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).
Technical summary and discussion of gearbox design alternatives and considerations.
| Identifier | ExFiles\Box 6\4\ 04-page251 | |
| Date | 29th April 1930 guessed | |
| -2- itself seems extremely good in several combinations. I had noticed the difficulty with 3 pinion driven trains of getting the 3rd. as high as we might wish, and examined most of the alternatives, but I rather concluded that with an easily available 3rd. we ought to have the top gear say 10% higher, and the drop rather greater than the present box, so that 74/100 x 100/110 = .67 - about what we should get with's trains of .3 Since, however, we can now easily go to 2nd. perhaps we can keep 3rd. also fast, and I think the 4 trains make the most silent and easiest made job, especially as all the planets can be large and slow speed, (and still give a ratio not less than .72) and the upper ones narrow and fine pitch so that they need not weigh much. Mr.Hardy's alternative of the Mavel .S is perhaps the best alternative to get the 3rd. but this type of gear is costly to get right; compared with stringing a lot of parallel gears on the end it is not good for production. The following summary may be useful :- (1) Having an easily available 3rd. the top gear can and should be higher, to avoid over-running the engine, foss, and bad petrol and oil consumption. An undergeared car is not pleasant. With our latest "twenties" I often attempt to change from top to something higher. (2) It should be realized that my suggestions avoid the high torque brakes that are necessary for Wilson/Lanchester scheme. By using a positive 1st. speed and reverse, so that if we use brakes on the 2nd. and 3rd. they will only need to have 1/1 engine torque, and 1 engine torque respectively, instead of 2 and 4 times with the Wilson/Lanchester gear. (3) We can use either jaw clutch or friction clutch of 1/3rd. engine torque for top gear. I should design for the latter if we use the control suggested in this memo. (4) For the 1st. speed my idea is to use silent ratchets to hold the annulus controlled by light brake. (5) For reverse we should use gear type jaw clutch (like direct drive present box) to hold planet cage (this type for safety). | ||