Annular Sensor Magnet With Stress Reducing Fixing Portion

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Solution Overview

Problem

Conventional methods for fixing sensor magnets to motor shafts often result in increased component count, assembly errors, and risk of cracking due to direct press-fitting or require additional components like sensor magnet holders.

Innovation Solution

An annular sensor magnet with a fixing portion and stress reducing portion, where the stress reducing portion can be an arc area or arms, is used to directly press-fit onto the motor shaft, reducing stress concentration and allowing for various shapes and configurations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If the sensor magnet is directly press-fit onto the motor shaft, then the assembly process is simplified and component count is reduced, but stress concentration occurs at the contact portion causing cracking

Engineering Contradiction:

Improvenumber of componentsVSAvoidstress resistance

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The sensor magnet is divided into functionally distinct portions: an annular portion providing magnetic poles and a fixing portion with contact portions for shaft engagement. This segmentation allows the contact portions to be specifically designed for stress distribution while maintaining direct fixation to the shaft

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The contact portions of the fixing portion are given special structural characteristics (rounded surfaces, specific geometry) to locally improve stress distribution properties at the critical contact areas with the shaft, while other portions maintain their primary functions

Inventive Principle:

Principle #3Local quality

2Strength

If a sensor magnet holder is used to fix the sensor magnet to the shaft, then stress concentration is reduced and cracking is prevented, but the number of components and assembly steps increases

Engineering Contradiction:

Improvestress resistanceVSAvoidnumber of components

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The fixing portion is integrated directly into the sensor magnet structure, merging the functions of the magnet body and the fixing mechanism into a single component. This eliminates the need for a separate sensor magnet holder while maintaining stress distribution capabilities through the designed contact portions

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The fixing portion serves multiple functions: it provides structural support, distributes stress across multiple contact portions, and enables direct fixation to the shaft. This multi-functionality replaces what would otherwise require separate components

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of operation

If the sensor magnet is directly press-fit onto the shaft, then assembly is simplified, but assembly errors are more likely to occur

Engineering Contradiction:

Improveassembly easeVSAvoidassembly precision

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The fixing portion is designed with asymmetric contact portions that correspond to specific features on the shaft, providing natural alignment and preventing incorrect assembly. The non-circular cross-section or specific contact point arrangement ensures proper orientation

Inventive Principle:

Principle #4Asymmetry

4Adaptability or versatility

If the sensor magnet is made with a bonded magnet structure, then manufacturing flexibility and shape variety are improved, but stress resistance may be reduced

Engineering Contradiction:

Improveshape flexibilityVSAvoidstress resistance

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The sensor magnet uses a bonded magnet structure combining magnetic material particles with a binder material, creating a composite that allows complex shapes while maintaining adequate strength. The contact portions are specifically designed to distribute stresses that would otherwise concentrate in the bonded structure

Inventive Principle:

Principle #40Composite materials

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 allows for direct fixation of the sensor magnet to the motor shaft without additional components, reducing assembly errors and stress concentration, enabling efficient manufacturing and reliable operation.

Implementation Method 1

a stress reducing portion for reducing a stress caused in a contact portion of the fixing portion that contacts the motor shaft when the motor shaft is press-fit onto the fixing portion

Methodology Applied

Scientific EffectStress reduction:

Implementation Method 2

The sensor magnet is magnetized such that its magnetic flux changes in accordance with the rotation of the rotor

Methodology Applied

Scientific EffectMagnetic flux change: Magnetism

Data Source

PatentUS11277057B2Sensor magnet of motor having a fixing portion to press-fit to a shaft without a sensor magnet holder

Publication Date: 2022.03.15 MABUCHI MOTOR CO LTD

AI summary

An annular sensor magnet to be fixed to a motor shaft by a press-fit includes an annular portion having magnetic poles alternately formed in an outer peripheral portion. The annular sensor magnet also includes a fixing portion extending from an inner peripheral portion of the annular portion toward a center to support and fix the motor shaft having been press-fit, and a stress reducing portion for reducing stress caused in a contact portion of the fixing portion that contacts the motor shaft when the motor shaft is press-fit onto the fixing portion. The sensor magnet includes a bonded magnet in which a magnetic material is dispersed in a plastic material.