Dual-Spool Superposition Gearbox for Low-Torque Engine Starting
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Solution Overview
Problem
Current gas turbine engine accessory drive systems face inefficiencies due to excessive power extraction from a single spool, which can limit operation and degrade overall engine performance and efficiency.
Innovation Solution
The implementation of a superposition gearbox with concentric or differently oriented tower shafts and one-way mechanical clutches allows for selective coupling of the ring gear to the tower shafts and fixed engine structure, enabling power distribution from both low and high speed spools to drive the accessory gearbox, optimizing power transfer during starting and operational conditions.
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 powered, but the engine performance and efficiency are degraded due to excessive power extraction from one spool
Solution Approach 1:
The invention divides the power extraction function into two separate paths: one from the high-speed spool through the first tower shaft, and another from the low-speed spool through the second tower shaft. This segmentation allows each spool to contribute appropriately to accessory drive power without one spool being overloaded, thereby maintaining engine performance while powering accessories.
Solution Approach 2:
The invention merges the power outputs from both the high-speed spool and low-speed spool through the superposition gearbox to drive the accessory components. By combining power from both spools, the system achieves sufficient power for accessories without excessive extraction from a single spool, thus resolving the contradiction between power availability and engine efficiency.
2Device complexity
If a traditional single spool drive system is used, then the structure is simpler, but the system cannot automatically adjust torque distribution based on operating conditions
Solution Approach 1:
The invention introduces dynamic adaptability through one-way mechanical clutches that automatically engage or disengage based on operating conditions. During engine starting, the clutches route power appropriately; during normal operation, they enable automatic torque distribution between the two spools. This dynamic behavior provides adaptability without requiring complex active control systems.
Solution Approach 2:
The superposition gearbox with one-way clutches is designed to automatically adjust torque distribution based on the relative speeds and power outputs of the two spools without external control. The system self-regulates the power flow paths, eliminating the need for complex control mechanisms while achieving adaptive torque distribution.
3Power
If power is extracted during engine starting from a single spool, then the starter can drive the engine spool, but the starting torque may be insufficient or create power limitations
Solution Approach 1:
During engine starting, the invention combines the starter torque with power from both the high-speed spool (through the first tower shaft) and low-speed spool (through the second tower shaft) in the superposition gearbox. This merging of multiple power sources provides sufficient starting torque while avoiding power limitations that would occur with single-spool extraction.
Data Source
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AI summary
A turbofan engine (20) includes a first spool (30) including a first turbine (46); a second spool (32) including a second turbine (54) disposed axially forward of the first turbine (46), a first tower shaft (76) engaged to the first spool (30), a second tower shaft (78) engaged to the second spool (32), and a superposition gearbox (66) including a sun gear (102), a plurality of intermediate gears (104) engaged to the sun gear (102) and supported in a carrier (106) and a ring gear (108) circumscribing the intermediate gears (104). The second tower shaft (78) is engaged to drive the sun gear (102). A starter (70) is selectively coupled to the sun gear (102) through a starter clutch (112). A first clutch (114) selectively couples the first tower shaft (76) to the ring gear (108) and a second clutch (116) selectively couples the ring gear (108) to a static structure (36) of the engine (20). An accessory gearbox (68) is driven by an output (110) of the superposition gearbox (66).