Patent ID: 8322130

Claim:
A method for controlling an exhaust gas purification system including an exhaust gas purification apparatus in which exhaust gas of an internal combustion engine is purified when the exhaust gas is in a lean air-fuel ratio state, and in which purification capability is regenerated when the exhaust gas is in a rich air-fuel ratio state, the method for controlling an exhaust gas purification system comprising performing, in a supply control of unburned fuel for making the exhaust gas into the rich air-fuel ratio state, both post-injection by which post-injection is performed as in-cylinder injection and in-exhaust-pipe direct injection by which fuel is injected directly into the exhaust pipe, including controlling, when an operating state of the internal combustion engine is under low load, the supply of the unburned fuel by using the post-injection without using the in-exhaust-pipe direct injection, controlling, when the operating state of the internal combustion engine is under medium load, the supply of the unburned fuel by using both the post-injection and the in-exhaust-pipe direct injection, controlling, when the operating state of the internal combustion engine is under high load, the supply of unburned fuel by using the in-exhaust-pipe direct injection without using the post-injection, and in the supply control of the unburned fuel under medium load, calculating a target addition amount of unburned fuel to be added for making the exhaust gas into the rich air-fuel ratio state by dividing an intake air amount by a target air-fuel ratio calculated from the operating state of the internal combustion engine, and by then subtracting, from the divided value, a fuel flow amount required depending on the operating state of the internal combustion engine, calculating a post-injection amount by calculating an addition amount ratio, which is a ratio between the post-injection amount and an in-exhaust-pipe direct injection amount, from the operating state of the internal combustion engine, and by then multiplying the target addition amount by the addition amount ratio, calculating the in-exhaust-pipe direct injection amount by subtracting the post-injection amount from the target addition amount, and supplying the unburned fuel in the calculated post-injection amount and the calculated in-exhaust-pipe direct injection amount.