JP7177442B2 - Permanent magnet rotors and rotating electrical machines - Google Patents

Description

The present invention relates to permanent magnet rotors and rotating electrical machines, and more particularly to permanent magnet rotors with permanent magnets embedded in the rotor core, and rotating electrical machines having such permanent magnet rotors.

2. Description of the Related Art In a rotating electric machine using a permanent magnet rotor, such as an embedded permanent magnet (IPM) motor, efforts are being made to improve output torque with the aim of achieving higher efficiency and miniaturization. In this type of rotary electric machine, the output torque can be improved by using a magnet material having high magnetic properties, such as introducing a grain boundary modification technology to the permanent magnet. In addition to the material properties of the permanent magnets themselves, the shape and arrangement of the permanent magnets embedded in the permanent magnet rotor also have a great effect on the torque properties of the rotary electric machine.

A spoke-type arrangement has been proposed as one arrangement of permanent magnets for improving the output torque of a rotating electrical machine. The spoke-type arrangement is disclosed, for example, in Patent Document 1. In a cross section perpendicular to the rotation axis of the permanent magnet rotor, rectangular permanent magnets having two sides parallel to the radial direction of the rotor are arranged around the rotor. Multiple are arranged in the direction. By increasing the length of the permanent magnet along the radial direction of the rotor, it is possible to increase the surface area of the permanent magnet and increase the amount of magnetic flux. As a result, output torque can be improved.

JP 2015-223079 A

In rotating electrical machines with permanent magnet rotors, one of the performance limiting factors is the irreversible demagnetization of the permanent magnets. For example, when the magnetic field generated by the stator coil is applied to the permanent magnet in the direction opposite to the magnetization direction of the permanent magnet, it acts as a reverse magnetic field and causes irreversible demagnetization of the permanent magnet. One method of reducing irreversible demagnetization is to use high coercivity materials as permanent magnets, such as those containing a large amount of heavy rare earth elements.

Irreversible demagnetization due to the magnetic field of the coil tends to occur at the radially outer (peripheral) position in a permanent magnet rotor that employs a spoke-type magnet arrangement. Therefore, in Patent Document 1, of the four corners of the permanent magnet with a rectangular cross section, the corners on the stator side, that is, on the radially outer side of the rotor, have a higher coercive force than the inner side in order to increase the demagnetization resistance. Forms are disclosed that provide for Grain boundary diffusion treatment using heavy rare earth elements such as Dy and Tb is mentioned as a method for forming regions with high coercive force locally in one permanent magnet.

High coercivity permanent magnets containing a large amount of heavy rare earth elements are expensive, and if used extensively to suppress irreversible demagnetization, the material cost of the permanent magnet rotor increases. As described in Patent Document 1, by locally providing a region with a high concentration of heavy rare earth elements in a permanent magnet, the amount of heavy rare earth elements used can be reduced. In addition to the need to use rare earth elements, preparation of a permanent magnet having a special distribution of coercive force due to grain boundary diffusion also requires labor and cost. It is desirable to be able to suppress irreversible demagnetization by improving the shape and arrangement of permanent magnets without relying on high coercive force of magnetic materials, and to be able to suppress irreversible demagnetization and achieve high output at the same time. be

The problem to be solved by the present invention is to provide a permanent magnet rotor capable of obtaining high output torque while suppressing irreversible demagnetization of permanent magnets, and a rotary electric machine having such a permanent magnet rotor. to do.

In order to solve the above-described problems, a permanent magnet rotor according to the present invention is a permanent magnet rotor having a rotor core and a plurality of permanent magnets embedded in the rotor core and forming magnetic poles. In a cross section orthogonal to each other, each of the permanent magnets has an arcuate shape that protrudes radially inward of the rotor core, and the magnetization direction of the permanent magnet is at least partially along the arcuate shape. It is inclined with respect to the radial direction centered on the arc-shaped focal point.

Here, it is preferable that the magnetization direction of the permanent magnet is inclined at least at the end of the arc with respect to the radial direction centered on the focal point of the arc. Also, the magnetization direction of the permanent magnet is preferably parallel to the radial direction centered on the focal point of the arc shape at the central portion along the arc shape. It is preferable that the permanent magnet has a semicircular arc shape.

Assuming that an axis passing through the arc-shaped focus and extending along the radial direction of the rotor core is the central axis of the magnet, the magnetization direction of the permanent magnet is set along the magnet central axis to the diameter of the rotor core rather than the arc-shaped focus. It is preferable that the radial direction is centered on a point on the outer side of the direction.

Further, the permanent magnets forming each of the magnetic poles are divided into a plurality of divided regions along the arc shape, and the magnetization directions of the permanent magnets in each divided region are parallel in the divided regions. I hope it is.

In this case, the number of divisions of the division area is 2, and the magnet center axis is an axis passing through the focus of the arc shape and extending along the radial direction of the rotor core. preferably inclines in a direction away from the magnet center axis from the radially outer side toward the inner side, and are symmetrical to each other with respect to the magnet center axis. Furthermore, in this case, the inclination angle of the magnetization directions in the two divided regions is preferably 30° or more and 60° or less with respect to the magnet central axis.

Alternatively, the number of divisions of the divided area is 3, and the inclination angle of the magnetization direction of the permanent magnet with respect to the magnet central axis is defined as an axis passing through the arc-shaped focus and extending along the radial direction of the rotor core. is preferably smaller in the central divided area along the arc shape than in the divided areas at both ends along the arc shape. In this case, the magnetization direction in the central divided area along the arc shape is parallel to the central axis of the magnet, and the magnetization direction in the divided areas at both ends along the arc shape is the radial direction of the rotor core. It is preferable that they are inclined in a direction away from the magnet center axis from the outside toward the inside and are symmetrical to each other with respect to the magnet center axis. Moreover, the inclination angle of the magnetization direction in the divided areas at both ends is preferably 20° or more with respect to the magnet central axis.

The permanent magnet is preferably a metal magnet.

A rotary electric machine according to the present invention has the permanent magnet rotor described above.

In the permanent magnet rotor according to the above invention, the permanent magnets embedded in the rotor core have an arcuate shape that protrudes radially inward (inner peripheral side) of the rotor core in a cross section orthogonal to the rotation axis of the rotor core. there is By making the permanent magnets arc-shaped, the surface area of the permanent magnets can be increased and the magnet magnetic flux can be increased, so that a large output torque can be obtained. In addition, in the permanent magnet rotor, the reverse magnetic field from the stator coil provided outside, which causes irreversible demagnetization, is likely to be applied in the arc-shaped thickness direction of the permanent magnet, but the magnetization direction of the permanent magnet is inclined with respect to the radial direction centered on the arc-shaped focal point, that is, the arc-shaped thickness direction, the resistance to irreversible demagnetization can be enhanced. In this way, by using arc-shaped permanent magnets and making the magnetization direction of the permanent magnets inclined with respect to the radial direction centered on the arc-shaped focal point, output torque is reduced while suppressing irreversible demagnetization. can be improved.

By improving the demagnetization resistance by regulating the arrangement of the permanent magnets and the magnetization direction, it is no longer necessary to use an expensive permanent magnet with high coercive force containing a large amount of heavy rare earth elements for the purpose of improving the demagnetization resistance. Also, the thickness of the permanent magnet can be reduced, and the amount of required magnets can be reduced. Furthermore, by increasing the output torque, it becomes possible to reduce the size of the permanent magnet rotor.

Here, when the magnetization direction of the permanent magnet is inclined with respect to the radial direction centering on the focus of the arc at least at the arc-shaped end, the arc-shaped end is the arc-shaped end. Among the permanent magnets, it is positioned radially outward of the rotor core and is likely to be subjected to a particularly large reverse magnetic field, so irreversible demagnetization is likely to occur. Irreversible demagnetization can be effectively suppressed by being inclined with respect to the radial direction, that is, the thickness direction of the permanent magnet.

Further, when the magnetization direction of the permanent magnet is parallel to the radial direction centered on the arc-shaped focal point at the central portion along the arc shape, in the central portion along the arc shape of the permanent magnet Irreversible demagnetization is less likely to occur because the magnetic field applied by the coil provided outside is weaker. The amount of magnetic flux going out in the direction can be increased. Therefore, it becomes easier to increase the output torque while maintaining high resistance to irreversible demagnetization.

When the permanent magnet has a semicircular arc shape, it is possible to suppress irreversible demagnetization and improve the output torque by using a relatively simple permanent magnet.

The axis passing through the arc-shaped focal point and extending along the radial direction of the rotor core is defined as the magnet central axis, and the magnetization direction of the permanent magnet is centered along the magnet central axis at a point radially outside the rotor core from the arc-shaped focal point. , the magnetization direction of the permanent magnets, except for the central portion of the arc, deviates from the radial direction centered on the arc-shaped focal point. In particular, the inclination angle of the magnetization direction with respect to the radial direction centering on the focus of the arc increases at a position closer to the end of the arc, where irreversible demagnetization tends to occur. Therefore, the effect of suppressing irreversible demagnetization of the permanent magnet is excellent. On the other hand, in the vicinity of the central portion of the arc, where irreversible demagnetization is unlikely to occur, the magnetization direction is close to the radial direction from the focus of the arc, and the amount of magnetic flux emitted from the permanent magnets to the radially outer side of the rotor core is reduced. Since it becomes large, it exhibits a high effect in improving the output torque.

In addition, when the permanent magnets forming each of the magnetic poles are divided into a plurality of divided regions along the arc shape, and the magnetization directions of the permanent magnets in each divided region are parallel in the divided regions. In order to suppress irreversible demagnetization and improve output torque, the magnetization direction is inclined with respect to the radial direction centered on the arc-shaped focus while the permanent magnet is simply manufactured. It is possible to achieve both.

In this case, the number of divided regions is 2, and the magnet center axis is the axis passing through the arc-shaped focal point and extending along the radial direction of the rotor core. With a form that is slanted inward in a direction away from the magnet center axis and that is symmetrical with respect to the magnet center axis, the arc-shaped focal point can be set by a simple division configuration and setting of the magnetization direction. By forming a state in which the magnetization direction is inclined with respect to the center radial direction, it is possible to achieve both suppression of irreversible demagnetization and improvement of output torque.

Furthermore, in this case, the output torque can be particularly easily increased if the inclination angle of the magnetization directions in the two divided regions is 30° or more and 60° or less with respect to the central axis of the magnet. Irreversible demagnetization can also be kept small.

Alternatively, the number of divisions of the divided area is 3, and the axis extending along the radial direction of the rotor core passing through the focal point of the arc is defined as the central axis of the magnet. If the divided area in the center along the arc is smaller than the divided areas at both ends along the arc shape, the divided area on the end side of the arc where irreversible demagnetization is likely to occur is centered on the arc-shaped focus. While the magnetization direction is tilted with respect to the radial direction of can. As a result, both suppression of irreversible demagnetization and improvement of output torque can be effectively achieved.

In this case, the magnetization direction in the central segmented region along the arc shape is parallel to the magnet center axis, and the magnetization direction in the segmented regions at both ends along the arc shape is radially inward from the rotor core. According to the configuration in which they are inclined away from the magnet central axis and are symmetrical with respect to the magnet central axis, the effects of suppressing irreversible demagnetization and improving the output torque can be particularly enhanced.

Further, when the inclination angle of the magnetization direction in the divided regions at both ends is 20° or more with respect to the central axis of the magnet, the effect of suppressing irreversible demagnetization can be further enhanced.

When the permanent magnet is a metal magnet, it has higher magnetic properties than magnets containing materials other than metal magnet materials, such as bonded magnets. , can be effectively enhanced. Metal magnets are more difficult to form into arc shapes than bonded magnets, but can be easily achieved by die sintering of metal magnet material powder. A metal magnet with a high magnetic component ratio is easier to magnetize into an arc shape than a bond magnet.

Since the rotary electric machine according to the above invention has the above permanent magnet rotor, it is possible to obtain a large output torque while avoiding irreversible demagnetization.

1 is a cross-sectional view showing the configuration of a permanent magnet rotor and a rotary electric machine according to an embodiment of the invention; FIG. 1 is a cross-sectional view of a part of a permanent magnet rotor having undivided permanent magnets according to a first embodiment of the present invention; FIG. It corresponds to the enlarged view of FIG. FIG. 10 is a cross-sectional view of a part of a permanent magnet rotor having two-split permanent magnets according to a second embodiment of the present invention; FIG. 11 is a cross-sectional view of a part of a permanent magnet rotor having three-split permanent magnets according to a third embodiment of the present invention; It is a figure which shows distribution of the demagnetization factor in a magnet, (a) is a case of radial orientation, (b) is a non-divided type and orientation angle (alpha)=40 degrees. In each figure, the coercive force Hcj is changed in three ways. FIG. 4 is a diagram showing the distribution of the demagnetization factor in the magnet, in which (a) is the case of the 2-split type and the orientation angle α=45°, and (b) is the case of the 3-split type and the orientation angle α=45°. In each figure, the coercive force Hcj is changed in three ways. FIG. 5 is a diagram showing the relationship between magnet coercive force and EMF reduction rate for five orientation angles α in the case of a two-split type. FIG. 4 is a diagram showing changes in (a) required coercive force and (b) output torque when 300% rated current is applied, depending on the orientation angle α, for each form. (b) shows normalized values, with the value for the spoke arrangement set to 1.

A permanent magnet rotor and a rotary electric machine according to embodiments of the present invention will be described in detail below with reference to the drawings. Three embodiments having different numbers of permanent magnet divisions and different magnetization directions will be described below. First, the configuration common to each embodiment will be described.

[Configuration of Rotating Electric Machine]
A schematic of a rotating electric machine 1 according to one embodiment of the present invention is shown in FIG. The rotary electric machine 1 has a permanent magnet rotor 10 according to an embodiment of the invention. In this specification, the case where the rotary electric machine 1 is a motor will be mainly described, but a similar configuration can be applied to a case where it is a generator.

The rotating electrical machine 1 is configured as an embedded permanent magnet (IPM) motor. The motor 1 has a hollow cylindrical stator (stator) 30 and a rotor (permanent magnet rotor) 10 coaxially supported in a hollow portion of the stator 30 so as to be axially rotatable.

The stator 30 has a stator core 31 and coils 32 . The stator core 31 is formed by laminating a plurality of layers of electromagnetic steel sheets, and has an annular back yoke portion 31a and a plurality of teeth 31b protruding from the back yoke portion 31a toward the inside of the annular shape. prepared for. A coil 32 is wound around the outer periphery of each tooth 31b.

The rotor 10 has a rotor core 11 having a substantially cylindrical outer shape and a plurality of permanent magnets M embedded in the rotor core 11 . A hollow portion is formed in the center of the rotor core 11 and a shaft 40 is inserted therethrough. An air gap 50 is secured between the teeth 31 b of the stator core 31 and the outer peripheral surface of the rotor core 11 while the rotor 10 is coaxially accommodated in the hollow portion of the stator 30 . Details of the configuration of the rotor 10 are described below.

[Overview of Configuration of Permanent Magnet Rotor]
The rotor (permanent magnet rotor) 10 has the rotor core 11 and the permanent magnets M as described above. The configuration of the rotor 10 is shown in FIGS. FIG. 2 shows one magnetic pole of the rotor 10 together with part of the magnetic poles on both sides. Rotationally symmetrical and continuous arrangement constitutes the overall structure of the rotor 10 as shown in FIG. In the following description, terms indicating directions in the rotating body such as "circumferential direction", "periphery", "radial direction", "outside", and "inside" refer to the directions with respect to the rotor core 11 unless otherwise specified. In addition, the concept of angles such as vertical and parallel includes errors generally allowed for this type of rotor, for example, up to a range of about ±5°.

The rotor core 11 is configured by laminating a plurality of electromagnetic steel sheets, and has a substantially cylindrical outer peripheral surface. Slots 13 are formed in the rotor core 11 as gaps extending through or recessed in the axial direction. A permanent magnet M is embedded in each of the slots 13 . In a second embodiment and a third embodiment described later, the permanent magnet M embedded in one slot 13 is divided into a plurality of divided areas (m1 and m2, m1' to m3'). However, it is assumed that the divided areas buried adjacent to each other in the same slot 13 and forming one magnetic pole are regarded as one permanent magnet M. As shown in FIG.

The permanent magnet M forming each magnetic pole has an arcuate shape that protrudes radially inward (rotational center side; inner peripheral side) of the rotor core 11 . The permanent magnet M has an arcuate shape that protrudes radially inward of the rotor core 11 in a cross section orthogonal to the rotation axis of the rotor 10, that is, a protruding portion that protrudes radially inward from the radially outer side (peripheral side) of the rotor core 11. Although the specific shape is not particularly limited as long as it has a gentle curved shape having only one have. Only one layer of the permanent magnets M is arranged from the radially outer side to the inner side of the rotor core 11 .

The composition of the permanent magnet M is not particularly limited, but the permanent magnet M is preferably made of a metal magnet. That is, except for the vicinity of the surface, it does not contain intentionally added metal oxides or organic compounds, and consists only of the metal magnet material. As a metal magnet, a sintered magnet obtained by orienting and sintering a powder of a metal magnet material can be exemplified. As a sintered magnet, a magnetic field is applied to the entire mold to orient the raw material particles, and the mold is sintered in a sintering chamber with a controlled atmosphere. It is preferable to use those obtained by the pressless method (PLP method).

[Magnetization direction in permanent magnet]
In the rotor 10 according to the embodiment of the present invention, the magnetization direction d of the arc-shaped permanent magnets M constituting each magnetic pole is centered on the arc-shaped focal point f in at least a part of the arc. It is inclined with respect to the radial direction. That is, the magnetization direction d of the permanent magnet M is directed in a direction different from the radial direction centered on the arc-shaped focal point f in at least a part of the arc-shaped portion. Here, the arc-shaped focal point f is, as shown in FIG. If M has the shape of an arc, it hits the center of the arc. The radial direction centered on the arc-shaped focal point f corresponds to the arc-shaped thickness direction, that is, the direction orthogonal to the outer surface M1 at each position of the permanent magnet M. Henceforth, when simply calling it a "radial direction", it shall refer to the radial direction centering on the arc-shaped focal point f.

In the rotor 10 according to the embodiment of the present invention, if the magnetization direction d of the permanent magnet M is inclined with respect to the radial direction in at least a part of the arc shape, the permanent magnet M There are no particular restrictions on the shape, arrangement, or specific magnetization direction d. However, below, as a suitable example, the permanent magnets M constituting one magnetic pole are integrally continuous and magnetized in the radial direction around one focal point Fm, and one magnetic pole is A configuration will be described in which the permanent magnet M is divided into a plurality of divided regions along an arc shape, and the magnetization directions d of the permanent magnets M in the respective divided regions are parallel within the divided regions.

(1) First Embodiment: When Permanent Magnets Are Integral and Continuous First, as a first embodiment, as shown in FIG. will be described. In this embodiment, the magnetization directions d of the permanent magnets M are radial directions centered on one focal point (referred to as a magnetization focal point Fm) at each portion along the arc shape. Here, the magnetization focal point Fm exists at a position different from the arc-shaped focal point f as a figure defining the shape of the permanent magnet M. FIG. Therefore, the magnetization direction d of the permanent magnet M differs from the radial direction centering on the arc-shaped focal point f at least in part.

More specifically, the axis passing through the arc-shaped focal point f and extending along the radial direction of the rotor core 11 is defined as the magnet central axis C, and the magnetization focal point Fm is located along the magnet central axis C from the arc-shaped focal point f. also exists at a radially outer position of the rotor core 11 . Therefore, the magnetization in each part of the permanent magnet M, except for the arc-shaped central part located on the central axis C of the magnet, has an inclination with respect to the radial direction centering on the arc-shaped focal point f. . The direction of inclination is the direction away from the magnet center axis C from the radially outer side of the rotor core 11 toward the inner side. The magnetization direction d in each part of the permanent magnet M is symmetrical on both sides of the magnet center axis C. As shown in FIG.

In the permanent magnet M, the inclination of the magnetization direction d with respect to the radial direction changes continuously along the arc shape. That is, the farther away from the magnet center axis C and closer to the end of the arc, the greater the inclination with respect to the radial direction, and the greater the inclination at both ends of the arc. Here, the angle of the magnetization direction d at the end of the arc with respect to the radial direction (the direction perpendicular to the magnet center axis C when the permanent magnet M is semi-arc) is defined as the inclination angle α (0 <α<90°). The farther the magnetization focus Fm is from the arc-shaped focus f to the outside of the rotor core 11 along the magnet center axis C, the larger the inclination angle α becomes. The inclination with respect to the direction increases. At the center of the arc shape, the magnetization direction d always faces the direction of the magnet central axis C and is parallel to the radial direction, regardless of the inclination angle α at the ends. That is, they are aligned in the radial direction. Assuming α=0°, the magnetization focus Fm coincides with the arc-shaped focus f of the permanent magnet M, and the magnetization direction d of the permanent magnet M is radial over the entire area around the arc-shaped focus f. direction.

In the rotor 10 according to the present embodiment, since the permanent magnets M have an arc shape, the amount of magnetic flux emitted from the permanent magnets M toward the radially outer side of the rotor core 11 can be increased. The amount of magnetic flux of the permanent magnets M increases as the permanent magnets M have a larger surface area. This is because the surface area, that is, the area of the outer surface M1 can be made larger than in the case of having a linear shape. By increasing the amount of magnetic flux of the permanent magnets M, the output torque when the rotor 10 is incorporated in the motor 1 can be improved. In particular, when the motor 1 is small, making the permanent magnets M arc-shaped secures a large surface area in the limited space in the rotor core 11, making it easier to improve the output torque.

Furthermore, in the rotor 10, the magnetization direction d is inclined with respect to the radial direction, so irreversible demagnetization can be suppressed. In the rotor 10, of the magnetic field emitted from the coil 32 of the stator 30, the vector component antiparallel to the magnetization direction d of the permanent magnet M causes irreversible demagnetization in the permanent magnet M. If irreversible demagnetization occurs in the permanent magnets M, the rotor 10 cannot obtain output characteristics as designed. In the arc-shaped permanent magnet M, a reverse magnetic field is likely to be applied along the thickness direction. Therefore, irreversible demagnetization is most likely to occur when the magnetization direction d of the permanent magnet M is in the radial direction. It will be. In the rotor 10 according to the present embodiment, the magnetization direction d is inclined with respect to the radial direction in at least a part of the permanent magnet M. In comparison, irreversible demagnetization is less likely to occur.

In this manner, the permanent magnets M are formed in an arcuate shape that protrudes toward the radially inner side of the rotor core 11, and the magnetization direction d of the arcuate permanent magnets M is inclined with respect to the radial direction. It is possible to improve the output torque while suppressing the magnetism. Suppression of irreversible demagnetization can also be achieved by using a magnet material with a large coercive force, such as one containing a large amount of heavy rare earth elements, as the permanent magnet M, but the magnet material containing a large amount of heavy rare earth elements is expensive. often. As in the present embodiment, the coercive force of the permanent magnet M (necessary coercive force) can be reduced. Therefore, it is possible to avoid using heavy rare earth elements in the permanent magnet M, or to reduce the content thereof. Then, the cost required for the permanent magnets M can be suppressed. It is also possible to reduce the thickness of the permanent magnets M used.

In the permanent magnets M of the rotor 10 , irreversible demagnetization is likely to occur particularly at radially outer positions of the rotor core 11 . This is because a strong reverse magnetic field is likely to be applied due to the proximity to the coils 32 of the stator 30 . In the arc-shaped permanent magnet M, the arc-shaped end is located on the outermost side with respect to the radial direction of the rotor core 11 . That is, the arc-shaped end portion of the permanent magnet M is the position where irreversible demagnetization is most likely to occur. Therefore, if the magnetization direction d of the permanent magnet M is inclined with respect to the radial direction at least at the arc-shaped end, irreversible demagnetization can be effectively suppressed. In the present embodiment, the magnetization direction d of each part of the permanent magnet M is a radial direction centered on the magnetization focus Fm, and the inclination of the magnetization direction d with respect to the radial direction is particularly large at the end of the arc shape. , excellent in the effect of suppressing irreversible demagnetization.

On the other hand, the central portion of the arc shape of the permanent magnet M is positioned radially inward of the rotor core 11, and thus is distant from the coil 32 of the stator 30, and is less likely to be subjected to a strong reverse magnetic field. Therefore, in the arc-shaped central portion of the permanent magnet M, there is little need to incline the magnetization direction d with respect to the radial direction from the viewpoint of suppressing irreversible demagnetization. Conversely, from the viewpoint of increasing the output torque, it is preferable that the magnetization direction d is close to the radial direction at the central portion of the arc shape. preferably. The closer the magnetization direction d is to the outer surface M1 through which the magnetic flux emitted from the permanent magnets M passes, the larger the equivalent cross-sectional area of the permanent magnets M becomes. This is because the amount of magnetic flux emitted toward the outside increases. As described above, the outer shape of the permanent magnet M is arc-shaped and the surface area is increased to improve the output torque. Output torque can be improved more effectively.

As described above, in the present embodiment, the magnetization direction d of the permanent magnet M is a radial direction centered on the magnetization focus Fm away from the arc-shaped focus f. , the magnetization direction d has a large inclination from the radial direction, while the magnetization direction d is parallel to the radial direction in the central portion of the arc shape. Therefore, irreversible demagnetization, which tends to occur at the ends, can be effectively suppressed, and the effect of increasing the output torque by the magnetic flux at the central portion is also excellent.

As will be shown in later examples, the demagnetization proof stress is higher than when the permanent magnets are arranged in spokes over the entire range of the inclination angle α of 0°<α<90°. The greater the value, that is, the greater the inclination of the magnetization direction d from the radial direction, the greater the demagnetization resistance. On the other hand, the smaller the tilt angle α, the larger the output torque. The specific inclination angle α may be determined in consideration of the required demagnetization resistance and output torque. can be effectively suppressed.

The arc-shaped permanent magnet M can be easily formed if it is a bond magnet. However, bond magnets tend to have low magnetic properties, and as described above, the permanent magnets M are preferably made of metal magnets. Arc-shaped metal magnets can be manufactured by sintering such as the PLP method. In the first embodiment, the magnetization direction d in each arc-shaped portion is directed radially around the magnetization focus Fm. , the magnetization is parallel in each divided region, but by sintering the magnetic material powder in a state of being oriented in the radial or parallel direction by an external magnetic field, such magnetization An arc-shaped permanent magnet M can be formed with direction d.

(2) Second Embodiment: When the Permanent Magnet is Divided into Two In the first embodiment, the permanent magnets M constituting each magnetic pole are integrally continuous, and the magnetization direction d is It was a radial direction centered on the magnetization focus Fm. On the other hand, in a second embodiment and a third embodiment described below, the permanent magnet M constituting each magnetic pole is divided into a plurality of regions along the arc shape, and the magnetization in each region Direction d is parallel within the region. Hereinafter, the points different from the first embodiment will be mainly described, and the description of the common points will be omitted.

FIG. 3 shows the configuration of the rotor 10 according to the second embodiment. Here, the number of divisions of the permanent magnet M is two, and the arc-shaped permanent magnet M forming one magnetic pole is divided into two. In other words, the two independent magnet pieces forming the divided regions m1 and m2 are embedded in the common slot 13 adjacent to each other.

In each of the two divided areas m1 and m2, the magnetization direction d is parallel throughout the divided area. That is, the magnetization direction d is the same at each position along the arc shape of the divided regions m1 and m2. The magnetization direction d of each divided area m1, m2 is inclined with respect to the magnet central axis C. As shown in FIG. The direction of inclination is the direction away from the magnet central axis C from the radially outer side to the inner side of the rotor core 11 . Although the ratio of the sizes of the two divided regions m1 and m2 is not particularly limited, in the illustrated embodiment, the permanent magnet M is divided at the center of the arc shape to form the two divided regions m1 and m2. The central angles of the arc shapes are equal. Also, the magnetization directions d in the two divided regions m1 and m2 are symmetrical with respect to the central axis C of the magnet. Here, the angle of the magnetization direction d of each divisional region m1, m2 with respect to the radial direction at the end of the arc (the direction perpendicular to the magnet central axis C when the permanent magnet M is semicircular) is Define the tilt angle α (0<α<90°).

In this embodiment, in the permanent magnet M composed of two divided regions m1 and m2, the magnetization direction d is directed in the thickness direction of the permanent magnet M, that is, the edge of the permanent magnet M is centered on the arc-shaped focal point f. The magnetization direction d has an inclination with respect to the radial direction over the entire area except for the position at the inclination angle .alpha. Irreversible demagnetization of the permanent magnet M can be suppressed by the inclination of the magnetization direction d. The permanent magnet M magnetized in the parallel direction over the entire area of the magnet piece can be manufactured relatively easily, like the divided areas m1 and m2 of the present embodiment.

In this second embodiment as well, as will be shown in later examples, the demagnetization resistance is higher than in the case of the spoke arrangement in the entire range of the inclination angle α of 0°<α<90°. , the greater the inclination angle α of the magnetization direction d, the greater the effect of improving the demagnetization resistance. On the other hand, the output torque exhibits a mountain-shaped behavior with respect to the inclination angle α, with α=45° as the peak. That is, the output torque reaches a maximum at α=45° and decreases in regions where the inclination angle α is larger and smaller. In general, high output torque is obtained in the range of α=45°±15° (30°≦α≦60°). The behavior in which the output torque increases at α=45° can be explained as follows. That is, in each region of the permanent magnet M, the larger the amount of magnetic flux emitted from the outer surface M1, the greater the output torque. . The equivalent cross-sectional area in each region of the permanent magnet M is obtained by projecting the surface area of the outer surface M1 in that region onto the magnetization direction d. The equivalent cross-sectional area in the entire area of the permanent magnet M is obtained by integrating the values in each area, and the integrated value becomes maximum when α=45°.

(3) Third Embodiment: When the Permanent Magnet is Divided into Three FIG. 4 shows the configuration of the rotor 10 according to the third embodiment. Here, the number of divisions of the permanent magnet M is three, and the arc-shaped permanent magnet M forming one magnetic pole is divided into three. In other words, three independent magnet pieces forming the divided areas m1', m2', m3' are embedded in the common slot 13 adjacent to each other. Along the arc shape of the permanent magnet M, end division regions m1' and m2' are arranged at both ends, and a central division region m3' is arranged at the center position. Although the ratio of the sizes of the divided areas m1′, m2′, and m3′ is not particularly limited, in the illustrated embodiment, the arc-shaped centers of the divided areas m1′, m2′, and m3′ The corners of the two end segments m1', m2' together are equal to the central segment m3'. The central angles of the two end divisions m1' and m2' are equal to each other, and the divisions m1', m2' and m3' are arranged symmetrically with respect to the magnet center axis C as the permanent magnet M as a whole. . When the permanent magnet M has a semicircular arc shape, the central angle of the arc is 45° in the two end divisions m1′ and m2′ and 90° in the central division m3′.

In each of the three divided areas m1', m2', m3', the magnetization direction d is parallel throughout the divided area. Here, the magnetization direction d in the central divisional region m3' has a smaller inclination with respect to the magnet center axis C than the magnetization direction d in the two end divisional regions m1' and m2'. Preferably, the magnetization direction d of the central segment m3' is parallel to the magnet central axis C, as shown. On the other hand, the magnetization directions d of the two end divisions m1' and m2' are inclined with respect to the central axis C of the magnet. The direction of inclination is the direction away from the magnet central axis C from the radially outer side to the inner side of the rotor core 11 . The magnetization directions d in the two end division regions m1' and m2' are symmetrical with respect to each other with the central axis C of the magnet interposed therebetween. Here, the magnetization direction d of the end division regions m1′ and m2′ has the radial direction at the arc-shaped end (the direction perpendicular to the magnet center axis C when the permanent magnet M is semicircular). The angle is defined as the tilt angle α (0<α<90°).

In the two end segments m1' and m2', the magnetization direction d has an inclination with respect to the radial direction over the entire area except for the position where the magnetization direction d is directed in the thickness direction of the permanent magnet M. ing. Irreversible demagnetization of the permanent magnet M can be suppressed by the inclination of the magnetization direction d. On the other hand, in the central divided region m3′, the magnetization direction d is parallel to the magnet central axis C, and at least at the central position of the arc shape existing on the magnet central axis C, the magnetization direction d is radial. parallel. Even at a position off the magnet center axis C, the magnetization direction d is close to the radial direction. As described in the first mode, irreversible demagnetization is less likely to occur in the vicinity of the central portion of the arc shape of the permanent magnet M, whereas the radial component of magnetization has the effect of increasing the amount of magnetic flux. Therefore, also in the present embodiment, the magnetization direction d in the central divided region m3′ is aligned with or close to the radial direction, thereby increasing the amount of magnetic flux and effectively contributing to the improvement of the output torque. can.

In the third embodiment, the demagnetization proof stress increases as the inclination angle α of the magnetization direction d increases, as shown in the examples below. In particular, in the region where α is approximately 20° or more, the demagnetization resistance is higher than in the case of the spoke arrangement. On the other hand, the output torque exhibits peak-shaped behavior, which is maximum near α=20° and decreases in regions where the inclination angle α is smaller and larger. In general, high output torque is obtained in the range of 20°≦α≦40°.

In each embodiment described above, the shape of the permanent magnet M is a simple circular arc shape, and the thickness is constant at each portion. However, a distribution may be formed in the thickness of each portion. For example, in the two divided regions m1 and m2 of the second embodiment and the two end divided regions m1′ and m2′ of the third embodiment, irreversible Since demagnetization is likely to occur, it is conceivable to make the thickness of such a portion larger than that of other portions to enhance the demagnetization suppressing effect. A boomerang shape in which the radius of curvature of the inner arc (outer surface M1) of the arc shape is larger than the radius of curvature of the outer arc can be given as an example of such an arc shape with a thicker middle portion.

The present invention will be described in detail below using examples. Here, simulation was used to evaluate demagnetization resistance and torque characteristics for each of the three embodiments described above.

[analysis method]
The following three types of rotor models were created.
- Undivided type: The rotor of the first embodiment shown in FIGS. The permanent magnet is not divided, and the magnetization direction is radial around the magnetization focus Fm over the entire area.
2-split type: The rotor of the second embodiment shown in FIG. 3 is used. The permanent magnet is divided into two, and the magnetization directions are parallel within each divided area.
- Three-split type: The rotor of the third embodiment shown in FIG. The permanent magnet is divided into three, and the magnetization directions are parallel within each divided area.

In any model, the simulation was performed while changing the inclination angle α of the magnetization direction. As described above, in each embodiment, the inclination angle α is in the range of 0°<α<90°, but the simulation was also performed in the region of α≦0°. In the non-divided rotor, in the region of α<0°, the magnetization focus Fm exists inside the arc-shaped focus f, and the magnetization direction is the magnet center axis from the radial outside to the inside of the rotor core. tilts toward In the two-segmented and three-segmented rotors, the magnetization directions in the segmented regions m1, m2, m1′, and m2′ are aligned with the magnet center axis from the radially outer side to the inner side of the rotor core in the region where α<0°. Tilt in the direction of approach.

Models of radially oriented and spoked rotors were also constructed for comparison with the above three models. The radial orientation type corresponds to a form in which α=0° in the undivided rotor. In the spoke-type model, permanent magnets with rectangular cross sections were arranged radially along the radial direction of the rotor. A non-uniform distribution of coercive force as in Patent Document 1 is not provided. In order to compare the demagnetization resistance and torque characteristics of the above three models, the radial orientation model and the spoke model, the surface areas of the permanent magnets were made uniform.

The magnet demagnetization rate and torque characteristics were analyzed while changing the coercive force of the permanent magnets for the rotors of the above models. The simulation was performed by electromagnetic field analysis using the finite element method (FEM). In the analysis of the magnet demagnetization rate, the reduction rate of the induced voltage when 450% rated current (4.5 times the rated current) was applied to the stator coil was evaluated as the demagnetization rate. Furthermore, the coercive force of the permanent magnet required to reduce the EMF reduction rate to 2.0% or less, which will be described later, is defined as the required coercive force. In the analysis of output torque, the magnitude of torque output when 300% rated current (three times the rated current) was applied was evaluated.

The parameters used for the simulation are summarized in Table 1 below.

[Analysis result]
(1) Spatial distribution of demagnetization rate Figs. 5(a), (b) and Figs. 45°) and three-part type (α=45°). The coercive force of the permanent magnet is 850 kA/m, 750 kA/m, and 650 kA/m.

First, looking at the spatial distribution in the radial orientation of FIG. 5(a), the demagnetization rate is large at the arc-shaped end (area a) of the permanent magnet located in the upper part of the figure. This is because the end of the arc shape is located on the outermost side of the rotor core and close to the stator, so that the reverse magnetic field due to the magnetic field from the coil acts greatly. Even in the case of the highest coercive force of 850 kA/m, a demagnetization rate close to 100% was observed at the end. Can not. Furthermore, the lower the coercive force of the permanent magnet, the greater the demagnetization rate. At the smallest coercive force of 650 kA/m, almost the entire permanent magnet is demagnetized.

Next, looking at the result of the case where the magnetization direction is shifted from the radial direction in the undivided type shown in FIG. Almost no magnetism occurs. In other words, the demagnetization resistance is higher than in the case of radial orientation, and it can be seen that demagnetization can be sufficiently suppressed even when using permanent magnets with lower coercive force than in the case of radial orientation. In the case of the lowest coercive force of 650 kA/m, the demagnetization factor increases at the arc-shaped end (area a) located in the upper part of the figure, but its magnitude is the same as the radial It is significantly smaller than in the case of orientation. Further, in the case of a coercive force of 650 kA/m, demagnetization occurs in the vicinity of the arc-shaped central portion (region b). In the vicinity of the central portion (region b) of the arc shape, the magnetization direction is the radial direction of the rotor core or a direction close to it, and coincides with or is close to the radial direction. Therefore, it is interpreted that demagnetization cannot be completely prevented.

Furthermore, looking at the results of the two-part type in FIG. 6(a), when the coercive force is 850 kA/m and 750 kA/m, , almost no demagnetization occurs. In other words, as in the case of the undivided type, it can be seen that the demagnetization resistance is higher than in the case of radial orientation. At the lowest coercive force of 650 kA/m, demagnetization of the permanent magnet occurs. However, the demagnetization rate of the end (area a) of the permanent magnet as a whole located in the upper part of the figure is smaller than in the case of radial orientation in FIG. 5(a).

In the case of a coercive force of 650 kA/m, demagnetization occurs not only at the arc-shaped end portion (region a) of the permanent magnet as a whole, but also at the middle portion (region c) of each divided region. The region (region c) where demagnetization occurs in the middle of each divided region is the region that is 45° inside the focus (f) of the circular arc from both ends of the circular arc as the entire permanent magnet. centrally distributed. That is, demagnetization occurs in the angular region corresponding to the magnetization direction α. In this region (region c), the direction of magnetization coincides with or is close to the thickness direction of the permanent magnet, that is, the radial direction, and it is interpreted that the opposite magnetic field from the stator coils is large. Even when the inclination angle α is set to other than 45°, the center is the area (area c) that is located inside the arc-shaped focal point (f) from both ends of the permanent magnet by an angle equal to the inclination angle α. In addition, it was confirmed that demagnetization tends to occur easily.

Finally, looking at the 3-part results in FIG. 6(b), for coercive forces of 850 kA/m and 750 kA/m, the entire area of the permanent magnet is , almost no demagnetization occurs. In other words, it can be seen that the demagnetization resistance is higher than in the case of the radial orientation, as in the case of the non-split type and the two-split type. At the lowest coercive force of 650 kA/m, demagnetization of the permanent magnet occurs. However, the demagnetization factor of the arc-shaped end portion located in the upper part of the figure is smaller than in the case of radial orientation in FIG. 5(a).

In the case of a coercive force of 650 kA/m, in addition to the arc-shaped end (region a) of the permanent magnet as a whole, from both ends of the arc-shaped to the arc-shaped focus (f), 45 ° inward Demagnetization also occurs in a region (region c) centered on the entry position. This region (region c) corresponds to a region that is located inside the arc-shaped focus (f) from both ends of the arc-shaped permanent magnet as a whole by an angle equal to the inclination angle α. In the configuration with the inclination angle α=45°, the region (region c) coincides with the boundary between the end segment and the central segment. In the case of a coercive force of 650 kA/m, the demagnetization rate also increases in the central portion (region d) of the central divisional region. In the region (region c) inside the arc-shaped end of the permanent magnet as a whole by an angle equal to the inclination angle α, and in the central portion (region d) of the central divided region, the magnetization direction is permanent. It is interpreted that the thickness direction of the magnet, that is, the radial direction, coincides with or is close to the magnet, and the reverse magnetic field from the stator coil increases, so the demagnetization rate increases. Also for cases other than α = 45°, a region (region c) that is located inside the arc-shaped focus (f) from the arc-shaped end of the permanent magnet as a whole by an angle equal to the inclination angle α, and in the central portion (region d) of the central divided region, the demagnetization rate tended to increase. However, when α > 45°, the central angle (45°) of the end segment exceeds the inclination angle α, so that the angle equal to the inclination angle α Since the position where the line enters is not in the end divisional region but in the central divisional region, and the magnetization direction does not match the thickness direction, no behavior that makes demagnetization likely to occur at that position is observed. That is, a region with a high demagnetization rate corresponding to region c is not formed.

FIG. 7 shows the EMF reduction rate obtained for each magnet coercive force with respect to five inclination angles α in the case of the two-split type. The EMF reduction rate represents the reduction rate of the fundamental wave amplitude of the induced voltage (EMF) before and after the demagnetization test. According to FIG. 7, at all tilt angles α, the higher the coercive force of the permanent magnet, the smaller the EMF reduction rate. That is, demagnetization is less likely to occur. In general, the larger the inclination angle α, the smaller the EMF reduction rate, and the better the demagnetization resistance. Although not shown, these tendencies are also obtained for the non-divided type and the three-divided type.

As indicated by the dashed line in FIG. 7, the magnet coercive force at which the EMF reduction rate becomes smaller than the target value of 2.0% (at the bottom of the graph) is the required coercive force Hc required to suppress demagnetization. , obtained for each inclination angle α are shown in FIG. 8(a). The required coercive force was similarly determined for the undivided type and the three-divided type, and is shown in the figure. FIG. 8(a) also shows the required coercive force level (860 kA/m) obtained in the same manner for the case of adopting the spoke-type magnet arrangement. The lower the required coercive force, the higher the demagnetization resistance. Even if a permanent magnet with a small coercive force is used, the influence of demagnetization can be sufficiently suppressed.

According to FIG. 8A, the required coercive force decreases as the inclination angle α increases in all of the non-divided type, the two-divided type, and the three-divided type. That is, the demagnetization resistance is increased. The required coercive force is smaller than that of the spoke type in the entire range of α>0° for the non-split type and the two-split type, and in the range of α≧20° for the three-split type. The magnetic resistance is higher than that of the spoke type. In the non-divided type, which corresponds to the radial orientation type, with α=0°, the required coercive force is almost the same as that of the spoke type.

Furthermore, FIG. 8(b) shows the output torque _T300 when 300% rated current is applied for each form. In the figure, normalized values are shown, assuming that the output torque estimated in the case of adopting the spoke-type magnet arrangement is 1.

According to FIG. 8(b), in any of the non-split type, the 2-split type, and the 3-split type, an output torque exceeding that of the spoke type is obtained over almost the entire range of the inclination angle α. However, the behavior of the output torque with respect to the inclination angle α differs in the three modes.

In the case of the undivided type, the output torque is the largest at α=0°, which is 32.6% higher than that of the spoke type. As α becomes larger away from 0°, the output torque becomes smaller. In general, in the region of 20°≦α≦40°, the output torque does not significantly decrease from the maximum value when α=0°. On the other hand, as shown in FIG. 8(a), in the region of 20°≦α≦40°, the required coercive force is much lower than in the case of α=0°. Therefore, in the case of the undivided type, it can be said that it is easy to achieve both suppression of irreversible demagnetization and improvement of output torque by setting 20°≦α≦40°.

In the case of the two-split type, the maximum output torque is obtained at α=45° in FIG. 8(b). The value is 25.4% higher than the spoke type. The output torque decreases almost symmetrically in the regions where the inclination angle α is greater than 45° and where it is smaller than 45°. Generally, in the region of α=45°±15°, the change in the output torque with respect to the inclination angle α is small, and a large output torque is stably obtained. Further, as can be seen from FIG. 8(a), the required coercive force is sufficiently reduced in the region of α=45°±15°. In this region, the amount of change in required coercive force within the region is also small. From these results, it can be said that, in the case of the two-split type, it is easy to achieve both suppression of irreversible demagnetization and improvement of output torque by setting 30°≦α≦65°.

In the case of the three-split type, in FIG. 8(b), the output torque is maximized at α=20°. The value is 27.8% higher than the spoke type. The output torque decreases substantially symmetrically in the region where the inclination angle α is larger than 20° and the region where the inclination angle α is smaller than 20°. In general, in the region of α=20°±20°, the change in the output torque with respect to the inclination angle α is small, and a large output torque is stably obtained. On the other hand, FIG. 8A shows that the required coercive force is smaller than that of the spoke type in the region of α≧20°. From these results, it can be said that, in the case of the three-split type, it is particularly easy to achieve both suppression of irreversible demagnetization and improvement of output torque by setting 20°≦α≦40°.

It can be said that the undivided type is superior in the sense that the largest output torque can be obtained when the three types are compared. The next best in terms of output torque is the three-split type. However, as shown in FIG. 8B, in any form, the larger the inclination angle α, the higher the demagnetization resistance. It is advantageous from the viewpoint of achieving both an improvement in output torque and an improvement in demagnetization resistance. From this point of view, it can be said that in the two-split type, the configuration in which 30°≦α≦65°, particularly α=45°, is excellent.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the gist of the present invention. For example, it is possible to divide the permanent magnet into four or more divided areas along the arc shape. Alternatively, the magnetization direction may be set by increasing the angle of inclination with respect to the central axis of the magnet.

1 motor (rotary electrical machine)
10 rotor (permanent magnet rotor)
11 rotor core 13 slot 30 stator (stator)
50 Air gap C Magnet center axis f Arc-shaped focus Fm Magnetization focus M Permanent magnet M1 Outer surface of permanent magnet m1, m2 Divided areas m1′, m2′ in the case of two divisions End division area m3′ in the case of three divisions Central division in case of 3 divisions

Claims (13)

A permanent magnet rotor having a rotor core and a plurality of permanent magnets embedded in the rotor core and forming magnetic poles,
In a cross section orthogonal to the rotation axis of the rotor core, each of the permanent magnets has an arcuate shape that protrudes radially inward of the rotor core, and
the permanent magnets constituting each of the magnetic poles are divided into a plurality of divided regions along the arc shape;
The magnetization direction of the permanent magnet is inclined in at least a part along the arc with respect to a radial direction centered on the focus of the arc , and
the magnetization directions of the permanent magnets in each of the divided areas are parallel within the divided area ;
In the divided areas located at both ends along the arc shape, the permanent magnet has a constant thickness along the radial direction centering on the focus of the arc shape, or the magnetization direction is in the thickness direction. A permanent magnet rotor that is thicker at the facing locations than elsewhere . 2. The permanent magnet rotor according to claim 1, wherein the magnetization directions of the permanent magnets are inclined, at least at the ends of the arc, with respect to radial directions about the focal point of the arc. 3. The permanent magnet rotor according to claim 1, wherein the magnetization direction of said permanent magnets is parallel to a radial direction centering on said arc-shaped focal point at a central portion along said arc-shaped portion. 4. The permanent magnet rotor according to any one of claims 1 to 3, wherein the permanent magnets as a whole of the magnetic poles have a semi-arc shape. 5. The permanent magnet rotor according to any one of claims 1 to 4, wherein in each of said divided areas, said permanent magnet has an arc shape. In the divided areas located at both ends along the arc shape, the permanent magnet has a shape in which the radius of curvature of the inner arc of the arc shape is larger than the radius of curvature of the outer arc, so that the magnetization direction is 4. The permanent magnet rotor according to any one of claims 1 to 3, wherein the thickness of the position facing the thickness direction is larger than that of other portions. The division number of the division area is 2,
With the axis passing through the arc-shaped focus and extending along the radial direction of the rotor core as the central axis of the magnet,
The magnetization directions in the two divided regions are inclined in a direction away from the magnet central axis from the radial outer side to the inner side of the rotor core, and are symmetrical with respect to the magnet central axis . A permanent magnet rotor according to any one of claims 1 to 6. 8. The permanent magnet rotor according to claim 7, wherein the inclination angles of the magnetization directions in the two divided regions are 30[deg.] or more and 60[deg.] or less with respect to the magnet central axis. The division number of the division area is 3,
With the axis passing through the arc-shaped focus and extending along the radial direction of the rotor core as the central axis of the magnet,
2. An inclination angle of the magnetization direction of the permanent magnet with respect to the central axis of the magnet is smaller in the central divided area along the arc shape than in both divided areas along the arc shape . 7. A permanent magnet rotor according to any one of claims 6 to 7 . The magnetization direction in the central divided area along the arc shape is parallel to the magnet center axis,
The magnetization directions in the divided areas at both ends along the arc shape are inclined from the radially outer side to the inner side of the rotor core in the direction away from the magnet central axis, and are symmetrical with respect to the magnet central axis. 10. The permanent magnet rotor of claim 9, wherein: 11. The permanent magnet rotor according to claim 9, wherein an inclination angle of the magnetization direction in said divided areas at both ends is 20[deg.] or more with respect to said magnet central axis. The permanent magnet rotor according to any one of claims 1 to 11, wherein the permanent magnets are metal magnets. A rotating electrical machine comprising a permanent magnet rotor according to any one of claims 1 to 12.

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