Emission control, function

General function requirements

 Circuit 61 ON

Exhaust gas cleaning, general

The task of the exhaust gas cleaning is observance of the limits for exhaust gas emissions set by the lawmaker in which the following pollutants in the exhaust gas are reduced:

- Nitrous oxide (NOX)

- Hydrocarbons (HC)

- Carbon monoxide (CO)

- Particulate matter (particles) (PM)

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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 (N3/9) reads in the following components:

- O2 sensor upstream of CAT (G3/2)

- Temperature sensor upstream of diesel particulate filter (B19/9)

- Temperature sensor upstream of turbocharger (B19/11)

- Pressure differential sensor (DPF) (B28/8)

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Function sequence

The exhaust gases expelled from the engine are cleaned in an oxidation catalytic converter (catalytic converter (CAT)) and a DPF. The catalytic converter reduces the amount of HC and CO and, by afterburning, produces the thermal energy required for the DPF regeneration phase. 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 alternatively 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 at 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 particles are retained in the honeycomb filter body of the DPF.

 The reduction of the PM share is approx. 99%.

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DPF regeneration with code (474) particulate filter

If the PM load exceeds the performance map value, the CDI control unit initiates the regeneration phase if the regeneration requirements are present. The CDI control unit receives the load condition of the DPF from the DPF pressure differential sensor.

Regeneration takes place via a periodical increase of the exhaust temperature. For this purpose, the following functions are taken over by the CDI control unit:

- Additional post injection

- DPF glow function

- Shift characteristics adjustment

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An increase in the exhaust gas temperature causes the PM retained in the DPF to be burnt to primarily produce carbon dioxide (CO2). The ash produced 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. 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 load in the DPF is determined using a performance map on the basis of pressure difference 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).

 Reduction of the soot share is approx. 99%.

 Interrupted regeneration is distributed over several driving cycles for short distances. Until the specified regeneration temperature is reached several heating-up phases are required. Regeneration occurs unnoticed by the customer.