Induction machine rotor and rotor cage winding assembly method

Abstract

To provide a rotor of an induction machine, and a method for assembling a cage winding of a rotor.SOLUTION: A rotor of an induction machine includes a rotor core structure (102) and a cage winding. The cage winding includes rotor bars (103, 104) in slots of the rotor core structure and end-rings (105, 106) connected to ends of the rotor bars. The ends of the rotor bars are attached to openings of the end-rings by expansion of the ends of the rotor bars in transverse directions of the rotor bars caused by axial press having been directed to the ends of the rotor bars. The material of the rotor bars is softer than the material of the end-rings. Thus, unwanted shape deformation of the end-rings can be avoided when the ends of the rotor bars are axially pressed. The material of the end-rings can be for example copper alloy with additions of chrome and zirconium, and the material of the rotor bars can be for example copper.SELECTED DRAWING: Figure 1a

Description

[Technical field]

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

[0002] Rotating electric machines, such as electric motors and generators, generally have a stator and a rotor, which are arranged so that a magnetic flux is generated between the two. The rotor of an induction machine usually has a rotor core structure, a shaft, and a cage winding. The cage winding has rotor bars and end-rings. The rotor bars are disposed in 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 usually a laminate-type structure made of ferromagnetic steel sheets that are electrically insulated from each other and stacked in the axial direction of the rotor. However, particularly in many high-speed induction machines, the rotor core structure is made of solid steel. The solid steel rotor core structure, together with the rotor shaft, may constitute a single piece of solid steel.

[0003] In many induction machines, the rotor bars and the 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 may be, for example, copper or aluminum. The rotor bars may be attached to the end rings, for example, by soldering, welding, brazing, or pressing the ends of the rotor bars in the axial direction, which expands the ends of the rotor bars in the cross-sectional direction to form a tight fit with the walls of the openings in the end rings through which the rotor bars pass. The above-mentioned attachment methods are not free from problems caused, for example, by temperature fluctuations and mechanical vibrations. Furthermore, the fit between the rotor bars and the slots of the rotor core structure must have a clearance to allow assembly. During operation, the rotor bars may move outward on the rotor, depending on the rotation speed. The movement of the rotor bars will affect the balance of the rotor and possibly result in increased mechanical vibrations and damage to the machine. Summary of the Invention

[0004] The following presents a simplified summary to provide a basic understanding of some embodiments of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention, nor is it intended to delineate the scope of the invention. The following summary is merely intended to present some concepts of the invention in a simplified form as a prelude to a more detailed description of example embodiments of the invention.

[0005] In this specification, the term "geometric" when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept may be, for example, a geometric point, a straight or curved geometric line, a geometric face, a non-flat geometric surface, a geometric space, or any other geometric entity that is 0, 1, 2, or 3 dimensional. In this specification, the term "between" is not limited to the case where an entity located between two other entities is in contact with these other entities, and the first mentioned entity may be separated from one or both of the other entities by a certain distance.

[0006] According to the present invention, a new rotor for an induction machine is provided. The rotor according to the present invention has the following features: - a rotor core structure; - a plurality of rotor bars within slots of a rotor core structure; - end rings electrically connecting the ends of the rotor bars to each other at both ends of a cage winding formed by the rotor bars and the end rings; has.

[0007] 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 cross-sectional direction of the rotor bars, which expansion is brought about by axial pressing directed at the ends of the rotor bars during the manufacture of the rotor. The material of the rotor bars is softer than the material of the end rings. Thus, undesirable shape deformation of the end rings can be avoided when the ends of the rotor bars are pressed in the axial direction and expanded in the cross-sectional direction. The advantage offered by the relatively hard end rings and the relatively soft rotor bars is that the mechanical strength of the cage winding is improved, while it is still possible to attach the rotor bars to the end rings by pressing the ends of the rotor bars in the axial direction. The material of the end rings may be, for example, a copper alloy with additions of chromium and zirconium, i.e. CuCrZr, and the material of the rotor bars may be, for example, copper.

[0008] The rotor according to the invention further comprises one or more ring-shaped disc springs surrounding the geometric axis of rotation of the rotor. The one or more ring-shaped disc springs are located axially between the end rings and radially between the rotor bars and the geometric axis of rotation of the rotor. The one or more ring-shaped disc springs are compressed in the axial direction and as a result of the axial compression, the one or more ring-shaped disc springs radially expand in pressure contact with the rotor bars such that the one or more ring-shaped disc springs are configured to radially press the rotor bars away from the geometric axis of rotation of the rotor. Thus, the rotor bars are constantly pressed outwards and therefore do not move due to centrifugal forces. Thus, the balance of the rotor can be maintained during rotation of the rotor.

[0009] According to the present invention, there is also provided a new induction machine. a stator having a stator winding; - a rotor according to the invention, the rotor being supported for rotation relative to a stator; has.

[0010] The present invention also provides a new method for assembling the cage windings of an induction machine rotor. The method according to the present invention comprises the steps of: - placing the rotor bars in slots of the rotor core structure such that the ends of the rotor bars protrude axially outwardly from the rotor core structure at the ends of the rotor core structure; - positioning the end rings such that the ends of the rotor bars extend axially through openings in the end rings; - applying an axial pressure to the ends of the rotor bars to fit them into the openings in the end rings due to an expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being brought about by the axial pressure and the material of the rotor bars being softer than the material of the end rings; has.

[0011] In the method according to the invention, one or more ring-shaped disc springs are arranged around the geometrical axis of rotation of the rotor and followed by the end rings, such that the one or more ring-shaped disc springs are located axially between the end rings and radially between the rotor bars and the geometrical axis of rotation of the rotor and the one or more ring-shaped disc springs are compressed in the axial direction, as a result of the axial compression the one or more ring-shaped disc springs radially expand in pressure against the rotor bars such that the one or more ring-shaped disc springs radially press the rotor bars away from the geometrical axis of rotation of the rotor.

[0012] Exemplary and non-limiting embodiments are set forth in the accompanying dependent claims.

[0013] Various illustrative and non-limiting embodiments, both as to structure and method of operation, together with further objects and advantages thereof, will be better understood from the following description of specific illustrative embodiments when read in conjunction with the accompanying drawings.

[0014] The verbs "to comprise" and "to include" are used in this specification as an open limitation which does not exclude and does not require the presence of features not recited. Features recited in the dependent claims may be freely combined with each other, unless expressly stated otherwise. Furthermore, it is to be understood that the use of "a" or "an", i.e. the singular, does not exclude the plural throughout this specification.

[0015] Exemplary and non-limiting embodiments and their advantages are described in more detail below, by way of example and with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0016] [Figure 1a] 1 illustrates a rotor according to an exemplary and non-limiting embodiment. [Figure 1b] 1 illustrates a rotor according to an exemplary and non-limiting embodiment. [Figure 1c] 1 illustrates a rotor according to an exemplary and non-limiting embodiment. [Diagram 2] 1 illustrates an electric machine according to an exemplary and non-limiting embodiment. [Diagram 3] 1 illustrates a flowchart of a method for assembling a cage winding of an induction machine rotor in accordance with an exemplary and non-limiting embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The specific examples provided in the description given below should not be construed as limiting the scope and / or applicability of the appended claims. Moreover, the lists and groupings of examples provided in the description given below should be understood to be non-exhaustive, unless expressly stated to the contrary.

[0018] 1a and 1b show cross-sectional views of a rotor 101 according to an exemplary and non-limiting embodiment. The cross-section shown in 1a is taken along the geometric line AA shown in 1b, such that the geometric cross-section plane is parallel to the yz-plane of the coordinate system 199. The cross-section shown in 1b is taken along the geometric line BB shown in 1a, such that the geometric cross-section plane is parallel to the xy-plane of the coordinate system 199. FIG. 1c shows an enlarged view of a portion 120 of FIG. 1a. The rotor 101 has 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 rotor shaft constitute a single piece of solid steel. However, it is also possible for the rotor according to an exemplary and non-limiting embodiment to have a rotor core structure with a stack of ferromagnetic steel sheets, such that the ferromagnetic steel sheets are electrically insulated from each other and are stacked on top of each other in the axial direction of the rotor.

[0019] The rotor 101 has a cage winding with a number of rotor bars arranged in slots of a ferromagnetic core structure 102. In Fig. 1a and Fig. 1b, two of the rotor bars are labeled with reference numbers 103 and 104. In this exemplary case, the slots of the rotor core structure 102 are open slots with the slot openings on the air gap surface of the rotor core structure 102. However, the rotor according to an exemplary and non-limiting embodiment can also have a rotor core structure with closed slots. The cage winding has two end rings 105 and 106. The end ring 105 electrically connects the ends of the rotor bars to each other at a first end of the rotor core structure 102. In a corresponding manner, the end ring 106 electrically connects the ends of the rotor bars to each other at a second end of the rotor core structure 102. The rotor bars are arranged in slots of the rotor core structure 102 at each end of the rotor core structure such that the ends of the rotor bars protrude axially outward from the rotor core structure 102 and pass axially through the openings of the end rings 105 and 106. The ends of the rotor bars are fitted into the openings of the end rings by expansion of the ends of the rotor bars in the cross-sectional direction of the rotor bars, the expansion being brought about by an axial pressing directed at the ends of the rotor bars during the manufacture of the rotor. In FIG. 1c, the axial pressing and the cross-sectional expansion are depicted by solid arrows. The tool for axially pressing the rotor bars can have, for example, a tip in the form of a point or a ridge in the form of a line, which presses against the end surface of the rotor bars being pressed axially. The material of the rotor bars is softer than the material of the end rings. Thus, undesirable shape deformation of the end rings can be avoided when the ends of the rotor bars are pressed axially and expanded in the cross-sectional direction. The material of the end rings may be, for example, a copper alloy with additions of chromium and zirconium, i.e., CuCrZr, and the material of the rotor bars may be, for example, copper, Cu.

[0020] The exemplary rotor 101 shown in Figures 1a-1c has ring-shaped disc springs 107 and 108 surrounding a geometric axis of rotation 121. The ring-shaped disc springs 107 and 108 are located axially between the rotor core structure 102 and the end rings and radially between the rotor bars and the geometric axis of rotation 121. The ring-shaped disc springs are axially compressed between the end rings and the rotor core structure and as a result of the axial compression the ring-shaped disc springs are radially expanded in pressure contact with the rotor bars such that the ring-shaped disc springs are configured to radially press the rotor bars away from the geometric axis of rotation 121. In Figure 1c the axial compression directed towards the ring-shaped disc springs 107 is depicted by dashed arrows and the radial pressing towards the bottom of the rotor bars 103 is depicted by dashed arrows.

[0021] In the exemplary rotor 101 shown in Figures 1a-1c, the outer circumference of the ring-shaped disc springs 107 and 108 is slotted such that the outer circumference of the ring-shaped disc spring has a radially extending locking slot that fits with the bottom of the rotor bar and prevents the ring-shaped spring from rotating relative to the rotor core structure 102. In Figure 1b, one of the locking slots is depicted by reference number 110. Furthermore, in the exemplary case, the outer circumference of the ring-shaped disc springs 107 and 108 has a radially extending decoupling slot located circumferentially between the rotor bars and radially deeper than the radially extending locking slot. In Figure 1b, two of the radially extending decoupling slots are depicted by reference number 111. Each portion of the ring-shaped disc spring between adjacent radially extending decoupling slots constitutes a spring arm which radially presses one of the rotor bars away from the geometrical axis of rotation 121. In FIG. 1b, one of the spring arms is depicted by reference number 112. A radial pressing force is maintained on each rotor bar individually due to the decoupling of the spring arms of the ring-shaped disc springs 107 and 108, i.e. each ring-shaped disc spring has its own spring arm for each rotor bar.

[0022] The example rotor 101 shown in Figures 1a-1c has locking nuts 113 and 114 that surround the rotor's geometric axis of rotation 121. As shown in Figure 1a, the locking nuts 113 and 114 are installed on the threaded portion of the rotor and are configured to press the end rings 105 and 106 axially toward the rotor core structure 102. However, different mechanical configurations can be used to secure the end rings. For example, a rotor according to one example and non-limiting embodiment can have 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 connection between the rotor bars and the end rings may be sufficient to keep the end rings in place.

[0023] In the exemplary rotor 101 shown in Figures 1a-1c, a first disc spring 107 of the ring-shaped disc springs is axially located between the rotor core structure 102 and a first end ring 105 of the end rings, and the first disc spring of the ring-shaped disc spring is axially compressed between the rotor core structure and the first end ring of the end rings, and a second disc spring 108 of the ring-shaped disc springs is axially located between the rotor core structure and a second end ring 106 of the end rings, and the second disc spring of the ring-shaped disc spring is axially compressed between the rotor core structure and the second end ring of the end rings.

[0024] Also, in a rotor according to an exemplary and non-limiting embodiment, in which the rotor core structure has axially continuous ferromagnetic elements, for example axially stacked sheets or plates, it is possible that one or more ring-shaped disc springs are located between the axially continuous ferromagnetic elements and are not in contact with the end rings. In this exemplary case, the one or more ring-shaped disc springs do not need to be located near the joint between the rotor bars and the end rings, and therefore a relatively small radial force provided by the one or more ring-shaped disc springs is sufficient to radially press the rotor bars away from the geometric rotation axis of the rotor. In a rotor according to an exemplary and non-limiting embodiment, there is only one ring-shaped disc spring in the middle of the rotor core structure. In another exemplary and non-limiting embodiment, there are three or more ring-shaped disc springs in axial succession between the end rings.

[0025] FIG. 2 illustrates an induction machine according to an exemplary and non-limiting embodiment. The induction machine includes a stator 215 and a rotor 201, according to an exemplary and non-limiting embodiment of the present invention. The rotor 201 is supported for rotation relative to the stator 215. In FIG. 2, the structure for supporting the rotor 201 for rotation relative to the stator 215 is not shown. The stator 215 includes a stator winding 216 that generates a rotating magnetic field in response to an alternating current being supplied thereto. The stator winding 216 may be, for example, a three-phase winding. The rotor 201 may be, for example, as shown in FIGS. 1a-1c.

[0026] 3 illustrates a flow chart of a method for assembling a cage winding of an induction machine rotor, according to an exemplary and non-limiting embodiment. The method includes: - operation 301: placing rotor bars in slots of a rotor core structure at the ends of the rotor core structure such that the ends of the rotor bars protrude axially outward from the rotor core structure; - action 302: positioning the end rings such that the ends of the rotor bars extend axially through openings in the end rings; - operation 303: directing an axial pressure on the ends of the rotor bars to fit them into the openings of the end rings due to an expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being caused by the axial pressure and the material of the rotor bars being softer than the material of the end rings; has.

[0027] In one exemplary and non-limiting embodiment method, 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.

[0028] A method according to an exemplary and non-limiting embodiment comprises softening the material of the rotor bars by annealing before placing them in the slots of the rotor core structure, in this exemplary case, depending on the material of the rotor bars, for example copper, the axial pressing and the deformation caused by the axial pressing can reharden the material of the rotor bars.

[0029] According to one exemplary and non-limiting embodiment, the method comprises: - one or more ring-shaped disc springs are located axially between the end rings, - one or more ring-shaped disc springs are located radially between the rotor bars and the geometric axis of rotation of the rotor, and - one or more ring-shaped disc springs are compressed in an axial direction and, as a result of the axial compression, the one or more ring-shaped disc springs expand in pressure contact with the rotor bars so as to press the rotor bars in a radial direction away from the geometric axis of rotation of the rotor; Thus, the method includes a step of arranging one or more ring-shaped disc springs to surround the geometric rotation axis of the rotor, and then arranging end rings.

[0030] In a method according to one exemplary and non-limiting embodiment, a first disc spring of the ring-shaped disc springs is axially disposed between the rotor core structure and a first one of the end rings, the first disc spring of the ring-shaped disc springs is axially compressed between the rotor core structure and the first one of the end rings, a second disc spring of the ring-shaped disc springs is axially disposed between the rotor core structure and a second one of the end rings, and the second disc spring of the ring-shaped disc springs is axially compressed between the rotor core structure and the second one of the end rings.

[0031] In one exemplary and non-limiting embodiment method, the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure.

[0032] In an exemplary and non-limiting embodiment of the method, the outer periphery of the ring-shaped disc spring has radially extending decoupling slots located circumferentially between the radially extending locking slots and radially deeper than the radially extending locking slots, and each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defines a spring arm that radially urges one of the rotor bars away from the geometric axis of rotation of the rotor.

[0033] A method according to an example and non-limiting embodiment includes installing a locking nut over a threaded portion of the rotor such that the locking nut surrounds the rotor's geometric axis of rotation and axially presses the end rings toward the rotor core structure.

[0034] The specific examples provided in the description given above should not be construed as limiting the scope and / or applicability of the appended claims. The lists and groupings of examples provided in the description given above are not exhaustive unless expressly stated to the contrary. The above-described embodiment can also be described as follows, but is not limited to the following. [Configuration 1] A rotor (101, 201) of an induction machine, - A rotor core structure (102); - a plurality of rotor bars (103, 104) in slots of the rotor core structure; - end rings (105, 106) electrically connecting the ends of the rotor bars to each other at both ends of the cage winding, the cage winding being constituted by the rotor bars and the end rings; having 1. A rotor, the ends of which are fitted into the openings of the end rings by expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being caused by an axial pressure directed towards the ends of the rotor bars, and the material of the rotor bars is softer than the material of the end rings, The rotor further comprises one or more ring-shaped disc springs (107, 108) surrounding the geometric axis of rotation of the rotor, the one or more ring-shaped disc springs being located axially between the end rings and radially between the rotor bars and the geometric axis of rotation of the rotor, the one or more ring-shaped disc springs being compressed in the axial direction and radially expanding in pressure contact with the rotor bars such that as a result of the axial compression, the one or more ring-shaped disc springs are configured to radially press the rotor bars away from the geometric axis of rotation of the rotor. [Configuration 2] 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; 2. The rotor according to configuration 1. [Configuration 3] a first disc spring (107) of the ring-shaped disc springs is located axially between the rotor core structure and a first end ring (105) of the end rings, and the first disc spring of the ring-shaped disc springs is compressed axially between the rotor core structure and the first end ring of the end rings; a second disc spring (108) of the ring-shaped disc springs is located axially between the rotor core structure and a second end ring (106) of the end rings, and the second disc spring of the ring-shaped disc springs is compressed axially between the rotor core structure and the second end ring of the end rings. 2. The rotor according to configuration 1. [Configuration 4] the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot (110) that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; 2. The rotor according to configuration 1. [Configuration 5] the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot (110) that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; 4. The rotor according to configuration 3. [Configuration 6] the outer periphery of the ring-shaped disc spring has radially extending decoupling slots (111) circumferentially located between the rotor bars and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm (112) configured to radially urge one of the rotor bars away from the geometric axis of rotation of the rotor; 5. The rotor according to configuration 4. [Configuration 7] the outer periphery of the ring-shaped disc spring has radially extending decoupling slots (111) circumferentially located between the rotor bars and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm (112) configured to radially urge one of the rotor bars away from the geometric axis of rotation of the rotor; 6. The rotor according to configuration 5. [Configuration 8] the rotor has a locking nut (113, 114) surrounding the geometric axis of rotation of the rotor, the locking nut being mounted on a threaded portion of the rotor and configured to press the end rings axially towards the rotor core structure; A rotor as described in any one of configurations 1 to 7. [Configuration 9] The rotor core structure (102) is made of solid steel. A rotor as described in any one of configurations 1 to 7. [Configuration 10] - a stator (215) having a stator winding (216); - A rotor (201) according to any one of configurations 1 to 7, rotatably supported relative to the stator; An induction motor having [Configuration 11] A method for assembling a cage winding of an induction machine rotor, comprising the steps of: - a step (301) of arranging rotor bars in slots of a rotor core structure, the rotor bars being arranged at ends of the rotor core structure such that the ends of the rotor bars protrude outwardly from the rotor core structure in an axial direction; - Positioning the end rings such that the ends of the rotor bars extend axially through openings in the end rings (302); - directing (303) an axial pressure on the ends of the rotor bars to seat the ends of the rotor bars against the openings in the end rings due to an expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being caused by the axial pressure; having the rotor bar material is softer than the end ring material; a method for arranging one or more ring-shaped disc springs around the geometric axis of rotation of the rotor, the one or more ring-shaped disc springs being 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 ring-shaped disc springs being compressed in the axial direction and, as a result of the axial compression, the one or more ring-shaped disc springs radially expand in pressure contact with the rotor bars to radially press the rotor bars away from the geometric axis of rotation of the rotor, and thereafter the end rings are arranged. [Configuration 12] softening the material of the rotor bars by annealing before placing the rotor bars in the slots of the rotor core structure. The method according to configuration 11. [Configuration 13] 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; The method according to configuration 11. [Configuration 14] the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; The method according to configuration 11. [Configuration 15] the outer periphery of the ring-shaped disc spring has radially extending decoupling slots located circumferentially between the radially extending locking slots and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm for radially urging one of the rotor bars away from the geometric axis of rotation of the rotor; The method according to configuration 14. [Configuration 16] 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 presses the end rings against the rotor core structure. 16. The method according to any one of claims 11 to 15.

Claims

1. A rotor (101, 201) of an induction machine, a rotor core structure (102), a number of rotor bars (103, 104) in slots of said rotor core structure; end rings (105, 106) electrically connecting the ends of the rotor bars to each other at either end of the cage winding, the cage winding being constituted by the rotor bars and the end rings; having 1. A rotor, the ends of which are fitted into the openings of the end rings by expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being caused by an axial pressure directed towards the ends of the rotor bars, and the material of the rotor bars is softer than the material of the end rings, the rotor further comprises one or more ring-shaped disc springs (107, 108) surrounding the geometric axis of rotation of the rotor, the one or more ring-shaped disc springs being 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 ring-shaped disc springs being compressed in the axial direction and radially expanding in pressure contact with the rotor bars such that as a result of the axial compression, the one or more ring-shaped disc springs are configured to be in direct contact with the rotor bars and to radially press the rotor bars away from the geometric axis of rotation of the rotor, the rotor bars being arranged in slots of the rotor core structure at each end of the rotor core structure such that the ends of the rotor bars protrude axially outward from the rotor core structure and pass axially through openings of the end rings.

2. 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; The rotor according to claim 1 .

3. a first disc spring (107) of the ring-shaped disc springs is located axially between the rotor core structure and a first end ring (105) of the end rings, and the first disc spring of the ring-shaped disc springs is compressed axially between the rotor core structure and the first end ring of the end rings; a second disc spring (108) of the ring-shaped disc springs is located axially between the rotor core structure and a second end ring (106) of the end rings, and the second disc spring of the ring-shaped disc springs is compressed axially between the rotor core structure and the second end ring of the end rings. The rotor according to claim 1 .

4. the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot (110) that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; The rotor according to claim 1 .

5. the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot (110) that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; The rotor according to claim 3.

6. the outer periphery of the ring-shaped disc spring has radially extending decoupling slots (111) circumferentially located between the rotor bars and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm (112) configured to radially urge one of the rotor bars away from the geometric axis of rotation of the rotor; The rotor according to claim 4.

7. the outer periphery of the ring-shaped disc spring has radially extending decoupling slots (111) circumferentially located between the rotor bars and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm (112) configured to radially urge one of the rotor bars away from the geometric axis of rotation of the rotor; The rotor according to claim 5.

8. the rotor has a locking nut (113, 114) surrounding the geometric axis of rotation of the rotor, the locking nut being located on a threaded portion of the rotor and configured to press the end rings axially towards the rotor core structure; A rotor according to any one of claims 1 to 7.

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

10. a stator (215) with a stator winding (216); - a rotor (201) according to any one of claims 1 to 7, supported for rotation relative to said stator; An induction motor having

11. A method for assembling a cage winding of an induction machine rotor, comprising the steps of: - arranging (301) rotor bars in slots of a rotor core structure, said rotor bars being arranged at the ends of said rotor core structure in such a way that their ends protrude outwardly from said rotor core structure in the axial direction; - positioning the end rings so that the ends of the rotor bars pass axially through openings in the end rings (302); - applying an axial pressure to the ends of the rotor bars (303) in order to attach them to the openings of the end rings by expansion of the ends of the rotor bars in a cross-sectional direction of the rotor bars, the expansion being brought about by an axial pressure; having the rotor bar material is softer than the end ring material; a method for arranging one or more ring-shaped disc springs axially between the end rings and radially between the rotor bars and the geometric axis of rotation of the rotor, the one or more ring-shaped disc springs being arranged to surround the geometric axis of rotation of the rotor, and thereafter the end rings being arranged such that the one or more ring-shaped disc springs are compressed axially and, as a result of the axial compression, the one or more ring-shaped disc springs radially expand while pressing against the rotor bars to radially press the rotor bars away from the geometric axis of rotation of the rotor.

12. softening the material of the rotor bars by annealing before placing the rotor bars in the slots of the rotor core structure. The method of claim 11.

13. 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; The method of claim 11.

14. the outer periphery of the ring-shaped disc spring is slotted such that the outer periphery of the ring-shaped disc spring has a radially extending locking slot that fits with the bottom of the rotor bar to prevent the ring-shaped disc spring from rotating relative to the rotor core structure; The method of claim 11.

15. the outer periphery of the ring-shaped disc spring has radially extending decoupling slots located circumferentially between the radially extending locking slots and radially deeper than the radially extending locking slots, each portion of the ring-shaped disc spring between adjacent ones of the radially extending decoupling slots defining a spring arm for radially urging one of the rotor bars away from the geometric axis of rotation of the rotor; The method of claim 14.

16. 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 presses the end rings against the rotor core structure.

16. The method according to any one of claims 11 to 15.

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