Exhaust gas recirculation system

Abstract

An open/close means M1 opens or closes an EGR passage. An engine load detecting means M2 detects an engine load, such as an intake air amount or an intake air pressure. Either an open. condition or a closed condition of the open/close means M1 is specified as a referential state, while the other is specified as a non-referential state. A memory means M3 memorizes engine loads at the referential state and the non-referential state. A constant acceleration judging means M4 makes a judgement as to whether or not the operational condition of the engine is in a constant accelerating condition. An open/close control means M5 switches the open/close means M1 from the referential state to the non-referential state in response to a constant accelerating condition detected by the constant acceleration judging means M4. An estimating means M8 calculates an estimated engine load to be measured if the open/close means M1 is maintained at the referential state under the continuous constant accelerating condition at the time an actual engine load is detected in the non-referential state, based on a plurality of detection values of the engine load values memorized in the referential state. An abnormality judging means M7 compares the estimated engine load calculated by the estimating means M6 with the actual engine load detected in the non-referential state, thereby making a judgement as to whether the exhaust gas recirculating operation is normal or abnormal.