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).
Car electrical ignition work, focusing on coil design and spark plug settings.
| Identifier | ExFiles\Box 178\3\ img130 | |
| Date | 5th April 1932 | |
| HS{Lord Ernest Hives - Chair}/WST. ) FROM R.{Sir Henry Royce} (At Le CanadelHenry Royce's French residence.) Sent from WW. 5.4.32. R/M/4.32. X3199 CAR ELECTRICAL WORK - IGNITION. I was not in favour of increasing the secondary turns on the coil because of increasing the risk of breakdown of the insulation of the coils and H.T. distributor, but thought those in contact with the work could judge better. Our car here with the special coil has been missing exactly like the London trials car, so that I had the plug electrodes scoured to remove the oxide, and the points put nearer together. They had been set by someone at .025 which is always too great for modern compression. I prefer .015 to a maximum of .020" - average = .018". Again this matter should be carefully examined because it is only at slow speed, full throttle, that the trouble occurs, and it seems to me that it is either leakage in the H.T. distributor over the surface of the insulation, or a spark jumping from say the rotor tail to the wrong cylinder. Dodd says he can hear a noise like a spark. Another possibility is mutual induction between the wires, and also it has occurred to me that the length of the secondary spark may be less at slow speed owing to the slow break at the L.T. contact maker, or the heating up of the ballast resistance. Now it is of no use my spending energy on this subject unless these notes bear some fruit. We know many reasons for lowering the safety margin, but the cause of this slow speed failure has never been found and reported. In the case of the new coil I cannot theorise on the magnetic circuit, but I should like many proportions of area and resistance of air gap investigated. Comparisons will even then be difficult to draw conclusions from. We all know that more section at a lower density means less hysterisis losses, so that increasing the section should be good, but decreasing the reluctance of the air gap may be good or bad. In the old days coils to give long sparks always had open magnetic circuits, but now transformers always have closed circuits, though it may be that many turns of wire are more efficient than a greater magnetic flux and fewer turns, for our purpose. R.{Sir Henry Royce} | ||