Superposition Gearbox for Dual-Spool Accessory Power Extraction
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Solution Overview
Problem
The loads from the accessory gearbox on the high spool in gas turbine engines reduce efficiency, as excessive power extraction from a single spool limits operation and degrades overall performance.
Innovation Solution
A superposition gearbox is introduced, which includes a sun gear, intermediate gears supported in a carrier, and a ring gear, allowing power distribution between the low speed and high speed spools through concentric or differently oriented tower shafts, with one-way mechanical clutches for selective coupling, to optimize power extraction and reduce idle thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power is extracted from a single spool to drive the accessory gearbox, then the accessory components can be driven, but the engine efficiency is reduced and overall performance is degraded
Solution Approach 1:
The invention divides the power extraction function into two separate spools (high-speed spool and low-speed spool), each driving separate tower shafts that feed into a common accessory gearbox. This segmentation allows power to be drawn from both spools simultaneously, preventing excessive load on a single spool and maintaining engine efficiency while still providing sufficient power to accessory components.
2Device complexity
If a single spool drives all accessories, then the system is simpler, but the operation is limited and performance is degraded
Solution Approach 1:
The accessory gearbox is designed with universal input capability from both high-speed and low-speed tower shafts, allowing it to function with power input from either spool or both simultaneously depending on operating conditions. This multi-functionality provides operational flexibility and adaptability across different flight regimes while maintaining a relatively simple overall system architecture.
3Power
If excessive power is extracted from one spool, then the accessory gearbox can be driven, but idle thrust is increased and efficiency is reduced
Solution Approach 1:
The power extraction function is segmented between two spools, with each spool contributing a portion of the total power required by the accessory gearbox. This distribution prevents excessive power extraction from a single spool, thereby reducing idle thrust and maintaining engine efficiency while still providing adequate power to all accessory components.
Data Source
AI summary
A gas turbine engine including a low speed spool including a low pressure compressor, a low speed output gear disposed on the low speed spool, a high speed spool including a high pressure compressor, a high speed output gear disposed on the high speed spool, a first tower shaft engaged to the low speed spool at the low speed output gear, a second tower shaft engaged to the high speed spool at the high speed output gear, and a superposition gearbox. The gas turbine engine further including a ring gear shaft coupled to drive the ring gear, a ring gear shaft drive gear. A low speed spool drive train gear ratio is between 0.5 to 2.0, the low speed spool drive train gear ratio being measured from the low speed output gear to the ring gear shaft drive gear.