Torque Limiting Device With Machined Torsion Spring
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Solution Overview
Problem
Existing torque limiting devices in aircraft actuator systems, such as those using multiple interleaved friction plates or torsion bars, result in weight penalties due to the need for oversized structures to handle maximum torque in case of jamming, which is undesirable.
Innovation Solution
A torque limiting device utilizing a machined torsion spring arranged around input and output shafts, with a jamming mechanism comprising ramp surfaces and roller elements, and an actuator with teeth to manage torque transmission, allowing for preload adjustment and absorption of excess torque to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional torque limiting devices (friction plates or torsion bars) are used, then torque limitation function is achieved, but device weight increases due to oversized structures
Solution Approach 1:
The patent changes the physical parameters of the torque limiting mechanism by using a torsion spring with adjustable preload instead of traditional friction plates or torsion bars. The preload force can be adjusted to set the torque limitation threshold, allowing optimization of the device weight while maintaining the torque limitation function. The torsion spring's stiffness and preload can be tuned to achieve the required torque limit with minimal weight.
Solution Approach 2:
The torque limiting function is segmented into distinct components: the torsion spring for torque storage and limitation, the roller elements for force transmission, and the ramp surfaces for mechanical advantage. This segmentation allows each component to be optimized independently for weight and function, rather than using a monolithic oversized structure.
2Strength
If oversized structures are used to handle maximum torque in case of jamming, then structural strength is sufficient, but aircraft weight increases
Solution Approach 1:
The torsion spring provides beforehand cushioning by storing elastic energy and providing a controlled torque limit before jamming occurs. When jamming happens, the torsion spring has already been pre-loaded to the maximum torque threshold, cushioning the system against excessive forces without requiring oversized structural components throughout the entire actuator system.
Solution Approach 2:
The torsion spring acts as an intermediary element between the power drive unit and the actuator. It mediates the torque transmission by allowing controlled slip or rotation when the torque exceeds the preload threshold, protecting the actuator and structure from damage without requiring them to be sized for maximum torque handling.
3Adaptability or versatility
If a torque limiting device with adjustable preload is used, then adaptability to different torque requirements is improved, but device complexity increases
Solution Approach 1:
The preload adjustment is performed as a preliminary action during assembly or maintenance, rather than requiring complex adjustment mechanisms during operation. The torsion spring can be pre-loaded to the required torque threshold before installation, or adjusted through simple mechanical means such as changing the spring winding or adjusting the mounting position, keeping the device complexity low while maintaining high adaptability.
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 solution effectively limits torque transmission, preventing damage to actuators and structures by quickly engaging the jamming mechanism upon jam detection, reducing weight penalties and ensuring safe operation, while maintaining compactness and ease of preload setting.
Implementation Method 1
a torque limiting mechanism arranged around the input shaft and the output shaft comprising a torsion spring
Implementation Method 2
The roller elements may be received between adjacent ramp surfaces on the input shaft
Data Source
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AI summary
A torque limiting device (24) comprises an input shaft (56), an output shaft (50) and a machined torsion spring (80) having a first end (82) and a second end (84). The first end (82) and the second end (84) of the torsion spring (80) are coupled to the both the input shaft (56) and the output shaft (50), whereby torque is transmitted between the input shaft (56) and output shaft (50) via the torsion spring (80). The couplings between the torsion spring (80) and the input shaft (56) and the output shaft (50) permit limited relative rotation between the input shaft (56) and the output shaft 50). The device further comprises a jamming mechanism (78) operable in response to relative rotation between the input shaft (56) and output shaft (50) to stop rotation of both the input shaft (56) and the output shaft (50).