Cage rotor for an electric asynchronous machine, asynchronous machine with such a cage rotor, and rail vehicle with a traction drive designed as such an asynchronous machine.

Abstract

The invention relates to a squirrel-cage rotor (7) for an electric asynchronous machine (3) for driving a rail vehicle (1). It comprises a rotor shaft (11) rotatable about a rotor axis (12), a rotor lamination stack (14) fixedly connected to the rotor shaft (11) and having several axially extending rotor slots (15), and a squirrel-cage cage (17) with short-circuit bars (18) arranged in the rotor slots (15). According to the invention, a bar cross-section (Q) of a short-circuit bar (18) has a rectangular outer area (QA) and an adjoining trapezoidal inner area (QI). The inner area (QI) is radially closer to the rotor axis (12) than the outer area (QA) and tapers radially towards the rotor axis (12). This optimizes the squirrel-cage rotor (7) with regard to both its electromagnetic properties and its mechanical strength properties.

Description

[0001] The invention relates to a cage rotor for an electric asynchronous machine for driving a rail vehicle according to the preamble of patent claim 1.

[0002] A cage rotor or squirrel cage rotor, together with a stator or stator, forms the active assembly of an asynchronous electrical machine, which can be used to drive a rail vehicle. A cage rotor of this type comprises a rotor shaft that can rotate about a rotor axis. The cage rotor further comprises a rotor lamination stack that is connected in a rotationally fixed manner to the rotor shaft. The rotor lamination stack can have a stack of axially stacked, magnetizable rotor laminations. The rotor lamination stack comprises a plurality of axially extending rotor slots that penetrate the, for example, cylindrical rotor lamination stack near its outer surface. The rotor slots can be distributed at equal intervals around the rotor lamination stack in a circumferential direction around the rotor axis. The cage rotor also comprises a squirrel cage with squirrel cage bars arranged in the rotor slots.The short-circuit bars end on both sides of the rotor core at a short-circuit ring of the short-circuit cage, to which they are electrically connected.

[0003] Such squirrel-cage rotors differ depending on the requirements placed on the electrical asynchronous machine, among other things, in the cross-section of the squirrel-cage bars. For example, rotor bars with rectangular, L-shaped, and trapezoidal cross-sections are known from published patent application DE 35 39 543 A1. There, it is proposed to provide the rotor bars along their upper edge, spaced longitudinally along the bars in the area of ​​the rotor core, with recesses extending transversely to the longitudinal extent of the bar. This is to force current paths along the upper edge into a wave-like course and thus extend the effective length of the current paths compared to that with a constant cross-section. This extension results in an additional increase in resistance and inductance due to current displacement.

[0004] European publication EP 3 598 618 A1 discloses a dynamoelectric rotary machine. This comprises a stator with a winding system arranged between the teeth of a magnetically conductive body, each winding system having a winding head on each end face of the stator. The machine also comprises a rotor with a squirrel cage, which is rotatably mounted about an axis and, during operation of the dynamoelectric rotary machine, interacts electromagnetically, either in a motor- or generator-like manner, via an air gap with the winding system of the stator arranged in the slots. The rotor has conductor bars, which point toward the air gap of the machine in closed or semi-open rotor slots. The conductor bars have a rectangular cross-sectional shape.

[0005] Such rectangular shorting bars have the disadvantage that the rotor teeth of the rotor core, which run between the rotor slots, are trapezoidal in shape with a narrower width in the area of ​​the tooth roots. This results in reduced strength, which can lead to breakage or even the loss of a rotor tooth, which in turn can cause damage to the stator winding or even failure of the machine. On the other hand, the trapezoidal shape of the rotor teeth results in a magnetically constricted rotor tooth, which offers less cross-section for current flow.

[0006] These disadvantages are overcome by a squirrel-cage rotor for an electrical machine, known from the international publication WO 2014 / 067756 A1. The rotor comprises a laminated core with a slot, a short-circuit ring cast onto one axial end of the laminated core, and a bar arranged in the slot. The bar is supported in the slot by a deformable bearing and has a wedge- or trapezoidal cross-section. The wedge shape of the bars results in rotor teeth with parallel tooth flanks, which provide greater strength in the area of ​​the tooth roots and a large tooth cross-section for current flow.

[0007] However, squirrel cage bars with a trapezoidal cross-section exhibit lower fatigue strength under very high loads, such as those typically encountered in traction drives, particularly traction bearing drives. The vibrations imprinted in the cage rotor in the circumferential direction generate the highest mechanical stresses due to the bending load on a squirrel cage bar at its widest point of the trapezoidal cross-section. These stress peaks are often the starting point for bar fractures. Thermal play occurring between the squirrel cage ring and the rotor laminations and the resulting radial forces can loosen the seat of a squirrel cage bar in its rotor slot. The resulting mechanical play between the squirrel cage and the rotor laminations over time can lead to vibrations, resulting resonances, and ultimately to damage to the machine.

[0008] The invention is therefore based on the object of providing a cage rotor of the type mentioned above which is optimized both with regard to its electromagnetic properties and its mechanical strength properties.

[0009] The object is achieved according to the invention by a generic cage rotor with the features specified in the characterizing part of patent claim 1.

[0010] According to the invention, a bar cross-section of a squirrel-cage rod has a rectangular outer region and an adjoining trapezoidal inner region. The inner region is radially closer to the rotor axis than the outer region. The trapezoidal inner region tapers radially towards the rotor axis. The merging composition of the bar cross-section from an outer rectangle and an inner trapezoid, which tapers in a wedge shape towards the rotor axis, makes it possible to design a squirrel-cage rod that is optimized both electromagnetically and in terms of strength. The rotor teeth arranged between the inner regions of adjacent squirrel-cage rods can thus be designed with parallel flanks and a wide design, which prevents overmagnetization of the rotor laminated core. Furthermore, an optimally large tooth cross-section with wide tooth roots is available, which makes the rotor teeth insensitive to tangential vibrations.In the outdoor area, the short-circuit bar can be designed relatively wide to provide a large cross-section for current flow as well as its mechanical strength. At the same time, the rectangular design of the short-circuit bar in the outdoor area avoids the stress peaks that occur in a trapezoidal bar. The rectangular design also prevents the short-circuit bar from loosening due to radial forces and micro-movements, as the wedge effect does not occur here.

[0011] In an advantageous embodiment of the cage rotor according to the invention, the cross-section of a rotor slot is congruent with the cross-section of a bar, with the short-circuit bars being inserted into the rotor slot without play by caulking. The positive fit achieved by the congruent cross-sections of the short-circuit bar and the rotor slot leads to a tight fit of the short-circuit bars in the rotor core. The caulking of the short-circuit bars can be performed using an appropriate tool.

[0012] In a further advantageous embodiment of the cage rotor according to the invention, the rotor core has axially extending slots that extend radially from an outer circumferential side of the rotor core to the rotor slots. The axial slots of the open rotor slots form scattering slots. Their cross-section can be rectangular and have a width of approximately one-third of the width of the rotor slot.

[0013] In a further advantageous embodiment of the cage rotor according to the invention, the ratio of a radially extending length of the outer region to a width of the outer region extending perpendicular to the length is between 3.0 and 3.4, preferably 3.2. The outer region of the bar cross-section forms a rectangle standing upright in the radial direction, which is more than three times as long as it is wide. The specific dimensions depend on the outer diameter of the rotor laminated core. The squirrel bars thus have a bar cross-section sufficiently large for the required strength. At the same time, the rotor teeth have a tooth width at their narrowest point that is 4 / 3 of the width of the outer region of the bar cross-section. This also allows the tooth cross-section to be designed to be sufficiently large.

[0014] In a further advantageous embodiment of the cage rotor according to the invention, the ratio of the longitudinal extension of the outer region to the radially extending height of the inner region is between 2.2 and 2.6, preferably 2.4. This means that the height of the trapezoidal inner region is only approximately 30% of the total rod height in the radial direction. The tapered inner region thus only insignificantly reduces the rod cross-section, so that the strength is not compromised.

[0015] In a further advantageous embodiment of the cage rotor according to the invention, the inner region has a base extension extending perpendicular to the vertical extension at a transition to the outer region, and a base extension extending perpendicular to the vertical extension at a radially inner groove base of a rotor slot. The base extension of the inner region corresponds to the width extension of the outer region. The ratio of the base extension to the base extension is between 0.8 and 0.9, preferably 0.87. The ratio of the base extension to the base extension is selected such that the two trapezoidal legs of the inner region enclose a taper angle that leads to parallelism between the trapezoidal legs of adjacent short-circuit bars. The taper angle can be, for example, 4.8°.This in turn means that the tooth flanks of the rotor teeth do not taper towards the base of the rotor groove and therefore also have a sufficiently large tooth cross-section.

[0016] In a further advantageous embodiment of the cage rotor according to the invention, the short-circuit bars have curves at the outer corners of the cross-section, with the ratio of the radius of the curves to the width of the outer area being between 0.18 and 0.19. The curves at the outer corners facilitate the caulking of the short-circuit bars into the rotor slots. Furthermore, the curves reduce the stress concentration in the area of ​​the outer corners of the rotor core under mechanical loads.

[0017] In a further advantageous embodiment of the cage rotor according to the invention, the short-circuit bars are made of copper. The short-circuit bars are made of a material with high electrical conductivity, preferably copper.

[0018] The invention further relates to an electric asynchronous machine for driving a rail vehicle. The machine comprises a machine housing, a hollow cylindrical stator with a stator core and a stator winding. The stator is mounted in the machine housing in a rotationally fixed manner thereto. According to the invention, the asynchronous machine comprises a cage rotor according to one of the preceding claims, the rotor shaft of which is rotatably mounted in the machine housing and the rotor core is rotatably arranged within the stator core, forming a radial air gap. The asynchronous machine can be designed to be more electromagnetically optimized while maintaining mechanical robustness. This also has a positive effect on the efficiency and size of the machine.

[0019] The invention also relates to a rail vehicle with a traction drive configured as an electric asynchronous motor according to the preceding claim. Electric asynchronous motors according to the invention can be used as traction drives in rail vehicles such as trams, metros, multiple units for regional and high-speed rail service, as well as diesel-electric and high-performance locomotives. Their robustness and efficiency combined with their compact size enable easier integration of the traction drive in the bogie area of ​​the rail vehicle, where space is typically very limited.

[0020] Further advantages and features of the invention will become apparent from the following description of an embodiment with reference to the drawings, in which Fig. 1 a rail vehicle according to the invention in side view, Fig. 2 shows an axial longitudinal section through a traction drive of the rail vehicle designed as an electric asynchronous machine according to the invention Fig. 1 and Fig. 3 shows an axial partial cross-section through a cage rotor according to the invention of the electrical asynchronous machine from Fig. 2 are illustrated schematically.

[0021] According to Fig. 1, a rail vehicle 1 designed, for example, as a locomotive, has electric asynchronous machines 3 integrated in bogies 2 as traction drive for driving wheel sets 4.

[0022] Such an electrical asynchronous machine 3 comprises according to Fig. 2 shows a machine housing 5 in which a stator 6 and a cage rotor 7 according to the invention are arranged. The stator 6 has a hollow cylindrical stator laminated core 8, which is connected in a rotationally fixed manner to the machine housing 5. The stator 6 further has a stator winding 10 running in stator slots and forming winding heads 9 on opposite end faces of the stator laminated core 8. The cage rotor 7 comprises a rotor shaft 11, which is mounted in the machine housing 5 via rolling bearings 12 for rotation about a rotor axis 12. Furthermore, the cage rotor 7 comprises a rotor laminated core 14, which is connected in a rotationally fixed manner to the rotor shaft 11. The rotor laminated core 14 can comprise a stack of axially stacked, magnetizable rotor laminations.

[0023] With reference also to Fig. 3, the rotor laminated core 14 comprises a plurality of axially extending rotor slots 15 which penetrate the, for example, cylindrical rotor laminated core 14 near its outer surface 16. The rotor slots 15 can be distributed at equal intervals over the rotor laminated core 14 with respect to a circumferential direction around the rotor axis 12. The cage rotor 7 also comprises a squirrel cage 17 with short-circuit bars 18 arranged in the rotor slots 15, which are preferably made of copper or another good electrical conductor material. The short-circuit bars 18 end on each end face on both sides of the rotor laminated core 14 at a short-circuit ring 19 of the squirrel cage 17, to which they are electrically conductively attached. The rotor laminated core 14 of the cage rotor 7 is rotatably arranged within the stator laminated core 8, forming a radial air gap 20.The operation of the electric asynchronous machine 3, which sets the cage rotor 7 in rotation through electromagnetic interaction with the stator 6, is well known and will therefore not be described in detail. Furthermore, numerous details, such as cooling devices, are described in . Fig. 2 not shown for the sake of simplicity.

[0024] The partial section through the rotor core 14 shows Fig. 3 three rotor slots 15, wherein a short-circuit bar 18 is inserted into each of the two outer rotor slots 15, while such a bar has been omitted from the middle rotor slot 15 for reasons of clarity. A bar cross-section Q of a short-circuit bar 18 according to the invention has a rectangular outer region QA and an adjoining trapezoidal inner region QI. The inner region QI is radially closer to the rotor axis 12 than the outer region QA. The trapezoidal inner region QI tapers in the radial direction towards the rotor axis 12. By merging the composition of the bar cross-section Q from an outer rectangle QA and an inner trapezoid QI, which tapers in a wedge shape towards the rotor axis 12, an electromagnetically and strength-optimized short-circuit bar 18 can be designed.The rotor teeth 21 arranged between the inner regions QI of adjacent short-circuit bars 18 can thus be designed with parallel flanks and a wide design, which prevents overmagnetization of the rotor core 14. Furthermore, an optimally large tooth cross-section with wide tooth roots 22 is available, which makes the rotor teeth 21 insensitive to tangential vibrations. In the outer region QA, the short-circuit bar 18 can be designed relatively wide in order to provide a large cross-section for the current flow as well as its mechanical strength. At the same time, the rectangular design of the short-circuit bar 18 in the outer region QA prevents the voltage peaks that occur in a trapezoidal bar. The rectangular cross-section design also prevents the short-circuit bar 18 from loosening due to radial forces and micro-movements, since the wedge effect does not occur here.

[0025] According to Fig. 3, a slot cross-section of a rotor slot 15 is congruent with a bar cross-section Q, wherein the short-circuit bars 18 are inserted into the rotor slot 15 without play by caulking. The positive fit achieved by congruent cross-sections of short-circuit bar 18 and rotor slot 15 leads to a firm fit of the short-circuit bars 18 in the rotor laminated core 14. The rotor laminated core 14 has axially running slots 23 which extend radially from the outer circumferential surface 16 of the rotor laminated core 14 to the rotor slots 15. The scattering slots 23 form open rotor slots 15. A cross-section of the slots 23 can be rectangular and have a slot width B23 of approximately one third of a width B15 of the rotor slot 15. A ratio of a radially extending length L of the outer region QA to a width B of the outer region QA extending perpendicular to the length L is between 3.0 and 3.4, preferably 3.2.The outer region QA of the bar cross-section Q forms a rectangle standing upright in the radial direction, which is more than three times as long as it is wide. The specific dimensions depend on the outer diameter of the rotor laminated core 14. The short-circuit bars 18 thus have a bar cross-section Q that is sufficiently large for the required strength. At the same time, the rotor teeth 21 have a tooth width B21 at their narrowest point that is 4 / 3 of the width B of the outer region QA of the bar cross-section Q. This means that the tooth cross-section can also be designed to be sufficiently large. The ratio of the length L of the outer region QA to a radially extending height h of the inner region is between 2.2 and 2.6, preferably 2.4. This means that the height h of the trapezoidal inner region QI is only approximately 30% of the total bar height H in the radial direction.The tapered inner region QI thus only slightly reduces the bar cross-section Q, so that the strength is not compromised. The inner region QI has a base extension b extending perpendicular to the height extension h at a transition 24 to the outer region QA (in . Fig.3 indicated by a dash-dot line) and a base extension g extending perpendicular to the height extension h at a radially inner slot base 25 of a rotor slot 15. The base extension b of the inner region QI corresponds to the width extension B of the outer region QA. A ratio of the base extension g to the base extension b is between 0.8 and 0.9, preferably 0.87. The ratio of the base extension g to the base extension b is selected such that the two trapezoidal legs 26 of the inner region QI enclose a taper angle α which leads to parallelism of trapezoidal legs 26 of adjacent short-circuit bars 18. The taper angle α can be 4.8°, for example. This in turn means that the tooth flanks 27 of the rotor teeth 21 do not taper towards the groove base 25 of the rotor groove 15 and thus also have a sufficiently large tooth cross-section.The short-circuit bars 18 have curves 28 at the outer corners of the bar cross-section Q, with the ratio of the radius R of the curves 28 to the width B of the outer area QA being between 0.18 and 0.19. The curves 28 at the outer corners facilitate the caulking of the short-circuit bars 18 into the rotor slots 14. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 35 39 543 A1

[0003] EP 3 598 618 A1

[0004] WO 2014 / 067756 A1

[0006]

Claims

[1] Cage rotor (7) for an electric asynchronous machine (3) for driving a rail vehicle (1), comprising - a rotor shaft (11) rotatable about a rotor axis (12), - a rotor core (14) connected to the rotor shaft (11) in a rotationally fixed manner and having a plurality of axially extending rotor grooves (15), and - a short-circuit cage (17) with short-circuit bars (18) arranged in the rotor slots (15), characterized by , - that a bar cross-section (Q) of a short-circuit bar (18) has a rectangular outer region (QA) and an adjoining trapezoidal inner region (QI), - wherein the inner region (QI) is located radially closer to the rotor axis (12) than the outer region (QA) and tapers in the radial direction towards the rotor axis (12). [2] Cage rotor (7) according to claim 1, - wherein a slot cross-section of a rotor slot (15) is congruent with a bar cross-section (Q) and the short-circuit bars (18) are inserted into the rotor slots (15) without play by caulking. [3] Cage rotor (7) according to claim 2, - wherein the rotor laminated core (14) has axially extending slots (23) which extend radially from an outer circumferential surface (16) of the rotor laminated core (14) to the rotor slots (15). [4] Cage rotor (7) according to one of the preceding claims, - wherein a ratio of a radially extending length dimension (L) of the outer region (QA) to a width dimension (B) of the outer region (QA) extending perpendicular to the length dimension (L) is between 3.0 and 3.4, preferably 3.

2. [5] Cage rotor (7) according to claim 4, - wherein a ratio of the length extension (L) of the outer region (QA) to a radially extending height extension (h) of the inner region (QI) is between 2.2 and 2.6, preferably 2.

4. [6] Cage rotor (7) according to claim 4 or 5, - wherein the inner region (QI) has a base extension (b) extending perpendicular to the height extension (h) at a transition (24) to the outer region (QA) and a base extension (g) extending perpendicular to the height extension (h) at a radially inner groove base (25) of a rotor groove (15), - where the base extension (b) of the inner area (QI) corresponds to the width extension (B) of the outer area (QA), and - wherein a ratio of the basic expansion (g) to the base expansion (b) is between 0.8 and 0.9, preferably 0.

87. [7] Cage rotor (7) according to one of the preceding claims, - wherein the short-circuit bars (18) have curves (28) at the outer corners of the cross-section (Q), - wherein a ratio of a radius (R) of the curves (28) to the width (B) of the outer area (QA) is between 0.18 and 0.

19. [8] Cage rotor (7) according to one of the preceding claims, - wherein the short-circuit bars (18) are made of copper. [9] Electric asynchronous machine (3) for driving a rail vehicle (1), comprising - a machine housing (5), - a stator (6) with a hollow cylindrical stator core (8) and with a stator winding (10), which is inserted in and rotationally fixed to the machine housing (5), - a cage rotor (7) according to one of the preceding claims, which is rotatably mounted in the machine housing (5) and whose rotor laminated core (14) is rotatably arranged within the stator laminated core (8) to form a radial air gap (20). [10] Rail vehicle (1) with a traction drive which is designed as an electric asynchronous machine (3) according to the preceding claim.

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