US2910606A - Low tension spark plugs - Google Patents

Description

Oct. 27, 1959 G. D. SUTER 2,910,606

' Low TENSION SPARK PLUGS Filed Sept. 26, 1955 INVENTOR. Gzoaas D. Su-reR wuw ATTORNEY LOW TENSION SPARK PLUGS George D. Suter, Thiensville, Wis, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Application September 26, 1955, Serial No. 536,329

1 Claim. (Cl. 313-431) This invention relates tospark-plugs; more particularly to the creepage gap type of spark plugs used in a low tension ignition system for an internal combustion engine.

Electrodes in plugs of this type are ordinarily subject to rapid erosion because the spark is of high amperage and energy level. This tends to materially decrease the useful life of the plug.

It is the object of this invention, therefore, to provide a spark plug of this type which will have a prolonged useful life within which its original firing characteristics are maintained.

This object is obtained by utilizing electrodes which are highly resistant to erosion, supporting such electrodes so as to have proper heat dissipation, arranging the sparking surfaces so that erosion will not adversely increase the gap, and using glass insulation in said gap bonded to said surfaces.

In general the sparking surfaces are a part of an electrode assembly with a glass insulation gap separating, but bonded to, the sparking surfaces. This assembly is relatively small and is inserted within the end of the steel shell of the plug from which it receives its mechanical support and heat dissipating properties. Thus the volume of special alloy is minimized. The encircling gap causes the erosion to take place radially inwardly without harmfully increasing the gap between sparking surfaces.

The features of the invention described herein which are considered new and useful and, therefore, patentable are set forth in the claim below. The details and scope of the invention itself can best be understood by reading the specification and analyzing the drawings, in which:

Fig. l is a sectional elevation view through the center of the low tension spark plug embodying this invention; and

Fig. 2 is an enlarged bottom View of the electrode assembly embodying this invention with parts broken away and shown in section to illustrate the relationship between the electrodes and the layers of insulation.

The particular adaptation of this invention shown by the drawings is incorporated in a spark plug of standard design, except for novel differences set forth hereinafter. A steel center terminal or stud 10 is sealed in place within a high alumina porcelain core 12. A nickel alloy connector 14 is connected to the terminal 10 and extends beyond the inner end of core 12. The inner end of this connector is slotted to provide a forked end 16 which makes contact with the electrode assembly. The core 12 is held within a threaded steel shell 18 against a gasket 20 by an aluminum seal 22 (see my Patent No.

2,632,431, dated March 24, 1953). The threaded end of the shell 18 has a bore with an inwardly facing shoulder 26 at its outer end. The electrode assembly hereinafter described is fixedly mounted in this bore against such shoulder with the forked end 16 connected to such assembly.

The principal feature of this invention resides in a United States Patent sparking surfaces.

2,910,606 Patented Oct. 27, 1959 solid electrode assembly consisting of a radially outer sleeve-like ground electrode 28 and a center electrode 30. The ground electrode 28 has an inturned outer flange 32 which forms an inwardly facing seat for a preformed high alumina porcelain bushing 34 forming part of such insulation. The center electrode 30 has a solid cylindrical body 36 which fits snugly Within the bushing 34. An outward projecting neck 38 on such body is center drilled to have a press fit on the forked end 16. Near the inner end such body has a larger diameter to form an outwardly facing shoulder 40 which engages the inner end of the bushing 34 to properly position the electrodes. At its inner end the body 36 has a radial flange 42 which has a diameter the same as that of the ground electrode 28. The sparking surfaces are the inward face and cor .ner on the ground electrode 28 and the outward face and corner of the flange 42. The space between the sparking surfaces is filled with glass 44 bonded 'to such surfaces and :forming another .part. of such insulation. Both electrodes are made of a metal such as a copper- .tungsten alloy, which is strong mechanically and resistant to spark erosion. When the spark plug is first placed in operation the spark creeps over the surface of the glass 44- from corner to corner. With continued usage the face of the glass will erode inwardly at a very slow rate exposing the inward and outward sparking surfaces to which the glass had been bonded. However, the special alloy material so resists erosion that those sparking surfaces do not recede from each other enough to make any change in the gap which effects the jumping of the spark. The bond between the insulation and the sparking surfaces prevents the sparking from creeping in between. Thus the plug can be used until the glass is eroded back to the radially inward edge of the sparking surface.

To make the electrode assembly, the bushing 34 is assembled in the ground electrode 28 and the body section 36 of center electrode 30 inserted part way into bushing 34. Insulating glass in powder form is then compacted around body 36 and between the sparking surfaces. The assembly is then placed in a fixture and heated until the glass becomes plastic after which body 36 of center electrode 30 is forced into bushing 34 until shoulder 40 comes to rest on the end of bushing 34. The dimensions of the components are such that upon cooling a gap of .005/ .010 is established between the The glass insulation has several very important characteristics. They are: (1) very high electrical resistance; (2) very high resistance to spark tracking and heat shock; (3) a coefficient of thermal expansion substantially the same as that of the electrode material; and (4) intimate bond with the sparking surfaces forming the gap. It should be noted that, in contrast to previous so-called creepage gap spark plugs, the insulation between the gap employs no semi-conducting material either as a surface coating or embedded particles. It has been found that such coatings and materials are erratic in behavior during the life of the plug under varying service conditions. In the described plug the available firing voltage is sufficient to jump the (.005 .010) gap with no need for lowering its resistance. After the electrode assembly is completed it is assembled into shell 18 as follows: the shell is heated to approximately 500 F. and the electrode assembly is forced with a light press fit into the shell bore. Upon cooling the shell shrinks slightly and holds the ground electrode 28 firmly. Thereafter the sub-assembly of stud 10, connector 14 and core 12 are assembled to the shell 18 in the usual manner. The forked end 16 fits into the drilled neck 38 and keeps constant contact by reason of its inherent resiliency. The overall coefficient of expansion 3 of the assembly is less than that of the shell 18. The spark plug shell 18, being a heat dissipating surface, will remain cooler than the ground electrode 28 and continue to hold the assembly firmly in place.

The spark plug described above has the following advantages: (1) the narrow gap of the electrode assembly can be accurately set before insertion into the shell of the spark plug; (2) the coeflicients of expansion are such that the thermal stresses are avoided in critical areas and the assembly is continuously held securely'within the shell at all temperatures; (3) the costly materials of the electrodes of the assembly are such that the spark erosion is minimized and such assembly lessens the amount of such materials in each plug; and (4) proportioning of all materials can be obtained to get the best thermal conductivity in the areas where heat dissipation is required.

Although only one specific embodiment of this invention has been shown and described, many modifications are possible. This invention, therefore, is not to be restricted except in so far as is necessitated by the prior art and by the spirit of the appended claim.

-I claim as my invention:

A spark plug including a steel shell with an internal bore at its lower end, said shell being provided with a shoulder in said bore, a connector having a forked lower end carried by and insulated from said shell and extending into said bore; an electrode assembly comprising a hollow cylindrical ground electrode of copper tungsten alloy having an inturned flange at its outer end, said ground electrode being received in said internal bore with said inturned flange in abutment with said shoulder, a bushing of high alumina porcelain insulating material seated inside said electrode against said inturned flange, a center electrode of copper tungsten alloy having a body with an outwardly facing shoulder fitted within said bushing with said shoulder in contact with said bushing, said center electrode having a radially projecting flange on the inner end thereof facing and spaced from the inner end of and of the same outside diameter as said ground electrode, said center electrode having a neck at the outer end thereof receiving said forked lower end of said connector, and insulating means between said radially projecting flange and said inner end of said ground electrode consisting of glass bonded and fuzed thereto.

References Cited in the file of this patent UNITED STATES PATENTS

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