Geared Turbofan Overspeed Protection With Weakened Shaft Link
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The straddle-mounted gear reduction in gas turbine engines poses challenges during component failure, particularly in the drivetrain, leading to potential overspeeding and undesirable conditions due to the lack of adequate resistance to axial and radial loads.
Innovation Solution
The implementation of a forward bearing and aft thrust bearing supports the gear reduction, with a catcher mechanism to resist movement of the gear reduction and fan rotor in case of bearing failure, utilizing a weakened link in the turbine drive shaft and a catcher structure to prevent overspeeding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a straddle-mounted gear reduction is used with bearings on both forward and aft sides, then the gear reduction is supported more stably during normal operation, but during component failure the lack of adequate resistance to axial and radial loads causes overspeeding and undesirable conditions
Solution Approach 1:
The weakened link is deliberately designed to fail in advance before the turbine can overspeed. This preliminary weakness creates a predetermined failure path that prevents the harmful overspeed condition from occurring, transforming the potential reliability problem into a controlled safety feature.
Solution Approach 2:
The weakened link acts as an intermediary element between the turbine and the gear reduction. It serves as a sacrificial component that absorbs the failure energy and prevents the turbine from accelerating beyond safe limits, thereby protecting the more critical gear reduction and bearing components.
2Ease of operation
If bearings are positioned both forward and aft of the gear reduction (straddle mount), then the gear reduction is better supported, but the arrangement creates challenges during drivetrain component failure due to inadequate resistance to axial and radial loads
Solution Approach 1:
The weakened link is deliberately positioned and designed to fail in advance, creating a predetermined safety mechanism that prevents the turbine from overspeeding. This preliminary weakness counteracts the potential harmful effect of inadequate load resistance during failure by ensuring failure occurs at a controlled location rather than allowing uncontrolled overspeeding.
3Volume of moving object
If the gear reduction is straddle mounted, then space utilization is improved, but the event of fan drivetrain component failure leads to potential overspeeding due to lack of adequate resistance
Solution Approach 1:
The weakened link serves as a preliminary safety mechanism that fails before the turbine can overspeed. By deliberately creating this weakness in the drive shaft, the design ensures that any drivetrain failure will occur at this predetermined location, preventing the harmful overspeed condition while maintaining the space-efficient straddle-mounted configuration.
Data Source
AI summary
A gas turbine engine has a fan drive turbine driving a gear reduction, the gear reduction, in turn, driving a fan rotor, the fan rotor delivering air into a bypass duct as bypass air and into a compressor section as core flow. A forward bearing is positioned between the gear reduction and the fan rotor and supports the gear reduction. A second bearing is positioned aft of the gear reduction and supports the gear reduction. The second bearing is a thrust bearing. A fan drive turbine drive shaft drives the gear reduction. The fan drive turbine drive shaft has a weakened link which is aft of the second bearing such that the fan drive turbine drive shaft will tend to fail at the weakened link, and at a location aft of the second bearing.