Torque-Limiting Fastener Clutch for High Removal Torque

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Solution Overview

Problem

Existing torque-limiting fasteners, such as those used in plumbing and electrical applications, suffer from limited coupling removal torque and rapid degradation of torque-carrying capacity, leading to difficulties in decoupling and increased risk of overtightening due to deformation of drive lugs after a few install and removal cycles.

Innovation Solution

A torque-limiting fastener design featuring a drive shell, driven fastener, and clutch with specific surface configurations and geometries, including drive-off and drive-on surfaces, driven-on and driven-off surfaces, and radially extending components, which allows for a rotational delay between the drive shell and driven nut to prevent overtightening and facilitate higher torque removal by deflection and audible/tactile feedback.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If drive lugs are designed to engage with driven lugs for torque transmission, then torque carrying capacity is improved, but the lugs deform and fail after a few install and removal cycles

Engineering Contradiction:

Improvetorque carrying capacityVSAvoiddurability across cycles

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The drive mechanism is segmented into separate components: a drive shell with drive lugs, a clutch assembly with driven lugs, and a driven fastener. This segmentation allows the drive lugs to be replaced or reset after each use, preventing cumulative deformation while maintaining torque transmission capability throughout multiple cycles.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The drive lugs on the drive shell are designed as consumable elements that can be easily replaced or reset. After a limited number of cycles, the drive lugs may deform, but the overall system remains reliable because the drive shell can be reset or the lugs replaced, rather than requiring replacement of the entire fastener assembly.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If torque is limited during installation to prevent overtightening, then reliability is improved, but coupling removal torque becomes too limited for practical removal

Engineering Contradiction:

Improveprevention of overtighteningVSAvoidremoval torque

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The clutch assembly incorporates a spring element that provides dynamic torque characteristics. During installation, the spring allows the clutch to slip at a predetermined torque threshold, preventing overtightening. During removal, the spring can be compressed or extended to allow higher torque application, enabling practical removal of the coupling.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The fastener is designed for periodic use cycles (installation and removal). The clutch mechanism is optimized for each phase: during installation, it limits torque to prevent damage; during removal, the mechanism can accommodate higher torque loads, allowing the coupling to be practically removed after use.

Inventive Principle:

Principle #19Periodic action

3Manufacturing precision

If drive lugs are made rigid for precise engagement, then manufacturing precision is improved, but the lugs deform rapidly over just a few cycles

Engineering Contradiction:

Improveengagement precisionVSAvoidservice life

Core Design Contradiction:

Manufacturing precisionVSDuration of action of moving object

Solution Approach 1:

The drive lugs are designed with specific geometric parameters including angled surfaces and controlled dimensions. The engagement surfaces are configured at specific angles to distribute loads optimally during engagement and disengagement, maintaining precision while reducing stress concentrations that would cause deformation over cycles.

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

The design provides a reliable and durable solution with an install torque limit between 1 Nm and 2.5 Nm and a removal torque limit greater than four times the install torque, maintaining performance across multiple cycles without significant degradation, thus overcoming the limitations of existing torque-limiting fasteners.

Implementation Method 1

a foot extending circumferentially and axially inwardly at an oblique angle

Methodology Applied

Scientific EffectMechanical Advantage: Mechanical Advantage

Implementation Method 2

drive-on surfaces on an interior side of the shell base wall and facing a second circumferential direction and extending substantially obliquely

Methodology Applied

Scientific EffectLever: Lever

Data Source

PatentUS20230015919A1Torque-limiting fastener and coupling

Publication Date: 2023.01.19 BRASSCRAFT MFG CO

AI summary

A torque-limiting fastener and a method of assembling the same includes a drive shell, a driven fastener carried by the drive shell, and a clutch axially between the fastener and the drive shell. The drive shell may have a shell base wall including drive-off surfaces, drive-on surfaces, and a shell skirt extending axially away from the shell base wall. The driven fastener may have a fastener base wall including driven-on surfaces, driven-off surfaces, drive tang pockets between the driven-on and driven-off surfaces, and driven-on beam pockets, and a radially outer wall extending in an axial direction away from the fastener base wall. The clutch may have a plate, a driven beam, and a driven tang, wherein the driven beam and the drive tang are cantilevered with respect to the plate. A drive shell, driven fastener, and clutch are individually disclosed.