Flexible Epicyclic Gear Support for Turbofan Engine

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Solution Overview

Problem

In gas turbine engines with epicyclic gear trains, backbone bending due to aero and maneuver loads causes transverse deflection, leading to misalignment of gear train elements and efficiency losses, as well as increased stress concentrations, which are exacerbated by high torque and speed inputs.

Innovation Solution

A flexible support structure is implemented to support the epicyclic gear system, with specific lateral and transverse stiffness values that are significantly lower than the gear mesh and frame stiffness, allowing for alignment adjustments and reduced stress on gear teeth during maneuvers, thereby maintaining efficiency and extending system life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a rigid support structure is used for the epicyclic gear system, then structural stability is improved, but misalignment and stress concentrations increase due to backbone bending deflections

Engineering Contradiction:

Improvestructural stabilityVSAvoidgear alignment and stress distribution

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The support structure's stiffness parameters are specifically adjusted to be lower than the gear mesh stiffness, allowing controlled flexibility that accommodates backbone bending while maintaining gear alignment. This parameter optimization resolves the contradiction between structural stability and gear reliability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The support structure is designed with dynamic flexibility to adapt to varying engine loads and deflections during operation. This dynamic characteristic allows the structure to maintain optimal gear alignment despite changes in backbone bending, resolving the stability-reliability contradiction.

Inventive Principle:

Principle #15Dynamics

2Manufacturing precision

If the support structure stiffness is increased to reduce deflection, then alignment is improved, but stress concentrations and efficiency losses increase due to high torque and speed inputs

Engineering Contradiction:

Improvegear alignmentVSAvoidefficiency losses and stress concentrations

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The support structure stiffness is optimized to a specific range that is lower than gear mesh stiffness but sufficient to maintain alignment. This parameter change reduces stress concentrations and energy losses while preserving manufacturing precision.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The flexible support structure acts as an intermediary element between the rigid gear mesh and the flexible engine backbone, mediating the stress and deflection forces to maintain alignment without causing excessive stress concentrations.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Duration of action of stationary object

If a flexible support structure is used to accommodate misalignment, then gear life is extended, but structural stability and torque transmission may be compromised

Engineering Contradiction:

Improvegear component lifeVSAvoidstructural stability and torque transmission

Core Design Contradiction:

Duration of action of stationary objectVSStability of the object's composition

Solution Approach 1:

The support structure stiffness parameters are carefully selected to provide sufficient flexibility for extending gear life while maintaining adequate structural stability and torque transmission capability. This parameter optimization resolves the contradiction between durability and stability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The flexible support structure is designed as a sacrificial element that can accommodate misalignment and deflection, protecting the more valuable gear components from premature failure. The support structure absorbs the wear and stress.

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 flexible support structure reduces engine weight, maintains torque transmission during maneuvers, and extends the life of gear components by accommodating misalignment and reducing stress variations, resulting in improved power density and efficiency.

Implementation Method 1

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS20230235715A1Geared architecture for high speed and small volume fan drive turbine

Publication Date: 2023.07.27 RTX CORP

AI summary

A turbofan engine includes a propulsor section that has a propulsor shaft in driving engagement with a propulsor. An epicyclic gear system has a gear mesh lateral stiffness and a gear mesh transverse stiffness. A gear system input 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 turbine section rotates at a first speed, and a second turbine rotates at a second speed that is faster than the first speed. A first performance quantity is defined as the product of the first speed squared and the first area of the first turbine, a second performance quantity is defined as the product of the second speed squared and the second area of the second turbine, and a performance quantity ratio is between 0.5 and 1.5.