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 testing and modification of an epicyclic 3rd speed gearbox following trials at Brooklands.
| Identifier | ExFiles\Box 6\2\ 02-page168 | |
| Date | 16th April 1931 | |
| X523 R.{Sir Henry Royce} FROM DA.{Bernard Day - Chassis Design} DA{Bernard Day - Chassis Design}1/M16.4.31. Copy to HS.{Lord Ernest Hives - Chair} EPICYCLIC 3rd. SPEED GEARBOX. We tried this box again yesterday at Brooklands. The modifications made were that the existing 5 tooth jaw pieces had had the angle of their faces reduced from 6° to 4°. (This also automatically increases the clearance between the jaws), and the original strong spring has been restored to the toggle mechanism. It is now possible to make changes in both directions with a certainty, and without the crashes that were apperently almost unvoidable before. It was however still possible for anyone not familiar with the correct procedure to get very bad crashes. Judging from the brief observation possible this seemed invariably to occur when there had been delay in accelerating the engine on changing from top to 3rd. It is suggested that this permits the sun wheel jaws to reach their maximum speed of ratcheting against the stationary 3rd. speed jaws with the result that the jaw clutch is flung momentarily into the top gear, where the conditions as to speeds are suitable for a 'crash' engagement, which however cannot be maintained because the toggle is pushing the jaws apart. Still further reduction of the angle of face is suggested. Derby say that they have in hand a set of jaws with 3 teeth and 2 1/2° angle as recently proposed. The noise of the ratchet as fitted is still rather more than one would think desirable. There are some indications that the power of the vacuum mechanism may not be quite sufficient. In changing in either direction, if the accelerator pedal is let up quickly, there is a certain amount of time required for the cylinder and toggle to function, but the over-run comes on immediately and the overrun load is sufficient at time to prevent the jaws from being disengaged. Touching or slightly opening the throttle of course remedies this. We do not think there is any reason to suppose that this mechanism cannot be made to work as well as the Maybach. We are looking in to the question of (a) a synchronising brake for 3rd. speed, (b) a Salerni baulk ring. Our light loads should facilitate making a success of it. In the meanwhile we suggest that the original scheme of a brake and clutch for the operation of this gear might be worth reconsidering. It has a great advantage that it gets over the Maybach patents. DA.{Bernard Day - Chassis Design} | ||