Dual-Spool Differential Transmission for Accessory Speed Matching
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Solution Overview
Problem
Aircraft engine manufacturers face challenges in extracting accessory power from the low pressure spool due to the difference in optimum speed ratios between the low pressure spool and high pressure spool, leading to high torque at low speeds and the need for complex multi-speed or variable-speed transmissions to condition the output speed for accessories.
Innovation Solution
A dual spool differential system that combines the low pressure spool and high pressure spool inputs using a gear assembly, including a ring gear and sun gear with planetary gears, to provide a smaller output speed range, and a direct drive assembly with clutches to selectively engage the rotational member, allowing for adjustable gear ratios and power extraction optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power is extracted from the low pressure spool, then accessory power supply is improved, but the output speed range becomes too wide and torque becomes too high at low speeds
Solution Approach 1:
The transmission system is segmented into multiple gear sets with different reduction ratios. The first gear set provides a first reduction ratio for high speed operation, while the second gear set provides a second reduction ratio for low speed operation. This segmentation allows the system to handle the wide speed range of the low pressure spool by switching between appropriate gear ratios, preventing excessive torque at low speeds while maintaining adequate power supply to accessories.
Solution Approach 2:
The transmission system dynamically switches between different gear sets based on operating conditions. A control system monitors the speed and torque requirements, and engages the appropriate gear set (first or second) to match the current operational demands. This dynamic adaptation allows optimal power transmission across the wide speed range of the low pressure spool, maintaining suitable torque levels at all speeds while ensuring continuous accessory power supply.
2Speed
If a multi-speed transmission is used to condition the low pressure spool output speed, then the output speed range is reduced, but the device complexity increases
Solution Approach 1:
The transmission system is designed with multi-functionality, where the same transmission assembly can operate in different modes (first gear set mode, second gear set mode, or direct drive mode) depending on clutch engagement. This universal design allows a single transmission system to handle multiple speed conditioning requirements without needing separate dedicated transmissions for each function, thereby reducing overall device complexity while still achieving the desired output speed range reduction.
Solution Approach 2:
The dual spool differential acts as an intermediary mechanism between the low pressure spool and the transmission assembly. It combines the low pressure spool input with the high pressure spool input to produce a modified output that has a narrower speed range than the low pressure spool alone. This intermediary function reduces the speed conditioning burden on the downstream transmission, allowing for a simpler transmission design while still achieving the required output speed range.
3Device complexity
If the low pressure spool directly drives the rotational member, then the transmission system is simplified, but the speed ratio mismatch between the spool and accessories remains
Solution Approach 1:
The system provides dynamic adaptability through multiple drive modes. When direct drive is selected, the low pressure spool directly drives the rotational member with a 1:1 ratio, simplifying the transmission. When speed conditioning is required, the system dynamically switches to gear-set-based drive modes that provide different reduction ratios. This dynamic capability allows the system to adapt to different accessory speed requirements while maintaining a relatively simple overall structure, resolving the contradiction between simplicity and adaptability.
Solution Approach 2:
The transmission assembly is designed with multi-functionality to serve both direct drive and gear-mediated drive modes. The same assembly can accommodate direct coupling when speed matching is not critical, or engage gear sets when specific speed ratios are required for accessories. This universal design allows a single system to provide both the simplicity of direct drive and the adaptability of speed-ratio-matched operation, depending on operational requirements.
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 system reduces the output speed range and torque at minimum speed, enabling efficient power extraction and simplifying the transmission system, allowing for a smaller, simpler transmission configuration and improved engine efficiency and stability.
Implementation Method 1
a gear assembly connected to the low pressure spool at a low pressure spool input and the high pressure spool at a high pressure spool input, the gear assembly configured to combine the low pressure spool input and the high pressure spool input into a combination output
Implementation Method 2
a direct drive assembly configured to allow selective direct engagement of a low pressure spool to directly drive a rotational member or to be directly driven by the rotational member
Implementation Method 3
each direct drive connection can be mounted to the rotational member by a respective clutch to selectively engage each direct drive connection to the rotational member
Data Source
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AI summary
A turbomachine dual spool transmission system (700) can include a direct drive assembly (701) configured to selectively allow bypassing of a dual spool differential combination output (107) to allow selective direct engagement of a low pressure spool (LS) to directly drive a rotational member (703; 109) or to be directly driven by the rotational member. The system can include the dual spool differential. The dual spool differential can include a gear assembly configured to combine a low pressure spool input and a high pressure spool input into a combination output to provide an output speed range smaller than a low pressure speed range alone.