Patent ID: 8079213

Claim:
An exhaust gas purification system for an internal combustion engine, comprising: an exhaust passage one end of which is connected to the internal combustion engine and through which exhaust gas from the internal combustion engine flows; a plurality of branch passages branching from said exhaust passage by a branching portion at some midpoint of said exhaust passage; an NOx storage reduction catalyst that stores NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and reduces NOx thus stored when the air-fuel ratio of the inflowing exhaust gas is rich and a reducing agent is present, said NOx storage reduction catalyst being provided in at least one of said plurality of branch passages; a reducing agent supply unit for supplying the reducing agent to the exhaust gas to be introduced into said NOx storage reduction catalyst; a plurality of flow rate control valves for changing the flow rate of exhaust gas flowing in each branch passage, at least one of the plurality of flow rate control valves being provided in each branch passage; a fuel injection valve for injecting fuel to be used in combustion in a cylinder of the internal combustion engine; a throttle valve for regulating a flow rate of intake air, the throttle valve being provided in an intake passage of the internal combustion engine; and a regeneration unit for, when a fuel cut request is made to the internal combustion engine, executing a performance regeneration process for regenerating performance of said NOx storage reduction catalyst by means of decreasing a quantity of fuel injected through the fuel injection valve and an opening degree of the throttle valve gradually, causing the reducing agent supply unit to supply the reducing agent to said NOx storage catalyst before a flow rate of exhaust gas which flows into said NOx storage catalyst is smaller than a predetermined flow rate, and causing the at least one of the plurality of flow rate control valves which is arranged in each branch passage provided with said NOx storage catalyst to close after the reducing agent supply unit supplied the reducing agent.