JP2010024934A - Exhaust device for engine and vehicle provided with the same - Google Patents

Abstract

An engine exhaust device having a simple and high noise reduction performance is provided.
An exhaust device includes a first exhaust pipe and a second exhaust pipe. The first exhaust pipe 61 is connected to the combustion chamber 36 of the engine 30. One end of the second exhaust pipe 62 is connected to the first portion 61d of the first exhaust pipe. The other end of the second exhaust pipe 62 is connected to the second portion 61 e of the first exhaust pipe 61. The second exhaust pipe 62 has a smaller flow area than the first exhaust pipe 61. The length of the second exhaust pipe 62 along the direction in which the tube center of the second exhaust pipe 62 extends is the first length of the first exhaust pipe 61 along the direction in which the tube center of the first exhaust pipe 61 extends. This is shorter than the length between the first portion 61d and the second portion 61e.
[Selection] Figure 1

Description

  The present invention relates to an engine exhaust device and a vehicle including the same.

Conventionally, various methods have been proposed as methods for reducing exhaust noise in an exhaust system of an engine. For example, Patent Document 1 discloses a method of providing a bypass pipe whose length can be adjusted with respect to a main exhaust pipe. In the exhaust device disclosed in Patent Document 1, the length of the bypass pipe is changed by the actuator so that the phase of the main component of the noise generated in the main exhaust pipe and the phase of the noise generated in the bypass pipe differ from each other by 180 °. Is adjusted. For this reason, the main component of the exhaust noise generated in the main exhaust pipe is canceled by the exhaust noise generated in the bypass pipe.
Japanese Patent Laid-Open No. 2001-50024

  The exhaust device disclosed in Patent Document 1 requires a device for analyzing the exhaust noise of the main exhaust pipe, an actuator for adjusting the length of the bypass pipe, and the like. For this reason, there exists a problem that an exhaust apparatus becomes complicated.

  The present invention has been made in view of this point, and an object of the present invention is to provide an engine exhaust device that is simple and has high noise reduction performance.

  The first engine exhaust system according to the present invention is connected to a combustion chamber of the engine. An exhaust system for a first engine according to the present invention includes a first exhaust pipe and a second exhaust pipe. The first exhaust pipe is connected to the combustion chamber. The first exhaust pipe has a first portion and a second portion. The second part is located downstream of the first part. The second part is bent toward the first part. One end of the second exhaust pipe is connected to the first portion of the first exhaust pipe. The other end of the second exhaust pipe is connected to the second portion of the first exhaust pipe. The second exhaust pipe has a smaller flow path area than the first exhaust pipe. The length of the second exhaust pipe along the direction in which the pipe center of the second exhaust pipe extends is equal to the length of the first portion of the first exhaust pipe along the direction in which the pipe center of the first exhaust pipe extends. Shorter than the length between the two parts.

  A second engine exhaust system according to the present invention is connected to a combustion chamber of the engine. An exhaust device for a second engine according to the present invention includes an exhaust pipe. The exhaust pipe is connected to the combustion chamber. An exhaust path is formed inside the exhaust pipe. An upstream portion and a downstream portion of the exhaust pipe are joined, and a communication hole that connects the upstream portion and the downstream portion of the exhaust path is formed at the joint portion. The area of the communication hole is smaller than the flow path area of the exhaust path.

  A first vehicle according to the present invention includes an engine having a combustion chamber and an exhaust device connected to the combustion chamber. The exhaust device includes a first exhaust pipe and a second exhaust pipe. The first exhaust pipe is connected to the combustion chamber. The first exhaust pipe has a first portion and a second portion. The second part is located downstream of the first part. The second part is bent toward the first part. One end of the second exhaust pipe is connected to the first portion of the first exhaust pipe. The other end of the second exhaust pipe is connected to the second portion of the first exhaust pipe. The second exhaust pipe has a smaller flow path area than the first exhaust pipe. The length of the second exhaust pipe along the direction in which the pipe center of the second exhaust pipe extends is equal to the length of the first portion of the first exhaust pipe along the direction in which the pipe center of the first exhaust pipe extends. Shorter than the length between the two parts.

  A second vehicle according to the present invention includes an engine having a combustion chamber and an exhaust device connected to the combustion chamber. The exhaust device includes an exhaust pipe. The exhaust pipe is connected to the combustion chamber. An exhaust path is formed inside the exhaust pipe. The exhaust pipe has a joint that joins the upstream portion and the downstream portion. A communication hole that connects the upstream portion and the downstream portion of the exhaust path is formed in the joint portion. The area of the communication hole is smaller than the flow path area of the exhaust path.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust apparatus of the engine which is simple and has high noise reduction performance is realizable.

(First embodiment)
Hereinafter, an example of a preferable embodiment in which the present invention is implemented will be described taking the motorcycle 1 shown in FIG. 1 as an example. In the following description, the front, rear, left, and right directions are directions viewed from a rider seated on the seat 15.

  As shown in FIGS. 1 to 3, the motorcycle 1 includes a body frame 10. The vehicle body frame 10 includes a head pipe 11, a main frame 12, a down frame 13, and a seat rail 14. The main frame 12 extends obliquely downward from the head pipe 11 toward the rear above the engine 30. The down frame 13 extends obliquely downward from the head pipe 11 toward the rear in front of the engine 30. The rear end portion of the down frame 13 and the rear end portion of the main frame 12 are connected to each other. A seat rail 14 is attached to the latter half of the main frame 12. The seat rail 14 extends slightly obliquely from the main frame 12 toward the rear. A seat 15 is attached on the seat rail 14.

  A steering shaft (not shown) is rotatably inserted into the head pipe 11. A steering wheel 19 and a pair of left and right front forks 20 are attached to the steering shaft. A front wheel 21 is rotatably attached to the lower ends of the pair of left and right front forks 20.

  A pivot shaft 16 is attached to the rear end portion of the main frame 12. A rear arm 17 is swingably attached to the pivot shaft 16. A suspension 45 is disposed between the rear arm 17 and the main frame 12. A rear wheel 18 is rotatably attached to the rear end portion of the rear arm 17. The rear wheel 18 is connected to the engine 30 by a power transmission mechanism 46 such as a chain.

  An engine 30 is suspended from the body frame 10. The engine 30 includes a crankcase 31. The crankcase 31 stores a crankshaft (not shown). A body cylinder 32 is attached to the front half of the crankcase 31. As shown in FIG. 4, a cylinder portion 32 a in which the piston 35 is accommodated is formed inside the body cylinder 32. In the present embodiment, the center axis of the cylinder portion 32a is inclined obliquely upward toward the rear as shown in FIG. That is, the body cylinder 32 is tilted backward.

  A head cylinder 33 is attached to the upper end of the body cylinder 32. As shown in FIG. 4, a combustion chamber 36 is defined by the head cylinder 33, the cylinder portion 32 a of the body cylinder 32, and the piston 35. An intake port 37 and an exhaust port 38 are formed in the head cylinder 33. The intake port 37 is opened and closed by an intake valve 43. On the other hand, the exhaust port 38 is opened and closed by an exhaust valve 44.

  A throttle body 39 is connected to the intake port 37. The throttle body 39 includes a throttle valve 40 and an injector 41. The amount of air supplied to the combustion chamber 36 is adjusted by the throttle valve 40. Fuel is supplied to the combustion chamber 36 by the injector 41. The throttle body 39 is connected to the air cleaner 42 shown in FIG. Air is supplied to the throttle body 39 through the air cleaner 42. The air cleaner 42 is disposed above and in front of the engine 30. The air cleaner 42 is disposed behind the head pipe 11.

  As shown in FIG. 4, the exhaust device 50 is connected to the combustion chamber 36 via the exhaust port 38. As shown mainly in FIG. 5, the exhaust device 50 includes an exhaust pipe 51 and an exhaust muffler 52. The exhaust pipe 51 includes a first exhaust pipe 61 and a second exhaust pipe 62. As shown in FIGS. 4 and 6, a main exhaust passage 53 is formed inside the first exhaust pipe 61. As shown in FIG. 6, a sub exhaust path 54 is formed inside the second exhaust pipe 62.

  As shown in FIGS. 1 and 3, the front end portion of the first exhaust pipe 61 is connected to the rear side of the engine 30. The rear end portion of the first exhaust pipe 61 is connected to the exhaust muffler 52. The central portion of the first exhaust pipe 61 is formed in a so-called toggro shape. Specifically, as shown in FIG. 5, the first exhaust pipe 61 includes a loop portion 61a that substantially forms a ring when viewed from the front.

  As shown in FIGS. 1 to 3, the loop portion 61 a is disposed on the rear side of the main frame 12. The loop portion 61 a is disposed below the seat 15. The loop portion 61a is arranged so that at least a portion thereof overlaps with the seat rail 14 in the front-rear direction.

  “Substantially forming a ring” means forming a substantial ring. Here, “substantially ring” includes a ring and a ring that is partially cut off. The “ring partially cut out” refers to a so-called horseshoe shape.

  As shown in FIGS. 1 and 5, the second exhaust pipe 62 is connected to the upstream side portion 61 d and the downstream side portion 61 e of the first exhaust pipe 61. More specifically, as shown in FIG. 5, the second exhaust pipe 62 is connected between the intersections of the first exhaust pipe 61 when viewed from the front. Therefore, the second exhaust pipe 62 connects the closest portions of the first exhaust pipe.

FIG. 6 is a schematic diagram showing a part of the exhaust pipe 51. As shown in FIG. 6, the second exhaust pipe 62 has a smaller flow area than the first exhaust pipe 61. Specifically, the area in the cross section of the sub exhaust path 54 formed inside the second exhaust pipe 62 is larger than the area in the cross section of the main exhaust path 53 formed inside the first exhaust pipe 61. Is also small. In the present embodiment, each of the first exhaust pipe 61 and the second exhaust pipe 62 is formed in a circular cross section. Therefore, the diameter D ₂ of the sub exhaust path 54 formed inside the second exhaust pipe 62 is smaller than the diameter D ₁ of the main exhaust passage 53 formed inside the first exhaust pipe 61.

In the present embodiment, the length L2 of the _second exhaust pipe 62 along the direction in which the tube center of the second exhaust pipe 62 extends is the first length along the direction in which the tube center of the first exhaust pipe 61 extends. an upstream-side portion 61d of the exhaust pipe 61, shorter than the length _{L 1} between the downstream portion 61e.

As described above, in the present embodiment, the upstream portion 61 d and the downstream portion 61 e of the first exhaust pipe 61 are connected by the second exhaust pipe 62. The second exhaust pipe 62 has a smaller flow area than the first exhaust pipe 61. Further, the length _{L 2} of the second exhaust pipe 62 is shorter than the length _{L 1} between the upstream portion 61d and the downstream portion 61e of the first exhaust pipe 61. Therefore, the exhaust noise of the engine 30 can be effectively reduced as demonstrated in the following embodiments.

  Further, unlike the exhaust device disclosed in Patent Document 1, the exhaust device 50 of the present embodiment requires an actuator for adjusting the length of the bypass pipe, a device for analyzing the exhaust noise of the main exhaust pipe, and the like. And not. In the present embodiment, exhaust noise can be effectively reduced only by providing the second exhaust pipe 62. Therefore, the exhaust device 50 of the present embodiment has a simple configuration, is small in size and low in cost.

  In other words, according to the present embodiment, it is possible to realize an engine exhaust device 50 that is simple, small, and low in cost and has high noise reduction performance.

  The exhaust device 50 of the present embodiment can also be used for vehicles other than motorcycles. However, the exhaust device 50 that can be miniaturized is particularly suitably used for a saddle-ride type vehicle, particularly a motorcycle, in which the exhaust device is disposed in a relatively small space.

The magnitude of the exhaust noise of the engine 30 correlates with the magnitude of the flow path area of the second exhaust pipe 62. Specifically, as will be demonstrated in the following embodiments, the exhaust noise of the engine 30 is effectively reduced as the flow path area of the second exhaust pipe 62 is larger. Therefore, from the viewpoint of further reducing the exhaust noise of the engine 30, it is preferable that the flow path area of the second exhaust pipe 62 is large. Specifically, the diameter D ₂ of the sub exhaust path 54 formed inside the second exhaust pipe 62 is larger is preferable. The diameter D1 of the _first exhaust pipe 61 is not particularly limited.

Further, the magnitude of the exhaust noise of the engine 30 correlates with the length L _{2 of} the second exhaust pipe 62. Specifically, as demonstrated in the following embodiment, the exhaust noise of the engine 30 is more effectively reduced as the length L2 of the _second exhaust pipe 62 is shorter. Therefore, from the viewpoint of further reducing the exhaust noise of the engine 30, the length L2 of the _second exhaust pipe 62 is preferably shorter.

  Further, when the second exhaust pipe 62 is provided, the torque of the engine 30 increases in the region where the rotational speed of the engine 30 is low, while the maximum torque of the engine 30 decreases, as will be demonstrated in the following embodiments. There is a tendency. For this reason, by providing the second exhaust pipe 62, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be increased. Further, by providing the second exhaust pipe 62, the torque characteristics of the engine 30 can be stabilized with respect to the rotational speed of the engine 30. In the following description, “the torque of the engine 30 in a region where the rotational speed of the engine 30 is low” may be abbreviated as “low-speed torque”.

  The low speed torque and the maximum torque of the engine 30 correlate with the size of the flow path area of the second exhaust pipe 62. Specifically, as demonstrated in the following examples, the larger the flow area of the second exhaust pipe 62, the higher the low-speed torque, while the lower the maximum torque. Therefore, the torque characteristics of the engine 30 can be easily adjusted by adjusting the size of the flow path area of the second exhaust pipe 62 as in the present embodiment.

The influence of the length L2 of the _second exhaust pipe 62 on the torque characteristics of the engine 30 is small.

  The reason why the torque characteristics of the engine 30 are changed by providing the second exhaust pipe 62 is considered as follows.

  FIG. 7 is a graph showing the relationship between the pressure of the exhaust port 38 and the crank angle when the rotational speed of the engine 30 is low. FIG. 8 is a graph showing the relationship between the pressure of the exhaust port 38 and the crank angle when the rotational speed of the engine 30 is high. 7 and 8, the solid line 70 represents the lift amount of the exhaust valve 44. A solid line 71 represents the lift amount of the intake valve 43. A thick line 72 represents the pressure of the exhaust port 38 when the second exhaust pipe 62 is provided. An alternate long and short dash line 73 represents the pressure in the exhaust port 38 when the second exhaust pipe 62 is not provided.

As shown in FIG. 7, in the region the rotational speed is low of the engine 30, the peak P ₁ is positioned within the region R both are opened between the intake port 37 and exhaust port 38. Here, as in the present embodiment, when the second exhaust pipe 62 is provided, the pressure of the exhaust port 38 at the peak P ₁ is lower than when the second exhaust pipe 62 is not provided. To do. That is, in the region R where both the intake port 37 and the exhaust port 38 are opened, the magnitude of the positive pressure of the exhaust port 38 is reduced. Therefore, exhaust of exhaust gas from the engine 30 is promoted. As a result, exhaust efficiency increases in a region where the rotational speed of the engine 30 is low. Accordingly, the torque of the engine 30 is increased.

On the other hand, as shown in FIG. 8, in the region high rotational speeds of the engine 30, the peak P ₂ is an intake port 37, located in region R where both are in the open and the exhaust port 38. Here, as in the present embodiment, the case of providing the second exhaust pipe 62, as compared with the case where the second exhaust pipe 62 is not provided, a high pressure of the exhaust port 38 at the peak P ₂ Become. That is, in the region where the rotational speed of the engine 30 is relatively high, the magnitude of the negative pressure of the exhaust port 38 in the region R where both the intake port 37 and the exhaust port 38 are opened becomes small. Therefore, in a region where the engine 30 has a maximum torque and the engine 30 has a high rotational speed, the exhaust efficiency is reduced, and therefore the torque of the engine 30 tends to decrease.

  As described above, by providing the second exhaust pipe 62 as in the present embodiment, in the region R where both the intake port 37 and the exhaust port 38 are opened in the region where the rotational speed of the engine 30 is low. The positive pressure of the exhaust port 38 tends to decrease. Further, in the region where the rotational speed of the engine 30 where the torque of the engine 30 is maximum is high, the negative pressure of the exhaust port 38 tends to decrease in the region R where both the intake port 37 and the exhaust port 38 are opened. It is in. Therefore, it is considered that the torque of the engine 30 in the region where the rotational speed of the engine 30 is low increases, while the torque of the engine 30 in the region where the rotational speed of the engine 30 is high tends to decrease.

The reason why the exhaust noise is reduced by providing the second exhaust pipe 62 is that the positive pressure of the exhaust port 38 at the peak P ₁ can be estimated from the attenuation characteristics of the exhaust device 50 shown in FIGS. On the other hand, the magnitude of the negative pressure of the exhaust port 38 at the peak P ₂ becomes small, and the pressure fluctuation of the exhaust port 38 becomes small.

  In the present embodiment, the first exhaust pipe 61 includes a loop portion 61a that substantially forms a ring when viewed from the front. For this reason, the distance between the nearest parts of the 1st exhaust pipe 61 can be shortened. Therefore, the second exhaust pipe 62 can be made shorter. As a result, the exhaust noise of the engine 30 can be more effectively reduced.

  Instead of the loop portion 61a of the present embodiment, a U-shaped U-shaped portion may be formed in the first exhaust pipe 61. Even in this case, the exhaust noise of the engine 30 can be more effectively reduced as in the present embodiment. Further, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be increased.

  The second exhaust pipe 62 is preferably connected between the intersections of the first exhaust pipe 61 when viewed from the front as in the present embodiment. According to this, the length of the second exhaust pipe 62 can be further shortened. Therefore, the exhaust noise of the engine 30 can be further effectively reduced.

  In particular, it is particularly preferable that the second exhaust pipe 62 connects the closest portions of the first exhaust pipe 61 to each other. According to this, the length of the second exhaust pipe 62 can be particularly shortened. Therefore, the exhaust noise of the engine 30 can be particularly reduced.

  Further, by forming the loop portion 61 a in the first exhaust pipe 61 as in the present embodiment, the length from the front end to the rear end of the first exhaust pipe 61 can be increased. Therefore, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be increased more effectively.

  In the present embodiment, the loop portion 61 a is disposed behind the main frame 12. According to this, the dead space formed behind the main frame 12 can be effectively utilized.

  Further, as in the present embodiment, the air cleaner 42 is disposed in front of the engine 30 and the exhaust device 50 is connected to the rear side of the engine 30, whereby the body cylinder 32 can be disposed relatively rearward. For example, the body cylinder 32 can be tilted backward. Therefore, mass concentration can be achieved in the motorcycle 1.

  Furthermore, by arranging the air cleaner 42 in front and above the engine 30, the intake efficiency of the engine 30 can be further improved.

  In the present embodiment, the motorcycle 1 shown in FIG. 1 has been described as an example of the vehicle according to the present invention. However, the vehicle according to the present invention is not limited to the motorcycle 1 shown in FIG. The vehicle according to the present invention may be a four-wheel vehicle or a straddle-type vehicle. Here, the “saddle-riding vehicle” refers to a vehicle on which a rider rides over a seat (鞍). The straddle-type vehicle includes an ATV (All Terrain Vehicle), a snowmobile, and the like in addition to the motorcycle. The four-wheeled vehicle also includes an off-road vehicle. An off-road vehicle may also be referred to as a side-by-side vehicle.

  In the present invention, the motorcycle is not limited to the type shown in FIG. In the present invention, “motorcycle” refers to a motorcycle in a broad sense. That is, in the present invention, the “motorcycle” includes a narrowly defined motorcycle, moped, scooter, off-road vehicle, and the like. Further, in the present specification, the motorcycle includes a vehicle in which at least one of the front wheel and the rear wheel is constituted by a plurality of wheels that rotate integrally, and the vehicle is inclined to change the traveling direction. To do.

(Second Embodiment)
In the above embodiment, the example in which the first exhaust pipe 61 is connected to the rear side of the engine 30 has been described. However, in the present invention, the connection position of the first exhaust pipe 61 to the engine 30 is not particularly limited. For example, as shown in FIGS. 9 and 10, the first exhaust pipe 61 may be connected to the front side of the engine 30.

  Hereinafter, the exhaust device 50 according to the present embodiment will be described with reference to FIGS. 9 and 10. In the following description, members having the same functions as those in the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

  As shown in FIGS. 9 and 10, in the present embodiment, the first exhaust pipe 61 is connected to the front side of the engine 30. The first exhaust pipe 61 includes a loop portion 61a that substantially forms a ring when viewed from the front. In the present embodiment, the loop portion 61 a is disposed on the front side of the down frame 13.

  As shown in FIG. 9, the loop part 61a is connected to the latter half part 61c. A rear end portion of the rear half portion 61c is connected to the exhaust muffler 52. The rear half 61c is arranged at a position higher than the crankcase 31.

  In the present embodiment, the first exhaust pipe 61 is connected to the front side of the engine 30. For this reason, the length of the 1st exhaust pipe 61 can be lengthened. Therefore, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be further increased.

  In the present embodiment, as shown in FIGS. 9 and 10, the loop portion 61 a is disposed in front of the down frame 13. For this reason, the dead space between the down frame 13 and the front wheel 21 can be effectively utilized.

(Third embodiment)
FIG. 11 is a perspective view illustrating a positional relationship among the engine 30, the exhaust device 50, and the vehicle body frame 10 according to the third embodiment. As shown in FIG. 11, in the present embodiment, the first exhaust pipe 61 is connected to the front side of the engine 30. The first exhaust pipe 61 includes a U-shaped portion 61b when viewed from the front. The U-shaped part 61 b is disposed on the front side of the down frame 13. The downstream end portion of the U-shaped portion 61b is connected to the rear half portion 61c. The rear half 61c is arranged at a position higher than the crankcase 31.

  In the present embodiment, the second exhaust pipe 62 is connected to the upstream end and the downstream end of the U-shaped portion 61 b of the first exhaust pipe 61.

  Even when the U-shaped portion 61b is formed in the first exhaust pipe 61 as in the present embodiment, as in the case where the loop portion 61a is formed, the closest portions of the first exhaust pipe 61 The distance between can be shortened. Therefore, the length of the second exhaust pipe 62 can be shortened. As a result, the exhaust noise of the engine 30 can be effectively reduced.

  Moreover, the length of the 1st exhaust pipe 61 can be lengthened by forming the U-shaped part 61b in the 1st exhaust pipe 61 like this embodiment. Therefore, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be further increased.

(Fourth embodiment)
In the third embodiment, the example in which the U-shaped portion 61 b of the first exhaust pipe 61 is disposed in front of the down frame 13 has been described. However, the arrangement position of the U-shaped portion 61b of the first exhaust pipe 61 is not particularly limited. For example, as shown in FIG. 12, the U-shaped portion 61 b may be disposed on the side of the engine 30. Even in this case, the length of the first exhaust pipe 61 can be increased while the positional buffering between the first exhaust pipe 61 and the engine 30 is suppressed, and the second exhaust pipe 62 can be lengthened. The length can be shortened. Therefore, the torque of the engine 30 in the region where the rotational speed of the engine 30 is low can be effectively increased. Further, the exhaust noise of the engine 30 can be effectively reduced.

(First modification)
In the first embodiment, as shown in FIG. 5, the example in which the second exhaust pipe 62 is formed in a curved shape has been described. However, the shape of the second exhaust pipe 62 is not particularly limited. For example, as shown in FIG. 13, the second exhaust pipe 62 may be formed in a linear shape. According to this, the length of the second exhaust pipe 62 can be further shortened. Therefore, the exhaust noise of the engine 30 can be more effectively reduced.

(Second modification)
In the first embodiment, the example in which the upstream portion 61d and the downstream portion 61e of the first exhaust pipe 61 are connected using the second exhaust pipe 62 has been described. However, in the present invention, the connection method between the upstream portion 61d and the downstream portion 61e of the first exhaust pipe 61 is not particularly limited. For example, as shown in FIG. 14, the upstream portion and the downstream portion of the main exhaust path 53 may be connected by directly joining the upstream portion 61d and the downstream portion 61e. Specifically, in this embodiment, as schematically shown in FIG. 15, a communication hole 64 is formed in the joint portion 63 between the upstream portion 61 d and the downstream portion 61 e. By this communication hole 64, the upstream side portion and the downstream side portion of the main exhaust path 53 are connected. The area of the communication hole 64 is smaller than the flow path area of the main exhaust path 53. In other words, the diameter D _{3 of the} communication hole 64 is smaller than the diameter D ₁ of the main exhaust path 53.

  The exhaust noise of the engine 30 can be particularly effectively suppressed by directly joining the upstream portion 61d and the downstream portion 61e as in this modification.

  In addition, the manufacturing method of the 1st exhaust pipe 61 in this modification is not specifically limited. For example, as shown in FIG. 16, first, the first pipe half 73 and the second pipe half 75 are joined. The method for joining the first pipe half 73 and the second pipe half 75 is not particularly limited. For example, the first pipe half 73 and the second pipe half 75 can be joined by welding. Next, a communication hole 64 is formed at the joint between the first pipe half 73 and the second pipe half 75. Thereafter, the first pipe half 73 and the third pipe half 72 are joined, and the second pipe half 75 and the fourth pipe half 76 are joined. As a result, a first pipe part 78 and a second pipe part 79 are formed.

  Then, the end portion 78 a of the first pipe portion 78 and the end portion 74 a of the third pipe portion 74 are connected. The end part 78b of the first pipe part 78 and the end part 71a of the fourth pipe part 71 are connected. The end 79b of the second pipe part 79 and the end 74b of the third pipe part 74 are connected. By connecting the end 79 a of the third pipe portion 79 and the end 77 a of the fifth pipe portion 77, the first exhaust pipe 61 can be produced.

(Example)
Various exhaust devices 50 having different flow path area sizes and lengths of the second exhaust pipe 62 are produced, and the damping characteristics of the exhaust device 50 and the torque characteristics of the engine 30 to which the exhaust device 50 is connected are measured. did. The measurement results of the attenuation characteristics of the exhaust device 50 are shown in FIGS. The measurement results of the torque characteristics of the engine 30 are shown in FIGS.

The data shown in FIGS. 17 to 20 are as follows.
Figures 17 and 18:
Solid line 81: No second exhaust pipe 62 Solid line 82: Diameter of the second exhaust pipe 62 is 20 mm, length is 100 mm
Solid line 83: the diameter of the second exhaust pipe 62 is 20 mm, and the length is 60 mm.
Solid line 84: the diameter of the second exhaust pipe 62 is 20 mm, and the length is 30 mm.
Solid line 85: the diameter of the second exhaust pipe 62 is 20 mm, and the length is 15 mm.
19 and 20:
Solid line 90: No second exhaust pipe 62 Solid line 91: Second exhaust pipe 62 diameter 15 mm, length 60 mm
Solid line 92: the diameter of the second exhaust pipe 62 is 20 mm, and the length is 60 mm.
Solid line 93: second exhaust pipe 62 having a diameter of 32 mm and a length of 60 mm
Solid line 94: second exhaust pipe 62 having a diameter of 36 mm and a length of 60 mm

17 and 19, if the pressure on the output side of the exhaust system 50 and _{P out,} the pressure on the input side of the exhaust system 50 and the _{P in,} the longitudinal axis "Magnitude" _{is, log (P} out _/ P _in ). When the magnitude is greater than or equal to zero, “amplification” occurs, and when the magnitude is less than or equal to zero, “attenuation” occurs.

  As shown in FIGS. 17 and 19, it can be seen that by providing the second exhaust pipe 62, it is possible to improve the damping characteristic of the exhaust device 50 as compared with the case where the second exhaust pipe 62 is not provided. Therefore, it can be seen that the exhaust noise of the engine 30 can be reduced by providing the second exhaust pipe 62.

  As shown in FIG. 17, it can be seen that the damping characteristic of the exhaust device 50 is enhanced by shortening the length of the second exhaust pipe 62. From this result, it can be seen that the exhaust noise of the engine 30 can be more effectively reduced by shortening the length of the second exhaust pipe 62.

  Further, as shown in FIG. 19, it can be seen that the damping characteristic of the exhaust device 50 is enhanced by increasing the diameter of the second exhaust pipe 62. From this result, it can be seen that the exhaust noise of the engine 30 can be reduced more effectively by increasing the size of the flow path area of the second exhaust pipe 62.

  As shown in FIGS. 18 and 20, the provision of the second exhaust pipe 62 increases the torque of the engine 30 in a region where the engine speed is low as compared with the case where the second exhaust pipe 62 is not provided. I understand. Moreover, it turns out that there exists a tendency for the maximum torque of the engine 30 to fall by providing the 2nd exhaust pipe 62. FIG. From the above, it can be seen that the torque of the engine 30 with respect to the engine rotation speed can be stabilized by providing the second exhaust pipe 62.

As shown in FIG. 18, it can be seen that the torque characteristics of the engine 30 do not change greatly even when the length L2 of the _second exhaust pipe 62 is changed.

  On the other hand, as shown in FIG. 20, when the diameter of the second exhaust pipe 62 is changed, it can be seen that the torque characteristics of the engine 30 change. Specifically, it can be seen that by increasing the diameter of the second exhaust pipe 62, the torque of the engine 30 in the region where the engine rotation speed is low becomes higher, while the maximum torque of the engine 30 becomes lower.

1 is a left side view of a motorcycle according to a first embodiment. 1 is a plan view showing a part of a motorcycle according to a first embodiment. 1 is a left side view showing a part of a motorcycle according to a first embodiment. It is sectional drawing showing a part of engine in 1st Embodiment. It is a part of exhaust apparatus in 1st Embodiment. It is a conceptual diagram of the exhaust apparatus in 1st Embodiment. It is a graph showing the relationship between the pressure of an exhaust port, and a crank angle when an engine speed is low. It is a graph showing the relationship between the exhaust port pressure and the crank angle when the engine speed is high. It is a right view showing the engine, the exhaust device, and the vehicle body frame in the second embodiment. It is front sectional drawing showing the engine, exhaust apparatus, and vehicle body frame in 2nd Embodiment. It is a perspective view showing the engine, exhaust system, and body frame 10 in a 3rd embodiment. It is a right view showing the engine, exhaust system, and body frame in a 4th embodiment. It is a side view of the exhaust apparatus in a 1st modification. It is a side view of the exhaust apparatus in the 2nd modification. It is a schematic diagram of the exhaust apparatus in the 2nd modification. It is a 1st exhaust pipe exploded perspective view in the 2nd modification. It is a graph showing the measurement result of the attenuation | damping property of an exhaust apparatus in case the diameter of a 2nd exhaust pipe is 20 mm. It is a graph showing the measurement result of the torque characteristic of an engine in case the diameter of a 2nd exhaust pipe is 20 mm. It is a graph showing the measurement result of the attenuation | damping property of an exhaust apparatus in case the length of a 2nd exhaust pipe is 60 mm. It is a graph showing the measurement result of the torque characteristic of an engine in case the length of a 2nd exhaust pipe is 60 mm.

Explanation of symbols

1 Motorcycles (vehicles, straddle-type vehicles)
11 Head pipe 12 Main frame 13 Down frame 30 Engine 36 Combustion chamber 50 Exhaust device 51 Exhaust pipe 53 Main exhaust path (exhaust path)
61 1st exhaust pipe 61a Loop part 61b U-shaped part 61d Upstream part (1st part)
61e Downstream part (second part)
62 2nd exhaust pipe 63 Joint 64 Communication hole

Claims (13)

An exhaust system connected to the combustion chamber of the engine,
A first exhaust pipe having a first portion and a second portion located on the downstream side of the first portion and bent toward the first portion; and connected to the combustion chamber; ,
One end is connected to the first part of the first exhaust pipe and the other end is connected to the second part of the first exhaust pipe, A second exhaust pipe having a smaller flow area than the exhaust pipe;
With
The length of the second exhaust pipe along the direction in which the tube center of the second exhaust pipe extends is the length of the first exhaust pipe along the direction in which the tube center of the first exhaust pipe extends. An exhaust system for an engine shorter than a length between one portion and the second portion. The engine exhaust system according to claim 1,
The first exhaust pipe is an engine exhaust device that includes a loop portion that substantially forms a ring when viewed from at least one direction. The exhaust system for an engine according to claim 2,
The exhaust system for an engine, wherein the second exhaust pipe is connected between the intersections of the first exhaust pipe when viewed from the one direction. The engine exhaust system according to claim 1,
The first exhaust pipe is an engine exhaust device including a U-shaped portion formed in a U-shape. The engine exhaust system according to claim 1,
The second exhaust pipe is an exhaust system for an engine in which the closest portions of the first exhaust pipe are connected to each other. An exhaust system connected to the combustion chamber of the engine,
An exhaust pipe connected to the combustion chamber and having an exhaust path formed therein;
The upstream portion and the downstream portion of the exhaust pipe are joined, and a communication hole that connects the upstream portion and the downstream portion of the exhaust path is formed in the joint portion,
The engine exhaust device has an area of the communication hole smaller than a flow passage area of the exhaust path. A vehicle comprising an engine having a combustion chamber and an exhaust device connected to the combustion chamber,
The exhaust device is
A first exhaust pipe having a first portion and a second portion located on the downstream side of the first portion and bent toward the first portion; and connected to the combustion chamber; ,
One end is connected to the first part of the first exhaust pipe and the other end is connected to the second part of the first exhaust pipe, A second exhaust pipe having a smaller flow area than the exhaust pipe;
With
The length of the second exhaust pipe along the direction in which the tube center of the second exhaust pipe extends is the length of the first exhaust pipe along the direction in which the tube center of the first exhaust pipe extends. A vehicle shorter than the length between the first part and the second part. The vehicle according to claim 7, wherein
Further comprising a head pipe and a main frame extending obliquely downward from the head pipe toward the rear above the engine;
The first exhaust pipe is connected to the rear side of the engine, and includes a portion that substantially forms a ring or a U shape when viewed from the front.
A vehicle that is substantially ring-shaped or U-shaped when viewed from the front of the first exhaust pipe is disposed behind the main frame. The vehicle according to claim 7, wherein
The first exhaust pipe is a vehicle connected to the front side of the engine. The vehicle according to claim 9, wherein
Further comprising a head pipe and a down frame extending obliquely downward from the head pipe toward the rear in front of the engine;
The first exhaust pipe includes a portion that substantially forms a ring or a U shape when viewed from the front,
A vehicle that is substantially ring-shaped or U-shaped when viewed from the front of the first exhaust pipe is disposed in front of the down frame. The vehicle according to claim 9, wherein
The first exhaust pipe includes a portion that substantially forms a ring or a U shape when viewed from the side,
A vehicle that is substantially ring-shaped or U-shaped when viewed from the side of the first exhaust pipe is disposed on the side of the engine. A vehicle comprising an engine having a combustion chamber and an exhaust device connected to the combustion chamber,
The exhaust device includes an exhaust pipe connected to the combustion chamber and having an exhaust path formed therein,
The exhaust pipe has a joint portion that joins an upstream portion and a downstream portion, and the joint portion has a communication hole that connects the upstream portion and the downstream portion of the exhaust path. Formed,
A vehicle in which the area of the communication hole is smaller than the flow path area of the exhaust path.   The vehicle according to claim 7 or 12, which is a saddle type vehicle.

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