Aircraft Braking System Constant Deceleration Control
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Solution Overview
Problem
Existing aircraft braking systems on the ground experience uneven deceleration due to variations in braking force caused by coefficient of friction, vertical load, and oscillation between braking and skidding, leading to attitude changes and structural mode excitation, resulting in uncomfortable rides and potential fatigue damage.
Innovation Solution
An advanced braking system that calculates and distributes braking force across wheels to achieve constant deceleration, monitoring slip ratios and friction coefficients in real-time, and controlling brake pressure to maintain optimal slip ratios, while ensuring even braking distribution and preventing overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional autobraking control is used with constant command signal, then braking simplicity is maintained, but deceleration uniformity deteriorates due to variations in friction coefficient and vertical load
Solution Approach 1:
The braking system dynamically adjusts the brake pressure command signal in real-time based on measured wheel deceleration, rather than using a fixed constant signal. The controller continuously modifies the braking force to maintain constant deceleration, adapting to variations in friction coefficient and vertical load conditions.
Solution Approach 2:
The system uses feedback from wheel deceleration measurements (obtained from tachometer data) to adjust the brake pressure command. The controller compares the measured deceleration with the target constant deceleration and modifies the brake pressure accordingly to eliminate deviations.
2Force
If high brake pressure is applied to achieve strong braking, then braking effectiveness is improved, but structural mode excitation worsens due to uneven deceleration
Solution Approach 1:
The system continuously measures wheel deceleration and uses this feedback to adjust brake pressure, ensuring that high braking force is applied smoothly and uniformly. This prevents sudden changes in deceleration that would excite structural modes, while still achieving the required braking effectiveness.
Solution Approach 2:
The system changes the braking control parameter from a constant command signal to a dynamically adjusted signal that maintains constant deceleration. This ensures that the braking force is applied in a manner that avoids exciting structural modes while achieving the required braking effect.
3Reliability
If brake pressure is increased to prevent skidding, then wheel slip control is improved, but brake overheating worsens due to excessive braking demand
Solution Approach 1:
The system uses feedback from wheel deceleration and slip ratio measurements to precisely control brake pressure, applying only the minimum necessary force to maintain optimal slip conditions. This prevents excessive brake pressure that would cause overheating while still effectively preventing skids.
Solution Approach 2:
The system optimizes the brake pressure parameter to maintain the wheel slip ratio within the optimal range (typically 10-30%), rather than applying excessive pressure. This ensures reliable skid prevention while minimizing unnecessary heat generation in the brakes.
4Ease of operation
If tachometer-based slip ratio control is used, then skid detection capability is maintained, but measurement precision deteriorates due to tachometer accuracy limitations
Solution Approach 1:
The system uses feedback from multiple sources including tachometer measurements of wheel speed and inertial navigation system data for ground speed. By combining these measurements and focusing on deceleration feedback, the system achieves accurate slip ratio control despite tachometer limitations.
Solution Approach 2:
The system uses an intermediary approach by measuring wheel deceleration (the derivative of wheel speed) rather than relying solely on absolute wheel speed measurements from the tachometer. This intermediary measurement approach reduces the impact of tachometer accuracy limitations on control precision.
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 achieves smooth, constant deceleration, reduces structural mode excitation, and prevents brake overheating, enhancing passenger comfort and maintaining aircraft stability by accurately managing braking forces across wheels.
Implementation Method 1
The wheel speed 6 (in the form of the speed of the rim) is measured by a tachometer
Implementation Method 2
The braking force provided by a ground wheel is equal to μFz where μ is the coefficient of friction between the wheel and the ground
Data Source
AI summary
An advanced braking system for an aircraft is disclosed. A controller calculates the braking required from each wheel in terms of force. A constant deceleration is achieved throughout a braking run by calculating the braking from other sources, principally aerodynamic drag, and commanding a complementary total level of braking from the wheel brakes. The performance of each wheel and brake are monitored during the braking run to determine whether their braking performance is limited by the brake discs or by the tire-ground interaction and to see whether the wheel is approaching the maximum slip ratio after which a skid occurs. The controller uses this information to distribute the total demand for braking amongst the wheels. In doing this, it also aims to keep the braking demand symmetrical across the aircraft and not to overheat the brakes. The controller further measures the braking force provided by a wheel and controls its brake pressure accordingly to achieve the force desired.