US 2318922 A
Description (OCR text may contain errors)
May 11, 1943. c. M. CARINGTON SPARKING PLUG Filed 001;. 19, 1940 Patented May 11, 1943 SPARKING PLUG Charles Molyneux Carington, London, England, assignor to K. L. G. Sparking Plugs Limited, London, England, a British company Application October 19, 1940, Serial No. 361,965 In Great Britain October 21, 1939- 6 Claims.
This invention relates to sparking-plugs for in ternal combustion engines, of the kind provided with an insulator of ceramic material, such as fused alumina, through which passes an electrode, the insulator being held within an earthed metal plug body. It is impracticable to form such an insulator with a smooth or accurately dimensioned bore for receiving the electrode, and a difficulty therefore arises in ensuring intimate contact between the electrode and the wall of the bore which is necessary to secure good heat conductivity between it and the electrode.
An object of the invention is to provide a combined insulator and electrode in which a path of high thermal conductivity is secured between the wall of the bore and the electrode, and for this purpose there is employed a composite elecftrode of known form, such as a steel core with a copper sheath on it, which was used to obtain improved heat conductivity. In using such an electrode advantage is taken of the fact that copper melts at a lower temperature than steel, so that for the purposes of this invention the composite electrode comprises a relatively infusible core with a relatively fusible sheath on it. The fusible metal forming the sheath, for the purposes of the present invention, should have, as have copper and silver, good electrical and heat conductivities as well as a relatively low melting point, which however is not below temperatures appertaining in the cylinders of internal combustion engines.
The invention therefore includes in one aspect the method of manufacturing sparking-plugs comprising the steps of securing a firing tip on the infusible core of a composite electrode, inserting said composite electrode into the bore of a ceramic insulator, and heating the assembly to melt the fusible metal sheath, whereby it flows into intimate contact with the bore of the insulator and with the infusible core, and a good heat conducting path is secured between th wall of the bore and the electrode.
According to a feature of the invention the firing tip is butt-welded on to the end of the core. Alternatively, a firing tip is placed end-to-end with the core and a sleeve of a metal, such as steel, is welded to the adjacent ends of the core and firing tip.
The invention includes, in another aspect, the provision in or for a sparking-plug of the combination with a composite central electrode comprising an infusible core with a corrosion-resisting firing'tip secured thereon, of a ceramic insulator, wherein the sheath of fusible metal be- Cit tween the core and the insulator is melted after the electrode has been inserted in the insulator, to give intimate contact and good thermal conductivity between them.
According to a feature of th invention, the electrode is provided with a firing tip of corrosion-resisting metal close to one end of the bore, characterized by the end of the bore being closed by a corrosion-resisting metal.
This has the advantage that in making the combined insulator and electrode the fusible metal may be prevented from flowing out of the bore whilst in the molten state, and, moreover, the fusible metal is protected against the corrosive action of the hot cylinder gases.
Two embodiments of the invention will now be described by way of example, reference being had to the accompanying drawing, in which- Figure 1 is a longitudinal section through a sparking-plug comprising a combined insulator and electrod according to the invention;
Figure 2 is an enlarged longitudinal sectional view of the end of the combined insulator and electrode, and
Figure 3 is a view corresponding to Figure 2 showing a modified form of the invention.
Referring to Figures 1 and 2, a sparking-plug embodying the combined insulator and electrode according to the invention comprises a two-part body I0, ll, formed of metal such as steel, the lower part 10 carrying earthed electrodes I2 and the upper part II having an axial extension l3 provided with an insulator lining I4 surrounding th upper end of the combined insulator and central electrode unit which is held in position by the two parts H), H interengaging by means of a screw-thread. A copper washer I6 i inserted between the two parts [0, H of the plug body to provide a seal to prevent the escape of gases around the outside of the combined insulator and electrode unit l5. Steel packing sleeves 30 are provided for a similar purpose between the plug body ID, I l and the combined insulator and electrode unit.
The insulator I5 is provided with a central bore I! accommodating an electrode having a core N3 of steel surrounded by a sheath of copper IS, the lower end of the bore being closed by a suitably constructed platinum firing tip 21 and steel sleeve 22. The firing tip 2| abuts the end of the core Is to which it is secured by the exteriorly-tapered steel sleeve 22 which surrounds the butting ends of the core I8 and firing tip 2| and is spot-welded to each of them so as to provide a good electrically-conducting path between the core and firing point. The firing tip 2| may be recessed circumferentially and the sleeve 22 swaged on to it. The steel sleeve 22 has its wider end close to the end of the bore l1 and is made at this end of such diameter that it substantially closes the space between the firing tip 21 and the wall of the bore.
The upper end of the bore I! is widened and provided with a coarse thread 23 in which engages a plug-terminal member 24 which is in good electrical contact with the upper end of the core 18 of the electrode.
In the manufacture of the sparking-plug just described, the combined electrode and insulator unit I5 is made as follows. A steel rod of about I8 gauge having a copper sheath on it is reduced in cross-section at one end to the diameter of the firing tip 2! and the firing tip 2! with the steel sleeve 22 swaged into the groove is placed end to end with the reduced portion of the core I8 so that a part of the sleeve 22 surrounds the reduced portion of the core l8. The steel sleeve is then spot-welded to the core l8 and firing tip 2|. The rod, together with the firing tip secured at one end, is then inserted into the bore of the insulator l5 so that the wider end of the tapered sleeve 22 lies flush with the end of the bore and substantially closes the bore. The assembly is mounted in a suitable furnace with the firing tip downwards, and heated to a temperature sufficient to melt the copper so that it flows into intimate contact with the bore in the insulator and also makes intimate contact with the core IS. The insulator and electrode are then removed from the furnace and allowed to cool.
It will be seen that the copper sheath [9 thus provides a path of high heat conductivity between the wall of the bore l1 and the electrode, and also prevents gases from penetrating along the bore.
It will be seen, moreover, that since the steel sleeve 22 substantially closes the end of the bore, it will be impossible for the molten metal to flow out through the bore. Also, since the copper flows downwardly, a space will be formed between the upper end of the core 18 and the wall of the insulator bore into which space may be inserted a suitable sealing composition to provide an additional seal against leakage of cylinder gases. The sealing composition may be a heat-insulator to prevent the excessive conduction of heat to the terminal 24, where it could cause damage to the insulation of the ignition cable, especially where the ignition system is of the kind which is enclosed in an electricallyconducted screen for the purpose of minimising interference with radio transmission. It will be seen that the space formed by the flow of the copper as above described provides a gap in the copper which would otherwise provide a path of high heat conductivity extending from the firing tip to the terminal. In this form of the invention, the only heat conducting path to the terminal is through the steel core l8 and the insulator.
In the construction of combined insulator and electrode unit illustrated in Figure 3 the firing tip is constituted by a cylindrical platinum point 23 having swaged thereon intermediate its ends a nickel bush 21, a groove being provided in the cylindrical platinum portion for this purpose; the diameter of the nickel bush is such that it occupies substantially the whole cross-section of the bore in the insulator 5. The firing tip 26 is secured by butt-welding to the core :8 of the electrode within the insulator, and is arranged so as to be accommodated partly within the bore and so that the outer end of the nickel bush 21 lies fiush with the end of the insulator [5. The nickel bush 2! thus prevents hot gases within the cylinder of an internal combustion engine from reaching and corroding the copper.
1. A composite central electrode for a sparking plug comprising a metal core, a corrosion-resisting firing tip secured to one end of the core, a ceramic insulator surrounding the core and a sheath of a metal having a considerably lower melting temperature than the core or the insulator, which sheath is located between the core and the insulator, and has been melted after the core has been inserted into the insulator to give intimate contact and good thermal conductivity between the core and the insulator.
2. A composite central electrode for a sparking plug comprising a ceramic insulator formed with a bore, a metal core extending through the bore and smaller in cross-section than the bore to provide an annular space between it and the insulator, a corrosion-resisting firing tip secured to one end of the core and extending from one end of the bore, a corrosion-resisting sleeve surrounding the firing tip within the bore and closing one end of the bore, and a sheath of a metal having a lower melting temperature than the other parts of the article, which sheath is located in the annular space and has been melted after the article has been assembled to give intimate contact and good thermal conductivity between the core and the insulator.
3. A central electrode assembly for a sparkin plug, comprising a ceramic insulator formed with a bore, and a composite electrode having a metal core with a sheath of relatively fusible metal and a corrosion-resisting firing tip secured to one end of the core, which composite electrode has been inserted into the bore so that the firing tip projects from one end of the bore and then heated to a temperature sufficient to fuse the sheath only so as to give intimate contact and good thermal conductivity between the electrode and the insulator.
4. A central electrode assembly for sparking plugs comprising a ceramic insulator formed with a bore, and a composite electrode comprised of a metal core, a relatively fusible metal sheath surrounding the core except at one end, a corrosionresisting firing tip abutting said end of the core, and a corrosion-resisting sleeve surrounding the junction between the core and the firing tip and welded to both said parts, which composite electrode has been inserted into the bore with the firing tip projecting from one end of the bore and said end closed by the sleeve and has then been heated to melt the sheath to give intimate contact and good thermal conductivity between the electrode and the insulator.
5. A central electrode assembly for sparking plugs comprising a ceramic insulator formed with a central bore and a composite electrode having a steel core sheathed in copper to fit into the bore but with one end of the core bare, a corrosionresisting firing tip and a steel sleeve into which the firing tip partly extends and to which the firing tip is secured, which sleeve has been fitted over the bare end of the core so that the firing tip and core abut and are welded to both said parts, and which composite electrode has been fitted within the bore so that the sleeve closes one end thereof and the firing tip projects therefrom and has then been heated to melt the copper to and swaged thereto, which electrode has been inserted into the bore with the outer end of the bush flush with the end of the insulator and the firing tip projecting from the insulator and then heated to fuse the copper so as to give intimate contact and good thermal conductivity between the electrode and the insulator.
CHARLES MOLYNEUX CARINGTON.