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Exhaust Gas Cleaning, Function - GF49.20-D-3000TSC

Engine 642.8 in model 907 

Block diagram 

G13787744

Function requirements for exhaust treatment, general points 

Exhaust treatment, general 

The task of exhaust treatment is to reduce the exhaust emissions:

Pollutant reduction is supported by the following subfunctions:

Function sequence for exhaust treatment 

The following subsystems are involved in exhaust treatment:

Function sequence for oxidation catalytic converter 

The oxidation catalytic converter ensures the reduction of hydrocarbon

The CDI control unit reads in information from the following signals:

(CH), carbon monoxide (CO), and nitrogen oxides (NOx) and, on vehicles with diesel particulate filter, generates the required thermal energy for the DPF regeneration phase by means of afterburning.

Function sequence for diesel particulate filter 

The diesel particulate filter consists of a ceramic honeycomb filter body made out of silicon carbide, which is coated with rare metal 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 content exceeds a characteristics 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 soot 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:

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.

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

Through the exhaust pressure lines upstream of the DPF 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 characteristics map on the basis of the pressure differential and the exhaust mass calculated by the CDI control unit. Necessary maintenance of the DPF is signaled by the engine diagnosis indicator lamp (A1e58) in the instrument cluster via the drive CAN, powertrain control unit, suspension FlexRay, EZS control unit, and user interface CAN.

IMPORTANTOn short-distance trips, regeneration is interrupted and distributed over several driving cycles. This means that preheating phases up to the required regeneration temperature will occur more frequently. Regeneration occurs unnoticeably for 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.

Oxidation in the oxidation catalytic converter converts CO and hydrocarbon (CH) 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 rare metal platinum.

The AdBlue® reduction 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).

There is a mixing element between the AdBlue® metering valve and the SCR catalytic converter. This improves the hydrolysis of the AdBlue® reduction agent and ensures more uniform distribution of the AdBlue® upstream of the SCR catalytic converter.

In the SCR catalytic converter, the NOx contained in the exhaust is converted in the SCR catalytic converter together with the NH3  into molecular nitrogen (N2) and water H2O.

The required amount of reducing agent is calculated according to a performance map by the CDI control unit and sent via the CAN drive train sensor to the AdBlue reducing agent. This control unit then initiates map-based injection of the calculated quantity of AdBlue® reducing agent through the AdBlue® metering valve.

IMPORTANT The conversion rate of the NOx percentage in the exhaust is temperature dependent and is up to 80 %. The reduction in the soot present is about 99 %.

Function sequence for intake port shutoff 

The intake port shutoff (EKAS) achieves the best possible relation between eddy and air mass in all load conditions of the engine. For intake port shutoff the CDI control unit also reads in the following signals:

After evaluating the input signals, the CDI control unit actuates the intake port shutoff actuator with a pulse width modulated 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 engine speed and load increases, the closed intake ports open continuously, so that the best possible relation between air eddying and air mass is provided for each operating phase of the engine. In this way, the exhaust characteristics and the engine performance are optimized.

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

IMPORTANT If the "Reserve" fill level in the AdBlue® container is reached, the driver is informed by an acoustic signal and via the AdBlue® Reserve (A1e42) warning light in the instrument cluster that he/she should contact workshop and that appropriate maintenance must be carried out.

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

Electrical function schematic for exhaust treatment PE49.20-D-2051-97TSC 
Overview of system components for common rail diesel injection (CDI) GF07.16-D-9997TSC
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