ROTOR FOR AN ELECTRIC MACHINE

A rotor for an electric machine includes at least one inner sheet package arranged on a rotor shaft defining a rotor longitudinal axis and buried magnets arranged radially around the at least one inner sheet package, which are arranged in a radial direction between the inner sheet package and correspondingly arranged outer sheet packages and fixed by a casting compound. The rotor further includes a plurality of surface magnets arranged on the outer sheet packages, each surface magnet forming a rotor pole in conjunction with a respective one of the outer sheet packages on which it is arranged and at least one of the buried magnets. At least one cooling channel extending along the rotor longitudinal axis is arranged in at least one of the inner or outer sheet packages and is sealed by a casting compound in a medium-tight manner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit to German Patent Application No. DE 10 2023 103 617.3, filed on Feb. 15, 2023, which is hereby incorporated by reference herein.

FIELD

The invention relates to a rotor for an electric machine and a method for producing the rotor according to the invention.

BACKGROUND

Various rotor topologies are presented in the prior art for electric machines, in particular for use in motor vehicles. A rotor topology with so-called buried magnets, which are provided in pockets or cavities within a rotor core, has proven to be advantageous with regard to efficiency.

FIGS.1aand1bshow schematic views of such a rotor topology known from the prior art.FIG.1ashows a perspective view of the embodiment, whileFIG.1bshows a cross-sectional view perpendicular to a rotor longitudinal axis x of the same embodiment in a detailed view. The rotor1comprises a rotor shaft2oriented along the rotor axis x. An inner sheet package11is arranged on the rotor shaft2, which has a star-shaped cross-section (perpendicular to the rotor longitudinal axis x). In the recesses of the star-shaped cross-section, buried magnets41are arranged in a v-shape, wherein the inner sheet package11comprises corresponding pockets and cut-outs for receiving the buried magnets41at the corresponding positions. These are then fixed to the corresponding positions with a casting compound50.

In the recesses of the star-shaped cross-section of the inner sheet package11, outer sheet packages12are arranged in the radial direction starting from the rotor shaft2on the buried magnets41, which in turn receive surface magnets42in recesses provided for this purpose. A rotor pole1ais located at the positions where the surface magnets42are arranged, so that the embodiment shown inFIGS.1aand1bhas six rotor poles1a.A rotor drum30is arranged in the radial direction of the rotor1on the very outer side, which surrounds the rotor1along the circumference and holds the sheet packages11,12and the magnets41,42together even at high revolutions and the resulting large centrifugal forces. The rotor drum30can be composed of different segments. In addition, cavities13can be provided in the sheet packages11,12for heat dissipation (cooling) and for reducing the mass.

The sheet packages11,12are made up of individual sheets, which are connected to one another. The inner sheet package11can be composed of a plurality of individual packages, which are connected to one another in either the circumferential direction or the longitudinal direction of the rotor1. In the context of the application, however, only an inner sheet package11is referred to and in the process, it is not differentiated whether it was composed of different segments or individual packages or only the corresponding cut-out sheets were connected to one another. The magnets41,42can also be produced from a plurality of individual magnets, which together form a magnetic unit or consist only of a single magnet. In the context of this application, both variants are subsumed under the term “magnet”.

In the development of electric motors, attention is paid to cooling, i.e., the heat dissipation from the sheet packages and the rotor. For this purpose, patent specification DE 10 2017 124 471 A1 discloses a rotor with encapsulated permanent magnets, wherein cooling channels are located in the casting compound. The cooling medium is moved from the radial inside to the radial outside of the rotor using centrifugal force.

The patent document JP 2012 139 074 A also discloses a rotor with cast permanent magnets, wherein cooling channels are located in the casting compound. A similar arrangement is also known from the patent document JP 2013 017 297 A, wherein a cooling channel is configured in a magnetic pocket specially formed for this purpose, which is sealed to the sheet package by a casting compound. The cooling medium is in direct contact with the magnet on one side.

SUMMARY

In an embodiment, the present disclosure provides a rotor for an electric machine comprising at least one inner sheet package arranged on a rotor shaft defining a rotor longitudinal axis and buried magnets arranged radially around the at least one inner sheet package, which are arranged in a radial direction between the inner sheet package and correspondingly arranged outer sheet packages and are fixed by a casting compound. The rotor further comprises a plurality of surface magnets arranged on the outer sheet packages, wherein each surface magnet forms a rotor pole in conjunction with a respective outer sheet package of the outer sheet packages on which it is arranged and at least one of the buried magnets. At least one cooling channel extending along the rotor longitudinal axis is arranged in at least one of the inner or outer sheet packages and is sealed by a casting compound in a medium-tight manner against the at least one of the inner or outer sheet packages in which it is located.

DETAILED DESCRIPTION

In an embodiment, the present invention provides a rotor for an electric machine, which has an alternative option for cooling the rotor. A method for producing the rotor according to embodiments of the invention is also provided. An electric machine comprising the rotor according to embodiments of the invention can be provided for use as a vehicle drive in a motor vehicle. Such an electric machine can thereby be used as an electric motor as well as an electric generator.

The rotor for an electric machine according to an embodiment of the invention comprises at least one inner sheet package arranged radially around a rotor shaft defining a rotor longitudinal axis, wherein buried magnets are arranged radially around the inner sheet package, which are arranged in a radial direction between the inner sheet package and correspondingly arranged outer sheet packages and fixed by a casting compound. Furthermore, the rotor according to an embodiment of the invention comprises a plurality of surface magnets, which are arranged on the outer sheet packages, preferably in recesses provided for this purpose in the outer sheet packages. Each surface magnet defines a rotor pole in conjunction with an outer sheet package on which it is arranged and at least one buried magnet. Preferably, a rotor drum surrounding the sheet packages and surface magnets in the circumferential direction is provided. According to an embodiment of the present invention, at least one cooling channel is arranged in at least one sheet package, which extends along the rotor longitudinal axis and is sealed against the sheet package in which it is located by a casting compound preferably made of plastic in a media-type manner. The cooling channel is preferably completely surrounded by the sheet package. Furthermore, preferably, the casting compound in the cooling channel corresponds to the casting compound for fixing the buried magnets. In the context of this application, the term “sealed against the sheet package in a media-tight manner” means that no medium, such as in particular a cooling liquid, can escape from the cooling channel in its radial direction and thus penetrate into the sheet package. The casting compound is therefore to be understood as a seal for the cooling channel.

A cooling medium can therefore flow through the configured cooling channel, which absorbs heat from the rotor and removes it from the rotor. Cooling can therefore reduce the temperature of the magnets and the sheet packages, which has a positive effect on the efficiency of the motor and in particular its continuous performance and the service life of the magnets and therefore the motor. The resulting improved thermal connection of the magnets to the cooling system can also be used in particular to deploy magnets with a lower proportion of heavy rare earths. These are less temperature stable.

In an advantageous embodiment of the invention, the cooling channel is configured to direct a cooling medium, in particular a cooling liquid, from a first balancing disk to a second balancing disk of the rotor, wherein the balancing disks are arranged on two opposite faces of the rotor in the direction of the rotor longitudinal axis. In other words, the cooling channel represents a continuous connection of the two end faces of the rotor, such that a cooling medium can enter on the one end face of the rotor and exit on the opposite end face, such that the two balancing disks are fluidically connected to each other. In this way, it can be ensured that the magnets, which also extend along the rotor longitudinal axis, are fully cooled in order to thus increase the effect of cooling.

In an advantageous embodiment of the invention, the first balancing disk comprises at least one cooling channel inlet configured to receive a cooling medium and direct it into the at least one cooling channel, and the second balancing disk comprises a cooling channel outlet configured to collect the cooling liquid from the cooling channel and discharge it from the rotor. Thus, the cooling medium enters one side of the rotor in the direction of the rotor longitudinal axis, is heated by the rotor heat and exits the other side of the rotor. In this way, a high cooling capacity can be ensured. In an embodiment, two cooling channels are provided, wherein the one cooling channel conveys a cooling medium from one direction to the other, and the other cooling channel conveys a cooling medium in the opposite direction, such that both balancing disks have both a cooling channel inlet and a cooling channel outlet. Preferably, the balancing disks have at least one radially outwardly extending cooling channel per rotor pole, such that the cooling medium is distributed in the balancing disk in a star shape from the inside out.

In an embodiment of the invention, the rotor comprises at least two cooling channels, wherein a balancing disk has a cooling channel inlet and a cooling channel outlet, and furthermore the second balancing disk has a cooling medium guide, which is configured to transfer the cooling medium from one cooling channel to another cooling channel of the rotor. In this way, the cooling medium is guided through the rotor twice, allowing it to absorb more heat and reducing the amount of cooling medium required. The cooling channel inlet and the cooling channel outlet are arranged on the same balancing disk.

In an advantageous embodiment of the invention at least one cooling channel is arranged in at least one outer sheet package. As the outer sheet packages are located between the surface magnets and the buried magnets, the heat load is greatest here, whereby cooling by means of the cooling channel has the greatest effect.

In an embodiment of the invention, at least one cooling channel is arranged in at least one inner sheet package.

Furthermore, in addition to at least one cooling channel in the sheet packages, at least one further cooling channel is arranged in the casting compound for fixing the buried magnets. In this way, the heat dissipation from the rotor can be further increased, thus increasing the cooling capacity.

In an embodiment of the invention, the casting compound in the at least one cooling channel in the sheet packages has a thickness of between 0.2 mm and 0.5 mm. With such a wall thickness, sufficient media tightness of the cooling channel can be ensured, wherein the cross-section of the cooling channel is not constricted too much at the same time. In addition, a sufficiently high heat transfer from the sheet packages to the cooling medium is ensured with such a thickness of the casting compound in this area.

In an embodiment of the invention, the at least one cooling channel in a sheet package has a trapezoidal, preferably additionally symmetrical, cross-section. In an embodiment, one side of the trapezoid is shorter than the other. Preferably, this is an embodiment in which the shorter side of the trapezoid faces outwards in the radial direction of the rotor. Such a cross-sectional shape can ensure that the guidance of the magnetic flux in the sheet packages is influenced as little as possible.

The method according to an embodiment of the invention for producing a rotor comprises several steps. First, an inner sheet package and a number of outer sheet packages corresponding to the number of poles are provided for this purpose. The provision comprises cutting out the sheets and assembling them into the corresponding sheet packages. According to a further method step, at least one cooling channel is cut into the inner sheet package and/or the outer sheets package in the finished sheet packages or in the individual sheets. The method step of cutting out the cooling channel can therefore take place during the method step of preparing the sheet packages when the cooling channel is cut out in the individual sheets and the sheets are subsequently brought together to form a sheet package. The cooling channel is cut out in such a way that the cooling channel, when assembled, directs a cooling medium from one end face of the rotor to an opposite end face of the rotor in the direction of the rotor longitudinal axis. Furthermore, the sheet packages are arranged together with buried magnets and surface magnets on a rotor shaft, such that the buried magnets are positioned between the inner sheet package and the outer sheet packages, and the surface magnets are arranged on the outer sheet packages. In a further method step, a rotor drum is preferably arranged around the sheet packages and the surface magnets, such that the rotor drum surrounds the sheet packages and the surface magnets in the circumferential direction. Furthermore, the buried magnets are fixed in their positions by a casting compound. Furthermore, the at least one cooling channel is lined with a casting compound. This should be understood to mean that the cooling channel is sealed from the sheet packages by the casting compound in a media-tight manner, such that a cooling medium flowing through the cooling channel does not enter the sheet packages. The casting compound used for this purpose preferably corresponds to the casting compound which is also used to fix the buried magnets.

An embodiment of the method according to the invention further comprises the method step according to which at least one further cooling channel is formed in the casting compound for fixing the buried magnets. In this way, the cooling effect can be further improved.

At this point, it should be noted that the embodiments of the device, i.e., the rotor, which are considered as advantageous embodiments, are hereby disclosed as preferred embodiments of the method according to the invention. Thus, the explained embodiments regarding the design of the cooling channel or the placement of the cooling channel as well as regarding the design of the balancing disks are also disclosed as corresponding advantageous embodiments of the method according to the invention.

In the following, advantageous aspects and embodiments of the invention will now be explained in further detail with reference to the accompanying figures.

FIGS.1aand1bhave already been discussed in further detail in the description of the prior art, for which reason at this point a further description of the figures will be omitted.

FIG.2shows a cross-sectional view perpendicular to the rotor longitudinal axis x of a first embodiment of the rotor1according to an embodiment of the invention. The rotor topology of the rotor1corresponds substantially to the rotor topology of the rotor1described in view ofFIGS.1aand1b. Thus, only the differences are discussed at this point.

In contrast to the rotor1shown inFIGS.1aand1b, the embodiment of a rotor1according to an embodiment of the invention according toFIG.2has six cooling channels20, which extend along the rotor longitudinal axis x (seeFIG.1a) through the rotor1from one end face to the other end face of the rotor1. A cooling channel20is provided on each rotor pole1a, which is cut into the corresponding outer sheet package12of the respective rotor pole1a. According to the method according to an embodiment of the invention, the cooling channels20are already cut into the outer sheet packages12during cutting out (preparation, e.g., punching) or during cutting out the of individual sheets.

The cooling channel20comprises a sealing layer21arranged on the cooling channel wall and made of a casting compound50. This preferably has a thickness of between 0.2 mm and 0.5 mm and seals the cooling channel20against the corresponding outer sheet packages12in a media-tight manner. Thus, a cooling medium directed through the cooling channels20cannot penetrate into the sheet packages12.

The cooling channels20further have a trapezoidal cross-section, wherein the sides of the trapezoid are rounded. In the context of this application, a trapezoidal cross-section is thus also to be understood as a trapezoid with round sides and rounded corners. The trapezoid has a long side and a short side and is also symmetrical. The legs connecting the sides of the trapezoid are the same length and also rounded. Since the cooling channels20have a different magnetic resistance than the outer and inner sheet packages11,12, this affects the guidance of the magnetic flux. By means of a described cross-sectional shape of the cooling channels20, it can be ensured that the guidance of the magnetic flux through the outer sheet packages12through the cooling channels is influenced as little as possible. Other cross-sectional shapes, such as oval, circular, triangular, rounded triangular, can also be provided, wherein the shape is preferably adapted to the position of the corresponding cooling channel20.

FIG.3shows an embodiment of a rotor1according to the invention, wherein the view corresponds to that ofFIG.2. The embodiment according toFIG.3corresponds to the embodiment according toFIG.2as far as possible, therefore only the differences between the two embodiments are discussed at this point.

In contrast to the embodiment shown inFIG.2, the embodiment according toFIG.3has further cooling channels20in the inner sheet package11instead of the cavities13. These are shaped the same as the cooling channels20in the outer sheet packages12and also have a corresponding sealing layer21made of a casting compound50. The cooling channels20in the inner sheet package11are arranged offset to the cooling channels20in the outer sheet packages12, and are thus positioned in the triangular jets of the star-shaped cross-section of the inner sheet package11between the buried magnets41of two rotor poles1a.With the embodiment shown, the cooling capacity can be significantly improved compared to the embodiment according toFIG.2and the temperature is kept constant in both the outer sheet packages12and the inner sheet package11.

FIG.4shows an embodiment of a rotor1according to the invention, wherein the view corresponds to that ofFIG.2. The embodiment according toFIG.4corresponds to the embodiment according toFIG.2as far as possible, therefore only the differences between the two embodiments are discussed at this point.

In contrast to the embodiment shown inFIG.2, the embodiment according toFIG.4has further cooling channels20in the casting compound50at the radially outer end of the rotor1upstream of the rotor drum30for fixing the buried magnets41. The additional cooling channels20can thereby ensure better cooling of the rotor1and thus further increase the cooling capacity. In the embodiment shown, the cooling channels20have a round cross-sectional shape, although other cross-sectional shapes can also be provided.

FIG.5shows an embodiment of a rotor1according to the invention, wherein the view corresponds to that ofFIG.4. The embodiment according toFIG.5corresponds to the embodiment in accordance withFIG.4as far as possible, wherein only further cooling channels20are provided in the casting compound50for fixing the buried magnets41. These cooling channels20are arranged between two buried magnets41of a rotor pole1aarranged in a v-shape. In this way, the cooling performance can be further improved.

It should be noted that any combination of the embodiments shown according toFIGS.2to5are also within the scope of the invention.

FIG.6shows an embodiment of the rotor1according to the invention.FIG.6shows a rotor1according to an embodiment of the invention with at least four cooling channels20, which are shown in cross-section in the rotor longitudinal direction x. Two cooling channels20are arranged radially further inside the rotor1than two further cooling channels20, wherein the rotor1is symmetrical in relation to the rotor longitudinal axis x. The rotor1rotates in a stator4and has a first balancing disk3aon one end face and a second balancing disk3bon the opposite end face.

The first balancing disk3acomprises a cooling channel inlet22. A cooling medium flows into the rotor1through the cooling channel input22and is distributed to the cooling channels22. The second balancing disk3b,on the other hand, has a cooling channel outlet23and collects the cooling medium directed through the cooling channels20and guides it out of the rotor1. It is also possible to reverse the flow direction of the cooling medium and thus arrange the cooling channel inlet22in the second balancing disk3band, correspondingly, the cooling channel outlet23in the first balancing disk3a.

It should be noted that such a guidance of the cooling medium could be implemented, for example in one of the embodiments according toFIG.2,3,4or5.

An embodiment is also provided in which both the first balancing disk3aand the second balancing disk3beach have a cooling channel inlet22and a cooling channel outlet23and thus the cooling medium is guided through the rotor1in different cooling channels20in opposite directions. In this way, uniform cooling of the rotor1could be ensured.

FIG.7shows an embodiment of a rotor1according to the invention, wherein the view corresponds to that ofFIG.6. The embodiment according toFIG.7corresponds to the embodiment according toFIG.6as far as possible, therefore only the differences between the two embodiments are discussed at this point.

In contrast to the embodiment shown inFIG.6, the first balancing disk3ain the embodiment according toFIG.7comprises both the cooling channel input22and the cooling channel output23. The cooling medium is therefore introduced into the first balancing disk3aand introduced on two of the four cooling channels20in the sheet packages11,12. The second balancing disk3bhas a cooling medium guide, which receives the cooling medium from the two filled cooling channels20and directs it into the two other cooling channels20, whereby the cooling medium is guided back to the first balancing disk3aand is discharged again there through the cooling channel outlet23.

The cooling medium is therefore passed twice through the rotor1and can therefore absorb a greater amount of energy in the form of heat. In this way, less cooling medium needs to be used to dissipate heat. In addition, the embodiment is suitable for installation situations of the rotor in which the coolant can only be supplied and discharged from one side of the rotor. It should be noted at this point that this embodiment of the cooling medium guide can also be applied to the embodiments according toFIGS.2,3,4and5.

Which of the two embodiments of the cooling medium guide shown inFIGS.6and7is better depends on the heat output to be dissipated and the design of the cooling channels20. Based on the embodiment shown inFIG.6, more heat can be dissipated due to the greater temperature difference between the cooling medium and the rotor if it is assumed that the cooling channels20individually and the sum of the cooling channels20can carry the same amount of cooling medium. However, such an embodiment results in an uneven heat transfer to the cooling medium, as the temperature difference in the inlet area of the cooling channels20is greater than in the outlet area of the cooling channels, as the longer the cooling medium remains in the cooling channel20, the more heat is absorbed by the cooling medium and therefore the temperature difference between the sheet package decreases.

However, according to the embodiment of the cooling medium guide shown inFIG.7, a lower amount of cooling medium can be used, which is advantageous when used in a motor vehicle as less mass must be transported.