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 note on servo efficiency, comparing the coefficient of friction (μ) for various models and its impact on brake proportions.
| Identifier | ExFiles\Box 95\4\ scan0155 | |
| Date | 2nd March 1938 | |
| To Da.{Bernard Day - Chassis Design} from Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} c. Hdy.{William Hardy} c. Sy/TAD. c. By/JRL. 341 Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale}7/MH.{M. Huckerby}2.3.38. SERVO EFFICIENCY. A few years ago, if we fitted a servo with discs having a coefficient of friction of 0.38, measured the ratio input/output, calculated back to find μ assuming 100% efficiency, μ appeared to be 0.30. If we do the same thing on a modern servo, either Ph.III, Wraith or Bentley 'M' Series, the apparent μ is 0.36. We think you ought to have this figure as it affects the calculated front/rear brake proportions. We have linings now which have apparent μ values of 0.31 or 0.40, which we use if desirable, but it is safest to assume μ = 0.36 in original designs. In obtaining these figures the strength of the servo push off spring has to be allowed for. The Bentley 50 servo may have a lower efficiency to begin with, but this will very likely rise again. We send this note because on GCD.457 you assume μ = 0.30. Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale} | ||