Function requirements for exhaust treatment, general points
Engine runs
The CDI control unit (N3/9) detects that the engine is running by evaluating the signals of the crankshaft Hall sensor (B70). The CDI control unit directly reads in the signals of the crankshaft Hall sensor.
Exhaust treatment, general
Exhaust gas cleaning reduces the harmful components of the combustion gases and residues emitted by the engine.
These are:
Nitrogen oxides (NOx)
Hydrocarbons (HC)
Carbon monoxide (CO)
Soot particles
Pollutant reduction is supported by the following functions:
Intake port shutoff (EKAS)
Diesel particulate filter (DPF) preheating
Exhaust gas recirculation (EGR)
AdBlue® injection (with code U77 (BlueTEC (SCR) diesel exhaust gas cleaning))
To do so, the CDI control unit processes the signals of the following sensors:
Outside temperature sensor (B14), transmitted by the front SAM control unit (N10/6) via the interior CAN (CAN B), electronic ignition lock control unit (N73), suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1)
Oxygen sensor upstream of catalytic converter (G3/2)
Vehicle with code U77 (BlueTEC (SCR) diesel exhaust gas cleaning):
Temperature sensor upstream of SCR catalytic converter (B16/15)
Temperature sensor upstream of catalytic converter (B19/7)
NOx sensor downstream of diesel particulate filter (N37/7b1), transmitted by NOx sensor control unit downstream of diesel particulate filter (N37/7) via drive train sensor CAN (CAN I)
NOx sensor downstream of SCR catalytic converter (N37/8b1), transmitted by NOx sensor control unit downstream of SCR catalytic converter (N37/8) via drive train sensor CAN
DPF:
Temperature sensor upstream of diesel particulate filter (B19/9)
DPF differential pressure sensor (B28/8)
Temperature sensor upstream of ATL (B19/11)
Vehicle with code 927 (Emissions standard EU6):
Soot particulate sensor (N74b1), transmitted by soot particulate sensor control unit (N74) via drive train sensor CAN
Exhaust gas cleaning in the diesel oxidation catalytic converter
The diesel oxidation catalytic converter reduces hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) through reduction and oxidation. Afterburning generates the thermal energy required for the DPF regeneration phase.
Exhaust gas cleaning in the DPF
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 exhaust gas flows into the DPF ducts opened to the front. It then flows through the porous filter walls of the honeycomb filter body into the ducts opened to the rear. The exhaust gas is then dissipated through the exhaust system. The soot particles are retained in the honeycomb filter body of the DPF.
If the soot content exceeds a specific value, the CDI control unit initiates the regeneration phase. The CDI control unit calculates the soot content in the DPF by evaluating the signals from the DPF differential pressure sensor.
The exhaust gas temperature is increased periodically for the regeneration phase. For this purpose, the CDI control unit initiates the following actions:
Additional post injection via:
Cylinder 1 fuel injector (Y76/1)
Cylinder 2 fuel injector (Y76/2)
Cylinder 3 fuel injector (Y76/3)
Cylinder 4 fuel injector (Y76/4)
Cylinder 5 fuel injector (Y76/5)
Cylinder 6 fuel injector (Y76/6)
The CDI control unit directly actuates the fuel injectors.
DPF glow function:
Cylinder 1 glow plug (R9/1)
Cylinder 2 glow plug (R9/2)
Cylinder 3 glow plug (R9/3)
Cylinder 4 glow plug (R9/4)
Cylinder 5 glow plug (R9/5)
Cylinder 6 glow plug (R9/6)
The CDI control unit transmits the request for the DPF glow function to the glow output stage (N14/3) via the drive LIN (LIN C1). The glow output stage actuates the glow plugs directly.
Shift curve offset
The CDI control unit transmits the request for shift curve offset via drive train CAN to the fully integrated transmission control unit (Y3/8n4).
The soot particles retained in the DPF are mostly burnt off to produce carbon dioxide (CO2) by increasing the exhaust gas temperature. The ash produced remains in the DPF. During regeneration, the exhaust gas temperature is recorded by the temperature sensor upstream of the exhaust gas turbocharger and by the temperature sensor upstream of the diesel particulate filter.
If the DPF requires maintenance, the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) lights up. The CDI control unit transmits the request to actuate the engine diagnosis indicator lamp via the drive train CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and the user interface CAN (CAN HMI) to the instrument cluster.
On short-distance trips, regeneration is interrupted and distributed over several driving cycles. As a result, the number of heating-up phases up to the required regeneration temperature increases. Regeneration occurs unnoticeably for the customer.
Exhaust gas cleaning in the SCR catalytic converter (with code U77 (BlueTEC (SCR) diesel exhaust gas cleaning))
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 (Y129) and the SCR catalytic converter. This serves to achieve improved hydrolysis and a more even distribution of the AdBlue® reduction agent 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 H2O.
The CDI control unit calculates the quantity of reduction agent required and requests it from the AdBlue® control unit (N118/5) via drive train sensor CAN. The AdBlue® control unit then actuates the AdBlue® metering valve accordingly.
The NOx sensors monitor the NOx concentration in the exhaust gas. The NOx sensors are heated to ensure that they reach their operating temperature quickly. The CDI control unit transmits the request for heating to the NOx sensor control units via the drive train sensor CAN. The NOx sensor control units then actuate the heating elements of the NOx sensors.
The conversion rate of the NOx percentage in the exhaust is temperature dependent and is up to 80 %. The reduction in the soot content present is about 99 %.
When the "Reserve" fill level is reached in the AdBlue® tank, a message is shown in the instrument cluster. This message contains the request to visit a workshop for maintenance. An acoustic signal is also issued.
When the AdBlue® tank is empty, the engine diagnosis indicator lamp in the instrument cluster lights up. The CDI control unit performs a plausibility check of this condition and stores an error in the fault memory.
The driver then has up to 20 engine starts available, with an assumed trip distance of 32 kilometers 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".
EKAS
Under all engine load conditions, the intake port shutoff tries to obtain the best possible relation between air turbulence and air mass.
To implement the intake port shutoff, the CDI control unit additionally reads in the signals of the following sensors:
Engine oil temperature sensor (B1)
Atmospheric pressure sensor
Accelerator pedal sensor (B37)
Crankshaft Hall sensor
The CDI control unit evaluates the incoming information and actuates the intake port shutoff actuator motor (M55) with pulse width modulated signals. In the lower engine speed and engine load range, half of the intake ports (2 intake ports available per cylinder) are closed with flaps. The flow rate in the open intake ports is increased. This leads to a higher swirl which creates a better vortex. This improves combustion, which contributes to reducing the soot particles in the exhaust gas.
As the engine speed and engine load increase, the closed intake ports are opened again continuously. This enables the best possible relation between air swirl and air mass for each operating phase of the engine.
If there is a fault or discontinuity in the supply voltage, the flaps are opened or kept open by means of spring force.