Patent ID: 6516612
Filing Date: 2003-02-11
Classification: B01D,F01N,F02D,Y02T

Abstract:
An exhaust gas purification device for an engine, comprising:a first front catalyst disposed in a first exhaust passage connected to a first cylinder group, said first front catalyst being adapted to trap oxygen present in exhaust gas flowing thereinto when an air-fuel ratio of the exhaust gas is lean relative to a stoichiometric air-fuel ratio and oxidize a reducing agent present in the exhaust gas by the oxygen trapped thereby when the air-fuel ratio of the exhaust gas is rich relative to the stoichiometric air-fuel ratio; a second front catalyst disposed in a second exhaust passage connected to a second cylinder group, said second front catalyst being adapted to trap oxygen present in exhaust gas flowing thereinto when an air-fuel ratio of the exhaust gas is lean relative to the stoichiometric air-fuel ratio and oxidize the reducing agent present in the exhaust gas by the oxygen trapped thereby when the air-fuel ratio of the exhaust gas is rich relative to the stoichiometric air-fuel ratio; a rear catalyst disposed in a rear exhaust passage which combines the exhaust of the first and second exhaust passages, said rear catalyst being adapted to trap nitrogen oxides (NOx) present in exhaust gas flowing thereinto when an air-fuel ratio of the exhaust gas is lean relative to the stoichiometric air-fuel ratio and reduce the NOx trapped thereby by the reducing agent present in the exhaust gas when the air-fuel ratio of the exhaust gas is rich relative to the stoichiometric air-fuel ratio; and a controller programmed to make the air-fuel ratio of the exhaust gas flowing into the first front catalyst rich relative to the stoichiometric air-fuel ratio and make the air-fuel ratio of the exhaust gas flowing into the second front catalyst a stoichiometric air-fuel ratio when the NOx trapped by the rear catalyst is reduced.