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).
Brake lining performance, servo characteristics, and mechanical efficiency tests.
| Identifier | ExFiles\Box 141\3\ scan0315 | |
| Date | 26th October 1934 | |
| -2- Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}7/KW.26.10.34. This shows the advantage of having the linings fully floating. However, we suspect that fully floating servos are more inclined to squeak than the old type in which the linings are stapled on and are not prevented from spreading outwards, and we intend to confirm this at a later date. This tendency to squeak is a serious disadvantage as the only linings with a constant /u of which we yet know are unsuitable because of squeaking. From the above results it is evident that a cooler running servo would be of assistance in maintaining a constant output. We are continuing the lining tests in an endeavour to find one with a constant or even a slightly rising characteristic. The servo is the one place in the braking system where a slightly rising characteristic is desirable as this would counteract the falling characteristic of the brakes. The brakes themselves definitely must not have rising characteristics. The efficiency tests carried out up to date have been done on the "direct to rear only" type of servo, and consist of a comparison of the spring ring torsional connection with the 3-pin connection and of the ball bearing bridge with the plain bridge bearing. The best way of showing the effect of the above modifications is by hysteresis loops. The results are shown on the attached Hs.{Lord Ernest Hives - Chair}1573. The hysteresis measured is that which occurs between the off side of the countershaft and the output lever on the servo shaft, so that it includes countershaft and cam friction. Both the spring ring and the ball bearing bridge cause a useful reduction of friction. The mechanical efficiencies are :- (1) Three pin and plain bridge bearing 67%. (2) Spring ring and plain bridge bearing 78%. (3) Spring ring and ball bearing bridge 84%. The remaining friction with the spring ring and ball bearing bridge is journal friction in the cams and the countershaft. We hope to do some further work on analysing and reducing this journal friction. Hs{Lord Ernest Hives - Chair}/F.J.Hardy. | ||