US2508354A - Spark plug or the like - Google Patents

Description

H. A. BRINSON SPARK PLUG OR THE LIKE May 23, 1950 Filed 001;. 21, 1944 IN VEN TOR. HG/"f'y A. BP/nson ATTORNEY Patented May 23, 1950 SPARK PLUG OR THE LIKE Harry A. Brinson, Sidney, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a

corporation of Delaware Application October 21, 1944, Serial No. 559,684

4 Claims.

This invention relates to sealing means and more particularly to means for sealing the bore of an insulator in a spark plug of the type used for igniting the combustible charges in the cylinders of internal combustion engines and the like.

One of the objects of the present invention is to provide a novel spark plug structure which is so constructed that leakage of gases between the center electrode and the insulation therefore is wholly or substantially eliminated at substantially all operating temperatures.

Another object of the invention is to provide novel sealing means adapted for use in the bore of an insulator or the like, particularly around a core such as an electrical conductor.

A further object is to provide novel means for sealing the bore of an insulator in the center electrode assembly of a spark plug which will also function as means for securing an electrode or a terminal or both in said bore.

Still another object is to provide novel sealing means for the bore of spark plug insulating means or the like which may be readily and efficiently installed therein and which will withstand high operating temperatures and wide or sudden changes in temperature.

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 drawings. It is to be expressly understood, however, that the drawings are for the purpose of iilustration only and are not intended to define the limits of the invention, reference for this latter purpos being had primarily to the appended claims.

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

Fig. 1 is a half sectional elevation view of one form of radio shielded spark plug embodying the present invention; and

Fig. 2 is a bottom end view of said spark plug.

The single embodiment of the invention illustrated in th drawings, by way of example, is shown in the form of a radio shielded spark plug of the general type universally used in presentday aircraft engines, but it will be understood that the features of the invention are equally applicable to other types of shielded spark plugs as well as to spark plugs which are not of the shielded type. In the form shown, the spark plug comprises a tubular metallic shell which is ex- ,ernally threaded at H for cooperation with a threaded opening in an engine cylinder (not shown) in a manner well understood in the art. The bore through shell I0 is provided with a tapered wall portion l2 for a purpose which will more fully appear hereafter. A ground electrode 13 having bendable prongs 2| or of any other suitable known construction is secured in the lower end of shell ID by means of silver solder or other suitable means.

Ground electrode I3 is in cooperative spark gap relation with the enlarged head portion [4 of a center electrode l5 which constitutes a part of the conducting means mounted in the differential bore l6, ll of a ceramic or like insulator l8 for conducting high tension electrical current therethrough. In the illustrated embodiment, the head H of the center electrode engages the lower end of insulator l8 and the elongated spindle l9 thereof extends through the small or reduced portion l6 of bore I6, I! and terminates in the larger portion II thereof. The upper end of spindle I9 is provided with one or more annular grooves 20, or other suitable deformations, for a purpose to appear hereafter.

Means are preferably provided for mounting center electrode IS in the bore of insulator l8 in a manner whereby accurate centering of the electrode in the insulator bore Hi and good heat conduction from the electrode to the insulator are insured without subjecting the insulator to the danger of being cracked by expansion of the electrode. As shown, spindle IQ of the center electrode has the diameter thereof slightly reduced for a major portion of its length in bore 16 to form shoulders 22, 22. The diameter of the parts of spindle l9 adjacent the ends of said reduced portion, 1. e., the diameter of said shoulders, is slightly less than the diameter of bore it, the exact clearance of these parts in the bore being determined by the accuracy with which the insulator I8 is constructed. The surface of the central reduced portion of spindle I9 is preferably roughened somewhat, such as by sand blasting, and several layers 23 of thin metallic foil, or the like, such as nickel or silver foil, are wrapped around the same, the number of layers or turns being just suflicient to provide a relatively tight sliding fit in bore IS.

A metallic terminal 24 adapted for suitable connection with an incoming supply cable carrying high voltage electrical current is installed in the upper end of the bore I! in insulator 18. The adjacent ends of terminal 24 and spindle l9 are spaced from one another and are electrically connected by means of a resistor 25 and a wire 26 2,sos,as4

of relatively small radial cross-section. Resistor 25 may be eliminated and replaced by other suitable conducting means or by an extension wire 26. If the resistor is used for the purpose of reducing erosion of the active parts l4 and 2! of the electrodes I 3 and iii, the same may have a resistance value of anywhere between approximately 75 ohms-to 10,000 ohms. The preferred value of resistor 25 is approximately between 500 ohm and 1,000 ohms. Conductor 26 may be made of any suitable type of wire, such as Nichrome or molybdenum, and preferably has a diameter of only a few thousandths of an inch. One end of said conductor is secured to the upper end of spindle l9 before the latter is inserted in insulator II and the free end thereof is preferably coiled to form a spring adapted to yieldably and electrically engage resistor 25 or terminal 24.

Novel means are provided in bore ll of insulator I! for sealing said bore against leakage of gases therethrough from the engine cylinder and for securing electrode I and terminal 24 in the insulator. The novel sealing material 21 is preferably, though not necessarily, electrically non-conductive and completely fills the annular space around the conducting elements I9, 24, 25 and 26. The sealing material has a high melting point and in its final form is a unitary rigid mass which has interlocking relation with spindle 19 at grooves 20 and with terminal 24 at groove 28 or other similar deformations. in said spindle and terminal to thereby hold the parts in assembled relation.

The novel sealing material 21 is formed by fusing a mixture of powdered bore-silicate glass or other similar material having a high melting point, such as "Pyrex glass, and one or more other powdered substances having lower melting points, such as lead oxide, for example. One suitable mixture which has been found to be practical and useful in forming a seal in bore i1 consists of one part by weight of powdered boro-silicate glass, such as Corning Pyrex glass No. 774, and one part by weight of powdered lead oxide. These proportions are not critical, however. It has been found practical, for example, to employ mixtures consisting of from 20 per cent to 60 per cent lead oxide and 80 per cent to per cent glass, the proportions being in terms of weight. One of the considerations, insofar as spark plugs are concerned, is to provide a sealing material which will be plastic-like or pasty only when heated to a temperature above the maximum operating temperature of the spark plug but below any temperature which might be detrimental to the spark plug parts, i. e., to the insulator I 8 and the parts installed in the bore thereof. This result may be obtained by using the above mixtures since the melting point of the glass component although not definite is above 1832 F., and that of lead oxide is 1630 F. The glass component will generally begin to soften at approximately 1472" F., but a considerably higher temperature is required to melt it. The mixture of the powdered glass and lead oxide is in effect a eutectic mixture which will soften at approximately 1400 F., a temperature below the softening and melting points of the constituents thereof. Accordingly, when the mixture is heated to temperatures between approximately 1500 F. to 1800" F., the same is reduced to a pasty or plastic-like compound. Although the melting point of the glass component is higher than 1500 F., the glass particles of the mixture soften somewhat at temperatures above approximately 1400 F. in the presence of the lead oxide and a certain amount of chemical reaction is believed to take place and unite the lead oxide particles with the Pyrex glass particles. The resulting material solidifies to a unitary homogeneous mass on cooling, said mass being a form of lead boro-silicate glass.

In forming the seal for the center electrode assembly of a spark plug it has been found suitable to make the boro-silicate glass component of the mixture by firing 80.5 parts by weight of silicon dioxide with 12.3 parts of sodium tetraborate, 7.8 parts of boric acid, 2.2 parts of aluminum oxide and .6 part of potassium carbonate. When this bore-silicate glass is mixed with equal parts of lead oxide and fused in the manner hereinafter pointed out, the resulting product has a chemical analysis of 40.25 per cent silicon oxide, 6.45 per cent boric oxide, .2 per cent potassium oxide, 1.9 per cent sodium oxide, 1.1 per cent aluminum oxide and 49.9 per cent lead oxide.

When the foil wrapped center electrode with conductor 26 secured thereto has been inserted into insulator I8, a predetermined quantity of the sealing material 21 in finely divided powder form is placed in bore ll of the insulator. The components of the sealing mixture should be thoroughly and intimately mixed and it is desirable that the same be sufficiently fine to pass a mesh screen. In order to insure good electrical contact between resistor 25 or terminal 24 and conductor 26, the latter should extend to or slightly beyond the upper surface of the powdered mixture at this stage of the assembly. After the powdered sealing material has been settled, such as by vibration of the assembly, tamping, or the like, the assembly is placed in a chuck on a press and resistor 25 is set on the surface of the powder in contact with the coiled end of conductor 26. Terminal 24 may be magnetically or otherwise suitably supported by the plunger of the press and lowered into engagement with the resistor 25. While a longitudinal compression pressure of approximately 50 pounds is being applied to the parts by the press, one or more flames are applied to the outer surface of insulator It, or other suitable means are employed to raise the temperature of the powdered mixture to the approximate temperatures heretofore mentioned for melting the-lead oxide or other equivalent component of the mixture and bringing about the chemical re action between the lead oxide and the Pyrex glass. The mixture is thus rendered pasty or plastic while resistor 25 and terminal 24 are forced into final position by the pressure applied by the press. When the parts reach the positions illustrated in the drawings, the source of heat is removed and as soon as the parts have cooled somewhat at normal room temperature the center electrode assembly, completed except for minor machining operations, is removed from the press for mounting in shell Hi.

The novel center electrode assembly when thus sealed against the leakage of gases is preferably mounted in shell ill in such a manner as to prevent any leakage of gases between insulator i8 and the shell. This mounting may be efiected, for example, by wedging a sleeve 30 of relatively soft metal such as copper between the surface of insulator l8 and tapered wall l2 in shell i0, said sleeve being held within the shell by a shielding barrel assembly consisting of a metallic barrel 3| surrounding a rigid sleeve 32. Barrel 3i may be silver soldered, as at 35, or otherwise suitably secured in shell ID or the same way may be formed integrally with the shell. Annular shims 33 made or" mica, asbestos, Or the like, may be interposed between insulating sleeve 32 and metallic sleeve 30 to insure proper longitudinal dimensions mam a novel sealing material which may be readily.

installed and which will be eflective at all temperatures to which the spark plug is subjected during engine operation. Also, the novel sealing.

means comprehended by the invention will withstand rough handling and may be installed readily and inexpensively in mass production by relatively unskilled workmen. Additionally, the novel sealing material has an amnity for and, hence, adheres well to the insulator l8, spindle l9, and terminal 24.

Although only a single embodiment of the invention is illustrated and described, it is 'to be expressly understood that the same is not limited thereto. For example, it will now be apparent to those skilled in the art that the invention may be practiced with other than ceramic insulators. Accordingly, the term ceramic, as used in the foregoing specification and the claims. is to be interpreted to include other similar insulators such as aluminum oxide or the like. will also be apparent to those skilled in the art that the invention is equally as applicable to unshielded spark plugs and other types of shielded spark plugs as it is to the specific type shown. The invention is also applicable to structures other than spark plugs when it is desired to seal a passage in materials having melting points below the assembly temperatures employed. The external contour of insulator Il may be greatly varied and the manner of mounting the same in the spark plug shell may be materially changed. It will also be apparent that materials other than those specifically mentioned as being suitable for the various elements of the spark plug may be used without departing from the invention. Various changes may also be made in the design and arrangement of the parts illustrated without departing from the spirit and scope of the invention. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

1. In the center electrode assembly oi a spark plug, an insulator having a bore therein, an electrical conductor in said bore, and sealing means filling a portion of said bore around said conductor consisting of a fused mixture of bore-silicate glass and lead oxide.

2. A center electrode assembly for a spark plug comprising an insulator having a bore therein, an electrical conductor in said bore, said conductor being smaller in transverse cross section than the part of the bore in which it is situated, and means sealing the space in said bore around said conductor and consisting essentially of glass and a fused metal oxide of the type useful in glass making having a melting point lower than the melting point of the glass.

3. The method of sealing the bore of a ceramic spark plug insulator that includes the steps of inserting in the bore a powdered mixture of borosilicate glass constituting about to 40% of the mixture, and of lead oxide constituting about 20 to 60% of the mixture, and heating the mixture to a temperature at which the lead oxide is molten and the glass is softened.

4. A spark plug having a conductor sealed within a ceramic insulator by a composition analyzing 40.25% S102, 6.45% 320:, 0.2% K20, 1.9% NazO, 1.1% A:, and 49.9% PbO.

HARRY A. BRINSON.

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

UNITED STATES PATENTS Number Name Date 1,508,455 Kraus Sept. 16, 1924 2,210,489 Lemmens Aug. 6, 1940 2,221,709 Hood Nov. 12, 1940 2,248,415 Schwartzwalder July 8, 1941 2,293,381 Carington Aug. 18, 1942 2,304,562 Gerisch Dec. 8, 1942 2,311,647 Doran Feb. 23, 1943 2,317,305 Schwartzwalder Apr. 20, 1943 2,349,432 Hopps May 23, 1944 2,351,128 Jeflery June 13, 1944 2,353,354 Nordberg July 11, 1944 2,355,163 Jackson Aug. 8, 1944 2,408,642 Hopps et a1. Oct. 1, 1948

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