EXHAUST PURIFICATION SYSTEM OF INTERNAL COMBUSTION ENGINE

摘要

An exhaust purification system of an internal combustion engine which has a plurality of cylinders is comprised of an exhaust purification catalyst, a downstream side air-fuel ratio sensor, and a control device which controls the average air-fuel ratio of the exhaust gas and the combustion air-fuel ratios of the cylinders. The control device performs average air-fuel ratio control where it alternately controls the average air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio and inter-cylinder air-fuel ratio control where it controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even when the average air-fuel ratio is controlled to the lean air-fuel ratio by average air-fuel ratio control. In average air-fuel ratio control, the average air-fuel ratio is controlled so that the lean shift amount when controlling the average air-fuel ratio to the lean air-fuel ratio becomes smaller than the rich shift amount when controlling the average air-fuel ratio to the rich air-fuel ratio.

主权项

1. An exhaust purification system of an internal combustion engine which has a plurality of cylinders comprising:
an exhaust purification catalyst which is arranged in an engine exhaust passage and which can store oxygen; a downstream side air-fuel ratio sensor which is arranged at a downstream side of the exhaust purification catalyst in a direction of flow of exhaust; and a control device which is to control combustion air-fuel ratios when combustion is performed in the cylinders, wherein the control device is configured to: perform average air-fuel ratio control which alternately controls an average air-fuel ratio of an average of the combustion air-fuel ratios of all cylinders between a rich air-fuel ratio which is richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio which is leaner than the stoichiometric air-fuel ratio and inter-cylinder air-fuel ratio control which controls the combustion air-fuel ratios of the cylinders so that the combustion air-fuel ratio becomes the rich air-fuel ratio at least at one cylinder among the plurality of cylinders even if the average air-fuel ratio is controlled to the lean air-fuel ratio by the average air-fuel ratio control; and control the average air-fuel ratio in the average air-fuel ratio control so that a lean shift amount of a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a lean air-fuel ratio becomes smaller than a rich shift amount of a difference between the average air-fuel ratio and stoichiometric air-fuel ratio when controlling the average air-fuel ratio to a rich air-fuel ratio.