Abstract: A servo valve direct driven by piezoelectric actuator using hydraulic amplification is researched. It takes advantage of the higher bandwidth and larger flow rate. A new hydraulic displacement amplifier structure is proposed to aim at the smaller displacement output and larger force output of piezoelectric(PZT). The structure is composed of input piston with larger area, output piston with smaller area and hermetic chamber. The larger stroke multilayer piezoelectric actuator is served as the drive element that drives the input piston with larger area of the hydraulic amplification. The change of pressure and volume drives the output piston directly connected to the spool to produce amplified displacement, which drive the spool to move. To satisfy the demand of sealing and low load, a diaphragm with flexure hinge structure is used for the piston with larger area. The structure and parameter is optimized by finite element method. Piezoelectric direct drive servo valve prototype is trial-manufactured and tested. The simulation results show that the displacement magnification times is 9, the governing error of valve spool is less than 1%, the bandwidth is up to 550 Hz. The flow curve obtained by experiment show the flow rate can reach to 17 L/min at pressure of 7 MPa.

Key words: Direct drive servo-valve, Finite element method, Flexure hinge, Hydraulic amplification, Piezoelectric ceramic