Permanent Magnet Embedded Motor Rotor Design to Reduce Demagnetization
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Solution Overview
Problem
Permanent magnets in motors used in refrigeration and air conditioning compressors tend to demagnetize due to high temperatures and reverse magnetic fields, leading to reduced efficiency and reliability, especially when using rare-earth magnets with low coercive force, which is exacerbated by the scarcity and cost of heavy rare-earth elements.
Innovation Solution
The design incorporates a rotor core with a combination of first and second electromagnetic steel plates, where the second plates have projections at the circumferential ends of magnet insertion holes to regulate magnet position and reduce magnetic flux leakage, and are positioned to overhang the stator core, thereby increasing demagnetization resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare-earth elements (Dy, Tb) are added to rare-earth magnets to improve coercive force and prevent demagnetization in high temperature atmosphere, then the motor resistance to demagnetization is improved, but the manufacturing cost increases due to scarcity and price hikes of heavy rare-earth elements
Solution Approach 1:
The rotor core is segmented into multiple electromagnetic steel plates stacked in the axial direction. Some plates have projections while others have recesses, creating a distributed structure that reduces magnetic flux leakage paths without requiring heavy rare-earth elements throughout the entire magnet assembly
Solution Approach 2:
Projections are provided only at specific locations (circumferential ends of magnet insertion holes in selected electromagnetic steel plates) rather than uniformly across all plates. This localized approach addresses magnetic flux leakage at critical points while minimizing the overall impact on magnet performance and cost
2Productivity
If projections are provided at circumferential ends of magnet insertion holes to position permanent magnets and reduce magnetic flux leakage, then magnetic flux leakage is reduced and motor efficiency is improved, but the distance between magnet surfaces becomes shorter causing increased magnetic flux short-circuiting in the magnet itself
Solution Approach 1:
The rotor core structure uses asymmetric stacking where electromagnetic steel plates alternate between having projections and having recesses. This asymmetric configuration creates an imbalance in magnetic path lengths that prevents symmetric flux leakage patterns, thereby reducing overall magnetic flux short-circuiting while maintaining magnet positioning
Solution Approach 2:
The alternating projection-recess structure acts as an intermediary mechanism between the magnets and the stator core. The recesses in one plate compensate for the projections in adjacent plates, creating a balanced magnetic circuit that reduces both leakage and short-circuiting effects
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 configuration significantly reduces demagnetization of permanent magnets, enhancing motor reliability and allowing the use of rare-earth magnets with lower coercive force, thereby reducing the need for expensive heavy rare-earth elements and improving efficiency and cost-effectiveness.
Implementation Method 1
a rotor core (34) including a plurality of electromagnetic steel plates (34a, 34b) that are stacked in an axial direction
Implementation Method 2
magnet insertion holes (36) that are made therein for inserting magnets (40) constituting magnetic poles of the rotor core (34)
Data Source
AI summary
A rotor core includes a plurality of first electromagnetic steel plates that are stacked in an axial direction and a plurality of second electromagnetic steel plates that are stacked in an axial direction at both ends of the electromagnetic steel plate group thereof. The first electromagnetic steel plates are provided therein with magnet insertion holes and first flux barriers. The second electromagnetic steel plates are provided therein with the magnet insertion holes, second flux barriers, and projections that regulate the positions of the magnets. The second electromagnetic steel plates are stacked at at least one of the axial direction ends of the electromagnetic steel plate group including the plurality of first electromagnetic steel plates and are provided at a position overhanging the axial direction end of a stator core.