Exhaust gas recirculation control device of engine

An exhaust gas recirculation (EGR) control device of an engine, comprising:

• an exhaust turbocharger having a turbine disposed in an exhaust passage of the engine and a compressor disposed in an intake passage;
• a low-pressure EGR passage connecting a part of the exhaust passage downstream of the turbine to a part of the intake passage upstream of the compressor;
• a low-pressure EGR valve disposed in the low-pressure EGR passage and for changing a cross-sectional area of the low-pressure EGR passage;
• a high-pressure EGR passage connecting a part of the exhaust passage upstream of the turbine to a part of the intake passage downstream of the compressor;
• a high-pressure EGR valve disposed in the high-pressure EGR passage and for changing a cross-sectional area of the high-pressure EGR passage;
• a valve control device for controlling openings of the low-pressure EGR valve and the high-pressure EGR valve so that an amount of exhaust gas of the engine recirculated by the low-pressure EGR passage becomes a low-pressure EGR target recirculation amount and an amount of exhaust gas of the engine recirculated by the high-pressure EGR passage becomes a high-pressure EGR target recirculation amount, respectively, the low-pressure and high-pressure EGR target recirculation amounts being set in advance according to an operating state of the engine;
• a total intake gas amount detector for detecting a total amount of intake gas introduced into the engine;
• a fresh air amount detector for detecting an amount of fresh air introduced into the engine;
• and
• a pressure difference detector for detecting a pressure difference between the exhaust passage side and the intake passage side of the high-pressure EGR valve in the high-pressure EGR passage,
• wherein while the engine is in a normal operation, when the exhaust gas is recirculated by the low-pressure EGR passage and the high-pressure EGR passage, the valve control device determines whether an actual total recirculation amount is normal/abnormal by comparing the actual total recirculation amount with a total target recirculation amount that is the sum of the low-pressure EGR target recirculation amount and the high-pressure EGR target recirculation amount, and the valve control device provisionally determines whether an actual high-pressure recirculation amount is normal/abnormal by comparing the actual high-pressure recirculation amount with the high-pressure EGR target recirculation amount, the actual total recirculation amount calculated by subtracting the fresh air amount detected by the fresh air amount detector, from the total intake gas amount detected by the total intake gas amount detector, the actual high-pressure recirculation amount calculated based on the pressure difference detected by the pressure difference detector and an actual opening of the high-pressure EGR valve,
• wherein while the engine is in the normal operation, when the exhaust gas is recirculated only by the low-pressure EGR passage, the valve control device determines whether an actual low-pressure recirculation amount is normal/abnormal by comparing the actual low-pressure recirculation amount with the low-pressure EGR target recirculation amount, the actual low-pressure recirculation amount calculated by subtracting the fresh air amount detected by the fresh air amount detector, from the total intake gas amount detected by the total intake gas amount detector, and
• wherein based on the determination result of whether the actual total recirculation amount is normal/abnormal and the determination result of whether the actual low-pressure recirculation amount is normal/abnormal, the valve control device reviews the provisional determination result of whether the actual high-pressure recirculation amount is normal/abnormal, and non-provisionally determines whether the actual high-pressure recirculation amount is normal/abnormal.