JPH11186077A - Ignition coil for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition coil which is capable of restraining the generation of cracks in an insulation layer in a bobbin and an area near it caused by thermal expansion and contraction. SOLUTION: An ignition coil 13 has a case 21, an igniter 21 arranged inside the case 20, a primary coil 30 and a secondary coil 40, an inside core 22, an outside core 23, etc. A secondary bobbin 41 formed of thermoplastic resin is divided equally into two in axial direction of the ignition coil 13. Each of the divided secondary bobbins 41a, 41b is arranged at a specified interval in a coaxial direction. Thermosetting resin is filled into the case 20 and hardened so as to form an insulation layer 24 which coats the circumference of the coils 30, 40 and the inside core 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine in which a bobbin on which a winding is wound is arranged in a case, and the case is filled with resin to form an insulating layer covering the bobbin. It relates to an ignition coil.

[0002]

2. Description of the Related Art As an ignition system in a spark ignition type internal combustion engine, a so-called DLI ignition system (Distributor Less Ignition system) in which an ignition coil is provided corresponding to an ignition plug of each cylinder is often used. . This is because the DLI ignition system has an advantage that a high voltage cord for supplying a high voltage from the distributor to the ignition plug is not required in addition to the distributor. In such a DLI ignition system, for example, as described in Japanese Patent Application Laid-Open No. 8-293418, an ignition coil may be housed in a plug hole for mounting an ignition plug.

FIG. 4 shows one configuration of the ignition coil housed in the plug hole as described above. As shown in FIG. 1, the ignition coil 100 includes a case 101 having a substantially bottomed cylindrical shape, and a primary coil 1 disposed in the case 101.
02 and the secondary coil 103 are provided. Case 10
An insulating layer 104 covering the coils 102 and 103 is formed by filling and curing a thermosetting resin in the inside 1, and the insulating property between the members in the case 101 is secured by the insulating layer 104. Have been. Further, each of the coils 102 and 103 has bobbins 107 and 108 on which windings 105 and 106 are wound, and these bobbins 107 and 108 are not thermosetting resins, but are formed in consideration of ease of moldability. Formed of a thermoplastic resin.

[0004]

By the way, in the ignition coil 100 housed in the plug hole as described above,
Because the outer diameter is limited by the diameter of the plug hole,
As shown in FIG. 4, each of the bobbins 107 and 108 has a long shape in the axial direction of the plug hole (the vertical direction in FIG. 4). While the outer diameter of the ignition coil 100 is set to a diameter that can be accommodated in the plug hole by reducing the thicknesses T1 and T2 of the winding layer, a portion where the winding is wound to secure a predetermined number of turns It is necessary to set the lengths L1 and L2 relatively long.

However, in such an ignition coil 100, the thermal expansion and contraction of the bobbins 107 and 108 in the axial direction becomes extremely large, and the thermal expansion and contraction of the bobbin 10
7, 108 is constrained by the insulating layer 104 covering the same. This is because the linear expansion coefficients of the thermoplastic resin forming the bobbins 107 and 108 and the thermosetting resin forming the insulating layer are different from each other.

As a result, excessive stress is concentrated on the insulating layer 104 at both ends of the bobbins 107 and 108 where the amount of movement due to thermal expansion and contraction is greatest, and the vicinity thereof.
There has been a problem that cracks occur in the bobbins 107 and 108 and the insulating layer 104. The occurrence of many such cracks causes a decrease in the mechanical strength of the ignition coil 100. In particular, the insulating layer 104 or the secondary layer in the vicinity of the secondary winding 106 of the secondary bobbin 108 where such cracks have a high potential If it occurs in the insulating layer 104 between the winding 106 and the primary winding 105 of the primary bobbin 107, the dielectric breakdown will occur. Although the ignition coil housed in the plug hole has been mentioned, the occurrence of the cracks described above is caused by the ignition coil in which the bobbin is covered with insulating layers having different linear expansion coefficients, in particular, the ignition coil having a longer bobbin. Is a common problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ignition coil capable of suppressing the generation of cracks in a bobbin and an insulating layer near the bobbin due to thermal expansion and contraction. .

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a bobbin on which a winding is wound is arranged in a case, and the case is filled with resin. In an ignition coil for an internal combustion engine in which an insulating layer covering a bobbin is formed, the bobbin is divided into a plurality in the axial direction, and the divided bobbins are arranged at predetermined intervals in the axial direction.

According to the above configuration, the thermal expansion and contraction amount of each of the divided bobbins is reduced as compared with the case where the divided bobbins are not divided, and the stress concentrated on the both end portions of the bobbin and the insulating layer near the bobbin is generated. Are distributed and generated near both ends of each divided bobbin.

According to the second aspect of the invention, in the ignition coil for an internal combustion engine according to the first aspect, an elastic body is interposed between each of the divided bobbins, and the elastic body is closely attached to each of the bobbins. I try to make it.

According to the above construction, in addition to the effect of the first aspect, the thermal expansion of each of the divided bobbins due to the deformation of the elastic body is absorbed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] An embodiment in which the present invention is embodied as an ignition coil provided in a four-cylinder engine will be described below with reference to FIGS.

As shown in FIG. 1, a cylinder head 11 of an engine 10 is formed with four plug holes 12 communicating with combustion chambers (not shown) of each cylinder. The ignition plug (not shown) inserted into the plug hole 12 is fixed to the cylinder head 11 such that its lower part projects into the combustion chamber.

The ignition coil 13 has a connection portion 14 located above the ignition coil 13 and a columnar insertion portion 15 located below the connection portion 14. The ignition coil 13 includes the insertion portion 1
5 is inserted into each plug hole 12, and is fixed in each plug hole 12 in a state where the lower part of the insertion part 15 is fitted to the upper part of the spark plug.

FIG. 2 is a sectional view showing the ignition coil 13. As shown in FIG.
0, igniter 21, primary coil 30, and secondary coil 4
0, an inner core 22, an outer core 23 and the like.

The case 20 is made of PBT which is a thermoplastic resin.
(Polybutylene terephthalate) is formed in a substantially cylindrical shape by a resin. A cylindrical inner core 22 is disposed at the center of the case 20. Case 2
An outer core 23 having a cylindrical shape is externally fitted to 0.
The outer core 23 may be inserted inside the case 20. Each of the inner core 22 and the outer core 23 is formed of silicon steel which is a ferromagnetic material, and each of the cores 22 and 23 forms a part of a magnetic circuit.

A substantially cylindrical secondary bobbin 41 is externally fitted to the inner core 22. The secondary bobbin 41 has a shape longer in the axial direction (vertical direction in FIG. 2) than in the radial direction of the ignition coil 13 (horizontal direction in FIG. 2). The secondary bobbin 41 is equally divided into two in the axial direction of the ignition coil 13, and each divided secondary bobbin 41 is divided into two.
a and 41b are arranged at predetermined intervals in the axial direction. A plurality of ribs 42 are formed on the outer periphery of each of the secondary bobbins 41a and 41b at predetermined intervals in the axial direction, and a secondary winding 43 is laminated and wound between the ribs 42. . These secondary bobbins 41 a and 41 b and the secondary winding 43 constitute a secondary coil 40.

A substantially cylindrical primary bobbin 31 is provided on the outer periphery of the secondary bobbins 41a and 41b.
It is arranged so as to surround b. This primary bobbin 3
A plurality of ribs 32 are formed on the outer circumference of the first rib at predetermined intervals in the axial direction thereof, and a primary winding 33 is provided between each rib 32.
Are stacked and wound. These primary bobbins 31 and 1
The primary coil 30 is constituted by the secondary winding 33. The primary bobbin 31 and the secondary bobbins 41a and 41b are formed of a PPE (polyphenylene ether) resin which is a thermoplastic resin.

An igniter 21 is disposed above the coils 30 and 40. The igniter 21 is electrically connected to a control device (not shown) via the external terminal 16 and the like.

The igniter 21, the coils 30, 40
The periphery of the inner core 22 is covered with an insulating layer 24. The insulating layer 24 is formed by filling an epoxy resin, which is a thermosetting resin, into the case 20 and curing the resin. This insulating layer 24 is for ensuring insulation between the members in the case 20.

A mounting hole 25 extending in the axial direction is recessed below the case 20, and a high-voltage connection terminal 27 is fixed so as to protrude into the mounting hole 25.
The high voltage connection terminal 27 is electrically connected to the secondary winding 43, and the high voltage generated in the secondary coil 40 is supplied to the ignition plug via the spring 28 and the like.

In the ignition coil 13 configured as described above, the primary coil 3 is controlled based on the ignition signal from the control device.
As the primary current of 0 is intermittently controlled by the igniter 21, the voltage of the battery (not shown) in the secondary coil 40 is increased to a high voltage for ignition. And
When the ignition high voltage is supplied to the ignition plug, a spark is generated between the electrodes of the ignition plug, and the air-fuel mixture in the combustion chamber is ignited.

As described above, in the present embodiment, the secondary bobbins 41a and 41b are equally divided in the axial direction. Therefore, the secondary bobbins 41a, 41b
, The amount of thermal expansion and contraction in each of the divided secondary bobbins 41a and 41b is reduced by half,
Stress is distributed and generated near both ends of each of the divided secondary bobbins 41a and 41b.

For example, if the thermal expansion / contraction amount of the entire bobbin 41 is 2 △ L when the secondary bobbin 41 is not divided, unlike the present embodiment, both ends of the bobbin 41 are each at ΔL. Only try to move in that axial direction. Here, the epoxy resin forming the insulating layer 24 is a secondary bobbin 4
Since the coefficient of linear expansion is smaller than that of the PPE resin forming No. 1, the thermal expansion and contraction amount in the axial direction of the secondary bobbin 41 is smaller than the expansion and contraction amount of the insulating layer 24 in the same direction even at the same temperature change. Become. As a result, the movement of both ends of the secondary bobbin 41 is restrained by the surrounding insulating layer 24, and both ends of the secondary bobbin 41 and the insulating layers 24 near the both ends are restricted.
, Excessive stress is concentrated and generated.

On the other hand, according to the present embodiment, the amount of expansion and contraction of each of the divided secondary bobbins 41a and 41b is ΔL, and both ends of each of the secondary bobbins 41a and 41b are Δ
Attempts to move in the axial direction by L / 2 respectively. Therefore, when the secondary bobbin 41 is not divided, the stress that has been concentrated near both ends of the secondary bobbin 41 is reduced to the respective secondary bobbins 41a, 4a.
1b are distributed to both ends, and the magnitude of the stress is reduced as compared with the case where no division is performed.

As a result, according to the present embodiment, excessive stress is prevented from acting on the secondary bobbins 41a and 41b and the insulating layer 24 in the vicinity thereof, and these members 24 and 41b are prevented from acting.
a, 41b can be suppressed from occurring.

Further, in this embodiment, the secondary bobbins 41a,
41b is equally divided in the axial direction so that the lengths of the divided secondary bobbins 41a and 41b are equal. Therefore, the thermal expansion and contraction amounts of the respective secondary bobbins 41a and 41b are all equal, and the stress is more evenly distributed in the vicinity of both ends of the respective secondary bobbins 41a and 41b. As a result, generation of cracks in the insulating layers 24 in the secondary bobbins 41a and 41b and in the vicinity thereof can be suppressed more reliably.

Since a high voltage is generated in the secondary bobbins 41a and 41b as described above, the bobbins 41a and 41b
The potential gradient in the insulating layer 24 at and near 1b is particularly high as compared with other portions. Therefore, the secondary bobbin 41
When a crack is generated in the insulating layer 24a and the insulating layer 24 in the vicinity thereof, the crack may grow and lead to dielectric breakdown.

In this regard, in this embodiment, the primary bobbin 31
Instead, the secondary bobbins 41a and 41b are divided, so that cracks are suppressed in the secondary bobbins 41a and 41b and the insulating layer 24 near the secondary bobbins 41a and 41b. It can be avoided reliably.

Further, as in the present embodiment, the secondary bobbin 4
In the ignition coil 13 having the igniter 21 built in the vicinity of 1a and 41b, as described above, the secondary bobbin 41
When the igniter 21 greatly expands and contracts in the axial direction, excessive stress is generated not only in the bobbin 41 and the insulating layer 24 but also in the igniter 21, which may cause damage to the igniter 21. In this regard, according to the present embodiment, such damage can be avoided, and the reliability of the igniter 21 can be improved.

Also, unlike the present embodiment, the difference between the linear expansion coefficient of the epoxy resin and the linear expansion coefficient of the PPE resin is changed by, for example, changing the amount of the curing agent added to the epoxy resin or the curing speed thereof. Even if adjusted to be smaller, 2
This is effective in reducing stress in the next bobbins 41a and 41b and the insulating layer 24 in the vicinity thereof.

However, in such a method, it is necessary to strictly control the amount of the curing agent and the temperature of the epoxy resin, which complicates the manufacturing process of the ignition coil, particularly, the process of forming the insulating layer 24. In this regard, according to this embodiment, the occurrence of cracks in the secondary bobbins 41a and 41b and the insulating layer 24 can be suppressed without complicating the manufacturing process as described above.

[Second Embodiment] Next, a second embodiment will be described focusing on differences from the first embodiment. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 3 shows an ignition coil 13 according to this embodiment.
FIG. As shown in FIG.
Is different from the configuration of the first embodiment in that an annular elastic member 50 is externally fitted so as to be located between the two divided secondary bobbins 41a and 41b. The elastic member 50 is provided with a divided secondary bobbin 41a,
The insulation layer 24 is not formed between the elastic member 50 and each of the secondary bobbins 41a and 41b. Also, this elastic member 50 is a secondary bobbin 41.
It is formed of a rubber material (for example, silicon rubber) having an elastic coefficient extremely smaller than that of the resin material forming the insulating layers 24 and a and 41b.

According to the present embodiment having such a configuration, the elastic expansion of the elastic member 50 in the axial direction of the secondary bobbin 41 absorbs the thermal expansion of each of the secondary bobbins 41a and 41b. Therefore, when each of the secondary bobbins 41a and 41b thermally expands, the respective ends of the bobbins 41a and 41b located on the elastic member 50 side move largely and come close to each other, but the respective ends on the opposite side are hardly formed. The position does not change. As a result, the occurrence of cracks in the secondary bobbins 41a, 41b and the insulating layer 24 due to the thermal expansion of the secondary bobbins 41a, 41b can be more reliably suppressed.

In particular, as in this embodiment, the plug hole 1
In the ignition coil 13, which is easily heated to a high temperature because it is housed in the inner space 2, the configuration in which the elastic member 50 is provided as described above suppresses generation of cracks in the secondary bobbins 41 a and 41 b and the insulating layer 24. It is effective in doing.

Each of the above embodiments can be implemented with the configuration changed as follows. In the above embodiments, the secondary bobbin 41 is divided. However, the primary bobbin 31 and both the bobbins 31, 41 may be similarly divided.

In each of the above embodiments, the secondary bobbin 41 is
Although the division is made, it may be divided into three or more bobbins. In addition, unequal division may be performed. A reinforcing material such as glass fiber may be added to the epoxy resin forming the insulating layer 24. As described above, the addition of the reinforcing material to the epoxy resin is effective in suppressing the occurrence of cracks in the insulating layer 24 whose thickness is limited because it is provided in the plug hole 12.

In each of the above embodiments, the case 20 is a PBT
Although the resin and the bobbins 31 and 41 are both formed of PPE resin, they may be formed of other thermoplastic resins such as PPS (polyphenylene sulfide) resin. Further, the insulating layer 24 may be formed of a thermosetting resin other than the epoxy resin.

In each of the above embodiments, the igniter 21 is incorporated in the connection portion 14 of the ignition coil 13, but the igniter 21 may be provided outside the ignition coil 13.

In each of the above embodiments, the primary coil 30 is
Although the arrangement is made outside the next coil 40, the arrangement of these coils 30, 40 may be reversed. In the above embodiments, the bobbins 31 and 41 are formed of a thermoplastic resin, and the insulating layer 24 is formed of a thermosetting resin. However, the materials for forming these members are not necessarily limited to combinations of the above resins. Not something. The occurrence of cracks in the bobbins 31, 41 and the insulating layer 24 as described above generally occurs when the coils 31, 41 and the insulating layer 24 covering the coils 31 and 41 have different coefficients of linear expansion. That's why.

That is, the present invention is not limited to the ignition coil housed in the plug hole as described in each of the above embodiments and the ignition coil used in the DLI ignition system. Can be applied to all ignition coils that are covered with insulating layers having different linear expansion coefficients. In particular, the present invention is effective for an ignition coil having a bobbin elongated in the axial direction and having a large difference between the linear expansion coefficient of the bobbin and the linear expansion coefficient of the insulating layer.

The technical ideas that can be grasped from the above embodiments are described below together with their effects. -In the ignition coil for an internal combustion engine according to claim 1,
Each of the divided bobbins has the same length in the axial direction.

According to the above configuration, each of the divided bobbins has the same thermal expansion and contraction amount. For example,
When the bobbin is divided into two parts, the amount of expansion and contraction of each divided bobbin is halved compared to the case where the bobbin is not divided, and the stress concentrated on both ends of the bobbin and the insulating layer near it is divided. The generated bobbins are distributed more evenly in the vicinity of both ends. As a result, in addition to the effect of the invention described in claim 1, the generation of cracks in the bobbin and the insulating layer in the vicinity thereof can be more reliably suppressed.

In the ignition coil for an internal combustion engine according to claim 1, the bobbin comprises a primary bobbin on which a primary winding is wound and a secondary bobbin on which a secondary winding is wound, and at least two bobbins are provided. The secondary bobbin is divided into a plurality in the axial direction, and the divided secondary bobbins are arranged at predetermined intervals in the axial direction.

According to the above configuration, the occurrence of cracks in the high potential portion of the ignition coil, such as the secondary bobbin and the insulating layer in the vicinity of the bobbin, is suppressed, and the occurrence of dielectric breakdown due to the cracks is suppressed. Can be avoided.

[0047]

According to the first aspect of the present invention, the bobbin is divided into a plurality of parts in the axial direction, and the divided bobbins are arranged at predetermined intervals in the axial direction. Therefore, the individual thermal expansion and contraction amount of each divided bobbin is reduced as compared with the case where the divided bobbin is not divided, and the stress concentrated on both ends of the bobbin and the insulating layer in the vicinity thereof is reduced. It is distributed and generated near both ends. As a result, it is possible to prevent an excessive stress from acting on the bobbin and the insulating layer near the bobbin, and to suppress the occurrence of cracks in these members.

According to the invention described in claim 2, an elastic body is interposed between the divided bobbins, and the elastic body is brought into close contact with each bobbin. Therefore,
Even when each bobbin thermally expands, the thermal expansion is absorbed by the deformation of the elastic body. As a result, claim 1
In addition to the effects of the invention described in (1), the occurrence of cracks in the bobbin and the insulating layer due to the thermal expansion of the bobbin can be suppressed more reliably.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an attached state of an ignition coil.

FIG. 2 is a sectional view showing the ignition coil according to the first embodiment;

FIG. 3 is a sectional view showing an ignition coil according to a second embodiment.

FIG. 4 is a sectional view showing a conventional ignition coil.

[Explanation of symbols]

13: ignition coil, 14: connection part, 15: insertion part, 20
... case, 21 ... igniter, 22 ... inner core, 23 ...
Outer core, 24 ... insulating layer, 30 ... primary coil, 31 ... 1
Primary bobbin, 33 ... primary winding, 40 ... secondary coil, 41
(41a, 41b) secondary bobbin, 43 secondary winding, 5
0 ... elastic member.

Claims (2)

[Claims] 1. An ignition coil for an internal combustion engine in which a bobbin on which a winding is wound is arranged in a case and a resin is filled in the case to form an insulating layer covering the bobbin. An ignition coil for an internal combustion engine, wherein the ignition coil is divided into a plurality of parts in the axial direction and the divided bobbins are arranged at predetermined intervals in the axial direction. 2. The ignition coil for an internal combustion engine according to claim 1, wherein an elastic body is interposed between each of the divided bobbins, and the elastic body is closely attached to each of the bobbins.