JP7632018B2 - Intake pipe structure - Google Patents

Description

The technology disclosed here belongs to the technical field of intake pipe structures.

A structure has been known in the past in which a chamber is attached to an intake pipe to smooth the flow of intake air through the intake pipe.

For example, in the intake pipe structure described in Patent Document 1, an intake chamber is provided midway through the intake duct body that communicates with the intake manifold, a bent portion is formed in the intake duct body that is inserted into the intake chamber, and multiple communication holes that open into the intake chamber are drilled in the area excluding the outer portion of the bent portion that faces the intake chamber.

The intake pipe structure of Patent Document 1 reduces intake pulsation by discharging the intake air from the communication hole into the intake chamber in the medium to low speed range where the intake flow speed is relatively slow.

JP 2002-130065 A

In recent years, engines are sometimes equipped with turbochargers in order to maximize engine output while keeping the engine compact. When an engine is equipped with a turbocharger, it is common to provide an intercooler in the intake pipe downstream of the turbocharger compressor. In this case, when the throttle valve is provided downstream of the intercooler, the volume of the intake pipe from the compressor to the throttle valve can be increased to a certain extent, but when the throttle valve is provided upstream of the intercooler, the volume of the intake pipe from the compressor to the throttle valve becomes smaller.

If the volume of the intake pipe from the compressor to the throttle valve is small, when the throttle valve is slightly closed, the pressure in the intake pipe from the compressor to the throttle valve becomes high. For this reason, when the throttle valve opens during engine transients, high-pressure intake air may suddenly flow into the cylinder, causing hunting. To suppress hunting, a configuration has been considered in which intake air is bled downstream of the compressor, but in that case, there will be less intake air in the intake pipe from the compressor to the throttle valve, making it difficult to generate a smooth intake flow during engine transients.

In particular, if there is a bend in the intake pipe from the compressor to the throttle valve, the intake air will separate at the bend, causing the intake flow to become turbulent, making control difficult during transients. As a result, hunting will be more likely to occur.

In Patent Document 1, a chamber is provided in the intake pipe upstream of the throttle valve, but no consideration is given to its positional relationship with the turbocharger or intercooler. Furthermore, even if a chamber such as that described in Patent Document 1 were placed in the intake pipe between the compressor and the throttle valve, the chamber in Patent Document 1 would need to cover the intake pipe, which would inevitably increase the size of the entire engine and make it difficult to achieve a compact configuration.

The technology disclosed here has been developed in light of these issues, and its purpose is to stabilize the intake flow during transients while keeping the engine configuration compact.

In order to solve the above problems, a first technology disclosed herein is directed to an intake pipe structure of an engine having a turbocharger compressor and an intercooler arranged downstream of the compressor in the intake direction, and is provided with a throttle valve arranged in the intake pipe at a position downstream of the compressor and upstream of the intercooler in the intake direction, and an expansion section that is arranged along an intermediate intake pipe, which is a portion of the intake pipe between the compressor and the throttle valve, and that bulges out from the intermediate intake pipe, expanding a volume of the intermediate intake pipe, the intermediate intake pipe having a curved section, and the expansion section is formed on the inner arc side of the curved section, and a first communication hole that communicates with the expansion section is provided in a separation region of the intermediate intake pipe where the intake flow separates from the wall surface , and the first communication hole is formed in the curved section .

With this configuration, the throttle valve is located downstream of the compressor and upstream of the intercooler, so the intermediate intake pipe itself, which is the portion of the intake pipe between the compressor and the throttle valve, has a relatively small volume. By providing an expansion section, however, the volume of the intermediate intake pipe can be increased by the amount of the expansion section. This makes it possible to prevent high pressure inside the intermediate intake pipe as much as possible, even when the throttle valve is slightly closed.

In addition, when the engine is in a transient state, turbulence in the intake air flow can be suppressed by drawing air out from the expansion section, and a smooth intake air flow can be generated. In particular, since the first communication hole is provided in the separation area where the intake air flow separates from the wall surface, the intake air can be efficiently drawn out from the expansion section by utilizing the negative pressure generated by the separation of the intake air.

Furthermore, because the extension is provided on the inner arc side of the curved portion of the intermediate intake pipe, the increase in size of the engine due to the extension can be minimized.

This allows the engine configuration to be compact while stabilizing the intake flow during transients.

In order to solve the above-mentioned problems, the second technology disclosed herein is directed to an intake pipe structure of an engine having a turbocharger compressor and an intercooler arranged downstream of the compressor in the intake direction, and includes a throttle valve arranged in the intake pipe at a position downstream of the compressor and upstream of the intercooler in the intake direction, and an expansion section that is arranged to extend along an intermediate intake pipe, which is a portion of the intake pipe between the compressor and the throttle valve, and to bulge from the intermediate intake pipe, thereby expanding a volume of the intermediate intake pipe, the intermediate intake pipe having a curved section and a straight section that extends linearly from the downstream end of the curved section, the expansion section being formed on the inner arc side of the curved section and along the curved section and the straight section, a first communication hole that communicates with the expansion section is provided in a separation region in the intermediate intake pipe where the intake flow separates from the wall surface, and the first communication hole is formed in a portion of the straight section in the vicinity of the curved section.

With this configuration, because the straight section extends from the downstream end of the curved section, separation of the intake air is particularly likely to occur near the boundary between the curved section and the straight section. In contrast, because the first communication hole is formed in the straight section near the curved section, the intake air can be efficiently sucked out of the expansion section by utilizing the negative pressure caused by the separation of the intake air. This makes it possible to further stabilize the intake air flow during transient periods.

In one embodiment, a second communication hole that communicates with the expansion section may be provided at a position downstream of the intake air from the first communication hole in the straight section.

With this configuration, intake air can also be drawn out through the second communication hole, making the intake air flow more stable during transients.

The intake pipe structure may be configured such that the extension section has multiple ribs extending in a direction intersecting the longitudinal direction of the extension section.

This configuration can suppress the membrane vibration that occurs when air is sucked out of the expansion section, and can suppress the generation of radiated sound. It can also increase the rigidity of the expansion section.

In the intake pipe structure, the expansion section may be configured to be composed of a main body section that is formed integrally with the intermediate intake pipe and has an opening on the side opposite the intermediate intake pipe, and a lid section that is formed separately from the main body section and closes the opening of the main body section.

With this configuration, the volume of the extension section can be easily changed by changing the volume of the lid section to match the engine configuration. As a result, it is possible to stabilize the intake flow during transients while keeping the configuration of various engines compact.

In the intake pipe structure, the compressor is provided on the exhaust side at the top of the engine, the throttle valve is provided on the intake side at the top of the engine, the intermediate intake pipe is provided on the upper side of the engine body so as to cross the engine body in a plan view, the curved portion is curved in the cylinder row direction of the engine body, and the expansion portion is provided on the inner arc side of the curved portion so as to bulge from the intermediate intake pipe in the cylinder row direction.

In other words, because both the compressor and the throttle valve are provided on the top of the engine and the intermediate intake pipe is arranged to cross the engine body, the length of the intermediate intake pipe is short. This makes the engine configuration more compact, but the volume of the intermediate intake pipe tends to be particularly small. Therefore, by providing an extension section, the effect of stabilizing the intake flow during engine transients can be adequately achieved.

In addition, because the curved portion is bent in the direction of the cylinder row and the extended portion bulges out from the intermediate intake pipe in the direction of the cylinder row, the engine can be appropriately prevented from expanding in the height direction. As a result, the engine configuration can be made more compact.

As explained above, the technology disclosed herein makes it possible to stabilize the intake flow during transients while keeping the engine configuration compact.

FIG. 1 is a schematic diagram of an engine having an intake pipe structure according to an exemplary embodiment. FIG. 2 is a perspective view of the engine. FIG. 3 is a plan view of the engine. FIG. 4 is a plan view of the intake pipe including the expansion portion. FIG. 5 is a cross-sectional view taken along a horizontal plane passing through the extension portion. FIG. 6 is a schematic diagram showing the flow of intake air, where (a) shows a case without an extension portion, and (b) shows a case with an extension portion. FIG. 7 is a cross-sectional view of an expanded portion of an intake pipe structure according to a modified example.

Below, an exemplary embodiment will be described in detail with reference to the drawings. In the following description, the front, rear, left, right, top, and bottom of the vehicle will simply be referred to as front, rear, left, right, top, and bottom, respectively. With respect to the left-right direction, the left side when looking from the rear to the front will be referred to as the left, and the right side will be referred to as the right.

Figure 1 shows a schematic diagram of an engine 1 having an intake pipe structure according to an exemplary embodiment. The engine 1 has an engine body 2. The engine body 2 has, for example, six cylinders (not shown) arranged in series. In this embodiment, the engine body 2 is placed vertically in an engine room at the front of the vehicle so that the cylinders are aligned in the front-to-rear direction.

The engine 1 has an intake pipe 10 and an exhaust pipe 20 connected to the cylinder head 2a of the engine body 2. As shown in Figures 2 and 3, the downstream end of the intake pipe 10 is connected to the left side surface of the cylinder head 2a. As shown in Figures 1 to 3, the intake pipe 3 has a compressor 4a of the turbocharger 4, a throttle valve 5, and an intercooler 6 inside the pipe. The intake pipe 10 is also provided with an expansion section 30, which will be described later. These are merely examples of some of the devices arranged in the intake pipe 10, and do not exclude other devices being arranged in the intake pipe 10. In addition, in this embodiment, the intake pipe 10 includes all of the parts that constitute the intake passage, and even if the parts in which the compressor 4a and the throttle valve 5 are arranged are chamber-shaped, these parts are also included in the intake pipe 10.

The compressor 4a is rotated by the turbine 4b rotating due to exhaust gas, compresses the intake air introduced into the intake pipe 10, and releases it downstream of the intake air. The intercooler 6 is arranged downstream of the compressor 4a and cools the intake air compressed by the compressor 4a. The intercooler 6 may be air-cooled or water-cooled. The throttle valve 5 is arranged in the intake pipe 10 at a position downstream of the compressor 4a and upstream of the intercooler 6. The throttle valve 5 changes its opening depending on the depression of the accelerator pedal arranged in the passenger compartment, thereby adjusting the amount of intake air introduced into the engine body 2.

The upstream end of the exhaust pipe 20 is connected to the right side surface of the cylinder head 2a. The exhaust pipe 20 has the turbine 4b of the turbocharger 4 inside the pipe. The turbine 4b is merely an example of a part of the devices that may be placed inside the exhaust pipe 20, and does not exclude devices other than the turbine 4b from being placed inside the exhaust pipe 20.

2 and 3, the portion of the intake pipe 10 from the compressor 4a to the intercooler 6 is arranged along the periphery of the engine body 2. Specifically, the compressor 4a is provided on the right side (exhaust side) of the upper part of the engine 1, the throttle valve 5 is provided on the left side (intake side) of the upper part of the engine 1, and the intercooler 6 is provided below the throttle valve 5 on the left side (intake side) of the engine 1. The intake pipe 10 has a first intermediate intake pipe 11 that connects the position where the compressor 4a is provided to the position where the throttle valve 5 is provided, and a second intermediate intake pipe 12 that connects the position where the throttle valve 5 is provided to the position where the intercooler 6 is provided.

The first intermediate intake pipe 11 is provided above the engine body 2, particularly above the cylinder head 2a, so as to cross the engine body 2 in a plan view. Because the compressor 4a and throttle valve 5 are provided at the top of the engine 1, the first intermediate intake pipe 11 is relatively short. The first intermediate intake pipe 11 is made of resin.

The second intermediate intake pipe 12 extends downward from the position of the throttle valve 5, then bends and extends forward. The second intermediate intake pipe 12 is made of resin.

Although not shown in the figures, the intake pipe 10 has an upstream intake pipe that forms a passage upstream of the position of the compressor 4a. The upstream intake pipe extends rearward from the position of the compressor 4a, and then extends leftward and forward to bypass the engine body 2. Only the intake downstream end of the upstream intake pipe is shown in Figures 2 and 3.

In this embodiment, the configuration of the first intermediate intake pipe 11 is particularly well thought out. The first intermediate intake pipe 11 will be described in detail below.

As shown in Figures 3 to 5, the first intermediate intake pipe 11 has a bent portion 11a that bends in the cylinder row direction of the engine body 2, and a straight portion 11b that extends linearly from the intake downstream end of the bent portion 11a. The bent portion 11a bends toward the rear. The straight portion 11b extends at an angle toward the rear toward the left so as to connect to the intake downstream end of the bent portion 11a.

The portion of the first intermediate intake pipe 11 on the inner arc side of the bent portion 11a, i.e., the rear portion of the first intermediate intake pipe 11, is provided with an expansion portion 30 that expands the volume of the first intermediate intake pipe 11. The expansion portion 30 is provided so as to follow the bent portion 11a and the straight portion 11b of the first intermediate intake pipe 11 and to bulge rearward from the first intermediate intake pipe 11. The expansion portion 30 is made of resin.

As shown in Figures 4 and 5, the extension section 30 is composed of a main body section 31 that is formed integrally with the first intermediate intake pipe and has an opening on the side opposite (rear side) the first intermediate intake pipe 11, and a cover section 32 that is formed separately from the main body section 31 and closes the opening of the main body section 31 from the rear.

The end of the main body 31 on the first intermediate intake pipe 11 side is integrally formed with the first intermediate intake pipe 11 over the entirety. As shown in Figs. 4 and 5, the main body 31 bulges in a direction substantially perpendicular to the pipe axis direction of the straight portion 11b. The open end of the main body 31 has a first parallel portion 31a extending parallel to the pipe axis direction from the right side in a plan view, an inclined portion 31b extending from the left end of the first parallel portion 31a toward the left side in a plan view, and a second parallel portion 31c extending parallel to the pipe axis direction from the left end of the inclined portion 31b in a plan view. A flange 31d is provided at the open end of the main body 31. A plurality of outer ribs 31e are formed in a mesh pattern on the entire outer peripheral surface of the main body 31 (only the outer ribs 31e on the upper surface portion are shown in Fig. 4).

As shown in FIG. 5, the lid 32 has an opening on the side of the main body 31. As shown in FIG. 3, the portion of the lid 32 opposite the opening (the rear portion) is curved and inclined to avoid surrounding components. A flange 32a is formed at the open end of the lid 32, corresponding to the flange 31d of the main body 31. A number of outer ribs 32b are formed on the outer peripheral surface of the lid 32.

The flanges 31d, 32a of the main body 31 and the lid 32 are overlapped with each other and the flanges 31d, 32a are welded to each other around the entire circumference to form the expansion section 30. As a result, the expansion section 30 is not connected to anything other than the first intermediate intake pipe 11.

As shown in FIG. 5, inside the expansion section 30, the main body 31 is provided with a plurality of (here, three) inner ribs 31f extending in a direction intersecting the longitudinal direction of the expansion section 30, specifically toward the lid section 32 side. The inner ribs 31f are provided at the position of the first parallel section 31a, the position of the inclined section 31b, and the position of the second parallel section 31c in the longitudinal direction of the expansion section 30. The end of each inner rib 31f on the lid section 32 side does not reach the opening of the main body 31, and is located on the first intermediate intake pipe 11 side of the opening. The end of each inner rib 31f on the first intermediate intake pipe 11 side is integrated with the first intermediate intake pipe 11. Inside the expansion section 30, the lid section 32 is provided with a plurality of (here, two) inner ribs 32c extending in a direction intersecting the longitudinal direction of the expansion section 30, specifically toward the main body 31. Each inner rib 32c is slightly offset from the inner rib 31f of the main body 31 in the longitudinal direction of the expansion section 30. The end of each inner rib 32c on the main body 31 side does not reach the opening of the lid 32, but is located just before the opening. This creates a gap between the inner rib 31f of the main body 31 and the inner rib 32c of the lid 32.

In the first intermediate intake pipe 11, downstream of the bent portion 11a and in the separation region R where the intake flow separates from the wall surface, a communication hole 33 that communicates with the inside of the extension portion 30 is provided. Specifically, the communication hole 33 is formed in the portion of the straight portion 11b near the bent portion 11a. By providing the communication hole 33, when the intake air passes through the first intermediate intake pipe 11, air can be sucked out from inside the extension portion 30, making the flow of the intake air smoother.

Figure 6 shows the flow of intake air as it passes through a curved section of the intake pipe. That is, as shown in Figure 6(a), when the intake air passes through a curved section, the intake air separates on the inner arc side of the curved section. If the communication hole 33 is not provided, a vortex will be generated by the intake air separation in the area where the intake air separation occurs, disturbing the intake air flow. On the other hand, as shown in Figure 6(b), if the communication hole 33 is provided in the separation area, when the intake air separation occurs, the negative pressure generated by the intake air separation can be used to suck air out from the communication hole 33. This makes it possible to suppress the formation of vortexes over a wide area and reduce the disturbance of the intake air flow. This makes it possible to smooth the intake air flow.

Here, if the throttle valve 5 is located upstream of the intercooler 6, as in this embodiment, the capacity of the portion of the intake pipe 10 between the compressor 4a and the throttle valve 5 (here, corresponding to the first intermediate intake pipe 11) becomes small. In particular, if the compressor 4a and the throttle valve 5 are located at the top of the engine 1 and the first intermediate intake pipe 11 is arranged to cross the upper side of the engine body 2, as in this embodiment, the first intermediate intake pipe 11 becomes short, so the capacity of the first intermediate intake pipe 11 becomes small. If the expansion section 30 is not provided and the volume of the first intermediate intake pipe 11 is small, the pressure in the first intermediate intake pipe 11 becomes high when the throttle valve 5 is slightly closed. In particular, since the turbocharger 4 rotates due to inertia even if the depression amount of the accelerator pedal becomes 0, the intake air compressed by the compressor 4a is pushed into the first intermediate intake pipe 11, resulting in high pressure. As a result, when the throttle valve 5 is open during engine 1 transients, high-pressure intake air may suddenly flow into the cylinder, causing hunting. In order to suppress hunting, it is possible to reduce the pressure in the first intermediate intake pipe 11 by venting the intake air in the first intermediate intake pipe 11. However, in this case, the amount of intake air in the first intermediate intake pipe 11 is reduced, making it difficult to generate a smooth intake flow during engine 1 transients. In particular, if the first intermediate intake pipe 11 has a bent portion 11a as in this embodiment, separation of the intake air occurs at the bent portion 11a, and the intake flow is likely to become turbulent, making control during transients difficult. As a result, hunting becomes more likely to occur.

In contrast, in this embodiment, the expansion section 30 is provided, and a communication hole 33 that communicates with the expansion section 30 is provided in the separation region R in the straight section 11b. This allows the volume of the first intermediate intake pipe 11 to be increased by the expansion section 30. This makes it possible to prevent the first intermediate intake pipe 11 from becoming high pressure as much as possible, even when the throttle valve 5 is slightly closed. In addition, during a transient state of the engine 1, the negative pressure generated by the separation of the intake air at the bent section 11a is used to suck air out of the expansion section 30, thereby suppressing turbulence in the intake flow and generating a smooth intake flow. Furthermore, since the expansion section 30 is provided on the inner arc side of the bent section 11a in the first intermediate intake pipe 11, it is possible to prevent the engine 1 from becoming large due to the expansion section 30 as much as possible. Therefore, it is possible to stabilize the intake flow during a transient state while keeping the configuration of the engine 1 compact.

In addition, in this embodiment, the extension section 30 is composed of a main body section 31 that is formed integrally with the first intermediate intake pipe 11 and has an opening on the side opposite the first intermediate intake pipe 11, and a lid section 32 that is formed separately from the main body section 31 and closes the opening of the main body section 31. This makes it easy to change the volume of the extension section 30 by changing the volume of the lid section 32 to match the configuration of the engine 1. As a result, it is possible to stabilize the intake flow during transients while making the configuration of various engines 1 compact.

In addition, in this embodiment, the expansion section 30 is provided with a plurality of inner ribs 31f, 32c extending in a direction intersecting the longitudinal direction of the expansion section 30. With this configuration, it is possible to suppress membrane vibrations that occur when air is sucked out of the expansion section 30, and it is possible to suppress the generation of radiated sound. It is also possible to increase the rigidity of the expansion section 30.

(Modification)
7 shows a modified example of this embodiment. In this modified example, the configuration of the first intermediate intake pipe 11 is different from that of the above embodiment. Specifically, as shown in FIG. 7, this modified example differs from the above embodiment in that a downstream communication hole 234 communicating with the expansion section 30 is provided at a position away from the communication hole 33 in the straight section 11b of the first intermediate intake pipe 11 on the intake downstream side. The downstream communication hole 234 communicates the downstream end of the expansion section 30 in the intake flow direction with the straight section 11b. By providing the downstream communication hole 234, intake air can also be sucked out from the downstream communication hole 234. This makes it possible to further stabilize the intake flow during the transient state of the engine 1.

Other Embodiments
The technology disclosed herein is not limited to the above-described embodiment, and may be substituted without departing from the spirit and scope of the claims.

For example, in the above embodiment, only one communication hole 33 was provided in the separation region R on the intake downstream side of the bent portion 11a in the first intermediate intake pipe 11. However, this is not limited to this, and multiple communication holes 33 may be provided as long as they are provided in the separation region R.

In addition, in the modified example of the embodiment described above, only one downstream communication hole 234 is provided. However, this is not limited to the above, and multiple downstream communication holes 234 may be provided as long as they are located downstream of the intake air from the communication hole 33 in the straight section 11b.

In the above-described embodiment, the first intermediate intake pipe 11 has a bent portion 11a as a curved portion. However, the curved portion may be curved in the cylinder row direction. The first intermediate intake pipe 11 may be composed of only a curved portion without having a straight portion 11b. In this case, the communication hole 33 is provided in the separation region on the intake downstream side of the curved portion of the first intermediate intake pipe 11.

The above-described embodiments are merely examples and should not be interpreted as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of equivalence of the claims are within the scope of the present disclosure.

The technology disclosed herein is useful as an intake pipe structure for an engine that has a turbocharger compressor and an intercooler located downstream of the compressor in the intake pipe.

Reference Signs List 1 Engine 2 Engine body 4 Turbocharger 4a Compressor 5 Throttle valve 6 Intercooler 10 Intake pipe 11 First intermediate intake pipe 11a Bent portion 11b Straight portion 30 Expanded portion 31 Main body portion 31f Inner rib 32 Lid portion 32c Inner rib 33 Communication hole (first communication hole)
234 downstream communication hole (second communication hole)

Claims (6)

An intake pipe structure of an engine having a compressor of a turbocharger and an intercooler arranged downstream of the compressor in an intake air flow direction,
a throttle valve disposed in an intake pipe at a position downstream of the compressor and upstream of the intercooler;
an expansion portion that is provided along an intermediate intake pipe that is a portion of the intake pipe between the compressor and the throttle valve and that expands from the intermediate intake pipe, and expands a volume of the intermediate intake pipe,
The intermediate intake pipe has a bent portion,
The expansion portion is formed on the inner arc side of the curved portion,
a first communication hole communicating with the expansion portion is provided in a separation region of the intermediate intake pipe where the intake air flow separates from a wall surface ,
An intake pipe structure , wherein the first communication hole is formed in the curved portion . An intake pipe structure of an engine having a compressor of a turbocharger and an intercooler arranged downstream of the compressor in an intake air flow direction,
a throttle valve disposed in an intake pipe at a position downstream of the compressor and upstream of the intercooler;
an expansion portion that is provided along an intermediate intake pipe that is a portion of the intake pipe between the compressor and the throttle valve and that expands from the intermediate intake pipe, and expands a volume of the intermediate intake pipe,
the intermediate intake pipe has a curved portion and a straight portion extending linearly from a downstream end of the curved portion,
The expansion portion is formed on the inner arc side of the curved portion and along the curved portion and the straight portion,
a first communication hole communicating with the expansion portion is provided in a separation region of the intermediate intake pipe where the intake air flow separates from a wall surface,
13. An intake pipe structure, comprising: a first communication hole formed in a portion of the straight portion adjacent to the curved portion . The intake pipe structure according to claim 2,
an intake pipe structure, characterized in that a second communication hole communicating with the expansion portion is provided at a position in the straight portion away from the first communication hole on the intake downstream side, the second communication hole being connected to the expansion portion; In the intake pipe structure according to any one of claims 1 to 3,
An intake pipe structure, characterized in that a plurality of ribs are provided within the expansion portion, the ribs extending in a direction intersecting with the longitudinal direction of the expansion portion. In the intake pipe structure according to any one of claims 1 to 4,
An intake pipe structure characterized in that the expansion portion is composed of a main body portion that is formed integrally with the intermediate intake pipe and has an opening on the side opposite the intermediate intake pipe, and a cover portion that is formed separately from the main body portion and closes the opening of the main body portion. In the intake pipe structure according to any one of claims 1 to 5,
The compressor is provided on the exhaust side at an upper portion of the engine,
The throttle valve is provided on the intake side of an upper portion of the engine,
The intermediate intake pipe is provided on an upper side of the engine body so as to cross the engine body in a plan view,
the curved portion is curved in a cylinder row direction of the engine body,
The expansion portion is provided on an inner arc side of the curved portion so as to bulge from the intermediate intake pipe in the cylinder row direction.

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