Case 621G Stage IV, Оригинальное руководство пользователя

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7 - MAINTENANCE
Selective Catalytic Reduction (SCR) system description
NHIL13ENG1393AA
9
(1) Intake air humidity and temperature sensor (10) Exhaust flap
(2) Air filter (11) Engine Control Unit (ECU)
(3) Supply module (12) SCR upstream temperature sensor
(4) DEF/A
D
B
LUE
® level and temperature sensor (13) Selective Catalyst Reduction (SCR) catalyst
(5) DEF/A
D
B
LUE
® quality sensor (14) SCR downstream temperature sensor
(6) Dosing module (15) NH
3
sensor
(7) DOC and mixer (16) Downstream NO
x
sensor
(8) DOC upstream temperature sensor (17) Engine
(9) Upstream NO
x
sensor
The humidity in the intake to the engine (17) affects the
emissions in the exhaust stream. The intake air humidity
sensor
(1) is located in the intake air piping to the engine
between the air filter (2) and the intake manifold. The
information from this sensor is sent directly to the Engine
Control Unit (ECU)
(11) .
Engine exhaust system temperature is critical to the cat-
alytic reactions that take place in the emissions control
components. To quickly increase the catalyst tempera-
ture at initial start-up and light operating loads, there is
an exhaust flap
(10) located in the exhaust stream near
the turbocharger. The maximum temperature of the ex-
haust flap is critical, therefore engine coolant is circulated
through the core of this valve. Limiting NO
x
emissions in
the exhaust stream is one of the major goals of the emis-
sion control system on these engines. The upstream NO
x
sensor (9) is located in the exhaust stream at the inlet to
the Diesel Oxidation Catalyst (DOC) (7) . The NO
x
sensor
transmits data to the ECU via the engine CAN data bus.
A temperature sensor (8) is located at the inlet to the DOC
to closely monitor temperature.
DEF/A
D
B
LUE
® fluid freezes at -11 °C ( 12 °F ). A
DEF/A
D
B
LUE
® fluid level and temperature sensor (4) is
installed in the tank and the instrument cluster displays
those levels.
The DEF/A
D
B
LUE
® quality sensor (5)
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 (6) 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 (3) at approx-
imately 9 bar ( 130 psi ).
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