Patent ID: 8522533

Claim:
An exhaust gas purification method for an exhaust gas purification system provided with an exhaust gas purification apparatus in which an oxidizing catalyst apparatus with an oxidizing catalyst and a diesel particulate filter are arranged in order from an upstream side in an exhaust passage of an internal combustion engine of a vehicle, or an exhaust gas purification apparatus in which a diesel particulate filter with an oxidizing catalyst is arranged in an exhaust passage of an internal combustion engine of a vehicle, comprising: measuring a sustaining time of a low rotation speed driving condition, when detecting that a driving condition of the internal combustion engine is the low rotation speed driving condition; setting a predetermined time for judgment depending on a remaining deposition amount that is a difference between a particulate matter tolerable amount of the diesel particulate filter and a particulate matter deposition estimation amount right before a start of the low rotation speed driving condition; dividing a tolerable deposition amount by the particulate matter deposition estimation amount per unit time at the low rotation speed driving condition to arrive at a divided value; making the divided value a tolerable sustaining time; making a difference between the tolerable sustaining time and the measured sustaining time at the start to be the predetermined time for judgment; and performing a forced regeneration control of the diesel particulate filter without being affected by a pressure difference between a front and a back of the diesel particulate filter, when the measured sustaining time exceeds the predetermined time for judgment.