Air-fuel ratio control apparatus

摘要

An exhaust system (30) includes an exhaust channel (34) having a main catalytic converter (38), a bypass channel (31) having a bypass catalytic converter (35), and a valve mechanism (37) disposed in the exhaust channel (34) to switch a pathway for exhaust gas from the exhaust channel (34) to the bypass channel (31). A pair of sensors (36,39) output signals indicative of air-fuel ratios of exhaust flowing in their respective channels. A controller (40) has first and second air-fuel ratio control sections that control an engine air-fuel ratio based on outputs of the sensors, respectively. The controller has a control mode switching section that switches control from the first air-fuel ratio control section to the second air-fuel ratio control section (S8,S9,S10) after a prescribed interval of time has elapsed from when the valve mechanism (37) is switched from a closed state to an open state (S6).