Sheath-core composite wire for motor and preparation method and application of sheath-core composite wire

Abstract

The invention discloses a sheath-core composite wire for a motor and a preparation method and application thereof, and belongs to the technical field of wires, the sheath-core composite wire for the motor comprises a sheath layer and a core layer, the sheath layer is a metal hollow tube, and the core layer is a carbon material. According to the invention, the carbon material is used as the core layer, and the carbon material has a weaker skin effect and lower resistivity, and can effectively ensure that current is uniformly distributed on the cross section of the core layer in a high-frequency environment, so that the area of a middle ineffective current region generated by the electromagnetic wire due to high frequency is reduced, and the charge density on the unit cross section is increased. Therefore, the problem that the effective current-carrying area of an existing metal wire in a high-frequency state is reduced can be solved.

Description

Technical Field

[0001] This invention relates to the field of conductor technology, and in particular to a core-sheath composite conductor for motors, its preparation method, and its application. Background Technology

[0002] As the demand for motor power in the new energy vehicle market continues to increase, the development trend of motors is also increasingly towards higher speeds. However, the high speed of motors makes the metal wires of the motor prone to skin effect. The skin effect reduces the effective current-carrying area of ​​the conductor, increases the equivalent resistance of the wire winding, and increases copper loss, which seriously affects the performance of the motor.

[0003] The conventional solution is to reduce the diameter of the conductor, such as by using multiple parallel thin stranded wires to reduce the skin effect of the metal conductor, thereby reducing AC copper losses. However, this method has an optimal frequency range (1kHz-3kHz). Beyond this range, the proximity effect of the conductor will replace the skin effect and dominate high-frequency losses. Therefore, this method has the problem of low effective current-carrying area of ​​the metal conductor at high frequencies. Summary of the Invention

[0004] The main objective of this invention is to provide a core-sheath composite conductor for motors, its preparation method, and its application, aiming to improve the problem of reduced effective current-carrying area of ​​existing metal conductors at high frequencies.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a core-skin composite conductor for an electric motor. The electric motor includes a stator core with stator slots evenly distributed circumferentially. The core-skin composite conductor is arranged in the stator slots. The core-skin composite conductor includes a sheath and a core, wherein the sheath is a hollow metal tube and the core is a carbon material.

[0006] In one embodiment, the carbon material includes at least one of carbon nanotubes, graphene, graphene oxide, and carbon fiber.

[0007] In one embodiment, the material of the metal hollow tube includes at least one of gold and its alloys, silver and its alloys, copper and its alloys, iron and its alloys, and aluminum and its alloys.

[0008] In one embodiment, the area ratio of the sheath to the cross-section of the core-sheath composite conductor is greater than the area ratio of the core to the cross-section of the core-sheath composite conductor; and / or,

[0009] The sheath accounts for a larger proportion of the mass of a core-sheath composite conductor than the core itself.

[0010] In one embodiment, the area ratio of the sheath to the core layer in the cross-section of the sheath-core composite conductor is (65-85):(15-45); and / or,

[0011] The mass ratio of the sheath to the core in the sheath-core composite conductor is (72-84):(18-26).

[0012] In one embodiment, at the cross-section of the core-sheath composite conductor, the core layer is symmetrically distributed along the centerline of the core-sheath composite conductor.

[0013] In one embodiment, the carbon material of the core layer is selected from one of the following: concentric stranded structure, concentric composite stranded structure, transposed composite stranded structure, parallel forming structure, single-winding forming structure, and braided forming structure.

[0014] In one embodiment, the outer peripheral shape of the hollow metal tube is selected from one of the following: rectangular, circular, elliptical, and trapezoidal; and / or,

[0015] The inner circumferential shape of the metal hollow tube is selected from one of the following: rectangular, circular, elliptical, or trapezoidal.

[0016] Secondly, the present invention provides a method for preparing a core-sheath composite conductor for an electric motor, comprising:

[0017] Carbon material wires are bundled into a hollow metal tube to form a sheath-core composite conductor for motors; or...

[0018] Carbon material wire is pre-placed on a metal strip, and a sheathed core composite wire for motors is produced using a coating welding process; or...

[0019] Carbon material wires are pre-placed in a crystallizer, and a continuous casting tubing process is used to produce composite wires for motors with sheath cores.

[0020] In one embodiment, "bundling carbon material wires into a hollow metal tube to form a core-sheath composite conductor for motors" includes:

[0021] One end of the carbon material wire is mounted on a magnetic traction head, and the carbon material wire is pulled through a metal hollow tube by a traction machine to form a core-shell composite wire for motors.

[0022] In one embodiment, "pre-setting carbon material wire on a metal strip and producing a core-coated composite conductor for motors using a coating welding process" includes:

[0023] The metal strip is gradually processed into a tube and wrapped around the outer periphery of the carbon material wire. The longitudinal seam of the tube is welded to form a wire blank. Then, the core-sheath composite wire for motors can be obtained by drawing and heat treatment.

[0024] In one embodiment, "pre-positioning carbon material wire in a crystallizer and producing core-coated composite wires for motors using a continuous casting tubing process" includes:

[0025] Carbon material wire is pre-placed in the crystallization mold of the crystallizer, and then molten metal is poured in. After the molten metal solidifies, it is continuously pulled out from the other end of the crystallizer to obtain the core-shell composite wire for motors.

[0026] Thirdly, the present invention provides the application of the above-mentioned core-sheath composite wire for motors or the core-sheath composite wire for motors prepared by the above-mentioned preparation method in motors.

[0027] In one embodiment, the motor windings are made of sheath-core composite wire to reduce the skin effect of the motor windings in high-frequency environments.

[0028] The present invention provides a composite wire for motors with a sheath and a core. The sheath is a hollow metal tube, and the core is made of carbon material. The carbon material in the core has a weaker skin effect and lower resistivity, which effectively ensures uniform current distribution across the cross-section of the core in high-frequency environments. This reduces the area of ​​the intermediate ineffective current region generated by high frequencies in the electromagnetic wire and increases the charge density per unit cross-section. Therefore, the present invention can improve the problem of reduced effective current-carrying area of ​​existing metal wires at high frequencies. Attached Figure Description

[0029] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0030] Figure 1 This is a schematic cross-sectional view of a core-sheath composite conductor for motors according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the stranded structure of the core carbon material in one embodiment of the present invention;

[0032] Figure 3 This is a schematic cross-sectional view of a core-sheath composite conductor for motors according to another embodiment of the present invention.

[0033] Explanation of icon numbers

[0034] 100. Sheath-core composite wire for motors; 11. Sheath; 12. Core. Detailed Implementation

[0035] It should be noted that if the embodiments of the present invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Furthermore, the use of "and / or" or "and / or" throughout the text implies three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied. In the embodiments of the present invention, "at least one" refers to one or more, and "more" refers to two or more.

[0036] In the description of the embodiments of this invention, if technical terms such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the embodiments of this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the embodiments of this application.

[0037] In the description of the embodiments of this invention, unless otherwise explicitly specified and limited, the technical terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0038] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0039] The increasing speed of electric motors makes their metal conductors prone to the skin effect. The skin effect occurs when alternating current flows through a conductor, and the alternating magnetic field generated around the conductor induces a current within the conductor, causing uneven current distribution that tends to concentrate near the outer surface. The skin effect reduces the effective current-carrying area of ​​the conductor, increasing the equivalent resistance of the windings. Furthermore, the eddy currents induced by the external magnetic field within the conductor increase copper losses in the windings, thus severely impacting motor performance.

[0040] There are two types of conductor windings for motors: flat wire and round wire. Under the same power, flat wire has advantages over round wire when used in new energy vehicle motors, such as high slot fill factor, low material cost, light weight, and high power density. Therefore, flat wire is widely used in new energy vehicle motors. However, flat wire is more prone to skin effect than round wire.

[0041] To address these issues, a conventional approach is to reduce the diameter of the conductor, such as by using multiple parallel stranded thin wires to reduce the skin effect of the metal conductor, thereby reducing AC copper losses. However, this method has an optimal frequency range (1kHz-3kHz). Beyond this range, the proximity effect of the conductor will replace the skin effect and dominate high-frequency losses. Therefore, this method suffers from the problem of low effective current-carrying area of ​​the metal conductor at high frequencies.

[0042] Compared with traditional metallic conductors, carbon materials have a lower skin effect, and their skin depth will saturate as the frequency increases, thus limiting the further increase of high-frequency resistance in carbon material structures.

[0043] Based on the above considerations, in order to improve the problem of reduced effective current-carrying area of ​​existing conductors in high-frequency environments, a composite conductor with a metal sheath and a carbon material core was designed. The carbon material in the core has a weaker skin effect and lower DC resistivity. In high-frequency environments, it can effectively ensure that the current is uniformly distributed across the cross-section of the core, thereby reducing the area of ​​the intermediate ineffective current region generated by the electromagnetic wire at high frequencies and increasing the charge density per unit cross-section.

[0044] According to some embodiments of the present invention, reference Figure 1 As shown, the present invention provides a core-skin composite conductor 100 for motors. The motor includes a stator core with stator slots evenly distributed along the circumference. The core-skin composite conductor is arranged in the stator slots. The core-skin composite conductor includes a sheath 11 and a core 12. The sheath 11 is a hollow metal tube, and the core 12 is a carbon material.

[0045] The stator core is an important component of the motor stator, typically made of laminated silicon steel sheets. The stator core provides a low-resistivity path for the motor's magnetic field. The core-sleeve composite conductors are arranged in the stator slots to form the stator windings; in other words, the stator core provides support and fixation for the stator windings.

[0046] A hollow metal tube is a tube made of metal with a hollow structure, which is used to fill the carbon material of the core layer 12. The skin layer 11, made of a hollow metal tube, can serve as a supporting skeleton, meeting the requirements of rigidity, conductivity, formability, and application conditions.

[0047] Carbon materials refer to a class of materials whose main component is carbon, and they possess excellent electrical conductivity. Using carbon material as the core layer 12 can improve the conductivity and current carrying capacity of the composite conductor at high frequencies, thereby increasing the electromagnetic conversion efficiency of the motor when used in motor windings. Furthermore, using carbon material as the core layer 12 can reduce the weight of the composite conductor, further reducing the overall weight of the motor when used in motor windings, thus improving the motor's operating efficiency.

[0048] The carbon material can be wire, which can be a single filament, a multi-strand filament made of one type of carbon material filament twisted together, a stranded filament made of at least two types of carbon material filament twisted together, or a bundled filament. This invention does not impose any specific limitations.

[0049] Carbon materials can also be in powder form. The powdered carbon material is filled into a hollow metal tube and compacted, or a mixture of powdered carbon material and adhesive is filled into a hollow metal tube and compacted.

[0050] A composite conductor for motors, consisting of a hollow metal tube and carbon material, effectively ensures uniform current distribution across the core cross-section in high-frequency environments. This reduces the area of ​​the intermediate ineffective current region generated by high frequencies and increases the charge density per unit cross-section. Therefore, this invention addresses the problem of reduced effective current-carrying area in existing metal conductors at high frequencies.

[0051] According to some embodiments of the present invention, the carbon material includes at least one of carbon nanotubes, graphene, graphene oxide, and carbon fiber.

[0052] Carbon nanotubes are seamless hollow tubular structures formed by coiling graphene sheets around a central axis at a specific helical angle. Carbon nanotubes exhibit excellent electrical conductivity, reaching up to 10⁻⁶. 8 S·m -1 Carbon nanotubes possess a current-carrying capacity two orders of magnitude higher than copper. Furthermore, they exhibit extremely high strength and toughness, with a tensile strength reaching 200 GPa. Carbon nanotubes can be either single-walled or multi-walled.

[0053] Graphene is a two-dimensional carbon nanomaterial composed of hexagonal, honeycomb-like lattice structures made of carbon atoms. It also possesses excellent electrical conductivity and extremely high mechanical strength. Graphene oxide is a two-dimensional nanosheet composed of highly oxidized carbon atoms, decorated with oxygen-containing functional groups on its edges and substrate plane. Although the electronic properties of graphene oxide are not as good as those of graphene, its electrical conductivity can be improved by reducing the number of functional groups.

[0054] Carbon fiber refers to high-strength, high-modulus fibers with a carbon content of over 90%. It is primarily made from raw materials such as polyacrylonitrile, pitch, viscose, lignin, phenolic resin, and other organic fibers, through high-temperature oxidation and carbonization. Carbon fiber possesses excellent electrical conductivity and electromagnetic shielding properties.

[0055] Carbon nanotubes, graphene, graphene oxide, and carbon fibers all have good electrical conductivity, low density, and light weight, which can increase the effective current-carrying area of ​​composite wires while reducing their weight.

[0056] According to some embodiments of the present invention, the material of the metal hollow tube includes at least one selected from gold and its alloys, silver and its alloys, copper and its alloys, iron and its alloys, and aluminum and its alloys.

[0057] The aforementioned conductive metals, while meeting conductivity requirements, also possess a certain strength, which can satisfy strength requirements under complex working conditions.

[0058] According to some embodiments of the present invention, the area ratio of the sheath 11 in the cross-section of the sheath-core composite conductor is greater than the area ratio of the core layer 12 in the cross-section of the sheath-core composite conductor; and / or, the mass ratio of the sheath 11 in the sheath-core composite conductor is greater than the mass ratio of the core layer 12 in the sheath-core composite conductor.

[0059] The area ratio of the sheath 11 in the cross-section of the sheath-core composite conductor refers to the cross-sectional area of ​​the tube wall of the metal hollow tube, and the area ratio of the core layer 12 in the cross-section of the sheath-core composite conductor refers to the cross-sectional area of ​​the hollow cavity of the metal hollow tube.

[0060] According to some embodiments of the present invention, the area ratio of the sheath 11 and the core 12 in the cross section of the sheath-core composite conductor is (65-85):(15-45); and / or, the mass ratio of the sheath 11 and the core 12 in the sheath-core composite conductor is (72-84):(18-26).

[0061] According to some embodiments of the present invention, reference Figure 1 As shown, at the cross-section of the core-sheath composite conductor, the core layer 12 is symmetrically distributed along the centerline of the core-sheath composite conductor.

[0062] The core layer 12 is symmetrically distributed along the center line of the core-skin composite conductor, meaning that the core layer 12 is located in the middle region of the skin layer 11. This can increase the current load in the middle region, thereby improving the uniformity of charge distribution at high frequencies.

[0063] According to some embodiments of the present invention, reference Figure 2 As shown, the carbon material of the core layer 12 is selected from one of the following: concentric stranded structure, concentric composite stranded structure, transposed composite stranded structure, parallel forming structure, single-winding forming structure, and braided forming structure.

[0064] by Figure 2 (a) For example, a concentric twisted structure is formed by spirally twisting multiple carbon material wires together around the same central axis according to certain rules. The wires in each layer are tightly arranged around the central axis, which increases the overall flexibility, strength, and conductivity. Figure 2 (b) For example, a concentric composite twisted structure refers to a structure formed by spirally twisting together multiple strands of carbon material in a concentric twisting manner according to certain rules. Figure 2 (c) For example, the transposition composite stranding structure refers to a structure obtained by periodically repositioning different strands during the stranding process. This method can make the stranding structure more uniform and avoid performance degradation due to stress concentration in a certain direction. Figure 2 (d) For example, the parallel forming structure arranges multiple carbon materials in parallel and fixes them through a specific process. This method can maintain the independence of each carbon material while providing high strength and performance in a specific direction. Figure 2 (e) For example, a single-winding structure refers to a structure formed by winding a single carbon material according to certain rules. Figure 2 (f) For example, the braided structure refers to the structure formed by using a weaving method similar to textiles. The braided carbon material has high strength and flexibility, and its performance is relatively uniform in all directions.

[0065] According to some embodiments of the present invention, the outer circumferential shape of the metal hollow tube is selected from one of a rectangle, a circle, an ellipse, and a trapezoid; and / or, the inner circumferential shape of the metal hollow tube is selected from one of a rectangle, a circle, an ellipse, and a trapezoid.

[0066] by Figure 1 For example, the outer circumference of the corrugated metal hollow tube 11 is rectangular, and the inner circumference is also rectangular. Figure 3 For example, the outer periphery of the metal hollow tube in the skin layer 11 is rectangular, and the inner periphery is circular. In other embodiments, the outer periphery of the metal hollow tube may also be circular and the inner periphery rectangular, or the outer periphery may be elliptical and the inner periphery rectangular. That is, the present invention does not impose specific limitations on the shape of the metal hollow tube.

[0067] According to some embodiments of the present invention, the present invention provides a method for preparing a core-shell composite conductor for motors, comprising: bundling carbon material wires into a hollow metal tube to form a core-shell composite conductor for motors; or, pre-positioning carbon material wires on a metal strip and producing a core-shell composite conductor for motors using a cladding welding process; or, pre-positioning carbon material wires in a crystallizer and producing a core-shell composite conductor for motors using a continuous casting tube process.

[0068] According to some embodiments of the present invention, "bundling carbon material wires into a metal hollow tube to form a core-shell composite wire for motors" includes: mounting one end of the carbon material wire on a magnetic traction head, and pulling the carbon material wire through the metal hollow tube by a traction machine to form a core-shell composite wire for motors.

[0069] The carbon fiber wire ends are secured by a magnetic traction head (magnetic cone) on the traction machine, and the carbon fiber wires are bundled into a hollow metal tube using a magnetic field. The traction machine can quickly bundle the carbon fiber wires into the hollow metal tube at a relatively stable speed and with a large traction force, enabling continuous operation. In addition, the uniform traction force of the traction machine ensures that the carbon fiber wires are arranged neatly and tightly in the hollow metal tube, avoiding looseness and disorder, and guaranteeing the quality of the bundling.

[0070] According to some embodiments of the present invention, "pre-place carbon material wire on a metal strip and produce a core-coated composite wire for motors using a cladding welding process" includes: gradually processing the metal strip into a tubular shape and cladding it around the outer periphery of the carbon material wire, welding the longitudinal seam of the tubular wire to form a wire blank, and then obtaining the core-coated composite wire for motors by drawing and heat treatment.

[0071] Clad welding allows for a tight bond between a hollow metal tube and a carbon material wire, forming a robust seal. Furthermore, cladding welding can produce composite wires of various shapes and sizes to meet the requirements of different applications.

[0072] According to some embodiments of the present invention, "pre-placing carbon material wire in a crystallizer and producing a core-coated composite wire for motors using a continuous casting tubing process" includes: pre-placing carbon material wire in a crystallization mold of a crystallizer, then pouring molten metal, and after the molten metal solidifies, continuously pulling it out from the other end of the crystallizer to obtain a core-coated composite wire for motors.

[0073] The core-shell composite conductor for motors formed using a continuous casting tubing process has a relatively smooth and flat surface, reducing surface defects and improving the appearance quality and corrosion resistance of the composite conductor. Furthermore, the hollow metal tube formed in this method has a more uniform and dense microstructure, which helps to improve the mechanical and electrical properties of the composite conductor.

[0074] In some embodiments, the hollow metal tube can be manufactured by one of the following processes: continuous casting tube process, drawing tube process, and cladding welding process.

[0075] Continuous casting pipe process package refers to continuously pouring molten metal into a crystallizer, and continuously pulling the solidified (shelled) casting out from the other end of the crystallizer to obtain hollow metal pipes of any length or a specific length.

[0076] The drawing tube manufacturing process refers to a method of processing hollow metal tubes by first pre-fabricating a hollow metal tube-shaped metal billet, and then applying external force to the front end of the metal billet to pull the metal billet out from a die hole smaller than the cross-section of the billet, so as to obtain a plastic hollow tube product with the corresponding shape and size.

[0077] The cladding welding process refers to the method of using a cladding welding device to gradually process a cleaned metal strip into a round tube shape, and then using argon arc welding to weld the longitudinal seam of the metal tube to form a wire blank. Finally, the desired hollow tube is obtained through drawing and heat treatment.

[0078] In some embodiments, the monofilaments of the carbon material wire can be processed by one of the following methods: wet spinning, dry spinning, dry-jet wet spinning, floating catalytic spinning, thin film winding, confined hydrothermal assembly, and array spinning. The resulting monofilaments have a tensile strength ≥1.0 GPa and an electrical conductivity ≥2.9 × 10⁻⁶. 4 S / cm; then two or more monofilaments are combined and twisted to form multiple bundled yarns or strands.

[0079] Thirdly, the present invention provides the application of the above-mentioned core-sheath composite wire for motors or the core-sheath composite wire for motors prepared by the above-mentioned preparation method in motors.

[0080] According to some embodiments of the present invention, the motor windings are made of sheath-core composite wires to reduce the skin effect of the motor windings in high-frequency environments.

[0081] The following description is based on specific embodiments.

[0082] Example 1

[0083] A composite wire for motors with a sheath and core, wherein the sheath is a copper alloy hollow tube with a rectangular outer circumference, the core is a single-walled carbon nanotube, the mass ratio of the sheath to the core is 95:5, and the cross-sectional area ratio of the sheath to the core is 80:20.

[0084] The preparation method of the core-sheathed composite conductor for motors includes the following steps:

[0085] (1) Single-walled carbon nanotubes are processed by wet spinning and then twisted to form two single-walled carbon nanotube wires. Multiple single-walled carbon nanotube wires are twisted into a core layer.

[0086] (2) A copper alloy hollow tube is processed by continuous casting tube process. Its external shape is a rectangle with a size of 3.2mm×2.0mm. The size and shape of the cavity are consistent with the size and shape of the sum of the outer diameters of the multi-strand twisted single-wall carbon nanotube fibers.

[0087] (3) Install one end of the single-walled carbon nanotube wire on the magnetic cone head, and pull the wire through the copper alloy hollow copper tube by the traction machine to form a copper alloy / carbon nanotube motor flat wire.

[0088] Example 2

[0089] A composite wire for motors with a sheath and core, wherein the sheath is an aluminum alloy hollow tube with a circular outer circumference, and the core is a multi-walled carbon nanotube. The mass ratio of the sheath to the core is 45:55, and the cross-sectional area ratio of the sheath to the core is 37:63.

[0090] The preparation method of the core-sheathed composite conductor for motors includes the following steps:

[0091] (1) Multi-walled carbon nanotubes are processed by carbon nanotube array spinning method, and then a twisting machine is used to prepare multiple multi-walled carbon nanotube filaments into a single multi-walled carbon nanowire.

[0092] (2) Aluminum alloy hollow tubes are processed by drawing tube making process. The outer shape is circular with a diameter of 3mm. The size and shape of the cavity are consistent with the outer size and shape of eight multi-walled carbon nanotubes.

[0093] (3) Install one end of the multi-walled carbon nanotube wire on the magnetic cone head, and pull the wire through the copper alloy hollow copper tube by the traction machine to form an aluminum alloy / carbon nanotube motor wire.

[0094] Example 3

[0095] A composite wire for motors with a sheath and core, wherein the sheath is a copper-silver alloy hollow tube with a circular outer circumference and a diameter of 3 mm, the core is graphene, the mass ratio of the sheath to the core is 87:13, and the cross-sectional area ratio of the sheath to the core is 59:41.

[0096] The preparation method of the core-sheathed composite conductor for motors includes the following steps:

[0097] (1) Graphene filaments are processed by thin film winding method, and then four graphene filaments are made into a single graphene wire by twisting machine.

[0098] (2) The cleaned copper-silver alloy strip is gradually formed into a round tube and wrapped around the outer periphery of multiple graphene wires. Then, the longitudinal seam of the copper-silver alloy tube is welded together by argon arc welding to form a wire blank. Finally, the copper-silver alloy / graphene motor round wire is obtained by drawing and heat treatment.

[0099] Example 4

[0100] A composite wire for motors with a sheath and core, wherein the sheath is a gold alloy hollow tube with a rectangular outer shape and dimensions of 3.2 mm × 2.0 mm, and the core is graphene and multi-walled carbon nanotubes. The mass ratio of the sheath to the core is 93:7, and the cross-sectional area ratio of the sheath to the core is 59:41.

[0101] The preparation method of the core-sheathed composite conductor for motors includes the following steps:

[0102] (1) Graphene filaments were processed by dry-jet wet spinning, multi-walled carbon nanotube filaments were processed by floating catalytic spinning, and then a twisting machine was used to twist four graphene filaments and one multi-walled carbon nanotube filament to prepare a graphene-multi-walled carbon nanotube hybrid wire.

[0103] (2) The prepared graphene-multi-walled carbon nanotube hybrid wire is pre-placed in the crystallization mold of the crystallizer, and then the gold alloy is cast. After the gold alloy solidifies, it is continuously pulled out from the other end of the crystallizer to obtain the gold alloy / graphene-carbon nanotube motor flat wire.

[0104] Comparative Example 1

[0105] The comparative example uses pure copper flat motor wire, measuring 3.2mm × 2.0mm.

[0106] Comparative Example 2

[0107] The copper alloy / carbon nanotube composite wire is formed by depositing a 5μm thick layer of copper alloy onto the surface of carbon nanotube wires. The preparation of the carbon nanotube wires involves wet spinning single-walled carbon nanotubes, followed by twisting to form two single-walled carbon nanotube wires as a single strand. The dimensions of the copper alloy / carbon nanotube composite wire are manufactured according to the design requirements of the motor product.

[0108] Comparative Example 3

[0109] Copper alloy / carbon nanotube composite wires are formed by physically entangled copper alloy wires and carbon nanotube wires together through twisting. The preparation of the carbon nanotube wires involves: wet spinning single-walled carbon nanotubes, followed by twisting to form two single-walled carbon nanotube wires as a single strand. The dimensions of the copper alloy / carbon nanotube composite wires are manufactured according to the design requirements of the motor product.

[0110] Performance testing

[0111] Density: Tested in accordance with national standard GB / T1423.

[0112] Tensile strength: Tested in accordance with industry standard SJ / T1123-2000.

[0113] Elongation: Tested in accordance with industry standard SJ / T1123-2000.

[0114] Minimum room temperature breakdown voltage: Tested in accordance with national standard GB / T4074.

[0115] AC resistance at different frequencies: Tested in accordance with industry standard SJ / T1123-2000.

[0116] Test Results

[0117] Table 1 Performance test results of the conductors in Examples 1-4 and Comparative Examples 1-3

[0118]

[0119]

[0120] As shown in Table 1, the AC resistance of the pure copper wire in Comparative Example 1 reached 51.8 Ω at 50 kHz and even 87.3 Ω at 100 kHz. This indicates that the equivalent resistance of the pure copper wire increases significantly at high frequencies, thereby reducing the effective current-carrying area of ​​the wire and affecting motor performance. In contrast, the composite wires prepared in Examples 1-4 of this invention maintain an AC resistance of less than 9 Ω at current frequencies above 50 kHz, demonstrating that this invention can significantly improve the problem of reduced effective current-carrying area of ​​existing metal wires at high frequencies.

[0121] Comparative Examples 1, 2, and 3 show that although depositing copper alloy on the surface of carbon nanotubes and twisting carbon nanotubes with copper alloy wires to form composite wires can reduce the AC resistance of the wires under high-frequency current, the effect is lower than that of the core-sheath composite wire for motors in this application.

[0122] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A composite conductor with sheathed core for motors, characterized in that, The motor includes a stator core with stator slots evenly distributed circumferentially. The core-skin composite conductor is arranged in the stator slots, wherein the core-skin composite conductor includes a sheath and a core, the sheath being a hollow metal tube and the core being a carbon material.

2. The composite wire for motors as described in claim 1, characterized in that, The carbon material includes at least one of carbon nanotubes, graphene, graphene oxide, and carbon fiber.

3. The composite wire for motors as described in claim 1, characterized in that, The material of the hollow metal tube includes at least one of gold and its alloys, silver and its alloys, copper and its alloys, iron and its alloys, and aluminum and its alloys.

4. The composite conductor for motors with sheathed core as described in any one of claims 1 to 3, characterized in that, The area ratio of the sheath layer in the cross-section of the core-sheath composite conductor is greater than the area ratio of the core layer in the cross-section of the core-sheath composite conductor; and / or, The sheath accounts for a larger percentage of the mass of the core in the sheath-core composite conductor than the core itself.

5. The composite wire for motors as described in claim 4, characterized in that, The area ratio of the sheath and core layers in the cross-section of the sheath-core composite conductor is (65-85):(15-45); and / or, The mass ratio of the sheath to the core in the sheath-core composite conductor is (72-84):(18-26).

6. The composite conductor for motors with sheathed cores as described in any one of claims 1 to 3, characterized in that, At the cross-section of the core-sheath composite conductor, the core layer is symmetrically distributed along the centerline of the core-sheath composite conductor.

7. The composite conductor for motors with sheathed core as described in any one of claims 1 to 3, characterized in that, The carbon material of the core layer is selected from one of the following: concentric stranded structure, concentric composite stranded structure, transposed composite stranded structure, parallel forming structure, single-winding forming structure, and braided forming structure.

8. The composite conductor for motors with sheathed core as described in any one of claims 1 to 3, characterized in that, The outer circumferential shape of the hollow metal tube is selected from one of the following: rectangular, circular, elliptical, and trapezoidal; and / or, The inner circumferential shape of the hollow metal tube is selected from one of the following: rectangular, circular, elliptical, and trapezoidal.

9. A method for preparing a core-sheathed composite conductor for motors, characterized in that, include: Carbon material wires are bundled into a hollow metal tube to form a core-sheath composite conductor for motors; or, Carbon material wire is pre-placed on a metal strip, and a sheathed core composite wire for motors is produced using a coating welding process; or... Carbon material wires are pre-placed in a crystallizer, and a continuous casting tubing process is used to produce composite wires for motors with sheath cores.

10. The method for preparing a core-sheathed composite conductor for motors as described in claim 9, characterized in that, The phrase "bundling carbon material wires into a hollow metal tube to form a core-sheathed composite conductor for motors" includes: One end of the carbon material wire is mounted on a magnetic traction head, and the carbon material wire is pulled through a metal hollow tube by a traction machine to form a core-shell composite wire for motors.

11. The method for preparing a core-sheathed composite conductor for motors as described in claim 9, characterized in that, The phrase "pre-positioning carbon material wires onto a metal strip and producing composite wires for motors using a coating welding process" includes: The metal strip is gradually processed into a tube and wrapped around the outer periphery of the carbon material wire. The longitudinal seam of the tube is welded to form a wire blank. Then, the core-sheath composite wire for motors can be obtained by drawing and heat treatment.

12. The method for preparing a core-sheathed composite conductor for motors as described in claim 9, characterized in that, The phrase "pre-positioning carbon material wires in a crystallizer and producing core-coated composite wires for motors using a continuous casting tubing process" includes: Carbon material wire is pre-placed in the crystallization mold of the crystallizer, and then molten metal is poured in. After the molten metal solidifies, it is continuously pulled out from the other end of the crystallizer to obtain the core-shell composite wire for motors.

13. The application of the core-sheathed composite wire for motors as described in any one of claims 1 to 8, or the core-sheathed composite wire for motors prepared by the preparation method described in any one of claims 9 to 12, in a motor.

14. The application as described in claim 13, characterized in that, The motor windings are made of sheath-core composite wire to reduce the skin effect of the motor windings in high-frequency environments.

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