Hyrdaulic Systems Simulation Tool |
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Eight different types of valves are available:
Each valve has the following inputs and outputs:
the valve current
the system pressures (is a two elements vector), coming from the accumulator block
the actuator pressures (is a two elements vector for 4 way valves), coming from the actuator block.
the valve input flows (is a two elements vector)
the valve controlled flows (is a two elements vector)
The servovalves dynamic is modelled on the basis of the MOOG catalogue schematic:
where
C1 |
is the torque motor gain [mm/mA] |
kw |
is the feedback wire stiffness [Nm/m] |
kf |
is the armature stiffness [Nm/m] |
sigma |
is the first stage natural frequency [rad/s] |
zita |
is the first stage damping factor |
C2 |
is the first stage flow gain [m3/s/m] |
A |
is the second stage spool end area [m2] |
It must be noted that the following expression shall be ever verified:
In addition the following parameters shall be defined:
xsm |
the maximum spool displacement [m] |
cd |
the discharge coefficient (0,61 is a good value for servovalve) |
w |
the port width [m] |
hs |
the radial clearance [m] |
ovss |
the overlap on supply side [m] |
ovrr |
the overlap on return side [m] |
kfs |
the first stage flow coefficient (ratio between first stage nominal flow and the square of the nominal pressure [(m3/s)/rad(Pa)] |
bias |
the bias current [mA] |
hist |
half hysteresis current band [mA] |
The port width can be evaluated on the basis of the following expression:
where
Q |
is the nominal flow |
D P |
is the nominal pressure drop through the valve |
r |
is the fluid density |
In the following table, possible values for MOOG servovalves Series 30, 31 and 32, relevant to a nominal current of 10 mA, are reported.
Description |
Unit |
Series 30 |
Series 31 |
Series 32 |
torque motor gain |
mm/mA |
2.825e-3 |
2.825e-3 |
2.825e-3 |
feedback wire stiffness |
Nm/m |
74.15 |
74.15 |
63.55 |
armature stiffness |
Nm/m |
378 |
511.5 |
559.6 |
first stage natural frequency |
rad/s |
5114 |
5114 |
4241 |
first stage damping factor |
|
0.4 |
0.4 |
0.4 |
first stage flow gain |
m3/s/m |
0.0908 |
0.096 |
0.1129 |
second stage spool end area |
m2 |
1.68e-5 |
1.68e-5 |
3.4193e-5 |
maximum spool displacement |
m |
0.381e-3 |
0.381e-3 |
0.445e-3 |
If the above data are not available, it is possible to use the simplified blocks that require only data reported on the valve catalogues.
The proportional valves can have a different gain between input current and spool position for positive or negative current. The pressure regulated proportional valve model is based on the following differential equilibrium equation:
with
x |
spool position |
s |
natural frequency |
z |
damping |
i |
current |
p |
regulated pressure |
ki |
current coefficient |
kp |
pressure coefficient |
The block ‘Line resistance’ substitutes the valve block in the hydraulic circuit where a variable displacement motor is directly connected to the supply pressure. The inputs and the outputs are the same of the other valves.