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).
Investigation into indentation on the Phantom III Servo cams, identifying causes and proposing solutions.
| Identifier | ExFiles\Box 95\4\ scan0118 | |
| Date | 14th January 1936 | |
| To E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to Hdy.{William Hardy} c. to RHC.{R. H. Coverley - Production Engineer} 4341 Hs{Lord Ernest Hives - Chair}/PJH.11/KW.14.1.36. Phantom III Servo. When 32-EX was dismantled after the first 20,000 miles test the servo cams were found to have been badly indented on both the inclined surfaces and the thrust races at the ends. The indentations on the inclined surfaces corresponded to the off position of the brakes where there is no appreciable load on the cams. It was thought that this indentation wasdue to chattering of the cams while the brakes were off, due to relative movement between the gearbox and the brake pedal. This was known to occur on the Bentley where similar trouble with the servo cams has been experienced. Accordingly, on 31-EX, the second 10,000 miles test car, the standard brake pedal stop was removed and, in its place, a stop was fitted behind the inner scissor lever of the cams. The effect of this is to make the pedal pull off spring hold the cams stationary against this stop and the relative movement is accommodated by small movements of the brake pedal. When 31-EX returned it was found that there was no indentation of the thrust races and none on the inclined faces in the "off" position. There was, however, some indentation in the loaded position. The only explanation we can find for this is that, before the car started its test, some very heavy loads, approx. 275 lbs., were applied to the brake pedal for the purpose of measuring sponge, and in confirmation of this we have since found that this load does cause indentation of the cams. The position is, therefore, that there are two possible causes of indentation on Ph.III - chattering and heavy pedal loads. The former can be overcome by the altered position of the pedal stop and the latter, in all probability, by increased depth of casehardening or improvement of material. | ||