Flexible Support for Geared Gas Turbine Engine
Solution Overview
Problem
In gas turbine engines, transverse deflection due to aero and maneuver loads causes misalignment of gear train elements, leading to efficiency losses and reduced life from increased stresses at journal bearings and gear teeth mesh.
Innovation Solution
A flexible support structure with specific lateral and transverse stiffness ratios is implemented to accommodate misalignment, using a flexible mount arrangement that segregates vibrations and reduces design loads, allowing the gear system to 'float' during maneuvers and minimizing gear tooth stress variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid support structure is used for the gear system, then structural stability is improved, but the gear train elements become misaligned under transverse deflection causing efficiency losses and increased stresses
Solution Approach 1:
The support structure transitions from a rigid static configuration to a dynamic flexible mounting system that allows controlled movement. The gear system is mounted on flexible supports that enable the gear train elements to maintain proper alignment despite transverse deflections of the engine case during flight maneuvers.
Solution Approach 2:
The stiffness characteristics of the support structure are modified to optimize performance. The flexible mounting system has specific lateral and transverse stiffness ratios that allow it to accommodate misalignment while maintaining gear mesh integrity, changing the mechanical parameters from rigid to flexible within controlled limits.
2Ease of manufacture
If the gear system is rigidly mounted to the engine case, then manufacturing and assembly are simplified, but the concentrated stresses at journal bearings and gear teeth increase reducing component life
Solution Approach 1:
Flexible mounting elements are introduced as intermediary components between the rigid gear system and the engine case. These intermediaries absorb and distribute the stresses generated during operation, preventing concentrated loads at critical locations while maintaining the simplicity of the gear system itself.
Solution Approach 2:
The flexible support structure provides pre-established stress distribution paths that cushion against concentrated loads before they can damage critical components. The mounting system is designed to handle expected stress ranges, protecting journal bearings and gear teeth from excessive stresses that would reduce component life.
3Reliability
If the gear system is isolated with flexible mounts to reduce stresses, then component life is improved, but the overall structural support requirement increases complexity
Solution Approach 1:
Flexibility is applied locally only where needed for stress distribution, rather than making the entire support structure complex and flexible. The flexible mounts are concentrated at specific mounting points, maintaining simplicity in the overall structure while providing reliability where stresses occur.
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 overall engine weight by more than 17%, increases system life and reliability, and maintains constant torque transmission during maneuvers by isolating gears from engine loads.
Implementation Method 1
A flexible support structure with specific lateral and transverse stiffness ratios is implemented to accommodate misalignment
Data Source
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AI summary
A gas turbine engine includes a flex mount for a Fan Drive Gear System defined by a lateral and transverse stiffness relationship. Epicyclic gearboxes with planetary or star gear trains may be used in gas turbine engines for their compact designs and efficient high gear reduction capabilities. Planetary and star gear trains generally include three gear train elements: a central sun gear, an outer ring gear with internal gear teeth, and a plurality of planet gears supported by a planet carrier between and in meshed engagement with both the sun gear and the ring gear.