Patent GB-693357-A (GB)
Title: Improvements in and relating to ratio-selecting couplings of change-speed gearing
Inventor: SHORT PHILIP JOHN
IPC: F16D23/10
Filed: 1950-02-17
Abstract: 693,357. Change-speed gear; clutches positive and ratchet; resilient couplings; locking rotary elements. S.S.S. GEARS, Ltd. Feb. 6, 1951 [Feb. 17, 1950], No. 4201/50. Classes 80 (ii) and 80 (iv). Relates to a toothed clutch of the kind, e.g. as described in Specifications 410,083 and 486,589, used as a ratio-selecting clutch or stop, wherein a common, or two or more linked helix members 20, move on a helical spline 19 on a driven (or driving) shaft 6, to engage clutchteeth 22 on its periphery selectively with axiallyspaced clutch-teeth 18 or 15 on driving (or driven) wheels 4, 5 (giving respectively low and second speed), such helical movement being induced, whilst the helix-member 20 is in an intermediate position, by appropriate changes in the direction of relative rotation of driving and driven members (as by accelerator-manipulation on a vehicle), which acts through the clutchteeth 15 or 18 on subsidiary pawls 23, 26 mounted on the front and rear faces of the helix member 20, to screw the helix member in the appropriate direction for synchronous engagement of its teeth 22 with the clutch-teeth 15 or 18. The subsidiary pawls 23, 26 are normally loaded only sufficiently to screw the helixmember 20 on its shaft, and, according to this invention, to avoid damaging overload on the pawls due to abnormal locally-circulating torque (described below) a torsionally resilient coupling is introduced in the drive to the second-speed clutch-teeth 15, either in the wheel 5 or in a meshing wheel 2. The change-speed gear shown comprises an input shaft 3, carrying fast low and second-speed wheels 1, 2, meshing wheels 4, 5 freely mounted on a countershaft 6 and clutchable thereto by the helix-member 20. Fast on the countershaft is a wheel 7 which drives a wheel 9 on a final parallel output shaft 10, through a wheel 8 freely mounted on the input shaft 3 and clutchable thereto by a friction disc-clutch 11 for highspeed. Forward drive-torque tends the screw the helix member 20 forwards (to the left of Fig. 1) on the spline 19 and, to maintain engagement with the second-speed teeth 15, the helix-member is locked to the shaft 6 by rearward movement of a lock-sleeve 29 splined to the helix member 20 and meshed with splines 32 on the shaft 6. In low-speed, forward movement of the helix member is prevented by a shaft-collar 34. Downshift from second to low is effected by preselectively biasing, through a spring-loaded shiftfork 33, the lock-sleeve 29 to the forward release-position shown, into which it moves on release of drive - torque (accelerator - release) whereupon the input shaft is accelerated to cause the front pawls 23 to screw the helix member 20 into synchronous engagement with the low-speed teeth 18. Rearward upshift movement to second - speed is by decelerating the input shaft to synchronism, whereupon the rear pawls 26 screw the helix member 20 into engagement with the second-speed teeth 15. Pawl-overload conditions may arise e.g. when the helix member 20 is central, with both pawls 23, 26 engaging the teeth 18, 15; the lock-sleeve 29 unlocked and the output shaft 10 turned slightly (e.g. by movement of the vehicle), with the input stationary (e.g. in servicing). Drag in the clutch 11 may then induce relative rotation between the low and second speed wheels, thus producing a heavy torque circulating locally through the pawls 23, 26. The resilient coupling prevents damage thereto. In Figs. 3 and 4 this coupling comprises a ring 37 carying the second-speed clutch-teeth 15 and having a lostmotion spline connection 36, 38 in a sleeve 14 fast to the second-speed wheel 5. Compressed coil springs 43, arranged in circumferential recesses in the sleeve 14, thrust on axial pins 42 on the ring 37 to maintain positive abutment between the splines 36, 38 in that direction (anti-clockwise from front) in which the wheel 4 normally drives the shaft 6, but the springs permit torsional yield in the opposite direction sufficiently to permit disengagement of one of the pawls 23 or 26. In Figs. 5 and 6 (not shown), a similar coupling is arranged between the hub and rim of the second speed fast wheel 2. In Fig. 7 (not shown), a ring carrying the second-speed clutch-teeth 15 is mounted in a helical spline for rearward movement in opposition to axial compression coil-springs, the movement being sufficient to disengage its teeth from the rear pawls 26. The Provisional Specification states also that the selective device may be. in the form of a, clutch and reaction-stop in a two-speed over- or under-drive planet train, the resilient coupling being in the stop or clutch.