Geared Turbofan Fan Shaft Mounting for Tip Clearance and Vibration
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Solution Overview
Problem
Designing a gas turbine engine with a larger fan diameter for increased thrust efficiency poses challenges in mounting the fan shaft within the engine, requiring careful consideration of component properties and stiffness ratios to maintain efficient operation and prevent excessive load transmission and vibrations.
Innovation Solution
A gas turbine engine design featuring a fan shaft mounting structure with specific radial and tilt stiffness ratios, defined by axial distances and stiffness values, to ensure proper fan location and isolation from loads while minimizing weight and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a larger fan diameter is used to increase thrust efficiency, then power output is improved, but mounting the fan shaft within the engine becomes problematic and device complexity increases
Solution Approach 1:
The fan shaft mounting structure is divided into separate functional components: supporting bearings for radial support, positioning features for axial and radial location, and isolation mechanisms for vibration control. This segmentation allows each component to be optimized independently for the challenges posed by larger fan diameters.
Solution Approach 2:
The patent addresses mounting challenges by utilizing multiple spatial dimensions - axial distance specifications (≥0.35m) create separation in the axial dimension, while stiffness ratios control behavior in radial and tilt dimensions. This multi-dimensional approach resolves the complexity of mounting large fans within constrained engine spaces.
2Manufacturing precision
If fan shaft stiffness is increased to improve location control, then manufacturing precision is improved, but load transmission to the gearbox increases and weight increases
Solution Approach 1:
The patent optimizes fan shaft performance by precisely controlling stiffness parameters - specifying radial bending stiffness ratios ≥1.0×10⁻³ and tilt stiffness ratios ≥1.5×10⁻³. These parameter changes achieve adequate location control while preventing excessive stiffness that would increase weight and load transmission.
Solution Approach 2:
Different sections of the fan shaft system are given different stiffness characteristics. The supporting bearings provide localized radial support, while the shaft itself maintains controlled flexibility. This local differentiation allows precise location control without requiring uniformly high stiffness throughout the entire shaft assembly.
3Reliability
If fan-gearbox axial distance is increased to reduce load transmission, then reliability is improved, but engine length increases
Solution Approach 1:
The patent introduces flexible couplings and carefully designed shaft sections as intermediary elements between the fan and gearbox. These intermediaries provide load isolation and vibration damping without requiring large axial separations, thus maintaining compact engine length while improving reliability through reduced load transmission.
4Reliability
If supporting bearings are added to improve fan shaft support, then reliability is improved, but device complexity increases
Solution Approach 1:
The supporting bearings are designed to perform multiple functions simultaneously: providing radial support for the fan shaft, establishing precise positioning references for assembly, and serving as mounting points for isolation mechanisms. This multi-functionality reduces overall device complexity despite adding bearing components.
Data Source
AI summary
Gas turbine engine for aircraft including: engine core including turbine, compressor, and core shaft connecting turbine to compressor; fan located upstream of engine core, including plurality of fan blades; gearbox receives input from core shaft and outputs drive to fan shaft to drive fan at lower rotational speed than core shaft; and fan shaft mounting structure arranged to mount fan shaft within engine. Fan shaft mounting structure includes at least two supporting bearings connected to fan shaft. Gearbox's output is at gearbox output position and fan's input is at fan input position. First bearing separation distance is defined as axial distance between input to fan and closest bearing of at least two supporting bearings in rearward direction from fan. First bearing separation ratio of:thefirstbearingseparationdistance(d1)theaxialdistancebetweenthefaninputpositionandthegearboxoutputposition(d4)is greater than or equal to 1.6×10−1, and the axial distance between the fan input position and the gearbox output position (d4) is greater than or equal to 0.43 m.