ignition coil

Abstract

Ignition coil (1) comprising: a primary coil (11) and a secondary coil (12) which are magnetically coupled to each other; a core (2) defining a closed magnetic circuit (C) in which a magnetic flux generated by energizing the primary coil (11) flows, the core (2) having a gap (4) formed therein through which the magnetic circuit (C) passes; and a magnet (3) which is arranged in the gap (4) of the core (2), wherein the magnet (3) has magnetization vectors (5), at least a part of which is inclined relative to a gap direction, wherein the core (2) includes a central core (6) and an outer peripheral core (7), wherein the central core (6) is arranged inside the inner peripheries of the primary coil (11) and the secondary coil (12), wherein the outer peripheral core (7) is arranged outside the outer peripheries of the primary coil (11) and the secondary coil (12), the central core (6) includes a body (61) and a flange (62), the central core (6) having a length with a first end (66) and a second end (67) which are opposite to each other in the gap direction, which is a longitudinal direction of the central core (6), the flange (62) extending from the first end (66) of the central core (6) in a direction perpendicular to the gap direction, the magnet (3) is arranged to face the first end (66) of the central core (6) in the gap direction, and the magnet (3) comprises at least a first magnet and a second magnet, at least one of which is opposite to the flange (62) in the gap direction and has magnetization vectors (5), at least a part of which is inclined relative to the gap direction and obliquely in a direction opposite to a direction in which the flange (62) protrudes from the first end (66) of the central core (6), and wherein one of the magnets, one and two, is opposite the body (61) of the central core (6) in the gap direction and has the magnetization vectors (5), at least a part of which is oriented substantially parallel to the gap direction.

Description

BACKGROUND1 TECHNICAL FIELD

[0001] This disclosure relates to an ignition coil in general. 2 BACKGROUND TO THE TECHNOLOGY

[0002] The first publication of JP H08 - 45 753 A discloses an ignition coil which is equipped with a primary coil, a secondary coil which is magnetically coupled to the primary coil, and a central core which is arranged inside the primary and secondary coil.

[0003] The central core and the outer peripheral core form a closed magnetic path, through which a magnetic flux, generated by electrical excitation of the primary coil, flows. The ignition coil serves to block the supply of electrical current to the primary coil in order to change the amount of magnetic flux in the closed magnetic path, thereby inducing a high secondary voltage in the secondary coil.

[0004] The previous ignition coil also includes a magnet arranged in an air gap between the center core and the outer peripheral core in an axial direction of the turns of the primary and secondary coils. The magnet is used to magnetically bias the closed magnetic path to increase secondary voltage and secondary energy. The magnet is magnetized in a direction opposite to a direction of a magnetic field generated in the closed magnetic path when the primary coil is energized, thereby increasing a change in the amount of magnetic flux in the closed magnetic path when the primary coil is no longer energized. This increases the secondary voltage and secondary energy in the ignition coil.

[0005] The center core of the ignition coil has a flange formed at one end of the center core, opposite the magnet, and extending radially outward. This results in an enlarged cross-sectional area of ​​the flanged end of the center core near the magnet. This allows the magnet to have an enlarged cross-sectional area opposite the flanged end of the center core, thereby enhancing a magnetic field generated by the magnetic bias.

[0006] However, the previous ignition coil faces the disadvantage that energy loss may occur when primary electrical energy supplied to the primary coil is converted into secondary electrical energy generated in the secondary coil. This will be explained below with reference to the Fig. 26 to 28. In the following explanation, a force that causes magnet 93 to generate a magnetic flux is referred to as a magnetomotive force Fmag. A force that generates a magnetic flux resulting from the excitation of primary coil 91 is referred to as a coil magnetomotive force Fcoil.

[0007] Fig. Figure 26 schematically illustrates the ignition coil 9, which has a structure similar to that taught in the previous publication. The magnetomotive force of the magnet Fmag and the magnetomotive force of the coil Fcoil are, as shown in Fig. 26 can be seen, opposite to each other. This calls, as in Fig. 27, it is clear that the magnetomotive force of the magnet Fmag immediately after the excitation of the primary coil 91 is greater than the magnetomotive force of the coil Fcoil, so that the magnetic flux φcoil generated by the magnetomotive force of the magnet Fmag is generated in the central core 96 and the outer peripheral core 97 without the occurrence of a magnetic flux generated by the magnetomotive force of the coil Fcoil. The primary current I1 flowing into the primary coil 91 is proportional to the product of an inverse of the magnetic flux φcoil generated by the magnetomotive force of the coil Fcoil and the time t (i.e., I1 ~ t / φcoil). This causes the primary current I1, as shown in Fig. 29, until the time t1 of excitation of the primary coil 91 is rapidly increased.

[0008] Then, as in Fig. 28, when the magnetomotive force of the coil Fcoil exceeds the magnetomotive force of the magnet Fmag, the magnetic flux φcoil in the center core 96 and the outer peripheral core 97 decreases. This results in a decrease in the rate of increase of the primary current I1 after the time t1.

[0009] As previously described, in a period between the start of energization of the primary coil 91 and time t1, in which the magnetomotive force of the magnet Fmag is greater than the magnetomotive force of the coil Fcoil, no magnetic flux generated by the magnetomotive force of the coil Fcoil exists in the central core 96 and the outer peripheral core 97. The primary energy supplied to the primary coil 91 between the start of energization of the primary coil 91 and time t1 is therefore a loss that does not contribute to the generation of secondary energy. The primary current I1 increases, as can be seen in Fig. 29, rapidly between the start of excitation of the primary coil 91 and time t1, resulting in an increase in energy loss. Fig. 29 the energy loss is indicated by hatching.

[0010] Further prior art is disclosed in the following documents.

[0011] JP H07-320960 A discloses an ignition coil for an internal combustion engine. The ignition coil for an internal combustion engine is equipped with a core, a primary coil, a secondary coil, and a permanent magnet. The core consists of a pair of core components that are nearly U-shaped. The primary coil is wound around a core in the direction perpendicular to the core's axis and causes the core to generate a magnetic flux along the axis when an electric current is supplied to the coil. The secondary coil is wound around the core and, when the supply of electric current to the coil is stopped, generates a voltage for igniting an internal combustion engine following the change in the magnetic flux caused by the interruption of the current supply. The permanent magnet has a plate-like shape and is arranged between the core components so that its magnetic poles cross the axis obliquely.The magnet generates a different magnetic flux with a component opposite to that generated by the core. The side surface of the magnet is located near the side surface of the core.

[0012] JP 6 061 284 B2 discloses an ignition coil. The ignition coil includes a primary coil in which ON / OFF control is performed via an electrical state, a secondary coil electromagnetically coupled to the primary coil, and a central iron core forming a closed magnetic flux path connected to the primary coil and the secondary coil. In the central core, connecting surfaces of a first core and a second core directly or indirectly abut each other. In the first core, a proximal portion extending to the connecting surface with the second core is thick and orthogonal to a magnetic flux direction.

[0013] JP H10-340821 A discloses an ignition coil. The ignition coil is provided with a magnetic core and a primary-side coil former and a secondary-side coil former, on each of which a primary coil and a secondary coil are wound. A magnetic body consisting of several, in this case two, quadrilateral plate-shaped permanent magnets is inserted into a magnetic gap provided in the magnetic core. The residual magnetization of the magnetic core by the magnetic field of the primary coil is canceled by the reverse bias magnetic field of the magnetic body. Since the magnetic body consists of several permanent magnets, a strong bias magnetic field is generated. SUMMARY

[0014] It is therefore an object of this disclosure to provide an ignition coil designed to minimize energy loss when converting primary energy into secondary energy.

[0015] This object is achieved by the features of claims 1 and 2. Further advantageous embodiments and further developments are the subject of the following claim 3.

[0016] According to one aspect of this disclosure, an ignition coil is provided, comprising: (a) a primary coil and a secondary coil, which are magnetically coupled to each other; (b) a core defining a closed magnetic circuit in which a magnetic flux generated by energizing the primary coil flows, the core having a gap formed therein through which the magnetic circuit passes; and (c) a magnet disposed in the gap of the core. The magnet has magnetization vectors, at least a portion of which is inclined relative to a gap direction, which will be specifically defined later. The core includes a center core and an outer peripheral core, the center core being disposed inside the inner peripheries of the primary coil and the secondary coil, and the outer peripheral core being disposed outside the outer peripheries of the primary coil and the secondary coil.the center core includes a body and a flange, the center core having a length with a first end and a second end opposite to each other in the gap direction, which is a longitudinal direction of the center core, the flange extending from the first end of the center core in a direction perpendicular to the gap direction, the magnet being arranged to oppose the first end of the center core in the gap direction, and the magnet including at least a first magnet and a second magnet, at least one of which opposes the flange in the gap direction and has magnetization vectors, at least a part of which is inclined relative to the gap direction and obliquely in a direction opposite to a direction in which the flange protrudes from the first end of the center core, and one of the magnets, one and two,opposite the body of the central core in the gap direction and having magnetization vectors, at least a part of which is oriented substantially parallel to the gap direction.

[0017] The magnet, as previously described, has magnetic regions with magnetization vectors, at least a portion of which is inclined relative to the gap direction. A magnetomotive force of the magnet, generated by the magnet, is oriented in the same direction as the magnetization vectors. A magnetomotive force of the coil, generated by the primary coil and acting on the magnet, is oriented in the gap direction. If an angle subtended by the magnetization vectors with the gap direction is defined as an angle θ, the magnetomotive force of the magnet has a component opposite to the magnetomotive force of the coil (i.e., a component of the magnetomotive force of the magnet that is oriented in the gap direction). This component is therefore smaller than the magnetomotive force of the magnet.

[0018] This causes the coil's magnetomotive force to quickly exceed the previous component of the magnet's magnetomotive force, so that the coil's magnetomotive force quickly generates a magnetic flux throughout the core. This minimizes energy loss when primary energy is converted to secondary energy in the ignition coil.

[0019] After the primary coil is no longer energized, a strong magnetomotive force of the magnet, oriented along the magnetization vectors, is exerted on the core by the magnet, resulting in an increased amount of change in the magnetic flux when the primary coil changes from an energized state to a non-energized state.

[0020] The previous structure of the ignition coil can therefore minimize energy loss when the primary energy is converted into the secondary energy.

[0021] Reference numerals in the claims are used only to indicate correspondences to parts explained in the following embodiments and do not limit the technical scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be more fully understood from the detailed description given hereinafter and the accompanying drawings of embodiments illustrating the invention, which, however, are not to be construed as limiting the invention to the specific embodiments, but are to be used only for purposes of explanation and understanding.

[0023] It shows: Fig. 1 is a sectional view taken along a Z direction of an ignition coil according to the first embodiment; Fig. 2 is a sectional view taken along a direction perpendicular to a Y direction of an ignition coil according to the first embodiment; Fig. 3 is an exploded perspective view of a center core and a magnet of an ignition coil in the first embodiment; Fig. 4 is a sectional view taken along a direction perpendicular to a Z direction, illustrating flows of magnetic fluxes generated in an ignition coil in the first embodiment upon energization of a primary coil; Fig. 5 is an explanatory enlarged view illustrating a region around a magnet and showing a magnetomotive force generated by the magnet and a magnetomotive force generated by the coil; Fig. 6 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil in the first embodiment, showing flows of magnetic fluxes generated after the energization of a primary coil is turned off; Fig. 7 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the second embodiment; Fig. 8 is an exploded perspective view illustrating a center core and a magnet of an ignition coil in the second embodiment; Fig. 9 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the third embodiment; Fig. 10 is an exploded perspective view illustrating a center core and magnet of an ignition coil in the third embodiment; Fig. 11 is a partially enlarged sectional view illustrating a portion around a magnet and a core of an ignition coil in the third embodiment, and showing the orientation of the passages of magnetic fluxes and magnetization vectors generated in the core; Fig. 12 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the fourth embodiment; Fig. 13 is an exploded perspective view illustrating a center core and magnet of an ignition coil in the fourth embodiment; Fig. 14 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the fifth embodiment; Fig. 15 is a sectional view taken along a direction perpendicular to a Y direction of an ignition coil according to the fifth embodiment; Fig. 16 is an exploded perspective view illustrating a center core and magnet of an ignition coil in the fifth embodiment; Fig. 17 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the sixth embodiment; Fig. 18 is an exploded perspective view illustrating a center core and magnet of an ignition coil in the sixth embodiment; Fig. 19 is a partially enlarged sectional view showing an area around a flange of a center core of the ignition coil of Fig. 17 and shows the orientation of the magnetic fluxes, as well as the simple direction of magnetization in the central core; Fig. 20 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the seventh embodiment; Fig. 21 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the eighth embodiment; Fig. 22 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the ninth embodiment; Fig. 23 is a sectional view taken along a direction perpendicular to a Z direction of an ignition coil according to the tenth embodiment; Fig. 24 is a graph illustrating secondary energy generated in test samples in a first experimental example; Fig. 25 is a graph illustrating secondary energy generated in the test samples in a second experimental example; Fig. 26 is a sectional view illustrating a conventional ignition coil; Fig. 27 shows a part of a sectional view of the ignition coil from Fig. 26 and it shows the magnetic flux generated after energization of a primary coil; Fig. 28 shows a part of a sectional view of the ignition coil from Fig. 26 and it shows the magnetic flux generated t1 ms after the excitation of a primary coil; and Fig. 29 is a graph showing a relationship between an ON duration of a primary coil and a primary current generated by the primary coil in a conventional ignition coil; DESCRIPTION OF THE EMBODIMENTS EXPLAINING THE INVENTION FIRST EMBODIMENT

[0024] The ignition coil 1 according to the first embodiment will be described with reference to the Fig. 1 to 6. The ignition coil 1, as described in detail in the Fig. 1 and Fig. 2, includes the primary coil 11, the secondary coil 12, the core 2 and the magnet 3.

[0025] The primary coil 11 and the secondary coil 12 are magnetically coupled. The core 2, as shown in the Fig. 4 and Fig. 6, creates closed magnetic circuits C through which the magnetic flux generated by excitation of the primary coil 11 passes. Fig. Figure 4 illustrates the closed magnetic circuits C through which the magnetic flux generated after excitation of the primary coil 11 passes. Fig. Figure 6 illustrates the closed magnetic circuits C through which the magnetic flux generated after switching off the excitation of the primary coil 11 passes.

[0026] The magnet 3 is arranged in the gap 4 formed in the core 3 and is located in the closed magnetic circuits C. In other words, the gap 4, through which the magnetic circuits C pass, is formed in the core 2. The magnet 3 is magnetized to have magnetic regions, at least a portion of which have magnetization vectors 5 inclined relative to a gap direction, which will be described in more detail later.

[0027] The ignition coil 1 is described in more detail below. The ignition coil 1 can be used in internal combustion engines of motor vehicles or combined heat and power systems. During operation, the ignition coil 1 is connected to a spark plug (not shown) installed in the internal combustion engine and serves to apply a high voltage to the spark plug.

[0028] The ignition coil 1 is designed to induce a high voltage in the secondary coil 12 upon a change in the electrical current in the primary coil 11 over time. The primary coil 11 is supplied with electrical power from an external power source located outside the ignition coil 1. The secondary coil 12 is electrically connected to the spark plug, to which the ignition coil 1 is connected.

[0029] The primary coil 11 and the secondary coil 12 are, as can be seen in the Fig. 1 and Fig. 2, are arranged coaxially with each other. The secondary coil 12 is arranged radially outwardly of the primary coil 11. In the following explanation, a direction in which the center axes of the windings of the primary coil 11 and the secondary coil 12 extend is also referred to as an X direction.

[0030] The core 2, as seen in the Fig. 1 and Fig. 2, contains the central nucleus 6 and the outer peripheral nucleus 7. Both the central nucleus 6 and the outer peripheral nucleus 7 are, as exactly in Fig. 2, it is made of a stack of magnetic steel sheets that are placed so that they overlap each other in the Z direction perpendicular to the X direction. Each of the magnetic steel sheets is made of a soft magnetic material. Both the center core 6 and the outer peripheral core 7 have a certain thickness in the Z direction.

[0031] The central core 6 is arranged radially inside the inner peripheries of the primary coil 11 and the secondary coil 12. The central core 6 is, as shown in the Fig. 1 to 3, is shaped to have a length extending in the X direction.

[0032] The outer peripheral nucleus 7 is, as shown in the Fig. 1 and Fig. 2, arranged radially outside the outer peripheries of the primary coil 11 and the secondary coil 12. The outer peripheral core 7 has, as can be seen in Fig. 1, has a rectangular cylindrical shape that surrounds the central core 6 in four directions perpendicular to the X-direction. In other words, the outer peripheral core 7 includes a pair of first side walls 71 that are opposite to each other in the X-direction and a pair of second side walls 72 that are opposite to each other in the Y-direction and perpendicular to both the X-direction and the Z-direction. The outer peripheral core 7 is, as shown in Fig. 2, is shaped to have a size larger than that of the center core 6 and has portions located outside the center core 6 in the Z direction.

[0033] The central core 6, as in the Fig. 1 and Fig. 2, has a certain length, with the first end 66 (ie a left end, as in the Fig. 1 and Fig. 2) and the second end 67 (ie a right end, as in the Fig. 1 and Fig. 2), which are opposite to each other in the X direction. The first end 66 of the center core 6 faces the first side walls 71 of the outer peripheral core 7 in the X direction through the gap 4. In other words, the gap 4 is formed in the X direction between the center core 6 and the outer peripheral core 7.

[0034] In this disclosure, the previously described gap direction is defined as a direction in which surfaces of the core 2 oppose each other through the gap 4, and in other words, surfaces of the core 2 defining the gap 4 between them oppose each other with a minimum distance therebetween. Specifically, in this embodiment, the first end 66 of the center core 6 opposes an adjacent one of the first side walls 71 of the outer peripheral core 7 at a minimum distance apart in the X direction (i.e., the longitudinal direction of the center core 6).

[0035] In this embodiment, the gap direction may be defined to be identical to the X direction, which is an axial direction of the windings of the primary coil 11 and the secondary coil 12. In this embodiment, the gap may also be defined as a direction in which the closed magnetic circuit C passes through the magnet 3 and a portion (i.e., the center core 6) of the core 2, which is aligned with the magnet 3 and surrounded by the primary coil 11 and the secondary coil 12.

[0036] The magnet 3 is arranged in the gap 4. In the following explanation, a direction from the center core 6 toward the magnet 3 in the X direction is also referred to as a forward direction X1, while a direction opposite to the forward direction X1 is also referred to as a reverse direction X2. The terms "forward" and "reverse" are used for the purpose of simplification, regardless of the orientation of the internal combustion engine or the ignition coil 1 installed in the vehicle.

[0037] The magnet 3 serves to magnetically bias the center core 6 to increase a rate of change in the magnetic flux after turning off the excitation of the primary coil 11, to amplify a voltage induced in the secondary coil 12, to amplify an output voltage (ie, a secondary voltage) developed by the ignition coil 1. The magnet 3, as shown in the Fig. 1 to 3, has a specific thickness in the X direction. The magnet 3 has a shape that is substantially shaped to match that of the first end 66 of the center core 6, as viewed in the X direction. The magnet 3 occupies the entire first end 66 of the center core 6.

[0038] The magnet 3, as in the Fig. 1, Fig. 3 and Fig. 5, has, in the magnetic regions thereof, the magnetization vectors 5 oriented in the same direction. An orientation from an initial point to an end point of each of the magnetization vectors 5 is obliquely directed in one of the opposite directions in the Y direction. In other words, each magnetization vector 5 is inclined at a certain angle (excluding zero) relative to the first end of the center core 6 or the inner surface of the first side wall 71. An acute angle θ subtended by each magnetization vector 5 of the magnet 3 with the X direction is selected to satisfy a relationship of 0° < θ > 90°. In this embodiment, the angle θ satisfies a relationship of 10° < θ < 30°.For example, the magnet 3 may be manufactured by magnetizing a base material in a first direction and cutting the base material in a second direction which is oblique to the first direction.

[0039] The primary coil 11, the secondary coil 12, the center core 6, the outer peripheral core 7, and the magnet 3 are arranged in a resin case, not shown, and are sealed by, for example, a thermosetting resin within the case.

[0040] The magnetic flux generated after energizing or de-energizing the primary coil 11 is described below with reference to the Fig. 4 to 6. For the purpose of simplification, the Fig. 4 and Fig. 5 the magnetization vectors 5 and the magnetomotive force of the magnet Fmag (i.e., the force that causes the magnet 3 to generate a magnetic flux) using the same arrows. The magnetic flux generated by exciting the primary coil 11 is first plotted with reference to the Fig. 4 and Fig. 5 described.

[0041] The excitation of the primary coil 11 causes the magnetomotive force of the coil Fcoil to act on the central core 6 and the outer peripheral core 7, thereby generating a magnetic flux in the closed magnetic circuit C in the central core 6 and the outer peripheral core 7, as shown schematically in Fig. 4. The magnetomotive force of the coil Fcoil acting near the magnet 3 is oriented in the X direction in a direction opposite to a direction of the magnetization vectors 5 in the magnet 3. The magnetization vectors 5 in the magnet 3 are, as shown in Fig. 5, is inclined to the X-direction at an angle θ. The magnetomotive force of the magnet Fmag is oriented parallel to the magnetization vectors 5, i.e., it is inclined relative to the X-direction at an angle θ.

[0042] The magnetomotive force of the magnet Fmag therefore has a component Fmagcosθ opposite to the magnetomotive force of the coil Fcoil, as in Fig. 5. The component Fmagcosθ of the magnetomotive force of the magnet Fmag, which is opposite to the magnetomotive force of the coil Fcoil, is therefore smaller than the magnetomotive force of the magnet Fmag. This causes the magnetomotive force of the coil Fcoil to quickly exceed the component Fmagcosθ of the magnetomotive force of the magnet Fmag in the X direction after the primary coil 11 is energized, so that the magnetomotive force of the coil Fcoil can quickly generate the magnetic flux in the center core 6 and the outer peripheral core 7. The magnetic energy is therefore quickly stored in the center core 6 and the outer peripheral core 7 after the primary coil 11 is energized. Accordingly, the magnetic energy is stored in the center core 6 and the outer peripheral core 7 without an undesirable increase in the primary energy consumed by the primary coil 11.

[0043] Next, the magnetic flux generated after turning off the excitation of the primary coil 11 will be described below with reference to Fig. 6 described.

[0044] When the primary coil 11 is no longer energized, a coil magnetomotive force produced in the center core 6 and the outer peripheral core 7 after the energization of the primary coil 11 is caused to disappear, so that the magnetic flux in the core 2 is formed by the magnetomotive force Fmag of the magnet, which is oriented in the same direction as the magnetization vectors 5. This causes the secondary voltage to be formed in the secondary coil 12 as a function of the amount of change in the magnetic flux between the states when the primary coil 11 is energized and when the primary coil 11 is not energized.

[0045] The previous structure of the ignition coil 1 offers the following useful advantages.

[0046] The ignition coil 1 is designed to have at least one of the magnetization vectors 5 in the magnet 3, which is inclined relative to the gap direction (i.e., a direction in which the central core 6 and the outer peripheral core 7 face each other with a minimum distance through the gap 4 in which the magnet 3 is arranged). The magnetomotive force of the magnet Fmag produced by the magnet 3 is oriented in the same direction as the magnetization vectors 5, while the magnetomotive force of the coil Fcoil acting on the magnet 3 is oriented in the gap direction. Accordingly, the inclination of the magnetization vectors 5 at an angle θ relative to the gap direction causes the magnetomotive force of the magnet Fmag to have the component Fmagcosθ, which is equal to the magnetomotive force of the coil Fcoil, i.e.,in the gap direction, and is smaller than the magnetomotive force of the magnet Fmag. This causes the magnetomotive force of the coil Fcoil to quickly exceed the component Fmagcosθ of the magnetomotive force of the magnet Fmag immediately after the primary coil 11 is energized, so that the magnetomotive force of the coil Fcoil quickly generates the magnetic flux in the entire core 2 after the primary coil 11 is energized, thereby minimizing energy loss when the primary energy is converted into the secondary energy.

[0047] When the primary coil 11 is no longer energized, this causes the large magnetomotive force of the magnet Fmag to be exerted by the magnet 3 on the core 2 along the magnetization vectors 5 in the magnet 3, resulting in a large amount of change in the magnetic flux compared to when the primary coil 11 is energized. The magnitude of the magnetomotive force of the magnet Fmag depends on the product of the thickness and the magnetic coercivity of the magnet 3. The energy loss that occurs when the primary energy is converted to the secondary energy can be reduced by orienting the magnetization vectors 5 in the magnet 3 parallel to the X direction and also by reducing the thickness of the magnet 3, but this results in an undesirably reduced magnitude of the magnetomotive force of the magnet Fmag, leading to insufficient bias of the center core 6.To mitigate such a disadvantage, the magnetic coercive force of the magnet 3 can be increased. However, a magnet used in typical ignition coils is made of a neodymium magnet, which has a high residual magnetic flux density Br and a high magnetic coercive force Hcj. Therefore, it is practically difficult to manufacture the magnet 3 from a material having a residual magnetic flux density Br and a magnetic coercive force Hcj higher than that of the neodymium magnet.

[0048] Reducing the energy loss when converting primary energy to secondary energy will also reduce the undesirable contribution of thermal energy generated in the ignition coil 1. Therefore, an ignition device designed to stop supplying electrical power to the primary coil 11 when the temperature of the ignition coil 1 exceeds a certain value can increase the excitation duration of the primary coil 11 by reducing the undesirable amount of thermal energy generated in the ignition coil 1, thereby increasing the secondary energy.

[0049] Increasing the secondary energy allows the magnet 3 to be made from a wider variety of different materials, thereby allowing the magnet 3 to be made from a cost-effective material.

[0050] As can be seen from the previous explanation, the ignition coil 1 in this embodiment can minimize an energy loss that occurs when the primary energy is converted into the secondary energy. SECOND EMBODIMENT

[0051] The Fig. 7 and Fig. 8 illustrate the ignition coil 1 according to the second embodiment, which differs in the configuration of the center core 6 from the first embodiment.

[0052] The central core 6 contains, as exactly in Fig. 8 illustrates the body 61 and a pair of flanges 62. The body 61 has a certain length extending in the X direction. Specifically, the body 61 has a quadrangular prism shape extending in the X direction and having a uniform cross-section along its length.

[0053] The flanges 62 project outwardly along the Y-direction in opposite directions from one end of the body 61 opposite the adjacent first side wall 71 of the outer peripheral core 7. The end of the body 61 and the flanges 62 define the first end 66 of the center core 6. Each of the flanges 62 extends from the entirety of one of the sides of the end of the body 61 in the Y-direction.

[0054] Each of the flanges 62 has a rear side facing in the rear direction X2 and inclined obliquely in the forward direction X1 from the outer periphery of the body 61. Each of the flanges 62 has a front side facing in the forward direction X1 and flush with the end of the body 61 opposite the first side wall 71, thereby defining the first end 66 of the center core 6. In this embodiment, the body 61 and the flanges 62 are integrally formed with each other. In other words, the magnetic steel plates constituting the center core 6 constitute both the body 61 and the flanges 62.

[0055] The magnet 3 has a rectangular plate shape and has a thickness in the X direction. The magnet 3 has a shape substantially shaped to coincide with that of the first end 66 of the center core 6 when viewed in the X direction. In other words, the magnet 3 covers or overlaps the entirety of the first end 66 (i.e., the front side) of the center core 6. The magnet 3 has the magnetization vectors 5 oriented in the same direction. An orientation from an initial point to an end point of each magnetization vector 5 is directed in an opposite direction along the Y direction. Other arrangements of the ignition coil 1 are identical to those of the first embodiment, and detailed explanations thereof are omitted here.The same reference numerals in the second and subsequent embodiments as in the previous embodiments refer to the same or similar parts unless otherwise stated.

[0056] The structure of the ignition coil 1 in the second embodiment offers the same useful advantages as that of the first embodiment. THIRD EMBODIMENT

[0057] The Fig. 9 to 11 illustrate the ignition coil 1 according to the third embodiment, which differs from the second embodiment only in the structure of the magnet 3.

[0058] The ignition coil 1 is, as shown in the Fig. 9 and Fig. 10, is equipped with a plurality of magnets 3. The magnets 3 are arranged aligned with each other in a direction (i.e., the Y direction) perpendicular to the X direction and face the first end 66 of the center core in the X direction. Each of the magnets 3 has the magnetization vectors 5 inclined from the first side wall 71 in a direction opposite to a direction in which the adjacent flange 62 protrudes from the end of the center core 6 relative to the X direction (i.e., the longitudinal center line of the center core 6). In other words, the magnetization vectors 5 are directed radially obliquely inward at a certain angle (excluding zero) relative to the longitudinal center line of the center core 6. At least one of the magnetization vectors 5 of at least one of the magnets 3 can be directed in the previously inclined orientation.

[0059] The magnets 3 in this embodiment include the first magnet 31 and the second magnet 32, which are aligned with each other in the Y direction. In the following explanation, a region in which the first magnet 31 is located and which is located farther away from the second magnet 32 ​​in the Y1 direction (ie, one of the opposite directions along the Y direction) is also referred to as a Y1 side, while an opposite side is also referred to as a Y2 side.

[0060] The first magnet 31 covers a surface of the first end 66 of the center core 6, which is located on the Y1 side. The second magnet 32 ​​covers a surface of the first end 66 of the center core 6, which is located on the Y2 side. In the illustrated example, a boundary between the first and second magnets 31 and 32 is aligned with the longitudinal center line (i.e., the center axis) of the center core 6. The first magnet 31 at least partially opposes one of the flanges 62 adjacent thereto in the X direction. Similarly, the second magnet 32 ​​at least partially opposes one of the flanges 62 adjacent thereto in the X direction.

[0061] The first magnet 31 is designed to have magnetization vectors 5 oriented in the same direction. An orientation from an initial point to an end point of each of the magnetization vectors 5 is oriented backward obliquely in the direction Y2.

[0062] Similarly, the second magnet 32 ​​has magnetization vectors 5 oriented in the same direction. An orientation from an initial point to an end point of each of the magnetization vectors 5 is oriented backwards obliquely in the direction Y1. In other words, the magnetization vectors 5 in the second magnet 32 ​​are oriented in a direction opposite to that in which the magnetization vectors 5 are oriented in the first magnet 31.

[0063] Further arrangements are identical to those of the second embodiment.

[0064] As can be seen from the previous explanation, the first magnet 31 and the second magnet 32, which oppose the flange 62 in the gap direction (i.e., X-direction), have the magnetization vectors 5 oriented obliquely toward the longitudinal center line (i.e., the axis) of the center core 6, or in other words, in directions opposite to directions in which the flange 62 extends outward from the center core 6. The previous orientation of the magnetization vectors 5 in the first and second magnets 31 and 32 enables an increase in a change amount of the magnetic flux after turning off the excitation of the primary coil 11. This will also be described below.

[0065] When the supply of electrical power to the primary coil 11 is interrupted, it causes, as shown by arrows in Fig. 11 indicates that magnetic fluxes φ1 generated in the flange 62 by the magnetomotive force of the magnet Fmag act along the magnetization vectors 5 in the magnet 3, so that they are oriented obliquely in the reverse direction X2 toward the longitudinal centerline of the body 61 of the central core, so that the magnetic fluxes φ1 in the flange 62 flow evenly into the body 61, thereby ensuring an increased amount of magnetic flux flowing through the entire central core 6, i.e., the core 2. This results in an increased amount of change in the magnetic flux after the excitation of the primary coil 11 is turned off.

[0066] This embodiment therefore offers substantially the same useful advantages as those in the second embodiment. FOURTH EMBODIMENT

[0067] The Fig. 12 and Fig. 13 illustrate the ignition coil 1 according to the fourth embodiment, which differs from the third embodiment only in the structure of the magnet 3. Other arrangements are substantially the same as those of the third embodiment.

[0068] The ignition coil 1 in this embodiment is arranged with three magnets 3 aligned with each other in the Y direction. Specifically, the magnets 3 include the first magnet 31, the second magnet 32, and the third magnet 30. The first magnet 31 faces one of the flanges 62, which is located closer to the Y1 side and is also referred to as a first flange. The second magnet 32 ​​faces one of the flanges 62, which is located closer to the Y2 side and is also referred to as a second flange. The third magnet 30 faces the body 61 of the center core 6 in the X direction and is also referred to as a body-facing core magnet.

[0069] The first magnet 31 is positioned so that it overlaps or completely covers the entire front face of the first flange 62 located on the Y1 side. The second magnet 32 ​​is positioned so that it overlaps or completely covers the entire front face of the second flange 62 located on the Y2 side. The core magnet 30 facing the body is positioned so that it overlaps or completely covers the entire front face of the body 61 of the center core 6.

[0070] The first magnet 31 has the magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the first magnet 31 is directed in the reverse direction X2 and obliquely in the direction Y2.

[0071] The second magnet 32 ​​has magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the second magnet 32 ​​is directed in the reverse direction X2 and obliquely in the direction Y1. The magnetization vectors 5 in the first magnet 31 are oriented in a direction opposite to a direction in which the magnetization vectors 5 are oriented in the second magnet 32.

[0072] The core magnet 30 facing the body has magnetization vectors 5 oriented in the same direction. Specifically, the magnetization vectors 5 in the core magnet 30 facing the body extend in the gap direction (i.e., the X direction). An orientation from an initial point to an end point of each of the magnetization vectors 5 is directed from the front side X1 to the back side X2.

[0073] Other arrangements of the ignition coil 1 are substantially the same as those of the third embodiment.

[0074] As can be seen from the previous explanation, the first magnet 31 and the second magnet 32, which are opposite to the flanges 62 in the gap direction (i.e., X-direction), have the magnetization vectors 5 which, as in the third embodiment, are oriented obliquely in the direction of the longitudinal center line (i.e., the axis) of the center core 6, in other words, in directions opposite to directions in which the flanges 62 extend outward from the center core 6. The magnetization vectors 5 in the core magnet 30 opposite the body 61 of the center core in the X-direction extend substantially parallel to each other in the X-direction. The magnetization vectors 5 in the first magnet 31, the second magnet 32, and the third magnet 30 (i.e.,The magnetization vectors 5 in the first to third magnets 31, 32, and 30 are therefore directed toward a specific portion of the body 61 of the central core 6, which is defined around the longitudinal centerline of the central core 6. Such an orientation of the magnetization vectors 5 in the first to third magnets 31, 32, and 30 enables an increase in the amount of change in the magnetic flux after the primary coil 11 is turned off. This will also be described below.

[0075] When the supply of electric power to the primary coil 11 is interrupted, magnetic fluxes generated in the flange 62 by the magnetomotive force Fmag produced by the magnets 3 (i.e., the first and second magnets 31 and 32) facing the flanges 62 are caused to be inclined in the reverse direction X2 obliquely toward the body 61 of the center core 6. The magnetic fluxes generated by the magnetomotive force Fmag produced by the magnet 3 (i.e., the third magnet 30) facing the body 61 of the center core 6 flow in the X direction.The use of magnets 31, 32, and 30 enables the merging of magnetic fluxes from flanges 62 along the length of body 61 of center core 6 in the reverse direction X2 after de-energization of primary coil 11, resulting in an increased amount of magnetic flux flowing in body 61 of center core 6 in the reverse direction X2, that is, an increased amount of change in magnetic flux after de-energization of primary coil 11.

[0076] This embodiment therefore offers substantially the same useful advantages as those of the third embodiment. FIFTH EMBODIMENT

[0077] The Fig. 14 to 16 illustrate the ignition coil 1 according to the fifth embodiment, which differs from the fourth embodiment only in the structure of the flanges 62 of the center core 6 and the magnets 3. The other arrangements are substantially identical to those of the fourth embodiment.

[0078] Viewed in the Z direction, the flanges 62 extend outward from the body 61 of the center core 6 in opposite directions along the Y direction. Viewed in the Y direction, each of the flanges 62 also extends or protrudes outward from the body 61 in one of the opposite directions (i.e., the Z1 direction) along the Z direction. A region farther away from the body 61 in the Z1 direction is also referred to as a Z1 side. A region farther away from the body 61 in the Z2 direction is also referred to as a Z2 side.

[0079] For the purpose of simplification, the flanges 62 are divided into five flanges in the following explanation: first flange 621, second flange 622, third flange 623, fourth flange 624 and fifth flange 625. The first flange 621, as detailed in the Fig. 14 and Fig. 16, extends from the front side of the body 61, which is opposite to the first side wall 71 of the outer peripheral core 7, to the side Y1. The second flange 622 extends from the front side of the body 61 to the side Y2. The third flange 623, as can be seen in the Fig. 15 and Fig. 16, extends from the front of the body 61 to the side Z1. The fourth flange 624, as can be seen in Fig. 16, continues both the first flange 621 and the third flange 623. The fifth flange 625 continues both the second flange 622 and the third flange 623.

[0080] The first flange 621 and the fourth flange 624 are formed to have cross sections extending perpendicular to the Z direction, which have a configuration identical to each other. The first flange 621 and the fourth flange 624 have front sides that are flat in a direction perpendicular to the Z direction and flush with each other in the Z direction. The first flange 621 and the fourth flange 624 have rear sides that extend in the Y direction (i.e., the Y1 direction) from the side surface of the body 61 of the center core 6 and are inclined obliquely in the forward direction X1.

[0081] The second flange 622 and the fifth flange 625 are formed to have cross sections extending perpendicular to the Z direction, which have a configuration identical to each other. The second flange 622 and the fifth flange 625 have front surfaces that are flat in a direction perpendicular to the Z direction and flush with each other in the Z direction. The second flange 622 and the fifth flange 625 have rear surfaces that extend in the Y direction (i.e., the Y2 direction) from the side surface of the body 61 of the center core 6 and are inclined obliquely in the forward direction X1.

[0082] The third flange 623 is shaped to have front and rear surfaces that are flat and oriented in a direction (i.e., the X direction) perpendicular to the Z direction. The rear surface of the third flange 623 has ends that are opposite to each other in the Y direction and are connected to the rear surfaces of the fourth flange 624 and the fifth flange 625. The front surfaces of the first flange 621 through the fifth flange 625 are flush with the front surface of the body 61 of the center core 6. The front surfaces of the first flange 621 through the fifth flange 625 and the front surface of the body 61 define a rectangular flat surface of the front end 66 of the center core 6. The magnets 3 oppose or cover the surface of the front end 66 of the center core 6.

[0083] The ignition coil 1 is equipped with six magnets 3. Specifically, the ignition coil 1 is equipped with the core magnet 30 facing the body, the first magnet 31, the second magnet 32, the third magnet 33, the fourth magnet 34, and the fifth magnet 35.

[0084] The core magnet 30 opposite the body, as shown in the Fig. 14 to 16, faces the front side of the body 61 of the central core 6. The entirety of the core magnet 30 facing the body completely covers or overlaps the entirety of the front side of the body 61 in the X direction. The core magnet 30 facing the body has the magnetization vectors 5 oriented in the same direction. Specifically, the magnetization vectors 5 in the core magnet 30 facing the body extend in the X direction. An orientation from an initial point to an end point of each of the magnetization vectors 5 is directed from the front side X1 to the back side X2.

[0085] The first magnet 31, as shown in the Fig. 14 and Fig. 16, faces the front side of the first flange 621. The first magnet 31 is placed so as to completely cover or overlap the entire front side of the first flange 621 in the X direction. The first magnet 31 has the magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the first magnet 31 is directed in the reverse direction X2 and obliquely in the Y2 direction.

[0086] The second magnet 32 ​​faces the front side of the second flange 622. Specifically, the second magnet 32 ​​is positioned so as to cover or completely overlap the entire front side of the second flange 622 in the X direction. The second magnet 32 ​​has magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the second magnet 32 ​​is oriented in the reverse direction X2 and obliquely in the Y1 direction.

[0087] The third magnet 33, as shown in the Fig. 15 and Fig. 16, faces the front side of the third flange 623 in the X direction. Specifically, the third magnet 33 is placed so as to cover or completely overlap the entire front side of the third flange 623 in the X direction. The third magnet 33 has the magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the third magnet 33 is directed in the reverse direction X2 and obliquely in the direction Z2, which is opposite to the direction Z1 along the X direction.

[0088] The fourth magnet 34, as shown in Fig. 16, faces the front side of the fourth flange 624 in the X direction. Specifically, the fourth magnet is placed so as to cover or completely overlap the entire front side of the fourth flange 624 in the X direction. The fourth magnet 34 has the magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the fourth magnet 34 is directed in the reverse direction X2 and oblique to both the Y2 direction and the Z2 direction.

[0089] The fifth magnet 35 faces the front side of the fifth flange 625 in the X direction. Specifically, the fifth magnet 35 is positioned so as to cover or completely overlap the entire front side of the fifth flange 625 in the X direction. The fifth magnet 35 has the magnetization vectors 5 oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 is directed in the reverse direction X2 and obliquely in both the Y1 direction and the Z2 direction.

[0090] As can be seen from the previous explanation, the magnetization vectors 5 in each of the first to the fifth magnet extend in the reverse direction X2 and obliquely toward the body 61 (e.g., the longitudinal center line of the body 61) of the central core 6.

[0091] Further arrangement of the ignition coil 1 is identical to that of the fourth embodiment.

[0092] As can be seen from the previous explanations, the first to fifth magnets 31 to 35, which face the flanges 62 in the X direction, have magnetization vectors 5 oriented in the reverse direction X2 and obliquely toward the longitudinal line (i.e., the axis) of the center core 6. The magnetization vectors 5 in the body-facing core magnet 30, which faces the body 61 of the center core 6 in the X direction, extend substantially parallel to each other in the X direction. The magnetization vectors 5 in the first to fifth magnets 31 to 35 and in the body-facing core magnet 30 are therefore converged in a specific portion of the body 61 of the center core 6, which is defined around the longitudinal center line of the center core.Such an orientation of the magnetization vectors 5, as in the fourth embodiment, enables an increase in an amount of change of the magnetic flux after switching off the excitation of the primary coil 11.

[0093] Also, the previous structure of the ignition coil 1 according to this embodiment offers substantially the same useful advantages as those of the fourth embodiment. SIXTH EMBODIMENT

[0094] The Fig. 17 to 19 illustrate the ignition coil 1 according to the sixth embodiment, which differs from the fourth embodiment only in the structure of the flanges 62 of the center core 6. Other arrangements are substantially identical to those of the fourth embodiment.

[0095] The central core 6 includes the body 61, the first flange 621 and the second flange 622, which, as shown in the Fig. 17 and Fig. 18, are separated from each other. Specifically, the magnetic steel plates constituting the body 61, the first flange 621, and the second flange 622 are separated from each other.

[0096] The body 61 is designed to have magnetic regions whose easy magnetization directions 8 are oriented in the same direction. The easy magnetization direction 8, as referred to herein, is a direction in which the body 61 is easily magnetized. Specifically, the body 61 has magnetic regions whose easy magnetization directions 8 are parallel to the magnetization vectors 5 in sections or magnetic regions of the core magnet 30 facing the body and are oriented in the same direction as the magnetization vectors 5 in the magnetic regions of the core magnet 30 facing the body. In other words, the easy magnetization directions 8 of the body 61 are oriented in the X direction (i.e., the reverse direction X2).

[0097] The first flange 621 has magnetic regions whose easy magnetization directions 8 are oriented in the same direction. Specifically, the easy magnetization directions 8 in the first flange 621 are parallel to the magnetization vectors 5 in the magnetic regions of the first magnet 31 and are oriented in the same direction as the magnetization vectors 5 in the first magnet 31. Specifically, the easy magnetization directions 8 of the first flange 621 are oriented in the reverse direction X2 and obliquely in the direction Y2 (i.e., in the direction of the longitudinal center line of the body 61 of the center core 6).

[0098] The second flange 622 has magnetic regions whose easy magnetization directions 8 are oriented in the same direction. In particular, the easy magnetization directions 8 in the second flange 622 are parallel to the magnetization directions 5 in the magnetic regions of the second magnet 32 ​​and are oriented in the same direction as the magnetization vectors 5 in the second magnet 32. In particular, the easy magnetization directions 8 of the second flange 622 are oriented in the reverse direction X2 and obliquely in the direction Y1 (i.e., in the direction of the longitudinal center line of the body 6 of the central core 6).

[0099] As can be seen from the previous explanation, the easy magnetization directions 8 in magnetic regions of the first flange 621 and the second flange 622 are oriented in the reverse direction X2 and obliquely toward the body 61 of the center core 6.

[0100] Further arrangements of the ignition coil 1 are identical to those of the fourth embodiment.

[0101] The easy magnetization directions 8 in the flange 62 (i.e., the first flange 621 and the first flange 622) are, as previously described, oriented away from the magnets 3 in the reverse direction X2 and obliquely in a direction perpendicular to the X direction toward the body 61 of the center core 6, in other words, obliquely at a certain angle (excluding zero) relative to the longitudinal center line (i.e., the axis) of the body 61, thereby enabling an increase in a change amount of the magnetic flux after the excitation of the ignition coil 11 is turned off. This will also be described below.

[0102] When the supply of electric power to the primary coil 11 is interrupted, it causes magnetic fluxes φ1, as shown in Fig. 19, is generated in each of the flanges 62. The magnetic fluxes φ1 flow along the easy magnetization directions 8 in the flange 62; in other words, they are oriented in the reverse direction X2 and obliquely toward the body 61 of the center core, converging the magnetic fluxes φ1 in the body 61 of the center core. This results in an increase in the amount of change in the magnetic flux in the entire core 2 after the excitation of the primary coil 11 is turned off.

[0103] In addition, when the primary coil 11 is no longer excited, it causes magnetic fluxes φ2, as shown in Fig. 19, are generated in the body 61 of the central core 6. The magnetic fluxes φ2 flow in the reverse direction X2 along the easy magnetization directions 8 in the body 61 (i.e., along a magnetic path in the body 61). This also results in an increase in the magnitude of the magnetic flux in the central core 6, i.e., the entire core 2, thereby increasing the magnitude of the change in the magnetic flux in the core 2 after the excitation of the primary coil 11 is turned off.

[0104] The magnetization directions 8 in each of the flanges 62 are, as previously described, oriented in the same direction as the magnetization vectors 5 in one of the adjacent magnets 3. The easy magnetization directions 8 in the body 61 are oriented in the same direction as the magnetization vectors 5 in the core magnet 30 opposite the body. This also allows for an increase in the amount of magnetic flux that occurs in the entire central core 6 after the excitation of the primary coil 11 is switched off, thereby increasing the amount of change in the magnetic flux in the core 2 after the excitation of the primary coil 11 is switched off.

[0105] The structure of the ignition coil 1 in this embodiment offers the same useful advantages as in the fourth embodiment. SEVENTH EMBODIMENT

[0106] Fig. 20 illustrates the ignition coil 1 according to the seventh embodiment, which differs in the structure of the outer peripheral core 7 from the first embodiment.

[0107] The outer peripheral core 7 has a C- or U-shape when viewed in the Z direction and opens in one of the opposite directions along the Y direction. The outer peripheral core 7 has the open end portion 73 in which the center core 6 and the magnet 3 are arranged.

[0108] Further arrangements of the ignition coil 1 are identical to those in the first embodiment.

[0109] The previous structure of the ignition coil 1 offers substantially the same useful advantages as those in the first embodiment. EIGHTH EMBODIMENT

[0110] Fig. 21 illustrates the ignition coil 1 according to the eighth embodiment, which differs in the structure of the center core 6 and the magnets 3 from the seventh embodiment.

[0111] The central core 6 includes the body 61 and the flange 62. The flange 62 extends from the body 61 in a direction leading along the Y direction away from the opening of the outer peripheral core 7.

[0112] The magnets 3 include two magnets: the sixth magnet 36 and the seventh magnet 37. The sixth magnet 36 is positioned so that it is at least partially opposite the flange 62. The seventh magnet 37 is aligned with the sixth magnet 36 in the Y direction and is completely opposite the body 61 of the center core 6.

[0113] The sixth magnet 36 has an outer end and an inner end opposite to the outer end in the Y direction. The outer end is flush with an outer end (a protruding end) of the flange 62. The inner end of the sixth magnet 36 is aligned with the length of the body 61 in the X direction. The sixth magnet 36 has magnetic regions whose magnetization vectors 5 are oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the sixth magnet 36 is directed in the reverse direction X2 and obliquely in the Y direction, that is, in the direction of the axis of the body 61 of the center core 6.

[0114] The seventh magnet 37 has an inner end and an outer end opposite to the inner end in the Y direction. The inner end of the seventh magnet 37 is adjacent to the inner end of the sixth magnet 36. The outer end of the seventh magnet 37, which is farther from the sixth magnet 36, is placed flush with an outer surface of the body 61 facing away from the flange 62, or in other words, it is exposed outside the outer peripheral core 7. The seventh magnet 37 has the magnetic regions whose magnetization vectors 5 are oriented in the same direction. Specifically, an orientation from an initial point to an end point of each of the magnetization vectors 5 in the seventh magnet 37 is oriented in the reverse direction X2.

[0115] Further arrangements of the ignition coil 1 are identical to those of the seventh embodiment.

[0116] The previous structure of the ignition coil 1 offers substantially the same useful advantages as those in the fourth or seventh embodiment. NINTH EMBODIMENT

[0117] Fig. 22 illustrates the ignition coil 1 according to the ninth embodiment, which differs in the structure of the core 2 from the first embodiment.

[0118] The core 2 has a closed hollow rectangular shape as viewed in the Z direction and has four sides. One of the four sides of the core 2 is arranged inside the primary coil 11 and the secondary coil 12 and is also referred to as the side inside the coil 21. One of the four sides of the core 2 which is opposite to the side inside the coil 21 in the Y direction is also referred to as the coil opposite side 22. The coil opposite side 22 has the gap 4 formed in a portion of a length thereof. The magnet 3 is arranged in the gap 4. The magnet 3 has magnetic regions whose magnetization vectors 5 are oriented obliquely in the gap direction of the coil opposite side 22 (i.e., the X direction), in other words, are inclined at a certain angle (excluding zero) relative to the length of the coil opposite side 22.

[0119] Further arrangements of the ignition coil 1 are identical to those of the first embodiment.

[0120] The previous structure of the ignition coil 1 offers substantially the same useful advantages as those in the first embodiment. TENTH EMBODIMENT

[0121] Fig. 23 illustrates the ignition coil 1 according to the tenth embodiment, which differs in the arrangement of the gap 4 from the ninth embodiment.

[0122] The core 2, as in the ninth embodiment, has a closed hollow rectangular shape and has the side 23 adjacent to the side located inside the coil 21. The side 23 has the gap 4 formed in a portion of a length thereof and extending in the X direction. The side 23 has the length extending in the Y direction, which is an axial direction of the turns of the primary coil 11 and the secondary coil 12 and perpendicular to the X direction. In this embodiment, the gap direction is the Y direction. The magnet 3 is arranged in the gap 4. The magnet 3 has the magnetic regions whose magnetization vectors 5 are inclined at a certain angle (excluding zero) relative to the length of the side 23 (i.e., the X direction).

[0123] Further arrangements of the ignition coil 1 are identical to those of the ninth embodiment.

[0124] The previous structure of the ignition coil 1 offers substantially the same useful advantages as those in the ninth embodiment. EXPERIMENT 1

[0125] We have performed simulations related to the secondary energy in the ignition coil 1 having the structure of the first embodiment as a function of the rotational speed of an internal combustion engine for different values ​​of the inclination angle θ of the magnetization vectors 5 in the magnet 3 relative to the gap direction.

[0126] We prepared four test samples of the ignition coil 1, which differ from each other in the value of the angle θ, which are referred to below as test samples A1 to A3 and as a comparative example A0. Test sample A1 has an angle θ of 10°. Test sample A2 has an angle θ of 20°. Test sample A3 has an angle θ of 30°. The comparative test sample A0 has an angle θ of 0°, that is, it has the magnetization vectors 5 in the magnet 3 that extend parallel in the gap direction. We evaluated the secondary energy in each of the test samples A0 to A3 at an engine speed of 3,200 to 7,000 rpm. The simulation results are shown in a graph in Fig. 24 shown.

[0127] The graph in Fig. 24 shows that the test samples A1 to A3 in which the angle θ is larger than 0° have a higher secondary energy output to the secondary coil 12 at each engine speed, whereby the test samples A1 to A3 are able to generate an increased amount of secondary energy compared with the case in which the angle θ is 0°. EXPERIMENT 2

[0128] We performed simulations of secondary energy in the ignition coil 1 with the structure in the first to sixth embodiments in the same way as in Experiment 1. We prepared five types of test samples, test samples B1 to B5, and a comparative test sample B0. Test sample B1 has the same structure as that of the ignition coil 1 in the second embodiment. Test sample B2 has the same structure as that of the ignition coil 1 in the third embodiment. Test sample B3 has the same structure as that of the ignition coil 1 in the fourth embodiment. Test sample B4 has the same structure as that of the ignition coil 1 in the fifth embodiment. Test sample B5 has the same structure as that of the ignition coil 1 in the sixth embodiment.Comparative Example B0 has basically the same structure as that of the ignition coil 1 in the second embodiment, except that it has magnetization vectors 5 in the magnetic regions of the magnet 3 that are oriented parallel to the gap direction. We evaluated the secondary energy generated in each of the test samples B1 to B0 at rotational speeds from 3,200 to 7,000 rpm. The experimental results are shown in a graph in . Fig. 25 shown.

[0129] The graph in Fig. 25 shows that the test samples B1 to B5 (ie, the second to sixth embodiments) have higher secondary energy output to the secondary coil 12 than the comparative test sample B0 in which the magnetization vectors 5 in the magnet 3 are parallel to the gap direction.

[0130] The graph also shows that the test sample B5 (ie, the sixth embodiment) has a higher secondary energy at each speed than all the other test samples B1 to B4, as well as B0, and thus shows that the secondary energy is increased by orienting the easy magnetization direction 8 in each of the flanges 62 in the same direction as that of the magnetization vectors 5 in an adjacent one of the magnets 3.

Claims

[1] Ignition coil (1) comprising: a primary coil (11) and a secondary coil (12) which are magnetically coupled to each other; a core (2) defining a closed magnetic circuit (C) in which a magnetic flux generated by energizing the primary coil (11) flows, the core (2) having a gap (4) formed therein through which the magnetic circuit (C) passes; and a magnet (3) which is arranged in the gap (4) of the core (2), wherein the magnet (3) has magnetization vectors (5), at least a part of which is inclined relative to a gap direction, wherein the core (2) includes a central core (6) and an outer peripheral core (7), wherein the central core (6) is arranged inside the inner peripheries of the primary coil (11) and the secondary coil (12), wherein the outer peripheral core (7) is arranged outside the outer peripheries of the primary coil (11) and the secondary coil (12), the central core (6) includes a body (61) and a flange (62), the central core (6) having a length with a first end (66) and a second end (67) which are opposite to each other in the gap direction, which is a longitudinal direction of the central core (6), the flange (62) extending from the first end (66) of the central core (6) in a direction perpendicular to the gap direction, the magnet (3) is arranged to face the first end (66) of the central core (6) in the gap direction, and the magnet (3) comprises at least a first magnet and a second magnet, at least one of which is opposite to the flange (62) in the gap direction and has magnetization vectors (5), at least a part of which is inclined relative to the gap direction and obliquely in a direction opposite to a direction in which the flange (62) protrudes from the first end (66) of the central core (6), and wherein one of the magnets, one and two, is opposite the body (61) of the central core (6) in the gap direction and has the magnetization vectors (5), at least a part of which is oriented substantially parallel to the gap direction. [2] Ignition coil (1) comprising: a primary coil (11) and a secondary coil (12) which are magnetically coupled to each other; a core (2) defining a closed magnetic circuit (C) in which a magnetic flux generated by energizing the primary coil (11) flows, the core (2) having a gap (4) formed therein through which the magnetic circuit (C) passes; and a magnet (3) which is arranged in the gap (4) of the core (2), wherein the magnet (3) has magnetization vectors (5), at least a part of which is inclined relative to a gap direction, wherein the core (2) includes a central core (6) and an outer peripheral core (7), wherein the central core (6) is arranged inside the inner peripheries of the primary coil (11) and the secondary coil (12), wherein the outer peripheral core (7) is arranged outside the outer peripheries of the primary coil (11) and the secondary coil (12), the central core (6) includes a body (61) and a flange (62), the central core (6) having a length with a first end (66) and a second end (67) which are opposite to each other in the gap direction, which is a longitudinal direction of the central core (6), the flange (62) extending from the first end (66) of the central core (6) in a direction perpendicular to the gap direction, the magnet (3) is arranged to face the first end (66) of the central core (6) in the gap direction, and the magnet (3) comprises at least a first magnet and a second magnet, at least one of which is opposite to the flange (62) in the gap direction and has magnetization vectors (5), at least a part of which is inclined relative to the gap direction and obliquely in a direction opposite to a direction in which the flange (62) protrudes from the first end (66) of the central core (6), and wherein the flange (62) has easy magnetization directions, at least a part of which is oriented away from the magnet (3) and is inclined obliquely towards a longitudinal center of the body (61) of the central core (6). [3] Ignition coil (1) according to claim 1 or 2, wherein the core (2) has surfaces which are opposite to each other through the gap (4), and wherein the gap direction is a direction in which the surfaces of the core (2) are opposite to each other through the gap (4).

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