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).
Secret memo discussing design calculations, problems, and theories related to four-wheel brake systems and servo assistance.
| Identifier | ExFiles\Box 182\M20\M20.1\ img015 | |
| Date | 4th April 1924 | |
| TO BA. & E.{Mr Elliott - Chief Engineer} FROM R.{Sir Henry Royce} S E C R E T Copy to - RG.{Mr Rowledge} RH.{R. Hollingworth} HS.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. 49940 FOUR WHEEL BRAKES. RG{Mr Rowledge}'s memo. is disappointing about the above. In the new design there should be no doubt about brake coming off even with 35º thread or inclined faces. There should be no difficulty in getting about 3 to 4 times the output in energy from the servo; but we must bear in mind that our pedal lever (input) travels 2" while the servo pin travels 3" so that if torque from servo were twice pull from pedal we ought to get total of 2" X 1 = 2 plus 3" X 2 = 6 total ~~output / input = 6 / 2 = 3~~, or 4 times, which I should say was too much for safety. I should prefer this to be 3 times - i.e. one third braking without servo. Many times I have asked if servo is fitted with bonded or other Ferodo as the co-efficient seems to be 2 to 1. I assume that co-efficient does not alter with pressure. The results I have shew that it does not materially vary with rubbing velocity, but does twice the pressure produce twice the friction? RG.{Mr Rowledge} says we have made no progress with improving the protection of the operating parts on the front brakes against mud. Surely we can at once do all that is possible and at least make them as good as the back brakes. There are six good draughtsmen at WW. yet one hears nothing is done. RR Regarding jaggers, RG.{Mr Rowledge} reports that these have reappeared. I do not know on which car. I understand that if the front brakes were put on principally by servo which was running proportionately slowly - i.e. speed X angle, same as Hispano, there was no further trouble, and this was our second reason for using the slow speed servo. Has this theory been exploded? We have had various theories. (1) Spring control of axles. This may be so but against this we have thousands of other cars, all the best makers, and our own Goshawk back axle. (2) Wind on and wind off. We never had wind on (Packard has in one model I saw yesterday). Wind off has been tested I understand, and proved no advantage (might be confirmed.) (3) Ferodo material having co-efficient varying with speed. The sheet sent me shews this to be insufficient to be of any serious harm, but it may vary in many samples, or when new. (4) My long rigid shoe theory, although shortening the shoes seemed to cure the trouble, it however was reported to be so because it destroyed the efficiency of the brakes. (Semi-flexible shoes, shorter shoes, and floating fulcrum should again be tested) (1) | ||