Rotor assembly and motor

Abstract

The invention provides a rotor assembly and a motor. The rotor assembly comprises a rotor punching sheet which is provided with a first weight reduction groove; the plurality of first weight reduction grooves are uniformly arranged along the circumferential direction of the rotor punching sheet. Each first weight reduction groove is symmetrically arranged along the q axis of the rotor punching sheet; the minimum distance between the first weight reduction grooves and the outer periphery of the rotor punching sheet is set as d, the diameter of the rotor punching sheet is set as D, and the ratio of d / D is 0.11-0.14. The first weight reduction grooves are formed in the rotor punching sheet, the distance between the first weight reduction grooves and the outer periphery of the rotor punching sheet is limited, it is clear that the first weight reduction grooves are away from the high flux density area of the rotor, the electromagnetic performance of the motor is not affected, and meanwhile the problem that the first weight reduction grooves are close to the center hole, and consequently stress concentration of the magnetic isolation bridge occurs is solved.

Description

Technical Field

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

[0002] Permanent magnet synchronous motors are gradually becoming one of the mainstream motors in automotive drive systems due to their excellent characteristics such as high efficiency, high power factor and high power density. In the design process of permanent magnet synchronous motors, the motor must be able to operate safely within the speed range required by the performance indicators. For this reason, the mechanical strength of the motor rotor structure must be checked to ensure that the motor rotor does not suffer serious deformation and damage under the action of centrifugal force when rotating at high speed.

[0003] The built-in permanent magnet rotor of the permanent magnet synchronous motor will generate centrifugal force when it rotates at high speed. This centrifugal force mainly acts on the rotor's magnetic isolation bridge, which can easily lead to damage to the rotor's magnetic isolation bridge. Although increasing the width of the magnetic isolation bridge can enhance the mechanical strength of the magnetic isolation bridge, as the width of the magnetic isolation bridge increases, the motor leakage increases and the electromagnetic performance of the permanent magnet motor decreases. Summary of the invention

[0004] Therefore, the present application provides a rotor assembly and a motor, which can solve the problem in the prior art that the magnetic isolation bridge of the rotor is very easy to be damaged.

[0005] In order to solve the above problems, the present application provides a rotor assembly, comprising: The rotor punching is provided with a first weight-reducing groove; a plurality of the first weight-reducing grooves are evenly arranged along the circumference of the rotor punching; each of the first weight-reducing grooves is symmetrically arranged along the q axis of the rotor punching; The minimum distance between the first weight-reducing groove and the outer periphery of the rotor punching is set to d, and the diameter of the rotor punching is set to D, satisfying a ratio of d / D of 0.11-0.14.

[0006] In some embodiments, The contour of the first weight-reducing groove is set to be an isosceles triangle, and adjacent sides are connected by chamfered corners; the distance between the bottom edge of the first weight-reducing groove and the outer periphery of the rotor punching sheet is the smallest.

[0007] In some embodiments, Four magnetic steel grooves are arranged symmetrically about the rotor punching d axis between adjacent q axes, and the four magnetic steel grooves form a double V-shaped structure, and the V-shaped opening faces the outer periphery of the rotor punching.

[0008] In some embodiments, The angle between the straight line where the waist of the first weight-reducing groove is located and the straight line where the side of the magnetic steel groove close to the first weight-reducing groove is located is set to a, satisfying a=53°-58°.

[0009] In some embodiments, The rotor punching is provided with a second weight-reducing groove, and a plurality of the second weight-reducing grooves are evenly arranged along the circumference of the rotor punching; each of the second weight-reducing grooves is symmetrically arranged along the d axis of the rotor punching, and is located between adjacent first weight-reducing grooves and close to one end of the center hole of the rotor punching.

[0010] In some embodiments, The contour of the second weight-reducing groove is formed by connecting the first arc and the second arc with rounded corners; the center of the first arc is located in the second weight-reducing groove, and the center of the second arc coincides with the center of the center hole; the second arc is closer to the center hole than the first arc.

[0011] In some embodiments, The distance between the center of the first arc and the center of the center hole is set to E, satisfying the ratio of E / D of 0.20-0.23.

[0012] In some embodiments, When the first weight-reducing groove has an isosceles triangle profile, the fillet radius at the vertex is set to r, and the radius of the first arc is set to R1, satisfying a ratio of R1 / r of 0.75-0.86.

[0013] In some embodiments, The radius of the second arc is set to R2, and the radius of the center hole is set to R0, satisfying R2-R0=12-16mm.

[0014] According to another aspect of the present application, a motor is provided, comprising the rotor assembly as described above.

[0015] A rotor assembly provided in the present application includes: a rotor punching, provided with a first weight-reducing groove; a plurality of the first weight-reducing grooves are provided and are evenly arranged along the circumference of the rotor punching; each of the first weight-reducing grooves is symmetrically arranged along the q axis of the rotor punching; the minimum distance between the first weight-reducing groove and the outer periphery of the rotor punching is set to d, and the diameter of the rotor punching is set to D, satisfying a ratio of d / D of 0.11-0.14.

[0016] This application has the following beneficial effects: By arranging the first weight reducing groove on the rotor punching sheet and limiting the distance between the first weight reducing groove and the outer periphery of the rotor punching sheet, the first weight reducing groove is clearly away from the high magnetic flux density area of ​​the rotor and does not affect the electromagnetic performance of the motor. At the same time, the first weight reducing groove is prevented from being close to the center hole, which would cause stress concentration problems on the magnetic isolation bridge. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the implementation methods or the prior art descriptions. The drawings described below are merely exemplary, and for those of ordinary skill in the art, other implementation drawings can be derived from the provided drawings without creative work.

[0018] Figure 1 This is a schematic diagram of the structure of the rotor punching sheet according to an embodiment of the present application; Figure 2 This is a schematic diagram of the structure of the rotor punching sheet according to an embodiment of the present application; Figure 3 For the embodiment of this application Figure 2 A partial enlarged view of Figure 4 is a stress simulation diagram of a rotor punching without the first weight-reducing groove; Figure 5 This is a stress simulation diagram of a rotor punching provided with a first weight-reducing groove in an embodiment of the present application; Figure 6 This is a stress simulation diagram of a rotor punching provided with a first weight-reducing groove and a second weight-reducing groove in an embodiment of the present application.

[0019] The reference numerals are: 1. Rotor punching; 2. Second magnetic steel slot; 3. First magnetic steel slot; 4. first weight reduction groove; 41. bottom edge; 42. waist; 5. Second weight-reducing groove; 51. First arc; 52. Second arc; 6. Center hole. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0022] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0023] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

[0024] See also Figures 1 to 6 As shown, according to an embodiment of the present application, a rotor assembly includes: The rotor punching 1 is provided with a first weight-reducing groove 4; the first weight-reducing groove 4 is provided with a plurality of grooves evenly arranged along the circumference of the rotor punching 1; each of the first weight-reducing grooves 4 is symmetrically arranged along the axis of the rotor punching 1q; The minimum distance between the first weight-reducing groove 4 and the outer periphery of the rotor punching 1 is set to d, and the diameter of the rotor punching 1 is set to D, satisfying a ratio of d / D of 0.11-0.14.

[0025] The present application sets a first weight reducing groove 4 on the rotor punching sheet 1, limits the distance between the first weight reducing groove 4 and the outer periphery of the rotor punching sheet 1, clarifies that the first weight reducing groove 4 is away from the high magnetic flux density area of ​​the rotor and does not affect the electromagnetic performance of the motor. At the same time, it prevents the first weight reducing groove 4 from being close to the center hole 6, which would cause stress concentration problems on the magnetic isolation bridge.

[0026] The first weight-reducing groove 4 is symmetrically arranged about the q-axis of the rotor punching sheet 1 , which can effectively reduce the mass of the rotor punching sheet 1 , reduce iron loss, and improve motor efficiency.

[0027] like Figure 4 As shown, the maximum stress on the conventional rotor punching sheet 1 is mainly concentrated on the magnetic isolation bridge between the first magnetic steel slots 3. In the present application, the first weight reduction slot 4 is arranged on the rotor punching sheet 1, especially the first weight reduction slot 4 is close to the magnetic steel slot. Such arrangement optimizes the stress concentration problem of the magnetic isolation bridge rotor here. Figure 5 As shown in the figure, the maximum stress of rotor punching 1 is reduced from 359MPa to 300MPa, and the rotor strength is increased by 16%.

[0028] For a motor rotor with a rotor punching sheet 1 having a diameter D of 150-200 mm, d can be selected to be 20-22 mm.

[0029] In some embodiments, The contour of the first weight-reducing groove 4 is set to be an isosceles 42 triangle, and adjacent sides are connected by chamfered corners; the distance between the bottom edge 41 of the first weight-reducing groove 4 and the outer periphery of the rotor punching 1 is the smallest.

[0030] The first weight-reducing groove 4 is symmetrically arranged along the axis of the rotor punching 1q. The present application specifically adopts an isosceles 42-triangular first weight-reducing groove 4, and adjacent edges are connected by chamfered corners to reduce stress concentration. The bottom edge 41 of the first weight-reducing groove 4 is at the smallest distance from the outer periphery of the rotor punching 1, so that the center of the first weight-reducing groove 4 is close to the outer periphery, thereby preventing stress from being concentrated on the magnetic isolation bridge.

[0031] In some embodiments, Four magnetic steel grooves are arranged symmetrically about the rotor punching sheet 1d axis between adjacent q axes, and the four magnetic steel grooves form a double V-shaped structure, and the V-shaped opening faces the outer periphery of the rotor punching sheet 1.

[0032] The present application adopts a double V configuration of four magnetic steel slots, which expands the number of magnetic isolation bridges, thereby further dispersing the problem of stress concentration and optimizing the distribution of stress.

[0033] In some embodiments, The angle between the straight line where the waist 42 of the first weight-reducing groove 4 is located and the straight line where the side of the magnetic steel groove close to the first weight-reducing groove 4 is located is set to a, satisfying a=53°-58°.

[0034] There is a straight line angle relationship between the first weight-reducing groove 4 and the adjacent first magnetic steel groove 3 , so that the first weight-reducing groove 4 can achieve the best effect of reducing the rotor stress and mass, while ensuring that the electromagnetic performance of the motor is not affected by the first weight-reducing groove 4 .

[0035] In some embodiments, The rotor punching 1 is provided with a second weight-reducing groove 5, and a plurality of the second weight-reducing grooves 5 are evenly arranged along the circumference of the rotor punching 1; each of the second weight-reducing grooves 5 is symmetrically arranged along the axis of the rotor punching 1d, and is located between adjacent first weight-reducing grooves 4, close to one end of the center hole 6 of the rotor punching 1.

[0036] The partial area of ​​the rotor core close to the center hole 6 contributes less to the electromagnetic performance. Excessive weight will increase the centrifugal load, reduce the fatigue life of the rotor core, and increase the design cost.

[0037] In order to further reduce the mass of the rotor punching 1, the present application provides a second weight-reducing groove 5 on the rotor punching 1 near the center hole 6. The second weight-reducing groove 5 is arranged on the d-axis position of the rotor punching 1 and is symmetrically arranged along the d-axis. It can effectively block the armature direct-axis magnetic circuit, reduce the direct-axis inductance, increase the salient pole ratio, increase the reluctance torque, reduce the leakage flux at this location, and improve the motor efficiency.

[0038] The second weight-reducing groove 5 and the first weight-reducing groove 4 are staggered in the radial direction of the rotor punching 1, so that the overall mass distribution of the rotor punching 1 is uniform, and thus the stress distribution is also uniform, thereby avoiding the problem of stress concentration.

[0039] In some embodiments, The contour of the second weight-reducing groove 5 is formed by connecting the first arc 51 and the second arc 52 with rounded corners; the center of the first arc 51 is located in the second weight-reducing groove 5, and the center of the second arc 52 coincides with the center of the center hole 6; the second arc 52 is closer to the center hole 6 than the first arc 51.

[0040] The second weight-reducing groove 5 is formed by two transitionally connected arcs to avoid stress concentration in the second weight-reducing groove 5 itself. The center of the second weight-reducing groove 5 is located close to the center hole 6, which can reduce the mass near the center hole 6 and reduce the magnetic density there, which is beneficial to the motor efficiency.

[0041] In some embodiments, The distance between the center of the first arc 51 and the center of the center hole 6 is set to E, satisfying the ratio of E / D of 0.20-0.23.

[0042] Setting the distance between the center of the first arc 51 and the center of the center hole 6 and the ratio of the diameter of the entire rotor punching 1 can make the second weight-reducing groove 5 as close to the center hole 6 as possible, which is beneficial to reducing rotor stress without affecting electromagnetic performance.

[0043] Specifically, for a motor structure in which the outer edge diameter of the rotor punching sheet 1 is 150-200 mm, the distance between the center of the first arc 51 and the center of the center hole 6 may be 35-37 mm.

[0044] In some embodiments, When the contour of the first weight-reducing groove 4 is an isosceles 42-angle triangle, the fillet radius at the vertex is set to r, and the radius of the first arc 51 is set to R1, satisfying the ratio of R1 / r of 0.75-0.86.

[0045] The ratio between the fillet radius of the top corner of the first weight-reducing groove 4 and the radius of the first arc 51 of the second weight-reducing groove 5 can form a gap between the first weight-reducing groove 4 and the second weight-reducing groove 5, and prevent the gap from being too small, which would lead to stress concentration, and prevent the gap from being too large, which would lead to reduced weight-reducing and stress-reducing effects of the second weight-reducing groove 5.

[0046] Combination Figure 5 and 6 As shown, the structure having both the first weight-reducing groove 4 and the second weight-reducing groove 5 can further reduce the stress of the magnetic bridge between the first magnetic steel grooves 3, so that the maximum stress of the rotor is reduced from 300 MPa to 2714 MPa, and the maximum stress of the rotor is reduced by 8.6%.

[0047] In some embodiments, The radius of the second arc 52 is set to R2, and the radius of the center hole 6 is set to R0, satisfying R2-R0=12-16.

[0048] More specifically, the distance between the second arc 52 of the second weight-reducing groove 5 and the center hole 6 is set based on the fact that the second arc 52 and the center hole 6 are concentric. In fact, the distance between the outer edge of the center hole 6 and the second arc 52 is the difference in radius between the two. This constraint relationship prevents the second weight-reducing groove 5 from being close to the center hole 6, which would cause stress concentration problems.

[0049] Specifically, for a motor structure in which the outer edge diameter of the rotor punching sheet 1 is 150-200 mm, the difference between the radius of the center hole 6 and the radius of the second arc 52 is 12-16 mm.

[0050] According to another aspect of the present application, a motor is provided, comprising the rotor assembly as described above.

[0051] This application adopts the above-mentioned rotor assembly, which can solve the problems of insufficient strength of the rotor punching 1, large rotor core mass, and low efficiency when the drive motor is at high speed. Weight reduction grooves are added to the area near the rotating shaft on the rotor core to reduce the rotor mass while ensuring electromagnetic performance and optimize stress distribution. By optimizing the coordination of the weight reduction grooves and the magnetic steel grooves, the stress of the magnetic isolation bridge is reduced, the distribution of the rotor magnetic lines of force is improved, and the harmonic content is reduced. The final beneficial effect is: while ensuring electromagnetic performance, the maximum rotor stress is reduced from 359MPa to 274MPa, a reduction of 23%; the motor efficiency is increased from 95.6% to 96.1%, and the efficiency optimization is increased by 0.5%.

[0052] The structure of the rotor assembly is described in detail below by taking a motor structure in which the outer edge diameter of the rotor punching 1 is 150-200 mm as an example.

[0053] The rotor punching 1 comprises a first magnetic steel slot 3, a second magnetic steel slot 2, a first weight-reducing slot 4, a second weight-reducing slot 5 and a center hole 6. All the magnetic steel slots and weight-reducing slots are evenly and spacedly distributed in the circumferential direction of the rotor punching 1.

[0054] like Figure 1 As shown, the first weight-reducing groove 4 is an isosceles triangular groove 42, which is surrounded by a base 41 and a waist 42. The connection between the base 41 and the waist 42 is connected by a chamfer, wherein the radius of the chamfers at the three connections is r, r=8~9mm. This constraint relationship makes the chamfers large enough to prevent stress concentration problems and helps to diffuse stress at the connection. At the same time, it prevents the chamfers from being too large, which would lead to a small weight-reducing groove.

[0055] The first weight-reducing groove 4 is symmetrical about the q-axis of the rotor punching sheet 1 , which can effectively reduce the rotor mass, reduce iron loss, and improve motor efficiency.

[0056] The distance between the bottom edge 41 of the first weight-reducing groove 4 and the outer edge of the rotor punching 1 is d, d=20-22mm. This constraint relationship keeps the weight-reducing groove away from the high magnetic density area of ​​the rotor and does not affect the electromagnetic performance of the motor. At the same time, it prevents the weight-reducing groove from being close to the center hole 6, which causes stress concentration problems on the side of the weight-reducing groove close to the center hole 6.

[0057] The angle between the waist 42 of the first weight-reducing groove 4 and the side of the first magnetic steel groove 3 is a, a=53°~58°. This constraint relationship optimizes the weight-reducing groove to reduce the rotor stress and mass, while ensuring that the electromagnetic performance of the motor is not affected by the weight-reducing groove. The maximum rotor stress is mainly concentrated on the magnetic isolation bridge between the first magnetic steel grooves 3. The setting of the first weight-reducing groove 4 optimizes the rotor stress concentration problem of the magnetic isolation bridge here. The maximum rotor stress is reduced from 359MPa to 300MPa, and the rotor strength is increased by 16%.

[0058] The second weight-reducing groove 5 is semicircular in shape and is composed of a first arc 51 and a second arc 52. The first arc 51 and the second arc 52 are connected by a chamfered corner for easy processing. The second weight-reducing groove 5 is symmetrically arranged about the d-axis of the rotor punching sheet 1, which can effectively block the armature direct-axis magnetic circuit, reduce the direct-axis inductance, increase the salient pole ratio, increase the magnetic resistance torque, reduce the leakage flux at this location, and improve the motor efficiency.

[0059] The distance between the center of the first arc 51 of the second weight-reducing groove 5 and the center of the center hole 6 is R2, R2=35~37mm. This constraint relationship makes the second weight-reducing groove 5 located on the proximal side, which is beneficial to reducing rotor stress without affecting the electromagnetic performance of the motor.

[0060] The radius of the first arc 51 of the second weight-reducing groove 5 is R1, and the radius of the chamfer of the first weight-reducing groove 4 is r, wherein there is a constraint relationship: R1=(0.75~0.86)r. This constraint relationship forms a gap between the semicircular second weight-reducing groove 5 and the first weight-reducing groove 4 to prevent the gap from being too small, which would lead to stress concentration, and also prevent the gap from being too large, which would lead to reduced weight-reducing and stress-reducing effects of the second weight-reducing groove 5.

[0061] The radius of the second arc 52 of the second weight-reducing groove 5 is R2, the center of the second arc 52 coincides with the center of the center hole 6, the radius of the center hole 6 is R0, R2=R0+(12~16)mm, and this constraint relationship prevents the second weight-reducing groove 5 from being close to the center hole 6, resulting in stress concentration problems on the side of the weight-reducing groove close to the center hole 6. Compared with the rotor with only the first weight-reducing groove 4, the provision of the second weight-reducing groove 5 further reduces the stress on the magnetic bridge between the first magnetic steel slots 3, reducing the maximum rotor stress from 300MPa to 274MPa, and the maximum rotor stress is reduced by 8.6%.

[0062] By adding the plurality of weight-reducing grooves to the rotor core, the rotor mass can be reduced while ensuring electromagnetic performance, saving material costs, optimizing stress distribution, reducing iron loss, and improving efficiency.

[0063] It is easy for those skilled in the art to understand that the above-mentioned implementation modes can be freely combined and superimposed without conflict.

[0064] The above is only a preferred embodiment of the present application and is 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 is only a preferred implementation 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: include: A rotor punching (1) is provided with a first weight-reducing groove (4); a plurality of the first weight-reducing grooves (4) are evenly arranged along the circumference of the rotor punching (1); each of the first weight-reducing grooves (4) is symmetrically arranged along the q axis of the rotor punching (1); The minimum distance between the first weight-reducing groove (4) and the outer periphery of the rotor punching sheet (1) is set to d, and the diameter of the rotor punching sheet (1) is set to D, satisfying a ratio of d / D of 0.11-0.

14.

2. The rotor assembly according to claim 1, characterized in that: The contour of the first weight-reducing groove (4) is set to be an isosceles (42) triangle, and adjacent sides are connected by chamfered corners; the distance between the bottom edge (41) of the first weight-reducing groove (4) and the outer periphery of the rotor punching sheet (1) is the smallest.

3. The rotor assembly according to claim 2, characterized in that: Four magnetic steel grooves are arranged symmetrically about the d axis of the rotor punching (1) between adjacent q axes, the four magnetic steel grooves forming a double V-shaped structure, and the V-shaped opening faces the outer periphery of the rotor punching (1).

4. The rotor assembly according to claim 3, characterized in that: The angle between the straight line where the waist (42) of the first weight-reducing groove (4) lies and the straight line where the side of the magnetic steel groove close to the first weight-reducing groove (4) lies is set to a, satisfying a=53°-58°.

5. The rotor assembly according to any one of claims 1 to 4, characterized in that: The rotor punching (1) is provided with a second weight-reducing groove (5), and a plurality of the second weight-reducing grooves (5) are evenly arranged along the circumference of the rotor punching (1); each of the second weight-reducing grooves (5) is symmetrically arranged along the d axis of the rotor punching (1), and is located between adjacent first weight-reducing grooves (4) and close to one end of the center hole (6) of the rotor punching (1).

6. The rotor assembly according to claim 5, characterized in that: The contour of the second weight-reducing groove (5) is formed by connecting the first arc (51) and the second arc (52) with rounded corners; the center of the first arc (51) is located in the second weight-reducing groove (5), and the center of the second arc (52) coincides with the center of the center hole (6); the second arc (52) is closer to the center hole (6) relative to the first arc (51).

7. The rotor assembly according to claim 6, characterized in that: The distance between the center of the first arc (51) and the center of the center hole (6) is set to E, satisfying the ratio of E / D of 0.20-0.

23.

8. The rotor assembly according to claim 6 or 7, characterized in that: When the first weight-reducing groove (4) has an isosceles (42) triangle profile, the fillet radius at its vertex is set to r, and the radius of the first arc (51) is set to R1, satisfying a ratio of R1 / r of 0.75-0.

86.

9. The rotor assembly according to claim 6 or 7, characterized in that: The radius of the second arc (52) is set to R2, and the radius of the center hole is set to R0, satisfying R2-R0=12-16mm.

10. A motor, characterized in that: Comprising a rotor assembly as claimed in any one of claims 1 to 9.

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