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).
Problem of 'creeping gears' in gearboxes and potential solutions.
| Identifier | ExFiles\Box 178\3\ img190 | |
| Date | 30th May 1932 | |
| HS.{Lord Ernest Hives - Chair} ) FROM R.{Sir Henry Royce} C. to BG. WOR.{Arthur Wormald - General Works Manager} C. to DY.{F R Danby} Eng. ORIGINAL GEARBOXES. CREEPING GEARS. R4/M/30.5.32. x5'S10. x7S10. It will be remembered that we patented several means of keeping the gears still on the shaft. In our schemes we endeavoured to get the full twist of the gear on the splines right under the gear in such a way that there was no movement of the gear on the splines due to the torque or angle of pressure of the teeth. As we have lately stated in another memo. this is quite easy when the gear is relatively large to the shaft, but in the case of the small gears used as drivers on the 1st. and 2nd. speeds it is only just possible to keep the gears from moving, and the following points should be noted: (1) If the gear is made coarser or the angle of action of the gear is increased say from 14.5 to 20° there is more tendency to push the gear about on the splines, and if it moves it may creep in or out of gear according to the circumstances, which seems rather difficult to foretell. (2) To keep it as still as possible on the splines the length of the serrations should be balanced and symmetrical on each side of the teeth. We think there is no advantage in cutting this length down and it may be that it would be better to keep it as long as is practical. (3) In cases of difficulty the splines themselves might be acme form or even Vee serrations, so that the torque would tend to centralise the wheel. (4) We pointed out to DA{Bernard Day - Chassis Design}/HDY.{William Hardy} that gears running on a smooth shaft (most reverse gears) may have a tendency to creep in or out, but in this case of a smooth stationary shaft the force exerted would only be small compared with any force due to epicyclic action, (as becomes the case with a serrated shaft,) or a wheel revolving with its shaft, in which case it depends largely upon the bore being parallel, whereas in the case of a reverse pinion running on a stationary shaft it is a question of the several shafts being parallel, and the extremely heavy force exerted with epicyclic rolling has been experienced with long roller bearings. (5) As regards the synchronous mesh gears I have written in another memo. that these should be tested as worn gears with slack before we can rely upon their driving sleeves not creeping in or out. Gear creep is dangerous because it throws excessive load on the corners of the teeth, and it may be that in some cases unless the gear is pushed central it will have a tendency to work out, and I think for this reason we have in some cases endeavoured to make it creep inwards under load. We see no reason why if creeping inwards the creep should not be limited by the gear coming up against a collar on its shaft. The control gear must be sufficiently accommodating to permit of th'. R.{Sir Henry Royce} | ||