Exhaust gas purifying system for vehicle

Abstract

An exhaust gas purifying system for a vehicle may include a three-way catalyst into which an exhaust gas from an engine is introduced, an SCR catalyst positioned downstream from the three-way catalyst and reducing NO x , an oxidizing catalyst positioned downstream from the three-way catalyst, a rear oxygen sensor positioned behind the three-way catalyst and a controller receiving signals from the rear oxygen sensor and controlling a catalyst purge, where the controller ends the catalyst purge while the signals still show a lean state, after starting the catalyst purge following end of a fuel-cut.

What is claimed is: 
     
         1 . An exhaust gas purifying system for a vehicle, comprising:
 a three-way catalyst into which an exhaust gas from an engine is introduced;   an SCR catalyst positioned downstream from the three-way catalyst and reducing NO x ;   an oxidizing catalyst positioned downstream from the three-way catalyst;   a rear oxygen sensor positioned behind the three-way catalyst; and   a controller receiving signals from the rear oxygen sensor and controlling a catalyst purge; wherein the controller ends the catalyst purge while the signals still show a lean state after starting the catalyst purge following end of a fuel-cut.   
     
     
         2 . The exhaust gas purifying system for a vehicle of  claim 1 , wherein the oxidizing catalyst is positioned upstream of the SCR catalyst. 
     
     
         3 . The exhaust gas purifying system for a vehicle of  claim 1 , wherein the oxidizing catalyst is positioned downstream of the SCR catalyst. 
     
     
         4 . A method of controlling the exhaust gas purifying system for a vehicle according to  claim 1 , the method comprising:
 a purge start checking step of determining whether catalyst purge starts after fuel-cut;   a monitoring step of monitoring an output value of the rear oxygen sensor at downstream from the three-way catalyst to determine whether the output value shows a lean state after the catalyst purge starts; and   a purge ending step of ending the catalyst purge while it is determined in the monitoring step that the output of the rear oxygen sensor shows the lean state.   
     
     
         5 . The method of  claim 4 , wherein the purge ending step includes ending the catalyst purge when the output value of the rear oxygen sensor is close to being out of the lean state.