Abstract:
A spark plug comprising a housing, a ceramic insulator and a sleeve is provided. The housing has an inner cavity while the ceramic insulator encloses a central electrode. The ceramic insulator is disposed inside the inner cavity and maintain from the housing with a gap. The sleeve is provided enclosing an inner wall of the housing and corresponds to an opening of the inner cavity. The level of an edge surface of the housing corresponding to the opening of the inner cavity is disposed higher than the level of an edge surface of the central electrode, and the level of the center electrode is also higher than the level of the edge surface of the ceramic insulator.

Description:
[0001]    This application claims priority based on both Taiwanese patent applications No. 096215065 filed on Sep. 7, 2007 and No. 097209856 filed on Jun. 4, 2008. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a spark plug, and more particularly to a spark plug that can protect a discharge spark. 
         [0004]    2. Description of the Relative Art 
         [0005]    A motorcycle or gasoline vehicle&#39;s engine is equipped with spark plugs to ignite fire and generate power. Generally, when spark plugs form a high discharge voltage, the engine introduces air via an intake manifold to form a fuel-air mixture into a cylinder almost at the same time, and generates power by igniting fuel-air mixture by discharge spark. However, the forms of the spark plug are different according to engine&#39;s design. 
         [0006]      FIG. 1  shows a conventional spark plug  10 . As shown in  FIG. 1 , the spark plug  10  includes a housing  12 , a ceramic insulator  14 , and a central electrode  16 . One end of the housing  12  extends and forms a ground contacted electrode  18 . The ground contacted electrode  18  is perpendicular to the central electrode  16  and is apart from the central electrode  16  with a gap  24 . The gap  24  is where a high voltage discharge spark formed (not shown). Besides, the other end of the spark plug  10  covers by an insulator  20  for preventing a short circuit or electric leakage. The insulator  20  further connects to a connecting head  22 . The ceramic insulator  14  may enclose a sealing material such as aluminum oxide and a seal ring between the ceramic insulator  14  and the housing  12  in assembly such that the ceramic insulator  14  and the housing  12  may form an air-seal structure for preventing pressure from leaking out from the engine while assembles the housing  12 . 
         [0007]    Referring to  FIG. 2 , the conventional spark plug  10  is disposed on an engine  30 , and a discharge spark  26  forms between the central electrode  16  and the ground contacted electrode  18 . When fuel-air mixture  40  enter into a combustion chamber  32  and the piston  34  go up to Top Center Point, the air fuel mixture  40  ignites by the exposed discharge spark  26  in the combustion chamber  32  of the engine  30  directly, thereby drives a piston  34  of the engine  30  to generate power. However, when stepping on the gas pedal heavily to speed up suddenly or other circumstances, a large amount of high pressure fuel-air mixture  40  will enter into the combustion chamber  32  speedily and breach the discharge spark  26 . Therefore, the discharge spark  26  may snuff out and affect the ignited efficiency of the spark plug  10 , such that causes the moving motorcycle or vehicle cannot speed up smoothly. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an objective of the present invention to provide a spark plug that can enable a moving vehicle to speed up smoothly. 
         [0009]    It is another objective of the present invention to provide a spark plug with a long life span. 
         [0010]    It is still another objective of the present invention to provide a spark plug that can protect a discharge spark form. 
         [0011]    It is another objective of the present invention to provide a spark plug whose discharge spark is not affected by the fuel-air mixture. 
         [0012]    A spark plug of the present invention includes a housing, a ceramic insulator and a sleeve. The housing has an inner cavity while the ceramic insulator encloses a central electrode. The ceramic insulator is disposed in the inner cavity and maintain from the housing with a gap. The sleeve encloses an inner wall and corresponds to the opening of the inner cavity. The level of the housing corresponding to the edge surface of the opening of the inner cavity is higher than the level of the edge surface of the central electrode, and the level of the edge surface of the central electrode is also higher than the level of the edge surface of the ceramic insulator. 
         [0013]    In other words, the housing corresponding to the outer sidewall of the opening of the inner cavity protrudes out from the edge surface of the central electrode, and the edge surface of the central electrode also protrudes out from the edge surface of the ceramic insulator. From another point of view, the level of the edge surface of the central electrode is lower than the level of the edge surface of the housing corresponding to opening of the inner cavity, and the level of the edge surface of the ceramic insulator is also lower than the level of the edge surface of the central electrode. 
         [0014]    In the preferable embodiment, the housing further has a protrusion and corresponds to the opening of the inner cavity. The level of the protrusion is higher than the edge surface of the central electrode, and the inner diameter of the protrusion is smaller than the inner diameter of the inner cavity. An inclined surface is disposed outside the edge surface of the housing and has a top end surface. The protrusion has a plane connects to the top end surface, and the plane is parallel to a central axis of the central electrode. The sleeve has a bending portion in contacts with the top end surface for positioning on the inner wall of the protrusion. Moreover, the side of the housing is further machined process at least one through hole. The through hole is parallelly communicated with the gap from the outer sidewall of the housing, and the level of the through hole is lower than the edge surface of the ceramic insulator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates a perspective view of a spark plug of the prior art; 
           [0016]      FIG. 2  illustrates a perspective view of the spark plug disposed on an engine of the prior art; 
           [0017]      FIG. 3  illustrates a first embodiment view of the spark plug of the present invention; 
           [0018]      FIG. 4  illustrates a second embodiment view of the spark plug of the present invention; 
           [0019]      FIG. 5  illustrates a perspective view of the fuel-air mixture entering from the through hole of the spark plug of the present invention; 
           [0020]      FIG. 6  illustrates a perspective view of the spark plug occurring a discharge spark according to the present invention; 
           [0021]      FIG. 7  illustrates a perspective view of the sleeve assembled the spark plug of the present invention; 
           [0022]      FIG. 8   a  illustrates a first movement view of pressing the sleeve of the present invention; 
           [0023]      FIG. 8   b  illustrates a second movement view of pressing the sleeve of the present invention; 
           [0024]      FIG. 8   c  illustrates a perspective view of taking apart from a machine tool and further assembled the ceramic insulator of the present invention; and 
           [0025]      FIG. 9  illustrates an embodiment view of the spark plug disposed on the engine of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    The present invention provides a spark plug that can enable a smooth ignition process of an engine even when a large amount of fuel-air mixture is generated suddenly. In other words, when hardly stepping (Kick down) on the gas pedal (e.g. speeding up or climbing a slope), a discharge spark would not snuff out by of the breach of the large amount of fuel-air mixture and thereby the ignition process is smoothly without interruption. In the preferable embodiment, the spark plug can be applied to motorcycles, vehicles, internal combustion engines and agricultural car. The preferred embodiments of the present invention are illustrated hereunder with attached drawings. 
         [0027]    Referring to  FIG. 3 , a spark plug  100  of the present invention includes a housing  102 , a ceramic insulator  120 , and a sleeve  300 . The housing  102  is shaped a hollow shell and forms an inner cavity  100  thereof. The inner cavity  110  accommodates the ceramic insulator  120  and a central electrode  130  enclosed by the ceramic insulator  120 . In the present embodiment, the outer sidewall of the housing  102  has an inclined surface  104  and an outside screw  108 . The inclined surface  104  preferably intersects the horizontal with a 60-degrees angle. However, the angle may include between 45 degrees and 60 degrees by the inclined surface  104  and the horizontal, and the inclined surface  104  may be shaped cruciform or other shapes. The outside screw  108  connects with the inclined surface  104  for engaging with the engine (not shown). The central electrode  130  is preferably a straight stick; however, in other embodiments, the central electrode  130  may be shaped a cone at the top end or in other shapes. A gap forms  132  between the ceramic insulator  120  and the housing  102  and with a certain level. 
         [0028]    The housing  102  corresponding to the edge surface of the opening of the inner cavity  110  is preferably higher than the level of the edge surface of the central electrode  130 , and the level of the edge surface of the central electrode  130  is also higher than the level of the edge surface of the ceramic insulator  120 . In other words, the housing  102  corresponding to the outer sidewall  105  of the opening of the inner cavity  110  protrudes out from the edge surface of the central electrode  130 , and the edge surface of the central electrode  130  may also protrude out from the edge surface of the ceramic insulator  120 . In the present embodiment, the outer sidewall  105  of the housing  102  protrudes out from the edge surface of the central electrode  130  including 5 mm to 20 mm. From another point of view, the level of the edge surface of the central electrode  130  is lower than the level edge surface of the housing  102  corresponding to the opening of the inner cavity  110 , and the level of the edge surface of the ceramic insulator  120  may also lower than the level of the edge surface of the central electrode  130 . Therefore, when the spark plug  100  is electrically conducted, the discharge spark (not shown) may form inside the inner cavity  110 . In other words, the discharge spark is hided inside the housing of the spark plug  100 . 
         [0029]      FIG. 4  illustrates another embodiment of the present invention. In the present embodiment, the housing  102  includes at least one through hole  150 . However, in the embodiment shown in  FIG. 5 , the housing  102  may include a plurality of through holes  150 . The through hole  150  is parallelly communicated through the gap  132  from the outer sidewall  105  of the housing  102 , and the level of the through hole  150  is disposed lower than the level of the edge surface of the ceramic insulator  120 . However, in other embodiments, the level of the through hole  150  may also be disposed the same as the level of the edge surface of the ceramic insulator  120 . In the embodiment shown in  FIG. 4 , the diameter of the through hole  150  is preferably between 2 mm and 14 mm. 
         [0030]    Moreover, the inclined surface  104  of the housing  102  further connects to the top end surface  106 . The top end surface  106  is a plane parallel to the horizontal. The housing  102  further has a protrusion  160  corresponding to the inner cavity  110 . The level of the protrusion  160  is disposed higher than the edge surface of the central electrode  130 , and an inner diameter of the protrusion  160  is smaller than an inner diameter of the inner cavity  110 . In the present embodiment, the protrusion  160  further has a plane  162  and an inclined surface  164 . The plane  162  connects with the top end surface  106  and is preferably perpendicular to the top end surface  106 . The inclined surface  164  connects with the plane  162 . However, in other embodiments, the plane  162  may be a plane not perpendicular to the horizontal, and the inclined surface  164  may be parallel to the horizontal. One end of the sleeve  300  further has a bending portion  310  in contacts with the top end surface  106 , so as to position at the inner sidewall of the housing  102 . 
         [0031]    The mentioned-above of the sleeve  300  is preferably be a rivet, and the material of the sleeve  300  preferably includes nickel, nickel alloy, nickel copper alloy, titanium alloy, yttrium alloy, chromium alloy, platinum, or other conductive materials. 
         [0032]    Due to the point discharge phenomenon of electricity forms selectively an electric current at the position of the lowest resistance when the spark plug  100  is electrically conducted. However, in other circumstances, the electricity may form selectively a discharge spark along a shortest path. As  FIG. 5  shown, when the spark plug  100  conducts and form an electric circuit, the discharge spark  170  may form between an end of the sleeve  300  and the edge surface of the central electrode  130 , i.e. the bending portion  310  corresponding to a point between the plane  162  of the wall surface of the sleeve  300  and the edge surface of the central electrode  130  ( 170   a. ) However, in other embodiments, the discharge spark  170   a  may form between the sleeve  300  corresponding to any points of the inner wall surface of the plane  162  and the edge surface of the central electrode  130 . 
         [0033]    The discharge spark  170   b  may form along a point of the shortest path between the edge surface of the central electrode  130  and the sleeve  300 . In the embodiment of shown in  FIG. 5 , the discharge spark  170   b  preferably forms between the bending point of the sleeve  300  and the edge surface of the central electrode  130 . The mentioned-above of the bending point of the sleeve  300  is a point which connects corresponding to the surface  162  of the protrusion  160  and the inclined surface  164 . 
         [0034]    Furthermore, in the preferable embodiment, a plurality of through holes  150  are disposed on the housing  102 , and the level of the through hole  150  is lower than the level of the edge surface of the ceramic insulator  120 . The fuel-air mixture may enter from the opening of the inner cavity  110  or enter from the through hole  150  while a large of the fuel-air mixture diffuse all around of the spark plug  100 . When the fuel-air mixture  230  enter from the through hole  150 , the fuel-air mixture  230  may impact the sidewall of the ceramic insulator  120  and would not directly affects the discharge sparks  170   a,    170   b  which forms between the edge surface of the central electrode  130  and the inner sidewall of the sleeve  300  or between the edge surface of the central electrode  130  and the bending point of the sleeve  300 . Besides, the disposed of the through hole  150  may help the fuel-air mixture  230  entering into the inner cavity  110  and assists the spark plug  100  to ignite fire. The accumulation of greasy filth may overfill form the through hole  150  and would not affect the formed discharge spark  170 . 
         [0035]    When the fuel-air mixture  230  enter from the opening of the inner cavity  110 , the fuel-air mixture  230  may enter into the inner cavity  110  before impact the plane  104  indirectly, and then ignites fire with the formed discharge spark  170 , thus the fuel-air mixture  230  would not affect the discharge spark  170  directly. In addiction, the protrusion  160  of the housing  102  protrudes towards the inner cavity  110 , so as to increase the moveable length of the fuel-air mixture  230 . In other words, the disposed of the protrusion  160  can increase the protection of the discharge spark  170  and would not snuff out by the large amount of the fuel-air mixture  230 . 
         [0036]    As  FIG. 6  shown, an inclined continuous surface  180 , the discharge spark  170 , is preferably formed between the inner sidewall of the sleeve  300  and the edge surface of the central electrode  130 . The mentioned-above of the continuous surface  180  includes forming in the inner cavity  110  at any ranges for 360 degrees. In fact, the range of angles of the discharge spark  170  may depend on the different electricity, the material of the sleeve  300  or other facts. Therefore, in other embodiments, the discharge spark  170  formed on the continuous surface  180  may also be a portion, a segment or other incompleted discharge spark. 
         [0037]      FIG. 7  illustrates a perspective view of the sleeve assembling the spark plug of the present invention. The step of assemble methods of the sleeve  300  are, the sleeve  300  assembles upwards from bottom end of the inner cavity  110  of the housing  102  until engages with the protrusion  160  of the housing  102 . As  FIG. 8   a  and  FIG. 8   b  shown, the housing  102  may fabricate on a machine tool  600 , and utilizes a pressed device  500  to press a top end of the sleeve  300 , the top end of the sleeve  300  becomes a bending portion  310  so as to position at the inner sidewall of the housing  102 , shows in  FIG. 8   b.  As  FIG. 8   c  shown, after finished the pressing method, they can be assembled the ceramic insulator  120 , the central electrode  130  and other elements. 
         [0038]      FIG. 9  illustrates an embodiment view of the spark plug disposed on the engine of the present invention. The spark  100  engages with a cylinder of the engine  200  by uses the outside screw  108  of the housing  102 . When the fuel-air mixture  230  enters into the combustion chamber  210 , the inclined surface  104  will guide the fuel-air mixture  230  spread rapidly, and speedily contacts and ignites the formed discharge spark  170 . More particularly, when treads on the gas pedal hardly, the large amount of the high pressure fuel-air mixture  230  will enter into the combustion chamber  210  rapidly. Because the protection of the protrusion  160  of the housing  102 , the discharge spark  170  which hides and forms between the inner sidewall of the sleeve  300  and the central electrode  130  would not impact or snuffed out by the fuel-air mixture  230  directly. 
         [0039]    The fuel-air mixture  230  may indeed enter into the inner cavity  110  from the through hole  150  rapidly, but block by the ceramic insulator  120  to reduce the impaction of the large amount of the fuel-air mixture  230 . In other words, the spark  100  may still ignite fire smoothly and the engine  200  may keep on operating in this circumstance. 
         [0040]    Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.