Sliding Mode Observer Antilock Braking Torque Control
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Solution Overview
Problem
Conventional antilock brake systems (ABS) for aircraft and land vehicles face challenges in determining an appropriate threshold differential wheel torque, especially under variable braking conditions, which can lead to sub-optimal braking performance and directional control issues due to wheel lock conditions.
Innovation Solution
The system employs a Sliding Mode Observer (SMO) to estimate differential wheel torque from measured wheel speed, using extrema detection to directly calculate an actuator control signal, eliminating the need for a threshold comparison and allowing for optimal braking control by maintaining peak ground/tire friction during heavy braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a threshold differential wheel torque comparison method is used to control brake application, then the braking system can regulate brake torque to prevent wheel lock, but the system complexity increases due to the need for continuous threshold computation and comparison algorithms
Solution Approach 1:
The patent extracts the threshold computation and comparison functionality from the control system by using the extrema detector to directly identify peak differential wheel torque conditions. This eliminates the need for continuous threshold algorithms, reducing computational complexity while maintaining wheel lock prevention capability through direct extremum detection and actuator control signal generation.
Solution Approach 2:
The Sliding Mode Observer automatically generates the differential wheel torque estimate and the extrema detector automatically identifies peak conditions without requiring external threshold references. The system serves itself by using its own measured wheel speed data to generate control signals, eliminating the need for separate threshold computation modules.
2Reliability
If continuous threshold computation and comparison is performed to determine brake application, then braking regulation can be achieved, but the processing time and computational load increase
Solution Approach 1:
The patent skips the intermediate steps of continuous threshold computation and comparison by directly detecting extrema in the differential wheel torque estimate. The extrema detector identifies peak conditions instantaneously and generates actuator control signals without requiring iterative threshold evaluations, significantly reducing processing time while maintaining effective braking regulation.
Solution Approach 2:
The Sliding Mode Observer continuously estimates differential wheel torque in advance, and the extrema detector is prepared to immediately detect peak conditions as they occur. This preliminary preparation of the estimation and detection mechanisms ensures rapid response to braking conditions without requiring real-time threshold computation during critical braking events.
3Speed
If the brakes are applied and released in binary on-off manner based on threshold comparison, then the control system can respond rapidly to wheel lock conditions, but the braking control precision is reduced compared to continuous modulation
Solution Approach 1:
The patent employs periodic on-off brake application controlled by extrema detection, where the brakes are applied when the differential wheel torque estimate reaches a peak and released when it falls below the peak value. This periodic control action, driven by the oscillating nature of wheel slip during ABS operation, achieves both rapid response and improved precision by timing brake application to the natural oscillation cycles of the wheel-brake system.
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 approach enables efficient and safe braking by maintaining friction near its peak value, effectively preventing wheel lock and ensuring optimal deceleration across various braking conditions, suitable for both switched and proportional actuators.
Implementation Method 1
employing a sliding mode observer (SMO) incorporated into an ABS algorithm and control system employing measurement of wheel speed to regulate the application of the wheel brakes
Implementation Method 2
Brake systems, whether for aircraft or land vehicles, function by applying a retarding torque to the braked wheels of the vehicle that is in a direction opposite to the rotational direction of the wheel
Implementation Method 3
This braking force is directed opposite to the vehicle velocity vector and results from sliding friction between the tire and the ground surface
Data Source
AI summary
Improved anti-lock brake systems (ABS) employed on aircraft and land vehicles and methods of operating same employing a sliding mode observer (SMO) incorporated into an ABS algorithm requiring only measurement of wheel speed to regulate the application of braking torque are disclosed. Braking is optimized simply by maintaining an SMO estimate of differential wheel torque (road/tire torque minus applied brake torque) derived from wheel speed at an extremum via applying or releasing the brakes as the extremum is passed through.