Exhaust gas purifying system for internal combustion engine

Abstract

The exhaust gas purifying system ( 1 ) for the internal combustion engine, comprising the first exhaust gas purifying device ( 31 ) provided with the NOx occlusion reduction type catalyst arranged in the exhaust gas passage ( 30 ) of the internal combustion engine ( 10 ), and also comprising the respective oxygen concentration sensors ( 34, 35 ) arranged at the upstream and downstream of the first exhaust gas purifying device ( 31 ), and which controls to end the rich control when a difference between the oxygen concentrations detected by both of said oxygen concentration sensors ( 34, 35 ) falls not higher than a predetermined judgment value during the rich control for restoring the catalytic ability of the first exhaust gas purifying device ( 31 ), is provided with the second exhaust gas purifying device ( 32 ) for cleaning HC and CO at the downstream of said first exhaust gas purifying device ( 31 ). In such a manner, HC and CO can be prevented from being discharged into the atmospheric air at the time of ending the rich control.

What is claimed is:  
     
         1 . An exhaust gas purifying system for an internal combustion engine, comprising a first exhaust gas purifying device composed of a NOx occlusion reduction type catalyst arranged in the exhaust passage of an internal combustion engine, and also comprising the respective oxygen concentration sensors arranged at the upstream and downstream of the first exhaust gas purifying device, and which controls to end the rich control when a difference between the oxygen concentrations detected by both of said oxygen concentration sensors falls not higher than a predetermined judgment value during the rich control for restoring the catalytic ability of the first exhaust gas purging device, wherein a second exhaust gas purifying device for purifying HC and CO is arranged at the downstream of said first exhaust gas purifying device.  
     
     
         2 . An exhaust gas purifying system as claimed in  claim 1 , wherein said second exhaust gas purifying device is composed of any one of the NOx occlusion reduction type catalyst, a DPF supporting thereon the NOx occlusion reduction type catalyst, a three-way catalyst, and an oxidation catalyst with an oxygen occlusion function, or composed of a combination of some of these.