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).
Letter from Cadillac Motor Car Company discussing transmission gear design for silence.
| Identifier | ExFiles\Box 22\4\ Scan023 | |
| Date | 17th April 1935 | |
| X4708 COPY CADILLAC MOTOR CAR COMPANY, DETROIT, MICHIGAN. April 17th,1935. Mr. W.A. Robotham, Rolls-Royce Ltd., Derby, England. Dear Rn.{Mr Robinson}, In reply to your question about our transmission gears, here are two reports by Ed{J. L. Edwards} Nyland on the Cadillac and LaSalle gears respectively. Apparently it was gears ground on the Pratt and Whitney which attracted your attention. Briefly the points for silence appear to be: (1) Helix angle close to 45 degrees. (2) Adequate face width. Short transmissions in which the face width has been reduced to save cost and weight are more expensive to produce to a given standard of silence because the involute requires to be more accurate as the face width is reduced. Gears which are cut helical and mounted on helical splines of the same lead - a practice introduced by Dodge and now used on LaSalle and Packard 120 first speed gears - are a disappointment, although they save weight. The trouble is that at the moment the gear engages or disengages before it has enough tooth in contact to know that it is a helical gear, it behaves exactly like a straight spur gear with rounded teeth mounted on helical splines. In other words, according to the "hand" of the helical splines and the relative drag on the two rotating gears, the engagement tends either to suck in or squirt out. The only escape is to use about 30 degrees helix on the gear which gives a spline angle which with normal friction is not too violent in its action. But 30 degrees helix angle gears are very expensive to get silent, so that the final cost saving over a fixed gear with dog clutch or synchromesh engagement is imaginary. Best regards, (Sgd.) Maurice Olley. | ||