Patent GB-641710-A (GB)
Title: Improvements in ignition units comprising a combined spark plug and transformer
IPC: F02P13/00
Filed: 1945-09-19
Abstract: 641,710. Ignition systems; sparking-plugs. BRITISH THOMSON - HOUSTON CO., Ltd. Sept. 19, 1945, No. 24311. Convention date, Jan. 1. 1943. [Class 7(iv)] .[Also in Group XXXV] A combined sparking-plug and ignition transformer comprises a barrel having a spark electrode electrically connected to it, a high frequency transformer having a primary winding and a secondary winding arranged in the barrel, one terminal of the secondary winding being electrically connected to a second spark electrode, means for insulating the primary winding from the secondary winding, an element of insulating material having a portion which supports the secondary winding and a portion in which the second spark electrode is mounted so that it is insulated from the barrel and is arranged to provide a spark discharge gap with the tirst mentioned electrode, means for electrically connecting one terminal of the primary winding to the barrel and means for providing an electrical connection between the other terminal of the primary winding and a source of electrical power supply. As shown in Fig. 1 an insulating member 25 which carries the central electrode 36 supports a transformer the secondary winding 30 being wound around the member 25 and the primary being around the secondary and insulated from it by an insulating layer 31. The member 25 is held in the barrel 10 of the plug by means of a sleeve 29 around it and by a ring 42 and electrodes 43 which bear against a lip 44 formed on the lower end of the barrel 10. The ring 42 holds the sleeve and the insulating member against a shoulder 41 in the interior of the barrel. One end of the primary winding is earthed by connecting it to the sleeve 29 while the other end is connected to a terminal 24 which is electrically connected to a high tension supply cable 12 by a connector 16, 22. One end of the secondary 30 is connected to the terminal 24 and the other to the central electrode 36. A screening conduit 13 is provided for the cable 12 and this and an insulating member 15 at the upper end of the barrel are held in place by a nut 19. In the embodiment shown in Fig. 2 a quenched spark-gap and condenser of an ignition system are incorporated in the barrel in addition to the transformers. The spark-gap comprises a pair of similar spark discharge buttons 51, 52 with sparking faces 53, 54 of suitable material such as cadmium. A high tension supply cable 66 is connected to one side of the spark-gap by terminals 68, 67 and the cup-shaped metal casing member 49 of the spark-gap housing. The other side of the spark-gap by means of the cup-shaped member 48 of its housing is connected to an input terminal 45 of the transformer. A condenser 69 is connected to the barrel by an extension 70 and to the input terminal 68. The spark-gap is insulated from the barrel by a member 65. A coupling nut at the top of the barrel holds the extension 70 and this extension bears on the insulation 65 and serves to hold this and the sparkgap in position. In a modification, Fig. 3 (not shown), the transformer windings and the central electrode are supported by a single insulating element of lead borosilicate glass which is moulded around these parts within the barrel. A spark-gap similar to that of Fig. 2 is incorporated in the barrel and held in place by an insulating bush which in turn is held by a nut screwed to the barrel top. An extension of the barrel which houses a condenser in a similar manner to the arrangemnt of Fig. 2 is held in place by the same nut. A U- shaped spring inside the top of the extention bears on the condenser and urges it towards the spark-gap so that a terminal attached to the condenser makes contact with one side of the spark-gap. The material of the insulating element has a coefficient of expansion substantially the same as that of the barrel.