Permanent Magnet Rotor Core Geometry for Lower Cogging Torque
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Solution Overview
Problem
Radial flux electric machines with permanent magnet rotors experience undesirable noise due to pole-to-pole dissymmetry and cogging torque harmonics, leading to vibrations and structural resonance, which affect the performance and noise levels of electric motors.
Innovation Solution
The design incorporates a permanent magnet rotor core with circumferentially-spaced rotor poles, radial apertures for magnet placement, and protrusions or bridges to secure magnets and maintain symmetry, along with dummy slots and strategically positioned openings to minimize cogging torque and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If magnets are inserted into larger magnet slots to allow insertion, then ease of manufacture is improved, but magnet movement during operation occurs causing noise and performance degradation
Solution Approach 1:
A magnet retention component is introduced as an intermediary element between the magnet and the slot. This retention component fills the gap between the magnet and slot walls, preventing magnet movement while allowing easy magnet insertion during manufacturing. The retention component acts as a mediator that simultaneously satisfies both the ease of manufacture and reliability requirements.
2Object-affected harmful factors
If rotor poles are formed with precise symmetry to prevent noise, then noise reduction is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The magnet retention component introduces a controlled asymmetric element into the otherwise symmetric rotor pole structure. By strategically placing the retention component in specific locations, the design compensates for potential asymmetries in pole formation, thereby reducing noise while relaxing the stringent manufacturing precision requirements for perfect pole symmetry.
3Ease of manufacture
If radial apertures are made larger to facilitate magnet insertion, then ease of manufacture is improved, but cogging torque harmonics increase causing vibrations and noise
Solution Approach 1:
The magnet retention component is designed with varying local properties - it provides a larger overall aperture for easy magnet insertion, while incorporating localized retention features (such as protrusions or interference fit regions) that minimize the effective gap between magnet and slot. This local quality variation allows large apertures for manufacturing ease while maintaining small effective gaps to reduce cogging torque harmonics.
Data Source
AI summary
A permanent magnet rotor core includes a plurality of rotor poles circumferentially-spaced about a central axis and including a first rotor pole and an adjacent second rotor pole that each include an outer wall, and wherein the rotor core includes a rotor diameter. The rotor core also includes a plurality of radial apertures alternately-spaced with the plurality of rotor poles. The rotor core also includes a first protrusion extending from the first rotor pole into a first radial aperture of the plurality of radial apertures positioned between the first rotor pole and the second rotor pole. The rotor core further includes a second protrusion extending from the second rotor pole into the first radial aperture such that a circumferential opening is defined between the first protrusion and the second protrusion. The opening extends a first length of between approximately 0.052% and approximately 0.058% of the rotor diameter.