US Patent 7114328 Control method of exhaust gas purifying system

In an exhaust gas purifying system wherein an NOx occlusion reduction type catalyst (30) including a catalytic metal and an NOx occluding substance is installed in an exhaust passage (3) of an engine (10), a restore processing against the sulfur poisoning of the NOx occlusion reduction type catalyst (30) is executed, by performing a lax rich control for controlling the air/fuel ratio of the exhaust gas to the theoretical air/fuel ratio or slightly lower than the theoretical air/fuel ratio, when the NOx occlusion reduction type catalyst (30) is heated equal or superior to the sulfur purge temperature.