4
DIMENSIONS, 30 cc PUMP EDC
Dimensions of the MCV111B EDC for 30 cc Pumps in Millimeters (Inches).
1790
CONTROL
LINKAGE
9,9
(0.39)
19,3
(0.76)
166,12
(6.54)
153,42
(6.04)
131,06
(5.16)
99,06
(3.90)
44,7
(1.76)
5,6
(0.22)
8,26
(0.33)
30,99
(1.22)
32,26
(1.27)
41,66
(1.64)
81,28
(3.20)
99,57
(3.92)
7,14 DIA 6 PLACES
(0.28) DIA
8,6 REF
(0.34)
103,25
(4.07)
7,1
(0.28)
181,03
(7.13)
MANUAL OPERATOR
SAE
SERVO PORT
FITTING X1
SAE
SERVO PORT
FITTING X2
NEUTRAL
ADJUST
LOCK
NUT
PACKARD
WEATHER-PACK
CONNECTOR
OPTION
MS CONNECTOR
OPTION
THEORY OF OPERATION
A command source such as a joystick, control handle or
electronic controller applies current signals to the pilot stage
of the MCV111B Electrical Displacement Control, which
results in flow out of the pump. 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
polarized together with two pole pieces form a frame for the
magnetic bridge. At null the armature is centered in the air
gaps between the magnets’ opposing poles by the
equivalence of their magnetic forces and the null adjust
centering springs. As the input differential current rises to the
dual coils, the end of the armature becomes biased either
north or south, depending on the magnitude of the current
differential. The resulting armature movement is determined
by the amperage of control current, the spring constant and
the differential pressure feedback forces, explained 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
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 pilot stage is silicone oil filled for protection
against the environment and for proper valve operation.
The second stage of the EDC uses a unique spool-barrel
feedback arrangement that serves to separate the null
deadband from the feedback, giving both safety against null
drift and quick dynamic response to command changes.
The second stage’s null adjust is set with a feedback spring
compressed to a 16 psi threshold (measured at the center of
the hysteresis loop), which is the amount of differential
pressure required to begin to move the actuator spool one
direction or the other. The threshold is a factory setting. By
tightening or loosening the main null adjust screw, the fixed
deadband is adjusted so that the pump starts to stroke with
equal output current on either side of null.
As differential control pressure input from the pilot rises
beyond the 16 psi deadband, the spool moves in one
direction or the other, opening one of the control ports to
supply charge pressure to the pump’s servo-cylinders,
moving the swashplate. As the swashplate moves, the
linkage follows, moving the barrel in the opposite direction of
the spool’s original motion. The barrel’s feedback movement
tends to drive the spool back toward neutral through its
internal feedback spring. Oil returns from the servo cylinders
through the spool to the case.
BLN-95-8995-4
