Anisotropic Sensor Magnet Improves Motor Position Detection
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Solution Overview
Problem
The accuracy of detecting the position of a field magnet in electric motors is limited due to the use of isotropic sensor magnets, which restricts the precision of magnetic field detection and torque generation.
Innovation Solution
The electric motor employs a rare earth anisotropic sensor magnet magnetized in multiple poles, which improves the detection accuracy of the field magnet position by enhancing the surface magnetic flux density distribution, allowing for more precise control of drive current and torque generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an isotropic sensor magnet is used, then the device complexity is reduced and manufacturing is easier, but the detection accuracy of the field magnet position is limited
Solution Approach 1:
The patent changes the magnetic property parameter of the sensor magnet from isotropic to anisotropic. This parameter change enables the magnet to have different magnetic permeability in different directions, allowing magnetic force lines to be concentrated at the pole surfaces rather than passing through the magnet body, thereby significantly improving the detection accuracy of the field magnet position.
Solution Approach 2:
The patent employs a composite magnetic structure where anisotropic magnet material is used in specific regions (sensor magnet) while maintaining the overall motor structure. This selective use of anisotropic material in the sensor magnet component achieves improved detection accuracy without requiring the entire magnetic system to be complex.
2Manufacturing precision
If an isotropic sensor magnet is used, then the manufacturing cost is lower, but the magnetization accuracy near pole boundaries is difficult to achieve
Solution Approach 1:
By changing the magnetic property parameter from isotropic to anisotropic, the patent fundamentally alters how magnetization behaves near pole boundaries. The anisotropic material's directional magnetic permeability naturally concentrates flux at the poles, making the magnetization process more controllable and accurate near boundaries without requiring complex manufacturing processes.
3Speed
If drive current is changed over based on limited detection accuracy, then the control response is faster, but the torque ripple increases and drive efficiency decreases
Solution Approach 1:
The patent implements a feedback mechanism where the Hall sensor continuously detects the position of the field magnet through the improved anisotropic sensor magnet. This accurate position feedback enables precise control of the drive current switching timing, ensuring that current is changed over at the optimal moment. This resolves the contradiction by maintaining fast response speed while improving drive efficiency and reducing torque ripple through accurate position-based control.
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 solution enhances the detection accuracy of the field magnet position, leading to improved drive efficiency and reduced torque ripple, while also reducing manufacturing costs by using a cheap Hall sensor for position detection.
Implementation Method 1
A sensor such as a Hall sensor for use in the electric motor detects a change in magnetic field
Implementation Method 2
a sensor magnet that is a substantially ring-like rare earth anisotropic magnet and magnetized in multiple poles
Implementation Method 3
lines of magnetic force pass through the inside of the magnet when magnetic force is produced
Data Source
AI summary
In a motor, an sensor magnet is attached to a shaft and three Hall sensors for detecting the position of the sensor magnet are mounted on a circuit board. By using neodymium-iron-boron base rare earth magnet having radial anisotropy as a sensor magnet, the detection accuracy for the position of a field magnet via the sensor magnet by the Hall sensor can be improved.