An exhaust purification device of an engine

摘要

An exhaust purification device of an engine having an exhaust passage, comprising: a NOx absorbent (18) arranged in the exhaust passage (17); air-fuel ratio control means (20) for controlling the air-fuel ratio of the exhaust gas flowing into the NOx absorbent to temporarily change the air-fuel ratio of the exhaust gas flowing into the NOx absorbent from lean to rich at certain time intervals to release NOx from the NOx absorbent; deterioration detecting means (22) for detecting the degree of deterioration of the NOx absorbent; wherein said NOx releasing control means controls at least one of a time period at which the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is changed from lean to rich and a rich time period during which the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is made rich to make one of said time periods shorter as the degree of deterioration of the NOx absorbent becomes higher, wherein said air-fuel ratio control means comprises a first air-fuel ratio control means for changing the air-fuel ratio of the exhaust gas flowing into the NOx absorbent temporarily from lean to rich at said cycle, controlled by said NOx releasing control means just so as to cause the release of NOx from the NOx absorbent and second air-fuel ratio control means for changing the air-fuel ratio of the exhaust gas flowing into the NOx absorbent temporarily from lean to rich so as to cause the NOx to be released from the NOx absorbent and to detect the degree of deterioration of the NOx absorbent by said deterioration degree detecting means.