Patent GB-764028-A (GB)
Title: Improvements in spark plugs
Filed: 1955-01-07
Abstract: 764,028. Sparking plugs. GENERAL MOTORS CORPORATION. Jan. 7, 1955 [Jan. 26, 1954], No. 491/55. Class 7 (4). [Also in Group XXXVI] In a sparking plug comprising an insulator 11, Fig. 1, and a centre electrode, having relatively high and low temperature coefficients of linear expansion, respectively, and a shell 3, an element, such as a sleeve 37, of a relatively high temperature coefficient of expansion is interposed between a pair of axially opposed surfaces for example shoulders 7 and 25 on the shell and insulator, respectively, at least one of which has a lower temperature coefficient of linear expansion than the element so that with increasing plug temperature the pressure between another pair of surfaces, such as insulator shoulder 23 and the rolled over shell top 1, is increased. The insulator 11, houses the nickel centre-electrode 13 and the terminal screw 15, the electrode 13 being tubular and closed at the active end and containing a good heat conducting metal such as copper or silver; a sintered copper-glass sealing powder 29 is located in the insulator bore around the forked end of the electrode and the adjacent end of the terminal screw. Earth electrodes 31 are welded to the shell 3 which latter is grooved 33 so that it can be collapsed upon the application of heat and axial pressure to clamp the insulator upon a nickel or copper gasket 35 co-operating with the shoulder 25; a soft metal gasket not shown is interposed between the shell top 1 and the shoulder 23. One end of the stainless steel sleeve 37 is seated on a gasket 38 located on the shoulder 7 whilst the other sleeve end abuts the gasket 35; the sleeve includes 18 per cent. chromium, 8-12 per cent. nickel and traces of colombium and titanium, the percentages being by weight. The total linear expansion of the sleeve 37 and insulator 11 is at least equal to that of the shell 3. In a modification, the low-expansion insulator 109, Fig. 2, is formed with shoulders 115 and 117 by which it is retained in the tubular shell 103. The nickel centre electrode 111 has a nut 127 threaded or brazed near its upper end and an ignition button 123 on its other end whilst a high-expansion metal sleeve 125, slidable on the electrode, to ensure a gas tight joint between the insulator and centre electrode, is positioned between the nut 127 and a shoulder 126 in the insulator bore; softmetal gaskets 129, 131 are inserted between the button 123 and the insulator and under the sleeve 125. The sleeve 125 and associated parts may be replaced by the sealing sleeve arrangement of Fig. 1. In another modification, the centre electrode sleeve is dispensed with and the nut is copper brazed or threaded onto the electrode after the temperature of the assembly has been raised above the normal plug operating temperature (1900F), the nut being loaded into abutment with the co-operating part of the insulator bore throughout the operation. In order to ensure a gas-tight seal between the pressurized ignition cable 135 and plug shell 103 a sleeve 133 is threaded upon the latter, a ferrule 137 of high-expansion metal, such as stainless steel, incorporating shoulders 141, 143 is fitted on the cable, the shoulders co-operating, through gaskets, with a part of a low-expansion nut 147 threaded on the upper part of the sleeve 133 ; the ferrule 137 expands more than the nut 147 whereupon it is forced with greater pressure against the nut and sleeve as the temperature rises. The nut may be arranged intermediate the ends of sleeve 133.