Output-Responsive Torque Limiter for Aircraft Actuators
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Solution Overview
Problem
Conventional torque limiting mechanisms in geared rotary actuators for aircraft control surfaces are inefficient due to reliance on friction, which is sensitive to lubrication changes, leading to potential lock-ups and increased weight from oversized components to account for higher torque limits.
Innovation Solution
A torque limiter that responds to output torque instead of input torque, utilizing a gear assembly and lockout mechanism to prevent excessive torque transmission, eliminating friction-based solutions and reducing viscous drag.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction-based torque limiting is used, then torque transmission can be limited, but the friction coefficient becomes sensitive to lubrication changes causing unreliable torque limiting
Solution Approach 1:
The patent replaces the friction-based mechanical torque limiting system with a mechanical lockout mechanism using pawls and gear teeth. This substitution eliminates dependence on friction coefficients and lubrication conditions, providing reliable torque limiting through positive mechanical engagement instead of frictional contact.
Solution Approach 2:
The torque limiting function is segmented into discrete mechanical elements (pawls, gear teeth, lockout rings) that engage at specific torque thresholds. This segmentation allows the system to respond to output torque in discrete steps rather than continuously through friction, improving reliability by eliminating lubrication sensitivity.
2Reliability
If disc brake pack is provided with adequate lubrication, then torque limiting function is maintained, but viscous drag increases causing inefficiency and higher limit loads
Solution Approach 1:
The patent replaces the lubricated friction-based disc brake pack with a dry mechanical lockout mechanism using pawls and gear teeth. This substitution eliminates viscous drag entirely since the lockout mechanism engages through positive mechanical contact rather than friction, removing the source of energy loss and inefficiency while maintaining reliable torque limiting.
3Reliability
If torque limiter responds to input torque, then torque transmission can be limited, but the lock-up torque limit must be set significantly higher than maximum operating torque increasing GRA weight
Solution Approach 1:
The patent inverts the conventional approach by having the torque limiter respond to output torque instead of input torque. This inversion allows the lockout mechanism to engage at or near the maximum operating torque level rather than requiring a significantly higher threshold, enabling the use of smaller, lighter GRA components while maintaining reliable torque limiting protection.
4Reliability
If friction-based torque limiter is used, then torque can be limited, but the system becomes less efficient and imposes higher limit loads on downstream components
Solution Approach 1:
The patent replaces the inefficient friction-based torque limiter with a mechanical lockout mechanism using pawls and gear teeth. This substitution improves system productivity by eliminating the continuous energy loss associated with friction, allowing the system to operate efficiently under normal conditions while providing reliable torque limiting when needed through positive mechanical engagement.
Data Source
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AI summary
A torque limiter limits transmission of torque between an input shaft an output shaft. The torque limiter may be incorporated in a geared rotary actuator for actuating an aircraft control surface. The torque limiter is responsive to output torque associated with the output shaft instead of input torque associated with the input shaft. The torque limiter includes a structural ground and a gear assembly for transmitting rotational motion of the input shaft to the output shaft. The gear assembly includes a reference gear coupled to the structural ground such that movement of the reference gear relative to the structural ground is dependent upon an output torque at the output shaft. The reference gear is stationary relative to the structural ground when the output torque is below an output torque limit, and the reference gear moves relative the structural ground when the output torque exceeds the output torque limit.