Permanent Magnet Rotor Anisotropy Control for Torque Density
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Solution Overview
Problem
Permanent magnet rotators face challenges in reducing cogging torque while maintaining high torque density, especially with anisotropic magnetic poles of small thickness, which are difficult to segment and manufacture with high precision, leading to increased noise and vibration in motors.
Innovation Solution
A permanent magnet rotator with continuous direction control for anisotropy is achieved by modifying magnetic poles to have a sinusoidal distribution of anisotropy direction with respect to the mechanical angle, using rare-earth magnet particles and a coupling agent to increase energy density and torque density without increasing cogging torque, through precise control of shear stress and magnetizing field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the energy density (BH) max of the magnet is increased to increase torque density, then the torque density increases, but the cogging torque increases causing increased vibration and noise
Solution Approach 1:
The patent applies local quality by varying the thickness of magnetic poles across different locations. The magnetic pole thickness is designed to be maximum at the center and minimum at both ends, creating a thickness deviation pattern. This local variation in thickness allows the airgap magnetic flux density distribution to approach sinusoidal wave shape, thereby reducing cogging torque while maintaining high torque density through the use of high energy density magnet materials.
2Object-generated harmful factors
If the thickness of magnetic poles is reduced to minimize cogging torque, then the cogging torque decreases, but the torque density decreases
Solution Approach 1:
Instead of uniformly reducing magnetic pole thickness, the patent applies local quality by creating a non-uniform thickness distribution. The magnetic poles have maximum thickness at the center and minimum thickness at the ends, which allows the overall torque density to be maintained while the local flux distribution is optimized to reduce cogging torque. This localized thickness variation resolves the contradiction between reducing cogging torque and maintaining torque density.
3Manufacturing precision
If magnetic poles are segmented to control anisotropy direction, then the direction control precision improves, but the manufacturing difficulty increases due to fragile mechanical properties
Solution Approach 1:
The patent applies segmentation by dividing magnetic poles into multiple sections along the circumferential direction. Each segmented magnetic pole can have independently controlled anisotropy direction, allowing precise control of the magnetic flux distribution. This segmentation enables the realization of sinusoidal airgap flux density distribution while maintaining manufacturability through a systematic division of the magnetic pole structure.
Solution Approach 2:
The patent employs composite materials by combining magnetically anisotropic materials with different anisotropy directions in each segmented region. This composite structure allows each segment to contribute differently to the overall magnetic field distribution, achieving precise direction control while the composite nature provides mechanical support to mitigate fragility issues during manufacturing.
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
The solution allows for a significant increase in torque density while reducing cogging torque, enhancing motor performance, power efficiency, and resource utilization in small motors used in home appliances and information devices.
Implementation Method 1
uses a magnet having the ability to attract or repel other magnetic materials and the ability to permanently generate a static magnetic field without using external energy
Implementation Method 2
using rare-earth magnet particles and a coupling agent to increase energy density and torque density
Implementation Method 3
through precise control of shear stress and magnetizing field
Implementation Method 4
effective magnetization M is left even after removal of an external magnetic field
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3B
AI summary
A motor generally has a contradictory relation between decrease of cogging torque and increase of torque density. To overcome this problem, continuous direction control is provided for anisotropy with modification of magnetic poles so that the average absolute value of differences between Mθ and 90×sin[φ{2π/(360/p)}] is set to be 3° or less, where Mθ is a direction of anisotropy with respect to a radial tangent line of a magnetic pole plane, φ is a mechanical angle, and p is the number of pole pairs.