Function requirements for exhaust treatment, general points
Circuit 87M (engine management ON)
Engine runs
Exhaust treatment, general
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)
Exhaust gas recirculation (EGR)
Injection of the AdBlue® reduction 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)
Temperature sensor upstream of turbocharger (B19/11)
DPF differential pressure sensor (B28/8)
Oxygen sensor upstream of catalytic converter (G3/2)
Front SAM control unit (N10/6), outside temperature via interior CAN (CAN B), electronic ignition lock control unit (N73), chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)
Control unit for NOx sensor downstream of diesel particulate filter (N37/7), signal of NOx sensor downstream of diesel particulate filter (N37/7b1) via drive train sensor CAN (CAN I)
NOx sensor control unit downstream of SCR catalytic converter (N37/8), signal of NOx sensor downstream of SCR catalytic converter (N37/8b1) via drive train sensor CAN
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 diesel particulate filter, generates the required thermal energy for the DPF regeneration phase by means of 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 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 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 over the drive train LIN (LIN C1) over the glow output stage (N14/3) to the glow plugs (R9)
Shifting curve shift via the drive train CAN by 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 temperature. The ash produced remains in the DPF.
During regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the exhaust gas turbocharger and by the temperature sensor upstream of the diesel particulate filter.
Through the exhaust 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 characteristics map on the basis of the pressure differential and the exhaust mass calculated by the CDI control unit. When DPF maintenance is required, this is signaled via drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) by the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1).
On short-distance 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 SCR catalytic converter
The exhaust expelled from the engine is cleaned in an oxidation catalytic converter, a diesel particulate filter (DPF) and an SCR catalytic converter.
Oxidation in the oxidation catalytic converter converts the CO and HC 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 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 higher exhaust temperature burns off the retained soot particles.
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 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 together with the NH3 to molecular nitrogen (N2) and H2O.
The CDI control unit calculates the quantity of reduction agent required based on a characteristics map and sends it via drive train sensor CAN to the AdBlue® control unit (N118/5). This control unit then initiates characteristic map-dependent injection of the calculated quantity of AdBlue® reduction agent through the AdBlue® metering valve.
The conversion rate of the NOx portion in the exhaust is dependent on the temperature and can be up 80%. The reduction in the soot present is about 99%.
The CDI control units determines the load condition of the DPF via the DPF differential pressure sensor. 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. Regeneration is performed by periodically raising the exhaust temperature with another post injection.
Raising the exhaust temperature causes most of the soot particles stored in the DPF to be burnt off to CO2.
The noncombustible ash remains in the DPF. During regeneration, the exhaust temperature is monitored by the temperature sensor upstream of the exhaust gas turbocharger and by 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® tank is reached, the driver is informed by means of an audible signal and at the same time over the instrument cluster that he/she should find a workshop and have the required maintenance work carried out.
If the "Empty" fill level is reached in the AdBlue® tank, 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 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".
Intake port shutoff shown schematically |
1 | Filler inlet port |
2 | Intake port |
3 | Intake ports |
4 | Outlet duct |
M16/6 | Throttle valve actuator |
M55 | Intake port shutoff actuator motor |
A | Fill inlet port intake air |
B | Intake port intake air |
P09.20-2327-76
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.
The CDI control unit additionally reads the following sensors for intake port shutoff:
Atmospheric pressure sensor (integrated in the CDI control unit), for the atmospheric pressure
Accelerator pedal sensor (B37), for load detection
Crankshaft Hall sensor (B70), for engine speed
For every cylinder, two separate intake ports, the fill inlet port and the intake port, are planned in the intake manifold. The fill inlet port can be plugged using a flap in the intake port shutoff actuator motor. Following this, only the intake ports are still available for filling the cylinders, which leads to an increase of the flow rate and larger eddy.
As engine speed and load increase, the closed fill inlet ports open continuously so that the best possible relationship between air swirl 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.
Referenced documents
- gf0716p9997orb Overview of system components for common rail diesel injection (CDI)