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Lambda Control, Function - GF07.10-P-1010MNA

Engine 177.9 in model 205, 253 

Engine 177.9 in model 213 

up to model year 2021 

Function requirements, general 

Lambda control, general points 

The mixture composition is controlled within the narrowest limits of approx. λ = 1 in order to achieve high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters.

The ME-SFI [ME] control unit (N3/10) reads in the signals of the following sensors for this purpose:

The mixture composition is mainly changed by modifying the injection duration and the injection pressure.

The ME-SFI [ME] control unit distributes the required fuel quantity to each cylinder by actuating the following components of the fuel injection system:

Exhaust gas conversion in three-way catalytic converter 

G13770163Courtesy of MERCEDES-BENZ USA

Lambda control 

Lambda control is described in the following points:

Closed-loop control circuit 

The sensor elements of the oxygen sensors upstream of the catalytic converter react to the proportion of oxygen in the exhaust. The ME-SFI [ME] control unit reads in the signals of the sensor elements of the oxygen sensors upstream of the catalytic converter directly.

The ME-SFI [ME] control unit reduces the injection quantity when the oxygen content in the exhaust is low (λ < 1) and modifies the mixture composition in the direction of "lean". The oxygen content in the exhaust increases, and the lambda value is modified in the direction of λ = 1.

The ME-SFI [ME] control unit increases the injection quantity when the oxygen content in the exhaust is high (λ > 1) and modifies the mixture composition in the direction of "rich". The oxygen content in the exhaust drops, and the lambda value is modified in the direction of λ = 1.

This process is repeated (control loop). The ME-SFI [ME] control unit alters the mixture composition with a time delay in order to prevent any risk of jerking.

IMPORTANT A diagnostic tester can be used to display the regulation status as a lambda regulating factor which alters in a positive direction for leaning of the mixture and in a negative direction for enriching of the mixture.

Additional function requirements for two-sensor control 

Two-sensor control 

The two-sensor control monitors the functionality of the oxygen sensors upstream of the catalytic converter and the effect of the catalytic converters.

The ME-SFI [ME] control unit reads in the signals from the following sensors to do this:

The ME-SFI [ME] control unit determines the mean lambda value using the signals of the oxygen sensor elements downstream of the catalytic converter. This value is compared with a stored value. If the deviation is too large after several measurements, a correction value is calculated for the lambda control.

Using the correction value (value for new oxygen sensors upstream of catalytic converter = 0), aging of the oxygen sensors upstream of the catalytic converter is corrected to a certain extent. The correction value is achieved by the ME-SFI [ME] control unit by adapting the injection duration of the fuel injectors. If the correction value exceeds the prescribed limit value and if the following error causes of error are excluded for the mixture formation then the oxygen sensor upstream of the catalytic converter must be replaced.

The following errors can, for example, occur during mixture formation:

If the specified limit value is exceeded or if the plausibility check of the oxygen sensor signals (upstream or downstream of catalytic converter) is negative, the instrument cluster (A1) issues a fault message. The ME-SFI [ME] control unit transmits the relevant request via the engine CAN (CAN C), the powertrain control unit (N127), the chassis FlexRay (Flex E), the electronic ignition lock control unit (N73) and the user interface CAN (CAN HMI) to the instrument cluster.

IMPORTANT Exceeding of the limit value is stored in the fault memory of the ME-SFI [ME] control unit and can be read out and deleted using the diagnostic tester.

Oxygen sensor heater 

The oxygen sensors are heated for rapid attainment of the operating temperature. The heating also prevents damage to the oxygen sensor ceramics.

The ME-SFI [ME] control unit directly actuates the following components of the oxygen sensors:

When the exhaust system is extremely cold (condensation present), the oxygen sensor heaters are switched off to prevent damage (due to thermal shock).

Additional function requirements self-adjustment of the mixture formation 

Self adaptation of mixture formation 

For regulated catalytic converters, the lambda control determines the injection period so exactly that a specified air/fuel ratio (λ) is maintained under all operating conditions.

Self-adjustment ensures that the mixture composition in the open-loop operation (e.g. warm-up phase) is neither too rich nor too lean. This also prevents the lambda control from reaching the control limit at high altitudes.

If faults occur, the ME-SFI [ME] control unit corrects the mixture formation independently. In this case, the lambda characteristics map is shifted within the specified control limits so that the lambda control is not at the upper or lower control limit.

If the mixture composition is constantly drifting out of the middle controlled range, the ME-SFI [ME] control unit shifts the lambda characteristics map under certain operating conditions until the lambda control factor is about 0%.

Shifting of the lambda characteristics map 

G13770164Courtesy of MERCEDES-BENZ USA

Presentation of self-adjustment values using the diagnostic tester 

The following information can be read out with the diagnostic tester:

Representation takes place in the form of a factor, and means that the measured air mass value must be multiplied by the factor.

Additional function requirements for catalytic converter monitoring 

Example:

The ME-SFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h1.1) to determine the injection period (fuel injection quantity).

The maximum correction values are -0.68 to 1.32.

Catalytic monitoring 

The law maker requires that the hydrocarbon (HC) emissions do not exceed a certain value. It is therefore necessary to constantly check the catalytic converters for aging. Aging of a catalytic converter is caused by the oxygen storage capacity reducing over time and the reduced HC conversion resulting from this. The catalytic converter stores oxygen during the leaning of the mixture (control loop) and releases it again during enrichment of the mixture for HC conversion. To check the oxygen storage capacity, the fuel/air mixture is enriched (λ < 1), until the sensor elements of the oxygen sensors downstream of the catalytic converter reach a certain maximum value and the majority of the oxygen has dissipated.

Then the fuel/air mixture is leaned out (λ > 1) and the time it takes for the sensor elements of the oxygen sensors downstream of the catalytic converter to reach a certain minimum value and for the catalytic converter to fill up its oxygen storage is measured. If the time that is measured lies below a stored characteristic, the oxygen storage capacity is insufficient and a fault is stored in the ME-SFI [ME] control unit.

  Electrical function schematic for lambda control Engine 177.9 in model 205, 253 PE07.10-P-2710-97FBD
    Engine 177.9 in model 213 up to model year 2021 PE07.10-P-2710-97DBG
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    Engine 177.9 in model 213 up to model year 2021 GF07.70-P-9998MNE
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