JP6392596B2 - Engine exhaust system - Google Patents

Description

  The present invention relates to an engine exhaust apparatus including a plurality of exhaust pipes whose base end portions are connected to a plurality of exhaust ports to derive exhaust gas.

  For example, in a parallel multi-cylinder engine mounted on a motorcycle, an exhaust pipe connected to the exhaust port has a circular cross section. Therefore, the exhaust port formed on the front surface of the engine is generally configured in a circular shape in accordance with the cross-sectional shape of the exhaust pipe (for example, Patent Document 1).

JP 2007-016672 A

  In the case of a four-valve engine, if the exhaust port and the exhaust pipe are circular, the cross section of the passage changes suddenly, and the smooth flow of exhaust gas may be hindered. If the diameters of the exhaust port and the exhaust pipe are increased, the change in the cross-sectional shape can be suppressed, but the degree of freedom in the arrangement of the exhaust pipe and peripheral parts is limited.

  An object of the present invention is to provide an exhaust system for an engine that can realize a smooth flow of exhaust gas and improve the degree of freedom of equipment arrangement.

  In order to achieve the above object, an exhaust system for an engine according to the present invention includes a plurality of exhaust pipes whose base end portions are connected to a plurality of exhaust ports of the engine and lead out exhaust gas, and the plurality of exhaust ports includes: The exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft, each exhaust port is a non-circular shape that is long in the width direction, and the base end portion of the outer exhaust pipe located outside the width direction is the exhaust port A non-circular exhaust inlet that is long in the width direction and connected to the outside, and an outer surface that curves smoothly inward in the width direction from the exhaust inlet toward the downstream side of the exhaust, and the curved base end portion The cross-sectional shape of the outer exhaust pipe is a circular shape whose axis is offset to the inner side in the width direction compared to before the curve. Here, “non-circular” includes an ellipse or an ellipse.

  According to the above configuration, since the exhaust port is non-circular in the width direction, the exhaust passage area is increased and the pipe resistance is reduced. When there are a plurality of exhaust valves, the exhaust port is non-circular, and the base end of the exhaust pipe has an outer surface that smoothly curves inward in the width direction toward the downstream side of the exhaust. The cross-sectional change of the passage can be moderated and the exhaust gas can be discharged smoothly. Furthermore, since the shaft center of the cross-sectional shape of the outer exhaust pipe after the bending is offset inward in the width direction as compared with that before the bending, it is easy to secure a space for arranging other parts on the outer side of the exhaust pipe. As a result, the degree of freedom of device arrangement is improved.

  In the present invention, the base end portion is set so as to lead the exhaust gas downward, and further includes a bracket that connects the base end portion to the exhaust port, and the bracket is connected to the exhaust port by a fastening member. It is preferable that at least one fastening member is disposed at a position displaced downward from the center of the exhaust port on the outer side in the width direction of the base end portion. According to this configuration, since the base end portion of the outer exhaust pipe is curved inward in the width direction, it is easy to perform a fastening operation even if the fastening member is disposed close to the inner side in the width direction. Therefore, even if each exhaust port has a non-circular shape that is long in the width direction, it is possible to suppress the engine to which the fastening member is attached from becoming large in the width direction.

  When the bracket is attached by the fastening member, the bracket is displaced from the center of the exhaust port on the outer side in the width direction of the base end portion, and the exhaust port on the inner side in the width direction of the base end portion. It is preferable that the exhaust port is attached to the peripheral portion of the exhaust port by a fastening member at a position displaced upward from the center of the exhaust port. According to this configuration, since the fastening member is not disposed on the outer side in the vehicle width direction of the exhaust port, the width of the bracket can be reduced and the engine can be suppressed from increasing in the width direction.

  In the present invention, the inner surface includes four exhaust pipes, and the two inner exhaust pipes on the inner side in the width direction each have a base end portion smoothly curved outward in the width direction toward the downstream side of the exhaust gas. An inner bracket for an inner exhaust pipe that has a circular cross-sectional shape of the inner exhaust pipe at the downstream end of the curved base end portion, and each base end portion of the inner exhaust pipe is connected to the exhaust port. Is a position that is offset downward from the center of the exhaust port on the inner side in the width direction of the base end portion, and a position that is offset upward from the center of the exhaust port on the outer side in the width direction of the base end portion. It is preferable that the exhaust port is attached to the peripheral portion of the exhaust port by a fastening member. According to this structure, since the fastening position of the bracket of an adjacent exhaust pipe approaches, fastening work can be made efficient.

  When the four exhaust pipes are provided, the distance between the axial centers of the downstream ends of the base ends of the two inner exhaust pipes is adjacent to the axial center of the downstream end of the base end of the outer exhaust pipe. It is preferable that the distance between the base end portion of the inner exhaust pipe and the axial center of the downstream end is larger than the distance between the inner exhaust pipe and the axial center. For example, when the engine is mounted on a motorcycle and a round type radiator whose rear surface is curved toward the rear is arranged in front of the exhaust pipe, the distance between the axes of the two inner exhaust pipes is increased. It is easy to secure the installation space for the exhaust pipe by offsetting each inner exhaust pipe to the outside.

  In the present invention, the plurality of exhaust pipes merge at the collecting pipe, and an opening edge forming a downstream end of each exhaust pipe is inclined toward the upstream side in the exhaust gas flow direction toward the radially outer side of the collecting pipe. It is preferable that the downstream ends of the exhaust pipes are arranged so as to be shifted in the exhaust gas flow direction. According to this configuration, since the opening edge of the downstream end of each exhaust pipe is inclined on the upstream side of the collecting pipe, the change in the passage area when flowing from the exhaust pipe into the collecting pipe can be reduced. As a result, the exhaust gas flow becomes smooth. Furthermore, since the opening edge of the downstream end of each exhaust pipe is displaced in the exhaust gas flow direction, the downstream end of the longer exhaust pipe can function as a partition wall. As a result, the passage area increases in two stages, and a sudden passage change is avoided, so that the flow of exhaust gas becomes smoother.

  According to the exhaust system for an engine of the present invention, by making the exhaust port non-circular, the cross-sectional change of the exhaust passage can be moderated and the exhaust gas can be discharged smoothly. In addition, it is easy to secure a space for arranging other parts outside the exhaust pipe. As a result, the degree of freedom of device arrangement is improved.

1 is a side view showing a motorcycle including an engine exhaust device according to an embodiment of the present invention. It is a front view which expands and shows the front surface of the cylinder head of the same engine. FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1 showing the cylinder head. It is a front view which shows the exhaust pipe of the engine. It is a bottom view which shows the collecting pipe of the same exhaust pipe. (A) is a horizontal sectional view showing the collecting pipe, and (B) is a horizontal sectional view showing a conventional collecting pipe. It is a front view which shows the state which attached the exhaust pipe to FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The left and right directions in this specification refer to the left and right as viewed from a rider riding a motorcycle.

  FIG. 1 is a side view of a rear portion of a motorcycle equipped with an engine exhaust device according to an embodiment of the present invention. The body frame FR of the motorcycle has a main frame 1 constituting the front half and a rear frame 2 connected to the rear part of the main frame 1 and constituting the rear half of the body frame FR. A front wheel is supported on a front end portion of the main frame 1 via a front fork (not shown).

  A swing arm bracket 4 is provided below the rear end of the main frame 1, and a swing arm 6 is supported on the swing arm bracket 4 via a pivot shaft 5 so as to be swingable up and down. A rear wheel 8 is supported at the rear end of the swing arm 6. An engine E is supported at the center lower portion of the main frame 1, and the rear wheel 8 is driven by the engine E through a power transmission member 10 such as a chain. The engine E is a 4-valve parallel multi-cylinder 4-cycle engine. However, the format of the engine E is not limited to this. A radiator 9 for dissipating engine cooling water is disposed in front of the engine E.

  The engine E has a crankcase 14 that supports the crankshaft CS, a cylinder block 15 that protrudes upward from the upper surface of the crankcase 14, and a cylinder head 20 above the cylinder block 15. The engine E of this embodiment is equipped with a supercharger 12. Specifically, the supercharger 12 is disposed above the rear portion of the crankcase 14 of the engine E, and the intake air pressurized by the supercharger 12 is disposed in the intake chamber disposed above the supercharger 12. After being stored in 16, it is supplied to the engine E from the intake port 22 formed on the rear surface of the cylinder head 20 of the engine E via the throttle body 18.

  After the four steel exhaust pipes 26 connected to the exhaust port 24 at the front part of the cylinder head 20 of the engine E are gathered at the junction 25 below the engine E, the exhaust chamber 27 and the inlet pipe 35 are connected. To the exhaust muffler 28. The exhaust muffler 28 is disposed on the outer side of the rear wheel 8, for example, on the right side. The exhaust chamber 27 and the exhaust muffler 28 are covered with a cover 31 from the outer side.

  As shown in FIG. 2, the four exhaust ports 24 are arranged side by side in the width direction along the rotational axis of the crankshaft CS (FIG. 1). Here, the width direction of the engine E coincides with the vehicle body width direction. Each exhaust port 24 is non-circular in the width direction. Specifically, each exhaust port 24 includes a pair of left and right first and second ports 32, 34. The first and second ports 32, 34 are D-shaped and are connected to two exhaust valve outlets of each cylinder. Communicate. Thereby, each exhaust port 24 has an oval shape that is long in the width direction as a whole.

  Specifically, each exhaust port 32, 34 has an arc portion and a straight portion, and the straight portions of the first and second exhaust ports 32, 34 face each other to partition between the exhaust ports 32, 34. Part. The distance L2 from the center C1 of the exhaust port 24 to the bulging portion of the arc portion is larger than the distance L1 from the center C1 of the exhaust port 24 to the end of the port along the straight line portion. The combined shape of the arc portions of the first and second exhaust ports 32 and 34 forms an oval shape that is long in the width direction.

  A cam angle sensor 38 is attached above the exhaust port 24 at the center in the vehicle width direction on the front surface of the cylinder head 20. A cylinder head 20 and a cylinder block 15 below the cylinder head 20 are connected to a crankcase 14 (FIG. 1) by a head bolt 21.

  Exhaust pipe mounting portions 40 are formed on the upper and lower sides of each exhaust port 24 on the front surface of the cylinder head 20. Specifically, the exhaust pipe mounting portion 40 is formed outside and below the center C1 and inside and above each of the two exhaust ports 24 and 24 on the outer side in the vehicle width direction. Each of the two exhaust ports 24, 24 on the inner side in the vehicle width direction is formed outside and above the center C1, and inside and below. Each exhaust pipe mounting portion 40 is formed of a boss formed integrally with the cylinder head 20 by molding, and has a screw hole 40a opened forward.

  As shown in FIG. 3, each exhaust port 24 communicates with exhaust holes 30, 30 which are a pair of exhaust valve outlets provided in each cylinder of the engine E. Specifically, each exhaust port 24 and a pair of exhaust holes 30, 30 communicate with each other by a pair of exhaust passages 33, 33 formed inside the cylinder head 20, and are discharged from the exhaust holes 30, 30. The exhaust gas G is led from the exhaust port 24 to the exhaust pipe 26 (FIG. 1) through the exhaust passages 33 and 33.

  As shown in FIG. 4, the four exhaust pipes 26 include first and second outer exhaust pipes 42 and 44 positioned on the outer side in the width direction, and first and second inner exhaust pipes 46 positioned on the inner side in the width direction, 48. Specifically, the first outer exhaust pipe 42, the first inner exhaust pipe 46, the second inner exhaust pipe 48, and the second outer exhaust pipe 44 are arranged in this order from the left side.

  The first and second outer exhaust pipes 42 and 44 are respectively connected to the exhaust port 24 (FIG. 2) of the engine E, and the first and second proximal end portions 52 and 54, respectively. , 54 have first and second main body portions 62, 64 connected to the tips (downstream ends). The first and second base ends 52 and 54 are connected to the exhaust port 24 (FIG. 2) by first and second brackets 72 and 74.

  Similarly, the first and second inner exhaust pipes 46 and 48 also have third and fourth base ends 56 and 58 connected to the exhaust port 24 (FIG. 2), respectively, and third and fourth base ends 56. , 58 and third and fourth main body portions 66, 68 connected to the distal ends (downstream ends), and the third and fourth base end portions 56, 58 are connected by the third and fourth brackets 76, 78. , Connected to the exhaust port 24 (FIG. 2).

  Each base end portion 52, 54, 56, 58 is made of a steel pipe material, and is set so as to lead the exhaust gas G downward. The first to fourth base end portions 52, 54, 56, 58 have oval first to fourth exhaust introduction ports 52 a, 54 a, 56 a, 58 a that match the exhaust port 24 (FIG. 2) at their upstream ends. Respectively.

  The first and second base ends 52 and 54 of the first and second outer exhaust pipes 42 and 44 are smoothly curved inward in the width direction from the first and second exhaust introduction ports 52a and 54a toward the downstream side, respectively. The outer end surfaces 52b and 54b are curved, and the cross-sectional shape is circular at the downstream ends 52c and 54c of the curved first and second base end portions 52 and 54. The inner surface opposite to the curved side extends linearly. Thereby, the passage cross section of the first and second base end portions 52 and 54 smoothly changes from the oval shape on the upstream side to the circular shape on the downstream side.

  The third and fourth base ends 56, 58 of the first and second inner exhaust pipes 46, 48 are smoothly curved outward in the width direction from the third and fourth exhaust introduction ports 56a, 58a toward the downstream side, respectively. The inner side surfaces 56b and 58b are curved, and the cross-sectional shape is circular at the downstream ends 56c and 58c of the curved third and fourth base end portions 56 and 58. The outer surface opposite to the curved side extends linearly. Thereby, the passage cross section of the third and fourth base end portions 56 and 58 smoothly changes from the oval shape on the upstream side to the circular shape on the downstream side.

  The axial center C2 at the downstream end of the first and second base end portions 52, 54 of the first and second outer exhaust pipes 42, 44 is the axis C1 before bending, that is, upstream of the base end portions 52, 54. It is offset inward in the width direction as compared with the axial center C1, and the downstream side of the curved portion in the first to fourth base end portions 52, 54, 56, 58 is a passage relative to the upstream side of the curved portion. The area is getting smaller. As described above, the axial center C2 at the downstream end of the first and second base end portions 52, 54 is offset inward in the width direction, and the first to fourth base end portions 52, 54, 56, 58 are made to be more than the curved portions. By reducing the diameter downstream, the degree of freedom in the arrangement of the exhaust pipe 26 and the arrangement of the engine peripheral components is improved.

  Further, the distance between the axial centers C3 and C3 at the downstream ends of the third and fourth base end portions 56 and 58 of the first and second inner exhaust pipes 46 and 48 is set to be the first and second outer exhaust pipes 42 and 44. The axial center C2 at the downstream end of the first and second base end portions 52, 54 and the third and fourth base end portions 56, 58 of the first and second inner exhaust pipes 46, 48 adjacent thereto, respectively. It is set to be larger than the distance between the downstream end axis C3.

  For example, when the round-type radiator 9 whose rear surface is curved rearward is disposed in front of the exhaust pipes 42, 44, 46, and 48, the vehicle body in the width direction behind the radiator 9 (near the center in the width direction of the vehicle body) ) Is pressed by the rear surface of the radiator 9. However, by increasing the distance between the axial centers C3, C3 of the first and second inner exhaust pipes 46, 48, that is, by offsetting the inner exhaust pipes 46, 48 from the center in the width direction of the vehicle body, It is easy to secure an installation space for the inner exhaust pipes 46 and 48.

  The first to fourth brackets 72, 74, 76, and 78 are fixed to the upstream ends of the first to fourth base end portions 52, 54, 56, and 58 by welding, and from the base end portions 52, 54, 56, and 58, respectively. It protrudes like a bowl outward in the radial direction.

  The first and second brackets 72, 74 of the first and second outer exhaust pipes 42, 44 are positioned outside the first and second base end portions 52, 54 in the width direction and are more than the axial center C 1 of the exhaust port 24. Bolt insertion holes 72a and 74a extending in the front-rear direction are provided at positions displaced downward and positions displaced upward inward in the width direction of the first and second base end portions 52 and 54, respectively. Here, “the outer side in the width direction of the first and second base end portions 52, 54” means that the center of the bolt insertion holes 72 a, 74 a is wider than the outer surface of the first and second base end portions 52, 54. Says outside.

  The third and fourth brackets 76 and 78 of the first and second inner exhaust pipes 46 and 48 are located on the inner side in the width direction of the third and fourth base end portions 56 and 58 than the axis C1 of the exhaust port 24. Bolt insertion holes 76a and 78a extending in the front-rear direction are provided at a position displaced downward and a position displaced upward on the outer side in the width direction of the third and fourth base end portions 56 and 58, respectively. Here, “the inner side in the width direction of the third and fourth base end portions 56, 58” means that the center of the bolt insertion holes 76 a, 78 a is wider than the inner side surfaces of the third and fourth base end portions 56, 58. Says inside.

  The upstream ends 62a, 64a, 66a, 68a of the first to fourth body portions 62, 64, 66, 68 are respectively connected to the downstream ends 52c, 54c, 56c, 58c of the first to fourth base ends 52, 54, 56, 58. Are connected by welding. The first to fourth main body portions 62, 64, 66, and 68 are formed of cylindrical pipes having the same inner and outer diameters, and the cross-sectional shape is the downstream end of the first to fourth base end portions 52, 54, 56, and 58. It is a circle that matches 52c, 54c, 56c, and 58c.

  Adjacent main body portions 62, 64, 66, 68 are connected by a connecting pipe 50 having a smaller diameter. Specifically, the first main body 62 and the third main body 66, the third main body 66 and the fourth main body 68, and the fourth main body 68 and the second main body 64 are connected by the connecting pipe 50, respectively. Yes. Thereby, torque adjustment is performed smoothly.

  As shown in FIG. 5, the downstream ends of the four exhaust pipes 26 merge at the junction 25. The four exhaust pipes 26 are gathered into two by the two left and right first collecting pipes 60, 60 and then gathered into one by the second collecting pipe 70. Specifically, the first outer exhaust pipe 42 and the first inner exhaust pipe 46 are gathered by the left first collecting pipe 60, and the second outer exhaust pipe 44 and the second inner exhaust pipe 48 are gathered by the right first collecting pipe 60. Is assembled. Thereafter, the left and right first collecting pipes 60, 60 are assembled in the second collecting pipe 70.

  As shown in FIG. 6 (A), the opening edges 60b, 60b including the downstream ends 60a, 60a of the first collecting pipes 60, 60 are directed radially outward of the second collecting pipe 70 in the flow direction of the exhaust gas G. It is formed so as to incline to the upstream side (front side). Further, the downstream end 60a of one of the two first collecting pipes 60, 60 (the lower side in FIG. 6A) is more in the exhaust gas flow direction than the downstream end 60a of the other (the upper side in FIG. 6A). It is shifted to the upstream side (rear side).

  As shown in FIG. 6B, when the opening edge 100b of the downstream end 100a of the exhaust pipe 100 is not inclined, the passage area increases rapidly when the collecting pipe 102 joins. 6A, since the opening edge 60b of the downstream end 60a of the first collecting pipe 60 is inclined, the change in passage area when flowing from the first collecting pipe 60 into the second collecting pipe 70 is achieved. Can be reduced. As a result, the flow of the exhaust gas G becomes smooth.

  On the other hand, by providing the partition plate 104 indicated by a two-dot chain line in FIG. 6B with the downstream end 100a of the exhaust pipe 100, the change in passage area when flowing from the exhaust pipe 100 into the collecting pipe 102 is reduced. Although there is a structure, it is necessary to fix the partition plate 104 to the downstream end 100a of the exhaust pipe 100 by welding, which increases the number of parts and the number of work steps. Further, according to the configuration of FIG. 6A, the downstream ends 60a, 60a of the two first collecting pipes 60, 60 are arranged so as to be shifted in the exhaust gas flow direction. The downstream end 60a of 60 (lower side in FIG. 6A) functions as a partition plate. As a result, the passage area of the exhaust gas G exiting each first collecting pipe 60 is increased in two stages, and a sudden passage change is avoided, so that the flow of the exhaust gas G becomes smoother.

  FIG. 7 shows a state in which the exhaust pipe 26 is attached to the engine E. A fastening member 69 is used to attach the exhaust pipe 26 to the engine E. Specifically, the fastening member 69 is inserted into the bolt insertion holes 72a, 74a, 76a, 78a of the brackets 72, 74, 76, 78 of each exhaust pipe 26 of FIG. 4, and the cylinder head 20 exhaust pipe mounting portion shown in FIG. Tighten to 40 screw holes 40a. Thereby, each exhaust pipe 26 of FIG. The fastening member 69 is, for example, a hexagon socket head bolt. When a hexagon socket head cap screw is used as the fastening member 69, the attachment in a narrow space becomes easy.

  According to the above configuration, as shown in FIG. 2, since the exhaust port 24 has an oval shape that is long in the width direction, a space is secured above the exhaust port 24 on the front surface of the cylinder head 20, and a cam is formed in the empty space. An angle sensor 38 is arranged. Further, since the exhaust port 24 is oval, the pair of exhaust passages 33 and 33 from the two exhaust valve outlets shown in FIG. 3 are joined not in the cylinder head 20 but in the exhaust pipe 26 of FIG. Can do. As a result, the exhaust gas G can be discharged smoothly by making the cross-sectional change of the exhaust passage gentler than in the case of merging in the exhaust port 24.

  Furthermore, since the base end portions 52 and 54 of the outer exhaust pipes 42 and 44 have outer surfaces 52b and 54b that smoothly curve inward in the width direction toward the downstream side, the overall width dimension of the exhaust pipe 26 is reduced. Get smaller. Thereby, the space which arrange | positions other components, for example, the hoses of the radiator 9, etc. to the outer side of the outer side exhaust pipes 42 and 44 is ensured easily.

  The exhaust port 24 is located at a position where the first and second brackets 72 and 74 of the first and second outer exhaust pipes 42 and 44 are displaced downward on the outer side in the width direction of the first and second base end portions 52 and 54. It is attached to the peripheral part of this by the fastening member 69. Since the first and second base end portions 52 and 54 of the first and second outer exhaust pipes 42 and 44 are curved inward in the width direction, the fastening can be performed even if the fastening member 69 is arranged inward in the width direction. The member 69 is easy to operate. Therefore, even if each exhaust port 24 is formed in an oval shape that is long in the width direction, the engine E to which the fastening member 69 is attached can be prevented from becoming large in the width direction.

  Since the head bolt 21 for connecting the cylinder head 20 to the cylinder block 15 and the crankcase 14 is disposed on the upper outside of the exhaust port 24 on the outer side in the width direction, the space is small. The position where the first and second brackets 72, 74 of the second outer exhaust pipes 42, 44 are displaced downward on the outer side in the width direction of the first and second base end portions 52, 54 and the upper side on the inner side in the width direction. It is attached by a fastening member 69 at a position displaced. As a result, the fastening member 69 is not arranged on the outer side in the vehicle width direction of the exhaust port 24, so that the width of the first and second brackets 72, 74 can be reduced, and the engine E is attached for mounting the brackets 72, 74. Can be prevented from increasing in the width direction.

  Further, the positions where the third and fourth brackets 76, 78 of the first and second inner exhaust pipes 46, 48 are displaced downward inward in the width direction of the third and fourth base end portions 56, 58, and the width. The exhaust port 24 is attached to the peripheral portion of the exhaust port 24 by a fastening member 69 at a position displaced upward in the direction outside. Thereby, since the fastening position of each adjacent exhaust pipe 26 approaches, fastening work can be made efficient.

  The first to fourth base end portions 52, 54, 56, 58 are connected to the engine E by a fastening member 69 via first to fourth brackets 72, 74, 76, 78. At least one of the fastening members 69 is attached to the lower side of the exhaust port 24 on the curved side of the base end portions 52, 54, 56, 58. Thus, the fastening member 69 can be easily tightened by arranging the fastening portion below the curved side.

  The outer side surfaces 52b and 54b are curved in the outer exhaust pipes 42 and 44, and the inner side surfaces 56b and 58b are curved in the inner exhaust pipes 46 and 48. That is, the opposite side surfaces of the outer exhaust pipes 42 and 44 and the inner exhaust pipes 46 and 48 are curved. A fastening member 69 is attached to the lower side of the exhaust port 24 on the curved side of each exhaust pipe 42, 44, 46, 48, and a fastening member 69 is attached to the upper side of the exhaust port 24 on the non-curved side. Thereby, the fastening position of adjacent exhaust pipes approaches and the time required for fastening work can be shortened.

  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 embodiment, the exhaust port 24 has an oval shape, but may be any non-circular shape that is long in the width direction, and may be, for example, an oval shape. In the above embodiment, the brackets 72, 74, 76, 78 are provided for each of the four exhaust pipes 26. However, a single bracket may be provided for the four exhaust pipes 26.

  Furthermore, the number of exhaust pipes 26 should just be two or more, and is not limited to four. For example, when there are two exhaust pipes, the two exhaust pipes constitute an outer exhaust pipe and no inner exhaust pipe is provided. When there are three exhaust pipes, the two exhaust pipes constitute an outer exhaust pipe, and there is one inner exhaust pipe. In this case, the base end portion of the inner exhaust pipe may be curved to the left or right side, or may not be curved.

  In the above embodiment, a four-valve engine with two intake / exhaust valves has been described. However, any engine having a plurality of exhaust ports may be used. For example, an engine with one intake valve and three exhaust valves may be used. .

  In the above embodiment, the passage area of the first to fourth base end portions 52, 54, 56, and 58 is smaller on the downstream side than the curved portion compared to the upstream side. 2 The axial center C2 at the downstream end of the first and second base end portions 52, 54 of the outer exhaust pipes 42, 44 only needs to be offset inward in the width direction as compared to the axial center C1 before bending. The area need not be small. This also improves the degree of freedom in the arrangement of the exhaust pipe 26 and the arrangement of engine peripheral parts. The present invention can also be applied to an engine in which the width direction of the engine and the width direction of the vehicle body are different. Therefore, such a thing is also included in the scope of the present invention.

24 exhaust port 26 exhaust pipe 42 first outer exhaust pipe 44 second outer exhaust pipe 46 first inner exhaust pipe 48 second inner exhaust pipe 52 first base end (base end of outer exhaust pipe)
52a First exhaust inlet (exhaust inlet of the outer exhaust pipe)
52b, 54b Outer surface 54 of the outer exhaust pipe Second base end portion (base end portion of the outer exhaust pipe)
54a Second exhaust inlet (exhaust inlet of the outer exhaust pipe)
56 3rd base end part (base end part of inner side exhaust pipe)
56b, 58b Inner side surface 58 of the inner exhaust pipe Fourth base end (base end of the inner exhaust pipe)
69 Fastening member 70 Second collecting pipe 72 First bracket (outer exhaust pipe bracket)
74 Second bracket (outer exhaust pipe bracket)
76 Third bracket (inner exhaust pipe bracket)
78 Fourth bracket (inner exhaust pipe bracket)
CS Crankshaft E Engine G Exhaust gas

Claims (6)

A plurality of exhaust pipes whose base end portions are connected to a plurality of exhaust ports of the engine and lead out exhaust gas; and a collecting portion that is disposed below the engine and collects the plurality of exhaust pipes.
The plurality of exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft,
Each exhaust port is a non-circular shape that is long in the width direction,
A base end portion of an outer exhaust pipe located on the outer side in the width direction is connected to the exhaust port and is a non-circular exhaust inlet that is long in the width direction, and smoothly from the exhaust inlet toward the downstream of the exhaust. Having an outer surface curved inward in the width direction and an inner surface extending linearly ,
The proximal end extends downward from the exhaust port;
At the downstream end of the curved base end portion, the cross-sectional shape of the outer exhaust pipe is a circle whose axis is offset inward in the width direction compared to before the curve,
The base end portion is set to lead the exhaust gas downward,
Furthermore, it has a bracket for connecting the base end to the exhaust port,
The bracket is attached to a peripheral portion of the exhaust port by a fastening member;
At least one of the fastening members is disposed at a position displaced downward from the center of the exhaust port on the outer side in the width direction of the base end portion;
The fastening device disposed below the exhaust port is an exhaust device for a motorcycle engine disposed on the curved side of the base end portion . 2. The exhaust device according to claim 1 , wherein the bracket is deviated downward from the center of the exhaust port on the outer side in the width direction of the base end portion, and the exhaust port on the inner side in the width direction of the base end portion. An exhaust system for an engine of a motorcycle, which is attached to a peripheral portion of the exhaust port by a fastening member at a position displaced upward from the center. Comprising four exhaust pipes whose base end portions are connected to a plurality of exhaust ports of the engine and lead out exhaust gas;
The four exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft,
Each exhaust port is a non-circular shape that is long in the width direction,
A base end portion of an outer exhaust pipe located on the outer side in the width direction is connected to the exhaust port and is a non-circular exhaust inlet that is long in the width direction, and smoothly from the exhaust inlet toward the downstream of the exhaust. An outer surface curved inward in the width direction,
At the downstream end of the curved base end portion, the cross-sectional shape of the outer exhaust pipe is a circle whose axis is offset inward in the width direction compared to before the curve,
The base end portion is set to lead the exhaust gas downward,
Furthermore, it has a bracket for connecting the base end to the exhaust port,
The bracket is attached to a peripheral portion of the exhaust port by a fastening member;
At least one of the fastening members is disposed at a position displaced downward from the center of the exhaust port on the outer side in the width direction of the base end portion;
A position where the bracket is deviated downward from the center of the exhaust port on the outer side in the width direction of the base end portion; and a position where the bracket is deviated upward from the center of the exhaust port on the inner side in the width direction of the base end portion. , Attached to the peripheral portion of the exhaust port by a fastening member,
Each of the two inner exhaust pipes on the inner side in the width direction has an inner surface whose base end portion smoothly curves outward in the width direction toward the downstream side of the exhaust gas ,
At the downstream end of the curved base end, the inner exhaust pipe has a circular cross-sectional shape,
Each of the base end portions of the inner exhaust pipe is located at a position where an inner bracket for the inner exhaust pipe connected to the exhaust port is displaced downward from the center of the exhaust port on the inner side in the width direction of the base end portion. At a position displaced upward from the center of the exhaust port on the outer side in the width direction of the base end, it is attached to a peripheral portion of the exhaust port by a fastening member,
The distance between the axial centers of the downstream ends of the base ends of the two inner exhaust pipes is the distance between the axis of the downstream end of the base end of the outer exhaust pipe and the base end of the inner exhaust pipe adjacent thereto. An exhaust system for an engine that is set to be larger than the distance between the shaft center at the downstream end. A plurality of exhaust pipes whose base ends are connected to a plurality of exhaust ports of the engine and lead out exhaust gas;
The plurality of exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft,
Each exhaust port is a non-circular shape that is long in the width direction,
A base end portion of an outer exhaust pipe located on the outer side in the width direction is connected to the exhaust port and is a non-circular exhaust inlet that is long in the width direction, and smoothly from the exhaust inlet toward the downstream of the exhaust. An outer surface curved inward in the width direction,
At the downstream end of the curved base end portion, the cross-sectional shape of the outer exhaust pipe is a circle whose axis is offset inward in the width direction compared to before the curve,
The plurality of exhaust pipes merge at a collecting pipe,
An opening edge forming a downstream end of each exhaust pipe is formed so as to incline toward the upstream side in the exhaust gas flow direction toward the radially outer side of the collecting pipe,
An exhaust system for an engine, wherein a downstream end of each exhaust pipe is shifted in the exhaust gas flow direction. Comprising four exhaust pipes whose base end portions are connected to a plurality of exhaust ports of the engine and lead out exhaust gas;
The four exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft,
Each exhaust port is a non-circular shape that is long in the width direction,
A base end portion of an outer exhaust pipe located on the outer side in the width direction is connected to the exhaust port and is a non-circular exhaust inlet that is long in the width direction, and smoothly from the exhaust inlet toward the downstream of the exhaust. An outer surface curved inward in the width direction,
At the downstream end of the curved base end portion, the cross-sectional shape of the outer exhaust pipe is a circle whose axis is offset inward in the width direction compared to before the curve,
Each of the two inner exhaust pipes on the inner side in the width direction has an inner surface whose base end portion smoothly curves outward in the width direction toward the downstream side of the exhaust gas,
At the downstream end of the curved base end, the inner exhaust pipe has a circular cross-sectional shape,
Each of the base end portions of the inner exhaust pipe is located at a position where an inner bracket for the inner exhaust pipe connected to the exhaust port is displaced downward from the center of the exhaust port on the inner side in the width direction of the base end portion. At a position displaced upward from the center of the exhaust port on the outer side in the width direction of the base end, it is attached to a peripheral portion of the exhaust port by a fastening member,
The distance between the axial centers of the downstream ends of the base ends of the two inner exhaust pipes is the distance between the axis of the downstream end of the base end of the outer exhaust pipe and the base end of the inner exhaust pipe adjacent thereto. An exhaust system for an engine that is set to be larger than the distance between the shaft center at the downstream end. A plurality of exhaust pipes whose base ends are connected to a plurality of exhaust ports of the engine and lead out exhaust gas;
The plurality of exhaust ports are arranged side by side in the width direction along the rotation axis of the crankshaft,
The plurality of exhaust pipes merge at a collecting pipe,
An opening edge forming a downstream end of each exhaust pipe is formed so as to incline toward the upstream side in the exhaust gas flow direction toward the radially outer side of the collecting pipe,
An exhaust system for an engine, wherein a downstream end of each exhaust pipe is shifted in the exhaust gas flow direction.

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