US2350396A - Spark plug electrode - Google Patents

Description

June 6, 1944. J. R JG'RETZINGR ETAL 2,350,396

{ PARK PLUG ELECT umanam- E.:

n 226307/ @n sz% MW l(lttcarnegs Patented June 6, 1944 sraax PLUG ELEcraonE John B.. Gretzlnger, Alexander J. Battey, and Hector Rabenana. Flint, Mich., assignors to General Motors Corporation. Detroit, Mich., a corporation of Delaware Application September 22, 1941, Serial No. 411,814

6 Claims.

This invention relates to spark plugs, particularly to spark plug electrodes.

With many types of plugs made today some difllcultyhas been experienced with the sparking end of the insulator. Because of the diillculty of obtaining a cement having a satisfactory coeillcient of expansion, it has been found expedient to mount the electrode in the insulator so that it is spaced from .the insulator by an air gap through a substantial part of the sparking end of its length. To increase the dielectric path between the conductor shell and the insulator, it is desirable to provide clearance space between the sparking end of the insulator and the shell, leaving that end of the insulator unsupported. It has further been found advantageous to make electrodes which`are separate from the spark plug terminal, and to seal the electrode in the insulator by means of a material which'bonds itself to both the electrodev and the insulator to form a substantially gas tight joint. This sealing material is electrically conductive to complete the circuit between the terminal and the electrode. It has been found, however, that with plugs of this, type, shocks or jars transmitted to the plug tend to cause vibration of the electrode in the course of which the free or sparking end of the electrode may strike the thin, unsupported tip of the insulator, resulting in chipping of said tip.

Figure 3 is a section on line 3-3 of Figure 2.

Figures 4-10 illustrate alternative methods of practising this invention.

Figure 1 shows a spark plug having a conductor shell 2. An insulator 4 of any suitable material is secured in conductor shell 2 between gaskets 6 and 8. The lower portion III of insulator 4 is tapered as shown to provide a clearance space between shell 2 and tapered portion II. This clearance space is desirable to increase the dielectric surface between insulator I0 and shell 2.

A center'wire or electrode I2 is mounted in a longitudinal opening or bore I4 of insulator 4. Electrode I2 is smaller than bore I4, leaving a clearance space. Because of the differences in the coeillcients of expansion of the insulator and available cements, it has been found desirable to leave this clearance space free to avoid cracking of the insulator. The upper portion of the 1ongitudinal bore through the insulator is enlarged as indicate'dat I6. The juncture of the diilerent diameter openings I4 and I6 forms a shoulder Il.

It is the object of this invention to provide a spark plug having the advantages of the plug set forth above but without the tendency to chip ping of the insulator. More speciilcally, it is the object of this invention to provide `means on the electrode near the sparking end but back from the insulator tip a short distance which will prevent contact between the electrode and the insulator tip during the said vibration. In fact, said means is intended to and does limit such vibration by materially decreasing the clearance between the insulator and the electrode at a given point. The said means comprises a raised portion on the electrode back a short distance from the insulator tip to prevent contact between the insulator tip and the electrode. This raised portion may conveniently be made up of a plurality of closely spaced projections, which may be formed by knurling.

Figure l shows a longitudinal sectional view of a complete spark plug made according to this invention.

Figure 2 is a detail view of the sparking end of the insulator `and electrode made according to this invention.

A collar 2li is provided on electrode I2. 'I'his collar cooperates with shoulder Il to position electrode I2 longitudinally in bore I4. A seal 22 is bonded to insulator 4 and collar 2li to hold electrode I2 in place in opening I4 and to make a gas tight joint. The material of which seal 22 is made is preferably a glass having a low coeilicient of expansion such as magnesium borate glass. This glass is 4preferably mixed with a 1111er which serves as an electrical conductor. 'Ihe illler may be graphite, with or without metal inclusions or metallic compounds. A seal of Vthis type is described in Patent 2,106,578 to Karl Schwartzwalder and William Shuford Kirk, issued January 25, 1938.

Secured in the large diameter bore Ii is a suitable terminal 24. Terminal 24 is likewise held in place by the sealing material'22, some of which is shown as having passed upward along the lower end of screw 24 to fill in the annular space between screw 24 and insulator 4.

Near the lower end of electrode I2 we have disposed a plurality of circumferential projections which are shown in Figures 1-4 as a vertical knurl 26. This knurl may be made by any suitable machining process, well known to those skilled in the art. The various projections provided on electrode I2 by the knurl 26 provide a plurality of supports whereby the electrode contacts the walls of opening I4 when laterally displaced.

Figure 4 illustrates another application of this invention. In this gure electrode I2 is reduced in Figure 4 is the same as that illustrated in Figures 1-3.

Figure 5 illustrates an electrode having what is known as a horizontal knurl 2l in which the projections may comprise parallel concentric v rings on electrode I2.

The knurl is the preferred form of projection or support. This is true because, as is easily seen from the drawing, the knurl furnishes a plurality of contact points which engage the walls of opening Il in case of vibration or other displacement of the electrode sidewise. Ii' the blow on the spark plug is severe enough, these contact points may distort orA dei'orm somewhat. thus taking up the shock which in the absence of/any projections might have to be taken up in impact between the electrode and the insulator tip.

In Figure 6 electrode i2 has been pinched at spaced intervals to form raised portions Il which function in much the same manner to protect the insulator as the above discussed knurl.

In Figure 7 the support comprises an annular ring of any suitable wire '32 disposed in an annular groove in electrode I2.

Figure 8 shows a raised portion comprising a plurality of fine projections made by prickpunching electrode I2 to form an annular band 34.

In Figure 9 electrode I2' has been stepped down at l2 to a smaller diameter, as shown in Figure 4. Since the smaller diameter is on the electrode at the insulator tip, displacement of electrode l2 sidewise will result merely in contact of the shoulder 34 against the, side oi' opening I4.-

Figure 10 shows a heiically wrapped wire 36 forming annular supports about electrode l2 to eect contact above the insulator tip to prevent chipping.

We claim: 1. In a spark plug7 an insulator, said insulator being tapered near the sparking end, a longitutudinal opening through the insulator, an electrode in the sparking end of said opening out of contact with the walls thereof, a terminal in the other end of the opening, a plurality of closely spaced. outwardly extending projections on the electrode near its sparking end. and a bonded seal to form an electrical and mechanical joint between the electrode and the terminal and to hold the electrode in centered position in the opening.

2. In a spark plus, an insulator, said insulator being tapered near the sparking end, a longitudinal opening through, the insulator, said 'opening having a relatively smaller diameter at the sparking end,a shoulder at the juncture of the two vdiameter openings. an electrode in the smaller diameter part ci' the opening out of contact, with the walls thereof, an enlargement on said electrode in engagement with said shoulder. a plurality of closely spaced, outwardly extending projections on the electrode near the sparking end, a terminal'in the larger diameter part oi the opening, andan electrically conductive seal in the inner end of the larger diameter part of the opening to form an electrical and mechanical Joint between the electrode and the terminal, said seal being bonded to both the electrode and the insulator.

3. The combination of claim 1, the sparking end of the electrode below the projections being of a smaller diameter than that portion of the electrode above said' projections.

4. 'I'he combination of claim 2, the sparking end of the electrode below the projections being of a smaller diameter than that portion of the electrode above said projections.

5. In a spark plug: an insulator having a lozgitudinal opening therethrough and an electrode in said opening out of contact with the Walls of' the opening; said electrode having its sparking end projecting from one end of said opening and having a plurality of closely spaced, outwardly extending projections near its sparking end within the said one end of the opening in the insulator.

6. A spark plug as in claim 5 in which the sparking end of the electrode below the projections is of a smaller diameter than that portion of the electrode above the projections.

HECTOR RABEzzANA. ALEXANDER J. BA'ITEY. JOHN a; GRE'IjzrNGER.

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