JP2014072924A - Permanent magnet embedded motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent magnet embedded motor in which the coercive force on the outer peripheral side of a rotor of which outer peripheral side has a larger reverse magnetic field due to the rotating magnetic field of a stator and can be demagnetized more easily comparing with the inner peripheral side of the rotor, can be raised while reducing the amount of coercive force material used.SOLUTION: A permanent magnet embedded motor includes a rotor 1 having a rotor core 2 provided with a plurality of magnet insertion holes 21 formed at a predetermined pitch in the circumferential direction (arrow A1 direction), and permanent magnets 3 being inserted into the plurality of magnet insertion holes 21, respectively. The permanent magnets 3 are formed in two layers in the circumferential direction (arrow A1 direction), and when the permanent magnet 3 arranged on the outer peripheral side of the rotor 1 is a first permanent magnet 31 and the permanent magnet 3 arranged on the inner peripheral side of the rotor 1 is a second permanent magnet 32, out of the permanent magnets 3 in two layers, the first permanent magnet 31 contains a larger amount of coercive force material than the second permanent magnet 32 contains.

Description

  The present invention relates to an embedded permanent magnet motor in which a permanent magnet is embedded in a rotor core.

  As an example of the permanent magnet embedded type electric motor, for example, the invention described in Patent Document 1 can be cited. In this invention, the rare earth magnet of the block body is inserted in the rotor core of the motor, and the rare earth magnet has a portion in which the concentration of the fluorine compound (iron or cobalt and fluorine) is higher than the other portions. ing. Then, by applying a fluoride treatment to a portion to which a relatively large reverse magnetic field is applied, the coercive force is increased compared to a portion not subjected to the fluoride treatment.

JP 2011-029293 A

  However, in the invention described in Patent Document 1, since the magnet of the block body is partially fluoride-treated, it is not easy to accurately grasp the fluorine permeability of the portion subjected to the fluoride treatment. For this reason, it is difficult to accurately grasp the coercive force of the portion subjected to the fluoride treatment, and the coercive force of the portion subjected to the fluoride treatment is higher than that of the portion not subjected to the fluoride treatment. It is unclear whether the degree has improved.

  Further, in order to increase the demagnetization resistance against a reverse magnetic field, a method of increasing the radial thickness of the rare earth magnet can be considered. However, this method increases the amount of the rare coercive material used, resulting in an increase in cost.

  The present invention has been made in view of the above circumstances, and the coercive force on the outer peripheral side of the rotor is easily demagnetized because the reverse magnetic field due to the rotating magnetic field of the stator is large compared to the inner peripheral side of the rotor. It is an object of the present invention to provide an embedded permanent magnet electric motor that can reduce the amount of coercive material used.

  The embedded permanent magnet electric motor according to claim 1, a rotor core in which a plurality of magnet insertion holes are formed at a predetermined pitch in the circumferential direction, and a permanent magnet inserted into each of the plurality of magnet insertion holes, Each of the permanent magnets is formed in two layers in the circumferential direction, and is disposed on the outer peripheral side of the rotor among the two layers of permanent magnets. When the permanent magnet to be used is the first permanent magnet and the permanent magnet disposed on the inner peripheral side of the rotor is the second permanent magnet, the content of the coercive force material of the first permanent magnet is the second permanent magnet. It is characterized in that it is larger than the coercive force material content.

  The embedded permanent magnet motor according to claim 2 is the embedded permanent magnet motor according to claim 1, wherein the coercive force material of the first permanent magnet is grain boundary diffused, and the first permanent magnet is used. The radial thickness of the magnet in the rotor is formed thinner than the radial thickness of the second permanent magnet in the rotor.

  According to a third aspect of the present invention, there is provided the embedded permanent magnet motor according to the first or second aspect, wherein the coercive force material of the first permanent magnet is completely grain boundary diffused.

  According to the embedded permanent magnet electric motor according to claim 1, the permanent magnet is formed in two layers in the circumferential direction, and contains the coercive force material of the first permanent magnet arranged on the outer peripheral side of the rotor. The amount is larger than the content of the coercive force material of the second permanent magnet disposed on the inner peripheral side of the rotor. Therefore, compared with the inner peripheral side of the rotor, the coercive force on the outer peripheral side of the rotor can be increased because the reverse magnetic field due to the rotating magnetic field of the stator is large and is easily demagnetized. Further, since the reverse magnetic field on the inner peripheral side is smaller than the outer peripheral side of the rotor, the content of the coercive material of the second permanent magnet is reduced compared to the content of the coercive material of the first permanent magnet. Can do. Therefore, a necessary coercive force can be secured while suppressing the amount of rare coercive material used.

  According to the interior permanent magnet motor of the second aspect, the radial thickness of the rotor of the first permanent magnet is formed thinner than the radial thickness of the rotor of the second permanent magnet. Therefore, compared to the second permanent magnet, the coercive material of the first permanent magnet can be easily diffused at the grain boundary, and the coercive material can be diffused from the magnet surface of the first permanent magnet to the deep inside of the magnet. Can do. Therefore, it is easy to increase the coercive force of the first permanent magnet as compared with the second permanent magnet.

  According to the permanent magnet embedded type electric motor of the third aspect, since the coercive material of the first permanent magnet is completely grain boundary diffused, the coercive force on the outer peripheral side of the rotor can be reliably improved. . In addition, since the coercive material of the first permanent magnet is completely grain boundary diffused, it is easy to grasp the coercive force of the first permanent magnet and to ensure magnetic characteristics such as magnetic flux density and coercive force. it can.

FIG. 4 is a partial cross-sectional view of the rotor and the stator as viewed in the axial direction according to the first embodiment. It is explanatory drawing which concerns on 1st Embodiment and shows an example of magnetic flux distribution. FIG. 10 is a partial cross-sectional view of the rotor and the stator as viewed in the axial direction according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Common portions of the embodiments are denoted by common reference numerals, and redundant description is omitted. Each figure is a conceptual diagram and does not define the dimensions of the detailed structure.

(1) First Embodiment FIG. 1 is a partial sectional view of a rotor 1 and a stator 4 as viewed in the axial direction. The embedded permanent magnet electric motor of this embodiment includes a stator 4 and a rotor 1 that is arranged to be rotatable with respect to the stator 4. In the figure, a part of the rotor 1 and the stator 4 is schematically shown. In practice, the rotor 1 and the stator 4 each have a substantially cylindrical shape. Note that the rotation axis of the rotor 1 is an axis AX1. In this embodiment, it is a 20-pole permanent magnet embedded electric motor.

<Rotor>
The rotor 1 has a rotor core 2 and a permanent magnet 3. The rotor core 2 is formed in a cylindrical shape by laminating a plurality of thin electromagnetic steel plates in the direction of the axis AX1. For example, a silicon steel plate can be used as the electromagnetic steel plate. A shaft portion (shaft) (not shown) is fitted to the inner peripheral side of the rotor core 2, and the shaft portion is pivotally supported by a bearing provided on a housing (not shown). Thereby, the rotor core 2 is rotatable in the circumferential direction (arrow A1 direction).

  Each electromagnetic steel plate of the rotor core 2 is provided with magnet insertion holes 21 for a predetermined magnetic pole at a predetermined pitch in the circumferential direction (arrow A1 direction), and penetrates each magnet insertion hole 21 in the direction of the axis AX1. The permanent magnet 3 is embedded. Each magnet insertion hole 21 is formed in two rows in the circumferential direction (arrow A1 direction) so that the permanent magnets 3 formed in two layers can be inserted. In this specification, the magnet insertion hole 21 formed on the outer peripheral side of the rotor 1 is referred to as a first magnet insertion hole 211, and the magnet insertion hole 21 formed on the inner peripheral side of the rotor 1 is referred to as a second magnet insertion hole. It is called 212.

The permanent magnet 3 is a rectangular parallelepiped permanent magnet. For example, a known rare earth sintered magnet such as a neodymium magnet (Nd—Fe—B magnet such as Nd ₂ Fe ₁₄ B) can be used. In addition to neodymium Nd, various rare earth elements such as praseodymium Pr and samarium Sm can be used as the rare earth element, and a plurality of rare earth elements can also be included. Moreover, the permanent magnet 3 can also contain a reforming element and inevitable impurities.

  Examples of the modifying element include cobalt Co, lanthanum La, which contributes to improvement of heat resistance of the permanent magnet 3, aluminum Al, silicon Si, titanium Ti, vanadium V, chromium Cr, which contributes to improvement of magnetic properties such as coercive force. , Transition elements such as manganese Mn, nickel Ni, copper Cu, yttrium Y, zirconium Zr, niobium Nb, molybdenum Mo, and the like. Inevitable impurities are elements that are difficult to remove in production, and examples thereof include oxygen O, nitrogen N, and carbon C.

  The permanent magnet 3 is formed in two layers in the circumferential direction (arrow A1 direction). In this specification, the permanent magnet 3 disposed on the outer peripheral side of the rotor 1 out of the two layers of permanent magnets 3 is referred to as a first permanent magnet 31, and the permanent magnet 3 disposed on the inner peripheral side of the rotor 1 is referred to as the first permanent magnet 31. The second permanent magnet 32 is referred to. The first permanent magnet 31 is inserted into the first magnet insertion hole 211, and the second permanent magnet 32 is inserted into the second magnet insertion hole 212. The first permanent magnet 31 and the second permanent magnet 32 are each magnetized so that the magnetization direction is the same as the radial direction (arrow B1 direction).

  When the first permanent magnet 31 is inserted into the first magnet insertion hole 211 so that the N pole side of the first permanent magnet 31 is on the stator 4 side, the N pole side of the second permanent magnet 32 is on the stator 4 side. In this manner, the second permanent magnet 32 is inserted into the second magnet insertion hole 212. Conversely, when the first permanent magnet 31 is inserted into the first magnet insertion hole 211 so that the south pole side of the first permanent magnet 31 is on the stator 4 side, the south pole side of the second permanent magnet 32 is the stator 4. The second permanent magnet 32 is inserted into the second magnet insertion hole 212 so as to be on the side.

  The method for fixing the permanent magnet 3 is not particularly limited. For example, the permanent magnet 3 can be fixed to the rotor core 2 with an adhesive. In addition, an elastic member can be provided separately, and the permanent magnet 3 can be fixed to the rotor core 2 by the biasing force of the elastic member. For example, the elastic member presses the inner surface of the first permanent magnet 31 in the radial direction (arrow B1 direction) against the inner surface of the first magnet insertion hole 211 in the radial direction (arrow B1 direction). May be urged inward in the radial direction (arrow B1 direction). The same applies to the second permanent magnet 32. Thereby, when the rotor core 2 and the permanent magnet 3 generate heat, the difference in thermal expansion between both members can be absorbed, and the fixed portion can be prevented from peeling off.

  The permanent magnet 3 includes a coercive material, and the content of the coercive material of the first permanent magnet 31 is larger than the content of the coercive material of the second permanent magnet 32. Note that the content of the coercive force material of the second permanent magnet 32 can be zero. The coercive force material is a rare earth element that increases the coercive force of the permanent magnet 3, and for example, dysprosium Dy, terbium Tb, or the like can be used. As the coercive force material, various rare earth elements can be used besides these, and a plurality of kinds of rare earth elements can also be included.

  The method of incorporating the coercive material into the permanent magnet 3 is not limited, but it is preferable to diffuse the coercive material at grain boundaries. In the present embodiment, the first permanent magnet 31 and the second permanent magnet 32 have the same kind of coercive force material diffused at the grain boundaries. Further, the method for diffusing the coercive material at the grain boundary is not particularly limited. For example, a known method such as a vapor deposition method, a vapor method, or a coating method can be used.

  In the vapor deposition method, sputtering is performed using a coercive force material as a target, and the coercive force material is diffused at grain boundaries inside the magnet. In the steam method, a coercive material is disposed in the vicinity of a magnet in a heating furnace, and the magnet and the coercive material are heated. Then, by directly exposing the magnet to the vapor of the coercive force material, the coercive force material is diffused at the grain boundaries inside the magnet. In the coating method, the coercive force material is applied to the surface of the magnet and heated, so that the coercive force material diffuses at the grain boundaries inside the magnet. For example, the depth at which the coercive force material diffuses at the grain boundaries can be adjusted by adjusting the temperature at the time of heating, the heating time, and the like.

  The radial thickness t1 of the rotor 1 of the first permanent magnet 31 (hereinafter simply referred to as the radial thickness t1 of the first permanent magnet 31) and the radial thickness t2 of the rotor 1 of the second permanent magnet 32 (hereinafter referred to as “herein”). The radial thickness t2 of the second permanent magnet 32 is simply set to a thickness at which the first permanent magnet 31 and the second permanent magnet 32 are not demagnetized. For example, a reverse magnetic field applied to the first permanent magnet 31 and the second permanent magnet 32 is estimated by magnetic field analysis, and the diameter of the first permanent magnet 31 is increased so that the coercive force is increased with respect to the estimated reverse magnetic field. The direction thickness t1 and the radial direction thickness t2 of the second permanent magnet 32 are set.

  The radial thickness t1 of the first permanent magnet 31 is preferably formed thinner than the radial thickness t2 of the second permanent magnet 32. In this case, compared with the second permanent magnet 32, the coercive material of the first permanent magnet 31 can be easily diffused at the grain boundary, and the coercive material is granulated from the surface of the first permanent magnet 31 to the inside of the magnet. Can be field diffused. Therefore, it is easy to increase the coercive force of the first permanent magnet 31 compared to the second permanent magnet 32.

  In particular, the radial thickness t1 of the first permanent magnet 31 is preferably 3.0 mm or less. Thereby, the coercive force material of the first permanent magnet 31 can be completely grain boundary diffused. Complete grain boundary diffusion refers to a state where the coercive force material is diffused from the surface of the first permanent magnet 31 to the center of the magnet. If the radial thickness t1 of the first permanent magnet 31 is too thin, the necessary coercive force material cannot be diffused at the grain boundaries. On the other hand, when the radial thickness t1 of the first permanent magnet 31 is greater than 3.0 mm, the coercive force material does not diffuse to the grain boundary to the magnet center. The radial thickness t1 of the first permanent magnet 31 is preferably 2.5 mm to 3.0 mm. In the present embodiment, the radial thickness t1 of the first permanent magnet 31 is 2.5 mm, and the radial thickness t2 of the second permanent magnet 32 is 3.0 mm.

  The length of the first permanent magnet 31 in the circumferential direction (arrow A1 direction) is the first circumferential length L1, and the length of the second permanent magnet 32 in the circumferential direction (arrow A1 direction) is the second circumferential length L2. The first permanent magnet 31 has a radial thickness t1 of 3.0 mm or less regardless of the first circumferential length L1 and the second circumferential length L2 and the type of coercive force material. The coercive force material of the magnet 31 can be completely grain boundary diffused. In the present embodiment, the first circumferential length L1 and the second circumferential length L2 are both 26 mm.

  Whether or not the coercive material is completely grain boundary diffused can be determined, for example, by analyzing the permanent magnet 3 with an electron beam microanalyzer (EPMA) and observing the obtained EPMA image.

  In the present embodiment, since the coercive force material of the first permanent magnet 31 is completely grain boundary diffused, the coercive force on the outer peripheral side of the rotor 1 can be reliably improved. Further, since the coercive material of the first permanent magnet 31 is completely grain boundary diffused, it is easy to grasp the coercive force of the first permanent magnet 31 and guarantees magnetic characteristics such as magnetic flux density and coercive force. be able to.

<Stator>
The stator 4 has a stator core 5 and a stator winding 6. The stator core 5 is formed by laminating a plurality of thin electromagnetic steel plates in the direction of the axis AX1. For example, a silicon steel plate can be used as the electromagnetic steel plate. The stator core 5 is disposed inside a substantially cylindrical casing (not shown). The stator core 5 includes a yoke part 51 extending in the circumferential direction (arrow A1 direction), and a plurality of magnetic pole tooth parts 52 protruding inward in the radial direction (arrow B1 direction) from the inner circumferential surface of the yoke part 51. ,have. Each magnetic pole tooth part 52 is arranged at a predetermined interval in the circumferential direction (arrow A1 direction).

  In the stator winding 6, the conductor surface of the three-phase winding is covered with an insulating layer such as enamel. The stator winding 6 is wound by distributed winding in the slot portion between the magnetic pole tooth portions 52, and the stator winding 6 is Y-connected. An AC voltage is applied to the stator winding 6, thereby generating a rotating magnetic field in the stator 4. The cross-sectional shape of the stator winding 6 is not particularly limited, and can be an arbitrary cross-sectional shape. For example, the stator winding 6 may be a winding having various cross-sectional shapes such as a round wire having a circular cross-section and a square wire having a polygonal cross-section. Also, a combination of a plurality of winding wires can be used. Note that the stator winding 6 may be concentrated winding or Δ connection.

<Summary>
FIG. 2 is an explanatory diagram showing an example of the magnetic flux distribution. This figure shows the magnetic flux distribution of the permanent magnet embedded motor shown in FIG. The magnetic flux distribution can be derived, for example, by magnetic field analysis. The outer peripheral side portion G1 of the rotor 1 indicated by the broken line in FIG. Therefore, the permanent magnet 3 is easy to demagnetize.

  In this embodiment, the permanent magnet 3 is formed in two layers in the circumferential direction (arrow A1 direction), and the content of the coercive force material of the first permanent magnet 31 disposed on the outer peripheral side of the rotor 1 is rotated. The content is larger than the content of the coercive force material of the second permanent magnet 32 disposed on the inner peripheral side of the child 1. Therefore, compared with the inner peripheral side of the rotor 1, the coercive force on the outer peripheral side of the rotor 1 can be increased because the reverse magnetic field due to the rotating magnetic field of the stator 4 is large and easily demagnetized. Further, since the reverse magnetic field on the inner peripheral side is smaller than that on the outer peripheral side of the rotor 1, the content of the coercive material of the second permanent magnet 32 is smaller than the content of the coercive material of the first permanent magnet 31. Can be reduced. Therefore, a necessary coercive force can be secured while suppressing the amount of rare coercive material used.

(2) 2nd Embodiment This embodiment differs in the shape of the magnet insertion hole 21 and the insertion method of the permanent magnet 3 compared with 1st Embodiment. The composition, shape, coercive material content, coercive material diffusion method, and the like of the permanent magnet 3 are the same as those in the first embodiment. Parts that are the same as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 3 is a partial cross-sectional view of the rotor 1 and the stator 4 as viewed in the axial direction. In the present embodiment, the magnet insertion holes 21 are formed in one row in the circumferential direction (arrow A1 direction). The radial direction (arrow B1 direction) length of the magnet insertion hole 21 is the radial direction (arrow B1 direction) length of the first magnet insertion hole 211 and the radial direction (arrow B1 direction) of the second magnet insertion hole 212 in the first embodiment. ) The length is added to the length. The 1st permanent magnet 31 and the 2nd permanent magnet 32 which adjoin a radial direction (arrow B1 direction) are fixed with the adhesive agent, for example, and are inserted in the magnet insertion hole 21, and are being fixed. Also in this embodiment, the same effects as those described in the first embodiment can be obtained.

(3) Others The present invention is not limited to the embodiment described above and shown in the drawings, and can be implemented with appropriate modifications within a range not departing from the gist. For example, two permanent magnets can be provided per magnetic pole and arranged in a substantially V shape. That is, when viewed in the axial direction, the two permanent magnets can be arranged in a substantially V shape that widens from the axis AX1 of the rotor 1 toward the stator 4 side.

  In this case, each of the two permanent magnets is formed in two layers. The permanent magnet arranged on the outer peripheral side of the rotor 1 corresponds to the first permanent magnet 31 in the first embodiment and the second embodiment. The permanent magnet disposed on the inner peripheral side of the rotor 1 corresponds to the second permanent magnet 32 in the first embodiment and the second embodiment. Even in this case, the same effects as described above can be obtained in the first embodiment.

  The embedded permanent magnet electric motor of the present invention has a high demagnetization resistance against a reverse magnetic field during driving and can obtain a high torque, so that it can be used, for example, as a driving motor for an electric vehicle or a hybrid vehicle. it can. Besides these, it can be widely used as various electric motors for industrial equipment such as servo motors and compressor motors.

1: rotor,
2: Rotor core, 21: Magnet insertion hole,
3: Permanent magnet
31: 1st permanent magnet, 32: 2nd permanent magnet,
t1: radial thickness of the first permanent magnet 31;
t2: radial thickness of the second permanent magnet 32

Claims (3)

A permanent magnet embedded type electric motor comprising a rotor having a rotor core in which a plurality of magnet insertion holes are formed at a predetermined pitch in the circumferential direction, and a permanent magnet inserted into each of the plurality of magnet insertion holes. And
Each of the permanent magnets is formed in two layers in the circumferential direction,
Of the two layers of permanent magnets, the permanent magnet disposed on the outer peripheral side of the rotor is the first permanent magnet, and the permanent magnet disposed on the inner peripheral side of the rotor is the second permanent magnet. A permanent magnet embedded type electric motor characterized in that the content of the coercive material of one permanent magnet is larger than the content of the coercive material of the second permanent magnet. The coercive material of the first permanent magnet is grain boundary diffused,
2. The embedded permanent magnet electric motor according to claim 1, wherein a radial thickness of the first permanent magnet in the rotor is thinner than a radial thickness of the second permanent magnet in the rotor.   3. The embedded permanent magnet electric motor according to claim 1, wherein the coercive force material of the first permanent magnet is completely grain boundary diffused.

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