JP6997966B2 - Engine exhaust structure - Google Patents

Description

The present invention relates to an engine exhaust structure, and more particularly to an engine exhaust structure in which an exhaust port mechanism for exhausting exhaust gas is integrally formed in a cylinder head.

Conventionally, in order to avoid exhaust interference, a plurality of cylinders whose exhaust order is not continuous are collected and grouped, and the exhaust passages of each cylinder in the group are gathered in the collective exhaust passage through the gathering part, and the collective exhaust of each group is performed. A structure is known in which the passages are finally assembled in a common exhaust passage.
The exhaust passage formed in the cylinder head, the so-called exhaust port, collects only the exhaust gas discharged from the exhaust valve hole corresponding to the same cylinder (combustion chamber) inside the cylinder head, and collects the exhaust gas from the other cylinders. The discharged exhaust gas is collected by a separate exhaust manifold connected to the vertical wall of the cylinder head.

On the other hand, with the aim of making the engine compact, a technique has been proposed in which the exhaust gas discharged from each cylinder is collected inside the cylinder head without using a separate exhaust manifold.
In the multi-cylinder engine of Patent Document 1, the exhaust ports extending from the six combustion chambers arranged along the cylinder arrangement direction are integrally assembled at the exhaust collecting portion, and the first and second collective exhausts are formed in the cylinder head. It has a port and a first and second exhaust pipes fastened to the first and second collective exhaust ports, respectively, and the first and second exhaust pipes are integrally provided with a catalyst and are integrally connected to each other.
In this multi-cylinder engine, the exhaust gas of the first cylinder to the third cylinder is collected at the first collective exhaust port, the exhaust gas of the fourth cylinder to the sixth cylinder is collected at the second collective exhaust port, and the firing order is the first. The order is 1 cylinder → 5th cylinder → 3rd cylinder → 6th cylinder → 2nd cylinder → 4th cylinder.

Japanese Unexamined Patent Publication No. 2000-265905

In the multi-cylinder engine of Patent Document 1, the cylinders having continuous exhaust strokes are arranged so as not to be adjacent to each other in the cylinder arrangement direction, and the exhaust gas discharged from each cylinder is collected inside the cylinder head, so that the exhaust pulsation We are trying to reduce the size while offsetting the positive and negative pressure waves that accompany it.
However, the technique of Patent Document 1 may not be able to sufficiently secure engine performance due to its structure.

In the multi-cylinder engine of Patent Document 1, since the first and second collective exhaust ports are integrally formed in the cylinder head, the downstream end of the first exhaust port communicating from the first combustion chamber to the exhaust outlet which is the collective portion. And the downstream end of the third exhaust port that communicates from the third combustion chamber to the exhaust outlet face each other, and the downstream end of the fourth exhaust port that communicates from the fourth combustion chamber to the exhaust outlet and the sixth combustion. It is arranged so as to face the downstream end of the sixth exhaust port that communicates from the chamber to the exhaust outlet.
That is, due to the structure of the cylinder head, the length of the exhaust port until the exhaust gas is collected is short, so that the flow velocity of the exhaust gas flowing through the first (sixth) exhaust port is inevitably increased, and the exhaust gas is the cylinder. A component that flows back to the third (fourth) exhaust port facing the first (sixth) exhaust port is generated without flowing to the exhaust manifold (downstream of the collecting portion) connected to the head.
If the stagnant exhaust gas is generated due to the backflow and the internal pressure of the exhaust port becomes high, there is a possibility that the intake filling efficiency is lowered as a result.

Moreover, when the cylinders having continuous exhaust strokes are arranged so as not to be adjacent to each other in the cylinder arrangement direction and the cylinders having non-continuous exhaust strokes are grouped, the exhaust stroke of the first (sixth) exhaust port is completed. Since the time interval until the start of the exhaust stroke of the third (fourth) exhaust ports facing each other becomes long, there is a concern that the backflow tendency of the exhaust gas is further promoted.
That is, at present, it is not easy to secure sufficient exhaust efficiency of the engine while reducing the size of the engine.

An object of the present invention is to provide an engine exhaust structure or the like capable of ensuring exhaust efficiency while reducing the size of the engine.

The exhaust structure of the engine according to claim 1 is a collecting portion for collecting exhausts discharged from the first and second combustion chambers arranged in the cylinder arrangement direction, and a first exhaust communicating from the first combustion chamber to the collecting portion. In an engine exhaust structure in which an exhaust port mechanism including a port and a second exhaust port communicating from the second combustion chamber to the collecting portion is integrally formed in a cylinder head, the first and second exhaust ports are used. The central axis extension line of the first exhaust port is formed so as to intersect at an blunt angle in a plan view, and the central axis extension line of the first exhaust port is connected to one of the upper half or the lower half of the assembly portion and the second It is characterized in that the extension line of the central axis of the exhaust port is connected to the other of the upper half portion or the lower half portion of the gathering portion.

In the exhaust structure of this engine, since the extension lines of the central axes of the first and second exhaust ports are formed so as to intersect at an obtuse angle in a plan view, the first and second exhaust ports are integrated in the cylinder head. The engine can be made compact.
The central axis extension line of the first exhaust port is connected to either the upper half or the lower half of the gathering portion, and the central axis extension line of the second exhaust port is the upper half or the lower half of the gathering portion. Since it is connected to the other of the collecting parts, the traveling direction component of the exhaust gas flowing through the exhaust port is converted into a turning direction component centered on the center of the collecting part by using the confluence shape with respect to the collecting part, and the exhaust from one exhaust port to the other. Exhaust gas flowing back to the port is suppressed.

The invention of claim 2 is the third combustion chamber installed between the first and second combustion chambers in the cylinder arrangement direction in the invention of claim 1, wherein the first and first combustion chambers are installed in the combustion cycle. A third combustion chamber having a slower exhaust stroke than the second combustion chamber is provided, and the exhaust port mechanism is arranged between the first and second exhaust ports and communicates from the third combustion chamber to the collecting portion. The central axis extension line of the exhaust port having the third exhaust port and having the earlier exhaust stroke among the first and second exhaust ports is connected to the upper half of the gathering portion and the first and second exhausts are exhausted. Among the ports, the extension line of the central axis of the exhaust port having the slower exhaust stroke is connected to the lower half of the gathering portion.
According to this configuration, the exhaust efficiency can be improved regardless of the order of the exhaust stroke.
That is, the exhaust gas staying in the first and second exhaust ports due to the backflow caused by the exhaust stroke of the third exhaust port is swept by the flow of the exhaust gas of the third exhaust port. Of these, the exhaust gas in the exhaust stroke performed after the exhaust stroke of the third exhaust port, that is, the exhaust port having the earlier exhaust stroke among the so-called first and second exhaust ports, does not have much stagnant exhaust gas. On the other hand, of the first and second exhaust ports, the exhaust port having the slower exhaust stroke is subjected to the exhaust stroke in a situation where the exhaust efficiency is low (there is stagnant exhaust gas).
Further, since the exhaust gas has a high temperature, the upper velocity component is larger than the lower velocity component, and the main flow of the flow is formed in the upper portion. Therefore, the exhaust port to which the central shaft extension line is connected to the upper half of the gathering portion swivels the traveling direction component of the exhaust gas more than the exhaust port to which the central shaft extension line is connected to the lower half of the gathering portion. The turning direction conversion efficiency is high.
Therefore, in order to reduce the stagnant exhaust gas of the exhaust port having the slower exhaust stroke of the first and second exhaust ports, the turning direction conversion efficiency of the exhaust port of the first and second exhaust ports having the faster exhaust stroke Is high.

The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, the engine includes a plurality of the exhaust port mechanisms.
According to this configuration, it is possible to secure the miniaturization of the engine and the exhaust efficiency regardless of the number of cylinders.

The invention of claim 4 is characterized in that, in the invention of any one of claims 1 to 3, the vertical cross section of the gathering portion is formed in a substantially circular shape.
According to this configuration, the turning direction conversion efficiency can be further increased.

The invention of claim 5 is formed in the invention of any one of claims 1 to 4, so that the exhaust strokes of the combustion chambers in the same exhaust port mechanism among the plurality of exhaust port mechanisms are not continuous. It is characterized by that.
According to this configuration, the positive pressure wave and the negative pressure wave accompanying the exhaust pulsation can be canceled out, and the exhaust efficiency can be improved.

According to the exhaust structure of the engine of the present invention, it is possible to secure the exhaust efficiency while reducing the size of the engine by structurally changing the exhaust port.

It is a perspective view of the engine provided with the exhaust structure of the engine which concerns on Example 1. FIG. It is a side view of the exhaust side of a cylinder head. It is a top view of a cylinder head. It is a top view of the exhaust port mechanism. It is a front view of the exhaust port mechanism. It is a rear view of the exhaust port mechanism. It is explanatory drawing of the gathering part. It is a figure corresponding to FIG. 6 which concerns on a comparative example. It is a figure which shows the flow analysis result of the exhaust gas which concerns on the exhaust port mechanism of Example 1, (a) is a plan view, (b) is a front view. It is a figure which shows the flow analysis result of the exhaust gas which concerns on the exhaust port mechanism of the comparative example, (a) is a plan view, (b) is a front view.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The following description exemplifies the application of the present invention to the exhaust structure of the in-line 6-cylinder engine E, and does not limit the present invention, its application, or its use.

Hereinafter, Example 1 of the present invention will be described with reference to FIGS. 1 to 10.
As shown in FIG. 1, the engine E has an aluminum alloy cylinder block 1 connected to the upper part of the oil pan 3, an aluminum alloy cylinder head 2 connected to the upper part of the cylinder block 1, and the cylinder head 2. It is an in-line 6-cylinder reciprocating engine equipped with a synthetic resin head cover 4 or the like that covers the upper part of the engine. The cylinder block 1 and the cylinder head 2 are manufactured by an aluminum casting method.

The cylinder block 1 has a front-rear direction (cylinder arrangement direction) from the cylinder corresponding to the first cylinder # 1 located at the front end (not shown) to the cylinder corresponding to the sixth cylinder # 6 located at the rear end (not shown). Six cylinders are formed in. Pistons (not shown) are slidably inserted into each cylinder, and these pistons and the lower portion of the cylinder head 2 cooperate with each other to form six first to sixth combustion chambers c1 to c6. (See FIG. 3) are provided respectively.
Hereinafter, in the figure, the arrow F direction will be described as forward, the arrow L direction as left, and the arrow U direction as upward. Further, reference numerals # 1 to # 6 indicate cylinders 1 to 6.

As shown in FIG. 3, in the combustion chambers c1 to c6, a pair of front and rear intake valve holes 5 are formed on the upper right side, a pair of front and rear exhaust valve holes 6 and a spark plug hole 7 are formed on the upper left side, respectively. ing.
Each intake valve hole 5 facing the combustion chambers c1 to c6 is opened and closed by an intake valve (not shown) driven by a valve operating system, and each exhaust valve hole 6 is an exhaust valve driven by a valve operating system (not shown). ) Is opened and closed. Each spark plug hole 7 is opened in a substantially central portion of the combustion chambers c1 to c6, and an ignition plug (not shown) is attached.
In the combustion cycle of the engine E, the firing order is as follows: 1st cylinder # 1 → 5th cylinder # 5 → 3rd cylinder # 3 → 6th cylinder # 6 → 2nd cylinder # 2 → 4th cylinder # 4. ..
As a result, the cylinders having continuous exhaust strokes are arranged so as not to be adjacent to each other, so that the positive pressure wave and the negative pressure wave accompanying the exhaust pulsation cancel each other out.

As shown in FIGS. 2 and 3, the cylinder head 2 is formed in the right side portion and is connected to each of the combustion chambers c1 to c6, and is formed in the left side portion and is connected to each of the combustion chambers c1 to c6. Six exhaust ports 11 to 16, a first exhaust port mechanism Pa, and a second exhaust port mechanism Pb are integrally provided.
Each intake port 8 is formed in a substantially Y-shape for each cylinder so as to communicate the six openings formed in the right wall portion of the cylinder head 2 and the pair of intake valve holes 5. An intake manifold (not shown) is connected to the six openings.

The first exhaust port mechanism Pa includes a first collecting portion 10a that collects exhaust gas discharged from combustion chambers c1 to c3 of the first to third cylinders # 1 to # 3, and a first collecting portion 10a from the combustion chamber c1. The first port 11 (first exhaust port) communicating with the above, the second port 12 (third exhaust port) communicating from the combustion chamber c2 to the first collecting portion 10a, and the combustion chamber c3 to the first collecting portion 10a. The third port 13 (second exhaust port) and the like that communicate with the above are the main components.
The second exhaust port mechanism Pb collects the exhaust gas discharged from the combustion chambers c4 to c6 of the fourth to sixth cylinders # 4 to # 6, and the second collecting part 10b and the combustion chambers c4 to the collecting part 10b. The main components are a fourth port 14 that communicates, a fifth port 15 that communicates from the combustion chamber c5 to the second assembly portion 10b, a sixth port 16 that communicates from the combustion chamber c6 to the second assembly portion 10b, and the like. It is supposed to be.

Since the second exhaust port mechanism Pb is plane-symmetrical with the first exhaust port mechanism Pa with respect to the plane orthogonal to the front-rear direction at the front-rear center position, the first port 11, the sixth port 16, and the second port 12 The fifth port 15, the third port 13, and the fourth port 14 have the same configuration.
Further, since the first and second exhaust port mechanism Pa is composed of the space formed in the cylinder head 2, the space corresponding to the first exhaust port mechanism Pa is mainly taken out from the cylinder head 2 for convenience. It will be explained by the model diagram.

As shown in FIGS. 1 to 3, the gathering portions 10a and 10b are provided on the left wall portion of the cylinder head 2, respectively, and their vertical cross sections are formed in a substantially circular shape. Exhaust manifolds (not shown) are connected to the left end portions of the collecting portions 10a and 10b, respectively, and are finally assembled by a common exhaust pipe.

As shown in FIGS. 4 to 6, the first port 11 is curved backward so as to approach the first gathering portion 10a, and the second port 12 is substantially linear to the left and right so as to approach the first gathering portion 10a. The third port 13 is formed so as to be curved forward so as to approach the first gathering portion 10a, and the port lengths of the third ports 13 are set to be substantially equal to each other.
As a result, the output characteristics of each cylinder # 1 to # 6 are equalized.
Further, the upstream end portions of the first to third ports 11 to 13 are bent downward toward the exhaust valve holes 6 respectively.

As described above, the exhaust strokes of the combustion chambers c1 to c3 of the first exhaust port mechanism Pa are formed so as not to be continuous. That is, the exhaust stroke of the first exhaust port mechanism Pa and the exhaust stroke of the second exhaust port mechanism Pb are executed alternately.
As shown in FIG. 4, the intersection angle θ in the plan view of the central axis extension line L1 of the first port 11 and the central axis extension line L3 of the third port 13 is configured to be an obtuse angle (90 ° <θ). There is.
In this embodiment, the intersection angle θ between the extension line L1 and the extension line L3 is set to 120 ° or more in a plan view with the aim of making the cylinder head 2 compact.

Since the intersection angle θ between the extension line L1 and the extension line L3 is an obtuse angle, the downstream end of the first port 11 and the downstream end of the third port 13 are in a positional relationship facing each other.
In the exhaust stroke, the exhaust gas flowing through the first port 11 is difficult to flow in the downstream direction of the first collecting portion 10a whose traveling direction angle is smaller than the crossing angle θ, so that it travels to the third port 13 facing the first port 11 (backflow). ) Is generated, and the exhaust gas stays on the exhaust valve of the third port 13. Therefore, since the exhaust stroke of the third port 13 is performed in the presence of the stagnant exhaust gas, the exhaust efficiency of the third port 13 is lowered.
On the other hand, the exhaust gas staying on the exhaust valve of the first port 11 is scavenged by the flow negative pressure of the exhaust gas caused by the exhaust stroke of the second port 12 before the exhaust stroke of the first port 11. There is.

As shown in FIG. 6, the first port 11 is offset-connected to the upper side of the first gathering portion 10a, and the third port 13 is offset-connected to the lower side of the first gathering portion 10a.
Specifically, the intersection of the extension line L1 of the first port 11 and the vertical line passing through the center C of the first gathering portion 10a is set higher than the center C, and the extension line L3 of the third port 13 and the first set. The intersection with the vertical line passing through the center C of the portion 10a is set lower than the center C.
Further, as shown in FIG. 7, a stepped portion 10s curved toward the center C of the first gathering portion 10a is formed at the lower end portion of the connection between the first port 11 and the first gathering portion 10a, and the third port is formed. At the upper end of the connection between the 13 and the first gathering portion 10a, a stepped portion 10t curved toward the center C of the first gathering portion 10a is formed.

Since the exhaust gas flowing through the first port 11 has a high temperature, the main flow of the exhaust gas is formed in the upper half of the first port 11. Therefore, as shown by the arrow in FIG. 7, since the main flow of the exhaust gas is guided along the wall shape of the first collecting portion 10a, the traveling direction component of the exhaust gas toward the third port 13 is first set. It is converted into a turning direction component centered on the center C of the portion 10a.
This reduces the exhaust gas that stays on the exhaust valve of the third port 13.

Next, the action and effect of the exhaust structure of the engine will be described.
A verification experiment was conducted to explain the action and effect.
In this verification experiment, a three-dimensional CFD (Computational Fluid Dynamics) model with the first exhaust port mechanism Pa of the same specifications as in Example 1 and the exhaust port mechanism M of the comparative example is prepared, and for example, the finite element method and the finite volume method are prepared. Alternatively, the pressure distribution of the exhaust gas in the exhaust port is calculated using the numerical analysis of the Navier-Stokes equation by the difference method or the like.
As shown in FIG. 8, the exhaust port mechanism M of the comparative example is configured such that the extension line La of the first port and the extension line Lb of the third port pass through the center C of the first gathering portion 10a, and other specifications. Is the same as the first exhaust port mechanism Pa. The exhaust stroke of the first port was verified by assuming that the engine speed was 3000 rpm and the pressure inside the combustion chamber was constant.

9 and 10 show the verification results.
9 (a) is a plan view of the pressure distribution of the first exhaust port mechanism Pa, and FIG. 9 (b) is a front view of the pressure distribution of the first exhaust port mechanism Pa. 10 (a) is a plan view of the pressure distribution of the exhaust port mechanism M, and FIG. 10 (b) is a front view of the pressure distribution of the exhaust port mechanism M.
As shown in FIGS. 9 and 10, the first exhaust port mechanism Pa has a stronger tendency to swivel in a vertical spiral around the central portion at the gathering portion than the exhaust port mechanism M, and the first exhaust port mechanism Pa has a stronger tendency to swirl from the gathering portion toward the exhaust manifold. It can be seen that the amount of exhaust gas flowing is large. Further, according to the calculation result, in the exhaust port mechanism M, 37.9% of the exhaust gas discharged from the first port flowed back to the third port, whereas in the first exhaust port mechanism Pa, the first port. It was confirmed that 9.7% of the exhaust gas discharged from the port was flowing back to the third port.

According to the exhaust structure of the engine E, since the extension lines L1 and L3 of the first and third ports 11 and 13 are formed so as to intersect at an obtuse angle in a plan view, the first and third ports 11 and 13 are formed in the cylinder head 2. The third ports 11 and 13 can be integrally arranged, and the engine E can be made compact. Since the extension line L1 of the first port 11 is connected to the upper half of the first assembly portion 10a and the extension line L3 of the third port 13 is connected to the lower half of the first assembly portion 10a, the first assembly portion 10a The traveling direction component of the exhaust gas flowing through the first and third ports 11 and 13 is converted into a turning direction component centered on the center C of the first collecting portion 10a by utilizing the confluence shape with respect to, and one port is converted to the other. Exhaust gas flowing back to the port is suppressed.

The second combustion chamber c2 installed between the first and third combustion chambers c1 and c3 in the cylinder arrangement direction, and the exhaust stroke is slower than the first and third combustion chambers c1 and c3 in the combustion cycle. A second port 12 is provided with a second combustion chamber c2, and the first exhaust port mechanism Pa is arranged between the first and third ports 11 and 13 and communicates from the second combustion chamber c2 to the first collecting portion 10a. The extension line L1 of the first port 11 having a faster exhaust stroke among the first and third ports 11 and 13 is connected to the upper half of the first collecting portion 10a and the first and third ports 11 and 13 are connected. Of these, the extension line L3 of the third port 13, which has a slower exhaust stroke, is connected to the lower half of the first assembly portion 10a.
According to this configuration, the exhaust efficiency can be improved regardless of the order of the exhaust stroke.
That is, since the exhaust gas staying in the first, third ports 11 and 13 is scavenged by the exhaust stroke of the second port 12, the stagnant exhaust is performed in the first port 11 performed after the exhaust stroke of the second port 12. There isn't much gas. On the other hand, in the third port 13, the exhaust stroke is performed in a situation where the exhaust efficiency is low.
Further, the upper velocity component of the exhaust gas is larger than the lower velocity component, and the main flow of the flow is formed in the upper portion. Therefore, the first port 11 to which the extension line L1 is connected to the upper half of the first gathering portion 10a exhausts more than the third port 13 to which the extension line L3 is connected to the lower half of the first gathering portion 10a. The turning direction conversion efficiency of converting the traveling direction component of the gas into the turning direction is high.
Therefore, the stagnant exhaust gas of the third port 13 can be reduced.

Since the engine E is provided with a plurality of exhaust port mechanisms Pa and Pb, it is possible to secure the miniaturization and exhaust efficiency of the engine E regardless of the number of cylinders.

Since the vertical cross section of the first gathering portion 10a is formed in a substantially circular shape, the turning direction conversion efficiency can be further improved.

Of the multiple exhaust port mechanisms Pa and Pb, the exhaust strokes of the combustion chambers c1, c2, and c3 in the same exhaust port mechanism Pa are formed so as not to be continuous, so that the positive pressure wave and the negative pressure wave accompanying the exhaust pulsation are offset. And the exhaust efficiency can be improved.

Next, a modified example in which the embodiment is partially modified will be described.
1] In the above embodiment, an example of an in-line 6-cylinder longitudinal reciprocating engine has been described, but a transverse reciprocating engine or a V-type engine may be used.
Further, it may be applied to a 2-cylinder engine, a 3-cylinder engine, a 4-cylinder engine, and can be applied to other multi-cylinder engines as long as it has at least facing exhaust ports.

2] In the above embodiment, in the in-line 6-cylinder engine, the extension line of the first (sixth) port is connected to the upper half of the gathering portion, and the extension line of the third (fourth) port is below the gathering portion. The example of being connected to the half part has been described, but the extension line of the first (fourth) port is connected to the upper half part of the gathering part, and the extension line of the third (sixth) port is the lower half part of the gathering part. May be connected to.
It is also possible to reverse the above connection pattern according to the ignition timing.

3] In the above embodiment, an example in which two exhaust valve holes are provided in the port in each cylinder has been described, but a single exhaust valve hole may be provided, and three or more exhaust valve holes may be provided. Is also possible.

4] In addition, a person skilled in the art can carry out the present invention in a form in which various modifications are added to the above-described embodiment or in a combination of the respective embodiments without departing from the spirit of the present invention. It also includes various modified forms.

10a 1st assembly part 11 1st port 12 2nd port 13 3rd port Pa 1st exhaust port mechanism Pb 2nd exhaust port mechanism c1 1st combustion chamber c2 2nd combustion chamber c3 3rd combustion chamber L1 (1st port) Extension line L3 (3rd port) Extension line

Claims (5)

A collecting part that collects exhaust discharged from the first and second combustion chambers arranged in the cylinder arrangement direction, a first exhaust port that communicates from the first combustion chamber to the collecting part, and the second combustion chamber to the above. In the exhaust structure of an engine in which an exhaust port mechanism including a second exhaust port that communicates to the collecting part is integrally formed in the cylinder head.
The extension lines of the central axes of the first and second exhaust ports are formed so as to intersect at an obtuse angle in a plan view.
The central axis extension line of the first exhaust port is connected to either the upper half or the lower half of the gathering portion, and the central axis extension line of the second exhaust port is the upper half or the lower half of the gathering portion. The exhaust structure of the engine characterized by being connected to the other side of the. A third combustion chamber installed between the first and second combustion chambers in the cylinder arrangement direction, which has a slower exhaust stroke than the first and second combustion chambers in the combustion cycle. And
The exhaust port mechanism has a third exhaust port which is arranged between the first and second exhaust ports and communicates from the third combustion chamber to the collecting portion.
The central axis extension line of the exhaust port having the earlier exhaust stroke of the first and second exhaust ports is connected to the upper half of the gathering portion, and the one of the first and second exhaust ports having the slower exhaust stroke. The exhaust structure of the engine according to claim 1, wherein the central axis extension line of the exhaust port of the above is connected to the lower half portion of the gathering portion. The engine exhaust structure according to claim 1 or 2, wherein the engine includes a plurality of the exhaust port mechanisms. The exhaust structure of an engine according to any one of claims 1 to 3, wherein the vertical cross section of the gathering portion is formed in a substantially circular shape. The engine exhaust structure according to claim 2, wherein the exhaust strokes of the combustion chambers in the same exhaust port mechanism among the plurality of exhaust port mechanisms are formed so as not to be continuous.

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