Air-fuel ratio control apparatus for an internal combustion engine

摘要

An air-fuel ratio control apparatus for an internal combustion engine of the present invention determines whether or not a lean request has occurred, based on a comparison between a value correlating with an output value of the downstream air-fuel ratio sensor disposed downstream of the catalyst (downstream air-fuel ratio sensor output correlating value) and a predetermined lean request determining value, and determines whether or not a rich request has occurred, based on a comparison between the downstream air-fuel ratio sensor output correlating value and a predetermined rich request determining value. Further, the air-fuel ratio control apparatus calculates a total amount of oxygen (released oxygen amount) released from the catalyst in the rich request occurring period, and calculates an integrated value (present stored oxygen amount) of oxygen stored in the catalyst after a start of the lean request occurring period which follows the rich request occurring period. The apparatus changes the rich request determining value in such a manner that a point in time at which it is determined that the rich request has occurred comes much earlier as the present stored oxygen amount comes closer to the released oxygen amount.

主权项

1. An air-fuel ratio control apparatus for an internal combustion engine, comprising:
a catalyst disposed in an exhaust passage of the engine; a downstream air-fuel ratio sensor disposed in said exhaust passage and at a position downstream of said catalyst; an air-fuel ratio request determining section configured to determine whether or not a lean request has occurred, based on a comparison between a downstream air-fuel ratio sensor output correlating value which is a value correlating with an output value of said downstream air-fuel ratio sensor and a predetermined lean request determining value, and to determine whether or not a rich request has occurred, based on a comparison between the downstream air-fuel ratio sensor output correlating value and a predetermined rich request determining value; and an air-fuel ratio control section configured to control an air-fuel ratio of a mixture supplied to said engine so as to have said air-fuel ratio of said mixture become equal to a lean air-fuel ratio which is an air-fuel ratio larger than a stoichiometric air-fuel ratio in a lean request occurring period from a point in time at which it is determined that said lean request has occurred and to a point in time at which it is determined that the rich request has occurred, and to control said air-fuel ratio of said mixture so as to have said air-fuel ratio of said mixture become equal to a rich air-fuel ratio which is an air-fuel ratio smaller than the stoichiometric air-fuel ratio in a rich request occurring period from a point in time at which it is determined that said rich request has occurred and to a point in time at which it is determined that the lean request has occurred; wherein, said air-fuel ratio request determining section is configured so as to: calculate, based on an air-fuel ratio of a gas flowing into said catalyst, a released oxygen amount which is a total amount of oxygen which has been released from said catalyst in said rich request occurring period; calculate, based on said air-fuel ratio of said gas flowing into said catalyst, a present stored oxygen amount which is an integrated amount of oxygen which is stored in said catalyst after a start of said lean request occurring period which follows said rich request occurring period; and change said request determining value such that the determination whether or not said rich request has occurred can be made at an earlier point in time as said present stored oxygen amount comes closer to said released oxygen amount.