Patent ID: 8028514

Claim:
An exhaust gas purification system for an internal combustion engine, comprising: an exhaust gas passage, one end of which is connected to the internal combustion engine and through which exhaust gas from the internal combustion engine passes, and which is divided into a plurality of branch passages; an exhaust gas purification device provided in each of the plurality of branch passages, each exhaust gas purification device purifying the exhaust gas that passes through the branch passage in which it is provided; an exhaust gas flow volume control valve provided in each of the plurality of branch passages, each exhaust gas flow volume control valve controlling a flow volume of the exhaust gas that passes through the branch passage in which it is provided; a reducing agent addition section provided in each of the plurality of branch passages upstream from the exhaust gas purification device, each reducing agent addition section adds a reducing agent to the exhaust gas that passes through the branch passage in which it is provided; a purification ability regeneration control section, wherein when the reducing agent is supplied to the exhaust gas purification device that is provided in one of the plurality of branch passages and regeneration processing of the purification ability of the exhaust gas purification device is carried out, in the branch passage where the exhaust gas purification device is provided in which the regeneration processing is to be carried out, an opening angle of the exhaust gas flow volume control valve is set to a prescribed first opening angle that is closer to being closed than the opening angle was before the regeneration processing started; the reducing agent is added from the reducing agent addition section during a period when the opening angle of the exhaust gas flow volume control valve is maintained at the first opening angle; and after addition of the reducing agent is complete, the opening angle of the exhaust gas flow volume control valve is set to a prescribed second opening angle that is closer to being closed than the first opening angle; and a prescribed no-adding-of-reducing-agent interval, during which the reducing agent is not added, is provided during at least one of a time before and a time after the period when the reducing agent is added during the period when the opening angle of the exhaust gas flow volume control valve is maintained at the first opening angle.