JP2011229329A - Permanent magnet motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the use of a heavy rare earth element by optimizing the use of the heavy rare earth element, and thereby to suppress the cost.SOLUTION: A permanent magnet motor comprises: a rotor having a permanent magnet embedded in a rotor core 100; and a stator arranged to face the rotor via a predetermined gap. The permanent magnet is a plurality of sintered magnet segments 10a and 10b obtained by dividing a sintered magnet 10, which is made by segregating a heavy rare earth element at a crystal grain boundary near a surface of the magnet 10, along a face perpendicular to a magnetization direction. The plurality of sintered magnet segments 10a and 10b is embedded in the rotor core 100 in such a manner that a surface having a relatively high concentration of the heavy rare earth element is arranged on an outer peripheral surface side of the rotor.

Description

  The present invention relates to a permanent magnet type motor, and more particularly to improvement of the holding force of a permanent magnet embedded in a rotor or mounted on a rotor surface.

  In an electric vehicle or a hybrid vehicle, how to reduce the cost of a battery or a drive motor is a very big problem. One approach to lowering motor manufacturing costs is to improve the permanent magnets embedded within the rotor or mounted on the rotor surface. For example, when a permanent magnet is embedded in the rotor, the external magnetic field entering from the stator side is relatively higher than the inside of the magnet on the stator side surface of the permanent magnet. Therefore, a relatively high holding force is required. On the other hand, since the external magnetic field is relatively weak inside the magnet, the holding force as close to the side surface is not required, but the magnetic flux density contributing to the torque performance of the motor needs to be relatively high. The coercive force and the magnetic flux density tend to conflict with each other, and a material that can satisfy both physical quantities at the same time is relatively expensive.

  In Patent Document 1, an external magnet formed from a material having a relatively low magnetic flux density and a relatively high holding force, and a material formed from a material having a relatively large magnetic flux density and a relatively low holding force. A technique for forming a composite magnet from an internal magnet and embedding the composite magnet in a rotor is disclosed. It is disclosed that a material obtained by adding dysprosium (Dy) and heavy rare earth element to neodymium (Nd) is used for the outer magnet, and Nd is used for the inner magnet.

  Further, in Patent Document 2, each of the permanent magnet segments embedded in the rotor or attached to the surface of the rotor is composed of an assembly of permanent magnets, and each of the divided permanent magnets. There is disclosed a rotor for a permanent magnet type rotating machine in which the holding force in the vicinity of the surface of the permanent magnet is larger than the holding force inside the divided permanent magnets. Further, the divided permanent magnet is an Nd-based rare earth sintered magnet, and the holding force gradient from the surface to the inside of the Nd-based rare earth sintered magnet diffuses Dy or Tb from the magnet surface to the inside. It is disclosed that it is manufactured.

JP 2006-261433 A JP 2009-254092 A

  By the way, the Nd-based sintered magnet has excellent heat resistance and holding power over a certain level and has excellent magnetic characteristics, but it is only near the outer periphery of the rotor that is easily demagnetized by the demagnetizing field from the stator. In the vicinity of the inner peripheral portion of the rotor, it is not necessary to increase the holding force so much. However, if a permanent magnet segment is composed of an assembly of permanent magnets manufactured by diffusing Dy or Tb from the magnet surface toward the inside, Since the heavy rare earth is segregated also in the vicinity of the peripheral portion, the use of the heavy rare earth is not optimized, resulting in an increase in cost.

  An object of the present invention is to provide a permanent magnet motor that can minimize the use of heavy rare earths by optimizing the use of heavy rare earths, thereby reducing costs.

  A permanent magnet motor according to the present invention includes a rotor in which a permanent magnet is embedded in a rotor core or mounted on a rotor core surface, and a stator that is disposed with respect to the rotor via a predetermined gap. , A plurality of sintered magnet segments obtained by dividing a sintered magnet in which heavy rare earth elements are segregated at crystal grain boundaries near the surface on a plane perpendicular to the magnetization direction, and the plurality of sintered magnet segments are respectively The rotor core is configured such that a surface having a relatively high concentration of the heavy rare earth element is positioned on the outer peripheral surface side of the rotor and a surface having a relatively low concentration of the heavy rare earth element is positioned on the inner peripheral surface side of the rotor. Embedded in or mounted on the surface of the rotor core.

  In one embodiment of the present invention, the permanent magnet includes a plurality of sintered magnets obtained by dividing a sintered magnet obtained by segregating a heavy rare earth element into a grain boundary near the surface into two equal parts on a plane perpendicular to the magnetization direction. It is a magnet segment.

  In another embodiment of the present invention, the permanent magnet includes a plurality of sintered magnets obtained by segregating a heavy rare earth element into a crystal grain boundary near the surface and dividing it into four equal parts in a plane perpendicular to the magnetization direction. It is a sintered magnet segment.

  According to the present invention, the use of heavy rare earths can be minimized by optimizing the use of heavy rare earths, thereby reducing costs.

It is explanatory drawing of the permanent magnet embedding process in embodiment. It is explanatory drawing of the permanent magnet embedding process in other embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1. First, the basic configuration of the motor in this embodiment will be described. The motor of this embodiment is an IPM (Internal Permanent Magnet) motor, and includes a rotor (rotor) and a stator (stator), and the rotor has a plurality of permanent magnets on a rotor core in which electromagnetic steel plates are laminated. Embedded and configured. The number of poles of the rotor is arbitrary. The stator has a structure in which electromagnetic steel plates are laminated, and a coil is wound around each tooth. The permanent magnet embedded in the rotor is an Nd-based rare earth sintered magnet, which is manufactured by roughly pulverizing, finely pulverizing, molding, and sintering a base metal, and a Dy or Tb oxide powder or Dy or Tb oxide powder on the magnet surface. An alloy powder containing fluoride powder and Dy and Tb is applied, and then the magnet is heat-treated at a temperature lower than the sintering temperature to diffuse Dy and Tb only in the grain boundary part. The sintered magnet on which heavy rare earth such as Dy is segregated (diffusion soaked) is inserted into a hole formed in the rotor to form the rotor of the IPM motor.

  With a sintered magnet in which heavy rare earth such as Dy is segregated (diffusion soaked), as disclosed in Japanese Patent Application Laid-Open No. 2009-254092, the holding power is efficiently increased with little reduction in residual magnetic flux density. As a result, a distribution occurs in the holding force of the sintered magnet. That is, the holding force in the vicinity of the magnet surface is relatively higher than the holding force inside the magnet in a plane parallel to the magnetization direction.

  In this embodiment, the rotor of the IPM motor is formed by using such a holding force distribution in a sintered magnet in which heavy rare earth such as Dy is segregated (diffusion dipped).

2. Method for Manufacturing Rotor FIG. 1 schematically shows a method for manufacturing a rotor for an IPM motor in this embodiment. FIG. 1A is a cross-sectional view of a rectangular parallelepiped Nd-based heavy rare earth sintered magnet 10 cut along a plane parallel to the magnetization direction. In sintered magnets in which heavy rare earth such as Dy is segregated (diffusion soaked), for example, NdFeB magnets, the concentration of heavy rare earth elements in the vicinity of the magnet surface in a plane parallel to the magnetization direction is more relative to the concentration of heavy rare earth elements in the magnet. Become expensive. Here, the cross section is divided into four areas a, b, c, and d for each heavy rare earth concentration. Of course, such division is merely for convenience, and the actual concentration changes continuously. The concentration of heavy rare earth is area a> area b> area c> area d.

  When such a sintered magnet 10 is simply inserted into a hole formed in the rotor and embedded, a region with a high concentration of heavy rare earth exists also on the inner peripheral side of the rotor. Since the demagnetizing field is relatively weak on the inner circumference side of the rotor, a large holding force is not required.In this way, it is useless to increase the concentration of heavy rare earth on the inner circumference side of the rotor. This increases the cost.

  Therefore, as shown in FIG. 1B, the rectangular parallelepiped sintered magnet 10 is divided into two equal parts by a plane perpendicular to the magnetization direction and divided into a sintered magnet segment 10a and a sintered magnet segment 10b. In the figure, assuming that the magnetization direction is the vertical direction of the paper surface, the sintered magnet 10 is divided into two equal parts on a surface perpendicular to the paper surface. Specifically, the sintered magnet 10 is cut along a plane perpendicular to the magnetization direction and cut using a grindstone, a cutting blade, a wire saw, or the like. Each of the sintered magnet segments 10a and 10b obtained by dividing into two halves includes areas a, b, c and d having different heavy rare earth concentrations. For example, the sintered magnet segment 10a has an area a on the front surface, and an area b, an area c, and an area d in a multilayered manner as it goes to the back surface. On the other hand, the sintered magnet segment 10b has an area d on the front surface, and the areas c, area b, and area a exist in multiple layers as it goes to the back surface. The size of each sintered magnet segment 10a, 10b is, for example, 20 mm long and 5 mm wide. Then, the sintered magnet segments 10a and 10b obtained by dividing into two in this way are inserted into holes formed in the rotor core.

  FIG. 1 (c) shows a configuration per pole of the rotor. As shown in FIG. 1C, the sintered magnet segments 10a and 10b are inserted into the two holes 102 formed in the rotor core 100, respectively. At this time, the insertion is performed so that the area a is positioned on the outer peripheral side of the rotor core 100 and the area d is positioned on the inner peripheral side of the rotor core 100. That is, when the sintered magnet segment 10 a is inserted into the hole 102, the area a side surface of the sintered magnet segment 10 a is positioned on the outer peripheral side of the rotor core 100, and the area d side surface is positioned on the inner peripheral side of the rotor core 100. Thus, the direction of the sintered magnet segment 10 a is adjusted and inserted into the hole 102. The same applies to the sintered magnet segment 10b, and the sintered magnet segment 10b has a surface on the area a side positioned on the outer peripheral side of the rotor core 100 and a surface on the area d side positioned on the inner peripheral side of the rotor core 100. The direction of the segment 10 b is adjusted and inserted into the hole 102.

  By inserting the sintered magnet segments 10a and 10b into the holes 102 of the rotor core 100 in this way, the area a having a relatively high heavy rare earth concentration is positioned near the rotor outer periphery, and the heavy rare earth concentration is relatively high. The low area d is located in the vicinity of the inner periphery of the rotor. Accordingly, the concentration of heavy rare earth is relatively increased near the rotor outer periphery where the demagnetizing field is strong to increase the holding force, while the concentration of heavy rare earth is relatively decreased near the inner periphery of the rotor where the demagnetizing field is weak. Can be wasted.

3. Other Method for Manufacturing Rotor FIG. 2 schematically shows a method for manufacturing a rotor for an IPM motor according to another embodiment. 2A is a cross-sectional view of the rectangular parallelepiped sintered magnet 10 cut along a plane parallel to the magnetization direction, and is the same as FIG. In a sintered magnet in which heavy rare earth is segregated (diffusion soaked), the concentration of heavy rare earth elements in the vicinity of the magnet surface is relatively higher than the concentration of heavy rare earth elements inside the magnet in a plane parallel to the magnetization direction. In the cross section, each heavy rare earth concentration is divided into four areas a, b, c, and d. The concentration of heavy rare earth is area a> area b> area c> area d.

  Next, as shown in FIG. 2B, the rectangular parallelepiped sintered magnet 10 is divided into four equal parts by a plane perpendicular to the magnetization direction, and the sintered magnet segment 10a, the sintered magnet segment 10b, and the sintered magnet segment are divided. 10c and sintered magnet segment 10d. The sintered magnet segments 10a and 10d are both provided with areas a, b and c in a multilayered manner, and the sintered magnet segments 10b and 10c are both provided with areas a, b, c and d in a multilayered manner.

  FIG. 2C shows a configuration per rotor pole. As shown in FIG. 2C, the sintered magnet segments 10a, 10b, 10c, and 10d are inserted into a total of four holes 102 formed in two layers in the rotor core 100, respectively. The sintered magnet segments 10a and 10d are inserted into the holes 102 on the outer peripheral side of the rotor, and the sintered magnet segments 10b and 10c are inserted into the holes 102 on the inner peripheral side of the rotor. At this time, the insertion is performed so that the area a is positioned on the outer peripheral side of the rotor core 100 and the area c or the area d is positioned on the inner peripheral side of the rotor core 100. That is, when the sintered magnet segment 10a is inserted into the hole 102 on the outer peripheral side, the surface on the area a side in the sintered magnet segment 10a is on the outer peripheral side of the rotor core 100, and the surface on the area c side is the inner periphery of the rotor core 100. The direction of the sintered magnet segment 10 a is adjusted so as to be positioned on the side, and is inserted into the hole 102. The same applies to the sintered magnet segment 10d, and the sintered magnet segment 10d is positioned so that the area a side surface is positioned on the outer peripheral side of the rotor core 100 and the area c side surface is positioned on the inner peripheral side of the rotor core 100. The direction of the segment 10 b is adjusted and inserted into the hole 102. Further, when the sintered magnet segment 10b is inserted into the hole 102 on the inner peripheral side, the surface on the area a side in the sintered magnet segment 10b is on the outer peripheral side of the rotor core 100, and the surface on the area d side is on the inner side of the rotor core 100. The direction of the sintered magnet segment 10b is adjusted so as to be positioned on the peripheral side, and is inserted into the hole 102. The same applies to the sintered magnet segment 10c, and the sintered magnet segment 10c has a surface on the area a side positioned on the outer peripheral side of the rotor core 100 and a surface on the area d side positioned on the inner peripheral side of the rotor core 100. The direction of the segment 10 c is adjusted and inserted into the hole 102.

  Thus, by inserting the sintered magnet segments 10a, 10b, 10c, and 10d into the holes 102 of the rotor core 100, the area a having a relatively high heavy rare earth concentration is located in the vicinity of the outer periphery of the rotor. An area d having a relatively low value is positioned in the vicinity of the inner periphery of the rotor. Accordingly, the concentration of heavy rare earth is relatively increased near the rotor outer periphery where the demagnetizing field is strong to increase the holding force, while the concentration of heavy rare earth is relatively decreased near the inner periphery of the rotor where the demagnetizing field is weak. Can be wasted.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible.

  For example, in this embodiment, an IPM motor in which a magnet is embedded in the rotor is illustrated, but the present invention can be similarly applied to a motor in which a permanent magnet is mounted on the surface of the rotor. That is, when the sintered magnet segments 10a and 10b obtained by dividing into two parts as shown in FIG. 1B are mounted on the surface of the rotor, the area a is located in the vicinity of the rotor outer periphery and the area d is the rotor. Adjust the orientation so that it is located on the inner circumference side.

  Further, in this embodiment, in a sintered magnet in which heavy rare earth is segregated (diffusion soaked) at grain boundaries near the surface, a surface having a relatively high heavy rare earth concentration is positioned on the outer periphery side of the rotor. The concentration value of the heavy rare earth on the surface where the concentration of heavy rare earth is relatively high may be such that a holding force large enough not to demagnetize by the demagnetizing field of the stator is obtained, and the concentration of heavy rare earth is The concentration on the relatively low surface, that is, the concentration inside the sintered magnet before the division, is located on the inner circumference side of the rotor where the demagnetizing field is weak, so it may be lower than the conventional concentration. In this sense, the amount of heavy rare earth elements used Can be reduced.

  Further, in the present embodiment, the rectangular parallelepiped sintered magnet 10 is divided into two equal parts in a plane perpendicular to the magnetization direction in FIG. 1, but “two equal parts” does not necessarily mean strictly equal to two equal parts. Rather, it means approximately bisected, and the sintered magnet segment 10a and the sintered magnet segment 10b may be divided so that they can be substantially identical to each other.

  In FIG. 2, the rectangular parallelepiped sintered magnet 10 is divided into four equal parts in a plane perpendicular to the magnetization direction corresponding to the two-layer structure of the rotor. However, when the rotor has a three-layer structure, it is perpendicular to the magnetization direction. In this case, it may be divided into 6 equal parts. Similarly, in the case of n layers, it may be divided into 2n equal parts.

  In the present embodiment, the sintered magnet obtained by equally dividing the rectangular parallelepiped sintered magnet 10 is referred to as a sintered magnet segment. However, the shape of the sintered magnet segment is not necessarily a rectangular parallelepiped shape. The curved surface may correspond to the curvature of the rotor.

  10 Sintered magnets 10a to 10d Sintered magnet segment, 100 rotor core, 102 holes.

Claims (3)

A rotor with a permanent magnet embedded in the rotor core or mounted on the surface of the rotor core;
A stator disposed via a predetermined gap with respect to the rotor;
With
The permanent magnet is a plurality of sintered magnet segments obtained by dividing a sintered magnet obtained by segregating heavy rare earth elements into crystal grain boundaries in the vicinity of the surface along a plane perpendicular to the magnetization direction,
Each of the plurality of sintered magnet segments has a surface having a relatively high concentration of the heavy rare earth element located on the outer peripheral surface side of the rotor, and a surface having a relatively low concentration of the heavy rare earth element is an inner surface of the rotor. The permanent magnet motor is embedded in the rotor core or mounted on the surface of the rotor core so as to be positioned on the circumferential surface side. The motor according to claim 1, wherein
The permanent magnet is a plurality of sintered magnet segments obtained by dividing a sintered magnet obtained by segregating heavy rare earth elements into a grain boundary near the surface into two equal parts on a plane perpendicular to the magnetization direction. Permanent magnet motor. The motor according to claim 1, wherein
The permanent magnet is a plurality of sintered magnet segments obtained by dividing a sintered magnet obtained by segregating heavy rare earth elements into crystal grain boundaries near the surface into four equal parts on a plane perpendicular to the magnetization direction. Permanent magnet motor.

Images