The electrohydraulic servo valve (EHSV) is a core component of servo control systems. Due to its advantages such as high level of control precision, quick response, light weight, small volume and high immunity to load variations, EHSV has been applied in many fields, such as astronavigation, aviation, navigation, and military equipment. EHSV is one of the most failure prone components, and has a direct and significant impact on the performance and reliability of the entire servo control system. Thus, it is very important to analyze the failure mode, failure effects, failure mechanism and failure rate of EHSV.
The key driving factors for the electro hydraulic servo valves are growing demand for quality and smart control. There have been many design innovations as it has been implied across the sectors to control air/fluid flow. The aerospace industry was the driver in earlier times but growing industrial use has been on the higher side in the recent times.
What are Electro Hydraulic Servo Valves?
The term servo valve traditionally refers to mechanical feedback valves, where a spring element (feedback wire) connects a torque motor to the main-stage spool. Servo valve has come to mean a valve whose main spool is positioned in proportion to the electrical input to the valve, where the spool movement is achieved through internal hydraulic actuation. The size of metering orifices is controlled by the spool movement thus enabling the valve to control flow; however this flow is dependent on the pressure difference across the orifice unless some form of pressure compensation is used. Spool displacement causes the wire to impart a torque onto the pilot-stage motor. The spool keeps position when the torque from an electromagnetic field induced by the current through the motor coil equals torque from the feedback wire's deflection. These two-stage valves contain a pilot stage or torque motor, and a main or second stage. Sometimes the main stage is referred to as the power stage and there may be more than two stages also involved in regulation.
A Hydraulic Servo Valves is a device that maneuvers the flow of fluid (oils) in response to an electrical input signal or command to control position, velocity, pressure or force in some type of machine or device (usually through a piston or cylinder). Servo Valves are closed-loop control devices that can be single stage, two-stage or three stage designs.
Flow control servo valves produce hydraulic flow output proportional to electrical current input. p/Q valves control flow and regulate pressure (upper or lower limiting pressure) and can be used for both pressure regulation as well as applying a pressure-limit. They are used to regulate emissions, increase productivity and reliability at the same time. More and more functionalities are controlled by software that reduces complexity and enables regional design, manufacturing and customer specific variants.
What are the major applications for Electro Hydraulic Servo Valves?
Embryonic electro hydraulic servo valves where developed for military applications in the Second World War, such as for automatic fire control (gun aiming).Such servo valves typically consisted of a solenoid driven spool with spring return. These were able to modulate flow, but with poor accuracy and a slow response.
Servo valve development in the 1950’s, was largely driven by the needs of the aerospace industry (particularly missiles). The technical status and available products at that time are well documented in a series of reports commission by the US Air Force.
The electro hydraulic servo valve finds applications in wide range of industries such as steel industry, power industry, chemical industry, construction sector and still more.
Market Research and Market Trends of Electro Hydraulic Servo Valves Ecosystem
- There has been a thorough research on alternative valve designs for the improved response, reducing leakage from the valves by various manufacturers and also to achieve ease in manufacturability process.
- Most investigations have involved new ways of actuating the spool, often using active materials such as piezoelectric crystals have been used on certain experimental models to achieve better dynamic response. It is difficult to use them because of high susceptibility to vibration, temperature changes, and electrical noise and because of the difficulty in obtaining sufficiently large displacements from the crystals.
- Magnetostriction is a material phenomenon which can be used to create a ‘smart‘ actuator. Magnetostrictive spool valve is another way to actuate valves action. The challenges for this technology introduction to actuate the valves are similar to piezoelectric actuation, including limited displacement, hysteresis, and temperature sensitivity.
- The torque motor still finds applications in providing an alternative, although there have been breakthroughs in piezoelectric actuator technology, including drive electronics and hysteresis compensation methods. There are other reliable options available such as electronic automation controls which pose a tough competition to valve market.
- Many manufacturing constraints for e.g. in designing valve bodies and other hydraulic components are not present due to additive manufacturing, particularly where manufacturing volumes are not too large (such as in aerospace). These provides a constraint free environment to innovators to further research and develop new ways to implement these motors and keeps the window open for new manufacturing technologies to be exhibited in future.
- A further continuing trend in electro hydraulic servo valve market is increased valve intelligence. Integration of self-tuning functions, condition monitoring, and increased communication capability are continuously being adopted in industrial application side of the valves and are now being incorporated into aerospace field also.
Who are the Major Players in Electro Hydraulic Servo Valves market?
The key companies to the market mentioned in report include Moog Inc., Bosch Rexroth AG, Parker Hannifin Corporation, Honeywell International Inc., Eaton Corporation Plc, Woodward, Inc., Voith GmbH, Schneider Kreuznach, Aviation Industry Corporation of China (AVIC), Oilgear Company
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