Flexible Gear Support Structure for Turbine Shaft Misalignment

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Solution Overview

Problem

In gas turbine engines, backbone bending due to aero and maneuver loads causes misalignment of gear train elements, leading to efficiency losses and reduced life from increased stresses, particularly in epicyclic gear trains with planetary or star gear systems.

Innovation Solution

A flexible support structure is introduced to support the geared architecture, with specific stiffness ratios defined for the frame, gear mesh, and input coupling, ensuring that the flexible support and input coupling stiffness are significantly lower than the frame stiffness, allowing for lateral and transverse flexibility to accommodate misalignment and reduce stress on gear teeth.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a rigid support structure is used for the geared architecture, then structural strength and stability are improved, but gear misalignment and stress concentration increase due to backbone bending

Engineering Contradiction:

Improvestructural strengthVSAvoidgear alignment stability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent applies the dynamics principle by designing a flexible support structure that allows the geared architecture to dynamically adapt to backbone bending. The flexible support enables the gear train to maintain proper alignment despite engine deflections during flight maneuvers, resolving the contradiction between structural strength and gear alignment stability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the stiffness parameter of the support structure from rigid to flexible. By specifically designing the flexible support with appropriate compliance, the system can accommodate backbone bending while maintaining gear alignment, thus resolving the contradiction between strength and reliability.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If the flexible support stiffness is increased to reduce deflection, then structural stability improves, but torque transmission variability increases during maneuvers

Engineering Contradiction:

Improvestructural stabilityVSAvoidtorque transmission consistency

Core Design Contradiction:

Stability of the object's compositionVSPower

Solution Approach 1:

The patent optimizes the stiffness parameter of the flexible support to achieve a balance between structural stability and torque transmission consistency. By carefully selecting the support stiffness to be significantly lower than frame stiffness, the system maintains stable torque transmission while accommodating necessary deflections.

Inventive Principle:

Principle #35Parameter changes

3Strength

If the ring gear stiffness is increased to reduce gear tooth stress, then gear strength improves, but overall system flexibility decreases

Engineering Contradiction:

Improvegear tooth strengthVSAvoidsystem flexibility

Core Design Contradiction:

StrengthVSAdaptability or versatility

Solution Approach 1:

The patent applies local quality by differentiating the stiffness requirements of different components. The ring gear is designed with sufficient stiffness to handle gear tooth loads, while the flexible support is designed with lower stiffness to accommodate backbone bending. This localized differentiation resolves the contradiction between gear strength and system flexibility.

Inventive Principle:

Principle #3Local quality

4Manufacturing precision

If the input coupling stiffness is increased to reduce misalignment, then gear alignment improves, but stress concentration at the coupling increases

Engineering Contradiction:

Improvegear alignment precisionVSAvoidcoupling stress concentration

Core Design Contradiction:

Manufacturing precisionVSStress or pressure

Solution Approach 1:

The patent optimizes the input coupling stiffness parameter to balance alignment precision and stress concentration. By designing the input coupling with appropriate compliance (stiffness significantly lower than frame stiffness), the system achieves sufficient alignment while distributing stresses to prevent concentration at the coupling.

Inventive Principle:

Principle #35Parameter changes

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 design loads by over 17%, enhances system life and reliability, and maintains constant torque transmission during maneuvers by isolating gears from engine loads, thereby minimizing gear tooth stress variations.

Implementation Method 1

A flexible support supports the geared architecture and defines a flexible support stiffness. The flexible support stiffness and the input coupling stiffness are each less than about 11% of the frame stiffness.

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS12163582B2Flexible support structure for a geared architecture gas turbine engine

Publication Date: 2024.12.10 RTX CORP

AI summary

A gas turbine engine including a drive shaft that drives a propulsor. A frame which supports the drive shaft is a K-frame bearing support. A gear system is connected to the drive shaft. The gear system includes a gear mesh that defines a gear mesh lateral stiffness and a gear mesh transverse. A flexible support supports the gear system that defines a flexible support transverse stiffness and a flexible support lateral stiffness. The flexible support lateral stiffness is less than 8% of the gear mesh lateral stiffness.