Theoretical analysis and experimental study on two-dimensional cartridge servo valve

Since the conventional servo valve's pilot stage and power stage are in parallel placement and could not realize cartridge, a new type of two-dimensional (2D) cartridge servo valve is studied. Its pilot stage and power stage are integrated in the two degrees of freedom of the 2D spool and the torque motor is mounted coaxially with the spool at the end of the spool. To control the output flow of the servo valve, the rotational motion of the spool is driven directly by the torque motor, and then the power is amplified and the straight motion of the spool is driven by the servo screw mechanism. To improve valve's control performance, the closed loop control of the spool is realized by detecting the displacement of the spool by Linear Variable Differential Transformer (LVDT). To explore its open-loop characteristics, the mathematical models for the torque motor and 2D valve are established, computing their transfer function. Then the effects of the key parameters on the valve's dynamic characteristics are simulated and analyzed. Finally, an experiment is carried out to verify the feasibility of the valve design. The experimental results show that under the open-loop control, the hysteresis loop of the valve is about 5%; the resolution is not more than 1%; the rising time of step response is about 10 ms; and the frequency width is approximately 35 Hz at full-scale input, significantly improving the performance under close-loop condition. It is concluded that the 2D cartridge servo valve has a simple structure, small size, light weight, fast response, and high control accuracy, showing broad applicability in aerospace and aeronautics industries. © 2019, Press of Chinese Journal of Aeronautics. All right reserved.