To early start exhaust-emission control by guiding exhaust gas onto a bypass catalyst converter 18 side immediately after start in a cold condition and to prevent HC from flowing out when exhaust gas leaks through a flow passage switch-over valve 4.
Upstream side main passages 2 are mutually connected per cylinder 1, upstream side main passages of cylinders in which exhaust processes are not continuous join as an intermediate main passage 3, and they become one downstream side main passage 7 finally. A main catalyst converter 8 is provided in a halfway section of the downstream side main passage 7. The flow passage switch-over valve 4 is provided between the upstream side main passage 2 and the intermediate main passage 3. Upstream side bypass passages 11 are branched from each of the upstream side main passages 2 as bypass passages and become one downstream side bypass passage 16 finally. The bypass catalyst converter 18 is provided in a halfway section of the downstream side bypass passage 16. An HC trap 21 is provided on the upstream side more than a join point 17 of the downstream side main passage 7 to adsorb HC in the leaked exhaust gas.
INOUE TAKAO
Hiromichi Kobayashi
Tomioka Kiyoshi