Air Turbine Starter Decoupler for Backdrive Torque Protection
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Solution Overview
Problem
Backdrive events can occur when the engine drives the output shaft of the air turbine starter, leading to over-spinning of the turbine rotor, which existing systems struggle to prevent effectively.
Innovation Solution
A decoupler assembly is introduced, featuring a shear pin retainer that disconnects the output shaft from the accessory gearbox interface when an overrunning torque exceeds a certain threshold, preventing further backdrive and potential damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air turbine starter remains engaged with the engine during backdrive events, then the engine can continue functioning, but the turbine rotor will over-spin and suffer damage
Solution Approach 1:
A decoupler assembly is introduced as an intermediary component between the output shaft and the accessory gearbox interface. This decoupler includes a shear pin that acts as a sacrificial element, allowing torque transmission during normal operation but shearing off when backdrive torque exceeds a threshold, thereby protecting the turbine rotor from damage while enabling engine continuation
Solution Approach 2:
The system changes the torque transmission parameter dynamically by using a shear pin with a specific shear strength. During normal operation, the pin transmits torque; during backdrive events, when torque exceeds the pin's shear strength parameter, the pin fails and torque transmission is interrupted, protecting the turbine rotor
2Reliability
If a decoupler assembly is added to prevent backdrive, then turbine rotor damage is prevented, but device complexity increases
Solution Approach 1:
The decoupler assembly uses a shear pin as a disposable, low-cost component that is designed to fail under backdrive conditions. This simple sacrificial element provides effective protection without requiring complex active control systems or multiple moving parts, thus minimizing the increase in device complexity
Solution Approach 2:
The harmful backdrive torque is extracted from the system by introducing the decoupler assembly that isolates the turbine rotor from the accessory gearbox interface during backdrive events. The shear pin specifically extracts and dissipates the excessive torque through its controlled failure
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 assembly effectively prevents backdrive events by disengaging the air turbine starter from the engine, reducing the risk of over-spinning and associated damage, while allowing the engine to continue functioning.
Implementation Method 1
A decoupler assembly is introduced, featuring a shear pin retainer that disconnects the output shaft from the accessory gearbox interface when an overrunning torque exceeds a certain threshold
Data Source
AI summary
An air turbine starter with a housing; a turbine member located within the housing; a drive shaft operably coupled to the turbine member, and having an interior portion. The air turbine starter output shaft extending between a first end and a second end, the output shaft movable between a first position, where the first end is coupled to the engine, and a second position, where the second end is retained within the interior portion and the first end is uncoupled from the engine. A decoupler assembly is included for decoupling the output shaft from the engine.