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).
The design, performance, and construction of an experimental gearbox.
| Identifier | ExFiles\Box 137\5\ scan0075 | |
| Date | 17th April 1929 guessed | |
| - 2 - Through the courtesy of the designer and chief engineer we have been permitted to see and try out this box in one of their experimental cars, and we have every reason to believe that this design is fully equal to the best that the internal gear transmissions can offer, is more robust, lighter, and far less expensive to produce. The shift can be made instantly though not entirely without shock, at any speed at which the engine will run, about 55 m.p.h. in the lower gear, and 75 m.p.h. in high, and in either direction "up" or "down". Even when thoroughly warm the gears are so silent on drive and overrun, that I cannot say after driving 60 miles whether I ever really heard or felt anything but the increased engine speed. There is no idling noise. The gears in this box are not ground or lapped in any way except by a short running-in with soft abrasive. The engineer assures me that out of the first lot of 50 boxes in production only one was turned down as being in any way below their standard of practical silence. Sketch SK-315 shows the design of the 4 speed box. The new "standard box" is 3 speed, and is exactly similar except for the omission of the "emergency-low" gear. The design consists of two trains of double-helical gears constantly in mesh, and a dog-clutch shift. The dog clutch is conventional consisting of internal and external gears with every second tooth cut back for easy engagement. The teeth are not rounded, and I think they should be, to reduce shock. The gears are hobbed on a Brown & Sharpe machine in two halves, the Sykes double herring-bone gears having been found inaccurate. Material is SAE-3250 (50 carbon, 39-60 manganese, 1.5 - 2.0 nickel, .90 - 1.25 chrome) heat treated after cutting to 70 scleroscope. A feature which has been found important though not fully understood (it is also patented) is the use in one train of two different pitches on the same gear, as shown. Apparently the fact that 30, 40, and 50 teeth mesh in the same interval of time tends to "blur" out harmonics. The third-speed driven gear is mounted on a hardened steel spool which revolves when idle directly on the third motion shaft, with only a spiral oil groove to help lubricate it. -continued- | ||