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 TM 9-8000
injector, is varied by changing the position of the plunger
5-16.
Distributor-Type Injection System.
lever between the stop pins in the cam rocker lever.
The position of the plunger lever is adjusted by the
a. General System Operation (Fig. 5-11). The
governor (para 5-25) through the control lever.
distributor injection system used in automotive diesel
engines is classed as a low-pressure system in that
d. Injectors (Fig. 5-13). The injector consists of
pumping, metering, and distribution operations take
a forged body with a properly fitted plunger.
This
place at low pressure. The high pressure required for
plunger is forced down against spring action by the
Injection is built up by the injector at each cylinder. A
engine camshaft through a rocker arm and push rod.
suction pump lifts fuel from the tank and delivers it to the
There is a fuel cup mounted on the end of the body
float chamber. From here a second low-pressure pump
combined with a hole-type nozzle (para 5-14).
delivers the fuel to the distributor. Fuel passes through
the distributor to the metering pump, where it is divided
(1) The fuel metering pump forces a precisely
into measured charges. The fuel charges then are
measured fuel charge into the cup on the intake stroke of
delivered back to the distributor, where they are sent to
the engine. The quantity of the fuel charge is based on
the injectors in the proper sequence. The measured
the speed and load requirements of the engine. The
charges then are sprayed into the engine cylinders at the
operation of this system depends on the injector delivery
proper time and under high pressure by the fuel
line being full of fuel. Then it will naturally follow that any
injectors.
fuel added by the fuel metering pump will discharge an
equal amount of fuel at the other end of the line into the
b. Distributor. The distributor consists of a rotating
injector.
disk and a stationary cover to which the fuel lines to the
individual injectors are connected.
The disk and the
(2) The fuel lies in the cup during the
cover have a series of holes that, when properly indexed,
compression stroke of the engine, and the compressed
form passages from the fuel supply pump to the
air is forced through the small spray holes in the cup.
metering pump. The disk is timed so that this occurs
The fuel in the tip of the cup is exposed to the intense
when the metering plunger Is moving down on its suction
heat of compression. The turbulence caused by the air
stroke, thus permitting the metering pump to be filled
rushing in through the holes in the nozzle tip serves to
with oil. As the disk continues to rotate, it lines up with
break the fuel charge into droplets.
the correct discharge hole in the cover just as the
metering plunger begins its delivery stroke, forcing the
(3) A few degrees before top dead center, at
fuel into the proper injector line.
As it continues to
the beginning of the power stroke, the injector plunger is
rotate, the disk works in the same timed sequence in
forced down, causing the fuel charge to be sprayed out
conjunction with the metering pump to feed fuel to the
of the cup, through the nozzle holes, and into the
remaining cylinders. The rotating disk turns at one-half
combustion chamber. The downward movement of the
crankshaft
speed
because
power strokes occur
injector plunger is spread out through the entire power
every other crankshaft revolution in a four-stroke cycle
stroke.
diesel engine.
(4) There is a small check valve located in the
c. Metering Unit (Fig. 5-12). The metering unit is
inlet passage of the injector body. Its purpose is to allow
a closely fitted reciprocating pump, obtaining its motion
fuel to enter the injector cup but block high combustion
through a link from the plunger lever. The plunger lever
chamber pressure from blowing air into injector delivery
is operated by a vertical lever, controlled in turn by an
lines.
eccentric rocker lever running directly off a cam on the
fuel pump main shaft. The position of the vertical lever
5-17.
Unit Injection System (Fig. 5-14).
in the eccentric of the rocker lever determines the travel
of the plunger lever and, in turn, the travel of the
a. Overall System Operation. The unit injection
metering pump plunger. As the pump plunger starts
system operates in the same manner as the
upward on its controlled stroke, it pushes fuel to the
injector through passages formed by the rotating
distributor disk.
The stroke of the metering plunger,
which determines the amount of fuel going to each
5-16
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