Flexible Gear Support for Turbofan Misalignment Stress

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Solution Overview

Problem

In gas turbine engines, the deflection caused by aero and maneuver loads leads to misalignment of gear train elements, resulting in efficiency losses and reduced life due to increased stresses, particularly in epicyclic gear trains with high torque and speed inputs.

Innovation Solution

A flexible support structure with reduced stiffness compared to the frame, which includes a flexible coupling and gear mesh, is used to partially support the gear system, allowing for lateral and transverse flexibility to accommodate misalignment and reduce stress concentrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a rigid frame supports the gear system, then structural stability is improved, but misalignment stress increases due to backbone bending deflection

Engineering Contradiction:

Improvestructural stabilityVSAvoidgear train reliability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent changes the stiffness parameter of the support structure from rigid to flexible. The flexible support structure has reduced stiffness compared to a rigid frame, allowing it to accommodate deflections and misalignments caused by backbone bending while maintaining structural stability. This parameter change resolves the contradiction by enabling the support to adapt to structural deformations without transmitting excessive stress to the gear train.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a flexible support structure is used, then misalignment stress is reduced, but structural stability decreases

Engineering Contradiction:

Improvegear train reliabilityVSAvoidstructural stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies local quality by creating a support structure with non-uniform stiffness characteristics. The flexible support structure has reduced stiffness in specific directions (lateral and transverse) to accommodate misalignment, while maintaining sufficient overall stability. This localized flexibility allows the structure to be compliant where needed (at the gear support points) while remaining stable overall, resolving the contradiction between flexibility and stability.

Inventive Principle:

Principle #3Local quality

3Power

If high torque and speed are transmitted through the gear train, then power density is improved, but misalignment-induced stress increases

Engineering Contradiction:

Improvepower densityVSAvoidmisalignment-induced stress

Core Design Contradiction:

PowerVSStress or pressure

Solution Approach 1:

The patent implements beforehand cushioning by designing a flexible support structure that anticipates and cushions against misalignment stresses before they reach the gear train. The flexible support acts as a buffer that absorbs and distributes the stresses caused by backbone bending, protecting the gear train from high misalignment-induced stresses while still transmitting the high torque and speed required for high power density.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS11635043B2Geared architecture for high speed and small volume fan drive turbine

Publication Date: 2023.04.25 RTX CORP

AI summary

A turbofan engine includes a fan section that drives air along a bypass flow path in a bypass duct. An epicyclic gear system in driving engagement with the fan shaft and has a gear mesh lateral stiffness and a gear mesh transverse stiffness. A gear system input to the gear system defines a gear system input lateral stiffness and a gear system input transverse stiffness. The gear system input lateral stiffness is less than 5% of the gear mesh lateral stiffness. A first performance quantity is defined as the product of a first speed squared and a first area and a second performance quantity is defined as the product of a second speed squared and a second area. A performance quantity ratio of a first performance quantity to a second performance quantity is between 0.5 and 1.5.