Patent Description:
In the related art, as an exhaust device of a straddle-type vehicle, a device in which a primary catalyst case is disposed in front of an engine and a secondary catalyst case is disposed on a lower side of the engine is known (for example, see Patent Literature <NUM>). A starter catalyst is accommodated in the primary catalyst case, and a main catalyst is accommodated in the secondary catalyst case. Exhaust gas is sent from a pair of exhaust ports to the primary catalyst case through an exhaust pipe on an upstream side, and the exhaust gas is sent from the primary catalyst case to the secondary catalyst case through an exhaust pipe on a downstream side. The primary catalyst case is brought close to the exhaust port and activated at an early stage, and the secondary catalyst case is activated at an early stage by the exhaust gas heated by a catalyst reaction.

Patent Literature <NUM>: <CIT>, <CIT> relates to an exhaust system that exhausts exhaust gas from an engine, <CIT> relates to an exhaust gas purifying apparatus for a motor vehicle and a respective motor vehicle comprising such an exhaust gas purifying apparatus, <CIT> relates to vehicles, and, more particularly, to an exhaust system of a vehicle.

However, in the exhaust device disclosed in Patent Literature <NUM>, the lower side of the engine is occupied by the secondary catalyst case, and it is difficult to secure a muffling chamber with a sufficient volume on an upstream side of a muffler. Therefore, a volume of the muffling chamber in the muffler is increased, and a size of the muffler is increased.

The present invention has been made in view of this point, and an object of the present invention is to provide an exhaust device capable of securing a muffling chamber on a lower side of an engine and reducing a size of a muffler.

The problem is solved by a straddle-type vehicle as defined in claim <NUM>.

According to the exhaust device of one aspect of the present invention, the primary catalyst case is disposed in the front space of the engine, and the secondary catalyst case is disposed on the front part of the lower space of the engine. Since the primary catalyst case and the secondary catalyst case are compactly disposed in front of the engine, the lower space of the engine is not occupied by the secondary catalyst case. The chamber is disposed in a wide range of the lower space of the engine, and the exhaust noise is reduced by the muffling chamber of the chamber. By securing the muffling chamber on an upstream side of the muffler, it is possible to reduce a size of the muffler.

An exhaust device according to one aspect of the present invention guides exhaust gas from an exhaust pipe in front of an engine to a muffler in a rear of the engine. A primary catalyst case is provided downstream of the exhaust pipe, and a primary catalyst that purifies the exhaust gas downstream of the exhaust pipe is accommodated in the primary catalyst case. A secondary catalyst case is provided downstream of the primary catalyst case, and a secondary catalyst that purifies the exhaust gas downstream of the primary catalyst is accommodated in the secondary catalyst case. A chamber is provided downstream of the secondary catalyst case, and a muffling chamber that reduces an exhaust noise is formed in the chamber. 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, and the chamber is configured to occupy at least a rear part of the lower space of the engine. Since the primary catalyst case and the secondary catalyst case are compactly disposed in front of the engine, the lower space of the engine is not occupied by the secondary catalyst case. The chamber is disposed in a wide range of the lower space of the engine, and the exhaust noise is reduced by the muffling chamber of the chamber. By securing the muffling chamber on an upstream side of the muffler, it is possible to reduce a size of the muffler.

Hereinafter, a present embodiment will be described in detail with reference to the accompanying drawings. <FIG> is a right side view of a straddle-type vehicle according to the present embodiment. In the following drawings, an arrow FR indicates a vehicle front, an arrow RE indicates a vehicle rear, an arrow L indicates a vehicle left side, and an arrow R indicates a vehicle right side.

As shown in <FIG>, a straddle-type vehicle <NUM> is formed by mounting various components such as an engine <NUM> and an electrical system on a cradle type vehicle body frame <NUM>. The vehicle body frame <NUM> includes a main tube <NUM> that extends rearward from a head pipe <NUM> and then bends downward, and a down tube <NUM> that extends downward from the head pipe <NUM> and then bends rearward. A rear side of the engine <NUM> is supported by the main tube <NUM>, and a front side and a lower side of the engine <NUM> are supported by the down tube <NUM>. A fuel tank <NUM> is supported on the main tube <NUM>, and a rider seat <NUM> and a pillion seat <NUM> are provided in a rear of the fuel tank <NUM>.

A pair of front forks <NUM> are supported by the head pipe <NUM> via a steering shaft (not shown), and a front wheel <NUM> is rotatably supported on lower portions of the front forks <NUM> so as to be steered. A swing arm (not shown) is swingably supported at a rear half portion of the main tube <NUM>, and a rear wheel <NUM> is rotatably supported at a rear end of the swing arm. The engine <NUM> is connected to the rear wheel <NUM> via a transmission mechanism, and power from the engine <NUM> is transmitted to the rear wheel <NUM> via the transmission mechanism. An exhaust device <NUM> is connected to the engine <NUM>, and exhaust gas from the engine <NUM> is discharged to the outside through the exhaust device <NUM>.

A method of expanding a catalyst capacity of a catalyst case disposed on a lower side of the engine, a method of disposing the primary catalyst case in front of the engine and disposing the secondary catalyst case on the lower side of the engine, and the like are used in order to comply with exhaust gas regulations in recent years. In these methods, the lower side of the engine is used to expand the catalyst capacity, and it is difficult to secure a muffling chamber with a sufficient volume upstream of a muffler unless a basic structure of the vehicle body frame or the engine is changed. Therefore, the size of the muffler is increased, a degree of freedom in designing a muffler appearance is reduced, and an influence of heat damage to a rider and other components is increased.

Therefore, in the exhaust device <NUM> of the present embodiment, a front space of the engine <NUM> and a front part of a lower space of the engine <NUM> are effectively used, and a catalyst case is compactly disposed in front of the engine <NUM> in comparison with a general exhaust device. In the lower space of the engine <NUM>, a chamber <NUM> (see <FIG>) having only a muffling function without a catalyst is disposed, and a muffling chamber having a sufficient volume is secured on an upstream of a muffler <NUM> by the chamber <NUM>. Accordingly, it is possible to reduce a size of the muffler <NUM> by reducing the muffling chamber in the muffler <NUM> while minimizing changes to a basic structure of the vehicle body frame <NUM> or the engine <NUM>.

Hereinafter, the engine and the exhaust device will be described with reference to <FIG>. <FIG> is a front view of the engine according to the present embodiment. <FIG> is a side view of the engine according to the present embodiment. <FIG> is a bottom view of the engine according to the present embodiment. <FIG> are cross-sectional views of a bent pipe according to the present embodiment. <FIG> shows a state where the bent pipe of <FIG> is cut along a line A-A, and <FIG> shows a state where the bent pipe of <FIG> is cut along a line B-B.

As shown in <FIG> and <FIG>, the engine <NUM> is a parallel two-cylinder engine and is formed by assembling a cylinder block <NUM>, a cylinder head <NUM>, and a head cover <NUM> on a crankcase <NUM>. A drive component such as a crankshaft <NUM> is accommodated in the crankcase <NUM>, and the cylinder block <NUM> is attached to an upper portion of the crankcase <NUM>. A pair of aligned cylinder bores (not shown) disposed in a left-right direction are formed in the cylinder block <NUM>, and a piston (not shown) connected to the crankshaft <NUM> is disposed in each cylinder bore. The cylinder head <NUM> is attached to an upper portion of the cylinder block <NUM>.

A pair of intake ports (not shown) connected to the pair of cylinder bores are formed on a rear surface side of the cylinder head <NUM>, and a pair of exhaust ports <NUM> and 36R connected to the pair of cylinder bores are formed on a front surface side of the cylinder head <NUM>. The head cover <NUM> is attached to an upper portion of the cylinder head <NUM>, and a valve gear or the like is accommodated in the cylinder head <NUM> and the head cover <NUM>. An oil pan <NUM> that stores oil for lubrication and cooling is attached to a lower portion of the crankcase <NUM>. An oil filter <NUM> that removes a foreign matter from the oil is attached to a lower portion of a front surface of the crankcase <NUM>.

The engine <NUM> is assembled inside the vehicle body frame <NUM>. The down tube <NUM> of the vehicle body frame <NUM> includes an upper down tube <NUM> extending downward from the head pipe <NUM> (see <FIG>) in a center of the engine <NUM> in the left-right direction, and a pair of lower down tubes <NUM> and 15R branching left and right from a lower end of the upper down tube <NUM> and extending obliquely downward. The lower down tubes <NUM> and 15R are bent rearward on the lower side of the engine <NUM>, and are joined to the main tube <NUM> at rear end portions of the lower down tubes <NUM> and 15R. The oil filter <NUM> is positioned between the lower down tubes <NUM> and 15R.

A pair of exhaust pipes <NUM> and 51R extend from a front surface of the cylinder head <NUM> so as to avoid the upper down tube <NUM> and the lower down tubes <NUM> and 15R, and the exhaust device <NUM> that guides exhaust gas from the exhaust pipes <NUM> and 51R to a muffler <NUM> in a rear of the engine <NUM> is provided. The exhaust device <NUM> is provided with a small primary catalyst <NUM> that functions as a starter catalyst and a large secondary catalyst <NUM> that functions as a main catalyst. The exhaust gas enters the exhaust device <NUM> from the exhaust ports <NUM> and 36R, and the primary catalyst <NUM> and the secondary catalyst <NUM> purify air pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen compounds (NOx) in the exhaust gas.

In the exhaust device <NUM>, the exhaust pipes <NUM> and 51R, a collecting pipe <NUM>, a primary catalyst case <NUM>, a bent pipe <NUM>, a secondary catalyst case <NUM>, the chamber <NUM>, an exhaust pipe <NUM>, and the muffler <NUM> form an exhaust passage that wraps around from the front to the lower side of the engine <NUM> and extends to the rear. The exhaust pipe <NUM> extends forward from the exhaust port <NUM> and is connected to the collecting pipe <NUM>, and the exhaust pipe 51R extends forward from the exhaust port 36R and then extends to a left and is connected to the collecting pipe <NUM>. Thus, the exhaust pipe <NUM> is shorter than the exhaust pipe 51R, and pipe lengths of the exhaust pipes <NUM> and 51R are different. The exhaust pipes <NUM> and 51R have a circular cross section.

An upstream side of the collecting pipe <NUM> is bifurcated, and a downstream side of the collecting pipe <NUM> is formed in a cylindrical shape. The exhaust pipes <NUM> and 51R are connected to the upstream side of the collecting pipe <NUM>, and the primary catalyst case <NUM> is connected to a downstream end of the collecting pipe <NUM>. The exhaust gas that passes through the exhaust pipes <NUM> and 51R is collected by the collecting pipe <NUM> and sent to the primary catalyst case <NUM>. A first oxygen sensor <NUM> is disposed between the exhaust pipes <NUM> and 51R on a wall surface of the collecting pipe <NUM>, and an average oxygen concentration of the exhaust gas flowing in from the exhaust pipes <NUM> and 51R is detected by the first oxygen sensor <NUM>. A detection result of the first oxygen sensor <NUM> is used for feedback control of a fuel injection amount.

The primary catalyst case <NUM> is formed in a cylindrical shape, and is connected to the collecting pipe <NUM> in a substantially vertical posture. Since the exhaust pipe <NUM> is shorter than the exhaust pipe 51R, the primary catalyst case <NUM> and the collecting pipe <NUM> are disposed on a left side (one side in the left-right direction) of a center line C1 of the engine <NUM> extending in an upper-lower direction. The primary catalyst <NUM> for purifying the exhaust gas that passes through the exhaust pipes <NUM> and 51R is accommodated in the primary catalyst case <NUM>. The primary catalyst <NUM> is formed by adhering a catalyst substance to a surface of a honeycomb-shaped or lattice-shaped partition plate, and when the exhaust gas flowing in from the collecting pipe <NUM> passes through the primary catalyst <NUM>, the air pollutant reacts with oxygen and is purified.

Since the pipe length of the exhaust pipe <NUM> is short, high-temperature exhaust gas flows into the primary catalyst case <NUM> from the exhaust port <NUM>, the primary catalyst <NUM> in the primary catalyst case <NUM> is warmed up in a short time, and a purification performance of the exhaust gas from the exhaust port <NUM> is improved. In this case, the pipe length of the exhaust pipe 51R is long and a temperature of the exhaust gas is likely to decrease, but the primary catalyst <NUM> is warmed up in a short time by the high-temperature exhaust gas from the exhaust pipe <NUM>, and a purification performance of the exhaust gas from the exhaust port 36R is also improved. Thus, an early activation of the primary catalyst <NUM> is implemented by intentionally adding a difference in the pipe lengths to the exhaust pipes <NUM> and 51R.

The bent pipe <NUM> is formed in an L-shaped tubular shape in which a vertical tubular portion <NUM> on an upstream side and a horizontal tubular portion <NUM> on a downstream side are connected. A cross-sectional shape of the bent pipe <NUM> gradually changes from a circular shape to an elliptical shape from an upstream end toward a downstream end (see <FIG>). In this case, a major axis of an elliptical cross section of the downstream side of the bent pipe <NUM> is larger than a diameter of a circular cross section of the upstream end of the bent pipe <NUM>, and a minor axis of the elliptical cross section of the downstream side of the bent pipe <NUM> is smaller than the diameter of the circular cross section of the upstream end of the bent pipe <NUM>. At a bent portion at a boundary between the vertical tubular portion <NUM> and the horizontal tubular portion <NUM>, a major axis of the bent pipe <NUM> is oriented substantially horizontally, and a minor axis of the bent pipe <NUM> faces a bending radial direction of the bent pipe <NUM>.

The primary catalyst case <NUM> is connected to the upstream end of the vertical tubular portion <NUM> having a circular cross section, the secondary catalyst case <NUM> is connected to the downstream end of the horizontal tubular portion <NUM> having an elliptical cross section. The exhaust gas that passes through the primary catalyst <NUM> is guided to the secondary catalyst <NUM> on the lower side of the engine <NUM> by the bent pipe <NUM>. Compared with a configuration in which the primary catalyst case <NUM> and the secondary catalyst case <NUM> are connected by a plurality of exhaust pipes, a gap between the exhaust pipes is not required, and left and right spaces are not compressed. A second oxygen sensor <NUM> is disposed on a wall surface of the horizontal tubular portion <NUM>, and an oxygen concentration of the exhaust gas that passes through the primary catalyst case <NUM> is detected by the second oxygen sensor <NUM>. A detection result of the second oxygen sensor <NUM> is used for feedback control of the fuel injection amount and diagnosis of catalyst deterioration.

As shown in <FIG> and <FIG>, the secondary catalyst case <NUM> is formed in an elliptical cylindrical shape, and is connected to the bent pipe <NUM> in a substantially horizontal posture. At this time, the secondary catalyst case <NUM> extends obliquely rearward from the left side toward a right side (the one side to the other side in the left-right direction). The secondary catalyst <NUM> for purifying the exhaust gas that passes through the bent pipe <NUM> is accommodated in the secondary catalyst case <NUM>. The secondary catalyst <NUM> is formed by adhering the catalyst substance to a surface of a honeycomb-shaped or lattice-shaped partition plate, and when the exhaust gas flowing in from the bent pipe <NUM> passes through the secondary catalyst <NUM>, the air pollutant reacts with oxygen and is purified.

The chamber <NUM> is formed in an elliptical cylindrical shape, and is connected to the secondary catalyst case <NUM> in a substantially horizontal posture. A muffling chamber <NUM> (see <FIG>) for reducing the exhaust noise is formed in the chamber <NUM>. The chamber <NUM> extends in a front-rear direction, and an upstream end of the chamber <NUM> is joined to an outer wall surface of the secondary catalyst case <NUM> so as to cover the outer wall surface of the secondary catalyst case <NUM>. The chamber <NUM> is disposed on a right side (the other side in the left-right direction) of a center line C2 of the engine <NUM> extending in the front-rear direction. A tapered pipe <NUM> connected to a downstream end of the secondary catalyst case <NUM> and a punching pipe <NUM> connected to a downstream end of the tapered pipe <NUM> are provided inside the chamber <NUM>.

A cross-sectional shape of the tapered pipe <NUM> gradually changes from an elliptical shape to a circular shape from an upstream end toward the downstream end. A large number of small holes are formed in a peripheral surface of the punching pipe <NUM>, and an inner side of the punching pipe <NUM> and the muffling chamber <NUM> are connected to each other through the large number of small holes. When the exhaust gas enters the muffling chamber <NUM> from the punching pipe <NUM>, the exhaust gas is expanded in the muffling chamber <NUM>, so that the exhaust noise is reduced. An outer wall of the chamber <NUM> has a double-cylinder structure, and a gap between an inner cylinder and an outer cylinder is filled with glass wool for sound absorption. The chamber <NUM> is supported by the vehicle body frame <NUM> via a bracket <NUM>.

The exhaust pipe <NUM> is formed in a cylindrical shape and extends rearward from a downstream end of the chamber <NUM>. The muffler <NUM> (see <FIG>) is positioned on a right side of the rear wheel <NUM>, and is connected to a downstream end of the exhaust pipe <NUM>. A muffling chamber (not shown) for reducing the exhaust noise is formed in the muffler <NUM>, and a rear end of the muffling chamber is connected to the outside through an exhaust port. Although a structure of the muffler <NUM> is not particularly limited, one muffling chamber may be formed, or a plurality of muffling chambers may be formed inside the muffler <NUM>. Thus, the exhaust noise is reduced in two stages by the chamber <NUM> and the muffler <NUM> in the exhaust device <NUM>.

An arrangement configuration of the catalyst case and the chamber will be described with reference to <FIG>. <FIG> is a cross-sectional view of the secondary catalyst case according to the present embodiment, and shows a state where the secondary catalyst case of <FIG> is cut along a line C-C. <FIG> is a cross-sectional view of the chamber according to the present embodiment, and shows a state where the chamber of <FIG> is cut along a line C-C. In <FIG>, the primary catalyst is omitted.

As shown in <FIG>, the lower down tubes <NUM> and 15R branching from the lower end of the upper down tube <NUM> extend obliquely downward. A branching point of the lower down tubes <NUM> and 15R are positioned below the exhaust ports <NUM> and 36R and above a height position O1 at a center of the crankshaft <NUM>. Accordingly, a space is formed on left and right sides of an upper portion of the engine <NUM> avoiding the upper down tube <NUM>, and the exhaust pipes <NUM> and 51R are easily extended forward from the exhaust ports <NUM> and 36R. A space is formed between the lower down tubes <NUM> and 15R in a lower portion of the engine <NUM>, and the bent pipe <NUM>, the secondary catalyst case <NUM>, and the chamber <NUM> are easily disposed.

A V-shaped space is formed between the lower down tubes <NUM> and 15R on the front surface of the crankcase <NUM>. An oil filter <NUM> is provided in the V-shaped space, and the oil filter <NUM> is positioned on the center line C1 of the engine <NUM> extending in the upper-lower direction. Since the oil filter <NUM> is positioned at a center of a vehicle body, an oil passage inside the engine <NUM> is formed simply. Since the exhaust device <NUM> passes through a left side and a lower side of the oil filter <NUM> avoiding a front of the oil filter <NUM>, an entry path for a tool to the oil filter <NUM> is secured.

The oil pan <NUM> is attached to a lower surface of the crankcase <NUM>. A bottom surface of the oil pan <NUM> is formed at a deep bottom on the left side (the one side in the left-right direction), and is inclined so that the bottom surface of the oil pan <NUM> becomes shallow from a deep bottom portion <NUM> toward the right side (the other side in the left-right direction) (see <FIG>). A right side of the bottom surface of the oil pan <NUM> is recessed in an arch shape, and the exhaust device <NUM> passes through a recess of the oil pan <NUM>. Thus, on the lower side of the engine <NUM>, a space for disposing the exhaust device <NUM> is formed on a right side of the deep bottom portion <NUM> of the oil pan <NUM>. A positional relationship between the exhaust device <NUM> and the oil pan <NUM> will be described in detail later.

As shown in <FIG> and <FIG>, the primary catalyst case <NUM> overlaps the lower down tube <NUM> in a front view. An upstream end of the primary catalyst case <NUM> substantially coincides with the height position O1 at the center of the crankshaft <NUM>. The bent pipe <NUM> is bent in an L shape from the downstream end of the primary catalyst case <NUM> to the right side, and a downstream end of the bent pipe <NUM> is positioned below the oil filter <NUM>. Since the bent pipe <NUM> extends obliquely to reduce an occupied area in the front and rear, the secondary catalyst case <NUM> connected to the downstream end of the bent pipe <NUM> is compactly disposed in the front. A rearmost portion of the downstream end of the secondary catalyst case <NUM> substantially coincides with a front-rear position O2 at the center of the crankshaft <NUM>.

As shown in <FIG>, the secondary catalyst case <NUM> is disposed between the lower down tubes <NUM> and 15R so as to overlap the oil pan <NUM>. The secondary catalyst case <NUM> extends obliquely rearward from the left side to the right side, and the secondary catalyst case <NUM> intersects the center line C2 of the engine <NUM> extending in the front-rear direction. Since the secondary catalyst case <NUM> is obliquely disposed, an occupied area of the secondary catalyst case <NUM> in the front-rear direction can be reduced, and an occupied area of the chamber <NUM> can be widely secured in a rear of the secondary catalyst case <NUM>. The secondary catalyst <NUM> accommodated inside the secondary catalyst case <NUM> is also obliquely disposed similarly to the secondary catalyst case <NUM>.

The chamber <NUM> extends in the front-rear direction, and is disposed on the right side of the center line C2 of the engine <NUM> extending in the front-rear direction. The upstream end of the chamber <NUM> is positioned in front of the front-rear position O2 at the center of the crankshaft <NUM>, and the downstream end of the chamber <NUM> extends to a bridge <NUM> connecting the lower down tubes <NUM> and 15R. An entire length of the chamber <NUM> is set to a size that does not interfere with a center stand (not shown). The catalyst is not accommodated in the muffling chamber <NUM> in the chamber <NUM>, and the muffling chamber <NUM> is an expansion space of the exhaust gas. The chamber <NUM> functions as a primary muffler that assists a muffling function of the muffler <NUM>.

The upstream end of the chamber <NUM> is joined to the outer wall surface of the secondary catalyst case <NUM>, and the muffling chamber <NUM> in the chamber <NUM> is widely secured to improve the muffling performance. More specifically, the chamber <NUM> is continuously connected to the secondary catalyst case <NUM>, and a space around the tapered pipe <NUM> (outside in a radial direction) disposed inside the chamber <NUM> is also used as the muffling chamber <NUM>. The exhaust gas flows smoothly from the secondary catalyst case <NUM> toward the chamber <NUM> by directly connecting the secondary catalyst case <NUM> and the chamber <NUM> without interposing another member such as a connecting pipe between the secondary catalyst case <NUM> and the chamber <NUM>.

Thus, the primary catalyst case <NUM> is disposed in the front space of the engine <NUM>, the secondary catalyst case <NUM> is disposed on the front part of the lower space of the engine <NUM>, and the chamber <NUM> is disposed on the rear part of the lower space of the engine <NUM>. More specifically, most of the primary catalyst case <NUM> is disposed in front of the engine <NUM> below the center of the crankshaft <NUM>, and most of the secondary catalyst case <NUM> is disposed on a front side of the center of the crankshaft <NUM> (see <FIG>). Then, most of the chamber <NUM> is disposed on the lower side of the engine <NUM> and on a rear side of the center of the crankshaft <NUM>, and the muffling chamber <NUM> (see <FIG>) having a sufficient volume is secured on the rear part of the lower space of the engine <NUM> in the exhaust passage.

In the exhaust device <NUM>, a required volume of the muffling chamber is secured by the chamber <NUM> and the muffler <NUM>. Since the chamber <NUM> serves as the primary muffler, a volume of the muffler <NUM> downstream of the chamber <NUM> can be reduced. In a state where a muffling performance of the exhaust device <NUM> is maintained, a risk of heat damage is reduced by reducing a surface area of the muffler <NUM>, and a degree of freedom in designing of the muffler <NUM> is improved. In addition, the risk of the heat damage is reduced by intensively disposing the high-temperature catalyst in the vicinity of the engine <NUM>. Further, a weight balance is optimized by positioning a center of gravity of the secondary catalyst <NUM> on the front side of the center of the crankshaft <NUM>.

As shown in <FIG>, the secondary catalyst case <NUM> is positioned inside an arch-shaped recess of the oil pan <NUM>. The secondary catalyst case <NUM> has an elliptical cross-sectional shape having a width larger than a height of the secondary catalyst case <NUM>. A major axis of the secondary catalyst case <NUM> is oriented in a substantially horizontal direction, and a minor axis of the secondary catalyst case <NUM> is oriented in a substantially vertical direction. An upper surface <NUM> of the secondary catalyst case <NUM> faces a bottom surface <NUM> of the oil pan <NUM> in a wide range, and heat dissipation from the upper surface <NUM> of the secondary catalyst case <NUM> is propagated to the bottom surface <NUM> of the oil pan <NUM>. In addition, a side surface <NUM> of the secondary catalyst case <NUM> faces an inclined portion <NUM> of the oil pan <NUM>, and heat dissipation from the side surface <NUM> of the secondary catalyst case <NUM> is propagated to the inclined portion <NUM> of the oil pan <NUM>.

As shown in <FIG>, the chamber <NUM> is positioned inside the arch-shaped recess of the oil pan <NUM>. The chamber <NUM> has an elliptical cross-sectional shape having a width dimension larger than a height dimension. A major axis of the chamber <NUM> is oriented in a substantially horizontal direction, and a minor axis of the chamber <NUM> is oriented in a substantially vertical direction. An upper surface <NUM> of the chamber <NUM> faces the bottom surface <NUM> of the oil pan <NUM> in a wide range, and heat dissipation from the upper surface <NUM> of the chamber <NUM> is propagated to the bottom surface <NUM> of the oil pan <NUM>. In addition, a side surface <NUM> of the chamber <NUM> faces the inclined portion <NUM> of the oil pan <NUM>, and heat dissipation from the side surface <NUM> of the chamber <NUM> is propagated to the inclined portion <NUM> of the oil pan <NUM>.

In a front view, the secondary catalyst case <NUM> overlaps the deep bottom portion <NUM> of the oil pan <NUM> (see <FIG>). More specifically, the secondary catalyst case <NUM> crosses a front of the deep bottom portion <NUM> of the oil pan <NUM> (see <FIG>), and heat dissipation of the secondary catalyst case <NUM> is propagated to the oil pan <NUM> by running wind. Since the heat dissipation from the secondary catalyst case <NUM> and the chamber <NUM> is propagated to the oil pan <NUM>, the oil in the oil pan <NUM> is increased to a suitable temperature in a short time. Since the minor axes (heights) of the secondary catalyst case <NUM> and the chamber <NUM> are small, the engine <NUM> is low, vehicle body stability during traveling is improved, and capacities of a fuel tank and an air cleaner are easily secured.

Next, an arrangement configuration of the first and second oxygen sensors will be described with reference to <FIG> and <FIG>.

As shown in <FIG> and <FIG>, the first oxygen sensor <NUM> is disposed in the collecting pipe <NUM> in front of the engine <NUM>. The first oxygen sensor <NUM> is erected on the collecting pipe <NUM> in a state of facing the rear (the engine <NUM> side) between the exhaust pipes <NUM> and 51R. Since the first oxygen sensor <NUM> is sandwiched between the exhaust pipes <NUM> and 51R and the first oxygen sensor <NUM> is brought close to the engine <NUM>, early activation of the first oxygen sensor <NUM> is achieved by heat dissipation from the exhaust pipes <NUM> and 51R and the engine <NUM>. When the exhaust gas from the exhaust pipes <NUM> and 51R is substantially uniform at a detection end of the first oxygen sensor <NUM>, a detection accuracy of the oxygen concentration by the first oxygen sensor <NUM> is improved.

Since the first oxygen sensor <NUM> is disposed on a rear side of the collecting pipe <NUM>, the first oxygen sensor <NUM> is protected from a flying object from the front by the collecting pipe <NUM>. Since the bent pipe <NUM> is present below the first oxygen sensor <NUM>, the first oxygen sensor <NUM> is protected from a flying object from below by the bent pipe <NUM>. The upper down tube <NUM> is positioned on a right side of the first oxygen sensor <NUM>, and the first oxygen sensor <NUM> overlaps the upper down tube <NUM> in a side view. Accordingly, since wiring is laid along the upper down tube <NUM>, the wiring is easily connected to the first oxygen sensor <NUM>.

The second oxygen sensor <NUM> is disposed on the horizontal tubular portion <NUM> downstream of a bent portion of the bent pipe <NUM>. The second oxygen sensor <NUM> is erected on the horizontal tubular portion <NUM> in a state of facing upward (the engine <NUM> side). When the second oxygen sensor <NUM> is brought close to the engine <NUM>, early activation of the second oxygen sensor <NUM> is achieved by the heat dissipation from the engine <NUM>. In the front view, the second oxygen sensor <NUM> overlaps the vertical tubular portion <NUM> upstream of the bent portion of the bent pipe <NUM>. The second oxygen sensor <NUM> is protected from a flying object from below by the horizontal tubular portion <NUM>, and the second oxygen sensor <NUM> is protected from a flying object from above by the vertical tubular portion <NUM>.

The second oxygen sensor <NUM> is positioned between the lower down tubes <NUM> and 15R, and the second oxygen sensor <NUM> overlaps the lower down tubes <NUM> and 15R in the side view. The second oxygen sensor <NUM> is protected from a flying object from the left and right sides by the lower down tubes <NUM> and 15R. Since the second oxygen sensor <NUM> is closer to the left side and wiring is laid along the lower down tube <NUM>, the wiring is easily connected to the second oxygen sensor <NUM>. Since the first and second oxygen sensors <NUM> and <NUM> are disposed on a left side of the engine <NUM>, a deviation of the first and second oxygen sensors <NUM> and <NUM> in the left-right direction is reduced, and the wiring is easily collected.

The oil filter <NUM> is positioned on a right side of the second oxygen sensor <NUM>, and the second oxygen sensor <NUM> overlaps the oil filter <NUM> in the side view. The second oxygen sensor <NUM> is protected from a flying object from the right by the oil filter <NUM>. The oil filter <NUM> protrudes toward the front from the front surface of the crankcase <NUM>, and the second oxygen sensor <NUM> is positioned in a rear of a front end of the oil filter <NUM>. Accordingly, the second oxygen sensor <NUM> protruding directly upward from the horizontal tubular portion <NUM> does not cross front space of the oil filter <NUM>, and the entry path for the tool to the oil filter <NUM> is secured.

As described above, according to the present embodiment, the primary catalyst case <NUM> is disposed in the front space of the engine <NUM>, and the secondary catalyst case <NUM> is disposed on the front part of the lower space of the engine <NUM>. Since the primary catalyst case <NUM> and the secondary catalyst case <NUM> are compactly disposed in front of the engine <NUM>, the lower space of the engine <NUM> is not occupied by the secondary catalyst case <NUM>. The chamber <NUM> is disposed in a wide range of the lower space of the engine <NUM>, and the exhaust noise is reduced by the muffling chamber <NUM> of the chamber <NUM>. By securing the muffling chamber <NUM> on an upstream side of the muffler <NUM>, it is possible to reduce the size of the muffler <NUM>.

In the present embodiment, the chamber is positioned on the right side of the deep bottom portion of the oil pan, but a shape of the chamber is not particularly limited. For example, as long as an attachment portion of the center stand can be relocated, as shown in a modification of <FIG>, a rear portion of a chamber <NUM> protrudes to a left side in a rear side of the oil pan <NUM>, and the muffling chamber in the chamber <NUM> may be further widened. In this case, the muffler on a side of the rear wheel can be eliminated to centralize a mass, the reduction of the risk of the heat damage due to a surface of the muffler, and an improvement of the degree of freedom in designing the muffler appearance can be achieved.

In the present embodiment, most of the secondary catalyst case is disposed on the front side of the center of the crankshaft, but the secondary catalyst case may be disposed on the front part of the lower space of the engine. Accordingly, by disposing the chamber in the wide range of the lower space of the engine, it is possible to further improve the muffling performance. The front part of the lower space of the engine refers to a space on a front side of an intermediate position in the front-rear direction in the lower space of the engine.

In the present embodiment, most of the chamber is disposed on the rear side of the center of the crankshaft, but the chamber may occupy at least the rear part of the lower space of the engine. For example, the chamber may be disposed on the front side and the rear part of the lower space of the engine. The rear part of the lower space of the engine refers to a space on a rear side of the intermediate position in the front-rear direction in the lower space of the engine.

In the present embodiment, a press component may be used for a pipe of the exhaust device. The number of components and welding points can be reduced.

In the present embodiment, the left side of the bottom surface of the oil pan is formed at the deep bottom, but a part of the bottom surface of the oil pan may be formed at the deep bottom. For example, if the exhaust device does not interfere with the oil pan, the right side of the bottom surface of the oil pan may be formed at the deep bottom.

In the present embodiment, the upstream end of the chamber is joined to the outer wall surface of the secondary catalyst case, but the chamber and the secondary catalyst case may be separated from each other, and the chamber and the secondary catalyst case may be connected to via a connecting pipe.

In the present embodiment, the engine is the parallel two-cylinder engine, but a type of engine is not particularly limited, and for example, the engine may be a single-cylinder engine.

In the present embodiment, the cross-sectional shape of the secondary catalyst case and the chamber is formed in an elliptical shape, but the cross-sectional shape of the secondary catalyst case and the chamber may be formed in a cross-sectional shape having the width larger than the height. Depending on a shape of the frame, a shape of a bottom surface of the engine, and a minimum ground clearance, the cross-sectional shape of the secondary catalyst case and the chamber may be formed in a circular shape.

In the present embodiment, the secondary catalyst case crosses the front of the deep bottom portion of the oil pan, but a positional relationship between the secondary catalyst case and the deep bottom portion of the oil pan is not particularly limited. When the heat dissipation from the secondary catalyst case is propagated to the oil pan by the running wind, the secondary catalyst case may overlap the deep bottom portion of the oil pan in the front view.

In the present embodiment, the secondary catalyst case extends obliquely rearward from the left side to the right side, but the secondary catalyst case may extend in the front-rear direction.

In the present embodiment, the oxygen sensor is illustrated as a gas sensor, but the gas sensor may be any sensor that can detect an average characteristic of the exhaust gas, and may be, for example, an exhaust noise sensor that detects the exhaust noise of the exhaust gas.

The exhaust device of the present embodiment is not limited to the engine of the above straddle-type vehicle, but may be adopted for an engine of another type of straddle-type vehicle. The straddle-type vehicle is not limited to general vehicles on which a driver rides in a posture of straddling a seat, and includes a scooter-type vehicle on which the driver rides without straddling the seat.

As described above, the exhaust device (<NUM>) of the present embodiment is an exhaust device that guides the exhaust gas from the exhaust pipe (<NUM>, 51R) in front of the engine (<NUM>) to the muffler (<NUM>) in the rear of the engine, and includes the primary catalyst case (<NUM>) in which the primary catalyst (<NUM>) that purifies the exhaust gas downstream of the exhaust pipe is accommodated; the secondary catalyst case (<NUM>) in which the secondary catalyst <NUM> that purifies the exhaust gas downstream of the primary catalyst is accommodated; and the chamber (<NUM>) in which the muffling chamber (<NUM>) that reduces the exhaust noise is formed is provided downstream of the secondary catalyst, in which the primary catalyst case is disposed in the front space of the engine, the secondary catalyst case is disposed on the front part of the lower space of the engine, and the chamber is configured to occupy at least the rear part of the lower space of the engine. According to this configuration, the primary catalyst case is disposed in the front space of the engine, and the secondary catalyst case is disposed on the front part of the lower space of the engine. Since the primary catalyst case and the secondary catalyst case are compactly disposed in front of the engine, the lower space of the engine is not occupied by the secondary catalyst case. The chamber is disposed in the wide range of the lower space of the engine, and the exhaust noise is reduced by the muffling chamber of the chamber. By securing the muffling chamber on the upstream side of the muffler, it is possible to reduce the size of the muffler.

In the exhaust device of the present embodiment, the front part of the lower space of the engine is on the lower side of the engine and on the front side of the center of the crankshaft (<NUM>), and the rear part of the lower space of the engine is on the lower side of the engine and on the rear side of the center of the crankshaft. According to this configuration, the chamber can be disposed in the wide range of the lower space of the engine by an amount that the secondary catalyst case is disposed on the front side of the center of the crankshaft.

In the exhaust device of the present embodiment, the secondary catalyst case extends obliquely rearward from the one side toward the other side in the left-right direction of the engine. According to this configuration, since the secondary catalyst case is obliquely disposed, the occupied area of the secondary catalyst case in the front-rear direction can be reduced, and the occupied area of the chamber can be widely secured in the rear of the secondary catalyst case. As compared with a case where the secondary catalyst case is oriented in the left-right direction of the engine, it is possible to prevent a pipe connected to the secondary catalyst case from protruding in the left-right direction of the engine.

Claim 1:
A straddle-type vehicle (<NUM>) comprising:
an exhaust device (<NUM>) configured to guide exhaust gas from an exhaust pipe (<NUM>, 51R) in front of an engine (<NUM>) of the straddle-type vehicle to a muffler (<NUM>) in a rear of the engine (<NUM>), the exhaust device (<NUM>) including:
a primary catalyst case (<NUM>) accommodating a primary catalyst (<NUM>) configured to purify the exhaust gas at a downstream side from the exhaust pipe (<NUM>, 51R); and
a secondary catalyst case (<NUM>) accommodating a secondary catalyst (<NUM>) configured to purify the exhaust gas at a downstream side from the primary catalyst (<NUM>), characterized in that
the exhaust device (<NUM>) includes a chamber (<NUM>) formed with a muffling chamber (<NUM>) configured to reduce an exhaust noise at a downstream side from the secondary catalyst (<NUM>),
the primary catalyst case (<NUM>) is disposed in a front space of the engine (<NUM>),
the secondary catalyst case (<NUM>) is disposed on a front part of a lower space of the engine (<NUM>),
the chamber (<NUM>) is disposed so as to occupy at least a rear part of the lower space of the engine (<NUM>),
characterized in that a tapered pipe (<NUM>) is connected to a downstream end of the secondary catalyst case (<NUM>) and a punching pipe (<NUM>) is connected to a downstream end of the tapered pipe (<NUM>) provided inside the chamber (<NUM>), and
a cross-sectional shape of the tapered pipe (<NUM>) gradually changes from an elliptical shape to a circular shape from an upstream end of the tapered pipe (<NUM>) toward a downstream end of the tapered pipe (<NUM>), a large number of small holes are formed in a peripheral surface of the punching pipe (<NUM>), and an inner side of the punching pipe (<NUM>) and the muffling chamber (<NUM>) are connected to each other through the large number of small holes such that when the exhaust gas enters the muffling chamber (<NUM>) from the punching pipe (<NUM>), the exhaust gas is expanded in the muffling chamber (<NUM>), so that the exhaust noise is reduced.