CN221042428U

CN221042428U - Rotor core, rotor assembly and motor

Info

Publication number: CN221042428U
Application number: CN202322019378.3U
Authority: CN
Inventors: 位海洋; 郑军; 段世英; 明希军; 毕晓帅
Original assignee: Suzhou Huichuan Control Technology Co Ltd
Current assignee: Suzhou Huichuan Control Technology Co Ltd
Priority date: 2023-07-28
Filing date: 2023-07-28
Publication date: 2024-05-28
Anticipated expiration: 2033-07-28

Abstract

The utility model discloses a rotor core, a rotor assembly and a motor, wherein the rotor core comprises a plurality of sector iron core parts which are arranged at intervals along the circumferential direction, two adjacent sector iron core parts define a magnetic steel groove for installing magnetic steel, the magnetic steel groove is provided with an opening part, the sector iron core parts on two sides of the opening part are respectively provided with a convex part towards each other, the convex parts partially cover the opening part to form a notch part, the central angle formed by the notch part and the center of the rotor core is beta 1, and the central angle formed by the opening part and the center of the rotor core is beta, wherein the 1/6 beta is less than or equal to beta 1 and less than or equal to 2/3 beta. The part of the magnetic steel groove corresponding to the edge of the rotor forms an outer magnetic bridge, and the outer magnetic bridge is cut off through the arrangement of the notch part, so that magnetic leakage is reduced, meanwhile, the contact surface between the magnetic steel and the outer magnetic bridge is ensured, the length of the magnetic steel along the radial direction of the rotor core can be reduced under the same output condition, and the magnetic steel cost is reduced.

Description

Rotor core, rotor assembly and motor

Technical Field

The utility model relates to the technical field of motors, in particular to a rotor core, a rotor assembly and a motor.

Background

The servo system needs to accurately control the position and the speed, so that the requirements on the rotation speed fluctuation and the torque fluctuation of the servo are high, the torque and the rotation speed fluctuation are reduced by adopting a surface-mounted structure by the traditional motor, the motor with a built-in rotor structure starts to appear along with the rapid development of the motor in recent years, and compared with the surface-mounted motor, the built-in motor has higher torque density and lower cost. However, the built-in rotor has serious magnetic leakage due to the existence of a plurality of magnetic isolation bridges, so that the usage amount of the magnetic steel is increased.

Disclosure of utility model

The utility model mainly aims to provide a rotor core, a rotor assembly and a motor, and aims to optimize the rotor core so as to reduce magnetic leakage and the dosage of magnetic steel and reduce cost.

In order to achieve the above object, the present utility model provides a rotor core, the rotor core includes a plurality of fan-shaped core portions arranged at intervals along a circumferential direction, two adjacent fan-shaped core portions define a magnetic steel groove for mounting magnetic steel, the magnetic steel groove is provided with an opening portion, the fan-shaped core portions on two sides of the opening portion are respectively provided with a convex portion toward each other, the convex portion partially covers the opening portion to form a notch portion, a central angle formed by the notch portion and a center of a circle of the rotor core is beta 1, and a central angle formed by the opening portion and the center of a circle of the rotor core is beta, wherein 1/6beta is less than or equal to beta 1 is less than or equal to 2/3beta.

In a specific embodiment, a central angle β1 corresponding to the notch is an angle formed by opposite side ends of the notch and a center of the rotor core; and/or, the central angle beta corresponding to the opening part is an angle formed by the two intersection points formed by the convex parts extending to the magnetic steel groove and the convex parts and the center of the rotor core.

In a specific embodiment, the rotor core further includes an inner annular portion provided with a central shaft hole, and each of the segment core portions is disposed outside the inner annular portion and connected to the inner annular portion through an inner magnetic bridge.

In a specific embodiment, the dimension of each inner magnetic bridge along the circumferential direction of the rotor core is w1, and the dimension along the radial direction of the rotor core is L1, and 3 is less than or equal to L1/w1 is less than or equal to 6; and/or the dimension of each inner magnetic bridge along the circumferential direction of the rotor core is w1, and the thickness of each rotor lamination is h1, and w1/h1 is more than or equal to 0.5 and less than or equal to 1.5.

In a specific embodiment, two side walls of the opening of the magnetic steel groove are concavely arranged relatively to form two magnetic barrier grooves respectively, and an air gap space is formed between the magnetic barrier grooves and the magnetic steel arranged in the magnetic steel groove.

In a specific embodiment, the dimension of the magnetic barrier groove along the radial direction of the rotor core is L2, and the dimension of each magnetic steel groove along the radial direction of the rotor core is L3, wherein, L2 is more than or equal to 1/10L3 and less than or equal to 1/6L3; and/or the size of the magnetic barrier groove along the circumferential direction of the rotor core is w2, and the size of each magnetic steel groove along the circumferential direction of the rotor core is h2, wherein w2 is more than or equal to 1/3h2 and less than or equal to 1/2h2.

In a specific embodiment, at least part of the outer side surface of each of the fan-shaped core portions is located at a distance from the center of the rotor core by a different dimension.

In a specific embodiment, the distance between the outer side surface of each sector-shaped core part and the center of the rotor core is gradually reduced in the direction from the center of the outer side surface of the sector-shaped core part to the two ends of the outer side surface.

In a specific embodiment, a first cambered surface section, two second cambered surface sections connected with two ends of the first cambered surface section and two inclined surface sections connected with two ends of the second cambered surface section are formed on the outer side surface of each fan-shaped iron core section, the appearance of the first cambered surface section is used for being matched with the annular stator assembly, the notch part, the two inclined surface sections and the two second cambered surface sections close to the notch part form a shape trimming part together, and the shape trimming part is used for forming a variable air gap with the annular stator assembly.

In a specific embodiment, the total length of the modification part along the circumferential direction of the rotor core is T, and the sum of the lengths of the two second cambered surface sections in the modification part is T1, wherein T1 is more than or equal to 1/3T.

In a specific embodiment, a central angle formed by the shaping part and the center of the rotor core is alpha, wherein alpha is more than or equal to 50/p and less than or equal to 160/p, and p is the pole pair number of the motor.

In a specific embodiment, opposite sides of the two adjacent fan-shaped core parts are respectively provided with a limiting part at one side far away from the notch part, and the two limiting parts are abutted with the sides of the magnetic steel in the magnetic steel groove.

In a specific embodiment, a kevlar wire is wound around a circumferential side of the rotor core.

The utility model also provides a rotor assembly which comprises the rotor iron core and magnetic steel arranged in the magnetic steel groove.

The utility model also provides a motor which comprises the rotor assembly and the annular stator assembly, wherein the annular stator assembly is arranged outside the rotor assembly.

According to the technical scheme, the rotor core and the magnetic steel are matched to realize the function when the rotor core and the magnetic steel are matched to perform high-speed rotation under the driving force, the outer side faces of the two adjacent fan-shaped core parts are provided with the notch parts, the outer magnetic bridge is cut off, so that magnetic leakage is reduced, the length of the magnetic steel along the radial direction of the rotor core can be reduced under the same force condition, the magnetic steel cost is reduced, meanwhile, the design of the size of the notch parts is related to the size of the magnetic steel and/or the magnetic steel groove along the circumferential direction of the rotor core, the central angles beta 1 and beta are limited to be less than or equal to 1/6beta and less than or equal to 2/3beta, the magnetic leakage is reduced, the surface stress of the contact surface of the magnetic steel and the outer magnetic bridge is ensured to be larger, and the central angles formed by the two and the rotor core are controlled in a size relation, so that a more optimized design effect can be obtained.

Drawings

In order to more clearly illustrate the embodiments of the present utility model or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present utility model, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic view of an embodiment of a rotor core according to the present utility model;

FIG. 2 is an enlarged partial schematic view of the rotor core of FIG. 1;

FIG. 3 is a schematic view of the mating surface of FIG. 1;

Fig. 4 is a schematic view of the rotor core and annular stator assembly of fig. 1 mated.

Reference numerals illustrate:

Reference numerals	Name of the name	Reference numerals	Name of the name
				1	Rotor core	12	Limiting part
11	Magnetic steel groove	131	A first cambered surface section
				111	Notch portion	132	Second cambered surface section
112	Magnetic barrier groove	133	Bevel section
				11a	A first annular part	2	Magnetic steel
11b	A second annular part	3	Inner magnetic bridge

The achievement of the objects, functional features and advantages of the present utility model will be further described with reference to the accompanying drawings, in conjunction with the embodiments.

Detailed Description

The following description of the embodiments of the present utility model will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the utility model. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.

In the case where a directional instruction is involved in the embodiment of the present utility model, the directional instruction is merely used to explain the relative positional relationship, movement condition, etc. between the components in a specific posture, and if the specific posture is changed, the directional instruction is changed accordingly.

In addition, if there is a description of "first", "second", etc. in the embodiments of the present utility model, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present utility model.

The servo system needs to accurately control the position and the speed, so that the requirements on the rotation speed fluctuation and the torque fluctuation of the servo are high, the torque and the rotation speed fluctuation are reduced by adopting a surface-mounted structure by the traditional motor, the motor with the built-in rotor core starts to appear along with the rapid development of the motor in recent years, and compared with the surface-mounted motor, the built-in motor has higher torque density and lower cost. However, the built-in rotor has serious magnetic leakage due to the existence of a plurality of magnetic isolation bridges, so that the usage amount of the magnetic steel is increased.

In view of this, the present utility model provides a rotor core, a rotor assembly and a motor, which aim to optimize the rotor core, thereby reducing magnetic leakage, reducing the amount of magnetic steel, and thus reducing the cost. Fig. 1 to 4 are embodiments of a rotor core provided by the present utility model.

Referring to fig. 1 to 3, a rotor core 1 includes a plurality of fan-shaped core portions arranged at intervals along a circumferential direction, two adjacent fan-shaped core portions define a magnetic steel groove 11 for mounting magnetic steel 2, the magnetic steel groove 11 is provided with an opening portion, the fan-shaped core portions on two sides of the opening portion are provided with protrusions toward each other, the protrusions partially cover the opening portion to form a notch portion 111, a central angle formed by the notch portion 111 and a center of the rotor core 1 is β1, and a central angle formed by the opening portion and the center of the rotor core 1 is β, wherein 1/6β is equal to or less than β1 is equal to or less than 2/3β.

In a specific embodiment, the central angle β1 corresponding to the notch 11 is an angle formed by opposite side ends of the notch 111 and the center of the rotor core 1.

In a specific embodiment, the central angle β corresponding to the opening portion is an angle formed by the two intersection points formed by the convex portions and the convex portions extending to the magnetic steel groove 11 and the center of the rotor core 1.

According to the technical scheme, the rotor core 1 and the magnetic steel 2 are matched to realize functions when being subjected to high-speed rotation by a driving force, the outer ends of the two adjacent fan-shaped core parts are provided with the notch parts 111, the outer magnetic bridge is cut off, so that magnetic leakage is reduced, the length of the magnetic steel 2 along the radial direction of the rotor core 1 can be reduced under the same output condition, the cost of the magnetic steel 2 is reduced, meanwhile, the design of the size of the notch parts 111 is related to the size of the magnetic steel 2/the magnetic steel groove 11 along the circumferential direction of the rotor core 1, the central angles beta 1 and beta are defined to be less than or equal to 1/6beta and less than or equal to 2/3beta, the magnetic leakage is reduced, meanwhile, the surface stress of the contact surface of the magnetic steel and the outer magnetic bridge is avoided to be larger, and the central angles formed by the two and the rotor core 1 are controlled in a size relation, so that a more optimal design effect can be obtained. In the embodiment of the utility model, the length and width dimensions of the magnetic steel 2 and the magnetic steel groove 11 are basically consistent, and no air gap exists between the magnetic steel 2 and the magnetic steel groove 11 after the magnetic steel 2 is inserted into the magnetic steel groove 11. It will be appreciated that only a portion of the outer magnetic bridges may be provided in a disconnected configuration, or all of the outer magnetic bridges may be provided in a disconnected configuration.

It should be understood that, in the radial direction of the rotor core 1, one side near the center thereof is the inner side, and the other side is the outer side, so that the positions of the notch portion 111 and the outer side of the magnetic steel 2 can be determined.

Further, the rotor core 1 further includes an inner annular portion provided with a central shaft hole, each of the fan-shaped core portions is disposed at an outer side of the inner annular portion, and each of the fan-shaped core portions is connected to the inner annular portion through an inner magnetic bridge 3, and it should be noted that the inner magnetic bridge 3 may have a structure with a certain width or may be formed by a plurality of narrow structures arranged at intervals.

In the technical solution of this embodiment, the rotor core 1 includes a plurality of rotor laminations stacked in sequence, each rotor lamination has a first annular portion 11a and a second annular portion 11b disposed at the periphery of the first annular portion 11a, and a plurality of hollowed-out portions are disposed on the second annular portion 11b to form a plurality of fan-shaped core portions when the plurality of rotor laminations are stacked, and the first annular portion 11a is used for being fixedly sleeved outside the rotating shaft. In this structure, the plurality of notched portions 111 of the plurality of rotor laminations facing each other in the height direction communicate with each other, and in this embodiment, the first annular portion 11a is smaller in size in the radial direction than the second annular portion 11b.

It will be appreciated that the cutouts 111 may be provided at different locations of different rotor laminations to form the isolated outer magnetic bridges, but still need to be able to perform the corresponding function.

It should be noted that, the size of each inner magnetic bridge along the circumferential direction of the rotor core 1 is w1, the size along the radial direction of the rotor core 1 is L1,3 is less than or equal to L1/w1 is less than or equal to 6, that is, when the size of the inner magnetic bridge is designed, the length and width of the inner magnetic bridge are designed according to the above ratio relation, for products with different specifications, specific size values of the inner magnetic bridge are different, for example, w1 of 60 machine bases takes 0.17-0.53 mm, L1 takes 0.51-3.18 mm, w1 of 130 machine bases takes 0.25-0.75 mm, L1 takes 0.75-4.5 mm, the machine bases refer to square flanges for connection positioned at the front side of the front end cover, and the corresponding 60 machine bases are square flanges with side lengths of 60 mm.

In other embodiments, the dimension of each inner magnetic bridge along the circumferential direction of the rotor core 1 is w1, and the thickness of each rotor lamination is h1, 0.5.ltoreq.w1/h 1.ltoreq.1.5. For example, a 60-stand conventionally designed rotor lamination has a thickness h1 of 0.35mm, w1 of 0.17 to 0.53mm, and a 130-stand conventionally designed rotor lamination has a thickness h1 of 0.5mm, w1 of 0.25 to 0.75mm.

In the technical scheme of the embodiment, the aspect ratio value of the inner magnetic bridge is defined to be more than or equal to 3 and less than or equal to L1/w1 and less than or equal to 6, and the ratio of the inner magnetic bridge to the thickness of the rotor lamination is more than or equal to 0.5 and less than or equal to w1/h1 and less than or equal to 1.5.

After the external magnetic bridge is disconnected, the anti-demagnetizing capability of the magnetic steel 2 is weakened when the external magnetic bridge is in weak magnetism, in one embodiment, two magnetic barrier grooves 112 are concavely formed at positions of two opposite side walls of the magnetic steel groove 11, which are close to the opening 111, and an air gap space is formed between each magnetic barrier groove 112 and the magnetic steel 2 arranged in the magnetic steel groove 11. The risk of local demagnetization of the magnet steel 2 is reduced by the design of the magnetic barrier groove 112, and it should be understood that after assembly, the air is in the magnetic barrier groove 112, and the magnet steel 2 does not extend to the position to shield the position.

Further, in order to ensure the effect of the magnetic barrier groove 112, in one embodiment, the dimension of the magnetic barrier groove 112 along the radial direction of the rotor core 1 is L2, and the dimension of each magnetic steel 2/magnetic steel groove 11 along the radial direction of the rotor core 1 is L3, wherein 1/10L3 is equal to or less than L2 is equal to or less than 1/6L3; in other embodiments, the dimension of the magnetic barrier groove 112 along the circumferential direction of the rotor core 1 is w2, and the dimension of each magnetic steel 2 along the circumferential direction of the rotor core 1 is h2, wherein 1/3h2 is equal to or less than w2 is equal to or less than 1/2h2. In the present embodiment, the shape of the magnetic barrier groove 112 is not limited, and may be a regular or irregular shape, and only the dimensions of the groove depth and the groove width thereof are correlated with the dimensions corresponding to the magnetic steel 2, thereby providing the same.

Furthermore, in the embodiment of the present utility model, at least part of the outer ends of the respective sector cores are positioned differently from the size of the space between the centers of the rotor core 1. Namely, by arranging the appearance of the rotor core 1, the air gap formed between the rotor core and the annular stator assembly is unevenly arranged, and the design mode can reduce cogging torque and torque fluctuation and improve motor performance.

The present utility model is not limited to the non-uniform design of the air gap, and in one embodiment, the distance between at least part of the outer side surface of each sector-shaped core part and the center of the rotor core 1 is gradually reduced in the direction from the center of the outer side surface of the sector-shaped core part to both sides of the outer side surface. That is, in the whole rotor core 1 structure, the uniformity distribution of the air gap between the rotor core 1 and the annular stator assembly is separated by the notch 111, so that a plurality of air gap sections are uniformly distributed, and the air gap between the notch 111 and the annular stator assembly is changed, and the outer edge of the air gap is in an irregular circular arc shape through the structural change of the sector core, so that the change of the air gap is more reasonable, and the rotation resistance is avoided.

Further, in this embodiment, referring to fig. 3 to 4, a first cambered surface section 131, two second cambered surface sections 132 connected to two ends of the first cambered surface section 131, and two inclined surface sections 133 connected to the two second cambered surface sections 132 are formed on the outer side surface of each fan-shaped core section, and the shape of the first cambered surface section 131 is adapted to the annular stator assembly. The notch 111 and the two inclined surface sections 133 and the two second cambered surface sections 132 arranged near the notch 111 together form a shape modification part, and the shape modification part is used for forming a variable air gap with the annular stator assembly, namely, when the rotor core 1 is designed, the shape modification part adopts a combination of three parts of an arc shape, a straight line and the notch 111. Due to the arrangement of the second cambered surface section 132 and the inclined surface section 133, the harmonic content of the air gap flux density can be reduced, and torque fluctuation is reduced.

Referring to fig. 4, in this example, the air gap between the first cambered surface section 111 and the annular stator assembly is the smallest, and gradually increases along the direction in which the center of the edge of the fan-shaped core part points to the two notch parts 111 adjacent thereto.

Based on the structural form, the central angle formed by the shaping part and the center of the rotor iron core 1 is alpha, wherein alpha is more than or equal to 50/p and less than or equal to 160/p, p is the pole pair number of the motor, and the unit of alpha is degree. It should be understood that the included angle α should include the central angle β1.

Further, the total length of the shaping portion along the circumferential direction of the rotor core 1 is T, and the sum of the lengths of the two second cambered surface sections 132 in the shaping portion is T1, wherein T1 is greater than or equal to 1/3T. The size range of each paragraph is constrained through ratio design, and the overall distribution of the air gap is ensured.

Further, two opposite sides of the adjacent fan-shaped core parts are respectively provided with a limiting part 12 at one side far away from the notch part 111, the two limiting parts 12 are in butt joint with the side faces of the magnetic steel 2 inserted into the magnetic steel groove 12, and the installation limiting of the magnetic steel 2 is realized through the two limiting parts 12, namely, when the magnetic steel 2 is fixedly installed, the contact between the magnetic steel 2 and the limiting parts 12 is ensured, and the risk of position deviation caused by the positioning of the notch part 111 is avoided.

In order to improve the reliability of the rotor, kevlar wires are wound around the circumferential side surface of the rotor core 1. When the outer magnetic bridge is disconnected, the kevlar wire is wound on the outer side of the rotor core 1 to fasten the rotor core, so that the mechanical strength of the rotor core 1 can be increased, and the reliability can be improved.

It will be appreciated that the number of layers of the winding of the kevlar wire depends on the size of the air gap between the rotor core 1 and the inner bore of the annular stator assembly, preferably the minimum value of the air gap between the core and the inner bore of the annular stator assembly should be greater than 0.2mm, so as to ensure the winding space of the kevlar wire.

The utility model also provides a rotor assembly, which comprises the rotor core 1 and the magnetic steel 2 arranged in the magnetic steel groove 11, and the rotor assembly comprises all the technical characteristics of the rotor core 1, so that the rotor assembly also has the technical effects brought by all the technical characteristics, and the technical effects are not repeated one by one.

The utility model also provides a motor, which comprises the rotor assembly and the annular stator assembly, wherein the rotor assembly comprises all the technical characteristics of the rotor core 1, so that the motor also has the technical effects brought by all the technical characteristics, and the technical effects are not repeated here. The motor further comprises an annular stator assembly, the rotor core 1 is positioned in an inner hole of the annular stator assembly, and an air gap is formed between the circumferential side surface of the rotor core 1 and the annular stator assembly.

The foregoing description is only of the preferred embodiments of the present utility model and is not intended to limit the scope of the utility model, and all equivalent structural changes made by the description of the present utility model and the accompanying drawings or direct/indirect application in other related technical fields are included in the scope of the utility model.

Claims

1. The rotor core is characterized by comprising a plurality of fan-shaped iron core parts which are arranged at intervals along the circumferential direction, wherein two adjacent fan-shaped iron core parts define a magnetic steel groove for installing magnetic steel, the magnetic steel groove is provided with an opening part, the fan-shaped iron core parts on two sides of the opening part are respectively provided with convex parts towards each other, the convex parts partially cover the opening part to form a notch part, the central angle formed by the notch part and the center of the rotor core is beta 1, and the central angle formed by the opening part and the center of the rotor core is beta, wherein the 1/6 beta is less than or equal to beta 1 and less than or equal to 2/3 beta.

2. The rotor core according to claim 1, wherein a central angle β1 corresponding to the notch is an angle formed by opposite side ends of the notch and a center of the rotor core;

And/or, the central angle beta corresponding to the opening part is an angle formed by the two intersection points formed by the convex parts extending to the magnetic steel groove and the convex parts and the center of the rotor core.

3. The rotor core according to claim 1, further comprising an inner annular portion provided with a central shaft hole, each of the segment core portions being provided outside the inner annular portion and connected to the inner annular portion by an inner magnetic bridge.

4. A rotor core according to claim 3, wherein each of said inner magnetic bridges has a dimension w1 in a circumferential direction of said rotor core, and a dimension L1 in a radial direction of said rotor core, 3.ltoreq.l1/w 1.ltoreq.6; and/or the number of the groups of groups,

The size of each inner magnetic bridge along the circumferential direction of the rotor core is w1, the rotor core comprises a plurality of rotor laminations which are sequentially stacked, and the thickness of each rotor lamination is h1, and w1/h1 is more than or equal to 0.5 and less than or equal to 1.5.

5. The rotor core as claimed in claim 1, wherein two side walls of the opening of the magnetic steel slot are concavely arranged to form two magnetic barrier slots, respectively, and an air gap space is provided between the magnetic barrier slots and the magnetic steel arranged in the magnetic steel slot.

6. The rotor core according to claim 5, wherein the dimension of the magnetic barrier grooves in the radial direction of the rotor core is L2, and the dimension of each magnetic steel groove in the radial direction of the rotor core is L3, wherein 1/10L3 is equal to or less than L2 is equal to or less than 1/6L3; and/or the number of the groups of groups,

The size of the magnetic barrier groove along the circumferential direction of the rotor core is w2, and the size of each magnetic steel groove along the circumferential direction of the rotor core is h2, wherein w2 is more than or equal to 1/3h2 and less than or equal to 1/2h2.

7. The rotor core as set forth in claim 1, wherein at least a portion of the outer side surface of each of the sector-shaped core portions is located at a different size from the pitch of the center of the rotor core.

8. The rotor core as set forth in claim 7, wherein the outer side surfaces of the respective sector-shaped core portions are disposed at a gradually decreasing interval from the center of the rotor core in a direction from the center of the outer side surfaces of the sector-shaped core portions toward both ends of the outer side surfaces.

9. The rotor core as set forth in claim 7, wherein each of the fan-shaped core portions has a first cambered surface section formed on an outer side thereof, two second cambered surface sections connected to both ends of the first cambered surface section, two inclined surface sections connected to both ends of the two second cambered surface sections, the first cambered surface section being shaped to fit with the annular stator assembly, the notch portion and the two inclined surface sections and the two second cambered surface sections disposed adjacent to the notch portion together forming a modified portion for forming a varying air gap with the annular stator assembly.

10. The rotor core according to claim 9, wherein the overall length of the shaping portion in the circumferential direction of the rotor core is T, and the sum of the lengths of two of the second cambered surface sections in the shaping portion is T1, wherein T1 is not less than 1/3T.

11. The rotor core of claim 9, wherein a central angle formed by the shaping portion and a center of the rotor core is α, wherein α is greater than or equal to 50/p and less than or equal to 160/p, and p is a pair of pole pairs of the motor.

12. The rotor core according to claim 1, wherein opposite side surfaces of the adjacent two fan-shaped core portions are each provided with a protruding portion on a side away from the notch portion, and the two protruding portions are abutted against side surfaces of the magnetic steel in the magnetic steel groove.

13. The rotor core according to claim 1, wherein a kevlar wire is wound around a peripheral side surface of the rotor core.

14. A rotor assembly comprising a rotor core as claimed in any one of claims 1 to 13 and magnetic steel disposed in the magnetic steel groove.

15. An electric machine comprising a rotor assembly as claimed in claim 14 and an annular stator assembly provided externally of the rotor assembly.