Electrohydraulic Servo Valve Fail-Fixed Position Holding
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Solution Overview
Problem
Existing systems fail to effectively maintain the last commanded position of a device controlled by a two-way, four-stage electrohydraulic servo valve (EHSV) during power interruptions without adding cost, complexity, size, or weight, and existing fail-fixed valve configurations are complex and inefficient.
Innovation Solution
A system comprising a fail-fixed valve body and a two-stage EHSV with a servo valve element that moves between control positions and an electrical null bias fail-fixed position, utilizing flow restrictions and dynamic seals to maintain the last commanded position by isolating fluid communications and using a fail-fixed control pressure port to lock the piston, thereby preventing fluid flow and maintaining position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fail-fixed valve is added to maintain position during power interruption, then position stability is improved, but device complexity increases
Solution Approach 1:
The fail-fixed valve is integrated with the existing two-stage EHSV by utilizing the second stage spool and its lands to perform dual functions: normal position control and fail-fixed position holding. The valve body is merged into the existing servo valve structure, sharing common ports and fluid passages, thereby avoiding the need for a completely separate fail-fixed valve system.
Solution Approach 2:
The second stage spool is designed to perform multiple functions: during normal operation, it controls fluid flow to position the actuator; during power interruption, it automatically transitions to block fluid flow paths to maintain the last commanded position. The same physical component serves both control and safety functions, reducing overall system complexity.
2Reliability
If a fail-fixed valve is added to prevent fluid flow during power interruption, then position holding capability is improved, but cost increases
Solution Approach 1:
The fail-fixed functionality is merged into the existing EHSV structure by utilizing the second stage spool and valve body that already exist in the system. No separate fail-fixed valve component is manufactured or purchased, eliminating additional material costs and assembly expenses.
Solution Approach 2:
The system uses its own existing components (second stage spool, valve body, fluid passages) to provide the fail-fixed position holding function. The spool automatically blocks fluid flow paths using its own structure and the existing hydraulic fluid, without requiring external power or additional active components.
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 effectively maintains the last commanded position of the device during power interruptions with minimal additional cost, complexity, size, or weight, using a simple and efficient fail-fixed valve configuration that minimizes drift and ensures hydraulic locking of the actuator.
Implementation Method 1
the fail-fixed valve element is moveable therein between a first position, in which the first inlet port is in fluid communication with the first outlet port and the second inlet port is in fluid communication with the second outlet port, and a second position, in which the first inlet port is not in fluid communication with the first outlet port and the second inlet port is not in fluid communication with the second outlet port
Implementation Method 2
The servo valve element is disposed within the servo valve body and is moveable therein between a centered control position and a plurality of non-centered control positions
Implementation Method 3
maintains the last commanded position of the device during power interruptions with minimal additional cost, complexity, size, or weight, using a simple and efficient fail-fixed valve configuration that minimizes drift and ensures hydraulic locking of the actuator
Data Source
AI summary
A system uses a two-stage electrohydraulic servo valve that includes an additional control port that commands a fail-fixed valve to lock the position of a device in the last commanded position. The additional port is modulated by an existing land on the EHSV valve element, adding little to no complexity. Major technical benefits of the disclosed system are that it adds little to no cost, complexity, size, or weight the device being controlled. The disclosed configuration allows for the use of a relatively small and simple fail-fixed valve, and the control ports on the controlled device keep “drift” to a minimum, when transitioning between normal operating mode and fail-fixed operating mode.