Decoupler Assembly for Engine Starter Back Drive Protection
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Solution Overview
Problem
Existing air turbine starter systems face issues with back drive events due to overrunning clutch failures, which can lead to over-spinning of the turbine rotor and require a mechanism to decouple the starter from the gas turbine engine effectively.
Innovation Solution
A decoupler assembly featuring a drive hub with teeth, an output shaft with mating teeth, a shear pin with a shear fuse, and a sheath surrounded by a biasing mechanism, which allows axial movement of the output shaft away from the drive hub during back driving torque transmission and shears the shear fuse during failure events to disengage the shafts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the shear pin is designed to fail at a predetermined threshold, then protection against over-spinning is provided, but the shear pin must be replaced after failure
Solution Approach 1:
The shear pin is designed as a disposable sacrificial component with a shear fuse that fails at a predetermined torque threshold. This cheap short-living object is intentionally designed to be replaced after failure, protecting the more expensive turbine rotor while accepting the need for periodic replacement of the shear pin itself
2Ease of operation
If the second set of teeth slide on the first set of teeth during back driving, then axial movement of the output shaft away from the drive hub is achieved, but wear on the teeth increases
Solution Approach 1:
The harmful sliding contact between the teeth is extracted and isolated to a controlled mechanism. The teeth are designed to engage only during normal operation for torque transmission, while the shear pin failure mechanism extracts the decoupling function during back drive events, minimizing unnecessary tooth sliding and wear
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 back driving and minimizes wear on components, increasing the lifespan of parts, reducing maintenance costs, and ensuring reliable operation by ensuring the starter and engine remain decoupled during failures.
Implementation Method 1
a shear pin operably coupled at a first end to the drive hub and operably coupled at a second end to the output shaft and having a shear fuse
Implementation Method 2
a biasing mechanism configured to compress during back driving and retain the sheath on the drive hub
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. A gear train is drivingly coupled with the turbine member, a drive train is operably coupled with the gear train, and an output shaft is selectively operably coupled to rotate with the engine via a decoupler.