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).
Gearbox noise and issues with gear changes, specifically concerning the epicyclic third and Maybach dogs.
| Identifier | ExFiles\Box 182\M19\ img138 | |
| Date | 31th March 1931 | |
| (2) two pairs of helicals are revolving more slowly for the same engine speed and make less noise, but the epicyclic noise counteracts this. The epicyclic third is very noisy under load much more objectionable than our present standard spur third gear at speeds up to 35 MPH, over this speed it becomes quieter. The quietest gear, apart from the top, is the helical 2nd, which is as quiet as a good standard 3rd. speed gear, if however this is used in series with the epicyclic third, the resultant noise is very unpleasant. When in top gear the noise from the two pairs of helicals is prominent at all speeds. Clicking noise from the dogs is much too great even with the reduced toggle spring load, this of course can be reduced to a reasonable minimum by reducing the face angle of the Maybach dogs. (b) Gear Change by Maybach dogs controlled by vacuum cylinder. Changing from top to epicyclic third or vice versa requires a great amount of skill otherwise the Maybach dogs engage when engine and road speeds are far from synchronous. This is perhaps the most disappointing feature of the gearbox, the noise emanating from the box when this happens is most distressing. What appears to happen is that when the Maybach dogs are disengaging say from top gear, the sun wheel to which is attached the Maybach sliding dog is entirely unrestricted as to rotational motion, its direction of rotation and speed is determined by the tightness of the gears in mesh with it, and the dogs will engage irrespective as to whether the planetary system speed (to which the road wheels are engaged) is in correct synchronism with the annulus. To make a good change from top to third gear it is necessary to increase engine speed immediately the clicking of the dogs is heard, if the dogs are allowed to overrun for a short time, non synchronous engagement results. Changing up from third to top non synchronous engagement takes place if the accelerator pedal is depressed before the engine has dropped to its correct top gear speed. Other objectionable features are - (a) Difficulty in changing from third to top gear when the rear box is in neutral - i.e. car stationary, the chances of doing this are about 1 in 10. | ||