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 memo detailing ratio limitations and clutch design considerations for the Cotal Gearbox.
| Identifier | ExFiles\Box 136\2\ scan0290 | |
| Date | 2nd August 1940 | |
| To Rm.{William Robotham - Chief Engineer} c. to Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/FJH.{Fred J. Hardy - Chief Dev. Engineer} Ev{Ivan Evernden - coachwork}/Tln.2/JH.2.8.40. Cotal Gearboxes. We give below for future reference, all we know about the Cotal Gearbox. (1) Ratio limitations. The ratios of the indirect gears cannot be independently chosen. The smaller the car and the lower the 1st. speed ratio, the more unsuitable are the intermediate ratios. For Myth (PL.232) we chose these ratios :- Direct 1.000, 3rd. .671, 2nd. .420, 1st. .243. On the Cotal box we may choose :- Direct 1.000, 3rd. .671, 2nd. .362, 1st. .243 or :- Direct 1.000, 3rd. .578, 2nd. .420, 1st. .243 or compromise with Direct 1.000, 3rd. .625 2nd. .389, 1st. .243 In this last case 2nd. and 3rd. are both 7% lower than we desire. (2) Economical radius for magnetic clutches. The large outside diameter of the Cotal box is a great disadvantage when accommodating the box in a motorcar; and we shall suggest later that it may be possible to reduce the diameter of the gear trains. For these reasons it was desirable to know in what way this design of clutch was dependent on the mean radius of the clutch. An approximate analysis showed that for a given torque capacity, the combined weight of copper and iron in the clutch increases very rapidly with reduction in mean radius. Thus it is very important to keep up the diameter of the Cotal box in order to keep down its weights. | ||