Theory Of Operation - Danfoss MCV109A Manual

DIMENSIONS
47,50
(1.87)
MAX
71,12
(2.8) MAX

THEORY OF OPERATION

A command source such as a joy stick, control handle, or
electronic controller applies a dc current signal to the pilot
stage of the MCV109A. The input current commands the
pilot's torque motor stage, a bridge network consisting of an
armature mounted on a torsion pivot and suspended in the
air gap of a magnetic field. Two permanent magnets polar-
ized in parallel and a connecting plate form a frame for the
magnetic bridge. At null the armature is centered in the air
gap between the magnets' opposing poles by the equiva-
lence of their magnetic forces and the null adjust centering
springs. As input current rises, the end of the armature
becomes biased either north or south, depending on the
direction of the current. The resulting armature movement is
determined by the amperage of control current, the spring
constant and the differential pressure feedback forces ex-
plained below. See Internal Workings Schematic.
The magnetic bridge output, flapper torque, in turn controls
the hydraulic bridge ratio. At null, the flapper is centered
between two nozzles. Upstream from each nozzle is an
orifice which provides a nominal pressure drop when the
system is at null. Between the nozzle and the orifice on each
side is a control port. As the torque motor shifts the flapper
away from one nozzle toward the other, a differential control
pressure results, the high side being the one nearer the
flapper. Fluid pressure rises on this side and moves the
FOLLOWING
CONFIGURATIONS
ONLY AS SHOWN
3XXX
EXCEPT 33, 34
4XXX
& 36
7XXX
SERIES
8XXX
PUMPS
24,89
(.98)
REF
Dimensions of the MCV109A in Millimeters (Inches).
5
3/8 O.D. TUBE FITTING O-RING
PORT PER SAE - J514 - 9/16-18 UNF
2 PLACES. (PLUGS INSTALLED)
190,5
(7.5) MAX
flapper back towards null. When the torque output from the
motor equals the torque output from the pressure feedback,
the pilot system is in equilibrium. It is this pressure feedback
that makes the pilot a stand-alone, closed loop, pressure
control valve.
The second stage's null adjust is set with the modulating
spring compressed to the equivalent of 95 psi, which is the
amount of differential pressure required to move the actuator
spool. This is a factory setting that determines the threshold
point at which the motor will begin to destroke. By tightening
or loosening the null adjust screw, the motor can be accu-
rately phased with a pump.
As differential control pressure (C2-C1) rises beyond the 95
psi threshold, the actuator spool moves, pivoting the cross-
link about its center. The pivoting cross-link pushes the
porting spool in the opposite direction of the actuator spool.
When the porting spool has moved far enough, oil is ported
to the motor servo cylinder, moving the swashplate. As the
swashplate moves, the drag linkage follows, pivoting the
cross-link about the stationary end of the actuator spool,
driving the porting spool back to its neutral position. Because
the feedback signal is entered into the control loop after the
command has been input, response time and accuracy are
enhanced.
193,0
(7.6) MAX
NULL
ADJUST
SCREW
1445A
BLN-95-8985-1