| 摘要 |
PROBLEM TO BE SOLVED: To suppress the deterioration of a catalyst while suppressing the deterioration of an exhaust emission. SOLUTION: An exhaust pipe 3 is branched into a first exhaust pipe 4 and a second exhaust pipe 5. A first catalyst 6 consisting of Pt-Rn (platinum- rhodium) having characteristics that a degree of deterioration becomes large when exposed to a lean atmosphere, is arranged in the inside of the first exhaust pipe 4, and a second catalyst 7 consisting of Pd-Rn (palladium-rhodium) having characteristics that a degree of deterioration becomes large when exposed to a rich atmosphere, is arranged in the inside of the second exhaust pipe 5. A switching valve 9 to change over an exhaust gas flow is arranged at a branch point. Then, the switching valve 9 is controlled by a signal from an ECU 20, so that, according to an air-fuel ratio of exhaust gas, the first exhaust pipe 4 is closed when lean and the second exhaust pipe 5 is closed when rich. |
