JP2018003718A - Arrangement structure for exhaust gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arrange an exhaust gas sensor between the front and rear of a catalyst without impairing detection accuracy.SOLUTION: An arrangement structure for the exhaust gas sensor includes a muffler (7) provided downstream of an exhaust pipe (6), a catalyst (8) provided in the muffler for purifying exhaust gas from an engine (2), and an exhaust gas sensor (9) for detecting components of the exhaust gas from th engine, the catalyst having a sub catalyst (8b) arranged on the upstream side of the muffler, and a main catalyst (8a) arranged downstream of the sub catalyst, the exhaust gas sensor being arranged between the front and rear of the sub catalyst.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.

  An exhaust gas sensor arrangement structure according to the present invention includes a muffler provided downstream of an exhaust pipe, a catalyst provided in the muffler for purifying engine exhaust gas, an exhaust gas sensor for detecting an exhaust gas component of the engine, and The catalyst has a sub-catalyst disposed upstream of the muffler and a main catalyst disposed downstream of the sub-catalyst, and the exhaust gas sensor is disposed before and after the sub-catalyst. It is characterized by being.

  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 perspective 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 an enlarged view of the exhaust gas sensor periphery which concerns on this Embodiment. It is a perspective view which shows the arrangement structure of the exhaust gas sensor which concerns on a 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 exhaust gas sensor arrangement structure according to the present invention is applied to a scooter type motorcycle will be described. However, 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, and the rear of the vehicle is indicated by an arrow RE. 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, the scooter type motorcycle 1 is configured by suspending an engine 2 on an underbone body frame 11. The vehicle body frame 11 includes a main frame 13 that extends rearward and downward from the head pipe 12 and a pair of seat rails 14 that extend rearward and upward from the rear end of the main frame 13. The engine 2 is composed of, for example, a single cylinder engine and is disposed below the main frame 13.

  Various covers as a vehicle body exterior are mounted on the vehicle body frame and the engine 2. Specifically, a front cowl 15 is provided on the vehicle front side. A center frame cover 16 is provided behind the front cowl 15. A side cowl 17 that covers the vehicle side surface is provided behind the center frame cover 16. A seat 18 is provided on the upper side of the side cowl 17.

  The engine 2 is configured by attaching a cylinder 21, a cylinder head 22, and a cylinder head cover (not shown) in this order in front of a crankcase 20 in which various components such as a crankshaft (not shown) are accommodated. The cylinder 21 is arranged so that the axial direction is inclined forward and faces the substantially horizontal direction. An air cleaner 25 is connected to the intake port of the cylinder head 22 via an intake pipe 23 and a throttle body 24. The air cleaner 25 is disposed below the head pipe 12.

  A front fork 26 is rotatably supported on the head pipe 12 via a steering shaft (not shown). A handlebar 28 for steering the front wheel 27 is provided above the front fork 26. A front wheel 27 is rotatably supported on the lower portion of the front fork 26. An upper portion of the front wheel 27 is covered with a front fender 29.

  A clutch cover 30 is provided on the right side of the crankcase 20, and a magnet cover (not shown) is provided on the left side of the crankcase 20. A swing arm 31 extending in the substantially horizontal direction toward the rear is provided at the rear portion of the crankcase 20. A rear wheel 32 is rotatably provided at the rear end of the swing arm 31. The rear upper side of the rear wheel 32 is covered with a rear fender 33.

  A pair of footrest brackets 34 are provided on both sides of the swing arm 31. The footrest bracket 34 extends rearward from the rear end of the engine 2 and has a substantially triangular shape in side view. A pillion footrest 35 is provided at the rear end of each footrest bracket 34. A center stand 36 is provided below the crankcase 20 and the swing arm 31. A brake pedal 37 and a driver's footrest 38 are provided side by side on the right side of the engine 2. The brake pedal 37 is disposed on the front side of the footrest 38.

  In addition, 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 32 in a side view.

  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.). 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.

  Although details will be described later, the catalyst 8 according to the present embodiment is configured by a so-called divided catalyst having a main catalyst 8a and a sub catalyst 8b. The sub catalyst 8 b is disposed on the upstream side of the muffler 7. The main catalyst 8a is disposed downstream of the sub catalyst 8b. 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 the exhaust gas component of the engine and determining the deterioration of the catalyst 8 is disposed before and after the sub catalyst 8b. Specifically, the exhaust gas sensor 9 includes an upstream sensor 90 provided upstream of the sub catalyst 8b and a downstream sensor 91 provided downstream of the sub catalyst 8b. 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). 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.

  Particularly in the 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.

  Moreover, with a scooter, it is possible to arrange | position an exhaust-gas sensor directly to a 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 inventors have adopted a configuration in which a divided catalyst is employed in the scooter type motorcycle 1 and the main catalyst 8 a and the sub catalyst 8 b are disposed in the muffler 7. Further, exhaust gas sensors 9 are arranged before and after the sub catalyst 8b. Specifically, an upstream sensor 90 is disposed in the exhaust pipe 6 immediately before the sub catalyst 8b, and a downstream sensor 91 is disposed in the muffler 7 immediately after the sub catalyst 8b.

  According to this configuration, the upstream sensor 90 can detect the exhaust gas before passing through the sub catalyst 8b, and the downstream sensor 91 can detect the exhaust gas after passing through the sub catalyst 8b. it can. Therefore, it is possible to determine the deterioration of the sub catalyst 8b based on the outputs of the upstream sensor 90 and the downstream sensor 91. Further, it is possible to determine the deterioration of the main catalyst 8a from the deterioration state of the sub catalyst 8b. The sub-catalyst 8b is provided to determine the deterioration of the main catalyst 8a, and the outer diameter and the density of the honeycomb portion are set smaller than those of the main catalyst 8a. In this case, the exhaust gas that has not been sufficiently purified by the sub-catalyst 8b can be purified by the main catalyst 8a.

  Thus, even if it is a divided catalyst, the exhaust gas sensor 9 can be arrange | positioned, without impairing the exhaust gas purification performance, and the arrangement | positioning freedom degree can be improved. Further, since the exhaust gas sensors 9 are arranged in the middle of the piping, the exhaust gas contacts each exhaust gas sensor 9 without being diffused. As a result, an output can be stably obtained, and the detection accuracy of the exhaust gas sensor 9 is not impaired. Further, 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.

  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, the exhaust system according to the present embodiment includes an exhaust pipe 6 connected to the exhaust port of the engine 2 (see FIG. 2), and a muffler provided downstream of the exhaust pipe 6. 7. The exhaust pipe 6 protrudes downward from the exhaust port, then bends backward and extends in a substantially horizontal direction.

  The muffler 7 increases in diameter as it goes rearward from the rear end of the exhaust pipe 6, and extends in a cylindrical shape with an outer diameter sufficiently larger than that of the exhaust pipe 6. Specifically, the muffler 7 includes a first half 70 that forms the first half and a second half 71 that is connected to the first half 70 and forms the second half. The front half part 70 is further configured by a straight pipe part 72 and a tapered part 73 connected to the straight pipe part 72.

  The straight pipe portion 72 extends linearly from the rear end of the exhaust pipe 6 to the rear. The front end of the straight pipe portion 72 has a tapered shape so as to be larger than the outer diameter of the exhaust pipe 6. The taper portion 73 extends in a cylindrical shape so as to have a larger diameter than the straight pipe portion 72 as it goes rearward from the rear end of the straight pipe portion 72, and the outer surface has a truncated cone shape.

  The rear half 71 extends in a cylindrical shape toward the rear while maintaining the outer diameter at the rear end of the tapered portion 73. The rear end portion of the rear half 71 is slightly reduced in diameter. A circular first baffle plate 74 a is provided at the boundary between the front half 70 and the rear half 71. Thereby, the space in the muffler 7 is partitioned forward and backward. Here, a space in the front half 70 on the front side of the first baffle plate 74a is defined as a space S1. Although details will be described later, the main catalyst 8a is disposed through the upper half of the first baffle plate 74a. A crescent-shaped communication hole 77 is formed in the lower half of the first baffle plate 74a.

  The space in the rear half 71 is partitioned into three spaces in the front-rear direction by a circular second baffle plate 74b and a third baffle plate 74c. The second baffle plate 74b is disposed slightly rearward of the center of the rear half 71 in the front-rear direction. The third baffle plate 74c is disposed further rearward than the second baffle plate 74b. Here, a space between the first baffle plate 74a and the second baffle plate 74b is a space S2, and a space between the second baffle plate 74b and the third baffle plate 74c is a space S3, and the third baffle plate 74c. A space on the rear side is defined as a space S4.

  As described above, the catalyst 8 is disposed in the muffler 7. Specifically, the sub-catalyst 8 b is disposed on the upstream side of the straight pipe portion 72, and the main catalyst 8 a is disposed at a boundary portion between the front half portion 70 and the rear half portion 71. The sub-catalyst 8 b has a cylindrical shape with an outer diameter slightly smaller than the inner diameter of the straight pipe portion 72. The upstream end of the sub catalyst 8b is connected to the downstream end of the exhaust pipe 6 via the first connecting pipe 75a. The first connecting pipe 75 a is formed in a tapered shape so as to follow the inner wall of the straight pipe portion 72.

  A straight second connecting pipe 75b and a tapered third connecting pipe 75c are connected to the downstream end of the sub catalyst 8b. The second connecting pipe 75 b extends rearward with the same outer diameter along the inner wall of the straight pipe portion 72. Further, the rear end portion of the second connecting pipe 75 b enters the tapered portion 73. The third connection pipe 75 c is connected to the rear end of the second connection pipe 75 b and extends rearward with a gentler taper shape than the taper portion 73. The main catalyst 8a is connected to the rear end of the third connecting pipe 75c. In the front half part 70, a gap is formed between the straight pipe part 72 and the taper part 73 and the first to third connection pipes 75 a to 75 c and the catalyst 8.

  The main catalyst 8a is set to have a larger outer diameter and density of the honeycomb portion than the sub catalyst 8b. The main catalyst 8a is disposed so as to penetrate substantially the upper half including the center of the circular first baffle plate 74a. The first half of the main catalyst 8a is exposed in the space S1, while the second half of the main catalyst 8a is exposed in the space S2. Further, the space S1 and the space S2 are communicated with each other through the communication hole 77 formed in the first baffle plate 74a.

  As described above, the exhaust gas sensors 9 are disposed before and after the sub catalyst 8b. 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.

  Specifically, the upstream sensor 90 is attached to the downstream end of the exhaust pipe 6 in front of the sub catalyst 8b. The upstream sensor 90 is attached so that one end side penetrates into the exhaust pipe 6 and the other end side is directed upward.

  The downstream sensor 91 is attached to the downstream end of the straight pipe portion 72 behind the sub catalyst 8b. Specifically, the downstream sensor 91 is attached so that one end side penetrates the straight pipe portion 72 and the second connecting pipe 75b, and the other end side is directed upward.

  In the second half 71, a plurality of communication pipes (baffle pipes) are provided so as to communicate with a space partitioned by a plurality of baffle plates. Specifically, the communication pipe includes a first baffle pipe 76a that penetrates the second baffle plate 74b and the third baffle plate 74c, a second baffle pipe 76b that penetrates the third baffle plate 74c, a third baffle plate 74c, and the latter half. And a third baffle pipe 76c that penetrates the portion 71.

  The first baffle pipe 76a extends in the front-rear direction and is disposed below the center of the second baffle plate 74b and the third baffle plate 74c. The front end of the first baffle pipe 76a is exposed in the space S2, while the rear end of the first baffle pipe 76a is exposed in the space S4. Thereby, space S2 and space S4 are connected.

  The second baffle pipe 76b extends in the front-rear direction and is disposed on the right side of the center of the third baffle plate 74c. The front end of the second baffle pipe 76b is exposed in the space S3, while the rear end of the second baffle pipe 76b is exposed in the space S4. Thereby, space S3 and space S4 are connected.

  The third baffle pipe 76c extends rearward and is bent slightly rearward and downward. The tip of the third baffle pipe 76c is disposed on the upper left side from the center of the third baffle plate 74c, and is exposed in the space S3. On the other hand, the rear end of the third baffle pipe 76 c is exposed to the outside from the rear end of the rear half 71. Thereby, space S3 and external space are connected.

  In the exhaust system configured as described above, 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 sub catalyst 8b and the main catalyst 8a, and then flows into the space S2. Then, the exhaust gas moves rearward via the first baffle pipe 76a and flows into the space S4.

  In the space S4, the flow path of the exhaust gas is reversed so as to go forward. The exhaust gas moves forward via the second baffle pipe 76b and flows into the space S3. In the space S3, the flow path of the exhaust gas is reversed so as to go rearward. The exhaust gas is discharged outside through the third baffle pipe 76c. Thus, the exhaust gas flow path can be formed to be folded back and forth by a plurality of baffle pipes. As a result, the flow path length of the exhaust gas can be ensured, and the effect of silencing exhaust gas is enhanced.

  Further, the oxygen concentration of the exhaust gas is detected by the upstream sensor 90 and the downstream sensor 91, and the ECU 10 can determine the deterioration of the sub catalyst 8b and the main catalyst 8a based on the detected value.

  Further, since the communication hole 77 is formed in the first baffle pipe 76a, the exhaust gas after purification flows into the space S2 and then flows into the space S1 through the communication hole 77. As described above, in the front half part 70 that forms the space S1, the straight pipe part 72 and the taper part 73 that constitute the outer wall, the first to third connection pipes 75a to 75c and the catalyst arranged in the front half part 70. A gap is formed between the two. That is, the volume of the muffler 7 can be secured by the gap. Therefore, it is possible to contribute to the silencing effect of the muffler 7 and the improvement of the output.

  In addition, since the catalyst 8 is biased toward the front half portion 70 of the muffler 7, the temperature increase of the catalyst 8 can be promoted on the upstream side of the exhaust gas, which is considered to have a relatively high temperature. As a result, early activation of the catalyst 8 can be realized. Further, the arrangement of the catalyst 8 in the muffler 7 can simplify the configuration as compared with a configuration in which the catalyst is arranged in the middle of the exhaust pipe 6, for example.

  Further, as shown in FIG. 2, the exhaust gas sensor 9 is disposed at a position away from the brake pedal 37 and the footrest 38 behind the engine 2. For this reason, it can prevent that a passenger | crew's leg contacts the exhaust gas sensor 9. FIG. Moreover, since the component parts are not close to the periphery of the exhaust gas sensor 9, a space for attaching the muffler 7 is secured, and the assembling property is improved.

  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 sub catalyst 8b. For example, the configuration shown in FIG. FIG. 5 is a perspective view showing an arrangement structure of exhaust gas sensors according to a modification.

  In the modification shown in FIG. 5, the upstream sensor 90 is also attached to the straight pipe portion 101 of the muffler 7 in the same manner as the downstream sensor 91. Specifically, the straight pipe part 101 and the first connection pipe 102 are extended forward, and one end side of the downstream sensor 91 is attached so as to penetrate the straight pipe part 101 and the first connection pipe 102. Even in this case, the exhaust gas sensor 9 can be disposed close to the front and back of the sub catalyst 8b. In particular, since the straight pipe portion 101 and the first connecting pipe 102 are extended forward, the volume in the space S1 can be further secured.

  Further, in the above-described embodiment, the straight pipe portions 72 and 101 have a cylindrical shape extending in the front-rear direction with the same outer diameter, but are not limited to this configuration. For example, the straight pipe portions 72 and 101 may have a tapered shape that increases in diameter toward the rear.

  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 2 Engine 6 Exhaust pipe 7 Muffler 70 Front half 71 Rear half 72, 101 Straight pipe part 73 Tapered part 8 Catalyst 8a Main catalyst 8b Sub catalyst 9 Exhaust gas sensor 90 Upstream sensor 91 Downstream sensor

Claims (4)

A muffler provided downstream of the exhaust pipe;
A catalyst provided in the muffler for purifying engine exhaust gas;
An exhaust gas sensor for detecting an exhaust gas component of the engine,
The catalyst has a sub catalyst disposed upstream of the muffler, and a main catalyst disposed downstream of the sub catalyst.
An exhaust gas sensor arrangement structure, wherein the exhaust gas sensor is arranged before and after the sub-catalyst. The exhaust gas sensor has an upstream sensor provided upstream of the sub-catalyst, and a downstream sensor provided downstream of the sub-catalyst,
The first half of the muffler has a straight pipe part and a tapered part connected to the downstream side of the straight pipe part,
The exhaust gas sensor arrangement structure according to claim 1, wherein the tapered portion has a diameter larger than that of the straight pipe portion as it goes rearward. The sub-catalyst is disposed in the straight pipe portion,
The exhaust gas sensor arrangement structure according to claim 2, wherein the main catalyst is arranged in the tapered portion.   The exhaust gas sensor arrangement structure according to any one of claims 1 to 3, wherein the exhaust gas sensor is arranged behind the engine.

Images