MAGNETIC MAKE-AND-BREAK SYSTEM
Fig. 19.—Magnetic Igniter.
Fig. 20.—Wiring Diagram of Magnetic Igniter System.
The flaming spark produced by the make-and-break system has many advantages for ignition over the jump spark produced by the high-tension system, but these are largely offset by the mechanical complication of cams, tappets, springs, etc. A make-and-break system in which the igniters are operated by magnetism has been perfected by the Bosch company, and is giving good results. The magneto used is of the ordinary low-tension type, equipped with an interrupter, while all of the igniter parts are contained in a plug that screws into the cylinder wall like a jump-spark plug. The plug is shown in diagram in Fig. 19. The sleeve that screws into the cylinder supports an iron core, the two being thoroughly insulated by blocks and washers of heat-proof insulating material. The upper portion of the core has a flat side, on which is formed a projection that serves as a pivot. A hammer bar is balanced on this pivot, its long end passing through the plug and coming into contact with an anvil attached to the screwed sleeve. A long horseshoe-shaped spring holds the two in light contact, and the hammer bar then forms the only path by which an electric current may pass from the core to the screwed sleeve and to the engine ground. When the hammer bar is moved on its pivot this connection is broken. Surrounding the core is a coil consisting of a few layers of wire covered with heat-proof insulation. The upper part of the plug is incased in a light iron casing screwed to the core, which completely incloses the core, hammer bar, spring and coil, and in which there is no opening that would permit the escape of compression from the combustion chamber. One terminal of the coil is connected to the binding post, and the other is grounded on the iron casing. The current generated in the magneto passes to a distributer and thence to the binding post of the plug, as shown in Fig. 20. It flows through the coil to the core, and thence by the hammer bar to the engine ground and back to the magneto. As the current establishes itself in the coil, the core becomes magnetized, and attracts to it the flat end of the hammer bar. When the hammer bar moves on its pivot, its connection with the anvil is broken, and this break in the circuit produces a flaming spark that is in every way identical with the spark of the ordinary mechanical make-and-break igniter. The casing that contains the coil may be unscrewed from the core without disturbing the screwed sleeve, and this makes it an easy matter to give the moving parts the inspection and cleaning that they should receive every few weeks. The spark occurs in the plug at the instant that the interrupter operates, and the setting up of the system is identical with that of the high-tension magneto systems.