E-Bike One-Way Clutch Spigot Joint for Stable Pawl Engagement

Solution Overview

Problem

Existing drive units for electrically assisted bicycles face challenges in maintaining stable rotation of the one-way clutch due to potential center misalignment between the inner and outer members, which can lead to decreased accuracy of engagement between clutch pawls and teeth.

Innovation Solution

The implementation of a 'boss/recess' spigot joint structure between the inner and outer members of the one-way clutch ensures center alignment, allowing stable rotation even when the clutch pawls and teeth configuration may experience center misalignment. This structure enables relative rotation between the members while maintaining alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the number of clutch pawls is decreased to reduce weight and production cost, then manufacturing cost and weight are reduced, but center misalignment occurs between the inner member and the outer member, decreasing engagement accuracy

Engineering Contradiction:

Improveproduction costVSAvoidengagement accuracy

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The boss protruding from the inner member acts as an intermediary alignment element that fits into the recess of the outer member. This mediator ensures precise center alignment between the inner and outer members, preventing misalignment issues that would otherwise occur with fewer clutch pawls.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the structural parameters by adding the boss-recess alignment feature, which modifies the geometric relationship between inner and outer members. This parameter change enables accurate engagement even when the number of clutch pawls is reduced.

Inventive Principle:

Principle #35Parameter changes

2Weight of moving object

If the number of clutch pawls is decreased to reduce weight, then weight is reduced, but center misalignment occurs between the inner member and the outer member, decreasing engagement accuracy

Engineering Contradiction:

ImproveweightVSAvoidengagement accuracy

Core Design Contradiction:

Weight of moving objectVSManufacturing precision

Solution Approach 1:

The boss protruding from the inner member acts as an intermediary alignment element that fits into the recess of the outer member. This mediator ensures precise center alignment between the inner and outer members, preventing misalignment issues that would otherwise occur with fewer clutch pawls.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the structural parameters by adding the boss-recess alignment feature, which modifies the geometric relationship between inner and outer members. This parameter change enables accurate engagement even when the number of clutch pawls is reduced.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If a ratchet mechanism with multiple clutch pawls is used to prevent center misalignment, then engagement accuracy is maintained, but the one-way clutch weight and complexity increase

Engineering Contradiction:

Improveengagement accuracyVSAvoidclutch structure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The boss protruding from the inner member acts as an intermediary alignment element that fits into the recess of the outer member. This mediator ensures precise center alignment between the inner and outer members, preventing misalignment issues that would otherwise occur with fewer clutch pawls.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the structural parameters by adding the boss-recess alignment feature, which modifies the geometric relationship between inner and outer members. This parameter change enables accurate engagement even when the number of clutch pawls is reduced.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12202571B2Drive unit and electrically assisted bicycle

Publication Date: 2025.01.21 YAMAHA MOTOR CO LTD

AI summary

A drive unit for an electrically assisted bicycle includes a one-way clutch including an inner member linked to an end of a connecting shaft and an outer member linked to a drive sprocket wheel. The inner member includes clutch pawls and a boss. The outer member includes clutch teeth that are able to engage with the clutch pawls and an extension to be coupled to the drive sprocket wheel. The extension includes a recess to accept the boss at an inner member side thereof. The recess has an inner peripheral surface that is able to slide against an outer peripheral surface of the boss.