Exhaust Gas Cleaning, Function - GF49.20-S-3000TRJ
Engine 274 in model 447.6/7
with code XM0 (Facelift)
Function requirements for exhaust treatment, general points
- Circuit 87M ON (Engine management ON)
- Engine running.
Exhaust treatment, general
The task of exhaust treatment is to reduce the exhaust emissions:
- Nitrogen oxides (NOx )
- Hydrocarbon (Cx Hy )
- Carbon monoxide (CO)
Y49The ME-SFI [ME] control unit (/34) actuates the intake camshaft solenoid (Y49/10) and the and exhaust camshaft solenoid (N3/11) to determine the valve overlap. The exhaust gas recirculation rate is thereby controlled by internal exhaust gas recirculation.
Function sequence for exhaust treatment
The following subsystems are involved in exhaust treatment:
- Function sequence for catalytic converter
- Function sequence for upshift delay (with an A/T)
- Function sequence for monitoring the catalytic converter efficiency
Function sequence for catalytic converter
The pollutants emitted by the engine in the exhaust gases are chemically converted by the catalytic converter at an air-fuel ratio of lambda (λ) = 1.
Through oxidation, carbon monoxide is converted to carbon dioxide (CO2 ), and hydrocarbon is converted to water (H2 O) and carbon dioxide.
Through reduction, the nitrogen oxides are converted to nitrogen (N2 ) and carbon dioxide.
Additional function requirements for upshift delay
- Coolant temperature during start < 50°C
- Vehicle speed < 53 km/h
Function sequence for upshift delay (with an A/T)
The upshift delay brings the CAT downstream of the engine start more rapidly up to operating temperature. The ME-SFI [ME] control unit controls the upshift delay according to the following sensor and signal:
- Coolant temperature sensor (B11/21), coolant temperature
- Electronic Stability Program (ESP) control unit (N30/4) for wheel speed
The upshift delay is active for max. 160 s and is solely realized electronically.
The ME-SFI [ME] control unit prompts the fully integrated transmission control (VGS) electric controller unit (N15/11) (with code G42 (7G-TRONIC PLUS) and/or the fully integrated transmission control (VGS) electric controller unit (N15/15) with code G43 (9G-TRONIC)) to move the shift lines.
The partial load switchings then take place at a higher vehicle speed.
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
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 signals from the following sensors to monitor the catalytic converter efficiency:
- Crankshaft Hall sensor (B70/2)
- Lambda sensor downstream of the catalytic converter (G3/21)
- Oxygen sensor upstream of catalytic converter (G8/6)
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 (G3/21) 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 operable, then the oxygen sensor signals upstream of the CAT (G8/6) and the oxygen sensor signal downstream of the CAT are the same size.
The measurements take place in the lower partial-load range and are compared with a characteristics map in the ME-SFI [ME] control unit.
In the case of fault detection, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1/1e58) in the instrument cluster. Recognized fault are stored in fault memory of the ME-SFI [ME] control unit. These can be read out and cleared with XENTRY Diagnosis.
| Function schematic for exhaust gas cleaning | PE49.00-S-2500-97TRM | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-S-9998TRJ |