Patent ID: 8371114

Claim:
An exhaust gas purification apparatus for an internal combustion engine, comprising: an NO x catalyst disposed in an exhaust gas passage of an internal combustion engine; and a reducing agent injecting unit, injecting a reducing agent into the exhaust gas passage which is on an upstream side of the NO x catalyst, wherein a narrowed portion, in which a cross-sectional area of a flow passage is smaller than a cross-sectional area of the exhaust gas passage and of the NO x catalyst, is provided on a downstream side of an injecting position by the reducing agent injecting unit and on the upstream side of the NO x catalyst, a reducing agent diffusing means formed using a metallic material which includes both a perforated plate having a plurality of flaps and a swirl type static mixer, or either, is provided on the narrowed portion, a downstream-side guide portion for guiding the exhaust gas to the NO x catalyst being provided between the narrowed portion and the NO x catalyst, an upstream-side guide portion for preventing the reducing agent from crystallizing by adhering to a location other than the narrowed portion being provided on an upstream side of the narrowed portion, and the exhaust gas passage having a curved section in the upstream side of the NO x catalyst, the downstream-side guide portion being fitted so as to cover an entrance of the NO x catalyst at the curved section and is provided with an exhaust gas inlet at a portion thereof, so that a flow direction of the exhaust gas that flows from the exhaust gas inlet into the downstream-side guide portion changes along the direction in which the exhaust gas passage curves.