Coil device

Abstract

To provide a coil device capable of reducing a heat stress generated in a core.SOLUTION: A coil device includes: a core containing a magnetic body; and a wire arranged in a coil shape around at least a part of the core. The core includes: a middle leg part at which a winding part of the wire is arranged; and a first base part that is arranged at one end of the middle leg part along a winding axis of the winding part so as to be separated by a predetermined distance. 70%, preferably 80% or more, more preferably 90% or more, or 95% or more of a volume of the middle leg part is positioned below an atmosphere open surface of a heat radiation resin.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a coil device that can be suitably used as, for example, a transformer. [Background technology]

[0002] In order to improve the heat resistance of the coil device, for example, in Patent Document 1, a part of the core is immersed in a heat dissipating resin to enhance the cooling effect. However, this technique has a problem in that the part covered with the heat dissipating resin is small, and sufficient heat dissipation effect cannot be expected.

[0003] Therefore, it is possible to cover most of the core with heat dissipating resin, but this would make the case for storing the heat dissipating resin too large, which goes against the demand for a compact coil device. Therefore, the case for storing the heat dissipating resin may be made small so that the wire winding part is immersed in the resin to the minimum extent necessary. In this case, part of the core, for example, the core part located above along the winding axis of the wire, may be exposed outside the heat dissipating resin.

[0004] In such a case, the core will have parts that are cooled by the heat dissipating resin and parts that are not cooled by the heat dissipating resin, which may cause thermal stress in the core and significantly reduce its durability. In particular, with the recent increase in current in coil devices, reducing the thermal stress generated in the core has become an issue.

[0005] Furthermore, even if a portion of the core is not exposed from the heat dissipating resin, if there is a large difference in the cooling temperature of the heat dissipating resin along the winding axis of the wire, excessive thermal stress may be generated in the core, which will also reduce the durability of the core. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-36194 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coil device capable of reducing thermal stress generated in a core. [Means for solving the problem]

[0008] In order to achieve the above object, a coil device according to the present invention comprises: A core including a magnetic material; a wire coiled around at least a portion of the core, The core is a middle leg portion on which the wire winding portion is disposed; a first base portion disposed at a predetermined distance from one end of the middle leg portion along a winding axis of the winding portion; 70% or more, preferably 80% or more, more preferably 90% or more, or even 95% or more of the volume of the center leg is located below the air-opening surface of the heat-dissipating resin.

[0009] In this coil device, most of the volume of the center leg is located below the air-opening surface of the heat-dissipating resin, so that most of the volume of the center leg and the winding of the wire arranged around the center leg are cooled by the heat-dissipating resin, improving heat dissipation. Moreover, since the first base is arranged at a predetermined distance from one end of the center leg along the winding axis of the winding, even if a part of the first base is exposed from the heat-dissipating resin, stress such as thermal expansion force generated in the center leg is not transmitted to the first base. Therefore, excessive thermal stress that could be generated in the first base can be reduced.

[0010] The first base portion may have a volume of 30% or more, 50% or more, 80% or more, or 95% or more exposed from the heat dissipating resin. By exposing most of the first base portion, it is possible to reduce the size of the case that contains the heat dissipating resin and also the amount of heat dissipating resin. Even in this case, the first base portion is disposed at a predetermined distance from one end of the center leg portion along the winding axis of the winding portion, so that stress such as thermal expansion force generated in the center leg portion is not transmitted to the first base portion. Therefore, it is possible to reduce excessive thermal stress that may be generated in the first base portion.

[0011] The core may further include a second base portion formed contiguous with the other end of the middle leg along the winding axis, or the core may further include a second base portion disposed at a predetermined distance from the other end of the middle leg along the winding axis.

[0012] The second base portion may be close to a cooling wall surface of the case filled with the heat dissipating resin. For example, when the cooling wall surface of the case is the bottom surface of the case, the core is housed inside the case so that the axis of the wound portion of the wire is approximately perpendicular to the bottom surface of the case. When the cooling wall surface of the case is the side surface of the case, the core is housed inside the case so that the axis of the wound portion of the wire is approximately parallel to the bottom surface of the case.

[0013] Preferably, an air gap of 1.9 mm or less exists between the first base portion and the one end of the center leg portion. By having an air gap between the first base portion and the one end of the center leg portion, stress such as thermal expansion force generated in the center leg portion is more reliably not transmitted to the first base portion. In addition, by making the gap of the air gap a predetermined value or less, it becomes easier to form a magnetic circuit between the center leg and the base portion.

[0014] The one end of the center leg may be located below the air-opening surface of the heat dissipation resin. With this configuration, the heat dissipation of the center leg and the portion of the wire wound therearound is improved.

[0015] The one end of the center leg may be located above the air-opening surface of the heat dissipation resin. With this configuration, an air layer of 1.9 mm or less can be easily formed between the first base portion and the one end of the center leg.

[0016] Preferably, the air-opening surface of the heat dissipating resin is located at a position where the heat dissipating resin covers the wound portion of the wire disposed around the center leg. With this configuration, heat dissipation is improved.

[0017] An adhesive or the heat dissipating resin may be at least partially interposed between the other end of the center leg and the surface of the second base portion. Also, the other end of the center leg and the second base portion may be formed integrally.

[0018] A cylindrical portion of a bobbin may be disposed between the center leg and the wound portion of the wire, or a wound portion of the wire (e.g., an air-core coil) may be disposed around the center leg without disposing a bobbin.

[0019] The coil device may further include a terminal block for holding a lead portion of the wire, The terminal block may be attached to a bobbin, a case that houses the heat dissipating resin, or the first base portion. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic perspective view of a coil device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic exploded perspective view of the coil device shown in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. 1, in which the terminals are omitted. [Figure 4A] FIG. 4A is a schematic cross-sectional view taken along line IV-IV of the core shown in FIG. [Figure 4B] FIG. 4B is a schematic cross-sectional view of a modified example of the core shown in FIG. 4A. [Figure 4C] FIG. 4C is a schematic cross-sectional view of another modified example of the core shown in FIG. 4A. [Figure 4D] FIG. 4D is a schematic cross-sectional view of still another modified example of the core shown in FIG. 4A. [Figure 4E] FIG. 4E is a schematic cross-sectional view of still another modified example of the core shown in FIG. 4A. [Diagram 5] FIG. 5 is a sectional perspective view of a main part of the bobbin shown in FIG. [Figure 6] FIG. 6 is a perspective sectional view of a main portion showing a modification of the bobbin shown in FIG. [Figure 7] FIG. 7 is a partially exploded perspective view of the bobbin and the cores shown in FIG. 2, with some of the cores removed, as viewed from a different angle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the contents shown in the drawings are merely schematic and illustrative for understanding the present invention, and the appearance and dimensional ratios may differ from the actual product. In addition, the present invention is not limited to the following embodiment.

[0022] (First embodiment) A coil device 1 according to an embodiment of the present invention shown in Fig. 1 functions as, for example, a leakage transformer and is used in a power supply circuit of an in-vehicle charger or various electric devices. As shown in Fig. 2, the coil device 1 has a core 2, a bobbin 3, a terminal block 7 combined with a connection lower cover 70, and a case 8. In the drawing, the X-axis, the Y-axis, and the Z-axis are mutually perpendicular, and the Z-axis is parallel to the height direction of the coil device 1 (the winding axis direction of the coil). In the following description, for each of the X-axis, the Y-axis, and the Z-axis, the direction toward the center of the coil device 1 is called the inside, and the direction away from the center of the coil device 1 is called the outside.

[0023] 3, a main bulkhead flange 31 for insulating the primary coil and the secondary coil is provided at a midpoint along the Z axis of the tubular portion 30 of the bobbin 3 so as to protrude radially from the outer circumferential surface of the tubular portion 30. A plurality of sub-bulhead flanges 32 are provided at upper positions along the Z axis of the main bulkhead flange 31 so as to protrude radially from the outer circumferential surface of the tubular portion 30 at predetermined intervals along the Z axis. A first wire 4 is wound between the main bulkhead flange 31 and the sub-bulhead flange 32 and between the sub-bulhead flanges 32 to form a first wire winding portion 40.

[0024] Similarly, below the main partition flange 31 along the Z axis, a plurality of sub-partition flanges 32 are provided at predetermined intervals along the Z axis so as to protrude radially from the outer circumferential surface of the tubular portion 30. A second wire 5 is wound in the partition gaps between the main partition flange 31 and the sub-partition flange 32 and in the partition gaps between the sub-partition flanges 32, forming second wire winding portions 50.

[0025] The partition gaps along the Z-axis between the main partition flange 31 and the sub-partition flange 32 and the partition gaps between the sub-partition flanges 32 are formed to be slightly larger than the outer diameter of the first wire 4 or the second wire 5, and each of these partition gaps is a gap that can accommodate only one row of the wire 4 or 5 along the Z-axis. This allows the wire 4 or 5 to be wound orderly around the outer circumferential surface of the tubular portion 30 of the bobbin 3.

[0026] At least one radial notch is formed along the circumferential direction of each of the secondary partition flanges 32, the notch extending from the outer periphery of the flange 32 to the outer periphery of the tubular portion 30. Through this notch, the wire 4 or 5 can be moved along the Z axis to the adjacent partition gap, enabling continuous winding of the wire 4 or 5. The winding method of the wire 4 or 5 is not particularly limited, and examples thereof include normal winding and α winding.

[0027] In this embodiment, the second wire winding portion 50 is disposed below the first wire winding portion 40 along the Z axis, but the opposite is also possible. In this embodiment, for example, the first wire winding portion 40 serves as a primary coil of a transformer, and the second wire winding portion 50 serves as a secondary coil of the transformer, but the opposite is also possible. The first wire winding portion 40 and the second wire winding portion 50 are separated in the Z axis direction by the main bulkhead flange 31, and the coupling coefficient and the like are adjusted.

[0028] In this embodiment, the first wire 4 and the second wire 5 are each made of a conductive wire, and may not be insulated, but are preferably insulated. The type of conductive wire is not particularly limited, and may be a conductive core wire such as a round wire, a rectangular wire, a twisted wire, a Litz wire, or a braided wire. The material of the fusion layer or insulating layer that covers the core wire is not particularly limited, and examples thereof include polyurethane, polyamideimide, polyimide, and polyester.

[0029] In this embodiment, both the first wire 4 and the second wire 5 are made of a self-bonding wire, but only one of them may be a self-bonding wire, or both may be made of other wires. At least one of the first wire winding portion 40 and the second wire winding portion 50 may be a flat coil. The wire diameters of the first wire 4 and the second wire 5 may be the same or different, and are not particularly limited, but are preferably within the range of 1.0 to 3.0 mm, for example.

[0030] Lead portions 41a, 41b are formed on both ends of the first wire 4 constituting the first wire winding portion 40, and the respective lead portions 41a, 41b are drawn out from the first winding portion 40 to the upper side along the Z axis and connected to the respective terminals 6, 6 shown in Fig. 1. Also, lead portions 51a, 51b are formed on both ends of the second wire 5 constituting the second wire winding portion 50 shown in Fig. 3, and the respective lead portions 51a, 51b are drawn out from the second winding portion 50 to the upper side along the Z axis and connected to the respective terminals 6, 6.

[0031] The terminals 6 to which the lead portions 41a, 41b, 51a, 51b are respectively connected are attached to a pair of terminal blocks 7. A wire connection cover 70 is attached to each terminal block 7. By combining the wire connection cover 70 with the terminal block 7, the pair of terminals 6 are fixed to the terminal block 7 at a predetermined interval along the Y axis. The terminal block 7 and the wire connection cover 70 are preferably made of insulating material such as synthetic resin, and may be made of the same insulating material or different insulating materials.

[0032] 1, in this embodiment, the terminal block 7 is attached to the upper end of a side plate 81 of the case 8 together with the wire connection bottom cover 70. For example, the wire connection bottom cover 70 has a bottom plate piece 71 that covers the wire connection parts 61 of the terminals 6 embedded in the terminal block 7 from below along the Z axis, and a side plate piece 72 that is integrally formed substantially perpendicular to the bottom plate 71, and the side plate piece 72 is provided with an attachment groove 73.

[0033] The mounting groove 73 of the side plate piece 72 is shaped to match the shape of the upper end of the side plate 81 so that upper ends 81a of the side plates 81 located on both sides along the X-axis of the case 8 fit into the mounting groove 73 of the side plate piece 72. Each of the connection wire lower covers 70 is attached to the case 8 by the upper ends of the side plates 81 located on both sides along the X-axis of the case 8 fitting into the mounting groove 73 of the side plate piece 72.

[0034] The terminal block 7 is preferably separate from the under-wire connection cover, and when connecting each of the lead parts 41a, 41b, 51a, and 51b to the connection part 61 of the terminal 6, it is easier to work if the under-wire connection cover is separated from the terminal block. Any of the lead parts 41a, 41b, 51a, and 51b is connected to the connection part 61 by crimping, thermocompression bonding, laser welding, soldering, or the like. After any of the lead parts 41a, 41b, 51a, and 51b is connected to the connection part 61 of each terminal 6, the terminal block 7 and the under-wire connection cover 70 are preferably combined and attached to the case 8 and / or the bobbin 3.

[0035] In this embodiment, each terminal 6 is preferably insert molded with respect to the terminal block 7 so that the connection portion 61 and the external connection portion 62 are exposed. Each terminal 6 is fixed to the terminal block 7 so that the connection portion 61 protrudes outward from the terminal block 7 along the X-axis, and the external connection portion 62 protrudes upward from the terminal block 7 along the Z-axis. The external connection portion 62 is a portion that is connected to an external connection terminal (not shown) or a terminal connection recess of a circuit board. The terminal 6 having the connection portion 61 and the external connection portion 62 is formed, for example, by pressing a single metal plate.

[0036] 2, in this embodiment, the core 2 can be disassembled into a first core 21 disposed on the upper side along the Z axis, a second core 22 disposed on the lower side of the first core 21 along the Z axis, and a center leg portion 23 disposed between the first core 21 and the second core 22. In addition, the first core 21 is divided into two first divided cores 21α along the X axis, and similarly, the second core 22 is divided into two second divided cores 22α along the X axis.

[0037] Each of the first divided cores 21α has a flat first base portion 21a and side legs 21b, 21b that protrude downward along the Z axis from both sides of the first base portion 21a along the Y axis. Each of the second divided cores 22α has a flat first base portion 22a and side legs 22b, 22b that protrude upward along the Z axis from both sides of the first base portion 22a along the Y axis.

[0038] In this embodiment, the first divided core 21α and the second divided core 22α are each made of a U-shaped core that is substantially U-shaped in cross section parallel to a plane including the Z-axis and the Y-axis, and have the same shape as each other, but may be different from each other. For example, one core may be a U-shaped core and the other core may be an I-shaped core.

[0039] Before the core retainer 92 is attached to the bobbin 3, the first base portions 21a of the pair of first split cores 21α are attached to the outer surface of the partition flange 32 provided at the upper end of the cylindrical portion 30 of the bobbin 3. The outer surface (upper surface 32a) of the partition flange 32 located at the upper end of the cylindrical portion 30 is provided with a positioning protrusion 33, which makes it possible to form a gap between the adjacent first base portions 21a, 21a. By forming such a gap, it is expected that heat dissipation performance will be improved.

[0040] The second base portions 22a of the pair of second split cores 22α are attached to the outer surface of a partition flange 32 provided at the lower end of the cylindrical portion 30 of the bobbin 3. The outer surface (lower surface 32b) of the partition flange 32 located at the lower end of the cylindrical portion 30 is provided with a positioning protrusion 33, which makes it possible to form a gap between the adjacent second base portions 22a, 22a. By forming such a gap, it is expected that the heat dissipation performance will be improved.

[0041] 2, core guide walls 34 are provided on both sides along the X-axis of partition flange 32 located at the upper end along the Z-axis of tubular portion 30 of bobbin 3. Core holders 92 are disposed on the inside of core guide walls 34. Before each core holder 92 is disposed on the inside of core guide walls 34, center leg portion 23 is first inserted from above in the Z-axis direction into a through hole formed in the inner peripheral surface of tubular portion 30 of bobbin 3.

[0042] Thereafter, the base portion 21a of the first core 21 consisting of a pair of first split cores 21α is placed on the outer surface (upper surface) of the partition flange portion 32 located between the pair of core guide walls 34. The side leg portions 21b of the first core 21 cover the upper portion along the Z axis on both sides along the Y axis of the bobbin 3. Then, inside the core guide wall 34, a core retainer 92 is inserted into the gap between the wall 34 and the core 21.

[0043] As shown in Fig. 7, a partition flange 32 located at the lower end along the Z axis of the tube portion 30 of the bobbin 3 is provided with core guide walls 35 on both sides along the X axis. A base portion 22a of a second core 22 consisting of a pair of second split cores 22α is provided on the outer surface (lower surface) of the partition flange portion 32 located between a pair of core guide walls 34. Side legs 22b of the second core 22 cover the lower portion along the Z axis on both sides along the Y axis of the bobbin 3. A tip portion 22b1 of each side leg 22b is butted against a tip portion 21b1 of a side leg 21b of the first core 21 and joined by an adhesive as necessary.

[0044] On the inner peripheral surface of the partition flange 32 located at the lower end along the Z axis of the tube portion 30 of the bobbin 3, inward convex pieces 36 protruding inward from the inner peripheral surface of the tube portion 30 are formed at a plurality of locations along the circumferential direction. These inward convex pieces 36 protrude from the inner peripheral surface of the tube portion 30 to an extent that they do not block the lower end along the Z axis of the through hole formed by the inner peripheral surface of the tube portion 30, and as shown in FIG. 3, they abut on the lower end outer peripheral portion along the Z axis of the center leg portion 23. As a result, a gap 37 can be formed between the lower end along the Z axis of the center leg portion 23 and the second base portion 22a of the second core 22. A heat dissipating resin 82 is allowed to enter into the gap 37. The interval of the gap 37 can be adjusted by changing the design thickness along the Z axis of the inward convex pieces 36.

[0045] In addition, by adjusting the length of middle leg portion 23 along the Z-axis to be shorter by a predetermined length relative to the height of tube portion 30 along the Z-axis from the inward convex piece 33 to the upper surface 32a of partition flange 32 located at the uppermost end, a gap 38 can be formed between the upper end of middle leg portion 23 along the Z-axis and first base portion 21a of first core 21.

[0046] In this embodiment, the air-opening surface 82a of the heat-dissipating resin 82 filled inside the case 8 is determined in relation to the volume of the middle leg 23 and the like so that the heat-dissipating resin 82 does not enter at least a part of the gap 38 and the middle leg 23 is sufficiently cooled. That is, the air-opening surface 82 is set so that 70% or more, preferably 80% or more, more preferably 90% or more, or 95% or more of the volume of the middle leg 23 is located below the air-opening surface 82a of the heat-dissipating resin 82 and is located lower along the Z axis than the lower surface of the base portion 21a. By configuring in this way, an air layer is formed in the gap 38 so that the heat-dissipating resin 82 does not enter.

[0047] The air-opening surface 82a of the heat-dissipating resin 82 is determined so that the winding portion 50 of the second wire 5 is sufficiently soaked in the heat-dissipating resin 82, and preferably 80% or more, more preferably 95% or more, or substantially 100% or more of the winding portion 40 of the first wire 4 is soaked in the heat-dissipating resin 82. With this configuration, the heat generated in the winding portion 40 or 50 of the wire 4 or 5 is also cooled by the heat-dissipating resin 82. In this embodiment, the heat transferred from the winding portion 40 or 50 of the wire 4 or 5 or the core 2 to the heat-dissipating resin 82 is transferred through the case 8 to a cooling member (for example, a cooling block with a cooling passage) installed on the lower surface of the bottom plate 80 of the case 8, and dissipated. The air-opening surface 82a is a surface formed by pouring the heat-dissipating resin 82 in a fluid state into the case 8 and solidifying the liquid surface.

[0048] In this embodiment, cores 21, 22 and center leg 23 are not particularly limited as long as they are each a core having a magnetic material, and are made of, for example, ferrite, a metallic magnetic material, or a resin containing magnetic powder.

[0049] 1, the case 8 has a substantially rectangular bottom plate 80, and side plates 81 that rise upward along the Z axis from the four sides of the bottom plate 80 to form a bottomed storage space inside, and an upper opening is formed in the upper part along the Z axis. The case 8 is preferably made of a metal such as aluminum that has excellent thermal conductivity, but may also be made of resin.

[0050] Heat dissipating resin 82 is also called potting resin, and is made of silicone resin, urethane resin, epoxy resin, or the like that remains soft even after injection, and the potting resin preferably has a longitudinal elastic modulus of 0.1 to 100 MPa. In this embodiment, for example, heat generated in first winding portion 40, second winding portion 50, and core 2 can be efficiently dissipated from the bottom of case 8 to the outside via heat dissipating resin 82 and case 8, thereby improving the cooling efficiency of coil device 1.

[0051] In addition, the heat dissipating resin 82 may be filled in advance inside the case 8, and then the bobbin (wound with wire) 3 with the core 2 attached as shown in FIG. 2 may be housed inside the case 8, or the heat dissipating resin 82 may be poured into the inside of the case 8 after the bobbin (wound with wire) 3 with the core 2 attached is housed inside the case 8.

[0052] In the coil device 1 according to the present embodiment, as shown in FIG. 3, most of the volume of the middle leg 23 of the core 2 is located below the atmospheric open surface 82a of the heat dissipating resin 82, so that most of the volume of the middle leg 23 and the windings 40, 50 of the wires 4, 5 arranged around the middle leg 23 are cooled by the heat dissipating resin 82, improving heat dissipation. Moreover, since the first base portion 21a is arranged at one end (upper end) of the middle leg 23 along the Z axis with a gap 38 of a predetermined distance therebetween, even if a part of the first base portion 21a is exposed from the heat dissipating resin 82, stress such as thermal expansion force generated in the middle leg 23 is not transmitted to the first base portion 21a. Therefore, excessive thermal stress that could be generated in the first base portion 21a can be reduced.

[0053] Incidentally, conventionally, the core 2 housed inside the case 8 was generally a core in which the base portion 21a, located at the top along the Z axis, and the middle leg portion 23 were integrated together. As a result, when the temperature difference between the base portion 21a and the middle leg portion 23 became large, stress was concentrated particularly in the base portion, which could result in problems such as cracking or chipping of the core.

[0054] In this embodiment, even if the temperature difference between the base portion 21a and the center leg portion 23 becomes large, a gap with an air layer is provided between the base portion 21a and the center leg portion 23, so that stress is less likely to concentrate on the base portion, and the risk of problems such as cracking or chipping of the core can be reduced. According to experiments by the inventors, it was confirmed that the maximum back stress generated in the base portion of the core of this embodiment is reduced by about 25% or more compared to the maximum back stress generated in the base portion of a conventional core.

[0055] In this embodiment, 30% or more, 50% or more, 80% or more, or 95% or more, preferably 100% or more of the volume of the first base portion 21a is exposed from the heat dissipating resin 82. By exposing most of the first base portion 21a, the case 8 that houses the heat dissipating resin 82 can be made smaller, and the amount of the heat dissipating resin 82 can be reduced. Even in this case, the first base portion 21a is disposed at the upper end of the middle leg portion 23 along the Z axis, separated by a predetermined distance 38, so that stress such as thermal expansion force generated in the middle leg portion 23, which is prone to trapping heat, is not transmitted to the first base portion 21a. Therefore, excessive thermal stress that could be generated in the first base portion 21a can be reduced.

[0056] The core 2 may further have a second base portion 22a formed continuously with the other end (lower end) of the middle leg portion 23 along the Z axis, but in this embodiment, the core 2 further has a second base portion 22a arranged at the lower end of the middle leg portion 23 along the Z axis, separated by a gap 37 of a predetermined distance.

[0057] The second base portion 22a is located close to the bottom plate 80, which is the cooling wall surface of the case 8 filled with a heat dissipating resin 82. In this embodiment, since the cooling wall surface of the case 8 is the bottom surface of the case 8, the core 2 is housed inside the case 8 such that the axes of the winding portions 40, 50 of the wires 4, 5 are approximately perpendicular to the bottom surface of the case 8. Note that in another embodiment, when the cooling wall surface of the case 8 is the side surface (side plate 81) of the case 8, the core 2 may be housed inside the case 8 such that the axes of the winding portions 40, 50 of the wires 4, 5 are approximately parallel to the bottom surface of the case 8.

[0058] In this embodiment, an air gap of 1.9 mm or less exists in the gap 38 between the first base portion 21a and the upper end of the middle leg portion 23. The presence of the air gap in which the heat dissipating resin 82 does not enter the gap 38 more reliably prevents stress such as thermal expansion force generated in the middle leg portion 23 from being transmitted to the first base portion 21a. In addition, by setting the gap 38 air gap to a predetermined value or less, it becomes easier to form a magnetic circuit between the middle leg 23 and the base portion 21a. As shown in FIG. 4A, the gap 38 gap 38 gap 37 gap 37 gap 37 may be the same or different, but preferably both are 3 mm or less, 2 mm or less, or 1.9 mm or less.

[0059] In this embodiment, the upper end of the center leg 23 may be located below the air-opening surface 82a of the heat dissipating resin 82 along the Z axis. This configuration improves the heat dissipation of the center leg and the wire windings disposed therearound. Even in this case, it is preferable that the air-opening surface 82a is located midway through the gap 38 so that an air layer is formed in the gap 38.

[0060] Alternatively, the upper end of the center leg portion 23 may be located above the atmosphere open surface 82a of the heat dissipating resin 82. With this configuration, an air layer of 1.9 mm or less can be easily formed in the gap 38.

[0061] In this embodiment, the air-opening surface 82a of the heat dissipating resin 82 is located at a position where the heat dissipating resin 82 covers the winding portions 40, 50 of the wires 4, 5 arranged around the middle leg portion 23. By configuring in this manner, the heat dissipation performance is further improved.

[0062] In this embodiment, an adhesive or heat dissipating resin 82 may be at least partially interposed between the lower end of center leg 23 along the Z axis and the surface of second base portion 22a. Also, the lower end of center leg 23 and second base portion 22a may be formed integrally.

[0063] Furthermore, in this embodiment, the tubular portion 30 of the bobbin 3 is arranged between the center leg portion 23 and the winding portions 40, 50 of the wires 4, 5, but the winding portions (e.g., air-core coils) 40, 50 of the wires 4, 5 may be arranged around the center leg portion 23 without placing the bobbin 3.

[0064] In addition, in this embodiment, the coil device 1 further has a terminal block 7 that holds the lead portions 41a, 41b, 51a, and 51b of the wires 4 and 5, and the terminal block 7 is held by the bobbin 3 or the case 8, but may be fixed or attached directly to the first base portion 21a of the core 2.

[0065] Second embodiment As shown in Fig. 6, the coil device of this embodiment is similar to the coil device 1 of the above-described embodiment, except for the following points, and provides similar functions and effects. That is, in this embodiment, a convex frame 39 that continues from the inner peripheral surface of the tube portion 30 is formed around the through hole so as to protrude from the surface of the partition flange 32 located at the top along the Z axis of the bobbin 3. The top surface of the convex frame 39 protrudes, for example, onto the inner surface of the base portion 21a shown in Fig. 3. Therefore, the protruding height of the convex frame 39 also contributes to adjusting the spacing of the gap 38 along the Z axis.

[0066] Due to the presence of this convex frame 39, even if the air-opening surface 82a of the heat dissipating resin 82 is higher than the upper surface 32a of the partition wall flange 32, the heat dissipating resin 82 is less likely to enter the gap 38 from around the convex frame 39, making it easier to form an air layer in the gap. The other configurations and effects are the same as those of the above-mentioned embodiment, and a description of the overlapping parts will be omitted.

[0067] Third embodiment 4B, the coil device of this embodiment is similar to the coil device 1 of the first or second embodiment described above, and provides similar operational effects, except as described below. That is, the coil device of this embodiment has a similar configuration and provides similar operational effects, except that it has a core 2A different from the core 2 of the above-mentioned embodiment.

[0068] Core 2A of this embodiment differs from core 2 of the previously described embodiment in that stepped protrusion 24 is formed on the inner surface of base portion 21a facing the upper end or lower end along the Z axis of center leg portion 23. The protruding height (along the Z axis) of stepped protrusion 24 is not particularly limited, and it is sufficient that a gap 38 or 37 is formed between the tip of stepped protrusion 24 along the Z axis and the upper end or lower end of center leg portion 23.

[0069] However, it is desirable that the protruding height of the stepped protrusion 24 facing the upper end of the middle leg 23 is as small as possible. In order to form an air layer in the gap 38, it is preferable to position the air-opening surface 82a of the heat dissipating resin within the range of height positions along the Z axis of the gap 38, but it is preferable to adjust the protruding height of the stepped protrusion 24 so that the air-opening surface 82a is not too low. The other configurations and effects are the same as those of the above-mentioned embodiment, and a description of the overlapping parts will be omitted.

[0070] (Fourth embodiment) 4C, the coil device of this embodiment is similar to the coil device 1 of the first to third embodiments described above, and provides similar operational effects, except as described below. That is, the coil device of this embodiment has a similar configuration and provides similar operational effects, except that it has a core 2B different from the core 2 or 2A of the embodiments described above.

[0071] The core 2B of this embodiment is different from the core 2 of the above-mentioned embodiment in that the first core 21 has a first base portion 21a independent of the side leg portion 25, and the second core 22 has a second base portion 22a independent of the side leg portion 25. The side leg portion 25 has a configuration in which the side leg portion 21b and the side leg portion 22b facing each other along the Z-axis direction of the above-mentioned embodiment are integrated and separated and independent from the respective base portions 21a and 22a. The other configurations and effects are the same as those of the above-mentioned embodiment, and a description of the overlapping parts will be omitted.

[0072] Fifth embodiment 4D, the coil device of this embodiment is similar to the coil device 1 of the first to fourth embodiments described above, and provides similar operational effects, except as described below. That is, the coil device of this embodiment has a similar configuration and provides similar operational effects, except that it has a core 2C different from the core 2, 2A or 2B of the embodiments described above.

[0073] The core 2C of this embodiment differs from the core 2 of the above-described embodiment in that the lower end of the center leg portion 23C is integrally formed with the second base portion 22a of the second core 22. The other configurations and effects are the same as those of the above-described embodiment, and a description of the overlapping parts will be omitted.

[0074] Sixth embodiment 4E, the coil device of this embodiment is similar to the coil device 1 of the first to fourth embodiments described above, and provides similar operational effects, except as described below. That is, the coil device of this embodiment has a similar configuration and provides similar operational effects, except that it has a core 2D different from the core 2, 2A, 2B, or 2C of the embodiments described above.

[0075] Core 2D of this embodiment differs from core 2B of the embodiment shown in Fig. 4C described above in that the lower end of center leg portion 23C is integrally formed with second base portion 22a of second core 22. Other configurations and effects are similar to those of the above-mentioned embodiment, and description of overlapping parts will be omitted.

[0076] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention.

[0077] For example, in the above-described embodiment, core 2 is configured by combining a core with five divisions and a core with seven divisions, but the number of divisions is not limited to these, and it can also be configured by combining cores with two divisions, three divisions, four divisions, or other numbers of divisions.

[0078] Also, as mentioned above, the bobbin 3 may not be necessary, and an air-core coil consisting of the first wire winding portion 40 and the second wire winding portion 50 may be arranged around the middle leg portion 23 without the bobbin 3 interposed therebetween.

[0079] When the tube portion 30 of the bobbin 3 is not present and the wire winding portion 40 or 50 is disposed directly around the central portion 23 of the core 2, the first wire 4 and the second wire 5 are preferably configured as self-bonding conductive wires having a fusion layer and an insulating layer. Also, the first winding portion 40 around which the first wire 4 is wound and the second winding portion 50 around which the second wire 5 is wound are each preferably formed into a coil shape in advance, and are preferably provided in the form of, for example, an air-core coil.

[0080] The terminal block 7 having the wire connection lower cover 70 may be attached to the case 8, or may be attached directly to the base portion 21a of the core 2 located on the upper side along the Z axis. The means for directly fixing the terminal block 7 to the core 2 is not particularly limited, and examples of the means include adhesion, fusion, and tape fixing, and includes all fixing means other than fixing by a bobbin.

[0081] Furthermore, in the above-described embodiment, for example as shown in Fig. 2, the heat sink divisions 9a, 9a of the heat sink 9 are arranged to cover the base portions 21a, 21a and the side legs 21b, 22b of the core 2, but the configuration of the heat sink 9 is not limited to the example shown in the figure. For example, the heat sink divisions 9a of the heat sink 9 shown in Fig. 2 each have a top plate portion 90 and a side plate portion 91, but the pair of heat sink divisions 9a may be continuous. Alternatively, the heat sink 9 may not be arranged. [Explanation of symbols]

[0082] 1...Coil device 2,2A~2D…Core 21…First core 21α…First split core 21a…First base part 21b...Side leg 21b1...tip 22…Second core 22α…First split core 22a…Second base part 22b...Side leg 22b1...tip 23,23C…middle leg 24…Step-shaped convex part 25...Side leg 3…Bobbin 30...Cylinder part 31…Main bulkhead flange 32...Secondary bulkhead flange 32a…Top end 32b…lower end 33…Positioning protrusion 34,35…Core guide wall 36...Inward convex piece 37,38…Gap 39…Convex frame 4…First wire 40…First wire winding portion 41a, 41b...Lead section 5…Second wire 50...Second wire winding section 51a, 51b...Lead section 6…Terminal 61...Connection section 62…External connection part 7…Terminal block 70…Connection bottom cover 71...Bottom plate piece 72...Side plate piece 73…Mounting groove 8. Case 80...Bottom plate 81…Side panel 81a…Top end 82…Heat dissipating resin 82a…Open to the atmosphere 9…Heat sink 9a…Radiation plate division body 90…Tabletop 91...Side plate part 92…Core holder

Claims

1. A core including a magnetic material; a wire coiled around at least a portion of the core, The core is a middle leg portion on which the wire winding portion is disposed; a first base portion disposed at a predetermined distance from one end of the middle leg portion along a winding axis of the winding portion; A coil device in which 70% or more of the volume of the center leg is located below the atmospheric open surface of the heat dissipation resin.

2. The coil device according to claim 1 , wherein 30% or more of the volume of the first base portion is exposed from the heat dissipation resin.

3. The coil device according to claim 1 , wherein the core further includes a second base portion formed continuously with the other end of the middle leg portion along the winding axis.

4. 2. The coil device according to claim 1, wherein the core further comprises a second base portion disposed at a predetermined distance from the other end of the middle leg portion along the winding axis.

5. 5. The coil device according to claim 3, wherein the second base portion is disposed adjacent to a cooling wall surface of a case filled with the heat dissipating resin.

6. The coil device according to claim 1 , wherein an air gap of 1.9 mm or less exists between the first base portion and the one end of the center leg portion.

7. The coil device according to claim 6 , wherein the one end of the center leg portion is located below the air-opening surface of the heat dissipating resin.

8. The coil device according to claim 6 , wherein the one end of the center leg portion is located above the air-opening surface of the heat dissipating resin.

9. 9. The coil device according to claim 7, wherein the surface of the heat dissipating resin open to the atmosphere is located at a position where the heat dissipating resin covers the wound portion of the wire disposed around the center leg.

10. The coil device according to claim 4 , wherein an adhesive or the heat dissipating resin is at least partially interposed between the other end of the center leg portion and the surface of the second base portion.

11. 2. The coil device according to claim 1, wherein a cylindrical portion of a bobbin is disposed between the center leg portion and the wound portion of the wire.

12. 2. The coil apparatus of claim 1, further comprising a terminal block for holding leads of said wires.

13. The coil device according to claim 12 , wherein the terminal block is attached to a bobbin, a case that houses the heat dissipating resin, or the first base portion.

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