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).
Starter motor to engine gear ratio, questioning the proposed 32 to 1 reduction.
| Identifier | ExFiles\Box 64\1\ scan0108 | |
| Date | 20th March 1923 | |
| (Handwritten: X8620) SECRET To E.{Mr Elliott - Chief Engineer} from EFC. c. Ry. EFC3/T20.3.23. E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. X.9660 - STARTER MOTOR. (Handwritten: X4383) Referring to E1/M28.2.23, we are surprised that the ratio of starter motor to engine is fixed as high as 32 to 1. - the 40/50 being 23.3 to 1 and the Goshawk 8.4 to 1. This means that unless the motor is designed for high speed, heavy current, and quick acceleration, there may be some difficulties with the starting gear. We should like to turn the engine at 75 R.P.M. but this implies a motor speed of 2400 R.P.M. The quantities on the 40/50 for rolling condition, with the engine normally cold, we consider to be:- Engine torque 1085 lb-inches. Transmission efficiency 85% (Handwritten note: (Chain wheel to engine)) Motor torque 55 lb-inches Motor speed 1030 r.p.m. Engine speed 44 Amperes 111 Motor efficiency 64%. (Handwritten values aligned with the above list: 1085, 85, 55, 980, 42, 120, 57.5%) In adopting a 32 to 1 reudction ratio we consider we are going to a further extreme than on the 40/50 and it is queried whether this is intended. If, on the other hand we keep the engine speed and the motor speed lower, as we do on the 40/50, we are not really (as on the 40/50) using the weight of material in the motor to anything like its full capacity. If this reduction ratio of 32 to 1 is quite in order, we would like you to say at what speed the motor should Contd. | ||