US1940325A - Shielded spark plug - Google Patents

Description

Dec. 19, 1933. RABEZZANA 1,940,325

SHIELDED SPARK PLUG Filed April 4. 1932 III 190201 fiaezzana 3% M WY Patented Dec. 19, 1933 SHIELDED SPARK PLUG Hector Rabezzana, Flint, Mich, assignor to A 0 Spark Plug Company, Flint,

0! Michigan Mich a company Application April 4, 1932. Serial No. 602,892 3 Claims. (01.123-169) This invention relates to ignition systems for internal combustion engines and particularly to improvements in spark plugs.

It is a primary object of the invention to provide a spark plug especially adapted for use on an engine which is to be operated in the vicinity of radio apparatus, and which plug, in its preferred form, incorporates as a part of the ground-' ed shell an integral extension or skirt enclosing the outer portion.of the insulator core and central electrode, and serving as a support and.

ground connection for a shield surrounding current conducting cable leading to the plug. With the arrangement provided, radio apparatus near, by is shielded from electrical radiations incidentv to the operation of the ignition system and which otherwise would interfere with communication. An important feature of the integral struc-' ture is the absence of any hindrance to the tree heat flow from the shell into the engine block. That is, the heat from the shell is transferred through the customary sealing gasket directly to the block without having to pass through any intermediate body such as a separate core shield formed independently of the plug proper and interposed between the shell and block. It also aids materially in reducing costs.

The invention includes certain structural details all to be described hereinafter in connection with various embodiments illustrated in the accompanying drawing, wherein Figure 1 is a vertical sectional view of one type of plug and cover; Figure 2 is an elevation with parts in section to show the application of the invention to another type of plug; Figures 3 and 4 are sectional views illustrating alternative assemblies, and Figure 5 is a detail perspective view showing one of the retainer parts assembled in'the plug structure of Figure 4.

Referring to the drawing, the central core as- I sembly includes an insulator 1 of porcelain or the like, surrounding a central electrode and having intermediate its ends an enlargement 2 positioned within an inner metal shell 3'having at opposite ends inwardly extending flanges 4 and 5, respectively, providing seats {or the shoulders afforded by the enlargement 2. Sealing gaskets 6 and 7 are preferably interposed between the shoulders and retainer flanges to prevent leakage. The ,assembly of these parts is preferably completed by first inserting the core in the inner'shell and then bending inwardly the flange 5 from a previous upstanding position. This inner shell is threaded into an outer shell body 8 v for engagement within a spark plug opening in the wall 12 of the engine combustion chamber. From the opposite end of the plug body 8 extends an enlarged cylindrical portion or skirt 13 surrounding the outer portion of the core 1 and having on its exterior a series of peripheral ribs or cooling fins 14. These cooling fins assist in.

the dissipation of heat, although most of the heat is transferred to the wall 12 in the usual fashion.

Seated on the upper end of the skirt 13 is a cover or cap 15, preferably molded of bakelite, hard rubber or the like, and provided on its exterior with a metallic coating or covering 16, preferably electro-deposited, which extends over the seat portion of the cover and in contact as'at 17 with the skirt l3. Embedded in the top of the cover is armetal seat 18 having a depression that receives a ball or roller 19 carried by a swinging bail 20 which is pivotally carried by the spark plug shell, as is most clearly shown in Figure 2, whereby to securely and detachably hold the cover in position over the outer end of the skirt. Within the cover 15 is formed a passageway 21 for the reception of an end of an insulated current conducting cable 22, forming a part of the engine ignition system. The cable 22 is held in place by means of a screw stud or keeper 23 extending from the inside of the cap and having a conical outer end extending into the opening 21, piercing the cable insulation and contacting with the current conducting wires. The screw stud 23 also serves as a mounting for the coil spring 24 contacting with the terminal head 25 of the central electrode for the passage of current from the cable 22 to the spark plug. At the outer end of the passageway 21 the cover is provided with a integral skirt 13 projects outwardly from the.

outermost portion of the shell proper, it will be obvious that the ready transference to the wall 12 of heat taken up by the plug parts is unchecked thereby.

The application oi the shielding to the so called mica plug is illustrated in Figure 2 where the cover 15 is mounted on the outer end of the skirt or cylindrical extension 30 of the metal shell 31, and the shell screw threadedly receives the gland 32, forming a part of the core assembly between the mica bodies 33 and 34, which surround and insulate the central electrode.

Instead oi proviidng a separate retainer shellfor the insulator core, the core may be permanently secured in the shell proper, as illustrated in Figure 3', where the central opening or bore 01' the shell 35 receives the central enlargement 36 or the insulator core 37 and the shell is provided initially with an upwardly extending lip 38, which is bent inwardly and over the enlargement 36 to retain the core in the shell.

'In lieu of the integral lip just referred to, the structure shown in Figure 4 may be employed to removably retain a core enlargement 39 in the shell 40. Here the skirt or shell 41 is provided with an annular grove 42 on its interior surface to receive a split ring 43 which forms a bearing for a retainer collar 44. The inner margin of the collar 44, as shown particularly in the detail view, Figure 5, forms a circular seat 45 for the core enlargement 39, and irom the seat 45 the collar extends angularly upwardly with portions cut away at spaced intervals to present a series of spring fingers 46. The assembly and removal of the parts involves merely the manipulation of the split ring retainer into or out of its seating groove to either hold the parts in the relation shown in the drawing or permit their separation.

I claim:

1. In the ignition system of an internal combustion engine, a spark plug having inner and outer sub-assembly units, said inner sub-assembly including an insulator core surrounding an electrode and having mounting means intermediate its ends, and said outer sub-assembly having as a unitary structure an intermediate portion to mountably receive the mounting means or the inner assembly, a skirted portion receivable within an engine spark plug opening and provided outer sub-assembly units, said inner assembly including as an integral part thereof an exteriorly threaded gland, and said outer assembly comprising a metallic shield having an exteriorly threaded end portion carrying a ground electrode, an interiorly threaded intermediate portion to receive said gland oi the inner assembly and an integral shielding portion in spaced relation to the inner assembly to receive and ground therethrough a terminal of a shielded cable.

3. In the ignition system of an internal combustion engine, a spark plug having an insulator core surrounding an electrode and having an intermediate shouldered portion, a shielding shell carrying a ground electrode near one end and having a counterbored intermediate portion to receive the shouldered portion of the core, together with a shielding portion surrounding the upper end of the core, and means to hold the shouldered core portion in the counterbore oi the shell including a retaining ring engaging the shoulder and a snap ring bearing for the retainer removably engaging a seat in said shielding portion.

HECTOR RABEZZANA.

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