METHOD FOR PRODUCING A SQUIRREL-CAGE ROTOR OF AN ASYNCHRONOUS MACHINE

Abstract

In a method for producing a squirrel-cage rotor of an asynchronous machine, conductor bars of a first conductive material are inserted into slots of a magnetically conductive body such as to project out of at least one end side to form a projection. A short-circuiting disc of a second conductive material is positioned under pressure on the projection with a clearance fit of approximately 0.1 mm relative to a radially outwardly open recess of the short-circuiting disc. The short-circuiting disc is heated while the conductor bars virtually contact the short-circuiting disc. At least the projection of the conductor bars is coated with a third material at a layer thickness to form an alloy with the first and second materials after heating so that the third material is fully dispersed in the first and second materials as a result of the third material being diffused into the first and second materials.

Claims

1.-20. (canceled)

21. A method for producing a squirrel-cage rotor of an asynchronous machine, said method comprising: inserting conductor bars of a first conductive material into substantially axially running slots of a substantially cylindrically shaped magnetically conductive body, in particular a laminated rotor core, such that the conductor bars project out of at least one end side of the magnetically conductive body to form a projection; axially positioning a short-circuiting disc of a second conductive material under pressure on the projection of the conductor bars such that the projection has a clearance fit, in particular a peripheral clearance fit, of approximately 0.1 mm relative to a radially outwardly open recess of the short-circuiting disc; heating, in particular hot-forming, the short-circuiting disc while the conductor bars virtually contact the short-circuiting disc; and coating at least the projection of the conductor bars with a third material at a layer thickness to form an alloy with the first and second materials after heating so that the third material is fully dispersed in the first and second materials as a result of the third material being diffused into the first and second materials.

22. The method of claim 21, wherein the conductor bars project out of both end sides of the magnetically conductive body to form projections, respectively.

23. The method of claim 21, wherein the conductor bars are coated with the third material.

24. The method of claim 21, wherein the projection of the conductor bars is coated only in a portion which is ultimately located in the short-circuiting disc.

25. The method of claim 21, wherein the layer thickness of the third material on the projection of the conductor bars is between 2 μm and 5 μm.

26. The method of claim 21, further comprising pickling the conductor bars before being coated with the third material.

27. The method of claim 26, wherein the conductor bars are coated immediately after the conductor bars undergo pickling.

28. The method of claim 21, wherein the third material has a melting point which is lower than a melting point of the first material and the second material.

29. The method of claim 21, wherein the first material has a melting point which is higher than a melting point of the second material.

30. The method of claim 21, wherein the short-circuiting disc is heated by induction heating.

31. The method of claim 30, wherein the induction heating is realized by an inductor such as to generate a temperature gradient which decreases axially outwards on the short-circuiting disc.

32. The method of claim 31, wherein the temperature gradient is generated by varying a distance of the inductor from the short-circuiting disc and/or by varying a number of windings of the inductor.

33. The method of claim 21, wherein the short-circuiting disc is constructed in a segmented manner circumferentially and/or axially.

34. The method of claim 21, wherein the conductor bars in a formed state occupy 30% to 70% of a total axial height of the recess of the short-circuiting disc.

35. The method of claim 21, wherein the conductor bars have an additional contour, at least in the projection, in order to establish an additional positive fit with the short-circuiting disc when undergoing hot-forming.

36. The method of claim 21, wherein the first material is copper or a copper alloy, the second material is aluminum or an aluminum alloy, and the third material comprises tin.

37. The method of claim 21, wherein the conductor bars have chamfered ends or are configured to have a cone.

38. The method of claim 21, wherein at least one of the conductor bars is made of drawn electrocopper with a conductance of at least 58 MS/m.

39. The method of claim 21, wherein the short-circuiting disc is heated such as to increase a proof stress.

40. The method of claim 21, further comprising cutting a disc from an extruded part to produce the short-circuiting disc.

41. An asynchronous machine, comprising a squirrel-cage rotor produced by a method as set forth in claim 21, said squirrel-cage rotor comprising: a substantially cylindrically shaped magnetically conductive body including substantially axially running slots; conductor bars inserted in the axial slots such that the conductor bars project out of at least one end side of the magnetically conductive body to form a projection; a short-circuiting disc made of a second conductive material and axially positioned under pressure on the projection of the conductor bars such that the projection has a clearance fit of approximately 0.1 mm relative to a radially outwardly open recess of the short-circuiting disc, said projection axially occupying only a specifiable fraction of an axial height of the recess of the short-circuiting disc; and a coating made of a third material and applied on at least the projection of the conductor bars at a layer thickness to form an alloy with the first and second materials.

42. A drive system, in particular a compressor, conveyor system, machine tool or vehicle, comprising an asynchronous machine as set forth in claim 41.

Description

[0088] The invention and advantageous embodiments thereof are explained in greater detail below with reference to schematically illustrated exemplary embodiments in which:

[0089] FIG. 1 shows a schematic longitudinal section of an asynchronous machine,

[0090] FIG. 2 shows an arrangement of conductor bars,

[0091] FIG. 3 shows a laminated core of a rotor,

[0092] FIG. 4 shows a short-circuiting disc,

[0093] FIG. 5 shows a segmented short-circuiting disc,

[0094] FIG. 6 shows a partial section of the rotor,

[0095] FIG. 7 shows an illustration of the heating principle,

[0096] FIG. 8 shows a schematic illustration of the axial joining,

[0097] FIG. 9 shows an illustration of the layers of the conductive materials,

[0098] FIG. 10 shows a perspective illustration of the rotor,

[0099] FIG. 11 shows a detail illustration of the finished rotor,

[0100] FIG. 12 shows a perspective illustration of the rotor and shaft,

[0101] FIG. 13 shows a detail view of the contacting of conductor bar and short-circuiting disc,

[0102] FIG. 14 shows a squirrel-cage rotor with long conductor bars,

[0103] FIG. 15 shows a squirrel-cage rotor with short-circuiting disc arranged at a distance.

[0104] FIG. 1 shows a schematic longitudinal section of an asynchronous machine 1 with a stator 2 forming at its end sides a winding system 3 which has winding overhangs of a winding system 3 there. The winding system 3 in this case can be composed of e.g. chorded coils, former-wound coils or tooth-wound coils having differing or identical coil widths.

[0105] A rotor 4 is so arranged as to be separated from the stator 2 by an air gap 18 of said asynchronous machine 1. This squirrel-cage rotor 4 has a magnetically conductive body which is made of sinter material or as a laminated core 5. In the region of its end sides 20 is located at least one short-circuiting ring in each case, in particular a short-circuiting disc 7. The short-circuiting ring, in particular the short-circuiting disc 7, connects and contacts conductor bars 6 which are arranged in slots 8 (not shown) of the laminated core 5.

[0106] The short-circuiting ring, in particular the short-circuiting disc 7, is in contact with a shaft 16 in this case as shown in FIG. 1, thereby effecting a thermal interface and hence a cooling of the short-circuiting ring during operation of the asynchronous machine 1. The rotor core is also in contact with the shaft 16 in a rotationally conjoint manner, thereby effecting a thermal interface and hence a cooling likewise.

[0107] According to FIG. 1, the short-circuiting ring, in particular the short-circuiting ring disc 7, is in contact with i.e. fits closely against both the end side 20 of the laminated core 5 and the shaft 16.

[0108] The short-circuiting disc 7 of the squirrel-cage rotor 4 can be arranged at a distance from the shaft 16 and/or the end side 20.

[0109] The short-circuiting ring, in particular a short-circuiting ring disc 7, can therefore be arranged at a distance from the end side 20 of the laminated core 5 and/or from the shaft 16 in order to improve cooling or prevent leakage losses in the laminated core, for example.

[0110] As a result of electromagnetic interaction between the stator 2, this being exposed to an electrical current, and a short-circuiting cage of the rotor 4, this comprising the conductor bars 6 and the short-circuiting discs 7, a rotation of the shaft 16 occurs.

[0111] During operation of the asynchronous machine 1, the rotor 4 therefore rotates with the rotationally conjoint shaft 16 about an axis of rotation 17.

[0112] FIG. 2 shows an arrangement of conductor bars 6 without the magnetically conductive body, i.e. the laminated core 5. The conductor bars 6 are preferably made of drawn copper or a copper alloy and have a drop-shaped cross section. This arrangement also implicitly indicates that the slots 8 are canted along the axial length of the laminated core 5. The cross sectional shape of the conductor bars 6 corresponds substantially to the cross section of the slots 8 in this case. The conductor bars 6 also have a cone 28 which aids axial insertion.

[0113] FIG. 3 shows a magnetically conductive body which is embodied as a laminated core 5 of electrical sheet and, in the region of its shaft hole 10, has elements 21 for connecting to the shaft 16 in a rotationally conjoint manner. The slots 8 are arranged in the radially outer region of the laminated core 5 and designed to be peripherally closed. However, they can also be half-open or open in design.

[0114] FIG. 4 shows a short-circuiting disc 7 which has recesses 9 which are open radially to the outside and correspond to the spacing of the slots 8 of the laminated core 5 in such a way that the conductor bars 6 arranged in the slots 8 can be inserted into said recesses 9. Projections 23 of the conductor bars 6, at least in the region of the recesses 9, preferably form a clearance fit of approximately 0.1 mm to 0.05 mm or even less.

[0115] In a further embodiment, FIG. 5 shows segments of short-circuiting discs 7 as can be used e.g. for machines having larger shaft heights. Two or more segments as per FIG. 5 form a short-circuiting disc 7, the two segments being mechanically connected at the joining points by a type of dovetail.

[0116] In the case of said segmented structure of the short-circuiting discs 7, these are advantageously formed using multiple layers in an axial direction also, such that the joining points 24 are offset in a similar manner to masonry, which ultimately also establishes the electrical connectivity in the short-circuiting ring as a result of axial pressing operations.

[0117] FIG. 6 shows the arrangement in the region of the end side 20 during the hot-forming, in particular inductive heating, when the conductor bars 6 are positioned in the laminated core 5 and have been inserted into the short-circuiting discs 7 as a clearance fit with their preferably already coated projections 23.

[0118] The heating therefore takes place, preferably by means of a temperature gradient 11 in the heating operation, before the hot-forming or at least for a time during the hot-forming.

[0119] A temperature drop occurs starting from that end side 20 of the short-circuiting disc 7 which is oriented towards the laminated core 5 and continuing axially outwards.

[0120] In this way, the temperature remains higher in the region of that side of the short-circuiting disc 7 which is oriented towards the laminated core 5, such that the first deformation occurs in the form of an upsetting deformation at the locating face to the coated projection 23 of the conductor bars 6. The further upsetting generates frictional heat which continues axially outwards. It is thereby possible to avoid thermal overload of the material and to effect the deformation in a linear manner axially outwards from the inside.

[0121] FIG. 7 shows an exemplary induction arrangement 12 which surrounds the short-circuiting disc 7 in which the coated projections 23 of the conductor bars 6 are arranged and are subjected to the heating process.

[0122] By way of example, FIG. 8 shows the joining process when the conductor bars 6 are situated in the laminated core 5. The projections 23 are provided with a coating 15 which is in the range of 2-5 μm. In this case, an insertion depth 26 of the projections 23 into the short-circuiting disc 7 is present which is less than the height 25 of the short-circuiting disc 7. 30% to 100% according to the required contact surface.

[0123] The axial joining is preferably performed simultaneously, to a specifiable insertion depth 26, for all conductor bars 6 projecting from an end side 20 of the laminated core 5.

[0124] In order to simplify the joining process, the conductor bars 6 are conically shaped or tapered at the conductor bar ends projecting from the laminated core 5 in order to aid the joining process.

[0125] FIG. 9 shows a schematic illustration of the coating 15 on the first material 13 at the projection 23 in particular and, separated therefrom by a clearance fit 31, the second material 14. During the heating operation 11, the coating 15 is melted or melted on and ultimately disperses completely or almost completely due to the hot-forming process and the resulting diffusion and/or reflow process and associated alloying.

[0126] FIG. 10 shows a perspective illustration of the rotor core 4 with the conductor bars 6 showing the insertion depth 26 in the short-circuiting disc 7.

[0127] FIG. 11 shows a detail illustration from FIG. 10, in which the recesses 9 of the short-circuiting disc 7 are visibly open radially to the outside.

[0128] FIG. 12 shows the squirrel-cage rotor 4 connected to the shaft 16 in a rotationally conjoint manner.

[0129] However, the shaft 16 can also be connected to the laminated core 5 in a rotationally conjoint manner before the joining operation of conductor bars 6 to the short-circuiting discs 7.

[0130] By virtue of the reduced insertion depth 26 relative to the height 25, ventilator-like effects are produced during operation of the machine.

[0131] Likewise, ventilator-like blades can also be developed by extending the conductor bars 6 axially through the short-circuiting disc 7. The projection 23 then extends axially beyond the height 25 of the short-circuiting disc 7.

[0132] It is also possible for a plurality of reciprocally isolated short-circuiting rings or short-circuiting discs 7 to be arranged on each end side 20 of the laminated core 5. Short-circuiting cages which are electrically isolated from each other in the rotor 4 reduce the harmonic waves in the air gap 18 of the asynchronous machine 1, particularly if the stator 2 has a winding system 3 with tooth-wound coils, wherein each tooth of the stator 2 is surrounded by a tooth-wound coil.

[0133] FIG. 13 shows a detail illustration of the contact areas 27 between conductor bar 6 and short-circuiting disc 7. In this case, the alloying preferably occurs only at the contact areas 27 which have the clearance fit 31 at the beginning of the production process. The process of the hot-forming can be implemented particularly effectively there. The further openings between conductor bar 6 and short-circuiting disc 7 can inter alia assist the cooling.

[0134] The contact area 27 of a conductor bar 6 in a recess 9 is derived from e.g. the peripheral length of the clearance fit 31 in the recess 9 multiplied by the insertion depth 26 of the conductor bar 6 in the short-circuiting disc 7.

[0135] FIG. 14 shows a squirrel-cage rotor 4 whose conductor bars 6 project axially beyond the short-circuiting disc 7 and thus form ventilator blades. Furthermore, the short-circuiting disc 7 is not in direct contact with the shaft 16 (as in FIG. 1), but abuts the end side 20 of the laminated core 5.

[0136] FIG. 15 shows a squirrel-cage rotor 4 whose short-circuiting disc 7 or short-circuiting ring is arranged at a distance from the end side 20 of the laminated core 5. This allows cooling via axial cooling channels 29 in the laminated core 5.

[0137] A method according to the invention for producing a squirrel-cage rotor 4 or an asynchronous rotor comprising a cage rotor of an asynchronous machine 1 is therefore effected, in consideration of the relationships described above, by means of the following steps: [0138] A substantially cylindrically shaped magnetically conductive body is provided, in particular a laminated rotor core 5, which has substantially axially running slots 14. The laminated core is constructed from axially layered electrical sheets. The slots 14 are closed, half-open or open in the peripheral direction. [0139] The conductor bars 6 are then inserted, preferably axially, into the slots 14. The conductor bars 6 are composed of a first conductive material 13, in particular drawn copper. The conductor bars 6 are inserted in such a way that they project out of the end sides 20 of the magnetically conductive body, in particular the laminated rotor core 5, and thereby form at least one projection 23 on one side, in particular a projection on both sides in each case. The complete conductor bars 6 but at least those sections of the projections 23 which are subsequently contacted with the short-circuiting discs 7 are coated before insertion, preferably with tin. The coating is between 2 μm and 5 μm in this case. The cross section of the conductor bars 6 corresponds substantially to the cross section of the slots 14. Therefore no significant friction occurs between conductor bar 6 and inner side of the slot 14 during the insertion. [0140] The short-circuiting disc 7 composed of a second conductive material 14, in particular aluminum, with recesses which are open radially to the outside 9, is also provided. The recesses 9 can also be closed, half-open or open. Said short-circuiting disc 7 can be constructed from multiple parts axially and/or circumferentially. It can therefore be either segmented circumferentially and/or layered axially. The parts are connected together beforehand in this case. The short-circuiting disc 7 is however preferably composed of a single part which has been cut from an extruded profile 19 and consequently has the required height 25. [0141] The short-circuiting disc 7 is then positioned axially on the projection or projections of the respective conductor bars 6, with a maximum clearance fit of 0.1 mm, which project out of the end side 20 of the magnetically conductive body, in particular the laminated rotor core 5. This takes place by means of cold joining, wherein no significant friction or indeed deformation of conductor bar 6 or recess 9 of the short-circuiting disc 7 occurs. [0142] The subsequent heating of the short-circuiting disc 7 can be effected by means of an inductor or in a furnace. Using the inductor, it is possible selectively to heat the short-circuiting disc to 450° C. to 500° C. within approximately 30 s depending on the short-circuiting disc. Optional screening of the inductor in the direction of the laminated rotor core 5 prevents any unnecessary heating of the laminations at the end side 20. [0143] The press is used to effect hot-forming, under pressure, of the short-circuiting disc 7 onto the projections 23 for approximately one minute, depending on process parameters such as materials used, size of the squirrel-cage rotor 4, etc. An almost simultaneous contacting of the conductor bars 6 with at least specifiable sections of the short-circuiting disc 7 is effected in this case. The clearance fit is “closed down” in this way and electrical contacting is effected in those sections where the clearance fit was present between recess 9 and coated projection 23. The gaps which initially exist at least between projection and recesses of the short-circuiting discs (clearance fit) in the case of cold joining (temperature range between room temperature and max. 100° C.) are no longer present after this process. With cold joining, almost no friction and/or deformation occurs between the conductor bars 6 and the short-circuiting discs 7. The hot-forming causes at least the gaps of the clearance fit to close. As a result of the heating, in particular the hot-forming temperatures, there also occurs a reflow process of the coating 15 to the short-circuiting disc 7. The coating 15 composed of the third material, in particular tin, disperses completely. The coating material, in particular tin, diffuses into the surfaces in the region of the specifiable section of the projection 23 of the conductor bar 6 and the surface that is to be contacted in the recess 9 of the short-circuiting disc 7. Therefore the desired contacting occurs only where the clearance fit was present between projection 23 and recess 9, i.e. the desired contact area.

[0144] The complete dispersal of this coating 15 during the production process (diffusion) in the region of the contact areas 27 is essential for the quality of the contacting between conductor bar 6 and short-circuiting disc 7. As a result of the complete dispersal, accumulations of the coating material are no longer present in the gap. In the case of specific materials such as e.g. tin, when running the asynchronous machine in a temperature range of approximately −40° C. to 200° C., unwanted transformations of beta tin into alpha tin or gamma tin would otherwise occur as explained previously. This would result in tin grain with a comparatively poor electrical conductance. The contacting between conductor bar 6 and short-circuiting disc 7 would then be comparatively poor, and this would lead to unnecessary thermal increases during operation of the asynchronous machine 1 and to diminished efficiency.

[0145] As a result of this diffusion and alloying, in particular of the tin into the first and second conductive materials of conductor bar 6 and short-circuiting disc 7, e.g. copper and aluminum or alloys thereof, the previously described phase transformation of the coating material is prevented.

[0146] By virtue of the reflow and diffusion processes, a material-fit connection between conductor bars 6 and short-circuiting disc 7 is achieved without the application of current as used in the production of a squirrel-cage rotor by means of resistance welding.

[0147] In addition to the inter alia electrical connection that is produced by forming, an additional material-fit connection is also obtained by means of diffusion.

[0148] Asynchronous machines with a squirrel-cage rotor 4 that is produced according to the invention have a stator into the stator hole of which is inserted the squirrel-cage rotor 4. The shaft 16 to which the squirrel-cage rotor 4 is connected in a rotationally conjoint manner is mounted in a housing on one side or on both sides.

[0149] Machines produced according to the invention have a broad spectrum of use and are used inter alia for both standard and high-speed applications, e.g. in the field of compressors, ventilators and pumps, materials handling, machine tool engineering, the food industry, and drives in rail-borne and non-rail-borne vehicle engineering.

[0150] These machines can be produced reliably, efficiently and easily. They can also be used for further drive requirements.