Engine air-fuel ratio controller

An air-fuel ratio controller for an engine having a combustion chamber, an intake pipe providing air to said combustion chamber, means for supplying fuel to said combustion chamber, an exhaust pipe expelling a burnt gas in said combustion chamber, means for measuring a volume of the air provided by said intake pipe, means for setting a fuel supply amount of said supplying means in proportion with said measured air volume, a three-way catalytic converter provided in said exhaust pipe, an oxygen sensor detecting whether or not the ratio of the air and fuel in said combustion chamber is rich or lean with respect to a theoretical value, means for determining from said detection whether said air-fuel ratio has changed over to lean or rich, means for computing a correction amount based on said change-over state, said amount being a step fraction during said change-over and an integral fraction smaller than said step fraction at times other than during said change-over, and means for correcting said fuel supply amount by said correction amount, said controller comprising:

• means for detecting engine start-up,
• means for measuring the time elapsed from the engine start-up,
• means for detecting engine temperature during the engine start-up,
• means for setting a warm-up correction amount according to said engine temperature during the start-up,
• means for reducing said warm-up correction amount according to the time elapsed after start-up, and
• means for adding said reduced amount to said step fraction.