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).
Bench test results and on-road performance of the 'SS' servo leverage.
| Identifier | WestWitteringFiles\T\2January1929-June1929\ Scan026 | |
| Date | 12th January 1929 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} c. to BJ. SG.{Arthur F. Sidgreaves - MD} c. to Wor.{Arthur Wormald - General Works Manager} DA.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} ORIGINAL Hs{Lord Ernest Hives - Chair}/Rml/LG12.1.29. X7370 'SS{S. Smith}' SERVO LEVERAGE. We have now carried out bench tests to determine the efficiency of the SS.{S. Smith} servo. We give you the results herewith compared with some figures we obtained when we were developing the Phantom servo. It will be observed that the average torque multiplication of the SS.{S. Smith} servo is only 1.43. As all the calculations for the leverages on N.sch.2539 assumed a torque multiplication of 2.5, we think that the very much lower measured output of the servo explains why we have had to alter the leverage on our experimental cars to get adequate braking. The effective co-efficient of friction for this servo giving a torque multiplication of 1.43 is no more than .16 which is even lower than that obtained on the 20 HP. servo but is about what we anticipated from the behaviour of the brakes on the road. We have had three 'SS{S. Smith}' cars running on the road for considerable distances and all the brakes and servos have confirmed the original characteristics. The only variation therefrom has been in wet weather when the rear brakes have become inefficient through the error, now rectified, in the mud-shield. All the experimental cars at present are running about with the servo output doubled by 30° cams but the input to the servo and the direct braking reduced 25%. contd :- | ||