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).
The results and methodology of starter motor brake efficiency and static torque tests.
| Identifier | WestWitteringFiles\G\June1921\ Scan55 | |
| Date | 22th June 1921 | |
| RR-STARTER MOTOR BRAKE TEST RESULTS. ORIGINAL EFCL/T22.6.21. r To R & E.{Mr Elliott - Chief Engineer} from EFC. c. to CJ. & PN.{Mr Northey} c. to En. & Ev.{Ivan Evernden - coachwork} c. to EP.{G. Eric Platford - Chief Quality Engineer} & De. c. R.R. of America Inc. X.3082 - R.R. STANDARD STARTER MOTOR BRAKE x3009 EFFICIENCY TESTS. We are now sending you curves of brake efficiency and static torque tests of the R.R. standard starter motor. There are four sheets of curves. Three sheets refer to one of the standard type starter motors built up in the Expl. Dept. early on. The remaining sheet of curves refers to a brake efficiency test taken on a starter motor borrowed from production about August, 1919. These results were taken some little while ago now but we have only gradually been able to get them into a condition for issue. In the case of the curves (blue prints) referring to the brake efficiency test of the experimental motor, these are given on both torque and speed bases, but later we have decided that curves of this nature on a speed base are unnecessary as the whole performance of the motor is very well shown by curves on a torque base arranged in the present manner; we have accordingly made this manner our standard for showing the performance of various starter motors. The motors were tested with the epicyclic gear in place and a large brake wheel of 24" diameter. The figures for the torque base referred to were obtained from the actual torque on the brake wheel by dividing by 6, and therefore do not (owing to the slight inefficiency of the epicyclic gear) represent exactly the motor torque, but what the motor torque would be if the gear were 100% efficient. Hence in applying these curves in any particular case, we need only allow the efficiency of the remainder of the reduction to the engine. ✓ We judge that in the motor epicylcic reduction gear there is 3% lost torque, in the chain drive another 3% loss, in the epicyclic reduction gear on the gear box another 3%, and in the 3 to 5 step up in the gear box and the remainder of the transmission 4% loss, so that the efficiency from motor armature to engine is 87%, but from motor chain wheel to engine 90%. Since the speed ratio is 23.3 to 1, the effective overall torque ratios comes out as 20.2 to 1, and the torque ratio to be used in applying the curves is 21.0 to 1. Contd. | ||