Identification and Modelling of Some Electrohydraulic Servo-Valve Non-Linearities

Abstract

An experiment is designed to investigate electrohydraulic servo-valves with mechanical feedback, excluding the effects of lap conditions and flow forces on the spool. Equilibrium of the armature–flapper assembly is modelled using exact expressions of the decentering magnetic torque on the armature and the hydraulic reaction on the flapper. Evidence is furnished that the feedback wire stiffness must not be constant as it is usually assumed. The parameters used to describe this hitherto unidentified non-linearity are accurately determined by computer simulation. This phenomenon is furthermore found to account for anomalies observed in the no-load flow gain characteristics of similar valves. Thus, a new criterion for quality and performance of electrohydraulic servo-valves could be established. Derivation of the stall-pressure gain characteristics of first-stage hydraulic amplifiers including a drain orifice is given in the Appendix.