JP7724659B2 - Coil Device - Google Patents

Description

This disclosure relates to a coil device.

Conventionally, the cores of coil devices that make up inductors and the like are often formed by compacting a mixed powder whose main components are metal-based magnetic powder or ferrite-based magnetic powder. Cores made from such compacted powder bodies are formed by compacting the mixed powder in a press and then heat-treating or sintering it at a predetermined temperature.

In coil devices capable of handling large currents, larger cores are required as the coils become larger. However, when forming cores using the powder compaction method described above, if the press's pressure capacity is insufficient for the core's size, the necessary mechanical strength cannot be ensured. This poses the problem that the press's pressure capacity hinders the core's size from being increased.

To address the demand for larger sizes while maintaining the core's mechanical strength, cores made from magnetic resin are being considered. Cores made from magnetic resin are made by mixing magnetic powder, such as metal powder, with liquid resin and then hardening it, so they can be formed into the desired shape and size while maintaining mechanical strength.

For example, Patent Document 1 discloses a coil device that includes a magnetic core that is placed inside and outside the coil to form a closed magnetic circuit, with the magnetic core being made of a composite material containing soft magnetic powder and resin. In this coil device, the coil is placed in a resin injection mold, and a molten mixture containing soft magnetic powder and raw resin is injected to integrally mold the coil and magnetic core.

JP 2016-96227 A

However, cores made from magnetic resin, as in Patent Document 1, tend to have lower magnetic permeability and higher core loss than cores made from powder compacts. Therefore, the coil device described in Patent Document 1 has the problem that it is more difficult to improve the magnetic properties of the coil device compared to coil devices with cores made from powder compacts.

This disclosure has been made to solve the above problems, and aims to provide a coil device that can accommodate larger cores and effectively improve magnetic properties.

A coil device according to a first aspect of the present disclosure comprises a cylindrical coil, a columnar inner core arranged inside the coil, and an outer core arranged outside the coil, the inner core being made of a powder compact, the outer core having an outer core arranged along the outer periphery of the coil, and at least the outer core being made of magnetic resin obtained by mixing magnetic powder and liquid resin and then hardening the mixture.

In the coil device according to the present disclosure, a magnetic circuit is formed by a cylindrical inner core placed inside a cylindrical coil and an outer core placed outside the cylindrical coil. The inner core placed inside the coil has a smaller diameter than the outer core, and even when the inner core is made of a powder compact, it is easy to ensure the pressurizing capacity of the press during the molding process. On the other hand, the outer coil placed outside the coil is larger than the inner core. In particular, the portion of the outer core that is placed along the outer periphery of the coil has a larger diameter, and when the outer core is made of a powder compact, it may be difficult to ensure the desired pressurizing capacity.

In this disclosure, at least the outer core, which is positioned along the outer periphery of the coil, is made of magnetic resin. The magnetic resin is formed by mixing magnetic powder with liquid resin and then hardening it, so it can be formed to the desired size while maintaining mechanical strength. This allows for larger cores.

In addition, by constructing the inner core from a powder compact, the magnetic properties of the coil device are effectively improved. In other words, since it is difficult to increase the volume of the inner core placed inside the coil due to space constraints, the magnetic permeability and core loss of the inner core have a significant impact on the magnetic properties of the coil device. Therefore, the inner core is constructed from a powder compact, and the core material, which is the main component in determining the magnetic properties of the coil device, is constructed from a material with high magnetic permeability and low core loss. This optimizes the placement of the core, which is made from a powder compact, and can accommodate larger cores, effectively improving the magnetic properties of the coil device.

FIG. 1 is a perspective view of a coil device according to an embodiment of the present disclosure. 2 is a cross-sectional view of the coil device taken along line II-II in FIG. 1. FIG. 2 is an exploded perspective view of the coil device according to the embodiment. FIG. 2 is a plan view of a coil case according to the embodiment. 1A to 1C are cross-sectional views of coil devices corresponding to Examples A to C of the present disclosure. 10A to 10C are cross-sectional views of coil devices corresponding to Examples D to F of the present disclosure. 10A to 10I are cross-sectional views of a coil device according to another embodiment of the present disclosure. 10A to 10C are cross-sectional views of coil devices corresponding to comparative examples A to C. 10 is a graph showing the magnetic permeability of coil devices corresponding to Examples A to C. 10 is a graph showing core losses of coil devices corresponding to Examples A to C. 10 is a graph showing μ-H characteristics of Example A. 10 is a graph showing the Pcv-Bm characteristics of Example A. 1 is a graph showing the magnetic properties of Example A and Examples D to F.

The coil device 10 according to this embodiment of the present invention will be described below with reference to Figures 1 to 4. For ease of explanation, the directions indicated by the up/down, left/right, and front/rear arrows shown in each figure will be defined as the up/down direction, left/right direction, and front/rear direction, respectively. Furthermore, some reference numerals may be omitted in each figure to make the drawings easier to understand.

As shown in Figures 1 to 4, the coil device 10 of this embodiment constitutes, as an example, a choke coil. The coil device 10 includes a cylindrical coil 20, a coil case 30 that houses the coil 20, and a core 50 that constitutes a magnetic circuit.

The coil 20 is composed of a long, conductive plate material (e.g., copper plate). The coil 20 has a cylindrical winding portion 22 formed by spirally winding the plate material, and a pair of lead-out terminal portions 24A, 24B drawn out from the start and end of the winding portion 22. The pair of lead-out terminal portions 24A, 24B are plate-shaped with the thickness direction extending vertically, and extend parallel to each other radially outward from both axial ends of the winding portion 22. When the coil 20 is housed in the coil case, the cylindrical winding portion 22 is housed inside the coil case 30, and the pair of lead-out terminal portions 24A, 24B are drawn out to the outside of the coil case 30.

The coil case 30 is a box made of an insulating material (e.g., resin). The coil case 30 has a cylindrical portion 32 arranged inside the coil 20 (winding portion 22), a first side wall portion 34 arranged radially outward from the cylindrical portion 32, and a second side wall portion 36 arranged radially outward from the first side wall portion 34.

The tubular portion 32 is formed in a cylindrical shape with its axis extending vertically, and the winding portion 22 of the coil 20 is arranged along the outer peripheral surface of the tubular portion 32. When the core 50 is attached to the coil case 30, a columnar inner core 52 is arranged inside the tubular portion 32. A flange-shaped bottom wall portion 38 is provided at the lower end of the tubular portion 32, extending radially outward from the outer peripheral surface of the tubular portion 32.

The first side wall portion 34 is formed in a cylindrical shape with a larger diameter than the tubular portion 32 and stands upward from the bottom wall portion 38 radially outside the tubular portion 32. The coil case 30 defines a coil accommodating portion 44 that opens to the upper side of the case by the above-mentioned tubular portion 32, bottom wall portion 38, and first side wall portion 34. The tubular winding portion 22 that constitutes the coil 20 is accommodated inside the coil accommodating portion 44. When the winding portion 22 is accommodated in the coil accommodating portion 44, the first side wall portion 34 is disposed along the outer periphery of the coil 20 (winding portion 22), and a pair of lead-out terminal portions 24A, 24B extending from the winding portion 22 are led out to the outside of the coil case 30 via terminal lead-out portions 40A, 40B formed integrally with the first side wall portion 34.

Here, the terminal lead-out portions 40A, 40B are openings formed to communicate between the inside and outside of the coil accommodating portion 44, and are formed in two locations along the circumferential direction of the first side wall portion 34. The two terminal lead-out portions 40A, 40B are composed of a first terminal lead-out portion 40A corresponding to the lead-out terminal portion 24A extending from the axial upper end of the winding portion 22, and a second terminal lead-out portion 40B corresponding to the lead-out terminal portion 24B extending from the axial lower end of the winding portion 22. Furthermore, the first and second terminal lead-out portions 40A, 40B are integrally formed with terminal guide portions 42A, 42B that guide the pair of lead-out terminal portions 24A, 24B, respectively.

The two terminal guide portions 42A, 42B protrude from the coil case 30 and each have a base portion 421A, 421B and a pair of guide walls 422A, 422B. The base portions 421A, 421B are formed like a table that protrudes radially outward from the outer periphery of the coil case 30, covering the undersides of the corresponding draw-out terminal portions 24A, 24B and allowing support from below. The pair of guide walls 422A, 422B extend parallel to each other radially outward from the outer periphery of the coil case 30, covering the side surfaces of the corresponding draw-out terminal portions 24A, 24B from both sides and allowing rotation of the coil 20 to be restricted. Furthermore, by protruding from the coil case 30, the terminal guide portions 42A, 42B are configured to effectively ensure insulation between the draw-out terminal portions 24A, 24B.

The second side wall portion 36 is cylindrical and has a larger diameter than the first side wall portion 34, and is positioned radially outward of the first side wall portion 34. Specifically, the second side wall portion 36 is composed of a first arc portion 36A formed inside the two terminal guide portions 42A, 42B at the front of the case, and a second arc portion 36B formed outside the two terminal guide portions 42A, 42B. The first and second arc portions 36A, 36B are each wall portions that are curved in an arc shape when viewed axially of the coil case 30, and both circumferential ends are connected to the two terminal guide portions 42A, 42B, respectively.

Here, in the coil case 30, the space formed between the first side wall portion 34 and the second side wall portion 36 serves as the core filling portion 46. Specifically, the core filling portion 46 is composed of a first core filling portion 461 formed between the first side wall portion 34 and the first arc portion 36A, and a second core filling portion 462 formed between the first side wall portion 34 and the second arc portion 36B, each of which is a space that penetrates the case in the vertical direction. The first and second core filling portions 461, 462 are filled with magnetic resin that constitutes the outer core 60 (described below) and are integrated with the coil case 30.

Next, the core 50 attached to the coil 20 will be described. The core 50 comprises an inner core 52 arranged inside the coil 20 and an outer core 54 arranged outside the coil 20. As described above, the inner core 52 is formed in a cylindrical shape with its axial direction extending vertically, and when assembled into the coil device 10, it is arranged inside the cylindrical portion 32 of the coil case 30 and inside the winding portion 22 of the coil 20. This inner core 52 is made from a powder compact.

Here, a powder compact is a magnetic body formed by mixing magnetic powder with a powdered binder (binding material) for shape retention, pressurizing the mixed powder, and then sintering or heat treating the resulting powder. In this embodiment, the magnetic powder is composed of a metallic magnetic powder whose main component is iron. Note that, hereinafter, a powder compact made using metallic magnetic powder will be referred to as a "metallic powder compact," and a powder compact made from a magnetic material obtained by sintering ferrite will be referred to as a "ferrite powder sintered compact."

The outer core 54 is composed of three core components: an upper flange core 56, a lower flange core 58, and an outer core 60. The upper flange core 56 and the lower flange core 58 are formed in a disk shape with their thicknesses extending vertically, and are disposed at the upper and lower ends of the inner core 52, respectively. The upper flange core 56 and the lower flange core 58 are each formed with a larger diameter than the inner core 52. When assembled into the coil device 10, the outer peripheries of the upper flange core 56 and the lower flange core 58 protrude in a flange-like manner from the outer periphery of the inner core 52. The upper flange core 56 and the lower flange core 58 are formed from a metal powder compact similar to the inner core 52 described above, and their outer surfaces are coated with an insulating coating 62 (see Figure 2) to ensure insulation from the outside. Note that the coating 62 is omitted from the illustrations of Figures 1 and 3.

The outer core 60 is arranged along the outer periphery of the coil 20 and is formed into a generally cylindrical shape overall. This outer core 60 is made of magnetic resin. Magnetic resin is a magnetic material formed by hardening liquid resin mixed with magnetic powder. In this embodiment, the coil case 30 is formed by injection molding a resin material, and then the liquid magnetic resin is filled into the core filling section 46 (461, 462) of the coil case 30 and hardened. As a result, the magnetic resin filled into the core filling section 46 (461, 462) forms the outer core 60, which is integrated with the coil case 30. When assembled into the coil device 10, the outer core 60 is arranged along the outer periphery of the coil 20 so as to connect the upper flange core 56 and the lower flange core 58. In this state, the outer periphery of the upper flange core 56 is positioned to cover the top surface of the coil 20, so a ring-shaped insulating sheet 70 is placed between the coil 20 and the upper flange core 56 to ensure insulation between the coil 20 and the upper flange core 56.

In this embodiment, the magnetic powder contained in the magnetic resin is, as an example, composed of metal-based magnetic powder whose main component is iron.

In the coil device 10 configured as described above, a magnetic circuit is formed that runs from the inner core 52 through the upper flange core 56, outer flange core 60, and lower flange core 58. In this magnetic circuit, the outer flange core 60, which is arranged along the outer periphery of the coil 20, has the largest outer diameter and a complex cylindrical shape. Therefore, in large coil devices that can handle large currents, if the outer flange core is molded using a typical powder compact, it may be difficult to ensure the press's pressure capacity during pressure molding. In contrast, in this embodiment, the outer flange core 60 is made of magnetic resin, which allows it to be molded into the desired shape and size using methods such as injection molding, while also ensuring mechanical strength.

In cores made from powder compacts, heat treatment can remove processing distortions that occur during molding, making it possible to suppress core loss (magnetic loss). In contrast, cores made from magnetic resins are subject to distortion caused by internal stresses when the liquid resin hardens, making it difficult to suppress core loss. Furthermore, because liquid resin is used as a binder, the interparticle distances in the magnetic powder increase, making it difficult to increase magnetic permeability. Furthermore, the influence of demagnetizing fields increases. Therefore, cores made from magnetic resins tend to have lower magnetic properties, such as permeability and core loss, compared to cores made from powder compacts.

The inventors therefore devised a way to efficiently improve the magnetic properties of a coil device 10 in which the outer core 60 is made of magnetic resin by combining different core materials made of either a powder compact or a magnetic resin. In particular, it is difficult to increase the volume of the inner core placed inside the coil 20 due to space constraints, so it is expected that a decrease in the magnetic properties of the inner core will have a significant impact on the magnetic properties of the entire core. Therefore, by constructing at least the inner core 52 placed inside the coil 20 from a powder compact, as in the above embodiment, they have succeeded in effectively improving the magnetic properties. Below, we will explain the configurations and magnetic properties of Examples A to F of the present disclosure, including the above embodiment.

Figure 5 shows a schematic cross-section of the coil device 10 of Examples A to C, in which the inner core 52 is made of a metal powder compact.

[Example A]
5A, the coil device 10A according to Example A includes a core 50 in which the inner core 52, upper flange core 56, and lower flange core 58 are made of a metal powder compact, and the outer core 60 is made of a magnetic resin. In Example A, the volume ratio of the core portion made of a metal powder compact to the magnetic path length of the magnetic circuit is set to about 73%.

[Example B]
5B, the coil device 10B according to Example B includes a core 50 in which the inner core 52 and the lower flange core 58 are made of a metal powder compact, and the upper flange core 56 and the outer core 60 are made of a magnetic resin. In Example B, the volume ratio of the core portion made of a metal powder compact to the magnetic path length of the magnetic circuit is set to about 50%.

[Example C]
5C, a coil device 10C according to Example C includes a core 50 in which an inner core 52 is made of a metal powder compact, and an upper flange core 56, a lower flange core 58, and an outer core 60 are made of magnetic resin. In Example C, the volume ratio of the core portion made of a metal powder compact to the magnetic path length of the magnetic circuit is set to about 27%.

Here, the magnetic characteristics of Examples A to C will be explained in comparison with Comparative Examples A to C shown in Figure 8. The coil devices 300A to 300C of Comparative Examples A to C have the same basic structure as the coil device 10 of this embodiment, but differ from Examples A to C in that the inner core 302 is made of magnetic resin. In each of the figures shown in Figure 8, components that are the same as those in the coil device 10 are assigned the same numbers and their description will be omitted.

[Comparative Examples A to C]
8A, in the coil device 300A of Comparative Example A, the inner core 302 and the outer core 308 are made of magnetic resin, and the upper flange core 304 and the lower flange core 306 are made of metal powder compacts. In this Comparative Example A, the volume ratio of the metal powder compacts to the magnetic path length is about 46%.
8B , in the coil device 300B of Comparative Example B, the inner core 302, the upper flange core 304, and the outer core 308 are made of magnetic resin, and the lower flange core 306 is made of a metal powder compact. In this Comparative Example B, the volume ratio of the metal powder compact to the magnetic path length is set to about 23%.
8C , in the coil device 300C of Comparative Example C, the inner core 302, the upper flange core 304, the lower flange core 306, and the outer core 308 are made of magnetic resin. In this Comparative Example C, the volume ratio of the metal powder compact to the magnetic path length is set to 0%.

Next, referring to Figure 9, the relationship between the volume ratio of the metal powder compact and the magnetic permeability of the entire core will be explained for Examples A to C, in comparison with Comparative Examples A to C. The horizontal axis of Figure 9 represents the volume ratio [%] of the metal powder compact to the magnetic path length. The vertical axis of Figure 9 represents the magnetic permeability μ [H/m] of the entire core when not energized. As shown in Figure 9, a comparison of the magnetic permeability μ of Examples A to C reveals that the greater the volume ratio of the metal powder compact to the magnetic path length, the more the magnetic permeability μ of the entire core improves.

It can also be seen that the magnetic permeability μ of Examples A to C exceeds that of Comparative Examples A to C across the entire range of values shown in Figure 9. Therefore, for example, comparing the magnetic permeability μ of Example C (Figure 5(C)) and Comparative Example A (Figure 8(A)), the volume ratio of the metal powder compact to the magnetic path length is 27% in Example C, while it is 46% in Comparative Example A. Despite this higher volume ratio than Example C, Example C exhibits a higher magnetic permeability μ of the entire core. Therefore, it can be seen that in Examples A to C, by constructing the inner core 52, which is placed inside the coil 20, from a metal powder compact, the magnetic permeability μ of the entire core is effectively increased compared to Comparative Examples A to C. The relationship between the volume ratio of the metal powder compact and the magnetic permeability of the entire core shown in Figure 9 was similar even when the inner core 52 in Examples A to C was constructed from a ferrite powder sintered compact.

Next, referring to Figure 10, the relationship between the volume ratio of the metal powder compact and the core loss of the entire core will be explained for Examples A to C, comparing them with Comparative Examples A to C. The horizontal axis of Figure 10 represents the volume ratio [%] of the metal powder compact to the magnetic path length. The vertical axis of Figure 10 represents the core loss Pcv [mW/cc] of the entire core. As shown in Figure 10, comparing the core loss Pcv of Examples A to C reveals that the overall core loss Pcv decreases as the volume ratio of the metal powder compact to the magnetic path length increases. Furthermore, throughout the entire range of values shown in Figure 10, the core loss Pcv values of Examples A to C are lower than those of Comparative Examples A to C. Therefore, as can be seen from comparing the core loss Pcv values of Example C (Figure 5(C)) and Comparative Example A (Figure 8(A)), despite the larger volume ratio of the metal powder compact in Comparative Example A, the core loss Pcv value is smaller in Example C. Therefore, in Examples A to C, by constructing the inner core 52, which is placed inside the coil, from a metal powder compact, it is clear that the core loss Pcv of the entire core is more effectively suppressed than in Comparative Examples A to C. Furthermore, the relationship between the volume ratio of the metal powder compact and the core loss of the entire core shown in Figure 10 was similar even when the inner core of Examples A to C was constructed from a sintered ferrite powder compact.

Next, referring to Figure 11, we will explain the μ-H characteristics of Example A, in which the inner core 52 is composed of a powder compact (metal powder compact). The horizontal axis of Figure 11 represents the magnetic field strength H [A/m], and the vertical axis of Figure 11 represents the magnetic permeability μ [H/m] of the entire core. Furthermore, in Figure 11, the μ-H characteristics of Example A are shown by a solid line, and the μ-H characteristics of Comparative Example C are shown by a dashed line. As shown in this figure, Example A exhibits stable high permeability over a wide range, and can maintain high permeability even when a large current flows through the coil. It can also be seen that the magnetic permeability of Example A exceeds that of Comparative Example C across the entire range of values shown in Figure 11.

Next, referring to Figure 12, we will explain the Pcv-Bm characteristics of Example A, in which the inner core 52 is composed of a powder compact (metal powder compact). The horizontal axis of Figure 12 represents magnetic flux density Bm [mT], and the vertical axis of Figure 12 represents core loss Pcv [mW/cc]. Also, in Figure 12, the Pcv-Bm characteristics of Example A are shown by a solid line, and the Pcv-Bm characteristics of Comparative Example C are shown by a dashed line. As shown in this figure, in Example A, the increase in core loss Pcv with increasing magnetic flux density Bm is more gradual than in Comparative Example C. Furthermore, the core loss of Example A is lower than that of Comparative Example C across the entire range of values shown in Figure 11. Therefore, it can be seen that Example A effectively suppresses increases in core loss, even when a large current flows through the coil.

Furthermore, the inventors noticed that, in terms of magnetic permeability and low core loss in the low current range, powder compacts made from ferrite powder sintered compacts generally have better magnetic properties than metal powder compacts, and they considered constructing a magnetic circuit by combining core members made from ferrite powder sintered compacts.

On the other hand, ferrite powder sintered compacts also have magnetic properties that cause their magnetic permeability to decrease when large currents flow. Therefore, by optimizing the combination of a core member made of a metal powder compact, a ferrite powder sintered compact, and a magnetic resin, the inventors succeeded in devising a core 50 configuration that improves magnetic properties and can handle large currents.

Below, with reference to Figure 6, Examples D to F will be described, in which the core 50 is constructed using a metal powder compact, a ferrite powder sintered compact, and a magnetic resin.

[Example D]
As shown in Figure 6 (A), the coil device 10D of Example D includes a core 50 in which the inner core 52 is made of a metal powder compact, the upper flange core 56 and the lower flange core 58 are made of a ferrite powder sintered body, and the outer core 60 is made of a magnetic resin.

[Example E]
As shown in Figure 6 (B), the coil device 10E of Example E includes a core 50 in which the inner core 52 is made of a ferrite powder sintered body, the upper flange core 56 and the lower flange core 58 are made of a metal powder compact, and the outer core 60 is made of a magnetic resin.

[Example F]
As shown in Figure 6 (C), the coil device 10E of Example E includes a core 50 in which the inner core 52, the upper flange core 56, and the lower flange core 58 are made of ferrite powder sintered body, and the outer core 60 is made of magnetic resin.

Next, the magnetic characteristics of Examples D to F will be described with reference to Figure 13. Figure 13 shows a bar graph representing the magnetic characteristics of Example A, in which the core 50 was constructed from a metal powder compact and magnetic resin, and Examples D to F. In Figure 13, for each Example, the solid line represents the magnetic permeability μ0A/m [H/m] of the entire core when the coil 20 is not energized, the dashed line represents the magnetic permeability μ5000A/m [H/m] of the entire core when a current of 5000 amperes is passed through the coil 20, and the dashed-dotted line represents the core loss Pcv [mW/cc] of the entire core.

As shown in Figure 13, the core loss Pcv values for Examples D to F are lower than the core loss Pcv value for Example A, which does not include a ferrite powder sintered compact in the core 50. Therefore, it can be seen that by constructing a portion of the core 50 from a ferrite powder sintered compact, the core loss Pcv can be suppressed.

Furthermore, when comparing the core loss Pcv values for the entire core in Example D and Example E, Example D, in which the upper flange core 56 and lower flange core 58 are made of ferrite powder sintered compact, has a larger volume ratio of ferrite powder sintered compact to the magnetic path length than Example E, in which only the inner core 52 is made of ferrite powder sintered compact. However, since the core loss Pcv value is lower in Example E than in Example D, it can be seen that by placing a ferrite powder sintered compact in the inner core 52, the magnetic properties of the ferrite powder sintered compact are significantly enhanced.

Furthermore, when comparing the core loss Pcv values for Example E and Example F, it can be seen that, compared to Example E, in which only the inner core 52 is composed of a ferrite powder sintered compact, Example F, in which the upper flange core 56 and lower flange core 58 are also composed of a ferrite powder sintered compact in addition to the inner core 52, has an even lower core loss Pcv value.

The above trend is also evident for the magnetic permeability μ0A/m when no current is applied and the magnetic permeability μ5000A/m when a current of 5000 amperes is applied. In other words, the magnetic permeability μ0A/m values of Examples D to F are higher than the magnetic permeability μ0A/m value of Example A, which does not include a ferrite powder sintered compact in the core 50, and this characteristic is more pronounced when a ferrite powder sintered compact is placed in the inner core 52. Furthermore, in Examples D to F, the magnetic permeability μ5000A/m value when a large current is applied is lower than the magnetic permeability μ5000A/m value of Example A, which does not include a ferrite powder sintered compact in the core 50, and this characteristic is more pronounced when a ferrite powder sintered compact is placed in the inner core 52.

Thus, Examples E and F, in which the inner core 52 is made of a sintered ferrite powder compact, are superior in terms of reducing the core loss Pcv value, but also exhibit a significant magnetic characteristic in which the magnetic permeability decreases significantly when a large current flows, making it difficult to handle large currents. On the other hand, Example D is superior to Example A in terms of the core loss Pcv value and magnetic permeability μ0A/m value, and has a magnetic permeability μ5000A/m value equivalent to Example A. Therefore, it can be seen that the configuration of Example D is optimized from the perspective of improving magnetic properties and handling large currents.

(Action and effect)
As described above, in the coil device 10 of this embodiment, the inner core 52 is made of a pressed powder compact (pressed powder sintered body), and in the outer core, at least the outer core arranged along the outer periphery of the coil is made of magnetic resin, thereby making it possible to accommodate an increase in core size and effectively improve magnetic properties.

In addition, in this embodiment, the outer core 54 is composed of an upper flange core 56, a lower flange core 58, and an outer core 60. Therefore, while the outer core 60 is made of magnetic resin, the materials of the upper flange core 56 and the lower flange core 58 can be changed, allowing the magnetic properties of the outer core 54 to be adjusted.

For example, as shown in Figure 5(B), in the coil device 10B of embodiment B, by constructing the lower flange core 58 from a powder compact and the upper flange core 56 from magnetic resin, it is possible to obtain magnetic characteristics with high magnetic permeability and low core loss compared to a configuration in which the outer core 54 is constructed only from magnetic resin.

Furthermore, as in Example A shown in Figure 5(A) and Example E shown in Figure 6(B), by constructing the upper flange core 56 and the lower flange core 58 from a powder compact made of a metal powder compact, it is possible to improve the magnetic properties corresponding to the magnetic properties of the metal powder compact compared to when the outer core 54 is constructed only from magnetic resin.

Furthermore, as in Example D shown in Figure 6(A) and Example F shown in Figure 6(C), by constructing the upper flange core 56 and the lower flange core 58 from a powder compact made of ferrite powder sintered compact, it is possible to improve the magnetic properties corresponding to the magnetic properties of ferrite powder sintered compact compared to when the outer core 54 is constructed only from magnetic resin.

In addition, in the coil device 10 of this embodiment, the coil case 30 and the outer core 60 are integrated. Specifically, the coil case 30 has a core filling portion 46 between the first side wall portion 34 and the second side wall portion 36, which is positioned radially outward of the first side wall portion 34, and the outer core 60 is integrated with the coil case 30 by filling the core filling portion 46 with magnetic resin. This reduces the clearance between the coil case 30 and the outer core 60, allowing for the miniaturization of the coil device 10. Furthermore, because the side surfaces of the outer core 60 are covered by the side surfaces of the coil case 30, deterioration of the outer core 60 due to rust can be suppressed.

Furthermore, by reducing the clearance between the coil case 30 and the outer core 60, the magnetic path length of the magnetic circuit can be shortened, thereby increasing the AL value of the coil device 10.

[supplementary explanation]
The present embodiment and examples have been described above, but in this disclosure, the core materials used to form the inner core and outer core can be changed in various ways without departing from the spirit of the present disclosure.

For example, the present disclosure includes a coil device 10G according to Example G shown in FIG. 7(A). The coil device 10G has an inner core 52G made of a metal powder compact, and an upper flange core 56G, a lower flange core 58G, and an outer core 60G made of magnetic resin. In the coil device 10G, both axial ends of the cylindrical inner core 52G are inserted into through holes 501 formed in the centers of the ring-shaped upper flange core 56G and lower flange core 58G. Note that the reference numerals for the coil 20 and coil case 30 have been omitted from the drawings in FIG. 7.

The present disclosure also includes a coil device 10H according to Example H shown in Figure 7(B). The coil device 10H has an inner core 52H made from a metal powder compact, and an upper flange core 56H, a lower flange core 58H, and an outer core 60H made from magnetic resin. In the coil device 10H, both axial ends of the columnar inner core 52H are inserted into recesses 502 provided on the opposing surfaces of the disk-shaped upper flange core 56H and lower flange core 58H.

The present disclosure also includes a coil device 10I according to Example I shown in FIG. 7(C). The coil device 10I has an inner core 52I, an upper flange core 56I, and a lower flange core 58I made from a metal powder compact, and an outer core 60I and a frame core 503 made from magnetic resin. In the coil device 10I, ring-shaped frame cores 503 are arranged at both ends of the cylindrical outer core 60I, and the columnar inner core 52I, and the upper flange core 56I and lower flange core 58I arranged at both ends of the inner core 52I are housed inside the frame core 503.

The present disclosure also includes a coil device 10J according to Example J shown in FIG. 7(D). The coil device 10J includes an upper flange core 56J and a lower flange core 58J made of a metal powder compact, and an outer core 60J and a frame core 503 made of magnetic resin. In the coil device 10J, ring-shaped frame cores 503 are disposed at both ends of the cylindrical outer core 60J. Inside the frame core 503, an upper flange core 56J integrally formed with a cylindrical upper inner core 561J and a lower flange core 58J integrally formed with a cylindrical lower inner core 581J are housed. In other words, the inner core disposed inside the coil is integrally formed with the upper flange core 56J and the lower flange core 58J. In this case, a predetermined gap may be formed between the upper inner core 561J and the lower inner core 581J that constitute the inner core.

The present disclosure also includes a coil device 10K according to Example K shown in Figure 7(E). The coil device 10K has an inner core 52K made from a metal powder compact, an upper flange core 56K and a lower flange core 58K made from a ferrite powder sintered compact, and an outer core 60K and a frame core 503 made from magnetic resin. In the coil device 10K, ring-shaped frame cores 503 are disposed at both ends of the cylindrical outer core 60K, and inside the frame core 503, a columnar inner core 52K is disposed inside the coil, and disk-shaped upper flange cores 56K and lower flange cores 58K are disposed at both ends of the inner core 52K.

The present disclosure also includes a coil device 10L according to Example L shown in FIG. 7(F). The coil device 10L includes an inner core 52L made of a metal powder compact, an upper flange core 56L and a lower flange core 58L made of a ferrite powder sintered compact, and an outer core 60L and a frame core 503 made of magnetic resin. In the coil device 10L, ring-shaped frame cores 503 are disposed at both ends of the cylindrical outer core 60L. A columnar inner core 52L is disposed inside the frame core 503 and inside the coil. The inner core 52L is sandwiched between an upper flange core 56L integrally formed with a columnar upper inner core 561L and a lower flange core 58L integrally formed with a columnar lower inner core 581L.

The present disclosure also includes a coil device 10M according to Example M shown in Figure 7 (G). The coil device 10M includes an inner core 52M made of a metal powder compact, an upper flange core 56M, a lower flange core 58M, and an outer core 60M made of magnetic resin, and a central core 504 made of a sintered ferrite powder compact. In the coil device 10M, the cylindrical inner core 52M is disposed inside the coil, and the ring-shaped upper flange core 56M and lower flange core 58M are disposed at both ends of the inner core 52M. Furthermore, a disk-shaped central core 504 is disposed in through holes 501 formed in the centers of the upper flange core 56M and the lower flange core 58M.

The present disclosure also includes a coil device 10N according to Example N shown in Figure 7 (H). The coil device 10N has an inner core 52N made of a sintered ferrite powder compact, and an upper flange core 56N, a lower flange core 58N, and an outer core 60N made of magnetic resin. In the coil device 10N, the disc-shaped upper flange core 56N and lower flange core 58N are disposed at both ends of the cylindrical inner core 52N.

The present disclosure also includes a coil device 10P according to Example P shown in FIG. 7(I). The coil device 10P includes an upper flange core 56P and a lower flange core 58P made of a sintered ferrite powder compact, and an outer core 60P and a frame core 503 made of magnetic resin. In the coil device 10P, ring-shaped frame cores 503 are disposed at both ends of the cylindrical outer core 60P. Inside the frame core 503, an upper flange core 56P integrally formed with a cylindrical upper inner core 561P and a lower flange core 58P integrally formed with a cylindrical lower inner core 581P are housed. In other words, the inner core disposed inside the coil is integrally formed with the upper flange core 56P and the lower flange core 58P. In this case, a predetermined gap may be formed between the upper inner core 561P and the lower inner core 581P that constitute the inner core.

In the coil case 30 of the above embodiment, the outer core 60 is formed by filling the core filling portion 46 formed between the first side wall portion 34 and the second side wall portion 36 with magnetic resin, but the present disclosure is not limited to this. From the perspective of ensuring insulation between the coil 20 and the outer core 60, the outer core only needs to be configured integrally with the first side wall portion, and the coil case may be configured without a second side wall portion.

The coil device in the above embodiment was a choke coil, but this is not limited thereto. The configuration of the coil device disclosed herein can also be applied to coil devices such as transformers. That is, a primary coil and a secondary coil formed in a cylindrical shape may be stacked and housed in the coil housing portion 44 of the coil case 30 with an insulating member interposed between them.

Furthermore, the coil windings are not limited to copper plates, and may be made of wire or Litz wire. Furthermore, in the embodiments and examples, a metal powder compact containing a magnetic powder primarily composed of iron has been described as an example, but the present disclosure is not limited to this, and metal powder compacts containing known metal-based magnetic powders can be combined as appropriate.

10 Coil device (10A to 10N, 10P)
20 coil 52 inner core 54 outer core 60 outer core 56 upper flange core 58 lower flange core 30 coil case 32 cylindrical portion 34 first side wall portion 36 second side wall portion 46 core filling portion (461, 462)

Claims (3)

A cylindrical coil,
a cylindrical inner core disposed inside the coil;
an outer core disposed outside the coil,
the inner core is formed from a powder compact,
The outer core has an outer core arranged along the outer periphery of the coil, and at least the outer core is made of magnetic resin obtained by mixing magnetic powder and liquid resin and then hardening the mixture ,
the outer core includes a plate-shaped upper flange core and a plate-shaped lower flange core, respectively, disposed at both ends of the inner core, and the outer core, which is disposed along the outer periphery of the coil so as to connect the upper flange core and the lower flange core;
One of the upper flange core and the lower flange core is made of the magnetic resin, and the other of the upper flange core and the lower flange core is made of a powder compact . The outer core is integrally formed with a coil case that houses the coil,
The coil case is
a cylindrical portion around which the coil is wound;
The coil device according to claim 1 , further comprising: a first side wall portion disposed along an outer periphery of the coil and integrated with the outer core. the coil case further includes a second side wall portion disposed radially outward of the first side wall portion, and a core filling portion formed between the first side wall portion and the second side wall portion,
The coil device according to claim 2 , wherein the outer core is formed by filling the core filling portion with a magnetic resin.