Patent ID: 7104047

Claim:
An air-fuel ratio control device for an internal combustion engine, comprising: an upstream detector part provided in an exhaust system of said internal combustion engine, for detecting a concentration of a particular component in an exhaust gas in an upstream side of a catalytic converter for cleaning the exhaust gas; a downstream detector part provided in said exhaust system, for detecting a concentration of a particular component in the exhaust gas in a downstream side of said catalytic converter; an air-fuel-ratio adjusting part for adjusting an air-fuel ratio by controlling an amount of a fuel supply to said internal combustion engine; a control part for controlling said air-fuel-ratio adjusting part so that an output value of said upstream detector part and an upstream target value match each other; a target-value varying part for changing said upstream target value using a proportional operation and an integral operation so that an output value of said downstream detector part and a downstream target value match each other; a state-detecting part for detecting a fuel cutoff state in which a fuel supply to said internal combustion engine is stopped; a cumulative-amount detecting part for detecting a cumulative amount of air taken into said internal combustion engine from a time at which said fuel cutoff state is removed; and a stop/restart part for stopping said integral operation in response to detection of said fuel cutoff state by said state-detecting part, and restarting said integral operation in response to attainment of said cumulative air amount to a predetermined air amount.