Rotor of an induction motor and method for assembling a cage winding of a rotor

Abstract

A rotor of an induction motor and a method for assembling a cage winding of the rotor. The rotor of the induction motor comprises a rotor core structure (102) and a cage winding. The cage winding comprises rotor bars (103, 104) and end rings (105, 106), wherein the rotor bars (103, 104) are located in slots of the rotor core structure, and the end rings (105, 106) are connected to the ends of the rotor bars. The ends of the rotor bars are attached to the openings of the end rings by expansion of the ends of the rotor bars in the transverse direction of the rotor bars, the expansion being caused by axial extrusion that has been directed to the ends of the rotor bars. The material of the rotor bars is softer than that of the end rings. Thus, undesirable shape deformation when the ends of the rotor bars are axially extruded can be avoided. The material of the end rings can be, for example, a copper alloy with chromium and zirconium added, while the material of the rotor bars can be, for example, copper.

Description

Technical Field

[0001] The present disclosure generally relates to rotating electric machines. More specifically, the present disclosure relates to a rotor of an induction electric machine. Furthermore, the present disclosure relates to an induction electric machine and a method for assembling a cage winding of a rotor of an induction electric machine. Background Art

[0002] Rotating electrical machines such as motors and generators generally include a stator and a rotor, which are arranged so that a magnetic flux is generated between the two. The rotor of an induction motor generally includes a rotor core structure, a shaft and a cage winding. The cage winding includes rotor bars and end rings. The rotor bars are located in the slots of the rotor core structure. The end rings are connected to the ends of the rotor bars at the end regions of the rotor core structure. The rotor core structure is typically a laminated structure consisting of ferromagnetic steel plates that are electrically insulated from each other and stacked in the axial direction of the rotor. However, particularly in many high-speed induction motors, the rotor core structure is made of solid steel. The rotor core structure made of solid steel can constitute a single piece of solid steel together with the shaft of the rotor.

[0003] In many induction machines, the rotor bars and end rings are manufactured as separate pieces of conductive material, and the end rings are attached to the ends of the rotor bars by conductive joints. The material of the rotor bars and the end rings can be, for example, copper or aluminum. The rotor bars can be attached to the end rings, for example, by brazing, welding, brazing, or axially pressing the ends of the rotor bars to expand the ends of the rotor bars in the lateral direction, thereby forming a tight fit with the walls of the opening of the end ring through which the rotor bars protrude. The above-mentioned attachment methods are not exempt from challenges caused by, for example, temperature changes and mechanical vibrations. In addition, the fit between the rotor bars and the slots of the rotor core structure needs to have a gap to allow assembly. During operation, the rotor bars will move outward on the rotor depending on the rotational speed. The movement of the rotor bars will affect the balance of the rotor and may lead to an increase in mechanical vibrations and damage to the machine. Summary of the invention

[0004] A simplified overview is provided below to provide a basic understanding of some embodiments of the present invention. The overview is not an extensive review of the present invention. It is not intended to identify key or important elements of the present invention, nor is it intended to describe the scope of the present invention. The following overview only presents some concepts of the present invention in a simplified form, as a preface to a more detailed description of an illustrative embodiment of the present invention.

[0005] In this document, the word "geometry" when used as a prefix denotes a geometric concept, which is not necessarily part of any physical object. A geometric concept may be, for example, a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity of zero, one, two or three dimensions. In this document, the word "between" is not limited to the case where an entity is located between two other entities and in contact with the other entities, but the first mentioned entity can be at a distance from one or both of the other entities.

[0006] According to the present invention, a novel rotor for an induction motor is provided. The rotor according to the present invention comprises:

[0007] - rotor core structure,

[0008] - a plurality of rotor bars located in slots of the rotor core structure, and

[0009] - End rings which electrically connect the ends of the rotor bars to one another at both ends of a cage winding consisting of the rotor bars and the end rings.

[0010] The ends of the rotor bars are attached to the openings of the end rings by expansion of the ends of the rotor bars in the transverse direction of the rotor bars, the expansion being caused by axial extrusion that has been directed to the ends of the rotor bars during manufacture of the rotor. The material of the rotor bars is softer than the material of the end rings. Thus, when the ends of the rotor bars are axially extruded and expanded in the transverse direction, undesirable shape deformation of the end rings can be avoided. The advantage provided by the harder end rings and the softer rotor bars is that the mechanical strength of the cage winding is improved while the rotor bars can still be attached to the end rings by axial extrusion of the ends of the rotor bars. The material of the end rings can be, for example, a copper alloy with chromium and zirconium added, i.e., CuCrZr, and the material of the rotor bars can be, for example, copper.

[0011] The rotor according to the invention further comprises one or more annular disc springs, which surround the geometric axis of rotation of the rotor. The one or more annular disc springs are axially located between the end rings and radially located between the rotor bars and the geometric axis of rotation of the rotor. The one or more annular disc springs are axially compressed and, because of the axial compression, the one or more annular disc springs are radially expanded against the rotor bars, so that the one or more annular disc springs are arranged to press the rotor bars radially away from the geometric axis of rotation of the rotor. Thus, the rotor bars are always pressed outwards, so that the centrifugal force does not move the rotor bars. Therefore, the balance of the rotor can be maintained during the rotation of the rotor.

[0012] According to the present invention, a novel induction motor is also provided. The induction motor according to the present invention comprises:

[0013] - a stator comprising stator windings, and

[0014] - According to the invention, the rotor is supported in a rotatable manner relative to the stator.

[0015] According to the present invention, there is also provided a new method for assembling a cage winding of a rotor of an induction motor. The method according to the present invention comprises:

[0016] - placing the rotor bars into the slots of the rotor core structure such that at the ends of the rotor core structure the ends of the rotor bars protrude axially from the rotor core structure,

[0017] - placing the end rings so that the ends of the rotor bars protrude axially through the openings of the end rings, and

[0018] - Introducing axial extrusion to the ends of the rotor bars to attach the ends of the rotor bars to the openings of the end rings by expansion of the ends of the rotor bars in the transverse direction of the rotor bars, the expansion being caused by the axial extrusion and the material of the rotor bars being softer than the material of the end rings.

[0019] In the method according to the invention, one or more annular disc springs are placed around the geometrical rotation axis of the rotor, and then end rings are placed so that the one or more annular disc springs are axially located between the end rings and radially between the rotor bars and the geometrical rotation axis of the rotor, and the one or more annular disc springs are compressed in the axial direction. Due to the axial compression, the one or more annular disc springs are radially expanded against the rotor bars, so that the one or more annular disc springs press the rotor bars radially away from the geometrical rotation axis of the rotor.

[0020] Illustrative and non-limiting embodiments are described in the attached dependent claims.

[0021] Various illustrative and non-limiting embodiments, both as to constructions and methods of operation, together with further objects and advantages thereof, will be best understood when the following description of specific illustrative embodiments is read in conjunction with the accompanying drawings.

[0022] The verbs "comprise..." and "include..." are used in this document as open limitations, which neither exclude nor require the existence of unrecited features. Unless expressly stated otherwise, the features recited in the dependent claims are all freely combinable with each other. Furthermore, it should be understood that the use of "a", "an", or the singular form throughout this document does not exclude a plurality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the following, exemplary and non-limiting embodiments and advantages are explained in more detail by way of example and with reference to the accompanying drawings, in which:

[0024] Figure 1a , Figure 1b and Figure 1c shows a rotor according to an illustrative and non-limiting embodiment,

[0025] Figure 2 An electric machine according to an exemplary and non-limiting embodiment is shown, and

[0026] Figure 3 A flow chart of a method for assembling a cage winding of a rotor of an induction motor is shown according to an illustrative and non-limiting embodiment. DETAILED DESCRIPTION

[0027] The specific examples provided in the description given below should not be construed as limiting the scope and / or applicability of the appended claims. In addition, it should be understood that the lists and groups of examples provided in the description given below are not exhaustive unless explicitly stated otherwise.

[0028] Figure 1a and Figure 1b A cross-sectional view of a rotor 101 is shown according to an illustrative and non-limiting embodiment. Figure 1a The cross-sectional view shown in FIG. Figure 1b The geometric line AA shown in is intercepted so that the geometric section plane is parallel to the yz plane of the coordinate system 199. Figure 1b The cross section shown in Figure 1a The geometric line BB shown in is intercepted so that the geometric section plane is parallel to the xy plane of the coordinate system 199 . Figure 1c Shows Figure 1a 120 . The rotor 101 comprises a rotor core structure 102. In this exemplary case, the rotor core structure 102 is made of solid ferromagnetic steel, and the rotor core structure and the shaft of the rotor constitute a single piece of solid steel. However, the rotor according to an exemplary and non-limiting embodiment may also comprise a rotor core structure, wherein the rotor core structure comprises a stack of ferromagnetic steel plates, such that the ferromagnetic steel plates are electrically insulated from each other and are stacked on each other in the axial direction of the rotor.

[0029] The rotor 101 includes a cage winding including a plurality of rotor bars located in slots of a ferromagnetic core structure 102. Figure 1a and Figure 1b, two of the rotor bars are indicated by reference numerals 103 and 104. In this schematic case, the slots of the rotor core structure 102 are open slots having slot openings on the air gap surface of the rotor core structure 102. However, the rotor according to the illustrative and non-limiting embodiment may also include a rotor core structure having closed slots. The cage winding includes two end rings 105 and 106. The end ring 105 electrically connects the ends of the rotor bars to each other at the first end of the rotor core structure 102. Correspondingly, the end ring 106 electrically connects the ends of the rotor bars to each other at the second end of the rotor core structure 102. The rotor bars are located in the slots of the rotor core structure 102 so that at each end of the rotor core structure, the ends of the rotor bars protrude axially from the rotor core structure 102 and protrude axially through the openings of the end rings 105 and 106. The ends of the rotor bars are attached to the openings of the end rings by expansion of the ends of the rotor bars in the transverse direction of the rotor bars, wherein the expansion is caused by axial compression introduced to the ends of the rotor bars during manufacture of the rotor. Figure 1c In the figure, axial extrusion and lateral expansion are shown by solid arrows. The tool for axially extruding the rotor bars may include, for example, a point-shaped tip or a linear ridge, which abuts against the end surface of the rotor bars being axially extruded. The material of the rotor bars is softer than that of the end rings. Thus, when the ends of the rotor bars are axially extruded and laterally expanded, undesirable shape deformation of the end rings can be avoided. The material of the end rings may be, for example, a copper alloy with chromium and zirconium added, i.e., CuCrZr, and the material of the rotor bars may be, for example, copper Cu.

[0030] Figure 1a to Figure 1c The schematic rotor 101 shown in comprises annular disc springs 107 and 108 around a geometric axis of rotation 121. The annular disc springs 107 and 108 are axially located between the rotor core structure 102 and the end rings, and radially located between the rotor bars and the geometric axis of rotation 121. The annular disc springs are axially compressed between the end rings and the rotor core structure, and due to the axial compression, the annular disc springs expand radially against the rotor bars, so that the annular disc springs are arranged to press the rotor bars radially away from the geometric axis of rotation 121. In Figure 1c In FIG. 1 , the axial compression directed to the annular disc spring 107 is shown by the dashed arrows, and the radial extrusion directed to the bottom of the rotor bar 103 is shown by the dashed arrows.

[0031] exist Figure 1a to Figure 1c In the schematic rotor 101 shown in FIG. 1 , the outer circumferences of the annular disc springs 107 and 108 are slotted, so that the outer circumferences of the annular disc springs have radially extending locking slots, which cooperate with the bottoms of the rotor bars to prevent the annular disc springs from rotating relative to the rotor core structure 102. Figure 1b In the diagram, a locking slot is indicated by reference numeral 110. Furthermore, in this schematic case, the outer circumference of the annular disc springs 107 and 108 has a radially extending disengagement slot, which is located between the rotor bars in the circumferential direction and is deeper in the radial direction than the radially extending locking slot. Figure 1b In FIG. 1 , two radially extending disengagement slots are indicated by reference numeral 111. The parts of the annular disc spring located between adjacent radially extending disengagement slots in the radially extending disengagement slots constitute spring arms, each of which presses one of the rotor bars in the radial direction away from the geometrical rotation axis 121. Figure 1b In the figure, a spring arm is indicated by reference numeral 112. Due to the disengagement of the spring arms of the annular disc springs 107 and 108, a radial compressive force is maintained on each rotor bar, respectively, that is, each annular disc spring includes a rotor bar-specific spring arm for each rotor bar.

[0032] Figure 1a to Figure 1c The schematic rotor 101 shown in FIG. 1 includes locking nuts 113 and 114 that surround the geometric rotation axis 121 of the rotor. Figure 1a As shown in , locking nuts 113 and 114 are mounted on the threaded portion of the rotor, and the locking nuts 113 and 114 are arranged to squeeze the end rings 105 and 106 axially toward the rotor core structure 102. However, different mechanical means may also be used to secure the end rings. The rotor according to an illustrative and non-limiting embodiment may include, for example, bolts that extend axially through the end rings to the rotor core structure. In some cases, such as when there are no disc springs between the rotor core structure and the end rings, the joints between the rotor bars and the end rings may be sufficient to hold the end rings in place.

[0033] exist Figure 1a to Figure 1c In the schematic rotor 101 shown in the figure, the first annular butterfly spring 107 of the annular butterfly springs is axially located between the rotor core structure 102 and the first end ring 105 of the end rings, the first annular butterfly spring of the annular butterfly springs is axially compressed between the rotor core structure and the first end ring of the end rings, the second annular butterfly spring 108 of the annular butterfly springs is axially located between the rotor core structure and the second end ring 106 of the end rings, and the second annular butterfly spring of the annular butterfly springs is axially compressed between the rotor core structure and the second end ring of the end rings.

[0034] In a rotor according to an exemplary and non-limiting embodiment in which the rotor core structure includes axially continuous ferromagnetic elements (e.g., axially stacked sheets or plates), it is also possible that one or more annular disc springs are located between the axially continuous ferromagnetic elements and do not contact the end rings. In this exemplary case, the one or more annular disc springs do not need to be close to the joint between the rotor bars and the end rings, so the radial force caused by the one or more annular disc springs to squeeze the rotor bars radially away from the geometric rotation axis of the rotor is small. In a rotor according to an exemplary and non-limiting embodiment, there is only one annular disc spring in the middle of the rotor core structure. In a rotor according to another exemplary and non-limiting embodiment, there are three or more annular disc springs axially continuously between the end rings.

[0035] Figure 2 An induction motor according to an exemplary and non-limiting embodiment is shown. The induction motor includes a stator 215 and a rotor 201 according to an exemplary and non-limiting embodiment of the present invention. The rotor 201 is rotatably supported relative to the stator 215. Figure 2 The device for supporting the rotor 201 in a rotatable manner relative to the stator 215 is not shown. The stator 215 includes a stator winding 216, which is used to generate a rotating magnetic field in response to the application of an alternating current. The stator winding 216 can be, for example, a three-phase winding. The rotor 201 can be, for example, Figure 1a to Figure 1c As shown in .

[0036] Figure 3 A flow chart of a method for assembling a cage winding of a rotor of an induction motor according to an exemplary and non-limiting embodiment is shown. The method comprises the following actions:

[0037] - action 301 : placing rotor bars into slots of the rotor core structure such that at the ends of the rotor core structure, the ends of the rotor bars protrude axially from the rotor core structure,

[0038] - Action 302: Placing the end ring so that the ends of the rotor bars protrude axially through the openings of the end ring, and

[0039] - Action 303: directing axial extrusion to the ends of the rotor bars to attach the ends of the rotor bars to the openings of the end rings by expansion of the ends of the rotor bars in a transverse direction of the rotor bars, the expansion being caused by the axial extrusion and the material of the rotor bars being softer than the material of the end rings.

[0040] In a method according to an illustrative and non-limiting embodiment, the material of the end rings is a copper alloy with additions of chromium and zirconium, and the material of the rotor bars is copper.

[0041] The method according to an exemplary and non-limiting embodiment includes softening the material of the rotor bars by annealing before placing the rotor bars into the slots of the rotor core structure. In this exemplary case, depending on the material of the rotor bars (e.g., copper), the axial extrusion and the deformation caused by the axial extrusion may re-harden the material of the rotor bars.

[0042] The method according to an exemplary and non-limiting embodiment comprises placing one or more annular disc springs around the geometric axis of rotation of the rotor and subsequently placing end rings such that:

[0043] - the one or more annular disc springs are located axially between the end rings,

[0044] - the one or more annular disc springs are located radially between the rotor bars and the geometrical axis of rotation of the rotor, and

[0045] The one or more annular disc springs are axially compressed and, due to the axial compression, radially expand against the rotor bars such that the one or more annular disc springs press the rotor bars radially away from the geometrical rotation axis of the rotor.

[0046] In a method according to an illustrative and non-limiting embodiment, a first of the annular butterfly springs is axially placed between a rotor core structure and a first end ring of the end rings, the first annular butterfly spring is axially compressed between the rotor core structure and the first end ring, a second of the annular butterfly springs is axially placed between the rotor core structure and a second end ring of the end rings, and the second annular butterfly spring is axially compressed between the rotor core structure and the second end ring.

[0047] In a method according to an illustrative and non-limiting embodiment, the outer circumference of the annular disc spring is slotted so that the outer circumference of the annular disc spring has radially extending locking slots that cooperate with the bottom of the rotor bars to prevent the annular disc spring from rotating relative to the rotor core structure.

[0048] In the method according to the exemplary and non-limiting embodiment, the outer circumference of the annular disc spring has radially extending escape slots, which are located between the radially extending locking slots in the circumferential direction and are radially deeper than the radially extending locking slots. The portion of the annular disc spring located between adjacent ones of the radially extending escape slots constitutes a spring arm, each of which presses one of the rotor bars in the radial direction away from the geometric rotation axis of the rotor.

[0049] A method according to an exemplary and non-limiting embodiment includes installing a lock nut on a threaded portion of a rotor such that the lock nut surrounds a geometric axis of rotation of the rotor and axially compresses the end ring toward the rotor core structure.

[0050] The specific examples provided in the description given above should not be construed as limiting the scope and / or applicability of the appended claims.Unless explicitly stated otherwise, neither the lists nor the groups of examples provided in the description given above are exhaustive.

Claims

1. A rotor (101, 201) for an induction motor, the rotor comprising: - a rotor core structure (102), - a plurality of rotor bars (103, 104) located in slots of the rotor core structure, and - end rings (105, 106) which electrically connect the ends of the rotor bars to each other at both ends of a cage winding, wherein the cage winding is composed of the rotor bars and the end rings, wherein the ends of the rotor bars are attached to the openings of the end rings by expansion of the ends of the rotor bars in a transverse direction of the rotor bars, the expansion being caused by axial compression that has been directed to the ends of the rotor bars, and wherein the material of the rotor bars is softer than the material of the end rings, Characterized in that the rotor further comprises one or more annular disc springs (107, 108), the one or more annular disc springs (107, 108) surrounding the geometric rotation axis of the rotor, the one or more annular disc springs (107, 108) being axially located between the end rings and radially located between the rotor bars and the geometric rotation axis of the rotor, and the one or more annular disc springs being axially compressed, and due to the axial compression, the one or more annular disc springs are radially expanded against the rotor bars, so that the one or more annular disc springs are arranged to press the rotor bars radially away from the geometric rotation axis of the rotor.

2. The rotor according to claim 1, wherein: The material of the end rings is a copper alloy to which chromium and zirconium are added, and the material of the rotor bars is copper.

3. The rotor according to claim 1, wherein: The first annular disc spring (107) among the annular disc springs is axially located between the rotor core structure and the first end ring (105) among the end rings, and the first annular disc spring is axially compressed between the rotor core structure and the first end ring, and the second annular disc spring (108) among the annular disc springs is axially located between the rotor core structure and the second end ring (106) among the end rings, and the second annular disc spring is axially compressed between the rotor core structure and the second end ring.

4. The rotor according to claim 1, wherein: The outer circumference of the annular disc spring is provided with a narrow groove, so that the outer circumference of the annular disc spring has a radially extending locking groove (110), and the radially extending locking groove (110) cooperates with the bottom of the rotor guide bar to prevent the annular disc spring from rotating relative to the rotor core structure.

5. The rotor according to claim 3, wherein: The outer circumference of the annular disc spring is provided with a narrow groove, so that the outer circumference of the annular disc spring has a radially extending locking groove (110), and the radially extending locking groove (110) cooperates with the bottom of the rotor guide bar to prevent the annular disc spring from rotating relative to the rotor core structure.

6. The rotor according to claim 4, wherein: The outer circumference of the annular disc spring has a radially extending disengagement slot (111), the radially extending disengagement slot (111) is located between the rotor bars in the circumferential direction and is radially deeper than the radially extending locking slot, and the portion of the annular disc spring between adjacent radially extending disengagement slots in the radially extending disengagement slot constitutes a spring arm (112), each spring arm (112) is arranged to press one of the rotor bars in the radial direction away from the geometric rotation axis of the rotor.

7. The rotor according to claim 5, wherein: The outer circumference of the annular disc spring has a radially extending disengagement slot (111), the radially extending disengagement slot (111) is located between the rotor bars in the circumferential direction and is radially deeper than the radially extending locking slot, and the portion of the annular disc spring located between adjacent radially extending disengagement slots of the radially extending disengagement slot constitutes a spring arm (112), each spring arm (112) is arranged to press one of the rotor bars in the radial direction away from the geometric rotation axis of the rotor.

8. A rotor according to any one of claims 1 to 7, wherein: The rotor comprises a locking nut (113, 114) which is mounted on a threaded portion of the rotor about the geometrical axis of rotation of the rotor and is arranged to press the end ring axially towards the rotor core structure.

9. A rotor according to any one of claims 1 to 7, wherein: The rotor core structure (102) is made of solid steel.

10. An induction motor comprising: - a stator (215), said stator (215) comprising a stator winding (216), and - A rotor (201) according to any one of claims 1 to 7, the rotor (201) being supported in a rotatable manner relative to the stator.

11. A method for assembling a cage winding of a rotor of an induction motor, the method comprising: - placing (301) rotor bars into slots of a rotor core structure such that, at the ends of the rotor core structure, the ends of the rotor bars protrude axially from the rotor core structure, - placing (302) an end ring so that the ends of the rotor bars protrude axially through openings in the end ring, and - directing (303) an axial extrusion to the end of the rotor bar to attach the end of the rotor bar to the opening of the end ring by expansion of the end of the rotor bar in a transverse direction of the rotor bar, the expansion being caused by the axial extrusion, The material of the rotor bars is softer than that of the end rings. Characterized in that one or more annular disc springs are placed around the geometric rotation axis of the rotor, and the end rings are subsequently placed so that the one or more annular disc springs are axially located between the end rings and radially located between the rotor bars and the geometric rotation axis of the rotor, and the one or more annular disc springs are compressed in the axial direction, and due to the axial compression, the one or more annular disc springs are radially expanded against the rotor bars, so that the one or more annular disc springs press the rotor bars radially away from the geometric rotation axis of the rotor.

12. The method according to claim 11, wherein: The method includes softening the material of the rotor bars by annealing prior to placing the rotor bars into the slots of the rotor core structure.

13. The method according to claim 11, wherein: The material of the end rings is a copper alloy to which chromium and zirconium are added, and the material of the rotor bars is copper.

14. The method according to claim 11, wherein: The outer circumference of the annular disc spring is provided with a slot, so that the outer circumference of the annular disc spring has a radially extending locking slot, and the radially extending locking slot cooperates with the bottom of the rotor guide bar to prevent the annular disc spring from rotating relative to the rotor core structure.

15. The method according to claim 14, wherein: The outer circumference of the annular disc spring has a radially extending disengagement slot, the radially extending disengagement slot is located between the radially extending locking slots in the circumferential direction and is radially deeper than the radially extending locking slot, and the portion of the annular disc spring located between adjacent radially extending disengagement slots in the radially extending disengagement slots constitutes a spring arm, each spring arm is used to radially press one of the rotor bars away from the geometric rotation axis of the rotor.

16. The method according to any one of claims 11 to 15, wherein: The method includes installing a lock nut on a threaded portion of the rotor such that the lock nut surrounds the geometric axis of rotation of the rotor and axially compresses the end ring toward the rotor core structure.

Images