US2691971A - Spark plug construction - Google Patents

Description

Oct. 19, 1954 R, J. L. DUTTERER SPARK PLUG CONSTRUCTION Filed Sept. 21, 1951 MGM IN VEN TOR. %6/i M16. /a//z/ e/ Patented Oct. 19, 1954 SPARK PLUG CONSTRUCTION Rex 3. L. Dutterer, Hastings, MiclL, assignor to Hastings Manufacturing Company, Hastings,

Mich.

Application September 21, 1951, Serial No. 247,600

9 Claims.

This invention relates to improvements in spark plug construction.

This application is a continuation in part oi my copending application for Spark Plug and Method of Manufacture Therefor, Serial No. 728,421 filed February 14, 1947, Patent Number 2,634,716 issued April 14, 1953.

The principal. objects of this invention are:

First, to provide a spark plug which is particularly easy to assemble.

Second, to provide a spark plug which can be manufactured with varied but accurately controllable operating characteristics.

Third, to provide a spark plug which is particularly durable, especially in the performance of its central seal and current conducting elements.

Fourth, to provide a novel form of seal and electrical connection between the sections of a sectional center electrode of a spark plug.

Fifth, to provide a spark plug in which the center insulated electrode may be formed of inexpensive base metals without endangering the seal of the center electrode or the insulator to breakage.

Sixth, to provide a coiled metallic intermediate connector between the sections of a sectional electrode, which connector forms a positive and continuous electrical connection between the electrode sections and which is protected and restrained against deterioration and movement by a solidified seal that also seals the central bore of the insulator in which the electrode is mounted.

Other objects and advantages of my invention will be apparent from a consideration of the following description and claims.

The drawings, of which there is one sheet illustrate a highly practical form of my spark plug.

Fig. 1 is an elevational view of the completed spark plug.

Fig. 2 is a longitudinal cross-sectional view through the insulator of the spark plug illustrating the center or insulated electrode in elevation.

Fig. 3 is an enlarged fragmentary cross-sectional view through the insulator and center elec-- trode of the spark plug in finished assembled condition.

Fig. 4 is an enlarged fragmentary longitudinal cross-sectional view through the insulator illustrating the sections of the center electrode in partially assembled position within the insulator.

Fig. 5 is an enlarged fragmentary elevational view of the lower section of the center electrode with the spiral intermediate connector mounted thereon.

Spark plug manufacturers have recognized for some time that different internal combustion engines require spark plugs having different operating characteristics. Not only must the insulated center electrode of the spark plug provide continuous electrical contact for the passage of ignition current therethro-ugh and be sealed to the insulator to prevent the escape of combustion gases along the center electrode, but the center electrode must dissipate heat through the insulator of the spark plug at different predictable rates in order that the temperature of the inner tip of the center electrode will remain at the desired level during operation. A spark plug which does not dissipate sufiicient heat from its center electrode may become so overheated in some engines as to cause pre-ignition. Such a plug is designated as a hot plug. A plug which dissipates a large amount of heat from its center electrode will have an inner tip that is so cool in some engines that partially burned fuel and oil collects on the tip and fouls the plug. Such a plug is designated as a cold plug. My present invention is directed toward providing a standard form of spark plug having standardized major elements which can be easily and inexpensively manufactured and assembled to have predeterminable operative characteristics ranging from the above described hot plugs to cold plugs.

Fig. 1 illustrates the principal elements of my plug which includes an insulator of insulating ceramic material retained within a metallic sleeve 2. The sleeve 2 is provided with a nutlike head 3 and a threaded inner tip 4 for mounting the same in an engine as is common practice. The sleeve carries a grounded electrode '5 that cooperates with a center or insulated electrode extending through the insulator. The insulated electrode includes an inner tip 6 cooperative with the grounded electrode, and an outer terminal tip 7 adapted to receive a connector wire from the distributor of an engine.

As is more particularly illustrated in Fig. 2 the insulator l includes a central portion 8 of thickened cross-section or diameter and a tapered inner end 9 that extends inwardly through the tip 4 of the sleeve. Throughout this description the elements of the spark plug will be oriented by reference to their usual position with respect to the cylinder of an engine. Thus the tip of the insulated electrode 6 is disposed inwardly of the cylinder, while the terminal 1 is disposed outwardly of the cylinder. The insulator l defines a center bore I0 extending therethrough, the bore being provided with a threaded portion il which is desirably positioned entirely within the thickened portion 8 of the insulator. Inwardly of the threaded portion i I the bore 19 provides a cavity l2 which is also located within the thickened portion ii of the insulator. The inner end of the cavity I2 terminates in an inwardly tapered shoulderJS merging with an inner portion 14 of the central bore of reduced diameter.

The insulated center electrode of the spark plug includes an outer rod-like section IE on which the terminal tip I is formed. The inner end of the outer section i5 is threaded as at is to threadingly engage the threaded portion ll of the insulator. It is pointed out that the threads in the insulator bore are of substantially greater diameter than the threads on the outer electrode section so, that a loose engagement is obtained between the threaded elements. A collar IT on the outer end of the outer electrode section en.- gages the outer end of the insulator to limit the movement of the outer electrode section into the insulator.

The inner tip 6 of the insulated; electrode consists of the inner end of a pin-like inner electrode section 18 that extends through the reduced portion I4 of the central bore in the: insulator. The inner electrode section is provided with a collar 19 having an inwardly tapered under edge 29 which seats upon the tapered shoulder l 3 at the bottom ofthe cavity 12in the insulator. Aboye the collar [9 the inner electrode section is plovided with an outwardly extending centering projection 2|. It will be noted from Figs. 2 and 3 that the inner end of the outer electrode section i8 is spaced substantially from the outer end of the centering projection 2| in the assem' bled positions of the electrode sections.

Electrical continuity in the insulated electrode is provided between the inner electrode section if; andthe outer electrode section by a spirally coiled metallic connector section 22; The spiral connector 22 is guidingly received around the centering projection 2l of the inner electrode sectipn and projects outwardly therefrom. It is desirable that the gauge of wire used in the spiral connector and the diameter of the centering projection 2| be such that the spiral connector 22 is spaced substantially inwardly from the walls of the cavity l2 as illustrated. In its uncompressed condition the spiral connector 22 projects outwardly substantially beyond its final position as will be noted by a comparison of Figs. 3 and 4. The outer electrode section-is providedwith a tapered inner end 23 which centeringlyengages the outerend of the spiral connector-as the outer; electrode section is threaded intothe insulator, and compresses the spiral connector into positive electrical contact with each of 1 the innerand outer electrode sections. The compression in the spiralconnector- 22 also serves to firmly seat the inner electrode section within the bottom of the cavity I2.

In assembling the above described standard elements of my spark plug I prefer to fit the spiral connector 22 on thecentering projection 2| on the inner electrode section, and drop thetwo elements as a sub-assembly into the bore of the insulator. Desirably the spiral connector has sufficient gripping engagement with the projection 2| soas not to become disengaged therefrom. After the inner electrode section and spiral connector are in place I inject a predetermined and measured amount of a semi-fluid or plastic sealing material 24 into the cavity l2-and around the connector 22; The sealingmaterial is desirably a chemically setting ceramic cement including a silicate. of soda binder, andv desirably has a. coefiicient of expansion approximating the coefiicient of expansion of the insulator 1, although this is not of great importance, as the sealing material is located within the thickened portion 8 of the insulatorwhere the insulator has the greatest strength andv ability to resist any tendency of the sealing material to crack the insulator.

After the sealing material 24 is in place the outer electrode section I5 is threaded into the insulator as above described to contact and compress the spiral connector 22. In so doing the inner tip of the outer electrode section wipingly engages the outer end of the spiral connector in a rotary motion to obtain good electrical con- 4 tact therewith. The inner tip of; the outer electrode section also penetrates and displaces a quantity of the sealing material 24 upwardly between the loosely engaged threads on the insulator and the outer electrode section as is indicated at 25 in Fig. 3.

The amount of sealing material thus displaced and forced upwardly in the insulator bore is of course determined by the quantity of sealing material originally introduced into the cavity l2. Thepresence of the sealing material between the insulated center electrode and the wall of the insulator of course increases the rate of radiation of heat from the electrode to the insulator, and by increasing the amount of sealing material and thedistance through which it rises along the threads II I am able to increase the rate of heat dissipation from the spark plug. Thus a great amount of sealing material provides a cooler spark plug, While the reduced amount of sealing material provides a hotter spark plug. It will be noted that the penetration of the outer electrode section into the sealing material also forces the sealing material uniformly around the outer end of the inner electrode section and the spiral connector 22.

It will be noted that the inner electrod is of such a diameter that there is substantial clearance between it and the wall of the bore below the shoulder. The beveled shoulders of the bore and of the inner electrode section result in an effective centering of the inner electrode section in the bore and also close engagement to insure that the sealing material i not forced between the shoulders and between the body portion of the inner electrode and the insulator bore which should be kept free from the sealing material. The intermediate electrode section being of springable material, such as the coil spring illustrated, forces the connecting shoulders together when the outer electrode section is threaded into engagementwith the internal threads of the insulator bore and this also insures a good electrical conducting contact between the intermediate and inner and outer electrode sections.

The sealing cement embeds the portion of the inner electrode section above the shoulder of the bore and keeps the inner electrode centered. It also embeds the intermediate electrod section and the lower end of the outer electrode section so thatno relative movement of these parts can take place after the sealing cement has set. As stated, aself-setting sealing mixture is desirably used. which eliminates the necessity for applying heat to set the sealing mixture. The loose engagement of the outer electrode sectio with the threads of the insulator bore is desirable not only from the standpoint of tolerances in manufacture and difficulty in securing accurate threads in the molded insulator body but it also permits the. sealing mixture forming an effective seal between. the outer electrode and the insulator andinsures that the outer electrode is effectively retained.

Attention is called to the fact that the dimensions of the insulator, theinner electrode section, and the outer electrode section are not particularly critical to the performance of the finished spark plug, as the performance is controlled largely by the amount of sealing material in the plug. It is therefore possible to economically manufacture the. standardized elements of the plug within reasonably accurate limits, and withoutexpensive tolerance controls and inspections. s emb o the. men th a -l1; l s s.

relatively simple and can b carried out without the use of heat or expensive jigs and apparatus.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent is:

1. A spark plug comprising an insulator having a central bore therethrough, said bore having an inner portion of reduced diameter with an outwardly facing beveled shoulder around the outer end thereof, said bore being internally threaded in outwardly spaced relation to said shoulder, an inner electrode section disposed in the reduced portion of said bore and having a beveled shoulder seated upon the outwardly facing shoulder of said bore, the diameter of the inner electrode being such that there is substantial clearance between'it and the bore below the said shoulder, the said inner electrode section having a centering projection extendnig outwardly from its said shoulder and spaced from the wall of the bore, a coiled initially springable metallic intermediate electrode section having its inner end sleeved upon said centering projection and centered thereby, an outer electrode section having loose threaded engagement with the threads of said bore and compressibly engaging the outer end of said springable intermediate section and urging the shoulder of said inner section upon said beveled shoulder of said bore and centering the inner section in the reduced portion of said bore, and a self-setting cementatious mixture filling the said bore between said inner and outer sections and embedding said intermediate section, said mixture surrounding the inner end of said outer section and extending I outwardly between at least a portion of the threads of the outer section and the bore.

2. A spark plug comprising an insulator having a central bore therethrough, said bore having an inner portion of reduced diameter with an outwardly facing shoulder around the outer end thereof, said bore being internally threaded in outwardly spaced relation to said shoulder, an inner electrode section disposed invthe reduced portion of said bore and having a shoulder seated upon the outwardly facing shoulder of said bore,

the said inner electrode section having a centering projection extending outwardly from its said shoulder and spaced from the wallv of the bore, a coiled initially springable metallic intermediate electrode section having its inner end sleeved upon said centering projection and centered thereby, an outer electrode section having loose threaded'engagement with the threads of said bore and compressibly engaging the outer end of said springable intermediat section and urging the shoulder of said inner section upon said shoulder of said bore, and a self-setting cementa tious mixture filling the said bore between said inner and outer sections and embedding said intermediate section, said mixture surrounding the inner end of said outer section and extending outwardly between at least a portion of the threads of the outer section and the bore.

3. A spark plug comprising an insulator having a central bore therethrough, said bore having an inner portion of reduced diameter with an outwardly facing beveled shoulder around the outer end thereof, saidbore having internal projections in outwardly spaced relation to said shoulder, an inner electrode section disposed in the reduced portion of said bore and having a shoulder seated upon the outwardly facing shoulder of said bore, the diameter of the inner electrode being such that there is substantial clearance between it and the bore below the said shoulder, the said inner electrode section having a centering projection extending outwardly from its said shoulder and spaced from the wall of the bore, a coiled initially springable metallic intermediate electrode section having its inner end sleeved around said centering projection and centered thereby, an outer electrode section having projections coacting with the projections of said bore in axially overlapping relation, said outer electrode section compressibly engaging said springable intermediate section and urging the shoulder of said inner section upon said shoulder of said bore and centering the inner section in the reduced portion of said bore, and a sealing mixture filling the said bore between said inner and outer sections and embedding said intermediate section.

4. A spark plug comprising an insulator having a central bore therethrough, said bore having an inner portion of reduced diameter with an outwardly facing shoulder around the outer end thereof, said bore having internal projections in outwardly spaced relation to said shoulder, an inner electrode section disposed in the reduced portion of said bore and having a shoulder seated upon the outwardly facing shoulder of said bore, the said inner electrode section having a centering projection extending outwardly from its said shoulder andspaced from the wall of the bore, a coiled initially springable metallic intermediate electrode section having its inner end engaged with said centering projection and centered thereby, an outer electrode section having projections coacting with the projections of said bore in axially overlapped relation, said outer electrode section compressibly engaging said springable intermediate section and urging the shoulder of said inner section upon said shoulder of said bore, and a sealing mixture filling the said bore between said inner and outer sections and embedding said intermediate section.

5. A spark plug comprising an insulator having a central bore formed therethrough and having a thickened intermediate section adapted to be received in a metal shell, said bore having an inner portion of reduced diameter with an outwardly facing shoulder around the outer end thereof and located within the thickened intermediate section of the insulator and substantially inwardly from the outer end of said thickened portion, threads formed around a portion of said bore and spaced outwardly from said shoulder and within the thickened portion of the insulator, an inner electrodev section projecting through the inner reduced portion of said bore and having a collar seated against said shoulder, a centering projection on said inner electrode section extending outwardly from said collar and spaced from the wall of said bore, an outer electrode section extending into said bore from the outer end thereof, the inner end of said outer electrode section being spaced from said centering projection, a coiled metallic connector section sleeved around said centering projection and compressed between the collar on said inner electrode section and the inner end of said outer electrode section, said connector being spaced from the wall of said bore, threads formed around said outer electrode section and engaging the threads in said bore, the threads in said bore being of greater diameter than the threads on said outer electrode section whereby a loose threaded engagement is obtained therebetween, and a sealing mixture including a 2,091 ,QY-Eli chemically setting cement. filling; said bore be-- tween; said; inner and outer electrode-sections and surrounding said connector sectiomsaidseale ing mixture extending outwardly between the;

threads on said outer electrode section; and the threadsin said bore.

6. A spark plug comprising an insulator having acentral bore-formed-therethrough and having a thickened intermediate sectionadapted to:-b.e; received in a metal shell, said borehaving an tion projectingthrough the inner reduced portion.

of said bore and having a collar seated. against. said shoulder; a centering projection on said inner electrode section extending outwardly fromsaid collar and spaced from the wall of said bore, an-

outer electrode section extending intosaid. bore. from the outer end thereof and having a. collar engaging the outer end of said insulator, the

inner end of said outer.v electrode. section being,

tapered and spaced'from said centering. projection, a coiled metallic connector section sleeved around said centering projection and compressed.

between the collar on said inner electrode section;

and the inner tapered end of said outer electrode section, said connector beingspaced from the wall.

of said bore, radial serrations formed around said outer electrode section and engaging the serrations in said bore, the serration in said bore being of greater diameter than the. serrationsonsaid outer electrode section whereby a loose.inter.-

locking engagement is obtained therebetween,.

and a sealing mixture including a chemically setting cement filling said bore between said inner and outer electrode sections and surrounding said connector section, said sealing mixture extending outwardly between the serrationson said outer. electrode section and the serrationsin said bore.

7. A spark plug comprising an insulator having a. central bore formed therethrough, said bore having an inner portion of reduced diameter with an outwardly facing beveled shoulder around the outer end thereof, radial serrations formed around a portion of said bore and spacedoutwardly from said shoulder, an inner electrode section projecting through the inner reduced portion. of saidbore andv havinga collar seated against said shoulder, a centering projection on said inner electrode section extending outwardly from said collar and spaced from thewall of said bore, an outer electrode section extending into said bore from the outer end thereof and having a collar engaging the outer end of said insulator, the inner end of said outer electrode section being tapered and spaced from said centering projection, a coiled metallic connector section sleeved.

around said centering projection and compressed between .the collar on said inner electrode section' and the inner tapered end of said outer electrode section, said connector being spaced from the wall.

of said bore, radial serrations formed around said outer electrode section and engaging the serrations in said bore, the serrations in said bore being of greater diameter than the serrations on said.

outer electrode section whereby a loose interlocking engagement is obtained therebetween, andv a sealing mixture. including; a. chemically setting cementfilling saidrbore between saiduinner' andiouter electro desections: andsurrounding. said' connector section; .saidsealing mixture extending outwardly between the serrations on said: outer electrode section and the serrations in saidbore.

8; A spark plugcomprising an insulator having a central bore formed therethrough, said bore havingan inner portion of reduced diameter with anoutwardlyfaoing; shoulder around the outer end thereof, axially spaced radial projections formed alonga portion of said bore and spaced outwardly. from said shoulder, an'inner electrode section proj ecting. through 'theinner reduced portionv of said bore and having a collar seated against said shoulder, a centering projection on said inner electrode sectionwextending outwardly from-said-collar and spaoedfrom. the wall of said bore, an outer electrode sectionextending into said bore from the outer end thereof and having a collar engaging'the outer-endof said insulator, the'innerrend'ofisaid outer. electrode section being spaced from saidcentering projection, a coiled metallic connector. section sleeved around said centering projection and compressed between the collar onsaid inner. electrode section and the inner end ofsaidouter electrode section, said connector being spaced from the wall of said bore;.radially projecting ribs'formed around said outer electrode section and. spaced between the projections in said'bore' in axially overlapping relation; anda sealing mixture including a chemically setting; cement filling said bore between said inner and outer electrode sections and surrounding said connector section, said sealing mixture extending outwardly between the ribs on-said outer electrode section and the 'projectionsin said bore.

9. A spark'plugr comprising; an-insula-tor having a central: bore formed: therethrough, saidbore having aniaxially inner portion of reduced-diam-- eter', axially spaced radial: projections formed along-a portion of 'said'bore and spacedoutwardly from said-reduced: portion: of said vbore, an inner electrode section projecting: through the inner reduced portion of said'bore andseating therein, a centeringprojection. on. said inner electrode section extending outwardly from said reduced portion'of' sa-id'bore, an outer electrode'section extending into said bore from the outer end there-- of and havingacollar; engaging the outer end of said insulator, the inner 'end of :said: outer electrode-sectionbeingtapered and spaced from said centering projection; a coiledmetallic connector section'jsleeved. aroundfsaid centering projection and compressedbetweensaidiinner electrode.section and the inner taperedend-ofsaid-outer electrode section, said connector being spaced from.

the wall of said bore; radial ribsformed around. said outer electrode section and. positioned.between the projections in said here in axially over= lapping relation, and asealing mixture including a chemically setting cement filling said bore between said inner and outer electrode sections and:

surrounding said connector'section', said sealing mixture extending outwardly'between the ribs on said outer electrode section andthe projections in said bore.

References, Cited in the file of this patent.

UNITED "STATES PATENTS Number Name Date 2,071,571 Rabezzanazet' a1: Feb; 23; 1937 2,246,948 McCarty-etal -June 24, 19.41. 2,317,305 Schwartzwalderet a1; Apr. 20,1943 2353348 Tognola etal ..Nov; 2, 19482

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