Development and Verification of a Two-Stage Flow Control Servovalve Model

Abstract

Abstract A sixth-order nonlinear mathematical model of a two-stage servovalve is developed based on physical quantities, such as the flapper nozzle diameters and the stiffness of feedback wire. This model does not linearize the torque motor dynamics and the force applied on the flapper by flows out of the flapper nozzles. The model incorporates fluid compressibility, variation of spool control volumes due to spool motion, leakage, flow forces on the spool and viscous friction. The validity of the model is demonstrated by comparing its step responses with experimental results for various amplitude valve commands. The effects of flow forces on the servovalve performance are also discussed. The model is useful as a design tool since all of the parameters used in the model are physical quantities. This capability is important for analyzing and designing electrohydraulic systems since servovalves are crucial components of such systems. This nonlinear sixth-order model has a significantly smaller response error than that for the typical linear third-order model used in industry (4.1% vs. 25%).