US2597978A - Spark plug - Google Patents

Description

R. F. DORAN May 27, 1952 III:

\1 4h JP is VII.. l m l/ w IN V EN TOR. Raineri /Z' Dorf/11 Patented May 27, 1 952 SPARK PLUG Robert F. Doran, Floral Park, N. Y., assignorto Sylvania Electric V'1"1oductsI`nc., a corporation of Massachusetts Applicationxluly 1 6, 1948, Serial'No. 39,115

5 Claims.

This invention relates to spark plugs andto their methods of manufacture.

Although it is well recognized that porous seals between the electrode and the ceramicbody of aspark plug are undesirable, there are no commercially available automobile spark plugs in which the seal is .not porous. This is true in spite ofthefact that hermetically sealed'plugs are being madetoday for theaviationindustry. The present method of manufacturing these plugs for the aviation industry is, however, .so slow and time consuming that the sales price of these .plugs is necessarily many times higher than -could be tolerated in Vthe automobile industry.

In accordance with the present method of making such plugs for the aviation industry, the electrode which is to be hermetically sealed to the ceramic body is rst surrounded with a metallic powder which is dipped into the small cylindrical opening by means of a specialtool requiring numerous clippings as well as aseries of tamping operations between each clipper-full of metal powder. This is followed by the introduction `of powdered glass in much the same manner in which the powdered glass is fed into the small cylindrical opening by means .of a specialtool and successive tamping operations, whereupon a plug of metal powder's -inserted on top of the glass powder by means'of a similar series of steps. The composite obtained in this manner is' subsequently' passed through a heating `furnace in which the"temperatureis sufciently high to hize the glass and bring about ammi-hermetic .porous looking seal between the electrode and 'the ceramic shell. However, since each of these threelling operations'is necessary and since eachof these lling operations, Ywhen carried on by a skilled operator with the special Ytools designed for this purpose, can only process approxi- Y mately '1200 spark plugs per Aday per teamY 'of Il skilledoperators, one'can readily understand why l this process results in a costly spark plug.

It-is an object of this'invention to design a spark plug in which the sealed portion is isolated from that portion of the plug which is likely to be subjected to mechanical stresses through the electrode.

Another object of this invention is to design a spark plug which is adapted for manufacture by modern highjjspeed techniques which will enable the production of non-porous plugs at prices whichwill be attractive in thev automobile eld.

In accordance with this invention, it has been found that these and other advantages can be attained'if that portion of the electrode comprising the .sealing material and a current carrying electrodeis made into a sub-assembly prior to its introduction into the ceramic body.

vIn the drawings whichillustrate a preferred embodiment containing'ffea'tures of this inven'v tion,

Fig. 1 is. a Vfront Velevation partly in. .section showing the component parts ofthe spark plug in assembled position;

` Fig.' 2 .is a .front elevation .partly in section .of a sub-assembly vof the electrode. andi the sealing material.

Since the normal stresses on electrodes istorsional. there is real advantage in.is`olatingthese forces from the seal because of the point ofloadf ing characteristic of torsional forces on a seal `oi" this particulary geometry.

Preferred embodiments of the. spark. vplug, of this invention`,therefore, havetheir center current carrying electrode portion made up 'offa plurality of parts in which ythe 'electrode portion lil extending' from the ceramic body "l2-lat Athe' end projectingY from the motor whenin use,is. not rigidly attached to the sparking pointv i4, 'of the electrode which is hermetically sealed tov 'the ceramic body by means of a sealing material such as showny at' i6. 'The sparking point IA lcan be kept in good electrical contact with the electrode l0 through the sealing material by means .Gian electrical conductor'l, a pin'2 and a` spring 2,2.

The sparking point vIll is preferably made'of a metal which will stand corrosion at hightemcperatures in both reducing and oxidizing atmospheres. The essentialV characteristics are, of course, that its crossfsectional area remain as constant as possible and thatits surface remain free of contaminants which would interfere with its current `,carrying capacity. 'The wire 'IB shown in ltheY preferred embodment'illustrated in the Vdrawingis preferably one which can. carry a'substantial current at a high tmperature and which'is relatively flexible and not Veasily 'broken even when drawn into a relatively thin wire. In preferred embodiments of thespark plugl of this invention, molybdenum wire is used for this purpose. The lpin 2l) is .preferably :but not necessarily made of 'a kmetal suitable for making good lalassio-'metal seals. The spring' 22 seri/esa the sealing' material whi'ch is'l preferably I riadev `offglass inthe'formof a glass bead or tubin i is made up into a sub-'assemblyin order to take advantage of a forming technique.' inasmuch as such forming technique or operation usually consists of the pressing .0f the softenedseal material between mold faces which act as the .sup-

porting medium for the more rigid portion ofthe composite, Vit has been found advisable to lea-ve a portion of the `forming mold inthe body. "This is particularly necessary and desirable in lthe spark plug because of the excessive heating of the forming mold and because of the necessity of heating theA glass through the rather thick Wall of the plug body, this type of indirect heating would not make it possible to obtain the concentrated localized heating of the glass which is normally used in the sealing art. For this reason the sub-assembly is also provided with the upset pin 20 which is in electrical contact with the sparking point I4 through the wire I8 Welded to each of the two aforementioned parts.

In making the sub-assembly in accordance with the preferred embodiments of this invention, illustrated in the drawings, it is preferable to start out with the upset pin 20 and weld thereto a length of wire I8. A determined length of glass tubing 30 is then slipped over the wire and prong portion of the upset pin and sealed thereon in order to insure the best possible seal. An auxiliary piece of glass tubing 32 may be telescoped into the larger tubing as needed. The free end of the rWire I8 is then Welded to the end of the sparking point at the end provided with the shoulder I5. This completes the subassembly which is now ready for insertion into the ceramic body. This is accomplished by dropping it into the ceramic body in such a manner that the contact point protrudes from the end 'I3 of the ceramic body with its offset portion properly seated on ledge I'I provided therefor within the ceramic portion I2 and pulled down in order to seat properly on the oifset portion I of the contact pin. As so assembled, the plug body may then be placed in a sealing spindle preferably on a high speed index machine where the heat can be introduced to the body in an amount sufficient to render the glass `very soft. A prepress operation in the amount of approximately 10 to 55 pounds per square inch may then be made by introducing a pressure ram down against the top of the pin 20. The composite may be heated further and a final pressing operation of approximately 60 to 80 pounds a square inch can then be applied. This pressure is suicient to introduce the sealing glass into a groove II, provided on the inside surface of the ceramic body I2 and to insure a good gas tight type of seal made of a dense clear glass. The amount of glass usedcan beso chosen that at the time of the iinal press, the upset pin will locate on the offset 2| provided therefor in the interior of the ceramic body.

After the composite has been properly cooled, a spring 22 may be dropped in to seat on the flat top pin or to locate about a small tit 24 which extends from the top of pin 20 as shown.

The contact portion of the electrode may then be properly threaded into the cement containing threaded section 26 and a pressure contact made through the spring 22 with the contact pin 20.

When a pre-assembly technique of the type described is used, all the steps in the fabrication of the spark plug are such as are adapted to high speed manufacturing techniques in which manual operation can be kept to a minimum. Furthermore, by using such sub-assembly techniques it is possible to pre-inspect a portion of the seal and thereby obtain a better control of the completed unit'. Furthermore, the particular construction shown and described herein permits the use of a considerable amount of heat and molding pressure thus insuring good seals, Without, however, giving rise to danger of glass sticking to the molds. At the same time the design provides for the isolation of the sealed 4 portion from mechanical stresses which. are likely to be transmitted through the contact portion of the electrodes. This portion in normal service is subjected to torsional stresses in view of the point loading characteristics of the torsional istics that the gas-tight seal is not subjected to such forces.

While the above description and drawings submitted herewith disclose preferred and practical embodiments of this invention, it will be understood by those skilled in the art that the specific details of construction and arrangement of parts as shown and described are by way of illustration and are not to be construed as limiting the invention.

What is claimed is:

1. A sub-assembly suitable for use in the manufacture of spark plugs by high speed techniques comprising a sparking electrode, a pin having an upset head, a wire connecting said electrode to said pin, a solid glass sleeve surrounding a portion of said pin and said wire, said glass body having a diameter not substantially greater than said head of said pin.

2. A sub-assembly suitable for use in the manufacture of spark plugs by high speed techniques comprising a sparking electrode, a pin having an upset head, a wire connecting said electrode to said pin, a glass sleeve surrounding a portion of said pin and an auxiliary glass sleeve surrounding said Wire, said auxiliary glass sleeve also being surrounded by said first mentioned glass sleeve.

3. A sub-assembly suitable for use in the manufacture of spark plugs by high speed techniques comprising a sparking electrode, a pin having an upset head, a wire connecting said electrode to said pin, a solid glass sleeve sealed to and surrounding a portion of said pin and said wire.

4. A sub-assembly suitable for use in the manufacture of spark plugs by high speed techniques comprising a sparking electrode, a pin having an upset head, a wire connecting said electrode to said pin, a glass sleeve sealed to and surrounding a portion of said pin, and an auxiliary glass sleeve surrounding said wire, said auxiliary glass sleeve also being surrounded by said first mentioned glass sleeve.

5. In the method of making spark plugs the. steps comprising welding wire to a pin, slipping a glass sleeve over the wire and pin, sealing said sleeve to said pin, welding the free end of said wire to a sparking electrode, inserting the composite of pin, wire, glass sleeve and sparking f electrode into a ceramic body and sealing said glass sleeve to said ceramic body by heat and pressure means.

ROBERT F. DORAN.

REFERENCES CITED The following references are of record inthe file Vof this patent:

UNITED STATES PATENTS

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