JPH03148808A - Ignition coil for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable the title ignition coil to be made compact by a method wherein a closed magnetic path is formed by containing the secondary coil bobbin in a hollow part and a stepped cylindrical body having a large and small sectional holes likewise the primary coil in the large sectional hole of the secondary bobbin as well as cores in the peripheral part and the small sectional hole. CONSTITUTION:An ignition coil 10 forms a closed magnetic path including a permanent magnet 18. Said coil 10 is composed of the first and second cores 11, 12 fitted with the primary and the secondary bobbins 23, 24 respectively wound around with the primary and the secondary coils. The hollow part of the bobbin 24 is formed into a stepped hole comprising a large sectional hole 24a and a small sectional hole 24b to form flange parts 24d, 24e wherein the coil 22 is to be arranged. The bobbin 23 having the similar hollow part to that of the small sectional hole 24b of the bobbin 24 forms the other flange parts 23d, 23e wherein the coil 21 is to be arranged while the input wires and the output of the coil 22 are respectively connected to terminals 25a, 25b and a secondary connector 32. Through these procedures, the title coil can be made compact by boosting the output voltage and minimizing the sectional areas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ignition coil for an internal combustion engine, and particularly to an ignition coil that has a large discharge energy per unit volume, is small, and is suitable for a coil distribution ignition system.

[Prior Art] An ignition device for an internal combustion engine intermittents the primary current of the ignition coil.
A high voltage generated on the secondary side in response to changes in magnetic flux within the coil is applied to each spark plug to ignite the air-fuel mixture in the cylinder. For this reason, in the past, a power distributor was provided to distribute the high voltage generated by the ignition coil to each spark plug. On the other hand, as the performance of internal combustion engines has improved in recent years, a technology has been adopted in which the power distributor is eliminated and an ignition coil is attached to each spark plug, which is known as a coil distribution ignition system.

When such an ignition device is installed in an internal combustion engine, a double overhead camshaft in which two camshafts are disposed above the combustion chamber is used, for example, as described in Japanese Patent Application Laid-open No. 1983-15F2F-8. (commonly known as DOHe), it is difficult to install it in an internal combustion engine, leading to an increase in the size of the engine. Therefore, in the same publication, in order to avoid restrictions on the internal combustion engine side, the DOH
An ignition system has also been proposed for the C engine in which an ignition coil can be disposed between the camshafts. Specifically, the partition wall provided in the oil chamber is removed, the ignition coil is placed directly in the oil chamber of the casing that houses it, and a seal is created between the cylinder Rad cover and the casing, as well as between the spark plug mounting hole and the casing. ing.

Incidentally, in the same publication, the spark plug mounting hole is described as a brag boss.

[Problems to be Solved by the Invention] The ignition coil used in the ignition device described in the above publication is required to be small while maintaining a predetermined output voltage and discharge energy. As a countermeasure to this problem, it is possible to downsize the ignition coil by reducing the cross-sectional area of the cross section perpendicular to the axial direction of the core, but this inevitably results in a decrease in the ignition performance in terms of the output voltage of the secondary coil and the discharge energy. Furthermore, if the cross-sectional area of the core is increased and the number of turns of the secondary coil wound around the core is increased, the ignition coil becomes large.

Regarding this, Japanese Utility Model Application No. 48-49425 also states that in order to increase the output voltage of the secondary coil, it is necessary to increase the number of turns of the secondary coil or increase the magnetic flux passing through the magnetic core. This is explained.

As a means to solve this problem, the publication proposes an ignition coil in which a magnet having a magnetizing force in the opposite direction to the direction of magnetization generated when the switch is closed is inserted into the magnetic path.

As described above, in recent ignition coils, it is necessary to simultaneously satisfy the conflicting demands of improved ignition performance and miniaturization.

- Therefore, the present invention relates to an ignition coil installed in an internal combustion engine, and an object of the present invention is to further reduce the size of the ignition coil while maintaining at least the ignition performance.

[Means for Solving the Problems 1] In order to achieve the above-mentioned object, the ignition coil for an internal combustion engine of the present invention consists of a cylinder having a hollow portion with stepped holes of a large cross-section hole and a small cross-section hole. A secondary bobbin in which a secondary coil is wound around the outer surface of a cylindrical body; a primary bobbin in which a primary coil is wound around the outer surface of the cylindrical body and accommodated in a large cross-section hole of the secondary bobbin; A core is housed in a small cross-section hole of the secondary bobbin that communicates with the hollow part, and is arranged around the secondary bobbin to form a substantially closed magnetic path.

In the ignition coil for an internal combustion engine, the axial length of the primary bobbin is the same as the axial length of the large cross-sectional hole of the secondary bobbin, and the cross-sectional shape of the hollow part of the primary bobbin and the axial length of the secondary bobbin are the same. The cross-sectional shape of the small cross-section hole is the same,
The core includes two portions having substantially the same cross-sectional shape as the hollow portion of the primary bobbin and the small cross-sectional hole of the secondary bobbin, and the two portions are arranged in a predetermined position within the hollow portion of the primary bobbin. It is preferable that the toothpicks be arranged facing each other with a gap between them, and that a groove be formed so that a permanent magnet is interposed in the gap.

The primary coil may be configured such that one layer is wound from one end of the primary bobbin to the other end, and then a second layer is wound from the other end to one end.

[Operation] In the ignition coil of the present invention configured as described above, the intermittent primary current supplied to the primary coil causes a core magnetic flux change, and a high voltage is induced in the secondary coil.

In particular, the ignition coil of the present invention is configured such that the primary bobbin containing the primary coil is housed in a large cross-section hole of the secondary bobbin, and the core is housed in the hollow part of the primary bobbin and the small cross-section hole of the secondary bobbin. has been done. Therefore, the discharge energy per unit volume is larger than that of conventional ignition coils, and not only is the axial length reduced, but the cross-sectional area perpendicular to the axial direction is also reduced, making the ignition coil as a whole smaller. . Furthermore, in the case where a permanent magnet is interposed between the two parts of the core within the primary coil, the permanent magnet is arranged so that magnetic flux is generated in the opposite direction to the magnetic flux caused by the primary coil, and due to the presence of this magnetic flux of the permanent magnet, Since the change in the intersecting magnetic flux of the secondary coil becomes large and the output voltage becomes large, the cross-sectional area of the cross section perpendicular to the axial direction of the core can be reduced, resulting in further compactness.

[Embodiments] Hereinafter, preferred embodiments of the ignition coil for an internal combustion engine of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the ignition coil of the present invention.
The ignition coil 10 includes a primary coil 21 and a secondary coil 22 wound around first and second cores 11.12 that include a permanent magnet 18 and form a substantially closed magnetic path. The primary coil 21 is wound around a primary bobbin 23, and the secondary coil 22 is wound around a secondary bobbin 24. The primary bobbin 23 and the secondary bobbin 24 are made of synthetic resin and are each formed into a cylindrical body with a substantially rectangular cross section, and the former is formed to be accommodated in the hollow portion of the latter.

The hollow part of the secondary bobbin 24 is formed into a stepped hole consisting of a large cross-sectional hole 24a having a large cross-sectional area and a small cross-sectional hole 24b having a smaller cross-sectional area than this large cross-sectional hole 24a, and is formed at both ends in the axial direction. Flange portions 24d and 24e having a substantially rectangular outer shape are formed on the sides. The winding of the secondary coil 22 is wound between these collar portions 24d and 24e.

The primary bobbin 23 has a hollow portion 23a having the same cross-sectional shape as the small cross-sectional hole 24b of the secondary bobbin 24, and collar portions 23d and 23e having a substantially rectangular outer shape are formed at both ends in the axial direction. The external shapes of these collar portions 23d and 23e are substantially the same as the cross-sectional shape of the large cross-sectional hole 24a of the secondary bobbin 24, and both nail portions 23d.

After the winding of the primary coil 21 is wound between the coils 23e, the primary coil 21 and the primary bobbin 23 are housed in the large cross-section hole 24a.

The primary coil 21 is wound in one layer from the upper end to the lower end of the primary bobbin 23, and then a second layer is wound from the lower end toward the upper end. That is, the primary coil 21 is wound in two layers, both ends of which are located at the upper end in FIG.
It is connected to terminals 25a and 25b shown in the figure. Therefore, for example, in a single-layer primary coil, a lead wire extending in the axial direction of the primary coil from the lower end to the upper end is required to connect both ends of the winding to the upper end terminal, whereas in this embodiment, Since the primary coil 21 is connected to both terminals 25a and 25b only by the central winding, no wasted lead wire or space is required.

A first core 11 and a second core 12 are magnetically coupled to each other in the axial center of the hollow portion 23a of the primary bobbin 23 via a permanent magnet 18. Both the first core 11 and the second core 12 are laminates of silicon steel plates, and the first core 11 is formed in a T-shape when viewed from the front, and the second core 12 is formed into a substantially E-shape when viewed from the front. Both are attached to the secondary bobbin 24 as shown in FIG.
It is joined around the circumference. That is, the first core 11 and the second core 11
A stepped portion is formed at each end to which the core 12 is joined, and the first core 11 is press-fitted into the second core 12 and magnetically coupled. Hollow part 2 in first core 11
The cross-sectional shape of the leg portion 11a accommodated in the hollow portion 23
It is made the same as the cross-sectional shape of the leg part 12a accommodated in the small cross-section hole 24b of the 2nd core 12, and is made the same as the cross-sectional shape of a.

A permanent magnet 18 is interposed between these leg portions 11a and 12a. This permanent magnet 18 is arranged so as to be in the opposite direction to the direction of the magnetic flux formed in JM1 and the second core 11.12 when the primary coil 21 is energized. The permanent magnet 18 is samarium-cobalt (Sm-co)
A rare earth magnet made of a metal sintered body is used, but a rare earth plastic magnet may also be used.

Each of the above components is housed in a cylindrical case 30, one end of the winding of the primary coil 21 is connected to a battery (not shown) via a terminal 25a, and the other end is connected to a control circuit (not shown) via a terminal 25b. connected to the igniter. One end of the winding of the secondary coil 22 is connected to the terminal 25a together with one end of the winding of the primary coil 21, and the other end is connected to the case 3.
The secondary connector 32 is connected to an electrode (not shown) in a secondary connector 32 formed into a 0-body. This electrode is the third
It is electrically connected to a spark plug 60 shown in the figure.

Furthermore, the case 30 is filled with a thermosetting synthetic resin and hardened to form a resin portion 31. As a result, the primary coil 21 and the secondary coil 22 are impregnated and fixed, and insulation that can withstand the high voltage output from the secondary coil 22 is ensured.

A control circuit (not shown) supplies a primary current to the primary coil 21 of the ignition coil 10 configured as described above, and when this is interrupted at a predetermined frequency, a magnetic flux change occurs in the closed magnetic path including the permanent magnet 18.

This generates a predetermined high voltage in the secondary coil 22, and this high voltage is supplied directly from the secondary connector 32 to the spark plug 60 shown in FIG.

In this case, the permanent magnet 18 interposed between the first core 11 and the second core 12 can ensure a large change in effective magnetic flux. In the part where the permanent magnet 18 is inserted, the closed magnetic circuit is separated, and the magnetic field formed by the permanent magnet 18 and the primary coil 21 are separated.
Since the magnetic field formed by the magnetic field tends to repel each other and disperse, leakage of magnetic flux can occur particularly from this part. However, in this embodiment, the permanent magnet 18 is connected to the primary coil 2.
Since the magnetic flux from the primary coil 21 is concentrated on the permanent magnet 18, leakage magnetic flux is extremely small. The magnetic flux of the secondary coil 22 becomes large, and the output voltage of the secondary coil 22 becomes large.

4 and 5 show two ignition coils 10a according to the present applicant's invention for comparison with this embodiment.

tob.

In the ignition coil 10a shown in FIG. 4, the legs of the T-shaped 341 cores 111 and the E-shaped second core 112 are accommodated in the hollow part of the primary bobbin 123, and the primary bobbin 123 is connected to the secondary bobbin 123. It is accommodated in the hollow part of 124. The axial lengths of the primary bobbin 123 and the secondary bobbin 124 are approximately equal, and the rest of the structure is the same as that of the embodiment shown in FIG. The winding of the primary coil 121 is wound around the primary bobbin 123 in a single layer, and the secondary coil 121 is wound around the secondary bobbin 124.
is wrapped in multiple layers.

The ignition coil tab in FIG. 5 has a T-shaped first core 211 and an E-shaped second core 21 in the hollow part of the bobbin 223.
The primary coil 221 and the secondary coil 222 are axially divided and wound through a flange formed in the axially intermediate portion of the bobbin 223. .

Ignition coil 10a shown in FIGS. 4 and 5 above.

When the same number of turns of the primary coil and the secondary coil are wound around tob and the ignition coil 10 of this embodiment, the overall length of the core portion including the first and second cores has the relationship shown in FIG. 6. In the same figure, A indicates the ignition coil 10a% B indicates the ignition coil tab% C indicates the ignition coil 10 of this embodiment (hereinafter, the same applies to FIGS. 7 to 9), that is, the ignition coil 10a has a primary coil 121 wound in one layer, so the overall length of the core portion is the longest, and ignition coil 10b has a primary coil 221 and a secondary coil 222 arranged side by side in the axial direction, but has a multi-layered winding, so it is the shortest.

Each ignition coil 10a, 10b in the above state.

The measurement results of the ignition performance of lO are shown in FIGS. 7 and 8. In other words, the output voltage of the secondary coil is approximately the same value for each ignition coil, as shown in the vertical axis of FIG. 10a is the maximum and each ignition coil tab is the minimum. This difference is due to the difference in energy conversion efficiency of each ignition coil.

Therefore, by setting the number of turns of the primary coil and secondary coil so that the output voltage and discharge energy of the secondary coil between each ignition coil are equal, and comparing the total length of the core part,
As shown in FIG. 9, the overall length of the core portion of the ignition coil 10 of this embodiment is the shortest. At this time, when the ignition coil 10a is used as a reference, the thickness of the permanent magnet 18 of the ignition coil tab is greatly increased, and the number of turns of the primary coil 221 and the secondary coil 222 is increased while the turn ratio remains the same. will be increased to Furthermore, in the ignition coil lO of this embodiment, the thickness of the permanent magnet 18 is slightly increased, and the primary coil 21
The number of turns of both secondary coils 22 and 22 is slightly increased while the turn ratio of the secondary coil 22 remains the same. In this way, when ensuring the same ignition performance, the ignition coil 10 of this embodiment is formed in the smallest size.

That is, when comparing the ignition coil 10 of this embodiment with the ignition coil tab of FIG. 5, which can structurally have the shortest axial length as shown in FIG. Since the conversion efficiency is high, the number of turns of the primary coil 21 and the secondary coil 22 can be reduced, and the total length of the core portion can therefore be shortened.

Next, in order to compare the ignition coil 10 of this embodiment with the ignition coil 10a of FIG. 4, the dimensional relationship in the ignition coil lOa will be described. Ignition coil 10 as a prerequisite
The outer diameter of a is set to a predetermined value, and the first and second cores 1
When the cross-sectional area of cores 11 and 112 is set to a predetermined value, the value of the gap P between the first and second cores ttt and ttz is determined.

When the current It (A) of the primary coil 121 is set to obtain a predetermined discharge energy E (J), the following (1
) and (2) determine the number of turns N1 of the primary coil 121.

Here, Ll represents the self-inductance (H) of the primary coil 121, and Φ represents the magnetic flux (wb).

In order to obtain a predetermined secondary generated voltage V2 (V), the number of turns N2 of the secondary coil 122 is determined by the following equation (3).

Vz /Vt = N2 /Nt = (3) Note that vl is the voltage (V) of the primary coil 121 and is set according to conditions on the control circuit side (not shown).

Furthermore, as shown in FIG. 4, since the thickness Q of the secondary bobbin 124 and the thickness R of the resin portion 31 are set to the thicknesses necessary to ensure withstand voltage, the winding of the secondary coil 122 The thickness T after winding is determined. Therefore, the secondary bobbin is necessary for winding the winding of the secondary coil 122 with N2 turns! The axial length 12 of 24 is determined. Further, the number of turns N of the primary coil 121 is tightly wound, and the axial length 1 of the primary bobbin 123 is also determined.

The axial length J of the above primary coil 121 and secondary coil 122! t, f2 is u, <41. Generally, this relationship is established, and in the ignition coil 10a, due to the structure shown in FIG. 3g4, the primary coil 121 is wound sparsely, resulting in wasted space around the primary bobbin 123. Conversely, the axial length is 11. u, is fi
In the case where t > 12, if the thickness T of the winding of the secondary coil 122 after winding is set to be 411 = IL2, the axial length of the ignition coil tab is only long. Therefore, the thickness R of the resin portion 31 becomes larger than necessary, resulting in wasted space.

In contrast, in this embodiment, by appropriately setting the axial length ratio of the large cross-section hole 23a and the small cross-section hole 23b, the above-mentioned waste is avoided in the relationship C between the primary coil 21 and the secondary coil 22. no space is created, i.e.
The ignition coil 10 of this embodiment is the ignition coil 10a shown in FIG.
The volume can be made smaller compared to . Therefore, although the energy conversion efficiency of the ignition coil 10 of this embodiment is slightly lower than that of the ignition coil 10a, by increasing the number of turns N,, N, the secondary generated voltage and discharge energy can be made equal to that of the ignition coil 10a. Even if it is made to be, the overall length of the core portion will be shorter than the ignition coil 10a as shown in FIG.

FIG. 3 shows an embodiment in which the ignition coil 1o is attached to a radial cover to a cylinder of an internal combustion engine, and shows a cross section of the cylinder head of one cylinder. The internal combustion engine 1 in this embodiment includes a plurality of cylinders arranged in series, and an ignition coil IO is attached to each cylinder.

A cylinder head 2 made of aluminum alloy of the internal combustion engine 1 is provided with a pair of intake boats 4 and an exhaust boat 5 that open into the combustion chamber 1a for each cylinder, and each of these has an intake valve 6 and an exhaust valve 7, respectively. Although they are installed, only the inner set of these is shown in FIG. That is, in this embodiment, a pair of intake valves 6 and exhaust valves 7 are installed for each cylinder, for a total of four valves, making it a so-called four-valve engine.

A pair of camshafts 8.9 are rotatably supported above the cylinder rod 2 by bearing members 3b and 3C, and are configured to directly drive the intake valve 6 and exhaust valve 7. There is.

In other words, it has a direct-drive double overhead camshaft valve train. Moreover, the rad cover 3 is joined to the upper part of the cylinder rad 2 and the cylinder made of rainbow aluminum alloy, and an oil chamber 52 is defined between the two.

A stepped mounting hole 2a is formed between the intake valve 6 and the exhaust valve 7 of the cylinder head 2, extending from the oil chamber 52 toward the combustion chamber 1a. An ignition plug 60 is screwed into a small diameter hole on the side of the combustion chamber la of this mounting hole 2a, and its electrode portion is connected to the combustion chamber la side.
It is fixed and exposed inside. - On the other hand, an insertion hole 3a is opened at the top of the cylinder rad cover 3, facing the opening of the mounting hole 2a to the oil chamber 52.
is formed, and a stepped portion is formed on the inner surface of the insertion hole 3a. A shielding cylinder 40, which is a cylindrical member made of a non-magnetic material, is inserted into the mounting hole 2a through the insertion hole 3a,
One end thereof is fixed near the lower end of the mounting hole 28 by press fitting or the like. The other end of the shielding cylinder 40 protrudes outward from the rad cover 3 from the insertion hole 3a into the cylinder, and has a threaded groove formed at its tip.

Then, after the annular sealing member 50 is fitted into the shielding cylinder 40 and placed in the step in the insertion hole 3a of the rad cover 3 into the cylinder, the nut 40a is screwed into the screw groove of the shielding cylinder 40. . The sealing member 50 is pressed against the stepped portion of the insertion hole 3a and the outer peripheral surface of the shielding cylinder 40 by this nut 40a,
The insertion hole 3a is sealed. As a result, the storage chamber and the oil chamber 52 inside the shielding cylinder 40 are completely separated, and the oil chamber 52 is completely separated.
The ignition coil 10 and a cylindrical body whose one end is connected to the secondary connector 32 at its tip are connected to a storage chamber within the shielding cylindrical body 40 so that the oil droplets inside the shielding cylindrical body 40 do not enter into the shielding cylindrical body 40. The member 28 is inserted and the other end of the connecting member 28 is connected to the terminal portion of the spark plug 60. Thereby, the ignition coil 10 and the ignition plug 60 are electrically connected via the connecting member 28.

The ignition coil 10 is connected to the secondary connector 3 as described above.
2 is inserted into the shielding cylinder 40 and bolted to the top of the rad cover 3 to the cylinder by a bracket 51.

When the internal combustion engine 1 is started and the camshaft 8.9 rotates, the intake valve 6 and the exhaust valve 7 open at a predetermined period.
The intake port 4 and the exhaust boat 5 are opened and closed. The primary current of the ignition coil 10 is controlled by the ignition signal output in a predetermined order according to the rotation of the internal combustion engine l,
As mentioned above, a predetermined high voltage is generated in the secondary coil 22. This high voltage is directly applied to 60 spark plugs via the secondary connector 32 and connecting member 28, and
Spark discharge occurs at the electrode at the tip of 0, and the combustion chamber! a
The compressed mixture inside is aged.

As described above, the ignition coil 10 of the above embodiment is small, has a small outer diameter, and can be easily accommodated in the shielding cylinder 40, so that it can be installed even in an internal combustion engine with a small valve angle.

In the above embodiment, 341 and the second core 11.
Although the permanent magnet 18 is interposed between the permanent magnets 12 and 12, a minute air gap may be used instead of interposing the permanent magnet 18.

Further, in the above embodiment, both the primary bobbin 23 and the secondary bobbin 24 are cylinders with a rectangular cross section, but they may also be cylinders with a circular cross section, and the core of 'i41 is formed into a shape that is a combination of a disk and a cylinder. , the second core may be a cylindrical body with a cylinder in the hollow part, and the primary bobbin and the secondary bobbin of the cylindrical body each having a disk-shaped permanent magnet may be accommodated in the sealed space formed by both. good.

[Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

That is, according to the ignition coil of the present invention, the primary bobbin is housed in the large cross-section hole of the secondary bobbin, and the core is housed in the hollow part of the primary bobbin and the small cross-section hole of the secondary bobbin. As a result, the discharge energy per unit volume is larger than in the past, and the axial length of the ignition coil as a whole can be reduced, and the cross-sectional area of the cross section perpendicular to the axial direction can be reduced, making it possible to create a compact ignition coil. can. Therefore, it is suitable for a coil distribution ignition system of an internal combustion engine, and can be easily installed even in an internal combustion engine with a narrow valve angle.

In addition, in the case of a permanent magnet interposed between the cores in the primary coil, the output voltage of the secondary coil becomes large and the cross-sectional area of the cross section perpendicular to the axial direction of the core can be reduced, making it even more effective. Miniaturization is possible.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an ignition coil according to an embodiment of the present invention, FIG. 2 is a plan view of the same, and FIG. 4 is a longitudinal sectional view of the ignition coil of 's1 for comparison with the ignition coil of the embodiment shown in FIG. 1, FIG. 5 is a longitudinal sectional view of the second ignition coil, and FIG. A graph comparing the total length of the core part when the number of coil turns is the same in the ignition coil of the example and the first and second ignition coils, FIG. 7 is a graph showing the output voltage of the secondary coil in each ignition coil, FIG. 8 is a graph showing the discharge energy, and FIG. 9 is a graph showing the total length of the core portion of each ignition coil when the ignition performance is the same. ! ...Internal combustion engine, 2-...Cylinder head. 10.10a, 10b...Ignition coil. 11-...first core, 12...second core. 11 a = leg, 12 a... leg. 18--Permanent magnet, 21--Primary coil. 22--Secondary coil, 23--Primary bobbin. 23 a---Hollow part, 24---Secondary bobbin-
. 24a---Large cross-section hole, 24b---Small cross-section hole.

Claims (2)

[Claims] (1) A secondary bobbin consisting of a cylindrical body having a hollow section with stepped holes of a large cross-sectional hole and a small cross-sectional hole, with a secondary coil wound around the outer surface of the cylindrical body, and a primary coil wound around the outer surface of the cylindrical body. A primary bobbin that is housed in a large cross-section hole of the secondary bobbin, a hollow portion of the primary bobbin, a small cross-section hole of the secondary bobbin that communicates with the hollow portion, and is arranged around the secondary bobbin. An ignition coil for an internal combustion engine, comprising a core that forms a closed magnetic path. (2) The axial length of the primary bobbin is the same as the axial length of the large-section hole of the secondary bobbin, and the cross-sectional shape of the hollow part of the primary bobbin and the cross-section of the small-section hole of the secondary bobbin the core has two parts having substantially the same cross-sectional shape as the cross-sectional shape accommodated in the hollow part of the primary bobbin and the small cross-sectional hole of the secondary bobbin, and the two parts are connected to the primary bobbin. 2. The ignition coil for an internal combustion engine according to claim 1, wherein the ignition coils are arranged to face each other with a predetermined gap in between, and a permanent magnet is interposed in the gap.