Aircraft Brake Servo Valve Calibration for Stable Pressure Control
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Solution Overview
Problem
Aircraft braking systems face challenges in maintaining precise pressure control and stability due to servo valve degradation and manufacturing tolerances, leading to undesirable pressure oscillations and potential fault detection issues in closed-loop systems.
Innovation Solution
A brake control system that calibrates the servo valve to generate a transfer function for open-loop operation, recalibrating at predetermined intervals, and switching to closed-loop operation if calibration is unsuccessful, eliminating pressure feedback interactions to maintain stable and consistent pressure response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop mode with pressure feedback signals is used to maintain commanded braking pressure, then pressure control precision is improved, but pressure oscillations and fault detection issues occur due to servo valve degradation and manufacturing tolerances
Solution Approach 1:
The system performs preliminary calibration of the servo valve before normal braking operation. During calibration, the system establishes a transfer function that maps servo valve currents to actual braking pressures, accounting for manufacturing tolerances and initial valve characteristics. This preliminary action enables the subsequent open-loop operation to achieve precise pressure control without the instability caused by continuous feedback during actual braking.
Solution Approach 2:
The system dynamically switches between closed-loop and open-loop modes based on operational conditions. During calibration phase, closed-loop mode is used to accurately map current-pressure relationships. During actual braking, the system transitions to open-loop mode using the pre-established transfer function, thereby avoiding pressure oscillations while maintaining precision. This dynamic adaptation resolves the contradiction between precision and stability.
2Reliability
If servo valve calibration is performed frequently to account for degradation and tolerances, then pressure control reliability is improved, but system complexity and operation time increase
Solution Approach 1:
The system performs servo valve calibration as a preliminary action during aircraft ground operations when brakes are not actively engaged. By completing the calibration process before flight, the system establishes accurate transfer functions that account for valve characteristics and degradation. This timing strategy improves reliability without adding operational complexity during critical braking phases.
Solution Approach 2:
The calibration process is designed to be automatically executed by the brake control system itself during designated operational windows. The system self-calibrates by commanding a series of test pressures, measuring actual responses, and updating its transfer function without requiring manual intervention or additional hardware. This self-service approach maintains reliability while minimizing system complexity.
3Measurement precision
If calibration is performed when aircraft is stationary on ground, then calibration accuracy is improved, but calibration can only be done during limited operational windows
Solution Approach 1:
The system exploits ground operation time before flight to perform preliminary calibration. During this window, the aircraft is stationary and brakes are not under load, providing ideal conditions for accurate calibration. The system completes the calibration process during this preliminary phase, storing the transfer function for use during flight operations. This approach maximizes calibration accuracy while accepting the time constraint by performing calibration only during available ground time.
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 system provides precise pressure control, reduces pressure oscillations, and avoids erroneous fault detection, improving manufacturing yield and reducing costs by operating effectively in both open-loop and closed-loop modes.
Implementation Method 1
a servo valve configured to receive a hydraulic fluid and provide the hydraulic fluid to apply a braking force to a wheel via a hydraulic line, and configured to receive an electric current for varying the hydraulic pressure
Implementation Method 2
Typical braking systems operate in a closed-loop mode and utilize pressure feedback signals for adjusting the electric current supplied to the servo valve to maintain the braking pressure at the commanded pressure
Data Source
AI summary
A brake control system of the present disclosure calibrates a servo valve and calculates a calibrated transfer function associated with the servo valve for precise braking in open-loop mode. The calibration steps may include determining i) whether an aircraft is on a ground surface, ii) whether the aircraft is not moving relative to the ground surface, and iii) whether braking is applied to a brake system of the aircraft. The brake control unit may calibrate the servo valve in response to the brake control unit determining that i) the aircraft is on the ground surface, ii) the aircraft is not moving relative to the ground surface, and iii) the braking is not applied to the brake system of the aircraft. The calibration process includes sending two or more test currents to the servo valve, and determining braking pressures associated with those test currents to calculate the transfer function.