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).
Improvements to the Phantom III gearbox, including comparisons to the Wraith model and potential design changes.
| Identifier | ExFiles\Box 94\2\ scan0202 | |
| Date | 13th April 1937 | |
| 328 Da.{Bernard Day - Chassis Design} C. Sg.{Arthur F. Sidgreaves - MD} Hs.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} Ev.{Ivan Evernden - coachwork} Rm.{William Robotham - Chief Engineer} E/HDY.{William Hardy}1/HP.13.4.37. Phantom III Gearbox. With reference to the suggestion in Rm{William Robotham - Chief Engineer}/96.3.37 from America that we should improve the gear change of the Phantom III by fitting a Wraith gearbox, we should like to remark that an unfavourable difference between the Phantom III and other cars is almost certainly mainly due to the inertia of the clutch plate and fabric coupling. The inertia is almost three times as great as on the Wraith. A reduction to 1.5 times would be made by the use of a 12" clutch disc as used on the large American cars assuming that the type of plate remained unaltered, of course. As regards the gearbox, theoretically the Wraith box is only better than the Phantom III by reason of 9° cones instead of 10° and a leverage of 6.35 instead of 5.65. Offsetting these is a smaller diameter of cone giving a net improvement of 10%. Both of the above improvements have been instructed for the Phantom III. The 9° cones were instructed on the 17.10.35, and have been referred to in memos by us three times subsequently, but are only now on test experimentally. They make an 11% improvement. We have not yet been successful in using the small angles found on some American and British cars without experiencing sticking of the cones. Instructions for increased leverage were issued by us on the 11.11.36 and are now, we understand, about to be tried. If the design of the new overdrive box for the Phantom III had been done by us we should have increased the cone diameter, and have recommended a gear lever travel of 4" into top and 3rd (Wraith has 3.5"). By these means we should have secured, with 9° cones, a total improvement of 53% compared with the standard box. If in addition we could use a 12" clutch disc we ought to secure an actuation very nearly as easy as that of the Wraith. E/HDY.{William Hardy} | ||