US2372867A - Spark plug - Google Patents

Description

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/' INVENTOR ATTORNEY T. TOGNOLA April 3, 1945.

SPARK PLUG Filed Dec. 10, 1941 PatentedApr. 3, 1945 umrso STATES PATENT OFFICE i amass SPARK PLUG Tullio Tognola, Sidney, N. 1., alaignor to Bendix Aviation Corporation, South Bend, Ind a corporation of Delaware Application December 10, 1941, Serial lilo. 422,383

Claims. (CL 123-489) This invention relates to ignition apparatus and more particularly to spark plugs for internal combustion engines and insulating means adapted for use therein.

This application is a continuation-in-part of my copending application Serial No. 344,506, filed July 9, 1940, for Ignition apparatus and method of making the same."

Spark plugs are quite generally recognized as the weakest links in the ignition systems of modern internal combustion engines, particularly on high compression aircraft engines which must operatecontinuously for long periods of time at high speeds and under heavy loads. One of the chief difficulties has been in providing proper electrical insulation which will withstand the high heat to which the plugs are subjected during use and yet prevent gas leakage and flashovers.

I One of the objects of the present invention is to provide a spark plug of novel construction wherein the foregoing difficulties are substantially obviated.

Another object of the invention is to provide a spark plug wherein novel means are employed for facilitating the conduction of heat from the center electrode to the outer metallic parts thereof.

Still another object is to provide a novel spark plug whereby the heat conductivity from the ceramic or insulating parts to the metal parts is enhanced.

A further object is to provide a spark plug having a novel electrode assembly.

A- still further object is to provide a novel spark plug employing ceramic insulating means and cushioning means for the latter to minimize breakage thereof during assembly and use.

The above and further objects and novel features of the invention will more fully appear from the following detailed description of the invention when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for thepurpose of illustration only and is not intended as a definition of the limits of the invention, reference for, this latter purpose bein had primarily to the appended claims.

In the drawing, wherein like reference characters refer to like parts throughout the several views,

Fig. l is a sectional view taken substantially along line i- -l of Fig. 2, showing one form of spark plug embodying the invention;

Fig. 2 is a'bottom view of the spark plug shown in Fig. 1; and,

Fig. 3 is a view similar to Fig. 1, showing a modification or the invention, the upper portion of said figure being broken away.

Two embodiments of the invention are illustrated in the drawing, by way of example, in the form of radio-shielded spark plugs which are particularly adapted for use on aircraft engines.

It will be understood, however, that the invention is also applicable to unshielded spark plugs and other electrical devices. As shown in Fig. 1, one form of the spark plug embodying the invention comprises a metallic shell in which carries a novel ground electrode means II, to be more fully described hereafter, in the lower end thereof and is externally threaded at I2 for cooperation with a threaded opening in an engine cylinder (not shown). Threaded into the outer end of shell I0 is a nut or body portion is having a tubular radio'shielding barrel H formed integrally therewith or otherwise suitably secured thereto and an internal shoulder i5 intermediate the ends thereof for supporting a novel center electrode assembly. A washer or gasket Illa may be provided between the upper end of shell I 0 and the nut portion f member i3, said shell, washer and member together forming what may hardened to as the body of the spark plug.

In the form illustrated, the center electrode assembly comprises a metallic cylindrical spindle It provided at its lower end with a head portion ll of enlarged diameter, said head portion being positioned for cooperation with ground electrode means H, as hereinafter described. Spindle i6 is tightly wrapped in a. sleeve l8 of sheet mica or other suitable insulating material which serves to insulate the center electrode from nut l3.

Novel insulating means whereby electrical and gas leaks are minimized and whereby heat conductlon between electrode i6, 87 and member i3 is materially enhanced are provided around insulated spindle, l8, it between shoulder l5 and the upper surface of head ll. As shown in Fig. 1, said insulating means comprise an insulating sleeve l9 constituted by or consisting primarily of a suitable ceramic material, such as porcelain or aluminum oxide, said sleeve surrounding the lower end of spindle 56 between head 51 and a metallic sleeve or liner 26 in body portion i3. An

external shoulder it on said liner is adapted to' seat on an internal shoulder 22 provided in the wall of body portion t3. Both of the sleeves I5 and 20 have a tight fit around mica cigarette i8 which surrounds spindle l8, and sleeve 20 has a tight sliding fit in the bore of member 93.

In order to insure good heat conductivity between the engaging ends of sleeves l9 and 20, said per end of sleeve 25 and a washer or plate 24.

Washer stack 23 is tightly compressed in a suitable press and secured in position by peening the countersunk end of spindle l6 outwardly into contact with the upper surface of washer 24. Shielding barrel l4 may be lined with a suitable insulating materialisuch as mica liner 25, to prevent fiashovers between the upper end of the center electrode and said barrel, said liner being secured in positionby suitable means, such as a washer 26. The latter engages the upper end of said liner and is held by the peened upper end of barrel l4.

Ground electrode means I l comprises novel elements, two being shown in the illustrated embodiment, mounted diametrically opposite each other, each' of said elements subtending an angle of approximately 90. Each of said elements is formed from a metallic strip, preferably rectangular in cross-section, ends lla (Fig. 2) .of

each strip being radially disposed relative to the axis of member l3 and being suitably secured to the lower end of said member, for example, by

being silver soldered or brazed in slots provided therefor in said member. Central portion lib of each of said elements or strips is arcuate in shape and is preferably concentric with the cylindrical wall of central electrodehead I1, the space between portions lib and electrode head I? con stituting the spark gap. 7

In assembling sleeves l9 and 2d oninsulated electrode l6, it, the same are preferably placed end to end in telescoping relation and pressed toether while one is moved angularly with respect to the other until the relatively hard ceramic material grinds for itself a perfect seat in the relatively soft metal of sleeve 20, the latter being made of copper or similarly soft metal having high heat conductivity. Good contact between sleeves l9 and 2B and, hence, a good heat conducting J int therebetween are thus formed, whereby heat from electrode l6 may be readily conducted to body I 3.

During the installation of the center electrode assembly in nut l3 and use, the axial pressure exerted on ceramic insulating sleeve I9 is cushioned by mica stack 23 which yields under pressure, thereby minimizing the possibility of any cracking, chipping or breaking of said sleeve. The mica Washers also tend to expand radially against nut l3 and sleeve it when compressed and, hence, contribute to the formation of a tight gas seal to prevent gas leakage along the center electrode oraround the insulating parts.

In order to provide further assurance against gas leakage from the engine cylinder through the spark plug, the voids or spaces between the various insulating'and metallic partssurrounding the upper end of spindle l6 may be filled Witha suitable high heat resistant insulating compound in accordance with a novel n :thod fully described in my 'copending application Serial No. 344,507,

fi1ed July. 9, 1940, for Spark plug and method of making the same. In general, said method consists. in placing the spark plug, completely assembled except for washer 24 and, in some instances, spindle IS," in a vacuum chamber and introducing the insulating compound in liquid form into barrel M. The liquid is thus caused to flow into and fill the minute spaces around and between the upper end of spindle l6, sleeve l8, mica stack 23 and liner 25. One compound which has been found suitable for this purpose is a cashew-nut-shell-oil product. After the compound has been applied to the plug in this manner, the latter is removed from the vacuum chamber, any excess compound is removed therefrom, and washer 24 is installed in the manner heretofore described. The assembled spark plug is then baked for various lengths of time at temperatures increasing from 200 F. to 500 F. until the compound is thoroughly dried and set, said temperature being kept at all times below the boiling point of the compound, which point varies as the compound dries or sets.

In Fig. 3, there is illustrated a spark plug which is similar to the above-described structure, except for the construction of the upper end of sleeve i9 and the provision of a conventional electrode head 27 at the lower end of insulated spindle l6, l8 and a conventional type ground electrode 28 in spark gap relation to said head. Parts which are substantially alike and which perform like functions in the two embodiments are designated by like numerals. Sleeve i9 is provided at its upper end with a surface consisting of metal impregnated ceramic material,

as indicated in the drawing at 29, or with a sleeve under a flame by a method known commercially as the Schori process The provision of a metal impregnated surface or a layer of metal on the upper end of sleeve l9 tends to improve the contact between said sleeve and sleeve 20 and to enhance the heat conductivity therebetween. In the fabrication of sleeve I9 with the metal impregnated upper end surface 29, the dry ceramic powder for the sleeve may be mixed, dampened and positioned as a plastic mass in a mold of the desired shape. A second mass consisting of a dampened mixture of ceramic powder and metallic powder is then applied to the mass in the mold to form a coating at the upper end thereof. The masses of material are pressed together into a unitary mass, removed from the mold, dried out by heating at a relatively low temperature,v and then baked or fired at a temperature of approximately 2,200 F. This baking temperature may, of course, vary, but

temperatures between 2,000 F. and 2,500 F. have successful, one part of metallic powder having a fineness, of about 200 mesh was thoroughly mixed with three parts of ceramic material, such as aluminum oxide (Alfrax), also in powder form and having a fineness of about 300 mesh. Finer or somewhat coarser powders may be used but the finer the powders the better the contact between adjacent particles and, hence, the better the heat conducting capacity thereof. The relative percentages of metallic'and ceramic powders may, of course, be varied, the highest proportion of metal being limited chiefly by the ability of the ceramic to function as a binding medium therefor.

There is thus provided a novel spark plug wherein use is made of ceramic materials for in-' sulating means and wherein said means are combined in a novel manner with metallic means to improve the conduction of heat from the central electrode to the outer metallic body of the plug be understood that the invention is not limited.

thereto but that various other modifications embodying the features of the invention may be made. For example, the shape of the engaging faces of sleeves l9 and may be varied. Various other changes, particularly in the design and arrangement of parts illustrated. and in the metallie and ceramic materials above suggested as being suitable, may be made without departing from the spirit and scope of the invention as will be now understood by those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1. In a spark plug. a metallic body comprising a member having a differential bore therein and a tubular soft metal liner slidably fitted in said d fferential here, said liner having a cone-like recess in one end thereof, an insulated electrode slidably extending through said liner, and a rigid insulating sleeve surrounding said electrode and interposed between an enlarged portion of the latter and the recessed end of said liner, said sleeve having a cone-l ke portion filling said recess and having intimate contact with the walls thereof.

2. In a sparkplug, a body member having a bore therein, a tubular soft metal liner in said bore, an insulated electrode slidably extending through said liner, and a molded insulating sleeve surrounding said electrode between an enlarged portion of the latter and said liner, said sleeve and liner having telescoping portions, the engaged surfaces of which have intimate contact.

3. In a spark plug, a body member having a bore therein, a tubular soft metal liner in said bore, an insulated electrode slidably extending through'said liner, and a rigid insulating sleeve surrounding said electrode between an enlarged portion of the latter and said liner, the end surface of said sleeve adjacent said liner being coated with metal.

4. In a spark plug, a body member having a bore therein, a tubular soft metal liner in said bore, an insulated electrode slidably extending through said liner, and a rigid insulating sleeve surrounding said electrode between an enlarged portion of the latter and said liner, the end of said sleeve which contacts said liner being.impregnated with metallic powder.

5. In a spark plug. a metallic body member having a bore therethrough. a tubular l ner of relatively soft metal in said bore, an insulated electrode slidably extending through said liner, and a rigid unitary insulating sleeve surrounding a portion of said insulated electrode, said plug at relatively low sleeve having a tapered external surface engaging a tapered internal surface of said liner.

6. In a spark plug, a metallic body member having a bore therethrough, a tubular liner of relatively soft metal in said bore, an insulated electrode slidably extending through said liner, and rigid insulating means surrounding a portion of said electrode and contacting said liner, .the contacting surfaces of said liner and insulating means being tapered.

7. In a spark plug, a tubular sleeve of relatively soft metal, and a rigid tubular insulating sleeve in end to end relation, the end of said insulating sleeve in contact with said metallic sleeve being at least partially composed of metal.

8. In a spark plug, a metallic body portion, a center electrode mounted in and insulated from said body portion, and ground electrode means mounted in said body portion comprising at least one elongated metallic strip, the ends of said strip being set into slots in said body portion and secured thereto, and an intermediate portion oi said strip being bent in a plane perpendicular to the longitudinal axis of said center electrode to follow the contour of an external peripheral surface of said center electrode in spark gap relation therewith.

9. In a spark plug, a metallic body comprising a member having a bore therein and a relatively soft metal liner slidably fitted in said bore, saio liner having a recess in one end thereof, an insulatcd-electrod slidably extending through said liner, and a rigid insulating sleeve surrounding said electrode and interposed between an enlarged portion of the latter and the recessed end of said liner, said sleeve having a portion shaped to fit said recess and have intimate contact with substantially the entire area of the Walls of said recess.

10. In a spark plug having a central electrode and a metallic body, ground electrode means carried by said body, said electrode means comprising at least one strip of metal secured at the ends thereof to said body and having the major portion thereof intermediate said ends in the form of an arc concentric with the longitudinal axis of said electrode and in spark gap relation with an external peripheral surface of said electrode.

11. In a spark plug having a central electrode, and a metallic body, ground electrode means mounted in the lower end of said body, said electrode means comprising at least one strip of metal secured at its ends to said body and having the major portion thereof intermediate said ends in spark gap relation with an external peripheral surface of said central electrode.

12. In a spark plug, a metallic body comprising a member having a bore therein and a soft metal liner fitted in said bore, said liner having a recess in one end thereof, an insulated electrode extending through said liner, and a rigid insulating sleeve surrounding said electrode and interposed between the head of the latter and the recessed end of said liner, said sleeve having a portion thereof extending into and engaging the walls of said recess.

13. In a spark plug, a body member having a bore therein, a tubular soft metal liner in said bore, an insulated electrode slidably extending through said liner, and a rigid insulating sleeve surrounding said electrode between an enlarged head portion of the latter and said liner.

14. In the method of making a spark plug, the steps of making a metal tube having high heat conductivity, making a tube consisting chiefly of ceramic material, placing said tubes and to end in axial alignment, and simultaneously pressing adjacent ends of said tubes together and imparting relative angluar motion thereto to grind a seat on said metal tube for said ceramic tube.

1.5. In a spark plug, a metallic body, a central electrode having a cylindrical head portion mounted in and insulated from said body, and ground electrode means carried by said body, said electrode means comprising at least one elongated metallic strip, the ends of said strip being secured to said body portion and'a major portion thereof intermediate said ends extending circumferentially of said head portion for a substantial angular distance in spark gap relation with the outer peripheral surface of said cylindrical head portion, the adjacent surfaces of said strip and head portion being surfaces of revolution generated by parallel straight lines revolving about the longitudinal axis of said central electrode.

0 TOGNOLA.

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