JP2019015256A - Exhaust device for engine, and motorcycle comprising the same - Google Patents

Abstract

To provide an exhaust device for an engine capable of obtaining a sound that is near an original sound of an exhaust sound, during low-speed engine rotation while ensuring muffling performance during high-speed engine rotation.SOLUTION: In a case 44 of an exhaust device 40, two exhaust passages P1 and P2 having different lengths are formed between a lead-in port 52 and a lead-out port 54. Regarding a lead-in pipe 56 forming the lead-in port 52, a cross-sectional area S2 of an exit 56b of the lead-in pipe 56 is set smaller than a cross-sectional area S1 of the lead-in port 54. The exit 56b of the lead-in pipe 56 and the lead-out port 54 are formed in a second expansion chamber 62, and the exit 56b of the lead-in pipe 56 faces the lead-out port 54. A lateral hole 72 is formed on a sidewall 56c of the lead-in pipe 56, and communicates with a first expansion chamber 60. An opening area S3 of the lateral hole 72 is larger than a passage area S2 of the exit 56b of the lead-in pipe 56. Between the two exhaust passages P1 and P2, the exhaust passage P1 from the exit 56b of the lead-in pipe 56 to the lead-out port 54 is shortest.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust device that silences exhaust gas of an engine and a motorcycle equipped with the exhaust device.

  An engine mounted on a vehicle such as a motorcycle includes an exhaust device that silences exhaust gas (for example, Patent Document 1). The exhaust device has a plurality of expansion chambers therein. The exhaust gas is muffled by repeating expansion and contraction inside the exhaust device.

Japanese Patent Laying-Open No. 2015-081522

  On the other hand, there is a case where a powerful exhaust sound close to the original sound of the exhaust sound is required at the time of engine low-speed rotation where the necessity of noise reduction of the exhaust gas is low. Such a demand is particularly required for an engine for a vehicle such as a motorcycle. However, in the exhaust device as disclosed in Patent Document 1, since the exhaust gas is silenced by expansion and contraction, an exhaust sound close to the original sound of the exhaust sound does not remain.

  It is an object of the present invention to provide an engine exhaust device that can obtain a sound close to the original sound of the exhaust sound at the time of engine low speed rotation while ensuring the silence at the time of engine high speed rotation.

  In order to achieve the above object, an exhaust system for an engine according to the present invention is an exhaust system including a case having an introduction port through which exhaust gas of the engine is introduced and a discharge port through which the exhaust gas is led out. A plurality of exhaust paths having different lengths are provided between the introduction port and the outlet port, and an introduction pipe that forms the introduction port is provided, and the outlet of the introduction pipe is cut off more than the cross-sectional area of the introduction port. A small area is set, the outlet of the introduction pipe and the outlet are arranged in the same expansion chamber, and a part of the virtual opening in which the opening of the outlet of the introduction pipe is projected in the axial direction is part of the outlet. A lateral hole having an opening area larger than the passage area of the outlet of the introduction pipe is formed on the side wall of the introduction pipe, which is in communication with the expansion chamber in the case. Out of the introduction pipe Exhaust path toward the outlet from the shortest.

  According to this configuration, a part of the virtual opening obtained by projecting the opening of the outlet of the introduction pipe in the axial direction thereof overlaps with a part of the outlet, and among the plurality of exhaust paths, the outlet of the introduction pipe The exhaust path to the outlet is the shortest. Therefore, at the time of engine low speed rotation, exhaust gas flows directly from the introduction pipe toward the outlet. That is, the exhaust gas is exhausted from the outlet port through almost no expansion / contraction and exhaust interference. Accordingly, it is possible to obtain a sound close to the original sound of the exhaust sound at the time of engine low speed rotation. In addition, at the time of engine low speed rotation, since the exhaust volume is small, the necessity for muffling is low.

  On the other hand, since the exhaust pressure increases during high-speed engine rotation, passage resistance increases at the outlet of the introduction pipe having a small cross-sectional area. Therefore, at the time of high-speed engine rotation, most of the exhaust gas flows from the lateral hole having a large passage area toward the outlet through the expansion chamber. That is, the exhaust gas is sufficiently silenced through expansion / contraction and exhaust interference, and then exhausted from the outlet. In this way, it is possible to obtain a sound close to the original sound of the exhaust sound at the time of engine low speed rotation while ensuring the necessary noise reduction at the time of engine high speed rotation.

  In the exhaust apparatus of the present invention, the introduction pipe may have a reduced diameter portion that decreases in diameter toward the downstream in the exhaust gas flow direction. According to this configuration, since the exhaust pressure is small at the time of engine low speed rotation, the passage resistance in the introduction pipe is also small. Accordingly, the exhaust gas having a small flow rate passes through the reduced diameter portion and smoothly flows directly toward the outlet. On the other hand, since the exhaust pressure increases during high-speed engine rotation with a large exhaust gas flow rate, the passage resistance increases at the reduced diameter portion. Therefore, most of the exhaust gas flows from the lateral hole toward the outlet through the expansion chamber. As a result, the necessary silence is ensured.

  In the exhaust device of the present invention, the inlet may further include a lead pipe that forms the lead outlet, and at least a part of the inlet of the lead pipe may be located on the axis of the outlet of the lead pipe. According to this configuration, the exhaust gas that has passed through the introduction pipe can easily go directly to the outlet pipe during low-speed engine rotation. As a result, it becomes easier to obtain a sound close to the original sound of the exhaust sound.

  In the exhaust device of the present invention, a partition that partitions the first expansion chamber on the upstream side and the second expansion chamber on the downstream side, and the first expansion chamber and the second expansion chamber that are provided in the partition are provided. A communication passage that communicates, the introduction pipe passes through the first expansion chamber and penetrates the partition wall, the outlet opens to the second expansion chamber, and the lateral hole extends to the first expansion chamber. You may communicate. According to this configuration, when the engine rotates at a low speed, the exhaust gas flows into the second expansion chamber without passing through the first expansion chamber and is discharged from the outlet. When the engine rotates at high speed, the exhaust gas flows into the first expansion chamber from the lateral hole of the introduction pipe, flows into the second expansion chamber through the communication path, and is then discharged from the outlet. As described above, with a simple configuration, that is, space saving and low cost, it is possible to obtain a sound close to the original sound of the exhaust sound when the engine is rotated at a low speed and to obtain a high noise reduction effect when the engine is rotated at a high speed.

  When the first expansion chamber and the second expansion chamber are partitioned by the partition wall, the introduction pipe has a reduced diameter portion that is reduced in diameter toward the downstream in the exhaust gas flow direction, and a downstream side of the reduced diameter portion. A straight pipe section on the side, and the straight pipe section may be supported by the partition wall through the partition wall. According to this configuration, since the introduction pipe is supported by the partition wall at the straight pipe portion on the tip side of the reduced diameter portion, the support of the introduction pipe is stabilized.

  When the communication passage is provided, the passage area of the lateral hole may be larger than the passage area of the communication passage. Here, when a plurality of lateral holes are provided, the “lateral passage area” means the total of the passage areas of the plurality of lateral holes. According to this configuration, at the time of high-speed rotation of the engine, the exhaust gas flows into the first expansion chamber from the lateral hole, and the contraction when flowing into the second expansion chamber through the communication path is increased. As a result, the silencing effect during high-speed engine rotation is improved.

  When the communication path is provided, the introduction pipe may be disposed closer to one side in the case, and the communication path may be disposed closer to the other side. According to this structure, a communicating path can be provided in the space near the other side secured by arranging the introduction pipe closer to one side in the case. Thereby, a large expansion space is secured in the space closer to the other side provided with the communication passage, and the space in the case of the exhaust device can be effectively used while setting the silencing effect high.

  In the exhaust device of the present invention, the case may be configured by joining the first case half and the second case half at a joint portion, and the lateral hole may face the joint portion. According to this configuration, since the high-temperature exhaust gas can collide with the joint having high rigidity, the vibration of the case half due to the collision of the exhaust gas can be suppressed.

  A motorcycle according to the present invention includes the exhaust device according to the present invention below the engine, the case has a rectangular parallelepiped shape, an introduction pipe having the introduction port is attached to a front wall of the case, and the rear of the case An outlet pipe having the outlet is attached to the wall, and the first expansion chamber and the second expansion chamber are arranged side by side in the front-rear direction. Here, the “cuboid” includes those having rounded corners. According to this configuration, the exhaust gas smoothly flows from the front to the rear of the motorcycle.

  In the motorcycle according to the present invention, the introduction pipe is disposed on one side of an oil pan below the engine, the exhaust device is disposed between the engine and a rear wheel, and a silencer is disposed behind the exhaust device. May be connected. According to this configuration, the space below the engine can be used effectively.

  According to the exhaust system for an engine of the present invention, it is possible to obtain a sound close to the original sound of the exhaust sound at the time of engine low speed rotation while ensuring the necessary noise reduction at the time of engine high speed rotation.

1 is a side view showing a motorcycle including an engine exhaust device according to a first embodiment of the present invention. It is a perspective view which shows the exhaust apparatus. It is a top view which shows the exhaust apparatus. It is a perspective view which shows the exhaust apparatus. It is a top view which shows the flow of the exhaust gas of the same exhaust apparatus. It is a top view which shows the exhaust apparatus of the engine which concerns on 2nd Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification, “left side” and “right side” refer to the left and right sides as viewed from the driver who gets on the vehicle. The “up and down direction” refers to the up and down direction as viewed from the driver who has boarded the vehicle. Furthermore, the “front-rear direction” refers to the traveling direction of the vehicle, that is, the longitudinal direction of the vehicle.

  FIG. 1 is a side view of a motorcycle having an engine exhaust device according to an embodiment of the present invention. A body frame FR of the motorcycle has a main frame 1 that forms a front half and a rear frame 2 that forms a rear half. The main frame 1 has a main frame piece 1a extending obliquely downward and rearward from a head pipe 4 provided at the front end. A pair of left and right main frame pieces 1a are provided. The left and right main frame pieces 1a, 1a are connected by a cross member 1b extending in the vehicle width direction at the rear part.

  The rear frame 2 has a seat rail 2a and a reinforcing pipe 2b below the seat rail 2a. The seat rail 2a extends rearward from the cross member 1b. The front end of the reinforcing pipe 2b is connected to the rear end of the main frame piece 1a, and extends rearward and obliquely upward from the front end and is connected to the lower surface of the seat rail 2a. A pair of left and right seat rails 2a and reinforcing pipes 2b are also provided.

  A front fork 8 is pivotally supported on the head pipe 4 via a steering shaft (not shown). A steering handle 6 is fixed to the upper end of the front fork 8. A front wheel 10 is rotatably attached to a lower end portion of the front fork 8.

  A swing arm bracket 9 is provided at the rear end of the main frame 1. A swing arm 12 is pivotally supported around a pivot shaft 16 attached to the swing arm bracket 9 so as to be swingable up and down. A rear wheel 14 is rotatably supported at the rear end of the swing arm 12. An engine E is mounted below the main frame 1 and on the front side of the swing arm bracket 9. The engine E of this embodiment is a 4-cycle 4-cylinder engine. However, the format of the engine E is not limited to this. The engine E drives the rear wheel 14 via a power transmission member 11 such as a chain.

  A fuel tank 15 is disposed above the main frame piece 1 a of the main frame 1. A rider's seat 18 and a passenger's seat 20 are supported on the seat rail 2 a of the rear frame 2.

  The engine E includes a crankcase 21 that rotatably supports the crankshaft 19, a cylinder block 23 connected to the top of the crankcase 21, a cylinder head 25 connected to the top of the cylinder block 23, And an oil pan 27 attached to the lower portion. A combustion chamber is formed inside the cylinder block 23 and the cylinder head 25.

  A throttle body 28 is connected to the intake port 26 at the rear of the cylinder head 25. Inside the throttle body 28, an air / fuel mixture is generated, and this mixture is supplied from the intake port 26 to the fuel chamber. The air-fuel mixture is combusted in the fuel chamber and discharged as exhaust gas G from the exhaust port 30 on the front surface of the cylinder head 25.

  Four exhaust pipes 32 are connected to the exhaust port 30. The four exhaust pipes 32 extend downward in front of the engine E and merge below the engine E. Specifically, two of the four exhaust pipes 32 merge at the two intermediate collecting pipes 34. Further, the two intermediate collecting pipes 34 join at the collecting pipe 36 behind the two intermediate collecting pipes 34. The collecting pipe 36 extends rearward under the engine E.

  Specifically, the oil pan 27 has a left side deep portion 27a and a right side shallow portion 27b, and the collecting pipe 36 is on the right side (one side) of the deep portion 27a of the oil pan 27. It arrange | positions under the shallow part 27b. A catalyst 38 is accommodated in the collecting pipe 36. The catalyst 38 purifies harmful substances in the exhaust gas G. An exhaust gas sensor 39 is attached to the upper surface of the collecting pipe 36. The exhaust gas sensor 39 detects the component of the exhaust gas G upstream of the catalyst 38 in the collecting pipe 36.

  The collecting pipe 36 is connected to a rear exhaust device 40. The exhaust device 40 silences the exhaust gas G and discharges it to the outside. In the present embodiment, the exhaust device 40 is disposed between the engine E and the rear wheel 14. The exhaust pipe 32, the intermediate collecting pipe 34, the collecting pipe 36, and the exhaust device 40 form an exhaust passage for the exhaust gas G of the engine E.

  As shown in FIG. 2, the exhaust device 40 has a rectangular parallelepiped case 44. Case 44 of this embodiment is comprised by the rectangular parallelepiped which has roundness in a corner | angular part. Specifically, the case 44 has a flat shape with a small vertical dimension, a larger vehicle width direction (left-right direction) dimension, and a larger front-rear dimension than the vehicle width direction dimension. The case 44 is made of a steel plate material, and the mounting bracket 42 is fixed to the upper surface of the case 44 by welding. The exhaust device 40 of the present embodiment is detachably attached to the swing arm bracket 9 (FIG. 1) by a fastening member (not shown) using a mounting bracket 42. However, the material of the case 44 and the support structure of the exhaust device 40 are not limited to this.

  The case 44 has an upper first case half 46 and a lower second case half 48, and the first and second case halves 46, 48 are joined at a joint 50. The case 44 has an introduction port 52 through which the exhaust gas G is introduced and a lead-out port 54 through which the exhaust gas G is derived.

  Specifically, as shown in FIG. 3, the introduction pipe 56 is attached to the front wall 44 f of the case 44, and the outlet pipe 58 is attached to the rear wall 44 r of the case 44. In the present embodiment, the introduction pipe 56 and the outlet pipe 58 are joined to the case 44 by welding. The introduction pipe 56 is made of a steel pipe, and its upstream end (front end) is connected to the collecting pipe 36. The opening (inlet) 56a at the upstream end of the introduction pipe 56 constitutes the introduction port 52 of the case 44 described above. The outlet 56 b at the downstream end of the introduction pipe 56 opens into the internal space of the case 44. Details of the introduction pipe 56 will be described later.

  The outlet pipe 58 is also made of a steel pipe, and an inlet 58 a at the upstream end thereof opens to the internal space of the case 44, and an outlet 58 b at the downstream end opens to the outside of the case 44. The inlet 58a of the outlet pipe 58 constitutes the outlet 54 of the case 44 described above.

  Inside the case 44, an upstream first expansion chamber 60 and a downstream second expansion chamber 62 are formed. The first expansion chamber 60 and the second expansion chamber 62 are arranged side by side in the front-rear direction. The first expansion chamber 60 and the second expansion chamber 62 are partitioned by a partition wall 64. The partition wall 64 is joined to the inner surface of the case 44 by, for example, welding. A sound absorbing material 65 is attached to a portion of the inner surface of the case 44 that contacts the expansion chambers 60 and 62. The sound absorbing material 65 is, for example, glass wool. However, the sound absorbing material 65 is not limited to this.

  A communication path 66 that connects the first expansion chamber 60 and the second expansion chamber 62 is formed in the partition wall 64. In the present embodiment, the communication path 66 is configured by a communication pipe 68 that penetrates the partition wall 64. The communication pipe 68 is a straight steel pipe having a constant cross-sectional area in the axial direction, and is joined to the mounting hole 64b of the partition wall 64 by welding. However, the communication path 66 is not limited to this, and may be, for example, a through hole provided in the partition wall 64. Further, the number of communication paths may be one or plural. The shape (cross-sectional shape) of the communication path is preferably circular, but may be other shapes. The circular shape is advantageous in terms of strength because it is difficult for stress to concentrate.

  In the present embodiment, the introduction pipe 56 and the outlet pipe 58 are disposed on the right side (close to one side) in the case 44, and the communication path 66 is disposed on the left side (close to the other side). However, the arrangement of the introduction pipe 56 and the communication path 66 is not limited to this. For example, the introduction pipe 56 may be disposed in the center in the left-right direction, and the communication path 66 may be disposed on both the left and right sides of the introduction pipe 56. Further, the communication path 66 may be arranged on the right side (one side), and the introduction pipe 56 and the outlet pipe 58 may be arranged on the left side (the other side) in the case 44. Further, the introduction pipe 56 and the lead-out pipe 58 and the communication path 66 may be arranged side by side in the vertical direction.

  The introduction pipe 56 passes through the first expansion chamber 60 and penetrates the partition wall 64, and the outlet 56 b opens to the second expansion chamber 62. A portion of the introduction pipe 56 that penetrates the partition wall 64 is press-fitted into a through hole 64 a provided in the partition wall 64. That is, the outlet 56 b and the outlet 54 of the introduction pipe 56 are arranged in the same second expansion chamber 62. As described above, both the outlet 56 b and the outlet 54 of the introduction pipe 56 are disposed on the right side (one side in the left-right direction) in the case 44 and are disposed in the same second expansion chamber 62. . That is, the outlet 56b and the outlet 54 of the introduction pipe 56 are disposed close to each other.

  Specifically, as shown in FIG. 4, a part of the virtual opening V obtained by projecting the opening of the outlet 56 b of the introduction pipe 56 in the axial direction C <b> 1 overlaps a part of the outlet 54. In other words, when viewed from the axial direction C1, the outlet 56b of the introduction pipe 56 and the outlet 54 partially overlap. Thereby, a part of the exhaust gas G from the outlet 56 b of the introduction pipe 56 flows directly into the outlet pipe 58 from the inlet 58 a without being diffused into the second expansion chamber 62 and rapidly expanding. Furthermore, at least a part of the inlet 58a (outlet 54) of the outlet pipe 58 may be positioned on the axis C1 of the outlet 56b of the inlet pipe 56, and the overlapping portion of both the outlets 56b and 58a may be enlarged.

  The sectional area (passage area) S2 of the outlet 56b of the introduction pipe 56 is set smaller than the sectional area (passage area) S1 of the inlet 56a (introduction port 52) of the introduction pipe 56 (S1 <S2). Specifically, as shown in FIG. 3, the introduction pipe 56 has a reduced diameter portion 69 and a straight pipe portion 70 on the downstream side thereof. The diameter-reduced portion 69 of the present embodiment decreases in a taper shape toward the downstream in the flow direction of the exhaust gas G. When the reduced diameter portion 69 is tapered, the exhaust gas G flows smoothly through the reduced diameter portion 69. However, the reduced diameter portion 69 is not limited to the tapered shape, and may have a shape in which the cross-sectional area gradually decreases. The straight pipe portion 70 has a substantially constant passage area. The straight pipe portion 70 penetrates the partition wall 64 and is supported by the partition wall 64, and the downstream end of the straight pipe portion 70 constitutes the outlet 56 b of the introduction pipe 56.

  In the present embodiment, the passage area at the upstream end of the reduced diameter portion 69 shown in FIG. 4 is the same as the passage area S1 of the introduction port 52, and the passage area at the downstream end is the same as the passage area S2 of the outlet 56b of the introduction pipe 56. is there.

  A lateral hole 72 that communicates the internal space of the introduction pipe 56 and the internal space of the case 44 is formed in the side wall 56 c of the introduction pipe 56. The lateral hole 72 of the present embodiment communicates with the first expansion chamber 62. In the present embodiment, two lateral holes 72 and 72 are provided in the reduced diameter portion 69. Each lateral hole 72 has an opening area S3 larger than the passage area S1 of the outlet 56b of the introduction pipe 56 (S1 <S3). However, the number of the horizontal holes 72 and 72 is not limited to this, and may be one or three or more.

  One of the two lateral holes 72, 72 opens on the right side (one side) in FIG. 3, and the other opens on the left side (the other side). Since the introduction pipe 56 of the present embodiment is disposed on the right side (one side) inside the case 44, the right lateral hole 72 faces the inner surface of the case 44, and the left lateral hole 72 is the first expansion chamber. It opens toward 60 wide spaces. In the present embodiment, the right lateral hole 72 faces the joint 50 having high rigidity in the first and second case halves 46 and 48. It is preferable that the right lateral hole 72 and the joint 50 overlap each other in a side view. In the present embodiment, the right lateral hole 72 and the left lateral hole 72 are formed 180 degrees apart in the circumferential direction of the axis A1. The introduction pipe 56 and the outlet pipe 58 may be disposed on the left side inside the case 44.

  The number and position of the horizontal holes 72 are not limited to this embodiment. However, when the case 44 has a flat shape with a small vertical dimension as in the present embodiment, if the horizontal hole 72 is formed in the vertical direction, the exhaust gas G from the horizontal hole 72 is formed on the upper wall or the lower wall. The case 44 is vibrated and vibrates, which is not preferable. Therefore, the lateral hole 72 is preferably opened in a direction in which the size of the case 44 is large and in a direction orthogonal to the flow direction of the exhaust gas G (in the present embodiment, the left-right direction).

  In addition, from the viewpoint of efficiently discharging the exhaust gas G from the horizontal hole 72, it is preferable that a pair of the horizontal holes 72 is provided around the introduction pipe 56 at positions where the phases are different by 180 °. When the introduction pipe 56 is disposed on one side inside the case 44 as in the present embodiment, the one side lateral hole 72 is close to the side wall 44 s of the case 44. As described above, since the lateral hole 72 on one side is opposed to the joint portion 50 having a high strength, the vibration of the case 44 hardly occurs.

  In the present embodiment, the passage area S4 of the horizontal hole 72 is set larger than the passage area S5 of the communication passage 66 (S4> S5). Here, when a plurality of the horizontal holes 72 are provided, the passage area S4 of the horizontal holes 72 is the total of the opening areas S3 of the horizontal holes 72. Therefore, in this embodiment with two horizontal holes 72, the passage area S4 of the horizontal hole 72 is larger than the passage area S5 of the communication passage 66 (S4 = (S3 + S3)> S5).

  Inside the case 44, a plurality of exhaust paths having different lengths, that is, two exhaust paths P1 and P2 in the present embodiment, are formed between the inlet 52 and the outlet 54. The first exhaust path P1 is a path from the introduction port 52 to the outlet 54 directly through the outlet 56b of the introduction pipe 56. The second exhaust path P <b> 2 is a path that enters the first expansion chamber 60 from the introduction port 52 through the lateral hole 72, and further travels from the communication path 66 to the outlet port 54 through the second expansion chamber 62. Therefore, the first exhaust path P1 is shorter than the second exhaust path P2.

  The exhaust gas G flowing into the case 44 from the introduction port 52 passes through the first and second exhaust paths P1 and P2, and all the exhaust gas G is discharged from the outlet port 54. Hereinafter, the flow of the exhaust gas G will be described with reference to FIG. 5 indicates the flow of the exhaust gas G when the engine E rotates at low speed, and the arrow G2 indicates the flow of the exhaust gas G when the engine E rotates at high speed.

  As indicated by an arrow G1 in FIG. 5, at the time of engine low speed rotation, the exhaust gas G mainly flows through the first exhaust path P1. Specifically, the exhaust gas G flowing into the introduction pipe 56 from the introduction port 52 flows from the reduced diameter portion 69 of the introduction pipe 56 through the straight pipe portion 70. Since the exhaust pressure of the exhaust gas G is low at the time of engine low speed rotation, the passage resistance is small even in the reduced diameter portion 69 where the passage area gradually decreases and the straight pipe portion 70 where the passage area S2 is small. Therefore, the exhaust gas G flows smoothly.

  The exhaust gas G that has passed through the reduced diameter portion 69 and the straight pipe portion 70 is led out from the outlet 56 b of the introduction pipe 56. Since the outlet 56b of the introduction pipe 56 is disposed so as to be close to and opposed to the outlet 54, most of the exhaust gas G led out from the outlet 56b of the inlet pipe 56 directly enters the outlet 54. It flows toward. The remainder (a part) of the exhaust gas G enters the second expansion chamber 62 and diffuses. The exhaust gas G flowing into the outlet pipe 58 from the outlet 54 is discharged to the outside of the case 44 through the outlet 58 b of the outlet pipe 58.

  As indicated by an arrow G2 in FIG. 5, the exhaust gas G mainly flows through the second exhaust path P2 during high-speed rotation of the engine. More specifically, since the exhaust pressure of the exhaust gas G is large during high-speed engine rotation, the passage resistance of the straight pipe portion 70 having a small passage area S2 increases. Therefore, only a part of the exhaust gas G flowing into the introduction pipe 56 from the introduction port 52 flows through the straight pipe portion 70, and most of the exhaust gas G is from the lateral hole 72 having an opening area S 3 larger than the passage area S 2 of the straight pipe portion 70. It flows into the first expansion chamber 60. The exhaust gas G is suddenly expanded and silenced in the first expansion chamber 60, and is further absorbed by the sound absorbing material 65, and then flows into the second expansion chamber 62 through the communication path 66. When passing through the communication path 66, the exhaust gas G contracts.

  The exhaust gas G is rapidly expanded and silenced when it flows into the second expansion chamber 62 from the communication path 66, and is further absorbed by the sound absorbing material 65 on the inner surface of the case 44, and then is discharged from the outlet 54 to the outlet pipe 58. Inflow. Thereafter, the exhaust gas G is discharged from the outlet 58 b of the outlet pipe 58 to the outside of the case 44.

  According to the above configuration, most of the exhaust gas G flows directly from the introduction pipe 56 toward the outlet 54 at the time of engine low speed rotation in FIG. That is, the exhaust gas G is exhausted from the outlet 54 with little expansion / contraction and exhaust interference inside the case 44. Therefore, a sound close to the original sound of the exhaust sound can be obtained in the engine low speed rotation region where the exhaust sound is small. Here, the “sound close to the original sound of the exhaust sound” is a sound having a low frequency and having a plurality of order components (peaks). In other words, it is a low-frequency low-pitched sound and a powerful sound with many order components. By feeling such a sound close to the original sound of the exhaust sound, it becomes possible to obtain a driver's favorite exhaust sound. In addition, since the exhaust noise is small at the time of engine low speed rotation, the necessity for noise reduction is low.

  6, most of the exhaust gas G flows from the lateral hole 72 toward the outlet 54 via the first expansion chamber 60, the communication passage 66, and the second expansion chamber 62. That is, the exhaust gas G is sufficiently silenced in the first and second expansion chambers 60 and 62 through expansion / contraction and exhaust interference, and then discharged from the outlet 54. In this way, it is possible to obtain a sound close to the original sound of the exhaust sound in the engine low-speed rotation region where the exhaust sound is low while ensuring the necessary silence in the engine high-speed rotation region where the exhaust sound is large.

  The introduction pipe 56 has a reduced diameter portion 69 that decreases in diameter toward the downstream in the flow direction of the exhaust gas G. Since the exhaust pressure is small during low-speed engine rotation, the passage resistance in the introduction pipe 56 is also small. Therefore, the exhaust gas G smoothly flows directly toward the outlet 54 through the reduced diameter portion 69. On the other hand, since the exhaust pressure increases during high-speed rotation of the engine, the passage resistance increases at the reduced diameter portion 69. Therefore, most of the exhaust gas G flows from the lateral hole 72 toward the outlet 54 via the first and second expansion chambers 60 and 62. As a result, the necessary silence is ensured.

  As shown in FIG. 3, a part of the inlet 58 a of the outlet pipe 58 is located on the axis A <b> 1 of the outlet 56 b of the inlet pipe 56. As a result, the exhaust gas G that has passed through the introduction pipe 56 at the time of low-speed rotation of the engine can be easily directed directly to the outlet pipe 58. As a result, it becomes easier to obtain a sound close to the original sound of the exhaust sound.

  The introduction pipe 56 passes through the first expansion chamber 60 and penetrates the partition wall 64, and the outlet 56 b opens to the second expansion chamber 62. Further, the lateral hole 72 communicates with the first expansion chamber 60. Thus, during high-speed rotation of the engine, the exhaust gas G flows into the first expansion chamber 60 from the lateral hole 72 of the introduction pipe 56, flows into the second expansion chamber 62 through the communication path 64, and then from the outlet 54. Discharged. Thereby, a high silencing effect can be obtained during high-speed engine rotation. Further, since the introduction pipe 56 is supported by the partition wall 64 through the partition wall 64 at the straight pipe portion 70 on the tip side of the reduced diameter portion 69, the support of the introduction pipe 56 is stabilized.

  The passage area S4 of the horizontal hole 72 is set larger than the passage area S5 of the communication passage 66. As a result, during high-speed engine rotation, the exhaust gas G flows into the first expansion chamber 60 from the lateral hole 72 and expands / contracts when flowing into the second expansion chamber 62 through the communication path 66. As a result, the silencing effect during high-speed engine rotation is improved.

  Further, the introduction pipe 56 is disposed on the right side in the case 44, and the communication path 66 is disposed on the left side. Thus, the communication path 66 can be provided in the space on the left side secured by arranging the introduction pipe 56 on the right side in the case 44. Thereby, a large expansion space is secured in the space on the left side where the communication path 66 is provided, and the space in the case 44 can be used effectively while setting the silencing effect high. Furthermore, since the lateral hole 72 on one side faces the joint 50, the high-temperature exhaust gas G can collide with the joint 50 having high rigidity. As a result, the vibration of the case 44 is suppressed, and a decrease in the durability of the case 44 can be avoided.

  As shown in FIG. 1, the exhaust device 40 is disposed below the engine E, the introduction pipe 56 is attached to the front wall 44f of the case 44 shown in FIG. 3, and the outlet pipe 58 is attached to the rear wall 44r. Moreover, the 1st expansion chamber 60 and the 2nd expansion chamber 62 are arrange | positioned along with the front-back direction. As a result, the exhaust gas G flows smoothly from the front to the rear of the motorcycle.

  As shown in FIG. 1, an introduction pipe 56 is disposed on the right side of the oil pan 27 below the engine E, and an exhaust device 40 is disposed between the engine E and the rear wheel 14. According to this configuration, the space below the engine E can be used effectively.

  FIG. 6 shows an exhaust device 40A according to the second embodiment of the present invention. The exhaust device 40A of the second embodiment has a silencer 75 connected to the rear thereof. Specifically, a silencer 75 is connected to the rear end of the outlet pipe 58. Providing the silencer 75 further improves the silence performance during high-speed engine rotation. The exhaust device 40A of the second embodiment has a simple structure in which a tail pipe 78 having a plurality of punching holes 80 is housed in an internal space of a casing 76 having a sound absorbing material 82 attached to the inner surface. With such a structure, most of the exhaust gas G flowing into the silencer 75 from the outlet pipe 58 during low-speed rotation of the engine flows through the tail pipe 78 without being discharged from the punching hole 80 and is discharged to the outside. . As a result, it is possible to obtain a sound close to the original sound of the exhaust sound at the time of engine low speed rotation. Other structures are the same as those of the first embodiment, and the same effects as those of the first embodiment are achieved.

  The present invention is not limited to the above-described embodiment, and various additions, modifications, or deletions can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the horizontal hole 72 is provided in the reduced diameter portion 69, but when there is no reduced diameter portion 69 or when there is a cylindrical portion on the upstream side of the reduced diameter portion 69, It may be provided. Further, there may be three or more exhaust paths. In this case, the exhaust path from the outlet 56b of the introduction pipe 56 to the outlet 58 may be the shortest among the three or more exhaust paths. Further, the exhaust device of the present invention is suitably used for a motorcycle in which the arrangement space is limited. However, the exhaust device of the present invention is also applicable to vehicles other than motorcycles, such as tricycles and four-wheel buggies. Therefore, such a thing is also included in the scope of the present invention.

14 Rear wheel 27 Oil pan 40, 40A Exhaust device 44 Case 44f Case front wall 44r Case rear wall 46 First case half 48 Second case half 50 Joint 52 Inlet 54 Outlet 56 Introducing pipe 56c Introducing pipe Side wall 58 Lead pipe 58a Lead pipe inlet 60 First expansion chamber 62 Second expansion chamber 64 Bulkhead 66 Communication passage 69 Reduced diameter portion 70 Straight pipe portion 72 Horizontal hole 75 Silencer A1 Center axis E of introduction pipe outlet E Engine G Exhaust gas P1 First exhaust path P2 Second exhaust path S1 Cross-sectional area of introduction port S2 Cross-sectional area of exit of introduction pipe (passage area)
S3 Horizontal hole opening area S4 Horizontal hole passage area S5 Communication passage area V Virtual opening

Claims (10)

An exhaust system comprising a case having an inlet for introducing exhaust gas of an engine and a lead-out port for exhausting the exhaust gas,
A plurality of exhaust paths having different lengths are provided between the inlet and the outlet.
An introduction pipe forming the introduction port is provided;
The cross-sectional area of the outlet of the inlet pipe is set smaller than the cross-sectional area of the inlet,
The outlet of the introduction pipe and the outlet are arranged in the same expansion chamber;
A part of the virtual opening obtained by projecting the opening of the outlet of the introduction pipe in the axial direction thereof overlaps with a part of the outlet.
A lateral hole having an opening area larger than a passage area of the outlet of the introduction pipe is formed in the side wall of the introduction pipe, communicating with the expansion chamber in the case.
An exhaust system for an engine having the shortest exhaust path from the outlet of the introduction pipe to the outlet of the plurality of exhaust paths.   2. The exhaust system according to claim 1, wherein the introduction pipe has a reduced diameter portion that decreases in diameter toward a downstream side in an exhaust gas flow direction. The exhaust apparatus according to claim 1 or 2, further comprising a lead-out pipe whose inlet forms the lead-out port,
An exhaust system for an engine, wherein at least a part of an inlet of the outlet pipe is located on an axial center of an outlet of the inlet pipe. 4. The exhaust device according to claim 1, further comprising: a partition that divides an upstream first expansion chamber and a downstream second expansion chamber; and the partition provided on the partition. A communication passage communicating the expansion chamber and the second expansion chamber;
The introduction pipe passes through the first expansion chamber and penetrates the partition; the outlet opens into the second expansion chamber;
An exhaust system for an engine, wherein the lateral hole communicates with the first expansion chamber. The exhaust device according to claim 4, wherein the introduction pipe includes a reduced diameter portion that is reduced in diameter toward a downstream side in an exhaust gas flow direction, and a straight pipe portion that is downstream of the reduced diameter portion,
An exhaust system for an engine, wherein the straight pipe portion penetrates the partition and is supported by the partition.   6. The exhaust system according to claim 4 or 5, wherein a passage area of the lateral hole is larger than a passage area of the communication path.   The exhaust system according to any one of claims 4 to 6, wherein the introduction pipe is disposed closer to one side in the case, and the communication path is disposed closer to the other side. The exhaust device according to any one of claims 1 to 7, wherein the case is configured by joining a first case half and a second case half at a joint portion,
An exhaust system for an engine in which the lateral hole faces the joint. A motorcycle comprising the exhaust device according to any one of claims 4 to 7 below the engine,
The case has a rectangular parallelepiped shape,
An introduction pipe having the introduction port is attached to the front wall of the case,
A lead-out pipe having the lead-out port is attached to the rear wall of the case,
A motorcycle in which the first expansion chamber and the second expansion chamber are arranged side by side in the front-rear direction. The motorcycle according to claim 9,
The introduction pipe is arranged on one side of the lower oil pan of the engine,
The exhaust device is disposed between the engine and the rear wheel,
A motorcycle in which a silencer is connected to the rear of the exhaust device.

Images