A rotor for an electric motor

Abstract

The present disclosure relates to a rotor (1) for an electric motor comprising a cylindrical rotor core (2), a plurality rotor poles (3) arranged to receive rotor windings (4). Each each pole (3) comprises a dividing plane (p1) extending along said radial direction of said pole (3), each dividing (p1) plane partitioning said pole into a first and a second segment (s1, s2). The first segment and the second segment (s1, s2) of at least one pole (3) of said plurality of rotor poles (3) are mirror asymmetric relative each other about said dividing plane (p1).

Description

[0001] A ROTOR FOR AN ELECTRIC MOTOR

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a rotor for an electric motor, an electric motor comprising such a rotor, and an electric vehicle comprising such a rotor.

[0004] BACKGROUND

[0005] Torque density and torque ripple are important aspects in electric motor design and significantly impact the efficiency of the electric motor. High torque density allows for the development of compact and lightweight motors with increased power output, making them ideal for space-constrained applications. Minimizing torque ripple ensures smooth operation, reducing vibrations and mechanical stress while enhancing overall performance of the electric motor.

[0006] The torque produced by electrical machines is driven by magnetic flux. In synchronous machines, the flux producing torque will be synchronous with the rotor and fluctuations in the torque, i.e torque ripple is produced by the harmonic content in the flux in the air gap present between the stator and the rotor.

[0007] For automotive applications, the torque density, which represents a ratio of torque to volume, has been a key attribute for electrical machines and therefore permanent magnet machines has been the most common motor of choice for most automotive manufacturers. Improved torque density allows for improved packaging solutions, can bring lower losses as a result of a smaller package and allow for more efficient material utilization which can bring down partprice.

[0008] Generally, electric motors having electrically excited rotors with windings may output less torque density compared to rotors with permanent magnets. At the same time, permanent magnets used in rotors are not considered environmentally friendly for several reasons. First, the production of permanent magnets involves mining and refining of rare earth elements, which can cause environmental degradation and pollution. Also, permanent magnets can pose challenges in recycling and disposal, as they contain hazardous materials that can potentially harm the environment if not handled properly. Therefore, while permanent magnets have many technological benefits, their production and use can have negative environmental implications that need to be carefully managed. Hence, electrically excited rotors using windings around the rotor core are considered to be more environmental friendly compared to permanent magnet rotors but lack benefits of rotors with permanent magnets such as optimized torque density.

[0009] Therefore, there is room for electrically excited rotors in the present art to explore the domain to provide an electrically excited rotor that is improved in terms of efficiency. Specifically, improved in terms of torque density and / or torque ripple. By improving the efficiency of electrically excited rotors, such rotors would be perceived as a more viable option for being used in an electric motor.

[0010] Accordingly, it would be desirable to provide a rotor that address requirements related to efficiency when implemented in an electric motor. Specifically, it would be desirable to provide a rotor that is improved in torque density and / or reduces torque ripple.

[0011] SUMMARY

[0012] It is therefore an object of the present disclosure to alleviate at least some of the mentioned drawbacks to provide a rotor that is improved in efficiency. Further, the disclosure provides an electric motor and an electric vehicle comprising such a rotor. This object is achieved by means of a rotor as defined in the appended claims. The present disclosure is at least partly based on the insight that by providing an asymmetric rotor, the rotor will be improved in efficiency.

[0013] The present disclosure relates to a rotor for an electric motor comprising a cylindrical rotor core extending in an axial direction. The rotor comprises a plurality rotor poles arranged to receive rotor windings, each pole extending outwards in a radial direction along a radial axis thereof from an outer circumference of said rotor core. The poles being circumferentially spaced from each other. Further, each pole comprises a pole neck extending radially away from said rotor core. Also, each pole comprises a pole hat extending in said radial direction (as an extension) from an end of said pole neck and beyond a width of said neck in a first direction perpendicular to said radial direction.

[0014] Each pole comprises a dividing plane (may also be referred to as central line) extending along said radial direction of said pole, each dividing plane partitioning said pole into a first and a second segment. The first segment and the second segment of at least one pole of said plurality of rotor poles are (mirror) asymmetric relative each other about said / with respect to said dividing plane. In other words, the first segment and the second segment are disproportional relative each other.

[0015] An advantage of the rotor of the present disclosure is that torque density is increased and torque ripple is reduced.

[0016] The asymmetry of the rotor according to the present disclosure may be provided by different variations in said rotor, each variation advantageously affecting torque density and torque ripple. It should be noted that at least one pole of the rotor may be asymmetric or a plurality of said poles are asymmetric, or all poles of the rotor are asymmetric

[0017] In some aspects (1), the at least one pole is asymmetric at least by that part of said pole hat of the first segment has a greater extension in said first direction relative part of said pole hat of said second segment, or vice versa.

[0018] In some aspects (2), the pole is asymmetric at least by that part of said pole neck of the first segment has a greater extension in said first direction relative part of said pole neck of said second segment, or vice versa.

[0019] In some aspects (3), the at least one pole is asymmetric at least by that a first corner defined by an intersection between said pole hat and said pole neck of said first segment comprises a radius / defines a fillet. Hence, the other corner may define an acute intersection.

[0020] In some aspects (4), the first corner has a greater radius than a second corner defined by an intersection between said pole hat and said pole neck of said second segment. Hence, both corners may comprise fillets, one of said fillets establishing a greater radius than the other.

[0021] In some aspects (5), said at least one pole comprises, at an underside of said hat, a first and a second underside surface, the first underside surface being (positioned) at said first segment, the second underside surface being at said second segment, the underside surfaces extending in said first direction. Further, the rotor core may comprise at least one tangent plane being perpendicular to the radial axis of said pole. The pole may be asymmetric at least by that a first extension in the direction of said radial axis from said first underside surface to said tangent plane is greater than a second extension in the direction of said radial axis from said second underside surface to said tangent plane, or vice versa. In some aspects (6), the first and second underside surface may be non-parallel.

[0022] In some aspects (7), the at least one pole may have a solid shape. In other words, the at least one pole may be free from any perforations, holes, grooves etc.

[0023] In some aspects (8), the at least one pole is asymmetric at least by that a first edge of the pole hat in the first segment is acute and an opposing second edge of the pole hat in the second segment is flat. The edge may be flat such that is extends parallel with the direction of the radial extension of the pole.

[0024] In some aspects (9), the pole hat comprises a top surface. Part of the top surface in the first segment comprises a first top portion, part of the top surface in the second segment comprises a second top portion. Thus, the pole may then be asymmetric at least by that at least the first top portion defines a radius centre point that is offset from the dividing plane in said first direction. The first top portion and the second top portion may jointly define the top surface of the pole hat. However, as noted, the first and the second top portion may have different curvatures (leading to that the radius differs). Accordingly, an intersection between the first top portion and the second top portion (at the dividing plane) may form an edge / indentation towards the rotor core based on differing curvatures.

[0025] In some aspects (10), the second top portion defines a radius centre point being offset from the dividing plane in said first direction. Hence, both first and second top portion may have offset radius centre points. Then the rotor may be asymmetric in that they are offset by different distances relative the dividing plane.

[0026] In some aspects (11), the asymmetry is provided at least by that second top portion defines a radius centre point being aligned with the dividing plane, while the first top portion defines a radius centre point being offset from the dividing plane.

[0027] In some aspects herein (12) said at least one pole hat comprises a top surface, part of the first segment comprises a first top portion, part of the top surface in the second segment comprises a second top portion, wherein said pole is asymmetric at least by that an arc angle of the first top portion being greater than an arc angle of said second top portion.

[0028] In some aspects herein (13), the pole hat comprises / defines a first and a second opposing protruding portions defined by opposing extensions of the hat beyond the width of the pole neck in opposing directions. Each first protruding portions being at said first segment and each second protruding portion being at said second segment. The pole may then be asymmetric at least by that the first protruding portion comprises a greater volume than the second protruding portion.

[0029] In some aspects herein (14), the at least one pole hat comprises a top surface, wherein said pole is asymmetric at least by that, a point at the top surface, at which a minimum air gap is established between said top surface and a stator inner surface arranged to enclose said rotor, is offset, in said first direction, from said dividing plane.

[0030] In some aspects herein (15), the pole is asymmetric at least in that the first underside surface is non-parallel with the second underside surface.

[0031] In some aspects herein (16), the pole is asymmetric at least in that a first (flat) surface of the pole neck is non-parallel with an opposite second (flat) surface of the pole neck. The flat surfaces may be parallel to the dividing plane.

[0032] In some aspects herein (17) the pole is asymmetric at least in that the first or the second underside surface comprises an insert. The insert may be covering the corresponding underside surface with at least 50%. In some aspects the insert may cover less than 100% of the underside surface, but more than 50% of said surface. The insert may be shaped as a block. The insert may comprise the same material as the rotor (i.e. rotor laminate material) or any other suitable material. Accordingly, the insert may be formed by metal, steel or any other material. The insert may be attached to the surface by e.g. adhesive, bonding or any other suitable fastening means.

[0033] In some aspects (18) the at least one pole is asymmetric at least in that a width of the pole neck along said first direction is greater in the first segment compared to the second segment, or vice versa. Accordingly, the pole hat may be shifted in relation to the pole neck.

[0034] Although different aspects herein may be disclosed separately. Some preferable embodiments of the present disclosure may combine the aspects herein. Accordingly, all aspects herein may be combined in different ways. Hence, aspects may be combined such that any variation are within the scope of the invention. As noted each above-mentioned aspects are numbered, 1-18 for simplifying while referring to different aspects. Each of the aspects 1-18, may combined. For example, aspects 1 and 14 may be combined, or aspects 1, 3 and 11 may be combined within the scope of the present disclosure.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] These and other features and advantages of the present disclosure will now be further clarified and described in more detail, with reference to the appended drawings;

[0037] Figure 1A illustrates a side cross-sectional view of a rotor in accordance with aspects herein;

[0038] Figure 1B-3B illustrates a side cross-sectional view of a pole in accordance with aspects herein;

[0039] Figure 4 illustrates a side cross-sectional cutout view of a rotor pole and a stator in accordance with aspects herein;

[0040] Figure 5A illustrates a side cross-sectional view of an electric motor / electric machine in accordance with aspects herein;

[0041] Figure 5B illustrates a side schematic view of a vehicle in accordance with aspects herein;

[0042] Figure 6 illustrates two graphs providing simulation results wherein one graph illustrates results for a motor having an asymmetric rotor and one graph illustrates results for a motor having a symmetric rotor;and

[0043] Figures 7A-B illustrates a side cross-sectional view of a pole in accordance with aspects herein.

[0044] DETAILED DESCRIPTION

[0045] In the following detailed description, some embodiments of the present disclosure will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. Even though in the following description, numerous specific details are set forth to provide a more thorough understanding of the present disclosure, it will be apparent to one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well known constructions or functions are not described in detail, so as not to obscure the present disclosure.

[0046] It is also to be understood that the terminology used herein is for purpose of describing particular aspects only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may refer to more than one unit in some contexts, and the like. Furthermore, the words "comprising", "including", "containing" do not exclude other elements or steps. It should be emphasized that the term "comprises / comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components. It does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. The term "and / or" is to be interpreted as meaning "both" as well and each as an alternative. More specifically, the wording "one or more" of a set of elements (as in "one or more of A, B and C" or "at least one of A, B and C") is to be interpreted as either a conjunctive or disjunctive logic. Put differently, it may refer either to all elements, one element or combination of two or more elements of a set of elements. For example, the wording "A, B and C" may be interpreted as A or B or C, A and B and C, A and B, B and C, or A and C.

[0047] It will also be understood that, although the term first, second, etc. may be used herein to describe various elements or features, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the embodiments. The first element and the second element are both elements, but they are not the same element.

[0048] The term "electric vehicle" as used herein may refer to an all-electric vehicle, also referred to as an EV, a plug-in hybrid vehicle, also referred to as a PHEV, or a hybrid vehicle, also referred to as a HEV, where a hybrid vehicle refers to a vehicle utilizing multiple propulsion sources one of which is an electric drive system. The term "rotor" herein may refer to and be interchanged with "an electrically excited rotor". An electrically excited rotor being a rotor that is magnetized by an external electrical source. The electrically excited rotor comprising windings that are arranged to receive (DC) power to thereby create a (static) magnetic field.

[0049] The expression "vice versa" herein refers to that a depicted asymmetry may be reversed. E.g., if a first corner is described as having a greater radius than a second corner. Vice versa may refer to that in some aspects the second corner may have a greater radius than said first corner.

[0050] Expression denoted as "the first", "the second", etc herein may be interchanged with other denotation within the scope of the present disclosure.

[0051] The figures IB-3 accompanying the disclosure are merely provided to, with the aid of the disclosure, describe or depict asymmetries that may be present in aspects herein. It should be noted that aspects herein may be combined in manners not depicted by the figures IB-3.

[0052] Figure 1A illustrates a side cross-sectional view of a rotor 1 for an electric motor. The rotor 1 comprises a cylindrical rotor core 2 extending in an axial direction along a central axis al of said rotor core (i.e. the rotor core 2 comprises a depth not shown in Figure 1A). The core 2 comprising a plurality rotor poles 3 arranged to receive rotor windings 4, each pole 3 extending outwards in a radial direction along a radial axis rl thereof from an outer circumference of said rotor core 2. The poles 3 being circumferentially spaced from each other, each pole 3 comprising a pole neck 3a extending radially away from said rotor core 2 and a pole hat 3b extending in said radial direction from an end of said pole neck 3a.

[0053] As illustrated in Figure 1A, the rotor 1 comprises a plurality of poles 3. It should be noted that the present disclosure is not limited to the amount of poles illustrated in Figure 1A. The rotor 1 herein may be a 6 pole rotor, 8 pole rotor, 12 pole rotor or any other type of rotor. Further, as illustrated the rotor windings 4 may be any suitable type of winding suitable for an electrically excited rotor.

[0054] Figure IB illustrates a side cross-sectional view of a single pole 3 of the rotor as shown in

[0055] Figure 1A. Figure IB illustrates that the pole head 3b extend beyond a width wl of said neck in a first direction xl perpendicular to said radial direction which is along the radial axis rl. An extension of the radial axis rl may be intersecting with said rotor core central axis al. The central axis al may also be referred to as the axis of rotation of said rotor core 2.

[0056] Figure IB illustrates that each pole 3 comprises a dividing plane pl extending along said radial direction of said pole 3, each dividing pl plane partitioning each pole into a first and a second segment si, s2. Hence, the dividing plane pl may refer to an imaginary plane that equally partitions each pole 3 into segments si, s2. The first segment and the second segment si, s2 of at least one pole 3 of said plurality of rotor poles 3 are mirror asymmetric relative each other about said dividing plane pl. The dividing plane pl may be arranged to be centered relative each pole 3, so to extend along the radial axis rl. Nonetheless, any placement of the dividing plane pl will result in said first and second segments si, s2 being asymmetric. The dividing plane pl may extend along the full depth of the pole 3.

[0057] The at least one pole 3 may be asymmetric at least by that a part of said pole hat 3b of the first segment si has a greater extension in said first direction xl relative part of said pole hat 3b of said second segment s2 or vice versa (as depicted by the double headed dotted arrow at the second segment s2). The expression "a part of said pole hat of the X segment" may refer to the part of the pole hat situated in the X segment. The extension may be 0.5%-20% greater, or 5-10% greater, or 0.5-5% greater, or 2-8% greater, or 3-10% greater.

[0058] Further, the pole 3 may be asymmetric at least by that part of said pole neck 3a of the first segment si has a greater extension in said first direction xl relative part of said pole neck 3a of said second segment s2. This is illustrated in the enlarged section A in Figure IB showing that the extension of the first segment is 'a', and the extension of the second segment is 'b'. Accordingly, 'a' may be greater than 'b' or 'b' may be greater than a. Accordingly, 'a' may be 0.5%-20% greater, or 5-10% greater, or 0.5-5% greater, or 2-8% greater, or 3-10% greater than 'b', or vice versa.

[0059] Figure IB further illustrates that the at least one pole 3 may be asymmetric by that a first edge el of the pole hat 3b in the first segment si is flat and an opposing second edge e2 of the pole hat 3b in the second segment si is acute. In some aspects, this may be provided the other way round.

[0060] Figure 2 illustrates a side cross-sectional view of said pole 3 and illustrates in an enlarged section B the pole 3 is asymmetric by that a first corner 6a defined by an intersection between said pole hat 3b and said pole neck 3a of said first segment si comprises a radius. However, this may be provided the other way round. As shown, the other corner 6b does not have a rad i us / fi Het and is e.g. forming an acute angle of e.g. 90 degrees.

[0061] It should be noted, although not depicted in Figure 2 that said first corner 6a and second corner 6a may both have a fillet / radius whereas the first corner 6a has a greater radius than a second corner 6b. The radius of the first corner 6a may be 0.5%-20% greater, or 5-10% greater, or 0.5-5% greater, or 2-8% greater, or 3-10% greater than the radius of the second corner 6b, or vice versa.

[0062] Figure 3A illustrates, similar to Figures IB-2, a side cross-sectional view of a pole 3. Figure 3A illustrates that each pole 3 comprises, at an underside of said hat 3b (i.e. a surface associated with and partially in contact with the winding), a first and a second underside surface ula, ulb. The first underside surface ula being / positioned at said first segment si, the second underside surface ulb being / positioned at said second segment s2. Both underside surfaces ula, ulb extending in said first direction xl. Further, Figure 3A illustrates that rotor core 2 (note only a part of the core 2 is shown in all Figures 1B-3B) comprises at least one tangent plane tl being perpendicular to the radial axis rl of said pole. The pole 3 may be asymmetric by that a first extension (may also be referred to as a first underside extension) in the direction of said radial axis rl from said first underside surface ula to said tangent plane tl is greater than a second extension (may also be referred to as a second underside extension) in the direction of said radial axis rl from said second underside surface ulb to said tangent plane tl. In other words, this may allow the pole 3 to be asymmetric in that the pole hat 3b thickness in the radial direction is differing in the first and second segment si, s2 (as shown by the dotted double headed arrow depicting how part of the hat 3b in the second segment s2 may be thicker compared to part of the hat 3b in the first segment si). The first extension may be 0.5%-20% greater, or 5-10% greater, or 0.5-5% greater, or 2-8% greater, or 3-10% greater than the second extension, or vice versa.

[0063] Figure 3A also illustrates a side cross-sectional view of a pole 3. Figure 3A illustrates that the part of the top surface ol positioned in the first segment si comprises a first top portion tri, part of the top surface ol in the second segment s2 comprises a second top portion tr2.

[0064] The tangent plane tl as referred to herein may refer to a tangent plane of said rotor core 2. Figure 3B illustrates a cross-sectional side view of a pole 3. Figure 3B illustrates that the pole hat comprises a first and a second opposing protruding portions 10a, 10b defined by opposing extensions beyond the width wl of the pole neck 3b in opposing directions, said first protruding portions 10a being located at said first segment si and said second protruding portion 10b being located at said second segment s2. Accordingly, the pole 3 may be asymmetric by that the first protruding portion 10a comprises a greater volume / cross- sectional area than the second protruding portion 10b, or vice versa. The volumes and / or cross-sectional areas may differ by 0.5%-20%, or 5-10%, or 0.5-5%, or 2-8%, or 3-10%.

[0065] Figure 3B further illustrates that the pole 3 may in some aspects be asymmetric by that at least the first top portion tri defines a radius center point cl that is offset from the dividing plane in said first direction xl. The expression "radius center point" may refer to that, if the surface tri would form a full circle, the center of the circle would define the radius center point. Accordingly, as illustrated in Figure 3A, the radius center point cl may be offset from the dividing plane pl in the first direction xl. In Figure 3B also the radius center point c2 of the second top portion tr2 is offset from the plane pl. Then, the pole 3 may be asymmetric in that they are offset by different magnitudes, such that center point cl is 0.5%-20%, or 5-10%, or 0.5-5%, or 2-8%, or 3-10% more offset relative the second center point c2, or vice versa.

[0066] In some aspects the asymmetry is defined by that the first center point cl is offset from the dividing line pl and the second center point c2 is aligned with the dividing line, or vice versa.

[0067] Figures 3A-3B illustrate top surface (ol) which may be divided by the dividing line pl into a first top portion tri (in first segment si) and second top portion tr2 (in segment s2). Then, the pole 3 may be asymmetric by that an arc angle / radius of the first top portion tri being greater than an arc angle / radius of said second top portion tr2 or vice versa. The angles may differ by 0.5%-20%, or 5-10%, or 0.5-5%, or 2-8%, or 3-10%.

[0068] Figure 4 illustrates a side cross sectional cut-out view of a rotor pole 3 enclosed by a stator 100. The stator 100 may comprise slots with a winding having a plurality of turns per slot. The stator winding may be a hairpin winding. Figure 4 is merely for illustrative purposes and the scale may be varied when realized. Figure 4 illustrates that the pole hat 3b comprises a top surface ol, wherein said pole 3 is asymmetric by that a point at the top surface ol, at which a minimum air gap gl is established between said top surface ol and a stator inner surface 101 arranged to enclose said rotor 1, is offset, in said first direction xl, from said dividing plane pl. The minimum air gap gl may refer to a point at the top surface ol that has the least distance to the stator inner surface.

[0069] Figure 5A illustrates an electric motor 200 comprising a stator 100 and the rotor 1 according to any aspect herein, wherein the stator 100 encloses the rotor 1. The rotor 1 may have one, two or more asymmetric poles 3. In some aspects a plurality of poles are asymmetric. In some aspects a plurality of poles are asymmetric while at least two of said plurality of poles have different asymmetries. The motor 200 may be an electrically excited motor 200, the rotor 1 being a rotor 1 that is magnetized by an external electrical source (such as a battery module of the vehicle). Hence, the rotor winding may be arranged to receive DC power transformed by a rectifier device. The stator winding may be configured to receive AC power. The rotor 1 may comprise a rotor shaft (not illustrated) such that the rotor 1 and the shaft rotate together. As illustrated in Figure 5A, all poles may be solid such that no slits / apertures are formed therein.

[0070] Figure 5B schematically illustrates an electric vehicle 300 comprising an electric motor 200 having the rotor 1 in accordance with any aspect herein. The electric vehicle 300 comprises a battery module 201 a number of other electrical components, including an electrical current transmission system, safety system, battery management system, current management system, inverter(s) and a battery busbar interconnecting the various components. Further, the electric vehicle 300 may comprise an electronic control unit (ECU) 202 in order to control the electric motor 200. The ECU 202 or components thereof can comprise or include various modules, each of which is constructed, programmed, configured, or otherwise adapted to autonomously carry out a function or set of functions.

[0071] Figure 6 illustrates two graphs in which simulations have been performed to compare peak torque and torque ripple of an electric motor having a symmetric rotor design with an electric motor having an asymmetric rotor design, wherein the rotor is an electrically excited rotor. The comparison of Figure 6 compares optimized designs for a symmetric vs an optimized design for asymmetric rotor. Figure 6 illustrates that the electric motor having an asymmetric rotor design provide improved peak torque and reduced torque ripple compared to the electric motor having a symmetric rotor design. Figure 7A illustrates a side cross-sectional view of a single pole 3 of the rotor as shown in Figure 1A. The pole in Figure 7A is asymmetric in that the pole 3 comprises a second underside surface ulb at said second segment s2, the second underside surface ulb being perpendicular to the dividing plane pl so that it is parallel with axis xl. Accordingly, the first underside surface ula is non-parallel with the second underside surface ulb. Hence, first underside surface ula is non-parallel with axis xl.

[0072] Figure 7B illustrates a side cross-sectional view of a single pole 3 of the rotor as shown in Figure 1A. The pole in Figure 7B is asymmetric in that the pole 3 comprises an insert 33 attached to the second underside surface ulb. Furthermore, the pole 3 is asymmetric by that a first surface 31 of the pole neck 3a is non-parallel with an opposite second (flat) surface of the pole neck 3a. Accordingly, the surface 32 in Figure 7B is parallel to the dividing plane pl and the surface 31 is non-parallel with the dividing plane pl. In other words, the surface 31 is angled relative to the dividing plane pl.

[0073] Tables 1-3 below discloses a simulation of a rotor according to some aspects of the present disclosure. The simulation is performed by utilizing finite element analysis in the simulation software J MAG.

[0074] The purpose of the simulation is to further describe the disclosure as presented herein accompanied with advantages thereof. It should be noted that the simulations are based on embodiments for a disclosing purpose, however it is not limited to said embodiments and may be varied within the present disclosure. Generally, the purpose of the simulation is to depict the gradual increase in torque obtained by introducing asymmetries to the pole designs. The simulation is performed for an electric motor, wherein each pole of the rotor of the electric motor comprises at least one asymmetry.

[0075] The label A is an asymmetry where the width of each pole hat 3b along said first direction xl is greater in the first segment si compared to the second segment s2, or vice versa (not illustrated). Accordingly, the hat 3b of each pole 3 has a greater extension along axis xl in one of the segments si, s2 compared to the other segment si, s2.

[0076] The label B is an asymmetry as depicted in Figure 3A where each pole 3 is asymmetric by that a first extension in the direction of said radial axis rl from said first underside surface ula to a tangent plane tl (associated to each pole 3) is greater than a second extension in the direction of said radial axis rl from said second underside surface ulb to said tangent plane tl, or vice versa. The extensions may be referred to as slot height. Accordingly, the slot height may differ in the first and second segments si, s2.

[0077] The label C is an asymmetry where the extension of each pole hat 3b along the direction rl differs in the first and the second segments si, s2, as illustrated in Figure 3A with the double dashed arow indicating that part of the pole hat 3b of the second segment s2 may have a greater extension along axis rl than part of the pole hat 3b in the first segment si.

[0078] The label D is an asymmetry in which, referring to Figure 3A now, a first top portion tri of each pole 3 comprises a radius which is greater than / differs with a radius of the second top portion tr2 of each pole.

[0079] The label E is an asymmetry in which the width of each pole neck 3a along said first direction xl is greater in the first segment si compared to the second segment s2, as il lustrated / i ndicated in for example section A of Figure IB where 'a' and 'b' in section A may have different extensions.

[0080] Accordingly, the tables 1-3 compare each asymmetry A-E alone compared to a symmetric rotor. Also, tables 1-3 compare the symmetric rotor to different combinations of the asymmetries A-E.

[0081] Table 1 depicts simulations for peak torque achieved for the different asymmetries under maximum load conditions of a simulated motor comprising a rotor according to some aspects of the present invention. Table 2 depicts corresponding simulations, but for medium load conditions of the simulated motor, and Table 3 depicts these simulations for low load conditions of the simulated motor.

[0082] Table 1.

[0083] Table 2.

[0084] Table 3.

[0085] The tables 1-3 illustrate that the combinations of asymmetries A-E result in the greatest peak torque. Further, the combinations of asymmetries A-C result in the greatest torque for medium load torque and the combination of asymmetries A-C result in the greatest torque for low load torque.

Claims

CLAIMS1. A rotor (1) for an electric motor comprising: a cylindrical rotor core (2) extending in an axial direction; a plurality rotor poles (3) arranged to receive rotor windings (4), each pole (3) extending outwards in a radial direction along a radial axis (rl) thereof from an outer circumference of said rotor core (2), the poles (3) being circumferentially spaced from each other, each pole (3) comprising a pole neck (3a) extending radially away from said rotor core (2) and a pole hat (3b) extending in said radial direction from an end of said pole neck (3a) and beyond a width (wl) of said neck in a first direction (xl) perpendicular to said radial direction; wherein each pole (3) comprises a dividing plane (pl) extending along said radial direction of said pole (3), each dividing (pl) plane partitioning said pole into a first and a second segment (si, s2); wherein the first segment and the second segment (si, s2) of at least one pole (3) of said plurality of rotor poles (3) are mirror asymmetric relative each other about said dividing plane (pl).

2. The rotor (1) according to claim 1, wherein said at least one pole (3) is asymmetric at least by that; part of said pole hat (3b) of the first segment (si) has a greater extension in said first direction (xl) relative part of said pole hat (3b) of said second segment (s2).

3. The rotor (1) according to claim 1 or 2, wherein said pole (3) is asymmetric at least by that; part of said pole neck (3a) of the first segment (si) has a greater extension in said first direction (xl) relative part of said pole neck (3a) of said second segment (s2).

4. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) is asymmetric at least by that;a first corner (6a) defined by an intersection between said pole hat (3b) and said pole neck (3a) of said first segment (si) comprises a radius, or, that said first corner (6a) has a greater radius than a second corner (6b) defined by an intersection between said pole hat (3b) and said pole neck (3a) of said second segment (s2).

5. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) comprises, at an underside of said hat (3b), a first and a second underside surface (ula, ulb), the first underside surface (ula) being at said first segment (si), the second underside surface (ulb) being at said second segment (s2), the underside surfaces (ula, ulb) extending in said first direction (xl) the rotor core (2) comprising at least one tangent plane (tl) being perpendicular to the radial axis (rl) of said pole, wherein the pole (3) is asymmetric at least by that; a first extension in the direction of said radial axis (rl) from said first underside surface (ula) to said tangent plane (tl) is greater than a second extension in the direction of said radial axis (rl) from said second underside surface (ulb) to said tangent plane (tl).

6. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) has a solid shape.

7. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) is asymmetric at least by that; a first edge (el) of the pole hat (3b) in the first segment (si) is flat and an opposing second edge (e2) of the pole hat (3b) in the second segment (s2) is acute.

8. The rotor according to any one of the preceding claims, wherein said pole hat (3b) comprises a top surface (ol), part of the top surface in the first segment (si) comprises a first top portion (tri), part of the top surface (ol) in the second segment (s2) comprises a second top portion (tr2), wherein said pole (3) is asymmetric at least by that;at least the first top portion (tri) defines a radius centre point (cl) that is offset from the dividing plane in said first direction (xl).

9. The rotor according to claim 8, wherein the second top portion (tr2) defines a radius centre point (c2) being offset from the dividing plane (pl) in said first direction (xl).

10. The rotor according to claim 8, wherein the second top portion (tr2) defines a radius centre point (c2) being aligned with the dividing plane (pl).

11. The rotor according to any one of the preceding claims, wherein said at least one pole hat (3b) comprises a top surface (ol), part of the first segment (si) comprises a first top portion (tri), part of the top surface (ol) in the second segment (s2) comprises a second top portion (tr2), wherein said pole (3) is asymmetric at least by that; an arc angle of the first top portion (tri) being greater than an arc angle of said second top portion (tr2).

12. The rotor (1) according to any one of the preceding claims, wherein the pole hat comprises a first and a second opposing protruding portions (10a, 10b) defined by opposing extensions beyond the width (wl) of the pole neck (3b) in opposing directions, said first protruding portions (10a) being at said first segment (si) and said second protruding portion (10b) being at said second segment (s2), wherein said pole (3) is asymmetric at least by that; the first protruding portion (10a) having a greater volume than the second protruding portion (10b).

13. The rotor (1) according to any one of the preceding claims, wherein said at least one pole hat (3b) comprises a top surface (ol), wherein said pole (3) is asymmetric at least by that, a point at the top surface (ol), at which a minimum air gap (gl) is established between said top surface (ol) and a stator inner surface (101) arranged to enclose said rotor (1), is offset, in said first direction (xl), from said dividing plane (pl).

14. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) comprises, at an underside of said hat (3b), a first and a second underside surface (ula, ulb), the first underside surface (ula) being at said first segment (si), the second underside surface (ulb) being at said second segment (s2), wherein the first and the second underside surfaces (ula, ulb) are nonparallel.

15. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) is asymmetric at least in that a first surface (31) of the pole neck (3a) is nonparallel with an opposite second surface (32) of the pole neck (3b).

16. The rotor (1) according to any one of the preceding claims, wherein said at least one pole (3) comprises, at an underside of said hat (3b), a first and a second underside surface (ula, ulb), the first underside surface (ula) being at said first segment (si), the second underside surface (ulb) being at said second segment (s2), wherein said at least one pole (3) is asymmetric at least in that one of the underside surfaces (ula, ulb) comprises an insert (33).

17. An electric motor (200) comprising: a stator (100) and the rotor (1) according to any one of the preceding claims, wherein the stator (100) encloses the rotor (1).

18. An electric vehicle (300) comprising the electric motor (200) according to claim 17.

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