GF14.00-P-3000OGB Exhaust Treatment Function

GF14.00-P-3000OGB Exhaust Treatment Function
ENGINES 642.8 in MODEL 212.0, 2
- with CODE (U42) BlueTEC (SCR) diesel exhaust treatment

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

Exhaust treatment, general points
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 (with code (474) Particulate filter)
- Exhaust gas recirculation (EGR)
- Injection of the AdBlue(R) reducing agent

The CDI control unit (N3/9) reads in the following sensors:

- Temperature sensor upstream of SCR catalytic converter (B16/15)
- Temperature sensor upstream of catalytic converter (B19/7)
- Temperature sensor upstream of diesel particulate filter (B19/9) (with code (474) Particulate filter)
- Temperature sensor upstream of turbocharger (B19/11)
- DPF differential pressure sensor (B28/8) (with code (474) Particulate filter)
- DPF differential pressure sensor for OBD (B28/16), with code (494) USA version)
- Oxygen sensor upstream of catalytic converter (G3/2)
- Nitrogen oxides control unit downstream of diesel particulate filter (N37/7), NOX sensor signal downstream of diesel particulate filter (N37/7b1) via the drive train sensor CAN (CAN I)
- Nitrogen oxides control unit downstream of SCR catalytic converter (N37/8), NOX sensor signal downstream of SCR catalytic converter (N37/8b1) via the drive train sensor CAN
- Front SAM control unit with fuse and relay module (N10/1), outside temperature via the chassis CAN (CAN E)

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 SCR catalytic converter
^ Function sequence for intake port shutoff

Function sequence for oxidation catalytic converter
The oxidation catalytic converter reduces the amount of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx, and, on vehicles with code (474) Particulate filter, generates the required thermal energy for the DPF regeneration phase by afterburning.

Function sequence for diesel particulate filter (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:

- One additional post injection via the fuel injectors (Y76)
- DPF glow function via the drivetrain LIN (LIN C1) over the glow output stage (N14/3) to the glow plugs (R9)
- Shift of shift characteristic curve via the drive train CAN (CAN C) by the fully integrated transmission control controller unit (Y3/8) (with code (427) 7-speed automatic transmission)

Soot content is reduced by approx. 99%.

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. On vehicles with code (474) Particulate filter, the exhaust temperature is monitored during regeneration by the temperature sensor upstream of the 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. Necessary service/maintenance of the DPF is indicated by the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1).
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 SCR catalytic converter
The exhaust gases expelled from the engine are cleaned in an oxidation catalytic converter, a diesel particulate filter (DPF) and a reduction catalytic converter (Selective Catalytic Reduction (SCR) catalytic converter).
By oxidation in the oxidation catalytic converter, the CO and HC are converted to CO2 and water (H2O). 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.
The soot particles are retained in the honeycomb filter body of the DPF. During the DPF regeneration phase, the exhaust temperature is raised to burn off the retained soot particles.
The AdBlue(R) reducing agent is injected upstream of the SCR catalytic converter, and is converted to ammonia (NH3) through thermal decomposition (heat-induced chemical reaction) and hydrolysis (water-induced chemical reaction).
Between the AdBlue(R) metering valve (Y129) and the SCR catalytic converter is a mixing element. This improves the hydrolysis of the AdBlue(R) reducing agent and ensures more uniform distribution of the AdBlue(R) upstream of the SCR catalytic converter.
In the SCR catalytic converter, the NOX contained in the exhaust gas is converted with the NH3 to nitrogen (N2) and H2O molecules.

The CDI control unit calculates the quantity of reducing agent required based on a characteristics map, and sends it over the drive train sensor CAN to the AdBlue(R) control unit (N118/5). This control unit then initiates map-based injection of the calculated quantity of AdBlue(R) reducing agent through the AdBlue(R) metering valve.

The conversion rate of the NOX portion in the exhaust is about 80%. Soot content is reduced by approx. 99%.

The load condition of the DPF is determined by the CDI control unit via the DPF differential pressure sensor and DPF differential pressure sensor for OBD (B28/16) (with code 494 USA version). If the soot load exceeds the map-based value, the CDI control unit will start the regeneration phase provided the prerequisites for regeneration are given. Regeneration is performed by periodically raising the exhaust temperature with another post injection.

By raising the exhaust temperature, the soot particles stored in the DPF are mostly burnt off to CO2.
The noncombustible ash remains in the DPF. During the regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the turbocharger and the temperature sensor upstream of the diesel particulate filter.
Necessary maintenance of the DPF is signaled by the engine diagnosis indicator lamp in the instrument cluster.

If the "Reserve" fill level in the AdBlue(R) container is reached, the driver is informed by an audible signal and by a "Service Required" message on the multifunction display (A1p13), in which case the driver should contact the workshop to obtain the appropriate maintenance.

If the "empty" level is reached in the AdBlue(R) container, the plausibility of the "empty" level is checked through a computer model. If the plausibility check also results in an "empty" fill level, an audible signal is given, an entry is made in the fault memory of the control unit (CDI), and the engine diagnosis indicator lamp is lit on the instrument cluster. The driver then has up to 20 engine starts available, with an assumed trip distance of 32 kilometers in each case. The number of remaining starts is displayed in the instrument cluster. The vehicle can no longer be started after the last remaining "Start".

Function sequence for intake port shutoff
The intake port shutoff (EKAS) achieves the best possible relation between air swirl and air mass in all load conditions of the engine.

The CDI control unit additionally reads the following sensors for intake port shutoff:

- Oil temperature sensor (B1)
- Atmospheric pressure sensor, for the atmospheric pressure
- Accelerator pedal sensor (B37), for load detection
- Crankshaft Hall sensor (B70), for engine speed

After evaluating the input signals, the CDI control unit actuates the actuator motor for the intake port shutoff switchover valve (M55) 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.