Component description for a O2 sensor - GF07.04-P-6100TU
ENGINE 642.920 in MODEL 211.022 with CODE (494) USA version
ENGINE 642.920 in MODEL 211.024
Location
The O2 sensor upstream of TWC is located at the front in the NOX catalytic converter, behind the turbocharger. The O2 sensor downstream of TWC is located behind the NOX catalytic converter.
Task of the O2 sensor upstream of TWC
The O2 sensor upstream of TWC detects the residual oxygen content in the exhaust and passes on an appropriate signal to the CDI control unit (N3/9). Secondary injection amounts for regeneration operation of the NOX catalytic converter is regulated depending on the determined residual oxygen content.
Task of the O2 sensor downstream of TWC
The O2 sensor upstream of TWC detects the residual oxygen content in the exhaust downstream of the NOX catalytic converter and passes on an appropriate signal to the CDI control unit. The period of regeneration operation of the NOX catalytic converter is regulated depending on the determined residual oxygen content.
Design
The O2 sensor used upstream TWC is designed as a wideband oxygen sensor. The wideband oxygen sensor consists of a pump cell, a concentration cell and a heating element. The heating element maintains the temperature of the ceramic probe body constant at 780°C. The conductivity of the ceramic probe body is temperature-dependent.
Function
Via a small gas entry hole in the pump cell, the exhaust gas reaches the measuring chamber of the concentration cell. The oxygen from the exhaust is pumped into a reference chamber which serves as the oxygen reference. By application of a voltage to the platinum electrodes of the pump call. oxygen can be pumped into or out of the reference chamber. An evaluation module in the CDI control unit regulates the voltage applied to the pump cell so that the mixture composition in the measuring chamber is continuously adjusted to the value λ = 1. In the case of lean exhaust gas the pump cell pumps oxygen out of the measuring chamber. The pump flow is thus positive.
If, however, the exhaust gas is rich, then oxygen at the platinum electrodes is pumped via the catalytic decomposition of carbon dioxide (CO2) and water out of the ambient exhaust gas into the measuring chamber. The pump flow is thus negative. If λ = 1 is available in the measuring housing, oxygen must not be transported. In this case the pump flow = 0 mA. The respective required pump flow is the measurement for the oxygen:air ratio and is processed in the CDI control unit for the corresponding functionality.