TM 5-6115-465-34
TO 35C2-3-446-2
NAVFAC P-8-625-34
TM 06858B/06859D-34
to the
average current from the transistor and moves
4-7.1
UNIT
(MEP-114A).
GOVERNOR CONTROL
in proportion to position the engine throttle. The
output transistor is switched on-and off to reduce
General.
a.
power dissipation.
(1) The electric governing system is a speed
b.
Malfunction.
(frequency) sensing system used to maintain constant
engine speed and generator output frequency during
The following procedures are to be performed with
periods of unchanging load and when load additions
the Governor Control Unit in the generator set.
or deletions occur. The system consists of a
control unit, magnetic pickup and an electric
(1) Connect the breakout cable between
throttle actuating unit. The engine speed signal
wiring harness plug P17 (1, figure 4-30.2) and the
is obtained from a magnetic pickup mounted in the
flywheel housing in close proximity to the flywheel
electric governor.
ring gear. The frequency of the pickup signal is
(2) Using a
digital voltmeter, make the
proportional to engine speed. Figure 4-30.1 shows
voltage readings
in table 4-4 at the breakout
the functional theory of operation.
cable plug. All
readings are measured between
the terminal and
ground. Terminals F, G, H and T
(2) The control unit has four distinct cir-
are ground.
cuits; pickup signal amplifier, frequency reference
oscillator, phase comparator and output circuit.
c.
Removal.
(a) The Frequency Reference Oscillator is
voltage controlled. The frequency setting Is
(1) Disconnect electrical connector P17
(1, figure 4-30.2).
adjusted by applying zero to 10 volts at the
Frequency Reference Oscillator input. The internal
(2) Remove 4 hex head screws (2), lock
frequency adjust provides this voltage setting when
washers (3) and nuts (4).
the control unit is in operation. The Reference
Oscillator does not maintain a constant frequency.
(3)
Remove
the
control
unit.
It deviates from its nominal frequency as the engine
speed changes during load changes. The Reference
d.
Installation.
Oscillator is forced by the Phase Comparator to
track the amplified pickup signal representing
Install the Governor Control Unit in reverse order
engine speed. The voltage representing speed
of removal procedures.
error is the amount of voltage required to drive
the Reference Oscillator off frequency in propor-
e. Adjustment Procedure.
tion to the engine speed deviation.
(1) Disconnect the actuator linkage rod from
(b) The Phase Comparator Circuit receives
the engine fuel shutoff lever.
signals from the Pickup Signal Amplifier and the
Reference Frequency Oscillator and compares the
(2) P1 ace the generator set START-RUN-STOP
difference in frequency. The Phase Comparator
switch (located on the generator set control panel)
measures the amount the engine signal is ahead
in the RUN position.
or behind the Reference Oscillator signal. Its
voltage output is used to force the Reference
(3) Place the generator set BATTLE SHORT
Oscillator to the same frequency as the signal
SWITCH (located on the generator set control panel)
from the engine. The Phase Comparator output
in the ON (override) position.
is proportional to the speed error. The gain
control is used to couple the Phase Comparator
(4) Beginning at the fully counterclockwise
output to the Reference Oscillator. By increas-
position, rotate the engine fuel shutoff lever in
ing the coupling, a small voltage change from
a clockwise direction until a slight resistance is
the Phase Comparator represents a large frequency
felt; hold the lever in this position.
change and vice-versa.
NOTE
(c) The Output Circuit allows governing by
introducing a temporary drop during a load change
This resistance Is the fuel Injection
for stability purposes. It has an adjustable means
pump's internal governor linkage hook
to control the magnitude and time constant of the
engaging the metering valve arm.
drop to match the dynamic characteristics of the
engine. The output current switching portion of
(5) Move the actuator lever to the "full fuel"
the circuit provides current to drive the actuator.
position. This is the direction against the spring
The output transistor is switched on and off at a
resistance (fully counterclockwise).
frequency of 200 Hz. This is above the natural
frequency of the actuator. The actuator responds
4-40.1
Change 5
