US2162062A - Manufacture of spark plugs - Google Patents

Description

June 13, 1939. D. H. CORBIN MANUFACTURE OF SPARK PLUGS 7 Filed March 17, 1958 Fig. '1.

Patented June 13, 1939 UNITED STATES MANUFACTURE OF SPARK PLUGS Douglas Haynes Corbin, Dunstable, England, as-

signor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application March 17, 1938, Serial No. 196,309 In Great Britain March 19, 1937 11 Claims.

This invention relates to the manufacture of spark plugs for internal combustion engines.

The object of the invention is to provide a simple and effective process of manufacturing a high efficiency spark plug.

According to the invention, which in its various aspects is indicated in the appended claims, a spark plug is made by positioning an electrode of corrosion-resisting material on or in the insulator, and it is them firmly attached thereto by introducing a metal into the central bore of the insulator in such a manner that it contacts with a part of the electrode in a molten state, and then cooling the metal.

Good heat conductivity metals having a comparatively low melting point such as copperand silver may be used for the central bore: it forms the conducting portion of the central electrode and therefore of course should have a melting point such that it will not be adversely affected under operating conditions.

The sparking portion of the central electrode is made of corrosion-resisting material, and for this nickel-chrome alloys may be used although platinum and platinum alloys. are preferred. Platinum-rhodium, platinum-indium, and pure platinum indicates the order of preference.

Further features of the invention will be apparent from the following description taken in conjunction with the accompanying drawing in which:

Figure 1 is a part section of a spark! plug having parts made according to this invention; and

Figures 2 to 7 illustrate various forms of electrode and insulator assemblies.

The same reference characters indicate like parts in the various figures.

The form of spark plug shown in Figure 1 is merely illustrative of the invention which can be appiied to many different forms of plugs. The particular form shown therefore need not be de scribed in detail, and it is sufficient to indicate the structure as comprising an outer screw-threaded shell a, an inner shield member b having an inner insulating lining c, and an inner sleeve d holding the central insulator e. This latter extends inside the lining c and carries a connecting cap I for connecting a spring (not shown) to the central electrode structure formed of a screwed-in member 9, a central conducting piece h and sparking electrode points i which cooperate with a ring of nickel or platinum alloyon the inside of the shell a.

In the preferred embodiment the insulator e (Cl. l23169) is made of a highlymefractory oxide or oxides sintered into a dense mass, the electrode conducting piece 12 is made of silver, and the points i are made of fine wires of platinum-rhodium alloy. The tip of the insulator assembly is shown in Figure 2.' v

The manner of making this assembly is as follows:

The insulator e is made with a central bore and with a plurality of communicating divergent channels of just sufiicient size to permit the insertion of the fine wires 1' as shown in Figures 1 and 2. Prior to insertion the ends of the wires which are to project into the central bore are plated with chromium and then heated to a red heat 15 to form a protective coating. The end tip of each wire is then nipped off, and the wires are inserted in their respective channels so as to project into the central bore. To help hold the wires in po-'- sition during the casting process, and also to stop any silver from running down between the wires and the sides of the hole, the wires and the end of the insulator are sealed off with a protective ceramic cement, which has a melting point higher than the fusing point of the metal used for sealing, yet with enough adhesion to hold the wires in place. The silver is then introduced into the bore in such a manner as to contact with the ends of the wires in a molten condition. This may be done bypouring molten silver intothe bore but the preferred method is toaplace a piece of'solid silver in the bore and then heat the whole. assembly to a temperature sumcient to melt the silver. This heating may be effected in air, or in a vacuum or in an inert atmosphere.

The assembly is then allowed to cool and in so doing the silver moulds itself to the bore and also firmly retains the wires in position. There is a fused connection between the silver and the wire at the unprotected surface of the latter.

The constructions shown in the remaining Figures 3 to 7 are made in a similar manner.

In Figure 3 the sparking electrode is formed as a cylindrical cap it crimped over the tip of the insulator e, and the silver is in contact therewith 45 through a plurality of channel pieces I.

The construction of Figure 4 is obviously a modification of that in Figures 1 and 2.

In the form shown in Figure 5 cylindrical cap is fits directly into the end of the central bore 50 and is retained therein by set silver.

In the form shown in Figure 6 the sparking electrode is made in the general form of a cylindrical cap 9' which is crimped onto the end of the insulator, and is provided with a plurality of pro- .55

iectlons m forming the sparking points. Between the bore and the cap I: are a plurality of communicating channeLpieces 1 formed when the silver is in the molten condition.

In a further form shown in Figure 7 the sparking electrode is made in the form of a star memher 1: having a central dished portion which fits into the end of the bore and which forms in elect a key with the silver therein.

In all the forms shown in Figures 3 and 5 to 'i the sparking electrode piece may be treated to form a protective coating except where fusion I with the silver is required, similarly to the treatment of the fine wires, above described. Thus. according to the invention, the usual central electrode takes the form of a cast or moulded metal piece, and this piece not only acts as the conductor, but also as the retaining and fixing means for the sparking electrode positioned at the end of the insulator.

1. A method of making a spark plug having an insulator with a central bore and an electrode which comprises positioning on the insulator an electrode made of a platinum alloy so as tobe in communication with the central bore, introducing silver into the bore and. bringing it into contact with said electrode whilst in a molten state. then letting the silver cool so as to retain the electrode in position.

2. A method of making a spark plug which comprises forming an insulator with a central bore, and a pluralityof communicating bores at the end-thereof, positioning at the end of the insulator an electrode member made of a platinum alloy so as to be in part within one of the bores, introducingsilver into the central bore so as to contact with the electrode in a molten state, and then cooling the silver so as to retain the electrode in position.

3. A method of making a spark plug which comprises forming an insulator with a central bore, and a plurality of communicating bores at the end thereof, fitting at the end of the insulator an electrode member of cylindrical form and made of a platinum alloy soas to be in part in communication with the bores, introducing silver into the central bore so as to contact at the ends of the communicating bores with the electrode in a molten state, and then cooling the silver so as to retain the electrode in position. 4. A method of making a spark plug which comprises forming an insulator with a central bore and with a plurality of fine channels at the tip thereof, communicating with the bore, inserting a fine wire electrode in each of the channels so as to project therefrom at each end, introducing a metal-into the bore so as to bring it into contact in a molten state, with the ends of the fine wires in the bore, and then cooling the metal to retain the wires in position.

5. A method of making a spark plug which comprises forming an insulator. with a central bore and with a plurality of fine channels at the tip thereof, communicating with the bore forming a protective coating on a plurality of fine wires inserting one of said fine wires in each of the channels so as to project therefrom at each end, introducing a metal into the bore so as to bring it into contact in. a molten state with the ends oi the fine wires in the bore so as to form a fused connection between them and the molten metal over only a limited area, and then cooling the metal to retain the wires in position.

6. A method of making a spark plug which comprises forming an insulator with a central bore and with a plurality of fine channels at the tip thereof, communicating with the bore forming a protective coating on a plurality of fine wires of a platinum alloy inserting one of said fine wires in each of the channels so as to project therefrom at each end, introducing silver into the bore so as to bring it into contact in a molten state with the ends of the iine wires in the bore, tov form a fused connection between them and the molten silver over only a limited area, and then cooling the silver to retain the wires in position.

insulator with a central bore, which comprises fitting the electrode into the end of the central bore so as to project in part therefrom, introducing silver into the bore and bringing it into contact with said electrode whilst in a molten state, then letting the silver cool so as to retain the electrode in position.

8. A method of making a spark plug having an insulator with a central bore which comprises fitting on the insulator an electrode of corrosionresisting material in the form of a star-shaped member having a central portion, so that said portion fits in said central bore, introducing siliver into the bore and bringing it into contact with said central portion whilst in a molten state,

then letting the silver cool so as to retain the trode fitted at the tip of the insulator in fused connection with the silver in the central-bore. 10. A spark plug comprising an insulator formed of a highly refractory oxide, a central bore and communicating channels in the tip of said insulaton'said bore being filled with silver, and a plurality of fine wire platinum alloy electrodes fitted in said channels in fused connection at their inner ends with the silver'in the central bore.

11. A spark plug'comprising an insulator having a longitudinal bore therein, anelectrode tip of metal resistant to heat and corrosion fitted to the lower end 'of the plug and extending a short distance only into the lower end of the bore, the

DOUGLAS HAYNES connm."

Images