Abstract:
Spark plugs in an internal combustion engine may have an encapsulated spark gap allowing for improved emissions and efficiency. However, increased temperatures in an ignition chamber about the spark gap may cause pre-ignition of a air fuel mixture in a combustion chamber. A purge passage allows hot exhaust gas to be expelled from the ignition chamber and thus reduce likelihood of pre-ignition.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates generally to a spark ignition device for an internal combustion engine and more particularly to an encapsulated spark plug.  
         BACKGROUND  
         [0002]    Emissions and efficiency continue driving technology to improve combustion of air and fuel mixtures. Many improvements have come through greater control of air flows and fuel flows. Generally, these controls have improved atomization and mixing of the fuel and air.  
           [0003]    Spark ignited engines may additionally control a combustion event through initiation of a spark. Encapsulated spark plugs combine improvements gained by improving mixing of fuel and air along with improvements gained by controlling initiation of the spark. An encapsulated spark plug includes an ignition chamber defined by an interior portion of the plug shell. The ignition chamber surrounds an electrode gap between a first electrode and a second electrode. As a piston compresses an air/fuel mixture in the combustion chamber, at least a portion of the air/fuel mixture passes through an orifice in the plug shell into the ignition chamber.  
           [0004]    In the ignition chamber, a spark across the electrode gap causes the portion of air/fuel mixture to combust resulting in a pressure rise in the ignition chamber. Hot gasses escape from ignition chamber into the air/fuel mixture in the combustion chamber as the pressure in the ignition chamber overcomes pressures in the combustion chamber. The hot gasses act like a torch penetrating further into the combustion chamber than a typical spark plug. Further penetration by the torch causes combustion to occur more evenly throughout the combustion chamber to reduce a mass of unburned air/fuel mixture. Both U.S. Pat. No. 4,937,868 issued 29 Jan. 1991 and U.S. Pat. No. 5,105,780 issued 21 Apr. 1992 to Richardson show encapsulated spark plugs.  
           [0005]    Operating the encapsulated spark plugs may require higher temperatures resulting in pre-ignition of the fuel/air mixture. In general, electrical demands are greater than those in a standard spark plug. These higher electrical demands may cause the encapsulated spark plugs to operate at higher temperatures. Pre-ignition of the fuel/air mixture in the ignition chamber may occur at these higher temperatures. U.S. Pat. No. 6,460,506 issued to Nevinger on Oct. 8, 2002 discloses one aspect of increased temperatures as being an increased heat transfer resistance between a tip portion of a spark plug shell and the cylinder head. In Nevinger, the assignee (the same as in the present case) attempts to reduce the temperature at an orificed region by increasing heat transfer to the cylinder head.  
           [0006]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0007]    In an embodiment of the present invention a spark plug has a spark plug shell. An insulator is placed in an interior portion of the spark plug shell with a first electrode passing through the insulator.  
           [0008]    An end cap connects with the spark plug shell. A second electrode connects with at least one of the end cap or spark plug shell. The spark plug shell, end cap and insulator define an ignition chamber including a purge portion above an ignition plane. A purge passage fluidly connects the purge portion with a combustion chamber.  
           [0009]    In another embodiment of the present invention an end cap for a spark plug includes a first end portion, second end portion, interior portion, and exterior portion. The first end portion connects with a spark plug shell. An ignition plane is formed between the first end portion and the second end portion. A purge passage fluidly connects the interior portion at or above the ignition plane with the exterior portion. A second passage connects the interior portion with the exterior portion at or near the second end portion.  
           [0010]    Further, the present invention may also be characterized as a method of reducing pre-ignition in a spark plug where a mixture of fuel and air are introduced into an ignition chamber of a spark plug. The fuel and air are ignited in an ignition plane of the spark plug. At least a portion of the combustion gas is expelled into the combustion chamber through a jet passage. Another portion of the combustion gas is expelled from a purge portion of the ignition chamber where the purge portion is a volume at or above the ignition plane. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a cross section view of a spark ignited internal combustion engine including a spark plug having an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of a spark plug having an embodiment of the present invention; and  
         [0013]    [0013]FIG. 3 is a cross-sectional view of a spark plug having an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]    In FIG. 1 a spark ignited combustion engine  10  has a cylinder head  12  sealingly connecting with a cylinder block  14 . A combustion chamber  16  is defined by a cylinder wall  18  in the cylinder block  14 , the cylinder head  12 , and a piston  20 . The piston  20  slidingly engages the cylinder wall  18  in a conventional manner.  
         [0015]    The cylinder head  12  has at least one port (not shown) fluidly connecting the combustion chamber  16  with a fuel conduit (not shown), an inlet conduit  24 , and an exhaust conduit  26 . For this application, the engine  10  has a first inlet port  28 , a second inlet port (not shown), a first exhaust port  30 , and a second exhaust port (not shown). The inlet ports  28  fluidly connect to the inlet conduit  24 . The exhaust ports  30  fluidly connect to the exhaust conduit  26 . While the fuel conduit may connect directly with the combustion chamber  16 , this application has the fuel conduit connecting with inlet conduit  24  upstream of the inlet port  28 . An inlet valve  32  is movably positioned in the inlet port  28  and an exhaust valve  34  is movably positioned in the exhaust port  30 . The engine may have multiple inlet valves  32  and exhaust valves  34  for each combustion chamber  16 . Each engine  10  may have multiple combustion chambers  16  arranged in numerous manners such as inline, V, flat, or radial configurations.  
         [0016]    The cylinder head  12  further includes a spark plug well  35  having a connection portion  36 . In this application, the connection portion  36  is threaded. However, the connection portion  36  may be any conventional connection mechanism able to withstand pressures, temperatures, and chemistry compatibility typical of a combustion process. The spark plug well  35  may also include cooling channels (not shown). A spark plug  38  sealingly connects with the cylinder head  12 .  
         [0017]    [0017]FIG. 2 shows the spark plug  38  having a spark plug shell  240 , insulator  242 , first electrode  244 , and a second electrode  246 . The first electrode  244  has a first portion  248  for connecting with a power source (not shown) and a second portion  250  distal from the first portion. The first electrode  244  may be made of a material having good electrical conductivity and heat resistance such as a nickel alloy. The insulator  242  electrically isolates the first electrode  244  from the second electrode  246  while still maintaining structural integrity in a high temperature environment. The insulator  242  may be made of a ceramic. The insulator  242  connects with and generally covers the first electrode  244  between the first portion  248  and second portion  250 .  
         [0018]    The spark plug shell  240  has an interior portion  252  and exterior portion  254 . The interior portion  252  of the spark plug shell  240  is adjacent to the insulator  242 . The exterior portion  254  of the spark plug shell  240  is positioned in the spark plug well  35  in a conventional manner.  
         [0019]    In the present embodiment, an end cap  256  is connected with the spark plug shell in a conventional manner such as press fitting or welding. The end cap  256  may include a jet passage  258 , a purge passage  260 , a first end portion  262 , and a second end portion  264 . The first end portion  262  is above the second end portion  264  and proximate the cylinder head  12 . For this application, “above” means the first end portion  262  is closer to the first portion  248  of the first electrode  244  compared with the second end portion  264 . The jet passage  258  may be a single orifice below the first electrode  250 . In this embodiment, the jet passage  258  includes multiple orifices  266 . Preferably the multiple orifices  266  are angled at least partially toward the piston  20  or downward.  
         [0020]    Connecting the end cap  256  with the spark plug shell  240  forms an ignition chamber  268 . The end cap  256  may act as the second electrode  246  as shown. An ignition plane  270  is formed generally about a spark gap  271  between the second portion  250  of the first electrode  244  and the second electrode  246 . The “plane” is generally perpendicular to a longitudinal axis  273  between the first portion  248  and second portion  250  of the first electrode  244 . The “plane” may have a thickness perpendicular to the “plane” equivalent a longitudinal length of the spark gap  271 . A purge portion  272  of the ignition chamber  268  is formed at or above the ignition plane  270 . The purge passage  260  fluidly connects the purge portion  272  with the combustion chamber  16 . Alternatively, the purge passage  260  may also be connected with an external gas source or sink such as atmosphere, a suction line, or a compressed air line.  
         [0021]    In an alternative embodiment shown in FIG. 3, the end cap  356  is integral with the spark plug shell  340 . For this embodiment, the element numbering starts with a “3” instead of “2” to reflect alternative embodiments of similar elements. The end cap  356  includes a single jet passage  358  positioned below the second portion  350  of the first electrode. The end cap  356  may be hemispherical. The end cap  356  may be integral with the spark plug shell  340  or attached to the spark plug shell in a conventional manner such as press fitting, threading, or welding. The second electrode  346  is connected to the spark plug shell  340  to form a spark gap  371  with the second portion  350  of the first electrode  344 . The purge passage  360  has a first end  361  above a second end  363 . The first end  361  is adjacent the purge portion  372  and the second end  363  is adjacent the combustion chamber  16 . The first end  361  may also be at or above a bottom portion  313  of the head  12  where “bottom” means the portion adjacent the block  14 . As shown in this embodiment, multiple purge passages  360  may be used. Further, the purge passages  360  may be angled with respect to both the longitudinal axis and with respect to a radius of the spark plug shell  340 .  
       INDUSTRIAL APPLICABILITY  
       [0022]    As pressures rises in the combustion chamber  16 , a portion combustion gas may remain in the ignition chamber  268  if no purge passage  260  is provided. These residual gasses may contribute to pre-ignition of the ignition chamber  268  as well as problems starting a cold engine. In a cold engine, the residual gasses may contain vapor that condenses out as water droplets as the engine cools. Vapor may pose a problem with re-starting the engine.  
         [0023]    Using the purge passage  260  promotes exchange of gasses with the combustion chamber  16 . Movement of the piston  20  through its exhaust stroke causes combustion gasses to move through the jet passage  258  into the ignition chamber  268 . As pressures rises again in the ignition chamber  268  during a compression stroke, a fresh charge mixture passes through the purge portion  272  as residual gasses escape through the purge passage  260 . The fresh charge typically is cooler than the residual gasses during normal engine operation. The fresh charge mixture may also pass through the purge passage  260  during the induction stroke. The purge portion  272  in particular will have a gas composition and temperature similar to that of the rest of the ignition chamber  268  including lower temperatures.  
         [0024]    Using the purge passage in FIG. 3, the purge passage  360  additionally allows a larger volume of the purge portion  272  to be in contact with the cylinder head  12  to enhance heat transfer. Using multiple, angled purge passages  360  may enhance mixing of gasses within the purge portion  272  and further reduces likelihood of pre-ignition of the ignition chamber  272  by the residual gasses.  
         [0025]    Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosures, and the appended claims.