Oxygen Sensor
The oxygen sensor in the C 14 SE engines is located in the exhaust pipe very close to the cylinder head. Quick warm-up guarantees that the engine operates in a closed oxygen sensor loop after a brief period of time.
The mixture adaptation accuracy required can only be attained by this closed loop, which continually determines the residual oxygen content of the combusted mixture and correspondigly corrects the feed fuel composition.
This is only possible with the oxygen sensor. With a stochiometric mixture (l = 1), the voltage jumps by about 800 mV if the mixture changes from the lean range to the rich range or from rich to lean (voltage with rich mixture 800 to 1000 mV, with lean mixture approx. 100 mV, transition from lean to rich is at 450 mV).
The function of the sensor is simple. One part of a ceramic body (zirconia) is in contact with ambient air, the other with exhaust gas. The surfaces of this body are covered on both sides with a gas-permeable platinum layer. A further porous ceramic layer protects the exhaust side of the sensor from contamination from combustion residue.
Zirconia conducts oxygen ions (ion = electrically charged atom or molecule) at approx.
350 °C/660 °F. If the oxygen concentration at the two contact points is unequal, a potential slope occurs between them. This voltage is directly proportional to the difference between the oxygen content in the ambient air and the residual oxygen content in the exhaust gas.
At an exact stochiometric fuel/air ratio, this voltage is approx. 450 mV.
As the residual oxygen content depends directly on the fuel/air mixture being fed to the combustion engine, it is possible to use it as a dimension for the fuel/air mixture.
Therefore: If the fuel/air mixture is richer than l = 1, the oxygen sensor voltage increases to a value larger than 450 mV. If it is lean, the value sinks to below 450 mV.
Oxygen Sensor (continued)
The oxygen sensor voltage is used together with other sensor information to attain the desired air/fuel mixture.
Oxygen sensor properties
- Attains operating temperature quickly
- Simple construction
| Fehler! Datei kann nicht geöffnet werden! | |||
|---|---|---|---|
| .P. D2428.tif | 9 | 7,5 | tiff;; |
Diagnosis
For diagnosis with TECH 1, the following must be observed:
With the ignition switched on, the integrator value can deviate from 128 steps when the engine is stationary and at operating temperature.