Exhaust device

Abstract

Disclosed is an exhaust device comprising: an exhaust chamber 65 that is installed so as to overlap with an internal combustion engine 3 in a top view; an exhaust pipe 61 that passes below the internal combustion engine from an exhaust port 36 of the internal combustion engine and has an opening 61c in the exhaust chamber; a catalyst retaining pipe 80 that is retained in the exhaust pipe, has at least a portion thereof installed in the exhaust chamber, and is filled with a catalyst 8; and an exhaust gas sensor 91 that is installed on a sensor mounting boss 93 provided to the exhaust pipe so as to penetrate the exhaust chamber and a rear exhaust pipe 61b that constitutes the exhaust pipe, is accommodated in the exhaust chamber, and retains the catalyst retaining pipe. As a result, when providing the exhaust gas sensor in front of or behind the catalyst in the exhaust pipe in order to suitably diagnose deterioration of the catalyst for treating exhaust gas, it is possible to improve the detection accuracy of the exhaust gas sensor while configuring the exhaust path to have a compact length in the front-rear direction, thereby improving emissions and thus contributing to mitigating or reducing the impact of climate change.

Description

exhaust system

[0001] The present invention relates to an exhaust system, and more particularly to an exhaust system for an internal combustion engine mounted on a saddle-ride type vehicle.

[0002] Efforts to mitigate or reduce the impact of climate change have been ongoing for some time, and research into improving emissions has been conducted to achieve this. In particular, regulations on environmental impact have become stricter in recent years, making it mandatory to monitor the status of exhaust gas control. Monitoring items may include diagnosing the deterioration of catalysts that purify exhaust gas. For example, as shown in Patent Document 1 below, the state of catalyst deterioration is determined based on the output values ​​of exhaust gas sensors attached before and after the catalyst. Even in straddle-type vehicles that have an exhaust chamber in the exhaust path, a known arrangement is to attach exhaust gas sensors to the exhaust pipe before and after a catalyst attached upstream of the exhaust chamber, as shown in Patent Document 2 below. In order to properly perform such catalyst deterioration diagnosis, it is important to ensure the detection reliability and accuracy of the exhaust gas sensors.

[0003] However, when a catalyst is installed upstream of the exhaust chamber and an exhaust gas sensor downstream of the catalyst, the exhaust path becomes longer in the longitudinal direction of the vehicle, and it may be difficult to ensure clearance with the rear wheel, swing arm, etc. While the longitudinal length can be made more compact by installing part of the catalyst inside the exhaust chamber, when the exhaust gas sensor is installed inside the exhaust chamber, the air in the exhaust chamber mixes with the exhaust gas that has passed through the catalyst, making it difficult to expose the exhaust gas that has passed through the catalyst directly to the exhaust gas sensor, which may reduce detection accuracy.

[0004] Japanese Patent Publication No. 2003-206784 (Fig. 1) Japanese Patent Publication No. 2017-214904 (Figs. 1 to 4)

[0005] In the case of improving emissions, when installing exhaust gas sensors before and after a catalyst in an exhaust pipe to properly diagnose the deterioration of the catalyst for treating exhaust gas, it is necessary to install an exhaust system with a compact longitudinal length, while allowing the exhaust gas to directly hit the exhaust gas sensor before it mixes with the air in the exhaust chamber and the exhaust gas that has passed through the catalyst, thereby improving the detection accuracy of the exhaust gas sensor.The present invention aims to provide an exhaust system that can solve this problem, and ultimately contributes to mitigating or reducing the impact of climate change.

[0006] In order to solve the above problems, the present invention provides an exhaust system having an exhaust chamber installed so that at least a portion of it overlaps with an internal combustion engine when viewed from above; an exhaust pipe that runs from an exhaust port of the internal combustion engine, passing below the internal combustion engine, and has an opening into the exhaust chamber; a catalyst holding pipe that is held by the exhaust pipe, has at least a portion installed within the exhaust chamber, and is filled with a catalyst; and an exhaust gas sensor that is installed in a sensor mounting boss portion provided on the exhaust pipe so as to penetrate through the exhaust chamber and a rear exhaust pipe that constitutes the exhaust pipe, is stored in the exhaust chamber, and holds the catalyst holding pipe.

[0007] According to the above configuration, when exhaust gas sensors are provided before and after a catalyst in the exhaust pipe to properly diagnose the deterioration of the catalyst for treating exhaust gas, by installing at least a portion of the catalyst holding pipe, which limits the longitudinal length of the exhaust device, inside the exhaust chamber, the longitudinal length of the exhaust path can be made compact, and by installing the exhaust gas sensor in the exhaust pipe that holds the catalyst holding pipe downstream of the catalyst holding pipe, the exhaust gas can be directly exposed to the exhaust gas sensor before it mixes with the air in the exhaust chamber and the exhaust gas that has passed through the catalyst, thereby improving detection accuracy, thereby improving emissions and ultimately contributing to mitigating or reducing the impact of climate change.

[0008] According to a preferred embodiment of the present invention, the catalyst holding pipe is installed at an angle with respect to the center line of the vehicle in the longitudinal direction of the vehicle, and by installing the catalyst holding pipe at an angle, the longitudinal dimension of the exhaust path can be made compact.

[0009] According to a preferred embodiment of the present invention, the downstream end of the exhaust pipe where the exhaust gas sensor is installed is installed along the inner wall surface of the exhaust chamber so as to be in contact with it, and by installing the exhaust gas sensor closer to the inner wall surface of the exhaust chamber, the amount of depression in the exhaust chamber required for installing the exhaust gas sensor can be reduced compared to when the exhaust gas sensor is installed in the center of the exhaust chamber, thereby improving the detection accuracy of the exhaust gas sensor while maintaining the capacity of the exhaust chamber.

[0010] According to a preferred embodiment of the present invention, the downstream end of the exhaust pipe has a reduced diameter structure. If water gets on the detection section of the exhaust gas sensor, it may be rapidly cooled, which may cause a decrease in the detection accuracy of the detection section of the exhaust gas sensor. However, by adopting a reduced diameter structure, water accumulated in the exhaust chamber when gas backflow occurs due to exhaust pulsation, or outside air entering through a drain hole, is less likely to come into contact with the exhaust gas sensor, thereby preventing the sensing accuracy of the exhaust gas sensor from being affected.

[0011] According to a preferred embodiment of the present invention, the reduced diameter structure at the downstream end of the exhaust pipe is asymmetrical with respect to the center line of the exhaust chamber of the exhaust pipe when viewed in a direction perpendicular to the flow direction of exhaust gases flowing through the exhaust pipe. This makes the exhaust gas sensor less susceptible to the effects of water and gases, preventing an impact on sensing accuracy, and by making the reduced diameter structure asymmetrical, the downstream end of the exhaust pipe is not excessively narrowed, which makes it less likely to cause resistance to the flow of exhaust gases and improves drivability.

[0012] According to a preferred embodiment of the present invention, in a top view of the exhaust system, the exhaust gas sensor is installed offset with respect to a center extension line passing through the longitudinal center of the catalyst holding pipe, and the downstream end of the exhaust pipe on the side where the exhaust gas sensor is installed has a diameter that is tapered so as to asymptotically approach the center extension line. By tapering the downstream end of the exhaust pipe on the side where the exhaust gas sensor is installed so as to asymptotically approach the center extension line, it is possible to relatively reduce the flow velocity of the gas flow on the exhaust gas sensor side, making it easier to sense the exhaust gas.

[0013] According to the exhaust system of the present invention, when exhaust gas sensors are provided before and after a catalyst in an exhaust pipe to properly diagnose the deterioration of the catalyst for treating exhaust gas, by installing at least a portion of the catalyst holding tube, which limits the longitudinal length of the exhaust system, inside the exhaust chamber, the longitudinal length of the exhaust path can be made compact, and by installing the exhaust gas sensor in the exhaust pipe that holds the catalyst holding tube downstream of the catalyst holding tube, the exhaust gas can be directly exposed to the exhaust gas sensor before the air in the exhaust chamber and the exhaust gas that has passed through the catalyst mix, thereby improving detection accuracy, thereby improving emissions and ultimately contributing to mitigating or reducing the impact of climate change.

[0014] FIG. 1 is a schematic left elevation view of a motorcycle according to this embodiment, with a partial cross section excluding the body cover. FIG. 2 is a left side view showing only the exhaust system, taken from the direction shown in FIG. 1. FIG. 3 is a plan view of the exhaust system as seen from arrow III in FIG. 2, i.e., as seen from above. FIG. 4 is an enlarged side cross-sectional view of the exhaust pipe and exhaust chamber as seen from arrows IV-IV in FIG. 3. FIG. 5 is a partial enlarged view of the exhaust pipe and exhaust chamber as seen from the direction shown in FIG. 3, i.e., as seen from above. FIG. 6 is a perspective view of the front of the exhaust chamber, seen diagonally from above and in the front left. FIG. 7 is a schematic cross-sectional view of the vehicle body, generally looking forward from arrows VII-VII in FIG. 1.

[0015] An exhaust system according to one embodiment of the present invention will be described with reference to Figures 1 to 7. In this embodiment, the internal combustion engine is an internal combustion engine mounted on a saddle-ride type vehicle, and the saddle-ride type vehicle is a motorcycle. Directions such as front, rear, left, right, up, and down in the claims and the description of this specification correspond to directions of the motorcycle in this embodiment. In the drawings, arrows FR, LH, RH, and UP indicate the front, left, right, and top of the vehicle, respectively.

[0016] Fig. 1 is a schematic left elevation view, partially in cross section, of a motorcycle 1 according to this embodiment, excluding a body cover. As shown in Fig. 1, the body frame 2 of the motorcycle 1 according to this embodiment includes a pair of left and right main frames 21 that extend slightly downward rearward from a head pipe 20, then further bend downward at a bent portion 21a in side view, forming a steeply inclined portion 21b, and connect to a pivot frame 22. A pair of left and right down frames 23 also extend obliquely downward from the head pipe 20 at a steep angle, generally parallel to the steeply inclined portion 21b of the main frame 21 in side view. A pair of left and right seat rails 24 extend rearward from the bent portion 21a of the main frame 21, and are supported by a pair of left and right backstays 25 that connect the rear portions of the seat rails 24 to the pivot frame 22. The left and right main frames 21, the left and right bent portions 21a, the left and right steeply inclined portions 21b, and the left and right seat rails 24 are connected by a plurality of cross members 26 provided at appropriate positions.

[0017] In the body frame 2 as described above, a front fork 11 is pivotally supported on the head pipe 20, and a front wheel 12 is journalled at its lower end. A swing arm 13, the front end of which is supported on a pivot frame 22 connected to the lower part of the steeply inclined portion 21b of the main frame 21, extends rearward, and a rear wheel 14 is journalled at its rear end, with a rear cushion 15 interposed between the swing arm 13 and the body frame 2. A fuel tank 16 is mounted in front of the main frame 21, and a passenger seat 17 is supported on seat rails 24 behind the fuel tank 16.

[0018] In this embodiment, the motorcycle 1 is equipped with an internal combustion engine 3 below the main frame 21 and in front of the steeply inclined portion 21b. The internal combustion engine 3 is suspended with the front portion of its crankcase 30 fastened to a bracket 23a attached to the lower end of the down frame 23, and the rear portion of the crankcase 30 fastened to the pivot frame 22.

[0019] The internal combustion engine 3 of this embodiment is equipped with a transmission 4 at the rear of the crankcase 30, constituting a so-called power unit, and is an air-cooled, single-cylinder, four-stroke cycle internal combustion engine mounted on the motorcycle 1 with its crankshaft 31 oriented in the vehicle width direction, i.e., the left-right direction, of the motorcycle 1.

[0020] A main shaft (not shown) and a countershaft 42 of the transmission 4 are provided in parallel to the crankshaft 31 at the rear of the crankcase 30. The countershaft 42 penetrates the crankcase 30 to the left and protrudes to the outside, serving as the final output shaft of the power unit, with an output sprocket 43 at its protruding portion. A drive chain 44 is wound around the output sprocket 43 and is stretched over a driven sprocket 45 on the rear wheel 14 side, forming a chain transmission mechanism that transmits power to the rear wheel 14.

[0021] The internal combustion engine 3 is suspended on the crankcase 30 with the cylinder axis tilted slightly forward and the cylinder block 32, cylinder head 33, and cylinder head cover 34 in an upright position. An intake pipe 51 extends rearward from the cylinder head 33 of the internal combustion engine 3, connecting to the intake port 35. An intake system path leads to an air cleaner case 55 via an intake member 50 consisting of the intake pipe 51, throttle body 52, connecting tube 53, etc. An exhaust pipe 61 extends forward from the cylinder head 33, connecting to the exhaust port 36, bends downward, and extends rearward below the internal combustion engine 3, forming an exhaust system 6 whose exhaust path passes through an exhaust chamber 65 and reaches a muffler 69 on the right side of the rear wheel 14.

[0022] Figure 2 is a left side view showing only the exhaust system 6, including the exhaust pipe 61, exhaust chamber 65, and muffler 69, taken from the direction shown in Figure 1. Figure 3 shows the exhaust system 6 as viewed from above, i.e., as seen from arrow III in Figure 2. Figure 4 is an enlarged side cross-sectional view of the exhaust pipe 61 and exhaust chamber 65 as viewed from arrows IV-IV in Figure 3. Figure 5 is a partial enlarged view of the exhaust pipe 61 and exhaust chamber 65 as viewed from above, i.e., as seen from the direction shown in Figure 3.

[0023] As shown in FIG. 2 , in the exhaust system 6 of this embodiment, a front exhaust pipe (referred to as the "exhaust pipe" in the present invention) 61a of the exhaust pipe 61 connected to the exhaust port 36 extends below the internal combustion engine 3 and connects to the exhaust chamber 65. As shown in FIG. 3 , the exhaust chamber 65 is installed so that at least a portion of it overlaps with the internal combustion engine 3 in a top view. As shown in FIG. 4 , the exhaust gas flow rear end 62 of the front exhaust pipe 61a constituting the exhaust pipe 61 is fitted into an opening 66 formed in an outer shell 65a of the exhaust chamber 65, and a portion of the fitted portion forms a front exhaust pipe fixing portion 73a that fixes the exhaust pipe 61 to the outer shell 65a of the exhaust chamber 65 by welding or the like. A drain hole (not shown) is provided at the bottom of the exhaust chamber 65 to drain moisture from the exhaust gas condensed within the exhaust chamber 65.

[0024] A rear exhaust pipe (referred to as the "exhaust pipe" in this invention) 61b, which constitutes the exhaust pipe 61, is housed within the exhaust chamber 65 with a predetermined clearance in the extension direction of the rear end 62 of the front exhaust pipe 61a and is held on the inner surface of the outer shell 65a of the exhaust chamber 65. The exhaust gas flow front end 63 of the rear exhaust pipe 61b, which is housed within the exhaust chamber 65 and holds a catalyst holding pipe 80 (described below), is connected to the exhaust chamber 65 by an exhaust pipe slide holder 71, which allows the exhaust pipe 61 to slidably fit into an opening 66 of the exhaust chamber 65. This allows for expansion and contraction of the rear exhaust pipe 61b in the axial direction due to thermal expansion relative to the opening 66. In this embodiment, the exhaust pipe slide holder 71 is formed at the front end 63 of the rear exhaust pipe 61b, but it may be offset downstream from the front end 63.

[0025] The rear end of the rear exhaust pipe 61b, i.e., the downstream end 64 of the exhaust pipe 61, has an opening 61c in the exhaust chamber 65. As shown in Figure 5, the rear exhaust pipe 61b has a rear exhaust pipe fixing portion 73b that is fixed to the outer shell 65a of the exhaust chamber 65 by partial welding or the like near a downstream sensor mounting boss 93 (described below), preventing misalignment of the outer shell 65a of the exhaust chamber 65 with respect to the downstream sensor mounting boss 94. Note that although the front exhaust pipe 61a and the rear exhaust pipe 61b are separated at a point within the exhaust chamber 65 in this embodiment, they function as a single unit as the exhaust pipe 61, and hereinafter, including in the claims, they will both be collectively referred to as the exhaust pipe 61.

[0026] A catalyst holding pipe 80 is held inside the exhaust pipe 61 (61a, 61b), fixed inside the front exhaust pipe 61a and extending into the rear exhaust pipe 61b, with its upstream end 80a fixed to the inner surface of the front exhaust pipe 61a. The catalyst holding pipe 80 is slidably fitted onto the inner surface of the rear pipe 61b, forming a catalyst slide holding portion 72 and connecting to it. This allows expansion and contraction of the catalyst holding pipe 80 in the axial direction relative to the rear pipe 61b due to thermal expansion. As shown in FIG. 3, the catalyst holding pipe 80 is installed at an angle with respect to the vehicle center line X in the longitudinal direction of the vehicle, thereby making the longitudinal length of the exhaust path compact.

[0027] The catalyst holding tube 80 is filled with a catalyst 8 for treating exhaust gas, such as a three-way catalyst that purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst 8 is not limited to a three-way catalyst, and may include cases where different types of catalysts are arranged along the length of the catalyst 8 shown in the figure. The catalyst 8 in this embodiment is supported on a honeycomb structure so that reaction can occur as exhaust gas passes through. The catalyst holding tube 80 is held across the inner surfaces of the front exhaust pipe 61a and the rear exhaust pipe 61b, and therefore a portion of the catalyst holding tube 80 is installed within the exhaust chamber 65.

[0028] When exhaust gas sensors 91 are provided in front of and behind the catalyst 8 for exhaust gas treatment to properly diagnose deterioration of the catalyst 8, if part of the catalyst 8 in the exhaust pipe 61 is located inside the exhaust chamber 65 to limit the longitudinal length of the exhaust device 6, the downstream exhaust gas sensor 91 must be installed by penetrating multiple components such as the exhaust chamber 65 and the exhaust pipe 61, which creates problems with expansion / contraction and distortion of each component due to heat. However, the connection between the rear exhaust pipe 61b and the exhaust chamber 65 forms the exhaust pipe slide holder 71, and the connection between the catalyst holder pipe 80 and the rear exhaust pipe 61b forms the catalyst slide holder 72, so displacement of each component caused by thermal expansion can be avoided, and distortion that occurs in the downstream sensor mounting boss 93 of the exhaust gas sensor 91 that is provided in the exhaust pipe 61 so as to penetrate both the exhaust chamber 65 and the exhaust pipe 61 can be alleviated. This reduces the load on the downstream sensor mounting boss 93, thereby improving the durability of the exhaust gas sensor 91 and its detection reliability and accuracy.

[0029] This embodiment will be described in further detail below. Exhaust gas sensors 91 are provided in the exhaust pipe 61 on the upstream and downstream sides of the catalyst 8 to detect the state of exhaust gas purification by the catalyst 8 and also to detect deterioration of the catalyst 8. The exhaust gas sensors 91 are, for example, an O2 sensor or an LAF sensor (air-fuel ratio sensor), but the type is not limited in this embodiment. As shown in Figures 2 and 3, the upstream exhaust gas sensor is installed in an upstream sensor mounting boss 92 provided at the front end of the front exhaust pipe 61a, but the upstream exhaust gas sensor itself is not shown in the figures.

[0030] 4, the downstream exhaust gas sensor 91 is mounted on a downstream sensor mounting boss 93 provided on the rear exhaust pipe 61b, which extends downstream from the downstream end 80b of the catalyst holding pipe 80 within the exhaust gas chamber 65, and the downstream sensor mounting boss 93 is provided on the rear exhaust pipe 61b, penetrating the rear exhaust pipe 61b and the exhaust gas chamber 65. Because the catalyst holding pipe 80 is held in the rear exhaust pipe 61b via the catalyst slide holder 72, expansion and contraction in the axial direction of the rear exhaust pipe 61b caused by thermal expansion of the catalyst holding pipe 80 is suppressed, and strain generated in the downstream sensor mounting boss 93, which is provided to penetrate both the exhaust chamber 65 and the rear exhaust pipe 61b, can be alleviated. By reducing the load on the downstream sensor mounting boss 93, the durability of the exhaust gas sensor 91 and the detection reliability and accuracy can be improved.

[0031] As described above, by installing at least a portion of the catalyst holding pipe 80 inside the exhaust chamber 65, the longitudinal length of the exhaust path can be made compact, and by installing the exhaust gas sensor 91 in the rear exhaust pipe 61b downstream of the catalyst holding pipe 80, the exhaust gas can be directed directly at the exhaust gas sensor 91 before it mixes with the air in the exhaust chamber 65 and the exhaust gas that has passed through the catalyst 8, thereby improving the detection accuracy of the exhaust gas sensor 91.

[0032] 3, in this embodiment, the front exhaust pipe 61a is spaced away from the vehicle center line X to the right in the vehicle width direction at the upstream end 80a of the catalyst holding pipe 80, and has a bent portion 61d that bends upstream of the catalyst 8, and the bent portion 65d forms an expanded diameter structure 65e. By providing the bent portion 65d in this manner, the exhaust pipe 61 can ensure the necessary exhaust pipe length while shortening the front-to-rear arrangement distance, and by providing the expanded diameter structure 65e at the bent portion 65d, the exhaust gas flow that is unevenly distributed within the front exhaust pipe 61a upstream of the catalyst 8 can be uniformly dispersed within the front exhaust pipe 61a, and by uniformly hitting the upstream end face of the catalyst 8, uneven flow of exhaust gas against the catalyst 8 is suppressed, and the detection accuracy of the exhaust gas sensor 91 after passing through the catalyst 8 can be improved.

[0033] 4 and 5, the downstream end 61c of the rear exhaust pipe 61b is reduced in diameter. When exhaust pulsation causes a backflow of exhaust gas, water that has accumulated in the exhaust chamber 65 or outside air that has entered through the drain hole comes into contact with the exhaust gas sensor 91, causing it to cool rapidly, which could cause a decrease in the detection accuracy of the detection unit 91a of the exhaust gas sensor 91. However, this can be prevented by reducing the diameter of the downstream end 64, and the sensing accuracy of the exhaust gas sensor 91 can be prevented from being affected. This also improves the durability of the exhaust gas sensor 91 as well as its detection reliability and accuracy.

[0034] 5, the reduced diameter structure of the downstream end 64 of the rear exhaust pipe 61b is formed asymmetrically in a top view with respect to the center line Y of the exhaust chamber of the rear exhaust pipe 61b. This prevents the downstream end 64 of the rear exhaust pipe 61b from being excessively narrowed, making it less likely to cause resistance to the flow of exhaust gas and improving drivability.

[0035] 5, the exhaust gas sensor 91 is installed at a position offset from a center extension line Z that passes through the longitudinal center of the catalyst holding pipe 80 in a top view, and the portion of the downstream end 64 of the rear exhaust pipe 61b on the side where the exhaust gas sensor 91 is installed, downstream of the exhaust gas sensor 91, is tapered in diameter so as to asymptotically approach the center extension line Z. This makes it possible to relatively reduce the flow velocity of the exhaust gas on the exhaust gas sensor 91 side, making it easier to sense the exhaust gas.

[0036] Furthermore, the downstream end 64 of the rear exhaust pipe 61b on the side where the exhaust gas sensor 91 is installed is installed along the inner wall surface 65b of the exhaust chamber 65 so as to be in contact with it when viewed from above. Therefore, heat from the high-temperature rear exhaust pipe 61b is dissipated through the exhaust chamber 65, suppressing movement of the rear exhaust pipe 61b due to temperature changes and mitigating distortion that occurs in the downstream sensor mounting boss 93 of the exhaust gas sensor 91. By reducing the load on the downstream sensor mounting boss 93, the durability, detection reliability, and accuracy of the exhaust gas sensor 91 can be improved. Furthermore, by installing the exhaust gas sensor 91 closer to the inner wall surface of the exhaust chamber 65, the amount of depression in the exhaust chamber 65 required for installation of the exhaust gas sensor 91 can be reduced compared to when the exhaust gas sensor 91 is installed in the center of the exhaust chamber 65. This allows the capacity of the exhaust chamber 65 to be maintained while improving the detection accuracy of the exhaust gas sensor 91.

[0037] Figure 6 is a perspective view of the front of the exhaust chamber 65, seen diagonally from above and to the front left. As shown in Figures 2, 3, and 6, a recess 65c recessed from above and to the left is formed on the left side of the exhaust chamber 65, and the exhaust gas sensor 91 is installed in the recess 65c with its detection portion 91a facing downward. Providing the recess 65a in the exhaust chamber 65 improves accessibility with tools when installing the exhaust gas sensor 91. The recess 65a is also shaped so that it slopes slightly downward toward the left, making it difficult for water from rain or other sources to accumulate in the exhaust chamber 65 and allowing it to flow away easily.

[0038] Figure 7 is a schematic cross-sectional view of the vehicle body viewed generally along arrows VII-VII in Figure 1 and facing forward, showing a cross section of the rear of the downstream sensor mounting boss portion 93 in the exhaust chamber 65. As shown in Figure 7, the harness 91b of the exhaust gas sensor 91 mounted in the recess 65a of the exhaust chamber 65 is engaged with a stay 26a that extends upward and is fixed to the nearby cross member 26. By temporarily engaging the harness 91b with the stay 26a in this way, it is possible to easily accommodate changes to the placement of the exhaust gas sensor 91 in the exhaust chamber 65, and the harness 91b is routed stably and safely.

[0039] The exhaust device 6 of the present embodiment described above has the following features: it has an exhaust chamber 65 that is installed so that at least a portion of it overlaps with the internal combustion engine 3 in a top view, an exhaust pipe 61 that runs from the exhaust port 36 of the internal combustion engine 3 below the internal combustion engine 3 and has an opening 61c within the exhaust chamber 65, a catalyst holding pipe 80 that is held by the exhaust pipe 61 and has at least a portion located within the exhaust chamber 65 and is filled with catalyst 8, and an exhaust gas sensor 91 that is installed in a sensor mounting boss 93 that is provided on the rear exhaust pipe 61b so as to penetrate through the exhaust chamber 65 and a rear exhaust pipe 61b that constitutes the exhaust pipe 61, is housed within the exhaust chamber 65, and holds the catalyst holding pipe 80.

[0040] When exhaust gas sensors 91 are provided in front of and behind the catalyst 8 in the exhaust pipe 61 to properly diagnose deterioration of the catalyst 8 for treating exhaust gas, it becomes necessary to reduce the longitudinal length of the exhaust device 6. However, by installing at least a portion of the catalyst holding pipe 80 inside the exhaust chamber 65, the longitudinal length of the exhaust device 6 can be made compact, and by installing the exhaust gas sensor 91 in the rear exhaust pipe 61b downstream of the catalyst holding pipe 80, the exhaust gas can be made to directly hit the exhaust gas sensor 91 before it mixes with the air in the exhaust chamber 65 and the exhaust gas that has passed through the catalyst 8, thereby improving detection accuracy. This results in improved emissions, which in turn contributes to mitigating or reducing the impact of climate change.

[0041] As shown in FIG. 3, the catalyst holding pipe 80 is installed at an angle with respect to the vehicle center line X in the longitudinal direction of the vehicle. By installing the catalyst holding pipe 80 at an angle, the longitudinal distance of the exhaust path can be made compact.

[0042] As shown in Figure 5, the downstream end 64 of the rear exhaust pipe 61b, where the exhaust gas sensor 91 is installed, is installed along and in contact with the inner wall surface 65b of the exhaust chamber 65. By installing the exhaust gas sensor 91 closer to the inner wall surface 65b of the exhaust chamber 65, the amount of depression in the exhaust chamber 65 required to install the exhaust gas sensor 91 can be reduced compared to when the exhaust gas sensor 91 is installed in the center of the exhaust chamber 65. This makes it possible to improve the detection accuracy of the exhaust gas sensor 91 while maintaining the capacity of the exhaust chamber 65.

[0043] The downstream end 64 of the rear exhaust pipe 61b has a reduced diameter structure 67. If water gets on the detection section 91a of the exhaust gas sensor 91, it may be cooled rapidly, which may cause a decrease in the detection accuracy of the detection section 91a of the exhaust gas sensor 91. However, by using the reduced diameter structure 67, water that has accumulated in the exhaust chamber 65 when a gas backflow occurs due to exhaust pulsation, or outside air that has entered through the drain hole, is less likely to come into contact with the exhaust gas sensor 91, preventing the sensing accuracy of the exhaust gas sensor 91 from being affected.

[0044] The diameter-reducing structure 67 of the downstream end 64 of the rear exhaust pipe 61b is asymmetrical with respect to the center line Y of the exhaust chamber of the rear exhaust pipe 61b when viewed in a direction perpendicular to the flow direction F of the exhaust gas flowing inside the exhaust pipe 61. Therefore, the exhaust gas sensor 91 is less susceptible to the effects of water and gas, preventing an impact on sensing accuracy, and by making the diameter-reducing structure 67 asymmetrical, the downstream end 64 of the rear exhaust pipe 61b is not narrowed too much, which makes it less likely to cause resistance to the flow of exhaust gas and improves drivability.

[0045] In a top view of the exhaust device 6, the exhaust gas sensor 91 is installed offset with respect to a center extension line Z that passes through the longitudinal center of the catalyst holding pipe 80, and the downstream end 64 of the rear exhaust pipe 61b on the side where the exhaust gas sensor 91 is installed has a diameter that is reduced so that the portion downstream of the exhaust gas sensor 91 asymptotically approaches the center extension line Z. By reducing the diameter of the downstream end 64 of the rear exhaust pipe 61b on the side where the exhaust gas sensor 91 is installed so that it asymptotically approaches the center extension line Z, the flow velocity of the gas flow on the exhaust gas sensor 91 side can be relatively reduced, making it easier to sense the exhaust gas.

[0046] While one embodiment of the exhaust system of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various other modifications are possible within the scope of the gist of the present invention. For convenience of explanation, the left-right arrangement of the system has been described in accordance with the illustrated embodiment, but the left-right arrangement may be reversed.

[0047] DESCRIPTION OF SYMBOLS 1...Motorcycle, 2...Vehicle body frame, 3...Internal combustion engine, 6...Exhaust device, 8...Catalyst, 26...Cross member, 26a...Stay, 33...Cylinder head, 36...Exhaust port, 61...Exhaust pipe, 61a...Front exhaust pipe ("exhaust pipe" in the present invention), 61b...Rear exhaust pipe ("exhaust pipe" in the present invention), 61c...Opening, 61d...Bent portion, 61e...Expanded diameter structure, 62...Rear end, 63...Front end, 64...Downstream end, 65...Exhaust chamber, 65a...Outer Shell, 65b...inner wall surface, 65c...recess, 66...opening, 69...muffler, 71...exhaust pipe slide holding portion, 72...catalyst slide holding portion, 73a...front exhaust pipe fixing portion, 73b...rear exhaust pipe fixing portion, 91...exhaust gas sensor, 91a...detection portion, 91b...harness, 92...upstream sensor mounting boss portion, 93...downstream sensor mounting boss portion, X...vehicle center line, Y...exhaust chamber interior center line (of rear exhaust pipe 61b), Z...center extension line (of catalyst holding pipe 80)

Claims

1. (After correction) an exhaust chamber (65) disposed so that at least a portion thereof overlaps with the internal combustion engine (3) when viewed from above; an exhaust pipe (61) extending from an exhaust port (36) of the internal combustion engine (3) and passing below the internal combustion engine (3), and having a downstream end (64) at its rear end having an opening (61c) that opens into the exhaust chamber (65); a catalyst holding tube (80) held in the exhaust pipe (61), at least a portion of which is disposed in the exhaust chamber (65), and which is filled with a catalyst (8); a rear exhaust pipe (61b) that constitutes the exhaust pipe (61), is housed in the exhaust chamber (65), and holds the catalyst holding pipe (80); and an exhaust gas sensor (91) installed in a sensor mounting boss portion (93) that is provided on the exhaust pipe (61) so as to penetrate through the exhaust chamber (65), a downstream end (64) of the exhaust pipe (61) having a diameter-reducing structure (67), and the opening (61c) opening into the exhaust chamber (65) is provided at the downstream end of the diameter-reducing structure (67).

2. 2. The exhaust system according to claim 1, wherein the catalyst holding pipe (80) is disposed obliquely with respect to a center line (X) of the vehicle in the longitudinal direction of the vehicle.

3. 3. The exhaust system according to claim 1, wherein the downstream end portion (64) of the exhaust pipe (61) where the exhaust gas sensor (91) is installed is installed along an inner wall surface (65b) of the exhaust chamber (65) so as to be in contact with the inner wall surface (65b).

4. An exhaust device as described in claim 1, characterized in that the reduced diameter structure (67) of the downstream end (64) of the exhaust pipe (61) is asymmetrical left and right when viewed vertically with respect to the center line (Y) within the exhaust chamber of the exhaust pipe (61) and the flow direction (F) of the exhaust gas flowing within the exhaust pipe (61).

5. In a top view of the exhaust system, with respect to a center extension line (Z) passing through the longitudinal center of the catalyst holding pipe (80), The exhaust gas sensor (91) is installed offset, 5. The exhaust system according to claim 4, wherein the diameter of the downstream end (64) of the exhaust pipe (61) on the side where the exhaust gas sensor (91) is installed, downstream of the exhaust gas sensor (91), is reduced so as to asymptotically approach the center extension line (Z).