Break Away Spline Coupling for Torque Limiting and Misalignment

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Solution Overview

Problem

In small aircraft, mechanical drives lack the fail-safes provided by belt drives, leading to potential damage to engine and accessory components due to excessive torques from catastrophic failures like seized bearings or broken rotor shafts, causing the entire system to seize up.

Innovation Solution

A torque-limiting coupling with a break-away spline mechanism that separates from the coupling in case of excessive torque, preventing damage to engine gearing and other components, and includes misalignment compensation to reduce side load and wear, conforming to standard aircraft mounting conventions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mechanical drive system is used to power accessories from the engine, then reliability against belt wear and slippage is improved, but the risk of catastrophic damage to engine and accessory components increases due to excessive torques from component failures

Engineering Contradiction:

Improvereliability against belt wear and slippageVSAvoidexcessive torques from component failures

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The drive shaft is segmented into a modular coupling system with a driving portion and a driven portion connected by a torque-limiting mechanism. This segmentation allows the system to maintain mechanical drive reliability while incorporating a failure protection feature that limits excessive torques through controlled disengagement of the coupling elements when overload occurs

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A torque-limiting coupling acts as an intermediary element between the engine and accessories. This coupling includes a driving portion with driving engagement elements and a driven portion with driven engagement elements, connected through a torque-limiting mechanism that mediates torque transmission and prevents catastrophic damage by disengaging when excessive torque is detected

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If precision shafts with little bearing clearance are used, then manufacturing precision is improved, but side load and wear increase when misalignment occurs

Engineering Contradiction:

Improveprecision shaft alignmentVSAvoidside load and wear from misalignment

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The coupling employs dynamic misalignment compensation through cam lobes that can rotate or shift position to accommodate angular and parallel misalignment between shafts. This dynamic adjustment mechanism allows the rigid precision shafts to operate with minimal bearing clearance while automatically compensating for misalignment, thereby reducing side load and wear

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS8708830B2Break away spline misalignment coupling

Publication Date: 2014.04.29 JONES ROBERT M

AI summary

A torque-limiting coupling may be used to provide a torsion drive between an engine or motor and a driven accessory. If an accessory should experience a catastrophic failure a torsion limit is exceeded and a spline breaks away from the coupling. This guarantees that the internal engine gearing used to drive the accessory is not compromised and interfering with essential moving parts inside the engine. Further, a misalignment compensation limits the side load and wear that occurs when coupling two precision shafts with little clearance on the bearings. With a misalignment coupling, the mount can be slightly out of parallel with no negative effects.