EGR control method and EGR controller

An EGR controller for a system that comprises an internal combustion engine comprising an intake pipe, an exhaust pipe, and an EGR passage circulating a part of an exhaust gas of the exhaust pipe in the intake pipe as an EGR gas;

• an EGR valve in the EGR passage, the EGR valve configured to adjust an EGR gas amount flowing in the EGR passage when the engine is in an EGR region;
• a differential pressure device in the intake pipe, the differential pressure device configured to adjust a front-and-back differential pressure of the EGR valve;
• the EGR controller comprising:
• a control unit configured to:
• determine whether or not an exhaust gas pressure of an inlet portion of the EGR passage is equal to or larger than a predetermined pressure,
• in response to determining that the exhaust gas pressure is equal to or larger than the predetermined pressure, fully open the differential pressure device and control an opening of the EGR valve according to a target EGR rate that is set to increase as an engine revolution speed and an engine load increase, and
• in response to determining that the exhaust gas pressure is less than the predetermined pressure, control an opening of the differential pressure device according to an opening degree that is set to increase as the engine revolution speed and the engine load increases and control the opening of the EGR valve according to the target EGR rate.