Spark plug

Application filed January 39, 1932. Serial No. 589,677.·

This invention relates to a spark plug and more particularly to the construction of porcelain type core for a plug. The invention lias for its purpose to provide a spark plug with a core which wjill 'have the various portions thereof maintained at proper working tempei'ature under the conditions for which the plug is intended.

In high compression and high duty internal combustion motors the temperatures to which the inwardly projecting end of the spark plug core is subjected are relatively high, and there is danger of portions of the core becoming so highly heated that preignition results. In order to prevent overheating of the inner end of the core the heat must be carried off fairly rapidly. Any sharp line of division between the hotter and cooler portions of the core is apt to result in breaking or splitting of the core. For this reason a proper heat gradient between the several portions of the core must be mainlined.

When portions of the core are maintained below a certain temperature, carbon is deposited thereon. As the core becomes hotter, such carbon deposits are burned off until a certain point is passed, after which carbon is again condensed upon the core in a form known as incrusted carbon. In modern practice the inner end of the core is usually heated to such an extent that there is incrusted carbon. In order to properly cool the core and prevent preignition, the portion of the core adjacent its seat in the shell is usually cool enough to have thereon a deposit of carbon. If the incrusted carbon reaches close to the deposited carbon, the insulation of the core is reduced to such an extent as to destroy the usefulness of the plug. It is, therefore, necessary to provide a material length of core which will oe normally free from either incrusted or deposited carbon, as defined above.

The purpose of the present invention is to provide a core and shell properly related so as to guard against preignition arid to provide an ample length of core which will be normally free from either incrusted or deposited carbon and eliminate any region where the temperature gradient between successive portions of the core is so steep as to split the core. With these and other objects in view a plug has been provided, the construction and advantages of which will 55 appear more fully as the description proceeds.

In the accompanying drawings forming a part of this specification·—

Figure 1 is a longitudinal section through 60 a plug embodying one form of the invention and in which the inner end of the core extends beyond the surrounding shell; and

Figure 2 is a view similar to Fig. 1, but showing a plug having its shell extending 65 beyond the inner end of the core.

The plug disclosed in Fig. 1 coriiprises a shell 10 of common type having an inner screw threaded end 11 adapted to be screwed into, the combustion chamber of an internal com- 70 bustion motor. The shell is provided with a slightly restricted end portion 12 and has a shoulder 13 supporting a gasket 14 on which there rests a core 15. The core is provided with a downwardly facing seating 75 surface 16 upon its shoulder 17, which seating surface is adapted to rest upon gasket 14. The shoulder has an upwardly facing seating surface 18 against which a gasket 19 is pressed by a sleeve 20 screwed into the so upper portion of shell 10. An electrode 21 passes through the core- and extends at its inner end 22 into sparking relation with an electrode 23 attached to the inner end of the shell. 85

The construction as thus far described is common, and is merely indicated for the purpose of showing the setting of the improvement constituting the present invention.

The lower end of the core as shown in Fig. 9C 1 extends at 25 beyond the inper end of the shell, and from its lower end flares outwardly in a substantially conical shape, as indicated at 26, until it reaches a bulge 27, which is within the restricted portion 12 of the lower 95 end of the shell. Immediately above the bulge 27 there is an inwardly tapering portion 28 which is shorter than portion 26 and has a somewhat steeper gradient. Above portion 28 there is a substantially cylindrical ¹⁰⁰

1,802,265 portion 29 extending for a material distance, of the surface of the core are all gradual so Preferably this cylindrical portion is longer as to prevent either an external angle, which than portion 28 but not of greater length than is likely to become overheated and cause preportion 26. Above portion 29 the core flares ignition, or a reentrance angle sufficiently _g outwardly at 30 upward to the seat 16. In the sharp to make a distinct line where the tern- 70 ' ’------- “ - ------- perature gradient is so steep as to cause splitting of the core.

As previously indicated, it has been found preferable, where the core is extended below the shell, to locate the bulge 27 within re- 75 stricted portion 26 of the core. Less satisfactory results are obtained from having this bulge either below or above the restriction under such circumstances; but where the inner end of the tip does not extend beyond ⁸⁰ , the shell, it is found preferable to have the bulge above the restricted portion of the shell, as indicated in Fig. 2.

While the particular shape of the core indicated in the figures is the best embodiment ⁸⁸of the invention at present known for the majority of motors now in use, it will be understood that some changes may be made, particularly to suit varying conditions, within the scope of the appended claims, it being ⁸⁰particularly borne in mind that increasing the diameter of ®the core above a given point tends to decrease the temperature at said point, while decreasing the cross section of the core above a given point tends to increase ⁸⁸the temperature at said point. It. will be further understood that any conducting material contacting the outer surface of the core between its seat and tip not only interrupts the insulating surface upon which depend- ¹⁰⁸ence is placed to insulate the central electrode from the shell, but also is objectionable because of its greater heat conductivity and consequent disturbance of proper heat distribution in the core. While reference has ¹⁰⁵been made to a porcelain core, it will be understood that the invention applies to other materials having similar characteristics as heat conductivity, etc.