602,319. Change-speed gearing ; friction clutches. HOBBS, H. F. Nov. 7, 1044, No. 21885. [Class 80 (ii)] In a change-speed gear, at least two friction devices, such as nested clutches 16, 17 and/or brakes, which are varied selectively alone to introduce at least two ratios, and in conjunction with engaging toothed members such as one or more dog-clutches 46, 47 and/or detents or sliding gear-wheels, for at least one additional ratio, are so controlled that, when the introduction of a new ratio is such as to require engagement or disengagement of the toothed members, operation of one or more of the friction devices is varied so as to cause or tend to cause the toothed members to rotate at varying relative speeds, whereby either their teeth are relieved of torque-loading for disengagement, or synchronized for engagement, which takes place without further variation in the engagement of the friction devices, engagement of which latter may then be further varied to drive through the required power path. During upshift, this temporary variation in engagement of the friction devices maintains uninterrupted power transmission in one embodiment, or maintains a braking torque on the input shaft, for unloading and synchronizing, in another embodiment. The dog-clutches 46, 37 have balk-rings 50 and are operated through springs 80, 81, Fig. 2, which give snap-action engagement when synchronization frees their balk-rings. All-countershaft, allepicyclic, and combined countershaft and epicyclic gears are described, control being hydraulic or mechanical. In the 5-speed and reverse gear shown in Figs. 1-3, there are two concentric intermediate shafts 29, 30, the outer, 30, of which is driven directly from an input shaft 10 through one nested friction-clutch 17 and drives through a wheel-pair 35, 37 a countershaft 38 which drives the output shaft 32 through wheel-pairs 41, 43 or 42, 44 selected by a double dog-clutch 46, 47. The inner intermediate shaft 29 is permanently connected by teeth 31 to the aligned output shaft 32 and carries a side-wheel 26 of a bevel differential gear, the other side-wheel 27 of which is secured to the outer intermediate shaft 30, whilst its carrier 25 is secured to the driven plate of the other nested friction clutch 16. The friction clutch 17 alone gives first and third speeds through wheel-pairs 43, 44 or 41, 43 and dog-clutch 47, 46 respectively. Second and Fourth speeds are obtained using the friction-clutch 16 alone to drive differentially direct through the inner intermediate shaft 29 and simultaneously through outer intermediate shaft 30 and the same wheel-pairs 42, 44 or 41, 43 as in first and third speeds. Fifth-speed, direct-drive is by engaging both clutches 16, 17 together to lock the differential gear, both dog clutches being disengaged. On a motor-vehicle the axle-ratio may be such as to permit the fifth ratio being regarded as an overdrive. Reverse is by sliding an idler to mesh wheels 58, 59, or by sliding the countershaft-wheel 42 to mesh the idler. Some of the gear-wheels may be mounted on free-wheels.. The friction clutches 16, 17 are engaged by fluid-pressure acting on diaphragms 18, 19 and, when disengagement is required, pressure is cut off and the diaphragm-chamber allowed to drain through fixed peripheral holes or through holes which are only opened when pressure is cut off. Disengagement is gradual since centrifugal force on the liquid still to be drained maintains engagement after pump-pressure is cut off. Oil is fed to the clutch surfaces when disengaged so as to provide a progressive slip period during engagement. An additional friction clutch may be provided on the inner intermediate shaft 29. Pressure-fluid is supplied to the frictionclutches 16, 17 by a pump 20 through pistonvalves 65, 66 operated through levers 68, 69 by a selector-cam 70, Figs. 2 and 3, which also has a cam-groove 72 operating a selectorfork 60 controlling the dog-clutch 46, 47, Fig. 1. The selector-cam 70 turns with, but is axially slidable on a rockshaft 71, connected to controlmeans, not shown, the cam 70 being centred in a normal axial position on the control-shaft 71 by loading-springs 80, 81. To make a shift, the control shaft 71 is turned, but if the shift involves disengagement of one of the dogclutches 46, 47 and drive torque prevents such disengagement, the cam 70, turning with the selector-shaft 71, is moved axially against one of the springs 80 or 81 which thus biasses the dog-selector fork 60 in the appropriate direction whilst the movement of the cam 70 operates the selector-valve levers 68, 69 of the frictionclutches 16, 17 to cause the required relative speed variation between input and output shafts during the shift interval. The previously engaged dog-clutch is thereby unloaded of drive torque and is moved by the spring 80 or 81 first to the balked position for the new speed and later, when synchronism is complete, with a snap action into the engaged position, the accompanying movement of the cam 70 serving to operate the selector-valve levers 68, 69 to produce non-slip engagement of the friction clutch or clutches 16, 17 required for the new speed. The only upshift involving change from one dog-clutch (47) to the other (46) is that from second to third speeds, and to unload the dogs 47 of drive torque and subsequently synchronize the dogs 46, both friction-clutches 16, 17 are allowed simultaneous slipping engagement during this shift interval, so as to tend to drive in fifth speed, thus slowing down the input shaft 10 and also maintaining uninterrupted power transmission between input and output shafts during the shift. Downshift from fifth to fourth speed is by cutting off the supply to the friction clutch 17 which progressively disengages, permitting the engine to speed up whilst still transmitting drive to the load, the dog-clutch 46 engaging under the spring 81 when synchronism is reached. The only downshift involving change of dog-clutches 46, 47 is that from third to second and this is effected in one case by cutting of the supply. to both friction clutches 16, 17 and in another by supplying both. To prevent the synchronizing action during a downshift if the engine throttle should be closed (in which case the engine would not speed up to unload the dogs of drive-torque, a tappet 84, Fig. 3, is provided to keep the valve 66 of the clutch 16 closed, preventing its engagement until the throttle is opened. An axially-fixed cam 74 on the control shaft 71 operates the reverse selector fork 62. A first modification providing three speeds and reverse, Fig. 4 (not shown) omits the differential gear, the clutch-disc 16 being mounted directly on the inner intermediate shaft. Wheels 44, 59 and the dog-clutch 47 are also omitted, the wheel 58 being slidable into mesh with the countershaft wheel 42, mesh being synchronized as above described. A second modification, providing four speeds and reverse, Fig. 6 (not shown), retains the double clutch 46, 47 and omits the differential gear as before. In both these forms the selector-forks slide on striker-rods on which they are centralized by bias-springs similar to 80, 81, Fig. 2, and the ends of the strikerrods directly control valve-ports feeding the friction-clutches 16, 17. In the second form the striker-rod has a helical connection with its selector-fork so as to cause the rod also to turn when the fork is unable to move axially. In the all-epicyclic form, Fig. 5, a doubletoothed detent-sleeve 96, with balk-rings, in its forward position holds a ring-gear 95; whereupon a first reduced speed is imparted to the driven carrier 102 when a sun 90 is clutched to the driving shaft 10 by the friction clutch 16. A second reduced speed is obtained when the detent is moved back to hold a second sun 93, and the ring-gear 95 is driven through the friction clutch 17, whilst direct-drive is obtained with the detent 96 in a central inoperative position and both clutches 16, 17 are engaged together to lock the planet-gear solid. An overdrive fourth or reverse, according to wheel-sizes, is obtained with the frictionclutch 16 engaged and the sun 93 held by the detent 96. A fluid-operated brake may replace the overdrive detent teeth, and free-wheel detents may be used. Synchronization is effected during detent changes by engaging both clutches 16, 17 together. Where brakes are used instead of the friction clutches, the arrangement may be that shown in Fig. 2 of Specification 602,318, which is also described in the Provisional Specification. Specifications 549,988 and 594,408 are referred to in the Complete Specification and the Provisional Specification refers also to Specification 560,379.