Exhaust gas recirculation system for internal combustion engine

An exhaust gas recirculation system for an internal combustion engine, comprising:

• means defining an exhaust gas recirculation passage for fluidly connecting an intake air passageway and an exhaust gas passageway of the engine;
• an exhaust gas recirculation control valve disposed in said exhaust gas recirculation passage, said exhaust gas recirculation control valve including a diaphragm defining a vacuum chamber into which a signal vacuum is supplied, and means for controlling an amount of exhaust gas flowing through the exhaust gas recirculation passage in response to said signal vacuum;
• a vacuum control valve including a diaphragm defining an atmospheric chamber and an exhaust pressure chamber respectively on the opposite sides of said diaphragm, said exhaust pressure chamber being supplied with an exhaust gas pressure prevailing in said exhaust gas recirculation passage downstream of said exhaust gas recirculation control valve, means defining an atmospheric air introduction port which is opened to said atmospheric chamber and communicated with said vacuum chamber of said exhaust gas recirculation control valve, a valve member secured on said diaphragm and located facing said atmospheric air introduction port, said valve member being capable of closing and opening said atmospheric air introduction port so as to modify said signal vacuum, spring means for biasing said diaphragm in a direction of movement relative to said atmospheric air introduction port, and a stepper motor for changing a biasing force of said spring means;
• means for controlling the stepper motor in accordance with an engine operating condition, said controlling means including first control means for controlling the stepper motor in a first manner to regulate an amount of exhaust gas passing through the exhaust gas recirculation passage, and second control means for controlling said stepper motor in a second manner to maintain said valve member at a position remote from said atmospheric air introduction port during stopping of the engine.