Stator core, stator, rotating electric machine, and method for manufacturing a stator core

Abstract

Provided is a stator core used in an axial-gap dynamo-electric machine, wherein: the stator core has a peripheral surface of each of a plurality of teeth, a first end surface of each of the plurality of teeth, and at least one second end surface on the side opposite from the first end surface; each of the plurality of teeth is configured from a powder magnetic core; the powder magnetic core is provided with a plurality of coated particles; each of the plurality of coated particles has a metal particle and an insulating coating; the first end surface has first regions configured from a cross-section of the metal particles, and second regions configured from the insulating coating between the first regions; the peripheral surface is configured from an oxide including constituent elements of a soft magnetic material; the average thickness of the oxide in the peripheral surface is 10 μm or less; and the difference between the maximum value and the minimum value of a plurality of first heights is 0.02 mm or less.

Description

Technical Field

[0001] The present disclosure relates to a stator core, a stator, a rotating electric machine, and a method for manufacturing a stator core. This application claims priority based on Japanese Patent Application No. 2021-102187 filed on June 21, 2021, and incorporates all the descriptions described in the Japanese application.

Background Art

[0002] Patent Document 1 discloses an axial-gap type rotating electric machine. The axial-gap type rotating electric machine includes a rotor and a stator. The rotor and the stator are arranged facing each other in the axial direction of the rotor. The stator includes a stator core and a plurality of coils.

[0003] The stator core has a yoke and a plurality of teeth. The yoke is an annular plate-shaped member. Each tooth is a columnar member protruding in the axial direction of the yoke. The teeth are arranged spaced apart in the circumferential direction of the yoke. Each coil is arranged on each tooth.

[0004] The stator core is composed of a powder core in which the yoke and the teeth are integrally formed. The powder core is obtained by compression molding a plurality of coated particles. The coated particles have metal particles made of a soft magnetic material and an insulating coating covering the metal particles.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The stator core of the present disclosure is a stator core used in an axial-gap type rotating electric machine, comprising a plurality of columnar teeth arranged on the circumference, The stator core is, Each of the circumferential surfaces of the plurality of teeth, The first end face of each of the plurality of teeth, It has at least one second end face which is the face opposite to the first end face, Each of the aforementioned multiple teeth is composed of a powdered porcelain core, The compacted magnetic core comprises a plurality of coating particles, Each of the plurality of coated particles is Metal particles composed of soft magnetic material, The metal particles are covered by an insulating coating, The first end face is, A first region consisting of the cross-section of the metal particles, The first regions are separated by a second region formed by the insulating coating, The circumferential surface is composed of an oxide containing the constituent elements of the soft magnetic material, The average thickness of the oxide on the circumferential surface is 10 μm or less. The difference between the maximum and minimum values ​​at multiple first heights is 0.02 mm or less. The plurality of first heights is the length between the first end face and the second end face of each of the plurality of teeth.

[0007] The status of this disclosure is, A stator for an axial gap type rotating electric machine, The stator core of this disclosure and The system comprises a coil positioned on each of the aforementioned plurality of teeth.

[0008] The rotating electric machine described herein is An axial gap type rotating electric machine, This disclosure includes the status.

[0009] The method for manufacturing the stator core described herein is: A process of producing a powder molded body by pressure molding multiple coated particles, The process of heat-treating the powder molded body, A step of grinding the heat-treated powder compact is provided. Each of the plurality of coated particles is composed of metal particles made of a soft magnetic material and has an insulating coating covering the metal particles. The powder compact has a plurality of columnar teeth arranged on the circumference. Each of the plurality of teeth has a peripheral surface and a first end surface. The pressure during the pressure molding is 500 MPa or more. Under the conditions of the heat treatment, the atmosphere is an oxidizing atmosphere, the temperature is 350°C or more and 800°C or less. The oxygen concentration in the oxidizing atmosphere is 20,000 ppm or less by volume ratio. The grinding is performed on the first end surface of each of the plurality of teeth without performing it on the peripheral surface of each of the plurality of teeth in the heat-treated powder compact.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic perspective view showing an example of a stator core according to Embodiment 1. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of the powder core in FIG. 1. [Figure 3] FIG. 3 is a schematic cross-sectional view schematically showing the vicinity of the first end surface of a tooth provided in the stator core according to Embodiment 1. [Figure 4] FIG. 4 is a schematic cross-sectional view schematically showing the vicinity of the peripheral surface of a tooth provided in the stator core according to Embodiment 1. [Figure 5] FIG. 5 is a schematic cross-sectional view showing an example of a powder compact produced in Step A in the manufacturing method of the stator core according to Embodiment 1. [Figure 6] FIG. 6 is a schematic cross-sectional view showing an example of a heat-treated body produced in Step B in the manufacturing method of the stator core according to Embodiment 1. [Figure 7] FIG. 7 is an explanatory diagram for explaining an example of Step C in the manufacturing method of the stator core according to Embodiment 1. [Figure 8] FIG. 8 is a schematic perspective view showing an example of a stator core according to Embodiment 2. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX of the dust core of FIG. 8. [Figure 10] FIG. 10 is a schematic perspective view showing an example of a stator according to Embodiment 3. [Figure 11] FIG. 11 is a schematic cross-sectional view showing an example of a rotating electrical machine according to Embodiment 4. [Figure 12] FIG. 12 is a schematic cross-sectional view showing an example of a rotating electrical machine according to Embodiment 5. [Figure 13] FIG. 13 is a schematic cross-sectional view schematically showing a state in which a portion where metal particles are connected to each other is formed near the first end surface of the teeth in the stator core.

MODE FOR CARRYING OUT THE INVENTION

[0011] [PROBLEMS TO BE SOLVED BY THE PRESENT DISCLOSURE] There is a demand for the development of a stator core capable of constructing an axial gap type rotating electrical machine with low noise and vibration and low loss.

[0012] One of the objects of the present disclosure is to provide a stator core and a stator capable of constructing an axial gap type rotating electrical machine with low noise and vibration and low loss. Another object of the present disclosure is to provide an axial gap type rotating electrical machine with low noise and vibration and low loss. Another object of the present disclosure is to provide a method for manufacturing a stator core capable of manufacturing a stator core capable of constructing an axial gap type rotating electrical machine with low noise and vibration and low loss.

[0013] [EFFECTS OF THE PRESENT DISCLOSURE] The stator core and the stator of the present disclosure can construct an axial gap type rotating electrical machine with low noise and vibration and low loss.

[0014] The rotating electrical machine of the present disclosure has low noise and vibration and low loss.

[0015] The method for manufacturing a stator core described herein can produce a stator core that enables the construction of an axial-gap type rotating electric machine with low noise and vibration and low losses.

[0016] Description of Embodiments in this Disclosure The inventors investigated the causes of increased noise and vibration, as well as increased losses, in axial gap type rotating electric machines. As a result, the following was found.

[0017] As mentioned above, the stator core, which is composed of a compacted magnetic core, is manufactured by pressure molding multiple coating particles. In the as-pressure-molded state, it is difficult to achieve a uniform height between the lower surface of the yoke and the end faces of each tooth. If the difference between the maximum and minimum heights is large, the difference between the maximum and minimum gap lengths between the rotor and the end faces of each tooth will be large in an axial-gap type rotating electric machine. A large difference between the maximum and minimum gap lengths increases the noise and vibration of the rotating electric machine.

[0018] Grinding the end faces of each tooth to reduce the difference between the maximum and minimum heights damages the insulating coating of the coating particles near the end faces. Grinding causes the metal particles of the coating particles near the end faces to flow. Exposed metal particles whose insulating coatings are damaged may connect to adjacent exposed metal particles through this flow. When metal particles connect to each other, the loss increases due to an increase in eddy current losses.

[0019] The inventors of this invention have diligently investigated methods for manufacturing stator cores and have obtained the following findings: By performing a specific sequence of steps, in which a powder molded body produced by pressure molding multiple coated particles is heat-treated under specific conditions and then ground, the number of points where metal particles connect to each other as described above can be reduced.

[0020] The present invention is based on the above findings. The embodiments of this disclosure will be described first by listing them.

[0021] (1) A stator core relating to one aspect of this disclosure is: A stator core used in an axial gap type rotating electric machine, It has multiple columnar teeth arranged around the circumference, The stator core is, Each of the circumferential surfaces of the plurality of teeth, The first end face of each of the plurality of teeth, It has at least one second end face which is the face opposite to the first end face, Each of the aforementioned multiple teeth is composed of a powdered porcelain core, The compacted magnetic core comprises a plurality of coating particles, Each of the plurality of coated particles is Metal particles composed of soft magnetic material, The metal particles are covered by an insulating coating, The first end face is, A first region consisting of the cross-section of the metal particles, The first regions are separated by a second region formed by the insulating coating, The circumferential surface is composed of an oxide containing the constituent elements of the soft magnetic material, The average thickness of the oxide on the circumferential surface is 10 μm or less. The difference between the maximum and minimum values ​​at multiple first heights is 0.02 mm or less. The plurality of first heights is the length between the first end face and the second end face of each of the plurality of teeth.

[0022] The above stator core can be used to construct a low-loss axial-gap type rotating electric machine. Each first end face has no connections between adjacent metal particles. A stator core having these first end faces makes it easier to reduce eddy current losses caused by the connection of metal particles when constructing the above rotating electric machine. Furthermore, a compacted magnetic core with an average thickness of oxide on the circumferential surface of 10 μm or less makes it easier to suppress the increase in hysteresis loss when constructing the above rotating electric machine. This is because the amount of oxide that increases hysteresis loss is small when the average thickness of the oxide on the circumferential surface is 10 μm or less. Therefore, the above stator core makes it easier to reduce losses in the above rotating electric machine.

[0023] The above-described stator core facilitates the construction of an axial-gap type rotating electric machine with low noise and vibration. This is because a stator core with a difference of 0.02 mm or less makes it easier to create a uniform gap between the first end face of each tooth and the magnets on the rotor when constructing the above-described rotating electric machine. A rotating electric machine with this uniform gap easily reduces torque ripple. A rotating electric machine with low torque ripple easily reduces noise and vibration. Therefore, the above-described stator core facilitates the reduction of noise and vibration in the above-described rotating electric machine.

[0024] (2) In the stator core described in (1) above, Equipped with a ring-shaped yoke, The aforementioned yoke is Inner surface and, Outer surface and, The upper surface connected to the inner surface, the outer surface, and each of the circumferential surfaces of the plurality of teeth, The lower surface connected to the inner surface and the outer surface, It has, The lower surface is the second end surface, The yoke may be composed of the compacted magnetic core which is integrally molded with the plurality of teeth.

[0025] The above-described stator core is suitable for reducing losses in axial gap type rotating electric machines, specifically in double stator / single rotor type or single stator / single rotor type rotating electric machines.

[0026] (3) In the stator core of (1) or (2) above, The parallelism between the first end face and the second end face of each of the plurality of teeth may be 0.02 mm or less.

[0027] The above-mentioned stator core facilitates the construction of axial-gap type rotating electric machines with low noise and vibration. This is because a stator core with a parallelism of 0.02 mm or less makes it easier to maintain a uniform distance between the first end face of each tooth and the magnets on the rotor when constructing an axial-gap type rotating electric machine.

[0028] (4) In any of the stator cores described in (1) to (3) above, The relative density of the compacted magnetic core may be 90% or higher.

[0029] Compacted magnetic cores with a relative density of 90% or higher are more easily improved in terms of magnetic properties such as saturation magnetic flux density. Compacted magnetic cores with a relative density of 90% or higher are also more easily improved in terms of mechanical properties such as strength.

[0030] (5) In any of the stator cores described in (1) to (4) above, The first end face of each of the plurality of teeth has a third region between the second regions that is composed of an oxide containing the constituent elements of the soft magnetic material, The average depth of the third region may be 100 μm or more.

[0031] The stator core described above, having a third region on its first end face, makes it easier to suppress the bonding of adjacent metal particles. The average depth of the third region being 100 μm or more particularly helps to suppress the bonding of adjacent metal particles. Therefore, the stator core described above makes it easier to reduce eddy current losses when constructing the rotating electric machine described above.

[0032] (6) In any of the stator cores described in (1) to (5) above, The aforementioned metal particles are composed of pure iron or an iron-based alloy. The iron-based alloy may be an Fe-Si alloy, an Fe-Al alloy, or an Fe-Si-Al alloy.

[0033] Metal particles composed of pure iron have a high saturation magnetic flux density. Therefore, a compacted magnetic core containing metal particles composed of pure iron easily achieves an improved saturation magnetic flux density. Furthermore, metal particles composed of pure iron have excellent formability. Therefore, a compacted magnetic core containing metal particles composed of pure iron easily achieves a higher relative density.

[0034] Metal particles composed of iron-based alloys easily reduce iron losses such as eddy current losses. Therefore, powdered magnetic cores containing metal particles composed of iron-based alloys easily reduce losses.

[0035] (7) A stata relating to one aspect of this disclosure is A stator for an axial gap type rotating electric machine, One of the stator cores from (1) to (6) above, The system comprises a coil positioned on each of the aforementioned plurality of teeth.

[0036] Because the stator described above is equipped with the stator core, it is possible to construct an axial-gap type rotating electric machine that has low noise and vibration and low losses.

[0037] (8) A rotating electric machine relating to one aspect of the present disclosure is An axial gap type rotating electric machine, It is equipped with the stator described in (7) above.

[0038] Because the above-mentioned rotating electric machine is equipped with the above-mentioned stator, it has low noise and vibration and low losses.

[0039] (9) A method for manufacturing a stator core according to one aspect of the present disclosure is: A process of producing a powder molded body by pressure molding multiple coated particles, The process of heat-treating the powder molded body, The process includes grinding the heat-treated powder molded body, Each of the plurality of coated particles is Metal particles composed of soft magnetic material, The metal particles are covered by an insulating coating, The powder molded body has a plurality of columnar teeth arranged on its circumference, Each of the plurality of teeth has a circumferential surface and a first end surface, The pressure used during the aforementioned pressure molding is 500 MPa or higher. In the aforementioned heat treatment conditions, the atmosphere is an oxidizing atmosphere, and the temperature is 350°C or higher and 800°C or lower. The oxygen concentration in the aforementioned oxidizing atmosphere is 20,000 ppm or less by volume. The grinding process is performed on the first end face of each of the plurality of teeth in the heat-treated powder molded body, but not on the circumferential surface of each of the plurality of teeth.

[0040] The above method for manufacturing a stator core can produce a compacted magnetic core that can be used to construct a low-loss axial-gap type rotating electric machine. The above method for manufacturing a compacted magnetic core involves grinding a powder molded body that has been heat-treated under specific conditions. Due to the heat treatment under specific conditions, oxides containing the constituent elements of metal particles are formed on the first end face and circumferential surface of the powder molded body. The grinding process after heat treatment removes material from the vicinity of the first end face of the powder molded body. It is thought that the oxides make it easier to suppress the load due to sliding during grinding. Therefore, it is possible to suppress the bonding between adjacent metal particles. The circumferential surface of the powder molded body is not removed by the grinding process after heat treatment. In other words, the above method for manufacturing a compacted magnetic core can produce the above-mentioned compacted magnetic core. If the oxygen concentration is 20,000 ppm or less, it is easier to suppress the increase in hysteresis loss associated with oxidation.

[0041] (10) As one form of the method for manufacturing the stator core described in (9) above, The oxygen concentration in the oxidizing atmosphere may be 500 ppm or more by volume.

[0042] If the oxygen concentration is 500 ppm or higher, it is easier to manufacture a stator core having the first end face and circumferential surface described above.

[0043] (11) As one embodiment of the method for manufacturing the stator core described in (9) or (10) above, The grinding process may be surface grinding.

[0044] Surface grinding facilitates the manufacture of stator cores having the aforementioned first end face.

[0045] Details of the embodiments of this disclosure The embodiments of this disclosure are described below. The same reference numerals in the figures indicate the same parts.

[0046] Embodiment 1 [Stator core] The stator core 1 according to Embodiment 1 will be described with reference to Figures 1 to 7. As shown in Figure 1, the stator core 1 of this embodiment comprises an annular plate-shaped yoke 3 and a plurality of columnar teeth 2. The yoke 3 and the plurality of teeth 2 are made of integrally molded compacted magnetic core. The compacted magnetic core is an aggregate of a plurality of coated particles 100 as shown in Figures 3 and 4. Each coated particle 100 has a metal particle 101 and an insulating coating 102. The insulating coating 102 covers the metal particle 101. One of the features of the stator core 1 of this embodiment is that it satisfies the following requirements (a) and (b). (a) The stator core 1 comprises a specific circumferential surface 21 shown in Figure 4, a specific first end surface 22 shown in Figure 3, and a second end surface 12 which is the surface opposite to the first end surface 22. (b) The difference between the maximum and minimum values ​​of the first height H1 of the stator core 1 shown in Figure 2 is within a specific range.

[0047] [yoke] As shown in Figure 1, the yoke 3 magnetically connects adjacent teeth 2 among the teeth 2 arranged circumferentially on the yoke 3. The shape of the yoke 3 is an annular plate. The yoke 3 has an inner circumferential surface 30i, an outer circumferential surface 30e, a planar upper surface 31, and a planar lower surface 32. The upper surface 31 is connected to the inner circumferential surface 30i, the outer circumferential surface 30e, and the circumferential surface 21 of the teeth 2, which will be described later. The lower surface 32 is connected to the inner circumferential surface 30i and the outer circumferential surface 30e. The lower surface 32 is the second end surface 12 of the stator core 1. Here, "upper" and "lower" refer to the two opposing surfaces of the yoke 3, with the teeth 2 on one surface being called the upper surface, and with the teeth 2 on the other surface being called the lower surface. As will be described later with reference to Figure 11, these "upper" and "lower" surfaces do not necessarily coincide with the "upper" and "lower" surfaces of the rotating electric machine 9 when the stator core 1 is used to construct the rotating electric machine 9. The yoke 3 has an axial hole 39 in its central part that penetrates the upper surface 31 and the lower surface 32.

[0048] The upper surface 31 is not ground, as shown in the manufacturing method of the stator core described later. The unground upper surface 31 is composed of layered oxide 211a, similar to the circumferential surface 21, which will be described later with reference to Figure 4. The lower surface 32 may be ground, as shown in the manufacturing method of the stator core described later, or it may not be ground, similar to the upper surface 31. If it is ground, the difference between the maximum and minimum values ​​of the first height H1, which will be described later with reference to Figure 2, becomes smaller. The ground lower surface 32 has the same configuration as the first end surface 22, which will be described later with reference to Figure 3. The ground lower surface 32 has grinding marks. The grinding marks on the lower surface 32 are similar to the grinding marks 25 shown in Figure 1. The grinding marks 25 will be described later. When a rotating electric machine 9 is constructed using the stator core 1 of this embodiment, as will be described later with reference to Figure 11, the lower surface 32 is in contact with the inner surface of the case 92 shown in Figure 11.

[0049] [Teeth] When constructing the stator 8, which will be described later with reference to Figure 10, the coil 80 is provided on tooth 2. There can be multiple teeth 2. The specific number of teeth 2 can be selected as appropriate. Figure 1 shows an example of a stator core 1 with 6 teeth 2.

[0050] Multiple teeth 2 are arranged circumferentially, as shown in Figure 1. Each tooth 2 is positioned at a predetermined interval in the circumferential direction of the yoke 3. In this embodiment, each tooth 2 is positioned at equal intervals in the circumferential direction of the yoke 3. Each tooth 2 is connected to the upper surface 31. In this embodiment, each tooth 2 and the yoke 3 are formed from a compacted magnetic core that is integrally constructed. No gaps that would form a magnetic gap are created between the yoke 3 and each tooth 2. Therefore, magnetic flux passes smoothly from each tooth 2 to the yoke 3.

[0051] Each tooth 2 is identical in shape and size. Each tooth 2 is either prismatic or cylindrical. Prismatic or cylindrical means that the cross-sectional shape when cut by a plane perpendicular to the axial direction of the tooth 2 is polygonal or circular. The axial direction of the tooth 2 is the direction perpendicular to the lower surface 32. A polygon is, for example, a triangle or a quadrilateral. A triangle is, for example, an equilateral triangle or an isosceles triangle. A quadrilateral is, for example, a trapezoid or a rectangle. A circular shape is, for example, a perfect circle or an ellipse. Polygons and circular shapes include not only geometrically defined corners and circles, but also a range that can be substantially considered as corners and circles. Polygons include, for example, shapes with rounded corners. The above cross-sectional shape is uniform in the axial direction of the tooth 2. Each tooth 2 may be configured in a tapered shape that narrows towards the tip.

[0052] The shape of the teeth 2 in this embodiment is trapezoidal. The cross-sectional shape of the teeth 2 in this embodiment is trapezoidal. The cross-sectional shape of the teeth 2 in this embodiment is uniform in the axial direction of the teeth 2. The trapezoidal shape of the teeth 2 makes it easy to secure a large cross-sectional area. The trapezoidal shape of the teeth 2 makes it easy to reduce the dead space of the stator core 1 and makes it easy to construct a stator 8 with a high space factor.

[0053] Each tooth 2 has a circumferential surface 21 and a first end surface 22. The circumferential surface 21 is the surface surrounding the axis of the tooth 2. The axis of the tooth 2 is parallel to the axis of the stator core 1 and passes through the center of gravity of the first end surface 22 of the tooth 2. The axis of the stator core 1 is the axis passing through the center of the inscribed or circumscribed circles of the multiple teeth 2 arranged on the circumference. The axis of the stator core 1 coincides with the rotation axis of the rotor 90, which will be described later. The circumferential surface 21 is the surface that connects the first end surface 22 to the upper surface 31. The first end surface 22 is the surface that connects to the upper end of the circumferential surface 21. The upper end of the circumferential surface 21 is located on the opposite side from the point where it connects to the upper surface 31.

[0054] [First end face] Each first end face 22 is ground as shown in the stator core manufacturing method described later. Due to the grinding process, the difference between the maximum and minimum values ​​of the first height H1, described later with reference to Figure 2, is small. Each ground first end face 22 has grinding marks 25, as shown in Figure 1. For the sake of explanation, Figure 1 shows the grinding marks 25 on one first end face 22 in an exaggerated manner. Figure 1 also shows the grinding marks on other first end faces 22 in an omitted manner. The grinding marks 25 are streak-like irregularities that occur during the grinding process. The streaks of the grinding marks 25 are formed along the relative direction of movement between the first end face 22 and the grinding machine 400 shown in Figure 7 during the grinding process. Each circumferential surface 21, unlike each first end face 22, is not ground.

[0055] The first end face 22 has a first region 221 and a second region 222, as shown in Figure 3. The first end face 22 may further have a third region 223.

[0056] The first region 221 is composed of cross-sections of metal particles 101. That is, the first region 221 is composed of the regions of individual metal particles 101 that are exposed from the insulating coating 102. When the first end face 22 is viewed from above, the first region 221 consists of numerous island-like regions that are dispersed and spaced apart from one another.

[0057] The second region 222 is composed of the cross-section of the insulating coating 102. The second region 222 is the region adjacent to the first region 221, between two first regions 221. That is, the second region 222 is in contact with the first region 221. When the first end face 22 is viewed from above, the second region 222 is a plurality of annular regions surrounding each first region 221. Adjacent second regions 222 may be in contact with each other at some points, but not at others.

[0058] The third region 223 is the region between multiple coating particles 100, that is, the region between adjacent second regions 222. The third region 223 is provided at the points where adjacent second regions 222 do not touch each other. The third region 223 is usually interrupted at a specific point in the depth direction from the first end face 22. That is, beyond the specific point, the third region 223 does not exist, and only the second region 222 exists. When the first end face 22 is viewed from above, the third region 223 is a mesh-like region surrounding each individual second region 222. The third region 223 is composed of oxide 223a. The oxide 223a contains the constituent elements of the metal particles 101. The composition of the oxide 223a is different from the composition of the insulating coating 102. The oxide 223a is, for example, an iron oxide. Specific iron oxides are Fe2O3 or Fe3O4.

[0059] [Peripheral surface] The circumferential surface 21 is not ground. That is, the circumferential surface 21 does not have grinding marks 25. The circumferential surface 21 does not have exposed metal particles 101 like the first end face 22. The circumferential surface 21 is composed of oxide 211a. That is, a layer of oxide 211a is provided between the circumferential surface 21 and the coating particle 100 closest to the circumferential surface 21. The composition of oxide 211a is the same as that of oxide 223a. Here, "same" means that the oxides share common constituent elements of the soft magnetic material. The ratio of the constituent elements to oxygen may differ between oxide 223a and oxide 211a. Oxide 223a is formed between the coating particles 100 near the circumferential surface 21.

[0060] The average thickness of the layered oxide 211a is 10 μm or less. A stator core 1 with an average thickness of oxide 211a of 10 μm or less is more likely to suppress an increase in hysteresis loss. This is because a lower average thickness of oxide 211a means a smaller amount of oxide that increases hysteresis loss. Oxides that increase hysteresis loss are those with high coercivity, such as Fe3O4. The average thickness of oxide 211a may be even lower, up to 8 μm, and especially 6 μm or less. The lower limit of the average thickness of oxide 211a is, for example, 0.5 μm. If the average thickness of oxide 211a is 0.5 μm or more, the insulating coating 102 of the coating particles 100 near the circumferential surface 21 is easier to mechanically protect. Therefore, even if the coil 80 and the circumferential surface 21 come into contact when constructing the stator 8, which will be described later with reference to Figure 10, the insulating coating 102 is less likely to be damaged. The average thickness of oxide 211a may be 1.0 μm or more, and particularly 2.0 μm or more. That is, the average thickness of oxide 211a may be 0.5 μm or more and 10 μm or less, and further 1.0 μm or more and 8 μm or less, and particularly 2.0 μm or more and 6 μm or less.

[0061] The average thickness of oxide 211a is determined as follows: A cross-section perpendicular to the circumferential surface 21 is taken. This cross-section is observed using an optical microscope. More than 100 observation fields are taken in the cross-section. Each observation field is taken so as to include the circumferential surface 21 and more than 5 coating particles 100 near the circumferential surface 21. The size of each observation field is 450 μm × 450 μm. In each field, the shortest distance between each coating particle 100 near the circumferential surface 21 and the circumferential surface 21 is measured. The average value of all shortest lengths is taken as the average thickness of oxide 211a.

[0062] The average depth of oxide 223a is, for example, 100 μm or more. If the average depth is 100 μm or more, it is easier to further suppress the bonding of adjacent metal particles 101. Therefore, the stator core 1 makes it easier to reduce eddy current losses when constructing the rotating electric machine 9. The upper limit of the average depth of oxide 223a is, for example, 1000 μm. If the average depth of oxide 223a is 1000 μm or less, the increase in losses can be suppressed. That is, the average depth of oxide 223a is 100 μm or more and 1000 μm or less. The average depth of oxide 223a may further be 150 μm or more and 800 μm or less, and especially 200 μm or more and 600 μm or less.

[0063] The average depth of oxide 223a is determined as follows: A cross-section is taken perpendicular to the circumferential surface 21. This cross-section is observed using an optical microscope. More than 20 observation fields are taken on the cross-section. Each observation field is taken so that the entire length of oxide 223a in the depth direction is included within the field of view. The size of each observation field is 2000 μm × 2000 μm. In each field of view, the length of each oxide 223a along the direction perpendicular to the circumferential surface 21 is measured. The average value of all measured lengths is taken as the average depth of oxide 223a.

[0064] [First height] The difference between the maximum and minimum values ​​of the first height H1 shown in Figure 2 is 0.02 mm or less. The above difference in the first height H1 is the difference between the maximum and minimum values ​​among multiple first heights H1. Each first height H1 is the length between the bottom surface 32 and each first end surface 22. A stator core 1 in which the above difference in the first height H1 is 0.02 mm or less makes it easier to make each spacing b uniform when constructing the rotating electric machine 9 described later with reference to Figure 11. The spacing b is the length between each first end surface 22 and the magnets 95 of the rotor 90. This stator core 1 makes it easier to construct a rotating electric machine 9 with low torque ripple. A rotating electric machine 9 with low torque ripple makes it easier to reduce noise and vibration. Figure 11 shows the spacing b in an exaggerated manner for ease of explanation. The smaller the above difference in the first height H1, the easier it is to make each spacing b uniform. The above difference in the first height H1 may be 0.01 mm or less, more specifically 0.008 mm or less, and especially 0.005 mm or less.

[0065] A micrometer is used to measure each first height H1. Multiple measurement points are selected on each first end face 22. The measurement points are set on a straight line drawn from the centroid of the first end face 22 to the center of the yoke 3, when the first end face 22 is viewed from above. Three or more measurement points are selected on the above straight line. In particular, the measurement points include the centroid of the first end face 22, the first edge of the first end face 22, and the second edge of the first end face 22 on the above straight line. The first edge of the first end face 22 is the edge located near the center of the yoke 3. The second edge of the first end face 22 is the edge located far from the center of the yoke 3. Each first height H1 is the average length of the straight line connecting the bottom surface 32 and each measurement point, which is perpendicular to the first end face 22.

[0066] [Second height] The difference between the maximum and minimum values ​​of the second height H2 shown in Figure 2 may be 0.02 mm or less, similar to the first height H1. The above difference in the second height H2 is the difference between the maximum and minimum values ​​among multiple second heights H2. Each second height H2 is the length between the top surface 31 and each first end surface 22. A stator core 1 with the above difference in the second height H2 of 0.02 mm or less makes it easier to appropriately arrange the coils 80 on each tooth 2 when constructing the stator 8 described later with reference to Figure 10, and the rotating electric machine 9 described later with reference to Figure 11. A stator core 1 with the above difference in the second height H2 of 0.02 mm or less makes it easier to achieve a uniform length in the magnetic circuit composed of each tooth 2. A smaller above difference in the second height H2 makes it easier to appropriately arrange the coils 80 on each tooth 2. The above difference in the second height H2 may be 0.01 mm or less, even 0.008 mm or less, and especially 0.005 mm or less.

[0067] Each second height H2 is determined by "first height H1 - thickness of yoke 3". A micrometer is used to measure the thickness of yoke 3. Multiple measurement points are selected on the top surface 31. The measurement points are set on a straight line drawn from the centroid of each first end face 22 to the center of yoke 3, when viewing the stator core 1 in plan. Two or more measurement points are selected on the above straight line. In particular, the measurement points include the inner peripheral edge and the outer peripheral edge of the top surface 31 on the above straight line. The thickness of yoke 3 is the average length of the straight line connecting the bottom surface 32 to each measurement point, which is a straight line perpendicular to the top surface 31.

[0068] [Parallelism] The parallelism between the lower surface 32 and each first end surface 22 may be 0.02 mm or less. A stator core 1 with the above parallelism of 0.02 mm or less makes it easier to make the spacing b uniform when constructing the rotating electric machine 9 described later with reference to Figure 11. The smaller the above parallelism, the easier it is to make the spacing b uniform. The above parallelism may be 0.01 mm or less, even 0.008 mm or less, and especially 0.005 mm or less.

[0069] The above parallelism is determined as follows: A height gauge equipped with a Grade 0 surface plate is used. The stator core 1 is placed on the surface plate so that the first end face 22 faces upward. Multiple measurement points are selected on each first end face 22. The measurement points are set on a straight line drawn from a plan view of the stator core 1, passing through the centroid of the first end face 22 and the center of the yoke 3. Three or more measurement points are selected on the above straight line. The measurement points include the centroid of the first end face 22, the first edge of the first end face 22, and the second edge of the first end face 22 on the above straight line. The parallelism between the lower surface 32 and each first end face 22 is the difference between the maximum and minimum lengths of the straight lines connecting the surface plate and each measurement point, which are perpendicular to the surface plate.

[0070] [Size] The size of the yoke 3 and the size of each tooth 2 can be appropriately selected according to the specifications of the rotating electric machine 9. The size of the yoke 3 is the inner diameter, outer diameter, and thickness, etc. The size of each tooth 2 is the cross-sectional area and height, etc. The inner diameter of the yoke 3 is, for example, 5 mm to 150 mm. The outer diameter of the yoke 3 is, for example, 30 mm to 300 mm. The thickness of the yoke 3 is, for example, 1.0 mm to 10 mm, and further 1.5 mm to 7.0 mm. The inner diameter of the yoke 3 is the diameter of the shaft hole 39. The cross-sectional area of ​​the tooth 2 is, for example, 5 mm 2 800mm or more 2 The following applies: The height of tooth 2 is, for example, between 3 mm and 50 mm. The cross-sectional area of ​​tooth 2 here refers to the area of ​​the cross-section obtained by cutting tooth 2 with a plane perpendicular to its axial direction. The height of each tooth 2 here refers to the second height H2.

[0071] [Component materials] The compacted magnetic core is composed of an aggregate of multiple coated particles 100 as shown in Figure 3. Each coated particle 100 has a metal particle 101 and an insulating coating 102.

[0072] (metal particles) The metal particles 101 are composed of a soft magnetic material. The soft magnetic material is pure iron or an iron-based alloy. Pure iron means that its purity is 99% or higher. That is, pure iron means that the iron (Fe) content is 99% by mass or higher. Metal particles 101 composed of pure iron have a high saturation magnetic flux density. Therefore, a powder magnetic core having metal particles 101 composed of pure iron is easy to improve the saturation magnetic flux density. In addition, metal particles 101 composed of pure iron have excellent formability. Therefore, a powder magnetic core having metal particles 101 composed of pure iron is easy to increase the relative density.

[0073] An iron-based alloy is one that contains additive elements, with the remainder being Fe and unavoidable impurities. Iron-based alloys contain the most Fe. An iron-based alloy is, for example, at least one selected from the group consisting of Fe-Si (silicon) alloys, Fe-Al (aluminum) alloys, Fe-Si-Al alloys, and Fe-Ni (nickel) alloys. An example of a Fe-Si alloy is silicon steel. An example of a Fe-Si-Al alloy is Sendust. An example of a Fe-Ni alloy is permalloy. The electrical resistance of an iron-based alloy is greater than that of pure iron. Therefore, metal particles 101 composed of an iron-based alloy easily reduce iron losses such as eddy current losses. Thus, a powder magnetic core having metal particles 101 composed of an iron-based alloy easily reduces losses. A powder magnetic core may contain both metal particles 101 composed of pure iron and metal particles 101 composed of an iron-based alloy.

[0074] (Insulating coating) The insulating coating 102 covers the metal particles 101. The insulating coating 102 can reduce iron losses such as eddy current losses. A powder core equipped with the insulating coating 102 is prone to loss reduction. The material of the insulating coating 102 is, for example, an oxide such as phosphate, silica, magnesium oxide, or aluminum oxide. Phosphates have excellent adhesion to the metal particles 101 and also have excellent deformability. Therefore, an insulating coating 102 composed of phosphate can easily deform in accordance with the deformation of the metal particles 101 in the process of manufacturing a powder molded body in the stator core manufacturing method described later, and is not easily damaged. Thus, such a powder core is prone to loss reduction.

[0075] The average thickness of the insulating coating 102 is, for example, between 10 nm and 1000 nm. An insulating coating 102 of 10 nm or more readily insulates adjacent metal particles 101 from each other. An insulating coating 102 of 1000 nm or less readily increases the relative density of the compacted magnetic core. The average thickness of the insulating coating 102 is further between 20 nm and 700 nm, and especially between 30 nm and 500 nm.

[0076] The average thickness of the insulating coating 102 is determined as follows: A cross-section of the stator core 1 is taken. This cross-section is observed using a TEM (transmission electron microscope), and the observed image is analyzed to determine the average thickness. More than 20 observation fields are taken in the cross-section. The magnification of each observation field is between 50,000x and 300,000x. The average value of the thickness of all fields is calculated from the average value of the thickness of each field, and this average value of all fields is taken as the average thickness of the insulating coating 102.

[0077] [Relative density] The relative density of the compacted magnetic core may be 90% or higher. Compacted magnetic cores with a relative density of 90% or higher are more likely to have improved saturation magnetic flux density. Compacted magnetic cores with a relative density of 90% or higher are more likely to have improved mechanical properties such as strength. The relative density may be 93% or higher, and even 95% or higher. The relative density may be 99% or lower.

[0078] The "relative density of a compacted magnetic core" refers to the ratio (%) of the actual density of a compacted magnetic core to its true density. That is, the relative density of a compacted magnetic core can be calculated by [(actual density of compacted magnetic core / true density of compacted magnetic core) × 100]. The actual density of a compacted magnetic core can be determined by immersing it in oil to impregnate it with oil, and then calculating [oil-impregnated density × (mass of compacted magnetic core before oil impregnation / mass of compacted magnetic core after oil impregnation)]. The oil-impregnated density is (mass of compacted magnetic core after oil impregnation / volume of compacted magnetic core after oil impregnation). That is, the actual density of a compacted magnetic core can be determined by (mass of compacted magnetic core before oil impregnation / volume of compacted magnetic core after oil impregnation). The volume of a compacted magnetic core after oil impregnation can typically be measured by the liquid displacement method. The true density of a compacted magnetic core is the theoretical density assuming that there are no voids inside.

[0079] [Method for manufacturing a stator core] The stator core 1 according to this embodiment can be manufactured by a method for manufacturing a stator core comprising the following steps A to C. Step A is the process of producing a powder molded body. Step B involves heat-treating a powder molded body to produce a heat-treated body. Process C involves grinding a specific surface of the heat-treated body.

[0080] [Process A] Powder molded bodies can be produced by pressurizing the raw powder.

[0081] The raw material powder contains multiple coated particles. The coated particles have metal particles and an insulating coating. The materials of the metal particles and the insulating coating are as described above. At the raw material stage, the coated particles are substantially covered over the entire surface of the metal particles by the insulating coating. In addition to the coated particles, the raw material powder may also contain a binder and a lubricant. A lubricant may be applied to the inner surface of the die, which will be described later.

[0082] The average particle size of metal particles is, for example, between 20 μm and 350 μm. Metal particles with an average particle size within the above range are easy to handle and easy to mold by pressure. The average particle size of soft magnetic powder is further between 40 μm and 300 μm, and especially between 40 μm and 250 μm. The average particle size of metal particles is determined by measuring it using a laser diffraction / scattering particle size distribution analyzer, and is defined as the particle size whose cumulative mass is 50% of the total mass of all particles.

[0083] Press molding machines can be used for the pressure molding of raw material powder. A press molding machine comprises a die, a core rod, an upper punch, and a lower punch. The die, core rod, and lower punch form a cavity into which the raw material powder is filled. In a press molding machine, for example, the yoke is formed at the top and the teeth at the bottom by the upper and lower punches. The inner surface of the die forms the outer surface of the yoke. The outer surface of the core rod forms the inner surface of the yoke. The lower punch comprises one first lower punch and multiple second lower punches. The first lower punch is cylindrical in shape. The first lower punch has one first hole and multiple second holes. The core rod is placed in the first hole. A second lower punch is placed in each second hole. The end face of the first lower punch forms the upper surface of the yoke. The inner surface of the second hole of the first lower punch forms the circumferential surface of each tooth. Each second lower punch is columnar in shape. The end face of each second lower punch forms the first end face of each tooth. The upper punch forms the lower surface of the yoke. The raw material powder is filled into the cavity by a powder feeder. The upper and lower punches press-form the raw material powder filled into the cavity.

[0084] Conventional powder dispensers supply powder into the cavity by moving linearly back and forth over the die. In this type of dispenser, the amount of raw material powder that fills the point where the powdering starts on the die tends to be greater than the amount of raw material powder that fills the point where the dispenser reverses direction.

[0085] A powder molded body is manufactured comprising an annular plate-shaped yoke and multiple columnar teeth. The raw material powder in the cavity is pressure-molded to produce the powder molded body. The height between the first end face of the teeth formed at the point where powder feeding begins and the bottom surface of the yoke tends to be higher than the height between the first end face of the teeth formed at the point where the powder feeder folds back and the bottom surface of the yoke.

[0086] A powder molded body of this type is shown in Figure 5. The powder molded body 200 in Figure 5 shows an example where the height between the lower surface 32 of the yoke 3 and the first end face 22 of the right tooth 2 is higher than the height between the lower surface 32 of the yoke 3 and the first end face 22 of the left tooth 2. As shown in Figure 5, a difference a is likely to occur between the first end face 22 on the right side and the first end face 22 on the left side.

[0087] The pressure during compression molding is, for example, 500 MPa or higher. If the pressure during compression molding is 500 MPa or higher, compacted magnetic cores with a high relative density can be manufactured. The pressure during compression molding is, for example, 2000 MPa or lower. If the pressure during compression molding is 2000 MPa or lower, the insulating coating on the coated particles is less likely to be damaged. The pressure during compression molding is further between 700 MPa and 1800 MPa, and especially between 800 MPa and 1500 MPa.

[0088] [Process B] The heat-treated body can be manufactured by heat-treating a powder-molded body. The heat treatment temperature is, for example, between 350°C and 800°C. The heat treatment holding time is, for example, between 5 minutes and 60 minutes. The atmosphere during heat treatment is an oxidizing atmosphere.

[0089] If the heat treatment temperature in an oxidizing atmosphere is 350°C or higher and the holding time is 5 minutes or longer, oxide 223a, as shown in Figure 3, is formed between the coating particles near the surface of the powder molded body, and oxide 211a, as shown in Figure 4, is formed over the entire surface of the powder molded body. In particular, oxide 223a is thought to be formed from the surface of the powder molded body to a predetermined depth. Depth is the length along the direction perpendicular to the surface of the powder molded body. The predetermined depth is, for example, 0.1 mm or more. The predetermined depth is further 0.15 mm or more, and especially 0.2 mm or more. The upper limit of the predetermined depth is, for example, 1.0 mm. That is, the predetermined depth is 0.1 mm or more and 1.0 mm or less, further 0.15 mm or more and 0.8 mm or less, and especially 0.2 mm or more and 0.6 mm or less. If the heat treatment temperature in an oxidizing atmosphere is 800°C or lower and the holding time is 60 minutes or less, the destruction of the insulating coating of the coating particles by the heat treatment can be suppressed. Therefore, the increase in eddy current loss can be suppressed. The above temperature is further defined as 400°C to 750°C, and more specifically, 450°C to 700°C. The above holding time is further defined as 10 minutes to 45 minutes, and more specifically, 15 minutes to 30 minutes.

[0090] The oxygen concentration in the oxidizing atmosphere may be 20,000 ppm or less. Here, the oxygen concentration refers to the volume percentage. If the above oxygen concentration is 20,000 ppm or less, it is easier to suppress the increase in hysteresis loss associated with oxidation. The above oxygen concentration may be 500 ppm or more. If the above oxygen concentration is 500 ppm or more, the above oxides 223a and 211a are easily formed. The above oxygen concentration is further 700 ppm to 10,000 ppm, 1,000 ppm to 7,500 ppm, and especially 2,000 ppm to 5,000 ppm.

[0091] Figure 6 shows the heat-treated body 250. The heat-treated body 250 in Figure 6 was manufactured by heat-treating the powder molded body 200 shown in Figure 5. The heat-treated body 250 in Figure 6 maintains the difference a described above with reference to Figure 5. The entire surface of this heat-treated body 250 is coated with oxide 211a as shown in Figure 4. In addition, oxide 223a as shown in Figure 4 is provided between the coating particles 100 in the vicinity of the entire surface of the heat-treated body 250.

[0092] [Process C] Grinding is performed, for example, using a grinding machine 400 as shown in Figure 7. The grinding may be surface grinding. Surface grinding makes it easier to form the planar first end face 22 as explained with reference to Figure 3.

[0093] As shown in Figure 7, the heat-treated body 250 described with reference to Figure 6 is ground. The areas to be ground are at least the first end faces 22 of each tooth 2. Grinding makes it easier to reduce the difference between the maximum and minimum values ​​of the first height H1 to 0.02 mm or less. Grinding may also be performed on the lower surface 32 of the yoke 3. Grinding the lower surface 32 of the yoke 3 makes it easier to reduce the above difference in the first height H1 to 0.02 mm or less. Grinding is not performed on the circumferential surfaces 21 and the upper surface 31.

[0094] When grinding, the end of each tooth 2 on the circumferential surface 21 side may be fixed. For example, a plate-shaped member 300 as shown in Figure 7 can be used to fix the above end of each tooth 2.

[0095] The plate-shaped member 300 is provided with a plurality of through holes 310. Each through hole 310 is a hole into which the end of each tooth 2 can be inserted. The number of through holes 310 corresponds to the number of teeth 2. The shape of the through holes 310 is similar to the shape of the teeth 2. The size of the through holes 310 can be appropriately selected so that the end of the tooth 2 can be inserted, and the gap between the through hole and the circumferential surface 21 is small when the end of the tooth 2 is inserted. The shape and size of each through hole 310 are the same.

[0096] Each through-hole 310 is fitted into each tooth 2. The inner circumferential surface of each through-hole 310 holds the circumferential surface 21 of the tooth 2 near the first end face 22. Grinding is performed while the tooth 2 is held in place. The plate-shaped member 300 is fixed by grinding so that the difference between the maximum and minimum values ​​of the first height H1 shown in Figure 2 is 0.02 mm or less. For the sake of explanation, Figure 7 shows an exaggerated view of the area exposed from the plate-shaped member 300 on each tooth 2. By fixing the area near the first end face 22 of each tooth 2 with the plate-shaped member 300, it is possible to prevent chipping of the edge between the first end face 22 and the circumferential surface 21 of each tooth 2 during grinding.

[0097] As described above, the height between the first end face 22 and the bottom surface 32 of the stator core formed at the point where powder feeding begins is likely to be higher than the height between the first end face 22 and the bottom surface 32 of the stator core formed at the point where the powder feeder folds back. For example, in Figure 5, the height is highest for the right tooth 2, and gradually decreases towards the left tooth 2. Due to this difference in height, the amount of material processed on the tooth 2 is greatest for the tooth 2 located at the point where powder feeding begins. The amount of material processed on the tooth 2 decreases towards the tooth 2 located at the point where the powder feeder folds back. In the grinding process, the plate-shaped member 300 may also be ground together.

[0098] The first end face 22, which has been ground, has a first region 221 and a second region 222, as described with reference to Figure 3, and a grinding mark 25, as described with reference to Figure 1. That is, the oxide formed on the first end face 22, the insulating coating 102 near the first end face 22, and the metal particles 101 are removed by grinding. The oxide 223a formed between the coating particles 100 near the first end face 22 by heat treatment suppresses the plastic flow of the metal particles 101 near the first end face 22 that occurs during grinding. By suppressing plastic flow, the number of places where adjacent metal particles 101 are connected can be reduced.

[0099] The circumferential surface 21 remains formed on the oxide 211a, as described with reference to Figure 4.

[0100] When the lower surface 32 of the yoke 3 is ground, the lower surface 32 will have the same configuration as the first end surface 22, although this is not shown in the illustration.

[0101] The stator core 1 of this embodiment facilitates the construction of a low-loss rotating electric machine 9. The first end faces 22 of each tooth 2 are such that adjacent metal particles 101 are not connected to each other. In particular, when the first end face 22 has a third region 223, the third region 223 maintains the spacing between adjacent first regions 221. Therefore, the stator core 1 makes it easier to reduce eddy current losses when constructing a rotating electric machine 9. Furthermore, the average thickness of the layered oxide 211a on the circumferential surface 21 of each tooth 2 is 10 μm or less. Therefore, the stator core 1 makes it easier to reduce hysteresis losses when constructing a rotating electric machine 9. Consequently, the stator core 1 makes it easier to reduce losses in the rotating electric machine 9.

[0102] The stator core 1 of this embodiment makes it easy to construct a rotating electric machine 9 with low noise and vibration. The reason is as follows: A stator core 1 in which the difference between the maximum and minimum values ​​of the first height H1 is 0.02 mm or less makes it easy to make each spacing b uniform when constructing the rotating electric machine 9 shown in Figure 11. A rotating electric machine 9 with uniform spacing b makes it easy to reduce torque ripple. A rotating electric machine 9 with low torque ripple has low noise and vibration. Therefore, the stator core 1 makes it easy to reduce the noise and vibration of the rotating electric machine 9.

[0103] The manufacturing method for the stator core of this embodiment allows for the production of the stator core 1 of this embodiment by following a specific sequence of steps, which involves heat treatment under specific conditions followed by grinding. The heat treatment under specific conditions forms oxide 211a on the entire surface of the powder molded body 200. Furthermore, oxide 223a may also form between the coating particles 100 near the surface of the powder molded body 200. Grinding after the heat treatment removes material from the vicinity of the first end face 22 of the heat-treated body 250. The oxide 211a is thought to make it easier to suppress the sliding load during grinding compared to the case where oxide 211a is absent. Therefore, even if the insulating coating 102 near the first end face 22 is damaged by grinding, the plastic flow of the metal particles 101 associated with grinding is suppressed. In particular, if oxide 223a is formed between the coating particles 100, the oxide 223a makes it easier to suppress the plastic flow of the metal particles 101 near the first end face 22 associated with grinding. Therefore, even if the insulating coating 102 covering the metal particles 101 near the first end face 22 is damaged and the metal particles 101 are exposed from the insulating coating 102, it is possible to suppress the bonding of adjacent metal particles 101 to each other. Furthermore, the circumferential surface 21 of the heat-treated body 250 is not ground. As a result, the oxide 211a on the circumferential surface 21 maintains its surface properties immediately after heat treatment even after grinding. In addition, grinding the first end face 22 reduces the difference between the maximum and minimum values ​​of the first height H1. Accordingly, the method for manufacturing a stator core of this embodiment can produce the stator core 1 having the above-described first end face 22 and circumferential surface 21, and having a difference between the maximum and minimum values ​​of the first height H1 of 0.02 mm or less. In other words, the method for manufacturing a stator core of this embodiment can produce a stator core 1 that can construct an axial gap type rotating electric machine with low noise and vibration and low loss.

[0104] Embodiment 2 [Stator core] The stator core 1 of Embodiment 2 will be described with reference to Figures 8 and 9. The stator core 1 of this embodiment differs from the stator core 1 of Embodiment 1 in that it does not have a yoke 3, but has multiple teeth 2. The following description will focus on the differences from Embodiment 1. A description of the configuration similar to that of Embodiment 1 will be omitted.

[0105] Each tooth 2 has a circumferential surface 21, a first end surface 22, and a second end surface 23. The first end surface 22 is connected to the first end of the circumferential surface 21. The second end surface 23 is connected to the second end of the circumferential surface 21. The circumferential surface 21 and the first end surface 22 are as described in Embodiment 1 above. The second end surface 23 may have the same configuration as the first end surface 22, or it may have the same configuration as the circumferential surface 21. If ground, the first end surface 22 and the second end surface 23 will have the same configuration. If not ground, the circumferential surface 21 and the second end surface 23 will have the same configuration. In this embodiment, the first height H1 is the length between the first end surface 22 and the second end surface 23, as shown in Figure 9. In this embodiment as well, the difference between the maximum and minimum values ​​of the first height H1 is 0.02 mm or less. A stator core 1 in which the above-mentioned difference in the first height H1 is 0.02 mm or less makes it easier to make each spacing b uniform when constructing the rotating electric machine 9 described later with reference to Figure 12. The preferred range for the above-mentioned difference in the first height H1 is as described above.

[0106] The stator core 1 of this embodiment facilitates the construction of a rotating electric machine 9 with low torque ripple. A rotating electric machine 9 with low torque ripple makes it easier to reduce noise and vibration.

[0107] Embodiment 3 [Status] Referring to Figure 10, the stator 8 of Embodiment 3 will be described. The stator 8 of this embodiment comprises the stator core 1 of Embodiment 1 and a plurality of coils 80. Unlike this embodiment, the stator 8 may comprise the stator core 1 of Embodiment 2 and a plurality of coils 80. Each coil 80 is arranged on the outer circumference of each tooth 2. The stator 8 is used in an axial gap type rotating electric machine.

[0108] Each coil 80 has a cylindrical portion. The cylindrical portion is formed by winding the wire spirally. The coil 80 in this embodiment is a trapezoidal cylindrical edgewise wound coil. The wire is a coated flat wire. In Figure 8, for the sake of explanation, only the cylindrical portion is shown, and both ends of the wire are omitted from the illustration.

[0109] Since the stator 8 of this embodiment is equipped with the stator core 1 of Embodiment 1, a low-loss axial-gap type rotating electric machine can be constructed. This stator 8 can be used to construct an axial-gap type rotating electric machine with low torque ripple. This stator 8 can be used to construct an axial-gap type rotating electric machine with low noise and vibration.

[0110] Embodiment 4 [Rotating Electric Machinery] The rotating electric machine 9 of Embodiment 4 will be described with reference to Figure 11. Figure 11 is a cross-sectional view of the rotating electric machine 9 cut by a plane parallel to the rotation axis 91. The rotating electric machine 9 of this embodiment is an axial gap type rotating electric machine. The rotating electric machine 9 can be used as a motor or a generator. The rotating electric machine 9 of this embodiment is a double stator, single rotor type rotating electric machine. The rotating electric machine 9 of this embodiment comprises one rotor 90 and two stators 8. In the rotating electric machine 9 of this embodiment, the rotor 90 is sandwiched between the stators 8 on both sides in the axial direction of the rotation axis 91. A gap is provided between the rotor 90 and each stator 8. At least one of the two stators 8 shown in Figure 11 is the stator 8 described in Embodiment 3.

[0111] The stator 8 and rotor 90 are housed in a case 92. The case 92 has a cylindrical internal space. The stator 8 and rotor 90 are housed in this internal space. The case 92 comprises a cylindrical portion 921 and two plate portions 922.

[0112] The cylindrical portion 921 surrounds the outer circumference of the stator 8 and rotor 90. Plate portions 922 are positioned on both sides of the cylindrical portion 921. The stator 8 and rotor 90 are housed in the case 92 so as to be sandwiched between the two plate portions 922. The stator 8 is fixed to the case 92 by the outer surface of the yoke 3 of the stator core 1 fitting into the steps of the plate portions 922 of the case 92. Through holes are provided in the center of both plate portions 922. Bearings 93 are provided in the through holes. The rotating shaft 91 is inserted through the bearings 93. The rotating shaft 91 passes through the inside of the case 92.

[0113] The rotor 90 comprises a rotor body and at least one magnet 95. The rotor body supports the magnet 95. The rotor body is an annular plate-shaped member. The rotor body is rotatably supported relative to the case 92 by a rotation shaft 91. The magnet 95 is fixed to the rotor body. There may be one or more magnets 95. If there is one magnet 95, the shape of the magnet 95 is an annular plate. This magnet 95 has alternating south poles and north poles in the circumferential direction. If there are multiple magnets 95, the number of magnets 95 is the same as the number of teeth 2. The multiple magnets 95 are arranged at equal intervals in the circumferential direction of the rotor body. The shape of each magnet 95 is, for example, a flat plate. The planar shape of each magnet 95 is, for example, the same as the planar shape of the first end face 22 of the teeth 2. Each magnet 95 is magnetized in the axial direction of the rotation shaft of the rotor 90. The magnetization directions of the adjacent magnets 95 on the rotor body are opposite to each other. The rotor 90 rotates as the rotating magnetic field generated by the stator 8 causes the magnets 95 to repeatedly attract and repel each tooth 2.

[0114] The rotating electric machine 9 of this embodiment is equipped with the stator 8 of Embodiment 3, making it easier to reduce losses. This rotating electric machine 9 also makes it easier to reduce torque ripple. A rotating electric machine 9 with low torque ripple makes it easier to reduce noise and vibration.

[0115] Embodiment 5 [Rotating Electric Machinery] The rotating electric machine 9 of Embodiment 5 will be described with reference to Figure 12. Figure 12, like Figure 11, is a cross-section of the rotating electric machine 9 cut by a plane parallel to the rotation axis 91. The rotating electric machine 9 of this embodiment differs from the rotating electric machine 9 of Embodiment 4 mainly in that it is a single-stator, double-rotor type axial gap motor equipped with two rotors 90 and one stator 8. The following description will focus on the differences from Embodiment 4. A description of the configuration similar to that of Embodiment 4 will be omitted.

[0116] The rotating electric machine 9 of this embodiment comprises one stator 8 and two rotors 90. In the rotating electric machine 9 of this embodiment, one stator 8 is sandwiched between the two rotors 90 on both sides in the axial direction of the rotating shaft 91. A gap is provided between the stator 8 and each rotor 90. The one stator 8 and the two rotors 90 are housed in the case 92 described in Embodiment 4.

[0117] Each rotor 90 comprises a rotor body, a plurality of magnets 95, and a back yoke 98. The rotor body and the plurality of magnets 95 are as described in Embodiment 4 above. The back yoke 98 is provided between the rotor 90 and the plate portion 922. The back yoke 98 is an annular plate-shaped member. The back yoke 98 is made of a compacted powder molded body or laminated steel plate similar to the stator core 1 described above.

[0118] The stator 8 comprises the stator core 1 described in Embodiment 2 and a plurality of coils 80. The stator 8 comprises a plurality of teeth 2 arranged in an annular shape, coils 80 arranged on the outer circumference of each tooth 2, and a support member that holds the plurality of teeth 2. The support member is not shown in the illustration. The coils 80 are as described in Embodiment 3 above. The support member holds the plurality of teeth such that the spacing between each tooth 2 is equal. This support member prevents adjacent teeth in the circumferential direction from contacting each other. The support member is fixed to the case 92 so as not to rotate.

[0119] The rotating electric machine 9 according to Embodiment 5 is equipped with a stator 8 having the stator core 1 of Embodiment 2, and therefore, like the rotating electric machine 9 of Embodiment 4, it is easy to reduce losses. This rotating electric machine 9 is easy to reduce torque ripple. A rotating electric machine 9 with low torque ripple is easy to reduce noise and vibration.

[0120] [Example Test] We evaluated the differences in the magnitude of stator core loss due to different manufacturing methods for stator cores. Two stator cores were fabricated for each sample.

[0121] [Samples No. 1 to No. 5] The stator cores of samples No. 1 to No. 5 were manufactured by following steps A to C in order, in the same manner as the stator core manufacturing method described above.

[0122] [Process A] A powder molded body of a predetermined shape was produced by pressure molding the raw material powder. The raw material powder contained multiple coated particles. Each coated particle had a metal particle composed of pure iron and an insulating coating composed of iron phosphate and silica. The thickness of the insulating coating was 50 nm. The pressure during pressure molding was 441 MPa or 785 MPa, as shown in Table 1. This powder molded body is a molded body in which an annular plate-shaped yoke and six columnar teeth are integrated, similar to powder molded body 200 described with reference to Figure 5.

[0123] [Process B] A heat-treated body was prepared by heat-treating a powder-molded body. The heat treatment atmosphere was an oxidizing atmosphere. The oxygen concentration in the oxidizing atmosphere ranged from 500 ppm to 20,000 ppm by volume, as shown in Table 1. The heat treatment temperature was 650°C. The heat treatment holding time was 15 minutes.

[0124] [Process C] The first end face of each tooth of the heat-treated body was surface-ground as described with reference to Figure 7.

[0125] [Samples No. 101 to No. 107] The stator cores of samples No. 101 to No. 107 were manufactured in the same manner as sample No. 1, except for at least one difference: the magnitude of the pressure in step A, the type of atmosphere in step B, and the absence of surface grinding in step C, as shown in Table 1. In the nitrogen atmosphere shown in Table 1, the oxygen concentration was 0 ppm.

[0126] [Relative density] The relative density of the compacted magnetic core constituting the stator core of each sample was determined as described above using the formula [(actual density of compacted magnetic core / true density of compacted magnetic core) × 100]. The results are shown in Table 1.

[0127] 〔loss〕 The losses of the stator cores of each sample were investigated. Two stator cores were set up one above the other so that the first end faces of their teeth were in contact with each other. In this setup, the pair of teeth whose first end faces are in contact is called a bobbin. Two bobbins were selected from a set of bobbins. Test components were fabricated by placing a 60-turn primary coil and a 30-turn secondary coil in each bobbin. The losses in the fabricated test components were measured in the resulting closed magnetic circuit at a magnetic flux density of 1.0 T and a frequency of 1 kHz. The results are shown in Table 1.

[0128] [First height] The difference between the maximum and minimum values ​​of the first height of the stator core of each sample was investigated. A micrometer was used to measure each first height. Multiple measurement points were selected on the first end face of each tooth. The measurement points were set on a straight line drawn from the centroid of the first end face to the center of the yoke, when the first end face is viewed from above. Three measurement points were selected on the above straight line. The first measurement point was the centroid of the first end face. The second measurement point was the edge of the first end face near the center of the yoke. The third measurement point was the edge of the first end face far from the center of the yoke. Each first height was defined as the difference between the maximum and minimum values ​​of the length of the straight line connecting the bottom surface of the yoke and each measurement point, which is perpendicular to the first end face. The difference between the maximum and minimum values ​​of the first height for multiple teeth was calculated. The results are shown in Table 1.

[0129] [Parallelism] The parallelism between the lower surface of the yoke and the first end face of each of the multiple teeth in the stator core of each sample was examined. A height gauge equipped with a Grade 0 surface plate was used. The stator core was placed on the surface plate so that the first end faces of the teeth faced upward. Multiple measurement points were selected on the first end face of each tooth. The measurement points were set on a straight line drawn from the centroid of the first end face to the center of the yoke, when the stator core was viewed from above. Three measurement points were selected on the above straight line. The first measurement point was the centroid of the first end face of the tooth on the above straight line. The second measurement point was the edge of the first end face located near the center of the yoke. The third measurement point was the edge of the first end face located far from the center of the yoke. The parallelism between the lower surface of the yoke and each first end face was taken as the average length of the straight line connecting the surface plate and each measurement point, which was perpendicular to the surface plate. The results are shown in Table 1.

[0130] [Table 1]

[0131] As shown in Table 1, samples No. 1 to No. 5 exhibit a small difference between the maximum and minimum values ​​of the first height, low parallelism, and low loss.

[0132] Samples No. 101, No. 102, and No. 105 through No. 107 exhibited low loss, but the difference between the maximum and minimum values ​​of the first height, as well as the degree of parallelism, was large. Sample No. 103 exhibited large differences between the maximum and minimum values ​​of the first height, high parallelism, and high loss. Sample No. 104 showed a small difference between the maximum and minimum values ​​of the first height, as well as a small degree of parallelism, but exhibited significant losses.

[0133] [Surface observation] The first end face and circumferential surface of the teeth in samples No. 1 to No. 5 were observed. The first end face and circumferential surface were observed by taking cross-sections perpendicular to each surface.

[0134] In samples No. 1 to No. 5, the first end face of the ground teeth was composed of a surface as described with reference to Figure 3. Specifically, the first end face of the teeth had a first region 221, a second region 222, and a third region 223, as shown in Figure 3. The insulating coating 102 of the coated particles 100 was damaged. As a result of the damage to the insulating coating 102, the metal particles 101 were exposed. The exposed metal particles 101 were not connected to adjacent metal particles 101. Figure 13 shows a schematic diagram of a state in which a portion where the metal particles 101 are connected to each other has been formed. It is thought that the loss was lower in samples No. 1 to No. 5 because a portion where the metal particles 101 are connected to each other as shown in Figure 13 was not formed.

[0135] In samples No. 1 to No. 5, the circumferential surface of the teeth was composed of a surface as described with reference to Figure 4. Specifically, as shown in Figure 4, a layered oxide 211a was formed on the circumferential surface of the teeth, covering the surface of multiple coating particles 100. The composition of oxide 211a and oxide 223a was analyzed using a TEM (JEM2100F) manufactured by JEOL Ltd. These oxides 211a and 223a were oxides containing the constituent elements of the metal particle 101. Specifically, they were Fe2O3 and Fe3O4. The average depth of oxide 223a on the circumferential surface of the teeth was determined as described above. The results are shown in Table 1. In all samples No. 1 to No. 5, the average depth of the oxide was 100 μm or more.

[0136] The average thickness of the layered oxide 211a was determined as described above. The results are shown in Table 1. For all samples No. 1 to No. 5, the average thickness of oxide 211a was 10 μm or less.

[0137] The present invention is not limited to these examples, but is intended to include all modifications within the meaning and scope of the claims as shown, and within the meaning and scope of the equivalents of the claims.

[0138] For example, the rotating electric machine, although not shown in the illustration, may be a single-stator, single-rotor type rotating electric machine. This rotating electric machine comprises one rotor and one stator. [Explanation of Symbols]

[0139] 1 Stator Core 12 Second end face 2 teeth 21 peripheral surface, 211a oxide 22 First end surface 221 First area, 222 Second area 223 Third region, 223a oxide 23 Second end face 25 Grinding marks 3 York 30e outer surface, 30i inner surface 31 top, 32 bottom 39 Shaft hole 8 stators, 80 coils 9 Rotating Electric Machines 90 rotor, 91 rotating shaft, 92 Case, 921 Cylindrical section, 922 Plate section 93 Bearing, 95 Magnet, 98 Back yoke 100 Coating particles, 101 Metal particles, 102 Insulating coating 200 powder molded bodies, 250 heat-treated bodies 300 Plate-shaped member, 310 Through hole 400 Grinding Machine H1 is the first height, H2 is the second height. a. Difference, b. Interval

Claims

1. A stator core used in an axial gap type rotating electric machine, It has multiple columnar teeth arranged around the circumference, The stator core is, Each of the circumferential surfaces of the plurality of teeth, The first end face of each of the plurality of teeth, It has at least one second end face which is the face opposite to the first end face, Each of the aforementioned multiple teeth is composed of a powdered porcelain core, The compacted magnetic core comprises a plurality of coating particles, Each of the plurality of coated particles is Metal particles composed of soft magnetic material, The metal particles are covered by an insulating coating, The first end face is, A first region consisting of the cross-section of the metal particles, Between the first regions, there is a second region formed by the insulating coating, The second regions are separated by a third region composed of an oxide containing the constituent elements of the soft magnetic material, The circumferential surface is composed of an oxide containing the constituent elements of the soft magnetic material, The average thickness of the oxide on the circumferential surface is 10 μm or less. The difference between the maximum and minimum values ​​at multiple first heights is 0.02 mm or less. The plurality of first heights is the length between the first end face and the second end face of each of the plurality of teeth. Stator core.

2. Equipped with a ring-shaped yoke, The aforementioned yoke is Inner surface and, Outer surface and, The upper surface connected to the inner surface, the outer surface, and each of the circumferential surfaces of the plurality of teeth, It has an inner circumferential surface and a lower surface connected to the outer circumferential surface, The lower surface is the second end surface, The stator core according to claim 1, wherein the yoke is composed of the compacted magnetic core integrally molded with the plurality of teeth.

3. The stator core according to claim 1 or claim 2, wherein the parallelism between the first end face and the second end face of each of the plurality of teeth is 0.02 mm or less.

4. The stator core according to claim 1 or claim 2, wherein the relative density of the compacted magnetic core is 90% or more.

5. The stator core according to claim 1 or claim 2, wherein the average depth of the third region is 100 μm or more.

6. The aforementioned metal particles are composed of pure iron or an iron-based alloy. The stator core according to claim 1 or claim 2, wherein the iron-based alloy is an Fe-Si alloy, an Fe-Al alloy, or an Fe-Si-Al alloy.

7. A stator for an axial gap type rotating electric machine, A stator core according to claim 1 or claim 2, A coil is placed on each of the plurality of teeth, stata.

8. An axial gap type rotating electric machine, The stator is provided according to claim 7. Rotating electric machine.

9. A process of producing a powder molded body by pressure molding multiple coated particles, The process of heat-treating the powder molded body, The process includes grinding the heat-treated powder molded body, Each of the plurality of coated particles is Metal particles composed of soft magnetic material, The metal particles are covered by an insulating coating, The powder molded body has a plurality of columnar teeth arranged on its circumference, Each of the plurality of teeth has a circumferential surface and a first end surface, The pressure used during the aforementioned pressure molding is 500 MPa or more. In the aforementioned heat treatment conditions, the atmosphere is an oxidizing atmosphere, and the temperature is 350°C or higher and 800°C or lower. The oxygen concentration in the aforementioned oxidizing atmosphere is 500 ppm or more and 20,000 ppm or less by volume. The grinding process is performed on the first end face of each of the multiple teeth, rather than on the circumferential surface of each of the multiple teeth in the heat-treated powder molded body. A method for manufacturing a stator core.

10. The method for manufacturing a stator core according to claim 9, wherein the grinding process is surface grinding.

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