CN108791509B

CN108791509B - Vehicle body front structure

Info

Publication number: CN108791509B
Application number: CN201810377597.XA
Authority: CN
Inventors: 喜多僚; 吉本毅
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2017-04-26
Filing date: 2018-04-25
Publication date: 2020-12-22
Anticipated expiration: 2038-04-25
Also published as: JP6469753B2; JP2018184089A; CN108791509A

Abstract

Provided is a vehicle body front structure which can cause the dropping of a subframe during a collision with a simple structure and can suppress the reduction of the support rigidity of the subframe during a normal state. The vehicle body front structure has a pair of left and right front side frames (14), a cowl cross member (50), and a subframe (54). The dash cross member (50) has a cross member body (51) and a pair of right and left subframe attachment portions (52). The subframe attachment portion (52) has a subframe fastening hole (52f) through which a bolt (B) for fastening the subframe attachment portion (52) and a subframe (54) is inserted, and a crack generation portion (52g) formed between the subframe fastening hole (52f) and the front side frame (14).

Description

Vehicle body front structure

Technical Field

The present invention relates to a vehicle body front structure.

Background

Various structures for a front portion of a vehicle body have been developed in which a subframe is detached from the vehicle body in the event of a frontal collision of the vehicle.

For example, patent document 1 discloses an invention in which a subframe and a tunnel frame (tunnel frame) are fastened and fixed by bolts, and a pin provided in the subframe is inserted into a hole formed in the tunnel frame. The clearance between the bolt hole and the bolt is set larger than the clearance between the pin and the opening hole. According to the invention of patent document 1, at the time of a frontal collision, the pin expands the hole to reduce the support rigidity around the bolt hole, and then the bolt expands the bolt hole to drop the bolt and the nut, thereby enabling the subframe to drop from the tunnel frame.

Patent document 2 discloses an invention in which a subframe and a front side frame are fastened and fixed by bolts and a cutout is formed in an edge of a bolt hole of the front side frame. According to the invention of patent document 2, a crack is generated from the cut top portion at the time of a frontal collision, and the bolt hole is expanded, whereby the bolt and the nut are disengaged, and the sub frame can be disengaged from the front side frame.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5471559

Patent document 2: japanese patent No. 5278105

Disclosure of Invention

In the invention of patent document 1, it is difficult to design and manage the positional accuracy of the pin and the bolt hole. Further, the pin is required to have high strength to such an extent that the hole is expanded, which causes problems of increased cost and increased weight.

In the invention of patent document 2, since the edge of the bolt hole is cut, there is a problem that the support rigidity of the subframe is lowered in a normal state.

The present invention has been made in view of the above, and an object thereof is to provide a vehicle body front structure that can cause the subframe to fall off during a collision with a simple structure and can suppress a decrease in the support rigidity of the subframe during a normal state.

In order to solve the above problems, the present invention includes: a pair of left and right front side frames extending in the vehicle front-rear direction; a dash cross member (dash cross member) extending in the vehicle width direction and connecting the pair of front side frames to each other; and a sub-frame disposed below the front side frame and disposed forward of the cowl cross member. The cowl cross member includes: a beam main body; and a pair of left and right subframe attachment portions that connect the vehicle-widthwise outer end portions of the cross member main body to the front side frames. The subframe mounting section includes: subframe fastening holes through which fastening members for fastening the subframe mounting portion and the subframe are inserted; and at least one crack generation part formed between the subframe fastening hole and the front side frame.

Effects of the invention

According to the vehicle body front structure of the present invention, the dropping off of the subframe at the time of collision can be caused by a simple structure, and the reduction of the support rigidity of the subframe at the time of a flat state can be suppressed.

Drawings

Fig. 1 is a bottom view of a vehicle to which a vehicle body front portion structure according to an embodiment of the present invention is applied.

Fig. 2 is a sectional view taken along line II-II of fig. 1.

Fig. 3 is a sectional view taken along line III-III of fig. 1.

Fig. 4 is an enlarged sectional view showing the subframe mounting portion of fig. 3.

Fig. 5 is a cross-sectional view taken along line V-V of fig. 1.

Fig. 6 is an enlarged bottom view showing the subframe mounting portion.

Fig. 7 is a sectional perspective view taken along line VII-VII of fig. 1.

Fig. 8 is a bottom view showing a state in which a vehicle to which the vehicle body front portion structure of the embodiment of the present invention is applied has a frontal collision.

Fig. 9 is an enlarged bottom view showing a state of the subframe attachment portion at the time of a frontal collision of the vehicle, in which fig. 9 (a) shows a state in which a crack travels from the crack generation portion to the subframe fastening hole, and fig. 9 (b) shows a state in which a crack travels from the crack generation portion to the crack enlargement portion.

Fig. 10 is a cross-sectional view showing a state of the subframe and the subframe mounting portion at the time of a frontal collision of the vehicle, in which fig. 10 (a) shows a state in which the subframe fastening hole is expanded, and fig. 10 (b) shows a state in which the bolt and the nut are released from the subframe fastening hole.

Description of the reference numerals

10 vehicle (vehicle body front structure)

14 front side frame

24 side frame body

24a support part

24b inclined part

26 outer frame

28 inner frame

30 branch part

40 outrigger

50 cowl cross member

51 Beam body

52 subframe mounting section

52f subframe fastening holes

52g crack generation part

52h crack enlargement

52j first sliding surface

54 subframe

55a second sliding surface

57 baffle

58 front fastening part

59 rear fastening part

59b collar

60 mounting bracket

64 stabilizer

P Branch Point

B bolt (fastening parts)

N nut

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings as appropriate. In the drawings, "front-rear" indicates a vehicle front-rear direction, "left-right" indicates a vehicle width direction (left-right direction), and "up-down" indicates a vertical up-down direction.

As shown in fig. 1, a vehicle 10 to which the vehicle body front portion structure of the embodiment of the present invention is applied has a vehicle body 12 formed of a monocoque body (monocoque body). The vehicle body 12 is disposed in bilateral symmetry with respect to a center line, not shown, that passes through the center in the vehicle width direction of the vehicle 10 and extends in the vehicle front-rear direction.

The vehicle body 12 mainly includes a pair of left and right front side frames 14, a dash cross member 50, and a sub-frame 54.

The pair of left and right front side frames 14, 14 are metal members located on the left and right sides of the front portion of the vehicle body and extending in the vehicle front-rear direction. Each front side frame 14 has a side frame body 24, an outer frame 26, and an inner frame 28. The outer frame 26 and the inner frame 28 are provided so as to branch from a branch point P of a branch portion 30 located on the vehicle rear side of each front side frame 14. A pair of left and

right side sills

16, 16 extending in the vehicle front-rear direction are disposed on the vehicle width direction outer sides of the outer frame 26. A floor panel 19 is disposed between the pair of left and

right side sills

16, 16.

The outer frame 26 and the inner frame 28 each have a hat-shaped cross section (see fig. 3 for the outer frame 26), and the end flange is fixed to the lower surface of the bottom panel 19 by, for example, welding. The outer frame 26 branches in the vehicle width direction obliquely outward from the branch point P of the branch portion 30, and the rear end portion thereof is fixed to the side sill 16. On the other hand, the inner frame 28 branches in the vehicle width direction obliquely inward from the branch point P of the branch portion 30, and the rear end portion thereof is fixed to the front seat support cross member 18.

The side frame body 24 is positioned further forward than the branch point P of the branch portion 30 in the vehicle, and is provided so as to extend toward the vehicle front. With respect to the side frame body 24, detailed description will be made later.

A bumper beam 34 extending in the vehicle width direction is bridged between the vehicle front ends of the pair of left and right front side frames 14, 14. A dash panel 36 that partitions a power loading compartment 66 and a vehicle cabin is disposed between the pair of left and right front side frames 14, 14 along the vehicle width direction. A power unit U including an engine, a transmission, and the like is disposed in the power mounting chamber 66. Left and right damper bases 37, 37 for supporting upper ends of left and right dampers, not shown, are disposed in front of the dash panel 36 and on both sides in the vehicle width direction.

A pair of left and

right outriggers

40, 40 and a cowl cross 50 interposed between the pair of left and

right outriggers

40, 40 are disposed on both sides in the vehicle width direction of a branch portion 30 that is a branch point P between the outer frame 26 and the inner frame 28. In other words, the pair of left and

right outriggers

40, 40 and the dash cross member 50 are arranged substantially linearly in the vehicle width direction across the pair of front side frames 14, 14. Further, a reinforcement cover 43 is attached to a joint portion between the pair of left and

right outriggers

40, 40 and the branch portion 30.

The subframe 54 is a metal member extending in the vehicle width direction and the vehicle front-rear direction. The sub-frame 54 is disposed below the front side frame 14 and in front of the dash cross member 50. The subframe 54 has: a subframe upper member 55 (see fig. 4), a subframe lower member 56, a pair of left and right partition plates 57, a pair of left and right front fastening portions 58, and a pair of left and right

rear fastening portions

59, 59. The subframe upper member 55 and the subframe lower member 56 are joined to each other by welding or the like. The partition plate 57 is provided between the subframe upper member 55 and the subframe lower member 56, and extends in the vehicle front-rear direction.

The pair of

front fastening portions

58, 58 are portions for fastening and fixing the subframe 54 to the front side frame 14. The

front fastening portions

58, 58 are provided at front portions at both ends of the subframe 54 in the vehicle width direction. The front fastening portion 58 extends outward and upward of the vehicle toward the front side frame 14. The front fastening portion 58 has bolt holes 58 a. The front fastening portion 58 is fastened and fixed to the front side frame 14 by bolts (not shown).

The pair of

rear fastening portions

59, 59 are portions for fastening and fixing the subframe 54 to the dash cross-member 50. The

rear fastening portions

59, 59 are provided at rear portions at both ends of the subframe 54 in the vehicle width direction. The rear fastening portion 59 extends rearward toward the dash cross member 50. The rear fastening portion 59 has bolt holes 59 a. The rear fastening portion 59 is fastened and fixed to the subframe attachment portion 52 adjacent to or near the branch portion 30 by a bolt (not shown).

The dash cross member 50 is a metal member that extends in the vehicle width direction and connects the pair of front side frames 14, 14 to each other. The cowl cross member 50 has: a cowl cross member main body 51 (hereinafter also referred to as "cross member main body 51") disposed at the center in the vehicle width direction, and a pair of left and right

subframe attachment portions

52, 52 that connect the vehicle width direction outer end portions of the cross member main body 51 to the front side frames 14, 14.

The cross member main body 51 shown in fig. 2 is recessed (hat-shaped) in a side cross section and is open on both sides and above in the vehicle width direction. The cross member main body 51 is configured to include a main body bottom surface 51a, a main body front surface 51b, and a main body rear surface 51 c.

The body bottom surface 51a is a plate-shaped portion extending in the vehicle front-rear direction and the vehicle width direction. The body bottom surface 51a shown in fig. 3 has an arch shape protruding upward when viewed from the vehicle front-rear direction. Therefore, the height dimensions of the body front surface 51b and the body rear surface 51c continuous with the body bottom surface 51a are formed to gradually decrease from the outer side toward the center side in the vehicle width direction. Body

outer flanges

51d, 51d are formed at both ends of the body bottom surface 51a in the vehicle width direction. A bottom panel 19 is disposed above the beam main body 51. Two mounting

brackets

60, 60 having hat-shaped cross sections are fixed to the upper surface of the floor panel 19 at intervals in the vehicle width direction. The mounting bracket 60 is a member for mounting a vehicle body member (e.g., a steering hanger) to the vehicle width direction center of the floor panel 19. The top portion (central portion in the vehicle width direction) of the body bottom surface 51a is flat, and is joined to the mounting bracket 60 by welding via the bottom panel 19.

As shown in fig. 2, the body front surface 51b is a plate-like portion extending obliquely upward and forward from the front end of the body bottom surface 51 a. A body front flange 51e joined to the lower surface of the dash panel 36 by welding is formed at the upper end of the body front surface 51 b.

The body rear surface 51c is a plate-like portion extending obliquely upward and rearward from the rear end of the body bottom surface 51 a. A body rear flange 51f joined to the lower surface of the bottom panel 19 by welding is formed at the upper end of the body rear surface 51 c.

The subframe attachment portion 52 shown in fig. 5 is recessed (hat-shaped) in a side cross-sectional view, and opens to both sides and upward in the vehicle width direction. The subframe mounting portion 52 is configured to include a mounting bottom surface 52a, a mounting front surface 52b, and a mounting rear surface 52 c.

The mounting bottom surface 52a is a plate-shaped portion extending in the vehicle front-rear direction and the vehicle width direction. An attachment inner flange 52d to be joined to the body outer flange 51d is formed at an inner end portion in the vehicle width direction of the attachment bottom surface 52a shown in fig. 4. An outer mounting flange 52e joined to the lower surface of the inner frame 28 is formed at the vehicle-widthwise outer end portion of the mounting bottom surface 52 a.

As shown in fig. 6, the subframe mounting portion 52 has a subframe fastening hole 52f, a crack-generating portion 52g, and a crack-enlarging portion 52h in the mounting bottom surface 52 a. In fig. 6, the subframe 54 is depicted by a two-dot chain line, and the bolts are omitted.

The subframe fastening holes 52f are portions through which bolts B (see fig. 5) for fastening the subframe attachment portion 52 and the subframe 54 are inserted. The subframe fastening holes 52f are through holes that vertically penetrate the mounting bottom surfaces 52 a. A nut N communicating with the subframe fastening hole 52f is fixed to the upper side of the mounting bottom surface 52a by welding. The subframe fastening holes 52f have a circular shape when viewed from the bottom. Reference numeral W in fig. 6 schematically shows a welded portion that fixes the nut N to the mounting bottom surface 52 a. A plurality of (three in the present embodiment) welded portions W are formed so as to surround the subframe fastening holes 52 f. An imaginary line L1 connecting the centers of the three welded portions W has a regular triangle shape when viewed from the bottom. The number and arrangement of the welded portions W may be changed as appropriate. The weld breaking load of the nut N is set to be greater than the plate cutting load (breaking load) of the subframe attachment portion 52 in the present embodiment. That is, the thickness of the subframe attachment portion 52, the arrangement of the subframe fastening holes 52f and the crack generation portions 52g, and the like are set so that cracks in the subframe attachment portion 52 occur earlier than the weld fracture of the nut N at the time of a frontal collision.

The crack-generating portion 52g is a portion that becomes a starting point of generation of a crack at the time of a frontal collision. The crack-generating portion 52g is not particularly limited as long as it can generate a crack in the mounting bottom surface 52a at the time of a frontal collision, and is configured by a through-hole penetrating the mounting bottom surface 52a in the vertical direction in the present embodiment. The crack initiator 52g has a circular shape when viewed from the bottom. The crack generation portion 52g is formed to have a smaller diameter than the subframe fastening hole 52 f. The number of the crack generators 52g is not particularly limited, and one crack generator is formed in the present embodiment. The crack-producing portion 52g is formed between the subframe fastening hole 52f and the front side frame 14 (the mounting outer flange 52 e). The sub-frame fastening holes 52f and the front side frames 14 are portions where shear force is concentrated at the time of a frontal collision, as will be described later. In the following description, this portion is also referred to as a "shear force concentration portion S". The crack generators 52g are formed on the vehicle exterior side and behind the subframe fastening holes 52f with a gap.

The crack enlargement portion 52h is a portion for enlarging a crack that is generated starting from the crack generation portion 52 g. The crack enlargement portion 52h is not particularly limited as long as it can enlarge a crack, and in the present embodiment, is formed of a through hole penetrating the attachment bottom surface 52a in the vertical direction. The crack enlargement portion 52h has a circular shape when viewed from the bottom surface. The diameter of the crack enlargement portion 52h is formed smaller than the subframe fastening hole 52 f. The number of the crack enlargers 52h is not particularly limited, and one crack enlarger is formed in the present embodiment. The crack enlargement portion 52h is disposed on the opposite side of the crack generation portion 52g with respect to the subframe fastening hole 52 f. The crack enlargement portions 52h are formed on the vehicle inner side and rear side at a distance from the subframe fastening holes 52 f. That is, the subframe fastening holes 52f are disposed forward of the crack-generating portion 52g and the crack-enlarged portion 52 h. A virtual line L2 connecting the center of the crack initiator 52g and the center of the crack enlargement 52h with respect to the center of the subframe fastening hole 52f has a substantially V-shape protruding forward.

As shown in fig. 5, the mounting front surface 52b is a plate-like portion extending obliquely upward and forward from the front end of the mounting bottom surface 52 a. At an upper end of the mounting front surface 52b, a mounting front flange 52i that engages with the lower surface of the dash panel 36 is formed. On the lower side of the mounting front surface 52b, a first sliding surface 52j gently inclined compared to the upper side is formed. The first sliding surface 52j is formed forward of the subframe fastening hole 52 f. The first sliding surface 52j is inclined downward toward the rear. The sub frame upper member 55 is formed with a second sliding surface 55a that can be brought into sliding contact with the first sliding surface 52j at the time of a frontal collision. The second sliding surface 55a is formed forward of the rear fastening portion 59. The second sliding surface 55a is inclined downward toward the rear. A stabilizer 64 is provided on the upper surface of the sub frame upper member 55 via a fixing bracket 62 having a hat-shaped cross section. The stabilizer 64 is cylindrical and extends in the vehicle width direction.

The mounting rear surface 52c is a plate-like portion extending obliquely upward and rearward from the rear end of the mounting bottom surface 52 a. A mounting rear flange 52k that engages the lower surface of the bottom panel 19 is formed at the upper end of the mounting rear surface 52 c.

The following describes the fixing structure of the subframe 54, the partition plate 57, and the subframe mounting portion 52 in detail.

The rear fastening portion 59 of the subframe 54 is a portion through which the bolt B is inserted, and includes two upper and lower bolt holes 59a and a collar (collar) 59B. The bolt holes 59a, 59a have a circular shape when viewed from the bottom. The upper bolt hole 59a vertically penetrates the subframe upper member 55, and the lower bolt hole 59a vertically penetrates the subframe lower member 56. The two

bolt holes

59a, 59a are spaced apart from each other in the up-down direction. The collar 59b is cylindrical and is disposed between the two

bolt holes

59a, 59 a.

The partition plate 57 is a metal plate-like member for reinforcing the subframe 54. The partition 57 has a cross-section in the shape of コ. A bolt hole 57a is formed in a rear portion of the upper wall of the partition plate 57. The bolt hole 57a has a circular shape when viewed from the bottom surface. The bolt hole 57a is disposed between the upper bolt hole 59a and the collar 59 b. The spacer 57 is coupled to the collar 59B by a bolt B. The partition 57 extends forward from the collar 59 b.

The three

bolt holes

59a, 57a, the collar 59b, and the subframe fastening hole 52f communicate with each other. Bolts B are inserted through the

bolt holes

59a, 57a, the collar 59B, and the subframe fastening holes 52f from below. The front end side of the bolt B is screwed into a nut N fixed to the upper side of the subframe fastening hole 52f, whereby three members, i.e., the subframe 54, the partition plate 57, and the subframe attachment portion 52, are integrally fastened and fixed.

The side frame body 24 will be described in detail with reference to fig. 7.

The side frame body 24 includes a support portion 24a and an inclined portion 24 b. The support portion 24a is a portion extending substantially horizontally in the vehicle front-rear direction. A front side frame side fastening portion 24c is provided hanging down from the support portion 24 a. The front fastening portion 58 (see fig. 1) of the subframe 54 is fastened and fixed to the front side frame side fastening portion 24c by a bolt (not shown). The front fastening portion 58 may be fastened and fixed to the inclined portion 24 b.

The inclined portion 24b is a portion that continues from the rear end of the support portion 24a and is inclined downward toward the rear along the inclination of the dash panel 36. The inclined portion 24b is joined to the dash panel 36 by welding.

The vehicle 10 to which the vehicle body front portion structure of the present embodiment is applied is basically configured as described above. Next, the operation and effect thereof will be described with reference to fig. 8 to 10.

As shown in fig. 8, when the vehicle 10 of the present embodiment undergoes a frontal collision, the front side frame 14 is subjected to bending deformation by a frontal collision load F. By this deformation, the support portion 24a of the front side frame 14 is released from the front fastening portion 58 of the sub frame 54.

In addition, when the vehicle 10 undergoes a frontal collision, a power unit U (see fig. 1) such as an engine and a transmission moves rearward, and the subframe 54 is pressed rearward by the power unit U. When the subframe 54 is pressed rearward, as shown in fig. 9a, the bolt B presses the hole wall of the subframe fastening hole 52f and the nut N rearward, and therefore the subframe 54 and the dash cross-member 50 move rearward relative to the front side frame 14 (see arrow Y1 in fig. 9 a).

At this time, since the pair of left and right front side frames 14 are coupled by the cowl cross member 50, a shear force is concentrated between the sub-frame fastening hole 52f and the front side frame 14 due to a phase difference in the traveling direction between the cowl cross member 50 that is to be relatively moved rearward and the front side frame 14 that is to be relatively moved forward (see arrows Y1 and Y2 in fig. 9 (a)).

In the present embodiment, since the crack-generating portion 52g is formed at the shear force concentrated portion S, the crack C is generated with the crack-generating portion 52g as a starting point. The crack C travels from the crack-generating portion 52g inward in the vehicle width direction and reaches the subframe fastening hole 52 f. As shown in fig. 9 (b), the crack C further advances from the subframe fastening hole 52f inward in the vehicle width direction and reaches the crack enlargement portion 52 h. Thus, the mounting bottom surface 52a is broken so that the crack-generating portion 52g, the subframe fastening hole 52f, and the crack-enlarging portion 52h are connected, and the nut N is exposed downward.

When the fracture of the attachment bottom surface 52a progresses further, as shown in fig. 10 (a) and (B), the bolt B and the nut N fall out from the fracture portion including the subframe fastening hole 52f, and the subframe 54 falls out from the vehicle body 12. In this case, in the present embodiment, the second sliding surface 55a of the subframe 54 is in sliding contact with the first sliding surface 52j of the subframe attachment portion 52, and therefore the subframe 54 is likely to move in the direction of falling under the floor. Thereby, the bolt B and the nut N are detached from the broken portion, and the subframe 54 is easily detached from the vehicle body 12.

As shown in fig. 8, the frontal collision load F input to the front end of the front side frame 14 is branched from the branch point P of the branch portion 30 and transmitted to the outer frame 26 as a load F1. On the other hand, the frontal collision load F is branched from the branch point P of the branch portion 30 and transmitted as a load F2 to the inner frame 28. The frontal collision load F is branched from the branch point P of the branch portion 30 and transmitted as a load F3 to the outrigger 40. The frontal collision load F is branched from the branch point P of the branch portion 30 and transmitted as a load F4 to the dash cross-member 50. In this way, the frontal collision load F input to the front side frame 14 is transmitted to the four frames of the inner frame 28, the outer frame 26, the outrigger 40, and the dash cross-member 50 while being dispersed into loads F1 to F4.

According to the present embodiment described above, as shown in fig. 6, the crack-generating portion 52g is formed at the shear force concentrated portion S between the subframe fastening hole 52f and the front side frame 14. Therefore, the crack C can be caused to travel from the crack generation portion 52g to the subframe fastening hole 52 f. Thus, the bolt B is disengaged from the subframe fastening hole 52f, the subframe 54 can be disengaged, and interference between the subframe 54 and the dash panel 36 disposed rearward thereof can be suppressed. That is, the subframe 54 can be caused to fall off at the time of a collision with a simple structure. Further, since the crack generation portions 52g are formed independently of the subframe fastening holes 52f, and the subframe fastening holes 52f themselves are not subjected to processing such as cutting, a reduction in the support rigidity of the subframe 54 during a normal state can be suppressed.

Further, according to the present embodiment, as shown in fig. 6, the nut N is welded and fixed to the mounting bottom surface 52a of the subframe mounting portion 52, and the weld breaking load of the nut N is set to be larger than the plate cutting load of the subframe mounting portion 52. Thus, compared to the weld fracture of the nut N, the crack C is generated from the periphery of the nut N of the subframe attachment portion 52, and the subframe attachment portion 52 can be stably fractured.

In addition, according to the present embodiment, as shown in fig. 6, the subframe attachment portion 52 has a crack enlargement portion 52h on the opposite side of the crack generation portion 52g with respect to the subframe fastening hole 52 f. This makes it easy for the crack C to advance, and therefore, the subframe attachment portion 52 can be easily broken, and the subframe 54 can be easily detached.

Further, according to the present embodiment, as shown in fig. 6, the subframe fastening hole 52f is disposed forward of the crack generators 52g and the crack enlargers 52h, and a virtual line L2 connecting the crack generators 52g and the crack enlargers 52h to the subframe fastening hole 52f has a substantially V-shape protruding forward. Thus, the crack C of the subframe attachment portion 52 caused by the phase difference in the traveling direction travels so as to bypass the subframe fastening hole 52f, so that the subframe attachment portion 52 can be easily broken, and the subframe 54 can be easily detached.

Further, according to the present embodiment, as shown in fig. 5, the subframe attachment portion 52 has the first sliding surface 52j inclined downward as it goes rearward, and the subframe 54 has the second sliding surface 55a inclined downward as it goes rearward and capable of sliding contact with the first sliding surface 52 j. As a result, the second sliding surface 55a of the subframe 54 comes into sliding contact with the first sliding surface 52j of the subframe attachment portion 52 during a frontal collision, so that the subframe 54 is easily moved in a direction to fall under the floor, and the subframe 54 can be easily removed.

Further, according to the present embodiment, as shown in fig. 3 and 5, the stabilizer 64 is provided on the upper surface of the subframe 54, and the body bottom surface 51a of the cross member body 51 has an arch shape protruding upward. Thus, when the subframe 54 falls off from the subframe attachment portion 52 and moves further rearward, interference between the stabilizer 64 provided on the upper surface of the subframe 54 and the cross member main body 51 can be suppressed. Therefore, the subframe 54 moves smoothly backward, and the crack C moves smoothly.

When the body bottom surface 51a of the beam body 51 is formed in an arch shape, the sectional area is reduced, and therefore, the strength and rigidity may be reduced. However, according to the present embodiment, as shown in fig. 3, the cross member main body 51 is joined to the mounting bracket 60 that mounts the vehicle body member at the vehicle width direction center of the floor panel 19 via the floor panel 19, and therefore, it is possible to suppress a decrease in strength and rigidity.

Further, according to the present embodiment, as shown in fig. 8, the front side frame 14 includes an outer frame 26 and an inner frame 28 that branch from a branch point P located at the rear end of the side frame body 24, and an outrigger 40 and a cowl cross 50 are respectively coupled to both sides in the vehicle width direction of a branch portion 30 that is the branch point P of the outer frame 26 and the inner frame 28. Thus, since the collision load applied to the front side frame 14 is transmitted dispersedly to the four frames of the inner frame 28, the outer frame 26, the outrigger 40, and the dash cross-member 50, the deformation of the floor panel 19 can be suppressed even in a collision with a large input load such as an offset collision in addition to a full flat collision.

Further, according to the present embodiment, as shown in fig. 1, the front portion is fixed to the support portion 24a at both ends of the subframe 54 in the vehicle width direction, and the rear portion is fixed to the subframe attachment portion 52 adjacent to or near the branch portion 30 which is the branch point P between the outer frame 26 and the inner frame 28 at both ends of the subframe 54 in the vehicle width direction. Therefore, when the support portion 24a and the inclined portion 24b bend and the fixation of the front portion of the subframe 54 is released at the time of a frontal collision, the subframe 54 is pushed rearward. This makes it possible to easily break the subframe attachment portion 52 and to easily drop the subframe 54.

Further, according to the present embodiment, as shown in fig. 5, the subframe 54 includes a collar 59B through which the bolt B is inserted, and a partition plate 57 which is coupled to the collar 59B via the bolt B and extends forward from the collar 59B. As a result, a load is easily applied to the bolt B through the partition plate 57 at the time of a frontal collision, and therefore the subframe attachment portion 52 can be more easily broken, and the subframe 54 can be more easily detached.

The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited thereto, and can be modified as appropriate within a range not departing from the gist of the invention.

In the present embodiment, the crack-generating portion 52g and the crack-enlarging portion 52h are formed by through-holes, but the present invention is not limited thereto, and may be, for example, a thin portion, a slit, a cut-out, or the like. In the present embodiment, the subframe fastening holes 52f, the crack generators 52g, and the crack enlargers 52h are arranged in a substantially V shape protruding forward, but may be arranged linearly along the vehicle width direction, for example. In the present embodiment, the body bottom surface 51a is formed in an arch shape protruding upward, but may be formed linearly along the vehicle width direction, for example.

Claims

1. A vehicle body front structure is characterized by comprising:

a pair of left and right front side frames extending in the vehicle front-rear direction;

a cowl cross member extending in the vehicle width direction and connecting the pair of front side frames to each other; and

a sub-frame disposed below the front side frame and disposed forward of the cowl cross member,

the cowl cross member has:

a beam main body; and

a pair of left and right sub-frame mounting portions for connecting the vehicle-widthwise outer end portions of the cross member main body to the front side frames,

the sub-frame mounting portion has:

a subframe fastening hole through which a fastening member for fastening the subframe mounting portion and the subframe is inserted; and

at least one crack-generating portion formed between the sub-frame fastening hole and the front side frame,

the front side frame has a front side frame main body, and an outer frame and an inner frame branching from a branch point located at the rear end of the front side frame main body,

an outrigger and the cowl cross member are coupled to both sides in the vehicle width direction of a branch portion that is the branch point of the outer frame and the inner frame.

2. The vehicle body front structure according to claim 1,

a nut is welded and fixed on the bottom surface of the auxiliary frame mounting part,

the weld breaking load of the nut is set to be greater than the plate cutting load of the sub-frame mounting portion.

3. The vehicle body front structure according to claim 1 or 2,

the subframe attachment portion has a crack enlargement portion on the opposite side of the crack generation portion with respect to the subframe fastening hole.

4. The vehicle body front structure according to claim 3,

the subframe fastening hole is disposed forward of the crack-generating portion and the crack-enlarging portion,

the joint portion may be formed in a substantially V-shape protruding forward from an imaginary line connecting the crack-generating portion and the crack-enlarging portion to the subframe fastening hole.

5. The vehicle body front structure according to claim 1,

the sub frame mounting portion has a first sliding surface formed at a front side of the sub frame fastening hole and inclined downward toward a rear side,

the subframe has: a rear fastening portion through which the fastening member is inserted; and a second sliding surface formed forward of the rear fastening portion, inclined downward toward the rear, and capable of sliding contact with the first sliding surface.

6. The vehicle body front structure according to claim 1,

having a stabilizer provided on an upper surface of the sub frame,

the bottom surface of the beam main body is in an arch shape protruding upward.

7. The vehicle body front structure according to claim 6, characterized by comprising:

a bottom panel disposed above the beam body; and

a mounting bracket fixed to an upper surface of the floor panel and used for mounting a vehicle body component at a vehicle width direction center of the floor panel,

the cross member main body is joined to the mounting bracket via the bottom panel.

8. The vehicle body front structure according to claim 1,

the front side frame has:

a support portion extending in a vehicle front-rear direction;

an inclined portion that is continuous with a rear end of the support portion and that is inclined downward toward the rear along the inclination of the dash panel; and

an outer frame and an inner frame branching from a branch point located at the rear end of the inclined portion,

the front part of the auxiliary frame is fixed on the supporting part or the inclined part,

a rear portion of the sub-frame is fixed to the cowl cross member adjacent to a branch portion that is the branch point of the outer frame and the inner frame.

9. The vehicle body front structure according to claim 1,

the subframe includes a collar through which the fastening member is inserted, and a partition plate that is connected to the collar via the fastening member and extends forward from the collar.