Exhaust gas purifying system for internal combustion engine

Abstract

An exhaust gas purifying system for an internal combustion engine has a relatively simple construction and is capable of accurately calculating the amount of SOx deposited on a NOx catalyst. A CO2 sensor having a detection electrode containing BaCO3 is disposed in an intake pipe at a location downstream of a confluent portion. A catalyst SOx deposition amount is calculated according to an EGR rate and a sensor deposition amount, based on the fact that the relationship between the sensor deposition amount detected by the CO2 sensor and the catalyst SOx deposition amount is determined according to the EGR rate.

1 . An exhaust gas purifying system for an internal combustion engine, for purifying exhaust gases discharged from the engine to an exhaust passage, comprising:
 a NOx catalyst disposed in the exhaust passage, for purifying NOx in exhaust gases;   an EGR passage that branches from the exhaust passage on an upstream side of said NOx catalyst and joins an intake passage, for recirculating part of exhaust gases discharged into the exhaust passage into the intake passage;   a CO2 sensor that is disposed in the intake passage at a location downstream of a confluent portion where said EGR passage joins the intake passage, and includes a detection electrode containing BaCO3, for detecting a CO2 concentration in intake air sucked into the engine;   EGR rate-calculating means for calculating a recirculation rate of exhaust gases recirculated via said EGR passage as an EGR rate; and   SOx deposition amount-calculating means for calculating an amount of SOx deposited on said NOx catalyst as a SOx deposition amount, according to the calculated EGR rate and a detection value detected by said CO2 sensor.   
     
     
         2 . The exhaust gas purifying system as claimed in  claim 1 , further comprising average value-calculating means for calculating an average value of the EGR rate over a predetermined time period, and
 wherein said SOx deposition amount-calculating means calculates the SOx deposition amount using the calculated average value of the EGR rate.   
     
     
         3 . The exhaust gas purifying system as claimed in  claim 1 , further comprising atmospheric CO2 concentration-obtaining means for obtaining an atmospheric CO2 concentration;
 error-calculating means for calculating an error of the detection value detected by said CO2 sensor, the error being caused by a deposition of SOx on said detection electrode of said CO2 sensor, according to the CO2 concentration detected by said CO2 sensor when no exhaust gases are being recirculated via said EGR passage, and the obtained atmospheric CO2 concentration; and   correction means for correcting the detection value detected by said CO2 sensor according to the calculated error.