Patent ID: 7448203

Claim:
A method for purifying exhaust gas provided with a NO x occlusion reduction type catalyst in an exhaust passage of a diesel engine, comprising: executing a normal control operation; detecting a regeneration control initiation timing for said catalyst; executing a rich-burn control operation and generating an exhaust gas which is in a fuel-rich state, accompanying recirculation of EGR gas; and activating a catalyst metal of said catalyst immediately before said rich-burn control operation is performed, wherein said catalyst includes a NO x occluding substance that is transformed into nitrate as a result of occluding activities, which is then regenerated back to allow continuation of NO x occlusion, and wherein said catalyst activation control operation executes a burning control operation in the condition of an EGR valve being totally closed, and at the same time, controlling the torque generation of the diesel engine by an intake control to reduce the torque variation during the transition from the normal control operation to the catalyst activation control operation.