EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINES

摘要

A three-way catalyst (8a) is connected to a first group of cylinders (1a) whereby exhaust gas discharged from the first group of cylinders (1a) and passing through the three-way catalyst (8a) and exhaust gas discharged from a second group of cylinders (1b) are conducted to an exhaust gas purifying catalyst (14). The second group of cylinders (1b) are operated with a lean gas. The first group of cylinders (1a) are operated with a rich gas, so that NH3 is generated from NOx in the exhaust gas of the first pump of cylinders (1a) by means of the three-way catalyst (8a). The exhaust gas purifying catalyst (14) causes NH3 from the three-way catalyst (8a) to purify NOx in the exhaust gas of the second group of cylinders (1b). An amount of HC flowing into the three-way catalyst (8a) is found, and when the amount of HC exceeds a set amount, the first group of cylinders (1a) is temporarily operated with a lean gas, thereby maintaining a favorable catalytic activity of the three-way catalyst (8a).