JPH0684664A - Ignition coil for internal-combustion engine - Google Patents

Abstract

PURPOSE:To reduce the size and weight of ignition coil for internal-combustion engine while preserving specified ignition performance. CONSTITUTION:The ignition coil for internal-combustion engine comprises a first core 2, primary and secondary coils 12, 22 to be applied on the first core 2, a second core 3 juxtaposed to the primary and secondary coils on the outside thereof while being jointed to the first core 2, and a permanent magnet 5 interposed between the first and second cores. The permanent magnet 5 is bonded to the end face of the first core 2 on the high voltage output side of the secondary coil 22. Gap between the secondary coil 22 and the second core 3 is set at a predetermined maximum value in the vicinity of the high voltage output side of the secondary coil 22 while the cross-sectional area at the juxtaposing part of the second core 3 is set at a predetermined manimum value in the vicinity of the high voltage output side of the secondary coil 22 and the outer side face at the juxtaposing part of the second core 3 is shaped such that the distance of the secondary coil 22 from the axis thereof in the vicinity of the high voltage output side is maximized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition coil for an internal combustion engine, and more particularly to an ignition coil in which a primary coil and a secondary coil are wound around a core and a permanent magnet is provided in a magnetic path.

[0002]

2. Description of the Related Art An ignition coil of an internal combustion engine has a core wound with a primary coil and a secondary coil. The primary coil is connected to a control circuit for controlling a primary current through a connector, and the secondary coil is It is connected to a spark plug via a high voltage terminal. Specifically, both ends of the winding of the primary coil are connected to the pair of primary terminals, and one end of the winding of the secondary coil is connected to the primary terminal and the other end is connected to the high voltage terminal.

Regarding such an ignition coil, it has been conventionally proposed to increase energy by interposing a permanent magnet in the magnetic path, for example, Japanese Patent Laid-Open No. 2-377.
No. 05 publication.

[0004]

In the ignition coil including the ignition coil described in the above publication and having the core arranged in parallel on the outer side of the secondary coil, in order to secure a predetermined withstand voltage to the secondary coil, The dimensions of the cores arranged side by side with respect to the secondary coil are set based on the gap between the core and the secondary coil on the high voltage output side. For example, in the ignition coil described in the above publication, a rectangular annular outer core having the same width is provided, but since the distance from the secondary coil is set with reference to the gap on the high voltage output side, the other side (Low voltage side)
Then, it will be set to a larger value than necessary.

With respect to the outer core 3P surrounding the core 2P around which the primary coil and the secondary coil (not shown) shown in FIG. 13 are wound, a juxtaposed portion with the core 2P is formed with a uniform cross-sectional area. When the magnetic flux densities at the A, B and C positions are measured, the maximum value is shown at the A position near the permanent magnet 5P as shown in FIG. Therefore, at the position C separated from the permanent magnet 5P, there is a margin in the cross-sectional area, and the cross-sectional area can be minimized on condition that a predetermined gap is secured with respect to the secondary coil. On the contrary, when the core 3p having the uniform cross-sectional area of the juxtaposed portion is formed based on the minimum magnetic flux density at the C position,
The magnetic flux density at the position A near the permanent magnet 5P becomes excessive.

Therefore, according to the present invention, the primary coil and the secondary coil are wound around the first core, the second core is arranged in parallel to the outer side of the secondary coil, and the first core is provided via the permanent magnet. It is an object of the present invention to reduce the size and weight of an ignition coil for an internal combustion engine that is joined to the core while maintaining a predetermined ignition performance.

[0007]

In order to achieve the above object, the present invention provides a first core, a primary coil and a secondary coil wound around the first core, and the primary coil and the secondary coil. Ignition for internal combustion engine provided with a second core arranged in parallel to the outside of the coil and joined to the first core, and a permanent magnet interposed between the second core and the first core In the coil, the permanent magnet is joined to the end surface of the first core on the side opposite to the high voltage output side of the secondary coil, and the second core is arranged in parallel with the secondary coil. The gap between the installation portion and the secondary coil is set to a predetermined maximum value in the vicinity of the high voltage output side of the secondary coil, and the cross-sectional area of the juxtaposed portion of the second core is set to that of the secondary coil. The outer surface of the juxtaposed part of the second core is set to a predetermined minimum value in the vicinity of the high voltage output side. , The distance from the axis of the secondary coil in the high voltage output side near the secondary coil in which was formed to have a maximum.

In the ignition coil for an internal combustion engine, the second core may be formed so as to surround the first core and the primary coil and the secondary coil.

[0009]

In the ignition coil for an internal combustion engine of the present invention, the second core is provided in parallel with the first core and the primary coil and the secondary coil wound around the first core, and the secondary coil has a high voltage. It is joined to the first core via a permanent magnet on the side opposite to the output side. Then, the cross-sectional area of the juxtaposed portion of the second core, the gap with the secondary coil, and the distance from the axis of the secondary coil of the outer surface to the second core near the high voltage output side of the secondary coil Since it is set based on the required specifications,
The second core has a required minimum size. Thus, when a small ignition coil is configured and the primary current supplied to the primary coil is intermittent, a magnetic flux change occurs in the first and first cores, and a high voltage is induced in the secondary coil.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an ignition coil for an internal combustion engine of the present invention will be described below with reference to the drawings. 1 to 3 show an embodiment of an ignition coil according to the present invention, which has a T-shaped core 2 and an annular core 3 forming a substantially day-shaped magnetic path, and the core 2 is a primary coil. Built in the assembly 10, the core 3 is housed in the case 30. Then, when the secondary coil assembly 20 is assembled to the primary coil assembly 10 and is housed in the case 30, these are surrounded by the core 3. Hereinafter, these will be described along with manufacturing and assembling procedures.

The case 30 is a housing made of synthetic resin in which the core 3 is integrally housed by insert resin molding, and a space for housing the primary coil assembly 10 and the secondary coil assembly 20 is defined inside the core 3. Has been done. A secondary connector portion 31 is formed at the bottom of the case 30, and the high voltage terminal 7 having a hole 7a in the center is accommodated therein.
Further, the case 30 has an opening on the left side in FIG. 3 (a surface serving as an upper surface at the time of arrangement), an opening 32 is formed on the side wall, and a flange 33 is formed on the side opposite to the opening 32. A collar 34 is embedded in the flange portion 33 by insert resin molding, and a mounting bolt 35 is inserted through a washer. The support portion 15 of the primary coil assembly 10 is fitted into the opening portion 32 as described later.

The core 3 is an annular iron core and is formed by laminating a plurality of non-oriented silicon steel sheets, but a grain-oriented silicon steel sheet may be used. The joint portion 3a of the core 3 that is joined to the core 2,
As shown in FIG. 1, a joint portion 3a of the joint portion 3b extends inwardly and is formed wide, and a recess portion 3e is formed inside the joint portion 3b, and the inner surface of each joint portion 3b is exposed to the internal space. The shape of the core 3 will be described later with reference to FIG. An elastic member such as an elastomer is coated on the inner side surfaces of the parallel portions 3c and 3d of the core 3 parallel to the core 2 to form an elastic member layer 4. The elastic member layer 4 absorbs a difference in thermal expansion between the core 3 and the case 30 surrounding the core 3. In the present embodiment, only a part of the inner surface is covered with the elastomer, but the entire elastic member layer 4 is covered. It may be configured to cover the surface. On the other hand, the core 2 has a columnar main body 2 as shown in FIG.
It is a T-shaped iron core having a and a joint portion 2b integrally formed at an end portion of the main body portion 2a and extending in a direction orthogonal to the axis. The core 2 is formed by laminating a plurality of grain-oriented silicon steel plates whose rolling direction is the axial direction of the main body 2a.

With respect to the primary coil assembly 10, the core 2 and the terminals 6a to 6e (and the conductor portion between them) are integrally housed by insert resin molding, and as shown in FIGS. The holding portion 13, the connecting portion 14, the supporting portion 15, and the connector portion 16 are formed. The primary bobbin 11 is formed around the main body portion 2a of the core 2 and is integrally formed with the holding portion 13 to form a collar portion 11b.
A collar portion 11a is formed at a predetermined distance from. As is apparent from FIGS. 4 and 6, the collar portion 11a has locking pieces 11e projectingly formed on two opposing sides. Further, a pair of grooves 11g is formed on each of the other two opposite sides, and the end surface of the collar portion 11a between the pair of grooves 11g is configured to fit into the hollow portion of the secondary bobbin 21 described later. There is. The locking piece 11e restricts the movement of the primary coil assembly 10 in the axial direction, and is locked by a protrusion 21h (shown in FIGS. 1 and 3) formed in the hollow portion of the secondary bobbin 21. Further, when the groove 11g is formed with the resin portion 9 described later,
The resin is allowed to flow into the hollow portion of the secondary bobbin 21. The primary bobbin 11 further has a covering portion 11c for covering the flange portion 11a to the end portion of the main body portion 2a of the core 2, and ribs are formed on both side ends of the one surface and the core 2 is formed.
An extending portion 11d extending in the axial direction from the end surface of the is formed. As shown in FIGS. 4 and 6, a pair of convex portions 11f is formed so as to extend outward from the two opposite sides of the flange portion 11b and project in the axial direction from the holding portion 13.

The holding portion 13 adjacent to the primary bobbin 11 is
The permanent magnet 5 is held so as to be in contact with the joint portion 2b of the core 2, and is formed so that the end face in the longitudinal direction of the joint portion 2b is exposed as shown in FIG. A recess 13b whose lower side surface is open is formed, and holding pieces 13a are formed at both longitudinal ends of the recess 13b. As a result, when the permanent magnet 5 is inserted into the recess 13b from the lower side in FIG. 5, the permanent piece 5 is held at a predetermined position by the holding piece 13a and is brought into close contact with the joint portion 2b of the core 2.
It should be noted that the permanent magnet 5 is used for the cores 2, 3 when the primary coil 12 is energized.
Are arranged so as to be in the direction opposite to the direction of the magnetic flux formed in. In addition, a cutout 13c is formed in the holding portion 13 and the flange portion 11b in the axial direction.

Thus, the holding portion 13 is formed so that its longitudinal direction is orthogonal to the axis of the primary bobbin 11, and the one side end portion (the upper side end portion in FIG. 5) is connected to the axis of the primary bobbin 11. A plate-shaped connecting portion 14 extending in parallel is formed, and further extends in a direction orthogonal to the plate surface of the connecting portion 14, that is, in a direction parallel to the plate surface of the permanent magnet 5 held by the holding portion 13. The supporting portion 15 is formed, and thus the holding portion 13, the connecting portion 14, and the supporting portion 15 form a U-shaped cross section as shown in FIG. Further, a connector portion 16 is formed in connection with the support portion 15, terminals 6a, 6b, 6c are erected on the connection portion 14, and terminals 6d, 6e are formed in the connector portion 6 and these terminals 6a and 6e are formed. The conductor that integrally connects the terminal 6e and the conductor that integrally connects the terminals 6b and 6c and the terminal 6d are the connecting portion 14, the supporting portion 15, and the connector portion 16.
It is buried in.

Then, as shown in FIGS. 7 to 9, the primary coil 12 is wound around the primary bobbin 11 to form the primary coil assembly 10. That is, the collar portions 11a and 11b
In the meantime, the windings of the primary coil 12 are wound in two or four layers. Both ends 12a and 12b of the winding of the primary coil 12 are guided and led out to the notches 13c, respectively, and are respectively connected to the terminal 6
It is wound around a and 6b and soldered. The terminal 6d is connected to a battery (not shown), and the terminal 6e is connected to a control circuit (not shown), commonly called an igniter.

The permanent magnet 5 mounted on the holding portion 13 is rectangular, and the width of one side thereof is set to be slightly larger than the width of one side of the cross section of the joint portion 2b of the core 2 as shown in FIG. 3 is set to a value slightly larger than the width of the other side of the cross section of the joint 2b as shown in FIG. Therefore, the cross-sectional area of the permanent magnet 5 is larger than the cross-sectional area of the joint portion 2b of the core 2, and as shown in FIG.
From the joint portion 2b of. This permanent magnet 5
As the rare earth magnet, a samarium-cobalt (Sm-Co) -based metal or a neodymium-iron-boron-based metal sintered body having a large residual magnetic flux density and hardly demagnetized is used.
In the above description, the permanent magnet 5 is attached to the holding portion 13 before the primary coil 12 is wound, but the order may be reversed, and the secondary coil assembly 20 which will be described later is also used.
The permanent magnet 5 may be mounted immediately before being housed in the case 30 after assembly.

On the other hand, the secondary coil assembly 20 is formed by winding a secondary coil 22 around a secondary bobbin 21. The secondary bobbin 21 is a resin cylindrical body having a substantially rectangular cross section in which a plurality of collar portions 21a are formed at predetermined intervals in the axial direction, and a plurality of grooves 21b are formed between these collar portions 21a. The winding of the secondary coil 22 is sequentially wound in the groove 21b from the upper side to the lower side in FIG. Collar 21a of the secondary bobbin 21
One of them is a wide brim portion 21d, and a projecting portion 21e is formed on this brim portion 21d, and a terminal 23b is fitted in a groove formed at the tip thereof.

On one end surface of the secondary bobbin 21, the concave portion 2 into which the convex portion 11f (FIGS. 4 and 6) of the primary bobbin 11 is fitted.
1 g (FIG. 1) is formed. Then, when the primary bobbin 11 portion of the primary coil assembly 10 is inserted into the hollow portion of the secondary bobbin 21, the locking piece 11 of the collar portion 11a is formed.
e rides over the projection 21h of the secondary bobbin 21 and is locked, and the projection 11f is fitted into the recess 21g. As a result, the primary bobbin 11 is supported at both ends with respect to the secondary bobbin 21, and relative movement in the axial direction and the width direction between the primary bobbin 11 and the secondary bobbin 21 is restricted, so that a stable joining state is achieved.

As shown in FIGS. 2 and 3, the collar portion 2 at the upper end
A projecting portion 21c is formed in the axial direction of the la 1a, and a terminal 23a is fitted in a groove formed in the projecting portion 21c. The winding start of the winding of the secondary coil 22 is wound around the terminal 23a and soldered. The winding end of the secondary coil 22 is wound around the terminal 23b and soldered thereto as shown in FIGS. 3 and 10. This terminal 23b has a long lead 23
c is joined and extends in a direction orthogonal to the axis of the secondary bobbin 21, and when assembled to the case 30 later,
The lead 23c is inserted into the hole 7a of the high voltage terminal 7.

Then, the secondary coil assembly 20 is assembled to the primary coil assembly 10 and the leads 8a and 8b of the diode 8 are soldered to the terminals 23a and 6c. The diode 8 prevents a spark plug (not shown) from flying due to a voltage of 1 to 3 kV generated when the primary coil 12 is energized. It should be noted that the solder joining in the primary coil assembly 10 and the secondary coil assembly 20 described above may be performed simultaneously with this solder joining, but in either case, the primary coil assembly 10 and the secondary coil assembly 20 are housed in the case 30. Solder joining is performed before the soldering.

When the primary coil assembly 10 and the secondary coil assembly 20 are housed in the case 30 as shown in FIG. 10, the leads 23 are provided as shown in FIG.
c is inserted into the hole 7a of the high voltage terminal 7, and the case 3
The support 1 of the primary coil assembly 10 in the opening 32 of 0
5 is fitted, the core 2 and the permanent magnet 5 are fitted inside the core 3. That is, when the joint portion 3a of the core 3 is fitted to the U-shaped cross-section portion of the holding portion 13, the connecting portion 14, and the supporting portion 15 of the primary coil assembly 10,
The connecting portion 14 comes into contact with the plate surface of the core 3, the extension portion 11d comes into contact with the plate surface of the core 3, and the permanent magnet 5 comes into contact with the inner laminated surface of the joint portion 3a of the core 3 so that the core 2 Junction 2c
Fits into the concave portion 3e of the core 3 and abuts on the laminated surface.
Therefore, the core 2, the core 3, and the permanent magnet 5 are surely in a predetermined positional relationship. The permanent magnet 5 is a recess 13 b of the holding portion 13.
Since the end portion 5a is housed inside and is held by the holding piece 13a, it is arranged at a predetermined position between the joint portions 2b and 3a of the cores 2 and 3, respectively.

After being assembled in this way, the lead 23
The tip of c and the high voltage terminal 7 are joined by solder 7c and electrically connected. Then, a space inside the case 30 is filled with a thermosetting synthetic resin, for example, an epoxy resin, and is cured to form a resin portion 9 as shown in FIG.
In FIG. 3, the surface of the resin portion 9 is shown by a broken line). This allows
The primary coil 12 and the secondary coil 22 are impregnated and fixed, and at the same time, the insulating property capable of withstanding the output high voltage of the secondary coil 22 is secured. In this case, in the hollow portion of the secondary bobbin 21, the notch 13c (FIGS. 4 and 6) of the holding portion 13, the groove 11g of the collar portion 11a, and the gap between the collar portions 11a and 11b and the hollow portion are provided. Since the resin is filled, the resin portion 9 is reliably formed without forming a void in the hollow portion. Moreover, the cores 2, 3 are formed by the covering portion 11c, the extending portion 11d, and the like.
Since the acute-angled portion of each side of the resin does not come into direct contact with the resin portion 9, the resin portion 9 is prevented even under severe environmental conditions.
It does not crack. Furthermore, since the solder joining to the leads 6a and the like is performed before the assembling to the case 30, the work is easy, and the solder lump or the flux does not adhere to the resin portion 9 during the solder joining.

FIG. 11 shows the core 2 and the core 3 in this embodiment.
And the permanent magnet 5, both of which are symmetrical with respect to the axis of the core 2. Although the secondary coil 22 and the like are omitted in FIG. 11, since the axis of the secondary coil 22 coincides with the central axis of the core 2, the core 3 and the secondary coil 2 will be described below.
The positional relationship between the core 3 and the core 2 will be replaced with the positional relationship between the core 3 and the core 2. Further, since the parallel portions 3c and 3d of the core 3 corresponding to the juxtaposed portion in the present invention have the same positional relationship with the secondary coil 22, only the parallel portion 3c will be described below as a representative of both. To do.

In FIG. 11, the high voltage output side of the secondary coil 22 is the portions indicated by 2ah and 3ch of the main body portion 2a of the core 2 and the parallel portion 3c of the core 3, respectively. The gap Gh between the main body portion 2a of the core 2 and the parallel portion 3c of the core 3 in this portion is set to the maximum value, and the parallel portion 3c of the core 3 is
The cross-sectional area Sh of is set to the minimum value. That is, the gap Gh is set so as to ensure the maximum withstand voltage, and the magnetic flux density distribution of the core 3 is as shown in FIG.
The cross-sectional area of the core 3 is set so that the magnetic flux densities are equal at the positions A, B, and C of 1.

Therefore, the permanent magnet 5 is arranged on the side opposite to the high voltage output side of the secondary coil 22, and 3c in the vicinity thereof.
Since the cross-sectional area Ss of the parallel portion 3c in the portion indicated by s is larger than the above-mentioned cross-sectional area Sh and the thickness of the entire core 3 is uniform, the width of the 3ch portion is 3 as shown in FIG.
The width is smaller than the width of cs. The outer surface of the parallel portion 3c of the core 3 is formed so that the distance Lh from the axis of the core 2 in the portion of 3ch is maximized.

The outer surface of the parallel portion 3c of the core 3 is
It will be decided based on the 3ch part of the core 3, as shown in FIG.
The shape becomes closer to the main body portion 2a side of the core 2 than the outer surface of the parallel portion 3c 'of uniform width indicated by 1 in FIG. 1, and the overall size and weight are reduced. At this time, 3 cs of the parallel portion 3c
The inner side surface of the portion 2 is closer to the main body portion 2a side of the core 2 than the parallel portion 3c ′ having a uniform width shown by the chain double-dashed line, but the portion 3cs is on the low voltage side of the secondary coil 22. Therefore, the insulating property is maintained.

In the ignition coil of this embodiment having the above-mentioned structure, for example, the upper side of the permanent magnet 5 in FIG. 1 is the N pole, and the flow of magnetic flux circulates in the cores 2 and 3 to form a closed loop. There is. When the primary coil 12 is energized by a control circuit (not shown) and a primary current is supplied, the magnetic flux flows in the direction opposite to the magnetization direction of the permanent magnet 5. Then, when the primary current is cut off, a counter electromotive force is induced in the secondary coil 22.
A high voltage of up to 40 kV is generated. At this time, core 2,
A large effective magnetic flux change can be secured by the permanent magnet 5 interposed between the three. Therefore, the magnetic flux density formed in the primary coil 12 becomes large with respect to the magnetomotive force due to the supply of the primary current, the discharge energy increases, and the change in the magnetic flux interlinking with the secondary coil 22 becomes large. The output voltage of the coil 22 becomes large, and good ignition performance can be secured. The output voltage of the secondary coil 22 is applied to an ignition plug (not shown) via the terminal 23b, the lead 23c, and the high-voltage terminal 7, and spark discharge is generated at the electrode portion at the tip of the ignition plug, causing a combustion chamber (see FIG. (Not shown)
The compressed mixture inside is ignited.

[0029]

Since the present invention is constructed as described above, it has the following effects. That is, in the ignition coil for an internal combustion engine of the present invention, the second core is provided side by side outside the first core and the primary coil and the secondary coil wound around the first core, and the high voltage output of the secondary coil is provided. On the side opposite to the side, the second core is joined to the first core via a permanent magnet, and the gap between the second core and the secondary coil is close to the high voltage output side of the secondary coil. It is set to the maximum value, the cross-sectional area is set to a predetermined minimum value near the high voltage output side of the secondary coil, and the outer surface is the distance from the axis of the secondary coil near the high voltage output side of the secondary coil. Is formed so as to have a maximum value, the second core can have a minimum required size, and therefore, the ignition coil can be formed small and lightweight while maintaining a predetermined ignition performance. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an ignition coil according to an embodiment of the present invention.

FIG. 2 is a plan view of an ignition coil according to an embodiment of the present invention.

FIG. 3 is a vertical sectional view of an ignition coil according to an embodiment of the present invention.

FIG. 4 is a plan view showing a state before winding the primary coil of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 5 is a partial cross-sectional front view showing a state before winding the primary coil of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 6 is a side view showing a state before winding the primary coil of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 7 is a plan view of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 8 is a front view of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 9 is a side view of the primary coil assembly in the ignition coil according to the embodiment of the present invention.

FIG. 10 is a side view showing a state in which the primary coil assembly and the secondary coil assembly in the ignition coil according to the embodiment of the present invention are housed in the case.

FIG. 11 is a first core and a second core according to an embodiment of the present invention.
FIG. 6 is a plan view showing a joined state of the core and the permanent magnet of FIG.

FIG. 12 is a graph showing the magnetic flux density of the second core in the example of the present invention.

FIG. 13 is a plan view showing a bonded state of a first core, a second core, and a permanent magnet which are comparison targets.

14 is a graph showing the magnetic flux density of the second core in the comparison object shown in FIG.

[Explanation of symbols]

2 cores, 2a body part, 2b, 2c joint part 3 cores, 3a, 3b joint part, 3c, 3d parallel part 5 permanent magnets 6a, 6b, 6c terminal 7 high voltage terminal, 7a hole 8 diode 9 resin part 10 primary coil assembly 11 primary bobbin, 11a, 11b collar part 12 primary coil 13 holding part, 13a holding piece 14 connecting part 15 supporting part 16 connector part 20 secondary coil assembly 21 secondary bobbin, 21a flange part, 21b groove 22 secondary coil 23a, 23b Terminal 30 Case 31 Secondary Connector Part 32 Opening Part 33 Flange Part

Claims (2)

[Claims] 1. A first core, a primary coil and a secondary coil which are wound around the first core, and the first core and the secondary coil are arranged side by side on the outside of the primary coil and the secondary coil and are arranged on the first core. In an ignition coil for an internal combustion engine comprising a second core to be joined and a permanent magnet interposed between the second core and the first core, an opposite side to a high voltage output side of the secondary coil The permanent magnet is joined to the end surface of the first core, and the gap between the permanent magnet and the secondary coil in the juxtaposed portion of the second core juxtaposed to the secondary coil is set to the secondary coil. Is set to a predetermined maximum value in the vicinity of the high voltage output side of the secondary coil, and the cross-sectional area of the juxtaposed portion of the second core is set to a predetermined minimum value in the vicinity of the high voltage output side of the secondary coil. The outer surface of the juxtaposed part of the second core is the secondary coil near the high voltage output side of the secondary coil. An ignition coil for an internal combustion engine, which is formed so that the distance from the axis of the coil is maximized. 2. The ignition coil for an internal combustion engine according to claim 1, wherein the second core is formed so as to surround the first core and the primary coil and the secondary coil.