JP2008098289A - Powder magnetic core and method of manufacturing the same - Google Patents

Abstract

A high magnetic flux density is obtained by reducing hysteresis loss and eddy current loss of a dust core.
A stator core 20 as a dust core is formed by compression molding a composite powder 22 and then sintering as a heat treatment. The composite powder 22 includes a powder 25 mainly composed of soft iron, a metal layer 26 covering the surface 25b of the particles 25a of the powder 25, and an insulating layer 27 covering the surface 26b of the metal layer 26. . The insulating layer 27 includes at least one of glass and metal oxide. The metal layer 26 includes a hard but high-permeability iron alloy. Thereby, the hysteresis loss as the whole powder magnetic core can be further reduced. Even if the high permeability iron alloy is hard, the composite powder 22 is easily deformed as a whole by the relatively soft iron, so that the compression density of the compression molding can be increased, and the powder core has a high magnetic flux density as a whole. Can be achieved. Since the inside of the dust core is finely insulated by the insulating layer 27, eddy current loss can be suppressed.
[Selection] Figure 2

Description

  The present invention relates to a dust core and a method for manufacturing the same.

The dust core is used for products using an electromagnetic action such as a motor and a transformer. As a method of manufacturing a dust core, a technique for obtaining a magnetic core by molding magnetic powder is known (for example, see Patent Document 1). In Patent Document 1, a magnetic core is formed using metal particles made of iron coated with an insulating coating as the above-described magnetic powder. Alternatively, metal particles made of an iron alloy coated with an insulating coating are used as the magnetic powder.
Japanese Patent Laid-Open No. 11-238614

By the way, since a dust core is installed in an alternating magnetic field, loss occurs according to its frequency. There are two types of loss, hysteresis loss proportional to the first order of frequency and eddy current loss proportional to the second order of frequency, and it is desired to reduce both.
Further, as a method for reducing hysteresis loss, it is considered to use a high permeability alloy. However, since the high magnetic permeability alloy is hard, the density of a molded product obtained by compression molding the powder of the high magnetic permeability alloy is lowered, so that a high magnetic flux density cannot be obtained.

  Accordingly, an object of the present invention is to provide a dust core capable of reducing hysteresis loss and eddy current loss and obtaining a high magnetic flux density, and a method of manufacturing the same.

  The powder magnetic core (20) of the present invention is a powder magnetic core formed by compressing and molding the composite powder (22), and the composite powder is composed of a powder (25) containing iron as a main component, A metal layer (26) covering the surface (25b) of the iron-based powder, and an insulating layer (27) covering the surface (26b) of the metal layer. 27a) and / or metal oxide (27b). According to the present invention, since the composite powder has a three-layer structure, for example, an iron alloy that is hard as a metal layer but has a high magnetic permeability, and iron as a main component are provided in the inner portion of the insulating layer. Both soft iron and powder can be used. As a result, the hysteresis loss as a whole of the dust core can be further reduced by the iron alloy having a relatively high magnetic permeability as compared with the conventional dust core made of iron. Moreover, even if the high permeability iron alloy is hard, the composite powder is easily deformed as a whole due to relatively soft iron, so that the compression density of compression molding can be increased, and the conventional one made of a hard iron alloy. Compared with the powder magnetic core, a high magnetic flux density can be achieved as a whole of the powder magnetic core. Furthermore, since the inside of the dust core is finely insulated by the insulating layer, eddy current loss can be suppressed.

  In the present invention, the metal layer may contain at least one of metals (26c) other than iron capable of forming an iron alloy. In this case, when the heat treatment is performed, for example, the above-described metal other than iron diffuses into the powder containing iron as a main component, and the iron alloy having a small hysteresis loss spreads, so that the hysteresis loss can be further reduced. The metal layer may be an iron alloy, or may be a metal other than iron that is a component metal of the iron alloy.

  The dust core of the present invention is a dust core formed by compressing and then heat-treating a composite powder. The composite powder comprises an alloy powder (28) and a surface (28b) of the alloy powder. A coated iron-based layer (29) and an insulating layer coated on the surface of the iron-based layer (29b), the insulating layer comprising at least one of glass and metal oxide It may be characterized by including. According to the present invention, since the composite powder has a three-layer structure, for example, an iron alloy that is hard as an alloy powder but has a high magnetic permeability, and iron as a main component are formed in the inner portion of the insulating layer. It is possible to use soft iron together as the layer. As a result, the hysteresis loss as a whole of the dust core can be further reduced by the iron alloy having a relatively high magnetic permeability as compared with the conventional dust core made of iron. Moreover, even if the high permeability iron alloy is hard, the composite powder is easily deformed as a whole due to relatively soft iron, so that the compression density of compression molding can be increased, and the conventional one made of a hard iron alloy. Compared with the powder magnetic core, a high magnetic flux density can be achieved as a whole of the powder magnetic core. Furthermore, since the inside of the dust core is finely insulated by the insulating layer, eddy current loss can be suppressed.

The alloy powder may contain an iron alloy. In this case, when the heat treatment is performed, the component metal of the iron alloy diffuses into the layer containing iron as a main component, and the region including the iron alloy with less hysteresis loss is expanded, so that the hysteresis loss can be further reduced. .
Further, the production method of the present invention comprises a composite powder comprising a powder containing iron as a main component, a metal layer covering the surface of the powder containing iron as a main component, and an insulating layer covering the surface of the metal layer. A second step of compressing the composite powder obtained in the first step to obtain a green compact (23), and a third step of heat-treating the compressed green compact And a process.

  Further, the production method of the present invention includes a composite powder comprising an alloy powder, a layer mainly composed of iron covering the surface of the alloy powder, and an insulating layer covering the surface of the layer mainly composed of iron. A first step of obtaining a green compact by compression molding the composite powder obtained in the first step, and a third step of heat-treating the green compact thus obtained. It may be characterized by including. By these production methods of the present invention, the above-described dust core of the present invention can be obtained.

  In the above description, the alphanumeric characters in parentheses indicate reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, a description will be given based on the case where the dust core is applied to a steering assisting electric motor of an electric power steering apparatus. Note that the dust core can also be applied to an electric motor for uses other than the electric power steering device and electromagnetic devices other than the electric motor.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus in which the dust core according to the first embodiment of the present invention is applied to an electric motor. Referring to FIG. 1, an electric power steering apparatus 1 includes a steering shaft 4 that transmits a steering torque applied to a steering wheel 3 as a steering member in order to steer a steered wheel 2, and a steering torque from the steering shaft 4. For example, a steering mechanism 5 composed of a rack and pinion mechanism for steering the steered wheels 2, and an intermediate shaft 6 provided between the steering shaft 4 and the steering mechanism 5 as a shaft coupling for transmitting rotation therebetween. And have.

  The steering shaft 4 is inserted into the steering column 7 and is rotatably supported by the steering column 7. The steering column 7 is supported on the vehicle body 9 via a bracket 8. A steering wheel 3 is connected to one end of the steering shaft 4 and is rotatably supported. An intermediate shaft 6 is connected to the other end of the steering shaft 4.

The intermediate shaft 6 includes a power transmission shaft 10, a universal joint 11 provided at one end of the intermediate shaft 6, and a universal joint 12 provided at the other end of the intermediate shaft 6.
The steering mechanism 5 supports a pinion shaft 13 as an input shaft, a rack bar 14 as a steered shaft extending in a lateral direction of the automobile (a direction orthogonal to the straight traveling direction), the pinion shaft 13 and the rack bar 14. And a rack housing 15.

The electric power steering apparatus 1 can obtain a steering assist force according to the steering torque. That is, the electric power steering device 1 includes a torque sensor 16 that detects steering torque, an ECU (Electronic Control Unit) 17 as a control unit, an electric motor 18 for assisting steering, and a deceleration as a gear device. Machine 19.
The ECU 17 controls the electric motor 18 based on a torque detection result detected by the torque sensor 16 or a vehicle speed detection result given from a vehicle speed sensor (not shown).

  When the steering wheel 3 is operated, the steering torque is detected by the torque sensor 16, and the electric motor 18 generates a steering assist force according to the torque detection result and the vehicle speed detection result. The steering assist force is transmitted to the steering mechanism 5 via the speed reducer 19. At the same time, the movement of the steering wheel 3 is also transmitted to the steering mechanism 5. As a result, the steering wheel 2 is steered and the steering is assisted.

  The electric motor 18 includes a motor housing 18a as a frame, an output shaft 18b that is rotatably supported by the motor housing 18a via a bearing (not shown), and an output shaft 18b that rotates integrally with the output shaft 18b. And a cylindrical stator 18d fixed in the motor housing 18a so as to face the outer peripheral surface of the rotor 18c in the radial direction. The electric motor 18 is configured as a brushless motor.

The rotor 18c has a rotor magnet (not shown). The rotor magnet is composed of an annular permanent magnet. Magnetic poles of N poles and S poles are alternately formed on the outer peripheral surface of the rotor magnet at a plurality of locations in the circumferential direction.
The stator 18 d has a single stator core 20 that forms an annular shape as a dust core, and a plurality of coils 21. The stator core 20 has a cylindrical yoke and a plurality of teeth. Specifically, the teeth protrude radially inward from the inner peripheral surface of the yoke, and are equally spaced apart from each other with a predetermined interval in the circumferential direction. Each coil 21 is wound around the teeth of the stator core 20.

2A, 2B, and 2C are schematic views showing a method of manufacturing the stator core as the dust core shown in FIG. 1, and the process proceeds in the order of FIGS. 2A, 2B, and 2C.
The stator core 20 is a first production intermediate and compression-molds a composite powder 22 as a material powder, thereby obtaining a green compact 23 as a second production intermediate, and then the green compact. The body 23 is subjected to a sintering treatment as a heat treatment. In the sintering process, the green compact 23 is sintered into a sintered body 24. The sintered body 24 is an aggregate of a large number of sintered particles 24a as heat-treated powder (particles). These sintered particles 24a are bonded to each other.

A specific manufacturing method includes a first step of obtaining the composite powder 22 (see FIG. 2A), a second step of compressing the composite powder 22 to obtain a green compact 23 (see FIG. 2B), and a green compact. And a third step (see FIG. 2C) in which the body 23 is sintered as a heat treatment. The first, second and third steps are performed in the order described.
First, in the first step, the composite powder 22 is manufactured. The composite powder 22 includes a powder 25 containing iron as a main component, a metal layer 26 covering the surface 25b of particles 25a of the powder 25 containing iron as a main component, and an insulation covering the surface 26b of the metal layer 26. Layer 27. The powder 25 containing iron as a main component has a large number of particles 25a containing iron as a main component. The composite powder 22 is an aggregate of a large number of material particles 22a. These material particles 22a are movable with respect to each other and are not coupled to each other.

  Each material particle 22a is a granular mother particle in the center of the material particle 22a and has a center layer 22b as a first layer. The center layer 22b is formed by forming at least one of the above-described particles 25a mainly composed of iron into a granular shape. The entire surface of the center layer 22b is covered with a metal layer 26 as a second layer. Further, the entire outer surface 26b of the metal layer 26 is covered with an insulating layer 27 as a third layer.

  In the present embodiment, the case where the center layer 22b is composed of a single particle 25a will be described. The particle size of the particles 25a of the powder 25 containing iron as a main component in the composite powder 22 is relatively large, and is set, for example, within a predetermined range in which the median value of the particle size is 150 μm. The particle size of the particles 25a is set to a size within the range of 10 to 1000 times the average particle size of the fine powder of the metal layer 26 described later. The particles 25a containing iron as a main component are, for example, so-called pure iron particles.

Here, as said pure iron, the content rate of iron (Fe) in the powder 25 should just be a value within the range of 99.8%-99.99% by weight ratio. Moreover, as the powder 25 which has the above-mentioned iron as a main component, not only the above-mentioned pure iron but the iron content rate may be steel with less than 99.8%.
The metal layer 26 includes an iron alloy of a soft magnetic material having a high magnetic permeability, and is made of a fine powder of this iron alloy. The fine powder is an aggregate of a large number of relatively small particles 26a which are iron alloy particles. The particle size of the particles 26a is, for example, in the range of 0.1 μm to 10 μm. The fine powder coats the particles 25a of the center layer 22b of the material particles 22a with mechanochemicals. Here, to coat the mechanochemical is to apply a mechanical force and to apply a binding force by a mechanochemical reaction between the particles to coat the fine powder onto relatively large particles.

The iron alloy of the soft magnetic material may be, for example, an alloy containing iron and silicon as main components, an alloy containing iron and cobalt, an alloy containing iron and nickel, or iron and silicon. An alloy containing aluminum as a main component may be used. In the present embodiment, the metal layer 26 will be described in the case where the metal layer 26 is made of fine powder of an iron alloy containing iron and silicon as main components.
The insulating layer 27 includes an insulating glass and is made of a fine powder of this glass. The particle size of the fine powder of the insulating layer 27 is set similarly to the particle size of the fine powder of the metal layer 26. The glass fine powder particles 27a cover the metal layer 26 with mechanochemicals.

  In the second step, the composite powder 22 obtained in the first step is filled in a mold, and the filled composite powder 22 is compression-molded by a compression device with a high-pressure compression force. Thereby, the green compact 23 is obtained. The green compact 23 has a plurality of particles 23a. The material particles 22 a of the composite powder 22 are compressed into particles 23 a of the green compact 23. By being compressed, the particles 23a are coupled to each other, and the gap between the particles 23a is reduced. The particles 23 a have a central layer 23 b including at least one particle 25 a mainly containing iron, a metal layer 26, and an insulating layer 27. The green compact 23 has the same shape as the stator core 20 or a shape approximate to this shape.

  In the third step, the green compact 23 is heated in a sintering furnace at a predetermined sintering time and a predetermined sintering temperature, and the particles 23a of the green compact 23 are bonded to each other. The particles contained in 23a are bonded to each other. As a result, a sintered body 24 is obtained. In addition, with the bonding of the particles in each particle 23a, the component elements of each particle diffuse into the adjacent particles. For example, a component metal of the particle 26a of the metal layer 26, for example, a component metal other than iron, which is a component metal of an iron alloy, diffuses into the particle 25a having iron as a main component of the center layer 23b. As a result, an iron alloy is generated in the center layer 23b. As a result, the particles 25a of the central layer 23b become particles 25c mainly composed of iron and an iron alloy.

By the sintering process, each particle 23 a of the green compact 23 becomes a sintered particle 24 a of the sintered body 24. Each sintered particle 24a includes iron and an iron alloy as a main component, a central layer 24b as a first layer in the center, a metal layer 26 as a second layer covering the surface of the central layer 24b, and the metal And an insulating layer 27 as a third layer covering the outer surface of the layer 26.
Specifically, the center layer 23b of the particles 23a of the green compact 23 becomes the center layer 24b of the sintered particles 24a by the sintering process. Accordingly, the particles 25a containing iron as a main component in the central layer 23b become particles 25c containing iron and an iron alloy as main components in the central layer 24b. Further, the metal layer 26 of the particles 23a of the green compact 23 becomes the metal layer 26 of the sintered particles 24a. The insulating layer 27 of the particles 23a of the green compact 23 becomes the insulating layer 27 of the sintered particles 24a.

  The center layer 24b of the sintered particles 24a includes at least one particle 25c whose main component is iron and an iron alloy. The center layer 24b has a center portion 24b1 made of pure iron and a diffusion portion 24b2 including an iron alloy formed on the surface 24b3 of the center layer 24b. In the diffusion part 24b2, the component metal of the iron alloy of the metal layer 26 of the particles 23a of the green compact 23 is diffused into the iron at a predetermined depth from the surface 24b3.

  The stator core 20 as the powder magnetic core of the present embodiment is a powder magnetic core formed by compressing and molding the composite powder 22 and then heat-treating, and the composite powder 22 includes a powder 25 containing iron as a main component, A metal layer 26 covering the surface 25b of the particles 25a of the powder 25 containing iron as a main component and an insulating layer 27 covering the surface 26b of the metal layer 26 are included. The insulating layer 27 includes glass (corresponding to the particles 27a).

  According to this embodiment, since the composite powder 22 has a three-layer structure, for example, a hard but high-permeability iron alloy as the metal layer 26 and iron are formed on the inner side of the insulating layer 27. Both soft iron and powder 25 as a main component can be used. As a result, the hysteresis loss as a whole of the dust core can be further reduced by the iron alloy having a relatively high magnetic permeability as compared with the conventional dust core made of iron. Moreover, even if the high permeability iron alloy is hard, the composite powder 22 is easily deformed as a whole by relatively soft iron, so that the compression density of compression molding can be increased, and the hard powder is made of a hard iron alloy. Compared with a conventional dust core, a high magnetic flux density can be achieved as a whole. Furthermore, since the inside of the dust core is finely insulated by the insulating layer 27, eddy current loss (iron loss) can be suppressed.

  Since the insulating layer 27 includes glass, the insulating layer 27 can withstand a high temperature. As a result, the temperature of the heat treatment can be increased. Therefore, distortion and grain boundaries in the green compact 23 generated during compression molding can be eliminated. As a result, hysteresis loss due to strain and grain boundaries can be reduced. Further, when heat treatment at a high temperature is performed so that the component metal of the iron alloy is diffused, the iron alloy having a high magnetic permeability in the metal layer 26 or the component metal of the iron alloy becomes the iron particles of the center layer 23b. The diffusion part 24b2 as a metal layer that can be diffused to 25a and has little hysteresis loss is expanded. In addition, since the metal layer 26 is coated with mechanochemical, the above-described component metals are easily diffused into the iron particles 25a by high-temperature heat treatment, and hysteresis loss is effectively reduced.

When the metal layer 26 contains an iron alloy, when heat treatment is performed, an iron alloy or a metal component other than iron (for example, silicon) diffuses into the powder 25 containing iron as a main component. Further, since the iron alloy as the metal layer having a small hysteresis loss is formed to be expanded, the hysteresis loss can be further reduced.
In addition, the method for manufacturing a dust core according to the present embodiment includes a powder 25 containing iron as a main component, a metal layer 26 covering the surface 25b of particles 25a of the powder 25 containing iron as a main component, and the metal layer. A first step (see FIG. 2A) for obtaining a composite powder 22 including an insulating layer 27 covering the surface of 26 and compression molding the composite powder 22 obtained in the first step to obtain a green compact 23. A second step (see FIG. 2B) and a third step (see FIG. 2C) in which the compression-molded green compact 23 is heat-treated are included. Thereby, the powder magnetic core of the present embodiment can be obtained.

Further, in the electric motor 18 using the stator core 20 as the dust core of the present embodiment, the iron loss and the hysteresis loss are suppressed to a small amount, so that the heat generation amount can be reduced. As a result, it is possible to suppress the occurrence of a thermal demagnetization phenomenon in which the generated magnetic force decreases due to a high temperature. Further, it is not necessary to restrict the amount of energization in order to suppress the heat generation amount, which contributes to an improvement in output.
Further, by applying such an electric motor to the electric power steering apparatus, it is possible to realize an electric power steering apparatus that is small and has a good steering feeling. Moreover, since the hysteresis loss of the stator core 20 can be reduced, the loss torque when the steering wheel 3 is started to be turned from the steered state (when the motor is not energized) can be reduced. As a result, the steering feeling can be enhanced.

Moreover, the following modifications can be considered about this embodiment. In the following description, differences from the above-described embodiment will be mainly described, and the same components are denoted by the same reference numerals and description thereof is omitted.
For example, in the first embodiment, the central portion 24b1 of the central layer 24b of the sintered particles 24a is made of pure iron, but is not limited thereto. For example, there may be a case where the entire center layer 24b of the sintered particles 24a contains an iron alloy due to the progress of diffusion described above.

  3A, 3B, and 3C are schematic views showing a method of manufacturing a dust core according to the second embodiment of the present invention, and the process proceeds in the order of FIGS. 3A, 3B, and 3C. In the second embodiment, the insulating layer 27 of the composite powder 22 includes a metal oxide having an insulating property instead of the glass of the first embodiment. For example, the insulating layer 27 includes fine powder particles 27b of a metal oxide. An insulating layer 27 covers the metal layer 26 with mechanochemicals. The insulating layer 27 may be made of a metal oxide film (not shown), and this film may be formed on the surface 26b of the metal layer 26 by chemical conversion treatment to cover the surface 26b. Further, the insulating layer 27 may contain both glass and metal oxide. Thus, when a metal oxide is included as the insulating layer 27, the same effects as when glass is included can be obtained. In short, the insulating layer 27 only needs to contain at least one of glass and metal oxide.

4A, 4B, and 4C are schematic views showing a method of manufacturing the stator core 20 as a dust core according to the third embodiment of the present invention, and the processes proceed in the order of FIGS. 4A, 4B, and 4C. . The metal layer 26 of the composite powder 22 of the present embodiment is made of the following powder, and includes the following fine powder particles 26c instead of the fine powder particles 26a of the iron alloy of the first embodiment.
That is, the metal layer 26 is a component metal of each iron alloy as the soft magnetic material described above and is at least one metal other than iron (for example, silicon, cobalt, nickel, which is a component metal of each iron alloy described above, And aluminum)). The fine powder may be a pure metal fine powder of the component metal, an alloy of the component metal and an alloy other than the above-described iron alloy, or a fine powder of a compound containing the component metal. Good.

  For example, when the iron alloy is an alloy containing iron and silicon as main components, the metal layer 26 may be fine silicon powder. When the iron alloy is an alloy containing iron, silicon, and aluminum as main components, the metal layer 26 may be a fine powder of an alloy of silicon and aluminum. In the present embodiment, the case where the metal layer 26 is made of fine powder of silicon, which is a component metal, will be described.

  In the present embodiment, when heat treatment is performed in the third step, the silicon (component metal of the iron alloy) of the particles 26c of the metal layer 26 is iron in the central layer 23b of the particles 23a in the green compact 23. Is diffused into the particles 25a containing as a main component and combined with iron in the particles 25a. Thereby, an iron alloy is generated in the center layer 23b. At the same time, the iron of the particles 25a of the central layer 23b diffuses into the particles 26c of the metal layer 26 and bonds to the silicon of the particles 26a of the metal layer 26. Thereby, an iron alloy is generated in the metal layer 26. As a result, sintered particles 24a of the sintered body 24 are obtained in the same manner as in the first embodiment.

  Thus, in this embodiment, the metal layer 26 is a metal capable of forming an iron alloy having a high magnetic permeability and includes at least one metal other than iron. In this case, when the heat treatment is performed, for example, the above-mentioned metal diffuses into the powder 25 containing iron as a main component, and an iron alloy as a metal layer having a small hysteresis loss is formed and spreads, so that the hysteresis loss is further reduced. can do.

  In addition, as the metal layer 26 of the composite powder 22, the above-described three kinds of fine powder containing the component metals explained in the third embodiment and the four kinds of fine powders of iron alloy explained in the first embodiment are used. You may use at least 2 sorts of fine powder simultaneously. Further, when using at least two kinds of fine powders as described above, these fine powders may be fine powders corresponding to different iron alloys. Further, the metal layer 26 may be only one of the above four types. In short, the metal layer 26 may include at least one of metals other than iron capable of forming an iron alloy having a high magnetic permeability.

  5A, FIG. 5B, and FIG. 5C are schematic views showing a method for manufacturing the stator core 20 as a dust core according to the fourth embodiment of the present invention, and the steps proceed in the order of FIG. 5A, FIG. 5B, and FIG. . The composite powder 22 of the present embodiment covers the alloy powder 28, the iron layer 29 as a layer mainly composed of iron covering the surfaces 28 b of the particles 28 a of the alloy powder 28, and the surface 29 b of the iron layer 29. Insulating layer 27 is included.

  The alloy powder 28 includes an iron alloy of the metal layer 26 of the material particles 22a of the first embodiment, and is made of this iron alloy powder. This powder has a plurality of particles 28a of an iron alloy. The center layer 22b of the material particles 22a of the present embodiment uses an iron alloy instead of the pure iron of the first embodiment, and is configured in the same manner as the center layer 22b of the first embodiment except for this component. Has been. The surface of the center layer 22b is covered with an iron layer 29 as a second layer.

The iron layer 29 is made of fine powder mainly composed of iron. The components of the fine powder are the same as the components of the powder 25 containing iron as a main component in the composite powder 22 of the first embodiment. Regarding the points other than the components, the iron layer 29 is configured in the same manner as the metal layer 26 of the first embodiment.
When the composite powder 22 is compressed, the particles 28a of the alloy powder 28 are included in the center layer 23b of the particles 23a of the green compact 23, and when further heat-treated, the particles 28a of the alloy powder 28 are converted into the sintered body 24. The sintered particles 24a are included in the central layer 24b.

  When the composite powder 22 is compressed, the iron layer 29 covers the center layer 23b of the particles 23a of the green compact 23. When the heat treatment is further performed, the iron layer 29 of the green compact 23 becomes an alloy layer 30 that covers the surface 24b3 of the central layer 24b of the sintered particles 24a of the sintered body 24. That is, in the heat treatment in the third step, the component metal of the iron alloy particles 28a of the central layer 23b of the green compact 23 and different from the iron is the pure iron particles of the iron layer 29 of the green compact 23. It diffuses to 29a. As a result, an iron alloy of the alloy layer 30 is generated. The alloy layer 30 includes a plurality of particles mainly composed of iron and an iron alloy, and these particles are bonded to each other.

  Thus, in this embodiment, the powder magnetic core is a powder magnetic core formed by compressing and then heat-treating the composite powder 22, and the composite powder 22 includes the alloy powder 28 and particles of the alloy powder 28. An iron layer 29 mainly composed of iron covering the surface 28b of 28a, and an insulating layer 27 covering the surface 29b of the iron layer 29 mainly composed of iron. The insulating layer 27 is made of glass (particle 27a corresponds to the above)).

  Since the composite powder 22 has a three-layer structure, for example, a hard but high-permeability iron alloy as the alloy powder 28 and an iron layer 29 containing iron as a main component are formed in a portion inside the insulating layer 27. Can be used together with soft iron. As a result, the hysteresis loss as a whole of the dust core can be further reduced by the iron alloy having a relatively high magnetic permeability as compared with the conventional dust core made of iron. Moreover, even if the high permeability iron alloy is hard, the composite powder 22 is easily deformed as a whole by relatively soft iron, so that the compression density of compression molding can be increased, and the hard powder is made of a hard iron alloy. Compared with a conventional dust core, a high magnetic flux density can be achieved as a whole. Furthermore, since the inside of the dust core is finely insulated by the insulating layer 27, eddy current loss can be suppressed.

The alloy powder 28 contains an iron alloy. In this case, the component metal of the iron alloy diffuses into the iron layer 29 containing iron as a main component during the heat treatment. As a result, the alloy layer 30 is formed as a region including the iron alloy with a small hysteresis loss, and the region including the iron alloy is expanded, so that the hysteresis loss can be further reduced.
In addition, the method for manufacturing a powder magnetic core according to the fourth embodiment includes an alloy powder 28, an iron layer 29 mainly composed of iron covering the surface 28b of the alloy powder 28, and a surface 29b of the iron layer 29. A first step (see FIG. 5A) for obtaining the composite powder 22 including the coated insulating layer 27 and a second step for obtaining the green compact 23 by compression molding the composite powder 22 obtained by the first step. (See FIG. 5B) and a third step (see FIG. 5C) of heat-treating the green compact 23 that has been compression-molded. Thereby, the dust core of the third embodiment can be obtained.

6A, 6B, and 6C are schematic views showing a method of manufacturing a dust core according to the fifth embodiment of the present invention, and the processes proceed in the order of FIGS. 6A, 6B, and 6C. The fifth embodiment is obtained by applying the second embodiment to the fourth embodiment. The insulating layer 27 of the composite powder 22 includes metal oxide fine powder particles 27b having insulating properties similar to those of the second embodiment.
In each of the above-described embodiments, the insulating layer 27 of the composite powder 22 includes at least one of glass and metal oxide. However, the present invention is not limited to this, and material particles that become glass or metal oxide by heat treatment are used. May be included.

  Further, the dust core is not limited to the stator core, and may be, for example, a divided core obtained by dividing the stator core into a plurality of parts in the circumferential direction, or a part of the stator core or a part of the divided core. It may be. In addition, various design changes can be made within the scope of matters described in the claims.

It is a figure showing a schematic structure of an electric power steering device of a 1st embodiment of the present invention. 2A, 2B, and 2C are schematic views showing a method of manufacturing the stator core as the dust core shown in FIG. 1, and the process proceeds in the order of FIGS. 2A, 2B, and 2C. 3A, 3B, and 3C are schematic views showing a method of manufacturing a dust core according to the second embodiment of the present invention, and the process proceeds in the order of FIGS. 3A, 3B, and 3C. 4A, 4B, and 4C are schematic views showing a method of manufacturing a dust core according to the third embodiment of the present invention, and the processes proceed in the order of FIGS. 4A, 4B, and 4C. 5A, 5B, and 5C are schematic views showing a method of manufacturing a dust core according to the fourth embodiment of the present invention, and the processes proceed in the order of FIGS. 5A, 5B, and 5C. 6A, 6B, and 6C are schematic views showing a method of manufacturing a dust core according to the fifth embodiment of the present invention, and the processes proceed in the order of FIGS. 6A, 6B, and 6C.

Explanation of symbols

20 ... stator core (powder magnetic core), 22 ... composite powder, 23 ... green compact, 25 ... powder (powder containing iron as a main component), 25b ... surface, 26 ... metal layer, 26a ... particles (iron alloy), 26b ... (metal layer) surface, 26c ... particles (metal other than iron), 27 ... insulating layer, 27a ... particles (glass), 27b ... particles (metal oxide), 28 ... alloy powder, 28b ... (alloy powder) ) Surface, 29... Iron layer (layer mainly composed of iron), 29 b... (Surface of iron layer)

Claims (6)

A powder magnetic core formed by compression molding a composite powder and then heat-treating,
The composite powder includes a powder containing iron as a main component, a metal layer covering the surface of the powder containing iron as a main component, and an insulating layer covering the surface of the metal layer. A dust core comprising at least one of glass and metal oxide.   2. The dust core according to claim 1, wherein the metal layer includes at least one metal other than iron capable of forming an iron alloy. A powder magnetic core formed by compression molding a composite powder and then heat-treating,
The composite powder includes an alloy powder, a layer containing iron as a main component covering the surface of the alloy powder, and an insulating layer covering the surface of the layer containing iron as a main component. A dust core comprising at least one of glass and metal oxide.   4. The dust core according to claim 3, wherein the alloy powder includes an iron alloy. A first step of obtaining a composite powder comprising a powder containing iron as a main component, a metal layer covering the surface of the iron-based powder, and an insulating layer covering the surface of the metal layer;
A second step of compression molding the composite powder obtained in the first step to obtain a green compact;
And a third step of heat-treating the compacted powder compact. A method for producing a compact magnetic core, comprising: A first step of obtaining a composite powder comprising an alloy powder, a layer mainly composed of iron covering the surface of the alloy powder, and an insulating layer covering the surface of the layer mainly composed of iron;
A second step of compression molding the composite powder obtained in the first step to obtain a green compact;
And a third step of heat-treating the compacted powder compact. A method for producing a compact magnetic core, comprising:

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