Electro-Hydraulic Servo Valve Spool Layout for Predictable Fail States
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Solution Overview
Problem
Electro-hydraulic servo valves (EHSV) often fail in unpredictable directions due to electrical or hydromechanical failures, causing connected effectors to move to either physical limit, which is undesirable as it depends on the failure state, and existing solutions only protect against loss of power scenarios.
Innovation Solution
The design incorporates a failsafe mechanism where the valve spool is configured to always drive the control valve in a predetermined direction during failures, utilizing additional positions and fluid duct configurations to ensure consistent effector movement, regardless of failure direction, by preventing fluid flow among specific ports under abnormal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional EHSV configuration is used, then the valve can operate under nominal conditions, but during failures the effector moves to unpredictable directions (either physical limit)
Solution Approach 1:
The valve spool is designed with asymmetric positioning where the first and third positions (opposite ends of stroke) both connect the first fluid port to the second fluid port, while the second position (intermediate) connects the first fluid port to the third fluid port. This asymmetric configuration ensures that regardless of which end position the spool reaches during failure, the same fluid connection is established, making the effector movement direction predictable and consistent.
Solution Approach 2:
The valve spool stroke is segmented into distinct positions (first, second, and third positions) with specific fluid connection functions. By dividing the continuous stroke into discrete functional segments, the system ensures that failure to any position results in a known fluid connection state, thereby improving reliability during failure conditions.
2Reliability
If null bias is used to protect against loss of power, then the control valve moves to a known stop, but this only protects against zero current failure and not other failure modes
Solution Approach 1:
The valve spool configuration serves multiple functions: under normal operation it controls fluid flow bidirectionally, and under failure conditions (whether zero current, non-zero current, or other failures driving the spool to extremes) it consistently establishes the same safe fluid connection. This multi-functionality extends protection beyond just loss of power scenarios to cover various failure modes, making the system more versatile in handling different failure conditions.
3Reliability
If the valve spool is configured with multiple positions, then failsafe operation is achieved, but the device complexity increases
Solution Approach 1:
The first and third fluid ports are both connected to the second fluid port when the valve spool is at either extreme position. This merging of fluid connections at failure positions ensures that regardless of which extreme the spool reaches, the same safe state is achieved, simplifying the overall control logic while maintaining failsafe 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
This configuration ensures consistent and predictable effector movement during failures, providing failsafe operation and known states, which can be tailored for specific application requirements, such as always extending or retracting, thereby enhancing system reliability.
Implementation Method 1
an electrohydraulic valve configured to urge the valve spool into at least the first position, the second position, and the third position
Implementation Method 2
The second port and the third port can be in fluidic communication with a fluid actuator, and the fluid actuator can be configured to actuate in a first direction based on fluid flow in a first direction through the second port, and actuate in a second direction opposite the first direction based on fluid flow in a first direction through the third port
Data Source
AI summary
The subject matter of this specification can be embodied in, among other things, a fluid valve assembly that includes a first fluid port, a second fluid port, a third fluid port, a valve spool configured to be positioned at a first position, a second position away from the first position, a third position away from the first position opposite the second valve position, the valve spool defining a first fluid duct configured to fluidly connect the first fluid port to the second fluid port in the first valve position, a second fluid duct configured to fluidly connect the first fluid port to the third fluid port in the second valve position, and a third fluid duct configured to fluidly connect the first fluid port to the second fluid port in the third valve position.