Patent Publication Number: US-7712686-B2

Title: Fuel injection valve

Description:
CROSS REFERENCE TO THE RELATED APPLICATION 
   This application is based on and claims the benefit of priority of Japanese Patent Application No. 2004-265251 filed on Sep. 13, 2004, the disclosure of which is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   This invention relates to a fuel injection valve that injects a fuel into an internal-combustion engine. 
   BACKGROUND OF THE INVENTION 
   Conventional fuel injection valves are disclosed in Japanese Patent Documents. The conventional fuel injection valves disclosed therein actuate a valve member by an electromagnetic force between a fixed core and a movable core that slidably moves in an axially reciprocating motion. The electromagnetic force between the fixed core and the movable core can be increased by increasing a cross-sectional area of those cores (refer to a Japanese Patent Document JP-A-H11-500509, and a Japanese Patent Document JP-A-2002-528672). The increased cross-sectional area of the fixed core and the movable core receives an increased amount of magnetic flux. Therefore, the fixed core  34  and the movable core attract each other by an increased magnetic attractive force. 
   However, the increased cross-sectional area of the movable core leads to an increased mass. The increased mass of the movable core deteriorates responsiveness of the movable core when a current is supplied to actuate the movable core. As a result, an amount of injected fuel cannot be precisely controlled. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to provide a fuel injection valve that has high responsiveness in actuation to precisely deliver a desired amount of fuel by using an increased magnetic attractive force between the fixed core and the movable core. 
   The fuel injection valve of the present invention has a coil portion where the number of windings of winding wire increases toward the movable core side in the coil. The magnetic attractive force between the fixed core and the movable core relates to the amount of magnetic flux generated between the fixed core and the movable core. The increase in number of windings of the winding wire on the movable core yields the increase of magnetic flux between the fixed core and the movable core, thereby increases the magnetic attractive force applied therebetween. Further, the amount of the magnetic flux spilled in the fixed core of the coil decreases as the number of windings of the winding wire decreases at a distance from the movable core because of a radially dispersing distribution of the magnetic flux in the coil. That is, the amount of the magnetic flux between the fixed core and the movable core increases when the number of windings of the winding wire on the coil increases toward the movable core side. In this manner, the magnetic attractive force between the fixed core and the movable core can be increased without increasing the cross-sectional area of the movable core for increased reception of the magnetic flux. Therefore, improved preciseness of the amount of the injected fuel can be achieved based on the improvement of the responsiveness of the movable core that has the same amount of mass for increased reception of the magnetic flux. 
   The fuel injection valve of the present invention has the coil portion that is formed in a trapezoid shape or in a triangular shape in an axial cross section. In this manner, the axial cross section of the coil portion has a longer radius toward the movable core side. A cross-sectional area of the coil portion that is perpendicular to the axis of the coil portion also increases toward the movable core side. Therefore, the amount of the magnetic flux between the fixed core and the movable core is smoothly increased to totally yield the increased amount of the magnetic attractive force between those cores. 
   The fuel injection valve of the present invention has the coil portion that has an outer circumference being tilted against the axis of the coil portion. In this manner, an inner circumference of the bobbin can be made substantially parallel to the axis of the coil when the cross section of the coil has a trapezoid form or a triangular form. Therefore, the coil portion and the fixed core can be arranged in a close proximity. That is, the magnetic attractive force between the fixed core and the movable core will be increased in this manner. 
   The coil portion of the conventional fuel injection valve has a cylindrical shape. Therefore, a magnetic member that covers the coil portion has to be cylindrically shaped with both axial ends extending radially inward toward the axis of the coil portion. However, it is difficult to integrally mold the magnetic member of the above-described shape. That is, the process of integrally molding the above-described shape requires more steps. Thus, the magnetic member is formed by an upper part and a lower part in the axial direction for the ease of the molding process of each part. As a result, the increased number of parts of the coil portion creates inconvenience in manufacturing process. The fuel injection valve of the present invention has the coil portion that has the winding wire being increased in the number of windings toward the movable core side. Therefore, the coil portion has the outer circumferential surface being tilted against the axis of the coil. As a result, the coil portion approximately has a conically cylindrical shape. In this manner, a holder and a housing that cover the coil portion can be easily formed in molding, thereby being integrally molded to contribute to the decrease of the number of parts. 
   The fuel injection valve of the present invention has an integrally molded holder and housing having a window on its circumference. That is, the integrated holder and housing has an umbrella like shape having an opening on its circumference. Therefore, the integrated holder and housing can be easily placed on an outside of the coil portion. Thus, the number of parts can be decreased to have a simple structure. 
   The fuel injection valve of the present invention has the bobbin and the winding wire in the coil portion. The winding wire has an increased number of windings from one end toward the other end. Therefore, the coil portion of the fuel injection valve has a different number of windings of the winding wire in a different axial position. In this manner, the winding wire yields a greater magnetic field on an end having a greater number of windings of the winding wire when an electric current is supplied to the coil portion. The magnetic field of the other end that has a fewer number of windings spills the smaller amount of the magnetic flux. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which: 
       FIG. 1  is a cross-section of an injector in a first embodiment of the present invention; 
       FIG. 2  is a schematic perspective view of a coil portion of the injector in the first embodiment; 
       FIG. 3  is a diagram of a relationship between a voltage applied to the coil portion and a magnetic attractive force; 
       FIG. 4  is a modification of the injector in the first embodiment of the present invention; 
       FIG. 5  is a schematic perspective view of a modification of the coil portion of the injector in the first embodiment of the present invention; 
       FIG. 6  is a cross-section of the injector in a second embodiment of the present invention; and 
       FIG. 7  is a schematic perspective view of a magnetic member of the injector in the second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described with reference to the drawings. 
   First Embodiment 
   A fuel injection valve in a first embodiment of the present invention is shown in  FIG. 1  (The fuel injection valve is called as ‘Injector’ hereinafter). The injector  10  in the first embodiment injects, for example, a fuel into an intake air provided to a combustion chamber of a gasoline engine. The injector  10  may be used in a direct-gasoline injection engine that directly injects gasoline into the combustion chamber, or may be used in a diesel engine. 
   A reception pipe  11  of the injector  10  has a thin-walled cylindrical shape. The reception pipe includes a first magnetic portion  12 , a non-magnetic portion  13  and a second magnetic portion  14 . The non-magnetic portion  13  prevents magnetic short-circuit between the first magnetic portion  12  and the second magnetic portion  14 . The reception pipe  11  has a fuel port  15  on one end. The fuel port  15  receives a fuel from a fuel pump not shown in the figure. The fuel provided to the fuel port  15  flows into the reception pipe  11  through a fuel filter  16 . The fuel filter  16  is disposed on the end of the reception pipe  11  to filter foreign matter in the fuel. 
   A valve body  20  is disposed on an inner circumference of the first magnetic portion  12  that is opposite to the fuel port  15  of the reception pipe  11 . The valve body  20  is formed in an approximately cylindrical shape, and is fixed on an inner wall of the first magnetic portion  12 . The valve body  20  has a valve seat  21  on a conical inner wall whose radius decreases toward a pointed end. The valve body  20  has a nozzle plate  22  on an end that is opposite to the reception pipe  11 . The nozzle plate  22  has a nozzle hole  23  that connects a face on the valve body  20  side of the nozzle plate  22  and a face on the opposite side of the nozzle plate  22 . 
   A needle  24  as a part of a valve member is accommodated in the first magnetic portion  12  and the valve body  20 . The needle  24  is disposed substantially coaxially with the reception pipe  11  and the valve body  20 . The needle  24  has a seal portion  25  in a proximity of an end on the nozzle plate  22  side. The seal portion  25  abuts on a valve seat  21  formed on the valve body  20 . The needle  24  and the valve body  20  define a fuel vessel  26 . The seal portion  25  of the needle  24  takes off from the valve seat  21  for the fuel vessel  26  to communicate with the nozzle hole  23 . The needle  24  in the present embodiment is formed in a cylindrical shape. The needle  24  includes a fuel vessel  27  formed therein. The needle  24  also includes a fuel hole  28  and  29  for letting the fuel pass between the fuel vessel  27  and the fuel vessel  26 . The needle  24  may be formed in a cylindrical shape having a void formed therein or having no void. 
   The injector  10  includes an actuator  30  for actuating the needle 24 . The actuator  30  electro-magnetically actuates the needle  24 . The actuator  30  includes a coil portion  40 , a housing  31 , a holder  32 , a fixed core  33  and a movable core  34 . The housing  31  and the holder  32  are made from a magnetic material. The housing  31  covers an outer surface of the coil portion  40 . The holder  32  is disposed outside of the reception pipe  11 , and supports the coil portion  40  on the nozzle hole  23  side. The housing  31  and the holder  32  are made from a magnetic material, and are magnetically connected. The coil portion  40 , the housing  31 , the holder  32  and the reception pipe  11  are covered by a resin mold  35  on their outer surface. The coil portion  40  is electrically connected to a terminal  38  on a connector  37  through wiring  36 . 
   The fixed core  33  is fixed on an inner side of the coil portion  40  having the reception pipe  11  bound therebetween. The fixed core  33  is formed in an approximately cylindrical shape by using a material such as an iron or the like. The fixed core  33  is disposed with a gap toward the movable core  34 . The size of the gap between the fixed core  33  and the movable core  34  corresponds to a lift of the needle  24 . 
   The movable core  34  is accommodated in an inner side of the reception pipe  11 . The movable core  34  is slidable in an axial direction of the reception pipe  11 . The movable core  34  is formed in an approximately cylindrical shape by using a material such as an iron or the like. The needle  24  is fixed on an inner side of the movable core  34  by an end that is opposite to the seal portion  25 . In this manner, the needle  24  and the movable core  34  integrally move in the axial direction in a reciprocating motion. 
   The movable core  34  abuts on a spring  17  that serves as an elastic member. The spring  17  is in contact with the movable core  34  on one end, and is in contact with an adjusting pipe  18  on the other end. The adjusting pipe  18  is fixed on an inner side of the fixed core  33 . The spring  17  has an extending force in an axial direction. Therefore, the spring  17  having a fixed end presses the movable core  34  and the needle  24  in a mass toward the valve seat  21  on the other end. Lord of the spring  17  is controlled by adjustably press-fitting the adjusting pipe  18  into the fixed core  33 . The movable core  34  and the needle  24  are pressed in a mass toward the valve seat  21  when no electric current is supplied to the coil portion  40 . In this manner, the seal portion  25  abuts on the valve seat  21 . 
   Next, the coil portion  40  is described in detail. 
   The coil portion  40  includes a bobbin  41  and a winding wire  42 . The bobbin  41  is formed in a cylindrical shape by using a resin. The bobbin  41  includes a cylinder portion  43  and a support portion  44  as shown in  FIG. 4 . The cylinder portion  43  has a cylinder shape, and has a winding wire  42  on an outer surface. The support portion  44  rises in an axial direction from the cylinder portion  43 . The support portion  44  holds wiring  45  as shown in  FIG. 1 . The wiring  45  is electrically connected to the winding wire  42  on one end, and is connected to the wiring  36  on the other end. The wiring  42  is made of a publicly known conductive material, and is wound on an outer surface of the cylinder portion  43 . The coil portion  40  is disposed on an outer side of the fixed core  33  having the reception pipe  11  bound therebetween. The cylinder portion  43  of the bobbin  41  receives the reception pipe  11 . Gap between the winding wire  42 , the housing  31  and the holder  32  is filled with a resin  46 . The resin  46  insulates the winding wire  42  from the housing  31  and the holder  32 . 
   The winding number of the winding wire  42  wound on the bobbin  41  changes from one end to the other end in an axial direction. The winding wire  42  in the present embodiment has a smaller winding number of the winding wire  42  on one end of the axis. That is, the coil portion  40  assembled to the injector  10  has a greater winding number of the winding wire  42  on the movable core  34  side. Therefore, the coil portion  40  has an approximately conically cylindrical shape, or has an approximately truncated conical shape as shown in  FIG. 2 . The winding number of the winding wire  42  increases stepwise in an axial direction as shown in  FIG. 1 . Thus, the coil portion  40  has an axial cross section of an approximately trapezoid shape. 
   The coil portion  40  is substantially in a conical shape. That is, outline of the winding wire  42  is tilted against an axis of the coil portion  40 . The tilted outer side of the winding wire  42  makes it possible to have the cylinder portion  43  of the bobbin  41  to be parallel with the axis of the coil portion  40 . The cylinder portion  43  can be put in a proximity of the outer surface of the reception pipe  11 . In this manner, the coil portion  40  and the fixed core  33  sits close to each other. Thus, spill of magnetic flux generated therein is decreased and most of the magnetic flux generated therein penetrates the fixed core  33  smoothly. 
   The increased number of windings of the winding wire  42  towards the movable core  34  generates a greater electromagnetic attractive force between the fixed core  33  and the movable core  34  when the current is supplied to the coil portion  40 . The magnetic attractive force between the fixed core  33  and the movable core  34  is related to an amount of the magnetic flux between the two cores  33  and  34 . The amount of the magnetic flux increases when the number of windings of the winding wire  42  increases. Therefore, the magnetic flux between the fixed core  33  and the movable core  34  can be increased by increasing the number of windings of the winding wire  42  on the movable core  34  side. The magnetic attractive force between the fixed core  33  and the movable core  34  can be increased in this manner. 
   The magnetic flux of the coil portion  40  flows radially outwardly. Therefore, an even distribution of the winding wire  42  in the axial direction creates an even reception of the magnetic flux that flows from the coil portion  40  to the fixed core  33 . The magnetic flux received by the fixed core  33  in a remote position from the movable core  34  does not contribute much to the magnetic attractive force between fixed core  33  and the movable core  34 . As a result, the even distribution of the winding wire  42  in the axial direction makes the amount of the spill of the magnetic flux more substantially to the contribution to the magnetic attractive force in the remote position of from the movable core  34 . Therefore, decrease of the winding number of the winding wire  42  in the remote position from the movable core  34  create less amount of the spill of the magnetic flux to the fixed core  33 . That is, the number of windings of the winding wire  42  can be increased to have a relative increase of the amount of the magnetic flux between the fixed core  33  and the movable core  34 . 
   Relationship between the number of windings of the winding wire  42  and the magnetic attractive force between the fixed core  33  and the movable core  34  is explained with reference to  FIG. 3 . A comparative example 1 (broken line) is yielded from a coil portion that has an even distribution of the winding wire in the axial direction. A comparative example 2 (dashed line) is yielded from a coil portion that has an increased number of windings on a far side from the movable core  34 , which is contrary to the present embodiment of the invention. A total number of windings of the winding wire is the same in all of the present invention, the comparative example 1 and the comparative example 2. 
   The coil portion  40  in the present invention in  FIG. 3  generates a greater magnetic attractive force than the comparative example 1 or the comparative example 2. Further, the magnetic attractive force in the comparative example 1 is greater than that of the comparative example 2. The windings of the winding wire  42  on the movable core  34  side is greatest in number in the present embodiment, and smallest in number in the comparative example 2, with the comparative example 1 in between. Therefore, the magnetic attractive force becomes stronger when the number of windings on the movable core  34  side is greater. 
   Operation of the injector  10  described above is explained. 
   The fixed core  33  and the movable core  34  do not magnetically attract each other when an electric current is not supplied to the coil portion  40 . Therefore, the movable core  34  moves away from the fixed core  33  by a force applied by the spring  17 . That is, the movable core  34  and the needle  24  in a mass move away from the fixed core  33 . Therefore, the seal portion  25  of the needle  24  is seated on the valve seat  21 . In this manner, injection of the fuel from the nozzle hole  23  is stopped. 
   The electric current supplied to the coil portion  40  generates the magnetic field to create the magnetic flux in the housing  31 , the second magnetic portion  14 , the fixed core  33 , the movable core  34 , the first magnetic portion  12  and the holder  32 . Therefore, the magnetic attractive force is generated between the fixed core  33  and the movable core  34  being separated by a force applied by the spring  17  when the electric current is supplied to the coil portion  40 . The movable core  34  and the needle  24  in a mass take off from the valve seat  21  toward the fixed core  33  when the magnetic attractive force conquers the force from the spring  17 . That is, the seal portion  25  of the needle  24  takes off from the valve seat  21 . The movable core  34  and the needle  24  integrally move up until the movable core  34  abut on the fixed core  33  in  FIG. 1 . 
   The fuel provided to the fuel port  15  flows into the injector  10  through the fuel filter  16 , the inner side of the reception pipe  11 , the inner side of the adjusting pipe  18 , the inner side of the fixed core  33 , the inner side of the movable core  34 , the fuel vessel  27  on the inner side of the needle  24 , the fuel hole  28  and  29  toward the fuel vessel  26 . The fuel in the fuel vessel  26  further flows toward the nozzle hole  23  from the gap between the needle  24  and the valve body  20  taking off from the valve seat  21 . In this manner, the fuel is injected from the nozzle hole  23 . 
   The magnetic attractive force between the fixed core  33  and the movable core  34  disappears when the electric current to the coil portion  40  is interrupted. Then, the movable core  34  and the needle  24  in a mass move in a direction that is opposite to the fixed core  33  by the force applied by the spring  17 . Therefore, the seal portion  25  abuts on the valve seat  21 , and the flow of the fuel between the fuel vessel  26  and the nozzle hole  23  is stopped. As a result, injection of the fuel is stopped. 
   The coil portion  40  in the first embodiment has the greater number of windings of the winding wire  42  on the movable core  34  side. Therefore, the magnetic field generated therefrom is greater on the movable core  34  side. In this manner, the magnetic attractive force between the fixed core  33  and the movable core  34  increases. Therefore, the magnetic attractive force between the fixed core  33  and the movable core  34  can be increased without increasing a cross sectional area or a volume of the movable core  34 . That is, the weight of the movable core  34  does not increase. The movable core  34  is made lighter in this manner, thereby the movable core  34  and the needle  25  in a mass has an improved responsiveness. Further, the improved responsiveness of the movable core  34  and the needle  24  in a mass contributes to a precise control of an amount of the injected fuel by promptly opening and closing the gap between the fuel vessel  26  and the nozzle hole  23 . 
   Modification 
   Modification of the first embodiment is shown in  FIGS. 4 and 5 . 
   The number of windings of the winding wire  42  gradually changes in coil portion  40  in an axial direction. An axial cross section of the coil portion  40  has a triangular shape in a part that bears the winding wire  42 . In this manner, the coil portion  40  is formed in a conical outer shape. 
   Second Embodiment 
   The injector  10  in a second embodiment of the present invention is shown in  FIG. 6 . Like parts have like numbers as used in the first embodiment, and descriptions of the like parts are omitted. 
   The coil portion  40  has a magnetic member  60  on an outer surface. The magnetic member  60  is made of a magnetic material. The magnetic member  60  has two ends, that is, one end  61  in an axial direction that is in contact with the first magnetic portion  12  of the reception pipe  11 , and the other end  62  that is in contact with the second magnetic portion  14 . In this manner, the magnetic member  60  is magnetically connected to the first magnetic portion  12  and the second magnetic portion  14  of the reception pipe  11 . That is, the magnetic member  60  includes the housing  31  and the holder  32  in the first embodiment in an integrated form. Further, the magnetic member  60  accommodates the coil portion  40  in the body. The magnetic member  60  has an opening in a circumferential direction as shown in  FIG. 7 . In this manner, the magnetic member  60  partially covers the coil portion  40  in the circumferential direction. 
   The magnetic member  60  is formed in a shape that fits an outer circumference of the coil portion  40 . Therefore, an inner radius and an outer radius of the magnetic member  60  at an end  61  on the first magnetic portion  12  side are greater than the inner radius and the outer radius at an end  62  on the second magnetic portion  14  side. As a result, the magnetic member  60  takes a conically cylindrical shape having an opening in a circumferential direction, that is, an umbrella like shape with an opening in the circumferential direction. The coil portion  40  is accommodated in a cylindrical magnetic member  60 . 
   The coil portion  40  has a greater number of windings of the winding wire  42  on the movable core  34  side as in the first embodiment. Therefore, the coil portion  40  has a conical shape having a tilted outer side against the axis. The magnetic member  60  can be formed in a conically cylindrical shape with the coil portion  40  formed in a conical shape. The magnetic member  60  has a conically cylindrical shape for the ease of molding. 
   The magnetic member  60  must be formed in a cylindrical shape when the coil portion  40  is formed in a cylindrical shape. However, the magnetic member  60  formed in the cylindrical shape must have a sector form extending inward on both ends in an axial direction of the cylindrical shape. That is, the magnetic member  60  in the cylindrical shape takes a complicated form, and the cylindrical shape is difficult to be formed in an integral molding. Therefore, the magnetic member in the conventional injector is divided into two parts, that is, the housing and the holder in an upper axial direction and a lower axial direction. 
   However, the coil portion  40  in the present embodiment is formed in a conical shape. Therefore, the magnetic member  60  is formed in a conically cylindrical shape with an opening in the circumferential direction. That is, the magnetic member  60  can be integrally formed without a seam. 
   The magnetic member  60  that covers the coil portion  40  in the second embodiment is integrally formed without a seam in the axial direction. Therefore, structure of the injector  10  is simplified, and the number of parts in the injector  10  is decreased. 
   Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. 
   For example, the nozzle hole  23  may be disposed directly on the valve body  20 , instead of the nozzle hole  23  formed in the nozzle hole plate  22  at an end of the valve body  20  in the above-described embodiments. 
   Further, the winding wire  42  has an even thickness in the above-described embodiments. Therefore, the conical shape is formed by increasing the number of windings on the movable core  34  side in the coil portion  40 . However, the thickness of the winding wire  42  may be made thinner toward the movable core  34  side to form a substantially cylindrical shape of the coil portion  40  having an increased number of windings of the winding wire  42  on the movable core  34  side. 
   Further, the needle is used as the valve member in the above-described embodiments. However, the valve member may be formed in an arbitrary form such as a ball valve or the like. 
   Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.