Rotor of a synchronous motor with internal permanent magnets and synchronous motor with internal permanent magnets

Abstract

Rotor of a synchronous motor with internal permanent magnets, comprising: a rotor core (10) which rotates with respect to an axis (L0) and which has a cylindrically shaped outer circumferential surface (10b) over its entire circumference; a plurality of slots (20) formed in the rotor core at a plurality of locations in a circumferential direction and extending parallel to the axis; and a plurality of permanent magnets (30) which are housed in the plurality of slots and have rectangular shapes in cross-section, wherein the plurality of permanent magnets is housed such that in the slots which are adjacent to each other in the circumferential direction, opposite poles are positioned in a diametrical direction, wherein Each of the numerous slots includes: a holding section (21) formed between a first outer diameter surface (211) extending in the circumferential direction and a first inner diameter surface (212) opposite the first outer diameter surface and extending in the circumferential direction at an inner side of the first outer diameter surface in the diametrical direction to hold each of the plurality of permanent magnets, and an opening section (22) formed on both sides of the retaining section in the circumferential direction, wherein the opening section is formed by a second outer diameter surface (221) extending from the first outer diameter surface in the circumferential direction, a second inner diameter surface (222) extending from the first inner diameter surface in the circumferential direction, and a curved connecting surface (223) connecting the second outer diameter surface and the second inner diameter surface, and wherein a section on the outside of the opening section (22) in the diametrical direction towards the outer circumferential surface (10b) of the rotor is defined by a bridge section (24), and the second outer diameter surface is formed into a curved shape, such that the distance to an outer circumferential surface (10b) of the rotor core in the diametral direction from both ends of the second outer diameter surface in the circumferential direction to an intermediate section in the circumferential direction becomes progressively smaller such that a first diametral length (ΔL1) is greater than or equal to a second diametral length (ΔL2) and a third diametral length (ΔL3) is smaller than both the first diametral length (ΔL1) and the second diametral length (ΔL2). where: - the first diametral length (ΔL1) is defined at a first end (241) of the bridge section (24), wherein the first end (241) is defined by a point (P2) of the greatest curvature of the curved connecting surface (223) of the opening section (22), and wherein the first diametral length (ΔL1) extends in a diametral direction (S2) from the first end (241) towards the outer circumferential surface (10b) of the rotor (10), - the second diametral length (ΔL2) is defined at a second end (242) of the bridge section (24), wherein the second end (242) is defined by a transition point (P1) from the first outer diameter surface (211) of the retaining section (21) to the second outer diameter surface (221) of the opening section (22), and wherein the second diametral length (ΔL2) extends in a diametral direction (S1) from the second end (242) towards the outer circumferential surface (10b) of the rotor (10), and - the third diametral length (ΔL3) is defined in an intermediate section (243) between the first end (241) and the second end (242), wherein the third diametral length (ΔL3) extends in a diametral direction from the second outer diameter surface (221) of the opening section (22) towards the outer circumferential surface (10b) of the rotor (10), where: the curved connecting surface comprises a curved surface that projects outwards towards an outside of the opening section in the circumferential direction, so that the cross-section of the opening section is essentially triangular, a maximum length (D2) of the opening section in the diametrical direction is longer than a thickness (D3) of the permanent magnet in the diametrical direction, a length (D1) of the opening section which is the shortest distance from the point (P2) of the greatest curvature of the curved connecting surface (223) of the opening section (22) to an end face (303) of the permanent magnet in the circumferential direction, i) greater than the maximum length (D2) of the opening section in the diametrical direction, and ii) longer than the thickness (D3) of the permanent magnet in the diametrical direction, and the rotor core has a section (23) without a slot between each pair of opening sections that adjoin each other in the circumferential direction, wherein: - a q-axis tooth width (W) of the section (23) without a slot between the points (P2) of the greatest curvature of the curved connecting surfaces (223) of the pair of opening sections (22) becomes minimal, and - the section (23) without a slot does not have a straight section of constant width in the circumferential direction.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to a rotor of a synchronous motor with internal permanent magnets that can rotate at a high speed and a synchronous motor with internal permanent magnets. 2. Description of the related art

[0002] A synchronous motor with internal permanent magnets is known, which provides a plurality of magnet holding holes in the circumferential direction of a substantially cylindrically shaped rotor core, and embeds permanent magnets in the magnet holding holes to form a rotor. For example, in the electric motor described in Japanese Patent JP 3533209 B (filed as JP 2004-72845 A), each magnet holding hole is formed by opposing, straight-shaped outer and inner walls, end walls extending from the ends of the outer wall in the circumferential direction, and passage walls connecting the end walls and the inner wall. Furthermore, a magnet is embedded between the outer wall and the inner wall. Gaps are formed on both sides of the magnet in the circumferential direction (inner diameter sides of the end walls).Furthermore, the outer peripheral surface of the rotor core is provided with recessed portions parallel to the end walls in the diametrical direction at the outer sides of the end walls. Bridge portions of constant thickness are formed between the end walls and the recessed portions in the diametrical direction.

[0003] The rotor described in JP 3533209 B has thin bridge sections of constant thickness on the outer sides of the gaps in the diametrical direction. The cross-sectional shape of the rotor core changes rapidly at the two ends of the end walls in the circumferential direction. Therefore, the load is concentrated at the two ends of the end walls of the rotor core, and thus, when the rotor is caused to rotate, the centrifugal force may cause the thin bridge sections to fracture.

[0004] The publication US 2010 / 0 117 475 A1 discloses a lightweight rotor consisting of circular disc sheets with a very large inner diameter with entire tangential magnets.

[0005] The document JP 2002- 359 942 A discloses a lightweight rotor consisting of circular disc sheets with a very large inner diameter with split tangential magnets with a web.

[0006] The documents DE 103 57 502 A1, DE 10 2008 004 225 A1, DE 10 2008 032 172 A1, DE 10 2010 043 224 A1, DE 11 2006 001 929 T5, US 2011 / 0 204 742 A1, JP 2011- 15 572 A, JP 2010- 206 884 A, JP 2004- 254 466 A, JP 2011- 135 726 A, JP 2008- 154 299 A and JP 2010- 88 219 A disclose further rotors. Summary of the invention

[0007] According to the invention, a device according to the independent claim is provided. Developments are presented in the dependent claims.

[0008] Preferably, a synchronous motor with internal permanent magnets is provided, comprising: a rotor core that rotates with respect to an axis; a plurality of slots formed in the rotor core at a plurality of locations in a circumferential direction and extending parallel to the axis; and a plurality of permanent magnets housed in the plurality of slots, wherein the plurality of permanent magnets are housed such that mutually different poles are positioned in a diametrical direction in the slots adjacent to each other in the circumferential direction. Each of the plurality of slots of this rotor core preferably includes a holding portion formed between a first outer diameter surface extending in the circumferential direction and a first inner diameter surface.which faces the first outer diameter surface and extends in the circumferential direction at an inner side from the first outer diameter surface in a diametrical direction to hold each of the plurality of permanent magnets, and an opening portion formed on both sides of the holding portion in the circumferential direction, wherein the opening portion is formed by a second outer diameter surface extending from the first outer diameter surface in the circumferential direction, a second inner diameter surface extending from the first inner diameter surface in the circumferential direction, and a connecting surface connecting the second outer diameter surface and the second inner diameter surface. Furthermore, the second outer diameter surface is preferably formed in a curved shape such thatthat a distance to an outer peripheral surface of the rotor core in the diametrical direction from both ends of the second outer diameter surface in the circumferential direction toward an intermediate portion in the circumferential direction gradually becomes smaller.,

[0009] Furthermore, an internal permanent magnet synchronous motor according to an example includes the rotor described above and a stator arranged around the rotor. Short description of the drawings

[0010] The objects, features, and advantages of the invention will become clearer from the following description of embodiments in relation to the accompanying drawings. Fig. 1 is a cross-sectional view showing the schematic structure of an internal permanent magnet synchronous motor according to an embodiment of the invention; Fig. 2 an enlarged view showing the basic structure of a rotor according to Fig. 1 shows; Fig. 3 a view showing a comparative example according to Fig. 2 shows; Fig. 4 a view showing a comparative example according to Fig. 2 shows; Fig. 5 a view showing the setting of lengths of the opening sections according to Fig. 2 in the circumferential direction and the diametrical direction; Fig. 6 a view showing a modification according to Fig. 1 shows; Fig. 7 a view showing a comparative example according to Fig. 6 shows; and Fig. 8 a view showing a modification according to Fig. 2 shows. Detailed description

[0011] Hereinafter, a synchronous motor with internal permanent magnets according to an embodiment of the invention will be described with reference to Fig. 1 to Fig. 8 are described. Fig. 1 shows a cross-sectional view showing a schematic structure of a synchronous motor with internal permanent magnets according to an embodiment of the invention. The electric motor 100 shown in Fig. 1 includes a substantially cylindrically shaped rotor 1 rotating about an axis L0, and a substantially cylindrically shaped stator 2 (illustration of this portion in the circumferential direction is omitted) arranged around the rotor 1 to surround the entire circumference of the rotor 1. The stator 2 includes a stator core 3 made of electrical steel sheets stacked in the axial direction. On the inner peripheral surface of the stator core 3, a plurality of slot recesses 3a are formed in the circumferential direction toward the outside in the diametrical direction. A coil 4 is arranged in the slot recesses 3a.

[0012] The rotor 1 includes a rotor 10 made of electrical steel sheets stacked in the axial direction, and having a cylindrically shaped inner peripheral surface 10a and an outer peripheral surface 10b over its entire circumference, a plurality of slots 20 formed on the rotor core 10 at a plurality of locations in the circumferential direction and extending parallel to the axis L0, and a plurality of permanent magnets 30 fitted (embedded) in the slots 20. The magnets 30 are housed such that mutually different poles are positioned in the diametrical direction in the slots 20 adjacent to each other in the circumferential direction. Therefore, north poles and south poles are alternately formed along the outer peripheral surface 10b of the rotor core 10. In the figure, the number of poles is twelve.The rotor 1 rotates in synchronization with a rotating magnetic field by passing a three-phase alternating current through the coil 4 to generate a rotating magnetic field.

[0013] The electric motor 100 according to the embodiment is inserted, for example, into a spindle of a machine tool as a built-in motor. That is, the inner peripheral surface 10a of the rotor core 10 is attached to the outer peripheral surface of the spindle by shrink fitting, etc. In general, the spindle of a machine tool must have high rigidity to ensure sufficient machining accuracy. In order to increase the rigidity of the spindle, it is necessary to increase the size of the spindle and increase the secondary torque in the cross section. For this reason, the rotor 1 has a comparatively large inner diameter corresponding to the diameter of the spindle. On the other hand, the rotor 1 must have the function of causing the spindle to rotate at a high speed. Therefore, it is necessary to suppress the maximum load on the rotor 1 acting due to the centrifugal force.

[0014] Fig. Fig. 2 is an enlarged view showing the structure of main sections of the rotor 1 according to Fig. 1, and in particular shows the shape of one end of a slot 20. As in Fig. 2, the slot 20 has a holding portion 21 in which a magnet 30 is held, and an opening portion 22 connected to the holding portion 21 and open toward the side of the holding portion 21. As shown in Fig. 1, the slot 20 and the magnet 30 have symmetrical shapes in the circumferential direction. The opening portion 22 is formed at both sides of the holding portion 21 in the circumferential direction. For this reason, as shown in Fig. 2, the rotor core 10 has a tooth portion 23 (q-axis tooth portion) extending from the inner peripheral surface 10a to the outer peripheral surface 10b in the diametrical direction between an opening portion 22 and an opening portion 22 adjacent to each other in the circumferential direction.

[0015] The tooth portion 23 contributes to the generation of a reluctance torque of the rotor 1. Therefore, in order to increase the reluctance torque, it is preferable that the width W in the circumferential direction (q-axis tooth width) be as large as possible. Conversely, if the q-axis tooth width is increased, the width of the magnets 30 becomes narrower. As a result, the magnetic flux decreases, the inductance increases, and the voltage may become insufficient. The q-axis tooth width is set with this in mind. That is, if the degree of utilization of the reluctance torque is increased, the q-axis tooth width is increased. If it is not necessary to increase the degree of utilization of the reluctance torque, the q-axis tooth width is made narrower.

[0016] The opening portions 22 are provided to prevent a short circuit of the magnetic flux on the sides of the magnets 30. For example, as in Fig. As shown in Figure 3, if there are no opening sections 22 on the sides of the magnets 30, parts of the magnetic flux do not pass through the stator 2, but, as shown by the arrows in the figure, scatter to the opposite pole sides of the magnets 30. That is, the magnetic flux shorts. Such a short circuit of the magnetic flux does not contribute to the generation of torque, so that a short circuit of the magnetic flux can be suppressed to the greatest extent possible. Therefore, in the embodiment as shown in Fig. As shown in Figure 2, portions (opening portions 22) in which no electrical steel sheets (so-called iron cores) are present are provided at the sides of the magnets 30 so that the magnetic flux efficiently passes through the stator 2. The opening portions 22 may be simple spaces or may be filled with a resin or other non-magnetic material.

[0017] In such an internal permanent magnet electric motor 100, the areas where the stress acting on the rotor core 10 tends to increase as the rotor 1 rotates are the portions on the outer side of the opening portions 22 in the diametrical direction (hereinafter referred to as the "bridge portions 24") and the iron core portions on the inner diameter side of the slots 20 (hereinafter referred to as the "slot inner diameter portions 25"). Among these, the portions on the inner diameter side of the slots 20 experience greater stress, particularly at the portions of the slot inner diameter portions 25 where the thickness in the diametrical direction (cross-sectional area) becomes the smallest. The maximum stress on the slot inner diameter portions 25 can be reduced by making the inner diameter of the rotor 1 smaller or otherwise appropriately changing the cross-sectional area.

[0018] On the other hand, considering the bridge portions 24, even if the inner diameter of the rotor 1 is reduced, no effect of stress reduction can be obtained. This is because, due to the centrifugal force generated by the mass of the magnets 30 and the centrifugal force generated by the mass of the portions of the slots 20 of the rotor core 10 on the outer side in the diametrical direction, a tensile stress in the circumferential direction mainly acts on the bridge portions 24. In particular, since the rotor 1 rotates at a high speed in the embodiment, the stress acting near the bridge portions easily becomes large. Therefore, the rotor 1 in the embodiment is constructed as follows to reduce the maximum stress acting near the bridge portions. A breakage at the slot inner diameter portions 25 causes great damage to the electric motor as a whole.Therefore, the rotor is preferably constructed such that the maximum load on the slot inner diameter sections 25 is smaller than the maximum load on the bridge sections 24.

[0019] As in Fig. As shown in Figure 2, the holding portion 21 of the slot 20 is formed of an outer diameter side holding edge 211 extending in the tangential direction of a circle with respect to the axis L0, and an inner diameter side holding edge 212 extending in the tangential direction of a circle with respect to the axis L0 on the inner diameter side from the outer diameter side holding edge 211 and facing the outer diameter side holding edge 211. The pair of holding edges 211 and 212 extend parallel to each other in straight shapes. A magnet 30 with a rectangular cross-section is fitted into the holding portion 21.

[0020] The lengths of a pair of pole faces 301 and 302, which form a north pole and a south pole of the magnet 30, are longer than the pair of side faces 303 that intersect the pole faces 301 and 302, and each magnet 30 has a rectangular shape in cross-section. If the orientation of the magnet 30 is defined by the center line L1 passing through the centers of the pole faces 301 and 302, the magnet 30 (center line L1) extends in the tangential direction of a circle with respect to the axis L0.

[0021] The magnet 30 is preferably made of a magnet with greater magnetic energy than a ferrite magnet, for example, a rare earth magnet. For the rare earth magnet, a rare earth magnet based on neodymium-iron-boron can be used, for example. Due to this, it is possible to reduce the thickness of the magnet 30 and easily increase the inner diameter of the rotor 1. Furthermore, if the magnet 30 is made thin, the centrifugal force due to the mass of the magnet 30 is reduced, making it possible to reduce the load acting on the bridge portion 24.

[0022] Each opening portion 22 of a slit 202 is formed by an outer diameter side opening edge 221 extending from the outer diameter side retaining edge 211 in the circumferential direction, an inner diameter side opening edge 222 facing the outer diameter side opening edge 221 and extending from the inner diameter side retaining edge 212 in the circumferential direction, and a connecting edge 223 connecting the outer diameter side opening edge 221 and the inner diameter side opening edge 222. The slit 202 extends parallel to the axis L0, while the edges 211, 212, and 221 to 223 are formed according to Fig. 2 Define surfaces that extend in the axial direction.

[0023] A dashed line S1 in the figure is a line connecting a connecting point P1 between the outer diameter side retaining edge 211 and the outer diameter side opening edge 221 to the axis L0, while the dashed line S2 is a line connecting a point P2 on the connecting edge 223, where the width W of the tooth portion 23 becomes the smallest, to the axis L0. The area surrounded by these dashed lines S1 and S2, the outer diameter side opening edge 221, and the outer peripheral surface 10b of the rotor core 10 becomes the bridge portion 24.

[0024] The outer diameter side opening edge 221 is formed by a smooth curve radiating outward in the diametrical direction (e.g., a circular arc with a radius of curvature of r = 1). The outer diameter side opening edge 221, the outer diameter side retaining edge 211, and the connecting edge 223 are smoothly connected. The radius of curvature r1 of the outer diameter side opening edge 221 is smaller than the length from the axis L0 to the outer diameter side opening edge 221. Therefore, the length in the diametrical direction from the outer diameter side opening edge 221 to the outer peripheral surface 10b of the rotor core 10 gradually becomes smaller from the two ends 241 and 242 of the bridge portion 24 in the circumferential direction toward the intermediate portion 243 in the circumferential direction.That is, the diametrical direction length ΔL3 at the intermediate portion 243 is smaller than the lengths ΔL1 and ΔL2 of the bridge portion 24 on the dashed lines S1 and S2, while the bridge portion 24 assumes the smallest thickness at the intermediate portion 243. The lengths ΔL1 and ΔL2 at the two ends 241 and 242 of the bridge portion 24 are substantially equal to each other.

[0025] The outer diameter side opening edge 221 may be formed not from a single circular arc, but from a smooth composite curve composed of a plurality of circular arcs combined with each other. In this case, it is sufficient that the maximum radius of the curve is smaller than the length from the axis L0 to the outermost diameter portion of the outer diameter side opening edge 221, in other words, smaller than the radius of curvature of the circular arc offset from the outer peripheral surface 10b of the stator core 10 to the inner diameter side by exactly the amount of the minimum thickness ΔL3. Here, "smooth" means forming the curve of the outer diameter side opening edge 221 to suppress stress concentration.For example, when connecting a plurality of curves different in radii of curvature to form the outer diameter side opening edge 221, it is preferable to connect them such that two curves are differentiable in their relationship, that is, such that two curves have common tangents at the connecting points of the two curves.

[0026] The connecting edge 223 is formed by extending toward the outside of the opening portion 22 in the circumferential direction. The opening portion 22, surrounded by the outer diameter-side opening edge 221, the inner diameter-side opening edge 222, and the side surface 303 of the magnet 30, has a substantially triangular shape overall. The connecting edge 223 can be constructed by a curve consisting of a single circular arc or by a smoothly compound curve consisting of a plurality of mutually combined circular arcs. The radius of curvature of the circular arc forming this connecting edge 223 (in the case of a compound curve, the minimum value of the radius of curvature) is smaller than the radii of curvature of the opening sides 221 and 222. In the embodiment, the end of the inner diameter-side opening edge 222 is provided with a protruding portion 22b.However, without considering the protruding portion 22b, the radius of curvature of the connecting edge 223 becomes smallest in the edges forming the opening portion 22.

[0027] By forming the connecting edge 223 in a protruding shape, the tooth portion 23 is formed with a narrowed portion (point P2). For this reason, the tooth portion 23 does not have a straight portion of a constant width in the circumferential direction. The tooth portion width W (q-axis tooth width) becomes the smallest at the narrowed portion. In contrast, as shown in Fig. 4 showing the comparative example of the embodiment, if the opening portion 22 is formed by the pair of edges 221a and 222a of the outer diameter side and the inner diameter side and the edge 223a extending in the diametrical direction, the tooth portion 23 will have a straight portion with a constant width W.

[0028] As in Fig. As shown in FIG. 2, the inner diameter side opening edge 222 includes a straight portion 22a inclined from the connecting edge 223 toward the inner diameter side, and a protruding portion 22b projecting outward toward the outside in the diametrical direction at the boundary portion of the opening edge 222 and the retaining edge 212. The inner diameter side opening edge 222 is smoothly connected by the connecting edge 223 to the straight portion 22a, the protruding portion 22b, and the inner diameter side retaining edge 212.

[0029] By providing the straight portion 22a at an inclination with respect to the inner diameter side, it is possible to reduce the maximum length of the opening portion 22 in the diametrical direction ( Fig. 5, D2). The protruding portion 22b functions as a positioning portion that restricts the position of the magnet 30 in the holding portion 21. Since the protruding portion 22b is provided at the inner diameter side opening edge 222, where the load is smaller than at the outer diameter side opening edge 221, the load near the protruding portion 22b becomes smaller than the maximum load acting on the bridge portion 24.

[0030] In the electric motor 100 according to the embodiment constructed as described above, when the rotor 1 rotates, a load acts on the bridge portion 24 due to the centrifugal force of the magnet 30 and partially at the outside of the slot 20 in the diametrical direction. In this case, the cross-sectional shape of the bridge portion 24 changes rapidly at the end of the outer diameter-side opening edge 221 (for example, the end 241 on the connecting edge 223 side). However, the opening portion 22 assumes a substantially triangular shape, so the length ΔL1 of the end 241 in the diametrical direction is longer than the length ΔL3 of the intermediate portion 243 in the diametrical direction. For this reason, the load becomes maximum at the intermediate portion 243 where the cross-sectional area of ​​the bridge portion 24 becomes the smallest.

[0031] In the embodiment, the outer diameter side opening edge 221 is configured by a smooth curve in which no straight portion is included. For this reason, stress concentration at the intermediate portion 243 can be suppressed, and the maximum load of the bridge portion 24 can be reduced. That is, the load acting on the bridge portion 24 gradually decreases toward the two ends 241 and 242 from the intermediate portion 243 as the center. A change range is formed in which the load gradually changes over a wide range in the entire region of the bridge portion 24. Due to this, it is possible to suppress the maximum load of the intermediate portion 243, and the rotor 1 can rotate at a high speed.

[0032] In contrast, as in Fig. 4, if the edge 221a of the outer diameter side is constructed so that the diametrical direction length ΔL of the bridge portion 24 becomes constant over the circumferential direction, the cross-sectional shape of the bridge portion 24 changes rapidly at the two ends A1 and A2 of the edge 221a in the circumferential direction. In this case, the maximum load occurs at the two ends A1 and A2 of the bridge portion 24. The radii of curvature of the portions A1 and A2 at which this maximum load occurs are smaller than the radii of curvature of the portion at which the maximum load occurs in the embodiment (intermediate portion 243), so that in the structure according to Fig. 4, the maximum load easily increases. As a result, the bridge section 24 breaks, starting at the two locations of A1 and A2. The broken sections may be ejected in a diametrical direction, and the electric motor 100 may be severely damaged.

[0033] When the edge 221a of the opening portion 22 according to Fig. 4 is formed, for example, in a straight shape along the tangential direction of the circle with respect to the axis L0, the two ends of the bridge section 24 become the smallest in terms of cross-sectional area. For this reason, the maximum load at A1 and A2 becomes much larger, and the bridge section 24 is more likely to break, starting from A1 and A2.

[0034] In the rotor of the embodiment, the lengths of the opening portion 22 in the circumferential direction and the diametrical direction are preferably constructed as follows. Fig. Fig. 5 is a view showing the adjustment of the lengths of the opening portion 22 in the circumferential direction and the diametrical direction. As in Fig. 5, the shortest distance from a point P2 on the connecting edge 223 at which the width of the tooth portion 23 becomes minimum to the side surface 303 of the magnet 30 is defined as D1, the maximum value of the length of the opening portion 22 in the diametrical direction is defined as D2, and the thickness of the magnet (distance between the pole faces) is defined as D3.

[0035] At this time, D1 is longer than D2, whereas D2 is longer than D3. For example, D1 is 1.5 times or more of D3. Therefore, the opening portion 22 has sufficient lengths in the circumferential direction and the diametrical direction. For this reason, as indicated by the arrow in FIG. Fig. 5, if a magnetic field acts on the rotor 1 in the demagnetization direction, the demagnetization field passes through the bridge portion 24 where the magnetoresistance is smaller than the opening portion 22, and it becomes more difficult to demagnetize the magnet 30.

[0036] In contrast, as in Fig. 4, when the lengths of the opening portion 22 in the circumferential direction and the diametrical direction are shorter than the thickness of the magnet 30, the magnetoresistance of the opening portion 22 does not become sufficiently large, and the demagnetizing field passes through the opening portion 22 as shown by the arrows in FIG. Fig. 4. As a result, the corner portions of the magnet 30 may be demagnetized.

[0037] According to the embodiment, the following functions and effects can be obtained: (1) The slot 20 of the rotor 1 is provided with a holding portion 21 in which the magnet 30 is to be held, and opening portions 22 formed on both sides of the holding portion 21 in the circumferential direction. That is, the opposing outer diameter side holding edge 211 and the inner diameter side holding edge 212 extending in the circumferential direction are used to form the holding portion 21. In addition, the outer diameter side opening edge 221 extending from the outer diameter side holding edge 211 in the circumferential direction, the inner diameter side opening edge 222 extending from the inner diameter side holding edge 212 in the circumferential direction, and the connecting edge 223 connecting the opening edges 221 and 222 are used to form the opening portion 22.Furthermore, the outer diameter side opening edge 221 is formed in a curved shape such that the length from the outer diameter side opening edge 221 to the outer peripheral surface 10b of the rotor core 10 in the diametrical direction gradually becomes smaller from both ends 241, 242 in the circumferential direction toward the intermediate portion 242 in the circumferential direction. That is, the outer diameter side opening edge 221 is formed by branching outward toward the outside in the diametrical direction, and the thickness of the bridge portion 24 at the intermediate portion 243 in the diametrical direction is made smallest.

[0038] Due to this, the bridge portion 24 is formed such that the cross-sectional area in the diametrical direction becomes smallest at the intermediate portion 243, and the maximum load acts at the intermediate portion 243 where the cross-sectional shape gradually changes. As a result, the maximum load acting on the bridge portion 24 can be reduced, and the rotor 1 can be caused to rotate at a high speed. The maximum load acts at a single location (the intermediate portion 243) of the bridge portion 24 instead of a plurality of locations, so that even if the portion breaks, the bridge portion 24 can be prevented from being thrown out to the stator 2 side. (2) The connecting edge 223 is formed in a curved shape that protrudes outwardly toward the outside of the opening portion 22 in the circumferential direction, so that it is possible to easily increase the cross-sectional area of ​​the end 241 of the bridge portion 24 in the circumferential direction and reduce the stress on the end 241 in the circumferential direction. Furthermore, since the opening portion 22 assumes a substantially triangular shape, the magnetic flux can be made to efficiently flow along the outer diameter side opening edge 221 and the inner diameter side opening edge 222 of the opening portion 22. (3) The outer diameter side holding edge 221 and the inner diameter side holding edge 212 constituting the holding portion 21 of the slot 20 are formed flat and parallel to each other, so that the holding portion 21 has no unevenness, and stress concentration at the holding portion 21 can be suppressed. Furthermore, since it is possible to use a magnet 30 with a rectangular cross section corresponding to the shapes of the holding portion 21, the structure of the magnet 30 is also easy. (4) The rotor core 10 has a circular-arc-shaped outer peripheral surface 10b that is free of unevenness over the entire circumference, so that the thickness of the bridge portion 24 changes smoothly in the diametrical direction and stress concentration can be facilitated. Furthermore, mold-like stress concentration on the outer peripheral surface 10b can also be prevented. (5) If the magnets 30 are constructed with rare earth magnets with higher magnetic energy than ferrite magnets, it is possible to achieve the required magnetic flux with fewer magnets and possibly keep the volume of the magnets 30 small to achieve the required torque. As a result, the centrifugal force acting due to the mass of the magnets 30 is reduced, and the rotor 1 can be operated at a higher speed. (6) The length D1 of the opening portion 22—from the point P2 on the connecting edge 223, where the width W of the tooth portion 23 of the rotor core 10 becomes the smallest, to the side surface 303 of the magnet 30—is made longer than the thickness D3 of the magnet 30 in the diametrical direction. As a result, the magnetoresistance at the opening portion 22 becomes larger. Therefore, when a magnetic field acts in the demagnetization direction, it is possible to reduce the demagnetization field passing through the corner portions of the magnet 30 and the opening portion 22 to the tooth portion 23. (7) The maximum length D2 of the opening portion 22 in the diametrical direction is made longer than the thickness D3 of the magnet 30 in the diametrical direction, so that the magnetoresistance at the opening portion 22 also increases in the diametrical direction. Therefore, the demagnetization effect at the corner portions of the magnet 30 can be kept small. (8) The inner diameter side opening edge 222 of the opening portion 22 is provided with a protruding portion 22b that springs outward toward the outside in the diametrical direction, so that the protruding portion 22b can be used to easily position the magnet 30 at the holding portion 21. In this case, the inner diameter side of the opening portion 22 is larger in thickness in the diametrical direction compared to the outer diameter side, and the generated stress is small, so the stress near the protruding portion 22 need not become excessive. (9) The inner diameter side opening edge 222 is provided with a straight portion 22a extending straight in the circumferential direction, so that magnetic flux can easily pass to the inner diameter side pole face 302. That is, the magnetic flux runs along the shortest distance without describing an excessive arc, and is therefore efficient.

[0039] In the above-described embodiment, the number of poles of the rotor 1 is twelve. However, the number of poles can be increased or decreased. For example, when four poles, six poles, eight poles, or any other small number of poles is used, the widths of the magnets 30 in the circumferential direction become larger, the mass of the magnets 30 increases, and the load acting on the bridge portions 24 also increases. In this case, by bifurcating the slots 20 and the magnets 30 in the circumferential direction and interposing the rotor core 10 between the divided pairs of slots 20 and 20, it is possible to ease the load acting on the bridge portions 24. This point will be described below.

[0040] Fig. Fig. 6 is a view showing an example of a rotor 1 that divides the slots 20 and the magnets 30 in the circumferential direction. As shown in Fig. As shown in Figure 6, the slots 20 are divided into two by intermediate portions in the circumferential direction, i.e., the dividing portions 26 of the rotor core 10. Pairs of slots 201 and 202 (first slots 201, second slots 202) are aligned along tangential directions of a circle with respect to the axis L0. The first slots 201 and the second slots 202 accommodate magnets 31 and 32 such that the same poles are positioned in the diametrical direction.

[0041] If partitioning portions 26 are provided in the rotor core 10 in this way to divide the slots 20 into first slots 201 and second slots 202 in the circumferential direction, it is possible to allow the partitioning portions 26 to receive the centrifugal force. As a result, the load acting on the bridge portions 24 is lightened, and the maximum load on the bridge portions 24 can be reduced.

[0042] Furthermore, the first slots 201 and the second slots 202 are aligned straight along the tangential direction of a circle centered on the axis L0, so that the partitioning portions 26 can be positioned near the outer diameter of the rotor core 10, the inner diameter of the rotor core can be easily enlarged, and the generation of excessive stress at the inner diameter portion of the rotor core 10 can be prevented. That is, as shown in, for example, Fig. As shown in Fig. 7, if the pair of slots 201a and 202a are arranged in a V-shape, the wall thickness ΔL of the rotor core 10 at the end A of the slots 20 in the circumferential direction becomes extremely small, and excessive stress acts on the end A. To avoid this, it is necessary to reduce the inner diameter of the rotor core 10 and increase the wall thickness ΔL. Therefore, an increase in the inner diameter of the rotor core 10 is prohibited.

[0043] In the embodiment described above ( Fig. 2) The outer diameter side retaining edge 211 (first outer diameter surface) and the inner diameter side retaining edge 212 (first inner diameter surface) are formed in straight shapes. However, as long as they oppose each other and extend in the circumferential direction, the structure of the first outer diameter surface and the first inner diameter surface, that is, the structure of the retaining portion 21, is not limited to the above description.Furthermore, although the outer diameter side opening edge 221 (second outer diameter surface) extending from the outer diameter side holding edge 211 in the circumferential direction, the inner diameter side opening edge 222 (second inner diameter surface) extending from the inner diameter side holding edge 212 in the circumferential direction, and the connecting edge 223 (connecting surface) connecting the opening edges 221 and 222 are formed in the opening portion 21, the structures of these second outer diameter surface, second inner diameter surface, and connecting surface, that is, the structure of the opening portion 22, are not limited to the above description.

[0044] In the above-described embodiment, the connecting edge 223 is formed protruding toward the outer side in the circumferential direction, and the opening portion 22 is formed in a substantially triangular shape. However, as long as the outer diameter-side opening edge 221 is formed in a curved shape such that the distance in the diametrical direction from the outer diameter-side opening edge 222 to the outer peripheral surface 10b of the rotor core 10 (length of the bridge portion 24 in the diametrical direction) gradually becomes smaller from the two ends 241 and 242 in the circumferential direction toward the intermediate portion 243 in the circumferential direction, the shape of the opening portion 22 is not limited to the above description. For example, it may be substantially square-shaped.Therefore, the shape of the tooth portion 23 (portion without slots) between a pair of opening portions 22 adjacent to each other in the circumferential direction is not limited to the above description. Even if the tooth portion 23 has a straight portion, the length D1 of the opening portion 22 from the point on the connecting edge 223 where the width W of the tooth portion 23 becomes the smallest to the side surface 303 of the magnet 30 is preferably longer than the thickness D3 in the diametrical direction of the magnet 30.

[0045] In the above-described embodiment, the inner diameter side opening edge 222 is provided with a straight portion 22a and a protruding portion 22b for positioning purposes. However, various shapes of the inner diameter side opening edge 222 may be considered. As shown in Fig. As shown in Figure 8, instead of the straight portion 22a, for example, it is possible to provide a curved portion 22c projecting outwardly in the inner side of the diametrical direction. Also, through it, the magnetic flux smoothly flows to the inner diameter side pole face 302, and efficient flow of the magnetic flux is possible. The inner diameter side opening edge 222 may include both a straight portion 22a and a curved portion 22c. In the above-described embodiment, the outer peripheral surface 10b of the rotor core 10 is formed in a circular arc shape without unevenness over the entire circumference. However, as long as the outer peripheral surface of at least the bridge portion 24 in the outer peripheral surface 10b is formed in a circular arc shape without unevenness, unevenness may be present at other locations.For example, it is possible to provide a recess portion at the outer peripheral surface of the tooth portion 23, in which the effect of the load condition is small.

[0046] The rotor core 10 is formed in a single piece by stacking a plurality of electrical steel sheets in the axial direction. The plurality of electrical steel sheets are preferably made of bonded steel sheets joined together by a bonding agent. For example, the surfaces of the electrical steel sheets (the entire surfaces other than the slots 20) are coated with a thermoplastic bonding agent, and then the plurality of electrical steel sheets are stacked. The stacked electrical steel sheets are subjected to a predetermined compressive force in the axial direction using a fixture, etc. Furthermore, the electrical steel sheets subjected to the compressive force are placed in an electric furnace, heated to a temperature at which the bonding agent melts, and then cooled and removed from the electric furnace.As a result, a plurality of electrical steel sheets are bonded together by a bonding agent. If a bonding agent is used to form a rotor core 10 in this way, there is no need for a structural joining portion for bonding the plurality of electrical steel sheets together, and it is possible to minimize the occurrence of new stress concentrations.

[0047] As another method for joining the electrical steel sheets, for example, joining them by swaging and joining them by a bolt (anchor bolt) can be considered. When swaging is used to join the electrical steel sheets, first, portions of the electrical steel sheets (for example, inner peripheral edges) are sheared by a forming die. The sheared portions are bent in the axial direction and plastically deformed to form protruding portions and to form recessed parts at the inner peripheral edges of the electrical steel sheets. The protruding portions are pressed into the recesses of the joined electrical steel sheets to join the electrical steel sheets. In this case, the protruding portions and the recessed portions become swaged portions.The pressed sections are located at a variety of locations in the circumferential direction. Stress concentration occurs at the pressed sections, making press-fit joining unsuitable for use with a rotor core 10 rotating at high speed.

[0048] Furthermore, when using an anchor bolt to connect the electrical steel sheets, each electrical steel sheet is drilled to form a through hole. An anchor bolt is inserted into the through holes of the stacked electrical steel sheets along the entire axial direction and secured with nuts at the ends of the anchor bolt. If the plurality of electrical steel sheets are secured with an anchor bolt in this way, the through holes become new stress concentration sites, so this case is also unsuitable for application to a rotor core 10 rotating at high speed.

[0049] As long as the stator 2 is arranged around the rotor 1 to form a synchronous motor with internal permanent magnets 100, the electric motor is not limited in structure to the description of the Fig.1. In the above-described embodiment, the synchronous motor 100 with internal permanent magnets is used to drive the spindle in a machine tool. However, it can be similarly applied to other machines.

[0050] The embodiment described above can be freely combined with one or more of the modifications.

[0051] According to the invention, the second outer diameter surface of the opening portion of the slot is formed in a curved shape such that the distance from the outer peripheral surface of the rotor core in the diametrical direction gradually decreases toward the intermediate portion in the circumferential direction. Therefore, the cross-sectional area in the diametrical direction becomes smallest at the intermediate portion of the bridge portion where the cross-sectional shape gradually changes, and the maximum load acting on the bridge portion can be reduced.

Claims

[1] Rotor of a synchronous motor with internal permanent magnets, comprising: a rotor core (10) which rotates with respect to an axis (L0) and which has a cylindrically shaped outer peripheral surface (10b) over its entire circumference; a plurality of slots (20) formed in the rotor core at a plurality of locations in a circumferential direction and extending parallel to the axis; and a plurality of permanent magnets (30) accommodated in the plurality of slots and having rectangular shapes in cross section, the plurality of permanent magnets being accommodated such that mutually different poles are positioned in a diametrical direction in the slots adjacent to each other in the circumferential direction, wherein each of the plurality of slots includes: a holding portion (21) formed between a first outer diameter surface (211) extending in the circumferential direction and a first inner diameter surface (212) facing the first outer diameter surface and extending in the circumferential direction at an inner side from the first outer diameter surface in the diametrical direction, for holding each of the plurality of permanent magnets, and an opening portion (22) formed on both sides of the holding portion in the circumferential direction, wherein the opening portion is formed by a second outer diameter surface (221) extending from the first outer diameter surface in the circumferential direction, a second inner diameter surface (222) extending from the first inner diameter surface in the circumferential direction, and a curved connecting surface (223) connecting the second outer diameter surface and the second inner diameter surface, and wherein a portion on the outside of the opening portion (22) in the diametrical direction toward the outer circumferential surface (10b) of the rotor is defined by a bridge portion (24), and the second outer diameter surface is formed into a curved shape such that a distance to an outer peripheral surface (10b) of the rotor core in the diametrical direction from both ends of the second outer diameter surface in the circumferential direction to an intermediate portion in the circumferential direction gradually becomes smaller such that a first diametrical length (ΔL1) is greater than or equal to a second diametrical length (ΔL2) and a third diametrical length (ΔL3) is smaller than both the first diametrical length (ΔL1) and the second diametrical length (ΔL2), where: - the first diametrical length (ΔL1) is defined at a first end (241) of the bridge portion (24), wherein the first end (241) is defined by a point (P2) of the greatest curvature of the curved connecting surface (223) of the opening portion (22), and wherein the first diametrical length (ΔL1) extends in the diametrical direction (S2) from the first end (241) toward the outer peripheral surface (10b) of the rotor (10), - the second diametrical length (ΔL2) is defined at a second end (242) of the bridge portion (24), wherein the second end (242) is defined by a transition point (P1) from the first outer diameter surface (211) of the holding portion (21) to the second outer diameter surface (221) of the opening portion (22), and wherein the second diametrical length (ΔL2) extends in the diametrical direction (S1) from the second end (242) toward the outer circumferential surface (10b) of the rotor (10), and - the third diametrical length (ΔL3) is defined in an intermediate section (243) between the first end (241) and the second end (242), the third diametrical length (ΔL3) extending in the diametrical direction from the second outer diameter surface (221) of the opening section (22) towards the outer peripheral surface (10b) of the rotor (10), where: the curved connecting surface comprises a curved surface projecting outwardly toward an outer side of the opening portion in the circumferential direction, so that the cross section of the opening portion is substantially triangular, a maximum length (D2) of the opening portion in the diametrical direction is longer than a thickness (D3) of the permanent magnet in the diametrical direction, a length (D1) of the opening portion, which is the shortest distance from the point (P2) of greatest curvature of the curved connecting surface (223) of the opening portion (22) to an end face (303) of the permanent magnet in the circumferential direction, i) is greater than the maximum length (D2) of the opening portion in the diametrical direction, and ii) is longer than the thickness (D3) of the permanent magnet in the diametrical direction, and the rotor core has a slotless portion (23) between each pair of opening portions adjacent to each other in the circumferential direction, wherein: - a q-axis tooth width (W) of the section (23) without a slot between the points (P2) of the greatest curvature of the curved connecting surfaces (223) of the pair of opening sections (22) becomes minimal, and - the section (23) without a slot does not have a straight section of constant width in the circumferential direction. [2] The rotor of the internal permanent magnet synchronous motor according to claim 1, wherein the length (D1) of the opening portion, which is the shortest distance from the point (P2) of greatest curvature of the curved connecting surface (223) of the opening portion (22) to an end face (303) of the permanent magnet in the circumferential direction, is 1.5 times the thickness (D3) of the permanent magnet in the diametrical direction or more. [3] The rotor of the internal permanent magnet synchronous motor according to claim 1 or 2, wherein the first outer diameter surface and the first inner diameter surface are formed to be flat and parallel to each other. [4] The rotor of the internal permanent magnet synchronous motor according to at least one of claims 1 to 3, wherein the outer peripheral surface (10b) of the rotor (10) is in a circular arc shape without unevenness over its entire circumference. [5] Rotor of the synchronous motor with internal permanent magnets according to at least one of claims 1 to 4, wherein the rotor core has dividing sections (26) which divide the plurality of slots into first slots (201) and second slots (202) in the circumferential direction, and the permanent magnets are housed in the first slots and the second slots such that the same poles are positioned in the diametrical direction. [6] The rotor of the internal permanent magnet synchronous motor according to claim 5, wherein the first slots and the second slots are aligned along tangents in a circumferential direction of a circle centered with respect to the axis. [7] The rotor of the synchronous motor with internal permanent magnets according to at least one of claims 1 to 6, wherein the permanent magnets are rare earth magnets having a higher magnetic energy than ferrite magnets. [8] The rotor of the internal permanent magnet synchronous motor according to at least one of claims 1 to 7, wherein the second inner diameter surface has a protruding portion (22b) protruding outwardly toward an outer side in the diametrical direction to position the permanent magnet. [9] The rotor of the internal permanent magnet synchronous motor according to any one of claims 1 to 8, wherein the second inner diameter surface has at least one of a straight portion and a curved portion projecting outward toward an inner side in the diametrical direction in the circumferential direction. [10] The rotor of the internal permanent magnet synchronous motor according to any one of claims 1 to 9, wherein the rotor core comprises a plurality of electrical steel sheets stacked on each other, and the electrical steel sheets joined to each other in the axial direction are joined by a bonding agent. [11] Synchronous motor with internal permanent magnets, comprising a rotor (1) according to at least one of claims 1 to 10, and a stator (2) arranged around the rotor.

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