US3431450A - Spark plug with adjustable electrode gap - Google Patents

Description

March 4, 1969 G. J. ERRICO 3,431,450

SPARK PLUG WITH ADJUSTABLE ELECTRODE GAP Filed April 7, 1967 Sheet 1 of 5 March 4, 1969 G. J. ERRICO SPARK PLUG WITH ADJUSTABLE ELECTRODE GAP Sheet g of 3 Filed April 7, 1967 INVENTOR Gus J. [rm'co March 4, 1969 cs. J. ERRICO SPARK PLUG WITH ADJUSTABLE ELECTRODE GAP Sheet Filed April 7, 1967 INVENTOR Gus frrc'q United States Patent O 1 Claim ABSTRACT OF THE FISCLOSURE A spark plug having a central stem surrounded by cold setting cement which may be glass filled. Secured to the stem by a screw connection is an electrode having a bent tip defining a gap with a surrounding metal shell. An adjustable gland nut in the metal shell adjusts the gap between the electrode tip and metal shell.

Spark plugs conventionally used in internal combustion engines of automobiles and other automotive vehicles as well as in stationary apparatus such as pumps, electric generators, and the like, have a number of important shortcomings. The conventional type of spark plugs in general use employs a center electrode spaced from a ground electrode attached to the cylindrical shell of the plug. This structure requires that a radial ground electrode be welded to the shell of the plug. This is costly in material and labor; also the ground electrode is an element where operational failure often occurs. The center electrode is attached to a long wire which extends axially through the plug from the center electrode at one end to the nose tip at the other end. Installation of this wire requires a number of complex operations; the wire uses costly material; and the several connections of the wire at opposite ends are subject to breakage resulting in operational failure of the plug.

Complex, critical processes are required to force a thermosetting sealing cement into the center of the plug between the center electrode and an outer cylindrical or conical porcelain insulator. To set the cement requires high baking temperatures in a furnace which in itself introduces several difficulties. The insulator may come out of the process with fine cracks which later lead to operational failure of the plug. Also it is very difficult to maintain the few thousandths of an inch clearance between wire and insulator allowed for expansion of parts. This clearance is often non-uniform and not enough resulting in fracture of the insulator due to thenmal shock. Sometimes thermal shock results in small internal fissures in the porcelain insulator. These fissures accumulate carbon and metallic salts and carry electric current causing partial or complete short circuiting of the plug electrodes,

reducing operational efliciency or stopping operation altogether.

The conventional spark plug has a very high voltage applied to the nose tip or terminal. Since the distance from the nose tip to the grounded engine head to which the ground electrode is connected, is very short, arcing or fiashover frequently occurs, particularly when the porcelain insulator becomes wet or moist, or even if the ambient humidity is high. This results in operational failure of the engine in which the spark plug is installed. Rubber jackets provided at the insulator do not solve this problem since the jackets themselves act as conductiye paths for arcing and fiashover when the jackets become wet or damp. Another dificulty encountered in conventional spark plugs is known as corona discharge. This involves current leakage along the surface of the porcelain insulator, particularly when it becomes coated 3,431,45fi Patented Mar. 4, 1969 with grease, dirt and moisture. Other difiiculties in conventional spark plugs are caused by the fact that the large mass of the plug absorbs heat rapidly leaving the small tip of the central electrode cold. This causes fouling of the electrode, misfiring, and the disparity in temperatures causes thermal shock during which the insulator is fractured or cracked. Another problem encountered in conventional spark plugs arises from the central location of the gap between center and ground electrodes. This gap is located in alignment with the path of greatest explosive force in the engine cylinder. This results in a high rate of erosion of the electrodes, oil fouling and carbon collection. Also a condition known as flame arrest occurs which is rnost undesirable. Due to the conditions mentioned and others which exist, conventional sparks plugs must be frequently removed, cleaned and regapped which involves a laborious, expensive, time consuming process. Furthermore the spark plugs must be replaced frequently due to progressive failure, which imposes a great economic burden on engine users. Between times of servicing and replacement, faulty operating spark plugs cause hard starting of engines, poor fuel economy, loss of engine power and overall degradation of engine efliciency.

The present invention is directed at overcoming the above and other difiiculties and disadvantages in conventional spark plugs, and does so with a spark plug which is simpler in construction and more economical to manu facture. According to the invention, a spark plug is provided which has a cylindrical porcelain insulator housing in which is a central stern held in place in a porcelain shell by a threaded connection with the shell. The stem is surrounded by cold setting electrical and thermal insulating cement. An adjustable gland nut is set in an outer shell for adjusting the gap between the central electrode and metal shell. A double tip can be provided for the electrode to ensure positive ignition under critical, heavy duty operating conditions. A capacitive adapter can be provided to remove carbon deposits at the gap between electrode and shell.

It is therefore a principal object of the invention to provide a spark plug of simplified, more reliable construction having a longer useful life than conventional spark plugs. A further object is to provide a spark plug with a central stern having screw connections to an electrode and porcelain housing.

Another object is to provide a spark plug with a central stem sealed by cold setting thermal and electrical insulative cement.

Another object is to provide a spark plug as described with a metal shell having a gland nut interposed between the shell and porcelain housing for adjusting the gap between the shell and electrode.

A further object is to provide a spark plug with an electrode having a double tip.

A further object is to provide a spark plug with a capacitive adapter to facilitate burning oif debris fouling the air gap.

Another object is to provide a spark plug with an adjusable set screw defining a gap between the screw and electrode forming part of a central stem.

For further comprehension of the invention, and of the objects and advantages thereof, reference will be had to the following description and accompanying drawings, and to the appended claim in which the various novel features of the invention are more particularly set forth.

In the accompanying drawings forming a material part of this disclosure:

FIG. 1 is a side elevational view of a spark plug assembly embodying the invention, the spark plug being shown mounted on a wall of an engine cylinder.

FIG. 2 is an enlarged bottom view end of the spark plug per se.

FIG. 3 is a central longitudinal view taken on line 33 of FIG. 2.

FIG. 4 is an exploded perspective view of parts of the spark plug assembly.

FIG. 5 is a central longitudinal sectional view of part of another spark plug assembly showing a modification of the invention.

FIG. 6 is a side elevational view on a reduced scale of another spark plug.

FIG. 7 is a longitudinal sectional view similar to FIG. 3 of still another spark plug.

FIG. 8 is an exploded perspective view of parts of the spark plug of FIG. 7.

Referring first to FIGS. 1-4, there is shown a spark plug 10 having a cylindrical porcelain or ceramic insulator 12 with a cylindrical chamber 14 open at the top. The lower part 16 of the insulator is enlarged radially and formed with an upper annular ledge or seat 18. In the enlarged part 16 of the insulator is a threaded cavity 20 communicating with chamber 14. A tapered frusto-conical annular ledge or seat 22 is formed at the bottom of part 16 of the insulator. The insulator has a conical bottom end 24 integral with enlarged part 16. In end 24 of the insulator is a narrow bore 25 communicating with cavity 20.

The spark plug is provided with a central axial stem 26 which may be threaded throughout its length. It terminates at its lower end in an enlargement 28 which is externally threaded to screw into and seat on the curved bottom 29 of cavity 20. The enlargement 28 has a threaded central bore 30 in which screws the upper end 31 of a rod which serves as the electrode 32 of the spark plug. The body of the electrode extends through bore 30 and terminates outside the insulator 12. The electrode is formed with a radially extending tip 34 perpendicular to upper part of the electrode.

In order to mount the spark plug to the wall 35 of an engine cylinder as indicated in FIG. 1, there is provided a tubular metal shell 36 having a lower externally threaded end 38 which screws into threaded hole 39 in the engine wall 35. The shell has a fiat, annular end surface 40. The end of electrode tip 34 is slightly spaced from surface 40 to define a gap G at which ignition of a combustible gas mixture takes place in the engine cylinder.

The shell 36 has a cylindrical bore 42 formed with a tapered ledge 44 on which seats the wall 22 of the insulator. A conical metal washer 46 made of copper or other pliable metal is interposed between wall 22 and ledge 44. The lower part 42a of bore 42 is smaller in diameter than the upper part. Insulator end 24 extends through bore part 42a.

The upper part of bore 42 is formed with an internal thread 48 in which seats an externally threaded gland nut 50. This nut bears down upon the ledge 18 of the insulator enlargement 16. Interposed between the ledge 18 and bottom end of the nut is a washer or retainer ring 52. Nut 50 has. external lands 54 which can be engaged by a wrench for turning the nut. Shell 36 has external lands 56 which can be engaged by a wrench for screwing the shell into the hole 39 of the engine wall 35, for removing the spark plug from the engine wall, and for holding the shell while nut 50 is turned with respect to the shell. When nut 50 is turned with respect to the shell, the insulator along with the stem 26 and electrode 32 will move axially of the shell so that the gap G can be changed in width.

On the upper end of stem 26 is screwed or force fitted a metal electrical terminal 60. This terminal may have a ferrule 62 which extends into chamber 14 of the insulator. On terminal engages cable 63 provided with a cylindrical spring clip 64 to hold the cable in tight but detachable engagement with the spark plug. Central wire or conductor 65 of the cable makes direct electrical contact with terminal 60 at bore 66 of the terminal.

A sealing body 68 made of a cold setting plastic compound containing silicone or other thermal and electrical insulating substance, fills the chamber 14 and completely surrounds stem 26. This sealing body expands on setting so that a hermetic seal is provided between electrode 32 and the exterior of the spark plug at its upper end. The body 68 may contain glass as a filling material to improve electrical and thermal insulation properties.

By the arrangement described, there is a direct electrical connection between the electrode 32 and terminal 60 which cannot he accidentally broken. The stem is hermetically sealed. Also if necessary the nut 50 can be turned with respect to the shell 36 to vary the gap G between electrode tip and shell. Generally not more than a fraction of a turn of the nut, about 10 angularly, will be required to vary the gap a few ten thousandths of an inch, which will be all the adjustment required. The pliable washer 46 will yield and may be forced slightly into bore 42:: to effect the required gap adjustment, when the nut 50 is turned.

In FIG. 5 is shown part of a spark plug 10A which is similar to spark plug 10 with corresponding parts identically numbered. In this spark plug, electrode 321:. has an auxiliary short tip 34a disposed radially inside of bore 42a of the shell and slightly spaced from its cylindrical wall. There are thus provided two gaps G and G at tips 34 and 34a. By this arrangement double assurance is bad that ignition will be effected in the engine cylinder even under very rugged operating conditions.

Both spark plugs 10 and 10A are arranged so they have self-renewing properties. It is possible by loosening nut 50 to rotate the insulator 12 with respect to the shell 36. This will locate the tip 34 or both tips 34 and 34a at a different point of the wall of bore 42a. Thus if the bore wall becomes pitted and fouled of the wall 40 or of both wall 40 and the wall of bore 42a. Thus if the wall 40 and wall of bore 42a become pitted and fouled, the turning of the electrode to another position with respect to shell 36 will provide fresh points for gaps G and G.

FIG. 6, 7 and 8 show another spark plug 10B in which parts corresponding to those of spark plugs 10 and 10A are identically numbered. In this spark plug, electrode 32b has no radial tips and terminates at its lower end 34 inside the bore 42a of shell 36a. A set screw 70 is fitted into a radial threaded hole 72 in the threaded bottom part 38 of the shell. A gap G is defined between the inner end of the screw and the free end 34 of the electrode. By turning the screw with a suitable wrench inserted in the polygonal hole 74 of the screw, adjustment of the size of gap G" can be easily effected.

At its upper end stem 26' is fitted into bore 75 of a capacitive plug 76. The plug has a stem 78 interfitted with tip 10a. The plug can be externally threaded to engage with internally threaded portion 79 of the wall of chamber 14 in insulator 12'. This plug serves the following purposes.

Some engines develop a tendency to burn oil. This is caused by seepage of oil into the engine cylinder past loosely fitting piston rings or poorly fitting valves. The burned oil causes fouling of the electrode in the conventional spark plug. In the present spark plug it is possible to burn off the debris fouling the gap G by employing plug 76. The plug serves as a dielectric element between terminal 60a and stem 26'. When a pulsating voltage is applied to wire 65 the voltage builds up in gap G". When the voltage is maximum a spark discharge of maximum energy content takes place causing a fat spark between electrode tip 34 and screw 70 in the engine cylinder. While the time duration of the spark is less than if the plug 76 were absent, the current flows at a higher magnitude causing effective burnout or clearance of the fouling condition. Plugs having different axial thickness than plug 76 can be used depending on the design parameters of the engine cylinder. The electrode 34' can be rotatably adjusted and axially moved by turning nut 50 in the same way as previously described for spark plugs and 10A even though the plug 76 is present. If desired plug 76 can be used with stem 26 in spark plugs 10 and 10A for the same purposes as in spark plug 10B.

While I have illustrated and described the preferred embodiments of my invention, it is to be understood that I do not limit myself to the precise construction herein disclosed and that various changes and modifications may be made within the scope of the invention and defined in the appended claim.

What is claimed is:

1. A spark plug assembly, comprising a generally cylindrical insulator having a central cylindrical cavity open at one end, said insulator having an enlarged portion spaced from said one end and formed with annular radially extending ledges at opposite ends of said enlarged portion, said insulator having a conical free other end integral with and axially spaced from said enlarged portion, said enlarged portion and said conical end of the insulator having axially aligned bores communicating with the other end of said cavity; an electrically conductive stem extending axially of said chamber and seated in said enlarged portion of the insulator; an electrode extending axially of the bore in said conical end of the insulator engaged at one end with the stem and having its other end extending outwardly of said conical end of the insulator; a generally cylindrical metal shell having an interior annular wall; said shell having an internally threaded portion at one end; said insulator being disposed axially of the shell with said enlarged portion enclosed in the shell, one of said ledges facing said annular wall; a pliable washer interposed between said one ledge and said annular wall; an externally threaded nut engaged in said threaded end portion of the shell and having one end extending outwardly thereof, so that the nut can be turned with respect to the shell to move the nut axially of the shell, the other end of the nut bearing on the other ledge of said enlarged portion of the insulator, said other end of the electrode being spaced from the other end of the shell to define a gap, whereby turning of the nut with respect to the shell advances the insulator and electrode axially of the shell to change the size of said air gap; an electrical terminal at said one end of the insulator electrically connected to said stem so that the electrode is directly connected electrically to said terminal; and a cold setting cement compound filling said chamber and surrounding said stern so that the electrode is hermetically sealed off from said terminal, said one ledge, said annular wall and said pliable washer being all frusto-conical in form, said washer having one end exposed to the interior of the shell to expand therein when the nut is tightened in the shell to widen said gap between the electrode and other end of the shell.

References Cited UNITED STATES PATENTS 932,338 8/1909 Sleaford 3l3125 1,164,082 12/1915 Gallant 315-58 X 1,870,981 8/1932 Auzin 313- X 2,226,414 12/1940 Kapp 313 3,320,461 5/1967 Feins 3l3-125 ROB ERT SEGAL, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

U.S. C1.X.R. 3l3136, 141, 145

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