JP2008277536A - Ignition coil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition coil in a dual ignition system without causing any deviation in output balance by a difference in stray capacity on wiring for connecting a secondary output terminal and an ignition plug. <P>SOLUTION: The ignition coil in the dual ignition system has a secondary coil 27a directly connected to an ignition plug, and a secondary coil 27b connected to the other ignition plug in the same cylinder via a high-tension cord. In this case, a center 19a in the winding width of a primary coil 19 is shifted to the side of the secondary coil 27b connected to the other ignition plug in the same cylinder via the high-tension cord by a prescribed width W to a middle tap 17 that is the center of the winding width of a secondary coil 27, a coil connection coefficient at the side of the secondary coil 27b is set larger than that at the side of the secondary coil 27a, and a decrease in output which is caused by an increase in the stray capacity by the high-tension cord is offset, thus balancing outputs in two primary coils. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dual ignition type ignition coil applied to a cylinder having two ignition plugs, and more particularly, to the same cylinder through an output terminal and a high tension cord that are mounted in an engine plug hole and directly connected to the ignition plug. The present invention relates to an ignition coil having an output terminal connected to another spark plug.

  In an internal combustion engine such as an automobile engine, for example, an ignition coil and a spark plug are applied as a detonator for burning gasoline as fuel.

  As the ignition coil, for example, a dual ignition type ignition coil applied to a cylinder having two ignition plugs is known.

  For example, Patent Literature 1 and Patent Literature 2 may be cited as prior art documents relating to a dual ignition type ignition coil or a diagnostic device thereof.

Conventionally, in the ignition coil of the dual ignition system, since the mainstream is that the two output terminals are directly connected to the adjacent spark plug in the same cylinder, the deviation of the output balance between the two output terminals becomes a problem There were few.
Japanese Patent Publication No. 63-28238 Japanese Patent Publication No.51-38046

  However, the output of the two secondary output terminals may be shifted due to the difference in the arrangement position of the ignition coil. In some cases, one secondary output terminal is directly connected to the spark plug, and the other secondary output terminal is connected to another spark plug in the same cylinder via a high tension cord. However, there is a problem that the output balance is easily shifted due to the difference in the stray capacitance on the wiring from the secondary output terminal to the spark plug.

  An object of the present invention is to provide an ignition that can achieve output balance by eliminating a deviation in output balance caused by a difference in stray capacitance between wirings connecting a secondary output terminal and a spark plug in a dual ignition type ignition coil. To provide a coil.

  In order to achieve the above object, an ignition coil according to claim 1 is a coil in which a core that forms a magnetic path is inserted in a central space of a coil pair having a primary coil and a secondary coil arranged concentrically. In a dual ignition type ignition coil in which an assembly is housed in a coil case and filled with an insulating resin between constituent members, the secondary coils are wound in opposite directions with respect to the center of the winding width. The coil comprises two (reversely wound) coils, and the center of the winding width of the primary coil with respect to the center of the winding width of the secondary coil is shifted by a predetermined width to balance the outputs of the two secondary coils. And

  The ignition coil according to claim 2 is the ignition coil according to claim 1, wherein the output end of one of the two secondary coils is directly connected to the spark plug, and the other secondary coil. The output end of the coil is connected to another spark plug in the same cylinder through a high tension cord, and the center of the winding width of the primary coil is the other in the same cylinder through the high tension cord. The secondary coil connected to the ignition coil is shifted by a predetermined width.

  The ignition coil according to claim 3 is the ignition coil according to claim 1 or 2, wherein the deviation width is 1.5 to 3.0 mm.

  The ignition coil according to claim 4 is the ignition coil according to any one of claims 1 to 3, wherein a terminal is provided at the center of the winding width of the secondary coil, and the terminal is a positive electrode of the battery. It is connected to the side or ground.

  The ignition coil according to claim 5 is the ignition coil according to claim 4, wherein the terminal at the center of the winding width of the secondary coil is connected to the anode of the diode, and the cathode of the diode is connected to the positive electrode side of the battery or to the ground. It is what is connected.

  The ignition coil according to claim 6 is the ignition coil according to any one of claims 1 to 5, wherein the core forms a closed magnetic circuit having a center core and a side core, and the center core is The coil pair is fitted into the center space.

  According to the ignition coil of the first aspect, since the winding width center of the primary coil with respect to the winding width center of the secondary coil composed of two coils is shifted by a predetermined width, the center of the winding width of the primary coil is, for example, By displacing the secondary coil to the secondary coil connected to the wiring with a large stray capacitance among the two secondary coils, the coupling coefficient between this secondary coil and the primary coil is the coupling between the other secondary coil and the primary coil. Thus, the potential difference at the connection point between the two secondary coils and the spark plug due to the difference in stray capacitance can be eliminated to balance the output.

  According to the ignition coil of the second aspect, in the ignition coil having a secondary coil directly connected to the ignition plug and a secondary coil connected to another ignition plug through a high tension cord, the primary coil is wound. Since the center of the width is shifted by a predetermined width toward the secondary coil connected to the spark plug via the high tension cord, the coupling coefficient between the secondary coil and the primary coil is directly connected to the spark plug. It becomes larger than the coupling coefficient between the secondary coil and the primary coil, thereby making it possible to balance the two secondary outputs by compensating for the output decrease due to the stray capacitance of the high tension cord.

  According to the ignition coil of the third aspect, since the deviation width is set to 1.5 to 3.0 mm, the output is increased by the output corresponding to the output necessary for recovering the output decrease due to the difference in the stray capacitance. Since the coil coupling coefficient can be set to, the two secondary outputs can be well balanced.

  According to the ignition coil of the fourth aspect, since the terminal at the center of the winding width of the secondary coil is connected to the positive electrode side of the battery or the ground, the center of the secondary coil is added to the effect of the invention described above. Thus, a stable secondary output can be obtained by reliably maintaining the potential at a low potential.

  According to the ignition coil of the fifth aspect, since the terminal at the center of the winding width of the secondary coil is connected to the anode of the diode and the cathode of the diode is connected to the positive electrode side of the battery or the ground, In addition to the effects of the invention, when the primary coil is switched, it is possible to prevent the spark plug from being discharged due to the rise of the on-current that first flows through the primary coil.

  According to the ignition coil of the sixth aspect, since the core forms a closed magnetic path having a center core and a side core, and the center core is inserted into the central space of the coil pair, in addition to the effects of the above invention The secondary output can be prevented from decreasing when the stray capacitance increases and the output decreases.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an assembly diagram of an ignition coil for an internal combustion engine according to an embodiment of the present invention.

  In FIG. 1, the ignition coil is a dual ignition type ignition coil having two secondary output terminals, and includes a housing 1 as a coil case, and a coil assembly 10 fitted into the housing 1. Is mainly composed of

  The coil assembly 10 has a substantially cylindrical primary coil bobbin 11 around which a primary coil (not shown) is wound, and a secondary coil (not shown) around which a substantially cylindrical shape whose diameter is larger than that of the primary coil bobbin 11. The secondary coil bobbin 12 is provided with a secondary coil bobbin 12, and the secondary coil bobbin 12 around which the secondary coil is wound is disposed concentrically outside the primary coil bobbin 11 around which the primary coil is wound. Thereby, the primary coil and the secondary coil form a coil pair arranged concentrically.

  Primary terminals 13 and 14 are press-fitted into one end of the primary coil bobbin 11, and the winding start end and winding end end of the primary coil are connected to the primary terminals 13 and 14, respectively, by fusing or the like. The primary terminals 13 and 14 are inserted into the connector 15 from one end, and the connector 15 is fixed to a predetermined position of the secondary coil bobbin 12.

  In the central space of the primary coil bobbin 11 along the central axis of the coil pair in which the primary coil and the secondary coil are concentrically arranged, the center core portion of the core 18 that forms the magnetic path is fitted, whereby the primary coil And the coil assembly 10 which mainly consists of the secondary coil and the core 18 is comprised.

  The upper opening end of the housing 1 as a coil case is provided with a notch portion 2 into which the connector 15 is fitted. The notch portion 2 is located at a position facing the notch portion 2 across the central axis of the housing 1. A cutout portion 3 is provided in which an H / T tower 4 that is a take-out end of the next output is fitted. A mounting flange 5 for fixing the ignition coil to the engine block is provided on the outer surface of the housing 1, and a plug cap 7 having a spring 6 built in is provided at the lower end of the housing 1 in FIG. Mated.

  Next, the coil assembly will be described in detail. FIG. 2 is a plan view of the secondary coil bobbin 12 which is a constituent member of the coil assembly.

  In FIG. 2, the secondary coil bobbin 12 includes, for example, a cylindrical secondary coil bobbin main body 21 made of modified PPO (polyphenylene oxide) resin, and first secondary output terminals provided at both ends in the length direction. 22 and a second secondary output terminal 23.

  The outer surface of the secondary coil bobbin main body 21 is a winding region 24 around which the secondary coil is wound, and an intermediate tap 17 as a terminal is provided at the approximate center of the winding width of the winding region 24. The intermediate tap 17 divides the winding region 24 into a first winding region 24a and a second winding region 24b. The winding regions 24a and 24b are partitioned, for example, at equal intervals by a plurality of partition plates 26 extending along the normal direction of the outer peripheral surface.

  In the first winding region 24a and the second winding region 24b, coils are wound in opposite directions with the intermediate tap 17 as a boundary, and two secondary coils 27a and 27b wound in opposite directions to each other. Is formed.

  Ends of the coil bobbins of the secondary coils 27a and 27b on the center side in the length direction are respectively connected to the intermediate tap 17 as a terminal. On the other hand, the other end of the first secondary coil 27 a is connected to the first secondary output terminal 22, and the other end of the second secondary coil 27 b is connected to the second secondary output terminal 23. The two secondary output terminals 22 and 23 are respectively connected to the spark plug through the plug cap when the coil assembly 10 is inserted into the housing 1, and H / H as a secondary high voltage terminal of the housing 1. It is connected to a terminal connected to the T tower 4.

  Any partition plate (four in FIG. 2) among the plurality of partition plates 26 that partitions the winding regions 24a and 24b at equal intervals, for example, from the intermediate tap 17 in the first winding region 24a and the second winding region 24b. The second partition plate and the outermost partition plate are rib-partition plates 26a provided with protrusions (not shown) to be a plurality of positioning guide ribs on the outer periphery thereof. When the coil assembly 10 formed using the secondary coil bobbin 12 having such a configuration is inserted into the housing 1, the secondary coil bobbin 12 that faces the mounting flange 5 on the outer surface across the wall surface of the housing 1. On the surface, there is formed a restricted area where no guide rib is provided. Thereby, generation | occurrence | production of the crack resulting from the distortion in the joint surface of the insulating resin and guide rib which the casting material solidified is suppressed.

  Next, features of the present invention will be described in detail. FIG. 3 is a connection diagram of the coil assembly in the present embodiment.

  In FIG. 3, the primary coil 19 and the secondary coil 27 (27a, 27b) face each other at a predetermined interval, and the primary terminal 13 that is the winding start end of the primary coil 19 controls the conduction of the primary coil. Connected to the control circuit. On the other hand, the primary terminal 14 that is the winding end of the primary coil is connected to the + (plus) side of the battery (not shown). The primary terminal 14 is connected to the cathode of a diode 16 having an anode connected to an intermediate tap 17 that is a connecting portion between the secondary coils 27a and 27b. Therefore, the intermediate tap 17 of the secondary coil is connected to the + (plus) side of the battery (not shown) via the diode 16 and the primary terminal 14.

  The outer end of the secondary coil 27a is connected to the secondary output terminal 22, and the secondary output terminal 22 is directly connected to the spark plug via a plug cap (not shown). On the other hand, the outer end of the secondary coil 27b is connected to the secondary output terminal 23, and the secondary output terminal 23 is connected to another spark plug via an H / T tower and a high tension cord (not shown). Yes.

  The stray capacitance on the secondary output terminal 23 side connected to the spark plug via the high tension cord is larger than the stray capacitance on the secondary output terminal 22 side directly connected to the spark plug, and from the output terminal having a large stray capacitance. Has been found to be lower than the output voltage from the output terminal having a small stray capacitance.

  Therefore, in this embodiment, in order to eliminate such an output imbalance, the winding width center 19a of the primary coil 19 is set to a secondary output having a larger stray capacitance than the center of the winding width of the secondary coil. The secondary coil 27b connected to the terminal 23 is shifted toward the secondary coil 27b by a predetermined width, whereby the coupling coefficient Kb between the secondary coil 27b and the primary coil 19 is larger than the coupling coefficient Ka between the secondary coil 27a and the primary coil 19. This compensates for a decrease in secondary output caused by an increase in stray capacitance.

  That is, in FIG. 3, the winding width center 19 a of the primary coil 19 is shifted to the secondary coil 27 b side by, for example, 2 mm (W) with respect to the intermediate tap 17 that is the center of the winding width of the secondary coil 27. Yes.

  As described above, the secondary coil 27b is a coil connected to the spark plug via the secondary output terminal 23 and a high tension cord (not shown), and stray capacitance increases due to the high tension cord. The next output is reduced. However, by shifting the center 19a of the winding width of the primary coil 19 to the secondary coil 27b side, the coupling coefficient Kb between the primary coil 19 and the secondary coil 27b is relatively coupled to the primary coil 19 and the secondary coil 27a. This is larger than the coefficient Ka, thereby canceling the output drop, and the two secondary outputs are balanced.

  In the present embodiment, the shift width W when the center 19a of the primary coil 19 is shifted to the secondary coil (for example, 27b) side where the stray capacitance increases with respect to the intermediate tap 17 that is the center of the secondary coil 27 is as follows. Determine as follows.

  That is, a plurality of experimental ignition coils in which the deviation width W of the center width 19a of the primary coil 19 with respect to the intermediate tap 17 that is the center of the winding width of the secondary coil 27 is changed, and the cylinder to which the ignition coil is applied. In this state, an optimum deviation width W is determined from the plurality of ignition coils so that the secondary output voltages of both coincide with each other.

  In this way, the deviation width W is determined, and the deviation width W of the center 19a of the primary coil 19 with respect to the intermediate tap 17 of the secondary coil 27 is normally 1.5 to 3.0 mm. If the deviation width W is smaller than 1.5 mm, the output that is reduced due to the stray capacitance due to the high tension cord cannot be compensated. If it is larger than 3.0 mm, the two outputs are balanced once. The output of the secondary coil on the side where the center 19a of the primary coil 19 is shifted gradually becomes larger than the output of the other secondary coil, and the output balance is lost. Therefore, in the present embodiment, the shift width W is set to 1.5 mm to 3.0 mm.

  Next, the core 18 that is a constituent member of the coil assembly 10 will be described. FIG. 4 is a perspective view of the core 18 as a constituent member of the coil assembly.

  In FIG. 4, the core 18 includes two substantially U-shaped core members 181 and 182. By combining the core members 181 and 182, for example, a rectangular closed magnetic circuit is formed on the front view.

  One joint portion between the core members 181 and 182 is an inclined joint portion that is inclined at a predetermined angle, for example, 10 to 20 degrees with respect to the joining direction, that is, the vertical direction in FIG. That is, the core members 181 and 182 have inclined joint surfaces 181a and 182a, respectively. A plate-like permanent magnet (magnet) 20 is interposed between the inclined joint surfaces 181a and 182a. This reverse biases the magnetic flux through the core 18 and increases the secondary output.

  The joint portion other than the one joint portion is, for example, a joint portion into which an uneven surface is fitted, the core member 181 has, for example, a convex joint surface 181b, and the core member 182 has, for example, a concave joint. It has a surface 182b.

  Most of the surfaces of the core members 181 and 182 are covered with mold resin. As the mold resin, for example, an insulating polypropylene resin is used.

  The mold resin 1813 around the inclined joint surfaces 181a and 182a in the core members 181 and 182 is partially at a predetermined height from each inclined joint surface, that is, a height corresponding to the thickness of the magnet 20, for example, 0.5-2. When the core members 181 and 182 are combined with each other, the protruding mold resin 1813 covers the entire circumference of the inclined bonding surface, and is surrounded by the inclined bonding surfaces 181a and 182a and the protruding mold resin 1813. An accommodation space for the magnet 20 is formed.

  FIG. 5 is an explanatory diagram of a coil assembly in which the above-described core 18 is inserted into the central space of the coil pair. In FIG. 5, the coil pair is shown as a cross-sectional view, but the core 18 is shown as a front view for convenience.

  In FIG. 5, the primary coil 19 is wound around the primary coil bobbin 11, and the secondary coil 27 is wound around the secondary coil bobbin 12. The diameter of the secondary coil bobbin 12 is larger than the diameter of the primary coil bobbin 11, and the secondary coil bobbin 12 is disposed concentrically outside the primary coil bobbin 11. The primary coil 19 and the secondary coil 27 form a coil pair arranged concentrically.

  The core 18 is an assembly composed of a combination of core members 181 and 182, the magnet 20 is interposed between the inclined joint surface 181 a of the core member 181 and the inclined joint surface 182 a of the core member 182, and the core member The core 18 having a closed magnetic path is formed by joining the convex joint surface 181b of 181 and the concave joint surface 182b of the core member 182 (see FIG. 4).

  A center core 18a, which is a part of the core 18, is inserted into the center space of the coil pair, that is, the center space of the primary coil bobbin 11 as a coil support member, and the side core 18b parallel to the center core 18a It arrange | positions along the outer surface of the secondary coil bobbin 12 as a structural member. Since the core 18 is an assembly of the core members 181 and 182, the assembly when a part of the core 18 is fitted into the central space of the coil assembly is facilitated.

  In addition, since the core 18 includes the center core 18a and the side core 18b, and the center core 18a and the side core 18b form a closed magnetic circuit, the leakage magnetic flux is eliminated, and the magnetic flux can be used effectively. Therefore, the output fall of the secondary coil 27 can be suppressed.

  In the ignition coil according to the present embodiment, when the core members 181 and 182 forming the core 18 are covered with the mold resin, the pin mark formed on the mold resin film is further filled with the mold resin and the surface of the ignition coil is covered. Unevenness is relaxed.

  When insert molding the core member, i.e., when the core member is coated with mold resin, the retaining pin mark for holding the core member in the mold remains on the surface as a concave portion, and the ignition coil is caused by the concave portion. Cracks may occur in the insulating resin in which the casting material is solidified. Therefore, in the present embodiment, in order to eliminate such a problem, after the core member is once coated with the mold resin, for example, the molding is performed twice in order to eliminate the pin mark formed at the time of coating, and the concave portion of the surface is formed. Is blocked with mold resin, thereby preventing the occurrence of cracks.

  In the ignition coil according to the present embodiment, the surface of the center core 18a of the core 18 has projections 40 as guide ribs for positioning the surface of the center core 18a with respect to the inner wall surface of the primary coil bobbin 11, for example, in the length direction and the outer circumferential direction. (See FIG. 5). The protrusions 40 have the same height, for example, protrude from the surface of the center core 18 a by about 0.05 to 0.6 mm, and the tip portions thereof are in contact with the inner wall surface of the primary coil bobbin 11.

  As a result, the gaps between the inner wall surface of the primary coil bobbin 11 and the surface of the center core 18 a are made uniform, and the surface of the center core 18 a is accurately positioned with respect to the inner wall surface of the primary coil bobbin 11. The protrusions 40 as the guide ribs are simultaneously formed in, for example, a resin molding process.

  In the present embodiment, one end of the core 18 forming the closed magnetic path is covered with an elastic member.

  When the coil assembly 10 is inserted into one end of the core 18, for example, the housing 1, the magnetic material is exposed at the end of the core 18 located on the opening end side of the housing 1 due to insert molding. When the casting material is filled while leaving the exposed portion of the magnetic material as it is, for example, when a grain-oriented silicon steel plate is applied as the core 18, the cast material hardens the C end 18c (see FIG. 5) of the grain-oriented silicon steel plate after hardening. Therefore, there is a problem that the influence of magnetostriction cannot be ignored and, for example, a predetermined secondary output cannot be obtained. Therefore, in the present embodiment, the D end 18d (see FIG. 5) of the core 18 is covered with insert-molded insulating resin, and the magnetic material exposed end (C end) 18c described above is covered with an elastic member.

  In this case, for example, the mold resin 1813 that covers the periphery of the end surface of the core 18 is raised from the exposed end surface of the magnetic material by a predetermined height, for example, about 1 to 2 mm, which is the thickness of the elastic member, so as to surround the exposed surface of the magnetic material. It is preferable that the core end face be the bottom face of the recess. And an elastic member is arrange | positioned in the recessed space enclosed with mold resin, and this elastic member is heat-clamped by the mold resin 1813, for example.

  As the elastic member, for example, a foam sponge made of silicon rubber is suitably used. The foamed sponge as an elastic member is preferably provided with a through hole penetrating in the thickness direction. Thereby, a void and a casting material can be smoothly passed at the time of filling with a casting material.

  In the present embodiment, the coil assembly 10 is inserted into the housing 1 in which the H / T tower 4 is fitted into the notch 3, the connector 15 of the coil assembly 10 is fitted into the notch 2, and the H / T One secondary output terminal 23 is joined to the T tower 4, and a plug cap 7 having a spring 6 is provided at one end (lower end in FIG. 1) of the housing 1 as a connector for the other secondary output terminal 22. The ignition coil is formed by fitting and filling an insulating resin between the constituent members. The ignition coil is fixed at a predetermined position of the engine block, and one secondary output terminal 22 is attached to a plug hole of the engine and directly connected to an ignition plug attached to, for example, the lower end of the housing 1. The other secondary output terminal 23 is connected to another spark plug disposed in the same cylinder via a high tension cord, and acts as an ignition source for an engine that outputs a balanced secondary output voltage.

  According to the present embodiment, the center 19a of the primary coil 19 is placed on the side of the secondary coil 27b connected to the other ignition coil in the same cylinder through the high tension cord of the two secondary coils 27a and 27b. Since the shift is made, the coupling coefficient Kb between the primary coil 19 and the secondary coil 27b is made larger than the coupling coefficient Ka between the primary coil 19 and the secondary coil 27a, so that the output decrease due to the increase in stray capacitance due to the high tension cord is reduced. Can be compensated for, thereby balancing the two secondary outputs.

  In the present embodiment, the intermediate tap 17 at the center of the winding width of the secondary coil 27 can be connected to the anode of the diode 16 and the cathode of the diode 16 can be connected to the ground of the battery. As a result, a stable secondary output can be obtained while the potential at the center terminal of the secondary coil is reliably kept at a low potential. In addition, when the primary coil is switched, it is possible to prevent the spark plug from being discharged due to the rise of the on-current that first flows through the primary coil.

1 is an assembly diagram of an ignition coil for an internal combustion engine according to an embodiment of the present invention. It is a top view of the secondary coil bobbin which is a structural member of a coil assembly. It is a connection diagram of the coil assembly of FIG. It is a perspective view of the core as a structural member of a coil assembly. It is explanatory drawing of the coil assembly which inserted the core in the center space of a coil pair.

Explanation of symbols

1 Housing (coil case)
2 notch 3 notch 4 H / T tower 5 mounting flange 6 spring 7 plug cap 10 coil assembly 11 primary coil bobbin 12 secondary coil bobbin 13 primary terminal 14 primary terminal 15 connector 16 diode 17 intermediate tap 18 core 18a center core 18b side core 181 Core member 181a Inclined joint surface 181b Convex joint surface 182 Core member 182a Inclined joint surface 182b Concave joint surface 1813 Mold resin 19 Primary coil 19a Primary coil winding width center 20 Magnet 21 Secondary coil bobbin body 22 Secondary output terminal 23 Secondary output terminal 24 Winding region 24a First winding region 24b Second winding region 26 Partition plate 26a Partition plate 27 with ribs Secondary coil 27a Secondary coil 27b Secondary coil 40 Projection

Claims (6)

A coil assembly in which a core that forms a magnetic path is inserted into the central space of a coil pair having a concentric primary coil and a secondary coil is housed in a coil case and insulated between each component. In the dual ignition type ignition coil filled with resin,
The secondary coil is composed of two coils wound in the opposite directions around the center of the winding width,
An ignition coil characterized in that the outputs of the two secondary coils are balanced by shifting the center of the winding width of the primary coil with respect to the winding width center of the secondary coil by a predetermined width. The output end of one of the two secondary coils is directly connected to the spark plug, and the output end of the other secondary coil is connected to another ignition in the same cylinder via a high tension cord. Is connected to the plug,
The center of the winding width of the primary coil is shifted by a predetermined width toward the secondary coil connected to the other ignition coil in the same cylinder via the high tension cord. Ignition coil.   The ignition coil according to claim 1 or 2, wherein the deviation width is 1.5 to 3.0 mm.   4. The terminal according to claim 1, wherein a terminal is provided at the center of the winding width of the secondary coil, and the terminal is connected to the positive electrode side of the battery or to the ground. The ignition coil as described.   5. The ignition according to claim 4, wherein a terminal at the center of the winding width of the secondary coil is connected to an anode of a diode, and a cathode of the diode is connected to a positive electrode side of the battery or a ground. coil.   6. The core according to claim 1, wherein the core forms a closed magnetic path having a center core and a side core, and the center core is fitted in a central space of the coil pair. The ignition coil according to item.