Electric motor with asymmetric permanent magnet layout

Abstract

The motor includes a stator and a rotor. The rotor includes a rotor core and a plurality of permanent magnets each disposed in one of the plurality of rotor cavities. The rotor core includes a plurality of pole pieces arranged annularly around a rotational axis. The plurality of permanent magnets includes a first permanent magnet and a second permanent magnet. A first permanent magnet is disposed in the first rotor cavity. A second permanent magnet is disposed in the second rotor cavity. The rotor core is included in an in-pole bridge in each of the plurality of pole pieces. The first permanent magnet has a first surface area. The second permanent magnet has a second surface area. The second surface area is larger than the first surface area.

Description

Technical Field

[0001] The present disclosure relates to an electric motor having an asymmetric permanent magnet layout. Background Art

[0002] This introduction generally introduces the background of the present disclosure. To the extent described in this introduction, the work of the presently named inventors and aspects of the description that may not constitute prior art at the time of filing are neither expressly nor impliedly admitted to be prior art to the present disclosure.

[0003] Some vehicles include electric motors for propulsion. To enhance the propulsion of the vehicle, it is necessary to maximize the torque generated by the electric motor while minimizing energy consumption. Summary of the Invention

[0004] The present disclosure describes an electric motor for maximizing torque while minimizing energy consumption. The electric motor includes a stator having a plurality of electrical conductors. The electric motor also includes a rotor concentrically disposed relative to the stator. The rotor is rotatable relative to the stator about a rotation axis. The rotor is spaced apart from the stator to define an air gap between the stator and the rotor. The rotor includes a rotor core defining an outermost rotor surface and an innermost rotor surface opposite the outermost rotor surface. The rotor core includes a plurality of pole pieces arranged annularly about the rotation axis. Each pole piece represents a magnetic pole of the electric motor. At least one of the plurality of pole pieces defines a plurality of rotor cavities. The plurality of rotor cavities includes a first rotor cavity and a second rotor cavity spaced apart from each other.

[0005] The rotor includes a plurality of permanent magnets, each of which is disposed in one of a plurality of rotor cavities. The plurality of permanent magnets includes a first permanent magnet and a second permanent magnet located in each pole piece. In the depicted embodiment, there are only two magnetic layers, each having a V-shape. However, it is conceivable that the rotor may include more magnetic layers (for example, three magnetic layers or four magnetic layers). Each magnetic layer may have two permanent magnets. The first permanent magnet is disposed in the first rotor cavity. The second permanent magnet is disposed in the second rotor cavity. The rotor core includes an intrapole bridge located in each of the plurality of pole pieces. The intrapole bridge separates the first rotor cavity from the second rotor cavity. Thus, the electric motor may have five permanent magnets. The first permanent magnet has a first surface area. The second permanent magnet has a second surface area. The second surface area is larger than the first surface area.

[0006] In one aspect of the present disclosure, a first permanent magnet has a first length and a first width. A second permanent magnet has a second length and a second width. The first width is equal to the second width. The second length is greater than the first length. An intrapole bridge has a bridge width extending from the first rotor cavity to the second rotor cavity. The first length of the first permanent magnet is greater than the bridge width, and the second length of the second permanent magnet is greater than the bridge width. The intrapole bridge has a bridge length. The first permanent magnet has a first linear wall and a second linear wall opposite the first linear wall. The first width extends from the first linear wall to the second linear wall. The first linear wall is closer to the outermost rotor surface than the second linear wall. The second linear wall is closer to the innermost rotor surface than the first linear wall. The second permanent magnet has a first linear boundary and a second linear boundary opposite the first linear boundary. The second width extends from the first linear boundary to the second linear boundary. The first linear boundary is closer to the outermost rotor surface than the second linear boundary. The second linear boundary is closer to the innermost rotor surface than the first linear boundary. The bridge length extends the first linear wall of the first permanent magnet along the bridge direction to the second linear boundary of the second permanent magnet. The second width of the second permanent magnet is less than the bridge length. The first linear boundary is spaced apart from the second linear boundary along the bridge direction, and the second width of the second permanent magnet is defined as extending from the first linear boundary to the second linear boundary along the bridge direction. The bridge length is less than the first width of the first permanent magnet. The first permanent magnet has a third linear wall and a fourth linear wall, and the first length of the first permanent magnet extends from the third linear wall to the fourth linear wall. The first permanent magnet defines a first axis extending through the third linear wall and the fourth linear wall. The first axis intersects the third linear wall at a perpendicular angle. The first axis intersects the fourth linear wall at a perpendicular angle. The second permanent magnet has a third linear boundary and a fourth linear boundary. The second length extends from the third linear boundary to the fourth linear boundary. The second permanent magnet defines a second axis extending from the third linear boundary to the fourth linear boundary. The second axis intersects the third linear boundary at a perpendicular angle. The second axis intersects the fourth linear boundary at a perpendicular angle. An angle is defined as extending from the first axis to the second axis. The angle is an oblique angle. This angle can be greater than ten degrees and less than ninety degrees.

[0007] The present disclosure also describes a propulsion system for a vehicle. The propulsion system includes the battery described above and an electric motor. The electric motor is electrically connected to the battery.

[0008] The present disclosure also describes a vehicle. The vehicle includes the vehicle body described above and an electric motor. The electric motor is coupled to the vehicle body.

[0009] Further areas of applicability will become apparent from the description provided in this disclosure.It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of this disclosure.

[0010] The above-described features and advantages and other features and advantages of the presently disclosed systems and methods are readily apparent from the following detailed description, including the claims and exemplary embodiments, when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0012] Figure 1 is a schematic diagram of a vehicle including an electric motor.

[0013] Figure 2 It is along Figure 1 The section line 2-2 is taken Figure 1 A schematic cross-sectional view of the motor is shown.

[0014] Figure 3 It is around Figure 2 FIG. 1 is a schematic enlarged cross-sectional view of the motor taken at area A.

[0015] Figure 4 The permanent magnets with asymmetric angles are shown Figure 1 An enlarged schematic diagram of the motor.

[0016] Figure 5 It is an enlarged schematic diagram of an electric motor without an inner-pole bridge. DETAILED DESCRIPTION

[0017] Reference will now be made in detail to several examples of the present disclosure, which are illustrated in the accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and the description to refer to the same or similar parts or steps.

[0018] Referring to the drawings, wherein like reference numerals refer to like parts, Figure 1 A vehicle 10 is shown that includes an electric motor 12 (i.e., an electric motor) configured to propel the vehicle 10. The electric motor 12 can be configured to provide torque or force to another component of the vehicle 10, thereby propelling the vehicle 10. Thus, the electric motor 12 is part of a propulsion system 13 of the vehicle 10. In addition to propelling the vehicle 10, the electric motor 12 can also be used to power other suitable devices. The electric motor 12 can be a brushless electric motor and includes six substantially identical interconnected segments 12A arranged side by side along a rotational axis X, which is defined along the length of the electric motor 12. However, it is contemplated that the electric motor 12 may include more or fewer segments 12A. The number of interconnected segments 12A is directly related to the torque of the electric motor 12, which is capable of powering the vehicle 10. The vehicle 10 includes a body 11, and the electric motor 12 is coupled to the body 11.

[0019] The vehicle 10 includes a transmission 14 having a transmission and a drive shaft (not shown). The transmission 14 is operatively connected between the motor 12 and the drive wheels 16 via one or more suitable couplings, such as constant velocity joints (not shown). The operative connection between the motor 12 and the transmission 14 allows the motor 12 to supply torque to the drive wheels 16 to propel the vehicle 10.

[0020] The propulsion system 13 also includes a battery (or battery pack) 18, which is configured to supply electrical energy to the electric motor 12 and other vehicle systems (not shown). To this end, the battery 18 is electrically connected to the electric motor 12. Due to this electrical connection, the electric motor 12 is configured to receive electrical energy from the battery 18 and can operate as a generator when driven by a power energy source of the vehicle 10 external to the electric motor 12. This external power energy can be provided, for example, by an internal combustion engine (not shown) or by the drive wheels 16 via vehicle inertia.

[0021] Figure 2 1 shows a cross-sectional view of a portion of the motor 12 taken along a virtual plane P. The motor 12 includes a stator 20 having a stator core 19. The stator core 19 has a hole 22, and the stator 20 includes an electrical conductor 24 disposed in the hole 22. The electrical conductor 24 is electrically connected to the battery 18 ( Figure 1 This electrical connection allows the energy storage device 18 ( Figure 1 ) supplies electrical energy to the electrical conductors 24. The stator 20 may have a substantially annular shape and may be disposed about an axis of rotation X. Furthermore, the stator 20 may define an outermost stator surface 23 and an innermost stator surface 25 opposite the outermost stator surface 23. Both the outer stator surface 23 and the inner stator surface 25 may define a circumference about the axis of rotation X. The apertures 22 may be disposed closer to the inner stator surface 25 than the outer stator surface 23, and each aperture 22 may be shaped and dimensioned to receive one or more electrical conductors 24. As used herein, the term "aperture" includes, but is not limited to, a slit, slot, opening, or any cavity in the stator 20 configured and shaped to receive at least one electrical conductor 24. The electrical conductors 24 may be made of a suitable conductive material, such as a metallic material such as copper and aluminum. The electrical conductors 24 may be configured as rods or windings and may have any suitable shape, such as a substantially rectangular, cubic, or cylindrical shape. Regardless of their shape, each electrical conductor 24 is shaped and dimensioned to be received within one aperture 22.

[0022] The electric motor 12 also includes a rotor 26 disposed about an axis of rotation X and positioned within the stator 20. The stator 20 may be concentrically disposed with the rotor 26. The rotor 26 includes a rotor core 21 formed entirely or partially of a metallic material, such as stainless steel, and may have a substantially annular shape. The rotor 26 defines a plurality of rotor cavities 30 and a plurality of permanent magnets 32 disposed within the rotor cavities 30. It is contemplated that the rotor cavities 30 may be configured as slots. The permanent magnets 32 fit tightly within the rotor cavities 30 and may include an alloy of a rare earth element, such as neodymium or samarium, or any other suitable ferromagnetic material. Suitable ferromagnetic materials include neodymium iron boron (NdFeB) alloys and samarium cobalt (SmCo) alloys. The permanent magnets 32 may be annularly disposed about the axis of rotation X and configured to magnetically interact with the electrical conductor 24. During operation of the electric motor 12, the rotor 26 rotates relative to the stator 20 about the axis of rotation X in response to magnetic flux generated between the electrical conductor 24 and the permanent magnets 32, thereby generating drive torque to power the vehicle 10.

[0023] The rotor 26 defines an outermost rotor surface 27 and an innermost rotor surface 29 opposite the outermost rotor surface 27. The outermost rotor surface 27 and the innermost rotor surface 29 may each define a circumference about the rotation axis X. The motor 12 may define an air gap 31 between the innermost stator surface 25 and the outermost rotor surface 27. The air gap 31 may have a substantially annular shape and span the rotor 26. The rotor 26 includes a plurality of pole pieces 42 arranged annularly about a rotor center C, which may coincide with the rotation axis X. Each pole piece 42 represents a magnetic pole of the motor 12. Although the figures show eight pole pieces 42, the rotor 26 may include more or fewer pole pieces 42. Interpolar bridges 44 separate consecutive pole pieces 42 and may extend along corresponding interpolar axes 46. Each interpolar axis 46 extends through the rotor center C and substantially through the middle of a corresponding interpolar bridge 44, defining a dividing line between two consecutive pole pieces 42. The consecutive pole pieces 42 have opposite magnetic polarity. Each pole piece 42 also defines a central polar axis 49 that extends through the rotor center C and substantially through the middle of the pole piece 42. The central polar axis 49 of each pole piece 42 may also intersect the axis X of rotation.

[0024] Each pole piece 42 has a plurality of magnetic layers 33. In the illustrated embodiment, in each pole piece 42, the plurality of magnetic layers 33 include a first magnetic layer 35 and a second magnetic layer 37. The second magnetic layer 37 is closer to the outer rotor surface 27 than the first magnetic layer 35. The first magnetic layer 35 is closer to the innermost rotor surface 29 than the second magnetic layer 37. In the illustrated embodiment, the first magnetic layer 35 is the magnetic layer 33 closest to the innermost rotor surface 29. Therefore, no other magnetic layer 33 is closer to the innermost rotor surface 29 than the first magnetic layer 35.

[0025] Each magnetic layer 33 includes a plurality of permanent magnets 32, and the plurality of permanent magnets 32 are arranged in the rotor cavity 30. The rotor cavity 30 is arranged in the cavity layer 48 corresponding to the magnetic layer 33. In each pole piece 42, the magnetic layers 33 are spaced apart from each other in the radial direction (as shown by arrow R). Although the drawings show two magnetic layers 33, each pole piece 42 may include more or fewer magnetic layers 33. In the illustrated embodiment, each magnetic layer 33 includes only two permanent magnets 32 spaced apart from each other in the tangential direction (as shown by arrow T). In other words, as a non-limiting embodiment, each magnetic layer 33 includes only two permanent magnets 32 to maximize the reluctance torque of the motor 12 without increasing the rotational loss. The tangential direction (as shown by arrow T) may be perpendicular to the radial direction (as shown by arrow R). Each permanent magnet 32 ​​may be a unitary structure (i.e., a one-piece structure).

[0026] refer to Figure 3 , the first magnetic layer 35 (which is the innermost magnetic layer) includes a first permanent magnet 41 and a second permanent magnet 42, each of which is disposed in a corresponding rotor cavity 30 (i.e., a first rotor cavity 51 and a second rotor cavity 52). That is, the first permanent magnet 41 is disposed inside the first rotor cavity 51, and the second permanent magnet 42 is disposed inside the second rotor cavity 52. ​​The rotor core 21 includes a single intra-pole bridge 54 in each pole piece 42 to minimize magnetization under light load. Only the first magnetic layer 35 includes the intra-pole bridge 54. The intra-pole bridge 54 asymmetrically divides the first rotor cavity 51 and the second rotor cavity 52, thereby defining an asymmetric rotor design for a permanent magnet leakage path. This asymmetric rotor design maximizes the torque generated in the motor 12 and minimizes the zero-flux density. Specifically, the asymmetric rotor design increases the ratio of the maximum torque to the zero-flux density of the motor 12. Therefore, the efficiency of the motor 12 is maximized when operating under light load to minimize energy consumption. Under light loads, the magnetic flux from the permanent magnets 32 partially flows through the leakage path. Furthermore, the asymmetric rotor design minimizes magnetization of the stator 20. Furthermore, the larger size of the inter-pole bridges 54 enhances the mechanical strength of the rotor 26, thereby allowing for a higher rotational speed of the rotor 26. Under high loads, the stator flux saturates the leakage path. The magnetic flux can be partially restored to link the stator coils.

[0027] The inner-pole bridge 54 creates a leakage path that is saturated with q flux (i.e., torque-generating flux) and negative d flux. As described above, the inner-pole bridge 54 is located only in one permanent magnet block 55 (which includes only the first permanent magnet 41 and the second permanent magnet 42) to achieve the above-mentioned benefits and does not act as a flux barrier to the torque-generating flux. In the permanent magnet block 55, the inner-pole bridge 54 is positioned closer to the outermost rotor surface 27 than the innermost rotor surface 29. As described above, the inner-pole bridge 54 is placed only in the first magnetic layer 31 (which is the innermost magnetic layer).

[0028] Due to the intra-pole bridge 54 , the first permanent magnet 41 and the second permanent magnet 42 have different surface areas along the imaginary plane P. The first permanent magnet 41 has a first surface area A1, and the second permanent magnet 42 has a second surface area A2. The second surface area A2 is larger than the first surface area A1 to optimize the torque output and zero magnetic flux density of the motor 12.

[0029] The first permanent magnet 41 has a first length L1 and a first width W1. The second permanent magnet 42 has a second length L2 and a second width W2. The first width W1 is equal to the second width W2. The second length L2 is greater than the first length L1. In the illustrated embodiment, the first permanent magnet 41 and the second permanent magnet 42 have a rectangular shape. Therefore, the first surface area A1 is equal to the first length L1 multiplied by the first width W1, and the second surface area A2 is equal to the second length L2 multiplied by the second width W2. The first width W1 is equal to the second width W2. However, the second length L2 is greater than the first length L1. For example, the second length L2 can be twice the first length L1 to define the asymmetric rotor design described above.

[0030] The in-pole bridge 54 has a bridge width BW extending from the first rotor cavity 51 to the second rotor cavity 52. ​​The first length L1 of the first permanent magnet 41 is greater than the bridge width BW. The second length L2 of the second permanent magnet 42 is greater than the bridge width BW. For example, the first length L1 is three times the bridge width BW, and the second length L2 is six times the bridge width BW.

[0031] The first permanent magnet 41 has a first linear wall 61 and a second linear wall 62 opposite the first linear wall 61. A first width W1 extends from the first linear wall 61 to the second linear wall 62. The first linear wall 61 is closer to the outermost rotor surface 27 than the second linear wall 62. The second linear wall is closer to the innermost rotor surface 29 than the first linear wall 61. The second permanent magnet 42 has a first linear boundary 71 and a second linear boundary 72 opposite the first linear boundary 71. A second width W2 extends from the first linear boundary 71 to the second linear boundary 72. The first linear boundary 71 is closer to the outermost rotor surface 27 than the second linear boundary 72. The second linear boundary 72 is closer to the innermost rotor surface 29 than the first linear boundary 71. A bridge length BL extends along a bridge direction BD from the first linear wall 61 of the first permanent magnet 41 to the second linear boundary 72 of the second permanent magnet 42. The second width W2 of the second permanent magnet 42 is greater than the bridge length BL. For example, the bridge length BL is 0.75 times the second width W2. The first linear boundary 71 is spaced apart from the second linear boundary 72 along the bridge direction BD, and the second width W2 of the second permanent magnet 42 is defined from the first linear boundary 71 to the second linear boundary 72 along the bridge direction BD.

[0032] refer to Figure 4The first permanent magnet 41 has a third linear wall 63 and a fourth linear wall 64 opposite the third linear wall 63. The first permanent magnet 41 has a first length L1 extending from the third linear wall 63 to the fourth linear wall 64. The first permanent magnet 41 defines a first axis 65 extending through the third linear wall 63 and the fourth linear wall 64. The first axis 65 is parallel to the first length L1 and intersects the third linear wall 63 at a perpendicular angle. Furthermore, the first axis 65 intersects the fourth linear wall 64 at a perpendicular angle. The second permanent magnet 42 has a third linear boundary 73 and a fourth linear boundary 74. The second length L2 extends from the third linear boundary 73 to the fourth linear boundary 74. The second permanent magnet 42 defines a second axis 75 extending from the third linear boundary 73 to the fourth linear boundary 74. The second axis 75 is parallel to the second length L2 and intersects the third linear boundary 73 at a perpendicular angle. The second axis 75 intersects the fourth linear boundary 74 at a perpendicular angle. An angle θ is defined from the first axis 65 to the second axis 75. Angle θ is an oblique angle to minimize air gap magnetic flux density harmonics. Angle θ can be greater than ten degrees and less than ninety degrees. For example, angle θ can be fifteen degrees.

[0033] Figure 5 An electric motor 12 is shown that is substantially similar to the electric motor 12 described above. However, in this embodiment, the electric motor 12 does not include an intra-pole bridge 34 to minimize saturation by increasing the magnetic flux path.

[0034] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in this specification are descriptive rather than restrictive, and it is understood that various modifications may be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments may be combined to form additional embodiments of the currently disclosed systems and methods that may not be explicitly described or illustrated. Although various embodiments may be described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those skilled in the art recognize that one or more features or characteristics may be compromised to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, lifecycle cost, marketability, appearance, packaging, size, applicability, weight, manufacturability, ease of assembly, and the like. Therefore, embodiments described as being less ideal than other embodiments or prior art implementations with respect to one or more characteristics do not exceed the scope of this disclosure and may be desirable for specific applications.

[0035] The accompanying drawings are simplified and not drawn to exact scale. Directional terms such as top, bottom, left, right, up, above, above, below, below, rear, and front may be used with respect to the accompanying drawings for convenience and clarity of description only. These and similar directional terms should not be construed as limiting the scope of the present disclosure in any way.

[0036] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and that other embodiments may take various alternative forms. The drawings are not necessarily drawn to scale; certain features may be enlarged or minimized to show details of particular components. Therefore, the specific structural details and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to employ the systems and methods of the present disclosure in different ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the figures may be combined with features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combinations of features shown provide representative embodiments of typical applications. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desirable for particular applications or implementations.

[0037] This description is merely illustrative in nature and is in no way intended to limit the present disclosure, its application, or use. The broad teachings of the present disclosure can be implemented in many forms. Therefore, although this disclosure includes specific examples, the true scope of the disclosure should not be so limited, as other modifications will become apparent upon a study of the drawings, the specification, and the appended claims.

Claims

1. An electric motor comprising: a stator comprising a plurality of electrical conductors; as well as a rotor concentrically disposed relative to the stator, wherein the rotor is rotatable relative to the stator about a rotation axis, the rotor being spaced apart from the stator to define an air gap between the stator and the rotor, and comprising: a rotor core defining an outermost rotor surface and an innermost rotor surface opposite the outermost rotor surface, wherein the rotor core includes a plurality of pole pieces annularly arranged about the rotation axis, at least one of the plurality of pole pieces defining a plurality of rotor cavities, and the plurality of rotor cavities including a first rotor cavity and a second rotor cavity spaced apart from each other; and a plurality of permanent magnets, each permanent magnet disposed in one of the plurality of rotor cavities, the plurality of permanent magnets comprising a first permanent magnet disposed in the first rotor cavity and a second permanent magnet disposed in the second rotor cavity; The rotor core includes an intra-pole bridge located in each of the plurality of pole pieces, the intra-pole bridge separating the first rotor cavity from the second rotor cavity, the first permanent magnet having a first surface area, the second permanent magnet having a second surface area, and the second surface area being greater than the first surface area.

2. The electric motor according to claim 1, wherein The first permanent magnet has a first length and a first width, the second permanent magnet has a second length and a second width, the first width is equal to the second width, and the second length is greater than the first length.

3. The electric motor according to claim 2, wherein The in-pole bridge has a bridge width extending from the first rotor cavity to the second rotor cavity, a first length of the first permanent magnet is greater than the bridge width, and a second length of the second permanent magnet is greater than the bridge width.

4. The electric motor according to claim 3, wherein The in-pole bridge has a bridge length, the first permanent magnet has a first linear wall and a second linear wall opposite to the first linear wall, the first width extends from the first linear wall to the second linear wall, the first linear wall is closer to the outermost rotor surface than the second linear wall, and the second linear wall is closer to the innermost rotor surface than the first linear wall, the second permanent magnet has a first linear boundary and a second linear boundary opposite to the first linear boundary, the second width extends from the first linear boundary to the second linear boundary, the first linear boundary is closer to the outermost rotor surface than the second linear boundary, and the second linear boundary is closer to the innermost rotor surface than the first linear boundary, the bridge length extends the first linear wall of the first permanent magnet along the bridge direction to the second linear boundary of the second permanent magnet, and the second width of the second permanent magnet is greater than the bridge length.

5. The electric motor according to claim 4, wherein The first linear boundary is spaced apart from the second linear boundary along the bridge direction, a second width of the second permanent magnet is defined from the first linear boundary to the second linear boundary along the bridge direction, and the bridge length is 0.75 times the second width.

6. The electric motor according to claim 5, wherein The bridge length is less than the first width of the first permanent magnet.

7. The electric motor according to claim 5, wherein The first permanent magnet has a third linear wall and a fourth linear wall, a first length of the first permanent magnet extends from the third linear wall to the fourth linear wall, the first permanent magnet defines a first axis extending through the third linear wall and the fourth linear wall, the first axis intersecting the third linear wall at a perpendicular angle, and the first axis intersecting the fourth linear wall at a perpendicular angle, the second permanent magnet has a third linear boundary and a fourth linear boundary, the second length extends from the third linear boundary to the fourth linear boundary, the second permanent magnet defines a second axis extending from the third linear boundary to the fourth linear boundary, the second axis intersecting the third linear boundary at a perpendicular angle, and the second axis intersecting the fourth linear boundary at a perpendicular angle, an angle defined from the first axis to the second axis, the angle being an oblique angle, and the angle being greater than ten degrees and less than ninety degrees.

8. A propulsion system for a vehicle, comprising: Battery; an electric motor electrically connected to the battery, wherein the electric motor comprises: a stator comprising a plurality of electrical conductors; and a rotor concentrically disposed relative to the stator, wherein the rotor is rotatable relative to the stator about a rotation axis, the rotor being spaced apart from the stator to define an air gap between the stator and the rotor, and The rotor comprises: a rotor core defining an outermost rotor surface and an innermost rotor surface opposite the outermost rotor surface, wherein the rotor core includes a plurality of pole pieces annularly arranged about the rotation axis, at least one of the plurality of pole pieces defining a plurality of rotor cavities, and the plurality of rotor cavities including a first rotor cavity and a second rotor cavity spaced apart from each other; and a plurality of permanent magnets, each permanent magnet disposed in one of the plurality of rotor cavities, the plurality of permanent magnets comprising a first permanent magnet disposed in the first rotor cavity and a second permanent magnet disposed in the second rotor cavity; The rotor core includes an intra-pole bridge in each of the plurality of pole pieces, the first permanent magnet has a first surface area, the second permanent magnet has a second surface area, and the second surface area is greater than the first surface area.

9. The propulsion system according to claim 8, wherein: The first permanent magnet has a first length and a first width, the second permanent magnet has a second length and a second width, the first width is equal to the second width, and the second length is greater than the first length.

10. The propulsion system according to claim 9, wherein: The in-pole bridge has a bridge width extending from the first rotor cavity to the second rotor cavity, the first permanent magnet has a first length greater than the bridge width, and the second permanent magnet has a second length greater than the bridge width and twice the first length.

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