Patent Publication Number: US-7907040-B2

Title: Ignition coil and method for manufacturing the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-279363 filed on Oct. 26, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ignition coil that applies voltage to an ignition plug for an internal combustion engine, and relates to a manufacturing method for manufacturing the above ignition coil. 
     2. Description of Related Art 
     A conventional method for molding a resin molded body having a coil body embedded therein during the manufacture of an ignition coil has been known (see, for example, JP-A-2003-243236). Specifically, in the above molding method, a coil body, which has at least a primary coil and a secondary coil, is placed in a cavity of a die, and then a resin material, which is in a liquid or melted condition, is introduced into the cavity such that the resin material is cured to be hardened. 
     When the resin molded body of JP-A-2003-243236 having the coil body embedded therein is molded, the resin material is introduced into the cavity by a sufficient pressure such that the resin material is uniformly filed into an entirety of the cavity in a short time. Thus, in order to improve the productivity, it is important to place the coil body at a position in the cavity for limiting the displacement of the coil body due to the pressure during the introduction of the resin material. 
     In the above, the coil body of the ignition coil of JP-A-2003-243236 is not provided with a positioning portion that is configured to position the coil body in the cavity. Accordingly, in the manufacture of the above ignition coil of JP-A-2003-243236 having the coil body, in which a center core wounded with a primary coil is exposed to an exterior of the resin molded body, the center core is assumed to be held between dies for positioning the coil body in the cavity. However, in the above ignition coil, the center core made of a magnetic material, which core is exposed to the exterior of the resin molded body, may rust after the molding, and thereby performance degradation of the ignition coil may be caused. Therefore, there has been needed improvement. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above disadvantages. Thus, it is an objective of the present invention to address at least one of the above disadvantages. 
     To achieve the objective of the present invention, there is provided an ignition coil includes a coil body, a primary resin molded body, and a secondary resin molded body. The coil body has a primary coil and a secondary coil. The primary resin molded body has the coil body therein in a fixed relation, and the primary resin molded body has a plurality of exposed side portions that hold the coil body therebetween. The secondary resin molded body is molded to have the coil body and the primary resin molded body embedded therein. The secondary resin molded body is configured to allow the plurality of exposed side portions of the primary resin molded body to be exposed to an exterior of the secondary resin molded body. 
     To achieve the objective of the present invention, there is also provided a method for manufacturing the above ignition coil. In the method, a die assembly, in a cavity of which the primary resin molded body is placed, is closed such that the die assembly holds the plurality of exposed side portions, which holds the coil body of the primary resin molded body therebetween. A resin material is introduced into the cavity of the die assembly to mold the secondary resin molded body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view illustrating an ignition coil according to the first embodiment of the present invention; 
         FIG. 2  is a perspective view illustrating a primary resin molded body of the ignition coil of the first embodiment of the present invention; 
         FIG. 3  is a front view illustrating the ignition coil of the first embodiment of the present invention; 
         FIG. 4  is a schematic cross-sectional view illustrating a die assembly used in a method for manufacturing the ignition coil of the first embodiment of the present invention; 
         FIG. 5  is a schematic cross-sectional view of a die taken along line V-V in  FIG. 4 ; 
         FIG. 6  is a schematic diagram used for explaining the method for manufacturing the ignition coil of the first embodiment of the present invention; 
         FIG. 7  is another schematic diagram used for explaining the method for manufacturing the ignition coil of the first embodiment of the present invention; 
         FIG. 8  is still another schematic diagram used for explaining the method for manufacturing the ignition coil of the first embodiment of the present invention; 
         FIG. 9  is a cross-sectional view illustrating an ignition coil according to the second embodiment of the present invention; 
         FIG. 10  is a perspective view illustrating a primary resin molded body of the ignition coil of the second embodiment of the present invention; 
         FIG. 11  is a schematic diagram for explaining a method for manufacturing the ignition coil of the second embodiment of the present invention; and 
         FIG. 12  is a schematic cross-sectional view illustrating a die assembly used in a method for manufacturing an ignition coil of the third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Multiple embodiments of the present invention will be described with reference to accompanying drawings. It should be noted that similar components of an ignition coil of one embodiment, which are similar to components of the other ignition coils of the other embodiments, will be indicated by the same numerals, and the explanation thereof will be omitted. 
     First Embodiment 
     As shown in  FIG. 1 , an ignition coil  1  of the first embodiment of the present invention includes a coil body  10  that integrally has a center core  13 , a secondary spool  15 , an outer peripheral core  18 , a primary coil  14 , and a secondary coil  16 . 
     The center core  13  is made by, for example, pressure molding the magnetic powder, and has a generally column shape. The primary coil  14  having a hollow cylindrical shape is wound around a radially outer surface of the center core  13 . The primary coil  14  includes a primary conductor wire of, for example, 0.3 to 0.8 mm in diameter, which wire is wound number of turns of 100 to 230. The primary conductor wire has a leading end and a trailing end that are electrically connected with an igniter  19  provided to the ignition coil  1 . It should be noted that although the primary conductor wire may employ an enamel coated wire, the primary conductor wire is not limited to the above wire provided that the adjacent primary conductor wires are electrically insulated from each other. Also, the center core  13  may be alternatively formed by arranging magnetic plates, such as a silicon steel plate, onto one another, instead of being formed by pressure molding. In the above alternative case, the primary coil  14  is not directly wound around the center core  13 , however, the primary coil  14  may be alternatively wound around the center core  13  via a primary spool. 
     The secondary spool  15  is made of a resin material, and has a generally tubular shape. The secondary spool  15  is fixedly fitted with the center core  13  on a radially outer side of the center core  13  and the primary coil  14 , and is coaxial with the center core  13  and the primary coil  14 . The secondary coil  16  having a hollow cylindrical shape is wound around a radially outer surface of the secondary spool  15 . The secondary coil  16  has a secondary conductor wire of, for example, 40 to 50 μm in diameter, which wire is wound number of turns of 10000 to 20000. The secondary conductor wire has a leading end that is electrically connected with the igniter  19 . In contrast, the secondary conductor wire has a trailing end that is electrically connected with a high-voltage terminal (not shown) provided to the ignition coil  1 . It should be noted that the secondary coil  16 , which has larger number of turns than the primary coil  14 , and which thereby generates substantially high voltage, may be, for example, slantly wound in order to limit the electric insulation breakdown of the secondary conductor wire caused by the voltage of the secondary conductor wire. 
     The outer peripheral core  18  is made of a magnetic plate, such as a pure iron, and has a U-shape form. The outer peripheral core  18  is fixed to an outer surface of the secondary spool  15 , and the center core  13  is fixed to an inner surface of the secondary spool  15 . As a result, the outer peripheral core  18  supports the primary coil  14 , the secondary spool  15 , and the secondary coil  16 . In the above, the outer surface of the outer peripheral core  18  is provided with a fitting recess  18   a , which will be described later. It should be noted that the outer peripheral core  18  may be also alternatively formed by arranging magnetic plates, such as a silicon steel plate, onto one another similar to the center core  13 . 
     In the ignition coil  1 , the coil body  10  is fixedly fitted inside a primary resin molded body (frame)  20 , which is molded of a hard resin material, such as PBT, to have a frame shape. As shown in  FIG. 2 , the primary resin molded body  20  includes four side wall portions  20   a ,  20   b ,  20   c ,  20   d , an igniter receiving portion  23 , a connector portion  22 , and a fixation portion  21 . The side portions  20   a ,  20   b ,  20   c ,  20   d  configure a rectangular frame. The igniter receiving portion  23  projects from the side portion  20   a . The connector portion  22  further projects from the igniter receiving portion  23 , and the fixation portion  21  projects from the side portion  20   c.    
     In the primary resin molded body  20  shown in  FIGS. 1 ,  2 , the side portion  20   a  (covered side portion) and the side portion  20   c  (third exposed side portion) are arranged to oppose to each other with the coil body  10  disposed between the side portion  20   a  and the side portion  20   c . Also, the side portion  20   b  (first exposed side portion) and the side portion  20   d  (second exposed side portion) are arranged to oppose to each other with the coil body  10  disposed between the side portion  20   b  and the side portion  20   d . In other words, the side portion  20   a  is provided on a side of the coil body  10  opposite to the side portion  20   c , and the side portion  20   b  is provided on a side of the coil body  10  opposite to the side portion  20   d . The side portion  20   c  has an inner surface, which is provided with two fitting protrusions  25 , and the protrusions  25  are fitted with the fitting recess  18   a  of the outer peripheral core  18 . Also, a plate suspension portion  24  is provided between the side portion  20   b  and the side portion  20   d  such that the suspension portion  24  bridges the side portions  20   b ,  20   d . The suspension portion  24  supports the coil body  10  received in the primary resin molded body  20 . 
     The igniter receiving portion  23  projects externally from the side portion  20   a  and is fixedly fitted with the igniter  19 . The connector portion  22 , which projects from the igniter receiving portion  23  in a direction away from the side portion  20   a , includes a terminal  28  embedded therein, which terminal  28  is configured to electrically connect the coil body  10  with an external power source (not shown) via the igniter  19 . 
     The fixation portion  21  externally projects from the side portion  20   c  in a direction away from the side portion  20   a  and is fixed with a tubular metal bush  21   a . The metal bush  21   a  is in threaded engagement with a bolt (not shown) that fixes the ignition coil  1  to the internal combustion engine. In the above, specifically, the fixation portion  21  of the present embodiment projects from an inner side portion of an outer surface of the side portion  20   c , which outer surface outwardly faces in a longitudinal direction of the center core  13 . More specifically, the inner side portion of the outer surface is located radially inward relative to a outer peripheral edge of the outer surface of the side portion  20   c.    
     As shown in  FIGS. 1 ,  3 , the primary resin molded body  20  is embedded in a main body portion  32  of a secondary resin molded body (casing)  30  together with the coil body  10 . The secondary resin molded body  30  is molded of an electrically insulating resin material  30   a , such as an epoxy resin, and includes the main body portion  32  having a square column shape. Specifically, in the present embodiment, the side portions  20   b ,  20   d , between which the coil body  10  is provided, and the side portion  20   c , which provides connection between the side portions  20   b ,  20   d , are exposed to an exterior out of an outer surface of the main body portion  32  of the secondary resin molded body  30 . Also, the side portion  20   a  is covered with the main body portion  32 . In other words, the side portion  20   a  corresponding to a covered side portion. Also, in the present embodiment, the fixation portion  21  outwardly projects from the side portion  20   c  toward an exterior of the main body portion  32  of the secondary resin molded body  30  such that the fixation portion  21  is exposed to the outside. Also, the connector portion  22  and the igniter receiving portion  23  are configured to be exposed to the outside of the main body portion  32 . It should be noted that as shown in  FIG. 1  the resin material  30   a  that forms the secondary resin molded body  30  is sufficiently filled into corners of the coil body  10  embedded in the primary resin molded body  20 , and thereby the electrical insulation of the secondary coil  16 , which generates substantially high voltage, is achieved. 
     The secondary resin molded body  30  has a high voltage tower portion  31 , which projects from the main body portion  32 , and which has a cylindrical shape. A high-voltage terminal is embedded in the high voltage tower portion  31  and is connected with the secondary coil  16 . The high voltage tower portion  31  has a radially outer surface that is provided with an annular engaging portion  31   a . The engaging portion  31   a  is configured to be engaged with an inclusion member (not shown) that encapsulates a conductive member (not shown). In the above, the conductive member of the inclusion member is configured to electrically connect an ignition plug (not shown) with the high-voltage terminal in the ignition coil  1 . 
     In the above ignition coil  1 , signals from a control unit (not shown) or a power source are supplied through the terminal  28  of the connector portion  22 . When the electric current that flows through the primary coil  14  is stopped by the igniter  19 , mutual induction by the primary and secondary coils  14 ,  16 , generates high voltage of, for example, 30 to 35 kV, in the secondary coil  16 . The high voltage generated in the secondary coil  16  as above is introduced to the ignition plug through the high-voltage terminal in the high voltage tower portion  31  and through the conductive member in the inclusion member such that spark discharge is generated at a tip end of the ignition plug. 
     (Manufacturing Method of Ignition Coil) 
     A manufacturing method for manufacturing the ignition coil  1  of the present embodiment will be described. The manufacturing method employs a die assembly  200  having a movable die  200   a  and a stationary die  200   b  as shown in  FIGS. 4 ,  5 . The die assembly  200  includes a cavity  201  and releasing spaces  202 ,  203 . The cavity  201  is configured to mold the secondary resin molded body  30 , and the releasing spaces  202 ,  203  are configured to receive the connector portion  22  and the fixation portion  21  of the primary resin molded body  20 , respectively, such that the connector portion  22  and the fixation portion  21  extend from the cavity  201  when the primary resin molded body  20  is placed at a position in the cavity  201 . In the above, specifically, the die assembly  200  of the present embodiment has four inner surfaces  204   a ,  204   b ,  204   c ,  204   d  for forming the main body portion  32  of the secondary resin molded body  30 . The releasing space  202  for the connector portion  22  opens at the inner surface  204   a , and the releasing space  203  for the fixation portion  21  opens at the inner surface  204   c , which opposes to the inner surface  204   a.    
     In the manufacturing method of the ignition coil  1  by using the above die assembly  200 , firstly, in a die closing step, the primary resin molded body  20 , to which the coil body  10  and the igniter  19  are fixed, is placed in the cavity  201  of the stationary die  200   b  as shown in  FIG. 6  such that the side portion  20   d  of the molded body  20  is brought into contact with the inner surface  204   d  of the stationary die  200   b . Then, by displacing the movable die  200   a  closer toward the stationary die  200   b  in order to close the die assembly  200 , the inner surface  204   b  of the movable die  200   a  is brought into contact with the side portion  20   b  of the primary resin molded body  20 . 
     As a result, the side portions  20   b ,  20   d , between which the coil body  10  is provided in the primary resin molded body  20 , are provided between the inner surfaces  204   b ,  204   d  of the die assembly  200 . Also, the fixation portion  21  is received in the releasing space  203  with a clearance between an outer peripheral face of the fixation portion  21  and an inner peripheral face of the releasing space  203 . The side portion  20   c  of the primary resin molded body  20 , from which portion  20   c  the fixation portion  21  projects, contacts the inner surface  204   c  of the die assembly  200 . As a result, the releasing space  203  is separated from the cavity  201 . Also, the connector portion  22  is received in the releasing space  202  with a clearance between an outer face of the connector portion  22  and an inner face of the releasing space  202 . The igniter receiving portion  23 , which is provided on a side of the connector portion  22  toward the side portion  20   a , is fitted with an opening  202   a  of the releasing space  202 , which opening  202   a  is formed at the inner surface  204   a  of the die assembly  200 . Thus, the releasing space  202  is separated from the cavity  201 . According to the above configuration, in a case of molding the secondary resin molded body  30 , a segment of the side portion, which segment is the radially outer area of the side portion relative to the fixation portion  21 , is brought into contact with the die assembly for the positioning of the primary resin molded body  20 . 
     Next, in a molding step, the resin material  30   a , for example, epoxy resin, in a liquid or melted condition is introduced into the cavity  201  under a predetermined pressure (introducing pressure) through a gate (not shown), which is provided as a flow channel for communication with the cavity  201 . In the above case, because the side portions  20   b ,  20   d  are provided between the inner surfaces  204   b ,  204   d  of the die assembly  200 , the primary resin molded body  20  is limited from being displaced in an opposing direction (lateral direction), in which the side portions  20   b ,  20   d  are arranged to oppose to each other. Also, because the side portion  20   c  is pressed against the inner surface  204   c  of the die assembly  200  due to the above introducing pressure applied to the side portion  20   a , which is spaced apart from the inner surface  204   a  of the die assembly  200 , the primary resin molded body  20  is limited from being displaced in another opposing direction (longitudinal direction), in which the side portions  20   c ,  20   a  are arranged to oppose to each other. Furthermore, the resin material  30   a  is limited from entering into the releasing spaces  203 ,  202  because of the pressing of the side portion  20   c  against the inner surface  204   c , and because of the fitting of the igniter receiving portion  23  into the opening  202   a  of the inner surface  204   a . It should be noted that the above introducing pressure, under which the resin material  30   a  is introduced into the cavity  201  in the molding step, is determined such that the resin material  30   a  in the cavity  201  in a liquid or melted condition is limited from forming air voids therein, and such that the resin material  30   a  is sufficiently filled into the corners of the coil body  10  in the primary resin molded body  20 . 
     As above, after the cavity  201  has been filled with the resin material  30   a , the die assembly  200  is heated or cooled to cure the resin material  30   a  in the molding step. The above process is able to mold the secondary resin molded body  30 , in which the side portions  20   b ,  20   d ,  20   c , the fixation portion  21 , the connector portion  22 , and the igniter receiving portion  23  of the primary resin molded body  20  are exposed to the exterior out of the main body portion  32  as shown in  FIGS. 7 ,  8 . It should be noted that after the above, the inclusion member encapsulating the conductive member is engaged with the engaging portion  31   a  of the high voltage tower portion  31  of the secondary resin molded body  30  such that the ignition coil  1  is completed. 
     According to the above first embodiment, when the resin material  30   a  is introduced into the die assembly  200  in the molding step executed after the die closing step, the primary resin molded body  20  is accurately positioned by using the die assembly  200  to support the primary resin molded body  20 , and the coil body  10  and the igniter  19  of the primary resin molded body  20  are also positioned accurately. Due to the above, manufacturing errors are limited, and thereby the productivity is more improved. Also, although the primary resin molded body  20  is exposed to the exterior out of the secondary resin molded body  30  obtained in the molding step, the coil body  10  is completely covered with the secondary resin molded body  30 . As a result, the performance degradation, which may be otherwise caused in a conventional art, is limited in the present embodiment. Therefore, in the first embodiment, the productivity is improved, and also at the same time, the performance is effectively and sufficiently achieved. 
     Second Embodiment 
     The second embodiment of the present invention is a modification of the first embodiment. 
     As shown in  FIGS. 9 ,  10 , a primary resin molded body  120  of the second embodiment, a contact ridge  120   e  is provided to extend across the side portions  20   b ,  20   c ,  20   d , which are exposed to the exterior of the secondary resin molded body  30 . Specifically, the contact ridge  120   e  projects from an outer surface of each of the side portions  20   b ,  20   c ,  20   d  toward the exterior of the secondary resin molded body  30 , and has a generally triangular shape in a cross section. There is defined a first boundary between the side portion  20   b  and the side portion  20   c . There is defined a second boundary between the side portion  20   c  and the side portion  20   d . The contact ridge  120   e  of the present embodiment continuously extends along the outer peripheral edges of the side portions  20   b ,  20   c ,  20   d  except for the above first and second boundaries between the side portions  20   b ,  20   c ,  20   d  to have an annular shape. In other words, the contact ridge  120   e  is configured to have an annular shape that extends along a radially outer side of the fixation portion  21 , which projects from the side portion  20   c . In other words, the contact ridge  123   a  extends along the outer peripheral edge of a U-shaped configuration, which is made by generally orthogonally arranging the side portion  20   c  between end portions of the parallelly arranged side portions  20   b ,  20   d.    
     Also, in the primary resin molded body  120  of the second embodiment, an igniter receiving portion  123 , which is exposed to the exterior from the secondary resin molded body  30 , is also provided with a contact ridge  123   a . Specifically, the contact ridge  123   a  projects from a radially outer surface of the igniter receiving portion  123  of an exterior of the secondary resin molded body  30 , and has a generally triangular shape in a cross section. Also, the contact ridge  123   a  of the present embodiment is configured to have an annular shape that continuously extends around the radially outer surface of the igniter receiving portion  123 . 
     In the above second embodiment, in the die closing step, the contact ridge  120   e , which extends across the side portions  20   b ,  20   c ,  20   d  of the primary resin molded body  120  to extend around the fixation portion  21 , contacts the inner surfaces  204   b ,  204   c ,  204   d  of the die assembly  200  as shown in  FIG. 11 . As a result, the contact pressure at the contact boundary surface becomes high. Thus, a gap between (a) the side portion  20   c , from which the fixation portion  21  extends, and (b) the die assembly  200 , and the other gaps between (a) the side portions  20   b ,  20   d  and (b) the die assembly  200  are substantially sealed in the molding step, and thereby degradation of the positioning accuracy caused by the entering of the resin material  30   a  into the above gaps is effectively limited. 
     Also, in addition to the sealing of the above gaps between (a) the side portion  20   c ,  20   b ,  20   d  and (b) the die assembly  200 , because the contact ridge  123   a , which is provided to the receiving portion  123 , contacts the opening  202   a  of the releasing space  202  in the inner surface  204   a  under a high contact pressure, a gap between the igniter receiving portion  123  and the die assembly  200  is also sufficiently sealed. As a result, in the molding step, the entering of the resin material  30   a  into the releasing spaces  203 ,  202  is effectively limited. 
     Third Embodiment 
     The third embodiment of the present invention is a modification of the first embodiment. 
     In the primary resin molded body  20  of the first embodiment, if there are changes in a physical or positional relation between the side portions, from which the fixation portion  21  and the connector portion  22  project, respectively, there should be prepared different dies, each of which has the releasing spaces  202 ,  203  at positions correspondingly to the above changes in the physical relation. As a result, productivity may deteriorate due to the preparation of the different dies. 
     Thus, as shown in  FIG. 12 , a die assembly  2200  of the third embodiment includes releasing spaces  2203   b ,  2203   d  in addition to the releasing space  203  that opens at the inner surface  204   c . Each of the releasing spaces  2203   b ,  2203   d  is configured to provide space for the fixation portion  21  of the primary resin molded body  20  in the die assembly  2200 , and open at the inner surfaces  204   b ,  204   d . It should be noted that in the present embodiment the releasing spaces  203 ,  2203   b ,  2203   d  may be connected with each other in a direction, in which the inner surfaces  204   b ,  204   c ,  204   d  are arranged in series. Also, the releasing spaces  203 ,  2203   b ,  2203   d  may be alternatively separate from each other in the direction. 
     In a die closing step of the above third embodiment, because the primary resin molded body  20  is held between the inner surfaces  204   b ,  204   d  in a state, where the side portions  20   b ,  20   d  of the primary resin molded body  20  contact the inner surfaces  204   b ,  204   d , the releasing spaces  2203   b ,  2203   d  correspondingly formed on the inner surfaces  204   b ,  204   d  are separated from the cavity  201 . As a result, even in a product, in which the fixation portion  21  projects from a radially inner side of the outer peripheral edge of the side portion  20   b  instead of projecting from the side portion  20   c , by making the fixation portion  21  be received in the releasing space  2203   b  opening at the inner surface  204   b , which the side portion  20   b  contacts, the entering of the resin material  30   a  into the releasing space  2203   b  is effectively limited in the molding step. Also similarly, even in a product, in which the fixation portion  21  projects from the radially inner side of the outer peripheral edge of the side portion  20   d , by making the fixation portion  21  be received in the releasing space  2203   d  opening at the inner surface  204   d , which the side portion  20   d  contacts, the entering of the resin material  30   a  into the releasing space  2203   d  is effectively limited in the molding step. 
     In the above third embodiment, even in any products, in which the fixation portion  21  projects from any one of the side portions  20   b ,  20   c ,  20   d , because a common die assembly  2200 , which is able to be shared by any projects, is employed for manufacturing, costs of production is effectively reduced. 
     As above, multiple embodiments of the present invention are explained. However, the interpretation of the present invention is not limited to the above embodiments, and the present invention is applicable to various embodiments provided that the embodiments are not deviating from the gist. 
     In the above embodiments, the outer peripheral edge of each of the side portions indicates an outer edge of the side portion along a plane, on which the side portion extends. Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.