IPM Rotor Magnet Assembly via Grain Boundary Diffusion

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Solution Overview

Problem

The assembly of rotor magnet segments in interior permanent magnet (IPM) rotary machines is inefficient due to material loss and increased machining costs, particularly when grain boundary diffusion treatments enhance coercive force and heat resistance, which are then abraded during finish grinding.

Innovation Solution

A method where magnet pieces are inserted loosely into the rotor yoke bores, stacked axially, and then securely bound, eliminating the need for finish grinding and preserving the subsurface region with enhanced coercive force and heat resistance, using a coercive force profile created by diffusing Dy or Tb from the surface toward the interior via grain boundaries.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If magnet pieces undergo grain boundary diffusion treatment to enhance coercive force and heat resistance, then the magnetic performance is improved, but the enhanced subsurface region is abraded away during finish grinding

Engineering Contradiction:

Improvecoercive force and heat resistanceVSAvoidmagnet material loss

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The grain boundary diffusion treatment is performed in advance on magnet pieces before assembly, creating an enhanced subsurface region. The invention then eliminates the finish grinding step that would remove this enhanced layer, preserving the beneficial properties while still achieving proper fit and finish through alternative means.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention extracts or removes the harmful finish grinding step from the manufacturing process. By eliminating this step, the enhanced subsurface region created by diffusion treatment is preserved, avoiding material loss while maintaining the improved magnetic performance.

Inventive Principle:

Principle #2Taking out (Extraction)

2Manufacturing precision

If magnet pieces are assembled by traditional methods requiring finish grinding, then precise dimensional fit is achieved, but manufacturing cost and material loss increase

Engineering Contradiction:

Improvedimensional fitVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The invention removes the finish grinding operation from the manufacturing process. By eliminating this costly and material-intensive step, manufacturing cost is reduced while the necessary dimensional fit is achieved through alternative assembly methods that do not require removal of the diffusion-treated surface.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If Dy or Tb is substituted for Nd to increase coercive force, then demagnetization resistance is improved, but remanence decreases

Engineering Contradiction:

Improvecoercive forceVSAvoidremanence

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

Instead of uniformly substituting Dy or Tb throughout the magnet, the invention uses grain boundary diffusion to concentrate these elements specifically at the grain boundaries and subsurface regions. This localized approach increases coercive force where it is most needed (at grain boundaries and surfaces) while minimizing the overall amount of Dy/Tb used, thereby preserving remanence.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the distribution parameter of Dy/Tb elements from uniform substitution to localized diffusion concentration. By controlling the spatial distribution of these elements through diffusion processes, the magnetic properties are optimized with higher coercive force at critical regions while maintaining overall remanence.

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 method reduces material loss and machining costs while maintaining high coercive force and heat resistance, resulting in a rotor with improved heat resistance and output efficiency for IPM rotary machines.

Implementation Method 1

a coercive force profile from the surface toward the interior, which is created by letting Dy or Tb diffuse from the surface toward the interior of the magnet piece

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentEP2306623B1Manufacturing method of an electric machine rotor comprising embedded permanent magnets

Publication Date: 2019.10.30 SHIN ETSU CHEMICAL CO LTD

Figure 1
Figure 2A~3B
Figure 4A~4B

AI summary

An interior permanent magnet (IPM) rotary machine comprises a rotor comprising a rotor yoke (11) having bores (11a) and a plurality of permanent magnet segments (12) disposed in the bores (11a) of the rotor yoke (11), each permanent magnet segment (12) consisting of a plurality of magnet pieces (12a). The rotor is assembled by inserting the plurality of unbound magnet pieces (12a) in each bore for stacking the magnet pieces, and fixedly securing the stacked magnet pieces (12a) in the bore (11).