Segmented IPM Rotor Structure for Lower Cogging Torque

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Solution Overview

Problem

Existing permanent magnet brushless direct current (PM BLDC) motors with interior permanent magnet (IPM) rotors face challenges in reducing noise and weight while maintaining efficient magnetic flux, particularly due to high cogging torque and magnet flux leakage.

Innovation Solution

The design incorporates a rotor with a shaft, hub, and rotor core segments alternately arranged with magnets, where the hub and covers are integrally formed using an inserting molding process, featuring tapered ribs, wedge-shaped locking slots, and an uneven air gap between the rotor and stator teeth, reducing magnet flux leakage and cogging torque.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If interior permanent magnet (IPM) rotors are used to maintain efficient magnetic flux, then motor performance is improved, but magnet flux leakage increases causing noise and weight issues

Engineering Contradiction:

Improvemotor performanceVSAvoidmagnet flux leakage

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The rotor core is divided into multiple rotor core segments with magnet insertion spaces between them. This segmentation allows magnets to be embedded in controlled positions, reducing flux leakage while maintaining magnetic efficiency. The segments are arranged alternately with magnets in the circumferential direction, creating a structured magnetic path.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The air gap between rotor core segments is designed to be non-uniform, with different gap widths at different circumferential positions. This local variation in air gap quality optimizes magnetic flux distribution, reducing leakage at critical positions while maintaining overall motor performance.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If conventional rotor structures are used, then manufacturing is simpler, but cogging torque increases causing noise

Engineering Contradiction:

Improve rotor structure simplicityVSAvoidcogging torque

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The rotor core is segmented into multiple sections with magnets inserted between segments. This segmentation creates a more complex structure that reduces cogging torque through optimized magnetic flux paths, while the modular design allows for manageable manufacturing processes including inserting molding for hub and covers.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The rotor core segments have asymmetric designs with tongue structures and non-uniform air gaps. The air gap width varies circumferentially, being smaller at certain positions and larger at others, which asymmetrically distributes magnetic flux to minimize cogging torque while maintaining制造 feasibility.

Inventive Principle:

Principle #4Asymmetry

3Device complexity

If magnets are mounted on the surface of the rotor core, then the structure is simpler, but magnet flux leakage increases

Engineering Contradiction:

Improvemagnet mounting structureVSAvoidmagnet flux leakage

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

Magnets are nested within magnet insertion spaces formed between rotor core segments, rather than being mounted on the outer surface. This nested configuration embeds magnets within the rotor structure, reducing exposed magnetic flux and minimizing leakage while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #7Nested doll (Nesting)

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 noise and weight by minimizing magnet flux leakage and cogging torque, allowing the use of cheaper ferrite magnets while maintaining motor performance, making it suitable for applications like washing machines and clothes drying machines.

Implementation Method 1

The windings generate a magnetic field which coacts with the permanent magnets to drive the rotor to rotate relative to the stator

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The windings generate a magnetic field which coacts with the permanent magnets to drive the rotor to rotate relative to the stator

Methodology Applied

Scientific EffectLorentz force: Lorentz Force

Implementation Method 3

the hub and covers are integrally formed on the rotor core segments by an inserting molding process

Methodology Applied

Scientific EffectInserting molding:

Data Source

PatentUS8987966B2Electric motor

Publication Date: 2015.03.24 JOHNSON ELECTRIC INTERNATIONAL AG

AI summary

An electric motor has a wound stator and a permanent magnet rotor. The rotor includes a shaft, a hub fixed on the shaft, a plurality of rotor core segments and magnets fixed around the hub, and a pair of covers fixed to axial ends of the rotor core segments. The hub and covers are formed on the rotor core segments by inserting molding and one of the covers has openings to allow the magnets to be inserted into spaces formed between adjacent rotor core segments such that the rotor core segments and magnets are alternately arranged in a circumferential direction of the rotor.