A rotor structure of an outer rotor permanent magnet motor

Abstract

This invention belongs to the field of permanent magnet motor design technology and discloses a rotor structure for an external rotor permanent magnet motor, comprising: a rotor core, circumferentially arranged permanent magnets, a carbon fiber sheath, and end pressure plates. The rotor core includes multiple magnetically conductive steel rotor core units arranged circumferentially along the permanent magnets. Each magnetically conductive steel rotor core unit includes a main body and bosses located at both axial ends of the main body, each boss having a positioning hole. The inner side of the main body of each magnetically conductive steel rotor core unit is attached to the outer surface of the permanent magnets, and the carbon fiber sheath is wound around the outer side of the main body of each magnetically conductive steel rotor core unit. The end pressure plates are assembled at opposite ends of the rotor core, and the positioning holes on the end pressure plates cooperate with the positioning holes on the end bosses of each magnetically conductive steel rotor core unit, and are positioned and fixed by fixing components. This invention can improve the torque density of the motor.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet motor design technology, and more specifically, relates to a rotor structure for an external rotor permanent magnet motor. Background Technology

[0002] Electric vertical takeoff and landing (EVTOL) aircraft, as a practical vehicle for low-altitude economic development, are currently a hot research topic. Unlike traditional helicopters, electric propulsion systems are power-to-size independent, allowing EVTOL aircraft to achieve superior aerodynamic efficiency and flight performance through distributed propulsion architecture and optimized external structure. However, the mission conditions of EVTOL aircraft are extremely complex, with lift requirements during vertical takeoff and landing reaching approximately 20 times that of the cruise phase. This places higher demands on the peak torque density of direct-drive electric propulsion systems, rendering some design methods and experiences from high-power-density electric propulsion motors in traditional electric vehicles inapplicable.

[0003] Compared to the focus on power density and cost in traditional electric vehicle propulsion motors, electric vertical takeoff and landing (EVTOL) aircraft propulsion motors prioritize torque density and overload capacity at low speeds. Permanent magnet synchronous motors (PMSMs), with their high power density and efficiency, are the preferred type of motor for such aerospace electric drive systems. Meanwhile, external rotor PMSMs, due to their larger air gap radius and the ability to further integrate within the stator, offer superior torque output capabilities, making them an excellent topology choice for direct-drive electric propulsion motors. In the traditional external rotor PMSM rotor structure, from the inside out, the components are permanent magnets, rotor core, and housing. In this topology, the mechanical structural strength of the rotor is a critical consideration. On one hand, excessively light rotor housing weight can severely reduce the rotor's structural reliability, even causing significant deformation during the heat-fitting process in assembly, compromising motor safety. On the other hand, excessively heavy rotor housing weight can significantly reduce the volume of the motor's effective components, impairing its torque output capability. While using a Halbach permanent magnet array can significantly reduce reliance on the rotor core, a small amount of rotor core is still needed as the rotor yoke to improve torque density and permanent magnet utilization. However, this introduces a new problem: the rotor core yoke is typically very thin, drastically increasing the difficulty of assembling the lightweight housing with the rotor core yoke. This is because the rotor core and housing are usually fixed using a heat-shrink method during assembly, but since both are thin-walled components, either part is highly susceptible to irreversible deformation after fixing. Therefore, in traditional external rotor Halbach permanent magnet motor designs, to meet the mechanical strength and structural reliability requirements of the assembly process, the rotor yoke core is usually designed to be thicker, resulting in low saturation in this area. From a torque output performance perspective, this is a "waste" of materials and weight, limiting further improvements in motor torque density. Therefore, how to continue to increase the rotor radius and improve torque output capability while ensuring the safety and reliability of the external rotor permanent magnet motor is one of the key aspects of this type of electric propulsion motor design.

[0004] Existing technology also discloses an outer rotor with a polygonal dovetail-shaped spliced ​​magnet structure. This structure involves splicing multiple permanent magnets with isosceles triangular or quadrilateral cross-sections together to form a closed-loop rotor magnet. Using a Helbeck magnetization method, the electromagnetic force on the stator coil within each stator slot forms a closed loop tangentially along the circumference, thus providing a stable torque to the outer rotor and achieving stable rotation. However, this rotor structure is overly complex, potentially leading to insufficient mechanical strength. Furthermore, this design only uses "reinforcing ribs" on the motor housing for fixation, while the axial segmentation of the magnets severely compromises installation stability. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides an external rotor permanent magnet motor rotor structure. The purpose is to provide an external rotor permanent magnet motor rotor structure with a simple structure, which can improve the torque density of the motor and solve the problem that deformation will damage the reliability of the motor structure during the assembly of the two "thin-walled parts" of the housing and rotor core in the external rotor permanent magnet motor.

[0006] To achieve the above objectives, the present invention provides an external rotor permanent magnet motor rotor structure, comprising: a rotor core, circumferentially arranged permanent magnets, a carbon fiber sheath, and an end pressure plate;

[0007] The rotor core comprises multiple magnetically conductive steel rotor core units arranged circumferentially along the permanent magnet. Each magnetically conductive steel rotor core unit includes a main body and bosses located at both axial ends of the main body, with positioning holes on each boss. The inner side of the main body of each magnetically conductive steel rotor core unit is attached to the outer surface of the permanent magnet, and the carbon fiber sheath is wound around the outer side of the main body of each magnetically conductive steel rotor core unit. The end pressure plates are assembled at opposite ends of the rotor core, and the positioning holes on the end pressure plates cooperate with the positioning holes on the end bosses of each magnetically conductive steel rotor core unit, and are positioned and fixed by fixing components.

[0008] Furthermore, the rotor core also includes multiple silicon steel sheet rotor core units; each of the silicon steel sheet rotor core units and the magnetically conductive steel rotor core units are arranged circumferentially along the permanent magnet.

[0009] Furthermore, the magnetically conductive steel rotor core units are arranged symmetrically along the circumference of the permanent magnet.

[0010] Furthermore, the rotor core is disposed on the main magnetic circuit of the rotor.

[0011] Furthermore, the positioning holes on the end pressure plate and the positioning holes on the end bosses of each magnetic steel rotor core unit are bolt holes, and the fixing component is a bolt that mates with the bolt holes.

[0012] Furthermore, the end pressure plate has a circular ring structure, and the positioning hole is provided along the circumference of the circular ring structure.

[0013] Furthermore, an end structure support is provided within the annular structure of at least one of the end pressure plates.

[0014] Furthermore, a high-strength magnetic adhesive is used for fixing between the rotor core and the permanent magnet;

[0015] The permanent magnet is magnetized by parallel magnetization or by Halbach permanent magnet array.

[0016] The present invention also provides an external rotor radial flux permanent magnet motor, including the external rotor permanent magnet motor rotor structure as described in any of the above claims.

[0017] The present invention also provides an aviation electric propulsion motor system, including an external rotor radial flux permanent magnet motor as described above.

[0018] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0019] (1) This invention provides a simple external rotor permanent magnet motor rotor structure. By using a carbon fiber sheath and a segmented rotor core structure, the dependence on the motor rotor housing is completely eliminated, the rotor mass is reduced, and the utilization rate and torque density of the motor rotor are improved. Specifically, a segmented magnetic steel rotor core is adopted. The magnetic steel has certain magnetic permeability while having good mechanical strength and stress resistance. Therefore, the magnetic steel is used as a functional reuse component, serving as both the magnetic rotor core structure in the electromagnetic field and the strength support component in the mechanical structure. Meanwhile, utilizing the advantages of carbon fiber materials such as high strength and low coefficient of thermal expansion, and because the carbon fiber sheath experiences outward force under centrifugal force during rotor rotation, it can provide good protection and fixation when wound around the outside of the rotor core. Furthermore, the protrusions and end plates at the ends of the magnetic rotor core units cleverly provide outward support during fixing and positioning, facilitating the fixing of each magnetic rotor core unit body and the permanent magnet through the winding of the carbon fiber sheath. This completely eliminates the traditional rotor housing, reducing the motor rotor mass and significantly improving the motor rotor utilization rate and torque density. It also avoids the problem of deformation damaging the motor structure during the assembly of the two "thin-walled parts," the housing and the rotor core, in external rotor permanent magnet motors, and offers good stability. The main components of the designed external rotor permanent magnet motor rotor structure include only permanent magnets, segmented rotor cores, carbon fiber sheaths, and end pressure plates. The rotor structure is simple, and the segmented magnetic steel rotor core structure does not involve roundness issues during installation, which can reduce the difficulty of rotor processing and assembly without compromising the reliability of the motor.

[0020] (2) Preferably, the segmented rotor core also includes multiple high-performance silicon steel sheet rotor core units. The two types of rotor core materials work together to allow the motor to utilize both the high magnetic permeability of the high-saturation magnetic density silicon steel sheets and the high mechanical strength of the magnetic steel. Specifically, the magnetic steel is a multifunctional component, serving both as the magnetic rotor core structure in the electromagnetic field and as a strength support component in the mechanical structure, thereby improving mechanical strength; the silicon steel sheet rotor core units only serve as rotor cores for enhanced electromagnetic performance, achieving high saturation magnetic density and further improving output torque density.

[0021] (3) As a preferred option, the magnetic steel rotor core units are arranged symmetrically along the circumference of the permanent magnet, which can further improve the mechanical strength of the rotor.

[0022] (4) Preferably, the rotor core is placed on the main magnetic circuit of the rotor to obtain the maximum output torque.

[0023] (5) Preferably, an end structure support is provided in the annular structure of at least one end pressure plate, which can further improve the mechanical strength of the rotor.

[0024] In summary, the external rotor permanent magnet motor rotor structure proposed in this invention features a circumferentially segmented rotor core design. Carbon fiber sheaths are used to fix the rotor core and permanent magnets, ensuring mechanical strength and reliability. The rotor core is only located within the main magnetic circuit of the rotor, improving its utilization rate. The segmented magnetic steel rotor core structure eliminates roundness issues during installation, reducing the difficulty of rotor machining and assembly without compromising motor reliability. Furthermore, it significantly liberates the design freedom of the rotor yoke core, effectively avoiding the deformation problems that occur during the assembly of traditional rotor core yokes and housings ("thin-walled parts against thin-walled parts"). The magnetically conductive steel rotor core serves a multifunctional purpose, acting as both an electromagnetic component to guide the main magnetic circuit of the rotor and a structural component to ensure the structural strength of the motor rotor. The bosses on the magnetically conductive steel rotor core, in conjunction with the end pressure plates, provide positioning and fixation while also offering internal support for the winding of the carbon fiber sheath. The combination of the magnetically conductive steel rotor core, end pressure plates, and carbon fiber sheath eliminates the need for a traditional rotor housing, reducing the motor rotor mass and significantly improving rotor utilization and torque density. This invention can be applied to low-speed, high-torque external rotor radial flux permanent magnet motor topologies, enabling the motor to achieve even higher torque density. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of an external rotor permanent magnet motor rotor in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the segmented magnetic steel rotor core unit structure in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the carbon fiber sheath structure in an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the assembly of the end structure support and the rotor structure in an embodiment of the present invention;

[0029] Figure 5 This is a schematic diagram of the segmented high-saturation magnetic flux density rotor core silicon steel sheet structure in an embodiment of the present invention;

[0030] Figure 6This is a schematic diagram of another structure of the external rotor permanent magnet motor rotor in an embodiment of the present invention;

[0031] Figure 7 for Figure 6 The end face front view of the rotor structure of the external rotor permanent magnet motor shown;

[0032] Figure 8 This is another end face front view of the rotor structure of an external rotor permanent magnet motor;

[0033] Figure 9 This is a cross-sectional view of the rotor structure of an external rotor permanent magnet motor according to an embodiment of the present invention;

[0034] Figure 10 This is a schematic diagram of the structure of a rotor core and a permanent magnet in an embodiment of the present invention;

[0035] Figure 11 This is a schematic diagram of the magnetic field lines of the main magnetic circuit of the external rotor permanent magnet motor in an embodiment of the present invention;

[0036] Figure 12 This is a schematic diagram of the Halbach permanent magnet array structure in an embodiment of the present invention;

[0037] Figure 13 This is an exploded view of the assembled rotor structure in an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Example 1

[0040] This invention focuses on achieving the ultimate low-speed, ultra-high torque density capability of external rotor permanent magnet motors, and proposes a rotor structure for such motors. Figure 1 and Figure 2As shown, the rotor structure of the external rotor permanent magnet motor in this embodiment of the invention includes a rotor core, circumferentially arranged permanent magnets, a carbon fiber sheath, and end pressure plates. The rotor core is a segmented structure, comprising multiple magnetically conductive steel rotor core units arranged circumferentially along the permanent magnets. Each magnetically conductive steel rotor core unit includes a main body and bosses located at both axial ends of the main body, each boss having a positioning hole. The inner side of the main body of each magnetically conductive steel rotor core unit is attached to the outer surface of the permanent magnet, and the carbon fiber sheath is wound around the outer side of the main body of each magnetically conductive steel rotor core unit. The end pressure plates are mounted on both sides of the opposite ends of the rotor core, and the end pressure plates have positioning holes that mate with the positioning holes on the end bosses of each magnetically conductive steel rotor core unit. The positioning holes on the end pressure plates and the corresponding positioning holes on the end bosses of the magnetically conductive steel rotor core units are positioned and fixed by fixing components. The number of magnetically conductive steel rotor core units is determined according to the required mechanical strength and electromagnetic performance of the rotor.

[0041] like Figure 3 As shown, due to the low density, low coefficient of thermal expansion and high stress of carbon fiber, and because the carbon fiber sheath is subjected to outward force due to centrifugal force when the rotor rotates, it can play a better role in protection and fixation.

[0042] Specifically, the end pressure plate has a circular ring structure with positioning holes along its outer circumferential direction. Preferably, the positioning holes on the end pressure plate and the positioning holes on the end bosses of each magnetic steel rotor core unit are bolt holes, and the fixing components are bolts that mate with the bolt holes.

[0043] like Figure 4 As shown, preferably, an end structure support is provided within the annular structure of at least one end pressure plate to further enhance the mechanical strength of the rotor. The end structure support is preferably a reinforcing rib, and the shape of the reinforcing rib is not fixed; it needs to be further determined based on actual structural strength simulation and weight requirements.

[0044] As a preferred option, the rotor core and the permanent magnet are fixed together using high-strength magnetic adhesive.

[0045] like Figure 5 As shown, as a preferred embodiment, the segmented rotor core includes not only multiple magnetic steel rotor core units, but also multiple high-performance silicon steel sheet rotor core units. The multiple magnetic steel rotor core units and the multiple high-performance silicon steel sheet rotor core units are arranged circumferentially along the permanent magnet.

[0046] Generally, silicon steel sheets with high saturation magnetic flux density have superior magnetic permeability compared to magnetically conductive steel, thus theoretically enabling greater torque output. However, silicon steel sheets are manufactured by laminating multiple sheets, and their mechanical strength and fatigue resistance cannot meet the strength requirements for high torque output. This is one of the reasons why traditional external rotor permanent magnet motors require a rigid housing. Magnetically conductive steel, on the other hand, possesses both good magnetic permeability and excellent mechanical strength and stress resistance, thus serving as a structural support to ensure the mechanical reliability of the motor rotor. Based on this idea, such as... Figure 6 As shown, in the segmented rotor core structure proposed in this embodiment of the invention, high-performance silicon steel sheet rotor core units and magnetically conductive steel rotor core units are arranged sequentially along the circumference. Furthermore, the silicon steel sheets are not limited to silicon steel magnetic materials and can be replaced with any high-performance soft magnetic core material manufactured using a lamination method, such as iron-cobalt alloy 1J22. In addition, the number of each material along the circumference is not fixed, but depends on the actual mechanical strength and electromagnetic performance requirements. Figure 7 The quantities shown are in the format "magnetic steel - silicon steel sheet - magnetic steel - silicon steel sheet..." where the number of magnetic steel cores is equal to the number of silicon steel cores and they are arranged symmetrically; alternatively, they can be as follows: Figure 8 The image shows "Magnetic steel - silicon steel sheet - silicon steel sheet - silicon steel sheet - magnetic steel - silicon steel sheet - silicon steel sheet - silicon steel sheet...".

[0047] In this embodiment of the invention, the magnetic steel is a multifunctional component, serving both as the magnetic rotor core structure in the electromagnetic field and as a strength support component in the mechanical structure. Therefore, the number of magnetic steel rotor core units needs to correspond to the mechanical structure simulation. Preferably, the magnetic steel rotor core units are arranged symmetrically along the circumference to further enhance mechanical strength. The number of silicon steel sheet rotor core units is not fixed; they only need to be arranged circumferentially with the magnetic steel rotor core units. They serve only as rotor cores for enhanced electromagnetic performance, achieving high saturation magnetic flux density and further improving output torque density. (See figure) Figure 9 The figure shows a cross-sectional view of the rotor structure of the external rotor permanent magnet motor proposed in an embodiment of the present invention. Figure 10 This is a schematic diagram of the rotor core and permanent magnet.

[0048] Because the rotor core has a segmented structure, only the individual segmented rotor core units (magnetic steel rotor core units, or magnetic steel rotor core units and silicon steel sheet rotor core units) need to be placed in the main magnetic circuit of the rotor, while permanent magnets are placed in other positions on the rotor, to obtain maximum torque output. Figure 11As shown, this completely eliminates the design limitations of the rotor yoke size. Therefore, the rotor yoke thickness can be zero or any size, meaning there's no need to consider the yoke thickness limitation; the design should simply follow the principles of motor size constraints and maximizing torque output performance. Correspondingly, the shape of the permanent magnet is adjusted to match the shape of the rotor core attached to its surface. The magnetization direction of the permanent magnet can use either traditional parallel magnetization or a Halbach permanent magnet array with higher torque performance, such as... Figure 12 As shown.

[0049] In this embodiment of the invention, to achieve maximum torque output, the number of silicon steel sheet rotor core units and magnetic steel rotor core units is not related to the number of permanent magnets. The circumferential angle occupied by each silicon steel sheet rotor core unit and the circumferential angle occupied by each magnetic steel rotor core unit have considerable design freedom; through optimization, the required mechanical strength and output torque density can be achieved. Figure 13 An exploded view of the rotor structure in this embodiment of the invention after assembly is given.

[0050] This invention proposes a segmented modular rotor core structure with a carbon fiber sheath. When different rotor core units are made of different materials, the motor simultaneously utilizes the high magnetic permeability of high-saturation magnetic density silicon steel sheets and the high mechanical strength of magnetically conductive steel. Furthermore, the segmented core design significantly liberates the design freedom of the rotor yoke core. Combined with the carbon fiber sheath and end pressure plates, it effectively avoids the deformation problems that occur during the assembly of traditional rotor core yokes and housings, which are typically "thin-walled parts." The proposed magnetically conductive steel rotor core unit structure with axial bosses allows different rotor core units and permanent magnets to be fixed together by winding with carbon fiber sheaths, completely eliminating the need for a traditional rotor housing. This reduces the rotor mass and significantly improves rotor utilization and torque density. The boss design of the magnetically conductive steel rotor core unit, combined with the end pressure plates, enables the magnetically conductive steel rotor core unit to achieve functional reuse: it acts as both an electromagnetic component to guide the main magnetic circuit of the rotor and a structural component to ensure the structural strength of the motor rotor. The end pressure plate, structural support components, and magnetic steel rotor core unit are positioned and fixed with bolts, reducing the difficulty of rotor processing and assembly without compromising motor reliability. This invention aims to achieve the ultimate low-speed, ultra-high torque density output capability of permanent magnet synchronous motors. The external rotor permanent magnet motor designed based on this low-speed, high-torque capability external rotor structure can be applied to aerospace direct-drive electric propulsion systems.

[0051] Example 2

[0052] This invention provides an external rotor radial flux permanent magnet motor, including the external rotor permanent magnet motor rotor structure in Embodiment 1 above.

[0053] The relevant technical solutions are the same as above, and will not be repeated here.

[0054] Example 3

[0055] This invention provides an aviation electric propulsion motor system, including the external rotor radial flux permanent magnet motor of embodiment 2.

[0056] The relevant technical solutions are the same as above, and will not be repeated here.

[0057] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rotor structure for an external rotor permanent magnet motor, characterized in that, include: Rotor core, circumferentially arranged permanent magnets, carbon fiber sheath and end pressure plate; The rotor core comprises multiple magnetically conductive steel rotor core units arranged circumferentially along the permanent magnet. Each magnetically conductive steel rotor core unit includes a main body and bosses located at both axial ends of the main body, with positioning holes on each boss. The inner side of the main body of each magnetically conductive steel rotor core unit is attached to the outer surface of the permanent magnet, and the carbon fiber sheath is wound around the outer side of the main body of each magnetically conductive steel rotor core unit. The end pressure plates are assembled at opposite ends of the rotor core, and the positioning holes on the end pressure plates cooperate with the positioning holes on the end bosses of each magnetically conductive steel rotor core unit, and are positioned and fixed by fixing components. The rotor core also includes multiple silicon steel sheet rotor core units; each of the silicon steel sheet rotor core units and the magnetically conductive steel rotor core units are arranged circumferentially along the permanent magnet; the rotor core is set on the main magnetic path of the rotor.

2. The rotor structure of the external rotor permanent magnet motor according to claim 1, characterized in that, The magnetically conductive steel rotor core units are arranged symmetrically along the circumference of the permanent magnet.

3. The rotor structure of the external rotor permanent magnet motor according to claim 1, characterized in that, The positioning holes on the end pressure plate and the positioning holes on the end bosses of each magnetic steel rotor core unit are bolt holes, and the fixing component is a bolt that mates with the bolt holes.

4. The rotor structure of the external rotor permanent magnet motor according to claim 3, characterized in that, The end plate is a ring-shaped structure, and the positioning hole is provided along the circumference of the ring-shaped structure.

5. The rotor structure of the external rotor permanent magnet motor according to claim 4, characterized in that, An end structure support is provided within the annular structure of at least one of the end pressure plates.

6. The rotor structure of the external rotor permanent magnet motor according to claim 1, characterized in that, The rotor core and the permanent magnet are secured with high-strength magnetic adhesive. The permanent magnet is magnetized by parallel magnetization or by Halbach permanent magnet array.

7. A permanent magnet motor with an external rotor radial flux, characterized in that, Including the external rotor permanent magnet motor rotor structure as described in any one of claims 1-6.

8. An aircraft electric propulsion motor system, characterized in that, Including the external rotor radial flux permanent magnet motor as described in claim 7.

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