Variable Speed Epicyclic Gearbox for Electromechanical Brake Actuation
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Solution Overview
Problem
Electromechanical braking systems in aerospace applications face a challenge in matching the response speed of hydraulic braking systems due to the trade-off between actuation speed and torque, often resulting in reduced running clearance positions leading to dragging brakes.
Innovation Solution
An epicyclic gearbox with a gear ratio of at least 25:1 is used in an electromechanical actuator, allowing a controller to selectively engage high-speed or high-torque outputs based on load measurements, using a voice coil to adjust the gearbox settings and optimize actuation speed and torque for efficient braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a gear train is used to increase motor torque in electromechanical braking, then the available torque at the output is increased, but the output actuation speed is decreased by the same ratio
Solution Approach 1:
The patent applies a variable ratio transmission mechanism that dynamically changes the gear ratio during actuation. The mechanism transitions from a higher gear ratio (providing higher torque multiplication) to a lower gear ratio (providing higher speed multiplication) as the actuation progresses. This dynamic adjustment resolves the contradiction by providing both high torque during the initial phase and high speed during the final phase of brake application.
Solution Approach 2:
The transmission mechanism changes its mechanical parameter (gear ratio) during operation. The variable ratio transmission allows the system to switch between different torque-speed characteristics, enabling the electromechanical actuator to achieve both high torque and high speed performance that would be impossible with a fixed gear ratio.
2Speed
If the targeted actuation speed of an EMA is selected to meet desired characteristics, then the response speed is improved, but the available torque at the output is reduced
Solution Approach 1:
The variable ratio transmission mechanism dynamically adjusts the gear ratio based on the actuation phase. During initial actuation when high torque is needed, the mechanism uses a higher gear ratio. As the actuation progresses and speed becomes more critical, the mechanism shifts to a lower gear ratio, providing higher speed multiplication while maintaining sufficient torque.
Solution Approach 2:
The transmission process is segmented into different phases with different gear ratios. The variable ratio transmission divides the actuation cycle into multiple stages, each optimized for specific requirements (torque-rich initial phase, speed-rich final phase), resolving the contradiction between speed and torque.
3Length of moving object
If a reduced running clearance position is used to reduce the distance that an EMA actuates, then the actuation distance is decreased, but dragging brakes occur
Solution Approach 1:
The variable ratio transmission mechanism provides higher speed multiplication during the final phase of actuation, enabling the system to quickly complete the remaining actuation distance. This allows the use of a reduced running clearance position without causing dragging brakes, as the high-speed phase ensures rapid brake application and release.
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 enables faster actuation with reduced dragging brakes by dynamically adjusting the gearbox settings in response to load thresholds, achieving quicker brake engagement and higher efficiency compared to standard electromechanical actuators.
Implementation Method 1
the mechanism to selectively engage the first output or the second output may comprise a voice coil
Data Source
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AI summary
An electromechanical actuator is provided comprising a housing (114), a rotor (116) disposed in the housing, an selective gearbox (104) mechanically coupled to the rotor and disposed in the housing, a first output of the selective gearbox configured to rotate at a different speed than the rotor, and a second output of the selective gearbox configured to rotate at a same speed as the rotor. Furthermore the present application refers to a braking system, comprising: a non-transitory memory communicating with a controller, the non-transitory memory having instructions stored thereon that, in response to execution by the controller, cause the controller to perform operations comprising: measuring, by the controller, a load on an electromechanical actuator (182); comparing, by the controller, the load to a threshold value (184); and selecting, by the controller, a gear of a selective gearbox in the electromechanical actuator in response to a result of the comparison (186, 188).