JP7550527B2 - Reactor - Google Patents

Description

This disclosure relates to a reactor.

In power supply devices mounted on motor-driven vehicles such as hybrid cars and electric cars, solar power generation devices, etc., reactors are used as components for stepping up and down voltage. It is known that core loss occurs in reactors during voltage conversion, which reduces the efficiency of various devices. As such, reactors are important components for performing voltage conversion with high efficiency, and in recent years, there has been active technological development of reactors, as shown in, for example, Patent Documents 1 to 3. Recently, reactors are used at high currents or high frequencies due to the demand for smaller reactors, and the amount of heat generated by the magnetic core due to core loss increases, making the reactor prone to high temperatures. If the reactor becomes too hot, there is a risk that the magnetic properties will deteriorate and reliability will decrease due to thermal degradation. Therefore, technology to improve heat dissipation is required.

JP 2016-32042 A JP 2008-98292 A JP 2015-53369 A

However, no matter which conventional technology was applied, the improvement in heat dissipation was not necessarily sufficient because resin components such as sealing materials and bobbins were used, and new technology to improve heat dissipation was eagerly desired.
The present disclosure has been made in view of the above-mentioned circumstances, and has an object to improve heat dissipation. The present disclosure can be realized in the following forms.

[1] A core including a core body portion made of a powder magnetic core and a surface layer portion formed on at least a part of the surface of the core body portion;
A coil wound around the outer periphery of the core;
A reactor including a heat dissipation portion that dissipates heat of the core body portion,
The surface layer portion is mainly composed of ceramics,
The surface portion is in contact with the heat dissipation portion.

[2] The reactor described in [1], in which the ceramic contains ceramic particles, and the ceramic particles include particles having a particle diameter smaller than the arithmetic mean roughness Ra of the surface of the core body.

[3] The reactor described in [1] or [2], in which the thickness of the surface layer is 0.1 mm or more and 3 mm or less.

[4] The reactor according to any one of [1] to [3], wherein the core body is formed by joining a plurality of divided bodies together with an inorganic adhesive to form an integrated body.

[5] A reactor according to any one of [1] to [4], in which the surface layer is formed between the coil and the core body.

According to the above configuration [1], the presence of the surface layer portion mainly made of ceramics gives the reactor a higher heat dissipation property than a surface layer portion mainly made of resin. Specifically, when winding a coil around a core, the surface layer portion is required to have a predetermined electrical resistance or more. Generally, ceramics have a higher electrical resistance than resin. Therefore, when the surface layer portion obtains an electrical resistance of a predetermined value or more, the thickness of the surface layer portion mainly made of ceramics can be made thinner than that of the surface layer portion mainly made of resin. Therefore, compared to the surface layer portion mainly made of resin, the reactor having the surface layer portion mainly made of ceramics has a smaller thermal resistance and therefore a higher heat dissipation property.
Furthermore, since the thermal conductivity of the ceramic material itself is generally higher than that of resin, a reactor with a ceramic surface layer has higher heat dissipation properties than a reactor with a surface layer mainly made of resin.
According to the above configuration [2], the ceramic particles contain particles having a particle diameter smaller than the arithmetic mean roughness Ra of the surface of the core body portion, so that the ceramic particles can penetrate into the fine irregularities on the surface of the core body portion, improving the adhesion between the core body portion and the surface layer portion and smoothing the conduction of heat between the core body portion and the surface layer portion, thereby improving heat dissipation.
According to the above configuration [3], the thermal conductivity of the surface layer is increased to improve heat dissipation, and sufficient electrical resistance of the surface layer can be secured.
According to the above configuration [4], when the core body is made up of a plurality of divided bodies, the divided bodies are bonded to each other with an inorganic adhesive, so that sufficient thermal conductivity can be ensured at the joints.
According to the above-mentioned configuration [5], since the coil and the core body can be insulated by the surface layer of ceramics with high insulation resistance, the coil can be wound directly on the core body, and therefore there is no need to use a resin with low thermal conductivity.

FIG. 4 is a perspective view showing an example of a core body portion. FIG. 2 is a perspective view of an example of a reactor. 3 is a cross-sectional view taken along line XX in FIG. 2. 3 is a schematic diagram of a cross section of a surface of a core body portion. FIG. FIG. 11 is a cross-sectional view of another example of a reactor.

The present invention will be described in detail below. In this specification, when a numerical range is described using "to", it is intended to include the lower limit and the upper limit unless otherwise specified. For example, the description "10 to 20" is intended to include both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Overall Configuration The reactor 1 includes a core 7 including a core body 3 made of a powder magnetic core and a surface layer 5 formed on at least a part of a surface 3A of the core body 3, a coil 9 wound around the outer periphery of the core 7, and a heat dissipation portion 11 that dissipates heat from the core body 3. The surface layer 5 is mainly composed of ceramics. The surface layer 5 is in contact with the heat dissipation portion 11.

(1) Core body portion 3
The core body 3 is a magnetic core. As shown in FIG. 1, the core body 3 is composed of a pair of legs 15, 17 arranged substantially parallel to each other, and a pair of joints 19, 21 connecting the ends of the legs 15, 17. The legs 15, 17 and the joints 19, 21 form a ring-shaped magnetic path. The powder magnetic core constituting the core body 3 is not particularly limited as long as it is made by compacting magnetic powder. The powder magnetic core can reduce core loss in the high frequency band, and is excellent in saturation magnetic flux density, freedom of shape, mass productivity, etc. The magnetic powder used in the powder magnetic core is not particularly limited. For example, pure iron powder, Fe-Si alloy powder, Fe-Ni alloy powder, Fe-Si-Al alloy powder, Fe-Ni-Mo alloy powder, amorphous alloy powder, nanocrystalline alloy powder, etc. can be used as the magnetic powder. The surface of the magnetic powder may be covered with an insulating material. The coating material is not particularly limited, but for example, at least one material selected from the group consisting of phosphoric acid, resin, glass, and alumina materials can be suitably used.
When the core body 3 is composed of a plurality of divided bodies (e.g., the legs 15, 17 and the joints 19, 21), it is preferable that the divided bodies are bonded together with an inorganic adhesive to form an integrated body. Bonding in this manner improves the strength of the core body 3. Bonding with an inorganic adhesive also eliminates gaps between the divided bodies, facilitating heat transfer between the divided bodies, thereby improving heat dissipation.
The inorganic adhesive is not particularly limited. Examples of the inorganic adhesive include an inorganic adhesive mainly composed of silicon dioxide (SiO ₂ ), an inorganic adhesive mainly composed of Al ₂ O ₃ , and an inorganic adhesive mainly composed of ZrO ₂ . Here, the main component refers to a substance whose content (mass %) is 50 mass % or more.

(2) Surface layer 5
The surface layer 5 is mainly composed of ceramics. When the main component of the surface layer 5 is ceramics, the thermal conductivity of the surface layer 5 is improved, and as a result, the heat of the core body 3 is easily transferred to the surface layer 5 and released from the heat dissipation section 11. Since ceramics also have high electrical resistance, the coil 9 can be directly wound around the portion where the surface layer 5 is formed. Here, the main component refers to a substance whose content (mass%) is 50 mass% or more. The content of ceramics in the surface layer 5 is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more. The content of ceramics in the surface layer 5 may be 100 mass%.
The type of ceramic is not particularly limited, but the ceramic is preferably at least one selected from the group consisting of Al ₂ O ₃ , AlN, SiO ₂ , and SiC, from the viewpoint of having high thermal conductivity and high electrical resistance.
In order to improve the strength and heat dissipation of the surface layer 5, it is preferable that the surface layer 5 contains one or more selected from the group consisting of Al ₂ O ₃ and AlN, and the total content of Al ₂ O ₃ and AlN is preferably 50 mass% or more and 99 mass% or less, more preferably 70 mass% or more and 95 mass% or less, and even more preferably 85 mass% or more and 90 mass% or less.
The surface layer portion 5 preferably contains SiO ₂ so that it can be sintered at a low temperature and improves the strength of the surface layer portion 15. When the surface layer portion 5 contains SiO ₂ , the SiO ₂ content is preferably 5 mass% or more and 80 mass% or less, more preferably 10 mass% or more and 50 mass% or less, and even more preferably 15 mass% or more and 45 mass% or less.
When _AlN is used, _Y2O3 may be added as a sintering aid.

The ceramic contains ceramic particles, and the ceramic particles preferably include particles having a particle diameter smaller than the arithmetic mean roughness Ra of the surface 3A of the core body 3. This configuration provides the following effects. As shown in FIG. 4, fine ceramic particles indicated by the symbol A enter the fine recesses on the surface 3A of the core body 3, improving the adhesion between the core body 3 and the surface layer 5. Therefore, the heat of the core body 3 is well transferred to the surface layer 5, and is easily released from the heat dissipation portion 11. The symbol B in FIG. 4 indicates other ceramic particles (e.g., _SiO2 particles) different from the ceramic particles indicated by the symbol A.
The arithmetic mean roughness Ra of the surface of the core body 3 can be measured and calculated using a non-contact laser microscope. The particle size of the ceramic particles can be measured using a particle size distribution meter.

The thickness of the surface layer 5 is not particularly limited. The thickness of the surface layer 5 is preferably 0.1 mm or more and 3 mm or less, more preferably 0.15 mm or more and 1 mm or less, and even more preferably 0.2 mm or more and 0.5 mm or less. By setting the thickness of the surface layer 5 within this range, high thermal conductivity can be obtained and heat dissipation can be improved. Furthermore, by setting the thickness within this range, sufficient electrical resistance can be ensured.

The surface layer 5 may be formed on the surface 3A of the core body 3 via an inorganic primer layer. The inorganic primer layer improves adhesion between the surface layer 5 and the surface 3A of the core body 3. This allows heat from the core body 3 to be efficiently transferred to the surface layer 5 and easily released from the heat dissipation section 11. There are no particular limitations on the inorganic primer layer. A suitable example of the inorganic primer layer is a layer of a hardened silane-based primer.

(3) Coil 9
The coil 9 is wound around the core 7 and is made of a continuous wire, for example a rectangular wire. The coil 9 is preferably an edgewise coil made by winding a rectangular wire in a spiral shape. The configuration of the coil 9 is not limited to an edgewise coil. However, an edgewise coil is preferable from the viewpoint of handling a large current and from the viewpoint of miniaturization of the coil 9. The coil 9 may be wound around the core 7 via a flexible insulating material, such as an insulating sheet.

(4) Heat dissipation section 11
2 and 3, the heat dissipation portion 11 is disposed so as to be in contact with the surface layer portion 5 of the core body portion 3. The material of the heat dissipation portion 11 is not particularly limited, but from the viewpoint of good heat dissipation, it is preferable that the heat dissipation portion 11 is made of a metal, for example, stainless steel, copper, aluminum, tungsten, or molybdenum. The shape of the heat dissipation portion 11 is not particularly limited, and may be appropriately changed depending on the shape of the core body portion 3, etc. The heat dissipation portion 11 is preferably in the form of a flat plate or fin in order to enhance heat dissipation.
5, a coil surface layer 23 may be provided on the surface of the coil 9, so that the coil surface layer 23 comes into contact with the heat dissipation portion 11. The coil surface layer 23 may have the same configuration as the above-mentioned surface layer 5. That is, the above-mentioned explanations of the components, thickness, etc. of the surface layer 5 can be directly applied to the coil surface layer 23. By providing the coil surface layer 23, the heat of the core body 3 is transferred to the heat dissipation portion 11 also through the coil surface layer 23, further improving the heat dissipation performance.

2. Method for forming the surface layer 5 There is no particular limitation on the method for forming the surface layer 5. The surface layer 5 is formed, for example, as follows.
(2.1) Preparation of ceramic slurry for forming surface layer 5 An example of a suitable method for preparing a ceramic slurry is shown below. Ceramic powder is added to a solvent. A dispersant and a binder (for example, at least one selected from the group consisting of PVA (polyvinyl alcohol), acrylic resin, and butyral resin) are added thereto and mixed. The solvent used can be appropriately selected depending on the type of binder, and for example, at least one solvent selected from the group consisting of water, ethanol, toluene, and MEK (methyl ethyl ketone) can be used. The obtained mixture is dispersed and mixed using a known mixing method such as a ball mill to obtain a ceramic slurry.

(2.2) Application of ceramic slurry and firing The ceramic slurry is applied to the molded body that will become the core body 3. The method of application is not particularly limited. Examples of the application method include application with a spatula, dip coating, a dispenser, spray application, and the like.
After application, the coating is dried to volatilize the solvent, and sintering is performed to form the surface layer 5 on the surface of the core body 3 .
The core body 3 is heat-treated at a relatively low temperature of 600° C. to 900° C. Therefore, it is preferable to add silica powder to the ceramic slurry in order to sinter at a low temperature and ensure the strength of the surface layer 5. A coupling agent such as a silane coupling agent or an aluminum coupling agent may be added to the ceramic slurry in order to improve the adhesion between the surface layer 5 and the core body 3, or may be applied to the surface layer 5 in advance.
For ceramics that have a high sintering temperature and cannot be sintered at the same time as the core, a sintered ceramic thin plate (surface layer 5) may be prepared in advance and bonded to the surface of the core body 3 using an inorganic adhesive or the like. The ceramic thin plate can be obtained by forming the ceramic slurry into a sheet by a known method and sintering it.

The present invention will now be described more specifically with reference to examples.
1. Reactor for evaluation (evaluation sample)
Pure iron was used as the magnetic powder.
Table 1 shows the presence or absence of a surface layer and the composition in the examples and comparative examples.
The details of the composition of the surface layer are as follows: The composition of the surface layer can be determined by composition analysis using SEM-EDS.

<Details of the composition of the surface layer>
Example 1 _Al2O3 : _SiO2 = _80:20 (mass ratio)
Example 2 AlN: ( _{Y2O3 + SiO2} ) = 90:10 (mass ratio)
Example 3 AlN: ( _{Y2O3 + SiO2} ) = 90:10 (mass ratio)
Example 4 AlN:( _Y2O3 + _SiO2 )=90 _: 10 (mass ratio)
Comparative Example 1: No surface layer Comparative Example 2: No surface layer

In Example 4, a primer layer using a silane-based primer is formed as a base on the core body, and the surface layer is formed on the primer layer. In the other examples and comparative examples, no primer layer is formed.
Each reactor had a magnetic path length of 0.1 m and a magnetic path volume of 8.6×10 ⁻⁶ m ³ .
The minimum particle size in the surface layer was controlled by the particle sizes of the raw materials Al ₂ O ₃ particles and AlN particles as shown in Table 1. The thickness of the surface layer was controlled by the coating amount of the ceramic slurry as shown in Table 2.
The arithmetic mean roughness Ra of the surface of the core body was controlled by the particle size of the magnetic powder.
The joining method in Table 2 refers to the joining method of the legs in the core body. The legs are bonded with an inorganic adhesive (Examples 3 and 4) or tied with a tie band (Examples 1 and 2, Comparative Examples 1 and 2) to form the core body.
The core around which the coil is wound is fixed to the heat dissipation part (stainless steel plate) with adhesive.

2. Measurement method (1) Particle diameter of ceramic particles The particle size of the ceramic particles ( _{Al2O3 particles} , AlN particles, _SiO2 particles) used in the surface layer was determined by observing the cross section of the surface layer of each sample with an FE-SEM (e.g., JSM-6330F) and calculating the area-equivalent circle diameter from the particle area, and determining the minimum particle diameter of the ceramic particles in the surface layer.

(2) Arithmetic mean roughness Ra of the surface of the core body
The arithmetic mean roughness Ra of the surface of the core body was measured using a non-contact laser microscope (VR-5000 manufactured by Keyence Corporation) and calculated.

(3) Thermal Conductivity The thermal conductivity of the core body and the surface layer was measured by cutting a rectangular parallelepiped block of each material, measuring 3 cm x 3 cm x 1 cm, and using a thermal conductivity measuring device (TCi manufactured by RIGAKU Corporation).

(4) Thickness of Surface Layer The thickness of the surface layer was measured by observing the cross section of the reactor with a SEM.

3. Evaluation (1) Evaluation method The reactor was evaluated based on the degree of temperature rise when the reactor was operated under specified conditions. The smaller the temperature rise, the higher the efficiency of heat dissipation from the heat dissipation part and the better the heat dissipation performance.
The reactor temperature was measured by installing a thermocouple on the surface of the core that did not face the heat sink and using a data logger. The temperature was measured when the reactor was operated at 0.2 T and 100 kHz. If the enamel on the coil surface turned black, the measurement was not possible.

(2) Evaluation Results The evaluation results are shown in Table 2.
From the results of Examples 1 to 4, it was confirmed that when the surface layer is made of ceramics as the main component, the temperature rise is suppressed and the coil is not damaged.
Among Examples 1 to 4, Examples 2 to 4, which contained ceramic particles with a particle size smaller than the arithmetic mean roughness Ra of the surface of the core body, showed greater suppression of the temperature rise.
Among Examples 1 to 4, in Examples 3 and 4 in which the thickness of the surface layer portion was 0.1 mm or more and 3 mm or less, the temperature rise was more suppressed.

4. Effects of the embodiment The reactor of the embodiment has high heat dissipation properties. That is, the reactor of the embodiment has a surface layer mainly made of ceramic, and therefore has high heat dissipation properties compared to a surface layer mainly made of resin.

The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the claims.
(1) In the above embodiment, an example of the core body 3 having a specific shape is shown, but the shape of the core body is not particularly limited. In Fig. 1, the cross section of the legs 15, 17 is circular, but it may be other shapes, for example, polygonal or elliptical. In Fig. 1, the joints 19, 21 are rectangular parallelepiped, but they may be other shapes. For example, the joints 19, 21 may be rectangular parallelepiped with uneven portions, notches, etc. In addition, the joints 19, 21 may be polygonal prisms.
(2) In the above embodiment, the coil 9 is made of rectangular wire. However, the cross-sectional shape of the wire is not particularly limited. A round wire may be used for the coil 9.

1 ... reactor 3 ... core body portion 3A ... surface 5 ... surface layer portion 7 ... core 9 ... coil 11 ... heat dissipation portion 15 ... leg portion 17 ... leg portion 19 ... joint portion 21 ... joint portion 23 ... coil surface layer portion

Claims (5)

A core including a core body portion made of a powder magnetic core and a surface layer portion formed on at least a part of a surface of the core body portion;
a coil wound around the outer periphery of the core and having a coil surface layer on a surface thereof ;
A reactor including a heat dissipation portion that dissipates heat of the core body portion,
the surface layer portion and the coil surface layer portion are mainly composed of ceramics,
the surface layer portion and the coil surface layer portion are in direct contact with the heat dissipation portion,
The ceramics are two or more types selected from the group consisting of Al ₂ O ₃ , AlN, SiO ₂ , and SiC, and one of the types must be SiO ₂ . The reactor according to claim 1, wherein the ceramic contains ceramic particles, and the ceramic particles include particles having a particle diameter smaller than the arithmetic mean roughness Ra of the surface of the core body. The reactor according to claim 1 or 2, wherein the thickness of the surface layer is 0.1 mm or more and 3 mm or less. The reactor according to any one of claims 1 to 3, wherein the core body is made up of multiple divided bodies that are bonded together with an inorganic adhesive to form an integrated body. The reactor according to any one of claims 1 to 4, wherein the surface layer is formed between the coil and the core body.

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