Epicyclic Gearbox Carrier Stiffness for Load Sharing and Alignment
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Solution Overview
Problem
Gas turbine engine gearboxes face challenges in maintaining gear alignment and load distribution due to manufacturing tolerances and wear, leading to potential distortion and reduced gearbox reliability.
Innovation Solution
The gearbox incorporates a planet carrier with specific stiffness ranges for radial bending, tilt, and torsional stiffness, allowing for compensation of misalignment while maintaining even load distribution across gears, thereby reducing the risk of distortion and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the planet carrier is made rigid to maintain gear alignment, then manufacturing precision is improved, but the gearbox becomes sensitive to misalignment and wear
Solution Approach 1:
The planet carrier's stiffness parameters are optimized to specific ranges (radial bending stiffness: 0.5-2.0×10^6 N/m, tilt stiffness: 0.3-1.5×10^6 Nm/rad, torsional stiffness: 0.2-1.0×10^6 Nm/rad) to achieve the right balance between alignment maintenance and misalignment accommodation
Solution Approach 2:
The planet carrier is designed with controlled flexibility rather than complete rigidity, allowing it to dynamically adjust to misalignment conditions while maintaining operational reliability
2Strength
If the planet carrier stiffness is increased to reduce distortion, then strength is improved, but load distribution across gears becomes uneven
Solution Approach 1:
The stiffness parameters are precisely controlled within specific ranges rather than maximized, ensuring the carrier is strong enough to handle loads while remaining flexible enough to maintain even load distribution across all planet gears
Solution Approach 2:
Rather than making the carrier excessively stiff, the design uses partial stiffness - enough to provide structural strength but limited enough to allow load equalization through controlled deformation
3Adaptability or versatility
If the planet carrier is made more flexible to accommodate misalignment, then adaptability is improved, but gear alignment and load distribution deteriorate
Solution Approach 1:
The carrier stiffness parameters are optimized to specific ranges that provide just enough flexibility for misalignment accommodation while maintaining sufficient rigidity for gear alignment and load distribution
Solution Approach 2:
The planet carrier exhibits dynamic behavior with controlled flexibility, adapting to misalignment conditions through elastic deformation within acceptable limits while maintaining operational precision
Data Source
AI summary
An engine for an aircraft has an engine core having a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan having a plurality of fan blades; and a gearbox. The gearbox for an aircraft is arranged to receive an input from a core shaft and to output drive to a fan so as to drive the fan at a lower rotational speed than the core shaft. The gearbox is an epicyclic gearbox and has a sun gear, a plurality of planet gears, a ring gear, and a planet carrier having a plurality of pins, each pin being arranged to have a planet gear of the plurality of planet gears mounted thereon. A ratio of planet carrier torsional stiffness to pin stiffness is within a specified range.