Patent ID: 7963103

Claim:
An exhaust gas purification method comprising: in regeneration control of an exhaust gas purification system that comprises a NOx occlusion reduction type catalyst that occludes NOx when an air/fuel ratio of exhaust gas is in a lean state, and releases and reduces the occluded NOx when it is in a rich state, and performs the regeneration control for recovering a NOx occluding ability of the NOx occlusion reduction type catalyst if it is determined that an estimated NOx occlusion amount that is estimated to be occluded in the NOx occlusion reduction type catalyst reaches a predetermined criterion value, the method comprising the steps of; determining whether or not an engine operating condition is in a first engine operating region where an exhaust gas temperature becomes equal to or less than a predetermined mode determination temperature, if the engine operating condition is in the first engine operating region, performing EGR rich control in which the air/fuel ratio of the exhaust gas is brought into the rich state by controlling an EGR amount, or if the engine operating condition is not in the first engine operating region, performing exhaust pipe injection rich control in which the air/fuel ratio of the exhaust gas is brought into the rich state by directly injecting fuel into an exhaust pipe; determining whether or not a vehicle mounted with the exhaust gas purification system is in acceleration if the EGR rich control is performed; and postponing the regeneration control until a determination that the vehicle is in acceleration is complete, if it is determined that the vehicle is in acceleration.