Patent ID: 6223525
Filing Date: 2001-05-01
Classification: F01N,F02D,Y02A,Y02T

Abstract:
An air fuel ratio controlling device for an internal combustion engine, comprising:a NOx absorbent catalyst which is disposed in an exhaust system of an internal combustion engine, and which, in an exhaust gas-lean state, absorbs NOx in an exhaust gas, and, in an exhaust gas-rich state, reduces NOx which has been absorbed;a three-way catalyst which is disposed in the exhaust system:an air-fuel ratio detector which is disposed in the exhaust system;an air-fuel ratio controller for controlling an air-fuel ratio of an air-fuel mixture being supplied to the engine, substantially to a stoichiometric air-fuel ratio based on an output of the air-fuel ratio detector,a NOx amount estimator for estimating an amount of NOx absorbed in said NOx absorbent catalyst based on an output of said air-fuel ratio detector during a period where the air-fuel ratio of the air-fuel mixture is controlled bv the air-fuel ratio controller; andan air-fuel ratio enricher for enriching the air-fuel ratio of the air-fuel mixture to a value which is richer than the richer air-fuel ratio that is controlled by the air-fuel ratio controller when the NOx amount, estimated by said NOx amount estimator, reaches a predetermined value during said period.