JP2005075167A - Front part vehicle body structure of vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a front part vehicle body structure of a vehicle capable of sufficiently buckling and deforming a front frame without displacement (inward fall) of a front end position of the front frame to a vehicle body inward side, even when larger load is inputted in the front part vehicle body structure of the vehicle adopting the so-called trifurcated frame. <P>SOLUTION: In this structure, an inward side member 113 is greatly extended to an upper side on a vehicle center side, a swollen part 113d extending to an oblique upper side on the vehicle center side is formed in the extended part, and a closed section part 34 is constituted between the swollen part 113d and a dash panel 31. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a front body structure of a vehicle, and more particularly to a front body structure of a vehicle configured to connect a rear end of a front frame to a tunnel panel, a side sill, and a floor frame of a floor panel.

  Conventionally, it is known to improve the collision performance of a vehicle by appropriately distributing a load input to the front frame during a frontal collision to a plurality of member members extending in the vehicle front-rear direction. (For example, refer to Patent Document 1).

  That is, as described in Patent Document 1, the front frame rear end is configured to be trifurcated so as to be connected to three members of a tunnel member, a side sill, and a floor frame extending in the vehicle front-rear direction. It is known that the collision load input to the front frame is appropriately transmitted to three members to disperse the collision load and improve the collision performance of the vehicle.

JP2003-63455A.

  By the way, since the collision load absorption of the front frame is generally performed by buckling deformation, it is better that the front end of the front frame is not displaced left and right and up and down as it is from the initial stage of the collision to the middle and late stage.

  In this regard, in the case of the vehicle body structure employing the so-called trifurcated frame described above, the rear end of the frame is certainly divided into three sides, so that the front end of the front frame is difficult to be displaced left and right and up and down during a frontal collision.

  However, looking at the members that receive impact loads, the side sill and floor frame are composed of completely closed cross-section member members with sufficient cross-sectional area, whereas the member members provided in the tunnel section are In order to secure vehicle volume (for example, exhaust pipe, propeller shaft, etc.) and vehicle compartment volume, a sufficient cross-sectional area cannot be ensured, and sufficient rigidity cannot be obtained.

  As described above, since only the member member of the tunnel portion does not have a sufficient cross-sectional area, even when a three-branch frame is employed, when a large collision load is input, the rear end of the front frame is relatively There is a problem that the rigidity on the tunnel side is weaker than that on the side sill side, and the front end of the front frame is displaced (inward) to the inside of the vehicle body, so that the front frame cannot be sufficiently buckled. It was.

  In particular, such a problem is likely to occur in a vehicle such as an open car that can receive a collision load only with an underbody.

  Therefore, the present invention is a front body structure of a vehicle that employs a so-called three-branch frame, and even when a larger load is input, the front end position of the front frame is not displaced (inwardly tilted) to the vehicle body inward side. An object of the present invention is to provide a vehicle front body structure capable of sufficiently buckling and deforming a frame.

  A vehicle front body structure according to the present invention includes a dash panel forming a front end wall of a passenger compartment, and a floor panel extending from the lower end of the dash panel to the rear of the vehicle. Forming a tunnel portion extending in the vehicle width direction of the floor panel and providing a side sill extending in the vehicle front-rear direction, and providing a floor frame extending in the vehicle front-rear direction on the bottom surface of the floor panel between the tunnel portion and the side sill, Further, the vehicle has a front vehicle body structure that includes a front frame that extends in front of the dash panel in the vehicle front-rear direction and has a rear end coupled to the tunnel portion, side sill, and floor frame. A load transmission increasing means for increasing the load transmission with respect to the dash panel is provided at the end of the tunnel connecting portion. That.

  That is, in a vehicle front body structure configured as a so-called trifurcated frame in which the rear end of the front frame is connected to the tunnel portion, the side sill and the floor frame, the load that increases load transmission to the dash panel at the tunnel portion connecting portion. A transmission increasing means is provided to transmit the collision load transmitted to the tunnel side to the dash panel.

  According to the above configuration, since the collision load transmitted to the tunnel portion side by the load transmission increasing means is also transmitted to the dash panel, a part of the collision load on the tunnel portion side can be received by the dash panel.

  Therefore, the relatively low rigidity of the tunnel part can be increased by utilizing the rigidity of the dash panel.

  As specific embodiments of the load transmission increasing means, a configuration in which the thickness of the tunnel portion connecting portion at the rear end of the front frame is increased, or another panel material is used for the tunnel portion connecting portion at the rear end of the front frame. The structure which sticks, the structure which forms several rib extended with respect to a dash panel in the tunnel part connection part of the rear end of a front frame etc. can be considered.

  In one embodiment of the present invention, the load transmission increasing means is configured as a closed cross section extending from the rear end of the front frame to the dash panel.

  According to the above configuration, since the closed cross-section portion is used as the load transmission increasing means, the load transmission can be performed to the dash panel without increasing the plate thickness or increasing the vehicle body weight as compared with the case where another member is provided. Can do.

  Therefore, the relatively low rigidity of the tunnel portion can be increased without increasing the vehicle body weight.

  In one embodiment of the present invention, the closed cross section is configured to extend obliquely upward toward the vehicle center side.

  That is, the closed cross-section portion that transmits the load to the dash panel is formed to be inclined so as to extend obliquely upward on the vehicle center side.

  According to the above configuration, the position for transmitting the load to the dash panel is set obliquely above the vehicle center side relative to the front frame position, so the side sill and the floor frame installation position (vehicle side and vehicle bottom) Thus, the load is transmitted just at the position facing the front frame.

  In this way, by transmitting the load to the dash panel at a position obliquely above the center of the vehicle, which is the position where the side sill and the floor frame face each other, the rigidity in the vertical and horizontal directions of the rear end of the front frame becomes even more uniform. Further, the displacement (inward tilt) of the front end of the front frame on the inner side of the vehicle body is suppressed, and the front frame can be reliably buckled and deformed.

  In one embodiment of the present invention, a tunnel reinforcing member extending in the vehicle front-rear direction is provided behind the dash panel, a second closed cross section is formed between the tunnel reinforcing member and the dash panel, and the second The closed cross section is set on the vehicle rear side of the load transmission increasing means.

  According to the above configuration, the second closed cross-section formed by the tunnel reinforcing member is set on the vehicle rear side of the load transmission increasing means, so that even if load transmission to the dash panel is increased by the load transmission increasing means, Since the rigidity of the dash panel can be sufficiently secured, the load transmission increasing means can function more reliably.

  In one embodiment of the present invention, a pair of left and right front frames are provided, and the pair of left and right front frames are connected by the load transmission increasing means and the second closed cross section.

  According to the above configuration, the frame rigidity can be further increased in the vehicle width direction by connecting the pair of left and right front frames by the load transmission increasing means and the second closed cross section, and the torsional rigidity between the left and right frames can be increased. Can also be increased. Therefore, the vehicle body rigidity of the entire vehicle can also be improved.

  According to this invention, in the front body structure of the vehicle configured as a so-called trifurcated frame, a load transmission increasing means for increasing load transmission with respect to the dash panel is provided in the tunnel portion connecting portion, and transmitted to the tunnel portion side. By adopting a configuration in which the collision load is increased and transmitted to the dash panel, the dash panel can partially receive the collision load on the tunnel side, and the relatively low rigidity of the tunnel side can be reduced. It can be increased using rigidity.

  Therefore, in the front body structure of a vehicle that employs a three-branch frame, even when a larger load is input, the front end position of the front frame is not displaced (inwardly tilted) toward the vehicle body, and the front frame is satisfactorily seated. A front body structure of a vehicle that can be bent and deformed can be provided.

An embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic plan view of a lower vehicle body structure of a vehicle employing the front vehicle body structure of the present invention.

  The vehicle of the present embodiment is a so-called open car having an open body at the upper part of the passenger compartment, and is configured to absorb a collision load with a lower vehicle body that is an underbody.

  That is, as a specific vehicle body structure, as shown in FIG. 1, a pair of left and right front side frames 11, 11 is provided on the front side of the vehicle, and the pair of left and right front side frames 11, 11 includes an intermediate portion and a front portion. Is configured as a vehicle body rigid member extending in the front-rear direction of the vehicle, and at the rear end portion of the front side frame 11, a main portion 11a extending in the front-rear direction and an inwardly wide portion 11b extending in the vehicle width direction The vehicle wide direction outer wide portion 11c is integrally or integrally formed, and the inner wide width portion 11b is provided with an extension portion 11c extending rearward along the vehicle outer surface of the tunnel portion (see FIG. 2). It is integrally formed.

  Further, a floor frame portion 12 and a rear side frame 13 are integrally extended toward the rear on an extension line of the main portion 11a of the pair of left and right front side frames 11, 11. Here, the above-mentioned floor frame portion 12 is a vehicle body rigid member that is joined to the lower vehicle outer surface of the floor panel 17 (see FIG. 2) to form a closed cross section and extends in the front-rear direction of the vehicle. The main part 11a is connected to the floor frame part 12.

  As shown in FIG. 1, a front cross member (so-called No. 1 cross member) 14 extending in the vehicle width direction is provided between the front portions of the front side frames 11 and 11, and corresponds to the lower portion of the dash panel. Thus, a torque box 15 extending in the vehicle width direction is provided on the outer side of the rear end portion of the front side frame 11, and the outer end portion of the torque box 15 is substantially parallel to the floor frame portion 12 in the vehicle front-rear direction. An extending side sill 16 is attached.

  As shown in FIG. 1, the outer wide portion 11 c of the front side frame 11 described above extends in the vehicle width direction along a front vehicle outer side surface of a dash panel 31 described later, and the vehicle width direction side portion thereof is a torque box 15. And the side sill 16. Here, the aforementioned torque box 15 is a vehicle body rigid member extending in the vehicle width direction so as to connect the floor frame portion 12 and the side sill 16.

  On the other hand, the inner wide portion 11b of the front side frame 11 also extends in the vehicle width direction along the front vehicle outer surface of the dash panel 31 described later, and the center portion in the vehicle width direction is joined to the tunnel portion 18 side.

  In addition, the above-described extensions 11d and 11d extending rearward from the wide portion 11b are joined to upper corner portions (corner portions) on the outer side of the lower surface of the tunnel portion 18 having a hat-like section (portion-shaped gate shape), and a pair of closed portions. A cross section is formed.

  The above-described tunnel portion 18 is formed so as to protrude substantially upward at the center of the floor panel 17 and extend in the front-rear direction of the vehicle. A member 19 (a so-called high-mount backbone frame) is attached, and closed sections 20 and 20 (shown in FIGS. 2 and 5) extending in the front-rear direction of the vehicle are formed between the tunnel portion 18 and the tunnel member 19. The vehicle body rigidity is improved. Here, the tunnel member 19 described above extends in the front-rear direction of the vehicle along the tunnel portion 18.

  Further, a tunnel reinforcement 21 is installed in front of the tunnel member 19 so as to extend and connect the vehicle compartment side surface of the dash panel and the front end of the tunnel member in the vehicle front-rear direction. By this tunnel reinforcement 21, the collision load at the time of the frontal collision can be transmitted to the tunnel member 19.

  As shown in FIG. 1, the rear end portion of the tunnel member 19 and the rear side frames 13 and 13 are connected by a rear connection frame 22, and the rear portion of the side sill 16 and the tunnel portion 18 are connected. They are connected by a rear cross member 23 extending in the vehicle width direction.

  Next, the detailed structure of the front body structure of the vehicle will be described in detail with reference to FIGS. 2 is a plan view of the main part showing the front body structure, FIG. 3 is a front view of the front body structure, FIG. 4 is a detailed perspective view of the rear end of the front side frame, and FIG. FIG. 6 is a cross-sectional view taken along line AA in FIG.

  First, the dash panel 31 that forms the front wall of the passenger compartment extends in the vehicle width direction and in the vertical direction, and at the center in the vehicle width direction, a lower portion thereof is recessed upward so as to correspond to the tunnel portion 18 described above. A recess 31a that is recessed toward the rear of the vehicle is also formed at the top. A dash cross member 32 extending in the vehicle width direction is joined to the side surface of the dash panel 31 on the passenger compartment side. The dash cross member 32 forms a closed cross section with the dash panel 31 and is joined to a height substantially coincident with the rear end of the front frame 11 described above, and both ends thereof are connected to the tunnel portion 18 and the torque box 15. Via the side sill 16 (not shown in FIGS. 2 to 6).

  A floor panel 17 extending in the vehicle width direction and in the front-rear direction is joined to the lower end of the dash panel 31. The floor panel 17 is formed with a tunnel portion 18 extending in the front-rear direction at the center in the vehicle width direction as described above. In the front part of this tunnel part, in order to house a part of the power unit such as the engine / transmission in the interior (outside of the passenger compartment), the amount of protrusion in the upward direction and the vehicle width direction is set large.

  Further, the tunnel member 19 and the tunnel reinforcement 21 are joined to the upper portion of the tunnel portion 18 so as to extend in the front-rear direction. Among these, the tunnel reinforcement 21 is joined to the dash panel 31 side from the rear side of the joining portion 32a of the dash cross member 32 on the tunnel portion 18 side, and the joining flange 21a at the front end thereof is joined. The left and right dash cross members 32 are connected at the front end.

  Note that an insertion hole 19a is formed in the center of the tunnel member 19 so as to insert a shift lever extending from the transmission (see FIG. 5).

  In addition, the floor frame portion 12 is joined to the lower surface of the floor panel 17 so as to extend in the front-rear direction in a pair of left and right, while the tunnel portion 18 and the side sill 16 are provided in the vehicle width direction on the upper surface of the floor panel 17. A pair of floor members 33 (see FIG. 5) that extend and connect are joined in pairs.

  The pair of left and right front side frames 11 are arranged on the vehicle front side of the dash panel 31 so as to extend in the front-rear direction. As described above, the rear end of the front side frame 11 has the main portion 11a as the floor frame portion 12, the vehicle width direction outer wide portion 11c as the torque box 15 and the side sill 16, and the vehicle width direction inner wide portion. The so-called trifurcated structure is formed by joining the 11b and the extension portion 11d to the tunnel portion 18 (see FIG. 2).

  That is, as shown in FIGS. 3 and 4, the rear end of the front side frame 11 constitutes the side wall of the main part member member 111 constituting the main part 11 a of the front side frame and the wide part 11 c outside in the vehicle width direction. The outer side member member 112, the inner side member member 113 constituting the side wall of the wide portion 11b in the vehicle width direction, and the upper side located above the member member and constituting the upper wall of the rear end of the front side frame. The side plate member 114 is composed of four members.

  These four members are joined to the front surface of the dash panel 31 by the respective joining flanges 111a to 114a, and form a closed cross section with the dash panel at each of the bulging portions 111b to 113b, and the rear end of the front side frame 11 The frame cross section is configured. Moreover, these four members are mutually joined by joining flanges 111c to 114c between them, and constitute the rear end of the front side frame 11 as a unit.

  In addition, a reinforcing member 115 is joined in front of the joining position between the main member member 111 and the floor frame portion 12 to increase the joining strength between the main member member 111 and the floor frame portion 12.

  Here, the above-described inner member member 113 is further provided with a closed cross-sectional portion 34 that increases load transmission to the recess 31a above the dash panel. That is, the inward member member 113 is greatly extended above the center of the vehicle (see FIG. 3), and a bulging portion 113d extending obliquely upward in the center of the vehicle is formed in the extended portion. A closed cross section 34 is formed between 113 d and the dash panel 31.

  The closed cross section 34 is formed so that its front end rises smoothly from the side surface of the rear end 11 of the front side frame, and its rear end is formed so as to be orthogonal to the vertical wall of the recess 31a above the dash panel. A collision load from the front of the front side frame 11 is transmitted to the recess 31a above the dash panel (see FIG. 4).

  Thus, the collision load is increased and transmitted to the dash panel 31, so that the collision load that the inner side member member 113 handles is positively transmitted to the dash panel 31 other than the tunnel portion 18, and the tunnel portion. The collision load transmitted to is reduced.

  On the rear side of the dash panel 31 of the closed section 34, a second closed section 35 configured between the tunnel reinforcement 21 and the dash panel 31 is set as shown in FIG. The second closed cross-section portion 35 is positioned behind the above-described closed cross-section portion 34, so that the rigidity of the recess 31a of the dash panel can be increased and the collision load increased by the closed cross-section portion 34 can be appropriately received.

  The second closed cross-section portion 35 is positioned above the tunnel portion 18 and is set to connect the pair of left and right closed cross-section portions 34. That is, the pair of left and right front side frames 11 are configured to be connected by the pair of left and right closed cross-section portions 34 and the second closed cross-section portion 35. By connecting the left and right front side frames 11 in this way, the frame rigidity in the vehicle width direction can be increased, and the torsional rigidity between the left and right frames can also be increased.

  Further, a third closed cross-section portion 36 formed between the dash panel 31 and the dash cross member 32 is set between the closed cross-section portion 34 and the second closed cross-section portion 35 as shown in FIG. Yes. Since the third closed cross-section portion 36 extends in the vehicle width direction and restricts the position of the dash panel 31 in the vehicle width direction, the rigidity of the concave portion 31a of the dash panel can be further increased.

  In addition, 37 shown in FIG. 2 is a front pillar which fixes the hinge etc. of a front door.

  Next, the operation and effect of the front body structure of the vehicle of the present embodiment configured as described above will be described in detail.

  As described above, the front vehicle body structure of the present embodiment includes the dash panel 31 that forms the front end wall of the vehicle compartment, and the floor panel 17 that extends rearward from the lower end of the dash panel. A tunnel portion 18 extending in the vehicle front-rear direction is formed at the center, a side sill 16 extending in the vehicle front-rear direction is provided at the vehicle width direction end of the floor panel, and a floor panel 17 under the floor panel 17 between the tunnel portion 18 and the side sill 16 is provided. A front frame 11 having a floor frame portion 12 extending in the vehicle front-rear direction and extending in the vehicle front-rear direction in front of the dash panel and having a rear end coupled to the tunnel portion 18, the side sill 16, and the floor frame portion 12 is provided. In the front body structure of the vehicle with the tunnel portion 18 connecting portion at the rear end of the front side frame 11, It is provided with a closed cross-section portion 34 to increase the load transmitted to the serial dash panel 31.

  That is, in the vehicle front body structure configured as a so-called trifurcated frame in which the rear end of the front side frame 11 is connected to the tunnel portion 18, the side sill 16, and the floor frame portion 12, an inner member member that is a connecting portion of the tunnel portion 18. 113 is provided with a closed cross-sectional portion 34 for increasing load transmission to the dash panel 31, and the collision load transmitted to the tunnel portion 18 side is also increased and transmitted to the dash panel 31.

  According to the above configuration, since the collision load transmitted to the tunnel portion 18 side by the closed cross-section portion 34 is also transmitted to the dash panel 31, the collision load on the tunnel portion 18 side is partially received by the dash panel 31. Can do.

  Therefore, the relatively low rigidity on the tunnel portion 18 side can be increased by utilizing the rigidity of the dash panel 31.

  As described above, when a relatively large load is input in the front body structure of the vehicle employing the three-branch frame by increasing the rigidity of the relatively low tunnel portion 18 side by utilizing the rigidity of the dash panel 31. However, the front end position of the front side frame 11 is not displaced (inwardly tilted) toward the vehicle body inner side, and the front side frame 11 can be sufficiently buckled and deformed.

  In addition to this closed cross section, other embodiments for increasing load transmission include a configuration in which the thickness of the tunnel portion connecting portion at the rear end of the front side frame is increased, and a tunnel portion connecting portion at the rear end of the front side frame. The structure which affixes another panel material, the structure which further forms the rib extended with respect to a dash panel in the tunnel part connection part of the rear end of a front side frame etc. can be considered.

  Further, in this embodiment, the means for increasing load transmission is configured as a closed cross section 34 extending from the rear end of the front side frame 11 to the dash panel 31.

  According to the above configuration, since the closed cross-section portion 34 is a means for increasing load transmission, the load is transmitted to the dash panel 31 without increasing the plate thickness or increasing the weight of the vehicle body as compared with the case where another member is provided. be able to.

  Therefore, the relatively low rigidity on the tunnel portion 18 side can be increased without increasing the vehicle body weight.

  Further, in this embodiment, the closed cross section 34 is configured to extend obliquely upward toward the vehicle center side.

  That is, the closed cross-sectional portion 34 that transmits the load to the dash panel 31 is formed to be inclined so as to extend obliquely upward on the vehicle center side.

  According to the above configuration, the position for transmitting the load to the dash panel 31 is set obliquely above the vehicle center side relative to the position of the front side frame 11, so that the installation positions of the side sill 16 and the floor frame portion 12 (vehicles) The load is transmitted to the position facing the side portion and the vehicle lower portion with the front side frame 11 therebetween.

  In this way, by transmitting the load to the dash panel 31 at a position obliquely above the center of the vehicle, which is a position where the side sill 16 and the floor frame portion 12 face each other, the vertical and horizontal rigidity of the rear end of the front side frame 11 is more uniform. Therefore, the displacement (inward tilt) of the front end of the front side frame 11 on the inner side of the vehicle body is further reliably suppressed, and the front side frame 11 can be reliably buckled and deformed.

  In this embodiment, a tunnel reinforcement 21 extending in the vehicle front-rear direction is provided behind the dash panel 31, and a second closed section 35 is formed between the tunnel reinforcement 21 and the dash panel 31. In addition, the second closed section 35 is set on the vehicle rear side of the closed section 34.

  According to the above configuration, the second closed cross-section portion 35 formed by the tunnel reinforcement 21 is set on the vehicle rear side of the closed cross-section portion 34, thereby increasing the load transmission to the dash panel 31 by the closed cross-section portion 34. Even so, since the rigidity of the dash panel 31 can be sufficiently secured, the closed section 34 can be functioned more reliably.

  Further, in this embodiment, a pair of left and right front side frames 11, 11 are provided, and the pair of left and right front frames 11, 11 are connected by the closed cross section 34 and the second closed cross section 35. It is composed.

  According to the above configuration, by connecting the pair of left and right front side frames 11, 11 by the closed cross section 34 and the second closed cross section, the frame rigidity can be further increased in the vehicle width direction, The torsional rigidity between the frames can also be increased. Therefore, the vehicle body rigidity of the entire vehicle can also be improved.

  In this embodiment, the open car body structure is described. However, a general closed body car body structure may be used.

As described above, in the correspondence between the configuration of the present invention and the above-described embodiment,
The front frame of the present invention corresponds to the front side frames 11 and 11 of the embodiment,
Similarly,
The load transmission increasing means corresponds to the closed cross section 34,
The floor frame corresponds to the floor frame portion 12,
The tunnel reinforcement member corresponds to the tunnel reinforcement 21,
The present invention is not limited to the configuration of the above-described embodiment.

The schematic plan view of the lower body structure which employ | adopted this invention. The top view of the principal part which shows a front vehicle body structure. The front view of a front body structure. The detailed perspective view of the rear end of a front side frame. The detailed perspective view of the vehicle interior side of the front body structure. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3.

Explanation of symbols

11. Front side frame (front frame)
12 ... Floor frame (floor frame)
16 ... Side sill 18 ... Tunnel 31 ... Dash panel 34 ... Closed section (load transmission increasing means)

Claims (5)

A dash panel constituting the front end wall of the passenger compartment,
A floor panel extending rearward from the lower end of the dash panel,
A tunnel portion extending in the vehicle front-rear direction is formed at the center of the floor panel in the vehicle width direction,
While providing a side sill extending in the vehicle longitudinal direction at the vehicle width direction side end of the floor panel,
A floor frame extending in the vehicle front-rear direction is provided on the lower surface of the floor panel between the tunnel portion and the side sill,
Further, in the front body structure of the vehicle including a front frame that extends in front of the dash panel in the vehicle front-rear direction and has a rear end coupled to the tunnel portion, the side sill, and the floor frame,
A vehicle front body structure in which load transmission increasing means for increasing load transmission with respect to the dash panel is provided at a tunnel portion connecting portion at a rear end of the front frame. The vehicle front body structure according to claim 1, wherein the load transmission increasing means is configured as a closed cross section extending from the rear end of the front frame to the dash panel. The vehicle front body structure according to claim 2, wherein the closed cross-section portion is configured to extend obliquely upward toward the vehicle center side. A tunnel reinforcing member extending in the vehicle front-rear direction is provided behind the dash panel, a second closed cross section is formed between the tunnel reinforcing member and the dash panel, and the second closed cross section is used as the load transmission increasing means. The vehicle front body structure according to claim 1, 2 or 3 set on the vehicle rear side. 5. The front body structure of a vehicle according to claim 4, wherein a pair of left and right front frames are provided, and the pair of left and right front frames are connected by the load transmission increasing means and the second closed cross section.

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