Specifications

Technology
NOZZLE FLAPPER TORQUE MOTOR DESCRIPTION
An electrical command signal (flow rate set point) is applied to
the torque motor coils and creates a magnetic force which acts
on the ends of the pilot stage armature.This causes a deflection
of armature/flapper assembly within the flexure tube. Deflection
of the flapper restricts fluid flow through one nozzle which is
carried through to one spool end, displacing the spool. [Spool
actuation relative to valve operation is detailed on page 17]
Movement of the spool opens the supply pressure port (P)
to one control port while simultaneously opening the tank port
(T) to the other control port.The spool motion also applies a
force to the cantilever spring, creating a restoring torque on the
armature/flapper assembly.
Once the restoring torque becomes equal to the torque
from the magnetic forces, the armature/flapper assembly moves
back to the neutral position, and the spool is held open in a state
of equilibrium until the command signal changes to a new level.
In summary, the spool position is proportional to the input
current and, with constant pressure drop across the valve, flow to
the load is proportional to the spool position.
SERVOJET
®
DESCRIPTION
The ServoJet
®
pilot stage consists mainly of torque motor, jet pipe
and receiver.A current through the coil displaces the jet pipe
from its neutral position.This displacement, combined with the
special shape of the jet pipe, directs a focused fluid jet towards
one side of the receiver.
The jet now produces a pressure difference across the ends
of the spool.This pressure difference causes a spool displacement
which, in turn, results in control port flow.The pilot stage drain is
through the annular area around the nozzle to tank.
LINEAR FORCE MOTOR DESCRIPTION
Moog’s Direct Drive Valves use our proprietary linear force
motor. A linear force motor is a permanent magnet differential
motor.The permanent magnets provide part of the required
magnetic force.The linear force motor has a neutral mid-position
from which it generates force and stroke in both directions. Force
and stroke are proportional to current.
High spring stiffness and the resulting centering force, plus
external forces (i.e. flow forces, friction forces due to contamina-
tion), must be overcome during outstroking. During backstroking
to center position, the spring force adds to the motor force and
provides additional spool driving force making the valve less
contamination sensitive.The linear force motor requires very low
current in the spring centered position.
ELECTROHYDRAULIC VALVE PILOT STAGE AND
SPOOL ACTUATION TECHNOLOGIES
PlugArmatureCoilBearing
Permanent
Magnets
Cable
Hole
Centering
Springs
Annular
Area
Nozzle
Receiver
Jet
Pipe
Feedback
Wire
Nozzle
Flapper
Armature
Coils
Technology
Technology
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