WOODWARD PSG GOVERNORS
SYSTEMS OPERATION
INTRODUCTION
The Woodward PSG (Pressure compensated Simple
Governor) can operate as an isochronous or a speed
droop type governor. It uses engine lubrication oil,
increased to a pressure of 175 psi (1200 kPa) by a gear
type pump inside the governor, to give hydra/mechanical
speed control.
PILOT VALVE OPERATION
The fuel injection pump camshaft drives a governor
drive unit. This unit turns pilot valve bushing (13)
clockwise as seen from the drive unit end of the
governor. The pilot valve bushing is connected to a
spring driven ballhead. Flyweights (7) are fastened to
the ballhead by pivot pins. The centrifugal force caused
by the rotation of the pilot valve bushing causes the
flyweights to pivot out. This action of the flyweights
changes the centrifugal force to axial force against
speeder spring (5). There is a thrust bearing (9)
between the toes of the flyweights and the seat for the
speeder spring. Pilot valve (12) is fastened to the seat
for the speeder spring. Movement of the pilot valve is
controlled by the action of the flyweights against the
force of the speeder spring.
The engine is at the governed (desired) rpm when
the axial force of the flyweights is the same as the force
of compression in the speeder spring. The flyweights will
be in the position shown. Control ports (14) will be
closed by the pilot valve.
Fuel Increase
When the force of compression in the speeder.
spring increases (operator increases desired rpm) or the
axial force of the flyweights decreases (load on the
engine increases) the pilot valve will move in the
direction of the drive unit. This opens control ports (14).
Pressure oil flows through a passage in the base to
chamber (B). The increased pressure in chamber (B)
causes power piston (6) to move. The power piston
pushes strut assembly (4), that is connected to output
shaft lever (3). The action of the output shaft lever
causes clockwise rotation of output shaft (2). This
moves fuel control linkage (15) in the FUEL ON direction.
PSG GOVERNOR INSTALLED
2. Output shaft. 15. Fuel control linkage.
As the power piston moves in the direction of return
spring (1) the volume of chamber (A) increases. The
pressure in chamber (A) decreases. This pulls the oil
from the chamber inside the power piston, above buffer
piston (11) into chamber (A). As the oil moves out from
above buffer piston (11) to fill chamber (A) the buffer
piston moves up in the bore of the power piston.
Chambers (A and B) are connected respectively to the
chambers above and below the pilot valve compensating
land (10). The pressure difference felt by the pilot valve
compensating land adds to the axial force of the
flyweights to move the pilot valve up and close the
control ports. When the flow of pressure oil to chamber
(B) stops so does the movement of the fuel control
linkage.
Fuel Decrease
When the force of compression in the speeder spring
decreases (operator decreases desired rpm) or the axial
force of the flyweights increases (load on the engine
decreases) the pilot valve will move in the direction of
speeder spring (5). This opens control ports (14). Oil
from chamber (B) and pressure oil from the pump will
dump through the end of the pilot valve bushing. The
decreased pressure in chamber (B) will let the power
piston move in the direction of the drive unit. Return
spring (I) pushes against strut assembly (4). This moves
output shaft lever (3). The action of the output shaft
lever causes counterclockwise rotation of output shaft
(2). This moves fuel control linkage (15) in the FUEL
OFF direction.
7
