US2147730A - Spark plug - Google Patents

Description

' Feb. 21, 1939. R A BELL 2,147,730

SPARK PLUG Filed Dec. 24, 1937 INVENTOR Patented Feb. 21, 1939 UNITED STATES PATENT OFFICE Rajah Company, tion of New Jersey Bloomfield, N. J., a corpora- Application December 24, 1937, Serial No. 181,659

5 Claims.

This invention relates to spark plugs for ignition of combustible gas mixtures, e. g., in internal combustion engines.

Spark plugs as commonly made prior to the present invention commonly comprise a core having a central electrode wire and conductor surrounded by an insulator of porcelain or other refractory insulating material and a metallic shell in which porcelain is mounted and by which the plug as a whole is handled for insertion and removal into the motor or other location in which it is used. This shell also serves as the ground connection to which the spark jumps from the center electrode wire of the core. According to the prior art, the bottom of the shell has ordinarily been provided with a wire or with a cage having fingers projecting towards the center electrode, which serve respectively as a second electrode for the spark and particularly to definitely predetermine and locate with respect to the bottom of the spark plug the position at which the spark occurs so as to give most efiective ignition. It has been the practice prior to my invention to secure such electrode members to the lower edge of the shell by drilling a hole into which the electrode wire is inserted and secured or by cutting a recess therein into which a cage electrode can be secured, e. g, by swaging. Recently, however, the tendency has been to decrease very substantially the dimensions permitted to spark plugs in the modern engine and this has been carried to such an extent that the cutting required for such mounting of the electrode may produce an objectionable weakening of the end of the plug. For this reason it has been necessary in commercial practice to resort to spot welding of such electrodes onto the ends of the shell.

It is an object of my present invention to provide a plug in which the electrode is securely mounted with a simple and efficient construction, superior in operation and length of useful service to other known electrode structures.

Another object of my invention is to protect the shell around the electrode from corrosion, burning, sputtering, etc., which ordinarily result from severe conditions to which such plugs are subjected.

Another object of my invention is to provide a simple spark plug construction with an interchangeable electrode so that the heat range of the plug can be adjusted by use of different electrodes.

Another object of my invention is to provide a simple spark plug construction in which the electrodes may be replaced as simply as the plug is cleaned and thus damage which may result from burning of the electrode may be easily repaired.

Other objects and advantages of my present 5 invention will appear from the following description and claims.

In the accompanying drawing and the following description I have shown and described a preferred embodiment of my invention and certain modifications thereof. It is to be understood that these are given for purposes of illustration in order that others may readily understand the principles of the invention and the manner of embodying it in practical use. These are not intended to be exhaustive nor limiting of the invention but on the contrary are given for the purpose of enabling others skilled in the 'art to modify and adapt the invention and to embody it in numerous practical forms each as may be best suited to the conditions of any particular use.

In the drawing:

Fig. 1 is a view in longitudinal section of a plug embodying my invention;

Fig. 2 is a bottom plan View. I

Referring to the drawing, the core of the plug consists of a refractory porcelain insulator I0, with a central electrode wire running therethrough. On the upper end of the electrode wire is the connector stud 3 and near its lower end the porcelain is formed with an enlarged portion M the lower face of which is substantially conical for seating of the soft copper gasket l5 and the upper face of which is substantially horizontal for engagement by the centering ring IS.

The shell I1 is made in substantially the usual form with its lower portion threaded as shown at l8 for screwing into the motor in which the plug is to be used and its upper portion 9 formed with 4 flat faces for engagement by a suitable wrench and is internally threaded for engagement of the clamping nut 9. A bore 20 extends through the small lower end of the shell and is enlarged or recessed near its upper end, as shown at 2|, for a purpose which will be later described.

Above the recess 2| a conical seat 22 is formed for the gasket l5 which thus serves to seal the space between the shell and the part M of the core.

Within the bore 20 and the recess 2| is fitted a thimble shaped cage electrode 23. This electrode, as shown, is formed of sheet metal stamped into a thimble shape with a peripheral projection extending radially from its upper edge and fitting into the recess 2|. The sides of the electrode thimble 23 fit closely to the inside of the bore 2!] and constitute a lining for the shell in that part which is exposed to the hot burning gases. The end of the electrode thimble is punched out, as clearly shown in Fig. 2, to give circumferentially spaced openings 25 between which are left the integral fingers 26 extending into close proximity to the central electrode ll of the core and constituting, therefore, the electrodes proper of the shell.

As will be clearly apparent from the drawing, these electrode fingers 26 are of a form such that they can be readily adjusted by bending so as to give accurately the spark gap of desired dimension but to avoid accidental bending or substantial change in the spark gap due to heating.

The opening 25 permits the passage of gases into and out of the space between the thimbleshaped electrode so as to assure the presence of an explosive mixture surrounding the electrode when the spark occurs. The cage form of the electrode, however, serves to hold any part of the porcelain which may be cracked or chipped off by the heat or other action and thus to prevent any possible scoring of the cylinder if this should occur. Moreover, since in the preferred embodiment of my invention this thimble electrode is made of a metal more resistant to high temperature than the steel of the shell l!, e. g., of Nichrome, the lining of the shell with this material avoids the scaling and disintegration which sometimes occurs on the inside of the shell, and especially the sputtering of any disintegrated materials from the shell onto the porcelain where it may result in deterioration of the insulating quality of the porcelain.

It will be observed that the assembly of this electrode thimble in the shell is accomplished simply by dropping the thimble into the bore 26 on the inside of the shell and pushing it through the bore until its peripheral projection 24 lies in the recess 2|. In this condition the upper edge of the electrode thimble is substantially plugged with and. forms a continuation of the gasket seat 22 and when the plug is assembled as shown in Fig. 1 the gasket 15 overlying the top of the electrode thimble holds the latter securely in position.

It is an advantage of my invention that these electrodes are readily interchangeable and replaceable. If, when a plug is cleaned, it is found that the points are burned or otherwise damaged, the electrode thimble may be removed and replaced by a new one and likewise if a hotter or cooler plug is required a longer or a shorter thimble may be used so as to move the position at which the spark occurs farther into the cylinder or back into the bore 20 of the plug.

What I claim is:

1. A spark plug which comprises a shell, a core extending into the shell, having a refractory insulator and an electrode wire extending beyond the insulator, a cage electrode surrounding the inner end of the core and spaced from its electrode wire, said cage electrode being thimbleshaped with a short radial projection at its periphery to engage the shell, openings circumferentially arranged about the center adapted for passage of gases into and out of the space between the cage and the core, and electrode portions extending between said openings toward the electrode wire of the core, and said shell having a bore adapted to receive said cage electrode from the inner end of the shell and said bore being cut back from its inner end to form an annular seat, said seat being recessed to receive the radial projection on the cage and thereby to position the cage at a predetermined position with respect to the bore, a gasket engaged between the core and said seat annularly beyond said recess, and means for pressing the core toward said seat whereby the gasket is compressed to an air-tight seal.

2. A spark plug as defined in claim 1., in which the recess is substantially fitted to the projection on the cage, whereby said projection is brought substantially flush with said seat and the gasket extends annularly over both said seat and the end and projection of said cage whereby the cage is held by the gasket when the parts are assembled.

3. A spark plug as defined in claim 1, in which the cage electrode is a sheet metal stamping of a metal more resistant to high temperatures than the material of the shell, and the bottom of the electrode has at least three circumferentially spaced holes therein and at least three integral 1 fingers extending between the holes toward the electrode wire of the core.

4. A spark plug which comprises a shell, a core extending into the shell and having an electrode and a refractory insulator therefor, and a sleeve between the shell and the insulator extending at least throughout the space in which the burning of gases may occur and made of a material more refractory than the metal of said shell, whereby to prevent sputtering or sublimation of the material of the shell onto the insulator.

5. A spark plug which comprises a shell, a core extending into the shell having an electrode and refractory insulator therefor, and a refractory nickel-chromium alloy sleeve between the shell and the insulator extending at least through the space in which the burning of gases may occur, whereby to prevent sputtering or sublimation of the material of the shell on the insulator, and terminating in an electrode portion extended toward said electrode to establish a spark gap and being cut away to provide for passage of gases into and out of said sleeve.

ROBERT A. BELL.

Images