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).
Peregrine dynamo speed, addressing issues with high RPM operation, excessive brush wear due to sparking, and necessary ratio adjustments.
| Identifier | ExFiles\Box 62\3\ scan0320 | |
| Date | 25th January 1933 | |
| X6005 To R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} c. Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} By.{R.W. Bailey - Chief Engineer} [Text has a line struck through it] HS{Lord Ernest Hives - Chair}/West. By/RD. E.6/HP.25.1.33. [Stamp: RECEIVED XII I] [Stamp over text: 1938] Peregrine Dynamo Speed. When the Peregrine was first designed it was never anticipated that the engine would operate up to 5000 r.p.m. and the dynamo ratio was fixed at what we normally use - namely 1 1/2 times engine speed. Owing to the speed however of which this little engine is able to run without fuss on the lowest of the range of back axle gears produced for this chassis we have been led into rather high dynamo revs. Mechanically the dynamo has stood up very well. There has however been an undue amount of brush wear but this we attribute to sparking rather than increased rubbing speed. The experience of the Lucas Co. on dynamo brush wear is rather on the same lines as our own and confirms that excessive wear on the brushes on high speed machines is caused mainly by sparking. Messrs. Lucas have not much experience beyond the dynamo speed of about 4500, and their practice on small high speed engines is to run the dynamo at engine speed. They consider a brush wear of about .020 for 10,000 miles running quite reasonably good, but this is nearly twice what we should expect for the same distance on our own machines - actually the brushes wore about ten times the normal amount on the last Peregrine 10,000 mile test car. We have since found on the new high speed bench rig that the dynamo commences to spark badly at 5500, but does not seem to get much worse above that speed. We think it will be necessary to reduce the dynamo speed on the Peregrine but in fixing the new ratio we have to balance two opposing considerations one against the other, namely cutting in speed and maximum dynamo revs. With regard to cutting in speed, this must be made sufficiently early to satisfy the conditions of a car being used in town for shopping and theatre work in which the road speed is often very low and there is a considerable amount of parking. We know from experience what this cutting in speed should be. | ||