Page 38
DESCRIPTION AND OPERATION
This engine uses double solenoid unit injectors.
Unlike systems that require separate components
for delivering, pressurizing and injecting, this unit
injector combines these functions. These
injectors precisely control the fuel delivery
because of the two solenoids. The solenoids,
pump and nozzle are in a single body in close
proximity to each other.
The injector is set in a pressurized fuel gallery
where the fuel temperature is constant. Uniform
fuel temperature means uniform quantity in each
injection which means uniform power output from
each cylinder.
The fuel pump pressurizes the gallery so that fuel
rushes into each injector when it opens. Gallery
pressure is regulated by a valve that delivers
excess fuel back to the tank.
Copper sleeves, acting as coolant jackets, line
the bottoms of the injector bores. Engine coolant
circulates around these sleeves aiding the
process of controlling injection temperature.
There are four phases to the injector cycle of
operation. These include:
앫 Fill Phase
앫 Spill Phase
앫 Injection Phase
앫 Pressure Drop Phase
25
Figure 25 — Unit Injector — Fill and Spill Phases
Fill phase (A): During the filling phase, the pump
plunger is on its way up, the camshaft lobe is
passing its highest point and the rocker arm is on
its way toward the camshaft base circle. The fuel
valve is open, allowing fuel to flow into the unit
injector from the lower fuel gallery. Fuel flows into
the cylinder head and the unit injector pump
cylinder. Filling continues until the pump plunger
reaches its upper position.
Spill phase (B): The spill phase begins when the
camshaft lobe forces the rocker arm to push the
pump plunger down. The fuel can now flow
through the fuel valve, through the holes in the
unit injector and out through the fuel gallery. The
spill phase continues as long as the fuel valve is
open.
1. Pump Plunger
2. Fuel Gallery
3. Injector Nozzle
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