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).
Causes of ignition coil failure and potential design improvements.
| Identifier | WestWitteringFiles\V\October1930-February1931\ Scan207 | |
| Date | 15th January 1931 | |
| EFC. ) FROM R.{Sir Henry Royce} HS.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} ) (At Le CanadelHenry Royce's French residence.) C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} PN.{Mr Northey} IGNITION COILS. AS R.{Sir Henry Royce} UNDERSTANDS THEY EXIST. I presume that coil failure is not due to moisture being either in or on the insulation when the coils are being made, or moisture being absorbed by the insulation from the atmosphere which may happen at such a place as WW. during the autumn months. I also presume it is in no way connected with bakelite cases, as so surprisingly happened in the early days of this material. Our form of coil (outside secondary) has always been considered the best type for insulation, though not the most economical for the fine wire because the more expensive wire has the greater perimeter. It is usually thought that open magnetic circuit is best for an induction coil used under our conditions, but we originally (and still) made hedgehog ends as invented by J.{Mr Johnson W.M.} Swinburne 30 or more yrs. ago, but it may be that still nearer, or actually a closed circuit, may be better. The wireless coils of Ferranti may suggest something, but to make a series of experiments might be worth while to see if we could use less of the expensive fine secondary wire. Then we must assume that breakdowns occur through local or general breaking down internally of the secondary winding either between convolutions, or layers, or general perforation throughout the mass of the secondary insulation, often towards the ends of the layers commencing with the early ones. My impression is that every layer of winding is carefully insulated with a piece of oiled paper or silk; all these fit closely between the end flanges and have a lap of about .5". The longer the layer the greater the voltage towards the ends of the layers between the layers but one would have expected that the layer of oiled paper was ample for the voltage of 2 layers. I believe that we strain our coils more than others, because we use too large a spark gap in the plugs for the compression ratio we now use. I think this gap setting should be between .015 and .020, not .025 and .030", as the feeler gauges would suggest, because of the unavoidable oxidising occurring. I am very definitely not in favour of increasing the number of secondary turns because it would seem that we should be increasing the voltage and the tendency for the coil to break down. It would be far better to be content in case of miss-fires to reduce the distance between the points. (1) Handwritten/Stamped text: ORIGINAL (STAMPED) X6058 X918 EFC. | ||