JP4400320B2 - Exhaust device for multi-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust device for a multi-cylinder internal combustion engine that performs exhaust purification using a catalytic converter, and in particular, immediately after a cold start when the main catalytic converter is not activated, guides exhaust to the bypass channel side provided with another catalytic converter. The present invention relates to an improvement of an exhaust device of the type.

  As conventionally known, in a configuration in which the main catalytic converter is disposed relatively downstream of the exhaust system such as under the floor of a vehicle, the temperature of the catalytic converter rises and is activated after a cold start of the internal combustion engine. In the meantime, a sufficient exhaust purification action cannot be expected. 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 1, a bypass flow path is provided in parallel with the upstream portion of the main flow path including the main catalytic converter, and another bypass catalytic converter is interposed in the bypass flow path. However, an exhaust device has been conventionally proposed in which exhaust gas is guided to the bypass flow path side immediately after the cold start by a switching valve for switching between the two. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust purification can be started from an earlier stage. it can.
JP-A-5-321644

  In the conventional exhaust apparatus, the bypass flow path branches off from the main flow path on the downstream side of the junction of the exhaust manifold. That is, in the multi-cylinder internal combustion engine, the main flow path and the bypass flow path are arranged in parallel at the downstream side of the junction where the exhaust flow paths of the cylinders merge into one flow path. ing. Therefore, although the bypass catalytic converter interposed in the bypass flow path is located upstream from the main catalytic converter, the distance from the exhaust port of each cylinder is considerably large, and exhaust purification can be started immediately after starting. Can not.

  In addition, since it branches to the bypass flow path downstream of the exhaust manifold, the temperature of the exhaust gas flowing into the bypass flow path is lowered by the heat capacity of the exhaust manifold, which is a large part, and the exhaust purification by the bypass catalytic converter is started accordingly. Will be delayed.

  In particular, recent exhaust manifolds are designed in consideration of avoidance of exhaust interference. For example, in an in-line four-cylinder engine, the so-called “four-two-one-one” type is the # 1, # 4 cylinder. Then, after the # 2 and # 3 cylinders are assembled together, the two are assembled into one, and therefore the distance to the confluence that becomes one flow path tends to be longer. Therefore, the position of the bypass catalytic converter is necessarily downstream. As the shape of the exhaust manifold becomes complicated, the heat capacity of the exhaust manifold described above becomes even larger.

The exhaust system for a multi-cylinder internal combustion engine according to the present invention includes, as a main flow path, an upstream main passage for each cylinder connected to each cylinder of the four-cylinder internal combustion engine, and a plurality of upstream main passages. A downstream main passage joined to the flow path, and a main catalytic converter interposed in the middle of the downstream main passage. Further, as the bypass flow path, there are an upstream bypass path for each cylinder branching from the upstream portion of the upstream main path and having a smaller cross-sectional area than the upstream main path, and the plurality of upstream bypass paths. A downstream bypass passage that merges into one flow path, and a bypass catalytic converter interposed in the middle of the downstream bypass passage. The downstream end of the downstream bypass passage is connected to the downstream main passage at a position upstream of the main catalytic converter. And the flow path switching means which opens and closes the said upstream main channel | path side so that the exhaust_gas | exhaustion discharged | emitted from each cylinder may flow into the said upstream bypass channel | path is provided.
The flow path switching means includes a switching valve provided at a merging portion of a plurality of upstream main passages, and is arranged such that the upstream main passages of the respective cylinders are respectively located at the quadrangle vertex positions in the merging portion. In addition, the switching valve has valve bodies supported by two rotatable shafts positioned on both sides of the square, and the upstream main passages are not in communication with each other when the switching valve is closed. It becomes.

  The exhaust system of the present invention includes the same number of upstream bypass passages as the number of cylinders, and branches from the main flow path, that is, the upstream main path, at a position upstream from the junction of the main flow paths. Therefore, the bypass catalytic converter can be arranged on the upstream side without being restricted by the position of the confluence of the main flow path. Further, since the point branching to the bypass flow path side is a position close to each cylinder, the exhaust flows into the bypass flow path side relatively without being cooled by the heat capacity of the main flow path 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.

  In one aspect, in the multi-cylinder, the upstream bypass passages of two cylinders adjacent to each other are joined together as intermediate bypass passages, and a plurality of intermediate bypass passages are joined as the downstream bypass passages. Will be. In this case, the entire passage length to the bypass catalytic converter (the sum of the bypass passages of each cylinder) can be shorter than that in which a plurality of upstream bypass passages are assembled at one point immediately before the bypass catalytic converter.

  On the other hand, for the main flow path, a piping layout considering the avoidance of exhaust interference is possible. For example, in one aspect, in the multi-cylinder, the upstream main passages of two cylinders in which the exhaust stroke is not continuous are joined together as intermediate main passages, and a plurality of intermediate main passages are used as the downstream main passages. Have joined.

  Specifically, in the case of an in-line four-cylinder internal combustion engine, desirably, as a main flow path, an intermediate main path formed by joining the upstream main paths of the # 1 and # 4 cylinders and an upstream of the # 2 and # 3 cylinders An intermediate main passage formed by joining the main main passages, and the two intermediate main passages merge into one as the downstream main passage. As the bypass flow path, the upstream bypass passages of the # 1 and # 2 cylinders merge as intermediate bypass passages, and the upstream bypass passages of the # 3 and # 4 cylinders merge as intermediate bypass passages. The intermediate bypass passage merges as one downstream bypass passage. In other words, the main flow path has a piping layout that considers avoidance of exhaust interference, while the bypass flow path has a piping layout that minimizes the total path length to the bypass catalytic converter rather than avoiding exhaust interference. ing.

  The upstream bypass passage can be branched as a passage inside the cylinder head from an exhaust port of each cylinder forming a part of the upstream main passage. Alternatively, each of the branch portions of the exhaust manifold connected to the exhaust port of the cylinder head can be branched from the upstream main passage.

If the switching valve serving as the flow path switching unit is closed, the exhaust gas flows from the upstream bypass passage to the bypass catalytic converter. When the switching valve is opened, the bypass cross-sectional area is small on the bypass flow path side and a bypass catalytic converter is interposed. Does not flow.

Then, in the present invention, the closing of the switching valve, the upstream main passageway ing and Hiren communication with each other. If the upstream main passages are in communication with each other when the switching valve is in the closed state, the exhaust strokes sequentially arrive at each cylinder. Therefore, the upstream main passages of the other cylinders from the upstream main passage of one cylinder. A phenomenon occurs in which the exhaust gas flows into the passage. Therefore, heat easily escapes to the outside, and the temperature rise of the bypass catalytic converter is hindered. Even when the switching valve is arranged at the junction, this wraparound phenomenon can be avoided by making the upstream main passages out of communication with each other when the switching valve is closed.

  The upstream bypass passage is desirably set to have a small passage cross-sectional area so that exhaust interference caused by the communication of a plurality of cylinders is below a predetermined level. On the other hand, if the passage cross-sectional area of the upstream bypass passage is excessively small, for example, it becomes impossible to secure a required flow rate during operation immediately after the cold start, so it is desirable to set the passage cross-sectional area in consideration of both.

  According to the present invention, it is possible to dispose the bypass catalytic converter more upstream, that is, at a position close to each cylinder, without being restricted by the position of the confluence of the main flow path that is generally configured as an exhaust manifold. Since the cooling action due to the heat capacity of the exhaust manifold or the like constituting the flow path is reduced, the exhaust purification action can be obtained early after the cold start.

  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 flow path has a piping layout that is gathered in the 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 is branched 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.

  In the present invention, a configuration in which the four upstream bypass passages 11 are assembled as one downstream bypass passage 16 immediately before the bypass catalytic converter 18 without being assembled as the intermediate bypass passage 14 is also possible. When the position of the branch point 12 and the position of the bypass catalytic converter 18 are compared with each other, the two intermediate bypasses on the upstream side as in the above embodiment, rather than the four upstream bypass passages 11 being routed longer. When the passages are grouped together, the overall passage length (the sum of the bypass passages of each cylinder) becomes shorter, and the heat capacity of the piping itself and the heat radiation area for the outside air become smaller.

  The bypass catalytic converter 18 includes two monolith catalyst carriers, that is, a first catalyst 18a and a second catalyst 18b, which are divided in the front and rear directions. 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, at the stage where 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 flow path 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. Further, 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, it proceeds warm-up of the engine, when the engine temperature or exhaust temperature becomes sufficiently high, the switching valve 4 is released to open. Thus, 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 flow path side is not particularly shut off, but the bypass flow path side has a smaller passage cross-sectional area than the main flow path side, and the bypass catalytic converter 18 is interposed. Most of the exhaust flow passes through the main flow path side and hardly flows into the bypass flow path side. Therefore, the thermal deterioration of the bypass catalytic converter 18 is sufficiently suppressed. In addition, since the bypass flow path side is not completely blocked, a part of the exhaust flow flows through the bypass flow path side at a high speed and high load where the exhaust flow rate becomes large, so that a reduction in charging efficiency due to back pressure can be avoided.

  Further, as described above, the main flow path side has a “4-2-1” piping layout in consideration of avoidance of exhaust interference, so that it is possible to obtain an effect of improving the filling efficiency by the exhaust dynamic effect. Here, the bypass channel side communicates and aggregates in a manner that does not particularly consider exhaust interference avoidance, but by making the cross-sectional area of the upstream bypass passage 11 sufficiently small, exhaust by communication of each cylinder is achieved. Interference can be reduced to a level that is substantially negligible. If the passage 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, and conversely if smaller than a certain lower limit dimension, the switching valve 4 is in the closed state. 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.

  Furthermore, 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 bypass catalytic converter 18. At this time, even if part of the exhaust gas flows from the downstream main passage 7 to the exhaust gas recirculation passage 20 so as to flow backward through the downstream bypass passage 16, it is taken out from the exhaust gas recirculation passage 20 to the intake system. Since the recirculated exhaust gas becomes clean exhaust gas after passing through the second catalyst 18b, deposits and fouling in the exhaust recirculation control valve and the intake system are also prevented. In addition, since the flow speed when the second catalyst 18b flows back in this way is relatively slow and the residence time (passing time) in the second catalyst 18b becomes longer, as shown in the figure, the second catalyst 18b The axial length can be set shorter than the axial length of the first catalyst 18a.

  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 flow path are disposed in a space below the main flow path 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 opened and closed simultaneously. 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 configurations can be used. From the viewpoint of reducing the heat capacity that hinders the exhaust gas temperature increase immediately after the cold start, it is desirable that the switching valve 4 is located as upstream as possible.
Note that FIG. 7 is not a merging unit, each of the upstream main path 2 of four shows a reference example in which a switching valve 4 for opening and closing the respective upstream main passageways 2 individually.

  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 keeping the exhaust temperature higher.

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 reference 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 channel of this Example.

Explanation of symbols

2 ... Upstream side main passage 3 ... Intermediate main passage 4 ... Switching valve 8 ... Main catalytic converter 11 ... Upstream side bypass passage 14 ... Intermediate bypass passage 16 ... Downstream side bypass passage 18 ... Bypass catalytic converter

Claims (8)

An upstream main passage for each cylinder connected to each cylinder of a four-cylinder internal combustion engine ;
A plurality of upstream main passages joined together into one flow passage;
A main catalytic converter interposed in the middle of the downstream main passage;
An upstream bypass passage for each cylinder branching from the upstream portion of the upstream main passage and having a smaller sectional area than the upstream main passage;
A plurality of upstream bypass passages merged into one flow path, and a downstream end of which a downstream end is connected to the downstream main passage at a position upstream of the main catalytic converter;
A bypass catalytic converter interposed in the middle of the downstream bypass passage;
A switching valve provided at a merging portion of the plurality of upstream main passages as a passage switching means for opening and closing the upstream main passage side so that the exhaust discharged from each cylinder flows to the upstream bypass passage;
Equipped with a,
The upstream main passages of the cylinders are arranged at the apex positions of the quadrilaterals at the junction, and the switching valves are respectively supported by two rotatable shafts located on both sides of the quadrilateral. An exhaust system for a multi-cylinder internal combustion engine , wherein the upstream main passages are not in communication with each other when the switching valve is closed .   In the multi-cylinder, the upstream bypass passages of two cylinders adjacent to each other are joined together as intermediate bypass passages, and further, the plurality of intermediate bypass passages are joined as the downstream bypass passages. The exhaust device for a multi-cylinder internal combustion engine according to claim 1, wherein the exhaust device is a multi-cylinder internal combustion engine.   In the multi-cylinder, the upstream main passages of two cylinders whose exhaust strokes are not continuous are joined together as intermediate main passages, and a plurality of intermediate main passages are joined as the downstream main passages. The exhaust system for a multi-cylinder internal combustion engine according to claim 1 or 2, wherein the exhaust system is a multi-cylinder internal combustion engine. An intermediate main passage formed by joining the upstream main passages of the # 1 and # 4 cylinders, and an intermediate main passage formed by joining the upstream main passages of the # 2 and # 3 cylinders. An exhaust system used in an in-line four-cylinder internal combustion engine in which a main passage is joined as one downstream main passage,
The upstream bypass passages of the # 1 and # 2 cylinders merge as intermediate bypass passages, and the upstream bypass passages of the # 3 and # 4 cylinders merge as intermediate bypass passages, and these two intermediate bypass passages are downstream bypasses 2. The exhaust system for a multi-cylinder internal combustion engine according to claim 1, wherein the passages merge into one passage.   5. The multi-passage according to claim 1, wherein the upstream bypass passage branches off from an exhaust port of each cylinder forming a part of the upstream main passage as a passage inside the cylinder head. Exhaust device for cylinder internal combustion engine.   5. The upstream bypass passage is branched from the upstream main passage at each branch portion of an exhaust manifold connected to an exhaust port of a cylinder head. Exhaust device for multi-cylinder internal combustion engine.   2. The upstream bypass passage branches off at a branch portion between the upstream main passage and the upstream bypass passage of each cylinder so as to form an acute angle with respect to the flow of the upstream main passage. The exhaust device for a multi-cylinder internal combustion engine according to any one of claims 6 to 10. The upstream bypass passage, so that the exhaust interference due to the plurality of cylinders are communicated becomes a predetermined level or less, according to any one of claims 1 to 7, characterized in that the cross-sectional area is set smaller Exhaust system for multi-cylinder internal combustion engine.

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