Patent ID: 7788909

Claim:
An exhaust gas purification method in an exhaust gas purification system, comprising: providing an exhaust gas purification device, having an oxidation catalyst device with an oxidation catalyst and a diesel particulate filter, in an exhaust passage of an internal combustion engine; obtaining a predetermined determining temperature based on an engine speed of the internal combustion engine, which predetermined determining temperature is a temperature necessary to oxidize an unburned fuel supplied to the oxidation catalyst device; comparing a catalyst temperature index temperature, indicating a temperature of the oxidation catalyst, with the predetermined determining temperature; when the catalyst temperature index temperature becomes equal to the predetermined determining temperature or above, raising a temperature of the diesel particulate filter by supplying the unburned fuel to the oxidation catalyst to have the unburned fuel oxidized by the oxidation catalyst, and when the catalyst temperature index temperature is lower than the predetermined determining temperature, raising an exhaust gas temperature, wherein the predetermined determining temperature is obtained based on the engine speed of the internal combustion engine after the exhaust gas temperature is raised; and comparing the obtained predetermined determining temperature with the catalyst temperature index temperature.