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).
Magneto design, comparing revolving armature with revolving magnet types like the Scintilla.
| Identifier | ExFiles\Box 4\5\ 05-page279 | |
| Date | 29th May 1924 | |
| Contd. -4- 29.5.24. compromise in which the magneto is capable of satisfactorily coping with only moderately leaky conditions. This higher voltage requirement necessitates particularly good insulation of the secondary winding, especially in the last few layers, in fact insulation of such a degree that is not easy to attain in an ordinary revolving armature type magneto. For this reason it is thought that the magneto to be developed along these lines will be one in which the permanent magnet is the revolving element, the armature being stationary. It is possible in that case to use an automatic advance mechanism housed between the poles of the revolving magnet and operating as previously suggested only upon contact breaker and distributor. The magneto known must nearly to approach the present suggestions is that known as the Scintilla, though the machines which we have tested do not come up to our tentative specification in a number of respects. The principal respect in which the Scintilla falls short, is that there is no means provided in this magneto for rendering the low sparking speed at retard at least as good as the low sparking speed at advance. In fact it is considerably worse and nowhere near as good as the 190 r.p.m. which we specify, and which figure we may say can be taken as quite definite, with very little possibility of modification. If only a comparatively short range of total advance were required, the absence of such a means would not be such a serious matter as the most suitable timing range of the magneto could be selected from the total available range. Our remarks, however, regarding the Scintilla, refer only to the range provided by the makers, which range is itself considerably less than that for which we ask in the specification. Hence, there is all the more necessity of some such means of equalising the time functioning of the magneto for different positions of advance (hand and automatic). Another point about the advance mechanism housed in the magneto is that it is altogether much neater to have the whole thing in one unit. Then again, it is doubtful as to whether very much room could be allowed for external automatic advance mechanism, so that it might suffer from being stinted in this respect. Contd. | ||