Geared Turbofan Shaft Weak Link Behind Thrust Bearing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Gas turbine engines with gear reductions face challenges in managing overspeed conditions due to failure of components in the drivetrain, particularly when straddle-mounted bearings are used, which can lead to undesirable conditions like turbine overspeeding or fan rotor movement.
Innovation Solution
The implementation of a weakened link in the fan drive turbine drive shaft aft of the second bearing, combined with a catcher mechanism to resist movement of the gear reduction and fan rotor in the event of bearing failure, ensures controlled failure and prevents overspeeding by allowing the turbine to disengage and move aft, thus preventing unsafe rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a straddle-mounted gear reduction is used with bearings positioned both forward and aft, then the gear reduction is supported more stably, but the risk of turbine overspeeding increases upon component failure
Solution Approach 1:
A weakened link is intentionally created in the drive shaft at a predetermined location aft of the second bearing. This preliminary structural weakness ensures that in the event of bearing failure, the drive shaft will fail at this controlled location rather than allowing the turbine to overspeed, thus resolving the contradiction between stable support and overspeed protection.
Solution Approach 2:
The weakened link acts as an intermediary safety mechanism between the second bearing and the turbine. When the second bearing fails, the weakened link serves as a controlled failure point that prevents the harmful effect (turbine overspeed) from occurring, while still allowing the straddle-mounted configuration to provide stable support during normal operation.
2Strength
If the drive shaft is made stronger to prevent failure, then structural integrity is improved, but the ability to provide controlled failure for overspeed protection is reduced
Solution Approach 1:
The drive shaft is designed with non-uniform strength distribution. The majority of the drive shaft maintains high strength for structural integrity, while a specific localized region (the weakened link) has reduced strength. This allows the drive shaft to be both strong overall and capable of controlled failure at the predetermined location when needed for overspeed protection.
3Device complexity
If bearings are positioned close to the gear reduction for compact design, then device complexity is reduced, but the risk of fan rotor movement upon bearing failure increases
Solution Approach 1:
The weakened link serves as an intermediary safety mechanism positioned between the second bearing and the turbine. When the second bearing fails, the weakened link fails first, preventing the harmful effect of fan rotor movement by disconnecting the drive train at a controlled location, thus resolving the contradiction between compact design and safety.
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.