Air Turbine Starter Decoupler for Backdrive Torque Disengagement
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Solution Overview
Problem
Existing air turbine starters face challenges in preventing backdrive events, which can lead to over-spinning of the turbine rotor and potential damage, as they lack effective mechanisms to decouple from the gas turbine engine during abnormal torque conditions.
Innovation Solution
A backdrive decoupler mechanism featuring a threaded shaft and retention mechanism, including a shear pin, that selectively decouples the output member from the gear train when overrunning torque exceeds a certain level, preventing re-engagement and allowing the air turbine starter to disengage from the gas turbine engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an overrunning clutch is used to prevent back drive, then the turbine rotor can be protected from over-spinning, but the system cannot effectively decouple during backdrive events resulting in potential damage
Solution Approach 1:
The system is divided into two functional segments: the overrunning clutch for normal protection and the decoupler mechanism for emergency decoupling. The decoupler separates the turbine rotor from the engine-driven components, allowing independent movement during backdrive events. This segmentation enables the system to handle both normal over-spinning protection and abnormal backdrive conditions effectively.
Solution Approach 2:
The decoupler acts as an intermediary element between the turbine rotor and the engine-driven components. During backdrive events, this intermediary mechanism engages to decouple the turbine rotor from the engine, preventing the transmission of harmful forces while allowing the turbine to continue rotating independently. The decoupler thus mediates between the conflicting requirements of maintaining connection during normal operation and separating during abnormal conditions.
2Duration of action of moving object
If the air turbine starter remains coupled to the gas turbine engine, then continuous operation is maintained, but overrunning torque causes damage to the starter components
Solution Approach 1:
The decoupler mechanism introduces dynamic adaptability to the system, allowing it to automatically transition between coupled and decoupled states based on operating conditions. During normal operation, the decoupler remains engaged to maintain continuous operation. When abnormal overrunning torque is detected, the decoupler dynamically disengages to protect components, enabling the system to adapt its connectivity state in response to changing conditions.
Solution Approach 2:
The decoupler mechanism is designed as a sacrificial protective element that can be replaced after experiencing extreme backdrive events. While the main turbine and engine components are expensive and critical, the decoupler serves as a more replaceable component that absorbs the damage from abnormal conditions, protecting the more valuable parts of the system.
3Object-affected harmful factors
If a decoupler mechanism is added to prevent backdrive damage, then protection during abnormal conditions is improved, but the device complexity increases
Solution Approach 1:
The decoupler mechanism is designed to automatically engage and disengage based on the mechanical conditions of the system, without requiring external control systems or complex sensing mechanisms. The overrunning torque itself activates the decoupling action through the mechanical design of the decoupler, allowing the system to self-regulate its protective state in response to abnormal conditions.
Solution Approach 2:
The decoupler extracts the protective function from the main clutch mechanism, creating a separate dedicated system for handling backdrive events. This extraction allows the overrunning clutch to focus on normal over-spinning protection while the decoupler handles extreme backdrive conditions, distributing the protective functions across specialized components rather than overcomplicating a single mechanism.
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
Effectively decouples the air turbine starter from the gas turbine engine during backdrive events, reducing the risk of damage and enabling continued operation by preventing the transfer of overrunning torque, thus minimizing the need for costly repairs.
Implementation Method 1
when overrunning torque is transmitted below a certain level the output member, retention mechanism, and threaded shaft are loaded and when the overrunning torque reaches a certain level the retention mechanism uncouples the output member and the first end of the threaded shaft
Implementation Method 2
a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas
Data Source
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AI summary
A method and decoupler for disengaging an output shaft from an engine in a back drive event with a backdrive decoupler. The backdrive decoupler includes a threaded shaft and a retention mechanism selectively coupling the output shaft to the threaded shaft. In a backdrive event, the decoupler decouples the output shaft from a drive shaft.