Air Turbine Starter Shear-Pin Decoupler for Backdrive Isolation
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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 overrunning torque, using a retainer that shears off when the torque exceeds a certain threshold, allowing smooth 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 engine can continue to operate, but the turbine rotor will over-spin and suffer damage
Solution Approach 1:
The decoupler assembly segments the power transmission path by introducing a removable retainer component that connects the drive shaft assembly to the output shaft. This segmentation allows the system to isolate the turbine rotor from backdrive forces while maintaining engine operation, resolving the contradiction between engine continuity and rotor protection
Solution Approach 2:
The retainer acts as an intermediary element between the drive shaft assembly and the output shaft. It selectively engages during normal operation to transmit power, then shears off during backdrive events to protect the turbine rotor, serving as a sacrificial mediator that resolves the conflict between maintaining operation and preventing damage
2Reliability
If a decoupler assembly with retainer is added to prevent backdrive, then turbine rotor protection is improved, but device complexity increases
Solution Approach 1:
The decoupler assembly extracts the protection function from the main starter mechanism by using a separate, removable retainer component. This extracted protective element can be independently designed and replaced without affecting the core starter system, adding protection while minimizing overall complexity
Solution Approach 2:
The retainer is designed as a disposable, sacrificial component that shears off during backdrive events to protect the expensive turbine rotor. By using a low-cost, replaceable element instead of a complex active protection system, the patent achieves reliable protection while keeping the overall device complexity manageable
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 damage and allowing for simpler and less costly maintenance by isolating the output shaft from further stress.
Implementation Method 1
a retainer selectively operably coupling the output shaft to the engine; wherein when a driving torque is transmitted from the drive shaft to the output shaft the retainer is not loaded, when an overrunning torque is transmitted below a torque limit the retainer is loaded, and when the overrunning torque reaches the torque limit the retainer uncouples the output shaft from the engine
Data Source
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AI summary
An air turbine starter (100) with a housing (108, 122); a turbine member (116) located within the housing (108, 122); a drive shaft assembly (135) operably coupled to the turbine member (116), and having an interior portion (154). The air turbine starter (100) output shaft (156) extends between a first end (164) and a second end (166), the output shaft (156) is movable between a first position (168), where the first end (164) is coupled to the engine, and a second position (166), where the second end (166) is retained within the interior portion (154) and the first end (164) is uncoupled from the engine. A decoupler assembly (150) is included for decoupling the output shaft (156) from the engine.