GB867031A - Spark discharge device - Google Patents

Abstract

867,031. Sparking plugs. BENDIX CORPORATION. Feb. 3, 1960 [Feb. 12, 1959], No. 3895/60. Class 7(4). [Also in Group XXXVI] A sparking plug has a monitor electrode or probe 19, 19<SP>1</SP> for detecting a discharge at the spark gap, the monitor probe being spaced from the gap and provided with an insulated lead extending within the plug shell to terminal means 47, 471 adjacent the outer end of the plug. In Fig. 1 an annular semiconductive ceramic insert 30 surrounds the inner end of the central electrode 22. The ininsulator 25 carries a ceramic washer 31 which centres the insulators 24 and 25 in the shell located within a central recess 34 is a flexible metal diaphragm 32 which is brazed at its smaller end to the electrode 22 and at its larger end to the metallized wall of the recess 34. The flexible metal diaphragm 35 has a larger end brazed to the inner wall of the shell portion 14 and its smaller end brazed to the metallized peripheral surface of the insulator 24. A retainer ring 36 fitting between the wall portion 14 and the diaphragm 35 is brazed to both. The lead wire 37 extends outwardly in one complete turn about the insulator 24. A ceramic sleeve 46 has a central bore the surface of which is metallized A metallic tube 47 made for example of an iron nickel alloy such as that known by the Registered Trade Mark "Kovar" snugly fits within and is brazed to the inner surface of sleeve 46. In assembling the device the mating surfaces of the recess 26 in the insulator 24 and boss 27 are coated with a refractory cement such as that known as "Sauereisen," the inner periphery of the washer is coated with a similar cement and the members are assembled as shown. The refractory insert 30 is held in the recess in the insulator 25 by a refractory cement. In Fig. 5 the means maintaining the probe electrode lead electrically isolated from the shell comprises wrappings or servings 55 of heat resistant cord or the like. Cord made of heat resistant glass fibres may be employed. Washer 59 is made of heat softenable material such as glass. A seal may be made after the device has been assembled by heating the shell 11<SP>1</SP> locally as with a torch applied to the outer surface thereof. The device is especially useful in initiating combustion in a missile rocket or the like.