Exhaust Gas Purifying Device for Internal Combustion Engine

Abstract

An NO X occluding and reducing catalyst 7 is arranged in an exhaust gas passage 2 of an engine 1 so as to occlude, reduce and purify NO X contained in an exhaust gas. An H2 sensor 33 is arranged in the exhaust gas passage on a downstream side of the NO X occluding and reducing catalyst 7 and a hydrogen component concentration of the exhaust gas is detected. When an amount of NO X occluded in the NO X occluding and reducing catalyst is increased to a predetermined value, an electronic control unit (ECU) 30 of the engine operates the engine at a rich air-fuel ratio, and a regenerating operation, by which a rich air-fuel ratio exhaust gas is supplied to the NO X occluding and reducing catalyst, is executed so as to reduce and purify NO X which is occluded in the NO X occluding and reducing catalyst. At the time of executing the regenerating operation, when the H 2 sensor 33 detects hydrogen components in the exhaust gas, ECU 30 finishes the regenerating operation. Due to the foregoing, it is possible to accurately judge the time for terminating the regenerating operation of the NO X occluding and reducing catalyst.

1 . An exhaust gas purifying device for an internal combustion engine comprising: an NO X  occluding and reducing catalyst disposed in an exhaust passage of an internal combustion engine, the NO X  occluding and reducing catalyst occluding NO X  contained in exhaust gas by one of the absorption and the adsorption or by both the absorption and the adsorption when an air-fuel ratio of the exhaust gas flowing into the catalyst is lean, and reducing and purifying the occluded NO X  with a reducing component contained in the exhaust gas when an air-fuel ratio of the exhaust gas is a stoichiometric air-fuel ratio or a rich air-fuel ratio; and
 an H 2  sensor disposed in at least one of the exhaust gas passages on the inlet side and the outlet side of the NO X  occluding and reducing catalyst for detecting a hydrogen component concentration of the exhaust gas, wherein   the exhaust gas purifying device executes a regenerating operation in which the exhaust gas of a rich air-fuel ratio or a stoichiometric air-fuel ratio is supplied to the NO X  occluding and reducing catalyst for a predetermined period of time when the NO X  occluding and reducing catalyst is to reduce and purify the NO X  occluded in the NO X  occluding and reducing catalyst and, during the regenerating operation, the exhaust gas purifying device controls the air-fuel ratio of the exhaust gas flowing into the NO X  occluding and reducing catalyst based on the hydrogen component concentration, in the exhaust gas, detected by the H 2  sensor.   
   
   
       2 . An exhaust gas purifying device for an internal combustion engine according to  claim 1 , wherein the H 2  sensor is arranged in an exhaust gas passage on an outlet side of the NO X  occluding and reducing catalyst, and at the time of executing the regenerating operation, a time for terminating the regenerating operation is judged according to a hydrogen component concentration in the exhaust gas detected by the outlet side H 2  sensor. 
   
   
       3 . An exhaust gas purifying device for an internal combustion engine according to  claim 1 , wherein the H 2  sensor is arranged in at least an exhaust gas passage on the outlet side of the NO X  occluding and reducing catalyst, the regenerating operation includes operations for first supplying the exhaust gas of a rich air-fuel ratio to the NO X  occluding and reducing catalyst and then supplying the exhaust gas of a stoichiometric air-fuel ratio to the NO X  occluding and reducing catalyst and, the time at which the exhaust gas air-fuel ratio is switched from the rich air-fuel ratio to the stoichiometric air-fuel ratio is determined in accordance with the hydrogen component concentration detected by the outlet side H 2  sensor. 
   
   
       4 . An exhaust gas purifying device for an internal combustion engine according to  claim 1 , wherein the H 2  sensor is arranged in an exhaust gas passage on the inlet side of the NO X  occluding and reducing catalyst, and at the time of executing the regenerating operation, an air-fuel ratio of the exhaust gas flowing into the NO X  occluding and reducing catalyst is controlled so that a hydrogen component concentration in the exhaust gas detected by the inlet side H 2  sensor can be a predetermined target value. 
   
   
       5 . An exhaust gas purifying device for an internal combustion engine according to  claim 4 , wherein the target value of the hydrogen component concentration is high at the time of starting the regenerating operation, and then the target value of the hydrogen component concentration is gradually decreased with the lapse of time. 
   
   
       6 . An exhaust gas purifying device for an internal combustion engine according to  claim 2 , wherein according to the lapse of time from the start of the regenerating operation to the end of the regenerating operation which is judged according to the hydrogen component concentration in the exhaust gas detected by the downstream side H 2  sensor, a degree of deterioration of the NO X  occluding and reducing catalyst is judged. 
   
   
       7 . An exhaust gas purifying device for an internal combustion engine comprising an NO X  occluding and reducing catalyst disposed in an exhaust passage of an internal combustion engine, the NO X  occluding and reducing catalyst occluding NO X  contained in exhaust gas by one of the absorption and the adsorption or by both the absorption and the adsorption when an air-fuel ratio of the exhaust gas flowing into the catalyst is lean and reducing and purifying the occluded NO X  with a reducing component contained in the exhaust gas when an air-fuel ratio of the exhaust gas is a stoichiometric air-fuel ratio or a rich air-fuel ratio,
 the exhaust gas purifying device for an internal combustion engine further comprising:   NO X  occluding and reducing catalysts arranged in series to each other on the upstream side and the downstream side of the exhaust gas passage of the internal combustion engine; and an H 2  sensor, which is arranged in series to each other in the exhaust gas passage between the upstream side NO X  occluding and reducing catalyst and the downstream side NO X  occluding and reducing catalyst, for detecting a hydrogen component concentration in the exhaust gas, wherein   when the NO X  occluding and reducing catalyst is to reduce and purify NO X  occluded during a lean air-fuel ratio operation of the engine, at the time of executing a regenerating operation in which the exhaust gas of a rich air-fuel ratio or a stoichiometric air-fuel ratio is supplied to the NO X  occluding and reducing catalyst for a predetermined period of time, according to the hydrogen component concentration in the exhaust gas detected by the H 2  sensor, an air-fuel ratio of the exhaust gas flowing into the upstream side NO X  occluding and reducing catalyst is controlled.   
   
   
       8 . An exhaust gas purifying device for an internal combustion engine according to  claim 7 , wherein an NO X  occlusion capacity of the upstream side NO X  occluding and reducing catalyst is larger than that of the downstream side NO X  occluding and reducing catalyst, an O 2  storage capacity of the upstream side NO X  occluding and reducing catalyst is smaller than that of the downstream side NO X  occluding and reducing catalyst, and an amount of platinum components carried on the upstream side NO X  occluding and reducing catalyst is larger than that carried on the downstream side NO X  occluding and reducing catalyst. 
   
   
       9 . An exhaust gas purifying device for an internal combustion engine according to  claim 7  or  8 , wherein a time for terminating the regenerating operation is judged according to the hydrogen component concentration in the exhaust gas detected by the H 2  sensor at the time of executing the regenerating operation. 
   
   
       10 . An exhaust gas purifying device for an internal combustion engine according to  claim 7  or  8 , wherein the device further executes a poisoning regeneration treatment in order to desorb sulfur oxide occluded in the NO X  occluding and reducing catalyst together with NO X  from the NO X  occluding and reducing catalyst by making the air-fuel ratio of the exhaust gas flowing into the NO X  occluding and reducing catalyst to be a rich air-fuel ratio and, at the same time, raising the temperature thereof and,
 wherein an air-fuel ratio of the exhaust gas flowing into the upstream side NO X  occluding and reducing catalyst is controlled according to the hydrogen component concentration in the exhaust gas detected by the H 2  sensor in the process of executing the poisoning regeneration treatment.   
   
   
       11 . An exhaust gas purifying device for an internal combustion engine, according to  claim 10 , wherein a time for terminating the poisoning regeneration treatment is judged according to the hydrogen component concentration in the exhaust gas detected by the H 2  sensor at the time of executing the poisoning regeneration treatment. 
   
   
       12 . An exhaust gas purifying device for an internal combustion engine according to  claim 8 , wherein a degree of deterioration of the upstream side NO X  occluding and reducing catalyst is judged according to a period of time from the start of the regenerating operation to the end of the regenerating operation which is judged according to the hydrogen component concentration, in the exhaust gas, detected by the H 2  sensor.