US3800179A

US3800179A - Self-cleaning spark plug

Info

Publication number: US3800179A
Application number: US00294476A
Authority: US
Inventors: P Louzecky
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1972-10-02
Filing date: 1972-10-02
Publication date: 1974-03-26
Anticipated expiration: 1991-03-26

Abstract

An improved spark plug adapted for use in rotary engines in order to eliminate misfiring in the engine caused by shorting of the electrodes as a result of the build up of oils, carbon and other products of combustion on the electrodes, comprising an insulator and center electrode assembled in conventional manner within a metal shell, the lower end of which cooperates with the center electrode to form a sparking gap, the gap being located in the restricted cross-section outlet of a combustion cavity formed within the lower end of the shell between the inner wall surface of the shell and the outer surface of the insulator, the combustion cavity having a volume of from 1-3% of the volume of the engine combustion chamber and the outlet area being such as to produce an exiting combustion gas velocity from the cavity upon ignition of the fuel-air mixture therein such as will maintain the electrodes in a clean condition.

Description

United States Patent 1 1 3, Louzecky or. 26, 197% SELF-CLEANING SPARK PLUG Primary Examiner-Alfred L. Brody [75] Inventor: Paul J. Louzecky, Troy, Mich. Attorney Agent or pirmhsldney Carter [73] Assigne'e: General Motors Corporation, A

Detroit, Mich. [571 ABSCT [22] F] d Oct 2 1972 An improved spark plug adapted for use in rotary en- App]. No.: 294,476

gines in order to eliminate misfiring in the engine caused by shorting of the electrodes as a result of the build up of oils, carbon and other products of combustion on the electrodes, comprising an insulator and center electrode assembled in conventional manner within a metal shell, the lower end of which cooperates with the center electrode to form a sparking gap, the gap being located in the restricted cross-section outlet of a combustion cavity formed within the lower end of the shell between the inner Wall surface of the shell and the outer surface of the insulator, the combustion cavity having a volume of from 13% of the volume of the engine combustion chamber and the outlet area being such as to produce an exiting combustion gas velocity from the cavity upon ignition of the fuel-air mixture therein such as will maintain the electrodes in a clean condition.

1 Claim, 1 Drawing Figure 1 SELF-CLEANING SPARK PLUG the lower end thereof between the shell and the insulator is not new as shown by the patent to G. F. Wright et al. No. 2,702,537 dated Feb. 22, 1955 and the patent to Testerini No. 3,215,131 dated Nov. 2, 1965. Neither is the use of a conventional type spark plug in a rotary engine new as shown by the patent to Shibagaki et al. No. 3,597,648 dated Aug. 3, 1971. Each of these pa tents, however, has an entirely different structure and operation than that disclosed and claimed by applicant.

In accordance with my invention, a spark plug of the self-cleaning type is provided. The electrodes are maintained in a clean condition by the self-cleaning action of the plug resulting from the hot scrubbing of the electrodes by the ignition of the fuel-air mixture within the lower end of the plug upon each sparking cycle of the plug, the hot combustion gases exiting from the plug and sweeping over the electrodes positioned in the plug exit.

The features and operation of my invention are apparent from the following description taken in conjunction with the accompanying drawing in which there is shown a longitudinal half-section view of the plug taken through the centerbore axis as installed in a radial engine shown in partial view.

As shown in the drawing, the spark plug 1 comprises a metal shell 3 in which there is positioned in sealed relationship therewith a ceramic insulator 5 having a centerbore 7 axially through the center thereof. A center electrode 9 is positioned within the centerbore with its sparking end portion 11 extending beyond the end of the insulator. As shown, the spark plug assembly is threaded into the housing 13 of the rotary engine with the plane of the end of the spark plug being limited to the plane of the surface of the combustion chamber or trochoid surface in the area of the spark plug aperture formed in the housing 13 in order to avoid any interference with the rotor apex seals 14 in the engine.

As can be readily understood from consideration of the mode of operation of a rotary engine, the seals provided in the ends of the engine rotor in order to seal the several portions of the engine cavity from each other through each cycle of rotation, act to sweep, or shovel lubricating oil and solid combustion products into the lower end of the spark plug shell, thus tending to quickly foul the electrodes with resultant misfiring of the plug. In order to control this misfiring tendency, applicant has designed his plug in order to provide a combustion cavity 15 within the lower end of the spark plug, cavity 15 being formed between the small diameter lower end 17 of the insulator and the radially inwardly tapering surface 19 of the shell, the radius of the inner surface of the shell decreasing progressively from the inner end 16 of the cavity 15 to the restricted crosssection circular outlet end 21. The portions defining the combustion cavity 15 are so proportionedas to produce a combustion cavity volume of from about 1-3 percent of the volume of the engine combustion chamher.

As is shown, the sparking end portion 11 of the center electrode is positioned within the restricted crosssection circular outlet end 21 of the shell 3 with which it cooperates to form a spark gap. As shown in the pre ferred embodiment, the spark gap is annular in shape. However, the gap may be alternatively formed as in the conventional automotive pin type spark plug by the provision of a ground electrode secured to the end of the shell and projecting toward but spaced from the side of the center electrode in order to maintain the spark gap in the restricted cross-section outlet from the combustion cavity.

It is the purpose of my invention that the electrodes be positioned in the restricted cross-section outlet 21 of the spark plug in order that the products of combustion from within the combustion cavity 15 sweep by the electrodes through the gap area in order to clean the oil and combustion products from the electrodes.

As is shown in the drawing, in the preferred embodiment of my spark plug the small diameter lower end 17 of the insulator projects partially into a tubular extension portion 23 of the shell 3, the tubular extension forming the restricted cross-section circular outlet end of the plug and of the combustion cavity 15. By so designing the parts, an annular venturi-like throat is formed through which the combustion gases from the cavity 15 pass at a relatively high velocity. The velocity of the gases iassingthrough the exit and through the sparkgap is from about 900m l000 feet per second at its peak upon ignition of the combustible gases within the cavity 15. The design of the combustion cavity is no problem to those skilled in the art in view of my teachings as set forth above. By way of example, a suitable sgk plugfor use in a rotaryengineln which the combustion chamber volume is about 30 cubic inchesincludes a combustion cavity 15 having a volume of 060 cubic inch or 2 percent of the engine combustion chamber volume. The annular cross-section area of the restricted outlet at the exit end of the cavity is approximately 0.04 sq. in. based on the tubular extension portion 23 having an inside diameter of about 0.28 inch and the small diameter portion 117 of the insulator extending into the tubular extension 23 having a diameter of about 0.16 inch, the engine compression ratio being from about 8 to 9.521. The width of the spark gap is similar to that in conventional automotive type plugs and is about 0.035 inch.

Though my invention has been described to include a tapered outer surface portion on the lower end of the spark plug shell, it is apparent that the outer surface might equally well be cylindrical as is conventional. Equivalents as regards other features will also be apparent to those skilled in the art and such equivalents are intended to be within the scope of the claims which follow.

What is claimed is:

l. A self-cleaning spark plug comprising a metal shell having a tubular firing end portion of circular crosssection, a ceramic insulator secured therein in gas-tight relationship therewith and having a centerbore therethrough, the surface of the lower portion of said insulator being tapered and spaced apart from said shell and of circular cross-section throughout its length with the firing end thereof extending into said tubular end portion concentrically and coaxially therewith to form an positioned in said centerbore, said firing end portion cooperating with said center electrode to form an annular spark gap in said outlet adjacent the venturi-like throat, the cross-sectional area of said annular spark gap being such as to produce an initial velocity of combustion gases out of said cavity and through said spark gap of from about 900 to 1000 feet per second in order to keep the electrodes scubbed clean.

Claims

1. A self-cleaninG spark plug comprising a metal shell having a tubular firing end portion of circular cross-section, a ceramic insulator secured therein in gas-tight relationship therewith and having a centerbore therethrough, the surface of the lower portion of said insulator being tapered and spaced apart from said shell and of circular cross-section throughout its length with the firing end thereof extending into said tubular end portion concentrically and coaxially therewith to form an annular venturi-like throat therebetween of uniform width, the inner wall surface of said shell and the surface of the lower portion of said insulator forming a combustion cavity of from about 1 to 3 percent of the volume of the engine combustion chamber volume, said inner wall surface of said shell defining said combustion cavity being tapered radially inwardly to said tubular end portion to form a restricted cross-section outlet at the exit end of said cavity, a center electrode positioned in said centerbore, said firing end portion cooperating with said center electrode to form an annular spark gap in said outlet adjacent the venturilike throat, the cross-sectional area of said annular spark gap being such as to produce an initial velocity of combustion gases out of said cavity and through said spark gap of from about 900 to 1000 feet per second in order to keep the electrodes scubbed clean.