Case 721G Stage IV, Руководство оператора

Страница: 275 / 522

7 - MAINTENANCE
DEF/A
D
B
LUE
® fluid freezes at -11 °C ( 12 °F ). A DEF/A
D
B
LUE
® fluid level and temperature sensor (15) is installed in
the tank and the instrument cluster displays those levels. The DEF/A
D
B
LUE
® quality sensor (14) monitors the quality
of the DEF/A
D
B
LUE
® fluid.
To precisely control the quantity of DEF/A
D
B
LUE
® fluid injected from the DEF/A
D
B
LUE
® tank into the exhaust stream,
a DEF/A
D
B
LUE
® dosing module (9) is integrated in the outlet area of the DOC canister. The dosing valve is Pulse
Width Modulation (PWM) controlled by the ECU. The ECU determines the amount of DEF/A
D
B
LUE
® fluid to inject
based on inputs from sensors in the exhaust stream. Pressurized DEF/A
D
B
LUE
® fluid is supplied to the dosing module
from the Supply Module (7) at approximately 9 bar ( 130 psi ).
Removal of NO
x
requires a chemical reaction. This chemical reaction takes place in the SCR (11) . DEF/A
D
B
LUE
®
reacts with the SCR catalyst to convert NO
x
to harmless nitrogen and water vapor.
The physical filtration of the Particulate Matter (PM) occurs in the SCRoF (10) .
To assure that the emission system is functioning correctly, a downstream NO
x
sensor (22) is located in the exhaust
stream at the outlet of the SCR.
Temperature and pressure are very important to the chemical reactions that take place in the emission control system.
An SCR upstream temperature sensor
(19) is located in the exhaust stream at the inlet of the SCR and compares the
reading of the SCR downstream temperature sensor (21) located in the exhaust stream at the outlet of the SCR. The
catalyst requires about 230 °C ( 446 °F ) for the chemical reaction to take place.
While a delta pressure (dp) sensor (20) , located on the SCR catalyst monitors the pressure of the exhaust gas at the
inlet and at the outlet of the SCR catalyst.
7-37