WO2025141386A1

WO2025141386A1 - Rotor for electric motor

Info

Publication number: WO2025141386A1
Application number: PCT/IB2024/062694
Authority: WO
Inventors: Alessio MIOTTO; Luca D'URSO
Original assignee: Brembo SpA
Current assignee: Brembo SpA
Priority date: 2023-12-27
Filing date: 2024-12-16
Publication date: 2025-07-03
Anticipated expiration: 2026-06-27

Abstract

A rotor assembly (2) for an electric motor, comprising a rotor (1 ) comprising a rotor body (3) extending about a rotor axis (4), wherein the rotor body (3) comprises a first surface (5), transverse to the rotor axis (4); a second surface (6), transverse to the rotor axis (4) and opposite to the first surface (5); an outer surface (7) extending about the rotor axis (4), preferably coaxial to the rotor axis (4), from the first surface (5) to the second surface (6), wherein the rotor assembly (2) comprises a plurality of permanent magnets (9), wherein the rotor body (3) comprises a plurality of housing seats (8), for housing a plurality of permanent magnets (9), wherein the housing seats (8) are shaped to make an undercut connection with the permanent magnets (9) in the direction radial to the rotor axis (4), and the housing seats (8) are formed on the outer surface (7), and are open in the direction radial and opposite to the rotor axis (4).

Description

“Rotor for electric motor”

[0001] Field of the invention

[0002] The present invention relates to a rotor for an electric motor, in particular an electric motor with permanent magnets.

[0003] Background art

[0004] Electric motors are known, comprising a plurality of permanent magnets associated with a rotor by coupling means, ensuring the connection and positioning of the plurality of permanent magnets with the rotor during actuation of the motor.

[0005] The need is felt to provide simplified electric motors, in which the connection of the permanent magnets with the rotor is achievable in an easier, simplified manner and with a reduction of the components needed for the connection and a reduction of the overall size.

[0006] The need is also felt to provide electric motors comprising a rotor which allows a connection of different types of permanent magnets, e.g., having different shapes and dimensions, without needing to modify the rotor, or in which the shape of the rotor does not require particular geometric or dimensional constraints for the permanent magnets.

[0007] The need is also felt to combine the aforesaid needs with the need to ensure a strong and safe connection between the permanent magnets and the rotor of the electric motor.

[0008] Solution

[0009] It is the object of the present invention to provide a rotor for an electric motor and an electric motor, such as to obviate at least some of the drawbacks highlighted in the prior art.

[0010] It is a further particular object of the present invention to provide a rotor for an electric motor and an electric motor, having a connection of the permanent magnets with the rotor in an easier and more simplified manner, and with a reduction in the components needed for the connection and a reduction in the overall size.

[0011] It is a further particular object of the present invention to provide a rotor for an electric motor and an electric motor, which allow a connection of different types of permanent magnets, e.g., having different shapes and dimensions, without needing to modify the rotor, or in which the shape of the rotor does not require particular geometric or dimensional constraints for the permanent magnets.

[0012] It is a further particular object of the present invention to provide a rotor for an electric motor and an electric motor, which ensure a strong and safe connection between the permanent magnets and the rotor of the electric motor.

[0013] These and other objects are achieved by a braking system according to claim 1.

[0014] The dependent claims relate to preferred and advantageous embodiments of the present invention.

[0015] Figures

[0016] In order to better understand the invention and appreciate the advantages thereof, some non-limiting exemplary embodiments thereof will be described below with reference to the accompanying drawings, in which:

[0017] - figure 1 is an exploded perspective view of a rotor assembly of an electric motor, comprising a plurality of permanent magnets and a lamination stack and a rotor shaft, according to an embodiment of the invention;

[0018] - figure 2 is a front view of a lamination stack of a rotor, according to an embodiment of the invention;

[0019] - figure 3 is a perspective view of a permanent magnet of an electric motor, according to an embodiment of the invention.

[0020] Description of preferred embodiments

[0021] With reference to the figures, a rotor is generally indicated by reference numeral 1. The rotor 1 is enclosed in a rotor assembly 2. The rotor assembly 2 can be enclosed or assembled in an electric motor.

[0022] The rotor 1 is thus suitable for being enclosed in an electric motor.

[0023] The rotor 1 comprises a rotor body 3 extending about a rotor axis 4.

[0024] The rotor body 3 comprises a first surface 5, transverse to the rotor axis 4.

[0025] Furthermore, the rotor body 3 comprises a second surface 6, transverse to the rotor axis 4. The second surface 6 is opposite to the first surface 5.

[0026] The rotor body 3 further comprises an outer surface 7. The outer surface 7 extends about the rotor axis 4, preferably coaxial to the rotor axis 4. Furthermore, the outer surface 7 extends from the first surface 5 to the second surface 6.

[0027] The rotor assembly 2 comprises a plurality of permanent magnets 9.

[0028] The rotor body 3 comprises a plurality of housing seats 8, for housing the plurality of permanent magnets 9.

[0029] According to an aspect of the invention, the housing seats 8 are shaped to make an undercut connection with the permanent magnets 9 in the direction radial to the rotor axis 4. [0030] Furthermore, the housing seats 8 are formed in the outer surface 7 and are open in the direction radial and opposite to the rotor axis 4.

[0031] Specifically, the outer surface 7 defines the housing seats 8 open in the direction radial and opposite to the rotor axis 4.

[0032] Advantageously, a rotor 1 thus configured allows an easier and stronger connection of the permanent magnets 9, and has a small size as compared to the prior art, in particular with the same arrangement of the permanent magnets.

[0033] Further advantageously, a rotor 1 thus configured allows a connection of different types of permanent magnets 9, e.g., having different shapes and dimensions, without needing to modify the rotor 1 . In fact, the rotor 1 thus configured does not require particular dimensional or geometric constraints for the permanent magnets 9.

[0034] Specifically, since the housing seats 8 are formed at the outer surface 7 and are open towards the outside of the rotor 1 , making an undercut connection with the permanent magnets 9, the connection of the permanent magnets 9 with the rotor 1 thus configured only requires that a connection portion of the permanent magnets 9 is insertable into and couplable with the respective housing seat 8, so that the permanent magnet 9 is constrained to the rotor body 3 in the radial direction, while the remaining portion of the permanent magnets 9, outside the housing seat 8 and thus the rotor 1 , can have different shapes and dimensions, not constrained by the rotor or by the shape of the housing seats 8.

[0035] Each permanent magnet 9 comprises a magnet body 10. The first magnet body comprises a first magnet surface 11 and an opposite second magnet surface 12.

[0036] The first magnet surface 1 1 or the second magnet surface 12 or both the first magnet surface 11 and the second magnet surface 12 preferably extend along planes circumferential or tangential to the rotor axis 4.

[0037] The permanent magnet 9 comprises a coupling body 13. The coupling body 13 projects from the second magnet surface 12 in a direction substantially transverse to the second magnet surface 12. In the connected configuration, the coupling body 13 extends along a direction substantially radial to the rotor axis 4.

[0038] The coupling body 13 is shaped to be insertable into the housing seats 8 and form a shape coupling, in particular with undercut, with the housing seats 8 of the rotor body 3.

[0039] Advantageously, the magnet body 10 of the permanent magnet 9, positioned outside the outer surface 7 of the rotor body 3, can have different shapes and sizes and however be couplable to the same housing seats 8, without needing to modify the rotor body 3, as long as the coupling body 13 remains couplable to the housing seats 8. [0040] According to an embodiment, the housing seats 8 are dovetail-shaped.

[0041] According to this embodiment, the coupling body 13 of the permanent magnets

9 is dovetail-shaped.

[0042] According to this embodiment, the housing seats 8 are configured to make a dovetail interlock with the permanent magnets 9, and in particular with the coupling bodies 13 of the permanent magnets 9.

[0043] Advantageously, the dovetail interlock allows inserting the permanent magnets 9 into the housing seats 8 along an axial direction parallel to the rotor axis 4, and it constrains the permanent magnets 9 to the housing seats 8 in the direction radial to the rotor axis 4. Therefore, the dovetail interlock allows a relative translation between the rotor body 3 and the permanent magnets 9 along an axial direction parallel to the rotor axis 4, but it prevents a relative translation between the rotor body 3 and the permanent magnets 9 along a direction radial to the rotor axis 4.

[0044] A dovetail shape is understood to mean that the housing seats 8 and the coupling bodies 13, in the cross-section with respect to the rotor axis 4, define a dovetail shape.

[0045] According to an embodiment, the housing seats 8 are open on the first surface 5.

[0046] According to an embodiment, the housing seats 8 are open on the second surface 6.

[0047] According to an embodiment, the housing seats 8 are open on the first surface 5 and on the second surface 6.

[0048] Advantageously, such a configuration allows inserting the permanent magnet 9 into the respective housing seat 8 through the opening formed, for example, on the second surface 6, along an axial direction parallel to the rotor axis 4. By means of such an insertion and the undercut shape of the housing seat 8 and the coupling body 13, the permanent magnet 9 is couplable and constrainable to the housing seat 8.

[0049] According to an embodiment, the housing seats 8 are open on the second surface 6 and closed on the first surface 5.

[0050] According to this embodiment, the rotor body 3 comprises an abutment wall 14 formed at the first surface 5.

[0051] The abutment wall 14 faces the respective housing seat 8 so as to close the housing seat 8 at the first surface 5. [0052] According to an embodiment, the abutment wall 14 extends along a plane transverse to the rotor axis 4.

[0053] Advantageously, a rotor 1 thus configured allows inserting the permanent magnet 9 of the respective housing seat 8 through the opening formed, for example, on the second surface 6, along an axial direction parallel to the rotor axis 4, and positioning the permanent magnet 9 to abut against the abutment wall 14. The rotor 1 thus ensures a correct positioning and coupling between the permanent magnet 9 and the housing seat 8, by means of the abutment of the permanent magnet 9, in particular of the coupling body 13, against the abutment wall 14 of the rotor body 3.

[0054] According to an embodiment, the rotor body 3 comprises from four to sixteen housing seats 8.

[0055] According to an embodiment, the rotor body 3 comprises from six to fourteen housing seats 8.

[0056] According to an embodiment, the rotor body 3 comprises from eight to twelve housing seats 8.

[0057] According to an embodiment, the rotor body 3 comprises from eight to ten housing seats 8.

[0058] According to an embodiment, the rotor body 3 comprises only ten housing seats 8.

[0059] According to an embodiment, the housing seats 8 extend through the rotor body 3 along respective axial directions parallel to the rotor axis 4.

[0060] According to an embodiment, the magnet body 10 is prismatic in shape.

[0061] According to an embodiment, the magnet body 10 is prismatic in shape with a substantially trapezoidal section. Specifically, the magnet body 10 substantially forms a trapezoid in a cross-section with respect to the motor axis 4.

[0062] According to an embodiment, the second magnet surface 12 has a longer extension than the first magnet surface 1 1 .

[0063] According to an embodiment, the magnet body 10 is substantially ingotshaped, having a larger lower base than an opposite upper base, and inclined side walls. [0064] According to an embodiment, the second magnet surface 12 is flat.

[0065] According to an embodiment, the second magnet surface 12 is positionable to abut against the outer surface 7 of the rotor body 3.

[0066] According to an embodiment, the outer surface 7 comprises at least one backing surface 17 adjacent to a respective housing seat 8. [0067] According to this embodiment, the second magnet surface 12 is positionable to abut against the backing surface 17 of the outer surface 7.

[0068] According to an embodiment, each housing seat 8 is formed between two opposite backing surfaces 17. Specifically, each housing seat 8 extends in a radially inner direction with respect to the backing surfaces 17, between two opposite backing surfaces 17.

[0069] According to an embodiment, the backing surface 17 is flat. Specifically, the backing surface 17 extends on a plane tangential to the rotor axis 4.

[0070] The outer surface 7 thus defines a plurality of flat backing surfaces 17, extending on planes tangential to the rotor axis 4, and a plurality of housing seats 8 formed between the flat backing surfaces 17 and extending into the rotor body 3 in the direction radial to the rotor axis 4.

[0071] According to an embodiment, the rotor body 3 comprises a plurality of injection holes 15.

[0072] The injection holes 15 extend from the first surface 5 to the second surface 6, passing through the rotor body 3.

[0073] The injection holes 15 preferably extend passing through the rotor body 3 along respective axial directions parallel to the rotor axis 4.

[0074] The injection holes 15 are configured to allow an injection of a filler material or an overmolding fluid therein.

[0075] Specifically, the outer surface 7 defines the injection holes 15.

[0076] After assembling the permanent magnets 9 to the rotor body 3 by means of an undercut connection, the rotor assembly 2 is positionable inside a mold for an overmolding operation. Advantageously, it is possible to inject the overmolding fluid into the rotor 1 thus configured through the injection holes 15 and distribute it in the mold on the permanent magnets 9 and on the rotor body 3, so as to make a rotor housing overmolded on the rotor assembly 2.

[0077] According to a further connection mode, after assembling the permanent magnets 9 to the rotor body 3 by means of an undercut connection, the rotor assembly 2 is positionable inside a mold for injecting a filler material, through the injection holes 15, for fixing the permanent magnets 9 to the rotor body 3.

[0078] According to an embodiment, the injection holes 15 are different from the housing seats 8.

[0079] Advantageously, the separation between the injection holes 15 and the housing seats 8 simplifies the assembly of the rotor 1 and the subsequent injection of filler material.

[0080] According to an embodiment, at least one injection hole 15 is positioned interposed between two housing seats 8.

[0081] According to an embodiment, each injection hole 15 is positioned interposed between two housing seats 8. The rotor body 3 thus forms an alternating arrangement of housing seats 8 and injection holes 15. According to this embodiment, the rotor body 3 comprises a number of injection holes 15 equal to the number of housing seats 8.

[0082] According to an embodiment, the injection holes 15 are formed on the outer surface 7 and are open in the direction radial and opposite to the rotor axis 4.

[0083] Advantageously, such a configuration makes a quicker and more even dispersion and distribution of filler material on the rotor body 3 and the permanent magnets 9.

[0084] According to an embodiment, the injection holes 15 are formed between two opposite backing surfaces 17.

[0085] According to an embodiment, the injection holes 15 extend, in the direction radial to the rotor axis 4, deeper than the housing seats 8.

[0086] According to an alternative embodiment, the housing seat 8 forms at least one outer recess, preferably extending in the direction radial to the rotor axis 4, forming the injection hole 15.

[0087] Advantageously, such configuration is particularly suitable for rotors requiring a greater reduction in size, since the injection hole 15 does not require any additional space on the circumferential portion of the rotor body 3, but is formed as a recess of a respective housing seat 8.

[0088] According to an embodiment, the rotor body 3 comprises from six to fourteen injection holes 15.

[0089] According to an embodiment, the rotor body 3 comprises from eight to twelve injection holes 15.

[0090] According to an embodiment, the rotor body 3 comprises only ten injection holes 15.

[0091] According to an embodiment, the injection holes 15 have a cross-section which is substantially circular in shape or shaped like an arc of a circle.

[0092] According to an embodiment, the permanent magnets 9 are fixed to the respective housing seats 8 by means of a filler material or an overmolding fluid. [0093] Advantageously, the undercut interlock combined with the fixing by means of the filler material or the overmolding fluid ensures a strong and safe connection between permanent magnets 9 and the rotor body 3.

[0094] The fixing and particularly the injection of filler material for such a fixing can preferably be carried out through the injection holes 15 described above.

[0095] According to an embodiment, the permanent magnets 9 are glued inside the respective housings 8.

[0096] Advantageously, the undercut interlock combined with gluing ensures a strong and safe connection between permanent magnets 9 and the rotor body 3.

[0097] According to an embodiment, the rotor assembly 2 comprises an annular component or a tubular containment component positioned circularly outside the permanent magnets 9 and configured to tighten and fix the permanent magnets 9 inside the housing seats 8.

[0098] The annular component or tubular component is made of a different material from that of the permanent magnets 9, it is preferably made of a paramagnetic material, e.g., aluminum. Alternatively, the annular component or the tubular component can be made of different materials, by way of example it is made as a heat shrink tube or of a composite material or of a fiber reinforced material (e.g., fiberglass) or stainless steel.

[0099] Advantageously, the undercut interlock combined with binding by means of the annular or tubular containment component ensures a strong and safe connection between permanent magnets 9 and the rotor body 3.

[00100] According to an embodiment, the permanent magnets 9 are fixed inside the respective housing seats 8 by both by gluing and binding.

[00101] According to an embodiment, the rotor body 3 is laminated. Specifically, the rotor body 3 consists of a stack of ferromagnetic foils stacked along an axial direction parallel to the rotor axis 4. A first foil and an opposite last foil preferably define the first surface 5 and the opposite second surface 6.

[00102] According to an embodiment, the rotor body 3 comprises an axial hole, extending through the rotor body 3 between the first surface 5 and the second surface 6, at the rotor axis 4.

[00103] The rotor 1 further comprises a rotor shaft 16 inserted into the axial hole and positioned coaxial to the rotor axis 4 and fixed to the rotor body 3.

[00104] According to a further aspect of the invention, an electric motor, in particular for actuating a braking system of the Brake-By-Wire type, comprises a rotor assembly 2 as described above.

[00105] According to an embodiment, the electric motor comprises a rotor housing overmolded on the rotor assembly 2. The rotor housing is made of a polymer material.

[00106] Clearly, those skilled in the art will be able to make changes or adaptations to the present invention, without however departing from the scope of the following claims.

List of reference numerals

1 . Rotor

2. Rotor assembly

3. Rotor body

4. Rotor axis

5. First surface

6. Second surface

7. Outer surface

8. Housing seat

9. Permanent magnet

10. Magnet body

11 . First magnet surface

12. Second magnet surface

13. Coupling body

14. Abutment wall

15. Injection hole

16. Rotor shaft

17. Backing surface

Claims

1. A rotor assembly (2) for an electric motor, comprising a rotor (1 ) comprising a rotor body (3) extending about a rotor axis (4), wherein the rotor body (3) comprises:

- a first surface (5), transverse to the rotor axis (4);

- a second surface (6), transverse to the rotor axis (4) and opposite to the first surface (5);

- an outer surface (7) extending about the rotor axis (4), preferably coaxial to the rotor axis (4), from the first surface (5) to the second surface (6), wherein the rotor assembly (2) comprises a plurality of permanent magnets (9), wherein the rotor body (3) comprises a plurality of housing seats (8), for housing the plurality of permanent magnets (9), characterized in that the housing seats (8) are shaped to make an undercut connection with the permanent magnets (9) in the direction radial to the rotor axis (4), and in that the housing seats (8) are formed in the outer surface (7), and are open in the radial direction and opposite to the rotor axis (4).

2. A rotor assembly (2) according to claim 1 , wherein each permanent magnet (9) comprises a magnet body (10) with a first magnet surface (1 1) and an opposite second magnet surface (12), wherein the permanent magnet (9) comprises a coupling body (13) projecting from the second magnet surface (12) in a direction substantially transverse to the second magnet surface (12), wherein the coupling body (13) is shaped to be insertable into the housing seats (8) and form a shape coupling with undercut with the housing seats (8).

3. A rotor assembly (2) according to claim 1 or 2, wherein the housing seats (8) have a dovetail shape.

4. A rotor assembly (2) according to any one of the preceding claims, wherein the housing seats (8) are open on the first surface (5) and/or the second surface (6).

5. A rotor assembly (2) according to one of claims 1 to 3, wherein the housing seats (8) are open on the second surface (6) and are closed on the first surface (5), wherein the rotor body (3) comprises an abutment wall (14) formed at the first surface (5), and facing the respective housing seat (8) so as to close the housing seat (8) at the first surface (5), wherein, optionally, the abutment wall (14) extends along a plane transverse to the rotor axis (4).

6. A rotor assembly (2) according to any one of the preceding claims, comprising four to sixteen housing seats (8), or comprising six to fourteen housing seats (8), or comprising eight to twelve housing seats (8), or comprising eight to ten housing seats (8), or comprising only ten housing seats (8).

7. A rotor assembly (2) according to any one of the preceding claims, wherein the housing seats (8) extend through the rotor body (3) along respective axial directions parallel to the rotor axis (4).

8. A rotor assembly (2) according to claim 2, wherein the magnet body (10) has a prismatic shape with a substantially trapezoidal section, and/or wherein the second magnet surface (12) has a longer extension than the first magnet surface (1 1 ), and/or wherein the second magnet surface (12) is flat and positionable to abut against the outer surface (7) of the rotor body (3).

9. A rotor assembly (2) according to any one of the preceding claims, wherein the outer surface (7) comprises at least one backing surface (17) adjacent to a respective housing seat (8), wherein a second magnet surface (12) of a permanent magnet (9) is positionable to abut against the backing surface (17) of the outer surface (7), wherein, preferably, each housing seat (8) is formed between two opposite backing surfaces (17), and wherein, preferably, the backing surface (17) is flat.

10. A rotor assembly (2) according to any one of the preceding claims, wherein the rotor body (3) comprises a plurality of injection holes (15) extending from the first surface (5) to the second surface (6), passing through the rotor body (3), preferably along respective axial directions parallel to the rotor axis (4), wherein the injection holes (15) are configured to allow for an injection of a filler material or an overmolding fluid inside them.

11. A rotor assembly (2) according to claim 10, wherein the injection holes (15) are distinct from the housing seats (8), wherein at least one injection hole (15) is positioned to be interposed between two housing seats (8), or wherein each injection hole (15) is positioned to be interposed between two housing seats (8) so that the rotor body (3) forms an alternating arrangement of housing seats (8) and injection holes (15).

12. A rotor assembly (2) according to claim 10 or 1 1 , wherein the injection holes (15) are formed on the outer surface (7) and are open in the radial direction and opposite to the rotor axis (4), wherein, preferably, the injection holes (15) are formed between two opposite backing surfaces (17) of the outer surface (7), and wherein, preferably, the injection holes (15) extend, in the radial direction with respect to the rotor axis (4), deeper than the housing seats (8).

13. A rotor assembly (2) according to claim 10 or 1 1 , wherein the housing (8) forms at least one outer recess, extending in the radial direction with respect to the rotor axis (4), forming the injection hole (15).

14. A rotor assembly (2) according to one of claims 10 to 13, comprising six to fourteen injection holes (15), or comprising eight to twelve injection holes (15), or comprising only ten injection holes (15), and/or wherein the injection holes (15) have a cross section which is substantially circular in shape or shaped as an arc of a circle.

15. A rotor assembly (2) according to any one of the preceding claims, wherein the permanent magnets (9) are fixed to their respective housing seats (8) by means of a filler material or overmolding fluid, and/or wherein the permanent magnets (9) are glued inside the respective housing (8), and/or wherein the rotor assembly (2) comprises an annular component or a tubular containment component positioned circularly outside the permanent magnets (9) and configured to tighten and fix the permanent magnets (9) in the housing seats (8), wherein the annular component or tubular component is made of a diamagnetic material.

16. A rotor assembly (2) according to any one of the preceding claims, wherein the rotor body (3) consists of a stack of ferromagnetic foils stacked along an axial direction parallel to the rotor axis (4), and/or wherein the rotor body (3) comprises an extending axial hole passing through the rotor body (3) between the first surface (5) and the second surface (6), at the rotor axis (4), and wherein the rotor (1 ) comprises a rotor shaft (16) inserted into the axial hole and positioned coaxially to the rotor axis (4), fixed to the rotor body (3).

17. An electric motor, for actuating a braking system of the Brake-By-Wire type, comprising a rotor assembly (2) according to any one of the preceding claims.

18. An electric motor according to claim 17, comprising a polymer rotor housing overmolded on the rotor assembly (2).