Patent ID: 7207171
Filing Date: 2007-04-24
Classification: F02D

Abstract:
1. An exhaust gas purifying method, using an exhaust gas purifying system which performs NOx purification by a NOx occluding reduction type catalyst and PM purification by a DPF for exhaust gas of an internal combustion engine and has a control unit, the control unit being provided with a regeneration start judgment means of a NOx catalyst, a NOx catalyst regeneration control means, a sulfur purge start judgment means, a DPF regeneration start judgment means, and a DPF regeneration control means, comprising the steps of: judging whether the sulfur purge of a NOx occluding reduction type catalyst is required, further judging whether the PM accumulation quantity collected in the DPF exceeds a predetermined value when the sulfur purge is judged to be required, and performing a sulfur purge control after performing the DPF regeneration control when the PM quantity exceeds the predetermined value; wherein the predetermined value is a value different from a regeneration start judgment value by which, when PM accumulated in the DPF is burned, a temperature rise of the exhaust gas and consumption of oxygen in the exhaust gas entering the NOx occluding reduction type catalyst is estimated.