US3529837A - Gasket - Google Patents

Description

' C. J. EATON ET AL 1 Sept. 22,1970

, v GASKET Filed Dec. 2, 1968 INVENTORS EARL J EATLW,

JAMES J. H FFMAN.-

United States Patent O M 3,529,837 GASKET Carl J. Eaton and James F. Hoffman, Toledo, Ohio, as-

signors to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Filed Dec. 2, 1968, Ser. No. 780,405 Int. Cl. F16j 9/00; F02f /00 U.S. Cl. 22726 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Considerable difficulty has been encountered in removing spark plugs from threaded engagement with internal combustion engines, particularly engines with aluminum heads, after installation of the plugs and operation of the engine. The problem has been found to be particularly severe after initial installation of spark plugs in aluminum heads of internal combustion engines, and somewhat less severe when second and subsequent spark plugs have been similarly engaged. The greater difficulty in removing the first set of spark plugs suggests that irregularities attributable to original threading of the head may be involved in a seizure between the threaded portion of the head and the engaged spark plug portion. In any event, the problem exists, and numerous attempts at solutions therefor have all proved to be less than complete.

THE PRESENT INVENTION The present invention is based upon the discovery that removal of spark plugs, particularly after initial installation in a new engine having an aluminum head and opera tion of the engine, can be significantly facilitated by a gasket having a plurality of facing surfaces so inter-connected that, when the gasket is compressed, the facing surfaces are resiliently urged apart, provided that the facing surfaces are coated with a material which, at temperatures not higher than about 200 F., are thermally decomposable or thermoplastic. It will be appreciated that a spark plug, when installed in an internal combustion engine, must be tightened sufiiciently that a gasket, interposed between the exterior of the spark plug and a cooperating seat on the head of the associated engine, is deformed into substantially continuous contact with both a seat on the exterior of the shell of the plug and the seat on the head of the engine. Usually, an installation torque of from approximately to foot pounds is required to assure that the necessary deformation occurs in all instances. In a spark plug assembly according to the present invention, upon installation in the normal manner, facing surfaces of the gasket coated with a ther mally decomposable or thermoplastic material are urged toward one another until the coatings contact one another; thereafter, as additional torque is applied, the coatings on the facing surfaces prevent contact therebetween, and the force necessary to cause seating deformation is transmitted, in part, through the coatings.

Similarly, after installation is complete, a part of the force exerted by the gasket between the two seats is 3,529,837 Patented Sept. 22, 1970 ice transmitted through the abutting coatings. However, during operation of the engine in which the plug is installed, the gasket quickly reaches a temperature of at least 200 F., and thereby causes either softening or decomposition of the coatings; as a consequence, the force exerted by the gasket between the two seats is reduced. In retrospect, it is believed that this reduction is responsible for the ultimate desired result; a decrease in the torque required for removal of the spark plug after operation for a more or less extended period of time.

OBJECTS OF THE INVENTION It is, therefore, an object of the invention to provide an improved spark plug.

It is a further object of the invention to provide a spark plug which is improved by virtue of a gasket having a plurality of facing surfaces coated with a material which is thermally decomposable or thermoplastic at temperatures not higher than about 200 F.

Other objects and advantages will be apparent from the description which follows, reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of a spark plug according to the invention, with parts broken away to show details of construction.

FIG. 2 is a plan view of a gasket which is a part of the spark plug of FIG. 1.

FIG. 3 is a view in vertical elevation, taken along the line 33 of FIG. 2.

FIG. 4 is a greatly enlarged, fragmentary view of the spark plug of FIG. 1, and shows details of the gasket of FIGS. 2 and 3, and its assembly with the plug of FIG. 1.

FIG. 5 is a fragmentary view showing the spark plug of FIG. 1 installed in an internal combustion engine.

FIG. 6 is a plan view similar to FIG. 2, but showing a modified gasket.

FIG. 7 is a vertical sectional view taken along the line 7-7 of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION Referring now, in more detail to the drawings, and, in particular, to FIG. 1, a spark plug according to the invention is indicated generally at 10. The spark plug 10 comprises a metal shell .11 in which an insulator 12 is appropriately seated and engaged, a center electrode' resides in a coating on a gasket 17, as subsequently discussed in more detail.

Referring now to FIGS. 2 and 3, the gasket 17 is so shaped as to have a plurality of facing surfaces, {18-18 and '19-19 which are interconnected by arcuate portions 20 and 21, respectively. The gasket 17 also includes a flange 22 which is directed radially inwardly from the portion of the gasket 17 which has one of the facing surfaces 1-9.

Referring now to FIG. 4, the gasket 17 is shown greatly enlarged and, in the solid line position, ready for assembly with the spark plug 10, and, in the broken line position, after such assembly. It will be noted that assembly involves deformation of the flange 22 so that a surface 23 thereof has a diameter less than the major diameter of the threads of the threaded portion 16. As

3 shown in FIG. 4, at least the surfaces 118-18 and 19-19 of the gasket 17 carry a coating 24 which, in a specific embodiment, can be an acrylic lacquer which is thermoplastic at a temperature below 200 F., and which is in the vicinity of of an inch in thickness.

Referring to FIG. 5, the spark plug 10 is shown fragmentarily, operatively engaged with an internal combustion engine which is also shown fragmentarily, and designated 25. It will be noted that the gasket "17, when the spark plug 10 is operatively engaged with the engine 25, has been collapsed from the position shown in FIG. 4 so that the facing surfaces v18-48 and 19 19 are in virtual contact, but separated by about of an inch, the thickness of two layers of the coating 24. Whenthe gasket 17 is compressed, as shown in FIG. 5, resilience of the arcuate portions 20 and 21 tends to urge the surfaces 18-18 and the surfaces '19-19 away from one another, thereby tending to urge the spark plug 10 axially away from the associated engine 25. In addition, however, another force tends to urge the spark plug 10 in the same direction relative to the engine this force is transmitted through the four abutting layers of the coating 24. Upon operation of the engine 25, the four abutting layers of the coating 24' are heated to a temperature of at least about 200 F. and, as a consequence of the heating, become thermoplastic so that the force which was previously transmitted therethrough no longer tends to urge the spark plug 10 axially away from the engine 25. As a consequence, the total force by which such relative movement of the spark plug .10 is urged, is diminished as soon as the coating 24 is softened. It is believed that this diminution in force minimizes the possibility of seizure between irregularities on a threaded portion of the engine 25 with which the threaded portion 16 of the spark plug 110 is engaged, and that reduction or elimination of such seizure is responsible for a reduction in the torque necessary to remove the spark plug 10 from the engine 25, in particular after initial installation and operation of the engine for a greater or lesser period of time. In any event, such a reduction, and of significant magnitude, has been observed in practice, as is subsequently discussed in more detail.

Referring to FIGS. 6 and 7, as gasket 26, which has been found to be operable in a spark plug according to the invention as an equivalent for the previously discussed gasket 17, differs from the gasket 17 principally in that it has five slots 27 in an engaging flange 28 which performs substantially the same function as the flange 22 in the gasket 17.

Various tests have been performed to demonstrate the reduction in removal of break-away torque attributable to coatings of varying thicknesses on gaskets in spark plug assemblies according to the invention. In one series of tests, spark plugs with coated gaskets according to the invention were installed in newly drilled and threaded aluminum heads, using an installation torque of 20 foot pounds. The heads, with the installed plugs, were then heated for two hours at 250 F. or for two hours at 450 F, and the break-away torque, or the torque required to disengage the plugs from the head was then determined. The assemblies investigated were those shown in FIGS. 1 through 5 of the drawings, and the thickness of the coating 24!- was varied by changing the solids content in an acrylic lacquer used to produce the coating by immersion and subsequent air drying. The specific acrylic lacquer used was a methylmethacrylate polymer which softens at about 150 F. The direct measurement of the thickness of the coating 24 has not yet been accomplished, but thickness has been estimated by applying coatings of the various solids contents used to fiat steel plates, allowing the coatings to air dry, and then by microscopic techniques determining the thickness of the coatings on the flat plates. In Tables I and 11, below, break-away torque in foot pounds is reported as a function of coating thickness, the thickness reported, in each case, being the microscopically determined thickness of a coating, on a flat steel plate, of a solution of the lacquer of the same solids content at which the reported break-away torque was determined. It will be appreciated that the coating thicknesses reported in Tables I and II are approximations, but sufficiently close approximations to indicate that coating thicknesses ranging from about 0.3 to about 5 ten thousandths of an inch, preferably from about 0.5 to about 3 ten thousandths of an inch, are operable in spark plug assemblies according to the invention. In any event the coatings should be sufiiciently thick that removal torque, after engine operation, is not greater than installation torque.

TABLE I.ASSEMBLIES HEATED AT 450 F.

Thickness of Break-away torque coating 24: foot pounds 0 22 Not determined 16 0.00005 inch 14 0.0001 inch 10 0.0003 inch 6 See footnotes at bottom of Table II.

TABLE II.ASSEMBLIES HEATED AT 250 F.

Thickness of Break-away torque coating 24: foot pounds 0 27 Not determined 20 0.00005 inch 17 0.0001 inch 11 0.0003 inch 11 t Average of numerous determinations on plugs of various ypes.

'lhe lacquer was diluted to half the solids content which produced a coating 0.00005 inch thick; the coating was too thin for a microscopic determination of thickness with available equipment.

In another series of tests, installation torque was varied, and spark plugs inserted as described above were treated for two hours at 25 0 R, and break-away torque was then determined. The results of this series of tests are presented in Table III, below: coating thickness in each case was estimated to be one ten thousandth of an inch.

TABLE III Installation torque 1 Break-away torque 1 15 8 20 10 25 l4 3 0 l5 /2 35 l7 1 In foot pounds.

It has also been found that various materials other than the acrylic lacquer used for the tests reported above can be the constituent of the coating 24. For example, various household glues have been found to be operable, as have layers of paper and of regenerated cellulose adhered so that, when the gasket is compressed during installation of a plug, a part of the force is transmitted through the paper or regenerated cellulose, as described above. Preferably, the coating is one which can be applied by immersion of gaskets therein, and which will air dry within a relatively short period of time, but the specific identity thereof is not critical so long as it either softens or decomposes to reduce force, as described.

It will be apparent that various changes and modifications can be made from the specific details shown therewith without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A gasket for use between a spark plug and an engine cylinder head comprising a body having a plurality of facing surfaces, said body being formed from a resilient material which continues to exert a substantially unreduced force between the spark plug and its seat, and a coating on said facing gasket surfaces, said coating being formed from a thermoplastic material which softens or thermally decomposes at a temperature below 200 F., said coating being present in a layer great enough in thickness that the torque required to remove the spark plug after it has been operated in the engine and the coating modified by the heat of operation is not greater 10 than the installation torque.

2. A gasket as claimed in claim 1 wherein said thermoplastic material is an acrylic.

3. A gasket as claimed in claim 1 wherein said coating 6 4. A gasket as claimed in claim 1 wherein said coating is from about 0.5 to about 3 ten thousandths of an inch in thickness.

References Cited UNITED STATES PATENTS 1,211,476 1/1917 Miller 27726 2,127,372 8/1938 Victor et a1. 27721l 3,091,472 5/1963 Balfe 277206 3,099,456 7/1963 Hopp 277166 SAMUEL ROTHBERG, Primary Examiner US. Cl. X.R.

is from about 0.3 to about 5 ten thousandths of an inch 15 277 166 235; 117-132 in thickness.

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