Parallel Electrohydraulic Servo Valves for Failure-Tolerant Actuators
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Solution Overview
Problem
Conventional systems for hydraulic control of end effectors, such as those used in aircraft actuators, require two full-sized electrohydraulic servo valves (EHSVs) for normal and backup operations, which results in increased weight, envelope, and leakage.
Innovation Solution
A system utilizing two parallel, smaller electrohydraulic servo valves (EHSVs) connected through transfer valves and solenoid valves, allowing for normal operation in parallel and backup operation with a single EHSV when the other fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two full-sized EHSVs are used for normal and backup operations, then reliability is improved, but weight increases
Solution Approach 1:
The single backup EHSV is segmented into two separate smaller EHSVs that operate in parallel during normal conditions. Each EHSV handles partial load, and together they provide full capability. This segmentation allows using smaller, lighter valves while maintaining the same backup capability, as failure of one smaller EHSV still leaves the other functional.
Solution Approach 2:
Two smaller EHSVs are merged to work in parallel during normal operation, combining their output to match the capability of a single full-sized EHSV. This merging approach allows the system to achieve full operational capability using lighter components, reducing overall actuator weight while maintaining reliability through redundancy.
2Reliability
If two full-sized EHSVs are used for normal and backup operations, then backup operation capability is improved, but envelope increases
Solution Approach 1:
The backup function is segmented into two smaller EHSVs that operate in parallel. Each valve is smaller in size, and when positioned in parallel configuration, they occupy less overall volume than a single full-sized EHSV, reducing the actuator envelope while maintaining backup capability.
Solution Approach 2:
The system transitions from a series arrangement (one backup valve) to a parallel arrangement (two smaller valves). This dimensional reconfiguration allows the valves to be positioned more efficiently in space, reducing the overall envelope of the actuator while maintaining the same functional capability.
3Reliability
If two full-sized EHSVs are used for normal and backup operations, then backup operation capability is improved, but leakage increases
Solution Approach 1:
The single backup EHSV is divided into two smaller EHSVs. Each smaller valve has reduced internal leakage paths and smaller sealing surfaces, resulting in lower individual leakage rates. When operating in parallel, the total leakage is less than that of a single full-sized EHSV, while still providing backup capability.
Solution Approach 2:
The system uses smaller, simpler EHSV components that are easier to manufacture with tighter tolerances and better sealing characteristics. These smaller valves inherently leak less due to their reduced size and simpler internal geometry, providing a cost-effective solution that reduces hydraulic fluid loss.
4Weight of moving object
If two smaller EHSVs operate in parallel, then weight is reduced, but device complexity increases
Solution Approach 1:
The control system uses a universal switching mechanism that can route commands to either EHSV or both EHSVs depending on operational mode. The same control architecture handles both normal parallel operation and backup single-valve operation, reducing the need for separate control circuits and simplifying the overall system despite having two valves.
Solution Approach 2:
The system dynamically reconfigures its operation mode based on valve availability and system demands. During normal operation, both EHSVs work in parallel; during backup operation, the system automatically switches to single-valve mode. This dynamic adaptability allows the control system to manage complexity by having a single flexible architecture rather than multiple dedicated control paths.
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 reduces actuator weight, envelope, and leakage while maintaining control of the end effector during EHSV failures, allowing continued operation at reduced power and locking the actuator in case of overpressure.
Implementation Method 1
two parallel electrohydraulic servo valves (EHSVs) each sized for full capability on its own
Implementation Method 2
The switch between the normal EHSV and the backup EHSV was via a transfer valve and a transfer EHSV/solenoid
Implementation Method 3
A first solenoid valve can be operatively connected to actuate the first transfer valve
Implementation Method 4
An actuator includes an extend chamber in fluid communication with both of the first and second extend actuator lines, and a retract chamber in fluid communication with both of the first and second retract actuator lines for extending an end effector
Data Source
Figure 1
Figure 2
AI summary
A system includes a first electrohydraulic servo valve, EHSV (102), configured to be in fluid communication with a pressure supply (104) and with a pressure return (106). The first EHSV (102) includes a first actuator extend line (114) and a first actuator retract line (112). A second EHSV (116) is configured to be in fluid communication with the pressure supply (104) and with the pressure return (106). The second EHSV (116) includes a second actuator extend line and a second actuator retract line. An actuator includes an extend chamber (126) in fluid communication with both of the first and second extend actuator lines, and a retract chamber (124) in fluid communication with both of the first and second retract actuator lines for extending an end effector when the first and second EHSVs (102, 116) pressurize the extend chamber (126), and for retracting the end effector when the first and second EHSVs (102, 116) pressurize the retract chamber (124).