There is provided a straddle-type vehicle. An exhaust pipe includes a first portion extending downward from an exhaust port through a region in front of an engine and on one lateral side of a down frame in the left-right direction, a second portion extending upward through a region in front of the engine and on the other lateral side of the down frame in the left-right direction after extending from a downstream side end portion of the first portion to the other lateral side of the down frame in the left-right direction through a region in front of or to the lower front of the down frame. The catalyst device is disposed in a portion of the second portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2022-075990 filed on May 2, 2022, the contents of which are incorporated herein by way of reference.

TECHNICAL FIELD

The present invention relates to a straddle-type vehicle including an internal combustion engine as an engine.

BACKGROUND

In general, straddle-type vehicles include those designed to be suitable for on-road traveling, that is, traveling on a paved road and a regular road, and those designed to be suitable not only for on-road traveling but also for off-road traveling, that is, traveling on an unpaved road or an irregular road. Straddle-type vehicles designed to be suitable for on-road traveling include a naked vehicle, a super sports vehicle, a cruiser vehicle, and the like. Straddle-type vehicles designed to be suitable for both on-road traveling and off-road traveling include a dual-purpose vehicle, an adventure vehicle, an on/off model vehicle, a scrambler vehicle, and the like. Some straddle-type vehicles are designed for off-road racing such as motocross, trial, and enduro.

Hereinafter, a straddle-type vehicle designed to be suitable for on-road traveling will be referred to as an “on-road vehicle”. A straddle-type vehicle designed to be suitable for both on-road traveling and off-road traveling and a straddle-type vehicle designed for off-road racing will be referred to as an “off-road vehicle”.

An off-road vehicle has a higher minimum ride height and a longer suspension stroke than an on-road vehicle. In many off-road vehicles, an exhaust pipe and a muffler are disposed at high positions away from the ground in the vehicle.

Here, regarding the arrangement of the exhaust pipes, an on-road vehicle and an off-road vehicle will be compared in detail. Generally, an exhaust pipe of an on-road vehicle extends downward from an exhaust port opened in a front surface of a cylinder head of an engine through a front side of each of the cylinder head, a cylinder, and a crankcase of the engine, bends backward, and then extends backward in a substantially horizontal direction at least to a position beyond the crankcase through a lower side of the crankcase (between the ground and a bottom surface of the crankcase). On the other hand, an exhaust pipe of an off-road vehicle (in particular, a straddle-type vehicle for off-road racing) once extends downward from an exhaust port opened in a front surface of a cylinder head through a front side of the cylinder head, but immediately bends laterally, then bends backward, and then extends backward in a substantially horizontal direction at least to a position beyond a cylinder or the cylinder head through a lateral side of the cylinder head or the cylinder. A significant difference in the arrangement of an exhaust pipe between an on-road vehicle and an off-road vehicle is that the exhaust pipe of the on-road vehicle passes below a crankcase, whereas the exhaust pipe of the off-road vehicle passes through a lateral side of a cylinder head or a cylinder. When traveling on an off-road, stones and the like on the ground are frequently wound up by wheels and scattered. By disposing an exhaust pipe at a high position away from the ground, it is possible to make it difficult for such flying stones to hit the exhaust pipe, and thus it is possible to protect the exhaust pipe. From this point of view, in many off-road vehicles, an exhaust pipe is disposed so as to pass through a lateral side of a cylinder head or a cylinder without passing below the crankcase.

On the other hand, in order to preserve the global environment, it is required to suppress discharge of air pollutants such as nitrogen oxides from an engine. Accordingly, a straddle-type vehicle includes a catalyst device in which a catalyst is supported on a monolith carrier having a honeycomb structure, for example, and the catalyst device is used to reduce air pollutants in exhaust gas.

In a straddle-type vehicle in the related art, in many cases, a catalyst device is provided in a muffler or in a portion of a back portion (downstream side) of an exhaust pipe that is close to the muffler. However, in recent years, there have been an increasing number of straddle-type vehicles in which a catalyst device is provided in a front portion (upstream side) of an exhaust pipe.

A temperature of a catalyst of the catalyst device is increased and the catalyst is activated by the exhaust gas discharged from an engine flowing through the catalyst device. When the catalyst device is provided at a position far away from an exhaust port of the engine, such as inside the muffler, a temperature of the exhaust gas is decreased during a period in which the exhaust gas is discharged from the exhaust port of the engine, flows through the exhaust pipe, and reaches the catalyst device, and as a result, the exhaust gas having a low temperature flows through the catalyst device. Therefore, the increase in the temperature of the catalyst becomes gentle, and therefore, the time from the start of the engine to the activation of the catalyst becomes long. As a result, when the engine is started, an amount of air pollutants may not be sufficiently reduced by the catalyst. On the other hand, when the catalyst device is provided in the front portion of the exhaust pipe, a distance between the catalyst device and the exhaust port of the engine is shortened. Therefore, since the exhaust gas having a high temperature immediately after being discharged from the exhaust port flows through the inside of the catalyst device, the temperature of the catalyst can be increased within a short period of time, and the catalyst can be activated at an early stage when the engine is started. As a result, even when the engine is started, the amount of air pollutants can be sufficiently reduced by the catalyst. In recent years, with an increasing demand for global environmental preservation, the spread of straddle-type vehicles in which a catalyst device is provided in a front portion of an exhaust pipe expands in order to enhance exhaust gas purification performance of a catalyst when the engine is started.

JP2008-64068A (Patent Literature 1) describes a straddle-type vehicle which is an off-road vehicle. In the straddle-type vehicle, an exhaust pipe extends forward from an exhaust port of an engine, then bends backward, then passes through a position to the right of the engine and above a crankcase of the engine, and extends backward. The straddle-type vehicle includes a main catalyst and a pre-catalyst, the main catalyst is disposed in a muffler, and the pre-catalyst is disposed in a portion of the exhaust pipe immediately after passing above the crankcase.

As described below, it is not easy to appropriately provide a catalyst device inside a front portion of an exhaust pipe in a straddle-type vehicle having a structure in which the exhaust pipe does not pass below an engine but passes through a lateral side of the engine, such as a lateral side of a cylinder or a cylinder head of the engine, as in the above off-road vehicle.

In the straddle-type vehicle having a structure in which an exhaust pipe passes a lateral side of an engine, the front portion of the exhaust pipe is a portion of the exhaust pipe from an exhaust port of the engine to the lateral side of the engine, and a portion of the exhaust pipe passing through the lateral side of the engine.

First, there is the following problem when a catalyst device is provided in the portion of the exhaust pipe from the exhaust port of the engine to the lateral side of the engine.

In the straddle-type vehicle having a structure in which an exhaust pipe does not pass below an engine but passes through a lateral side of the engine as in the off-road vehicle, the exhaust pipe once extends downward from the exhaust port opened in a front surface of the cylinder head through a front side of the cylinder head, but immediately bends laterally, then bends backward, and reaches the lateral side of the engine. Therefore, the portion of the exhaust pipe from the exhaust port of the engine to the lateral side of the engine has a short pipe length. Therefore, it is difficult to provide the catalyst device inside the portion.

Next, there is the following problem when a catalyst device is provided in a portion of an exhaust pipe passing through a lateral side of an engine.

In the straddle-type vehicle having a structure in which an exhaust pipe passes a lateral side of an engine, the exhaust pipe passes through the lateral side of the engine, and then passes through a position that is on an inner side of a leg of a rider seated on a seat and that is extremely close to the leg. For example, when the exhaust pipe passes through a right side of the engine, the exhaust pipe passes through the right side of the engine, and then passes through a position that is to the left of a knee or a calf of a right leg of a rider seated on a seat and that is extremely close to the knee or the calf. The straddle-type vehicle having a structure in which an exhaust pipe passes through a lateral side of an engine is generally provided with a heat shield plate for protecting legs of a rider from heat from the exhaust pipe. The heat shield plate is provided in a region between the leg of the rider and a portion of the exhaust pipe passing through the lateral side of the engine as well as a portion immediately after the portion so as to shield between the exhaust pipe and the leg of the rider.

When a diameter of the catalyst device is larger than a normal diameter of the exhaust pipe, a diameter of the portion of the exhaust pipe where the catalyst device is provided is larger than the normal diameter of the exhaust pipe (diameter of a portion of the exhaust pipe where the catalyst device is not provided). Therefore, when such a catalyst device is provided in the portion of the exhaust pipe passing through the lateral side of the engine, a portion of the exhaust pipe passing through the inner side of the leg of the rider may have a large diameter. In this case, since a portion between a right leg and a left leg of the rider seated on the seat is widened in the straddle-type vehicle, the rider needs to ride the straddle-type vehicle in a posture in which the legs are widened, and a riding posture of the rider is worsened. Worsening of the riding posture leads to deterioration of maneuverability of the straddle-type vehicle.

When a catalyst device having a diameter smaller than a normal diameter of an exhaust pipe is provided in the exhaust pipe, a diameter of a portion of the exhaust pipe where the catalyst device is provided may not be larger than the normal diameter of the exhaust pipe. However, by providing the catalyst device inside the exhaust pipe, the portion of the exhaust pipe in which the catalyst device is provided tends to have a higher temperature than a portion of the exhaust pipe in which the catalyst device is not provided. Therefore, even when the catalyst device having a diameter smaller than the normal diameter of the exhaust pipe is provided in the portion of the exhaust pipe passing through the lateral side of the engine, it is necessary to increase a distance between the exhaust pipe and the shield plate in order to protect the legs of the rider from the heat from the exhaust pipe, and as a result, there is a possibility that the riding posture of the rider is worsened as when the catalyst device having a diameter larger than the normal diameter of the exhaust pipe is provided in the portion of the exhaust pipe passing through the lateral side of the engine. Since the catalyst device having a diameter smaller than the normal diameter of the exhaust pipe has lower exhaust gas purification performance than the catalyst device having a diameter larger than the normal diameter of the exhaust pipe, the exhaust gas may not be sufficiently purified.

In the straddle-type vehicle described in JP2008-64068A (Patent Literature 1), the exhaust pipe passes through a lateral side of a cylinder or a cylinder head of an engine, and then extends backward through a center side of the straddle-type vehicle in a left-right direction with respect to the cylinder or the cylinder head of the engine. A catalyst device having a diameter larger than a normal diameter of the exhaust pipe is provided in a portion of the exhaust pipe extending backward through the central side of the straddle-type vehicle in the left-right direction with respect to the cylinder or the cylinder head of the engine (seeFIG.3of the same publication). According to this configuration, by providing the catalyst device inside the exhaust pipe, it may be possible to suppress a portion of the straddle-type vehicle between a right leg and a left leg of a rider seated on a seat from becoming wide to some extent even when a portion of the exhaust pipe passing through an inner side of the leg of the rider has a large diameter. However, in a case of this configuration, it is necessary to expand a space surrounded by a main frame, a rear cushion, and the cylinder of the engine in order to pass the exhaust pipe to the central side of the straddle-type vehicle in the left-right direction, the exhaust pipe having a large diameter by providing the catalyst device, and as a result, the straddle-type vehicle may be increased in size.

The present invention is made in view of, for example, the above problem, and an object of the present invention is to appropriately provide a catalyst device in a front portion of an exhaust pipe in a straddle-type vehicle having a structure in which the exhaust pipe does not pass below an engine but passes through a lateral side of the engine.

SUMMARY

There is provided a straddle-type vehicle including: a head pipe; a main frame extending backward from the head pipe; a down frame extending downward from the head pipe; an engine including a crankcase, a cylinder provided above the crankcase, and a cylinder head provided above the cylinder, the engine being disposed below the main frame and behind the down frame; a muffler disposed behind the engine and configured to reduce exhaust noise of exhaust gas that is discharged from an exhaust port provided in the cylinder head; an exhaust pipe configured to connect the exhaust port and the muffler and to send the exhaust gas discharged from the exhaust port to the muffler; and a catalyst device provided in an intermediate portion of the exhaust pipe and configured to purify the exhaust gas flowing through the exhaust pipe. The exhaust port is disposed in a front portion of the cylinder head, and is opened forward while being inclined to one side in a left-right direction. The exhaust pipe includes a first portion extending downward from the exhaust port through a region in front of the engine and on one lateral side of the down frame in the left-right direction, a second portion extending upward through a region in front of the engine and on the other lateral side of the down frame in the left-right direction after extending from a downstream side end portion of the first portion to the other lateral side of the down frame in the left-right direction through a region in front of or to the lower front of the down frame, a third portion extending backward from a downstream side end portion of the second portion through a region on the other lateral side of the engine in the left-right direction, and a fourth portion extending from a downstream side end portion of the third portion and reaching the muffler.

The catalyst device is disposed in a portion of the second portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction.

DESCRIPTION OF EMBODIMENTS

A straddle-type vehicle according to an embodiment of the present invention includes a head pipe, a main frame extending backward from the head pipe, a down frame extending downward from the head pipe, and an engine disposed below the main frame and behind the down frame. The engine includes a crankcase, a cylinder provided above the crankcase, and a cylinder head provided above the cylinder. Further, the straddle-type vehicle according to the embodiment of the present invention includes a muffler that reduces exhaust noise of exhaust gas discharged from an exhaust port of the engine, an exhaust pipe that sends the exhaust gas discharged from the exhaust port of the engine to the muffler, and a catalyst device that purifies the exhaust gas flowing through the exhaust pipe.

In the straddle-type vehicle according to the embodiment of the present invention, the exhaust port of the engine is disposed in a front portion of the cylinder head, and is opened forward while being inclined to one side in a left-right direction. The muffler is disposed behind the engine. The exhaust pipe connects the exhaust port of the engine and the muffler. The exhaust pipe includes a first portion extending downward from the exhaust port of the engine through a region in front of the engine and on one lateral side of the down frame in the left-right direction, a second portion extending upward through a region in front of the engine and on the other lateral side of the down frame in the left-right direction after extending from a downstream side end portion of the first portion to the other lateral side of the down frame in the left-right direction through a region in front of or to the lower front of the down frame, a third portion extending backward from a downstream side end portion of the second portion through a region on the other lateral side of the engine in the left-right direction, and a fourth portion extending from a downstream side end portion of the third portion to reach the muffler. The catalyst device is provided in the intermediate portion of the exhaust pipe. Specifically, the catalyst device is disposed in a portion of the second portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction.

According to the straddle-type vehicle according to the embodiment of the present invention, the catalyst device can be appropriately provided in a front portion (upstream side) of the exhaust pipe.

That is, as described above, since a pipe length of a portion of an exhaust pipe from an exhaust port of an engine to a lateral side of the engine is short in a straddle-type vehicle in the related art having a structure in which the exhaust pipe passes through the lateral side of the engine, there is a problem that it is difficult to provide a catalyst device in this portion. However, the exhaust pipe of the straddle-type vehicle according to the present embodiment includes the first portion extending downward from the exhaust port of the engine through the region in front of the engine and on one lateral side of the down frame in the left-right direction, and the second portion extending upward through the region in front of the engine and on the other lateral side of the down frame in the left-right direction after extending from the downstream side end portion of the first portion to the other lateral side of the down frame in the left-right direction through the region in front of or to the lower front of the down frame. According to this configuration, it is possible to secure a pipe length sufficient for providing a catalyst device in a portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction, and it is possible to easily provide the catalyst device in this portion. In particular, a large-sized catalyst device having a diameter larger than a normal diameter of an exhaust pipe and having high exhaust gas purification performance can be easily provided at the portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction.

As described above, when a catalyst device having a diameter larger than a normal diameter of an exhaust pipe is provided in a portion of the exhaust pipe passing through a lateral side of an engine in the straddle-type vehicle in the related art having the structure in which the exhaust pipe passes through the lateral side of the engine, a portion between a right leg and a left leg of a rider seated on a seat becomes wide in the straddle-type vehicle, and thus there is a problem that a riding posture of the rider is worsened. Even when a catalyst device having a diameter smaller than the normal diameter of the exhaust pipe is provided in the portion of the exhaust pipe passing through the lateral side of the engine, it is necessary to increase a distance between the exhaust pipe and a shield plate in order to protect the legs of the rider from heat from the exhaust pipe, and thus there is a problem that the riding posture of the rider may be worsened. However, since the catalyst device is provided in the portion of the second portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction in the straddle-type vehicle according to the present embodiment, such a problem does not occur. That is, according to the straddle-type vehicle according to the present embodiment, it is possible to suppress the riding posture of the rider from worsening due to provision of the catalyst device inside the front portion of the exhaust pipe.

As described above, in the straddle-type vehicle described in JP2008-64068A (Patent Literature 1), a catalyst device having a diameter larger than a normal diameter of an exhaust pipe is provided in a portion of the exhaust pipe extending backward from a cylinder or a cylinder head of an engine through a center side of the straddle-type vehicle in a left-right direction, whereby it is necessary to expand a space surrounded by a main frame, a rear cushion, the cylinder of the engine, and the like, and as a result, there is a problem that the straddle-type vehicle may be increased in size. However, since the catalyst device of the straddle-type vehicle according to the present embodiment is disposed in the portion of the second portion of the exhaust pipe that is located in front of the engine and on the other lateral side of the down frame in the left-right direction, such a problem does not occur.

In the straddle-type vehicle according to the present embodiment, the exhaust port of the engine is disposed in the front portion of the cylinder head, and is opened forward while being inclined to one side in the left-right direction. Accordingly, the exhaust pipe can be easily connected to the exhaust port without providing a locally bent portion with a large curvature at an upstream end side portion (first portion) of the exhaust pipe. The exhaust pipe can extend from the exhaust port to a position in front of or to the lower front of the down frame without providing a complicated bent portion such as an S-shaped or crank-shaped bent portion at the upstream end side portion (first portion) of the exhaust pipe.

Embodiment

An embodiment of a straddle-type vehicle according to the present invention will be described with reference to the drawings. In the following embodiment, directions including front (Fd), back (Bd), up (Ud), down (Dd), left (Ld), and right (Rd) are described based on arrows drawn at the lower right in each drawing.

FIG.1shows an entire straddle-type vehicle1according to the embodiment of the present invention as viewed from the right. InFIG.1, only outer shapes of a seat and a cowl are indicated by two-dot chain lines, and some components provided in the straddle-type vehicle1, such as a fuel tank, a brake caliper, a rear cushion, and a drive chain, are not shown.FIGS.2to6show a portion where an engine31is provided in the straddle-type vehicle1, and specifically,FIG.2shows a state where the portion is viewed from the right,FIG.3shows a state where the portion is viewed from the front,FIG.4shows a state where the portion is viewed from the left,FIG.5shows a state where the portion is viewed from above, andFIG.6shows a state where the portion is viewed from below. InFIGS.2to6, a steering shaft, a front fork15, a handle18, a swing arm19, and the like are removed. InFIGS.5and6, radiators42and43are further removed.

InFIG.1, the straddle-type vehicle1is an off-road vehicle, specifically, a straddle-type vehicle for off-road racing. The straddle-type vehicle1includes a vehicle body frame2that forms a framework thereof, and the vehicle body frame2includes a head pipe3, a pair of main frames4, a down frame5, a pair of under frames6, and a pair of seat rails7.

As shown inFIGS.2and3, the head pipe3is disposed at the center of a front upper portion of the straddle-type vehicle1in a left-right direction.

Of the pair of main frames4, one main frame4extends from the front upper portion of the straddle-type vehicle1to a lower portion of an intermediate portion of the straddle-type vehicle1in a front-back direction through a right portion of the straddle-type vehicle1. Specifically, as shown inFIG.5, a front portion4A of the one main frame4extends rightward and backward from the head pipe3, then gently bends, and then extends backward. As shown inFIG.2, the front portion4A of the one main frame4extends backward through an upper right portion of the straddle-type vehicle1while being inclined downward. As shown inFIG.2, a back portion4B of the one main frame4extends downward through a right portion of the intermediate portion of the straddle-type vehicle1in the front-back direction while being slightly inclined backward. The other main frame4extends from the front upper portion of the straddle-type vehicle1to the lower portion of the intermediate portion of the straddle-type vehicle1in the front-back direction through a left portion of the straddle-type vehicle1. As shown inFIGS.4and5, the shape and arrangement of the other main frame4are bilaterally symmetrical to the shape and arrangement of the one main frame4. A front end portion of each main frame4is coupled to the head pipe3.

As shown inFIGS.2and3, the down frame5extends downward from the front upper portion of the straddle-type vehicle1to a front lower portion of the straddle-type vehicle1through a center of the straddle-type vehicle1in the left-right direction while being slightly inclined backward. An upper end portion of the down frame5is coupled to the head pipe3. A position of a lower end of the down frame5is higher than a position of a lower end of the back portion4B of the main frame4.

Of the pair of under frames6, one under frame6extends from the front lower portion of the straddle-type vehicle1to the lower portion of the intermediate portion of the straddle-type vehicle1in the front-back direction through the right portion of the straddle-type vehicle1. Specifically, as shown inFIGS.3and6, the one under frame6extends downward, rightward, and backward from a lower end portion of the down frame5, gently bends, and then extends backward in a substantially horizontal direction through a lower right portion of the straddle-type vehicle1as shown inFIG.2. The other under frame6extends from the front lower portion of the straddle-type vehicle1to the lower portion of the intermediate portion of the straddle-type vehicle1in the front-back direction through the left portion of the straddle-type vehicle1. As shown inFIGS.3,4, and6, the shape and arrangement of the other under frame6are bilaterally symmetrical to the shape and arrangement of the one under frame6. A front end portion of each under frame6is coupled to the lower end portion of the down frame5. As shown inFIG.6, a back end portion of each under frame6is coupled to a bridge frame8that is bridged between lower end portions of the back portions4B of the pair of main frames4.

As shown inFIGS.1,2, and4, the pair of seat rails7extend from an upper portion of the intermediate portion of the straddle-type vehicle1in the front-back direction to an upper portion of a back end of the straddle-type vehicle1through the left and right portions of the straddle-type vehicle1. A reinforcing frame9that reinforces a front portion of the vehicle body frame2is provided between the down frame5and each main frame4(seeFIGS.2and4), and a reinforcing frame10that reinforces a back portion of the vehicle body frame2is provided between the lower portion of the back portion4B of each main frame4and the seat rail7(seeFIG.1).

As shown inFIG.1, the steering shaft is rotatably provided in the head pipe3, and the front fork15is attached to the steering shaft via a bracket. A front wheel16is rotatably attached to a lower end portion of the front fork15. A front fender17is provided above the front wheel16. The handlebar18is provided above the head pipe3, and the handlebar18is attached to the steering shaft via a bracket. The swing arm19is swingably attached to a lower side portion of the back portion4B of each main frame4, and a back wheel20is rotatably attached to a back end portion of the swing arm19.

The straddle-type vehicle1includes an engine31which is a power source for traveling. An internal combustion engine is used as the engine31. The engine31according to the present embodiment is a four-cycle, water-cooling, and single-cylinder gasoline engine. The engine31is disposed at a substantially central portion in the front-back direction and a substantially central portion in the left-right direction of the straddle-type vehicle. The engine31is surrounded by the pair of main frames4, the down frame5, and the pair of under frames6. Specifically, the engine31is disposed below the front portions4A of the pair of main frames4, in front of the back portions4B of the pair of main frames4, behind the down frame5, and above the pair of under frames6. The engine31is supported by these frames via engine mounts.

As shown inFIG.4, the engine31includes a crankcase32, a cylinder33, a cylinder head34, and a cylinder head cover35. The crankcase32is disposed at a lower portion of the engine31, and a crankshaft is provided in the crankcase32. The engine31is a so-called power unit integrated with a transmission, and a transmission device is provided at a back portion in the crankcase32. The cylinder33is provided above the crankcase32, and a piston is provided in the cylinder33. The cylinder head34is provided above the cylinder33. An intake port (not shown) through which an air-fuel mixture is sent to the cylinder33is formed in a back portion of the cylinder head34. An exhaust port36through which combustion gas (exhaust gas) is discharged to the outside of the cylinder33is formed in a front portion of the cylinder head34(seeFIG.7). An intake valve, an exhaust valve, a camshaft, and the like are provided in the cylinder head34, and a spark plug (not shown) and the like are attached to the cylinder head34. The cylinder head cover35covers an upper portion of the cylinder head34.

FIG.7shows the engine31as viewed from the front. As shown inFIG.7, the exhaust port36of the engine31is disposed on a front surface of the cylinder head34at a position to the left of the center of the cylinder head34in the left-right direction. In a front view of the straddle-type vehicle1, only a part of a right end side of the exhaust port36overlaps with the down frame5. The exhaust port36is opened forward in the front surface of the cylinder head34while being inclined to a left direction (one side in the left-right direction), that is, an opening direction of the exhaust port36is the left front. An one-dot chain line L inFIG.5is a straight line that passes through the center of the straddle-type vehicle1in the left-right direction and extends in the front-back direction. An one-dot chain line M inFIG.5is a straight line that passes through the center of the exhaust port36and extends in the opening direction of the exhaust port36. An angle a formed by the one-dot chain line L and the one-dot chain line M indicates an inclination angle of the exhaust port36in the left direction. In the present embodiment, the exhaust port36is inclined to the left direction by about36degrees as shown inFIG.5. The inclination angle of the exhaust port36in the left direction is not limited to 36 degrees, but is preferably about 20 degrees or more and about 70 degrees or less. A minimum value of the inclination angle of the exhaust port36at which an upstream side end portion of an exhaust pipe60can be easily connected to the exhaust port36from the left of the down frame5is about 20 degrees, and a maximum value of an angle at which a first portion61of the exhaust pipe60can be easily routed so as not to protrude leftward from the leftmost portion of the engine31(left surface of a magneto cover39) is about 70 degrees.

As shown inFIG.2, a water pump37that circulates cooling water mainly for cooling the engine31is provided on an outer surface side of a right front portion of the crankcase32. A clutch is provided at a right back portion in the crankcase32, and a clutch cover38that covers the clutch is provided at an outer surface side of the right back portion of the crankcase32. As shown inFIG.4, a generator that generates electric power using rotation of the crankshaft is provided at a left front portion in the crankcase32, and the magneto cover39that covers the generator is provided on an outer surface side of the left front portion of the crankcase32.

In the straddle-type vehicle1, an air cleaner40is provided behind and above the engine31as shown inFIG.1, and an intake pipe41is provided between the air cleaner40and the intake port of the engine31as shown inFIG.4. Although not shown in detail, a throttle device, a fuel injector, and the like are provided around the intake port of the engine31.

In the straddle-type vehicle1, two radiators42and43are provided in front of the cylinder head34of the engine31as heat exchangers that mainly cool, by traveling wind, cooling water for cooling the engine31. As shown inFIG.3, the radiator42is disposed to the right of an upper portion of the down frame5, and the radiator43is disposed to the left of the upper portion of the down frame5. The radiators42and43are attached to the upper portion of the down frame5via radiator mounts, respectively.

A step44for a right foot and a brake pedal45are provided at the lower portion of the back portion4B of the right main frame4(seeFIG.2). A step44for a left foot and a shift pedal46are provided at the lower portion of the back portion4B of the left main frame4(seeFIG.4). A seat47on which a rider sits is provided at the upper portion of the intermediate portion of the straddle-type vehicle1in the front-back direction, and a cowl48is provided in front of and behind the seat47(seeFIG.1).

Exhaust Pipe and Muffler

The straddle-type vehicle1includes a muffler51that reduces exhaust noise of exhaust gas discharged from the exhaust port36of the engine31, and the exhaust pipe60that sends the exhaust gas discharged from the exhaust port36to the muffler51.

The muffler51is disposed behind the engine31, specifically, behind the air cleaner40that is disposed behind the engine31, as shown inFIG.1. The muffler51is disposed between the right seat rail7and the back wheel20such that a discharge port through which exhaust gas is discharged to the outside air faces backward. The muffler51is supported by the right seat rail7via a stay.

The exhaust pipe60is a pipe that connects the muffler51and the exhaust port36formed in the cylinder head34of the engine31, and is formed of a metal material such as steel. The exhaust pipe60includes the first portion61extending downward from the exhaust port36through a region in front of the engine31and to the left (one lateral side in the left-right direction) of the down frame5as shown inFIG.4, a second portion62extending upward through a region in front of the engine31and to the right (the other lateral side in the left-right direction) of the down frame5after extending from a downstream side end portion of the first portion61to the right of the down frame5(the other lateral side in the left-right direction) through a region to the lower front of the down frame5as shown inFIG.3, a third portion63extending backward from a downstream side end portion of the second portion62through a region to the right of the engine31as shown inFIG.2, and a fourth portion64extending from a downstream side end portion of the third portion63to the muffler51as shown inFIG.1.

FIG.8is a view showing the exhaust pipe60, the muffler51, and the components provided at the exhaust pipe60extracted from the straddle-type vehicle1. An one-dot chain line K inFIG.8is a line passing through the center of the exhaust pipe60. In the exhaust pipe60inFIG.8, a portion from a position a to a position b is the first portion61, a portion from the position b to a position c is the second portion62, a portion from the position c to a position d is the third portion63, and a portion from the position d to a position e is the fourth portion64.

Each part of the exhaust pipe60will be described in more detail. An upstream side end portion of the first portion61of the exhaust pipe60is connected to the exhaust port36that is opened leftward and forward at a position to the left of the front surface of the cylinder head34. As shown inFIG.3, the first portion61of the exhaust pipe60is located to the left of the down frame5. In the front view of the straddle-type vehicle1, the first portion61of the exhaust pipe60extends leftward and downward from the exhaust port36and then extends rightward and downward. In addition, in the front view of the straddle-type vehicle1, the first portion61of the exhaust pipe60is gently curved so as to draw an arc-shaped locus bulging leftward with a diameter of a lower portion of the down frame5as a whole, and the upstream side end portion and the downstream side end portion of the first portion61of the exhaust pipe60are close to the down frame5, whereas an intermediate portion of the first portion61of the exhaust pipe60is separated from the down frame5. The downstream side end portion of the first portion61of the exhaust pipe60is located in front of the crankcase32and to the lower left front of the down frame5. Specifically, the downstream side end portion of the first portion61of the exhaust pipe60is located to the lower left of the lower end of the down frame5, and is located in front of an upper end side portion of the left under frame6in the front view of the straddle-type vehicle1. As shown inFIG.4, in a left side view of the straddle-type vehicle1, the first portion61of the exhaust pipe60extends downward from the exhaust port36while being inclined forward, and the upstream side end portion of the first portion61of the exhaust pipe60is located behind the down frame5, but the downstream side end portion of the first portion61of the exhaust pipe60is located in front of the down frame5. As shown inFIG.5, the intermediate portion of the first portion61of the exhaust pipe60protrudes leftward (outward in the left-right direction) from the left main frame4, but is located to the right (inner side in the left-right direction) of the leftmost portion of the engine31(left surface of the magneto cover39). The first portion61of the exhaust pipe60has a constant diameter over the entire length thereof. The first portion61of the exhaust pipe60is formed by bending a pipe.

As shown inFIG.3, in the front view of the straddle-type vehicle1, the second portion62of the exhaust pipe60extends rightward from the downstream side end portion of the first portion61of the exhaust pipe60that is located to the left of the down frame5through the lower front of the down frame5, and then extends rightward and upward through the right of the lower portion of the down frame5. An upstream side portion of the second portion62of the exhaust pipe60is gently curved so as to draw an arc, and an extension direction of the second portion62of the exhaust pipe60gradually changes from the right to the upper right due to the curve. The upstream side portion of the second portion62of the exhaust pipe60passes through a front side of the upper end side portion of the right under frame6. As shown inFIG.2, in a right side view of the straddle-type vehicle1, an intermediate portion of the second portion62of the exhaust pipe60extends upward and backward through the right of the lower portion of the down frame5, and a downstream side portion of the second portion62of the exhaust pipe60is curved so as to approach the horizontal. A portion of the second portion62of the exhaust pipe60from the intermediate portion to the downstream side portion extends in an up-down direction from a substantially intermediate position of the crankcase32to a position of a boundary between the cylinder33and the cylinder head34beyond a position of a boundary between the crankcase32and the cylinder33. The portion of the second portion62of the exhaust pipe60from the intermediate portion to the downstream side portion extends in the front-back direction from a position in front of the down frame5to a position behind the down frame5. As shown inFIG.5, in a top view of the straddle-type vehicle1, the portion of the second portion62of the exhaust pipe60from the intermediate portion to the downstream side portion is located to the right front (outer side) of the front portion4A of the right main frame4and extends along the front portion4A of the right main frame4. As shown inFIG.2, the position of the downstream side end portion of the second portion62of the exhaust pipe60in the up-down direction is substantially equal to the position of the boundary between the cylinder33and the cylinder head34. The position of the downstream side end portion of the second portion62of the exhaust pipe60in the front-back direction is substantially equal to the position of a front surface of the cylinder33. The position of the downstream side end portion of the second portion62of the exhaust pipe60in the left-right direction is, as shown inFIG.3, to the right (outer side in the left-right direction) of the right surface of the cylinder33and to the right of a right surface of the cylinder head34, and as shown inFIG.5, to the right of the right main frame4and to the left (inner side in the left-right direction) of the rightmost portion of the engine31(rightmost portion of the water pump37). As will be described later, the second portion62of the exhaust pipe60is provided with a first catalyst device accommodating portion73.

As shown inFIG.2, the third portion63of the exhaust pipe60extends backward in the substantially horizontal direction from the downstream side end portion of the second portion62of the exhaust pipe60through the right of the boundary portion between the cylinder33and the cylinder head34. As shown inFIG.5, an upstream side portion of the third portion63of the exhaust pipe60is located to the right of the front portion4A of the right main frame4, but a downstream side portion of the third portion63of the exhaust pipe60is slightly bent to the right (inner side in the left-right direction) from the vicinity beyond the cylinder33and extends backward through the left (inner side in the left-right direction) of the back portion4B of the right main frame4. The third portion63of the exhaust pipe60has a constant diameter over the entire length thereof. The diameter of the third portion63of the exhaust pipe60is substantially equal to the diameter of the first portion61of the exhaust pipe60. The third portion63of the exhaust pipe60is formed of a pipe. A heat shield plate65that suppresses heat of the exhaust pipe60from being transmitted to the right leg of the rider is provided to the right of the third portion63of the exhaust pipe60. The heat shield plate65covers an outer surface of a right portion of the third portion63over a wide range. The heat shield plate65is attached to the third portion63via a spacer or the like.

The fourth portion64of the exhaust pipe60extends backward below the right portion of the air cleaner40from the downstream side end portion of the third portion63of the exhaust pipe60. An upstream side portion of the fourth portion64of the exhaust pipe60is formed integrally with the third portion63of the exhaust pipe60, and a portion of the exhaust pipe60from the upstream side end portion of the third portion63to a substantially intermediate portion of the fourth portion64is formed by one pipe. As described later, a downstream side portion of the fourth portion64of the exhaust pipe60is provided with a second catalyst device accommodating portion85. A downstream side end portion of the fourth portion64of the exhaust pipe60is connected to an inlet through which the exhaust gas flows in the muffler51.

Catalyst Device and Catalyst Device Accommodating Portion

The straddle-type vehicle1includes two catalyst devices, that is, a first catalyst device71and a second catalyst device72that purify exhaust gas discharged from the exhaust port36of the engine31and flowing through the exhaust pipe60. Each of the first catalyst device71and the second catalyst device72is a three-way catalyst, and is formed by, for example, loading a catalyst on a monolith carrier having a honeycomb structure. The first catalyst device71has a columnar outer shape, and a diameter thereof is larger than a diameter of the first portion61of the exhaust pipe60and larger than a diameter of the third portion63of the exhaust pipe60. The second catalyst device72has a columnar outer shape, and a diameter thereof is larger than a diameter of the upstream side portion of the fourth portion64of the exhaust pipe60.

The first catalyst device71and the second catalyst device72are both provided in the intermediate portion of the exhaust pipe60. Specifically, as shown inFIGS.2and3, the first catalyst device71is provided in the second portion62of the exhaust pipe60. More specifically, the first catalyst device71is provided in a portion of the second portion62of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5. The first catalyst device71is disposed at a position higher than the lower end of the down frame5and lower than the exhaust port36of the engine31. The first catalyst device71is disposed above the under frame6. On the other hand, as shown inFIG.1, the second catalyst device72is provided in the downstream side portion of the fourth portion64of the exhaust pipe60. The first catalyst device71is a specific example of a “catalyst device” in the claims.

The second portion62of the exhaust pipe60is provided with the first catalyst device accommodating portion73that accommodates the first catalyst device71. As shown inFIGS.2and3, the first catalyst device accommodating portion73includes a cylindrical enlarged diameter portion74whose diameter increases from the upstream side toward the downstream side of the second portion62of the exhaust pipe60, a cylindrical large diameter portion75connected to a downstream side end portion of the enlarged diameter portion74, and a cylindrical reduced diameter portion76which is connected to a downstream side end portion of the large diameter portion75and whose diameter decreases from the upstream side toward the downstream side of the second portion62of the exhaust pipe60. In the present embodiment, the entire second portion62serves as the first catalyst device accommodating portion73. That is, the upstream side portion of the second portion62of the exhaust pipe60is the enlarged diameter portion74, the intermediate portion of the second portion62of the exhaust pipe60is the large diameter portion75, and the downstream side portion of the second portion62of the exhaust pipe60is the reduced diameter portion76. The first catalyst device accommodating portion73is a specific example of a “catalyst device accommodating portion” in the claims.

An upstream side end portion of the enlarged diameter portion74is connected to the downstream side end portion of the first portion61of the exhaust pipe60. The third portion63of the exhaust pipe60is connected to a downstream side end portion of the reduced diameter portion76. The first catalyst device71is disposed in the large diameter portion75such that an axis of the first catalyst device71coincides with an axis of the large diameter portion75.

A diameter of the large diameter portion75is constant from an upstream side end portion to the downstream side end portion thereof. The diameter of the large diameter portion75is larger than the diameter of the first catalyst device71. The diameter of the large diameter portion75is larger than the diameter of the first portion61of the exhaust pipe60and larger than the diameter of the third portion63of the exhaust pipe60. For example, the diameter of the large diameter portion75is set to a value slightly larger than the diameter of the first catalyst device71so that the first catalyst device71can be accommodated and fixed in the large diameter portion75. A diameter of the upstream side end portion of the enlarged diameter portion74is equal to the diameter of the first portion61of the exhaust pipe60, and a diameter of the downstream side end portion of the enlarged diameter portion74is equal to the diameter of the large diameter portion75. A diameter of an upstream side end portion of the reduced diameter portion76is equal to the diameter of the large diameter portion75, and a diameter of the downstream side end portion of the reduced diameter portion76is equal to the diameter of the third portion63of the exhaust pipe60.

The enlarged diameter portion74is increased in diameter and extends from a region in front of the crankcase32and to the lower front of the down frame5to a region in front of the crankcase32and to the right of the down frame5while being bent upward, rightward, and backward. That is, as shown inFIG.3, the upstream side end portion of the enlarged diameter portion74is located in front of the crankcase32and to the lower left front of the down frame5. Specifically, the upstream side end portion of the enlarged diameter portion74is located to the lower left of the lower end of the down frame5, and is located in front of the upper end side portion of the left under frame6in the front view of the straddle-type vehicle1. The enlarged diameter portion74is gradually increased in diameter while being gently curved so as to draw an arc. The enlarged diameter portion74passes through a front side of the upper end side portion of the right under frame6. The downstream side end portion of the enlarged diameter portion74is located in front of the crankcase32and to the lower right front of the down frame5.

The large diameter portion75linearly extends upward, rightward, and backward through a region in front of the crankcase32and to the right of the down frame5. The large diameter portion75and the first catalyst device71in the large diameter portion75are located substantially just to the right of the lower end portion of the down frame5. The large diameter portion75and the first catalyst device71in the large diameter portion75are located substantially directly below the right radiator42.

The reduced diameter portion76is decreased in diameter and extends from a region in front of the crankcase32and to the right of the down frame5toward a region to the right of the cylinder33or the cylinder head34while being bent backward so as to be close to the horizontal direction. The reduced diameter portion76is gradually decreased in diameter while being gently curved so as to draw an arc. As shown inFIG.2, a position of the downstream side end portion of the reduced diameter portion76in the up-down direction is substantially equal to the position of the boundary between the cylinder33and the cylinder head34, and a position of the downstream side end portion of the reduced diameter portion76in the front-back direction is substantially equal to the position of the front surface of the cylinder33. A position of the downstream side end portion of the reduced diameter portion76in the left-right direction is to the right (outer side in the left-right direction) of the right surface of the cylinder33and to the right of the right surface of the cylinder head34as shown inFIG.3, and is to the right of the right main frame4as shown inFIG.5.

When the first catalyst device accommodating portion73is viewed as a whole, the first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76(downstream side end portion of the first catalyst device accommodating portion73) is located above and behind the upstream side end portion of the enlarged diameter portion74(upstream side end portion of the first catalyst device accommodating portion73). The first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76is located above and to the right of the upstream side end portion of the enlarged diameter portion74. That is, as shown inFIG.2, the first catalyst device accommodating portion73extends from a position in front of the down frame5to a position behind the down frame5in the right side view of the straddle-type vehicle1. The first catalyst device accommodating portion73extends from the substantially intermediate position of the crankcase32to the position of the boundary between the cylinder33and the cylinder head34beyond the position of the boundary between the crankcase32and the cylinder33in the right side view of the straddle-type vehicle1. As shown inFIG.3, the first catalyst device accommodating portion73extends from a position to the left of the down frame5to a position to the right of the down frame5in the front view of the straddle-type vehicle1. As shown inFIG.5, the first catalyst device accommodating portion73extends along the front portion4A of the right main frame4through the outside of the front portion4A of the right main frame4in the top view of the straddle-type vehicle1.

In the present embodiment, the rightmost portion of the first catalyst device accommodating portion73is a right surface of an upstream side portion of the reduced diameter portion76. As can be seen fromFIGS.3and6, the position of the rightmost portion of the first catalyst device accommodating portion73is located to the left of the rightmost portion of the engine31(rightmost portion of the water pump37) and to the left of a right surface of the clutch cover38. In the present embodiment, the lowermost portion of the first catalyst device accommodating portion73is a lower surface of the intermediate portion of the enlarged diameter portion74. As can be seen fromFIG.2, a position of the lowermost portion of the first catalyst device accommodating portion73in the up-down direction is substantially equal to a position of the step44or a front end portion of the brake pedal45in the up-down direction.

The first catalyst device accommodating portion73is disposed below the right radiator42in a state of being inclined in the front-back direction such that the upstream side end portion of the enlarged diameter portion74is in front of a front surface of the right radiator42and the downstream side end portion of the reduced diameter portion76is behind a back surface of the right radiator42. The rightmost portion of the first catalyst device accommodating portion73is located to the left of a right surface of the right radiator42.

In a lower left portion ofFIG.8, a state in which the first catalyst device accommodating portion73is disassembled is shown. The first catalyst device accommodating portion73has a monaka structure, and is formed by coupling, for example, four metal plates77to80as shown in the lower left portion ofFIG.8. In the present embodiment, the enlarged diameter portion74is formed by welding the two press-formed metal plates77and78to each other, a structure in which the large diameter portion75and the reduced diameter portion76are integrated is formed by welding two press-formed metal plates79and80to each other, and the first catalyst device accommodating portion73is formed by welding the enlarged diameter portion74and the structure in which the large diameter portion75and the reduced diameter portion76are integrated to each other. The first catalyst device71is sandwiched between the two metal plates79and80. For example, the upstream side end portion of the enlarged diameter portion74of the first catalyst device accommodating portion73is welded to the downstream side end portion of the first portion61of the exhaust pipe60, and the downstream side end portion of the reduced diameter portion76of the first catalyst device accommodating portion73is welded to the upstream side end portion of the third portion63of the exhaust pipe60.

The second catalyst device accommodating portion85is provided at the downstream side portion of the fourth portion64of the exhaust pipe60. The second catalyst device accommodating portion85is formed in a cylindrical shape having a diameter larger than a diameter of the second catalyst device72and the diameter of the upstream side portion of the fourth portion64of the exhaust pipe60. The second catalyst device72is provided in the second catalyst device accommodating portion85.

In the exhaust pipe60, a first exhaust gas sensor91is provided upstream of the first catalyst device71, and a second exhaust gas sensor92is provided downstream of the first catalyst device71. The first exhaust gas sensor91is a sensor that detects a state of the exhaust gas inside a portion of the exhaust pipe60upstream of the first catalyst device71, and is, for example, an oxygen sensor. The second exhaust gas sensor92is a sensor that detects a state of exhaust gas inside a portion of the exhaust pipe60downstream of the first catalyst device71, and is, for example, an oxygen sensor. The straddle-type vehicle1performs fuel injection control and the like based on detection signals output from the first exhaust gas sensor91and the second exhaust gas sensor92, in order to increase the purification rate of the exhaust gas by the first catalyst device71. The first exhaust gas sensor91is a specific example of an “exhaust gas sensor” in the claims.

The first exhaust gas sensor91is provided at a portion of the exhaust pipe60passing through a region in front of the down frame5. Specifically, as shown inFIG.3, the first exhaust gas sensor91is provided at a downstream side portion of the first portion61of the exhaust pipe60, and protrudes upward, rightward, and backward from an upper surface of the downstream side portion of the first portion61. The first exhaust gas sensor91is disposed such that the entire first exhaust gas sensor91overlaps with the first catalyst device accommodating portion73in the side view of the straddle-type vehicle1. As shown inFIG.2, the first exhaust gas sensor91is completely hidden by the first catalyst device accommodating portion73in the right side view of the straddle-type vehicle1. The first exhaust gas sensor91is disposed such that the entire first exhaust gas sensor91overlaps with the first portion61of the exhaust pipe60in the side view of the straddle-type vehicle1. As shown inFIG.4, the first exhaust gas sensor91is completely hidden by the first portion61of the exhaust pipe60in the left side view of the straddle-type vehicle1. As shown inFIG.3, the first exhaust gas sensor91overlaps with the upper end side portion of the left under frame6in the front view of the straddle-type vehicle1.

The second exhaust gas sensor92is provided at the upstream side portion of the third portion63of the exhaust pipe60, and protrudes upward from an upper surface of the upstream side portion of the third portion63. The second exhaust gas sensor92is located to the right of the cylinder head34, and the entire second exhaust gas sensor92overlaps with the cylinder head34in the side view of the straddle-type vehicle1.

As described above, in the straddle-type vehicle1according to the embodiment of the present invention, the exhaust pipe60includes the first portion61extending downward from the exhaust port36of the engine31through the region in front of the engine31and to the left of the down frame5, the second portion62extending upward through the region in front of the engine31and to the right of the down frame5after extending from the downstream side end portion of the first portion61to the right of the down frame5through the region to the lower front of the down frame5, the third portion63extending backward from the downstream side end portion of the second portion62through the region to the right of the engine31, and the fourth portion64extending from the downstream side end portion of the third portion63and reaching the muffler51, and the first catalyst device71is disposed in the portion of the second portion62of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5. Accordingly, the first catalyst device71can be appropriately provided in a front portion of the exhaust pipe60.

That is, in a straddle-type vehicle in the related art having a structure in which an exhaust pipe passes through a lateral side of an engine, since a pipe length of a portion of the exhaust pipe from an exhaust port of the engine to the lateral side of the engine is short, there is a problem that it is difficult to provide a catalyst device in this portion. However, the exhaust pipe60of the straddle-type vehicle1according to the present embodiment includes the first portion61extending downward from the exhaust port36through the region in front of the engine31and to the left of the down frame5, and the second portion62extending upward through the region in front of the engine31and to the right of the down frame5after extending from the downstream side end portion of the first portion61to the right of the down frame5through the region to the lower front of the down frame5. With this configuration, it is possible to secure a sufficient pipe length for providing the first catalyst device71in a portion of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5, and it is possible to easily provide the first catalyst device71in this portion. In particular, the large-sized first catalyst device71having a diameter larger than the diameter of each of the first portion61and the third portion63of the exhaust pipe60and having high exhaust gas purification performance can be easily provided at the portion of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5.

More specifically, a path of the exhaust pipe60is a path from the left of the down frame5to the right of the down frame5through the lower front of the down frame5, whereby the direction of the second portion62of the exhaust pipe60at the lower right of the down frame5can be brought close to a vertically upward direction in the front view of the straddle-type vehicle1without increasing a curvature of the curve of the upstream side portion of the second portion62of the exhaust pipe60. Accordingly, the second portion62of the exhaust pipe60can be extended linearly for a long distance from the lower right of the down frame5to the front right of the cylinder33of the engine31, and the downstream side end portion of the second portion62of the exhaust pipe60can be suppressed from protruding rightward from the rightmost portion of the engine31. As a result, it is possible to provide the large diameter portion75extending linearly in a portion of the second portion62of the exhaust pipe60that extends linearly from the lower right of the down frame5to the front right of the cylinder33, to accommodate the large-sized first catalyst device71having a large diameter and a certain length in an axial direction in the large diameter portion75, and to dispose the first catalyst device accommodating portion73in which such a large-sized first catalyst device71is accommodated so as not to protrude from the rightmost portion of the engine31in the front view of the straddle-type vehicle1.

In a straddle-type vehicle in the related art having a structure in which an exhaust pipe passes through a lateral side of an engine, when a catalyst device having a diameter larger than a normal diameter of the exhaust pipe is provided in a portion of the exhaust pipe passing through the lateral side of the engine, a portion of the straddle-ride type vehicle between a right leg and a left leg of a rider seated on a seat becomes wide, and thus there is a problem that a riding posture of the rider is worsened. Even when a catalyst device having a diameter smaller than the normal diameter of the exhaust pipe is provided in the portion of the exhaust pipe passing through the lateral side of the engine, it is necessary to increase a distance between the exhaust pipe and a shield plate in order to protect the legs of the rider from heat from the exhaust pipe, and thus there is a problem that the riding posture of the rider may be worsened. However, since the first catalyst device71is provided in the portion of the second portion62of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5in the straddle-type vehicle1according to the present embodiment, such a problem does not occur. That is, according to the straddle-type vehicle1according to the present embodiment, it is possible to suppress the riding posture of the rider from worsening due to the provision of the first catalyst device71inside the front portion of the exhaust pipe60.

As described above, in the straddle-type vehicle described in JP2008-64068A (Patent Literature 1), a catalyst device having a diameter larger than a normal diameter of an exhaust pipe is provided in a portion of the exhaust pipe extending backward through a center side of the straddle-type vehicle in the left-right direction with respect to a cylinder of an engine or a cylinder head, whereby it is necessary to expand a space surrounded by a main frame, a rear cushion, the cylinder of the engine, and the like, and as a result, there is a problem that the straddle-type vehicle may be increased in size. However, since the first catalyst device71of the straddle-type vehicle1according to the present embodiment is disposed in the portion of the second portion62of the exhaust pipe60that is located in front of the engine31and to the right of the down frame5, such a problem does not occur.

In the straddle-type vehicle1according to the present embodiment, the exhaust port36of the engine31is disposed in the front portion of the cylinder head34, and is opened forward while being inclined leftward. Accordingly, the exhaust pipe60can be easily connected to the exhaust port36without providing a locally bent portion with a large curvature at an upstream end side portion (first portion61) of the exhaust pipe60. The exhaust pipe60can extend from the exhaust port36to a position to the lower front of the down frame5without providing a complicated bent portion such as an S-shaped or crank-shaped bent portion at the upstream end side portion (first portion61) of the exhaust pipe60. When the exhaust port36of the engine31is opened forward without being inclined leftward or rightward, and the down frame5passes ahead in the opening direction of the exhaust port36, it is necessary to secure an interval for disposing the upstream end side portion of the exhaust pipe60between the front portion of the engine31and the down frame5. However, in the present embodiment, since the exhaust port36of the engine31is opened forward while being inclined leftward, the opening direction of the exhaust port36can be deviated from the down frame5, and it is possible to dispose the upstream end side portion of the exhaust pipe60without securing such an interval. Therefore, the interval between the front portion of the engine31and the down frame5can be reduced, and the size of the straddle-type vehicle1can be reduced. In addition, since the exhaust port36of the engine31is opened forward while being inclined leftward, the first portion61of the exhaust pipe60can be suppressed from protruding leftward from the leftmost portion of the engine31.

In the straddle-type vehicle1according to the present embodiment, the first catalyst device71is disposed, in front of the engine31and to the right of the down frame5, at a position higher than the lower end of the down frame5and lower than the exhaust port36of the engine31. Since the first catalyst device71is disposed at a position higher than the lower end of the down frame5, the lowermost surface of the second portion62of the exhaust pipe60can be suppressed from being lowered. Therefore, even when the front wheel16moves in a direction approaching the front fender17caused by contraction of the front fork15due to the front wheel16moving over a large stone on the irregular ground or a step on the road, the front wheel16can be suppressed from coming into contact with the second portion62of the exhaust pipe60. In addition, since the first catalyst device71is disposed at a position lower than the exhaust port36of the engine31, the uppermost surface of the second portion62of the exhaust pipe60can be suppressed from becoming high, and the second portion62of the exhaust pipe60can be sufficiently separated from each portion of the body of the rider seated on the seat47.

In the straddle-type vehicle1according to the present embodiment, the second portion62of the exhaust pipe60is provided with the first catalyst device accommodating portion73including the enlarged diameter portion74, the large diameter portion75, and the reduced diameter portion76. Accordingly, the large-sized first catalyst device71having a diameter larger than the diameter of each of the first portion61and the third portion63of the exhaust pipe60and having high exhaust gas purification performance can be provided at the second portion62of the exhaust pipe60.

In the straddle-type vehicle1according to the present embodiment, the first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76is located above and behind the upstream side end portion of the enlarged diameter portion74. Accordingly, the curvature of the reduced diameter portion76can be reduced. The first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76is located above and to the right of the upstream side end portion of the enlarged diameter portion74. Accordingly, the curvature of the enlarged diameter portion74can be reduced. The first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76is located above, behind, and to the right of the upstream side end portion of the enlarged diameter portion74, whereby the first catalyst device accommodating portion73capable of accommodating the large-sized first catalyst device71can be disposed in a region from the lower front of the down frame5to the right of the down frame5without forming a locally bent portion with a large curvature at the first catalyst device accommodating portion73. By inclining the first catalyst device accommodating portion73in this manner, it is possible to suppress an increase in the size of the straddle-type vehicle1while providing the first catalyst device accommodating portion73in front of the engine31and to the right of the down frame5.

In the straddle-type vehicle1according to the present embodiment, the enlarged diameter portion74is increased in diameter and extends from a region in front of the crankcase32and to the lower front of the down frame5toward a region in front of the crankcase32and to the right of the down frame5while being bent upward and backward. With this configuration, the downstream side end portion of the first portion61of the exhaust pipe60that is located to the lower left of the lower end of the down frame5and the large diameter portion75of the first catalyst device accommodating portion73can be easily connected via the enlarged diameter portion74, the large diameter portion75being disposed at a position to the right of the down frame5, higher than the lower end of the down frame5, and lower than the exhaust port36of the engine31, and having a diameter larger than that of the downstream side end portion of the first portion61of the exhaust pipe60. The first catalyst device accommodating portion73has a monaka structure, whereby the enlarged diameter portion74that is bent and increased in diameter can be easily manufactured.

In the straddle-type vehicle1according to the present embodiment, the reduced diameter portion76is decreased in diameter and extends from a region in front of the crankcase32and to the right of the down frame5toward a region to the right of the boundary between the cylinder33and the cylinder head34while being bent backward so as to be close to the horizontal direction. With this configuration, the large diameter portion75of the first catalyst device accommodating portion73and the upstream side end portion of the third portion63of the exhaust pipe60that is located to the right of the boundary between the cylinder33and the cylinder head34can be easily connected to each other via the reduced diameter portion76, the large diameter portion75being disposed at a position to the right of the down frame5, higher than the lower end of the down frame5, and lower than the exhaust port36of the engine31, and having a diameter larger than that of the upstream side end portion of the third portion63of the exhaust pipe60. The first catalyst device accommodating portion73has a monaka structure, whereby the reduced diameter portion76that is bent and decreased in diameter can be easily manufactured.

In the straddle-type vehicle1according to the present embodiment, the first catalyst device accommodating portion73is disposed below the right radiator42in a state of being inclined in the front-back direction such that the upstream side end portion of the enlarged diameter portion74is in front of the front surface of the right radiator42and the downstream side end portion of the reduced diameter portion76is behind the back surface of the right radiator42. Accordingly, a radiator having a large size in the up-down direction and therefore having a large core area can be adopted as the right radiator42. Therefore, the cooling performance of the radiator42on the cooling water can be enhanced. That is, when the first catalyst device accommodating portion73is disposed below the right radiator42so as to stand upright in the vertical direction, a radiator having a small size in the up-down direction and therefore having a small core area can be adopted as the right radiator42in order to avoid contact between the downstream side end portion of the reduced diameter portion76provided at an upper portion of the first catalyst device accommodating portion73and a lower end portion of the right radiator42. On the other hand, in the straddle-type vehicle1according to the present embodiment, since the first catalyst device accommodating portion73is inclined such that the downstream side end portion of the reduced diameter portion76is located behind the back surface of the right radiator42, even when the lower end portion of the right radiator42is located below the reduced diameter portion76of the first catalyst device accommodating portion73, contact between the lower end portion of the right radiator42and the first catalyst device accommodating portion73can be avoided (for example, the lower end portion of the right radiator42can extend downward to a position immediately before the large diameter portion75of the inclined first catalyst device accommodating portion73). Therefore, a radiator having a large size in the up-down direction and therefore having a large core area can be adopted as the right radiator42. When a radiator having a small size in the up-down direction is adopted as the right radiator42, the right radiator42can be separated from the first catalyst device accommodating portion73, and it is difficult to transmit the radiant heat from the first catalyst device accommodating portion73to the right radiator42.

In the straddle-type vehicle1according to the present embodiment, the first exhaust gas sensor91is provided at a portion of the exhaust pipe60passing through the region in front of the down frame5, and is disposed such that the entire first exhaust gas sensor91overlaps with the first catalyst device accommodating portion73in the side view of the straddle-type vehicle1. Since the first exhaust gas sensor91is provided at the portion of the exhaust pipe60passing through the region in front of the down frame5, the first exhaust gas sensor91can be easily attached to and detached from the exhaust pipe60. Since the first exhaust gas sensor91is disposed such that the entire first exhaust gas sensor91overlaps with the first catalyst device accommodating portion73in the side view of the straddle-type vehicle1, the first catalyst device accommodating portion73can be made to function as a partition wall that suppresses flying stones flying from the right from hitting the first exhaust gas sensor91, and the first exhaust gas sensor91can be protected by the first catalyst device accommodating portion73. In the straddle-type vehicle1according to the present embodiment, the first exhaust gas sensor91is disposed such that the entire first exhaust gas sensor91overlaps with the first portion61of the exhaust pipe60in the side view of the straddle-type vehicle1. Accordingly, the first portion61of the exhaust pipe60can be made to function as a partition wall that suppresses flying stones flying from the left from hitting the first exhaust gas sensor91, and the first exhaust gas sensor91can be protected by the first portion61of the exhaust pipe60.

In the straddle-type vehicle1according to the present embodiment, since the first catalyst device accommodating portion73is located to the left of the rightmost portion of the engine31and the first portion61of the exhaust pipe60is located to the right of the leftmost portion of the engine31, it is possible to suppress an increase in the size of the straddle-type vehicle1.

In the above embodiment, the second portion62of the exhaust pipe60(enlarged diameter portion74of the first catalyst device accommodating portion73) extends from the downstream side end portion of the first portion61of the exhaust pipe60to the right of the down frame5through the region to the lower front of the down frame5. However, when the present invention is applied to a straddle-type vehicle having a long down frame5, the second portion62of the exhaust pipe60(enlarged diameter portion74of the first catalyst device accommodating portion73) may extend from the downstream side end portion of the first portion61of the exhaust pipe60to the right of the down frame5through the region in front of the down frame5.

In the above embodiment, the entire second portion62of the exhaust pipe60serves as the first catalyst device accommodating portion73. However, the present invention is not limited thereto, and a portion of the second portion62of the exhaust pipe60may serve as the first catalyst device accommodating portion73. For example, the first catalyst device accommodating portion73may be provided such that the upstream side end portion of the enlarged diameter portion74of the first catalyst device accommodating portion73is disposed at a portion of the second portion62of the exhaust pipe60that is located to the right front or the right lower front of the lower end portion of the down frame5.

In the above embodiment, the first catalyst device71is disposed at a position higher than the lower end of the down frame5. However, when the present invention is applied to a straddle-type vehicle having a short down frame5, the first catalyst device71may be disposed such that the lower end of the first catalyst device71is lower than the lower end of the down frame5.

The present invention can also be applied to a straddle-type vehicle that does not include the second catalyst device72. The present invention can also be applied to a straddle-type vehicle that neither includes the first exhaust gas sensor91nor the second exhaust gas sensor92. The present invention can also be applied to a straddle-type vehicle that does not include the left or right radiator42.

In the straddle-type vehicle according to the present invention, an exhaust port of an engine may be inclined rightward and opened forward, the exhaust pipe may include a first portion extending downward from the exhaust port of the engine through a region in front of the engine and to the right of the down frame, a second portion extending upward through a region in front of the engine and to the left of the down frame after extending from a downstream side end portion of the first portion to the left of the down frame through a region in front of or to the lower front of the down frame, a third portion extending backward from a downstream side end portion of the second portion through a region to the left of the engine, and a fourth portion extending from a downstream side end portion of the third portion to reach a muffler, and the catalyst device may be disposed in a portion of the second portion of the exhaust pipe that is located in front of the engine and to the left of the down frame.

In the above embodiment, the first catalyst device71having a diameter larger than that of each of the first portion61and the third portion63of the exhaust pipe60is provided at the second portion62of the exhaust pipe60. However, the present invention is not limited thereto, and a catalyst device having a diameter equal to that of the first portion61or the third portion63of the exhaust pipe60, or a catalyst device having a diameter smaller than that of each of the first portion61and the third portion63of the exhaust pipe60may be provided at the second portion62of the exhaust pipe60. When a catalyst device having a diameter smaller than that of each of the first portion61and the third portion63of the exhaust pipe60is provided at the second portion62of the exhaust pipe60, the diameters of the first portion61, the second portion62, and the third portion63of the exhaust pipe60can be made equal to one another, and in this case, the first catalyst device accommodating portion73including the enlarged diameter portion74, the large diameter portion75, and the reduced diameter portion76may not be provided at the second portion62of the exhaust pipe60.

In the above embodiment, the straddle-type vehicle1in which the third portion63of the exhaust pipe60passes through a right side of the boundary between the cylinder33and the cylinder head34of the engine31is taken as an example of a straddle-type vehicle having a structure in which an exhaust pipe passes through a lateral side of an engine without passing below the engine, but the present invention is not limited thereto. The present invention can also be applied to a straddle-type vehicle in which an exhaust pipe passes a lateral side of an upper portion of a crankcase of an engine, a lateral side of a cylinder, or a lateral side of a cylinder head.

The present invention can be applied not only to a straddle-type vehicle for off-road racing but also to a straddle-type vehicle designed to be suitable for both on-road traveling and off-road traveling. When there is a straddle-type vehicle designed to be exclusively suitable for on-road traveling and having a structure in which an exhaust pipe passes a lateral side of an engine, the present invention can also be applied to such a straddle-type vehicle.

The present invention can be appropriately changed without departing from the gist or concept of the invention which can be read from the claims and the entire description, and a straddle-type vehicle accompanied with such a change is also included in the technical concept of the present invention.