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).
Article from 'THE AUTOCAR' magazine explaining the workings of a magneto with diagrams.
| Identifier | ExFiles\Box 4\5\ 05-page034 | |
| Date | 2nd November 1912 | |
| THE AUTOCAR, November 2nd, 1912. 791 How the Magneto Works. must be taken not to drop it, otherwise the shock may demagnetise the magnets. "The magnets are not likely to fail on the road?" "No. That is practically impossible. After two or three years' running the magneto would probably be improved by being remagnetised. It is best to return it to the maker's, as they will make a thorough job of it." Fig. 2. - Complete end view of a Simms magneto with the cover plate and armature removed. "I have heard that it is bad to let water or oil drop on the magneto. Will these affect the magnets?" "No. Only a blow and long usage will demagnetise them. The objection to allowing water to have access to the magneto is that it may leak into some of the mechanical parts other than the magnets. But water on them does not have any effect, and you cannot obtain a shock by touching them." "I see there are two magnets in these magnetos. Is that always the number used?" "No, the number varies. The power of the magneto depends to a certain extent on the strength of its magnets, and the strength of the magnets varies with their surface. Thus, if a magneto to give a powerful spark at low speeds is wanted, there may be more than two magnets, and they are arranged on top of one another or side by side. These medium-powered magnetos are fitted to medium-powered cars, but for big engines which cannot be started quite so easily a bigger magneto is necessary. When once the engine is started the smallest magneto will work as well as the biggest one. The advantage of the large one is only obtained at low speeds and at starting." Now this magneto from which I have removed the armature (see fig. 2) shows the arrangement of the magnets very well, and also the brass base to which they are attached. "What are those curved blocks attached to the magnets?" Fig. 1. - The armature of a Simms magneto. "They are what are termed the pole pieces. They are merely used to fill in the space between the armature and the magnets. The important part of the magneto is the armature (fig. 1), and you will do well to examine it closely. You will find it is fairly heavy, being practically all of metal. It is slotted out at the centre, and in the slotted part is arranged a lot of wiring carefully wrapped up in silk and varnished so as to be rendered waterproof." "Yes, but all those wires are out of sight, and if anything goes wrong with them I am hung up." "It is practically impossible for anything to go wrong with the armature. As you will see, the wires are very carefully protected, and are to all intents and purposes solid with the armature. They cannot move and they are wonderfully protected. I have never known of an armature failing, so you can really ignore the composition of it. As a matter of fact, the actual winding of it is rather a complicated process, but is one which need not bother you. In the very remote possibility of an armature going wrong it will be outside the capabilities of almost any repairer to put it right, and the only thing to do is to return it to the maker's. As I say, I have never known one to fail, so you need not consider it as a possibility in your case." Fig. 4. - Diagram showing the usual order in which the cylinders fire, i.e., starting next to the radiator, 1, 3, 4, 2. "Then I do not require to know the actual construction of the armature and why it is constructed in this special manner?" "No. If you did, that knowledge would not help you at all towards looking after the magneto, as it is knowledge which would be of no use to you as a motorist. If you were going to undertake the repair or construction of magnetos, then, of course, an intimate knowledge of all the details of the armature would be essential. All that you require to understand is that, when the armature is revolved in its place between the magnets, a current is generated in that bundle of wires. You will see that one end of the wires passes out at the point we will call X. Although one cannot actually see it, the wire X is attached to a brass ring which is called the slip ring. Each side of the ring is a fibre disc. Outside the fibre disc is arranged a ball bearing, while at the other extreme end of the armature spindle is another ball bearing, and between this and the armature is a gear wheel. All these parts revolve with the armature, which is, of course, supported by the ball bearings. The ball bearings run in ball races carried by the end plates, which are fixed to the base plate (see fig. 2)." | ||