Rotor for electric motor

Abstract

An example of a rotor for an electric motor is disclosed, taking into consideration the possibility of slippage occurring on the circumferential surface between the cylindrical rotor core and the bonded magnet layer. [Solution] The rotor 3 comprises a rotor shaft 31 and a substantially cylindrical rotor body 32 that is supported and rotated by the rotor shaft 31, and the rotor body 32 has four or more even-numbered sintered magnets 33, bonded magnets 34, and a core portion 35 integrated with the rotor shaft 31. The multiple sintered magnets 33 are arranged on the outside of the core portion 35, and the bonded magnets 34 are formed to cover the outside of the core portion 35. Furthermore, when the number of sintered magnets 33 is n, the cross-sectional shape of the core portion 35 is configured as a polygonal shape having n or more corners (including corners with C-chamfers and R-chamfers). This can suppress the occurrence of slippage at the interface between the core portion 35 and the bonded magnets 34.

Description

Technical Field

[0001] The present disclosure relates to a rotor for an electric motor having a sintered magnet and a bonded magnet.

Background Art

[0002] For example, in the rotor for an electric motor described in Patent Document 1, a plurality of sintered magnets for field excitation are embedded in a bonded magnet layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the invention described in Patent Document 1, the cylindrical rotor core portion and the bonded magnet layer are in contact with each other on the circumferential surface. Therefore, there is a risk of slippage occurring on the circumferential surface. The present disclosure discloses an example of a rotor for an electric motor in view of this point.

Means for Solving the Problems

[0005] The rotor for an electric motor preferably includes at least one of the following constituent elements, for example. That is, the constituent element is a rotor shaft (31) and a substantially cylindrical rotor body (32) supported by the rotor shaft (31) and rotating, the rotor body (32) having four or more even-numbered sintered magnets (33), a bonded magnet (34), and a core portion (35) integrated with the rotor shaft (31).

[0006] Furthermore, multiple sintered magnets (33) are arranged on the outside of the core portion (35), and the bonded magnet (34) is formed to cover the outside of the core portion (35). In addition, when the number of sintered magnets (33) is n, the cross-sectional shape of the core portion (35) is configured as a polygonal shape having n or more corners (including corners with chamfered edges and rounded edges).

[0007] This makes it possible to suppress slippage at the interface between the core portion (35) and the bonded magnet (34) in the rotor for the electric motor. Incidentally, the symbols in each of the parentheses above are just examples showing the correspondence with the specific configurations etc. described in the embodiments described later, and this disclosure is not limited to the specific configurations etc. indicated by the symbols in the parentheses above. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing an electric motor according to the first embodiment. [Figure 2] This is a diagram showing a rotor according to the first embodiment. [Figure 3] This is a diagram showing a rotor according to the first embodiment. [Figure 4] This is an explanatory diagram of the corner section of the core. [Figure 5] This is a diagram showing a rotor according to the first embodiment. [Figure 6] This is a diagram showing a rotor according to the first embodiment. [Figure 7] This figure shows a rotor according to the second embodiment. [Figure 8] This figure shows a rotor according to the second embodiment. [Figure 9] This is a diagram showing a rotor according to the third embodiment. [Figure 10] This is a diagram showing a rotor according to the third embodiment. [Figure 11] This is a diagram showing a rotor according to the fourth embodiment. [Figure 12] This is a diagram showing a rotor according to the fifth embodiment. [Figure 13] This figure illustrates the rotor according to the sixth embodiment.

Best Mode for Carrying Out the Invention

[0009] The following "Embodiments of the Invention" show an example of embodiments belonging to the technical scope of the present disclosure. That is, the invention-specific matters described in the claims are not limited to the specific configurations, structures, etc. shown in the following embodiments.

[0010] Note that the arrows, slashes, etc. indicating directions attached to each figure are described to facilitate understanding of the relationship between the figures and the shape of each member or part. Therefore, the invention shown in the present disclosure is not limited to the directions attached to each figure. The figure with slashes does not always show a cross-sectional view.

[0011] At least one member or part described with a reference sign is provided at least one, unless otherwise stated such as "one". That is, when there is no statement such as "one", two or more of the members may be provided. The rotor shown in the present disclosure includes at least one of the components such as the members or parts described with a reference sign and the structural parts shown in the drawings.

[0012] (First Embodiment) <1. Overview of the Electric Motor> In this embodiment, an example of a rotor for an electric motor according to the present disclosure is applied to an electric motor for driving a water pump. As shown in FIG. 1, the electric motor 1 is an inner rotor type electric motor in which a rotor 3 is housed in a stator 2.

[0013] The stator 2 has at least a stator core 2A and a plurality of coils 2B, etc. The rotor 3 includes at least a rotor shaft 31 and a rotor body 32, etc. as shown in FIG. 2. The rotor shaft 31 is a shaft portion that supports the rotor body 32.

[0014] The rotor main body 32 is a substantially cylindrical rotating body supported by the rotor shaft 31 and rotates. As shown in FIG. 3, the rotor main body 32 has at least a sintered magnet 33, a bonded magnet 34, and a core portion 35.

[0015] Four or more even numbers (in this embodiment, four) of sintered magnets 33 are provided. The core portion 35 is a polygonal columnar shape with a cross-sectional shape configured as a polygon (see FIG. 2). The number of corners of the polygon is the same as or greater than the number of sintered magnets 33.

[0016] As shown in FIG. 4, the corner R of the polygon means that it also includes a chamfered corner (see the broken line) and a rounded corner (see the two-dot chain line). Note that the cross-sectional shape of the core portion 35 according to this embodiment is a quadrangle with a C-chamfer at each corner.

[0017] That is, the core portion 35 according to this embodiment has the same number of corners as the sintered magnets 33. Hereinafter, a portion of the outer peripheral surface of the core portion 35 that is a planar portion and excludes the C-chamfered portion is referred to as a side portion 35A.

[0018] The core portion 35 is integrated with the rotor shaft 31. The core portion 35 according to this embodiment is configured by laminating a large number of electromagnetic steel sheets in the longitudinal direction of the rotor shaft 31 (hereinafter, also referred to as the axial direction).

[0019] As shown in FIG. 3, the plurality of sintered magnets 33 are arranged on the outer side in the radial direction of the core portion 35. The bonded magnet 34 is formed so as to cover the outer side in the radial direction of the core portion 35. Note that the radial direction is a direction orthogonal to the axial direction, that is, the diameter direction of the rotor main body 32.

[0020] And each sintered magnet 33 is magnetized so as to coincide with the direction orthogonal to the side portion 35A. The bonded magnet 34 is magnetically anisotropically oriented so that magnetic field lines (thick arrows in FIG. 3) that make a U-turn on the core portion 35 side are generated.

[0021] In the region of the bonded magnet 34 that lies on the extension of the magnetization direction of each sintered magnet 33, the magnetization direction of each sintered magnet 33 and the magnetization direction of the bonded magnet 34 substantially coincide. Furthermore, the end faces on one end and the other end of the rotor body 32 in the direction of the central axis, as well as the outer circumferential surface of the rotor body 32, are covered with resin (in this embodiment, the binder for the bonded magnet 34).

[0022] <2. Rotor Details> In the rotor 3 according to this embodiment, each of the multiple sintered magnets 33 is configured in a plate shape (see Figure 2), and the plate surface 33A of each sintered magnet 33 is in surface contact with substantially the entire area of ​​the corresponding edge portion 35A in a state parallel to the edge portion 35A (see Figures 2 and 3).

[0023] Furthermore, when a virtual plane perpendicular to the axial direction is used as the projection plane, the dimension L1 of the portion of each sintered magnet 33 projected onto the projection plane that is parallel to the edge portion 35A is the same as the dimension L2 of the edge portion 35A projected onto the projection plane.

[0024] In other words, dimension L1 is the length of the portion of the sintered magnet 33 that is in contact with the edge portion 35A, as projected onto the projection surface. Dimension L2 is the dimension of the portion excluding the chamfer, if there is a chamfer at the corner.

[0025] Furthermore, when there is no chamfering at the corners, dimension L2 is the distance between the tops of adjacent corners in the circumferential direction. In addition, in this embodiment, the dimensions and density of each part of the sintered magnet 33, bonded magnet 34, and core part 35 satisfy at least the following requirements.

[0026] <Requirements> The variation in the inertia of the rotor 3 is smaller than the variation in the inertia when the cross-sectional shape of the core portion 35 is circular, as shown by the dashed line in Figure 5. Note that the cross-sectional shape of the core portion 35 is circular, meaning that the cross-sectional shape is an inscribed circle that is tangent to each plate surface 33A.

[0027] "Variation in inertia" refers to the difference between the moment of inertia of the area where the sintered magnet 33 is present (hereinafter referred to as the first moment of inertia Iz1) and the moment of inertia of the area where the sintered magnet 33 is absent (hereinafter referred to as the second moment of inertia Iz2).

[0028] That is, the first moment of inertia Iz1 = I1 + I2 + I3, and the second moment of inertia Iz2 = I1 + I4 + I5. Incidentally, the density of electrical steel sheet is approximately 1.6 times that of bonded magnets.

[0029] I1: Moment of inertia of the portion inscribed within the sintered magnet I2: Moment of inertia of the sintered magnet portion I3: Moment of inertia of the bonded magnet portion I4: Moment of inertia of the part of the core of the rectangle that is outside the inscribed circle. I5: Moment of inertia of the part outside the rectangular core The difference Δ1 between the first moment of inertia and the second moment of inertia is as follows:

[0030] Δ1 = Iz1 - Iz2 = (I2 + I3) - (I4 + I5) Here, assuming that the cross-sectional shape of the core is circular, if we denote the moment of inertia of the part outside the core as I6, then the third moment of inertia Iz3 when the core is circular will be I1 + I6.

[0031] The difference Δ2 between the first moment of inertia and the third moment of inertia is as follows: Difference Δ2 = (I2 + I3) - I6 Therefore, the difference between difference Δ1 and difference Δ2 is as follows:

[0032] Δ1-Δ2=[(I2+I3)-(I4+I5)]-[(I2+I3)-I6] =I6-(I4+I5) In this embodiment, the dimensions of the sintered magnet 33, bonded magnet 34, and core portion 35 are selected such that Δ1-Δ2<0. Therefore, the variation in the inertia of the rotor 3 according to this embodiment is smaller than the variation in the inertia when the cross-sectional shape of the core portion 35 is circular.

[0033] <3. Features of the rotor according to this embodiment> The cross-sectional shape of the core portion 35 according to this embodiment is configured as a polygon. This makes it possible to suppress the occurrence of slippage at the interface between the core portion 35 and the bonded magnet 34 in this embodiment.

[0034] In this embodiment, each of the multiple sintered magnets 33 is configured in a plate shape, and each plate surface 33A is arranged to be parallel to the edge portion 35A. As a result, in this embodiment, it becomes possible to select the dimensions of each part of the sintered magnet 33, bonded magnet 34, and core portion 35 such that Δ1-Δ2<0. Consequently, in this embodiment, the variation in inertia can be made smaller than the variation in inertia when the cross-sectional shape of the core portion 35 is circular.

[0035] Incidentally, if the invention described in Patent Document 1 is applied to a rotor having four sintered magnets 33, the outer diameter of the core portion, that is, the inscribed circle S1 that is in contact with the inside of the four sintered magnets 33, will be as shown in Figure 6, and the inside of the sintered magnets 33 will be arc-shaped so as to be in contact with the inscribed circle S1.

[0036] However, in this configuration, as shown in part A of Figure 6, two adjacent sintered magnets 33 interfere with each other in the circumferential direction. The reason for this is that the core-side surface of the sintered magnet 33 in this configuration is a curved surface that contacts the outer circumferential surface of the core.

[0037] In other words, the sintered magnet 33 in this configuration has the shape shown by the shaded area in Figure 6. Therefore, in this configuration, the shaded areas of two adjacent sintered magnets 33 overlap. In other words, in this configuration, two adjacent sintered magnets 33 interfere with each other in the circumferential direction.

[0038] To avoid this interference, the inscribed circle that contacts the inside of the sintered magnet 33 should be S2 in Figure 6. This inscribed circle S2 is a circle that passes through point J where the extensions L3 of the long-side end faces of two adjacent sintered magnets 33 intersect.

[0039] However, the core portion determined by the inscribed circle S2 interferes with the sintered magnet 33, as shown in Figure 6. Therefore, in order to avoid interference between the core portion and the sintered magnet 33 without increasing the diameter of the rotor, the short side dimension, i.e., the thickness dimension, of the sintered magnet 33 must be reduced.

[0040] When the short side dimension of the sintered magnet 33 decreases, the magnetic field generated in the short side direction becomes smaller. Therefore, it is difficult to apply the rotor described in Patent Document 1 to a rotor having four sintered magnets 33.

[0041] Incidentally, if the dimension of the longer side of the sintered magnet 33, that is, the dimension L1 of the part parallel to the side 35A, is reduced, the intersection J will come into contact with the inscribed circle S2, and the above interference can be avoided. However, this avoidance method reduces the dimension of the longer side of the sintered magnet 33, so it is difficult to say that this avoidance method is effective.

[0042] In contrast, the multiple sintered magnets 33 according to this embodiment have a rectangular cross-section with a long side dimension, i.e., the dimension L1 of the portion parallel to the side portion 35A, being the same as the dimension L2 of the side portion 35A of the core portion 35, and having the same short side dimension throughout the entire long side direction. Therefore, in this embodiment, the problem of two adjacent sintered magnets 33 interfering with each other does not occur.

[0043] In other words, in this embodiment, in the core portion 35 of the rotor having four sintered magnets 33, adjacent edges 35A are perpendicular to each other. Therefore, the long-side end faces of two adjacent sintered magnets 33 do not intersect. Consequently, the problem of two adjacent sintered magnets 33 interfering with each other does not occur.

[0044] In this embodiment, the dimensions of each part are selected such that the intersection point J is located outside the inscribed circle S2. Specifically, when the dimension LS1 is the distance from the center of the rotor body 32 to the sintered magnet 33, that is, the radius of the inscribed circle S2, and the chamfer dimension Lx is the distance between adjacent side portions 35A, the following relationship holds true in this embodiment.

[0045] LS1<2 1 / 2 ×LS1-Lx Furthermore, in the rotor 3 according to this embodiment, sintered magnets 33 having the same short-side dimensions throughout the entire long-side direction can be used without increasing the rotor diameter. In other words, the rotor 3 according to this embodiment is suitable for a rotor having four sintered magnets 33.

[0046] It should be noted that the rotor 3 according to this embodiment can be applied to 6 or 8 sintered magnets 33, etc. The reason for this is that as the number of sintered magnets 33 increases, the angle between adjacent sides increases, making it more difficult for the extensions L3 of the long-side end faces of two adjacent sintered magnets 33 to intersect.

[0047] (Second Embodiment) In the rotor 3 according to the above embodiment, dimensions L1 and L2 were the same. In contrast, the rotor 3 according to this embodiment, as shown in Figures 7 and 8, is a rotor 3 in which dimension L1 is smaller than dimension L2.

[0048] Note that components identical to those in the above-described embodiments are denoted by the same reference numerals. Therefore, redundant explanations are omitted in this embodiment. Incidentally, Figure 7 shows an example in which a chamfered edge (C chamfer) is provided on the corner. Figure 8 shows an example in which an R chamfered edge (R chamfer) is provided on the corner.

[0049] Furthermore, in this embodiment, since dimension L1 is smaller than dimension L2, it becomes possible to effectively utilize the reluctance torque generated in the core portion 35. When the rotational speed of the rotor 3 is high, utilizing the reluctance torque can reduce motor losses.

[0050] (Third embodiment) <Configuration of the rotor according to this embodiment> The core portion 35 in the above-described embodiment was made of electrical steel sheet. In contrast, the core portion 35 in this embodiment is made of resin. Furthermore, as shown in Figure 9, each sintered magnet 33 is positioned opposite to a corner of the resin core portion 35 (hereinafter referred to as the resin core 35) and is in contact with that corner.

[0051] Specifically, the diagonal line L4 crosses the sintered magnet 33, and the corner portion is in contact with the sintered magnet 33 while the diagonal line L4 intersects the sintered magnet 33. The diagonal line L4 is an imaginary line that passes through two opposing corner portions on either side of the center of the rotor shaft 31.

[0052] Each sintered magnet 33 is magnetized in a direction perpendicular to the edge portion 35A. The bonded magnet 34 is polarly anisotropically oriented so that magnetic field lines (thick arrows in Figure 9) make a U-turn on the resin core 35 side.

[0053] Note that components identical to those in the above-described embodiments are denoted by the same reference numerals. Therefore, redundant explanations are omitted in this embodiment. Incidentally, the density of the resin core 35 is approximately 1 / 3 of the density of the bonded magnet.

[0054] <Features of the rotor according to this embodiment> In this embodiment as well, the dimensions of each part of the sintered magnet 33, bonded magnet 34, and resin core 35 are selected to satisfy the requirement that Δ1-Δ2<0. Therefore, in the rotor 3 according to this embodiment, the variation in inertia can be made smaller than the variation in inertia when the cross-sectional shape of the resin core 35 is circular.

[0055] That is, as shown in Figure 10, the first moment of inertia Iz1 = I1 + I2 + I3 + I4, and the second moment of inertia Iz2 = I1 + I5. I1: Moment of inertia of the inscribed circle portion of the rectangular resin core I2: Moment of inertia of the contact area between the sintered magnet and the resin core, as seen from the inscribed circle. I3: Moment of inertia of the sintered magnet portion I4: Moment of inertia of the bonded magnet portion I5: Moment of inertia of the part outside the square resin core The difference Δ1 between the first moment of inertia and the second moment of inertia is as follows:

[0056] Difference Δ1 = Iz1 - Iz2 = (I2 + I3 + I4) - I5 Here, assuming that the cross-sectional shape of the resin core is circular, if we denote the moment of inertia of the part outside the resin core as I6, then the third moment of inertia Iz3 when the resin core is circular is I1 + I2 + I6. Note that this circle is an inscribed circle within each sintered magnet 33.

[0057] The difference Δ2 between the first moment of inertia and the third moment of inertia is as follows: Difference Δ2 = (I3 + I4) - I6 Therefore, the difference between difference Δ1 and difference Δ2 is as follows:

[0058] Δ1-Δ2=[(I2+I3+I4)-I5]-[(I3+I4)-I6] =I2-(I5-I6) where I5>I6 In this embodiment, the dimensions of the sintered magnet 33, bonded magnet 34, and core portion 35 are selected such that Δ1-Δ2<0. Therefore, in the rotor 3 according to this embodiment, the variation in inertia can be made smaller than the variation in inertia when the cross-sectional shape of the core portion 35 is circular.

[0059] Furthermore, since a larger bonded magnet portion (see portion B in Figure 9) is formed between two adjacent sintered magnets 33 in the circumferential direction compared to the above embodiment, it may be possible to generate a large torque in this embodiment.

[0060] (Fourth Embodiment) The corners of the core portion 35 (including the resin core 35) according to this disclosure are corners that are convex radially outward (including corners with chamfered edges and corners with rounded edges). Therefore, for example, the resin core 35 shown in Figure 11 is also an example of the core portion 35 according to this disclosure.

[0061] In other words, Figure 11 shows an example where the center of adjacent corners of the resin core 35 is recessed towards the rotor shaft 31. And in this embodiment as well, the same functions and effects as in the third embodiment can be achieved.

[0062] (Fifth embodiment) In the rotor 3 according to the above-described embodiment, the number of corners in the core portion 35 (including the resin core 35) was the same as the number of sintered magnets 33. In contrast, as shown in Figure 12, the rotor 3 according to this embodiment has a configuration in which the number of corners in the core portion 35 (including the resin core 35) is greater than the number of sintered magnets 33.

[0063] Note that components identical to those in the above-described embodiments are denoted by the same reference numerals. Therefore, redundant explanations are omitted in this embodiment. (Sixth Embodiment) In the above-described embodiment, as shown in Figure 13A, each sintered magnet 33 was oriented in anisotropic direction such that the magnetization directions of adjacent sintered magnets 33 were opposite, and the bonded magnet 34 located between the sintered magnets 33 was oriented in anisotropic direction such that magnetic field lines (thick arrows in Figure 13A) made a U-turn on the core portion 35 (including the resin core 35) side.

[0064] However, as shown in Figure 13B, each sintered magnet 33 may have the same magnetization direction as adjacent sintered magnets 33. In such a case, bonded magnets 34 located between sintered magnets 33 with the same magnetization direction may be polarly asymmetrically oriented so that magnetic field lines are generated along the radial direction of the rotor body 32, while bonded magnets 34 located between sintered magnets 33 with different magnetization directions may be polarly asymmetrically oriented so that magnetic field lines (thick arrows in Figure 13B) make a U-turn on the core portion 35 (including the resin core 35).

[0065] In other words, the number of poles of rotor 3 shown in Figure 13A matches the number of sintered magnets 33. In contrast, the number of poles of rotor 3 shown in Figure 13B does not match the number of sintered magnets 33. Specifically, the number of poles of rotor 3 shown in Figure 13B is 4.

[0066] Note that components identical to those in the above-described embodiment are denoted by the same reference numerals. Therefore, redundant explanations are omitted in this embodiment. Incidentally, Figures 13A and 13B show an example of application to a rotor 3 in which the number of sintered magnets 33 is 8 and the number of core portions 35 is 8.

[0067] (Other embodiments) The electric motor 1 in the above-described embodiment was for a water pump. However, this disclosure is not limited to this. That is, this disclosure can be applied to applications other than water pumps, such as lawnmowers.

[0068] In the embodiments described above, the end faces on one and the other end faces in the direction of the central axis of the rotor body 32, as well as the outer circumferential surface of the rotor body 32, were covered with resin. However, the disclosure is not limited thereto. That is, the disclosure may also include, for example, a configuration in which only the outer circumferential surface of the rotor body 32 is covered with resin, or a configuration in which the outside of the rotor body 32 is not covered with resin.

[0069] The sintered magnet 33 in the above-described embodiment was plate-shaped. However, this disclosure is not limited thereto. That is, the disclosure may also have a configuration that is curved to follow the outer circumferential surface of the rotor body 32, for example.

[0070] The sintered magnet 33 according to the above-described embodiment was configured to be in contact with the core portion 35 (including the resin core 35). However, this disclosure is not limited thereto. That is, the disclosure may, for example, have a resin layer between the sintered magnet 33 and the core portion 35 (including the resin core 35).

[0071] In the above-described embodiment, the core portion 35 (including the resin core 35) was configured such that the dimensions of the sintered magnet 33, bonded magnet 34, and core portion 35 were selected to satisfy the above requirements. However, this disclosure is not limited thereto.

[0072] In the embodiment described above, the resin covering the outer circumferential surface of the rotor body 32 was the binder for the bonded magnet 34. However, the disclosure is not limited thereto. The outer circumferential surface of the rotor body 32 may be covered with a resin different from the aforementioned resin.

[0073] Furthermore, this disclosure is not limited to the embodiments described above, but is sufficient to be consistent with the intent of the disclosures described in the embodiments described above. Therefore, it may be a configuration in which at least two of the embodiments described above are combined, or a configuration in which any of the illustrated components or components described with reference numerals in the embodiments described above are omitted. [Explanation of symbols]

[0074] 3… Rotor 31… Rotor shaft 32… Rotor body 33… Sintered magnets 34… Bonded magnets 35… Core section

Claims

1. In a rotor for an electric motor, Rotor shaft and A substantially cylindrical rotor body that rotates supported by the rotor shaft, comprising a rotor body having four or more even-numbered sintered magnets, bonded magnets, and a core portion integrated with the rotor shaft, Multiple sintered magnets are arranged outside the core portion. The bonded magnet is formed to cover the outside of the core portion, Furthermore, when the number of sintered magnets is n, the cross-sectional shape of the core portion is configured as a polygonal shape having n or more corners, which is the rotor for an electric motor.

2. The core portion is constructed by laminating a large number of electromagnetic steel sheets. The number of corners and the number of sintered magnets are the same. Furthermore, when the planar portion of the outer circumferential surface of the core is defined as the edge portion, each of the plurality of sintered magnets is configured in a plate shape, and each plate surface is arranged to be parallel to the edge portion, as described in claim 1.

3. The plurality of sintered magnets are in contact with the edges, Furthermore, when a virtual plane perpendicular to the axial direction of the rotor shaft is used as the projection plane, the dimensions of the portion of the plurality of sintered magnets projected onto the projection plane that is parallel to the edge portion are the same as the dimensions of the edge portion projected onto the projection plane, as described in claim 2 for electric motor rotor.

4. The core portion is constructed by laminating a large number of electromagnetic steel sheets. When the planar portion of the outer circumferential surface of the core is defined as the edge, each of the plurality of sintered magnets is configured in a plate shape, and each plate surface is arranged in contact with the edge. Furthermore, when a virtual plane perpendicular to the axial direction of the rotor shaft is used as the projection plane, the dimensions of the portion of the plurality of sintered magnets projected onto the projection plane that is parallel to the edge portion are smaller than the dimensions of the edge portion projected onto the projection plane, as described in claim 1 for electric motor rotor.

5. The core portion is made of resin, The number of corners and the number of sintered magnets are the same. Furthermore, the rotor for an electric motor according to claim 1, wherein each of the plurality of sintered magnets is configured in a plate shape and is positioned opposite to the corner of the core portion.

6. The rotor for an electric motor according to any one of claims 1 to 5, wherein the end face on one end in the direction of the central axis of the rotor body, the end face on the other end, and the outer circumferential surface of the rotor body are covered with resin.

7. The rotor for an electric motor according to claim 6, wherein the resin is a binder for the bonded magnet.

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