System for controlling engine

Claim 1

A fuel injection control system for an internal combustion engine equipped with a fuel injector through which fuel is sprayed directly into a combustion chamber of the internal combustion engine and a catalyst disposed in an exhaust passage which contains a NO x trapping substance operative to absorb NO x in an exhaust gas containing oxygen in excess and to release NO x into the exhaust gas when the oxygen content of the exhaust gas lowers, said fuel injection control system comprising: detecting means for detecting a value relating to an amount of NO x absorbed by said NO x trapping substance which represents a trapped amount of NO x ; fuel injection control means for repeatedly performing fuel injection through primary fuel injection which is made at a primary fuel injection timing near a top dead center of a compression stroke when said trapped amount of NO x is larger than a specified amount and post-fuel injection at a post-fuel injection timing retarded by a predetermined time from said top dead center of compression stroke after said primary fuel injection when causing a fall in said oxygen concentration so as to release NO x from said NO x trapping substance; wherein said control means controls a retardation of said post-fuel injection timing so as to be large for a specified period of time from a detection of said trapped amount of NO x larger than said specified amount than after a lapse of said specified period of time so as thereby to make an amount of HC in an exhaust gas from said combustion chamber larger for a period of time from said detection of said trapped amount of NO x larger than said specified amount to said lapse of said specified period of time than after said lapse of said specified period of time.