| 摘要 |
PROBLEM TO BE SOLVED: To improve the lean burning exhaust gas purifying performance while effectively preventing the contamination of the lean NOx catalyst with SOx by providing an SOx catching material and a lean NOx catalyst in an exhaust gas flow passage, and raising temperature of the SOx catching material in the reducing atmosphere. SOLUTION: During the operation of an engine provided with an SOx catching material 17 and a lean NOx catalyst 18 in order in an exhaust system thereof, an ECU 25 evaluates the engine operating condition and the condition of the lean NOx catalyst 18 so as to decide the air-fuel ratio, and controls an injector 5. After eliminating the SOx in the exhaust with the SOx catching material, at the time of theoretical air-fuel ratio operation, NOx, HC and CO in the exhaust gas are purified by a catalystic converter rhdium function of the lean NOx catalyst 18, and at the time of lean burning operation, NOx is purified by the NOx catching ability, and while HC and CO are oxidized for purifying by the catalyst function, and at the same time, a part of the NOx is deoxidized for purifying. When the NOx purifying ability is lowered, air-fuel ratio is shifted to a rich side so as to restore the NOx adsorbing ability of the lean NOx catalyst. |
