Patent Application
20230223805
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2022-003046, filed on Jan. 12, 2022, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a rotor and a rotary electric machine.
In an embedded magnet type rotary electric machine in which permanent magnets are embedded in a rotor to form magnetic poles, the combined torque of the magnet torque generated by the permanent magnets and the reluctance torque generated based on the magnetic anisotropy of the rotor core is output torque. Conventionally, in order to increase the output torque, a technique has been proposed in which permanent magnets are arranged in a plurality of layers along the radial direction of the rotor as disclosed in, for example, International Publication No. 2020/057847 (Patent Document 1) and Japanese Patent Application Publication No. 2020-137139 (Patent Document 2).
The rotary electric machine in which permanent magnets are arranged in a plurality of layers along the radial direction of the rotor can increase the output torque. However, magnet mounting holes for disposing the permanent magnets therein are provided in the rotor core, and stress concentration due to centrifugal force caused by the rotation of the rotor occurs in the bridge portions formed between the magnet mounting holes. The centrifugal force that causes stress concentration increases as the rotation speed of the rotor increases. Therefore, in order to increase the rotational speed of the rotor in the conventional rotary electric machine, there is room for improvement in the mechanical strength of the rotor of rotary electric machines including the rotary electric machines disclosed in Patent Documents 1 and 2.
Therefore, an object of the present disclosure is to provide a rotor having mechanical strength strong enough for high-speed rotation of a rotary electric machine.
In one aspect of the present disclosure, there is provided a rotor that is rotatably and concentrically disposed inside a stator and in which a plurality of magnetic poles arranged in a circumferential direction with a q-axis interposed therebetween are formed, the rotor including: a rotor core in which magnet mounting holes, which are provided in a plurality of layers along a radial direction and are arranged symmetrically in the circumferential direction about a d-axis, are formed for each of the magnetic poles; and magnets disposed in the magnet mounting holes, respectively, wherein the rotor core includes a first bridge portion, a second bridge portion, a third bridge portion, and a fourth bridge portion, where the first bridge portion is provided between a pair of first magnet mounting holes, which are included in the magnet mounting holes and are adjacent to each other across the d-axis, the second bridge portion is provided between a pair of second magnet mounting holes, which are located further inward than the pair of first magnet mounting holes in the radial direction and are adjacent to each other across the d-axis, the third bridge portion is provided between an outer peripheral surface of the rotor core and the first magnet mounting hole, and the fourth bridge portion is provided between the outer peripheral surface of the rotor core and the second magnet mounting hole, and wherein when a smallest width of the first bridge portion is represented by L1, a smallest width of the second bridge portion is represented by L2, a smallest width of the third bridge portion is represented by L3, and a smallest width of the fourth bridge portion is represented by L4, a relationship of L3<L1<L4<L2 is satisfied.
In the above rotor, the rotor core may further satisfy a relationship of 3.0≤L2/L1≤3.5.
In the above rotor, the rotor core may further satisfy a relationship of 1.5≤L2/L4≤2.2.
In the above rotor, in one of the magnetic poles, the first magnet mounting holes may be provided symmetrically in the circumferential direction about the d-axis across the first bridge portion through which the d-axis passes, and at least one of the magnets may be disposed in each of the first mounting holes.
In the above rotor, in one of the magnetic poles, the second magnet mounting holes may be provided symmetrically in the circumferential direction about the d-axis across the second bridge portion through which the d-axis passes, and at least one of the magnets may be disposed in each of the second magnet mounting holes.
In the above rotor, two or more of the magnets may be disposed in each of the second magnet mounting holes.
In the above rotor, magnets having different dimensions when viewed in an axial direction may be disposed in the second magnet mounting holes.
In the above rotor, in one of the magnetic poles, each of the second magnet mounting holes may have a polygonal line shape having one or more bending points when viewed in the axial direction, and at least one of the magnet may be provided in each of regions on both sides of the bending points.
In the above rotor, the magnets may have a curved shape when viewed in the axial direction.
In another aspect of the present disclosure, there is provided a rotary electric machine including the above rotor.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of the respective portions may not be illustrated so as to completely coincide with actual ones. In addition, details may be omitted in some drawings.
[Configuration of Rotary Electric Machine]
The rotary electric machine 10 includes a substantially cylindrical stator 12, the rotor 14 disposed concentrically inside the stator 12, and a rotating shaft 16 fixed to the center of the rotor 14. The stator 12 includes a substantially cylindrical stator core 18 having a plurality of teeth (not illustrated) formed on the inner periphery thereof, and stator coils 20 wound around the respective teeth. A gap G having a substantially uniform distance is formed between the outer peripheral surface of the rotor 14 and the inner peripheral surface of the stator 12.
In the present embodiment, the stator 12 has three phases: a U phase, a V phase, and a W phase, and the stator coil 20 is wound by distributed winding (not illustrated). The stator core 18 is provided with 24 slots in the circumferential direction, and coils are arranged in the respective slots. That is, the rotary electric machine 10 of the present embodiment forms a 24-slot 8-pole motor.
In the rotor 14, magnetic poles 24 (see
As illustrated in
The first magnet mounting holes 30 are arranged symmetrically in the circumferential direction about the d-axis in each magnetic pole, and each first magnet mounting hole 30 is a hole penetrating through the rotor core 22 in the axial direction. Each of the first magnet mounting holes 30 has a substantially rectangular outer shape elongated in one direction when viewed in the axial direction. Each first magnet mounting hole 30 is inclined so as to be farther from the d-axis at closer distances to the outer peripheral edge of the rotor 14, whereby the two first magnet mounting holes 30 form a substantially V-shape as illustrated in
Similarly to the first magnet mounting hole 30, each outer magnet 32 has a substantially rectangular outer shape when viewed in the axial direction. Each outer magnet 32 is magnetized in its thickness direction (the short axis direction). The dimension of the outer magnet 32 in the width direction (the long axis direction) is sufficiently smaller than the dimension of the first magnet mounting hole 30 in the width direction. Therefore, when the outer magnet 32 is mounted in the first magnet mounting hole 30, gaps are formed at both sides of the outer magnet 32 in the width direction. This gap functions as a flux barrier that inhibits the flow of magnetic flux.
The second magnet mounting holes 34 are located further in than the first magnet mounting holes 30 in the radial direction, and a pair of the second magnet mounting holes 34 arranged symmetrically in the circumferential direction about the d-axis are provided so as to form a substantially V shape or a substantially U shape. Similarly to the first magnet mounting holes 30, each second magnet mounting hole 34 is a hole that penetrates through the rotor core 22 in the axial direction. However, the second magnet mounting hole 34 has an outer shape of a polygonal line shape having one or more bending points 40 when viewed in the axial direction. More specifically, the second magnet mounting hole 34 of the present embodiment has a substantially V-shaped outer shape having a center-side portion 34c extending from the bending point 40 toward the center of the magnetic pole 24 and an outer-side portion 34o extending from the bending point 40 toward the outer peripheral edge of the rotor 14. A second bridge portion 52, which is a part of the rotor core 22, is provided between the two second magnet mounting holes 34. The second bridge portion 52 will be described in detail later.
Two inner magnets 36 are mounted in the second magnet mounting hole 34. The two inner magnets 36 are disposed at both sides of the bending point 40. That is, the inner magnet 36a is mounted in the center-side portion 34c of the second magnet mounting hole 34, and the inner magnet 36b is mounted in the outer-side portion 34o. Similarly to the outer magnets 32, the inner magnets 36a and 36b also have a substantially rectangular outer shape when viewed in the axial direction, and are magnetized in its thickness direction (the short axis direction).
Next, the magnetic flux flowing through the rotor 14 of the present embodiment will be described with reference to
The magnet torque increases as the amount of the magnet magnetic flux 48 flowing through the outer magnets 32 and the inner magnets 36a and 36b increases in the rotor core 22. In the present embodiment, the first magnet mounting hole 30 and the second magnet mounting hole 34 are provided, and the outer magnet 32 and the inner magnets 36a and 36b are mounted in the respective magnet mounting holes to form a two layer structure. Therefore, it is possible to increase the number of permanent magnets and increase the total amount of the magnet magnetic flux 48 as compared with the case of a single-layer arrangement. In the present embodiment, two inner magnets 36a and 36b are mounted in one second magnet mounting hole 34. As a result, the number of permanent magnets can be increased and the magnet magnetic flux 48 can be increased as compared with the case in which only one permanent magnet is mounted in one second magnet mounting hole 34. By increasing the amount of the magnet magnetic flux 48, the output torque of the rotary electric machine 10 can also be improved. Leakage magnetic flux may be generated in which the magnet magnetic flux emitted from the north pole of one outer magnet 32 flows directly to the south pole of the one outer magnet 32. Similarly, leakage magnetic flux may be also generated in the inner magnets 36a and 36b. The leakage magnetic flux does not contribute to the output of the rotary electric machine 10. The leakage magnetic flux will be described in detail later.
Here, the first bridge portion 50, the second bridge portion 52, a third bridge portion 54, and a fourth bridge portion 56 provided in the rotor core 22 will be described with reference to
The first bridge portion 50 is provided between a pair of the first magnet mounting holes 30 adjacent to each other across the d-axis. The smallest width of the first bridge portion 50 is L1. In the present embodiment, the opposed side edges of the pair of the first magnet mounting holes 30 are parallel to the d-axis, but in the case that the opposed side edges are inclined with respect to the d-axis, the width of the part where the opposed side edges are closest to each other is defined as the smallest width L1.
The second bridge portion 52 is provided between a pair of the second magnet mounting holes 34 adjacent to each other across the d-axis. The smallest width of the second bridge portion 52 is L2. In the present embodiment, the opposed side edges closest to the d-axis of the pair of the second magnet mounting holes 34 are parallel to the d-axis. However, in the case that the opposed side edges are inclined with respect to the d-axis, the width of the part where the opposed side edges are closest to each other is defined as the smallest width L2.
The third bridge portion 54 is provided between a first outer peripheral surface 22a of the rotor core 22 and the first magnet mounting hole 30. The first outer peripheral surface 22a is an outer peripheral surface located further outward than the first magnet mounting hole 30 in the radial direction. The smallest width of the third bridge portion 54 is L3.
The fourth bridge portion 56 is provided between a second outer peripheral surface 22b of the rotor core 22 and the second magnet mounting hole 34. The second outer peripheral surface 22b is an outer peripheral surface located further outward than the second magnet mounting hole 34 in the radial direction. The smallest width of the fourth bridge portion 56 is IA.
Both the first outer peripheral surface 22a and the second outer peripheral surface 22b have arcs having the same radius centered on the rotation center axis AX. Both of the first outer peripheral surface 22a and the second outer peripheral surface 22b form a gap G with the stator 12 positioned outside the rotor 14 (see
The smallest width L1 of the first bridge portion 50, the smallest width L2 of the second bridge portion 52, the smallest width L3 of the third bridge portion 54, and the smallest width IA of the fourth bridge portion 56 have a relationship represented by the following expression (1).
L3<L1<L4<L2 (1)
In
Therefore, in the present embodiment, the smallest width L1 of the first bridge portion 50, the smallest width L2 of the second bridge portion 52, the smallest width L3 of the third bridge portions 54, and the smallest width L4 of the fourth bridge portions 56 in the rotor core 22 have the relationship presented in expression (1). That is, the smallest width L2 of the second bridge portions 52, which is the most severe portion in terms of stresses, is configured to be the largest, and the other bridge portions are also configured in accordance with the order of stresses.
The rotor 14 of the present embodiment can support high-speed rotation of the rotary electric machine 10 by satisfying the relationship defined by expression (1).
Since almost no stresses is applied to the third bridge portion 54, the smallest width L3 of the third bridge portion 54 can be made very thin as compared with the smallest widths of the other bridge portions. In other words, the smallest width L3 is only required to satisfy the relationship of L3≤L1.
Next, with reference to
Therefore, the ranges of the L2/L1 ratio and the L2/L4 ratio are set so that the stress is within the mechanical strength of the electromagnetic steel plate constituting the rotor core 22 and the rotary electric machine 10 can operate in a high-output and low-loss state. The reason why the smallest width L3 of the third bridge portion 54 is not taken into consideration is that, as described above, almost no stresses acts on the third bridge portion 54, and the smallest width L3 of the third bridge portion 54 can be made very thin compared with the smallest widths of the other bridge portions.
First, the L2/L1 ratio will be described. In
In
On the other hand, the torque [P.U.]=1.0 indicates the required torque of the rotary electric machine 10, and when the torque [P.U.] becomes lower than 1.0, the rotary electric machine 10 cannot output the required torque. On the other hand, when the torque [P.U.] is 1.0 or greater, the rotary electric machine 10 can output the required torque. The torque [P.U.] decreases as the L2/L1 ratio increases, that is, as the smallest width L2 increases. When the L2/L1 ratio becomes larger than 3.5, the torque [P.U.] becomes smaller than 1.0. This is because the leakage magnetic flux 49 increases as the smallest width L2 increases, and the output efficiency of the rotary electric machine 10 thereby decreases.
Therefore, the rotor 14 of the present embodiment has a relationship represented by the following expression (2).
3.0≤L2/L1≤3.5 (2)
Next, the L2/L4 ratio will be described. As illustrated in
In
On the other hand, the torque [P.U.]=1.0 indicates the required torque of the rotary electric machine 10, and when the torque [P.U.] becomes lower than 1.0, the rotary electric machine 10 cannot output the required torque. On the other hand, when the torque [P.U.] is 1.0 or greater, the rotary electric machine 10 can output the required torque. The torque [P.U.] decreases as the L2/L4 ratio increases, that is, as the smallest width L2 increases. When the L2/L4 ratio becomes larger than 2.2, the torque [P.U.] becomes smaller than 1.0. This is because the leakage magnetic flux 49 increases as the smallest width L2 increases, and the output efficiency of the rotary electric machine 10 thereby decreases.
Therefore, the rotor 14 of the present embodiment has a relationship represented by the following expression (3).
1.5≤L2/L4≤2.2 (3)
As described above, the rotor 14 of the present embodiment can obtain a high output without losing the magnetic force because an increase in the leakage magnetic flux 49 is reduced while the mechanical strength of the rotor core 22 is ensured. The rotor 14 can support high-speed rotation of the rotary electric machine 10 because the mechanical strength of the rotor core 22 is ensured.
The magnitude of the centrifugal force applied to one electromagnetic steel plate forming the rotor core 22 is the same even when the length of the rotor core 22 in the axial direction changes. Therefore, as long as the rotor core 22 has a shape that satisfies the above-described conditions when viewed in the axial direction, the length of the rotor core 22 in the axial direction may be different and may be set in various ways. In other words, the length of the rotor core 22 in the axial direction can be appropriately set, but the shape of the rotor core 22 when viewed in the axial direction is required to satisfy the above-described conditions.
Next, variations will be described with reference to
<First Variation>
As illustrated in
In the rotor 114 having such a configuration, the relationship among the smallest width L1 of the first bridge portion 50, the smallest width L2 of the second bridge portion 52, the smallest widths L3 of the third bridge portion 54, and the smallest width L4 of the fourth bridge portion 56 is set so as to satisfy the above expression (1). This configuration ensures the mechanical strength of the rotor 114, and allows the rotor 114 to support high-speed rotation of the rotary electric machine 10. Further, by satisfying the relationships of expression (2) and expression (3), it is possible to suppress an increase in the leakage magnetic flux 49 while ensuring the mechanical strength of the rotor core 22, and to obtain a high output without losing the magnetic force.
<Second Variation>
As illustrated in
In the rotor 214 having such a configuration, the relationship among the smallest width L1 of the first bridge portion 50, the smallest width L2 of the second bridge portion 52, the smallest width L3 of the third bridge portion 54, and the smallest width L4 of the fourth bridge portion 56 is set so as to satisfy the above expression (1). This configuration ensures the mechanical strength of the rotor 114, and allows the rotor 114 to support high-speed rotation of the rotary electric machine 10. Further, by satisfying the relationships of expression (2) and expression (3), it is possible to suppress an increase in the leakage magnetic flux 49 while ensuring the mechanical strength of the rotor core 22, and to obtain a high output without losing the magnetic force.
Although some embodiments of the present invention have been described in detail, the present invention is not limited to the specific embodiments but may be varied or changed within the scope of the present invention as claimed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-003046 | Jan 2022 | JP | national |
