Abstract: A turbine housing has a scroll part, an outlet pipe, and an inlet pipe. A bypass passage is formed on an inner peripheral side of a twisting form leading from the inlet pipe toward the scroll part so as to allow communication between an inlet passage and an outlet passage. Viewing the turbine housing in an axial direction, an opening center of an outlet opening of the bypass passage is located in a quadrant where a mounting flange is located among four quadrants defined by a first imaginary plane that passes through a rotational center and that is parallel to a surface of the mounting flange, and a second imaginary plane that passes through the rotational center and that is orthogonal to the first imaginary plane.

Abstract: When a waste gate valve (7) is forcibly fully closed for learning control at the time of start, the drive force of an electric actuator (20) is initially set to a large first level, and when a predetermined position (L1) immediately before seating is reached, the driving force is reduced to a second level. As a result, a valve body (7a) is gently seated. When a predetermined time (TM1) passes, the driving force is increased to a third level. Consequently, the electric actuator (20) presses the valve body (7a) onto a seat surface (34a) while displacing a spring member (37). As a result, a reliable sealability is obtained.

Abstract: A waste gate valve (7) of a turbocharger (3) is fully opened during idling after warm-up is completed in order to reduce exhaust resistance. However, during idling in an engine cold state when a cooling water temperature (TW) is below a threshold value (TW1), the waste gate valve (7) is open-loop controlled to an intermediate opening degree that is smaller than full opening. An ignition timing is delayed (retarded) for catalyst warm-up. When the cooling water temperature (TW) reaches (t3) the threshold value (TW1), the opening degree of the waste gate valve (7) is set to full opening. When an accelerator opening degree (APO) becomes large (t4) before warm-up is completed, the limitation of the opening degree is released.

Abstract: When a waste gate valve (7) is forcibly fully closed for learning control at the time of start, the drive force of an electric actuator (20) is initially set to a large first level, and when a predetermined position (L1) immediately before seating is reached, the driving force is reduced to a second level. As a result, a valve body (7a) is gently seated. When a predetermined time (TM1) passes, the driving force is increased to a third level. Consequently, the electric actuator (20) presses the valve body (7a) onto a seat surface (34a) while displacing a spring member (37). As a result, a reliable sealability is obtained.

Abstract: A waste gate valve (7) of a turbocharger (3) is fully opened during idling after warm-up is completed in order to reduce exhaust resistance. However, during idling in an engine cold state when a cooling water temperature (TW) is below a threshold value (TW1), the waste gate valve (7) is open-loop controlled to an intermediate opening degree that is smaller than full opening. An ignition timing is delayed (retarded) for catalyst warm-up. When the cooling water temperature (TW) reaches (t3) the threshold value (TW1), the opening degree of the waste gate valve (7) is set to full opening. When an accelerator opening degree (APO) becomes large (t4) before warm-up is completed, the limitation of the opening degree is released.