Engine exhaust gas purification device

Claim 1

An engine exhaust gas purification device in an engine exhaust passage, said device comprising: an NO x absorbent arranged in the exhaust passage and absorbing NO x when an air-fuel ratio of exhaust gas flowing into the NO x absorbent is lean, said NO x absorbent releasing absorbed NO x when said air-fuel ratio of the exhaust gas becomes rich; and control means for controlling the temperature of said NO x absorbent to maintain the temperature of said NO x absorbent within a predetermined range in which a high NO x absorbing ability of said NO x absorbent is obtained, wherein the control means includes one of a heating means for heating the exhaust gas flowing into the NO x absorbent and a cooling means for cooling the exhaust gas flowing into the NO x absorbent to control the temperature of the exhaust gas flowing into the NO x absorbent, the heating means comprising a fuel injector for injecting fuel into the exhaust gas flowing into the NO x absorbent only when the temperature of the exhaust gas flowing into the NO x absorbent becomes lower than a first temperature of the predetermined range and wherein the cooling means comprises an air injector for injecting air into the exhaust gas flowing into the NO x absorbent only when the temperature of the exhaust gas flowing into the NO x absorbent becomes higher than a second temperature of the predetermined range, wherein the second temperature is higher than the first temperature.