A low-cogging axial flux motor rotor
By designing arc-shaped grooves and staggered through-grooves on the rotor disk of the axial flux motor, combined with magnets and reinforcing rings, the problem of high eddy current loss is solved, achieving efficient heat dissipation and low-cost motor design, which is suitable for high-performance axial flux motors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HANGZHOU ZONHOW ELECTRIC TECH CO LTD
- Filing Date
- 2026-04-02
- Publication Date
- 2026-06-09
AI Technical Summary
In high-performance axial flux motors, the fractional slot concentrated winding design suffers from high eddy current losses, leading to overheating of the permanent magnet and rotor temperature rise, which affects motor performance and lifespan. Existing solutions, such as low-loss materials and lamination processes, suffer from high costs and poor manufacturability.
The rotor disk features an arc-shaped groove design with multiple through slots arranged radially in a staggered pattern. Combined with the magnets and reinforcing rings of the fan-ring structure, a closed and insulated air duct is formed, which efficiently blocks the eddy current path through precision machining technology.
It significantly reduces eddy current losses, improves motor efficiency and reliability, enhances heat dissipation, reduces material costs, and is suitable for mass production.
Smart Images
Figure CN122178603A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of motor technology, and in particular to a rotor for an axial flux motor with low eddy current loss. Background Technology
[0002] Axial flux permanent magnet (AFPM) motors have their main magnetic flux direction parallel to the motor shaft. Their core feature is the axially stacked, disc-shaped stator and rotor. Furthermore, the flat structure of AFPM motors allows for dual-air-gap, dual-stator, or dual-rotor configurations, resulting in a large effective heat dissipation area and enabling extremely high power and torque output within a compact space.
[0003] Specifically designed for the mainstream high-performance topology of Double Stator Single Rotor (DSSR). In this structure, a rotor disk with permanent magnets attached to both sides is sandwiched between two stators, forming two effective working air gaps. This topology maximizes the utilization of permanent magnets, resulting in extremely high magnetic load and electromagnetic torque density, making it an ideal choice for high-end applications such as electric vehicle main drive and aerospace electric propulsion. The motor example described in this invention is further specified as a DSSR-AFPM employing fractional-slot concentrated windings. This design offers significant advantages in increasing slot fill factor, reducing cogging torque, and shortening end winding dimensions.
[0004] However, the DSSR-AFPM with fractional-slot concentrated windings contains numerous spatiotemporal harmonic magnetic field excitation sources. These include abundant low-order spatial harmonics in the magnetomotive force harmonics of the fractional-slot concentrated windings; high-frequency current harmonics caused by switching actions during pulse-width modulation (PWM) motor driving; and tooth harmonics of specific frequencies generated by the modulation of the motor's main magnetic field by stator slotting. When these harmonic-rich, time-varying magnetic fields act on the rotor's conductive components, eddy currents are induced, resulting in Joule heat loss, leading to localized overheating of the permanent magnets (risk of demagnetization) and rotor disk temperature rise, severely threatening motor performance and lifespan.
[0005] To reduce rotor eddy current losses, low-loss soft magnetic composite materials (SMC) or laminated iron cores are typically used instead, which can effectively suppress eddy currents. However, SMC has a low saturation magnetic flux density and insufficient mechanical strength, while the lamination process for axial motor rotor discs is extremely complex, requiring solutions to axial pressing, resistance to centrifugal force, and reliability of interlayer insulation under high voltage and high frequency, resulting in high costs and poor manufacturability.
[0006] Therefore, in the pursuit of high efficiency, high power density, and high reliability in DSSR-AFPM motors, especially for designs using fractional slot concentrated windings, there is an urgent need for a new rotor disk structure that can more thoroughly block the three-dimensional eddy current path while taking into account magnetic circuit performance, mechanical strength, and processing feasibility. Summary of the Invention
[0007] This invention addresses the shortcomings of existing technologies by providing a rotor for an axial flux motor with low eddy current loss.
[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A low eddy current loss axial flux motor rotor includes a rotor disk with multiple through slots. The through slots are arc-shaped wire slots and are distributed circumferentially along multiple coils coaxial with the rotor disk. The through slots on adjacent coils are staggered in the radial direction of the rotor disk.
[0009] Preferably, magnets are installed on both the front and rear sides of the rotor disk. The magnets are all of fan-ring structure, and the magnets on the same side are circumferentially distributed on the rotor disk.
[0010] Preferably, the arc length of the through slot on different coils is L. m The calculation formula is as follows: Where m is the sequence number of the coils distributed radially from the inside to the outside along the rotor disk, p is the number of magnet pole pairs, and R i R is the inner diameter of the magnet. o Let N be the outer diameter of the magnet, k be a constant, and N be the total number of turns of the coil.
[0011] Preferably, the value of k is between 0.7 and 0.9.
[0012] Preferably, the radius of the slot array on the same coil is R. m The calculation formula is as follows: Where m is the sequence number of the coils distributed radially from the inside to the outside along the rotor disk, and R i R is the inner diameter of the magnet. o Where is the outer diameter of the magnet, and N is the total number of turns of the coil.
[0013] Preferably, the magnets are insulated neodymium iron boron magnets; the magnets located on the front and rear sides of the rotor disk are symmetrically arranged about the rotor disk; the arc length of the magnets is greater than or equal to the arc length of the through slots, the magnets cover the outside of the through slots, and the magnets completely cover the through slots on the odd-numbered coils (i.e., the first turn, the third turn, and so on).
[0014] Preferably, the width of the through groove is 0.5-1.5mm.
[0015] Preferably, it also includes multiple pre-divided insulated permanent magnets; the upper and lower sides of the rotor disk are covered by permanent magnets and form a closed insulated air duct or filling space inside the motor.
[0016] Preferably, the outer ring surface of the rotor disk is provided with reinforcing rings that protrude forward and backward respectively.
[0017] Preferably, the height of the reinforcing ring is no higher than the upper surface of the permanent magnet; the distance between the through slot and the reinforcing ring is D, and its calculation formula is: Where Ri is the inner diameter of the magnet, Ro is the outer diameter of the magnet, and N is the total number of turns of the coil.
[0018] Preferably, the through-slot array is located in the inner disk area surrounded by the reinforcing ring structure, and the outermost ring of the through-slot array maintains a safe distance from the inner wall of the reinforcing ring to ensure the structural integrity and strength of the reinforcing ring.
[0019] This invention, employing the above technical solutions, achieves significant technical effects: Through a quadruple design of "radial multi-turns," "circumferential discreteness," "axial penetration," and "interlaced adjacent turns," it physically severs any large-area continuous loops that eddy currents might form in three spatial dimensions (radial, circumferential, and axial). Eddy currents are confined within tiny, isolated "conductive islands" formed by the slot array, resulting in extremely short flow paths and extremely high resistance, thus achieving a precipitous decrease in eddy current losses. Magnetic circuit influence is minimized: the slots are discretely distributed, and their arc length matches the width of the permanent magnet; the interlaced layout avoids concentrated weakening of specific areas of the magnetic circuit. Magnetic flux can still flow smoothly radially through the "solid ribs" between the slots, with minimal impact on the main air gap magnetic flux density and reluctance torque. Natural heat dissipation and lightweight channels: the axial through-slots form a through-rotor airflow channel, facilitating air convection and enhancing rotor heat dissipation. Simultaneously, material removal achieves rotor lightweighting. High process feasibility: The slot array can be completed with high precision in one go using modern processing technologies such as precision laser cutting, water jet cutting or cluster EDM drilling, making it suitable for mass production. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the structure of the present invention.
[0021] Figure 2 This is an exploded view of the present invention.
[0022] Figure 3 This is a schematic diagram of the rotor disk of the present invention.
[0023] Figure 4 This is a table comparing eddy current losses in rotor disks in finite element simulation.
[0024] Figure 5 This is a schematic diagram of the vortex path of a solid disk in the prior art.
[0025] Figure 6 This is a schematic diagram of the vortex path of the staggered slotted disk of the present invention.
[0026] The parts referred to by the numbers in the attached diagram are as follows: 1—rotor disc, 2—through slot, 3—magnet, 11—reinforcing ring. Detailed Implementation
[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Example 1
[0028] A low eddy current loss axial flux motor rotor, as shown in the figure, includes a rotor disk 1. The rotor disk 1 is provided with multiple through slots 2. The through slots 2 are arc-shaped wire slots. The through slots 2 are distributed circumferentially along multiple coils coaxial with the rotor disk 1. The through slots 2 located on adjacent coils are staggered in the radial direction of the rotor disk 1.
[0029] The array of through slots 2 between adjacent coils has partial overlap or complete offset in radial projection. Its fundamental purpose is to ensure that in any large continuous area of rotor disk 1, there is no conductive path that is not separated by slots and allows eddy currents to flow long distances in the circumferential or radial directions.
[0030] Magnets 3 are installed on both the front and rear sides of the rotor disk 1. The magnets 3 are all fan-ring structures, and the magnets 3 on the same side are circumferentially distributed on the rotor disk 1. Example 2
[0031] Similar to Example 1, except that the arc length of the through slot 2 on the different coils is L. m The calculation formula is as follows: Where m is the coil number distributed radially from the inside to the outside along rotor disk 1 (i.e., the coil number from the inside to the outside; for example, the first innermost coil is m=1), p is the number of 3 pole pairs of the magnet, and R i R is the inner diameter of magnet 3. o Let be the outer diameter of magnet 3, k be a constant, and N be the total number of turns of the coil.
[0032] The value of k ranges from 0.8. Example 3
[0033] Similar to Example 1, except that the radius of the array of through slots 1 on the same coil is R. m The calculation formula is as follows: Where m is the sequence number of the coils distributed radially from the inside to the outside along rotor disk 1, and R i R is the inner diameter of magnet 3. o Where is the outer diameter of magnet 3, and N is the total number of turns of the coil.
[0034] Taking a 16-pole, 18-slot dual-stator single-rotor axial motor as an example, the rotor disk 1 is forged from No. 10 steel, and an integrated reinforcing ring 11 is machined on its outer edge. The axial height of the reinforcing ring 11 is not higher than the upper surface of the permanent magnet, and the radial thickness of the reinforcing ring 11 is sufficient to meet the structural strength requirements. N represents the total number of turns of the coil containing the through slot 2. When N is 3, meaning the through slot 2 is arranged sequentially along three coils: the first coil contains 16 arc-shaped through slots 2, with the slot centerline aligned with the magnetic pole centerline of the magnet 3; the second coil contains 16 arc-shaped through slots 2, with the slot centerline offset by 11.25° (half a magnetic pole angle) relative to the slot centerline of the first coil, aligning with the magnetic pole gap; the third coil contains 16 arc-shaped through slots 2, arranged in the same way as the first coil, with the slot centerline aligned with the magnetic pole centerline of the magnet 3.
[0035] Finite element simulation analysis shows that under a load condition of 3800 rpm and 16A, the rotor disk eddy current loss of the above rotor structure is as follows: Figure 4 As shown, the eddy current loss of the solid disk is 5.1W, while the eddy current loss of the staggered slotted disk designed in this application is 3.2W, which reduces the eddy current loss by 37% compared with the solid rotor disk of the same size, and the reduction in loss increases with the increase of the number of slots.
[0036] Its vortex distribution is as follows Figure 5 and Figure 6 As shown, the staggered slot array effectively blocks the eddy current path and suppresses the eddy current loss of the rotor disk. Example 4
[0037] Similar to Example 1, except that the magnet 3 is an insulated neodymium iron boron magnet; the magnets 3 located on the front and rear sides of the rotor disk 1 are symmetrically arranged about the rotor disk 1; the arc length of the magnet 3 is greater than or equal to the arc length of the through slot 2, the magnet 3 covers the outside of the through slot 2, and the magnet 3 completely covers the through slot 2 of the odd number of coils, i.e., the first turn, the third turn, and so on. Example 5
[0038] Similar to Example 1, except that the width of the through groove 2 is 1 mm. Example 6
[0039] Similar to Embodiment 1, but with the difference that it also includes multiple pre-divided insulated permanent magnets; the upper and lower sides of the rotor disk 1 are covered by permanent magnets and form a closed insulated air duct or filling space inside the motor. Example 7
[0040] Similar to Embodiment 6, except that the outer ring surface of the rotor disk 1 is provided with reinforcing rings 11 that protrude forward and backward respectively.
[0041] The height of the reinforcing ring 11 is no higher than the upper surface of the permanent magnet; the distance between the through groove 2 and the reinforcing ring 11 is D, and its calculation formula is: Among them, R i R is the inner diameter of magnet 3. o Where is the outer diameter of magnet 3, and N is the total number of turns of the coil.
[0042] The through-slot 2 array is located in the inner disk area surrounded by the reinforcing ring 11 structure, and the outermost ring of the through-slot 2 array maintains a safe distance from the inner wall of the reinforcing ring to ensure the structural integrity and strength of the reinforcing ring.
[0043] In summary, the above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the present invention.
Claims
1. A rotor for a low-eddy current loss axial flux motor, comprising a rotor disk (1), characterized in that: The rotor disk (1) is provided with multiple through slots (2). The through slots (2) are arc-shaped wire slots. The through slots (2) are distributed circumferentially along multiple coils coaxial with the rotor disk (1). The through slots (2) located on adjacent coils are staggered in the radial direction of the rotor disk (1).
2. The rotor of a low eddy current loss axial flux motor according to claim 1, characterized in that: Magnets (3) are installed on both the front and rear sides of the rotor disk (1). The magnets (3) are all fan ring structures, and the magnets (3) are distributed circumferentially on the rotor disk (1).
3. The rotor of a low eddy current loss axial flux motor according to claim 2, characterized in that: The arc length of the through slot (2) on different coils is L m The calculation formula is as follows: Where m is the sequence number of the coil distributed radially from the inside to the outside along the rotor disk (1), p is the number of pole pairs of the magnet (3), and R i R is the inner diameter of the magnet (3). o is the outer diameter of the magnet (3), k is a constant, and N is the total number of turns of the coil.
4. The rotor of a low eddy current loss axial flux motor according to claim 3, characterized in that: The value of k ranges from 0.7 to 0.
9.
5. A low eddy current loss axial flux motor rotor according to claim 2, characterized in that: The radius of the array of through slots (1) on the same coil is R m The calculation formula is as follows: Where m is the sequence number of the coils distributed radially from the inside to the outside along the rotor disk (1), and R i R is the inner diameter of the magnet (3). o is the outer diameter of the magnet (3), and N is the total number of turns of the coil.
6. A low eddy current loss axial flux motor rotor according to claim 2, characterized in that: The magnet (3) is an insulated neodymium iron boron magnet; the magnets (3) located on the front and rear sides of the rotor disk (1) are symmetrically arranged about the rotor disk (1); the arc length of the magnet (3) is greater than or equal to the arc length of the through slot (2), and the magnet (3) covers the outside of the through slot (2).
7. A low eddy current loss axial flux motor rotor according to claim 1, characterized in that: The width of the through groove (2) is 0.5-1.5mm.
8. A low eddy current loss axial flux motor rotor according to claim 1, characterized in that: It also includes multiple insulated permanent magnets; the upper and lower sides of the rotor disk (1) are covered by permanent magnets and form a closed insulated air duct or filling space inside the motor.
9. A low eddy current loss axial flux motor rotor according to claim 8, characterized in that: The outer ring surface of the rotor disk (1) is provided with a raised reinforcing ring (11).
10. A low eddy current loss axial flux motor rotor according to claim 9, characterized in that: The height of the reinforcing ring (11) is not higher than the upper surface of the permanent magnet; the distance between the through groove (2) and the reinforcing ring (11) is D, and its calculation formula is: Among them, R i R is the inner diameter of the magnet (3). o is the outer diameter of the magnet (3), and N is the total number of turns of the coil.