Rotor assembly for an axial flux motor, and axial flux motor comprising a rotor assembly

Abstract

Rotor assemblies (10) for an axial flux motor (100) are known, which comprise a rotor body (12) having a plurality of permanent-magnetic magnet sectors (20) which are arranged adjacent to one another along the circumference of the rotor body (12) and between which in each case one pole boundary (26) extends, wherein the magnet sectors (20) are magnetised in such a way that, at least on one axial end face (14) of the rotor body (12), in each case two different magnetic poles (22, 24), separated by a pole boundary portion (28), are arranged adjacent to one another alternately in the circumferential direction. According to the invention, the pole boundary portions (28) have a curved profile, as a result of which the cogging torque and the torque fluctuations resulting therefrom are reduced, which leads to the minimisation of undesired interference noises.

Description

[0001] DESCRIPTION

[0002] Rotor arrangement for an axial flux motor and axial flux motor with a rotor arrangement

[0003] The present invention relates to a rotor arrangement for an axial flux motor.

[0004] A rotor assembly for an axial flux motor typically comprises a rotor body containing a permanent magnet ring magnet with a plurality of pole segments arranged adjacent to each other in the circumferential direction of the rotor body. Two pole segments of opposite magnetic polarity are always arranged directly adjacent to one another. A pole boundary runs between each pair of adjacent pole segments, magnetically separating them.

[0005] Such a rotor arrangement is known, for example, from CN 114640202 A. The pole boundary sections on the end faces of the rotor body run obliquely with respect to the radial direction, which is intended to reduce the so-called cogging torque of the axial flux motor. Consequently, torque fluctuations, which can cause unwanted torsional vibrations and resulting noise during operation, are reduced.

[0006] Furthermore, the present invention relates to an axial flux motor with such a rotor arrangement. Such an axial flux motor has a stator arrangement with several stator poles, each formed by a pole tooth, with each pole tooth carrying a stator winding. The pole teeth extend axially in the direction of the axially adjacent rotor arrangement. The magnetic flux lines in the so-called air gap arranged between the stator arrangement and the rotor arrangement thus run in the axial direction in the axial flux motor.

[0007] The present invention is based on the objective of creating a rotor arrangement for an axial flux motor which is improved compared to the prior art with regard to cogging torque and the resulting occurrence of torque fluctuations.

[0008] This problem is solved according to the invention by a rotor arrangement having the features of claim 1.

[0009] The rotor arrangement according to the invention for an axial flux motor comprises a rotor body with several permanent magnet sectors arranged adjacent to one another in the circumferential direction of the rotor body. The rotor body can be formed in one piece or in multiple pieces. The magnet sectors can be designed as individual and separate permanent magnet elements inserted into the rotor body. Preferably, however, the magnet sectors are designed as permanent magnet sections of a one-piece ring magnet, which is magnetized differently sector by sector.

[0010] Between the magnetic sectors there is a pole boundary, which in the case of separate magnetic elements represents a physical separation of the adjacent magnetic elements, or in the case of a one-piece ring magnet represents a magnetic separation at which the magnetic field lines change direction, with the field lines of two adjacent magnetic sectors running in opposite directions to each other.

[0011] In principle, in a rotor assembly for an axial flux motor, the magnetic sectors are magnetized such that the magnetic field lines enter or exit the axial end face facing the stator in the axial direction, depending on the magnetization direction. In both the single-piece and multi-piece versions, the magnetic sectors are magnetized such that at least on one axial end face—namely, the axial end face of the rotor body facing the stator of the axial flux motor—two different magnetic poles are always arranged adjacent to each other in the circumferential direction, with the magnetic poles being separated from each other by a pole boundary section.

[0012] Thus, the magnetic north and south poles alternate circumferentially, so that the magnetic field lines enter a first magnetic sector, which forms a magnetic south pole, axially and exit the adjacent second magnetic sector, which forms a magnetic north pole, axially, i.e., they run in opposite directions to each other. Each pole boundary segment therefore separates the magnetic north pole from the circumferentially adjacent magnetic south pole at the axial end face of the rotor body.

[0013] According to the invention, the pole boundary sections have a curved profile. In a conventional rotor arrangement according to the prior art, the pole boundary sections run linearly along the axial end faces, whereas in the prior art, the pole boundary sections can run at an angle with respect to the radial direction. This results in a less abrupt transition between two adjacent magnetic poles of the rotor when they move from the magnetic field of a first stator winding across the stator slot into the magnetic field of an adjacent second stator winding. The following magnetic pole of the rotor in the direction of rotation is thus gradually guided into the effective range of the magnetic field of the stator winding following in the direction of rotation and therefore does not enter its effective range abruptly with its entire radial width, as is the case with purely radially extending pole boundary sections.By skew the pole boundary sections, the cogging torque of the axial flux motor is reduced, thus minimizing torque fluctuations. This effect increases with increasing skew angle.

[0014] Simulations and initial prototype tests have shown that a curved pole boundary further enhances this effect, thus further reducing the cogging torque and the resulting torque fluctuations, which leads to an additional minimization of unwanted noise and consequently improves the so-called noise, vibration, and harshness (NVH) behavior of the axial flux motor.

[0015] The polar boundary section can be curved such that, starting from the radially innermost endpoint on the axial end face of the annular rotor body, for example in the case of a purely leftward curvature of the polar boundary section, the polar boundary section initially extends outwards to the right of a radial running purely radially from the rotor center, moving away from the radial in the circumferential direction. Due to the leftward curvature, the polar boundary section moves away from the radial until a reversal point whose tangent is parallel to the radial. From there, the polar boundary section approaches the radial again, and upon reaching the radially outer edge of the axial end face of the rotor body, the polar boundary section either does not reach the radial, ends precisely on it, or intersects it.In the case of a pure rightward curvature of the polar boundary segment, the polar boundary segment can accordingly run at least partially to the left of the radials.

[0016] Alternatively, starting from the radially innermost point, the polar boundary section can, in the case of pure leftward curvature, run exclusively to the left of the radials passing through the innermost point, or, in the case of pure rightward curvature, run exclusively to the right of these radials, so that, viewed from the inside out, the polar boundary section moves further and further away from the radials in the circumferential direction.

[0017] Generally, the polar boundary section on an axial end face is preferably curved in only one direction. Alternatively, the polar boundary section on an axial end face can also be curved in both directions and thus be S-shaped.

[0018] The curvature direction of the pole boundary section is fundamentally independent of the rotor's direction of rotation. However, in certain applications, a relationship between these factors can be advantageous.

[0019] In a particularly preferred embodiment of the invention, the rotor body is designed as a one-piece ring magnet. The ring magnet can, for example, be a rare-earth magnet produced by a sintering process. The ring magnet is magnetized sector by sector such that alternating, differently polarized magnetic sectors are arranged adjacent to one another, their magnetic field lines running in opposite directions, with the magnetic field lines generally entering and exiting the magnetic sectors in an axial direction. By using a one-piece ring magnet, the entire rotor body can be formed as a single piece, thus eliminating the need for a return ring, which is necessary, for example, for coupling individual, separate magnetic elements.

[0020] In a further particularly preferred embodiment of the invention, each pole boundary section additionally runs at a skew angle with respect to a purely radially extending line. The skew angle is defined as follows: If the two endpoints of the pole boundary section were connected by a straight line, which is henceforth referred to as the chord of curvature, the skew angle would describe the angle between the chord of curvature and the radial that extends radially outward from the center of the rotor body, which lies on the axis of rotation of the rotor body, through the radially inner endpoint of the pole boundary section on the axial end face of the rotor body.

[0021] A particularly preferred angle of inclination is that originating from a radially inner end of the pole boundary section and directed in the direction of curvature relative to the radial. Starting from the radially innermost point of the pole boundary section on the axial end face of the rotor body, the chord of curvature extends to the left of the radial for a left-hand curved pole boundary section, whereas for a right-hand curved pole boundary section, the chord of curvature lies to the right of the radial. The additional inclination of the curved pole boundary section leads to a further improvement in torque characteristics and a reduction in torque fluctuations.

[0022] The helix angle is preferably greater than 1°, with the helix angle being particularly preferably between 5° and 45°. In particular, with a helix angle between 10° and 30°, the additional helix of the curved pole boundary section has the strongest effect on improving the torque characteristics.

[0023] In a further particularly advantageous embodiment, the pole boundary section has a constant radius of curvature. Consequently, the pole boundary section is designed as a circular arc, which has a beneficial effect on the manufacturability of the magnetic sectors.

[0024] In a further embodiment of the invention, the radii of curvature of all pole boundary sections are identical. This results in a relatively uniform torque behavior over the circumference of the rotor body.

[0025] In a further preferred embodiment of the invention, the curvatures of all pole boundary sections on the same axial end face of the rotor body exhibit the same direction of curvature. Preferably, the magnet sectors are designed such that if the pole boundary sections on a first axial end face of the rotor body have a leftward curvature, the pole boundary sections on the opposite axial end face of the rotor body have a rightward curvature. This is advantageous, for example, in an axial flux motor that has a stator arrangement on each of the two axial sides of the rotor assembly.

[0026] In a further particularly preferred embodiment of the invention, the curvature height is at least 5% of the curvature length. The curvature length denotes the length of the already defined chord of curvature, i.e., the direct distance between the radially inner and the radially outer endpoints of the pole boundary segment. The curvature height, on the other hand, denotes the distance perpendicular to the chord of curvature of the furthest point on the pole boundary segment. In the case of a circular arc, this is the distance between the chord of curvature and the tangent parallel to it on the circular arc. The curvature height, in combination with the curvature length, thus defines the radius of curvature. From a curvature height of 5% of the curvature length, significant improvements are observed with regard to the cogging torque and the resulting torque fluctuations.

[0027] Furthermore, the invention comprises an axial flux motor with a rotor arrangement according to the invention. The axial flux motor includes a stator arrangement arranged axially adjacent to the rotor arrangement. The stator arrangement has a stator body with several pole teeth. The pole teeth extend axially from a common return ring in one direction towards the rotor arrangement, with an axial air gap formed between the stator and rotor arrangements. The pole teeth have stator windings, which are preferably wound around the pole teeth in a plane arranged perpendicular to the axis of rotation. The magnetic field lines therefore run axially through the air gap between the stator poles and the magnetic poles of the rotor arrangement.

[0028] In a further embodiment, the stator assembly comprises a stator body formed from a spirally wound strip of sheet metal. This strip has teeth extending parallel to one another in the transverse direction on one side, spaced apart such that, after winding the strip, a three-dimensional stator body with pole teeth extending axially on one side is formed. This allows the stator body, and consequently the stator assembly, to be manufactured relatively cost-effectively.

[0029] Furthermore, the axial flux motor can have two stator arrangements that are arranged on axially opposite sides of the rotor arrangement and thus jointly drive the rotor arrangement in between.

[0030] Furthermore, the axial flux motor can have several axially stacked rotor arrangements, between each of which at least one stator arrangement is arranged, thereby increasing the drive power of the axial flux motor.

[0031] An embodiment of the present invention is described below with reference to the accompanying figures. These show:

[0032] Figure 1 shows a schematic representation of a rotor arrangement according to the invention in a top view, and

[0033] Figure 2 shows a schematic representation of an axial flux motor with the rotor arrangement according to the invention shown in Figure 1 in a perspective view.

[0034] Figure 1 shows a rotor assembly 10 for an axial flux motor 100, which is shown in Figure 2 and can be used, for example, in an electric water pump for a motor vehicle. The rotor assembly 10 comprises a rotor body 12, which is designed as a one-piece permanent magnet ring magnet 13 and has several permanent magnet sectors 20, between each of which a pole boundary 26 runs.

[0035] The ring magnet 13 is magnetized sector by sector such that on both axial end faces 14 of the rotor body 12, two different magnetic poles 22, 24 are alternately arranged adjacent to each other in the circumferential direction, wherein the magnetic poles 22, 24 on each axial end face 14 are magnetically separated by a pole boundary section 28, which extends from a radially inner edge 23 of the rotor body 12 to a radially outer edge 25 of the rotor body 12.

[0036] The pole boundary section 28 thus separates a magnetic north pole 22 formed by a first magnetic sector 20 from a magnetic south pole 24 formed by a second immediately adjacent magnetic sector 20. The magnetic sectors 20 are magnetized such that the magnetic field lines exit or enter the magnetic north pole 22 in an axial direction at the end faces of the magnetic sectors 20.

[0037] The ring magnet 13 is further magnetized such that the pole boundary sections 28 on the axial end faces 14 have a curved profile. All pole boundary sections 28 of the first axial end face 14 shown in Figure 1 are each formed as circular arcs and therefore have a constant radius of curvature R. This radius is identical for all pole boundary sections 28. Furthermore, all pole boundary sections 28 on this axial end face 14 exhibit a purely left-hand curvature, whereas the pole boundary sections 28 on the opposite axial end face (not shown) exhibit a right-hand curvature.

[0038] A radially inner endpoint 281 of the pole boundary section 28 at the radially inner edge 23 of the rotor body 12 and a radially outer endpoint 282 of the pole boundary section 28 at the radially outer edge 25 of the rotor body 12 are dimensionally connected by a chord of curvature KS, the length of which is designated as the curvature length L. Furthermore, the curvature height H denotes the perpendicular distance of the pole boundary section 28 from the chord of curvature KS. The curvature height H is approximately 15% of the curvature length L. Each pole boundary section 28 also runs at an angle α relative to a radial B extending purely in the radial direction. The radial B extends radially outward from the center point M of the rotor body 12, which lies on the axis of rotation, through the inner endpoint 281 of the pole boundary section 28.The helix angle a defines the angle between the radial B and the curvature chord KS, both of which pass through the radially inner endpoint 281 of the pole boundary section 28. The helix angle a is directed in the direction of curvature with respect to the radial B, such that the curvature chord KS extends to the left of the radial B.

[0039] In this case, the inclination angle α is approximately 20°. As a result, the left-curved polar boundary section 28, viewed from the inside out, initially extends to the right of the radial B passing through the inner endpoint 281, then crosses the radial B and subsequently runs to the left of the radial B.

[0040] Figure 2 shows an axial flux motor 100 with a rotor arrangement 10 according to the invention, which can be used, for example, as a drive motor for an electric water pump of a motor vehicle. The axial flux motor 100 comprises a stator arrangement 110, which is arranged axially adjacent to the rotor arrangement 10. The stator arrangement 110 has a stator body 112, wherein the stator body 112 is formed by a plurality of pole teeth 113 extending axially in the direction of the rotor arrangement 10 and having a pie-shaped cross-section, which are magnetically connected to one another by a common integral return ring 114.

[0041] The pole teeth 113 are each provided with a stator winding 116 wound around the pole teeth 113, the stator windings 116 being, for example, wound on winding carriers 118 that are at least partially mounted on the pole teeth 113. The stator body 112 is formed by a spirally wound strip of sheet metal, which is wound around the central axis of the stator assembly 110 from the inside out to form the three-dimensional stator body 112 shown in Figure 2.

Claims

PATENT CLAIMS 1. Rotor arrangement (10) for an axial flux motor (100), comprising: a rotor body (12) with several permanent magnet sectors (20) arranged adjacent to each other in the circumferential direction of the rotor body (12) and between which a pole boundary (26) runs, wherein the magnet sectors (20) are magnetized such that at least on an axial end face (14) of the rotor body (12) two different magnetic poles (22, 24) are alternately arranged adjacent to each other in the circumferential direction, separated from each other by a pole boundary section (28), characterized in that the pole boundary sections (28) have a curved profile.

2. Rotor arrangement (10) according to claim 1, wherein the rotor body (12) is designed as a one-piece ring magnet (13).

3. Rotor arrangement (10) according to one of the preceding claims, wherein each pole boundary section (28) additionally extends at an angle of inclination (a) with respect to a radial (B) extending purely in the radial direction.

4. Rotor arrangement (10) according to claim 3, wherein the helix angle is directed in the direction of curvature starting from a radially inner end of the pole boundary section (28) with respect to the radial (B).

5. Rotor arrangement (10) according to claim 3 or 4, wherein the helix angle (a) is preferably greater than 1° and particularly preferably between 5° and 45°.

6. Rotor arrangement (10) according to one of the preceding claims, wherein the pole boundary section (28) has a constant radius of curvature (R).

7. Rotor arrangement (10) according to claim 6, wherein the radii of curvature (R) of all pole boundary sections (28) are identical.

8. Rotor arrangement (10) according to one of the preceding claims, wherein the curvatures of all pole boundary sections (28) on the same end face of the rotor body (20) have the same direction of curvature.

9. Rotor arrangement (10) according to one of the preceding claims, wherein a curvature height (H) is at least 5% of a curvature length (L).

10. Axial flux motor (100) with a rotor arrangement (10) according to one of the preceding claims, comprising: a stator arrangement (110) which is arranged axially adjacent to the rotor arrangement (10).

11. Axial flux motor (100) according to claim 10, wherein the stator arrangement (110) has a stator body (112) formed from a spirally wound strip of sheet metal.

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