ROTORAN ORDER

Abstract

Rotor arrangement (20) for an electrical device, the rotor arrangement comprising: a plurality of electrical steel sheets (22), each defining a plurality of grooves (24) arranged at an angle around a central axis (26) and equidistant to it, wherein the plurality of electrical steel sheets (22) are arranged adjacent to each other to define a stacked pile (28) with a first end face (30) and a second end face (32) spaced apart from the first end face (30) along the central axis (26), wherein the plurality of grooves (24) are aligned to define a plurality of longitudinal grooves (34) in the stacked pile (28); a plurality of conductor bars (36), wherein one of the plurality of conductor bars (36) is arranged in each of the plurality of longitudinal grooves (34), each of the plurality of conductor bars (36) comprising a first end (38) extending axially along the central axis (26) beyond the first end face (30) of the layered stack (28); and a first end ring (52) which is arranged at and adjacent to the first end surface (30) and at least partially surrounds and electrically connects the first end (38) of each of the plurality of conductor bars (36); wherein the first end (38) of each of the plurality of conductor bars (36) contains a structured surface (46) with microscopic surface irregularities (48) which mechanically lock with the first end ring (52); wherein the microscopic surface irregularities (48) of the structured surface (46) contain a minimum radius R which is defined by the equation: R = 2 γ P where γ is the surface tension of a liquid material used to cast the first end ring (52) and / or the second end ring (54), and P is the pressure applied to the liquid material during solidification.

Description

TECHNICAL AREA

[0001] The invention relates generally to a rotor arrangement for an electrical device. BACKGROUND

[0002] Rotor assemblies for an electrical device comprising, but not limited to, an electric induction motor typically include a stacked pile of electrical steel sheets supporting a plurality of conductor bars arranged in longitudinal grooves defined by the stacked electrical steel sheets. The conductor bars extend outward beyond axial end faces of the stacked electrical steel sheets. The rotor assembly includes a first end ring and a second end ring arranged at opposite axial end faces of the stacked electrical steel sheets. The first end ring and the second end ring electrically connect the ends of the conductor bars at their respective axial end faces of the stacked electrical steel sheets. The end rings and the conductor bars may be encapsulated simultaneously.Alternatively, the first end ring and the second end ring made of aluminium can be cast over the ends of preformed conductor rods that are positioned in the longitudinal grooves of the layered stack.

[0003] US Patent 6,088,906 A discloses a method for manufacturing squirrel-cage rotors in which conductor bars are inserted into slots of a rotor core, with the ends of the conductor bars extending from opposite end faces of the rotor core. The ends of the conductor bars are connected to end rings, the end rings being pressurized to improve contact and reduce areas of poor or uneven contact between the ends of the conductor bars and the end rings.

[0004] In US patent application 2005 / 0040726A1, a rotor for an induction motor is disclosed in which end rings are manufactured from an aluminum alloy plate and conductor bars are cast into holes with external slots in a rotor core, such that the ends of the conductor bars engage in support holes in the end rings. The support holes in the end rings have engagement projections around the perimeter of the inner surfaces of the support holes with which the ends of the conductor bars engage.

[0005] US Patent 3,842,303 A discloses a stiffening device for winding end sections of stator coil conductors, in which two wedge-shaped elements interact to stiffen the respective winding end sections. The wedge-shaped elements each have serrations on their inclined surfaces, which serve to lock the wedge-shaped elements against each other and thus stiffen the winding end sections.

[0006] In US patent 2,784,333 A, a method for casting end rings of a squirrel cage rotor around the ends of previously cast conductor bars is disclosed, wherein the ends of the conductor bars have locking grooves and serrations to achieve both a good mechanical connection and a good electrical connection between the conductor bars and the end rings.

[0007] US Patent 5,389,847 A discloses a squirrel-cage rotor for an induction motor with an iron core having through-holes on its outer circumference into which conductor bars are pressed, protruding from the iron core at opposite ends. The protruding ends of the conductor bars are received in end rings and have axial bores into which snap pins are pressed to fasten the end rings to the iron core.

[0008] The object of the invention is to improve a mechanical and electrical connection between end rings and conductor bars of a rotor for an induction motor.

[0009] This problem is solved by the rotor arrangement according to claim 1. SUMMARY

[0010] A rotor assembly for an electrical device is provided. The rotor assembly contains a plurality of electrical steel sheets. Each of the plurality of electrical steel sheets defines a plurality of slots. The plurality of slots are arranged at an angle around a central axis and equidistant from it. The plurality of electrical steel sheets are arranged adjacent to one another to define a stacked pile with a first end face and a second end face. The second end face is spaced apart from the first end face along the central axis. The plurality of slots are aligned to define a plurality of longitudinal grooves in the stacked pile. The rotor assembly further contains a plurality of conductor bars. One of the plurality of conductor bars is arranged in each of the plurality of longitudinal grooves.Each of the multiple conductor bars contains a first end that extends axially along the central axis beyond the first end face of the stacked array. A first end ring is located at and adjacent to the first end face. The first end ring at least partially surrounds the first end of each of the multiple conductor bars and electrically connects them. The first end of each of the multiple conductor bars features a structured surface with microscopic surface irregularities that mechanically interlock with the first end ring.

[0011] A rotor assembly for an electrical device is also provided. The rotor assembly comprises a plurality of electrical steel sheets. Each of the plurality of electrical steel sheets defines a plurality of grooves arranged at an angle around a central axis and equidistant from it. The plurality of electrical steel sheets are arranged adjacent to one another to define a stacked pile with a first end face and a second end face. The second end face is spaced apart from the first end face along the central axis. The plurality of grooves is oriented to define a plurality of longitudinal grooves in the stacked pile, extending along the central axis. The rotor assembly further comprises a plurality of conductor bars. One of the plurality of conductor bars is arranged in each of the plurality of longitudinal grooves. Each of the plurality of conductor bars has a first end and a second end.The first end of each of the plurality of conductor bars extends axially along the central axis beyond the first end face of the stacked pile. The second end of each of the plurality of conductor bars extends axially along the central axis beyond the second end face of the stacked pile. A first end ring is located at and adjacent to the first end face, and it at least partially surrounds and electrically connects the first end of each of the plurality of conductor bars. A second end ring is located at and adjacent to the second end face, and it at least partially surrounds and electrically connects the second end of each of the plurality of conductor bars. The first and second ends of each of the plurality of conductor bars contain a structured surface with microscopic surface irregularities. The microscopic surface irregularities of the structured surface interlock with the first end ring and the second end ring, respectively.the second end ring mechanically. The first and second end rings are cast over the first and second ends, respectively, of the plurality of conductor bars, and the conductor bars are pre-formed before the casting of the first and second end rings. The microscopic surface irregularities of the structured surface include a roughness, measured parallel to a longitudinal axis of the conductor bars, which is less than 1 µm, and an amplitude, measured perpendicular to the longitudinal axis of the conductor bars, which is less than 50 µm.

[0012] A method for manufacturing a rotor assembly for an electrical device is also provided. The method comprises forming a plurality of conductor bars to define a structured surface with microscopic surface irregularities at a first end of each plurality of conductor bars. The method further comprises stacking a plurality of electrical steel sheets to define a stacked pile with a first end face and a second end face spaced apart from the first end face along a central axis, and a plurality of longitudinal grooves extending along the central axis between the first end face and the second end face. The plurality of grooves are arranged at an angle around the central axis and equidistant from it.The method further comprises positioning one of the plurality of conductor bars in each of the plurality of longitudinal grooves such that the first end of each of the plurality of conductor bars extends outwards beyond the first end face of the layered stack. The method further comprises casting a first end ring around the microscopic surface irregularities of the structured surface of the first end of each of the plurality of conductor bars such that it at least partially surrounds the first end of each of the plurality of conductor bars and electrically connects them.

[0013] Accordingly, the microscopic surface irregularities of the structured surface at the first end and second end of each of the conductor bars mechanically lock with the encapsulated first end ring and the encapsulated second end ring, respectively, to provide a stronger mechanical connection between them and to improve the electrical connection between each of the conductor bars and the first end ring and the second end ring.

[0014] The foregoing features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the best ways of carrying out the invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic perspective exploded view of a rotor assembly. Fig. Figure 2 is a schematic top view of an electrical steel sheet of the rotor assembly. Fig. Figure 3 is a schematic top view of a layered stack of electrical steel sheets. Fig. Figure 4 is an enlarged schematic perspective view of one end of a ladder rod. Fig. Figure 5 is an enlarged schematic partial view from above of the engine arrangement. DETAILED DESCRIPTION

[0015] With reference to the figures, in which the same reference numerals denote the same parts in the different views, a rotor arrangement is generally shown at 20. The rotor arrangement 20 is for an electrical device that includes, but is not limited to, an electric induction motor. The rotor arrangement 20 can generally be described as a squirrel-cage rotor arrangement 20.

[0016] The rotor arrangement 20 contains a plurality of electrical steel sheets 22. With reference to Fig. 2 defines a plurality of grooves 24 for each of the electrical steel sheets 22. The grooves 24 are arranged near an outer circumference of the electrical steel sheets 22 at an angle around a central axis 26 and equidistant from it. With reference to Fig. 1 and Fig. In the 3, the electrical steel sheets 22 are arranged adjacent to each other and concentrically around the central axis 26 to define a stacked pile 28. The stacked pile 28 includes a first end face 30 and a second end face 32. The second end face 32 is spaced apart from the first end face 30 along the central axis 26. The first end face 30 and the second end face 32 define opposing axial end faces of the stacked pile 28 of electrical steel sheets 22. The grooves 24 are oriented such that they define a plurality of longitudinal grooves 34 in the stacked pile 28. The longitudinal grooves 34 extend between and connect the first end face 30 and the second end face 32. As is known, the longitudinal grooves 34 can be slightly chamfered along a length of the stacked pile 28 of electrical steel sheets 22.The electrical steel sheets 22 may contain and be made of low carbon and high silicon iron to reduce eddy current loss, and they may be coated with an insulating mixture to reduce circulating current which may lead to further eddy current loss.

[0017] The rotor assembly 20 further comprises a plurality of conductor bars 36. One of the conductor bars 36 is arranged in each of the plurality of longitudinal grooves 34. The conductor bars 36 may contain and be made of, but are not limited to, pure aluminum, an aluminum forging alloy, an aluminum composite, copper, a copper alloy, or another conductive material. Each of the plurality of conductor bars 36 comprises a first end 38 and a second end 40. The first end 38 extends axially along the central axis 26 beyond the first end face 30 of the stacked pile 28. The second end 40 extends axially along the central axis 26 beyond the second end face 32 of the stacked pile 28. Accordingly, the conductor bars 36 comprise a conductor length 42 along the central axis 26 that is greater than a stack length 44 of the stacked pile 28 of electrical steel sheets 22 along the central axis 26.

[0018] Each of the conductor bars 36 can have a uniform cross-sectional shape perpendicular to the central axis 26 between the first end face 30 and the second end face 32 of the stacked pile 28. As shown, the uniform cross-sectional shape of the conductor bars 36 between the first end face 30 and the second end face 32 is rectangular. However, it should be noted that the uniform cross-sectional shape can have a different shape, which is neither shown nor described here.

[0019] With reference to Fig. The first end 38 and the second end 40 of each of the conductor bars 36 contain a structured surface 46 with microscopic surface irregularities 48. The term microscopic, as used here, encompasses feature dimensions in the range of 0.001 µm to 100 µm and that are smaller than a normal focus scale, i.e., features that are only visible when magnified. The microscopic surface irregularities 48 in the structured surface 46 may include any suitable surface irregularity and / or deformation capable of mechanically locking with a cast end ring, including, but not limited to, grooves 34, trenches, bumps, ridges, waves, etc.

[0020] The microscopic surface irregularities 48 of the structured surface 46 comprise a roughness measured parallel to a longitudinal axis 50 of the conductor bars 36. The roughness is preferably less than 1 µm. Even more preferably, the roughness of the microscopic surface irregularities 48 of the structured surface 46 is less than 0.5 µm.

[0021] Furthermore, the microscopic surface irregularities 48 of the structured surface 46 have an amplitude that is measured perpendicular to the longitudinal axis 50 of the conductor bars 36. The amplitude is preferably less than 50 µm. Particularly preferably, the amplitude of the microscopic surface irregularities 48 of the structured surface 46 is less than 5 µm. However, it should be noted that the roughness and the amplitude of the microscopic surface irregularities 48 can be greater than the values ​​described above.

[0022] With reference to Fig. 1 and Fig. 5 The second end ring 54 is arranged at and adjacent to the first end face 30 of the stacked pile 28 of electrical steel sheets 22. The second end ring 54 at least partially surrounds the first end 38 of each of the conductor bars 36 and connects them electrically. In a similar way, the first end ring 52 (only in Fig. (1 shown) is arranged on and borders the second end face 32 of the stacked pile 28 of electrical steel sheets 22. The first end ring 52 at least partially surrounds the second end 40 of each of the conductor bars 36 and connects them electrically.

[0023] The first end ring 52 and the second end ring 54 are each cast over the first ends 38 of the conductor bars 36 and the second ends 40 of the conductor bars 36, respectively. Preferably, the first end ring 52 and the second end ring 54 are cast from pure aluminum or a cast aluminum alloy. However, it should be noted that the first end ring 52 and the second end ring 54 can be cast from another conductive material. The first end ring 52 and the second end ring 54 can be cast using any suitable casting process known to those skilled in the art, including, but not limited to, a compression molding process, a high-pressure injection molding process, a low-pressure injection molding process, or a sand casting process.

[0024] The microscopic surface irregularities 48 of the structured surface 46 at the first end 38 of each of the conductor rods 36 mechanically lock with the encapsulated first end ring 52. Similarly, the microscopic surface irregularities 48 of the structured surface 46 at the second end 40 of each of the conductor rods 36 mechanically lock with the second end ring 54.

[0025] The microscopic surface irregularities 48 of the structured surface 46 are microscopic geometric features that allow the potting compound of the first end ring 52 and the second end ring 54 to flow into and interlock with the microscopic surface irregularities 48 of the structured surface 46, thereby improving the mechanical and electrical bond between the conductor bars 36 and the first end ring 52 or the second end ring 54. The minimum radius of the microscopic surface irregularities 48 of the structured surface 46 can be determined by Equation 1: R=2γP where R is the minimum radius of the microscopic surface irregularities 48, measured in micrometers; γ is the surface tension of the liquid material used to cast the first end ring 52 and / or the second end ring 54, measured in N / m; and P is the pressure applied to the liquid material during solidification, measured in ATM. The minimum radius of the microscopic surface irregularities 48 is the minimum size that will allow the liquid material forming the first end ring 52 and / or the second end ring 54 to flow completely into and fill the microscopic surface irregularities 48 of the structured surface 46, thereby ensuring a proper mechanical interlock between the microscopic surface irregularities 48 of the structured surface 46 and the cast first end ring 52 and / or the cast second end ring 54.

[0026] At a pressure of one atmosphere, such as in the sand casting process with gravity casting, the minimum radius R of the microscopic surface irregularities must be greater than 18 µm. However, at a higher pressure, such as the pressure of 68.95 MPa (10,000 psi) achieved during the high-pressure injection molding process, the minimum radius R of the microscopic surface irregularities must be greater than only 0.027 µm.

[0027] A method for manufacturing the rotor assembly 20 is also disclosed. The method comprises stacking the plurality of electrical steel sheets 22 together to define the stacked pile 28. As described above, the stacked pile 28 includes the first end face 30 and the second end face 32. The second end face 32 is axially spaced from the first end face 30 along the central axis 26. The electrical steel sheets 22 are stacked together such that the grooves 24 in each of the electrical steel sheets 22 cooperate to define the longitudinal grooves 34, which extend along the central axis 26 between the first end face 30 and the second end face 32, the grooves 34 being spaced at an angle around the central axis 26 and equidistant from it.

[0028] The method further comprises shaping the conductor bars 36. The conductor bars 36 are shaped to have a conductor length 42 greater than the stack length 44 of the layered stack 28 of electrical steel sheets 22, such that the first end 38 and the second end 40 of each of the conductor bars 36 extend outwards beyond the first end face 30 and the second end face 32, respectively. The conductor bars 36 are also shaped to define the microscopic surface irregularities 48 in the structured surface 46 at the first end 38 and the second end 40 of each of the conductor bars 36. The microscopic surface irregularities 48 in the structured surface 46 can be shaped in any suitable manner, which includes, but is not limited to, a waterjet cutting process or an electric / mechanical polishing process known to those skilled in the art.The conductor bars 36 and in particular the microscopic surface irregularities 48 in the structured surface 46 are pre-formed before casting the first end ring 52 and / or the second end ring 54 over the first ends 38 and the second ends 40 of the conductor bars 36.

[0029] The method further comprises positioning one of the conductor bars 36 in each of the longitudinal grooves 34. The conductor bars 36 are positioned such that the first end 38 and the second end 40 of each of the plurality of conductor bars 36 extend outwards beyond the first end face 30 and the second end face 32 of the stacked pile 28, respectively.

[0030] The method further comprises placing the layered stack 28, with the plurality of conductor bars 36 positioned therein, in a mold. The mold defines the first end ring 52 and / or the second end ring 54. The mold can be of any suitable shape and / or size for casting the first end ring 52 and / or the second end ring 54 and may depend on the casting process used to cast the first end ring 52 and / or the second end ring 54.

[0031] The process further comprises encasing the microscopic surface irregularities 48 in the structured surface 46 of the first end 38 of each of the plurality of conductor bars 36 in the first end ring 52 µm, and encasing the microscopic surface irregularities 48 in the structured surface 46 of the second end 40 of each of the plurality of conductor bars 36 in the second end ring 54. The first end ring 52 and the second end ring 54 are cast such that they at least partially surround and electrically connect the first end 38 of each of the plurality of conductor bars 36 to the first end ring 52, and that they at least partially surround and electrically connect the second end 40 of each of the plurality of conductor bars 36 to the second end ring 54.

[0032] The casting of the first end ring 52 and / or the second end ring 54 comprises injecting molten material into the mold and around the microscopic surface irregularities 48 in the structured surface 46 at the first end 38 of each of the plurality of conductor bars 36 and / or around the microscopic surface irregularities 48 in the structured surface 46 at the second end 40 of each of the conductor bars 36. The first end ring 52 and the second end ring 54 are preferably cast from aluminum or an aluminum alloy. However, another conductive material may be used.The casting of the first end ring 52 and / or the second end ring 54 may further include allowing the molten material to flow into and around the microscopic surface irregularities 48 in the structured surface 46 in order to mechanically lock it to the microscopic surface irregularity of the structured surface 46 during solidification.

[0033] The casting of the first end ring 52 and / or the second end ring 54 may further include compressing the molten material as it solidifies. Compressing the molten material as it solidifies during the casting process reduces the porosity in the finished casting and also improves the mechanical properties of the finished product.

[0034] The method can further include vibrating each of the conductor bars 36 at an ultrasonic frequency for a predefined period of time during the solidification of the molten material of the cast first end ring 52 and / or second end ring 54. Preferably, the ultrasonic frequency is approximately equal to or greater than 20 kHz. The conductor bars 36 can be vibrated for a period of less than 20 seconds and preferably for a period of between 5 and 10 seconds. Vibrating the conductor bars 36 during the solidification of the molten material during the casting process can break up aluminum oxides located on an outer surface of the first ends 38 and the second ends 40 of the conductor bars 36 and improves the wetting between the liquid molten material used in the casting process and the preformed conductor bars 36.

[0035] Although the best ways of carrying out the invention have been described in detail, those skilled in the field relating to this invention will recognize various alternative designs and embodiments for putting the invention into practice within the scope of the attached claims.

Claims

[1] Rotor arrangement (20) for an electrical device, the rotor arrangement comprising: a plurality of electrical steel sheets (22), each defining a plurality of grooves (24) arranged at an angle around a central axis (26) and equidistant to it, wherein the plurality of electrical steel sheets (22) are arranged adjacent to each other to define a stacked pile (28) with a first end face (30) and a second end face (32) spaced apart from the first end face (30) along the central axis (26), wherein the plurality of grooves (24) are aligned to define a plurality of longitudinal grooves (34) in the stacked pile (28); a plurality of conductor bars (36), wherein one of the plurality of conductor bars (36) is arranged in each of the plurality of longitudinal grooves (34), each of the plurality of conductor bars (36) comprising a first end (38) extending axially along the central axis (26) beyond the first end face (30) of the layered stack (28); and a first end ring (52) which is arranged at and adjacent to the first end surface (30) and at least partially surrounds and electrically connects the first end (38) of each of the plurality of conductor bars (36); wherein the first end (38) of each of the plurality of conductor bars (36) contains a structured surface (46) with microscopic surface irregularities (48) which mechanically lock with the first end ring (52); wherein the microscopic surface irregularities (48) of the structured surface (46) contain a minimum radius R which is defined by the equation: R=2γP where γ is the surface tension of a liquid material used to cast the first end ring (52) and / or the second end ring (54), and P is the pressure applied to the liquid material during solidification. [2] Rotor arrangement (20) according to claim 1, wherein each of the plurality of conductor bars (36) comprises a second end (40) extending axially along the central axis (26) beyond the second end surface (32) of the layered stack (28), and further comprising a second end ring (54) arranged at and adjacent to the second end surface (32) and at least partially surrounding and electrically connecting the second end (40) of each of the plurality of conductor bars (36), wherein the second end (40) of each of the plurality of conductor bars (36) comprises a structured surface (46) with microscopic surface irregularities (48) which mechanically lock with the second end ring (54). [3] Rotor arrangement (20) according to claim 2, wherein the first end ring (52) and the second end ring (54) are each encased over the first end (38) and the second end (40) of each of the plurality of conductor bars (36). [4] Rotor arrangement (20) according to claim 3, wherein the first end ring (52) and the second end ring (54) contain and are made of pure aluminum or an aluminum forging alloy of the classification for electrical conductors or an aluminum casting alloy or a combination thereof. [5] Rotor arrangement (20) according to claim 1, wherein the microscopic surface irregularities (48) of the structured surface (46) include a roughness measured parallel to a longitudinal axis (50) of the conductor bars (36) which is less than 1 µm and an amplitude measured perpendicular to the longitudinal axis (50) of the conductor bars (36) which is less than 50 µm. [6] Rotor arrangement (20) according to claim 5, wherein the roughness of the microscopic surface irregularities (48) of the structured surface (46) is less than 0.5 µm. [7] Rotor arrangement (20) according to claim 5, wherein the amplitude of the microscopic surface irregularities (48) of the structured surface (46) is less than 5 µm.

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