From October 2003, in the left-hand drive vehicles shown, 4-cylinder diesel engines (OM646) are now available with optional diesel particulate filter (DPF), Code 474, in combination with the EURO 4 Standard engine version. The 6-cylinder (OM648) engine is available from January 2004.
The Mercedes-Benz diesel particulate filter (DPF), also referred to in the press as a “soot filter”, allows the almost complete suppression of the particulate emissions produced by the diesel fuel combustion process. The
Mercedes-Benz DPF works without any further additives and, in combination with measures adaptations inside the engine, meets the exacting EURO 4 Standard. Depending on the particular operational profile of the vehicle, the DPF can be used over long mileages with no additional maintenance.
GT14_40_0008_C81
Catalytic converter Diesel particulate filter
C-Klasse Limousinen C 200 CDI C 220 CDI BM 203.007 BM 203.008 Sportcoupé C 200 CDI C 220 CDI BM 203.707 BM 203.708 E-Klasse Limousinen E 200 CDI
E 220 CDI E 320 CDI
BM 211.004 BM 211.006 BM 211.026 S-Klasse Limousine S 320 CDI BM 220.025
Components of the emission control system
1 Catalytic converter (120/1)
2 Seal
3 Diesel particulate filter (114) B19/7 TWC temperature sensor B19/8 Temperature sensor after TWC
B28/8 Differential pressure sensor of diesel particulate filter G3/2 Oxygen sensor in front of TWC
(does not affect operation of the diesel particulate filter)
Components in engine compartment
B60 Exhaust back pressure sensor M16/5 Throttle valve actuator
Diesel particulate filter operation
The diesel particulate filter (114) consists of a ceramic honeycomb filter body, which is made of silicon carbide coated with the rare metal
platinum. The ports in the diesel particulate filter are opened alternated at the front and rear, and separated by the porous filter walls (C) in the honeycomb body.
The unfiltered exhaust gas (A) flows into the open ports at the front of the diesel particulate filter (114), and filters through the porous walls of the honeycomb filter body (silicon carbide) to the open ports at the rear.
The filtered exhaust gas (B) then passes through the exhaust system. In this way, the diesel particulates are physically retained in the body of the diesel particulate filter, where they are burned during the regeneration (self-cleaning) phase. Fouling of the diesel particulate filter is detected by the CDI control unit by means of the
differential pressure sensor (TWC) (B28/8). 114 Diesel particulate filter (DPF) A Unfiltered exhaust gas B Filtered exhaust gas C Filter walls
An oxidation catalytic converter is mounted upstream of the diesel particulate filter, to absorb hydrocarbon (HC) and carbon monoxide (CO).
The diesel particulate filter (114) is screwed together with the oxidation catalytic as a single unit, which is located on the right of the engine behind the turbocharger.
Input/Output signals
1 Exhaust gas pressure line before DPF 2 Exhaust gas pressure line after DPF 114 Diesel particulate filter (DPF) 120/1 Oxidation catalytic converter B19/7 TWC temperature sensor B19/8 Temperature sensor after TWC B28/8 Differential pressure sensor of diesel
particulate filter
B60 Exhaust back pressure sensor CAN Data bus
(Controller Area Network) G3/2 Oxygen sensor before TWC M16/5 Throttle valve actuator N3/9 CDI control unit
Y27/9 Exhaust gas recirculation positioner Y76 Fuel injectors
Y100/1 Right boost pressure regulator
P14.40-2005-06
Differential pressure sensor
The differential pressure sensor (B28/8) is located at the right rear of the engine compartment, behind the heat shield. Through the exhaust gas pressure lines, it detects the difference in gas pressure before and after the diesel particulate filter. In this way, it can detect soot or ash fouling in the DPF.
If the DPF is full, there is a relatively high pressure in front of the diesel particulate filter, and a
pressure slightly above atmospheric pressure after the DPF.
The exhaust gas pressure before the DPF acts on the active side of the silicon diaphragm in the differential pressure sensor (TWC).
The exhaust gas pressure after the DPF is passed to the rear side of the silicon diaphragm.
The deflection of the diaphragm due to the
different pressures is measured, and the pressure differential deduced.
Temperature sensors before/after TWC
The temperature sensor before the TWC (B19/7) is located in the oxidation catalytic converter, above the threaded connection.
The temperature sensor after the TWC (B19/8) is located in front of diesel particulate filter, under the threaded connection.
Since the maximum permissible temperature in the TWC should be 750°C, a sensor is mounted in front of the TWC to monitor the temperature. The temperature in the diesel particulate filter (DPF) should not go above 700°C. A temperature sensor is therefore mounted behind the TWC (or in front of the diesel particulate filter). These
temperatures are reached only during the regeneration phase.
Exhaust back pressure sensor (B60)
This pressure sensor measures the gas back pressure in the exhaust gas recirculation channel, in order to adjust the boost pressure according to the load on the diesel particulate filter. If the exhaust gas back pressure rises, the guide vanes in the turbocharger are adjusted to keep the boost pressure constant.
By means of the exhaust gas back pressure sensor, the CDI control unit (N3/9) can
distinguish between a higher back pressure and a malfunction.
The exhaust gas back pressure sensor is located at the left rear of the engine compartment, in the exhaust gas recirculation channel in front of the exhaust gas recirculation positioner (Y27/9).
Throttle valve actuator (M16/5)
P14.20-2111-02 P14.20-2110-01
The throttle valve actuator (M16/5) is actuated by a PWM signal from the CDI control unit (N3/9), and controls the quantity of fresh air by means of the throttle valve (1).
The throttle valve actuator is active during the regulating phase, to assist the recirculation of warm exhaust gases. This helps the catalytic converter to warm up.
The fresh intake air is mixed with the recirculated exhaust gas by means of the exhaust gas
recirculation connection with mixing throttle (3). The pressure for the pressure sensor (intake manifold) is taken from the pressure
measurement connection (2).
The throttle valve actuator is located at the left front of the engine compartment (Model 211), in front of the intake manifold.
1 Throttle valve
2 Pressure measurement connection for the pressure sensor (intake manifold) 3 Exhaust gas recirculation connection with mixing throttle
4 Electrical connection M16/5 Throttle valve actuator
Regeneration (self-cleaning)
The self-cleaning process of the diesel particulate filter is performed automatically by the CDI control unit (N3/9). This is done according to the values measured at the differential pressure sensor (B28/8), but every 1000 km at least. The CDI control unit (N3/9) burns off the particulates deposited in the filter by raising the exhaust gas temperature.
The regeneration process can be interrupted by the CDI control unit (N3/9), and restarted later (for example, if the engine is switched off).
To start the regeneration process, both the minimum and maximum conditions must be present.
Maximum conditions:
* Differential pressure in the diesel particulate filter * Mileage (km)
Regeneration
Minimum conditions:
* Vehicle speed > 10 km/h * Exhaust gas temperature > 150°C
* Tank fill level > Reserve
* Operating point Idle up to 4000 rpm * No related fault entry in the CDI control unit
Duration of regeneration
Depending on exhaust gas temperature, the regeneration phase lasts between 400 and 1000 seconds.