Electrohydraulic servovalves are compact, accurate, broad-bandwidth modulating valves, which are widely used in several industrial applications that need high power and rapid response. Electrohydraulic servovalves can proportionally transform electric analog or digital input signals into stepless hydraulic output signals and they can be single-stage or two-stage servovalves. The first stage (pre-stage) of such servovalves may assume a variety of forms, such as a sliding spool, a nozzle-flapper, a jet-pipe and a deflector-jet.
The present designs of pilot operated servovalves are either of a nozzle-flapper type or of a jet pipe type, and the design aspects and various configurations of servovalves, particularly of a nozzle-flapper type, are available in many references.
However, there have been few studies on the deflector-jet type servovalves. Furthermore, no detailed design approaches and modeling of a deflector-jet type servovalve have been reported so far. Conventional design methods for structural parameters of the fluidic amplifier in the deflector-jet servovalve (DJSV) are confined in their applications due to the lower resolution and narrower working bandwidth of the deflector-jet type servovalve.
Hence, it is very important to develop a new type of electro hydraulic servovalve that has more ideal characteristics. To improve the characteristics of resolution and working bandwidth of DJSV, the most reasonable flow amplification coefficient and pressure amplification coefficient of a fluidic amplifier should be obtained, by properly determining the structural parameters of fluidic amplifiers in the pre-stage.
In order to obtain the most ideal coefficients (pressure amplification coefficient and flow rate amplification coefficient) of fluidic amplifier in the DJSV, Pang In Ho, a researcher at the Robotics Institute, conducted a computer simulation of the effects of the geometric parameters of a fluidic amplifier on the two coefficients.
First, he decided that the important geometric parameters which give the greatest effect on the characteristics of fluidic amplifier are the area and shape of the returning channel of receive ports. Then, he studied the characteristics of the fluidic amplifier, while changing the area of the discharging channel by changing its height.
He built 3D and fluid models for the fluidic amplifier in the DJSV using SolidWorks. He used ANSYS CFD 15.0 to solve the 3D continuity and momentum equations for incompressible flows. The results showed that the pressure amplification coefficient was Kp≈25MPa/mm and the flow rate amplification coefficient was KQ≈0.127L/s·mm-1, which means better sensitivity and better linearity.
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