Fail-Safe Pilot Valves for Reliable Electro-Hydraulic Steering
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Solution Overview
Problem
Electro-hydraulic control systems for steering actuators face reliability issues due to potential malfunction of pilot valves, leading to uncontrollable actuators, which can result in dangerous situations, especially in vehicle steering systems.
Innovation Solution
An electro-hydraulic control system with fail-safe pilot valves that drain fluid to a low-pressure reservoir if a spool becomes stuck, and a redundant setup with parallel-connected pilot valves and electronic controllers to ensure continuous operation and monitoring for early detection of failures, including spool position and pressure sensors for fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single pilot valve is used to control the main valve, then the device complexity is reduced, but the reliability deteriorates because a malfunction can make actuators uncontrollable
Solution Approach 1:
The control system is segmented into multiple independent pilot valves (first and second pilot valves) that separately control different aspects of the main valve. This segmentation allows the system to maintain control functionality even if one pilot valve fails, as the other can still influence the main valve operation.
Solution Approach 2:
The system incorporates preliminary fail-safe mechanisms where pilot valves are designed with automatic draining capability and redundant pathways. When a pilot valve malfunctions, the system has pre-established alternative routes through the second pilot valve and direct tank connections to maintain control, preventing complete system failure before it occurs.
2Reliability
If redundant pilot valves are added to improve reliability, then the reliability improves, but the device complexity increases
Solution Approach 1:
The first and second pilot valves are merged into a coordinated control system where both valves work together to control the main valve. They share common control signals from the electronic controller and are integrated through the main valve's control architecture, allowing redundant functionality without proportionally increasing overall system complexity.
Solution Approach 2:
The main valve acts as an intermediary that receives control signals from multiple pilot valves and integrates their effects. This intermediary component allows the system to process inputs from redundant pilot valves in a unified manner, managing the complexity of having multiple control pathways through a single integration point.
3Object-affected harmful factors
If pilot valves are made fail-safe with automatic draining, then the safety improves, but the device complexity increases due to additional draining mechanisms
Solution Approach 1:
The pilot valves are designed with self-service fail-safe capabilities where the valves automatically detect and respond to their own malfunction conditions. When a pilot valve becomes stuck in the actuated position, it automatically drains through its own internal or external pathways to the tank, without requiring external detection or intervention systems.
Solution Approach 2:
The potential harmful effect of a stuck spool in the actuated position is converted into a beneficial fail-safe mechanism. By providing automatic draining pathways, the system transforms the harmful stuck condition into a self-correcting event where the valve automatically returns to a safe state by draining to the tank, eliminating the hazard rather than just detecting it.
4Reliability
If parallel pilot valves are used with shuttle valves, then the reliability improves through backup capability, but the device complexity increases due to parallel architecture
Solution Approach 1:
The control system is divided into parallel segments with the first and second pilot valves operating in parallel configurations. Each valve segment has its own control pathway to the main valve, and the shuttle valve segments separately manage the switching between these parallel pathways, allowing independent operation and failure isolation.
Solution Approach 2:
Shuttle valves serve as intermediary switching components that manage the parallel pilot valve architecture. These intermediaries automatically select which pilot valve pathway is active based on pressure differentials or control signals, simplifying the management of parallel redundancy by providing automatic switching without requiring complex control logic.
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 system prevents faulty pilot valves from overriding the control system, ensuring continuous operation and reducing wear on redundant valves by automatically draining stuck spools and providing immediate backup pressure, thus enhancing safety and reliability.
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.
Implementation Method 3
A direction input to a pilot valve may for instance correspond to a left or right steering indication when the control system is used in a steering system. The automatic draining of the fail-safe pilot valve in case of spool becomes stuck in an actuated position removes the risk
Data Source
AI summary
The disclosure relates to an electro-hydraulic control system for directing fluid to at least one hydraulic actuator, the system comprising at least one electronic controller; first and second pilot valves being electrically connected to the at least one electronic controller which is arranged to control the operation of the first and second pilot valves, third and fourth pilot valves being electrically connected to the at least one electronic controller which is arranged to control operation of the third and fourth pilot valves. A pilot operated main valve is configured to control fluid flow to at least one hydraulic actuator. 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 to a low pressure reservoir if a spool of the fail-safe pilot valve becomes stuck in an open state.