GB606186A - Improvements in or relating to a combined spark plug and transformer - Google Patents

Abstract

606,186. Transformers. BENDIX AVIATION CORPORATION. Aug. 1, 1945, No. 19789. Convention date, July 1, 1944. [Class 38 (ii)] [Also in Group XXVII] The invention relates to a combined transformer and sparking-plug in which the tubular metal body of the plug and a tubular metallic shield connected thereto form an enclosure, an electrode assembly includes an insulator in which the central electrode is mounted and the transformer consists of an inner tubular core of magnetic material carrying first the secondary and then the primary windings. The primary and secondary windings extend into an annular space around the outer end of the insulator forming part of the electrode assembly. The inner tubular core surrounds the outer end of this insulator. As shown, the transformer comprises a secondary winding 28 and primary winding 29 within a shielding barrel 24 which forms an extension of the sparking-plug body 10. The insulator 18 for the central electrode extends upwardly into the centre of the transformer. The secondary winding is wound around a magnetic core 26 which comprises a few turns of sheet metal and an insulating layer is provided between the core and the winding. The several layers of the coil are separated by thin layers of insulating sheet material. A further insulating layer separates the outside of the secondary winding and the primary winding and still further insulating layers are provided between the outside of the primary and a split magnetic sleeve which surrounds it and between the sleeve and the shielding barrel. One end of the secondary winding is connected to the adjacent end of the primary winding while the other end of the secondary 34 is connected to a terminal 40 which is in contact with the central electrode. One end of the primary is connected to the earthed body of the plug and the other to a terminal 36 arranged to be connected to a high tension supply lead. The terminal 36 is mounted in an insulating bush 39 at the upper end of the barrel. The barrel carries a member threaded externally'for receiving a union for holding the high-tension lead and its screening conduit in position. The magnetic sleeve is split longitudinally to avoid providing an easy path for eddy currents around the coil. The whole of the interior of the shielding barrel may be filled with an insulating compound such as polymerized cashew-nut-shell oil and a drying agent as described in Specification 549,580, [Group XXVII]. The filling may be done under pressure or vacuum. The layers of insulating material are suitably of woven glass fibre cloth impregnated with silicon. To assist the insulation the core 26 may be coated with enamel. The invention is shown as applied to a sparking- plug of the type disclosed in Specification 586,014, [Group XXVII].