ELECTRIC MACHINE WITH PERMANENT MAGNETS AND ITS CONTROL

Description

State of the art

[0001] DE 10 2013 222 208 A1 relates to a method for estimating the temperature of magnets on a rotating element of a rotating electrical machine. It is provided that, if at least the rotating element of the rotating electrical machine is cooled by a coolant, a magnet temperature estimator estimates the magnet temperature based on the temperature of the coolant and a loss of the rotating element including the magnets.

[0002] US 2010 / 0289366 A1 discloses a generic rotor core assembly. Core and advantages of the invention

[0003] Rotating electrical machines, especially permanent magnet rotating electrical machines, are used in various designs and sizes, as well as power classes (e.g., window lifts, micromotors, traction drives in automobiles, and generators in wind turbines, etc.). They are characterized by high power density (per mass or volume) and are therefore particularly important for non-stationary applications.

[0004] The permanent excitation in these machines is generated using permanent magnets (also called hard magnets or permanent magnets). In machines with high power densities, neodymium-iron-boron alloys or samarium-cobalt alloys are typically used as the material for the permanent magnets.

[0005] The permanent magnets are magnetized by an external magnetic field at the end of the manufacturing process or already in the rotor core or motor. Due to their specific magnetic properties (hysteresis behavior and high coercive field strength or demagnetization resistance), these materials retain their magnetization after the external magnetic field is removed and exhibit a so-called stray field, i.e. a magnetic field outside the permanent magnet that emanates from the permanent magnet. This stray field is exploited for application in permanently excited rotating electrical machines. Permanent magnetic materials have a characteristic temperature T c (Curie temperature). If this temperature is exceeded, the material undergoes a phase transition, changing from the ferromagnetic to the paramagnetic state and thus losing its directional magnetization relevant for the application.If the temperature subsequently falls below the Curie temperature Tc, the material becomes ferromagnetic again. However, once the Curie temperature Tc is exceeded, it no longer retains the magnetization initially imparted by an external magnetic field and thus irreversibly loses its properties relevant for use in a rotating electrical machine. Therefore, during design and operation, care is taken to ensure that the permanent magnets are not exposed to temperatures that irreversibly reduce or influence the permanent magnetic properties. Due to statistical processes, the temperature at which such irreversible changes (partial demagnetization) occur can sometimes be below the nominal Curie temperature Tc of the permanent magnet.

[0006] The invention relates to a rotor core assembly, a rotor assembly, a rotating electrical machine and a method for controlling a rotating electrical machine.

[0007] An advantage of the invention with the features of the independent patent claims is that temperature measurement is carried out wirelessly and in a space-saving manner directly on the permanent magnet, wherein the temperature measuring device can be implemented with little additional effort. In particular, no complex cuts in the rotor laminated core (lamination pack) and no large gaps around the permanent magnets are required, whereby the magnetic field of the permanent magnet is not disturbed and thus the performance of the rotating electrical machine is advantageously maintained. A further advantage is that the present invention can be used to detect when a threshold temperature is exceeded and / or undershot. In particular, it is thus possible to initiate measures, for example to reduce the temperature, via a control unit in order to maintain the performance of the rotating electrical machine.

[0008] This is achieved with a rotor core assembly according to claim 1.

[0009] The rotor lamination arrangement preferably comprises at least two permanent magnets, wherein at least one of the two permanent magnets has a functional layer.

[0010] A very good flux-conducting ferrosilicon (Fe-Si) material is typically used as electrical sheet material for the rotor core.

[0011] The permanent magnets can be arranged in pockets provided in the cross-section of the rotor core or on the core itself. This variant is particularly advantageous for synchronous machines with high-speed rotors, as the buried magnets can be used to generate the field, thus better managing the extreme loads caused by the high centrifugal forces.

[0012] When the Curie temperature of a material is exceeded, it undergoes a reversible phase transition from its ferromagnetic to its paramagnetic state, with the spontaneous or directional magnetization of crystal regions disappearing above the Curie temperature. When the temperature falls below the Curie temperature, the material regains its magnetic properties, i.e., the Weiss domains spontaneously magnetize, provided no external magnetic field acts on the material. However, the permanent magnet no longer regains magnetization initially imprinted by an external magnetic field once the temperature falls below the Curie temperature. Thus, once the Curie temperature is exceeded, it has irreversibly lost its magnetic properties relevant for use in a rotating electrical machine. Consequently, permanent magnets can only be used reliably as magnetic materials well below their Curie temperature.

[0013] Due to statistical processes, partial demagnetization can sometimes occur even below the Curie temperature of the permanent magnet, limiting the performance of a rotating electrical machine. The threshold temperature of the permanent magnet (also referred to as the temperature threshold, threshold temperature, or limit temperature) is a temperature below the Curie temperature of the permanent magnet at which no irreversible changes in the magnetic properties of the permanent magnet occur. For example, the threshold temperature can be at least 100°C or at least 150°C below the Curie temperature of the permanent magnet.In particular, the threshold temperature should be chosen to be sufficiently different from the Curie temperature of the permanent magnet, so that the permanent magnet has sufficient time to respond to an adjustment of the operating parameters of the rotating electrical machine, including the permanent magnet, to prevent a further increase in the temperature of the permanent magnet. This can prevent irreversible changes in the magnetic properties of the permanent magnet. The magnetic properties of the functional layer can be understood to include, in particular, the magnetization, polarization, and / or magnetic permeability of the functional layer.

[0014] The functional layer changes its magnetic properties, in particular magnetization, polarization, and magnetic permeability, abruptly and significantly when its material-characteristic temperature Tc (Curie temperature) is exceeded and / or undershot. The Curie temperature of the functional layer is preferably below the Curie temperature of the permanent magnet. In particular, the Curie temperature of the functional layer can correspond to the threshold temperature. The change in the magnetic properties of the functional layer due to the phase transition from ferromagnetic to paramagnetic, or from paramagnetic to ferromagnetic in the event of the Curie temperature of the functional layer being undershot, affects the magnetic circuit comprising the permanent magnet, the functional layer, and the electrical steel sheet. This can be detected via the machine data during operation, and measures can be initiated via the motor control system if necessary.

[0015] One advantage of the functional layer for temperature monitoring of the permanent magnet is the acquisition of direct information on the surface temperature of the permanent magnet or the information on whether a certain temperature threshold has been exceeded and / or undershot. This information can be used to protect the system from overheating of the permanent magnets. Due to the precise and local detection of exceeding the temperature threshold, a machine can be designed and operated much closer to this temperature threshold. No safety buffers are required. The phase transition of the material of the functional layer is fully reversible and can be repeated as required. Since the temperature monitoring of the permanent magnet only requires a functional extension of the permanent magnet and an adaptation of the machine software to detect the effect, no adaptation of other components (e.g.of the plate pack), electronics, or new components are required. This advantageously allows existing designs, geometries, and processes to be retained.

[0016] The thickness of the functional layer should not be too thick, so that during normal operation, i.e., at temperatures below the Curie temperature of the functional layer (T < T c of the functional layer), it does not excessively shield the magnetic field of the permanent magnet to which it is applied, thereby negatively impacting the function of the machine. To ensure this, the layer thickness of the functional layer is preferably less than or equal to 200 µm, preferably less than or equal to 50 micrometers (µm), in particular less than or equal to 20 µm.

[0017] The functional layer consists of a material which is in the ferromagnetic state at the desired operating temperatures of the rotating electrical machine comprising the rotor core assembly and has a Curie temperature T c which corresponds to the desired temperature threshold.

[0018] For typical motor applications using neodymium-iron-boron magnets as permanent magnets, whose Curie temperature is between 310°C and 340°C, the maximum operating temperatures are limited to below 200°C, usually between 100°C and 160°C (depending on the magnet class).

[0019] For samarium-cobalt magnets, whose Curie temperature lies between 750°C and 825°C, typical operating temperatures of up to 350°C can be achieved (special Sm 2 Co 17 alloys up to 550°C). In the case of neodymium-iron-boron magnets as permanent magnets, a material with a Curie temperature below 250°C, particularly in the range of 100°C to 200°C (depending on the magnet class), is particularly suitable as a functional layer. The Curie temperature of the functional layer can be precisely determined during production, for example, through the alloy composition.In the case of samarium-cobalt magnets, a material is particularly suitable as the functional layer which has a Curie temperature in the range of less than or equal to 500°C, in particular in the range from 250°C to 350°C (where 250°C and 350°C are included), and for which the Curie temperature of the functional layer can be precisely determined during production, for example by the alloy composition. In order that the material from which the functional layer is made conducts the magnetic flux of the permanent magnet as well as possible (i.e. reduces the magnetic resistance in the magnetic circuit), it is furthermore advantageous for the material of the functional layer to have a high magnetization M, polarization J and a high permeability µ, in particular a saturation polarization J s greater than 0.5 Tesla (T), preferably greater than 1 T. The relative permeability µ r should in particular be greater than 500, preferably greater than 1000.

[0020] Alloys that can be used as a functional layer for temperature monitoring of the permanent magnet and which have Curie temperatures that are suitable as threshold temperatures are, for example, the following: Iron aluminide alloys (Fe-Al alloys) such as Fe 3 Al with a Curie temperature of Tc~300°C; depending on the composition, iron-aluminum alloys with a Curie temperature Tc in the range of 100-200°C (including the boundary values) can also be realized. Fe-Al-X alloys, such as (Fe x V 1-x ) 3 Al, whose Curie temperature can be adjusted via the vanadium content (V content), whereby Curie temperatures of -200°C and 500°C or a value between -200°C and 500°C can be achieved via the choice of vanadium content (Source: Gautam Ghosh and MSIT ®®< ; Effenberg, G. (Ed.); SpringerMaterials; 10.19028.2.9 (Springer-Verlag GmbH, Heidelberg, 2004) Nickel (Ni), which has a Curie temperature of 354°C and is particularly suitable as a functional layer for temperature monitoring of a permanent magnet made of a samarium-cobalt alloy Iron-nickel compounds (Fe-Ni compounds), if necessary.with additions of molybdenum (Mo) and / or copper (Cu) and / or other chemical elements, enabling Curie temperatures of the functional layer of 100°C, 500°C, or a value between 100°C and 500°C, depending on the composition of the iron-nickel compound and the optional additives. Ferrites with Curie temperatures ranging from 100°C to 450°C.

[0021] Further examples of materials that can be used as a functional layer for temperature monitoring of the permanent magnet are: MnFeP 1-x Si x with Curie temperatures of 70°C, 110°C or a value between 70°C and 110°C (depending on the composition, ie the choice of the value x) Amorphous compounds such as (Fe,Co) 83 (Si,B) 17 with a Curie temperature of about 430°C Ti(FeCo) 2.3 : with a Curie temperature of -70°C to 400°C (depending on the cobalt content) Ce 2 (FeCo) 17 with a Curie temperature of about 0°C to 800°C (depending on the cobalt content)

[0022] The above list is merely exemplary and not exhaustive. Other materials whose Curie temperature is suitable as the threshold temperature of the permanent magnet can be used as functional layers for temperature monitoring of the permanent magnet.

[0023] In addition to the actual functional crystallographic phase (with a Curie temperature corresponding to the threshold temperature), the functional layer may also contain other crystallographic phases to a certain extent (preferably <50 vol%), especially if these cannot be avoided by the manufacturing process and do not restrict the function.

[0024] The functional layer can be applied to the permanent magnet using conventional methods such as chemical coating processes, vapor deposition processes, sputtering processes, vacuum deposition processes, spraying or injection processes, dipping processes, application by means of a dispersion, etc.

[0025] In one embodiment, the permanent magnet comprises a protective layer, wherein the protective layer is applied between the permanent magnet and the functional layer or on a side of the functional layer facing away from the permanent magnet. In particular, the protective layer can comprise an oxidation protection layer. The oxidation protection layer can, for example, comprise copper-nickel (Cu-Ni), as a single or multilayer, with a layer thickness of less than 10 µm. Either the oxidation protection layer or the functional layer can be applied first, depending on what is more advantageous from a process engineering perspective. Alternatively or additionally, the protective layer can comprise a passivation layer, wherein the passivation layer can, for example, comprise a zinc layer having a layer thickness of a few micrometers, in particular 5 µm to 40 µm, preferably 8 µm to 12 µm.

[0026] Alternatively or additionally, the functional layer can act as a protective layer, in particular, as oxidation protection. One advantage is that this keeps the magnetic resistance in the magnetic circuit low and reliably transmits the magnetic flux of the permanent magnet.

[0027] In one embodiment, the rotor core comprises a first functional layer and a second functional layer, wherein the first functional layer is arranged on a first surface of the permanent magnet and wherein the second functional layer is arranged on a second surface of the permanent magnet facing away from the first surface. The first and second functional layers are thus applied to two surfaces of the permanent magnet facing away from one another. In particular, the surface normals of the functional layers advantageously point in the direction of the preferred magnetic direction of the typically used anisotropic permanent magnets. One advantage is that the usable magnetic field emerging from the permanent magnet is thus not reduced. Furthermore, coating only two opposing surfaces is significantly simpler and more cost-effective for process-related reasons.

[0028] According to one embodiment, the functional layer can be formed as a particle layer comprising functional particles and a binding material, wherein the functional particles are at least partially encased by the binding material. The binding material, for example a plastic, can encase the functional particles and hold them together. The particles consist, for example, of one or more of the above-mentioned materials with the desired T c . The advantage of this embodiment is that particles in a suspension or adhesive mass can be injected into a gap between the permanent magnet and the electrical steel sheet. In some machine designs, the permanent magnets in the rotor laminated core are additionally fixed by injecting epoxy into this gap in order to withstand the high centrifugal forces. The addition of functional particles can advantageously be integrated into the process.

[0029] According to one embodiment, the permanent magnet of the rotor core assembly can be formed from a neodymium-iron-boron alloy and the Curie temperature of the functional layer can have a value less than or equal to 250° Celsius, in particular a value between 100° Celsius and 200° Celsius.

[0030] According to one embodiment, the permanent magnet of the rotor core assembly may be formed from a samarium-cobalt alloy and the Curie temperature of the functional layer may have a value of 350° Celsius or 500° Celsius or a value between 350° Celsius and 500° Celsius.

[0031] According to the invention, the functional layer comprises a first sublayer having a first Curie temperature and a second sublayer (10512) having a second Curie temperature, and wherein the first Curie temperature and the second Curie temperature differ from one another. One advantage is that such a functional layer consisting of at least two sublayers forms a multilayer system, which enables the implementation of several, even different, threshold temperatures (= Curie temperatures of the functional sublayers) if a multi-stage signal is desired. This advantageously enables precise temperature monitoring; in particular, it can be determined in which temperature interval the temperature of the permanent magnet lies, and if necessary, countermeasures can be initiated via the motor control.

[0032] The advantages of a rotor arrangement comprising a rotor core assembly according to one of the aforementioned embodiments result from the advantages of the rotor core assembly.

[0033] A rotating electrical machine designed as above preferably comprises a control unit for controlling the rotating electrical machine, further comprising a receiving unit which is configured to receive an input signal, wherein the input signal represents a magnetic variable by means of which the exceeding and falling below of the threshold temperature of the permanent magnet can be detected, a comparison unit which compares the input signal with a reference curve and, depending on the detected exceeding and falling below of the threshold temperature of the permanent magnet, provides a control signal for setting at least one operating parameter of the rotating electrical machine, and an output unit for outputting the control signal for setting at least one operating parameter of the rotating electrical machine depending on the detected exceeding and falling below of the threshold temperature of the permanent magnet.

[0034] The receiving unit, the comparison unit, and / or the output unit can be designed as part of an engine control unit that handles the control, regulation, and monitoring of engine functions. The engine control unit can, for example, have a microcontroller for executing computing operations (such as signal comparison), wherein the microcontroller has access to an internal and / or external memory (RAM, ROM, and flash memory) in which, for example, the reference curve or reference data is stored. Furthermore, the engine control unit can also comprise ASICs and / or FPGAs. In particular, the receiving unit and / or the output unit can comprise interfaces integrated into the engine control unit for analog and digital input signals from sensors and output signals for actuators. For example, adjustments to the operating state of the electrically rotating machine (e.g., energy-saving mode) can be made via the engine control unit.

[0035] One advantage of the control unit is that it allows for easy temperature monitoring of the rotating electrical machine, as it only monitors a single magnetic variable, which can be used to detect whether the threshold temperature of the permanent magnet in the rotor assembly of the rotating electrical machine has been exceeded or not reached. If the threshold temperature is detected by comparing the magnetic variable (e.g., magnetic resistance of the magnetic circuit, magnetic flux, current / voltage curve, electrical power, etc.) with a reference curve, measures can be initiated directly via the motor control system, for example, to reduce the machine's power and reduce the temperature. The control unit thus prevents the permanent magnets from overheating (see above), thus ensuring reliable operation of the rotating electrical machine.If the temperature subsequently falls below the threshold, the rotating electrical machine can be returned to its normal operating mode via the control signal. This enables efficient, reliable operation of the rotating electrical machine.

[0036] The B(H) characteristic curve of the functional layer cannot be measured directly during machine operation. From the two B(H) characteristic curves of the two states (paramagnetic and ferromagnetic), which can be characterized, for example, on the pure material outside, a difference in the expected machine signal can be calculated in one embodiment by calculating the overall magnetic circuit in the rotating electrical machine. Alternatively or additionally, this signal when the Curie temperature is exceeded can also be recorded for various operating points before use in the rotating electrical machine, its characteristics stored in the software, and thus serve as a reference. Only signals at the machine level are suitable for evaluation, such as characteristic curves (power, current, voltage, etc.) or combinations of several parameters that provide an overall picture.The change in this overall picture of the parameters when the threshold temperature is exceeded must be stored as a reference, as described above. The reference curve can be, in particular, the electrical power or the voltage / current curve of the rotating electrical machine below the Curie temperature (ferromagnetic) and / or above the Curie temperature (paramagnetic), stored in a storage unit internal or external to the rotating electrical machine and retrieved by the comparison unit. An example of such a reference curve is shown in . Fig. 5 shown. The magnetic field strength H is plotted on the x-axis of the B-(H) characteristic curve, and the degree of magnetization B is plotted on the y-axis. The functional layer is located in the magnetic field of the permanent magnet. Depending on whether the functional layer is in the ferromagnetic or paramagnetic state, the functional layer has a different degree of magnetization in the magnetic field. By comparing the degree of magnetization, which is represented by an input signal and transmitted to the receiving unit, with the reference curve, it can be determined whether the functional layer is in the ferromagnetic or paramagnetic state, i.e., whether the surface of the permanent magnet has a temperature above (functional layer is paramagnetic) or below the threshold temperature (functional layer is ferromagnetic).

[0037] Furthermore, the magnetic resistance, as which the functional layer acts in the magnetic circuit, depends on whether the functional layer is in the ferromagnetic state (corresponding to a low magnetic resistance) or in the paramagnetic state (corresponding to a low magnetic resistance compared to the magnetic resistance in the ferromagnetic state). A change in the magnetic resistance can be detected, for example, as a change in the magnetic flux density, whereby an input signal representing the magnetic flux density can be, for example, an electrical voltage, Hall voltage, etc. The magnetic flux can be measured using magnetometers, Hall sensors, or measuring coils, for example. This can be used to determine whether the threshold temperature has been exceeded or not reached based on the machine's operating data.

[0038] The operating parameters of the rotating electrical machine include, for example, the rotational speed of the rotor arrangement, the torque of the rotor arrangement or a coil current which flows through the copper windings of the stator of the rotating electrical machine and which causes the rotor arrangement to rotate.

[0039] The advantages of a rotating electrical machine, comprising the rotor assembly, result from the advantages of the rotor core assembly and the rotor assembly.

[0040] A rotating electrical machine, such as an electric motor or a generator, generally consists of a stator and a rotor assembly rotatably mounted therein. Such a rotor assembly typically contains a plurality of rotor laminations joined together to form a so-called rotor lamination stack, as well as a drive unit comprising a drive shaft. A rotating electrical machine can operate as a three-phase electric motor or as a generator that generates three-phase current. The rotating electrical machine has a stator winding, usually located on the outside, which generates a rotating magnetic field and in which an electrical voltage is induced. The rotor, usually located on the inside (pole wheel), carries permanent magnets to generate the field.

[0041] According to the invention, the rotating electric machine comprises the control unit described above, wherein the control unit is configured to provide a control signal for adjusting at least one operating parameter of the rotating electric machine when the threshold temperature of the permanent magnet is exceeded or undershot. The advantages arise from the advantages of the control unit described above.

[0042] A method for controlling the rotating electrical machine comprises the steps: Determining whether the threshold temperature of the permanent magnet is exceeded and / or undershot, adjusting at least one operating parameter of the rotating electrical machine when the threshold temperature of the permanent magnet is exceeded and / or undershot.

[0043] This advantageously enables efficient, reliable operation of the rotating electrical machine. Short description of the drawings

[0044] Embodiments of the invention, as well as embodiments not forming part of the invention ("forms" hereinafter), are illustrated in the drawings and explained in more detail in the following description. The same reference numerals in the figures denote the same or equivalent elements.

[0045] It shows Fig. 1 a section of a cross section of a rotor arrangement comprising a rotor core assembly, Fig. 2 a section of a cross-section of a rotating electrical machine, Fig. 3a a cross-section of a permanent magnet with a first functional layer and a second functional layer, Fig. 3b a cross-section of a permanent magnet with a particle layer comprising functional particles and a binding material, Fig. 3c a cross-section of a permanent magnet comprising a functional layer comprising a first sublayer and a second sublayer, Fig. 4 a cross-section of a permanent magnet, comprising a protective layer applied to a side of the functional layer facing away from the permanent magnet, Fig. 5 an example B-(H) characteristic curve of the functional layer, Fig. 6 a sketch of the magnetic field of the permanent magnet in a section of the rotor core assembly and Fig. 7 a flowchart of a method for controlling a rotating electrical machine.

[0046] Embodiments of the invention and forms Fig. 1 shows a section of an exemplary, schematic cross-section of a rotor assembly 111, comprising a rotor core assembly 100. The rotor core assembly 100 comprises a rotor core assembly 101 and, in this form, a plurality of permanent magnets 102, which are arranged in the rotor core assembly 101. These are so-called buried permanent magnets 102. The rotor core assembly 100 is arranged on a drive shaft 103.A functional layer 105 for detecting an exceedance of and / or undershoot of a threshold temperature of the permanent magnet 102 is arranged on a surface of the permanent magnets 102 facing the drive shaft and on a surface of the permanent magnets 102 facing away from the drive shaft. The functional layer 105 changes its magnetic properties when the threshold temperature is exceeded or undershot, whereby the exceedance of and / or undershoot of the threshold temperature of the permanent magnet 102 can be detected. In particular, the Curie temperature of the functional layer 105 corresponds to the threshold temperature. The permanent magnets can, for example, be cuboid-shaped as a rectangular magnet, with at least one surface provided with the functional layer 105. In this shape, the permanent magnets 102 are seated in pockets 104 provided in the cross-section of the rotor core 101.The permanent magnets 102 are inserted and clamped there. Furthermore, they can be additionally or supplementarily bonded to the rotor core 101 with an adhesive, such as epoxy resin, so that the pocket 104 between the rotor core 101 and the permanent magnet 102, or between the rotor core 101 and the functional layer 105, is at least partially filled with epoxy resin.

[0047] Alternatively or additionally, the permanent magnets can also be arranged on the rotor core 101 or arranged in recesses at least partially in the rotor core 101.

[0048] Fig. 2 shows a section of a rotating electrical machine 300. The section shows the rotor core assembly 100 and a stator 301 surrounding the rotor core assembly 100 with copper windings 302, wherein the stator 301 is spaced from the rotor core assembly 100 by a gap 112, in particular an air gap.

[0049] The magnetic field of the permanent magnets 102, whose direction 107 is indicated by the arrows in Fig. 2 is indicated, is brought via the rotor core 101 into the gap 112 and further guided into the stator core 301 or interacts with an electromagnetic field generated by the tooth winding 302 of the stator across the gap 112. Therefore, for the conduction of the magnetic field of the permanent magnet 102 towards the air gap, it is of interest to generate the lowest possible magnetic resistance, i.e., in general, but especially for the functional layer 105, to use materials with high magnetization M or polarization J, high permeability µ and high electrical resistance (to reduce dynamic losses). Typically, the magnets are provided with a passivation layer (Zn layer, phosphate layer, a few micrometers thick) and / or an oxidation protection layer (Cu-Ni, single or multilayer, < 10 micrometers) (in Fig. 2 (not shown). A highly flux-conducting Fe-Si material is typically used as the material for the rotor core. An unavoidable minimal gap (air gap or epoxy resin) is created by the fit of the permanent magnet 102 into the pocket 104 in the rotor core 101.

[0050] The functional layer 105 is as in Fig. 3a shown applied to the surface of the permanent magnet 102. If the functional layer 105 itself functions as oxidation protection 106, it is sufficient to apply only the functional layer 105. A combination with an oxidation protection layer 106 is possible and in Fig. 4 shown schematically. Either the oxidation protection layer (not shown) or the functional layer can be applied first (see Fig. 4 ), depending on what is more advantageous from a process engineering point of view.

[0051] The functional layer 105 consists of a material that is in a ferromagnetic state at the desired operating temperatures of the rotating electrical machine and has a Curie temperature T c that corresponds to the desired threshold temperature. To ensure that the material conducts the magnetic flux of the permanent magnet 102 as effectively as possible (i.e., reduces the magnetic resistance in the magnetic circuit), it is further advantageous for the material of the functional layer to have a high magnetization M, polarization J, and permeability µ.

[0052] In the Fig. 1, 2 , 3a and 4The functional layer 105 is applied only to the top and bottom of the permanent magnet 102. A first functional layer 1051 is arranged on a first surface 1071 of the permanent magnet 102, and a second functional layer 1052 is arranged on a second surface 1072. The first surface 1071 and the second surface are opposite surfaces of the permanent magnet. As can be seen from Fig. 2 These are clearly the relevant areas for the magnetic flux in the direction of the gap 112 between the rotor core assembly 100 and the stator 301. This direction also corresponds to the preferred magnetic direction 107 of the typically used anisotropic permanent magnets 102. With a complete coating of the surface, it may happen under certain circumstances that a portion of the magnetic flux escaping in the direction of the air gap 112 returns via the coating, thus reducing the usable field. Coating only the top and bottom surfaces 1071, 1072 prevents this and, for process-related reasons, can also be implemented much more simply and cost-effectively.

[0053] In Fig. 3b a form of the functional layer 105 is shown in cross section, in which the functional layer 105 is formed as a particle layer, which functional particles 109 are embedded in a binding material 110. In one embodiment, alternatively or additionally, such a particle layer, comprising functional particles 109 and the binding material 110 or another functional layer 105, is on the underside, ie on one of the in Fig. 3b shown functional layer 105 opposite surface of the permanent magnet 102.

[0054] Fig. 3c shows an embodiment of the functional layer 105 in cross-section, wherein the functional layer 105 comprises several sub-layers 10511, 10512 (multilayer system). The first sub-layer (10511) has a first Curie temperature and a second sub-layer 10512 has a second Curie temperature. According to the invention, the first Curie temperature and the second Curie temperature differ from one another. Thus, several, even different, threshold temperatures of the permanent magnet can be detected, wherein the first and second Curie temperatures correspond to the different threshold temperatures. In particular, it is thus possible to determine in which temperature interval the temperature of the permanent magnet 102 is located and thus, if necessary, measures for adapting the operating mode (e.g., energy-saving mode) can be more specifically tailored to the current temperature.For example, measures can be initiated at an early stage to prevent a further increase in temperature and, based on the further threshold temperatures, it can be determined whether the measures have been effective, ie the temperature is falling or being maintained, or whether the temperature continues to rise and therefore more stringent measures must be initiated by adjusting the operating parameters.

[0055] In Fig. 5 The magnetization characteristics (magnetic induction 200 over an external magnetic field 201) for a ferromagnetic material 202, a paramagnetic material 203, and for the vacuum 204 are shown schematically and by way of example. The ferromagnetic material has a magnetic permeability µ f that is typically several orders of magnitude higher than that of a paramagnetic material µ p . Therefore, a paramagnetic material in a magnetic circuit represents a comparable magnetic resistance to an air gap. Accordingly, the magnetic circuit is significantly influenced by the transition from the highly magnetically conductive ferromagnetic state of the functional layer 105 to the poorly magnetically conductive paramagnetic state. This sudden change in the magnetic flux can be reliably detected in the machine data during operation.The thickness of the functional layer should not be too thick, so that during normal operation (temperature < T c of the functional layer), it does not excessively shield the magnetic field of the permanent magnet 102 and thus negatively impact the function of the rotating electrical machine. The layer thickness is preferably in the range <50 µm, and is also advantageous in the range <20 µm.

[0056] Fig. 6 shows a sketched course of the magnetic field lines 205 of the permanent magnet 102 in the rotor laminated core arrangement 100. The field lines run from the permanent magnet 102 through the functional layer 105 and the space (pocket) 104 between the functional layer and the rotor laminated core 101 and through the rotor laminated core.

[0057] Fig. 7shows a flowchart of a method 404 for controlling the rotating electrical machine 300. A control unit 400, for example a motor controller, receives an input signal 4010 from the rotating electrical machine 300 via a receiving unit 401. The input signal 4010 represents a magnetic variable by means of which the exceeding and / or falling below the threshold temperature of the permanent magnet 102 can be detected. The input signal 4010 can be a sensor signal representing the magnetic variable, for example the magnetic flux of the permanent magnet. The sensor can be, for example, a magnetometer, a Hall sensor, etc. The receiving unit 401 forwards the input signal 4010 to the comparison unit 402, where it is compared with a reference curve 4020.Depending on the detected exceedance and undershoot of the threshold temperature of the permanent magnet 102, a control signal 4021 for adjusting at least one operating parameter of the rotating electrical machine 300 is provided by the comparison unit 402.

[0058] If the comparison shows that the functional layer 105 is in the ferromagnetic state and the rotating electrical machine 300 is operating in normal mode, the operating parameters are not adjusted by means of the control signal 4021.

[0059] If the comparison reveals that the functional layer 105 is in the ferromagnetic state and the rotating electrical machine 300 is operating in a special mode (e.g., energy-saving mode or shutdown), the rotating electrical machine 300 can be returned to normal operation using the control signal 4021, since it can be concluded from the ferromagnetic state of the functional layer 105 that the permanent magnet 102 has a temperature below the Curie temperature of the functional layer 105 and thus below the threshold temperature of the permanent magnet 102 and is therefore not at risk of overheating. Normal operation is therefore possible.

[0060] If the comparison shows that the functional layer 105 is in the paramagnetic state and the rotating electrical machine 300 is operating in normal mode, the rotating electrical machine 300 can be put into a special mode (e.g. energy saving mode, adjusted operating parameters or switching off the rotating electrical machine 300) by means of the control signal 4021.

[0061] If the comparison reveals that the functional layer 105 is in a paramagnetic state and the rotating electrical machine 300 is operating in special mode (e.g., energy-saving mode), further measures to reduce the temperature, such as switching off the rotating electrical machine 300 or further adjusting the operating parameters, can be initiated using the control signal 4021. Examples of operating parameters of the rotating electrical machine include the rotational speed of the rotor assembly, the torque of the rotor assembly, or a coil current flowing through the copper windings of the stator of the rotating electrical machine and causing the rotor assembly to rotate. For example, the coil current can be reduced, thus reducing the Joule heat, which also leads to heating of the permanent magnets.

[0062] An output unit 403 outputs the control signal 4021 to the rotating electrical machine 300 for setting at least one operating parameter of the rotating electrical machine 300 as a function of the detected exceedance and / or undershoot of the threshold temperature of the permanent magnet 102.

Claims

1. Rotor laminated core arrangement (100) comprising at least one permanent magnet (102) which has a functional layer (105, 1051, 1052) for detecting an exceedance and an undershoot of a threshold temperature of the permanent magnet (102), wherein the functional layer (105, 1051, 1052) changes its magnetic properties when the threshold temperature is exceeded and undershot, as a result of which the exceedance and the undershoot of the threshold temperature of the permanent magnet (102) can be detected, wherein the threshold temperature is a temperature lower than the Curie temperature of the permanent magnet (102), at which no irreversible changes of the magnetic properties of the permanent magnet (102) occur, characterized by a rotor laminated core (101) on or in which the at least one permanent magnet (102) is arranged, wherein the functional layer (105, 1051, 1052) comprises a first sublayer (10511) which has a first Curie temperature and a second sublayer (10512) which has a second Curie temperature, and wherein the first Curie temperature and the second Curie temperature differ from one another.

2. Rotor laminated core arrangement (100) according to Claim 1, characterized in that the permanent magnet (102) comprises a protective layer (106), wherein the protective layer (106) is applied between the permanent magnet (102) and the functional layer (105, 1051, 1052) or to a side of the functional layer (105, 1051, 1052) facing away from the permanent magnet (102).

3. Rotor laminated core arrangement (100) according to either of the preceding claims, characterized in that the rotor laminated core (101) comprises a first and a second functional layer (105, 1051, 1052), wherein the first functional layer (1051) is arranged on a first surface (1071) of the permanent magnet (102) and wherein the second functional layer (1051) is arranged on a second surface (1072) of the permanent magnet (102) facing away from the first surface (1071).

4. Rotor laminated core arrangement (100) according to one of the preceding claims, characterized in that the functional layer (105, 1051, 1052) is formed as a particle layer which comprises functional particles (109) and a binder material (110), wherein the functional particles (109) are at least partially enveloped by the binder material (110).

5. Rotor laminated core arrangement (100) according to one of the preceding claims, characterized in that the permanent magnet (102) is formed from a neodymium-iron-boron alloy and the Curie temperature of the functional layer has a value less than or equal to 250° Celsius, in particular a value between 100° Celsius and 200° Celsius.

6. Rotor laminated core arrangement (100) according to one of Claims 1 to 4, characterized in that the permanent magnet (102) is formed from a samarium-cobalt alloy and the Curie temperature of the functional layer has a value less than or equal to 500° Celsius or in particular a value between 250° Celsius and 350° Celsius.

7. Rotor laminated core arrangement (100) according to one of the preceding claims, characterized in that the permanent magnet (102) with the functional layer (105, 1051, 1052) is arranged in a pocket in the rotor laminated core (101).

8. Rotor arrangement (108) comprising a rotor laminated core arrangement (100) according to one of the preceding claims.

9. Rotating electric machine (300) comprising a rotor arrangement (108) according to Claim 8.

10. Rotating electric machine (300) according to Claim 9, comprising a control unit (400) for controlling the rotating electric machine (300), comprising • a receiving unit (401) which is configured to receive an input signal (4010), wherein the input signal (4010) represents a magnetic value which can be used to detect the exceedance and undershoot of the threshold temperature of the permanent magnet (102), • a comparison unit (402) which is designed to compare the input signal (4010) with a reference curve (4020) and, in dependence on the detected exceedance and undershoot of the threshold temperature of the permanent magnet (102), to provide a control signal (4021) for setting at least one operating parameter of the rotating electric machine (300), and • an output unit (403) for outputting the control signal (4021) for setting at least one operating parameter of the rotating electric machine (300) in dependence on the detected exceedance and undershoot of the threshold temperature of the permanent magnet (102).

11. Method (404) for controlling a rotating electric machine (300) according to Claim 10, comprising the steps of: • ascertaining an exceedance and undershoot of the threshold temperature of the permanent magnet (102), • adapting at least one operating parameter of the rotating electric machine (300) upon exceedance and undershoot of the threshold temperature of the permanent magnet (102).