Rotor of an electric machine, as well as an electric machine comprising such a rotor

Abstract

The present invention relates to a rotor (10) for an electric machine (12), and to an electric machine (12) with a base body (18) extending concentrically around an axial rotor shaft (14), wherein magnetic pockets (20) are formed in the base body (18) in which permanent magnets (22) comprising FeN material are received, and the permanent magnets (22) have an extent (24) in the tangential direction (9) which is greater than their dimension (26) in the radial direction (7), and the permanent magnets (22) are magnetized in the tangential direction (9).

Description

[0001] The invention relates to a rotor of an electric machine, and to an electric machine comprising such a rotor according to the preamble of the independent claims. State of the art

[0002] From DE 10 2010 061 778A1, an electric motor with a rotor comprising a laminated core is known, wherein magnets are arranged in recesses in the laminated core. The magnets are longer in the radial direction than in the tangential direction and are held in the recess by spring-loaded tabs. The rotor body is composed of two types of laminates, one type of laminate holding the magnets in the recesses by means of the spring-loaded tabs, and the other type of laminate connecting the laminated core to the rotor shaft. In this embodiment, the laminated core is connected to the rotor shaft, for example, by means of an injection-molded plastic to prevent magnetic flux to the metal rotor shaft. Rare-earth magnets, which are relatively expensive, are typically used in such designs. The object of the invention is to produce rotors with a less expensive magnet material but with comparable flux densities. Disclosure of the invention

[0003] The rotor and the electric machine according to the invention, with the features of the independent claims, have the advantage that the manufacturing costs of electric machines can be significantly reduced by using FeN magnets compared to rare-earth magnets, without reducing the magnetic flux density. However, to prevent demagnetization of these FeN magnets during operation, they can be arranged so that the magnetic flux must flow along their greatest extent. This ensures that the field strength in the FeN magnet remains high enough to prevent it from falling below a critical demagnetizing field strength. As a result, the induced opposing fields cannot damage the FeN magnet.

[0004] The measures listed in the dependent claims enable advantageous further developments and improvements of the embodiments specified in the independent claims. It is particularly advantageous to align the permanent magnets with their greatest extent in the tangential direction and to magnetize them tangentially as well. This causes the magnetic field lines to run tangentially through the permanent magnets and be deflected radially outwards at the magnetic poles between the magnets. Two adjacent permanent magnets are magnetized in opposite directions, so that either the north poles or the south poles of two adjacent permanent magnets point towards each other. This creates radially outward-facing magnetic poles between the permanent magnets on the rotor, with north and south poles alternating around the circumference.The radial outer surface of the magnetic poles can be designed in such a way that the emerging magnetic flux is adapted to the corresponding application of the electric machine.

[0005] The permanent magnets are advantageously arranged in magnetic pockets, which are, for example, punched out of the sheet metal. The magnetic pockets are open on their radially outer side, thus preventing a magnetic short circuit in the tangential direction through the rotor body. Retaining elements can be formed on both sides of the radial opening of the magnetic pocket with respect to the tangential direction, by means of which the permanent magnet is fixed in the magnetic pocket. For example, the retaining elements can be designed as elastic spring tabs that press the permanent magnet radially inwards into the magnetic pocket. This may eliminate the need for adhesive to fix the permanent magnets in the rotor.

[0006] FeN magnets with a rectangular cross-section relative to the radial plane of the rotor can be manufactured particularly easily, and their axial length can be readily adapted to the rotor's axial length. To effectively prevent demagnetization of the FeN magnets, their extent in the magnetizing direction is at least 1.2 times greater—and in particular at least 1.5 times greater—than their extent perpendicular to the magnetizing direction. The magnetizing direction here corresponds to the tangential direction, so the FeN magnets have a greater extent in the tangential direction than in the radial direction. Preferably, approximately cuboid-shaped permanent magnets are inserted axially into the receiving pockets in the rotor body.The extent of the permanent magnets is greater in the tangential direction than in the radial direction, with the permanent magnets exhibiting opposite magnetization in the tangential direction, causing adjacent permanent magnets to repel each other in the tangential direction. As a result, the magnetic field lines of the permanent magnets extend radially outwards through the rotor pole regions to the outer contour of the rotor, such that polar caps with a north pole alternate with polar caps exhibiting a south pole in the circumferential direction.

[0007] The permanent magnets are preferably not arranged centrally with respect to the radial dimensions of the base body, but rather offset radially inwards towards the rotor shaft. This means, in particular, that the magnet pockets are arranged radially inside, immediately adjacent to the rotor shaft. This minimizes negative leakage flux through the base body on the radial inner side of the permanent magnets, thereby increasing the power density of the electric machine.

[0008] The rotor's magnetic poles advantageously feature a pole separation, which, for example, deviates from a circular arc and is shaped according to a so-called "Richter" contour or a sinusoidal contour on the radial outer surface. This allows the cogging torque of the electric machine to be optimized for the respective application. The magnetic poles extend to the tangential retaining ribs on the magnet pockets, with the radial air gap to the stator ring being larger in the circumferential region of the retaining ribs than in the tangential center of the rotor poles. The rotor's circumference deviates from a perfect circle, so that the rotor radius is smaller in the circumferential regions of the permanent magnets than in the circumferential regions of the pole areas between the permanent magnets.

[0009] The rotor body can be manufactured particularly cost-effectively from stamped sheet metal lamellae, which are joined together axially, for example, by means of stamped stacks or adhesive. The magnet pockets with the spring-loaded retaining tabs for the permanent magnets can be stamped directly from the sheet metal material.

[0010] The rotor body is preferably arranged on a rotor shaft that is inserted into a central recess in the rotor body. For example, the rotor body can be pressed onto the rotor shaft or joined by injection molding. The outer circumference of the rotor shaft can also be designed with flat contact surfaces for the permanent magnets.

[0011] To achieve a sufficient magnetic flux density, sintered iron nitrate magnets are preferably used. These contain a significant amount of Fe. 16N2, which can provide particularly high magnetic flux densities, is used. Iron and nitrogen are practically unlimited in quantity on Earth. This eliminates dependence on the very limited resources of rare earth elements.

[0012] Such a rotor according to the invention is preferably arranged within a stator that is part of an electric machine. The electric machine is preferably designed as an electrically commutated electric motor, in which the stator has an electronically commutated winding that sets the rotor with the permanent magnets in rotational motion. Such an EC motor is preferably used as an electric drive unit of a windshield wiper system, but can also be used for other adjustment drives of corresponding components in motor vehicles or for rotary drives. Such an electric machine can also be used for applications outside of motor vehicles.

[0013] Since, when using iron nitrate magnets in the electric machine, the FeN magnets in the rotor are arranged in such a way that the magnetic flux runs along the maximum dimension of the FeN magnets in a tangential direction, demagnetization of the FeN magnets can be effectively prevented in the normal operating state of the electrically commutated motor. Brief description of the drawings

[0014] Preferred embodiments of the invention are explained in more detail in the following description with reference to the accompanying drawings, in which corresponding elements are provided with matching reference numerals. The drawings show: Fig. 1 a sectional view of an electrical machine according to a first embodiment, and Fig. 2. Schematic representation of the magnetic field strengths occurring during operation according to the design. Fig. 1. Embodiments of the invention

[0015] In Fig. Figure 1 shows a cross-section of an electric motor 12 in which a rotor 10 is arranged radially within a stator 50. The rotor 10 has a rotor body 18, which is, for example, fixedly mounted on a rotor shaft 14. Several magnet pockets 20 are formed in the rotor body 18, into which permanent magnets 22 are inserted. The permanent magnets 22 have a tangential extent 24 along the tangential direction 9 that is larger than their radial dimension 26 in the radial direction 7. For example, the tangential extent 24 is larger by a factor of at least 1.2 – in particular by a factor of at least 1.5 – than the radial dimension 26 of the permanent magnet 22. In the embodiment according to Fig. The permanent magnets 22 have a rectangular cross-section in the radial plane perpendicular to a rotor axis 15. The magnet pockets 20 are open radially outwards on a radial outer surface 21 of the permanent magnets 22 to prevent a magnetic short circuit. The permanent magnets 22 are arranged radially as far inwards as possible – radially within a radial center – on the base body 18 to minimize a magnetic short circuit on a radial inner surface 28 of the permanent magnet 22 as well. The permanent magnets 22 are magnetized tangentially 9, with the north and south poles of directly adjacent permanent magnets 22 pointing towards each other. This directs the magnetic field lines 33 of the rotor 10 radially outwards towards the surface 32 of the rotor 10 in the circumferential regions between the permanent magnets 22.This creates magnetic poles 30 between the permanent magnets 22, the surface 32 of which is radially convex on the outside. Preferably, the magnetic poles 30 have a pole separation 42, such that a radial air gap 44 between the rotor 10 and the surrounding stator 50 increases on both sides from the center 31 of the magnetic poles 30 in the circumferential direction 9. The magnetic flux flows through the permanent magnets 22 essentially along their entire tangential extent 24. Due to the larger tangential extent 24 in the tangential direction 9 – compared to the radial width 26 – of the permanent magnets 22, the magnetization direction ensures that no significant demagnetization occurs in the permanent magnets 22. The permanent magnets 22 have FeN as the magnetic material, which is significantly less expensive than rare-earth magnets. These permanent magnets 22 contain at least a certain proportion of Fe. 16N2 phase, and are preferably manufactured as sintered magnets. These iron nitrate-containing permanent magnets 22 have a flux density comparable to rare-earth magnets, but have a lower resistance to demagnetization.

[0016] Tangential retaining ribs 25 are formed radially on the outer surface of the magnetic poles 30, serving as fixing elements 23 for the permanent magnets 22. These tangential retaining ribs 25 overlap the permanent magnets 22 in a tangential direction 9, for example, by at least 10% on each side, or in particular by at least 20% of the tangential extent 24 of the permanent magnets 22. This results in the magnetic pocket 20 having a radial opening 35 on its radial outer surface 21, the tangential length 36 of which corresponds, for example, to at least half of the tangential extent 24 of the permanent magnet 22. The retaining ribs 25 can, in particular, be radially resilient, so that they press the permanent magnets 22 radially inwards against the magnetic pocket 20. The base body 18 is preferably made up of individual sheet metal lamellae 17 which are axially connected to each other, for example by means of stamping or gluing.The magnetic pockets 20 are punched out of the sheet metal lamellae 17, whereby the shape of the magnetic pockets 20 can also deviate from a rectangle. The base body 18 is rotationally fixed to the rotor shaft 14, for example by being pressed onto it. In . Fig. In this case, the rotor shaft 14 has a circular cross-section; however, the rotor shaft 14 can also have a rounded outer circumference on which the permanent magnets 22 are radially excited. For example, exactly six permanent magnets 22 are arranged evenly distributed around the circumference of the rotor. The stator 50 here has nine stator teeth 54, each of which is wound with individual tooth coils as an electrical winding 52. The stator teeth 54 form nine stator poles, which interact accordingly with the six rotor poles 30. The electrical winding 52 has, for example, three phases that are electronically commutated.

[0017] Fig. Figure 2 schematically shows the flux through the electric motor 12 when energized. For example, here the three individual tooth coils of a specific electrical phase are energized, so that three stator poles 54 are activated evenly distributed around the circumference. Fig. Areas 2 with higher magnetic flux B are shown hatched, where there is no risk of demagnetization. It can be seen that all permanent magnets 22, including their edges, lie within these areas 61, which are not critical for demagnetization. The permanent magnets 22 are inserted into the magnetic circuit in such a way that the magnetic flux completely penetrates them along their greatest extent. This ensures that the magnetic field strength within the permanent magnets 22 remains high enough that there is no risk of demagnetization due to opposing magnetic fields. Fig. 2. It is evident that tangentially between the permanent magnets 22, and also in radially outer regions of the base body 18 of the rotor 10, areas 62 with lower field strengths are formed, in which there would be a risk of demagnetization. These critical areas 62 are in Fig. Figure 2 shows a checkered pattern. However, no permanent magnets 22 are arranged in these critical areas 62. This specific choice of rotor geometry with longitudinally magnetized FeN magnets 22 allows, for example, rare-earth magnets to be replaced in certain applications. Such an electric machine 12 can, for example, drive windshield wipers and other components in motor vehicles.

[0018] It should be noted that with regard to the embodiments shown in the figures and in the description, numerous combinations of the individual features are possible. For example, the specific number, position, and design of the magnetic poles 30 and the stator poles 54 can be adapted to the requirements of the electric machine 12 and the manufacturing possibilities. Likewise, the specific design, arrangement, and number of the magnetic pockets 20, as well as the permanent magnets 22 arranged therein and the fixing elements 35 for the permanent magnets 22, can be varied. The specific design of the sintered iron nitride magnets with the corresponding Fe 16The N2 phase can be adapted to existing manufacturing capabilities. The invention is particularly suitable for the rotary drive of components or the adjustment of parts in motor vehicles, but can also be used for other applications, such as the drive of bicycles or scooters. The electric machine 12 with the FeN magnets is preferably designed as an electronically commutated EC motor. 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] DE 10 2010 061 778A1

[0002]

Claims

[1] Rotor (10) for an electric machine (12), with a base body (18) extending concentrically around an axial rotor shaft (14), wherein magnet pockets (20) are formed in the base body (18) in which permanent magnets (22) having FeN material are received, and the permanent magnets (22) have a tangential extent (24) (9) which is greater than their radial extent (26) (7), and the permanent magnets (22) are magnetized in the tangential direction (9). [2] Rotor (10) according to claim 1, characterized by , that between two adjacent permanent magnets (22) a magnetic pole (30) is formed which has a circumferentially curved surface (32) on the radially outer circumference of the base body (18), and magnetic field lines (33) of the magnetic pole (30) emerge approximately in the radial direction (7) from the curved surface (32) in order to interact with a stator field. [3] Rotor (10) according to any of the preceding claims, characterized by , that the magnetic pockets (20) are designed to be radially open to the outside, wherein fixing elements (23) are arranged on radially outer sides (21) of the magnetic pockets (20) as tangentially extending retaining webs (25) - which in particular press the permanent magnets (22) radially resiliently inwards into the magnetic pockets (20). [4] Rotor (10) according to any of the preceding claims, characterized by , that the permanent magnets (22) have an approximately rectangular cross-section (40) in the radial plane, and immediately adjacent permanent magnets (22) are magnetized in opposite directions. [5] Rotor (10) according to any of the preceding claims, characterized by , that the extent (24) in the tangential direction (9) is at least 1.5 times greater than the dimension (26) in the radial direction (7). [6] Rotor (10) according to any of the preceding claims, characterized by, that the permanent magnets (22) are arranged radially inwards off-center with respect to the radial direction (7) of the base body (18) - whereby in particular a magnetic short circuit on the radial inside (28) of the permanent magnets (22) is minimized. [7] Rotor (10) according to any of the preceding claims, characterized by , that the magnetic poles (30) have pole lifts (42) on both sides tangential to the retaining webs (25) in order to reduce the cogging torque of the rotor (10) and to adjust the desired shape of the induced voltage, thereby increasing the radial air gap (44) to the stator (50) at the retaining webs (25) - in particular according to a “Richter pole contour”. [8] Rotor (10) according to any of the preceding claims, characterized by , that the base body (18) is composed of axially stacked sheet metal lamellae (19) from which the magnet pockets (20) are punched out. [9] Rotor (10) according to any of the preceding claims, characterized by , that the base body (18) has a central through-opening (16) which is pressed onto a rotor shaft (14) which is approximately magnetically non-conductive. [10] Rotor (10) according to any of the preceding claims, characterized by , that the permanent magnets (22) are sintered - and in particular have nitrided FeN material with an Fe16N2 phase. [11] Rotor (10) according to any of the preceding claims, characterized by , that the permanent magnets (22) are designed as plastic-bonded magnets - and in particular nitrided FeN material with an Fe 16 exhibit N2 phase. [12] Electric machine (12), in particular electric motor, wherein the rotor (10) is arranged radially within a stator (50) according to one of the preceding claims, which has stator teeth (54) with an electronically commutated electrical winding (52). [13] Electric machine (12) according to claim 12, wherein the geometric arrangement of the permanent magnets (22) in the base body (18) of the rotor (10) ensures that a critical demagnetizing field strength in the permanent magnets (22) is not exceeded during operation by the excitation of the stator (50).

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