US2267571A - Spark plug - Google Patents

Description

Dec. 23, 1941. T. G. MCDOUGAL SPARK PLUG Filed July 27, 1940 3maentor Patented Dec. 23, 1941 SPARK PLUG Taine G. McDougal, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application July 27, 1940, Serial No. 348,056

9 Claims.

This invention has to do with spark plug electrodes and method of assembling and sealing same in the usual bore in the insulator. It is an improvement on the invention described and claimed in Patent No. 2,106,578 igranted to Schwartzwalder and Kirk on January 25, 1938. In that patent there is disclosed an electrode consisting of two axially separated parts secured to each other and to the insulator by an intermediate conducting glass seal. The lower electrode part cooperates with the usual side electrode to provide a spark gap while the upper electrode part constitutes the terminal to which the spark plug lead is secured. In the assembly in the upper end of the bore. Thereafter the assembly is heated to partially fuse or soften the glass whereupon the upper part of the electrode is forced down into the glass causing it to be squeezed into the space between the electrode and the insulator bore. The glass adheres fairly well to the electrode parts and tenaciously to the insulator and, upon hardening, forms a strong, tight seal and at the same time, owing to its conducting property, allows passage of current to the sparking end of the electrode.

An important feature of my invention consists in the provision of means to limit the extent of movement of theupper part of the electrode into the insulator bore during assembly. This not only insures uniformity in the product but in sures the presence of conducting glass between the ends of the electrode sections rather than metal to metal contact. This glass, while soft, accommodates itself to any variations in length of the sections of the electrode.

It is also frequently desirable to employ an electrode having an enlarged end at the spark gap. The head is preferably of such shape as to form a tight seal with the end of the insulator preventing hot combustion gases from entering the insulator bore and attacking the electrode metal. With such constructions it is necessary to provide some means for gripping the upper end or the electrode section to hold it in place. Because the bonding of the glass seal to the upper end of the lower electrode section may not remain stable in service for this purpose I have preferred to provide as an additional safeguard some form of mechanical interlock. Thus the upper end of the lower section may be expanded sition. Such insulators are ornvetedovertolocktheelectrodelectionin place or it may be so shaped or roughened as to mechanically interlock with the glass seal. It may be desirable to provide a washer 0r gasket, preferably of soft metal, around the lower electrode section and resting on thebottom ofthe upper part of the electrode bore to prevent the glass seal when softened during assembly from penetrating into the lower part of the electrode bore.

In application Serial No. 343,808 filed on July 3, 1940, by Schwartzwalder and Rulka it is proposed to employ two glass pellets instead of one for forming the seal. One pellet is of such composition that it softens but slightly during assembly. This pellet is placed in the lower part of the insulator bore, secures the electrode in place and forms a good seal with the insulator. The upper pellet is less heat resistant and becomes more fluid upon heating during assembly, and flows about the upper section of the electrode and forms a good bond with the electrode metal, the insulator and the remainder of the glass. Another feature of my invention consists in the use of concentric glass pellets, one of the pellets being of such composition as to grip the ends of the electrode sections and the other being especially adapted to bond to the insulator, the two glass compositions uniting with each other on assembly.

Other objects and advantages of the invention will be pointed out during the course of the following description taken in connection with the accompanying drawing in which:

Figure 1 is a longitudinal vertical section through the insulator with the electrode assembled in it.

Figure 2 is a similar ilcation. v

Figure 3 is a fragmentary view similar to Figure 1 showing a modified construction as it appears prior to final assembly.

Figure 4 is a view corresponding to Figure 3 showing the parts as they appear after final assembly.

Figures 5 and 6 are views similar to Figures 3 and ishowing a further modification.

Figure 7 is an enlarged section through the sealing pellet employed in Figure 3.

view showing a modi- Figure 8 is a corresponding section through the sealing pellet shown in-Figure 5.

In Figures 1 to 6, It indicates the spark plug insulator which may be of any desired compocustomarily made of porcelain but may be made ofsintered oxides or mixtures oi oxides and silicates. Theinsu- I in assembling the insulators.

' cated at 30.

lator of Figures 1 and 2 is provided with a bore consisting of an enlarged upper portion I2 and areduced lower portion I4 connected by shoulder I6. In the enlarged portion I2 is provided the upper electrode section I8 preferably having its lower end roughened as by means of threads or the like. The lower electrode section 22 is provided with an enlarged head 24 having sealing engagement at 26 with the lower end of the insulator. The upper end of the lower electrode section 22 is preferably provided with a gasket 28 which may be of any suitable metal or other heat resistant material. The gasket is held in place by heading or riveting over the upper end of the electrode section 22 as shown. 32 indicates conducting sealing material bonded to the electrode sections and to the insulator. In order to obtain a degree of mechanical interlocking with the insulator the latter may be provided with a threaded or otherwise roughened surface as indicated at 34. The conducting material preferably consists of heat resistant glass, such as Pyrex, mixed with powdered copper and fused in place as described in the copending application of Schwartzwalder and Rulka, Serial No. 343,808, previously referred to.

In assembling the parts shown in Figure 1 the method described in the Schwartzwalder and Kirk Patent 2,106,578 and the previously mentioned application is preferably employed, that is, the sealing composition either in powdered form or pellet form is inserted in the bore between the two electrode sections, the assembly is heated to soften the sealing material and thereafter the electrode section I8 is pressed into place. i It is important to note that electrode section I8 is provided with a shoulder 36 which limits the extent of insertion of the electrode section into the insulator bore. This insures uniformity Furthermore the sealing composition, when soft, yields to allow for any variations in the length of the electrode parts thereby doing away with thenecessity for accurate machining.

With the described construction the lower electrode section 22 is held in place by the grip on the insulator resulting from the riveting indi- Consequently there is tight sealing engagement between the electrode and the insulator at 26 and at the same time the washer 28 prevents the sealing composition 32 from entering the lower portion of the insulator bore. The upper electrode section 20 is securely held in place by the sealing composition.

In this and the succeeding designs, it is desirable to make the lower electrode section of metal or alloy that is resistant to heat and corrosion. The upper electrode. section 20 may be made of good heat conducting material such as l'copper or the like.

The modification shown in Figure 2 is substantially the same as that descibed except that the washer 28' is merely a tight fit on'the lower electrode section 22. Another difference is that a mechanical interlock is provided between the upper end of the lower electrode section and the sealing composition. This may take the form of grooves or notches asindicated at 38 into which the sealing composition is forced on assembly so that it grips the electrode section and prevents its displacement.

Another difference in construction'consists in parts, a central part 2I and a surrounding terminal portion 23 having a flange 25 corresponding to flange 36 of the form shown in Figure 1. The part 2| is headed or riveted over'as shown at 21 to retain terminal 23.

In the modification shown in Figures 3 and 4 the electrode is indicated as made of three parts. The lower part I22 is made of heat resistant metal or alloy and is provided with shoulder I24 to limit its insertion into the lower end of the insulator bore, and with an undercut portion I26 for interlocking engagement with the sealing composition I28. The sealing composition is preferably prepared in the form of a central cylinder I30 with a surrounding cylindrical shell I32. The portion I30 may be made of a mixture of glass and metal characterized by ability to bond well to the electrode metal. For'this purpose the following composition may be used:

Percent Lead borosilicate glass 50 Copper 50 The shell I32 is preferably of a similar glassmetal composition characterized by ability to bond Well to the insulator as well as to the sealing composition I30. The following is a satisfactory composition for this purpose:

. Percent Borosilicate glass 55-30 Copper 45-70 134 indicates an intermediate electrode section having a lower reduced and undercut portion I36 similar to the part I26 of the lower section I22, except that thereduced portion has a gradually tapered connection with the body of the electrode section.

Electrode section I34 may have its upper end slotted as shown and seated in an enlarged portion I40 of the insulator bore. Electrode section I34 may be suitably bonded to upper electrode section I 42 by sealing composition I44 in the manner previously described. The sealing is accomplished in the manner previously described, that is, the assembled parts are heated to soften the sealing material and thereafter the electrode sections are forced into the bore until the lower electrode section assumes its position shown in Figure 4. In this embodiment the glass interlockswith the ends of the electrode sections to hold the parts assembled.

The form of the invention shown in Figures 5 and 6 is substantially the same as that shown in Figures 3 and 4 except that the sealing composition is made in the form of concentric pellets I50 and I52 adapted to encircle the adjacent reduced and undercut portions I26 and I28 of the electrode sections. After final assembly the parts assume the position shown in Figure 6.

I claim:

1. A spark plug comprising an insulator having a bore therein, an electrode in said bore making the upper electrode section 20' in two comprising a lower section having an end serving as a sparking electrode, an upper section having a terminal for connection with a suitable lead and an intermediate electrically conducting seal interposed between said electrode sections, and means on said upper section for limiting the extent of insertion of the upper section into the bore so as to insure a gap filled with said conducting seal between said sections.

2. A spark plug comprising an insulator having a bore therein, an electrode in said bore comprising a lower section having an end serving as a sparking electrode, an upper section having a terminal for connection with a suitable lead and an intermediate electrically conducting glass seal interposed between said electrode sections,

and an annular flange on said upper section for limiting the extent of insertion of the upper section into the bore so as to keep said electrode sections out of direct contact.

3. A spark plug comprising an insulator having a bore therein, an electrode in said bore comprising a lower section having an end serving as a sparking electrode, means on said section cooperating with said bore to prevent said section from passing out through the sparking end of said bore, an upper section having an end serving as a terminal for connection with a suitable lead, an intermediate conducting seal, said upper section being provided with stop means cooperating with the upper end of the insulator to limit the extent of insertion of the upper section into the bore so as to keep said sections out of direct contact.

4...A spark plug comprising an insulator having a bore therein and'an electrode in said bore comprising a lower section having an enlarged end serving as a sparking electrode and engaging the lower end of the insulator to seal the bore against the entrance of hot combustion gases,' means adjacent the upper 'end of said section cooperating with said bore to prevent said section from passing out through the lower' end of the bore, an upper section having a terminal for connection with a suitable lead, and an intermediate-conducting seal bonded to the electrode sections and the insulator.

5. A spark plug comprising an insulator having a bore therein, the lower portion of the bore being of reduced diameter, an electrode in said bore comprising a lower section having an enlarged en d serving as a sparking electrode and having gas-tight sealing engagement with' the lower end of the insulator, means on said section above said reduced portion of the bore'engaging the shoulder between said bore portions to prevent said section from passing out through the lower end of the bore, an upper electrode section having a terminal for connection-with a suitable lead and an intermediate conducting seal bonded to the electrode sections and to the insulator. 1

6.'A spark plug comprising an insulator having a bore therein and an electrode in said bore comprising a lower section having an enlarged end serving as a sparking electrode and engaging the lower end 'of' the insulator to seal the bore against the entrance of hot combustion gases, means adjacent the upperend of said section cooperating with said bore to prevent said section from'passing out through the lower end of the bore, an upper section having a terminal for connection with a suitable lead, and an intermediate conducting seal bonded to the electrode sections and the insulator, said upper'section being provided with stop means cooperating with the upper end of the insulator to limit the extent of insertion of the upper electrode section into the bore so as to keep said electrode sections out of direct contact.

7. A spark plug comprising an insulator having a bore therein, an electrode in said bore com prising a lower section having a sparking electrode portion and an upper section having a terminal portion, ing seal separating said portions and bonded to the electrode sections and the insulatonone of said sections being formed to mechanically interlock with said seal to prevent its withdrawal from the bore.

8. A spark plug comprising an insulator having a bore therein, an electrode in said bore comprising a lower section having a portion serving as a sparking electrode, an upper section having a terminal portion, and an intermediate conducting seal separating said portions and bonded to the electrode sections and the insulator, said seal comprising a central portion especially adapted to bond to the electrode sections and the surrounding portion especially adapted to bond to said insulator, said portions being integrally joinedtmeach other.

9. The method of assembling electrodes in spark plug insulators which consists in providing an insulator with a bore therein, inserting an electrode in the lower end of the bore, thereafter inserting in said bore fusible electrically conducting sealing material composed of a central portion especially adapted to bond to the electrode material and a surrounding portion especially adapted to bond to the insulator and then inserting in said bore the,upper electrode section; heating the parts so assembled to soften said fusible sealing material and thereafter pressing one of said electrodes into the bore to cause the sealing material to flow about the ends of said electrodes and the surrounding portions of the bore and thereafter permitting said assembly to cool so that the sealing material hardens and forms a gas-tight bond with the electrode sections and the insulator.

TAJNE G. McDOUGAL.

and an intermediate conduct

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