S14.00-3000-12
Position
The O2 sensor (R22) is installed in the exhaust system upstream of the catalytic converter.
Task
Detecting the residual oxygen content in the exhaust and informing the PEC control module
Design
The active sensor ceramic (3) consists of gas-impermeable ceramic body made off zirconium dioxide. A protective tube (8) with several slots protects the ceramic body from mechanical stresses (shocks) and from temperature jumps.
The platinum electrode (5) at the exhaust side acts like a mini catalyst, in other words the impacting exhaust gas is catalytically post-treated at this point and brought into the stochiometric equilibrium. The inner, open space (7) is in contact with the ambient air.
1 Electrical connection
2 Sensor housing
3 Active sensor ceramic
4 Electrode (inner)
5 Electrode (outer)
6 Heating element
7 Inner, open space
8 Protective tube
R22 O2 sensor
S14.00-3001-01
Function
The operation is based on the principle of a galvanic oxgen concentration cell with a solid electrolyte.
The ceramic material used is conductive for oxygen ions from about 300 °C. If the oxygen concentration at both electrodes (4, 5) of the O2 sensor (R22) differs, this produces an electric voltage. The voltage output by the O2 sensor (R22), which depends on the residual oxygen content in the exhaust, attains in the case of:
– Rich fuel-air mixture (λ < 1) 800 – 1000 mV
– Lean fuel-air mixture (λ > 1) approx. 100 mV
Rich fuel-air mixture
Lean fuel-air mixture
In addition to the residual oxygen content in the exhaust, the temperature of the active sensor ceramic (3) also plays a major role as this determines the conductivity for oxygen ions. Consequently, the pattern of the voltage output as a function of the air index λ is greatly influenced by the temperature. The figures stated therefore apply to an operating temperature of approx. 600 °C. But, the response time for a voltage change if there is a variation to the mixture composition, is also greatly dependent on temperature. If these response times at a temperature below 300 °C are within the seconds range, the sensor alreay reacts after a time of < 50 ms at the optimal operating temperature of around 600 °C. After the engine is started, therefore, the lambda closed-loop control is inhibited (open-loop mode) until the minimum operating temperature of the O2 sensor (R22) of about 300 °C is reached.
The O2 sensor (R22) is heated electrically in order to ensure that it reaches its operating temperature as rapidly as possible, and to also maintain a constant operating temperature. The heating element (6) of the O2 sensor (R22) is supplied with the voltage by the PEC control module during the entire driving cycle, in other words the O2 sensor is heated all the time the vehicle is driven.