US2331748A - Spark plug - Google Patents

Description

Oct. 12. 1943. T. ToGNo-LA S PARK PLUG Filed .July SQ 1940 //4v l@ W Z mms @m Patented Oct. l2, -1943 UNITED STATES PATENT OFFICE SPARK'PLUG A i Tullio Tognola, Sidney, N. Y., assignor to Bendix Aviation Corporation poration of Delaware Application July 9, 1940, Serial No. 344,506

13 Claims.

high heat to which the plugs are subjected during use and yet prevent gas leakage and flashovers.

One of the objects of the present invention is to provide a novelly constructed spark. plug wherein the foregoing difculties are substantially obviated.

Another object of the invention is toP 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 novel electrical insulating means and method of 'making same, said means being adapted for use in spark plugs and other devices wherein high heat conductivity is desired. v

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

A still further object is to provide a novel spark plug and method of making the same South Bend, Ind., a cor- Fig. 2 isa bottom view of the spark plug shown.

in Fig. l; and, Figs. 3, 4, 5 and 6 are viewssimilar to Fig. 1 showing other modifications and embodiments of the invention with the upper portions thereof broken away.

Various 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, thatthe invention is also applicable to unshielded spark plugs and other electrical devices. Asshown in Fig. 1, one form of spark plug embodying the invention comprises a metallic shell I Il which carries a ground electrode II in the'lower end thereof and is externally threaded at I2 for cooperation with a threadedl opening in`an'engine cylinder (not shown) in the usual manner.v

Threaded into'the outer end of shell I0 is a nut or body portion I3 having a tubular radio shielding barrel I4 formedv integrally therewith or otherwise suitably secured thereto and an inter- "nal llange I5 intermediate the ends thereof for supporting a novel center electrode assembly.

Shell III and member yI' 3 .together form what may be referred to as the body of the spark plug and in some instances, as shown in Fig. 6, may be formed as .one piece.

In the form illustrated, said center electrod assembly comprises a metallic cylindrical spindle whereby the heat conductivity from ceramic parts to metal parts is enhanced.

The above and further objects and novel fea.- tures of the invention will more fully appear from the following detailed description of the invention when the latter is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not I6 provided at its 4lower end with'a head portion' I'I which is shaped and positioned for cooperation with ground electrode II in a manner wellV understood in the art. Spindle I6 is tightlyd` wrapped in `a sleeve I8 of vsheet mica or other suitable insulating material which serves'to insulate the center electrode from nut I3 and the insulated spindle has a tight sliding fit in the reduced bore surrounded by internal flange I5.

Novel insulating means whereby electrical and gas leaks are minimized and whereby heat conduction between electrode i6, I1 and nut I3, I5 is materially enhanced are provided around insulated spindle I6, I8 between the upper surface of head I'I and the lower surfaceof flange` I5. Said insulatingmeans, in the-'form shown in Fig. 1, comprises a small stack of mica washers I9 and a novelly fabricated insulating sleeve 20.

The inner portion 2| of sleeve 20 is constituted by a .mixture comprising a suitable ceramic mamaterial. The proportions of metal and ceramic material employed in portion 2| are preferably such that the mixture, when molded and baked in, the manner hereinafter described, is a nonconductor or at most a very poor conductor of electricity, but is a materially better conductor of heat than pure ceramic material.

The metal dust employed in insulating sleeve 20 may consist of nickel, tungsten, or other suitable high heat resisting metallic materials, or a mixture of suitable metals. In one embodiment which has proved successful, one part of metallic powder having a flneness 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 flneness 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 ability thereof. The relative percentage of metallic and ceramic powders may be varied, depending upon the portion of the plug in which the mixture is used, the highest proportion of metal being limited chiefly by the ability of the ceramic to function as the binding agent therefor. v

In the fabrication of sleeve 20, the dry metallic and ceramic powders for portion 2| are first very thoroughly mixed and just enough water added thereto to dampen it or form a stiff paste. The dampened mixture is then placed in a cylindrical mold around a core corresponding in size to insulated spindle I6, I8 and a plain ceramic paste consisting of dampened ceramic powder is placed in a second and larger cylindrical mold surrounding the first mold which serves as a core therefor. The rst or inner mold is then removed and the concentric cylinders of different pastes or materials are pressed together to form the unitary sleeve structure 20 which is then removed from'the mold, dried out by heating at a relatively low temperature 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 2,500F. have been found preferable. After removal of the baked sleeve from the oven, the outer surface thereof may, if desired, be glazed by any suitable method known in the art, and the insulated center electrode I6, I8 then fitted therein.

Surrounding the upper end of insulated spindle I6, I8 and interposed between the upper surface of flange I5 and a washer or plate 22 is a stack 23 of mica,washers. The latter and stack I9 are tightly compressed in a suitable press and secured in position by peening the countersunk end of spindle I5 outwardly into contact with the upper surface of washer 22. Shielding barrel I4 may be lined with suitable insulating material,such as mica liner 24; to prevent flash-overs between the upper end of thevcenter electrode and said barrel.

During the installation of the vcenter electrode assembly in nut I3, the axial pressure exerted on ceramic insulating sleeve 20 is cushioned by mica stacks I8 and 23 which yield lunder pressure, thereby minimizing the possibility' of any cracking, chipping or breaking of said sleeve. The mica. washers also tend to expand radially against nut I3 and sleeve I8 when compressed and hence contribute to the formation of a tight gas seal to prevent gas leakage alongthe center electrode or around the insulating parts. Additionally, the mica insulation tends to cushion the ceramic insulator and prevent'the breaking or cracking thereof which often results in ceramic plugs heretofore provided by reason of the differential between the coefficients of expansion ofthe ceramic and metallic 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 parts surrounding the upper end of (spindle I6 may be filled with a suitable high heat resistant insulating compound in accordance with a novel method fully described and claimed in my copending application Serial No. 344,507 led 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 22 and, in some instances, spindle I6, in a vacuum chamber and introducing the insulating compound in liquid form into barrel I4. The liquid is thus caused to flow into and fill the minute spaces around and between the upper end of spindle I6, sleeve I8, mica stack 23 and liner 24. 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 22 is installed in the manner heretofore described. The assembled spark plug is then baked for various lengths of time at temperatures increasing from approximately 200 F. to 500 F. until the compound is thoroughly dried and sets, said temperature being kept at all times below the boiling point of the compound, which point varies as the compound dries.

In Fig. 3, there is illustrated a spark plug which is identical with the above-described structure, except for the c-onstruction of ceramic insulating sleeve 20 and the provision of a ceramic sleeve 23' which replaces the upper portion of the stack of mica washers 23. Sleeve 20', as shown, comprises a lower portion of plain ceramic material and an upper portion 2| constituted by the novel metal impregnated ceramic heretofore described. Said upper and lower portions are prepared in the same mold while damp and, hence, form an integral unitary sleeve structure. It will be noted that in the embodiment of Fig. 3 the metallic and ceramic mixture is well removed from the otherwise uninsulated portion of center electrode I6, I1 and has direct contact with nut I3, thereby materially facilitating the conduction of heat from the center of the plug to the outer air-cooled surfaces thereof to obviate overheating while minimizing the possibility of flash-overs. In this form, the metallic content in portion 2l' may be somewhat greater than in the embodiment of Fig. l.

In the embodiment of Fig. 4, a. molded insulated sleeve 25. extends substantially the full length of spindle I6 and through the reduced bore of a nut I3' which corresponds with nut I3 of Fig. 1. The upper and lower portions of sleeve 25 are composed of plain ceramic material, while the central portion 26 thereof, preferably that portion which contacts nut I3', consists of a mixture of ceramic material and metal of the character above-described. Insulator 25 is preferably molded in a. single mold as a, unitary sleeve and machined'to flt tightly into nut I3', an extef'- nal shoulder 21 on the insulator being adapted to seat on an internal shoulder 28 on the nut. Surrounding the upper end of insulator 25 in the space formed by the latter, insulating sleeve 2| and washer 22, there is provided suitable. insulating means, such as a stack of mica washers 29. In other respects, the spark plug shown in Fig. 4 is the same as that shown in Fig. 1.

In the embodiment of Fig. 5, an insulating sleeve 30 consisting primarily of a suitable ceramic material, such as porcelain or aluminum oxide, surrounds the lower end of spindle I6 between head and a metallic sleeve or liner 3| in body member I3'. Both oi the sleeves 30-and 3| have a tight iit around mica cigarette I8 which surrounds spindle I6, and sleeve 3| has a tight sliding lt in the bore of member |3', shoulder 28 on the latter being engaged by an external shoulder 21 on the metal sleeve.

In order to insure good heat conductivity between the engaging ends of sleeves 30 and 3|, said ends are shaped and assembled in a novel manner to provide good contact between relatively large engaging surfaces. Preferably, the upper end of sleeve 30 is conical and lits into a similarly shaped recess in the lower end of sleeve 3| thereby providing a relatively large contact,

area for heat transfer. In assembling sleeves 30 and 3| on insulated electrode I6, I8, the same are placed end to end and pressed together 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 metah of sleeve 3|, the latter being made of copper or similarly soft metal having high heat conductivity. Good contact between sleeves 30 and 3| and, hence, a good heat conducting joint therebetween whereby heat from electrode I6 may be readily conducted to body I3. If desired, the conical end of ceramic sleeve 30 may be provided with a surface consisting of metal impregnated ceramic material, as indicated in the drawing at 32, or the surface may have a coating of suitable metal, such as copper, applied thereto under a flame by a method known commercially as the Schori process. The upper end of metallic sleeve 3| is preferably ilush with an internal shoulder 33 in nut |35 and a cushioning stack of mica washers 23 is seated against the same and said shoulder. That portion of the plug which is broken away may be of the same construction illustrated in is thus formed, K

Figs. 1 or 3.\It will be understood, however, that shielding barrels I4 are not necessary parts of any of the embodiments and may be dispensed with, if desired.

A. smaller type of spark plug which is commercially known as a 10 mm. plug is illustrated in Fig. 6. In this type, a one-piece metallic body 34 is employed with ground electrodes 35 installed in the lower end thereof for cooperation with the lower end of a center electrode IB'. The latter has a collar or enlarged portion 'above which it is surrounded by an insulating sleeve I8'. Surrounding spindle I6 between collar 1 and a shoulder 36 in body-34 is a cushion;

ing stack of mica washers 31 and a ceramic insulating sleeve 38, the latter having a portion 39 with an enlarged bore extending downwardly beyond collar I1' to a point adjacent ground electrodes 35. The upper portion of the spark plug shown in Fig. 6, is illustrated as being similar to the corresponding structure in Fig. 3. It will be understood that portions of ceramic insulators 38 and 23' may, if desired, be impregnated with metallic dust or powder for increasing the heat conducting ability thereof.

There is thus provided a novel spark plug wherein use is made of ceramic materials for insulating means and wherein said means are and thereby obviate breaking and cracking ot the latter during assembly of the plugs and during actualuse thereof. There is also provided novel metallic limpregnated ceramic insulating means and method for making the same,. the heat conductivity of hich is relatively greater than that of plain ce amic material, while the- 10 electrical insulating qualities thereof are not materially less than those of plain ceramic materials. ing he same are also provided whereby good heat nductivity between ceramic' and metallic parts is assured. Additionally, the features of the present invention may be incorporated in simply constructed spark plugs at relatively low cost.

Although a limited number of embodiments ofv the invention are illustrated and abovedescribed, it will be understood that the same is not limited thereto but that various other modifications embodying features of the invention may be made. For example, sleeves 20 and 20', shown in Figs. 1 and 3, are interchangeable in the types .of plugs illustrated in said figures, and one or both of the stacks of cushioning washers shown in the severa1 embodiments may A novel spark plug and method of mak be dispensed with, if desired. 'Ihe shape of the engaging faces of sleeves 30 and 3| in Fi'g.v 5

may also be varied. Various other changes, particularly in the design and arrangement of parts illustrated and' in the metallic and ceramic materials above suggested as being suitable, may

also be made-without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art. For a definition of the limitsvof the inventionfreference is had primarily to the appended claims.

40 What is claimed is:

bore vtherethrough and an annular internal iiange intermediate the ends thereof forming a reduced bore, a center electrode in said-bore comprising a spindle andan enlarged head por.

tion, an'insulating sleevesurrounding said spindle and having a close sliding iit in said reduced bore, insulating means surrounding said sleeve between vsaid head portion and one side of said 1.In a spark plug, a metallic body having a 2. In a sparkplug, a metallic body having ,aV

`bore therein, a center electrode in said bore, a

- sleeve surrounding a part ofA said electrode for' electrically insulating the samefrom said body, insulating means surrounding said sleeve and interposed between said body and an enlarged portion of said electrode, said insulating means o5 comprising compressible insulating means and a. rigid tube Vconsisting of insulating material with scattered, -finely dividedV metallic particles therein, and means for holdingsaid body, velectrode and insulating means in assembled relation.

3. In a spark p1ug,a metallic body having a dinerential bore therein, avcenter electrode in said bore comprising aspindle andan enlarged portion, a sleeve surrounding said spindle-for electrically insulating the same from said body,l insulating means surrounding said sleevel and interposed between said body and said enlarged portion of the electrode, said insulating means including a yieldable stack of insulating washers and a substantially rigid tube consisting at least in part of metal impregnated insulating material, and means for holding said body, electrode and insulating means in assembled relation.

4. In a spark plug, a metallic body having a bore therein, an electrode comprising a spindle and an enlarged portion, an insulating sleeve surrounding said spindle and having a close sliding t in the smallest portion of said bore, insulating means surrounding said sleeve on opposite sides of the smallest portion of said bore, said insulating means including at least one stack of ilexible insulating Washers and a substantially rigid insulating tube comprising finely divided metallic particles dispersed therein, and means for holding said body, insulation and electrode in assembled relation with said stack of Washers under compression.

5. In a spark plug, a body having a bore therethrough, an electrode extending through said bore, an insulating sleeve surrounding a 'portion of said electrode' for insulating the same from said body, insulating means surrounding said sleeve at opposite ends of the smallest portion of said bore, said insulating means comprising cornpressible insulating means and a substantially rigid insulating tube having finely divided metallic particles dispersed therein, and means for holding said body, electrode and insulation in assembled relation.

6. In a spark plug, a body having a bore therein, an electrode in said bore, and means for electrically insulating said electrode from said body comprising a substantially rigid tube surrounding a portion of said electrode, the outer portion of said tube consisting of plain insulating material and the inner portion consisting of metal impregnated insulating material.

7. In a spark plug, a body having a bore therein, an electrode extending through said bore, and means for electrically insulating said electrode from said body comprising a substantially rigid insulating tube surrounding a portion of said electrode, one end of said tube consisting of plain insulating material and the other end thereof consisting of metal impregnated insulating material.

8. In a spark plug, a body having a bore therethrough, an electrode in said bore, and means for electrically insulating said electrode from said body comprising compressible insulating means and a substantially rigid insulating tube surrounding said electrode and interposed between an enlarged portion of the latter and said body, one end of said tube consisting of plain insulating material and the other end thereof consisting of insulating material having iine metallic particles dispersed therein.

9. In a spark plug, a body having a differential bore therein, an electrode extending through said bore, and a rigid insulating sleeve surrounding said electrode and having a close sliding t in said bore, at least a portion of said sleeve in contact with said body lconsisting of a molded mixture of i'lnely divided insulating and metallic materials.

10. In a spark plug, a body having a bore therethrough, an electrode extending through said bore, a ,substantially rigid insulating sleeve surrounding said electrode and having aclose sliding t in said bore, an enlarged portion of said sleeve being interposed between a shoulder in said body and an enlarged portion of said electrode, at least a portion of said sleeve in contact with said body consisting of a molded mixture of powdered insulating and metallic materials, and means for holding-said body, sleeve and electrode in assembled relation.

11. In a spark plug, a metallic body having a bore therein, an electrode extending through said bore, and means for electrically insulating said electrode from said body comprising a' substantially rigid insulating tube surrounding a portion of said electrode, said tube consisting of molded insulating material having nely divided metallic particles dispersed therein.

12. In a spark plug, a metallic body having a bore therein, an electrode extending through said bore, and means for electrically insulating said electrode from said body comprising aV substantially rigid insulating-tube surrounding a portion of said electrode, said tube consisting of molded insulating material having nely divided particles of an electrically conductive material dispersed therein.

13. In a spark plug, a metallic body having a bore therein, an electrode extending through said bore, and means for electrically insulating said electrode from said body comprising a substantially rigid insulating tube surrounding a portion of. said electrode, said tube consisting of insulating material, such as of a ceramic having dispersed therein nely divided particles of a material having greater heat conductivity than said insulating material.

TULLIO TOGNQLA.

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