EP4671509A1

EP4671509A1 - EXHAUST SYSTEM

Info

Publication number: EP4671509A1
Application number: EP23930468.6A
Authority: EP
Inventors: Junichi Nakano; Shigeru Kita
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2023-03-29
Filing date: 2023-03-29
Publication date: 2025-12-31
Also published as: EP4671509A4; WO2024201830A1; JPWO2024201830A1; CN120917218A

Abstract

An exhaust device is disclosed, including: an exhaust chamber 65 disposed to overlap with an internal combustion engine 3 in a top view; an exhaust pipe 61, which passes below the internal combustion engine from an exhaust port 36 of the internal combustion engine, and which includes an opening portion 61c in the exhaust chamber; a catalyst holding pipe 80, which is held in the exhaust pipe, at least a part of which is disposed in the exhaust chamber, and which is filled with a catalyst 8; and an exhaust gas sensor 91 disposed on a sensor attachment boss portion 93, which is provided on the exhaust pipe so as to penetrate into a rear exhaust pipe 61b and the exhaust chamber, the rear exhaust pipe 61b constituting the exhaust pipe, being stored in the exhaust chamber, and holding the catalyst holding pipe. Thus, in providing the exhaust gas sensor at the front and the rear of the catalyst in the exhaust pipe in order to appropriately make a degradation diagnosis of the catalyst for exhaust gas treatment, detection accuracy of the exhaust gas sensor can be improved, while a length in a front-rear direction of the exhaust passage is made compact. Emission improvement is achieved, and contribution to mitigating or reducing the influence on climate change is made, accordingly.

Description

[Technical Field]

The present invention relates to an exhaust device, and more particularly to an exhaust device for an internal combustion engine mounted on a straddle type vehicle.

[Background Art]

Efforts for the purpose of mitigating or reducing the influence on climate change have been continuously made conventionally, and research and development on emission improvement are being conducted in order to achieve the purpose.
In particular, in recent years, regulations on environmental load have become strict, and it is obligated to monitor a control situation of the exhaust gas. As a monitoring item, a degradation diagnosis of a catalyst for purifying the exhaust gas is included as an item, in some cases. For example, as disclosed in Patent Document 1 to be listed below, a degradation state of the catalyst is determined, based on output values of exhaust gas sensors each attached at the front and the rear of the catalyst.
Also, in a straddle type vehicle including an exhaust chamber on an exhaust passage, the arrangement in which the exhaust gas sensor is attached to an exhaust pipe at the front and the rear of the catalyst attached on an upstream side of the exhaust chamber is known, for example, as disclosed in Patent Document 2 to be listed below.
In order to appropriately make the catalyst degeneration diagnosis in such a manner, it is important to ensure detection reliability and accuracy of the exhaust gas sensors.
In a case where the catalyst is attached on the upstream side of the exhaust chamber and the exhaust gas sensor is attached on the downstream side of the catalyst, however, the exhaust passage becomes long in a vehicle front-rear direction, and it may be difficult to ensure a clearance to a rear wheel, a swing arm, or the like.
By disposing a part of the catalyst in the exhaust chamber, it is possible to make a front-rear length compact. However, in a case where the exhaust gas sensor is disposed in the exhaust chamber, air in the exhaust chamber and the exhaust gas that has passed through the catalyst are mixed together. Hence, it is difficult to directly bring the exhaust gas that has passed through the catalyst into contact with the exhaust gas sensor, and detection accuracy may be lowered.

[Prior Art Document]

[Patent Document]

Patent Document 1: JP 2003-206784 A (Fig. 1)
Patent Document 2: JP 2017-214904 A (Figs. 1 to 4)

[Summary of the Invention]

[Underlying Problems to be solved by the Invention]

In the emission improvement, by the way, in providing the exhaust gas sensor at the front and the rear of the catalyst in the exhaust pipe in order to appropriately make a degradation diagnosis of the catalyst for exhaust gas treatment, there is a problem in that before the air in an exhaust chamber and the exhaust gas that has passed through the catalyst are mixed together, the exhaust gas can be brought into contact with the exhaust gas sensor and detection accuracy of the exhaust gas sensor is improved, while a length in a front-rear direction of the exhaust device is made compact.
An object of the present invention is to achieve an exhaust device capable of solving such a problem, and the present invention contributes to mitigating or reducing the influence on climate change, accordingly.

[Means to solve the Problems]

In order to solve the above problem, the present invention provides an exhaust device including:

an exhaust chamber disposed such that at least a part of the exhaust chamber overlaps with an internal combustion engine in a top view;
an exhaust pipe, which passes below the internal combustion engine from an exhaust port of the internal combustion engine, and which includes an opening portion in the exhaust chamber;
a catalyst holding pipe, which is held in the exhaust pipe, at least a part of which is disposed in the exhaust chamber, and which is filled with a catalyst; and
an exhaust gas sensor disposed on a sensor attachment boss portion, which is provided on the exhaust pipe so as to penetrate into a rear exhaust pipe and the exhaust chamber, the rear exhaust pipe constituting the exhaust pipe, being stored in the exhaust chamber, and holding the catalyst holding pipe.

According to the above configuration,
in providing the exhaust gas sensor at the front and the rear of the catalyst in the exhaust pipe in order to appropriately make a degradation diagnosis of the catalyst for exhaust gas treatment, at least a part of the catalyst holding pipe that suppresses the front-rear length of the exhaust device is disposed in the exhaust chamber, and while a length in a front-rear direction of the exhaust device is made compact, the exhaust gas sensor is disposed in the exhaust pipe that holds the catalyst holding pipe on the downstream side of the catalyst holding pipe, so that the exhaust gas can be directly brought into contact with the exhaust gas sensor, before the air in the exhaust chamber and the exhaust gas that has passed through the catalyst are mixed together, and the detection accuracy can be improved. In addition, emission improvement is achieved, and contribution to mitigating or reducing the influence on climate change is made, accordingly.
In a preferred embodiment of the present invention,
the catalyst holding pipe is disposed obliquely with respect to a vehicle center line in a vehicle front-rear direction. By disposing the catalyst holding pipe obliquely, the distance in the front-rear direction of the exhaust path can be made compact.
In a preferred embodiment of the present invention,
a downstream end portion of the exhaust pipe, in which the exhaust gas sensor is disposed, is disposed along an inner wall surface of an exhaust chamber.
By disposing the exhaust gas sensor to be close to the inner wall surface of the exhaust chamber, a recess amount of the exhaust chamber for disposing the exhaust gas sensor can be reduced, as compared with a case where the exhaust gas sensor is disposed at the center of the exhaust chamber, and the detection accuracy of the exhaust gas sensor can be improved while the capacity of the exhaust chamber is ensured.
In a preferred embodiment of the present invention,
a downstream end portion of the exhaust pipe has a reduced diameter structure.
When water is splashed on the detection unit of the exhaust gas sensor, the detection unit may be rapidly cooled to cause a decrease in detection accuracy of the detection unit of the exhaust gas sensor. However, by adopting the reduced diameter structure, water accumulated in the exhaust chamber at the time of gas backflow due to exhaust pulsation, outside air that has entered through a drain hole, or the like is hardly brought into contact with the exhaust gas sensor, and it becomes possible to prevent influence on sensing accuracy of the exhaust gas sensor.
In a preferred embodiment of the present invention,
the reduced diameter structure of the downstream end portion of the exhaust pipe is left-right asymmetric with respect to a center line in the exhaust chamber of the exhaust pipe, when viewed in a direction perpendicular to a flow direction of an exhaust gas flowing in the exhaust pipe.
Therefore, the exhaust gas sensor is hardly influenced by water or gas, while preventing the influence of water or gas on the sensing accuracy, and the reduced diameter structure is made left-right asymmetric. Thus, the downstream end portion of the exhaust pipe is not excessively narrowed, and thus resistance of the exhaust gas flow hardly occurs, and drivability is improved.
In a preferred embodiment of the present invention,
in a top view of the exhaust device, the exhaust gas sensor is disposed to be offset with respect to a center extension line which passes through a center in a longitudinal direction of the catalyst holding pipe, and
a downstream part, relative to the exhaust gas sensor, of the downstream end portion of the exhaust pipe, on a side where the exhaust gas sensor is disposed, is reduced in diameter to gradually approach the center extension line.
By reducing the diameter of the downstream end portion of the exhaust pipe on the side where the exhaust gas sensor is disposed so as to gradually approach the center extension line, the flow velocity of the gas flow on the exhaust gas sensor side can be relatively lowered, and the exhaust gas is easily sensed.

[Effects of the Invention]

According to the exhaust device in the present invention,
in providing the exhaust gas sensor at the front and the rear of the catalyst in the exhaust pipe in order to appropriately make a degradation diagnosis of the catalyst for exhaust gas treatment, at least a part of the catalyst holding pipe that suppresses the front-rear length of the exhaust device is disposed in the exhaust chamber, and while a length in a front-rear direction of the exhaust device is made compact, the exhaust gas sensor is disposed in the exhaust pipe that holds the catalyst holding pipe on the downstream side of the catalyst holding pipe, so that the exhaust gas can be directly brought into contact with the exhaust gas sensor, before the air in the exhaust chamber and the exhaust gas that has passed through the catalyst are mixed together, and the detection accuracy can be improved. In addition, emission improvement is achieved, and contribution to mitigating or reducing the influence on climate change is made, accordingly.

[Brief Description of Drawings]

Fig. 1 is a schematic left elevation view of a motorcycle according to the present embodiment, partially including a cross-section except for a vehicle body cover.
Fig. 2 is a left side view illustrating only an exhaust device that is taken out, in a direction illustrated in Fig. 1.
Fig. 3 is a plan view of the exhaust device, when viewed in a direction of an arrow III in Fig. 2, that is, a top view.
Fig. 4 is an enlarged cross-sectional side view of an exhaust pipe and an exhaust chamber taken along line IV-IV in Fig. 3.
Fig. 5 is a partially enlarged view of the exhaust pipe and the exhaust chamber, in a direction illustrated in Fig. 3, that is, a top view.
Fig. 6 is a perspective view of a front portion of the exhaust chamber, when viewed from obliquely left front upper.
Fig. 7 is a schematic cross-sectional view of a vehicle body substantially taken along line VII-VII in Fig. 1 and directed toward a forward side of a vehicle.

[Modes for carrying out the Invention]

An exhaust device according to one embodiment of the present invention will be described with reference to Figs. 1 to 7.
In the present embodiment, an internal combustion engine is an internal combustion engine mounted on a straddle type vehicle, and the straddle type vehicle indicates a case of a motorcycle 1, and directions such as front, rear, left, right, and up and down in the claims and the description of the present specification respectively correspond to the directions of the motorcycle in the present embodiment.
In the drawings, an arrow FR indicates the front of the vehicle, LH indicates the left of the vehicle, RH indicates the right of the vehicle, and UP indicates the top of the vehicle.
Fig. 1 is a schematic left elevation view of a motorcycle 1 according to the present embodiment, partially including a cross-section except for a vehicle body cover.
As illustrated in Fig. 1, in a vehicle body frame 2 of the motorcycle 1 in the present embodiment, a pair of main frames 21 slightly extend downward from a head pipe 20 to the rear, then further form bent portions 21a to bend downward in a side view, form steep inclined portions 21b, and reach a pivot frame 22.
In addition, a pair of left and right down frames 23 extending downward from the head pipe 20 at an obliquely steep angle are in substantially parallel with the steep inclined portions 21b of the main frames 21 in a side view.
A pair of left and right seat rails 24 extend rearward from the bent portions 21a of the main frames 21, and a pair of left and right back stays 25, which couple rear portions of the seat rails 24 to the pivot frame 22, support the seat rails 24.
The left and right main frames 21, the left and right bent portions 21a, the left and right steep inclined portions 21b, and the left and right seat rails 24 are connected by a plurality of cross members 26, which are provided at appropriate positions.
In the vehicle body frame 2 as described above, a front fork 11 is pivotally supported by the head pipe 20, and a front wheel 12 is pivotally supported by a lower end of the front fork 11.
On the pivot frame 22, which is connected with a lower portion of the steep inclined portion 21b of the main frame 21, a swing arm 13 having a front end supported extends rearward, a rear wheel 14 is pivotally supported on a rear end of the swing arm 13, and a rear cushion 15 is interposed between the swing arm 13 and the vehicle body frame 2.
A fuel tank 16 is bridged on front portions of the main frames 21, and a passenger seat 17 is provided on the rear of the fuel tank 16 so as to be supported by the seat rails 24.
In the present embodiment, in the motorcycle 1, the internal combustion engine 3 is mounted below the main frames 21 and at the front of the steep inclined portions 21b. In the internal combustion engine 3, a front portion of a crankcase 30 is fastened to a bracket 23a, which is attached to a lower end of the down frame 23, and a rear portion of the crankcase 30 is fastened to the pivot frame 22, and is suspended.
The internal combustion engine 3 in the present embodiment includes a transmission 4 at a rear portion in the crankcase 30 to constitute a so-called power unit, and is an air-cooled single-cylinder four-stroke cycle internal combustion engine mounted on the motorcycle 1 with a crankshaft 31 oriented in a vehicle width direction of the motorcycle 1, that is, a left-right direction.
A main shaft, not illustrated, and a counter shaft 42 of the transmission 4 are provided in a rear portion in the crankcase 30 in parallel with the crankshaft 31, and the counter shaft 42 penetrates through the crankcase 30 to the left, and protrudes to the outside to be a final output shaft of the power unit, and includes an output sprocket 43 at a protrusion portion. A drive chain 44, which is wound around the output sprocket 43, is bridged over a driven sprocket 45 on the rear wheel 14 side to constitute a chain transmission mechanism, and dynamic power is transferred to the rear wheel 14.
The internal combustion engine 3 is suspended in an attitude in which a cylinder block 32, a cylinder head 33, and a cylinder head cover 34 are made upright while slightly inclining a cylinder axis forward on the crankcase 30.
An intake pipe 51, in connection with an intake port 35, extends rearward from the cylinder head 33 of the internal combustion engine 3, and an intake system passage reaches an air cleaner case 55 via an intake member 50 including the intake pipe 51, a throttle body 52, a connecting tube 53, and the like.
On the front of the cylinder head 33, an exhaust device 6 is configured such that an exhaust pipe 61, in connection with an exhaust port 36, extends and bends downward, and extends rearward below the internal combustion engine 3, and an exhaust passage reaches a muffler 69 on the right side of the rear wheel 14 through an exhaust chamber 65.
Fig. 2 is a left side view illustrating only the exhaust device 6, which includes the exhaust pipe 61, the exhaust chamber 65, and the muffler 69, and which is taken out, in a direction illustrated in Fig. 1.
Fig. 3 is a plan view of the exhaust device 6, when viewed in a direction of an arrow III in Fig. 2, that is, a top view.
Fig. 4 is an enlarged cross-sectional side view of the exhaust pipe 61 and the exhaust chamber 65 taken along line IV-IV in Fig. 3.
Fig. 5 is a partially enlarged view of the exhaust pipe 61 and the exhaust chamber 65, in a direction illustrated in Fig. 3, that is, a top view.
As illustrated in Fig. 2, in the exhaust device 6 in the present embodiment, a front exhaust pipe (an "exhaust pipe" in the present invention) 61a of the exhaust pipe 61, in connection with the exhaust port 36, extends below the internal combustion engine 3, and is connected with the exhaust chamber 65.
As illustrated in Fig. 3, at least a part of the exhaust chamber 65 is disposed to overlap with the internal combustion engine 3 in a top view.
As illustrated in Fig. 4, an exhaust gas flow rear end 62 of the front exhaust pipe 61a constituting the exhaust pipe 61 is fit with an opening 66, which is formed in an outer shell 65a, with respect to the exhaust chamber 65, and a part of the fit portion forms a front exhaust pipe fixing portion 73a, which fixes the exhaust pipe 61 and the outer shell 65a of the exhaust chamber 65 by welding or the like.
Note that a drain hole, not illustrated, for discharging moisture of the exhaust gas condensed in the exhaust chamber 65 is provided at a bottom portion of the exhaust chamber 65.
A rear exhaust pipe (the "exhaust pipe" 61 in the present invention) 61b, which constitutes the exhaust pipe 61 with a predetermined clearance in an extension direction of a rear end 62 of the front exhaust pipe 61a is extended and stored in the exhaust chamber 65, and is held on an inner surface of the outer shell 65a of the exhaust chamber 65.
A connection portion between the exhaust chamber 65 and the exhaust gas flow front end portion 63 of the rear exhaust pipe 61b, which is stored in the exhaust chamber 65, and which holds a catalyst holding pipe 80 to be described later, forms an exhaust pipe slide holding portion 71 in which the exhaust pipe 61 is slidably fit in the opening 66 of the exhaust chamber 65. Thus, it becomes possible to permit the opening 66 to expand or contract in a pipe axial direction caused by thermal expansion of the rear exhaust pipe 61b.
Note that in the present embodiment, the exhaust pipe slide holding portion 71 is formed at the front end portion 63 of the rear exhaust pipe 61b, but may be offset in a downstream direction from the front end portion 63.
The rear end of the rear exhaust pipe 61b, that is, a downstream end portion 64 of the exhaust pipe 61 includes an opening portion 61c in the exhaust chamber 65.
As illustrated in Fig. 5, the rear exhaust pipe 61b includes a rear exhaust pipe fixing portion 73b, which is fixed to the outer shell 65a of the exhaust chamber 65 by partial welding or the like in the vicinity of a downstream sensor attachment boss portion 93 to be described later, and prevents positional displacement of the outer shell 65a of the exhaust chamber 65 with respect to the downstream sensor attachment boss portion 93.
Note that in the present embodiment, the front exhaust pipe 61a and the rear exhaust pipe 61b are partially separated from each other in the exhaust chamber 65. However, they integrally function as the exhaust pipe 61. Hereinafter, they will be collectively referred to as the exhaust pipe 61, including the description in claims.
The catalyst holding pipe 80 is fixed in the front exhaust pipe 61a, extends over the inside of the rear exhaust pipe 61b, and is held inside the exhaust pipe 61 (61a, 61b). Its upstream end 80a is fixed to an inner surface of the front exhaust pipe 61a. The catalyst holding pipe 80 is slidably fit with the inner surface of the rear exhaust pipe 61b, forms a catalyst slide holding portion 72, and is connected. This permits expansion or contraction in the pipe axial direction of the rear exhaust pipe 61b caused by thermal expansion of the catalyst holding pipe 80.
Note that as illustrated in Fig. 3, the catalyst holding pipe 80 is disposed obliquely with respect to a vehicle center line X in the vehicle front-rear direction, and the length in the front-rear direction of the exhaust passage is made compact.
The catalyst holding pipe 80 is filled with a catalyst 8 for exhaust gas treatment, for example, a three-way catalyst for purifying hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) all together.
Note that the catalyst 8 is not limited to the three-way catalyst, and includes a case where different types of catalysts are disposed in a longitudinal direction of the catalyst 8, which is illustrated. In addition, the catalyst 8 in the present embodiment is supported on a honeycomb structure so that the exhaust gas can react while passing through.
The catalyst holding pipe 80 is held over the inner surfaces of the front exhaust pipe 61a and the rear exhaust pipe 61b, and a part of the catalyst holding pipe 80 is disposed in the exhaust chamber 65.
In providing the exhaust gas sensor 91 at the front and the rear of the catalyst 8 in order to appropriately make a degradation diagnosis of the catalyst 8 for exhaust gas treatment, in a case where a part of the catalyst 8 in the exhaust pipe 61 is disposed in the exhaust chamber 65 in order to suppress the front-rear length of the exhaust device 6, it is necessary to dispose the exhaust gas sensor 91 on the downstream side so as to penetrate into a plurality of members such as the exhaust chamber 65 and the exhaust pipe 61, thereby causing problems of expansion or contraction and distortion of each member due to heat.
However, a connection portion between the rear exhaust pipe 61b and the exhaust chamber 65 forms the exhaust pipe slide holding portion 71, and a connection portion between the catalyst holding pipe 80 and the rear exhaust pipe 61b forms the catalyst slide holding portion 72. Therefore, it becomes possible to release the displacement of each member caused by the thermal expansion, and to mitigate the distortion that occurs at the downstream sensor attachment boss portion 93 of the exhaust gas sensor 91, which is provided in the exhaust pipe 61 so as to penetrate into both the exhaust chamber 65 and the exhaust pipe 61, so that durability, detection reliability, and accuracy of the exhaust gas sensor 91 can be improved by reducing the load that occurs at the downstream sensor attachment boss portion 93.
The present embodiment will be further specifically described below.
On the exhaust pipe 61, the exhaust gas sensor 91 is provided on the upstream side and the downstream side of the catalyst 8 in order to detect a state of exhaust gas purification by the catalyst 8 and also detect degradation of the catalyst 8.
The exhaust gas sensor 91 is, for example, an O2 sensor or an air-fuel ratio sensor (LAF sensor), but the type is not limited in the present embodiment.
As illustrated in Figs. 2 and 3, the exhaust gas sensor on the upstream side is disposed on an upstream sensor attachment boss portion 92, which is provided on a front end of the front exhaust pipe 61a, but the exhaust gas sensor itself on the upstream side is not illustrated.
As illustrated in Fig. 4, the exhaust gas sensor 91 on the downstream side is disposed on the downstream sensor attachment boss portion 93, which is provided on the rear exhaust pipe 61b extending on the downstream side of a downstream end 80b of the catalyst holding pipe 80 in the exhaust gas chamber 65, but the downstream sensor attachment boss portion 93 penetrates into the rear exhaust pipe 61b and the exhaust chamber 65, and is provided on the rear exhaust pipe 61b.
The catalyst holding pipe 80 is held by the rear exhaust pipe 61b via the catalyst slide holding portion 72, and thus expansion and contraction in the pipe axial direction of the rear exhaust pipe 61b caused by thermal expansion of the catalyst holding pipe 80 is suppressed, so that distortion that occurs at the downstream sensor attachment boss portion 93, which is provided to penetrate into both the exhaust chamber 65 and the rear exhaust pipe 61b, can be mitigated, and durability, detection reliability, and accuracy of the exhaust gas sensor 91 can be improved by reducing the load that occurs at the downstream sensor attachment boss portion 93.
As described above, by disposing at least a part of the catalyst holding pipe 80 in the exhaust chamber 65, the length in the front-rear direction of the exhaust passage is made compact. By disposing the exhaust gas sensor 91 on the rear exhaust pipe 61b on the downstream side of the catalyst holding pipe 80, the exhaust gas can be directly brought into contact with the exhaust gas sensor 91 before the air in the exhaust chamber 65 and the exhaust gas that has passed through the catalyst 8 are mixed together, so that the detection accuracy of the exhaust gas sensor 91 can be improved.
As illustrated in Fig. 3, in the present embodiment, the front exhaust pipe 61a includes a bent portion 61d, which is spaced apart to the right in the vehicle width direction from the vehicle center line X on the upstream end 80a side of the catalyst holding pipe 80, and is bent on the upstream side of the catalyst 8, and a bent portion 65d forms an enlarged diameter structure 65e.
The provision of the bent portion 65d in such a manner makes it possible to ensure a necessary exhaust pipe length of the exhaust pipe 61 while shortening a front-rear arrangement distance. The provision of the enlarged diameter structure 65e in the bent portion 65d makes it possible to uniformly disperse, in the front exhaust pipe 61a, the exhaust gas flow unevenly present in the front exhaust pipe 61a on the upstream side of the catalyst 8. By uniformly bringing the exhaust gas into contact with an upstream end surface of the catalyst 8, the uneven flow of the exhaust gas to the catalyst 8 can be suppressed, and the detection accuracy of the exhaust gas sensor 91 that has passed through the catalyst 8 can be improved.
As illustrated in Figs. 4 and 5, the downstream end portion 61c of the rear exhaust pipe 64 is reduced in diameter. When water accumulated in the exhaust chamber 65 at the time of backflow of the exhaust gas due to exhaust pulsation, outside air that has entered through a drain hole, or the like comes into contact with the exhaust gas sensor 91, rapid cooling may cause a decrease in detection accuracy of a detection unit 91a of the exhaust gas sensor 91. However, this can be prevented by the reduced diameter of the downstream end portion 64, and influence on sensing accuracy of the exhaust gas sensor 91 can be prevented.
Accordingly, durability, detection reliability, and accuracy of the exhaust gas sensor 91 are improved.
Furthermore, as illustrated in Fig. 5, the reduced diameter structure of the downstream end portion 64 of the rear exhaust pipe 61b is formed to be left-right asymmetric in a top view with respect to a center line Y in the exhaust chamber of the rear exhaust pipe 61b. Accordingly, the downstream end portion 64 of the rear exhaust pipe 61b is not excessively narrowed, and thus resistance of the exhaust gas flow hardly occurs, and drivability is improved.
Further, as illustrated in Fig. 5, the exhaust gas sensor 91 is disposed at a position offset with respect to a center extension line Z, which passes through the center in the longitudinal direction of the catalyst holding pipe 80 in a top view. A downstream part, relative to the exhaust gas sensor 91, of the downstream end portion 64 of the rear exhaust pipe 61b, on the side where the exhaust gas sensor 91 is disposed, is reduced in diameter to gradually approach the center extension line Z.
Therefore, the flow velocity of the exhaust gas flow on the exhaust gas sensor 91 side can be relatively lowered, and sensing of the exhaust gas is facilitated.
Furthermore, the downstream end portion 64 of the rear exhaust pipe 61b, on the side where the exhaust gas sensor 91 is disposed, is disposed to be in contact with an inner wall surface 65b of the exhaust chamber 65 in a top view.
Therefore, the heat of the rear exhaust pipe 61b at a high temperature is dissipated through the exhaust chamber 65, and thus the movement of the rear exhaust pipe 61b due to a temperature change is suppressed, so that the distortion that occurs at the downstream sensor attachment boss portion 93 of the exhaust gas sensor 91 can be mitigated, and durability, detection reliability, and accuracy of the exhaust gas sensor 91 can be improved by reducing the load that occurs at the downstream sensor attachment boss portion 93.
In addition, by disposing the exhaust gas sensor 91 to be closer to the inner wall surface of the exhaust chamber 65, a recess amount of the exhaust chamber 65 for disposing the exhaust gas sensor 91 can be reduced, as compared with a case where the exhaust gas sensor 91 is disposed at the center of the exhaust chamber 65, so that the detection accuracy of the exhaust gas sensor 91 can be improved while the capacity of the exhaust chamber 65 is ensured.
Fig. 6 is a perspective view of the front portion of the exhaust chamber 65, when viewed from obliquely left front upper.
As illustrated in Figs. 2, 3, and 6, the recess portion 65c, which is recessed from above and from a left lateral side, is formed in a left side portion of the exhaust chamber 65. The exhaust gas sensor 91 is disposed in the recess portion 65c such that the detection unit 91a faces downward.
Note that the recess portion 65c is provided in the exhaust chamber 65, and thus access performance of a tool in disposing the exhaust gas sensor 91 is improved.
In addition, the recess portion 65c has a shape inclined to have a slightly downward gradient toward the left lateral side. When water such as rain is splashed on the exhaust chamber 65, the water is hardly accumulated, and easily flows.
Fig. 7 is a schematic cross-sectional view of the vehicle body substantially taken along line VII-VII in Fig. 1 and directed toward a forward side of the vehicle, and illustrates a cross-section on a rear side of the downstream sensor attachment boss portion 93 in the exhaust chamber 65.
As illustrated in Fig. 7, a harness 91b of the exhaust gas sensor 91, which is attached to the recess portion 65c of the exhaust chamber 65, is locked to a stay 26a, which is fixed to the cross member 26 extending upward and present in the vicinity. By locking the harness 91b to the stay 26a once in such a manner, even though the arrangement setting of the exhaust gas sensor 91 of the exhaust chamber 65 is changed, it is possible to handle easily, and the harness 91b is stably and safely routed.
The exhaust device 6 in the present embodiment that has been described above has the following characteristics.
That is, the exhaust chamber 65, which is disposed such that at least a part of the exhaust chamber 65 overlaps with the internal combustion engine 3 in a top view; the exhaust pipe 61, which passes below the internal combustion engine 3 from the exhaust port 36 of the internal combustion engine 3, and which includes the opening portion 61c in the exhaust chamber 65; the catalyst holding pipe 80, which is held in the exhaust pipe 61, and at least a part of which is disposed in the exhaust chamber 65, and which is filled with the catalyst 8; and the exhaust gas sensor 91 disposed on the sensor attachment boss portion 93, which is provided in the rear exhaust pipe 61b so as to penetrate into the rear exhaust pipe 61b and the exhaust chamber 65, the rear exhaust pipe 61b constituting the exhaust pipe 61, being stored in the exhaust chamber 65, and holding the catalyst holding pipe 80 are included.
In providing the exhaust gas sensor 91 at the front and the rear of the catalyst 8 in the exhaust pipe 61 in order to appropriately make a degradation diagnosis of the catalyst 8 for exhaust gas treatment, it is necessary to suppress the front-rear length of the exhaust device 6. However, at least a part of the catalyst holding pipe 80 is disposed in the exhaust chamber 65, while a length in a front-rear direction of the exhaust device 6 is made compact, the exhaust gas sensor 91 is disposed in the rear exhaust pipe 61b on the downstream side of the catalyst holding pipe 80, so that the exhaust gas can be directly brought into contact with the exhaust gas sensor 91, before the air in the exhaust chamber 65 and the exhaust gas that has passed through the catalyst 8 are mixed together, and the detection accuracy can be improved. In addition, emission improvement is achieved, and contribution to mitigating or reducing the influence on climate change is made, accordingly.
As illustrated in Fig. 3, the catalyst holding pipe 80 is disposed obliquely with respect to the vehicle center line X in the vehicle front-rear direction. By disposing the catalyst holding pipe 80 obliquely, the distance in the front-rear direction of the exhaust path can be made compact.
As illustrated in Fig. 5, the downstream end portion 64 of the rear exhaust pipe 61b, in which the exhaust gas sensor 91 is disposed, is disposed in contact with the inner wall surface 65b of the exhaust chamber 65. By disposing the exhaust gas sensor 91 to be close to the inner wall surface 65b of the exhaust chamber 65, a recess amount of the exhaust chamber 65 for disposing the exhaust gas sensor 91 can be reduced, as compared with a case where the exhaust gas sensor 91 is disposed at the center of the exhaust chamber, and the detection accuracy of the exhaust gas sensor 91 can be improved while the capacity of the exhaust chamber 65 is ensured.
The downstream end portion 64 of the rear exhaust pipe 61b has the reduced diameter structure 67.
When water is splashed on the detection unit 91a of the exhaust gas sensor 91, the detection unit 91a may be rapidly cooled to cause a decrease in detection accuracy of the detection unit 91a of the exhaust gas sensor 91. However, by adopting the reduced diameter structure 67, water accumulated in the exhaust chamber 65 at the time of gas backflow due to exhaust pulsation, outside air that has entered through a drain hole, or the like is hardly brought into contact with the exhaust gas sensor 91, and it becomes possible to prevent influence on sensing accuracy of the exhaust gas sensor 91.
The reduced diameter structure 67 of the downstream end portion 64 of the rear exhaust pipe 61b is left-right asymmetric with respect to the center line Y in the exhaust chamber of the rear exhaust pipe 61b, when viewed in a direction perpendicular to a flow direction F of the exhaust gas flowing in the exhaust pipe 61.
Therefore, the exhaust gas sensor 91 is hardly influenced by water or gas, while preventing the influence of water or gas on the sensing accuracy, and the reduced diameter structure 67 is made left-right asymmetric. Thus, the downstream end portion 64 of the rear exhaust pipe 61b is not excessively narrowed, and thus resistance of the exhaust gas flow hardly occurs, and drivability is improved.
In a top view of the exhaust device 6, the exhaust gas sensor 91 is disposed to be offset from a center extension line Z, which passes through the center in the longitudinal direction of the catalyst holding pipe 80, and a downstream part, relative to the exhaust gas sensor 91, of the downstream end portion 64 of the rear exhaust pipe 61b, on a side where the exhaust gas sensor 91 is disposed, is reduced in diameter to gradually approach the center extension line Z.
By reducing the diameter of the downstream end portion 64 of the rear exhaust pipe 61b on the side where the exhaust gas sensor 91 is disposed so as to gradually approach the center extension line Z, the flow velocity of the gas flow of the exhaust gas sensor 91 can be relatively lowered, and the exhaust gas is easily sensed.
Heretofore, although the exhaust device according to an embodiment of the present invention has been described, the present invention is not limited to the above-described embodiment, and in addition to the above-described embodiment, various modifications may be made without departing from the gist of the present invention.
Note that, for convenience of description, left and right arrangements of the device have been described in accordance with the illustrated embodiment, but without being limited to this, the left and right arrangements may be reversed.

[Reference Signs List]

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 portion
61d: Bent portion
61e: Enlarged diameter structure
62: Rear end
63: Front end portion
64: Downstream end portion
65: Exhaust chamber
65a: Outer shell
65b: Inner wall surface
65c: Recess portion
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 unit
91b: Harness
92: Upstream sensor attachment boss portion
93: Downstream sensor attachment boss portion
X: Vehicle center line
Y: Center line in exhaust chamber (of rear exhaust pipe 61b)
Z: Center extension line (of catalyst holding pipe 80)

Claims

An exhaust device comprising:
an exhaust chamber (65) disposed such that at least a part of the exhaust chamber (65) overlaps with an internal combustion engine (3) in a top view;

an exhaust pipe (61), which passes below the internal combustion engine (3) from an exhaust port (36) of the internal combustion engine (3), and which includes an opening portion (61c) in the exhaust chamber (65);

a catalyst holding pipe (80), which is held in the exhaust pipe (61), at least a part of which is disposed in the exhaust chamber (65), and which is filled with a catalyst (8); and

an exhaust gas sensor (91) disposed on a sensor attachment boss portion (93), which is provided on the exhaust pipe (61) so as to penetrate into a rear exhaust pipe (61b) and the exhaust chamber (65), the rear exhaust pipe (61b) constituting the exhaust pipe (61), being stored in the exhaust chamber (65), and holding the catalyst holding pipe (80).
The exhaust device as claimed in claim 1, wherein the catalyst holding pipe (80) is disposed obliquely with respect to a vehicle center line (X) in a vehicle front-rear direction.
The exhaust apparatus as claimed in claim 1 or 2, wherein a downstream end portion (64) of the exhaust pipe (61), in which the exhaust gas sensor (91) is disposed, is disposed along an inner wall surface (65b) of an exhaust chamber (65).
The exhaust device as claimed in claim 1, wherein a downstream end portion (64) of the exhaust pipe (61) has a reduced diameter structure (67).
The exhaust device as claimed in claim 4, wherein the reduced diameter structure (67) of the downstream end portion (64) of the exhaust pipe (61) is left-right asymmetric with respect to a center line (Y) in the exhaust chamber of the exhaust pipe (61), when viewed in a direction perpendicular to a flow direction (F) of an exhaust gas flowing in the exhaust pipe (61).
The exhaust device as claimed in claim 5, wherein
in a top view of the exhaust device, the exhaust gas sensor (91) is disposed to be offset with respect to a center extension line (Z) which passes through a center in a longitudinal direction of the catalyst holding pipe (80), and

a downstream part, relative to the exhaust gas sensor (91), of the downstream end portion (64) of the exhaust pipe (61), on a side where the exhaust gas sensor (91) is disposed, is reduced in diameter to gradually approach the center extension line (Z).