JP4385874B2 - Exhaust device for internal combustion engine - Google Patents

Description

  The present invention provides an exhaust system for an internal combustion engine that includes a catalytic converter for purifying exhaust gas and an exhaust gas recirculation passage that recirculates part of the exhaust gas to the intake system, and in particular, a main passage and a bypass passage are provided in parallel. The present invention relates to an improvement of an exhaust system in which a catalytic converter is interposed on the bypass passage side.

  An exhaust gas recirculation device that recirculates part of the exhaust gas to the intake system is widely known for improving the fuel consumption of the internal combustion engine and reducing NOx. However, the exhaust gas contains foreign matters, unburned fuel components, and the like. Therefore, there is a problem that these adhere to and accumulate on the exhaust gas recirculation passage, intake system parts, etc., resulting in fouling and clogging.

  On the other hand, in Patent Document 1, an exhaust gas recirculation passage is connected to a downstream position of an upstream catalytic converter in which exhaust of some cylinders is guided, and exhaust gas after removing HC by the catalytic converter is taken as an intake system A configuration for refluxing is disclosed. According to this configuration, foreign matters and unburned components in the exhaust are removed in advance by the catalytic converter, and contamination of the exhaust gas recirculation control valve and the like is suppressed.

  On the other hand, in recent years, there has been a strong demand for an improvement in the exhaust composition immediately after the start of the internal combustion engine. However, as conventionally known, a configuration in which a catalytic converter is disposed on the relatively downstream side of the exhaust system such as under the floor of a vehicle Then, after the cold start of the internal combustion engine, sufficient exhaust purification action cannot be expected until the temperature of the catalytic converter rises and is activated. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

Therefore, as disclosed in Patent Document 2, a bypass passage is provided in parallel with the upstream portion of the main passage, and a catalytic converter is interposed in the bypass passage, and the flow of exhaust gas is switched by a switching valve. Immediately after the cold start, exhaust is guided to the bypass passage side to activate the catalyst at an early stage, exhaust purification is started from an early stage, and after warm-up is completed, the exhaust is guided to the main passage side to Conventionally, an exhaust device that suppresses an excessive temperature rise of the converter has been proposed. In this case, the second catalytic converter (main catalytic converter) is generally provided further downstream of the main passage.
Japanese Patent Laid-Open No. 10-317950 JP-A-5-321644

  In the configuration in which the main passage is provided in parallel with the bypass passage having the catalytic converter as in Patent Literature 2, if the exhaust gas recirculation passage is connected to the downstream position of the catalytic converter in accordance with the teaching of Patent Literature 1, Exhaust gas flowing in the forward direction passes through the catalytic converter and then travels to the exhaust gas recirculation passage. For example, in a situation where the exhaust mainly flows through the main passage side by a switching valve, the main exhaust downstream of the bypass passage The exhaust gas flows backward from the main passage to the bypass passage via the junction with the passage and flows into the exhaust gas recirculation passage as it is. That is, the exhaust gas is taken into the exhaust gas recirculation passage without passing through the catalytic converter. Therefore, it is not possible to completely prevent the intake system parts from being contaminated or clogged by foreign matters or unburned fuel components in the exhaust.

  An exhaust system for an internal combustion engine according to the present invention includes a main passage through which exhaust exhausted from the internal combustion engine flows, a branch from the main passage on the upstream side so as to bypass a part of the main passage, and a downstream side. A bypass passage that merges with the main passage, and a first catalyst and a second catalyst that are arranged in series as a catalytic converter are interposed in the bypass passage. One end of an exhaust gas recirculation passage that guides the recirculated exhaust gas to the intake system is connected between the first catalyst and the second catalyst.

  Preferably, flow path switching means for switching the flow of exhaust gas between the main passage side and the bypass passage side is provided. As the flow path switching means, various types such as one that selectively opens one of the passages at the branching portion or the merge portion, and one that opens and closes one of the passages in the middle of the passage are possible. In one preferred embodiment, the flow path switching means comprises a switching valve that opens and closes the main passage in a portion of the main passage that is parallel to the bypass passage. In this case, if the switching valve is closed, the exhaust flows only through the bypass passage and passes through the first catalyst and the second catalyst. At this time, the exhaust gas after passing through the first catalyst is introduced into the exhaust gas recirculation passage. In the state where the switching valve is opened, due to the difference in passage resistance, the exhaust mainly flows on the main passage side, and the exhaust hardly flows on the bypass passage side. At this time, the exhaust gas flowing through the main passage flows back into the bypass passage from the downstream junction to the bypass passage, and the exhaust gas that has flowed back passes through the second catalyst on the downstream side. And then flows into the exhaust gas recirculation passage.

  That is, regardless of the direction of flow in the bypass passage, the exhaust gas from which foreign matters and the like after passing through the catalyst are removed is introduced into the exhaust gas recirculation passage.

  Although the first catalyst and the second catalyst can be configured as two catalytic converters having individually independent casings, in one embodiment, the first catalyst and the second catalyst are respectively separate monoliths. Both are made of a catalyst carrier and are accommodated in one casing. That is, it can be configured as a substantially single catalytic converter. Such integration is advantageous in reducing the heat capacity that affects early activation.

  Preferably, the capacity of the second catalyst located on the downstream side is set smaller than the capacity of the first catalyst located on the upstream side.

  Alternatively, the axial length of the second catalyst located on the downstream side is set shorter than the axial length of the first catalyst located on the upstream side.

  That is, paying attention to the flow of exhaust gas taken into the exhaust gas recirculation passage, when the exhaust main flow flows in the forward direction in the bypass passage, it passes through the first catalyst at a relatively high speed. Compared to this, when the exhaust gas flows back to the exhaust gas recirculation passage from the downstream junction of the main passage to the bypass passage as described above, the speed of the exhaust gas flowing backward through the second catalyst is relatively high. Very late. As a result, the residence time (passage time) in the second catalyst becomes longer, so the axial length of the second catalyst can be set shorter than the axial length of the first catalyst. The capacity can be made smaller than the capacity of the first catalyst.

  In one specific aspect of the present invention, the main passage includes an upstream main passage for each cylinder connected to each cylinder, and the plurality of upstream main passages merge into one flow passage. An upstream bypass passage for each cylinder that branches from the upstream portion of the upstream main passage and has a smaller sectional area than the upstream main passage. And a plurality of upstream bypass passages merged into one flow path, and a downstream bypass passage having a downstream end connected to the downstream main passage, and the first catalyst and the first Two catalysts are interposed in the downstream bypass passage.

  Such an exhaust device includes the same number of upstream bypass passages as the number of cylinders, and branches from the upstream main passage at a position upstream of the merging point of the upstream main passage. Therefore, it is possible to dispose the first and second catalysts serving as bypass catalytic converters on the upstream side without being restricted by the position of the confluence of the main passages of the plurality of cylinders. Further, since the point branching to the bypass passage side is a position close to each cylinder, the exhaust flows into the bypass passage side relatively without being cooled by the heat capacity of the main passage immediately after cold start.

  Since the upstream bypass passage finally joins one downstream bypass passage, there is a concern about exhaust interference, but by setting the passage cross-sectional area of the upstream bypass passage sufficiently small, the pipe layout (each Regardless of the cylinder's exhaust flow aggregate layout), it is possible to suppress the exhaust interference to a level that does not impede practical use. In other words, it is possible to have a piping layout that minimizes the length of the passage to the bypass catalytic converter without being restricted by the point of exhaust interference.

  According to the present invention, in the configuration including the main passage and the bypass passage that are parallel to each other, the exhaust after passing through the catalyst can be taken out to the exhaust gas recirculation passage regardless of which passage the exhaust main flow passes through. This makes it possible to avoid foreign matters in the exhaust gas and unburned fuel components from flowing into the exhaust gas recirculation passage. Therefore, it is possible to completely prevent the intake system parts from being contaminated or clogged by foreign matters or unburned fuel components in the exhaust gas.

  Hereinafter, an embodiment in which the present invention is applied as an exhaust system for an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view schematically showing the piping layout of the exhaust device. First, the configuration of the entire exhaust device will be described with reference to FIG.

  An upstream main passage 2 is connected to each cylinder 1 including # 1 cylinder to # 4 cylinder arranged in series. Among the four cylinders, the upstream main passage 2 of the # 1 cylinder and the upstream main passage 2 of the # 4 cylinder where the exhaust stroke is not continuous merge as one intermediate main passage 3, and the exhaust stroke is similarly performed. The upstream main passage 2 of the # 2 cylinder and the upstream main passage 2 of the # 3 cylinder are joined together as one intermediate main passage 3. Here, a switching valve 4 is provided at each junction where the two upstream main passages 2 join each other. The switching valve 4 is closed when it is cold. When the switching valve 4 is closed, the upper and lower communication between the upstream main passage 2 and the intermediate main passage 3 is blocked and the two upstream main passages 2 are connected. It is the structure which makes a communication state non-communication between. A pair of switching valve 4 is comprised as one valve unit 5 so that it may mention later. The two intermediate main passages 3 positioned downstream of the valve unit 5 merge with each other at a junction 6 to form one downstream main passage 7. A main catalytic converter 8 is interposed in the middle of the downstream main passage 7. The catalyst in the main catalytic converter 8 includes a three-way catalyst and an HC trap catalyst. The main catalytic converter 8 has a large capacity arranged under the floor of the vehicle. The upstream main passage 2, the intermediate main passage 3, the downstream main passage 7, and the main catalytic converter 8 constitute a main passage through which exhaust flows during normal operation. This main passage has a piping layout that gathers in a well-known “4-2-1” form in an in-line four-cylinder internal combustion engine, and therefore, an improvement in charging efficiency utilizing the exhaust dynamic effect is realized.

  On the other hand, an upstream bypass passage 11 branches from each of the upstream main passages 2 as bypass passages. The upstream bypass passage 11 has a sufficiently smaller passage cross-sectional area than the upstream main passage 2, and the branch point 12 serving as the upstream end of the upstream bypass passage 11 is set at a position as upstream as possible in the upstream main passage 2. Has been. The upstream bypass passage 11 of the # 1 cylinder and the upstream bypass passage 11 of the # 2 cylinder, which are adjacent to each other, merge with each other as a single intermediate bypass passage 14 at the merge point 13. The upstream bypass passage 11 of the # 3 cylinder and the upstream bypass passage 11 of the # 4 cylinder which are adjacent to each other join each other as a single intermediate bypass passage 14 at the junction 13. In FIG. 1 schematically showing each passage, each upstream bypass passage 11 is drawn relatively long, but in practice it is as short as possible. In other words, it merges as the intermediate bypass passage 14 with the shortest distance. The two intermediate bypass passages 14 join each other as one downstream bypass passage 16 at the junction 15. The downstream end of the downstream bypass passage 16 joins the downstream main passage 7 at a junction 17 upstream of the main catalytic converter 8 in the downstream main passage 7. In the middle of the downstream bypass passage 16, a bypass catalytic converter 18 using a three-way catalyst is interposed. The bypass catalytic converter 18 is disposed as upstream as possible in the bypass flow path. That is, the intermediate bypass passage 14 is as short as possible.

  A configuration in which the four upstream bypass passages 11 are gathered as one downstream bypass passage 16 at a position immediately before the bypass catalytic converter 18 without being gathered as the intermediate bypass passage 14 is also possible. When the positions of the bypass catalytic converter 18 and the position of the bypass catalytic converter 18 are compared, the two upstream bypass passages 11 are combined into two intermediate bypass passages 14 on the upstream side as in the above-described embodiment, rather than the four upstream bypass passages 11 being routed longer. However, the overall passage length (the sum of the bypass passages of each cylinder) becomes shorter, and the heat capacity of the pipe itself and the heat radiation area for the outside air become smaller.

  The bypass catalytic converter 18 includes two catalysts divided in the front-rear direction, that is, an upstream first catalyst 18a and a downstream second catalyst 18b. These first and second catalysts 18a and 18b are both made of a cylindrical monolith catalyst carrier, and are accommodated in the same casing 18c apart from each other so that a slight gap 19 is formed in the middle. One end of the exhaust gas recirculation passage 20 is connected to the gap 19 between the first catalyst 18a and the second catalyst 18b. The other end of the exhaust gas recirculation passage 20 extends to the engine intake system via an exhaust gas recirculation control valve (not shown). That is, the gap 19 serves as a recirculation exhaust outlet. The bypass catalytic converter 18 has a small capacity as compared with the main catalytic converter 8, and a catalyst excellent in low temperature activity is desirably used.

  In the exhaust system configured as described above, when the engine temperature or the exhaust temperature after the cold start is low, the switching valve 4 is closed via an appropriate actuator, and the main passage is shut off. Therefore, the entire amount of exhaust discharged from each cylinder 1 flows from the branch point 12 to the bypass catalytic converter 18 through the upstream bypass passage 11 and the intermediate bypass passage 14. Since the bypass catalytic converter 18 is located upstream of the exhaust system, that is, close to the cylinder 1 and is small in size, the bypass catalytic converter 18 is activated quickly and exhaust purification is started at an early stage. At this time, when the switching valve 4 is closed, the upstream main passages 2 of the cylinders 1 are not in communication with each other. Therefore, a phenomenon in which the exhaust discharged from a certain cylinder wraps around the upstream main passage 2 of the other cylinder is prevented, and a decrease in the exhaust gas temperature due to this wraparound is surely avoided.

  When exhaust gas recirculation is performed with the switching valve 4 closed, the recirculated exhaust gas taken out from the exhaust gas recirculation passage 20 to the intake system is clean exhaust gas after passing through the first catalyst 18a, that is, foreign matter and unburned components. Therefore, deposits and fouling in the exhaust gas recirculation control valve and the intake system are prevented.

  On the other hand, when the warm-up of the engine proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, the switching valve 4 is released. As a result, the exhaust discharged from each cylinder 1 mainly passes from the upstream main passage 2 through the intermediate main passage 3 and the downstream main passage 7 and through the main catalytic converter 8. At this time, the bypass passage side is not particularly cut off, but the bypass passage side has a smaller passage cross-sectional area than the main passage side, and the bypass catalytic converter 18 is interposed. Most of the exhaust flow passes through the main passage side and hardly flows into the bypass passage side. Therefore, the thermal deterioration of the bypass catalytic converter 18 is sufficiently suppressed. In addition, since the bypass passage side is not completely shut off, at high speed and high load where the exhaust flow rate becomes large, a part of the exhaust flow flows through the bypass passage side, thereby avoiding a reduction in charging efficiency due to back pressure.

  Further, as described above, since the main passage side has a “4-2-1” piping layout in consideration of avoiding exhaust interference, it is possible to obtain an effect of improving the charging efficiency by the exhaust dynamic effect. Here, the bypass passage side communicates and aggregates in a manner that does not particularly consider exhaust interference avoidance. However, by making the passage cross-sectional area of the upstream bypass passage 11 sufficiently small, exhaust by the communication of each cylinder. Interference can be reduced to a level that is substantially negligible. Note that if the cross-sectional area of the upstream bypass passage 11 is larger than a certain upper limit dimension, the charging efficiency is reduced due to the exhaust interference described above. The exhaust flow rate is limited to be too small, and the operable region is excessively narrowed. Therefore, the optimum value of the passage cross-sectional area of the upstream bypass passage 11 is within a range between a predetermined upper limit dimension and a lower limit dimension corresponding to the engine displacement. As an example, in an internal combustion engine having a total displacement of about 2000 cc, good results were obtained when the equivalent diameter was in the range of 5 mm to 15 mm.

  When exhaust gas recirculation is performed under the open state of the switching valve 4, the recirculated exhaust gas is also taken out from the intermediate gap 19 of the bypass catalytic converter 18 through the exhaust gas recirculation passage 20. At this time, at least a part of the exhaust flows from the downstream main passage 7 to the exhaust gas recirculation passage 20 in such a manner as to flow back through the downstream bypass passage 16 via the junction 17. Passes through the second catalyst 18b in the reverse direction and is introduced into the exhaust gas recirculation passage 20. Accordingly, since the recirculated exhaust gas taken out from the exhaust recirculation passage 20 to the intake system becomes clean exhaust gas after passing through the second catalyst 18b, deposit adherence and contamination in the exhaust recirculation control valve and the intake system are surely prevented. Is done.

  Here, as described above, the flow rate of the second catalyst 18b when flowing backward is relatively slow, and the residence time (passing time) in the second catalyst 18b becomes longer. The axial length of 18b is set shorter than the axial length of the first catalyst 18a. With the difference in length, the capacity of the second catalyst 18b becomes smaller than the capacity of the first catalyst 18a. Therefore, the exhaust gas taken out from the exhaust gas recirculation passage 20 can be reliably purified while minimizing the capacity of the bypass catalytic converter 18 as a whole including the first and second catalysts 18a and 18b.

  FIG. 2 shows the exhaust device described above as a more specific form. An internal combustion engine 31 having a cylinder block 32 and a cylinder head 33 is mounted in a so-called horizontal arrangement in an engine room of a vehicle. An exhaust manifold 34 that mainly constitutes the upstream main passage 2 is attached to a side surface of the cylinder head 33 that is the rear of the vehicle. A valve unit 5 having a pair of switching valves 4 is attached to an outlet portion of the exhaust manifold 34, and a front tube 35 serving as a downstream main passage 7 is connected downstream thereof. A part of the upstream side of the front tube 35 is internally partitioned into two passages, that is, the intermediate main passage 3 described above. The main catalytic converter 8 is provided in the middle of the front tube 35.

  The bypass catalytic converter 18 and the like serving as a bypass passage are disposed in a space below the main passage extending from the cylinder head 33 toward the rear of the vehicle. Since the bypass catalytic converter 18 is located in the engine room and in front of the front tube 35 with respect to the vehicle traveling direction, the bypass catalytic converter 18 is effectively cooled by the traveling wind during traveling, and the bypass catalytic converter 18 is excessively cooled. Temperature rise is prevented.

  Further, the upstream bypass passage 11 is branched so as to form an acute angle with respect to the upstream main passage 2, so that when the switching valve 4 is closed, the exhaust gas smoothly flows to the bypass passage side.

  3 and 4 show a more specific embodiment of the exhaust manifold 34. FIG. 3 is a bottom view seen from below, and FIG. 4 is a top view seen from above. As shown in these drawings, the exhaust manifold 34 has four branch portions 41 to 44 that serve as the upstream main passage 2, and upstream portions of the branch portions 41 to 44 (the cylinder head mounting flanges 45 and 46. A small-diameter pipe that becomes the upstream bypass passage 11 is branched from the position immediately after). The upstream bypass passage 11 composed of the four pipes joins as the intermediate bypass passage 14 with the shortest distance as described above, and is connected to the catalytic converter mounting flange 47 at the center.

  5 and 6 show an embodiment of the valve unit 5 connected to the flange 48 at the downstream end of the exhaust manifold 34. FIG. The valve unit 5 is provided with four openings 52 to 55 to which the upstream main passage 2 of each cylinder is connected in a casing 51. In particular, the opening 52 for the # 1 cylinder and the # 4 cylinder are provided. Each opening 52 to 55 is positioned at the apex of the quadrangle in such a manner that the opening 55 for the cylinder is adjacent to each other and the opening 53 for the # 2 cylinder and the opening 54 for the # 4 cylinder are adjacent to each other. Has been placed. Each switching valve 4 includes a shaft 56 driven in the rotational direction by an actuator (not shown), an arm 57 attached to the shaft 56, and a rectangular valve body 58 supported by the arm 57. The valve body 58 of one switching valve 4 simultaneously opens and closes the two openings 52 and 55 for the # 1 and # 4 cylinders, and the valve body 58 of the other switching valve 4 is # 2, # 3. The two openings 53 and 54 for the cylinder are simultaneously opened and closed. In the state where the valve body 58 is closed, the openings 52 to 55 are individually closed over the entire circumference, so that the two adjacent openings 52, 55, 53, and 54 do not communicate with each other. A partition wall 59 is provided between the two switching valves 4 so as to partition the inside of the front tube 35 connected downstream of the valve unit 5 into two intermediate main passages 3. This partition wall 59 partitions openings 52 and 55 for # 1, # 4 cylinders and openings 53, 54 for # 2, # 3 cylinders. In FIG. 5, for the sake of explanation, one valve body 58 is shown in an open state and the other valve body 58 is shown in a closed state, but the two shafts 56 are linked by an appropriate link, Two valve bodies 58 are simultaneously opened and closed by an actuator (not shown).

  The switching valve 4 is not limited to the illustrated embodiment, and various types of configurations can be used. From the viewpoint of reducing the heat capacity that hinders an increase in exhaust gas temperature immediately after the cold start, it is desirable that the switching valve 4 is positioned as upstream as possible. Therefore, for example, as shown in FIG. 7, each of the four upstream main passages 2 may be provided with a switching valve 4 that opens and closes each upstream main passage 2. As the passage length upstream of the switching valve 4 or the passage volume is smaller, the exhaust temperature on the bypass passage side immediately after the cold start is more likely to rise.

  FIGS. 8 and 9 show an embodiment in which the bypass catalytic converter 18 is directly attached to the side surface of the cylinder head 33 so that the position of the bypass catalytic converter 18 is on the upstream side. In this embodiment, the upstream bypass passage 11 is configured as an internal passage of the cylinder head 33 and is branched from an exhaust port 61 that forms part of the upstream main passage 2 of each cylinder. In this case, in order to facilitate the formation of the upstream bypass passage 11, each upstream bypass passage 11 extends to the inlet of the bypass catalytic converter 18, and the four upstream bypass passages 11 include the bypass catalytic converter 18. It is the structure which joined at the position just before. According to such a configuration, immediately after the cold start, the exhaust catalytic converter 18 can be introduced into the bypass catalytic converter 18 while maintaining the exhaust temperature higher.

  Although one embodiment in which the present invention is applied to an in-line four-cylinder internal combustion engine has been described above, the present invention relates to various types of internal-combustion engines such as an in-line multi-cylinder internal combustion engine other than the in-line four-cylinder engine or a V-type multi-cylinder internal combustion engine. It can be applied as an exhaust device. In the above embodiment, the upstream end of the bypass passage is connected to each cylinder. However, as in Patent Document 2, one bypass passage is provided in parallel with the main passage merged into one by the exhaust manifold. In addition, as in Patent Document 2, the present invention can be similarly applied to a configuration in which the bypass passage side is closed by a switching valve when the exhaust main flow is guided to the main passage side. is there.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows one Example of the exhaust apparatus which concerns on this invention. The side view of the exhaust apparatus shown more concretely. The bottom view which shows the specific Example of an exhaust manifold. Similarly top view. Sectional drawing of the vicinity of the valve unit. The front view of a valve unit. Structure explanatory drawing which shows the Example which provided the switching valve in each of the upstream main channel | paths. Sectional drawing of the principal part of the Example which attached the bypass catalytic converter to the cylinder head. Explanatory drawing which shows the layout of the upstream bypass passage of this Example.

Explanation of symbols

2 ... Upstream main passage 3 ... Intermediate main passage 4 ... Switching valve 7 ... Downstream main passage 8 ... Main catalytic converter 11 ... Upstream bypass passage 14 ... Intermediate bypass passage 16 ... Downstream bypass passage 18 ... Bypass catalytic converter 18a ... 1st catalyst 18b ... 2nd catalyst

Claims (6)

A main passage through which exhaust gas discharged from the internal combustion engine flows;
A bypass passage branching from the main passage on the upstream side and joining the main passage on the downstream side so as to bypass a part of the main passage;
A first catalyst and a second catalyst arranged in series while being interposed in the bypass passage;
An exhaust gas recirculation passage having one end connected between the first catalyst and the second catalyst and leading the recirculated exhaust gas to the intake system;
Flow path switching means for switching the flow of exhaust gas to the main passage side and the bypass passage side;
An exhaust system for an internal combustion engine, comprising: The flow path switching means, in the portion of the main passage in parallel with the bypass passage, an exhaust system for an internal combustion engine according to claim 1, characterized in that it consists of switching valve for opening and closing the main passage. 3. The exhaust system for an internal combustion engine according to claim 1, wherein the first catalyst and the second catalyst are made of separate monolithic catalyst carriers, and both are accommodated in one casing. 4. . The main passage includes an upstream main passage for each cylinder connected to each cylinder, and a downstream main passage formed by joining the plurality of upstream main passages into one flow passage,
The bypass passage branches from the upstream portion of the upstream main passage, and has an upstream bypass passage for each cylinder having a smaller passage cross-sectional area than the upstream main passage, and one upstream bypass passage. And a downstream bypass passage having a downstream end connected to the downstream main passage,
The exhaust device for an internal combustion engine according to any one of claims 1 to 3 , wherein the first catalyst and the second catalyst are interposed in the downstream bypass passage. The exhaust system for an internal combustion engine according to any one of claims 1 to 4 , wherein a capacity of the second catalyst located on the downstream side is set smaller than a capacity of the first catalyst located on the upstream side. Internal combustion according to any one of claims 1 to 5, characterized in that the axial length of the second catalyst located downstream is set to be shorter than the axial length of the first catalyst positioned upstream Engine exhaust system.

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