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 3161 GOVERNOR
SYSTEMS OPERATION
movement of the power piston, and the output shaft, is
Decrease In Speed Setting
now stopped.
When the speed setting shaft is turned
The continued decrease of engine speed to its
counterclockwise, the speed setting of the governor is
steady-state setting, results in a continued increase in
decreased. The low idle screw limits the low speed
downward force of the speeder spring on the pilot valve
setting of the governor. As the speed setting shaft is
plunger as the ballhead flyweights move in. At the same
turned counterclockwise, the force of the speed setting
time, the pressure difference on each side of the buffer
lever on the floating lever is removed. This lowers the
piston (and at top and bottom of the compensation land)
compression of the speeder spring. Centrifugal force
is being released by the flow of oil through the needle
from the ballhead flyweights lifts the pilot valve plunger to
valve orifice. This controlled discharge allows the buffer
open the control port in the rotating bushing. Control oil
piston to return slowly to its normal, "centered" position.
under the power piston now drains to the sump and lets
The speeder spring continues to push down on the pilot
the power piston move down. The output shafts are
valve plunger until the spring force and ballhead flyweight
turned in the "decrease" fuel direction and the engine
force become equal. At the same time the controlled
speed is decreased.
reduction of the pressure difference on the two sides of
the compensation land occur exactly at the same rate
Before the engine gets to the new set speed, the
(while the pilot valve plunger remains centered) until the
compensation system starts to move the pilot valve
engine is again at the on-engine speed condition at the
plunger back to its center position and put the governor
new speed setting.
under stable control as follows.
When the pilot valve plunger is lifted the oil
NOTE: An increase or decrease in engine load will give
under the power piston is released to drain back to the
the similar governor movement as an increase or
governor sump. Pump pressure oil on the bottom of the
decrease in governor speed setting.
buffer piston now forces the buffer piston up. The oil
above the buffer piston then puts a force on the top of
Shutdown
the power piston to move the power piston down.
The limit/shutdown pilot valve is located in the
The movement of the buffer piston up increases
pump oil pressure supply line to the ballhead pilot valve.
the compression of the upper buffer piston spring. The
When the engine shutdown system is activated, the
force of the upper spring works against the buffer piston
limit/shutdown rod pushes the limit/ shutdown pilot valve
movement and this results in a small increase to the
plunger below the supply passage. This drains oil from
pump oil pressure on the lower side of the buffer piston
the supply to the ballhead pilot valve plunger. Control oil
and on the top surface of the pilot valve plunger
from under the power piston now drains past the control
compensation land. This small increase is greater than
land of the pilot valve plunger. The power piston then
the pressure sent to the bottom surface of the
moves down and the output shaft is turned in the
compensation land. This pressure difference on the two
"decrease fuel" direction.
As the engine speed
sides of the compensation land makes a force (greater at
decreases, the ballhead flyweights move in and this
the top) to push the pilot valve plunger back down to the
lowers the ballhead pilot valve. Oil from under the power
center position.
piston is now drained to the governor sump at a faster
rate. As the power piston continues to move down, the
When the output shaft has turned far enough to
output shaft is turned to the shutdown position until the
satisfy the new fuel setting, the force of the pressure
engine is stopped.
difference on the compensation land puts the pilot valve
plunger in its center position (even though the engine
speed is not yet completely back to normal). The
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