JP2936239B2 - Ignition coil for internal combustion engine - Google Patents

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 for increasing an output voltage by interposing a permanent magnet in a magnetic path.

[0002]

2. Description of the Related Art With respect to an ignition coil of an internal combustion engine, an increase in output voltage and discharge energy is required with the recent increase in output of the internal combustion engine. For this reason, it is necessary to take measures such as increasing the cross-sectional area of the core and increasing the number of turns of the coil wound around the core. However, in such a case, the ignition coil becomes large and it becomes difficult to mount the ignition coil on the internal combustion engine.

On the other hand, as means for increasing the output voltage of the secondary coil, it has been proposed to interpose a permanent magnet magnetized in the direction opposite to the exciting direction of the primary coil in the magnetic path. In 2-37705,
The specification of the core and the permanent magnet interposed between the cores is defined.

[0004]

As described in the above publication, in an ignition coil in which a permanent magnet is interposed in a magnetic path, a change in magnetic flux when the primary current is interrupted is large, and an output voltage generated in the secondary coil is large. It is larger than the conventional ignition coil. However, in the ignition coil described in the above publication, no consideration is given to the leakage magnetic flux. That is, in this type of ignition coil, since a large amount of leakage magnetic flux is generated when the primary coil is energized, most of the increased magnetic flux is canceled out, and the increase in the magnetic flux is small.

In particular, in an ignition coil in which a permanent magnet is disposed outside the coil as described in the above-mentioned publication, the leakage magnetic flux becomes large. Further, when the secondary coil is wound around the primary coil as described in the above publication, the coil winding portion becomes large, and when the coil is mounted on an internal combustion engine, the dimension in the vertical direction (thickness) ) Is a great constraint on the design of the internal combustion engine. However, simply reducing the thickness of the coil winding increases the leakage magnetic flux. On the other hand, if it is necessary to secure a necessary magnetic flux, the core must be increased, resulting in an increase in size.

Accordingly, the present invention relates to an ignition coil in which a permanent magnet is interposed in a magnetic path, and an object thereof is to suppress leakage of magnetic flux and secure predetermined ignition performance without increasing the size of the ignition coil.

[0007]

In order to achieve the above object, an ignition coil for an internal combustion engine according to the present invention comprises a pair of U-shaped cores having a first leg and a second leg. A pair of cores arranged such that an end face of each first leg and an end face of each second leg face each other, and a primary wound around each first leg of the pair of cores. A coil, a secondary coil wound around the second leg of each of the pair of cores, and a magnetic flux interposed between the end faces of the first leg of each of the pair of cores when the primary coil is energized And a permanent magnet that generates a magnetic flux in the opposite direction.

In the ignition coil for an internal combustion engine, it is preferable that the permanent magnet is disposed at an axial center of the primary coil.

In the ignition coil for an internal combustion engine, the pair of cores may be a laminate of directional silicon steel sheets having the same shape, and a cross-sectional area of the first leg may be determined by cutting a cross-sectional area of the second leg. Area and the cross-sectional area of the permanent magnet
It is desirable that the cross-sectional area of the legs is substantially the same.

In particular, the sectional area of the permanent magnet is Sm,
When the residual magnetic flux density of the permanent magnet is Br (Tesla) and the cross-sectional area of the minimum cross-section of the pair of cores is Sc,
The area ratio Sm / Sc may be set to be 1.8 Tesla / Br. The value of the area ratio Sm / Sc is 1.
5 to 2.6 is preferred.

[0011]

In the ignition coil for an internal combustion engine according to the present invention, the primary current supplied to the primary coil is interrupted to cause a magnetic flux change in the core, and a high voltage is induced in the secondary coil. You.

At this time, due to the presence of the permanent magnet which generates a magnetic flux in the opposite direction to the magnetic flux when the primary coil is energized, the change of the interlinkage magnetic flux of the secondary coil becomes large and the output secondary voltage becomes large. In particular, since the permanent magnet is arranged at an appropriate position in the primary coil, for example, at the center in the axial direction, local magnetic saturation is eliminated, and leakage magnetic flux is reduced.

The core is a laminated body of grain-oriented silicon steel sheets, the cross-sectional area of the first leg is larger than the cross-sectional area of the second leg, and the cross-sectional area of the permanent magnet is the first leg. And the cross-sectional area of the permanent magnet Sm
And the area ratio Sm / of the cross-sectional area Sc of the minimum cross-section of the pair of cores.
In the case where Sc is set to 1.8 Tesla / Br, the demagnetization of the permanent magnet is prevented, and a predetermined magnetic flux linkage to the secondary coil is ensured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an ignition coil for an internal combustion engine according to the present invention will be described below with reference to the drawings. FIGS. 1 to 4 show an embodiment of an ignition coil according to the present invention. An ignition coil 1 has a pair of U-shaped cores 2 and 3, and a primary coil assembly 10 and a secondary coil assembly 2 are respectively attached to both legs. The next coil assembly 20 is mounted.

The cores 2 and 3 are respectively connected to first legs 2a and 3a.
A U-shaped iron core having second leg portions 2b and 3b, and a plurality of directional silicon steel plates whose rolling direction is the vertical direction in FIG. As is well known, a grain-oriented silicon steel sheet exhibits extremely good magnetic properties in the rolling direction, but the magnetic properties deteriorate at an angle different from the rolling direction. For this reason, in the cores 2 and 3, the width of the connecting portions 2c and 3c orthogonal to the rolling direction is set to be 1.5 to 1.8 times the width of the second legs 2b and 3b in the rolling direction. For example, when allowing a magnetic flux density of 1.7 T (tesla) in the rolling direction, 45 ° with respect to the rolling direction
In the direction of, the magnetic flux density of 1.1T is the limit.
The width Wc of the connecting portions 2c, 3c extending in a direction perpendicular to the longitudinal direction of the legs 2b, 3b of the second arm 2
The width Wb of b, 3b is set so that Wc ≒ Wb × 1.7 / 1.1.

The surfaces of the cores 2 and 3 are covered with an elastic member such as an elastomer, and an elastic member layer 4 is formed. The elastic member layer 4 absorbs a difference in thermal expansion between the cores 2 and 3 and components surrounding the cores 2 and 3 and is made of, for example, a polyolefin-based thermoplastic elastomer. This elastomer has the same elasticity as ordinary rubber, and is a high-molecular-weight substance formed by the same processing method as a thermoplastic resin.

In this embodiment, the first legs 2a,
Although the elastomer is double-coated only on the front and back surfaces on the 3a side and only on both side surfaces on the second leg portions 2b and 3b side, the entire surface may be covered. The elastic member layer 4 is
It is also possible to mix a predetermined ratio of a modifier having excellent adhesiveness and affinity with the elastomer. As this modifier, a terpolymer of ethylene, acrylic acid ester, and maleic anhydride is known, and when this is mixed with an elastomer, it is greatly affected by a difference in thermal expansion between cores 2 and 3. And good adhesion is obtained.

As the permanent magnet 5, a rare earth magnet of a sintered body of a samarium-cobalt (Sm-Co) -based metal having a large residual magnetic flux density and being hardly demagnetized is used. For example,
Normal magnetic flux density is 0.8T (tesla) and temperature is 150T.
Even if the magnetic flux density in the opposite direction when the primary coil 12 is energized becomes 0.7 T (tesla) even at ° C., a material that does not demagnetize is used.

The permanent magnet 5 has a substantially square shape, and the width of one side thereof is within a range of 1.5 to 2.6 times the width of one side of the cross section of the second legs 2b, 3b of the cores 2, 3. It is set to about twice in this embodiment, and is equal to the width of one side of the cross section of the first leg portions 2a and 3a. The width of the other side of the permanent magnet 5 is set to be the same as the width (thickness) of the other side of the cross section of the second legs 2b, 3b of the cores 2, 3, so that the cross-sectional area of the permanent magnet 5 is The cross-sectional area of the first and second leg portions 2a and 3a is the same as that of the second and third leg portions 2b and 3b, and is approximately twice the cross-sectional area of 1.5 to 2.6 times the cross-sectional area of the second leg portions 2b and 3b. . The permanent magnet 5 is arranged so as to be in the direction opposite to the direction of the magnetic flux formed in the cores 2 and 3 when the primary coil 12 is energized.

A primary coil assembly 10 is mounted around the first legs 2a, 3a of the cores 2, 3. The primary coil assembly 10 includes a primary coil 1 on a primary bobbin 11.
2 are wound, and primary terminals 13a and 13b shown in FIG. The primary bobbin 11 is a resin cylinder having a substantially rectangular cross section, and has flanges 1 at both ends.
1a are formed, between which the windings of the primary coil 12 are wound in two or four layers.

Both ends of the primary coil 12 are connected to primary terminals 13a and 13b, respectively.
3a and 13b are connector terminals 6a of the connector 6,
6b by resistance welding. The connector 6 is a connector terminal 6 formed by insert resin molding.
a and 6b are formed therein, and are fitted into openings formed in the side surface of the case 30. The connector terminal 6a is connected to a not-shown battery, and the connector terminal 6b is connected to a not-shown control circuit, commonly called an igniter.

A secondary coil assembly 20 is mounted around the second legs 2b, 3b of the cores 2, 3. The secondary coil assembly 20 includes the secondary bobbin 21 and the secondary coil 2.
2, a secondary terminal 23a is fixed to the secondary bobbin 21, and a secondary terminal 23b shown in FIG. The secondary bobbin 21 has a plurality of flanges 21a formed at predetermined intervals in the axial direction, and thus a plurality of grooves 21b are formed therebetween.
1b, the winding of the secondary coil 22 is sequentially wound from the upper side to the lower side in FIGS.

As shown in FIG. 3, a support portion 21c is formed in the flange 21a at the upper end so as to extend in the axial direction, and a secondary terminal 2 is formed in a groove (not shown) formed in the support portion 21c.
3a is fitted. The start of the winding of the secondary coil 22 is connected to the secondary terminal 23a. The secondary terminal 23a is connected to a lead 8a at one end of the diode 8 shown in FIG.
Are joined by resistance welding. The end of the winding of the secondary coil 22 is connected to the secondary terminal 23b. The secondary terminal 23b is provided with a hole having a claw, into which a connecting portion 7a of the high-voltage terminal 7 described later is press-fitted. The diode 8 is used to prevent a spark plug 40, which will be described later, from igniting due to a voltage of 1 to 3 kv generated when the primary coil 12 is energized, and a lead 8b is connected to a claw 6c provided on the connector terminal 6b.
Are joined by resistance welding, and then the lead 8a is joined as described above.

The case 30 is a housing made of synthetic resin, and has a secondary connector portion 30a formed at the bottom. A high-voltage terminal 7 having a bottomed cylindrical body is accommodated in the secondary connector portion 30a by insert resin molding, and a connection portion 7a extending and formed at the bottom portion penetrates through the bottom surface of the secondary connector portion 30a to form a case. It extends into 30. This connection part 7a
Is press-fitted into a hole formed in the secondary terminal 23b,
It is electrically connected.

The space inside the case 30 is filled with a thermosetting synthetic resin, for example, an epoxy resin, and cured to form a resin portion 9. As a result, the primary coil 12 and the secondary coil 22 are impregnated and fixed, and the insulation property that can withstand the output high voltage of the secondary coil 22 is secured.

The manufacturing and assembling process of the ignition coil 1 having the above structure will be described. First, a predetermined number of directional silicon steel sheets are laminated, pressed into a U-shape, and the steel sheets are joined by stacking. And a core 2
Form 3 After performing magnetic annealing in order to cope with the deterioration of the magnetic characteristics due to this processing, the elastic member layer 4 of the elastomer is coated.

On the other hand, a primary bobbin 11 having a cylindrical body provided with primary terminals 13a and 13b by insert resin molding.
And the primary coil 12
Wrap. Both ends of the winding of the primary coil 12 are flanged 11a
Primary terminals 13a, 13 through notches 11c
b, and then soldered. Thereby, the primary coil assembly 10 is formed.

Similarly, the secondary terminal 23b is provided by insert resin molding, and a plurality of secondary terminals 23b (7 in this embodiment) are provided.
The secondary bobbin 21 is formed as a cylindrical body having a flange 21a, and the secondary coil 22 is wound around each groove 21b. Further, a support portion 21c having a groove is integrally formed at one end of the flange portion 21a, and the secondary terminal 23a is fitted into the groove. One end of the winding of the secondary coil 22 is wound around the secondary terminal 23a and then soldered, and the other end is wound around the secondary terminal 23b and soldered. Thus, the secondary coil assembly 20 is formed.

Further, a case 30 containing the high voltage terminal 7 is formed by insert resin molding. As shown in FIG.
Is formed so that the tip of the connecting portion 7a is exposed.

The primary coil assembly 10 and the secondary coil assembly 20 are juxtaposed, and the first and second legs 3a, 3b of one core 3 are inserted into the respective hollow portions, and are permanently set in the primary bobbin 11. After housing the magnet 5, the first and second legs 2a and 2b of the other core 2 are inserted. This allows
A permanent magnet 5 is provided for each of the first legs 2a, 3a of each of the cores 2, 3.
Sandwiched between. These assemblies are housed in the case 30, and the secondary terminal 23b is engaged with the high voltage terminal 7 to be in an electrically connected state.

The connector 6 attached to the case 30
Are connected to the primary terminals 13a and 13b of the primary coil assembly 10 by resistance welding. Further, the secondary terminal 23a of the secondary coil assembly 20 and the connector terminal 6b are joined via the diode 8 by resistance welding. Finally, the space in the case 30 is filled with an epoxy resin, and cured by heat to impregnate and fix.

As described above, in this embodiment, the width of one side of the permanent magnet 5 is about twice the width of one side of the cross section of the second legs 2b, 3b of the cores 2, 3, and the other side is the second side. Legs 2b, 3b
Is the same width as the width of the other side of the cross section of
The area ratio is about twice as large as the cross section of the leg portions 2b and 3b, and the optimum area ratio is set as follows. In the following example, it is assumed that a samarium-cobalt rare earth magnet is used as the permanent magnet 5, directional silicon steel sheets are used for the cores 2 and 3, and the leakage magnetic flux is 20%. Further, the permanent magnet 5 used has a magnetic flux density of 0.8 T (tesla) when the primary current is interrupted and is not demagnetized until the magnetic flux density in the opposite direction when the primary current is applied becomes 0.7 T. The cores 2 and 3 are 1.8T
The magnetic flux density is higher than that of the magnetic flux density.

That is, since the grain-oriented silicon steel sheets are used for the cores 2 and 3, the saturation magnetic flux density at the time of primary current application is 1.8 T or more, and the magnetic flux density of the permanent magnet 5 at that time is -0.7T.
T, which is smaller than 0.8 T when no current is supplied temporarily. Thus, the residual magnetic flux density of the permanent magnet 5 is Br
(Tesla), the area ratio S of the cross-sectional area Sm of the permanent magnet 5 and the cross-sectional area Sc of the second legs 2b, 3b of the cores 2, 3
m / Sc is set to satisfy the following relationship. Sm / Sc = 1.8T / Br

In the rare earth magnet including the permanent magnet 5 in this embodiment, the residual magnetic flux density Br can be set to 0.7T to 1.2T, and when this is substituted into the above equation, the area ratio Sm / Sc Has a value of 1.5 to 2.6. Thus, the thickness of the permanent magnet 5, the leakage flux,
In consideration of the magnetic saturation region of the cores 2 and 3 and the demagnetization region of the permanent magnet 5, an area ratio Sm / at which a predetermined output secondary voltage can be secured.
When Sc is determined, a value in the range of 1.5 ± 10% to 2.6 ± 10% is optimal.

FIG. 6 shows the relationship between the area ratio Sm / Sc and the output secondary voltage (kV).
This shows a change in the output secondary voltage when c is constant, the sectional area Sm of the permanent magnet 5 is increased, and the area ratio Sm / Sc is increased. In the figure, the residual magnetic flux density Br is 1.
The output characteristic at 2T (tesla) is indicated by a broken line,
The characteristic at T is indicated by a solid line, and the characteristic at 0.7T is indicated by a dashed line. As shown in FIG.
If the residual magnetic flux density Br is determined by the characteristics of (1), the area ratio Sm / Sc at which the output secondary voltage becomes maximum is approximately 1.5 to 2.
6 is set. From the viewpoint of preventing the demagnetization of the permanent magnet 5, the area ratio Sm / Sc is increased. However, to reduce the size while considering the prevention of demagnetization, 2.25 is required.
(= 1.8 / 0.8).

The ignition coil 1 is mounted on a cylinder head cover 53 of an internal combustion engine 50 for each cylinder as shown in FIG. The internal combustion engine 50 in this embodiment includes a plurality of cylinders arranged in series, and FIG. 5 shows a cross section of a cylinder head of one of the cylinders. The cylinder head 52 of the internal combustion engine 50 is integrally formed with an intake port and an exhaust port that open to the combustion chamber 51 for each cylinder, and a pair of an intake valve 56 and an exhaust valve 57 are mounted on these, respectively. , FIG. 5 shows only one of these sets. That is, in the present embodiment, a so-called four-valve engine is provided with a pair of intake valve 56 and exhaust valve 57 for each cylinder, that is, a so-called four-valve engine. It has become.

In the internal combustion engine 50, the cylinder head 5
A cylinder head cover 53 is joined to the upper part of the cylinder head 2, and an oil chamber 55 is defined between the two. Cylinder head 5
A mounting hole 54 is formed between the second intake valve 56 and the exhaust valve 57 from the oil chamber 55 toward the combustion chamber 51.
A spark plug 4 is inserted into a small diameter hole of the mounting hole 54 on the combustion chamber 51 side.
0 is screwed, and the electrode portion is fixed in a state where it is exposed inside the combustion chamber 51.

On the other hand, on the top of the cylinder head cover 53,
A mounting recess 53a is formed to face the opening of the mounting hole 54 to the oil chamber 55, and an insertion hole 53b is formed in the bottom of the mounting recess 53a. A cylindrical shielding cylinder 41 formed of metal is inserted into the mounting hole 54,
One end is fixed to the vicinity of the lower end of the mounting hole 54 by press fitting or the like. The other end of the shielding cylinder 41 protrudes from the mounting hole 54 and extends to the insertion hole 53b of the mounting recess 53a.

The ignition coil 1 has a secondary connector 30
After an annular seal member 42 is fitted around the outer periphery of the cylinder a, the annular seal member 42 is inserted into the shielding cylinder 41, and its main body is accommodated in the mounting recess 53 a of the cylinder head cover 53. As a result, the secondary connector 30a of the ignition coil 1 is electrically connected to one end of the connecting member 43, and the other end is electrically connected to the ignition coil 40. As described above, the ignition coil 1 of the present embodiment is small in size, and particularly the main body is formed thin, so that it can be easily housed in the cylinder head cover 53. Further, the storage chamber in the shielding cylinder 41 and the oil chamber 55 are completely separated from each other, and the oil droplets in the oil chamber 55 do not enter the shielding cylinder 41.

The operation of this embodiment will be described. The internal combustion engine 50 is started, and the intake valve 56 and the exhaust valve 57 are driven at a predetermined cycle. Then, the primary current of the ignition coil 1 is controlled by an ignition signal output in a predetermined order according to the rotation of the internal combustion engine 50, and a predetermined high voltage is generated in the secondary coil 22. This high voltage is applied to the high voltage terminal 7
And applied to the ignition plug 40 via the connecting member 43,
Spark discharge occurs at the electrode portion at the tip of the spark plug 40, and the compressed air-fuel mixture in the combustion chamber 51 is ignited.

In the ignition coil 1, for example, the upper part of the permanent magnet 5 in FIG. 1 is an N pole, and the flow of magnetic flux circulates in the cores 2 and 3 to form a closed loop. There is almost no leakage of magnetic flux in this state. When the primary coil 12 is energized by a control circuit (not shown) and a primary current is supplied, the magnetic flux flows in a direction opposite to the magnetization direction of the permanent magnet 5. And
When the primary current is cut off, a back electromotive force is induced in the secondary coil 22, and a high voltage of 30 to 40 kv is generated. This high voltage is applied to the ignition plug 40 via the secondary terminal 23b and the high voltage terminal 7.

In the ignition coil 1 of this embodiment, a large change in effective magnetic flux can be secured by the permanent magnet 5 interposed between the cores 2 and 3. In particular, since the permanent magnet 5 is accommodated in the primary coil 12 and arranged at an appropriate position in the center in the axial direction, the concentration of magnetic flux reduces the leakage magnetic flux as compared with the conventional case, and the local magnetic There is no saturation. In addition, the minimum cross section of the cores 2 and 3 (second
Cores 2 and 3 are saturated before the magnetic field generated by the primary coil 12 reaches the demagnetization limit of the permanent magnet 5 because the cross-sectional area of the permanent magnet 5 is about twice the cross-sectional area of the legs 2b and 3b). It does not occur that the magnetic flux density is reached and the permanent magnet 5 is demagnetized. Accordingly, the magnetic flux density formed in the primary coil 12 becomes large with respect to the magnetomotive force generated by the application of the primary current, so that the discharge energy increases and the secondary coil 22
Therefore, the output voltage of the secondary coil 22 increases.

In the above embodiment, the first leg 2
Although the cross-sectional area of the first leg 2a is larger than that of the second leg 2b, 3b, the cross-sectional area of the first leg 2a is larger than that of the second leg 2b.
The end portions a and 3a may be formed in a tapered shape until the cross-sectional area gradually decreases as the distance from the end surface increases and becomes the same as the cross-sectional area of the second leg portions 2b and 3b. This makes it possible to reduce the weight of the cores 2 and 3 while ensuring a predetermined ignition performance.

[0044]

Since the present invention is configured as described above, the following effects can be obtained. That is, according to the ignition coil of the present invention, the primary coil is wound around the first leg of the pair of U-shaped cores, and the secondary coil is wound around the second leg. It is possible to reduce the thickness, and since the permanent magnet is provided in the primary coil, the leakage flux is reduced, the change in the flux linkage of the secondary coil becomes large, and a large output secondary voltage is generated. can get.

In particular, in the case where the permanent magnet is arranged at the axial center position in the primary coil, the leakage magnetic flux can be effectively reduced and the pair of cores can be formed in the same shape. Mounting is easy.

The pair of cores is a laminated body of grain-oriented silicon steel sheets, and the cross-sectional area of each first leg is larger than the cross-sectional area of the second leg, and the cross-sectional area of the permanent magnet is the first. When the sectional area is substantially the same as the sectional area of the leg, particularly, the sectional area Sm of the permanent magnet
Ratio Sm / Sc between the cross-sectional area Sc of the core and the minimum cross-sectional area of the core
Is set to be 1.8 Tesla / Br,
A decrease in the output secondary voltage due to demagnetization is reliably avoided. Therefore, the ignition coil can be made small while ensuring good ignition performance.

[Brief description of the drawings]

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

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

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

FIG. 4 is a front view of an ignition coil according to one embodiment of the present invention.

FIG. 5 is a sectional view of an internal combustion engine provided with an ignition coil according to one embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between an area ratio between a minimum cross-sectional area of a core and a cross-sectional area of a permanent magnet and an output secondary voltage of an ignition coil in one embodiment of the present invention.

[Explanation of symbols]

1 ignition coil 2 core, 2a first leg, 2b second leg,
2c connecting part 3 core, 3a first leg, 3b second leg,
3c connection part 4 elastomer 5 permanent magnet 6 connector, 6a, 6b connector terminal 7 high voltage terminal, 7a connection part 8 diode 9 resin part 10 primary coil assembly 11 primary bobbin, 11a, 11b flange, 11c
Notch 12 Primary coil 13a, 13b Primary terminal 20 Secondary coil assembly 21 Secondary bobbin, 21a Flange, 21b groove,
21c Support part 22 Secondary coil 23a, 23b Secondary terminal 30 Case 30a Secondary connector part

Claims (4)

(57) [Claims] 1. A pair of U-shaped cores having a first leg and a second leg, wherein an end surface of each first leg and an end surface of each second leg are respectively formed. A pair of cores disposed so as to face each other, a primary coil wound around a first leg of each of the pair of cores, and a secondary coil wound around a second leg of each of the pair of cores And a permanent magnet interposed between the end faces of the first legs of each of the pair of cores to generate a magnetic flux in a direction opposite to a magnetic flux when the primary coil is energized. Ignition coil. 2. The apparatus according to claim 1, wherein the permanent magnet is arranged at an axial center of the primary coil.
An ignition coil for an internal combustion engine as described in the above. 3. The pair of cores is a laminate of grain-oriented silicon steel sheets having the same shape, wherein a cross-sectional area of the first leg is larger than a cross-sectional area of the second leg, and 2. The ignition coil according to claim 1, wherein a sectional area of the magnet is substantially the same as a sectional area of the first leg. 4. When the sectional area of the permanent magnet is Sm, the residual magnetic flux density of the permanent magnet is Br (tesla), and the sectional area of the minimum sectional portion of the pair of cores is Sc, the area ratio Sm / 4. The ignition coil according to claim 3, wherein Sc is set so as to satisfy the following relationship. Sm / Sc = 1.8 Tesla / Br