Fail-Safe Pilot Valves for Stuck-Spool Hydraulic Control
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Solution Overview
Problem
Electro-hydraulic control systems for steering actuators lack reliability, leading to uncontrollable situations when a pilot valve malfunctions, as they do not effectively manage stuck spools or fluid pressure imbalances, potentially causing dangerous outcomes.
Innovation Solution
The system employs fail-safe pilot valves connected in parallel with shuttle valves to automatically drain high-pressure fluid to a low-pressure reservoir if a spool becomes stuck, and uses differential pressure monitoring to detect malfunctions, ensuring continuous operation by activating redundant pilot valves and incorporating dual electronic controllers for enhanced redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single pilot valve is used to control the main valve, then the system structure is simple, but the reliability deteriorates because the actuator becomes uncontrollable when the pilot valve malfunctions
Solution Approach 1:
The control system is segmented into multiple independent pilot valves (first and second pilot valves) that can operate independently. Each pilot valve has its own solenoid and spool, allowing one valve to take over if the other fails, thereby improving reliability without requiring a completely redundant dual-valve system.
Solution Approach 2:
The system is configured with pilot valves and shuttle valves in advance to detect and respond to malfunction conditions before they lead to complete system failure. The differential pressure monitoring and automatic switching mechanisms are pre-established to activate immediately upon detecting a stuck spool or pressure imbalance.
2Reliability
If pilot valves are added to improve reliability, then system reliability improves, but the device complexity increases
Solution Approach 1:
Multiple pilot valves are merged into a single functional unit where the first and second pilot valves work together with the shuttle valve to provide fail-safe control. The merging allows the system to maintain simplicity by using a single main valve while incorporating redundancy at the pilot valve level through the shuttle valve mechanism.
Solution Approach 2:
The shuttle valve acts as an intermediary between the first and second pilot valves and the main valve. It automatically selects which pilot valve signal to transmit to the main valve based on system conditions, simplifying the control logic while providing redundancy. The electronic controller also serves as an intermediary that monitors differential pressure and manages the switching between pilot valves.
3Ease of operation
If the pilot valve spool becomes stuck in open state, then fluid continues to flow to the main valve, but this causes harmful effects by overriding subsequent direction inputs
Solution Approach 1:
The system uses differential pressure monitoring across the first and second pilot valves to detect abnormal conditions such as stuck spools. When a pressure imbalance is detected, the electronic controller receives feedback and automatically switches to the other pilot valve or activates the fail-safe draining function, restoring proper control responsiveness.
Solution Approach 2:
The fail-safe pilot valve design converts the harmful effect of a stuck spool into a beneficial automatic draining function. When the spool remains stuck in the open state, the regulated outlet port automatically drains to the low-pressure reservoir, which prevents the harmful override effect and restores system controllability.
4Reliability
If redundant pilot valves are implemented, then system reliability improves, but fluid consumption and wear increase
Solution Approach 1:
The system dynamically switches between the first and second pilot valves based on operational needs and detected conditions. The electronic controller monitors system state and activates only the necessary pilot valve, preventing continuous operation of both valves and thereby reducing fluid consumption and wear while maintaining reliability through the availability of redundant valves when needed.
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 configuration prevents faulty pilot valves from overriding the system, maintains control by automatically switching to backup valves, and reduces wear and fluid consumption, ensuring reliable operation even in failure modes.
Implementation Method 1
Each of the first and second pilot valves and the third and fourth pilot valves is a fail-safe pilot valve arranged to drain a regulated outlet port of said pilot valve to a low pressure reservoir if a spool of the fail-safe pilot valve becomes stuck in an open state
Implementation Method 2
The first pilot valve and the third pilot valve are connected in parallel via a first shuttle valve to the main valve. The second pilot valve and the fourth pilot valve are connected in parallel via a second shuttle valve to the main valve
Data Source
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AI summary
The disclosure relates to an electro-hydraulic control system (1) for directing fluid to at least one hydraulic actuator (10), the system (1) comprising at least one electronic controller (3, 4); first and second pilot valves (5, 6) being electrically connected to the at least one electronic controller (3, 4) which is arranged to control the operation of the first and second pilot valves (5, 6), third and fourth pilot valves (7, 8) being electrically connected to the at least one electronic controller (3, 4) which is arranged to control operation of the third and fourth pilot valves (7, 8). A pilot operated main valve (9) is configured to control fluid flow to at least one hydraulic actuator (10). Each of the first and second pilot valves (5, 6) and the third and fourth pilot valves (7, 8) is a fail-safe pilot valve arranged to drain a regulated outlet port to a low pressure reservoir (15) if a spool of the fail-safe pilot valve (5, 6, 7, 8) becomes stuck in an open state.