Rotor for use in an electric machine, electric machine and method for manufacturing a rotor

Abstract

The invention relates to a rotor (2) for use in an electric machine (1), wherein the rotor (2) has one or more permanent magnets (5) forming the poles of the rotor (2). One or at least one of the several permanent magnets (5) is a segmented permanent magnet comprising at least two segments (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h), wherein at least one of the at least two segments (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h) comprises a first material, in particular consisting of a material other than that, and at least one other segment (5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h) comprises a second material, in particular consisting of a material other than that. The first material has a higher coercive field strength than the second material. The invention further relates to a method for manufacturing a rotor and an electric machine.

Description

[0001] The present invention relates to a rotor for an electrical machine. Background of the invention

[0002] In rotors of electrical machines such as permanent magnet synchronous machines, as used in electric vehicles, permanent magnets made of a neodymium-iron-boron (NdFeB) alloy can be used because they have a very high magnetization.

[0003] The stator of an electric machine generates an alternating magnetic field due to the currents flowing through it. Even though the fundamental wave of this alternating field rotates synchronously with the rotor, the rotor experiences a magnetic field that changes over time due to harmonics in the field, particularly very high-frequency harmonics caused by the pulse-width modulation (PWM) clocking of the inverter. This time-varying magnetic field induces eddy currents in the rotor iron and within the permanent magnets within the rotor. To keep these eddy currents as low as possible, the rotor can consist of a laminated core or have one. To reduce the eddy currents within the permanent magnets, these can be segmented.

[0004] When manufacturing segmented permanent magnets, the individual segments can first be sawn from larger blocks and then joined together to form the segmented permanent magnet.

[0005] While permanent magnets made of an NdFeB alloy, for example, can have a very high magnetization, they have the disadvantage of a relatively low coercive field strength, which decreases further when the permanent magnet becomes hot.

[0006] This can lead to the permanent magnets being (partially) demagnetized during operation if a sufficiently strong opposing field is generated by the stator, which can occur particularly in the case of an active short circuit.

[0007] To increase the coercive field strength of NdFeB permanent magnets, for example, terbium and dysprosium, so-called heavy rare earth elements, can be added. These can either be added during the alloying of the magnet material or subsequently diffused into the magnets.

[0008] Permanent magnets of the highest classes in terms of demagnetization resistance, i.e. with a high coercive field strength, cannot usually be manufactured without such heavy rare earths. Disclosure of the invention

[0009] According to the invention, a rotor for use in an electrical machine, an electrical machine, and a method for producing a rotor are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0010] The invention is based on a rotor with one or more permanent magnets, forming the rotor's poles. The rotor can, for example, have recesses for the permanent magnets into which permanent magnets are inserted. Furthermore, segmented permanent magnets, i.e., permanent magnets with multiple segments, e.g., consisting of individual permanent magnets joined together, are used to reduce eddy currents. To further reduce demagnetization of the permanent magnets, the individual permanent magnets could be made of an alloy containing rare heavy earths, or could contain such an alloy or rare heavy earths in general.

[0011] The invention is based on the finding that, in order to prevent demagnetization, not all segments of such a segmented permanent magnet have to have an alloy with an increased demagnetization strength or coercive field strength, but it is sufficient to produce only some of the segments with such an alloy and the remaining segments with an alloy with a lower coercive field strength.

[0012] This allows resources and costs to be saved in the production of permanent magnets, as the amount of expensive heavy rare earths required to produce the permanent magnets can be reduced.

[0013] According to the invention, a rotor for use in an electrical machine is proposed, in which a segmented permanent magnet with at least two segments is used for one or at least one of the plurality of permanent magnets, wherein at least one of the segments has a first material, in particular consists thereof, and at least one other of the segments has a second material, in particular consists thereof. The first and the second material are different. Thus, the first and the second material have, in particular, different magnetic properties. Particularly preferably, the first material has a higher coercive field strength than the second material, e.g., a coercive field strength that is at least 10% or at least 20% higher. In addition to the coercive field strength, the first and second materials can alternatively or additionally also differ in one or more other magnetic properties, e.g.the remanence or properties of the hysteresis curve.

[0014] The first material is in particular an alloy comprising neodymium, iron and boron, to which terbium and / or dysprosium is further added, wherein the second material is an alloy containing neodymium, iron and boron, wherein the second material has less terbium and / or dysprosium than the first material, or which does not contain any terbium and / or dysprosium at all, i.e. has no terbium and / or dysprosium.

[0015] This allows the amount of heavy rare earth elements such as terbium and / or dysprosium required for demagnetization protection to be reduced, thus saving costs and resources and achieving demagnetization protection in a simple and efficient manner.

[0016] In one embodiment, the one or more permanent magnets have an elongated shape, with a length that is greater than a width, for example in the form of an elongated cylinder or cuboid.

[0017] In one embodiment, the one or more permanent magnets are divided into at least two segments along their width. In such a case, each permanent magnet can, for example, have two segments in the shape of a half-cylinder or a cuboid. The half-cylinders are joined together at their flat surfaces. One of the segments comprises the first material, while the other segment comprises the second material.

[0018] It is also conceivable for the permanent magnet to have three segments, with two segments made of the first material and one segment made of the second material. The segment made of the second material is joined, for example, to two opposite outer surfaces, each with a segment made of the first material.

[0019] In one embodiment, the one or more permanent magnets have at least three segments and are divided into the at least three segments along their length, wherein in particular the segments arranged at the ends in the longitudinal direction have the first material, in particular consist thereof. It is also possible for only one of the segments at the ends to have the first material. The one or more permanent magnets are arranged in the rotor in such a way that the segment having the first material is located as far radially outward as possible. For example, the permanent magnet can have three segments, two with the first material and one with the second material. The one segment having the second material can in particular be longer than the two segments made of the first material, wherein one segment made of the first material is attached to each segment at one end in the longitudinal direction.

[0020] It is also conceivable for the segments to all be the same size, and for two, three, six, or any number of segments made of the second material to be joined together to form an elongated permanent magnet. A segment made of the first material is attached to one or both ends in the longitudinal direction. However, the number of segments made of the first material at each end in the longitudinal direction is not limited to one, but can also be two, three, or more.

[0021] Permanent magnets designed in this way not only prevent demagnetization of the permanent magnets in a simple, efficient and cost-effective manner, but also reduce eddy currents in the permanent magnets caused by the time-varying magnetic field generated by the stator.

[0022] The invention further relates to a method for producing a rotor for use in an electrical machine, wherein, in the method, first segments for permanent magnets comprising a first material and second segments for permanent magnets comprising a second material are firstly produced, and then at least one first segment and at least one second segment are joined together, in particular by gluing, to produce at least one segmented permanent magnet, wherein the first segments and the second segments form at least two segments of the permanent magnet. Subsequently, the at least one segmented permanent magnet is introduced or attached into or to the rotor.

[0023] This makes it easy to produce a rotor with the advantages mentioned above.

[0024] The invention further relates to an electrical machine, in particular a permanent magnet synchronous machine, which can be or is installed in a vehicle, for example, and which comprises a rotor according to one of the preceding embodiments.

[0025] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0026] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing. Short description of the drawings Fig. 1 shows a schematic representation of an electrical machine to explain the invention, Fig. 2 shows a schematic representation of an embodiment of a rotor of an electric machine in sectional view, and Fig. 3a, Fig. 3b and Fig. 3c show schematic representations of different embodiments of the segmented permanent magnets. Embodiment(s) of the invention

[0027] In Fig. 1 shows a schematic representation of an electrical machine 1 with a rotor 2 and a stator 3. The rotor 2 has a rotor shaft 4 and is arranged within the stator 3 so as to be rotatable about a rotation axis R. The rotation axis R is oriented in the z-direction, for example. A main or forward rotation direction is designated U here, for example; this is also a circumferential direction of the rotor 2. A gap or air gap is formed between an outer side of the rotor 2 and an inner side of the stator 3.

[0028] The electric machine 1 may be an electric machine according to the invention, although the design of the permanent magnets 5 is not shown here. Reference is made to the following figures.

[0029] Fig. Figure 2 shows a schematic representation of an embodiment of a rotor 2 of an electric machine 1 in a sectional view. Here, as in Fig. 1, the main or forward direction of rotation U, which also forms a circumferential direction of the rotor 2, as well as the axis of rotation R. Only one angular segment of the rotor 2 is shown; the rotor can, for example, have several of them, which are arranged next to one another in the forward direction of rotation U. By way of example, two recesses 2a are shown in the rotor 2, in which permanent magnets 5 are inserted. The permanent magnets 5 each have eight segments 5a, 5b and are joined together, in particular by gluing, in such a way that an elongated permanent magnet 5 with a length L and a width B is formed. The ends of the permanent magnet 5 are formed from segments 5a (marked with hatching) which comprise the first material and therefore have a higher coercive field strength than the segments 5b arranged further inwards (with respect to the permanent magnet itself), which comprise the second material.The permanent magnets 5 are further arranged at an angle to the radial direction of the rotor 2.

[0030] Fig. 3a, Fig. 3b and Fig. 3c show schematic representations of different embodiments of the segmented permanent magnets 5.

[0031] Fig. Figure 3a shows a permanent magnet 5 with three segments 5a, 5b. The permanent magnet 5 is divided into three segments 5a, 5b in the width direction B. Each of the segments 5a, 5b has an elongated shape, with the middle segment 5b comprising the second material, while the two outer segments 5a (marked with hatching) comprise the first material and therefore have a higher coercive field strength.

[0032] Fig. Figure 3b shows an embodiment in which the permanent magnet 5 is again divided into three segments 5a, 5b. The division takes place in Fig. 3b, however, takes place along the length L of the permanent magnet 5. The two segments 5a arranged at the ends in the longitudinal direction (marked with hatching) comprise the first material and therefore have a higher coercive field strength than the segment 5b arranged in the middle, which comprises the second material. The middle segment 5b is longer than the two segments 5a arranged at the ends. This makes it possible to reduce demagnetization of the permanent magnet 5, while at the same time simplifying the manufacture of the permanent magnet 5, since only three segments 5a, 5b need to be joined together. However, this comes at the expense of reducing the eddy currents induced by the time-varying magnetic field generated by the stator.

[0033] To further reduce these eddy currents, the permanent magnet 5 can be arranged as shown in Fig. 3c shown to be constructed from a plurality of segments 5a, 5b. In Fig. Figure 3c shows eight segments 5a, 5b, two of which (segments 5a) comprise the first material and six (segments 5b) comprise the second material. The segments 5a, 5b are arranged such that a segment 5a comprising the first material (indicated by hatching) is located at each end of the elongated permanent magnet 5.

[0034] The further inner segments 5b, however, comprise the second material. However, the number and arrangement of the segments 5a, 5b are not intended to be limiting. For example, segments 5a made of the first material can also be arranged inside. For example, it is conceivable that segments 5a made of the first material and segments 5b made of the second material are arranged alternately. A total of four, six, ten, or more segments 5a, 5b can also be combined to form a permanent magnet 5.

[0035] The reduction in demagnetization by segments 5a made of the first material arranged longitudinally at the ends was confirmed by simulations. It was determined that the maximum torque that can be generated by the electric machine 1 after an active short circuit, which can demagnetize the magnets, for a permanent magnet 5 made entirely of the first material corresponds to approximately 99.4% of the torque before the active short circuit. For a corresponding permanent magnet 5 made entirely of the second material, the maximum torque drops to approximately 98.8% of the original maximum value.

[0036] With a corresponding permanent magnet 5, which has a configuration like that in Fig.3c, i.e., six segments comprising the second material, and at each end in the longitudinal direction, one segment comprising the first material, the maximum torque after the active short circuit, i.e., after demagnetization, drops to approximately 99.4% of the maximum torque. It follows that the configuration proposed by the invention offers the same protection against demagnetization as a permanent magnet 5 consisting entirely of the first material, but with less consumption of the first material.

Claims

[1] Rotor (2) for use in an electrical machine (1), wherein the rotor (2) has one or more permanent magnets (5), whereby poles of the rotor (2) are formed, wherein the one or at least one of the plurality of permanent magnets (5) is a segmented permanent magnet having at least two segments (5a, 5b), wherein at least one of the at least two segments (5a, 5b) comprises a first material, in particular consists thereof, and at least one other of the at least two segments (5a, 5b) comprises a second material, in particular consists thereof, wherein the first material is different from the second material. [2] Rotor (2) according to claim 1, wherein the first material has a higher coercive field strength than the second material. [3] Rotor (2) according to claim 1 or 2, wherein the one or more permanent magnets (5) have an elongated shape with a length (L) that is greater than a width (B). [4] Rotor (2) according to claim 3, wherein the one or at least one of the plurality of permanent magnets (5) is divided along the widths into the at least two segments (5a, 5b). [5] Rotor (2) according to claim 3, wherein the one or at least one of the plurality of permanent magnets (5) has at least three segments (5a, 5b) and is divided into the at least three segments (5a, 5b) along the length (L). [6] Rotor (2) according to claim 5, wherein at least one of the segments (5a) arranged at the ends in the longitudinal direction comprises the first material, in particular consists thereof. [7] Rotor (2) according to one of the preceding claims, wherein the first material is an alloy comprising, in particular consisting of, neodymium, iron and boron, and furthermore at least one heavy rare earth, in particular terbium and / or dysprosium. [8] Rotor according to one of the preceding claims, wherein the second material is an alloy comprising, in particular consisting of, neodymium, iron and boron, and comprising less terbium and / or dysprosium than the first material, or comprising no terbium and / or dysprosium. [9] A method for producing a rotor (2) for use in an electrical machine (1), the method comprising: Producing first segments for a permanent magnet comprising a first material and second segments for permanent magnets comprising a second material, Joining at least one first segment and at least one second segment to produce at least one segmented permanent magnet (5), wherein the first segments and the second segments form at least two segments (5a, 5b) of the permanent magnet (5), and Inserting or attaching at least one segmented permanent magnet to the rotor. [10] The method of claim 9, wherein joining comprises gluing together at least one first segment and at least one second segment. [11] Electrical machine (1) comprising a rotor (2) according to one of claims 1 to 8. [12] Electrical machine (1) according to the preceding claim, wherein the electrical machine (1) is a permanent magnet synchronous machine.

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