A straddle-type vehicle comprises an engine which generates driving power and emits an exhaust gas; an exhaust device including: a catalyst which cleans the exhaust gas, an inner tube in which the catalyst is disposed and through which the exhaust gas flows, the inner tube extending to a location downstream of the catalyst; and an outer tube which covers an outer peripheral surface of the inner tube in an axial direction of the inner tube, and has a muffling space through which the exhaust gas discharged from the inner tube is flowed to reduce an exhaust noise radiated from the engine; at least one exhaust pipe through which the exhaust gas is led to the catalyst; and a downstream oxygen sensor which detects an oxygen concentration of the exhaust gas after flowing through the catalyst, at a location downstream of the catalyst in the inner tube.

A vehicle, such as a straddle-type vehicle, can include an engine, a catalyst and an air cleaner. The catalyst can be disposed in an expansion chamber of the vehicle. At least a part of the air cleaner can be disposed above a swing arm of the vehicle, and at least a part of the expansion chamber can be disposed below the swing arm. The air cleaner can further be disposed to the rear of a shock absorber of the vehicle. Thus, the influence of heat from the catalyst and the engine on the air cleaner can be reduced. Consequently, efficiency of air induction into the engine can be increased, thereby improving engine output.

An exhaust gas sensor arrangement structure includes a catalyst which purifies exhaust gas of an engine; and exhaust gas sensors which detect an exhaust gas component of the engine; the catalyst is provided under the engine; and the exhaust gas sensors are provided within a width of the engine in a front/rear direction so that the catalyst is provided between the exhaust gas sensors at front and rear sides of the catalyst.

Mufflers with unique configurations which, in certain (but not all) embodiments, improve engine performance. In other embodiments, improved manufacturing processes and methods for making mufflers. In particularly preferred embodiments, methods for making motorcycle mufflers with swaging techniques. In still other preferred embodiments, swaged motorcycle mufflers with improved exhaust flow. In still other embodiments, aftermarket mufflers which can be assembled to a variety of engine exhaust systems utilizing a universal coupler.

An exhaust structure for a straddle-type vehicle includes a muffler having an outer tube constituting an outer circumferential member of the muffler; first and second separators defining expansion chambers in the outer tube; a body end member arranged at the downstream end of the outer tube; and glass wool provided on the inner circumference of the outer tube. The muffler further includes a resonator chamber provided in the most downstream portion of the muffler. The resonator chamber is formed by the outer tube, the body end member and the second separator situated closest to the body end member. The surroundings of the resonator chamber are surrounded by the glass wool. Such exhaust structure of a straddle-type vehicle is capable of taking measures against exhaust heat and exhaust sound even with a configuration where there is only one, single resonator chamber.

Gas flow and sound control valve for an exhaust system of an internal combustion engine comprising a housing including an inlet, a first outlet, and a second outlet, and a valve member arranged within the housing for forming a first conduit connecting the inlet to the first outlet and/or a second conduit from the inlet to the second outlet, wherein the valve member can be moved relative to the housing between a first predetermined position in which the valve member closes the second conduit and a second predetermined position in which the valve member closes the first conduit, whereby the valve member is rotatable around a valve axis aligned parallel, in particular coaxial, to a centerline of the inlet.

An abnormality detection device determines abnormality in an exhaust gas sensor, disposed in an exhaust passage of an engine to detect a component in exhaust gas. The abnormality detection device includes: a responsiveness determination unit configured to calculate responsiveness of the exhaust gas sensor on the basis of a timewise change of output values of the exhaust gas sensor; and an abnormality determination unit configured to determine that the exhaust gas sensor has abnormality when the responsiveness calculated by the responsiveness determination unit is lower than a predetermined responsiveness threshold. The abnormality determination unit determines if the exhaust gas sensor has abnormality, excluding an excluded period during which a slope of the output values becomes zero or is inversed with respect to a preceding trend of the timewise change while the output values of the exhaust gas sensor timewisely change between a predetermined first and second determination values.

An air exhausting device includes a muffler internally divided into a plurality of chambers by a separator, an inlet pipe that couples an exhaust pipe of an engine to the muffler, and an outlet pipe that is a path to discharge an exhaust gas inside the muffler to outside air. The muffler is configured of an expansion chamber to which a downstream end of the inlet pipe opens, and a resonator chamber communicated with only the expansion chamber via a plurality of resonator pipes. Any of or both of lengths and thicknesses of the plurality of resonator pipes are different.

Provided is a novel palladium catalyst capable of efficiently purifying carbon monoxide (CO) and total hydrocarbons (THC) under a fuel-rich atmosphere even when palladium (Pd) is used as a catalyst active component. Proposed is a palladium monolayer catalyst for an exhaust gas from a saddle-riding-type vehicle, which is an exhaust gas purification catalyst for a saddle-riding-type vehicle to be installed in an exhaust gas passage in an internal combustion engine. The palladium monolayer catalyst includes a substrate, and a catalyst layer that has the form of a monolayer and contains palladium acting as a catalyst active component, an inorganic porous body acting as a catalyst carrier, ceria (CeO.sub.2) particles acting as a promoter component, and barium.

A motorcycle has a crankcase containing a crank shaft and a balancer shaft, and a cylinder and a cylinder head positioned above the crankcase, and an exhaust pipe extends from the cylinder head. The balancer shaft is positioned in front of the crank shaft, and the crankcase has a balancer shaft housing supporting the balancer shaft thereinside, and has a recessed part depressed rearward in a front end center part of the balancer shaft housing. The balancer shaft has balancer shaft weights apart from each other in one side and in the other side in an axis direction.