electric machine

Abstract

The application relates to an electric machine, which comprises a rotor, the rotor comprising a rotor core having an outer side wall provided with a plurality of spaced recesses penetrating the outer side wall along an axial direction of the rotor core, wherein the recesses have a preset inclination angle relative to the axial direction so that the recesses can guide fluid from one side of the rotor core to the other side along the axial direction when the rotor core rotates. The rotor and the electric machine can have a good heat dissipation effect without occupying additional space of the electric machine, thereby avoiding the problems of performance reduction and service life shortening of the electric machine due to excessively high temperature of the electric machine.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric machines, in particular to an electric machine. BACKGROUND

[0002] The electric machine has high running accuracy and adjustable and controllable speed, and is a kind of driving device for converting voltage signals into torque and speed. A large amount of heat is generated during long-time operation of the electric machine in actual use, and the heat will affect the working performance of the electric machine, especially the encoder, and reduce the accuracy thereof. The current servo motor mainly relies on natural air cooling for heat dissipation, and the application occasion of the servo motor is limited, resulting in a small installation space and poor external air flow. When the external air flow is insufficient, the heat generated by the servo motor cannot be timely conducted outward, the heat is accumulated on the servo motor, and the encoder is greatly affected, the accuracy of the servo motor is affected, and the service life of the servo motor is reduced. SUMMARY

[0003] The purpose of the present application is to provide a rotor and an electric machine, which have good heat dissipation effect without occupying additional space of the electric machine, and avoid the problems of performance degradation and service life shortening of the electric machine due to excessive temperature thereof.

[0004] To this end, in a first aspect, an embodiment of the present application provides a rotor for an electric machine, comprising:

[0005] A rotor core has an outer side wall, and the outer side wall is provided with a plurality of recesses arranged at intervals, and the recesses penetrate the outer side wall along an axial direction of the rotor core,

[0006] The extension direction of the recesses has a preset inclination angle relative to the axial direction, so that when the rotor core rotates, the recesses can guide the fluid from one side of the rotor core to the other side along the axial direction.

[0007] In a possible implementation, the recesses of any cross section along the extension direction have the same morphology,

[0008] The recesses are first grooves recessed inward relative to the axis of the rotor core, and the first grooves have a preset maximum depth.

[0009] In a possible implementation, the preset maximum depth is not greater than 1.5 mm.

[0010] In a possible implementation, the first grooves are arc-shaped grooves, and along the axial direction, the recesses form a first recessed track and a second recessed track at both ends of the outer side wall, respectively, the first recessed track has a first axis, and the second recessed track has a second axis,

[0011] An angle between a line connecting the first axis and the second axis and an axis of the rotor core is the preset inclination angle, and the preset inclination angle is not greater than 30°.

[0012] In a possible implementation, the preset inclination angle ranges between 20° and 28°.

[0013] In a possible implementation, the outer side wall is provided with a plurality of second grooves arranged at intervals, the second grooves penetrating the outer side wall along the axial direction, and the second grooves and the recesses are arranged alternately.

[0014] In a possible implementation, along a circumferential direction of the outer side wall, a minimum distance between an edge of the recess and an edge of an adjacent second groove is greater than 5 mm.

[0015] In a possible implementation, the rotor core is further provided with a plurality of through holes arranged circumferentially, and along a radial direction of the rotor core, the through holes are opposite to the second grooves,

[0016] A minimum thickness between the through hole and an adjacent recess is not less than 10 mm.

[0017] In a second aspect, an embodiment of the present application provides an electric machine, comprising:

[0018] A housing having an inner cavity, the housing comprising a first end cover and a second end cover, the first end cover being provided with an air inlet communicating with the inner cavity, and the second end cover being provided with an air outlet communicating with the inner cavity;

[0019] A drive assembly arranged in the inner cavity, the drive assembly comprising a rotor shaft; and

[0020] The rotor described in the above is sleeved on an outer circumferential side of the rotor shaft.

[0021] In a possible implementation, the air inlet and the air outlet are respectively provided in a plurality of numbers, and along the axial direction, the air inlet and the air outlet are respectively located on two sides of the rotor,

[0022] An axis of the air inlet is parallel to an axis of the rotor, and an axis of the air outlet has a preset angle with the axis of the rotor.

[0023] In a possible implementation, the preset angle ranges between 30° and 60°.

[0024] In a possible implementation, fluid in the inner cavity between the rotor and the first end cover has a first pressure p1, fluid in the inner cavity between the rotor and the second end cover has a second pressure p2, the preset inclination angle and the preset maximum depth of the recess are calculated according to the following formula:

[0025] W = (p2-p1) / p + (c2 2-c1 2) / 2;

[0026] EK = mv 2 / 2;

[0027] wherein W is total kinetic energy of the rotor, p is fluid density, c1 is absolute speed of fluid at the air outlet at a first temperature, c2 is absolute speed of fluid at the air outlet at a second temperature, the second temperature is greater than the first temperature, EK is change in kinetic energy, m is mass of the rotor, and v is rotational speed of the rotor.

[0028] In a possible implementation, a dust screen is further included, and the dust screen is arranged at a position corresponding to the air inlet and the air outlet, respectively.

[0029] According to the rotor and the motor provided in the embodiments of the present application, the plurality of recesses with the preset inclination angle are arranged on the outer side wall of the rotor core, so that the plurality of recesses combine to form a spiral sector chute structure on the outer side wall of the rotor. When the rotor works in the motor, the rotor rotates, and a local vacuum is formed around the rotor core, so that the air around the rotor core is sucked into the recesses, and an air flow effect is generated. In addition, the recesses are arranged to make the direction of the air flow parallel to the axial direction, so that the air flow can flow into and out of the rotor core along the axial direction. Therefore, the recesses arranged on the rotor core can have a good heat dissipation effect without occupying additional space of the motor, and can avoid the problems of performance degradation and service life shortening of the motor caused by excessively high temperature of the motor. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings. In addition, the same components are marked with the same reference numerals in the drawings, and the drawings are not drawn according to the actual proportion.

[0031] Figure 1 A cross-sectional front view of a motor is shown, wherein the direction indicated by the arrow H is the axial direction;

[0032] Figure 2 Fig. 1 shows a schematic diagram of a rotor structure according to an embodiment of the present application;

[0033] Figure 3 Fig. 2 shows a schematic diagram of a second end cover structure in a motor according to an embodiment of the present application;

[0034] Figure 4 Fig. 3 shows a schematic diagram of a first end cover structure in a motor according to an embodiment of the present application;

[0035] Figure 5 Fig. 4 shows a schematic diagram of an air flow direction in a motor according to an embodiment of the present application.

[0036] Legend of reference signs:

[0037] 100, motor; 1, second end cover; 11, air outlet; 111, air outlet passage; 2, first end cover; 21, air inlet; 211, air inlet passage; 3, inner cavity; 4, driving assembly; 41, rotor shaft; 42, rotor; 42a, rotor core; 421, recessed part; 422, second recess; 423, through hole; 5, dust screen. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0039] Figure 1 Fig. 5 shows a cross-sectional front view of a motor according to an embodiment of the present application, wherein the direction indicated by arrow H is the axial direction. Figure 2 Fig. 1 shows a schematic diagram of a rotor structure according to an embodiment of the present application;

[0040] Referring to Figure 1 and Figure 2 , the present application provides a motor 100, which can be a servo motor, for example, and the following will not emphasize it separately. The servo motor refers to a motor for controlling the movement of mechanical elements in a servo system, and is an auxiliary motor indirect speed changing device, and its application fields can include robots, motors, etc., and its specific application scenarios are not limited here.

[0041] The application also provides a rotor. The motor 100 comprises a housing having an inner cavity 3, the housing comprises a first end cover 2 and a second end cover 1 connected to each other, the first end cover 2 and the second end cover 1 are detachably connected in the axial direction H and form the inner cavity 3 after being connected. The inner cavity 3 is used to arrange a driving assembly 4, the driving assembly 4 comprises a rotor shaft 41, the rotor shaft 41 is coaxially provided with a rotor 42, the rotor 42 is sleeved on the outer circumferential side of the rotor shaft 41. It can be understood that the driving assembly 4 also comprises a stator and other matching components matched with the rotor 42, which will not be described in detail here.

[0042] The first end cover 2 is provided with an air inlet 21 communicating with the inner cavity 3, and the second end cover 1 is provided with an air outlet 11 communicating with the inner cavity 3. The rotor 42 comprises a rotor core 42a having an outer side wall provided with a plurality of recesses 421 arranged at intervals, and the recesses 421 penetrate the outer side wall in the axial direction H of the rotor core 42a. By arranging the recesses 421 on the rotor 42 and the air inlets 21 and air outlets 11 corresponding to the recesses 421 arranged on the first end cover 2 and the second end cover 1 respectively, heat dissipation can be achieved for the inside of the motor 100, without the need to additionally arrange corresponding heat dissipation devices in the motor 100, and without the need to additionally occupy space.

[0043] Among the plurality of recesses 421 arranged on the outer side wall of the rotor core 42a, the extension direction of the recesses 421 has a preset inclination angle relative to the axial direction H, so that when the rotor core 42a rotates, the recesses 421 can guide the fluid from one side of the rotor core 42a to the other side in the axial direction H. By arranging a plurality of recesses 421 with a preset inclination angle on the outer side wall of the rotor core 42a, the plurality of recesses 421 combine to form a spiral sector chute structure on the outer side wall of the rotor 42. Thus, when the rotor 42 rotates during operation of the motor 100, a local vacuum is formed around the rotor core 42a, air around the rotor core 42a is sucked into the recesses 421, and an air flow effect is generated. Moreover, the direction of the air flow is parallel to the axial direction H, so that the air flow can flow into and out of the rotor core 42a in the axial direction H. Therefore, by arranging the recesses 421 on the rotor core 42a, a better heat dissipation effect can be achieved without additionally occupying space in the motor 100, and the problems of performance degradation and short service life caused by excessive temperature of the motor 100 can be avoided.

[0044] In an optional embodiment, referring to Figure 2Along the extending direction, the recessed portion 421 of any cross-section has the same shape. The recessed portion 421 is a first groove recessed inward relative to the axis of the rotor core 42a, and the first groove has a preset maximum depth. That is, along the extending direction of the recessed portion 421, the shape and size of the recessed trajectory formed by the recessed portion 421 of each cross-section are the same, and the maximum depth of each part relative to the rotor core 42a is the same. This design is used to limit the depth of the recessed portion 421 relative to the rotor core 42a, so as to ensure that when the rotor core 42a rotates, the recessed portion 421 rotates accordingly to form eddies, thereby realizing air flow inside the motor 100. In conjunction with the air inlet and air outlet provided on both sides, heat dissipation inside the motor 100 is achieved.

[0045] It is understood that the fluid can be air, or other flowing gases or liquids, and no specific limitation is made here. In the embodiments of this application, the fluid refers to air, and will not be emphasized separately thereafter.

[0046] Optionally, the preset maximum depth is no more than 1.5mm. It is understood that the preset maximum depth is a preferred implementation method. The preset maximum depth will be adjusted according to different models and specifications of motor 100, as well as the position and size of inlet and outlet, etc., and no specific limitation is made here.

[0047] In an optional embodiment, the first groove is an arc-shaped groove along the axial direction H. The recessed portion 421 forms a first recessed trajectory and a second recessed trajectory at both ends of the outer wall. The first recessed trajectory has a first axis, and the second recessed trajectory has a second axis. The angle between the line connecting the first and second axes and the axis of the rotor core 42a is a preset inclination angle. This allows the first groove to be configured as an inclined groove on the outer wall at a certain angle relative to the axial direction H. Multiple inclined grooves form a spiral groove on the outer wall, so that when the rotor core 42a rotates, the rotation of the multiple inclined grooves creates a vacuum around the rotor core 42a, allowing the surrounding air to form vortices, thereby achieving a heat dissipation effect.

[0048] It is understandable that the first groove can also be set as a square groove, an elliptical groove, or other shapes, as long as it can meet the requirements of the tilt angle and depth mentioned above. No specific limitation is made here.

[0049] Optionally, the preset tilt angle is no greater than 30°. Preferably, the preset tilt angle is in the range of 20°-28°. In this embodiment, the preset tilt angle is set to 25°, and no specific limitation is made here.

[0050] The specific structure of the rotor provided in the embodiments of this application will be further described in detail below with reference to the accompanying drawings.

[0051] With reference to Figure 2 The rotor provided by the embodiment of the present application is based on a cylindrical rotor core 42a, and a plurality of second grooves 422 are arranged on the outer side wall of the rotor core 42a. The second grooves 422 penetrate the outer side wall in the axial direction H, and the second grooves 422 and the recesses 421 are arranged alternately. The second grooves 422 are air holes arranged on the rotor 42. When the recesses 421 are arranged on the outer side wall of the rotor core 42a, the recesses 421 and the second grooves 422 need to be designed to avoid interference, and the distance between the recesses 421 and the second grooves 422 is a certain distance.

[0052] Optionally, the minimum distance between the edge of the recess 421 and the edge of the adjacent second groove 422 along the circumference of the outer side wall is greater than 5 mm.

[0053] In an optional embodiment, the rotor core 42a is further provided with a plurality of through holes 423 arranged in the circumferential direction. The through holes 423 are opposite to the second grooves 422 in the radial direction of the rotor core 42a. The through holes 423 are used to arrange the stator, which will not be described in detail here.

[0054] When a plurality of recesses 421 are arranged, in order to avoid the distance between the arranged recesses 421 and the through holes 423 being too close, which causes the local part of the rotor core 42a to be relatively weak, and further affects the strength of the rotor core 42a itself, the minimum thickness between the through hole 423 and the adjacent recess 421 is not less than 10 mm. It can be understood that the rotor core 42a arranged on the motor 100 of different models and specifications will also be different, and the minimum thickness arranged according to different needs will also be different, which can be adjusted adaptively according to the actual situation, and will not be specifically limited here.

[0055] Optionally, the number of recesses 421 arranged on the rotor core 42a can be adaptively selected according to the maximum depth of the recess 421, the inclination angle, and the actual situation of the model of the motor 100, and will not be specifically limited here. In the embodiment of the present application, the number of recesses 421 is 10.

[0056] The motor 100 can realize heat dissipation inside the motor 100 by arranging the recesses 421 on the rotor 42 and cooperating with the air inlet 21 and the air outlet 11, thereby avoiding damage to the encoder. The recesses 421 arranged on the rotor 42 can be adaptively matched according to the above-mentioned limitations combined with the specific model of the motor 100, and will not be described in detail here. Alternatively, the recesses 421 arranged on the rotor 42 can also be calculated as follows:

[0057] In a specific embodiment, with reference to Figures 3 to 5, the fluid in the inner cavity 3 between the rotor 42 and the first end cover 2 has a first pressure p1, the fluid in the inner cavity 3 between the rotor 42 and the second end cover 1 has a second pressure p2, the preset inclination angle and the preset maximum depth of the recess 421 are calculated according to the following formula:

[0058] W = (p2-p1) / p + (c2 2-c1 2) / 2;

[0059] EK=mv 2 / 2;

[0060] Wherein, W is the total kinetic energy of the rotor, p is the fluid density, c1 is the absolute speed of the fluid at the air outlet 11 at the first temperature, c2 is the absolute speed of the fluid at the air outlet 11 at the second temperature, the second temperature is greater than the first temperature, EK is the change of kinetic energy, m is the mass of the rotor 42, v is the rotational speed of the rotor 42.

[0061] Optionally, the first temperature and the second temperature are the corresponding measured values of the motor 100 at two different temperatures, for example, the second temperature can be 60°, and the first temperature can be 40°, which will not be described in detail here.

[0062] It can be understood that the above calculation formula can be obtained based on Bernoulli's principle and Euler's equation as the theoretical basis, and the detailed derivation process will not be described in detail here. According to the law of conservation of energy, W=EK, the mass of the rotor core 42a is obtained, and then the number, depth and shape of the recess 421 are designed according to the actual situation, which will not be described in detail here.

[0063] The inclination angle of the recess 421 can be selected adaptively by referring to the working principle of the electric fan as the theoretical basis, and combining the specific situation of the motor 100, and the specific derivation process and selection process will not be described in detail here.

[0064] Regardless of the way of obtaining the rotor 42 with the recess 421, the specific arrangement of the air inlet 21 and the air outlet 11 in the first end cover 2 and the second end cover 1 will be adaptively adjusted when the rotor 42 is arranged in the inner cavity 3 of the motor 100.

[0065] In an optional embodiment, the air inlets 21 and the air outlets 11 are respectively provided in plurality, and are respectively located on two sides of the rotor 42 along the axial direction H, the axis of the air inlets 21 is parallel to the axis of the rotor 42, and the axis of the air outlets 11 has a preset included angle with the axis of the rotor 42. The air inlets 21 and the air outlets 11 are arranged to cooperate with the recesses 421 of the rotor 42, and the arrangement of the air inlets 21 and the air outlets 11 can ensure a faster air inlet and outlet speed during the rotation of the recesses 421 to flow air, so as to ensure a better heat dissipation effect.

[0066] Optionally, the preset included angle is in a range of 30°-60°. Preferably, the preset included angle of the air outlets 11 is 45°.

[0067] It can be understood that the number of the air inlets 21 and the air outlets 11 arranged in the first end cover 2 and the second end cover 1 can be the same or different, which is not specifically limited here.

[0068] In an optional embodiment, the corresponding air inlet and outlet amounts can be calculated according to the recesses 421 of the rotor 42, and then the air inlets 21 and the air outlets 11 with appropriate diameters and numbers can be adaptively selected according to the air inlet and outlet amounts. Alternatively, on this basis, the number of air inlets and outlets can be adaptively increased or reduced in combination with the power of the selected motor 100. Preferably, the number of the air inlets 21 is 6, and the number of the air outlets 11 is 10.

[0069] Optionally, the maximum diameter enclosed by the plurality of air inlets 21 is a first diameter with the axis of the rotor core 42a as the center, the minimum diameter enclosed by the plurality of air outlets 11 is a second diameter, the second diameter is greater than the first diameter, and the first diameter of the air inlets 21 matches or approaches the minimum diameter enclosed by the plurality of recesses 421, which is not specifically limited here.

[0070] In an optional embodiment, the air inlets 21 form air inlet channels 211 extending along the axial direction H in the first end cover 2, and the air outlets 11 form air outlet channels 111 inclined outward by a preset included angle relative to the axial direction H in the second end cover 1. The diameters of the positions in the air inlet channels 211 and the air outlet channels 111 can be the same or different, and the minimum diameters thereof respectively serve as the air inlets 21 and the air outlets 11, which is not specifically limited here.

[0071] Optionally, a dust screen 5 is further included, and the dust screen 5 is arranged at positions corresponding to the air inlet 21 and the air outlet 11 respectively. That is, the dust screen 5 can be arranged in the air inlet channel 211 and the air outlet channel 111, or can be arranged outside the air inlet channel 211 and the air outlet channel 111, as long as the dust screen 5 can play a role of dust filtering, which is not limited in detail herein. It can be understood that other structures capable of having a dust filtering effect can also be arranged, and are not limited to the dust screen 5. Alternatively, a dust filtering screen can be arranged outside the first end cover 2 and the second end cover 1 to achieve the purpose of dust and water prevention, which is not described in detail herein.

[0072] It should be noted that the rotor 42 and the motor 100 provided in the embodiments of the present application are not limited to be applied to industrial robots and the field of aerospace, but can also be applied to other scenes that require transmission precision, large speed ratio, small size and simple structure, such as the field of precision equipment manufacturing, and the like, and will not be described herein.

[0073] It should be noted that the "one embodiment", "embodiment", "exemplary embodiment", "some embodiments" and the like mentioned in the specification mean that the described embodiments can include a specific feature, structure or characteristic, but not necessarily every embodiment includes the specific feature, structure or characteristic. In addition, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure or characteristic is described in connection with an embodiment, it is within the knowledge of those skilled in the art to realize such feature, structure or characteristic in connection with other embodiments described explicitly or implicitly.

[0074] It should be readily understood that "on", "above", and "over" in the present disclosure are to be interpreted in the broadest context to mean not only "directly on something", but also to include the meaning of "on something" with intervening features or layers therebetween, and "above" or "over" not only includes the meaning of "above" or "over" something, but also can include the meaning of "above" or "over" something without intervening features or layers therebetween (i.e., directly on something).

[0075] In addition, spatial relative terms, such as "below", "under", "lower", "above", "upper" and the like, can be used herein for ease of description to describe a relationship of one element or feature to another element or feature as illustrated in the drawings. The spatial relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the drawings. The device can have other orientations (rotated 90 degrees or otherwise) and the spatial relative terms used herein can be interpreted accordingly.

[0076] It should be noted that, in the present document, relational terms such as "first" and "second", and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0077] Finally, it should be noted that the above-described embodiments are merely intended for describing and illustrating, not limiting, the technical solutions of the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some or all of the technical features; and such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments.

Claims

1. An electric machine characterized in that, The shell has an inner cavity, and the shell comprises a first end cover and a second end cover, the first end cover is provided with an air inlet communicating with the inner cavity, and the second end cover is provided with an air outlet communicating with the inner cavity; The driving assembly is arranged in the inner cavity, and the driving assembly comprises a rotor shaft; and The rotor is arranged on the outer periphery of the rotor shaft; the rotor comprises a rotor core, and the rotor core has an outer side wall provided with a plurality of recesses arranged at intervals; the recesses penetrate the outer side wall along the axial direction of the rotor core, Wherein, the extension direction of the recess has a preset inclination angle relative to the axial direction, so that when the rotor core rotates, the recess can guide the fluid from one side of the rotor core to the other side along the axial direction; the recess is a first groove recessed inward relative to the axis of the rotor core, and the first groove has a preset maximum depth; The fluid in the inner cavity between the rotor and the first end cover has a first pressure p1, the fluid in the inner cavity between the rotor and the second end cover has a second pressure p2, and the preset inclination angle and the preset maximum depth of the recess are calculated according to the following formula: W=(p2-p1) / ρ+(c2²-c1²) / 2; EK=mv² / 2; Wherein, W is the total kinetic energy of the rotor, ρ is the fluid density, c1 is the absolute speed of the fluid at the air outlet at the first temperature, c2 is the absolute speed of the fluid at the air outlet at the second temperature, the second temperature is greater than the first temperature, EK is the change of kinetic energy, m is the mass of the rotor, and v is the rotational speed of the rotor. Along the extension direction, the recess morphology of any cross section is the same.

2. The electric machine of claim 1, wherein, The preset maximum depth is not greater than 1.5 mm.

3. The electric machine of claim 1, wherein, The first groove is an arc-shaped groove, and the recess forms a first recess track and a second recess track at both ends of the outer side wall along the axial direction, the first recess track has a first axis, and the second recess track has a second axis, 4. The electric machine of claim 1, wherein, The included angle between the line connecting the first axis and the second axis and the axis of the rotor core is the preset inclination angle, and the preset inclination angle is not greater than 30°. The preset inclination angle ranges between 20° and 28°.

5. The electric machine of claim 1, wherein, The outer side wall is provided with a plurality of second grooves arranged at intervals, the second grooves penetrate the outer side wall along the axial direction, and the second grooves and the recesses are arranged alternately.

6. The electric machine of any of claims 1-5, wherein, Along the circumferential direction of the outer side wall, the minimum distance between the edge of the recess and the edge of the adjacent second groove is greater than 5 mm.

7. The electric machine of claim 6, wherein, The rotor core is also provided with a plurality of through holes arranged circumferentially, and the through holes are opposite to the second grooves along the radial direction of the rotor core, 8. The electric machine of claim 6, wherein, The minimum thickness between the through hole and the adjacent recess is not less than 10 mm. The air inlet and the air outlet are respectively provided as a plurality of air inlets and a plurality of air outlets, and the air inlets and the air outlets are respectively located on both sides of the rotor along the axial direction, 9. The electric machine of claim 1, wherein, ​ The axis of the air inlet is parallel to the axis of the rotor, and the axis of the air outlet has a preset included angle with the axis of the rotor.

10. The electric machine of claim 9, wherein, The preset included angle is in the range of 30°-60°.

11. The electric machine of claim 1, wherein, A dustproof screen is further included, which is arranged at the position corresponding to the air inlet and the air outlet respectively.

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