Permanent Magnet Motor Rotor Slit Design for Vibration Noise
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Solution Overview
Problem
Existing permanent magnet motors experience increased motor vibration noise due to local excessive magnetic flux density in the air gap, which worsens with increased output and reduced size, canceling out the advantages of IPM motors in terms of size reduction and output increase.
Innovation Solution
A permanent magnet motor design featuring a rotor core with slits in the field pole, where the interval between central lines of slits increases towards the outer peripheral side, and the first slit is centrally positioned with second and third slits disposed within 20% of the permanent magnet's circumferential direction width, to manage electromagnetic excitation force and torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the air gap is enlarged or motor current is reduced to decrease electromagnetic excitation force, then motor vibration noise is reduced, but torque density decreases
Solution Approach 1:
The field pole is segmented into multiple regions by forming slits that divide it radially into a first region and a second region. This segmentation allows different electromagnetic excitation force densities to be applied in different regions, reducing peak excitation forces that cause vibration noise while maintaining overall torque output.
Solution Approach 2:
The first region (closer to the air gap) is designed with higher electromagnetic excitation force density, while the second region (farther from the air gap) has lower excitation force density. This local quality differentiation optimizes the distribution of electromagnetic forces to reduce vibration noise without sacrificing torque density.
2Power
If IPM motor design is adopted to increase output and reduce size, then torque density increases, but local excessive magnetic flux density in air gap increases causing worsened vibration noise
Solution Approach 1:
The field pole is divided radially into multiple regions through slits, creating a first region closer to the air gap and a second region farther away. This segmentation enables differentiated electromagnetic excitation force density distribution, reducing peak flux density in the air gap while maintaining overall torque output.
Solution Approach 2:
The electromagnetic excitation force density is designed to be asymmetric across the field pole thickness, with the first region (near air gap) having higher density and the second region (far from air gap) having lower density. This asymmetric distribution optimizes magnetic flux density in the air gap to reduce vibration noise.
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 design effectively reduces motor vibration noise while maintaining reduced size and increased output, achieving a balance between electromagnetic excitation force and torque ripple, thereby improving motor performance.
Implementation Method 1
a face opposing a stator inner diameter forms a rotor core with high magnetic permeability, because of which a magnetic flux that crosses a magnetic pole surface in a circumferential direction increases, and an air gap magnetic flux density is more liable to become locally excessive
Implementation Method 2
a magnetic flux that crosses a magnetic pole surface in a circumferential direction increases
Data Source
AI summary
A permanent magnet motor includes a rotor having a field pole of a rotor core, wherein the field pole has a radius smaller than an arc centered on a shaft of the rotor, a multiple of slits are formed in the field pole, the multiple of slits are disposed so that an interval between a first central line positioned between a multiple of the slits and a second central line positioned between a neighboring multiple of the slits increases as the first central line and the second central line head toward an outer peripheral side of the rotor core, and of the multiple of slits of the field pole, a first slit disposed in a central position of the field pole, and a second slit and a third slit disposed on either side of the first slit, are disposed within 20% of a circumferential direction width of the permanent magnet.