Roller Selectable Clutch for Smooth Lock-Free Switching

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Solution Overview

Problem

Existing selectable clutches face challenges in switching from lock mode to free mode due to residual torque load, leading to potential damage and friction loss, and are often large and prone to chipping, with accessibility issues and high surface pressure on torque-receiving surfaces.

Innovation Solution

A selectable clutch design featuring a cylindrical inner and outer race with rollers biased by a resilient member, inclined roller-holding surfaces, and a selector for easy mode switching, reducing friction and noise while allowing high-torque transmission in a compact size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If pawls are biased by springs in the locking direction, then the clutch can maintain lock mode reliably, but switching from lock mode to free mode becomes difficult due to residual torque load

Engineering Contradiction:

Improvelock mode stabilityVSAvoidmode switching difficulty

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The selector is designed to preliminarily separate from the rollers before complete mode switching occurs. This preliminary action reduces the torque load on the rollers during transition, making it easier to switch from lock mode to free mode while maintaining reliable locking when engaged

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The clutch transitions from a static spring-biased pawl system to a dynamic roller system where the selector can move between engaged and separated states. This dynamic configuration allows the rollers to be pushed into pocket parts for locking while enabling easy release by separating the selector

Inventive Principle:

Principle #15Dynamics

2Volume of moving object

If the selector is disposed on the inner race side, then the clutch structure is compact, but the selector becomes less accessible from drive sources such as actuators

Engineering Contradiction:

Improveclutch compactnessVSAvoidselector accessibility

Core Design Contradiction:

Volume of moving objectVSEase of operation

Solution Approach 1:

The selector is positioned in the axial direction adjacent to the inner race rather than radially inside it. This dimensional repositioning maintains the compact radial profile while improving axial accessibility to the selector for actuator engagement

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Device complexity

If pawls are provided on the inner race side, then the clutch structure is simplified, but the pawls are subjected to centrifugal force during rotation

Engineering Contradiction:

Improveclutch structure simplicityVSAvoidpawl durability under centrifugal force

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

Instead of placing torque transmission members on the inner race side as in conventional designs, the rollers are placed on the outer race side in pocket parts. This inversion allows the inner race to rotate without subjecting the torque transmission members to excessive centrifugal force while maintaining structural simplicity

Inventive Principle:

Principle #13The other way round (Inversion)

4Volume of moving object

If small surface area torque transmission members are used, then the clutch size is reduced, but chipping and wear occur due to high surface pressure

Engineering Contradiction:

Improveclutch sizeVSAvoidresistance to chipping and wear

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The torque transmission members are changed from angular pawls with small contact surfaces to cylindrical rollers with larger curved contact surfaces. This spherical/curved geometry increases the contact area between rollers and pocket parts, reducing surface pressure and resistance to chipping and wear while maintaining compact clutch dimensions

Inventive Principle:

Principle #14Spheroidality (Curvature)

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

The design enables smooth switching between lock and free modes with reduced friction and noise, extends service life, and allows for high-torque transmission in a compact size, with improved durability and accessibility.

Implementation Method 1

a resilient member radially biasing the rollers

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

The roller-holding surface of each pocket part and the roller-holding surface of each support groove are formed with an inclination angle such that, when a roller is held therebetween, a force acts on the roller in a direction to move the roller toward a corresponding pocket part

Methodology Applied

Scientific EffectMechanical Force: Mechanical Force

Data Source

PatentUS12196276B2Selectable clutch

Publication Date: 2025.01.14 TSUBAKIMOTO CHAIN CO

AI summary

A selectable clutch with a selector is provided, in which support grooves are formed to one of an inner race and an outer race, while pocket parts are formed to the other. A resilient member is provided to bias rollers disposed between the inner race and outer race toward the pocket parts. A roller-holding surface of the support groove and a roller-holding surface of the pocket part are formed with an inclination angle such that, when the rollers are held therebetween, a force acts on the rollers in a direction to move the rollers toward the pocket parts. In the lock mode, the rollers are each held by the support groove, pocket part, and selector.