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Operation of a Servovalve in aHydraulic Actuator
December R. Cowen
University of Illinois - UC
March 6, 2002
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Outline
General Uses of Hydraulic Actuators
Basic Hydraulic System Operation
Servovalve Location and Components
Servovalve Operation
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General Uses of Hydraulic
Actuators
Static, Psuedodynamic, and Dynamic Testing
Load or Position Control
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Basic Hydraulic System
Operation
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Servovalve Location
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Role of Servovalve in System
Servovalve reacts to an input signal from a valve
driver or valve controller by porting hydraulic fluid
in a direction and amount determined.
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Servovalve Components
Torque Motor
Two Stages of Hydraulic
Regulation
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Servovalve Components
Torque Motor
Coils
Upper and Lower Pole Pieces
Armature
Two Magnets
Converts input signal from a valve driver or valve controller
into a physical movement for the armature
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Servovalve Components
Second Stage of Regulation
A spool that controls the hydraulic fluid flow to and from
actuator A feedback wire which provides the closed loop control
between the armature and spool
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Servovalve Operation
The control signal energizes the coils causing the armature to
rotate.
The armature rotates clockwise or counter clockwisedepending upon the polarity of the signal. The rate at which the
armature rotates is dependent upon the magnitude of the signal.
As the armature/flapper assembly rotates it controls the flow
of hydraulic fluid from the two nozzles.This is an inversely proportional manner; as the flow from one
nozzle increases, the flow from the other decreases.
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Servovalve Operation
This resultant change in flow of hydraulic fluid creates a
differential pressure which is used to position the second stage
spool. As the spool moves in response to the differences in pressure,
the feedback wire exerts an opposite torque on the
armature/flapper assembly trying to re-center the flapper.
The spool will continue to move until the feedback wire torqueequals the control signal torque and re-centers the flapper.
Now both nozzle openings are equal.
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Servovalve Operation
This causes the pressure at the ends of the spool to equalize
and then the spool will stop.
For any level of input control signal there will be a
corresponding spool position dependent upon the magnitude and
polarity of the control signal.
Therefore, the position of the spool controls the amount, rate,
and duration of flow to the actuator.
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Servovalve Operation
When the control signal decreases to zero, the flapper
creates a pressure imbalance to the opposite end of the
spool.
In response to the pressure imbalance, the spool movesuntil the pressure is equalized. The spool moves to a
position that stops the flow of the hydraulic fluid to the
actuator.
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Acknowledgements
Greg Banas, Lab Director for NCEL
MTS Training Manual