JP2016127609A - Rotary electric machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict demagnetization of a permanent magnet while hindering a decrease in saturation flux density, in a rotary electric machine in which a permanent magnet and a coil are arranged facing each other.SOLUTION: A rotary electric machine is provided with a stator core (21) having a plurality of teeth (211) and having slots (213) between the teeth (211). The rotary electric machine is provided with coils (23, 24) wound around the teeth (211) and accommodated in the slots (213). A permanent magnet (22) is provided in a predetermined slot (213) so as to be in contact with the coil (23) in this slot (213). The permanent magnet (22) is a sintered magnet using a rare-earth element, and the coercive field force of the face (S) of it, which is in contact with the coil (23), is made greater than the coercive field force of the interior part thereof.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a rotating electric machine such as an electric motor.

  Some electric motors, which are a type of rotating electrical machine, have a structure in which both a winding and a permanent magnet are provided on a stator, and the magnetic flux of the permanent magnet flows from the stator to the rotor (for example, Patent Document 1). reference). In the example of Patent Document 1, the predetermined winding (field winding) is provided in contact with the permanent magnet, and the flow of magnetic flux of the permanent magnet is controlled by controlling the direct current conduction state to the field winding. And the AC power is supplied to another winding (armature winding) to rotate the rotor.

JP 2013-2018869 A

  However, in the example of Patent Document 1, a so-called rare earth magnet (neodymium magnet or the like) is used as the permanent magnet, and when the winding in contact with the permanent magnet is energized, There is a possibility of demagnetization.

  For this, for example, by introducing a heavy rare earth element (for example, dysprosium (Dy)) into the particles (main phase) constituting the rare earth magnet, the coercive force can be obtained in the entire magnet, but the saturation magnetic flux Density decreases.

  The present invention has been made paying attention to the above problems, and in a rotating electric machine having a structure in which a permanent magnet and a winding are arranged facing each other on a stator, a decrease in saturation magnetic flux density is suppressed. However, it aims at suppressing the demagnetization of a permanent magnet.

In order to solve the above problems, the first invention is
A stator core (21) having a plurality of teeth (211) arranged at predetermined intervals in the circumferential direction of an annular stator yoke (212) and having slots (213) formed between these teeth (211) When,
A rotor core (11) opposed to the stator core (21) with a predetermined air gap;
Windings (23, 24) wound around the teeth (211) and accommodated in the slots (213);
A permanent magnet (22) provided in contact with a winding (23) in the slot (213) in a predetermined slot (213);
With
The permanent magnet (22) is a sintered magnet using a rare earth element, and is characterized in that the coercive force on the surface (S) in contact with the winding (23) is larger than the internal coercive force.

  In this configuration, the permanent magnet (22) has a higher demagnetization resistance on the surface (S) in contact with the winding (23) than in the interior of the permanent magnet (22).

The second invention is the first invention, wherein
The permanent magnet (22) has the coercive force adjusted by diffusing heavy rare earth elements so that the content decreases from the surface of the permanent magnet (22) toward the inside. It is characterized by that.

  In this configuration, the coercive force is adjusted by the heavy rare earth element. Further, since the content of the heavy rare earth element is smaller in the permanent magnet (22) than on the surface side, it is easy to secure a desired magnetic flux density in the permanent magnet (22).

The third invention is the second invention, wherein
The permanent magnet (22) has a region where the heavy rare earth element is not diffused.

Further, a fourth invention is any one of the second to third inventions,
The heavy rare earth element is diffused from a surface (S) in contact with the winding (23).

  In this configuration, the demagnetization resistance on the surface (S) in contact with the winding (23) is the largest.

In addition, a fifth invention is any one of the second to fourth inventions,
The heavy rare earth element is dysprosium (Dy) or terbium (Tb).

  In this configuration, the coercive force is adjusted by dysprosium (Dy) or terbium (Tb).

  According to the first invention, in the rotating electric machine, it is possible to take measures against demagnetization of the permanent magnet while suppressing a decrease in saturation magnetic flux density.

  Further, according to the second invention, it is possible to take a countermeasure against demagnetization of the permanent magnet while ensuring a desired magnetic flux density.

  Moreover, according to the third aspect, it becomes easy to secure a desired magnetic flux density.

  In addition, according to the fourth invention, the amount of heavy rare earth elements used can be reduced.

  Moreover, according to the fifth aspect, the coercive force can be easily adjusted.

FIG. 1 is a cross-sectional view showing a configuration of an electric motor according to Embodiment 1 of the present invention. FIG. 2 is a diagram for explaining the gradient of the content distribution of heavy rare earth elements. FIG. 3 shows the magnetic flux of the permanent magnet when no current is flowing through the field winding. FIG. 4 shows the magnetic flux of the permanent magnet in a state where a current is flowing through the field winding. FIG. 5 is a cross-sectional view showing a configuration of an electric motor according to Embodiment 2 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are essentially preferable examples, and are not intended to limit the scope of the present invention, its application, or its use.

Embodiment 1 of the Invention
Below, the example of an electric motor is demonstrated as an example of the rotary electric machine of this invention. FIG. 1 is a cross-sectional view showing a configuration of an electric motor (1) according to Embodiment 1 of the present invention. As shown in FIG. 1, the electric motor (1) includes a rotor (10) and a stator (20), and is accommodated in a casing (not shown). The electric motor (1) can be used for, for example, a car, a compressor of an air conditioner, and the like. A drive shaft (12) provided on the rotor (10) is used to transmit a car or a compressor of an air conditioner. Drive etc.

  Below, the structure of an electric motor (1) is demonstrated. Of the terms used in the following description, the axial direction refers to the direction of the axis (P) of the drive shaft (12), and the radial direction refers to the direction orthogonal to the axis (P). The outer peripheral side is the side farther from the axis (P), and the inner peripheral side is the side closer to the axis (P).

<Rotor>
The rotor (10) includes a rotor core (11) and a drive shaft (12). The rotor core (11) is made of a soft magnetic material. Specifically, the rotor core (11) is a laminated core in which a large number of core members created by punching electromagnetic steel sheets by press working are laminated in the axial direction. As shown in FIG. 1, the rotor core (11) is formed with a through hole (113) into which the drive shaft (12) is inserted.

  The rotor core (11) is provided with a plurality of protrusions (111) protruding toward the outer peripheral side. The protrusions (111) are arranged at an equal pitch in the circumferential direction of the rotor core (11). That is, the rotor core (11) has a gear shape when viewed from the axial direction.

<stator>
The stator (20) includes a stator core (21), a permanent magnet (22), a field winding (23), and an armature winding (24).

  The stator core (21) is made of a soft magnetic material. Specifically, the stator core (21) is a laminated core in which a number of core members created by punching electromagnetic steel sheets by pressing are laminated in the axial direction. As shown in FIG. 1, the stator core (21) includes a stator yoke (212) and a plurality of teeth (211). The stator yoke (212) is a portion formed on the outer peripheral side of the stator core (21) having an annular shape. Each tooth (211) is a portion protruding from the inner peripheral surface of the stator yoke (212) toward the inner peripheral side. In the example of FIG. 1, an even number of teeth (211) are provided, and these teeth (211) are arranged at a predetermined pitch around the axis (P). Thereby, a space is formed between the respective teeth (211).

  These spaces function as slots (213) in which windings (described later) are accommodated. There are two types of slots (213), a field slot (213a) and an armature slot (213b), and a plurality of slots of any type are provided. Specifically, the field slot (213a) is a pair of slots adjacent to each other in the circumferential direction by skipping one of the slots (213). The armature slot (213b) is a slot excluding the field slot (213a) among the slots (213). That is, the field slot (213a) and the armature slot (213b) are alternately arranged in the circumferential direction.

<Winding>
There are two types of windings for the stator (20): field windings (23) and armature windings (24).

−Field winding (23) −
The field winding (23) is wound around the tooth (211) and accommodated in the field slot (213a). More specifically, the field winding (23) includes a pair of teeth (211) sandwiched between a pair of field slots (213a) adjacent to each other in the circumferential direction (hereinafter referred to as a pair of field teeth (211a)). Is called). Specifically, the field winding (23) is wound around the pair of field teeth (211a) with the axis along the radial direction as a winding axis. That is, the pair of field teeth (211a) is regarded as one tooth, and the field winding (23) is wound around this with concentrated winding. These field windings (23) are DC-excited as will be described later.

− Armature winding (24) −
The armature winding (24) is wound around the teeth (211) and accommodated in the armature slot (213b). More specifically, the armature winding (24) is also referred to as a pair of teeth (211) sandwiched between a pair of armature slots (213b) adjacent in the circumferential direction (hereinafter also referred to as a pair of armature teeth (211b)). ). Specifically, the armature winding (24) is wound around the pair of armature teeth (211b) using a shaft along the radial direction as a winding shaft. That is, the pair of armature teeth (211b) is regarded as one tooth, and the armature winding (24) is wound around this with concentrated winding.

<permanent magnet>
The stator (20) is provided with a plurality of permanent magnets (22). Each permanent magnet (22) is a so-called rare earth magnet using a rare earth element, and in this example, is a sintered magnet mainly composed of neodymium, iron, and boron. This permanent magnet (22) has a square cross section (surface visible in FIG. 1) in a direction perpendicular to the axis (P) (in this example, approximately square). The axial length of the permanent magnet (22) is substantially the same as the axial length of the stator core (21). That is, the permanent magnet (22) of this embodiment is a rectangular parallelepiped.

-Arrangement of permanent magnet (22) (Relation with winding)-
Each permanent magnet (22) is disposed in the field slot (213a). That is, the permanent magnet (22) and the field winding (23) are disposed in the field slot (213a). As shown in FIG. 1, in the stator (20), the permanent magnet (22) is in the radial direction so that the permanent magnet (22) is on the inner peripheral side (rotor (10) side) than the field winding (23). The surface (S) on the outer peripheral side of the permanent magnet (22) is in contact with the field winding (23).

  On the other hand, looking at the relationship between the permanent magnet (22) and the armature winding (24), the permanent magnet (22) is surrounded by the armature winding (24) along the radial direction.

  In addition, each permanent magnet (22) is disposed so that the magnetic pole faces of the same polarity face each other in the circumferential direction. That is, the permanent magnets (22) are magnetized along the circumferential direction, and these permanent magnets (22) are arranged with magnetic pole faces of different polarities alternately directed toward one side in the circumferential direction. Yes.

-Countermeasure against permanent magnet (22) demagnetization-
The permanent magnet (22) of the present embodiment is configured such that the coercive force on the surface (S) in contact with the field winding (23) is larger than the internal coercive force. Specifically, heavy rare earth elements (specifically, dysprosium (Dy) or terbium (Tb)) are moved inward from the surface (S) in contact with the field winding (23) by the grain boundary diffusion method. The gradient of the coercive force distribution is realized by diffusing so as to reduce its content. In the present embodiment, the particles (main phase) constituting the permanent magnet (22) itself do not contain heavy rare earth elements.

  FIG. 2 is a diagram for explaining the gradient of the content distribution of heavy rare earth elements. In this example, the permanent magnet (22) diffuses the heavy rare earth element from the surface (S) in contact with the field winding (23). Further, a region where the heavy rare earth element is not diffused exists in the permanent magnet (22). Specifically, in FIG. 2, the three points A, B, and C inside the permanent magnet (22) picked up in order from the surface (S) are the points A, B, and C. When the contents of the heavy rare earth elements are Rm (A), Rm (B), and Rm (C), there is a relationship of Rm (A)> Rm (B)> Rm (C). In this example, Rm (C) = 0. With this configuration, the permanent magnet (22) can obtain a sufficient coercive force on the surface (S) in contact with the field winding (23) and in the vicinity thereof (surface layer having a predetermined thickness of the permanent magnet (22)). It becomes possible.

<Operation of motor (1) (excitation of winding)>
FIG. 3 shows the magnetic flux (hereinafter also referred to as magnet magnetic flux) of the permanent magnet (22) in a state where no current flows through the field winding (23). In FIG. 3, a part of the electric motor (1) (one quarter centered on the drive shaft (12)) in a cross section perpendicular to the axis (P) is illustrated, and the magnetic flux is indicated by solid arrows. is there. As shown in FIG. 3, when no current flows through the field winding (23), most of the magnetic flux passes through a pair of armature teeth (211b) and a part of the stator yoke (212). Flowing. That is, when no current flows through the field winding (23), the amount of magnetic flux flowing from the stator core (21) to the rotor core (11) is small.

  FIG. 4 shows the magnetic flux of the permanent magnet (22) in a state where current flows through the field winding (23). FIG. 4 shows a part of the electric motor (1) (one-fourth centered on the drive shaft (12)) in a cross section perpendicular to the axis (P), and the magnetic flux of the permanent magnet (22). And the magnetic flux by the field winding (23) (hereinafter also referred to as winding magnetic flux) are indicated by solid line arrows and broken line arrows, respectively.

  In the example of FIG. 4, a direct current is passed through the field winding (23) so that the magnetic flux passes through the rotor core (11) (see FIG. 4). Specifically, in the field winding (23), the field winding (23) is arranged so that the winding magnetic flux flows in the opposite direction to the magnet magnetic flux shown in FIG. 3 in the stator yoke (212). The current is passed through. By doing so, in this example, the magnetic flux passes through a part of the stator yoke (212) and the teeth (24) that straddle the armature winding (24) adjacent to the permanent magnet (22). 211), and further flows from the teeth (211) to the rotor core (11). In FIG. 4, the direction of the current flowing through the field winding (23) is shown by known symbols (a symbol with a black circle inside the circle and a symbol with a cross inside the circle).

  Note that the flow of the magnet magnetic flux and the winding magnetic flux in FIG. 4 is an example, and the paths through which the magnetic flux and the winding magnetic flux flow may differ depending on the rotational position of the rotor core (11) (position of the protrusion (111)). . However, even if the rotational position of the rotor core (11) is changed, the magnet magnetic flux and the winding magnetic flux flow through the rotor core (11).

  Thus, the magnet magnetic flux and the winding magnetic flux flow through the rotor core (11) and act as field magnetic flux. Therefore, the magnitude of the field magnetic flux can be controlled by controlling the direct current flowing through the field winding (23). For example, to increase the field magnetic flux size during low-speed rotation and perform strong field control that outputs a large torque, and to reduce field flux size during high-speed rotation and perform field-weakening control to improve the rotation speed Can do. Various types of power supplies for supplying DC power to the field winding (23) can be used. For example, by using a chopper circuit (for example, a step-down circuit, a step-up circuit or a step-up / step-down circuit), it is possible to easily control the direct current flowing through the field winding (23).

  In the electric motor (1), an alternating current is passed through the armature winding (24) to apply a rotating magnetic field to the rotor (10). For example, when a three-phase armature winding is employed as the armature winding (24), a three-phase alternating current flows through the armature winding (24). The alternating current flowing through the armature winding (24) can be controlled by, for example, an inverter circuit. Since the magnetic flux of the armature winding (24) is an alternating magnetic flux, an eddy current is generated due to this. Further, due to the harmonic component generated in the alternating current, a harmonic component is also generated in the alternating magnetic flux. The harmonic component of this alternating magnetic flux also causes eddy currents.

-Heat conduction of winding-
As described above, in the electric motor (1), the magnitude of the field magnetic flux is controlled by controlling the direct current supplied to the field winding (23). The field winding (23) generates heat while a current flows through the field winding (23). Part of the heat of the field winding (23) is transmitted to the stator core (21), and the stator core (21) dissipates heat to the surrounding air and the casing of the electric motor (1), for example, and permanent magnets. Transfer heat to (22). Further, since the permanent magnet (22) is in contact with the field winding (23) on the surface (S), the heat of the field winding (23) is directly transmitted to the permanent magnet (22).

  Since the heat transferred from the field winding (23) to the stator core (21) is dissipated halfway as described above, the demagnetization effect due to the heat via the stator core (21) is mitigated. It is done. On the other hand, the heat directly transmitted from the field winding (23) to the permanent magnet (22) is likely to demagnetize the permanent magnet (22) if no measures are taken. In addition, when a chopped current flows through the field winding (23), an eddy current is generated in the permanent magnet (22), and the permanent magnet (22) contacts the field winding (23) due to the skin effect. This part is particularly heated.

<Effect in this embodiment>
However, the permanent magnet (22) of the present embodiment has the surface (S) in contact with the field winding (23) by diffusing the heavy rare earth element from the surface (S) in contact with the field winding (23). ) Is larger than the coercive force inside the permanent magnet (22).

  Therefore, in this embodiment, the demagnetization of the permanent magnet (22) due to heat from the surface (S) in contact with the field winding (23) is caused by the diffused heavy rare earth element to the surface (S) and its vicinity ( It becomes possible to suppress in the surface layer of the permanent magnet (22) having a predetermined thickness. Further, although the amount of diffusion of the heavy rare earth element is small in the permanent magnet (22) (inside the surface layer), there is no problem of demagnetization. This is because the temperature of the permanent magnet (22) is considered to be lower in the permanent magnet (22) than in the vicinity of the surface (S).

  In general, when the diffusion amount of the heavy rare earth element is increased as a countermeasure against demagnetization, the saturation magnetic flux density tends to decrease. In the electric motor (1) having a structure in which the magnetic flux of the permanent magnet (22) flows from the stator (20) to the rotor (10) as in this embodiment, the saturation magnetic flux density by the permanent magnet (22) is larger. Since it is desirable, a decrease in the saturation magnetic flux density of the permanent magnet (22) is desired to be avoided. In this regard, in the present embodiment, the content of the heavy rare earth element decreases as it goes toward the inside of the permanent magnet (22), so that a decrease in saturation magnetic flux density can be suppressed.

  Therefore, in the present embodiment, it is possible to take measures against demagnetization of the permanent magnet while suppressing a decrease in the saturation magnetic flux density of the permanent magnet. In addition, by using the distribution of heavy rare earth elements as described above, it is possible to reduce the amount of heavy rare earth elements used and to reduce the cost of the electric motor (1).

<< Embodiment 2 of the Invention >>
FIG. 5 is a cross-sectional view showing the configuration of the electric motor (1) according to Embodiment 2 of the present invention. In this example, the positional relationship between the permanent magnet (22) and the field winding (23) is different from the example of the first embodiment. In this embodiment, both are adjacent to each other in the radial direction so that the field winding (23) is on the inner peripheral side (rotor (10) side) than the permanent magnet (22), and the permanent magnet (22 ) Is in contact with the field winding (23).

  Also in this embodiment, the permanent magnet (22) is configured such that the coercive force on the surface (S) in contact with the field winding (23) is larger than the internal coercive force. Specifically, as in Embodiment 1, the heavy rare earth element (dysprosium (Dy) or terbium (Tb)) is diffused from the surface (S) in contact with the field winding (23), whereby a permanent magnet ( The gradient of the heavy rare earth element content is provided so that the content of the heavy rare earth element decreases from the outer peripheral surface to the inside in (22).

<Heat conduction in winding>
Also in this embodiment, the heat of the field winding (23) is transmitted to the permanent magnet (22) through the stator core (21) and directly to the permanent magnet (22). Also in this example, the heat transferred from the field winding (23) to the stator core (21) is dissipated in the middle as described above, so the demagnetization effect due to the heat via the stator core (21) is mitigated. It is thought that. On the other hand, the heat directly transmitted from the field winding (23) to the permanent magnet (22) is likely to demagnetize the permanent magnet (22) if no measures are taken.

<Effect in this embodiment>
However, also in this embodiment, the permanent magnet (22) has the surface (23) in contact with the field winding (23) by diffusing the heavy rare earth element from the surface (S) in contact with the field winding (23). The coercive force in S) is larger than the internal coercive force.

  Therefore, also in this embodiment, it is possible to suppress demagnetization due to heat from the surface (S) in contact with the field winding (23). In addition, since the content of the heavy rare earth element is given a gradient, a decrease in saturation magnetic flux density can be suppressed. That is, this embodiment can also obtain the same effect as that of the first embodiment.

<< Other Embodiments >>
Note that the heavy rare earth element may be diffused into the permanent magnet (22) also from the surface (S) other than that in contact with the field winding (23). In short, it is necessary to make a gradient of the content of the heavy rare earth element so that the content of the heavy rare earth element decreases from the outer peripheral surface of the permanent magnet (22) toward the inside.

  The method for introducing the heavy rare earth element is not limited to the grain boundary diffusion method. For example, the permanent magnet material may be included as an alloy.

  Moreover, you may form a rotor core (11) with a compact. Similarly, the stator core (21) may also be formed of compacted powder.

  Further, the number of teeth (211) of the stator (20) and the number of protrusions (111) of the rotor (10) are also examples, and are not limited to the example of the above embodiment.

  The configuration of each of the above embodiments can be applied not only to the electric motor but also to the generator.

  The present invention is useful as a rotating electric machine such as an electric motor.

1 Electric motor (rotary electric machine)
11 Rotor core 21 Stator core 22 Permanent magnet 23 Field winding (winding)
24 Armature winding (winding)
211 Teeth 212 Stator yoke 213 Slot

Claims (5)

A stator core (21) having a plurality of teeth (211) arranged at predetermined intervals in the circumferential direction of an annular stator yoke (212) and having slots (213) formed between these teeth (211) When,
A rotor core (11) opposed to the stator core (21) with a predetermined air gap;
Windings (23, 24) wound around the teeth (211) and accommodated in the slots (213);
A permanent magnet (22) provided in contact with a winding (23) in the slot (213) in a predetermined slot (213);
With
The permanent magnet (22) is a sintered magnet using a rare earth element, and the coercive force on the surface (S) in contact with the winding (23) is larger than the internal coercive force. machine. In claim 1,
The permanent magnet (22) has the coercive force adjusted by diffusing heavy rare earth elements so that the content decreases from the surface of the permanent magnet (22) toward the inside. Rotating electrical machine characterized by that. In claim 2,
The rotating electric machine according to claim 1, wherein the permanent magnet (22) includes a region where the heavy rare earth element is not diffused. In any one of Claim 2 to Claim 3,
The rotating electric machine according to claim 1, wherein the heavy rare earth element is diffused from a surface (S) in contact with the winding (23). In any one of Claims 2-4,
The rotary electric machine, wherein the heavy rare earth element is dysprosium (Dy) or terbium (Tb).

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