US3344304A - Creepage spark type plug having low voltage igniter seal - Google Patents

Description

Sept. 26, 1967 G. F. RADEMACHER CREEPAGE SPARK TYPE PLUG HAVING LOW VOLTAGE IGNITER SEAL Filed June 25, 1965 f/fl United States Patent C 3,344,304 CREEPAGE SPARK TYPE PLUG HAVING LQW VOLTAGE IGNITER SEAL Gustav F. Rademacher, Davison, Mich., assigner to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed June 23, 1965, Ser. No. 466,334 9 Claims. (Cl. 313-131) ABSTRACT F THE DISCLSURE This invention relates to a low voltage igniter having a conductive glass seal positioned `between the firing tip portion of the center electrode and the lower portion of the tubular semiconductor which encircles the tiring tip portion. This conductive metal-glass seal causes the spark to originate at the desired location at the end of the tiring tip portion of the center electrode thereby eliminating fracturing of the center electrode at points above the end of the tiring tip.

This invention relates to a low voltage igniter, and more particularly to a low voltage igniter employing a flush gap between the center electrode and the ground electrode.

It is well recognized that low voltage igniters have a short life due to the rapid erosion of the center electrode and/ or the semiconductor. Erosion which causes fracturing of the center electrode and/or the semiconductor is particularly deleterious because the fractured pieces can cause extensive damage to the turbine.

In low voltage igniters employing a shielded or nonush gap between the center electrode and the ground electrode, that is, where the sparking end of the center electrode has an enlarged head below the lower surface of the semiconductor, the problem commonly encountered is the undercutting by erosion of the center electrode enlarged head.

In low voltage igniters employing a ush gap between the center electrode and the ground electrode, the problem of fracturing the center electrode still exists despite the absence of the enlarged head below the lower surface of the semiconductor. Ideally, the center electrode and the semiconductor are in intimate contact with eac-h other along the shaft yof the lower portion of the center electrode thereby resulting in sparking at the designed location; namely, where the electrode emerges at the face of the semiconductor. Normally, however, during the manufacture of ilush gap igniters the center electrode is inserted through the semiconductor material thereby requiring a certain degree of clearance between these two parts. This clearance space causes the sparking to occur in places other than the designed location. Frequently, especially in the presence of gap quenching -fuel oil, the spark originates then at some point above the tip where good contact exists. This type of sparking which occurs in the clearance space -between the semiconductor and the center electrode instead of on the firing tip end of the center electrode results in ring-shaped erosion above the electrode tip, fracture of the semiconductor and/ or fracture of the center electrode tip.

It is a basic object of this invention to provide an improved low voltage igniter having a ush gap design in which the spark originates at that portion of the center electrode which emerges at the face of the semiconductor. It is another object of this invention to provide a conductive seal means to ll the clearance space between the semiconductor and the center electrode to prevent the spark from originating in the clearance space between the semiconductor and the center electrode. It is still another object of this invention to reduce ring-shaped erosion above the electrode tip Iand the accompanying fracturing of the center electrode tip.

These and other objects are accomplished by filling the clearance space separating the semiconductor from the center electrode with a conductive metal-glass seal which hermetically bonds the center electrode to the semiconductor. Specifically, in the illustrated embodiments disclosed herein, the low voltage igniter comprises a metal shell, the lower end thereof constituting the ground electrode and a tubular semiconductor positioned within and in intimate electrical contact with the ground electrode. A center electrode is positioned within the tubular semiconductor and is sealed to the semiconductor by means of an electrical conductive metal-glass seal. When this low Voltage igniter is energized, the spark will originate on that portion of the center electrode which emerges at the face of the semiconductor. The glass-metal seal causes the spark to originate at the desired location at the end of the center electrode there'by eliminating fracturing of the center electrode at points above the firing tip.

Other objects `and advantages of this invention will be apparent from the following detailed description, reference `being made to the accompanying drawings wherein several preferred embodiments of this invention are shown.

In the drawings:

FIGURE 1 is a side View of an improved flush gap low voltage igniter plug having a cylindrical center electrode partly in cross section and partly in elevation;

FIGURE 2 is a side view of a firing tip portion of an improved flush gap low voltage igniter having a cylindrical center electrode with an enlarged end portion partly in cross section and partly in elevation;

FIGURE 3 is a side View of a tiring tip portion of au improved flush gap low voltage igniter having an enlarged center electrode tip portion partly in cross section and partly in elevation;

FIGURE 4 is a side View of the flush gap low voltage igniter plug during the manufacture thereof just prior to pressing the insulator into position partly in cross section and partly in elevation.

Referring to FIGURE 1 of the drawings, the low voltage igniter 10 comprises a conventional outer tubular metal shell 12 having the lower end portion thereof constituting an annular ground electrode 14. The ground electr-ode 14 may be made of any suitable high temperature erosion resistant metal or metal alloy. Inconel containing approximately 76% nickel, 16% chromium and 6% iron was used in the preferred embodiment.

Positioned within the ground electrode 14 is a tubular semiconductor 16. Semiconductor materials presently being used in low voltage igniters may be used in this invention. The patent to Edwards 3,052,814 describes in detail the silicon nitride-bonded silicon carbide semiconductor which perrorms satisfactorily. The semiconductor 16 has an inwardly extending lower portion 18 thereof in electrical contact with the inwardly extending lower portion Ztl of said ground electrode 14. rThe internal dimensions of the tubular semiconductor will be hereinafter discussed. The vertically extending portion of the semiconductor 16 is separated from the ground electrode 14 by a glass seal 22. Glass seal compositions typically used in spark plugs and igniters may be used for this application. The composition of the glass seal 22 used in the preferred embodiment consists of 65% S102, 25% B203, 5% A1203 and 7% NaZO, however, this invention is not limited to this composition.

Positioned within the tubular semiconductor 16 is the center electrode 24. The tiring tip portion of the center electrode may be of any high temperature erosion resistant metal or alloy, such as Inconel, tungsten, platinum and/ or iridium. The center electrode 24 may be of a onepiece construction of a single metal or it may consist of two parts, the tiring tip portion comprising a high temperature erosion resistant metal or alloy and the upper portion comprising another metal such as Kovar. Kovar is a low expansion iron base alloy containing 28 to 30% nickel, 15 to 18% cobalt and fractional percentages of manganese. The shape of the center electrode 24 will be hereinafter discussed.

The clearance space between the semiconductor 16 and the lower portion of the center electrode 24 is filled with a conductive metal-glass seal 26. The seal 26 is hermetically bonded to semiconductor 16 and center electrode 24. The function of the conductive metal-glass seal 26 which hermetically fills the clearance space between the center electrode and the semiconductor is to direct the sparks from the tip 28 of the center electrode 24 to the lower surface 30 of the semiconductor 16 and to the ground electrode 14. The conductive glass seal 26 prevents igniters having the flush gap design from sparking at points on the center electrode 24 above the ring tip portion 28. The spark, as a result, originates at the designed location and eliminates the problem of center electrode fracturing which can cause expensive turbine damage.

The composition of the metal-glass seal used in the preferred embodiment is 50 weight percent tungsten and 50 weight percent glass. The chemical analysis of the glass used was 65% SiOZ, 25% B203, 5% A1203 and 7% NaZO. Suitable glasses having different chemical analysis may be used. In addition, a metal-glass seal may contain binders and/ or iiuxes. Other suitable metals which may be used in the conductive metal seal are nickel, copper, platinum, and iridium. The concentration of the metal in the metal-glass seal may vary from 25 weight percent up to 90 weight percent. The minimum amount of metal required in the metal-glass seal is approximately 25 weight percent. This amount is necessary in order to insure suicient conductivity so that current may travel across the metal-glass seal. Glasses having metal concentrations below this amount do not have suicient conductivity, and as a result, are insulators which require the spark to jump across the seal. If the metal-glass seal is non-conductive or insulative, a higher voltage is required for the spark to jump across this metal-glass gap from the center electrode to the semiconductor. The upper limit of the metal concentration is approximately 90 weight percent. The maximum amount of metal in such a case is governed by the ease of ilow of the metal-glass seal, and it has been found that it requires or more of glass in order to insure sufficient owability of the metal-glass mixture. Mixtures having more than 90% metal or less than 10% glass were found to have insufiicient owability for the purposes of this invention.

The internal dimensions of the tubular semiconductor 16 depend upon the shape of the lower portion of the center electrode 24. The semiconductor 16 and the center electrode 24 should have dimensions which cooperate to form a constriction, thereby providing a passageway conducive for the iluid metal-glass mixture to ow downward and ll the clearance space completely near the opening in the tiring tip region between 30 and 28. For example, as shown in FIGURE 1, where the center electrode is a uniform cylinder, it is necessary to have a semiconductor design in which the internal diameter dimension gradually `decreases as the firing tip portion is approached to form a constriction about the center electrode. Decreasing the internal diameter of the tubular semiconductor from a given width 17 to a narrower width 19 and a still narrower width 21 about the firing tip portion of the center electrode enables the fluid metalglass mixture 16 to flow uniformly about the firing tip portion of the center electrode between 28 and 30.

As shown in FIGURE 2, the firing tip portion 34 of the center electrode 36 is in the form of an enlarged cylinder. The conductive metal-glass seal 38 is positioned between the semiconductor 40 and the center electrode 36 and the firing tip portion 34. The semiconductor 40 has a uniform internal diameter. The outer electrode 36 starts with the diameter 37 which is increased gradually as the firing tip portion is approached as shown at 39 until it has a larger diameter as indicated at 41. The constriction formed by the electrode tapering along the slope of the electrode as shown at 39 and the vertical inner wall of the semiconductor 40 provides the necessary constriction which insures adequate llowability in the clearance area about the firing tip portion 34.

The inwardly extending lower exterior portion 43 of the semiconductor 40 is in electrical contact with the inwardly extending portion 45 of the ground electrode 42. Glass seal 44 is positioned between the vertical extending portions of the semiconductor 40 and the ground electrode 42.

FIGURE 3 shows a tiring tip assembly in which the center electrode and the semiconductor have still another configuration. The relationship between the ground electrode 52, the glass seal 54 and the semiconductor 56 is the same as described in FIGURES 1 and 2. The semiconductor 56 has a lower inwardly extending portion 58. The center electrode 60 has an enlarged tiring tip portion 62. The ring tip portion 62 has an inwardly extending end portion 64. The conductive metal-glass seal 66 is positioned between the semiconductor 56 and the center electrode 60 and the firing tip portions 62 and 64. The constriction is formed by the inwardly tapered lower portion 64 of the center electrode 6) and the inwardly tapered lower end 58 of the semiconductor 56. The tapered end portions of the firing tip 64 and the semiconductor S8 are not parallel and tend to come closer together at the bottom of the igniter. lIn other words, the distance between the semiconductor 58 and the center electrode firing tip portion 64 is greater at point 68 than it is at point '70. This constriction insures adequate metal-glass flow about the firing tip end portion 64 of the center electrode 60.

FIGURES 2 and 3 show a center electrode having an enlarged mass at the firing tip in order to extend the life of the igniter. The conductive metal-glass seal functions in the same manner in FIGURES 1, 2 and 3, regardless of the shape of the firing tip portion of the center electrode. The conductive metal-glass seal fills the clearance space, which has been enlarged in FIGURES 2 and 3 for illustrative purposes, between the center electrode and the semiconductor and insures intimate contact between the semiconductor and the center electrode at the end of the firing tip, which is the designed tiring location. When the sparking occurs at the designed location, that is, at the end of the firing tip portion of the center electrode, there is no fraeturing of the center electrode at points above the tiring tip end.

In the manufacture of a low voltage igniter 10' having a llush gap design, the following procedure is used. An igniter shell 12 is positioned in an upright position, thereby resting on the ground electrode 14 as shown in FIG- URE 4. The semiconductor 16 is inserted into the top of the shell 12 and positioned so that the semiconductor portion 18 is in electrical Contact with the inwardly extending portion 20 of the ground electrode 14. The center electrode 24 is then inserted in the shell 12 and positioned so the lower end of the center electrode 24 is positioned within the tubular semiconductor 16. A measured amount of the conductive metal-glass powder mixture 26 is inserted between the semiconductor 16 and the center electrode 24 and tamped. The quantity of the conductive metal-glass 26 used is not critical as long as there is suiiicient metal-glass seal available in the sparking region. Normally, however, a large portion of the clearance space between the semiconductor 16 and the center electrode 24 is filled with the conductive metal-glass mixture 26. Glass powder 22 is then inserted between the semiconductor 16 and the ground electrode 14 as well as on top of the metal-glass powder 26. The insulator 11 is then inserted in the shell and positioned on top of the glass powder 22. This assembly is then placed in a warm oven and the temperature of the oven `is raised to l700 F. The assembly is kept at a temperature of 1700 F. for 3 minutes in order to melt the glass powder and the glass in the metal-glass powder mixture. As soon as the assembly is removed from the oven, pressure is applied to the insulator 11 forcing the fluid metal-glass 26 mixture to iill the clearance space 27 around the iiring tip portion ofthe center electrode. FIGURE 1 shows the position of the insulator after the metal-glass mixture 26 has been forced into the clearance space. The iiuid glass 22 is forced into the space separating the shell 12 from the insulator 11 and the space between the ground electrode 14 and the semiconductor 16.

While the invention has been described in terms of preferred embodiments, it is to be understood that the scope of the invention is not limited thereby except as deiined in the following claims.

I claim:

1. A low voltage igniter plug having a flush gap tiring tip assembly comprising an outer annular ground electrode, a tubular semiconductor positioned longitudinally within said ground electrode and being in electrical contact with said electrode, a center electrode positioned longitudinally within said tubular semiconductor, conductive sealing means positioned between said center electrode and said semiconductor and being bonded thereto, said sealing means directing a spark from the lower end of said center electrode when said igniter plug is energized.

2. A low voltage igniter plug having a ilush gap tiring tip assembly comprising an outer annular ground electrode, a tubular semiconductor positioned longitudinally within said ground electrode and being in electrical contact with said electrode, a center electrode positioned longitudinally in said tubular semiconductor, a conductive metal-glass seal positioned between said center electrode and said semiconductor and being bonded thereto, said conductive metal-glass seal directing a spark from the lower end of said center electrode when said igniter plug is energized.

3. An igniter plug as described in claim 2 wherein said conductive metal seal comprises 25 weight percent to 90 weight percent of a metal powder.

4. An igniter plug as described in claim 2 wherein said conductive metal-glass seal comprises a metal taken from the group consisting of tungsten, copper, nickel, iron, Kovar, platinum and iridium.

5. A low voltage igniter plug comprising a tubular metal shell having a lower end constituting an annular ground electrode, said ground electrode having a lower portion extending inwardly, a tubular semiconductor positioned within said tubular metal shell and having an inwardly extending annular lower portion in electrical contact with the inwardly extending portion of said ground electrode, a center electrode positioned in said semiconductor, a conductive metal-glass seal positioned between said center electrode and said semiconductor and being bonded thereto, said conductive seal directing -a spark from the lower end of said center electrode when said igniter plug is energized.

6. A low voltage igniter plug comprising a tubular metal shell having a lower end constituting an annular ground electrode, said ground electrode having a lower portion extending inwardly, a tubular semiconductor positioned within said tubular metal :shell and having an inwardly extending annular lower portion in electrical contact with the inwardly extending portion of said ground electrode, a center electrode positioned in said semiconductor, -a conductive metal-glass seal positioned between said center electrode and said semiconductor and being bonded thereto, said center electrode and said semiconductor being in spaced relationship with each other to form a vconstriction adjacent the firing tip end of the center electrode thereby insuring that said seal completely iills the space between the semiconductor and the firing tip end of the center electrode, said conductive seal directing a spark from the lower end of said lower electrode when said igniter plug is energized.

7. An igniter plug as dened in claim 6 wherein said semiconductor is tapered inwardly toward said center electrode to form a constriction between said semiconductor and said center electrode.

8. A low voltage igniter plug as described in claim 6 wherein said center electrode is tapered outwardly toward said semiconductor to form a constriction between said semiconductor and said center electrode.

9. An igniter plug as dened in claim 6 wherein both said semiconductor and said center electrode taper inwardly in the tiring tip region to form a constriction between said semiconductor and said center electrode.

References Cited UNlTED STATES PATENTS 2,831,993 4/1958 entz S13-11.5 2,836,756 5/1958 Smits 313-137 X 2,867,740 1/1959 Segall 313-131 X 2,874,321 2/1959 Summerer 313-131 X JAMES W. LAWRENCE, Primary Examiner. C. R. CAMPBELL, Assistant Examiner.

Claims (1)

1. A LOW VOLTAGE IGNITER PLUG HAVING A FLUSH GAP FIRING TIP ASSEMBLY COMPRISING AN OUTER ANNULAR GROUND ELECTRODE, A TUBULAR SEMICONDUCTOR POSITIONED LONGITUDINALLY WITHIN SAID GROUND ELECTRODE AND BEING IN ELECTRICAL CONTACT WITH SAID ELECTRODE, A CENTER ELECTRODE POSITIONED LONGITUDINALLY WITHIN SAID TUBULAR SEMICONDUCTOR, CONDUCTIVE SEALING MEANS POSITIONED BETWEEN SAID CENTER ELECTRODE AND SAID SEMICONDUCTOR AND BEING BONDED THERETO, SAID SEALING MEANS DIRECTING A SPARK FROM THE LOWER END OF SAID CENTER ELECTRODE WHEN SAID IGNITER PLUG IS ENERGIZED.

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