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).
Servo efficiency tests, analyzing the effect of temperature on the coefficient of friction in brake linings.
Identifier | ExFiles\Box 141\3\ scan0314 | |
Date | 26th October 1934 | |
HR/PJH. 7/KW. 26.10.34. Servo Efficiency Tests. We are carrying out a large number of experiments on the Bentley and 20/25 HP. servo to determine the mechanical efficiency and the effect of temperature on the coefficient of friction in the linings. The experiments were originally begun for the purpose of finding the causes of the mechanical losses in the servo, but it was immediately found that the /u (coefficient of friction) of the linings fell considerably as the linings became hot. This made accurate friction loss tests impossible and, of course, is the principal cause of fading brakes on R.R. cars. A search was therefore begun for a lining material that would maintain its /u at high temperatures. The temperature attained by the servo under hard driving conditions on the road was measured by a thermo-couple in the part of the servo drum which runs between the two linings. The max. temperature was found to be 350°F.{Mr Friese} A method of testing lining materials on a rig was then evolved so that we could obtain characteristic curves of /u against temperature. Up to the present we have tried 22 kinds of servo lining without finding one whose /u drops less than 20% when hot and which is suitable in other respects for use on a car. The present standard RAD.13 material loses 47% of its /u when hot. The attached table is a summary of lining results so far obtained. Attached are also two curves which are representative of the behaviour of the linings. In the case of V.M.30 it can be seen that the lining has to be run in up to 350°F.{Mr Friese} and allowed to cool before its characteristic becomes stable. This is typical of most of the linings. In some cases the stable state is not reached till the 3rd or 4th run. If a lining is made slightly greasy when being stapled on to the pressure plate, the attainment of a stable characteristic is delayed by one or two runs. | ||