Patent GB-731938-A (GB)
Title: Improvements in or relating to vehicle differential transmissions
Inventor: HILL CLAUDE
IPC: B60K17/346
Filed: 1952-06-09
Abstract: 731,938. Differential gearing: freewheel clutches. FERGUSON RESEARCH, Ltd., H. June 8, 1953 [June 9, 1952; Sept. 24, 1952; May 14, 1953], Nos. 14442/52, 23910/52 and 13470/53. Class 80 (2). [Also in Group XXXI] A motor vehicle transmission system comprises a power input member 7, Fig. 2, power output members 11, 12 driving respectively front and rear road wheels, and gearing 10 between these members permitting a limited range of free differential action between the output members and effective automatically to lock the output members together when either tends to overrun the other beyond a predetermined rate, e.g. when a road wheel tends to spin &c. In the form shown in Fig. 2, planet gears 17A on a driving carrier 17 mesh bevel sun gears 18F, 18R, the former being geared through a train 19F, 20F to the overrunning part of a freewheel clutch 23 connected to the propeller shaft 11 which transmits drive through bevel gearing 21F to the crown wheel of a known differential gear, not described, and thence to the front road wheels, while the latter sun gear 18R is integral with the overrunning part of a freewheel 24 geared through a train 19R, 20R to the propeller shaft 12 which similarly transmits drive through bevel gearing 21R and another differential to the rear road wheels. The freewheels 23, 24 are of the type permitting their overrunning elements to rotate freely in either direction and are arranged so that they allow overrunning of the shaft 11 and gear 19R respectively. The ratios of the bevel gearings 21F, 21R are different and arranged so that with all four road wheels rotating at equal speeds the shaft 11 overruns the shaft 12, and the ratios of the gears 19F, 20F, 19R, 20R are such that the gear 19R then overruns the planet carrier 17. If the rear wheels spin, the freewheel 23 locks the differential gearing 10 and effectively connects the rear wheels to the front wheels. Conversely, if the front wheels spin, the freewheel 24 locks. In the form shown in Fig. 5, a countershaft 25 is driven by the engine and carries gears 26, 27, 28, the gear 27 meshing an annulus- 34 secured to a carrier 32 supporting planet gears 30 meshing sun gears 29 on the ends of the shafts 11, 12. The gears 26, 28 mesh the overrunning elements 38, 39 of two similar freewheels 36, 37. The freewheel 37 comprises an overrunning element 39, Fig. 6, having a cylindrical inner surface 43, and a driving element 40, secured to the shaft 12, having an exterior surface with flats 42. Between these two surfaces are disposed rollers 44 in the fingers 45 of a cage 46 subjected to drag by a spring-mounted brake block 48. Thus relative rotating of the driving element 40 in either direction jams the rollers against the overrunning element 39, while the overrunning element can be freely rotated in either direction relative to the driving element without causing jamming. In this case the gearing to the road wheels is arranged so that the shafts 11, 12 rotate at equal speeds with all four road wheels rotating at the same speed, and the ratios of gear pairs 26, 39; 27, 34; 28, 38 are different. The ratios can be such that, eg., the rear shaft 12 has to rotate only 2.7 per cent faster than the front shaft 11 before the freewheel 36 and the differential lock, whereas the front shaft 11 must rotate 14.58 per cent faster than the rear shaft before locking occurs. In the form shown in Fig. 7, the differential is situated between front and rear propeller shafts 58, 69, the front shaft 58 normally overrunning the rear and sun gears 63 fast on these shafts meshing planets in a carrier 62 driven from the engine by means not shown. The overrunning element 64 and driving element 65 of a freewheel of the type described are connected to the two propeller shafts and lock if a rear wheel spins, and the overrunning and driving parts 69, 66 of another freewheel are connected through gear gear trains 71, 70 and 68, 67 to these two shafts and lock if a front wheel spins. The provision of an intermediate differential of any of the above forms enables the power distribution between the front and rear wheels to be varied, e.g. to give greater power at the rear wheels. Further, with independent brakes, one at each wheel of the vehicle, a differential arrangement of the type described will prevent one of the wheels from locking while the others rotate, so that under these conditions all four brakes remain active. In Fig. 2 of the second Provisional Specification, a modification of Fig. 2 above is shown with the freewheel 24 in a countershaft train having gears meshing the gears 19F, 19R, to obtain equal torque distribution between the front and rear wheels.