PGEV and PGE Locomotive Governors. Manual - part 10

Manual 36703

PGEV and PGE Locomotive Governors

Woodward

Lube Oil Pressure Shutdown at Alarm

(See Figure 3-4)

Engine oil pressure is directed to the oil-pressure diaphragm. The shutdown-
valve plunger is connected to the diaphragm which has three forces acting on it;
load-spring and engine-oil pressures act to move it to the right, governor speed-
setting-servo oil acts to move it to the left. Normally, load-spring and engine-oil
pressures hold the diaphragm and shutdown-valve plunger to the right, permitting
oil to the left of the shutdown piston to drain to sump. When engine lube-oil
pressure drops below a safe level, speed-setting-servo oil pressure (which is
dependent on the speed setting and on the rate of the speed-setting servo
spring) overcomes the load spring and engine-oil pressure forces and moves the
diaphragm and shutdown-valve plunger to the left. Governor pressure oil is
directed around the shutdown-valve plunger to the shutdown piston and moves it
to the right. The shutdown piston moves the inner spring and shutdown plunger
to the right. The differential piston allows a high engine-lube oil-pressure trip
point without a corresponding increase in the speed-setting-servo oil pressure.
The engine-lube oil pressure required to initiate shutdown is increased. When the
shutdown plunger moves sufficiently, it trips the alarm switch.

In addition, oil trapped above the governor speed-setting-servo piston flows
around the smaller diameter on the left end of the shutdown plunger and drains
to sump. This action allows the speed-setting-servo spring to raise the speed
setting servo piston. When the piston moves up sufficiently, the piston rod lifts
the shutdown nuts and rod. The shutdown rod lifts the governor pilot-valve
plunger. When it is lifted above its centered position, oil trapped below the power
piston drains to sump and the power piston moves to the fuel off position

The shutdown plunger must be pushed back in to restart the engine
except on modulating governors.

Adjustment of the spring seat in the field is not recommended. This adjustment
biases the lube-oil-pressure required for shutdown. Adjust the spring seat on a
test stand during testing after an overhaul. No further adjustment should be
necessary.

Water Pressure Shutdown at Alarm

A water box monitors engine water pressure to shut down the engine when water
pressure is too low. This device operates like the Lube Oil Shutdown device
described above except that low water pressure initiates shutdown of the engine.

Bypass Valve

Governor pressure oil is supplied to the shutdown piston in one of two ways,
depending on the speed setting. At rated speed settings, the bypass valve is
moved down off its seat by the speed-changing mechanism. Governor pressure
oil passes directly to the shutdown piston and immediately initiates engine
shutdown in the event of lube-oil failure.

PGEV and PGE Locomotive Governors

Manual 36703

Woodward

Figure 3-4. Lube Oil Pressure Shutdown and Alarm

Manual 36703

PGEV and PGE Locomotive Governors

Woodward

When starting and at idle speeds, the bypass valve is closed and governor
pressure oil travels through an intermittent-flow orifice in the rotating speed-
setting-pilot-valve bushing. With each rotation of the bushing, a slot in the
bushing registers with an oil-supply passage in the governor column and a hole
in the adjustment sleeve. Thus, intermittent pressure oil is passed to the
shutdown-valve plunger. The adjustment sleeve may be turned (by readjusting
the time-delay pointer) so the cross-sectional area of the oil passage is increased
or decreased. Thus, the volume of oil supplied with each rotation of the bushing
is increased or decreased. Turning the pointer cw increases volume and
decreases the time required to pass sufficient oil to initiate shutdown.

Fuel Limiter

General

The fuel limiter is an auxiliary system designed primarily for use on Woodward
PG load control governors installed on turbo-supercharged locomotive engines. It
is used with manifold air pressure as a reference. This governor is equipped with
a load-control-overriding solenoid and provisions for fast unloading.

The function of the load control is independent of the fuel limiter. They are related
only through an optional common reference to manifold air pressure. Figure 3-6a
illustrates the basic fuel limiter, the load-control override and bias linkages
installed on a locomotive governor equipped with load control, an overriding
solenoid, and solenoid speed setting.

During acceleration, on turbo-supercharged engines, it is possible to supply more
fuel to the engine than can be burned with the available air. This results from the
normal lag of supercharger speed, and consequently manifold air pressure
decreases with respect to engine speed.

The fuel limiter restricts the movement of the governor power piston toward the
increase-fuel direction, limiting engine fuel during acceleration as a function of
manifold air pressure (an approximation of the weight of air available at any
instant). Fuel limiting improves the fuel-to-air ratio and, during acceleration,
allows complete combustion. This improves acceleration and reduces smoke.
Fuel limiting also protects the engine if the turbo-supercharger fails or reductions
in engine air supply occur.

Figure 3-5 illustrates the unlimited, limited, and steady-state fuel schedules for a
typical engine together with a typical acceleration transient from one steady-state
condition to another.

Figure 3-5. Typical Limited Acceleration Fuel Schedule Curve

PGEV and PGE Locomotive Governors

Manual 36703

Woodward

Description

The fuel limiter (Figure 3-6a) is essentially a floating lever, a bellcrank, a
pressure sensor and cam, and a hydraulic amplifier together with a feedback
lever and a fuel-limit lever. The right end of the floating lever is connected to the
tailrod of the governor power piston and pivots about one leg of the bellcrank.
The left end of the floating level rests on the right end of the hydraulic-amplifier
feedback lever. The position of the bellcrank, and therefore the position of the
floating-lever pivot point, is determined by the position of the fuel-limit cam.
Raising the floating-lever pivot as manifold air pressure increases, allows the
governor power piston to move upward a proportionally greater distance before
fuel limiting occurs.

The pressure sensor is a force-balance device consisting of an inlet check valve,
an orifice-pack restriction, a piston-and-cam assembly, a restoring spring, a
bleed valve, and either a gauge-pressure or an absolute-pressure bellows
arrangement. The sensor establishes a corresponding piston (and cam) position
for each different manifold air pressure. The relationship between manifold air
pressure and governor power-piston position (fuel flow) where limiting occurs is
determined by the profile and angular tilt of the cam. Cam profiles are either
linear or non-linear depending on engine and turbo-supercharger characteristics.
The hydraulic amplifier is a pilot-operated, single-acting hydraulic cylinder. The
amplifier provides the force necessary to overcome the resistance of the speeder
spring, lift the shutdown rod and re-center the governor pilot-valve plunger when
the fuel limit is reached for a given manifold air pressure.

Operation

Pressured oil enters the fuel limiter through the inlet check valve. Oil is directed
to the upper side of the sensor piston and through the orifice-pack restriction to
the under side of the sensor piston. The inlet check valve prevents siphoning of
the oil from the limiter housing during shutdown periods and omits the time lag to
refill the orifice pack and piston cylinder. This prevents the sensor piston from
going to maximum-fuel position during start-up. The bleed valve regulates the
rate of oil flow from the area under the sensor piston to sump as a function of
manifold air pressure. When the bleed valve bypasses a greater flow of oil from
this area than is admitted through the orifice pack, the sensor piston moves
downward. Conversely, reducing the bypass-oil flow to less than that admitted
causes the sensor piston to rise. When the inflow and outflow of oil are equal, the
piston remains stationary.

The sensing element of the absolute-pressure-type fuel limiter consists of two
opposed, flexible, metallic bellows of equal effective area. The upper bellows is
evacuated, and the lower bellows senses manifold air pressure. A spacer joins
the bellows at the center while the outer end of each bellows is restrained to
prevent movement. Manifold air pressure acting internally on the sensing bellows
produces a force causing the spacer to move toward the evacuated bellows. The
evacuated bellows provides an absolute reference, therefore, the sensing-
bellows force is directly proportional to the absolute manifold-air pressure.
Movement of the bellows spacer is transmitted through an output strap and a
bleed-valve pin to the bleed-valve diaphragm.

The sensing element of the gauge-pressure-type fuel limiter consists of a single,
flexible, metallic bellows. Movement of the gauge-pressure bellows is transmitted
directly to the bleed-valve pin. The bellows force tends to open the bleed valve
while the restoring-spring force tends to close the valve.

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