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, features, and testing of a new silent gearbox.
| Identifier | ExFiles\Box 137\5\ scan0076 | |
| Date | 17th April 1929 guessed | |
| - 3 - If these gears were lapped by the Copeland or other suitable process, the designer is confident that absolute silence in production could be acheived at little extra cost, even with case-hardened gears. The effect of slight modifications of the gears on noise is not understood and over 40 different gear combinations were tried before the present design was arrived at. The third speed gears are made equal, for convenience in using two pitches. The gear teeth are 14-1/2° pressure angle with standard proportions in every way. An important feature claimed for this box is that the first step is easily made 1.5, 1.7, or more. As shown it is 1.67. The internal gear boxes so far have got into trouble with noise when the first step is made over 1.45. This step is not large enough to enable the axle ratio to be raised and at the same time permit all normal driving to be done on the two silent gears. It will be noticed that equal meshing of the double helical gears is permitted by allowing the side shaft and third speed driven gear to be located end ways by the meshing of the teeth. With the box described above the axle ratio has been raised 20% and normal driving is still done in the two silent gears. This box appears to have been thoroughly well tested on 3 ton speed-trucks, on road and track etc. The box I tried had just returned from 6000 miles on the Indianapolis speedway. The 3 speed box scheduled for production is 1-1/2" longer than the standard box, a few pounds heavier, and will cost in production only about one and a half dollars more to produce. We think Mr. Royce will be interested in this design if only because it is such a small change and relatively simple to try out. Very truly yours, ROLLS ROYCE OF AMERICA, INC. encl. Maurice Olley | ||