JP2017227157A - Exhaust gas sensor arrangement structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arrange an exhaust gas sensor in front and rear of a catalyst without deteriorating detection accuracy.SOLUTION: An exhaust gas sensor arrangement structure of this invention includes a muffler (7) disposed in the downstream side of an exhaust pipe (6), a catalyst (8) provided in the muffler and purifying exhaust gas of an engine, piping connected to the downstream side of the catalyst, and an exhaust gas sensor (9) for detecting an exhaust gas component of the engine. The exhaust gas sensor includes an upstream side sensor (90) provided in the upstream side of the catalyst, and a downstream side sensor (91) provided in the downstream side of the catalyst. The piping is located close to a wall of the muffler. The downstream side sensor is mounted so as to penetrate the muffler and the piping.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an arrangement structure of exhaust gas sensors.

  In an automobile, it is obliged to monitor the exhaust gas control status with an in-vehicle computer. As an item to be monitored, for example, a deterioration state of a catalyst that purifies exhaust gas can be cited (see Patent Document 1). In Patent Document 1, oxygen sensors are provided before and after the catalyst, respectively, and it is determined whether the catalyst has deteriorated based on the output values of these two oxygen sensors.

  Specifically, the number of output inversions between the rich leans of the two oxygen sensors is used. For example, when the catalyst is normal and can sufficiently adsorb oxygen, the number of output inversions of the downstream oxygen sensor approaches zero. For this reason, the ratio of the number of output reversals of the upstream oxygen sensor with respect to the downstream side is increased. On the other hand, when the catalyst deteriorates and the oxygen adsorption capacity decreases, the output reversal count of the downstream oxygen sensor approaches the output reversal count of the upstream oxygen sensor. For this reason, the ratio of the number of output inversions of the upstream oxygen sensor with respect to the downstream side becomes small. Therefore, it can be determined that the catalyst has deteriorated when the above ratio falls below a predetermined value.

JP 2003-206784 A

  By the way, when determining deterioration of a catalyst in a motorcycle, it is difficult to arrange two oxygen sensors before and after the catalyst while ensuring detection accuracy due to restrictions on the structure and layout of the exhaust pipe and muffler.

  The present invention has been made in view of the above points, and an object thereof is to provide an exhaust gas sensor arrangement structure in which exhaust gas sensors can be arranged before and after a catalyst without impairing detection accuracy.

  The exhaust gas sensor arrangement structure according to the present invention includes a muffler provided on the downstream side of the exhaust pipe, a catalyst provided in the muffler for purifying engine exhaust gas, and a pipe connected to the downstream side of the catalyst. An exhaust gas sensor for detecting an exhaust gas component of the engine, and the exhaust gas sensor has an upstream sensor provided on the upstream side of the catalyst and a downstream sensor provided on the downstream side of the catalyst. The piping is arranged close to the wall of the muffler, and the downstream sensor is attached so as to penetrate the muffler and the piping.

  According to the present invention, exhaust gas sensors can be arranged before and after the catalyst without impairing detection accuracy.

1 is a right side view showing a schematic configuration of a motorcycle to which an exhaust gas sensor arrangement structure according to the present embodiment is applied. 1 is a top view showing a configuration around an engine of a motorcycle according to the present embodiment. It is a perspective view of the exhaust system which concerns on this Embodiment. It is a front view of the exhaust system which concerns on this Embodiment. It is sectional drawing of the muffler which follows the AA line of FIG. It is sectional drawing which shows the internal structure of the muffler which concerns on a 1st modification. It is sectional drawing which shows the internal structure of the muffler which concerns on a 2nd modification.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, an example in which the arrangement structure of the exhaust gas sensor according to the present invention is applied to a small scooter type motorcycle will be described, but the application target is not limited to this and can be changed. For example, the exhaust gas sensor arrangement structure according to the present invention may be applied to other types of motorcycles, buggy type motorcycles, automobiles, and the like. Regarding the direction, the front of the vehicle is indicated by an arrow FR, the rear of the vehicle is indicated by an arrow RE, the left direction of the vehicle is indicated by an arrow L, and the right direction of the vehicle is indicated by an arrow R. In the following drawings, a part of the configuration is omitted for convenience of explanation.

  With reference to FIGS. 1 and 2, a schematic configuration of a motorcycle to which the exhaust gas sensor arrangement structure according to the present embodiment is applied will be described. FIG. 1 is a right side view showing a schematic configuration of a motorcycle to which an exhaust gas sensor arrangement structure according to the present embodiment is applied. FIG. 2 is a top view showing the engine peripheral configuration of the motorcycle according to the present embodiment.

  As shown in FIGS. 1 and 2, a small scooter type motorcycle 1 is configured by suspending an engine 2 on an underbone body frame (not shown). The engine 2 is composed of, for example, a single cylinder engine. In particular, in the present embodiment, a unit swing type engine in which a transmission mechanism for the engine 2, a transmission (CVT unit 23 described later) and a rear wheel 26 is integrated with a swing arm is employed.

  Various covers as a vehicle body exterior are mounted on the vehicle body frame and the engine 2. Specifically, a leg shield 11 that protects the driver's suspension is provided in front of the vehicle. A center frame cover 12 is provided behind the leg shield 11. A footboard 13 extending rearward is provided at the lower end of the center frame cover 12. A side frame cover 14 that covers the vehicle side surface is provided behind the footboard 13.

  A front fork 15 is rotatably supported in front of the vehicle via a steering shaft (not shown). A handlebar 17 for steering the front wheel 16 is provided above the front fork 15. A front wheel 16 is rotatably supported at the lower portion of the front fork 15.

  A seat 18 is provided on the upper side of the side frame cover 14. A rear fender 19 is provided at the rear of the side frame cover 14. An engine 2 as an internal combustion engine is disposed from the inner side to the rear side of the side frame cover 14.

  The engine 2 is configured by attaching a cylinder block 21 and a cylinder head cover 22 in which a cylinder and a cylinder head are integrated in this order in front of a crankcase 20 in which various components such as a crankshaft (not shown) are accommodated. The The cylinder is arranged such that the axial direction is inclined forward.

  A CVT unit 23 as a transmission is provided on the right side of the crankcase 20. The CVT unit 23 is constituted by a so-called belt-type continuously variable transmission, and realizes a shift by changing a belt winding radius.

  A transmission gear case 25 is provided at the rear of the crankcase 20 as a swing arm extending rearward in a substantially horizontal direction. Various gears for transmitting power to the rear wheel 26 are housed in the transmission gear case 25 side by side. A rear wheel 26 is rotatably provided at the rear end of the transmission gear case 25.

  An exhaust pipe 6 and a muffler 7 are connected to the exhaust port of the engine 2 as an exhaust system. The exhaust pipe 6 extends below the engine 2 toward the rear. The muffler 7 is connected to the rear end of the exhaust pipe 6 and is disposed so as to overlap the rear wheel 26 in a side view. A muffler cover 70 is provided on the right side surface of the muffler 7.

  In the present embodiment, the catalyst 8 is provided inside the muffler 7. The catalyst 8 is composed of, for example, a three-way catalyst, and converts pollutants (carbon monoxide, hydrocarbons, nitrogen oxides, etc.) in the exhaust gas into harmless substances (carbon dioxide, water, nitrogen, etc.). Exhaust gas generated by the combustion of the engine 2 is introduced into the muffler 7 through the exhaust pipe 6 and purified by the catalyst 8. And after exhaust noise is reduced, exhaust gas is discharged outside.

  Although details will be described later, an exhaust gas sensor 9 for detecting an exhaust gas component of the engine and determining deterioration of the catalyst 8 is disposed before and after the catalyst 8. Specifically, the exhaust gas sensor 9 includes an upstream sensor 90 provided on the front side (upstream side) of the catalyst 8 and a downstream sensor 91 provided on the rear side (downstream side) of the catalyst 8. The exhaust gas sensor 9 is composed of, for example, a zirconia oxygen sensor, and the output (current value) changes according to the oxygen concentration in the exhaust gas. The current value is output to the ECU 10 (Electronic Control Unit (see FIG. 4)). The exhaust gas sensor 9 is not limited to an oxygen sensor, and may be an air-fuel ratio sensor, for example. The layout of the exhaust gas sensor 9 will be described later.

  The ECU 10 performs overall control of various operations in the motorcycle 1. The ECU 10 includes a processor, a memory, and the like that execute various processes in the motorcycle 1. The memory is configured by a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory) according to the application. The memory stores a control program for controlling each part of the motorcycle 1. In particular, in the present embodiment, the ECU 10 determines the deterioration of the catalyst 8 based on the output of the exhaust gas sensor 9. For example, the deterioration of the catalyst 8 is determined based on the ratio of the number of output inversions between the rich lean of the upstream sensor 90 and the downstream sensor 91. In order to determine the deterioration of the catalyst 8, the output difference between the upstream sensor 90 and the downstream sensor 91 may be used without being limited to the case of using the ratio of the number of output inversions.

  As described above, in a motorcycle exhaust system, it is required to monitor a deterioration state of a catalyst as an exhaust gas purification device. In order to determine the deterioration of the catalyst, it is necessary to install exhaust gas sensors upstream and downstream of the catalyst.

  For example, it has heretofore been practiced to detect the oxygen concentration in the exhaust gas with an exhaust gas sensor (oxygen sensor) provided upstream of the catalyst and control the air-fuel ratio. However, if an exhaust gas sensor is arranged on the downstream side of the catalyst for the purpose of determining deterioration of the catalyst, the exhaust gas sensor is brought closer to the downstream side of the catalyst while ensuring a predetermined detection accuracy due to a layout restriction unique to the motorcycle. It was difficult.

  In this regard, in an automobile, since the catalyst can be arranged in a space where there is enough space, such as in the engine room, it is easy to arrange and protect the exhaust gas sensor. On the other hand, in a motorcycle, a catalyst is often arranged in a chamber or a muffler, and it is difficult to arrange the downstream sensor close to the catalyst because of the structure. Even when a catalyst is arranged in the middle of the exhaust pipe, the exhaust pipe and peripheral parts are often close to each other, and it is difficult to secure a space for arranging the exhaust gas sensor. Furthermore, since the exhaust system of the motorcycle is exposed to the outside, it may be assumed that the temperature of the catalyst is likely to decrease, for example, during winter or rainy weather, and sensor output cannot be obtained appropriately. Also, protection of the exhaust gas sensor becomes a problem.

  For example, when a catalyst is provided in a chamber or a muffler, it can be considered that the outer wall is recessed to secure a space for arranging the exhaust gas sensor. However, as a result of the volume of the chamber and muffler being reduced, the original function (output increase and noise reduction) may be affected. Although it is conceivable to arrange the catalyst itself on the front side of the vehicle, it is difficult to secure the catalyst arrangement space in the first place, and it is not practical because it requires a significant design change. Furthermore, various problems such as heat damage caused by the catalyst as a heat source approaching the rider, a decrease in output, a method for protecting an exhaust gas sensor, and deterioration in appearance design occur.

  In particular, in a small scooter, it is necessary to dispose the exhaust pipe in a narrow space between the engine and the frame, and the exhaust pipe is set to have a relatively thin pipe diameter. In this case, it is very difficult to arrange the catalyst and the exhaust gas sensor in the exhaust pipe while ensuring a gap with peripheral parts.

  In a small scooter, it is conceivable to arrange an exhaust gas sensor directly on the muffler. However, in the muffler (expansion chamber), it is difficult to accurately detect the oxygen concentration by the exhaust gas sensor due to the turbulent flow of the exhaust gas, so that the performance of the exhaust gas sensor cannot be sufficiently satisfied. Furthermore, the temperature of the exhaust gas decreases as it becomes downstream of the exhaust gas passage. For this reason, depending on the layout of the exhaust gas sensor, it takes time to reach the activation temperature region of the exhaust gas sensor. This becomes a factor that makes it difficult for the exhaust gas sensor to work when the engine is cold.

  Therefore, the present inventor has a configuration in which the exhaust gas sensor 9 is disposed before and after (upstream and downstream) of the catalyst 8 disposed in the muffler 7 in the small scooter type motorcycle 1. Specifically, the upstream sensor 90 is disposed on the exhaust pipe 6 on the upstream side of the muffler 7, and the downstream sensor 91 is directly attached to the left side surface of the muffler 7. In particular, the baffle pipe 76 (pipe) connected to the downstream side of the catalyst 8 is brought close to the wall of the muffler 7 (the outer wall portion 72b and the inner wall portion 72c described later), and the downstream side so as to penetrate the muffler 7 and the baffle pipe 76. The sensor 91 is attached.

  According to this configuration, even if the catalyst 8 is disposed in the muffler 7, the exhaust gas sensor 9 can be disposed before and after the catalyst 8. In particular, the downstream sensor 91 can be disposed close to the catalyst 8. For this reason, the exhaust gas detection accuracy is not impaired. Further, since the downstream sensor 91 is disposed in the baffle pipe 76 on the downstream side of the catalyst 8, the purified exhaust gas directly contacts the downstream sensor 91 without being diffused. As a result, an output can be stably obtained. Further, since the exhaust gas sensor 9 can be arranged inside the exterior cover, the exhaust gas sensor 9 can be made inconspicuous and the appearance design is not affected. Furthermore, since the exhaust gas sensor 9 can be arranged without greatly changing the existing (current) muffler arrangement and appearance, it is possible to contribute to a reduction in design man-hours.

  Further, in a specific area where a small scooter type motorcycle is used, it is customary to attach and detach the rear wheel with the muffler attached when replacing the rear wheel. In this case, in order to secure a space for removing the rear wheel, a gap is provided between the rear wheel and the muffler, and the outer surface of the muffler facing the rear wheel is formed flat. In view of this, the inventor of the present invention pays attention to a gap secured between the rear wheel and the muffler, and has a configuration in which the downstream sensor 91 is provided in the gap. Thereby, the downstream sensor 91 can be arranged inside the vehicle, and the downstream sensor 91 can be protected without using a dedicated cover. Furthermore, as described above, the appearance design is not affected.

  Next, a schematic configuration of the exhaust system according to the present embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a perspective view of the exhaust system according to the present embodiment. FIG. 4 is a front view of the exhaust system according to the present embodiment.

  As shown in FIGS. 3 and 4, in the exhaust system according to the present embodiment, the exhaust pipe 6 is connected to the exhaust port of the engine 2 (the cylinder block 21 (both see FIG. 2)) via the flange 60. . The exhaust pipe 6 protrudes downward from the exhaust port and then bends substantially to the right in the horizontal direction when viewed from the front. The exhaust pipe 6 extends rearward along the lower side of the engine 2 and the CVT unit 23 (see FIG. 2) in a side view.

  The muffler 7 has a rectangular tube shape whose outer shape is sufficiently larger than that of the exhaust pipe 6 and extends in the front-rear direction. Specifically, the muffler 7 is configured by welding and joining a left case 72 and a right case 73 which are divided into left and right parts, and has an axial direction in the front-rear direction. As shown in FIG. 4, the muffler 7 is formed in a substantially triangular shape when viewed from the front. Specifically, the left case 72 located inside the vehicle has a flat surface portion 72a that faces the rear wheel 26 (see FIG. 2). Further, the right case 73 is formed in a substantially V shape in a cross-sectional view when cut in a direction orthogonal to the axial direction of the muffler 7.

  Of the sides defining the triangular shape of the muffler 7, one side inside the vehicle is set longer than the other two sides. That is, the area of the plane part 72a of the left case 72 is larger than the two plane parts of the right case 73 formed in a V shape. Thus, by making the area of the plane part 72a facing the rear wheel 26 the largest, it is possible to easily secure a gap between the rear wheel 26 and the plane part 72a. Moreover, since the area of the plane part 72a is large, the arrangement | positioning freedom degree of the exhaust gas sensor 9 (downstream sensor 91) is raised, and an assembly | attachment property also improves. Although not particularly shown, the space in the muffler 7 is partitioned into a plurality of rooms in the front-rear direction by a plurality of partition walls (baffle plates).

  A bracket 71 for fixing the muffler 7 to the vehicle body side is provided at the front end portion of the muffler 7. A muffler cover 70 that protects the muffler 7 is provided on the right side of the muffler 7 (the outer surface of the right case 73) (not shown in FIG. 3). A tail pipe 74 that exhausts exhaust gas to the outside is provided at the rear end portion of the muffler 7.

  A catalyst 8 and a baffle pipe 76 (pipe) are disposed in the muffler 7. The catalyst 8 is disposed in the muffler 7 at substantially the center in the vertical direction. The exhaust pipe 6 is connected to the lower part of the mating surface of the left case 72 and the right case 73 at the front portion of the muffler 7. The exhaust pipe 6 further passes through the muffler 7 and is connected to the catalyst 8 in the muffler 7. A baffle pipe 76 is connected to the downstream end (rear end) of the catalyst 8.

  As described above, the exhaust gas sensor 9 is disposed before and after the catalyst 8. The exhaust gas sensor 9 is formed in a cylindrical shape having a predetermined length. One end side of the exhaust gas sensor 9 serves as a detection unit, and wiring (not shown) is connected to the other end side.

  The upstream sensor 90 is attached to the front side of the muffler 7 slightly behind the center of the exhaust pipe 6 in the front-rear direction. The upstream sensor 90 is attached so that one end side penetrates into the exhaust pipe 6 and the other end side is directed to the upper right.

  In particular, as shown in FIG. 4, the upstream sensor 90 is disposed inside the triangular shape of the muffler 7 in front view. For this reason, it can prevent that the upstream sensor 90 protrudes from the outer surface of the muffler 7, and does not affect a vehicle width. As described above, since the upstream sensor 90 is hidden by the exterior cover, the upstream sensor 90 can be made inconspicuous in appearance, and the upstream sensor 90 is protected from flying stones, water, and the like during traveling. can do.

  The downstream sensor 91 is attached to the left case 72 inside the vehicle in the space between the rear wheel 26 (see FIG. 2) and the muffler 7. Specifically, the downstream sensor 91 is attached so that one end side penetrates the left case 72 at a substantially central portion of the muffler 7 in the front-rear direction. The downstream sensor 91 has the axial direction directed horizontally and the other end directed to the left side (rear wheel side).

  Further, as shown in FIG. 2, the downstream sensor 91 is disposed within the front-rear width of the rear wheel 26 as viewed from the top of the vehicle. In the vicinity of the rear wheel 26 (particularly on the right side of the rear wheel 26), there is enough space, so there is no need to worry about the positional relationship with the peripheral components, and the layout of the downstream sensor 91 is easy. Further, since the downstream sensor 91 is disposed in the space between the rear wheel 26 and the muffler 7, it is possible to prevent the downstream sensor 91 from projecting to the outside of the vehicle.

  The gas after combustion in the engine 2 (see FIG. 2) is introduced into the muffler 7 through the exhaust pipe 6 from the exhaust port. In the muffler 7, the exhaust gas is purified by the catalyst 8, and then discharged outside from the tail pipe 74 at the rear end through a predetermined space in the baffle pipe 76 and the muffler 7. At this time, the exhaust gas sensor 9 detects the oxygen concentration of the exhaust gas, and the ECU 10 determines the deterioration of the catalyst 8 based on the detected value.

  Next, the internal configuration of the muffler according to the present embodiment will be described with reference to FIG. FIG. 5 is a cross-sectional view of the muffler along the line AA in FIG.

  As shown in FIG. 5, the left case 72 has a two-layer structure having an outer wall portion 72b and an inner wall portion 72c. In the muffler 7, the catalyst 8 is disposed close to the inner wall portion 72 c along the left case 72. The exhaust pipe 6 penetrating into the muffler 7 runs along the left case 72 and is connected to the upstream end of the catalyst 8 via the first cone portion 75. A baffle pipe 76 constituting an exhaust passage in the muffler 7 is connected to the downstream end of the catalyst 8.

  The first cone portion 75 is connected to the downstream end of the exhaust pipe 6 and is configured by a tapered pipe whose diameter increases toward the downstream (rear). The catalyst 8 is connected to the rear end of the first cone portion 75. The catalyst 8 is formed in a cylindrical shape extending in the front-rear direction and has an outer diameter larger than that of the exhaust pipe 6. The catalyst 8 is configured by covering a cylindrical honeycomb portion that oxidizes and reduces a predetermined component in exhaust gas with a cylindrical outer tube portion.

  As described above, the catalyst 8 is disposed close to the inner wall portion 72c of the left case 72 in the muffler 7. That is, the catalyst 8 is arranged in the muffler 7 so as to be biased toward the vehicle inner side. Since the catalyst 8 has a relatively high temperature in the muffler 7, the catalyst 8 can be separated from the outside of the vehicle that is easily in contact with a person. Therefore, the influence of heat on the passenger can be suppressed, and safety is improved.

  Further, the catalyst 8 is disposed in front of the center in the front-rear direction of the muffler 7 in a side view. In this case, the catalyst 8 can be arranged on the upstream side of the exhaust gas as much as possible. For this reason, exhaust gas can be introduced into the catalyst 8 in a state where the exhaust gas temperature is relatively high, and the temperature of the catalyst 8 is increased. As a result, purification of exhaust gas is promoted and purification performance is improved.

  The baffle pipe 76 includes a second cone part 77 connected to the downstream end of the catalyst 8 and a straight pipe part 78 connected to the second cone part 77. The 2nd cone part 77 is comprised by the taper-shaped piping which diameter-reduces as it goes downstream (back).

  Specifically, the second cone portion 77 is reduced in diameter only on one side (right side in the present embodiment) in the radial direction from the rear end of the catalyst 8 toward the downstream side. That is, the substantially left half portion of the second cone portion 77 extends rearward while maintaining the outer diameter of the catalyst 8, while the substantially right half portion of the second cone portion 77 is reduced in diameter to the left of the outer diameter of the catalyst 8. In this way, it extends backward.

  In this way, the second cone portion 77 is formed so as to be reduced in diameter toward the inner wall portion 72c side (left side) as it goes downstream. For this reason, the straight pipe part 78 connected to the rear end of the second cone part 77 can be arranged close to the inner wall part 72 c along the left case 72. The straight pipe part 78 extends rearward with the same diameter as the downstream end of the second cone part 77. Further, the central axis C1 of the straight pipe portion 78 is offset by a distance D from the central axis C2 of the catalyst 8 toward the inner wall portion 72c. Thereby, even when the outer diameter of the baffle pipe 76 is smaller than the outer diameter of the catalyst 8, the catalyst 8 and the baffle pipe 76 can be arranged along the left case 72 and close to the inner wall portion 72c. .

  The downstream sensor 91 is attached so as to penetrate the left case 72 and the second cone portion 77. Specifically, at the position where the second cone portion 77 is disposed, a circular recess 72d is formed in the outer wall portion 72b by embossing. The circular recessed portion 72d is recessed on the right side toward the second cone portion 77, and the bottom surface is a circular flat surface. A through hole 72e larger than the outer diameter of a nut 92 described later is formed in the center of the flat surface. The inner wall 72c is formed with a circular hole 72f that can receive the circular recess 72d.

  In the second cone portion 77, a circular convex portion 77a is formed by embossing at a position facing the circular concave portion 72d. The circular convex portion 77a bulges to the left side toward the left case 72, and the bulged end surface is a circular flat surface. The flat surface of the circular convex portion 77a is in contact with the flat surface of the circular concave portion 72d. In addition, a through hole 77b that is smaller than the outer diameter of the nut 92 and through which the detection portion (one end side) of the downstream sensor 91 can pass is formed at the center of the flat surface of the circular convex portion 77a. In addition, the flat surface of the circular convex portion 77a functions as a seating surface of the nut 92 for attaching the downstream sensor 91.

  The nut 92 is passed through the through hole 72e, and the bottom surface is in contact with the flat surface of the circular convex portion 77a. In this state, the nut 92 is welded all around, so that the outer wall portion 72b, the second cone portion 77, and the nut 92 are integrated, and the attachment portion of the downstream sensor 91 is formed. The muffler 7 is divided into two parts, and the left case 72 is provided with the flat surface portion 72a, so that the nut 92 can be welded by the left case 72 alone. Therefore, the weldability of the nut 92 and the assembly property of the muffler 7 are improved.

  The downstream sensor 91 is attached so that one end side is screwed into the nut 92 and the tip penetrates into the second cone portion 77 (through hole 77b). As a result, the exhaust gas flowing in the baffle pipe 76 (second cone portion 77) can be detected by the downstream sensor 91.

  Thus, in the present embodiment, the baffle pipe 76 is disposed along the inner wall portion 72c of the left case 72, and the downstream sensor 91 is provided at the contact portion between the outer wall portion 72b and the second cone portion 77. It was set as the structure which attaches the nut 92 for attachment. In particular, the contact portion between the outer wall portion 72b and the second cone portion 77 is crushed to secure the mounting seat surface of the nut 92, so that the nut 92 can be easily positioned and welded. Further, by simultaneously welding the outer wall portion 72b, the second cone portion 77, and the nut 92, it is possible to ensure the sealing performance of the welded portion. As described above, even if the catalyst 8 is arranged in the muffler 7, the downstream sensor 91 can be arranged as close to the downstream end of the catalyst 8 as possible.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the above-described embodiment, the upstream sensor 90 is disposed on the exhaust pipe 6, but the present invention is not limited to this configuration. The upstream sensor 90 may be disposed at any position as long as it is upstream of the catalyst 8. For example, it is good also as a structure shown in FIG. FIG. 6 is a cross-sectional view showing the internal configuration of the muffler according to the first modification. In addition, the cut part of a muffler is the same as FIG.

  In the modification shown in FIG. 6, the upstream sensor 90 is also attached to the left case 72 in the same manner as the downstream sensor 91. Specifically, the upstream sensor 90 is attached so as to penetrate the left case 72 and the first cone portion 75 on the upstream side of the catalyst 8. In addition, since the shape of the 1st cone part 75 is symmetrical with the shape of the 2nd cone part 77 in the front-back direction, description is abbreviate | omitted.

  The nut 92 is passed through the through hole 72e, and the bottom surface is in contact with the flat surface of the circular convex portion 75a. In this state, the nut 92 is welded all around, so that the outer wall portion 72b, the first cone portion 75, and the nut 92 are integrated, and the attachment portion of the upstream sensor 90 is formed. The upstream sensor 90 is attached so that one end side is screwed into the nut 92 and the tip penetrates into the first cone portion 75 (through hole 75b). As a result, the exhaust gas flowing in the baffle pipe 76 (first cone portion 75) can be detected by the upstream sensor 90. According to the first modification, since the upstream sensor 90 and the downstream sensor 91 can be arranged close to each other, wiring can be facilitated.

  In the above-described embodiment, the downstream sensor 91 is attached to the flat portion 72a of the left case 72. However, the present invention is not limited to this configuration. For example, the downstream sensor 91 may be attached to the flat portion of the right case 73. In this case, it is preferable to place the catalyst 8 close to the right case 73. Moreover, the structure shown in FIG. 7 may be sufficient. FIG. 7 is a cross-sectional view illustrating an internal configuration of a muffler according to a second modification. In addition, the cut part of a muffler is the same as FIG.

  In the present embodiment shown in FIG. 5, the second cone portion 77 is formed so as to be deviated toward the left side and reduce in diameter toward the downstream, whereas in the modification shown in FIG. 7, the second cone portion 77 is formed. Is formed to be reduced in diameter to the right. Specifically, the substantially right half portion of the second cone portion 77 extends rearward while maintaining the outer diameter of the catalyst 8, while the substantially left half portion of the second cone portion 77 extends outside the catalyst 8 toward the downstream. It extends rearward so as to reduce the diameter to the right of the diameter.

  In the second modification, the left case 72 (the outer wall portion 72b and the inner wall portion 72c) is inclined toward the right rear side along the tapered surface of the second cone portion 77. Thereby, the 2nd cone part 77 and the left case 72 can be closely approached, and the contact part of the 2nd cone part 77 and the left case 72 can be ensured. In addition, since the structure for attaching the downstream sensor 91 is the same as this Embodiment, description is abbreviate | omitted. Thus, the arrangement pattern of the downstream sensor 91 can be changed as appropriate in accordance with the shape of the muffler 7.

  In the above-described embodiment, the mounting seat surface of the nut 92 is formed as a flat surface. However, the present invention is not limited to this configuration. The mounting seat surface of the nut 92 may be formed with a tapered surface or a curved surface, for example.

  In the above-described embodiment, the muffler 7 has a triangular shape in front view. However, the present invention is not limited to this configuration. The muffler 7 may have any shape, and may be, for example, a circular shape or a rectangular shape when viewed from the front.

  In the above-described embodiment, the straight straight pipe portion 78 is connected to the rear end of the second cone portion 77. However, the present invention is not limited to this configuration. A curved pipe may be connected to the rear end of the second cone portion 77 instead of a straight line.

  Further, in the above-described embodiment, the downstream sensor 91 is attached so as to penetrate the second cone portion 77, but the present invention is not limited to this configuration. For example, the downstream sensor 91 may be attached so as to penetrate the straight pipe portion 78.

  In the above-described embodiment, the case where the muffler 7 has a two-layer structure including the outer wall portion 72b and the inner wall portion 72c has been described. However, the present invention is not limited to this configuration. The muffler 7 may be configured with a single layer structure, for example.

  As described above, the present invention has an effect that exhaust gas sensors can be arranged before and after the catalyst without impairing detection accuracy, and is particularly useful for an arrangement structure of exhaust gas sensors.

DESCRIPTION OF SYMBOLS 1 Motorcycle 26 Rear wheel 6 Exhaust pipe 7 Muffler 72 Left case 72a Plane part 72b Outer wall part (muffler wall)
72c Inner wall (muffler wall)
73 Right Case 76 Baffle Pipe (Piping)
77 2nd cone part (cone part)
78 Straight pipe section 8 Catalyst 9 Exhaust gas sensor 90 Upstream sensor 91 Downstream sensor

Claims (6)

A muffler provided downstream of the exhaust pipe;
A catalyst provided in the muffler for purifying engine exhaust gas;
Piping connected to the downstream side of the catalyst;
An exhaust gas sensor for detecting an exhaust gas component of the engine,
The exhaust gas sensor has an upstream sensor provided on the upstream side of the catalyst, and a downstream sensor provided on the downstream side of the catalyst,
The piping is arranged close to the muffler wall,
The exhaust gas sensor arrangement structure, wherein the downstream sensor is attached so as to penetrate the muffler and the pipe. The pipe has a cone part and a straight pipe part connected to the downstream side of the cone part,
The central axis of the straight pipe portion is offset to the wall side of the muffler from the central axis of the catalyst,
The exhaust gas sensor arrangement structure according to claim 1, wherein the downstream sensor is attached so as to penetrate the cone portion or the straight pipe portion.   The exhaust gas sensor arrangement structure according to claim 1, wherein the downstream sensor is arranged within a front-rear width of the rear wheel in a top view of the vehicle.   The exhaust gas sensor arrangement structure according to any one of claims 1 to 3, wherein the catalyst is arranged inside the muffler so as to be biased toward the inside of the vehicle. The muffler has a flat portion,
The exhaust gas sensor arrangement structure according to any one of claims 1 to 4, wherein the downstream sensor is attached to the flat portion.   The exhaust gas sensor arrangement structure according to claim 5, wherein the muffler is configured in two parts, and the flat part is provided on one side of the muffler divided into two parts.

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