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).
Testing of various servo lining materials, like Halo and cotton duck, to improve braking efficiency.
| Identifier | WestWitteringFiles\T\2July1929-December1929\ Scan058 | |
| Date | 21th September 1929 | |
| ORIGINAL To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/En. c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} c. to Sg.{Arthur F. Sidgreaves - MD} Hs{Lord Ernest Hives - Chair}/Bm.1/HW.21.9.29. x7370. In connection with the S.S. we have done a considerable amount of work on servos. It will be remembered that we were originally troubled with the S.S. servo efficiency falling off when the car had been on the road some little time. We traced this to the variation in the coefficient of the Halo with temperature. We therefore tried various other materials for a servo lining with a view to overcoming the disadvantage of Halo. We find that a cotton duck lining without any impregnating material gives good results for the light duties called for. It also appeared to be more consistent in operation than any materials that were impregnated. Our only trouble has been a slight tendency to squeak, which is not very easy to overcome. We made a further test on this woven cotton fabric, soaking it in oil. Normally, if an impregnated lining is soaked in oil it becomes gummy and gives inconsistent results. The woven cotton fabric however, gives remarkably smooth and consistent braking when it is oiled. The cam angle on the servo, has to be altered to make up for the drop in coefficient of friction. On the attached graph, curve (2) illustrates the servo we have standardised. Curve (1) similar servo having a lining soaked in oil. curve "B" the oil soaked servo | ||