Patent Publication Number: US-7710231-B2

Title: Ignition coil

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application No. 2007-200850 filed on Aug. 1, 2007, the contents of which are incorporated herein by reference in its entirety. 
   FIELD OF THE INVENTION 
   The present invention relates to an ignition coil that can be used for generating sparks between a pair of electrodes in a spark plug for an internal combustion engine, for example. 
   BACKGROUND OF THE INVENTION 
   In an ignition coil used for an internal combustion engine, a primary coil is wound on a resinous primary spool and a secondary coil is wound on a resinous secondary spool. The primary and secondary coils are accommodated in a resinous coil case to form the ignition coil. The primary coil can be formed in a cylindrical shape using a self-fusing copper wire without the primary spool. 
   For example, JP-A-8-55742 discloses a coil case of an ignition coil for an internal combustion engine. The coil case is constructed by integrally forming a container for accommodating therein a transformer for generating a high voltage, a cylindrical primary bobbin for holding a primary winding of the transformer, and a connector for connection of an electric signal with an external device for controlling the high voltage. The primary winding using the self-fusing wire is mounted on the primary bobbin. 
   However, in the conventional ignition coil as disclosed in JP-A-8-55742, a secondary spool (secondary bobbin) and the connector for connecting the ignition coil to an external electronic control unit (ECU) or the like are separately molded and assembled. This arrangement is not sufficient to decrease the number of components of the ignition coil. When the secondary spool is assembled to the connector, measures are required in order to stably connect a low-voltage side winding end of the secondary coil wound on the secondary spool to a terminal (or a fitting member) for connection with a conducting pin of the connector. 
   SUMMARY OF THE INVENTION 
   The invention has been made in view of the forgoing problems, and it is an object of the invention to provide an ignition coil that can simplify the structure of a wire connection portion of a secondary coil, thereby effectively decreasing the number of components of the ignition coil. 
   According to an aspect of the present invention, an ignition coil includes a coil body, a plug connection portion and a connector. The coil body includes a center core made of a soft magnetic material, a primary coil and a secondary coil, which are accommodated in a coil case. The plug connection portion is provided to protrude from the coil body, and is adapted to bring a high-voltage side winding end of the secondary coil into conduction with a spark plug. The connector is for electrically connecting the coil body to an outside of the coil case. In the ignition coil, the primary coil is arranged on an inner peripheral side of the secondary coil, and the center core is arranged on an inner peripheral side of the primary coil. The secondary coil includes a secondary electric wire having thereon an insulating film, wound around an outer periphery of a resinous secondary spool. In addition, the connector is formed integrally with an end of the secondary spool in an axial direction. 
   Accordingly, it is possible to eliminate a step of assembling the secondary spool and the connector. Thus, a terminal (a fitting member) for connecting a low-voltage side winding end of the secondary coil wound on the secondary spool to a conducting pin in the connector can be provided in an integrated molded member including the secondary spool and the connector, for example. In this case, in the secondary spool and the connector, there are no need to separately provide the terminals for connecting the low-voltage side winding end of the secondary coil to the conducting pin of the connector. 
   As a result, the ignition coil can simplify the structure of a wire connection portion of the secondary coil, thereby effectively decreasing the number of components in the ignition coil. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In which: 
       FIG. 1  is a schematic sectional view showing an entire structure of an ignition coil arranged in a plug hole according to an embodiment of the invention; 
       FIG. 2  is a schematic sectional view showing the ignition coil of the embodiment before being arranged in the plug hole; 
       FIG. 3  is another schematic sectional view showing the ignition coil of the embodiment before being arranged in the plug hole; 
       FIG. 4  is a schematic sectional view showing a secondary spool before being assembled to the ignition coil in the embodiment; 
       FIG. 5  is a schematic diagram showing a state in which terminals provided in electric connection portions of primary and secondary coils, conducting pins, and the like are formed in the embodiment; and 
       FIG. 6  is a schematic diagram showing a circuit configuration of the ignition coil in the embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   According to a preferred embodiment of the present invention, an ignition coil ( 1 ) includes a coil body ( 11 ), a plug connection portion ( 12 ) and a connector ( 31 ). The coil body ( 11 ) includes a center core ( 23 ) made of a soft magnetic material, a primary coil ( 21 ) and a secondary coil ( 22 ), which are accommodated in a coil case ( 4 ). The plug connection portion ( 12 ) is provided to protrude from the coil body ( 11 ), and is adapted to bring a high-voltage side winding end of the secondary coil ( 22 ) into conduction with a spark plug ( 7 ). The connector ( 31 ) is for electrically connecting the coil body ( 11 ) and the plug connection portion ( 12 ) to an outside of the coil case ( 4 ). In the ignition coil ( 1 ), the primary coil ( 21 ) is arranged on an inner peripheral side of the secondary coil ( 22 ), and the center core ( 23 ) is arranged on an inner peripheral side of the primary coil ( 21 ). The secondary coil ( 22 ) includes a secondary electric wire having thereon an insulating film, wound around an outer periphery of a resinous secondary spool ( 3 ). In addition, the connector ( 31 ) is formed integrally with an end of the secondary spool ( 3 ) in an axial direction (L). Accordingly, it is possible to eliminate the step of assembling the secondary spool ( 3 ) and the connector ( 31 ). 
   Preferably, the ignition coil ( 1 ) includes an igniter arrangement portion ( 32 ) for arranging an igniter ( 321 ) including a switching control circuit for energization and non-energization to the primary coil ( 21 ). In this case, the igniter arrangement portion ( 32 ) is formed integrally with the secondary spool ( 3 ), and the connector ( 31 ) is formed integrally with the igniter arrangement portion ( 32 ) and the secondary spool ( 3 ) while protruding from the igniter arrangement portion ( 32 ). Accordingly, the ignition coil ( 1 ) can simplify the structure of a wire connection portion of the secondary coil ( 22 ), thereby effectively decreasing the number of components in the ignition coil ( 1 ). 
   More preferably the ignition coil ( 1 ) includes conducting members ( 34 ,  35 ) insert-molded into the igniter arrangement portion ( 32 ) and the connector ( 31 ). For example, the conducting members ( 34 ,  35 ) are adapted to bring a positive side winding end and a negative side winding end of the primary coil ( 21 ) and a low-voltage side winding end of the secondary coil ( 22 ) into conduction with conducting pins ( 311 ,  322 ) of the igniter ( 321 ). In this case, the ignition coil ( 1 ) can simplify the structure of the wire connection portion of the primary coil ( 21 ), the secondary coil ( 22 ) and the igniter ( 321 ), by using the conducting members ( 34 ,  35 ) insert-molded into the igniter arrangement portion ( 32 ) and the connector ( 31 ). 
   For example, the ignition coil ( 1 ) further includes an outer peripheral core ( 24 ) made of a soft magnetic material and arranged on an outer peripheral side of the secondary coil ( 22 ), and an intermediate core ( 25 ) made of a soft magnetic material and arranged between the outer peripheral core ( 24 ) and an axial end of the center core ( 23 ). In this case, the intermediate core ( 25 ) is arranged in a core arrangement concave portion ( 323 ) that is provided between the axial end of the secondary spool ( 3 ) and the igniter arrangement portion ( 32 ). In this case, an electromagnetic circuit constructed of the center core ( 23 ), the outer peripheral core ( 24 ) and the intermediate core ( 25 ) can be formed by effectively using a space in the coil case ( 4 ). 
   The plug connection portion ( 12 ) can be arranged perpendicularly to the axial direction of the coil body ( 11 ) to protrude from an intermediate position in the axial direction of the coil body ( 11 ). In this case, the outer peripheral core ( 24 ) has a C-like sectional shape with a cutout portion ( 241 ) arranged on a side of the plug connection portion ( 12 ). Furthermore, the secondary spool ( 3 ) can be provided to have on the side of the cutout portion ( 241 ), a low-voltage side terminal ( 52 ) provided on one end side in the axial direction (L) and electrically connected to a low-voltage side winding end of the secondary coil ( 22 ), and a high-voltage side terminal ( 51 ) provided on the other end side in the axial direction (L) and electrically connected to a high-voltage side winding end ( 221 ) of the secondary coil ( 22 ). 
   Furthermore, the low-voltage side terminal ( 52 ) can be formed using a diode terminal connected to the secondary coil ( 22 ). In this case, because the diode terminal connected to the secondary coil ( 22 ) is used, it is unnecessary to additionally provide a low-voltage side terminal. 
   Preferably, the primary coil ( 21 ) includes a primary electric wire wound in a cylindrical shape and fusion-bonded by a fusing agent, and is directly arranged on an outer peripheral side of the center core ( 23 ). Generally, the coil case can be made of resin. 
   In the above ignition coil ( 1 ), the igniter arrangement portion ( 32 ), the secondary spool ( 3 ) and the connector ( 31 ) can be molded integrally by using resin, and the connector ( 31 ) can protrude from the igniter arrangement portion ( 32 ) in a direction approximately parallel with the axial direction (L). 
   Typical Example of Embodiment 
   Now, a typical example of an ignition coil according to an embodiment of the invention will be described below with reference to the accompanying drawings. 
   As shown in  FIG. 1 , an ignition coil  1  of this embodiment includes a coil body  11  for accommodating a primary coil  21  and a secondary coil  22  stacked on the respective inner and outer peripheral sides in a resinous coil case  4 . The ignition coil  1  also includes a plug connection portion  12  extending in a direction approximately perpendicular to an axial direction L of the coil body  11  and adapted to bring a high-voltage side winding end  221  of the secondary coil  22  into conduction with a spark plug  7 . In the ignition coil  1 , the plug connection portion  12  is arranged and inserted into a plug hole  83  provided in a cylinder head  81  and a cylinder head cover  82  of the engine, and the coil body  11  is transversely arranged near an opening of the plug hole  83  in the cylinder head cover  82 . 
   As shown in  FIGS. 2 and 3 , the primary coil  21  is arranged on the inner peripheral side of the secondary coil  22 . A center core  23  made of a soft magnetic material is arranged on the inner peripheral side of the primary coil  21 . The plug connection portion  12  is provided to protrude from an intermediate position in the axial direction L of the coil body  11 . In this example shown in  FIG. 1 , the plug connection portion  12  is located to protrude substantially from the center position of the coil case  4  in the axial direction L. 
   The secondary coil  22  is constructed by winding a secondary electric wire having an insulating film, around the outer periphery of a resinous secondary spool  3 . A connector  31  for electrically connecting the ignition coil  1  to an external electronic control unit (ECU) or the like is integrally formed with one end  301  of the secondary spool  3  in the axial direction L, as shown in  FIGS. 2 and 4 . 
     FIG. 1  shows an entire structure of the ignition coil  1  according to this embodiment.  FIGS. 2 and 3  show the ignition coil  1  before assembly of a spring  54  and a plug cap  55  as described later, and before being arranged in the plug hole  83 . 
   The ignition coil  1  of this embodiment will be described below in detail with reference to  FIGS. 1 to 6 . 
   As shown in  FIGS. 1 to 3 , the plug connection portion  12  in the ignition coil  1  of this embodiment includes a mounting base  45  formed to protrude from the outer periphery of the coil case  4 , a conducting terminal  53  provided in the mounting base  45 , a rubber plug cap  55  mounted onto the mounting base  45 , and the coil spring  54  arranged in the plug cap  55 . 
   The spark plug  7  is screwed into a bottom portion of the plug hole  83  of the cylinder head  81 , and the plug cap  55  of the ignition coil  1  is mounted to an insulator  71  of the spark plug  7 , so that the lower end of the coil spring  54  is brought into conduction with a terminal  72  positioned at the tip of the insulator  71  of the spark plug  7 . At this time, the high-voltage side winding end  221  of the secondary coil  22  is brought into conduction with the end of the spark plug  7  via a high voltage terminal  51 , the conducting terminal  53 , and the coil spring  54 . 
   As shown in  FIGS. 2 and 3 , an outer peripheral core  24  made of a soft magnetic material is arranged on the outer peripheral side of the secondary coil  22  in the coil body  11  of the ignition coil  1  of this embodiment. Intermediate cores  25  made of a soft magnetic material are arranged between the outer peripheral core  24  and the two ends of the center core  23  in the axial direction L. The outer peripheral core  24  has a C-like sectional shape with a cutout portion  241  arranged on the side of the plug connection portion  12 . 
   The center core  23  is formed to have a substantially circular sectional shape by laminating a plurality of plate-like electromagnetic steel plates (e.g., silicon steel plates or the like) in the radial direction R. As shown in  FIG. 2 , the radial direction R is a direction perpendicular to the axial direction L. The outer peripheral core  24  is constructed of a lamination of the electromagnetic steel plates (e.g., silicon steel plates or the like) in the radial direction R, each having a C-like sectional shape along the shape of the inner peripheral surface of the coil case  4 . The outer peripheral core  24  has the cutout portion  241  formed over the entire length thereof in the axial direction L. That is, as shown in  FIG. 3 , the cutout portion  241  is an opening formed in the outer peripheral core  24 . The cutout portion  241  is open in a direction facing the plug connection portion  12 . The outer peripheral core  24  is arranged on the inner peripheral surface of the coil case  4 . 
   The primary core  21  of this embodiment is constructed of a primary electric wire, which is a self-fusing wire, wound in a cylindrical shape without using the resinous primary spool and fusion-bonded by a fusing agent of the self-fusing wire. The primary core  21  is directly arranged on the outer peripheral side of the center core  23 . The primary electric wire is wound on a stick-like jig in a cylindrical shape, and then energized to be heated. Thus, the primary core is fusion-bonded by the fusing agent on the surface thereof to be molded in a cylindrical shape, so that the primary coil  21  can be formed by being removed from the jig. 
   As shown in  FIG. 2 , the secondary spool  3  with the secondary coil  22  wound thereon has flanges  303  and  304  located on both ends thereof in the axial direction L and protruding outward in the radial direction R. The secondary electric wire is wound between the flanges  303  and  304 . The secondary electric wire has a diameter smaller than that of the primary electric wire, and the number of winding of the secondary wire is larger than that of the primary electric wire. 
   As shown in  FIGS. 2 and 4 , an igniter arrangement portion  32  is integrally formed with the one end  301  of the secondary spool  3  in the axial direction L, in this embodiment. The igniter arrangement portion  32  is adapted to arrange an igniter  321  including a switching control circuit for energization and non-energization to the primary coil  21 . The connector  31  is integrally formed with the igniter arrangement portion  32  and the secondary spool  3 , while protruding from the igniter arrangement portion  32  in the axial direction L. A plurality of conducting pins  311  are insert-molded into the connector  31 . 
   A core arrangement concave portion  323  for arranging one intermediate core  25  is formed between the secondary spool  3  and the igniter arrangement portion  32 . The connector  31  is formed to protrude from the igniter arrangement portion  32 , and has the conducting pins  311  directed toward the axial direction L. 
     FIG. 4  shows the secondary spool  3  before being assembled to the ignition coil  1 . 
   As shown in  FIG. 2 , the coil case  4  has a bottom  42  on one end (e.g., right end in  FIG. 2 ) of a cylindrical outer peripheral portion  41  in the axial direction L, and an opening  43  at the other end thereof. At the inner surface of the bottom  42  of the coil case  4 , the other intermediate core  25  is arranged. The coil case  4  has a protruding outer peripheral portion  44  protruding from a part of the outer peripheral portion  41  outward the plug connection portion  12  in the radial direction R. The mounting base  45  is formed to protrude from the protruding outer peripheral portion  44 , in the plug connection portion  12 . 
   The connector  31  is arranged to protrude from the opening  43  of the coil case  4  in the axial direction L. 
   The secondary spool  3  has on the plug connection portion  12  side (i.e., on the cutout portion  241  side of the outer peripheral core  24 ), a low-voltage side terminal  52  which is electrically connected to a low-voltage side winding end  222  of the secondary coil  22 , and the high-voltage side terminal  51  which is electrically connected to the high-voltage side winding end  221  of the secondary coil  22 . 
   The secondary coil  22  of this embodiment is formed by wiring the secondary electric wire toward the other end of the secondary spool  3  in the axial direction L in a diagonally wound state where a reduced winding part and an enlarged winding part are superimposed on each other In the reduced winding part, the secondary electric wire is wound with a winding diameter decreasing from one end side to the other end side of the secondary spool  3  in the axial direction L. In the enlarged winding part, the secondary electric wire is wound with a winding diameter increasing from the other end side to the one end side of the secondary spool  3  in the axial direction L. 
   As shown in  FIG. 2 , the high-voltage side terminal  51  of this embodiment is formed to extend from the other flange  304  of the secondary spool  3  toward an intermediate position of the coil case  4 . That is, the high-voltage side terminal  51  extends from the other flange  304  to the conducting terminal  53  that is located in the mounting base  45 . 
   In the mounting base  45 , the conducting terminal  53  is provided for bringing the high-voltage side terminal  51  into conduction with the coil spring  54 . 
     FIG. 6  schematically shows a circuit configuration of the ignition coil  1  of this embodiment. A positive side winding end  211  of the primary coil  21  is connected to a battery power source VB, and a negative side winding end  212  of the primary coil  21  is connected to a switching element in the switching control circuit of the igniter  321 . The low-voltage side winding end  222  of the secondary coil  22  is connected to an anode terminal of a diode  521 , and a cathode terminal of the diode  521  is connected to the battery power source VB and the positive winding end  211  of the primary coil  21 . 
   As shown in  FIGS. 5 and 6 , the low-voltage side terminal  52  of this embodiment is formed by diverting a terminal  522  of the diode  521  such that an induced electromotive force caused in the secondary coil  22  is not applied to the spark plug  7  at start of energization to the primary coil  21 . The igniter arrangement portion  32  is provided with a first conducting member  34  for attaching the diode  521 . The diode  521  can be attached to the igniter arrangement portion  32  formed, and thus can be insert-molded into the igniter arrangement portion  32 . 
   One terminal  522  of the diode  521  is connected to the first conducting member  34 , and the other terminal  522  of the diode  521  is connected to the low-voltage side winding end  222  of the secondary coil  22 . The first conducting member  34  is connected to the positive side winding end  211  of the primary coil  21 . 
     FIG. 5  shows the formed state of the terminals  51  and  52 , the conducting pins  311  and  322 , and the like which are provided in electrical connection parts of the primary coil  21  and the secondary coil  22 . 
   In the igniter arrangement portion  32 , a second conducting member  35  connected to the negative side winding end  212  of the primary coil  21  is provided on the side opposite to the side of the first conducting member  34 . 
   The conducting pin  322  of the igniter  321  is connected to the conducting pin  311  of the connector  31  by welding or the like. Each of the first conducting member  34  and the second conducting member  35  is integrally formed with one of the conducting pins  311  of the connector  31 . 
   As shown in  FIGS. 2 and 3 , a clearance of the ignition coil  1  enclosed by the coil case  4  is filled with a thermosetting resin (e.g., epoxy resin or the like)  15  for fixing and insulating of respective components which include the primary coil  21 , the secondary coil  22 , the center core  23 , the outer peripheral core  24 , the intermediate core  25 , the igniter  321 , and the like. 
   After assembly of the respective components of the ignition coil  1 , the inside of the clearance of the ignition coil  1  is brought into a vacuum state, and then filled with the liquid thermosetting resin  15 , which becomes thereafter hardened. 
   When a command is received from an ECU in the ignition coil  1  of this embodiment to energize the primary coil  21  by the switching control circuit of the igniter  321 , a magnetic field is formed to pass through the center core  23 , the intermediate core  25 , and the outer peripheral core  24 . Then, when the energization to the primary coil  21  is interrupted, a voltage is generated in the primary coil  21  by a self-induction effect, while a high induced electromotive force is generated in the secondary coil  22  by a mutual induction effect, so that a spark can be made between a pair of electrodes  73  in the spark plug  7  that is provided in the ignition coil  1  (see  FIG. 1 ). 
   In the ignition coil  1  of this embodiment as described above, the igniter arrangement portion  32  and the connector  31  are integrally formed with the one end  301  of the secondary spool  3  in the axial direction L. 
   Accordingly, it is unnecessary to have a step of assembling the secondary spool  3  to the igniter arrangement portion  32  and the connector  31 . The first conducting member  34  is adapted to connect the low-voltage side winding end  222  of the secondary coil  22  and the positive side winding end  211  of the primary coil  21  to the conducting pin  311  in the connector  31 . The second conducting member  35  is adapted to connect the negative side winding end  212  of the primary coil  21  to the conducting pin  311  of the connector  31 . The first and second conducting members  34  and  35  can be insert-molded into the connector  31  and the igniter arrangement portion  32  which are integrally formed with the secondary spool  3  using the resin. Thus, there is no need to separately provide the first conducting member  34  and the second conducting member  35 , in each of the secondary spool  3  and the connector  31 . 
   Thus, the ignition coil  1  of this embodiment can simplify the structure of the wire connection portion of the secondary coil  22 , thereby effectively decreasing the number of components of the ignition coil  1 . 
   Although the present invention has been fully described in connection with the preferred embodiments 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. such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.