초록 ▼

A three-way catalyst (8a) is connected to a first cylinder group 1a. The exhaust gas of the first cylinder group (1a), which has passed through the three-way catalyst (8a), and the exhaust gas of a second cylinder group (1b) are introduced to an exhaust gas purifying catalyst (14). The second cylind

A three-way catalyst (8a) is connected to a first cylinder group 1a. The exhaust gas of the first cylinder group (1a), which has passed through the three-way catalyst (8a), and the exhaust gas of a second cylinder group (1b) are introduced to an exhaust gas purifying catalyst (14). The second cylinder group (1b) performs the lean operation. The first cylinder group (1a) performs the rich operation to synthesize NH.sub.3 from NO.sub.X in the exhaust gas of the first cylinder group (1a) in the three-way catalyst (8a). In the exhaust gas purifying catalyst (14), NO.sub.X in the exhaust gas of the second cylinder group 1b is purified by NH.sub.3 from the three-way catalyst (8a). The amount of HC flowing to the three-way catalyst (8a) is obtained. When the HC amount exceeds a predetermined amount, the first cylinder group 1a must perform the lean operation temporarily, to thereby maintain the excellent catalytic activity of the three-way catalyst (8a).

대표청구항 ▼

[ We claim:] [1.] A device for purifying an exhaust gas of an internal combustion engine having a plurality of cylinders divided into first and second cylinder groups, and first and second exhaust passages connected to the first and the second cylinder groups, respectively, the device comprising:an

[ We claim:] [1.] A device for purifying an exhaust gas of an internal combustion engine having a plurality of cylinders divided into first and second cylinder groups, and first and second exhaust passages connected to the first and the second cylinder groups, respectively, the device comprising:an NH.sub.3 synthesizing catalyst arranged in the first exhaust passage, the NH.sub.3 synthesizing catalyst synthesizing NH.sub.3 from at least of a part NO.sub.X in an inflowing exhaust gas when an exhaust gas air-fuel ratio of the inflowing exhaust gas is rich;first making-rich means for making the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst rich to synthesize NH.sub.3 ;an interconnecting exhaust passage interconnecting the first passage downstream of the NH.sub.3 synthesizing catalyst and the second exhaust passage to contact NH.sub.3 synthesized in the NH.sub.3 synthesizing catalyst and NO.sub.X from the second exhaust passage to each other, to reduce the NO.sub.X by the NH.sub.3 ; andfirst making-lean means for making the exhaust gas air-fuel ratio of the exhaust gas flowing into the NH.sub.3 synthesizing catalyst temporarily lean; wherein a cumulative amount of hydrocarbon (HC) flowing to the NH.sub.3 synthesizing catalyst when the exhaust gas air-fuel ratio of the exhaust gas flowing to the NH.sub.3 synthesizing catalyst is rich is obtained, and wherein the first making-lean means performs the making-lean operation when the cumulative amount of HC becomes larger than a predetermined upper threshold.