Exhaust treatment function - GF14.00-P-3000OG

ENGINE 642.8 in MODEL 204, 212 up to 8/31/14, 218 up to 8/31/14 without CODE U42 (BlueTEC diesel exhaust treatment (SCR)) 

ENGINE 642.8 in MODEL 207 up to 5/31/13 

Function requirements for exhaust treatment, general points 

• Circuit 87M ON (engine timing 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 particle

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)

The CDI control unit (N39) reads in the following sensors for purging:

• Oxygen sensor upstream of catalytic converter (G3/2)
• Temperature sensor upstream of diesel particulate filter (B19/9), on vehicles with code (474) Particulate filter
• Temperature sensor upstream of turbocharger (B19/11)
• DPF differential pressure sensor (B28/8), for vehicles with code (474) Particulate filter
• Front SAM control unit with fuse and relay module (N10/1), outside temperature via chassis CAN 1 (CAN E1)

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 reduces the amount of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NO_x ), 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:

• An additional post injection via the fuel injectors (Y76)
• DPF glow function via 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 IC (A1).

On short trips, regeneration is interrupted and distributed over several driving cycles. This means that more heating-up phases up to the required regeneration temperature will occur. Regeneration occurs unnoticeably by the customer.

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 and signals for intake port shutoff:

• Oil temperature sensor (B1)
• Front SAM control unit with fuse and relay module, outside temperature via chassis CAN 1
• 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 intake port shutoff actuator motor (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 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.

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