Patent GB-631386-A (GB)
Title: Improvements in or relating to low tension sparking plugs
IPC: H01T13/52
Filed: 1946-12-04
Abstract: 631,386. Sparking-plugs. SMITS, W. B. Dec. 4. 1946, No. 35961. Convention date, Dec. 14, 1945. [Class 7 (iv)] In a low-tension sparking-plug comprising . a holder 11, Fig. 2, a leading-in insulator 12, a conductor 13 passing through' said insulator and connected to a central-inner electrode 3, an annular-outer electrode 1, Fig. 1, surrounding the inner electrode, the electrodes being formed of material of high-thermal conductivity, there is a provided member 2 of insulating material, separating the electrodes and a synthetic rubber or other similar electrically-insulating organicsubstance 8 provided between the electrodes and the insulating member 2, the substance being elastic so as to take up the differences of expansion due to the differences between the coefficients of expansion of the electrodes and the member 2 when the temperature during operation varies, and keeping the joints between the parts gas-tight. The copper annular-outer electrode 1, which has a tapered bore is mounted upon a correspondingly-tapered tube 2 of ceramic material whilst upon the inside of the insulating tube 2 is the copper bolt-shaped central-inner electrode 3 the head of which constitutes the sparking surface. The central electrode 3 has a porcelain insulator 4 and a washer 5 fixed thereto by means of two nuts 6, 7, the co-efficient of expansion of the washer 5 being chosen so that this washer compensates for any difference in expansion between the electrodes 1, 3, and the porcelain insulator 4. An electrically-insulating elastic-organic optionally vulcanizable substance 8 or a synthetic rubber, such as that under the Registered Trade Mark " Buna " is inserted in the space enclosed between the electrode 1, tube 2, insulator 4 as well as between the washer 5, the insulator 4 thereby ensuring gas-tight joint between the parts in question ; the inner end of the outer electrode 1 is provided with slot 10. In a modification, the two electrodes are separated by insulating rings and a tube of good heat conducting material is mounted upon the central electrode. Around this latter electrode and above the outer electrode there is also provided a ring of synthetic rubber or other similar electrically-insulating elasticorganic substance, such as synthetic resin, in order to seal the joints, between the two electrodes 1, 3, and the first mentioned insulating ring. In another modification, a similar elastic substance, in addition to covering the tube of good heat conducting material, also forms the leading-in insulator. In a further modification, the outer electrode which is screwed into the holder is separated from the central electrode by a conical and a cylindrical tube, both of insulating material; the upper part of the central-inner electrode passes through an insulator of synthetic rubber or other similar electrically-insulating elastic-organic substance, such as synthetic resin. This latter material which is situated as remotely as possible from the sparking surfaces of the electrodes may also be vulcanizable. Specification No. 631,387 is referred to. The Specification as open to inspection under Sect. 91 also states that before the parts of the sparking plug are finally assembled they may be covered with a vulcanizable adhesive substance, the whole plug then being subjected to a vulcanizing process after the assembly. This subject-matter does not appear in the Specification as accepted.