Rotor for an electric motor

Abstract

The invention relates to a rotor (1) for an electric motor, comprising a rotor body (2) having magnet pockets (5) distributed about a central rotor axis (D) and having rotor magnets (6) inserted therein, wherein identically formed rotor end rings (7) are arranged on both end faces of the rotor body (2) and have axially oriented positioning pins (8), which engage in an associated free space (5b) of the respective magnet pocket (5), and wherein the respective rotor end ring (7) has a number of snap hooks (9), which catch into a recess (4) of the rotor body (2) running in the axial direction (A).

Description

[0001] Page 1

[0002] 2024 383 WO

[0003] Description

[0004] Rotor for an electric motor

[0005] The invention relates to a rotor for an electric motor, comprising a rotor body with a number of magnetic pockets arranged distributed along a circumferential direction, each pocket containing a permanent magnet rotor magnet. The invention further relates to an electric motor with such a rotor.

[0006] In a motor vehicle, especially a passenger car, electric motors are typically used in a variety of ways to drive different actuators or auxiliary units that do not directly contribute to the vehicle's propulsion. For example, electric motors are used as window regulator drives, sunroof or seat adjustment drives, steering drives (EPS, Electrical Power Steering), brake boosters (EBB, Electronic Brake Booster), radiator fan drives, or transmission actuators.

[0007] Such an electric motor, typically designed as a brushless direct current (BLDC) motor, essentially consists of a stationary stator with an electrical stator or rotating field winding containing a number of (motor) phases, which serves as the energy converter for electrical energy into mechanical energy. The electric motor also features a rotor with several permanent magnets, which is fixed to a rotor shaft. The rotor shaft is rotatably mounted around a rotor axis by means of one or more bearings. As a three-phase AC machine, the stator, or rather its rotating field winding, has three phases and thus at least three phase windings, each of which is supplied with an electric current out of phase to generate a rotating magnetic field in which the rotor, also called the runner, rotates around its axis. Page 2

[0008] The rotor typically features a central, often cylindrical, stamped laminated core as its rotor core or rotor body. This core, referred to below as the rotor body, is, for example, rigidly connected to the rotor or motor shaft of the electric motor. The rotor body may include recesses or slots, known as magnet pockets, in which the permanent magnets (rotor magnets) are arranged. An electric motor with such a rotor body is also called an interior permanent magnet motor (IPM motor).

[0009] In addition to magnetic torque, IPM motors also utilize reluctance due to magnetic resistance by embedding the permanent magnets within the rotor body. Therefore, IPM motors typically exhibit higher torque and efficiency than surface-mounted permanent magnet motors (SPM motors) with rotor magnets mounted on the outer surface of the rotor. This allows for particularly high torque and power density, as well as a compact design and thus lower manufacturing costs.

[0010] From DE 10 2022 203 959 A1, a rotor for an electric motor is known, wherein the rotor is a rotor body designed as a laminated core (rotor core) with a number of recesses distributed along a tangential direction, serving as magnet pockets, in each of which a permanent magnet rotor is inserted. A disk-shaped or ring-shaped rotor end plate is arranged on both end faces of the rotor core. This end plate has a number of retaining projections or pins corresponding to the number of recesses, which are integrally formed on the rotor end plate and engage in corresponding recesses to clamp and fix the respective rotor magnet in the recess. Page 3

[0011] The magnets are radially tensioned in the magnet pockets by means of the rotor end disks, which engage in a free space between the respective (rotor) magnet and the rotor package.

[0012] To secure the rotor end disks axially, one of the rotor end disks has additional pins that extend through the entire rotor assembly and the other rotor end disk. In an additional process step, known as hot air riveting, the protruding pin is melted and compressed, so that the two rotor end disks are positively locked together and surround the magnet axially.

[0013] The known concept therefore requires two different rotor end disks. Due to the pins engaging with the rotor assembly and one of the two rotor end disks, this concept is limited to an active part length determined by the length of these pins. Changing the active part length thus necessitates a corresponding change in the concept and consequently also a change in tooling. Scalability with this concept is therefore only possible with considerable effort.

[0014] The invention is based on the objective of providing a particularly suitable rotor for an electric motor. In particular, it aims to enable suitable magnet positioning and fixation of a plurality of permanent magnets in the designated magnet pockets of a rotor body (rotor stack), independent of the axial rotor length, and especially independent of the active part length, preferably for different length variants of such rotors or their rotor bodies. The invention is further based on the objective of providing a particularly suitable electric motor.

[0015] With regard to the rotor, the problem is solved according to the invention by the features of claim 1, and with regard to the electric motor by the features of claim 10. Advantageous embodiments and further developments are the subject of the dependent claims. The advantages mentioned with regard to the rotor and page 4

[0016] The same principles apply to electric motors and vice versa.

[0017] The rotor according to the invention is designed, suitable, and configured for use in an electric motor, particularly a brushless electric motor. The rotor comprises a rotor body (rotor core), for example, a laminated core. The substantially cylindrical rotor body has a number of magnet pockets arranged around a central rotor axis, each containing a permanent magnet rotor magnet. In other words, the rotor is preferably designed as an embedded permanent magnet rotor (IPM rotor).

[0018] The rotor magnets or magnet pockets are preferably arranged in pairs along the circumference as approximately V-shaped magnet pairs, with the rotor magnets of each pair having the same polarity. The magnet pockets preferably penetrate the rotor body completely in the axial direction. The magnet pockets are designed as axially open (through-)openings in the rotor or rotor body to accommodate a rotor magnet. The magnet pockets are preferably closed on the circumference and thus arranged completely within the rotor body. Alternatively, the magnet pockets can be open radially towards an inner (shaft) opening or radially towards the outer circumference of the rotor body.

[0019] In this and the following, "axial" or an "axial direction" refers specifically to a direction parallel (coaxial) to the central rotor axis or axis of rotation, i.e., perpendicular to the rotor's end faces. Similarly, in this and the following, "radial" or a "radial direction" refers specifically to a direction oriented perpendicular (transverse) to the central rotor axis or axis of rotation along a radius of the rotor. In this and the following, "circumferential" or a "circumferential direction" refers specifically to a direction along the circumference of the rotor (azimuthal direction). Page 5

[0020] A rotor end ring is arranged on each end face of the rotor body. The two rotor rings are preferably made of plastic, in particular injection-molded parts made of a thermoplastic. It is particularly advantageous if the rotor rings are identical, i.e., designed as identical parts.

[0021] Each rotor end ring has a number of axially oriented positioning pins corresponding to the number of magnet pockets. These pins engage in a designated recess within the respective magnet pocket to clamp the rotor magnet inserted therein radially. During assembly of the rotor end rings, the positioning pins indirectly press-fit the rotor magnets into the magnet pockets, with the insertion of the positioning pins being easily and reliably controlled by the process.

[0022] The positioning pins, which may be bolt-shaped or cylindrical, are preferably integrally formed, i.e., monolithically, on the rotor end rings. The axial length of the positioning pins engaging in the corresponding recesses of the magnet pockets preferably corresponds to approximately 15% or 1 / 7 of the axial length or height of the rotor body. In other words, the positioning pins preferably have an axial height or length that is less than the axial height of the recesses of the magnet pockets.

[0023] Each rotor end ring has a number of snap hooks, hereinafter also referred to as locking tongues with free-end locking hooks, which engage in an axially extending recess in the rotor body and lock into place with a detent or joining contour. The detent contour is preferably designed as a recess forming an undercut in the sheet metal layers of the rotor body. This allows for a more complex fastening of the rotor end rings and thus enables tool-reduced positioning and fixing of the rotor magnets in the magnet pockets of the rotor body. In the detent connection with the rotor body, the rotor end rings also fix the rotor magnets within the associated magnet pockets in the axial direction. Page 6

[0024] The rotor end rings are designed to be particularly material-efficient, with a smaller ring area compared to the prior art. Advantageously, each rotor end ring covers less than 50%, preferably less than (30 ± 10)% and more than (10 ± 5)% of the rotor body's end face. Additionally or alternatively, the ratio between the inner diameter and the outer diameter of the respective rotor end ring is greater than 0.5, preferably greater than (0.7 ± 0.15), and particularly preferably greater than (0.9 ± 0.05). The rotor end rings can therefore be produced particularly cost-effectively.

[0025] According to a preferred embodiment, a number of radially oriented cover tabs are provided, and in particular integrally formed, on the outside of each rotor end ring. The cover tabs suitably cover the rotor magnets seated in the magnet pockets only partially in the radial direction, preferably less than 50%, particularly less than 30%, and more preferably more than 10%, preferably (20 ± 5)%. The cover tabs are advantageously arranged circumferentially around the rotor body between adjacent snap hooks. The positioning pins are also suitably arranged circumferentially around the rotor body between adjacent snap hooks.

[0026] In the preferably paired, V-shaped magnet pockets and the rotor magnets inserted therein, the positioning pins of the respective rotor end ring are arranged side by side as pairs of pins, with one of the snap hooks being located between adjacent pairs of pins. Preferably, the cover tabs are located at the position of the paired positioning pins.

[0027] In an advantageous embodiment, the snap hooks between adjacent pairs of pins are formed radially inwardly offset on the inner circumference of the respective rotor end ring. Particularly advantageous is the formation of the cover tabs in the area of ​​the pin pairs, extending radially outward on the outer circumference of the respective rotor end ring. Page 7

[0028] The electric motor is intended for, suitable for, and configured for use in a motor vehicle. The electric motor features a rotor as described above. This means that the electric motor is preferably designed as an embedded permanent magnet motor (IP M motor). The electric motor is advantageously configured with a rotor whose rotor magnets are arranged in a V-shape. With this rotor topology, the electric motor is particularly well-suited for use as a traction drive in electric or electric two-wheeled vehicles (e2W).

[0029] The advantages achieved with the invention lie particularly in the fact that the same rotor end rings can always be used for different length variants of the rotor or its rotor body. In other words, it is possible to accommodate the variance of potentially different length variants with just one design of rotor end rings, which can be provided as identical parts, while simultaneously keeping product costs low, especially since only one tool is required. Furthermore, the snap-fit ​​connection enables a simple and reliable form-fit and force-fit fastening of the rotor end rings to the rotor body.

[0030] Further cost reductions are achieved through optimized material usage, reduced weight of the rotor end rings, and the elimination of an entire process step (hot air riveting). The advantageous partial coverage of the rotor magnets by the rotor end ring, achieved through its cover tabs with minimal radial dimensions, also simplifies process monitoring, especially since the rotor magnets remain visible even after the rotor end ring is joined.

[0031] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows:

[0032] Fig. 1 shows a perspective exploded view of an (IPM) rotor with a

[0033] Rotor body with V-shaped arranged magnetic pockets and rotor magnets that can be inserted into these pockets (page 8), as well as rotor rings designed as identical parts for magnet positioning and magnet fixation.

[0034] Fig. 2 shows a sectional view of the rotor in a partial exploded view with inserted rotor magnets and with a rotor end ring fixed to the rotor body, and

[0035] Fig. 3 shows a top view of the rotor with a rotor end ring schematically depicted in two different views, of which the mounting positions of partially shown positioning pins and snap hooks (without ring body surface) are visible to the right of a dashed dividing line.

[0036] Corresponding parts and sizes are always marked with the same reference symbols in all figures.

[0037] The rotor 1 of an electric motor (not shown in detail) is an internal rotor, shown in Figures 1 to 3, and in Figure 1 in an exploded view in a partially disassembled state. In this embodiment, the rotor 1 has a cylindrical rotor assembly as the rotor body or rotor base 2. This assembly is rigidly connected to a rotor shaft (motor shaft) (not shown in detail) or non-rotatably connected to the rotor shaft. In the assembled state, the rotor shaft, and thus the rotor 1, is rotatably mounted relative to a stationary stator of the electric motor that surrounds the rotor 1. In this embodiment, the rotor 1 is designed as an IPM rotor.

[0038] The rotor body 2 is formed, for example, from a number of unspecified rotor laminations, which are stacked and stamped together along an axial direction A illustrated in Fig. 1 to form a lamination stack (rotor lamination stack). The rotor body 2 has a central through-hole 3 for receiving the rotor shaft, which is rotatably mounted about a central rotor axis or axis of rotation D indicated in Fig. 2 in a manner not shown in detail. To reduce the moment of inertia of the rotor 1, the rotor body 2 in this embodiment has ten recesses 4 that penetrate the lamination stack. The recesses 4 are arranged evenly distributed around the central through-hole 3 or around the central rotor axis D along the circumferential direction U illustrated in Fig. 1. The recesses 4 have an approximately teardrop-shaped or triangular cross-sectional shape along the axial direction A.

[0039] The rotor body 2 has a number of magnet pockets 5 into which a corresponding number of permanent magnet rotor magnets 6 are inserted or can be inserted to generate a magnetic excitation field. The rotor magnets 6 are arranged in pairs as magnet pairs distributed along the circumferential direction U. The magnet pairs have an approximately V-shaped arrangement of the rotor magnets 6, with the angle between the V-legs or rotor magnets 6 being approximately (80 ± 10)°. The rotor magnets 6 of each magnet pair have the same polarization or magnetization, and the magnet pairs form the poles of the ten-pole rotor 1 in the exemplary embodiment.

[0040] As can be seen, for example, in Fig. 1, the magnet pockets 5 have an axial cross-sectional shape with an approximately rectangular magnet area or magnet chamber 5a and an approximately triangular free space 5b adjoining a radially inner narrow side of the magnet chamber 5a. The magnet chamber 5a is shaped essentially complementary to the outer contour of the rotor magnets 6. The rotor magnets 6 are inserted into their respective magnet chambers 5a with a precise fit and exhibit radial or tangential play within the magnet pocket 5 due to the free space 5b.

[0041] For positioning and securing or fixing the rotor magnets 6 in the magnet pockets 5, the rotor 1 has two identical rotor end rings 7 arranged on the end face of the rotor body 2. The rotor end rings 7, or their ring bodies, each have a number of positioning pins or clamping pins 8 on the flat surface facing the rotor body 4, corresponding to the number of magnet pockets 5. The positioning pins 8, designed as cylindrical clamping pins, are integrally formed with the respective rotor end ring 8 or its ring body and project upwards in the axial direction A towards the rotor body 2. Page 10

[0042] The positioning pins 8 engage in the corresponding free space 5b of the respective magnet pocket 5 during assembly or installation. This clamps the corresponding rotor magnet 6 in the magnet pocket 5, particularly in the radial direction R. The positioning pins 8 have an axial length that is less than the axial length of the magnet pockets 5 that penetrate the rotor body 2, in particular approximately 15% of the axial length of the rotor body 2.

[0043] Each rotor end ring 8 has a number of snap hooks 9, hereinafter also referred to as detent tongues with free-end detent hooks, which engage in the recesses 4 of the rotor body 2 extending in the axial direction A. Detent or joining contours 10 are provided in the recesses 4, into which the snap hooks 9 engage, forming a rear grip. The respective detent contour 10 is suitably designed as a recess forming an undercut in the rotor body 2 or in its sheet metal layers. The snap hooks 9 are integrally formed radially inwards on the inner circumference of each rotor end ring 7 between adjacent pairs of pins of the positioning pins 8.

[0044] The snap hooks 9 of the rotor end rings 8 and the corresponding locking contours 10 of the rotor body 2 provide a particularly efficient fastening of the rotor end rings 8, thus enabling tool-free positioning and fixing of the rotor magnets 6 in the magnet pockets 5 of the rotor body 2. In the snap-fit ​​connection with the rotor body 2, the rotor end rings 8 fix the rotor magnets 6 within the associated magnet pockets 5 in the axial direction A.

[0045] A number of radially oriented cover tabs 11 are integrally formed on the outer surface of each rotor end ring 7. The cover tabs 11 are arranged circumferentially U of the rotor body 2 between adjacent snap hooks 9. In the assembled state, the cover tabs 11 of the rotor end rings 7 partially cover the end-face magnetic chambers 5a of the magnet pockets 5 and secure the rotor magnets 6 against axial slippage out of the magnet pockets 5. The cover tabs 11 only cover approximately 20% of the rotor magnets 6 seated in the magnet pockets 5 in the radial direction R. The cover tabs 11 are integrally formed on the outer circumference of each rotor end ring 7, extending radially outwards in the area of ​​the paired positioning pins 8 or pin pairs.

[0046] The rotor end rings 7 cover only about 20% of the rotor body 2 at its end face. The ratio between the inner diameter di and the outer diameter da of each rotor end ring 8 is approximately 0.9. The rotor end rings 7, which are made, for example, of PA 6 GF 30, are primarily designed as (plastic) injection-molded parts.

[0047] In summary, the invention relates to a rotor 1 with magnet pockets 5 arranged around a central rotor axis D, with rotor magnets 6 inserted therein, wherein equal rotor end rings 7 with axially oriented positioning pins 8 are arranged on both end faces of the rotor body 2, which engage in an associated free space 5b of the respective magnet pocket 5, and wherein the respective rotor end ring 7 has a number of snap hooks 9 which latch in a recess 4 of the rotor body 2 extending in the axial direction A.

[0048] The claimed invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived by a person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all individual features described in connection with the various embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention. Page 12

[0049] Reference symbol list

[0050] 1 Rotor

[0051] 2 rotor bodies

[0052] 3 Feedthrough opening

[0053] 4 recesses

[0054] 5 magnetic pockets

[0055] 5a Magnetic area A space

[0056] 5b Free space

[0057] 6 Rotor magnet

[0058] 7 Rotor end ring

[0059] 8 Positioning pin / clamping pin

[0060] 9 snap hooks

[0061] 10 Raster / joining contour

[0062] 11 Cover flap

[0063] A Axial direction

[0064] D Rotor / rotational axis

[0065] R Radial direction

[0066] U circumferential direction

Claims

Page 13 Claims 1. Rotor (1) for an electric motor, comprising a rotor body (2) with a number of magnet pockets (5) arranged around a central rotor axis (D) with permanent magnetic rotor magnets (6) inserted therein, - wherein a rotor end ring (7), in particular of equal size, is arranged on each of the two end faces of the rotor body (2), - wherein the respective rotor end ring (7) has a number of axially oriented positioning pins (8) corresponding to the number of magnet pockets (5), which engage in an associated free space (5b) of the respective magnet pocket (5) and clamp the rotor magnet (6) inserted therein in the radial direction (R), and - wherein the respective rotor end ring (7) has a number of snap hooks (9) which engage in an axially extending recess (4) of the rotor body (2) and snap into place with a detent contour (10).

2. Rotor (1) according to claim 1, characterized in that, - that the respective rotor end ring (7) covers or obscures the rotor body (2) face by less than 50%, preferably less than (30 ± 10)%, and more than (10 ± 5)%, and / or - that the ratio between the inner diameter (di) and the outer diameter (da) of the respective rotor end ring (7) is greater than 0.5, preferably greater than (0.7 ± 0.15), particularly preferably (0.9 ± 0.05).

3. Rotor (1 ) according to claim 1 or 2, characterized in that a number of radially oriented cover tabs (11) are formed on the outside of the respective rotor end ring (7).

4. Rotor (1) according to claim 3, characterized in that, Page 14 that the cover flaps (11) only partially cover or obscure the rotor magnets (6) located in the magnet pockets (5) in the radial direction (R), preferably to less than 50%.

5. Rotor (1 ) according to claim 3 or 4, characterized in that the cover tabs (11) are arranged in the circumferential direction (U) of the rotor body (2) between adjacent snap hooks (9).

6. Rotor (1 ) according to one of claims 1 to 5, characterized in that the magnet pockets (5) and the rotor magnets (6) inserted therein are arranged in pairs in a V-shape.

7. Rotor (1 ) according to one of claims 1 to 6, characterized in that the positioning pins (8) of the respective rotor end ring (7) are arranged as pairs of pins next to each other, wherein the snap hooks (9) are arranged between adjacent pairs of pins.

8. Rotor (1 ) according to one of claims 1 to 7, characterized in that the snap hooks (9) are formed radially inwards on the inner circumference of the respective rotor end ring (2).

9. Rotor (1 ) according to one of the preceding claims, characterized in that the cover tabs (11) are formed radially outwards on the outer circumference of the respective rotor end ring (7) in the area of ​​the positioning pins (8) or pin pairs.

10. Electric motor for a motor vehicle, comprising a rotor (1) according to any one of claims 1 to 9.

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