Patent ID: 6263668
Filing Date: 2001-07-24
Classification: F01N,F02D

Abstract:
A control system for an internal combustion engine, comprising:air-fuel ratio control means for normally controlling an air-fuel ratio of air-fuel mixture supplied to the internal combustion engine to a lean side with respect to a stoichiometric ratio for a lean mixture combustion, and temporarily controlling the air-fuel ratio to a rich side with respect to the stoichiometric air-fuel ratio;NOx catalyst means for occluding NOx in an exhaust gas exhausted at the time of the lean mixture combustion and releasing the occluded NOx from the NOx catalyst by temporarily controlling the air-fuel ratio to the rich side for a rich mixture combustion;catalyst state detecting means for detecting an NOx purification state of the NOx catalyst;rich time updating means for updating a rich time for the rich mixture combustion so as to be shortened in a predetermined time period; andupdate cancelling means for canceling an update of the rich time so as to be shortened when the rich time at that time is discriminated as a limit value from the detected NOx purification state of the catalyst.