Reluctance-assisted axial flux electric motor

Abstract

Axial flux electric motor (14), comprising: a non-rotatable stator (30) defining a rotation axis (X) and having a plurality of conductive stator magnetic poles (30B) arranged radially around the rotation axis (X); a first rotor (32) axially spaced from one side of the stator (30), having a first rotor outer surface (32-1) facing the stator (30), and rotatably mounted coaxially with the rotation axis (X), wherein: the first rotor (32) comprises a first ferromagnetic rotor core (36) and a plurality of first alternating south and north pole permanent magnets (40, 42) arranged on the first ferromagnetic rotor core (36) symmetrically about the axis of rotation (X) and facing the stator (30); the first ferromagnetic rotor core (36) comprises a plurality of first core projections (38) extending to the first rotor outer surface (32-1); each of the first core projections (38) is arranged between a first south pole permanent magnet (40) and a first north pole permanent magnet (42); and the plurality of first core projections (38) are phase-shifted relative to the plurality of first alternating south and north pole permanent magnets (40, 42) to thereby change a magnetic reluctance of the electric motor, wherein each of the plurality of first alternating south and north pole permanent magnets (40, 42) is a respective permanent magnet set (40A, 42A) comprising a permanent magnet with a comparatively large radial span (40-1, 42-1) and a permanent magnet with a comparatively small radial span (40-2, 42-2), wherein each of the first core projections (38) is embedded in the respective permanent magnet set (40A, 42A) adjacent to the permanent magnet with a comparatively small radial span (40-2, 42-2).

Description

The disclosure relates to a magnetic reluctance-assisted axial flux electric motor.An electric motor is a machine that converts electrical energy into mechanical energy. The operation of an electric motor is based on an electromagnetic interaction between permanent magnets and the magnetic field generated by the selectively excited coils of the machine. Electric motors are classified into two categories according to the direction of the magnetic field: axial flux motors and radial flux motors. The arrangement of the gap between the rotor and the stator of the machine, which is arranged parallel to the axis of rotation in an axial flux motor and radially in a radial flux motor, determines the direction of the magnetic flux of the motor.Axial and radial flux motors can be designed as switched reluctance machines. Generally, a reluctance machine induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor of such a machine normally has no windings and generates the torque by magnetic reluctance. The subtypes of reluctance machines include synchronous, variable, switching and stepping motors. Reluctance motors can provide high power density, but at high load, significant torque ripple (difference between maximum and minimum torque during one revolution) may occur due to reluctance when combined with the torque of magnets, which may also produce noise.Typically, axial flow motors have a relatively denser and shorter flow path. In addition, the rotor magnets can be further away from the central axis of rotation of the axial motor in comparison to radial flux motors. As a result, axial flow engines generally have a higher ratio of torque to weight and torque to size compared to radial flow engines. The magnets on the rotor of an axial flux motor, like all forms of synchronous AC motors, are attracted to the rotating field generated by a surrounding ring of independent electromagnets in the stator. Since the switching of the magnets which causes the field to rotate is usually not perfectly uniform, the rotor suffers from torque ripple.CN114825696A discloses a hybrid permanent magnet asymmetric motor with embedded surface and convex pole belonging to the technical field of permanent magnet motors, comprising an outer stator core partially separated by an air gap in the center, and a three-phase armature winding provided on the stator core, and a rotor shaft surrounded by the rotor and arranged in the central axis of the motor. The rotor includes rotor cam pole teeth, a rotor yoke, a rotor inner air slot, a permanent magnet, and a rotor outer slot. The permanent magnet is offset in the outer rotor slot at an angle with respect to the central axis of the outer rotor slot. The peak of the permanent magnet torque and reluctance torque components can reach the maximum value at a similar current angle to improve the utilization rate of the torque components and thus increase the torque density.CN 2 10780279U discloses a rotor for a disk motor having a rotor holder and a neodymium-iron-boron permanent magnet. The neodymium-iron-boron permanent magnet is circumferentially distributed on a side wall of the rotor holder. The rotor further comprises a pole shoe arranged on the rotor holder. The pole shoe separates two adjacent neodymium-iron-boron permanent magnets. This reduces the chain reluctance of the motor q-axis, increasing the q-axis inductance, i.e., Lqis increased and the convexity is increased.US 2013 / 0 088 112 A1 discloses a motor comprising: a first rotor configured to be arranged on a first side of a stator and a second rotor configured to be arranged on a second side of the stator, opposite the first side. The first rotor includes: a plurality of first modules each including a pair of first permanent magnets spaced apart from each other; and a first connection unit connecting the ends of the first permanent magnets. The second rotor includes: a plurality of second modules each including a pair of second permanent magnets spaced apart from each other; and a second connection unit connecting the ends of the second permanent magnets to each other.CN 1 15498841 A discloses a high torque density disc rotor motor comprising a stator assembly and a rotor assembly. The stator assembly and the rotor assembly are coupled by an axial magnetic flux. The rotor assembly includes a rotor core, a first group of magnetic tiles, and a second group of magnetic tiles. The first group of magnetic tiles is mounted on the rotor core, distributed along the same circumference and axially magnetized. The second group of magnetic tiles is mounted on the rotor core, distributed along the same circumference and magnetized tangentially. The first group of tiles are in the vicinity of the stator assembly, the second group of tiles is far from the stator assembly, the first group of tiles and the second group of tiles are offset by a certain distance in the axial direction, the first group of tiles consists of N plates A distributed along the circumference, and the second group of tiles consists of N plates B distributed along the circumference, and N is an integer, and the centre lines of the two adjacent tiles A are L, and the tiles B are shifted from the centre line L by an angle α in the circular direction. The electrical angle difference between the maximum value of the permanent magnetic torque and the current angle corresponding to the occurrence of the maximum value of the torque is decreased to increase the maximum output torque of the motor.An axial flux electric motor includes a fixed stator defining an axis of rotation and having a plurality of conductive stator magnetic poles disposed radially about the axis of rotation. The axial flux electric motor also includes a first rotor axially spaced from a side of the stator, having a first rotor outer surface facing the stator, and rotatably mounted coaxially with the rotational axis. The first rotor includes a first ferromagnetic rotor core and a plurality of alternating south and north pole permanent magnets (PMs) arranged on the first ferromagnetic rotor core symmetrically about the axis of rotation and facing the stator. The first ferromagnetic rotor core includes a plurality of first core protrusions extending toward the first rotor outer surface. Each of the first core protrusions is disposed between a first south pole PM and a first north pole PM. The plurality of first core protrusions are phase-shifted relative to the plurality of alternating south and north pole PMs to thereby change the magnetic reluctance of the electric motor.The axial flux electric motor may additionally include a second rotor axially spaced from another side of the stator, having a second rotor outer surface facing the stator, and rotatably mounted coaxially with the rotational axis. The second rotor includes a second ferromagnetic rotor core and a second plurality of alternate south and north pole PMs disposed on the second ferromagnetic rotor core on the second rotor outer surface symmetrically about the axis of rotation. The second ferromagnetic rotor core may include a plurality of second core protrusions extending toward the second rotor outer surface. Each of the second core protrusions is disposed between a second south pole PM and a first north pole PM. The plurality of second core protrusions may be phase matched or phase shifted with the plurality of first core protrusions. The plurality of second alternating south and north pole PMs may be phase-shifted relative to the plurality of first alternating south and north pole PMs to thereby further change the magnetic reluctance of the motor.In each pair of alternating south and north poles of the first rotor, the respective first core protrusion may be angularly disposed closer to the corresponding south pole PM than the corresponding north pole PM.In each pair of alternating south and north pole PMs of the first rotor, the respective core protrusion may be angularly disposed closer to the corresponding north pole PM than the corresponding south pole PM.Each of the plurality of alternating south and north pole PMs of the first rotor is a corresponding PM set that includes a PM of relatively large radial span and a PM of relatively small radial span.In each PM set, the PM with a comparatively small radial span can be arranged radially closer to the axis of rotation than the PM with a comparatively large radial span.In each PM set, the PM with the PM with a comparatively large radial span may be arranged radially closer to the axis of rotation than the PM with a comparatively small radial span.Each of the first core protrusions is embedded in the respective PM set that abuts the PM with a comparatively small radial span.In each PM set, the comparatively large radial span PM and the comparatively small radial span PM may be radially arranged to create a radially straight PM set edge opposite the embedded protrusion.In each PM set, the embedded protrusion may extend to overlap an edge of the comparatively large radial span PM and / or the comparatively small radial span PM, thereby mechanically retaining the respective PM on the first rotor. FIG. 1 is a schematic illustration of a motor vehicle having a powertrain that uses an axial flow electric motor-generator to drive. FIG. 2 is a schematic, approximate partial perspective view of the motor-generator shown in FIG. 1, showing a stator assembly having first and second rotors that each alternately include south and north pole permanent magnets (PMs) and core protrusions disposed therebetween, according to an embodiment of the disclosure. FIG. 3A is a schematic cross-sectional partial side view of the first rotor assembly shown in FIG. 2, showing an embodiment of a phase angle shift between the first core protrusions and the plurality of alternating first south and north pole PMs, according to an embodiment of the disclosure. FIG. 3B is a schematic cross-sectional partial side view of the first rotor assembly shown in FIG. 2, showing another embodiment of the phase angle shift between the first core protrusions and the plurality of first alternating south and north pole PMs, according to an embodiment of the disclosure. FIG. 4A is a graph of the effects of the phase angle shift shown in FIG. 3A on the output torque of the electric motor according to the disclosure. FIG. 4B is a graph of the effect of the phase angle shift shown in FIG. 3B on the output torque of the electric motor according to the disclosure. FIG. 5A is a schematic cross-sectional partial front view of the first rotor shown in FIG. 2, showing an embodiment of alternating south and north pole PMs configured as a respective PM set having a comparatively large radial span PM and a comparatively small radial span PM, in accordance with the disclosure. FIG. 5B is a schematic cross-sectional partial front view of the first rotor shown in FIG. 2, showing another embodiment of alternating south and north pole PM sets, in accordance with the disclosure. FIG. 5C is a schematic cross-sectional partial front view of the first rotor shown in FIG. 2, showing respective south and north pole PM sets each having a radially straight PM set edge aligned with the respective embedded protrusion, the embedded protrusion mechanically retaining the respective PM, in accordance with the disclosure. FIG. 6 is a schematic partial perspective view of the motor-generator shown in FIG. 2, showing the second core protrusions in phase with the plurality of first core protrusions and the second plurality of alternating south and north pole PMs phase shifted relative to the first plurality of alternating south and north pole PMs, in accordance with the disclosure.FIG. 1 depicts a motor vehicle 10 having a drive train 12. The vehicle 10 may be, but is not limited to, a commercial vehicle, an industrial vehicle, a passenger vehicle, an aircraft, a watercraft, a train, or the like. It is also contemplated that the vehicle 10 may be a mobile platform, such as an aircraft, off-road vehicle (ATV), boat, personal mover, robot, and the like, to accomplish the purposes of this disclosure. The powertrain 12 includes a first energy source 14, shown as an electric motor-generator, configured to generate a first torque of the energy source T 1 (shown in FIG. 1 ) for propelling the vehicle 10 via driven wheels 16, for example, relative to a road surface. The motor-generator 14 is configured as a reluctance machine in which non-permanent magnetic poles are induced on the ferromagnetic rotor(s) of the motor, which will be described in detail below.As shown in FIG. 1, the powertrain 12 may also include a second power source 20, such as an internal combustion engine, configured to generate a second power source torque T 2. The power sources 14 and 20 are co-operable to propel the vehicle 10 and are operatively connected to a transmission assembly 22. The transmission assembly 22 may be configured to transmit the first and / or second drive torques T 1, T 2 to a final drive unit 24, which in turn may be connected to the driven wheels 16. The first energy source 14, referred to herein as a motor-generator, may be mounted, for example, to the second energy source 20, to the transmission assembly 22 (or integrated therein), to the final drive unit 24, or as a stand-alone assembly on the structure of the vehicle 10. As shown, the vehicle 10 additionally includes a programmable electronic control unit 26 configured to control the powertrain 12 to generate a predetermined power source torque T, as well as various other vehicle systems. The vehicle 10 also includes an energy storage system 28, such as one or more batteries, configured to generate and store electrical energy for operating the power sources 14 and 20.As shown in FIG. 2, the motor-generator 14 includes a non-rotating stator 30. the stator 30 defines an axis of rotation X and includes a stator core 30A and a plurality of magnetic poles 30B arranged radially about the axis of rotation. The stator 30 has two opposing sides - a first side 30-1 and a second side 30-2. The motor-generator 14 also includes a first rotor 32 axially spaced from the first side 30- 1 of the stator 30 and forming an air gap 34 therebetween. The first rotor 32 is rotatably supported coaxially with the rotation axis X and has a first rotor outer surface 32- 1 facing the stator 30. The first rotor 32 includes a first ferromagnetic rotor core 36. the first rotor core 36 may be constructed of a relatively soft magnetic material, such as laminated silicon steel, having a plurality of first core protrusions or protrusions 38 that act as magnetic poles via the magnetic reluctance. The magnetic reluctance is defined as the ratio of magnetomotive force (mmf) to magnetic flux, which is the resistance to magnetic flux, and generally depends on the geometry and composition of an object. As shown, the first core protrusions 38 extend to the first rotor outer surface 32- 1. During operation of the motor-generator 14, non-permanent magnetic poles are successively induced on the magnetic poles 38 of the motor to generate motor torque.The first rotor 32 also includes a plurality of first alternating south pole permanent magnets (PMs) 40 and north pole PMs 42. the south and north pole PMs 40, 42 are disposed on the first ferromagnetic rotor core 36 substantially symmetrically about the axis of rotation X and face the stator 30. Each pair of alternately arranged south and north pole PMs 40, 42 includes one of the first core protrusions 38 disposed therebetween. in other words, each of the first core protrusions 38 is disposed or sandwiched between a first south pole PM 40 and a first north pole PM 42. The plurality of first core protrusions 38 as a whole is phase-shifted from the plurality of first alternating south and north pole PMs 40, 42. A "phase shift" of the first core protrusions 38 relative to the PMs 40, 42 is defined herein as any core protrusion positioned at unequal or non-equal radial distance or angle θ from its two adjacent or bracketed PMs. For example, the angle θ 1 may be larger than the angle θ 2. In other words, in each pair of alternating south and north pole PMs 40, 42, the respective core protrusion 38 enclosed thereby is radially asymmetrically disposed between the respective south pole PM and the corresponding north pole PM, as shown in FIGS. 3A and 3B. The subjected phase angle shift of the first core protrusions 38 relative to the south and north alternating PMs 40, 42 is configured to change a magnetic reluctance of the motor generator 14 as compared to a motor generator structure having a symmetric arrangement of the core protrusions relative to the corresponding south and north alternating PMs.FIG. 3A shows a cross-sectional view of the rotor 32 wherein, in each pair of alternating south and north pole PMs 40, 42, the respective core protrusion 38 is angularly disposed closer to the corresponding south pole PM 40 than the corresponding north pole PM 42. The phase shift in question in FIG. 3A is indicated by the distance d 1, which is greater than the distance d 2. Alternatively, as shown in FIG. 3B, in each pair of alternating south and north pole PMs 40, 42, the respective core protrusion 38 may be angularly disposed closer to the corresponding north pole PM 42 than the corresponding south pole PM 40. The phase shift in question in FIG. 3B is indicated by the distance d 1, which is smaller than the distance d 2. The embodiment of the first rotor 32 shown in FIG. 3A is configured to increase the general torque output of the motor-generator 14 and also may affect torque ripple, while the embodiment of the first rotor 32 shown in FIG. 3B is configured to decrease the general torque output. Comparative torque diagrams are shown in FIGS. 4A and 4B, which show the orientation of PM torque (T 40, T 42) relative to reluctance torque (T 38) in a representative motor-generator, as a function of angular displacement between PMs 40 and 42 and sandwiched core boss 38. FIGS. 4A and 4B specifically show the increased torque output T 1 according to the embodiment of FIG. 3A and the reduced torque output T 1 according to the embodiment of FIG. 3B.As shown in FIGS. 5A and 5B, each of the plurality of first alternating south and north pole PMs 40, 42 may be identified as a respective PM set 40A and 42A. Each PM set 40A may include a PM 40- 1 having a comparatively large radial span and a PM 40- 2 having a comparatively small radial span. Similarly, each PM set 42A may include a comparatively large radial span PM 42- 1 and a comparatively small radial span PM 42- 2. As shown in FIG. 5A, in each PM set 40A, 42A, the comparatively small radial span PMs 40- 2, 42- 2 may be disposed radially closer to the rotational axis X than the corresponding comparatively large radial span PMs 40- 1, 42- 1. Alternatively, as shown in FIG. 5B, in each corresponding PM set 40A, 42A, the comparatively large radial span PM 40- 1, 42- 1 may be disposed radially closer to the rotational axis X than the corresponding comparatively small radial span PM 40- 2, 42- 2. Each PM set 40A and 42A may have a T-shape as a whole, as illustrated in FIG. 5A.Each of the first core protrusions 38 disposed between each pair of alternating south and north pole PMs 40, 42 may be embedded in the respective PM set 40A, 42A that abuts the corresponding relatively small radial span PM 40-2, 42-2 (shown in FIGS. 5A and 5B ). In each PM set 40A, 42A, the comparatively large radial span PM 40- 1, 42- 1 and the comparatively small radial span PM 40- 2, 42- 2 may be radially arranged to generate a corresponding PM set edge 41A opposite the corresponding embedded protrusion 38, an opposite side of the comparatively small radial span PM 40- 2, 42- 2, an edge 41B, and an opposite edge 41C, as shown in FIG. 5C. As shown, the PM set edge 41A may be constructed as being substantially straight radially, with the edges of the PMs 40- 1, 42- 1 aligned with each other and the edges of the PMs 40- 2, 42- 2 similarly aligned. Moreover, the opposing edges 41C of the PM sets 40A, 42A may also be substantially straight and may be aligned with the outer edge of the corresponding embedded protrusion 38. As shown in FIG. 5C, in each PM set 40A, 42A, the embedded protrusion 38 may extend to overlap the edge 41B of the comparatively small radial span PM 40- 2, 42- 2 and / or a portion of the adjacent comparatively large radial span PM 40- 1, 42- 1. The overlap between the protrusion 38 and the adjacent PM may be used to mechanically retain the respective PM on the first rotor 32.As shown in FIG. 2, the motor-generator 14 may additionally include a second rotor 46 axially spaced from the second side 30- 2 of the stator 30 and forming an air gap 48 therebetween. As shown, the second rotor 46 is rotatably supported coaxially with the rotational axis X and has a second rotor outer surface 46- 1 facing the stator 30. The second rotor 46 includes a second ferromagnetic rotor core 50 that is constructed generally like the first rotor core 36 and has a plurality of second core protrusions 52. The second core protrusions 52 extend to the second rotor outer surface 46- 1 and function as magnetic poles by magnetic reluctance. The second rotor 46 also includes a plurality of second alternating south and north poles PMs 54, 56 disposed on the second ferromagnetic rotor core 50 substantially symmetrically about the axis of rotation X and facing the stator 30.As shown and analogous to the first rotor 32, each of the second core protrusions 52 is disposed between a second south pole PM 54 and a second north pole PM 56. The second core protrusions 52 may be disposed in phase, i.e., not displaced, with the plurality of second south and north pole PMs 54, 56 such that the distances d 1 and d 2 shown in FIGS. 3A and 3B are substantially equal. As installed in the motor-generator 14, the plurality of second core protrusions 52 may also be in phase with the plurality of first core protrusions 38. On the other hand, the plurality of second alternating south and north PMs 54, 56 may be out of phase with the plurality of first alternating south and north PMs 40, 42 as shown in FIG. 6. The phase shift of the alternating south and north poles PMs 54, 56 relative to the alternating south and north poles PMs 40, 42 generates a position shift 58 of the first rotor PM relative to the second rotor PM along the axis of rotation X and acts to further change the magnetic reluctance of the electric motor 14.Moreover, the plurality of second core protrusions 52 may be phase-shifted relative to the plurality of first core protrusions 38, and such an arrangement may be combined with the phase-shifted PMs as described above. The phase angle shift of the second core protrusions 52 relative to the first core protrusions 38 generates a position shift (not explicitly shown, but seen in FIGS. 3A, 3B, and 6 ) of the first rotor protrusions relative to the second rotor protrusions along the rotational axis X to further change the magnetic reluctance of the electric motor 14. In another embodiment, the first and second rotors 32, 46 may be substantially identical, but when incorporated into the motor-generator 14, e.g., when the rotor 46 is a substantial duplicate of the rotor 32 shown in FIG. 3A, the phase angle shift between the respective PMs and protrusions of the two rotors will not be aligned. In other words, when two substantially identical first and second rotors 32, 46 are facing each other from opposite sides of the stator 30 (as shown in FIG. 2 ), the respective PMs and protrusions of the two rotors are phase-shifted relative to each other. Such substantially identical oppositely mounted rotors may be similarly employed to vary the magnetic reluctance of the electric motor 14.In summary, the axial flow motor generator 14 may have one or two rotors. A rotor has core protrusions phase-shifted relative to the south and north pole PMs to alter the magnetic reluctance of the motor and assist in torque generation in the electric motor 14. The alternating south and north pole PMs of the first rotor may be configured as individual PM sets each including a PM of comparatively large radial span and a PM of comparatively small radial span. Each of the first rotor protrusions may be embedded in a corresponding PM set adjacent to the PM with a comparatively small radial span, thereby achieving the desired phase angle shift. The second rotor may have core protrusions that are in phase with the first core protrusions, while the alternate south and north pole PMs of the second rotor may be phase shifted relative to the alternate south and north pole PMs of the first rotor. The second rotor can thereby further change the magnetic reluctance of the electric motor.

Claims

An axial flux electric motor (14) comprising: a non-rotating stator (30) defining an axis of rotation (X) and having a plurality of conductive stator magnetic poles (30B) arranged radially about the axis of rotation (X); a first rotor (32) axially spaced from a side of the stator (30), having a first rotor outer surface (32-1) facing the stator (30) and rotatably mounted coaxially with the axis of rotation (X), wherein: the first rotor (32) comprises a first ferromagnetic rotor core (36) and a plurality of first alternating south and north permanent magnets (40, 42) arranged on the first ferromagnetic rotor core (36) symmetrically about the axis of rotation (X) and facing the stator (30); the first ferromagnetic rotor core (36) includes a plurality of first core protrusions (38) extending toward the first rotor outer surface (32-1); each of the first core protrusions (38) being disposed between a first south pole permanent magnet (40) and a first north pole permanent magnet (42); and the plurality of first core protrusions (38) are phase-shifted relative to the plurality of first alternating south and north permanent magnets (40, 42) to thereby change a magnetic reluctance of the electric motor, each of the plurality of first alternating south and north permanent magnets (40, 42) being a respective permanent magnet set (40A, 42A) comprising a relatively large radial span permanent magnet (40-1, 42-1) and a relatively small radial span permanent magnet (40-2, 42-2), each of the first core protrusions (38) being embedded in the respective permanent magnet set (40A, 42A) adjacent to the relatively small radial span permanent magnet (40-2, 42-2).The axial flux electric motor (14) of claim 1, further comprising a second rotor (46) axially spaced from another side of the stator (30), having a second rotor outer surface (46-1) facing the stator (30) and rotatably mounted coaxially with the axis of rotation (X), wherein: the second rotor (46) has a second ferromagnetic rotor core (50) and a plurality of second alternating south and north permanent magnets (54, 56) disposed on the second ferromagnetic rotor core (50) symmetrically about the axis of rotation (X) and facing the stator (30); the second ferromagnetic rotor core (50) has a plurality of second core protrusions (52) extending to the second rotor outer surface (46-1); each of the second core protrusions (52) is disposed between a second south pole permanent magnet (54) and a second north pole permanent magnet (56); the plurality of second core protrusions (52) phase-align with or phase-shifted relative to the plurality of first core protrusions (38); and the plurality of second alternating south and north pole permanent magnets (54, 56) phase-shifted relative to the plurality of first alternating south and north pole permanent magnets (40, 42), thereby further varying the magnetic reluctance of the electric motor.The axial flux electric motor (14) of claim 1, wherein in each pair of first alternating south and north permanent magnets (40, 42), the respective first core protrusion (38) is angularly disposed closer to the respective south pole permanent magnet (40) than the respective north pole permanent magnet (42).The axial flux electric motor (14) of claim 1, wherein in each pair of first alternating south and north permanent magnets (40, 42), the respective first core protrusion (38) is angularly disposed closer to the respective north permanent magnet (42) than the respective south permanent magnet (40).The axial flux electric motor (14) according to claim 1, wherein in each permanent magnet set (40A, 42A), the permanent magnet with a comparatively small radial span (40-2, 42-2) is arranged radially closer to the rotation axis (X) than the permanent magnet with a comparatively large radial span (40-1, 42-1).The axial flux electric motor (14) according to claim 1, wherein in each permanent magnet set (40A, 42A), the permanent magnet with a comparatively large radial span (40-1, 42-1) is arranged radially closer to the rotation axis (X) than the permanent magnet with a comparatively small radial span (40-2, 42-2).The axial flux electric motor (14) according to claim 1, wherein in each permanent magnet set (40A, 42A), the permanent magnet of comparatively large radial span (40-1, 42-1) and the permanent magnet of comparatively small radial span (40-2, 42-2) are arranged to generate a radially straight permanent magnet set edge (41A) opposite to the embedded protrusion (38).The axial flux electric motor (14) according to claim 1, wherein in each permanent magnet set (40A, 42A), the embedded protrusion (38) extends to overlap an edge of the permanent magnet (40-1, 42-1) having a comparatively large radial span and / or the permanent magnet (40-2, 42-2) having a comparatively small radial span, thereby mechanically retaining the respective permanent magnet (40, 42) on the first rotor (32).

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