Device for detecting deterioration of NO.sub.x absorbent

A device for detecting deterioration of a NO.sub.x absorbent arranged in an exhaust passage of an engine, said NO.sub.x absorbent absorbing NO.sub.x and storing oxygen therein when an air-fuel ratio of exhaust gas flowing into the NO.sub.x absorbent is lean and releasing absorbed NO.sub.x and stored oxygen therefrom when the air-fuel ratio of exhaust gas flowing into the NO.sub.x absorbent becomes rich, said device comprising:

• air-fuel ratio detecting means arranged in the exhaust passage downstream of the NO.sub.x absorbent for producing an output signal indicating an air-fuel ratio of exhaust gas which flows out from the NO.sub.x absorbent;
• air-fuel ratio changing means for changing the air-fuel ratio of exhaust gas flowing into the NO.sub.x absorbent from lean to rich when an amount of NO.sub.x absorbed in the NO.sub.x absorbent is almost zero;
• and
• oxygen amount detecting means for detecting an amount of oxygen stored in the NO.sub.x absorbent on the basis of the output signal of said air-fuel ratio detecting means after the air-fuel ratio of exhaust gas flowing into the NO.sub.x absorbent is changed from lean to rich by said air-fuel ratio changing means.