JP7505382B2 - Ignition coil for internal combustion engine - Google Patents

Description

The present invention relates to an ignition coil for an internal combustion engine.

An ignition coil for an internal combustion engine (called an ignition coil) is used to ignite a mixture of fuel and combustion air in the combustion chamber of an internal combustion engine. The ignition coil includes a primary coil, a secondary coil that is arranged coaxially around the outer periphery of the primary coil and is magnetically coupled to the primary coil, an igniter that incorporates a switching element that switches current to and from the primary coil, and a core for passing magnetic flux generated by the primary coil and secondary coil. The primary coil, secondary coil, igniter, core, etc. are arranged in a coil case and are insulated and fixed by an insulating fixing resin filled in the coil case.

The primary coil is wound around the outer circumference of a plastic primary bobbin, and the secondary coil is wound around the outer circumference of a plastic secondary bobbin. The secondary coil winding (magnet wire) generates a high voltage for sparking, so the potential difference between the secondary coil windings is large. Therefore, to protect the insulating coating of the secondary coil winding from dielectric breakdown, multiple flanges are provided on the outer circumference of the secondary bobbin, lined up in the axial direction, and the secondary coil windings are placed in multiple recesses partitioned by these flanges.

In addition, in the ignition coil for an internal combustion engine of Patent Document 1, measures have been taken to improve the insulation between the wires of the secondary conductor (winding) of the secondary coil. In this ignition coil, the thickness of the insulating coating on the high-voltage side, which is the secondary conductor arranged on the high-voltage side of the secondary coil, is made thicker than the thickness of the insulating coating on the low-voltage side, which is the secondary conductor arranged on the low-voltage side of the secondary coil, thereby increasing the voltage resistance of the high-voltage side.

JP 2016-171098 A

The secondary coil of the ignition coil is wound around the secondary bobbin and fixed inside the coil case by the insulating adhesive resin inside the coil case. When a potential is generated in the secondary coil, capacitance is generated by the secondary coil windings that are lined up on the high voltage side and low voltage side with the flange of the secondary bobbin in between, and by the secondary coil windings and core with the insulating adhesive resin in between. The former is called series capacitance, and the latter is called capacitance to ground.

After a spark discharge occurs in the spark plug due to the induced electromotive force generated after the current to the primary coil is cut off, a surge voltage, which is a rebound voltage from the spark plug, is applied to the secondary coil. This surge voltage increases in the higher voltage side of the secondary coil winding. In the ignition coil of Patent Document 1, the withstand voltage of the high voltage side of the secondary conductor is increased, which simply improves the insulation between the windings.

In the ignition coil of Patent Document 1, increasing the thickness of the insulating coating on the secondary conductor may increase the overall capacitance of the secondary coil and secondary bobbin. If the overall capacitance of the secondary coil and secondary bobbin increases, the voltage loss in the secondary coil increases, making it difficult to increase the discharge voltage from the secondary coil. This leads to a decrease in the performance of the ignition coil. Furthermore, increasing the coating thickness increases the size of the ignition coil, leading to a decrease in the mountability of the ignition coil.

The inventor's research has revealed that the line potential (the potential shared by the windings) as the potential difference generated between the windings of the secondary coil varies greatly depending on the ratio of the capacitance to ground to the series capacitance. In particular, it has been found that in order to reduce the line potential in the high-voltage side of the secondary coil winding, it is effective to increase the series capacitance in this high-voltage side. The series capacitance in this high-voltage side is tiny compared to the capacitance of the entire secondary coil, and has little effect on the voltage loss in the secondary coil mentioned above.

The present invention was made in consideration of these problems, and aims to provide an ignition coil for an internal combustion engine that can reduce the line potential generated in the high-voltage side of the secondary coil winding while suppressing the deterioration of the ignition coil's performance and increase in size.

One aspect of the present invention is
an igniter (43) having a switching element;
A primary coil (2) in which current is applied and cut off by the switching element;
a secondary coil (3) arranged coaxially with the primary coil on the outer periphery of the primary coil, and generating an induced electromotive force when current to the primary coil is cut off;
A secondary bobbin (31) around which the secondary coil is wound;
a coil case (5) that accommodates the igniter, the primary coil, the secondary coil, and the secondary bobbin;
an insulating and fixing resin (6) that fills gaps in the coil case, insulates and fixes the igniter, the primary coil, the secondary coil, and the secondary bobbin, and has a relative dielectric constant higher than that of the secondary bobbin;
The secondary bobbin has a cylindrical portion (32) having a rectangular cylindrical shape, and a plurality of flange portions (33, 34) that protrude from the outer periphery of the cylindrical portion at a plurality of locations in the axial direction (L) on the outer periphery of the cylindrical portion and divide the outer periphery of the cylindrical portion into a plurality of recesses (321) arranged in the axial direction,
A single cross groove (35) is formed in each of the remaining intermediate flanges (34) of the flanges, excluding the end flanges (33) located at both ends, in which a winding (301) of the secondary coil is disposed and which crosses between the adjacent recesses;
At least one of the intermediate flanges, which is located on the high-voltage side (L1) in the axial direction (L) of the secondary coil relative to a center position (L0) in the axial direction (L) of the secondary coil, is cut out deeper than an outermost position (P) of the secondary coil winding and has at least one notched groove (36) filled with the insulating adhesive resin,
the notch groove is formed in a plurality of the intermediate flange portions located on the high-voltage side in the axial direction relative to the center position,
The present invention relates to an ignition coil for an internal combustion engine, in which, among the plurality of intermediate flange portions in which the notch grooves are formed, the intermediate flange portion located closer to the high-voltage side in the axial direction has a larger notch area of the notch groove when viewed from the axial direction .

In the ignition coil for an internal combustion engine (referred to as the ignition coil) of the above-mentioned embodiment, the shape of the intermediate flange located on the high-voltage side of the secondary bobbin is changed to increase the series capacitance generated in the high-voltage portion of the secondary coil winding. Specifically, at least one notch groove is formed in at least one intermediate flange located on the axial high-voltage side of the axial center position of the secondary coil. Then, by filling this notch groove with insulating adhesive resin, a part of the intermediate flange that separates the secondary coil winding in the axial direction is formed by the insulating adhesive resin.

The notch groove is cut deeper than the outermost peripheral position of the secondary coil winding, and is formed at a position adjacent to the secondary coil winding in the axial direction. Since the dielectric constant of the insulating adhesive resin is higher than the dielectric constant of the secondary bobbin, it is possible to increase the series capacitance of at least one intermediate flange located on the high voltage side and the secondary coil windings arranged in the axial direction via this intermediate flange. As a result, by simply forming a notch groove in part of the intermediate flange of the secondary bobbin, it is possible to reduce the line potential generated in the high voltage side part of the secondary coil winding.

And, without increasing the dimensions of each component, such as by increasing the thickness of the middle flange of the secondary bobbin or the thickness of the insulating coating on the secondary coil winding, the series capacitance of the high-voltage side of the secondary coil and secondary bobbin can be increased. This prevents the overall capacitance of the ignition coil from increasing, and prevents the ignition coil from deteriorating in performance and becoming bulkier.

The ignition coil of the above embodiment can reduce the line potential generated in the high-voltage side of the secondary coil winding while suppressing deterioration in the performance of the ignition coil and increase in size.

Note that the reference numerals in parentheses for each component shown in one aspect of the present invention indicate the corresponding reference numerals in the figures in the embodiment, but do not limit each component to the contents of the embodiment.

FIG. 1 is an explanatory diagram showing a cross section of an ignition coil according to a first embodiment. FIG. 2 is an explanatory diagram showing a cross section of the ignition coil according to the first embodiment before being filled with an insulating adhesive resin, as viewed in a direction perpendicular to FIG. FIG. 3 is an explanatory diagram showing the secondary bobbin according to the first embodiment as viewed from the mounting side of the spark plug. FIG. 4 is an explanatory diagram illustrating an enlarged view of the periphery of the notched groove in FIG. 2 according to the first embodiment. FIG. 5 is an explanatory diagram illustrating an enlarged view of the periphery of the connecting groove in FIG. 2 according to the first embodiment. FIG. 6 is an explanatory diagram showing a cross section of another secondary bobbin according to the first embodiment, which has a different cutout groove formation state from the secondary bobbin shown in FIG. 2, as viewed in a direction perpendicular to FIG. FIG. 7 is an explanatory diagram showing a cross section of still another secondary bobbin according to the first embodiment, which has a different cutout groove formation state from that of the secondary bobbin in FIG. 2, as viewed in a direction perpendicular to FIG. FIG. 8 is a graph showing the relationship between the ratio of the windings of the secondary coil and the voltage shared by each portion of the windings of the secondary coil according to the first embodiment. FIG. 9 is an explanatory diagram illustrating a schematic diagram of the capacitance to ground and the series capacitance according to the first embodiment.

A preferred embodiment of the above-mentioned ignition coil for an internal combustion engine will be described with reference to the drawings.
<Embodiment 1>
As shown in Figures 1 and 2, an ignition coil 1 for an internal combustion engine according to this embodiment (hereinafter referred to as ignition coil 1) includes an igniter 43, a primary coil 2, a secondary coil 3, a secondary bobbin 31, a coil case 5, and an insulating adhesive resin 6. The igniter 43 has a switching element. The primary coil 2 is configured so that current is applied and cut off by the switching element. The secondary coil 3 is disposed coaxially with the primary coil 2 on the outer periphery of the primary coil 2, and is configured to generate an induced electromotive force when current to the primary coil 2 is cut off.

The secondary bobbin 31 has the secondary coil 3 wound around its outer circumference. The coil case 5 houses the igniter 43, the primary coil 2, the secondary coil 3, the secondary bobbin 31, etc. The insulating adhesive resin 6 fills the gaps in the coil case 5 and insulates and fixes the igniter 43, the primary coil 2, the secondary coil 3, the secondary bobbin 31, etc. The relative dielectric constant of the insulating adhesive resin 6 is higher than that of the secondary bobbin 31.

Figure 1 shows the state in which the gaps in the coil case 5 of the ignition coil 1 have been filled with insulating adhesive resin 6. Figure 2 shows the state before the gaps in the coil case 5 of the ignition coil 1 have been filled with insulating adhesive resin 6.

As shown in Figures 1 to 3, the secondary bobbin 31 has a rectangular cylindrical tubular portion 32 and a plurality of flanges 33, 34 that protrude from the outer periphery of the tubular portion 32 at a plurality of locations in the axial direction L on the outer periphery of the tubular portion 32 and divide the outer periphery of the tubular portion 32 into a plurality of recesses 321 arranged in the axial direction L. In the plurality of flanges 33, 34, except for the end flanges 33 located at both ends, one crossing groove 35 is formed in which the winding 301 of the secondary coil 3 is arranged to cross between the adjacent recesses 321. At least one of the plurality of intermediate flanges 34, which is located on the high voltage side L1 in the axial direction L rather than the center position L0 of the secondary coil 3 in the axial direction L, is cut out deeper than the outermost peripheral position P of the winding 301 of the secondary coil 3 and is filled with insulating adhesive resin 6, and at least one notched groove 36 is formed.

The ignition coil 1 of this embodiment will be described in detail below.
(Ignition coil 1)
As shown in Fig. 1, an ignition coil 1 is disposed in a cylinder head cover 7 of an engine as an internal combustion engine of a vehicle, and is used to generate a spark discharge in a combustion chamber of the cylinder head from a spark plug disposed in the cylinder head. The ignition coil 1 of this embodiment is for mounting on a vehicle. The ignition coil 1 has a coil body 11 constituted by a primary coil 2, a secondary coil 3, a coil case 5, an igniter 43, etc., and a joint portion 12 protruding from the coil body 11 for electrically connecting the secondary coil 3 and the spark plug via a high-voltage terminal 45 and a spring 46. The coil body 11 is disposed in the cylinder head cover 7, and the joint portion 12 is disposed in a plug hole 71 of the cylinder head cover 7.

(Axial direction L, radial direction R, circumferential direction C, mounting direction D, width direction W)
1 to 5, the axial direction L in this embodiment refers to the direction in which the central axis extends as an imaginary line passing through the center (centre) of the cross section of the primary coil 2 and secondary coil 3. In the axial direction L, the side where high voltage is generated in the secondary coil 3 is called the high-voltage side L1, and the opposite side of the high-voltage side L1 is called the low-voltage side L2. The direction that spreads radially from the central axis of the primary coil 2 and secondary coil 3 is called the radial direction R. The direction around the central axis of the primary coil 2 and secondary coil 3 is called the circumferential direction C. The circumferential direction C in this embodiment refers to the direction around a rectangle.

In this embodiment, the mounting direction D is a direction perpendicular to the axial direction L, and refers to the direction in which the opening 52 and bottom 53 of the coil case 5 are aligned. In the mounting direction D of the coil case 5, the side on which the bottom 53 is located and the side on which the spark plug is arranged is called the mounting side D1, and the side on which the opening 52 is located is called the opening side D2. In addition, the direction perpendicular to both the axial direction L and the mounting direction D is called the width direction W.

(Primary coil 2)
1 and 2, the primary coil 2 is formed by winding a magnet wire as a winding 301 around the outer circumferential surface of a cylindrical portion of the primary bobbin 21. The primary coil 2 is repeatedly energized and cut off by a switching element of an igniter 43.

(Secondary coil 3)
1 and 2, the secondary coil 3 is disposed coaxially with the primary coil 2 on the outer periphery of the primary coil 2. The secondary coil 3 is formed by winding a magnet wire as a winding 301 around the outer periphery of the cylindrical portion 32 of the secondary bobbin 31. The winding 301 of the secondary coil 3 is thinner than the winding of the primary coil 2, and the number of windings of the secondary coil 3 is greater than the number of windings of the primary coil 2. The secondary coil 3 generates an induced electromotive force by mutual induction when the current to the primary coil 2 is cut off. The central axes of the primary coil 2 and the secondary coil 3 are oriented in a direction perpendicular to the opening 52 of the coil case 5.

As shown in Figures 3 to 5, the winding 301 of the secondary coil 3 is wound in multiple rows in the axial direction L of the secondary bobbin 31 in each recess 321 of the secondary bobbin 31, and is wound overlapping in multiple stages in the radial direction R of the secondary bobbin 31. In other words, the secondary coil 3 is formed by dividing one magnet wire into multiple recesses 321 and winding it continuously. The winding 301 of the secondary coil 3 is arranged in each recess 321 from the bottom stage position 301A, which is the innermost position in the radial direction R, to the outermost position in the radial direction R, overlapping sequentially. The number of stages of the winding 301 shown in Figures 4 and 5 is one example.

The winding 301 of the secondary coil 3 is passed between adjacent recesses 321 through the transition groove 35 of the intermediate flange 34. More specifically, the winding 301 of the secondary coil 3 is passed from the topmost position 301B of the multiple stages of winding 301 in the radial direction R in each recess 321 through the transition groove 35 to the bottommost position 301A in the radial direction R in the recess 321 adjacent to each recess 321 in the axial direction L.

The winding 301 of the secondary coil 3 is wound toward one side of the circumferential direction C in each recess 321. One end of the winding 301 of the secondary coil 3 is connected to the low voltage side L2 and is connected to the ground or power supply terminal of the igniter 43. The other end of the winding 301 of the secondary coil 3 is connected to the high voltage terminal 45 that is connected to the center electrode of the spark plug and is connected to the high voltage side L1.

The winding 301 of the secondary coil 3 is formed by rotating the secondary bobbin 31 relative to the magnet wire for forming the winding 301, or by rotating a jig that feeds out the magnet wire for forming the winding 301 around the central axis of the secondary bobbin 31.

(Central core 41)
1 and 2, a central core 41 is disposed on the inner periphery of the primary coil 2 for passing magnetic flux generated by the primary coil 2 and the secondary coil 3. The central core 41 in this embodiment is formed by laminating a plurality of plate-shaped electromagnetic steel sheets made of a soft magnetic material. The central core 41 is formed in a rectangular parallelepiped shape. The central core 41 may be formed by compression molding powder made of a soft magnetic material.

(Outer core 42)
1 and 2, an outer core 42 is disposed on the outer periphery of the secondary coil 3 to allow the magnetic flux generated by the primary coil 2 and the secondary coil 3 to pass therethrough. The outer core 42 in this embodiment is formed by laminating a plurality of plate-shaped electromagnetic steel sheets made of a soft magnetic material. The outer core 42 is formed in a square ring shape with the central core 41 disposed on the inside in a cross section seen from the mounting direction D. The outer core 42 may be formed by compression molding powder made of a soft magnetic material.

The central core 41 and the outer core 42 form a closed magnetic path through which magnetic flux passes. A permanent magnet 44 is disposed between the central core 41 and the outer core 42 to prevent magnetic saturation.

(Igniter 43)
As shown in Fig. 1, the igniter 43 is disposed adjacent to a part of the outer core 42 in the axial direction L of the primary coil 2 and the secondary coil 3. The igniter 43 is composed of an electronic board on which electronic components such as switching elements forming a switching circuit are provided, and a molded resin covering the electronic board. Conductor pins provided on the electronic board are drawn out of the molded resin. The conductor pins of the igniter 43 protrude from the molded resin to an opening side D2 in the mounting direction D. The switching element in the igniter 43 receives a command from an electronic control device disposed outside the ignition coil 1 and performs energization and cut-off of energization to the primary coil 2.

(Coil case 5)
As shown in Fig. 1 and Fig. 2, the coil case 5 is formed as a molded product of thermoplastic resin. The coil case 5 has a housing portion 51 that houses the primary coil 2, the secondary coil 3, the central core 41, the outer core 42, the igniter 43, etc. The opening 52 of the coil case 5 is formed at the end of the opening side D2 of the housing portion 51 in the mounting direction D. The opening 52 is formed on the opposite side of the mounting side D1 on which the spark plug is mounted in the mounting direction D. The coil assembly, including the primary coil 2, the primary bobbin 21, the secondary coil 3, the secondary bobbin 31, the central core 41, the outer core 42, and the igniter 43, is disposed in the housing portion 51 through the opening 52. In addition, the liquid insulating adhesive resin 6 is injected into the gap in the coil case 5 through the opening 52.

A connector portion 24 is disposed in a portion of the coil case 5 for electrically connecting the igniter 43 to an external electronic control device. In this embodiment, the connector portion 24 is formed separately from the primary bobbin 21. The connector portion 24 may also be molded integrally with the primary bobbin 21.

A tower section 54 that constitutes the joint section 12 is formed on the bottom section 53 of the mounting side D1 of the coil case 5 in the mounting direction D. A seal rubber 55 is attached to the tower section 54 to seal the gap between the ignition coil 1 and the plug hole 71.

(Insulating adhesive resin 6)
1, the insulating fixing resin 6 is made of a thermosetting resin. After a coil assembly in which the primary coil 2, the primary bobbin 21, the secondary coil 3, the secondary bobbin 31, the center core 41, the outer core 42, the igniter 43, etc. are assembled is placed in the coil case 5, liquid thermosetting resin is injected into the gaps in the coil case 5, and the liquid thermosetting resin is hardened. The insulating fixing resin 6 made of a thermosetting resin fixes the primary coil 2, the primary bobbin 21, the secondary coil 3, the secondary bobbin 31, the center core 41, the outer core 42, the igniter 43, etc. in the coil case 5 to each other in an insulated state.

(Primary bobbin 21)
1 and 2, the primary bobbin 21 is formed by molding a thermoplastic resin. The primary bobbin 21 has a rectangular cylindrical portion and flanges formed on both ends of the cylindrical portion in the axial direction L. The winding of the primary coil 2 is wound around the outer circumferential surface between the flanges of the cylindrical portion of the primary bobbin 21. The connector portion 24 is provided with a connector conductor that is connected to a conductor pin of the igniter 43.

The igniter 43 is disposed in a space formed between the outer core 42 and the connector portion 24. The multiple conductor pins of the igniter 43 are disposed opposite the multiple connector conductors of the connector portion 24 at the position of the opening side D2 in the mounting direction D inside the coil case 5. The multiple conductor pins and the multiple connector conductors are joined to each other by soldering, welding, etc. The multiple conductor pins are also joined to the coil conductors connected to both ends of the winding of the primary coil 2 and to the coil conductor connected to the end of the low-voltage side L2 of the winding 301 of the secondary coil 3 by soldering, welding, etc.

(Secondary bobbin 31)
As shown in Fig. 2 and Fig. 3, the secondary bobbin 31 is formed by a molded product of a thermoplastic resin. The four corners of the rectangular cylindrical portion 32 of the secondary bobbin 31 are curved. The four corners of the multiple intermediate flanges 34 are formed as curved corners 343. A hollow hole 322 in which the primary coil 2 and the primary bobbin 21 are disposed is formed on the inner peripheral side of the cylindrical portion 32 of the secondary bobbin 31. The multiple intermediate flanges 34 are composed of a pair of linear first side portions 341 parallel to the mounting direction D, a pair of linear second side portions 342 perpendicular to the mounting direction D, and four curved corner portions 343 connecting the first side portions 341 and the second side portions 342. Fig. 3 shows the secondary bobbin 31 as viewed from the mounting side D1 of the mounting direction D.

As shown in FIG. 5, in one of the two curved corner portions 343 located on the mounting side D1 of the mounting direction D in each intermediate flange 34, a transition groove 35 through which the winding 301 of the secondary coil 3 passes is formed. The transition groove 35 is formed to allow the winding 301 of the secondary coil 3 arranged in each recess 321 in the secondary bobbin 31 to cross over to the recess 321 adjacent to each recess 321. The transition groove 35 is formed as a notch that cuts out a part of the intermediate flange 34 in the circumferential direction C. The transition groove 35 is cut out to the outer periphery of the tubular portion 32 of the secondary bobbin 31.

As shown in FIG. 3, the transition grooves 35 in this embodiment are formed on one side of the curved corners 343 of the intermediate flanges 34 in the width direction W, penetrating (aligned) in the axial direction L. The transition grooves 35 may be formed alternately on one side and the other side in the width direction W of the intermediate flanges 34 adjacent to each other.

As shown in FIG. 4, the notch grooves 36, which are intended to increase the capacitance of the secondary coil 3, are formed in a pair of second side portions 342, which are linear side portions facing each other, in the intermediate flange portion 34, separately from the transition grooves 35. The notch grooves 36 are cut out to the outer periphery of the cylindrical portion 32 of the secondary bobbin 31, and are formed adjacent to the axial direction L of the multiple stages of winding 301 from the lowest stage position 301A to the highest stage position 301B in the winding 301 of the secondary coil 3. It is sufficient that the notch grooves 36 are cut out deeper from the outer periphery of the intermediate flange portion 34 than the outermost periphery position P of the winding 301 of the secondary coil 3.

The notch groove 36 is formed as a notch that the winding 301 of the secondary coil 3 does not pass through and is entirely filled with insulating adhesive resin 6. Since the notch groove 36 and the transition groove 35 are all formed with an opening toward the mounting direction D, when the secondary bobbin 31 is molded, it is easy to remove the molded secondary bobbin 31 from the mold.

As shown in FIG. 3, the notch groove 36 in this embodiment is formed in three intermediate flanges 34 that are continuous from the intermediate flange 34 located on the highest voltage side L1 of the axial direction L of the secondary coil 3 to the low voltage side L2 of the axial direction L among the multiple intermediate flanges 34. The number of intermediate flanges 34 arranged in the axial direction L in the secondary bobbin 31 can be, for example, 3 to 8. The notch groove 36 can be formed in one to four intermediate flanges 34 that are continuous from the intermediate flange 34 located on the highest voltage side L1 of the axial direction L of the secondary coil 3 to the low voltage side L2 of the axial direction L among the multiple intermediate flanges 34. With this configuration, the series capacitance of the high voltage side L1 by the secondary coil 3 and the secondary bobbin 31 can be effectively increased. In FIG. 3, for ease of understanding, the areas around the jump groove 35 and the notch groove 36 in the intermediate flange 34 are shown hatched.

The center position L0 of the secondary coil 3 in the axial direction L refers to the center position L0 of the entire length Lx of the multiple divided winding parts of the secondary coil 3, which are divided and arranged in the multiple recesses 321 of the secondary bobbin 31. The high-voltage side L1 of the secondary coil 3 in the axial direction L is located on the side where the end of the winding 301 of the secondary coil 3 is connected to the spark plug. The low-voltage side L2 of the secondary coil 3 in the axial direction L is located on the side where the igniter 43 is arranged with respect to the end of the secondary coil 3 in the axial direction L, or on the side where the end of the winding 301 of the secondary coil 3 is connected to the igniter 43 or the connector part 24.

The width in the axial direction L of the multiple recesses 321 in the secondary bobbin 31 is smaller for the recesses 321 located on the high-voltage side L1 in the axial direction L. The width in the axial direction L of the split winding portion of the winding 301 of the secondary coil 3 arranged in each recess 321 is smaller for the split winding portion located on the high-voltage side L1 in the axial direction L.

As shown in FIG. 6, the notch grooves 36 may be formed in each of a pair of first side portions 341 as mutually opposing straight side portions and each of a pair of second side portions 342 as mutually opposing straight side portions in each intermediate flange portion 34 of the secondary bobbin 31. Also, as shown in FIG. 7, a plurality of notch grooves 36 may be formed in each of the first side portions 341 and the second side portions 342. The notch grooves 36 may be formed in various other ways. Also, the notch area in the protruding area of the entire intermediate flange portion 34 as viewed from the axial direction L may be made larger for the notch grooves 36 located on the high-voltage side L1 of the axial direction L.

(Dielectric constant)
The insulating and fixing resin 6 of this embodiment contains a thermosetting resin and a filler having a relative dielectric constant higher than that of the thermosetting resin. By using the filler, the mechanical strength, withstand voltage, etc. of the insulating and fixing resin 6 can be improved, and the relative dielectric constant of the insulating and fixing resin 6 can be increased. The thermosetting resin of this embodiment is made of epoxy resin or the like. The filler of this embodiment is made of alumina (aluminum oxide), silica containing silicon dioxide, or the like. The filler can be made of inorganic materials such as powder and fiber, ceramics, resin, wood powder, or the like. The filler is mixed into the thermosetting resin, for example, for the purpose of increasing the viscosity of the thermosetting resin.

The capacitance C is expressed as C = ε·S/d, where S is the area of the plates, d is the distance between the plates, and ε is the relative dielectric constant. The capacitance can be increased by increasing the relative dielectric constant.

The secondary bobbin 31 is made of a thermoplastic resin such as polyphenylene ether (PPE) resin. The relative dielectric constant of polyphenylene ether resin is about 3.0, while the relative dielectric constant of epoxy resin is about 3.5. Furthermore, the relative dielectric constant of alumina, which is a filler contained in epoxy resin, is about 8.5, and the relative dielectric constant of silicon dioxide is about 3.9.

In particular, the filler is likely to accumulate in the portion of the insulating resin 6 located near the bottom 53 of the coil case 5. The filler is also likely to accumulate in the portion of the insulating resin 6 located near the secondary coil 3 and the secondary bobbin 31. The relative dielectric constant of the insulating resin 6 near the secondary coil 3 and the secondary bobbin 31 is about 4 to 5. The high relative dielectric constant of the insulating resin 6 makes it possible to increase the electrostatic capacitance of the secondary coil 3 and the secondary bobbin 31 when the insulating resin 6 is filled into the notched groove 36 of the secondary bobbin 31.

(Capacitance and Line Potential)
After a spark discharge occurs in the spark plug due to an induced electromotive force generated after the power supply to the primary coil 2 is cut off, a surge voltage, which is a rebound voltage from the spark plug, is applied to the secondary coil 3. This surge voltage becomes larger in the portion of the winding 301 of the secondary coil 3 that is located on the high voltage side L1. The insulating coating provided on the winding 301 of the secondary coil 3 is designed to withstand the surge voltage acting as a line potential between the windings 301 by setting the material and thickness of the insulating coating.

The ignition coil 1 of this embodiment is designed to lower the line potential (potential shared by each winding 301) between the windings 301 of the secondary coil 3 by appropriately reducing the electrostatic capacitance around the secondary coil 3. When a step voltage simulating a surge voltage is applied to the secondary coil 3, the potential distribution in the windings 301 of the secondary coil 3 is shown by the relationship between the proportion of the windings 301 and the potential shared by each part of the winding 301, as shown in Figure 8.

The ratio of the winding 301 on the horizontal axis of Fig. 8 is 100% for the total number of turns, 0% for the high voltage side L1, and closer to 100% for the low voltage side L2. The potential Vn/V shared by each part of the winding 301 is expressed by Vn = V sinhα (1 - Xn/N)/sinhα, where V is the step voltage, N is the total number of turns, and Xn is the number of turns at each part of the winding 301. Here, the coefficient α is expressed by α = (C/K) ^1/2 , where C is the total capacitance to earth of the secondary coil 3, and K is the total series capacitance of the secondary coil 3. The total capacitance to earth C refers to the total capacitance to earth C, and is simply called the capacitance to earth C. The total series capacitance K refers to the total series capacitance K, and is simply called the series capacitance K.

Figure 9 shows a schematic diagram of the capacitance to earth C and the series capacitance K. As shown in Figure 9, the capacitance to earth C refers to the capacitance generated by the winding 301 of the secondary coil 3 and the outer core 42 with the insulating adhesive resin 6 in between. The series capacitance K refers to the capacitance of the part of the winding 301 of the secondary coil 3 that is arranged on the high voltage side L1 and the low voltage side L2 with the intermediate flange 34 of the secondary bobbin 31 in between. Usually, the capacitance to earth C is larger than the series capacitance K. And, as shown in Figure 8, the coefficient α takes a value of 2 or more, and the potential distribution in the winding 301 of the secondary coil 3 becomes curved.

The larger the coefficient α, the greater the curvature of the curve and the more the shared potential Vn/V is biased toward the portion of the winding 301 on the high-voltage side L1. If the shared potential Vn/V is biased toward the portion of the winding 301 on the high-voltage side L1, the line-to-line potential between the windings 301 becomes high, making it easier for current to leak into the windings 301. In order to lower the line-to-line potential at each portion of the winding 301, it is effective to increase the series capacitance K as much as possible so that the shared potential Vn/V is generated as evenly as possible across the entire winding 301 of the secondary coil 3.

(Action and Effect)
In the ignition coil 1 of this embodiment, the shape of the intermediate flange 34 located on the high-voltage side L1 of the secondary bobbin 31 is changed to increase the series capacitance generated in the portion of the winding 301 of the secondary coil 3 on the high-voltage side L1. Specifically, a plurality of notched grooves 36 are formed in at least one intermediate flange 34 located on the high-voltage side L1 in the axial direction L from the center position L0 of the secondary coil 3 in the axial direction L. Then, the notched grooves 36 are filled with insulating resin 6, so that a part of the intermediate flange 34 that divides the winding 301 of the secondary coil 3 in the axial direction L is formed by the insulating resin 6.

The notch groove 36 is cut deeper than the outermost position P of the winding 301 of the secondary coil 3, and is formed at a position adjacent to the axial direction L of the winding 301 of the secondary coil 3. Since the dielectric constant of the insulating adhesive resin 6 is higher than the dielectric constant of the secondary bobbin 31, it is possible to increase the series capacitance of at least one intermediate flange 34 located on the high voltage side L1 and the winding 301 of the secondary coil 3 arranged on the high voltage side L1 and the low voltage side L2 in the axial direction L through this intermediate flange 34. As a result, by a simple device such as forming the notch groove 36 in a part of the intermediate flange 34 of the secondary bobbin 31, it is possible to reduce the line potential generated in the part of the high voltage side L1 of the winding 301 of the secondary coil 3.

And, without increasing the dimensions of each component, such as by increasing the thickness of the intermediate flange 34 of the secondary bobbin 31 or by increasing the thickness of the insulating coating on the winding 301 of the secondary coil 3, the series capacitance at the high voltage side L1 of the secondary coil 3 and the secondary bobbin 31 can be increased. This prevents the overall capacitance of the ignition coil 1 from increasing, and prevents the performance of the ignition coil 1 from decreasing and the size of the ignition coil 1 from increasing.

If the overall capacitance of the ignition coil 1 becomes large, it becomes difficult to increase the discharge voltage of the secondary coil 3. Furthermore, if the shape is changed by thickening the insulating coating of the winding 301 of the secondary coil 3, by increasing the thickness of the axial direction L of the intermediate flange portion 34 of the secondary bobbin 31, or by increasing the number of recesses 321 (slots) of the secondary bobbin 31, the size of the ignition coil 1 will increase. Therefore, the configuration of the ignition coil 1 of this embodiment is effective in increasing the discharge voltage of the secondary coil 3 without increasing the size of the ignition coil 1.

The ignition coil 1 of this embodiment can reduce the line potential generated at the high-voltage side L1 of the winding 301 of the secondary coil 3 while preventing the overall capacitance of the ignition coil 1 from increasing, thereby preventing the performance degradation and increase in size of the ignition coil 1.

(Verification of effectiveness)
In this embodiment, the effect of forming the notched groove 36 in the intermediate flange portion 34 was confirmed by simulation.
The notched grooves 36 were formed in a pair of second side portions 342 of three intermediate flanges 34 located on the high voltage side L1 in the axial direction L among the five intermediate flanges 34 shown in FIG. 3. The thickness of the intermediate flanges 34 in the axial direction L was constant at 0.8 mm. The relative dielectric constant of the secondary bobbin 31 was set to 3.0, and the relative dielectric constant of the insulating adhesive resin 6 containing the filler was set to 5.0. The reduction amount of the maximum line-to-line potential was confirmed when the area reduction rate due to the notched grooves 36 and the jumper grooves 35 on the surface in the axial direction L of the intermediate flanges 34 was set to 25% and 50%. For comparison, the area reduction rate of a conventional secondary bobbin having an intermediate flange 34 formed only with the jumper grooves 35 was set to 4%. The maximum line-to-line potential refers to the value at the portion where the line-to-line potential is maximum in the entire winding 301.

The reduction in maximum line potential was about 10% when the area reduction rate was 25%, and about 18% when the area reduction rate was 50%. The discharge voltage as the output voltage required for conventional ignition coils is about 40 kV. For recent ignition coils 1, it is expected that the required output voltage will be about 45 kV. In this case, if the maximum line potential increases by 11.1% (45/40 x 100%), it was found that the required output voltage of about 45 kV can be met by setting the area reduction rate of the notch groove 36 in the intermediate flange portion 34 to 30% or more.

The present invention is not limited to the embodiments, and further different embodiments can be constructed without departing from the gist of the present invention. The present invention also includes various modified examples, modifications within the scope of equivalents, etc. Furthermore, the combinations and forms of the various components envisioned from the present invention are also included in the technical concept of the present invention.

REFERENCE SIGNS LIST 1 ignition coil 2 primary coil 3 secondary coil 31 secondary bobbin 32 cylindrical portion 34 intermediate flange portion 35 cross groove 36 notched groove

Claims (3)

an igniter (43) having a switching element;
A primary coil (2) in which current is applied and cut off by the switching element;
a secondary coil (3) arranged coaxially with the primary coil on the outer periphery of the primary coil, and generating an induced electromotive force when current to the primary coil is cut off;
A secondary bobbin (31) around which the secondary coil is wound;
a coil case (5) that accommodates the igniter, the primary coil, the secondary coil, and the secondary bobbin;
an insulating and fixing resin (6) that fills gaps in the coil case, insulates and fixes the igniter, the primary coil, the secondary coil, and the secondary bobbin, and has a relative dielectric constant higher than that of the secondary bobbin;
The secondary bobbin has a cylindrical portion (32) having a rectangular cylindrical shape, and a plurality of flange portions (33, 34) that protrude from the outer periphery of the cylindrical portion at a plurality of locations in the axial direction (L) on the outer periphery of the cylindrical portion and divide the outer periphery of the cylindrical portion into a plurality of recesses (321) arranged in the axial direction,
A single cross groove (35) is formed in each of the remaining intermediate flanges (34) of the flanges, excluding the end flanges (33) located at both ends, in which a winding (301) of the secondary coil is disposed and which crosses between the adjacent recesses;
At least one of the intermediate flanges, which is located on the high-voltage side (L1) in the axial direction (L) of the secondary coil relative to a center position (L0) in the axial direction (L) of the secondary coil, is cut out deeper than an outermost position (P) of the secondary coil winding and has at least one notched groove (36) filled with the insulating adhesive resin,
the notch groove is formed in a plurality of the intermediate flange portions located on the high-voltage side in the axial direction relative to the center position,
An ignition coil (1) for an internal combustion engine, wherein, among the plurality of intermediate flanges in which the notch grooves are formed, the intermediate flanges located closer to the high-voltage side in the axial direction have larger notch areas of the notch grooves when viewed in the axial direction . The ignition coil for an internal combustion engine according to claim 1, wherein the notch groove is formed in one to four intermediate flanges that continue from the intermediate flange located on the highest voltage side of the secondary coil in the axial direction toward the low voltage side in the axial direction. The ignition coil for an internal combustion engine according to claim 1 or 2, wherein the insulating adhesive resin contains a thermosetting resin and a filler having a relative dielectric constant higher than that of the thermosetting resin.

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