Rotor for a permanent magnet synchronous machine of a motor vehicle, motor vehicle and method for manufacturing a rotor

Abstract

The invention relates to a rotor (16) for a permanent magnet synchronous machine (12) of a motor vehicle (10), with a rotor body having a plurality of recesses, wherein respective permanent magnets (18) are arranged in the recesses, wherein in a first region (20) of the rotor (16), for which a higher temperature development during operation of the rotor (16) is predicted, permanent magnets (18) with a higher concentration of heavy rare earth elements are arranged than in a second region (22) of the rotor (16), for which a comparatively lower temperature development is predicted.

Description

[0001] The invention relates to a rotor for a permanent excitation synchronous machine of a motor vehicle, a motor vehicle and a method for manufacturing a rotor.

[0002] US patent 10 242 778 B2 discloses a manufacturing process for a rare-earth magnet based on the heat treatment of a fine powder.

[0003] Furthermore, US Patent 9,154,004 B2 discloses a sintered rare-earth magnet comprising a sintered rare-earth magnet core. This rare-earth magnet can be used in the rotor of a motor which, in addition to the rotor, has a stator with a plurality of stator windings.

[0004] The object of the present invention is to provide a solution which enables the provision of a permanent excitation rotor which has a particularly high performance and for whose permanent magnets there is a particularly low risk of demagnetization.

[0005] This problem is solved according to the invention by the subject matter of the independent claims. Further possible embodiments of the invention are disclosed in the dependent claims, the description, and the figures. Features, advantages, and possible embodiments set forth in the description for one of the subject matter of the independent claims are to be regarded, at least analogously, as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as of any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the dependent claims.

[0006] The invention relates to a rotor for a permanent magnet synchronous machine of a motor vehicle. The permanent magnet synchronous machine is, in particular, an electric traction machine of the motor vehicle, designed to propel the vehicle using electrical energy. In addition to the rotor, the permanent magnet synchronous machine can include a stator, relative to which the rotor can be rotated about an axis of rotation during operation. A synchronous machine is a rotating electric machine in which the rotor rotates synchronously with the rotating magnetic field of the stator. In the permanent magnet synchronous machine, the rotor carries permanent magnets for excitation. The use of permanent magnets results in a constant excitation field. The rotor comprises a rotor body with a plurality of recesses, in which individual permanent magnets are arranged.A permanent magnet is a magnet made from a single piece of hard magnetic material, such as alloys of iron, cobalt, nickel, or certain ferrites. A permanent magnet has and maintains a constant magnetic field without requiring electrical power, unlike electromagnets. To protect permanent magnets from demagnetization at elevated temperatures, heavy rare earth elements are used. Adding these elements increases the coercive field strength. However, heavy rare earth elements also reduce the remanence and thus the performance of the permanent magnet. Therefore, there is a trade-off between protecting permanent magnets from demagnetization and the reduction in remanence and performance resulting from the use of heavy rare earth elements. Furthermore, heavy rare earth elements are expensive.

[0007] To minimize the risk of demagnetization of the permanent magnets and to achieve particularly high performance and remanence, the design proposes that permanent magnets with a higher concentration of heavy rare earth elements be used in a first section of the rotor, where higher operating temperatures are predicted, compared to a second section where lower temperatures are expected. It is possible that the permanent magnets in the second section could be completely free of heavy rare earth elements.The heavy rare earth elements, or rather a higher concentration of heavy rare earth elements, are thus only used in the permanent magnets located in the first region, which is expected to be exposed to higher temperatures during operation. This is to protect these permanent magnets particularly well from demagnetization during operation due to high temperatures. In the described rotor, demagnetization of permanent magnets in risk areas can be particularly well prevented by adding heavy rare earth elements, or by increasing their concentration compared to other permanent magnets. This enables the permanent magnets in the first region to withstand a stator opposing field particularly well, especially at high temperatures.

[0008] In a possible further development of the invention, the first region is located at a greater axial distance from the nearest end face of the rotor body than the second region. Thus, with respect to the axial direction, the first region is closer to the axial center of the rotor than the second region. Heat can be dissipated from the rotor via the respective end faces, which can, for example, be actively cooled. Therefore, the closer a given region is to an end face of the rotor, the lower the temperature development in that region during rotor operation. It is thus intended that permanent magnets located closer to a central region of the rotor with respect to the axial direction will have a higher concentration of heavy rare earth elements than permanent magnets located further away from this central region in the axial direction.The closer a permanent magnet is positioned to the axial center of the rotor, the greater the temperature stress it experiences during operation due to high heat generation. The increased use of heavy rare earth elements in permanent magnets positioned particularly far towards the center provides them with superior protection against demagnetization during operation.

[0009] In a further possible embodiment of the invention, a first permanent magnet arranged in the first region overlaps a second permanent magnet arranged in the second region, at least partially, in the axial direction. This means that the first and second permanent magnets are arranged one behind the other in the axial direction, at least partially. Thus, several permanent magnets arranged in a line in the axial direction can have different concentrations of heavy rare earth elements. The rotor therefore does not have permanent magnets with a uniform concentration of heavy rare earth elements extending axially from one end face to the other end face of the rotor body.If the rotor has several permanent magnets arranged in series along this axial line, which have different concentrations of heavy rare earths, the rotor can be manufactured with a particularly low use of heavy rare earths while simultaneously having a particularly low risk of demagnetization of the permanent magnets, since only those permanent magnets which are arranged in the first axial areas of the rotor, in which an increased temperature development is to be expected during operation compared to second axial areas, have an increased concentration of heavy rare earths compared to permanent magnets arranged in second areas.

[0010] In this context, it is particularly possible for the first and second permanent magnets to be axially aligned. This allows the two permanent magnets to extend together over a particularly large axial length of the rotor. Specifically, instead of a single permanent magnet extending the entire axial length of the rotor, several permanent magnets with varying concentrations of heavy rare earth elements, selected according to the predicted temperature development in specific areas of the rotor during operation, can be arranged axially one behind the other, forming a kind of composite magnet extending the entire length of the rotor. This allows a particularly large portion of the rotor's volume to be provided by permanent magnets.

[0011] In a further possible embodiment of the invention, the heavy rare earth elements are provided for in a uniform distribution within the respective permanent magnets or are concentrated in at least one edge region of the respective permanent magnet. In other words, when heavy rare earth elements are used in a respective permanent magnet, they can be added to a base mixture of the permanent magnet to be sintered for its production, thereby distributing the heavy rare earth elements uniformly within the permanent magnet produced by sintering the base mixture. Alternatively, the respective rare earth elements can be introduced, for example, by surface diffusion only into the edge region of the respective permanent magnet.Introducing the heavy rare earth elements into the edge region of the respective permanent magnet allows the permanent magnet to contain the heavy rare earth elements only in the edge regions that are heavily stressed during operation, or to have an increased concentration of heavy rare earth elements, thus keeping the total amount of heavy rare earth elements used in this permanent magnet particularly low.

[0012] The invention further relates to a motor vehicle with a permanent magnet synchronous machine, which is configured to drive the motor vehicle using electrical energy. The permanent magnet synchronous machine comprises a stator and a rotor that, during operation, is rotatable relative to the stator about an axis of rotation, as already described in connection with the rotor according to the invention. The use of heavy rare earth elements provides particularly good protection against demagnetization for the rotor's permanent magnets, which, due to their position within the rotor, are exposed to high temperatures during operation.Simultaneously, the rotor uses very few heavy rare earth elements because the permanent magnets located in the second section, which is exposed to lower operating temperatures compared to the first section, contain a lower concentration of heavy rare earth elements, or in some cases, no heavy rare earth elements at all. This allows for exceptionally high rotor performance and, consequently, high performance of the vehicle powered by the permanent magnet synchronous machine.

[0013] The invention further relates to a method for manufacturing a rotor with a rotor body and a plurality of recesses for a permanent magnet synchronous motor vehicle. The method provides that a temperature development of the rotor is predicted for operation. Furthermore, the method provides that first permanent magnets with a higher concentration of heavy rare earth elements are arranged in recesses of a first region of the rotor for which a higher temperature development has been predicted. It further provides that second permanent magnets with a lower concentration of heavy rare earth elements, or without heavy rare earth elements, are arranged in recesses of a second region of the rotor for which a lower temperature development has been predicted compared to the first region.In other words, the process determines which areas of the rotor are likely to be exposed to higher temperature developments and thus higher temperatures during operation, and permanent magnets which are to be arranged in these areas are particularly well protected against demagnetization by using heavy rare earth elements.

[0014] In a possible further development of the invention, it is provided that the temperature development of the rotor is predicted by means of a simulation. A simulation is a reproduction of real-world scenarios for the purpose of analyzing systems, in this case the rotor, whose behavior is too complex for a theoretical, formulaic treatment. Within the framework of the simulation, a model of the rotor is created, this model is subjected to various influencing factors, and the resulting behavior of the rotor is examined. Using the simulation, the temperature development of the rotor during operation can be predicted particularly easily, precisely, and cost-effectively.

[0015] In a further possible embodiment of the invention, the heavy rare earth elements are added to a base mixture to be sintered for the production of a first permanent magnet. This allows the heavy rare earth elements to be incorporated into the first permanent magnet particularly easily. By adding the heavy rare earth elements to the base mixture to be sintered for the first permanent magnet, a concentration of heavy rare earth elements within the magnet can be achieved that is at least substantially uniform. The risk of undesirable accumulation of heavy rare earth elements within the first permanent magnet can thus be kept particularly low.

[0016] In a further possible embodiment of the invention, the heavy rare earth elements are introduced into the respective first permanent magnet by surface diffusion. In surface diffusion, the heavy rare earth elements diffuse from an outer surface of the first permanent magnet into at least a surface layer of the first permanent magnet. This results in a higher concentration of heavy rare earth elements in the surface layer compared to other areas of the first permanent magnet, such as the central region.Through edge layer diffusion, the heavy rare earth elements can be selectively introduced into at least one edge region of the respective first permanent magnet, which, when this first permanent magnet is arranged in the rotor body of the rotor, is oriented towards the stator of the permanent excitation synchronous machine and is therefore exposed to an increased risk of demagnetization.

[0017] Further features of the invention may become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures themselves, can be used not only in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0018] The drawing shows in: Fig. 1. A schematic perspective view of a motor vehicle, as well as enlarged views of the respective permanent magnets of a rotor of a permanent magnet synchronous machine of the motor vehicle; and Fig. 2. A process diagram for a process for manufacturing the rotor.

[0019] In Fig. Figure 1 shows a schematic perspective view of a motor vehicle 10 with a permanent magnet synchronous machine 12. The permanent magnet synchronous machine 12 comprises a stator 14 and a rotor 16 which, during operation, is rotatable about an axis of rotation relative to the stator 14. The rotor 16, in turn, comprises a rotor body with a plurality of recesses, which in Fig. 1 is not explicitly shown. Permanent magnets 18 are arranged in the recesses of the rotor body, which are in Fig. 1 are shown enlarged. In the enlarged view, you can see in Fig. 1. The relative position of all permanent magnets 18 to each other in their positions arranged in the respective recesses can be identified. For clarity, only some of the permanent magnets 18 are marked with their corresponding reference numerals. It is provided that the rotor 16 is divided into different zone types depending on the temperature development predicted for the operation of the rotor 16. In this case, it is provided that the rotor 16 is divided into several different zone types, wherein in Fig. 1. Three different types of regions are specifically identified and explained below. The respective first regions 20 of the rotor 16 are exposed to the highest temperature development during operation. The respective second regions 22 are exposed to the second highest temperature development during operation. The respective third regions 24 are exposed to the third highest temperature development during operation. The higher the temperature development in a respective region, the greater the risk of demagnetization for the respective permanent magnets 18 arranged in that region. It is therefore provided that the permanent magnets 18 arranged in the first region 20 of the rotor 16 have a higher concentration of heavy rare earth elements than the respective second regions 22 of the rotor 16 and the respective third regions 24 of the rotor 16.Furthermore, it is provided that the permanent magnets 18 arranged in the second areas 22 have a higher concentration of heavy rare earth elements than the permanent magnets 18 arranged in the third areas 24. This means that the higher the predicted temperature development of a particular area of ​​the rotor 16 during operation, the higher the concentration of heavy rare earth elements is selected for the permanent magnets 18 arranged in that area. The heavy rare earth elements can be uniformly distributed within the respective permanent magnets 18 or concentrated in at least one edge region of the respective permanent magnet 18.

[0020] As in Fig. 1. The respective first areas 20 are located further away from the respective end faces 26 of the rotor 16 than the respective second areas 22 and the respective third areas 24. The more centrally a respective area is arranged with respect to the axial direction A of the rotor 16, the higher the temperature development predicted for that area during the operation of the rotor 16. As in Fig. As can be further identified, permanent magnets 18 arranged in different areas 20, 22, 24 can be arranged one behind the other in axial direction A and thus overlapping each other. In particular, a permanent magnet 18 of the first area 20 can be in direct axial contact with a respective permanent magnet 18 of the second area 22.

[0021] In Fig.Figure 2 shows a process diagram for a method for manufacturing the rotor 16. In the first process step V1, the temperature development for different areas of the rotor 16 is predicted for operation. This temperature development prediction can be made, in particular, by means of a simulation. In a second process step V2, permanent magnets 18 with different concentrations of heavy rare earth elements are produced. For the production of a particular permanent magnet 18, heavy rare earth elements can be added to a base mixture to be sintered. Alternatively or additionally, heavy rare earth elements can be introduced into the respective permanent magnet 18 by surface diffusion.In a third process step V3 of the process, it is provided that in recesses of the first area 20 of the rotor 16, for which a higher temperature development has been predicted, first permanent magnets 18 with a higher concentration of heavy rare earths are arranged, and in recesses of the second areas 22 of the rotor 16, for which a lower temperature development compared to the at least one first area 20 has been predicted, second permanent magnets 18 with a lower concentration of heavy rare earths compared to the first permanent magnets 18, or without heavy rare earths, are arranged.

[0022] The described invention is based on the understanding that reducing the use of heavy rare earth elements is an economic and geopolitical development goal for traction drives. To reduce losses, the permanent magnets 18 of the rotor 16 can be tangentially segmented. These segments can be bonded together outside the rotor 16 and then inserted into the rotor body of the rotor 16. It is also possible to join the respective permanent magnets 18 arranged one behind the other in the axial direction A outside the rotor body to form a single magnet, which is then inserted into an axially extending recess in the rotor body of the rotor 16. The use of heavy rare earth elements in the permanent magnets 18 can increase the coercive field strength of the respective permanent magnets 18.

[0023] As simulations show, the temperature of the rotor 16 is not uniform in the axial direction A. Under externally symmetrical boundary conditions and central cooling of the rotor 16, a temperature hotspot would form in the center of the rotor 16 in the axial direction A. To protect the permanent magnets 18 of the rotor 16 from demagnetization, it is sufficient to insulate only those permanent magnets 18 located in areas at risk from increased temperature stress by adding heavy rare earth elements to the opposing fields of the stator 14. Therefore, permanent magnets 18 with a higher proportion of heavy rare earth elements, and consequently higher coercivity, are only used in those areas of the rotor 16 exposed to higher temperatures.In cooler operating regions of the rotor 16, permanent magnets 18 with a comparatively lower proportion of heavy rare earth elements are used, for example, in the area of ​​the end faces 26 of the rotor 16. This allows for a particularly small amount of heavy rare earth elements to be used for protection against demagnetization, enabling the rotor 16 to be manufactured very cost-effectively. Furthermore, the rotor 16 achieves particularly high performance because the very low overall proportion of heavy rare earth elements in all the permanent magnets 18 results in a particularly high remanence of the permanent magnets 18.The increased proportion of heavy rare earths in permanent magnets 18 located only in vulnerable areas of the rotor 16 can be achieved through local surface diffusion of heavy rare earths on the surfaces of the respective permanent magnets 18 facing the stator 14 during operation. Alternatively or additionally, one or more magnet segments can be arranged in the vulnerable area of ​​a respective permanent magnet 18, to which heavy rare earths have been added in the base mixture or into which heavy rare earths have been introduced by surface diffusion. The respective permanent magnet 18 exhibiting the increased concentration of heavy rare earths can thus be segmented, with the segments being stacked on top of each other, particularly in the radial direction of the rotor 16.In this context, radially outer segments of this permanent magnet 18 can exhibit a higher concentration of heavy rare earth elements than radially inner segments. These outer segments, which have a higher concentration of heavy rare earth elements compared to the inner segments, can act as a protective shield for the inner layers of the permanent magnet 18. The structure of this permanent magnet 18, consisting of multiple stacked magnet segments, particularly those arranged radially in the direction of the rotor 16, allows for exceptionally low eddy current losses.

[0024] Overall, the invention demonstrates how the use of heavy rare earths in permanent magnet synchronous machines 12 can be implemented according to demand. Reference symbol list 10 motor vehicle 12 permanent magnet synchronous machine 14 Stator 16 Rotor 18 permanent magnets 20 first area 22 second area 24 third area 26 Front V1 Prediction of the rotor's temperature development V2 Manufacturing permanent magnets V3 Arranging permanent magnets in recesses of the rotor A axial direction QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] US 10 242 778 B2

[0002] US 9 154 004 B2

[0003]

Claims

[1] Rotor (16) for a permanent excitation synchronous machine (12) of a motor vehicle (10), with a rotor body having a plurality of recesses, wherein respective permanent magnets (18) are arranged in the recesses, wherein in a first region (20) of the rotor (16), for which a higher temperature development during operation of the rotor (16) is predicted, permanent magnets (18) with a higher concentration of heavy rare earth elements are arranged than in a second region (22) of the rotor (16), for which a comparatively lower temperature development is predicted. [2] Rotor (16) according to claim 1, characterized by , that the first area (20) has a greater axial distance to a nearest end face (26) of the rotor body than the second area (22). [3] Rotor (16) according to claim 2, characterized by, that a first permanent magnet (18) arranged in the first region (20) overlaps a second permanent magnet (18) arranged in the second region (22) at least partially in the axial direction (A). [4] Rotor (16) according to claim 3, characterized by , that the first permanent magnet (18) and the second permanent magnet (18) are in axial direction (A) against each other. [5] Rotor (16) according to any one of the preceding claims, characterized by , that the heavy rare earth elements are uniformly distributed within the respective permanent magnets (18) or are concentrated in at least one edge region of the respective permanent magnet (18). [6] Motor vehicle (10) with a permanent excitation synchronous machine (12) comprising a stator and a rotor (16) rotatable about an axis of rotation relative to the stator during operation according to one of the preceding claims. [7] Method for manufacturing a rotor (16) with a rotor body having a plurality of recesses for a permanent magnet synchronous machine (12) of a motor vehicle (10), wherein - for operation of the rotor (16) a temperature development of the rotor (16) is predicted, - in recesses of a first area (20) of the rotor (16), for which a higher temperature development has been predicted, first permanent magnets (18) with a higher concentration of heavy rare earths are arranged, and - in recesses of a second area (22) of the rotor (16), for which a lower temperature development compared to the first area (20) has been predicted, second permanent magnets (18) with a lower concentration of heavy rare earths or without heavy rare earths compared to the first permanent magnets (18) are arranged. [8] Method according to claim 7, characterized by, that the temperature development of the rotor (16) is predicted by means of a simulation. [9] Method according to claim 7 or 8, characterized by , that the heavy rare earth elements for the production of the respective first permanent magnet (18) are added to a basic mixture to be sintered for the production of this first permanent magnet (18). [10] Method according to any one of claims 7 to 9, characterized by , that the heavy rare earths are introduced into the respective first permanent magnets (18) by boundary layer diffusion.

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