JP7263718B2 - Exhaust system and vehicle - Google Patents

Description

The present disclosure relates to exhaust systems and vehicles.

Generally, in a vehicle such as a motorcycle, exhaust gas is purified by a catalytic device, but sufficient exhaust gas purification performance cannot be obtained until the catalytic device reaches an activation temperature. For this reason, it is known to bring the catalytic device closer to the exhaust port so that the catalytic device is quickly warmed up by high-temperature exhaust gas (see, for example, Patent Document 1). In this exhaust system, an exhaust pipe extends from a pair of exhaust ports of an engine, a primary catalyst device is provided in the middle of one of the exhaust pipes, and a secondary catalyst device is provided at the junction of the pair of exhaust pipes. The primary catalyst is brought closer to the exhaust port and activated early, and the secondary catalyst is activated early by the exhaust gas heated by the catalytic reaction.

Japanese Unexamined Patent Application Publication No. 2014-137001

By the way, in the exhaust system described in Patent Document 1, the catalyst device in the middle of one of the exhaust pipes is mainly used for heating the exhaust gas, but it is possible to activate the catalyst device more quickly and improve the purification performance of the exhaust gas. Needs improvement. In this case, it is conceivable to provide a catalyst device for each of the pair of exhaust pipes, but it is difficult to realize in consideration of layout flexibility and cost.

The present disclosure has been made in view of this point, and it is an object of the present disclosure to provide an exhaust system and a vehicle that can achieve the effect of early activation of a catalyst device without increasing costs while ensuring a degree of freedom in layout. aim.

An exhaust system according to one aspect of the present disclosure is an exhaust system in which an engine is mounted on an airframe and purifies exhaust gas discharged from a plurality of exhaust ports of the engine, wherein the exhaust gas flows in from the plurality of exhaust ports. a plurality of upstream exhaust pipes, a common catalyst device into which exhaust gas flows from the outlets of the plurality of upstream exhaust pipes, and a downstream exhaust pipe to which the exhaust gas that has passed through the catalyst device is sent to the outside. wherein the catalyst device is positioned in front of the engine and is installed on one side in the width direction of the fuselage with respect to a center line extending in the vertical direction of the fuselage, and the plurality of upstream exhaust pipes are arranged on one side in the width direction of the fuselage. and an upstream exhaust pipe positioned on the one side and an upstream exhaust pipe positioned on the other side, wherein the upstream exhaust pipe positioned on the one side is formed shorter than the upstream exhaust pipe positioned on the other side , and The plurality of upstream exhaust pipes are a pair of upstream exhaust pipes into which exhaust gas flows from a pair of exhaust ports, and one of the pair of upstream exhaust pipes is an upstream exhaust pipe located on the one side, The other of the pair of upstream exhaust pipes is an upstream exhaust pipe positioned on the other side, and a main catalytic device into which exhaust gas flows from an outlet of the downstream exhaust pipe, wherein the downstream exhaust pipe is an airframe. A pair of downstream exhaust pipes consisting of a downstream exhaust pipe positioned on one side in the width direction and a downstream exhaust pipe positioned on the other side, wherein the downstream exhaust pipe positioned on the one side extends to the other side. It is characterized by being formed longer than the located downstream exhaust pipe .

According to the exhaust system of one aspect of the present disclosure, the catalyst device common to the plurality of upstream exhaust pipes is brought closer to some of the exhaust ports, and at least one upstream exhaust pipe is formed short. High-temperature exhaust gas flows into the catalyst device through the at least one upstream exhaust pipe, the catalyst device is warmed up in a short time, and early activation of the catalyst is achieved. Purification performance for the exhaust gas from the upstream side exhaust pipe having a long pipe length is also improved. In addition, cost can be reduced by connecting multiple upstream exhaust pipes to a single catalyst device, and by adjusting the length of multiple upstream exhaust pipes, the layout freedom of the catalyst device relative to the engine is increased. can be ensured.

FIG. 2 is a perspective view of the periphery of the engine according to the embodiment; It is a perspective view around the engine of a comparative example. 1 is a front view of an exhaust device according to an embodiment; FIG. 1 is a side view of an exhaust system according to an embodiment; FIG. FIG. 3 is an explanatory diagram of an installation layout of the exhaust device of the present embodiment; It is a perspective view of the exhaust device of a modification. FIG. 11 is a perspective view of an exhaust device of another modified example;

Hereinafter, this embodiment will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view of the periphery of an engine according to this embodiment. FIG. 2 is a perspective view of the periphery of the engine of the comparative example. In the following description, a configuration in which the technology of the present disclosure is applied to a motorcycle will be described, but it can be applied to other vehicles in which the catalyst device is installed. In the following figures, an arrow FR indicates the front of the vehicle, an arrow RE indicates the rear of the vehicle, L indicates the left side of the vehicle, and R indicates the right side of the vehicle.

As shown in FIG. 1, the engine 1 is, for example, a parallel two-cylinder engine, and is constructed by assembling a cylinder block 11, a cylinder head 12, and a head cover (not shown) on a crankcase 10. As shown in FIG. Drive components such as a crankshaft 14 are housed in the crankcase 10 , and pistons (not shown) connected to the crankshaft 14 are housed in the cylinder block 11 . The cylinder head 12 accommodates various devices such as a valve system device, a fuel injection device, and an ignition device. is formed.

Also, the engine 1 is mounted inside the vehicle body frame 21 with a predetermined gap from the front wheels 19 . The vehicle body frame 21 is a so-called cradle frame, which branches off from the middle of the down tube 22 into a pair of left and right lower tubes 23 and extends around the engine 1 below. An oil filter 16 is installed between a pair of left and right lower tubes 23 on the front surface of the crankcase 10 . An exhaust pipe extends from the front surface of the cylinder head 12 so as to avoid the down tube 22 and the lower tube 23 , and an exhaust device 30 for purifying the exhaust gas discharged from the exhaust port 15 is provided.

In the engine 1 configured in this way, the air-fuel mixture is sent into the combustion chamber through the intake port and ignited, so that the piston in the crankcase 10 is pushed down at once, and the downward movement of the piston moves to the crankshaft 14. transmitted. Exhaust gas is discharged from the exhaust port 15, and air pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in the exhaust gas are purified by the exhaust device 30. be. In the exhaust system 30, exhaust gas is purified by a primary catalyst device (catalyst device) 31 on the upstream side of the exhaust pipe, and exhaust gas is further purified by a secondary catalyst device (main catalyst device) 36 on the downstream side of the exhaust pipe. .

Immediately after starting the engine 70 shown in the comparative example of FIG. 2, the catalyst materials of the primary catalyst device 71 and the secondary catalyst device 72 are at a low temperature, and the performance of purifying air pollutants cannot be sufficiently exhibited. For this reason, in the engine 70 of the comparative example, a pair of left and right primary catalyst devices 71 are installed near a pair of exhaust ports 73, and each primary catalyst device 71 is activated for a short time by high-temperature exhaust gas discharged from each exhaust port 73. It is warmed up in the air and early activation is achieved. However, considering the cost and workability during maintenance, it is not realistic to install the pair of primary catalyst devices 71 in the narrow space between the front wheel 74 and the vehicle body frame 75 .

It is also conceivable to install a common primary catalyst device for the pair of exhaust ports 73, but if the primary catalyst device is simply installed in the center of the engine 70, the clearance with the oil filter 76, the front wheels 74, the radiator 77, etc. can't take enough. Therefore, as shown in FIG. 1, in the present embodiment, the pipe length of the exhaust pipe from each exhaust port 15 to the common primary catalyst device 31 is intentionally made different. Layout freedom is ensured. In addition, the primary catalyst device 31 is warmed up in a short time by the high-temperature exhaust gas from the short exhaust pipe, and the purification performance of the exhaust gas from the long exhaust pipe is also improved.

The exhaust system will be described below with reference to FIGS. 3 and 4. FIG. FIG. 3 is a front view of the exhaust system of this embodiment. FIG. 4 is a side view of the exhaust system of this embodiment. Although an exhaust system installed in a two-cylinder engine is illustrated here, the exhaust system of the present disclosure can also be applied to a multi-cylinder engine of two or more cylinders.

As shown in FIGS. 3 and 4, the exhaust system 30 is a pair of exhaust ports 15L of the engine 1 with a small primary catalyst device 31 functioning as a starter catalyst and a large secondary catalyst device 36 functioning as a main catalyst. , 15R to purify the exhaust gas. The exhaust ports 15L, 15R to the primary catalyst device 31 are connected by a pair of upstream exhaust pipes 41L, 41R, and exhaust gas is sent to the primary catalyst device 31 through the respective upstream exhaust pipes 41L, 41R. The primary catalyst device 31 to the secondary catalyst device 36 are connected by a pair of downstream side exhaust pipes 42L and 42R, and the exhaust gas that has passed through the primary catalyst device 31 is sent to the secondary catalyst device 36 through the respective downstream side exhaust pipes 42L and 42R. Sent.

The primary catalyst device 31 is connected to the upstream side exhaust pipes 41L and 41R in a substantially vertical posture, and is provided with a conical upper chamber 33 and a conical lower chamber 34 above and below a cylindrical portion 32 containing a catalyst. there is The upper chamber 33 is connected to the outlets of the upstream exhaust pipes 41L and 41R, and the lower chamber 34 is connected to the inlets of the downstream exhaust pipes 42L and 42R. The upper chamber 33 is a confluence point of the upstream side exhaust pipes 41L and 41R, and the upper chamber 33 mixes the exhaust gases flowing from the upstream side exhaust pipes 41L and 41R. The lower chamber 34 serves as a branching point for the downstream side exhaust pipes 42L and 42R, and the exhaust gas that has passed through the catalyst is branched to the downstream side exhaust pipes 42L and 42R.

The catalyst in the tubular portion 32 is a honeycomb or grid-like partition plate with a catalytic substance adhered to the surface thereof. Contaminants are purified by reacting with oxygen. The upper chamber 33 is provided with an oxygen sensor 35 as a gas sensor for detecting the oxygen concentration in the exhaust gas. The single oxygen sensor 35 detects the average oxygen concentration in the exhaust gas flowing from the upstream side exhaust pipes 41L and 41R, and the cost is reduced compared to a configuration in which a catalytic device and an oxygen sensor 35 are provided for each exhaust pipe. be. The detection result of the oxygen sensor is used for feedback control of the fuel injection amount so as to approach the stoichiometric air-fuel ratio.

The secondary catalyst device 36 is connected to the downstream side exhaust pipes 42L and 42R in a substantially lateral posture, and is provided with a conical front chamber 38 and a conical rear chamber 39 in front of and behind a tubular portion 37 containing the catalyst. ing. The outlets of the downstream side exhaust pipes 42L and 42R are connected to the front chamber 38, and the inlet of the collective exhaust pipe 43 is connected to the rear chamber 39. The front chamber 38 is a confluence point of the downstream side exhaust pipes 42L, 42R, and the front chamber 38 mixes the exhaust gases flowing from the downstream side exhaust pipes 42L, 42R. In addition, in the cylindrical portion 37 of the secondary catalyst device 36, a catalyst for purifying air pollutants having the same structure as the primary catalyst device 31 is provided.

The upstream exhaust pipe 41L extends forward from one of the exhaust ports 15L, bends downward in front of the primary catalyst device 31, and is connected to the upper chamber 33. As shown in FIG. The upstream side exhaust pipe 41R extends forward from the other exhaust port 15R, then extends leftward (horizontal direction) toward the primary catalyst device 31, and bends downward before the primary catalyst device 31 to open the upper chamber. 33 is connected. Thus, the upstream side exhaust pipe 41L is formed shorter than the upstream side exhaust pipe 41R, and the primary catalyst device 31 connected to the upstream side exhaust pipes 41L and 41R is arranged in the vehicle width direction with respect to the center line C extending in the vertical direction of the vehicle. is located on one side (left side).

In addition, since the length of the upstream exhaust pipe 41L is short, high-temperature exhaust gas flows into the upper chamber 33 from the exhaust port 15L, and the primary catalyst device 31 is warmed up in a short time, and the exhaust gas from the exhaust port 15L is exhausted. Purification performance is improved. In this case, the length of the upstream exhaust pipe 41R is long and the temperature of the exhaust gas drops. Purification performance of exhaust gas is also improved. Early activation of the primary catalytic device 31 is realized by deliberately providing a difference in the pipe lengths of the upstream side exhaust pipes 41L and 41R.

After extending downward from the lower chamber 34 of the primary catalyst device 31, the downstream exhaust pipe 42L extends obliquely rearward to the right toward the secondary catalyst device 36 and bends rearward in front of the secondary catalyst device 36. It is connected to the front chamber 38 . The downstream exhaust pipe 42R extends obliquely downward to the right from the lower chamber 34 of the primary catalyst device 31, then extends obliquely rearward to the right toward the secondary catalyst device 36, and extends rearward in front of the secondary catalyst device 36. It is bent and connected to the front chamber 38 . The downstream exhaust pipe 42L is formed longer than the downstream exhaust pipe 42R, and the secondary catalyst device 36 connected to the downstream exhaust pipes 42L and 42R is arranged on the other side (right side) of the center line C in the vehicle width direction. It is

In the primary catalyst device 31, exhaust gas is guided from the upstream side exhaust pipe 41L to the downstream side exhaust pipe 42L by the pores of the catalyst, and exhaust gas is guided from the upstream side exhaust pipe 41R to the downstream side exhaust pipe 42R. The downstream exhaust pipe 42L corresponds to the upstream exhaust pipe 41L, and these two exhaust pipes function as the left exhaust pipe. The downstream exhaust pipe 42R corresponds to the upstream exhaust pipe 41R, and these two exhaust pipes function as the right exhaust pipe. Therefore, the difference in pipe length between the upstream side exhaust pipes 41L and 41R is canceled by the difference in pipe length between the downstream side exhaust pipes 42L and 42R. well kept.

The installation layout of the exhaust device will be described below with reference to FIG. FIG. 5 is an explanatory diagram of an installation layout of the exhaust system according to the present embodiment. FIG. 6 is a perspective view of a modified exhaust device. FIG. 7 is a perspective view of an exhaust device of another modification.

As shown in FIG. 5, the primary catalyst device 31 is positioned on the left side of the center line C of the vehicle body on the front surface of the engine 1 . The upstream exhaust pipe 41</b>L extends from the left exhaust port 15</b>L of the down tube 22 and is connected to the primary catalyst device 31 . At this time, a portion of the primary catalyst device 31 is contained within a predetermined range A from the exhaust port 15L connected to the inlet of the upstream side exhaust pipe 41L to the center line C of the vehicle body. Therefore, since the upstream side exhaust pipe 41L extends substantially downward when viewed from the front, the length of the pipe from the exhaust port 15L to the primary catalyst device 31 is shortened, and the primary catalyst device 31 is warmed up in a short period of time. It is being activated.

The upstream exhaust pipe 41</b>R extends from the exhaust port 15</b>R on the right side of the down tube 22 and is connected to the primary catalyst device 31 across the front of the down tube 22 . At this time, since the upstream exhaust pipe 41R extends from the right side of the vehicle body and the primary catalyst device 31 is located on the left side of the vehicle body, the pipe length from the exhaust port 15R to the primary catalyst device 31 becomes long. However, the primary catalyst device 31 functions as a small starter catalyst, and can be warmed up in a short time only with the high-temperature exhaust gas from the upstream side exhaust pipe 41L. Lowering the temperature of the exhaust gas does not significantly affect the early activation of the catalyst.

The upstream side exhaust pipe 41L is formed shorter than the upstream side exhaust pipe 41R, and the primary catalyst device 31 is shifted to the left side of the vehicle body, so that the down tube 22, the oil filter 16, the front wheel 19 (see FIG. 1), etc. A clearance is secured between the member positioned at and the primary catalyst device 31 . Therefore, it becomes easier to access the members located on the center line C of the vehicle body, and for example, the maintainability of the oil filter 16 can be improved. Although the primary catalyst device 31 is positioned in front of the lower tube 23L, since the front wheel 19 is removed from the front of the lower tube 23L, the work space between the front wheel 19 and the engine 1 is not greatly narrowed by the primary catalyst device 31. .

Further, the upstream exhaust pipe 41L is slightly bent downward near the outlet, but mainly extends substantially forward from the front surface of the engine 1. As shown in FIG. Although the upstream side exhaust pipe 41R also bends slightly downward in the vicinity of the outlet, it mainly extends from the front surface of the engine 1 in a substantially lateral direction. Therefore, since the primary catalyst device 31 is positioned at a high position, collision with obstacles on the road can be avoided, and a decrease in the catalyst temperature of the primary catalyst device 31 due to flooded roads or water splashing can be suppressed. In addition, since the primary catalyst device 31 is brought closer to the radiator 18 (see FIG. 1) in the vertical direction, the catalyst temperature can be raised by the heat around the radiator 18 .

The primary catalyst device 31 to the secondary catalyst device 36 on the lower side of the engine 1 are connected by two downstream side exhaust pipes 42L and 42R, and output performance is required by the downstream side exhaust pipes 42L and 42R. The pipe length and cross-sectional area are secured. At this time, the downstream exhaust pipe 42L is formed longer than the downstream exhaust pipe 42R by the amount that the upstream exhaust pipe 41L is shorter than the upstream exhaust pipe 41R, and the output characteristics of the left and right exhaust pipes are aligned. . Further, by adjusting the pipe lengths of the downstream side exhaust pipes 42L and 42R, it is possible to adopt a known layout for the secondary catalyst device 36, and reduce costs by reducing design changes.

Since the oxygen sensor 35 is installed in the upper chamber 33 of the primary catalyst device 31 where the upstream exhaust pipes 41L and 41R join, the single oxygen sensor 35 detects the exhaust gas from the upstream exhaust pipes 41L and 41R. of average oxygen concentration can be detected. Further, an oxygen sensor may be provided in the lower chamber 34 of the primary catalyst device 31 or the front chamber 38 of the secondary catalyst device 36 to detect deterioration. Thus, by arranging the small-sized catalyst device at the optimum position on the front surface of the engine 1, the target purification performance can be realized with the minimum catalyst device and oxygen sensor 35. FIG.

In the present embodiment, the upstream exhaust pipe 41L is shorter than the upstream exhaust pipe 41R and the primary catalyst device 31 is arranged on the left side of the vehicle body, but the configuration is not limited to this. For example, like the exhaust system 50 shown in the modified example of FIG. may be shortened and the primary catalyst device 51 may be arranged on the right side of the vehicle body. Even with such a modified exhaust system 50, the primary catalyst device 51 and the exhaust port 54R can be brought closer to each other by the upstream side exhaust pipe 52R, and the same effects as those of the exhaust system 30 of the present embodiment can be obtained. It is possible.

Further, in the present embodiment, the primary catalyst device 31 and the secondary catalyst device 36 are connected by the two downstream exhaust pipes 42L and 42R, but the configuration is not limited to this. For example, as in the exhaust system 60 shown in the modification of FIG. As a result, the number of parts can be reduced, the cost can be reduced, and the weight can be reduced. Further, even in the exhaust device 60 of the modified example, by making the pipe lengths of the upstream side exhaust pipes 63L and 63R different, it is possible to obtain the same effect as the exhaust device 30 of the present embodiment. is.

As described above, according to the present embodiment, the primary catalyst device 31 is brought closer to the exhaust port 15L, and the upstream side exhaust pipe 41L is formed short. High-temperature exhaust gas flows into the primary catalyst device 31 through the upstream side exhaust pipe 41L, and the primary catalyst device 31 is warmed up in a short time, realizing early activation of the catalyst. In addition, purification performance for the exhaust gas from the upstream side exhaust pipe 41R having a long pipe length is also improved. In addition, since the upstream exhaust pipes 41L and 41R are connected to the single primary catalyst device 31, the cost can be reduced. The degree of freedom in layout of the catalyst device 31 can be ensured.

In this embodiment, the exhaust port and the primary catalyst device are connected by a pair of upstream exhaust pipes, but the configuration is not limited to this. The exhaust port and the primary catalyst device may be connected by three or more upstream exhaust pipes.

Further, in the present embodiment, the primary catalyst device and the secondary catalyst device are connected by a pair of downstream exhaust pipes, but the present invention is not limited to this structure. The primary catalyst device and the secondary catalyst device may be connected by three or more downstream exhaust pipes.

Further, in the present embodiment, the exhaust system is configured to include the primary catalyst device and the secondary catalyst device, but the configuration is not limited to this. The exhaust system may be provided with at least one catalyst device into which exhaust gas flows from outlets of a plurality of upstream exhaust pipes.

Moreover, in the present embodiment, an exhaust system for an engine mounted on a vehicle body is exemplified, but the configuration is not limited to this. The exhaust system may be an exhaust system of an engine mounted on a body other than the vehicle body.

Moreover, in the present embodiment, an oxygen sensor is exemplified as a gas sensor, but the configuration is not limited to this. The gas sensor may be any sensor that can detect the average characteristics of the exhaust gas that has flowed in from the plurality of upstream exhaust pipes, and may be, for example, an exhaust temperature sensor that detects the temperature of the exhaust gas.

Although the present embodiment has been described, other embodiments may be obtained by combining the above-described embodiments and modifications in whole or in part.

Also, the technology of the present disclosure is not limited to the above-described embodiments, and may be variously changed, replaced, and modified without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in another way by advancement of technology or another derived technology, the method may be used for implementation. Therefore, the claims cover all implementations that may fall within the scope of the technical concept.

Also, in the present embodiment, a configuration in which the technology of the present disclosure is applied to a four-wheeled motor vehicle has been described, but the present invention is not limited to this configuration. Other vehicles in which the catalytic device is installed, such as motorcycles and buggy-type three-wheeled vehicles, can also be appropriately applied to special equipment such as personal watercraft, lawn mowers, and outboard motors.

Characteristic points in this embodiment are summarized below.
The exhaust system described in the above embodiment is an exhaust system in which an engine is mounted on an airframe and purifies exhaust gas discharged from a plurality of exhaust ports of the engine, and the exhaust gas flows in from the plurality of exhaust ports. A plurality of upstream exhaust pipes, a common catalyst device into which exhaust gas flows from outlets of the plurality of upstream exhaust pipes, and a downstream exhaust pipe through which the exhaust gas that has passed through the catalyst device is sent to the outside, At least one of the plurality of upstream exhaust pipes is formed shorter than the rest of the upstream exhaust pipes. According to this configuration, the catalyst device common to the plurality of upstream exhaust pipes is brought closer to a part of the exhaust ports, and at least one upstream exhaust pipe is formed short. High-temperature exhaust gas flows into the catalyst device through the at least one upstream exhaust pipe, the catalyst device is warmed up in a short time, and early activation of the catalyst is achieved. Purification performance for the exhaust gas from the upstream side exhaust pipe having a long pipe length is also improved. In addition, cost can be reduced by connecting multiple upstream exhaust pipes to a single catalyst device, and by adjusting the length of multiple upstream exhaust pipes, the layout freedom of the catalyst device relative to the engine is increased. can be ensured.

In the exhaust system described in the above embodiment, the catalyst device is installed on one side in the width direction of the fuselage with respect to the center line extending in the vertical direction of the fuselage. According to this configuration, it is possible to secure a clearance between the member positioned on the center line of the fuselage and the catalytic device, thereby facilitating access to the member positioned on the center line of the fuselage.

In the exhaust system according to the above embodiment, a part of the catalyst device extends in the vertical direction of the engine from the exhaust port connected to the inlet of the outermost upstream exhaust pipe in the machine width direction among the plurality of upstream exhaust pipes. It is contained within a predetermined range up to the line. According to this configuration, it is possible to shorten the length of the outermost upstream exhaust pipe in the machine body width direction, warm up the catalyst device in a shorter time, and realize early activation of the catalyst.

In the exhaust system according to the above embodiment, the plurality of upstream exhaust pipes are a pair of upstream exhaust pipes into which exhaust gas flows from a pair of exhaust ports, and one of the pair of upstream exhaust pipes The upstream exhaust pipe is formed shorter than the other upstream exhaust pipe. According to this configuration, it is possible to warm up the catalyst device in a short time in a two-cylinder engine and realize early activation of the catalyst.

In the exhaust system described in the above embodiment, the other upstream exhaust pipe extends laterally from the exhaust port toward the catalyst device. According to this configuration, the other upstream exhaust pipe extends in the lateral direction and is connected to the catalytic device, so that the catalytic device can be positioned upward to avoid collision with obstacles on the road, flooded roads, and so on. It is possible to suppress a decrease in catalyst temperature due to water splashing.

The exhaust system according to the above embodiment includes a main catalyst device into which exhaust gas flows from the outlet of the downstream side exhaust pipe, and the downstream side exhaust pipe is a pair of downstream side exhaust pipes corresponding to the pair of upstream side exhaust pipes. One downstream exhaust pipe corresponding to one upstream exhaust pipe is formed longer than the other downstream exhaust pipe corresponding to the other upstream exhaust pipe. According to this configuration, the difference in pipe length between the pair of upstream exhaust pipes is offset by the difference in pipe length between the downstream exhaust pipes, thereby reducing variation in the pipe lengths of the entire plurality of exhaust pipes and improving the output characteristics of the engine. can be kept in

In the exhaust system described in the above embodiment, the gas sensor is attached to the catalyst device at the confluence point of the plurality of upstream exhaust pipes. According to this configuration, a single gas sensor can detect the average characteristics of the exhaust gas that has flowed into the catalyst device from a plurality of upstream exhaust pipes. can be reduced.

The vehicle described in the above embodiment is characterized by including the exhaust system described above. According to this configuration, it is possible to realize early warm-up of the catalyst device and improve the exhaust gas purification performance of the vehicle.

1: Engine 15: Exhaust port 30: Exhaust device 31: Primary catalyst device (catalyst device)
35: oxygen sensor (gas sensor)
36: Secondary catalyst device (main catalyst device)
41L: Upstream exhaust pipe 41R: Upstream exhaust pipe 42L: Downstream exhaust pipe 42R: Downstream exhaust pipe

Claims (5)

An exhaust system in which an engine is mounted on an airframe and purifies exhaust gas discharged from a plurality of exhaust ports of the engine,
a plurality of upstream exhaust pipes into which exhaust gas flows from the plurality of exhaust ports;
a common catalyst device into which exhaust gas flows from outlets of the plurality of upstream exhaust pipes;
a downstream exhaust pipe through which the exhaust gas that has passed through the catalyst device is sent to the outside,
The catalyst device is located in front of the engine and is installed on one side in the width direction of the fuselage with respect to a center line extending in the vertical direction of the fuselage,
The plurality of upstream exhaust pipes include an upstream exhaust pipe positioned on one side and an upstream exhaust pipe positioned on the other side in the machine width direction, and the upstream exhaust pipe positioned on the one side is positioned on the other side. formed shorter than the upstream exhaust pipe located at
The plurality of upstream exhaust pipes are a pair of upstream exhaust pipes into which exhaust gas flows from a pair of exhaust ports, and one of the pair of upstream exhaust pipes is an upstream exhaust pipe located on the one side. , the other of the pair of upstream exhaust pipes is an upstream exhaust pipe positioned on the other side,
A main catalyst device into which exhaust gas flows from the outlet of the downstream side exhaust pipe,
The downstream exhaust pipe is a pair of downstream exhaust pipes consisting of a downstream exhaust pipe positioned on one side and a downstream exhaust pipe positioned on the other side in the machine width direction,
The exhaust system , wherein the downstream exhaust pipe positioned on the one side is longer than the downstream exhaust pipe positioned on the other side . A part of the catalyst device is housed within a predetermined range from an exhaust port connected to an inlet of the outermost upstream exhaust pipe in the machine body width direction to a center line extending in the vertical direction of the engine, among the plurality of upstream exhaust pipes. The exhaust system according to claim 1, characterized in that: 3. The exhaust system according to claim 1, wherein the upstream exhaust pipe positioned on the other side extends laterally from the exhaust port toward the catalyst device. 4. The exhaust system according to any one of claims 1 to 3 , wherein a gas sensor is attached to said catalyst device at a junction of said plurality of upstream exhaust pipes. A vehicle comprising the exhaust system according to any one of claims 1 to 4 .

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