DESCRIPTION AND OPERATION
Page 43
Nitrous oxide (NOx) emission levels increase with
combustion temperature. The primary function of
the Exhaust Gas Recirculation (EGR) system is
to cool exhaust gas and send it back to the
combustion chamber to lower the combustion
temperature thereby reducing NOx.
EGR systems are configured differently for the
LCF and conventional chassis engines. The
mixer, where the recirculated exhaust joins the
inlet air, mounts at the front of the inlet manifold
for the conventional chassis; but for the LCF
chassis, it is located toward the rear of the
manifold. This requires differences in the piping
from the EGR cooler to the mixer.
EGR VALVE
This engine uses the EGR valve to recirculate
exhaust gases. Engine oil operates the EGR
valve. The EECU determines the desirable valve
opening based on inputs from a number of
sensors and commands the EGR valve solenoid
to open or close the valve.
Corrosion occurs in the inlet manifold if exhaust
gas condenses there. This can produce both
internal and external damage. To eliminate
corrosion, the EECU compares engine RPM,
torque load, ambient temperature, inlet manifold
temperature and EGR demand to calculate the
dew point in the inlet manifold. It then adjusts the
EGR opening to stay above the dew point.
Additionally, surfaces within the inlet manifold and
the mixing chamber are treated to resist
corrosion.
The EGR valve attaches to the rear section of the
exhaust manifold for reliable response and
turbocharger efficiency. This location also
protects the EGR cooler from harmful high
pressure exhaust pulses that occur during engine
braking.
EGR VALVE FUNCTION
A temperature sensor monitors exhaust
temperature sending the data to the EECU.
Excessively high temperature, or abnormally high
temperature for more than 30 minutes during an
hour, causes the EECU to limit engine power to
prevent engine damage.
When the EGR valve is open, exhaust gas
recirculates into the combustion chamber. The
valve is normally closed when engine coolant
temperature is below 65°C (149°F) unless the
EECU commands the valve open during
automatic cooler cleaning mode. When coolant
temperature exceeds 65°C (149°F), engine load
exceeds 50%, and RPM exceeds 1200, the
EECU opens the EGR valve to approximately
90% of its range.
At idle, the EECU monitors exhaust temperature
every three minutes. If it exceeds 98°C (208°F),
the valve opens to approximately 14% of its
range. Otherwise, it remains closed.
EGR COOLER INLET PIPE
32
Figure 32 — EGR Valve and Cooler Inlet Pipe
The cooler inlet pipe conducts the exhaust from
the EGR valve to the EGR cooler where its
temperature is reduced prior to being
reintroduced into the combustion chamber.
1. EGR Valve
2. Cooler Inlet Pipe
3. Clamps
4. EGR Cooler
5. Electrical Connector
6. Oil Supply Line
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