DE102022212655A1 - Vehicle, electrical machine, squirrel-cage rotor and method for producing a squirrel-cage rotor - Google Patents

Abstract

The invention relates to a squirrel-cage rotor, an electrical machine and a vehicle with a squirrel-cage rotor, and a method for producing a squirrel-cage rotor. The squirrel-cage rotor comprises a squirrel cage (200) with a plurality of rotor bars (220) and at least one short-circuit ring (210-1, 210-2) for connecting the rotor bars. At least one of the rotor bars has at least a first and a second section (221, 222), which are offset from one another (224) in a circumferential direction (241) of the squirrel-cage rotor.

Description

The invention relates to a squirrel-cage rotor, an electrical machine and a vehicle with a squirrel-cage rotor, and a method for producing a squirrel-cage rotor.

Electrical machines are playing an increasingly important role, particularly in vehicles but also in other applications. During operation, electrical machines, particularly induction power machines such as asynchronous machines (ASM), typically experience disturbing acoustic excitation. The typical cause of the acoustic excitation is a force fluctuation caused by the number and spacing of induction rods in the rotor. Such force fluctuations are also known as "torque ripple". One measure to counteract this is the continuous slanting of the induction rods of the rotor or stator. The slant is chosen to be large enough to bridge the gap between the stator slots for accommodating the induction rods or beyond the space between the induction rods. However, the slant can be accompanied by power losses.

There is therefore a need for an improved concept for squirrel-cage rotors. This need is taken into account by embodiments of the independent claims. Advantageous further developments are disclosed by the appended dependent claims.

Embodiments of the present disclosure provide a squirrel-cage rotor for an electrical machine. The squirrel-cage rotor comprises a squirrel cage with a plurality of rotor bars and at least one short-circuit ring for connecting the rotor bars. At least one of the rotor bars has at least a first and a second section, which are offset from one another in a circumferential direction of the squirrel-cage rotor. The offset of the first and second sections reduces a distance between rotor bars of the squirrel-cage rotor. This ensures a weakening of force fluctuations which act on the squirrel-cage rotor and a weakening of associated acoustic excitations.

Electrical machines with the proposed squirrel-cage rotor can therefore operate more quietly than other electrical machines. This means that the rotor bars do not need to be inclined in favor of a higher power density and less technical effort. Compared to solutions that provide for the inclination/inclination of rotor bars, the proposed concept also requires a smaller angular range as installation space, i.e. the rotor bars take up less space in the squirrel-cage rotor or the laminated core.

The offset in the circumferential direction can be dimensioned in such a way that force fluctuations that act on the first and second sections during operation of the squirrel-cage rotor are at least partially compensated. In an asynchronous machine, this can reduce stator/rotor field harmonics in the air gap, which can be noticed acoustically.

In practice, the force fluctuations can oscillate periodically. The offset can be dimensioned such that the force fluctuations acting on the first and second sections are 180° out of phase with each other. The force fluctuations acting on the first and second sections can therefore completely compensate each other within the framework of manufacturing tolerances. The torque ripple and acoustic excitations can thus be further reduced or, ideally, avoided.

In some embodiments, a cross-sectional area of a connecting section for connecting the first and second sections is at least as large as a cross-sectional area of the first or second section. This can prevent a current density and thus a temperature of the rotor bar in the connecting section from being greater than in the first or second section. This can therefore prevent, for example, a critical thermal load caused by a (local) temperature maximum in the connecting section.

The first section and/or the second section can run (across several laminations of the laminated core) obliquely or parallel to an axial direction of the squirrel-cage rotor. Depending on the dimensioning of the offset, an oblique course can further reduce the distance to other slots in favor of lower torque ripples.

The rotor bar can optionally have several sections that are offset from one another. For example, the rotor bar has a third section that is offset in the circumferential direction of the squirrel-cage rotor compared to the first and second sections. In this way, a step-by-step progression of the rotor bar can be achieved in some embodiments.

Further embodiments of the present disclosure provide an electrical machine comprising a squirrel-cage rotor according to the present disclosure.

The electric machine can be designed in different ways and for different purposes. In particular, the electric machine can be designed to drive a vehicle.

Further embodiments of the present disclosure thus relate to a vehicle comprising an electric machine according to the present disclosure.

The proposed squirrel-cage rotor can be manufactured using an appropriate process.

Embodiments of the present disclosure therefore relate in particular to a method for producing a squirrel-cage rotor. The method comprises providing a squirrel cage with at least one short-circuit ring and a plurality of rotor bars. The method further comprises providing a laminated core with a plurality of laminates arranged next to one another and a plurality of grooves for receiving the rotor bars. At least one of the grooves has at least a first and a second section. In addition, the first and the second section are offset from one another in a circumferential direction of the squirrel-cage rotor. In this way, a squirrel-cage rotor according to the present disclosure can be produced which has at least a lower torque ripple than other squirrel-cage rotors.

The provision of the squirrel cage can include producing the rotor bars using a casting process, and the at least one groove can serve as a casting space for at least one of the rotor bars in the casting process. In this way, a higher degree of filling of the groove with the rotor bar can be achieved than, for example, when using so-called "hair pin windings".

In the following, embodiments of the present disclosure will be explained in more detail using the accompanying figures.

• 1a-c einen Kurzschlussläufer mit gerade verlaufenden Läuferstäben;
• 2a, b schematisch ein Ausführungsbeispiel eines Kurzschlusskäfigs mit Läuferstäben mit versetzten Abschnitten; und
• 3 eine schematische Darstellung eines Ausführungsbeispiels eines Verfahrens zur Herstellung eines Kurzschlussläufers.

Show it:

• 1a -c a squirrel-cage rotor with straight rotor bars;
• 2a , b schematically shows an embodiment of a squirrel cage with rotor bars with offset sections; and
• 3 a schematic representation of an embodiment of a method for producing a squirrel-cage rotor.

In practice, squirrel-cage rotors can be used in particular in asynchronous machines (ASM). In order to develop a desired power density in an ASM, the aim is for the conductor bars/rotor bars/induction bars of the squirrel-cage rotor to have as large an overlap area as possible with the teeth of a stator of the ASM and for there to be as little or no angular offset as possible between the teeth and rotor bars, as this would reduce an induction current and thus power generation. During operation of asynchronous machines, fluctuations in the force excitation of the rotor bars occur. These fluctuations in the force excitation in turn cause disturbing acoustic excitation. In order to reduce the fluctuation, a continuous slant of the rotor bars can be provided, although this is associated with an impairment of the power density.

Electrical machines therefore provide a squirrel-cage rotor with straight slots, as can be seen from 1a , 1 b and 1c is explained in more detail.

1a shows a perspective oblique view of a squirrel-cage rotor 100 with a laminated core 120 and a squirrel-cage 110 connected thereto. Furthermore, the squirrel-cage rotor 100 provides a shaft 130 for power transmission.

As can be seen from a perspective oblique view of the squirrel cage 110 in 1b and a representation of the squirrel cage 110 in a plan view in 1c perpendicular to an axial direction 142 and a circumferential direction 141, the squirrel cage 110 comprises a plurality of rotor bars 112 which are distributed over a circumference of the squirrel cage 110. It is understood that the circumferential direction 141 in practice runs in an arc along a circumference of the squirrel cage 100, but is shown schematically as straight for the sake of simplicity. As shown, the rotor bars 112 are arranged next to one another and parallel in the circumferential direction 141. The rotor bars 112 run straight and parallel to the axial direction 142. There is therefore no offset within the rotor bars 112.

Furthermore, the short-circuit cage 110 comprises a first short-circuit ring 114-1 and a second short-circuit ring 114-2, which connect the rotor bars 112 to one another at respective opposite ends of the rotor bars 112 in an axial direction 142 in order to produce a short circuit between the rotor bars 112.

To connect the short-circuit cage 110 with the laminated core 120, the laminated core 120 Grooves for receiving the rotor bars 112. The rotor bars 112 are arranged accordingly in the grooves of the laminated core 120. The grooves are straight according to the course of the rotor bars 112 and also run parallel to the axial direction 142.

When the squirrel-cage rotor 100 is used in an electrical machine, the distances between the rotor bars 112 usually result in an uneven force effect of a stator magnetic field of the electrical machine on the rotor bars 112 during operation of the electrical machine. This results in force fluctuations and a torque ripple as well as acoustic excitations, which lead to undesirable noise during operation of the electrical machine.

With reference to further figures, an improved squirrel-cage rotor is therefore explained here, which enables a quieter motor operation of electrical machines.

In order to improve force fluctuations and thus in particular the acoustics, a so-called rotor staging is proposed in an electrical machine, e.g. an ASM. The concept explained here can therefore be understood in particular as an approach to realizing a rotor-side stepped offset to reduce noise excitation of an electrical induction power machine.

2a and 2 B show an embodiment of a squirrel cage 200 with rotor bars 220 with offset sections. 2a shows a perspective oblique view of the squirrel cage 200. 2 B shows a plan view perpendicular to an axial direction 242 and a circumferential direction 241. It is understood that the circumferential direction 241 in practice runs in an arc along a circumference of the squirrel cage 200 and is shown schematically in a straight line for the sake of simplicity.

As can be seen, the squirrel cage 200 comprises a plurality of rotor bars 220, which are distributed over a circumference of the squirrel cage 200. The rotor bars 220 are arranged next to one another and parallel in the circumferential direction 241. It is understood that the squirrel cage 200 can comprise any number of rotor bars in exemplary embodiments. In practice, the squirrel cage 200 is arranged in a squirrel cage (not shown). In exemplary embodiments, the squirrel cage comprises, for example, a laminated core (not shown) with grooves for receiving the rotor bars 220.

Furthermore, the short-circuit cage 200 comprises a first short-circuit ring 210-1 and a second short-circuit ring 210-2, which connect the rotor bars 220 to one another at opposite ends of the rotor bars 220 in the axial direction 242 (“front side”) in order to produce a short circuit between the rotor bars 220. In other embodiments, the short-circuit cage 200 can also comprise only a single or more than two short-circuit rings. As the person skilled in the art will understand, the short-circuit rings 210-1 and 210-2, like the rotor bars 220, consist at least partially of an electrically conductive material or an electrical conductor.

The rotor bars 220 have at least a first section 221 and a second section 222. The first section 221 and the second section 222 are arranged adjacent to one another in the axial direction 242 and run parallel to the axial direction 242. In other embodiments, the sections 221 and 222 can also run obliquely to the axial direction.

Furthermore, the first and second sections 221 and 222 have an offset 224 in the circumferential direction 241 of the squirrel cage 200. The first section 221 and the second section 222 are thus arranged offset from one another in relation to the circumferential direction 241 and are connected to one another via a connecting section 223 of the respective rotor bar. The respective rotor bar thus has at least one step in the circumferential direction 241. In embodiments, the offset can be provided for any part of the rotor bars 220 or all of the rotor bars 220. As in 2a and 2 B As can be seen, in the case of a plurality of offset rotor bars 220, the first and second sections 221 and 222 can each be offset in the same direction and/or by the same amount. Alternatively, the sections 221 and 222 of the rotor bars 220 can be alternately offset from one another in opposite directions.

In the present case, the connecting section 223 runs, for example, along the circumferential direction 241. For this purpose, the first and second sections 221 and 222 can overlap in the axial direction 242. In alternative embodiments, the connecting section 223 can also run obliquely to the circumferential direction 241.

In practice, sheets of the laminated core each have a plurality of recesses which are arranged in alignment with one another or at least overlapping one another in the circumferential direction 241 in order to form grooves for the sections 221 and 222 in the axial direction 242. This the groove sections for the sections 221 and 222 are formed, which extend in the axial direction 242 over several sheets of the laminated core.

To form a step of the groove for the offset 224, the recesses can be arranged offset by the intended offset of the sections 221 and 222 in the circumferential direction 241.

To form the step for the connecting section 223, the recesses in the area provided for the connecting section 223 have a greater extension in the circumferential direction 241 than in the area of the first and second sections 221 and 222. In practice, the recesses for the first and second sections 221 and 222 can be semicircular, for example, and the recesses for forming the connecting section 223 can be shaped like a half oval stretched in the circumferential direction 241. However, other shapes can also be considered for the recesses, for example a square shape.

It should be noted that the offset 224 can be provided at any point on the rotor bar. For the most complete compensation possible, the offset 224 can be provided centrally between the ends of the rotor bar in the axial direction or centrally between the short-circuit rings 210-1 and 210-2. In the present case, the sections 221 and 222 are therefore, for example, the same length.

During operation, an electric current is induced in the rotor bars 220. A problem with the proposed grading in the rotor arises from a possible cross-sectional tapering in the step area or connecting section 223, which results in current maxima and thus undesirable thermal hotspots in the squirrel-cage rotor. In order to prevent temperature maxima in the area of the connecting section 223, it can be provided that a cross-sectional area of the connecting section 223 (in the circumferential direction 241) is greater than or equal to a cross-sectional area of the first and/or second section 221 and/or 222. The cross-sectional area of the rotor bars 220 can be limited by the respective groove. In practice, the rotor bars 220 are cast into the grooves, for example. It is therefore understood that the grooves can be adapted accordingly.

The cross-sectional area of the groove is determined by the shape of the recesses for the connecting section 223 and by a number of sheets with recesses for the connecting section and/or their extension in the axial direction 242. The grooves can therefore be adapted accordingly to the intended cross-sectional area of the sections 221 and 222 and to the intended cross-sectional area of the connecting section 223.

In addition, the offset in the circumferential direction 241 or a width (e.g. angle, radian, length) by which the sections 221 and 222 are offset in the circumferential direction 241 can be determined arbitrarily. Force fluctuations that act on the sections 221 and 222 during operation can compensate each other more or less depending on the width of the offset. In other words, the width of the offset determines to what extent or to what extent the force fluctuations compensate each other. In embodiments, the offset is dimensioned such that force fluctuations that act on the first and second sections during operation of the squirrel-cage rotor at least partially compensate each other. Ideally, the offset is dimensioned such that the force fluctuations compensate each other almost completely (within the scope of manufacturing-related tolerances).

In practice, the force fluctuations can oscillate periodically. The offset can then be dimensioned for complete mutual compensation so that the force fluctuations acting on the first and second sections 221 and 222 are 180° out of phase with each other. The force fluctuations then act in opposite directions and can thus cancel each other out. This can prevent acoustic excitations and the associated noise when operating an electrical machine with a squirrel cage rotor.

For this purpose, the width of the offset in the circumferential direction 241 can be equal to half of a (center) distance to an adjacent rotor bar or its first or second section. As the person skilled in the art will appreciate, a different width can optionally be selected, taking into account a harmonic excitation of the stator magnetic field, so that the force fluctuations acting on the first and second sections 221 and 222 are 180° out of phase with each other and thus completely compensate each other.

In embodiments, multiple gradations of one or more rotor bars can optionally be provided.

For this purpose, a rotor bar has, for example, at least a third section, which has an offset in the circumferential direction of the squirrel-cage rotor compared to the first and/or second section. Features of the offset between the sections 221 and 222 can The offset of the third section should be implemented in an analogous manner.

The squirrel cage rotor 200 proposed here can be manufactured using a corresponding manufacturing process. Such a manufacturing process is described below by way of example using 3 explained in more detail.

3 shows a schematic representation of an embodiment of a method 300 for producing a squirrel-cage rotor.

The method 300 includes providing 310 a squirrel cage with at least one short-circuit ring and a plurality of rotor bars. As already explained, at least one of the rotor bars has at least a first and a second section, which are offset from one another in a circumferential direction of the squirrel cage. Optionally, it has additional features which are described in connection with the squirrel cage described above.

In practice, the squirrel cage is connected to a laminated core. As already explained, the laminated core has grooves to accommodate the rotor bars. The laminated core can be connected to a shaft for power transmission.

Optionally, at least one of the grooves has a first and a second groove section, which are offset from one another in the circumferential direction. The rotor bar with offset sections can then be produced using a casting process in which the at least one groove serves as a casting space for the rotor bar. For this purpose, a material of the rotor bar can be liquefied and poured into the groove in liquid form and hardened there. As the person skilled in the art will understand, the liquid material adapts to the groove during the casting process, whereby an offset is formed in the rotor bar according to the present explanations.

In practice, the material of the rotor bar can be an electrically conductive material, such as copper, brass, bronze, aluminum or other electrically conductive metals. The laminated core can therefore be designed for the casting process to be resistant to the melting temperature of the material for the rotor bars, at least in the area of the slots.

Alternatively, the runner bar can also be inserted into the groove in a solid form. For this purpose, the runner bar can be pre-formed, whereby the offset is introduced into the runner bar. For this purpose, the runner bar is, for example, cast, bent or cut out accordingly beforehand.

As the person skilled in the art will understand, the squirrel-cage rotor can be used in all electrical machines that are designed for operation with a squirrel-cage rotor. In particular, the squirrel-cage rotor can be used in asynchronous machines. Accordingly, embodiments of the present disclosure provide an electrical machine comprising a squirrel-cage rotor according to the present disclosure. Examples of the electrical machine can be provided for different purposes. In particular, examples of the electrical machine can be provided for driving machines, e.g. (motor) vehicles.

Embodiments therefore relate to a vehicle comprising an electric machine according to the present disclosure.

Reference symbols

100

Squirrel cage rotor

110

Squirrel cage

112

Runner bars

114-1

Short-circuit ring

114-2

Short-circuit ring

120

Sheet metal package

130

Wave

141

Circumferential direction

142

axial direction

200

Squirrel cage

210-1

Short-circuit ring

210-2

Short-circuit ring

220

Runner bars

221

first section

222

second part

223

Connecting section

224

Offset

241

Circumferential direction

242

axial direction

300

Proceedings

310

Providing a squirrel cage

Claims (10)

A squirrel-cage rotor for an electrical machine, the squirrel-cage rotor comprising: a squirrel cage (200) with a plurality of rotor bars (220) and at least one short-circuit ring (210-1, 210-2) for connecting the rotor bars, wherein at least one of the rotor bars has at least a first and a second section (221, 222), wherein the first and the second section have an offset (224) from one another in a circumferential direction (241) of the squirrel-cage rotor. The squirrel-cage rotor according to Claim 1 , wherein the offset in the circumferential direction is dimensioned such that force fluctuations acting on the first and second sections during operation of the squirrel-cage rotor are at least partially compensated. The squirrel-cage rotor according to Claim 2 , whereby the force fluctuations oscillate periodically and the offset is dimensioned such that the force fluctuations acting on the first and second sections are 180° out of phase with each other. The squirrel-cage rotor according to one of the preceding claims, wherein a cross-sectional area of a connecting portion (223) for connecting the first and second portions is at least as large as a cross-sectional area of the first or second portion. The squirrel-cage rotor according to one of the preceding claims, wherein the first section and/or the second section extend obliquely or parallel to an axial direction (242) of the squirrel-cage rotor. The squirrel-cage rotor according to one of the preceding claims, wherein the rotor bar has at least a third section, wherein the third section has an offset in the circumferential direction of the squirrel-cage rotor with respect to the first and second sections. An electrical machine comprising a squirrel-cage rotor according to any one of the preceding claims. A vehicle comprising an electric machine according to Claim 7 . A method (300) for producing a squirrel-cage rotor, the method comprising: Providing (310) a squirrel cage with at least one short-circuit ring and a plurality of rotor bars, wherein at least one of the rotor bars has at least a first and a second section, wherein the first and the second section have an offset from one another in a circumferential direction of the squirrel-cage rotor. The procedure according to Claim 9 , the provision of the squirrel cage comprising: providing a laminated core with at least one groove, which has a first and a second groove section, which are offset from one another in the circumferential direction; and producing the rotor bar using a casting process, wherein the at least one groove serves as a casting space for the rotor bar in the casting process.

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