JP2013209066A - Fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel tank which reduces flow sound due to sloshing in a front-back direction of fuel in a fuel tank.SOLUTION: A fuel tank 1 is constituted by putting a top plate 2 and a bottom plate 3 together. The fuel tank 1 includes: front wall faces 2a and 3a, and rear wall faces 2d and 3d extending in a vehicle width direction; right and left side wall faces 2b, 2c, 3b and 3c extending in back and forth direction of the vehicle; a top face 2e; and a bottom face 3e. A plurality of stripes of concave sections 5 recessed inward of the fuel tank 1 is extended and formed approximately in back and forth direction of the vehicle, in the boundary part of the front wall face 2a and the rear wall face 2d, and the top face 2e. The inner surface of the concave section 5 forms a smooth curved surface by which fuel flow that hits the front wall face 2a or the rear wall face 2d is dispersed to the right and left of the inner face of the concave section 5 in the vehicle width direction.

Description

  The present invention relates to a fuel tank, and more particularly to a fuel tank configured to suppress flow noise (collision noise) generated when fuel in the fuel tank rapidly flows.

The body of an automobile includes a fuel tank that stores fuel. Some of these fuel tanks are provided with a wave-dissipating part inside, and the wave-dissipating part is configured to suppress the flow noise generated when the fuel in the fuel tank suddenly flows.
For example, in Patent Document 1, in a fuel tank integrally molded with a synthetic resin, a hollow wave quenching plate is integrally molded as a wave-absorbing portion (absorber), and the fuel in the fuel tank rapidly flows in the front-rear direction of the vehicle. A technique for suppressing this is disclosed. The technique described in Patent Document 1 has a hollow wave extinguishing plate that protrudes downward or upward from the upper or lower wall of the fuel tank into the fuel tank, or a hollow wave extinguishing plate that communicates from the upper wall to the lower wall. A hollow wave extinguishing plate that communicates between the left and right side walls is provided to prevent the fuel in the fuel tank from suddenly flowing (sloshing) in the front-rear direction of the vehicle.

Patent Document 2 discloses a technique of providing a baffle plate suspended from the top surface of the fuel tank at a small interval from the front wall surface at the front portion of the fuel tank. The baffle plate is provided with a plurality of small-diameter holes to prevent the fuel from moving forward when the vehicle is decelerated.
Further, in Patent Document 2, in the configuration of the baffle plate in the front portion of the fuel tank described above, when the fuel level in the fuel tank decreases, the fuel is prevented from moving forward when the vehicle is decelerated. A technology is disclosed that improves the point that the reaction wave that is shaken back after the collision with the front wall of the fuel tank passes through the lower part of the baffle plate and collides with the rear wall of the fuel tank to produce a flow sound. Yes. In the improved technology, the rear wall surface of the fuel tank is formed in a planar shape so that it extends to the left and right front sides, the left and right center portions of the rear wall surface are located on the rear side of the fuel tank, and the depth of the fuel tank in that portion is The baffle plate is configured so as to be higher and provided with a baffle plate suspended from the top surface of the fuel tank at a small interval forward from the substantially central portion of the rear wall surface.
According to this improved technique, when the reaction wave of the fuel moves backward in the fuel tank, the fuel gathers at the left and right central portions and the wave front becomes high. As a result, even when the fuel level is lowered, the fuel flow momentum is suppressed by the baffle plate provided at a small interval forward from the substantially central portion of the rear wall surface, and the fuel wall strongly collides with the rear wall surface. It is possible to suppress the generation of a large flow noise by bouncing back to the rear end of the top surface of the tank.

  In Patent Document 3, in a resin resin fuel tank made of a resin that is attached to a vehicle body such as an automobile and stores fuel in the tank body, a projecting portion projects from the front wall of the tank body into the tank body. Is formed integrally with the front wall, and this overhanging portion is configured to suppress the fuel in the tank body from rising up to the upper surface along the front wall. .

Japanese Utility Model Publication No. 56-87926 (refer to FIGS. 1 to 6) Japanese Patent Laid-Open No. 08-156617 (see FIGS. 1 to 6) Japanese Patent Laying-Open No. 2005-263043 (see FIGS. 2 and 7, paragraphs [0054] to [0058])

However, in the technique disclosed in Patent Document 1, it is necessary to perform blow molding using a core for molding the hollow wave quencher, which is complicated and the capacity of the fuel tank is increased by the hollow wave quencher. There was a problem of being reduced.
Further, the technique disclosed in Patent Document 2 has a configuration in which the baffle plate is suspended from the top surface, and the configuration in which the baffle plate is provided is complicated, and there is a problem that the manufacturing cost of the fuel tank is increased.
Furthermore, in the technique disclosed in Patent Document 3, there is a problem that the capacity of the fuel tank is reduced by the amount of the overhanging portion by adopting a configuration in which the overhanging portion protrudes into the tank body.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a fuel tank that can mitigate flow noise caused by sloshing in the front-rear direction of fuel in the fuel tank.

  In order to solve the above problems, an invention according to claim 1 is a fuel tank of a vehicle, comprising front and rear wall surfaces extending in a vehicle width direction, left and right side wall surfaces extending in a vehicle front-rear direction, and a top surface. A plurality of recesses recessed inward of the fuel tank at the boundary with the top surface of at least one of the front wall surface and the rear wall surface, substantially in the longitudinal direction of the vehicle. The recess is formed to extend, and the concave portion forms a curved surface having a substantially semicircular cross section in the front-rear direction of the vehicle.

  According to the first aspect of the present invention, when the fuel suddenly moves (sloshing) in the fuel tank to the front side or the rear side and collides with the front wall surface or the rear wall surface, the inner side of the fuel tank. The plurality of recesses that are recessed in the surface form a curved surface having a substantially semicircular cross section in the front-rear direction of the vehicle. Dispersing the sound to the left and right can alleviate the flow noise.

  In addition, since the concave portion is provided at the boundary between the front wall surface or the rear wall surface and the top surface, the front and rear edge portions have the concave portion, resulting in the rigidity of the front and rear edge portions of the top surface. Enhanced. Therefore, when the fuel suddenly moves to the front side or the rear side of the vehicle and the wave front hits the front and rear edges of the top surface, the front and rear edges have concave portions, so that the top surface is The effect of generating drum sounds can be suppressed.

  According to a second aspect of the invention, in addition to the configuration of the first aspect, a plurality of recesses are formed adjacent to each other in the vehicle width direction, and an inner surface including the plurality of recesses forms a curved surface that smoothly undulates in the vehicle width direction. It is characterized by.

  According to the second aspect of the present invention, since the plurality of recesses are formed close to each other in the vehicle width direction, fuel having a certain width that collides with the recesses can be dispersed left and right in the vehicle width direction. Flow sound can be reduced.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, at least one of the front wall surface and the rear wall surface has its left and right wings inclined obliquely toward the center of the plane of the fuel tank. In addition, a plurality of recesses are formed on the left and right wings.

  According to the third aspect of the present invention, the reaction waves that are caused by the rapid flow of fuel that collides with the front wall surface or the rear wall surface whose left and right wings obliquely face the plane center side of the fuel tank are It can be directed to the center of the plane of the tank, where the reaction waves from both the left and right wings and the center of the left and right collide, and the momentum of the reaction waves is partially offset. As a result, the momentum when the reaction wave collides with the rear wall surface or the front wall surface can be reduced, and the flow sound caused by the reaction wave can be reduced.

  According to a fourth aspect of the invention, in addition to the configuration of the first aspect of the invention, the fuel tank includes a front wall surface and a rear wall surface extending in the vehicle width direction, and a vehicle front-rear direction. A fuel is formed by combining a bottom plate portion having left and right side wall surfaces and a bottom surface extending, a front wall surface and a rear wall surface extending in a vehicle width direction, and a top plate portion having left and right side wall surfaces and a top surface extending in a vehicle front-rear direction. At least the bottom surface of the bottom plate portion of the tank has a substantially flat shape.

  According to the invention described in claim 4, since at least the bottom surface of the fuel tank has a substantially flat shape, the capacity of the fuel tank can be reduced without greatly reducing the capacity of the fuel tank as in the prior art described in Patent Document 1. Flow noise caused by sudden movement (sloshing) in the fuel tank can be reduced.

  In the invention according to claim 5, in addition to the configuration of the invention according to claim 4, when the recess is formed in the top plate portion and is formed to extend substantially in the front-rear direction of the vehicle, both end portions in the front-rear direction Is a curved surface that smoothly merges with the flat part in the vicinity, and does not obstruct the flow in the front-rear direction of the fuel that collides toward the front wall surface or the rear wall surface at the inner surfaces of both ends in the front-rear direction of the recess. It is characterized by.

  According to the invention described in claim 5, since both end portions of the concave portion are smoothly fused with the adjacent flat portion, the flow of the fuel colliding with the front wall surface or the rear wall surface becomes an upward flow, and the wave front is Even if it collides with the end of the recess, a smooth curved surface is formed, so no flow noise is generated.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel tank which relieves the flow noise by the rapid movement (sloshing) of the fuel in the fuel tank in the front-back direction can be provided.

It is a top view of the fuel tank of an embodiment. It is the perspective view seen from the right rear direction of the fuel tank of an embodiment. It is explanatory drawing of a flow when the flow of the rapid movement of the fuel in a fuel tank collides with the recessed part of a front wall surface or a rear wall surface, (a) is a perspective view looking up diagonally upward of the XX arrow of FIG. The figure and (b) are YY arrow directional cross-sectional views in (a). It is explanatory drawing of a reaction wave when the flow of the rapid movement of the fuel in a fuel tank collides with a rear wall surface.

  Hereinafter, a fuel tank according to an embodiment of the present invention will be described in detail with reference to the drawings.

The fuel tank in the present embodiment will be described with reference to FIGS. 1 and 2.
FIG. 1 is a top view of the fuel tank of the embodiment, and FIG. 2 is a perspective view of the fuel tank of the embodiment as viewed from the right rear direction.
Incidentally, the front / rear, left / right, and up / down directions in the following description are displayed in the front / rear, left / right, up / down directions of the vehicle when the fuel tank 1 is mounted on the vehicle.
The fuel tank 1 shown in FIG. 1 is made of, for example, resin, and the upper and lower sides thereof are joined together at the joining surface A, and is composed of, for example, a blow-molded top plate portion 2 and bottom plate portion 3 and is substantially rectangular in plan view. Shape.
The top plate portion 2 has a front wall surface 2a, a left wall surface 2b, a right wall surface 2c, and a top surface 2e and is integrally formed.
As shown in FIG. 2, the bottom plate portion 3 has a front wall surface 3a, a left wall surface 3b, a right wall surface 3c, and a bottom surface 3e and is integrally formed.

  As shown in FIG. 1, the center portions of the rear wall surfaces 2d, 3d of the top plate portion 2 and the bottom plate portion 3 are flat in the left-right direction, but both left and right wings of the rear wall surfaces 2d, 3d of the top plate portion 2 and the bottom plate portion 3 are used. The portion is inclined obliquely toward the plane center side of the fuel tank 1 in plan view.

As shown in FIGS. 1 and 2, a portion extending from the upper part of the front wall surface 2a of the top plate 2 to the front edge of the top surface 2e is recessed toward the inner side of the fuel tank 1, and the longitudinal direction of the vehicle A plurality of recesses 5 are provided continuously in the left-right direction (corresponding to “the recess is provided at the front wall surface or the boundary between the rear wall surface and the top surface” in the claims). In the example of FIG. 1, two concave portions 5 are provided on the left and right wing portions on the front side of the top plate portion 2.
In addition, a recess 5 that is recessed inward of the fuel tank 1 and extends substantially in the front-rear direction of the vehicle at a portion from the upper portion of the rear wall surface 2d of the top plate 2 to the rear edge of the top surface 2e, A plurality of continuous portions are provided in the left-right direction (corresponding to “the concave portion is provided at the front wall surface or the boundary between the rear wall surface and the top surface” in the claims). In the example of FIG. 1, two concave portions 5 are provided on the left wing portion on the rear side of the top plate portion 2, and three concave portions 5 are provided on the right wing portion on the rear side of the top plate portion 2.

The recess 5 has a substantially semicircular cross-section in the front-rear direction, and smoothly in the left-right direction with the flat portion 6 of the edge of the top surface 2e adjacent to the left and right, the flat portion 6 of the front wall surface 2a, and the rear wall surface 2d. It is formed so as to form a curved surface (see FIG. 3).
Further, the concave portion 5 is formed so that the front and rear wall side end portions 5a of the concave portion 5 smoothly merge with the flat portion 6 of the front wall surface 2a or the rear wall surface 2d, and the top surface side end portion 5b of the concave portion 5 It is formed so as to smoothly merge with the flat portion 6 at the edge on the front side or the rear side of the top surface 2e (see FIG. 3A). Here, the front and rear wall surface side end portions 5a of the concave portion 5 and the top surface side end portion 5b of the concave portion 5 correspond to "both end portions in the front and rear direction of the concave portion" described in the claims.
Incidentally, the bottom surface 3e is a substantially flat plane.

As shown in FIG. 2, a fuel tank 11 and an air vent pipe 12 that are normally provided are connected to the fuel tank 1, and a fuel pump 13 and a fuel cut valve 14 are provided. The fuel cut valve 14 has a charcoal (not shown). A purge pipe 15 connected to the canister is connected.
In the example of FIGS. 1 and 2, almost half of the front side of the top plate 2 of the fuel tank 1 rises higher than the rear side, and a fuel cut valve 14 is arranged in the center of the top to purge the fuel vapor. It flows to the pipe 15 side.

In addition, almost half of the rear side of the top plate portion 2 of the fuel tank 1 has a substantially flat top surface 2e. For example, on the left and right sides of the fuel pump 13 in order to prevent the vertical drooping characteristic of the flat tank. The top and bottom surfaces 2e and the bottom surface 3e are swelled in a substantially cylindrical shape toward each other inward of the fuel tank 1 at a site separated from the fuel pump 13 by a predetermined distance in the left-right direction. It is provided.
The left and right positions in the fuel tank 1 in which the upper and lower welds 8 and 8 are arranged are the left and right of the plurality of recesses 5 provided in the region from the upper part of the front wall surface 2a to the front edge of the top surface 2e. It is a position shifted so as not to overlap the position in the horizontal direction and the position in the left-right direction of the plurality of recesses 5 provided in the region from the upper part of the rear wall surface 2d to the rear edge of the top surface 2e. That is, as shown in FIG. 1, the position is closer to the center in the left-right direction.

Next, referring to FIG. 3, the fuel in the fuel tank 1 suddenly moves backward when the vehicle starts, or the fuel in the fuel tank 1 suddenly moves forward when the vehicle stops. The function of the recess 5 when it collides with the rear wall surfaces 2d, 3d or the front wall surfaces 2a, 3a of the fuel tank 1 will be described.
FIG. 3 is an explanatory diagram of the flow when the flow of the rapid movement of the fuel in the fuel tank collides with the concave portion of the front wall surface or the rear wall surface, and (a) is an oblique view taken along the line XX in FIG. The perspective view which looks up upwards, (b) is a YY arrow sectional drawing in (a).

For example, the case where the fuel in the fuel tank 1 collides with the front wall surfaces 2a and 3a at the time of stopping will be described with reference to FIG. Even if the liquid level of the fuel is low and does not reach the front wall surface 2a, if the fuel in the fuel tank 1 suddenly moves forward, the liquid level reaches the front wall surface 2a and collides. Conventionally, a large lump of droplets generated at the time of the collision collides with the top surface 2e to generate a large flow sound (collision sound). However, according to the present embodiment, when the wave front TW collides with the front wall surface 2a, the concave portion 5 protrudes inward, and the flat portions 6 adjacent to the left and right of the concave portion 5 protrude outward, and in the left-right direction in FIG. Since a smooth curved surface (smoothly undulating curved surface) is formed, the flow colliding with the concave portion 5 is divided into right and left as shown by arrows, and flows from the opposite side in the portion indicated by C of the flat portion 6. Will collide with. The collision at the part C of the flow in the left and right direction partly cancels out the momentum of the fuel, and the momentum of the fuel that collides with the front side edge of the top surface 2e of the top plate 2 and the upper part of the front wall 2a. Get smaller. As a result, there is an effect of relieving the flow sound that is a drum sound mainly generated from the top surface 2e.
As the number of the recesses 5 is increased, more left-right flow can be generated at the front wall surface 2a, and a larger amount of forward fuel movement can be offset at the portion C. That is, since a plurality of recesses 5 are formed close to each other in the vehicle width direction, fuel having a certain width that collides with the recesses 5 can be dispersed left and right in the vehicle width direction. As a result, the effect of relaxing the flow noise is enhanced.
This effect is the same in the concave portion 5 of the rear wall surface 2d.

  In addition, by arranging the above-described upper and lower welded portions 8 and 8 substantially on both the left and right sides of the fuel pump 13, the fuel pump 13 and the fuel pump 13 are vertically moved together with the fuel pump 13 at the central portion in the left and right direction. Since the welded portions 8 and 8 are sufficiently effective in suppressing the sloshing of the fuel in the front-rear direction, the concave portion 5 is not provided in order to suppress a decrease in the fuel capacity of the fuel tank 1 even a little.

  By the way, the front and rear wall side ends 5a of the recess 5 and the top surface end 5b of the recess 5 are formed so as to smoothly merge with the flat portion 6, so that when the fuel level moves up and down, With respect to the flow in the front-rear direction of the fuel generated by the sloshing in the front-rear direction of the fuel, no large flow noise is generated at the front-rear wall-side end 5a and the top-side end 5b of the recess 5.

  Further, according to the present embodiment, the recess 5 extends from the upper part of the front wall surface 2a to the front edge of the top surface 2e or from the upper part of the rear wall surface 2d to the rear edge of the top surface 2e. Since it is provided in this way (the recess is provided at the boundary between the front wall surface or the rear wall surface and the top surface), as a result, the rigidity of the front edge and the rear edge of the top surface 2e is increased. Enhanced. Therefore, when the fuel suddenly moves to the front side or the rear side of the vehicle and the wave front hits the front and rear edges of the top surface 2e, the front and rear edges of the top surface 2e have the recesses 5, The top surface 2e suppresses the effect of generating drum sounds.

Next, referring to FIG. 4, a description will be given of the flow noise suppression effect due to the fact that the left and right blade portions of the rear wall surfaces 2 d and 3 d are configured obliquely toward the center of the plane in the plan view of the fuel tank 1. FIG. 4 is an explanatory diagram of the reaction wave when the flow of the rapid movement of the fuel in the fuel tank collides with the rear wall surface.
As shown in FIG. 4, for example, when the fuel starts and the fuel suddenly moves backward in the fuel tank 1, the wave front moves backward as shown by TW and collides with the rear wall 2 d. The direction of the colliding flow is indicated by thick arrows AC, AL, AR. The flow of the thick arrows AL and AR collide with each other in the recess 5 as indicated by the arrows of CL and CR, and part of the momentum of the flow is lost. This is a wave-dissipating effect like a wave-dissipating block on a coastal dike. Then, a reaction wave caused by the rear wall surface 2d is generated in the direction indicated by the white arrows RC, RL, RR with respect to the flow of the thick arrows AC, AL, AR, and the region B in the center of the fuel tank 1 in plan view Interfere with each other, and the momentum of the reaction wave is partially offset. As a result, it is possible to mitigate the flow noise when the reaction wave collides with the front wall surface 2a.

  In particular, in order to expect this effect, the bottom surface 3e of the bottom plate portion 3 is substantially flat, and the traveling speed of the reaction wave is almost the same for the white arrows RC, RL, RR, and interference occurs in the central region B. You can expect If the bottom surface 3e is not substantially flat but has a deep portion and a shallow portion in plan view, the wave speed increases as the wave speed increases from the deep portion of the bottom surface 3e to the shallow portion, and the phase of the wave shifts. This is because they do not work in the direction to cancel each other's waves.

  According to the present embodiment, the recess 5 extends from the upper part of the front wall surface 2a or the upper part of the rear wall surface 2d to the front edge or the rear edge (the front and rear edges of the top surface 2e) of the top surface 2e. (The concave portion is provided at the boundary between the front wall surface or the rear wall surface and the top surface), so that the baffle plate is not provided as in the prior art of Patent Document 2, In addition, the flow noise can be reduced without substantially reducing the capacity of the fuel tank 1.

In the present embodiment, the fuel tank 1 is not limited to the top surface 2e of the top plate portion 2 raised on the front side, and may be substantially flat.
In the case of such a flat type fuel tank 1, in order to ensure the same fuel capacity, the width in the front-rear direction of the fuel tank 1 is larger than that shown in FIG. 1, and the wave travel distance due to sloshing is long. Thus, since the momentum of the fuel that collides with the plurality of recesses 5 is also increased, the effect of suppressing the flow noise by the plurality of recesses 5 is further enhanced as compared with the case of the fuel tank 1 shown in FIG.
Further, in the fuel tank 1 of the present embodiment, the bottom surface 3e of the bottom plate portion 3 is substantially flat, but it may be one in which the left and right sides are divided substantially at the center like a bowl shape.

In the present embodiment, the fuel tank 1 is recessed inward of the fuel tank 1 in a portion extending from the upper portion of the front wall surface 2a of the top plate portion 2 to the front edge of the top surface 2e, in the longitudinal direction of the vehicle. A plurality of recessed recesses 5 are continuously provided in the left-right direction, and the interior of the fuel tank 1 is located at a portion from the upper portion of the rear wall surface 2d of the top plate portion 2 to the rear edge portion of the top surface 2e. Although a plurality of recesses 5 that are recessed in the lateral direction and extend substantially in the front-rear direction of the vehicle are provided continuously in the left-right direction, the present invention is not limited thereto.
The fuel tank 1 includes a portion from the top of the front wall 2a of the top plate 2 to the front edge of the top surface 2e, and a rear edge of the top 2e from the top of the rear wall 2d of the top plate 2 It is also possible to provide a structure in which a plurality of recesses 5 that are recessed inwardly of the fuel tank 1 and are extended substantially in the front-rear direction of the vehicle are provided continuously in the left-right direction. good.

  Furthermore, in the present embodiment, the fuel tank 1 is assumed that the left and right blade portions of the rear wall surfaces 2d and 3d of the top plate portion 2 and the bottom plate portion 3 are inclined obliquely toward the center of the plane in the plan view of the fuel tank 1. It is not limited to that. The fuel tank 1 may have a configuration in which the left and right wing portions of the front wall surfaces 2 a and 3 a of the top plate portion 2 and the bottom plate portion 3 are inclined obliquely toward the center of the plane in the plan view of the fuel tank 1.

DESCRIPTION OF SYMBOLS 1 Fuel tank 2 Top plate part 2a Front wall surface 2b Left side wall surface 2c Right side wall surface 2d Rear wall surface 2e Top surface 3 Bottom plate part 3a Front wall surface 3b Left side wall surface 3c Right side wall surface 3d Rear wall surface 3e Bottom surface 5 Recess 5a Top side end of recess 6 Flat part 8 Vertical welded part

Claims (5)

A fuel tank for a vehicle,
Front and rear wall surfaces extending in the vehicle width direction, left and right side wall surfaces extending in the front-rear direction of the vehicle, a top surface, and a bottom surface,
A plurality of recesses recessed inwardly of the fuel tank are formed extending substantially in the front-rear direction of the vehicle at the boundary with the top surface of at least one of the front wall surface and the rear wall surface. And
The said recessed part forms the curved surface from which the front-back direction cross section of a vehicle becomes substantially semicircle shape, The fuel tank characterized by the above-mentioned.   2. The fuel tank according to claim 1, wherein a plurality of the recesses are formed adjacent to each other in the vehicle width direction, and an inner surface including the plurality of recesses forms a curved surface that smoothly undulates in the vehicle width direction.   At least one of the front wall surface and the rear wall surface is characterized in that both left and right wings are inclined obliquely toward the plane center side of the fuel tank, and the plurality of recesses are formed in the left and right wings. The fuel tank according to claim 1 or 2. The fuel tank includes the front wall surface and the rear wall surface extending in the vehicle width direction, the bottom plate portion having the left and right side wall surfaces and the bottom surface extending in the vehicle front-rear direction, and the front wall surface and the rear wall surface extending in the vehicle width direction. And the top plate part having the left and right side wall surfaces extending in the front-rear direction of the vehicle and the top surface are formed together,
The fuel tank according to any one of claims 1 to 3, wherein at least the bottom surface of the bottom plate portion of the fuel tank has a substantially flat shape. The concave portion is formed in the top plate portion,
In forming the vehicle substantially extending in the front-rear direction, the front and rear sides of the fuel colliding toward the front wall surface or the rear wall surface are smoothly fused at the both ends in the front-rear direction. The fuel tank according to claim 4, wherein a curved surface that does not obstruct a flow in a direction is formed on an inner surface of both end portions of the recess in the front-rear direction.

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