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).
Design issues and suggested solutions for a 4-speed gearbox.
| Identifier | ExFiles\Box 6\4\ 04-page039 | |
| Date | 29th January 1925 | |
| X.5310 AJS. Hs.{Lord Ernest Hives - Chair}) E.{Mr Elliott - Chief Engineer} DA.{Bernard Day - Chassis Design}} FROM R.{Sir Henry Royce} RG.{Mr Rowledge} TO c. to CJ. BJ. BY.{R.W. Bailey - Chief Engineer} SECRET. R4/M29.1.25. U. S. A.{Mr Adams} 4-SPEED BOX. X.5310 Trouble with gearbox is surprising. I telegraphed Derby some of my views. I do not take the wear of the teeth seriously, as in use the first and reverse are not used for any length of time in 20 years at full engine torque, but the second and third must shew a reasonable life, which I believe will be found on test, if the gears stay in position and are really hard. Naturally the logical way to increase the life is to increase the width, but my way is to increase the dia. of the smaller wheels, which is easier, and under the circumstances is desirable, because the 4 speeds would then be more useful as it will be found that the first is unnecessarily low, and it has been found that the third is rather too high, so that if the steps are smaller it may do much good towards curing the fault for the following reason :- The gears 2nd, 1st, and reverse, are reported to have a tendency to creep out. I think this is due to the load and especially the thrust between the shafts causing the gears to move on the splined shaft and move along the shaft. This may have arisen in this box because we are sliding gears which are only slightly larger than the shaft, so that the pressure on the keys is not enough to resist the thrust between the gears, especially if they are 20° gears, hence my advice to :- (1) Increase the dia. of the sliding gears (increases the bind) (2) Use 14° angle teeth which reduces the thrust pushing the shafts apart and tending to move the wheels on the shafts. (3) One might also try splines on the shaft thus :- [drawing of a spline profile] Instead of [drawing of a different spline profile] (4) The idea of chambering the bore is to prevent the risk of the wheel fitting in the centre and rolling about, thus :- [drawing of a chambered bore] Suggested chamber. Unfortunately it seems difficult to see how we can get the binding under the first speed pinion because the shaft is more flexible than the hub of the double gear unless we could make each pinion torsionally free, but this we could contd :- | ||