| 摘要 |
PURPOSE:To prevent an air-fuel ratio sensor from its output decline by continu ously keeping open loop control for the specified time, when a rich air fuel ratio becomes theoretical air-fuel ratio due to open loop control after long-term continuation of the state of said rich air-fuel ratio. CONSTITUTION:A control circuit 60 takes in signals from a flow rate sensor 24, a water temperature sensor 56 and an O2 sensor 142, and controls an injector 12, an ignition coil 62, a bypass valve 61 and the like. Air-fuel ratio control by the control circuit 60 performs lean air-fuel ratio process if excess air-ratio is larger than 1, and checks whether the specified time has passed since rich air-fuel ratio was switched to the lean. If not, open loop control is carried out just for the specified time, then switching to close loop control is performed. A detecting function of an air-fuel ratio sensor due to sooth adhering caused by long-term operation in the state of being rich can be prevented from declining, and so an amount of close loop control can also be prevented from disorder.
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