Abstract: A technique of controlling an air-fuel ration for an engine, in which an air-fuel ratio feedback correction coefficient ? to correct an amount of fuel injection into the engine is computed based on an output from an air-fuel ratio sensor disposed on an upstream side of a catalytic converter. A gain of the air-fuel ratio feedback correction coefficient ? in respect to a detection result of the air-fuel ratio sensor is decreased as a delay in a transient response of the air-fuel ratio sensor occurs. Thus, an excessive increase in the amount of fuel injection immediately after fuel cuts is prevented.

Abstract: A feedback control of an air-fuel ratio of an internal combustion engine is performed in such a manner that when fuel injection is resumed from a condition where fuel injection is stopped due to deceleration running, air-fuel ratio feedback control is resumed once the output from an air-fuel ratio sensor indicates an air-fuel ratio less than or equal to a threshold value SL.

Abstract: A technique of controlling an air-fuel ration for an engine, in which an air-fuel ratio feedback correction coefficient ? to correct an amount of fuel injection into the engine is computed based on an output from an air-fuel ratio sensor disposed on an upstream side of a catalytic converter. A gain of the air-fuel ratio feedback correction coefficient ? in respect to a detection result of the air-fuel ratio sensor is decreased as a delay in a transient response of the air-fuel ratio sensor occurs. Thus, an excessive increase in the amount of fuel injection immediately after fuel cuts is prevented.

Abstract: When carrying out abnormality determination for an air-fuel ratio sensor 33 by comparison of an average value tave of all diagnostic values t(n) and an abnormality determination value C, the abnormality determination value C is corrected using an average value ?tave for the disturbance correction values ?t(n). A disturbance correction value ?t(n) is derived by subtracting a correction reference value A, which is a diagnostic value with a normal air-fuel ratio sensor 33 when there is no disturbance, from the diagnostic value t(n). The present invention provides the abnormality diagnosis device for the air-fuel ratio sensor that can acquire highly precise diagnosis results without lowering frequency of diagnosis accurately taking into consideration the influence of disturbance.

Abstract: When carrying out abnormality determination for an air-fuel ratio sensor 33 by comparison of an average value tave of all diagnostic values t(n) and an abnormality determination value C, the abnormality determination value C is corrected using an average value ?tave for the disturbance correction values ?t(n). A disturbance correction value ?t(n) is derived by subtracting a correction reference value A, which is a diagnostic value with a normal air-fuel ratio sensor 33 when there is no disturbance, from the diagnostic value t(n). The present invention provides the abnormality diagnosis device for the air-fuel ratio sensor that can acquire highly precise diagnosis results without lowering frequency of diagnosis accurately taking into consideration the influence of disturbance.

Abstract: Whether a misfire occurred is judged based on a comparison between diagnosis data that indicates a variation of an engine rotation speed and a threshold based on engine operating conditions. The misfire judgment is canceled based on a result of a comparison between data indicating an average correlation between the diagnosis data and the threshold, and a threshold for cancellation judgment.

Abstract: Whether a misfire occurred is judged based on a comparison between diagnosis data that indicates a variation of an engine rotation speed and a threshold based on engine operating conditions. The threshold is corrected based on data that indicates an average correlation between the diagnosis data and the threshold.

Abstract: A feedback control of an air-fuel ratio of an internal combustion engine is performed in such a manner that when fuel injection is resumed from a condition where fuel injection is stopped due to deceleration running, air-fuel ratio feedback control is resumed once the output from an air-fuel ratio sensor indicates an air-fuel ratio less than or equal to a threshold value SL.

Abstract: In a configuration where it is judged whether or not a misfire occurred, based on the comparison between diagnosis data indicating a variation of an engine rotation speed and a threshold based on engine operating conditions, the misfire judgment is canceled based on a result of the comparison between data indicating an average correlation between the diagnosis data and the threshold, and a threshold for cancellation judgment.

Abstract: In a configuration where it is judged whether or not a misfire occurred, based on the comparison between diagnosis data indicating a variation of an engine rotation speed and a threshold based on engine operating conditions, the threshold is corrected based on data indicating an average correlation between the diagnosis data and the threshold.