Patent Publication Number: US-8994256-B2

Title: Igniter for an internal combustion engine

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/504,852 titled “Igniter” and filed Jul. 6, 2011, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Exemplary embodiments of the present invention relate to a spark plug or igniter for an internal combustion engine, and more particularly to a spark plug or igniter that initiates combustion, facilitates combustion control and burns off soot deposits in a diesel engine. 
     Soot is a common byproduct of the incomplete combustion of fuel in internal combustion engines namely, diesel engines. In particular, conventional fuels are comprised of hydrocarbons, which after undergoing complete combustion, produce byproducts of only carbon dioxide and water. However, complete combustion does not typically occur in internal combustion engines since no known engine is entirely efficient. In addition, complete combustion can require a lean fuel-air mixture whereas typical engine conditions require richer fuel-air mixtures to produce a desired performance. 
     Further emission regulations are mandating the use of new engine combustion cycles such as homogeneous charge compression ignition (HCCI) and exhaust treatment systems for diesel engines. These new combustion cycles will require new methods for combustion sensing and control. There may also be certain engine load conditions where more conventional combustion cycles still work best. For these conditions, spark assist is one means of controlling the combustion process. This unique combination of needs for in-cylinder combustion sensing and combustion initiation can be supported with a spark plug designed to work well in the higher pressure diesel engine cylinder environment as an igniter and also as an ion sensor for combustion feedback and control. For exhaust treatment, better methods are needed to actively regenerate the particulate filters. One method for active regeneration is to provide a self contained burner system to add heat energy to the exhaust to initiate the regeneration cycle. This burner system requires a reliable igniter that can survive in the corrosive and turbulent diesel exhaust environment. 
     In addition, soot typically accumulates at a higher rate in diesel engines than in gasoline engines due to the different ways that fuel is injected and ignited. In particular, in gasoline engines, fuel is injected during the intake stroke and thoroughly mixed with air before ignition by a spark. Conversely, in diesel engines, fuel is injected during the compression stroke and ignited spontaneously from the pressure. In that respect, combustion occurs at the boundary of unmixed fuel, where localized pockets of rich fuel-air mixtures are ignited, thus producing soot. 
     Soot deposits can accumulate on insulator tips of conventional spark plugs used as an igniter in a burner system. The exposed surface of the insulator tip is typically located at or near the boundary of unmixed fuel. Moreover, the exposed surface of the insulator tip is not typically located in or about the spark gap between the side electrode and the center electrode. In particular, the typical spark plug includes a center electrode extending past an insulator tip and a side electrode extending past the center electrode. For these reasons, soot may accumulate on the insulator tip and may not be burned off. 
     Accordingly, it is desirable to provide a spark plug or igniter design that is more robust than conventional spark plug designs to high cylinder pressures and to the corrosive effects of the combustion chamber or exhaust. 
     SUMMARY OF THE INVENTION 
     In accordance with a non-limiting exemplary embodiment of the present invention, an igniter for an internal combustion engine includes a center electrode, an insulator disposed about the center electrode, and a ground shield disposed about the insulator, wherein the insulator includes a tip portion extending past an end portion of the ground shield and a tip portion of the center electrode extending through and away from the tip portion of the insulator. The igniter further includes a cap secured to the center electrode, wherein the cap extends past and covers a distal end of the tip portion of the center electrode and a distal end of the tip portion of the insulator. A spark gap is disposed between a peripheral edge of the cap and the end portion of the ground shield or threaded portion wherein the peripheral edge of the cap is spaced away from a surface of the tip portion of the insulator. 
     In accordance with another non-limited exemplary embodiment of the present invention, an igniter for an internal combustion engine includes a center electrode and an insulator disposed about the center electrode. The igniter further includes a threaded portion disposed about the insulator, the insulator having a tip portion extending past an end portion of the threaded portion and a tip portion of the center electrode extending through and away from the tip portion of the insulator. A cap is secured to the center electrode, wherein the cap extends past and covers a distal end of the tip portion of the center electrode and a distal end of the tip portion of the insulator. A spark gap is disposed between a peripheral edge of the cap and the end portion of the threaded portion, wherein the peripheral edge of the cap is spaced away from a surface of the tip portion of the insulator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of an igniter; 
         FIG. 1A  is an enlarged view of the igniter of  FIG. 1 ; 
         FIG. 2  is a view of an igniter constructed in accordance with a first exemplary embodiment of the present invention; 
         FIG. 2A  is an enlarged view of the igniter illustrated in  FIG. 2 ; 
         FIG. 2B  is an enlarged view of the igniter illustrated in  FIG. 2 ; and 
         FIG. 3  is a view of a further igniter constructed in accordance with a second exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present invention relate to an igniter or igniter/ion sensor for high compression engines and in particular, an igniter for use in a burner system for regenerating a filter (e.g., diesel particulate filter “DPF” or other equivalent filter requiring high temperature regeneration using an igniter). Exemplary embodiments of the present invention are related to U.S. Pat. No. 5,697,334, the contents of which are incorporated herein by reference thereto. 
     In accordance with an exemplary embodiment and as illustrated in the attached drawings, a “high thread” spark plug is provided with a circular side electrode shape that allows for the spark energy to pass over the ceramic insulator tip surface, thereby creating the igniter of exemplary embodiments of the present invention. In a non-limiting exemplary embodiment, the side electrode is made of a high nickel or stainless steel alloy having an 8 millimeter (mm) or a 10 mm diameter or any range therebetween as well as diameter greater or less than 8 and 10 mm. Although, the dimensions greater or less than the aforementioned diameters are considered to be within the scope of exemplary embodiments of the present invention. In addition and in accordance with non-limiting exemplary embodiments of the present invention, the distance between the tip of the center electrode and the side electrode has been in the range of 2 mm to 10 mm. Furthermore, the diameter of the center electrode tip may be increased by attaching a metal disk to improve ion sensing capability of the center electrode. 
     In accordance with one exemplary embodiment, the spark plug must be able to produce a sufficiently high energy spark over the non-conductive ceramic insulator tip to burn off the soot formed on the insulator tip. In accordance with another exemplary embodiment, the device described herein uses a center electrode with an ion sensing portion or annular disc portion to emit a spark along the insulator tip and to detect an ion current in a combustion cylinder into which the igniter is disposed. 
     Referring to  FIGS. 1-1A , there is shown an igniter or igniter/ion sensor  10  for a high compression engine. The igniter or igniter/ion sensor or spark plug  10  includes a center electrode  12  ( FIG. 1A ) disposed in a center bore of an insulator  14 . A ground shield  16  is disposed about the insulator  14 . In accordance with an exemplary embodiment of the present invention, a tip portion  18  of the insulator  14  extends past an end portion  20  of the ground shield  16 . A tip portion  22  of the center electrode  12  extends past the end of the insulator  14 . 
     Accordingly and as illustrated, a spark gap  24  extends from the tip portion  22  of the center electrode  12  to the ground shield  16 . The spark gap  24  also extends along a surface  26  of the tip portion  18  of the insulator  14 . In order to “burn off” or remove soot accumulated on the surface  26 , a high voltage is passed through the center electrode  12  to heat up the surface and burn away accumulated soot. 
     The spark gap  24  has a frustoconical shape defined by the tip portion  18  of the insulator  14 , wherein an outer periphery  28  of the tip portion  18  diverges between an inner end  29  of the tip portion  22  of the center electrode  12  and the end portion  20  of the ground shield  16 . 
     The ground shield  16  has an outer diameter OD that is between about 8 millimeters and about 10 millimeters. It is understood that the outer diameter OD can instead be more or less than this range. One non-limiting material for the ground shield  16  is a nickel alloy. However, it is contemplated that the ground shield  16  can instead be formed from stainless steel or various other suitable materials, as desired. 
     As depicted in  FIGS. 1 and 1A , the center electrode  12  also includes a ring portion  32 , which surrounds the tip portion  22  of the center electrode  12 . As illustrated, the ring portion  32  is an annular disc portion that extends from the center electrode  12  and has a width greater than a width of the center electrode  12 . Of course, other configurations of the ring portion  32  are considered to be with the scope of exemplary embodiments of the present invention. When the ring portion  32  (e.g., disc portion or other configuration) is disposed on the center electrode  12 , the spark gap  24  extends between an outer periphery  33  of the annular disc portion  32  and the end portion  20  of the ground shield  16 . 
     The ring portion  32  is also used as an ion sensing portion  33  as described in U.S. Pat. No. 8,053,965, the contents of which are incorporated herein by reference in their entirety. The ion sensing portion  33  is used to provide an ion sensing means as part of the igniter. In one embodiment, the annular disc portion is made from a nickel alloy and the ion sensing means is contemplated for use with a combustion control system (“system”) as exemplified in U.S. Pat. No. 8,053,965. 
     As illustrated in  FIGS. 1-1A  the arc of the spark travels around the corner  35  of the ceramic insulator  14  as depicted by arrows  37 . As the arc goes around the corner  35 , it may form a groove in the ceramic insulator  14 . If a formed groove becomes large enough, it may prevent ignition of the fuel or cause the ceramic insulator  14  to fail due to mechanical weakness. 
     Referring now to  FIGS. 2-2B  a high thread spark plug  10 ′ in accordance with an exemplary embodiment of the present invention is illustrated, wherein the design of the high thread spark plug  10 ′ minimizes formation of a groove or “channeling” in the ceramic insulator  14 . The ring  32  of the embodiment of  FIGS. 2-2B  is configured to have a cap, cup or inverted cup design  32 ′, wherein a rim portion or peripheral edge  40  of the cup extends past the ceramic tip and towards the end  20  of the ground shield  16  such that the cap or cup covers the corner  35  of the end of the insulator  14 . 
     In this configuration, the spark gap  24  will extend from a peripheral edge or rim portion  40  of the cap  32 ′ to the end  20  of the ground shield  16 , as illustrated by arrows  42 . As shown, the arrows  42  are spaced from the surface  26  of the insulator  14 . This spacing will eliminate the channeling at the ceramic corner and increase the surface for the spark surface. 
     As shown at least in  FIG. 2B  the peripheral edge  40  of the cap  32 ′ is spaced at least a distance X from the surface  26  of the insulator  14  extending past the ground shield  16 . This design guides the spark arc away from the surface of the ceramic insulator  14 , thereby reducing damage and wear on the ceramic insulator  14 . 
     The embodiment of  FIG. 3  is identical to the embodiments of  FIGS. 1-1A  and  2 - 2 B, respectively, except that igniter  10 ″ of  FIG. 3  is a conventional igniter. In particular, threaded portion  50  for attachment to a conventional engine block is disposed adjacent the insulator  14 . In this manner, the igniter  10 ″ of  FIG. 3  would function in the same manner as the embodiments of  FIGS. 1-1A  and  FIGS. 2-2B , respectively, and a spark gap  24  would be created between the ring portion  32  or the cap  32 ′, respectively, and the end  20 ′ of the threaded portion  50 . The threaded portion  50  acts as a ground electrode and is preferably made of steel, a nickel alloy, a stainless steel alloy, or any other material known in the art. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the present application.