In a vehicle, a rod of a waste gate valve actuator reciprocates along a virtual plane which is parallel to both the central axis of a connecting shaft of a turbocharger and the cylinder axis of a cylinder hole. When viewed in the left or right direction of the vehicle, a main catalyst of a catalyst portion is provided forward of the cylinder axis of the cylinder hole. The flow direction of the exhaust gas in the main catalyst intersects with the reciprocating direction of the rod of the waste gate valve actuator when viewed in a direction orthogonal to both the central axis of the connecting shaft of the turbocharger and the central axis of the cylinder hole.

An exhaust device includes an expansion chamber that expands an exhaust gas from an engine; a separator that partitions the expansion chamber; and a plurality of catalyst units arranged in the expansion chamber and supported in parallel by the separator. The separator is divided into upper and lower portions through a dividing plane, and the plurality of catalyst units are supported in such a manner as to be clamped from upper and lower sides at the dividing plane.

A straddle-type vehicle includes a driver seat on which a driver rides, a cylinder head of an engine arranged in a region in front of and below the driver seat, an exhaust pipe that is connected to an exhaust port formed on a front surface of the cylinder head and exhausts exhaust of the engine, and a control unit that is arranged in an engine front space formed in front of the cylinder head, above the exhaust pipe, and below an upper end surface of the engine and controls the straddle-type vehicle.

There is provided a muffler structure of a saddle-type vehicle. The muffler structure is disposed at a downstream side of an exhaust pipe extending from an exhaust port of a cylinder head. A pipe is connected to the exhaust pipe and inserted into a muffler main body. The pipe is provided with an expansion chamber having an inner diameter that is larger than an inner diameter of the exhaust pipe. At least a part of the expansion chamber is disposed in the muffler main body, and a plurality of through holes are formed on an outer peripheral surface of the expansion chamber disposed in the muffler main body.

There is provided a muffler structure of a saddle-type vehicle. The muffler structure is disposed at a downstream side of an exhaust pipe extending from an exhaust port of a cylinder head. A pipe is connected to the exhaust pipe and inserted into a muffler main body. The muffler main body includes a cylindrical portion and a reduced diameter portion joined to a downstream side end portion of the cylindrical portion and having a diameter reduced toward the downstream side thereof. The pipe includes a center pipe passing through the cylindrical portion, and a tail pipe disposed in the reduced diameter portion. An expansion chamber is formed by a space in the reduced diameter portion in the vicinity of the tail pipe.

An engine exhaust device includes an exhaust pipe attached to a vehicle engine and a silencer connected to a downstream side of the exhaust pipe; the silencer includes a first partition wall which partitions an internal space of the silencer into at least two spaces in a first direction and a second partition wall which partitions one of the at least two spaces into two spaces in a second direction that crosses the first direction; another one of the at least two spaces is larger in capacity than each of the two spaces defined by the second partition wall; and a downstream end of the exhaust pipe is open in the another one of the at least two spaces.

Methods, systems, and vehicles that control the temperature of a device included in the vehicle are presented herein. The temperature of the device is controlled by ventilating the device with drivetrain air, such as transmission cooling air. In some embodiments, the device is at a greater temperature than the drivetrain air, which cools the device. In other embodiments, the device is at a lesser temperature than the drivetrain air, which heats the device. The drivetrain air is provided to the device through an exhaust duct coupled to the vehicle's transmission. The drivetrain exhaust air is preferably circulated by the transmission. The transmission may be a continuously variable transmission. The device may be an oxygen sensor that is coupled to an engine exhaust pipe. The oxygen sensor is thermally coupled to the engine exhaust and the engine exhaust pipe, which are at greater temperatures than the transmission exhaust air.

There is provided a secondary air introduction device configured to introduce air into an exhaust port provided in a cylinder head of an engine by using a negative pressure in the exhaust port. A back-flow restriction member is provided between a reed valve and the exhaust port in an air introduction passage, and includes a plate part intersecting with an extension direction of the air introduction passage. The plate part has an air passing region in which the air flowing through the air introduction passage from an air intake unit toward the exhaust port is enabled to pass therethrough and a back-flow cutoff region in which exhaust air, which flows in a direction of directly colliding with at least a valve body of the reed valve, of exhaust air flowing back through the air introduction passage from the exhaust port is cut off.

An exhaust pipe structure for an in-line four-cylinder internal combustion engine includes: an in-line four-cylinder internal combustion engine; four exhaust pipes connected with respective exhaust ports in respective cylinders of the internal combustion engine; and a converging exhaust pipe connected with a converging portion at which downstream ends of all the exhaust pipes converge. In this exhaust pipe structure, the exhaust pipes are each configured as a dual pipe including an outer pipe and an inner pipe disposed inside the outer pipe. At the converging portion, the four exhaust pipes are arrayed linearly in parallel with each other, and the outer pipes of adjacent ones of the exhaust pipes are directly welded with each other at the downstream ends.

In an engine exhaust control valve of a saddle-riding vehicle in which an engine exhaust pipe has a main pipe portion and a branch pipe portion which are connected to an exhaust muffler at downstream sides thereof, a branching portion is provided at which the branch pipe portion is branched sideward from the main pipe portion, and a full-open to full-closed control of the main pipe portion at a downstream side of the branching portion is performed. The exhaust control valve includes: a valve shaft disposed in an intersecting manner with a center line of the main pipe portion; a valve plate mounted on the valve shaft and rotatably positioned within an inner peripheral surface of the main pipe portion; a valve rotational drive portion mounted on one shaft end of the valve shaft; a drive motor for driving the valve rotational drive portion; and a control unit for controlling the drive motor. Protruding portions, with which outer peripheral edges, of the valve plate are brought into contact at a rotational limit of the valve plate in a closing direction are formed on an inner peripheral surface of the main pipe portion. The above structure provides a high degree of sealing.