Squirrel-cage rotor for asynchronous machine, asynchronous machine having such squirrel-cage rotor, and rail vehicle having traction drive designed as such asynchronous machine

Abstract

The invention relates to a squirrel-cage rotor (7) for driving an asynchronous machine (3) of a rail vehicle (1). The rotor comprises a rotor shaft (11) rotatable about a rotor axis (12), a rotor laminated core (14) connected to the rotor shaft (11) in a rotationally fixed manner and having a plurality of axially extending rotor slots (15), and a shorting cage (17) having shorting bars (18) arranged in the rotor slots (15). According to the invention, the strip cross-section (Q) of the short-circuit strip (18) has a rectangular outer region (QA) and a trapezoidal inner region (QI) connected thereto. Wherein the inner region (QI) is radially closer to the rotor axis (12) than the outer region (QA) and tapers in a radial direction towards the rotor axis (12). As a result, the squirrel-cage rotor (7) is optimized in terms of its electromagnetic properties and in terms of its mechanical strength properties.

Description

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

[0002] The squirrel cage rotor or cage rotor together with the stator or fixed part forms an active arrangement of an asynchronous electric machine, which can be provided for driving a rail vehicle. Such a squirrel cage rotor comprises a rotor shaft, which is rotatable about a rotor axis. Furthermore, the squirrel cage rotor comprises a rotor lamination core, which is torsionally connected with the rotor shaft. The rotor lamination core can have a stack composed of magnetizable rotor laminations, which are axially laminated with one another. The rotor lamination core comprises a plurality of axially extending rotor slots, which run through the, for example, cylindrical rotor lamination core near an outer jacket surface of the rotor lamination core. The rotor slots can be distributed on the rotor lamination core with uniform spacing about a circumferential direction about the rotor axis. The squirrel cage rotor further comprises a short-circuit cage with short-circuit bars arranged in the rotor slots. The short-circuit bars each end on one short-circuit ring of the short-circuit cage on both sides of the rotor lamination core, on which the short-circuit bars are fixed electrically conductively.

[0003] Such cage rotors are distinguished in particular by the bar cross section of the short-circuit bars depending on the requirements placed on the asynchronous electric machine. From the publication DE 35 39 543 A1 it is known, for example, rotor bars with rectangular, L-shaped and trapezoidal cross-sectional shapes. It is proposed there that the rotor bars are provided with grooves running transversely to the longitudinal extension of the bars in the region of the rotor lamination stack at intervals along the upper edge of the bars in the longitudinal direction of the bars, in order to force the current path to run in a wave shape along the upper edge, thereby lengthening its effective length compared to the current path in the case of a constant cross section. This lengthening additionally increases the resistance and the inductance by the skin effect.

[0004] The European publication EP 3 598 618 A1 shows a rotary electric machine. The electric machine comprises a stator with a winding system arranged in slots between teeth of a magnetic conductor, which winding system has one winding end on each end side of the stator. The electric machine further comprises a rotor with a short-circuit cage, which rotor is arranged rotatable about an axis and forms an electromagnetic interaction with the winding system of the stator arranged in the slots in motor fashion or generator fashion when the rotary electric machine is in operation. The rotor has conductor bars, which conductor bars face the air gap of the electric machine in closed or half-open rotor slots. The conductor bars have a rectangular cross-sectional shape.

[0005] Such rectangular short-circuit bars result in the following disadvantage, that the rotor teeth of the rotor lamination core, which extend between the rotor slots, have a trapezoidal shape with a smaller width in the region of the tooth root. This is accompanied on the one hand by a lower strength, which can lead to a breaking or even a loss of the rotor teeth, which in turn can damage the stator winding or even lead to a machine failure. On the other hand, the trapezoidal shape of the rotor teeth results in magnetically constricted rotor teeth, which offer a smaller cross section for the current flow.

[0006] The cage rotor for an electric machine known from the international publication WO 2014 / 067756 Al overcomes these disadvantages, which has a rotor lamination pack with slots, short-circuit rings injection molded on the axial end of the rotor lamination pack, and bars arranged in the slots. The bars are supported in the slots by deformable supports and have a wedge-shaped or trapezoidal cross section. By the wedge shape of the bars, rotor teeth with parallel tooth flanks are obtained, which have a higher strength in the root region and provide a large tooth cross section for the current flow.

[0007] However, short-circuit bars with trapezoidal bar cross sections have a lower operating strength under very high loads, which occur, for example, typically in traction drives, in particular in hub drives. Vibrations that are introduced into the squirrel cage rotor in the circumferential direction produce the highest mechanical stresses by the bending load of the short-circuit bars at the wide side of their trapezoidal cross section. These stress peaks are often the starting point for a bar break. Thermal expansion gaps (Wärmespiele) that occur between the short-circuit ring and the rotor lamination core and the resulting radial forces can loosen the fit of the short-circuit bars in their rotor slots. The mechanical gaps that are thus created in the long term between the short-circuit bars and the rotor lamination core can lead to vibrations, resulting resonances and ultimately to damage to the electric machine.

[0008] The technical problem addressed by the present invention is therefore to provide a squirrel cage rotor of the type mentioned at the outset, which is optimized both in terms of its electromagnetic properties and in terms of its mechanical strength properties.

[0009] This technical problem is solved according to the invention by a squirrel cage rotor of the type mentioned at the outset, which has the features given in the characterizing part of claim 1.

[0010] According to the application, the bar cross-section of the short-circuit bar has a rectangular outer region and a trapezoidal inner region connected to the outer region. The inner region is located radially closer to the rotor axis than the outer region. The trapezoidal inner region tapers here in the radial direction towards the rotor axis. By the combination of the outer rectangle and the tapering inner trapezoid towards the rotor axis, an optimized short-circuit bar in terms of both the electromagnetic and the strength aspects can be designed. The rotor tooth arranged between the inner regions of adjacent short-circuit bars can thus be designed with parallel flanks and be relatively wide, which prevents overmagnetization of the rotor lamination core. In addition, an optimal large tooth cross-section with a wide tooth root is available, which makes the rotor tooth insensitive to tangential vibrations. In the outer region, the short-circuit bar can be designed relatively wide in order to provide a large cross-section for the current flow and its mechanical strength. At the same time, stress peaks occurring in trapezoidal bars are avoided due to the rectangular design of the short-circuit bar in the outer region. The rectangular design also prevents the short-circuit bar from loosening due to radial forces and micro-movements, since no wedge action occurs here.

[0011] In an advantageous embodiment of the squirrel-cage rotor according to the application, the slot cross-section of the rotor slot is configured identically to the bar cross-section, wherein the short-circuit bar is introduced into the rotor slot without play by means of a press fit. The form fit achieved by the congruent cross-section of the short-circuit bar and the rotor slot results in a secure fit of the short-circuit bar in the rotor lamination core. The press fit of the short-circuit bar can be achieved by means of a corresponding tool.

[0012] In a further advantageous embodiment of the squirrel-cage rotor according to the application, the rotor lamination core has axially extending slots which extend radially from the outer circumferential side of the rotor lamination core to the rotor slot. The axially extending slots of the open rotor slot form a leakage slot. The cross-section thereof can be designed rectangular and have a width of approximately one third of the width dimension of the rotor slot.

[0013] In a further advantageous embodiment of the squirrel-cage rotor according to the application, the ratio of the radially extending length dimension of the outer region to the width dimension of the outer region extending perpendicular to the length dimension is between 3.0 and 3.4, preferably 3.2. The outer region of the bar cross-section forms a rectangle which stands upright in the radial direction, the length of which is more than three times the width. The specific dimensions depend on the outer diameter of the rotor lamination core. The short-circuit bar thus has a large bar cross-section which is sufficient to meet the required strength. At the same time, the tooth width of the rotor tooth at its narrowest point is 4 / 3 of the width dimension of the outer region of the bar cross-section. The tooth cross-section can thus also be designed sufficiently large.

[0014] In a further advantageous embodiment of the squirrel cage rotor according to the application, the ratio of the length dimension of the outer region to the height dimension of the radial extension of the inner region is between 2.2 and 2.6, preferably 2.4. That is, the height of the trapezoidal inner region is only about 30% of the overall bar height as viewed in the radial direction. The tapered inner region thus only slightly reduces the bar cross section, so that the strength is not affected thereby.

[0015] In a further advantageous embodiment of the squirrel cage rotor according to the application, the inner region has a base dimension extending perpendicular to the height dimension at the transition to the outer region and a bottom dimension extending perpendicular to the height dimension at the radially inner slot bottom of the rotor slot. Therein, the base dimension of the inner region coincides with the width dimension of the outer region. The ratio of the bottom dimension to the base dimension is between 0.8 and 0.9, preferably 0.87. The ratio of the bottom dimension to the base dimension is chosen such that the two trapezoidal legs of the inner region are pinched into a convergence angle, which convergence angle makes the trapezoidal legs of adjacent short circuit bars parallel. The convergence angle can be, for example, 4.8°. This in turn means that the tooth flanks of the rotor tooth are not tapered towards the direction of the slot bottom of the rotor slot and thus also have a sufficiently large tooth cross section.

[0016] In a further advantageous embodiment of the squirrel cage rotor according to the application, the short circuit bar has a rounding at the outer corner of the cross section, wherein the ratio of the rounding radius to the width dimension of the outer region is between 0.18 and 0.19. The rounding at the outer corner facilitates the press fit of the short circuit bar into the rotor slot. Furthermore, the rounding reduces the notch effect in the area of the outer corner of the rotor lamination core in the case of mechanical loads.

[0017] In a further advantageous embodiment of the squirrel cage rotor according to the application, the short circuit bar is made of copper. The short circuit bar is made of a material having a high electrical conductivity, preferably of copper.

[0018] The application also relates to an asynchronous machine for driving a rail vehicle. The machine comprises a machine housing, a hollow cylindrical stator having a stator lamination core and stator windings. The stator is mounted in the machine housing torsionally fixed with respect to the machine housing. According to the application, the asynchronous machine comprises a squirrel cage rotor according to any of the preceding claims, whose rotor shaft is rotatably supported in the machine housing, whose rotor lamination core is rotatably arranged within the stator lamination core with a radial air gap. The asynchronous machine can be designed electromagnetically more optimally, while at the same time having mechanical robustness. This also has a positive effect on the efficiency and structural size of the machine.

[0019] The application also relates to a rail vehicle having a traction drive designed as an asynchronous machine according to the preceding claims. In rail vehicles such as trams, subways, multiple units for regional and high-speed traffic, and diesel-electric and high-power locomotives, the asynchronous machine according to the application can be used as a traction drive. Robustness and efficiency at a small structural size make it easier to integrate the traction drive in the bogie area of the rail vehicle, where only very narrow installation spaces are usually available.

[0020] Further advantages and features of the application result from the following description of embodiments with the aid of the drawings, in which:

[0021] Figure 1 a rail vehicle according to the application is shown schematically in a side view,

[0022] Figure 2 a sectional view is shown Figure 1 an axial longitudinal section of a traction drive of a rail vehicle designed as an asynchronous machine according to the application, and

[0023] Figure 3 a sectional view is shown Figure 2 an axial partial cross section of an asynchronous machine according to the application of a squirrel cage rotor resulting therefrom.

[0024] According to Figure 1 , a rail vehicle 1 designed as a locomotive has an integrated asynchronous machine 3 in a bogie 2 as a traction drive for driving a wheel set 4.

[0025] According to Figure 2 , such an asynchronous machine 3 comprises a machine housing 5 in which a stator 6 and a squirrel cage rotor 7 according to the application are arranged. The stator 6 has a hollow-cylindrical stator lamination core 8 which is torsionally connected to the machine housing 5. The stator 6 also has a stator winding 10 which extends in stator slots and forms winding ends 9 at opposite end sides of the stator lamination core 8. The squirrel cage rotor 7 comprises a rotor shaft 11 which is rotatably supported in the machine housing 5 about a rotor axis 12 by means of rolling bearings 12. Furthermore, the squirrel cage rotor 7 comprises a rotor lamination core 14 which is torsionally connected to the rotor shaft 11. The rotor lamination core 14 can have a stack consisting of axially laminated magnetizable rotor laminations.

[0026] Reference is also made to Figure 3The rotor lamination core 14 comprises a plurality of axially extending rotor slots 15 which run through the, for example, cylindrical rotor lamination core 14 near the outer jacket surface 16 of the rotor lamination core. These rotor slots 15 can be distributed at uniform intervals on the rotor lamination core 14 with respect to the circumference about the rotor axis 12. The squirrel-cage rotor 7 also comprises a short-circuit cage 17 with short-circuit bars 18 arranged in the rotor slots 15, which are preferably composed of copper or another good electrically conductive material. The short-circuit bars 18 each terminate on one of the short-circuit rings 19 of the short-circuit cage 17 on both sides of the rotor lamination core 14, to which the short-circuit bars are electrically conductively fixed. The rotor lamination core 14 of the squirrel-cage rotor 7 is arranged rotatably within the stator lamination core 8 with a radial air gap 20. The principle of operation of the asynchronous machine 3, i.e. the rotational movement of the squirrel-cage rotor 7 by electromagnetic interaction with the stator 6, is known and will therefore not be described in detail. Furthermore, for the sake of simplicity, Figure 2 Numerous details, for example cooling devices, are not shown in the figures.

[0027] According to Figure 3 Three rotor slots 15 are shown in a partial cross-section through the rotor lamination core 14, in each of which one of the short-circuit bars 18 is arranged in the two outer rotor slots 15, while such a short-circuit bar is omitted in the middle rotor slot 15 for the sake of clarity. The bar cross-section Q of the short-circuit bar 18 according to the application has a rectangular outer region QA and a trapezoidal inner region QI which is connected to the outer region. The inner region QI is located radially closer to the rotor axis 12 than the outer region QA. The trapezoidal inner region QI tapers here in the radial direction towards the rotor axis 12. By the transition combination of the outer rectangle QA and the inner trapezoid QI which tapers towards the rotor axis 12, an optimised short-circuit bar 18 in terms of both the electromagnetic and the strength aspects 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 are relatively wide, which prevents overmagnetisation of the rotor lamination core 14. In addition, the optimum large-tooth cross-section with a wide tooth root 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 and its mechanical strength. At the same time, stress peaks which occur in trapezoidal bars are avoided in the rectangular design of the short-circuit bar 18 in the outer region QA. The rectangular cross-section design also prevents the short-circuit bar 18 from loosening as a result of radial forces and micro-movements, since no wedge action occurs here.

[0028] According to Figure 3, the slot cross section of the rotor slot 15 is configured in conformity with the bar cross section Q, wherein the short-circuit bar 18 is introduced into the rotor slot 15 without play by press fit. The form fit achieved by the congruent cross sections of the short-circuit bar 18 and the rotor slot 15 results in a secure fit of the short-circuit bar 18 in the rotor lamination core 14. The rotor lamination core 14 has axially extending slots 23 which extend radially from the outer cover face 16 of the rotor lamination core 14 to the rotor slot 15. The leakage slots 23 form the open rotor slot 15. The cross section of the slots 23 can be designed as rectangular and has a slot width B23 which is approximately one third of the width dimension B15 of the rotor slot 15. The ratio of the radially extending length dimension L of the outer region QA to the width dimension B of the outer region QA which extends perpendicularly to the length dimension L is between 3.0 and 3.4, preferably 3.2. The outer region QA of the bar cross section Q forms a rectangle which stands upright in the radial direction, the length of which is more than three times the width. The specific dimensions depend on the outer diameter of the rotor lamination core 14. The short-circuit bar 18 thus has a large bar cross section Q which is sufficient to meet the required strength. At the same time, the tooth width B21 of the rotor tooth 21 at its narrowest point is 4 / 3 of the width dimension B of the outer region QA of the bar cross section Q. The tooth cross section can thus also be designed to be sufficiently large. The ratio of the length dimension L of the outer region QA to the radially extending height dimension h of the inner region is between 2.2 and 2.6, preferably 2.4. That is to say, the height h of the trapezoidal inner region QI is only approximately 30% of the overall bar height H viewed in the radial direction. The tapering inner region QI thus narrows the bar cross section Q only slightly, so that the strength is not affected thereby. The inner region QI has a base dimension b which extends perpendicularly to the height dimension h at the transition 24 to the outer region QA (shown in Figure 3 dot-dash line in the middle) and a bottom dimension g which extends perpendicularly to the height dimension h at the radially inner slot bottom 25 of the rotor slot 15. The base dimension b of the inner region QI coincides with the width dimension B of the outer region QA. The ratio of the bottom dimension g to the base dimension b is between 0.8 and 0.9, preferably 0.87. The ratio of the bottom dimension g to the base dimension b is chosen such that the two trapezoidal sides 26 of the inner region QI are pinched together at a tapering angle a which results in the trapezoidal sides 26 of adjacent short-circuit bars 18 being parallel. The tapering angle a can be, for example, 4.8°. This in turn means that the tooth flanks 27 of the rotor tooth 21 do not taper in the direction of the slot bottom 25 of the rotor slot 15 and thus also have a sufficiently large tooth cross section. The short-circuit bar 18 has a rounding 28 at the outer corner of the bar cross section Q, wherein the ratio of the radius R of the rounding 28 to the width dimension B of the outer region QA is between 0.18 and 0.19. The rounding 28 at the outer corner facilitates the press fit of the short-circuit bar 18 into the rotor slot 14.

Claims

1. A squirrel cage rotor (7) for an asynchronous electric machine (3) for driving a rail vehicle (1), comprising - a rotor shaft (11) rotatable about a rotor axis (12), - a rotor lamination core (14) in torsionally fixed connection with the rotor shaft (11), the rotor lamination core having a plurality of axially extending rotor slots (15), and - a short-circuit cage (17) having short-circuit bars (18) arranged in the rotor slots (15), characterized in that - the bar cross section (Q) of the short-circuit bars (18) has a rectangular outer region (QA) and a trapezoidal inner region (QI) connected to the outer region, - wherein the inner region (QI) is radially closer to the rotor axis (12) than the outer region (QA) and tapers in a radial direction toward the rotor axis (12).

2. The squirrel cage rotor (7) according to claim 1, - wherein, the slot cross section of the rotor slots (15) is configured congruently to the bar cross section (Q) and the short-circuit bars (18) are introduced into the rotor slots (15) without play by press fit.

3. The squirrel cage rotor (7) according to claim 2, - wherein the rotor lamination core (14) has axially extending slots (23) which extend radially from a cover face (16) of the rotor lamination core (14) to the rotor slots (15).

4. The squirrel cage rotor (7) according to any one of the preceding claims, - wherein the ratio of the radially extending length dimension (L) of the outer region (QA) to the width dimension (B) of the outer region (QA) which extends perpendicular to the length dimension (L) is between 3.0 and 3.4, preferably 3.

2.

5. The squirrel cage rotor (7) according to claim 4, - wherein the ratio of the length dimension (L) of the outer region (QA) to the radially extending height dimension (h) of the inner region (QI) is between 2.2 and 2.6, preferably 2.

4.

6. The squirrel cage rotor (7) according to claim 4 or 5, - wherein the inner region (QI) has a base dimension (b) which extends perpendicular to the height dimension (h) at the transition (24) to the outer region (QA) and a bottom dimension (g) which extends perpendicular to the height dimension (h) at a radially inner slot bottom (25) of the rotor slot (15), - wherein, the base dimension (b) of the inner region (QI) coincides with the width dimension (B) of the outer region (QA), and - wherein the ratio of the bottom dimension (g) to the base dimension (b) is between 0.8 and 0.9, preferably 0.

87.

7. The squirrel cage rotor (7) according to any one of the preceding claims, - wherein the short-circuit bars (18) have a rounding (28) at the outer corners of the cross section (Q), - wherein, the ratio of the radius (R) of the rounding (28) to the width dimension (B) of the outer region (QA) is between 0.18 and 0.

19.

8. The squirrel cage rotor (7) according to any one of the preceding claims, - wherein the short-circuit bars (18) are composed of copper.

9. An asynchronous electric machine (3) for driving a rail vehicle (1), comprising - a machine housing (5), - a stator (6) having a hollow-cylindrical stator lamination core (8) and a stator winding (10), which stator is mounted in the machine housing (5) and is torsionally fixed relative thereto, - a squirrel-cage rotor (7) according to any one of the preceding claims, which is rotatably supported in the machine housing (5) and whose rotor lamination core (14) is rotatably arranged within the stator lamination core (8) with a radial air gap (20) being formed.

10. A rail vehicle (1) having a traction drive which is designed as an asynchronous machine (3) according to the preceding claim.

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