Abstract: An exhaust system includes a turbine housing and an air-fuel ratio sensor. The turbine housing includes a first collecting exhaust pipe including a first passage, a second collecting exhaust pipe including a second passage, and a junction exhaust pipe including a junction passage. The first passage and the second passage are arranged in parallel. When an inner wall forming the junction passage is defined into a first continuous inner wall and a second continuous inner wall, the air-fuel ratio sensor is provided in the first continuous inner wall so as to protrude toward the center of the junction passage. A guide portion that protrudes toward the center of the junction passage is provided in the first continuous inner wall on the upstream side of the air-fuel ratio sensor.

Abstract: A flange joining structure comprises flanges of a cylinder head of an internal combustion engine and a turbine housing joined through a gasket. The flange of cylinder head has, in an end face thereof, end parts of a first collecting exhaust pipe and a second collecting exhaust pipe; the flange of turbine housing has, in an end face thereof, end parts of a first pre-merge exhaust pipe and a second pre-merge exhaust pipe corresponding to the end parts of the first collecting exhaust pipe and the second collecting exhaust pipe; and the gasket has, on a face on the cylinder head side, a bead formed into an edge-rounded rectangle having a straight part shorter than the radius of curvature thereof, and surrounding the end parts of the first collecting exhaust pipe and the second collecting exhaust pipe.

Abstract: An exhaust system includes a turbine housing and an air-fuel ratio sensor. The turbine housing includes a first collecting exhaust pipe including a first passage, a second collecting exhaust pipe including a second passage, and a junction exhaust pipe including a junction passage. The first passage and the second passage are arranged in parallel. When an inner wall forming the junction passage is defined into a first continuous inner wall and a second continuous inner wall, the air-fuel ratio sensor is provided in the first continuous inner wall so as to protrude toward the center of the junction passage. A guide portion that protrudes toward the center of the junction passage is provided in the first continuous inner wall on the upstream side of the air-fuel ratio sensor.