Exhaust Treatment Function - GF14.00-P-3000MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.354/954 

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 (NO_x )
• Hydrocarbon (HC)
• Carbon monoxide (CO)

To do so, among other things the three-way catalytic converter must be rapidly brought up to operating temperature in order to reduce the exhaust emissions during a cold start.

The ME-SFI [ME] control unit actuates the intake camshaft and exhaust camshaft solenoids (Y49/1, Y49/2) 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 three-way catalytic converter 
• Function sequence for upshift delay 
• Function sequence for monitoring the catalytic converter efficiency 

Function sequence for three-way catalytic converter 

The pollutants emitted by the engine are chemically transformed (converted) by the near-engine mounted three-way catalytic converter (firewall catalytic converter) at λ=1.

Through oxidation, carbon monoxide is converted to carbon dioxide (CO ₂ ) and hydrocarbon to water (H₂ O)+ carbon dioxide.

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

Additional function requirements for upshift delay 

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

Function sequence for upshift delay 

The upshift delay brings the three-way catalytic converter up to operating temperature more rapidly after starting the engine.

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

• Coolant temperature sensor (B11/4)
• Electronic Stability Program control unit (N30/4), wheel speed via suspension FlexRay (Flex E), powertrain control unit (N127) and drive train CAN (CAN C1)

The upshift delay is active for a maximum of 60 s and exclusively occurs electronically.

The ME-SFI [ME] control unit makes a request to the fully integrated transmission control unit (Y3/8n4) via drive train CAN to move the shift characteristic curves.

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 

• Three-way catalytic converter at operating temperature
• Lambda control released

Function sequence for monitoring the catalytic converter efficiency 

Hydrocarbon (HC) emissions must not exceed the limit specified by the legal requirements.

The purpose of monitoring the catalytic converter efficiency is to use the oxygen storage capacity of the three-way catalytic converter to determine the degree of aging, and therefore the degree of HC 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 (G3/1b1),
• Oxygen sensor element upstream of catalytic converter (G3/2b1), oxygen sensor signal
• Crankshaft Hall sensor (B70), 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 HC conversion capacity of the three-way 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 three-way catalytic converter has a low amplitude and is virtually constant.

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

If the three-way catalytic converter is no longer operable, then the oxygen sensor signal of the sensor element for oxygen sensor upstream of the catalytic converter and the oxygen sensor signal of the sensor element for oxygen sensor 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 [ME] control unit.

If a fault is detected, the ME-SFI [ME] control unit actuates the engine diagnosis symbol in the instrument cluster (A1) via the drive train CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit (N73) and 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 Mercedes' XENTRY Diagnostics.

	Electrical function schematic for exhaust treatment		PE14.00-P-2051-97FBH
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRH