Double Frangible Bearing Support for Aircraft Engine Imbalance

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Solution Overview

Problem

Aircraft engine fans can experience significant imbalance and vibration due to fan blade loss, leading to potential engine and aircraft damage during windmilling, as existing bearing support structures fail to effectively absorb and manage the resulting radial loads and vibrations.

Innovation Solution

A double frangible bearing support structure is implemented, featuring a fusible conical support for the first bearing and a thrust bearing with rolling elements and frangible bolts for the second bearing, designed to decouple from the stator structure under critical loads, thereby reducing the transmission of imbalance forces and vibrations to the engine and aircraft.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a rigid bearing support structure is used to maintain structural integrity, then strength and stability are improved, but the transmission of damaging loads and vibrations to the engine and aircraft increases during fan blade loss events

Engineering Contradiction:

Improvestructural integrityVSAvoidtransmission of damaging loads and vibrations

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The bearing support structure is segmented into multiple frangible elements (frangible bolts, fusible conical support) that can independently fail under critical loads. This segmentation allows the structure to progressively decouple from the rotor, absorbing harmful loads while maintaining overall structural integrity through the remaining bearing assemblies.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Frangible bolts and fusible conical supports act as intermediary elements between the rigid bearing support and the rotor. These intermediaries are designed to fail at predetermined loads, serving as a controlled weak link that protects the main engine structure from transmitting damaging vibrations and loads during abnormal operating conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If bearing support structures are designed to be rigid and permanent, then reliability under normal operation is improved, but the ability to absorb and manage radial loads during abnormal conditions deteriorates

Engineering Contradiction:

Improvereliability under normal operationVSAvoidability to absorb and manage radial loads during abnormal conditions

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The bearing support structure transitions from a static rigid design to a dynamic system with predetermined failure modes. The frangible bolts and fusible conical support are designed to remain intact during normal operation, providing reliable support, but automatically decouple when critical radial loads are exceeded, allowing the structure to adapt to abnormal conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The structural parameters of the bearing support (specifically the frangible connection elements) are designed with controlled weakness. By changing the material properties and geometric parameters of the frangible bolts and fusible support, the structure maintains high strength during normal operation but can undergo controlled structural changes when critical loads are reached.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If frangible elements are introduced to decouple under critical loads, then the transmission of harmful vibrations is reduced, but device complexity increases due to additional bearing assemblies and frangible components

Engineering Contradiction:

Improvetransmission of harmful vibrationsVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The frangible bolts and fusible conical support are designed as disposable protective elements that are relatively simple in construction compared to the main engine structure. These elements are intended to fail in a controlled manner during extreme events, providing a cost-effective solution to protect the valuable main engine and aircraft structures from damage.

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

The solution effectively reduces the transmission of damaging loads and vibrations to the engine and aircraft, minimizing the risk of damage and maintaining control during abnormal rotor imbalance events by decoupling the bearings from the stator structure, thus preventing engine and aircraft structural damage.

Implementation Method 1

a first bearing supported by a fusible conical support structure

Methodology Applied

Scientific EffectFusible material melting: Melting

Implementation Method 2

the outer race being connected to a second bearing support by frangible bolts

Methodology Applied

Scientific EffectFracture mechanics: Fracture Mechanics

Data Source

PatentUS9777596B2Double frangible bearing support

Publication Date: 2017.10.03 PRATT & WHITNEY CANADA CORP

AI summary

A double frangible bearing support structure supports a low pressure rotor of an aircraft engine. The support structure has a first bearing assembly including a first bearing supported by a first bearing support adapted to buckle or frange when subject to a predetermined critical load resulting from an abnormal rotor imbalance. The support structure has a second bearing assembly comprising a second bearing having rolling elements disposed between inner and outer races. The outer race is connected to a second bearing support by means of frangible bolts adapted to fail when subject to a predetermined critical load resulting from radial displacements and loads of the low pressure rotor following decoupling/franging at the first bearing support.