Soft magnetic wire / strip arrangements for motor stators and rotors

Abstract

A novel construction of motor rotors and stators in electric motor devices and other electromagnetic devices that uses soft magnetic wires and / or strips bundled and shaped to form desired magnetic flux paths.

Description

[Technical field]

[0001] <Contractual Background of Inventions> This invention was made with Government support under Grant Nos. DE-AC-02-07CH11358 and DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. <Field of the Invention> The present invention relates to the field of electric motors, and more particularly to the topology and arrangement of advanced soft magnetic materials in the manufacture of the stator or rotor of the motor. [Background technology]

[0002] <Background of the invention> The electric vehicle (EV) market is expanding rapidly, with several governments implementing ambitious plans to replace all internal combustion engine vehicles with EVs. Healthy growth in the EV market depends on government initiatives as well as further development of electric drive systems and traction motors to improve power and range. In its Electrical and Electronics Technology Team roadmap, the US DOE has set targets for electric traction motors in 2025 to increase power density by 8 times to 50kW / L and reduce costs by 30% to $3.3 / kW compared to 2020 figures.

[0003] The electric drive of an EV consists of an electric motor, electronics, transmission, and a battery. An electric motor is mainly made up of a rotor, a stator, windings, a housing, a shaft, and a cooling system. Depending on the motor type, the rotor and / or the stator are a collection of soft magnetic materials (SMM) and insulating materials. By using advanced SMM and improved thermal management techniques, the power density and thermal stability of electric motors can be significantly improved without sacrificing system efficiency.

[0004] Selecting an advanced SMM with a high degree of saturation increases the rated power of an electric motor. However, since SMMs are constantly exposed to alternating magnetic fields, the efficiency of the motor can be compromised if not properly managed. The largest energy loss in SMMs is eddy current loss caused by induced currents in a changing magnetic field, and eddy current loss increases with frequency. Therefore, increasing the motor speed to increase power density is only effective if eddy current losses can be minimized. Taking a 30 kW motor as an example, if the speed is increased from its rated 10,000 rpm to 15,000 rpm, the power output may increase to 45 kW, but the efficiency will decrease from the original 94% to about 90% due to increased eddy current losses [Reference 1].

[0005] The current motor industry employs a segmentation strategy to reduce eddy current losses by thinning the SMM laminate. However, making the SMM sheets thinner to achieve even higher operating frequencies reduces the packing density and magnetic flux density of the SMM because the insulating coating is already at a minimum thickness. For example, in a typical stator, the SMM laminate is about 0.4 mm and the insulating coating on both sides is about 8 μm. If the thickness of the SMM laminate is further reduced to 0.1 mm while keeping the insulating layer constant, the inactive volume will exceed 10%. Typical engineering approaches have reached their practical limits, and the best solution to keep core losses low at high speeds is to use an alternative SMM that has a much higher electrical resistivity than the currently most popular 3.2% Si steel (ρ=57 μΩ-cm). Efforts are underway to use advanced SMMs such as amorphous alloys (Metglas Fe78Si9B13) and nanocrystalline alloys (Nanoperm Fe88B4Zr7Cu1, ρ=120 μΩ-cm) for motor applications. Unfortunately, the inherent brittle nature of these advanced SMM materials makes it extremely difficult to fabricate laminates and assemble them to manufacture motors. In addition, the use of large amounts of expensive glass-forming elements such as B, Nb, Zr, and Cu results in high cost and weak magnetization. High silicon electrical steels have a relatively high resistivity (ρ=82 μΩ-cm), which provides high magnetization and low cost, but unlike amorphous or nanocrystalline alloys, crystalline high silicon electrical steels suffer from brittleness as a result of ordering [Reference 2]. An embodiment of the present invention involves mitigating this brittleness issue through rapid quenching techniques such as melt spinning, as described below. Summary of the Invention

[0006] In some embodiments of the present invention, an electric motor stator and / or rotor is provided that includes a plurality of individual wires and / or strips constructed of soft magnetic material arranged in an array (various configurations) to enhance the magnetic field generated by the copper windings and to act as pole pieces to conduct and concentrate the magnetic flux, forming the magnetic flux paths of the desired stator or rotor. The wires and / or strips may be coated with an electrically insulating material that may also act as a binder for subsequent molding of the stator or rotor.

[0007] In some embodiments, a stator or rotor is provided that may include multiple stator segments or multiple rotor segments, each of which is a bundle of multiple wires and / or strips, arranged side-by-side and joined to form a complete stator or rotor.

[0008] In some embodiments of the present invention, the soft magnetic wire and / or strip comprises a rapidly solidified wire or strip, the wire or strip including, but not limited to, at least one of high silicon steel, amorphous soft magnetic material, and nanocrystalline soft magnetic material.

[0009] The invention contemplates an electric motor including a stator or rotor as described above.

[0010] Additionally, the present invention contemplates components including multiple individual soft magnetic material wires and / or strips bundled together to conform to a desired magnetic flux path in a particular component application, including, but not limited to, a rotor or stator of a motor, a transformer core, or a power electronic component such as an inductor or choke. [Brief description of the drawings]

[0011] [Figure 1]Figure 1 shows the magnetic flux lines or paths that exist during peak torque conditions in a conventional outer rotor surface mounted permanent magnet and inner stator motor design (shown diagrammatically). The U-shaped magnetic flux lines or paths are typical of the magnetic flux lines that exist in a stator (the copper windings have been cut away in Figure 1 to show the magnetic flux lines).

[0012] [Diagram 2] FIG. 2 is a schematic front view of a stator constructed from a bundle of wires and / or strips according to an exemplary embodiment of the invention, with the stator windings shown relative to several stator teeth. [Figure 2A] 2A is a schematic partial perspective view showing a stator segment (two pole pieces) highlighting the orientation of the SMM (soft magnetic material) wires / strips. The SMM wires or strips are shown disposed in a matrix of an electrically insulating material or binder. [Figure 2B] FIG. 2B is a schematic diagram illustrating another embodiment of a stator constructed from individual segments. [Figure 2C] FIG. 2C is a schematic diagram of an individual segment.

[0013] [Figure 3a] FIG. 3a is a photographic image of the high silicon steel strip in the as-melt spun state. [Figure 3b] FIG. 3b is a photographic image of the soft magnetic strip that has been straightened by cold rolling. [Figure 3c] FIG. 3c is a photographic image of a high silicon (6.5 wt % Si) steel strip that has been truncated to a length.

[0014] [Figure 4a] FIG. 4a is a photographic image of a bundle of high silicon steel strips bonded by epoxy in the form of a rectangular prism with dimensions 50 mm×20 mm×1 mm. [Figure 4b] FIG. 4b is a photographic image of two U-shaped segments. [Figure 4c] FIG. 4c is a photographic image of the toroid cut in half to form the two U-shaped segments of FIG. 4b. [Figure 4d] FIG. 4d is a schematic line representation of the rectangular prism of FIG. 4a.

[0015] [Diagram 5] FIG. 5 is a schematic diagram showing an iron core of a wire bundle and an iron core of a strip bundle according to an embodiment of the present invention, in which the upper part is a schematic cross-sectional view of each of the wire bundle and the strip bundle, and the lower part is a schematic plan view with the binder partially removed to expose the wires or strips.

[0016] [Figure 6] FIG. 6 includes a magnetic properties table showing that Fe-6.5w / oSi strip (ribbon) bundles according to embodiments of the present invention have lower electrical energy loss compared to Fe-3.2w / oSi sheet samples of industrial grain-oriented silicon steel (GOSi steel). In the table, DCmax is the maximum permeability under DC test conditions. DC core loss is the core loss (hysteresis) under DC test conditions. B8, B25 and B50 are the magnetic flux density at a specific magnetic field (the values ​​in A / m listed are multiplied by 100 (e.g. B8 is the magnetic flux density at a magnetic field of 800A / m)). Hc is the coercive field in A / m. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] One of the essential components of an electric vehicle is the electric motor. To increase the power output and range of an electric vehicle, the power density and energy efficiency of the electric motor must be improved. The soft magnetic material (SMM) used in the iron core of an electric motor, whether in the form of a rotor or stator, amplifies and guides the magnetic field generated by the copper windings. The copper windings act as pole pieces where the core concentrates the magnetic flux. Currently, iron cores are made by closely stacking laminations along the axial direction of the motor. Each lamination is a monolithic piece, with slots drilled to accommodate either permanent magnets or windings. Due to the saturation limit of magnetization, the areas close to the magnets or windings are saturated, while other areas of the lamination are not. This effect of magnetic flux concentration leaves most of the laminations underutilized, reducing the power density of the motor.

[0018] To address the above-mentioned deficiencies, certain embodiments of the present invention assemble an iron core using ductile soft magnetic wires 10a and / or strips 10b (i.e., wires or strips or a combination of wires and strips, hereinafter referred to as wires and / or strips), where the elongated wires and / or strips are bent or otherwise formed to collectively form an ideal magnetic flux path. With reference to FIG. 5, the wires 10a can have a circular cross-section (e.g., diameter) or other curvilinear cross-section, and the strips 10b can have a rectangular or other planar cross-section. The term "strips" includes, but is not limited to, strips, ribbons, tapes, bands, and other similar elongated shapes.

[0019] When the wire 10a is manufactured and used, the wire diameter can be in the range of 0.01 mm to 1 mm, and the length can be in the range of 1 mm to 5000 mm. When the strip 10b is manufactured and used, the thickness can be in the range of 0.01 mm to 1 mm, the width can be in the range of 0.01 mm to 100 mm, and the length can be in the range of 1 mm to 5000 mm.

[0020] Exemplary embodiments of the present invention form a plurality of stator or rotor segments 12, each of which includes a plurality of SMM wire and / or strip bundles 10, which are joined together to form a complete stator or rotor. The SMM wire and / or strip bundles 10 are glued together, mechanically joined by fastening elements, or otherwise joined to form each bundle. The segments may have a U-shape or other shape to provide useful magnetic flux paths for the motor. Alternatively, a plurality of SMM wires and / or strips may be first formed into a ring shape and then cut in half to form two U-shaped wire and / or strip bundle stator (or rotor) segments that are joined to create the stator (or rotor).

[0021] In a further embodiment, the free (unglued) SMM wire 10a and / or strip 10b can be placed into a stator or rotor fixture with a cavity having a desired stator or rotor tooth shape. The cavity can then be filled or sprayed with a binder material to bond the wire and / or strip into a bundle, or the fixture can be made from a material such as shrink film resin and shrunk over the free SMM wire and / or strip to wrap it and form a complete stator or rotor.

[0022] In practicing the exemplary embodiment of the present invention, the wires 10a and / or strips 10b are coated with an electrical insulating binder material before or after bending or other shaping and then glued together into a horseshoe (U-shape) or other shape that fits snugly around the motor pole. The insulating binder may be an organic or inorganic material, including but not limited to epoxies, silicones, phenolics, silicates, fluorides, oxides, and the like. However shaped, the bundles (stator or rotor segments) are glued to the stator (or rotor) cylinder or disk in a radial or other oriented alignment, as shown in Figures 2 and 2B. The U-shaped wire and / or strip bundle configuration in certain embodiments of the present invention is useful for effectively utilizing the magnetic flux generated by the copper windings of the stator or rotor and also for providing space for cooling channels.

[0023] The properties and arrangement of the SMM wires 10a and / or strips 10b of the bundle 10 play a role in determining the energy density and energy efficiency of the electric motor. Advanced SMM alloys such as high silicon electrical steels (e.g., containing more than 3.2 wt. % Si, with the balance essentially consisting of Fe and other optional alloying elements such as B, Nb, Zr, Cu, etc.) and Fe-B electrical steels with high saturation magnetization and high electrical resistivity (electrical resistivity ρ greater than about 60 μΩ-cm, e.g., about 80 μΩ-cm or greater) can meet this requirement. However, because advanced SMMs are brittle, traditional material processing and motor assembly techniques cannot be directly applied to advanced SMMs. Rapid solidification can overcome the brittleness problem to prepare ductile SMMs. The soft magnetic wires and / or strips used in certain embodiments of the present invention include rapidly solidified wires or strips, including at least one of high silicon steels, amorphous soft magnetic materials, and nanocrystalline soft magnetic materials, but are not limited to these. Also, subsequent stamping or lamination is cost inefficient for SMM tapes. In contrast, the most common material forms for wire and strip are made from rapid solidification techniques such as melt spinning. Particular embodiments of the invention include using high silicon steel (electrical resistivity ρ of about 82 μΩ-cm) and other SMM wire and / or strip to manufacture iron cores for electric motors. Such motors include, but are not limited to, AC or DC motors with radial or axial gaps, self-commutated or externally commutated motors, induction motors, permanent magnet motors, synchronous or switched reluctance motors.

[0024] FIG. 1 shows a typical magnetic flux path FP present in a conventional radial flux motor. From this figure, it can be seen that the stator 2 induces and enhances the magnetic flux lines generated by the copper windings 6 shown in the figure. Limited by Gauss's law of saturation and magnetism in SMM, the magnetic flux lines are concentrated near the permanent magnet rotor 4 and the copper windings 6. Current stator structures use monolithic steel laminated stacks, so the magnetic properties are the same everywhere in each lamination. The effect of magnetic flux concentration results in a large portion of the laminations being underutilized, reducing the power density of the motor.

[0025] 2 shows a schematic representation of an embodiment of the present invention, which addresses the above drawbacks by using a U-shaped wire and / or strip bundle structure as the stator or rotor segments 12 according to an embodiment of the present invention, which makes more effective use of the magnetic flux generated by the stator or rotor copper windings and also provides space for cooling channels.

[0026] In particular, in an exemplary embodiment, the ductile SMM wire 10a and / or strip 10b is treated with an insulating coating and truncated to the desired length before being bent to form the ideal magnetic flux path required for the motor stator. Alternatively, multiple continuous SMM wires and / or strips can be wound or otherwise formed into a toroidal shape as described above and then cut in half to form a set of U-shaped stator or rotor segments. The U-shaped stator or rotor segment 12, however manufactured, is then formed into a horseshoe shape that fits snugly over the motor poles, creating two pole piece halves, as shown in Figures 2A and 2C. The electrically insulating coating on the individual wires 10a and / or strips 10b can serve as a binder 14 for the molding operation. The coating of the insulated wire and / or strip may be applied by dip coating, solution coating, spray coating, or chemical / physical vapor deposition and may include, but is not limited to, at least one of a polymeric material such as an epoxy resin, an inorganic insulator material, and a semiconductor material. A plurality of U-shaped wire and / or strip bundle segments 12 are then glued in a radial arrangement into a cylinder forming a stator or rotor, as shown in Figures 2 and 2B. EXAMPLES

[0027] The following examples are provided to further illustrate, but not limit, embodiments of the present invention. To obtain ductile high silicon steel (6.5 wt.% Si, balance essentially Fe) wire or strip, it is necessary to suppress the formation of ordered phases at temperatures below about 600°C. This can be done by rapid cooling techniques such as melt spinning, where molten metal is injected into a rotating copper wheel. The melt spinning process directly produces continuous ductile high silicon steel wire, strip, ribbon, tape, band. As noted above, the wire can have a circular or other cross section, and the strip includes, but is not limited to, ribbon, tape, band, or other similar elongated shapes. Melt spinning can produce strip widths typically between 0.5 mm and 220 mm, depending on process parameters and equipment capabilities.

[0028] For example, soft magnetic wires or narrower strips can be readily achieved using melt spinning techniques. FIG. 3a shows an assembly of ductile high silicon steel strips (approximately 1 mm wide) made by melt spinning using a wheel speed of 20 m / s. The width of the strips (or diameter of the wires) can range from 0.1 mm to 100 mm for use in practicing certain embodiments of the present invention, although strips (or wires) having widths (diameters) of about 0.5 mm to about 60 mm, or strips (or wires) having other width dimensions suitable for folding or otherwise forming into a U-shape or other shape, can also be used. The soft magnetic strips (or wires) can be reduced in size from the precursor (larger size) soft magnetic material by subjecting the precursor soft magnetic material to suitable processing, such as cutting, rolling, pressing, etc., including but not limited to cutting, rolling, pressing.

[0029] The strip in the quenched solidified state may curl or twist due to the limited size of the solidification chamber or other equipment parameters. Such strip can be straightened by mild cold rolling, as shown in FIG. 3b, and can be easily truncated (e.g., cut) to the desired length, as shown in FIG. 3c. In this embodiment, the strip is mixed with epoxy resin by dip coating and aligned in a die set. The epoxy resin polymer serves not only as an insulating material for the strip, but also as a binder 14 for structural integrity. The desired shape of the stator piece segment is maintained by cold pressing and curing the strip / epoxy mixture in a cold press die. After curing, the epoxy-bonded wire bundle stator segment is removed from the cold press die set. An exemplary epoxy bundle of high silicon steel strip in the form of a rectangular prism (dimensions 50 mm×20 mm×1 mm) was prepared and is shown in FIG. 4a. FIG. 4b shows two U-shaped stator segments and FIG. 4c shows an annulus cut in half to form the two U-shaped stator segments of FIG. 4b.

[0030] Referring to FIG. 5, when viewed in cross section, the wire or strip bundle structure effectively minimizes eddy current losses (see arrows) due to the small cross-sectional size of the wires 10a or strips 10b. When viewed in plan view, the wire or strip bundle structure provides a continuous magnetic flux path within the wire and / or strip bundle core, minimizing air gaps. As mentioned above, the SMM wire and / or strip bundle 10 can be bent or otherwise processed into shapes to maximize magnetic flux density, which is not possible with conventional steel laminate structures. Therefore, if densification can be maximized, the wire and / or strip bundle structure can be a more efficient structure in a motor stator.

[0031] Additionally, FIG. 6 includes a magnetic properties table showing that the energy loss of a strip (ribbon) bundle of Fe-6.5w / oSi according to an embodiment of the present invention is lower compared to the energy loss of a sheet sample of industrial grain-oriented silicon steel Fe-3.2w / oSi (GOSi steel).

[0032] Embodiments of the present invention contemplate electromagnetic devices that include the above wire and / or strip bundles to provide a particular required or desired 3D magnetic flux path, including but not limited to electromagnet yokes and electromagnet pole pieces, since the individual wires and / or strips of the bundle function as magnetic flux carriers.

[0033] Although preferred embodiments of the present invention have been illustrated above, modifications and variations can be made without departing from the spirit and scope of the invention as set forth in the appended claims.

[0034] The following references are incorporated herein by reference: [1]. Tangudu, J. et al., "Design, analysis and loss minimization of a fractional-slot concentrated winding IPM machine for traction applications." Energy Conversion Congress and Exposition (ECCE). IEEE, 2011. [2]. G. Ouyang, X. Chen, Y. Liang, C. Macziewski, J. Cui, Review of Fe-6.5 wt%Si high silicon steel - A promising soft magnetic material for sub-kHz application, J. Magn. Magn. Mater. 481 (2019) 234-250.

Claims

1. 1. A stator or rotor of an electric motor comprising a plurality of individual wires and / or strips made of soft magnetic material and arranged in an array to define a magnetic flux path in the stator or rotor.

2. 2. A stator or rotor as claimed in claim 1, comprising a plurality of stator segments or a plurality of rotor segments, each segment being a bundle of a plurality of said wires and / or strips, said segments being arranged to form a complete stator or rotor.

3. A stator or rotor as claimed in claim 2 , wherein adjacent segments are joined to form the complete stator or rotor.

4. A stator or rotor as claimed in claim 1 , wherein said wires or strips are electrically insulated from one another.

5. A stator or rotor according to claim 4 , wherein the wires and / or strips each have an electrically insulating coating thereon.

6. The stator or rotor of claim 5 , wherein the coating comprises at least one of a polymeric material, an inorganic insulator material, and a semiconductor material.

7. A stator or rotor as claimed in claim 1 , wherein the soft magnetic wires and / or strips have a non-linear shape.

8. A stator or rotor as claimed in claim 7 , wherein the non-linear shape comprises a curved shape.

9. 2. A stator or rotor as claimed in claim 1, wherein the bundle of wires and / or strips is U-shaped and forms a magnetic flux path.

10. A stator or rotor as claimed in claim 1 , wherein the soft magnetic wire and / or strip comprises rapidly solidified wire and / or strip.

11. The stator or rotor of claim 1 , wherein the soft magnetic material comprises at least one of silicon steel, an amorphous soft magnetic material, and a nanocrystalline soft magnetic material.

12. 2. A stator or rotor according to claim 1, wherein the silicon steel comprises greater than 3.2% Si by weight of the steel, the balance being essentially Fe.

13. 2. A stator or rotor as claimed in claim 1, wherein the amorphous or nanocrystalline soft magnetic material is melt spun or otherwise rapidly solidified to inhibit the formation of embrittled phases.

14. A stator or rotor as claimed in claim 1 , wherein the soft magnetic wires and / or strips are reduced in size from a larger size of soft magnetic material.

15. A stator or rotor segment that includes a bundle of multiple soft magnetic wires and / or strips formed into a shape that creates a desired magnetic flux path in a particular stator or rotor application.

16. The segment of claim 14 , wherein the bundle has a U-shape.

17. An electric motor including a stator or rotor according to claim 1.

18. 18. The electric motor of claim 17 comprising a radial flux motor or an axial flux motor or a hybrid radial-axial flux motor.

19. 20. The electric motor of claim 17, comprising an electric motor for a vehicle.

20. A component comprising a plurality of individual wires and / or strips of soft magnetic material bundled together to form a magnetic flux path within the component.

21. 21. The component of claim 20 comprising at least one of a rotor or stator of a motor, a transformer core, an inductor or choke of a power electronic component, and an electromagnet component.

22. 21. An electromagnetic device comprising the component of claim 20.

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