PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
is built up by the injector at each cylinder. A suction pump lifts fuel
from the tank and delivers it to the float chamber. From here a second low
pressure pump delivers the fuel to the distributor. Fuel passes through the
distributor to the metering pump, where it is divided into measured charges.
The fuel charges are then delivered back to the distributor, where they are
sent to the injectors in the proper sequence. The measured charges and then
sprayed into the engine cylinders, at the proper time and under high
pressure, by the fuel injectors.
(2) Distributor. The distributor consists of a rotating disk and a
stationary cover to which the fuel lines to the individual injectors are
connected. The disk and the cover have a series of holes which, when
properly indexed, form passages from the fuel supply pump to the metering
pump. The disk is timed so that this occurs when the metering plunger is
moving down on its suction stroke, thus permitting the metering pump to be
filled with oil. As the disk continues to rotate, it lines up with the
correct discharge hole in the cover just as the metering plunger begins its
delivery stroke, forcing the fuel into the proper injector line. As it
continues to rotate, the disk works in the same timed sequence in
conjunction with the metering pump to feed fuel to the remaining cylinders.
The rotating disk turns at onehalf crankshaft speed because power strokes
occur every other crankshaft revolution in a fourstroke cycle diesel
engine.
(3) Metering Unit (figure 48 on the following page). The metering
unit is a closely fitted reciprocating pump, obtaining its motion through a
link from the plunger lever. The plunger lever is operated by a vertical
lever, controlled in turn by an eccentric rocker lever running directly off
a cam on the fuel pump main shaft. The position of the vertical lever in
the eccentric of the rocker lever determines the travel of the plunger lever
and, in turn, the travel of the metering pump plunger. As the pump plunger
starts 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
injector, is varied by changing the position of the plunger lever between
the stop pins in the cam rocker lever. The position of the plunger lever is
adjusted by the governor through the control lever.
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