JPH04118909A - Ignition coil for internal combustion engine use - Google Patents

Abstract

PURPOSE:To reduce the leakage of a magnetic flux, to restrain the demagnetization of a permanent magnet and to ensure a prescribed ignition performance by a method wherein the area ratio of the permanent magnet to a cross section perpendicular to the axis of main body parts of individual cores constituting a center core is set to a prescribed value. CONSTITUTION:Three permanent magnets 17, 18, 19 whose front view is square are arranged in nearly middle points formed by dividing the inside of a primary bobbin 23 into three in its axial direction in such a way that N-poles are faced upward. Cores 11 to 14 whose front view is nearly I-shaped are arranged in such a way that the permanent magnets 17, 18, 19 are sandwiched and held between the individual cores. The permanent magnets 17, 18, 19 are arranged in such a way that the direction of generated magnetic fluxes is nearly the same direction and that the direction becomes a direction opposite to the direction of magnetic fluxes generated at the cores 11 to 14 when an electric current is applied to a primary coil 21. The permanent magnets 17, 18, 19 are formed to be in the same thickness; the width of their one side is set to a value within 1.5 to 2.5 times of the width of one side of main body parts of the cores 11 to 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ignition coil for an internal combustion engine, and more particularly to an ignition coil that increases output voltage by interposing a permanent magnet in a magnetic path.

[Conventional technology]

Ignition systems for internal combustion engines generally intermittent the primary current of the ignition coil, and apply a high voltage generated on the secondary side to the spark plug in response to changes in magnetic flux within the coil to ignite the air-fuel mixture in the cylinder. It is.

Regarding the above-mentioned ignition coil, as the output of internal combustion engines has recently increased, an increase in output voltage and discharge energy is required. 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, but this would result in a larger ignition coil, which goes against the demand for miniaturization of the ignition system as a whole. .

Utility Model Application Publication No. 48-49425 also explains that in order to increase the output voltage of the secondary coil, it is necessary to increase the number of windings in the secondary coil or increase the magnetic flux passing through the magnetic core. ing. 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. Similarly, the Special Public Interest Publication No. 41-208.2
The publication also discloses an ignition coil in which a permanent magnet is provided in the magnetic path of an iron core, that is, provides a magnetic flux that is different from the magnetic flux produced by the primary coil, that is, provides a magnetic flux in the opposite direction. In addition, JP-A-59-167006 and JP-A-60-218810 also disclose an ignition coil in which a permanent magnet is arranged in a gap provided in the core. In both of these conventional techniques, one or two gaps are formed in a core around which a primary coil and a secondary coil are wound, other than the area around which both coils are wound, and a permanent magnet is placed in this gap. We are planning to intervene.

By the way, in modern internal combustion engines, a technology has been adopted that eliminates the power distributor and installs an ignition coil for each spark plug.
This is known as the coil distribution ignition system. When installing such an ignition coil in an internal combustion engine, for example,
- As described in Publication No. 157278, it is difficult to install the double overhead camshaft (commonly known as DOHC) internal combustion engine in which two camshafts are arranged above the combustion chamber, and the size of the engine increases. will be invited. For this reason, the publication proposes an ignition system in which the ignition coil can be disposed between the camshafts even for DOHC engines with narrow valve angles, so as not to impose restrictions on the internal combustion engine. ing. Specifically, the partition wall provided in the oil chamber is removed, the casing containing the ignition coil is placed directly in the oil chamber, 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.

[Problem to be solved by the invention]

As described above, in an ignition coil in which a permanent magnet is interposed in the magnetic path, the change in magnetic flux when the primary current is interrupted is large, and the output voltage generated in the secondary coil is larger than that of a conventional ignition coil. However, in these ignition coils, since there is a large amount of leakage magnetic flux generated when the primary coil is energized, much of the increased magnetic flux is canceled out, and the increase in magnetic flux is small. especially,
For an internal combustion engine with a small valve angle as described in the above-mentioned publication, if the ignition coil is to be further miniaturized so that it can be inserted into the metal pipe provided in the cylinder head cover, the space provided will be The external dimensions are determined to match the above, and the cross-sectional area of the core necessary to ensure a predetermined output voltage is determined. As a result, the gap formed between the cores is inevitably determined, and for example, the size ratio of the axial gap to the radial gap becomes a value of 8 to 16.

This means that the ignition coil is considerably elongated and the gap in the radial direction is extremely small, as compared to a similar size ratio of 2 or less in a conventional ignition coil. For this reason,
A leakage of magnetic flux occurs between the central core and the outer core, which inevitably leads to a decrease in discharge energy and output, and eventually it becomes impossible to obtain the desired ignition performance. As a means for reducing such leakage magnetic flux, a mode can be considered in which a permanent magnet is further disposed within the coil and sandwiched between the cores. However, since permanent magnets are arranged so as to give a magnetic flux in the opposite direction to the magnetic flux produced by the primary coil, there is a risk that the permanent magnet may become demagnetized depending on the strength of the magnetic field produced by the primary coil. demagnetization can cause a decrease in ignition performance.

Therefore, the present invention relates to an ignition coil installed in an internal combustion engine, and an object of the present invention is to reduce leakage of magnetic flux, suppress demagnetization of a permanent magnet, and secure a predetermined ignition performance without increasing the size of the ignition coil. do.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an ignition coil for an internal combustion engine that induces a high voltage in a secondary coil by intermittent current flowing through the coil, in which the inside of the primary coil is divided into three equal parts in the axial direction. a central core consisting of three permanent magnets arranged approximately at the midpoint of and generating magnetic flux in the opposite direction to the magnetic flux produced by the primary coil, and four cores adjacent to each other via the permanent magnets within the primary coil; an outer core joined to both ends of a central core and arranged around the primary coil and the secondary coil, and an area ratio of the permanent magnet to a cross section perpendicular to the axis of the main body of each core constituting the central core; is set to 1.5 to 2.5.

In the above ignition coil for an internal combustion engine, a portion of each core constituting the central core adjacent to the permanent magnet is bulged to form a tapered shape, and the end face facing the permanent magnet is the same as the end face of the permanent magnet. It is good to have a shape.

[Effect]

In the ignition coil for an internal combustion engine of the present invention configured as described above, the intermittent primary current supplied to the primary coil causes a change in magnetic flux in the core, and a high voltage is induced in the secondary coil.

At this time, due to the presence of the magnetic flux of the three permanent magnets that generate magnetic flux in the opposite direction to the magnetic flux of the primary coil, the change in the interlinkage magnetic flux of the secondary coil becomes large, and the output secondary voltage becomes large.

In particular, since the permanent magnets are arranged at appropriate positions within the coil, local magnetic saturation is eliminated and leakage magnetic flux is reduced. Moreover, the area ratio of the permanent magnet to the cross section perpendicular to the axis of the main body of each core constituting the central core is 1.5.
Since it is set to 2.5 to 2.5, demagnetization of the permanent magnet is prevented and a predetermined flux linkage to the secondary coil is ensured.

〔Example〕

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

1 to 5 show an embodiment of the ignition coil of the present invention, in which the ignition coil 1O is a single-layer coil 21 wound around a bobbin 23 and a secondary coil wound around a secondary bobbin 24. A magnetic circuit is constituted by cores 11 to 14 and permanent magnets 17, 18, 19 and cores 15, 16 surrounding the coils.

In this embodiment, three permanent magnets 17, 18, and 19, which are square in plan view, are placed approximately at the midpoint of the portion where the inside of the primary bobbin 23 is divided into three equal parts in the axial direction, with the upper part in FIG. The cores 11 to 14, which are C-shaped in front view, are arranged so that the permanent magnets 17, 18, and 19 are sandwiched between the cores. These cores 11 to 14 constitute a central core according to the present invention, and among them, core 11 and core 14 have the same shape, and core 12 and core 13 have the same shape. That is, the core 11.14 further projects outward from the bobbin 23 and has projecting end portions 11a, 14b formed therein.
Arm portions 15a, 15b, 16a, and 16b of a core 15.16, which is an outer core according to the present invention and is C-shaped in front view, are joined to these. The other end 11b, 1 of the core LL, i4
4a and both ends 12a, 12b of each of the cores 12.13
, 13a, 13b are formed in a tapered shape that bulges laterally in FIG.
It is formed into a substantially square shape that is the same as the end face of.

The permanent magnets 17, 18, and 19 are arranged so that the direction of the magnetic flux generated is the same direction, and is opposite to the direction of the magnetic flux formed in the cores 11 to 14 when the primary coil 21 is energized. Ru. Also, permanent magnet 17.18.19
have the same thickness, and the width of the negative side is set to a value within the range of 5 to 2.5 times the width of one side of the main body of the cores 11 to 14, and in this embodiment, it is approximately twice is set to .

permanent magnet! 7, 18. The width of the other side of 19 is core 2 to 14
The width is set to be the same as the width of the other side of the main body (same width as both ends), so the core 11 of the permanent magnet 17° 18.19
The area of the surface facing any of cores 11 to 14 is
The area of the cross section perpendicular to the axis of the main body of No. 4 is 1.5 to 2.
It is approximately twice within the range of five times. Permanent magnet 17.1
8.19 is a rare earth magnet made of a sintered body of samarium-cobalt (Sm-Co) metal, which has a large residual magnetic flux density and is difficult to demagnetize. For example, even at a temperature of 150°C, the magnetic flux density in the opposite direction when the coil 21 is energized is 0.7.
A magnet that does not demagnetize until T (Tesla) is used is used.

The cores 11 to 16 described above are formed by laminating a plurality of grain-oriented silicon steel plates whose rolling direction is the vertical direction in FIG. 1. As is well known, grain-oriented silicon steel sheets exhibit extremely good magnetic properties in the rolling direction, but the magnetic properties deteriorate at angles different from the rolling direction. Therefore, the arm 15a is perpendicular to the rolling direction of the core 15.16.

The radius of 15b, 16a, 16b is in the rolling direction (longitudinal direction)
1.5~! , is set to 8 times.

For example, when a magnetic flux density of 1.7 T (Tesla) is allowed in the rolling direction, the magnetic flux density is limited to 1.1 T in a direction 45 degrees to the rolling direction, so the direction perpendicular to the longitudinal direction of the core 15.16 is Width Wa of arm portions 15a and 16a extending to
Wa#WbX1.
The relationship is set to 7/1.1. On the other hand, the smaller the inclination angle of the tapered surface with respect to the end surface that contacts the permanent magnet 17 etc. at the end 11b of the core 1N, the lighter the weight will be, and the longer the winding portion of the primary coil 21 will be, leading to improved performance. If the angle is less than a predetermined angle, the magnetic flux will be constricted and the magnetic resistance will increase, making it impossible to obtain the predetermined ignition performance. For this reason, in this embodiment, a tapered surface is formed from a position leaving a minimum required part (for example, 1M) for press working from the end face that comes into contact with the permanent magnet 17, etc.
The angle of inclination is set to a value of 25° to 35″, which is the minimum angle that can maintain good ignition performance.

The primary bobby Z/23 consists of members 23a and 23b of the same shape, each of which is a resin cylinder with a substantially rectangular cross section divided into two parts in the axial direction. That is, it is divided into two parts, front and rear in FIG. 1, and left and right in FIG. Cores 11 to 14 and permanent magnets 17, 18 . are placed inside one of these members 23a, 23b.
19 is housed, the other is joined to form a cylindrical body as seen in FIG. The coil 21 is wound around the primary bobbin 23 in two or four layers. In this embodiment, the winding of the primary coil 21 is a rectangular wire with a square cross section.

If the winding of the primary coil 21 is N and the total length of the winding of the first layer bobbin 23 is l, then the winding convergence W in the case of two-layer winding is
is I!/(N/2), and when comparing this result with the winding thickness Tw, if Wr < Tw, it is considered a four-layer winding, and the winding width Wr is I!/(N /4).The thickness Tw is determined from the radius W of the winding, the resistance R1 required for the primary film 21, the cross-sectional area S of the copper wire, and the specific resistance ρ of the copper. By using a rectangular wire as the winding wire (2), it is possible to further minimize the gap when winding the wire around the bobbin 23, thereby eliminating dead space and reducing the winding height of the winding portion.

Both ends of the primary coil 210 are connected to primary terminals 33b and 3, respectively.
3c is connected by soldering or the like. These primary terminals 33b and 33c are molded with insert resin to form a single-layer connector 33, and the primary terminal 33b is connected to a battery (not shown), and the primary terminal 33c is connected to a battery (not shown).
is connected to a control circuit (not shown), commonly known as an igniter.

Note that the winding direction of the winding of the secondary coil 21 is the same as that of the primary coil 21.
When energized, the permanent magnets 17, 18, and 19 are magnetized in a direction opposite to that of the permanent magnets 17, 18, and 19.

A secondary bobbin 24 around which a secondary coil 22 is wound is disposed outside the coil 21 . A plurality of grooves are formed in the secondary bobbin 24 at predetermined intervals in the axial direction, and the winding of the secondary coil 22 is sequentially wound from the upper groove to the lower groove in FIG.

The beginning of the winding of the secondary coil 22 is the terminal 33b.
It has the same potential as a battery (not shown). The end of the winding of the secondary coil 22 is connected to a lead 36a at one end of a diode 36 in the lower part of FIG. 4 by soldering or the like.

Arranged around the secondary coil 22 is a core 15.16 molded integrally with the holder 31.32 as described above. That is, cores 15 and 16 are molded with insert resin, and holders 31 and 32 having the same shape as shown in FIG. 5 are formed. Support parts 31a and 31b having a U-shaped cross section are formed at the upper and lower ends of the holder 31, and an insulating part 31c is formed inside the core 15 so as to be continuous with these parts in order to ensure a withstand voltage. The corner portions on both sides of this insulating portion 31c are stepped, and step portions aid and 31e are formed. still,
The holder 32 also has a similar structure. Thus, between the support portion 31a of the holder 31 and the support portion 32a of the holder 32, the protruding end portion 11a of the core 11 and the arm portion 15 of the core 15.
The joint ends 15c and 16c of the cores 15 and 16a are held together (see FIGS. 1 and 4), and similarly, the protruding end 14b of the core 14 and the joint ends of the arms 15b and 16b of the core 15 and 16 are held together. 15d and 16d are held between the lower support parts 31b and 32b of the holder 31.32.

The width of the upper joint ends 15c, 16c of the core 15.16 is greater than the width of the arms 15a, 16a of the core 15.16, and is the same width as the protruding end 11a of the core 11, The same relationship holds true for the end portions 15d and 16d.

As shown in FIG. 1, the protruding end 11a and the joining end 15c
, 16c are provided with holes 11e, 15e, 16e, respectively, and the supporting parts 31a, 32 of the holder 31.
The holders 31, 32 are thermally deformed by being heated and pressed from the sides of (from the lower left direction and the upper right direction in FIG. 5) and enter the holes 11e, 15e, 16e, and the cores 11, 15.
The upper part of 16 is firmly fixed. Core 14 and Core 15.
The lower part of 16 is also fixed in the same way.

A resin cover 35 consisting of a mounting part 35a and a support part 35b having a U-shaped cross section (as shown in FIG. 4) is sandwiched at the bottom of the support parts 31b and 32b. As shown in FIG. 4, the support portion 35b has a grooved protrusion 35c that protrudes downward.
, 35d are formed, and leads 36a and 36b of the diode 36 are sandwiched and fixed in these grooves. Further, the bent legs provided on both sides of the plate 37 are press-fitted into holes formed on both end surfaces of the support portion 35b,
A connecting portion 37a of the plate 37 is connected to a lead 36b of the diode 36 by soldering or the like.

These holders 31, 32, primary coil 21, secondary coil 22, and cores 11 to 16 are housed in a case 30 as shown in FIG. The case 30 has a vertical wall portion 30a
, 30b are arranged side by side to form an accommodating portion between them, flange portions 3°c and 30d are formed at the upper end, and a secondary connector portion 30e, which is a cylinder with a bottom, is formed at the lower end. and,
Steps (30f represents the four steps) are formed on both sides of the vertical walls 30a and 30b, and this step 30
The stepped portion 31d of the holder 31, 32, etc. are fitted into the holder 31, 32 and are configured to be in close contact with the holder 31, 32. A secondary terminal 34 is housed in the secondary connector portion 30e, and a protrusion 34a formed on the top surface thereof extends toward the core 14 through the bottom surface of the secondary connector portion 30e. And plate 3
Secondary terminal 34 is inserted into the circular hole drilled in the center of 7.
The protrusion 34a is press-fitted and electrically connected. The space defined by the case 30 and the holders 31 and 32 is filled with a thermosetting synthetic resin, such as an epoxy resin, and hardened to form the resin portion 38. Thereby, 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.

The procedure for assembling the ignition coil IO having the above configuration will be explained below.

First, the divided members 23a and 23 that constitute the primary bobbin 23
The cores 11 to 14 and the permanent magnet 1 are placed at predetermined positions between b.
7.18.19 Place and fix. This primary bobbin 2
The coil 21 is wound around the outer periphery of the coil 21 in two or four layers. Further, the secondary coil 22 is wound in each groove of the secondary bobbin 24 of the cylindrical body, and the primary coil 21 and the primary bobbin 2 are wound in the hollow part of the secondary bobbin 24.
3 is housed to form a coil subassy 10a shown in FIG. Meanwhile, cores 15 and 16 are molded with insert resin to form holders 31 and 32, respectively. These holders 31.32
The supporting parts 31a, 32a and the supporting parts 31b, 32b are brought into contact with each other so as to sandwich them from both sides of the coil subassy 10a, and the joint end of the protruding ends 11a, 14b of the core 11.14 and the core 15.16 is 15c, 15d, 16c, 1
Join 6d. In this state, attach the mounting portion 33a of the primary connector 33 to the protruding end 11a of the core 11 and the core 15.1.
6, and heat pressurizes the supporting parts 31a, 32a of the holder 31 from the sides to open the holes 1, 1, and 3.
5e and 16e and fix the upper part of the core 11.15.16. The lower part of the core 14, 15, 16 is also fixed to the supports 31b, 32b in a similar manner. This forms a coil assembly. Then, both ends of the winding of the primary coil 21 are connected to the terminals 33b and 33c. In addition, a diode 36 and a metal plate 3 are attached to the cover 35.
7 and connect the lead 36b to the connecting part 37a of the plate 37.
Connect. The mounting portion 35a of this cover 35 is attached to the core 14.
The protruding end 14b of the core 15.18 and the joining end 15d of the core 15.18
, 16d, and connects the end portion of the winding of the secondary coil 22 to the lead 36a.

Next, the secondary terminal 34 is integrally molded to form the secondary connector portion 30e and the vertical wall portion 30a.

A coil assembly including the above-mentioned coil sub-assembly 10a is inserted into the case 30 shown in FIG. Then, the space defined by the holder 31, 32 and the case 30 and formed between the coil subassembly 10a is filled with epoxy resin, and the epoxy resin is thermally cured to be impregnated and fixed.

The ignition coil IO is attached to the rad cover 3 to the cylinder of the internal combustion engine Ill, as shown in FIGS. 6 and 7. The internal combustion engine 1 in this embodiment has a plurality of cylinders arranged in series, and FIG. 7 shows a cross section of the cylinder head of the inner cylinder. The ignition coil 10 is attached to the cylinder head cover 3 by a mounting screw 39 for each cylinder.

An intake boat 4 and an exhaust port 5 that open into the combustion chamber 1a are integrally molded in the aluminum alloy cylinder head 2 of the internal combustion engine 1 for each cylinder, and a pair of intake valves 6 and exhaust valves 7 are attached to these, respectively. are installed, but 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. Above the cylinder head 2 is a bearing member 3b.

A pair of camshafts 8 and 9 are rotatably supported by 3c, and are configured to directly drive the intake valve 6 and exhaust valve 7. In other words, it is a direct drive double overhead camshaft system. Further, a rad cover 3 is joined to an aluminum alloy cylinder above the cylinder head 2, and an oil chamber 52 is formed between the two. Between the intake valve 6 and exhaust valve 7 of the cylinder head 2, there is a space between the oil chamber 52 and the combustion chamber 1.
A stepped mounting hole 2a is formed toward the direction a. A spark plug 60 is screwed into a small diameter hole on the combustion chamber la side of the attachment hole 2a, and is fixed with its electrode portion exposed inside the combustion chamber la.

On the other hand, an insertion hole 3a is formed at the top of the cylinder rad cover 3 and opens opposite to the opening of the mounting hole 2a to the oil chamber 52, and a stepped portion is formed on the inner surface of the insertion hole 3a. A cylindrical shielding body 40 made of a non-magnetic material is inserted into the attachment hole 2a through the insertion hole 3a, and one end thereof is fixed near the lower end of the attachment hole 28 by press fitting or the like. The other end of the shielding cylinder 40 projects outward from the cylinder head cover 3 through the insertion hole 3a. An annular sealing member 50 is fitted into the shielding cylinder 40 and placed at a stepped portion in the insertion hole 3a of the rad cover 3 into the cylinder. and,
Insert the ignition coil IO into the shielding cylinder 40 and screw the mounting screw 39
When tightening, the flange portions 80c, 30 of the case 30
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 the lower surface of the insertion hole 3a, thereby sealing the insertion hole 3a. As a result, the storage chamber in the shielding cylinder 40 and the oil chamber 52 are completely separated, and oil droplets in the oil chamber 52 will not enter into the shielding cylinder 40. This shielding cylinder 4
The ignition coil IO, a conductive spring 28 housed in a secondary terminal 34 at the tip thereof, and a connecting member 29 made of a rubber forum body are housed in the housing chamber inside the ignition coil IO. A secondary terminal 34 integrally formed on the case 30 is electrically connected to the ignition coil 60 via the spring 28. The connecting member 29 tightens the lower part of the ignition coil 10 and the upper part of the ignition plug 60 from the outside to connect the two, and also prevents leakage of high voltage to the shielding cylinder 4o.

When the internal combustion engine 1 is started and the camshaft 89 rotates, the intake valve 6 and the exhaust valve 7 are driven at a predetermined cycle, and the intake boat 4 and the exhaust boat 5 are opened and closed. and,
The primary current of the ignition coil IO is controlled by ignition signals output in a predetermined order according to the rotation of the internal combustion engine 1, and a predetermined high voltage is generated in the secondary coil 22. This high voltage is directly applied to the ignition plug 60 via the secondary terminal 34, and a spark discharge occurs at the electrode at the tip of the ignition plug 60, igniting the compressed air-fuel mixture in the combustion chamber Ia. In this way, the ignition coil 10 of this embodiment is small and has a shielding cylinder 4.
0, and can also be installed in the above-mentioned internal combustion engine l having a small valve angle.

In the ignition coil IO, as shown in FIG. 1, the upper part of the permanent magnets 17, 18, 19 is the north pole, and the flow of magnetic flux is from the core 14 to the core 11, and from the core 11 to the core 15, 16. It is a closed loop that branches to and returns to the core 14. There is almost no leakage of magnetic flux in this state. When the primary coil 2I is energized by a control circuit (not shown) and a primary current is supplied, the magnetic flux flows in a closed loop from the core 11 to the core 14 in the opposite direction to the magnetization direction of the permanent magnets 17, 18, 19. At this time, from core 11 to core 15.16, from core 15.16 to core 14, and then from core 12.1
3 and cores 15, 16. Magnetic flux leakage occurs between each other. 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 spark plug 60 via diode 36, plate 37 and secondary terminal 34.

The diode 36 further prevents the spark plug 60 from flying out due to a voltage of 1 to 3 kV generated when the coil 21 is energized.

In the ignition coil IO of this embodiment, cores 11 to 1
The permanent magnets 17, 18, and 19 interposed between the cores of 4 can ensure a large change in effective magnetic flux. In particular, since the permanent magnets 17, 18 and 19 are housed within the primary coil 21 and placed at appropriate positions, the leakage magnetic flux is reduced compared to the past due to concentration of magnetic flux, and local magnetic saturation in the cores 11 to 14 is reduced. disappears. Moreover, the core
Since the area ratio of the permanent magnets 17, 18, and 19 to the cross section orthogonal to the axis of the main body portions 1 to 14 is approximately twice,
The magnetic field caused by the primary coil 21 is a permanent magnet 17.18.19
Cores 11 to 14 reach the saturation magnetic flux density before reaching the demagnetization limit of permanent magnets! 7, 18, and 19 are never demagnetized. Therefore, the magnetic flux density formed in the primary coil 21 increases with respect to the magnetomotive force caused by the supply of the primary current, and the discharge energy increases. Moreover, since the magnetic flux change becomes large, the output voltage of the secondary coil 22 becomes large.

Figures 8 to 1O compare the amount of leakage magnetic flux and the output secondary voltage according to the number of permanent magnets arranged, based on the dimensional relationship of each core in the ignition coil 10 of the above embodiment of the present invention. The configuration is schematically shown with the coil, case, etc. omitted. Figure 8(a) relates to this embodiment, and three permanent magnets 17, 18, and 19 are arranged, and Figure 8(b) shows two permanent magnets 17, 18, and Figure 8(C). One permanent magnet 17 is placed at the center. As shown in Fig. 8, the dimensional relationship of each core is such that the dimensional ratio (A/B) of the gap between the cores is set to 8 to 16, and the similar dimensional ratio (A/B) of a conventional ignition coil is Although it is smaller than 2, it is elongated. As mentioned above, the ignition coil 1O of this example is to be installed in the limited space of an internal combustion engine with a narrow pulp angle, and the outer shape is determined to fit this, and the predetermined Since the necessary cross-sectional area of the core to ensure the output voltage is determined, the gap between each core is necessarily determined. For example, the longitudinal length of the core 15.16 is 70 to 100 m,
When the outer diameter is set to 23 to 27 m+, the gap between the cores is the longitudinal gap A or 65 to 95 m, and the radial gap B is 6 to 8 m, so the size ratio (A/B) is as described above. Thus, the numbers range from 8 to 16. Of course, conventional ignition coils cannot satisfy such a relationship, and simply changing the dimensional ratio will increase the leakage magnetic flux between the cores, making it impossible to ensure a predetermined ignition performance.

In each of FIGS. 8(a) to (c'), the dimensional ratio (A/B) of the gap between the cores maintains the above-mentioned value, and the area is approximately twice the width of the main body of cores 11 to 14. Permanent magnet 17 with about twice the ratio
．． 18.19 are arranged. The total thickness of these permanent magnets is set to be equal in all cases. Therefore, the thickness Te of the permanent magnet 17 in FIG. 8(a)
a is 1/3 of the thickness Tmc of the permanent magnet 17 in FIG. 8(C)
It becomes. The leakage magnetic flux amount L (%) is determined based on the following equation (1) from the maximum magnetic flux amount ΦWaX of the core portion and the magnetic flux amount Φ1ain of the permanent magnet portion showing the minimum magnetic flux amount.

As shown in the measurement results in Figure 9, the leakage magnetic flux increases as the size ratio (A/B) increases, but the absolute value and increase rate of the leakage magnetic flux are shown in Figure 8 (a). is the smallest. Therefore, as shown in Fig. 1θ, Fig. 8 (a
), the greater the number of permanent magnets, the greater the output secondary voltage can be obtained. Based on the above measurement results, if we focus on the number of permanent magnets, the more permanent magnets there are, the more the leakage magnetic flux will decrease, and the output secondary voltage will increase. As the number of permanent magnets increases, each permanent magnet becomes thinner and more likely to break, and the number of parts increases, making assembly more troublesome. Considering the rigidity of the permanent magnet and productivity including ease of assembly, the thickness of the permanent magnet is at most 0.5 m, and the optimum number of permanent magnets to be arranged is three as in this embodiment.

Next, the ignition coil lO of this embodiment is composed of four cores 11 to 14, and the inside of the primary coil 21 is divided into equal parts in the axial direction (in this embodiment, it is divided into three equal parts). Permanent magnets 17, 18, and 19 are arranged approximately at the midpoints of the respective permanent magnets.

That is, as shown in FIG. 8(a), a permanent magnet 17 is placed approximately at the midpoint of a portion where the portion surrounded by the coil 21 is divided into three equal parts.
゜18.19 is placed, so the permanent magnet 17.1
8. The leakage magnetic flux is less than when the 19s are arranged in the center or spaced apart at both ends.
Local magnetic saturation in the cores 11 to 14 is eliminated. Therefore, the core 11
The magnetic flux density of I6 to I6 becomes large, and large discharge energy can be obtained. Furthermore, since the change in magnetic flux becomes large, the output voltage becomes large.

As mentioned above, in this embodiment, permanent magnets I7.18.
19 has a side width of approximately 2 of the convergence of the main body of cores 11 to 14.
It is a square with the other side having the same width, and therefore has an area ratio approximately twice that of the main body portions of the cores 11 to 14. This optimal area ratio is set as follows. In the following example, a samarium-cobalt rare earth magnet is used as the permanent magnet, a grain-oriented silicon steel plate is used as the core, and the dimensional ratio (A
/B) is 12 and two permanent magnets are arranged in Figure 8 (b).
), the leakage magnetic flux is 20%.

For permanent magnets, the magnetic flux density when the primary current is off is 0.87 (Tesla), and the magnetic flux density in the opposite direction when the primary current is on is 0.
．． A magnet that is not demagnetized until it reaches 7T is used. Further, the core has the ability to pass a magnetic flux density of 1°8T (the magnetic flux density with the least leakage magnetic flux at point P in FIG. 8(b)), and magnetic saturation occurs above this value. In other words, the saturation magnetic flux density when the primary current is on is 1.8T, and the magnetic flux density of the permanent magnet at that time is -0.7T.The magnetic flux density of the core when the primary current is off is ΦC, and the relationship between the permanent magnet and the core is ΦC. When the area ratio of is set to H, the following equations (2) and (3) hold true.

(0,8+0.7)X H= (1,8+Φc)X (
1-0,2)-(2)H=Φc10.8
...(3) Then, by substituting equation (3) into equation (2), H#1.67 is obtained. In this way,
Considering the thickness of the permanent magnet, magnetic flux leakage, magnetic saturation area of the core, demagnetization area of the permanent magnet, etc., the area ratio H that can ensure the specified output voltage is found to be between 1.5 and 2°5. A range of values is optimal.

As described above, the ignition coil of this embodiment has various effects synergistically, is compact as a whole, has good ignition performance, and is easy to manufacture. That is, three permanent magnets 17
．． 18 and 19 are further placed in appropriate predetermined positions within the coil 21, the leakage flux is reduced. In addition, the area of the permanent magnets 17, 18, 19 is approximately twice the area of the cross section perpendicular to the axial direction of each core of the central cores 11 to 14, and the area adjacent to each permanent magnet of each core Since the permanent magnets 17, 18, and 19 are formed in a tapered bulge and are set at a taper angle or a minimum angle, demagnetization of the permanent magnets 17, 18, and 19 is suppressed, and the core area is minimized. Therefore, cores 11 to 1
In addition to the weight reduction of 4, since the number of windings of the primary coil 21 can be increased to the maximum, the ignition performance is improved accordingly. Although the outer cores 15 and 16 are integrally molded with the holder 31, the outer circumferential surface is exposed and is configured to form a continuous outer circumferential surface with the outer circumferential surface of the ignition coil IO, so that the conventional casing resin part is not present. It becomes small without it. Further, since a rectangular wire is used as the winding of the primary coil 21, the winding height is reduced, which also leads to miniaturization. Furthermore, the primary bobbin 23 has a cylindrical body divided into two parts 23a,
23b, the cores 11 to 14
Also, the permanent magnets 17, 18, and 19 can be easily positioned, and can be placed appropriately and quickly. Therefore, good workability can be obtained. The joining structure between the cores 11 and 14 of the central core and the outer core 15.16 is a structure that can absorb the tolerances of the cores 11 to 14 and the permanent magnets 17, 18.19, so assembly is easy. The cores are securely fixed.

〔Effect 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 central core housed in the primary coil is made up of four cores, and a total of three permanent magnets are provided between each core, so that the interlinkage of the secondary coil is prevented. The change in magnetic flux is large, and a large output voltage can be obtained.

In particular, since the permanent magnets are arranged at appropriate positions within the coil, local magnetic saturation is eliminated and leakage magnetic flux is reduced. Moreover, since the area ratio of the permanent magnet to the area of the cross section perpendicular to the axis of the main body of the core is set to 1.5 to 2.5, a drop in the output secondary voltage due to demagnetization is also avoided. Therefore, the ignition coil can be made compact while ensuring good ignition performance, and can be easily installed in an internal combustion engine.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of an ignition coil according to an embodiment of the present invention, Fig. 2 is a plan view of the ignition coil, and Fig. 3 is a -
■A line sectional view, FIG. 4 is a vertical cross-sectional view of an ignition coil according to an embodiment of the present invention as seen from the side, FIG. 5 is an exploded perspective view of an ignition coil according to an embodiment of the present invention, and FIG. FIG. 7 is a plan view of an internal combustion engine equipped with an ignition coil according to an embodiment of the invention; FIG. 7 is a cross-sectional view of the internal combustion engine; FIG. is a block diagram of a core with three permanent magnets, FIG. 8(b) is a block diagram of a core with two permanent magnets, and FIG. 8(C) is a core with - permanent magnets. FIG. 9 is a graph showing the relationship between the dimensional ratio of the gap between the cores and leakage magnetic flux, and FIG. 10 is a graph showing the relationship between the dimensional ratio of the gap between the cores and the output voltage. lO...Ignition coil. 1 to 14... Core (center core). 5, I6... Core (outer core). 7.18.19...Permanent magnet. l...Primary coil, 22...Secondary coil. 3...Primary bobbin, 24...Secondary bobbin.

Claims (2)

[Claims] (1) In an ignition coil for an internal combustion engine that induces a high voltage in a secondary coil by intermittent current flowing through the primary coil, the ignition coil is arranged approximately at the midpoint of a portion where the inside of the primary coil is divided into thirds in the axial direction. a central core consisting of three permanent magnets that generate magnetic flux in the opposite direction to the magnetic flux produced by the primary coil; and four cores adjacent to each other within the primary coil via the permanent magnets; The permanent magnet includes an outer core disposed around the primary coil and the secondary coil, and the area ratio of the permanent magnet to a cross section perpendicular to the axis of the main body of each core constituting the central core is 1.5 to 2.5. An ignition coil for an internal combustion engine, characterized in that it is set to (2) The portion of each core constituting the central core adjacent to the permanent magnet is bulged and formed into a tapered shape, and the end surface facing the permanent magnet is made to have the same shape as the end surface of the permanent magnet. An ignition coil for an internal combustion engine according to claim 1.