Patent Publication Number: US-2022231557-A1

Title: Electric machine and assembling method for electric machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Chinese Patent Application No. 201910440569.2, filed on May 24, 2019 and entitled “ELECTRIC MACHINE AND ASSEMBLING METHOD FOR ELECTRIC MACHINE”, which is incorporated herein by reference in its entirety. 
     FIELD 
     The disclosure relates to a technical field of electric machine, and in particular to an electric machine and an assembling method for an electric machine. 
     BACKGROUND 
     In large electric machines such as wind turbines, in order to ensure uniformity of an air gap between a stator and a rotor, an assembling coaxiality of the stator, the rotor and a shaft assembly is usually achieved by means of processing equipment. Due to a large number of components of the electric machine, in order to facilitate assembling, the components are usually manufactured only at a processing site, and then the respective components are transported to a wind power generation site and then assembled; therefore, it is also necessary to transport the processing equipment to the site, and after the assembling of the electric machine by means of the processing equipment, the processing equipment will be disassembled and transported back to a designated site, which increases the transportation cost and the assembling complexity. 
     SUMMARY 
     An object of the disclosure is to provide an electric machine and an assembling method for an electric machine, which can simplify the assembling process and reduce transportation cost. 
     In one aspect, the disclosure provides an electric machine including: a shaft assembly including a first shaft, a second shaft coaxially disposed within an inner circumference of the first shaft, and a bearing disposed between the first shaft and the second shaft; a first revolving body coaxially connected to the first shaft, wherein the first revolving body includes an annular first adapter bracket, and a tubular structural portion extending in an axial direction is disposed at an inner circumference of the first adapter bracket; a second revolving body coaxially connected to the second shaft and disposed around and at an outer circumference of the first revolving body; and a guiding assembly disposed between the tubular structural portion and the first shaft to restrict a movement of the first revolving body relative to the first shaft in a circumferential direction and a radial direction. 
     In another aspect, the disclosure provides an assembling method for any of the aforementioned electric machines, which includes: disposing a first shaft around and at an outer circumference of a second shaft; disposing a tubular structural portion of a first revolving body around and at an outer circumference of the first shaft through a guiding assembly; and connecting a second revolving body coaxially with the second shaft so that the second revolving body is disposed around and at an outer circumference of the first revolving body. 
     The electric machine and the assembling method for the electric machine according to the disclosure provide the guiding assembly between the stator and the stationary shaft or between the rotor and the rotational shaft, which improves a coaxiality of the stator or rotor and the shaft assembly and then improves an assembling quality of the electric machine; and since the guiding assembly is adopted to replace the processing equipment in prior art, it simplifies the assembling process of the electric machine and also reduces the assembling cost of the electric machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be better understood from the following description of the specific embodiments of the disclosure in conjunction with the accompanying drawings, wherein other features, objects and advantages of the disclosure will be more apparent by reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, and same or similar reference signs indicate same or similar features. 
         FIG. 1  is a three-dimensional schematic diagram of an electric machine according to embodiments of the disclosure; 
         FIG. 2  is an exploded schematic diagram of the electric machine shown in  FIG. 1 ; 
         FIG. 3  is a longitudinal sectional view of the electric machine shown in  FIG. 1 ; 
         FIG. 4  is a partial cross-sectional view of a stator module in a stator shown in  FIG. 2 ; 
         FIG. 5  is a schematic top view of a first adapter bracket in the stator shown in  FIG. 2 ; 
         FIG. 6  is an enlarged schematic diagram of a zone B in the first adapter bracket shown in  FIG. 5 ; 
         FIG. 7  is a schematic cross-sectional view of the first adapter bracket shown in  FIG. 5  along a C-C direction; 
         FIG. 8  is a schematic diagram of an assembled structure of a stationary shaft and a rotational shaft in the electric machine shown in  FIG. 2 ; 
         FIG. 9  is an enlarged schematic view of a zone A of the stationary shaft shown in  FIG. 8 ; 
         FIG. 10  is a schematic top view of a rotor shown in  FIG. 2 ; 
         FIG. 11  is an enlarged schematic diagram of a zone E of the rotor shown in  FIG. 10 ; 
         FIG. 12  is a schematic diagram of a magnetic pole module in the rotor shown in  FIG. 10 ; 
         FIG. 13  is a schematic diagram of a rotor of an electric machine according to embodiments of the disclosure; 
         FIG. 14  is a flowchart of an assembling method for an electric machine according to embodiments of the disclosure. 
     
    
    
     REFERENCE SIGNS IN THE DRAWINGS 
       1 —first revolving body;  11 —first adapter bracket;  111 —first inner flange;  112 —tubular structural portion;  113 —second double flange;  12 —first module;  121 —stator module bracket;  122 —iron core;  123 —first double flange; 
       2 —second revolving body;  21 —second adapter bracket;  211 —second inner flange;  22 —second module; 
       3 —shaft assembly;  31 —first shaft;  311 —first end surface;  312 —second end surface;  313 —first outer flange;  32 —second shaft;  321 —second outer flange; 
       4 —guiding assembly;  41 —first inserting portion;  411 —first guiding rib;  412 —second guiding rib;  42 —first socketing portion;  43 —second inserting portion;  44 —second socketing portion; 
       51 —adapter portion;  52 —connecting arm;  53 —rotor ring;  53   a —mounting surface;  53   b —mounting slot; 
       6 —magnetic pole module;  6   a  —substrate;  6   b  —magnet steel;  6   c  —mounting portion. 
     DETAILED DESCRIPTION 
     Features and exemplary embodiments according to various aspects of the disclosure will be described in detail below. Many specific details are disclosed in the following detailed description to facilitate a fully understanding of the disclosure. However, it will be apparent to those skilled in the art that the disclosure can be implemented without some of these specific details. The following description of embodiments is intended only to provide a better understanding of the disclosure by illustrating examples of the disclosure. The disclosure is by no means limited to any of the specific configurations and algorithms discussed below, but covers any modifications, replacements, and improvements to the elements, components, and algorithms without departing from the spirit of the disclosure. In the accompanying drawings and the following description, structures and techniques that are well known are not shown in order to avoid unnecessary ambiguity in the disclosure. 
     For a better understanding of the disclosure, electric machines and assembling methods for electric machines according to embodiments of the disclosure are described in detail below in conjunction with  FIGS. 1 to 14 . In the disclosure, the term “radial direction” refers to a direction of a diameter of a revolving body of the electric machine, the term “axial direction” refers to a direction of an axis of the revolving body of the electric machine, and the term “circumferential direction” refers to a direction of a circumference of the revolving body of the electric machine. 
     Referring to  FIGS. 1 to 3 , the disclosure provides an electric machine including: a first revolving body  1 , a second revolving body  2 , a shaft assembly  3  and a guiding assembly  4 . 
     The shaft assembly  3  includes a first shaft  31 , a second shaft  32  coaxially disposed within an inner circumference of the first shaft  31 , and a bearing (not shown in the drawings) disposed between the first shaft  31  and the second shaft  32 . An inner ring of the bearing is disposed at one of the first shaft  31  and the second shaft  32 , and an outer ring of the bearing is disposed at the other of the first shaft  31  and the second shaft  32 , such that the first shaft  31  can be rotated relative to the second shaft  32  about a central axis of the second shaft  32 ; and the bearing can be fixed in the shaft assembly  3  through, for example, a bearing retaining ring, such that the first shaft  31  and the second shaft  32  are unmovable with respect to each other in the axial direction. 
     The first revolving body  1  is coaxially connected to the first shaft  31 , and the first revolving body  1  includes an annular first adapter bracket  11 , and a tubular structural portion  112  extending in an axial direction is disposed at an inner circumference of the first adapter bracket  11 . 
     The second revolving body  2  is coaxially connected to the second shaft  32 , and the second revolving body  2  is disposed around and at an outer circumference of the first revolving body  1 . 
     The guiding assembly  4  is disposed between the tubular structural portion  112  and the first shaft  31  to restrict a movement of the first revolving body  1  relative to the first shaft  31  in a circumferential direction and a radial direction. 
     In some embodiments, the first revolving body  1  is a stator, the first shaft  31  is a stationary shaft, the second revolving body  2  is a rotor, and the second shaft  32  is a rotational shaft. In other words, the electric machine has a structure with an inner stator and an outer rotor. 
     In some embodiments, the first revolving body  1  is a rotor, the first shaft  31  is a rotational shaft, the second revolving body  2  is a stator, and the second shaft  32  is a stationary shaft. In other words, the electric machine has a structure with an inner rotor and an outer stator. 
     Thus, the guiding assembly  4  can improve a coaxiality of the stator and the rotational shaft or a coaxiality of the rotor and the rotational shaft, which then ensures a uniform air gap between the stator and the rotor and improves an assembling quality of the electric machine. 
     The electric machine according to the disclosure provides the guiding assembly  4  between the stator and the stationary shaft or between the rotor and the rotational shaft, which improves a coaxiality of the stator or rotor and the shaft assembly  3  and then improves an assembling quality of the electric machine; and since the guiding assembly  4  is adopted to replace the processing equipment in prior art, it simplifies the assembling process of the electric machine and also reduces the assembling cost of the electric machine. 
     In order to facilitate the description, the specific structure of the electric machine according to embodiments of the disclosure will be described in further detail below, by taking the electric machine having a structure with an inner stator and an outer rotor as an example. 
     Referring to  FIGS. 2, 4 and 5 , the first revolving body  1  is a stator, and the first shaft  31  is a stationary shaft. The first revolving body  1  also includes a first module  12  disposed around and at an outer circumference of the first adapter bracket  11 ; the first module  12  is a stator module of the electric machine; and the stator module includes a stator module bracket  121 , an iron core  122  disposed at an outer circumference of the stator module bracket  121 , and a stator winding (not shown in the drawings) mounted on the iron core  122 . 
     The first adapter bracket  11  and the stator module bracket  121  are usually made of steel materials such as Q235 steel, which is shaped in a welding, casting or other process and then machined. Optionally, the stator module bracket  121  has an internally hollow structure to improve its stiffness and also reduce its weight. A first double flange  123  is disposed at an inner circumference of the stator module bracket  121 , and a group of bolt holes are formed at the first double flange  123 ; a second double flange  113  is disposed at the outer circumference of the first adapter bracket  11 , and a group of bolt holes are formed at the second double flange  113 ; and the stator module bracket  121  and the first adapter bracket  11  may be connected together through a cooperation of the first double flange  123  and the second double flange  113 . The iron core  122  is usually made of laminated silicon steel sheets, and winding coils are installed in slots of the iron core  122 ; and the iron core  122  is mounted to dovetail slots (not shown in the drawings) on the outer circumference of the stator module bracket  121  and thus fixed to the stator module bracket  121 . 
     Referring to  FIGS. 6 to 9 , the guiding assembly  4  includes a first inserting portion  41  and a first socketing portion  42  that are engaged with each other, one of the first inserting portion  41  and the first socketing portion  42  is disposed at an inner circumference of the tubular structural portion  112  and extends in the axial direction, and the other of the first inserting portion  41  and the first socketing portion  42  is disposed at an outer circumference of the first shaft  31  and extends in the axial direction. There may be multiple first inserting portions  41  and multiple first socketing portions  42 . 
     A case in which the first inserting portion  41  is disposed at the inner circumference of the tubular structural portion  112  is taken as an example, the first inserting portion  41  includes a first guiding rib  411  protruding in the radial direction from the inner circumference of the tubular structural portion  112 ; and the first inserting portion  42  is a first guiding groove recessed in the radial direction from the outer circumference of the first shaft  31 , and the first guiding groove has a width along the circumferential direction matched with a width of the first guiding rib  411  along the circumferential direction, so that a movement of the tubular structural portion  112  of the stator in the circumferential direction relative to the stationary shaft is restricted, which prevents a case in which a first inner flange  111  and a first outer flange  313  cannot be assembled with their centers being aligned due to insufficient coaxiality and accuracy after the stator and rotor have been assembled with one being surrounded by another. 
     Furthermore, the first inserting portion  41  includes a second guiding rib  412  protruding in the radial direction from the inner circumference of the tubular structural portion  112 , the second guiding rib  412  has an inner diameter larger than an inner diameter of the first guiding rib  411 , and the second guiding rib  412  and the first guiding rib  411  are alternately arranged in the circumferential direction on the inner circumference, and the outer circumference of the first shaft  31  has an outer diameter matched with the inner diameter of the second guiding rib  412 . The first shaft  31  and the inner circumference of the second guide  412  form a shaft-hole fit, and its tolerance fit here is preferably a clearance fit to restrict the movement of the tubular structural portion  112  of the stator in the radial direction relative to the stationary shaft. 
     Furthermore, the first guiding rib  411  and the second guiding rib  412  can be connected to an inner wall of the tubular structural portion  112  through countersunk screws or in other ways. The first guiding rib  411  and the second guiding rib  412  can be made of engineering plastics, metals such as aluminum, or composite materials such as phenolic laminated sheet. Herein, it would be beneficial that the materials of the first guiding rib  411  and the second guiding rib  412  are different from the material of the first shaft  31  to avoid crawling phenomenon which occurs when the first shaft  31  slides relative to the first guiding rib  411  and the second guiding rib  412 . 
     Furthermore, a first inner flange  111  is further disposed at an axial end of the tubular structural portion  112  of the first revolving body  1  near the first adapter bracket  11 . The first inner flange  111  is a single flange, a group of bolt holes are formed at the single flange for connecting with the first shaft  31 . 
     The first shaft  31  is a stationary shaft, the first shaft  31  is usually made of steel materials such as low carbon steel, ductile iron, etc. which is shaped in a welding, casting or other process and then machined. The first shaft  31  includes a first end surface  311  and a second end surface  312  opposite to each other in its axial direction, a first outer flange  313  is disposed at the outer circumference of the first shaft  31  at a predetermined distance from the first end surface  311 , and the tubular structural portion  112  and the first shaft  31  are connected together through a cooperation of the first inner flange  111  and the first outer flange  313 . The cooperation of the first inner flange  111  and the first outer flange  313  may, for example, be a connection with a bolt and a stop. 
     In order to further improve the coaxiality of the stator and the shaft assembly, the guiding assembly  4  also includes a second inserting portion  43  and a second socketing portion  44  that are engaged with each other, the second inserting portion  43  is disposed at the outer circumference of the first shaft  31  near the first outer flange  313 , the second socketing portion  44  is disposed at the inner circumference of the tubular structural portion  112  near the first inner flange  111 , and the second socketing portion  44  has an inner diameter D 2  larger than an inner diameter D 1  of the first inserting portion  41 . 
     Furthermore, the second socketing portion  44  is formed by protruding in the radial direction from the inner circumference of the tubular structural portion  112 , the second inserting portion  43  is formed by protruding in the radial direction from the outer circumference of the first shaft  31 , an outer circumference of the second inserting portion  43  is matched with an inner circumference of the second socketing portion  44 , and a fitting precision of the second inserting portion  43  and the second socketing portion  44  is higher than a fitting precision of the first inserting portion  41  and the first socketing portion  42 . For example, if the shaft-hole fitting precision of the first inserting portion  41  and the first socketing portion  42  is H9/g9, the shaft-hole fitting precision of the second inserting portion  43  and the second socketing portion  44  is H7/f7. 
     The second inserting portion  43  is obtained by machining such as turning at the outer circumference of the first shaft  31 , and the inner circumference of the second socketing portion  44  and the second inserting portion  43  form a shaft-hole fit, and its tolerance fit here is preferably a clearance fit. In order to facilitate smoothly inserting of the first shaft  31  into the tubular structural portion  112 , the clearance between the first inserting portion  41  and the first socketing portion  42  needs to be chosen to be large. 
     In order to reduce a radial error between the stator and the stationary shaft after they are finally assembled, when the rotor and the rotational shaft are assembled in place, the second inserting portion  43  can be pulled into the second socketing portion  44  when the bolts are connected at the first inner flange  111 , which ensures that the coaxiality of the final assembly of the stator and the shaft assembly is at a high precision level. 
     Referring to  FIGS. 10 to 12 , the second revolving body  2  includes an annular second adapter bracket  21  and a second module  22  disposed at an outer circumference of the second adapter bracket  21 , a second inner flange  211  is disposed at an inner circumference of the second adapter bracket  21 , a second outer flange  321  is disposed at the outer circumference of the second shaft  32 , and the second revolving body  2  and the second shaft  32  are connected together through a cooperation of the second inner flange  211  and the second outer flange  321 . 
     Herein, the second revolving body  2  is a rotor, the second shaft  32  is a rotational shaft, and the second shaft  32  is usually made of steel materials such as low carbon steel, ductile iron, etc., which is shaped in a welding, casting or other process and then machined. The second inner flange  211  of the second adapter bracket  21  and the second outer flange  321  are connected with bolts and stops so that the rotor and the rotational shaft are connected together. The second adapter bracket  21  is usually made of steel materials such as Q235 steel, which is shaped in a welding, casting or other process and then machined. 
     The second adapter bracket  21  is a rotor bracket, and the second module  22  includes a plurality of magnetic pole modules  6 ; and the rotor bracket includes an adapter portion  51 , two or more connecting arms  52  distributed radially on an outer circumference of the adapter portion  51 , and a rotor ring  53  arranged coaxially with the two or more connecting arms  52 ; and the magnetic pole modules  6  are disposed at a mounting surface  53   a  of the rotor ring  53 . The adapter portion  51 , the connecting arms  52  and the rotor ring  53  can be fixed together by means of flange bolt connection, etc. 
     Furthermore, each of the rotor ring  53  and the connecting arms  52  are provided as a hollow internal structural member, which improves the stiffness of the rotor bracket. In particular, the internally hollow connecting arm  52  can theoretically prevent a problem of magnetic pole attraction at the air gap between the rotor and the stator when the rotor is being mounted around the outer circumference of the stator. 
     Furthermore, a plurality of mounting slots  53   b  extending in the axial direction are disposed at the mounting surface  53   a  of the rotor ring  53  at intervals; with respect to the electric machine having a structure with an inner stator and an outer rotor, the mounting surface  53   a  is the inner circumference of the rotor ring  53 . The magnetic pole module  6  includes a substrate  6   a  and at least one magnet steel  6   b  disposed at the substrate  6   a , and mounting portions  6   c  for matching with the mounting slots  53   b  are disposed at a side of the substrate  6   a  away from the magnet steel  6   b.    
     The magnetic pole module  6  is an excitation source of the electric machine, in which direct current coil excitation or permanent magnet excitation is commonly used; and permanent magnet excitation is used as an example in embodiments of the disclosure. The magnetic pole module  6  can be prefabricated at the factory. Herein, the magnet steel  6   b  is made of hard magnetic material such as NdFeB permanent magnet material, and several small-sized magnet steels  6   b  are assembled in the axial direction to form the magnetic pole module  6 . The magnet steels  6   b  are fixed to the substrate  6   a  by gluing, mechanical connection such as screw connection, etc. The surface of the magnet steel  6  is protected by glue injection, magnetic pole boxes, etc., to isolate it from the outside air and reduce the risk of failure. The substrate  6   a  is made of ferromagnetic materials such as low carbon steel, electric iron, silicon steel, etc. by machining, which provides a magnetic flux path between adjacent magnetic pole modules  6 . 
     The mounting portion  6   c  of the substrate  6   a  is made of ferromagnetic materials such as low carbon steel, electric iron, silicon steel, etc. by machining, and can be fixed to the substrate  6   a  by bolting, welding, etc.; or the mounting portion  6   c  may be a part of the substrate  6   a ; and the mounting portion  6   c  has a shape matching with that of the mounting slot  53   b  of the rotor ring  53  to form a sliding rail structure that can move in the axial direction, so that the magnetic pole module  6  can be conveniently mounted to the mounting surface  53   a  of the rotor ring  53  and thus arranged opposite to the iron core  122  and the stator winding of the stator to form a uniform air gap. 
     It will be understood that the above structure of the guiding assembly  4  can also applied to an electric machine having a structure with an inner rotor and an outer stator, and then the guiding assembly  4  is disposed between the rotor and the rotational shaft; in other words, the first revolving body  1  is a rotor, the first shaft  31  is a rotational shaft, the second revolving body  2  is a stator, and the second shaft  32  is a stationary shaft. 
     Referring to  FIG. 13 , a structural schematic diagram of a rotor of an electric machine having a structure with an inner rotor and an outer stator is shown. The rotor includes an annular first adapter bracket  11  and a plurality of magnetic pole modules  6  disposed at an outer circumference of the first adapter bracket  11 , a first inner flange  111  and a tubular structural portion  112  extending in the axial direction from the first inner flange  111  are disposed at an inner circumference of the first adapter bracket  11 . 
     Accordingly, the first shaft  31  in  FIG. 8  is a rotational shaft, and the guiding assembly  4  is disposed between the tubular structural portion  112  of the rotor and the rotational shaft to restrict a movement of the rotor relative to the rotational shaft in the circumferential direction and the radial direction. A first outer flange  313  is disposed at an outer circumference of the rotational shaft, and the tubular structural portion  112  and the rotational shaft are connected together through a cooperation of the first inner flange  111  and the first outer flange  313 . 
     Furthermore, similar to the structure in  FIGS. 6 and 7 , the guiding assembly  4  includes a first inserting portion  41  and a first socketing portion  42  that are engaged with each other, one of the first inserting portion  41  and the first socketing portion  42  is disposed at an inner circumference of the tubular structural portion  112  and extends in the axial direction, and the other of the first inserting portion  41  and the first socketing portion  42  is disposed at an outer circumference of the first shaft  31  and extends in the axial direction. There may be multiple first inserting portions  41  and multiple first socketing portions  42 . 
     The guiding assembly  4  also includes a second inserting portion  43  and a second socketing portion  44  that are engaged with each other, the second inserting portion  43  is disposed at the outer circumference of the first shaft  31  near the first outer flange  313 , the second socketing portion  44  is disposed at the inner circumference of the tubular structural portion  112  near the first inner flange  111 , and the second socketing portion  44  has an inner diameter D 2  larger than an inner diameter D 1  of the first inserting portion  41 . 
     Other structures of the guiding assembly  4  are similar to the aforementioned electric machine having a structure with an inner stator and an outer rotor to ensure that the coaxiality error of the rotor and the shaft assembly which have been finally assembled is at a high precision level, and will not be described again. 
     Furthermore, the rotor bracket includes an adapter portion  51 , two or more connecting arms  52  distributed radially on an outer circumference of the adapter portion  51 , and a rotor ring  53  arranged coaxially with the two or more connecting arms  52 ; magnetic pole modules  6  are disposed at a mounting surface  53   a  of the rotor ring  53 ; and with respect to the electric machines having a structure with an inner rotor and an outer stator, the mounting surface  53   a  is an outer circumference of the rotor ring  53 . 
     Furthermore, the stator structure is similar to the stator structure in  FIGS. 4 and 5 , with the difference that there is no tubular structural portion  112  at the inner circumference of the first adapter bracket  11 , the iron core  122  is disposed at the inner circumference of the stator module bracket  121 , and the stator winding is mounted on the iron core  122  so as to be disposed opposite to the magnetic pole module  6  at the outer circumference of the rotor bracket to form a uniform air gap. 
     Furthermore, each of the rotor ring  53  and the connecting arms  52  are provided as a hollow internal structural member, which improves the stiffness of the rotor bracket. In particular, the internally hollow connecting arm  52  can theoretically prevent a problem of magnetic pole attraction at the air gap between the rotor and the stator when the stator is being mounted around the outer circumference of the rotor. 
     Furthermore, for an electric machine with a large diameter, when a maximum diameter of its stator or rotor exceeds a road transportation limit of  5 m, it is necessary to prefabricate the stator and the rotor in a factory, and divide the stator into several stator sections and divide the rotor into several rotor sections before transportation. Herein, a maximum chord length of each stator section is smaller than an inner diameter of a paint dipping tank in the factory in order to ensure processing requirements of the stator winding. 
     To facilitate transportation, maximum widths of the stator section and the rotor section are smaller than the road transportation limit. After being transported to an assembling site, respective stator sections are then assembled into the stator, and respective rotor sections are assembled into the rotor. 
     Referring to  FIG. 14 , embodiments of the disclosure also provide an assembling method for any of the electric machines as described above, wherein the assembling method includes: 
     Step S 1 : disposing the first shaft  31  around and at the outer circumference of the second shaft  32 ; 
     Step S 2 : disposing the tubular structural portion  112  of the first revolving body  1  around and at the outer circumference of the first shaft  31  through the guiding assembly  4 . 
     Step S 3 : connecting the second revolving body  2  coaxially with the second shaft  32  so that the second revolving body  2  is disposed around and at the outer circumference of the first revolving body  1 . 
     Herein, the first revolving body  1  is a stator, the first shaft  31  is a stationary shaft, the second revolving body  2  is a rotor, and the second shaft  32  is a rotational shaft; or the first revolving body  1  is a rotor, the first shaft  31  is a rotational shaft, the second revolving body  2  is a stator, and the second shaft  32  is a stationary shaft. 
     Alternatively, the electric machine and the assembling method for the electric machine according to exemplary embodiments described above may be applied to various devices where an electric machine is required, such as but not limited to, wind turbines. 
     Those skilled in the art should understand that the above-mentioned embodiments are all illustrative but not restrictive. Different technical features in different embodiments can be combined to achieve beneficial effects. Those skilled in the art should understand and implement other modified embodiments of the disclosed embodiments after studying the drawings, description, and claims. In the claims, the term “comprise” does not exclude other devices or steps; the article is intended to include one or more articles when not modified by a quantifier, and may be used interchangeably with “one or more articles”; the terms “first”, “second” or the like are used to designate names and are not intended to indicate any particular order. Any reference sign in the claims should not be construed as limiting the scope of protection. The functions of multiple parts in the claims may be implemented by a single hardware or software module. The presence of certain technical features in different dependent claims does not mean that these technical features cannot be combined for beneficial effect.