Air Turbine Starter Decoupler for Back-Drive Disengagement
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Solution Overview
Problem
Conventional air-turbine starters (ATS) face reliability concerns due to mechanical clutch failures during back-drive events, leading to potential damage and the need for frequent replacement of decouplers, which increases maintenance costs and risks of unintended re-engagement.
Innovation Solution
A manually reversible decoupler mechanism that disengages during back-drive events without damaging components, allowing for re-engagement without replacing parts, featuring a locking shaft, connecting shaft, limiter cap, and dog clutch that move axially to prevent circumferential engagement, ensuring the ATS and accessory gearbox remain disengaged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional mechanical clutch is used for decoupling during back-drive events, then the decoupling function is achieved, but component damage occurs and frequent replacement is required
Solution Approach 1:
The decoupler mechanism transitions from a static mechanical clutch to a dynamic system where the locking shaft can axially move between engaged and disengaged positions. During normal operation, the locking shaft engages with output tabs to transmit torque. During back-drive events, axial movement of the locking shaft automatically disengages the connection, preventing damage while maintaining reliability.
Solution Approach 2:
The decoupler is divided into separate functional components: the locking shaft for engagement control, the connecting shaft for torque transmission, the limiter cap for axial movement restriction, and the dog clutch for additional decoupling assurance. This segmentation allows each component to perform its specific function efficiently and enables manual resetting without replacing entire assemblies.
2Reliability
If a mechanical clutch is used for decoupling, then back-drive protection is provided, but the system requires frequent part replacement increasing maintenance complexity
Solution Approach 1:
The decoupler mechanism provides self-protection during back-drive events through automatic disengagement. The axial movement of the locking shaft and connecting shaft occurs naturally in response to reverse torque, eliminating the need for external sensing or control systems. After the event, the mechanism can be manually reset without specialized tools or procedures.
3Reliability
If conventional decoupler components are used, then decoupling function is achieved, but unintended re-engagement risks occur after disengagement
Solution Approach 1:
The limiter cap is positioned to restrict the axial movement of the connecting shaft and locking shaft, preventing them from inadvertently returning to the engaged position after disengagement. The dog clutch with its tabs and slots provides an additional mechanical barrier that must be actively overcome for re-engagement to occur, ensuring that accidental re-engagement cannot happen.
Data Source
AI summary
An air turbine starter for starting an engine, comprising a housing defining an inlet, an outlet, and a flow path extending between the inlet and the outlet for communicating a flow of gas there through. A turbine member is journaled within the housing and disposed within the flow path for rotatably extracting mechanical power from the flow of gas and a gear train is drivingly coupled with the turbine member. A drive shaft is operably coupled with the gear train, and a decoupler is selectively coupled to the drive shaft for decoupling the air turbine starter from the engine.