Epicyclic Gearbox Stiffness Tuning for Geared Fan Load Sharing
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Solution Overview
Problem
Existing gearboxes in aircraft engines face challenges in accommodating small errors in gear alignment and shape, leading to uneven load share and wear, while excessive flexibility can result in reduced reliability and efficiency.
Innovation Solution
An epicyclic gearbox with a specific range of overall gear mesh stiffness (between 1.05×10^9 N/m and 8.0×10^9 N/m) is designed to provide flexibility for adjusting misalignments or shape errors, while maintaining optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gearbox is designed with high manufacturing precision to minimize alignment errors and gear tooth shape errors, then the gear mesh stiffness becomes too rigid, leading to uneven load share and excessive wear on gears
Solution Approach 1:
The patent applies parameter changes by deliberately controlling the gear mesh stiffness to fall within a specific range (1.05×10^9 N/m to 8.0×10^9 N/m). This parameter optimization allows the gearbox to accommodate manufacturing errors (up to 100 μm alignment errors and 10 μm tooth shape errors) while maintaining even load distribution across gear teeth, thus improving reliability without sacrificing manufacturing precision
2Adaptability or versatility
If the gearbox is designed with increased flexibility to accommodate misalignments and shape errors, then load share evenness improves, but excessive flexibility leads to increased gear tooth deformation and torsional vibrations
Solution Approach 1:
The patent resolves this contradiction by precisely controlling the gear mesh stiffness parameter within the range of 1.05×10^9 N/m to 8.0×10^9 N/m. This optimized stiffness provides sufficient flexibility to accommodate misalignments and shape errors (improving adaptability) while preventing excessive gear tooth deformation and torsional vibrations (maintaining stability)
3Strength
If the gear mesh stiffness is increased to reduce gear tooth deformation, then structural stability improves, but the gearbox becomes less able to accommodate manufacturing errors, leading to uneven wear
Solution Approach 1:
The patent applies parameter changes by optimizing gear mesh stiffness to a specific range (1.05×10^9 N/m to 8.0×10^9 N/m) that balances two opposing requirements: maintaining sufficient strength to resist gear tooth deformation while providing enough compliance to tolerate manufacturing errors up to 100 μm alignment errors and 10 μm tooth shape errors, thereby achieving both durability and error accommodation
Data Source
AI summary
A gas turbine engine for an aircraft comprising an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor. A fan located upstream of the engine core, the fan comprising a plurality of fan blades and having a fan diameter and a gearbox arranged to receive an input from the core shaft and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, thereby defining a gear ratio. The gearbox being an epicyclic gearbox. A gearbox diameter is defined as the pitch circle diameter of the ring gear; and a geared-fan value defined by a product of the fan diameter and gear ratio, which are divided by the gearbox diameter, being greater than 12.