Mechanical Shear Fuse for Clutch Failure Torque Protection
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Solution Overview
Problem
Aircraft engine starter motors are at risk of damage due to overspeed when the clutch fails to disengage the reduction gear train during engine startup, leading to excessive torque that can cause mechanical failure.
Innovation Solution
Incorporating a mechanical shaft fuse with specific dimensions and features, such as through holes and a hexagonal cross-sectional shape, into the drive line connecting the motor to the turbine engine, which can withstand normal operational torque but shear when the torque exceeds a selected value, thereby protecting the motor from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the clutch fails to disengage the reduction gear train, then the motor continues to drive the engine, but the motor is subjected to excessive torque and overspeed conditions causing damage
Solution Approach 1:
A mechanical shaft fuse is introduced as an intermediary component between the motor and the reduction gear train. This fuse element is designed to shear at a predetermined torque threshold, acting as a mediator that protects the motor from excessive torque by failing in a controlled manner when the clutch fails to disengage.
Solution Approach 2:
The mechanical shaft fuse is designed as a disposable protective element with a limited service life. Once it shears due to excessive torque, it is replaced rather than repaired, providing an economical solution to protect the expensive motor from damage.
2Reliability
If the mechanical shaft fuse is designed to withstand normal operational torque, then the motor is protected during normal operation, but the fuse must be designed with specific dimensions that may increase device complexity
Solution Approach 1:
The mechanical shaft fuse is designed with specific geometric parameters (diameter, length, material properties) that are carefully selected to withstand normal operational torque while shearing at excessive torque levels. By adjusting these parameters, the fuse can be tailored to different torque thresholds without changing the basic design concept.
Solution Approach 2:
The drive line is segmented into distinct functional zones: the motor, the protective fuse element, and the reduction gear train. This segmentation allows the fuse to be designed and optimized independently for its protective function, simplifying the overall system design.
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 mechanical shaft fuse effectively prevents motor damage by shearing when excessive torque is applied, indicating clutch failure, thus ensuring the motor's safety and integrity during normal operation and engine startup.
Implementation Method 1
The mechanical shaft fuse is capable to withstand a torque required for normal operation of a motoring system and is also configured to shear when the torque is greater than or equal to a selected value
Data Source
Figure 1~2
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Figure 6
AI summary
A motoring system (100) for a gas turbine engine (54) having: a reduction gear train (122) having an input (122a) and an output (122b); an electric motor (110) operably connected to the input (122a); a clutch (124) operably connected to the output (122b), the clutch (124) in operation engages and disengages the reduction gear train (122); and a mechanical shaft fuse (200) operably connecting the output (123b) to the clutch (124), the mechanical shaft fuse (200) in operation shears when torque on the mechanical shaft fuse (200) is greater than or equal to a selected value. The mechanical shaft fuse (200) includes a plurality of through holes (250).