Rotary electric machine

Abstract

To provide a rotary electric machine capable of suppressing demagnetization in high temperature ranges while ensuring a torque of the rotary electric machine.SOLUTION: A second magnet 36 of a rotor 14 has an outer magnet 36B located outside a magnet pole 24 than the bent portion 40 and an inner magnet 36A located closer to the center of the magnet pole 24 than the bent portion 40. The outer magnet 36B has a lower residual magnetic flux density and a higher coercive force compared to the inner magnet 36A and a first magnet 32, and the width of the outer magnet 36B is wider than the width of the inner magnet 36A when viewed in an axial direction.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a rotating electrical machine including a cylindrical stator and a rotor concentrically disposed inside the stator.

Background Art

[0002] Conventionally, as a rotating electrical machine, an embedded magnet type rotating electrical machine in which permanent magnets are embedded in a rotor core to form magnetic poles has been used. The rotating electrical machine can output a combined torque of a magnet torque generated by permanent magnets embedded in the rotor core and a reluctance torque generated based on the magnetic anisotropy of the rotor core. In order to increase this output torque, a technique of arranging permanent magnets in two layers along the radial direction of the rotor core has been proposed.

[0003] For example, in Patent Document 1, as a technique of two-layer arrangement, a rotor including a first magnet loading portion and a second magnet loading portion located on the inner peripheral side of the first magnet loading portion is arranged at each magnetic pole of the rotor. Here, the first magnet loading portion includes a first magnet hole and a first magnet loaded in the first magnet hole. The second magnet loading portion includes a pair of second magnet holes symmetrically arranged with respect to the magnetic pole center and second magnets loaded in each of the second magnet holes. The second magnet hole has a broken line shape with a bent portion in an axial view.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a rotor with embedded permanent magnets like the rotating electrical machine shown in Patent Document 1, when the magnet width is increased to improve torque, the torque of the rotating electrical machine increases. However, as the armature reaction increases, significant demagnetization occurs in the high-temperature range, which may lead to a decrease in motor torque.

[0006] An object of the present invention is to provide a rotating electrical machine capable of suppressing demagnetization in a high-temperature range while ensuring the torque of the rotating electrical machine.

Means for Solving the Problems

[0007] The present invention has been made in view of such points, and the rotating electrical machine according to the present invention is a rotating electrical machine including a cylindrical stator and a rotor concentrically arranged inside the stator, wherein the rotor has a plurality of magnetic poles arranged in the circumferential direction, and each of the magnetic poles has a first magnet loading portion and a second magnet loading portion located on the inner peripheral side of the first magnet loading portion. The first magnet loading portion includes a first magnet hole and a first magnet loaded in the first magnet hole. The second magnet loading portion includes a pair of second magnet holes symmetrically arranged with respect to the center of the magnetic pole and a second magnet loaded in each of the second magnet holes. Each of the second magnet holes has a broken-line shape with a bent portion in an axial view. Each of the second magnets has an outer magnet located outside the magnetic pole with respect to the bent portion and an inner magnet located closer to the center of the magnetic pole than the bent portion. The outer magnet has a lower residual magnetic flux density and a higher coercive force compared to the inner magnet and the first magnet, and in the axial view, the width of the outer magnet is wider than the width of the inner magnet.

[0008] In a preferred embodiment, the inner magnet and the first magnet are NdFeB-based magnets, and the outer magnet is a SmFeN-based magnet. Further, in a preferred embodiment, the residual magnetic flux density of the outer magnet is 1.00 to 1.35 T at 20°C, and the coercive force of the outer magnet is 730 to 980 kA / m at 150°C.

Effects of the Invention

[0009] According to the present invention, it is possible to suppress demagnetization in a high temperature range while ensuring the torque of the rotating electrical machine.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] Hereinafter, the configuration of the rotating electrical machine 10 will be described with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of the rotating electrical machine 10. Further, FIG. 2 is a cross-sectional view of the rotor 14, which is a cross-section obtained by cutting the rotor 14 at the portion where the permanent magnets are arranged. FIG. 3 is an enlarged view around one magnetic pole 24. In FIG. 2, in order to make the shape of the magnet holes easy to see, the illustration of the magnets is omitted in one magnetic pole 24. Further, in the following description, the "axial direction", "radial direction", and "circumferential direction" mean the rotor axial direction, the rotor radial direction, and the rotor circumferential direction.

[0012] This rotating electrical machine 10 is a permanent magnet synchronous rotating electrical machine in which first and second magnets 32, 36 (36A, 36B), which are permanent magnets, are embedded inside a rotor core 22. Such a rotating electrical machine 10 may be mounted on an electric vehicle, for example, as a driving power source. The rotating electrical machine 10 includes a substantially cylindrical stator 12, a rotor 14 concentrically disposed inside the stator 12, and a rotating shaft 16 fixed to the center of the rotor 14. The stator 12 has a substantially cylindrical stator core 18 having a plurality of teeth formed on its inner circumference, and stator coils 20 wound around each tooth. The rotor 14 is disposed concentrically with the stator 12 inside the stator 12. A gap G having a substantially uniform distance exists between the outer peripheral surface of the rotor 14 and the inner peripheral surface of the stator 12.

[0013] The rotor 14 has a substantially cylindrical rotor core 22 and magnetic poles 24 formed by permanent magnets 32, 36 embedded in the rotor core 22. The rotating shaft 16 is fixed to the center of the rotor core 22. The rotating shaft 16 is supported by bearings (not shown) and rotates together with the rotor 14.

[0014] The rotor 14 is provided with an even number (eight in the illustrated example) of magnetic poles 24 arranged at equal intervals in the circumferential direction. The polarities of the even number of magnetic poles 24 are alternately reversed in the circumferential direction. One magnetic pole 24 is composed of a plurality (six in the illustrated example) of permanent magnets 32, 36 (36A, 36B) loaded in a plurality of magnet holes 30, 34 (four in the illustrated example). This will be described with reference to FIG. 3.

[0015] Each magnetic pole 24 has a two-layer structure including a first magnet loading portion 26 and a second magnet loading portion 28 provided radially inward of the first magnet loading portion 26. The first magnet loading portion 26 is provided near the outer peripheral edge of the rotor 14 and has a pair of first magnet holes 30 symmetrically arranged with respect to the magnetic pole center (i.e., d-axis Ld), and first magnets 32 loaded in the respective first magnet holes 30. The first magnet hole 30 is a hole that penetrates the rotor core 22 in the axial direction and has a substantially rectangular outer shape that is elongated in one direction when viewed in the axial direction. Each first magnet hole 30 is arranged at a predetermined inclination angle θ1 (θ1 < 90°) with respect to the d-axis Ld. As a result, as shown in FIG. 3, the two first magnet holes 30 form a substantially V-shape that opens radially outward. An outer center bridge 50, which is a part of the rotor core 22, is interposed between the two first magnet holes 30.

[0016] The first magnets 32 are loaded one by one into the respective first magnet holes 30. Each first magnet 32 also has a substantially rectangular outer shape when viewed in the axial direction, similar to the first magnet hole 30. Further, each first magnet 32 is magnetized in its thickness direction (short side direction). The dimension of the first magnet 32 in the width direction (long side direction) is sufficiently smaller than the dimension of the first magnet hole 30 in the width direction. Therefore, when the first magnet 32 is loaded into the first magnet hole 30, gaps are formed on both sides in the width direction of the first magnet 32. This gap functions as a flux barrier 37 that inhibits the flow of magnetic flux. The thickness of this flux barrier 37 is substantially the same as the thickness of the first magnet 32.

[0017] The second magnet loading portion 28 is provided radially inside the first magnet loading portion 26, and includes a pair of second magnet holes 34 and a plurality of second magnets 36 (36A, 36B) loaded in the second magnet holes 34. The pair of second magnet holes 34 are symmetrically arranged with respect to the d-axis Ld so as to form a substantially V-shaped or substantially U-shaped opening toward the radially outer side. Each of the second magnet holes 34 is also a hole that penetrates the rotor core 22 in the axial direction, similar to the first magnet hole 30. However, the second magnet hole 34 has an outer shape of a broken line shape having a bent portion 40 in the axial view. The second magnet hole 34 has a substantially V-shaped outer shape having a central side portion 34c extending from the bent portion 40 toward the center side of the magnetic pole 24 and an outer side portion 34o extending from the bent portion 40 toward the outer peripheral edge of the rotor 14.

[0018] Between the first magnet loading portion 26 and the second magnet loading portion 28, as will be described later, it becomes a magnetic path through which magnetic flux flows. The shape of the second magnet hole 34 is such that the widths L1, L2, L3 of this magnetic path increase as they approach the magnetic pole center (d-axis Ld). Specifically, the inclination angle θ2 of the central side portion 34c with respect to the d-axis Ld and the inclination angle θ3 of the outer side portion 34o are made smaller than the inclination angle θ1 of the first magnet hole 30. Further, in this example, the inclination angle θ2 is made larger than the inclination angle θ3. That is, θ1 > θ2 > θ3.

[0019] Two second magnets 36, 36 (36A, 36B) are loaded in the second magnet hole 34. The two second magnets 36A, 36B are arranged on both sides with the bent portion 40 interposed therebetween. That is, the second magnet 36 has an outer magnet 36B outside the magnetic pole 24 with respect to the bent portion 40 and an inner magnet 36A inside the magnetic pole 24 with respect to the bent portion 40. Here, both the inner magnet 36A and the outer magnet 36B are loaded avoiding the bent portion 40, and the width direction ends of the second magnet 36 are separated from the bent portion 40.

[0020] The outer magnet 36B and the inner magnet 36A, which are the second magnets 36, also have a substantially rectangular outer shape when viewed in the axial direction, and are magnetized in the thickness direction (short side direction). In the present embodiment, the inner magnet 36A and the first magnet 32 have the same shape, and the width and thickness are also the same. The thickness of the outer magnet 36B is the same as the thickness of the inner magnet 36A. Further, in the present embodiment, the width W1 of the outer magnet 36B is wider than the width W2 of the inner magnet 36A. By satisfying such a relationship, the torque of the rotating electrical machine 10 can be improved. According to the analysis by the inventor, it is preferable that (width W1 of the outer magnet 36B) / (width W2 of the inner magnet 36A) is in the range of 1.1 to 1.7 times.

[0021] In the present embodiment, the widthwise dimension of the central portion 34c and the widthwise dimension of the outer portion 34o are sufficiently larger than the widthwise dimension of the second magnet 36. Therefore, gaps where no magnets exist are formed at both ends of the second magnet hole 34. These gaps function as flux barriers 37, 38 that inhibit the flow of magnetic flux. Among these, the flux barrier 38 on the center side of the magnetic pole 24 bulges on both sides in the thickness direction of the second magnet hole 34 and has a larger thickness than the second magnet 36, as shown in FIG. 3.

[0022] The outer magnet 36B has a lower residual magnetic flux density and a higher coercive force compared to the inner magnet 36A and the first magnet 32. The type is not particularly limited as long as these relationships are satisfied. Specifically, the first magnet 32 and the second magnet 36 (inner magnet 36A and outer magnet 36B) can include SmFeN (samarium iron nitride)-based magnets, NdFeB (neodymium)-based magnets, or SmCo (samarium cobalt)-based magnets. It is more preferable that the inner magnet 36A and the first magnet 32 are NdFeB-based magnets, and the outer magnet 36B is an SmFeN-based magnet. Generally, for two permanent magnets, the relationship of "low residual magnetic flux density" and "high coercive force" is satisfied if the temperature ranges from room temperature, which is the operating environment temperature of the rotating electrical machine, to about 150°C, which is a high temperature. Therefore, in the present invention, the temperature conditions are not specified on the premise of this relationship.

[0023] The rotating electrical machine 10 configured as described above can suppress demagnetization in a high-temperature range while ensuring the torque of the rotating electrical machine 10. Specifically, in the present embodiment, the torque of the rotating electrical machine 10 decreases by an amount corresponding to the reduction in the residual magnetic flux density of the outer magnet 36B compared to the inner magnet 36A. However, by making the outer magnet 36B wider than the inner magnet 36A, the torque of the rotating electrical machine 10 can be maintained. At high temperatures, there is a possibility that the ratio of the coercive force to the maximum demagnetizing field may decrease due to the increase in the maximum demagnetizing field caused by the wider width. However, demagnetization can be suppressed by making the coercive force of the outer magnet 36B higher than that of the inner magnet 36A at high temperatures.

Example

[0024] Examples will be described below. First, as magnets to be arranged on the rotor, magnets A, B, and magnets 1 to 3 with magnetic characteristics shown in Table 1 and FIGS. 4(a) and 4(b) below were prepared. The residual magnetic flux density and coercive force shown below are the residual magnetic flux density at 20°C and the coercive force at 150°C, respectively, and these were measured in accordance with JIS C2501:2019.

[0025]

Table 1

[0026] (Example 1) Using magnet A and magnet 1 with the characteristics shown in Table 1, a rotor core was fabricated as shown in Table 2 below. Specifically, magnet A with a high residual magnetic flux density Br (1.40 T) and a low coercive force Hk characteristic (630 kA / m at 150°C) was arranged as the inner magnet 36A of the first magnet 32 and the second magnet 36 in the rotor. Next, magnet 1 with a low residual magnetic flux density Br (1.35 T) and a high coercive force Hk characteristic (980 kA / m at 150°C) was made 1.4 times wider than the other magnets and partially arranged as the outer magnet 36B. A rotating electrical machine (motor) using this rotor was fabricated, and the maximum torque of the rotating electrical machine and the maximum demagnetizing field in the high-temperature range were measured, and the ratio of the torque to a specific value and the ratio of the coercive force to the maximum demagnetizing field were calculated, respectively. The results are shown in FIG. 5.

[0027] (Examples 2 and 3) A rotating electrical machine was fabricated in the same manner as in Example 1. The differences from Example 1 are that, as shown in Table 2 below, in Example 2, Magnet 2 having the magnetic characteristics shown in Table 1 was used for the outer magnet 36B, and in Example 3, Magnet 3 having the magnetic characteristics shown in Table 1 was used for the outer magnet 36B. For these, the ratio of torque and the ratio of coercive force / maximum demagnetizing field were calculated respectively. The results are shown in FIG. 5.

[0028] (Comparative Examples 1 and 2) A rotating electrical machine was fabricated in the same manner as in Example 1. The difference of Comparative Example 1 from Example 1 is that, as shown in Table 2 below, for the first magnet 32, the inner magnet 36A, and the outer magnet 36B, Magnet A having the magnetic characteristics shown in Table 1 was used, and the sizes and shapes of all the magnets were made the same. The difference of Comparative Example 2 from Example 1 is that for the first magnet 32, the inner magnet 36A, and the outer magnet 36B, Magnet A having the magnetic characteristics shown in Table 1 was used. For these, the ratio of torque and the ratio of coercive force / maximum demagnetizing field were calculated respectively. The results are shown in FIG. 5.

[0029] (Comparative Examples 3 and 4) A rotating electrical machine was fabricated in the same manner as in Example 1. The difference of Comparative Example 3 from Example 1 is that, as shown in Table 2 below, for the first magnet 32, the inner magnet 36A, and the outer magnet 36B, Magnet B having the magnetic characteristics shown in Table 1 was used, and the sizes and shapes of all the magnets were made the same. The difference of Comparative Example 4 from Example 1 is that for the first magnet 32, the inner magnet 36A, and the outer magnet 36B, Magnet B having the magnetic characteristics shown in Table 1 was used. For these, the ratio of torque and the ratio of coercive force / maximum demagnetizing field were calculated respectively. The results are shown in FIG. 5.

[0030] (Comparative Examples 5 - 7) A rotating electrical machine was fabricated in the same manner as in Example 1. The differences between Comparative Examples 5 to 7 and Example 1 are that, as shown in Table 2 below, magnets 1 to 3 with the magnetic characteristics shown in Table 1 were used for the first magnet 32, the inner magnet 36A, and the outer magnet 36B, respectively, and the sizes and shapes of all the magnets were made the same. For these, the ratio of torque and the ratio of coercive force / maximum demagnetizing field were calculated respectively. The results are shown in Fig. 5.

[0031]

Table 2

[0032] (Results and Discussion) Here, when the results of Comparative Example 1 and Comparative Example 2 are examined, in Comparative Example 2, compared with Comparative Example 1, the torque has improved by about 5% due to widening the outer magnet 36N of the second magnet 36 (see Fig. 5(a)). On the other hand, at high temperatures, the ratio of coercive force / maximum demagnetizing field decreases due to an increase in the maximum demagnetizing field (see Fig. 5(b)).

[0033] Similarly, in the results of Comparative Example 4, the torque has improved by about 5% due to widening the outer magnet 36B of the second magnet 36. On the other hand, at high temperatures, the ratio of coercive force / maximum demagnetizing field decreases due to an increase in the maximum demagnetizing field. Also, when the results of Comparative Example 1, Comparative Example 3, and Comparative Examples 5 to 7 are examined, the magnitude of the torque (see Fig. 5(a)) is approximately proportional to the magnitude of the residual magnetic flux density Br (see Fig. 4(a)).

[0034] Here, in Examples 1 to 3, compared with Comparative Example 1, there is a possibility that the torque may decrease due to reducing the residual magnetic flux density of the outer magnet 36B. However, in Examples 1 to 3, compared with Comparative Example 1, the torque is larger than that of Comparative Example 1 because the width of the outer magnet 36B is widened.

[0035] On the one hand, in Examples 1 to 3, compared with Comparative Example 1, by widening the outer magnet 36B, originally, at high temperatures, as in Comparative Example 2, at high temperatures, with the increase in the maximum demagnetizing field, there is a possibility that the ratio of coercive force to maximum demagnetizing field may decrease. However, since the magnets 1 to 3 of Examples 1 to 3 have a higher coercive force at high temperatures than the magnet A of Comparative Example 1, it is considered that, unlike Comparative Example 2, the decrease in the ratio of coercive force to maximum demagnetizing field did not occur.

[0036] From the above, it is considered that the rotating electrical machines of Examples 1 to 3 were able to suppress demagnetization in the high-temperature range while ensuring the torque of the rotating electrical machine. Here, if the outer magnet 36B has a lower residual magnetic flux density and a higher coercive force compared to the inner magnet 36A and the first magnet 32, such an effect can be expected. From the results described above, the residual magnetic flux density of the outer magnet 36B is preferably 1.00 to 1.35 T in the state of 20 °C, and the coercive force of the outer magnet 36B is preferably 730 to 980 kA / m in the state of 150 °C.

[0037] Furthermore, in the state of 20 °C, the residual magnetic flux density Br of the outer magnet 36B is preferably smaller in the range of 0.05 to 0.40 T compared to the residual magnetic flux density Br of the inner magnet 36A and the first magnet 32. Furthermore, in the state of 150 °C, the coercive force Hk of the outer magnet 36B is preferably larger in the range of 100 to 510 kA / m compared to the coercive force Hk of the inner magnet 36A and the first magnet 32. Also, (width W1 of the outer magnet 36B) / (width W2 of the inner magnet 36A) is 1.4 times, but according to the analysis by the inventor, it is known that the range of 1.1 to 1.7 times is preferable.

[0038] As described above, the embodiments of the present invention have been described in detail, but the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims.

Explanation of Reference Numerals

[0039] 10: Rotating electrical machine, 12: Stator, 14: Rotor, 16: Rotating shaft, 18: Stator core, 20: Stator coil, 22: Rotor core, 24: Magnetic pole, 26: First magnet loading portion, 28: Second magnet loading portion, 30: First magnet hole, 32: First magnet (permanent magnet), 34: Second magnet hole, 36: Second magnet (permanent magnet), 36A: Inner magnet, 36B: Outer magnet, 40: Bent portion

Claims

1. A rotating electrical machine comprising a cylindrical stator and a rotor concentrically disposed inside the stator, wherein the rotor has a plurality of magnetic poles arranged in the circumferential direction, each of the magnetic poles having a first magnet loading portion and a second magnet loading portion located on the inner circumferential side of the first magnet loading portion, the first magnet loading portion including a first magnet hole and a first magnet loaded in the first magnet hole, the second magnet loading portion including a pair of second magnet holes symmetrically arranged with respect to the center of the magnetic pole and a second magnet loaded in each of the second magnet holes, each of the second magnet holes having a broken line shape with a bent portion in an axial view, each of the second magnets having an outer magnet located outside the magnetic pole with respect to the bent portion and an inner magnet located closer to the center of the magnetic pole than the bent portion, the outer magnet having a lower residual magnetic flux density and a higher coercive force compared to the inner magnet and the first magnet, wherein, in the axial view, the width of the outer magnet is wider than the width of the inner magnet. A rotating electrical machine characterized by this.

2. The rotating electrical machine according to claim 1, wherein the inner magnet and the first magnet are NdFeB-based magnets, and the outer magnet is a SmFeN-based magnet.

3. The rotating electrical machine according to claim 1, wherein the residual magnetic flux density of the outer magnet is 1.00 to 1.35 T at 20°C, and the coercive force of the outer magnet is 730 to 980 kA / m at 150°C.

Images