Patent ID: 6370473
Filing Date: 2002-04-09
Classification: F02D

Abstract:
An apparatus for controlling the air-fuel ratio of a multicylinder internal combustion engine having all cylinders divided into a plurality of cylinder groups and an exhaust system including a plurality of auxiliary exhaust passages for discharging exhaust gases produced when an air-fuel mixture of air and fuel is combusted from said cylinder groups, respectively, a main exhaust passage joining said auxiliary exhaust passages together at downstream sides thereof, an exhaust gas sensor mounted in said main exhaust passage for detecting the concentration of a given component in the exhaust gases flowing through said main exhaust passage, and a catalytic converter connected to said auxiliary exhaust passages and/or said main exhaust passage upstream of said exhaust gas sensor, so that the air-fuel ratio of the air-fuel mixture combusted in each of said cylinder groups is controlled to converge an output from said exhaust gas sensor to a predetermined target value, said apparatus comprising:a plurality of air-fuel ratio sensors mounted respectively in said auxiliary exhaust passages upstream of said catalytic converter, for detecting the air-fuel ratio of the air-fuel mixture combusted in each of said cylinder groups; said exhaust system including an object exhaust system disposed upstream of said exhaust gas sensor and including said auxiliary exhaust passages and said catalytic converter, said object exhaust system being equivalent to a system for generating an output of said exhaust gas sensor from a combined air-fuel ratio determined by combining the values of air-fuel ratios of air-fuel mixtures combusted by the cylinder groups, respectively, according to a filtering process of the mixed model type; target combined air-fuel ratio data generating means for sequentially generating target combined air-fuel ratio data representing a target value for said combined air-fuel ratio which is required to converge the output from said exhaust gas sensor to said predetermined target value with said system equivalent to said object exhaust system serving as an object to be controlled; target air-fuel ratio data generating means for sequentially generating target air-fuel ratio data from the target combined air-fuel ratio data generated by said target combined air-fuel ratio data generating means according to a predetermined converting process based on characteristics of a filtering process identical to said filtering process of the mixed model type, said target air-fuel ratio data representing a target air-fuel ratio for the air-fuel mixture combusted in each of said cylinder groups, said target air-fuel ratio being shared by said cylinder groups, said target combined air-fuel ratio data being produced by subjecting said target air-fuel ratio data to said filtering process; and air-fuel ratio manipulating means for manipulating the air-fuel ratio of the air-fuel mixture combusted in each of said cylinder groups in order to converge an output of each of said air-fuel ratio sensors to the target air-fuel ratio represented by said target air-fuel ratio data generated by said target air-fuel ratio data generating means.