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).
Technical discussion on the reliability and design limitations of the De Normanville overdrive system.
| Identifier | ExFiles\Box 136\2\ scan0048 | |
| Date | 9th February 1939 | |
| c. Rm.{William Robotham - Chief Engineer} DE NORMANVILLE OVERDRIVE. With reference to Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls}7/MH.{M. Huckerby}7.2.39. and the remarks therein referring to what must be done to secure reliability of the hydraulic system, Da.{Bernard Day - Chassis Design} has called attention to the fact that complete reliability is not secured with our damper control system owing to foreign matter getting under the ball valves. Consequently we should prefer to use positively actuated piston valves in place of all ball valves for the gearbox control. Failure of the control pressure means not only the loss of the overdrive gear, but also that not more than top gear torque can be transmitted in reverse, unless we provide a stronger spring than is at present contemplated. Whether, with the use of piston valves, we could use filtered gearbox oil we cannot say, but it does not seem unlikely. Referring to the epicyclic gear train, we find that the planet pinions of the Warner overdrive are split into two lengths with a torsional spring between, apparently with the object of taking up slack in the teeth and avoiding rattles. De Normanville does not split the pinions, and whether we shall need to do this we do not yet know. It is rather more troublesome to us on account of the compounding we intend to have. The compound gear has another limitation in that the smaller gear of the two forming each planet pinion cannot be ground. However, it appears probable that we shall get sufficient silence with unground gears. Da{Bernard Day - Chassis Design}/Hdy.{William Hardy} | ||