Exhaust gas purification device for an engine and a/f ratio control for early activating a nox trapping catalyst

摘要

An exhaust gas purification device including three-way catalysts (40,44) connected to engine cylinder groups (12) and arranged in parallel, and a NOx trapping catalyst (48) connected with the three-way catalysts downstream thereof. A controller controls fuel injection for making an A/F ratio of exhaust gas flowing into one of the three-way catalysts rich relative to a stoichiometric A/F ratio when it is required to reduce the NOx trapped by the NOx trapping catalyst.