Exhaust gas recirculation system for an internal combustion engine

摘要

Disclosed is an exhaust gas recirculation system for an engine having a high compression ratio or with a supercharger. An outside EGR duct connecting the exhaust system (4) to the intake system (3) is provided with a first control valve (22), which has a second outside EGR duct (23) bypassing the first control valve. The second EGR duct has a second EGR control valve (24) and a cooler (25). When the engine exists in an extremely low load state, the first and second control valves are closed to inhibit the outside EGR. In the light load state, the first control valve is opened while the second control valve is closed, thereby allowing recirculation of the EGR gases having high temperature and reducing the pumping loss. In the high load state, the first control valve is being closed while opening the second control valve, thereby increasing a recirculation ratio of EGR gases cooled by the cooler and performing both an improvement of anti-knocking performance and a decrease in pumping loss, as well as reducing the heat load of the exhaust system and within the engine.