From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Design and scaling of a 'Junior Gearbox' to achieve weight savings for smaller cars.
| Identifier | ExFiles\Box 136\2\ scan0130 | |
| Date | 28th July 1939 | |
| 1153 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} c. DA.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Hdy.{William Hardy} Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls}7/MH.{M. Huckerby}28.7.39. JUNIOR GEARBOX. We have been considering the best size to make the Junior gearbox. Our reasons for doing this are that we think it essential that the smallest car in the range should be as light as possible. It is to have almost the same body space as the bigger cars, and it is therefore very important to keep the chassis weight down so as to get the complete car as light as possible. We have assumed that the latest drawing of the B.V. standard ratios box PD.477, is suitable for the 8-cylinder 5.6 litre car. The attached table shows what we have calculated the weight of the box will be when scaled down .875, .815 and .71. These sizes are suitable for 3.7-litres, 3 litres and 2-litres respectively. The drawing at present being made of the Junior box is .875 scale of the original B.V. and has an uneconomical torque-to-weight ratio. It will be seen from the table that by designing the box for 2-litres instead of 3-litres we should save 12 1/2 lbs. and it is, therefore, worth while considering whether it would not be advisable to use the present design on all the cars from 3-litres upwards and make a new little box for 2-litres downwards. Similar considerations, of course, apply to the Junior axle, but in this case we do not think it is possible to provide adequate differential pinions inside a crown wheel of less than 7". In compiling the table we have assumed that the weight of the gear trains varies as the cube of the linear scale, but the weight of the castings varies as the square, because, of course, the section does not vary. We find that the bearings also vary as the square and we have assumed that the change speed and selector mechanism does not vary at all because it is possible to be just as brutal with a small gearbox as with a large one. Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} | ||