Abstract:
The spark plug has been designed so as to, be capable of being disassembled for cleaning, have a substantially full shield for the spark gap end of the center electrode portion, enable the center electrode to be readily replaced, if desired, enable partial cleaning of the spark plug gap area without removal of the spark plug from an associated engine, and have a substantially full gas seal defined between the base of the spark plug and the spark plug insulative sleeve.

Description:
BACKGROUND OF THE INVENTION 
     The spark plug development throughout this century has moved along varied paths. In some instances spark plug construction has moved in a direction of spark plugs which may not be disassembled for cleaning purposes and in other instances the path of spark plug development has extended in the direction of spark plugs which may be disassembled for cleaning. Further, most spark plug development has moved along a path toward substantially fully exposed spark gap defining electrodes. Examples of previously patented spark plugs including structural features somewhat similar to the spark plug of the instant invention may be found in U.S. Pat. Nos. 885,864, 893,955, 1,098,637, 1,275,961, 1,356,954, 1,442,423, 1,448,656, 1,913,575, 1,912,109 and 3,417,275. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The spark plug of the instant invention has been specifically designed so as to be capable of being disassembled for cleaning and has further been designed to substantially fully shield the spark gap end of the center electrode portion thereof. Further, the spark plug of the instant invention has also been designed in a manner enabling the center electrode to be readily replaced, if desired, and to also enable partial cleaning of the spark plug spark gap area without removal of the spark plug from an associated engine. 
     The main object of this invention is to provide a spark plug including a center electrode having its spark gap defining end substantially fully shielded. 
     Another object of this invention is to provide a spark plug that may be readily disassembled for cleaning. 
     Yet another object of this invention is to provide a spark plug constructed in a manner whereby the center electrode thereof may be readily replaced. 
     Yet another object of this invention is to provide a spark plug constructed in a manner whereby a substantially full gas seal will be defined between the base of the spark plug and the spark plug insulative sleeve. 
     A final object of this invention to be specifically enumerated herein is to provide a spark plug in accordance with the preceding objects and which will conform to conventional forms of manufacture, be of simple construction and easy to clean so as to provide a device that will be economically feasible, long lasting and readily serviceable. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a spark plug constructed in accordance with the present invention; 
     FIG. 2 is an enlarged vertical sectional view taken substantially upon the plane indicated by the section line 2--2 of FIG. 1; and 
     FIG. 3 is an exploded perspective view of the various components of the spark plug. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more specifically to the drawings the numeral 10 generally designates a spark plug constructed in accordance with the present invention. The spark plug 10 includes a somewhat conventional tubular base referred to in general by the reference numeral 12, a tubular insulative body referred to in general by the reference numeral 14, a tubular thrust nut referred to in general by the reference numeral 16, a center electrode rod 18 constructed of carbon, an upper terminal 20 supported from the upper end of the tubular insulative body and in electrical contact with the electrode rod 18 and a lower electrode assembly referred to in general by the reference numeral 22 carried by the lower end of the body 12 and constructed of &#34;Stellite&#34; , which material is from a group of hard, corrosion resistant, non-ferrous alloys containing 40 to 80% cobalt, 20 to 35% chromium, 0 to 25% tungsten, 0.75 to 2.5% carbon and 0 to 3% silicon. 
     The body 12 includes a large diameter end portion 24 having a large diameter bore 26 formed therein and which is threaded as at 28. The base 12 further includes an externally threaded small diameter end portion 30 which is externally threaded as at 32 and has a small diameter bore 34 formed therethrough. The inner ends of the bores 26 and 34 are communicated and the bores 26 and 34 are coaxial. 
     The tubular insulative body 14 includes a diametrically enlarged mid-portion 36 and a short small diameter end portion 38 of the body 14 is loosely received within the bore 34 with the diametrically enlarged mid-portion 36 received in the bore 26. The base 12 defines an annular shoulder 40 at the inner end of the large diameter bore 26 and the shoulder 40 includes a mid-radial extent annular groove 42. The end of the diametrically enlarged mid-portion 36 of the insulative body 14 includes an endwise outwardly projecting annular rib 44 on its outer periphery seatingly received in the groove 42. 
     The electrode assembly 22 carried by the free end of the small diameter end portion 30 comprises a generally diametric U-shaped member 44 with the free ends of the legs of the U-shaped member 44 anchored to diametrically opposite portions of the end face of the small diameter end portion 30 and the mid-portion of the bight portion of the U-shaped member 44 includes a spherical enlargement 46. 
     The tubular insulative body 14 has a small diameter center bore 48 formed in the free end of the short small diameter end 38 thereof and the inner end of the bore 48 opens into a counterbore 50 extending from the inner end of the small diameter bore 48 through the diametric enlarged mid-portion 36 of the insulative body 14 and through the long small diameter end portion 52 of the insulative body. The outer end of the counterbore 50 is slightly diametrically reduced and threaded as at 54 and a threaded shank portion 56 of the terminal 20 is threadedly engaged therein. 
     The center electrode rod 18 is seated in the counterbore 50 with the inner end of the shank 56 of the terminal 20 abutted against the end of the rod 18 remote from the inner end of the counterbore 50. The tubular thrust nut 16 is telescoped downwardly over the long small diameter and portion 52 of the insulative body 14 and threaded into the threaded outer end portion 28 of the large diameter bore 26 formed in the large diameter end portion of the body 12 with the inner end of the thrust nut 16 abutted against the outer annular axial face 58 of the diametrically enlarged mid-portion of the insulative body 14. In this manner, the rib 44 of the mid-portion 36 is firmly seated in the groove 42 to form a substantially gas tight seal between the insulative body 14 and the base 12. 
     The outer end of the terminal 20 is defined by a spherical enlargement 60 having crossed intersecting small diameter bores 62 and 64 formed therethrough. The bores 62 and 64 lie along diameters of the enlargement 60 and the spring clip type terminal 66 carried by the spark plug end of a secondary ignition wire 68 may be readily removably electrically engaged with the terminal 20 in a manner which is believed to be obvious from a comparison of FIGS. 1 and 2 of the drawings. 
     The end of the electrode rod 18 adjacent the electrode assembly 22 is fully recessed within the insulative body 14 to the inner end of the bore 48 and thus the rod 18 is shielded against the intense heat of combustion. Of course, the length of the bore 48 and the spacing of the enlargement 46 from the outer end of the bore 48 determines the spark gap of the plug 10. 
     Inasmuch as the electrode 18 is fully recessed to the inner end of the bore 48 the spark jumping the gap between the adjacent portions of the electrode rod 18 and the spherical enlargement 46 must pass through the small diameter bore 48. The passage of the spark through the bore 48 will insure that the bore 48 remains unblocked by carbon and/or oil deposits. Further, it is believed that it may be readily appreciated that the spark plug 10 may be easily disassembled for cleaning purposes and replacement of any portion thereof in the event such replacement is deemed necessary. Further, it will be noted that upon removal of the terminal 20 the electrode rod 18 may be readily removed and replaced without removing the spark plug from an associated engine. Further, after the electrode rod 18 has been removed and before a new electrode rod 18 has been installed, a proper small diameter rod may be inserted downwardly through the counterbore 50 and bore 48 for contact with the spherical enlargement 46 to dislodge any carbon accumulation thereon, even when the spark plug 10 remains mounted on the associated engine. 
     The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.