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).
Comparing the mechanical efficiency of Girling and Bentley brake system cams.
| Identifier | ExFiles\Box 120\3\ scan0125 | |
| Date | 3rd January 1935 | |
| To E.{Mr Elliott - Chief Engineer} from HA/AFM.{Anthony F. Martindale} c.c. to WGR. c.c. to Ey. c.c. to Da.{Bernard Day - Chassis Design} Mechanical Efficiency of Brake System Components - Girling Cams. Further to our memo, Ha/AFM.{Anthony F. Martindale}4/KW.21.12.34, we are now in a position to supply data as to the efficiency of Girling cams. Various tests have been carried out, the results of two of them being attached in graph form. They are - (1) Efficiency of Girling cams with brake drum in position. (2) Efficiency of Girling cams measured against spring loaded clamp. The first of these affords a comparison with the test carried out on Bentley cams, a comparison graph being supplied herewith. While this test gives a good picture of what occurs when the brakes are being used on a car, it is thought to give a distorted picture of the mechanical efficiency of the cams themselves, and accordingly the second test was performed. The efficiencies recorded by this method are much higher, and are approximately constant at 87.5%, this figure agreeing closely with the calculated efficiency assuming normal frictional coefficients. The comparison of Girling and Bentley efficiencies shows the Girling system has a considerable advantage in this respect; but there is another aspect of the Girling brake that is distinctly unfavourable. It will be noticed that the "sponge" measured in experiment (1) is 43 thousandths, (the position of the clock is given on the graph); the total travel of the clock is only 125 thousandths; and that the clearance for two shoes at this radius is 47 thousandths, the residual available travel being therefore only 35 thousandths. | ||