US2891187A - Spark plug - Google Patents

Description

June 5 M. A. BREfscH ET AL 2,891,187

SPARK PLUG Filed Nair. 15,

INVENTORS I Mahae/ A. 5/6756/7 BY Faber) E A osfram I QTTURNEYS United States Patent SPARK PLUG Michael A. Bretsch and Robert F. Nostrant, Toledo, Ohio, 'assignors to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application November 15, 1956, Serial No. 622,350

8 Claims. (Cl. 313-136) This invention relates to a spark plug, and, more particularly, to a spark plug having an improved electrode assembly which enables satisfactory sparking in an engine operating at a high output.

It has been found that, for any given spark plug, there is a maximum output in any given engine, which can be measured in terms of indicated mean effective pres sure (I.M.E.P.), above which the plug will not spark satisfactorily. Spark plug failure in such case may be indicated by pre-ignition, which is early combustion of the fuel-air mixture being used, or it may be indicated merely by a failure of the plug to ignite the mixture. It has also been found that, other factors being equal, a spark plug having a short insulator nose end adjacent the center electrode will continue firing satisfactorily at higher engine outputs than will a plug with a longer insulator nose end. However, many other factors also affect substantially the maximum output, as measured by engine I.M.E.P., at which different spark plugs of the same design, and made of the same materials, become inoperative. Therefore, I.M.E.P. ratings, or maximum indicated mean effective pressures at which different spark plugs will spark satisfactorily, vary within relatively wide limits even among difierent spark plugs which are identical to one another within the limits of manufacturing tolerances. Also, it has been found that, other factors being equal, spark plugs having short insulator nose ends are more subject to fouling than are plugs having long nose ends. As a consequence, a dual problem exists in previously known spark plug designs; that of finding a spark plug structure which will enable satisfactory sparking with minimum fouling in engines operating under heavy loads, and that of finding a spark plug structure which can be produced in large quantities in such a way that engine load at which satisfactory sparking ceases is approximately uniform from plug to plug of a given design.

The instant invention is based upon the discovery of a spark plug including a particular electrode assembly which both increases themaximum load at which satisfactory sparking ceases for a given design and decreases the deviation from average engine load at which satisfactory sparking ceases in any given lot of spark plugs of the same design.

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 electrode assembly which will operate satisfactorily in engines running under a high load, or at a high I.M.E.P.

Itis still another object of the invention to provide spark plugs in which deviations from average engine load at which satisfactory sparking ceases are minimized by virtue of the inclusion therein of a particular electrode assembly.

Other objects and advantages will be apparent from the description which follows, reference being had to the accompanying drawings, in which- Fig. 1 is a fragmentary vertical sectional view of a spark plug electrode assembly according to the invention;

Fig. 2 is a fragmentary view in vertical section of a different embodiment of a spark plug electrode assembly according to the invention;

Fig. 3 is a vertical sectional view of a part of a spark plug showing an electrode assembly according to the invention which is similar to that of Fig. 1 except that various component parts are associated in different ways;

Fig. 4 is a fragmentary view in vertical section of a spark plug electrode assembly similar to that of Fig. 1, but showing still further modifications of the relationships among various component parts;

Fig. 5 is a fragmentary sectional view showing still further modified relationships among component parts of a spark plug electrode assembly according to the invention;

Fig. 6 is a sectional view showing a fragment of a spark plug electrode assembly in which the relationships among component parts are still further modified;

Fig. 7 is a sectional view along the line 7-7 of Fig. 1; and

Fig. 8 is a sectional view along the line 8-45 of Fig. 2.

According to the invention an improved spark plug assembly is provided. Such assembly, as shown in Fig. 1, comprises an appropriate ceramic insulator indicated generally at 11, of which only a fragment is shown. A firing tip 12 is seated in a central bore 13 which extends through the insulator 11. In an assembled spark plug the electrode firing tip 12 is in operative spaced relationship with an appropriate ground electrode. A tubular member 14 extends through the bore 13, in close proximity to the walls of the insulator which surround the bore, and, at its lower extremity, extends downwardly and surrounds and is in electrical contact with a cap 15 which is integral with the tip 12. A packing material 16, which is preferably in a finely divided form, and can be talc or other suitable resilient powdered material (see, for example, U.S. Patent 2,020,966), or could be copper powder, silver powder, aluminum powder, or other metal member 17 which extends downwardly into the upper portion of the tube 14, in electrical contact therewith.

At any desired position in the insulator bore 13 above the plug member 17 a suitable gas-tight seal, which can be a glass seal, a talc seal, or other suitable seal is provided, and appropriate electrical connections are made to the plug member 17. The relationships among the various parts are shown in horizontal section in Fig. 7.

An assembly which is preferred in some respects is shown in Fig. 2. This assembly comprises an appropriate ceramic insulator, a portion of which is designated generally at 18. A stepped central bore 19 extends through the insulator 155, with a firing tip 20 extending from the lower end thereof. A sleeve 21 is welded or otherwise rigidly attached to the firing tip 20, and extends upwardly therefrom, in close proximity to the walls of the insulator which surround the bore. A radial slit 22 which separates walls 23 and 24 of the sleeve 21 extends longitudinally from the top to the bottom thereof. A powdered material 25 is packed inside the sleeve 21. The sleeve 21 is flanged outwardly at its upper extremity to receive a plug member 26, with which it is in electrical contact. At any desired point above the upper extremity of the sleeve 21 an appropriate gas-tight seal is provided, and suitable electrical connections are made to the plug member 26. Relationships among the various parts are shown in horizontal section in Fig. 8.

An assembly shown in Fig. 3 is similar to that of Fig.

1, comprising an insulator indicated generally at 27 with a.

central bore 28 extending therethrough, a firing :tip29.

extending from the lower extremity of the bore 28, a tube 30 packed with a suitable powdered material 31 electrically interconnecting the firing tip 29 and a plug member 32. The firing tip 29 andthe plug member-.32 havereducedportions 33 and 34, respectively, which extend inside the tube 30 to provide the requisite structural integrity and electrical connections for the assembly. I

Still another assembly according to the invention, as shown in Fig. 4, comprises an insulator indicated generally at 35, a firing tip 36 extending from the lower portion of a bore 37, and a tube member 38 interconnecting the firing tip 36 and a plug member 39. The tube 38 is compressed radially inwardly around a cap 39 at the upper extremity of the firing tip 36, and is flanged outwardly .to receive the plug member 39. A center electrode 40 provides an electrical connection from the firing tip 36, through the interior of the tube 38, and through the plug member 3Q. Finely divided suitable packing material 41 is provided in the annular space between the center electrode 40 and the tube 38.

As is shown in Fig. 5, a plug member 42 can be employed in the assembly of Fig. 1. The plug member 42 is similar to that numbered 17 except that it fits tightly against the adjacent walls which define the bore .13, instead of being spaced therefrom.

Instead of using the plug member 17, the. structure of Fig. 1 can also be modified, as shown in Fig. 6, by substitution therefor of an upper electrode portion 43 which extends downwardly inside the tube 14, in electrical contact therewith, and also extends upwardly through a glass or other seal to provide a suitable electrical connector.

It will be appreciated that the instant invention provides, in its essential details, an electrode assembly comprising a firing tip seated in the nose end of the bore of an appropriate insulator, an annular bushing member at least mechanically connected to the firing tip and extending upwardly therefrom away from the nose end of the insulator, in close proximity to the walls thereof which define the central bore, a finely divided powdered mate rial packed into the bushing member, and a plug member closing an open upper end of the bushing.

It will he noted that, in the structures shown in Figs. 1-8, the tubes or sleeves shown extend away from the firing tip and the nose portion of the insulator to a position which is radially aligned with an enlarged portion of the insulator. When an assembly as illustrated in any of the drawings is incorporated in a spark plug, the insulator is seated in a metal shell which contacts the radially enlarged insulator portion. Although the invention is in no way limited to or by the following theoretical explanation, it is believed that, as the load on an engine is in creased, so that the average cylinder temperature is correspondingly increased, the amount of increase of temperature of the nose portion of a spark plug insulator positioned within the cylinder depends upon the thermal conductivity of the insulator material and the length of the path for heat conduction from the tip of the insulator, adjacent the electrode firing tip, to the point where the insulator is in contact with the metal shell. Since, in most engines, the metal shell is threaded into a water jacketed cylinder head, its temperature can be considered as independent of average cylinder temperature, with the result that the two indicated variables principally determine the temperature of the insulator tip. It is further believed that assemblies in accordance with the invention tend to increase the I.M.E.P. rating of any given spark plug by providing, when a tube or sleeve of high thermal conductivity material is employed, a more effective path for the transfer ofheat fromthe extreme tip end of the insulator to the portion thereof which, contacts the metal shell. When, as is usually preferred, an assembly according to the invention includesa tube or a sleeve composed of a high thermal conductivity metal, it is desirablethat such'tube or sleeve extend from the firing tip of the electrodefto a point in the insulator which is at least as far from such tip as a plane through the points of contact between the insulator and the metal shell in a completely fabricated spark plug. Most desirably, the tube or sleeve extends beyond such plane a distance sufficient to assure that variations in manufacturing operations will not result in some assemblies where the tube or sleeve extends a lesser distance. Ordinarily, there is no reason for the a tube or sleeve to extend a greater distance beyond such plane, although a greater length is not detrimental.

The foregoing discussion suggests an explanation for improved LMEP. ratings for spark plugs produced from electrode assemblies according to the invention. As has been indicated above, however, increasing the I.M.E.P.

rating of a spark plug has not, even heretofore, been a serious problem. It has been possible to increase the I.M.E.P. rating of spark plugs by changing the design thereof, and specifically by shortening the nose portion so that the path for heat transfer from the tip of the insulator to the portion thereof in contact with the metal shell is shortened.

However, there has not heretofore been any known way to minimize deviations from average I.M.E.P. rating in a lot of spark plugs all produced of the same materials, and to the same specifications. It has been found that such deviations are greatly reduced in spark plugs including an electrode assembly according to the invention. For example, a lot of spark plugs including an electrode assembly of the type shown in Fig. 3 of the drawings, and wherein the vertical distance from the tip of the insulators to the point on the insulator where it contacted the metal shell was 0.781 inch, was assembled and tested under varying conditions of engine load. It was found that the average indicated mean effective pressure at which these plugs failed to spark satisfactorily was 230 pounds per square inch gauge. The dif ference between maximum indicated mean effective pressure at which any plug failed to spark satisfactorily and the minimum was 9 pounds per square inch gauge.

, When, for purposes of comparison, but not in accordance with the invention, a lot of 5 spark plugs of the same general design as those described in the preceding paragraph, but with a solid conductor extending upwardly through the bore of the insulator from the firing tip instead of the tube 30, and with a substantially shorter insulator nose end so that the average I.M.E.P. at which the plugs ceased to operate was 224 pounds per square inch gauge, it was found that the difference between the maximum I.M.E.P. and the minimum at which satisfactory sparking ceased was 15 pounds per square inch gauge. It has also been found that insulator cracking in service is a serious problem when a solid conductor is used instead of the tube 30, for example. conductors have been produced by casting a metal of high thermal conductivity in the insulator bore, and also by merely inserting an appropriately shaped solid conductor.. In both cases, however, nose cracking is a serious problem.

It is believed that a snug fit between the tube or sleeve of an electrode assembly in accordance with the invention and the walls which define a central bore in an insulator is important. Accordingly, such an assembly including a sleeve as shown in Figs. 2 and 8 is a preferred embodiment of the invention. In preparing such an assembly it is possible to insert a tube having an appreciably smaller outside diameter than the interior diameter of the bore with which it is to fit snugly, and then to expand such sleeve into close fitting relationship with the bore, for example when the finely divided powdered material is packed thereinside.

It is also believed that the identity of the powdered material packed inside a tube or sleeve in an electrode assembly according to the invention is of relatively minor importance. For example, satisfactory results have been Such solid,

achieved using talc as the powdered packing material, but powdered metals, for example, copper, silver, aluminum, or the like can also be employed, as well as alumina, bentonite, silica, aluminum silicates, and the like.

It will be apparent that various changes and modifications can be made from the specific details disclosed in the attached drawings and discussed in connection therewith without departing from the spirit and scope of the attached claims. For example, any of the various electrical and mechanical connections shown between the firing tip electrode portion and a tube or sleeve, as well as between a stud member and the tube or sleeve, can be used in any of the several structures. A center electrode can be employed extending through the tube or sleeve as shown in Fig. 4, or electrical conductivity through the tube or sleeve can be relied upon for electrical contact as in the other views. Other changes and modifications will be apparent to one skilled in the art.

What we claim is:

1. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of the insulator, a generally cylindrical annular member connected to said firing tip and extending upwardly therefrom through the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided powdered material tightly compressed inside the cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

2. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of the insulator, a generally cylindrical annular member connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided powdered material tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

3. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal connected to said firing tip and extending upwardly therefrom through the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided powdered material tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

4. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided powdered material tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

5. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided talc tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

6. in a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided copper metal powder tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

7. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided aluminum metal powder tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

8. In a spark plug, an insulator having a central bore extending therethrough and exteriorly contoured to provide a seat for engagement with the interior of a metal shell, a center electrode firing tip seated in the nose end of the bore of said insulator, a generally cylindrical annular member composed of a high thermal conductivity metal, and having a longitudinally extending opening through the entire height of its side walls, said cylindrical member being connected to said firing tip and extending upwardly therefrom in close fitting relationship with the bore of said insulator, a substantial portion of said member being disposed toward said firing tip from the insulator seat, finely divided powdered material tightly compressed inside said cylindrical member, and a stud member closing the upper extremity of said cylindrical member.

References Cited in the file of this patent UNITED STATES PATENTS

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