JP7636733B2 - Engine intake system structure - Google Patents

Description

The present invention relates to the structure of an exhaust recirculation gas introduction section in a vehicle intake passage.

Many engines installed in vehicles are equipped with an EGR device (exhaust gas recirculation device) to improve exhaust performance. The EGR device has an EGR passage that connects the exhaust passage and the intake passage, and recirculates a portion of the exhaust (EGR gas) from the exhaust passage to the intake passage, lowering the oxygen concentration in the intake air. This lowers the temperature inside the engine's combustion chamber and suppresses NOx emissions from the engine.

The multi-cylinder engine described in Patent Document 1 is structured to introduce EGR gas (exhaust gas recirculation) near the point where the intake passage is divided into each cylinder, and adopts a configuration in which the EGR gas is introduced in a substantially tangential direction from the outer periphery of the intake passage. This generates a swirling flow of EGR gas in the intake passage, promoting the mixing of the EGR gas with the intake air.

Patent No. 3539246

However, when the intake air volume and EGR gas volume are small, for example during idling, even if EGR gas is introduced tangentially to the intake passage as in Patent Document 1, the swirling flow of EGR gas is weak and the EGR gas flows directly into the branch passages to each cylinder, which may result in uneven flow of EGR gas into some cylinders.

The present invention has been made in consideration of these problems, and its purpose is to provide an EGR introduction structure for an engine that can introduce intake air with a uniform concentration of exhaust recirculated gas into multiple cylinders.

In order to achieve the above object, the intake system structure of the engine according to the present invention is an intake system structure of an engine equipped with an exhaust gas recirculation device that recirculates a portion of the exhaust gas to an intake passage as exhaust gas recirculation gas, and includes a surge tank provided in the intake passage, an upstream intake pipe provided upstream of the surge tank and having an inlet through which the exhaust gas recirculation gas is introduced, and a downstream intake pipe provided downstream of the surge tank and supplying intake air to each cylinder of the engine, and the surge tank is provided on the upstream tank wall surface and is in contact with the upstream intake pipe. the tank inlet is provided on one side of the upstream tank wall surface and connected to the downstream intake pipe, and the tank outlet is provided on the downstream tank wall surface and connected to the downstream intake pipe, the tank inlet is provided displaced to one side in the extension direction of the upstream tank wall surface, the tank outlet is provided on the downstream tank wall surface and displaced to the other side in the extension direction of the upstream tank wall surface, the inlet is provided on the other side of the upstream intake pipe and opens toward the one side, and the exhaust recirculation gas flows into the upstream intake pipe from the other side toward the one side.

As a result, the tank inlet and tank outlet are offset in the surge tank, and the exhaust gas recirculation gas inlet in the upstream intake pipe opens toward the opposite side of the tank outlet, making it difficult for the exhaust gas recirculation gas introduced into the intake passage from the inlet to flow directly toward the tank outlet together with the intake air. This makes it easier for the intake air and the exhaust gas recirculation gas to mix in the surge tank.

Preferably, the exhaust recirculation device includes an exhaust recirculation passage inlet portion that extends tangentially to the upstream intake pipe in the extension direction and through which the exhaust recirculation gas is supplied, and the inlet is provided at the junction of the exhaust recirculation passage inlet portion.

This allows the exhaust recirculation gas to flow into the intake pipe in a direction different from the flow direction of the exhaust recirculation gas at the exhaust recirculation passage inlet, making it easier to mix the exhaust recirculation gas with the intake air in the upstream intake pipe.

Preferably, the exhaust recirculation device includes an exhaust recirculation passage extension extending circumferentially along the outer wall of the upstream intake pipe on the side opposite the exhaust recirculation passage inlet, and the inlet includes a first inlet provided at the junction of the exhaust recirculation passage inlet and a second inlet provided at the exhaust recirculation passage extension.

This allows exhaust recirculation gas to flow into the upstream intake pipe from two locations, the first inlet and the second inlet, i.e., from multiple directions, thereby promoting mixing of the exhaust recirculation gas and intake air in the upstream intake pipe.

Preferably, the downstream end of the upstream intake pipe extends into the surge tank toward the one side of the downstream tank wall.

This makes it easier for the exhaust recirculated gas and intake air mixed in the upstream intake pipe to collide with the downstream tank wall of the surge tank, further promoting mixing within the surge tank.

Preferably, the exhaust gas recirculation passage introduction portion is integrally formed with the upstream tank wall surface,
The downstream intake pipe may extend along the downstream tank wall surface to the one side of the upstream tank wall surface.

This allows the engine's intake system structure to be compact while ensuring the length of the downstream intake pipe in the extension direction of the upstream tank wall.

According to the engine intake system structure of the present invention, the tank inlet and tank outlet are offset in the surge tank, and the exhaust gas recirculation gas inlet in the upstream intake pipe opens toward the opposite side to the tank outlet, so that the exhaust gas recirculation gas introduced into the intake passage from the inlet is less likely to head directly toward the tank outlet together with the intake air, and the intake air and exhaust gas recirculation gas are more likely to mix in the surge tank. This makes it possible to introduce intake air with a uniform concentration of exhaust gas recirculation gas into each cylinder of the engine, improving the effectiveness of the exhaust gas recirculation device.

1 is a schematic configuration diagram of a front part of a vehicle according to an embodiment of the present invention. FIG. 2 is a vertical cross-sectional view of an intake system accessory of the engine. FIG. 2 is a vertical cross-sectional view of an intake system accessory of the engine. FIG. 2 is a cross-sectional view of an intake system accessory of the engine. FIG. 11 is a vertical cross-sectional view of an intake system accessory according to another embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
Fig. 1 is a schematic structural diagram of the front part of a vehicle 1 employing an intake system structure for an engine 3 according to an embodiment of the present invention. Fig. 2 is a vertical cross-sectional view of an intake system accessory disposed in front of the engine 3, as viewed from the left side in the vehicle width direction when mounted on the vehicle. Fig. 3 is a vertical cross-sectional view of the intake system accessory of the engine 3. Fig. 4 is a horizontal cross-sectional view of the intake system accessory of the engine 3. Fig. 3 is a cross-sectional view of the A-A portion shown in Fig. 2. Fig. 4 is a cross-sectional view of the B-B portion shown in Fig. 3.

As shown in Figure 1, a vehicle 1 incorporating the present invention is equipped with a power unit 4 including an engine 3 in an engine compartment 2 at the front. The vehicle 1 is a plug-in hybrid vehicle capable of operating in EV mode, series mode, and parallel mode.

The power unit 4 includes the engine 3 and a driving motor and a power generating motor generator (not shown). The driving motor and the power generating motor generator are arranged to the left of the engine 3 in the vehicle width direction. The power generating motor generator is also used as a starter motor for the engine 3.

The engine 3 is a four-cylinder engine, and is mounted transversely on the vehicle 1. An intake manifold 5 is provided on the front surface 3a of the engine 3, and an intake passage 6 is arranged therein. Meanwhile, an exhaust manifold 7 is provided on the rear surface side of the engine 3, and an exhaust passage 8 is arranged therein.

A throttle valve 10 is provided in the intake passage 6. A surge tank 11 is provided between the throttle valve 10 in the intake passage 6 and the intake manifold 5.

The throttle valve 10 is located at the upper part of the front surface 3a of the engine 3, and is disposed between a branch pipe 12 (downstream intake pipe) connected to the second cylinder located in the center of the engine 3 in the vehicle width direction, and a branch pipe 12 connected to the third cylinder.

The surge tank 11 is provided along the front surface 3a of the engine 3 and is disposed below the throttle valve 10. Branch pipes 12 of the intake manifold 5 are connected from the surge tank 11 to each cylinder. The branch pipes 12 bend from the underside of the surge tank 11 toward the front of the vehicle, extend upward adjacent to the front side of the surge tank 11, and are connected to the intake ports 13 of each cylinder provided at the top of the front surface 3a of the engine 3.

On the other hand, a front catalyst 20 is provided in the exhaust passage 8 downstream of the exhaust manifold 7. A rear catalyst 21 is also provided in the exhaust passage 8 downstream of the front catalyst 20. The front catalyst 20 and the rear catalyst 21 are exhaust purification catalysts such as three-way catalysts. The front catalyst 20 is relatively small, and is arranged adjacent to the rear surface of the engine 3. The front catalyst 20 is arranged close to the engine 3 so that exhaust gas flows in from the engine 3 immediately, in order to improve exhaust purification performance during cold operation, such as immediately after the engine is started. The rear catalyst 21 is relatively large, and is arranged, for example, under the floor of the vehicle 1.

Furthermore, the engine 3 is equipped with an EGR device 30 (exhaust gas recirculation device). The EGR device 30 recirculates a portion of the exhaust gas back into the intake passage 6, thereby reducing the oxygen concentration in the intake air and suppressing the rise in temperature in the combustion chamber of the engine 3. This reduces NOx in the exhaust gas from the engine 3.

The EGR device 30 has an EGR passage 31 (exhaust gas recirculation passage) that connects the intake passage 6 and the exhaust passage 8, an EGR valve 34 that is interposed in the EGR passage 31 and adjusts the opening area of the EGR passage 31, and an EGR cooler 32 provided in the EGR passage 31.

The EGR cooler 32 is a water-cooled cooler that lowers the temperature of EGR gas (exhaust gas recirculation gas), which is exhaust gas passing through the EGR passage 31, and is disposed along the rear surface of the engine 3. By lowering the temperature of the EGR gas, the EGR cooler 32 further suppresses the rise in the temperature of the intake air into which the EGR gas has been introduced, thereby improving the NOx reduction effect of the EGR device 30.

The EGR passage 31 runs from near the exhaust outlet of the front catalyst 20, passes through the EGR cooler 32, extends upward from the rear left of the engine, wraps around to the front of the engine 3, passes through the EGR valve 34 located at the upper left of the engine, and is connected to the intake passage 6 between the throttle valve 10 and the surge tank 11.

2 to 4, an adapter 40 and an EGR ring 41 (upstream intake pipe) are provided between the throttle valve 10 and the surge tank 11 as part of the intake passage 6 of the engine 3. The adapter 40 and the EGR ring 41 are cylindrical and have approximately the same diameter, and the lower end of the adapter 40 and the upper end of the EGR ring 41 are connected and extend vertically along the front surface of the engine 3. The upper end of the adapter 40 is connected to the throttle valve 10, and the lower end of the EGR ring 41 is connected to a tank inlet 42 provided in the upper wall 11a (upstream tank wall surface) of the surge tank 11.

The surge tank 11 is formed in a roughly rectangular box shape, with a tank inlet 42 provided slightly to the right in the vehicle width direction and toward the front of the vehicle (one side) from approximately the center position in the left-right direction (vehicle width direction) of the upper wall 11a.

Four tank discharge ports 43 (inlet ports) corresponding to the number of cylinders of the engine 3 are arranged side by side in the left-right direction at a position on the vehicle rear side (other side) of the lower wall 11b (downstream tank wall surface) of the surge tank 11. That is, in the surge tank 11, the tank inlet ports 42 and the tank discharge ports 43 are arranged offset in the vehicle front-rear direction.

From each tank outlet 43 of the surge tank 11, a branch pipe 12 of the intake manifold 5 extends adjacent to the lower and front sides of the surge tank 11 toward the intake port 13 of the corresponding left and right cylinders.

The connection point between the EGR passage 31 in the EGR device 30 and the intake passage 6, i.e., the point where the EGR gas is introduced into the intake passage 6, is located between the throttle valve 10 and the surge tank 11.

The EGR passage 31 downstream of the EGR valve 34 extends along the upper wall 11a of the surge tank 11 from the left to the right in the vehicle width direction, and has an EGR inlet passage portion 45 (exhaust gas recirculation passage inlet portion) formed to surround the side surface of the EGR ring 41.

The EGR introduction passage 45 is a tubular member having a rectangular vertical cross section formed integrally with the upper wall 11a of the surge tank 11, and has a front-to-rear width (e.g., a few cm) that is approximately the same as or slightly larger than the diameter of the EGR ring 41, and is rectangular in shape with a vertical width smaller than the front-to-rear width.

The EGR introduction passage 45 extends to the right in the vehicle width direction beyond the outer wall surface of the EGR ring 41 on the right side in the vehicle width direction. In addition, the EGR introduction passage 45 is arranged offset toward the rear of the vehicle with respect to the axis of the EGR ring 41. Furthermore, there is a gap of, for example, about 1 cm between the right inner wall surface at the tip end of the extension direction of the EGR introduction passage 45 and the right outer wall surface of the EGR ring 41, and between the rear inner wall surface of the EGR introduction passage 45 and the rear outer wall surface of the EGR ring 41. In addition, the front outer wall surface of the EGR ring 41 abuts against the front inner wall surface of the EGR introduction passage 45. That is, the internal space of the EGR introduction passage 45 faces the right, rear, and left parts of the outer wall surface of the EGR ring 41.

Furthermore, a ring hole 50 (first inlet) is provided in the rear part of the outer wall surface of the EGR ring 41 facing the internal space of the EGR introduction passage portion 45, and a ring hole 51 (second inlet) is provided in the right part. As a result, the EGR gas that has passed through the EGR valve 34 is introduced from the EGR introduction passage portion 45 through the ring holes 50 and 51 into the intake passage 6 in the EGR ring 41.

In detail, the EGR introduction passage 45 has a main body 45a (exhaust gas recirculation passage introduction portion) that extends tangentially from the EGR ring 41 to the left in the vehicle width direction, and an extension 45b (exhaust gas recirculation passage extension portion) that extends circumferentially along the outer wall of the EGR ring 41 on the right side in the vehicle width direction opposite the main body 45a. The EGR ring 41 has a ring hole 50 at the position on the vehicle rear side that is the contact point with the EGR introduction passage 45, and a ring hole 51 is provided in the extension 45b.

As described above, in this embodiment, the throttle valve 10 and intake manifold 5, which are intake system devices, are provided on the front surface 3a of the engine 3 mounted horizontally on the vehicle 1. In addition, a surge tank 11 is provided between the throttle valve 10 and the intake manifold 5. Branch pipes 12 of the intake manifold 5 are connected from the surge tank 11 to each cylinder, and the intake air is branched within the surge tank 11 and supplied to each cylinder via each branch pipe 12.

Furthermore, an EGR device 30 is provided which supplies EGR gas, which is a part of the exhaust gas, to the intake passage 6, and the EGR gas is introduced into the intake air at an EGR ring 41 provided in the intake passage 6 between the throttle valve 10 and the surge tank 11.

The EGR ring 41 has ring holes 50, 51 as inlets for EGR gas into the intake passage 6, with the ring hole 50 opening toward the front of the vehicle and the ring hole 51 opening toward the left in the vehicle width direction. On the other hand, each tank discharge port 43 that discharges the intake air from the surge tank 11 to the branch pipe 12 all faces upward.

Therefore, the EGR gas introduced into the intake passage 6 inside the EGR ring 41 from the ring holes 50, 51 is unlikely to flow directly toward either of the tank discharge ports 43, which are the inlets of the branch pipes 12.

In particular, the tank inlet 42 through which the intake air flows from the EGR ring 41 into the surge tank 11 is displaced toward the vehicle front side of the upper wall 11a of the surge tank 11, and the tank outlet 43 is displaced toward the vehicle rear side of the lower wall 11b, so that the tank inlet 42 and the tank outlet 43 are offset in the vehicle front-rear direction. Furthermore, the ring hole 50 is disposed on the vehicle rear side of the EGR ring 41 and opens toward the vehicle front side. As a result, the EGR gas that flows into the EGR ring 41 from the ring hole 50 toward the vehicle front is less likely to directly head toward the tank outlet 43 disposed on the vehicle rear side of the surge tank 11. As a result, the intake air and the EGR gas are easily mixed in the surge tank 11, and intake air with a uniform concentration of EGR gas can be introduced into each cylinder of the engine 3, improving the effect of the EGR device 30.

In addition, the EGR introduction passage 45, which is the most downstream part of the EGR passage 31 that guides the EGR gas to the intake passage 6, extends in the left-right direction of the vehicle, which is the tangent direction of the EGR ring 41, and the ring hole 50 is provided at the contact point of the EGR introduction passage 45, so that the EGR gas moving to the right in the vehicle width direction in the EGR introduction passage 45 changes direction from the ring hole 50 toward the front of the vehicle and flows into the EGR ring 41. As a result, the EGR gas is not directly introduced from the ring hole 50 into the EGR ring 41 but diffuses, promoting the mixing of the intake air and the EGR gas in the EGR ring 41.

In addition, the EGR ring 41 has two ring holes 50, 51, which are exhaust ports for the EGR gas, spaced apart from each other in the circumferential direction, making it easier to mix the EGR gas and the intake air within the EGR ring 41.

In particular, the ring hole 50 is provided at the junction between the EGR introduction passage portion 45 and the EGR ring 41 and opens toward the front of the vehicle, while the ring hole 51 is provided in the extension portion 45b and opens toward the left in the vehicle width direction. Therefore, EGR gas flows into the EGR ring 41 from different positions and in different directions, thereby promoting the mixing of the EGR gas and the intake air within the EGR ring 41.

In addition, the EGR introduction passage 45, which is the most downstream part of the EGR passage 31 that guides the EGR gas to the intake passage 6, extends from the left in the vehicle width direction toward the EGR ring 41 toward the right in the vehicle width direction. Therefore, the EGR gas flowing through the EGR introduction passage 45 toward the EGR ring 41 is likely to reach the part on the left side of the EGR ring 41 in the vehicle width direction (opposite the specified direction).

Here, if there is a ring hole on the right side of the EGR ring 41 in the vehicle width direction, more EGR gas will be discharged from this ring hole than from the other ring holes.

In this embodiment, the ring holes 50, 51 are provided on the vehicle rear side or vehicle right side of the outer peripheral wall surface of the EGR ring 41, and are not provided on the vehicle left side. Therefore, the EGR gas can be discharged from the multiple ring holes 50, 51 with less bias, and the mixing of the intake air and the EGR gas inside the EGR ring 41 can be further promoted.

In addition, the surge tank 11 has multiple tank discharge ports 43 arranged in the vehicle width direction, and the center of the EGR ring 41 is offset to the right in the vehicle width direction, which is the extension 45b side of the EGR introduction passage 45, from the vehicle width central position of the multiple tank discharge ports 43. This is because the intake air passing through the EGR ring 41 is displaced to the left in the vehicle width direction due to the influence of the throttle valve 10 located upstream, so that the displaced intake air is set to be located in the center in the vehicle width direction. The ring hole 51 is located on the opposite side, on the right side in the vehicle width direction, so that the displaced intake air does not inhibit the introduction of EGR gas by the displaced intake air.

The EGR introduction passage 45 has a piping shape that extends toward the right in the vehicle width direction and has a closed tip, and the EGR ring 41 penetrates the tip (right end) of the EGR introduction passage 45 at a distance from the inner wall of the tip, forming an introduction section for EGR gas.
This allows the introduction portion of the EGR gas into the intake passage 6 to be configured simply and compactly.

In addition, since the EGR introduction passage 45 is integrally formed with the upper wall 11a of the surge tank 11, the surge tank 11 and the EGR introduction passage 45 can be configured compactly. In addition, the branch pipe 12 is configured to extend along the lower wall 11b of the surge tank 11 toward the front side of the vehicle. Since the branch pipe 12 is connected to the rear side of the surge tank 11, the length of the branch pipe 12 in the vehicle front-rear direction can be secured and the bending radius can be increased, while the length of the surge tank 11 and the branch pipe 12 in the vehicle front-rear direction can be reduced. Therefore, the structure of the intake system of the engine 3 can be configured compactly while suppressing the intake resistance in the branch pipe 12.

In addition, the tank inlet 42, which is the opening position at the lower end of the EGR ring 41, is offset from the tank outlet 43, which is the opening position of the branch pipe 12 in the surge tank 11, in the vehicle fore-and-aft direction perpendicular to the inflow direction of the intake air from the tank inlet 42, and the bottom wall 11b of the surge tank 11 is located ahead of the opening side of the tank inlet 42.

Therefore, the intake air containing EGR gas that flows into the surge tank 11 from the tank inlet 42 collides with the lower wall 11b of the surge tank 11 and spreads in the vehicle's fore-and-aft and width directions, promoting the mixing of the EGR gas and the intake air within the surge tank 11 and suppressing bias in the EGR gas concentration of the intake air supplied to each cylinder.

Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the lower end of the EGR ring 41 is at approximately the same vertical position as the inner wall surface of the upper wall 11a of the surge tank 11. In contrast, as shown in FIG. 5, the EGR ring 41 may be extended downward, that is, the EGR ring 41 may be extended downward toward the portion of the lower wall 11b of the surge tank 11 on the vehicle front side, so that the lower end 41a of the EGR ring 41 protrudes downward from the inner wall surface of the upper wall 11a of the surge tank 11.

In this way, by extending the EGR ring 41 downward, the distance from the ring holes 50, 51, which are the EGR gas introduction positions in the EGR ring 41, to the inside of the surge tank 11 is extended, and the mixing of the intake air and the EGR gas in the EGR ring 41 can be promoted. In addition, since the distance between the lower end of the EGR ring 41 and the bottom wall 11b of the surge tank 11 is shortened, the intake air containing the EGR gas that flows from the EGR ring 41 into the surge tank 11 is more likely to collide with the bottom wall 11b of the surge tank 11. This promotes the mixing of the EGR gas in the surge tank 11 and further suppresses the bias of the EGR gas concentration of the intake air supplied to each cylinder from each tank outlet 43.

Alternatively, in the above embodiment, the adapter 40 and the EGR ring 41 are separate structures, but the adapter 40 and the EGR ring 41 may be integrally formed.

In addition, in this embodiment, multiple tank exhaust ports 43 are provided according to the number of cylinders of the engine 3, but this is not limited to the above and the number of tank exhaust ports 43 may be smaller than the number of cylinders of the engine 3. For example, only one exhaust port 43 may be provided and branched in the branch pipe 12 according to the number of cylinders of the engine 3, and intake air may be introduced into each cylinder.

In addition, in this embodiment, the present invention is applied to the engine 3 mounted on a plug-in hybrid vehicle, but it can also be applied to engines mounted on hybrid vehicles or gasoline vehicles, or engines other than those mounted on vehicles. The present invention can be widely applied to engines equipped with an EGR device.

3 engine 6 intake passage 11 surge tank 11a upper wall (upstream wall surface)
11b Lower wall (downstream wall surface)
12 Branch pipe (downstream intake pipe)
30 EGR device (exhaust gas recirculation device)
41 EGR ring (upstream intake pipe)
42 Tank inlet 43 Tank outlet (inlet)
45 EGR introduction passage section (exhaust gas recirculation passage introduction section)
45a Main body (exhaust recirculation passage introduction part)
45b Extension part (Exhaust recirculation passage extension part)
50 Ring hole (first inlet)
51 Ring hole (second inlet)

Claims (5)

An intake system structure of an engine equipped with an exhaust gas recirculation device that recirculates a part of the exhaust gas to an intake passage as exhaust gas recirculation gas,
a surge tank provided in the intake passage;
an upstream intake pipe provided upstream of the surge tank and having an inlet through which the exhaust gas recirculation gas is introduced;
a downstream intake pipe provided downstream of the surge tank and supplying intake air to each cylinder of the engine,
the surge tank has a tank inlet provided on an upstream tank wall surface and connected to the upstream intake pipe, and a tank outlet provided on a downstream tank wall surface and connected to the downstream intake pipe,
The tank inlet is provided displaced to one side in an extension direction of the upstream tank wall surface,
the tank discharge port is provided on the downstream tank wall surface, the tank discharge port being displaced to the other side in the extension direction of the upstream tank wall surface,
An intake system structure for an engine, characterized in that the inlet is provided on the other side of the upstream intake pipe and opens toward the one side, and the exhaust recirculation gas flows into the upstream intake pipe from the other side toward the one side. the exhaust gas recirculation device includes an exhaust gas recirculation passage introduction portion that extends in the extension direction in a tangential direction of the upstream intake pipe and to which the exhaust gas recirculation gas is supplied,
2. The engine intake system structure according to claim 1, wherein the inlet is provided at a junction of the exhaust gas recirculation passage inlet portion. the exhaust gas recirculation device includes an exhaust gas recirculation passage extension portion extending circumferentially along an outer wall of the upstream intake pipe on an opposite side to the exhaust gas recirculation passage introduction portion,
3. The engine intake system structure according to claim 2, wherein the inlet comprises a first inlet provided at the junction of the exhaust recirculation passage inlet and a second inlet provided at the exhaust recirculation passage extension. The engine intake system structure according to any one of claims 1 to 3, characterized in that the downstream end of the upstream intake pipe extends into the surge tank toward the one side of the downstream tank wall. the exhaust gas recirculation passage introduction portion is integrally formed with the upstream tank wall surface,
3. The engine intake system structure according to claim 2 , wherein the downstream intake pipe extends along the downstream tank wall surface to the one side of the upstream tank wall surface.

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