Patent Description:
In an exhaust system of a straddle-type vehicle, a silencing chamber is provided downstream of an exhaust pipe that extends from an engine. When the exhaust gas flows into the chamber from the exhaust pipe, the exhaust gas is expanded in the chamber and energy of an exhaust sound is attenuated. As an exhaust apparatus of this type, an exhaust apparatus in which a chamber is disposed below an engine is known (for example, see Patent Literature <NUM>). A plurality of expansion chambers are formed by partition walls inside the chamber described in Patent Literature <NUM>, and after expansion of the exhaust gas is repeated in a process of passing through the plurality of expansion chambers, the exhaust gas is discharged to an outside from the downstream expansion chamber through a tail pipe. Patent Literature <NUM> discloses arranging a silencer so that its discoloration due to high temperature exhaust gas is inconspicuous.

Since the chamber described in Patent Literature <NUM> is disposed below the engine, there is a case where a volume of the chamber cannot be sufficiently secured in relation to a bank angle or surrounding components. Although a silencing measure is taken by forming a plurality of expansion chambers inside the chamber, it is difficult to secure a large volume of the plurality of expansion chambers in a limited space below the engine because of a structure in which the plurality of expansion chambers are arranged in a front-rear direction. Therefore, the exhaust gas may not be fully expanded, and a silencing effect may be reduced.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a straddle-type vehicle having an exhaust apparatus that can obtain a sufficient silencing effect by effectively utilizing a limited space.

According to one advantageous aspect of the invention, there is provided a straddle-type vehicle as defined in claim <NUM>.

An exhaust apparatus according to an aspect of the present invention purifies exhaust gas exhausted from an engine through an exhaust pipe. A chamber is disposed below the engine, the exhaust gas is guided from the exhaust pipe to the chamber through an inlet pipe, and the exhaust gas is discharged from the chamber to an outside through a tail pipe. An inside of the chamber is partitioned into a pair of left and right spaces by a first partition wall, and one of the pair of left and right spaces is partitioned into a pair of front and rear spaces by a second partition wall. The other of the pair of left and right spaces serves as a first expansion chamber into which the inlet pipe enters, a rear space of the pair of front and rear spaces serves as a second expansion chamber disposed downstream of the first expansion chamber, and a front space of the pair of front and rear spaces serves as a third expansion chamber disposed downstream of the second expansion chamber, the tail pipe enters into the front space. In this way, inside the chamber, the first expansion chamber, and the second and third expansion chambers are separately formed on left and right sides, and the second expansion chamber and the third expansion chamber are separately formed on front and rear sides. A flow direction of the exhaust gas from the first expansion chamber to the second expansion chamber intersects with a flow direction of the exhaust gas from the second expansion chamber to the third expansion chamber. The exhaust gas is unlikely to directly flow from the first expansion chamber to the third expansion chamber, and the exhaust gas can be sufficiently expanded in the first to third expansion chambers. Even when the chamber is disposed in a limited space below the engine, the first to third expansion chambers are formed inside the chamber, so that the exhaust gas can be expanded stepwise to improve a silencing performance of the chamber.

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

As shown in <FIG> and <FIG>, an engine <NUM> is a parallel two-cylinder engine in which a cylinder block <NUM> is disposed on an upper portion of a crankcase <NUM>. A cylinder head <NUM> is attached to an upper portion of the cylinder block <NUM>, and a head cover (not shown) is attached to an upper portion of the cylinder head <NUM>. An oil pan <NUM> in which oil for lubrication and cooling is stored is attached to a lower portion of the crankcase <NUM>. A magneto cover <NUM> that covers a magneto chamber in the case is attached to a left side surface of the crankcase <NUM>, and a clutch cover <NUM> that covers a clutch chamber in the case is attached to a right side surface of the crankcase <NUM>.

The engine <NUM> is supported by a pair of left and right main frames <NUM> of a straddle-type vehicle. A swing arm <NUM> that supports a rear wheel (not shown) is swingably supported by the pair of main frames <NUM>. The swing arm <NUM> is connected to a rear suspension <NUM> for shock-absorbing the rear wheel. An upper end of the rear suspension <NUM> is connected to the main frames <NUM>, and a lower end of the rear suspension <NUM> is connected to the swing arm <NUM> via a link arm <NUM> and a link bracket <NUM>. Further, a chamber <NUM> of an exhaust apparatus <NUM> is supported by lower portions of the pair of main frames <NUM> via left and right brackets 42a and 42b.

Exhaust gas flows into the chamber <NUM> through a pair of exhaust pipes 31a and 31b, and the exhaust gas is exhausted to an outside from the chamber <NUM> through a muffler <NUM>. A plurality of expansion chambers are formed inside the chamber <NUM>, and energy of an exhaust sound is attenuated by the exhaust gas expanding stepwise in each expansion chamber. However, since the chamber <NUM> is disposed in a limited space below the engine <NUM>, it is difficult to secure a plurality of wide expansion chambers inside the chamber <NUM>. Therefore, in the chamber <NUM> of the present embodiment, the exhaust gas is unlikely to directly flow among the plurality of expansion chambers, and the exhaust gas is sufficiently expanded in each expansion chamber to improve silencing performance.

Hereinafter, a detailed configuration of the exhaust apparatus will be described with reference to <FIG>. <FIG> is a top view of the exhaust apparatus of the present embodiment. <FIG> is a side view of the exhaust apparatus of the present embodiment. <FIG> is a perspective view showing an internal structure of the chamber of the present embodiment. <FIG> is a perspective view of the chamber from which an upper outer body of the present embodiment is removed.

As shown in <FIG> and <FIG>, the exhaust apparatus <NUM> reduces the exhaust sound of the exhaust gas exhausted from the engine <NUM> (see <FIG>) through the exhaust pipes 31a and 31b, and purifies the exhaust gas. The exhaust pipes 31a and 31b extend downward from a front surface of the engine <NUM>, and the exhaust pipes 31a and 31b are collected by a collecting pipe <NUM> and connected to an inlet pipe <NUM>. An attachment boss <NUM> for an upstream exhaust gas sensor (not shown) is formed on an outer peripheral surface of the collecting pipe <NUM>. The upstream exhaust gas sensor detects an average oxygen concentration of the exhaust gas that flows in from the exhaust pipes 31a and 31b. A detection result of the upstream exhaust gas sensor is used for feedback control of a fuel injection amount.

The inlet pipe <NUM> connects a first catalyst <NUM> and a second catalyst <NUM> (see <FIG>) via a connection pipe <NUM>. An upstream side of the connection pipe <NUM> is outside the chamber <NUM>, and the first catalyst <NUM> is disposed on the upstream side of the connection pipe <NUM>. A downstream side of the connection pipe <NUM> enters the chamber <NUM>, and the second catalyst <NUM> is disposed on the downstream side of the connection pipe <NUM>. An attachment boss <NUM> for a downstream exhaust gas sensor (not shown) is formed between the first catalyst <NUM> and the second catalyst <NUM> on an outer peripheral surface of the connection pipe <NUM>. The downstream exhaust gas sensor detects the average oxygen concentration of the exhaust gas that flows in from the exhaust pipes 31a and 31b. A detection result of the downstream exhaust gas sensor is used for the feedback control of the fuel injection amount and diagnosis of catalyst deterioration.

When the exhaust gas flows into the inlet pipe <NUM> from the exhaust pipes 31a and 31b, air pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust gas are purified by the first and second catalysts <NUM> and <NUM>. Further, the exhaust gas flows into the chamber <NUM> from the inlet pipe <NUM>, so that the exhaust gas is expanded in each expansion chamber in the chamber <NUM>, and the exhaust sound is reduced. The muffler <NUM> (see <FIG>) is connected to a downstream side of the chamber <NUM> via a tail pipe <NUM>, and the exhaust gas that has passed through the chamber <NUM> is exhausted to an outside from the muffler <NUM>. Since the exhaust sound is reduced in the chamber <NUM>, an expansion chamber of the muffler <NUM> is reduced in size, so that a reduction in size of the muffler <NUM> is implemented.

The chamber <NUM> is positioned below the engine <NUM> and behind the oil pan <NUM> (see <FIG>). The chamber <NUM> has a box shape, the inlet pipe <NUM> is inserted into a right side of a front wall of the chamber <NUM>, and the tail pipe <NUM> extends rearward from a right side of a rear wall of the chamber <NUM>. The exhaust gas is guided to the chamber <NUM> from the exhaust pipes 31a and 31b by the inlet pipe <NUM>, and the exhaust gas is discharged to the outside from the chamber <NUM> by the tail pipe <NUM>. Further, the brackets 42a and 42b are provided on both left and right side walls of the chamber <NUM>, and the chamber <NUM> is attached to lower portions of the main frames <NUM> (see <FIG>) via the brackets 42a and 42b.

As shown in <FIG>, an inside of the chamber <NUM> is partitioned into a pair of left and right spaces by a first partition wall <NUM> that extends in a front-rear direction. Further, the left space of the pair of left and right spaces is partitioned into a pair of front and rear spaces by a second partition wall <NUM> that extends in a left-right direction. The right space of the pair of left and right spaces is a first expansion chamber <NUM> into which the inlet pipe <NUM> enters. The rear space of the pair of front and rear spaces is a second expansion chamber <NUM> downstream of the first expansion chamber <NUM>. The front space of the pair of front and rear spaces is a third expansion chamber <NUM> into which the tail pipe <NUM> enters downstream of the second expansion chamber <NUM>.

In this way, a rear side of the first expansion chamber <NUM> and the second expansion chamber <NUM> are adjacent to each other in the left-right direction, and a front side of the first expansion chamber <NUM> and the third expansion chamber <NUM> are adjacent to each other in the left-right direction. Further, the first expansion chamber <NUM> is formed to have the largest volume, the second expansion chamber <NUM> is formed to have the second largest volume, and the third expansion chamber <NUM> is formed to have the smallest volume. The inlet pipe <NUM> is provided on the front wall of the chamber <NUM>, the first catalyst <NUM> on an upstream side of the inlet pipe <NUM> is disposed outside the chamber <NUM>, and the second catalyst <NUM> on a downstream side of the inlet pipe <NUM> is disposed inside the chamber <NUM>. The second catalyst <NUM> is disposed parallel to the first partition wall <NUM> in the first expansion chamber <NUM>.

A straight first communication pipe <NUM> is provided on a rear end side of the first partition wall <NUM>, and a straight second communication pipe <NUM> is provided on a right end side (the other side in the left-right direction) of the second partition wall <NUM>. The first communication pipe <NUM> extends in the left-right direction and penetrates the first partition wall <NUM>, and the first expansion chamber <NUM> and the second expansion chamber <NUM> communicate with each other through the first communication pipe <NUM>. The second communication pipe <NUM> extends in the front-rear direction and penetrates the second partition wall <NUM>, and the second expansion chamber <NUM> and the third expansion chamber <NUM> communicate with each other through the second communication pipe <NUM>. Inside the chamber <NUM>, extending directions of the first and second communication pipes <NUM> and <NUM> are arranged so as to intersect each other.

The tail pipe <NUM> bent in a substantially crank shape is provided on a left end side (one side in the left-right direction) of the second partition wall <NUM>. The tail pipe <NUM> extends in the front-rear direction on a left side of the second communication pipe <NUM> and penetrates the second partition wall <NUM>, then extends in the left-right direction in front of the first communication pipe <NUM> and penetrates the first partition wall <NUM>, and further extends obliquely rearward to a right side and penetrates the rear wall of the chamber <NUM>. That is, the tail pipe <NUM> extends in the front-rear direction from the third expansion chamber <NUM> to the second expansion chamber <NUM>, extends in the left-right direction from the second expansion chamber <NUM> to the first expansion chamber <NUM>, and extends to an outside of the chamber <NUM> from a right corner of the rear wall of the first expansion chamber <NUM>.

A bottomed tubular cap <NUM> is mounted on a front end of the tail pipe <NUM>. A front end of the cap <NUM> is closed, and numerous punched holes are formed in an outer peripheral surface of the cap <NUM>. An inlet of the tail pipe <NUM> is formed by the numerous punched holes. A bulge portion <NUM> that expands the third expansion chamber <NUM> forward is formed on a left side of the front wall of the chamber <NUM>, and the cap <NUM> of the tail pipe <NUM> is positioned inside the bulge portion <NUM>. Since the inlet of the tail pipe <NUM> has the punched holes of the cap <NUM>, the inlet of the tail pipe <NUM> is narrowed, so that the exhaust gas is easily retained inside the bulge portion <NUM>.

As shown in <FIG> and <FIG>, a right half portion of an outer wall of the chamber <NUM> has a two-layer structure in which a sound-absorbing material <NUM> is filled between the outer body <NUM> and an inner body <NUM>, and a left half portion of the outer wall of the chamber <NUM> has a single-layer structure of the outer body <NUM>. The first expansion chamber <NUM> is surrounded by the outer wall of the two-layer structure, and the second expansion chamber <NUM> and the third expansion chamber <NUM> are surrounded by the outer wall of the single-layer structure. A pair of upper and lower large plates <NUM> that cover the outer body <NUM> from an inside are arranged in the second expansion chamber <NUM>, and a pair of upper and lower small plates <NUM> that cover the outer body <NUM> from the inside are arranged in the third expansion chamber <NUM>.

The upper large plate <NUM> extends from an upper surface to a left side surface of the second expansion chamber <NUM>, and the lower large plate <NUM> extends from a lower surface to the left side surface of the second expansion chamber <NUM>. The upper small plate <NUM> extends from an upper surface to a left side surface of the third expansion chamber <NUM>, and the lower small plate <NUM> extends from a lower surface to the left side surface of the third expansion chamber <NUM>. Shallow recesses <NUM> and <NUM> are formed in surfaces of the large plate <NUM> and the small plate <NUM>, and sound-absorbing materials (not shown) are filled in the recesses <NUM> and <NUM>. Although not shown in the drawings, numerous punched holes are formed in the large plate <NUM> and the small plate <NUM>.

A partition wall plate <NUM> is attached to a left side surface of the first partition wall <NUM> in a predetermined range from a rear end of the second catalyst <NUM> to a front side of the tail pipe <NUM>. A sound-absorbing material (not shown) is filled between the first partition wall <NUM> and the partition wall plate <NUM>. In this way, the first expansion chamber <NUM> having the largest volume is formed by the outer wall and the partition wall of the two-layer structure, and the second and third expansion chambers <NUM> and <NUM> are also partially formed by the outer wall and the partition wall of the two-layer structure. Therefore, silencing performance can be improved without increasing a size of the chamber <NUM>. Further, by minimizing the two-layer structure, an increase in weight is prevented and heat is unlikely to be retained. As the sound-absorbing material <NUM>, for example, glass wool is used.

Hereinafter, positional relationship of the members inside the chamber will be described with reference to <FIG> and <FIG>. <FIG> is a top view showing the internal structure of the chamber of the present embodiment. <FIG> is a rear view showing the internal structure of the chamber of the present embodiment.

As shown in <FIG>, the first expansion chamber <NUM> is formed in a right half portion of the chamber <NUM>, the second expansion chamber <NUM> is formed on a rear side of a left half portion of the chamber <NUM>, and the third expansion chamber <NUM> is formed on a front side of the left half portion of the chamber <NUM>. An outlet <NUM> of the inlet pipe <NUM> (second catalyst <NUM>) is positioned in a middle of the first expansion chamber <NUM> in the front-rear direction, and an inlet <NUM> of the first communication pipe <NUM> is positioned on a rear side of the first expansion chamber <NUM>. An outlet <NUM> of the first communication pipe <NUM> is positioned on a rear side of the second expansion chamber <NUM>, and an inlet <NUM> of the second communication pipe <NUM> is positioned in a middle of the second expansion chamber <NUM> in the front-rear direction. An outlet <NUM> of the second communication pipe <NUM> is positioned on a rear side of the third expansion chamber <NUM>, and the cap <NUM> of the tail pipe <NUM> is positioned inside the bulge portion <NUM>.

The exhaust gas flows into the first expansion chamber <NUM> from the outlet <NUM> of the inlet pipe <NUM>, and the exhaust gas flows into the inlet <NUM> of the first communication pipe <NUM> from the first expansion chamber <NUM>. The inlet pipe <NUM> is inclined so as to become higher toward a rear side, and an extending portion <NUM> of the tail pipe <NUM> in the left-right direction overlaps the outlet <NUM> of the inlet pipe <NUM> in front of the first communication pipe <NUM> in a rear view (see <FIG>). A flow of the exhaust gas is blocked by the extending portion <NUM> of the tail pipe <NUM> in the left-right direction in front of the first communication pipe <NUM>, so that the exhaust gas is unlikely to directly flow from the outlet <NUM> of the inlet pipe <NUM> to the inlet <NUM> of the first communication pipe <NUM>. Therefore, the exhaust gas is likely to sufficiently expand in the first expansion chamber <NUM>.

In a rear view, the inlet <NUM> of the first communication pipe <NUM> is positioned below the extending portion <NUM> of the tail pipe <NUM> in the left-right direction (see <FIG>), and the outlet <NUM> of the inlet pipe <NUM> and the inlet <NUM> of the first communication pipe <NUM> are displaced in an upper-lower direction. Further, directions of the inlet pipe <NUM> and the first communication pipe <NUM> intersect with each other, and the first communication pipe <NUM> partially overlaps the outlet <NUM> of the inlet pipe <NUM> in the first expansion chamber <NUM> in a rear view (see <FIG>). Accordingly, the exhaust gas is unlikely to directly flow from the outlet <NUM> of the inlet pipe <NUM> to the inlet <NUM> of the first communication pipe <NUM>, and the exhaust gas is more likely to expand in the first expansion chamber <NUM>.

The exhaust gas flows into the second expansion chamber <NUM> from the outlet <NUM> of the first communication pipe <NUM>, and the exhaust gas flows into the inlet <NUM> of the second communication pipe <NUM> from the second expansion chamber <NUM>. The second communication pipe <NUM> has substantially the same height as that of the extending portion <NUM> of the tail pipe <NUM> in the left-right direction, and the extending portion <NUM> of the tail pipe <NUM> in the left-right direction overlaps the inlet <NUM> of the second communication pipe <NUM> in front of the first communication pipe <NUM> in a rear view (see <FIG>). The flow of the exhaust gas is blocked by the extending portion <NUM> of the tail pipe <NUM> in the left-right direction in front of the first communication pipe <NUM>, and the exhaust gas is unlikely to directly flow from the outlet <NUM> of the first communication pipe <NUM> to the inlet <NUM> of the second communication pipe <NUM>. Therefore, the exhaust gas is likely to sufficiently expand in the second expansion chamber <NUM>.

In a rear view, the outlet <NUM> of the first communication pipe <NUM> is positioned below the extending portion <NUM> of the tail pipe <NUM> in the left-right direction (see <FIG>), and the outlet <NUM> of the first communication pipe <NUM> and the inlet <NUM> of the second communication pipe <NUM> are displaced in the upper-lower direction. Further, directions of the first communication pipe <NUM> and the second communication pipe <NUM> intersect with each other, and the first communication pipe <NUM> overlaps the inlet <NUM> of the second communication pipe <NUM> in the second expansion chamber <NUM> in a rear view (see <FIG>). Accordingly, the exhaust gas is unlikely to directly flow from the outlet <NUM> of the first communication pipe <NUM> to the inlet <NUM> of the second communication pipe <NUM>, and the exhaust gas is more likely to expand in the second expansion chamber <NUM>.

The exhaust gas flows into the third expansion chamber <NUM> from the outlet <NUM> of the second communication pipe <NUM>, and the exhaust gas flows into the cap <NUM> of the tail pipe <NUM> from the third expansion chamber <NUM>. As described above, the second communication pipe <NUM> is provided on the right end side of the second partition wall <NUM>, and an extending portion <NUM> of the tail pipe <NUM> in the front-rear direction is provided on the left end side of the second partition wall <NUM>. The front wall of the chamber <NUM> is formed with the bulge portion <NUM>, the outlet <NUM> of the second communication pipe <NUM> faces a foot portion of the bulge portion <NUM>, and the cap <NUM> of the tail pipe <NUM> faces a top portion of the bulge portion <NUM>. Therefore, the exhaust gas from the outlet <NUM> of the second communication pipe <NUM> is diffused not only to an inside of the bulge portion <NUM> but also to a wide range.

The outlet <NUM> of the second communication pipe <NUM> is positioned on the rear side of the third expansion chamber <NUM>, and the cap <NUM> of the tail pipe <NUM> is positioned on an inner side of the bulge portion <NUM> in front of the outlet <NUM> of the second communication pipe <NUM>. The second communication pipe <NUM> and the extending portion <NUM> of the tail pipe <NUM> in the front-rear direction extend in parallel to each other, and the outlet <NUM> of the second communication pipe <NUM> and the cap <NUM> of the tail pipe <NUM> are displaced in the front-rear direction. The exhaust gas is unlikely to directly flow from the outlet <NUM> of the second communication pipe <NUM> to the cap <NUM> of the tail pipe <NUM>, and the exhaust gas is likely to expand in the third expansion chamber <NUM>. Since the cap <NUM> is positioned on the inner side of the bulge portion <NUM>, the volume of the bulge portion <NUM> is effectively utilized for expansion of the exhaust gas.

In this way, the exhaust gas is unlikely to directly flow from the first expansion chamber <NUM> to the second expansion chamber <NUM>, the exhaust gas is unlikely to directly flow from the second expansion chamber <NUM> to the third expansion chamber <NUM>, and the exhaust gas is unlikely to directly flow from the third expansion chamber <NUM> to the tail pipe <NUM>. The exhaust gas is sufficiently expanded in the first to third expansion chambers <NUM> to <NUM>, and the silencing performance of the chamber <NUM> is improved. Since the exhaust gas is expanded stepwise in the first to third expansion chambers <NUM> to <NUM> and the energy of the exhaust sound is fairly attenuated, the chamber <NUM> can be disposed in the narrow space below the engine <NUM>.

The inlet pipe <NUM> and the second communication pipe <NUM> extend parallel to the extending portion <NUM> of the tail pipe <NUM> in the front-rear direction, and the first communication pipe <NUM> extends parallel to the extending portion <NUM> of the tail pipe <NUM> in the left-right direction. The extending portion <NUM> of the tail pipe <NUM> in the left-right direction crosses the inlet pipe <NUM> and the second communication pipe <NUM> in front of the first communication pipe <NUM>. The first communication pipe <NUM> is formed to be shorter than a distance L from a left end of the second communication pipe <NUM> to a right end of the inlet pipe <NUM> (second catalyst <NUM>) (see <FIG>). The extending portion <NUM> of the tail pipe <NUM> in the left-right direction is formed to be longer than the distance L from the left end of the second communication pipe <NUM> to the right end of the inlet pipe <NUM> (second catalyst <NUM>) in the left-right direction (see <FIG>).

As described above, in the first expansion chamber <NUM> and the second expansion chamber <NUM>, the flow of the exhaust gas is blocked by the extending portion <NUM> of the tail pipe <NUM> in the left-right direction in front of the first communication pipe <NUM>. The exhaust gas is unlikely to directly flow from the outlet <NUM> of the inlet pipe <NUM> to the inlet <NUM> of the first communication pipe <NUM>, and the exhaust gas is unlikely to directly flow from the outlet <NUM> of the first communication pipe <NUM> to the inlet <NUM> of the second communication pipe <NUM>. Therefore, the exhaust gas can be sufficiently expanded in the first and second expansion chambers <NUM> and <NUM>, and the silencing performance of the chamber <NUM> can be improved. The tail pipe <NUM> functions as a barrier that blocks the flow of the exhaust gas in the first and second expansion chambers <NUM> and <NUM>.

The first expansion chamber <NUM> is entirely surrounded by the outer wall of the two-layer structure, and the second and third expansion chambers <NUM> and <NUM> are partially surrounded by the outer wall of the two-layer structure. The large plates <NUM> of the second expansion chamber <NUM> are arranged so as to overlap an outlet <NUM> side of the first communication pipe <NUM> and an inlet <NUM> side of the second communication pipe <NUM> in a plan view. The outlet <NUM> of the first communication pipe <NUM> faces a side surface portion of the lower large plate <NUM> (see <FIG>). The small plates <NUM> of the third expansion chamber <NUM> are arranged so as to overlap an outlet <NUM> side of the second communication pipe <NUM> behind the bulge portion <NUM> in a plan view. A vicinity of the communication pipes <NUM> and <NUM> in which the exhaust gas is concentrated is formed in a two-layer structure, so that the silencing effect of the chamber <NUM> is enhanced.

As described above, according to the present embodiment, inside the chamber <NUM>, the first expansion chamber <NUM> and the second and third expansion chambers <NUM> and <NUM> are separately formed on left and right sides, and the second expansion chamber <NUM> and the third expansion chamber <NUM> are separately formed on front and rear sides. A flow direction of the exhaust gas from the first expansion chamber <NUM> to the second expansion chamber <NUM> intersects with a flow direction of the exhaust gas from the second expansion chamber <NUM> to the third expansion chamber <NUM>. The exhaust gas is unlikely to directly flow from the first expansion chamber <NUM> to the third expansion chamber <NUM>, and the exhaust gas can be sufficiently expanded in the first to third expansion chambers <NUM> to <NUM>. Even when the chamber <NUM> is disposed in the limited space below the engine <NUM>, the first to third expansion chambers <NUM> to <NUM> are formed inside the chamber <NUM>, so that the exhaust gas can be expanded stepwise to improve the silencing performance of the chamber <NUM>.

The first expansion chamber is formed on the right side of the chamber and the second and third expansion chambers are formed on the left side of the chamber in the present embodiment, but the first expansion chamber may be formed on the left side of the chamber and the second and third expansion chambers may be formed on the right side of the chamber.

In the present embodiment, the first communication pipe extends in the left-right direction, but the first communication pipe may communicate the first expansion chamber with the second expansion chamber. For example, the first communication pipe may extend obliquely.

In the present embodiment, the second communication pipe extends in the front-rear direction, but the second communication pipe may communicate the second expansion chamber with the third expansion chamber. For example, the second communication pipe may extend obliquely.

In the present embodiment, the outer wall of the chamber that surrounds the second and third expansion chambers partially has the two-layer structure, but the outer wall of the chamber that surrounds the second and third expansion chambers may have a single-layer structure as a whole. Further, the outer wall of the chamber may have a two-layer structure or a single-layer structure as a whole.

In the present embodiment, the partition wall plate is attached to the first partition wall in a predetermined range from the rear end of the second catalyst to the front side of the tail pipe, but the predetermined range in which the partition wall plate is attached can be appropriately changed. For example, the partition wall plate may be attached to the first partition wall in a predetermined range from a position in front of the inlet pipe to a position in front of the first communication pipe.

In the present embodiment, the extending portion of the tail pipe in the left-right direction is disposed in the first and second expansion chambers, but the tail pipe may not be disposed in the first and second expansion chambers. For example, the tail pipe may extend from the third expansion chamber to the outside of the chamber.

The bulge portion is formed in the chamber in the present embodiment, but the bulge portion may not be formed in the chamber as long as a volume of the third expansion chamber can be sufficiently secured.

In the present embodiment, the inlet of the tail pipe is formed by the punched holes of the cap, but the inlet of the tail pipe is not particularly limited as long as the inlet has a shape that enables the exhaust gas to flow in.

The exhaust apparatus of the present embodiment can be appropriately applied to other straddle-type vehicles such as a buggy-type automatic three-wheeled vehicle. Here, the straddle-type vehicle is not limited to a general vehicle on which a rider drives the vehicle in a posture of straddling a seat, and further includes a scooter-type vehicle on which a rider drives the vehicle without straddling a seat.

As described above, an exhaust apparatus (<NUM>) of the present embodiment is an exhaust apparatus configured to purify exhaust gas exhausted from an engine (<NUM>) through an exhaust pipe (31a, 31b), the exhaust apparatus (<NUM>) including: a chamber (<NUM>) disposed below the engine; an inlet pipe (<NUM>) configured to guide exhaust gas from the exhaust pipe to the chamber; a tail pipe (<NUM>) configured to discharge exhaust gas from the chamber to an outside; a first partition wall (<NUM>) configured to partition an inside of the chamber into a pair of left and right spaces; and a second partition wall (<NUM>) configured to partition one of the pair of left and right spaces into a pair of front and rear spaces, in which the other of the pair of left and right spaces is defined as a first expansion chamber (<NUM>) into which the inlet pipe enters, in which a rear space of the pair of front and rear spaces is defined as a second expansion chamber (<NUM>) downstream of the first expansion chamber, and in which a front space of the pair of front and rear spaces is defined as a third expansion chamber (<NUM>) into which the tail pipe enters downstream of the second expansion chamber. According to this configuration, inside the chamber, the first expansion chamber, and the second and third expansion chambers are separately formed on the left and right sides, and the second expansion chamber and the third expansion chamber are separately formed on the front and rear sides. The flow direction of the exhaust gas from the first expansion chamber to the second expansion chamber intersects with the flow direction of the exhaust gas from the second expansion chamber to the third expansion chamber. The exhaust gas is unlikely to directly flow from the first expansion chamber to the third expansion chamber, and the exhaust gas can be sufficiently expanded in the first to third expansion chambers. Even when the chamber is disposed in the limited space below the engine, the first to third expansion chambers are formed inside the chamber, so that the exhaust gas can be expanded stepwise to improve the silencing performance of the chamber.

The exhaust apparatus of the present embodiment further including: a first communication pipe (<NUM>) configured to extend in a left-right direction and penetrate the first partition wall; and a second communication pipe (<NUM>) configured to extend in a front-rear direction and penetrate the second partition wall, in which the first expansion chamber and the second expansion chamber communicate with each other through the first communication pipe, in which the second expansion chamber and the third expansion chamber communicate with each other through the second communication pipe, and in which the first communication pipe overlaps an inlet (<NUM>) of the second communication pipe in a rear view. According to this configuration, the directions of the first communication pipe and the second communication pipe intersect with each other, and the exhaust gas is unlikely to directly flow from the outlet of the first communication pipe to the inlet of the second communication pipe. Therefore, the exhaust gas can be sufficiently expanded in the second expansion chamber, and the silencing performance of the chamber can be improved.

In the exhaust apparatus of the present embodiment, the tail pipe extends in the front-rear direction and penetrates the second partition wall, then extends in the left-right direction and penetrates the first partition wall, and an extending portion (<NUM>) of the tail pipe in the left-right direction overlaps the inlet of the second communication pipe in front of the first communication pipe in a rear view. According to this configuration, the flow of the exhaust gas is blocked by the extending portion of the tail pipe in the left-right direction in front of the first communication pipe, and the exhaust gas is unlikely to directly flow from the outlet of the first communication pipe to the inlet of the second communication pipe. Therefore, the exhaust gas can be sufficiently expanded in the second expansion chamber, and the silencing performance of the chamber can be improved.

In the exhaust apparatus of the present embodiment, the extending portion of the tail pipe in the left-right direction overlaps an outlet (<NUM>) of the inlet pipe in front of the first communication pipe in a rear view. According to this configuration, the flow of the exhaust gas is blocked by the extending portion of the tail pipe in the left-right direction in front of the first communication pipe, and the exhaust gas is unlikely to directly flow from the outlet of the inlet pipe to the inlet of the first communication pipe. Therefore, the exhaust gas can be sufficiently expanded in the first expansion chamber, and the silencing performance of the chamber can be improved.

In the exhaust apparatus of the present embodiment, the extending portion of the tail pipe in the left-right direction is longer than a distance from one end of the second communication pipe in the left-right direction to the other end of the inlet pipe in the left-right direction. According to this configuration, in the first expansion chamber and the second expansion chamber, the flow of the exhaust gas is blocked by the extending portion of the tail pipe in the left-right direction in front of the first communication pipe. The exhaust gas is unlikely to directly flow from the outlet of the inlet pipe to the inlet of the first communication pipe, and the exhaust gas is unlikely to directly flow from the outlet of the first communication pipe to the inlet of the second communication pipe. Therefore, the exhaust gas can be sufficiently expanded in the first and second expansion chambers, and the silencing performance of the chamber can be improved.

In the exhaust apparatus of the present embodiment, an outer wall of the chamber is formed with a bulge portion (<NUM>) configured to expand the third expansion chamber forward, the extending portion of the tail pipe in a front-rear direction extends in parallel to the second communication pipe, and an inlet (cap <NUM>) of the tail pipe is positioned inside the bulge portion in front of an outlet (<NUM>) of the second communication pipe. According to this configuration, the volume of the third expansion chamber can be increased by the bulge portion. The second communication pipe and the extending portion of the tail pipe in the front-rear direction extend in parallel to each other, and the exhaust gas is unlikely to directly flow from the outlet of the second communication pipe to the inlet of the tail pipe. Further, since the inlet of the tail pipe is positioned inside the bulge portion, a volume of the bulge portion can be effectively utilized to bulge the exhaust gas. Therefore, the exhaust gas can be sufficiently expanded in the third expansion chamber, and the silencing performance of the chamber can be improved.

Claim 1:
A straddle-type vehicle comprising an exhaust apparatus (<NUM>) configured to purify exhaust gas exhausted from an engine (<NUM>) through an exhaust pipe (31a, 31b), the exhaust apparatus (<NUM>) comprising:
a chamber (<NUM>) disposed below the engine (<NUM>);
an inlet pipe (<NUM>) configured to guide exhaust gas from the exhaust pipe (31a, 31b) to the chamber (<NUM>);
a tail pipe (<NUM>) configured to discharge the exhaust gas from the chamber (<NUM>) to an outside;
a first partition wall (<NUM>) partitioning an inside of the chamber (<NUM>) to a pair of left and right spaces; and
a second partition wall (<NUM>) partitioning one of the pair of left and right spaces to a pair of front and rear spaces,
characterized in that
another of the pair of left and right spaces is defined as a first expansion chamber (<NUM>) into which the inlet pipe (<NUM>) enters,
a rear space of the pair of front and rear spaces is defined as a second expansion chamber (<NUM>) disposed downstream of the first expansion chamber (<NUM>), and
a front space of the pair of front and rear spaces is defined as a third expansion chamber (<NUM>) disposed downstream of the second expansion chamber (<NUM>), and the tail pipe (<NUM>) enters into the third expansion chamber (<NUM>).