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).
Performance of an experimental Phantom III Overdrive Gearbox and proposed design modifications.
| Identifier | ExFiles\Box 94\2\ scan0172 | |
| Date | 11th February 1937 | |
| Hs{Lord Ernest Hives - Chair} from Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} 328 Rm{William Robotham - Chief Engineer}/Gry{Shadwell Grylls}7/M.11.2.37. p.III Overdrive Gearbox. The overdrive box fitted to 36 EX has proved exceptionally silent on the indirect high gear. The object of this particular experimental box was to determine the silence of an indirect top gear. With the minimum of changes in the standard box we arranged this test with an overgear ratio of .82. The lowest possible 2nd and 1st speed ratios we could arrange were 1.32 and 2.05 respectively. Obviously these are not suitable for standardisation. The limiting factors were the smallest usable size of the 1st speed pinion and 3rd speed loose pinion. In order to obtain sensible 3 speed ratios of about 2.7, 1.5, 1 and .82 it is necessary to increase the shaft centres 3/10 of an inch. Accepting a change speed gate thus [Diagram of gear gate showing top row positions R, 2, 0 and bottom row positions 1, T] we can dispense with the mechanism which reverses the 1st and 2nd speed direction in the present box and save a few shillings. A new casting is required because of the increased shaft centres, also longer selector forks for the 2nd speed and reverse and new gear wheels throughout. The synchro mechanism is unaltered. We attach a scheme showing the shaft centres and spiral angles. We have made all the continuous gears of the same tooth form to save grinding tackle. We think a design for these changes could be made in ten days. Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} | ||