1.1 Working principle of electro-hydraulic servo valves
The schematic diagram of an electro-hydraulic servo valve is illustrated in Fig. 1. This electro-hydraulic servo valve consists of two stages, first stage is double nozzle–flapper valve which consists of a toque motor, a flapper, two nozzles, and a feedback spring, and the second stage is a precision ground 4 way spools. Fig. 1.
Schematic diagram of a two-stage electro-hydraulic servo valve.
The function of the nozzle–flapper valve driven by the torque motor through electrical signals is a hydraulic amplifier putting out a large hydraulic signal to control the position of the spool. Two variable throttle orifices are formed by the annular area between the nozzles and the flapper when the
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The total displacement of the feedback spring is xg − (r + b)θ – xv, and thus the force produced by the feedback spring can be given as:
Ff=Kf[(r+b)θ-xg+xv] (10) where Ff is the force produced by the feedback spring and kf is the stiffness of the feedback spring.
Apply Newton’s second law to the armature–flapper assembly. Equilibrium equations of torque and force on the armature–flapper assembly can be described as:
(11)
where J is the moment of inertia of the armature–flapper assembly, Br is the damping coefficient for rotation of the armature–flapper assembly, Tnozzle is the torque produced by the net flow force, m is the mass of the armature–flapper assembly, and Bt is the damping coefficient for translation of the armature–flapper assembly.
Changing the form of Eq. (11), the torque-motor stage dynamics can be written as a state-space equation:
(12) where , and p2 is the pressure on the right side of the spool.
Mathematical model of double nozzle-flapper valve
When the flapper deflects a displacement xg − rθ from the neutral position, the flows through the nozzles at both sides are given by
...Modelling: Rigging Patterns - The Carracks and Caravels." Jan's Sites: Navigation. N.p., 8 Mar. 2012. Web. 24 Nov. 2013.
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