Permanent Magnet Motor Slits Reduce Demagnetization

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Solution Overview

Problem

Permanent magnet electric motors face irreversible demagnetization due to demagnetizing magnetic fields, especially at the edge portions of permanent magnets, which can lead to reduced torque and efficiency, particularly when the demagnetizing field exceeds the nonlinear range of the B-H curve.

Innovation Solution

The design incorporates a rotor core with magnet insertion openings and projections to position permanent magnets, along with slits positioned radially outward, where the shortest distance between the slits and the magnet insertion opening is greater than the shortest distance between the slits and the rotor core's outer surface, reducing the demagnetizing magnetic field strength and enhancing resistance to demagnetization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If projections are provided at the edge portions of permanent magnet insertion openings for positional determination and fixing, then the permanent magnets are properly positioned and fixed, but the demagnetizing magnetic field is concentrated at the projections, causing irreversible demagnetization at the edge portions of the permanent magnets

Engineering Contradiction:

Improvepositioning precision of permanent magnetsVSAvoidresistance to demagnetization

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The rotor core is segmented by providing slits that divide the rotor core into multiple regions. These slits are positioned to separate the magnetic flux paths, preventing the concentration of demagnetizing magnetic fields at the projections while maintaining the positioning function of the projections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The slits act as intermediary elements that modify the magnetic flux distribution in the rotor core. By introducing these slits, the magnetic flux is redirected through alternative paths, reducing the demagnetizing field concentration at the permanent magnet edge portions while preserving the projections' positioning function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If slits are formed in the projecting portions with large width between slits and outer circumferential surface, then the structure is simplified, but the demagnetizing magnetic field strength at the locations between slits and outer circumferential surface increases, causing irreversible demagnetization

Engineering Contradiction:

Improvestructure complexity of rotor coreVSAvoidresistance to demagnetization

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent optimizes the parameters of the slits, specifically controlling the width and positioning of slits relative to the outer circumferential surface. By setting the width to be within a specific range and positioning the slits at appropriate distances from the outer surface, the magnetic flux distribution is controlled to prevent demagnetization while maintaining structural simplicity.

Inventive Principle:

Principle #35Parameter changes

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 effectively reduces the demagnetizing magnetic fields applied to the permanent magnets, preventing irreversible demagnetization and maintaining high torque and efficiency by increasing the magnetic reluctance of the rotor paths.

Implementation Method 1

increasing the magnetic reluctance of the rotor paths

Methodology Applied

Scientific EffectMagnetic reluctance: Magnetic Reluctance

Implementation Method 2

a plurality of projections are formed at least partially along an axial direction in the magnet insertion openings, the projection positioning both edges of the permanent magnet in the circumferential direction

Methodology Applied

Scientific EffectMechanical positioning: Mechanical Force

Implementation Method 3

a permanent magnet electric motor comprises: a rotor that comprises a rotor core around a circumferential direction of which a plurality of magnet insertion openings are formed, and a plurality of permanent magnets that are inserted in the plurality of magnet insertion openings; and a stator that comprises a stator core around a circumferential direction of which a plurality of slots are formed, and windings that are inserted into the plurality of slots

Methodology Applied

Scientific EffectElectromagnetic interaction: Electromagnetic Induction

Data Source

PatentUS10270303B2Permanent magnet electric motor having slits and projections to minimize irreversible demagnetization

Publication Date: 2019.04.23 HITACHI JOHNSON CONTROLS AIR CONDITIONING INC

AI summary

In a permanent magnet electric motor, a plurality of projections are formed at least partially along an axial direction in the magnet insertion openings, the projection positioning both edges of the permanent magnet in the circumferential direction so that vacant spaces are defined at each sides of the permanent magnet in the circumferential direction; a plurality of slits arranged along the circumferential direction are provided in regions, the region being positioned radially outward from the permanent magnet and being sandwiched at the edges of the permanent magnet in the circumferential direction by the projections; and the shortest distance between the slit and the magnet insertion opening is set to be greater than the shortest distance between the slit and an outer circumferential surface of the rotor core.