EXHAUST GAS PURIFICATION SYSTEM AND EXHAUST GAS PURIFICATION METHOD

摘要

When a catalyst temperature of a catalyst device is at or below a lower limit air-fuel ratio richness control is prohibited. When a first timing, where an estimated value of a NOx storage amount has reached an enrichment start threshold value, and a second timing, based on a set interval time in an enrichment interval time map, are both satisfied, the control is started. The second timing is corrected by multiplying the set interval time by an enrichment interval correction coefficient preset based on the catalyst temperature and a storage ratio of the estimated value of the NOx storage amount to an enrichment start threshold value of the NOx storage amount. The frequency of the air-fuel ratio richness control of a catalyst device configured to recover a purification capacity of a catalyst is reduced, and the catalyst temperature is raised while preventing white smoke development and hydrocarbon slip, to thereby achieve improvement in exhaust gas composition and improvement in fuel efficiency.

主权项

1. An exhaust gas purification system, comprising:
a catalyst device provided in an exhaust passage of an internal combustion engine and configured to recover a purification capacity of a catalyst by an air-fuel ratio richness control; and a controller configured to perform the air-fuel ratio richness control, wherein the controller is configured to
prohibit the air-fuel ratio richness control, when a catalyst temperature is at or below a preset lower limit catalyst temperature,start the air-fuel ratio richness control, when a first timing where an estimated value of a NOx storage amount has reached a preset enrichment start threshold value and a second timing based on a set interval time set in an enrichment interval time map are both satisfied, andpreset an enrichment interval correction coefficient based on the catalyst temperature of the catalyst device and on a storage ratio of the estimated value of the NOx storage amount to an enrichment start threshold value of the NOx storage amount, and correct the second timing by multiplying the set interval time by the enrichment interval correction coefficient.