine-power causes the second-speed clutch teeth 70 to move the nut 73 to the right, in which position the accelerating first-speed clutch-teeth 71 eventually pick up the nut-pawl 78, screwing the nut to the extreme right (as in Fig. 8) to clutch the firstspeed teeth 71 and freeing the lock-slee