US2503194A - Spark plug - Google Patents

Description

4l M .w w M M 9 a u m W, 4l. uns muws. u nl. m 5.. \Q.` .Q1 1 Lb w a 4 F [Ill Q a m. m. m w m fm April 4, 195o Patented Apr. 4, 1950 SPARK PLUG chuter Cipriani, kenneth l. nomen, ma Carl J. Eaton, Toledo, Ollio Application February 15, 194s, serial N. 51ans (ci 12s-iss) 8 Claims. 1

This invention relates to spark plugs, more particularly to the methods of sealing a center electrode in an insulator core and an insulator core in a shell of a spark plug.

To obtain satisfactory seals between a center electrode and the ceramic insulator core of a spark plug and also between the insulator core and the metallic shell in which the core is positioned has long presented problems. The solution of this problem is complicated by the fact that structures must be provided to obtain these seals which are capable of being applied in mass production so that the resulting seals formed between the component parts of the spark plug are substantially leak-proof and also that these seals may be formed with convenience and cheapness in a mass production line. The tolerances allowable in the dimensions of the components must be as flexible as possible and capable of being compensated for by the flexibility of the sealing material.

The present invention provides a method of sealing the component parts of a spark plug in which the sealing material is compacted to form a holding and vsealing body to provide a seal which is permanent and at the same time is suiiiciently ilexible to compensate for the diierent coeflicients of expansion of the materials used in the component parts of the plug. The inherent exibility of the compacted material also allows compensation for tolerance variation in the dimensions of the parts as made in large quantities so that many of the dimensions of the component parts of the spark plug are not critical but may vary relatively widely. This facilitates their production in large quantities and' at the same time makes possible a product which is cheap in price, yet fully suitable for the purposes for which it is intended.

In the prior art, compacted granular materials have been used to form holding and sealing bodies, such as powdered talc, but these materials have been subject to the great disadvantage that it has been diiiicult to position them between the component parts of the spark plug to form the holding and sealing bodies. It has been necessary to compact these granular materials in relatively shallow layers to obviate the bridging characteristic which prevents uniform compaction in deep layers. This makes the compacting process of granular materials ineiilcient in a production line.

The present invention contemplates the provision of a fibrous material such as asbestos to be compacted in position to form holding and sealing bodies. Flbrous material has the advantage oi providing a ilow characteristic which equalizes the pressure throughout the compacted bodies to give the holding and sealing body uniform characteristics and at the same time allows the body to be positioned in a spark plug by a single compression. This is a substantial advantage on a production line, particularly when more uniform bodies for holding and sealing the parts of a spark plug are provided. l

It is, therefore. a principal object of this invention to provide a sealing method for spark plugs which uses a. body of compacted material to form a holding and sealing bocLv between the component parts of the spark plug.

It is a further object of this invention to provide holding and sealing bodies between the component parts of a spark plug which are compacted in position so that the inherent iiexibility of the compacted material will compensate for variations in dimension arising from tolerances and also will compensate for the diierent coeiiicients of expansion of the material used in the spark plug.

It is a further object of this invention to provide holding and sealing bodies for the component parts of a spark plug which are readily compacted in position in mass production and will result in a product which is cheap in price and durable in service.

It is a further object oi this invention to provide holding and sealing bodies for the component parts of a spark plug which areof a fibrous nature and have good iiow characteristics to allow a holding and sealing body to be positioned by one compaction.

Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure, to various details of construction, to combinations of parts and to economies of manufacture, will be apparent to those skilled in the art upon consideration of the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is an elevational view in cross section of a spark plug to which the invention has been applied.

Figs. 2 and 3 are elevational views. in cross section, of shielded aviation plugs to which the invention has been applied.

Fig. 4 is an elevational view, partly in section,

showing an arrangement for compacting the shell seal.

usual type having an internal shoulder I2 against which rests the enlargement I4 of a ceramic insulator core I6 with a gasket I8 preferably of copper positioned between the metallic and ceramic surfaces. The enlargement I4 forms a shoulder 20 on the insulator which provides a narrow annular space 22 between the insulator core I 6 and the internal bore 24 of the shellv I0. compacted material is positioned in the annular space 22 to form a holding and sealing body between the insulator I6 and the shell I0 as will be described in greater detail hereinafter. To protect the compacted material from the effects of weather, etc., a gasket 26 is provided above the compacted material which is held in position by an inturned flange 28.

'I'he insulator core I6 is provided with an internal bore 30 which may have a shoulder 32 positioned adjacent the enlargement I4 for greater strength. A metallic center electrode 34 is positioned in the bore, being dimensioned to nt relatively closely in the bore below the shoulder 32, while it is substantially smaller than the bore above the shoulder to provide an annular space 36. An upset portion 38 is provided on the electrode to rest on the shoulder 32, and a body 40 of compacted material is positioned (to be described further hereinafter) in the bore above the shoulder 32 to -hold the upset portion thereagainst and to form a holding and sealing body between the electrode and the bore of the insulator. The lower end 42 of the center electrode may project from the bore of the insulator I6 to cooperate with a ground or shell electrode 44 to form the spark gap of the plug. The upper end of the bore 30 may be provided with a threaded portion 46 with which a threaded terminal 48 cooperates to close the bore. The terminal is provided with a bore 50 which houses the upper end 52 of the center electrode to form an electrical connection therewith.

The relative position of the enlargement Ill of the insulator and the shoulder 32 'of the bore in the type of spark plug disclosed in Fig. l is preferably such that the two bodies of compacted materials forming the shell and electrode seals are juxtaposed adjacent each other, so that a path for iiow of heat is established between the center electrode 34 and the shell I0 in a radial direction from the center electrode. This will give greater heat flow from the center electrode and tend to keep it cooler which is highly advantageous. The aforesaid juxtaposition of the two bodies of compacted materials has a further advantage in that by packing the shell seal first and thereafter the electrode seal, a compensation of forces may be obtained which will tend to reduce the tensile stress in the ceramic insulator. A cooperative relation between the seals may be had in this way.

The two bodies 22 and 40 of compacted material are formed of fibrous material, preferably of asbestos, commonly known in the trade as long fiber asbestos, which is a form of magnesium silicate. Any grade of asbestos ber is suitable, and may be somewhat impure without impairing the effectiveness of the holding and sealing body formed when compacted. In the most convenient and preferable form, the asbestos ber is combined with a binder, organic or inorganic, preferably sodium silicate, and formed into a tube of the desired dimensions to fit into the bore 24 of the shell or the bore 30 of the in sulator, being of sumcient wall thickness to snugly ll the annular spaces between the shell and the insulator, and the insulator and the center electrode. The tube may then be cut into short lengths or rings 54 (Fig. 6) for convenience in compacting, and if desired may be partially compacted as at 54a (Fig. '7) in a die of desired contour before positioned in the aforementioned annular spaces.

Then with the rings 54 in original tube condition, or in partially compacted condition 54a, they are dropped into position in the annular space for which they are intended and pressed or compacted into nal position in the annular spaces by a ram (56 and 56a) as shown in Figs. 4 and 5. The compacting may be accomplished either by a steady pressure of- 85,000 pounds per square inch, or by tamping, where a relatively lower load is used, preferably approximately half of the steady pressure. The actual load however due to the tamping action will probably be twice as high under these circumstances. Although the fibrous material has good flowing characteristics under load which would allow a seal to be made -by the compaction of a single large ring of material, it is usually preferable to position three or four smaller rings 5ta than one large one. This sequential positioning of several rings reduces the danger of insulator breakage and gives a more uniform compaction so that a better holding and sealing body results. The insulator I6 is held in an anvil 58 with reference to ram 56a, as shown in Fig. 5, where a manually operated press 60 is illustrated having a spring-pressed guide 6I cooperating with the top 52 of the center electrode, and shell i0 is also held in an anvil 62 as shown in Fig. 4. The lip 28 on the shell I0 is still in unturned condition until the compacting of the body 221s complete. Any convenient means manual or power operated can be used to obtain the desired pressures during the compacting period.

It is to be understood that the physical condition of the asbestos fiber is important during the compacting period, such as moisture content in physical combination, amount of binder, foreign materials, etc. The fugitive material in the rings having reference to the operating temperatures of the spark plug in service is preferably limited to 10% by weight to give the best results. The compacting pressures given above are to be preferred, however these pressures may vary from 12,000 to 90,000 pounds per square inch, which may result in a bulk modulus of elasticity from 200,000 pounds per square inch to 1,500,000 pounds per square inch.

In some applications of the invention, it may be desirable to form the holding and sealing body with one large ring, so that a pre-formed centering member '10 is advantageous as shown in Fig. 3 where a shielded type plug normally used in aviation service is disclosed. The centering member is a washer-like body made of the same material as the seal, except that it is highly compressed by pre-forming in a die with pressure of 110,000 pounds per square inch, which gives a relatively rigid body, through which the compressive force is applied. The member 1l is placed above the compactible material next to the ram, so that extrusion around the ram is obviated during the compression period. The ring or member 'l0 may also be made of a ductile metal such as copper, if desired.

In Figs. 2 and 3, the invention is shown as applied to shielded type of aviation plugs, having a two-piece insulator 12 and 1I as shown in Fig. 2, and a one-piece insulator Il as shown in Fig. 3. Both shell and electrode seals are again made with the compacted asbestos as described hereinbefore and the same general principlesare uti- Il zed as that disclosed in the modlilcation shown in Fig. 1. In Fig. 2 a one-piece shell 118 is utilized, while in Fig. 3 a two- piece shell 50 and 52 is shown Joined together at substantially a central location by acooperating outwardly extending ilange 84 and an intumed lip 05. Shell portion 82 is in the nature of a shielding sleeve. The center electrode 05 disclosed in Pig. 2 is positioned in a smooth bore in insulator 12, with the compacting of the seal occurring against a shoulder 00 on the electrode. Either electrode as shown in Figs. 2 or 3 is a composite electrode.

It is to be understood that the above detailed description of the present invention is intended to disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement 0f parts illustrated in the accompanying drawings, since the invention is capable of being practiced and carried out in various ways without departing from the spirit of the invention. The language used in the specification relating to the operation and function of the elements of the invention is employed for purposes of description and not of limitation, and it is not intended t0 limit the scope of the following claims beyond the requirements of the prior art.

Whatisclaimed:

1. In a spark plug, a metallic shell having an internal shoulder, an insulator body positioned in the shell having an external shoulder resting on the internal shoulder of the shell, and a dense homogeneous body of fibrous material positioned between the shell and the body to form a selfsustaining holding and sealing body therebetween said body of fibrous material having a bulk modulus of elasticity below 1,500,000 per square inch.

2. Aspark plug comprising a ceramic insulator and sn electrode secured thereto by an intermediate body consisting of dense asbestos forming a holding and sealing body gripping-the insulator and electrode and having a bulk modulus of elasticity of more than 200,000 pounds but less than 1,500,000 pounds persquare inch.

3. A spark plug comprising a ceramic insulatorand ametallicbodysecuredtheretobyanintermediate body consisting of dense asbestos forming a holding and sealing body, said asbestos having less than ten per cent fugitive materials at the operating temperature of the spark plug, and a bulk modulus of elasticity greater than 200,000 pounds but less than 1,500,000 pounds per square inch.

4. A spark plug comprising an electrode, a ceramic insulator about the electrode, a metallic shell about the insulator, a seal between the electrode and the insulator and between the insulator and the shell, said seals consisting of fibrous material forming holding and sealing bodiesv between the parts, said fibrous material having less than ten per cent fugitive materials at the operating temperature oi the spark plug and a bulk modulus of elasticity of over 200,000 pounds but less than 1,500,000 pounds per square inch.

5. A spark plug comprising an electrode, a ceramic insulator about the electrode, a metallic shell about the insulator, a seal between the electrode and the insulator and between the insulator and the shell, said seals consisting of dense asbestos forming holding and sealing bodies therebetween, said asbestos having less than ten per cent fugitive materials at the operating temperatures 0f the spark plug and a bulk modulus of elasticity over 200,000 pounds but less than 1,500,000 pounds per square inch.

6. A spark plug comprising a ceramic insulator and an electrode secured thereto by an intermediate body consisting of a dense fibrous material having a bulk modulus of elasticity from 200,000 to 1,500,000 pounds Der Square inch, gripping the bodies and forming a holding and sealing body having less than ten per cent of fugitive materials at the operating temperature of the spark plug.

7. In a spark plug, a metallic shell having an internal shoulder, an insulator body positioned in the shell having an external shoulder resting on the internal shoulder of the shell. said insulator defining an annular space with parallel walls with the inner wall of the shell above the shoulder, a dense self-sustaining body of ilbrous material positioned in the annular space gripping the walls and forming a holding and sealing body therebetween, said body of ilbrous material having a bulk modulus of elasticity above 200,000 but below 1,500,000 pounds per square inch.

il. A spark plug comprising a ceramic insulator and a metallic body secured thereto by an intermediate body consisting of a dense self-sustain- Y ing body of fibrous material having less than ten above 200,000 pounds but l per cent by weight of fugitive materials at the operating temperature of the spark plug and a bulk modulus of elasticity above 200,000 pounds but below 1,500,000 pounds per square inch, said body of fibrous material gripping the bodies and forming .a holding and sealing body therebetween.

KENNETH I. ROBINSON. CARL J. RATON.

REFERENCES CITED The following references are of record in the y ille of this patent:

UNITED STATES PA'I'INTB

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