JP7559637B2 - 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 is used to ignite a mixture of fuel and combustion air in the combustion chamber of the engine as 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 magnetically coupled to the primary coil, and an inner core and an outer core that allow the magnetic flux generated by the primary coil and secondary coil to pass through. Each component, such as the primary coil, secondary coil, inner core, and outer core, is arranged inside a coil case, and the gaps inside the coil case are filled with a filling resin that insulates and adheres each component.

When the current to the primary coil is cut off, the secondary coil generates a higher voltage in one direction closer to the spark plug. In order to prevent the ignition coil from becoming larger and to ensure the voltage resistance of the ignition coil, the following measures have been taken. That is, a number of flanges are provided on the outer circumference of the secondary spool around which the secondary coil is wound, with the axial spacing narrowing toward the high voltage side in the axial direction. In the recesses between the flanges, the diameter of the secondary coil wound around the recesses is made smaller toward the high voltage side in the axial direction of the secondary spool. This prevents the potential difference between the windings of the secondary coil from becoming large in the part located on the high voltage side of the secondary coil, and increases the distance from the core cover provided on the outer coil. An example of an ignition coil having such a structure is described in Patent Document 1.

JP 2017-45760 A

In the ignition coil described in Patent Document 1 and other publications, the thickness of the filled resin filled in the gap between the secondary coil and the core cover is greater in areas located on the high-voltage side of the secondary spool in the axial direction. Therefore, in the cooling and heating cycles during use of the ignition coil, the amount of thermal deformation (amount of thermal expansion and contraction) of the filled resin in the area located on the high-voltage side in the axial direction is greater than the amount of thermal deformation (amount of thermal expansion and contraction) of the filled resin in the area located on the low-voltage side in the axial direction. As a result, there is a risk of thermal stress being concentrated in the filled resin due to the difference in the amount of thermal deformation between the low-voltage side and the high-voltage side in the axial direction of the filled resin.

The present invention was made in consideration of these problems, and aims to provide an ignition coil for an internal combustion engine that can prevent the concentration of thermal stress in the filling resin.

One aspect of the present invention is
A primary coil (2);
a secondary spool (31) arranged concentrically outside the primary coil;
A secondary coil (3) that is wound around the outer periphery of the secondary spool in a radial direction (R) and an axial direction (L), and a voltage generated therein increases toward a high voltage side (L1) in the axial direction;
an inner core (41) disposed inside the primary coil;
an outer core (42) having a rectangular ring shape including a pair of side core portions (421) arranged parallel to the axial direction outside the side surface (411) of the inner core, and a pair of end surface core portions (422) arranged parallel to a width direction (W) perpendicular to the axial direction outside the end surface (412) of the inner core;
A core cover (6) provided on a surface of the outer core including an inner surface (423) located on the inside of at least a pair of the side core portions;
a coil case (5) having an opening (53) located on an opening side (D2) of the outer core and housing the primary coil, the secondary spool, the secondary coil, the inner core, the outer core, and the core cover;
A filling resin (7) is filled in the gap in the coil case,
The average radial thickness (u1) of the secondary coil at a portion located on the high-voltage side in the axial direction is smaller than the average radial thickness (u2) of the secondary coil at a portion located on the low-voltage side (L2) in the axial direction,
An ignition coil (1) for an internal combustion engine has an average cross-sectional area (a1) in a cross section perpendicular to the axial direction of a portion of the core cover provided on the inner surface of the high-voltage side of a pair of the side core portions in the axial direction, which is larger than an average cross-sectional area (a2) in a cross section perpendicular to the axial direction of a portion of the core cover provided on the inner surface of the low-voltage side of the pair of the side core portions in the axial direction.

In the ignition coil for an internal combustion engine of the above-mentioned embodiment, the shape of the core cover provided on the surface of the outer core is devised. Specifically, the average cross-sectional area of the portion of the core cover provided on the inner surface of the axial high-voltage side of the pair of side core parts in a cross section perpendicular to the axial direction is made larger than the average cross-sectional area of the portion of the core cover provided on the inner surface of the axial low-voltage side of the pair of side core parts in a cross section perpendicular to the axial direction. On the other hand, the average radial thickness of the portion of the secondary coil located on the axial high-voltage side is smaller than the average radial thickness of the portion of the secondary coil located on the axial low-voltage side.

With these configurations, the size of the gap between the secondary coil and the core cover at the high-voltage side in the axial direction can be made closer to the size of the gap at the low-voltage side in the axial direction. This makes it possible to make the average thickness of the filled resin filled between the secondary coil and the core cover closer to the area at the high-voltage side in the axial direction and the area at the low-voltage side in the axial direction. As a result, the amount of thermal expansion and contraction that occurs in the filled resin during the cooling and heating cycles when the ignition coil is in use can be made closer to the area at the high-voltage side in the axial direction and the area at the low-voltage side in the axial direction.

Therefore, with the ignition coil for an internal combustion engine of the above-mentioned embodiment, it is possible to prevent the concentration of thermal stress in the filling resin.

The "average radial thickness of the secondary coil at the high voltage side in the axial direction" may be the average value of the thickness of the secondary coil at the high voltage side of the center position over the entire axial length of the secondary coil. Also, the "average radial thickness of the secondary coil at the low voltage side in the axial direction" may be the average value of the thickness of the secondary coil at the low voltage side of the center position over the entire axial length of the secondary coil.

The "average cross-sectional area of the core cover at the surface on the high-voltage side of the pair of side core parts in the axial direction in a cross section perpendicular to the axial direction" may be the average value of the cross-sectional area of the core cover at the high-voltage side of the center position over the entire length of the core cover at the surface of the pair of side core parts. Also, the "average cross-sectional area of the core cover at the surface on the low-voltage side of the pair of side core parts in the axial direction in a cross section perpendicular to the axial direction" may be the average value of the cross-sectional area of the core cover at the low-voltage side of the center position over the entire length of the core cover at the surface of the pair of side core parts.

Note that the reference numerals in parentheses for each component shown in this invention indicate the corresponding relationship with the reference numerals in the figures in the embodiment, but do not limit each component to only 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 a coil assembly of an ignition coil according to the first embodiment. FIG. 3 is an explanatory diagram showing an enlarged cross section of the secondary coil, the outer core, the core cover, the filling resin, and the like according to the first embodiment. FIG. 4 is an explanatory diagram showing a cross section of the ignition coil at a position on the high voltage side in the axial direction, which corresponds to line IV-IV in FIG. 3, according to the first embodiment. FIG. 5 is an explanatory diagram showing a cross section of the ignition coil at a position on the low-voltage side in the axial direction, which corresponds to line VV in FIG. 3, according to the first embodiment. FIG. 6 is a perspective view showing a coil intermediate body in which a primary coil, a primary spool, a secondary coil, a secondary spool, an inner core, and the like are integrated together according to the first embodiment. FIG. 7 is a perspective view of a core cover according to the first embodiment. FIG. 8 is a graph showing the relationship between the position of each split coil part of the secondary coil and the strength of the electric field generated in a portion of the filling resin radially opposite the position of each split coil part in the first embodiment. FIG. 9 is a perspective view showing an outer core and a core cover according to the second embodiment. FIG. 10 is an explanatory diagram showing a cross section of the ignition coil at a position on the high voltage side in the axial direction, which corresponds to the line IV-IV in FIG. 3, according to the second embodiment. FIG. 11 is an explanatory diagram showing a cross section of the ignition coil at a position on the high voltage side in the axial direction, which corresponds to line VV in FIG. 3, according to the second embodiment. FIG. 12 is an explanatory diagram showing a state in which the coil assembly is disposed in a coil case according to the third embodiment. FIG. 13 is an explanatory diagram showing the periphery of the end portion on the low-voltage side in the axial direction of the core cover according to the third embodiment. FIG. 14 is an explanatory diagram showing the state in which a coil intermediate body in which a primary coil, a primary spool, a secondary coil, a secondary spool, an inner core, etc. are integrated together in embodiment 4 is assembled to a core cover attached to an outer core. FIG. 15 is an explanatory diagram showing another coil intermediate body in which a primary coil, a primary spool, a secondary coil, a secondary spool, an inner core, and the like are integrated together according to the fourth 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 Fig. 1, an ignition coil 1 for an internal combustion engine according to this embodiment includes a primary coil 2, a secondary spool 31, a secondary coil 3, an inner core 41, an outer core 42, a core cover 6, a coil case 5, and a filled resin 7. The primary coil 2 is adapted to turn on and off current. The secondary spool 31 is arranged concentrically on the outside of the primary coil 2. The secondary coil 3 is wound around the outer periphery of the secondary spool 31 in the radial direction R and the axial direction L, and the generated voltage increases toward the high voltage side L1 in the axial direction L.

2 to 5, the inner core 41 is disposed inside the primary coil 2. The outer core 42 has a rectangular ring shape with a pair of side core parts 421 arranged parallel to the axial direction L on the outside of the side surface 411 of the inner core 41, and a pair of end surface core parts 422 arranged parallel to the width direction W perpendicular to the axial direction L on the outside of the end surface 412 of the inner core 41. The core cover 6 is provided on the surface of the outer core 42, including the inner side surface 423 located on the inside of at least a pair of side surface core parts 421. The coil case 5 has an opening 53 located on the opening side D2 of the outer core 42, and houses the primary coil 2, the secondary spool 31, the secondary coil 3, the inner core 41, the outer core 42, and the core cover 6. The filling resin 7 is filled in the gaps in the coil case 5.

As shown in Figures 3 to 5, the average thickness u1 in the radial direction R of the secondary coil 3 at the high-voltage side L1 in the axial direction L is smaller than the average thickness u2 in the radial direction R of the low-voltage side L2 in the axial direction L. The average cross-sectional area a1 in the cross section perpendicular to the axial direction L of the core cover 6 at the inner surface 423 at the high-voltage side L1 in the axial direction L of the pair of side core portions 421 is larger than the average cross-sectional area a2 in the cross section perpendicular to the axial direction L of the core cover 6 at the inner surface 423 at the low-voltage side L2 in the axial direction L of the pair of side core portions 421.

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 8 in 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, 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 8, and the joint portion 12 is disposed in a plug hole 81 of the cylinder head cover 8.

(Axial direction L, mounting direction D, width direction W)
1 to 7, the axial direction L refers to the direction in which the central axes of the primary coil 2 and the secondary coil 3 extend. The side opposite to the high-voltage side L1 is referred to as the high-voltage side L1, and the side opposite to the high-voltage side L1 is referred to as the low-voltage side L2. In the mounting direction D of the coil case 5, the side on which the bottom portion 52 is located and on which the spark plug is arranged is called the bottom side D1, and the side on the opposite side of the bottom side D1 on which the opening 53 is arranged is called the bottom side D2. The side where the opening is located is referred to as the opening side D2. Also, the direction perpendicular to both the axial direction L and the mounting direction D is referred to as the width direction W.

(Radial direction R, circumferential direction C)
The direction extending radially from the central axis of the primary coil 2 and the secondary coil 3 is called the radial direction R. The direction around the central axis of the primary coil 2 and the secondary coil 3 is called the circumferential direction C. In this embodiment, the primary coil 2, the secondary coil 3, etc. are formed in a rectangular tube shape, and the circumferential direction C in this embodiment is the circumferential direction C of the rectangular ring shape. The mounting direction D and the width direction W are included in the radial direction R.

(Primary coil 2)
1 to 5, the primary coil 2 is formed by winding a magnet wire as a winding around the outer circumferential surface of the cylindrical portion 22 of the primary spool 21. The primary coil 2 is formed of a conductive conductor and an insulating coating layer provided around the conductor. The primary coil 2 is repeatedly energized and cut off by a switching element of an igniter 43 that receives a command from the engine control device.

(Secondary coil 3)
1 to 5, the secondary coil 3 is disposed coaxially with the primary coil 2 on the outside of the primary coil 2. The secondary coil 3 is formed by winding a magnet wire as a winding around the outer circumferential surface of the cylindrical portion 32 of the secondary spool 31. The secondary coil 3 is formed of a conductive conductor and an insulating coating layer provided around the conductor.

The secondary coil 3 has a thinner winding than the primary coil 2, and the number of windings is greater than that 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 secondary coil 3 are oriented in a direction perpendicular to the opening 53 of the coil case 5. The low-voltage side L2 end of the secondary coil 3 winding is connected to the ground or power supply terminal of the igniter 43. The high-voltage side L1 end of the secondary coil 3 winding is connected to a high-voltage terminal 45 that is connected to the center electrode of the spark plug.

(Inner core 41)
2 and 3, an inner core 41 is disposed inside (on the inner circumferential side) of the primary coil 2 to allow magnetic flux generated by the primary coil 2 and the secondary coil 3 to pass therethrough. The inner core 41 in this embodiment is formed by laminating a plurality of plate-shaped electromagnetic steel sheets made of a soft magnetic material. The inner core 41 is formed in a rectangular parallelepiped shape and has four side faces 411 parallel to the axial direction L and two end faces 412 perpendicular to the axial direction L. The inner core 41 may be formed by compression molding powder made of a soft magnetic material.

(Outer core 42)
2 to 5, an outer core 42 is disposed on the outside (outer periphery) of the secondary coil 3 to allow 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 inner 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 pair of side core parts 421 of the outer core 42 are located outside the secondary coil 3 and secondary spool 31 on both sides in the width direction W. The pair of end core parts 422 of the outer core 42 are located on both sides L1, L2 in the axial direction L of the secondary coil 3 and secondary spool 31 and are connected to the pair of side core parts 421. The igniter 43 is disposed facing the end core part 422 located on the low voltage side L2 of the secondary coil 3 in the axial direction L of the outer core 42. There is almost no gap between the igniter 43 and the end core part 422, and almost no filling resin 7 is disposed therein.

The inner 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 inner core 41 and the outer core 42 to prevent magnetic saturation.

(Igniter 43)
1 and 2, the ignition coil 1 includes an igniter 43 that repeatedly energizes and cuts off the primary coil 2 in response to a command from an engine control device. The igniter 43 is disposed facing the low-voltage side L2 of the end surface core portion 422 of the outer core 42 in the axial direction L of the primary coil 2 and the secondary coil 3. The igniter 43 is disposed between the connector portion 24 attached to the coil case 5 and the end surface core portion 422 of the outer core 42. The igniter 43 includes a circuit forming portion provided with electronic components such as switching elements that form a switching circuit, a heat sink integrated with the circuit forming portion, a molded resin that covers the circuit forming portion and the heat sink, and an igniter conductor 431 that is drawn out from the circuit forming portion to the outside of the molded resin.

(Primary spool 21)
As shown in Figs. 1 to 5, the primary coil 2 is wound around the outer periphery of the primary spool 21. The primary spool 21 is formed by a molded product of a thermoplastic resin. The primary spool 21 has a cylindrical tubular portion 22 around which the primary coil 2 is wound. In this embodiment, the primary spool 21 and the connector portion 24 are integrally molded as a spool molded body 210. The spool molded body 210 has a rectangular tubular portion 22, flange portions 221 formed on both ends of the tubular portion 22 in the axial direction L, the connector portion 24, and a relay portion 23 that relays the tubular portion 22 and the connector portion 24. The connector portion 24 may be formed as a connector separately from the tubular portion 22 of the primary spool 21.

The winding of the primary coil 2 is wound around the outer circumferential surface between the flanges 221 of the tubular portion 22 of the primary spool 21. The connector portion 24 is provided with a connector conductor 25 connected to the igniter conductor 431 of the igniter 43 by insert molding. The connector portion 24 is formed in a state in which it protrudes outside the coil case 5. The multiple igniter conductors 431 and the multiple connector conductors 25 are joined to each other by soldering, welding, etc. In addition, the multiple igniter conductors 431 are joined to the conductors connected to both ends of the winding of the primary coil 2 and to the conductor connected to the end of the low-voltage side L2 of the winding of the secondary coil 3 by soldering, welding, etc.

(Secondary spool 31)
As shown in Figs. 1 to 5, the secondary coil 3 is wound around the outer periphery of the secondary spool 31. The secondary spool 31 is formed by molding a thermoplastic resin. The secondary spool 31 has a cylindrical portion 32 having a rectangular cylindrical shape and a plurality of flange portions 33 that protrude outward around the entire circumference of the cylindrical portion 32 at a plurality of locations in the axial direction L. The flange portions 33 divide the outer periphery of the cylindrical portion 32 into a plurality of recesses (slots) 321 arranged in the axial direction L. A part of the thickness in the radial direction R of the portion forming the recess 321 located on the high voltage side L1 in the axial direction L in the cylindrical portion 32 of the secondary spool 31 is larger than the thickness in the radial direction R of the portion forming the recess 321 located on the low voltage side L2 in the axial direction L.

As shown in FIG. 3, the width in the axial direction L of the multiple recesses 321 located on the high-voltage side L1 in the axial direction L is smaller than the width in the axial direction L of the multiple recesses 321 located on the low-voltage side L2 in the axial direction L. In this embodiment, the width in the axial direction L of the multiple recesses 321 is smaller as they are located on the high-voltage side L1 in the axial direction L. The flange portion 33 is appropriately formed with a transition groove for the winding of the secondary coil 3 to cross between adjacent recesses 321.

The winding of the secondary coil 3 is wound in sequence as a split coil section 30 around a plurality of recesses 321 formed between the flanges 33. As shown in FIG. 4, the average thickness u1 in the radial direction R of the split coil section 30 arranged in the plurality of recesses 321 located on the high-voltage side L1 of the axial direction L is smaller than the average thickness u2 in the radial direction R of the split coil section 30 arranged in the plurality of recesses 321 located on the low-voltage side L2 of the axial direction L as shown in FIG. 5. In other words, the winding of the secondary coil 3 wound around the plurality of recesses 321 located on the high-voltage side L1 of the axial direction L is wound thinner in the radial direction R than the winding of the secondary coil 3 wound around the plurality of recesses 321 located on the low-voltage side L2 of the axial direction L.

Here, the average thickness u1 in the radial direction R of the split coil parts 30 arranged in the multiple recesses 321 located on the high-voltage side L1 in the axial direction L may be set to the average thickness u1 of the split coil parts 30 arranged in the multiple recesses 321 located on the high-voltage side L1 of the center position of the secondary coil 3 in the entire length in the axial direction L. The average thickness u2 in the radial direction R of the split coil parts 30 arranged in the multiple recesses 321 located on the low-voltage side L2 in the axial direction L may be set to the average thickness u2 of the split coil parts 30 arranged in the multiple recesses 321 located on the low-voltage side L2 of the axial direction L of the secondary coil 3 in the entire length in the axial direction L.

The split coil section 30 arranged in the recess 321 that includes the center position of the entire length of the secondary coil 3 in the axial direction L may be excluded from the average thickness u1 of the high-voltage side L1 and the average thickness u2 of the low-voltage side L2. The average thicknesses u1 and u2 may be the average values of the thicknesses of the multiple split coil sections 30.

In this embodiment, the thickness of the split coil section 30 in the radial direction R is smaller as it is located on the high voltage side L1 in the axial direction L. Also, the number of turns of the secondary coil 3 wound around the multiple recesses 321 is smaller for the recesses 321 located on the high voltage side L1 in the axial direction L. And the distance between the outer circumference of the secondary coil 3 and the side core section 421 of the outer core 42 is larger as it is located on the high voltage side L1 in the axial direction L.

(Core cover 6)
As shown in Fig. 4, Fig. 5 and Fig. 7, the core cover 6 is used to reduce the gap S between the secondary coil 3 and the outer core 42, thereby reducing the amount of the filling resin 7, and to more appropriately ensure insulation between the secondary coil 3 and the outer core 42. The core cover 6 is provided on the inside of the outer core 42 and on each surface of the bottom side D1 and the opening side D2 in the mounting direction D. More specifically, the core cover 6 has a pair of inner cover parts 61 arranged on the inner side surface 423 located on the inside of the pair of side core parts 421, and a pair of opening side cover parts 63 connected to the pair of inner cover parts 61 and arranged on the opening surface 425 located on the opening side D2 in the mounting direction D of the pair of side core parts 421. The core cover 6 of this embodiment also has a pair of bottom side cover parts 62 connected to the pair of inner cover parts 61 and arranged on the bottom surface 424 located on the bottom side D1 in the mounting direction D of the pair of side core parts 421.

The inner cover part 61 is connected to the part arranged on the inner side surface 423 of the pair of side core parts 421, and is also arranged on the inner side surface 423 of the end face core part 422 on the high voltage side L1 in the axial direction L. The opening side cover part 63 is connected to the part arranged on the opening surface 425 of the pair of side core parts 421, and is also arranged on the opening surface 425 of the end face core part 422 on the high voltage side L1 in the axial direction L. The bottom side cover part 62 is connected to the part arranged on the bottom surface 424 of the pair of side core parts 421, and is also arranged on the bottom surface 424 of the end face core part 422 on the high voltage side L1 in the axial direction L. In other words, the core cover 6 is arranged facing the inner side surface 423, the opening surface 425, and the bottom surface 424 of the pair of side core parts 421 and the end face core part 422 on the high voltage side L1.

As shown in FIG. 4, the average thickness t1 in the width direction W of the pair of inner cover parts 61 located on the high-voltage side L1 in the axial direction L is greater than the average thickness t2 in the width direction W of the pair of inner cover parts 61 located on the low-voltage side L2 in the axial direction L as shown in FIG. 5. With this configuration, the thickness of the inner cover part 61 in the width direction W is greater in the high-voltage side L1 part where the thickness of the secondary coil 3 in the radial direction R is smaller, and the variation in the size of the gap S filled with the filling resin 7 at each part in the axial direction L between the secondary coil 3 and the inner cover part 61 can be suppressed.

The average thickness t1 in the width direction W of the portion of the pair of inner cover parts 61 located on the high-voltage side L1 in the axial direction L may be the average value of the thicknesses of the portion located on the high-voltage side L1 of the inner cover part 61 relative to the center position over the entire length of the inner cover part 61 in the axial direction L. The average thickness t2 in the width direction W of the portion of the pair of inner cover parts 61 located on the low-voltage side L2 in the axial direction L may be the average value of the thicknesses of the portion located on the low-voltage side L2 of the inner cover part 61 relative to the center position over the entire length of the inner cover part 61 in the axial direction L.

As shown in FIG. 3, in the core cover 6 of this embodiment, the thickness in the width direction W of the pair of inner cover parts 61 is greater in the portion located on the high-voltage side L1 in the axial direction L. In other words, the thickness in the width direction W of the pair of inner cover parts 61 is greater in the portion located on the high-voltage side L1 in the axial direction L, to the extent that the thickness in the radial direction R of the secondary coil 3 is smaller in the portion located on the high-voltage side L1 in the axial direction L. In addition, the surface located on the inside of the inner cover part 61 is formed in a tapered shape that approaches the inside in the width direction W as it approaches the high-voltage side L1 in the axial direction L. With this configuration, it is possible to more effectively suppress the variation in the size of the gap S filled with the filling resin 7 at each portion in the axial direction L between the secondary coil 3 and the inner cover part 61.

As shown in Figures 4 and 5, the overall dimension of the opening side cover part 63 in the mounting direction D is greater than the dimension of the bottom side cover part 62 in the mounting direction D and the dimension of the inner cover part 61 in the width direction W. In this embodiment, the opening side cover part 63 is formed by a plurality of ribs 631 aligned in the mounting direction D. More specifically, two ribs 631 are formed side by side on the bottom side D1 and the opening side D2 in the mounting direction D, connected to the inner cover part 61, and a groove part 632 in which the filling resin 7 is filled is formed between the two ribs 631.

The surface of the opening side cover part 63 facing the opening surface 425 of the outer core 42 has a protrusion 633 for facilitating attachment of the core cover 6 to the outer core 42. The surface of the bottom side cover part 62 facing the bottom surface 424 of the outer core 42 also has a protrusion 621 for facilitating attachment of the core cover 6 to the outer core 42. The protrusions 621, 633 are formed at multiple locations in the axial direction L of the core cover 6. In addition, an opening hole 611 through which the inner core 41 is inserted is formed in the part of the inner cover part 61 arranged inside (low voltage side L2) of the end face core part 422 of the high voltage side L1.

As shown in FIG. 7, the outer core 42 is formed by combining two parts separated at a pair of end face core portions 422. The core cover 6 is formed by combining two parts separated at a portion facing the end face core portions 422 of the high voltage side L1.

(Coil case 5)
As shown in Fig. 1 and Fig. 4 to Fig. 6, the coil case 5 is formed as a molded product of a thermoplastic resin. The coil case 5 has a housing portion 51 that houses the primary coil 2, the secondary coil 3, the inner core 41, the outer core 42, the igniter 43, etc. The coil case 5 has an opening 53 for disposing the coil assembly 10 in the housing portion 51, and the opening 53 is formed at the end of the opening side D2 of the housing portion 51 in the mounting direction D. The coil assembly 10 is formed by assembling the primary coil 2, the primary spool 21, the secondary coil 3, the secondary spool 31, the inner core 41, the outer core 42, the core cover 6, the igniter 43, etc. In addition, the liquid filling resin 7 is injected into the gap in the coil case 5 from the opening 53.

As shown in Figures 1 and 6, the connector portion 24 of the spool molding 210 is disposed in a portion of the coil case 5 to electrically connect the igniter 43 to an external engine control device. The spool molding 210 is formed by resin insert molding in which the inner core 41 is disposed in the cylindrical portion 22 of the primary spool 21 and the connector conductor 25 is disposed in the connector portion 24.

The coil case 5 is formed with an attachment notch 56 into which the connector portion 24 of the spool molding 210 is attached. A portion of the wall of the coil case 5 is formed by the connector wall portion 241 of the connector portion 24. The end of the connector wall portion 241 on the bottom side D1 in the attachment direction D and on both ends in the width direction W are formed with clamping portions 242 that clamp the edge of the attachment notch 56 from both sides.

As shown in FIG. 1, a tower portion 57 that constitutes the joint portion 12 is formed on the bottom portion 52 located on the bottom side D1 of the mounting direction D of the coil case 5. A seal rubber 58 is attached to the tower portion 57 to seal the gap between the ignition coil 1 and the plug hole 81.

(Filling resin 7)
As shown in FIG. 1 and FIG. 3 to FIG. 5, the filled resin 7 is used as an insulating and fixing resin for insulating and fixing the components of the ignition coil 1, such as the primary coil 2, the primary spool 21, the secondary coil 3, the secondary spool 31, the inner core 41, the outer core 42, and the igniter 43, in the coil case 5. The filled resin 7 is made of a thermosetting resin. After the coil assembly 10, in which the primary coil 2, the primary spool 21, the secondary coil 3, the secondary spool 31, the inner core 41, the outer core 42, the core cover 6, the igniter 43, and the like are assembled, is arranged 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 filled resin 7 made of a thermosetting resin fixes the primary coil 2, the primary spool 21, the secondary coil 3, the secondary spool 31, the inner core 41, the outer core 42, the core cover 6, the igniter 43, and the like in the coil case 5 to each other in an insulated state.

(Action and Effect)
In the ignition coil 1 for an internal combustion engine of this embodiment, the shape of the core cover 6 provided on the surface of the outer core 42 is devised. Specifically, the cross-sectional area of the core cover 6 in a cross section perpendicular to the axial direction L is made larger toward the high-voltage side L1 in the axial direction L. In particular, in this embodiment, the cross-sectional area of the inner cover part 61 is made larger toward the high-voltage side L1 in the axial direction L. On the other hand, the thickness of the secondary coil 3 in the radial direction R is smaller toward the high-voltage side L1 in the axial direction L. In addition, the cross-sectional area of the gap S in the width direction W between the secondary coil 3 and the inner cover part 61 and the cross-sectional area of the filling resin 7 filled in this gap S are almost uniform throughout the axial direction L.

These configurations allow the size of the gap S between the secondary coil 3 and the inner cover part 61 to be as uniform as possible from the low voltage side L2 to the high voltage side L1 in the axial direction L. This allows the thickness of the portion of the filled resin 7 filled between the secondary coil 3 and the inner cover part 61 to be as uniform as possible from the low voltage side L2 to the high voltage side L1 in the axial direction L. As a result, the amount of thermal expansion and contraction that occurs in the filled resin 7 during the cooling and heating cycles when the ignition coil 1 is in use can be made as uniform as possible from the low voltage side L2 to the high voltage side L1 in the axial direction L.

Therefore, according to the ignition coil 1 for an internal combustion engine of this embodiment, it is possible to make it difficult for thermal stress to concentrate in the area of the filled resin 7 filled between the secondary coil 3 and the inner cover part 61. In addition, it is possible to make it difficult for cracks to occur in the area of the filled resin 7, and it is possible to ensure the insulation of the ignition coil 1 for a long time.

Figure 8 shows the relationship between the position of each split coil section 30 of the secondary coil 3 arranged in the multiple recesses 321 of the secondary spool 31 and the electric field strength [kV/mm] generated at the portion of the filled resin 7 facing the position of each split coil section 30 in the radial direction R for a conventional ignition coil (comparison product) and the ignition coil 1 of this embodiment (implemented product). The positions of the split coil sections 30 are indicated as N1 to N6, starting from the one located on the low-voltage side L2 in the axial direction L.

In the conventional ignition coil, the thickness in the radial direction R of the split coil section 30 arranged in each recess 321 is almost constant throughout the entire area from the low voltage side L2 to the high voltage side L1 in the axial direction L. In the ignition coil 1 of this embodiment, the thickness in the radial direction R of the split coil section 30 arranged in each recess 321 is smaller as it is located closer to the high voltage side L1 in the axial direction L.

The position of each split coil section 30 is shown as the center position of the split coil section 30 in the axial direction L. The strength of the electric field generated at the location of the filled resin 7 indicates the strength of the electric field generated in the pseudo capacitor formed by disposing the inner cover section 61 of the core cover 6 and the filled resin 7 between each split coil section 30 of the secondary coil 3 and the outer core 42.

In FIG. 8, in a conventional ignition coil (comparison product), the voltage is higher in the high-voltage side L1 of the secondary coil 3, so the strength of the electric field generated in the filled resin 7 is significantly stronger in the portion located on the high-voltage side L1 in the axial direction L. Also, there is a significant difference in the strength of the electric field generated in the filled resin 7 between the low-voltage side L2 portion and the high-voltage side L1 portion in the axial direction L. On the other hand, in the ignition coil 1 (embodiment product) of this embodiment, there is a smaller difference in the strength of the electric field generated in the filled resin 7 between the low-voltage side L2 portion and the high-voltage side L1 portion in the axial direction L.

Furthermore, in this embodiment of the ignition coil 1, by using a material for the core cover 6 that has a smaller relative dielectric constant than the material for the filled resin 7, it is possible to further reduce the difference in the strength of the electric field generated in the filled resin 7 between the low-voltage side L2 and the high-voltage side L1 in the axial direction L.

Specifically, the core cover 6 in this embodiment is made of polypropylene resin, and the filling resin 7 in this embodiment is made of epoxy resin. The relative dielectric constant of polypropylene resin is about 2.2 to 2.6, and the relative dielectric constant of the epoxy resin used in this embodiment is larger than the relative dielectric constant of polypropylene resin, being about 2.5 to 6.0.

In the ignition coil 1 of this embodiment, in the gap S between the split coil portion 30 located on the high-voltage side L1 in the axial direction L and the inner core 41 portion, the volume occupied by the inner cover portion 61 becomes large, while the volume occupied by the filled resin 7 becomes small. As a result, in the ignition coil 1 of this embodiment, the strength of the electric field generated in the filled resin 7 located on the high-voltage side L1 in the axial direction L becomes small, and it is thought that the difference in the strength of the electric field generated in the filled resin 7 between the part on the low-voltage side L2 and the part on the high-voltage side L1 in the axial direction L is further alleviated.

This also helps prevent deterioration of the portion of the filling resin 7 between the secondary coil 3 and the inner cover portion 61, and allows the insulation of the ignition coil 1 to be maintained for a long time.

<Embodiment 2>
As shown in Figures 9 to 11, this embodiment shows an example of a configuration in which the variation in the size of the gap S between the secondary coil 3 and the inner cover portion 61 in the axial direction L is reduced by using a core cover 6 different from the core cover 6 of embodiment 1.

In this embodiment of the core cover 6, the corner 64 formed by the inner cover part 61 and the opening side cover part 63 is formed in a curved shape that bulges outward. The curved corner 64 may have any shape that has a curved portion, and may be formed between the inner cover part 61 and an inclined surface on the opening side D2 of the opening side cover part 63 in the mounting direction D. In addition, the radius of curvature of the corner 64 may vary in a cross section perpendicular to the axial direction L, and may be expressed as the average value of the radius of curvature.

The opening side cover part 63 in this embodiment is not formed as a plurality of ribs 631, but is formed as a single block shape. As shown in FIG. 10, the average radius of curvature r1 of the corners 64 of the core cover 6 located on the high voltage side L1 in the axial direction L is smaller than the average radius of curvature r2 of the corners 64 of the core cover 6 located on the low voltage side L2 in the axial direction L as shown in FIG. 11. With this configuration, the thickness of the opening side cover part 63 in the width direction W is large in the high voltage side L1 part where the thickness of the secondary coil 3 in the radial direction R is small. As a result, in this embodiment, the amount of thermal expansion and contraction that occurs in the filling resin 7 during the cooling and heating cycle when the ignition coil 1 is used can be made more uniform from the low voltage side L2 part to the high voltage side L1 part in the axial direction L.

The average radius of curvature r1 of the corners 64 of the core cover 6 located on the high-voltage side L1 in the axial direction L may be the average value of the radii of curvature of the parts located on the high-voltage side L1 of the center position of the corners 64 between the inner cover part 61 and the opening side cover part 63 over the entire length in the axial direction L. The average radius of curvature r2 of the corners 64 of the core cover 6 located on the low-voltage side L2 in the axial direction L may be the average value of the radii of curvature of the parts located on the low-voltage side L2 of the center position of the corners 64 between the inner cover part 61 and the opening side cover part 63 over the entire length in the axial direction L.

In this embodiment of the core cover 6, the radius of curvature of the corner 64 formed by the inner cover part 61 and the opening side cover part 63 is smaller in the portion located on the high voltage side L1 in the axial direction L. With this configuration, the amount of thermal expansion and contraction that occurs in the filled resin 7 during the cooling and heating cycles when the ignition coil 1 is in use can be made more uniform from the portion on the low voltage side L2 to the portion on the high voltage side L1 in the axial direction L.

The configuration of the core cover 6 in this embodiment is used in combination with the configuration of the pair of inner cover parts 61 shown in embodiment 1 in which the thickness in the width direction W varies at each location in the axial direction L. In addition, the opening side cover part 63 in this embodiment may be formed as a plurality of ribs 631 shown in embodiment 1, as shown by the two-dot chain line in Figure 9.

Other configurations, functions, and effects of the ignition coil 1 of this embodiment are the same as those of the first embodiment. In this embodiment, the components denoted by the same reference numerals as those in the first embodiment are the same as those in the first embodiment.

<Embodiment 3>
This embodiment shows an example in which, as shown in Figures 12 and 13, even if a crack occurs in the portion of the filling resin 7 that fills the gap S between the secondary coil 3 and the core cover 6, the crack is prevented from extending to conductors such as the winding end 201 of the primary coil 2.

The primary spool 21 of this embodiment has a shape that prevents the propagation of cracks that occur in the filled resin 7. As shown in Figures 6, 12, and 13, the primary spool 21 has a protruding portion 26 that protrudes from the cylindrical portion 22 to the opening side D2 in the mounting direction D and faces the low-voltage side L2, which is the outer side in the axial direction L, of the opening side cover portion 63 of the core cover 6. The protruding portion 26 is formed facing the end of the low-voltage side L2 in the axial direction L of the pair of opening side cover portions 63. A holding portion 261 that holds the winding end 201 of the primary coil 2 is provided at a portion of the primary spool 21 that is located closer to the low-voltage side L2 in the axial direction L than the protruding portion 26.

As shown in FIG. 12, the amount of protrusion x1 of the opening side cover portion 63 from the opening surface 425 of the side core portion 421 to the opening 53 side of the coil case 5, in other words, from the opening surface 425 to the opening side D2 in the mounting direction D, is smaller than the amount of protrusion x2 of the protruding portion 26 of the primary spool 21 from the opening surface 425 to the opening side D2 in the mounting direction D.

When the ignition coil 1 of this embodiment is used in a cooling/heating cycle, if a crack occurs in the portion of the filling resin 7 that fills the gap S between the secondary coil 3 and the inner cover portion 61, the protrusion 26 prevents the crack from propagating to the low-voltage side L2 in the axial direction L. This prevents the crack from propagating to the conductors such as the winding end 201 of the primary coil 2.

Other configurations, functions, and effects of the ignition coil 1 of this embodiment are the same as those of the first and second embodiments. In this embodiment, the components denoted by the same reference numerals as those in the first and second embodiments are the same as those in the first and second embodiments.

<Embodiment 4>
12 and 14, this embodiment shows an example in which a coil intermediate body 100 in which the primary coil 2, the primary spool 21, the secondary coil 3, the secondary spool 31, the inner core 41, etc. are integrated with a core cover 6 attached to an outer core 42 is appropriately maintained in an assembled state. In this embodiment, the shape of the primary spool 21 constituting the coil intermediate body 100 is devised.

The primary spool 21 is formed with a spacing maintaining portion 27 that protrudes from the tubular portion 22 in the width direction W and is fitted between a pair of inner cover portions 61 of the core cover 6 to maintain the spacing between the pair of inner cover portions 61. In this embodiment, the spacing maintaining portion 27 is formed by a pair of tapered ribs 271 that protrude from the tubular portion 22 on both sides in the width direction W at the boundary between the tubular portion 22 and the relay portion 23 of the primary spool 21.

The width in the width direction W of the pair of tapered ribs 271 serving as the spacing maintaining portion 27 becomes smaller as it moves from the opening side D2 to the bottom side D1 in the mounting direction D. In other words, the end faces in the width direction W of the tapered ribs 271 are formed as tapered surfaces that are positioned inward in the width direction W as they move toward the bottom side D1. On the other hand, the inner surfaces 612 in the width direction W of the pair of inner cover portions 61 of the core cover 6 are formed as linear surfaces parallel to the mounting direction D.

When the width in the width direction W of the end of the bottom side D1 in the mounting direction D of the pair of tapered ribs 271 is w1, the width in the width direction W of the end of the opening side D2 in the mounting direction D of the pair of tapered ribs 271 is w2, and the width in the width direction W of the inner surface 612 of the pair of inner cover parts 61 is w3, the relationship is w1 < w3 < w2. Then, as shown in Figures 12 and 13, when the coil intermediate body 100 assembled with the primary coil 2, primary spool 21, secondary coil 3, secondary spool 31, inner core 41, etc. is placed in the core cover 6 attached to the outer core 42, the pair of tapered ribs 271 are fitted between the pair of inner cover parts 61 of the core cover 6.

The portion of the low-voltage side L2 in the axial direction L of the core cover 6 is located at the end of the U-shaped core cover 6, and is therefore expected to deform inward after the core cover 6 is molded using a molding die. Therefore, when the coil intermediate 100 is assembled to the core cover 6 attached to the outer core 42, the spacing between the pair of inner cover parts 61 can be appropriately maintained by the spacing maintaining part 27. This makes it possible to appropriately maintain the thickness in the width direction W of the filling resin 7 filled in the gap S between the secondary coil 3 and the pair of inner cover parts 61.

Also, as shown in FIG. 15, the spacing maintaining portion 27 may be formed by a pair of deformation protrusions 272 provided on the side surface of the primary spool 21 in the width direction W, instead of the pair of tapered ribs 271. In this case, the width w4 in the width direction W between the tips of the pair of protrusions 272 is made smaller than the width w3 in the width direction W of the inner side surface 612 of the pair of inner cover portions 61. Then, when the coil intermediate body 100 is inserted inside the core cover 6 of the outer core 42, the pair of protrusions 272 undergo plastic or elastic deformation, thereby appropriately maintaining the spacing between the pair of inner cover portions 61.

Other configurations, functions, and effects of the ignition coil 1 of this embodiment are the same as those of the first to third embodiments. In this embodiment, the components denoted by the same reference numerals as those in the first to third embodiments are the same as those in the first to third embodiments.

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 spool 41 inner core 42 outer core 5 coil case 6 core cover 7 filling resin

Claims (6)

A primary coil (2);
a secondary spool (31) arranged concentrically outside the primary coil;
A secondary coil (3) that is wound around the outer periphery of the secondary spool in a radial direction (R) and an axial direction (L), and a voltage generated therein increases toward a high voltage side (L1) in the axial direction;
an inner core (41) disposed inside the primary coil;
an outer core (42) having a rectangular ring shape including a pair of side core portions (421) arranged parallel to the axial direction outside the side surface (411) of the inner core, and a pair of end surface core portions (422) arranged parallel to a width direction (W) perpendicular to the axial direction outside the end surface (412) of the inner core;
A core cover (6) provided on a surface of the outer core including an inner surface (423) located on the inside of at least a pair of the side core portions;
a coil case (5) having an opening (53) located on an opening side (D2) of the outer core and housing the primary coil, the secondary spool, the secondary coil, the inner core, the outer core, and the core cover;
A filling resin (7) is filled in the gap in the coil case,
the average radial thickness (u1) of the secondary coil at a portion located on the high-voltage side in the axial direction is smaller than the average radial thickness (u2) of the secondary coil at a portion located on the low-voltage side (L2) in the axial direction;
An ignition coil (1) for an internal combustion engine, wherein an average cross-sectional area (a1) of a portion of the core cover provided on the inner surface of the pair of side core portions on the high-voltage side in the axial direction, in a cross section perpendicular to the axial direction, is larger than an average cross-sectional area (a2) of a portion of the core cover provided on the inner surface of the pair of side core portions on the low-voltage side in the axial direction, in a cross section perpendicular to the axial direction. The core cover has a pair of inner cover portions (61) arranged on the inner surfaces of the pair of side core portions, and a pair of opening side cover portions (63) connected to the pair of inner cover portions and arranged on opening surfaces (425) located on the opening side of the pair of side core portions,
2. The ignition coil for an internal combustion engine according to claim 1, wherein an average thickness (t1) in the width direction of a portion of the pair of inner cover parts that is located on a high-voltage side in the axial direction is larger than an average thickness (t2) in the width direction of a portion of the pair of inner cover parts that is located on a low-voltage side in the axial direction. A corner portion (64) formed by the inner cover portion and the opening side cover portion is formed in a curved shape,
3. The ignition coil for an internal combustion engine according to claim 2, wherein an average radius of curvature (r1) of the corners of a portion located on the high-voltage side in the axial direction is smaller than an average radius of curvature (r2) of the corners of a portion located on the low-voltage side in the axial direction. The secondary spool has a cylindrical portion (32) having a cylindrical shape and a plurality of flange portions (33) protruding outwardly around the entire circumference of the cylindrical portion at a plurality of locations in the axial direction,
The secondary coil is wound as split coil portions (30) in sequence around a plurality of recesses (321) formed between the flange portions,
4. An ignition coil for an internal combustion engine as described in claim 2 or 3, wherein the average radial thickness (u1) of the split coil portions arranged in the multiple recesses located on the high voltage side in the axial direction is smaller than the average radial thickness (u2) of the split coil portions arranged in the multiple recesses located on the low voltage side in the axial direction. a primary spool (21) having a cylindrical portion (22) around which the primary coil is wound, and a protrusion (26) protruding from the cylindrical portion and facing an outer side in the axial direction of the opening side cover portion of the core cover,
An ignition coil for an internal combustion engine as described in any one of claims 2 to 4, wherein a protrusion amount (x1) of the opening side cover portion from the opening surface toward the opening side of the coil case is smaller than a protrusion amount (x2) of the protrusion portion of the primary spool from the opening surface toward the opening side of the coil case. The ignition coil for an internal combustion engine according to claim 5, wherein the primary spool is formed with a spacing maintaining portion (27) that protrudes from the cylindrical portion in the width direction and is fitted between the pair of inner cover portions of the core cover to maintain the spacing between the pair of inner cover portions.

Images