US2356102A - Ignition apparatus and method of making the same - Google Patents

Description

Aug. 15, 1944. T. TOGNOLA IGNITION APPARATUS AND METHOD OF MAKING THE SAME Filed July 9, 1940 INVENTQFg 7 BY M ATTORNEY Patented Aug. 15, 1944 IGNITION APPARATUS AND METHOD OF MAKING THE SAME Tullio Tognoia, Sidney, N. Y., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application July 9, 1940, Serial No. 344,508

30 Claims.

This invention relates to ignition apparatus, and more particularly to spark plugs adapted for use in the ignition systems of internal combustion engines and methods of making the same. I

One of the objects of the present invention is to provide a novel spark plug adapted to withstand high operation temperatures and one wherein electrical losses and gas leakage are substantially eliminated.

Another object of the invention is to provide a novel heavy duty spark plug employing a unitary insulator around the center electrode made of ceramic or similar material and a novel method for fabricating the same.

Still another object is to provide a novel ceramic spark plug having replaceable center and ground electrodes.

A further object is to provide a novelty constructed spark plug wherein the conduction of heat from the center electrode to the outer shell of the plug is facilitated.

A still further object is to provide a spark showing another form of spark plug embodying features or the invention; and,

Fig. 4 is a sectional view similar to Fig. 1 of a portion of a modified form of spark plug embodying novel electrodes.

Three embodiments of the invention are illustrated in the drawing, by way of example, in the form of radio-shielded spark plugs of the general type now' commercially used in aircraft engines. It will be understood, however, that the invention is equally applicable to unshielded spark plugs and other types of shielded spark plugs. To render either of the illustrated plugs unshielded, it is only necessary to remove the upper portion of the shielding barrel and the v insulating lining therefor and provide a suitplug which is so constructed as to minimize the possibility of undesirable flash-overs therein and gas leakage therethrough.

Another object is to provide a novel spark plug that is, in effect, a unitary structure but which may be quite readily disassembled with suitable equipment for overhaul and repair.

Another object is to provide a spark plug constituted by a small number of simple and yet rugged parts and wherein novel means are employed for securing and supporting the center electrode assembly in the shell or body.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same 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 intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

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

Fig. 1 is a sectional view taken on line l-l of Fig. 2 and illustrating one form of spark plug embodying the present invention;

Fig. 2 is a sectional view of said spark plug taken on line 22 of Fig. 1;

Fig. 3 is a sectional view similar to Fig. 1

able terminal of any well-known type at the outer end of the center electrode.

In the form shown in Fig. 1, the invention comprises a tubular metallic shell 5, which is externally threaded at 6 for cooperation with a threaded opening in an engine cylinder (not shown) in the usual manner. Mounted in the lower end of shell 5 in any suitable manner known in the art is a ground electrode 1 which may be of any well-known type. For purposes to hereinafter appear, an intermediate portion of the bore through shell 5 is somewhat enlarged to provide an annular internal shoulder 8 and 80 is still further enlarged at the upper end thereof to provide an annular recess 9 in the assembled plug for silver solder or other suitable binding and sealing medium.

Mounted within shell 6 for cooperation with ground electrode 1 is a center electrode in which is incorporated in a novel center electrode assembly that is, in turn, supported by novel means in said shell. As shown, center electrode I0 is cylindrical and is provided with an enlarged portion or collar ll adjacent the lower end or head Ila thereof, which head is positioned in spark gap relation to ground electrode I. Said center electrode slidably extends through a central bore in a solid one-piece insulator I! made of ceramic 12, while the upper portion of said sleeve projects outwardly a short distance beyond the upper end of shell and has an annular groove it cut therein which is partially within said shell. Sleeve may be made of any suitable metal, such as copper, the heat conductivity of which is relatively high and may be applied to the insulating'body in any one of several ways. The insulator may, for example, have the surface thereof roughened by suitable treatment, such as by sand-blasting, and the sleeve or collar l4 may be disposed thereon by a method known as the Schori process, which may be practiced with the apparatus and in the manner disclosed in Fritz Schori U. S. Patents Nos. Re. 20,425 and 2,108,998. If desired, sleeve 14 may be shrink-fitted directly onto the insulator or onto a thin layer of metal applied to the insulator by said Schori process or similar method. In one embodiment it has been found suitable to applythe sleeve at a temperature of about 1,500 F. to obtain a .003" shrink fit on an insulator having an outside diameter of .375. Rapid heat conduction from the insulator to the metal sleeve or bushing I4 is thus assured and the gripping engagement of the sleeve on the insulator affords good support for the insulator and center electrode and prevents the passage of gases and moisture.

For radio-shielding the input terminal of the spark plug, there isprovided a metal barrel [1, preferably of relatively thin stainless steel which is in effect a part of the body of the plug. The outer end .of said barrel is lined with a tube or bushing ll of any suitable electrical insulating material having a radial thickness comparable to or somewhat less than that of collar H. The lower or inner end of barrel IT has a close sliding fit over collar l4 and, if desired, over a portion of insulating body l2, and has a close sliding fit into the intermediate portion of the bore in shell 5 immediately above shoulder 8. Said barrel is seated against shoulder 8 and has one or more holes IS in the wall thereof which register or communicate with groove 16 in sleeve II when the latter is in abutting relation with liner 28.

The above-described parts are novelly held in assembled relation, as illustrated in the drawing, by filling groove l6, holes I! and annular space 9 between the enlarged-bore of shell 5 and barrel I! with silver solder 20 or other suitable binding medium which is adapted to adhere to metal. As shown, liner l8 may be held in barrel I! by an internally flanged cap portion 2| which is secured to the outer end of said barrel by any suitable means, such as by solder 22, and is threaded for attachment with a well-known type of radio-shielded supply cable (not shown). Any of many well-known means may be employed for this latter purpose.

In order to insure against gas leakage from the engine cylinder along electrode l0 and against the entrance of moisture and the resulting possibility of flash-overs from washer or terminal l3 to grounded metallic parts of the spark plug, a space 23 between the upper portion of electrode l0 and insulating body l2 and the space 2| between insulator l2 and liner" are filled with a suitable high heat resistant, electrical insulating material 25. Preferably, this material is put into the plug under vacuum in liquid form and later dried or set by heating or baking to thus avoid the trapping of air and so that all voids or spaces between the assembled parts will be filled with the same. A novel method of injec in the 76 insulating compound 25 into the spark plug is fully described and claimed in my U. S. Patent No. 2,348,427. One compound or resin which has been found suitable for use in the above connection has a cashew nut shell oil base and when dried by proper heat treatment in accordance with the novel method described in the above-mentioned copending application is converted into a high heat resistant yieldable solid which serves as excellent electrical insulating means and means for preventing gas leakage and moisture accumulation.

The above-described spark plug is preferably fabricated in accordance with a novel method which comprises making the hollow insulating body I2, as by molding a ceramic material, such as porcelain, aluminum oxide or other suitable insulating material, into the desired shape. The outer and inner surfaces of said body may then b machined, if necessary, and the surfaces, particularly those which are exposed in the completed structure, may be glazed, if desired. Collar H, which has a slightly smaller inside diameter than the outside diameter of insulator l2 at normal temperatures is then heated to approximately 1500 F. and shrunk onto the insulator, either in direct contact with the insulator itself or in contact with a thin metal coating applied to the insulator by spraying in the manner abovementioned. If desired, collar ll may be wholly applied by the so-called Schori process, preferably after the surface of the insulator to be covered has been sand-blasted or roughened by other suitable means. By any of these methods an excellent bond or gripping action between the collar and insulator may be obtained.

The surface of groove IS in the assembled unit l2, II and the interior of barrel ll in the vicinity of holes I! are coated with a suitable soldering flux and, if desired, a ring of silver solder or the like may be placed in said groove. The unit comprising the collar and insulator is then placed in barrel l'l, 2| in abutting relation with insulating liner l8 and the whole is inserted into shell or body member 5. With the parts thus assembled and supported in an upright position, additional silver solder and soldering flux are placed in annular space 8 and around barrel H at the upper face of shell 5, and the whole is heated, preferably by electrical means, to approximately 1100 F. The solder is thus melted and fills groove I6 and annular space 9, thereby binding barrel l1 exteriorly to shell 5 and interiorly to collar I4. Solder 20 thus acts as a binding medium to support the center electrode assembly within the spark plug body and to provide absolute assurance against gas leakage around the latter. Collar H together with solder 20 may be considered as means for securing and supporting insulator l2 and electrode III in shell 5.

Center electrode l0 maybe inserted in the central bore of insulator I2 either before or after the foregoing assembly process. If said electrode is inserted after the soldering operation, as well as after ground electrode I has been mounted in body 5, the prongs la of the ground electrode may be temporarily bent outwardly a sumcient amount to allow for the passage of collar 1 l or other larger portion of the center electrode. Said prongs may be properly adjusted after the insertion oi electrode I0. When the latter has been inserted, the plug is placed in a vacuum chamber and insulating compound 25 is injected in a liquid state after evacuation of r the air. The plug is then taken out of the vacuum chamber, excess compound is removed, and a washer I3 is installed in a suitable press. Thereafter, the plug is placed in an oven for heat treatment of the insulating material 25 in the manner fully set out in the above-mentioned copending application. When the particular compound referred to above is used, the baking temperature is preferably increased at intervals over a period of approximately 88 hours from approximately 200 F. to a. maximum of approximately 500 F., the temperature being maintained at all times below the boiling point of the compound, which boiling point gets higher as the compound dries.

Insulating material 25 is preferably of such a nature that it does not become brittle when it sets and does not shrink appreciably during the drying process. The spaces between various parts of the plug will thus be completely filled and, hence, obviate gas leakage as well as the entrance of moisture, both of which are conducive to the occurrence of undesirable flashovers between the center electrode and the grounded parts of the plug. when such a compound is use'd," it is an easy matter after solder shell 26 having an annular internal shoulder or seat 21 therein and a ground electrode 20 mounted in said shell. A single, one-piece insulator 29 surrounding a center electrode 30 has a thin coating ll of metal applied to a central portion of the outer surface thereof by the so-called Schori process or other suitable method and a sleeve 32 of comparatively soft metaL-such as copper, shrunk onto said coating. Sleeve 32 is provided with an external flange 33 that rests on shoulder 21 and is engaged by the lower end of a nut 34 threaded into the outer end of shell 26 and having an upwardly extending shielding barrel 35. Flange 53 serves as a gasket to prevent gas leakage around the center electrode assembly as well as means for supporting the latter. An insulating material, such as compound 25, may be injected in the manner abovedescribed into the minute spaces between the upper end of electrode 20 and insulator 29 and between said insulator and an insulating liner 36 in barrel to obviate gas leakage along said electrode and to avoid the possibility of undesirable flash-overs.

In order to provide further assurance against gas leakage between collar 32 and insulator 29, the outer end of said collar may be provided with an enlarged bore to form an annular space 31 in which a suitable sealing material 38 may be compacted. One material found suitable for this purpose may be prepared by impregnating asbestos with liquid polymer of cashew nut shell oil, drying the impregnated material at approximately 300 F., and then grinding the same into powderform. Before the powder is pressed into recess 31, it may be heated to a gluey state.

If desired, the gluey material-may be pressed 7 into the recess beneath a rigid washer ll, and the end ll of collar 22 may be spun in to hold the washer and material in place. It will be understood that the sealing means thus provided in the spark plug of Fig. 3 may also be incorporated in the other forms of plugs illustrated.

A third embodiment of the invention which involves novel electrode structures is illustrated. with parts broken away, in Fig. 4. As shown, a novel center electrode constituted by a ferrous alloy body portion ll, having a platinum tip 42 fused to the lower end thereof, is mounted in the manner heretofore described in a molded ceramic insulator VM on which is shrunk or spray-coated a metallic collar 44. The lower end of said collar engages a gasket 45 resting on an internal shoulder or flange 45 in a tubular shell or body 41. Collar N, which is preferably made of some durable material, such as stainless steel, is provided with a flange II that fits into an enlarged portion of shell 41 and is engaged by a nut 45 threaded into shell 41 to press the collar against gasket 45 and thus form a gas-tight seal. Nut 49 may be provided with an upwardly extending shielding barrel lined with suitable insulation the same as is nut 34 in the embodiment of Fig. 3.

Mounted in the lower end of shell 41 for cooperation with electrode ll, 42 is a novelly constructed ground electrode which, as shown, comprises a ring or annular portion 50 having a plurality of inwardly and downwardly projecting prongs 5|. Mounted in each of said prongs, such as by silver soldering, is a platinum pinlike member or electrode 52 which is horizontally disposed and extends radially with respect to the platinum tip of the center electrode and into spark gap relation therewith.

There is thus provided a novel spark plug which is capable of withstanding high temperatures during long periods of use without appreciable deterioration of any of the parts therein, and wherein gas leakage and moisture accumulation, which initiate electrical losses, are substantially eliminated. Additionally, there is provided a novel method of making spark plugs so that both the ground and center electrodes thereof may be removed with comparative ease for reconditioning or renewal without destroying the more durable and more expensive parts of the structure. Novel means are also provided for preventing gas leakage between the parts of the center electrode assembly' of a spark plug. Furthermore, the invention comprehends novel electrode structures for a spark plug which materially increase the emciency and operating life of the plug.

Although only a limited number of embodiments and modifications of the invention are illustrated and described, it is to be expressly understood that the same is notlimited thereto.

For example, various features of the different embodiments illustrated, such as the electrode structure of Fig. 4, the sealing means of Fig. 3, and the coating and collar construction ii and 12 of Fig. 3 may be incorporated in other embodiments of the invention. Various other changes may also be made in the design and arrangement of parts illustrated, as well as in the materials suggested without departing from the spirit and scope of the invention as will now be apparent to 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, the combination of insulating means for a center electrode, a tubular metallic body member, means including a collar having a shrink fit on said insulating means for supporting the latter in said body member and means extending into a groove in said collar for supporting the latter in said body member.

2. In a spark plug, the combination of a unitary insulator for a center electrode, an annular metallic bushing having a shrink fit on said insulator for supporting the latter, a tubular body member for receiving said bushing, and a fusible solder for securing said bushing in said body member.

3. In a spark plug, the combination of insulating means for a center electrode, an annular metallic collar gripping said insulating means and having an annular recess in the surface thereof, a tubular shell having a diiferential bore. a metallic tube around said collar seated on an internal shoulder in said shell and having one or more openings in registry with said recess, and a fusible metal substantially filling said recess, openings and a space between said shell and tube for securing said collar, tube and shell together.

4. In a spark plug, the combination of a tubular shell, a metallic tube slidably fitted into said shell and secured thereto by a fusible metal, such as silver solder, and an assembly slidably fitted into said tube comprising a tubular insulator and a metallic collar fixed on said insulator and secured to said tube by a fusible metal, such as silver solder.

5. In a spark plug, a tubular shell, a metallic tube slidably fitted into said shell and soldered thereto, a center electrode assembly slidably fitted into said tube comprising a tubular insulator for a center electrode and a metallic collar fixed on said insulator for supporting the same and soldered to said tube, an insulating tube lining said metallic tube between the outer end of the latter and said collar, and a yieldable insulating material between said insulator and insulating tube and in said insulator around said electrode.

6. In a spark plug the combination of an assembly comprising a ceramic insulator for a center electrode and a metallic collar surrounding said insulator in gripping engagement therewith, a tubular metallic body member, means for supporting and securing said assembly in said member, a tubular metallic barrel surrounding the upper end of said assembly, a ceramic insulating lining for said barrel, and insulating material having a cashew nut shell-oil base filling the space between said ceramic insulator and said lining.

'7. In a spark plug having a tubular body, the combination of an insulator for a center electrode, a metallic coating on an annular surface of said insulator, and a metallic collar around said insulator in gripping engagement with said coating for supporting said insulator and electrode in said body.

8. In a spark plug having a tubular body, the combination of an insulator for an electrode, a metallic collar fixed on said insulator, said collar having an enlarged bore at one end thereof forming an annular space with said insulator, and a compactable material pressed into said space.

9. In a spark plug, the combination of an electrical insulator for an electrode, a metallic coating on an annular surface of said insulator,

and a metallic collar having a shrink fit on said coating.

10. In a spark plug, the combination of an insulator for an electrode, a cylindrical metallic collar fitted on said insulator, said collar having an enlarged bore at one end thereof forming an annular space with said insulator, and a heatresistant material packed in said space to form a gas seal.

11. In a spark plug, a tubular shell, 9. ground electrode mounted in said shell and comprising an annular member having an inwardly and downwardly projecting prong and a horizontally extending pin-like member mounted on said prong, a center electrode comprising a ferrous alloy body portion and a platinum tip fused to said body portion, and means for supporting said center electrode in said shell with said tip in spark gap relation with said pin.

12. In a spark plug, a tubular shell, a ground electrode mounted in said shell comprising an annular ferrous alloy member having a plurality of circularly arranged prongs and a radially extending pin-like platinum member mounted on each of said prongs, a center electrode comprising a ferrous alloy body portion and a platinum tip, and means for supporting said center electrode in said shell with said tip extending between the inner ends of said pin-like members.

13. In a spark plug, the combination of insulating means for an electrode, a tubular metallic body member, and means including a sprayed metallic collar on said insulating means for supporting the latter in said body member.

14. In a spark plug having a tubular shell, the combination of insulating means for insulating an electrode from said shell, and means for supporting said insulating means in said shell comprising a sprayed metallic coating on the outer surface of said insulating means.

15. The method of making a spark plug which includes the steps of making a tubular insulator having an annular portion of the outer. surface thereof roughened, applying an annular metallic coating on said roughened surface, and shrinkfitting a tubular metallic collar on said coating.

16. The method of making a spark plug which includes the steps of making a tubular insulator, inserting a center electrode in the bore of said insulator, and filling an annular space between said electrode and insulator with a pliable material having a cashew-nut-shell oil base.

17. The method of making a spark plug which comprises the steps of making a tubular insulator, fixing a tubular metallic collar on said insulator, inserting a center electrode in the bore of said insulator, filling an annular space between said electrode and insulator with a chemically setting liquid, securing said electrode and insulator together, and baking the assembled parts until said liquid sets as a solid.

18. In a spark plug having a tubular body member, the combination of insulating means for a center electrode. a metallic cylinder shrinksulator for an electrode, a metallic cylinder hav-,.

ing a shrink-fit on said insulator, a tubular metallic body for receiving said cylinder, and means engaging a groove in said cylinder intermediate the ends thereof for securing said body and cylinder together for positioning said insulator in said body.

20'. In a spark plug, the combination of a unitary ceramic insulator for an electrode having an external wall portion of substantially uniform diameter, an annular metallic collar fixed on said wall portion for supporting said insulator, a tubular shell, and means for securing said collar in said shell, said 1astnamed means including means having a fused bond with said shell.

21. In a spark plug, the combination of a univ tary insulator for an electrode, an annular metallic bushing fixed on said insulator for supporting the same, a tubular body member for receiving said bushing, and fusible means engaging said bushing and member for securing said bushing in said member.

22. A spark plug comprising insulating means fior a center electrode, a metallic cylinder having a shrink-fit on a portion of said insulating means having a uniform outside diameter whereby said insulating means is supported, a tubular shell, and means including means having a fused bond with said shell for supporting said cylinder in said shell. I

23. A spark plug comprising a tubular shell, insulating means for a center electrode, a metallic cylinder having a shrink-fit on said insulating means for supporting the latter, and fusible means having interlocking engagement with said cylinder for supporting the latter in said shell.

24. A spark plug comprising a tubular shell, a metallic tube extending into said shell, a metallic sleeve in said shell and tube for supporting insulating means for a center electrode, and fusible meansfor securing said shell, tube and sleeve in fixed relation to one another.

25. In apparatus of the class described, a tubular metallic shielding barrel, an insulating liner in said barrel, and means secured to the end of said barrel including a cylindrical portion engaging the external surface of the barrel and an internal flange having an internal diameter approximately the same or less than the internal diameter of said insulating lining.

26. A spark plug comprising insulating means for a center electrode, a metallic sleeve surrounding said insulating means, and a substance comprising asbestos filling an annular space between said sleeve and insulating means.

27. A spark .plug comprising insulating means for a center electrode, a metallic sleeve surrounding said insulating means, and a substance comprising asbestos and a cashew-nut-shell oil product filling an annular space between said sleeve and insulating means.

28. In a spark plug having a center electrode, the combination of a tubular shell, an annular member mounted in said shell and having a bendable prong thereon, and a pin-like member mounted on said prong and extending into spark gap relation with said center electrode.

29. A spark plug comprising a tubular shell,

insulating means for an electrode, a metallic sleeve around said insulating means for supporting the same, and means for securing said sleeve in said shell including a tubuiar element extending into said shell and joined thereto by fusible means.

30. In a spark plug, a tubular metallic shell, .tubular insulating means for an electrode, an

and tube.

TULLIO TOGNOLA.

Images