Electromechanical Brake Back Drive Mechanism
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Solution Overview
Problem
Conventional aircraft brake systems using electromechanical actuators (EMAs) face challenges in maintaining efficient brake clearance without power, as they rely on electromechanical drive for reverse rotation, which is not available during power loss, leading to potential dragging brakes and unsafe operations.
Innovation Solution
Incorporating a supplemental back drive mechanism with a torsion spring and clutch to accumulate and release back drive potential energy, allowing for reverse rotation and retraction of the ball nut piston without electromechanical actuation, ensuring safe brake clearance even in power loss scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electromechanical actuator relies on a motor and controller to create piston retraction, then braking control precision is improved, but the system becomes unable to back drive the piston to clearance position when power is lost
Solution Approach 1:
The torsion spring is pre-loaded during the forward braking stroke to accumulate potential energy, which is then released to automatically back-drive the piston to clearance position when power is lost, without requiring additional control systems
Solution Approach 2:
The system uses its own operational movements (forward braking stroke) to charge the torsion spring, making the backup mechanism self-sufficient and eliminating the need for external power or complex control systems during failure mode
2Reliability
If the electromechanical actuator uses reverse efficiency to back drive the piston during power loss, then failsafe operation is improved, but the response time and effectiveness are insufficient due to mechanical inefficiencies
Solution Approach 1:
The torsion spring provides more than sufficient force to overcome mechanical inefficiencies and back-drive the piston to full clearance position, ensuring rapid and complete brake release even under adverse conditions
Solution Approach 2:
The system alternates between charging the torsion spring during normal braking operations and discharging it during power loss events, creating a periodic energy storage and release cycle that ensures rapid response when needed
3Reliability
If a supplemental back drive mechanism with torsion spring is added, then failsafe operation during power loss is improved, but device complexity increases
Solution Approach 1:
The torsion spring back-drive mechanism is integrated into the existing actuator housing and shares common components such as the ball screw and ball nut, merging the backup mechanism with the primary actuation system to minimize additional complexity
Solution Approach 2:
The ball screw mechanism serves dual functions: it transmits motor-driven force during normal operation and converts torsion spring torque to linear piston retraction during power loss, eliminating the need for separate mechanical components
4Ease of manufacture
If the system allows lower efficiency drivetrain design with supplemental back drive, then manufacturing costs are reduced, but energy loss during normal operation increases
Solution Approach 1:
The system accepts higher energy loss during normal operation as a trade-off, converting what would be wasted energy into useful work by charging the torsion spring, which then provides free backup operation and enables simpler, cheaper drivetrain components
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 supplemental back drive mechanism provides a failsafe operation during power failures, reduces response time, and extends the operational life of EMAs by overcoming mechanical inefficiencies, while also allowing for a lower efficiency drivetrain design, decreasing complexity and costs.
Implementation Method 1
The supplemental back drive mechanism may comprise a torsion spring. Forward rotation of the ball screw in response to actuation of the electromechanical actuator may produce forward rotation of the rotating end of the torsion spring. A back drive potential energy may be accumulated in the torsion spring
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
An electromechanical actuator 200 in an aircraft brake system may include a stationary body, an actuator drive unit 210 in an actuator drive unit housing 211, a ball screw 206 coupled to the actuator drive unit 210, and a ball nut piston 204 coupled to the ball screw 206. A supplemental back drive mechanism may be disposed between the ball screw 206 and the stationary body. The supplemental back drive mechanism may comprise a spring 220 and a clutch 230. The spring 220 may store back drive potential energy when the electromechanical actuator is actuated to drive the ball nut piston 204 forward, and may supply back drive energy to the retract the ball nut piston 204.