Exhaust Gas Cleaning, Function - GF49.20-D-3000TSB

Engine 274 in model 907 

Block diagram 

Function requirements for exhaust treatment, general points 

• Circuit 87M (Engine management ON)
• Engine running.

Exhaust treatment, general 

The task of exhaust treatment is to reduce the exhaust emissions:

• Nitrogen oxides (NOx)
• Hydrocarbon (CxHy)
• Carbon monoxide (CO)

To do this, the near-engine mounted catalytic converter (three-way catalytic converter) must be rapidly brought up to operating temperature, amongst other things, in order to reduce the exhaust gas emissions during a cold start.

The ME-SFI [ME] control unit (N3/36) determines the valve overlap by actuating the intake camshaft adjustment solenoid (Y49/10) and the exhaust camshaft adjustment solenoid (Y49/11). The exhaust gas recirculation rate is thereby controlled by internal exhaust gas recirculation.

Function sequence for exhaust treatment 

The ME-SFI [ME] control unit controls the upshift delay according to the following sensor and signal:

• Coolant temperature sensor (B11/21), coolant temperature over direct line
• ESP® control unit, wheel speed via chassis FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C)

Upshift delay is active for a maximum of 60 s and is entirely electronic. The ME-SFI [ME] control unit makes the request via the drive train CAN (CAN C) to the fully integrated transmission control electric controller unit (VGS) (N15/15) to move the shift characteristics. Partial load gear shifts (1-2-1, 2-3-2) thus take place at higher engine speeds or at higher vehicle speeds.

Additional function requirements for monitoring the catalytic converter efficiency 

• Catalytic converter at operating temperature
• Lambda control released

Function sequence for monitoring the catalytic converter efficiency 

The following subsystems are involved in exhaust treatment:

• Function sequence for catalytic converter
• Function sequence for upshift delay (for A/T)
• Function sequence for monitoring the catalytic converter efficiency

Function sequence for catalytic converter 

The pollutants emitted by the engine are converted chemically by the catalytic converter for the fuel/air ratio (λ) = 1.

Through oxidation, carbon monoxide is converted to carbon dioxide (CO2) and hydrocarbon to water (H2O) + carbon dioxide.

Through reduction the nitrogen oxides are converted into nitrogen (N2  ) + carbon dioxide.

Additional function requirements for upshift delay (for automatic transmission) 

• Coolant temperature at start < 50 °C
• Vehicle speed < 53 km/h

Function sequence for upshift delay (for A/T) 

The upshift delay brings the CAT downstream of the engine start more rapidly up to operating temperature.

By law, hydrocarbon emissions must not go above prescribed limits. The purpose of monitoring the catalytic converter efficiency is to use the oxygen storage capacity of the catalytic converter to determine the degree of aging, and therefore the degree of hydrocarbon conversion. The ME-SFI [ME] control unit reads in the following signals to monitor the catalytic converter efficiency:

• Oxygen sensor element downstream of catalytic converter (g3/21 b1), oxygen sensor signal
• Oxygen sensor element upstream of catalytic converter (G8/6b1), oxygen sensor signal
• Crankshaft Hall sensor (B70/2), engine RPM

The oxygen stored during the "lean operating phase" is reduced totally or partially during the "rich operating phase". Aging reduces the oxygen storage capacity and hydrocarbon conversion capacity of the catalytic converter.

Due to the three-way catalytic converter's high oxygen storage capacity, the change in oxygen content is nearly fully dampened downstream of the three-way catalytic converter.

Consequently, the oxygen sensor signal downstream of the catalytic converter has a low amplitude and is virtually constant.

When the catalytic converter is at operating temperature and the lambda control enabled, the amplitude variables of the oxygen sensor signals downstream and upstream of the catalytic converter are compared.

If the catalytic converter is no longer operational, then the signals of the oxygen sensor element upstream of the catalytic converter and the signals of the oxygen sensor element downstream of the catalytic converter are the same size.

A number of measurements take place in the lower partial-load range in the specified RPM range. The results are compared with a characteristics map in the ME-SFI control unit. If a fault is detected, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit (N73/8) and the user interface CAN (CAN HMI).

Any faults detected are stored in the fault memory of the ME-SFI [ME] control unit. These can be read out and deleted with XENTRY Diagnostics.

Electrical function schematic for exhaust treatment	PE49.20-D-2051-97TSB
Overview of system components for gasoline injection and ignition system with direct injection	GF07.70-D-9998TSB