US2258810A - Shielded aircraft spark plug - Google Patents

Description

Och 1941- H. RABEZZANA ET AL 2,258,810

SHIELDED AIRCRAFT SPARK PLUG Filed Jan. 5, 1940 Snnenfors 920202 Waszzazza 4' I ttomegs Patented Oct. 14, 1941 I 2,258,810 SHIELDED AIRCRAFT SPARK PLUG Hector Rabezzana and Alexander J. Battey, Flint,

Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of-Delaware Application January 5, 1940, Serial No. 312,476

2 Claims.

Our invention relates to spark plugs designed to ignite the combustible mixture supplied to and burned within the working cylinder of an internal combustion engine, and particularly to spark plugs for use in shielded ignition systems wherein the conductor or lead wire through which current is supplied to the insulated electrode of the plug is enclosed in a metallic envelope which, in'

turn, is connected to the metallic shell or casing of the plug. The plug itself or, more strictly speaking, the casing thereof being screwed into a threaded opening in an engine cylinder, it follows that the envelope enclosing the supply lead is grounded to the engine structure through the metallic shell or casing of the plug; thus prevent-' ing the high tension oscillating current in the supply lead from interfering with the operation of radio receiving apparatus located adjacent the engine equipped with an ignition system having -overheating, than has been the case in spark plugs such as'have heretofore been used. To that end our invention consists in providing the usual shell or casing of the plug with an upwardly extending shield portion designed to be electrically connected with the metallic envelope enclosing the supplylead, in certain relationships between the shield'portion and the central insulated elec-- trode of the plug,. and various other features hereinafter described and claimed.

Our invention includes a tubular lining member of plastic insulating material molded in place within the upwardly extending shield portion of the shell or casing of the plug, and in intimate contact withthe interior thereof and with the exterior .of the upper portion of the insulating member of the plug, whereby a better heat conducting path and one of minimum resistance to the flow of heat fromv the central electrode and insulating member to the shell or casing, is secured.

In the drawing accompanying and forming a part of this specification:

Figure l is a view showing our improved spark v plug partly in elevation, and partly in section upon avertical central plane; the plug being shown about full size.

Figure 2 is a view similar to Figure 1 showing a supply cable secured to the plug so as to supply current thereto, and the metallic sheath of which 'cable is grounded to the shell or casing of the plug.

Figure 3 is a view illustrating one step of the method whereby a tubular lining member is molded in place within the shell or casing of the plug, .the plug being shown about twice the size it is shown in Figures 1 and 2.

Figure 4 is a view similar to Figure 3 but showing a later step of the method whereby the tubular lining member of our spark plug is molded in place within the exterior shell or casing thereof.

Referring now to the drawing, the tubular metallic shell or casing of our improved spark plug is threaded at its lower end 5 to screw into a threaded opening in an engine cylinder and comprises a lower portion 6 within which the enlarged central portion of the insulating member 1 of the plug is secured, and an upper tubular shield portion 8 shown as integral with the lower portion, but which may be separate therefrom and secured to the lower portion in any way so as to form a unitary shell or casing for the plug.

The insulating member is supported by an internal ledge 9 within the lower portion of the shell, and the upper end' thereof extends into the upper shield portion of the shell and is smaller in diameter than said shield portion, so as to provide an annular space between the two. The insulating member'is held in place within the lower portion 8 of the shell or casing by an externally threaded annular sleeve [0 in engagement with an internally threaded seat within the shield portion 8, as shown, and through which sleeve the upper end of said insulating member -vext-ends; an annular holding member being interposed between the sleeve and an annular shoulder ll upon the insulating member. This holding member is shown as in the form of a C-shaped gasket I2 made of spring steel so'that when the sleeve I0 is screweddownward the insulating member is forced against the ledge 9 t by pressure transmitted through the gasket [2 and shoulder H; the insulating member being thus permanently held in place within the lower portion 6 of the shell within which it is housed independently of the tubular lining member to be next described.

After the insulating member 1 has been assembled within the shell or casing and secured in place therein by the annular sleeve l0 and C- shaped gasket I2, as hereinbefore' explained, a

tubular lining member l3 of plastic material is molded in place within the upwardly extending shieldportion 8 of the shell; said member being molded in place under pressure so that intimate contact is secured between the periphery thereof and 'the interior of the shield portion 8, and between said lining member and the exterior of the upwardly extending portion of the insulating member. A portion of the material of the lining extends over the upper end of the insulating .iember and into contact with the upper end of .he insulated electrode M as indicated by the ziumeral l5. The intimate contactsthus secured provide a heat conducting path of minimum resistance to heat flow from the central electrode 54 and the upper portion of the insulating member to and into the lining member i3, and from said member to the shield portion 8 of the shell; from which the heat is dissipated into the surrounding atmosphere and a plug which operates at a lower temperature than heretofore is secured.

The numeral l6 designates a metallic voltage dispersing member, preferably cup-shaped in form as shown, in contact with the upper end of the central electrode of the plug and the periphery of which is embedded in the inner surface of th tubular lining member 53; the purpose of this member being to distribute the voltage present at the upper end of said electrode through an area equal to the circumference of said member times its height. The voltage at said upper end being thus dispersed (as distinguished from being concentrated at one .or more points of limited area), it follows that the wall of the lining member 83 is less likely to be injured, 'as' by a short circuit betweenthe upper end of the central electrode and the grounded shell portion a,

or otherwise, than is the case when such voltage is or may be concentrated at points of limited area upon the inner surface of said lining member.

In making a spark plug in accordance with our invention the insulating'member l and central electrode are assembled within the shell or casing and secured in place by the annular sleeve l6 and holding member I 2, as hereinbefore appears, and plastic material to form the tubular linin member i3 is put into theupper shield portion 8 of the shell, as indicated by the numeral ii in Figure 3. The plug is thenplaced upon asuitable annular anvil i8 and held in contact therewithby an annular holding member iii, the two being maintained in alignment by a die block 20; and a.plunger 2| which .is guided by holding member is as shown is forced into the shield part 3 thus displacing the plastic material ll and causing it to fill the shield portion of the shell or casing, as shown in Figure 4; with the result that intimate contact is secured between said plastic material and the interior of the shell,

and with the exterior of the upwardly extending part-of the insulating member. A cup-shaped member 22 is put upon the extremity of the plunger 2!, see Figure 3, before it is forced into the shield part 8;,and the bottom wall of this joint between the central electrode and the voltage dispersing member 56, which member becomes embedded in the inner surface of the tubular lining member at the end of the downward movement of the plunger and is left in place, see Figure 1, as the plunger is withdrawn after the completion of the molding operation.

The tubular lining member 53 preferably made of Bakelite in which case the plastic material I! placed in the shield portion 8 of the shell consists of a suitable amorphous and uncured material or composition from which a finished Bakelite article (the tubular lining member herein) may be formed; and the plunger 2! is depressed to accomplish moldingof the member 13 in situ, the same as heretofore explained. Thematerial used is commonly heated to a temperature of around 100 to 150 degrees centigrade before being supplied to the plug casing, and the plug with the lining molded in place is commonly kept at a temperature of around 150 degrees centigrade for around one minute after the molding operation to permit the Bakelite material to coalesce and form an integral and solid lining member.

Having" thus described and explained our invention, we claim and desire to secure by Letters Patent:

1. A spark plug comprising a hollow metallic shell or casing threaded at its lower end to screw into an opening an engine cylinder and having a lower portion for housing an insulating member, and having also an upper shield portion; an insulating member located within the lower and extending into the upper shield portion of said shell, and the upper end of which insulating member is smaller in diameter than the interior of said shield portion so as to provide an annular space between the two; means for securing said insulating member in place within the lower portion of -said shell; and a tubular lining member of plastic material molded in place within said annular space and in intimate contact with the interior of said shield portion and with the exterior of the upper end of said insulating member, and which lining extend above the upper end of said insulating member.

2; In a spark plug of the class described, a hollow metallic shell or casing threaded at its lower end to screw into an opening in an engine cylinder and having an internal supporting ledge, an internally'threaded seat, and a shield portion extending above said seat; an insulating member within said .shell and supported by said ledge,

and which member extends above said threaded seat and into said shield portion and has an annular shoulder; an externally threaded annular sleeve in engagement with said threaded-seat and through which the upper end of said insulating member extends; an annular holding member between said sleeve and the shoulder aforesaid of said insulating member; and a tubular lining member of plastic material molded in place within said shell and in intimate contact with the interior of the shield portion thereof and with the exterior of th upwardly extending portion of said insulating member.

HECTOR. RABEZZANA.

ALEXANDER J. BA'I'I'EY.

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