| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device and an air-fuel ratio control method for an engine obtaining excellent exhaust gas purifying performance from immediately after the opening/closing control of an exhaust gas flow control valve. Ž<P>SOLUTION: The air-fuel ratio control device for the engine includes an underfloor catalyst 21 provided in a main passage; a micro-catalyst 31 provided in a by-pass passage; and the exhaust gas flow control valve 40 capable of regulating the quantity of exhaust gas flowing through the main passage. The air-fuel ratio control device has an air-fuel ratio feedback correction quantity setting means B4 setting an air-fuel ratio feedback correction quantity in response to a signal from a by-pass passage air-fuel ratio sensor 32 when the exhaust gas flow control valve is closed and multiplying a signal from an underfloor air-fuel ratio sensor 22 by a predetermined correction quantity gain to set the air-fuel ratio feedback correction quantity when the exhaust gas flow control valve is open. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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