Nitrogen Oxides (NOx) Sensor

ENGINE CONTROL COMPONENTS

Nitrogen Oxides (NOx) Sensor
The NOx sensor detects the presence of oxygen (02) and NOx concentrations in the exhaust system. The NOx Sensor uses two measurement chambers to determine 02 and NOx concentrations. The 02 concentration is measured in the first measurement chamber. Exhaust gas enters the first chamber through a diffusion barrier. The sensor infers an air fuel ratio relative to the stoichiometric air fuel ratio by balancing the amount of oxygen pumped in or out of the measurement chamber. As the exhaust gases become richer or leaner, the amount of oxygen that must be pumped in or out to maintain a stoichiometric air fuel ratio in the measurement chamber varies in proportion to the air fuel ratio. The amount of current required to pump the oxygen in or out of the measurement chamber calculates the air fuel ratio. The calculated air fuel ratio is the output from the pumping current controller in the NOx module and not a signal directly from the sensor.

The NOx concentration measurement takes place in the second measurement chamber. Exhaust gas passes from the first measurement chamber through a second diffusion barrier into the second measurement chamber. The NOx present in the second measurement chamber is dissociated into nitrogen (N2) and 02. The excess 02 is pumped out of the measurement chamber by the pumping current. The amount of current required to pump the oxygen ions out of the measurement chamber calculates the NOx content. The calculated NOx content is the output from the pumping current controller in the NOx module and not a signal directly from the sensor.

The NOx sensor is equipped with a memory component which stores gain and offset characteristics of the sensor to compensate for part to part variation of the element during the manufacturing process.