초록 ▼

Disclosed is a method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine. The method employs a feedback control in which the control is made to maintain the air-fuel ratio at the stoichiometric level in accordance with the air-fuel ratio read thr

Disclosed is a method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine. The method employs a feedback control in which the control is made to maintain the air-fuel ratio at the stoichiometric level in accordance with the air-fuel ratio read through the detection of a component of the exhaust gas and, at least during the idling of the engine after the warming up of the same, a lean control in which the control is made to maintain the air-fuel ratio at the leaner side of the stoichiometric level. The lean control is allowed when the mean value of the engine speed over a predetermined period is greater than a predetermined reference value during the idling after warming up of the engine, while the feedback control is conducted when the mean value is below the predetermined reference value. Disclosed also is an apparatus suitable for carrying out this method.

대표청구항 ▼

A method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine having an injector by selectively using a feedback control in which the air-fuel ratio is maintained at the stoichiometric level and a lean control in which the air-fuel ratio is maintai

A method of controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine having an injector by selectively using a feedback control in which the air-fuel ratio is maintained at the stoichiometric level and a lean control in which the air-fuel ratio is maintained at a leaner side of the stoichiometric level at least during an idling of the engine after a warming up of the engine, said method comprising the steps of: calculating a mean value of the engine idling speed for a predetermined period of time; comparing the mean value thus calculated with a predetermined reference value; prohibiting said lean control at least when said comparing step determines that the mean value is less than the predetermined reference value, whereby the air-fuel ratio is feedback-controlled with said feedback control so as to be maintained at the stoichiometric ratio; computing a basic fuel injection time duration corresponding to a fuel injection rate of said injector in accordance with an engine speed and a load on the engine; and correcting said basic fuel injection time duration in the lean control by at least a lean correction coefficient and in the feedback control by at least a feedback correction coefficient to thereby determine a final injection time duration, said lean correction coefficient being determined in accordance with a load on the engine such that the air-fuel ratio is in a leaner side of the stoichiometric air-fuel ratio, and said feedback correction coefficient being determined in accordance with the actual air-fuel ratio such that the air-fuel ratio substantially becomes a stoichiometric level, wherein when the result of said comparing step is that the mean value is less than the predetermined reference value, a correction of the basic injection time duration by the lean correction coefficient is prohibited. An apparatus for controlling the air-fuel ratio of an air-fuel mixture to be supplied to an internal combustion engine, comprising: control means for selectively using feedback control to maintain said air-fuel ratio at a stoichiometric level and using lean control to maintain said air-fuel ratio at a leaner side of said stoichiometric level at least during idling of said engine after a warming up of said engine; means for calculating a mean value of idling speed of said engine for a predetermined period of time; means for comparing said mean value with a predetermined reference value; means for prohibing said lean control operation of said control means when said comparing means determines that said mean value is less than said predetermined reference value, so that said air-fuel ratio is maintained by said feedback control operation of said control means; an injector for said engine; means for computing a basic fuel injection time duration corresponding to a fuel injection rate of said injector in accordance with an engine speed and a load on said engine; and means for correcting said basic fuel injection time duration during said lean control operation by at least a lean correction coefficient and during said feedback control operation by at least a feedback correction coefficient to thereby determine a final injection time duration, said lean correction coefficient being determined in accordance with a load on said engine such that said air-fuel ratio becomes a leaner side of said stoichiometric air-fuel ratio, and said feedback correction coefficient being determined in accordance with an actual air-fuel ratio such that said air-fuel ratio substantially becomes stoichiometric level; and wherein said means for correcting, when said comparing means determines that said mean value is less than said predetermined reference value, prohibits correction of said basic injection time duration by said lean correction coefficient.