Patent ID: 7963101
Filing Date: 2011-06-21
Classification: F01N,F02D,Y02T

Abstract:
1. An exhaust gas purifying device for an internal combustion engine, comprising: a three-way catalyst having a reducing capability; a lean NOx catalyst provided downstream of the three-way catalyst, the lean NOx catalyst is adapted to trap NOx in a lean condition of air fuel ratio of an exhaust gas and reduce the trapped NOx in a rich condition of air fuel ratio of the exhaust gas; and an exhaust air fuel ratio control means for controlling an exhaust air fuel ratio to remove the NOx from the three-way and lean NOx catalysts, wherein, when the lean NOx catalyst is in an inactive state and the three-way catalyst is in an active state, the exhaust air fuel ratio control means conducts a lean control or a rich spike control in a selective manner depending on a prescribed operating condition under a low-load operating condition of the engine, and a continuous stoichiometric control or a weak rich control under a high-load operating condition of the engine.