Stub Shaft Failure Relief Assembly for Aircraft Generators

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Solution Overview

Problem

Bending failures of stub shafts in rotating machines, such as aircraft generators, lead to axial loads that can cause damage to the main rotor shaft and housing, resulting in potential uncontained failures and excessive vibration.

Innovation Solution

A failure relief assembly featuring a stub shaft without an outer flange and a lightly press-fitted knock-out plug within the main rotor shaft, allowing the stub shaft to enter the main rotor shaft and displace the plug during a bending failure, thereby preventing axial load transmission to the housing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the stub shaft is axially constrained in the gearbox output shaft with a flange, then the stub shaft is limited in movement, but the axial load from bending failure is transmitted via the flange to the main rotor shaft and housing, potentially causing damage

Engineering Contradiction:

Improvestub shaft positional stabilityVSAvoidaxial load transmission to housing

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The flange is removed from the stub shaft, extracting the harmful axial load transmission path. Without the flange to bear the axial load, the main rotor shaft and housing are protected from the damaging forces generated during bending failure, while the stub shaft remains functionally connected for power transmission.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

A knock-out plug is introduced as an intermediary component between the stub shaft and the main rotor shaft. This plug absorbs and contains the axial load during bending failure by being pushed into the main rotor shaft, preventing the load from being transmitted to the housing while still allowing normal operation when intact.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the stub shaft breaks at an inclined surface, then the two parts attempt to turn at different speeds creating axial load, but this axial load transmission causes potential uncontained failure and excessive vibration

Engineering Contradiction:

Improvefailure containmentVSAvoidexcessive vibration and uncontained failure

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The knock-out plug serves as a pre-positioned cushioning element that absorbs the axial load generated during bending failure. When the stub shaft fails, the plug is pushed into the main rotor shaft, cushioning the impact and containing the failure effects, thereby preventing uncontained failure and excessive vibration from propagating through the system.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Ease of operation

If a flange is present on the stub shaft to limit movement, then axial movement is constrained, but the housing becomes vulnerable to breakage from transmitted axial loads

Engineering Contradiction:

Improvestub shaft movement limitationVSAvoidhousing structural integrity

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The knock-out plug acts as a disposable sacrificial element that is designed to be pushed into the main rotor shaft during failure. This inexpensive component absorbs the axial load that would otherwise damage the expensive housing, serving as a cost-effective protective measure.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution effectively limits damage by preventing axial load transmission to the main rotor shaft and housing, reducing the risk of uncontained failures and excessive vibration.

Implementation Method 1

a knock-out plug inside the main rotor shaft and facing a distal end of an inside portion of the stub shaft, the knock-out plug press fit into the main rotor shaft lightly enough

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS7850532B2Axial impact shaft system

Publication Date: 2010.12.14 HONEYWELL INTERNATIONAL INC

AI summary

A stub shaft of a main rotor shaft of a generator has its flange or shoulder removed from its outer portion so in the event of a bending failure of the stub shaft the resulting axial load of the stub shaft is not transmitted to the main rotor shaft. Instead of a retention plug adjacent the distal end of the inside portion of the stub shaft, a knock out plug is lightly press-fit into the main rotor shaft. In the event of a failure, the outside portion of the stub shaft enters the main rotor shaft without applying an axial load onto the main rotor shaft, moves axially and displaces the knock-out plug without exiting the main rotor shaft.