Air Turbine Starter Decoupler for Overrunning 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 overrunning torque conditions.
Innovation Solution
A decoupler assembly with a retention mechanism, such as a shear pin or moveable element, is implemented to selectively decouple the output member from the drive shaft when overrunning torque reaches a certain level, preventing reengagement and allowing the air turbine starter to disengage from the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an overrunning clutch is placed between the air turbine starter output shaft and the air turbine starter gearbox section to prevent back drive, then back drive prevention is improved, but the device complexity increases and the clutch may fail under high overrunning torque conditions
Solution Approach 1:
The decoupler assembly segments the power transmission path by introducing a separate decoupling mechanism (shaft with retention mechanism) that operates independently from the overrunning clutch. This divides the back drive prevention function into two parts: the clutch handles normal overrunning conditions while the decoupler assembly handles high-torque back drive events, reducing the complexity burden on each individual component.
Solution Approach 2:
The decoupler assembly acts as an intermediary element between the air turbine starter output shaft and the engine. The shaft with retention mechanism serves as a mediator that can selectively engage or disengage the connection based on torque conditions, providing a simple mechanical solution that complements the overrunning clutch without adding significant complexity.
2Device complexity
If the air turbine starter remains engaged with the engine during back drive events, then the structure remains simple, but the turbine rotor may over-spin causing damage and increasing maintenance costs
Solution Approach 1:
The decoupler assembly implements preliminary anti-action by being pre-configured to automatically disengage when back drive torque exceeds the retention mechanism's holding capacity. This preventive mechanism activates before severe damage can occur to the turbine rotor, counteracting the harmful back drive effect in advance rather than relying solely on the overrunning clutch which may fail under extreme conditions.
Solution Approach 2:
The retention mechanism in the decoupler assembly provides beforehand cushioning by being designed to fail safely at a predetermined torque level. This protective feature acts as a mechanical fuse that sacrifices itself to protect the more critical turbine rotor from over-spin damage, enabling simpler overall structure while maintaining protection against catastrophic failure.
3Reliability
If a decoupler assembly with retention mechanism is added to prevent back drive, then the protection against over-spinning is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The decoupler assembly is designed as a separate, modular unit with distinct components (shaft, retention mechanism, receiving portion) that can be manufactured independently and assembled into the existing air turbine starter. This segmentation allows each component to be optimized for its specific function and manufactured using standard processes, reducing overall manufacturing complexity despite adding protective functionality.
Solution Approach 2:
The retention mechanism is designed as a sacrificial component that may fail under extreme back drive conditions, protecting the more expensive turbine rotor. By using a simpler, more economical retention mechanism that can be replaced if necessary, the overall system reliability is improved while keeping manufacturing costs lower than reinforcing the entire starter assembly.
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 decoupler effectively prevents backdrive events by disengaging the output member from the engine, reducing the risk of damage to the air turbine starter and minimizing the need for costly replacements, while ensuring the engine can continue operating safely.
Implementation Method 1
a turbine member journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas
Implementation Method 2
a retention mechanism extending axially through a portion of the output member and a portion of the shaft and selectively operably coupling the output member to a first end of the shaft; wherein when overrunning torque reaches a certain level the retention mechanism uncouples the drive shaft and the first end of the shaft
Data Source
AI summary
A method and decoupler for disengaging an output member from an engine in a back drive event with a backdrive decoupler. The backdrive decoupler includes a shaft and a retention mechanism selectively coupling the output member to the shaft. In a backdrive event, the decoupler decouples the member from a drive shaft.