Flexible Gear Mount Structure for Gas 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, input coupling, and flexible support, 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
Engineering Contradiction Analysis
1Strength
If a rigid support structure is used for the geared architecture, then structural strength and stability are improved, but misalignment of gear train elements occurs due to backbone bending, leading to efficiency losses and increased stresses
Solution Approach 1:
The patent applies parameter changes by modifying the stiffness characteristics of the support structure. Specifically, it uses flexible supports with controlled stiffness values (Kfs < 0.11 × Kframe and Kfs < 0.08 × Kgm) and compliant elements that allow controlled deflection. This enables the structure to accommodate backbone bending while maintaining gear alignment, resolving the contradiction between structural strength and gear reliability.
2Stability of the object's composition
If the frame stiffness is increased to reduce deflection, then structural stability is improved, but the flexible support and input coupling must be designed with specific stiffness ratios to maintain gear alignment
Solution Approach 1:
The patent establishes specific parameter relationships: Kfs < 0.11 × Kframe, Kfs < 0.08 × Kgm, and Kic < 0.05 × Kgm. These parameter changes create a hierarchical stiffness distribution that automatically accommodates deflections while maintaining alignment, reducing the complexity of detailed design adjustments.
Solution Approach 2:
The flexible support acts as an intermediary element between the rigid frame and the gear train. It mediates the mechanical interaction by providing controlled compliance, allowing the rigid frame to maintain stability while the flexible support absorbs deflections that would otherwise cause misalignment.
3Reliability
If flexible supports with low stiffness are used, then gear alignment is maintained during backbone bending, but the support structure must be carefully designed to maintain adequate structural strength
Solution Approach 1:
The patent defines specific stiffness parameter ranges: Kfs < 0.11 × Kframe and Kfs < 0.08 × Kgm. These parameter changes ensure the flexible support is compliant enough to maintain gear alignment during deflection while remaining strong enough to provide adequate support. The hierarchical stiffness distribution ensures neither extreme is reached.
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 reliability, and maintains torque transmission during maneuvers, effectively isolating gears from engine loads and 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.
Data Source
AI summary
A gas turbine engine includes a fan shaft that drives a fan that has fan blades. The fan delivers airflow to a bypass duct. A gear system is connected to the fan shaft and is driven through an input defining an input lateral stiffness and an input transverse stiffness. A gear system flex mount arrangement accommodates misalignment of the fan shaft and the input during operation. A frame for supporting the fan shaft defines a frame lateral stiffness and a frame transverse stiffness. The input lateral stiffness is less than 11% of the frame lateral stiffness and the input transverse stiffness is less that 11% of the frame transverse stiffness.