Patent ID: 6739122
Filing Date: 2004-05-25
Classification: F01N,F02D,Y02A,Y02T

Abstract:
An air-fuel ratio feedback controlling apparatus for an internal-combustion engine, comprising:an air-fuel ratio detector disposed in an exhaust system of the internal-combustion engine for detecting air-fuel ratio of exhaust gas; a NOx purifier for purifying NOx contained in the exhaust gas during lean operation; a downstream O2 sensor disposed downstream of the NOx purifier; an upstream O2 sensor disposed upstream of the NOx purifier; a feedback controller for performing feedback control of an air-fuel ratio of air fuel mixture to be supplied to the internal-combustion engine based on outputs of the air-fuel ratio detector; a diagnostic system for diagnosing the NOx purifier by changing the air-fuel ratio of the air-fuel mixture to be supplied to the internal combustion engine from lean to rich and detecting on the outputs of the downstream O2 sensor and the upstream O2 sensor; and a gain changer for reducing feedback control gain of the feedback controller when the diagnostic system changes the air-fuel ratio from lean to rich; and a three way catalyst disposed upstream of the NOx purifier, wherein the diagnostic system carries out the checking of the NOx purifier when the three way catalyst is determined to be normal.