Embedded Magnet Motor Compression Sections Reduce Flux Leakage

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Solution Overview

Problem

Conventional permanent magnet embedded electric motors suffer from magnetic flux leakage to the frame, leading to increased iron loss and efficiency drops, particularly with high magnetic flux density magnets, due to incomplete contact between the stator core and the frame, and deformation-induced magnetic flux paths through stress-receiving sections.

Innovation Solution

The implementation of a compression section group with strategically placed compression sections between the stator core's outer circumferential section and the frame's inner circumferential section, which undergoes higher compression stress than the back yoke, reducing magnetic permeability and flux leakage by equalizing compression stress and absorbing deformation forces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the outer circumferential section of the back yoke is fixed in contact with the inner circumferential section of the frame, then the stator core is securely positioned, but magnetic flux leaks to the frame causing increased iron loss

Engineering Contradiction:

Improvestator core positioningVSAvoidiron loss

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The outer circumferential section of the back yoke is divided into multiple compression sections (first, second, third compression sections) that can be independently deformed. This segmentation allows localized magnetic permeability reduction at specific flux leakage paths while maintaining overall structural integrity and stator core positioning.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different sections of the back yoke are given different properties: the compression sections are designed to have reduced magnetic permeability through deformation, while other portions maintain normal magnetic properties. This local quality change targets flux leakage reduction at critical areas without affecting overall stator performance.

Inventive Principle:

Principle #3Local quality

2Loss of energy

If stress relaxation slits are formed on the back yoke, then compression stress is reduced improving iron loss characteristics, but the sum of rotating direction widths exceeds frame thickness causing flux leakage through stress-receiving sections

Engineering Contradiction:

Improveiron lossVSAvoidmagnetic flux containment

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The width of compression sections is carefully controlled to be less than the frame thickness, changing the geometric parameter to prevent flux leakage. Additionally, the magnetic permeability of compression sections is reduced through deformation, creating a dual-parameter solution that addresses both iron loss and flux containment.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If high compression stress is applied to the back yoke, then magnetic permeability is reduced decreasing flux leakage, but the core case deforms more easily absorbing the pressing force

Engineering Contradiction:

Improveflux leakage reductionVSAvoidcore case resistance

Core Design Contradiction:

Loss of energyVSStrength

Solution Approach 1:

The frame is designed with local reinforcement at specific positions where compression sections contact the frame. This local quality enhancement allows the frame to withstand high compression forces without excessive deformation, enabling effective flux leakage reduction through compression stress.

Inventive Principle:

Principle #3Local quality

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 magnetic flux leakage and iron loss by 69% and 82% respectively, enhancing the electric motor's efficiency and reducing the risk of performance degradation.

Implementation Method 1

by being deformed by the pressing force generated between the frame and the back yoke, compression stress occurs that is higher than compression stress generated due to the pressing force in the back yoke

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

reducing magnetic permeability and flux leakage by equalizing compression stress and absorbing deformation forces

Methodology Applied

Scientific EffectMagnetic permeability change: Magnetic Field

Data Source

PatentUS10284030B2Permanent magnet embedded electric motor, compressor, and a refrigerating and air conditioning device

Publication Date: 2019.05.07 MITSUBISHI ELECTRIC CORP

AI summary

A permanent magnet embedded electric motor includes a stator core disposed inside the frame and having a back yoke and a plurality of magnetic pole teeth; a rotor disposed on an inner diameter side of the plurality of magnetic pole teeth; and compression sections in which compression stress higher than compression stress occurring in the back yoke due to pressing force generated between the frame and the back yoke occurs. A compression section group having a set of two or more compression sections and of the plurality of compression sections is disposed on an outer circumferential section of the stator core. A sum of the rotating direction widths of the plurality of compression sections constituting the compression section group is smaller than a radial direction thickness of the frame.