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).
Formidable challenges of the Spectre engine's battery ignition system.
| Identifier | ExFiles\Box 163\7\ img244 | |
| Date | 13th February 1934 | |
| Sg.{Arthur F. Sidgreaves - MD} From Hs{Lord Ernest Hives - Chair}/Wat. c. to Wor.{Arthur Wormald - General Works Manager} c. 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} 86184 Hs{Lord Ernest Hives - Chair}/Wat.2/MA.13.2.34. SPECTRECodename for Phantom III BATTERY IGNITION. The ignition problem on the SpectreCodename for Phantom III becomes formidable when it is realised that this engine will require twice as many sparks per minute as the Bentley. Thus at 5000 R.P.M. the rate of ignition will be 30,000 sparks per minute or 500 per second. The limitations to high speed working with battery ignition are as follows :- (a) The mechanical operation of the contact breaker. In order to keep the contact breaker contacts closed the whole period allowed by the cam, it is necessary to prevent flinging by reducing the moment of inertia of the contact lever about its pivot and by suitably designing the cam profile to produce minimum acceleration and decelleration forces at break and make. A cam and contact breaker which has given very satisfactory results was produced by E.{Mr Elliott - Chief Engineer} for the Bensport, but a number of preliminary experiments, which we have been conducting, shew that for the SpectreCodename for Phantom III ignition a still lighter contact lever with smaller spring pressure and other detail modifications will be required, and we understand the design Dept. have this matter well in hand. (b) The electrical characteristics of the ignition coil. Owing to the reduced time of make at the contact breaker at high speeds, insufficient time is allowed for the current in the primary winding of the coil to reach a value sufficiently large enough to produce a satisfactory spark at the plugs. | ||