Hyrdaulic Systems Simulation Tool

 Contents

 

 

Valves

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.

 

 

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