Planetary Fan Drive Gear System for Gas Turbine Engines
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Solution Overview
Problem
Gas turbine engines face limitations in achieving optimal thermal, transfer, and propulsive efficiencies, particularly in setting the gear ratio of the fan drive gear system to balance fan and turbine section speeds effectively.
Innovation Solution
A gas turbine engine employs a planetary fan drive gear system with a gear ratio of at least 2.5 and a bypass ratio greater than 11, including a sun gear, planetary gears, a ring gear, and a carrier, where the ring gear is fixed, and the low pressure turbine is mechanically attached to the sun gear, with the fan section attached to the carrier, to optimize fan tip speed and reduce stress levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a speed reduction device with a planetary fan drive gear system is utilized to drive the fan section at a reduced speed, then propulsive efficiency is improved, but the device complexity increases
Solution Approach 1:
The fan drive gear system is segmented into modular components including a planetary gear set with sun gear, planetary gears, ring gear, and carrier. This segmentation allows each component to be optimized independently while maintaining overall system efficiency, resolving the contradiction between improved propulsive efficiency and increased device complexity through structured modularity.
2Speed
If the gear ratio is set to at least 2.5 to optimize fan tip speed, then fan blade tip speed is reduced to below 1400 fps, but the stress levels in the rotor and fan blades increase
Solution Approach 1:
The patent applies parameter changes by setting the gear ratio to at least 2.5, which directly controls the fan blade tip speed to remain below 1400 fps. This parameter optimization balances the reduction of fan blade tip speed with the management of stress levels in the rotor and fan blades, resolving the contradiction between speed optimization and stress reduction.
3Productivity
If the bypass ratio is increased to greater than 11.0 to improve propulsive efficiency, then thermal and transfer efficiencies are enhanced, but the engine size and weight increase
Solution Approach 1:
The patent replaces a conventional direct-drive mechanical system with a planetary fan drive gear system that enables high bypass ratio operation (greater than 11.0) without proportionally increasing engine weight. The gear system allows for optimized component sizing and stress distribution, resolving the contradiction between improved propulsive efficiency and increased engine weight.
Data Source
AI summary
A gas turbine engine includes a fan section including a fan rotatable about an axis. A speed reduction device is connected to the fan. The speed reduction device includes a planetary fan drive gear system with a planet gear ratio of at least 2.5. A bypass ratio is greater than about 11.0.