Patent ID: 7779621
Filing Date: 2010-08-24
Classification: F01N,F02D

Abstract:
1. An air fuel ratio control apparatus for an internal combustion engine, comprising: a catalyst that is arranged in an exhaust system of an internal combustion engine for purifying an exhaust gas from said internal combustion engine; an upstream air fuel ratio sensor that is arranged at a location upstream of said catalyst for detecting an air fuel ratio of a mixture in the exhaust gas upstream of said catalyst; a variety of kinds of sensors that detect operating conditions of said internal combustion engine; a first air fuel ratio feedback control section that adjusts the air fuel ratio of the mixture supplied to said internal combustion engine in accordance with an output value of said upstream air fuel ratio sensor and a predetermined control constant thereby to make said air fuel ratio oscillate in rich and lean directions in a periodic manner; and an average air fuel ratio oscillation section; wherein said average air fuel ratio oscillation section operates said control constant based on an amount of oxygen occlusion of said catalyst so as to make an average air fuel ratio, which is obtained by averaging said periodically oscillating air fuel ratio, oscillate in the rich and lean directions, and wherein said average air fuel ratio oscillation section sets a first oscillation period of said average air fuel ratio at the start of oscillation thereof to a half of a finally set oscillation period of said average air fuel ratio.