Exhaust gas recirculation system having cooler

An exhaust gas recirculation system of an internal combustion engine having an exhaust gas recirculation cooler that is disposed in an exhaust gas recirculation passage and cools exhaust gas recirculated from an exhaust passage to an intake passage of the engine through the exhaust gas recirculation passage connecting the exhaust passage with the intake passage, the system comprising:

• cooling performance detecting means for detecting cooling performance of the cooler;
• cooling performance regeneration controlling means for performing a regenerating operation for regenerating the cooling performance of the cooler when the cooling performance detecting means detects degradation of the cooling performance;
• and
• intake pressure measuring means for measuring pressure of intake air,
• wherein the cooling performance detecting means determines that the cooling performance is degraded when the intake pressure measured by the intake pressure measuring means is lower than a normal intake pressure by at least a predetermined value, the normal intake pressure being estimated from an operating state of the engine.