JP2008180136A - Exhaust system structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust system structure capable of generating an exhaust sound having a powerful feeling, while securing a mounting space of an exhaust pipe. <P>SOLUTION: A vehicular exhaust system 10 comprises a right side exhaust line 18 and a left side exhaust line 20 for independently introducing exhaust gas up to a main muffler 14 from different banks 12A and 12B of an engine 12, and a spiral pipe 30 as a cooling means arranged only in the left side exhaust line 20 out of the right side exhaust line 18 and the left side exhaust line 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust system structure for exhausting exhaust gas from an internal combustion engine.

In a dual exhaust system in which first and second exhaust pipes connected independently of each other in different banks of the internal combustion engine are connected to a single muffler, the lengths of the first and second exhaust pipes There is known a technique for obtaining a powerful exhaust sound by differentiating the above (for example, see Patent Document 1).
JP 2006-57553 A Japanese Patent Laid-Open No. 2000-240445 JP-A-8-177454 JP 2004-300920 A

  However, the conventional technology as described above is difficult to apply to a vehicle in which it is difficult to secure a space for making the lengths of the two exhaust pipes different (lengthening one), such as a small vehicle. .

  In view of the above facts, an object of the present invention is to obtain an exhaust system structure capable of generating a powerful exhaust sound while ensuring a mounting space for an exhaust pipe.

  An exhaust system structure according to a first aspect of the present invention is provided in any one of a pair of exhaust pipes that are independently communicated with different exhaust parts of an internal combustion engine and the pair of exhaust pipes, and cools the exhaust gas. And a cooling means.

  In the exhaust system structure according to claim 1, the exhaust gas generated by the operation of the internal combustion engine passes through a pair of exhaust pipes independently connected to different exhaust parts (for example, left and right banks) of the internal combustion engine. , Discharged outside the system. Here, since any one of the pair of exhaust pipes is provided with a cooling means, the exhaust gas is cooled at the installation portion of the cooling means in one exhaust pipe, and the flow velocity of the exhaust gas changes (decreases). In addition, a powerful exhaust sound can be obtained as in the case where the exhaust pipe is made longer than the other. That is, a powerful exhaust sound can be obtained without depending on the configuration in which the lengths of the pair of exhaust pipes are different.

  Thus, the exhaust system structure according to claim 1 can generate a powerful exhaust sound while ensuring a space for mounting the exhaust pipe.

  An exhaust system structure according to a second aspect of the present invention produces a temperature difference between a pair of exhaust pipes that are independently communicated with different exhaust parts of an internal combustion engine and an exhaust gas that flows through the exhaust pipes of the pair of exhaust pipes. And a temperature difference generating means.

  In the exhaust system structure according to claim 2, the exhaust gas generated by the operation of the internal combustion engine passes through a pair of exhaust pipes independently connected to different exhaust parts (for example, left and right banks) of the internal combustion engine. , Discharged outside the system. At this time, the temperature of the exhaust gas flowing through the pair of exhaust pipes is made different by the temperature difference generating means, so that a difference in flow velocity occurs, and there is a feeling of force as in the case where the lengths of the pair of exhaust pipes are made different. Exhaust sound can be obtained. That is, a powerful exhaust sound can be obtained without depending on the configuration in which the lengths of the pair of exhaust pipes are different.

  Thus, the exhaust system structure according to claim 2 can generate a powerful exhaust sound while securing a mounting space for the exhaust pipe.

  The exhaust system structure according to a third aspect of the present invention is the exhaust system structure according to the first or second aspect, wherein the cooling means has at least a part of one of the pair of exhaust pipes as an inner peripheral surface. It is configured as a spiral tube having a spiral groove.

  In the exhaust system structure according to claim 3, since the exhaust gas passing through the spiral tube produces a spiral flow, the efficiency of heat exchange with the outside air through the tube wall is improved, and the exhaust gas is effective with a simple configuration. Cooling can be performed, or a temperature difference can be generated between the exhaust gases of the pair of exhaust pipes.

  The exhaust system structure according to a fourth aspect of the present invention is the exhaust system structure according to the third aspect, wherein the spiral pipe is gradually spiraled toward the upstream end at the upstream end in the exhaust gas flow direction. An upstream side removal portion where the depth of the groove is shallow is formed.

  In the exhaust system structure according to claim 4, since the upstream side exfoliation part is formed in the spiral pipe, the exhaust gas smoothly flows into the spiral pipe and suppresses the increase in the back pressure accompanying the installation of the spiral pipe. Can do.

  The exhaust system structure according to a fifth aspect of the present invention is the exhaust system structure according to the third or fourth aspect, wherein the spiral tube is gradually formed toward an end portion on the downstream side in the exhaust gas flow direction toward the downstream side. A downstream side removal portion is formed in which the depth of the spiral groove is shallow.

  In the exhaust system structure according to claim 5, since the downstream side exfoliation part is formed in the spiral pipe, the exhaust gas smoothly escapes from the spiral pipe, and the increase of the back pressure due to the installation of the spiral pipe is suppressed. can do.

  As described above, the exhaust system structure according to the present invention has an excellent effect that a powerful exhaust sound can be generated while securing a mounting space for the exhaust pipe.

  A vehicle exhaust system 10 to which an exhaust system structure according to an embodiment of the present invention is applied will be described with reference to FIGS. 1 to 9. For convenience of explanation, the directions indicated by the arrows FR, UP, and W shown in the drawings as appropriate are the forward direction (traveling direction), the upward direction, and the vehicle width of the vehicle to which the vehicle exhaust system 10 is applied, respectively. The direction. In the following description, upstream and downstream refer to upstream and downstream in the exhaust gas flow direction.

  FIG. 1 is a perspective view of a vehicle exhaust system 10. As shown in this figure, the vehicle exhaust system 10 is for exhausting the exhaust gas of the engine 12, which is an internal combustion engine, out of the system, and purifies and silences the exhaust gas of the engine 12. Yes. In this embodiment, the engine 12 is, for example, a V-type or horizontally opposed multi-cylinder (8-cylinder to 12-cylinder) engine, and the cran shaft (not shown) is rotated around an axis along the vehicle longitudinal direction. It is configured to be placed vertically at the front. Therefore, the engine 12 has a right bank 12A as a first bank and a left bank 12B as a second bank.

  The vehicle exhaust system 10 includes a main muffler 14 for silencing the exhaust sound of the exhaust gas. The main muffler 14 is disposed at the rear end of the vehicle body, and the introduced exhaust gas is discharged from the atmosphere open end 16 </ b> A of the end pipe 16. Although not shown, a plurality of expansion chambers including at least a first expansion chamber and a final expansion chamber are formed in the main muffler 14, and the upstream end of the end pipe 16 opens at the final expansion chamber.

  The vehicle exhaust system 10 includes a right exhaust line 18 that guides exhaust gas from the right bank 12A of the engine 12 to the main muffler 14 and a left exhaust line 20 that guides exhaust gas from the left bank 12B to the main muffler 14. It is configured as a so-called dual exhaust system. As shown in FIG. 1, each of the right exhaust line 18 and the left exhaust line 20 includes, in order from the upstream side, a catalytic converter 22 for purifying exhaust gas and a sub muffler 24 for silencing exhaust sound (especially high frequency side). These are arranged and communicated in series by an exhaust pipe 28. In this embodiment, the exhaust pipes 28 of the right exhaust line 18 and the left exhaust line 20 correspond to a pair of exhaust pipes in the present invention, but the right exhaust line 18 and the left exhaust line 20 themselves are a pair of exhaust pipes in the present invention. It is also possible to grasp that there is.

  In this embodiment, the catalytic converter 22 of the right exhaust line 18 has an upstream end directly connected (directly attached) to the exhaust manifold 12C of the right bank 12A, and the catalytic converter 22 of the left exhaust line 20 has an upstream end. Are directly connected to the exhaust manifold 12D of the left bank 12B. Each catalytic converter 22 in the left and right banks may be configured as a so-called tandem catalyst in which a first catalyst and a second catalyst are arranged in series.

  In this embodiment, an exhaust path is provided between the downstream end of the exhaust pipe 28 constituting the right exhaust line 18 and the left exhaust line 20 and the main muffler 14 when the engine 12 is at low speed and at high speed. A valve device 26 for switching is provided. The valve device 26 includes a high-rotation flow path 26A communicated with the final expansion chamber of the main muffler 14, a low-rotation flow path 26B communicated with the first expansion chamber of the main muffler 14, and a high-rotation flow path. The valve 26C opens the high-rotation flow path 26A when the rotational speed of the engine 12 exceeds a predetermined rotational speed (first threshold value). When the rotational speed of the engine 12 separately falls below a predetermined rotational speed (second threshold), the valve 26C closes the high-rotation flow path 26A. The second threshold value may be the same as or different from the first threshold value.

  In the vehicle exhaust system 10, the right exhaust line 18 and the left exhaust line 20 have substantially the same length of the exhaust gas flow path (a configuration in which the distance difference between the exhaust gas discharge paths is small). That is, in the vehicle exhaust system 10, the right exhaust line 18 and the left exhaust line 20 are linearly arranged along the longitudinal direction of the vehicle body, so that from the right bank 12 </ b> A (exhaust manifold 12 </ b> C) of the engine 12 to the main muffler 14. The distance from the left bank 12B (exhaust manifold 12D) to the main muffler 14 is substantially the same length (within 500 mm in length difference).

  The vehicle exhaust system 10 includes a spiral tube 30 as a cooling means provided only in one of the right exhaust line 18 and the left exhaust line 20. In this embodiment, the spiral tube 30 is disposed in series between the sub-muffler 24 and the valve device 26 in the left exhaust line 20. In this embodiment, the configuration in which the spiral pipe 30 is not provided in the right exhaust line 18 and the spiral pipe 30 is provided in the left exhaust line 20 corresponds to the temperature difference generating means in the present invention.

  As shown in FIGS. 2A and 2B, spiral grooves 30A and 30B having a spiral shape are formed inside and outside the pipe wall of the spiral tube 30. In this embodiment, four spiral grooves 30 </ b> A and 30 </ b> B are formed on the inner and outer peripheral surfaces of the spiral tube 30. Although the details will be described later together with the operation of the present embodiment, the spiral pipe 30 has a larger surface area than the cylindrical exhaust pipe 28 and generates a spiral flow in the exhaust gas, thereby passing the exhaust gas passing through the inside. And heat exchange with the outside air. That is, the spiral tube 30 is configured to function as a cooling unit that lowers the temperature of the exhaust gas that passes through the exhaust tube 28 as compared with the case where the exhaust gas passes through the exhaust tube 28 having the same length.

  Further, as shown in FIG. 3, the spiral tube 30 includes an upstream side gradually changing portion 32 in which a part of the upstream end side gradually becomes shallower toward the upstream side, and the depth of the spiral grooves 30A and 30B becomes shallower. Has been. Further, the spiral tube 30 is configured such that a part of the downstream end side thereof is a downstream side gradual change portion 34 in which the depth of the spiral grooves 30A and 30B gradually decreases toward the downstream side. Although details will be described later, the length L (see FIG. 3) of the upstream side gradual change portion 32 and the downstream side gradual change portion 34 in the exhaust gas flow direction is a distance X (160 mm in this embodiment) shown in FIG. Are equal (L≈X). Moreover, in this embodiment, the upstream side gradual change part 32 and the downstream side gradual change part 34 are each formed so that the maximum diameter of the spiral tube 30 may be made constant.

  The spiral pipe 30 has a maximum diameter larger than the diameter of the exhaust pipe 28 and a minimum diameter smaller than the diameter of the exhaust pipe 28. A tapered reducer may be interposed at the joint between the exhaust pipe 28 and the spiral pipe 30 (upstream gradual change portion 32, downstream gradual change portion 34). Further, the upstream side gradually changing portion 32 and the downstream side gradually changing portion 34 are formed so that the upstream end of the upstream side gradually changing portion 32 and the downstream end of the downstream side gradually changing portion 34 have substantially the same diameter as the exhaust pipe 28. You may do it. Further, for example, in the spiral tube 30, the upstream end of the upstream side gradually changing portion 32 may be directly joined to the downstream end of the sub muffler 24, and the downstream end of the downstream side gradually changing portion 34 is connected to the valve device 26. May be directly joined to the flange 36, or the sub-muffler 24 and the valve device 26 (flange 36) may be constituted by the spiral pipe 30 over the entire length instead of the exhaust pipe 28.

  Next, the operation of this embodiment will be described.

  In the vehicle exhaust system 10 having the above-described configuration, the exhaust gas of the engine 12 is purified by the respective catalytic converters 22 of the right exhaust line 18 and the left exhaust line 20, respectively, and the high-frequency component is mainly silenced by the sub muffler 24. The sound is further silenced at, and discharged from the end pipe 16 into the atmosphere in a purified state as described above. For example, when the engine speed is lower than a predetermined speed, the high-rotation flow path 26A of the valve device 26 is closed by the valve 26C, and the exhaust gas is expanded in the main muffler 14 from the first expansion chamber. Pass through to the room one after another and be well silenced and open to the atmosphere. On the other hand, for example, when the engine speed exceeds a predetermined speed, the high-rotation flow path 26A of the valve device 26 is opened, and the exhaust gas passes through the final expansion chamber from the high-rotation flow path 26A and flows into the end pipe 16. The atmosphere is released from the atmosphere opening end 16A. For this reason, the back pressure (exhaust resistance) at the time of high rotation is reduced.

  Here, in the vehicle exhaust system 10 that is a dual exhaust system, the spiral pipe 30 is provided in the left exhaust line 20, so that the exhaust gas passing through the left exhaust line 20 is cooled in the spiral pipe 30 and is The temperature becomes lower than that of the exhaust gas passing through the exhaust line 18.

  Therefore, an exhaust gas speed difference occurs between the right exhaust line 18 and the left exhaust line 20 due to the exhaust gas temperature difference, and exhaust gas exhaust from the right bank 12A to the main muffler 14 via the right exhaust line 18 is generated. Regarding the relationship between the sound quality (change with respect to the engine original sound) and the exhaust sound quality of the exhaust gas from the left bank 12B through the left exhaust line 20 to the main muffler 14, the lengths of the right exhaust line 18 and the left exhaust line 20 are expressed as follows. The relation can be made in the same manner as the configuration different from the predetermined value (eg, 700 mm or more). Thereby, in an automobile to which the vehicle exhaust system 10 is applied, it is possible to obtain (produce) a powerful exhaust sound (so-called rumble sound) when the engine 12 is rotated at a low speed.

  In the vehicle exhaust system 10, the spiral pipe 30 changes the temperature difference of the exhaust gas between the right exhaust line 18 and the left exhaust line 20 instead of the difference in length between the right exhaust line 18 and the left exhaust line 20. Since it is the structure which produces | generates the speed difference based, the mounting space to a vehicle body does not become large like the structure which made any one of the right side exhaust line 18 and the left side exhaust line 20 longer than the other. That is, in the vehicle exhaust system 10, it is possible to achieve a powerful exhaust sound in the configuration including the right exhaust line 18 and the left exhaust line 20 that are substantially equal in length.

  Next, the cooling effect of the exhaust gas by the spiral tube 30 will be supplemented. FIG. 4 shows the exhaust of the spiral pipe 30, the cylindrical pipe 100 shown in FIGS. 10A and 10B, and the U-shaped pipe 110 shown in FIGS. 11A and 11B. It is a numerical analysis result comparing gas cooling effects and the like. The broken line indicates the analysis result when the flow rate of the exhaust gas is doubled with respect to that indicated by the solid line. In this comparison, the diameter of the cylindrical pipe 100 is the same as the maximum diameter of the spiral pipe 30, and the spiral pipe 30 (the upstream side gradual change part 32 and the downstream side gradual change part 34 having the same length) is used. The pipe 100 and the U-shaped pipe 110 are used. From this figure, it can be seen that the spiral tube 30 has a larger cooling effect than the pipe 100 having a small surface area and a large cooling effect compared to the U-shaped pipe 110 having a surface area equal to or greater than that.

  When the flow of the exhaust gas in the spiral tube 30 is visualized (by numerical analysis), it becomes as shown in FIG. From this figure, it can be seen that a spiral flow of exhaust gas occurs in the spiral tube 30. 5A shows the temperature distribution on the outer surface of the spiral tube 30, and FIG. 5B shows the temperature distribution along the cross section inside the spiral tube 30 (the thinner the dots, the lower the temperature). Show that). From these figures, it can be seen that the cooling effect of the exhaust gas is small at the central portion in the spiral tube 30 and the cooling effect is large at the pipe wall side. Therefore, by generating a spiral flow along the spiral groove 30A formed in the pipe wall of the spiral tube 30, the heat exchange efficiency between the exhaust gas and the outside air through the pipe wall of the spiral tube 30 is improved, and the surface area is simply increased. It is presumed that an exhaust gas cooling effect higher than the above can be obtained.

  On the other hand, the spiral tube 30 that does not have the upstream side gradual change part 32 and the downstream side gradual change part 34 has pressure compared to a configuration in which fins (blades or the like), particularly spiral fins, are provided in order to obtain a cooling function. Although the loss (exhaust resistance) is small, as shown in FIG. 4, the spiral pipe 30 having no upstream side gradually changing portion 32 and downstream side gradually changing portion 34 is compared with the cylindrical pipe 100 and the U-shaped pipe 110. Thus, the pressure loss (back pressure) of the exhaust gas increases.

  Here, in the vehicle exhaust system 10, since the upstream side gradual change part 32 and the downstream side gradual change part 34 are provided in the spiral pipe 30, the introduction of exhaust gas into the spiral pipe 30 and the exhaust from the spiral pipe 30 are performed. The gas is smoothly discharged, and the pressure loss can be reduced as compared with the case where the upstream side gradual change part 32 and the downstream side gradual change part 34 are not provided.

  In FIG. 6, the pressure loss at each cross-sectional position in the exhaust gas flow direction of the spiral pipe 30 (without the upstream side gradual change part 32 and the downstream side gradual change part 34) is shown by a solid line. The pressure loss at 28 (the maximum diameter of the spiral tube 30 is also small) is indicated by a broken line. From this figure, it can be seen that the pressure loss between the spiral pipe 30 and the exhaust pipe 28 becomes comparable at a predetermined distance X from the exhaust gas inlet.

  In FIG. 7, the exhaust pipe 28, the spiral pipe 30 whose lengths of the upstream side gradual change part 32 and the downstream side gradual change part 34 are X, the upstream side gradual change part 32 and the downstream side gradual change part 34 are shown. The exhaust pipe cooling effect and pressure loss are shown by the spiral tube 30 having a length of X / 2 and the spiral tube 30 in which the upstream side gradual change part 32 and the downstream side gradual change part 34 are not provided. . These total lengths are set equal to each other. From this figure, there is no significant difference in the cooling efficiency of the exhaust gas depending on the presence / absence and length of the upstream side gradual change part 32 and the downstream side gradual change part 34, and the upstream side gradual change part 32 and the downstream side gradual change part It can be seen that as 34 is provided and the length L is longer, the pressure loss is reduced. In addition, about the analysis results shown in FIG.4, FIG.5, FIG.6, analysis conditions, such as a flow volume of exhaust gas and exhaust gas temperature, do not necessarily correspond.

  Thus, in the vehicle exhaust system 10, the upstream side gradual change part 32 and the downstream gradual change part 34 having the length L in the exhaust gas flow direction equal to the distance X shown in FIG. The pressure loss can be reduced while maintaining the above. This reduction in back pressure prevents a reduction in the maximum output of the engine 12.

  FIG. 8 shows the relationship between the rotational speed of the engine 12 and the sound pressure levels of the exhaust gas in the right exhaust line 18 and the left exhaust line 20. FIG. 9 shows the frequency distribution of the exhaust sound of the right exhaust line 18 and the left exhaust line 20 when the engine 12 is rotating at a low speed (2000 rpm). From these figures, it can be seen that the right exhaust line 18 and the left exhaust line 20 differ in sound pressure level and sound quality (tone color) of the exhaust sound. The vehicle exhaust system 10 produces a powerful exhaust sound (rumble sound) by making the sound quality (including sound pressure level) of the right exhaust line 18 and the left exhaust line 20 different. (Create).

  In particular, in the multi-cylinder engine 12, since the explosion interval is short, it is difficult to produce a powerful exhaust sound with a substantially equal length dual exhaust structure. However, in the vehicle exhaust system 10, the left exhaust line 20 is simply used. The spiral tube 30 is provided on the right exhaust line 18 (the spiral tube 30 is not provided on the right exhaust line 18), and can be applied to the multi-cylinder engine 12 to obtain a powerful exhaust sound. Therefore, the vehicle exhaust system 10 is suitably applied to a sports car or the like equipped with a small-sized engine (the arrangement space of the vehicle exhaust system 10 is small) and a high-output multi-cylinder engine. Can be produced.

  In the above-described embodiment, an example in which the spiral pipe 30 is provided in the left exhaust line 20 has been described. However, the present invention is not limited to this, and for example, the right exhaust line 18 and the left exhaust line 20 are mutually long. It is good also as a structure which provided the spiral pipe | tube 30 from which (cooling performance) differs.

  In the above embodiment, an example in which the spiral tube 30 is provided as the cooling means (temperature difference generating means) has been described. However, the present invention is not limited to this, and for example, the exhaust heat of the exhaust gas is used as the engine cooling water. An exhaust heat recovery device (heat exchanger), an EGR cooler, or the like for recovery may be used as a cooling means. For example, an outside air introduction duct (and a fan, etc.) for introducing outside air only to the left exhaust line 20 is provided. Further, as the temperature difference generating means, for example, a configuration in which the surface of the right exhaust line 18 is covered with a heat insulating material may be employed.

  Further, in the above-described embodiment, the example in which the valve device 26 is disposed between the right exhaust line 18 and the left exhaust line 20 and the main muffler 14 has been described. However, the present invention is not limited thereto, and the valve device is not limited thereto. Needless to say, the present invention can be applied to an exhaust system that does not include H.26.

  Furthermore, in the above-described embodiment, the example in which the upstream side gradually changing portion 32 and the downstream side gradually changing portion 34 have the same length L is shown. However, the present invention is not limited to this, for example, the upstream side gradually changing portion. The length L may be different between the portion 32 and the downstream side gradual change portion 34.

It is a perspective view which shows the exhaust system for vehicles which concerns on embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the spiral tube which comprises the exhaust system for vehicles which concerns on embodiment of this invention, Comprising: (A) is a perspective view partly notched, (B) is an axial orthogonal cross-sectional view. It is a sectional side view of the spiral pipe which comprises the exhaust system for vehicles which concerns on embodiment of this invention. It is a diagram which shows the cooling performance of the spiral pipe which comprises the exhaust system for vehicles which concerns on embodiment of this invention compared with a comparative example. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the spiral pipe which comprises the exhaust system for vehicles which concerns on embodiment of this invention, Comprising: (A) is a side view which shows the temperature distribution of this surface, (B) is sectional side view which shows internal temperature distribution (C) is a sectional side view schematically showing the flow of exhaust gas. It is a diagram which shows the relationship between the cross-sectional position of the spiral tube which comprises the exhaust system for vehicles which concerns on embodiment of this invention, and a pressure loss. It is a diagram which shows the cooling performance of the spiral pipe which comprises the exhaust system for vehicles which concerns on embodiment of this invention compared with the comparative example different from FIG. It is a diagram which shows the difference of the sound pressure level on either side which comprises the exhaust system for vehicles which concerns on embodiment of this invention. It is a diagram which shows the difference of the sound quality on either side which comprises the exhaust system for vehicles which concerns on embodiment of this invention. It is a figure which shows the pipe which concerns on the comparative example with the spiral pipe | tube which comprises the exhaust system for vehicles which concerns on embodiment of this invention, Comprising: (A) is a perspective view, (B) is an axis perpendicular sectional view. It is a figure which shows the U-shaped pipe which concerns on the comparative example with the spiral pipe | tube which comprises the exhaust system for vehicles which concerns on embodiment of this invention, Comprising: (A) is a perspective view, (B) is an axial orthogonal cross section.

Explanation of symbols

10 Vehicle exhaust system 12 Engine 18 Right exhaust line (the other of a pair of exhaust pipes)
20 Left exhaust line (one of a pair of exhaust pipes)
30 Spiral tube (cooling means, temperature difference generating means)
32 upstream gradual change part 34 downstream gradual change part

Claims (5)

A pair of exhaust pipes independently communicated with different exhaust parts of the internal combustion engine;
A cooling means provided on any one of the pair of exhaust pipes for cooling the exhaust gas;
Exhaust system structure with A pair of exhaust pipes independently communicated with different exhaust parts of the internal combustion engine;
A temperature difference generating means for generating a temperature difference in the exhaust gas flowing through the exhaust pipes of the pair of exhaust pipes;
Exhaust system structure with   The said cooling means or a temperature difference generation means is comprised as a spiral pipe | tube which has at least one part of either one of said pair of exhaust pipes and a helical groove | channel on an internal peripheral surface. Exhaust system structure.   4. The exhaust according to claim 3, wherein the spiral pipe is formed with an upstream removal portion where the depth of the spiral groove gradually decreases toward the upstream end at the upstream end in the exhaust gas flow direction. System structure.   The downstream side change part in which the depth of the spiral groove gradually decreases toward the downstream side is formed in the end part on the downstream side in the exhaust gas flow direction of the spiral pipe. 4. The exhaust system structure according to 4.

Images