Patent GB-452445-A (GB)
Title: Improvements in and relating to magnetos
IPC: H02K21/14
Filed: 1935-02-22
Abstract: 452,445. Magnetos. SPOHN CORPORATION, 19, Dover Green, Dover, Delaware, and SPOHN, M. E., Sidney, New York, both in U.S.A. Feb. 22, 1935, No. 5714. [Class 35] [See also Group XXXVII] A magneto comprises a number of rotor magnets each extending or having its poles spaced in the axial direction of the rotor with like poles connected at the ends, and a stator core extending or having its ends spaced in the axial direction with its pole-shoes located adjacent the paths of the rotor poles. The magneto is particularly suitable for ignition in multi-cylinder internal - combustion aircraft engines where two or more simultaneous sparks are required in each cylinder. Fig. 1 shows a machine adapted to be driven at half engine speed to give two sparks per cylinder in a nine cylinder engine. The bar magnets 2 are mounted parallel with the shaft 4 and are secured thereto by non- magnetic spiders 20, 22. In this form, all the magnets are arranged with their like poles at the same end and connected together by rings 6, 8 and 10, 12. Each ring is continuous at its inner periphery but is cut back at its outer periphery to form gaps between successive poles. Between the rings, laminated pole-shoes 16 are provided for each magnet. The rotor assembly is secured by bolts 38. Alternatively, die-casting may be employed to reduce the number of separate parts. Two stator elements are provided comprising axially disposed cores 52 and pole shoes 54, 56 perpendicular thereto held between the main end plates 40, 42. The arrangement is such that each rotor magnet will co-operate with each stator element to complete an independent magnetic circuit. The magneto housing is completed by lateral plates 76, 78 forming segments of a cylinder and the stators and the condenser 62 are enclosed in light U-shaped metal plates 82, 83. The housing is rotatably mounted on a base 88 by which it may be attached to the engine so that the ignition can be retarded or advanced. The base 88 is formed with a rib 90 with which engages a clamping plate 94 having a circumferential recess to hold a spring 98 bearing against one end of the recess and against a projection on the base 88 extending into the recess. The spring acts to maintain the magneto in the advanced spark position and adjustment is effected by a lever 102 pivoted between ears 104 on the lower housing plate 42. The interrupter and distributer mechanism is directly connected to the magneto shaft so as to be driven at the same speed. An insulating ring 112 surrounding a hub 108 on the upper plate 40 carries a pair of disc sectors 114, 115 on which are mounted interrupter contacts operated by a nine-pointed cam 124 on the shaft. The disc sectors are individually adjustable on the ring 112 which is itself adjustable on the plate 40 by the use of screws passing through curved slots. The distributer carrier comprises an insulating member 142 mounted on the camhub 140 and enclosed in an insulating housing 144 which also carries two rings of relatively angularly and axially displaced contacts 156, 158 with their terminal sockets 152, 154 for connection with the sparking plugs, brushes 168, 172 connected to the secondary coils of the magneto and a brush for connection to a booster magneto for starting purposes. The carrier 142 has moulded into its upper surface contact rings and distributer fingers for connecting the contact brushes with the appropriate sparking plug terminals. A safety sparkgap is provided in a vacuum tube. In a modification, eight rotor magnets are disposed so that north and south poles. alternate at the ends. As shown in Fig. 10, like poles are connected together by laminated spiders 203, 204 and laminated spaces 205 of greater depth are provided to maintain the spiders out of contact with each other. Nonmagnetic end plates 206 hold the structure together. In this construction, the stator cores are diametrically opposite each other, the condenser is arranged between the primary and secondary windings on the core, and the distributer carrier is a flat disc with one ring of contacts bearing on its upper face and the other ring around its periphery.