Bidirectional Gear Train Lubrication for Windmilling Turbofans
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Solution Overview
Problem
Gas turbine engines face challenges in lubricating gear reductions during windmilling operations, where the fan rotor can rotate in either direction, requiring efficient lubrication systems that occupy large space and must function under various adverse conditions such as windmilling in flight or on the ground, and negative gravity scenarios.
Innovation Solution
A gear train assembly with a main input drive gear connected to an oil pump through first and second pinion gears, utilizing directional clutches to ensure lubrication in either direction of rotation, allowing the engine to operate under windmill conditions for extended periods and in adverse conditions, featuring a rotatable oil pump about a common axis with the pinion gears and utilizing sprag clutches for efficient lubricant supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a gear reduction is included between the turbine and fan rotor to improve engine efficiency, then power transmission efficiency is improved, but lubrication reliability during windmilling operation deteriorates because the gear train may not receive adequate lubrication when the fan rotates in either direction during windmilling
Solution Approach 1:
The patent employs directional clutches (first and second clutches) that dynamically engage and disengage based on the rotation direction of the fan. When the fan rotates in a first direction, the first clutch engages to drive the oil pump; when the fan rotates in a second direction, the second clutch engages to drive the oil pump. This dynamic switching ensures continuous lubrication reliability regardless of rotation direction, resolving the contradiction between power transmission efficiency and lubrication reliability.
Solution Approach 2:
The patent introduces an intermediary oil pump driven by the fan through a gear train with directional clutches. This oil pump acts as a mediator that actively supplies lubrication to the gear train components during windmilling operation, ensuring that the gear reduction system maintains both high power transmission efficiency and reliable lubrication under varying operational conditions.
2Adaptability or versatility
If gear train components are designed to accommodate bidirectional windmilling rotation, then adaptability to windmilling conditions is improved, but device complexity increases due to the need for additional lubrication system components
Solution Approach 1:
The patent segments the lubrication drive system into two separate pathways: one for first-direction rotation (first pinion gear, first clutch, first gear) and one for second-direction rotation (second pinion gear, second clutch, second gear). This segmentation allows each pathway to be optimized for its specific rotation direction while collectively providing comprehensive bidirectional adaptability, managing complexity through modular organization.
Solution Approach 2:
The patent creates a universal lubrication system where the oil pump can be driven by the fan regardless of rotation direction through the gear train and directional clutches. This multi-functional design allows the same lubrication system to handle both forward and reverse windmilling conditions, improving adaptability without requiring entirely separate systems for each direction.
3Device complexity
If the oil pump is directly driven by the fan through a single gear train, then device complexity is reduced, but reliability of lubrication during bidirectional rotation deteriorates
Solution Approach 1:
The patent uses directional clutches that dynamically respond to rotation direction to reliably drive the oil pump. When the fan rotates in the first direction, the first clutch engages; when the fan rotates in the second direction, the second clutch engages. This dynamic engagement ensures the oil pump is reliably driven in both directions, resolving the contradiction between simplicity and reliability.
Solution Approach 2:
The system is designed to automatically select the appropriate clutch engagement based on rotation direction without external control. The directional clutches self-engage or disengage according to the fan's rotation direction, ensuring the oil pump is always driven correctly without requiring complex control systems, thus maintaining simplicity while ensuring reliability.
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 enables the gas turbine engine to maintain operation for extended periods during windmilling, prevent damage to gear components, and ensure continuous lubrication, allowing indefinite windmilling on the ground and flight under negative gravity conditions without seizing or wearing of bearings and gear teeth.
Implementation Method 1
The first clutch transmits rotation from the first pinion gear to the first gear when the fan is rotating in the first direction, and the first clutch not transmitting rotation from the first pinion gear to the first gear when the fan is rotating in the second direction
Data Source
AI summary
A gas turbine engine including a fan and an oil pump operatively connected to the fan by a main input drive gear, the drive gear rotating when the fan rotor rotates in either a first or second direction of the fan. Further included is a gear train intermediate the main input drive gear and the oil pump, the gear train including a first and second pinion gear, the first and second pinion gear each driven by the main input drive gear, the first pinion gear driving a first gear through a first clutch, the second pinion gear driving a second gear through a second clutch. Only one of the clutches transmits rotation from the respective pinion gear to the respective gear when the fan is rotating in the first direction, with the only the other clutch transmitting rotation when the fan is rotating in the second direction.