Spoiler Actuator Ratchet-Cam Layout for Feedback Torque Protection
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Solution Overview
Problem
Existing electromechanical actuators (EMAs) for aircraft require additional components like torque limiters to prevent damage from feedback torque, which increases weight and complexity.
Innovation Solution
The design incorporates an anti-extension device with a ratchet wheel and pivotable pawl, controlled by a cam mechanism that automatically disables the anti-extension device when the output rod is sufficiently retracted, eliminating the need for a torque limiter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a torque limiter is added to protect against feedback torque, then reliability is improved, but device complexity and weight increase
Solution Approach 1:
The patent combines the torque protection function with the existing anti-extension device by integrating a ratchet wheel and pawl mechanism into the load path between the motor and gearbox. This merging of functions eliminates the need for a separate torque limiter while maintaining protection against feedback torque, thereby reducing device complexity and weight.
Solution Approach 2:
The anti-extension device is designed to serve multiple functions: preventing load-induced extension of the output rod and simultaneously protecting the motor from feedback torque through the ratchet-pawl mechanism. This multi-functionality reduces the overall component count while maintaining reliability.
2Reliability
If a torque limiter is added to protect against feedback torque, then reliability is improved, but weight increases
Solution Approach 1:
The torque protection function is merged with the anti-extension device, eliminating the need for a separate torque limiter component. This integration removes the additional weight that would be required for a standalone torque limiter while maintaining the same level of motor protection against feedback torque.
3Reliability
If the anti-extension device is always engaged, then protection against feedback torque is improved, but ease of operation deteriorates
Solution Approach 1:
The patent makes the anti-extension device dynamic by allowing it to be automatically disengaged when the output rod is fully retracted. The ratchet wheel and pawl mechanism is positioned such that full retraction of the output rod causes disengagement, enabling smooth operation in the retracted position while maintaining protection when the rod is extended. This dynamic behavior ensures ease of operation throughout the full range of motion.
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
This solution reduces the overall weight and complexity of the actuator by eliminating the torque limiter, while ensuring protection against feedback torque through the cam-controlled anti-extension device.
Implementation Method 1
a cam (142) connected to the pivotable rod (44), the cam movable between a first cam position and a second cam position, wherein the cam is biased by a spring towards the first cam position
Implementation Method 2
A screw shaft (22) and a nut (24) mounted on the screw shaft; an output rod (26) connected to the nut
Implementation Method 3
a ratchet wheel (54) mounted on a shaft arranged to be driven by the motor; a pivotable rod (44) comprising a pawl (52); the pivotable rod being pivotable between a first position in which the pawl (52) engages with the ratchet wheel (54) to prevent rotation of the ratchet wheel
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present disclosure relates to an electromechanical actuator (100). The actuator comprises: a motor (12); a gearbox (18); an anti-extension device (140) mounted between the motor and the gearbox. The motor and anti-extension device are mounted on a housing (200) of the actuator. The actuator further comprises a screw shaft (22); a nut (24) mounted on the screw shaft; an output rod (26) connected to the nut, the output rod having a linear range of motion defined between full extension of the output rod at a first end point (A) and full retraction of the output rod at a second end point (C). The screw shaft, nut, and output rod are located in a cavity (204) of the housing. The output rod and nut are held against rotation relative to the housing, such that rotation of the screw shaft drives the output rod to move linearly within the housing. The anti-extension device (140) comprises: a ratchet wheel (54) mounted on a shaft (56) arranged to be driven by the motor; a pivotable rod (44) comprising a pawl (52); the pivotable rod being pivotable between a first rod position in which the pawl (52) engages with the ratchet wheel to prevent rotation of the ratchet wheel in one direction of rotation, and a second rod position in which the pawl does not prevent rotation of the ratchet wheel; and a cam (142) connected to the pivotable rod, the cam movable between a first cam position and a second cam position. The cam is biased by a spring (50) towards the first cam position in which a portion of the cam extends through an aperture (202) in the housing and into the cavity (204); wherein, in the second cam position, the cam holds the pivotable rod at the second rod position in which the pawl does not prevent rotation of the ratchet wheel. When an axial end (26b) of the output rod (26) is at a predetermined intermediate point (D) or between the intermediate point (D) and the second end point (C), the cam is moved to the second cam position by an outer surface (26a) of the output rod bearing against the cam. When the axial end of the output rod is between the intermediate point (D) and the first end point (A), the output rod does not bear against the cam. The actuator may be connected to an aircraft and used to control the position of a spoiler of the aircraft.