Aircraft Brake Return Valve Leak Path Against Cavitation
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Solution Overview
Problem
The existing hydraulic brake systems in aircraft often experience false fault reports and cavitation issues during routine testing and operation, leading to potential delays and unnecessary maintenance.
Innovation Solution
A hydraulic brake system with a valve that includes a leak path to maintain the pressure and volume of hydraulic fluid in the return line above a minimum acceptable level, reducing the risk of cavitation and false fault reports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a check valve is installed in the return line to prevent hydraulic fluid loss, then hydraulic fluid retention is improved, but cavitation occurs due to inability to replenish fluid in the return line
Solution Approach 1:
The check valve is modified to have different flow characteristics in different directions: it provides high resistance to forward flow (preventing fluid loss) while allowing controlled leakage in the reverse direction (preventing cavitation). This local differentiation of flow properties resolves the contradiction between fluid retention and cavitation prevention.
Solution Approach 2:
The valve transitions from a static check valve to a dynamic valve with a movable element that responds to pressure differential. The valve automatically adjusts its flow resistance based on operating conditions, allowing controlled leakage when needed while maintaining check valve functionality under normal operation.
2Loss of substance
If a check valve with high forward flow resistance is used to prevent hydraulic fluid loss, then fluid retention is improved, but false fault reports occur due to excessive pressure differential
Solution Approach 1:
The valve design changes the pressure differential parameter by allowing controlled reverse flow. This prevents excessive pressure buildup that would trigger false fault reports, while maintaining sufficient forward flow resistance to prevent hydraulic fluid loss during normal operation.
3Reliability
If a valve allowing high reverse flow is used to prevent cavitation, then cavitation risk is reduced, but hydraulic fluid loss increases
Solution Approach 1:
The valve provides asymmetric flow characteristics: high resistance to forward flow (preventing fluid loss) and controlled resistance to reverse flow (preventing cavitation). This local differentiation resolves the contradiction between preventing fluid loss and preventing cavitation.
4Loss of substance
If a restrictive leak path is added to the check valve to prevent fluid loss, then fluid retention is improved, but cavitation occurs in the return line
Solution Approach 1:
The leak path is designed with specific dimensional parameters that allow controlled flow. By carefully selecting the leak path dimensions, the valve provides sufficient flow to prevent cavitation while maintaining high enough resistance to prevent significant hydraulic fluid loss during normal operation.
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 solution effectively reduces the risk of cavitation and false fault reports, ensuring more accurate system testing and reducing the risk of hydraulic system failure during operation.
Implementation Method 1
maintain the pressure and volume of hydraulic fluid in the return line above a minimum acceptable level, reducing the risk of cavitation
Data Source
AI summary
A hydraulic brake system for activating the wheel brakes of an aircraft landing gear assembly includes a hydraulic fluid supply line and an associated return line. There is a valve which separates a source of hydraulic fluid from a portion of the return line and an associated leak path associated with the valve that in use maintains the pressure and/or volume of hydraulic fluid in the portion of the return line above a minimum acceptable level. The leak path may be provided by a hole drilled in a part (e.g. the poppet) of a non-return check valve.