Patent GB-602318-A (GB)
Title: Improvements in or relating to variable ratio power transmission apparatus
IPC: F16H37/04
Filed: 1944-11-07
Abstract: 602,318. Change-speed epicyclic gearing. HOBBS, H. F. Nov. 7, 1944, No. 21884. [Class 80 (ii)] Variable-ratio gearing includes a toothed or fluid differential enabling torque to be divided between 'two paths of different ratio, each introduced by a friction clutch or brake, at least two of which are engaged simultaneously in at least one ratio so as to share the load, the reaction-element of the differential being connected to a fixed member through a oneway detent or positive stop, whereby it can react on the fixed member only after it has been brought to rest. Where a fluid differential is used this may be the three-element fluid gear described in Specification 549,988. In Fig. 1, opposite side-wheels 63, 64 of a simple bevel differential gear, with planets carried by a driven shaft 60, are driven from a driving drum 50 through nested friction clutches 53, 54 respectively, the former driving directly, the latter through a countershaft reducing train 68. Four ratios are available, including directdrive through a third nested clutch 52, or a dog-clutch, one reduced ratio with both sidewheels driven together, and two further reduced ratios with the side-wheels driven separately, the side-wheels being provided with one-way roller-detents 73, 74 (the latter mounted on the countershaft) which may have dog-clutch locking-means, or balked dog-detents alone, to prevent backward rotation of the wheel not being driven. The train 63, 64 may be of the stepped planet type with spur, helical or bevel planets and the wheel 64 may be coupled to the output shaft. The planets may have three steps and an additional sun be provided for additional speeds. In an all-planetary form, Fig. 3, not shown, the carrier of a bevel differential is secured to the final output shaft, whilst its unequal side-wheels are secured to two concentric intermediate shafts such as 55, 56, the inner shaft being frictionally clutchable to the driving drum, the outer carrying a sun-wheel which can be held stationary by a balked positive detent and engages one step of a set of stepped spur planets carried by the driving drum, the other planet-step engaging a second sun which can be clutched frictionally to the driving drum or held fast by a friction brake. In direct-drive both friction-clutches are engaged and the whole of the gearing rotates solidly. In Fig. 2 the differential-gear comprises interengaging spur planets 32, carried by the driven shaft 10, which may be the rear-axle of a wheeled or tracked vehicle, and engaging sidewheels 39, 33 each driven from a hollow driving- sleeve 100 through a 2-speed epicyclic gear A, 13 and C, D respectively. Each 2-speed gear comprises two three-element trains in parallel, the planet carrier 19 of the first and connected ring-gear 18 of the second train being carried by the driving-sleeve 100, which is driven through bevel gearing 13 by a propeller-shaft 15. An increased. or reduced speed is imparted to the connected ring-gear 22 of the first train and planet-carrier of the second when either sun-wheel of the trains is braked at C or D respectively, the drive from the trains A, B or C, D being passed to the respective side-wheels 39 or 33 through toothed wheels K, J of different ratio. With the disposition shown four ratios are obtainable by combinations of the brakes A, B, C, D used two at a time to drive both side-wheels 39, 33 simultaneously. Four additional ratios are obtained using each brake A, B, C, D separately when the side-wheel 33 is locked to the driven shaft 10 by a balked positive clutch F, and two additional ratios using the brakes C, D separately with the other side-wheel 39 locked stationary by a balked positive brake E. The brakes C, D also provide two reverse ratios when the wheel J is slid axially to the left to mesh a second set of teeth on the gear 22 through an idler (not shown). Arrangements are referred to using seven or nine of these available ratios. Upshifts may be facilitated by momentarily engaging an additional one of the friction clutches or brakes A to D, to load the engine shaft, reducing its speed so that dog-clutch parts to be engaged are synchronized, without power interruption, and load can be removed from dog-clutch parts to be disengaged as described in Specification 602,319. Fig. 2 shows also a differential steering arrangement for a tracked vehicle, the final driven shaft 10 being connected to each aligned track-sprocket shaft through three-element epicyclic trains 143, the planets of each of which are carried by the sprocket-shafts, the ring-gears by the driven shaft 10, whilst the suns are geared at 141 to inner half-shafts 11, passing through the parallel driving-shaft 100 and connected to it by a differential-gear 139. Application of a brake to either sun-wheel shaft 106 retards the corresponding tracksprocket for steering the vehicle. The control may be hydraulic or manual, the latter using a combined pedal and lever arrangement, servo-assisted if required.