Fuel then goes through the center passage of
plunger (6) and the lower port during the remainder of
the downstroke. This sudden release of pressure as the
lower port is opened causes the fuel to hit the spill
deflector with a high force. The spill deflector gives
protection to the injector housing (nut) from erosion
(wear) because of the force of the released fuel. On the
return (UP) stroke, the chamber inside the injector barrel
is filled with fuel again.
The plunger can be turned by rack (5) at the
same time it is moved up and down by rocker arm (2).
The upper section of the plunger has a flat side that fits
in the gear, which is engaged with the rack. The plunger
slides up and down in the gear, which also has a flat side
on its inside diameter. The flat sides let the parts turn
together. The rack is engaged with the gear.
(Rocker Shaft Removed for Photo Illustration)
1. Injector. 3. Bellcrank. 5. Rack.
When the rack moves, it turns the plunger
through the gear. The rotation of plunger (6) controls
injection timing and the fuel output of the injector.
Rotation of the plunger changes the relation of the
The injector is held in position by clamp (3).
plunger scrolls to the ports in the barrel, and this
Fuel is injected when rocker arm (2) pushes the top of
increases or decreases the length of the effective stroke
the injector down. The movement of the rocker arm is
and the point at which injection takes place.
controlled by the camshaft through lifter assembly (7)
and push rod (4). The amount of fuel injected is
When rack (5) is moved all the way in against
controlled by rack (5). Movement of the rack causes
the injector body, no injection takes place during the
rotation of a gear fastened to plunger (6). Rotation of the
downstroke of the plunger. This is the fuel "SHUT-OFF"
plunger changes the effective stroke (that part of the
position. A small amount of rack movement "OUT" from
stroke during which fuel is actually injected) of the
the injection body is used as a "NO FUEL" movement or
"SHUTOFF" position for governing purposes. This "NO
FUEL" distance starts at the "ALL-THE-WAY-IN" position
Injection timing is a product of two factors; the
of the rack, and ends when the lower scroll opens the
angular location of camshaft (8) and the location of
lower port and the upper scroll closes the upper port.
plunger (6). The angular location of the camshaft is
Movement of the rack "OUT" from this point in the fuel
controlled by the camshaft drive gears at the rear of the
"ON" direction, gives an interval in the plunger stroke
engine. The location of the plunger can be adjusted with
when both ports are closed by the plunger and injection
takes place. As the rack is moved farther "OUT" in the
fuel "ON" direction, the quantity of fuel during the
injection stroke increases until a maximum is available at
full rack movement.
When the plunger is at the top of its stroke, fuel
flows from the fuel supply chamber, around the injector
The scrolls on plunger (6) are used to time the
and through both the lower and upper ports of the barrel.
start of injection and set the amount of fuel per injection
As plunger (6) is moved down by rocker arm (2), fuel is
stroke. The scrolls can change the start of injection in
pushed back into the supply chamber through the lower
relation to the engine piston position and the length of
port. The fuel can now go up through a passage in the
the effective stroke in relation to the different engine
center of the plunger and out through the upper port of
loads. The start of injection can be retarded (made later)
the barrel. As the lower port is closed by the end of
with a decrease or increase in injector output according
plunger (6), fuel can still flow through the upper port until
to the engine needs.
it is closed by the upper scroll on plunger (6). At this
point, injection starts and the effective stroke begins.
During the fuel injection stroke, fuel passes from
During the effective stroke, fuel is injected into the
the barrel chamber through a valve assembly. The valve
cylinder until the downward movement of plunger (6)
assembly has a spring-loaded needle valve with a cone
causes the lower scroll to open the lower port and
shaped end which operates against a seat. The angle of
release the fuel pressure.
the valve is slightly larger than that of the