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).
Potential improvements to gearbox and synchromesh design, including suggestions for a 4-speed configuration and adopting Packard's designs.
| Identifier | ExFiles\Box 94\2\ scan0082 | |
| Date | 23th November 1936 | |
| -2- As regards the internal mechanism of our gearbox, we can say that we ought to try a non-positive" synchromesh arrangement. We cannot make the present operation much lighter, and do not think that the fact that the non-positive type can be crashed by brutal changes will matter. We consider it of greater importance to have more driving length of splines. We were forced to the present top and 3rd gear sliding piece owing to the design of our synchro-mesh which has been copied on all boxes from the first 20/25 synchromesh box. We advocate rearranging the synchromesh so that the dogs of the sliding pieces do not overhang the splines, and these latter are of generous proportions. It should not then be necessary to correct an already expensive article which comes out of mesh with further complicated couplings, as we have had to do on both the 3rd and 2nd speed couplings on P.III. We now come to the question of justifying a 4-speed box chiefly on the grounds that it would be a retrograde step to have only 3 speeds. We suggest that 4 speeds would be of more use to the driver if they consisted of an ordinary 3 speed box and then an indirect higher gear giving about .75 of the present engine revs. The axle ratio would be unchanged and the direct top exactly as it is now. For fast driving the indirect top would be pleasanter owing to less engine fuss, and give a more economical consumption. The difficulties we have at present in balancing the parts that cause roughness are so great that we recommend designs are put in hand now of a unit construction box, containing synchromesh and sliding coupling arrangement, an exact copy of the Packard, and we suggest the gear ratios should be those outlined previously in this memo. Further we think that serious consideration should be given to the loose pinion mounting used by Packards to see whether we could not copy this at a reasonable cost. It cannot develop any play, the gear must run true, and there are no bushes to seize; all very useful assets. Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} | ||