Diesel Emissions Fluid (DEF) System: Description and Operation

GF14.40-S-0002SA Exhaust After Treatment, Function

ENGINES 642.8 in MODEL 906
- with CODE (MG5) Engine OM 642 DE 30 LA, 140 kW (190 hp) 3800 rpm
- except CODE (ZU7) National version for Canada
- except CODE (ZU8) National version for USA

ENGINES 642.8 in MODEL 639
- with CODE (XZ1)
- with CODE (MZ0) Blue EFFICIENCY

Illustrated on model 639

B2/14 Hot film mass air flow sensor
B4/17 Rail pressure sensor
B5/8 Boost pressure sensor
B11/19 Coolant temperature sensor
B16/11 Temperature sensor upstream of turbocharger
B17/15 Charge air temperature sensor
B19/19 Temperature sensor upstream of diesel particulate filter
B28/19 Intake manifold pressure sensor
B28/20 Diesel particulate filter differential pressure sensor
B37/3 Accelerator pedal module
B60/4 Exhaust back pressure sensor
B70/1 Crankshaft sensor
B85/3 Oxygen sensor
M16/48 Throttle valve positioner
M72/2 Inlet port shutoff positioner
N14/7 Glow output stage
N3/30 CDI control unit
R9/1 Cylinder 1 glow plug
R9/2 Cylinder 2 glow plug
R9/3 Cylinder 3 glow plug
R9/4 Cylinder 4 glow plug
R9/5 Cylinder 5 glow plug
R9/6 Cylinder 6 glow plug
Y27/13 Exhaust gas recirculation cooling solenoid valve
Y27/17 Exhaust gas recirculation positioner
Y76/18 Cylinder 1 injector
Y76/19 Cylinder 2 injector
Y76/20 Cylinder 3 injector
Y76/21 Cylinder 4 injector
Y76/22 Cylinder 5 injector
Y76/23 Cylinder 6 injector
LIN C1 Drive train LIN

Function requirements for exhaust treatment, general points
- 'Circuit 87 ON' (engine control ON)
- Engine running

Exhaust treatment, general
The task of exhaust treatment is to reduce the exhaust emissions:
- Nitrogen oxides (NOX)
- Hydrocarbons (HC)
- Carbon monoxide (CO)
- Soot particles

Pollutant reduction is supported by the following subfunctions:
- Intake port shutoff (EKAS)
- Diesel particulate filter (DPF) preheating
- Exhaust gas recirculation (EGR)

The CDI control unit reads in the following sensors for purging:
- Oxygen sensor
- Temperature sensor upstream of diesel particulate filter
- Temperature sensor upstream of turbocharger
- Diesel particulate filter differential pressure sensor
- via the engine compartment-CAN (CAN C) from the EZS control unit (N73) the signal from the outside air temperature sensor (B14) from the SAM control unit (N10) via the interior CAN (CAN B)

Function sequence for exhaust treatment
The following subsystems are involved in exhaust treatment:
- Function sequence for oxidation catalytic converter
- Function sequence for diesel particulate filter (DPF)
- Function sequence for intake port shutoff

Function sequence for oxidation catalytic converter
The oxidation catalytic converter lowers the hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOX) and generates the required thermal energy for the DPF regeneration phase by means of after burning.

Function sequence for DPF
The diesel particulate filter consists of a ceramic honeycomb filter body made out of silicon carbide, which is coated with platinum. The passages of the diesel particulate filter are opened alternately at the front and rear and are separated from each other through the porous filter walls of the honeycomb filter body.
The precleaned exhaust which has passed though the oxidation catalytic converter flows into the ducts of the DPF which are open to the front and passes through the porous filter walls of the honeycomb filter body into the ducts which are open to the rear. After this, the cleaned and filtered exhaust is dissipated through the exhaust system. The soot particles are retained in the honeycomb filter body of the DPF.
If the soot particle content exceeds a map-based value, the CDI control unit will start the regeneration phase provided the prerequisites for regeneration are given. The CDI control unit receives the information on soot particle content in the DPF via the DPF differential pressure sensor ().

Regeneration takes place by means of a periodical increase of the exhaust temperature. For this purpose, the following functions are initiated by the CDI control unit:
- An additional post injection over the injectors
- DPF glow function via drive LIN over glow output stage to glow plugs

The soot particles retained in the DPF are mostly burnt off to produce carbon dioxide (CO2) by increasing the exhaust temperature. The ash produced remains in the DPF.

Soot content is reduced by approx. 99%.

During regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the exhaust gas turbocharger and by the temperature sensor upstream of the diesel particulate filter.

Through the exhaust gas pressure lines upstream and downstream of the DPF, the DPF differential pressure sensor determines the pressure differential between the exhaust gas pressure upstream and downstream of the DPF.
The soot particle content in the DPF is determined using a characteristic map on the basis of the pressure differential and the exhaust mass calculated by the CDI control unit. If the diesel particulate filter requires maintenance, the EOBD indicator lamp (A1e17) in the instrument cluster (A1) will signal this.

On short trips, regeneration is interrupted and distributed over several driving cycles. Until the specified regeneration temperature is reached several heating-up phases are required. Regeneration occurs unnoticeably by the customer.

Function sequence for intake port shutoff
Under all engine load conditions, the intake port shutoff tries to obtain the best possible relation between air turbulence and air mass. The CDI control unit additionally reads the following sensors and signals for intake port shutoff:
- Engine oil sensor (B40/8)
- Outside temperature SAM control unit
- Accelerator pedal module, for load recognition
- Crankshaft sensor, for the engine rpm

After evaluating the input signals, the CDI control unit actuates the motor for the inlet port shutoff positioner () by means of a pulse width modulated (PWM) signal. In the lower engine speed and engine load range, half of the intake ports (2 intake ports per cylinder available) are closed by means of the intake port shutoff flaps.

In the open intake ports, the flow rate is thus increased. This leads to a higher swirl which creates a better vortex. This improves combustion and also contributes to reducing the soot particles in the exhaust gas. As the engine speed and engine load increase, the closed intake ports are continuously opened so that the best possible relationship between air swirl and air mass is available for every operating phase of the engine. In this way, the exhaust characteristics and the engine performance are optimized.

If there is a fault or discontinuity in the supply voltage, the flaps are opened by spring force.