Patent Publication Number: US-7222616-B2

Title: Stick ignition coil apparatus for ignition plug

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on and incorporates herein by reference Japanese Patent Applications No. 2004-218737 filed on Jul. 27, 2004 and No. 2005-152985 filed on May 25, 2005. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a stick ignition coil apparatus for an internal combustion engine. 
   2. Description of Related Art 
   A stick ignition coil apparatus includes a center core, an outer core, a primary coil arrangement and a secondary coil arrangement. By switching on and off of supply of an electric current to the primary coil arrangement, a high voltage is generated in the secondary coil arrangement. The high voltage, which is generated at the secondary coil arrangement, is supplied to an ignition plug by way of a high voltage terminal, which is located at a (lower) end of the secondary coil arrangement. 
   As shown in  FIG. 23A , a conventional stick ignition coil apparatus has a coil case  300 , which includes a center core  302 , a secondary coil arrangement  304 , which is located radially outward of the center core  302 , and a primary coil arrangement  308 , which is located radially outward of the secondary coil arrangement  304 . The secondary coil arrangement  304  includes a secondary spool  305  and a secondary winding  306 , which is wound around the secondary spool  305 . The primary coil arrangement  308  includes a primary spool  309  and a primary winding  310 , which is wound around the primary spool  309 . 
   A terminal plate (a second terminal element)  317 , which is shaped into a tubular form, is installed at a bottom end of the secondary spool  305 . A tubular-form high voltage terminal (a first terminal element)  315 , an opening of which faces downward, is held in a spring case  312 , which holds a spring  313 . The spring  313  is located between the high voltage terminal  315  and the ignition plug (not shown). An upwardly extending portion of the high voltage terminal  315  contacts the terminal plate  317 . Therefore, a bottom end of the secondary winding  306  is connected with the ignition plug, by way of the terminal plate  317 , the high voltage terminal  315  and the spring  313 . A space, which is formed by a bottom end of the coil case  300 , the spring case  312 , the high voltage terminal  315  and the like, is filled with dielectric resin  319  (see Unexamined Japanese Patent Publication No. 2000-133534). 
   However, in the above-described conventional art, a crack may be formed on the dielectric resin  319 . Here, the terminal plate  317 , which is a copper alloy, such as phosphor bronze, does not adhere well to the dielectric resin  319 , which is made of a thermosetting epoxy resin. Furthermore, a coefficient of linear thermal expansion of the terminal plate  317  differs from that of the dielectric resin  319 . Therefore, as shown in  FIG. 23B , when a thermal stress is generated in a radial direction at the time of starting and stopping of an engine, and the crack tends to be formed at a phase boundary  321  between the terminal plate  317  and the dielectric resin  319 . 
   An edge effect of the terminal plate  317  is added to the crack at the phase boundary. This means that the thermal stress is concentrated around an edge  317   a  and a resin portion therearound. Then, the dielectric resin  319  gets the crack  322 , which starts from the edge  317   a  of the terminal plate  317 . This may cause a dielectric breakdown. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a stick ignition coil apparatus, which limits generation of cracks in a dielectric resin (a potting material) of the stick ignition coil apparatus. 
   To achieve the objective of the present invention, there is provided a stick ignition coil apparatus for an ignition plug including a primary coil arrangement, a secondary coil arrangement, a center core, a coil case, a high voltage terminal, a spring case and dielectric resin. The primary coil arrangement includes a primary winding and a primary spool, wherein the primary winding is wound around the primary spool. The secondary coil arrangement is located radially inward of the primary coil arrangement, wherein the secondary coil arrangement includes a secondary winding and a secondary spool, the secondary winding is wound around the secondary spool, and an annular corner portion is formed on a distal projecting portion of the secondary spool. The center core is located radially inward of the secondary coil arrangement. The coil case is located radially outward of the primary coil arrangement. The high voltage terminal is located at a distal end of the secondary coil arrangement, wherein the high voltage terminal is shaped into a tubular form, an opening of which faces toward a proximal end of the stick ignition coil apparatus, and the high voltage terminal is electrically connected with one end of the secondary winding. The spring case holds a spring for electrically connecting the high voltage terminal with the ignition plug. The dielectric resin is filled in a space defined radially inward of the coil case, wherein an open end of the high voltage terminal is connected to the annular corner portion of the distal projecting portion of the secondary spool. 
   To achieve the objective of the present invention, there is also provided a stick ignition coil apparatus for an ignition plug including a primary coil arrangement, a secondary coil arrangement, a center core, a coil case, a spring case, a high voltage terminal and dielectric resin. The primary coil arrangement includes a primary winding and a primary spool, wherein the primary winding is wound around the primary spool. The secondary coil arrangement is located radially inward of the primary coil arrangement, wherein the secondary coil arrangement includes a secondary winding and a secondary spool, and the secondary winding is wound around the secondary spool. The center core is located radially inward of the secondary coil arrangement. The coil case is located radially outward of the primary coil arrangement. The spring case is located at a distal side of the coil case, wherein the spring case holds a spring, one end of which contacts the ignition plug to form an electrical connection therebetween. The high voltage terminal is located at a proximal end of a proximal cylindrical end portion of the spring case, wherein the high voltage terminal is shaped into a tubular form, an opening of which faces toward a proximal end of the stick ignition coil apparatus, the high voltage terminal is electrically connected with one end of the secondary winding, and the high voltage terminal is contacts the other end of the spring to form an electrical connection therebetween. The dielectric resin is filled in a space defined radially inward of the coil case, wherein an open end of the high voltage terminal contacts an inner peripheral surface of the proximal cylindrical end portion of the spring case. 
   To achieve the objective of the present invention, there is also provided a stick ignition coil apparatus for an ignition plug including a primary coil arrangement, a secondary coil arrangement, a center core, a coil case, a spring case, a high voltage terminal and dielectric resin. The primary coil arrangement includes a primary winding and a primary spool, wherein the primary winding is wound around the primary spool. The secondary coil arrangement, which is located radially inward of the primary coil arrangement, wherein the secondary coil arrangement includes a secondary winding and a secondary spool, and the secondary winding is wound around the secondary spool. The center core is located radially inward of the secondary coil arrangement. The coil case is located radially outward of the primary coil arrangement. The spring case is located at a distal side of the coil case, wherein the spring case holds a spring, one end of which contacts the ignition plug to form an electrical connection therebetween, and a proximal cylindrical end portion of the spring case is located at a proximal end of the spring case. The high voltage terminal contacts at least one of a distal end of the secondary coil arrangement and the proximal end of the spring case, wherein the high voltage terminal is shaped into a tubular form, an opening of which faces toward a proximal end of the stick ignition coil apparatus, the high voltage terminal is electrically connected with one end of the secondary winding, and the high voltage terminal contacts the other end of the spring to form an electrical connection therebetween. The dielectric resin is filled in a space defined radially inward of the coil case, wherein an open end of the high voltage terminal is surrounded by a distal projecting portion of the secondary spool and the proximal cylindrical end portion of the spring case. 
   To achieve the objective of the present invention, there is also provided a stick ignition coil apparatus for an ignition plug including a primary coil arrangement, a secondary coil arrangement, a center core, a coil case, a spring case, a high voltage terminal and dielectric resin. The primary coil arrangement includes a primary winding and a primary spool, wherein the primary winding is wound around the primary spool. The secondary coil arrangement is located radially inward of the primary coil arrangement, wherein the secondary coil arrangement includes a secondary winding and a secondary spool, and the secondary winding is wound around the secondary spool. The center core is located radially inward of the secondary coil arrangement. The coil case is located radially outward of the primary coil arrangement. The spring case is located at a distal side of the coil case, wherein the spring case holds a spring, one end of which contacts the ignition plug to form an electrical connection therebetween. The high voltage terminal is located on a proximal end of the spring case, wherein the high voltage terminal is shaped into a tubular form, an opening of which faces toward a distal end of the stick ignition coil apparatus, the high voltage terminal is electrically connected with one end of the secondary winding, and the high voltage terminal includes a first terminal element, which contacts the other end of the spring to form an electrical connection therebetween. The dielectric resin is filled in a space defined radically inward of the coil case, wherein an open end of the high voltage terminal is located in a space, which is not filled with the dielectric resin. 

   
     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 longitudinal sectional view of a stick ignition coil apparatus according to a first embodiment of the present invention; 
       FIG. 2A  is an enlarged view of a main part of the stick ignition coil apparatus of  FIG. 1 ; 
       FIG. 2B  is a schematic view of  FIG. 2A ; 
       FIG. 3  is a sectional view of a main part of a first modification of the first embodiment; 
       FIG. 4  is a sectional view of a main part of a second modification of the first embodiment; 
       FIG. 5  is a sectional view of a main part of a third modification of the first embodiment; 
       FIG. 6  is a sectional view of a main part of the stick ignition coil apparatus according to a second embodiment; 
       FIG. 7  is a sectional view of a main part of a first modification of the second embodiment; 
       FIG. 8  is a sectional view of a main part of a second modification of the second embodiment; 
       FIG. 9  is a sectional view of a main part of a third modification of the second embodiment; 
       FIG. 10  is a sectional view of a main part of a fourth modification of the second embodiment; 
       FIG. 11  is a sectional view of a main part of a fifth modification of the second embodiment; 
       FIG. 12  is a sectional view of a main part of a sixth modification of the second embodiment; 
       FIG. 13  is a sectional view of a main part of a seventh modification of the second embodiment; 
       FIG. 14  is a sectional view of a main part of the stick ignition coil apparatus according to a third embodiment; 
       FIG. 15  is a sectional view of a main part of a modification of the third embodiment; 
       FIG. 16  is a sectional view of a main part of the stick ignition coil apparatus according to a fourth embodiment; 
       FIG. 17  is a sectional view of a main part of a second modification of the fourth embodiment; 
       FIG. 18  is a sectional view of a main part of a third modification of the fourth embodiment; 
       FIG. 19  is a sectional view of a main part of a fourth modification of the fourth embodiment; 
       FIG. 20  is a sectional view of a main part of a fifth modification of the fourth embodiment; 
       FIG. 21  is a sectional view of a main part of a sixth modification of the fourth embodiment; 
       FIG. 22  is a sectional view of a main part of a seventh modification of the fourth embodiment; 
       FIG. 23A  is a longitudinal sectional view of a conventional stick ignition coil apparatus; and 
       FIG. 23B  is a schematic view of  FIG. 23A . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   (First Embodiment) 
   A structure of a stick ignition coil apparatus according to a first embodiment will be described. As shown in  FIG. 1 , the stick ignition coil apparatus includes a coil member  10 , a high voltage tower member (not shown) and a control member  60 . The coil member  10  is located at an axially middle portion of the stick ignition coil apparatus. The high voltage tower member is located at one end (a bottom end) of the stick ignition coil apparatus. The control member  60  is located at the other end (a top end) of the stick ignition coil apparatus. The coil member  10  is inserted into a plug hole (not shown) of an engine head and is connected to an ignition plug (spark plug) through the high voltage tower member (not shown) at the bottom end of the stick ignition coil apparatus. The control member  60  at the top end of the stick ignition coil apparatus is seated against a top surface of an engine head cover. 
   In the coil member  10 , a center core  11 , a secondary coil arrangement  13 , a primary coil arrangement  21 , case  25  and a radially outer core  32  are arranged in this order in a radial direction from a center to a radially outer part of the coil member  10 . The center core  11  is made of a magnetic material, and is shaped into a cylindrical bar form. The secondary coil arrangement  13  includes a secondary spool  14  and a secondary winding  15 . The secondary spool  14  is dielectric and is formed into a cylindrical body having a bottom. The secondary winding  15  is wound around the secondary spool  14 . A bottom cylindrical end portion (a distal cylindrical end portion)  18  is projected from a base portion  17  of the secondary spool  14  (see  FIG. 2 ). The primary coil arrangement  21  is concentrically arranged radially outward of the secondary coil arrangement  13 . The primary coil arrangement  21  includes a primary spool  22  and a primary winding  23 . The primary spool  22  is dielectric, and is a cylinder. The primary winding  23  is wound around the primary spool  22 . 
   The case  25 , which is made of the dielectric material, includes a coil case member  26  and a spring case member  35 , which is formed integrally with the coil case member  26 . The cylindrical coil case member  26  includes an intermediate portion  27 , a top end portion  28  and bottom end portion  29 . The radially outer core  32 , which has C-shaped cross section, is installed to an outer peripheral surface of the intermediate portion  27  to radially oppose the center core  11 . The top end portion  28  of the coil case member  26  is press fitted into a top case  61 , which will be described later. 
     FIG. 2A  is an enlarged view of a main part of  FIG. 1 , and  FIG. 2B  is a schematic view of  FIG. 2A . As shown in  FIGS. 2A and 2B , the spring case member  35 , which is connected to the bottom end portion  29 , includes a top cylindrical end portion (a proximal cylindrical end portion)  36 , a bottom end holding portion  37  and an intermediate connection portion  38 . An inner diameter of the top cylindrical end portion  36  is slightly larger than an outer diameter of the bottom cylindrical end portion  18  of the secondary spool  14 . The top cylindrical end portion  36  and the bottom cylindrical end portion  18  are slightly overlapping each other in the axial direction (height direction). Relevant components of  FIG. 2A , which directly associate with the present invention, are schematically depicted in  FIG. 2B . 
   A high voltage terminal  40  is located between the bottom cylindrical end portion  18  and the top cylindrical end portion  36 . The high voltage terminal  40 , which is made by drawing a copper-alloy circular plate material, includes a circular base wall portion  41  and a peripheral wall portion  44 , which rises perpendicularly from a rim of the base wall portion  41  and extends upward in the axial direction. At a center of the base wall portion  41 , a conic projection  42 , which is slightly projecting upward, is formed. A top end of the outer peripheral wall portion  44  of the high voltage terminal  40  extends upward (an opening of the high voltage terminal  40  faces upward) and an open end  45 , which is the top end of the outer peripheral wall portion  44 , is slightly bent radially outward. 
   An inner peripheral surface of the peripheral wall portion  44  is engaged with an outer peripheral surface of the bottom cylindrical end portion  18  of the secondary spool  14 . The open end  45  contacts an annular corner portion  20 , which is composed by the bottom cylindrical end portion  18  and a flange portion  19 . An annular projection  19   a , which axially projects downward, is formed on an outer rim of the flange portion  19 . A top surface of the base wall portion  41  contacts a bottom surface of the bottom cylindrical end portion  18 . Thus, the conic projection  42  is projected into a cavity of the bottom cylindrical end portion  18 . A top end of a spring  48 , which is held by the holding portion  37 , contacts the base wall portion  41  of the high voltage terminal  40  to form an electrical connection therebetween. Also, a bottom end of the spring  48  is connected resiliently with the ignition plug (not shown) to form an electrical connection therebetween. 
   In  FIG. 1 , a bottom press-fitting portion  52 , which is located at a top end of a cylindrical plug cap  51  of the high voltage tower member, is press fitted into the holding portion  37 . The control member  60  includes the top case  61  and an igniter  65 . The top case  61  includes a receiving portion  62 , a top press-fitting portion  63 , a connecting portion  64  and the like. 
   First dielectric resin (first potting material)  70  and second dielectric resin (second potting material)  72  are filled in the following spaces: a space between the primary winding  23  and the coil case member  26 , which is located radially outward of the primary winding  23 , a space between the secondary winding  15  and the primary spool  22 , which is located radially outward of the secondary winding  15 , a space between the bottom cylindrical end portion  18  of the secondary spool  14  and the top cylindrical end portion  36  of the spring case  35 , and a space between the igniter  65  and the receiving portion  62 . 
   A method of assembling the stick ignition coil apparatus will be described. The high voltage terminal  40  is installed on the bottom cylindrical end portion  18  of the secondary spool  14 . The center core  11  is inserted into a cavity of the secondary spool  14  from a top opening thereof. Then, a bottom end of the center core  11  contacts the base portion  17  of the secondary spool  14 . Then, the center core  11  and the secondary coil arrangement  13  are inserted into a cavity of the primary spool  22 . 
   Thereafter, an integrated member, which includes the center core  11 , the secondary coil arrangement  13  and the primary coil arrangement  21 , is inserted into the coil case member  26  until the bottom cylindrical end portion  18  of the secondary spool  14  contacts the top cylindrical end portion  36 . Before or after this, the radially outer core  32 , which has the C-shaped cross section, is installed over the intermediate portion  27  of the coil case  26 , by enlarging the lateral opening or slit of the radially outer core  32 . At the same time, the peripheral wall portion  44  is held between the bottom cylindrical end portion  18  and the top cylindrical end portion  36 . Also, the bent open end  45  contacts the annular corner portion  20 , which is a connection between the flange portion  19  and the bottom cylindrical end portion  18 . Then, the assembling of the coil member  10  is finished. Thereafter, the plug cap  51  of the high voltage tower member is installed at a bottom end of the coil member  10 . In this assembling process, the spring  48  is inserted into the top cylindrical end portion  36  of the coil case  26 , and the bottom press-fitting portion  52  of the plug cap  51  is pressed into the holding portion  37 , so that a top end of the spring  48  contacts a bottom surface of the base wall portion  41  of the high voltage terminal  40 . 
   Then, the igniter  65  and a terminal  66  are installed in the top case  61 . Atop end of the radially outer core  32  and a top portion  28  of the coil case member  26  are pressed into a radially inward side of the top press-fitting portion  63  of the top case  61 . Thereafter, the secondary winding  15  and the primary winding  23  are electrically connected with the terminal  66  and the like. Then, from the top case  61 , epoxy resin is injected into a space around the igniter  65  of the top case  61 . Thereafter, the epoxy resin travels to the coil case  26 , whereby the epoxy resin fills a space between the secondary winding  15  and the primary spool  22 , and a space between the secondary spool  14  and the top cylindrical end portion  36  of the coil case  26 . At this time, a space between the bottom cylindrical end portion  18  of the secondary spool  14  and the top cylindrical end portion  36  of the spring case  35  is communicated, and is filled with the epoxy resin. The epoxy resin is cured when heated, so that the epoxy resin becomes the first dielectric resin  70  of the top case  61  and the second dielectric resin  72  of the coil member  10 . 
   An operational effect will be described. The effect of the stick ignition coil apparatus is widely known and is not directly related to the present invention. Thus, an explanation of the effect of the stick ignition coil apparatus is omitted. According to the present stock ignition coil apparatus, firstly, a crack is not likely to be formed in the second dielectric resin  72  around the open end  45  of the high voltage terminal  40 . This is because the open end  45  is bent radially outward beforehand, and thereafter the bent open end  45  contacts the annular corner portion  20 , which includes the bottom cylindrical end portion  18  of the secondary spool  14  and the flange portion  19 . 
   Thus, as it is obviously shown in  FIGS. 2A and 2B  that the open end  45  is slightly bent radially outward. Therefore, stress is not likely to be concentrated on either an outer edge or an inner edge. Also, the second dielectric resin  72  does not substantially exist between the open end  45  and the bottom cylindrical end portion  18 , because the open end  45  contacts the outer peripheral surface of the bottom cylindrical end portion  18 . Also, because the open end  45  enters at the annular corner portion  20 , which is formed by the bottom cylindrical end portion  18  and the flange portion  19 , the open end  45  is not likely to detach from the bottom cylindrical end portion  18 . Therefore, a boundary surface is not likely to be generated. 
   As a second operational effect, because the coil case member  26  and the spring case member  35  are formed integrally, it is easy to mould a case  25 . As a third operational effect, because the base wall portion  41  of the high voltage terminal  40  includes the conic projection  42 , which is injected into the cavity of the bottom cylindrical end portion  18 , the high voltage terminal  40  is accurately positioned. 
     FIGS. 3 ,  4  and  5  are modifications of the first embodiment. In a first modification as shown in  FIG. 3 , on the flange portion  19  at the bottom portion  17  of the second spool  14 , the annular projection  19   a , which is formed in the first embodiment, is not formed. Instead, a bottom surface of the flange portion  19  is an annular inclined plane  19   b . The open end  45  of the peripheral wall portion  44  of the high voltage terminal  40  contacts the annular corner portion  20  at a root of the annular inclined plane  19   b . Other structure is the same as the first embodiment. 
   In a second modification as shown in  FIG. 4 , an open end  102  of a peripheral wall portion  101  of the high voltage terminal  100  is tapered and contacts the bottom surface of the flange portion  19 . In this structure, the open end  102  has only one edge, which contacts the bottom surface of the flange portion  19 . Thus, the crack is not likely to be upwardly generated in the second dielectric resin  72 . 
   In a third modification as shown in  FIG. 5 , an inner edge of the open end  45 , which is bent radially outward, of the peripheral wall portion  44  of the high voltage terminal  40  contacts an annular plate  105 . The annular plate  105  is composed of a soft material, which is softer than the secondary spool  14 . The annular plate  105  is pressed toward the bottom surface of the flange portion  19 . By this structure, the inner edge is slightly engaged in the annular plate  105 , and the second dielectric resin  72  does not substantially exist around the inner edge. Therefore, the crack is not likely to be generated. 
   (Second Embodiment) 
   A second embodiment of the present invention will be described with reference to the accompanying drawings. Similar components of a stick ignition coil apparatus of the present embodiment, which are similar to the components of the stick ignition coil apparatus of the first embodiment, will be indicated by the same numerals. 
   In the second embodiment, the open end of the outer peripheral wall portion contacts the top cylindrical end portion of the spring case. As shown in  FIG. 6 , the secondary spool  14  has almost the same structure as the first embodiment. At a center of a base wall portion  111  of a high voltage terminal  110 , a projection  112 , which projects toward the same direction (upward in  FIG. 6 ) as a peripheral wall portion  113  extends, is formed. The height (deepness) of the projection  112  is larger than the height of the peripheral wall portion  113 . An outer peripheral surface of the peripheral wall portion  113  is engaged with an inner peripheral surface of the top cylindrical end portion  36 . A top end of the top cylindrical end portion  36  extends toward the top end of the stock ignition coil apparatus further than an open end  114 . Here, there is a slight space between the projection  112  and the bottom cylindrical end portion  18 , which is included in the distal projecting portion of the secondary spool  14 . 
   In the second embodiment, an outer edge of the open end  114  of the high voltage terminal  110  contacts the inner peripheral surface of the top cylindrical end portion  36 . Thus, the second dielectric resin  72  does not substantially exist therebetween. Thus, the crack is not likely to be generated in the second dielectric resin  72  around the open end  45 . Also, an inner edge of the open end  114  is located adjacent to an outer peripheral surface of the bottom cylindrical end portion  18  of the secondary spool  14 . Therefore, the crack is not likely to be generated. 
   In  FIGS. 7 to 13 , modifications of the second embodiment are described. In a first modification as shown in  FIG. 7 , the peripheral wall portion  122  of a high voltage terminal  120  is engaged with the top cylindrical end portion  36  of the spring case  35 . An open end  123  is at the same position as a top end of the top cylindrical portion  36 , and an outer edge of the open end  123  contacts the top cylindrical end portion  36 . An annular intermediate component  124 , a section of which forms L shape, lies between a bottom surface of the bottom cylindrical end portion  18  and a base wall portion  121  of a high voltage terminal  120 , and lies between an outer peripheral surface of a bottom part of the bottom cylindrical end portion  18  and a peripheral wall portion  122  of the high voltage terminal  120 . An inner edge of the open end  123  contacts an outer peripheral surface of the intermediate component  124 . An outer edge of the open end  123  contacts the top cylindrical end portion  36 , and the inner edge of the open end  123  contacts the intermediate component  124 . Therefore, the crack is not likely to be generated on the second dielectric resin  72 . 
   In a second modification as shown in  FIG. 8 , a high voltage terminal  125  includes a base wall portion  126  and a peripheral wall portion  127 . Neither a recess portion nor a projection is formed on a surface of the flat base wall portion  126 . The peripheral wall portion  127  is engaged with an inner peripheral surface of the top cylindrical end portion  36  of the spring case  35 . An outer edge of an open end  128  contacts an inner peripheral surface of the top cylindrical end portion  36 . An inner edge of the open end  128  contacts an outer peripheral surface of the bottom cylindrical end portion  18 . As shown in a third modification in  FIG. 9 , a base portion  130  may be formed at a bottom end of the bottom cylindrical end portion  18  of the secondary spool  14 . 
   In a fourth modification as shown in  FIG. 10 , a high voltage terminal  135  includes a base wall portion  136  and a peripheral wall portion  137 . At a center of the base wall portion  136 , a projection  138  is projected in an opposite direction (downward in  FIG. 10 ) from the direction of the peripheral wall portion  137 . An outer edge of an open end  139  of the peripheral wall portion  137  contacts an inner peripheral surface of the top cylindrical end portion  36 . In an inner edge of the open end  139  is located closer to an outer peripheral surface of the bottom cylindrical end portion  18  of the secondary spool  14 . In a fifth modification as shown in  FIG. 11 , a base portion  140  is formed at a slightly upper side of the bottom end of the bottom cylindrical end portion  18  of the secondary spool  14 . Below the base portion  140 , a cavity  141  of the bottom cylindrical end portion  18  is formed. A high voltage terminal  143  includes a base wall portion  144  and a peripheral wall portion  145 . The peripheral wall portion  145  is held by the top cylindrical end portion  36  of the spring case  35 . An open end  146  contacts the inner peripheral surface of the top cylindrical end portion  36 . 
   In a sixth modification as shown in  FIG. 12 , a base portion  150  is formed at a bottom end of the bottom cylindrical end portion  18  of the secondary spool  14 . A peripheral wall portion  158  of a high voltage terminal  155  is held by the top cylindrical end portion  36  of the spring case  35 . On a base wall portion  156  of the high voltage terminal  155 , a projection  157 , which projects downward, is formed integrally. An open end  159  contacts the inner peripheral surface of the top cylindrical end portion  36 . Also, in a seventh modification as shown in  FIG. 13 , a base portion  160  is formed at a mid-point of the bottom cylindrical end portion  18  of the secondary spool  14 . A peripheral wall portion  168  of a high voltage terminal  165  is held by the top cylindrical end portion  36  of the spring case  35 . On a base wall portion  166  of the high voltage terminal  165 , a projection  167 , which projects downward, is formed integrally. An open end  169  contacts the inner peripheral surface of the top cylindrical end portion  36 . 
   The first to seventh modifications achieve the same effect as the second embodiment. 
   (Third Embodiment) 
   A third embodiment of the present invention will be described with reference to the accompanying drawings. Similar components of a stick ignition coil apparatus of the present embodiment, which are similar to the components of the stick ignition coil apparatus of the first embodiment, will be indicated by the same numerals. 
   In the third embodiment as shown in  FIG. 14 , the open end of the outer peripheral wall portion of the high voltage terminal is encircled by a bottom end of the secondary spool and a top end of the spring case. In other words, the dielectric resin around the open end is closed by the bottom end of the secondary spool and the top end of the spring case. This means that an outer diameter of a bottom half portion  170  of the bottom cylindrical end portion  18 , which is included in the distal projecting portion of the secondary spool  14 , of the secondary spool  14  is smaller than an outer diameter of a top half portion  171  of the bottom cylindrical end portion  18 . Thus, an annular step portion  173  is formed therebetween. 
   A peripheral wall portion  178  of a high voltage terminal  175  is engaged with an outer peripheral surface of the bottom half portion  171 , and also is engaged with the top cylindrical end portion  36  of the spring case  35 . An open end  179  of the peripheral wall portion  178  is located slightly away from the step portion  173 . A projection  177  of a base wall portion  176  is projected into the cavity of the bottom cylindrical end portion  18 . The top cylindrical end portion  36  of the spring case  35  is engaged with an outer peripheral surface of the peripheral wall portion  178 . A top end of the top cylindrical end portion  36  contacts the step portion  173 . 
   In the third embodiment, the open end  179  and the second dielectric resin  72  therearound are encircled by the bottom half of the bottom cylindrical end portion  18 , the step portion  173  and the top cylindrical end portion  36 . Therefore, the crack, which starts from outer and inner edges of the open end  179 , is limited from being generated. 
   In a modification of the third embodiment as shown in  FIG. 15 , there is a space (no contact) between the step portion  173  of the bottom cylindrical end portion  18  of the secondary spool  14  and the top cylindrical end portion  36  of the spring case  35 . An open end  183  of a peripheral wall portion  182  of a high voltage terminal  180  contacts the step portion  173 . The top cylindrical end portion  36  of the spring case  35  is engaged with an outer peripheral surface of the peripheral wall portion  182 . 
   (Fourth Embodiment) 
   A fourth embodiment of the present invention will be described with reference to the accompanying drawings. Similar components of a stick ignition coil apparatus of the present embodiment, which are similar to the components of the stick ignition coil apparatus of the first embodiment, will be indicated by the same numerals. 
   The fourth embodiment is described in  FIG. 16 . In the present embodiment, the high voltage terminal includes a first terminal element, which is shaped into a tubular form, and an annular second terminal element. An opening of the first terminal element faces downward. Specifically, at a bottom side of the bottom cylindrical end portion  18 , which is included in the distal projecting portion of the secondary spool  14 , of the secondary spool  14 , a circulation hole  200  for epoxy resin is formed in the radial direction. The first terminal element  202  includes a base wall portion  203  and a peripheral wall portion  205 . At a center of the base wall portion  203 , a projection  204  is projected in an opposite direction from the extending direction of the peripheral wall portion  205 . 
   An outer peripheral surface of the projection  204  is loosely engaged with an inner peripheral surface of the bottom cylindrical end portion  18 . An outer peripheral surface of the peripheral wall portion  205  is engaged with the top cylindrical end portion  36  of the spring case  35 . The annular second terminal element  208  lies between a base wall portion  203  and a bottom end of the bottom cylindrical end portion  18 . An inner diameter of the annular second terminal element  208  is slightly larger than an outer diameter of the projection  204 . Also, an outer diameter of the annular second terminal element  208  is slightly smaller than the outer diameter of the peripheral wall portion  205 . 
   The bottom end of the bottom cylindrical end portion  18  contacts a top surface of the second terminal element  208 . Therefore, the epoxy resin does not circulate between an inside and an outside of the secondary spool  14 . Thus, the epoxy resin circulates through the circulation hole  200 . 
   In the fourth embodiment, an opening of the peripheral wall portion  205  of the first terminal element  202 , which is shaped into a tubular form, faces downward. Thus, around an open end  206 , the dielectric resin  72  does not exist substantially. Therefore, the crack, which starts from an edge of the open end  206 , is not likely to be generated. Also, an outer rim of the second terminal element  208  contacts the base wall portion  203  of the first terminal element  202 . Thus, the crack is not likely to be generated in the second dielectric resin  72  therearound. 
   Modifications of the fourth embodiment will be described. In a first modification of the fourth embodiment, the circulation hole  200 , which is formed in the bottom cylindrical end portion  18  of the secondary spool  14 , may be alternatively located in an upper side of a middle part of the bottom cylindrical end portion  18 . Therefore, the circulation hole  200  may be alternatively located in an upper side than a top end of the projection  204 . 
   In a second modification as shown in  FIG. 17 , a circulation hole  215  is formed in the bottom side of the bottom cylindrical end portion  18  of the secondary spool  14 . At a center of a base wall portion  218  of a first terminal element  217 , a projection  221  is projected in the same direction as an extending direction of a peripheral wall portion  219  (downward in  FIG. 17 ). The peripheral wall portion  219  is engaged with the top cylindrical end portion  36  of the spring case  35 . In a third modification as shown in  FIG. 18 , the secondary spool  14  includes a base portion  225  at a bottom end of the bottom cylindrical end portion  18 . A circulation hole  226  is formed in the base portion  225  in a radial direction. A first terminal element  230  includes a peripheral wall portion  233  and a base wall portion  231 , which is equipped with a low projection  232 , which projects downward. 
   In a fourth modification as shown in  FIG. 19 , the secondary spool  14  includes a base wall portion  235  at an upper side of a bottom end of the bottom cylindrical end portion  18 . Bellow the base wall portion  235 A, a cavity  236  of the bottom cylindrical end portion  18  is formed. A circulation hole  237  is formed in a radial direction near the bottom end of the bottom cylindrical end portion  18 . A first terminal element  240  includes a base wall portion  241  and a peripheral wall portion  243 , which is engaged with the top cylindrical end portion  36  of the spring case  35 . A second terminal element  244  lies between the base wall portion  241  and a bottom end of the bottom cylindrical end portion  18 . 
   In a fifth modification as shown in  FIG. 20 , a circulation hole  246  is formed in a radial direction at a flange portion  245 , which is formed at a bottom end of the bottom cylindrical end portion  18  of the secondary spool  14 . A peripheral wall portion  253  of a first terminal element  250  is engaged with the top cylindrical end portion  36  of the spring case  35 . An outer diameter of a second terminal element  255  is smaller than an outer diameter of a base wall portion  251  of the first terminal element  250 . An outer rim of the second terminal element  255  is encircled by the flange portion  245  of the secondary spool  14 . 
   In a sixth modification as shown in  FIG. 21 , a sleeve  260  is engaged with an outer peripheral surface of the bottom cylindrical end portion  18  of the secondary spool  14 . A top end of the sleeve  260  contacts the step portion  173  and the bottom end of the sleeve  260  is leveled with the bottom cylindrical end portion  18 . A circulation hole  262  is formed in the bottom cylindrical end portion  18  and the sleeve  260 . A second terminal element  265  lies between a first terminal element  263  and the sleeve  260 . An outer diameter of the second terminal element  265  is selected in a rage between outer diameters of the bottom cylindrical end portion  18  and the sleeve  260 . A top edge of an outer rim of the second terminal element contacts the sleeve  260 , and a bottom edge of the outer rim of the second terminal element contacts a base wall portion  264 . 
   In a seventh modification as shown in  FIG. 22 , a circulation hole  278  is formed in the bottom end of the bottom cylindrical end portion  18  of the secondary spool  14 . A peripheral wall portion  273  of a first terminal element  270  is engaged with the top cylindrical end portion  36  of the spring case  35 . The top cylindrical end portion  36  extends upward further than a second terminal element  275 . The second terminal element  275  lies between a bottom end of the bottom cylindrical end portion  18  and a base wall portion  271 . A bottom edge of an outer rim of the second terminal element  275  contacts the base wall portion  271 , and a top edge of the outer rim of the second terminal element  275  is located adjacent to a top end of the top cylindrical end portion  36 : 
   The first to seventh modifications achieve the same effect as the fourth embodiment. 
   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.