Component Description For An Oxygen Sensor - GF07.04-S-6101SA

ENGINES 642.8 in MODEL 906 

with CODE (MG5) Engine OM 642 DE 30 LA, 140 kW (190 hp) 3800 RPM 

except CODE (ZU7) National version for Canada 

except CODE (ZU8) National version for USA 

ENGINES 642.8 in MODEL 639 

with CODE (XZ1) Model generation 1 

with CODE (MZ0) BlueEFFICIENCY 

Illustrated on model 906 

Task 

The oxygen sensor detects the residual oxygen content in the exhaust upstream of the catalytic converter with diesel particulate filter (DPF) for the following tasks:

• Injection control
• Zero quantity calibration
• Injection quantity correction
• Exhaust gas cleaning
• Function chain tests (for on-board diagnosis (OBD))

Schematic diagram 

Design 

The oxygen sensor is designed as a wideband sensor. It consists of a pump cell, a concentration cell and a heating element. The pump cell is connected with the concentration cell via a diffusion gap. The concentration cell is connected via the reference air duct with the ambient atmosphere.

The oxygen sensor is fitted with an optimized heater and protective pipe geometry. The heater output requirement and sooting tendency are thereby reduced.

Schematic diagram 

Function 

The exhaust in the measuring chamber for the concentration cell passes through the diffusion gap. Through application of the supply voltage to the platinum electrodes of the pump cell, oxygen is pumped into or out of the reference chamber. If λ = 1 is already available in the measuring housing, oxygen must not be transported. In this case, the pump current is 0 mA. The CDI control unit (N3/30) subsequently regulates the voltage in such a way that the mixture composition in the measuring housing is held constant at the value λ = 1. If the exhaust gas is lean, oxygen is pumped out of the measuring chamber through the pump cell.

This process is recognized by the CDI control unit based on the negative pump current. If the exhaust gas is rich, oxygen is pumped into the measuring chamber. The oxygen is generated by the catalytic decomposition of carbon dioxide (CO ₂ ) and water. This process is recognized by the CDI control unit based on the positive pump current. Thus the pump current required in each case is a measure for the Lambda air/fuel ratio.

The integrated heating element is actuated by the CDI control unit when necessary so that the oxygen sensor will quickly reach its operating temperature of about 600°C.