JP2008031925A - Exhaust passage structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas passage structure improved in filling efficiency of suction air by reducing exhaust gas interference with a simple structure in a multiple cylinder engine. <P>SOLUTION: The exhaust gas passage structure of an exhaust gas passage in which exhaust gas discharged from each cylinder of the multiple cylinder engine is collected and flows, is provided with a deflection part 72 formed in exhaust pipes 27, 32 in which exhaust gas from a cylinder #3 in which ignition is done later in two cylinders #3, #7 of which interval of discharged exhaust gas is shortest under a condition ignition order of each cylinder #1-#8 is successive with uneven interval in a specific collection step of exhaust gas flows. Since the deflection part 72 deflects part of pressure wave of blow down pressure wave flowing reversely against a flow direction of exhaust gas, exhaust gas interference at an exhaust port 13 is inhibited, and filling efficiency of suction air in suction stroke is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust passage structure of an engine.

  In a multi-cylinder engine, the exhaust gas flowing out from one cylinder and the exhaust gas flowing out from other cylinders interfere with each other in the exhaust passage, increasing the exhaust pressure in the exhaust port and reducing the intake charging efficiency. There's a problem.

In the invention described in Patent Document 1, a flap valve is provided in a part of the exhaust passage to form a huge portion in which the cross-sectional area of the exhaust passage becomes large and the equivalent pipe length of the exhaust passage is variable. By adjusting the flap valve opening, exhaust interference is reduced and engine output characteristics are improved.
No. 7-12671

  However, in the invention described in Patent Document 1, a huge portion and a flap valve are provided in the middle of the exhaust passage, so that the structure of the exhaust passage becomes complicated and the degree of freedom in layout is reduced.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an exhaust passage structure capable of reducing exhaust interference with a simple structure and improving intake charging efficiency in a multi-cylinder engine.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention is an exhaust passage structure of an exhaust passage that collects and exhausts exhaust gas discharged from each cylinder of a multi-cylinder engine, and the ignition sequence of each cylinder (# 1 to # 8) in a predetermined assembly stage of exhaust gas. Are exhaust pipes (27, 32) through which exhaust from the cylinder (# 3) to be ignited later is out of the two cylinders (# 3, # 7) in which the intervals of exhaust exhaust are the shortest. ) And a deflecting portion (72) for deflecting a pressure wave that flows backward with respect to the flow direction of the exhaust gas.

  According to the present invention, the deflection unit is formed in the exhaust pipe connected to the cylinder in which exhaust interference occurs. The deflecting unit can deflect a part of the blowdown pressure wave that flows backward with respect to the flow direction of the exhaust gas. As a result, exhaust interference at the exhaust port is suppressed, and an increase in exhaust pressure due to exhaust interference is suppressed, so that scavenging within the cylinder is efficiently performed, and thus intake charge efficiency in the intake stroke is improved. .

  In addition, since the deflecting portion is formed in the exhaust passage, the degree of freedom in layout is not lowered when the deflecting portion is formed.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an exhaust system of a V-type 8-cylinder engine 1 of the present embodiment. The left side of FIG. 1 shows the front of the vehicle.

  The V-type 8-cylinder engine 1 includes left and right banks composed of a plurality of cylinders, a right bank 10R, and a left bank 10L.

  In the right bank 10R of the V-type 8-cylinder engine 1, four cylinders of a first cylinder # 1, a third cylinder # 3, a fifth cylinder # 5, and a seventh cylinder # 7 are arranged in series. The cylinder head of the right bank 10R includes an exhaust port 11 that communicates with the first cylinder # 1, an exhaust port 13 that communicates with the third cylinder # 3, an exhaust port 15 that communicates with the fifth cylinder # 5, An exhaust port 17 communicating with the seventh cylinder # 7 is formed. Further, an exhaust manifold 2R that collects exhaust gas flowing out from the cylinders # 1, # 3, # 5, and # 7 is installed on the cylinder head side portion of the right bank 10R.

  The exhaust manifold 2R includes branch pipes 21, 23, 25, and 27. A common flange 29R is formed at the tips of the branch pipes 21, 23, 25, 27. The exhaust manifold 2R is installed on the side surface of the right bank 10R by fixing the flange 29R with a bolt or the like (not shown). The exhaust manifold 2R is connected to the exhaust pipe 31 via an exhaust purification catalyst 51 and connected to the exhaust pipe 32 via a catalyst 52. The catalysts 51 and 52 purify the exhaust gas flowing out from the cylinders # 1, # 3, # 5, and # 7 and flow it downstream.

  The branch pipe 21 is connected to the exhaust port 11 of the first cylinder # 1.

  The branch pipe 23 is connected to the exhaust port 13 of the third cylinder # 3. The branch pipe 23 merges with the branch pipe 21 at the collecting portion 20R. The branch pipe 23 is formed with a protrusion 60 (FIG. 5) on the inner wall for suppressing exhaust interference. Details of the protrusion 60 will be described later.

  The branch pipe 25 is connected to the exhaust port 15 of the fifth cylinder # 5.

  The branch pipe 27 is connected to the exhaust port 17 of the seventh cylinder # 7. The branch pipe 27 joins the branch pipe 25 at the gathering portion 20R.

  The exhaust pipe 32 joins the exhaust pipe 31 at a joining part 30R that is a downstream gathering part. The exhaust pipe 31 that merges with the exhaust pipe 32 is connected to the front pipe 41.

  On the other hand, in the left bank 10L, four cylinders of the second cylinder # 2, the fourth cylinder # 4, the sixth cylinder # 6, and the eighth cylinder # 8 are arranged in series. The cylinder head of the left bank 10L includes an exhaust port 12 communicating with the second cylinder # 2, an exhaust port 14 communicating with the fourth cylinder # 4, an exhaust port 16 communicating with the sixth cylinder # 6, and an eighth An exhaust port 18 communicating with the cylinder # 8 is formed. An exhaust manifold 2L that collects the exhaust gas flowing out from the cylinders # 2, # 4, # 6, and # 8 is installed on the cylinder head side portion of the left bank 10L.

  The exhaust manifold 2L includes branch pipes 22, 24, 26, and 28. Since the exhaust manifold 2L is substantially the same as the configuration of the exhaust manifold 2R of the right bank 10R, differences from the exhaust manifold 2R will be described.

  The exhaust manifold 2L is different from the exhaust manifold 2R in the manner in which the branch pipes 22, 24, 26, and 28 are assembled.

  The branch pipe 22 is connected to the exhaust port 12 of the second cylinder # 2. In the exhaust manifold 2 </ b> L, a protrusion 60 (FIG. 5) that suppresses exhaust interference is formed on the inner wall of the branch pipe 22. Details of the protrusion 60 will be described later.

  The branch pipe 26 is connected to the exhaust port 16 of the sixth cylinder # 6. In the exhaust manifold 2L, the branch pipe 26 joins the branch pipe 22 at the gathering portion 20L.

  The branch pipe 24 is connected to the exhaust port 14 of the fourth cylinder # 4.

  The branch pipe 28 is connected to the exhaust port 18 of the eighth cylinder # 8. The branch pipe 24 merges with the branch pipe 24 at the gathering portion 20R.

  The exhaust manifold 2L is connected to the exhaust pipe 33 via the exhaust purification catalyst 53 and connected to the exhaust pipe 34 via the catalyst 54.

  The flow of exhaust gas flowing out from each cylinder of the V-type 8-cylinder engine 1 will be described below.

  In the right bank 10R of the V-type 8-cylinder engine 1, the exhaust gas flowing out from the cylinders # 1 and # 3 flows through the branch pipes 21 and 23, joins at the collecting portion 20R, is purified by the catalyst 51, and flows into the exhaust pipe 31. . Further, the exhaust gas flowing out from the cylinders # 5 and # 7 flows through the branch pipes 25 and 27, joins at the collecting portion 20R, is purified by the catalyst 52, and flows into the exhaust pipe 32. The exhaust gas that has passed through the exhaust pipe 32 joins the exhaust pipe 31 at the junction 30R, flows into the front pipe 41, and is released to the atmosphere.

  On the other hand, the exhaust from the cylinders # 2 and # 6 of the left bank 10L flows through the branch pipes 22 and 26, joins at the collecting portion 20L, is purified by the catalyst 53, and flows to the exhaust pipe 33. Further, the exhaust from the cylinders # 4 and # 8 flows through the branch pipes 24 and 28, collects at the collecting portion 20L, is purified by the catalyst 54, and flows into the exhaust pipe 34. The exhaust gas that has passed through the exhaust pipe 34 joins the exhaust pipe 33 at the junction 30L and flows into the front pipe 42. The exhaust gas flowing into the front pipe 42 joins the front pipe 41 and is released to the atmosphere.

  Next, the relationship between the ignition sequence of each cylinder of the V-type 8-cylinder engine 1 according to this embodiment and the exhaust interval will be described.

  FIG. 2 is a diagram showing the ignition order of the cylinders # 1 to # 8 of the V-type 8-cylinder engine 1 of the present embodiment and the exhaust interval at that time.

  As shown in FIG. 2, the ignition order of the V-type 8-cylinder engine 1 is as follows: first cylinder # 1 → 8th cylinder # 8 → 7th cylinder # 7 → 3rd cylinder # 3 → 6th cylinder # 6 → 5th cylinder # 5 → 4th cylinder # 4 → 2nd cylinder # 2 → 1st cylinder # 1 →... Thus, since the ignition order is not alternately distributed to the cylinders of the banks 10R and 10L, the ignition intervals are unequal between the banks 10L and 10R. In other words, the firing order of each cylinder continues at unequal intervals at a predetermined collection stage of exhaust. Hereinafter, for ease of explanation, the explanation will focus on the flow of exhaust from the cylinders # 1, # 3, # 5, and # 7 of the right bank 10R.

  Since the crankshaft of the V-type 8-cylinder engine 1 of the present embodiment is a double plane type, the ignition intervals of the cylinders # 1, # 3, # 5, and # 7 in the right bank 10R are the first cylinder # 1 → the first cylinder. 180 ° for 7 cylinder # 7, 90 ° for 7th cylinder # 7 → 3rd cylinder # 3, 180 ° for 3rd cylinder # 3 → 5th cylinder # 5, 5th cylinder # 5 → 1st cylinder # 1 270 °. Then, since the exhaust is exhausted in the exhaust stroke after a certain period from ignition, after exhausting from the first cylinder # 1, it is exhausted from the seventh cylinder # 7 with a delay of 180 °, and after that, the third cylinder is delayed by 90 ° Exhaust from # 3, 180 ° later than the fifth cylinder # 5, then 270 ° later from the first cylinder # 1, and so on are repeated to obtain an exhaust interval corresponding to the ignition interval. Therefore, the exhaust gas flows out of the cylinders # 1, # 3, # 5, and # 7 intermittently in the exhaust stroke.

  As described above, when high-temperature and high-pressure exhaust flows from the cylinders # 1, # 3, # 5, and # 7, pressure waves (hereinafter referred to as “blowdown pressure waves”) are formed in the exhaust ports 11, 13, 15, and 17. .) Is formed. The blowdown pressure wave is pulsated and propagates to the branch pipes 21, 23, 25, 27 of the exhaust manifold 2R. In this way, the blowdown pressure wave formed in one cylinder collides with the inner wall of the passage at the collecting portion 20R of the exhaust manifold 2R and the merging portion 30R of the exhaust pipe 31 shown in FIG. An exhaust pipe and a branch pipe connected to other cylinders flow backward from the downstream side toward the upstream side. Therefore, the reflected wave that flows backward and the blow-down pressure wave of the exhaust from the cylinder with the slower ignition of the two cylinders in which the ignition sequence is continuous interfere with each other (hereinafter referred to as “exhaust interference”).

  That is, in the right bank 10R, the ignition order of the seventh cylinder # 7 and the third cylinder is continuous, the ignition interval is close to 90 °, and the upstream third cylinder # 3 is delayed from the exhaust of the seventh cylinder # 7. Exhausted from. Therefore, the reflected wave of the blowdown pressure wave from the seventh cylinder # 7 and the blowdown pressure wave of the exhaust from the third cylinder # 3 interfere with exhaust, and the exhaust pressure in the exhaust port 13 of the third cylinder # 3. Becomes higher.

  Similarly, in the left bank 10L, since the ignition order of the fourth cylinder # 4 and the second cylinder # 2 is continuous, the ignition interval is close to 90 °, and the reflected wave of the blowdown pressure wave from the fourth cylinder # 4 And the blowdown pressure wave of the exhaust gas flowing out from the upstream second cylinder # 2 cause the exhaust interference, and the exhaust pressure in the exhaust port 12 connected to the second cylinder # 2 increases.

  Thus, when the exhaust pressure in the exhaust ports 12 and 13 increases due to exhaust interference, the exhaust efficiency decreases. Then, the charging efficiency of the intake air in the second cylinder # 2 and the third cylinder # 3 in the intake stroke is lowered, and there is a problem that the output characteristics are lowered.

  Therefore, in the V-type 8-cylinder engine 1 of the present embodiment, the ignition interval is close in the same bank, and inside the branch pipes 22 and 23 connected to the intake ports 12 and 13 of the cylinders # 2 and # 3 where exhaust interference occurs. A protrusion having a step (a deflecting portion for deflecting a part of the reflected wave) that reduces the backflow of the reflected wave is formed.

  FIG. 3 shows a configuration of protrusions formed on the branch pipe.

  FIG. 3A shows a protrusion 60 formed on the branch pipe 23 connected to the exhaust port 13 of the third cylinder # 3 of the right bank 10R. FIG. 3B shows the operation of the protrusion 60.

  Note that the projection 60 formed on the branch pipe 22 connected to the exhaust port 12 of the second cylinder # 2 of the left bank 10L has the same configuration, and is therefore omitted for convenience of description.

  As shown in FIG. 3A, the protrusion 60 is formed to protrude from the inner wall of the branch pipe 23 connected to the exhaust port 13 of the right bank 10R. The protrusion 60 includes a reduced diameter portion 61 that gradually narrows the inner diameter of the branch pipe 23 in the exhaust flow direction, and a stepped portion 62 that reduces the backflow of the reflected wave of the blowdown pressure wave.

  The reduced diameter portion 61 of the protrusion 60 is formed with a length L in the middle of the branch pipe 23 so as to gradually narrow the inner diameter of the branch pipe 23 in accordance with the flow direction of the intake air. By adopting such a tapered shape, the exhaust resistance that is increased by forming the protrusion 60 on a part of the branch pipe 23 is suppressed as much as possible. The drawing ratio r of the reduced diameter portion 61 is expressed by the following equation (1) by the minimum inner diameter of the reduced diameter portion 61 and the inner diameter of the branch pipe 23.

  The stepped portion 62 of the protrusion 60 is formed so as to protrude perpendicular to the inner wall of the branch pipe 23. This stepped portion 62 reduces the backflow of the reflected wave of the blowdown pressure wave and suppresses exhaust interference. In the stepped portion 62, the amount of protrusion from the inner peripheral wall of the branch pipe 23 increases as the throttle ratio r in the equation (1) increases, and the effect of reducing the backflow of the reflected wave is improved.

  In order to reduce the backflow of the reflected wave as much as possible and reduce the increase in exhaust resistance during exhaust, it is desirable to set the range L for forming the protrusion 60 to about 15 mm and the aperture ratio r to about 85%. .

  In the right bank 10R, the reflected wave of the blowdown pressure wave from the seventh cylinder # 7 ignited 90 ° before the third cylinder # 3 is generated from the downstream of the branch pipe 23 as shown in FIG. Back flow upstream. A part of the reflected wave collides with the stepped portion 62 of the protrusion 60 and is deflected as indicated by an arrow A. Therefore, it is possible to suppress the reflected wave from flowing back upstream from the protrusion 60. As a result, exhaust interference is suppressed at the exhaust port 13, so that an increase in exhaust pressure at the exhaust port 13 is reduced, and the intake charging efficiency of the third cylinder # 3 in the intake stroke can be improved.

  FIG. 4 is a diagram showing the effect of reducing exhaust interference by the protrusion 60. The horizontal axis indicates the crank angle, and the vertical axis indicates the exhaust flow rate. A solid line indicates a case where the projection 60 is not provided on the branch pipe 23, and a broken line indicates the present embodiment.

  As shown by the solid line, when the protrusion 60 is not formed on the branch pipe 23, the exhaust gas flow rate rapidly increases immediately after the exhaust valve opening timing (hereinafter referred to as "EVO") elapses. Thereafter, the exhaust pressure in the exhaust port 13 increases due to the influence of the exhaust interference, and the exhaust flow rate rapidly decreases. In this way, when affected by exhaust interference, the total outflow amount of exhaust gas decreases, so that the charging efficiency of intake air decreases and the output characteristics deteriorate.

  On the other hand, when the projection 60 is formed on the branch pipe 23, the backflow of the reflected wave is reduced by the projection 60. Therefore, as shown by the broken line, after the exhaust flow rate increases rapidly immediately after the EVO, A sudden drop in the exhaust flow rate due to the interference is suppressed, and the exhaust is discharged smoothly. Therefore, the total outflow amount of the exhaust gas flowing out from the third cylinder # 3 is increased as compared with the case where the protrusion 60 is not formed. As a result, the charging efficiency of the intake air in the intake stroke is improved, and the output characteristics can be improved.

As described above, when the projection 60 is formed on the branch pipe 23, the reduction in filling efficiency due to the exhaust interference can be suppressed. However, the formation of the projection 60 in the branch pipe 23 inhibits the exhaust flow, and slightly Exhaust resistance increases. Then, the exhaust pressure inside the exhaust port 13 on the upstream side of the position where the projection 60 is formed increases, and the intake charging efficiency in the intake stroke decreases. Therefore, in the present embodiment, the protrusion 60 is formed at a position away from the third cylinder # 3 to suppress the deterioration of the intake charging efficiency caused by the protrusion 60. FIG. It is a figure which shows the position which forms the processus | protrusion 60 in a type | system | group.

  As shown in FIG. 5, the protrusion 60 is formed at a position away from the third cylinder # 3, that is, in the vicinity of the collective portion 20R of the branch pipe 23. Preferably, the branch pipe 23 having a reduced diameter portion 61 by narrowing the downstream end is connected to the joining destination passage to form the gathering portion 20 so that the passage downstream from the stepped portion 62 becomes the joining destination passage.

  Note that the protrusion 60 is also formed in the vicinity of the collective portion 20L of the branch pipe 22 in the left bank 10L, but the description is omitted for convenience.

  As described above, it has been confirmed through experiments that when the projection 60 is formed in the vicinity of the gathering portion 20R of the branch pipe 23, the inertia effect at the time of exhaust flow from the third cylinder # 3 can be largely maintained.

  When the inertial effect at the time of exhaust gas outflow increases, the negative pressure in the third cylinder # 3 generated when the exhaust gas flows out of the cylinder increases, so that the intake charging efficiency is improved. Therefore, even if the exhaust resistance is increased by forming the projection 60 on the branch pipe 23, it is possible to suppress the reduction of the charging efficiency of the intake air as much as possible and suppress the decrease of the output characteristics.

  As described above, the present embodiment can obtain the following effects.

  In the V-type 8-cylinder engine 1, projections 60 are formed on the branch pipe 22 connected to the exhaust port 12 of the second cylinder # 2 where exhaust interference occurs and the branch pipe 23 connected to the exhaust port 13 of the third cylinder # 3. The stepped portion 62 of the protrusion 60 deflects a part of the reflected wave of the blowdown pressure wave that flows backward from the downstream of the branch pipes 22 and 23. Therefore, exhaust interference at the exhaust ports 12 and 13 is suppressed, an increase in exhaust pressure at the exhaust ports 12 and 13 due to exhaust interference is suppressed, and intake charge efficiency in the intake stroke is improved.

  Further, the reduced diameter portion 61 of the protrusion 60 is formed so that the inner diameters of the branch pipes 22 and 23 are gradually narrowed according to the flow direction of the intake air, so that the increase in exhaust resistance during exhaust can be reduced as much as possible. it can.

  Furthermore, since the protrusion 60 is formed in the vicinity of the gathering portions 20R and 20L of the branch pipes 22 and 23, the inertial effect at the time of exhaust outflow can be largely maintained. Therefore, the negative pressure in the cylinder that is generated during exhaust can be increased, so that a reduction in intake charging efficiency caused by the protrusion 60 can be suppressed as much as possible.

  As described above, in the present embodiment, since the protrusion 60 is formed on the branch pipes 22 and 23, the degree of freedom in layout does not decrease when the protrusion 60 is formed.

  It is obvious that the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical idea.

  For example, the present invention is not limited to the V-type 8-cylinder engine 1 but a multi-cylinder engine having an exhaust passage that collects exhaust from each cylinder. The idea of the present invention can also be applied to the exhaust passage connected to.

  Further, in order to provide the stepped 63 of the protrusion 60, as shown in FIG. 6, an enlarged diameter portion 64 may be formed in a part of the branch pipe 23. In this case, since the reduced diameter portion 61 is not formed on the protrusion 60, an increase in exhaust resistance can be suppressed.

  Further, the protrusion 60 may be formed not on the branch pipes 22 and 23 but on the exhaust pipes 31 and 33.

  FIG. 7 is a diagram showing positions where the protrusions 60 are formed in the V-type 8-cylinder engine 1.

  As shown in FIG. 7A, the protrusion 60 may be formed not on the branch pipes 22 and 23 but on the exhaust pipes 31 and 33.

  Thus, by forming the protrusions 60 on the exhaust pipes 31 and 33, a part of the reflected wave of the blowdown pressure wave can be deflected and the backflow of the reflected wave can be reduced. Therefore, an increase in exhaust pressure due to exhaust interference can be suppressed, and the same effect as in the first embodiment can be obtained.

  Since this protrusion 60 is formed in the vicinity of the merging portions 30R and 30L of the exhaust pipes 31 and 33 away from the cylinders # 2 and # 3, the protrusion 60 is formed more than the case where the protrusion 60 is formed only on the branch pipes 22 and 23. Thus, an increase in exhaust resistance due to 60 can be suppressed, and a decrease in intake charging efficiency can be suppressed.

  Further, as shown in FIG. 7B, the protrusions 60 may be formed in the vicinity of the collecting portions 20R and 20L of the branch pipes 22 and 23 and in the vicinity of the merging portions 30R and 30L of the exhaust pipes 31 and 33, respectively. Good.

  In this way, by forming the protrusion 60 on each of the branch pipes 22 and 23 and the exhaust pipes 31 and 33, a part of the reflected wave of the blowdown pressure wave is deflected. The backflow of the reflected wave can be suppressed as compared with the case where the wave is formed.

  Since the projection 60 is formed on each of the branch pipes 22 and 23 and the exhaust pipes 31 and 33, exhaust resistance is slightly deteriorated, but the effect of suppressing increase in exhaust pressure due to exhaust interference is further improved. A decrease in efficiency can be suppressed.

It is a figure which shows the exhaust system of a V type 8 cylinder engine. It is a figure which shows the ignition order and exhaust interval of each cylinder of a V type 8 cylinder engine. The structure of the protrusion formed in the branch pipe is shown. It is a figure which shows the reduction effect of the exhaust interference by a protrusion. It is a figure which shows typically the exhaust system of a V type 8 cylinder engine. The structure of the protrusion formed in the branch pipe is shown. It is a figure which shows the position which forms protrusion.

Explanation of symbols

# 1 to # 8 1st cylinder to 8th cylinder 1 V-type 8-cylinder engine 2R, 2L Exhaust manifold 10R Right bank 10L Left bank 11-18 Exhaust ports 20R, 20L Collecting parts 21-28 Branch pipe (upstream exhaust pipe)
30R, 30L confluence 31-34 exhaust pipe (downstream exhaust pipe)
41, 42 Front pipes 51, 52, 53, 54 Catalyst 60 Projection 61 Reduced diameter part 62 Stepped (deflection part)
63 Expanded part

Claims (7)

An exhaust passage structure of an exhaust passage that collects and exhausts exhaust discharged from each cylinder of a multi-cylinder engine,
An exhaust pipe through which exhaust from the cylinder to be ignited later is flown out of the two cylinders in which the ignition sequence of the cylinders continues at unequal intervals and the interval of exhaust exhaust is the shortest at a predetermined collection stage of exhaust. A deflection unit configured to deflect a pressure wave that is formed and flows backward with respect to the flow direction of the exhaust gas;
An exhaust passage structure characterized by that. The multi-cylinder engine is a V-type 8-cylinder engine,
The cylinder that is ignited later is a cylinder that ignites at intervals of 90 deg CA after ignition of the cylinder that is ignited first in the same bank.
The exhaust passage structure according to claim 1. The exhaust pipe is
A first upstream exhaust pipe connected to the cylinder that is subsequently ignited;
A second upstream exhaust pipe that collects exhaust from the cylinders in the same bank different from the two cylinders in which the interval of the exhaust exhaust is the shortest in the first upstream exhaust pipe;
A downstream exhaust pipe that is connected downstream of the first upstream exhaust pipe in the exhaust flow direction and flows exhaust gas from the first upstream exhaust pipe and the second upstream exhaust pipe;
With
The deflection unit is formed in either one or both of the first upstream exhaust pipe and the downstream exhaust pipe.
The exhaust passage structure according to claim 2. The deflection unit is formed by expanding a part of the exhaust pipe.
The exhaust passage structure according to any one of claims 1 to 3, wherein: The deflecting portion is formed to protrude toward the inner diameter side of the exhaust pipe.
The exhaust passage structure according to any one of claims 1 to 3, wherein: The deflection unit includes a reduced diameter part that gradually reduces the inner diameter of a part of the exhaust pipe according to the flow direction of the exhaust gas.
The exhaust passage structure according to claim 5. The deflecting portion is formed in the vicinity of a collecting portion where exhaust collects.
The exhaust passage structure according to any one of claims 1 to 5, characterized in that:

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