JP7848156B2 - Rotating electric machine - Google Patents

Description

This invention relates to a rotating electric machine.

In electric vehicles, where the drive wheels are driven by the rotational force of a drive motor, torque pulsation caused by changes in magnetic flux resulting from changes in the opposing area between the motor's magnetic poles and teeth is a cause of noise and vibration (NV) in electric vehicles.

As a technique for suppressing torque pulsation, for example, Patent Document 1 discloses that a rotor core 252 comprises a core 301 formed on one side in the rotational direction and a core 302 formed on the other side in the rotational direction, and that the cross-sectional shapes of cores 301 and 302 have different positions for the magnetic gaps 258a and 258b. Furthermore, Patent Document 2 discloses a rotor core comprising a first rotor core 11A and a second rotor core 11B stacked in the axial direction, and that the arrangement of grooves in each rotor core 11A and 11B is changed.

Patent No. 4708448 Patent No. 6573654

However, when manufacturing rotor cores, producing multiple rotor cores with different groove positions in the circumferential direction increases manufacturing costs.

The objective of this invention is to provide a rotating electric machine that can reduce manufacturing costs in order to reduce torque pulsation.

In one embodiment, the rotating electric machine comprises a stator core, a three-phase coil, a magnet-embedded rotor having an iron core, and permanent magnets embedded in the rotor. The main magnetic flux direction of the rotor is defined as the d-axis direction, and the magnetic flux direction magnetically perpendicular to the d-axis is defined as the q-axis direction. The outer circumference of the rotor is provided with a d-axis groove through which the d-axis passes through the center, and a q-axis groove through which the q-axis passes through the center. The circumferential groove width of the q-axis groove is wider than the circumferential groove width of the d-axis groove. The bottoms of the d-axis groove and the q-axis groove are formed radially outward from the radial outer end of the flux barrier formed in the permanent magnet or the magnet insertion hole in which the permanent magnet is housed. The d-axis groove and the q-axis groove are alternately arranged between a pair of flux barriers in the circumferential direction. The pair of magnet insertion holes are symmetrical with respect to the d-axis and are formed in a V-shape that opens radially outward. The pair of permanent magnets are each housed in the V-shape along the pair of magnet insertion holes.

According to one embodiment, manufacturing costs for reducing torque pulsation can be reduced.

Figure 1 is a cross-sectional view showing an example of a motor. Figure 2 is an enlarged cross-sectional view showing an example of a motor. Figure 3 is a cross-sectional view showing an example of a rotor. Figure 4 is an enlarged perspective view showing an example of the side surface of a rotor. Figure 5 is an enlarged cross-sectional view showing an example of a rotor. Figure 6 is an enlarged cross-sectional view showing an example of a d-axis groove. Figure 7 is an enlarged cross-sectional view showing an example of a q-axis groove. Figure 8 is a graph showing a comparison of torque pulsation under no-load conditions. Figure 9 is a graph showing a comparison of torque pulsation under load conditions.

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the dimensional relationships and ratios of the elements in the drawings may differ from reality. There may also be differences in dimensional relationships and ratios between different parts of the drawings.

(Embodiment)
The rotating electric machine in the embodiment of the present invention is, for example, a drive motor 10 mounted on an electric vehicle (not shown). Figure 1 is a cross-sectional view showing an example of a motor. Figure 2 is an enlarged cross-sectional view showing an example of a motor. Figure 2 is an enlarged view of the portion shown in frame F1 of Figure 1. Note that a rotating electric machine other than a drive motor, such as a power generator motor, may have a configuration similar to that of the drive motor 10. Furthermore, the rotating electric machine may be mounted on equipment other than electric vehicles, such as hybrid vehicles or ships.

As shown in Figure 1, the drive motor 10 is a three-phase motor comprising a rotor 90 and a stator 80. The drive motor 10 is a so-called inner-rotor type motor, in which the rotor 90 is positioned radially inside the stator 80.

The stator 80 comprises a stator core 200 and coils 300. As shown in Figure 2, the coils 300 include a U-phase coil 310, a V-phase coil 320, and a W-phase coil 330. Note that coils 300 are an example of a three-phase coil for a rotating electric machine in this disclosure.

The stator core 200 is formed, for example, by stacking multiple sheets of electromagnetic steel of the same shape in the axial direction. In this case, the cross-sectional shape of the stator core 200 does not change in the axial direction.

The stator core 200 is provided with teeth 210 that project radially inward from the annular portion. As shown in Figure 1, the stator core 200 in this embodiment has 48 teeth 210.

Furthermore, slots 220 are formed between two adjacent teeth 210 in the circumferential direction. In this case, as shown in Figure 1, 48 slots 220 are formed in the stator core 200. Each slot 220 is radially oriented, and its inner end in the radial direction opens to the inner circumferential surface of the stator core 200, facing the outer circumferential surface of the rotor 90 in the radial direction.

As shown in Figures 1 and 2, each slot 220 houses a segment coil that constitutes the coil 300. In this embodiment, the coil 300 is a so-called distributed-winding coil formed by connecting multiple segment coils housed in the same slot or in slots spaced apart in the circumferential direction, as will be explained later. In this case, the coil 300 has two or more slots per pole per phase.

The rotor 90 is an 8-pole permanent magnet rotor comprising a rotor core 100 and permanent magnets 500. The rotor core 100 is formed, for example, by laminating press-formed electromagnetic steel sheets in the axial direction. In this embodiment, similar to the stator core 200, the cross-sectional shape of the rotor core 100 also does not change in the axial direction.

As shown in Figure 3, the rotor core 100 comprises a side circumferential surface 110 forming the outer circumference of the rotor core 100 and a through hole 190. Figure 3 is a cross-sectional view showing an example of a rotor. A rotating shaft (not shown) is inserted through the through hole 190. The rotor 90 rotates integrally with the rotating shaft. Note that the side circumferential surface 110 is an example of the outer circumference of the rotor in this disclosure.

Furthermore, as shown in Figure 3, a d-axis groove 111 and a q-axis groove 112, which will be described later, are formed on the side surface 110. In this embodiment, as shown in Figure 3, a hole 180 for suppressing the moment of inertia is formed in the rotor core 100 between the radial through hole 190 and the magnet insertion hole 120. Also, the d-axis groove 111 and q-axis groove 112 are not shown in Figure 1.

In the radial direction, eight pairs of magnet insertion holes 120 are formed between the side surface 110 of the rotor core 100 and the hole 180, as shown in Figure 3. Note that when distinguishing between the eight pairs of magnet insertion holes 120, they may be referred to as magnet insertion holes 121 to 128.

The pair of magnet insertion holes 120 are symmetrical with respect to the d-axis Ad and are formed in a roughly V-shape, opening radially outward, as shown in Figure 3. In this embodiment, the d-axis Ad refers to the axis set in the direction of the magnetic poles of the rotor 90. In this case, the main magnetic flux direction of the rotor 90 is defined as the d-axis direction. Furthermore, when distinguishing between the eight sets of d-axis Ads, they may be referred to as d-axis Ad1 to d-axis Ad8.

As shown in Figure 2, the pair of permanent magnets 500 are housed in the pair of magnet insertion holes 120. In other words, the rotor 90 is an IPM (Interior Permanent Magnet) rotor, with the permanent magnets 500 embedded inside.

Furthermore, as shown in Figure 2, flux barriers 120a and 120b are formed in the pair of magnet insertion holes 120 that house the pair of permanent magnets 500.

As shown in Figure 2, the pair of permanent magnets 500 are housed in the pair of magnet insertion holes 121 such that the magnetic pole portion 131 through which the d-axis Ad1 passes has a north pole. In this case, the magnetic flux flowing from the pair of permanent magnets 500 arranged in the magnet insertion holes 121 flows radially to the stator 80 via the magnetic pole portion 131. Note that the magnetic pole portion 131 is an example of the rotor core in this disclosure.

On the other hand, as shown in Figure 1, a pair of permanent magnets 500 are housed in one of the pair of magnet insertion holes 122 adjacent to the pair of magnet insertion holes 121 in the circumferential direction, such that the magnetic pole portion 131 through which the d-axis Ad2 passes has a south pole. Similarly, a pair of permanent magnets 500 are housed in the other pair of magnet insertion holes 128 adjacent to the pair of magnet insertion holes 121 in the circumferential direction, such that the magnetic pole portion 131 through which the d-axis Ad8 passes has a south pole.

In this case, the polarity of the d-axis passing through the pair of magnet insertion holes 121 is positive (N pole), while the polarity of the d-axis passing through the pair of magnet insertion holes 122 and 128 is negative (S pole). That is, magnetic flux flows from the stator 80 to the pair of permanent magnets 500 housed in the pair of magnet insertion holes 122 and 128 via the magnetic pole portion 131.

On the other hand, in the intermediate portion 132, which is sandwiched between two adjacent magnetic pole portions 131 in the circumferential direction, the north and south poles of the permanent magnet 500 face each other in the circumferential direction. Furthermore, a q-axis magnetic flux flows through the intermediate portion 132 along the magnetic pole surfaces of the permanent magnet 500. The direction in which the q-axis Aq extends is the magnetic flux direction magnetically perpendicular to the d-axis Ad. In this case, the angle between the adjacent d-axis Ad and q-axis Aq in the circumferential direction is 22.5° in mechanical angle and 90° in electrical angle, as shown in Figure 3.

Furthermore, as shown in Figure 1, coil 310 is formed to connect segment coils that are spaced 180° apart in electrical angles (45° apart in mechanical angles). Similarly, coils 320 and 330 are wound so that their winding pitch is 180° in electrical angles.

Furthermore, as shown in Figures 4 and 5, the rotor core 100 has d-axis grooves 111 and q-axis grooves 112 formed on its side surface 110. Figure 4 is an enlarged perspective view showing an example of the rotor's side surface. Figure 5 is an enlarged cross-sectional view showing an example of the rotor. Figure 5 is an enlarged view of the portion shown in frame F2 of Figure 3. Note that in Figure 4, the laminated structure on the side surface 110 of the rotor core 100 is omitted from the illustration.

As shown in Figure 5, the d-axis groove 111 is formed at the position through which the d-axis Ad passes, and the q-axis groove 112 is formed at the position through which the q-axis Aq passes. That is, the d-axis Ad passes through the center of the d-axis groove 111, and the q-axis Aq passes through the center of the q-axis groove 112.

As shown in Figure 2, the side surface 110 of the rotor core 100 and the teeth 210 of the stator 80 face each other in the radial direction. When the rotor 90 rotates, the area where the side surface 110 and the teeth 210 face each other changes, causing a change in the magnetic flux passing through the d-axis Ad or q-axis Aq, resulting in torque pulsation.

Pulsation occurs in the no-load state, i.e., when neither motor torque nor regenerative torque is generated in the drive motor 10, due to a change in the magnetic flux of the d-axis Ad as the rotor 90 rotates. This change in magnetic flux is compensated by the formation of the d-axis groove 111, shown in Figure 2, on the side surface 110 of the rotor core 100.

On the other hand, under load conditions, i.e., when the drive motor 10 is generating power torque or regenerative torque, the magnetic flux passing through the q-axis Aq changes in addition to the magnetic flux along the d-axis Ad. This change in magnetic flux is compensated by the formation of the q-axis groove 112, shown in Figure 2, on the side surface 110 of the rotor core 100.

Furthermore, in a magnet-embedded rotor, magnetic flux passes more easily in the q-axis direction than in the d-axis direction. Therefore, when a large torque is generated, the pulsation caused by the change in magnetic flux in the q-axis Aq direction may be greater than the pulsation caused by the change in magnetic flux in the d-axis Ad direction. Therefore, in this embodiment, as shown in Figures 6 and 7, by making the groove width W2 in the circumferential direction of the q-axis groove 112 larger than the groove width W1 in the circumferential direction of the d-axis groove 111, the pulsation in the q-axis direction can be further suppressed.

Figure 6 is an enlarged cross-sectional view showing an example of a d-axis groove. Figure 7 is an enlarged cross-sectional view showing an example of a q-axis groove. Figure 6 is an enlarged view of the portion shown in frame F11 of Figure 5, and Figure 7 is an enlarged view of the portion shown in frame F12 of Figure 5. Note that in Figures 6 and 7, the cross-section of the side surface 110 is shown as approximately straight, but the cross-section of the side surface 110 is approximately circular and actually slightly curved.

As shown in Figures 6 and 7, the groove width W2 of the q-axis groove 112 in the circumferential direction is greater than the groove width W1 of the d-axis groove 111. Note that groove width W1 is the distance between the imaginary points where the side surface 110 of the rotor core 100 intersects with the side surface of the d-axis groove 111, and groove width W2 is the distance between the imaginary points where the side surface 110 of the rotor core 100 intersects with the side surface of the q-axis groove 112.

With this configuration, as shown in Figures 8 and 9, torque pulsation associated with changes in magnetic flux can be suppressed in both the no-load state, where neither power torque nor regenerative torque is generated in the drive motor 10, and the load state, where power torque or regenerative torque is generated in the drive motor 10. Figure 8 is a graph showing a comparison of torque pulsation in the no-load state. Figure 9 is a graph showing a comparison of torque pulsation in the load state. As shown in Figures 8 and 9, torque pulsation in the load state is larger than torque pulsation in the no-load state, but according to this embodiment, the effect of suppressing torque pulsation in the load state is greater.

Furthermore, the greater the radial depth D2 of the q-axis groove 112, the greater the effect of suppressing torque pulsation. On the other hand, as shown in Figure 7, a portion of the q-axis groove 112 faces the magnet insertion hole 120 in the direction indicated by arrow T2. In this case, increasing the depth D2 of the q-axis groove 112 may reduce the thickness T2 of the bridge portion 133 sandwiched between the q-axis groove 112 and the magnet insertion hole 120, potentially reducing the strength of the rotor core 100.

Therefore, in this embodiment, as shown in Figures 6 and 7, the radial depth D1 of the d-axis groove 111 is deeper than the radial depth D2 of the q-axis groove 112. This allows for suppression of torque pulsation in the q-axis Aq direction while also ensuring the strength of the rotor core 100.

Furthermore, if the groove width W1 of the d-axis groove 111 and the groove width W2 of the q-axis groove 112 are too large, the magnetic resistance due to the gap between the stator 80 and rotor 90 in the radial direction will increase, which may lead to a decrease in torque.

Therefore, the groove width W1 in the circumferential direction of the d-axis groove 111 is set to be less than half of the tooth pitch width P1 shown in Figure 2. In the following, the tooth pitch width P1 represents the distance between two adjacent teeth 210 in the circumferential direction on the stator core 200, as shown in Figure 2. Furthermore, the sum of the circumferential widths of the d-axis groove 111 and the q-axis groove 112 (W1 + W2) is set to be less than the tooth pitch width P1 shown in Figure 2. This configuration suppresses torque pulsation and prevents a decrease in torque.

As described above, the rotating electric machine 10 in this embodiment consists of a stator core 200, a three-phase coil 300, a magnet-embedded rotor 90 equipped with an iron core 131, and permanent magnets 500 embedded in the rotor 90. The main magnetic flux direction of the rotor 90 is defined as the d-axis direction, and the magnetic flux direction magnetically perpendicular to the d-axis Ad is defined as the q-axis direction. The outer circumference 110 of the rotor 90 is provided with a d-axis groove 111 through which the d-axis Ad passes at its center, and a q-axis groove 112 through which the q-axis Aq passes at its center. The circumferential groove width W2 of the q-axis groove 112 is wider than the circumferential groove width W1 of the d-axis groove 111.

In this embodiment, the shape of the side circumferential surface 110 of the rotor core 100 does not change in the axial direction, as shown in Figure 4. That is, the d-axis groove 111 extends from one end face to the other end face in the axial direction of the rotor 90. Similarly, the q-axis groove 112 extends from one end face to the other end face in the axial direction of the rotor 90.

To reduce torque pulsation, when forming a rotor with grooves whose position and shape change in the axial direction, different shaped press molds are required, and different shaped electrical steel sheets need to be aligned, increasing manufacturing costs. According to this embodiment, since the groove positions are the same in the axial direction, the rotor core 100 can be formed from electrical steel sheets of the same shape, thus reducing manufacturing costs.

[Variations]
Although the configuration of this embodiment has been described above, the embodiment is not limited thereto. For example, other recesses or protrusions other than the d-axis groove 111 and q-axis groove 112 may be formed on the side circumferential surface 110 of the rotor core 100. In that case as well, it is preferable that the shape of the recesses or protrusions does not change in the axial direction, similar to the d-axis groove 111 and q-axis groove 112 shown in Figure 4.

Furthermore, the cross-sectional shape of the d-axis groove 111 and the q-axis groove 112 is, for example, a roughly curved shape as shown in Figure 6, but is not limited to this; for example, it may be a polygonal shape, etc. Also, the d-axis groove 111 and the q-axis groove 112 may be formed only in a portion of the axial direction.

Furthermore, while the coil 300 is formed, for example, by mounting a U-shaped conductor into the slot 220 and welding its axial end, it is not limited to this configuration; a pre-wound coil may also be inserted into the slot 220.

The embodiments of the present invention have been described above. However, these embodiments are presented as examples only and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment is included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as described in the claims.

1 Electric vehicle 10 Drive motor 80 Stator 90 Rotor 100 Rotor core 110 Side surface 111 d-axis groove 112 q-axis groove 120 Magnet insertion holes 120a-b Flux barrier 131 Magnetic pole section 132 Intermediate section 133 Bridge section 180 Hole section 190 Through hole 200 Stator core 210 Teeth 220 Slot 300 Coil 500 Permanent magnet Ad d-axis Aq q-axis D1, D2 Depth P1 Teeth pitch width T2 Thickness W1, W2 Groove width

Claims (4)

In a rotating electric machine comprising a stator core, a three-phase coil, a magnet-embedded rotor having an iron core, and permanent magnets embedded in the rotor,
The main magnetic flux direction of the rotor is defined as the d-axis direction, and the magnetic flux direction magnetically perpendicular to the d-axis is defined as the q-axis direction.
The outer circumference of the rotor is provided with a d-axis groove through which the d-axis passes in the center, and a q-axis groove through which the q-axis passes in the center.
The groove width of the q-axis groove in the circumferential direction is wider than the groove width of the d-axis groove in the circumferential direction.
The bottoms of the d-axis groove and the q-axis groove are formed radially outward from the radial end of at least one of the flux barriers formed in the permanent magnet and the magnet insertion hole in which the permanent magnet is housed, in the radial direction of the rotor.
The d-axis groove and the q-axis groove are arranged alternately between the flux barriers in the circumferential direction.
The pair of magnet insertion holes are symmetrical with respect to the d-axis and are formed in a V-shape that opens radially outward.
Each of the pair of permanent magnets is housed in the V-shape along the pair of magnet insertion holes.
Rotating electric machine. The rotating electric machine according to claim 1, wherein the radial depth of the d-axis groove is greater than the radial depth of the q-axis groove. The rotating electric machine according to claim 1 or 2, wherein the groove width of the d-axis groove in the circumferential direction is provided to be less than half the tooth pitch width of the stator core. The rotating electric machine according to claim 3, wherein the sum of the widths of the d-axis groove and the q-axis groove is less than the tooth pitch width.