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).
Braking systems, comparing servos for the Spectre and Phantom models, and proposing improvements.
| Identifier | ExFiles\Box 92\4\ scan0021 | |
| Date | 29th October 1934 | |
| -2- Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}1/KW. 29.10.34. The SpectreCodename for Phantom III is a luxury car and comfort of the rear passengers dictates less violent braking we recommend therefore reverting to the Phantom arrangement, but consider it essential to have a servo no smaller than the Phantom II. Reference to former memos, read "The reason we have had such difficulties with the S.S. brakes is due to the servo being smaller than on the Phantom I". The Exptl. Dept, complained bitterly of the Peregrine servo and have always wanted a bigger one on the 20/25. The Phantom II overall ratios, servo size and cam angles should provide good brakes. We realise, in asking for a system in which the front to rear ratio is dependent on servo output and therefore temperature, that this is inconsistent with recent memos. In order to maintain as near as possible a constant proportion of front and rear braking, the ratio of servo braking to direct braking should be as high as possible. A large torque multiplication is better obtained by an increase in servo size rather than cam angle, since there is a greater area of cooling and less losses through mechanical inefficiency. We have been measuring servo temperatures on the road and a separate report is attached of the results obtained. We know from the Repair Dept. that they have little trouble from the 40/50 servo and a considerable amount from the 20/25. If it is impossible to use a larger servo we recommend a multiplate one on the lines of the Peregrine, the connection between the driving members being of course by a "crinkly plate". We do not think that for a coefficient of 0.3 the torque multiplication should be less than 4. We think also we ought to try hydraulic brakes to the front, in conjunction with mechanical to the rear. Failure of the hydraulic part would not render the foot braking entirely inoperative, and need not prevent servo braking to the rear if we have a stop in the front mechanism. | ||