GB199879A - Improvements in or relating to induction coils - Google Patents

Abstract

199,879. British Lighting & Ignition Co., Ltd., and Turner, E. O. April 26, 1922. Transformers.-Induction coils, particularly intended for use as ignition coils for internal-combustion engines, are made with a nearly closed magnetic circuit, one or more air gaps being provided of a size just suflicient to ensure a low value for the idle flux and quick demagnetization on breaking the primary circuit. The theoretical considerations governing the dimensions of the gaps are discussed in the Specification, and it is shown that the total length of the gaps should not be less than 2.5 or more than 60 times the ratio of the length of the iron path to the maximum flux density developed at an air-gap face. A single gap in the middle of the core on which the coils are wound, or a central gap with additional gaps at the ends of this core, may be provided. In another arrangement, Fig. 1, gaps e are left between the central core a and the lateral cheeks d, d<1> and connecting members f, f<1>. In modifications of the arrangement the gaps are left between the central core a, and the lateral cheeks, the central core in some cases passing through holes in the cheeks, as shown in Fig. 10. In the arrangement shown in Fig. 6, the gaps e are formed between overlapping members g, g' secured to the central core a. The opposing faces of the air gaps may be so arranged that the flux passes across the gaps in the plane of the laminations composing the core.