Exhaust system for internal combustion engine, internal combustion engine and saddle-type vehicle

Abstract

To provide a constitution which can contribute to the installation of an EGR system on a saddle riding type vehicle.SOLUTION: An exhaust system 50 of an internal combustion engine 20 related to one embodiment includes an exhaust pipe 51c having an exhaust passage portion 66a through which exhaust gas discharged from a combustion chamber flows, and an EGR channel part 68a. The exhaust pipe 51c has a partition wall 71 which separates the exhaust passage portion 66a from the EGR channel part 68a.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an exhaust system for an internal combustion engine equipped with an EGR passage portion, an internal combustion engine equipped with the same, and a straddle-type vehicle equipped with the internal combustion engine. [Background technology]

[0002] Efforts to mitigate or reduce the impact of climate change have been ongoing for some time, and research and development into emissions improvement has been conducted to achieve this. Specifically, in internal combustion engines, exhaust gas recirculation (EGR), which returns a portion of exhaust gas back to the combustion chamber, is known to reduce emissions of harmful substances such as nitrogen oxides (NOx) and improve fuel efficiency, and has been widely put into practical use. One type of EGR is so-called external EGR, in which a portion of exhaust gas flowing through the exhaust passage is recirculated back to the intake passage via an EGR passage and sent to the combustion chamber. External EGR, which is put into practical use in, for example, four-wheeled automobiles, generally includes an EGR passage connecting the exhaust passage and the intake passage, an EGR valve provided in the EGR passage, and an EGR cooler provided in the EGR passage.

[0003] For example, Patent Document 1 discloses an exhaust gas recirculation device that supplies recirculated exhaust gas taken from downstream of a catalytic converter downstream of an exhaust manifold in an exhaust passage of a cross-flow multi-cylinder engine that takes in air from one side in a direction perpendicular to the cylinder row and exhausts from the other side via a water-cooled recirculation exhaust cooler and an exhaust gas recirculation control valve to an intake passage. According to the description in Patent Document 1, this engine is a transverse-mounted engine in an engine compartment at the front of a vehicle, with the cylinder row direction being approximately the vehicle width direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-98171 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the EGR device of Patent Document 1 is mounted on a four-wheeled automobile and is not intended for application to straddle-type vehicles such as motorcycles. Although EGR is effective in improving emissions in straddle-type vehicles, it is difficult to directly apply the EGR system of Patent Document 1 to straddle-type vehicles, for example, in terms of the installation space for an EGR system for performing external EGR.

[0006] In order to solve the above-mentioned problems, the present application aims to provide a configuration that can contribute to the installation of an EGR system in a saddle-ride type vehicle, which in turn contributes to mitigating or reducing the impact of climate change. [Means for solving the problem]

[0007] One aspect of the present invention is an exhaust passage portion through which exhaust gas discharged from the combustion chamber flows; EGR passage part and an exhaust pipe having The exhaust pipe has a partition wall that separates the exhaust passage portion and the EGR passage portion. An exhaust system for an internal combustion engine, characterized in that to provide.

[0008] According to the above configuration, the exhaust pipe has a partition wall separating the exhaust passage portion and the EGR passage portion, so that the EGR passage portion can be arranged adjacent to the exhaust passage portion in the exhaust pipe, thereby integrating the exhaust passage portion and the EGR passage portion in the exhaust pipe, thereby reducing dead space and contributing to a more compact EGR system. This contributes to the installation of an EGR system in a saddle-type vehicle. Additionally, because the exhaust pipe is configured with a partition wall separating the exhaust passage portion and the EGR passage portion, the appearance of the exhaust pipe can be made closer to or substantially the same as that of a conventional exhaust pipe, compared to, for example, a case in which an exhaust pipe forming the aforementioned exhaust passage portion and an EGR pipe forming the aforementioned EGR passage portion are provided.

[0009] Preferably, the partition wall is provided in the exhaust pipe so as to define the EGR passage portion outside the exhaust passage portion. With this configuration, the exhaust pipe can have, for example, a double-pipe structure, and the EGR passage portion adjacent to the exhaust passage portion can be effectively formed while ensuring a sufficient cross-sectional area of ​​the exhaust passage portion. Furthermore, an exhaust pipe with a double-pipe structure can be manufactured at relatively low cost, and this configuration is also excellent in terms of cost.

[0010] Preferably, the exhaust pipe includes a catalyst in the exhaust passage portion. With this configuration, the catalyst can be warmed up by exhaust gas flowing through the EGR passage portion. Also, with this configuration, when the EGR passage portion passes exhaust gas from the downstream side of the catalyst, the exhaust gas purified by the catalyst can flow into the intake system of the internal combustion engine.

[0011] The present invention also relates to an internal combustion engine equipped with the exhaust system for the internal combustion engine described above. Preferably, the internal combustion engine further includes an EGR pipe section that defines a second EGR passage section connected to the EGR passage section of the exhaust pipe and extends toward the engine body. This configuration allows the EGR pipe section to be arranged compactly around the engine body, which can contribute to, for example, making the EGR system more compact.

[0012] Preferably, the EGR pipe section is connected to the engine body. This configuration allows a portion of the EGR passage to be defined within the engine body, making it possible to further compact the EGR system. Alternatively, the EGR pipe section may pass around the engine body and be connected to the intake pipe. This allows the EGR pipe section to be compactly arranged around the engine body, making it possible to design a compact EGR system.

[0013] Preferably, the EGR pipe portion includes a heat dissipation portion, and this configuration makes it possible to more effectively cool the exhaust gas flowing through the EGR pipe portion, i.e., the EGR gas.

[0014] Preferably, the internal combustion engine includes an air-cooling fan provided at one end of the crankshaft and an air guide member that guides airflow from the air-cooling fan toward an exhaust port of the engine body, and the EGR pipe section is arranged next to the exhaust port of the engine body so that it can receive the air discharged from the air guide member. With this configuration, the EGR pipe section, and in particular the exhaust gas flowing therethrough, can be more effectively cooled.

[0015] The present invention also relates to a saddle-ride type vehicle equipped with the above-described internal combustion engine. Preferably, in this saddle-ride type vehicle, the exhaust pipe is disposed below the engine body in the vertical direction of the vehicle or in front of the engine body in the longitudinal direction of the vehicle, and at least a portion of the EGR passage portion is located on the opposite side of the engine body with the exhaust passage portion in between. With this configuration, it is possible to more actively apply airflow from the vehicle while the vehicle is traveling to the EGR passage portion of the exhaust pipe, thereby facilitating cooling of the exhaust gas, i.e., the EGR gas, flowing through the EGR passage portion. [Effects of the Invention]

[0016] According to the above aspect of the present invention, the above configuration is provided, which can contribute to making the EGR system more compact, and therefore can contribute to installing the EGR system in a saddle-ride type vehicle. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is an overall right side view of a motorcycle according to a first embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged right side view of a portion of the vehicle of FIG. [Figure 3] 2 is a side view of a power unit, an intake system device, and an exhaust system of the motorcycle of FIG. 1. [Figure 4] FIG. 4 is a plan view of a portion of FIG. 3. [Figure 5] FIG. 2 is a bottom view of a portion of the motorcycle. [Figure 6] FIG. 2 is a partial cross-sectional view taken along the crankshaft of the internal combustion engine of the power unit. [Figure 7]FIG. 2 is an overall left side view of the motorcycle of FIG. 1. [Figure 8] 2 is a perspective view of an engine body and part of an exhaust system of an internal combustion engine of the motorcycle of FIG. 1. FIG. [Figure 9] 2 is a perspective view of the engine body and part of the exhaust system of the internal combustion engine of the motorcycle of FIG. 1, seen from another angle. FIG. [Figure 10] 2 is an enlarged view of a connection portion of an exhaust device to a cylinder head of an internal combustion engine of the motorcycle of FIG. 1. [Figure 11] FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. [Figure 12] FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. [Figure 13] FIG. 2 is a cross-sectional view of a portion of an exhaust pipe. [Figure 14] 1, (a) is a schematic diagram of an EGR system in the internal combustion engine of the motorcycle of FIG. 1, (b) shows a modified example thereof, and (c) shows yet another modified example. [Figure 15] FIG. 10 is an overall left side view of a motorcycle according to a second embodiment of the present invention. [Figure 16] FIG. 16 is a front view of a portion of the motorcycle of FIG. [Figure 17] FIG. 16 is a perspective view of a portion of the internal combustion engine of the motorcycle of FIG. [Figure 18] FIG. 10 is a perspective view of a portion of a modified internal combustion engine. [Figure 19] FIG. 10 is a schematic cross-sectional view of an exhaust pipe according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a first embodiment of the present invention will be described. Fig. 1 shows a side view of a scooter-type motorcycle 1 according to this embodiment. In the explanations in this specification, the directions of front, back, left, right, and up and down will follow the usual standard of the straight-ahead direction of the motorcycle 1 in this embodiment being the forward direction, and in the drawings, FR indicates the forward direction, RE indicates the rearward direction, LH indicates the leftward direction, RH indicates the rightward direction, UP indicates the upward direction, and DW indicates the downward direction.

[0019] As shown in FIG. 1, a front body 1F and a rear body 1R are connected via a low floor portion 1C, and a body frame F that forms the skeleton of the body is generally composed of a down tube 3 and a main pipe 4. That is, a down tube 3 extends downward from a head pipe 2 at the front part 1F of the vehicle body, bends horizontally at its lower end and extends rearward below the floor part 1C, and is connected at its rear end to a pair of left and right main pipes 4, which form an inclined section 4a that extends diagonally upward and rearward from the connected section, and the upper part of the inclined section 4a is further bent to form a horizontal section 4b that extends rearward approximately horizontally.

[0020] In the front body portion 1F, the head pipe 2 and the vertically oriented portions of the down tube 3 are covered from the front and rear by the front cover 1a and leg shield 1b, in the floor portion 1C, the vertically oriented portions of the down tube 3 are covered by the lower side cover 1c, and in the rear body portion 1R, the main pipe 4 is covered on the left, right, and rear sides by the body cover 1d. The lower side cover 1c, which covers the underside of the vehicle, extends from the lower part of the front cover 1a toward the rear of the vehicle and covers part of the right side of the power unit P, as shown in Figures 2 and 7.

[0021] A storage box 5 and a fuel tank (not shown) are supported at the front and rear between the pair of main pipes 4, and a seat 7 is disposed above the storage box 5 and the fuel tank to cover them. On the other hand, at the front body 1F, a handlebar 8 is provided above and journalled on the head pipe 2, and a front fork 9 extends below and journalled at its lower end to a front wheel 10.

[0022] As shown in Fig. 1, a support bracket 11 is provided to protrude rearward, located approximately halfway along the longitudinal direction of the inclined portion 4a of the main pipe 4. As shown in Fig. 2, a hanger 22h is provided to protrude diagonally upward from the top of the power unit P. The support bracket 11 of the main pipe 4 and the hanger 22h are connected via a link member 12, and this link mechanism connects and supports the power unit P to the main pipe 4 so that it can swing.

[0023] 3, a single-cylinder, four-stroke, air-cooled internal combustion engine 20 is mounted at the front of the power unit P. A crankcase 22 supports a crankshaft 21 oriented in the vehicle width direction, and a cylinder block 23, a cylinder head 24, and a head cover 25 are stacked in this order from the crankcase 22, which projects forward in a position tilted forward to a nearly horizontal state. Here, the part including the crankcase 22, the cylinder block 23, the cylinder head 24, and the head cover 25 is referred to as an engine body B.

[0024] Referring to Figure 6, the crankcase 22 is split into left and right parts, a left crankcase part 22L and a right crankcase part 22R, and the crankshaft 21 oriented in the vehicle width direction is rotatably supported by the left crankcase part 22L and the right crankcase part 22R via main bearings 21b, 21b, respectively.

[0025] An AC generator 55 is provided on the right shaft portion of the crankshaft 21, and a centrifugal cooling fan 56 is integrally attached to an outer rotor 55r of the AC generator 55. A fan cover 57 that covers the right crankcase portion 22R from the right side houses the centrifugal cooling fan 56. Referring also to Figure 2, the fan cover 57 is formed with a grill 57g that serves as an outside air inlet facing the centrifugal cooling fan 56. In this way, the centrifugal cooling fan 56 is an air-cooled fan.

[0026] 6, the left crankcase 22L extends rearward and doubles as a transmission case, and a transmission case cover 65 covers the transmission case (left crankcase) 22L from the left side, with the belt-type continuously variable transmission 60 disposed inside. A drive chain sprocket 58 is provided adjacent to the main bearing 21b on the left shaft portion of the crankshaft 21, and a drive pulley 61 of the belt-type continuously variable transmission 60 is provided on the end of the left shaft.

[0027] Power is transmitted to the valve mechanism on the cylinder head 24 side by a cam chain 59 wound around a drive chain sprocket 58 . 1 and 3, the reduction gear output shaft of the reduction mechanism 64 provided at the rear of the belt-type continuously variable transmission 60 is the rear axle 28a, and the rear wheel 28 is provided on the rear axle 28a. A rear cushion (not shown) is interposed between the upper end of the rear part of the transmission case 22L that houses the reduction mechanism 64 and the upper bent part of the main pipe 4.

[0028] 3, a driven pulley 63 of the belt-type continuously variable transmission 60 is journaled on a reducer input shaft 64a of the reduction mechanism 64, a belt 62 is wound around a drive pulley 61 provided on the crankshaft 21 and the driven pulley 63 provided on the reducer input shaft 64a, and the power of the internal combustion engine 20 is transmitted to the driven pulley 63 via the belt 62, and the rotation of the driven pulley 63 is transmitted to the reducer input shaft 64a of the reduction mechanism 64 via a centrifugal clutch (not shown), and is then reduced in speed by the reduction mechanism 64 before being transmitted to the rear wheel 28. As shown in FIG. 6, an outside air intake fan 61F is formed on the left pulley half of the drive pulley 61.

[0029] A shroud 70, which is an air guide member as shown in Figure 6, surrounds the cylinder block 23 and the cylinder head 24, and the right side of the shroud 70 is connected to the fan cover 57. Therefore, air can be blown through the shroud 70 to various parts of the cylinder block 23 and the cylinder head 24, for example, around the outlet of the exhaust port 24b of the cylinder head 24 of the internal combustion engine 20.

[0030] 3, an intake port 24a is formed on the upper surface of a cylinder head 24 of an internal combustion engine 20 in the front part of a power unit P, and an inlet pipe 31 serving as an intake pipe extends upward from the intake port 24a. An exhaust port 24b is formed on the lower surface of the cylinder head 24, and an exhaust pipe 51 extends downward from the exhaust port 24b. An ignition plug 26 is inserted into the cylinder head 24 near the center of the head cover 25, and an oxygen concentration sensor 27 is inserted into the location where the exhaust passage E extends.

[0031] An intake device 30 that draws in outside air and sends it to the internal combustion engine 20 is connected to the intake port 24a of the internal combustion engine 20. The inside of the intake device 30 forms an intake passage through which the intake air sent to the internal combustion engine 20 passes, introducing the intake air into the combustion chamber 20a of the internal combustion engine 20. The intake device 30 comprises an air cleaner device 40 that takes in and purifies outside air, a connecting tube 36 connected to the air cleaner device 40, a throttle body 33 connected to the downstream side of the connecting tube 36, and an inlet pipe 31 connected to the upstream side of the throttle body 33, and these together form the intake system.

[0032] As shown in Figure 4, the air cleaner device 40 of the intake device 30 has an air cleaner case 41 which is made up of left and right unpurified chamber cases 42 and purified chamber cases 43, and is divided into an unpurified chamber Ca on the unpurified chamber case 42 side and a purified chamber Cb on the purified chamber case 43 side by a partition section disposed between the unpurified chamber case 42 and the purified chamber case 43 and in which an air cleaner element 44 is disposed. As shown in Figure 3, an air intake pipe 47, which takes in airflow from running, is disposed in the unpurified chamber case 42 with its opening 47a facing forward. The intake air introduced through the opening 47a passes through the unpurified chamber Ca, passes through the air cleaner element 44, is purified, and is sent to the purified chamber Cb. The purified chamber Cb of the air cleaner device 40 is connected to the throttle body 33 by an elastically deformable connecting tube 36 made of rubber. A fuel injection valve 37 is attached to the top of each of the throttle body 33 and the inlet pipe 31, and injects fuel into the intake passage.

[0033] 5, an exhaust device 50 is connected to the exhaust port 24b of the cylinder head 24. The exhaust device 50 includes an exhaust pipe 51 connected to the exhaust port 24b, a muffler 52 connected to the rear end of the exhaust pipe 51 and having an atmosphere opening port 52a facing rearward of the vehicle, and a catalytic converter 53 built into the exhaust pipe 51. Exhaust gas emitted from the internal combustion engine 20 flows into the exhaust pipe 51 from the exhaust port 24b, is purified by a catalytic device 53 installed midway along the exhaust pipe 51, passes through a muffler 52, and is discharged into the atmosphere through an air-opening port 52a.

[0034] The exhaust pipe 51 communicates with the exhaust port 24b, extends downward from the underside of the cylinder head 24, bends diagonally forward to the left, bends further from the rear to the right, bends from the left to the right of the lower part of the crankcase 22, extends rearward, and is connected to a muffler 52 disposed on the right side of the rear wheel 28.

[0035] The exhaust pipe 51 is composed of a catalytic device-accommodating exhaust pipe 51c in which a catalytic device 53 is built, an upstream exhaust pipe 51a connected to the upstream side of the catalytic device-accommodating exhaust pipe 51c, and a downstream exhaust pipe 51b connected to the downstream side of the catalytic device-accommodating exhaust pipe 51c.

[0036] The upstream exhaust pipe 51a is connected to the exhaust port 24b and extends downward from the underside of the cylinder head 24 (see also Figure 3), then bends diagonally forward to the left and then bends again from the rear to the right to be connected to the catalytic converter-accommodated exhaust pipe 51c.

[0037] The catalyst device-accommodating exhaust pipe 51c is located below the internal combustion engine 20 and is arranged so that exhaust gas flows in the vehicle width direction from the left side to the right side of the vehicle. The catalytic converter-accommodating exhaust pipe 51c is disposed so that its upstream end is located on the left side in the vehicle width direction and its downstream end is located on the right side in the vehicle width direction. The upstream end is connected to the upstream-side exhaust pipe 51a, and the downstream end is connected to the downstream-side exhaust pipe 51b.

[0038] A catalytic converter 53 is housed inside the catalytic converter-housed exhaust pipe 51c with its axis oriented in the vehicle width direction. The catalytic converter 53 is a honeycomb-shaped porous structure with numerous pores extending in the axial direction, and this porous structure supports a catalyst such as platinum, rhodium, or palladium as a component that decomposes exhaust gas. Here, the catalytic converter 53 may be simply referred to as a catalyst.

[0039] As shown in Fig. 5, the downstream exhaust pipe 51b is connected to the downstream side of the catalyst device-accommodating exhaust pipe 51c, extends in the vehicle width direction, and then curves toward the rear. In a bottom view of the vehicle, the downstream exhaust pipe 51b extends rearward in the vehicle front-to-rear direction on the outer side in the vehicle width direction from the crankcase 22 that constitutes the unit case Pc. Furthermore, as shown in Figs. 2 and 7, in a right side view of the vehicle body, the downstream exhaust pipe 51b extends rearward from the right side of the lower part of the power unit P, then bends diagonally upward, and extends, and is connected to a muffler 52 disposed on the right side of the rear wheel 28.

[0040] 2 is a right side view of the vicinity of power unit P, with a portion of the front side of fan cover 57 cut away. In this side view, downstream exhaust pipe 51b has two curved portions 51d, one on the upstream side and one on the downstream side. Of these curved portions 51d, upstream curved portion 51d1, which is closest to catalyst device-accommodating exhaust pipe 51c, is formed in downstream exhaust pipe 51b so that, in side view of the vehicle, upstream curved portion 51d1 is located forward of center of rotation C1 of the cooling fan in the vehicle longitudinal direction. The saddle-type vehicle of this embodiment has two curved portions 51d, but it is sufficient to have at least one curved portion 51d, and may have two or more curved portions 51d.

[0041] An exhaust gas sensor 54 is attached to the downstream exhaust pipe 51b and detects the oxygen concentration in the exhaust gas that has passed through the catalytic device 53. The exhaust gas sensor 54 may be either an LAF sensor or an O2 sensor.

[0042] As shown in FIGS. 2 and 6, a fan cover 57 constituting part of the unit case Pc is disposed near the downstream exhaust pipe 51b and the exhaust gas sensor 54, covering the right side of the centrifugal cooling fan 56. The fan cover 57 is integrally connected to a shroud 70 that surrounds a portion of the internal combustion engine 20, and covers the right side of the internal combustion engine 20. An eave portion 57d of the fan cover 57 is formed to cover the right side surface of the downstream exhaust pipe 51b. A notch 57e that opens forward in the vehicle longitudinal direction is formed at the edge of the eave portion 57d of the fan cover 57. The notch 57e is formed to avoid the exhaust gas sensor 54 attached to the downstream exhaust pipe 51b, and as shown in FIG. 2, the notch 57e and the exhaust gas sensor 54 overlap in a side view of the vehicle.

[0043] The motorcycle 1 is equipped with an ECU (electronic control unit), not shown. The ECU controls the internal combustion engine 20 and other components. The ECU is configured as a computer and includes a processor (e.g., a CPU) and memory (e.g., a ROM and a RAM), and receives output signals from various sensors. For example, an engine speed sensor, an engine load sensor such as a throttle opening sensor, an oxygen concentration sensor 27, and an exhaust gas sensor 54 are connected to the ECU. The ECU analyzes the operating state based on inputs from these sensors, and controls the operation of components such as the spark plug 26, the fuel injection valve 37, the throttle valve of the throttle body 33, and the EGR valve V, which will be described later, based on the analyzed operating state.

[0044] The exhaust device 50 of the internal combustion engine 20 will now be described in further detail. Figs. 8 and 9 show perspective views of a portion of the engine body B and the catalytic converter-accommodated exhaust pipe 51c that defines the exhaust passage E. Fig. 8 is a perspective view of the cylinder head 24 side of the engine body B, as viewed diagonally from the front right side of the vehicle, and Fig. 9 is a perspective view of the cylinder head 24 side of the engine body B, as viewed diagonally from the rear left side of the vehicle. Fig. 10 is an enlarged view of the portion of the exhaust device 50 that connects to the exhaust port 24b of the cylinder head 24. Figs. 11 to 13 show the upstream exhaust pipe 51a and the catalytic converter-accommodated exhaust pipe 51c of the exhaust pipe 51. Fig. 11 is a perspective cross-sectional view of the catalytic converter-accommodated exhaust pipe 51c taken along the exhaust flow direction, and Fig. 12 is a cross-sectional view of the catalytic converter-accommodated exhaust pipe 51c taken along the exhaust flow direction, with the exhaust flow direction, i.e., the axis 51ca of the catalytic converter-accommodated exhaust pipe 51c, parallel to the paper surface. Figure 13 is a cross-sectional view taken along line XIII-XIII in Figure 12, which is a plane perpendicular to the exhaust flow direction of the catalytic device-housed exhaust pipe 51c, and is a cross-sectional view in which the exhaust flow direction, i.e., the axis 51ca of the catalytic device-housed exhaust pipe 51c, is positioned perpendicular to the plane of the paper.

[0045] The internal combustion engine 20 is equipped with an EGR system S to perform EGR, particularly external EGR, which recirculates exhaust gas from the exhaust system to the intake system. The EGR system S includes an EGR passage Ep. The EGR system S also includes an EGR valve V. Here, the EGR valve V is attached directly to the cylinder head 24 so as to guide exhaust gas recirculated to the intake port 24a, i.e., EGR gas, but it may be provided at any location in the EGR passage Ep so as to guide the exhaust gas to an intake pipe such as an inlet pipe 31. Note that the EGR valve V is a poppet valve here, but may be another type of valve.

[0046] An EGR passage portion 68a, which is a part of the EGR passage Ep, is formed in the catalytic converter-housed exhaust pipe 51c. As shown in FIGS. 11 to 13, the catalytic converter-housed exhaust pipe 51c has a double-pipe structure. The catalytic converter-housed exhaust pipe 51c has an inner pipe portion 66 whose axis extends along the axis 51ca of the catalytic converter-housed exhaust pipe 51c, and an outer pipe portion 68 located outside the inner pipe portion 66. The inner pipe portion 66 has a substantially cylindrical passage and defines an exhaust passage portion 66a through which exhaust gas discharged from the exhaust port 24b to the exhaust passage E flows toward the muffler 52. The outer pipe portion 68 extends adjacent to and in contact with the periphery of the inner pipe portion 66, and extends along the axis 51ca of the catalytic converter-housed exhaust pipe 51c as its axis, defining a cylindrical space. The cylindrical space of the outer pipe portion 68 forms an EGR passage portion 68a through which recirculated exhaust gas, i.e., EGR gas, flows. The inner pipe portion 66 and the outer pipe portion 68 are integrated by a cylindrical partition wall 71. That is, the catalyst device-accommodating exhaust pipe 51c has the partition wall 71 that divides its interior into an exhaust passage portion 66a and an EGR passage portion 68a, and the EGR passage portion 68a is adjacent to the exhaust passage portion 66a within the catalyst device-accommodating exhaust pipe 51c via the partition wall 71. In particular, because the catalyst device-accommodating exhaust pipe 51c has a double-pipe structure, the EGR passage portion 68a is defined by the partition wall 71 outside the exhaust passage portion 66a within the catalyst device-accommodating exhaust pipe 51c. The partition wall 71 is a cylindrical pipe portion whose axis is the axis 51ca of the catalyst device-accommodating exhaust pipe 51c. As a result, the longitudinal directions of the exhaust passage portion 66a and the EGR passage portion 68a are generally aligned and generally parallel to each other.

[0047] The catalytic converter 53, which is equipped with a catalyst, is disposed in the exhaust passage portion 66a of the catalytic converter-accommodating exhaust pipe 51c. A communication passage 72 that connects the exhaust passage portion 66a and the EGR passage portion 68a is defined downstream of the catalytic converter 53 in the exhaust passage portion 66a. The communication passage 72 is formed at the downstream end of the catalytic converter-accommodating exhaust pipe 51c and is defined by a notch 74 formed at the downstream end of the partition wall 71. The communication passage 72 is a hole that extends radially about the axis 51ca of the catalytic converter-accommodating exhaust pipe 51c and enables a portion of the exhaust gas in the exhaust passage portion 66a to be drawn into the EGR passage portion 68a by negative pressure in the intake system.

[0048] A gas discharge section 76 is formed at the upstream end of the catalytic device-accommodating exhaust pipe 51c. The gas discharge section 76 enables exhaust gas in the EGR passage section 68a to be discharged from the EGR passage section 68a. The gas discharge section 76 defines a gas discharge path 76a that communicates with the EGR passage section 68a. Therefore, in the catalytic device-accommodating exhaust pipe 51c, the exhaust gas recirculated in the EGR passage section 68a, i.e., the EGR gas, flows in the opposite direction to the downstream flow direction of the exhaust gas in the exhaust passage section 66a.

[0049] An EGR pipe 78 is connected to the gas discharge section 76. The EGR pipe 78 is an example of an EGR pipe section and defines an EGR passage section (hereinafter, referred to as a second EGR passage section) 78a that connects to the EGR passage section 68a of the catalyst device-accommodated exhaust pipe 51c. The EGR pipe 78 is arranged to extend toward the engine body B. Here, as shown in FIGS. 5, 8, and 10, the EGR pipe 78 is directly connected to the cylinder head 24 of the engine body B, enabling EGR gas to be guided to the EGR passage section 24e defined within the engine body B. As shown in FIGS. 2, 5, 8 to 10, and 12, the EGR pipe 78 is arranged to extend generally within the area surrounded by the upstream exhaust pipe 51a and the catalyst device-accommodated exhaust pipe 51c, extends downward from the connection portion of the catalyst device-accommodated exhaust pipe 51c, then turns upward, and connects to the underside of the cylinder head 24. Therefore, the EGR pipe 78 is a substantially U-shaped pipe. The EGR passage portion 24e may be formed in the engine body B at a location other than the cylinder head 24.

[0050] FIG. 14(a) is a schematic diagram of an EGR system S. FIG. 14(a) shows the EGR system S of this embodiment. In the EGR system S, exhaust gas discharged from the engine body B flows sequentially through the exhaust port 24b and the upstream exhaust pipe 51a, passes through the catalytic converter 53 in the exhaust passage portion 66a of the catalytic converter-accommodating exhaust pipe 51c, and, when the ECU (not shown) controls the opening of the EGR valve V, flows through the communication passage 72 to the EGR passage portion 68a, and then flows out of the catalytic converter-accommodating exhaust pipe 51c from the gas discharge portion 76. Then, flows through the second EGR passage portion 78a of the EGR pipe 78 to the EGR passage portion 24e of the engine body B, and is recirculated through the EGR valve V to the intake passage, here the intake port 24a. As a result, the recirculated exhaust gas, i.e., EGR gas, is drawn into the combustion chamber 20a.

[0051] When exhaust gas is recirculated in this manner, a cooling means is provided midway through the EGR passage Ep. First, the EGR pipe 78, which is an EGR pipe section, is provided with a heat dissipation section 80. The heat dissipation section 80 is configured to increase the surface area of ​​the EGR pipe 78 exposed to the outside air, and is a pleated, or bellows-shaped pipe section. The EGR pipe 78 is exposed to the outside below the vehicle body where the wind flows while the vehicle is running, and is provided with the heat dissipation section 80, so it can provide a high cooling effect.

[0052] Furthermore, as described above, the shroud 70, which is an air guide member provided to surround the cylinder block 23 and the cylinder head 24, is connected to the fan cover 57 of the air-cooling fan, i.e., the centrifugal cooling fan 56, provided on one end of the crankshaft 21 of the internal combustion engine. As shown in FIG. 10 , one edge 70a of the shroud 70 opens around the outlet of the exhaust port 24b of the cylinder head 24 of the internal combustion engine 20, allowing the centrifugal cooling fan 56 to send air toward the exhaust port 24b, i.e., toward the upstream exhaust pipe 51a communicating with it. As shown in FIGS. 5 , 8 , and 10 , the EGR pipe 78 is arranged next to the upstream exhaust pipe 51a, i.e., the exhaust port 24b communicating with it, on the exhaust port 24b side of the cylinder head 24. The connection position of the EGR pipe 78 to the cylinder head 24 is located in the path of the air from the centrifugal cooling fan 56 flowing out from the shroud 70. Therefore, the EGR pipe 78 can receive the wind from the centrifugal cooling fan 56 that is discharged from one edge portion 70a of the shroud 70. The wind from the centrifugal cooling fan 56 that flows toward the EGR pipe 78 is schematically shown by arrow A1 in FIG.

[0053] The characteristic configurations of the exhaust device 50 of the internal combustion engine 20 and the like in the motorcycle 1, which is a straddle-type vehicle, having the above-described configuration, and the resulting actions and effects will be described below.

[0054] In the exhaust device 50 for the internal combustion engine 20 mounted on the motorcycle 1, the catalyst device-accommodating exhaust pipe 51c includes an exhaust passage portion 66a through which exhaust gas discharged from the combustion chamber 20a flows, and an EGR passage portion 68a. The catalyst device-accommodating exhaust pipe 51c has a partition wall 71 that separates the exhaust passage portion 66a and the EGR passage portion 68a. Therefore, the EGR passage portion 68a can be disposed adjacent to the exhaust passage portion 66a, which allows the exhaust passage portion 66a and the EGR passage portion 68a to be integrated into a single exhaust pipe 51c. This reduces the dead space between the exhaust passage portion 66a and the EGR passage portion 68a, contributing to a more compact EGR system S. The exhaust device 50 therefore contributes to the installation of the EGR system S on the motorcycle 1, which is a straddle-type vehicle. Additionally, the catalyst device-accommodating exhaust pipe 51c includes a partition wall 71 separating the exhaust passage portion 66a and the EGR passage portion 68a. This allows the EGR passage portion 68a to be positioned adjacent to the exhaust passage portion 66a in the catalyst device-accommodating exhaust pipe 51c. This allows the appearance of the catalyst device-accommodating exhaust pipe 51c to be closer to or substantially the same as that of a conventional circular exhaust pipe, compared to a case in which, for example, a catalyst device-accommodating exhaust pipe forming the exhaust passage portion 66a and an EGR pipe forming the EGR passage portion 68a are provided. In particular, the exhaust passage portion 66a and the EGR passage portion 68a are formed in the exhaust pipe 51c in a substantially parallel relationship, allowing the EGR passage portion 68a to be more integrated with the exhaust pipe 51c. Furthermore, the exhaust pipe 51c includes the communication passage 72, which serves as a communication portion, allowing the EGR passage portion 68a to be more integrated with the exhaust pipe 51c. In this way, the exhaust system 50 is significantly different from conventional exhaust systems in that it includes an exhaust pipe 51c having a configuration that combines an EGR passage section 68a with a normal exhaust passage section 66a, in that it includes an exhaust pipe 51c having a configuration that combines an EGR passage section 68a with the normal exhaust passage section 66a.

[0055] The partition wall 71 is provided in the catalyst device-accommodating exhaust pipe 51c to define the EGR passage portion 68a outside the exhaust passage portion 66a. In this example, the partition wall 71 is provided inside the exhaust pipe 51c so that the exhaust pipe 51c has a double-pipe structure. Therefore, the EGR passage portion 68a adjacent to the exhaust passage portion 66a can be effectively formed outside the exhaust passage portion 66a while ensuring a sufficient cross-sectional area, in other words, without compromising it. Furthermore, the exhaust pipe 51c with a double-pipe structure can be manufactured relatively inexpensively, making this configuration advantageous in terms of cost. Furthermore, because the exhaust pipe 51c has a double-pipe structure and the EGR passage portion 68a is formed therein, the EGR passage portion 68a is not visible from the outside, further preventing the additional formation of the EGR passage portion 68a from impairing the appearance of the exhaust pipe 51c.

[0056] Furthermore, the catalytic converter-accommodating exhaust pipe 51c is provided with a catalyst, i.e., the catalytic converter 53, in the exhaust passage portion 66a. Therefore, the catalyst can be warmed up by the exhaust gas flowing through the EGR passage portion 68a. Also, the catalytic converter-accommodating exhaust pipe 51c is provided with the above-mentioned communication passage 72 so that exhaust gas downstream of the catalytic converter 53 can flow into the EGR passage portion 68a, allowing exhaust gas purified by the catalytic converter 53 to flow into the intake system of the internal combustion engine. Furthermore, because the catalytic converter-accommodating exhaust pipe 51c is configured with the above-mentioned communication passage 72, the configuration of the EGR passage Ep can be simplified, and the EGR system S can be made even more compact.

[0057] Furthermore, the EGR pipe 78 that defines the second EGR passage portion 78a extends toward the engine body B. This makes it possible to compactly arrange the second EGR passage portion 78a, i.e., the EGR pipe 78, around the engine body B in each of the motorcycle 1 and the internal combustion engine 20, which in turn contributes to making the EGR system S more compact.

[0058] Furthermore, the EGR pipe 78 is directly connected to the cylinder head 24 of the engine body B, and defines an EGR passage portion 24e, which is a part of the EGR passage Ep, inside the engine body B. This allows the EGR system S to be made even more compact.

[0059] Furthermore, the EGR pipe 78 is provided with a heat dissipation section 80. This makes it possible to more effectively cool the exhaust gas, i.e., the EGR gas, flowing through the EGR pipe 78. However, this does not preclude the provision of an additional EGR cooler before, after, or midway through the EGR pipe 78, and an additional EGR cooler may be provided.

[0060] The internal combustion engine 20 also includes a centrifugal cooling fan 56 provided on one end of the crankshaft 21, and a shroud 70 which is an air guide member that guides the airflow from the centrifugal cooling fan 56 toward the exhaust port 24b of the engine body B. The EGR pipe 78 is arranged next to the exhaust port 24b of the engine body B so that it can receive the airflow discharged from the shroud 70. This allows the airflow from the centrifugal cooling fan 56 to more effectively cool the EGR pipe 78, i.e., the exhaust gas flowing inside it.

[0061] Furthermore, the catalyst device-accommodating exhaust pipe 51c is disposed below the engine body B in the up-down direction of the motorcycle 1. As a result, the catalyst device-accommodating exhaust pipe 51c is exposed below the motorcycle 1. Furthermore, as is clear from the fact that the catalyst device-accommodating exhaust pipe 51c has a double-pipe structure, at least a portion of the EGR passage portion 68a is located on the opposite side of the engine body B with the exhaust passage portion 66a in between. This makes it possible to more actively direct the wind generated by traveling at the catalyst device-accommodating exhaust pipe 51c including the EGR passage portion 68a, thereby facilitating the cooling of the exhaust gas, i.e., the EGR gas, flowing through the EGR passage portion 68a.

[0062] In the internal combustion engine 20 of the motorcycle 1, the EGR passage portion 24e connected to the second EGR passage portion 78a of the EGR pipe 78 is formed in the engine body B. However, the EGR passage portion 24e formed in the engine body B may not be provided, and the EGR pipe 78 may be connected to an intake pipe, such as the inlet pipe 31. FIG. 14(b) shows an EGR system Sa in which the EGR pipe 78 is directly connected to the EGR valve V. In this configuration of the EGR system Sa, the EGR pipe 78 passes around the engine body E and is connected to the inlet pipe 31, which is an intake pipe, via the EGR valve V. This may enable a compact arrangement of the EGR passage Ep. In FIG. 14(b), the EGR valve V is attached to the engine body B, but it may also be provided away from the engine body B to connect the EGR pipe 78 to an intake pipe, such as the inlet pipe 31.

[0063] Alternatively, as in an EGR system Sb shown in Figure 14(c), an EGR passage portion 82 may be defined in the upstream exhaust pipe 51a. In this case, an EGR pipe 78 is connected to the upstream exhaust pipe 51a, and a second EGR passage portion 78a of the EGR pipe 78 is connected to the EGR passage portion 82 of the upstream exhaust pipe 51a. In this case, the EGR passage portion 82 may be connected to the EGR passage portion 24e of the engine body B via an EGR passage portion 84a of an additional EGR pipe 84 as shown in Figure 14(c), or may be connected to the intake pipe via an EGR valve V without passing through the EGR passage portion 24e of the engine body B as shown in Figure 14(b).

[0064] Next, a second embodiment of the present invention will be described. A left side view of a motorcycle 101 according to the second embodiment is shown in Fig. 15, and a front view of a portion of the motorcycle 101 is shown in Fig. 16.

[0065] The motorcycle 101 includes a body frame 102 on which a power unit P and electrical components are mounted. The main tubes of the body frame 102 extend rearward from a head pipe 103 located at the front end. A down tube 104 of the body frame 102 is provided so as to extend diagonally downward and rearward from the head pipe 103. A fuel tank 105 containing fuel is disposed behind the head pipe 103. A seat 106 on which a rider sits is mounted behind this fuel tank 105. A footrest 107 on which the rider rests their feet while riding is provided below the seat 106.

[0066] A brake pedal 108 for the rear wheel WR, which is a drive wheel, is provided near a footrest 107 on the right side of the vehicle body shown in FIG. 15. The brake pedal 108 is pivotally supported at a rear end 108r located rearward of the footrest 107, and is provided so that a front end 108f located forward of the footrest 107 can swing up and down. In a side view of the motorcycle 101 in FIG. 15, the brake pedal 108 is initially slanted slightly downward and forward, then becomes generally horizontal, and then further slanted slightly upward and forward, forming a substantially U-shape, as it moves from the rear end 108r to the front end 108f. In other words, the brake pedal 108 extends in the front-to-rear direction without slanting in the up-and-down direction in a side view of the motorcycle 101. The front end 108f of the brake pedal 108 functions as a pedal portion, is located on the right side of the front end portion of the crankcase 109 described later, and is located at approximately the same height as the footrest 107, so that it can be depressed by the driver's foot placed on the footrest 107.

[0067] Furthermore, a kick pedal 110 is provided near the footrest 107 on the right side of the vehicle body shown in FIG. 15 , particularly above the footrest 107. The kick pedal 110 has a rear end 110r positioned diagonally rearward and upward of the footrest 107 and a front end 110f located near the rear of the cylinder head 112 of the engine body B of the internal combustion engine 111 of the power unit P. As the kick pedal 110 moves from the rear end 110r to the front end 110f, it first extends upward and then curves forward. When in use, the kick pedal 110 unfolds so as to extend outward in the vehicle width direction. The front end 110f of the kick pedal 110 functions as a pedal portion and is depressed by the driver's foot. This depression causes the kick pedal 110 to rotate within a predetermined range around the rear end 110r, thereby starting the internal combustion engine 111.

[0068] An engine body B of an internal combustion engine 111 is suspended between the main tubes and down tube 104 of the body frame 102. The engine body B includes a crankcase 109 supported on the down tube 104 via a bracket, and a cylinder block 113, a cylinder head 112, and a head cover 114, which are provided in this order above the crankcase 109. The cylinder block 113 is connected above the crankcase 109 in a forward-inclined state. Therefore, as shown in FIG. 15, the cylinder axes 111c of the cylinders of the engine body B are inclined obliquely forward from the crankshaft side of the crankcase 109 toward the cylinder head 112 side. The crankshaft extends in the vehicle width direction and is generally perpendicular to the up-down and front-rear directions. FIG. 15 shows a rotational axis 115 of the crankshaft.

[0069] An upper end (upstream end) of an upstream exhaust pipe 117 of an exhaust device 116 is connected to a cylinder head 112 of the engine body B. Exhaust gas discharged from a combustion chamber (not shown) flows through the upstream exhaust pipe 117 via exhaust ports in the cylinder head 112 and is discharged from a muffler 118 located to the right of the rear wheel WR, that is, located at the rear right side of the vehicle body. The exhaust ports of the cylinder head 112, the upstream exhaust pipe 117, the catalytic converter-accommodating exhaust pipe 120, the downstream exhaust pipe 121, and the muffler 118 are connected in this order in the exhaust flow direction, and each defines a part of an exhaust passage 122.

[0070] A front fork 123 is rotatably supported at the front end of the main tube via a steering shaft provided on the head pipe 103. A handlebar 124 is provided at the upper end of the steering shaft, and grips 125 are attached to both ends of the handlebar 124. A front wheel WF is rotatably supported at the bottom of the front fork 123. The upper part of the front wheel WF is partially covered by a front fender 126.

[0071] A rear wheel WR, to which power from the internal combustion engine 111 is transmitted via a swing arm, is rotatably supported behind the engine body B. A suspension 126 that absorbs shocks from the road surface is disposed between the swing arm and the body frame 102. A rear fender 127 is disposed above and behind the rear wheel WR and behind the seat 106.

[0072] As described above, the upstream exhaust pipe 117 of the exhaust device 116 is connected to the front wall of the cylinder head 112 of the engine body B, and downstream of that, the catalytic converter-accommodated exhaust pipe 120, which is an exhaust purification device, the downstream exhaust pipe 121, and the muffler 118 are arranged in this order from upstream. The catalytic converter-accommodated exhaust pipe 120 has the same configuration as the catalytic converter-accommodated exhaust pipe 51c described above, so a detailed description will not be given here, but it has a double-pipe structure and, as shown in Figure 17, is provided with a partition wall 128, and inside it are provided an exhaust passage portion 129 separated by the partition wall 128 from an EGR passage portion 130 on the outside, and a catalytic converter 131 is provided in the exhaust passage portion 129. Note that Figure 17 shows a part of the catalytic converter-accommodated exhaust pipe 120 in perspective.

[0073] 15 and 16 , the exhaust passage 122 continuing from the exhaust port of the cylinder head 112 of the engine body B extends to the front of the engine body B, then extends downward, and further extends rearward passing below the engine body B. In other words, the exhaust device 116 extends from the front of the engine body B of the internal combustion engine 111 downward, passes below the engine body B, and extends rearward. The catalytic converter-housed exhaust pipe 120 is positioned on the front side of the engine body B in the vehicle fore-and-aft direction, and is particularly positioned on the front side of the crankcase 109. Therefore, the catalytic converter-housed exhaust pipe 120 is located further forward of the front end 108f of the brake pedal 108. Here, because the exhaust passage 122 extends around the engine body B as described above, the catalytic converter-housed exhaust pipe 120 is disposed so as to extend obliquely in the same direction as the cylinder axis 111c in a side view of the motorcycle 101, and to extend obliquely rearward and downward from the upstream side to the downstream side. 16, which shows a partial front view of the motorcycle 101, when a central imaginary plane IS (a line extending in the vertical direction at the front wheel WF) is defined to extend from the front to the rear of the motorcycle 101, the catalyst device-accommodating exhaust pipe 120 is located on the right side of the plane, and in this case extends to the right of the front wheel WF, and is provided on the motorcycle 101 so that its downstream portion is slightly inward in the vehicle width direction relative to its upstream portion. Note that the central imaginary plane IS can be defined to be perpendicular to the vehicle width direction and to substantially bisect the front wheel WF and the rear wheel WR.

[0074] In the exhaust device 116 of the internal combustion engine 111 of the motorcycle 101, the catalyst device-accommodating exhaust pipe 120 has the same configuration as the catalyst device-accommodating exhaust pipe 51c described above. Therefore, an EGR pipe 132, which is an EGR pipe portion, is connected to the catalyst device-accommodating exhaust pipe 120 so as to guide exhaust gas flowing through an EGR passage portion 130 of the catalyst device-accommodating exhaust pipe 120 to the outside. Also, as in the first embodiment, the EGR pipe 132 is directly connected to the engine body B, and therefore a second EGR passage portion 132a of the EGR pipe 132 is connected to an EGR passage portion (not shown) of the engine body B. In this way, the EGR system Sc mounted on the internal combustion engine 111 of the motorcycle 101 has the same configuration as the EGR system S (see FIG. 14(a)). An EGR valve in the EGR system Sc is not shown. The EGR pipe 132 has a heat dissipation portion 133 (see FIG. 17) that is the same as the heat dissipation portion 80.

[0075] Therefore, the motorcycle 101, the internal combustion engine 111 mounted thereon, and its exhaust device 116 have the same configuration as those in the first embodiment described above, and similarly achieve the above-mentioned effects.

[0076] Additionally, in the motorcycle 101 of this embodiment, the catalytic converter-accommodating exhaust pipe 120 is disposed in front of the engine body B in the longitudinal direction of the motorcycle 101. Since the catalytic converter-accommodating exhaust pipe 120 has a double-pipe structure, a portion of the EGR passage portion 130 of the catalytic converter-accommodating exhaust pipe 120 is located on the opposite side of the engine body B with the exhaust passage portion 129 in between. In other words, a portion of the EGR passage portion 130 is located in front of the engine body B, and is located at the vehicle's most forward position within the catalytic converter-accommodating exhaust pipe 120. This makes it possible to more actively apply the wind generated by running to the catalytic converter-accommodating exhaust pipe 120 including the EGR passage portion 130, thereby facilitating the cooling of the exhaust gas flowing through the EGR passage portion 130, i.e., the EGR gas.

[0077] Furthermore, in the motorcycle 101, a portion of the EGR pipe 132 is exposed to the right front side without being hidden by the front wheel WF depending on the angle of the front wheel WF, as shown in FIG. 16. This further promotes cooling of the exhaust gas flowing through the EGR pipe 132. This allows the EGR system Sc to omit an EGR cooler. However, the EGR system Sc may also be provided with an EGR cooler.

[0078] The motorcycle 101, internal combustion engine 111, and exhaust system 116 can each be modified to have the various configurations described as modifications of the first embodiment, specifically the configurations shown in FIG. 14(b) and FIG. 14(c). For example, as shown in FIG. 18, the upstream exhaust pipe 117a may have a double-pipe structure and include an EGR passage portion 134. In this case, the EGR passage portion 130 of the catalyst device-accommodating exhaust pipe 120 and the EGR passage portion 134 of the upstream exhaust pipe 117a are connected by an EGR pipe 135, and the EGR passage portion 134 of the upstream exhaust pipe 117a and an EGR passage portion (not shown) of the engine body B are connected by an EGR pipe 136. The EGR pipe 136 has a heat dissipation portion 137. The EGR pipe 135 can also have a heat dissipation portion.

[0079] Although the embodiments and modifications of the present invention have been described above, the present invention is not limited thereto. Various substitutions and modifications are possible without departing from the spirit and scope of the present invention as defined by the claims of this application.

[0080] For example, the catalytic converter-accommodating exhaust pipe 51c, 120 has a double-pipe structure, in which the EGR passage portion 68a, 130 is separated from the exhaust passage portion 66a, 129 by a cylindrical partition wall 71, 128 and extends cylindrically outside the exhaust passage portion 66a, 129. However, the catalytic converter-accommodating exhaust pipe is not limited to this configuration and may have a partition wall with a shape other than a cylindrical shape. For example, the catalytic converter-accommodating exhaust pipe may have a flat partition wall inside, which divides the internal space into two spaces, one of which is the exhaust passage portion and the other is the EGR passage portion. Note that an exhaust pipe having an EGR passage portion and an exhaust passage portion is not limited to an exhaust pipe having a catalytic converter in its exhaust passage portion, and may also include an exhaust pipe without a catalytic converter in its exhaust passage portion.

[0081] FIG. 19 shows a catalytic device-accommodating exhaust pipe 150, which is a modification of the catalytic device-accommodating exhaust pipes 51c and 120. FIG. 19 is a cross-sectional schematic diagram of the catalytic device-accommodating exhaust pipe 150, cut downstream of the catalytic device 152, i.e., the catalyst, corresponding to the catalytic devices 53 and 131, and viewed upstream from the cut surface. The catalytic device-accommodating exhaust pipe 150 includes a partition wall 158 therein to define an exhaust passage portion 154 and an EGR passage portion 156. The partition wall 158 is flat and extends along the axis 150A of the exhaust pipe 150. The partition wall 158 is offset from the axis 150A, and the exhaust passage portion 154 is wider than the EGR passage portion 156. Therefore, the EGR passage portion 156 is essentially defined outside the exhaust passage portion 154. A communication portion 160 that connects the exhaust passage portion 154 and the EGR passage portion 156 is formed in the partition wall 158. In this way, by forming the partition wall 158, the exhaust passage portion 154 and the EGR passage portion 156 can be integrated into the exhaust pipe 150. This also makes it possible to give the exhaust pipe 150 an appearance similar to that of a conventional circular exhaust pipe. Note that in Figure 19, the gas discharge portion that defines a gas discharge path that communicates with the EGR passage portion 156, that is, the portion corresponding to the gas discharge portion 76, is not shown.

[0082] In the above embodiments, the partition walls 71, 128, 158 in the exhaust pipes 51c, 120, 150 are made up of a single wall member, but they may be made up of two or more wall members. For example, a pipe member that defines the exhaust passage portion and a pipe member that defines the EGR passage portion may be arranged adjacent to each other with their longitudinal directions aligned and pressed together to form a generally tubular shape, or may be further joined by welding, for example, to form a substantially single exhaust pipe 51c, 120, 150. In this case, the partition walls 71, 128, 158 are made up of a part of the pipe member that defines the exhaust passage portion and a part of the pipe member that defines the EGR passage portion. [Explanation of symbols]

[0083] 1, 101...Motorcycles 20, 111...Internal combustion engine 50, 116...Exhaust system 51a, 117, 117a...Upstream exhaust pipe 51c, 120, 150... Catalytic converter housing exhaust pipe 53, 131, 152...Catalyst 66a, 129, 154...Exhaust passage section 68a, 130, 156...EGR passage section 71, 128, 158…bulkhead 80, 133...heat dissipation part

Claims

1. an exhaust passage portion (66a, 129, 154) through which exhaust gas discharged from the combustion chamber (20a) flows; EGR passage portion (68a, 130, 156) and an exhaust pipe (51c, 120, 150) having the exhaust pipe (51c, 120, 150) is an internal combustion engine (20, 111) equipped with an exhaust system for an internal combustion engine, the exhaust pipe (51c, 120, 150) having a partition wall (71, 128, 158) separating the exhaust passage portion (66a, 129, 154) from the EGR passage portion (68a, 130, 156), an EGR pipe portion (78, 132) that defines a second EGR passage portion (78a, 132a) connected to the EGR passage portion (68a, 130) of the exhaust pipe (51c, 120) and extends toward an engine body (B); The internal combustion engine (20, 111) includes an air-cooling fan (56) provided at one end of a crankshaft (21), and an air guide member (70) that guides air from the air-cooling fan (56) toward an exhaust port (24b) of the engine body (B), the EGR pipe portion (78, 132) is arranged next to the exhaust port (24b) of the engine body (B) so as to be able to receive the airflow discharged from the air guide member (70); An internal combustion engine characterized by:

2. the partition wall (71, 128, 150) is provided in the exhaust pipe (51c, 120, 150) so as to define the EGR passage portion (68a, 130, 156) outside the exhaust passage portion (66a, 129, 154); 2. The internal combustion engine according to claim 1.

3. The exhaust pipe (51c, 120, 150) includes a catalyst (53, 131, 152) in the exhaust passage portion (66a, 129).

3. An internal combustion engine according to claim 1 or 2.

4. The EGR pipe portion (78, 132) is connected to the engine body (B), 2. The internal combustion engine according to claim 1.

5. ＜6＞ The EGR pipe portion (78, 132) passes around the engine body (B) and is connected to the intake pipe (31).

2. The internal combustion engine according to claim 1.

6. The EGR pipe section (78, 132) is provided with a heat dissipation section (80, 133).

2. The internal combustion engine according to claim 1.

7. An exhaust passage portion (66a, 129, 154) through which exhaust gas discharged from a combustion chamber (20a) flows; EGR passage portion (68a, 130, 156) and an exhaust pipe (51c, 120, 150) having the exhaust pipe (51c, 120, 150) is an internal combustion engine (20, 111) equipped with an exhaust system for an internal combustion engine, the exhaust pipe (51c, 120, 150) having a partition wall (71, 128, 158) separating the exhaust passage portion (66a, 129, 154) from the EGR passage portion (68a, 130, 156), A saddle-type vehicle (1, 101) equipped with an internal combustion engine (20, 111) further including an EGR pipe portion (78, 132) that defines a second EGR passage portion (78a, 132a) connected to the EGR passage portion (68a, 130) of the exhaust pipe (51c, 120) and extends toward an engine body (B), the exhaust pipe (51c, 120) is disposed below the engine body (B) in the up-down direction of the saddle riding type vehicle (1) or in front of the engine body (B) in the front-rear direction of the saddle riding type vehicle (101); At least a part of the EGR passage portion (68a, 130) is located on the opposite side of the engine body (B) across the exhaust passage portion (66a, 129). A saddle-type vehicle characterized by:

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