Patent Publication Number: US-6670740-B2

Title: High electrical stiction spark plug

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of application Ser. No. 09/552,184, filed Apr. 18, 2000 now abandoned, which claims the benefit of U.S. Provisional Application No. 60/133,778, filed May 12, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed generally to spark plugs, and more particularly to a spark plug employing matching opposing convex surfaces as the spark plug gap. 
     BACKGROUND OF THE INVENTION 
     Prior spark plugs typically provide gap electrodes that are flat and parallel or round and symmetrical (i.e., circular convex to circular concave). One such spark plug provides one or more prongs disposed over the tip of a center or sparking electrode. Such spark plugs generate a spark at the outermost tip of the center electrode which results in the gradual build-up of carbon on the tips of the central electrode and the prongs. The carbon build-up leads to a reduced capacity or failure in generating a spark for igniting the fuel/air mixture in an internal combustion engine. Further, the prongs tend to need re-gapping because of electrical use wear and any unwanted bending of the prongs which can occur during periodic cleaning of the spark plug electrodes. 
     In order to lengthen operational life, another type of spark plug has a disk-like terminal head concentrically located in spaced relation within a cylindrical ground electrode to provide an annular sparking gap between the ground electrode and the entire circumference of the disk-like terminal head of the sparking electrode. Thus, in this type of spark plug, firing may occur across the annular sparking gap anywhere along its circumferential length and therefore less fouling will occur as compared with spark plugs having a single point-to-point contact between a central electrode and a ground electrode prong. A drawback with spark plugs with annular sparking gaps, however, is that the center electrode and insulator are typically not exposed to enough of the fuel/air mixture to prevent fouling and are susceptible to damage resulting from, for example, accidental dropping of the spark plug. Further, the insulator member of such spark plugs typically does not have enough exposure to the fuel/air mixture for allowing sufficient cooling to prevent an associated insulator heat build-up which can in turn lead to cracking or insulator resistance breakdown. 
     In view of the foregoing, it is a general object of the present invention to provide a spark plug which overcomes the above-mentioned drawbacks associated with the use and operational life of prior art spark plugs. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicates with the first bore. The sparking electrode includes a firing tip defining a convex outer surface generally having a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode. 
     In a second aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicates with the first bore. The sparking electrode includes a firing tip defining a convex outer surface facing generally away from the connector end and generally has a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis;. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve such that the toroidal member is disposed slightly longitudinally outwardly from the firing tip. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode. 
     In a third aspect of the present invention, a spark plug includes an elongated electrical insulator body defining a first bore extending longitudinally along a central axis of the body from a connector end to a firing end. A sparking electrode communicating with the first bore. The sparking electrode includes a firing tip defining a convex outer surface facing generally toward the connector end and generally having a radius of curvature. The firing tip has an outermost point generally coinciding with the central axis. A ground electrode includes a sleeve having a support portion adjacent to the firing tip of the sparking electrode. The sleeve defines a second bore accommodating at least a longitudinal end portion of the insulator body adjacent to its firing end. The ground electrode further includes a toroidal member having a convex outer surface. The toroidal member is supported by and spaced from the support portion of the sleeve such that the toroidal member is disposed slightly longitudinally inwardly from the firing tip. The toroidal member forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis of the insulator body, whereby each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip. The toroidal member is a closest portion of the ground electrode relative to the firing tip. At least a portion of the outer surface of the toroidal member opposing the firing tip has a radius of curvature of about that of the firing tip for providing a spark along a path of least resistance from the firing tip of the sparking electrode to a point of contact on the opposing surface defined by the toroidal member of the ground electrode. 
     One advantage of the present invention is that the spark gap between electrodes need be set only once during the manufacture of the spark plug. 
     Another advantage of the present invention is that the connecting members and the toroidal member cooperate to form a cage or frustoconically shaped enclosure which protects the firing tip of the sparking electrode and the insulator body from mechanical damage resulting from, for example, accidentally dropping the spark plug. 
     A further advantage of the present invention is that the connecting members permit the insulator body to be exposed to the atmosphere and to cleaning from the fuel/air blast created by a spark to prevent the accumulation of carbon thereon. 
     A further advantage of the present invention is that the spark plug provides a plurality of generally radial spark paths terminating about the surface of the toroidal member which significantly extends the operational life of the spark plug. 
     Another advantage of the present invention is that the firing tip of the sparking electrode protects the longitudinal end of the insulator body from damage from the fuel/air blast. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a spark plug embodying the present invention. 
     FIG. 2 is a partial cross-sectional view of the firing end of the spark plug of FIG.  1 . 
     FIG. 3 is a partial cross-sectional view of the firing end of a spark plug in accordance with a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 2, a spark plug embodying the present invention is generally designated by the reference number  10 . The spark plug includes an elongated electrical insulator body  12 , a sparking electrode  14  and a ground electrode  16 . 
     The insulator body  12 , preferably a ceramic material, defines a first bore  18  extending longitudinally along a central axis C of the insulator body from a connector end  20  to a firing end  22  of the insulator body. The sparking electrode  14  has a terminal end  24  at the connector end  20  of the insulator body  12 , and at an opposite end an exposed firing tip  26 . The firing tip  26  defines a convex outer surface generally having a radius of curvature and is preferably in the form of a dome or half-sphere at least partly covering the firing end  22  of the insulator body  12  to provide maximum resistance to spark bleed off before spark firing, and to protect the insulator body  12  from damaging effects of the ignition of a fuel/air mixture in an internal combustion engine (not shown). As shown in FIGS. 1 and 2, the convex outer surface of the firing tip  26  faces generally away from the connector end  20  of the insulator body  12 . The sparking electrode  14  is substantially disposed within the first bore  18  such that the terminal end  24  extends slightly longitudinally outwardly from the connector end  20  of the insulator body  12  for connection to the boot of a spark plug cable (not shown), and the firing tip  26  extends slightly longitudinally outwardly from the firing end  22  of the insulator body for immersion in a fuel/air mixture in a firing chamber of an internal combustion engine. As shown in FIG. 2, the center of the firing tip  26  of the sparking electrode  14  coincides with the central axis C of the insulator body  12 . 
     The ground electrode  16  includes a sleeve  28  having a support portion  30  positioned adjacent to the firing tip  26  of the sparking electrode  14 . The sleeve  28  defines an external threaded surface for being threadably received in the cylinder head of an internal combustion engine (not shown), and defines a second bore  32  accommodating at least a longitudinal end portion  34  of the insulator body  12  adjacent to the firing end  22 . The ground electrode  16  further includes an electrically conductive toroidal member  36  having a convex outer surface, preferably in the form of a torus. At least two electrically conductive connecting members  38 ,  38 , preferably four as shown in FIG. 1, couple the toroidal member  36  to the support portion  30  of the ground electrode  16 . More specifically, each of the connecting members  38 ,  38  has a first end  40  coupled to the support portion  30  of the ground electrode  16 , and a second end  42  coupled to a portion of the toroidal member  36 . As best shown in FIG. 2, the connecting members  38 , 38  each taper inwardly toward the central axis C in a direction from the first end  40  to the second end  42 . As a result, the toroidal member  36  is the closest portion of the ground electrode  16  relative to the firing tip  26  of the sparking electrode  14 . At least a portion of the outer surface of the toroidal member  36  facing the firing tip  26  has a radius of curvature of about that of the firing tip, to thereby provide a spark path of least resistance from the firing tip of the sparking electrode to a point of contact on the toroidal member. It has been found that the firing tip  26  when in the form of a dome or half-sphere, and the toroidal member  36  both having a similar radius of curvature cooperate to provide inherent maximum electrical stiction (i.e., allows equivalent ball to ball spark firing) to prevent spark bleed off before a spark fires so that maximum spark enhancement (i.e., hottest spark) occurs. 
     As shown in FIGS. 1 and 2, the toroidal member  36  forms an annular curve disposed generally in a plane transverse to and having a radial center coinciding with the central axis C of the insulator body  12  such that each differential segment of the toroidal member radially thereabout is generally equidistant to the firing tip  26 . As a result, a spark path can be terminated at any point radially about the toroidal member  36 . Further, the toroidal member  36  is disposed longitudinally adjacent to, and more specifically as shown in FIGS. 1 and 2, slightly longitudinally outwardly from the firing tip  26  of the sparking electrode  14  such that the connecting members  38 ,  38  and the toroidal member cooperate to form a cage or frustoconically shaped vented enclosure. The frustoconically shaped vented enclosure about the firing tip  26  allows the pre-explosion fuel/air mixture to sufficiently cool the spark plug insulator end to eliminate hot spot problems (i.e., cracking the insulator) associated with prior radially directed spark plugs. The frustoconically shaped vented enclosure also creates an additional fuel/air mixture explosion wind around the firing tip  26  and the toroidal member  36  to substantially prevent carbon build-up on the tip and the toroidal member. Moreover, the enclosure protects the firing tip  26  of the sparking electrode  14  and the insulator body  12  from mechanical damage resulting from, for example, accidentally dropping the spark plug. 
     In operation, when a spark is generated between the electrodes  14  and  16 , it extends along a path of least resistance. The path of least resistance is generally the shortest path between the firing tip  26  of the sparking electrode  14  and the ground electrode  16 . As shown in FIGS. 1 and 2, the shortest distance generally is between a point of contact from a side portion circumferentially about the dome of the firing tip  26  and a point of contact radially about the toroidal member  36  from the portion of the outer surface of the toroidal member facing the firing tip. As mentioned above, a spark path has a termination point at a side portion of the dome of the firing tip  26  because the side portion is closer to the toroidal member  36  relative to the outermost point of the dome coinciding with the central axis C. 
     The exact termination points of a spark path at a first end radially about the dome and at a second end radially about the toroidal member are determined by a variety of factors including fuel fluctuations and slight point-to-point variations in distance between the firing tip  26  and the toroidal member  36 . For example, if a contact point for a spark on the toroidal member  36  deteriorates because of electrical spark contact corrosion (pitting), the spark gap will slightly increase which slightly lowers conductivity at this point. As a result, the path of least resistance now may be at another point on the toroidal member  36  that has not yet been contacted by a spark. 
     The provision of a plurality of contact points for each end of a spark path significantly extends the operational life of the spark plug  10 . Because the spark plug  10 , in effect, supplies new contact points, regapping which is common for conventional spark plugs using point-to-point electrodes is not necessary with the spark plug embodying the present invention. The gap between the firing tip  26  of the sparking electrode  14  and the toroidal member  36  of the ground electrode  16  need be set only once during manufacture, and such factory setting of the gap is sufficient for the operational life of the spark plug  10 . 
     FIG. 3 is a partial cross-sectional view of a firing end of a spark plug  100  in accordance with a second embodiment of the present invention. Like elements with the spark plug  10  of FIGS. 1 and 2 are designated by like reference numbers. 
     An insulator body  102  defines a first bore  104  extending longitudinally along a central axis C of the insulator body from a connector end (not shown) to a firing end  106  of the insulator body. A sparking electrode  108  has a terminal end (not shown) at the connector end of the insulator body  102 , and at an opposite end an exposed firing tip  110 . The firing tip  110  defines a convex outer surface generally having a radius of curvature and is preferably in the form of a dome or half-sphere at least partly covering the firing end  106  of the insulator body  102  to provide maximum resistance to spark bleed off before spark firing, and to protect the insulator body  102  from damaging effects of the ignition of a fuel/air mixture in an internal combustion engine (not shown). As shown in FIG. 3, the convex outer surface of the firing tip  110  faces generally toward the connector end of the insulator body  102 , as opposed to spark plug  10  of FIGS. 1 and 2 where the convex outer surface of the firing tip  26  faces generally away from the connector end  20  of the insulator body  12 . The sparking electrode  108  is substantially disposed within the first bore  104  such that a terminal end extends slightly longitudinally outwardly from the connector end (not shown) of the insulator body  102  for connection to the boot of a spark plug cable, and the firing tip  110  extends slightly longitudinally outwardly from the firing end  106  of the insulator body for immersion in a fuel/air mixture in a firing chamber of an internal combustion engine. As shown in FIG. 3, the center of the firing tip  110  of the sparking electrode  108  coincides with the central axis C of the insulator body  102 . 
     The spark plug  100  further includes a sleeve  28  having a support portion  30  positioned adjacent to the firing tip  110  of the sparking electrode  108 . A ground electrode  112  includes an electrically conductive toroidal member  36  having a convex outer surface, preferably in the form of a torus. At least two electrically conductive connecting members  114 ,  114  couple the toroidal member  36  to the support portion  30  of the ground electrode  112 . More specifically, each of the connecting members  114 ,  114  has a first end  116  coupled to the support port of the insulator body.