Machine with internal permanent magnets

Abstract

Machine (12) with internal permanent magnets, comprising: a stator (20) containing several electrical conductors (24); and a rotor (26) arranged concentrically with respect to the stator (20), the rotor (26) being configured to rotate about an axis of rotation (X) relative to the stator (20) and comprising several pole pieces (42) arranged in a ring around the axis of rotation (X), each pole piece (42) comprising a first magnetic layer (48; 52), a second magnetic layer (50), and a third magnetic layer (52; 48), each of the first (48; 52), second (50), and third (52; 48) magnetic layers being configured for magnetic interaction with the electrical conductors (24), the first magnetic layer (48; 52) having a parabolic shape, the second magnetic layer (50) having a semi-elliptical shape, and the third magnetic layer (52; 48) having a hyperbolic shape, and the second magnetic layer (50) being located between the first magnetic layer (48;52) and the third magnetic layer (52; 48); ; wherein the first magnetic layer (48; 52) contains a first permanent magnet (32A; 32E) and a second permanent magnet (32B; 32F), wherein the first (32A; 32E) and second (32B; 32F) permanent magnets together define the parabolic shape; wherein the second magnetic layer (50) contains a third permanent magnet (32C) and a fourth permanent magnet (32D), wherein the third permanent magnet (32C) and the fourth permanent magnet (32D) together define the semi-elliptical shape; wherein the third magnetic layer contains a fifth permanent magnet (32E; 32A) and a sixth permanent magnet (32F; 32B), where the fifth (32E; 32A) and sixth (32F; 32B) permanent magnets define the hyperbolic shape; wherein the rotor (26) further includes an intrapolar bridge (34; 56) that separates the first permanent magnet (32A; 32E) from the second permanent magnet (32B; 32F); and wherein an air gap (31) is defined between the rotor (26) and the stator (20) and a focal point (F) of the parabolic shape, the semi-elliptical shape and the hyperbolic shape is arranged in the air gap (31).

Description

TECHNICAL AREA

[0001] The present disclosure relates to machines with internal permanent magnets (IPM machines) and methods for manufacturing them. BACKGROUND

[0002] An internal permanent magnet (IPM) machine is a brushless electric motor with permanent magnets embedded in its rotor core. Permanent magnet electric motors are generally reliable, lightweight, and thermally efficient. Historically, however, permanent magnets have been used primarily in small, low-power electric motors due to the relative difficulty of finding a material capable of generating a strong magnetic field and the fact that rare-earth permanent magnet technology is still in its infancy.

[0003] Recent advances in materials technology have enabled the creation of high-intensity permanent magnets at lower costs. These technological advances have facilitated the development of compact, high-performance permanent magnet motors (IPMs) for high-volume applications, such as powering vehicles, i.e., hybrid or electric vehicles. IPMs are generally characterized by favorable output torque-to-size ratios and reduced input voltage. IPMs are typically reliable, largely because the permanent magnets are held in dedicated slots in the motor's rotor. When kinetic energy is supplied from an external source, an IPM can also function as a generator.As a result, IPM machines have gained increasing acceptance in the transport industry as viable units for electric and hybrid electric vehicles.

[0004] The publication DE 10 2013 215 222 A1 discloses a machine with internal permanent magnets in which arc-shaped rotor cavities are filled with arc-shaped magnets, wherein the arc centers of these magnets are spaced apart from each other.

[0005] In publication US 2003 / 0011265A1, a permanent magnet motor is disclosed with a rotor having permanent magnets in U-shape, trapezoidal shape or V-shape, which are subdivided and inserted into slots of the rotor to improve the mechanical stability of the motor.

[0006] The publication JP 2011-83 066 A discloses a synchronous reluctance motor with permanent magnet support, which has three arc-shaped slots with ferrite magnets in each rotor pole. The arc-shaped slots taper to triangular shapes at their ends to prevent demagnetization.

[0007] In the publication DE 601 08 424 T2, a permanent magnet rotor with arc-shaped or V-shaped grooves or layers is disclosed, which are filled with magnets made of the same material or of different materials.

[0008] The object of the invention is to improve the reluctance torque of a machine with internal permanent magnets.

[0009] This problem is solved by the machine with internal permanent magnets according to claim 1. Advantageous embodiments of the invention are described in the dependent claims. SUMMARY

[0010] The present disclosure relates to machines with internal permanent magnets. According to the invention, the machine with internal permanent magnets includes a stator containing several electrical conductors. The machine with internal permanent magnets further includes a rotor arranged concentrically with respect to the stator. The rotor is configured to rotate about an axis of rotation relative to the stator and includes several pole pieces arranged in a ring around the axis of rotation. Each of the pole pieces contains a first magnetic layer, a second magnetic layer, and a third magnetic layer, each of the magnetic layers being configured to interact magnetically with the electrical conductors. The first magnetic layer has a parabolic shape, the second magnetic layer has a semi-elliptical shape, and the third magnetic layer has a hyperbolic shape.The second magnetic layer is positioned between the first and third magnetic layers.

[0011] According to the invention, the first magnetic layer contains a first permanent magnet and a second permanent magnet. The first and second permanent magnets together define the parabolic shape. In one embodiment, the first and second permanent magnets are bonded magnets.

[0012] According to the invention, the rotor comprises a first magnetic layer and a second magnetic layer. The second magnetic layer contains a third permanent magnet and a fourth permanent magnet. The third and fourth permanent magnets together define a semi-elliptical shape. The rotor further comprises a third magnetic layer with a fifth permanent magnet and a sixth permanent magnet. The fifth and sixth permanent magnets define a hyperbolic shape. According to the invention, the rotor further comprises an intrapolar bridge that separates the first permanent magnet from the second permanent magnet. An air gap is defined between the rotor and the stator according to the invention. A focal point of the parabolic shape defined by the first magnetic layer, the semi-elliptical shape, and the hyperbolic shape is arranged in the air gap according to the invention.The intrapolar bridge can be stretched along a polar axis that intersects the axis of rotation and the focus.

[0013] The present disclosure also relates to vehicles. In one embodiment, the vehicle includes a final drive and a machine with internal permanent magnets, which is effectively connected to the final drive. The machine with internal permanent magnets includes a stator containing several electrical conductors. The machine with internal permanent magnets may further include a rotor, which is at least partially arranged within the stator and configured to rotate relative to the stator. The rotor contains several magnetic layers. Each magnetic layer has a conical cross-sectional shape with a focal point located between the stator and the rotor. Each magnetic layer contains a first arc-shaped permanent magnet and a second arc-shaped permanent magnet.

[0014] In one embodiment, the first and second arc-shaped permanent magnets can be bonded together. Each magnetic layer can contain only the first and second arc-shaped permanent magnets. The first arc-shaped magnet can be a mirror image of the second arc-shaped permanent magnet. The conical cross-sectional shape defined by each magnetic layer can be substantially semi-elliptical, substantially hyperbolic, or substantially parabolic. The magnetic layers can have substantially different shapes. The magnetic layers can have substantially identical shapes.

[0015] The present disclosure also relates to methods for manufacturing a machine with internal permanent magnets. In one embodiment, the method comprises placing a first glued magnet in a first rotor cavity of a first rotor and placing a second glued magnet in a second rotor cavity of the rotor. The first and second glued magnets together define a substantially conical cross-sectional shape, such as a substantially parabolic shape, a substantially hyperbolic shape, or a substantially semi-elliptical shape.

[0016] In one embodiment, the method further comprises placing a third glued magnet in a third rotor cavity of the rotor and placing a fourth glued magnet in a fourth rotor cavity of the rotor. The third and fourth glued magnets can jointly define a shape that differs from the substantially conical cross-sectional shape jointly defined by the first and second glued magnets.

[0017] In one embodiment, the method may further include placing a third glued magnet in a third rotor cavity of the rotor and placing a fourth glued magnet in a fourth rotor cavity of the rotor. The third and fourth glued magnets may together define a shape that is substantially identical to the substantially conical cross-sectional shape jointly defined by the first and second glued magnets.

[0018] The foregoing features and advantages and other features and advantages of the present invention will readily become apparent from the following detailed description of some of the best types and other embodiments for carrying out the invention, which is defined in the attached claims, when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a vehicle containing a machine with internal permanent magnets; Fig. 2 is a cross-sectional view from the front of the in Fig. 1 schematically shown machine with internal permanent magnets; and Fig. 3 is an enlarged cross-sectional view of a pole piece of the in Fig. 2. Machine shown with internal permanent magnets. DETAILED DESCRIPTION

[0019] With reference to the drawings, where the same reference symbols denote the same components, shows Fig. 1. A vehicle 10 comprising a motor or machine 12 with internal permanent magnets (IPM motor or IPM machine) configured to drive the vehicle 10. The IPM machine 12 may be configured to supply torque or power to another component of the vehicle 10, thereby driving the vehicle 12. Apart from driving the vehicle 10, the IPM machine 12 may be used to supply power to other suitable devices. The IPM machine 12 may be a brushless motor and comprises six substantially identical interconnected segments 12A arranged side by side along a rotational axis X defined along the length of the IPM machine 12. However, it is considered that the IPM machine 12 may contain more or fewer segments 12A.The number of interconnected segments 12A is directly related to the torque that the IPM machine 12 can generate to drive the vehicle 10.

[0020] The vehicle 10 includes a final drive 14 with a gearbox and a drive shaft (not shown). The final drive 14 is effectively connected between the IPM machine 12 and the drive wheels 16 via one or more suitable coupling elements, such as (not shown) constant-speed joints and universal joints. The effective connection between the IPM machine 12 and the final drive 14 enables the IPM machine 12 to deliver torque to the drive wheels 16 to propel the vehicle 10.

[0021] In addition to the final drive 14, the vehicle 10 includes an energy storage device 18 configured to supply electrical energy to the IPM machine 12 and other (not shown) vehicle systems. For this purpose, the energy storage device 18 is electrically connected to the IPM machine 12. Because of this electrical connection, the IPM machine 12 is configured to receive electrical energy from the energy storage device 18 and can operate as a generator when driven by a kinetic energy source of the vehicle 10 located outside the IPM machine 12. Such external kinetic energy can be supplied, for example, by an internal combustion engine (not shown) or by the drive wheels 16 via the vehicle's inertia.

[0022] Fig. Figure 2 shows a cross-sectional view of a part of the in Fig. Figure 1 schematically shows the IPM machine 12. The IPM machine 12 includes a stator 20 with openings 22 and electrical conductors 24 arranged in the openings 22. The electrical conductors 24 are connected to the energy storage device 18 ( Fig. 1) electrically connected. This electrical connection enables the energy storage device 18 ( Fig. 1) supplies electrical energy to the electrical conductors 24. The stator 20 can have a substantially ring-shaped form and can be arranged around the axis of rotation X. Furthermore, the stator 20 can define an outer stator surface 23 and an inner stator surface 25 opposite the outer stator surface 23. Both the outer stator surface 23 and the inner stator surface 25 can define a circumference around the axis of rotation X. The openings 22 can be located closer to the inner stator surface 25 than to the outer stator surface 23, and each is shaped and dimensioned to accommodate one or more electrical conductors 24. The term "openings," as used herein, includes without limitation slots, grooves, recesses, or any cavity in the stator 20 that is designed and shaped to accommodate at least one electrical conductor 24.The electrical conductors 24 can be made of a suitable electrically conductive material, such as metallic materials like copper and aluminum. The electrical conductors 24 can be configured as rods or coils and can have any suitable shape, such as essentially rectangular, cuboid, and cylindrical shapes. Regardless of its shape, each electrical conductor 24 is shaped and dimensioned to fit into an opening 22. Although the drawings show that the openings 22 contain two electrical conductors 24, each opening 22 can contain more or fewer electrical conductors 24.

[0023] The IPM machine 12 further comprises a rotor 26 arranged around the axis of rotation X and within the stator 20. The stator 20 is arranged concentrically to the rotor 26. The rotor 26 can be made entirely or partially of a metallic material such as stainless steel, it can have a substantially ring-shaped form, and it defines several rotor cavities 30 and several arc-shaped permanent magnets 32 arranged in the rotor cavities 30. The arc-shaped permanent magnets 32 are tightly fitted into the rotor cavities 30 and contain an alloy of a rare-earth element such as neodymium, samarium, or any other suitable ferromagnetic material. Suitable ferromagnetic materials include a neodymium-iron-boron alloy (NdFeB alloy) and a samarium-cobalt alloy (SmCo alloy).The arc-shaped permanent magnets 32 can be arranged in a ring around the axis of rotation X and are designed to interact magnetically with the electrical conductors 24. During operation of the IPM machine 12, the rotor 26 rotates relative to the stator 20 around the axis of rotation X in response to the magnetic flux that develops between the electrical conductors 24 and the arc-shaped permanent magnets 32, thereby generating drive torque to operate the vehicle 10.

[0024] In the illustrated embodiment, the rotor 26 defines an outer rotor end 27 and an inner rotor end 29 opposite the outer rotor end 27. Both the outer rotor end 27 and the inner rotor end 29 can define a circumference around the axis of rotation X. The IPM machine 12 defines an air gap 31 between the inner stator surface 25 and the outer rotor end 27. The air gap 31 can have a substantially annular shape and extends around the rotor 26. The rotor 26 contains several pole pieces 42 arranged in a ring around a rotor center point C, which can coincide with the axis of rotation X. Although the drawings show eight pole pieces 42, the rotor 26 can contain more or fewer pole pieces 42. Interpolar bridges 44 separate successive pole pieces 42 and can be extended along respective interpolar axes 46.Each interpolar axis 46 extends through the center point C of the rotor and substantially through the center of a respective interpolar bridge 44, defining the boundary line between two successive pole pieces 42. Successive pole pieces 42 have opposite polarities. Each pole piece 42 further defines a pole center axis 49, which extends through the center point C of the rotor and substantially through the center of the pole piece 42. The pole center axis 49 of each pole piece 42 may also intersect the rotation axis X.

[0025] With reference to Fig. Each pole piece 42 contains several arc-shaped permanent magnets 32 arranged in magnetic layers 48, 50, and 52, spaced apart from one another along a radial direction indicated by arrow R. Specifically, each pole piece 42 contains a first magnetic layer 48, a second magnetic layer 50, and a third magnetic layer 52. Although the drawings show three magnetic layers 48, 50, and 52, each pole piece 42 may contain more magnetic layers. Each magnetic layer 48, 50, or 52 contains a pair of arc-shaped permanent magnets 32 spaced apart from one another along a tangential direction indicated by arrow T. The tangential direction (indicated by arrow T) may be substantially perpendicular to the radial direction (indicated by arrow R).Although the drawings show that each magnetic layer 48, 50, and 52 has only two arc-shaped permanent magnets 32, the magnetic layers 48, 50, and 52 can each contain more arc-shaped permanent magnets 32. Each arc-shaped permanent magnet 32 ​​can be a monolithic structure.

[0026] All or some of the arc-shaped permanent magnets 32 may be bonded magnets. When used herein, the term “bonded magnets” excludes sintered magnets. Sintered magnets are prepared by melting the raw material in a furnace, pouring the molten raw material into a mold, and allowing the raw material to cool to form ingots. The ingots are then pulverized, and the resulting powder subsequently undergoes a liquid-phase sintering process, which magnetically aligns the powder into dense blocks. These blocks are then heat-treated, cut to shape, surface-treated, and magnetized. In contrast, to produce a bonded magnet, a thin strip of a ferromagnetic material (such as a neodymium alloy) is melt-spun. This strip is then pulverized, mixed with a polymer, and then cast into bonded magnets by either die-casting or injection molding.Bonded magnets offer less flux than sintered magnets and are therefore less efficient. However, bonded magnets can be formed into parts with complex shapes and exhibit lower eddy current losses than sintered magnets.

[0027] It is important to form complexly shaped permanent magnets (such as the arc-shaped magnets 32) to increase the reluctance moment of the IPM machine 12 and thus maximize its power output. Consequently, at least one of the magnetic layers 48, 50, or 52 has an essentially conical cross-sectional shape. As used herein, the term "conical cross-sectional shape" includes essentially parabolic, essentially hyperbolic, and essentially semi-elliptical shapes and excludes essentially semicircular shapes. Although the term "semi-elliptical shape" may, in a strictly mathematical sense, include semicircular shapes, as used herein, the term "semi-elliptical shape" excludes semicircular shapes. Similarly, the term "essentially semi-elliptical shape" in the present disclosure excludes essentially semicircular shapes.Due to their essentially conical cut shapes, the magnetic layers 48, 50 and 52 can be arranged further into the inner end of the rotor 29, thereby improving the reluctance moment of the IPM machine 12.

[0028] The first magnetic layer 48 can contain only a first permanent magnet 32A, arranged in a first rotor cavity 30A, and a second permanent magnet 32B, arranged in a second rotor cavity 30B. However, the first magnetic layer 48 can contain more or less arc-shaped permanent magnets 32. A first intrapolar bridge 34 separates the first permanent magnet 32A from the second permanent magnet 32B in the tangential direction indicated by arrow T. Furthermore, the first intrapolar bridge 34 can be extended along the pole center axis 49 and improves the structural integrity of the rotor 26.

[0029] In the illustrated embodiment, the first permanent magnet 32A and the second permanent magnet 32B jointly define a substantially parabolic shape. Consequently, the first magnetic layer 48 has a substantially parabolic shape. The substantially parabolic shape of the first magnetic layer 48 is defined around a focus or focal point F. The focal point F is located in the air gap 31 and is the focal point of the parabola jointly defined by the first permanent magnet 32A and the second permanent magnet 32B. The pole center axis 49 intersects the focal point F and coincides with an axis of symmetry of the parabola jointly defined by the first permanent magnet 32A and the second permanent magnet 32B. Consequently, the first permanent magnet 32A can be a mirror image of the second permanent magnet 32B.The first intrapolar bridge 34 is arranged between the first permanent magnet 32A and the second permanent magnet 32B and defines the vertex of the parabola defined by the first magnetic layer 48. The first magnetic layer 48 alternatively has an essentially hyperbolic or essentially semi-elliptical shape. In both cases, the focal point F defines the focal point of the hyperbola or semi-ellipse jointly defined by the first permanent magnet 32A and the second permanent magnet 32B, and the pole center axis 49 can define the axis of symmetry of the hyperbola or parabola defined by the first magnetic layer 48.

[0030] At least part of the second magnetic layer 50 is arranged closer to the inner end of the rotor 29 than the first magnetic layer 48. The second magnetic layer 50 can contain only a third permanent magnet 32C, arranged in a third rotor cavity 30C, and a fourth permanent magnet 32D, arranged in a fourth rotor cavity 30D. However, it is considered that the second magnetic layer 50 can contain more permanent magnets. A second intrapolar bridge 54 separates the third permanent magnet 32C from the fourth permanent magnet 32D along the tangential direction indicated by arrow T. Furthermore, the second intrapolar bridge 54 can be extended along the pole center axis 49 and improves the structural integrity of the rotor 26.

[0031] In the illustrated embodiment, the third permanent magnet 32C and the fourth permanent magnet 32D together define a substantially semi-elliptical shape. Consequently, the second magnetic layer 50 has a substantially semi-elliptical shape. The focal point F is the focal point of the semi-ellipse defined by the second magnetic layer 50, and the pole center axis 49 is the axis of symmetry of the semi-ellipse defined by the second magnetic layer 50. Consequently, the third permanent magnet 32C is a mirror image of the fourth permanent magnet 32D. The second intrapolar bridge 54 is arranged between the third permanent magnet 32C and the fourth permanent magnet 32D and defines the vertex of the semi-ellipse defined by the second magnetic layer 50. The second magnetic layer 50 can alternatively have a substantially parabolic or substantially hyperbolic shape.In both cases, the focal point F can define the focal point of the parabola or hyperbola defined by the second magnetic layer 50, and the pole center axis 49 defines the axis of symmetry of the parabola or hyperbola defined by the second magnetic layer 50.

[0032] At least part of the third magnetic layer 52 is located closer to the inner end of the rotor 29 than the second magnetic layer 50. The third magnetic layer 52 contains a fifth permanent magnet 32E, located in a fifth rotor cavity 30E, and a sixth permanent magnet 32F, located in a sixth rotor cavity 30F. Although the drawings show that the third magnetic layer 52 has only two permanent magnets, it can contain more. A third intrapolar bridge 56 separates the fifth permanent magnet 32E from the sixth permanent magnet 32F along the tangential direction indicated by arrow T. Furthermore, the third intrapolar bridge 56 can be extended along the pole center axis 49, thus improving the structural integrity of the rotor 26.

[0033] The fifth permanent magnet 32E and the sixth permanent magnet 32F together define an essentially hyperbolic shape. Consequently, the third magnetic layer 52 has an essentially hyperbolic shape. The focal point F is the focal point of the hyperbola defined by the third magnetic layer 52, and the pole-center axis 49 is the axis of symmetry of the hyperbola defined by the third magnetic layer 52. Consequently, the fifth permanent magnet 32E is a mirror image of the sixth permanent magnet 32F. The third interpolar bridge 56 is arranged between the fifth permanent magnet 32E and the sixth permanent magnet 32F and defines the vertex of the hyperbola defined by the third magnetic layer 52. Instead of an essentially hyperbolic shape, the third magnetic layer 52 may have an essentially semi-elliptical or parabolic shape.In any case, the focal point F defines the focal point of the semi-ellipse or parabola defined by the third magnetic layer 52, and the pole center axis 49 can define the axis of symmetry of the semi-ellipse or parabola defined by the third magnetic layer 52.

[0034] Although Fig.Since the pole piece 42 is shown to have magnetic layers with three different shapes, each of the pole pieces 42 of the rotor 26 can contain essentially identical magnetic layers. For example, each pole piece 42 can contain three magnetic layers, each having essentially parabolic shapes. It is considered that each pole piece 42 can contain two magnetic layers with essentially identical shapes and a third magnetic layer with a different shape. For example, one of the pole pieces 42 can contain two magnetic layers with essentially hyperbolic shapes and a third magnetic layer with an essentially semi-elliptical shape. Alternatively, one or more of the pole pieces 42 can contain two magnetic layers with essentially parabolic shapes and a third magnetic layer with an essentially hyperbolic shape.Each pole piece 42 can also contain magnetic layers, each of which has essentially different shapes.

[0035] It is also considered that the magnetic layers may be arranged in different positions relative to the rotor center C. For example, at least part of the third magnetic layer 52 may be arranged closer to the rotor outer end 27 than any other part of the first magnetic layer 48. In addition, the pole pieces 42 may contain other combinations of the first magnetic layer 48, the second magnetic layer 50, and the third magnetic layer 52.

[0036] The present disclosure also relates to methods for manufacturing the IPM machine 12. By using bonded permanent magnets, the manufacturing process is simplified, thereby minimizing manufacturing costs. In an exemplary embodiment, the method for manufacturing the IPM machine 12 comprises placing a first bonded magnet (e.g., the first permanent magnet 32) in the first rotor cavity 30A of the rotor 26; and placing a second bonded magnet (e.g., the second permanent magnet 32B) in the second rotor cavity 30B. In this method, the first and second bonded magnets (e.g., the first and second permanent magnets 32A, 32B) together define a substantially conical cross-sectional shape. This substantially conical cross-sectional shape can be a substantially parabolic shape, a substantially hyperbolic shape, or a substantially semi-elliptical shape.This manufacturing process can further include placing a third bonded magnet (such as the third permanent magnet 32C) in the third rotor cavity 30C and placing a fourth bonded magnet (such as the fourth permanent magnet 32D) in the fourth rotor cavity 30D. The third and fourth bonded magnets (such as the third and fourth permanent magnets 32C, 32D) together define a shape that is substantially identical to the substantially conical cross-sectional shape jointly defined by the first and second bonded magnets (such as the first and second permanent magnets 32A, 32B). Alternatively, the third and fourth bonded magnets (such as the third and fourth permanent magnets 32C, 32D) can together define a shape that differs from the shape jointly defined by the first and second bonded magnets (such as the first and second permanent magnets 32A, 32B).

[0037] The detailed description and the drawings or figures support and describe the invention, but the scope of the invention is defined only by the claims. Although some of the best ways and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for putting the invention defined in the accompanying claims into practice.

Claims

[1] Machine (12) with internal permanent magnets, comprising: a stator (20) containing a plurality of electrical conductors (24); and a rotor (26) arranged concentrically in relation to the stator (20), wherein the rotor (26) is configured to rotate relative to the stator (20) about a rotation axis (X) and includes a plurality of pole pieces (42) arranged annularly around the rotation axis (X), wherein each of the pole pieces (42) includes a first magnetic layer (48; 52), a second magnetic layer (50), and a third magnetic layer (52; 48), wherein each of the first (48; 52), second (50), and third (52; 48) magnetic layers is configured for magnetic interaction with the electrical conductors (24), wherein the first magnetic layer (48; 52) has a parabolic shape, the second magnetic layer (50) has a semi-elliptical shape, and the third magnetic layer (52; 48) has a hyperbolic shape, and wherein the second magnetic layer (50) is disposed between the first magnetic layer (48;52) and the third magnetic layer (52; 48); wherein the first magnetic layer (48; 52) includes a first permanent magnet (32A; 32E) and a second permanent magnet (32B; 32F), the first (32A; 32E) and second (32B; 32F) permanent magnets together defining the parabolic shape; wherein the second magnetic layer (50) contains a third permanent magnet (32C) and a fourth permanent magnet (32D), wherein the third permanent magnet (32C) and the fourth permanent magnet (32D) together define the semi-elliptical shape; wherein the third magnetic layer contains a fifth permanent magnet (32E; 32A) and a sixth permanent magnet (32F; 32B), wherein the fifth (32E; 32A) and sixth (32F; 32B) permanent magnets define the hyperbolic shape; wherein the rotor (26) further includes an intrapolar bridge (34; 56) separating the first permanent magnet (32A; 32E) from the second permanent magnet (32B; 32F); and wherein an air gap (31) is defined between the rotor (26) and the stator (20) and a focal point (F) of the parabolic shape, the semi-elliptical shape and the hyperbolic shape is arranged in the air gap (31). [2] The internal permanent magnet machine (12) of claim 1, wherein the first (32A; 32E) and second (32B; 32F) permanent magnets are bonded magnets. [3] The internal permanent magnet machine (10) of claim 1, wherein the intrapolar bridge (34, 54, 56) is extended along a pole center axis (49) intersecting the rotation axis (X) and the focal point (F).

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