Low-pressure exhaust gas recirculation system

A low-pressure exhaust gas recirculation (EGR) system for an engine having an intake passage which guides intake air into the engine, the system comprising:

• a low-pressure EGR passage that guides EGR gas into the intake passage;
• a low-pressure EGR regulating valve that is configured to regulate an opening degree of the low-pressure EGR passage;
• an electric actuator that is configured to drive the low-pressure EGR regulating valve;
• a low-pressure EGR opening sensor that is configured to detect an opening degree of the low-pressure EGR regulating valve;
• a control device that is configured to control energization of the electric actuator so as to control the opening degree of the low-pressure EGR regulating valve;
• an intake throttle valve that is configured to generate a negative pressure of intake air at a merging part of the intake passage and the low-pressure EGR passage;
• a linking device that is configured to change an output characteristic of the electric actuator so as to drive the intake throttle valve;
• a mechanical stopper that is provided for the linking device and is configured to limit a rotation range of the low-pressure EGR regulating valve at a limit opening degree of the low-pressure EGR regulating valve on its fully-open side and outside an EGR amount adjustment opening degree range of the low-pressure EGR regulating valve;
• and
• a failure detection unit that is provided for the control device, wherein after the engine is stopped, the failure detection unit rotates the low-pressure EGR regulating valve to its fully-open position to such an extent that rotation of the linking device is prevented by the mechanical stopper, and is configured to determine that a failure has occurred when the opening degree of the low-pressure EGR regulating valve detected by the low-pressure EGR opening sensor is different from the limit opening degree of the low-pressure EGR regulating valve.