Compound Epicyclic Gearbox Layout for Turbofan Misalignment Loads
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Solution Overview
Problem
Gas turbine engines face durability and lifespan issues due to loads imparted on gearboxes when transferring rotational energy from turbines to output shafts, particularly when reducing rotational speed for fans, leading to misalignments and increased sensitivity to angular misalignments.
Innovation Solution
A compound epicyclic gearbox with a sun gear, multiple compound gears, and a ring gear is designed, where the sun gear has a larger diameter than conventional gearboxes, and the gearbox includes up to seven compound gears, minimizing face widths and angular misalignments by optimizing gear ratios and configurations to reduce sensitivity to angular misalignments and loads.
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 rotational speed can be reduced for the fan, but the gearbox is subjected to increased loads and angular misalignments that reduce durability
Solution Approach 1:
The gearbox is divided into multiple gear stages (sun gear, planet gears, ring gear) that work together to achieve the speed reduction. This segmentation distributes the mechanical loads across multiple gear interfaces and bearing positions, reducing the stress concentration on any single component and improving overall gearbox durability
Solution Approach 2:
The patent combines the sun gear, planet gears, and ring gear into a single integrated epicyclic gear assembly that functions as one unified load-bearing structure. This merging allows the loads to be distributed across multiple gear mesh points simultaneously, reducing angular misalignments and improving reliability
2Reliability
If the sun gear diameter is increased to reduce sensitivity to angular misalignments, then the gearbox becomes more durable, but the overall gearbox size and complexity increase
Solution Approach 1:
The planet gears are nested between the sun gear and the ring gear, with the sun gear at the center and the ring gear enclosing the entire assembly. This nested configuration allows the large-diameter sun gear to be integrated into a compact gearbox structure without proportionally increasing the overall size, as the planet gears fill the space efficiently
Solution Approach 2:
The sun gear serves multiple functions: it acts as the input gear receiving torque from the turbine, provides the large diameter necessary for reduced misalignment sensitivity, and serves as the central structural element around which the planet gears rotate. This multi-functionality reduces the need for additional components, managing complexity
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 solution effectively reduces angular misalignments and loads on the gearbox, enhancing the durability and efficiency of gas turbine engines by minimizing face widths and using a compound star configuration that reduces rotational contributions to bearing loads, allowing for larger sun gear sizes and smaller face widths, thus improving the gearbox's operational stability and efficiency.
Implementation Method 1
The plurality of compound gears are coupled with the sun gear and spaced circumferentially around the reference axis from one another and each compound gear is driven in rotation by the sun gear
Implementation Method 2
The ring gear is coupled with each of the compound gears and the output shaft to transfer the rotational energy from the plurality of compound gears to the output shaft to drive rotation of the fan
Data Source
AI summary
A gas turbine engine includes an engine core, a fan and a gearbox interconnecting the engine core and the fan. The engine core is configured to drive rotation of at least one shaft. The power gearbox is configured to transfer torque from the at least one shaft to an output shaft at a reduced rate. The output shaft is coupled to the fan to drive the fan at the reduced rate and provide trust for the gas turbine engine.