INDUCTION MOTOR ROTOR AND A METHOD OF MANUFACTURING THE SAME

Abstract

A method of manufacturing an induction motor rotor assembly, the method includes the steps of: providing a rotor; machining a plurality of re-entrant slots axially along an outer surface of the rotor; positioning a sleeve concentrically over the outer surface of the rotor; applying a friction stir welding process to the sleeve along each re-entrant slot axially along the outer surface of the rotor to cause the sleeve material to plasticise and flow into the axial re-entrant slot to form an axial re-entrant slot bar; and providing an electrical connection at each of the opposing axial ends of the rotor between respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor.

Claims

1. A method of manufacturing an induction motor rotor assembly, the method comprising the steps of: providing a rotor; machining a plurality of re-entrant slots axially along an outer surface of the rotor; positioning a sleeve concentrically over the outer surface of the rotor; applying a friction stir welding process to the sleeve along each re-entrant slot axially along the outer surface of the rotor to cause the sleeve material to plasticise and flow into the axial re-entrant slot to form an axial re-entrant slot bar; and providing an electrical connection at each of the opposing axial ends of the rotor between respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor assembly.

2. The method as claimed in claim 1, wherein the step of providing an electrical connection at each of the opposing axial ends of the rotor between respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor assembly, comprises the step of: attaching an end ring to each of the opposing axial ends of the rotor to connect together respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor assembly.

3. The method as claimed in claim 1, wherein the step of providing an electrical connection at each of the opposing axial ends of the rotor between respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor assembly, comprises the steps of: machining a re-entrant slot circumferentially around the outer surface of the rotor at each axial end of the rotor; and applying a friction stir welding process to the sleeve along each re-entrant slot circumferentially around the outer surface of the rotor to cause the sleeve material to plasticise and flow into the circumferential re-entrant slot to form a circumferential re-entrant slot bar, to connect together respective ones of opposing ends of each of the axial re-entrant slot bars to thereby form the induction motor rotor assembly.

4. The method as claimed in claim 1, further comprising the additional step of: machining an outer surface of the sleeve to produce a machined surface.

5. The method as claimed in claim 1, wherein each of the re-entrant slots has a cross-sectional profile selected from the group comprising dovetails, ellipses, circles, teardrops and other re-entrant geometries.

6. The method as claimed in claim 5, wherein each of the re-entrant slots is a dovetail slot.

7. The method as claimed in claim 6, wherein each side of a base of each dovetail slot is provided with a base radius.

8. The method as claimed in claim 6, wherein an upper corner of each dovetail slot is provided with an upper corner radius.

9. The method as claimed in claim 1, wherein the axial re-entrant slots extend axially along an outer surface of the rotor at a skew angle to the axis of rotation of the rotor.

10. The method as claimed in claim 9, wherein the skew angle is in the range of 0 to 10 relative to the axis of rotation of the rotor.

11. An induction motor rotor assembly comprising: a rotor, having a first end and an opposite second end; a sleeve; and first and second electrical connection portions, the rotor comprising a plurality of axial, re-entrant slots machined axially along an outer surface of the rotor, the sleeve extending circumferentially around the outer surface of the rotor, the sleeve comprising a plurality of axial re-entrant slot bars extending radially inwardly from the sleeve, each re-entrant bar having a first end and an opposite second end, each axial re-entrant slot bar being accommodated in a respective one of the axial re-entrant slots, the first electrical connection portion being attached to the first end of the rotor and connecting together the first ends of each of the axial re-entrant slot bars, the second electrical connection portion being attached to the second end of the rotor and connecting together the second ends of each of the axial re-entrant slot bars.

12. The induction motor rotor assembly as claimed in claim 11, wherein each of the first electrical connection portion and the second electrical connection portion is formed as an end ring attached to each of the first and second ends of the rotor respectively, each respective end ring connecting corresponding first ends and second ends of the axial re-entrant bars.

13. The induction motor rotor assembly as claimed in claim 11, further comprising a re-entrant slot machined circumferentially around the outer surface of the rotor at each of the first end and the second end of the rotor, and additional circumferential re-entrant slot bars being accommodated in each of the circumferential slots, each of the additional circumferential re-entrant slot bars connecting together corresponding first ends and second ends of the axial re-entrant slot bars.

14. The induction motor rotor assembly as claimed in claim 11, wherein each of the re-entrant slots has a cross-sectional profile selected from the group comprising dovetails, ellipses, circles, teardrops and other re-entrant shapes.

15. The induction motor rotor assembly as claimed in claim 11, wherein each of the re-entrant slots is a dovetail slot.

16. The induction motor rotor assembly as claimed in claim 15, wherein each side of a base of each dovetail slot is provided with a base radius.

17. The induction motor rotor assembly as claimed in claim 15, wherein an upper corner of each dovetail slot is provided with an upper corner radius.

18. The induction motor rotor assembly as claimed in claim 11, wherein the axial re-entrant slots extend axially along an outer surface of the rotor at a skew angle to the axis of rotation of the rotor.

19. The induction motor rotor assembly as claimed in claim 18, wherein the skew angle is in the range of 0 to 10 relative to the axis of rotation of the rotor.

20. An induction motor comprising an induction motor rotor assembly as claimed in claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0098] There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

[0099] FIG. 1 shows a schematic perspective view of a squirrel cage induction motor rotor according to the prior art;

[0100] FIG. 2 shows a schematic perspective view of an induction motor rotor assembly according to an embodiment of the disclosure;

[0101] FIG. 3, shows a sectional view of the rotor assembly of FIG. 3;

[0102] FIG. 4 shows a further sectional view of the rotor assembly of FIG. 3;

[0103] FIG. 5 shows a schematic, partial sectional view of the rotor of the induction motor rotor assembly with the re-entrant slots;

[0104] FIG. 6 shows the view of FIG. 5 with the addition of the sleeve;

[0105] FIG. 7 shows the view of FIG. 6 during the friction stir welding process;

[0106] FIG. 8 shows the view of FIG. 7 with the sleeve material having been plasticised into one of the re-entrant slots;

[0107] FIG. 9 shows the view of FIG. 8 with the sleeve material having been plasticised into all of the re-entrant slots;

[0108] FIG. 10 shows the view of FIG. 9 with the excess sleeve material having been machined back to a machined surface;

[0109] FIG. 11 shows a schematic, partial sectional view of the re-entrant slot of the rotor of FIG. 5;

[0110] FIG. 12 shows a schematic, partial sectional view of various alternative re-entrant slot geometries; and

[0111] FIG. 13 shows a schematic plan view of the rotor of FIG. 5 showing the skew angle of the re-entrant slots.

[0112] It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

[0113] Referring to FIGS. 2 to 4, an induction motor rotor assembly according to an embodiment of the disclosure is designated generally by the reference numeral 100.

[0114] The induction motor rotor assembly 100 comprises a rotor 110, a sleeve 130 and first and second electrical connection portions 162,164.

[0115] The rotor 110 has a cylindrical geometry with an outer surface 112 and an axis of rotation 114. The rotor also has a first axial end 116 and a second opposite axial end 118.

[0116] The rotor 110 is made from steel. In other arrangements, the rotor 110 may be formed from an alternative material such as, for example, an aluminium alloy or a titanium alloy.

[0117] The rotor 110 comprises a plurality of re-entrant slots 120 machined axially along the outer surface 112 of the rotor 110. In the present embodiment, the cross-sectional profile 126 of each of the re-entrant slots 120 is a dovetail slot 127. In other arrangements of the disclosure, the cross-sectional profile 126 of these re-entrant slots 120 may be elliptical 128 or circular 129 as shown in FIG. 12.

[0118] Each of the dovetail slots 127 is arranged at a skew angle 122 to the axis of rotation 114 of the rotor 110, as shown in FIG. 13.

[0119] The sleeve 130 extends circumferentially around the outer surface 112 of the rotor 110. The sleeve 130 is formed from copper.

[0120] The material of the sleeve 130 extends into and fills each of the dovetail slots 127. The sleeve material that fills each of the dovetail slots 127 forms a corresponding axial re-entrant slot bar 140. Each of the re-entrant slot bars has a first end 142 and an opposite second end 144.

[0121] The first electrical connection portion 162 is attached to the first end 116 of the rotor 110 and connects together the first ends 142 of each of the axial re-entrant slot bars 140.

[0122] The second electrical connection portion 164 is attached to the second end 118 of the rotor 110 and connects together the second ends 144 of each of the axial re-entrant slot bars 140.

[0123] In the embodiment shown in FIGS. 2 to 4, the first and second electrical connection portions 162,164 are formed as circumferential re-entrant slots 124 machined circumferentially around each of the first and second ends 116,118 of the rotor 110.

[0124] Each of the circumferential re-entrant slots 124 has a cross-sectional profile 126 in the form of a dovetail 127. In other arrangements of the disclosure, the cross-sectional profile 126 of the circumferential re-entrant slots 124 may be elliptical 128 or circular 129, as shown in FIG. 12. The two circumferential re-entrant slots 124 are filled with the sleeve material to form circumferential re-entrant slot bars 150.

[0125] The circumferential re-entrant slot bars 150 provide an electrical connection between respective ones of opposing ends of each of the axial re-entrant slot bars 140.

[0126] FIGS. 5 to 10 illustrate the method of manufacturing the induction motor rotor assembly 100. As shown in FIG. 5, this starts with the machining of re-entrant slots 120, in the form of dovetail slots 127, in the rotor 110. In other arrangements of the disclosure, the cross-sectional profile 126 of these re-entrant slots 120 may be elliptical 128 or circular 129, as shown in FIG. 12.

[0127] The dovetail slots 127 may be prepared for bonding to copper by grit blasting to increase the surface roughness, followed by de-greasing in a solvent bath.

[0128] A copper sleeve 130 plate is then laid over the steel rotor 110 (see FIG. 6). In the present arrangement, the sleeve 130 is arranged to be an interference fit over the outer surface 112 of the rotor 110.

[0129] As illustrated in FIG. 7, a friction stir welding tool 180 is then rotated 182 and forced downwards 184 into the copper sleeve 130, while traversing along the axial length of the rotor 110 from the first end 116 to the second end 118. The rotation 182 and downwards pressure 184 of the tool 180 creates significant frictional heating (approximately 350 C. to 500 C.), which causes plastic flow 136 of the copper sleeve material into the dovetail slot 127.

[0130] When the friction stir welding tool 180 has passed along the length of the rotor 110, as shown in FIG. 8, the dovetail slot 127 is filled completely with the copper sleeve material. The friction stir welding process results in a good mechanical bond both between the copper sleeve material and the interior surface of the dovetail slot 127, and between the copper sleeve material and the surface of the steel adjacent to the dovetail slot 127.

[0131] The friction stir welding process is carried out along each dovetail slot 127 in turn until each dovetail slot 127 is filled with the copper sleeve material, and the radially inwardly facing surface of the sleeve 130 is bonded to the outer surface 112 of the rotor 110. This is shown in FIG. 9.

[0132] At this point, the outer surface 132 of the copper sleeve 130 has a series of depressions 133 extending axially along the rotor 110. These depressions correspond to the path taken by the friction stir welding tool 180 axially along the rotor 110. The volume of each depression 133 corresponds to the volume of material displaced downwards into corresponding dovetail slots 127 during the friction stir welding process.

[0133] The outer surface 132 of the copper sleeve 130 can now be removed by machining to a depth defined by the electromagnetic requirements of the induction motor and corresponding to the machined surface 134.

[0134] FIG. 10 illustrates the final arrangement of the sleeve 130 over the rotor 110.

[0135] The arrangement of dovetail slots 127 in the rotor 110 is such that the copper sleeve material approximates to the conventional squirrel cage but with the advantage that it is firmly attached to the steel rotor 110 by both the re-entrant dovetail slots 127 and the bond formed by the friction stir welding process.

[0136] Optionally, as shown in FIG. 11, each of the dovetail slots 127 could be rounded at the base 152 with each side of the base having a base radius 153. This base radius 153 reduces any stress concentrations in the lower region of the dovetail slots 127.

[0137] Similarly, the upper corners 154 may be rounded to radius 155 to improve the flow of the copper sleeve material into the dovetail slots 127.

[0138] Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

[0139] The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the disclosure as defined by the accompanying claims.