GF07.10-P-1010MMI Lambda Control, Function
GF07.10-P-1010MMI Lambda Control, Function
ENGINES 152.9 in MODEL 172.4
Function requirements for lambda control, general points
^ Circuit 87M (engine timing ON)
^ Engine running
^ Coolant temperature greater than-10°C
^ Operating temperature reached in LH and RH oxygen sensors upstream of catalytic converter (G3/3, G3/4)
^ Deceleration fuel shutoff not active.
For this purpose, the ME-SFI [ME] control unit (N3/10) reads the following sensors:
- Coolant temperature sensor (B11/4)
- Pressure sensor downstream of throttle valve (B28/7), engine load
- LH and RH oxygen sensor sensor elements upstream of catalytic converter (G3/3b1, G3/4b1)
Lambda control, general points
The mixture composition is controlled within the narrowest limits around Lambda = 1 in order to achieve high conversion of the exhaust gases (exhaust gas conversion) in the catalytic converters.
Exhaust gas conversion in the three way catalytic converter
A Exhaust gas emission
B Controlled range around Lambda=1 (catalyst window)
CO Carbon monoxide
HC Hydrocarbon
NOx Nitrogen oxides
Lambda Fuel air/fuel ratio
Function sequence for lambda control
Lambda control is described in the following points:
^ Function sequence for the lambda closed loop
^ Function sequence for two-sensor control
^ Function sequence for oxygen sensor heaters
^ Function sequence for self-adjustment of the mixture formation
^ Function sequence for catalytic converter monitoring
Function sequence for the lambda closed-loop control circuit
The LH and RH oxygen sensor sensor elements upstream of catalytic converter react to the oxygen contents in the exhaust and send corresponding signals to the ME-SFI [ME] control unit.
For Lambda less than 1 and a low oxygen content in the exhaust the sensor elements 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 Lambda=1.
For Lambda less than 1 and a high oxygen content in the exhaust the sensor elements 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 Lambda=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.
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
^ Operating temperature of catalytic converters reached
^ Lambda regulation active
^ Left and right oxygen sensors downstream of catalytic converter (G3/5, G3/6) are error-free
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 [ME] control unit reads the following sensors:
- LH and RH oxygen sensors sensor elements upstream of catalytic converter, oxygen sensor signals
- LH and RH oxygen sensors sensor elements downstream of catalytic converter (G3/5b1, G3/6b1), oxygen sensor signals
The ME-SFI [ME] control unit determines the Lambda mean value from signals LH and RH oxygen sensors sensor elements 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 = 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 sources of error are excluded for the mixture formation then the oxygen sensors upstream of catalytic converter must be replaced.
The following errors can, for example, occur during mixture formation: the oxygen sensors
- Wear or carbon deposits on the fuel injectors, - Damaged pressure sensor downstream of the throttle valve
- Damaged fuel pressure and temperature sensor (B4/25)
- Damaged oxygen sensors
- Defective purge control valve (Y58/1)
- Wear on the engine (e.g. valve leakage)
If the specified limit value is exceeded or if the plausibility check of the sensor signals (upstream or downstream of catalytic converter) is negative, the ME-SFI [ME] control unit actuates the engine diagnosis indicator lamp (A1e58) in the IC (A1) via the chassis CAN (CAN C) and the interior CAN (CAN B). The exceeded 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 diagnostic system.
Function sequence for oxygen sensor heaters
The LH and RH oxygen sensors heaters upstream of catalytic converter (G3/3r1, G3/4r1) and the LH and RH oxygen sensors heaters downstream of catalytic converter (G3/5r1, G3/6r1) bring the oxygen sensors more rapidly up to operating temperature. Controlled heating also prevents damage to the oxygen sensor ceramics.
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
^ Lambda regulation active
^ Engine at idle or on partial load
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 fuel-air ratio (Lambda) is maintained under all operating conditions.
Self-adjustment ensures that the mixture composition in the control mode (e.g. warming-up phase) 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 in the mixture formation. In this case, the lambda performance map is shifted within the specified limits so that the lambda control is not at the upper or lower end stop.
Shifting of the lambda performance map
a Controlled range of lambda control factor
b Shifting of the lambda performance map
c Position of lambda performance map prior to self-adjustment
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%.
Shown with self-adjustment value with Xentry diagnostics
The following can be read out with Xentry diagnostics:
- Shifting of the lambda performance map
- Direction of shift (rich or lean)
- Size of the shift
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/hour
Displayed factor in Xentry diagnostics: 1.1
To determine the injection duration (fuel injection quantity), the MESFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h X1.1).
The maximum correction values are -0.68 to +1.32.
Additional function requirements for catalytic converter monitoring
^ Operating temperature of catalytic converters reached
^ Lambda control active
Catalytic converter monitoring, general points
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 arises from the oxygen storage capacity reducing over time and the subsequent resultant reduced HC conversion.
The catalytic converter stores oxygen during the leaning of the mixture (lambda closed loop) and releases it again during enrichment of the mixture for HC conversion.
Function sequence for catalytic converter monitoring
In order to check the oxygen storage capacity a rich mixture (Lambda less than 1) is given out until the oxygen sensors downstream of catalytic converter have reached a certain maximum value and the largest part of the oxygen is removed.
A lean mixture (Lambda less than 1) is then given out and the time is measured to see how it takes until the LH and RH oxygen sensors sensor elements downstream of catalytic converter have reached a certain minimum value and the catalytic converter has filled up its oxygen storage capacity.
If the time measured lies below a stored characteristic then the oxygen storage capacity is inadequate and an error is stored in the ME-SFI [ME] control unit.
