| 摘要 |
PROBLEM TO BE SOLVED: To suppress the instability of combustion and deterioration of fuel economy due to the retard of ignition timing while preventing a step of torque produced when a flow passage selector valve 5 is opened at the completion of warmup. SOLUTION: A main passage 3 is connected to an exhaust port 2. A main catalytic converter 4 is disposed on the downstream side. The flow passage selector valve 5 opening and closing the main passage 3 is installed in the main passage 3. A bypass passage 7 with a small cross section is branched from the main passage 3, and a small bypass catalytic converter 8 is installed in the bypass passage. Immediately after cold starting, exhaust gases are guided to the bypass passage 7 for purifying the exhaust gases. When the flow passage selector valve 5 is opened at the completion of warmup, the step of torque is produced due to a reduction in back pressure. Therefore, a swirl control valve 31 is closed, and the retard of the ignition timing is corrected. The corrected amount of the retard angle is smaller than in the case that only the retard of the ignition angle is corrected, and surge due to the retard angle is suppressed by reinforcing the flow of the gases. COPYRIGHT: (C)2007,JPO&INPIT
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