Patent ID: 6766640
Filing Date: 2004-07-27
Classification: B01D,F01N,F02D,Y02T

Abstract:
An exhaust gas purification device for an engine, comprising:an exhaust passage of the engine; a first catalyst, installed in the exhaust passage, that stores and releases oxygen in exhaust gas in accordance with an air-fuel ratio of exhaust gas; a second catalyst, installed in the exhaust passage downstream of the first catalyst, that traps and releases NOx in exhaust gas in accordance with the air-fuel ratio of exhaust gas; and a microprocessor programmed to: compute a total oxygen amount stored in the first catalyst and the second catalyst, compute a required reducing agent amount based on the total oxygen amount, wherein the required reducing agent amount is increased with increase in the total oxygen amount, and perform a rich operation that controls the air-fuel ratio of exhaust gas to rich when trapped NOx in the second catalyst is to be released until an amount of supplied reducing agent due to the rich operation reaches the required reducing agent amount, and wherein the microprocessor is further programmed to compute a high speed component stored by a noble metal of the catalysts and a low speed component stored by an oxygen storage material of the catalysts separately, and to compute the total oxygen amount from the high speed component and the low speed component.