Autobrake Initialization Using Nose Gear Ground Verification
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Solution Overview
Problem
Existing aircraft braking systems lack a reliable mechanism to prevent uncommanded braking during takeoff and other maneuvers, particularly when the nose landing gear is not fully grounded, which can lead to damage or safety issues.
Innovation Solution
A brake control system that includes an AND gate to ensure that autobraking is only initiated when all landing gears, including the nose gear, are on the ground, using signals from throttle positions and landing gear sensors to control a shutoff valve, ensuring hydraulic pressure is applied only when all gears are properly grounded.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If autobraking is enabled without verifying nose gear grounding, then braking response time is improved, but uncommanded braking during takeoff may occur
Solution Approach 1:
The system performs preliminary verification of nose gear grounding status before enabling autobraking. The brake control unit checks the nose gear grounded signal in advance to ensure the gear is properly on the ground before allowing brake pressure application, preventing uncommanded braking during takeoff
Solution Approach 2:
A shutoff valve is introduced as an intermediary component between the brake control unit and the brake system. This valve acts as a safety gate that blocks brake pressure even when autobraking is commanded, unless the nose gear grounding condition is verified, thus preventing uncommanded braking while maintaining autobraking functionality
2Reliability
If nose gear grounding verification is added, then braking safety is improved, but system complexity increases
Solution Approach 1:
The shutoff valve serves multiple functions: it acts as a safety gate for nose gear verification, a control element for autobraking initialization, and a protection mechanism against uncommanded braking. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in system complexity
Solution Approach 2:
The nose gear grounding verification function is merged into the existing autobraking control logic. The brake control unit integrates the verification of nose gear status with the autobraking command processing, combining multiple safety checks into a unified control sequence rather than adding separate independent systems
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An autobrake brake control system includes a shutoff valve (40) configured to receive a hydraulic fluid, a servo valve (421,42r) configured to receive the hydraulic fluid from the shutoff valve and configured to provide the hydraulic fluid to apply braking force to a wheel via a hydraulic line, and a brake control unit (150) in electronic communication with the shutoff valve. The brake control unit is configured to detect a weight-on-wheel (WOW) condition of a nose landing gear, and the brake control unit controls the shutoff valve in response to detecting the WOW condition of the nose landing gear.