An exhaust device that guides exhaust gas from an exhaust pipe in front of an engine to a muffler in a rear of the engine is provided. The exhaust device includes a primary catalyst case accommodating a primary catalyst configured to purify the exhaust gas at a downstream side from the exhaust pipe, a secondary catalyst case accommodating a secondary catalyst configured to purify the exhaust gas at a downstream side from the primary catalyst, and a chamber formed with a muffling chamber configured to reduce an exhaust noise at a downstream side from the secondary catalyst. The primary catalyst case is disposed in a front space of the engine. The secondary catalyst case is disposed on a front part of a lower space of the engine. The chamber is disposed so as to occupy at least a rear part of the lower space of the engine.

An exhaust device in which an exhaust passage wraps around from a front side of an engine to a lower side of the engine and extends to a rear side is provided. The exhaust device includes a catalyst configured to purify exhaust gas in the exhaust passage and disposed in front of the engine, and a gas sensor disposed on a wall surface of the exhaust passage at an upstream side than the catalyst. The gas sensor is disposed in front of the engine so as to be directed toward the engine.

A catalyst deterioration determining device for use in a straddled vehicle having an engine, a transmission that transmits motive power of an engine, and a catalyst that cleans an exhaust gas from the engine. The catalyst deterioration determining device includes a running state acquirer that acquires a plurality of running states, a state determiner that stores a plurality of allowable conditions, each of which is a condition for determining work in regard to a degradation state of the catalyst to be executed and is based on a relationship among a plurality of gear ratios of the transmission, an intake state of the engine and a rotation speed of the engine, and determines whether the plurality of running states acquired by the running state acquirer satisfy the plurality of allowable conditions, and a determination executor that executes the determining work based on a result of the determination by the state determiner.

A catalyst degradation determining device for a straddled vehicle that includes an engine, a catalyst for cleaning an exhaust gas from the engine, and a throttle valve that is controllable by cruise control of the straddled vehicle to keep a traveling speed of the straddled vehicle constant. The catalyst degradation determining device includes a determiner that determines whether the cruise control is being executed, and an execution controller. The execution controller is configured to determine a degradation state of the catalyst while controlling an air-fuel mixture supplied through the throttle valve to the engine, in a case where the determiner determines that the cruise control is not being executed, and at least one running state of the straddled vehicle satisfies at least one predetermined allowable condition, and not to determine the degradation state of the catalyst in a case where the determiner determines that the cruise control is being executed.

A secondary air introduction device is configured to supply air into an exhaust passage of an engine to combust unburned gas contained in exhaust gas. The secondary air introduction device includes: an air introduction passage configured to introduce air into the exhaust passage; and a secondary air valve configured to be attached to an outer surface of a cylinder head of the engine and to control opening and closing of the air introduction passage. The secondary air valve is configured to be attached to an outer lateral surface of the cylinder head on one side in an axial direction of a crankshaft, and the secondary air valve includes an air introduction inlet formed in a position opposite to the outer lateral surface of the cylinder head in the axial direction of the crankshaft.

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.

A muffler structure contains: a body, a first cover unit, and a second cover unit. The body includes an accommodation tube, fiber cotton, and a first mesh portion. The accommodation tube has an accommodating space and an internal fence. The first cover unit includes a manifold connection portion, a first polygonal cap, a hollowly tubular mesh having multiple orifices, a second mesh portion, and a stainless steel mesh. The second cover unit is fixed on a rear end of the accommodation tube of the body opposite to the first cover unit, and the second cover unit includes a second polygonal cap and a silencer. The second polygonal cap is covered on the accommodation tube of the body, and the second polygonal cap has a receiving portion defined in a free end thereof and configured to accommodate the silencer.

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.

A secondary air introduction device is configured to supply air into an exhaust passage of an engine to combust unburned gas contained in exhaust gas. The secondary air introduction device includes: an air introduction passage configured to introduce air into the exhaust passage; and a secondary air valve configured to be attached to an outer surface of a cylinder head of the engine and to control opening and closing of the air introduction passage. The secondary air valve is configured to be attached to an outer lateral surface of the cylinder head on one side in an axial direction of a crankshaft, and the secondary air valve includes an air introduction inlet formed in a position opposite to the outer lateral surface of the cylinder head in the axial direction of the crankshaft.

A saddle-riding type vehicle exhaust structure includes: an exhaust pipe that is connected to an exhaust port connecting to a combustion chamber of an engine and has a circular cross-sectional shape which is orthogonal to an exhaust flow direction; and a muffler that is connected to a downstream side in the exhaust flow direction of the exhaust pipe, wherein the exhaust pipe includes a muffler connection part that is connected to the muffler, an exhaust pipe upstream part that is connected to an upstream side in the exhaust flow direction of the muffler connection part, and an exhaust pipe downstream part that is connected to a downstream side in the exhaust flow direction of the muffler connection part, a cross-sectional area that is orthogonal to the exhaust flow direction of the muffler connection part is larger than each of a minimum value of a cross-sectional area that is orthogonal to an exhaust flow direction of the exhaust pipe upstream part and a minimum value of a cross-sectional area that is orthogonal to an exhaust flow direction of the exhaust pipe downstream part, and a vehicle width direction size of the cross-sectional shape of the muffler connection part and a vertical direction size of the cross-sectional shape of the muffler connection part are different from each other.