Magnet arrangement structure of rotor for IPM motor and IPM motor

Abstract

To provide a magnet arrangement structure reducing an occurrence of unnecessary magnetic flux which does not contribute to a rotational torque of a rotor in a rotor for an IPM motor having a plurality of permanent magnets inside of a rotor core.SOLUTION: A rotor 3 for an IPM motor has a cylindrical rotor core 8 and a plurality of permanent magnets 10 arranged inside of the rotor core 8. The permanent magnets 10 are configured by arranging a plurality of circumferential direction magnets 11 in a circumferential direction fitted to the rotor core 8 so that a direction of a magnetic pole may follow the circumferential direction of the rotor core 8. The circumferential direction magnets 11 are respectively set so that a circumferential direction width closer to an outside of a radial direction may be larger than the circumferential direction width closer to an inside of the radial direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an embedded permanent magnet rotor and an IPM motor using the same, and in particular to a magnet arrangement structure that reduces the generation of unnecessary magnetic flux that does not contribute to rotational force. [Background technology]

[0002] In an electric motor with an inner rotor structure, in order to generate a strong magnetic field outside the magnet arrangement and reduce cogging torque and torque ripple, a technique is known in which a plurality of main magnets magnetized in the radial direction of the rotor and a plurality of auxiliary magnets magnetized in a direction other than the radial direction (for example, the circumferential direction), the main magnets are arranged at intervals in the circumferential direction on the outer circumferential surface of the rotor core, the auxiliary magnets are arranged between the main magnets, and these main magnets and auxiliary magnets are arranged in a Halbach array (see Patent Documents 1 and 2).

[0003] By adopting such a magnet arrangement, it is possible to create an electric motor with high torque and high efficiency. However, when using an SPM structure in which multiple main magnets and multiple auxiliary magnets are arranged on the outer peripheral surface of the rotor core, a process is required to bond the main magnets and auxiliary magnets to the outer peripheral surface of the rotor core using an adhesive or the like, and there is also concern that the magnets may crack, peel off, or shatter, resulting in a deterioration of the magnetic properties.

[0004] Therefore, an IPM structure has been considered in which magnets are embedded in the rotor while maintaining the Halbach arrangement of the magnets (see Patent Documents 3 and 4), and the present applicant has also previously proposed a rotor for an IPM motor that improves magnetic characteristics by reducing magnetic flux leaking inward from the magnet arrangement (Patent Document 5).

[0005] 6, this includes circumferential magnets (auxiliary magnets) 111 arranged so that the magnetic poles are oriented along the circumferential direction of rotor core 108, and radial magnets (main magnets) 112 arranged so that the magnetic poles are oriented along the radial direction of rotor core 108, and circumferential magnets 111 and radial magnets 112 are arranged in a Halbach array in the rotational direction of rotor core 108. Circumferential magnets 111 are formed in a rectangular cross section, and are arranged so that the long sides of this cross section are oriented along the radial direction of rotor core 108. Radial magnets 112 are also formed in a rectangular cross section, and are arranged at the radially inner end of circumferential magnet 111 so that the long sides of the cross section are oriented along the circumferential direction of rotor core 108. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-354721 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-014110 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-50179 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-150659 [Patent Document 5] Japanese Patent Publication No. 2020-72634 Summary of the Invention [Problem to be solved by the invention]

[0007] In the IPM motor previously proposed by the present applicant, of the magnetic flux extending from the circumferential magnets, the magnetic flux near the radially inner side is attracted by the magnetic flux of the radial magnets located before and after in the circumferential direction and is guided toward the stator located radially outward, thereby reducing the magnetic flux leaking inward and making it possible to increase the magnetic flux that contributes to motor torque.

[0008] However, because the radially outer vicinity of the circumferential magnet is separated from the radial magnet, the magnetic flux extending from the radially outer vicinity of the radially extending surface of the circumferential magnet (the end surface facing the circumferential direction) is not affected by the magnetic flux from the radial magnet, so it wraps around the radially extending back surface of the circumferential magnet (forming a small loop on the radially outer side of the auxiliary magnet) and does not contribute to torque. For this reason, there is room for further improvement from the perspective of increasing the magnetic flux that contributes to torque.

[0009] The present invention has been made in consideration of the above circumstances, and its main objective is to provide a magnet arrangement structure for a rotor for an IPM motor that can reduce the generation of unnecessary magnetic flux that does not contribute to the rotational torque of the rotor radially outside the circumferential magnets, and an IPM motor that uses a rotor equipped with this magnet arrangement structure. [Means for solving the problem]

[0010] In order to achieve the above object, the magnet arrangement structure of the rotor for an IPM motor according to the present invention comprises: A magnet arrangement structure of a rotor (3) for an IPM motor, comprising a cylindrical rotor core (8) and a plurality of permanent magnets (10) arranged inside the rotor core (8), the permanent magnet (10) includes a plurality of circumferential magnets (11) fitted in the rotor core (8) along the circumferential direction of the rotor core (8), and the circumferential magnets (11) are arranged in the rotor core (8) such that the direction of their magnetic poles is along the circumferential direction of the rotor core (8); The circumferential magnet (11) is set so that the circumferential width of the radially outer side is larger than the circumferential width of the radially inner side. It is characterized by the following.

[0011] Therefore, since the circumferential magnets are set so that the circumferential width on the radially outer side is larger than the circumferential width on the radially inner side, the magnetic flux extending from near the radially outer side is directed toward the stator without being returned to the back surface of the circumferential magnet, and can contribute to torque.

[0012] Here, the circumferential magnet (11) has asymmetrical surfaces (11a, 11c) on both sides facing the circumferential direction, and each of the plurality of circumferential magnets (11) is arranged on the rotor core (8) with its cross-sectional shape reversed in the circumferential direction so that the opposing surfaces (11a-11a, 11c-11c) of adjacent circumferential magnets (11) are mirror images of each other.

[0013] In addition, the circumferential magnet (11) preferably includes an arc-shaped convex surface (13) on one of its surfaces (11a) facing the circumferential direction, and the plurality of circumferential magnets (11) are preferably arranged so that their arc-shaped convex surfaces (13) face each other.

[0014] Furthermore, a radial magnet (12) fitted in the rotor core (8) may be arranged between adjacent circumferential magnets of the plurality of circumferential magnets (11) and near the radially inner end thereof so that the direction of the magnetic poles is along the radial direction of the rotor core (8), thereby forming a Halbach array.

[0015] Here, it is preferable that the circumferential magnets be ferrite magnets and the radial magnets be rare earth magnets.

[0016] It is preferable that an arcuate concave surface be formed from the radially inner side to the radially outer side of the circumferential magnet on the surface facing the circumferential direction opposite to the side on which the arcuate convex surface is provided.

[0017] Furthermore, a fixing means for fixing the laminated steel plates that make up the rotor core may be disposed between the arc-shaped concave surfaces of adjacent circumferential magnets that face each other in the circumferential direction. The fixing means may be, for example, rivets that penetrate the rotor core or crimping portions that crimp the laminated steel plates together.

[0018] In a more specific embodiment of the circumferential magnet, the circumferential magnet (11) comprises a first outer surface (11a) having the arcuate convex surface (13), a third outer surface (11c) having the arcuate concave surface (14) provided opposite the first outer surface (11a), a second outer surface (11b) connecting the radial outer end of the first outer surface (11a) to the radial outer end of the third outer surface (11c), and a fourth outer surface (11d) connecting the radial inner end of the first outer surface (11a) to the radial inner end of the third outer surface (11c), and adjacent circumferential magnets (11) whose arcuate concave surfaces 14 face each other may be arranged so that their fourth outer surfaces (11d) are approximately parallel to each other, and a radial magnet (12) may be arranged in the radially inner portion between these facing fourth outer surfaces (11d).

[0019] With this configuration, the magnetic flux extending from the radial magnet can pass between the parallel opposing fourth sides and be directed directly toward the stator. Furthermore, since a means for fixing the laminated steel plate is provided between the opposing arc concave surfaces, the magnetic path of the magnetic flux extending from between the parallel opposing fourth sides is not narrowed, and it can be guided to the stator. [Effects of the Invention]

[0020] As described above, according to the present invention, a plurality of circumferential magnets whose magnetic poles are oriented along the circumferential direction of the rotor core are arranged in the circumferential direction inside a cylindrical rotor core, and in each of the circumferential magnets, Since the circumferential width on the radially outer side is set to be larger than the circumferential width on the radially inner side, it is possible to reduce the magnetic flux that returns to the magnet instead of heading toward the stator on the radially outer side of the circumferential magnet, making it possible to reduce the generation of magnetic flux that does not contribute to the rotational torque of the rotor. [Brief explanation of the drawings]

[0021] [Figure 1] 1A and 1B are diagrams showing an IPM motor according to the present invention, in which (a) is a cross-sectional view taken along line BB of (b), and (b) is a cross-sectional view taken along line AA of (a). [Figure 2]1A and 1B are diagrams showing the components of an IPM motor according to the present invention, in which (a) is a perspective view showing a rotor core fitted with permanent magnets, (b) is a perspective view showing the permanent magnets fitted into the rotor core, and (c) is a perspective view showing the rotor core housed inside the stator. [Figure 3] FIG. 2 is an enlarged, partially cutaway view of the rotor core disposed inside the stator as viewed from the axial direction. [Figure 4] 1A is a diagram showing an end face of a circumferential magnet as viewed from the axial direction of the rotor core, and FIG. 1B is a diagram showing a circumferential magnet holding portion as viewed from the axial direction of the rotor core. [Figure 5] 4A and 4B are diagrams illustrating the magnetic flux distribution of the rotor and the stator of the present invention. [Figure 6] 10A and 10B are diagrams illustrating magnetic flux distributions in a conventional rotor and stator. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of an interior permanent magnet motor (IPM motor) according to the present invention will be described with reference to the accompanying drawings.

[0023] In FIG. 1, an IPM motor 1 includes a stator 2 and a rotor 3 .

[0024] The stator 2 includes a stator core 4 including a substantially cylindrical back yoke 4a and a plurality of (15 in this embodiment) teeth 4b formed radially inside the back yoke 4a, insulators 5 disposed at both axial ends of the stator core 4, and windings 6 wound around the teeth 4b via the insulators 5 and connected to a power supply (not shown). The windings 6 are configured to generate a rotating magnetic field for rotating the rotor 3 when a current is supplied from the power supply.

[0025] The rotor 3 is rotatably disposed inside the stator 2. As shown in Figures 2 and 3, the rotor 3 has a rotor core 8 that is fixed to the rotary shaft 7 and rotates integrally therewith, a plurality of permanent magnets 10 that are circumferentially arranged within the rotor core 8, and end plates 9 that are attached to both ends of the rotor core 8, and the rotor core 8 and the end plates 9 are axially fastened together with rivets 17 to form an integrated unit.

[0026] The rotor core 8 is formed into a cylindrical shape by laminating a plurality of disk-shaped steel plates made of, for example, silicon steel. A shaft hole 16 into which the rotating shaft 7 is inserted is formed in the center of the rotor core 8.

[0027] Between the axial hole 16 of the rotor core 8 and the outer peripheral surface, there are formed a plurality of circumferential magnet holding portions 21 that are arranged at predetermined intervals in the circumferential direction and extend in the axial direction of the rotating shaft 7 (axial hole 16), and a plurality of radial magnet holding portions 22 that are formed between adjacent circumferential magnet holding portions 21 and extend in the axial direction of the rotating shaft 7 (axial hole 16).

[0028] Here, circumferential magnet holding portions 21 are formed along the radial direction of rotor core 8 from near shaft hole 16 to near the outer circumferential surface. Radial magnet holding portions 22 are formed along the circumferential direction of rotor core 8 near shaft hole 16.

[0029] A circumferential magnet 11 is fitted into each of the circumferential magnet holding portions 21, and a radial magnet 12 is fitted into each of the radial magnet holding portions 22. The circumferential magnets 11 and the radial magnets 12 each constitute a permanent magnet 10 of the present invention.

[0030] Each circumferential magnet 11 has a cross-sectional shape perpendicular to the axis of the rotor core 8 as shown in Fig. 4(a). Here, in Figs. 3 and 4(a), the axis of the rotor core 8 is not shown, but is located below the circumferential magnets 11 in the figures (in this example, it is located radially inward of the circumferential magnets 11 on a line that passes through the circumferential center of a second outer surface 11b (described later) and is perpendicular to the second outer surface). Therefore, in Fig. 4(a), the up-down direction of the figure approximately coincides with the radial direction of the rotor 3, and the left-right direction of the figure approximately coincides with the circumferential direction of the rotor 3.

[0031] The circumferential magnet 11 has asymmetrically formed surfaces (11a, 11c) on both sides facing the circumferential direction. That is, the circumferential magnet 11 has a first outer surface 11a, which is one outer surface facing the circumferential direction and has an arc-shaped convex surface 13, and a third outer surface 11c, which is the other outer surface facing the circumferential direction and has an arc-shaped concave surface 14 that faces the arc-shaped convex surface 13 in the circumferential direction. It also has a second outer surface 11b formed between the radial outer end of the first outer surface 11a and the radial outer end of the third outer surface 11c, and a fourth outer surface 11d formed between the radial inner end of the first outer surface 11a and the radial inner end of the third outer surface 11c.

[0032] The arcuate convex surface 13 formed on the first outer surface 11a is formed over the entire range of the first outer surface 11a, i.e., from the radially inner end to the radially outer end of the first outer surface 11a. The arcuate concave surface 14 formed on the third outer surface 11c is formed over the entire range of the third outer surface 11c, i.e., from the radially inner end to the radially outer end of the third outer surface 11c. The second outer surface 11b and the fourth outer surface 11d are formed as substantially flat surfaces overall.

[0033] Furthermore, when the circumferential magnets 11 are fitted into the rotor core 8 (circumferential magnet holding portions 21), the distance from the axis of the rotor core 8 to the radial outer end of the first outer surface 11a is approximately equal to the distance from the axis of the rotor core 8 to the radial outer end of the third outer surface 11c, but the radial length of the third outer surface 11c is shorter than the radial length of the first outer surface 11a. Therefore, the first outer surface 11a has a portion that faces the third outer surface 11c in the circumferential direction and a portion that faces the fourth outer surface 11d in the circumferential direction.

[0034] Therefore, the circumferential magnet 11 is formed so that at least the circumferential width between the fourth outer surface 11d and the first outer surface 11a circumferentially opposing it gradually increases from the radially inner side toward the radially outer side.

[0035] Furthermore, the radius of curvature of the arcuate convex surface 13 may be the same as or different from the radius of curvature of the arcuate concave surface 14, but the circumferential width between the arcuate concave surface 14 and the arcuate convex surface 13 that faces it in the circumferential direction is also set to increase radially outward.

[0036] In this way, the circumferential magnet 11 is set so that the circumferential width on the radially outer side is larger than the circumferential width on the radially inner side.

[0037] Next, an example of the circumferential magnet holder 21 into which the circumferential magnet 11 is fitted will be described.

[0038] The cross-sectional shape of circumferential magnet holding portion 21 perpendicular to the axis of rotor core 8 is also shown in Figure 4(b). Here, although the axis of rotor core 8 is not shown, it is located below circumferential magnet holding portion 21 in the figure (in this example, it is located below circumferential magnet holding portion 21 on a straight line that passes through the center of an imaginary plane connecting the radially outer end of first inner surface 21a and the radially outer end of third inner surface 21c, which will be described later, and is perpendicular to this imaginary plane). Therefore, in Figure 4(b), the up-down direction of the figure approximately coincides with the radial direction of rotor 3, and the left-right direction of the figure approximately coincides with the circumferential direction of rotor 3.

[0039] This circumferential magnet holding portion 21 has a shape substantially the same as the outer shape of the circumferential magnet, and includes: one inner surface facing the circumferential direction, a first inner surface 21a, which faces the first outer surface 11a of the circumferential magnet; the other inner surface facing the circumferential direction opposite the first inner surface 21a in the circumferential direction, a third inner surface 21c, which faces the third outer surface 11c of the circumferential magnet; a second inner surface 21b formed between the radial outer end of the first inner surface 21a and the radial outer end of the third inner surface 21c, which faces the second outer surface 11b of the circumferential magnet; and a fourth inner surface 21d formed between the radial inner end of the first inner surface 21a and the radial inner end of the third inner surface 21c, which faces the fourth outer surface 11d of the circumferential magnet.

[0040] The first inner surface 21a has an arcuate concave surface 23 that is curved from the radially outer end toward the radially inner side in a shape substantially similar to the arcuate convex surface 13 of the circumferential magnet 11 and abuts against this arcuate convex surface 13, and a flat surface 26 that extends radially inward from this arcuate concave surface 23, is separated from the arcuate convex surface 13, and forms a magnetic shielding portion 27 between it and the arcuate convex surface 13.

[0041] The third inner surface 21c has an arcuate convex surface 24 that is curved in a shape substantially similar to the arcuate concave surface 14 of the circumferential magnet 11 over the entire range from the radially outer end to the radially inner end and abuts against this arcuate concave surface 14.

[0042] The second inner surface 21b may be formed continuously between the radial outer end of the first inner surface 21a and the radial outer end of the third inner surface 21c, but the middle portion is divided to block the magnetic flux that flows around the radial outer end portion of the circumferential magnet 11.

[0043] The fourth inner surface 21d may be formed to connect the radially inner end of the first inner surface 21a and the radially inner end of the third inner surface 21c, but in this example, in order to reduce the magnetic flux from flowing radially inward, the magnetic shielding portion 27 extends in the circumferential direction from the radially inner end of the first inner surface 21a to pass over the fourth inner surface 21d. Therefore, the fourth inner surface 21d is formed from the radially inner end of the third inner surface 21c to the magnetic shielding portion 27.

[0044] Each of the multiple circumferential magnets 11 arranged in the circumferential direction is arranged on the rotor core 8 with its cross-sectional shape reversed in the circumferential direction so that the facing surfaces (11a-11a, 11c-11c) of adjacent circumferential magnets 11 are mirror images.

[0045] That is, the circumferential magnet 11 has a first outer surface 11a and a third outer surface 11c facing in the circumferential direction that are formed asymmetrically, but adjacent circumferential magnets 11 in the circumferential direction are fitted into the rotor core 8 so as to be mirror-symmetric with respect to an imaginary plane that includes the center position therebetween and the axis of the rotor core 8. Therefore, the multiple circumferential magnets fitted into the rotor core 8 are formed such that portions where the first outer surfaces 11a (arcuate convex surfaces 13) face each other in the circumferential direction and portions where the third outer surfaces 11c (arcuate concave surfaces 14) face each other in the circumferential direction are alternately formed in the circumferential direction.

[0046] In this example, adjacent circumferential magnets 11, whose third outer surfaces 11c face each other in the circumferential direction, are arranged so that their fourth outer surfaces 11d are substantially parallel to each other. That is, each fourth outer surface 11d is a flat surface parallel to a plane including the axis of the rotor core 8 (the center of the shaft hole 16) and the midpoint between the adjacent circumferential magnets 11, whose fourth outer surfaces 11d face each other in the circumferential direction.

[0047] Additionally, adjacent circumferential magnet holding portions 21, whose first inner surfaces 21a face each other in the circumferential direction, are arranged so that the flat surfaces 26 of the first inner surfaces 21a are substantially parallel to each other. That is, the flat surfaces 26 of each first inner surface 21a are substantially parallel to a plane that includes the axis of rotor core 8 (the center of shaft hole 16) and the midpoint between adjacent circumferential magnet holding portions 21, whose first inner surfaces 21a face each other in the circumferential direction.

[0048] The spacing (circumferential separation distance) between the opposing fourth outer surfaces 11d of adjacent circumferential magnets whose fourth outer surfaces 11d face each other in the circumferential direction is formed to be approximately equal to the spacing (circumferential separation distance) between the flat surfaces 26 of the first inner surfaces 21a of adjacent circumferential magnet holding portions 21 whose first inner surfaces 21a face each other in the circumferential direction.

[0049] The radial magnets 12 are arranged between adjacent circumferential magnets 11, i.e., between the first outer surfaces 11a of adjacent circumferential magnets 11 whose first outer surfaces 11a face each other, and between the fourth outer surfaces 11d of adjacent circumferential magnets 11 whose fourth outer surfaces 11d face each other.

[0050] The radial magnet 12 extends parallel to the axial hole 16 and has a rectangular cross section similar to the cross section of the radial magnet holding portion 22, and is arranged so that the long side of the rectangular cross section is aligned with the circumferential direction of the rotor core 8.

[0051] The radial magnet 12 formed between adjacent circumferential magnets 11 whose first outer surfaces 11a face each other in the circumferential direction is arranged near the radial inner end between the facing first outer surfaces 11a via a magnetic shielding portion 27.

[0052] Furthermore, the radial magnet 12 formed between the adjacent circumferential magnets 11 whose fourth outer surfaces 11d face each other in the circumferential direction is disposed near the radially inner end between the mutually facing fourth outer surfaces 11d.

[0053] These radial magnets 12 are arranged at equal distances from the center of the axial hole 16, and a total of ten of them are provided at approximately equal intervals on concentric circles.

[0054] In this example, the radial magnets 12 are formed to be sufficiently smaller than the circumferential magnets 11. The circumferential magnets 11 are fitted so that the direction of their magnetic poles is along the circumferential direction (they are magnetized in the circumferential direction of the rotor core 8) and so that the magnetic pole facing an adjacent radial magnet 12 is the same polarity as the magnetic pole of that adjacent radial magnet 12 on the surface side of the rotor core 8. Therefore, each radial magnet 12 is fitted into the radial magnet holding portion 22 so that the direction of its magnetic poles is along the radial direction of the rotor core 8 and the magnetic poles on the surface side of the rotor core 8 are alternately different (reversed) in the circumferential direction.

[0055] Here, ferrite magnets are used for the circumferential magnets 11. In contrast, the radial magnets 12 are smaller than the circumferential magnets 11, but are made of rare earth magnets with strong magnetic force. An example of a rare earth magnet with strong magnetic force is a neodymium magnet.

[0056] Therefore, the circumferential magnets 11 and the radial magnets 12 are arranged in the rotation direction of the rotor 3 using a Halbach array, so that magnetic flux is generated mainly on the surface side of the rotor core 8.

[0057] In addition, in this example, rivet insertion holes 18 are formed between the third outer surfaces 11c of the circumferential magnets 11 whose third outer surfaces 11c face each other in the circumferential direction (between the third inner surfaces 21c of the circumferential magnet holding portions 21 whose third inner surfaces 21c face each other in the circumferential direction), through which rivets 17 for fastening end plates 9, etc. in the axial direction are inserted.

[0058] Also, 21f is a spring accommodating portion that is provided on the fourth inner surface 21d of the circumferential magnet holding portion 21 and that accommodates the leaf spring 8a that is provided on some of the steel plates of the rotor core 8 and biases the stacked steel plates.

[0059] In the above configuration, when a current is supplied from the power supply to the windings 6, a magnetic field is generated by the circumferential magnets 11 and the radial magnets 12. At this time, since the circumferential magnets 11 and the radial magnets 12 are arranged using the Halbach array, a large amount of magnetic flux is generated mainly on the surface side of the rotor 3.

[0060] If the circumferential width of the circumferential magnet on the radially outer side is the same as the circumferential width on the radially inner side, the circumferential width of the divided portion of the second inner surface 21b of the circumferential magnet holding portion 21 cannot be secured to be large, and more magnetic flux will circulate around the radially outer end portion of the circumferential magnet 11 without heading towards the stator 2 (magnetic flux circulating from the first outer surface 11a to the third outer surface 11c, or magnetic flux circulating from the third outer surface 11c to the first outer surface 11a), resulting in more magnetic flux that does not contribute to the rotation of the rotor.

[0061] In contrast, the circumferential magnet 11 according to this embodiment is configured so that its circumferential width increases from the radially inner side to the radially outer side, both at the portion where the fourth outer surface 11d of the first outer surface 11a faces in the circumferential direction and at the portion where the third outer surface 11c of the first outer surface 11a faces in the circumferential direction. Overall, the circumferential width closer to the radially outer side is larger than the circumferential width closer to the radially inner side. This, combined with the fact that the circumferential width of the divided portion of the second inner surface 21b of the circumferential magnet holding portion 21 can be secured large, makes it possible to direct most of the magnetic flux toward the stator, as shown in FIG. 5, and makes it possible to reduce the magnetic flux that turns around at the radially outer end portion of the circumferential magnet 11 without heading toward the stator 2 (magnetic flux that turns around from the first outer surface 11a to the third outer surface 11c, or from the third outer surface 11c to the first outer surface 11a).

[0062] Furthermore, the circumferential magnets 11 are arranged in the rotor core (8) with their cross-sectional shapes (arcuate convex surface 13 and arcuate concave surface 14) reversed in the circumferential direction for each magnet so that the facing surfaces (11a-11a, 11c-11c) of adjacent circumferential magnets (11) are mirror images. Therefore, between adjacent circumferential magnets whose arcuate convex surfaces 13 (first outer surface 11a) face each other, a magnetic path is formed whose circumferential width gradually widens from the radially inner side toward the circumferentially outer side. Although the magnetic flux flowing from the circumferential direction of the first outer surface 11a toward the stator becomes more concentrated as it goes radially outward, the magnetic path width also increases, making it possible to direct the magnetic flux smoothly and evenly toward the stator 2.

[0063] Furthermore, between adjacent circumferential magnets whose arc concave surfaces 14 (third outer surfaces 11c) face each other, a large space can be secured between the arc concave surfaces 14, so even if a rivet insertion hole 18 for inserting a rivet 17 is formed in this portion, the magnetic path will not be narrowed more than necessary.

[0064] Furthermore, since ferrite magnets are used for the circumferential magnets and rare earth magnets are used for the relatively smaller radial magnets, it is possible to reduce the amount of expensive rare earth magnets used. Furthermore, in the magnetic path between the opposing arc convex surfaces 13 of adjacent circumferential magnets 11, even if the radial magnets 12 are small, the magnetic flux can reach the stator 2 with the assistance of the circumferential magnets 11.

[0065] In the above example, a rivet insertion hole 18 through which a rivet 17 for fixing the end plate 9 is inserted is provided between the opposing third outer surfaces 11c (opposing third inner surfaces 21c). However, instead of the rivet insertion hole 18, a crimping portion (for example, a dowel for joining adjacent steel plates) for crimping and joining the stacked steel plates together may be provided in this portion.

[0066] In the above example, an example was shown in which one surface facing the circumferential direction is provided with an arcuate convex surface 13 and the other surface facing the circumferential direction is provided with an arcuate concave surface 14, as a shape in which the circumferential width on the radially outer side is larger than the circumferential width on the radially inner side, but this is not limited to this and other shapes may be adopted as long as the circumferential width of the radially outer part of the circumferential magnet 11 is made larger than the circumferential width of the radially inner part, and the function of reducing the leakage of magnetic flux on the radially outer side of the circumferential magnet 11 is prioritized. For example, the first outer surface 11a and the third outer surface 11c of the circumferential magnet 11 may be formed only with flat surfaces without any arcuate surfaces, and the circumferential width of the radially outer part may be formed larger than the circumferential width of the radially inner part. [Explanation of symbols]

[0067] 1 IPM motor 2 stator 3 rotors 7 Rotation Axis 8 rotor core 10 Permanent Magnets 11 Circumferential magnet 11a 1st outer surface 11b Second outer surface 11c 3rd outer surface 11d 4th outer surface 12 radial magnets 13 Convex arc 14 Concave arc 16 Shaft hole

Claims

1. A magnet arrangement structure of a rotor (3) for an IPM motor, comprising a cylindrical rotor core (8) and a plurality of permanent magnets (10) arranged inside the rotor core (8), The permanent magnet (10) includes a plurality of circumferential magnets (11) fitted in the rotor core (8) along the circumferential direction of the rotor core (8), and the circumferential magnets (11) are arranged in the rotor core (8) such that the direction of their magnetic poles is along the circumferential direction of the rotor core (8); The circumferential magnet (11) is set so that the circumferential width on the radially outer side is larger than the circumferential width on the radially inner side. The magnet arrangement structure of an IPM motor rotor (3) is characterized in that

2. The circumferential magnet (11) has asymmetric circumferentially facing opposite surfaces (11a, 11c), 2. The magnet arrangement structure of the rotor (3) for an IPM motor according to claim 1, characterized in that each of the plurality of circumferential magnets (11) is arranged in the rotor core (8) with its cross-sectional shape reversed in the circumferential direction for each magnet so that the facing surfaces (11a-11a, 11c-11c) of adjacent circumferential magnets (11) are mirror images of each other.

3. 3. The magnet arrangement structure of the rotor (3) for an IPM motor according to claim 2, characterized in that the circumferential magnet (11) includes an arc-shaped convex surface (13) on one surface (11a) facing the circumferential direction, and the multiple circumferential magnets (11) are arranged so that their respective arc-shaped convex surfaces (13) face each other.

4. 3. The magnet arrangement structure of a rotor (3) for an IPM motor according to claim 2, characterized in that a radial magnet (12) fitted in the rotor core (8) is arranged between adjacent circumferential magnets of the plurality of circumferential magnets (11) near the radially inner end thereof so that the direction of the magnetic poles is along the radial direction of the rotor core (8).

5. 5. The magnet arrangement structure of the rotor (3) for an IPM motor according to claim 4, wherein the circumferential magnets (11) are ferrite magnets, and the radial magnets (12) are rare earth magnets.

6. 4. The magnet arrangement structure of a rotor (3) for an IPM motor according to claim 3, characterized in that an arc-shaped concave surface (14) is formed from the radially inner side to the radially outer side on a surface (11 c) of the circumferential magnet (11) facing in the circumferential direction opposite to the side on which the arc-shaped convex surface (13) is provided.

7. 7. The magnet arrangement structure of a rotor (3) for an IPM motor according to claim 6, characterized in that a rivet (17) that passes through the rotor core (8) is arranged between the arc-shaped concave surfaces (14) of adjacent circumferential magnets (11) whose arc-shaped concave surfaces (14) face each other in the circumferential direction.

8. 7. The magnet arrangement structure of an IPM motor rotor (3) according to claim 6, characterized in that the circumferential magnet (11) comprises a first outer surface (11a) having the arcuate convex surface (13), a third outer surface (11c) having the arcuate concave surface (14) provided opposite the first outer surface (11a), a second outer surface (11b) connecting a radial outer end of the first outer surface (11a) to a radial outer end of the third outer surface (11c), and a fourth outer surface (11d) connecting a radial inner end of the first outer surface (11a) to a radial inner end of the third outer surface (11c), wherein adjacent circumferential magnets (11) whose arcuate concave surfaces (14) face each other are arranged so that their fourth outer surfaces (11d) are substantially parallel to each other, and a radial magnet (12) is disposed in a radially inner portion between the facing fourth outer surfaces (11d).

9. An IPM motor (1) having: a cylindrical stator (2) including a stator core (4) having a plurality of teeth (4b) and a winding (6) wound around each of the plurality of teeth (4b); and an IPM motor rotor (3) provided inside the stator (2) and including the magnet arrangement structure according to any one of claims 1 to 8.

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