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

Engine 276.8 in model 172.4 

Function requirements for exhaust treatment, general points

Exhaust treatment, general

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

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

IMPORTANT Exhaust gas recirculation rate The ME-SFI [ME] control unit (N3/10) determines the valve overlap through actuation of the left and right intake camshaft solenoids (Y49/4 and Y49/5) and the left and right exhaust camshaft solenoids (Y49/6 and Y497). 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

The pollutants in the exhaust emitted by the engine are converted chemically by the catalytic converter for A=1.

Through oxidation, carbon monoxide is converted to carbon dioxide (CO2 ) 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 (for automatic transmission)

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. The ME-SFI [ME] control unit controls the upshift delay dependent on the following signals:

Upshift delay is active for a maximum of 160 s and is entirely electronic.

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

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 firewall 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:

IMPORTANT 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 catalytic converter.

Changes in the oxygen content downstream of the catalytic converters are almost completely dampened by the high oxygen storage capacity of the catalytic converters. Consequently, the signals from the oxygen sensor sensor elements downstream of the catalytic converters have low amplitude and are virtually constant.

If the catalytic converters are no longer ready to operate then the signals from the oxygen sensor sensor elements upstream of the catalytic converter and the signals from the oxygen sensor 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 [ME] control unit.

For fault detection the engine diagnosis indicator lamp (A1e58) is actuated by the ME-SFI [ME] control unit in IC (A1) via the chassis CAN 1, the front SAM control unit with fuse and relay module (N10/1) and chassis CAN 2 (CAN E2).

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   PE14.00-P-2051-97TAH 
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