Air Turbine Starter Shear-Pin Decoupler for Backdrive Torque
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Solution Overview
Problem
Backdrive events can occur in air turbine starters, leading to over-spinning of the turbine rotor, which existing systems fail to effectively prevent, potentially causing damage and requiring costly replacements.
Innovation Solution
A decoupler assembly with a shear pin mechanism that disconnects the output shaft from the engine during excessive overrunning torque, using a shear pin with a threshold strength that remains intact under normal conditions but shears off during backdrive events, allowing seamless disengagement and preventing further damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air turbine starter remains engaged with the engine during backdrive events, then the starter can continue to function, but the turbine rotor will over-spin and suffer damage
Solution Approach 1:
The decoupler assembly segments the power transmission path by introducing a shear pin that can fail independently, separating the turbine rotor from the output shaft during backdrive events. This allows the turbine rotor to be protected while maintaining the rest of the starter system intact.
Solution Approach 2:
The shear pin acts as an intermediary element between the drive shaft assembly and the output shaft. It normally transmits power but fails as a protective measure during backdrive, serving as a sacrificial component that protects more valuable parts from damage.
2Reliability
If a decoupler assembly with shear pin is added to prevent backdrive damage, then turbine rotor protection is achieved, but device complexity increases
Solution Approach 1:
The shear pin is designed as a disposable, low-cost component with a specific strength threshold. It is intended to fail during backdrive events and be replaced, while protecting more expensive components like the turbine rotor from damage. This follows the principle of using cheap sacrificial elements to protect valuable assets.
Solution Approach 2:
The decoupler assembly provides beforehand protection by pre-installing the shear pin with a known failure threshold. Before a backdrive event occurs, the system is already prepared with a protective mechanism that will automatically activate when the torque exceeds the shear pin's strength, preventing damage in advance.
3Strength
If the shear pin is designed with high strength to withstand normal operation, then normal power transmission is reliable, but it may not shear during backdrive events
Solution Approach 1:
The shear pin's strength parameter is specifically designed to fall within a certain range - strong enough to withstand normal operational torques but weak enough to fail during backdrive events. This parameter optimization allows the pin to differentiate between normal and abnormal operating conditions, shearing only when necessary to protect the system.
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-induced over-spinning by disengaging the air turbine starter from the engine, reducing the risk of damage and allowing for simpler and less costly maintenance by isolating the affected components.
Implementation Method 1
a shear pin with a threshold strength that remains intact under normal conditions but shears off during backdrive events
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.