JP7784341B2 - rotating electrical machines - Google Patents

Description

The present invention relates to a rotating electric machine having a rotor structure that can reduce back electromotive force.

Rotating electric machines are used as electric motors in trains and automobiles. Rotating electric machines typically have a cylindrical stator and a rotor that is rotatably supported inside the stator. The rotor is formed by stacking electromagnetic steel sheets in the direction of the rotation axis. Multiple magnets are embedded in these electromagnetic steel sheets, with magnetic poles of different magnetic properties arranged alternately in the circumferential direction of rotation.

In rotating electrical machines consisting of a rotor and stator, magnetic changes caused by rotor rotation generate back electromotive force (line voltage) in the stator coil. If the maximum value of the back electromotive force becomes large, it becomes necessary to limit the upper limit of the voltage applied to the coil, which poses the problem of reduced motor torque.

Patent Document 1 describes a permanent magnet rotating electric machine in which deep recesses are provided on the surface of the rotor's outer periphery on the q-axis in order to reduce the maximum value of line voltage without reducing the torque constant. Patent Document 2 describes a rotating electric machine in which recesses are provided on the surface of the rotor core surrounded by magnets at each of the south and north poles of the rotor surface in order to reduce torque ripple.

JP 2012-16189 A Patent No. 2017-70040

Patent Document 1 provides magnetic resistance on the q-axis between the magnetic poles, making it difficult to apply to rotating electrical machines that utilize reluctance torque. Patent Document 2 provides magnetic resistance separately from the flux barrier, which raises concerns about an average reduction in torque.

A rotating electric machine according to the present invention comprises a stator having slots, and a rotor having magnetic poles formed by magnets embedded in flux barriers , the flux barriers extending circumferentially of the rotor about the d-axis and having tip regions on both sides facing the outer circumferential surface of the rotor, the magnets being embedded in portions of the rotor along the circumferential direction, the tip regions being formed as space where no magnets are embedded, each magnetic pole of adjacent magnetic pole pairs circumferentially of the rotor has a bridge in the tip region, the bridge being one of two types: an outer bridge formed on the outer circumferential surface of the rotor in the tip region , and an inner bridge located in a middle portion of the tip region on the inner diameter side of the outer bridge, the number of outer bridges and inner bridges in a magnetic pole pair is the same, and the arrangement of the outer bridges and inner bridges is symmetrical with respect to one of the d-axis and q-axis and asymmetrical with respect to the other axis.

Here, it is preferable that the rotating electric machine has an outer bridge and a middle bridge at one pole of the magnetic pole pair that are asymmetrical with respect to the d-axis, and an outer bridge and a middle bridge at the other pole of the magnetic pole pair that are symmetrical with respect to the q-axis with respect to the arrangement at one pole of the magnetic pole pair.

It is also preferable that in one pole of the magnetic pole pair, only the outer bridge is arranged symmetrically with respect to the d axis , and in the other pole of the magnetic pole pair, only the middle bridge is arranged symmetrically with respect to the d axis.

Here, the rotor of the rotating electric machine has multiple flux barriers in the radial direction, and the above-mentioned arrangement of the outer bridge and middle bridge is preferably applied to the flux barriers arranged on the inner, outermost side of the flux barriers.

Furthermore, when the open angle between adjacent teeth is α and the angle formed by the line connecting the circumferential center of the two bridges sandwiching the d-axis at the magnetic pole and the center of the rotation axis is β, it is preferable that the rotating electric machine satisfy the condition α×N≦β≦α×(N+1), where N is an integer greater than or equal to 1.

Furthermore, the rotor of a rotating electric machine may be formed by stacking partial rotors in the direction of the rotation axis, with the outer bridges and middle bridges interchanged.

The rotating electric machine of the present invention is capable of suppressing back electromotive force that occurs as the rotor rotates.

1 is a partial cross-sectional view of a rotating electric machine according to the present invention; 4 shows the relationship between the tooth opening angle and the bridge opening angle of the rotating electric machine of the present invention. 10 is a cross-sectional view showing the arrangement of bridges in the magnetic pole pairs of the rotors of Examples 1 to 4. FIG. 10 is a cross-sectional view showing the arrangement of bridges in the magnetic pole pairs of the rotors of Comparative Examples 1 to 3. FIG. 10A and 10B are cross-sectional views showing the arrangement of bridges in the magnetic pole pairs of the rotors of Comparative Examples 4 and 5. 1A and 1B are diagrams showing back electromotive force waveforms in Comparative Examples 1 to 3, where FIG. 1A is a waveform diagram for one electrical angle cycle, and FIG. 1B is an enlarged diagram for an electrical angle of 60°±30°. The back electromotive voltage waveforms for Examples 1 and 4 and Comparative Examples 1 and 2 are similar to those shown in FIG. 1A and 1B are diagrams comparing the back electromotive force waveforms of Examples 1 to 4, where FIG. 1A is a diagram comparing Examples 1 and 2, and FIG. 1B is a diagram comparing Examples 3 and 4. 10 is a graph comparing peak voltage/fundamental wave amplitude between an example and a comparative example. The back electromotive voltage waveforms for Example 1 and Comparative Examples 4 and 5 are similar to those shown in FIG. 1 is a diagram illustrating the positions where peak voltages occur in Example 1 and Comparative Examples 1 and 2. FIG. 10 shows the analysis results of the magnetic flux density distribution in Example 1. 10 shows the analysis results of the magnetic flux density distribution of Comparative Example 1. 10 shows the analysis results of the magnetic flux density distribution of Comparative Example 2. 7 shows a back electromotive force waveform similar to that shown in FIG. 6 for a configuration in which Example 1 and the comparative example are alternately stacked.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, specific shapes, materials, directions, numerical values, etc. are examples intended to facilitate understanding of the present invention and can be modified as appropriate to suit the application, purpose, specifications, etc. Furthermore, it is anticipated from the outset that the components of the embodiments and variations described below may be selectively combined.

Figure 1 shows a partial cross-sectional view of a rotating electric machine 10 of the present invention. The rotating electric machine 10 includes a stator 20 and a rotor 30. The rotating electric machine 10 is an electric motor that generates a rotating magnetic field in the stator 20 and rotates the rotor 30 around its axis of rotation. Figure 1 shows a cross-section of a sector-shaped portion of the stator 20 and rotor 30.

The stator 20 has a hollow cylindrical shape. It is formed by stacking multiple electromagnetic steel plates along the rotation axis direction. The stator 20 has a structure in which multiple slots 21 and teeth 22 are arranged alternately at equal intervals in the circumferential direction. Coils are wound around the slots 21. The teeth 22 face the outer periphery of the rotor 30 and act as surfaces that receive magnetic flux from the rotor 30. A back yoke 23 is arranged on the outer periphery of the slots 21 and teeth 22. The back yoke 23 is an iron core that connects the magnetic flux between each tooth 22 and forms a magnetic circuit.

The rotor 30 is cylindrical. It is arranged inside the hollow cylindrical stator 20 so that it can rotate around the rotation axis. The rotor 30 is arranged with a gap between its outer circumferential surface and the inner circumferential surface of the stator 20. The rotor 30 is constructed by stacking multiple electromagnetic steel plates along the rotation axis direction.

The rotor 30 has a flux barrier 32 with a magnet 31 embedded inside. The flux barrier 32 is an area with a lower magnetic permeability than the electromagnetic steel sheets that make up the rotor 30, and is composed, for example, of a space provided inside the rotor 30. The flux barrier 32 prevents the magnetic flux emitted from the magnet 31 from leaking out the side of the rotor 30, thereby increasing the magnetic flux density on the outer surface of the rotor 30.

Multiple flux barriers 32 may be provided for each magnetic pole. For example, multiple flux barriers 32 may be provided in the radial direction of the rotor 30. In this embodiment, the rotor 30 has two flux barriers, a first flux barrier 32a and a second flux barrier 32b, arranged along the radial direction.

The magnets 31 embedded in the flux barrier 32 form the magnetic poles 33 of the rotor 30. The magnets 31 are arranged so that the direction of the magnetic flux in each magnetic pole 33 is oriented radially around the rotor 30. In other words, the center of the magnetic flux in each magnetic pole 33 coincides with the d-axis. The magnets 31 are arranged so that the magnetization directions of adjacent magnetic poles 33 in the circumferential direction are different, and magnetic pole pairs, south magnetic poles 33S and north magnetic poles 33N, are formed alternately along the circumferential direction. In the rotor 30, the centers of the south magnetic poles 33S and north magnetic poles 33N coincide with the q-axis.

The flux barrier 32 extends circumferentially around the rotor 30, centered on the d-axis, with both ends curved toward the outer peripheral surface of the rotor 30. A bridge 35 is formed in the end regions 34 (first end region 34a, second end region 34b) at both ends of the first flux barrier 32a. The first end region 34a of the first flux barrier 32a in one magnetic pole 33 is adjacent to the second end region 34b of the first flux barrier 32a in another magnetic pole 33 adjacent to that magnetic pole 33.

In this embodiment, it is preferable that both ends of the first flux barrier 32a, which is the flux barrier 32 located on the outermost side of the rotor 30, be defined as tip regions 34 (first tip region 34a, second tip region 34b). However, both ends of other flux barriers, such as the second flux barrier 32b, may also be defined as tip regions 34 (first tip region 34a, second tip region 34b).

In this embodiment, two types of bridges 35 are used: outer bridges 35a and middle bridges 35b. The outer bridges 35a are parts that connect the outer peripheral surface of the rotor 30 to the tip of the flux barrier 32 near the outer peripheral surface of the rotor 30 where no recesses or the like are provided. The middle bridges 35b are parts that connect the tip of the flux barrier 32 to recesses provided on the outer peripheral surface of the rotor 30 or gaps provided inside the rotor 30. In other words, due to the recesses provided on the outer peripheral surface of the rotor 30 or the gaps provided inside the rotor 30, the middle bridges 35b are positioned more inward than the outer bridges 35a with respect to the outer peripheral surface of the rotor 30.

In each magnetic pole 33, the first tip region 34a and second tip region 34b of the first flux barrier 32a are positioned symmetrically with respect to the d-axis. Furthermore, the structure of each magnetic pole 33 is symmetrical with respect to the q-axis, except for the configuration of the bridge 35. Either an outer bridge 35a or an inner bridge 35b is applied to the first tip region 34a and the second tip region 34b, respectively. Furthermore, in consideration of the rotational balance of the rotor 30, it is preferable to arrange the bridges 35 periodically along the circumferential direction.

Figure 2 shows the relationship between the spacing angle of adjacent teeth 22 and the bridge spacing angle of the bridge 35. Here, the angle formed by a line connecting the radial center lines of adjacent teeth 22 and the rotation axis is defined as the tooth spacing angle α. When the outer bridge 35a is arranged in the first tip region 34a and the second tip region 34b, the angle formed by a line connecting the circumferential center of the outer bridge 35a and the center of the rotation axis is defined as the bridge spacing angle β. The bridge spacing angle β and tooth spacing angle α of the rotating electric machine 10 of the present invention are formed to satisfy α × N ≦ β ≦ α × (N + 1), where coefficient N is an integer greater than or equal to 1. Note that while Figure 2 shows that the middle bridge 35b is arranged in the second tip region 34b, the bridge spacing angle β is calculated assuming that the outer bridge 35a is arranged therein.

In this embodiment, the opening angle α of the teeth 22 is set to 7.5°, and the coefficient N is set to 2. Therefore, the bridge opening angle β of the bridge 35 is set to satisfy the condition 15°≦β≦22.5°. However, the relationship between the opening angle α of the teeth 22 and the bridge opening angle β of the bridge 35 is not limited to this, and it is sufficient that the above formula is satisfied.

The symmetry (symmetrical arrangement) in the arrangement of the bridges 35 is defined as follows.
"Symmetrical with respect to the d-axis" means that the types of bridges 35 arranged in the first tip region 34a and the second tip region 34b of the flux barrier 32 are the same.
"Asymmetric with respect to the d-axis" means that the types of bridges 35 arranged in the first tip region 34a and the second tip region 34b of the flux barrier 32 are different.
"Symmetrical with respect to the q-axis" means that in the magnetic pole pair, the same type of bridge 35 is arranged in the tip region 34 of each magnetic pole 33 at a symmetrical position with respect to the q-axis.
"Asymmetric with respect to the q-axis" means that in the magnetic pole pair, different types of bridges 35 are arranged in the tip regions 34 of the magnetic poles 33 at positions symmetric with respect to the q-axis.

The present invention was developed with the aim of suppressing back electromotive force by having the outer bridge 35a and middle bridge 35b, which are arranged at the south magnetic pole 33S and north magnetic pole 33N of the magnetic pole pair, have a specific symmetrical arrangement with respect to the d-axis and q-axis.

The arrangement of the bridges 35 in the rotor 30 will be described with reference to Figures 3(a) to 3(d). Figures 3(a) to 3(d) show the arrangement of the outer bridges 35a and middle bridges 35b in Examples 1 to 4, respectively.

Example 1
In the first embodiment, a center bridge 35b is disposed in the first tip region 34a of the south magnetic pole 33S. An outer bridge 35a is disposed in the second tip region 34b of the south magnetic pole 33S. An outer bridge 35a is disposed in the first tip region 34a of the north magnetic pole 33N. A center bridge 35b is disposed in the second tip region 34b of the north magnetic pole 33N.

In other words, different types of bridges 35 are arranged in the first tip region 34a of the south magnetic pole 33S and the first tip region 34a of the north magnetic pole 33N, and different types of bridges 35 are arranged in the second tip region 34b of the south magnetic pole 33S and the second tip region 34b of the north magnetic pole 33N.

Hereinafter, the bridge 35 arrangement will be represented by the initial letters of the types of bridges 35 arranged in the first and second tip regions 34a and 34b of the south magnetic pole 33S and the first and second tip regions 34a and 34b of the north magnetic pole 33N of the magnetic pole pair. Specifically, the bridge 35 arrangement in Example 1 will be represented as "inside-outside-inside."

Example 2
In Example 2, the outer bridge 35a and the inner bridge 35b in Example 1 are interchanged. That is, the arrangement of the bridges 35 in Example 2 is "outer-in-in-outer."

Example 3
In the third embodiment, a center bridge 35b is disposed between the first and second tip regions 34a and 34b of the south magnetic pole 33S. An outer bridge 35a is disposed between the first and second tip regions 34a and 34b of the north magnetic pole 33N.

In other words, the same type of bridge 35 is arranged in the first tip region 34a and the second tip region 34b of the south magnetic pole 33S, and a different type of bridge 35 is arranged in the tip region 34 of the north magnetic pole 33N than in the tip region 34 of the south magnetic pole 33S. The bridge 35 arrangement structure in Example 3 is "center-center-outside-outside."

Example 4
In Example 4, the outer bridge 35a and the inner bridge 35b in Example 3 are interchanged. That is, the arrangement of the bridges 35 in Example 4 is "outside-outside-inside-inside."

<Conditions for bridge arrangement structure>
The following two conditions are common to the magnetic pole pairs in Examples 1 to 4.
Condition (1): The number of outer bridges 35a is equal to the number of middle bridges 35b.
Condition (2): The arrangement of the outer bridge 35a and the middle bridge 35b is symmetrical with respect to either the d-axis or the q-axis, and is asymmetrical with respect to the other axis.
By configuring the outer bridge 35a and the middle bridge 35b in this manner in the magnetic pole pair, it is possible to suppress the back electromotive force.

Next, as comparative examples, Figures 4 and 5 show the arrangement of bridges 35 that do not satisfy the above condition (2). Figures 4(a), 4(b), 4(c), 5(a), and 5(b) show the arrangements of the outer bridges 35a and middle bridges 35b for Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5, respectively.

<Comparative Example 1>
Outer bridges 35a are arranged in the first and second tip regions 34a, 34b of the south magnetic pole 33S in comparative example 1. Outer bridges 35a are also arranged in the first and second tip regions 34a, 34b of the north magnetic pole 33N. In other words, the arrangement of the bridges 35 in comparative example 1 is "outside-outside-outside."

<Comparative Example 2>
In Comparative Example 2, a center bridge 35b is arranged in the first tip region 34a and the second tip region 34b of the south magnetic pole 33S. A center bridge 35b is also arranged in the first tip region 34a and the second tip region 34b of the north magnetic pole 33N. In other words, the arrangement structure of the bridges 35 in Comparative Example 2 is "center-center-center-center."

<Comparative Example 3>
Both outer bridges 35a and center bridges 35b are arranged in all tip regions 34 of the south magnetic pole 33S and north magnetic pole 33N of comparative example 3. In other words, comparative example 3 has the bridge 35 arrangement structures of both comparative examples 1 and 2. The bridge 35 arrangement structure of comparative example 3 is "outside-outside-outside/center-center-center."

<Comparative Example 4>
In Comparative Example 4, an outer bridge 35a is arranged in the first tip region 34a of the S magnetic pole 33S. A center bridge 35b is arranged in the second tip region 34b of the S magnetic pole 33S. An outer bridge 35a of the same type as the first tip region 34a of the S magnetic pole 33S is arranged in the first tip region 34a of the N magnetic pole 33N. A center bridge 35b of the same type as the second tip region 34b of the S magnetic pole 33S is arranged in the second tip region 34b of the N magnetic pole 33N. In other words, the arrangement structure of the bridges 35 in Comparative Example 4 is "outside-inside-outside-inside."

Comparative Example 5 has a configuration in which the outer bridge 35a and inner bridge 35b in Comparative Example 4 are swapped. In other words, the bridge 35 arrangement in Comparative Example 5 is "inside-outside-inside-outside."

As shown above, in Comparative Examples 1 to 5, the number of outer bridges 35a and the number of middle bridges 35b in each magnetic pole pair are the same, and condition (1) above is satisfied. On the other hand, the outer bridges 35a and middle bridges 35b are either symmetrical or asymmetrical with respect to the d-axis and q-axis, and do not satisfy condition (2) above.

The arrangement of the outer bridge 35a and middle bridge 35b in the magnetic pole pairs of Examples 1 to 4 and Comparative Examples 1 to 5 is summarized in Table 1.

Next, we will explain how the generation of back electromotive force differs depending on the arrangement of the bridge 35. Figures 6 to 9 show the simulation results of back electromotive force for the arrangement of the bridge 35 in the example and comparative example.

Figure 6 shows the simulation results of the back EMF voltage in the UV line voltage for Comparative Examples 1 to 3. In Figure 6, the horizontal axis represents the electrical angle, and the vertical axis represents the back EMF voltage in pu units. Figure 6(a) shows the back EMF waveform for one electrical angle cycle, and Figure 6(b) is an enlarged view of an electrical angle of 60°±30°, showing the waveform near the maximum amplitude of the fundamental wave.

In all of Comparative Examples 1 to 3, the peak voltage value was greater than the maximum value of the fundamental voltage at an electrical angle of approximately 60°. Therefore, it was necessary to limit the upper limit of the voltage applied to the coil, and the inverter DC voltage could not be effectively utilized.

In Comparative Example 2, the voltage increased near the electrical angle when the d-axis was parallel to the central axis of the teeth 22, i.e., the electrical angle (60°) at which the fundamental wave voltage of the line voltage was at its maximum value. On the other hand, the voltage decreased near 15° before and after the electrical angle of 60°, i.e., near the electrical angle corresponding to the electrical angle when the d-axis rotates from the central axis of the teeth 22 to the central axis of the slot 21.

In Comparative Examples 1 and 3, the voltage increased at an electrical angle shifted by approximately 15°, which corresponds to the electrical angle when the d-axis rotates from the central axis of the teeth 22 to the central axis of the slot 21, relative to the electrical angle of 60° at which the d-axis is parallel to the central axis of the slot 21, i.e., the maximum electrical angle of the fundamental wave voltage.

In Comparative Example 3, the maximum value of the fundamental wave voltage near an electrical angle of 60° was reduced. As a result, the torque of the rotating electric machine 10 in Comparative Example 3 decreased. In Comparative Example 3, both outer bridges 35a and inner bridges 35b were arranged in all tip regions 34 of the south magnetic poles 33S and north magnetic poles 33N. This is thought to be because the total number of bridges 35 was large, causing the magnetic flux of the magnets 31 to be confined within the rotor 30, reducing the amount of linkage with the stator 20. In Comparative Examples 2 and 1, which had fewer total numbers of bridges 35 than Comparative Example 3, the torque of the rotating electric machine 10 was greater than in Comparative Example 3. The torque ratio of Comparative Examples 1 to 3 was Comparative Example 2:Comparative Example 1:Comparative Example 3 = 100.0:98.5:96.2.

Figure 7 shows the simulation results of the back electromotive force (back EMF) for the UV line voltage in Examples 1 and 4 and Comparative Examples 1 and 2. In Figure 7, the horizontal axis represents the electrical angle, and the vertical axis represents the back electromotive force (in pu). Figure 7(a) shows the back electromotive force waveform for one electrical angle cycle, and Figure 7(b) is an enlarged view of an electrical angle of 60°±30°, showing the waveform near the maximum amplitude of the fundamental wave.

In Examples 1 and 4, the peak voltage near an electrical angle of 60° was reduced compared to Comparative Example 1, and the peak voltage near an electrical angle of 60°±15° was reduced compared to Comparative Example 2. In other words, in Examples 1 and 4, the peak voltage was reduced overall.

Figure 8(a) shows the simulation results of the back electromotive force in the UV line voltage for Examples 1 and 2, and Figure 8(b) shows the simulation results of the back electromotive force in the UV line voltage for Examples 3 and 4. The arrangement of the bridges 35 in Example 2 is the same as that of the bridges 35 in Example 1, rotated circumferentially by one magnetic pole, and Example 2 produced substantially the same back electromotive force waveform as Example 1. Furthermore, the arrangement of the bridges 35 in Example 4 is the same as that of the bridges 35 in Example 3, rotated circumferentially by one magnetic pole, and Example 3 produced substantially the same back electromotive force waveform as Example 4.

Examples 1 to 4 are characterized by having a back electromotive force intermediate between that of Comparative Example 1 and Comparative Example 2. Specifically, by adjusting the harmonic voltage, it was possible to make the maximum value of the back electromotive force close to the maximum value of the fundamental wave.

Figure 9 shows the calculation results for the value obtained by dividing the peak voltage by the amplitude of the fundamental wave (peak voltage/fundamental wave amplitude). In the rotating electric machine 10, torque increases according to the amplitude of the fundamental wave voltage. Therefore, the smaller the peak voltage/fundamental wave amplitude value, the closer the fundamental wave voltage amplitude and peak voltage value are, meaning that the fundamental wave voltage can be increased under the constraints of the voltage applied to the coil. In other words, the smaller the peak voltage/fundamental wave amplitude value, the easier it is to generate torque under voltage constraints. In Examples 1 to 4, the peak voltage/fundamental wave amplitude value is smaller than in Comparative Examples 1 and 2, and it can be said that it is easier to generate torque under voltage constraints than in Comparative Examples 1 and 2. Furthermore, Examples 1 and 2 have a slight advantage in torque output over Examples 3 and 4.

Figure 10 shows the simulation results of the back electromotive force in the UV line voltage for Example 1 and Comparative Examples 4 and 5. In Example 1 and Comparative Examples 4 and 5, the number of outer bridges 35a and the number of middle bridges 35b were equal for each magnetic pole 33. The bridges 35 were also arranged asymmetrically with respect to the d-axis. However, the difference is that the bridges 35 in Example 1 were arranged symmetrically with respect to the q-axis, whereas the bridges 35 in Comparative Examples 4 and 5 were arranged asymmetrically with respect to the q-axis.

In Comparative Example 4, the voltage increased and peaked near an electrical angle of 50°, exceeding the maximum amplitude of the fundamental wave voltage near an electrical angle of 60°. The voltage also increased and peaked at an angle slightly offset from 60° and at an electrical angle of 80°. In Comparative Example 5, the voltage also increased and peaked near an electrical angle of 72°, exceeding the maximum amplitude of the fundamental wave voltage near 60°. The voltage also increased and peaked near electrical angles of 60° and 42°. The voltage waveform in Comparative Example 5 resembled the voltage waveform in Comparative Example 4, inverted around an electrical angle of 60°. This is because the arrangement of the bridge 35 in Comparative Example 5 is equivalent to the arrangement of the bridge 35 in Comparative Example 4 inverted with respect to the d-axis.

As described above, the arrangement of the bridge 35 in Examples 1 to 4 was more effective in reducing back electromotive force than the arrangement of the bridge 35 in Comparative Examples 1 to 5.

<Qualitative explanation of the effects of the invention>
The back electromotive force tends to increase when the d-axis is parallel to the central axis of the teeth 22 and when the d-axis is parallel to the central axis of the slots 21. When the d-axis is parallel to the central axis of the teeth 22, the voltage (referred to as voltage A) at the phase of the maximum fundamental wave value of the back electromotive force (line voltage) increases or decreases. When the d-axis is parallel to the central axis of the slots 21, the voltage (referred to as voltage B) at a position shifted in phase from the maximum fundamental wave value relative to the electrical angle when the rotor 30 rotates from the central axis of the teeth 22 to the central axis of the slots 21 increases or decreases significantly.

In Comparative Example 2, only the middle bridge 35b is arranged, resulting in a high voltage A. In Comparative Example 1, only the outer bridge 35a is arranged, resulting in a high voltage B. The bridge 35 arrangements in Examples 1 to 4 are intermediate structures that use both the outer bridge 35a and the middle bridge 35b, and are able to suppress increases in the peak back electromotive force at voltages A and B.

Figure 11 shows the back electromotive force waveforms of Comparative Example 1, Comparative Example 2, and Example 1, along with the phases of Voltage A and Voltage B. Voltage A is the back electromotive force at an electrical angle of 60°, and Voltage B is the back electromotive force at electrical angles of 45° and 75°. In Example 1, Voltage A and Voltage B exhibit values intermediate between those of Comparative Example 1 and Comparative Example 2, and the peak voltage was reduced overall.

Figures 12 to 14 show the analysis results of the magnetic flux density distribution for Example 1, Comparative Example 1, and Comparative Example 2, respectively. In Figures 12 to 14, (a) shows the analysis results of the magnetic flux density distribution at an electrical angle of 45°, and (b) shows the analysis results of the magnetic flux density distribution at an electrical angle of 60°. Below, as shown in Figures 12 to 14, each tooth 22 is numbered #1 to #12, and explanations will use these numbers.

<Reason why magnetic flux fluctuation increases in the outer bridge 35a: electrical angle 45°>
As shown in FIG. 12A , at an electrical angle of 45° in the first embodiment, the outer bridge 35a is located between two teeth 22 (#3 and #4, #7 and #8). At this time, the magnetic flux from the magnet 31 tends to flow directly into the teeth 22 via the outer bridge 35a, which tends to cause large fluctuations in the magnetic flux flowing into the teeth 22. Fluctuations in the magnetic flux are also likely to occur due to the effect of magnetic flux cancellation, where the magnetic flux flowing into the rotor 30 from the two teeth 22 is canceled out by the outer bridge 35a. Furthermore, the center bridge 35b is located farther from the teeth 22 than the outer bridge 35a. Therefore, when the magnetic flux passes through the teeth 22 via the center bridge 35b, the change in magnetic resistance of the magnetic path is small, and magnetic flux fluctuations are less likely to occur compared to the outer bridge 35a. Therefore, at an electrical angle of around 45°, the outer bridge 35a tends to generate a large back electromotive force.

<Reason for increasing magnetic flux fluctuation in the middle bridge 35b: electrical angle 60°>
12B, at an electrical angle of 60° in the first embodiment, magnetic flux flows through the teeth 22 (#12, #10) adjacent to the teeth 22 (#1, #9), which tends to increase magnetic flux fluctuations in the teeth 22 (#1, #9) as the rotor 30 rotates. The outer bridge 35a allows magnetic flux to flow only through the opposing teeth 22 (#3, #7), making it difficult for magnetic flux fluctuations to occur. Therefore, at an electrical angle of around 60°, the middle bridge 35b tends to increase the back electromotive force.

As shown in FIG. 13(a), at an electrical angle of 45° in Comparative Example 1, outer bridges 35a are located between teeth 22 (#1, #2), between teeth 22 (#3, #4), between teeth 22 (#7, #8), and between teeth 22 (#9, #10). Therefore, compared to Example 1, in which outer bridges 35a are located between teeth 22 (#3, #4) and between teeth 22 (#7, #8), fluctuations in the magnetic flux flowing into the teeth 22 are more likely to be large. Furthermore, because the middle bridge 35b is not provided, magnetic flux fluctuations are less likely to occur near an electrical angle of 60°. Therefore, in Comparative Example 1, large back electromotive force is more likely to be generated near an electrical angle of 45°.

As shown in Figure 14(b), at an electrical angle of 60° in Comparative Example 2, magnetic flux flows through the teeth 22 (#12, #10) adjacent to the teeth 22 (#1, #9) and the teeth 22 (#4, #6) adjacent to the teeth 22 (#3, #7). Therefore, compared to Example 1, in which magnetic flux flows through the teeth 22 (#12, #10) adjacent to the teeth 22 (#1, #9), magnetic flux fluctuations associated with the rotation of the rotor 30 tend to be larger. Furthermore, because the outer bridge 35a is not provided, magnetic flux fluctuations are less likely to occur near an electrical angle of 45°. Therefore, in Comparative Example 2, a large back electromotive force is likely to be generated near an electrical angle of 60°.

<Reference example: Alternate lamination of rotor core>
In Example 1 and Example 2, the arrangement of the bridges 35 at the south magnetic pole 33S and the arrangement of the bridges 35 at the north magnetic pole 33N are swapped. That is, in Example 1 and Example 2, the structure of the rotor 30 excluding the magnet 31 is the same when rotated by one magnetic pole. Therefore, by stacking the rotor 30 having the bridge 35 arrangement of Example 1 and the rotor 30 having the bridge 35 arrangement of Example 2 along the rotation axis as partial rotors, it is possible to improve the weight balance during rotation of the rotor 30. The same applies to Example 3 and Example 4.

As shown in Figure 10, the arrangement of bridges 35 in Comparative Examples 4 and 5 alone did not have the effect of suppressing back electromotive force. However, by stacking them alternately in the axial direction as described below, the effect of reducing back electromotive force can be achieved.

The same effect as the bridge 35 structure of Example 1 can also be achieved by "Structure X: axially alternating stacking of bridge-arranged electromagnetic steel sheets in Comparative Examples 1 and 2, which had significant issues with back electromotive force when used alone," or "Structure Y: axially alternating stacking of bridge-arranged electromagnetic steel sheets in Comparative Examples 4 and 5, which had significant issues with back electromotive force when used alone." Structures X and Y are based on alternating stacking, and the disadvantage is that two types of electromagnetic steel sheets must be prepared to make up the rotor 30. Structure Y is mirror symmetrical with respect to the q axis, and has a shape in which the front and back of the electromagnetic steel sheets are reversed, and can be manufactured using the same mold. Therefore, it is believed that Structure Y can reduce production costs compared to Structure X.

The bridge arrangement of Example 1 can reduce back electromotive force even without alternately stacking the electromagnetic steel sheets in the bridge arrangement of Example 2. The same is true for Example 3. However, if the bridge arrangement electromagnetic steel sheets of Examples 1 and 2 must be alternately stacked in the axial direction to achieve rotational balance (Structure Z), the difference with Structure Y becomes smaller when considering only the back electromotive force suppression effect. However, Structure Z can stack the punched core by rotating it through an angle equivalent to one magnetic pole, whereas Structure Y must be stacked upside down, so Structure Z is advantageous in terms of production man-hours. As a reference example, Figure 15 shows the back electromotive force waveforms of Example 1, Structure X, and Structure Y. Both Structure X and Structure Y are able to suppress back electromotive force in the same way as Example 1.

The present invention is not limited to the above-described embodiment and its variations, and various modifications and improvements are possible within the scope of the claims of this application.

10 Rotating electric machine, 20 Stator, 21 Slot, 22 Teeth, 23 Back yoke, 30 Rotor, 31 Magnet, 32, 32a, 32b Flux barrier, 33 Magnetic pole, 33N N magnetic pole, 33S S magnetic pole, 34 Tip region, 34a First tip region, 34b Second tip region, 35 Bridge, 35a Outer bridge, 35b Middle bridge

Claims (6)

a stator;
a rotor having magnetic poles formed by embedding magnets in a flux barrier;
Equipped with
the blacks barrier extends along the circumferential direction of the rotor with the d-axis as its center, and has tip regions on both sides thereof that extend toward the outer circumferential surface of the rotor;
the magnets are embedded in a portion along the circumferential direction of the rotor, and the tip region is formed as a space in which the magnets are not embedded,
Each magnetic pole of a magnetic pole pair adjacent to each other in the circumferential direction of the rotor has a bridge in the tip region,
the bridge is one of two types: an outer bridge formed on the outer peripheral surface of the rotor in the tip region , and an intermediate bridge disposed in an intermediate portion of the tip region on the inner diameter side of the outer bridge,
The number of the outer bridges and the number of the middle bridges in the magnetic pole pair are the same,
A rotating electric machine characterized in that the outer bridges and the middle bridges are arranged symmetrically with respect to one of the d-axis and q-axis and asymmetrically with respect to the other axis. 2. The rotating electric machine according to claim 1,
In one of the magnetic poles of the magnetic pole pair, the arrangement of the outer bridge and the middle bridge is asymmetric with respect to the d axis,
a rotating electric machine, characterized in that the arrangement of the outer bridge and the middle bridge at the other magnetic pole of the magnetic pole pair is symmetrical with respect to the q axis to the arrangement at the one magnetic pole of the magnetic pole pair. 2. The rotating electric machine according to claim 1,
In one of the magnetic poles of the magnetic pole pair , only the outer bridge is arranged symmetrically with respect to the d axis,
A rotating electric machine, characterized in that, at the other magnetic pole of the magnetic pole pair, only the center bridge is arranged symmetrically with respect to the d axis. A rotating electric machine according to any one of claims 1 to 3,
the rotor has a plurality of the flux barriers in a radial direction,
A rotating electric machine characterized in that the arrangement of the outer bridge and the middle bridge is applied to the flux barrier arranged on the inner, outermost radial side of the flux barrier. A rotating electric machine according to any one of claims 1 to 3 ,
The stator has a plurality of teeth arranged at equal intervals in the circumferential direction,
When the open angle between the adjacent teeth is α and the angle formed by a line connecting the center of the rotation axis and the center of the circumferential direction of the two bridges sandwiching the d axis at the magnetic pole is β,
α×N≦β≦α×(N+1), where N is an integer of 1 or more.
A rotating electric machine characterized by satisfying the following: A rotating electric machine according to any one of claims 1 to 3 ,
The rotor is a rotating electric machine characterized in that it is formed by stacking partial rotors in the direction of the rotation axis, with the positions of the outer bridges and the middle bridges interchanged with each other.