Hydraulic Priority Valve Thrashing Control
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Solution Overview
Problem
Hydraulic systems in aircraft face issues with 'thrashing' due to previous priority control valves that fail to efficiently allocate limited fluid to high-priority actuators, leading to continuous resonant cycling harmful to the system.
Innovation Solution
A hydraulic system with a priority valve that automatically adjusts fluid flow between primary and secondary sections based on pressure levels, using a poppet and control spool mechanism to prevent thrashing by ensuring sufficient fluid is allocated to high-priority actuators while limiting flow to secondary actuators during fluid scarcity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a priority control valve is used to allocate limited hydraulic fluid to flight control actuators, then flight control actuators can operate with priority, but the valve exhibits thrashing behavior causing continuous resonant cycling
Solution Approach 1:
A control spool is introduced as an intermediary element between the priority valve poppet and the pressure sources. The control spool receives high-pressure fluid and modulates it to control the poppet position, preventing direct response to pressure fluctuations that cause thrashing. This intermediary mechanism filters out harmful pressure variations while maintaining priority control functionality.
Solution Approach 2:
The control chamber behind the poppet is pre-filled with hydraulic fluid and maintained at a controlled pressure through the control spool mechanism. This cushioning effect absorbs pressure fluctuations and prevents the poppet from rapidly oscillating between open and closed positions, eliminating thrashing before it can occur.
2Stress or pressure
If the priority control valve attempts to close in response to flow to secondary actuators, then pressure to primary actuators is maintained, but continuous open-close-open cycling occurs
Solution Approach 1:
The control spool is positioned to receive feedback from both the high-pressure source and the poppet position. When the poppet begins to close, it restricts flow to the control chamber, causing the control spool to shift and reopen passage to the control chamber. This feedback mechanism prevents complete closure and stabilizes the valve in a controlled state that maintains pressure without cycling.
Solution Approach 2:
The control spool creates a periodic modulation of fluid flow to the control chamber, preventing the valve from settling into a continuous oscillation pattern. By introducing controlled periodic flow adjustments, the system maintains stable pressure while avoiding the harmful continuous cycling that characterizes thrashing.
3Productivity
If sufficient hydraulic fluid is available, then all hydraulic actuators can operate simultaneously, but when fluid is limited, allocation to high priority functions must be enforced
Solution Approach 1:
The priority valve is designed with dynamic characteristics where the control spool and control chamber create a time-delayed response system. When fluid availability changes, the valve dynamically adjusts between fully open, partially open, and fully closed states based on pressure conditions, automatically allocating fluid without complex external control systems.
Solution Approach 2:
The control spool is actuated by the hydraulic fluid pressure itself rather than by an external actuator or control system. The high-pressure fluid automatically controls the spool position, which in turn controls the poppet, creating a self-regulating system that allocates fluid based on available pressure without external intervention.
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 or eliminates thrashing by ensuring high-priority actuators receive necessary fluid while minimizing oscillations, maintaining system stability and performance even with limited fluid availability.
Implementation Method 1
pressure adjacent the closed end of the spool bore moves the control spool
Implementation Method 2
A spring mechanism, such as one or more springs for example, biases the control spool toward the first position
Implementation Method 3
pressure is conveyed adjacent the closed end of the spool bore which creates a force that moves the control spool
Data Source
Figure 1~2
Figure 3~6
Figure 7~9
AI summary
A hydraulic system (10) has high priority hydraulic functions (17,18,19) connected to a primary supply line (15) that receives pressurized fluid from a source and low priority hydraulic functions (20) connected to secondary supply line (16). A priority valve (28) couples the primary supply line to the secondary supply line. The priority valve detects when the source is unable to furnish enough pressurized fluid to satisfy the demands of all the high and low priority hydraulic functions. In that case the priority valve reduces or eliminates fluid flow between the primary and secondary supply lines.