Power inductor and its manufacturing method

Abstract

To improve the heat dissipation performance and installation ease of a power inductor. The method for manufacturing a power inductor (1) that is integrally molded by injection molding includes a primary injection molding step in which a coil (2) and a center core (31) are integrated to form a primary molded product (A). forming and a secondary injection molding step of integrating the primary molded product A, the first outer leg core 32, the second outer leg core 33, the first connecting core 34, the second connecting core 35 and the pair of insulating ceramic plates 4 to form a rectangular parallelepiped-shaped power inductor 1.

Description

[Technical Field]

[0001] The present invention relates to a power inductor that is integrally molded by injection molding and a method for manufacturing the same. [Background technology]

[0002] With the trend toward electrification of automobiles, power inductors (reactors) are becoming increasingly important in applications such as high-power battery charging circuits and power conversion circuits from batteries to motor drives. Power inductors for such automotive applications operate at high frequencies and large currents, so they are required to have a heat dissipation structure with low thermal resistance to the heat sink while maintaining insulation between the coil and core or heat sink, and a durable structure that can withstand vehicle vibrations, shocks, heat, and other factors over the long term. In recent years, the mainstream automotive power inductors that meet these requirements are those that are integrally molded using PPS (polyphenylene sulfide) resin or the like (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-243211 Summary of the Invention [Problem to be solved by the invention]

[0004] However, such a power inductor has room for improvement in terms of heat dissipation performance and ease of installation. [Means for solving the problem]

[0005] The present invention was created in view of the above-described circumstances and with the aim of solving these problems. The invention of claim 1 is a power inductor that is integrally molded by injection molding, and comprises a coil that is composed of an edgewise coil in which a rectangular wire is wound at a right angle, and has a pair of parallel flat surfaces and a pair of parallel side surfaces, at least one of the pair of flat surfaces functioning as a heat dissipation surface; a center core that is inserted into the hollow part of the coil; a first outer core that is parallel to the center core and arranged along one of the side surfaces of the coil; and a second outer core that is parallel to the center core and arranged along the other side surface of the coil. The power inductor is characterized by comprising: a first connecting core that connects one ends of the center leg core, the first outer leg core, and the second outer leg core; a second connecting core that connects the other ends of the center leg core, the first outer leg core, and the second outer leg core; an insulating ceramic plate arranged along the heat dissipation surface; a primary molded resin part formed by primary injection molding that integrates the coil and the center leg core to form a primary molded product; and a secondary molded resin part formed by secondary injection molding that integrates the primary molded product, the first outer leg core, the second outer leg core, the first connecting core, the second connecting core, and the insulating ceramic plate to form the rectangular parallelepiped-shaped power inductor. The invention of claim 2 is a method for manufacturing a power inductor integrally molded by injection molding, the power inductor comprising: a coil configured by an edgewise coil wound at right angles with a rectangular wire, the coil having a pair of heat dissipation surfaces parallel to each other and a pair of side surfaces parallel to each other, at least one of the pair of flat surfaces functioning as a heat dissipation surface; a center core inserted through a hollow portion of the coil; a first outer core arranged in parallel with the center core and along one of the side surfaces of the coil; a second outer core arranged in parallel with the center core and along the other side surface of the coil; a first connecting core connecting one ends of the center core, the first outer core, and the second outer core; a second connecting core connecting other ends of the center core, the first outer core, and the second outer core; and an insulating ceramic plate arranged along the heat dissipation surfaces, and the manufacturing method of the power inductor includes a primary injection molding step of integrating the coil and the center core to form a primary molded product.molding and a secondary injection molding step of integrating the primary molded product, the first outer leg core, the second outer leg core, the first connecting core, the second connecting core and the insulating ceramic plate to form the rectangular parallelepiped-shaped power inductor. The invention of claim 3 is a method for manufacturing a power inductor according to claim 2, characterized in that in the primary injection molding step, injection molding is performed while pressing in at least one of the flat surfaces so that the thickness between the pair of flat surfaces of the coil becomes a predetermined thickness. Furthermore, the invention of claim 4 is a manufacturing method of a power inductor as described in claim 2, characterized in that in the secondary injection molding step, injection molding is performed while pressing the first outer leg core, the second outer leg core, the first connecting core, the second connecting core and the insulating ceramic plate toward the primary molded product. The invention of claim 5 is a manufacturing method of a power inductor as defined in claim 2, further comprising a coil lead-out wire bending step of bending one of a pair of coil lead-out wires drawn out from the primary molded product so that the one of the coil lead-out wires is drawn out in the same direction as the other of the coil lead-out wires, and is characterized in that in the secondary injection molding step, injection molding is performed while pressing in a portion of the one of the bent coil lead-out wires to embed it in resin. [Effects of the Invention]

[0006] According to the invention of claim 1 or 2, a rectangular parallelepiped power inductor with excellent installability can be integrally molded by two injection molding processes. Furthermore, the power inductor of the present invention has a coil heat dissipation surface that can be cooled via an insulating ceramic plate, so it can exhibit excellent heat dissipation performance while ensuring insulation. Furthermore, according to the invention of claim 3, in the primary injection molding step, injection molding is performed while pressing in at least one of the planes so that the thickness between the pair of planes of the coil becomes a predetermined thickness, thereby improving the flatness and parallelism of the coil plane, and as a result, increasing the degree of adhesion between the coil plane (coil heat dissipation surface) and the heat sink, thereby improving the cooling efficiency of the power inductor. According to claim 4, in the secondary injection molding step, the first outer leg core, the second outer leg core, the first connecting core, the second connecting core, and the insulating ceramic plate are injection molded while being pressed toward the primary molded product, so the cores are tightly fixed together without any gaps, preventing a decrease in magnetic performance due to gaps between the cores. Also, because the heat dissipation surface of the coil and the insulating ceramic plate are tightly fixed together, a decrease in heat dissipation performance due to gaps can be prevented. According to the invention of claim 5, the method further includes a coil lead-out wire bending step of bending one of a pair of coil lead-out wires drawn out from the primary molded product so that it is drawn in the same direction as the other coil lead-out wire, which facilitates electrical connection of the coil lead-out wires and further improves the installability of the power inductor. Also, in the secondary injection molding step, injection molding is performed while pressing in a portion of one of the bent coil lead-out wires to embed it in resin, thereby improving the insulation of the coil lead-out wires. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of a power inductor according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing components of a power inductor. [Figure 3] FIG. 2 is an explanatory diagram of a primary injection molding step. [Figure 4] FIG. [Figure 5] FIG. 1 is a perspective view showing components of a secondary injection mold. [Figure 6] FIG. 10 is an explanatory diagram of a secondary injection molding step. [Figure 7] FIG. 4 is a perspective view showing a secondary molded resin portion. [Figure 8] FIG. 10 is a perspective view showing a modified example of the center leg core. [Figure 9] FIG. 10 is a perspective view showing a power inductor according to a second embodiment. [Figure 10] FIG. 10 is a perspective view showing a power inductor according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Power inductor] 1 to 7, reference numeral 1 denotes a power inductor integrally molded by injection molding (insert molding) using an insulating resin material such as PPS resin, and the power inductor 1 includes a coil 2, a core body 3, two insulating ceramic plates 4, a primary molded resin portion 5, and a secondary molded resin portion 6.

[0009] The coil 2 is an edgewise coil formed by winding a rectangular wire at a right angle. The coil 2 has a generally rectangular cylindrical shape, and its outer periphery has a pair of parallel heat dissipation surfaces 2a and a pair of parallel side surfaces 2b. The coil 2 also has a first coil lead-out wire 2c extending from one end along the coil central axis and a second coil lead-out wire 2d extending from the other end along the coil central axis. The second coil lead-out wire 2d is longer than the first coil lead-out wire 2c and is bent so as to extend in the same direction as the first coil lead-out wire 2c.

[0010] The core body 3 is configured by combining a center leg core 31, a first outer leg core 32, a second outer leg core 33, a first connecting core 34, and a second connecting core 35.

[0011] The center core 31 is inserted into the hollow portion of the coil 2. The cross section perpendicular to the magnetic flux passage direction of each of the cores 31 to 35 is rectangular, but may be oval or elliptical. In addition, it is desirable that the center core 31 has a plurality of grooves 31a arranged in parallel on both the front and back surfaces thereof along the magnetic flux passage direction (coil insertion direction) in order to promote the fluidity of the resin in the primary injection molding.

[0012] The first outer leg core 32 is arranged along one side surface 2b of the coil 2 so as to be parallel to the center leg core 31. The second outer leg core 33 is arranged along the other side surface 2b of the coil 2 so as to be parallel to the center leg core 31. The first connecting core 34 is arranged to connect one ends of the center leg core 31, the first outer leg core 32, and the second outer leg core 33 to each other. The second connecting core 35 is arranged to connect the other ends of the center leg core 31, the first outer leg core 32, and the second outer leg core 33 to each other. Grooves 34a, 35a are formed in the first connecting core 34 and the second connecting core 35 for drawing out the coil lead wires 2c, 2d.

[0013] The two insulating ceramic plates 4 are arranged along the pair of heat dissipation surfaces 2a of the coil 2. The insulating ceramic plates 4 ensure insulation between the heat dissipation surface 2a of the coil 2 and a heat sink (not shown), while bringing the heat dissipation surface 2a of the coil 2 into close contact with the heat sink with low thermal resistance.

[0014] The primary molded resin portion 5 is formed by primary injection molding, and integrates the coil 2 and the center leg core 31 to form the primary molded product A. Specifically, as shown in Fig. 4, the primary molded resin portion 5 is filled between the inner peripheral surface of the coil 2 and the outer peripheral surface of the center leg core 31 during primary injection molding, and integrates the coil 2 and the center leg core 31 while insulating them from each other.

[0015] The secondary molded resin part 6 is formed by secondary injection molding, and integrates the primary molded product A, the first outer leg core 32, the second outer leg core 33, the first connecting core 34, the second connecting core 35 and the two insulating ceramic plates 4 to form a rectangular parallelepiped-shaped power inductor 1.

[0016] [Manufacturing method of power inductors] Next, a method for manufacturing the power inductor 1 will be described with reference to Figures 3 to 7. However, in the drawings, only the main part of the primary molding die 7 is shown, and the secondary molding die is not shown.

[0017] The manufacturing method of the power inductor 1 is a primary injection molding method in which the coil 2 and the center core 31 are integrated to form a primary molded product A. moldinga coil lead wire bending step in which one of a pair of coil lead wires 2c, 2d drawn out from the primary molded product A, the first outer leg core 32, the second outer leg core 33, the first connecting core 34, the second connecting core 35 and the two insulating ceramic plates 4 are integrated to form a rectangular parallelepiped-shaped power inductor 1.

[0018] According to this manufacturing method of the power inductor 1, a rectangular parallelepiped power inductor 1 with excellent installability can be formed by two injection molding steps. Furthermore, the power inductor 1 has a pair of coil heat dissipation surfaces 2a that can be cooled via the insulating ceramic plates 4, and therefore can exhibit excellent heat dissipation performance while ensuring insulation. Specific examples of each step in the manufacturing method of the power inductor 1 will be described below.

[0019] 3, the primary injection molding step is performed by placing the coil 2 and center leg core 31 in the primary molding die 7, then closing the primary molding die 7 and injecting resin between the coil 2 and the center leg core 31. At this time, in the primary injection molding step of this embodiment, injection molding is performed while pressing in at least one of the heat dissipation surfaces 2a so that the thickness between the pair of heat dissipation surfaces 2a of the coil 2 (thickness after molding) becomes a predetermined thickness W. This improves the flatness and parallelism of the heat dissipation surface 2a of the coil 2 and increases the degree of adhesion between the heat dissipation surface 2a of the coil 2 and the heat sink.

[0020] Specifically, as shown in FIG. 3, the primary molding die 7 includes at least a fixed die 71 having a first surface 71a that positions one end face of the center leg core 31 and a second surface 71b that positions one heat dissipation surface 2a of the coil 2, a first movable die 72 that sandwiches the coil 2 between itself and the second surface 71b of the fixed die 71, and a second movable die 73 that sandwiches the center leg core 31 between itself and the first surface 71a of the fixed die 71.

[0021] In the primary injection molding step, as shown in FIG. 3, the coil 2 and center leg core 31 are placed in a vertical position in the primary molding mold 7, and then the first movable mold 72 and the second movable mold 73 are moved to position the coil 2 and center leg core 31. Furthermore, the first movable mold 72 applies pressure to push in the heat dissipation surface 2a of the coil 2, and finally moves it to the final position shown in FIG. 3.

[0022] The thickness W1 of the coil 2 in its natural state (before primary molding) is slightly larger than the target thickness W after primary injection molding. Therefore, as shown in Figure 4, the shape of the coil 2 is slightly deformed and expanded in the width direction of the coil 2 (the direction between the side surfaces 2b) compared to before primary injection molding due to the pressing of the first movable mold 72. Thereafter, when high-temperature (e.g., around 300°C) PPS resin is poured into the gap between the coil 2 and the center leg core 31, the coil 2 and its coating are instantaneously heated by the resin temperature and soften slightly, so that the shape of the coil 2 also hardens as the resin solidifies, and a pair of heat dissipation surfaces 2a with high flatness and parallelism are created.

[0023] During the primary injection molding step and immediately thereafter, the coil lead wires 2c, 2d are drawn out linearly along the coil central axis direction. In the coil lead wire bending step, one of the pair of coil lead wires 2c, 2d drawn out from the primary molded product A, the coil lead wire 2d, is bent so as to be drawn in the same direction as the other coil lead wire 2c. For example, as shown in Fig. 6, in the second injection molding step, one coil lead wire 2d is bent at multiple locations (e.g., four locations) so as to wrap around the outer peripheries of the first connecting core 34, the first outer leg core 32, and the second connecting core 35 until it approaches the other coil lead wire 2c.

[0024] 5 and 6, the secondary injection molding step is performed by placing the primary molded product A, the first outer leg core 32, the second outer leg core 33, the first connecting core 34, the second connecting core 35, and the two insulating ceramic plates 4 in a secondary mold (not shown), and then closing the secondary mold to inject PPS resin. This secondary injection molding step is performed while pressing the first outer leg core 32, the second outer leg core 33, the first connecting core 34, the second connecting core 35, and the two insulating ceramic plates 4 toward the primary molded product A.

[0025] This secondary injection molding step allows the cores 31-35 to be tightly fixed together without any gaps, preventing a decrease in magnetic performance due to gaps between the cores 31-35. Furthermore, since the heat dissipation surface 2a of the coil 2 and the insulating ceramic plates 4 can be tightly fixed together, a decrease in heat dissipation performance due to gaps can also be prevented. The two insulating ceramic plates 4 are each attached in advance to the heat dissipation surface 2a of the primary molded product A (coil 2) using an adhesive or the like, and are then tightly fixed to the heat dissipation surface 2a by secondary injection molding using PPS resin.

[0026] 6, in the secondary injection molding step, injection molding is performed while pressing multiple locations of the bent one coil lead wire 2d onto the outer periphery of the cores 32, 34, and 35, thereby embedding the base of the one coil lead wire 2d in resin, thereby improving the insulation of the coil lead wire 2d.

[0027] As shown in FIG. 7, the secondary injection molding step forms a rectangular parallelepiped power inductor 1 whose periphery is covered with a secondary molded resin portion 6 or an insulating ceramic plate 4. Circular holes 6a and 6b are formed on the side surfaces of the power inductor 1 as the holes where the cores 32 to 35 and the coil lead wire 2d are pressed. A necessary insulation distance (distance from a heat sink or a metal chassis) is ensured between the circular holes 6a and 6b and the heat dissipation surface of the power inductor 1 (the installation surface of the insulating ceramic plate 4). However, the circular holes 6a and 6b may be filled with an insulating material to improve insulation. The insulation of the coil lead wire 2d can be changed by selecting a coating material for the coil winding (such as an enamel coating, PEEK, or a fluororesin (e.g., Teflon (registered trademark)).

[0028] [Variations] Next, a modified example of the power inductor 1 will be described with reference to Fig. 8. However, for configurations common to the above-described embodiment, the same reference numerals as those in the above-described embodiment will be used, and the description of the above-described embodiment may be used.

[0029] Although the center core 31 in the above-described embodiment does not have a gap, as shown in Fig. 8, a center core 31B having a gap may be used to adjust the characteristics of the power inductor 1. Such a center core 31 can be composed of, for example, a plurality of split cores 31b split in the magnetic flux passage direction and gap spacers 31c connecting the split cores 31b together.

[0030] The present invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the claims.

[0031] For example, in the above-described embodiment, PPS resin was exemplified as the resin material used for integrally molding the power inductor 1, but the resin material used is not limited to PPS resin, and may be resin such as PBT or nylon.

[0032] In addition, in the above-described embodiment, the two flat surfaces of the coil 2 are used as heat dissipation surfaces 2a, and insulating ceramic plates 4 are arranged along each heat dissipation surface 2a to realize an insulating heat dissipation structure, but the heat dissipation surface 2a may be either one of the two flat surfaces of the coil 2.

[0033] Furthermore, the insulating ceramic plate 4 may be used not only to insulate the coil 2 but also to insulate the core body 3 .

[0034] Furthermore, the lead-out paths and lead-out directions of the coil lead wires 2c, 2d are not limited to those in the above-described embodiment. For example, in the above-described embodiment, the coil lead wire 2d is arranged along the outer periphery of the core body 3, but as shown in Fig. 9, the coil lead wire 2d may be arranged along the inner periphery of the core body 3. This not only shortens the length of the coil lead wire 2d, but also reduces the number of bending steps.

[0035] Furthermore, in the above-described embodiment, the coil lead wires 2c, 2d are led out in the direction of the coil central axis, but the coil lead wires 2c, 2d may be led out in a direction perpendicular to the coil central axis, as shown in Fig. 10. In this way, the coil lead wires 2c, 2d can be led out in the same direction without bending the coil lead wire 2d after primary molding. [Explanation of symbols]

[0036] 1. Power inductor 2 coils 2a Heat dissipation surface (flat) 2b side 2c, 2d Coil leader wire 3 Core Body 31, 31B Mid-leg core 31a Groove 31b Split Core 31c Gap spacer 32 First outer leg core 33 Second outer leg core 34 1st linked core 34a groove 35 Second connected core 35a groove 4. Insulating ceramic plate 5 Primary molded resin part 6 Secondary molded resin part 6a, 6b round holes 7 Primary molding die 71 Fixed mold 71a 1st page 71b 2nd side 72 First Movable Mold 73 Second movable mold

Claims

1. A power inductor that is integrally molded by injection molding, a coil formed by an edgewise coil wound with a rectangular wire at a right angle, the coil having a pair of parallel flat surfaces and a pair of parallel side surfaces, at least one of the pair of flat surfaces functioning as a heat dissipation surface; a center core inserted into a hollow portion of the coil; a first outer leg core arranged in parallel with the center leg core and along one of the side surfaces of the coil; a second outer leg core arranged in parallel with the center leg core and along the other side surface of the coil; a first connecting core that connects one end of the center core, the first outer core, and the second outer core; a second connecting core that connects the other ends of the center core, the first outer core, and the second outer core; an insulating ceramic plate disposed along the heat dissipation surface; a primary molded resin portion formed by primary injection molding, which integrates the coil and the center leg core to form a primary molded product; a secondary molded resin portion formed by secondary injection molding, which integrates the primary molded product, the first outer leg core, the second outer leg core, the first connecting core, the second connecting core, and the insulating ceramic plate to form the rectangular parallelepiped-shaped power inductor.

2. A method for manufacturing a power inductor that is integrally molded by injection molding, comprising: The power inductor is a coil formed by an edgewise coil wound with a rectangular wire at a right angle, the coil having a pair of parallel flat surfaces and a pair of parallel side surfaces, at least one of the pair of flat surfaces functioning as a heat dissipation surface; a center core inserted into a hollow portion of the coil; a first outer leg core arranged in parallel with the center leg core and along one of the side surfaces of the coil; a second outer leg core arranged in parallel with the center leg core and along the other side surface of the coil; a first connecting core that connects one end of the center core, the first outer core, and the second outer core; a second connecting core that connects the other ends of the center core, the first outer core, and the second outer core; an insulating ceramic plate disposed along the heat dissipation surface, The method for manufacturing the power inductor includes: a primary injection molding step of integrating the coil and the center leg core to form a primary molded product; a secondary injection molding step of integrating the primary molded product, the first outer leg core, the second outer leg core, the first connecting core, the second connecting core, and the insulating ceramic plate to form the power inductor having a rectangular parallelepiped shape.

3. 3. The method for manufacturing a power inductor according to claim 2, wherein in the primary injection molding step, injection molding is performed while pressing in at least one of the flat surfaces so that the thickness between the pair of flat surfaces of the coil becomes a predetermined thickness.

4. 3. The method for manufacturing a power inductor according to claim 2, wherein in the secondary injection molding step, injection molding is performed while pressing the first outer leg core, the second outer leg core, the first connecting core, the second connecting core, and the insulating ceramic plate toward the primary molded product.

5. a coil lead-out wire bending step of bending one of a pair of coil lead-out wires drawn out from the primary molded product so that the one coil lead-out wire is drawn out in the same direction as the other coil lead-out wire, 3. The method for manufacturing a power inductor according to claim 2, wherein in the secondary injection molding step, injection molding is performed while pushing in a portion of one of the bent coil lead wires to embed the bent coil lead wire in resin.

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