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).
Comparative analysis of a Cadillac gearbox, focusing on its silent operation, materials, bearings, and gear bedding.
| Identifier | ExFiles\Box 125\1\ scan0219 | |
| Date | 15th March 1935 | |
| -2- HS{Lord Ernest Hives - Chair}/PJH.4/KW.15.3.35. The Cadillac box is very silent in operation and we have examined it very carefully to find the reason for this. The box is of cast-iron, and, if cast-iron is quieter than aluminium, then this is a point in its favour. As can be seen from the attached Rs.{Sir Henry Royce's Secretary}1821, the sides of the box consist of large flat areas. This should be against the silence of the box. The outer races of all ball races are a slack fit in the box, and must have been so in the first place because they have not been working round. It is possible that bearings that are a slack fit in their housings are less noisy under idling conditions. It would not be possible to fit the bearings in this way in an aluminium box owing to the differential expansion when hot. The layout of the gears is such, that the 1st and 2nd speed wheels are always spinning round on taper roller bearings. It is reasonable to expect these to be more noisy than the plain bearings used in R.R. boxes. The reverse pinion and its idler, which are straight gears, are always running in mesh. This is another possible source of noise. Shaft deflection under load is likely to be far greater in the Cadillac box than in our own boxes owing to the use of only two bearings spaced 12" apart. An examination of the bedding of the gears leads us to the conclusion that the grinding of the teeth is very good indeed and that this is the principal reason for the silence of the box. The tooth form has been corrected so that the bedding occurs mainly on the addendum of the driving gear and the root of the driven gear. A remarkable feature of the bedding is its uniformity. The attached photograph No. 2205C shows the bedding of the first speed wheel (driven side). Owing to the correction of the teeth the bedding consists of a band running along the root only, but the point at which the bedding fades out is of constant height from the base of the teeth, not only along the full length of a tooth, but also, is reproduced exactly on every tooth on the gear. This uniformity of marking is not obtained on R.R. production gears and it indicates a superior accuracy of grinding. We cannot identify the machine used for grinding the gears but have written to the Cadillac Motor Co. for information on this point. | ||