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Lambda control, function - GF07.10-P-1010MM

ENGINE 276.9 in MODEL 204 

ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 up to model year 2014 

Function requirements for lambda control, general points 

Lambda control, general points 

The mixture composition in homogeneous mode is controlled within the narrow limits around λ = 1 in order to achieve a high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters. For engine with code (920) Gasoline direct injection with stratified charge, the ME-SFI [ME] control unit (N3/10) regulates to a lean mixture λ>1 based on a characteristics map to lower the fuel consumption.

For this purpose, the ME-SFI [ME] control unit (N3/10) reads in the following sensors:

Exhaust conversion in three-way catalytic converter (for engine with homogeneous mode) 

Fig 1: Exhaust Conversion Three-Way Catalytic Converter Graph (For Engine With Homogeneous Mode)
G10049927Courtesy of MERCEDES-BENZ USA

Function sequence for lambda control 

Lambda control is described in the following points:

Function sequence for the lambda closed-loop control circuit 

The oxygen sensors upstream of the catalytic converter respond to the oxygen content in the exhaust and send corresponding signals to the ME-SFI [ME] control unit.

For λ <1 and a low oxygen content in the exhaust, the oxygen sensors transmit the signal "rich mixture" to the ME-SFI [ME] control unit. This then reduces the injection quantity through regulation of the fuel injectors (Y76) and alters the mixture composition in the direction "lean". The oxygen content in the exhaust increases and the value alters in the direction λ=1.

For λ <1 and a high oxygen content in the exhaust the oxygen sensors transmit the signal "lean mixture" to the ME-SFI [ME] control unit. This then increases the injection quantity through regulation of the fuel injectors and alters the mixture composition in the direction "rich". The oxygen content in the exhaust decreases and the value alters in the direction 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.

For an engine with code (920) Gasoline direct injection with stratified charge regulation takes place according to a stored characteristics map to a lean mixture with λ >1.

IMPORTANT Indication of the regulation status takes place in Xentry Diagnostics based on 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 

Function sequence for two-sensor control 

The two-sensor control monitors the function of the left and right oxygen sensors upstream of the catalytic converter and the effectiveness of the catalytic converters.

To do this, the ME-SFI control unit reads the following sensors:

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

Using the correction value (value for new left and right oxygen sensors upstream of catalytic converter is about 0), aging of the oxygen sensors upstream of the catalytic converter is adjusted for within certain limits. It depends on the characteristics map and the ME-SFI [ME] control unit applies it through adaptation of the injection time of the fuel injectors. If the correction value exceeds the prescribed limit value and if the following error causes are excluded for the mixture formation then the oxygen sensors upstream of CAT 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 on the oxygen sensor signals (upstream or downstream of the catalytic converter) is negative, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) via the chassis CAN 1 (CAN E). Exceeding of the limit value is stored in the fault memory by the ME-SFI [ME] control unit and can be read out and deleted using the Xentry Diagnostics.

Function sequence for oxygen sensor heater 

The oxygen sensor heaters bring the oxygen sensors up to operating temperature more quickly. With controlled heating, they also prevent damage to the oxygen sensor ceramics.

The oxygen sensor heaters differ according to lambda sensor type:

Wideband oxygen sensor 

The left and right oxygen sensors upstream of the catalytic converter are heated continuously when the engine is running, in order to keep them functioning.

Temperature control and temperature measurement (by measuring the internal resistance) is performed by special control electronics in the ME-SFI [ME] control unit.

Narrow band oxygen sensor 

Using a ground signal, the ME-SFI [ME] control unit actuates and synchronizes the oxygen sensor heaters for the left and right oxygen sensors downstream of the catalytic converter.

To do this the ME-SFI [ME] control unit reads in the signal from the coolant temperature sensor (model 204, 207, 212), coolant temperature sensor (model 218).

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

Additional function requirements self-adjustment of the mixture formation 

Function sequence for self-adjustment of the mixture formation 

For regulated catalytic converters, the lambda control determines the injection time 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) is neither too rich nor too lean. It also prevents the lambda control from coming to the end stop at high altitudes.

If a fault occurs, the ME-SFI [ME] control unit automatically makes a correction of the mixture formation. 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 end stop.

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 

Fig 2: Lambda Characteristics Map Graph
G10049928Courtesy of MERCEDES-BENZ USA

Shown with self-adjustment value with Xentry diagnostics 

The following can be read out with Xentry diagnostics:

Presentation takes place in the form of a factor and means that the measured air mass value is multiplied by the factor.

Example:

Measured air mass: 150.0 kg/h

Displayed factor in Xentry diagnostics: 1.1

To determine the injection duration (fuel injection quantity), the ME-SFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h X 1.1).

The maximum correction values are -0.68 to +1.32.

  Electrical function schematic for lambda control MODEL 204 PE07.10-P-2710-97FAK
MODEL 207 PE07.10-P-2710-97EAH
MODEL 212 PE07.10-P-2710-97DAI
Model 218 PE07.10-P-2710-97XAB
  Overview of system components for gasoline injection and ignition system with direct injection ENGINE 276.9 in MODEL 204
ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 up to model year 2014		 GF07.70-P-9998MM
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