Patent ID: 8272209
Filing Date: 2012-09-25
Classification: F01N,F02D,F02M,Y02T

Abstract:
1. An exhaust gas purification system for an internal combustion engine, comprising: an NOx storage reduction catalyst provided in an exhaust passage of the internal combustion engine; combustion mode switching unit for switching a combustion mode of said internal combustion engine into a low air-fuel ratio mode in which the air-fuel ratio of air-fuel mixture in said internal combustion engine is lower than that in a normal combustion mode in which reduction of oxide stored in the NOx catalyst is not performed; reducing agent supply unit for supplying reducing agent to exhaust gas flowing in said exhaust passage upstream of said NOx storage reduction catalyst; reduction execution unit for executing an NOx reduction control to reduce NOx stored in said NOx storage reduction catalyst, integrated NOx discharge amount calculation unit for calculating an integrated NOx discharge amount defined as an integrated amount of the quantity of NOx discharged from said internal combustion engine since the time of last execution of the NOx reduction control; and prediction unit for predicting, based on a decrease rate of the difference between said integrated NOx discharge amount and a specific NOx discharge amount serving as a threshold of execution of the NOx reduction control, a specific time defined as a time at which said integrated NOx discharge amount reaches said specific NOx discharge amount, wherein said reduction execution unit executes the NOx reduction control by switching the combustion mode of said internal combustion engine into the low air-fuel ratio mode by said combustion mode switching unit with such timing, prior to the specific time predicted by said prediction unit, as to make the air-fuel ratio of the exhaust gas low at said specific time, and executing supply of reducing agent by said reducing agent supply unit at the specific time.