Gearbox Positioning Device for Gas Turbine Engine Thermal Growth

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Solution Overview

Problem

Modern gas turbine engines face challenges in managing thermal growth and support linkage imbalance, which can lead to undesirable stress on the engine case due to the mounting of the gearbox, as existing solutions do not effectively relieve these issues without imposing additional loads.

Innovation Solution

A gearbox positioning device with a connecting cavity and coupling post arrangement that constrains lateral movement while allowing linear and angular movement, providing an isostatic support linkage to accommodate thermal growth and linkage imbalance without stressing the engine case.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the gearbox is rigidly mounted to the engine case, then the gearbox is stable and properly positioned, but thermal growth and support linkage imbalance create stress on the engine case

Engineering Contradiction:

Improvegearbox positioning stabilityVSAvoidstress on engine case

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The positioning device transitions from a rigid fixed connection to a dynamic connection that permits controlled movements. The connecting cavity and coupling post arrangement allows the gearbox to move axially and rotate slightly, accommodating thermal growth and linkage imbalance dynamically while maintaining operational stability through constrained lateral positioning.

Inventive Principle:

Principle #15Dynamics

2Stress or pressure

If the gearbox is allowed to float freely, then thermal growth and linkage imbalance are relieved, but the gearbox loses proper alignment and positioning

Engineering Contradiction:

Improvestress relief on engine caseVSAvoidgearbox alignment stability

Core Design Contradiction:

Stress or pressureVSStability of the object's composition

Solution Approach 1:

The positioning device applies different constraint qualities to different degrees of freedom. Lateral movement is constrained through the frictional engagement between the coupling post and connecting cavity walls, while axial movement and rotation are permitted. This local differentiation of constraint quality achieves both alignment stability and stress relief.

Inventive Principle:

Principle #3Local quality

3Strength

If a rigid support linkage is used, then the gearbox is firmly supported, but thermal expansion causes stress and potential damage to the engine case

Engineering Contradiction:

Improvesupport linkage strengthVSAvoidthermal growth stress

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The support linkage changes its effective stiffness parameter based on operational conditions. During normal operation, the frictional engagement provides strong lateral support. During thermal expansion, the clearance gap allows the linkage to become more compliant, reducing stress while maintaining overall structural strength.

Inventive Principle:

Principle #35Parameter changes

4Manufacturing precision

If the gearbox is constrained in all directions, then positioning precision is maximized, but thermal growth and rotation are prevented causing stress accumulation

Engineering Contradiction:

Improvegearbox positioning precisionVSAvoidstress-free operation reliability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The positioning constraints are segmented into different spatial directions. Lateral positioning precision is maintained through frictional engagement in the transverse direction, while axial and rotational degrees of freedom are left unconstrained. This directional segmentation of constraints achieves both positioning precision and stress-free operation.

Inventive Principle:

Principle #1Segmentation

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 relieves thermal growth and support linkage imbalance, ensuring the gearbox can move axially and rotationally, thereby reducing stress on the engine case and maintaining stability during operation.

Implementation Method 1

the connecting cavity being shaped relative to the coupling post such that, when the coupling post mates with the connecting cavity, the inner side wall of the connecting cavity constrains movement of the coupling post in a direction laterally transverse to the longitudinal axis of the gas turbine engine while permitting linear movement of the coupling post in the connecting cavity along said longitudinal axis as well as angular movement about a central longitudinal axis of the coupling post

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS9046041B2Gearbox positioning device

Publication Date: 2015.06.02 PRATT & WHITNEY CANADA CORP

AI summary

A gearbox positioning device to position a gearbox relative to an engine case of a gas turbine engine. The positioning device has a first and second part, with the first part having a connecting cavity of predetermined shape and being secured to the engine case. The second part has a coupling post received in the connecting cavity and constraining displacement of the gearbox in a laterally transverse direction with respect to the central longitudinal axis of the engine. The device permits movement of the gearbox in the axial direction of the engine as well as angular movement to prevent stressing the engine case during thermal growth of the engine case or support linkage imbalance. A gearbox positioning system incorporating the positioning device and the method of attaching same to the engine casing is also included.