Patent ID: 6796118
Filing Date: 2004-09-28
Classification: F02B,F02D,F02M,Y02T

Abstract:
An exhaust gas purification system for an internal combustion engine including:a NOx trap catalyst disposed in an exhaust passage of the engine for trapping NOx in an inflow exhaust gas when an air/fuel ratio of the exhaust gas is lean and releasing trapped NOx when the air/fuel ratio of the exhaust gas is rich; and a control unit for controlling the NOx trap catalyst in accordance with an activated condition of the NOx trap catalyst; the control unit comprising: a purification time determining section for determining whether it is the time for purifying NOx trapped by the NOx trap catalyst; a catalyst activation determining section for determining whether the Nox trap catalyst is activated; a combustion mode switching section for switching a combustion mode of the engine between a diffusion combustion mode and a premix combustion mode in accordance with an operating condition of the engine; and an air/fuel ratio control section for controlling an exhaust air/fuel ratio so that the exhaust air/fuel ratio is made rich in the premix combustion mode when it is the time for purifying trapped NOx of the NOx trap catalyst and the NOx trap catalyst is activated and that the exhaust air/fuel ratio is made rich in the diffusion combustion mode when it is the time for purifying trapped NOx of the Nox trap catalyst and the Nox trap catalyst is not activate.