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).
Optimal gear ratios and performance for a C.A.V. starter and a Liberty dynamo.
| Identifier | ExFiles\Box 37\2\ scan 105 | |
| Date | 22th December 1920 | |
| X.3306- To EP.{G. Eric Platford - Chief Quality Engineer} from EFU. EFC3/T22.12.20. X 3247 (crossed out) X 3306 RE C.A.V. STARTER & LIBERTY DYNAMO. We make out that the best gear ratio for the C.A.V. starter, operating upon 6 volts for the torque you require, would be 12 : 1 or 14 : 1. These two ratios give the same efficiency, but the 12 : 1 gives more power and takes more current from the battery. We estimate that the 12 : 1 ratio will take 87 amperes and drive the engine at 90 R.P.M., but the 14 : 1 will take 82 amperes and drive the engine at 84 R.P.M. These figures are, of course, on the assumption of the torque which you have given which seems rather lower than we should have thought. With reference to the Liberty dynamo, this puts up 6 volts at 650 R.P.M. in the cold condition, or 6.3 volts (balancing volts) at 660 R.P.M. in the hot condition 76°C. These figures must be increased by 100 R.P.M. The regulator can readily be altered to suit the lower voltage. EFC. | ||