Compound Epicyclic Gearbox for Turbofan Fan Speed Reduction
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Solution Overview
Problem
Gas turbine engines face durability and life span issues due to loads imparted on gearboxes when transferring rotational energy from turbines to output shafts, particularly in reducing rotational energy for fans, which can cause angular misalignments and increased loads.
Innovation Solution
The design incorporates a compound epicyclic gearbox with a large sun gear and smaller first- and second-stage gears, minimizing face widths and angular misalignments by using a compound star configuration with a higher number of planet gears, which do not contribute to centrifugal loads, allowing for larger sun gear diameters and reduced face widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a gearbox is used to transfer rotational energy from the turbine to the output shaft, then the fan can be rotated at a lower speed, but various loads are imparted on the gearbox which affect its durability and life
Solution Approach 1:
The gearbox is divided into multiple stages with sun gears, planet gears, and ring gears working in sequence. This segmentation allows the load to be distributed across multiple gear interfaces rather than concentrated in a single stage, reducing the stress on individual gear components and improving overall durability.
Solution Approach 2:
The patent combines multiple gear functions into a single integrated epicyclic gear system where sun gears, planet gears, and ring gears work together. This merging creates a compact structure that efficiently transfers rotational energy while distributing loads across multiple contact points, enhancing reliability.
2Manufacturing precision
If the sun gear diameter is increased to reduce angular misalignments, then the face widths of compound gears can be minimized, but the overall gearbox size increases
Solution Approach 1:
The patent transitions from a single-stage gear configuration to a multi-stage epicyclic arrangement, utilizing radial and axial dimensions more efficiently. By stacking gear stages radially around the sun gear and using axial spacing between planet gears, the design achieves precise angular alignment without proportionally increasing the overall volume.
Solution Approach 2:
The compound gears are nested within the epicyclic structure, with first-stage and second-stage gears arranged axially. This nesting allows multiple gear functions to occupy a compact radial and axial space, achieving the required angular precision without excessive overall dimensions.
Data Source
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AI summary
A gas turbine engine (10) includes an engine core (12), a fan (14) and a gearbox (16) interconnecting the engine core (12) and the fan (14). The engine core (12) is configured to drive rotation of at least one shaft (26). The gearbox (16) is configured to transfer torque from the at least one shaft (26) to an output shaft (30) at a reduced rate. The output shaft (30) is coupled to the fan (14) to drive the fan (14) at the reduced rate and provide thrust for the gas turbine engine (10).