Rotor assembly and alternating pole motor

Abstract

The present application provides a rotor assembly and an alternating pole motor. The rotor assembly includes a rotor core, the rotor core includes permanent magnetic poles and alternating poles arranged alternately along the circumferential direction, the permanent magnetic poles include mounting slots, permanent magnets are mounted in the mounting slots, the polarity of the permanent magnets facing the outer periphery of the rotor core is the same polarity, a first air slot and at least two second air slots are arranged on the rotor core radially outside the mounting slot, the first air slot is located on the center line of the magnetic pole, at least two second air slots are arranged at intervals along the circumferential direction and are located on both sides of the center line of the magnetic pole, along the radial direction away from the center of the rotor core, the spacing between the side walls of the at least two second air slots close to the center line of the magnetic pole gradually increases, and the first air slot is located in the expansion area of ​​the at least two second air slots. According to the rotor assembly of the present application, the problem of increased torque pulsation caused by the rich back-electromotive force harmonic content of the alternating pole motor can be effectively improved, the back-electromotive force harmonic content can be significantly reduced, and the motor performance can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of motors, and in particular to a rotor assembly and an alternating-pole motor. Background Art

[0002] The number of permanent magnets used in the alternating-pole permanent magnet synchronous motor is only half of that of the traditional permanent magnet synchronous motor. Therefore, it makes more complete use of the permanent magnets and can significantly reduce the amount of permanent magnets used, thereby reducing the cost of the motor.

[0003] However, its special magnetic circuit structure also brings many problems, including the decrease in output torque due to the reduction in the use of permanent magnets and the increase in torque fluctuation due to the asymmetric structure of adjacent magnetic poles, which limits the further promotion and application of alternating pole motors.

[0004] Some alternating pole motors in the prior art improve torque fluctuations by optimizing the pole arc coefficient, mainly targeting the torque fluctuations caused by the tooth slot torque, but have no effect on the torque pulsation caused by non-sinusoidal back EMF. Therefore, they have a poor effect on the problem of increased torque pulsation caused by the rich harmonic content of the back EMF of the alternating pole motor. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present application is to provide a rotor assembly and an alternating pole motor, which can effectively improve the problem of increased torque pulsation caused by the rich back-EMF harmonic content of the alternating pole motor, significantly reduce the back-EMF harmonic content, and improve the motor performance.

[0006] In order to solve the above problems, the present application provides a rotor assembly, including a rotor core, the rotor core including permanent magnetic poles and alternating poles arranged alternately along the circumferential direction, the permanent magnetic poles including mounting grooves, permanent magnets mounted in the mounting grooves, the polarities of the permanent magnets facing the outer periphery of the rotor core are the same polarity, a first air groove and at least two second air grooves are arranged on the rotor core radially outside the mounting grooves, the first air groove is located on the center line of the magnetic pole, at least two second air grooves are arranged at intervals along the circumferential direction and are located on both sides of the center line of the magnetic pole, along the radial direction away from the center of the rotor core, the spacing between the side walls of the at least two second air grooves close to the center line of the magnetic pole gradually increases, and the first air groove is located in the expansion area of ​​the at least two second air grooves.

[0007] Preferably, the side wall of the second air slot close to the center line of the magnetic pole includes a straight section and a bent section, the bent section extends obliquely outward in a direction away from the center line of the magnetic pole, and an expansion area is formed between the opposite bent sections of at least two second air slots.

[0008] Preferably, the extension line of the straight line segment passes through the central axis of the rotor core.

[0009] Preferably, the bending segment is a straight line segment or an arc segment, and the expansion area is V-shaped or U-shaped.

[0010] Preferably, a first extension section extending circumferentially in a direction away from the center line of the magnetic pole is provided on the rotor core at the end of the bent section.

[0011] Preferably, in a plane perpendicular to the central axis of the rotor core, the angle formed by the line connecting the endpoints of the radial outer edges of the two first extension segments away from the magnetic pole centerline and the center of the rotor core is a22, and the angle formed by the line connecting the radial outer endpoints of the two straight line segments and the center of the rotor core is a21, where a21 / a22=0.15~0.4.

[0012] Preferably, in a plane perpendicular to the central axis of the rotor core, the angle formed by the line connecting the two endpoints of the radial outer edge of the first air slot and the center of the rotor core is a1, and the angle formed by the line connecting the radial outer endpoints of the two straight line segments and the center of the rotor core is a21, where a1 / a21=0.9~1.1.

[0013] Preferably, the radial thickness of the first air groove is t1, the radial thickness of the second air groove is t2, and t1 / t2=0.1-0.3.

[0014] Preferably, third air grooves are respectively provided at both ends of the mounting groove, and the third air grooves extend circumferentially from the side wall toward the center line of the magnetic pole to form a second extension section.

[0015] Preferably, in a plane perpendicular to the central axis of the rotor core, the angle formed by the line connecting the endpoints of the radial outer edges of the two second extension segments close to the center line of the magnetic poles and the center of the rotor core is a31, and the angle formed by the line connecting the endpoints of the radial outer edges of the two third air slots located between adjacent permanent magnet poles close to the center line of the alternating poles and the center of the rotor core is a32, where a31 / a32=0.8~1.

[0016] Preferably, in a plane perpendicular to the central axis of the rotor core, the angle formed by the line connecting the endpoints of the radial outer edges of the two second extension segments close to the magnetic pole centerline and the center of the rotor core is a31, and the angle formed by the line connecting the two endpoints of the radial outer edges of the permanent magnet close to the magnetic pole centerline and the center of the rotor core is am, where a31 / am=0.7~0.95.

[0017] Preferably, when a first extension section is provided on the rotor core, in a plane perpendicular to the central axis of the rotor core, the angle formed by the line connecting the endpoints of the radial outer edges of the two first extension sections away from the magnetic pole centerline and the center of the rotor core is a22, and the angle formed by the line connecting the endpoints of the radial outer edges of the two second extension sections close to the magnetic pole centerline and the center of the rotor core is a31, wherein a22 / a31=0.4~0.6.

[0018] Preferably, the permanent magnet is V-shaped.

[0019] Preferably, there are two second air slots, and the two second air slots are symmetrical about the center line of the magnetic pole.

[0020] According to another aspect of the present application, an alternating-pole motor is provided, comprising a rotor assembly and a stator assembly, wherein the rotor assembly is the above-mentioned rotor assembly.

[0021] The rotor assembly provided in the present application includes a rotor core, the rotor core includes permanent magnetic poles and alternating poles arranged alternately along the circumferential direction, the permanent magnetic poles include mounting grooves, permanent magnets are mounted in the mounting grooves, the polarities of the permanent magnets facing the outer periphery of the rotor core are the same polarity, a first air groove and at least two second air grooves are arranged on the rotor core radially outside the mounting grooves, the first air groove is located on the center line of the magnetic pole, at least two second air grooves are arranged at intervals along the circumferential direction and are located on both sides of the center line of the magnetic pole, along the radial direction away from the center of the rotor core, the spacing between the side walls of the at least two second air grooves close to the center line of the magnetic pole gradually increases, and the first air groove is located in the expansion area of ​​the at least two second air grooves. The rotor assembly is capable of planning the magnetic lines of force passing through the rotor core by providing a first air slot located on the center line of the magnetic pole and two second air slots located on both sides of the center line of the magnetic pole. The second air slot has a shape feature that opens outward from the center and wraps the first air slot in the opened expansion area. The magnetic lines of force distribution in the center of the magnetic pole are adjusted by the second air slot, the magnetic lines of force are gathered in the center of the magnetic pole, and the magnetic lines of force are restricted from gathering on one side of the rotation direction. The gathered magnetic lines of force are slowly divided to both sides by the first air slot so that they are not too concentrated in the center of the magnetic pole, thereby avoiding an increase in the third harmonic of the back electromotive force. The peak position of the back electromotive force is advanced by the coordination of the first air slot and the second air slot, the even-order harmonic content is reduced, the sinusoidality of the back electromotive force is improved, and the problem of increased torque pulsation caused by the rich harmonic content of the back electromotive force of the alternating-pole motor is effectively improved, the harmonic content of the back electromotive force is significantly reduced, and the motor performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of a rotor assembly according to an embodiment of the present application;

[0023] Figure 2 This is a dimensional structure diagram of a rotor assembly according to an embodiment of the present application;

[0024] Figure 3 A magnetic field line distribution diagram of a rotor assembly according to an embodiment of the present application;

[0025] Figure 4 A comparison diagram of back-EMF waveforms of the rotor assembly of the embodiment of the present application and the rotor assembly of the prior art;

[0026] Figure 5 A comparison diagram of back-EMF harmonic content between the rotor assembly of the embodiment of the present application and the rotor assembly of the prior art;

[0027] Figure 6 A torque waveform comparison diagram of the rotor assembly of the embodiment of the present application and the rotor assembly of the prior art;

[0028] Figure 7 It is a curve diagram of the back electromotive force harmonics and electromagnetic torque content of the rotor assembly according to the embodiment of the present application as a21 / a22 changes;

[0029] Figure 8 This is a curve chart showing the torque fluctuation of the rotor assembly and the electromagnetic torque as a22 / a31 changes according to an embodiment of the present application.

[0030] The reference numerals are:

[0031] 1. Rotor core; 2. Mounting slot; 3. Permanent magnet; 4. First air slot; 5. Second air slot; 6. Third air slot; 7. Straight section; 8. Bend section; 9. First extension section; 10. Second extension section; 11. Stator assembly. DETAILED DESCRIPTION

[0032] See also Figures 1 to 8 As shown, according to an embodiment of the present application, the rotor assembly includes a rotor core 1, the rotor core 1 includes permanent magnetic poles and alternating poles arranged alternately in the circumferential direction, the permanent magnetic pole includes a mounting slot 2, a permanent magnet 3 is mounted in the mounting slot 2, the polarity of the permanent magnet 3 facing the outer periphery of the rotor core 1 is the same polarity, and a first air slot 4 and at least two second air slots 5 are arranged on the rotor core 1 radially outside the mounting slot 2, the first air slot 4 is located on the center line of the magnetic pole, at least two second air slots 5 are arranged at intervals in the circumferential direction and are located on both sides of the center line of the magnetic pole, along the radial direction away from the center of the rotor core 1, the spacing between the side walls of the at least two second air slots 5 close to the center line of the magnetic pole gradually increases, and the first air slot 4 is located in the expansion area of ​​the at least two second air slots 5. For the convenience of description below, the structure on the same permanent magnetic pole is used as an example for explanation.

[0033] The magnetic lines of force on the alternating poles of the alternating-pole motor lack the constraints of permanent magnets. Due to the armature reaction, the magnetic lines of force will gather to the side of the rotor rotation, causing the position of the back-EMF peak to not be where the q-axis is aligned with the u-phase winding, but to be delayed a little, which in turn leads to an increase in the even-order harmonics in the back-EMF harmonics and severe back-EMF distortion. Since the current passed through the winding is a sinusoidal wave, the effect of the current and the back-EMF with a large distortion rate causes an increase in torque pulsation.

[0034] In the present application, the rotor assembly is capable of planning the magnetic lines of force passing through the rotor core 1 by providing a first air slot 4 located on the center line of the magnetic pole and two second air slots 5 located on both sides of the center line of the magnetic pole. The second air slot 5 has a shape feature that opens outward from the center, and wraps the first air slot 4 in the opened expansion area. The distribution of the magnetic lines of force in the center of the magnetic pole is adjusted by the second air slot 5, and the magnetic lines of force are gathered in the center of the magnetic pole, and the magnetic lines of force are restricted from gathering to one side of the rotation direction. The gathered magnetic lines of force are slowly divided to both sides by the first air slot 4 so that they are not too concentrated in the center of the magnetic pole. Figure 3 As shown, while avoiding the increase of the third harmonic of the back electromotive force, the peak position of the back electromotive force is advanced by the cooperation of the first air slot 4 and the second air slot 5, as shown in FIG. Figure 4 As shown, the even-order harmonic content is reduced and the sinusoidality of the back EMF is improved, as shown in Figure 5 The above method can effectively improve the problem of increased torque pulsation caused by rich back-EMF harmonic content of the alternating-pole motor, significantly reduce the back-EMF harmonic content, and improve the motor performance.

[0035] The side wall of the second air slot 5 near the magnetic pole center line includes a straight section 7 and a bent section 8, the bent section 8 extends obliquely outward in a direction away from the magnetic pole center line, and an expansion area is formed between at least two opposite bent sections 8 of the second air slot 5. The bent section 8 extends obliquely outward in a direction away from the magnetic pole center line, specifically, the extension direction of the bent section 8 includes a circumferential direction away from the magnetic pole center line and a radial direction away from the center of the rotor core 1, and the bent section extends in a direction away from the magnetic pole center line and away from the center of the rotor core 1 at the same time.

[0036] Due to the outward expansion structure of the bending section 8, an expansion area can be formed in the middle area of ​​the two bending sections 8, so that the first air groove 4 can be conveniently set, so that the first air groove 4 is located in the expansion area, and at the same time, a gap is formed between the bending sections 8 on both sides of the circumferential direction, so that the magnetic lines of force can flow through the magnetic circuit formed at the gap.

[0037] The first air slot 4 is a long strip extending in the circumferential direction, and the radial outer peripheral wall of the first air slot 4 is an arc shape with the center of the rotor core 1 as the center. The first air slot 4 is, for example, rectangular, sector-shaped, or elliptical, etc. The first air slot 4 can also be circular.

[0038] Preferably, the first air slot 4 is symmetrical about the magnetic pole center line.

[0039] Preferably, the extension line of the straight segment 7 passes through the central axis of the rotor core 1, so that the magnetic lines of force can be arranged when entering the magnetic circuit in the middle area of ​​the two straight segments 7, thereby improving the uniformity of the magnetic lines of force distribution.

[0040] Preferably, the bending section 8 is a straight line section 7 or an arc section, and the expansion area is V-shaped or U-shaped. The expansion area may also be other shapes, as long as it can ensure that the distance between the side walls of the two second air slots 5 close to the center line of the magnetic poles gradually increases along the direction away from the central axis of the rotor core 1.

[0041] Preferably, a first extension section 9 extending circumferentially in a direction away from the center line of the magnetic pole is provided on the rotor core 1 at the end of the bending section 8. In this embodiment, the first extension section 9 is an arc section extending circumferentially, and the arc diameter of the radial outer peripheral wall of the first extension section 9 is the same as the arc diameter of the radial outer peripheral wall of the first air slot 4, and the radial outer peripheral walls of the two are located on the same circumference. Releasing the magnetic lines of force gathered by the two symmetrical straight line segments 7 and handing them over to the first air slot 4 for further arrangement can optimize the distribution of magnetic lines of force near the center line of the magnetic pole and reduce back electromotive force harmonics.

[0042] In a plane perpendicular to the central axis of the rotor core 1, the angle formed by the endpoints of the radial outer edges of the two first extension segments 9 away from the center line of the magnetic pole and the line connecting the center of the rotor core 1 is a22, and the angle formed by the radial outer endpoints of the two straight line segments 7 and the line connecting the center of the rotor core 1 is a21, where a21 / a22=0.15~0.4. The larger the external angle of the second air slot 5, the larger the space occupied by the second air slot 5, and the larger the magnetic resistance formed. If the magnetic resistance is too large, it will cause a sharp drop in the electromagnetic torque. The larger the internal angle of the second air slot 5, the more magnetic lines of force gather in the middle of the magnetic pole. Too much will cause distortion of the magnetic density waveform. Therefore, it is necessary to reasonably set the overall circumferential width and the minimum circumferential spacing of the two second air slots 5. Studies have shown that when a21 / a22=0.15~0.4, it can better prevent excessive magnetic resistance and distortion of the magnetic density waveform. Figure 7 shown.

[0043] In a plane perpendicular to the central axis of the rotor core 1, the angle formed by the two endpoints of the radial outer edge of the first air slot 4 and the line connecting the center of the rotor core 1 is a1, and the angle formed by the radial outer endpoints of the two straight line segments 7 and the line connecting the center of the rotor core 1 is a21, where a1 / a21=0.9~1.1. A large angle of the first air slot 4 will block the flow of magnetic lines modulated by the second air slot 5, reduce the output torque, and increase torque fluctuations. If the angle of the first air slot 4 is too small, its modulation effect will be weakened, and the air gap magnetic flux in the center of the magnetic pole will not be effectively weakened, resulting in a sharp protrusion of the magnetic flux in the center of the magnetic pole, that is, the increase of the third harmonic. Studies have shown that the best effect can be obtained when a1 / a21=0.9~1.1.

[0044] The radial thickness of the first air slot 4 is t1, and the radial thickness of the second air slot 5 is t2, and t1 / t2=0.1~0.3. Studies have shown that there is an optimal value for the thickness of the first air slot 4, which can not only appropriately weaken the air gap magnetic flux in the center of the magnetic pole, but also make the waveform of the entire magnetic flux just close to a sine wave, with the minimum harmonic content. The thickness of the second air slot 5 characterizes the ability to gather magnetic lines of force, and there is also an optimal value. Studies have shown that when t1 / t2=0.1~0.3, the thickness ratio of the first air slot 4 and the second air slot 5 is optimal, which can achieve better results in both the air gap magnetic flux waveform and the ability to gather magnetic lines of force in the center of the magnetic pole.

[0045] The third air slots 6 are respectively provided at both ends of the mounting slot 2, and the third air slots 6 extend circumferentially from the side wall to the center line of the magnetic pole to form a second extension section 10. The symmetry of the magnetic flux density distribution of the permanent magnetic pole and the alternating pole is adjusted by the third air slots 6. No matter which side of the magnetic flux density is too large or too small, it will cause the asymmetry of the adjacent magnetic flux density distribution and increase the torque fluctuation. By adding the first air slot 4 and the second air slot 5 in the center of the magnetic pole and making them interact with the third air slot 6, the magnetic flux density distribution can be effectively improved, so that the technical solution of the present application significantly reduces the torque fluctuation compared with the prior art. Figure 6 shown.

[0046] In a plane perpendicular to the central axis of the rotor core 1, the angle formed by the end points of the radial outer edges of the two second extension sections 10 close to the center line of the magnetic poles and the line connecting the center of the rotor core 1 is a31, and the angle formed by the end points of the radial outer edges of the two third air slots 6 located between adjacent permanent magnetic poles close to the center line of the alternating poles and the line connecting the center of the rotor core 1 is a32, wherein a31 / a32=0.8~1. This ratio characterizes the pole arc ratio of adjacent magnetic poles. The smaller the ratio, the larger the amplitude of the magnetic flux under the permanent magnetic pole, the smaller the magnetic flux under the alternating pole, and the increased magnetic flux asymmetry. On the contrary, the larger the ratio, the wider the width of the pole shoe under the permanent magnetic pole, the smaller the constraint on the magnetic flux lines, the smaller the magnetic flux, the larger the magnetic flux under the alternating pole, and the increased magnetic flux asymmetry. Studies have shown that a31 / a32=0.8~1 has the best magnetic flux symmetry.

[0047] In a plane perpendicular to the central axis of the rotor core 1, the angle formed by the end points of the radial outer edges of the two second extension segments 10 close to the magnetic pole centerline and the line connecting the center of the rotor core 1 is a31, and the angle formed by the line connecting the two end points of the radial outer edges of the permanent magnet 3 close to the magnetic pole centerline and the center of the rotor core 1 is am, where a31 / am=0.7-0.95. If the ratio is too large, it will lead to the inability to form an effective magnetic flux density under the permanent magnetic pole. If the ratio is too small, the second extension segment 10 will block too much magnetic flux, resulting in low utilization of the permanent magnet. Studies have shown that 0.7-0.95 has the best effect, which can not only form an effective magnetic flux density under the permanent magnetic pole, but also avoid blocking too much magnetic flux lines, thereby improving the utilization of the permanent magnet.

[0048] When the rotor core 1 is provided with a first extension section 9, in a plane perpendicular to the central axis of the rotor core 1, the angle formed by the line connecting the endpoints of the radial outer edges of the two first extension sections 9 away from the magnetic pole centerline and the center of the rotor core 1 is a22, and the angle formed by the line connecting the endpoints of the radial outer edges of the two second extension sections 10 close to the magnetic pole centerline and the center of the rotor core 1 is a31, wherein a22 / a31=0.4~0.6. The larger the ratio is, the more space the second air slot 5 occupies and the greater the magnetic resistance formed. A too large ratio will cause a decrease in electromagnetic torque. If the ratio is too small, the number of magnetic lines that can be adjusted by the second air slot 5 will decrease, thereby failing to effectively optimize torque fluctuations. Studies have shown that the best effect is when a22 / a31=0.4~0.6, such as Figure 8 shown.

[0049] Preferably, the permanent magnet 3 is V-shaped. The prior art mainly focuses on the optimization of the torque fluctuation of the alternating pole motor. Since the permanent magnets of the V-type permanent magnet alternating pole motor are deeply buried, it is difficult to effectively optimize the torque fluctuation of the existing strategy.

[0050] After adopting the scheme of the present application, the progressive magnetic flux sorting groove combination structure is used to gather the magnetic flux lines in the center of the magnetic pole and then hand them over to the second layer of magnetic flux sorting grooves for further adjustment. Therefore, the magnetic flux lines can be initially adjusted in the area with a larger burial depth by utilizing the characteristic that the expansion starting area of ​​the second air groove 5 occupies a smaller area. The magnetic flux lines can reach the expansion area under the influence of the second air groove 5, and can be adjusted in the expansion area through the first air groove 4 and the second air groove 5 to slowly separate the gathered magnetic flux lines to both sides so that they are not too concentrated in the center of the magnetic pole, thereby making torque adjustment for V-type permanent magnets a reality. Compared with the prior art, the torque fluctuation can be further reduced and the working performance of the motor can be improved.

[0051] Preferably, there are two second air slots 5 , and the two second air slots 5 are symmetrical about the magnetic pole center line.

[0052] The rotor core 1 is formed by laminating thin sheets of soft magnetic material.

[0053] According to an embodiment of the present application, the alternating-pole motor includes a rotor assembly and a stator assembly 11 , and the rotor assembly is the above-mentioned rotor assembly.

[0054] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed.

[0055] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above are only preferred implementations of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present application, and these improvements and variations should also be regarded as the protection scope of the present application.

Claims

1. A rotor assembly, characterized in that: The invention comprises a rotor core (1), wherein the rotor core (1) comprises permanent magnetic poles and alternating poles arranged alternately in the circumferential direction, wherein the permanent magnetic poles comprise mounting grooves (2), wherein permanent magnets (3) are mounted in the mounting grooves (2), wherein the polarities of the permanent magnets (3) facing the outer periphery of the rotor core (1) are the same polarity, and a first air groove (4) and at least two second air grooves (5) are arranged on the rotor core (1) radially outside the mounting grooves (2), wherein the first air groove (4) is located on the center line of the magnetic pole, and the at least two second air grooves (5) are arranged at intervals in the circumferential direction and are located on both sides of the center line of the magnetic pole, and along the radial direction away from the center of the rotor core (1), the spacing between the side walls of the at least two second air grooves (5) close to the center line of the magnetic pole gradually increases, and the first air groove (4) is located in the expansion area of ​​the at least two second air grooves (5).

2. The rotor assembly according to claim 1, characterized in that: The side wall of the second air slot (5) close to the magnetic pole center line comprises a straight section (7) and a bent section (8), the bent section (8) extending obliquely outward in a direction away from the magnetic pole center line, and the expansion area is formed between the opposite bent sections (8) of the at least two second air slots (5).

3. The rotor assembly according to claim 2, characterized in that: An extension line of the straight line segment (7) passes through the central axis of the rotor core (1).

4. The rotor assembly according to claim 2, characterized in that: The bending section (8) is a straight line section (7) or an arc section, and the expansion area is V-shaped or U-shaped.

5. The rotor assembly according to claim 2, characterized in that: The rotor core (1) is provided with a first extension section (9) circumferentially extending in a direction away from the center line of the magnetic pole at the end of the bending section (8).

6. The rotor assembly according to claim 5, characterized in that In a plane perpendicular to the central axis of the rotor core (1), the angle formed by the line connecting the endpoints of the radial outer edges of the two first extension segments (9) away from the magnetic pole centerline and the center of the rotor core (1) is a22, and the angle formed by the line connecting the radial outer endpoints of the two straight line segments (7) and the center of the rotor core (1) is a21, where a21 / a22=0.15~0.

4.

7. The rotor assembly according to claim 2, characterized in that: In a plane perpendicular to the central axis of the rotor core (1), the angle formed by the line connecting the two end points of the radial outer edge of the first air slot (4) and the center of the rotor core (1) is a1, and the angle formed by the line connecting the radial outer end points of the two straight line segments (7) and the center of the rotor core (1) is a21, wherein a1 / a21=0.9~1.

1.

8. The rotor assembly according to claim 1, characterized in that The radial thickness of the first air groove (4) is t1, the radial thickness of the second air groove (5) is t2, and t1 / t2=0.1-0.

3.

9. The rotor assembly according to any one of claims 2 to 7, characterized in that: A third air groove (6) is provided at both ends of the installation groove (2), and the third air groove (6) extends circumferentially from the side wall toward the magnetic pole center line to form a second extension section (10).

10. The rotor assembly according to claim 9, characterized in that In a plane perpendicular to the central axis of the rotor core (1), the angle formed by the line connecting the end points of the radial outer edges of the two second extension sections (10) close to the center line of the magnetic poles and the center of the rotor core (1) is a31, and the angle formed by the line connecting the end points of the radial outer edges of the two third air slots (6) located between adjacent permanent magnetic poles close to the center line of the alternating poles and the center of the rotor core (1) is a32, wherein a31 / a32=0.8-1.

11. The rotor assembly according to claim 9, characterized in that In a plane perpendicular to the central axis of the rotor core (1), the angle formed by the line connecting the endpoints of the radial outer edges of the two second extension segments (10) close to the magnetic pole center line and the center of the rotor core (1) is a31, and the angle formed by the line connecting the two endpoints of the radial outer edges of the permanent magnet (3) close to the magnetic pole center line and the center of the rotor core (1) is am, where a31 / am=0.7~0.

95.

12. The rotor assembly according to claim 9, characterized in that When the rotor core (1) is provided with a first extension section (9), in a plane perpendicular to the central axis of the rotor core (1), the angle formed by the line connecting the end points of the radial outer edges of the two first extension sections (9) away from the magnetic pole center line and the center of the rotor core (1) is a22, and the angle formed by the line connecting the end points of the radial outer edges of the two second extension sections (10) close to the magnetic pole center line and the center of the rotor core (1) is a31, wherein a22 / a31=0.4-0.

6.

13. The rotor assembly according to any one of claims 1 to 8, characterized in that: The permanent magnet (3) is V-shaped.

14. The rotor assembly according to any one of claims 1 to 8, characterized in that: There are two second air slots (5), and the two second air slots (5) are symmetrical about the magnetic pole center line.

15. An alternating-pole motor, comprising a rotor assembly and a stator assembly (11), characterized in that: The rotor assembly is the rotor assembly according to any one of claims 1 to 14.

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