To ensure the stability of an air-fuel ratio feedback control system at the time of low engine water temperature in an engine (internal combustion engine) performing the air-fuel ratio feedback control based on an output signal of an A/F sensor disposed in an exhaust passage.
The air-fuel ratio feedback control gain (proportional gain and integration gain) is set variably according to the cooling water temperature THW of an engine sensed by a water temperature sensor (steps ST203, ST204). By setting an appropriate air-fuel ratio feedback control gain corresponding to responsiveness decline of the A/F sensor output at the time of low engine water temperature (temperature lower than the engine warming-up temperature), stability of the control system is ensured by restraining hunting of the exhaust air-fuel ratio.
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Yoshiro Kurauchi
Kunitomi Go