Exhaust device

Abstract

To provide an exhaust device capable of improving cleaning performance while suppressing increase of a catalyst loading amount.SOLUTION: An exhaust device ED comprises: an exhaust chamber 32 that forms an expansion space SP in an exhaust passage EP in which exhaust gas G expands; a chamber inlet pipe 30 connected to the exhaust chamber 32, and having a downstream end that opens to the expansion space SP; a first catalyst 40 arranged upstream of the expansion space SP in the exhaust passage EP; and a second catalyst 42 arranged in the chamber inlet pipe 30 and facing the expansion space SP.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an exhaust device that constitutes a part of an exhaust passage through which exhaust gas from an engine flows, purifies the gas, and discharges the gas to the outside. [Background technology]

[0002] 2. Description of the Related Art In some engine exhaust systems, two catalysts for purifying exhaust gas are provided spaced apart from each other in the flow direction of the exhaust gas (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-046463 A Summary of the Invention [Problem to be solved by the invention]

[0004] Increasing the amount of catalyst carried can improve purification performance, but generally, increasing the amount of catalyst carried leads to increased costs.

[0005] The disclosure of the present application provides an exhaust device that can improve purification performance while suppressing an increase in the amount of catalyst carried. [Means for solving the problem]

[0006] The exhaust device disclosed herein is an exhaust device that forms an exhaust passage through which engine exhaust gas flows, purifies the exhaust gas, and discharges it to the outside. The exhaust device includes a case body that forms an expansion space in the exhaust passage for expanding the exhaust gas, a communicating pipe connected to the case body and having one end that opens to the outside of the expansion space and the other end that opens into the expansion space, a first catalyst that is arranged upstream of the expansion space in the exhaust passage, and a second catalyst that is arranged in the communicating pipe and faces the expansion space. Effect of the Invention

[0007] According to the exhaust device of the present disclosure, the exhaust gas diffused in the expansion space enters and leaves the second catalyst in response to the exhaust pulsation. In this way, the number of times the exhaust gas comes into contact with the second catalyst can be increased due to the pulsation. In other words, the exhaust gas after diffusing in the expansion space flows back and is guided to the second catalyst. By returning the diffused exhaust gas to the second catalyst in this way, it is possible to easily bring the exhaust gas that has not come into contact with the second catalyst into contact with the second catalyst again. In this way, the amount of exhaust gas that comes into contact with the second catalyst can be increased. As a result, the purification performance can be improved even if the amount of catalyst carried is small. [Brief description of the drawings]

[0008] [Figure 1] 1 is a side view showing a motorcycle, which is one type of vehicle, equipped with an exhaust system according to a first embodiment of the present disclosure. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a plan view showing the inside of an exhaust chamber of the exhaust device. [Figure 4A] FIG. 2 is a plan view illustrating a purification function of the exhaust system. [Figure 4B] FIG. 4 is another plan view illustrating the purification function of the exhaust system. [Figure 4C] FIG. 11 is still another plan view illustrating the purification function of the exhaust system. [Diagram 5] FIG. 11 is a plan view showing the inside of an exhaust chamber of an exhaust device according to a second embodiment of the present disclosure. [Figure 6] FIG. 11 is a horizontal cross-sectional view showing the inside of an exhaust chamber of an exhaust device according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the following description, "front" and "rear" refer to the "front" and "rear" as seen from the traveling direction of the vehicle. In other words, the front-rear direction coincides with the longitudinal direction of the vehicle. "Left" and "right" refer to the "left" and "right" as seen from the driver who is in the vehicle. In other words, the "left-right direction" coincides with the width direction of the vehicle.

[0010] 1 is a side view showing a motorcycle, which is a type of saddle-type vehicle, equipped with an exhaust system according to a first embodiment of the present disclosure. The exhaust system of the present disclosure is also applicable to vehicles other than motorcycles, such as three-wheeled vehicles, four-wheeled buggies, utility vehicles, and small personal watercraft.

[0011] The exhaust system disclosed herein has a silencing function that reduces exhaust noise. The exhaust system also has a so-called purification function that suppresses the emission of harmful substances contained in the exhaust gas into the atmosphere. Here, the "silencing function" refers to suppressing the pressure energy of the exhaust gas by forming multiple chambers that expand and contract repeatedly, or by using a resonant structure. The "purification function" uses platinum group elements (catalyst materials) such as rare precious metals platinum (Pt), palladium (Pd), and rhodium (Rh), and the harmful substances contained in the exhaust gas are converted into harmless substances by an oxidation-reduction reaction between the platinum group elements and the exhaust gas. Specifically, by exposing the exhaust gas to a platinum-based element, nitrogen oxides (NO X ), carbon monoxide (CO), and hydrocarbons (CH) are converted into harmless substances N2, CO2, and H2O, respectively.

[0012] The body frame FR of the motorcycle in Fig. 1 has a main frame 1 forming a front half and a rear frame 2 forming a rear half. The main frame 1 extends diagonally rearward and downward from a head pipe 4 at its front end. The main frame 1 curves downward at a rear end 1a and extends substantially downward. The rear frame 2 has its front end connected to the vicinity of the rear end 1a of the main frame 1 and extends rearward from the main frame 1.

[0013] A front fork 6 is rotatably supported by the head pipe 4 via a steering shaft (not shown). A steering handle 8 is fixed to the upper end of the front fork 6. A front wheel 10 is attached to the lower end of the front fork 6.

[0014] A swing arm bracket 9 is provided below the rear end portion 1a of the main frame 1. A swing arm 12 is supported around a pivot shaft 11 attached to the swing arm bracket 9 so as to be able to swing up and down freely. A rear wheel 14 is supported on the rear end portion of the swing arm 12.

[0015] An engine E, which is a drive source for the motorcycle, is disposed below and in front of the main frame 1 and attached to the main frame 1. The engine E drives a rear wheel 14 via a power transmission member 16 such as a drive chain. The engine E in this embodiment is a four-cylinder four-stroke engine E, but is not limited to this.

[0016] An intake port 17 is formed at the rear of the engine E, and an exhaust port 18 is formed at the front. A mixture of air and fuel introduced through the intake port 17 is burned in the combustion chamber, and exhaust gas G is discharged from the exhaust port 18. An exhaust device ED for the engine E is attached to the exhaust port 18. Details of the exhaust device ED will be described later.

[0017] A fuel tank 20 is supported by the main frame 1. Fuel for the engine E is stored in the fuel tank 20. The fuel tank 20 is disposed above the engine E. Behind the fuel tank 20, a seat 22 for a driver to sit on is supported by the rear frame 2.

[0018] The exhaust device ED of the present disclosure will be described below. The exhaust device ED constitutes an exhaust passage EP through which exhaust gas G of an engine E flows, and purifies the exhaust gas G and discharges it to the outside. In the following description, "upstream" and "downstream" refer to "upstream" and "downstream" in the flow direction of the exhaust gas G, respectively.

[0019] The exhaust device ED has an exhaust pipe 24 , a collecting pipe 26 , a catalyst pipe 28 , a chamber inlet pipe 30 , an exhaust chamber 32 , a chamber outlet pipe 34 , a connecting pipe 36 , and an exhaust muffler 38 .

[0020] An upstream end 24a of the exhaust pipe 24 is connected to the exhaust port 18. An exhaust pipe 24 is provided for each cylinder, and the engine E of this embodiment has four exhaust pipes 24. Each exhaust pipe 24 extends downward in front of the engine E and then curves rearward in front of the lower part of the engine E, and a downstream end 24b is connected to an upstream end 26a of a collecting pipe 26.

[0021] The four exhaust passages EP are collected into one exhaust passage EP by the collecting pipe 26. The collecting pipe 26 extends rearward below the engine E, and its downstream end 26b is connected to an inlet portion 28a at the upstream end of the catalyst pipe 28.

[0022] The catalyst pipe 28 is disposed in a region below the engine E. The exhaust chamber 32 is disposed between the engine E and the rear wheel 14. The exhaust chamber 32 is disposed below the swing arm 12. The exhaust chamber 32 is configured to straddle the center of the vehicle in the width direction.

[0023] The exhaust chamber 32 is formed with a larger passage cross-sectional area than the upstream portion. As a result, the exhaust gas guided into the exhaust chamber 32 expands, reducing the pressure energy of the exhaust gas. Furthermore, the exhaust chamber 32 has a plurality of spaces formed therein, and communication passages that connect the spaces are formed. As a result, the exhaust gas guided into the exhaust chamber 32 flows in different directions, reducing the pressure energy of the exhaust gas.

[0024] By providing the exhaust chamber 32 having such a sound-absorbing function, the exhaust muffler 38 can be made smaller than when the sound-absorbing function is achieved only by the exhaust muffler 38. The exhaust muffler 38 is disposed on the outer side of the rear wheels 14 in the vehicle width direction.

[0025] The collecting pipe 26 has a portion where the diameter gradually decreases toward the downstream side after collecting. The collecting pipe 26 further has a portion where the diameter gradually increases toward the downstream side from the narrowest portion. By connecting the portion where the diameter increases toward the catalyst pipe 28, the flow resistance is reduced and the exhaust gas can be easily guided to the catalyst pipe 28.

[0026] As shown in FIG. 2, the first catalyst 40 is housed inside the catalyst tube 28. The first catalyst 40 is made of the above-mentioned catalyst material and converts harmful exhaust gas contained in the exhaust gas G into harmless gas. The first catalyst 40 is supported on a catalyst carrier. In this embodiment, two first catalysts 40 are provided at a distance in the flow direction of the exhaust gas G. By providing two first catalysts 40, the exhaust gas that leaves the upstream catalyst 40 and merges with the downstream catalyst 40 flows into the downstream catalyst 40, making it easier to make the exhaust gas that comes into contact with the catalyst 40 different, and making it easier to improve the purification effect of the catalyst. However, the number of first catalysts 40 is not limited to this. In this embodiment, the upstream catalyst and the downstream catalyst that constitute the first catalyst 40 may be formed to have the same shape.

[0027] The first catalyst 40 is configured to be able to guide exhaust gas from the upstream side to the downstream side. For example, the first catalyst 40 is provided with partition walls that separate a plurality of passages, and a catalyst material is supported on the partition walls. Specifically, the first catalyst 40 may be formed into a honeycomb catalyst structure.

[0028] The catalytic tube 28 (first catalyst 40) is formed to have a cross-sectional area, specifically a diameter, larger than that of the upstream collecting tube 26. The length of the first catalyst 40 is set to be larger than that of the collecting tube 26. Here, the length of the first catalyst 40 refers to the combined length of the upstream catalyst and the downstream catalyst. The collecting tube 26 is disposed between the front end of the engine E and the rear end of the engine E. The first catalyst 40 is formed to have a purification performance (loading amount, volume) larger than that of a second catalyst 42 described later. However, the catalytic tube 28 may have a cross-sectional area smaller than that of the upstream collecting tube 26. Similarly, the length of the catalytic tube 28 may be shorter than that of the collecting tube 26.

[0029] An upstream end 30a of a chamber inlet pipe 30 is connected to an outlet portion 28b at the downstream end of the catalyst pipe 28. As shown in Fig. 4, the chamber inlet pipe 30 is joined to the exhaust chamber 32 at a middle portion in the flow direction of the exhaust gas G. That is, the upstream half of the chamber inlet pipe 30 is located outside the exhaust chamber 32, and the downstream half is located inside the exhaust chamber 32. In other words, the upstream end 30a of the chamber inlet pipe 30 opens to the outside of the exhaust chamber 32, and the downstream end 30b opens into the inside of the exhaust chamber 32.

[0030] In this embodiment, the upstream end 30a of the chamber inlet pipe 30 is made of a tapered section whose diameter gradually decreases toward the downstream side. A main body section 30c having a constant pipe diameter is connected to the downstream end of the tapered section 30a. The downstream end of the main body section 30c is expanded in diameter and connected to the downstream end section 30b of the chamber inlet pipe 30. That is, the downstream end section 30b of the chamber inlet pipe 30 is made of a large diameter section whose diameter is larger than that of the main body section 30c. In other words, the main body section 30c constitutes a reduced diameter section whose pipe diameter is smaller than that of the upstream end section (tapered section) 30a and the downstream end section (large diameter section) 30b. However, the downstream end section 30b of the chamber inlet pipe 30 may have the same diameter as the main body section 30c. As shown in FIG. 3, the downstream end section (large diameter section) 30 is disposed in the exhaust chamber 32. In other words, the main body section 30c of the chamber inlet pipe 30 is the penetrating section that penetrates the exhaust chamber 32.

[0031] The second catalyst 42 is housed in the large diameter section 30b at the downstream end of the chamber inlet pipe 30. Like the first catalyst 40, the second catalyst 42 is made of the above-mentioned catalytic material and decomposes harmful exhaust gas contained in the exhaust gas G by converting it into harmless gas. The second catalyst 42 is also supported on a catalyst carrier. The second catalyst 42 may have the same or different support ratio for each catalytic material as the first catalyst 40. In this embodiment, the support amount, volume, and purification capacity of the second catalyst 42 are set to be smaller than those of the first catalyst 40.

[0032] In the present disclosure, the second catalyst 42 is disposed inside the exhaust chamber 32. In detail, the second catalyst 42 is disposed so as to face the expansion space SP formed inside the exhaust chamber 32. Here, the "expansion space SP" refers to a space formed in the exhaust passage EP to expand the exhaust gas G. In addition, "facing the expansion space SP" includes the second catalyst 42 and the expansion space SP facing each other in the flow direction of the exhaust gas G, or the second catalyst 42 facing the expansion space SP. The expansion space SP is formed so that the gas passage cross-sectional area is larger than the passage cross-sectional area of ​​the chamber inlet pipe 30. For example, the passage area of ​​the expansion space SP facing the second catalyst 42 is formed to be 1.5 times or more, preferably 2 times or more, the passage area of ​​the chamber inlet pipe 30.

[0033] An expansion space SP is also formed on the opposite side in the flow direction of the second catalyst 42. In other words, exhaust gas is guided into the exhaust chamber 32 from the second catalyst 42, which is located away from the wall surface of the exhaust chamber 32. In the expansion space SP, exhaust gas is mixed from the radially outer region of the second catalyst 42 and from a region of the expansion space SP that is on the opposite side in the flow direction from the second catalyst 42. In this way, in this embodiment, the agitation and mixing effect of the exhaust gas leaving the second catalyst 42 is high.

[0034] In this embodiment, the exhaust chamber 32 constitutes a case body in which an expansion space SP is formed and in which a second catalyst 42 is provided facing the expansion space SP. Also, in this embodiment, the chamber inlet pipe 30 is connected to the case body, and constitutes a communicating pipe having one end open to the outside of the expansion space SP and the other end opening into the expansion space SP, at the other end of which the second catalyst 42 is disposed. The other end is disposed closer to the center of the chamber than the inner wall of the chamber. In this embodiment, the other end is disposed closer to the center of the chamber than the front inner wall of the chamber. However, the case body and the communicating pipe are not limited to the exhaust chamber 32 and the chamber inlet pipe 30.

[0035] In this way, the first catalyst 40 is disposed upstream of the expansion space SP and the second catalyst 42. The exhaust passage EP between the first catalyst 40 and the second catalyst 42 is narrowed in diameter by the tapered section 30a at the upstream end of the chamber inlet pipe 30, and then expanded in diameter by the large diameter section 30b at the downstream end. In other words, a small diameter section 30c where the pipe line is narrowed is formed between the first catalyst 40 and the second catalyst 42.

[0036] The second catalyst 42 is set to have a lower purification performance than the first catalyst 40. That is, the first catalyst 40 is a main catalyst, and the second catalyst 42 is a sub catalyst. Here, "low purification performance" may include any one of the following: the catalyst carrier is short, the catalyst carrier is small in diameter, and the amount of catalyst carried is small. In this embodiment, the second catalyst 42 is formed to be shorter and have a smaller diameter than the first catalyst 40, and to carry a smaller amount of catalyst. When the first catalyst 40 or the second catalyst 42 is composed of a plurality of catalysts, the length of the catalyst carrier is the sum of the lengths of the catalyst carriers. In this embodiment, the second catalyst 42 is set to be smaller in diameter and shorter than the first catalyst 40.

[0037] 2, the exhaust device ED of this embodiment has a first exhaust gas sensor 44 and a second exhaust gas sensor 46. The first and second exhaust gas sensors 44, 46 detect the state of the exhaust gas G flowing through the exhaust passage EP. In this embodiment, oxygen sensors that detect the oxygen concentration in the exhaust gas G are used as the first and second exhaust gas sensors 44, 46.

[0038] The first exhaust gas sensor 44 is disposed in the exhaust passage EP upstream of the first catalyst 40. In this embodiment, the first exhaust gas sensor 44 is attached to the collecting pipe 26. The first exhaust gas sensor 44 is used, for example, for air-fuel ratio control of the engine E.

[0039] As described above, the first exhaust gas sensor 44 is, for example, an oxygen sensor. By feedback-controlling the output value of the first exhaust gas sensor 44, it becomes easier to control the engine at an ideal air-fuel ratio that improves purification performance. The first exhaust gas sensor 44 is disposed in the narrowest lower portion of the collecting pipe 26. By disposing the first exhaust gas sensor 44 in a portion where exhaust gas is sufficiently collected, it becomes easier to obtain an average detection result of exhaust gas discharged from multiple cylinders.

[0040] 3, the second exhaust gas sensor 46 is disposed downstream of the first catalyst 40 in the exhaust passage EP and upstream of the second catalyst 42. In this embodiment, the second exhaust gas sensor 44 is attached to the main body 30c, which is the small diameter portion of the chamber inlet pipe 30. The second exhaust gas sensor 46 is used, for example, to monitor the deterioration degree of the first catalyst 40.

[0041] As described above, the second exhaust gas sensor 46 is, for example, an oxygen sensor. By feedback-controlling the output values ​​of the first exhaust gas sensor 44 and the second exhaust gas sensor 46, the engine can be controlled at an ideal air-fuel ratio that provides higher purification performance than when the first exhaust gas sensor 44 is used alone. In addition, by comparing the output values ​​of the second exhaust gas sensor 46 and the first exhaust gas sensor 44, the catalytic effect can be detected and the deterioration state of the first catalyst 40 can be estimated.

[0042] The second exhaust gas sensor 46 is disposed in the narrowest portion of the inlet pipe 30. By disposing the second exhaust gas sensor 46 in the portion where exhaust gas is sufficiently collected, it is easy to obtain an average detection result of the exhaust gas discharged from the first catalyst 40. The second exhaust gas sensor 46 is provided upstream of the exhaust chamber 32. In other words, the second exhaust gas sensor 46 is disposed between the catalyst pipe 28 and the exhaust chamber 32.

[0043] The second exhaust gas sensor 46 is disposed sufficiently away from the open end of the inlet pipe 30 on the exhaust chamber side. Specifically, it is disposed at a distance of at least twice, and more preferably at least three times, the length of the second catalyst 42. This makes it possible to prevent exhaust gas that has flowed back from the exhaust chamber 32 from reaching the second exhaust gas sensor 46, and to prevent a decrease in detection accuracy due to the backflow. Furthermore, by forming the inlet pipe 30 so as to be curved toward the downstream side in the flow direction, it is possible to prevent exhaust gas that has flowed back from the exhaust chamber 32 from reaching the second exhaust gas sensor 46, and to prevent a decrease in detection accuracy due to the backflow.

[0044] The exhaust chamber 32 shown in Fig. 2 has a divided structure formed by joining a plurality of divided bodies. In this embodiment, the exhaust chamber 32 has two divided bodies, a first and a second divided body 32a, 32b, which are joined by welding at a joint 32c. In detail, the exhaust chamber 32 has a two-part structure, with the upper first divided body 32a and the lower second divided body 32b joined at the joint 32c.

[0045] 3 is a plan view of the exhaust chamber 32 with the first divided body 32a removed. The exhaust chamber 32 is substantially rectangular in plan view, and the joint 32c is provided around the entire periphery of the exhaust chamber 32. The joint 32c of the first divided body 32a and the joint 32c of the second divided body 32b are butted together in the vertical direction and welded all around from the outside.

[0046] The chamber inlet pipe 30 in which the second catalyst 42 is disposed is joined to the first and second divisions 32a, 32b in a state where it is fitted into the joint 32c. In detail, semicircular insertion parts 48, 48 are formed at the joint 32c of the first division 32a and the joint 32c of the second division 32b. The lower half of the chamber inlet pipe 30 is fitted into the semicircular insertion part 48 of the lower second division 32b, and the semicircular insertion part 48 of the upper first division 32a is fitted into the upper half of the chamber inlet pipe 30. In this state, the chamber inlet pipe 30 is joined to the first and second divisions 32a, 32b by welding.

[0047] The chamber inlet pipe 30 is joined to the first and second divided bodies 32a, 32b by the small diameter main body portion 30c. By joining the chamber inlet pipe 30 to the first and second divided bodies 32a, 32b while being fitted into the joining portion 32c, the chamber inlet pipe 30 can be connected to the intake chamber 32 even when the large diameter portion 30b is disposed inside the intake chamber 32.

[0048] The chamber outlet pipe 34 is connected to the upper first divided body 32a. In detail, a pipe insertion hole 32aa is formed in the first divided body 32a, and the chamber outlet pipe 34 is welded to the first divided body 32a with the chamber outlet pipe 34 inserted through the pipe insertion hole 32aa.

[0049] A partition wall 50 is provided inside the intake chamber 32. The partition wall 50 is disposed inside the intake chamber 32 and divides the expansion space SP into a plurality of expansion chambers 52, 54. In this embodiment, the expansion space SP is divided by one partition wall 50 into a first expansion chamber 52 on the upstream side and a second expansion chamber 54 on the downstream side. However, the number of partition walls 50 and expansion chambers 52, 54 is not limited to this. The partition wall 50 is joined to the inner wall of the intake chamber 32 by welding. A rib 55 may be provided at the portion of the inner wall of the intake chamber 32 where the partition wall 50 is welded for reinforcement.

[0050] A communication hole 56 is formed in the partition wall 50. The communication hole 56 penetrates the partition wall 50 and communicates between the first expansion chamber 52 and the second expansion chamber 54. In this embodiment, one communication hole 56 is provided, but the number of communication holes 56 is not limited to this.

[0051] The downstream end 30b of the chamber inlet pipe 30 opens into the first expansion chamber 52. That is, the second catalyst 42 is located in the first expansion chamber 52 and communicates with the first expansion chamber 52. In this embodiment, the axis AX1 of the downstream end 30b of the chamber inlet pipe 30 is inclined with respect to the partition wall 50. Also, the chamber inlet pipe 30 opens toward a portion of the partition wall 50 that is spaced apart from the communication hole 56. In the example shown in the figure, the communication hole 56 is formed in the right portion of the partition wall 50, and the chamber inlet pipe 30 opens toward the left portion of the partition wall 50.

[0052] The axis AX1 of the downstream end 30b of the chamber inlet pipe 30 is misaligned with the axis AX3 of the communication hole 56. Specifically, the axis AX1 of the downstream end 30b of the chamber inlet pipe 30 and the axis AX3 of the communication hole 56 are separated when viewed in a cross section in the flow direction. In addition, the axis AX1 of the downstream end 30b of the chamber inlet pipe 30 and the axis AX3 of the communication hole 56 are not parallel.

[0053] The upstream end 34a of the chamber outlet pipe 34 is inserted into the intake chamber 32 and opens to the second expansion chamber 54. The downstream end 34b of the chamber outlet pipe 34 is connected to the upstream end 36a of the connecting pipe 36.

[0054] The connecting pipe 36 shown in Fig. 2 extends in the vehicle width direction (right side) and then curves and extends rearward, with its downstream end portion 36b being connected to an exhaust muffler 38. As shown in Fig. 1, the exhaust muffler 38 is disposed on the right side of the rear wheel 14. The exhaust gas G is muffled by the exhaust muffler 38 and then discharged to the outside.

[0055] Next, the flow of exhaust gas G in the exhaust device ED of this embodiment will be described. When the engine E starts, the exhaust gas G is discharged from the exhaust port 18 to the exhaust pipe 24. The exhaust gas G discharged from the four exhaust pipes 24 shown in FIG. 2 is joined in the collecting pipe 26. The exhaust gas G joined in the collecting pipe 26 is discharged to the catalyst pipe 28. At this time, the first exhaust gas sensor 44 detects the oxygen concentration in the exhaust gas.

[0056] The exhaust gas G introduced into the catalyst tube 28 passes through the first catalyst 40 and is purified. The exhaust gas G discharged from the catalyst tube 28 flows into the chamber inlet pipe 30. The exhaust gas G that flows into the chamber inlet pipe 30 shown in FIG. 3 passes through the main body 30c of the chamber inlet pipe 30, and then passes through the second catalyst 42 at the downstream end 30b and is purified. When passing through the main body 30c, the oxygen concentration in the exhaust gas is detected by the second exhaust gas sensor 46.

[0057] The exhaust gas G purified by the second catalyst 42 flows into the first expansion chamber 52 of the exhaust chamber 32 and expands. The exhaust gas G that flows into the first expansion chamber 52 collides with the partition wall 50 and is diffused. In addition, a portion G1 of the exhaust gas G diffused in the first expansion chamber 52 is guided to the second catalyst 42 by exhaust pulsation and is purified.

[0058] The exhaust gas G in the first expansion chamber 52 flows into the second expansion chamber 54 through the communication hole 56 and expands. This repeated expansion and contraction silences the exhaust gas G. The exhaust gas G in the second expansion chamber 54 passes through the chamber outlet pipe 34 and is discharged from the exhaust chamber 32.

[0059] The exhaust gas G discharged from the exhaust chamber 32 flows into the exhaust muffler 38 via the connecting pipe 36. The exhaust gas G that flows into the exhaust muffler 38 is silenced by the exhaust muffler 38 and then discharged into the atmosphere.

[0060] Next, the exhaust gas purification function of the exhaust device ED of this embodiment will be described with reference to Figures 4A and 4B. As shown in Figure 4A, the exhaust gas Ga purified by the second catalyst 42 flows into the first expansion chamber 52 of the exhaust chamber 32, where it expands and is diffused.

[0061] 4B, the exhaust gas Ga that flows out from the chamber inlet pipe 30 into the first expansion chamber 52 and diffuses therein is mixed with the exhaust gas Gb in the first expansion chamber 52. In the following description, the mixture of the exhaust gas Ga and the exhaust gas Gb is referred to as "mixed exhaust gas Gc."

[0062] As shown in Fig. 4C, when the mixed exhaust gas Gc flows backward due to exhaust pulsation, the mixed exhaust gas Gc is guided to the second catalyst 42 and purified. In this way, the exhaust gas Gc (mixed exhaust gas) different from the exhaust gas G that passed previously is purified again by the second catalyst 42, so the purification performance is improved compared to the case where the same exhaust gas Ga (exhaust gas purified by the second catalyst 42) is purified again. The mixed exhaust gas Gc purified by the second catalyst 42 flows into the first expansion chamber 52 of the exhaust chamber 32, expands, and diffuses. Thereafter, the same operation is repeated.

[0063] According to the above configuration, as shown in Fig. 3, the exhaust gases G, G1 diffused in the expansion space SP enter and exit the second catalyst 42 in response to the exhaust pulsation. In this way, the number of times the exhaust gas G comes into contact with the second catalyst 42 due to the pulsation can be increased. In other words, the exhaust gas G diffused in the expansion space SP is led to the second catalyst 42, so that the amount of the exhaust gases G, G1 that comes into contact with the second catalyst 42 increases. This makes it possible to improve purification performance even if the catalyst loading amount is small.

[0064] In this embodiment, the second catalyst 42 is provided at the downstream end 30b of the chamber inlet pipe 30, and the expansion space SP adjacent to the chamber inlet pipe 30 has a diameter perpendicular to the exhaust flow direction, i.e., the front-rear direction, that is larger than the diameter of the downstream end 30b of the chamber inlet pipe 30. In other words, the expansion space SP adjacent to the chamber inlet pipe 30 is larger than the diameter of the chamber inlet pipe 30. This makes it possible to obtain a rapid pressure change of the exhaust gas G before and after the chamber inlet pipe 30 and the expansion space SP. As a result, the flow of the exhaust gas G is disturbed, and the exhaust gas G after diffusing in the expansion space SP is led to the second catalyst 42. This increases the amount of exhaust gas G that comes into contact with the second catalyst 42, so that the purification performance can be improved even if the amount of catalyst carried is small.

[0065] In the present embodiment, the purification performance of the second catalyst 42 is set lower than that of the first catalyst 40. According to this configuration, by setting the purification performance of the main first catalyst 40 high and the purification performance of the sub second catalyst 42 low, excessive performance of the catalysts as a whole can be suppressed.

[0066] In this embodiment, a partition wall 50 is disposed inside the intake chamber 32 to divide the expansion space SP into a plurality of expansion chambers 52, 54, and the axis AX1 of the downstream end 30b of the chamber inlet pipe 30 is inclined with respect to the partition wall 50. With this configuration, the exhaust gas G discharged from the chamber inlet pipe 30 hits the partition wall 50 and diffuses. As a result, the flow of the exhaust gas G is disturbed, and the exhaust gas G after diffusing in the expansion space SP is led to the second catalyst 42. As a result, the amount of exhaust gas G that comes into contact with the second catalyst 42 increases, and therefore the purification performance can be improved even with a small amount of catalyst supported.

[0067] In this embodiment, a communication hole 56 that communicates the first expansion chamber 52 and the second expansion chamber 54 is formed in the partition wall 50, and the chamber inlet pipe 30 opens toward a portion of the partition wall 50 that is spaced apart from the communication hole 56. With this configuration, the exhaust gas G discharged from the chamber inlet pipe 30 does not flow toward the communication hole 56, but hits the partition wall 50 and diffuses. As a result, the flow of the exhaust gas G is disturbed, and the exhaust gas G that has diffused into the expansion space SP is led to the second catalyst 42. As a result, the amount of exhaust gas G that comes into contact with the second catalyst 42 increases, and therefore, even if the amount of catalyst supported is small, purification performance can be improved.

[0068] In this embodiment, the second catalyst 42 is disposed at the downstream end 30b of the chamber inlet pipe 30, and the second catalyst 42 has a smaller diameter than the first catalyst 40, and a small diameter portion 30c where the pipe is narrowed is formed between the first catalyst 40 and the second catalyst 42. According to this configuration, the exhaust gas G rectified by the first catalyst 40 is agitated when it is discharged from the small diameter portion 30c and flows into the second catalyst 42. This allows the exhaust gas G to come into contact with the entire second catalyst, thereby improving purification performance.

[0069] In this embodiment, the intake chamber 32 has a split structure formed by joining multiple split bodies 32a, 32b, and the chamber inlet pipe 30 is fitted into the joint portion 32c of the split bodies 32a, 32b. With this configuration, the intake chamber 32 can be assembled by joining the split bodies 32a, 32b with the chamber inlet pipe 30, in which the second catalyst 42 is arranged, fitted in place. This makes it possible to assemble the chamber inlet pipe 30 to the intake chamber 32 even if the downstream end portion 30b, in which the second catalyst 42 is arranged, is a large diameter portion.

[0070] 2, in this embodiment, a first exhaust gas sensor 44 is disposed upstream of the first catalyst 40 in the exhaust passage EP, and a second exhaust gas sensor 46 is disposed downstream of the first catalyst 40 and upstream of the second catalyst 42. With this configuration, the degree of deterioration of the first catalyst 40 can be grasped by using the two exhaust gas sensors 44, 46. In addition, since the second catalyst 42 does not affect the deterioration determination, it can be installed without considering the position of the sensors 44, 46, thereby increasing the degree of design freedom.

[0071] Other embodiments will be described below. In the description of each embodiment, the same components as those in the preceding embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0072] 5 shows a main part of an exhaust device ED according to a second embodiment of the present disclosure. In the first embodiment described above, the second catalyst 42 is provided at the downstream end 30b of the chamber inlet pipe 30, whereas in the second embodiment, the second catalyst 42 is provided at the upstream end 134a of the chamber outlet pipe 134, not at the chamber inlet pipe 130. That is, in the second embodiment, the chamber outlet pipe 134 is connected to the case body, and forms a communication pipe with one end open to the outside of the expansion space SP and the other end opening into the expansion space SP, at the other end of which the second catalyst 42 is disposed. The other configurations of the second embodiment are the same as those of the first embodiment.

[0073] 5, the chamber inlet pipe 130 of the second embodiment is not provided with the second catalyst 42, so the downstream end 130b of the chamber inlet pipe 130 is not a large diameter portion, but has the same diameter as the main body portion 130c. The structure of the upstream end 130a of the chamber inlet pipe 130, i.e., the tapered portion 130a, is the same as the tapered portion 30a of the first embodiment.

[0074] As described above, in the second embodiment, the second catalyst 42 is provided at the upstream end 134a of the chamber outlet pipe 134, and is disposed so as to face the expansion space SP inside the exhaust chamber 32. In addition, the axis AX2 of the chamber outlet pipe 134 is inclined with respect to the partition wall 50. The chamber outlet pipe 134 passes through the intake chamber 32, and is connected to the upstream end 36a of the connecting pipe 36 at the downstream end 134b.

[0075] The axis AX2 of the chamber outlet pipe 134 is misaligned with the axis AX3 of the communicating hole 56. Specifically, the axis AX2 of the chamber outlet pipe 134 and the axis AX3 of the communicating hole 56 are separated from each other when viewed in a cross section in the flow direction. In addition, the axis AX2 of the chamber outlet pipe 134 and the axis AX3 of the communicating hole 56 are not parallel to each other.

[0076] Next, the flow of exhaust gas G in the exhaust device ED of the second embodiment will be described. The flow is the same as in the first embodiment until it is discharged from the catalyst tube 28. The exhaust gas G discharged from the catalyst tube 28 flows into the chamber inlet tube 130. The exhaust gas G that flows into the chamber inlet tube 130 passes through the main body 30c of the chamber inlet tube 30, and then flows out from the downstream end 30b into the first expansion chamber 52 of the exhaust chamber 32, where it expands. When passing through the main body 30c, the second exhaust gas sensor 46 detects the oxygen concentration in the exhaust gas.

[0077] The exhaust gas G that flows out into the first expansion chamber 52 collides with the partition wall 50 and is diffused. The exhaust gas G in the first expansion chamber 52 flows into the second expansion chamber 54 through the communication hole 56 and expands. By repeating expansion and contraction in this manner, the exhaust gas G is silenced.

[0078] The exhaust gas G in the second expansion chamber 54 flows into the upstream end 134a of the chamber outlet pipe 134. The exhaust gas G that flows into the upstream end 134a of the chamber outlet pipe 134 passes through the second catalyst 42 and is purified. In addition, a portion G1 of the exhaust gas G that has passed through the second catalyst 42 is returned to the second expansion chamber 54 by exhaust pulsation. The exhaust gas G that has passed through the second catalyst 42 passes through the chamber outlet pipe 134 and is discharged from the exhaust chamber 32. After being discharged from the exhaust chamber 32, the process is the same as in the first embodiment.

[0079] According to the second embodiment, similarly to the first embodiment, the exhaust gases G, G1 in the expansion space SP enter and exit the second catalyst 42 in response to the exhaust pulsation. In this manner, the number of times the exhaust gas G comes into contact with the second catalyst 42 can be increased due to the exhaust pulsation. In other words, the exhaust gas G after diffusing into the expansion space SP is guided to the second catalyst 42, so that the amount of the exhaust gases G, G1 that comes into contact with the second catalyst 42 increases. This makes it possible to improve purification performance even if the catalyst loading amount is small.

[0080] 6 shows a main part of an exhaust device ED according to a third embodiment of the present disclosure. In the third embodiment, a chamber inlet pipe 58 extends rearward through the internal space of the exhaust chamber 32, penetrates the partition wall 50, and opens into the expansion space SP inside the exhaust chamber 32. That is, in the third embodiment, a first expansion chamber 52 is formed behind the partition wall 50, and a second expansion chamber 54 is formed in front of the partition wall 50. A communication hole 56 that communicates between the first expansion chamber 52 and the second expansion chamber 54 is formed in the partition wall 50.

[0081] An auxiliary catalyst pipe 60, inside which the second catalyst 42 is housed, is disposed so as to penetrate the partition wall 50. That is, the upstream end 60a of the auxiliary catalyst pipe 60 in the flow direction of the exhaust gas G is located in the second expansion chamber 54, and the downstream end 60b is located in the first expansion chamber 52. The upstream end 60a of the auxiliary catalyst pipe 60 opens into the second expansion chamber 54.

[0082] An upstream end 60a of the auxiliary catalyst pipe 60 is joined to the partition wall 50 by welding. In detail, the upstream end 60a of the auxiliary catalyst pipe 60 is supported by the partition wall 50 via a first rib 62 so as to be relatively displaceable. The first rib 62 is formed by bending a metal plate into a U-shaped cross section, and is joined to the partition wall 50 at a bottom 60a of the U-shape and to the auxiliary catalyst pipe 60 at branch portions 60b, 60b. The difference in thermal expansion between the auxiliary catalyst pipe 60 and the partition wall 50 is absorbed by the elastic deformation of the first rib 62 made of metal plate.

[0083] The downstream end 60b of the auxiliary catalyst pipe 60 is connected to the upstream end 66a of the chamber outlet pipe 66 via the connecting pipe 64. In detail, the upstream end 64a of the connecting pipe 64 is joined to the downstream end 60b of the auxiliary catalyst pipe 60 by welding, and the downstream end 64b of the connecting pipe 64 is joined to the upstream end 66a of the chamber outlet pipe 66 by welding. The chamber outlet pipe 66 in this embodiment is made of a straight pipe, and is supported by the exhaust chamber 32 at its middle part 66b, and is connected to the connecting pipe 36 outside the expansion space SP at its downstream end 66c.

[0084] In this manner, the auxiliary catalyst pipe 60 accommodating the second catalyst 42 has its upstream end 60a supported by the partition wall 50, and its downstream end 60b supported in the exhaust chamber 32 via the connecting pipe 64 and the chamber outlet pipe 66. In other words, the auxiliary catalyst pipe 60 is supported in the exhaust chamber 32 at both ends 60a, 60b.

[0085] In the third embodiment, the auxiliary catalyst pipe 60, the connecting pipe 64 and the chamber outlet pipe 66 form "a communicating pipe connected to the case body (exhaust chamber) 32, one end (downstream end) of which is open to the outside of the expansion space SP and the other end (upstream end) of which opens into the expansion space SP, and in which the second catalyst 42 is disposed at the other end (upstream end)."

[0086] In this embodiment, the auxiliary catalyst pipe 60 is arranged such that the axis AX4 of the auxiliary catalyst pipe 60 is bent with respect to the axis AX2 of the chamber outlet pipe 66. That is, in this embodiment, the connecting pipe 64 is configured as a curved pipe. This improves the degree of freedom in arranging the auxiliary catalyst pipe 60, making it easier to ensure the volume of the second catalyst 42. The other configurations of the third embodiment are the same as those of the first and second embodiments.

[0087] According to the third embodiment, similarly to the first and second embodiments, the exhaust gases G, G1 in the expansion space SP enter and exit the second catalyst 42 in response to the exhaust pulsation. In this manner, the number of times the exhaust gas G comes into contact with the second catalyst 42 due to the exhaust pulsation can be increased. In other words, the exhaust gas G after diffusing into the expansion space SP is guided to the second catalyst 42, so that the amount of the exhaust gases G, G1 that comes into contact with the second catalyst 42 increases. This makes it possible to improve purification performance even if the catalyst loading amount is small.

[0088] In the above embodiment, oxygen sensors that detect the oxygen concentration in the exhaust gas are used as the exhaust gas sensors 44, 46, but the present invention is not limited to this and may be, for example, temperature sensors that detect the temperature of the exhaust gas.

[0089] The exhaust system of the present disclosure can be applied to engines other than four-cylinder engines, and can also be applied to single-cylinder engines. In the above embodiment, the catalyst 40 is disposed downstream of the collecting pipe 26, but a catalyst may be provided for each cylinder of a multi-cylinder engine. In this case, the collecting pipe 26 does not need to be provided.

[0090] The positions of the exhaust chamber 32 and the exhaust muffler 38 are not limited to those in the embodiment. For example, the exhaust muffler 38 may be disposed on both sides of the rear wheel 38 in the vehicle width direction, or may be disposed above the rear wheel. In addition, the shape of the exhaust chamber 32 is not limited to that in the above embodiment as long as an expansion space is secured.

[0091] The catalyst material is not limited to the above embodiment, and various materials can be used. That is, the catalyst material may be a material other than the platinum group metals described above. The fuel for the engine E may be a material other than gasoline, and may contain ethanol or may be hydrogen.

[0092] The vehicle on which the exhaust system of the present disclosure is mounted may be, but is not limited to, a relatively small saddle-type vehicle in which a driver straddles a seat. For example, the vehicle may be applied to a four-wheeled vehicle in which passengers ride side-by-side in the width direction. The exhaust system of the present disclosure may also be applied to a hybrid vehicle having an internal combustion engine and an electric motor.

[0093] The present disclosure includes the following exhaust devices according to embodiments 1 to 8 and a vehicle according to embodiment 9. [Aspect 1] An exhaust device that configures an exhaust passage through which exhaust gas from an engine flows, purifies the exhaust gas, and discharges the exhaust gas to the outside, a case body that defines an expansion space in the exhaust passage for expanding the exhaust gas; a communication pipe connected to the case body, the communication pipe having one end open to the outside of the expansion space and the other end open to the expansion space; a first catalyst disposed upstream of the expansion space in the exhaust passage; a second catalyst disposed in the communicating pipe and facing the expansion space. [Aspect 2] In the exhaust system according to the first aspect, the second catalyst is provided at one end of the communication pipe, an expansion space adjacent to the communicating pipe, the diameter perpendicular to the exhaust flow direction being larger than the diameter of the one end of the communicating pipe; [Aspect 3] 3. The exhaust system according to claim 1, wherein the second catalyst is set to have a purification performance lower than that of the first catalyst. [Aspect 4] The exhaust device according to any one of aspects 1 to 3, further comprising a partition wall disposed inside the case body and dividing the expansion space into a plurality of expansion chambers; An exhaust device, wherein an axis of the communication pipe is inclined with respect to the partition wall. [Aspect 5] The exhaust device according to any one of aspects 1 to 4, further comprising a partition wall disposed inside the case body and dividing the expansion space into a plurality of expansion chambers; A communication hole that communicates with adjacent expansion chambers is formed in the partition wall, The communication pipe opens toward a portion of the partition wall spaced apart from the communication hole. [Aspect 6] In the exhaust system according to any one of aspects 1 to 5, the communication pipe is an inlet pipe having a downstream end that opens into the expansion space, The second catalyst is disposed at the downstream end of the inlet pipe; The second catalyst has a smaller diameter than the first catalyst, An exhaust device in which a reduced diameter portion where a pipe line is reduced in diameter is formed between the first catalyst and the second catalyst. [Aspect 7] In the exhaust device according to any one of aspects 1 to 7, the case body has a divided structure formed by joining a plurality of divided bodies, an exhaust system, wherein a pipe in which the second catalyst is disposed is fitted into the joint of the split body; [Aspect 8] The exhaust system of any one of the first to seventh aspects, further comprising: a first exhaust gas sensor disposed upstream of the first catalyst in the exhaust passage and configured to detect a state of the exhaust gas flowing through the exhaust passage; an exhaust gas sensor disposed in the exhaust passage downstream of the first catalyst and upstream of the second catalyst for detecting a state of the exhaust gas flowing through the exhaust passage; [Aspect 9] A vehicle comprising an exhaust system according to any one of the preceding embodiments.

[0094] The present disclosure is not limited to the above-described embodiments, and various additions, modifications, and deletions are possible without departing from the scope of the present disclosure. For example, therefore, such modifications are also included in the scope of the present disclosure. [Explanation of symbols]

[0095] 30 Chamber inlet pipe (connecting pipe) 30c Main body (small diameter part) 32 Exhaust chamber (case body) 32a 1st division body 32b Second division body 32c joint 40 First Catalyst 42 Second catalyst 44 First exhaust gas sensor 46 Second exhaust gas sensor 50 Partition Wall 56 Communication hole 60 Sub-catalyst pipe (communication pipe) 64 Connecting pipe (communicating pipe) 66 Chamber outlet pipe (communicating pipe) 134 Chamber outlet pipe (connecting pipe) AX1 Axis of chamber inlet pipe (connecting pipe) E-Engine ED exhaust system G. Exhaust gas EP exhaust passage SP Expansion Space

Claims

1. An exhaust device that configures an exhaust passage through which exhaust gas from an engine flows, purifies the exhaust gas, and discharges the exhaust gas to the outside, a case body that defines an expansion space in the exhaust passage for expanding the exhaust gas; a communication pipe connected to the case body, the communication pipe having one end open to the outside of the expansion space and the other end open to the expansion space; a first catalyst disposed upstream of the expansion space in the exhaust passage; a second catalyst disposed in the communication pipe and facing the expansion space.

2. 2. The exhaust system according to claim 1, wherein the second catalyst is provided at one end of the communication pipe, an expansion space adjacent to the communicating pipe, the diameter perpendicular to the exhaust flow direction being larger than the diameter of the one end of the communicating pipe;

3. 3. The exhaust system according to claim 1, wherein the second catalyst is set to have a purification performance lower than that of the first catalyst.

4. 3. The exhaust device according to claim 1, further comprising a partition wall disposed inside the case body and dividing the expansion space into a plurality of expansion chambers, An exhaust device, wherein an axis of the communication pipe is inclined with respect to the partition wall.

5. 3. The exhaust device according to claim 1, further comprising a partition wall disposed inside the case body and dividing the expansion space into a plurality of expansion chambers, A communication hole that communicates with adjacent expansion chambers is formed in the partition wall, The communication pipe opens toward a portion of the partition wall spaced apart from the communication hole.

6. 3. The exhaust system according to claim 1, wherein the communication pipe is an inlet pipe having a downstream end that opens into the expansion space, The second catalyst is disposed at a downstream end of the inlet pipe; The second catalyst has a smaller diameter than the first catalyst, An exhaust system comprising: a reduced diameter portion where a pipe line is reduced in diameter, between the first catalyst and the second catalyst.

7. 3. The exhaust system according to claim 1, wherein the case body has a split structure formed by joining a plurality of split bodies, an exhaust system, wherein a pipe in which the second catalyst is disposed is fitted into the joint of the split body;

8. The exhaust system according to claim 1 or 2, further comprising: a first exhaust gas sensor disposed upstream of the first catalyst in the exhaust passage and configured to detect a state of the exhaust gas flowing through the exhaust passage; an exhaust gas sensor disposed in the exhaust passage downstream of the first catalyst and upstream of the second catalyst for detecting a state of the exhaust gas flowing through the exhaust passage;

9. A vehicle equipped with an exhaust system according to claim 1 or 2.

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