Emission gas cleaning device of internal combustion engine

Abstract

In a system having an oxygen sensor arranged downstream of a NOx storage-reduction catalyst, a constant current is made to flow between sensor electrodes by a constant current circuit provided in the outside of the oxygen sensor, which makes it possible to change an output characteristic of the oxygen sensor. Further, during a lean combustion control of an engine, a sensing responsiveness to a lean component of the oxygen sensor is improved. In this way, when NOx (lean component) is emitted to the downstream of the catalyst, the NOx can be quickly sensed by the oxygen sensor. Meanwhile, during a rich combustion control of the engine, the sensing responsiveness to a rich component of the oxygen sensor is improved. In this way, when HC and CO (rich components) are emitted to the downstream of the catalyst, the HC and the CO can be quickly sensed by the oxygen sensor.

1 . An emission gas cleaning device of an internal combustion engine having a catalyst which cleans an emission gas of an internal combustion engine, and an emission gas sensor which is arranged on a downstream of the catalyst or in the catalyst and senses a concentration of a specified component in the emission gas by a sensor element having a solid electrolyte material provided between a pair of sensor electrodes one of which is exposed to the atmosphere, the emission gas cleaning device of an internal combustion engine comprising:
 a constant current supply portion making a constant current flow between the sensor electrodes to change an output characteristic of the emission gas sensor; and 
 a current control portion determining a direction of the constant current flowing between the sensor electrodes according to a change request for changing the output characteristic of the emission gas sensor or according to an operating state of the internal combustion engine, the current control portion controlling the constant current supply portion in such a way that the constant current flows in the direction. 
 
     
     
         2 . The emission gas cleaning device of an internal combustion engine as claimed in  claim 1 , wherein
 the catalyst is a NOx storage-reduction catalyst for adsorbing NOx in the emission gas when an air-fuel ratio of the emission gas flowing into the catalyst is lean and for reducing, cleaning, and discharging the NOx adsorbed by the catalyst when the air-fuel ratio of the emission gas flowing into the catalyst becomes rich.   
     
     
         3 . The emission gas cleaning device of an internal combustion engine as claimed in  claim 2 , wherein
 during a lean combustion control in which an air-fuel ratio of an air-fuel mixture to be supplied to the internal combustion engine is controlled to a lean value, the current control portion controls the constant current supply portion in such a way that the constant current flows in a direction in which a sensing responsiveness to a lean component of the emission gas sensor is improved, and   during a rich combustion control in which the air-fuel ratio of the air-fuel mixture to be supplied to the internal combustion engine is controlled to a rich value, the current control portion controls the constant current supply portion in such a way that the constant current flows in a direction in which a sensing responsiveness to a rich component of the emission gas sensor is improved.   
     
     
         4 . The emission gas cleaning device of an internal combustion engine as claimed in  claim 1 , wherein
 the catalyst is a three-way catalyst for cleaning CO, HC, and NOx in the emission gas.