An exhaust gas purification device for an engine

摘要

In the present invention, a NOX absorbent (18) is used for removing the NOX in the exhaust gas. The NOX absorbent (18) absorbs NOX in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and releases the absorbed NOX and reduces it to nitrogen when the air-fuel ratio of the exhaust gas is rich or stoichiometric. To prevent the NOX absorbent (18) from being saturated with the absorbed NOX, the NOX absorbent must (18) be regenerated periodically by causing the NOX in the absorbent (18) to be released and reduced. However, it is found that when the regenerating process by supplying a rich air-fuel ratio exhaust gas to the NOX absorbent (18) is carried out at high NOX absorbent temperature, a part of NOX flows out from the NOX absorbent at the beginning of the regenerating process without being reduced. In the present invention, this outflow of NOX is suppressed by, for example, carrying out the regenerating process only when the temperature of the NOX absorbent (18) is lowered to a predetermined temperature. This predetermined temperature is set low enough to ensure that the amount of the outflow of NOX is minimized.