Embedded Permanent Magnet Rotor Slits for Eddy Current Control
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Solution Overview
Problem
Conventional permanent magnet embedded electric motors experience increased loss and decreased efficiency due to eddy currents and demagnetization caused by magnetic flux variations and heat generation, as well as reduced demagnetization resistance due to slit design allowing diamagnetic fields to interlink with permanent magnets.
Innovation Solution
The motor design includes a rotor iron core with specific slit configurations and iron core portions that isolate magnetic fluxes from permanent magnets, reducing eddy current loss and enhancing demagnetization resistance by dispersing magnetic fluxes and allowing diamagnetic fields to pass through outer iron core portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If slits extend from the magnet insertion hole edge to near the rotor outer circumferential portion, then vibration and noise are suppressed, but demagnetization resistance deteriorates due to easy interlinking of diamagnetic fields with permanent magnets
Solution Approach 1:
The rotor iron core is segmented into multiple regions: magnet insertion holes for permanent magnets, first slits on the outer side of magnet insertion holes, second slits at positions opposed to and spaced apart from the first slits, inter-slit iron core portions between the first and second slits, outer side iron core portions between the second slits and the outer circumferential surface, and thin iron core portions extending in the rotating direction. This segmentation isolates magnetic fluxes from permanent magnets while maintaining vibration and noise suppression.
Solution Approach 2:
The inter-slit iron core portions and outer side iron core portions act as intermediary structures between the slits and the permanent magnets. These intermediary iron core portions guide and disperse magnetic fluxes, preventing direct interlinking between diamagnetic fields and permanent magnets, thereby improving demagnetization resistance while maintaining the benefits of slit design.
2Power
If magnetic fluxes pass through the iron core portion between magnet insertion holes and slits and interlink with permanent magnet surfaces, then motor operation is enabled, but eddy currents increase causing loss and heat generation that reduce efficiency and output
Solution Approach 1:
The rotor iron core is divided into multiple segmented regions including magnet insertion holes, first slits, second slits, inter-slit iron core portions, outer side iron core portions, and thin iron core portions. This segmentation interrupts continuous magnetic flux paths that would otherwise pass directly over permanent magnet surfaces, thereby reducing eddy current loops and associated energy losses while maintaining necessary magnetic coupling for motor operation.
Solution Approach 2:
The inter-slit iron core portions and outer side iron core portions serve as intermediary magnetic paths that redirect magnetic fluxes away from direct contact with permanent magnet surfaces. These intermediary structures provide alternative flux paths through the iron core, reducing eddy current induction in the permanent magnets while maintaining the magnetic coupling necessary for motor operation.
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 improves demagnetization resistance while maintaining efficiency and output, suppressing temperature rises and eddy current losses, and allows for the use of rare-earth magnets with lower coercive force to reduce costs.
Implementation Method 1
Magnetic fluxes flowing from the stator side to the rotor pass through an iron core portion between the magnet insertion holes and the slits, and interlink with an surface of the permanent magnets, wherein the magnetic fluxes vary with time to thereby cause an eddy current to flow in the permanent magnet, and increase the loss.
Implementation Method 2
The slits extend from an edge of the magnet insertion hole to near the rotor outer circumferential portion, whereby a diamagnetic field formed by the stator can easily interlink with the permanent magnets, and demagnetization resistance is deteriorated accordingly.
Data Source
AI summary
In a permanent magnet embedded electric motor, a rotor iron core of a rotor disposed on an inner diameter side of a stator includes: a plurality of first slits that are formed on a radial direction outer side of a magnet insertion hole, and communicate with the magnet insertion hole; a plurality of second slits formed at positions opposed to and spaced apart from the first slits; inter-slit iron core portions formed between the first slits and the second slits; outer side iron core portions formed between the second slits and an outer circumferential surface of the rotor iron core; space portions communicating with rotating direction end portions of the magnet insertion hole; and thin iron core portions that are formed between the space portions and the outer circumferential surface of the rotor iron core, and extend in a rotating direction.