Patent ID: 7051520

Claim:
A sulfur purge control method, using an exhaust gas purifying system for removing NOx by a NOx occlusion reduction type catalyst from the exhaust gas of an internal combustion engine, said exhaust gas purifying system having; an oxygen concentration detection means for detecting the oxygen concentration in the downstream of the NOx occlusion reduction type catalyst; a sulfur purge start judgment means; and a sulfur purge control means accompanying the control of the air-fuel ratio state of the exhaust gas; said sulfur purge control method comprising steps of: controlling the air-fuel ratio in the exhaust gas by setting a target air-fuel ratio to a predetermined first air-fuel ratio which is a rich air-fuel ratio by means of the sulfur purge control means after starting the sulfur purge; and thereafter, controlling the air-fuel ratio in the exhaust gas by changing the target air-fuel ratio to a predetermined second air-fuel ratio which is a stoichiometric air-fuel ratio, when the oxygen concentration measured by an oxygen concentration detection means in the downstream of a NOx occlusion reduction type catalyst becomes lower than a predetermined threshold.