Patent Publication Number: US-9897064-B2

Title: Ignition coil for internal combustion engine

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
     The present application claims the benefit of priority of Japanese Patent Application No. 2012-101260 filed on Apr. 26, 2012, the disclosure of which is totally incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This disclosure relates generally to an ignition coil working to produce an electric spark in a spark plug for use in internal combustion engines. 
     2. Background Art 
     Typical ignition coils for spark plugs installed in internal combustion engines are equipped with a high-voltage connector terminal which connects at an end thereof with a trailing end of a winding of a secondary coil and is placed in elastic abutment with a high-voltage output terminal disposed in a lower portion of a holder casing. An electric circuit, which extends from the trailing end of the secondary coil, to the high-voltage connector terminal, to the high-voltage output terminal, and to the spark plug, works to apply the high voltage to the spark plug. 
     Japanese Patent First Publication No. 2004-207582 discloses the above types of high-voltage connector terminal and high-voltage output terminal of the ignition coil. In order to ensure the stability in elastic contact between the high-voltage connector terminal and the high-voltage output terminal, the high-voltage output terminal has irregularities formed on an end surface thereof. Specifically, the irregularities increase an area of contact between the high-voltage connector terminal and the high-voltage output terminal to enhance the stability in elastic contact therebetween. 
     The above structure of the high-voltage output terminal, however, faces the drawback in that rubbing of the high-voltage connect terminal against the irregularities on the high-voltage output terminal facilitate ease of wear of the irregularities, which may lead to adhesion of foreign objects thereto, that is, contamination of surfaces of contact between the high-voltage connector terminal and the high-voltage output terminal. Such contamination results in instability of electric contact between the high-voltage connector terminal and the high-voltage output terminal and also accelerates the wear of them. The foreign objects may also be adhered to the secondary coil, thus resulting in a decrease in resistance thereof to voltage and degradation in reliability of operation of the ignition coil. Further, when the high-voltage connector terminal is disposed at an inclined orientation on the high-voltage output terminal during assembling processes of the ignition coil, it may cause the top of the high-voltage connector terminal to get stuck to the surface of the high-voltage output terminal, so that the high-voltage connector terminal may deform, which leads to damage to a bobbin of the secondary coil by which the high-voltage connector terminal is retained or lack in pressure required to ensure the stability in contact between the high-voltage connector terminal and the high-voltage output terminal. 
     SUMMARY 
     It is therefore an object to provide an improved structure of an ignition coil for use in an internal combustion engine which is designed to minimize the contamination of a high-voltage connector terminal and ensure stability in contact between the high-voltage connector and a high-voltage output terminal. 
     According to one aspect of an embodiment, there is provided an ignition coil for an internal combustion engine which comprises: (a) a coil unit equipped with a primary coil, a secondary coil which works to develop a high voltage as a function of an electric current flowing in the primary coil, and a high-voltage connector terminal which electrically connects with the secondary coil and is elastically deformable; (b) a high-voltage output terminal placed in contact with the high-voltage connector terminal for applying the high voltage, as developed by the secondary coil, to a spark plug installed in an internal combustion engine; (c) a holder casing in which the coil unit is disposed, the holder casing having a portion of the high-voltage output terminal exposed externally; and (d) a resinous insulator disposed in the holder casing to cover and fix the coil unit within the holder casing. 
     The high-voltage connector terminal has a first end and a second end opposite the first end, the high-voltage connector terminal including a connecting portion end which electrically connects at the first end with the secondary coil, a tip portion which is placed at the second end in contact with the high-voltage output terminal, and an arm portion which connects the connecting portion and the tip portion together. The tip portion has a rounded surface which is placed in contact with the high-voltage output terminal. 
     The rounded surface of the tip portion minimizes the wear of surfaces of contact between the high-voltage connector terminal and the high-voltage output terminal which arises from the rubbing therebetween, thus avoiding the adhesion of foreign objects to the contact surfaces. In other words, the tip portion of the high-voltage connector terminal does not have irregularities, that is, has a curved even surface to be placed in contact with the high-voltage output terminal, thus not exerting uneven pressure on the high-voltage connector terminal in a radial direction of the high-voltage output terminal and ensuring the stability in pressure required to achieve electric contact between the high-voltage connector terminal and the high-voltage output terminal. 
     The minimization of the adhesion of foreign objects to the surfaces of contact between the high-voltage connector terminal and the high-voltage output terminal avoids unwanted development of sparks upon application of high voltage to the spark plug. 
     Further, when the high-voltage connector terminal is disposed at an inclined orientation on the high-voltage output terminal during assembling processes of the ignition coil, the structure of the ignition coil does not cause the tip portion of the high-voltage connector terminal to get stuck with the surface of the high-voltage output terminal and avoids exertion of uneven load on the high-voltage connector terminal which would lead to undesired deformation thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only. 
       In the drawings: 
         FIG. 1  is a longitudinal sectional view which illustrates an ignition coil of the first embodiment; 
         FIG. 2  is a plan view which illustrates a high-voltage connector terminal disposed in the ignition coil of  FIG. 1 ; 
         FIG. 3  is a partially enlarged longitudinal sectional view which illustrates an electric and elastic contact between a high-voltage connector terminal and a high-voltage output terminal in the ignition coil of  FIG. 1 ; 
         FIG. 4  is a partially side view, as viewed from an arrow A in  FIG. 3 , which illustrates the case where a coil unit is disposed at an inclined orientation in a holder casing; 
         FIG. 5  is a sectional view which illustrates a high-voltage connector terminal according to the second embodiment; 
         FIG. 6( a )  is a partially plan view which illustrates a high-voltage connector terminal of the third embodiment; 
         FIG. 6( b )  is a side view of  FIG. 6( a ) ; 
         FIG. 7( a )  is a partially plan view which illustrates a high-voltage connector terminal of the fourth embodiment; 
         FIG. 7( b )  is a side view of  FIG. 7( a ) ; 
         FIG. 8( a )  is a partially sectional view which illustrates a modified form of a combination of a high-voltage connector terminal and a high-voltage output terminal; and 
         FIG. 8( b )  is a partially sectional view which illustrates the high-voltage connector terminal and the high-voltage output terminal of  FIG. 8( a )  before they are placed in contact with each other. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to  FIG. 1 , there is shown an ignition coil equipped with a high-voltage connector terminal  80  according to the first embodiment. The ignition coil is electrically connected to a spark plug  100  mounted in an internal combustion engine. 
     The ignition coil also includes a holder casing  10 , a coil unit  1 , a high-voltage output terminal  90 , and a resinous insulator  70 . The holder casing  10  is made of resin and has a greater opening and a smaller opening. The greater opening is formed in one of opposed ends of the holder casing  10  (i.e., an upper end, as viewed in  FIG. 1 ). The smaller opening is formed in the other end of the holder casing  10 . The coil unit  1  is disposed inside the holder casing  10 . The coil unit  1  consists essentially of a center core  20 , a primary coil  2 , a secondary coil  3 , an outer core  21 , the high-voltage connector terminal  80 , and an igniter  60 . The high-voltage output terminal  90  is connected electrically to the spark plug  100  through a conductor  101 . The coil unit  1  is covered with the resinous insulator  70  and fixed by the resinous insulator  70  firmly within the holder casing  10 . The primary coil  2  of the coil unit  1  is supplied with electric current from an external power source. The igniter  60  controls the current to be fed to the primary coil  2  to develop a high-voltage at the secondary coil  3 . The high-voltage at the secondary coil  3  is then applied to the high-voltage output terminal  90  through the high-voltage connector terminal  80  and to the spark plug  100  through the high-voltage output terminal  90  and the conductor  101 . 
     The coil unit  1  is, as described above, equipped with the primary coil  2 , the secondary coil  3 , the center core  20 , the outer core  21 , and the high-voltage connector terminal  80 . The primary coil  2  is made of a primary winding  30  wound around the center core  20 . The secondary coil  3  is made of a secondary winding  31  wound around a bobbin  40  and disposed around the outer periphery of the primary coil  2 . The center core  20 , the primary coil  2  and the secondary coil  3  are installed within the outer core  21 . The high-voltage connector terminal  80  is connected electrically to a trailing portion of the secondary winding  31  of the secondary coil  3 . The trailing portion of the secondary winding  31  is a portion thereof which has been wound last around the bobbin  40 . 
     The center core  20  is of a substantially hollow cylindrical shape and made by pressing soft magnetic powder consisting of, for example, iron, cobalt, and/or nickel. The primary winding  30  is electric wire which is made by baking insulating paint on conductive material such as copper. 
     The bobbin  40  is made of a resinous hollow cylinder. The secondary winding  31  is electric wire which is made by baking insulating paint on conductive material such as copper. The secondary coil  3  is disposed around the outer periphery of the primary coil  2  coaxially therewith. The secondary winding  31  of the secondary coil  3  is different in diameter of wire from the primary winding  30  of the primary coil  2 . Specifically, the diameter of the secondary winding  31  is smaller than that of the primary winding  30 . The number of turns of the secondary winding  31  is greater than that of the primary winding  30 . 
     The outer core  21  serves to form a magnetic circuit along with the center core  20 . The outer core  21  is of a substantially hollow cubic or rectangular prism shape made by pressing soft magnetic powder. The outer core  21  is a rectangular cuboid with an axis which extends perpendicular to the length or axis of the center core  20  and passes through an upper opening  11  and a bottom  12  of the holder casing  10 .  FIG. 1  illustrates only two of four side faces of the outer core  21  which face each other in the axial direction of the center core  20  for the brevity of illustration. One of such two faces of the outer core  21  is, as clearly illustrated in  FIG. 1 , placed in contact with the inner surface of the center core  20 , while the other face is placed away from the inner surface of the center core  20  through an air gap. With the air gap, a permanent magnet  211  is disposed so as to face an axial end face  201  of the center core  20  in order to enhance magnetic properties of the coil unit  1 . 
     The high-voltage connector terminal  80  is formed by elastically deformable conductor made of, for example, phosphor bronze in the form of a plate. The high-voltage connector terminal  80  is fit or retained in the bobbin  40  of the coil unit  1  and connects electrically with the secondary coil  3 . The use of phosphor bronze facilitates ease with which the high-voltage connector terminal  80  is welded to the secondary winding  31  and also increases the strength of such a weld. 
       FIG. 2  illustrates the high-voltage connector terminal  80  before installed in the coil unit  1 . The high-voltage connector terminal  80  is of a substantially T-shape and includes a connecting portion  83  which is to be joined electrically to the secondary coil  3 , a tip portion  82  which is to be placed in electric contact with the high-voltage output terminal  90  and an arm portion  81  which is in the form of a plate and connects between the tip portion  82  and the connecting portion  83 . The tip portion  82  has a spherical surface to be placed in contact with the high-voltage output terminal  90 . Specifically, the tip portion  82  includes a hollow hemispherical head  82   a  which bulges toward the high-voltage output terminal  90  to have a bowl-shaped recess facing away from the high-voltage output terminal  90 . The maximum outer diameter D 1  of the hemispherical head  82   a  is greater than the width d 1  of the arm portion  81 . The width d 1  is a dimension of the arm portion  81  in a direction perpendicular to the length-wise direction and the thickness-wise direction of the arm portion  81 . 
     The connecting portion  83  includes a holder portion  83   b , a wire-winding portion  83   a , and a connecting arm portion  83   c . The holder portion  83   b  is fit in the bobbin  40  to retain or hold the high-voltage connector terminal  80  on the bobbin  40 . The wire-winding portion  83   a  has the secondary winding  31  wound thereon to establish an electric joint between the high-voltage connector terminal  80  and the secondary coil  31 . The connecting arm portion  83   c  extends perpendicular to the arm portion  81 . Specifically, the holder portion  83   b  has a hole formed therein. The bobbin  40  has a protrusion such as a pin. The protrusion of the bobbin  40  is fit in the hole of the holder portion  83   b , thereby retaining the high-voltage connector terminal  80  on the bobbin  40 . Additionally, the connecting arm portion  83   c  is, as illustrated in  FIG. 3 , grasped firmly by a first bobbin fixing portion  41  and a second bobbin fixing portion  42  shown in  FIG. 4  to secure the high-voltage connector terminal  80  to the bobbin  40 . 
     The resinous insulator  70  is made of thermosetting resin such as epoxy resin. The formation of the resinous insulator  70  is achieved by pouring the thermosetting resin into the holder casing  10  from the upper opening  11  so as to cover or electrically insulate components such as the coil unit  1 , etc. completely without any air gap then heating it to fix the components within the holder casing  10 . 
     The holder casing  10  is substantially cuboid made of a thermoplastic resin such as polybutylene therephthalate (PBT). The holder casing  10  also includes a plug shell  14 , a bottom  12 , and the upper opening  11  facing the bottom  12  in a vertical direction of the holder casing  10 . The bottom  12  has a hollow cylindrical lower extension  13  facing downwardly, as viewed in  FIG. 1 . The plug shell  14  has disposed therein a plurality of plug terminals  61  and serves as a pin connector. The plug terminals  61  are made of pins and extend within the plug shell  14 . The plug terminals  61  are to be connected to an external connector to achieve an electric joint of the coil unit  1  to an ignition control device and a power supply. In the lower extension  13  of the bottom  12  of the holder casing  10 , the high-voltage output terminal  90  is fit in electric contact with the high-voltage connector terminal  80 . The lower extension  13  has formed on an outer periphery thereof a barbed protrusion  15  which achieves a snap-fit joint to an elastic cylinder (e.g., a plug cap) of the spark plug  100 . 
     The high-voltage output terminal  90  is plugged into the lower extension  13  in order to avoid the entrance of the thermosetting resin into the extension  13  when it is put in the holder casing  10  to form the resinous insulator  70 . Specifically, the high-voltage output terminal  90  partially protrudes inside the holder casing  10  toward the upper opening  11 , so that the upper end surface  91  and a portion of a peripheral side surface thereof are covered with the resinous insulator  70 , while the lower end surface  92  is exposed to the atmosphere within the lower extension  13 . 
     The high-voltage output terminal  90  connects electrically at the lower end surface  92  with the spark plug  100  through a spiral conductor  101 . The spiral conductor  101  is made of metal and wound at an end thereof on the spark plug  100  and placed at the other end in abutment with the lower end surface  92  of the high-voltage output terminal  90 . The high-voltage output terminal  90  works to apply high-voltage, as created by the ignition coil, to the spark plug  100 . 
     The igniter  60  is coupled electrically with the ignition control device of an external engine control system (not shown) through the plug terminals  61 . The igniter  60  works to control the application of electric current, as delivered from the power supply, to the primary coil  2  in response to an ignition signal outputted from the ignition control device. The igniter  60  includes a circuit board on which switching devices, such as insulated gate bipolar transistors, are fabricated and which is disposed within an insulating resin-made mold. 
     The operation and beneficial effects of the high-voltage connector terminal  80  of the ignition coil will be described below. 
     In the assembling process of the ignition coil, when the coil unit  1  is put into the holder casing  10  from the upper opening  11 , the tip portion  82  of the high-voltage connector terminal  80  first makes contact with the high-voltage output terminal  90 . In the initial stage where the tip portion  82  is just placed on the upper end surface  91  of the high-voltage output terminal  90 , the high-voltage connector terminal  80  does not yet deform elastically and contacts at the hemispherical head  82   a  of the tip portion  82  with a portion of the upper end surface  91  of the high-voltage output terminal  90  which is out of alignment with the longitudinal center line (i.e., the axis) of the high-voltage output terminal  90 . The initial stage is when the hemispherical head  82   a  of the high-voltage output terminal  80  makes contact with the upper end surface  91  of the high-voltage output terminal  90  before pressing the upper end surface  91 . 
     Subsequently, when the coil unit  1  is put more deeply in the holder casing  10 , pressure is exerted on both the high-voltage connector terminal  80  and the high-voltage output terminal  90  in the longitudinal direction of the high-voltage output terminal  90 . This will cause the joint  84  between the arm portion  81  and the connecting portion  83  to be, as can be seen in  FIG. 1 , bent so that the arm portion  81  is laid substantially parallel to the upper end surface  91  of the high-voltage output terminal  90 . During the bending of the joint  84 , the hemispherical head  82   a  of the tip portion  82  of the high-voltage connector terminal  80  is subjected to pressure in the longitudinal direction of the high-voltage output terminal  90  (i.e., a direction perpendicular to the length of the center core  20 ) and slides on the upper end surface  91  toward the center of the upper end surface  91  while exerting almost no pressure on the upper end surface  91  in a radial direction thereof. This minimizes the wear of the tip end portion  82  and the upper end surface  91  due to physical friction therebetween, thus avoiding the adhesion of foreign objects to the hemispherical head  82   a  or the upper end surface  91 . 
     The entry of foreign objects into between the high-voltage connector terminal  80  and the high-voltage output terminal  90  will result in a drop in resistance of, for example, the secondary coil  3  to voltage due to the adhesion of the foreign objects thereto and the wear of the high-voltage connector terminal  80  and the high-voltage output terminal  90  as well as the instability of contact between the high-voltage connector terminal  80  and the high-voltage output terminal  90 . The wear of the terminals may break the electrical communication between the high-voltage connector terminal  80  and the high-voltage output terminal  90 , which results in a failure in operation of the ignition coil and a drop in reliability thereof. 
       FIG. 4  is an illustration of the coil unit  1  and the high-voltage output terminal  90 , as viewed from an arrow A in  FIG. 3 , in the case where the high-voltage connector terminal  80  is put in the holder casing  10  at an inclined orientation due to a variation in dimension of the components of the ignition coil or an error in assembling thereof. When the coil unit  1  is put deeply in the holder casing  10  after the high-voltage connector terminal  80  touches the upper end surface  91  of the high-voltage output terminal  90 , it will result in concern that the tip portion  82  may get stuck with the upper end surface  91 , thus causing the high-voltage connector terminal  80  to experience uneven pressure, so that it deforms undesirably, which leads to damage to the bobbin  40  or lack in pressure required to ensure the stability in contact between the high-voltage connector terminal  80  and the high-voltage output terminal  90 . However, the hemispherical head  82   a  of the high-voltage connector terminal  80  has a rounded or domed surface, thus establishing smooth sliding of the tip portion  82  of the high-voltage connector terminal  80  on the upper end surface  91  of the high-voltage output terminal  90  and ensuring the stability in contact between the tip portion  82  and the upper end surface  91 . 
     The maximum outer diameter D 1  of the hemispherical head  82   a  of the high-voltage connector terminal  80  is, as descried above, set greater than the width d 1  of the arm portion  81 . This causes the hemispherical head  82   a  to touch the upper end surface  91  of the high-voltage output terminal  90  earlier than when either of side edges of the arm portion  81  touches the high-voltage output terminal  90  in the case where the coil unit  1  is disposed in the holder casing  10  at an inclined orientation, thus ensuring the stability of contact between the high-voltage connector terminal  80  and the high-voltage output terminal  90  and reliability in operation of the ignition coil. 
     The hemispherical head  82   a  of the high-voltage connector terminal  80 , as described above, has the bowl-shaped recess or cavity facing in a direction opposite the high-voltage output terminal  90 . In other words, the hemispherical head  82   a  is of a cup-shape with a given thickness. The formation of the resinous insulator  70  is achieved by pouring the thermosetting resin into the holder casing  10  from the upper opening  11 , so that the cavity of the hemispherical head  82   a  is filled with the thermosetting resin fully. This results in an increase in contact area of the resinous insulator  70  with the high-voltage connector terminal  80 , which minimizes positional misalignment of the high-voltage connector terminal  80 . The formation of the high-voltage connector terminal  80  is also achieved easily by plastically deforming or pressing a plate because the hemispherical head  82   a  is simply rounded. 
       FIG. 5  illustrates the high-voltage connector terminal  80  of the second embodiment. The hemispherical head  82   a  of the tip portion  82  ha a flange  82   c  extending from a portion or the whole of a circumferential edge  82   b  which does not directly connect with the arm portion  81 . The flange  82   c  may be formed using a flange remaining on the tip portion  82  after a plate is plastically deformed or extruded to make the high-voltage connector terminal  80 . It is preferable that the flange  82   c  is geometrically shaped or formed to occupy a portion of the circumference of the hemispherical head  82   a  so as not to touch the upper end surface  91  of the high-voltage output terminal  90  earlier than the outer surface of the hemispherical head  82   a.    
       FIGS. 6( a ) and 6( b )  illustrate the high-voltage connector terminal  80  of the third embodiment. The high-voltage connector terminal  80  is so shaped that the width d 2  of the arm portion  81  is greater than the maximum diameter D 2  of the hemispherical head  82   a . The hemispherical head  82   a  has, as clearly illustrated in  FIG. 6( a ) , a rectangular flange  82   d  formed therearound. The width of the top end portion  82  is identical with the width d 2  of the arm portion  83 . It is, like in the second embodiment, preferable that the flange  82   d  is geometrically shaped so as not to touch the upper end surface  91  of the high-voltage output terminal  90  earlier than the outer surface of the hemispherical head  82   a . The structure of the high-voltage connector terminal  80  also minimizes the damage to the high-voltage connector terminal  80  and the high-voltage output terminal  90  when the electric contact therebetween is made. 
       FIGS. 7( a ) and 7( b )  illustrate the high-voltage connector terminal  80  of the fourth embodiment. The tip portion  82  of the high-voltage connector terminal  80  is, as can be seen in the drawing, shaped to be spherical. The arm portion  81  is made in the shape of a bar. The tip portion  82 , like in the above embodiments, has a rounded outer surface to be placed in contact with the upper end surface  91  of the high-voltage output terminal  90 , thus minimizing the damage to the high-voltage connector terminal  80  and the high-voltage output terminal  90  when the electric contact therebetween is made. 
     Modifications 
     The high-voltage output terminal  90  may be, as illustrated in  FIG. 8( a ) , designed to have a rounded or domed recess  91   a  with which the tip portion  82  of the high-voltage connector terminal  80  is to be placed in contact. In other words, the electrical contact is made between the rounded surfaces of the high-voltage connector terminal  80  and the high-voltage output terminal  90 . This further minimizes the damage to the high-voltage connector terminal  80  and the high-voltage output terminal  90  and the adhesion of foreign objects to the tip portion  82  and the upper end surface  91 . The diameter R 2  of the domed recess  91   a  in the upper end surface  91  is, as illustrated in  FIG. 8( b ) , preferably greater than or equal to the diameter R 1  of the tip portion  82  of the high-voltage connector terminal  80  (i.e., an outer diameter of the hemispherical head  82   a ). This achieves smooth contact between the rounded outer surface of the tip portion  82  of the high-voltage connector terminal  80  and the domed recess  91   a  in the upper end surface  91  of the high-voltage output terminal  90  when the coil unit  1  is put in the holder casing  10 , and the tip portion  82  slides on the upper end surface  91  in the radial direction of the high-voltage output terminal  90 , thus enhancing the reliability of electrical contact between the high-voltage connector terminal  80  and the high-voltage output terminal  90 . 
     While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims. 
     The tip portion  82  of the high-voltage connector terminal  80  of the first embodiment is hemispherical, but may be shaped to have a curved or rounded surface to be placed in direct contact with the upper end surface  91  of the high-voltage output terminal  90 . For example, approximately one-fourth of the surface of the tip portion  82  that is an outer area of the tip portion  92  may be rounded, which will continue to contact with the upper end surface  91  of the high-voltage output terminal  90  for a period of time between when the coil unit  1  is put in the holder casing  10 , and when the tip portion  82  first touches the top end surface  91  and when the tip portion  82  finishes sliding on the top end surface  9 . Alternatively, more than half the outer surface of the tip portion  82  may be rounded or spherical. 
     In the first embodiment, the coil unit  1  is put in the holder casing  10  from the upper opening  11 , but may alternatively be disposed inside the holder casing  10  from the side thereof before the plug shell  14  is attached to the holder casing  10 . Specifically, the coil unit  1  is put in the holder casing  10 . The tip portion  82  of the high-voltage connector terminal  80  then touches the upper end surface  91  of the high-voltage output terminal  90 . The coil unit  1  is pushed deeply in the holder casing  10 , so that the rounded outer surface of the tip portion  82  smoothly slides on the upper end surface  91 . The connecting portion  84  of the high-voltage connector terminal  80  is bent to right angles, as illustrated in  FIG. 1 , to make an electric communication between the high-voltage connector terminal  80  and the high-voltage output terminal  90  without exerting uneven pressure on the high-voltage connector terminal  80  in the radial direction of the high-voltage output terminal  90 .