Spark Plug

Abstract

A spark plug in which the points are covered by a non-conducting material and in which a space between the non-conducting material constitutes the spark gap for ignition of a fuel mixture. In certain embodiments of the invention the spark plug has electrodes constructed and arranged to produce a plurality of sparks during each firing cycle of the plug.

Description

BACKGROUND OF THE INVENTION

In use, the electrodes of a spark plug are subjected to electric and chemical erosion which not only limits the useful life of the plug but, also, necessitates frequent cleaning of the electrode tips and adjustment of the spark gap length. Various arrangements have been proposed to overcome this problem.

U.S. Pat. No. 2,391,455, issued Dec. 25, 1945 to Franz R. Hensel discloses a spark plug in which the electrodes are made of various metal compositions having a high tensile strength and increased resistance to gaseous attack at high temperatures.

U.S. Pat. No. 1,515,866, issued Nov. 18, 1924 to L. F. Martin, discloses spark plug electrodes having tips plated with a metal having a high heat conductivity and providing a non-oxidizable surface.

The arrangements heretofore proposed for solving the problem of erosion of spark plug electrodes result in varying degrees of improved operating results as they are directed to decreasing the rate at which erosion takes place. However, they do not completely solve the problem as the spark for ignition of the fuel mixture jumps directly between two metal surfaces or points.

In a spark plug made in accordance with this invention, the ends of the electrodes across which the spark is generated are encased in a high temperature, non-conducting material, thereby eliminating electric and chemical erosion of the electrode ends, which results in a long operating life.

SUMMARY OF THE INVENTION

A spark plug having electrodes for connection to a source of ignition voltage, the electrodes having spaced tips imbedded in an electrical insulating material. An air gap is provided in the insulating material, which gap constitutes the spark gap for ignition of a fuel mixture. In specific embodiments of the invention, the spark plug includes more than two electrodes having tips imbedded in an insulating material, thereby to provide a plurality of sparks during each firing cycle of the plug.

An object of this invention is the provision of spark plug having electrodes constructed and arranged to eliminate erosion thereof during use.

An object of this invention is the provision of a spark plug in which the spark for ignition of a fuel mixture is generated across an air gap defined by spaced non-conducting materials.

An object of this invention is the provision of a spark plug having electrodes for providing a plurality of sparks during each firing cycle of the plug, each of the electrodes having tips covered with non-conducting material.

The above-stated and other objects and advantages of the invention will become apparent from the following description when taken with the accompanying drawings. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings wherein like reference characters denote like parts in the several views:

FIG. 1 is a side elevational view of a single gap spark plug made in accordance with one embodiment of this invention, certain parts being shown in section;

FIG. 2 is a fragmentary cross-sectional view showing a single gap spark plug made in accordance with another embodiment of this invention;

FIG. 3 is a bottom plan view showing a two-gap spark plug made in accordance with another embodiment of this invention, certain parts being broken away;

FIG. 4 is a fragmentary, cross-sectional view taken along the line 4--4 of FIG. 3;

FIG. 5 is a fragmentary, cross-sectional view of a three-gap spark plug made in accordance with another embodiment of this invention;

FIG. 6 is a bottom plan view of a two-gap spark plug made in accordance with still another embodiment of this invention; and

FIG. 7 is a fragmentary, cross-sectional view taken along the line 7--7 of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, the spark plug comprises a core 10 made of an insulating material, a metal shell 11 provided with a threaded portion 12, and a center electrode 13 terminating in a terminal 14 for connection of the plug to the ignition system of an internal combustion engine. The core has a conical end portion 15 which is spaced from the threaded portion of the shell. In a conventional spark plug, the center electrode 13 has a bare tip projecting from the core portion 15 and a bare ground electrode 16 having one end welded to the threaded shell portion 12 and the other end spaced from the exposed tip of the center electrode. The spacing between these two electrodes constitutes the normal air gap across which a spark is generated for ignition of a fuel mixture. In accordance with this invention, the center electrode tip is encased in a non-conducting coating identified by the numeral 17. Similarly, all or a major portion of the ground electrode 16 is encased in a non-conducting coating identified by the numeral 18. The non-conducting coatings may be formed by applying a ceramic paste or a high temperature glass over the electrode tips. In either case, the coating material is subjected to suitable high temperature, thereby to fuse the material to the electrodes. The two coatings are spaced apart to form an air gap (a). When a voltage of suitable magnitude is applied to the spark plug, a spark will jump from the center electrode 13, through the insulator coating 17, across the air gap (a), through the insulator coating 18, and to the ground electrode 16. The insulator coatings, which may be relatively thin, prevent chemical and electrical erosion of the electrode points.

In the FIG. 2 embodiment of the invention, the lower end of the center electrode 20 is encased in the conical portion 15 of the insulating core of the spark plug and the ground electrode 21 is covered with a non-conducting coating 22. The air gap (b) constitutes the spark gap for ignition of the fuel mixture.

A double-gap spark plug is shown in FIGS. 3 and 4. Here, the conical core portion 15 has two, cylindrical projections 24 and 25 extending therefrom. The lower portion of the center electrode 26 is offset with a tip 27 encased within the projection 24. The neutral electrode comprises a metal piece 28 encased within the projection 25. The ground electrode 29 is encased in a non-conducting coating 30. When the plug is fired, two sparks, in series, jump across the air gaps (c) and (d).

A triple-gap spark plug made in accordance with this invention is shown in FIG. 5. In this arrangement, the conical portion 15, of the core 10, has a helical groove 32 formed in the peripheral surface thereof. A first, generally-helical neutral electrode 33 is positioned in the helical groove and has a tip 34 spaced from the tip 35 of the center electrode, said tips 34 and 35 being encased within non-conducting coating 36 and 37, respectively. A second neutral electrode 38 is positioned in the helical groove. One end of the neutral electrode 38 is spaced from the end of the neutral electrode 33, and the other end of the neutral electrode 38 is spaced from the ground electrode 39 welded to the threaded portion 12 of the spark plug case. The portions of the neutral electrodes 33 and 38 which are disposed in the helical groove are covered with a ceramic paste as indicated by the reference numerals 40 and 41, which paste is then heat cured and maintains these electrodes in fixed position on the supporting core portion 15. It will be noted that the ceramic paste extends somewhat beyond the proximate ends of the two neutral electrodes. More specifically, these proximate ends of the neutral electrodes are completely encased with the ceramic but the ceramic is parted to form the air gap (e). That end of the neutral electrode 38 which is proximate to the ground electrode 39 also is completely encased in the ceramic. When a firing voltage is applied to the spark plug, three sparks, in series, will jump across the air gaps (f), (e) and (g).

FIGS. 6 and 7 show a two-gap spark plug made in accordance with another embodiment of this invention. A neutral electrode 43 is imbedded in a tubular member 44 made of a ceramic or a high temperature glass, said member 44 including a radially-extending leg 45 which is cemented in a diametrical slot formed in the end of the core 46. The center electrode 47 has a tip 48 extending toward the neutral electrode, which tip is encased within a non-conducting coating 49. The ground electrode 50 is welded to the threaded portion 12 of the spark plug shell and has a tip spaced from the neutral electrode, said tip being encased in a non-conducting coating 51. In this particular construction, the two spark gaps (h) and (i) are well spaced from each other. Also, the spark gaps lie on opposite sides of the tubular member 44 which serves as a combustion deflector. When the spark plug is installed on an internal combusion engine, initial ignition of the compressed fuel mixture takes place at the spark gap (h). Although measured in milliseconds, some period of time is required for combustion to take place in those areas of the fuel mixture which are remote from the point of initial ignition. The spacing of the spark gaps and the action of the deflector provide a sufficient time delay so that an ignitable fuel mixture is present at the spark gap (i) when the second spark occurs across such gap. The net result is a more complete combustion of the fuel which provides increased power to the piston of the engine with a corresponding reduction in pollutants exhausted into the atmosphere.

The coating of the electrode tips with a high temperature non-conducting material eliminates chemical and electrical erosion of the tips, whereby the electrodes may be made of an inexpensive base metal. Also, accumulated carbon deposits on the non-conductor surfaces can be removed easily and does not necessitate a re-adjustment of the effective spark gap length, as is the case when the eroded surface is removed from the tips of conventional electrodes.

Claims

Having now described the invention what I desire to protect by letters

1. A spark plug comprising,

a. a core of insulating material carried by a metal shell,

b. a main electrode carried by said core,

c. a ground electrode connected to said shell and having an end portion spaced from an end portion of the main electrode to form a spark gap

d. a non-conducting ceramic material covering the said end portion of the ground electrode, and

e. a non-conducting ceramic material covering the said end portion of the main electrode and spaced from the covering on the end portion of the

2. A spark plug as recited in claim 1, wherein the said non-conducting material is a high temperature glass.