WO2017161721A1

WO2017161721A1 - Stator lamination and electrical machine

Info

Publication number: WO2017161721A1
Application number: PCT/CN2016/087056
Authority: WO
Inventors: Tao Zhu; Shi Deng; Bastian Vogt; Xinhua Liu; Ralf Mendgen
Original assignee: Robert Bosch Gmbh
Priority date: 2016-03-24
Filing date: 2016-06-24
Publication date: 2017-09-28
Also published as: WO2017161527A1

Abstract

A stator lamination (29) for forming a stator core (3) of an electrical machine (1) and the electrical machine (1) are provided. The stator lamination (29) comprises: a body (30); a central aperture (31) formed in the body (30) and sized to receive a rotor (21) of the electrical machine (1); a series of slots (33) disposed about the central aperture (31) and formed in the body (30), each configured to hold a set of stator winding (25); and a series of closed openings (37) disposed about the series of slots (33) and formed in the body (30), each configured to allow the airflow to pass through, and a wall between the adjacent closed openings (37) forming an inner fin (39) which extends radially outward with respect to the central aperture (31). It is possible to improve the cooling efficiency of the electrical machine (1).

Description

Stator Lamination and Electrical Machine

FIELD OF THE INVENTION

The present invention relates generally to the field of electrical machines, which includes electrical motors and generators. More particularly, the present invention relates to the dissipation of heat in such electrical machines.

BACKGROUND OF THE INVENTION

Electrical machines, such as motors and generators, are commonly used in industrial, commercial, and consumer settings. In industry, such machines are employed to drive various kinds of devices, including pumps, conveyors, compressors, fans, and so forth, to mention only a few. The electrical machines generally include a stator surrounding a rotor and comprising a multiplicity of stator windings. By establishing an electromagnetic relationship between the rotor and the stator, electrical energy can be converted into kinetic energy, and vice-versa. During operation, conventional motors and generators produce heat. If left unabated, excess heat may degrade the performance of the electrical machine, reducing efficacy, for instance. Worst yet, excess heat may contribute to any number of malfunctions, leading to system down time and, in certain instances, requiring maintenance and/or replacement. Undeniably, reduced efficacy and increased malfunctions are undesirable events that may lead to increased costs.

In traditional electrical motors and generators, the stator core assembly is housed within a frame assembly having fins formed thereon. The frame assembly forms an intermediate structure between the stator core assembly and the surrounding environment. The intermediate structure decreases the efficacy of convective cooling techniques. To overcome this problem, US2006/0284511 provides an electrical machine comprising a stator core assembly that is formed of a plurality of stator laminations and that is, at least partially, an outer surface of the motor. Each stator lamination has a plurality of fins that extend radially outward. When assembled, the fins of adjacent laminations cooperate to form a plurality of fin sections extending the length of the stator core assembly. When a fan directs airflow to flow through a passage between two adjacent fin sections, heat exchange occurs between the airflow and the larger fins, the heat then is dissipated into the surrounding environment through the airflow to cool the electrical machine. However, since the cross section of the passage between two adjacent fin sections is generally U-shaped, the airflow driven by the fan may flow out of the passages so that heat can not be transferred from the further downstream portions of the fin sections to the airflow. As a result, the further downstream portions of the fin sections can not be cooled evenly and effectively and thus the cooling efficacy of the electrical machine is reduced.

There is a need, therefore, for an improvement on the conventional electrical machines, such as motors and generators.

SUMMARY OF THE INVENTION

The present invention provides a stator lamination for forming a stator core and an electrical machine which considerably improve the cooling efficacy of the electrical machine.

In accordance with certain exemplary embodiments, the present invention provides a stator lamination for forming a stator core of an electrical machine, comprising:

a body；

a central aperture formed in the body and sized to receive a rotor of the electrical machine；

a series of slots disposed about the central aperture and formed in the body, each configured to hold a set of stator winding； and

a series of closed openings disposed about the series of slots and formed in the body, each configured to allow the airflow to pass through, and a wall between the adjacent closed openings forming an inner fin which extends radially outward with respect to the central aperture.

As an exemplary embodiment, the present invention also provides an electrical machine, comprising:

a stator core at least partially defining an outer surface of the electrical machine, the stator core comprising a central chamber that extends axially thought the stator core, a plurality of winding slots that are disposed about the central chamber and extend axially through the stator core, and a plurality of inner airflow passages that are disposed about the winding slots and extend axially through the stator core；

a plurality of sets of windings disposed in the plurality of winding slots；

a first end cap and a second end cap disposed at opposite ends of the stator core；

a rotor located within the central chamber and fixedly mounted on a shaft rotatably supported by the first end cap and the second end cap； and

a fan disposed outside either of the first end cap and the second end cap to urge a cooling airflow to pass through the inner airflow passages.

These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing schematically an electrical machine according to an exemplary embodiment of the present invention；

FIG. 2 is another perspective view of the electrical machine of FIG. 1；

FIG. 3 is an axial cross-sectional perspective view of the electrical machine of FIG. 1, in which the electrical machine includes a stator core according to a first exemplary embodiment of the present invention；

FIG. 4 is a perspective view showing the stator core of the electrical machine of FIG. 3；

FIG. 5 is an exploded perspective view of a series of adjacent stator laminations forming the stator core of FIG. 4；

FIG. 6 is an axial cross-sectional view of the electrical machine of FIG. 3, in which the arrows A show the flow of the forced cooling airflow；

FIG. 7 is a perspective view showing a stator core according to a second exemplary embodiment of the present invention；

FIG. 8 is a partial side view of the stator core of FIG. 7；

FIG. 9 is a perspective view showing a stator core according to a third exemplary embodiment of the present invention；

FIG. 10 is a perspective view similar to FIG. 9, in which the stator core is partially cut off to show arrangement of inner fin sub-sections；

FIG. 11 is a perspective view showing four stator sub-cores forming the stator core of FIG. 9；

FIG. 12 is a perspective view showing schematically an electrical machine according to another exemplary embodiment of the present invention；

FIG. 13 is another perspective view of the electrical machine of FIG. 12；

FIG. 14 is an axial cross-sectional perspective view of the electrical machine of FIG. 12, in which the electrical machine includes a stator core according to a fourth exemplary embodiment of the present invention；

FIG. 15 is a perspective view showing the stator core of the electrical machine of FIG. 14；

FIG. 16 is an exploded perspective view of a series of adjacent stator laminations forming the stator core of FIG. 15；

FIG. 17 is an axial cross-sectional view of the electrical machine of FIG. 14, in which the arrows A show the flow of the forced cooling airflow； and

FIG. 18 is a side view of the electrical machine of FIG. 14, in which the arrows B show the flow of the natural cooling airflow.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a perspective view showing schematically an electrical machine according to an exemplary embodiment of the present invention, FIG. 2 is another perspective view of the electrical machine of FIG. 1 and FIG. 3 is an axial cross-sectional perspective view of the electrical machine of FIG. 1. As illustrated in FIGS. 1-3, an exemplary electrical machine 1 according to the present invention is envisaged as an induction motor. However, it is worth noting that the present invention is applicable to any electrical machines, including electrical motors and electrical generators. Moreover, although the following discussion focuses on AC electrical machines, the present invention is equally applicable to DC electrical machines. For example, devices in which the rotor's magnetic flux is produced as a result of the material employed and not by induction also benefit from the present invention.

The exemplary electrical machine 1 includes a stator core 3 capped at both ends by a first end cap 5 and a second end cap 7, respectively. Advantageously, the exemplary first end cap 5 and second end cap 7 may include mounting and transportation features (not shown) as well as heat dissipation features, such as the end cap cooling fins 9, 11. The first end cap 5 and the second end cap 7 and the stator core 3 are maintained in assembly by through-bolts 13 extending axially through the first end cap 5 and the second end cap 7 and the stator core 3. The tight fit and close tolerances between the assembled stator core 3 and the first and

second end caps

5 and 7 prevent the ingress of containments into the interior of the electrical machine 1. In other words, the exemplary first and

second end caps

5 and 7 and stator core 3 cooperate to present an assembly that is resistant to, but not sealed from the ingress of contaminants. Of course, a sealing pad may be disposed between the stator core 3 and the first end cap 5 as well as the stator core 3 and the second end cap 7. Moreover, the outer surface of the stator core 3 may be coated with resin to further improve the water-tightness of the electrical machine 1.

The exemplary electrical machine 1 further includes a shaft 15 rotatably supported by a first bearing 17 disposed in the first end cap 5 and a second bearing 19 disposed in the second end cap 7 as well as a rotor 21 fixedly mounted on the shaft 15 and located within a central chamber 23 defined by the stator core 3. To induce rotation of the rotor 21 located within the central chamber 23 defined by the stator core 3 if the electrical machine 1 is acting as an electric motor, alternating current is routed through stator windings 25 disposed in the stator core 3. The stator windings 25, of which only the end turns are shown in FIG. 3, are electrically interconnected to form groups that are, in turn, interconnected in a manner generally known in the pertinent art. These stator windings 25 are further coupled to terminal leads 27 that electrically connect the stator windings 25 to an external power source (not shown) . Routing electrical current from the external power source through the stator windings 25 creates electromagnetic relationships with the rotor 21 that cause rotation of the rotor 21, as is appreciated by those of ordinary skill in the art. The shaft 15 coupled to the rotor 21 also rotates in response to rotation of the rotor 21. Through the shaft 15, torque may be transmitted to any number of drive machine elements.

FIG. 4 is a perspective view showing the stator core of the electrical machine of FIG. 3 and FIG. 5 is an exploded perspective view of a series of adjacent stator laminations forming the stator core of FIG. 4. As illustrated in FIGS. 4 and 5, the stator core 3 comprises a plurality of stator laminations 29 aligned and assembled with respect to one another to form the contiguous stator core 3. Each stator lamination 29 includes a generally circular body 30. A central aperture 31 is formed in the body 30 and sized to receive the rotor 21. Disposed about this central aperture 31 and formed in the body 30 are a series of slots 33, each configured to hold an incremental portion of the stator winding 25. The slots 33 and the central aperture 31 essentially define the inner periphery 35 of the stator lamination 29. Disposed about the series of slots 33 and formed in the body 30 are a series of closed openings 37, each configured to allow the airflow to pass through. A wall between the adjacent closed openings 37 forms an inner fin 39 that extends radially outward with respect to the this central aperture 31 or the series of slots 33. Each stator lamination 29 also includes through-bolt receiving apertures 41 disposed about the series of slots 33.

Although the exemplary stator lamination 29 is shown to have a generally circular shape, it may have generally square, rectangular or any other suitable shape. Such stator laminations 29 can be fabricated via a stamping process, in which a material blank is stamped to produce the desired stator lamination.

When assembled, the stator laminations 29 cooperate to present a number of features and attributes. For example, the stator laminations 29 cooperate to define the central chamber 23 that extends axially thought the stator core 3 and in which the rotor 21 resides. These stator laminations 29 also cooperate to define winding slots 43 that are formed by the series of slots 33 and extend axially through the stator core 3 and that are configured to hold the sets of stator windings 25. Further still, these stator laminations 29 also cooperate to define a plurality of inner airflow passages 45 that are formed by the series of closed openings 37 and extend axially through the stator core 3 and that are configured to allow the airflow to pass through the stator core 3. The inner airflow passages 45 are opened only at two ends. At the same time, the inner fins 39 of adjacent stator laminations 29 cooperate to form cumulative inner fin sections 47 that extend the length of the stator core 3. Of course, these stator laminations 29 also cooperate to define continuous through-bolt receiving apertures 49 that are formed by the through-bolt receiving apertures 41 and extend axially through the stator core 3 and that are configured to receive the through-bolts 13.

To effectuate cooling, the exemplary electrical machine 1 includes a fan 51 disposed outside of the second end cap 7. It should be understood that the fan 51 may be disposed outside of the first end cap 5. The fan 51 is used to urge the airflow to pass through the inner airflow passages 45 formed in the stator core 3. To this end, a first hollowed-out region53 is formed in the first end cap 5 and a second hollowed-out region 55 is formed in the second end cap 7 so that the forced cooling airflow driven by the fan 51 flows through the second end cap 7, the inner airflow passages 45 and the first end cap 5 into the surrounding environment. Of course, it is also feasible that a series of first through-holes and a series of second through-holes which are aligned with the respective inner airflow passages 45 are formed in the first end cap 5 and the second end cap 7. Disposed about the fan 51 is a shroud 57 in which a plurality of vents 59 is formed. The shroud 57 directs airflow drawn in through the vents 59 toward the fan 51, thus directing the airflow to pass through the second end cap 7, the stator core 3 and the first end cap 5, to cool the electrical machine 1. Although the fan 51 may be mounted on the shaft 15 and rotates together with the shaft 15, it is preferable that the fan 51 is driven by a separate electrical motor 61 whose speed can be controlled according to the operating condition of the electrical machine 1.

FIG. 6 is an axial cross-sectional view of the electrical machine of FIG. 3, in which the arrows A show the flow of the forced cooling airflow. As illustrated in FIG. 6, the stator core 3 at least partially defines an external surface of the electrical machine 1. Thus, when the fan 51 rotates, the fan 51 directs the cooling airflow to pass through the second end cap 7, the stator core 3 and the first end cap 5 to conduct heat exchange with the inner fin section 47 of the stator core 3. On one hand, since there is no intermediate structure such as a frame assembly between the stator core 3 and the surrounding environment, some heat is dissipated directly into the surrounding environment from the external surface of the stator core 3. On the other hand, heat exchange occurs between the stator core 3 and the cooling airflow passing through the inner airflow passages 45 so that the whole stator core 3 can be cooled evenly and effectively. Thus, the present invention considerably improves the efficacy of cooling for dissipating heat generated in the electrical machine 1 during operation.

FIG. 7 is a perspective view showing a stator core according to a second exemplary embodiment of the present invention and FIG. 8 is a partial side view of the stator core of FIG. 7. The stator core 3 according to the second exemplary embodiment of the present invention is similar substantially to that shown in FIG 4 except the further inner fin sections formed on the inner fin sections. For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. As illustrated in FIGS. 7 and 8, the stator core 3 according to the second exemplary embodiment of the present invention further includes a plurality of further inner fin sections 63 extending from the inner fin sections 47 between adjacent the inner airflow passages 45 along the length of the stator core 3. By providing the further inner fin sections 63, the effective area for heat exchange with the cooling airflow passing through the inner airflow passages 45 is considerably increased. As a result, it is possible to allow more effective heat removal from the stator core without increasing the size of the stator core. Although the further inner fin sections 63 is shown to be flat and extend perpendicularly from the inner fin sections 47, it should be understood that the further inner fin sections 63 may take any other shape and extend slantways from the inner fin sections 47.

FIG. 9 is a perspective view showing a stator core according to a third exemplary embodiment of the present invention. FIG. 10 is a perspective view similar to FIG. 9, in which the stator core is partially cut off to show arrangement of inner fin sub-sections. FIG. 11 is a perspective view showing four stator sub-cores forming the stator core of FIG. 9. The stator core 3 according to the third exemplary embodiment of the present invention is similar substantially to that shown in FIG 4 except the arrangement of the inner fin sections. For the sake of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. As illustrated in FIGS. 9-11, the stator core 3 includes four

stator sub-cores

3a, 3b, 3c, 3d, each having

respective airflow sub-passages

45a, 45b, 45c, 45d and respective inner fin sub-sections. 47a, 47b, 47c, 47d. When the

stator sub-cores

3a, 3b, 3c, 3d are assembled together to form the stator core 3, the inner fin sub-sections of the

adjacent stator sub-cores

3a, 3b, 3c, 3d staggers with each other while the winding sub-slots 43a, 43b, 43c, 43d of the four

stator sub-cores

3a, 3b, 3c, 3d are aligned with each other. Specifically, as shown in FIG 10, the inner fin sub-section 47a of the stator sub-core 3a staggers with the inner fin sub-section 47b of the stator sub-core 3b, the inner fin sub-section 47b of the stator sub-core 3b staggers with the inner fin sub-section 47c of the stator sub-core 3c, and the inner fin sub-section 47c of the stator sub-core 3c staggers with the inner fin sub-section 47d of the stator sub-core 3d. When the cooling airflow flows through the inner airflow passages, the inner fin sub-sections staggered with each other render more adequate and more effective heat exchange with the cooling airflow.

Although the stator core 3 is shown to include four stator sub-cores, it should be understand that the stator core 3 may have less than or more than four stator sub-cores. Further, although the inner fin sub-section on the stator sub-core is shown to locate at the middle of two inner fin sub-sections on the adjacent stator sub-core, the inner fin sub-section on the stator sub-core may locate at any position between two inner fin sub-sections on the adjacent stator sub-core. Furthermore, the stator sub-core may further include a plurality of further inner fin sub-sections extending from the inner fin sub-sections, just as shown in FIGS 7 and 8.

To reduce the manufacturing cost, each of the stator sub-cores may be assembled by a plurality of stator laminations 29 having the same profile or shape. To this end, the stator lamination 29 is symmetrical about one axis XX which passes through a center O of the stator lamination. An angular pitch between the adjacent inner fins 39 equally spaced on the stator lamination 29 should have a value such that 360 degrees divided by this pitch results in an odd integer number. This odd integer number is the number of the inner fins 39 equally spaced on the stator lamination 29. When assembling the stator sub-cores having the stator laminations 29 to form the stator core 3, the immediate next stator sub-core is rotated by 180 degrees around this symmetrical axis so that the inner fin sub-sections of the adjacent stator sub-cores staggers with each other. For example, the stator sub-core 3b is rotated by 180 degrees around this symmetrical axis x-x relative to the stator sub-core 3a and the stator sub-core 3d is rotated by 180 degrees around this symmetrical axis x-x relative to the stator sub-core 3c while the

stator sub-cores

3a and 3c have the same orientation. When the stator laminations 29 are for example stamped, all the stator laminations 29 may be stamped by the same stamping die using the same stamping process.

FIG. 12 is a perspective view showing schematically an electrical machine according to another exemplary embodiment of the present invention. FIG. 13 is another perspective view of the electrical machine of FIG. 12. FIG. 14 is an axial cross-sectional perspective view of the electrical machine of FIG. 12, in which the electrical machine includes a stator core according to a fourth exemplary embodiment of the present invention. The electrical machine 1 according to another exemplary embodiment of the present invention as shown in FIGS. 12-14 is similar substantially to that shown in FIGS. 1-3 except a plurality of outer fins 65 extending circumferentially along the stator core 3 and a plurality of annular grooves 67 defined between the adjacent outer fins 65. For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted.

FIG. 15 is a perspective view showing the stator core of the electrical machine of FIG. 14. FIG. 16 is an exploded perspective view of a series of adjacent stator laminations forming the stator core of FIG. 15. As illustrated in FIGS 15 and 16, the stator laminations 29 forming the stator core 3 have a peripheral portion 69 outside of the series of closed openings 37. The stator laminations 29 have two types which different from each other at least by a size of the peripheral portion 69. In the present invention, the size of the peripheral portion 69 refers to a radial distance from an outer edge of the closed openings 37 to an outer edge of the stator laminations 29. The peripheral portion 69 of the first type of stator laminations 29 has a larger size than that of the second type of stator laminations 29. For example, the first type of stator laminations whose peripheral portion 69 has a larger size are indicated by numeral 29a while the second type of stator laminations whose peripheral portion 69 has a smaller size are indicated by numeral 29b. When the stator laminations are circular, the first type of stator laminations indicated by numeral 29a has a larger outer diameter than the second type of stator laminations indicated by numeral 29b.

When assembled, a first stator sub-core 71 formed by stacking a plurality of the first type of stator laminations 29a whose peripheral portion 69 has a larger size is inserted at an interval between two adjacent second stator sub-cores 73 formed by stacking a plurality of the second type of stator laminations 29b whose peripheral portion 69 has a smaller size. A plurality of first stator sub-cores 71 and a plurality of second stator sub-cores 73 together form the stator core 3. As a result, the peripheral portions 69 of the plurality of the first type of stator laminations 29a in each of the first stator sub-core 71 form the outer fin 65 extending circumferentially along the stator core 3 and the annular grooves 67 are defined between the adjacent outer fins 65.

FIG. 17 is an axial cross-sectional view of the electrical machine of FIG. 14, in which the arrows A show the flow of the forced cooling airflow. As illustrated in FIG. 17, the stator core 3 at least partially defines an external surface of the electrical machine 1. Thus, when the fan 51 rotates, the fan 51 directs the cooling airflow to pass through the second end cap 7, the stator core 3 and the first end cap 5 to conduct heat exchange with the inner fin section 47 of the stator core 3, thereby dissipating heat from the electrical machine 1 by forced convection cooling. FIG. 18 is a side view of the electrical machine of FIG. 14, in which the arrows B show the flow of the natural cooling airflow. The cooling airflow exchanges heat with the outer fins 65 extending circumferentially along the stator core 3 and flows upwardly along a direction indicated by the arrows B to dissipate heat from the electrical machine 1 by natural convection cooling. When cooling demand is high, both forced convection cooling and natural convection cooling are working in parallel to enhance the rate of heat dissipation. When cooling demand is low, the fan is switched off and only natural convection cooling is working to achieve energy saving.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

A stator lamination (29) for forming a stator core (3) of an electrical machine (1) , comprising:

a body (30) ；

a central aperture (31) formed in the body (30) and sized to receive a rotor (21) of the electrical machine (1) ；

a series of slots (33) disposed about the central aperture (31) and formed in the body (30) , each configured to hold a set of stator winding (25) ； and

a series of closed openings (37) disposed about the series of slots (33) and formed in the body (30) , each configured to allow the airflow to pass through, and a wall between the adjacent closed openings (37) forming an inner fin (39) which extends radially outward with respect to the central aperture (31) .
The stator lamination (29) as claimed in claim 1, further comprising a plurality of further inner fins extending from the inner fins (39) .
The stator lamination (29) as claimed in claim 1 or 2, wherein the stator lamination (29) is symmetrical about one axis (XX) passing through a center (O) of the stator lamination, and an angular pitch between the adjacent inner fins (39) has a value such that 360 degrees divided by this pitch results in an odd integer number.
The stator lamination (29) as claimed in claim 1 or 2, further comprising through-bolt receiving apertures (41) formed in the body (30) .
An electrical machine (1) , comprising:

a stator core (3) at least partially defining an outer surface of the electrical machine (1) , the stator core (3) comprising a central chamber (23) that extends axially thought the stator core, a plurality of winding slots (43) that are disposed about the central chamber (23) and extend axially through the stator core, and a plurality of inner airflow passages (45) that are disposed about the winding slots (43) and extend axially through the stator core；

a plurality of sets of windings (25) disposed in the plurality of winding slots (43) ；

a first end cap (5) and a second end cap (7) disposed at opposite ends of the stator core (3) ；

a rotor (21) located within the central chamber (23) and fixedly mounted on a shaft (15) rotatably supported by the first end cap (5) and the second end cap (7) ； and

a fan (51) disposed outside either of the first end cap (5) and the second end cap (7) to urge a cooling airflow to pass through the inner airflow passages (45) .
The electrical machine (1) according to claim 5, wherein the stator core (3) comprises a plurality of stator laminations (29) assembled together, each stator lamination comprising:

a body (30) ；

a central aperture (31) formed in the body (30) and sized to receive the rotor (21) of the electrical machine (1) ；

a series of slots (33) disposed about the central aperture (31) and formed in the body (30) , each configured to hold the set of stator winding (25) ； and

a series of closed openings (37) disposed about the series of slots (33) and formed in the body (30) , each configured to allow the airflow to pass through, and a wall between the adjacent closed openings (37) forming an inner fin (39) which extends radially outward with respect to the central aperture (31) ；

wherein the central apertures (31) of the plurality of stator laminations (29) forms the central chamber (23) , the slots (33) of the plurality of stator laminations (29) forms the winding slots (43) , the closed openings (37) of the plurality of stator laminations (29) forms the inner airflow passages (45) .
The electrical machine (1) according to claim 6, wherein the inner fins (39) on one of the plurality of stator laminations (29) align with the respective inner fins (39) on the adjacent stator laminations (29) to define a plurality of inner fin sections (47) that extend the length of the stator core.
The electrical machine (1) according to claim 7, further comprising a plurality of further inner fin sections (63) extending from the inner fin sections (47) along the length of the stator core.
The electrical machine (1) according to claim 5, wherein the stator core (3) includes a plurality of stator sub-cores (3a, 3b, 3c, 3d…) , each of the plurality of stator sub-cores (3a, 3b, 3c, 3d…) comprises a plurality of stator laminations (29) assembled together, each stator lamination comprising:

a body (30) ；

a central aperture (31) formed in the body (30) and sized to receive the rotor (21) of the electrical machine (1) ；

a series of slots (33) disposed about the central aperture (31) and formed in the body (30) , each configured to hold the set of stator winding (25) ； and

a series of closed openings (37) disposed about the series of slots (33) and formed in the body (30) , each configured to allow the airflow to pass through, and a wall between the adjacent closed openings (37) forming an inner fin (39) which extends radially outward with respect to the central aperture (31) ；

wherein each of the plurality of stator sub-cores comprises a plurality of winding slots (43a, 43b, 43c, 43d…) formed by the slots (33) , a plurality of airflow sub-passages (45a, 45b, 45c, 45d…) formed by the closed openings (37) and a plurality of inner fin sub-sections (47a, 47b, 47c, 47d…) formed by the inner fins (39) and extending the length of the stator sub-cores, the stator sub-cores are assembled together to form the stator core (3) in such a way that the inner fin sub-sections of the adjacent stator sub-cores stagger with each other.
The electrical machine (1) according to claim 9, further comprising a plurality of further inner fin sub-sections extending from the inner fin sub-sections along the length of the stator sub-cores.
The electrical machine (1) according to claim 9, wherein the stator lamination (29) is symmetrical about one axis (XX) passing through a center (O) of the stator lamination, and an angular pitch between the adjacent inner fins (39) has a value such that 360 degrees divided by this pitch results in an odd integer number.
The electrical machine (1) according to claim 5, wherein the stator core (3) comprises a plurality of outer fins (65) extending circumferentially along the stator core (3) and a plurality of annular grooves (67) defined between the adjacent outer fins (65) .
The electrical machine (1) according to claim 6, wherein the stator laminations (29) each have a peripheral portion (69) outside of the series of closed openings (37) , the stator laminations (29) comprise a first type of stator laminations whose peripheral portion (69) has a larger size and a second type of stator laminations whose peripheral portion (69) has a smaller size, a first stator sub-core (71) formed by stacking a plurality of the first type of stator laminations is inserted at an interval between two adjacent second stator sub-core (73) formed by stacking a plurality of the second type of stator laminations so that a plurality of outer fins (65) extending circumferentially along the stator core (3) are formed by the peripheral portions (69) of the plurality of the first type of stator laminations in each of the first stator sub-core (71) and an annular groove (67) is defined between two adjacent outer fins (65) .
The electrical machine (1) according to claim 5, wherein the first end cap (5) and the second end cap (7) are hollowed out in a region (53, 55) that align with the inner airflow passages (45) .
The electrical machine (1) according to claim 5, wherein the fan (51) is driven by a separate electrical motor (61) .