Axial Gap Rotor Magnet Segmentation and Surface Coercivity
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Solution Overview
Problem
Axial gap-type permanent magnetic rotating machines face challenges with demagnetization due to high temperatures from eddy currents, which are exacerbated by the difficulty in maintaining high coercive force and remanence in sintered Nd-base magnets, especially at the surface where heat generation is higher, leading to reduced performance and increased manufacturing costs.
Innovation Solution
Dividing sintered Nd-base magnets into pieces with a higher coercive force near the surface than in the interior, achieved by diffusing Dy or Tb from the surface into the magnet pieces via grain boundaries, using methods such as applying Dy or Tb oxide powder and heat treating, to enhance heat resistance and demagnetization resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sintered Nd-base magnets are used in axial gap-type rotating machines, then high remanence and magnetic performance are achieved, but the magnets are prone to demagnetization due to high temperatures from eddy currents and demagnetizing fields
Solution Approach 1:
The patent applies local quality by creating a non-uniform concentration distribution of heavy rare earth elements (Dy or Tb) within the magnet, specifically concentrating them at the grain boundaries and outer peripheral portions where they are most needed for demagnetization resistance, while maintaining higher remanence in the overall magnet structure
Solution Approach 2:
The patent uses composite materials by combining Nd-Fe-B base magnet material with heavy rare earth elements (Dy or Tb) to create a composite magnetic structure that leverages the high remanence of Nd-Fe-B and the high coercive force of heavy rare earth elements to simultaneously achieve both remanence and demagnetization resistance
2Loss of energy
If the magnet body is divided into smaller pieces to reduce eddy currents, then eddy current loss is reduced, but manufacturing cost increases and output decreases due to reduced magnet volume and increased interstices
Solution Approach 1:
The patent applies segmentation by dividing the magnet into multiple magnet pieces arranged in an array, which interrupts eddy current paths and reduces eddy current loss while maintaining sufficient magnetic volume and output through proper arrangement and sizing of the segments
3Reliability
If Dy or Tb is substituted for Nd to increase coercive force, then demagnetization resistance is improved, but remanence decreases due to reduced saturation magnetic polarization
Solution Approach 1:
The patent applies local quality by creating a non-uniform concentration distribution of heavy rare earth elements (Dy or Tb) within the magnet, specifically concentrating them at the grain boundaries and outer peripheral portions where they are most needed for demagnetization resistance, while maintaining higher remanence in the overall magnet structure
Solution Approach 2:
The patent uses parameter changes by controlling the concentration distribution of heavy rare earth elements through specific manufacturing parameters (diffusion time, temperature, surface coating thickness) to achieve the optimal balance between coercive force and remanence
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively minimizes demagnetization and maintains high output and heat resistance in axial gap-type rotating machines, ensuring the magnets' performance is improved without significant loss in remanence, particularly suitable for high-output applications.
Implementation Method 1
each magnet piece has a coercive force or heat resistance at a surface and an interior, and the coercive force or heat resistance near the surface of the magnet piece is higher than the coercive force or heat resistance in the interior of the magnet piece
Implementation Method 2
sintered Nd base magnets are conductors having an electric resistance of 100 to 200 μΩ-cm. As the rotor rotates, the magnet undergoes a variation of magnetic flux density, by which eddy currents flow
Implementation Method 3
Permanent magnets in axial gap-type rotating machines are exposed to high temperature due to the heat generated by windings and cores and have a likelihood of demagnetization by the demagnetizing field from the windings
Data Source
Figure 1A~1C
Figure 2A~3B
Figure 4A~4B
AI summary
An axial gap-type permanent magnetic rotating machine comprises a rotor comprising a rotating shaft having an axis of rotation, a rotor yoke of disc shape radially extending from the shaft, and a plurality of permanent magnet segments circumferentially arranged on a surface of the rotor yoke such that each permanent magnet segment may have a magnetization direction parallel to the axis of rotation, and a stator having a plurality of circumferentially arranged coils and disposed to define an axial gap with the rotor. In the rotor, each permanent magnet segment is an assembly of two or more divided permanent magnet pieces, and the coercive force near the surface of the magnet piece is higher than that in the interior of the magnet piece.