| 摘要 |
PROBLEM TO BE SOLVED: To accurately acquire an amount of vapor introduced in an intake passage when engine operation is switched from normal operation to rich/lean operation. SOLUTION: At normal times, the normal operation performing combustion based on a predetermined air-fuel ratio for each cylinder group is executed. When a reducing agent and air should be supplied to a catalyst 10 so that exhaust gas of a predetermined air-fuel ratio flows into the catalyst, the rich/lean operation is performed. In the rich/lean operation, rich combustion is performed in one cylinder group, and lean combustion is performed in the other cylinder group. A first air-fuel ratio sensors 11, 12 are respectively disposed to exhaust branch pipes 5, 6, and a second air-fuel ratio sensor 13 is disposed to a common exhaust pipe 7 upstream of the catalyst. For acquiring the amount of vapor introduced in the intake passage 4 during a purge control, an output value of the first air-fuel ratio sensor and a learning value of the vapor amount acquired in the normal operation are used during normal operation, and the output value of the second air-fuel ratio sensor and the learning value of the vapor amount acquired in rich/lean operation are used during the rich/lean operation. COPYRIGHT: (C)2007,JPO&INPIT
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