PGEV and PGE Locomotive Governors. Manual - part 7

Manual 36703

PGEV and PGE Locomotive Governors

Woodward

The greater of two opposing forces moves the pilot valve plunger up or down.
Flyweight force tends to lift the plunger while speeder spring force tends to lower
the plunger. When the engine is on speed at any speed setting, these forces are
balanced and the flyweights assume a vertical position. In this position, the
control land on the pilot valve plunger is centered over the regulating port(s) in
the rotating bushing. No oil, other than leakage make up, flows to or from the
buffer compensation system or power cylinder. A change in either of these two
forces will move the plunger from its centered position. The plunger will be
lowered (1) when the governor speed setting is unchanged but an additional load
slows the engine and governor (thereby decreasing flyweight force), or (2) when
engine speed is unchanged but speeder spring force is increased to raise the
governor speed setting. Similarly, the pilot valve plunger will be raised (1) when
the governor speed setting is unchanged but load is removed from the engine
causing an increase in engine and governor speed (and hence, an increase in
flyweight force), or (2) where engine speed is unchanged but speeder spring
force is reduced to lower the governor speed setting. When the plunger is
lowered (an underspeed condition), pressure oil is directed into the buffer
compensation system and power cylinder to raise the power piston and increase
fuel. When lifted (an overspeed condition), oil is permitted to drain from these
areas to sump and the power piston moves downward to decrease fuel.

The buffer piston, springs, and needle valve in the hydraulic circuits between the
pilot valve plunger and power cylinder make up the buffer compensation system.
This system functions to stabilize the governing action by minimizing over or
undershoot following a change in governor speed setting or a change in load on
the engine. It establishes a temporary negative feedback signal (temporary
droop) in the form of a pressure differential which is applied across the
compensation land of the pilot valve plunger. The flow of oil into or out of the
buffer system displaces the buffer piston in the direction of flow. This movement
increases the loading on one spring while decreasing the load on the other and
creates a slight difference in the pressures on either side of the piston with the
higher pressure on the side opposite the spring being compressed. These
pressures are transmitted to opposite sides of the plunger compensation land
and produce a net force, upward or downward, which assists in re-centering the
plunger whenever a fuel correction is made.

Speed Setting or Load Increase

Increasing the speed setting or increasing load on the engine at a given speed
setting have an identical effect. In either case, the flyweights move inward
(underspeed) due to the increase in speeder spring force or, to the decrease in
centrifugal force caused by the decrease in engine speed as load is added. The
movement of the flyweights is translated into a downward movement of the pilot
valve plunger. This directs pressure oil into the buffer system, causing the buffer
piston to move toward the power cylinder. The oil displaced by the movement of
the buffer piston forces the power piston to move upward in the increase fuel
direction. The oil pressures on either side of the buffer piston are simultaneously
transmitted to the plunger compensation land with the higher pressure on the
lower side. The net upward force thus produced is added to flyweight force and
assists in restoring the balance of forces and re-centering the pilot valve plunger.

PGEV and PGE Locomotive Governors

Manual 36703

Woodward

In effect, this enables the governor to cut off the additional fuel needed for
acceleration by stopping the power piston when it has reached a point
corresponding to that amount of fuel required for steady state operation at the
new higher speed or load. As the engine continues to accelerate toward the set
speed, the compensation force is gradually dissipated to offset the continuing
increase in flyweight force. This is done by equalizing the pressures on each side
of the compensation land through the needle valve at a rate proportional to the
continued rate of acceleration. The rate of dissipation is the same as the rate of
increase in flyweight force, the pressure differential is reduced to zero at the
instant flyweight force becomes exactly equal to speeder spring force. This
minimizes speed overshoot and permits the governor to quickly re-establish
stable operation. The needle valve setting determines the rate at which the
differential pressure is dissipated and allows the governor to be "matched" to the
characteristics of the engine. The compressed buffer spring returns the buffer
piston to its centered position as the pressure differential is dissipated.

Whenever large changes in speed setting or load are made, the buffer piston will
move far enough to uncover a bypass port in the buffer cylinder. This limits the
pressure differential across the buffer piston and permits oil to flow directly to the
power cylinder. Thus, the power piston is made to respond quickly to large
changes in speed setting or load.

Speed Setting or Load Decrease

Decreasing the speed setting or load on the engine at a given speed setting are
identical in effect and cause a reverse action to that described above. The
flyweights move outward (overspeed), lifting the pilot valve plunger and allowing
oil to drain from the buffer compensation system. The buffer piston moves away
from the power cylinder, permitting oil to drain from the area under the power
piston which then moves downward in the decrease fuel direction. The
differential pressures acting across the compensation land produce a net
downward force, assisting the speeder spring in re-centering the pilot valve
plunger slightly before the engine has fully decelerated. This stops power piston
movement when it has reached a point corresponding to that amount of fuel
required for steady state operation at the new lower speed or load. Dissipation of
the compensation force in the same manner as previously described and
minimizes speed undershoot.

Compensation Cutoff

With large decreases in speed or load, the power piston moves to the "no fuel"
position and blocks the compensation oil passage between the power cylinder
and needle valve to prevent normal equalization of the compensation pressures.
This holds the buffer piston off center and increases the level of the pressure
transmitted to the upper side of the plunger compensation land. The increased
pressure differential, added to the effect of the speeder spring, temporarily
increases the governor speed setting. The governor will thus begin corrective
action as soon as engine speed drops below the temporary speed setting and
start the power piston upward to restore the fuel supply in sufficient time to
prevent a large underspeed transient. The above action is sometimes referred to
as "compensation cutoff". When the upward movement of the power piston again
uncovers the compensation oil passage, normal compensating action will resume
and stabilize engine speed at the actual speed setting of the governor.

Manual 36703

PGEV and PGE Locomotive Governors

Woodward

Due to the location of the compensation cutoff port in the power
cylinder wall, the governor/fuel rack linkage must be adjusted so the
power piston "gap" does not exceed 1-1/32 inches (26.2 mm) at idle
no load.

Speed Setting Section

(Figure 3-1)

This section consists of a speed setting cylinder, a speed setting pilot valve
plunger housed within a rotating bushing, four speed setting solenoids, a
triangular plate, and a restoring linkage mechanism.

General

The speed setting section provides a method of changing the compression
(force) of the speeder spring which opposes flyweight centrifugal force. It does
this by controlling the position of the speed setting piston in the speed setting
cylinder. When control oil is admitted to the cylinder, the piston moves
downward, compressing the speeder spring and raising the speed setting, When
oil is allowed to drain from the cylinder, the piston spring forces the piston
upward, reducing speeder spring force and lowering the speed setting. The flow
of oil into or out of the speed setting cylinder is regulated by the speed setting
pilot valve plunger in the rotating bushing. The plunger is controlled by the
solenoids which provide incremental control of speed in equally spaced steps. An
integral gear on the governor flyweight head drives the bushing through a splined
mating gear on the lower end of the bushing.

The rate of movement of the speed setting piston over its full downward stroke
(idle to maximum speed) is usually retarded to occur over some specific time
interval to minimize exhaust smoke during accelerations. This is done by
admitting governor pressure oil into the rotating bushing through an orifice which
registers with the main supply port once in every revolution of the bushing. This
retards the rate at which oil is supplied to the control port in the bushing and thus,
the rate of oil flow to the speed setting cylinder. The diameter of the orifice
determines the specific time interval which may be anywhere within a nominal
range of 1 to 50 seconds. Typical engine acceleration periods for switching and
suburban service is approximately 5 seconds; for freight or passenger service,
approximately 15 to 30 seconds; turbo-supercharged engines the timing may be
as much as 50 seconds to permit the supercharger to accelerate with the engine.

On turbo-supercharged units, the rate of movement of the speed setting piston
over its full upward stroke (maximum to idle speed) is also retarded to prevent
compressor surge during decelerations. This timing may be anywhere within a
nominal range of 1 to 15 seconds. In this case, a vertical slot in the drain land of
the pilot valve plunger registers with a second orifice in the rotating bushing once
each revolution. This retards the rate at which the oil is allowed to drain from the
speed setting cylinder.

PGEV and PGE Locomotive Governors

Manual 36703

Woodward

Speed Setting

Three of the four speed setting solenoids, A, B, and C, actuate the pilot valve
plunger by controlling the movement of the triangular plate which rests on top of
the floating lever attached to the plunger. The fourth solenoid D controls the
position of the rotating bushing with respect to the plunger. Energizing the A, B,
and C solenoids, singly or in various combinations, depresses the triangular plate
a predetermined distance for each combination. The downward movement of the
plate is transmitted through the floating lever to un-center the plunger. This
directs intermittent oil pressure to the speed setting cylinder, forcing the speed
setting piston downward to increase the Governor speed setting. Energizing the
D solenoid pushes the rotating bushing downward and opens the control port to
drain oil from the speed setting cylinder and thus decrease the speed setting. An
identifying letter will be found on the solenoid bracket adjacent to each solenoid.

Figure 3-2 is an additional aid in understanding the various governor
components. The oil passages are simplified and color coded for ease in
following the oil flow through the system. The lower half of the governor functions
to maintain a constant engine speed by controlling fuel flow to the engine
cylinders. The upper half of the governor consists of the column and cover and
internal related parts for changing governor speed setting, the control valve for
the load regulator, and shutdown and protective devices.

Advancing or retarding the throttle control from one step to the next energizes or
de-energizes the solenoids in various combinations to increase or decrease
engine speeds in approximately equal increments.

Whenever a change in speed setting is made, the movement of the speed setting
piston, downward or upward, is transmitted or fed back through the restoring
linkage and floating lever to re-center the pilot valve plunger. This stops the flow
of oil into or out of the speed setting cylinder at a position corresponding to that
speed setting.

Speed Setting Increase

When one or more of the solenoids is energized (or de-energized) by moving the
throttle to a higher step, the solenoid plungers move downward and depress the
triangular plate and in turn the floating lever. Since the right end of the lever is
attached to the lower end of the restoring link, the left end of the lever is forced
downward to un-center (lower) the pilot valve plunger. This directs intermediate
pressure oil to the speed setting cylinder which forces the piston downward to
further compress the speeder spring and thereby increase the speed setting.

The downward movement of the piston is transmitted through the restoring
linkage to the right end of the floating lever and causes it to move downward a
proportional amount. This allows the loading spring under the pilot valve plunger
to raise the plunger, with the floating lever pivoting about the triangular plate.
This action will continue until the plunger is again re-centered, stopping the flow
of oil to the speed setting cylinder at the instant the piston reaches the new lower
position corresponding to the increased speed setting.

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