Ignition coil

Abstract

This invention provides a technology that can suppress the formation of voids near the secondary bobbin and secondary winding. [Solution] An ignition coil 104 for an internal combustion engine comprises a primary coil L1 in which a primary wire 81 is wound around a primary bobbin 41, a secondary coil L2 in which a secondary wire 82 is wound around a secondary bobbin 42, an iron core 60, and a resin part. The resin part fills the space outside the secondary bobbin 42 and inside the iron core 60. The iron core 60 has a central iron core 61 and an outer periphery iron core 62. The central iron core 61 is located radially inward from the primary coil L1 and the secondary coil L2 and extends axially. The outer periphery iron core 62 expands in an annular shape radially outward from the secondary coil L2 and connects the axial ends of the central iron core 61. The outer periphery iron core 62 has an uneven shape 660 on its inner circumferential surface 621 that contacts the resin part. This reduces the stress on the resin parts near the secondary bobbin 42 and secondary conductor 82 when the ignition coil 104 is driven.

Description

Technical Field

[0001] The present invention relates to an ignition coil for an internal combustion engine.

Background Art

[0002] Conventionally, an ignition device for an internal combustion engine uses an ignition coil that boosts a low voltage supplied from a power supply device to several thousand volts. The ignition coil includes a primary coil, a secondary coil, and a core for electromagnetic coupling between the primary coil and the secondary coil. Further, the primary coil, the secondary coil, and the core are housed in a case and fixed at predetermined positions within the case. A conventional ignition coil is described in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The ignition coil (100) of Patent Document 1 has a core in which a primary coil, a secondary coil, and an I-shaped central core (30) and a C-shaped outer peripheral core (40) are combined in a figure-eight shape. The primary coil is formed by winding a primary winding (16) about 100 turns around the outer periphery of a substantially rectangular prism-shaped primary bobbin (10) molded with resin. The secondary coil is formed by winding a secondary winding (24) thinner than the primary winding (16) about 8,000 to 15,000 turns around the outer periphery of a substantially rectangular prism-shaped secondary bobbin (20) molded with resin (paragraph 0026). Further, the ignition coil (100) is housed in a case (60). Further, the case (60) is filled with a mold resin (90) for achieving electrical insulation of the ignition coil (100) and physical fixation of each member (paragraph 0036).

[0005] As a result, in the ignition coil (100) of Patent Document 1, each component is connected via a molded resin (90). When a primary current is passed through the primary coil of the ignition coil (100) to energize it, or when a high voltage is induced in the secondary coil, each part generates heat and undergoes thermal expansion. In general, the coefficient of linear expansion of the outer iron core (40) is smaller than that of the molded resin (90). There is a large difference between the coefficient of linear expansion of the outer iron core (40) and the coefficient of linear expansion of the molded resin (90). Therefore, the molded resin (90) connected to the outer iron core (40) may have its movement restricted by the outer iron core (40), and mechanical stress may be applied to the molded resin (90). Furthermore, if this behavior is repeated, there is a risk that a gap will form between the secondary bobbin (20) and secondary winding (24) inside the mold resin (90) and the mold resin (90). If a gap forms, there is a risk that the insulation performance between the secondary windings (24) will decrease because air has low dielectric strength.

[0006] The object of the present invention is to provide a technology that can reduce the stress on the mold resin fixed to the secondary bobbin and secondary winding, and suppress the formation of voids near the secondary bobbin and secondary winding. [Means for solving the problem]

[0007] To solve the above problems, the first invention of the present application is an ignition coil for an internal combustion engine, comprising a primary coil, a secondary coil, an iron core, and a resin part. The primary coil is formed by winding a primary wire around a primary bobbin. The secondary coil is formed by winding a secondary wire around a secondary bobbin. The iron core electromagnetically couples the primary coil and the secondary coil. The resin part fills at least the space outside the secondary bobbin and inside the iron core. The iron core also comprises a central iron core and an outer circumferential iron core. The central iron core is located radially inward from the primary coil and the secondary coil and extends axially. The outer circumferential iron core expands in an annular shape radially outward from the secondary coil and connects the axial ends of the central iron core. The outer circumferential iron core has an uneven shape on its inner circumferential surface that contacts the resin part.

[0008] The second invention of this application is an ignition coil of the first invention, wherein the inner surface of the outer core has a flat, spreading planar portion and a curved portion. The uneven shape is formed in the curved portion.

[0009] The third invention of this application is an ignition coil according to the first or second invention, wherein the outer core is formed by laminating a plurality of steel plates in a direction perpendicular to the circumferential direction of the outer core. The uneven shape includes a plurality of grooves extending in the lamination direction of the plurality of steel plates.

[0010] The fourth invention of this application is an ignition coil according to any one of the first to third inventions, wherein the secondary bobbin is formed from modified PPE.

[0011] The fifth invention of this application is an ignition coil according to any one of the first to fourth inventions, wherein the resin portion is formed from epoxy resin. [Effects of the Invention]

[0012] According to the first to fifth inventions of this application, by providing an uneven shape on the inner surface of the outer core, when each part undergoes thermal expansion, the outer core and the resin part located inside the outer core can be intentionally separated. As a result, even if the coefficient of linear expansion of the outer core is smaller than that of the resin part, the stress on the resin part can be reduced. Consequently, the formation of a void between the secondary bobbin and the resin part can be suppressed.

[0013] In particular, according to the third invention of this application, an uneven shape can be formed on the inner surface of the outer core by laminating multiple steel plates. This improves the manufacturing efficiency of the outer core. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block diagram schematically showing the operating environment of the ignition system. [Figure 2] This is a perspective view of the ignition device according to the first embodiment. [Figure 3] This is a partial perspective view of the ignition device according to the first embodiment. [Figure 4] This is a cross-sectional view of the ignition coil according to the first embodiment. [Figure 5] This is a perspective view of the outer periphery of the iron core according to the first embodiment. [Figure 6] This is a perspective view of the cap according to the first embodiment. [Figure 7] This is a cross-sectional view of the ignition coil according to the second embodiment. [Figure 8] This is a longitudinal cross-sectional view of an ignition device according to the third embodiment. [Modes for carrying out the invention]

[0015] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the components described in these embodiments are merely illustrative and are not intended to limit the scope of the present invention to them alone. Furthermore, in the drawings, for ease of understanding, the dimensions and number of parts may be exaggerated or simplified as necessary.

[0016] <1. First Embodiment> <1-1. Configuration of Ignition Device> First, the configuration of the ignition device 1 for an internal combustion engine according to the first embodiment of the present invention will be described while referring to the drawings. FIG. 1 is a block diagram schematically showing the operating environment of the ignition device 1. The primary coil L1 and the secondary coil L2 of the ignition coil 104, which will be described later and are included in the ignition device 1, are coaxially arranged. However, in FIG. 1, for ease of explanation, they are shown adjacent to each other.

[0017] The ignition device 1 of this embodiment is, for example, a device that is mounted on an internal combustion engine such as a SI (spark ignition) reciprocating engine mounted on a vehicle body 100 such as an automobile, and applies a high voltage for generating a spark discharge to the spark plug 101. The ignition device 1 is provided for each of one or a plurality of cylinders of the internal combustion engine.

[0018] Also, as shown in FIG. 1, in addition to the ignition device 1, the internal combustion engine is equipped with the spark plug 101, and the vehicle body 100 is equipped with a power supply device 102 (battery) and an ECU 103 (Engine Control Unit). In a broad sense, the spark plug 101, the power supply device 102, and the ECU 103 can also be regarded as being included in the ignition device 1.

[0019] The spark plug 101 is a device for realizing an ignition operation in the combustion chamber of the internal combustion engine. The spark plug 101 is electrically connected to one end Eg2 of the secondary coil L2 of the ignition coil 104 via a conducting wire 121. The spark plug 101 is inserted between one end Eg2 of the secondary coil L2 and the ground point 151 (ground).

[0020] The spark plug 101 has a center electrode 141 and a ground electrode 142. When a high voltage is induced in the secondary coil L2 of the ignition coil 104, and the high voltage induced at one end Eg2 of the secondary coil L2 exceeds the dielectric breakdown voltage in the gap between the center electrode 141 and the ground electrode 142 of the spark plug 101 (hereinafter referred to as "plug gap d"), a discharge occurs in the plug gap d and a spark is generated. This ignites the fuel filled in the internal combustion engine. In other words, the spark plug 101 ignites the fuel by discharging in the plug gap d based on the high voltage induced at one end Eg2 of the secondary coil L2.

[0021] The power supply unit 102 is a storage battery capable of charging and discharging DC power. In this embodiment, the power supply unit 102 is electrically connected to one end Ep1 of the primary coil L1 of the ignition coil 104 via a conductor (hereinafter referred to as "power line 150"). The power supply unit 102 applies a DC voltage to one end Ep1 of the primary coil L1 of the ignition coil 104 via the power line 150.

[0022] The ECU103 is an existing computer that comprehensively controls the operation of the vehicle's transmission, engine, and other functions.

[0023] Figure 2 is a perspective view of the ignition device 1 according to this embodiment. Figure 3 is a perspective view of the case 106 with the main housing portion 71 (excluding the bottom portion 711) and the fixing portion 74 removed from Figure 2. Note that in Figures 2 and 3, several components are omitted from the illustration, such as the second resin portion 108 that fills the internal space 700 of the main housing portion 71 of the case 106, and the first resin portion 107 that fills the inside of the cap 109, which will be described later. As shown in Figure 2, the ignition device 1 has a three-dimensional shape in which the length in the longitudinal direction in the horizontal direction is longer than the length in the transverse direction. However, the shape of the ignition device 1 is not limited to this. Also, in Figures 2-3 and 2-8, "vertical direction" is defined for ease of explanation, but the orientation in which the ignition device 1 is positioned during manufacturing and use is not limited to this.

[0024] As shown in Figures 1 to 3, the ignition device 1 includes an ignition coil 104, an igniter 105, a case 106, a first resin part 107 (see Figure 4), a second resin part 108 (see Figure 4), a cap 109, and a diode 110. In a broader sense, the first resin part 107, the second resin part 108, and the cap 109 can also be considered as being included in the ignition coil 104.

[0025] The case 106 is an insulating resin container that forms the outer shape of the ignition device 1 and houses the various parts, including the ignition coil 104 and the igniter 105. The case 106 has a main housing section 71, a first connector section 72, a second connector section 73, and a fixing section 74.

[0026] The main housing section 71 is a container that opens to one side in the longitudinal direction. Hereinafter, the space inside the main housing section 71 will be referred to as the "internal space 700". The internal space 700 houses the ignition coil 104 and the igniter 105. The igniter 105 is positioned in the internal space 700 near the first connector section 72. The ignition coil 104 is positioned in the internal space 700 near the fixing section 74. The bottom surface 711 that constitutes the bottom of the case 106 faces the internal space 700 on its upper surface.

[0027] A first connector section 72 is formed on the side of the main housing section 71. Wiring extending from the igniter 105 and power lines 150 extending from one end Ep1 of the primary coil L1 of the ignition coil 104 are brought out to the outside of the case 106 through the internal space 720 of the first connector section 72 and connected to the ECU 103 and the power supply unit 102.

[0028] Below the main housing section 71, a second connector section 73 is formed. The second connector section 73 extends vertically in a cylindrical shape. Inside the second connector section 73, a conductor 121 connecting the secondary coil L2 and the spark plug 101, and a noise suppression resistor (not shown) interposed in the conductor 121 to reduce ignition noise in the ignition coil 104 are arranged.

[0029] Furthermore, a fixing portion 74 is formed on the side of the main housing portion 71 opposite to the first connector portion 72. The fixing portion 74 is a roughly triangular prism-shaped protruding part from the main housing portion 71 for attaching and fixing the ignition device 1 to the engine block.

[0030] Figure 4 is a cross-sectional view of the ignition coil 104 cut horizontally. Note that in Figure 4, the hatching of the secondary bobbin 42, outer core 62, first resin part 107, and second resin part 108, as well as the uneven shape 660, which will be described later, are only shown in the enlarged partial view. As shown in Figure 4, the ignition coil 104 has a bobbin 40, a primary coil L1, a secondary coil L2, and a core 60.

[0031] In the following description of the ignition coil 104, the direction parallel to the central axis Bc of the bobbin 40 will be referred to as the "axial direction," the direction perpendicular to the central axis Bc of the bobbin 40 will be referred to as the "radial direction," and the direction along the circumference of the central axis Bc of the bobbin 40 will be referred to as the "circumferential direction." Furthermore, the "parallel direction" includes a direction that is approximately parallel, and the "perpendicular direction" also includes a direction that is approximately perpendicular. In addition, the longitudinal direction of the ignition device 1 is approximately parallel to the axial direction. That is, as shown in Figure 4, the ignition coil 104 is housed in the internal space 700 of the main housing 71 with the axial direction of the ignition coil 104 approximately parallel to the horizontal longitudinal direction.

[0032] The bobbin 40 includes a primary bobbin 41 and a secondary bobbin 42 that can be connected to each other. The primary bobbin 41 and the secondary bobbin 42 each extend cylindrically along the central axis Bc. The secondary bobbin 42 is positioned radially outside the primary bobbin 41. The material used for the primary bobbin 41 and the secondary bobbin 42 is, for example, a resin that acts as an insulator. More specifically, the primary bobbin 41 and the secondary bobbin 42 are each formed from an engineering plastic such as modified PPE (polyphenylene ether).

[0033] The primary coil L1 is formed by winding a conductor around the outer surface of the primary bobbin 41 about 100 times in the circumferential direction around the central axis Bc, while simultaneously stacking it in multiple layers in the radial direction. Hereinafter, the conductor wound around the primary bobbin 41 will be referred to as the "primary conductor 81". In other words, the primary coil L1 is formed by winding the primary conductor 81 around the primary bobbin 41.

[0034] After the primary coil L1 is formed, a secondary bobbin 42 is positioned to cover the outer surface of the primary coil L1 and connected to the primary bobbin 41. Then, a different wire from the primary wire 81 is wound around the outer surface of the secondary bobbin 42 approximately 10,000 times in the circumferential direction around the central axis Bc, and stacked in multiple layers in the radial direction to form the secondary coil L2. Hereinafter, this different wire wound around the secondary bobbin 42 will be referred to as the "secondary wire 82". In other words, the secondary coil L2 is formed by winding the secondary wire 82 around the secondary bobbin 42.

[0035] The secondary bobbin 42 is provided with multiple flange portions 43 that expand radially. The secondary conductor 82 is wound around the outer circumferential surface of the secondary bobbin 42 between the axial directions of the multiple flange portions 43. The secondary conductor 82 is wound around the secondary bobbin 42 while covered with a coating material such as polyamide-imide.

[0036] In this way, by arranging the primary coil L1 and the secondary coil L2 in a stacked manner, the entire ignition coil 104 including them can be miniaturized. However, the primary coil L1 and the secondary coil L2 are not limited to being wound while stacked on top of each other in this manner; for example, they may be arranged adjacent to each other in the axial direction.

[0037] The core 60 has a structure in which a central core 61 and an outer core 62 are combined. That is, the core 60 has a central core 61 and an outer core 62. Figure 5 is a perspective view of the outer core 62. The central core 61 and the outer core 62 are each formed from laminated steel sheets in which a plurality of steel sheets 631 are stacked. The plurality of steel sheets 631 have substantially the same size and shape. In this embodiment, the stacking direction of the plurality of steel sheets 631 is substantially parallel to the vertical direction. In addition, for example, silicon steel sheets are used for the steel sheets 631. Generally, silicon steel sheets are electrical steel sheets formed by rolling steel that has been heat-treated with a few percent of silicon mixed into iron. However, steel sheets other than silicon steel sheets may be used for the steel sheets of the present invention.

[0038] As shown in Figure 4, the central core 61 extends substantially horizontally and columnarly along the central axis Bc. Furthermore, the central core 61 has a substantially I-shape in plan view. The central core 61 is inserted into the radially inner space 410 of the primary bobbin 41. That is, the central core 61 is located radially inward of the primary coil L1 and secondary coil L2, and extends axially.

[0039] The outer core 62 has a roughly square shape in plan view. In plan view, the outer core 62 surrounds the outside of the primary coil L1, secondary coil L2, central core 61, and cap 109 in an annular shape. Hereinafter, the direction in which the outer core 62 extends annularly around the outside of each part in plan view will be referred to as the "circumferential direction". The outer core 62 is formed by stacking multiple steel plates 631 that expand in the circumferential direction in the vertical direction. The outer core 62 also expands annularly radially outward from the secondary bobbin 42 and secondary coil L2, connecting both axial ends of the central core 61. As a result, the core 60 forms a closed magnetic circuit structure that electromagnetically couples the primary coil L1 and the secondary coil L2. In this embodiment, the core 60 has a shape that combines the roughly I-shaped central core 61 and the roughly square-shaped outer core 62 in a Japanese character shape. A more detailed description of the outer core 62 will be provided later.

[0040] As described above, a power line 150 extending from the power supply unit 102 is connected to one end Ep1 of the primary coil L1. The other end Eg1 of the primary coil L1, opposite to the end Ep1, is connected to the ground point 152 via the igniter 105. Controlled by the igniter 105, a low DC voltage from the power supply unit 102 is applied to the end Ep1 of the primary coil L1, and a gradually increasing primary current begins to flow through the primary coil L1.

[0041] One end Eg2 of the secondary coil L2 is connected to the spark plug 101. The diameter of the secondary conductor 82 is smaller than the diameter of the primary conductor 81. Also, the number of turns of the secondary conductor 82 in the secondary coil L2 is greater than the number of turns of the primary conductor 81 in the primary coil L1. For example, the number of turns of the secondary conductor 82 in the secondary coil L2 is about 100 times the number of turns of the primary conductor 81 in the primary coil L1. As a result, when the primary current is interrupted, the ignition coil 104 boosts the low-voltage DC power supplied from the power supply unit 102 to several thousand volts to tens of thousands of volts. That is, a high voltage is induced in the secondary coil L2. The secondary coil L2 then supplies the induced high-voltage power to the spark plug 101. This generates an electric spark at the spark plug 101, and the fuel is ignited.

[0042] As shown in Figure 1, the other end Ep2 of the secondary coil L2, opposite to the end Eg2 to which the spark plug 101 is connected, is electrically connected to the power supply unit 102 via a conductor 122. In this embodiment, the other end Ep2 of the secondary coil L2 is electrically connected to the power line 150 via the conductor 122. A diode 110 is interposed in the conductor 122. The diode 110 is connected in series with the secondary coil L2. The diode 110 is positioned such that the direction from the one end Eg2 of the secondary coil L2 to the other end Ep2 is the forward direction.

[0043] As a result, in the current control described later, when the primary coil L1 is energized by a primary current (ON state), the induced current caused by the voltage induced in the secondary coil L2 by the gradually increasing primary current is prevented from flowing in the reverse direction in the diode 110. As a result, this induced current is prevented from flowing to the spark plug 101, and thus, discharge at the spark plug 101 during the ON state, i.e., at an abnormal timing, can be suppressed.

[0044] The igniter 105 is a semiconductor device electrically connected to the primary coil L1 and controls the current flowing through the primary coil L1. The igniter 105 is also electrically connected to the ECU 103 and receives signals (hereinafter referred to as "EST signals") from the ECU 103. The igniter 105 includes a switching element 91 and a drive IC 92. The igniter 105 may be integrated with the electronic circuitry of the ECU 103.

[0045] For example, an insulated-gate bipolar transistor (IGBT) is used as the switching element 91. The switching element 91 is inserted in a wire 123 that connects the other end Eg1 of the primary coil L1 to the ground point 152. The collector (C) of the switching element 91 is connected to the other end Eg1 of the primary coil L1. The emitter (E) of the switching element 91 is connected to the ground point 152. The gate (G) of the switching element 91 is connected to the drive IC 92.

[0046] This allows the switching element 91 to switch between supplying or interrupting the primary current flowing from the power supply 102 to the primary coil L1. When the switching element 91 is closed, primary current flows from the power supply 102 to the primary coil L1. When the switching element 91 is open, the primary current flowing to the primary coil L1 is interrupted. However, other types of transistors, such as MOSFETs, may be used instead of IGBTs for the switching element 91.

[0047] The drive IC 92 is a control unit that controls the switching of the switching element 91 based on the EST signal received from the ECU 103. The drive IC 92 has a logic device connected to the switching element 91. The logic device includes, for example, a logic circuit, a processor, a CPLD (complex programmable logic device), an FPGA (field-programmable gate array), or an ASIC (application-specific integrated circuit). The logic device performs calculations to operate the ignition device 1 and ignite the spark plug 101.

[0048] Figure 6 is a perspective view of the cap 109. As shown in Figure 6, the cap 109 is a three-dimensional cover having a large opening 75, a small opening 76, and an upper lid portion 77. The material used for the cap 109 is, for example, an insulating resin. More specifically, the cap 109 is formed from, for example, modified PPE (polyphenylene ether).

[0049] In the manufacturing process of the ignition device 1, first, the primary coil L1 of the ignition coil 104 is formed, and then the secondary coil L2 is formed radially outside the primary coil L1. After that, the central core 61 is inserted into the radially inner space 410 of the primary bobbin 41. The primary coil L1 and secondary coil L2, with the central core 61 inserted, are then placed inside the cap 109. At this time, the central core 61 is positioned such that one end penetrates the large opening 75 and the other end penetrates the small opening 76.

[0050] Next, a thermosetting first molding resin is poured into the inside of the cap 109 to insulate and fix each part. For example, epoxy resin is used as the first molding resin. The first molding resin is filled inside the cap 109 so as to fill the gap between the outer surface of the secondary bobbin 42 and the inner surface 78 of the cap 109. As a result, after the first molding resin hardens, a first resin part 107 (see Figure 4) is formed that fills the gap between the outer surface of the secondary bobbin 42 and the inner surface 78 of the cap 109. The primary coil L1, the secondary coil L2, and the central iron core 61 are then held inside the cap 109. Hereinafter, the cap 109 and the primary coil L1, secondary coil L2, and central iron core 61 held inside the cap 109 will be referred to as the "coil assembly 111".

[0051] Next, the outer core 62 is fitted onto the outside of the coil assembly 111. At this time, the outer core 62 is positioned so that its circumferential direction is parallel to the upper cover portion 77 of the cap 109. As a result, both axial ends of the central core 61 are connected to the inner circumferential surface 621 of the outer core 62. In this embodiment, a magnet 64 is interposed between one of the axial end faces of the central core 61 and the inner circumferential surface 621 of the outer core 62 to increase the discharge energy released when the ignition coil 104 is discharged.

[0052] Next, the coil assembly 111, with the outer core 62 fitted inside, is placed in the internal space 700 of the main housing section 71 of the case 106. At this time, the coil assembly 111 with the outer core 62 fitted inside is positioned so that the circumferential direction of the outer core 62 and the top cover portion 77 of the cap 109 are parallel to the bottom surface portion 711 of the case 106. In addition, the igniter 105 is placed adjacent to the coil assembly 111 with the outer core 62 fitted inside.

[0053] Then, a thermosetting second molding resin is poured into the internal space 700 of the main housing 71 to insulate and fix each part. For example, epoxy resin is used as the second molding resin. The second molding resin is filled so as to cover each part that is placed in the internal space 700. The second molding resin is also filled so as to fill the gap between the outer surface 79 of the cap 109 and the inner surface 621 of the outer core 62. As a result, after the second molding resin hardens, a second resin part 108 (see Figure 4) is formed that fills the gap between the outer surface 79 of the cap 109 and the inner surface 621 of the outer core 62. The second resin part 108 is an example of a "resin part" in the present invention. That is, the "resin part" is formed from, for example, epoxy resin. In addition, each part, including the coil assembly 111 into which the outer core 62 is fitted and the igniter 105, is held in the appropriate position within the internal space 700.

[0054] However, the arrangement of each part in the internal space 700 of the case 106 and the position of the molded resin filling the internal space 700 are not limited to this. The ignition coil 104 only needs to have a "resin part" that fills the space outside the secondary bobbin 42 and inside the iron core 60.

[0055] <1-2. Operation of the ignition system> Next, the operation of the ignition device 1 will be explained. As described above, a DC voltage is applied to one end Ep1 of the primary coil L1 from the power supply unit 102 via the power line 150. The other end Eg1 of the primary coil L1 is connected to the switching element 91. The drive IC 92 controls the switching of the switching element 91 based on the EST signal received from the ECU 103.

[0056] When operating the ignition device 1, first, the signal level of the EST signal transmitted from the ECU 103 to the drive IC 92 is changed from L to H. Then, based on the EST signal, the drive IC 92 switches the switching element 91 from the open state to the closed state. As a result, a low DC voltage from the power supply 102 is applied to one end Ep1 of the primary coil L1. Then, a primary current flows through the primary conductor 81 that forms the primary coil L1, and a magnetomotive force is generated in the primary coil L1. Hereafter, this process in which the drive IC 92 generates a magnetomotive force by flowing a primary current through the primary coil L1 will be referred to as "energization control".

[0057] Furthermore, in this embodiment, when a DC voltage from the power supply 102 is applied to the primary coil L1 (ON), a positive electromotive force is induced in the secondary coil L2, which is electromagnetically coupled to the primary coil L1 via the iron core 60, from one end Eg2 to the other end Ep2. That is, when ON, the voltage at one end Eg2 of the secondary coil L2 is higher than that at the other end Ep2. The maximum voltage across one end Eg2 of the secondary coil L2 is, for example, several hundred volts. On the other hand, the minimum voltage across the other end Ep2 of the secondary coil L2 is, for example, several hundred volts.

[0058] Here, as described above, in the conductor 122 connecting the other end Ep2 of the secondary coil L2 to the power supply 102, the diode 110 is connected in series with the secondary coil L2. The diode 110 is positioned so that the forward direction is from one end Eg2 of the secondary coil L2 to the other end Ep2. Therefore, when a primary current flows through the primary coil L1, even if the voltage across one end Eg2 of the secondary coil L2 is large compared to the voltage across the other end Ep2 of the secondary coil L2, it is possible to suppress the flow of induced current (secondary current) from the power supply 102 side to the other end Eg2 of the secondary coil L2 via Ep2. As a result, it is possible to suppress discharge from occurring in the spark plug 101 when it is ON, i.e., at an abnormal timing, and to suppress the flow of induced current through the spark plug 101.

[0059] After the power supply control is performed, the signal level of the EST signal transmitted from the ECU 103 to the drive IC 92 is then changed from H to L. The drive IC 92 then switches the switching element 91 from the closed state to the open state, interrupting the primary current flowing from the power supply 102 to the primary coil L1. As a result, a large induced electromotive force is induced in the secondary coil L2, which is electromagnetically coupled to the primary coil L1 via the iron core 60, due to mutual induction. At this time, the voltage value applied to one end Eg2 of the secondary coil L2 ranges from several thousand volts to tens of thousands of volts relative to the ground point 151.

[0060] As a result, an electric spark is generated at the spark plug 101 connected to one end Eg2 of the secondary coil L2, igniting the fuel, and an induced current flows through the spark plug 101. This induced current first flows from the ground point 151, through the ground electrode 142 of the spark plug 101, to the center electrode 141 of the spark plug 101. Then, this induced current flows from one end Eg2 of the secondary coil L2 to the other end Ep2, and further flows to the ground point 153 (ground) through the power line 150 and the power supply unit 102 (see Figure 1). After the drive IC 92 performs the above-described "energy control," the process of interrupting the primary current flowing through the primary coil L1 and inducing a high voltage at one end Eg2 of the secondary coil L2, thereby causing a discharge at the plug gap d of the spark plug 101, is called "discharge control."

[0061] Subsequently, when the absolute value of the induced current due to the negative secondary voltage induced at one end Eg2 of the secondary coil L2 falls below the absolute value of the secondary current that can maintain discharge at the plug gap d of the spark plug 101, the discharge at the plug gap d of the spark plug 101 ends.

[0062] <1-3. Detailed structure of the outer core> Next, we will describe the structure of the outer core 62 in more detail.

[0063] As described above, the inner surface 621 of the outer core 62 contacts the second resin portion 108 which is filled between it and the outer surface 79 of the cap 109. Here, as shown in Figures 4 and 5, the inner surface 621 of the outer core 62 in this embodiment is provided with a flat portion 65 and a curved portion 66. The flat portion 65 is the flat, spreading portion of the inner surface 621 of the outer core 62. The curved portion 66 is the curved portion of the inner surface 621 of the outer core 62. The curved portion 66 is located near the axial end of the secondary bobbin 42 held inside the cap 109. In this embodiment, an uneven shape 660 is formed on the curved portion 66. In this embodiment, an uneven shape 660 is formed on each of the two curved portions 66 on the inner surface 621 of the outer core 62.

[0064] As described above, the outer core 62 is formed by stacking multiple steel plates 631 in a direction perpendicular to the circumferential direction of the outer core 62 (vertical direction). For ease of explanation, the multiple steel plates 631 forming the outer core 62 will be referred to as steel plate 631a, steel plate 631b, steel plate 631c, ... steel plate 631k in order along the stacking direction. As shown in Figure 5, each of the steel plates 631a, 631b, 631c, ... steel plate 631k has multiple recesses 67 provided at approximately equal intervals along the circumferential direction of the outer core 62 in the curved surface portion 66. Each of the multiple recesses 67 is recessed in the inner circumferential surface of each steel plate 631. Furthermore, each of the multiple recesses 67 extends from one end to the other in the vertical direction of each steel plate 631.

[0065] Furthermore, each recess 67 provided in the steel plate 631a, each recess 67 provided in the steel plate 631b, each recess 67 provided in the steel plate 631c, ..., each recess 67 provided in the steel plate 631k are located at the same position in the circumferential direction. Therefore, when multiple steel plates 631 are stacked, each recess 67 is connected in the stacking direction. As a result, grooves 68 are formed on the inner circumferential surface 621 of the outer core 62, where the recesses 67 are connected in the stacking direction. In addition, multiple grooves 68 are formed at approximately equal intervals along the circumferential direction. As a result, the above-described uneven shape 660 is formed. That is, the uneven shape 660 includes multiple grooves 68 extending in the stacking direction of the multiple steel plates 631. Thus, in this embodiment, an uneven shape 660 can be formed on the inner circumferential surface 621 of the outer core 62 by stacking steel plates 631 of the same shape, each having multiple recesses 67. This improves the manufacturing efficiency of the outer core 62.

[0066] However, the location where the uneven shape 660 is formed on the inner circumferential surface 621 of the outer core 62 is not limited to the curved surface 66. For example, the uneven shape 660 may be formed not only on the curved surface 66 but also on the flat surface 65. In other words, the outer core 62 only needs to have the uneven shape 660 on the inner circumferential surface 621 that contacts the second resin part 108.

[0067] When the above energization control or discharge control is performed in the ignition coil 104, each part generates a large amount of heat. At this time, the coefficient of linear expansion of the outer core 62 is smaller than that of the second resin part 108 fixed to the inner surface 621 of the outer core 62, the cap 109 fixed inside the second resin part 108, and the first resin part 107 fixed inside the cap 109. There is a large difference between the coefficient of linear expansion of the outer core 62 and that of the second resin part 108, the cap 109, and the first resin part 107. For this reason, in the case of a conventional ignition coil 104, when each part expands, the second resin part 108 fixed to the inner surface 621 of the outer core 62, the cap 109 fixed inside the second resin part 108, and the first resin part 107 fixed inside the cap 109 may have their movement restricted by the outer core 62. As a result, mechanical stress may be applied to the second resin part 108, the cap 109, and the first resin part 107. Furthermore, mechanical stress applied to the first resin part 107 around the secondary bobbin 42 and secondary coil L2 may cause delamination between the secondary bobbin 42 and secondary coil L2 and the first resin part 107. In addition, in the conventional ignition coil 104, repeated energization control or discharge control and stopping causes repeated thermal expansion and contraction of each part. As a result, a gap is created between the secondary bobbin 42 and secondary coil L2 and the first resin part 107, and since the dielectric strength of air is low, this may lead to a decrease in the insulation performance between the secondary conductors 82.

[0068] However, in this embodiment, as described above, an uneven shape 660 is formed on the inner circumferential surface 621 of the outer core 62. Therefore, when each part expands due to heat, the outer core 62 and the second resin part 108 can be intentionally separated. This suppresses the restriction of movement that the second resin part 108, the cap 109, and the first resin part 107 receive from the outer core 62. As a result, the stress on the second resin part 108, the cap 109, and the first resin part 107 can be reduced. This suppresses the formation of a gap between the secondary bobbin 42 and the secondary coil L2 and the first resin part 107, and allows the first resin part 107, which has high dielectric strength, to be continuously positioned near the secondary bobbin 42 and the secondary coil L2. As a result, the insulation performance between the secondary conductors 82 can be maintained.

[0069] Furthermore, in this embodiment, an uneven shape 660 is formed on the curved portion 66 of the inner circumferential surface 621 of the outer core 62. As described above, the curved portion 66 is located near the axial end of the secondary bobbin 42 held inside the cap 109. In the ignition coil 104, the fixing strength between the axial end of the secondary bobbin 42 and the first resin portion 107 tends to be lower than in other areas during the manufacturing process of the first resin portion 107. However, in this embodiment, when each part expands due to heat, the outer core 62 and the second resin portion 108 can be intentionally separated near the axial end of the secondary bobbin 42. This reduces the stress on the first resin portion 107 near the axial end of the secondary bobbin 42. As a result, the insulation performance between the secondary conductors 82 can be better maintained.

[0070] <2. Second Embodiment> Next, the configuration of the ignition device 1 according to the second embodiment of the present invention will be described. In the following description, the differences from the first embodiment will be the main focus, and parts equivalent to those in the first embodiment will be denoted by the same reference numerals, and some redundant explanations will be omitted. The ignition device 1 of this embodiment includes an ignition coil 104, an igniter 105, a case 106, a diode 110, and a resin part 112. Figure 7 is a cross-sectional view of the ignition coil 104 of this embodiment, cut horizontally. In Figure 7, the secondary bobbin 42, the outer core 62, and the hatching of the resin part 112, as well as the uneven shape 660, are shown only in the partially enlarged view.

[0071] The ignition device 1 of this embodiment does not have the first resin part 107, the second resin part 108, and the cap 109 that were provided in the first embodiment. In the manufacturing process of the ignition device 1 of this embodiment, first, the outer circumferential core 62 is fitted to the outside of the primary coil L1 and secondary coil L2 through which the central core 61 is inserted. As a result, both axial ends of the central core 61 are connected to the inner circumferential surface 621 of the outer circumferential core 62. This completes the assembly of the ignition coil 104.

[0072] Next, the ignition coil 104 is placed in the internal space 700 of the main housing 71 of the case 106. At this time, the ignition coil 104 is positioned so that the circumferential direction of the outer core 62 is parallel to the bottom surface 711 of the case 106. Also, the igniter 105 is placed adjacent to the ignition coil 104.

[0073] Then, a thermosetting molding resin is poured into the internal space 700 of the main housing 71 to insulate and fix each part. For example, epoxy resin is used as the molding resin. The molding resin is filled so as to cover each part that is placed in the internal space 700. The molding resin is also filled so as to fill the gap between the outer surface of the secondary bobbin 42 and the inner surface 621 of the outer core 62. As a result, after the molding resin hardens, a "resin part 112" is formed that fills the space outside the secondary bobbin 42 and inside the outer core 62. In addition, each part, including the ignition coil 104 and the igniter 105, is held in the appropriate position within the internal space 700.

[0074] The inner circumferential surface 621 of the outer core 62 contacts the resin portion 112 filled between it and the outer surface of the secondary bobbin 42. Here, as in the first embodiment, the inner circumferential surface 621 of the outer core 62 is provided with a flat portion 65 and a curved portion 66. The flat portion 65 is the flat, spreading portion of the inner circumferential surface 621 of the outer core 62. The curved portion 66 is the curved portion of the inner circumferential surface 621 of the outer core 62. The curved portion 66 is located near the axial end of the secondary bobbin 42. An uneven shape 660 is formed on the curved portion 66.

[0075] This allows the ignition coil 104 to perform the above-mentioned energization and discharge control, and when each part expands due to thermal expansion, it is possible to intentionally separate the outer core 62 and the resin part 112. As a result, the restriction on the movement of the resin part 112 from the outer core 62, which has a smaller coefficient of linear expansion than the resin part 112, can be suppressed. This reduces the stress on the resin part 112. As a result, it is possible to suppress the formation of air gaps between the secondary bobbin 42 and secondary coil L2 and the resin part 112, and the resin part 112, which has high dielectric strength, can be continuously placed near the secondary bobbin 42 and secondary coil L2. This maintains the insulation performance between the secondary conductors 82.

[0076] <3. Third Embodiment> Next, the configuration of the ignition device 1 according to the third embodiment of the present invention will be described. In the following description, the differences from the first and second embodiments will be the main focus, and parts equivalent to those in the first and second embodiments will be denoted by the same reference numerals, and some redundant explanations will be omitted. The ignition device 1 of this embodiment includes an ignition coil 104, an igniter 105, a case 106, a diode 110, and a resin part 112. Figure 8 is a vertical cross-sectional view of the ignition device 1 of this embodiment, cut in the vertical direction. In Figure 8, the hatching of the secondary bobbin 42 and the resin part 112, and the uneven shape 660 are shown only in the partially enlarged view.

[0077] As shown in Figure 8, the ignition coil 104 includes a bobbin 40, a primary coil L1, a secondary coil L2, and an iron core 60. The central iron core 61 has a roughly I-shape. On the other hand, the outer periphery iron core 62 has a roughly U-shape when viewed from the front. The outer periphery iron core 62 extends radially outward from the secondary bobbin 42 and secondary coil L2 in an annular shape, connecting both axial ends of the central iron core 61. As a result, the iron core 60 forms a closed magnetic circuit structure that electromagnetically couples the primary coil L1 and the secondary coil L2. In this embodiment, the iron core 60 has a shape that combines the roughly I-shaped central iron core 61 and the roughly U-shaped outer periphery iron core 62 in a square shape. In addition, the direction in which the outer periphery iron core 62 advances annularly on the outside of each part when viewed from the front is called the "circumferential direction".

[0078] In this embodiment, the case 106 has a main housing section 71, a first connector section 72, a second connector section 73, and a fixing section 74. The main housing section 71 is a container that opens upward. The internal space 700 inside the main housing section 71 houses the ignition coil 104 and the igniter 105. However, unlike the first and second embodiments, the ignition coil 104 is arranged such that the circumferential direction of the outer core 62 is perpendicular to the bottom surface 711 of the case 106.

[0079] In the manufacturing process of the ignition device 1 of this embodiment, with the ignition coil 104 and igniter 105 positioned in the internal space 700 of the main housing 71, a thermosetting molding resin is poured in to insulate and fix each part. For example, epoxy resin is used as the molding resin. The molding resin is filled up to near the opening at the upper end of the internal space 700. The molding resin is also filled so as to fill the gap between the outer surface of the secondary bobbin 42 and the inner surface 621 of the outer core 62. As a result, after the molding resin hardens, a "resin part 112" is formed that fills the space outside the secondary bobbin 42 and inside the outer core 62. Furthermore, each part, including the ignition coil 104 and igniter 105, is held in the appropriate position within the internal space 700.

[0080] The inner circumferential surface 621 of the outer core 62 contacts the resin portion 112 filled between it and the outer surface of the secondary bobbin 42. Here, as in the first and second embodiments, the inner circumferential surface 621 of the outer core 62 is provided with a flat portion 65 and a curved portion 66. The flat portion 65 is the flat, spreading portion of the inner circumferential surface 621 of the outer core 62. The curved portion 66 is the curved portion of the inner circumferential surface 621 of the outer core 62. The curved portion 66 is located near the axial end of the secondary bobbin 42. An uneven shape 660 is formed on the curved portion 66.

[0081] This allows the ignition coil 104 to perform the above-mentioned energization and discharge control, and when each part expands due to thermal expansion, it is possible to intentionally separate the outer core 62 and the resin part 112. As a result, the restriction on the movement of the resin part 112 from the outer core 62, which has a smaller coefficient of linear expansion than the resin part 112, can be suppressed. This reduces the stress on the resin part 112. As a result, it is possible to suppress the formation of air gaps between the secondary bobbin 42 and secondary coil L2 and the resin part 112, and the resin part 112, which has high dielectric strength, can be continuously placed near the secondary bobbin 42 and secondary coil L2. This maintains the insulation performance between the secondary conductors 82.

[0082] <4. Variation> Although exemplary embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above.

[0083] The ignition coil of the present invention can be installed not only in vehicles such as automobiles, but also in various devices such as generators and industrial machinery, and is used to generate an electric spark at the spark plug of an internal combustion engine to ignite fuel.

[0084] The shape and structure of the ignition coil described above may be modified as appropriate without departing from the spirit of the present invention. Furthermore, the elements that appeared in the above embodiments may be combined as appropriate without creating any inconsistencies. [Explanation of Symbols]

[0085] 1 Ignition device 40 bobbins 41 Primary bobbin 42 Secondary bobbin 60 Iron Heart 61 Central Iron Core 62 Outer core 65 (The flat portion of the inner surface of the outer core) 66 Curved surface (on the inner surface of the outer core) 68 Grooves (on the inner surface of the outer core) 81 Primary conductor 82 Secondary conductor 104 Ignition coil 105 Igniter 106 cases 107 First Resin Part 108 Second Resin Section 109 Cap 112 Resin part 621 Inner surface of outer core 631 Steel plate forming the outer core 660 (Irregular shape of the inner surface of the outer core) L1 Primary coil L2 Secondary Coil

Claims

1. An ignition coil for an internal combustion engine, A primary coil is formed by winding a primary wire around a primary bobbin, A secondary coil is formed by winding a secondary wire around a secondary bobbin, An iron core is used to electromagnetically couple the primary coil and the secondary coil, At a minimum, a resin portion fills the space outside the secondary bobbin and inside the iron core, It has, The aforementioned iron core is A central iron core is located radially inward from the primary coil and the secondary coil, and extends in the axial direction, An outer core extending radially outward from the secondary coil and connecting both axial ends of the central core, It has, The ignition coil wherein the outer core has an uneven shape on its inner surface that contacts the resin portion.

2. An ignition coil according to claim 1, The inner surface of the outer core is A flat, spreading surface, Curved surface section, It has, The aforementioned uneven shape is formed on the curved surface portion of the ignition coil.

3. An ignition coil according to claim 1 or claim 2, The outer core is formed by stacking a plurality of steel plates in a direction perpendicular to the circumferential direction of the outer core. The aforementioned uneven shape includes a plurality of grooves extending in the lamination direction of the plurality of steel plates, wherein the ignition coil.

4. An ignition coil according to claim 1 or claim 2, The aforementioned secondary bobbin is an ignition coil formed from modified PPE.

5. An ignition coil according to claim 1 or claim 2, The aforementioned resin part is an ignition coil formed from epoxy resin.

Images