Oxygen Sensor: Description and Operation

GF07.04-P-6100GZ Component Description For A O2 Sensor
ENGINE 642 in MODEL 164.1 /8 up to Model Year 2008
ENGINE 642 in MODEL 463 up to 31.5.12





Shown on model 164

G3/2 O2 sensor upstream of TWC

Location
The O2 sensor upstream of TWC (G3/2) is located at the front in the oxidation catalytic converter, behind the turbocharger.

Task
The O2 sensor upstream of TWC (G3/2) detects residual oxygen contained in the exhaust gas and emits a corresponding signal to the CDI control unit (N3/9).

Design
The O2 sensor used upstream of TWC (G3/2) is designed as a wide band oxygen sensor. The wide band 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 sensor ceramic 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. Through application of a voltage to the platinum electrodes of the pump cell oxygen can be pumped into or out of the reference chamber. An evaluation module in the CDI control unit (N3/9) regulates the voltage applied to the pump cell so that the mixture composition in the measuring chamber is continuously adjusted to the value Lambda = 1.
If the exhaust gas is lean, oxygen is pumped out of the measuring chamber via the pump cell. 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 Lambda = 1 is available in the measuring housing, oxygen must not be transported. In this case the pump flow = 0 mA. The pump flow required respectively is the measurement for the oxygen air ration and is processed in the CDI control unit (N3/9) for the corresponding functionality.