Patent GB-617086-A (GB)
Title: Improvements in and relating to sparking plugs
IPC: H01T13/05
Filed: 1946-03-04
Abstract: 617,086. Transformers. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). March 4, 1946, No. 6656. [Class 38 (ii)] [Also in Groups XXVII and XXXVI] A sparking plug comprises a transformer mounted in its metal barrel, an insulating element about which the transformer secondary is wound, a core of magnetic material within the insulating element, means, including a spring clip for retaining the core in position and for connecting the secondary winding to a spark electrode insulated from the barrel, means for sealing the space within the barrel about the transformer for substantially maintaining a predetermined pressure therein and means for providing an electrical connection between an electrical conductor external to the sealed space and the transformer primary winding. As shown, a sleeve 16 is attached to a sparking barrel 12 by a connecting sleeve 14 screwed to the barrel at 13. The sleeve 16 houses a transformer comprising a primary winding wound on an insulating sleeve 22 mounted in the barrel 12, and a secondary winding 48 wound on an insulator 26. The sleeve 22 is secured to the ceramic insulator 19 of the sparking plug by cement 23. The sleeve may be of ceramic material or a heat hardenable plastic material such as thermosetting silicone resin. The ungrounded end of the primary winding is connected to a socket 27 moulded in the insulating member 26, the socket making connection with a plug member 29 attached to the end of a supply cable 31. The plug member 29 extends through an insulating member 30 formed of a heat hardenable resin. The upper end of the sleeve is sealed by a bushing 39 which is fixed by a nut 40, against a flange 38 of the insulator 26 and by tightening a nut 46 which causes a flange 43 on the insulator 30 to be gripped between ribs 45 on a flange 36 and ribs 44 on the upper end of the sleeve 16. The sealing of the sleeve enables the interior to be maintained at a predetermined pressure and it is preferably maintained at sea level atmospheric pressure. A core 50 of magnetic material is inserted in a cavity 49 of the insulator 26 and held in place by cement 51. The core is also retained in position by a spring clip 62 which also serves to connect the high potential end of the secondary winding to the central electrode 18 of the sparking plug. Fig. 2 shows a modification in which the upper ends 55, 56 of the primary and secondary windings are connected together to a terminal rod 57. The rod 57 is surrounded by a sleeve 59 of electrically conductive material welded to it at 60. The current to the transformer is supplied by a lead 68 which is in contact with a spring finger 70 which in turn contacts the sleeve 59. The upper end of the sleeve 16 is sealed by a washer 62 and a glass seal 61 between the washer and the sleeve 59. The outer edges of the washer are welded at 63 to the upper edge of the barrel. In a further modification the sleeve 16 is welded directly to the sparking plug barrel and the upper end of the sleeve is sealed by an expansible glass-tometal seal. The seal includes an expansible U-section washer welded to the upper end of the sleeve 16 and fused to a glass element which is also fused to an electrically conductive tube extending through it. The tube is electrically connected to one end of the transformer primary winding by welding, the welding also providing a fluid-tight seal at the end of the tube. The secondary is also connected electrically to the tube. A terminal secured to the end of the electrical supply cable has spring fingers which connect it electrically to the tube.