Stator core and method for manufacturing a stator core

Abstract

We provide stator cores with superior assembly precision. [Solution] A stator core used in a motor comprising a shaft, a bearing that rotatably supports the shaft, a rotor fixed integrally with the shaft, and a stator positioned with a gap of a design length in the axial direction of the shaft relative to the rotor, wherein the stator core is made of a compacted body, the compacted body has a first surface facing the gap and a second surface provided on the opposite side of the first surface in the axial direction, and grinding marks are present on at least one of the first surface and the second surface.

Description

Technical Field

[0001] The present disclosure relates to a motor and a method for manufacturing the motor. This application claims priority based on Japanese Patent Application No. 2021-102188 filed on June 21, 2021, and incorporates all the descriptions set forth in the Japanese application.

Background Art

[0002] The axial-gap type rotating electric machine of Patent Document 1 includes a case, a stator, a rotor, a shaft, and bearings, as shown in FIG. 10 of Patent Document 1. The case includes a cylindrical peripheral wall portion and a pair of disk-shaped plates. The pair of plates are attached to both ends of the peripheral wall portion. A through hole is formed at the center of the pair of plates. A shaft is provided in the through hole. The stator and the rotor are arranged facing each other in the axial direction of the shaft within the case. The stator is arranged on the plate. The rotor is provided with a gap from the stator. The shaft is the rotation axis of the rotor. The bearings support the shaft rotatably.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The motor of the present disclosure includes a shaft, a bearing that rotatably supports the shaft, a rotor fixed integrally with the shaft, and a stator arranged with a gap of a designed length in the axial direction of the shaft with respect to the rotor. The stator has a stator core formed of a compacted powder body. The stator core has a first surface facing the gap and a second surface provided on the opposite side of the first surface in the axial direction. At least one of the first surface and the second surface has grinding marks.

[0005] A method for manufacturing a motor according to the present disclosure comprises the steps of adjusting the height of a stator in an axial gap type motor and assembling the parts of the motor, wherein the parts include a rotor, the stator, a shaft which is the rotation axis of the rotor, and a bearing which rotatably supports the shaft, the stator having a stator core made of a compacted powder molded body, the step of adjusting the height of the stator comprising the steps of determining the design height of the stator core considering the actual dimensions of the shaft and the bearing, and grinding at least one of the first surface and the second surface of the stator core to achieve the determined design height, wherein the design height is a height where the length of the gap between the rotor and the stator is the design length, the first surface is the surface facing the gap, and the second surface is the surface provided on the opposite side of the first surface in the axial direction of the shaft. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic cross-sectional view showing the motor according to Embodiment 1. [Figure 2] Figure 2 is a schematic cross-sectional view showing an enlarged view of region A in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing an enlarged example of another region A in Figure 1. [Figure 4] Figure 4 is a schematic perspective view of the stator core provided in the motor according to Embodiment 1. [Figure 5] Figure 5 is a cross-sectional view of Figure 4, VV section. [Figure 6] Figure 6 is a schematic cross-sectional view showing an enlarged view of region B in Figure 5. [Figure 7] Figure 7 is a graph showing the relationship between the load on the inner race of the first bearing and the amount of displacement of the inner race relative to the outer race of the first bearing. [Figure 8] Figure 8 illustrates an example of grinding in the motor manufacturing method according to Embodiment 1. [Figure 9]Figure 9 illustrates another example of grinding in the motor manufacturing method according to Embodiment 1. [Figure 10] Figure 10 is a schematic cross-sectional view showing the motor according to Embodiment 2. [Modes for carrying out the invention]

[0007] [Issues this disclosure aims to address] There is a need to improve the manufacturability of axial gap motors, which offer superior assembly precision.

[0008] One of the objectives of this disclosure is to provide a motor with excellent assembly precision. Another objective of this disclosure is to provide a motor manufacturing method that offers excellent manufacturability for the above-mentioned motor.

[0009] [Effects of this disclosure] The motor disclosed herein offers superior assembly precision.

[0010] The motor manufacturing method of the present disclosure offers excellent manufacturability for the motor.

[0011] Description of Embodiments in this Disclosure Axial gap motors are manufactured through two assembly processes: a preliminary assembly and a final assembly of the motor parts. The reason for the preliminary assembly is that it is difficult to determine the design length of the gap between the stator and rotor in a single assembly. The design length of the gap is the target value of the gap length determined based on the motor specifications. Therefore, the gap length of the motor manufactured through the preliminary assembly is measured. The difference between the measured gap length and the design length of the gap is calculated. After determining the measured gap length, the motor is disassembled.

[0012] The parts are assembled using a shim with the same thickness as the difference mentioned above. The shim is placed between the bearing and the plate. The placement of the shim causes the bearing to move away from the plate by the thickness of the shim. This shift in the bearing's position causes the shaft supported by the bearing to shift in the axial direction of the shaft. This shift causes the rotor to move away from the stator. This shift in the rotor causes the gap length to become longer than the measured length. In other words, the gap length becomes longer than the measured length by the thickness of the shim. Since the thickness of the shim is the same as the difference mentioned above, the gap length can be set to the design length.

[0013] The manufacturing method described above involves two assembly steps for the parts, making the manufacturing process more complicated. Furthermore, this method increases the number of parts due to the shims. Additionally, using shims may increase mechanical losses due to the increased bearing preload.

[0014] The inventors diligently studied methods for manufacturing motors without using shims. As a result, they have developed a manufacturing method that allows the gap length between the stator and rotor to be substantially the same as the design length by assembling the parts only once. Embodiments of this disclosure will be listed and described first.

[0015] (1) A motor according to one aspect of the present disclosure comprises a shaft, a bearing that rotatably supports the shaft, a rotor fixed integrally with the shaft, and a stator positioned with respect to the rotor at a gap of a design length in the axial direction of the shaft, wherein the stator has a stator core made of a compacted powder body, the stator core has a first surface facing the gap and a second surface provided on the opposite side of the first surface in the axial direction, and grinding marks are present on at least one of the first surface and the second surface.

[0016] The above motor has excellent assembly accuracy. Grinding marks are formed by the grinding process in the manufacturing process. Although the stator core is composed of a powder compact with lower dimensional accuracy than electromagnetic steel sheets, the stator core with a height where the gap length becomes the designed length can be obtained by the grinding process.

[0017] Since the above motor does not have a shim, an increase in the number of parts can be suppressed. Moreover, since the above motor can suppress an increase in the preload of the bearing, an increase in mechanical loss can be suppressed.

[0018] (2) In the motor of (1) above, the stator core has an annular plate-shaped yoke and a plurality of columnar teeth arranged at intervals in the circumferential direction of the yoke. The yoke has an outer peripheral surface, an inner peripheral surface, a planar upper surface and a planar lower surface connecting the outer peripheral surface and the inner peripheral surface. Each of the plurality of teeth has a side surface connected to the upper surface of the yoke and an end surface connected to an end portion on the side opposite to the side connected to the upper surface of the side surface. The lower surface is the second surface, the end surface is the first surface, and the difference between the maximum value and the minimum value of the height between the lower surface of the yoke and the end surface of each of the plurality of teeth may be 0.02 mm or less.

[0019] The above motor is easy to reduce noise and vibration. This is because when the above difference is 0.02 mm or less, torque ripple is likely to be reduced.

[0020] (3) In the motor of (1) or (2) above, the relative density of the powder compact may be 90% or more.

[0021] A powder compact with a relative density of 90% or more is likely to improve magnetic properties such as saturation magnetic flux density. Also, a powder compact with a relative density of 90% or more is likely to improve mechanical properties such as strength.

[0022] (4) In any of the motors described in (1) to (3) above, the compacted body comprises a plurality of coated particles, each of which comprises a metal particle made of a soft magnetic material and an insulating coating covering the metal particle, the metal particle being made of pure iron or an iron-based alloy, and the iron-based alloy may be an Fe-Si alloy, an Fe-Al alloy, or an Fe-Si-Al alloy.

[0023] The saturation magnetic flux density of pure iron is higher than that of iron-based alloys. Therefore, if the metal particles of a compacted body are composed of pure iron, the saturation magnetic flux density of the compacted body tends to be high. Furthermore, pure iron has better formability than iron-based alloys. Therefore, if the metal particles of a compacted body are composed of pure iron, the relative density of the compacted body tends to be high.

[0024] Iron losses, such as eddy current losses, in iron-based alloys are easier to reduce than those in pure iron. Therefore, if the metal particles in a compacted product are composed of an iron-based alloy, it is easier to reduce losses in the compacted product.

[0025] (5) Any motor described in (1) to (4) above may include a case having a first plane on which the stator is mounted, and a fastening member for fixing the first plane and the stator.

[0026] The above motor offers superior assembly precision because the fastening members can suppress misalignment between the stator and the first plane.

[0027] (6) In any of the motors described in (1) to (5) above, the number of stators and the number of rotors may be one each.

[0028] The above motor is a single-stator, single-rotor type. The above motor boasts excellent assembly precision.

[0029] (7) In any of the motors described in (1) to (5) above, the number of stators may be two and the number of rotors may be one.

[0030] The above motor is a double-stator, single-rotor type. The above motor boasts excellent assembly precision.

[0031] (8) A method for manufacturing a motor according to one aspect of the present disclosure comprises the steps of adjusting the height of a stator in an axial gap type motor and assembling the parts of the motor, wherein the parts include a rotor, the stator, a shaft which is the rotation axis of the rotor, and a bearing which rotatably supports the shaft, the stator having a stator core made of a powder-molded body, the step of adjusting the height of the stator comprising the steps of determining the design height of the stator core considering the actual dimensions of the shaft and the bearing, and grinding at least one of the first surface and the second surface of the stator core to achieve the determined design height, wherein the design height is a height where the length of the gap between the rotor and the stator is the design length, the first surface is the surface facing the gap, and the second surface is the surface provided on the opposite side of the first surface in the axial direction of the shaft.

[0032] The above motor manufacturing method includes a step of determining the design height and a step of grinding a predetermined surface of the stator core to achieve the determined design height, thereby enabling the production of a stator core with the design height. The design height is the height of the stator core such that the gap length is the design length. Furthermore, the above motor manufacturing method allows the motor to be assembled using parts including the stator core with the design height. Therefore, the above motor manufacturing method allows the gap length to be set to the design length by assembling the parts only once. Thus, the above motor manufacturing method is excellent in terms of the manufacturability of motors with excellent assembly accuracy, even without using shims.

[0033] (9) In the motor manufacturing method of (8) above, the rotor comprises an annular rotor body and at least one magnet fixed to the rotor body, wherein the rotor body has a first surface facing the magnet, and the magnet has a first end surface facing the stator, and the step of determining the design height may be performed by determining the design height by considering the actual length between the first surface of the rotor body and the first end surface of the magnet in the rotor to which the rotor body and the magnet are fixed.

[0034] The above motor manufacturing method allows for the determination of a precise design height, thus enabling the production of motors with superior assembly precision.

[0035] (10) In the motor manufacturing method described in (8) or (9) above, the process of assembling the parts is repeated, and the process of determining the design height is to determine the design height by considering the average value of the actual dimensions of the shaft and the bearing, which is less than the number of motors to be manufactured.

[0036] The above motor manufacturing method allows for the determination of a precise design height, thus enabling the production of motors with superior assembly precision.

[0037] (11) In any of the motor manufacturing methods described in (8) to (10) above, the grinding process may be surface grinding.

[0038] The above motor manufacturing method makes it easy to produce a stator core with the design height.

[0039] (12) In any of the motor manufacturing methods described in (8) to (11) above, the part includes a case having a first surface on which the stator is mounted, and the grinding step may be performed by grinding the second surface while the stator and the case are combined.

[0040] The above motor manufacturing method can produce motors with excellent assembly precision.

[0041] (13) In any of the motor manufacturing methods described in (8) to (11) above, the part includes a case having a first plane on which the stator is mounted, and the grinding step may be performed on at least one of the first surface and the second surface of the stator core when the stator and the case are not assembled.

[0042] The above motor manufacturing method facilitates the grinding of the stator core, and therefore allows for the production of motors with superior assembly precision. Furthermore, it facilitates the removal of grinding debris from the stator core.

[0043] 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.

[0044] Embodiment 1 [Motor] Motor 1 of Embodiment 1 will be described with reference to Figures 1 to 6. Figure 1 is a cross-sectional view of motor 1 cut by a plane parallel to the axial direction of shaft 4. Figure 1 illustrates a single-stator, single-rotor type axial gap motor as motor 1. A single-stator, single-rotor type is a motor in which there is one stator 2 and one rotor 3. An axial gap motor is a motor in which the stator 2 and rotor 3 face each other with a gap in the axial direction of shaft 4. Figure 4 is a perspective view showing only the stator core 21 of motor 1 for the sake of explanation.

[0045] The motor 1 of this embodiment comprises a stator 2, a rotor 3, a shaft 4, and a first bearing 51. The motor 1 has the stator 2, rotor 3, and shaft 4 housed in a case 7, which will be described later. The stator 2 and rotor 3 in the case 7 face each other with a gap in the axial direction of the shaft 4. The length of this gap along the axial direction satisfies the design length G1. The design length G1 is the target value of the design gap length determined based on the specifications of the motor 1. The design length G1 has a certain tolerance. One of the features of the motor 1 of this embodiment is that the stator 2 has a specific stator core 21.

[0046] [Stata] As shown in Figure 1, the stator 2 is positioned on the first plane 71f of the case 7. As shown in Figure 1, the stator 2 comprises a stator core 21 and a plurality of coils 25.

[0047] (Stator core) The stator core 21 comprises an annular plate-shaped yoke 22 and a plurality of columnar teeth 23.

[0048] <yoke> The yoke 22 magnetically couples adjacent teeth 23 among the teeth 23 arranged circumferentially around the yoke 22. As shown in Figure 2, the yoke 22 has a planar upper surface 22a, a planar lower surface 22b, an outer surface, and an inner surface. The upper surface 22a and the lower surface 22b are surfaces that connect the outer surface and the inner surface. The upper surface 22a is the surface that connects to the side surface 23b of the teeth 23. The lower surface 22b is the surface that is in contact with the first plane 71f. The lower surface 22b is the second surface 21s of the stator core 21. The second surface 21s is the surface of the stator core 21 that is located on the opposite side of the stator core 21 from the first surface 21f in the axial direction of the shaft 4. The first surface 21f of the stator core 21 is the surface that faces the gap. The terms "up" and "down" here do not necessarily coincide with the terms "up" and "down" of the motor 1.

[0049] <Teeth> As shown in Figure 1, each tooth 23 is provided with a coil 25. There are multiple teeth 23. Each tooth 23 is arranged at a predetermined interval in the circumferential direction of the yoke 22. Each tooth 23 protrudes perpendicularly to the upper surface 22a of the yoke 22, as shown in Figure 2. In this embodiment, each tooth 23 and the yoke 22 are made of a single compacted molded body. The compacted molded body will be described later. Each tooth 23 has the same shape and size. Each tooth 23 is either prismatic or cylindrical. Each tooth 23 has a side surface 23b and an end surface 23a. The side surface 23b is the surface connected to the upper surface 22a of the yoke 22. The end surface 23a is the surface connected to the side surface 23b. The end surface 23a is the first surface 21f. The end surface 23a faces the magnet 35 of the rotor 3, which will be described later.

[0050] <Grinding marks> At least one of the second surface 21s, the lower surface 22b, and the first surface 21f, the end surface 23a, has grinding marks. The grinding marks are formed by grinding during the manufacturing process. In Figure 4, for the sake of explanation, the grinding marks 231 on one end surface 23a are exaggerated. Figure 4 omits the grinding marks on the other end surface 23a. The grinding marks 231 are streaky irregularities that occur during grinding. The streaks of the grinding marks 231 are formed along the relative direction of movement between the end surface 23a and the grinding machine 1000, which will be described later with reference to Figures 8 and 9, during grinding. Grinding marks refer to streaky irregularities such as those that satisfy an arithmetic mean roughness Ra of 0.1 μm or more and 50 μm or less. The arithmetic mean roughness Ra is a value measured in accordance with JIS B 0601 (2013). The arithmetic mean roughness Ra may further satisfy the condition of being between 0.1 μm and 10 μm, and especially between 0.1 μm and 5 μm. Unlike the end faces 23a, each side surface 23b is not ground. If the second surface 21s is ground during the manufacturing process, grinding marks similar to those shown in Figure 4 (though not shown) will be provided on the second surface 21s.

[0051] <Hole> As shown in Figure 1, the stator core 21 has a hole. A fastening member 91 is provided in this hole. The fastening member 91 fixes the stator core 21 to the first plane 71f. The fastening member 91 suppresses misalignment between the stator 2 and the first plane 71f. An example of the fastening member 91 is a screw or a bolt. The hole is formed from the second surface 21s to the middle of the teeth 23. The number of holes may be less than the number of teeth 23, or it may be the same as the number of teeth 23.

[0052] <height> The height of the stator core 21 satisfies the design height H1, as shown in Figures 2, 3, and 5. The design height H1 is the height of the stator core 21 such that the gap length is the design length G1. The design height H1 has a certain tolerance width.

[0053] As shown in Figure 5, the difference between the maximum and minimum heights of the stator core 21 is small because at least one of the second surface 21s, which is the lower surface 22b, and the first surface 21f, which is the end surface 23a, is ground. This difference is the difference between the maximum and minimum lengths between each end surface 23a and the lower surface 22b.

[0054] A micrometer is used to measure the length between each end face 23a and the bottom surface 22b. Multiple measurement points are selected on each end face 23a. The measurement points are set, for example, on a straight line drawn from a plan view of the stator core 21, passing through the centroid of the end face 23a and the center of the yoke 22. Three or more measurement points are selected on the above straight line. In particular, the measurement points on the above straight line include the centroid of the end face 23a, the edge of the end face 23a closer to the center of the yoke 22, and the edge of the end face 23a further from the center of the yoke 22. The length between each end face 23a and the bottom surface 22b is the average length of the straight lines perpendicular to the bottom surface 22b that connect the bottom surface 22b to each measurement point.

[0055] The above difference may be 0.02 mm or less. If the above difference is 0.02 mm or less, the torque ripple of motor 1 is small. Therefore, the noise and vibration of motor 1 are small. A smaller above difference makes it easier to reduce torque ripple. The above difference may be 0.01 mm or less, even 0.008 mm or less, and especially 0.005 mm or less.

[0056] [Parallelism] The parallelism between the lower surface 22b and each end surface 23a may be 0.02 mm or less. If the above parallelism is 0.02 mm or less, the torque ripple of the motor 1 is small. Therefore, the noise and vibration of the motor 1 are small. A smaller parallelism makes it easier to reduce torque ripple. The above parallelism may be 0.01 mm or less, even 0.008 mm or less, and especially 0.005 mm or less.

[0057] The above parallelism is determined as follows: A height gauge equipped with a Grade 0 surface plate is used. The stator core 21 is placed on the surface plate so that the end faces 23a face upward. Multiple measurement points are selected on each end face 23a. The measurement points are set on a straight line drawn from a plan view of the stator core 21, passing through the centroid of the end face 23a and the center of the yoke 22. Three or more measurement points are selected on the above straight line. The measurement points on the above straight line include the centroid of the end face 23a, the edge of the end face 23a closer to the center of the yoke 22, and the edge of the end face 23a further from the center of the yoke 22. The parallelism between the lower surface 22b and each end face 23a is the average length of the straight line connecting the surface plate and each measurement point, which is perpendicular to the surface plate.

[0058] <Materials> The compacted powder body constituting the stator core 21 is composed of an aggregate of multiple coated particles 24 as shown in Figure 6. Each coated particle 24 has metal particles 241 and an insulating coating 242.

[0059] ·Metal particles The metal particles 241 are composed of a soft magnetic material. The soft magnetic material is pure iron or an iron-based alloy.

[0060] Pure iron is iron with a purity of 99% or higher. In other words, pure iron is iron (Fe) with a content of 99% by mass or higher. The saturation magnetic flux density of pure iron is higher than that of iron-based alloys. Therefore, if the metal particles 241 of a powder compact are composed of pure iron, the saturation magnetic flux density of the powder compact tends to improve. Also, the formability of pure iron is superior to that of iron-based alloys. Therefore, if the metal particles 241 of a powder compact are composed of pure iron, the relative density of the powder compact tends to increase.

[0061] An iron-based alloy is a material 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 an Fe-Si alloy is silicon steel. An example of an Fe-Si-Al alloy is Sendust. An example of an Fe-Ni alloy is permalloy. The electrical resistance of an iron-based alloy is greater than that of pure iron. Therefore, iron-based alloys make it easier to reduce iron losses such as eddy current losses. Thus, if the metal particles 241 of the compacted body are composed of an iron-based alloy, the losses of the compacted body are easily reduced. The compacted body may contain both metal particles composed of pure iron and metal particles composed of an iron-based alloy.

[0062] • Insulating coating The insulating coating 242 covers the metal particles 241. The insulating coating 242 can reduce iron losses such as eddy current losses. A compacted molded body equipped with the insulating coating 242 is more prone to loss reduction. The material of the insulating coating 242 is, for example, an oxide. Examples of oxides include phosphate, silica, magnesium oxide, or aluminum oxide. Phosphates have excellent adhesion to the metal particles 241 and also have excellent deformability. Therefore, if the insulating coating 242 is composed of phosphate, the insulating coating 242 is more likely to deform in accordance with the deformation of the metal particles 241 during the manufacturing process of the compacted molded body. Thus, the insulating coating 242 is less prone to damage. Because the insulating coating 242 is less prone to damage, the loss of the compacted molded body is more easily reduced.

[0063] <Relative density> The relative density of the compacted body may be 90% or higher. Compacted bodies with a relative density of 90% or higher are more likely to have improved saturation magnetic flux density. Compacted bodies 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.

[0064] The "relative density of a compacted material" refers to the ratio (%) of the actual density of the compacted material to its true density. That is, the relative density of a compacted material is calculated by [(actual density of compacted material / true density of compacted material) × 100]. The actual density of a compacted material can be determined by immersing it in oil to impregnate it with oil, and then calculating [oil-impregnated density × (mass of compacted material before oil impregnation / mass of compacted material after oil impregnation)]. The oil-impregnated density is (mass of compacted material after oil impregnation / volume of compacted material after oil impregnation). That is, the actual density of a compacted material can be determined by (mass of compacted material before oil impregnation / volume of compacted material after oil impregnation). The volume of a compacted material after oil impregnation can typically be measured by the liquid displacement method. The true density of a compacted material is the theoretical density assuming that there are no voids inside.

[0065] (coil) Each coil 25 has a cylindrical portion. The cylindrical portion is constructed by winding the wire spirally. The coil 25 in this embodiment is an edgewise wound coil. Coated flat wire is used for the winding of the coil 25. Each coil 25 is arranged on the outer circumference of the side surface 23b of the teeth 23. The cross-sectional shape of the cylindrical portion of each coil 25 corresponds, for example, to the cross-sectional shape of the teeth 23. The axial length of the cylindrical portion is slightly shorter than the length of the teeth 23. Note that in Figure 1, only the cylindrical portion is shown, and both ends of the winding are omitted from the illustration.

[0066] [Rotor] The rotor 3 is positioned with a gap between it and the stator 2. The rotor 3 is integrally fixed to the shaft 4. This fixation allows the rotor 3 to rotate integrally with the shaft 4 around its axis of rotation. The rotor 3 comprises a rotor body 31 and at least one magnet 35.

[0067] (Rotor body) The rotor body 31 is rotatably supported relative to the case 7 by the shaft 4. The rotor body 31 is an annular member. The rotor body 31 has a through hole in the center. The third shaft portion 43 of the shaft 4, which will be described later, is provided in this through hole. In this embodiment, the rotor body 31 and the shaft 4 are assembled by press-fitting the shaft 4 into the through hole. Because it is press-fitted, the runout of the rotor 3 tends to be small. The position of the rotor body 31 along the axial direction of the shaft 4 is determined by the rotor body 31 abutting against the second end face 42s of the second shaft portion 42, which will be described later.

[0068] As shown in Figure 2, the rotor body 31 has a first surface 31f, a second surface 31s, an inner circumferential surface, and an outer circumferential surface. The first surface 31f and the second surface 31s connect the inner circumferential surface and the outer circumferential surface. The first surface 31f is the surface facing the stator 2. The second surface 31s is the surface facing the second bearing 55 shown in Figure 1. The second bearing 55 will be described later. In this embodiment, a recess 32 is provided on the first surface 31f. The recess 32 opens toward the stator 2. A magnet 35 is fixed to the bottom surface 32a of the recess 32. The inner circumferential surface of the rotor body 31 is in contact with the third shaft portion 43 of the shaft 4. As shown in Figure 1, the outer circumferential surface of the rotor body 31 is not in contact with the inner circumferential surface of the peripheral wall portion 73 of the case 7. A gap is provided between the outer circumferential surface of the rotor body 31 and the inner circumferential surface of the peripheral wall portion 73 of the case 7.

[0069] (magnet) The magnet 35 is fixed to the rotor body 31. As shown in Figure 2, adhesive 38 is used to fix the magnet 35. There may be one magnet 35 or multiple magnets. If there is one magnet 35, the number of parts is fewer compared to when there are multiple magnets 35, making it easier to manufacture the rotor 3. Therefore, it is easier to improve the manufacturability of the motor 1. Moreover, it is easier to manufacture a motor 1 with excellent assembly precision.

[0070] If there is only one magnet 35, the shape of the magnet 35 is annular. The single magnet 35 has alternating south and north poles arranged in the circumferential direction. If there are multiple magnets 35, the specific number of magnets 35 is the same as the number of teeth 23. The multiple magnets 35 are arranged at equal intervals in the circumferential direction of the rotor body 31. The shape of each magnet 35 is, for example, a flat plate. The planar shape of each magnet 35 is, for example, the same as the planar shape of the end face 23a of the tooth 23. Each magnet 35 is magnetized in the axial direction of the rotation axis of the rotor 3. The magnetization directions of adjacent magnets 35 in the circumferential direction of the rotor body 31 are opposite to each other. The rotor 3 rotates as the magnets 35 are repeatedly attracted to and repelled by each tooth 23 by the rotating magnetic field generated by the stator 2.

[0071] Magnet 35 is a permanent magnet. Specific examples of permanent magnets include ferrite magnets, neodymium magnets, samarium-cobalt magnets, or bonded magnets. Neodymium magnets and samarium-cobalt magnets, in particular, have strong magnetic forces.

[0072] [shaft] The shaft 4 is the axis of rotation of the rotor 3. The shaft 4 is made of a solid round rod. As shown in Figure 1, the shaft 4 has multiple shaft portions with different outer diameters. The multiple shaft portions are integrally formed. In this embodiment, the shaft 4 has, in order from the first plate portion 71 toward the second plate portion 72 of the case 7, a first shaft portion 41, a second shaft portion 42, a third shaft portion 43, a fourth shaft portion 44, and a fifth shaft portion 45.

[0073] As shown in Figure 1, the first shaft portion 41 is provided inside the first bearing 51. As shown in Figure 2, the outer circumferential surface of the first shaft portion 41 is in contact with the inner circumferential surface of the inner race 52 of the first bearing 51.

[0074] As shown in Figure 1, the second shaft portion 42 has a larger diameter than the first shaft portion 41. As shown in Figure 2, the second shaft portion 42 has a first end face 42f and a second end face 42s. The first end face 42f is in contact with the first end face 52f of the inner race 52. The first end face 42f is not in contact with the outer race 53 of the first bearing 51. The second end face 42s is in contact with the first surface 31f of the rotor body 31.

[0075] As shown in Figure 1, the third shaft portion 43 is provided in a through hole of the rotor body 31. As shown in Figure 2, the outer circumferential surface of the third shaft portion 43 is in contact with the inner circumferential surface of the rotor body 31. As shown in Figure 1, the third shaft portion 43 has a smaller diameter than the second shaft portion 42. As shown in Figure 2, the third shaft portion 43 has an end face 43a. The end face 43a is in contact with the first end face of the inner race 56 of the second bearing 55.

[0076] As shown in Figure 1, the fourth shaft portion 44 is provided within the second bearing 55. The outer circumferential surface of the fourth shaft portion 44 is in contact with the inner circumferential surface of the inner race 56 of the second bearing 55. The fourth shaft portion 44 has a smaller diameter than the third shaft portion 43.

[0077] The fifth shaft portion 45 is provided in the through hole 72h of the second plate portion 72 of the case 7. The outer circumferential surface of the fifth shaft portion 45 is not in contact with the inner circumferential surface of the second plate portion 72. The fifth shaft portion 45 has a smaller diameter than the diameter of the fourth shaft portion 44.

[0078] [First bearing, second bearing] The first bearing 51 and the second bearing 55 support the shaft 4 so that it can rotate freely around its axis of rotation. The first bearing 51 is mounted on the first shaft portion 41 of the shaft 4. The second bearing 55 is mounted on the fourth shaft portion 44 of the shaft 4. The configurations of the first bearing 51 and the second bearing 55 may be the same or different.

[0079] The first bearing 51 is a radial bearing or an angular contact bearing. As shown in Figures 2 and 3, the first bearing 51 has an inner race 52 and an outer race 53. In this embodiment, the first bearing 51 is a ball bearing in which balls 54 are arranged between the inner race 52 and the outer race 53. The inner circumferential surface of the inner race 52 is in contact with the outer circumferential surface of the first shaft portion 41 of the shaft 4. The outer circumferential surface of the outer race 53 is in contact with the protrusion 71a, which will be described later.

[0080] The inner race 52 has a first end face 52f and a second end face 52s. The outer race 53 has a first end face 53f and a second end face 53s. The first end face 52f is in contact with the first end face 42f. The first end face 53f is not in contact with the shaft 4. The second end face 52s is not in contact with the case 7. In this embodiment, the second end face 52s is in contact with a fixing member, which is not shown. This fixing member mechanically fixes the first bearing 51 and the first shaft portion 41. An example of this fixing member is a retaining ring or a shaft nut. If a shaft nut is used as the fixing member, it is preferable to form a threaded portion on the outer circumferential surface of the first shaft portion 41. This fixing member is not required. In that case, the inner race 52 and the first shaft portion 41 are fixed by fitting them together. The second end face 53s is in contact with the first plane 71f. Figure 2 shows an example where the first end face 52f and the first end face 53f are not misaligned along the axial direction of the first bearing 51. Figure 3 shows an example where the first end face 52f and the first end face 53f are misaligned along the axial direction of the first bearing 51. As will be explained in more detail later, the first end face 52f and the first end face 53f may also be misaligned along the axial direction of the first bearing 51.

[0081] The second bearing 55 is a radial bearing or an angular contact bearing. The configuration of the second bearing 55 is the same as that of the first bearing 51. That is, as shown in Figures 2 and 3, the second bearing 55 has an inner race 56 and an outer race 57. As shown in Figure 1, the second bearing 55 is a ball bearing in which balls 58 are arranged between the inner race 56 and the outer race 57. The inner circumferential surface of the inner race 56 is in contact with the outer circumferential surface of the third shaft portion 43. The outer circumferential surface of the outer race 57 is in contact with the inner circumferential surface of the recess 72a. The recess 72a is provided in the second plate portion 72 of the case 7. Each of the inner race 56 and the outer race 57 has a first end face and a second end face. The first end face of the inner race 56 is in contact with the end face 43a. The second end face of the inner race 56 is not in contact with the elastic member 8 and the case 7, which will be described later. The second end face of the inner race 56 may or may not be in contact with a fixing member similar to that of the first bearing 51, because the outer race 57 is pressed toward the rotor 3 by the elastic member 8. The first end face of the outer race 57 is not in contact with the rotor 3 or the shaft 4. The second end face of the outer race 57 is in contact with the elastic member 8 shown in Figure 1.

[0082] [Elastic material] The elastic member 8 presses the second bearing 55 toward the rotor 3. The elastic member 8 is positioned between the outer race 57 and the bottom of the recess 72a. An example of the elastic member 8 is a spring washer, a disc spring washer, a corrugated washer, or a rubber O-ring.

[0083] [case] Case 7 houses the stator 2, rotor 3, part of the shaft 4, the first bearing 51, and the second bearing 55, among other things. Case 7 comprises a first plate section 71, a second plate section 72, and a peripheral wall section 73.

[0084] In this embodiment, the peripheral wall portion 73 and the second plate portion 72 are integrally constructed. In this embodiment, the peripheral wall portion 73 and the first plate portion 71 are separate components. Unlike this embodiment, the peripheral wall portion 73 and the first plate portion 71 may be integrally constructed, while the peripheral wall portion 73 and the second plate portion 72 may be separate components. Also, unlike this embodiment, the peripheral wall portion 73, the first plate portion 71, and the second plate portion 72 may be separate components. In this embodiment, the peripheral wall portion 73 and the first plate portion 71 are fixed to each other by fastening members 92. An example of fastening member 92 is a screw or bolt, similar to fastening member 91.

[0085] The peripheral wall portion 73 surrounds the outer circumference of the stator 2 and rotor 3. A hole is provided at the end face of the peripheral wall portion 73. A fastening member 92 is provided in this hole.

[0086] The first plate portion 71 has a first plane 71f, a projection 71a, a first through hole, a second through hole, and a third through hole. The stator 2 is positioned on the first plane 71f. The projection 71a is provided between the stator 2 and the first bearing 51. The projection 71a is connected to the first plane 71f. The shape of the projection 71a is, for example, cylindrical. The inner circumferential surface of the projection 71a is in contact with the outer circumferential surface of the outer race 53. The projection 71a can be used to position the first bearing 51. The outer circumferential surface of the projection 71a may or may not be in contact with the inner circumferential surface of the yoke 22. A part of the first shaft portion 41 is provided in the first through hole. A fastening member 91 is provided in the second through hole. The second through hole is provided at a location corresponding to the hole in the stator core 21. A fastening member 92 is provided in the third through hole. The third through hole is provided at a location corresponding to the hole in the peripheral wall portion 73.

[0087] The second plate portion 72 has a recess 72a in the center. A through hole 72h is provided at the bottom of the recess 72a. The fifth shaft portion 45 is provided inside the through hole 72h. The inner diameter of the through hole 72h is larger than the outer diameter of the fifth shaft portion 45. Therefore, the shaft 4 rotates without the inner circumferential surface of the through hole 72h coming into contact with the fourth shaft portion 44.

[0088] The motor 1 of this embodiment has excellent assembly precision. Although the stator core 21 is made of a powder-molded body with lower dimensional accuracy than electromagnetic steel sheet, the grinding process during manufacturing allows the stator core 21 to have a height where the gap length is equal to the design length H1. Since the motor 1 does not have shims, the increase in the number of parts can be suppressed. Furthermore, since the motor 1 can suppress the increase in bearing preload, the increase in mechanical loss can be suppressed.

[0089] [Motor manufacturing method] The motor manufacturing method of Embodiment 1 will be described with reference to Figures 2, 3, and 7 to 9. The motor manufacturing method of this embodiment comprises steps A and B. Step A involves adjusting the height of the stator. Process B involves assembling the motor parts.

[0090] Process A comprises process A1 and process A2. Step A1 is to determine the design height H1 of the stator core 21. Step A2 involves grinding at least one of the second surface 21s, which is the lower surface 22b, and the first surface 21f, which is the end surface 23a, of the stator core 21. This grinding process sets the height of the stator core 21 to the design height H1. The parts assembled in step B are the parts of the motor 1 described above, referring to Figures 1 to 3. In this embodiment, the parts include the stator 2, rotor 3, shaft 4, first bearing 51, second bearing 55, case 7, elastic member 8, fastening member 91, and fastening member 92.

[0091] The stator core 21 is manufactured by pressure molding of raw material powder. The raw material powder contains a plurality of 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. 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 circumferential surface of the die, which will be described later.

[0092] 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 and core rod form a cavity into which the raw material powder is filled. The upper and lower punches pressure-molde the raw material powder filled in the cavity.

[0093] The pressure during compression molding is, for example, between 500 MPa and 2000 MPa. If the pressure during compression molding is 500 MPa or higher, a compacted powder molded body with high relative density can be manufactured. 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 may further be between 700 MPa and 1800 MPa, or especially between 800 MPa and 1500 MPa.

[0094] [Process A] (Process A1) In process A1, the design height H1 of the stator core 21 manufactured as described above is determined. The design height H1 is determined by considering the actual dimensions of the shaft 4 and the first bearing 51. For example, the actual dimensions of the shaft 4 are the dimensions measured of the shaft 4 before assembly. The same approach to actual dimensions applies to the actual dimensions of the first bearing 51. Considering actual dimensions includes considering the actual dimensions themselves and considering calculated values ​​obtained from the actual dimensions. For example, the calculated value obtained from the actual dimensions of the shaft 4 is the average value of the actual dimensions of each shaft 4 obtained from multiple shafts 4. The same approach to calculated values ​​applies to the calculated value of the first bearing 51.

[0095] Referring to Figures 1 to 3, as in the motor 1 described above, when the first end face 35f is closer to the stator 2 than the first surface 31f, the design height H1 is determined by further considering the actual dimensions of the rotor 3. Unlike the motor 1 described above, when the first surface 31f and the first end face 35f are flush, the design height H1 is determined by considering the actual dimensions of the shaft 4 and the first bearing 51, as described above.

[0096] The number of measurements required to calculate the average value may be less than the number of motors manufactured. For example, consider the case where 1000 motors are manufactured. If one of a certain part is used in each motor, the number of measurements required to calculate the average actual dimensions of that part may be less than 1000. Even if two of a certain part are used, the number of measurements required to calculate the average actual dimensions of that part may still be less than 1000. More specifically, the average value can be calculated from the actual dimensions of 50 or fewer of a certain part. The average value may also be calculated for each lot of a particular part.

[0097] As shown in Figure 2, if the first end face 35f is closer to the stator 2 than the first end face 31f, and the first end face 52f and the first end face 53f are not misaligned along the axial direction of the first bearing 51, the design height H1 can be calculated as "length L1 + length L2 + length L3 - (length L4 + design length G1)". Although not shown in the figure, if the first end face 31f and the first end face 35f are flush, and the first end face 52f and the first end face 53f are not misaligned along the axial direction of the first bearing 51, the design height H1 can be calculated as "length L1 + length L2 - design length G1".

[0098] Length L1 is the height of the first bearing 51. Length L2 is the length of the second shaft portion 42. That is, length L2 is the length between the first end face 42f and the second end face 42s. Length L3 is the depth of the recess 32. That is, length L3 is the length between the first surface 31f and the bottom surface 32a. The length L4 is the thickness Tm of the magnet 35. If the magnet 35 and the rotor body 31 are fixed together with adhesive 38, the length L4 is the sum of the thickness Tm of the magnet 35 and the thickness Ta of the adhesive 38. All of these lengths are along the axial direction of shaft 4.

[0099] The actual length L1 may be either the actual height of the inner race 52 or the actual height of the outer race 53. Measuring the height of the outer race 53 is easier than measuring the height of the inner race 52. The actual height of either the inner race 52 or the outer race 53 shall be the average of the heights measured at multiple points. The measurement points shall be taken at equal intervals around the inner race 52 or outer race 53. There shall be at least three measurement points.

[0100] The actual length L2 shall be the average of the lengths measured at multiple measurement points. The measurement points shall be taken at equal intervals in the circumferential direction of the second shaft portion 42. There shall be three or more measurement points.

[0101] The actual length L3 is the average of the depths measured at multiple measurement points. The measurement points are taken at equal intervals on the circumferences of three concentric circles. The three circumferences are, when viewed from above, the circumference of the inner edge of the recess 32, the circumference of the outer edge of the recess 32, and the circumference at the midpoint between the inner and outer edges of the recess 32. There are three or more measurement points on each circumference. A measurement point on the inner circumference, a measurement point on the outer circumference, and a measurement point on the midpoint are located on a straight line along the radial direction of the rotor 3.

[0102] The actual length L4 is the average of the thicknesses Tm of multiple magnets 35 if there are multiple magnets 35. Each thickness Tm may be the thickness at one measurement point, or it may be the average of the thicknesses Tm at multiple measurement points. One measurement point is the centroid of the first end face 35f when the magnet 35 is viewed from above. Multiple measurement points are set on a straight line drawn from the centroid of the first end face 35f to the center of the rotor 3 when the magnet 35 is viewed from above. There are three or more multiple measurement points on the above straight line. In particular, the multiple measurement points on the above straight line include the centroid of the first end face 35f, the edge of the first end face 35f closer to the center of the rotor 3, and the edge of the first end face 35f further from the center of the rotor 3.

[0103] The actual length L4 is the average of the thickness Tm of multiple measurement points when there is one magnet 35 and the shape of the magnet 35 is annular. The measurement points are taken at equal intervals on the circumference of three concentric circles. The three circumferences are, when the magnet 35 is viewed from above, the circumference of the inner edge of the first end face 35f, the circumference of the outer edge of the first end face 35f, and the circumference of the midpoint between the inner and outer edges of the first end face 35f. There are three or more measurement points on each circumference. A measurement point on the inner edge circumference, a measurement point on the outer edge circumference, and a measurement point on the midpoint circumference are located on a straight line along the radial direction of the rotor 3. The thickness of each measurement point is the length along the axial direction of the rotor 3 at each measurement point.

[0104] The actual length L4 is the actual length when the rotor body 31 and the magnet 35 are fixed together, provided that adhesive 38 is applied. That is, the actual length L4 is the average length along the axial direction of the rotor 3 between the measurement point of the thickness Tm of the magnet 35 and the bottom surface 32a of the recess 32.

[0105] The design height H1 is determined by considering the displacement g of the first bearing 51 when the first end face 52f and the first end face 53f are misaligned along the axial direction of the first bearing 51, as shown in Figure 3. The displacement g is the length along the axial direction of the first bearing 51 between the first end face 53f and the first end face 52f.

[0106] The displacement amount g is determined by considering the load acting on the inner race 52 due to the weight of the shaft 4 and rotor 3, and the load acting on the inner race 52 due to the attractive force of the magnet 35 on the stator 2. The displacement amount g is further determined by considering at least one of the load acting on the inner race 52 due to the weight of the second bearing 55, and the load acting on the inner race 52 due to the pressing force of the elastic member 8 pressing the second bearing 55 toward the first bearing 51.

[0107] The inner race 52 is subjected to loads primarily from the weight of the shaft 4 and rotor 3, and from the attractive force of the magnet 35 toward the stator 2. The inner race 52 is also subjected to at least one of the following: the load from the weight of the second bearing 55, and the load from the pressing force of the elastic member 8 pressing the second bearing 55 toward the first bearing 51. Depending on the magnitude of the above loads, the first end face 52f may shift relative to the first end face 53f. In particular, the shift of the first end face 52f is greatly influenced by the attractive force of the magnet 35. That is, the stronger the magnetic force of the magnet 35, the greater the shift of the first end face 52f. The length of the gap becomes shorter than the design length G1 by the amount of shift g. Therefore, the amount of shift g should be taken into consideration.

[0108] The displacement amount g can be determined from a graph like the one shown in Figure 7. The load (N) on the vertical axis of Figure 7 represents the load on the inner race 52 of the first bearing 51. The displacement amount (mm) on the horizontal axis of Figure 7 represents the displacement g of the first end face 52f of the inner race 52 relative to the first end face 53f of the outer race 53 of the first bearing 51. It is advisable to prepare the graph in Figure 7 in advance. Specifically, the graph in Figure 7 can be determined by applying the axial load of the first bearing 51 to the inner race 52 while displacing it.

[0109] As shown in Figure 3, if the first end face 35f is closer to the stator 2 than the first end face 31f, and the first end face 52f and the first end face 53f are offset along the axial direction of the first bearing 51, the design height H1 is calculated by "(length L1 - offset g) + length L2 + length L3 - (length L4 + design length G1)". Although not shown in the figure, if the first end face 31f and the first end face 35f are flush, and the first end face 52f and the first end face 53f are offset along the axial direction of the first bearing 51, the design height H1 is calculated by "(length L1 - offset g) + length L2 - design length G1".

[0110] (Process A2) In process A2, grinding is performed by the amount of the difference between the design height H1 obtained in process A1 and the actual height of the stator core 21. When grinding both the lower surface 22b, which is the second surface 21s, and the end surface 23a, which is the first surface 21f, the total grinding length is set to be equal to the difference between the design height H1 obtained in process A1 and the actual height of the stator core 21.

[0111] The actual height of the stator core 21 is determined by the actual length between the bottom surface 22b and the end surface 23a. The actual length between the bottom surface 22b and the end surface 23a is determined by the same measurement method as described above for measuring the length between each end surface 23a and the bottom surface 22b.

[0112] The timing for performing process A2 is either before process B, which will be described later, or between process B2 and process B3. Figure 8 shows an example of grinding being performed before process B. Figure 9 shows an example of grinding being performed between process B2 and process B3. As shown in Figure 8, the stator core 21 is ground when the stator core 21 and the first plate portion 71 are not assembled. In this case, at least one of the lower surface 22b and the end surface 23a of the stator core 21 can be ground. Alternatively, as shown in Figure 9, the stator core 21 is ground when the stator core 21 and the first plate portion 71 are assembled. In this case, only the end surface 23a can be ground.

[0113] In both Figure 8 and Figure 9, a grinding machine 1000 can be used for grinding. The grinding may be surface grinding. Surface grinding makes it easier to align the end faces 23a of the stator core 21 in the height direction.

[0114] When grinding the end face 23a, the end face 23a may be ground while fixing the end of the side surface 23b of each tooth 23, as shown in Figure 8 or Figure 9. For fixing the end, for example, a plate-shaped member 1100 as shown in Figure 8 may be used.

[0115] The plate-shaped member 1100 is provided with a plurality of through holes 1110. Each through hole 1110 is a hole into which the end of each tooth 23 can be inserted. The number of through holes 1110 corresponds to the number of teeth 23. The inner circumferential shape of the through holes 1110 is similar to the outer circumferential shape of the teeth 23. The size of the through holes 1110 is such that the end can be inserted, and when the end is inserted, the gap between the side surface 23b and the inner circumferential surface of the through hole 1110 is minute. The inner circumferential shape and size of each through hole 1110 are the same.

[0116] As shown in Figure 8 or Figure 9, each tooth 23 is inserted into each through hole 1110. The inner circumferential surface of the through hole 1110 holds the side surface 23b. While held, the end surface 23a is ground. For ease of explanation, Figures 8 and 9 exaggerate the exposed area from the plate-like member 1100 of each tooth 23. By fixing the vicinity of the end surface 23a of each tooth 23 with the plate-like member 1100, it is possible to prevent chipping of the edge between the end surface 23a and the side surface 23b during grinding. The plate-like member 1100 may also be ground during the grinding process.

[0117] Grinding marks 231, as explained with reference to Figure 4, are formed on the ground end face 23a. When the lower surface 22b is ground, grinding marks similar to those 231 are formed on the lower surface 22b, although this is not shown in the figure.

[0118] [Process B] In assembly process B, each component is fixed in its designated position. By going through process B, motor 1 as shown in Figure 1 is manufactured. As an example of the order in which the parts are assembled, the process proceeds from process B1 to process B6 in order.

[0119] In step B1, the stator 2 and the first bearing 51 are placed on the first plane 71f of the first plate portion 71.

[0120] In step B2, the first plate portion 71 and the stator 2 are fixed together by fastening members 91. The fastening members 91 are provided in the second through hole of the first plate portion 71 and in the hole of the stator 2.

[0121] In step B3, the first shaft portion 41 of the shaft 4 is placed inside the first bearing 51. A rotor assembly, consisting of the rotor 3 and shaft 4, is prepared in advance. In step B3, the first shaft portion 41 of the rotor assembly is placed inside the first bearing 51. In this case, step B4 is skipped and step B31 is skipped. If the rotor assembly is not prepared and the rotor 3 and shaft 4 are prepared separately, step B31 is skipped before step B4. Step B31 involves fitting the rotor 3 onto the shaft 4, which has the first shaft portion 41 placed inside the first bearing 51.

[0122] In step B4, the second bearing 55 is fitted onto the fourth shaft portion 44 of the shaft 4.

[0123] In step B5, the elastic member 8 is placed on top of the second bearing 55.

[0124] In step B6, the through hole 72h of the second plate portion 72 is fitted into the fifth shaft portion 45 of the shaft 4, and the end face of the peripheral wall portion 73 is brought into contact with the first plate portion 71. The first plate portion 71 and the peripheral wall portion 73 are then fixed together with fastening members 92. The fastening members 92 are provided in the third through hole of the first plate portion 71 and the aforementioned hole in the peripheral wall portion 73.

[0125] [Process C] The motor manufacturing method of this embodiment may further include a step C for heat-treating the stator core 21. Step C is performed before step A, or between step A and step B.

[0126] The heat treatment temperature is, for example, 350°C to 800°C. The heat treatment temperature may further be 400°C to 750°C, or more specifically 450°C to 700°C. The heat treatment holding time is, for example, 5 minutes to 60 minutes. The heat treatment holding time may further be 10 minutes to 45 minutes, or more specifically 15 minutes to 30 minutes. The atmosphere in the heat treatment is, for example, an oxidizing atmosphere. The oxygen concentration in the oxidizing atmosphere is, for example, 500 ppm to 20000 ppm. The oxygen concentration here refers to the volume percentage. The oxygen concentration in the oxidizing atmosphere may further be 700 ppm to 10000 ppm, 1000 ppm to 7500 ppm, or more specifically 2000 ppm to 5000 ppm.

[0127] If process C is performed before process A, oxides are formed between the coating particles near the surface of the stator core 21. The formed oxides suppress the plastic flow of the metal particles 241 that occurs during grinding. Therefore, even if the insulating coating 242 is damaged by grinding, it is possible to prevent adjacent metal particles 241 from connecting with each other. On the other hand, if process C is performed between process A and process B, the ground surface is oxidized. That is, even if the insulating coating 242 is damaged by grinding and adjacent metal particles 241 connect with each other, the connected parts are oxidized. Therefore, adjacent metal particles 241 are insulated from each other by the oxide film. Thus, by performing process C, eddy current losses are reduced, and consequently, losses are reduced.

[0128] In this motor manufacturing method, the design height H1 of the stator core 21, which will have a design length G1, can be determined before assembling the parts. Furthermore, in this motor manufacturing method, the height of the stator core 21 can be set to the design height H1 by grinding before or during the assembly of the parts. Therefore, in this motor manufacturing method, the gap length can be set to the design length G1 by assembling the parts only once. Thus, in this motor manufacturing method, the motor 1 can be manufactured with excellent assembly accuracy without the use of shims.

[0129] As described above, the inner race 52 of the first bearing 51 may be misaligned with respect to the outer race 53. Even in this case, the motor manufacturing method of this embodiment can determine the design height H1 while taking into account the aforementioned misalignment amount g. Therefore, even if the inner race 52 is misaligned, the motor manufacturing method of this embodiment provides excellent manufacturability for the motor 1, which has excellent assembly accuracy.

[0130] The motor manufacturing method of this embodiment offers excellent manufacturability for multiple motors 1 with superior assembly precision, even when the assembly process of parts is repeated. Therefore, the motor manufacturing method of this embodiment can produce multiple motors 1 with small variations in performance. In particular, by determining the design height H1 by considering the average value of the actual dimensions of a certain part, which is less than the number of parts manufactured, it is easier to improve the manufacturability of the motor 1 compared to when the design height H1 is determined by considering the actual dimensions of a certain part, which is equal to the number of parts manufactured.

[0131] Embodiment 2 [Motor] Referring to Figure 10, the motor 1 of Embodiment 2 will be described. The motor 1 of Embodiment 2 differs from the motor 1 of Embodiment 1 mainly in that it is a double-stator, single-rotor type axial gap motor. A double-stator, single-rotor type is a motor 1 in which there are two stators 2 and one rotor 3. In a double-stator, single-rotor type, one rotor 3 is assembled so that it is sandwiched between the two stators 2 from the axial direction of the shaft 4. At least one of the two stators 2 is the stator 2 described in Embodiment 1. Both of the two stators 2 may be the stator 2 described in Embodiment 1. The following description will focus on the differences from Embodiment 1. Descriptions of configurations similar to those in Embodiment 1 may be omitted.

[0132] [Rotor] The rotor body 31 is an annular flat plate member. The rotor body 31 has a first through hole and at least one second through hole. The first through hole is located in the center. The third shaft portion 43 of the shaft 4 is provided in the first through hole. The second through hole is located on the outer circumference of the first through hole. A magnet 35 is provided in the second through hole. The number of second through holes is the same as the number of magnets 35.

[0133] As shown in Figure 10, in this embodiment, the thickness of the rotor body 31 and the thickness of the magnet 35 are the same. That is, the first surface of the rotor body 31 and the first end surface of the magnet 35 are flush. Also, the second surface of the rotor body 31 and the second end surface of the magnet 35 are flush. The first surface of the rotor body 31 and the first end surface of the magnet 35 are the surfaces closer to the first stator 2. The second surface of the rotor body 31 and the second end surface of the magnet 35 are the surfaces closer to the second stator 2. Here, the stator 2 shown on the lower side of Figure 10 is referred to as the first stator 2. Also, the stator 2 shown on the upper side of Figure 10 is referred to as the second stator 2. Although not shown in the illustration, the thickness of the rotor body 31 and the magnet 35 do not have to be the same.

[0134] [case] Case 7 of this embodiment comprises a pair of first plate portions 71 and a peripheral wall portion 73. The pair of first plate portions 71 and peripheral wall portion 73 are constructed as separate parts. The first first plate portion 71 and peripheral wall portion 73 are fixed together by a fastening member 92. The second first plate portion 71 and peripheral wall portion 73 are fixed together by a fastening member 92.

[0135] [Motor manufacturing method] In the motor manufacturing method, the design height of the first stator core 21 is determined by considering the actual dimensions of the shaft 4 and the first bearing 51 shown on the lower side of Figure 10. The design height of the first stator core 21 is determined by "actual height of the first bearing 51 + actual length of the second shaft portion 42 - design length G1".

[0136] The design height of the second stator core 21 is determined by considering the actual dimensions of the rotor 3, the shaft 4, and the first bearing 51 shown in the upper part of Figure 10. The design height of the second stator core 21 is determined by "actual height of the first bearing 51 + actual length of the third shaft portion 43 - (thickness of the magnet 35 + design length G1)".

[0137] The actual length of the third shaft portion 43 is the actual length between the end face 43a and the second end face 42s. The actual length of the third shaft portion 43 is the average value of the lengths at multiple measurement points. The measurement points are taken at equal intervals in the circumferential direction of the third shaft portion 43. There are three or more measurement points. The length of each measurement point is the length along the axial direction of the third shaft portion 43 at each measurement point.

[0138] The motor 1 of this embodiment, like that of Embodiment 1, has excellent assembly precision. The manufacturing method of the motor of this embodiment is excellent in terms of the manufacturability of the motor 1, which has excellent assembly precision, even without using shims.

[0139] 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 equivalents thereof.

[0140] For example, the yoke may be composed of multiple fan-shaped yoke segments. The number of teeth connected to each yoke segment may be one or more. [Explanation of symbols]

[0141] 1 motor 2 staters 21 Stator core, 21f First surface, 21s Second surface 22 Yoke, 22a top, 22b bottom 23 Teeth, 23a End face, 23b Side, 231 Grinding marks 24 coated particles, 241 metal particles, 242 insulating coating 25 coils 3 rotors 31 Rotor body, 31f First surface, 31s Second surface 32 recess, 32a bottom surface 35 magnet, 35f first end surface 38 Adhesives 4 shafts 41 First shaft part 42 Second shaft part, 42f first end surface, 42s second end surface 43 Third shaft part, 43a end face 44 Fourth shaft part, 45 Fifth shaft part 51 First bearing 52 Inner race, 52f First end face, 52s Second end face 53 Outer race, 53f First end face, 53s Second end face 54 Ball 55 Second bearing 56 Inner lace, 57 Outer lace 58 balls 7 cases 71 First plate portion, 71f First plane, 71a Protruding portion 72 Second plate portion, 72a Recess, 72h Through hole 73 Peripheral wall section 8 Elastic members 91, 92 Fastening members 1000 Grinding Machine 1100 Plate-shaped member, 1110 Through hole A, B area G1 Design length, g displacement H1 Design height L1, L2, L3, L4 Length Tm, Ta thickness

Claims

1. The shaft and A bearing that rotatably supports the aforementioned shaft, A rotor fixed integrally with the shaft, A stator core used in a motor comprising a rotor and a stator positioned with a gap of a design length in the axial direction of the shaft, The stator core is made of a compacted powder molded body, The compacted body has a first surface facing the gap and a second surface provided on the opposite side of the first surface in the axial direction. The first surface and the second surface have grinding marks on at least one of them. Stator core.

2. A ring-shaped yoke, The yoke has a plurality of columnar teeth arranged at intervals in the circumferential direction, The aforementioned yoke is Outer surface and, Inner surface and, It has a planar upper surface and a planar lower surface connecting the outer peripheral surface and the inner peripheral surface, Each of the aforementioned multiple teeth is The side surface connected to the upper surface of the yoke, It has an end face that connects to the end of the side opposite to the side that connects to the upper surface, The aforementioned lower surface is the second surface, The end face is the first face, The stator core according to claim 1, wherein the difference between the maximum and minimum heights between the lower surface of the yoke and the end faces of each of the plurality of teeth is 0.02 mm or less.

3. The stator core according to claim 1 or claim 2, having the grinding marks on both the first surface and the second surface.

4. The stator core according to claim 2, wherein the parallelism between the lower surface and the end faces of each of the plurality of teeth is 0.02 mm or less.

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

6. The compacted powder molded body comprises a plurality of coated 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 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. The process includes adjusting the height of the stator core in an axial gap type motor. The stator core is made of a compacted powder molded body, The step of adjusting the height of the stator core is: A step of determining the design height of the stator core by considering the actual dimensions of the shaft, which is the rotating axis of the rotor, and the bearing that rotatably supports the shaft, which are parts of the motor. The process includes the step of grinding at least one of the first and second surfaces of the stator core to achieve the required design height, The aforementioned design height is the height at which the length of the gap between the rotor and the stator core becomes the design length. The aforementioned first surface is the surface facing the gap, A method for manufacturing a stator core, wherein the second surface is a surface provided on the opposite side of the first surface in the axial direction of the shaft.

8. The method for manufacturing a stator core according to claim 7, wherein the grinding step involves grinding both the first surface and the second surface.

9. The rotor is The rotor body is an annular plate shape, It comprises at least one magnet fixed to the rotor body, The rotor body has a first surface facing the magnet, The magnet has a first end face facing the stator, The method for manufacturing a stator core according to claim 7 or claim 8, wherein the step of determining the design height is to determine the design height in the rotor to which the rotor body and the magnets are fixed, taking into consideration the actual length between the first surface of the rotor body and the first end surface of the magnets.

10. The method for manufacturing a stator core according to claim 7 or claim 8, wherein the grinding process is surface grinding.

11. The method for manufacturing a stator core according to claim 7, wherein the grinding step is performed by grinding the first surface while the stator core and a case having a first surface on which the stator core is mounted are combined.

12. The method for manufacturing a stator core according to claim 7, wherein the grinding step is performed by grinding at least one of the first surface and the second surface of the stator core while the stator core and the case having a first surface on which the stator core is mounted are not combined.

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