Abstract:
An impact-absorbing system and method which assures speed dependency of loads generated in side members at times of frontal collisions, and reduces repair costs at times of low-speed collisions. A reinforcing member spans along a vehicle width direction in a substantially linear form between front ends of a pair of side members. A region of a rear wall portion of an impact-absorbing member, which region is disposed so as to connect between end portions of the side members, is provided with a plurality of protrusion portions which are spaced by a predetermined interval in the vehicle width direction, and includes grooves at outer peripheries of base portions of the protrusion portions. Peak portions of the protrusion portions include hole portions along a length axis of the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2003-283602, the disclosure of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle bumper structure, and particularly relates to a vehicle bumper structure for an automobile or the like which is provided with an energy-absorbing member. 
     2. Description of the Related Art 
     Secondary structures at bumper structures of vehicles such as automobiles and the like have been known heretofore. There is a structure in which left and right side members extend in a front-rear direction of a vehicle, a bumper reinforcement which extends in a vehicle width direction spans between front ends of the left and right side members, a bumper cover is provided forward of this bumper reinforcement, and an extension member is fixed at a front wall of the bumper reinforcement and extends close to a rear face of the bumper cover. Thus, directly after a collision, an impact load is transmitted from the bumper cover through the extension member to the bumper reinforcement, and is further transmitted to the left and right side members. (See, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-001150.) 
     However, with this vehicle bumper structure, when there is a frontal collision, a load that is generated is concentrated at a vehicle width direction central portion of the bumper reinforcement, and buckles the bumper reinforcement toward the rear of the vehicle. Consequently, loads in the left-right direction are generated at the front ends of the left and right side members. As a result, buckling modes of the left and right side members vary in accordance with the collision speed, and a speed dependency of loads generated in the side members is reduced. Therefore, if an acceleration sensor for operation of an airbag is provided at a rear end of a side member, that airbag cannot be operated in optimum conditions. Furthermore, because the extension member is made of metal, costs for repairing an extension member when it has been deformed by a low-speed collision are high. 
     SUMMARY OF THE INVENTION 
     In consideration of the circumstances described above, provision of a vehicle bumper structure which assures speed dependency of a load that is generated in a side member at a time of frontal collision and which can reduce costs of repair when there is a low-speed collision is required. 
     One aspect of the present invention is a bumper absorber which is provided with a rear wall portion and with a plurality of protrusion portions which are arranged in a vehicle width direction of the rear wall portion. Lengths along a vehicle front-rear direction of at least some of this plurality of protrusion portions gradually get shorter toward outer sides in the vehicle width direction. 
     A vehicle bumper structure of another aspect of the present invention includes a bumper reinforcement which extends in the vehicle width direction and spans between front ends of left and right side members, which extend in the vehicle front-rear direction, and a bumper absorber which is disposed between the bumper reinforcement and a bumper cover. Further, a plurality of protrusion portions are provided at a region of this bumper absorber that oppose the bumper reinforcement, and grooves are provided at outer peripheries of base portions of the protrusion portions of the bumper absorber. 
     Hence, when the bumper cover frontally collides with a colliding body, a load is transmitted from the bumper cover through the bumper absorber to the bumper reinforcement, and is further transmitted to the side members. At this time, the collision load can be transmitted through the bumper reinforcement to the side members, directly after the collision, by the plurality of protrusion portions which are provided standing from the region of the bumper absorber that opposes the bumper reinforcement. Further, the protrusion portions at a vehicle width direction central portion of the bumper absorber, which protrude in a vehicle forward direction more than the protrusion portions at vehicle width direction outer side regions, are subjected to pressure sooner and, because of the grooves that are formed at the base portion outer peripheries of the protrusion portions, the protrusion portions consistently deform without affecting surrounding regions. As a result, a concentration of the load that is generated at the time of frontal collision at the vehicle width direction central portion of the bumper is prevented. Consequently, the generation of left-right direction loads at the front ends of the left and right side members can be prevented, and thus the speed dependency of loads that are generated in the left and right side members at times of frontal collisions is excellent. Furthermore, because the concentration of a load that is generated at a time of frontal collision at the vehicle width direction central portion of the bumper absorber can be prevented, deformation of the vehicle width direction central portion of the bumper reinforcement toward a vehicle length direction inner side at a time of low-speed collision can be prevented. Consequently, costs of repair when there is a low-speed collision can be reduced. 
     In the vehicle bumper structure of the present invention described above, peak portions of the protrusion portions may include hole portions and a region of the bumper absorber that opposes the bumper cover may include a plurality of recess portions, such that the holes and the recess portions are on coincident axes in the vehicle front-rear direction. 
     In such a case, because the recess portions at the bumper cover side of the bumper absorber and the hole portions at the peak portions of the protrusion portions at the bumper reinforcement side of the bumper absorber are coaxial in the vehicle front-rear direction, a load that is applied at the bumper cover side of the bumper absorber can be effectively transmitted through outer peripheral portions of the recess portions and the peak portions of the protrusion portions to the bumper reinforcement. Resultantly, it is possible, by adjusting shapes of the recess portions and the protrusion portions, to reliably implement control of applied loads. 
     A vehicle bumper structure of the present invention includes: the bumper reinforcement extending in the vehicle width direction, which spans between the front ends of the left and right side members which extend in the vehicle front-rear direction; the bumper absorber, which is disposed between the bumper reinforcement and the bumper cover; the plurality of protrusion portions disposed at the region of the bumper absorber that opposes the bumper reinforcement; and the grooves which are formed at the outer peripheries of the base portions of the protrusion portions of the bumper absorber. Consequently, the vehicle bumper structure has excellent effects in that the speed dependency at the side members of loads generated at times of frontal collisions is excellent, and in that the cost of repair when there is a low-speed collision can be reduced. 
     When, in the vehicle bumper structure of the present invention, the peak portions of the protrusion portions include the hole portions, the region of the bumper absorber that opposes the bumper cover includes the plurality of recess portions, and the holes and the recess portions are on coincident axes in the vehicle front-rear direction, the vehicle bumper structure has an excellent effect in that control of applied loads can be implemented consistently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional plan view showing a vehicle bumper structure relating to one embodiment of the present invention. 
         FIG. 2  is an enlarged sectional view cut along line  2 — 2  of  FIG. 1 . 
         FIG. 3  is an exploded perspective view, viewed from a diagonally rearward inner side of the vehicle, showing the vehicle bumper structure relating to the one embodiment of the present invention. 
         FIG. 4  is an exploded perspective view, viewed from the diagonally rearward inner side of the vehicle, showing a vehicle bumper structure relating to another embodiment of the present invention. 
         FIG. 5  is an exploded perspective view, viewed from the diagonally rearward inner side of the vehicle, showing a vehicle bumper structure relating to yet another embodiment of the present invention. 
         FIG. 6  is a sectional plan view showing the vehicle bumper structure relating to still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the vehicle bumper structure of the present invention will be described in accordance with  FIGS. 1 to 3 . 
     Here, the arrow FR in the drawings indicates a vehicle forward direction, the arrow UP indicates a vehicle upward direction, and the arrow IN indicates a vehicle inner side direction. 
     As shown in  FIG. 1 , a front bumper  12  is provided with a bumper cover  23  (a vehicle lateral direction member). A bumper absorber  16  (a first member at an inner side of the vehicle lateral direction member) is at an inner side of the bumper cover  23 . A bumper reinforcement  14  (a second member at an inner side of the first member) is provided extending in a substantially linear form along a width direction of the vehicle. In the present embodiment, the bumper reinforcement  14  of the front bumper  12  is provided to span between front ends  10 A of left and right front side members  10  (i.e., at least one pair of side members attached to the second member and running along a longitudinal direction of the vehicle), which extend in a front-rear direction of the vehicle. 
     As shown in  FIG. 2 , a cross-sectional form of the bumper reinforcement  14  cut in a direction intersecting the length direction of the bumper reinforcement  14 , that is, viewed in the vehicle width direction, has a grid or grille form in which horizontal wall portions  14 E and  14 F, which are joined with a front wall portion  14 C and a rear wall portion  14 D between an upper wall portion  14 A and a lower wall portion  14 B, are formed to be parallel with the upper wall portion  14 A. 
     At a region of the front wall portion  14 C of the bumper reinforcement  14  at which it is anticipated that collisions will occur (i.e., a vehicle forward direction or vehicle longitudinal direction end portion), the bumper absorber  16  is provided along the vehicle width direction to serve as an energy-absorbing member, which is structured of a restorable or resilient material, such as a resin such as polypropylene with a low expansion ratio or the like, a rubber or the like. 
     As shown in  FIG. 1 , a form of a front wall portion  16 A of the bumper absorber  16  as viewed from a vehicle vertical direction has a circular arc form which bulges in the vehicle forward direction, so as to increase a degree of freedom of design and so as to lengthen a front-rear length of the bumper absorber  16  and increase an energy absorption amount thereof. 
     At a region between the left and right front side members  10 , a plurality of recess portions  20  are formed in the front wall portion  16 A of the bumper absorber  16 , from the vehicle forward side toward the vehicle rearward side. The recess portions  20  are formed with predetermined intervals therebetween in the vehicle width direction. Here, the recess portions  20  have truncated pyramid forms. 
     As shown in  FIG. 2 , the recess portions  20  are formed in two rows, one above and one below, with a predetermined spacing therebetween in the vehicle vertical direction. The front wall portion  16 A of the bumper absorber  16  in which the recess portions  20  are formed opposes an upper portion  23 A of the bumper cover  23  in the vehicle front-rear direction. 
     As shown in  FIG. 1 , at a region of a rear wall portion  16 B of the bumper absorber  16  between the front side members  10 , which region opposes the front wall portion  14 C of the bumper reinforcement  14 , a plurality of protrusion portions  24  are formed with predetermined intervals therebetween in the vehicle width direction. Lengths of the plurality of protrusion portions  24  along the vehicle front-rear direction gradually get shorter from a vehicle width direction central portion toward the vehicle width direction outer sides, in correspondence with a circular arc form of the rear wall portion  16 B of the bumper absorber  16 , which bulges toward the vehicle forward direction. 
     As shown in  FIG. 3 , the plurality of protrusion portions  24  are formed in two rows, one above and one below, with a predetermined spacing therebetween in the vehicle vertical direction, and have truncated pyramid forms. Circular holes  26  are formed in peak portions  24 A of the protrusion portions  24 , from the vehicle rearward side toward the vehicle forward side. When the protrusion portions  24  are deformed by compression, the holes  26  will collapse. Thus, an energy absorption amount is increased, and a crushing residual is reduced. Further, grooves  28  are formed at outer peripheries of base portions of the protrusion portions  24 . Thus, when the protrusion portions  24  are deformed, the protrusion portions  24  can reliably deform without affecting surrounding regions of the bumper absorber  16 . 
     As shown in  FIGS. 1 and 2 , the recess portions  20  and the holes  26  of the protrusion portions  24  that are formed at the bumper absorber  16  are on coincident axes in the vehicle front-rear direction, and the protrusion portions  24  are provided at the bumper absorber  16  in the vehicle rearward direction relative to respective outer peripheral portions of the recess portions  20 . 
     As shown in  FIG. 2 , the peak portions  24 A of the protrusion portions  24  abut against the front wall portion  14 C of the bumper reinforcement  14  at locations forward, respectively, of the upper wall portion  14 A, the lower wall portion  14 B, the horizontal wall portion  14 E and the horizontal wall portion  14 F. Further, at a vertical direction central portion of the bumper absorber  16 , a shallow recess portion  25  is formed along the vehicle width direction. It is possible to dispose a harness in the recess portion  25 . 
     As shown in  FIG. 3 , a protrusion portion  30  for positioning is formed toward the vehicle rearward direction at a vicinity  16 C of each vehicle width direction end portion of the rear wall portion  16 B of the bumper absorber  16 . This protrusion portion  30  is inserted into a positioning hole  32 , which is formed at a vicinity of each vehicle width direction end portion of the front wall portion  14 C of the bumper reinforcement  14 . 
     As shown in  FIG. 1 , a cross-member  36  is provided spanning between kick portions  10 B of the left and right front side members  10 . A front end portion of a floor tunnel  38  is joined to a vehicle width direction central portion  36 A of the cross-member  36 . An airbag deployment control circuit  40  is provided at a front portion of the floor tunnel  38 . An acceleration sensor, which constitutes collision detection means, is incorporated at the airbag deployment control circuit  40 . 
     Next, operation of the present embodiment will be described. 
     In the present embodiment, when the bumper cover  23  frontally collides with a body, loads F 5 , F 6  and F 7 , as shown in  FIG. 1 , are transmitted from the bumper cover  23  through the bumper absorber  16  to the bumper reinforcement  14 , and are further transmitted to the front side members  10 . At this time, because the plurality of protrusion portions  24  are formed at the region of the bumper absorber  16  that faces the bumper reinforcement  14 , the collision loads can be transmitted through the bumper reinforcement  14  to the front side members  10  directly after the collision. 
     Further, with the vehicle structure shown in  FIG. 1 , in order for accelerations which are dependent on collision speeds of the vehicle to be reliably generated at the acceleration sensor which is incorporated in the airbag deployment control circuit  40 , it is necessary that loads F 1  and F 2  which are generated in the left and right front side members  10  are dependent on the collision speeds. 
     Therefore, it is necessary that buckling of a vehicle width direction central portion of the bumper reinforcement  14  toward the vehicle rearward direction (to a vehicle longitudinal direction inner side) at the time of a frontal collision is avoided, and that the generation of loads F 3  and F 4  in vehicle width inner side directions at the front ends  10 A of the left and right front side members  10  is avoided. 
     With the present embodiment, when the protrusion portions  24  at the vehicle width direction central portion of the bumper absorber  16 , which in plan view protrudes in the vehicle forward direction in the circular arc form relative to the vehicle width direction outer side regions, are subjected to pressure early in a collision, the protrusion portions  24  are reliably deformed without affecting surrounding regions, because of the grooves  28  formed at the base portion outer peripheries of the protrusion portions  24 . Further, the protrusion portions  24  are also reliably deformed by the holes  26  collapsing. 
     As a result, at a time of frontal collision, concentration of the generated load F 5  at the vehicle width direction central portion of the front bumper  12  can be avoided. That is, at the time of frontal collision, the load F 5  that is generated at the vehicle width direction central portion of the bumper reinforcement  14  can be made smaller relative to the loads F 6  and F 7  that are generated at the respective vehicle width direction end portions of the bumper reinforcement  14 . Consequently, the vehicle width direction inward direction loads F 3  and F 4 , which act on the left and right front side members  10 , can be suppressed. Thus, a change in buckling modes of the left and right front side members  10  in accordance with collision speeds and a reduction in speed dependence of the loads F 1  and F 2  generated in the front side members  10  can be prevented. Therefore, the speed dependence of the loads F 1  and F 2  generated at times of frontal collision is excellent, and an airbag(s) can be operated in optimal conditions. 
     Furthermore, with the present embodiment, because concentration of a generated load at the vehicle width direction central portion of the bumper absorber  16  at a time of frontal collision can be avoided, deformation toward the vehicle rearward direction of the vehicle width direction central portion of the bumper reinforcement  14  when there is a low-speed collision can be avoided. Consequently, costs for repair at times of low-speed collisions can be lowered. 
     Further still, with the present embodiment, because the holes  26  formed in the peak portions  24 A of the protrusion portions  24  of the bumper absorber  16  are on coinciding axes in the vehicle front-rear direction with the recess portions  20  of the bumper absorber  16 , a load that is applied to the bumper absorber  16  from the bumper cover  23  is transmitted through the recess portions  20  and the protrusion portions  24  to the bumper reinforcement  14  effectively. As a result, it is possible, by adjusting shapes of the recess portions  20  and the protrusion portions  24 , to reliably implement control of applied loads. 
     Further still, loads are transmitted from the protrusion portions  24  of the bumper absorber  16  to the upper wall portion  14 A, the lower wall portion  14 B and the horizontal wall portions  14 E. In other words, loads of the protrusion portions  24  can disperse toward the upper wall portion  14 A, the lower wall portion  14 B and the horizontal wall portions  14 E. 
     In the above descriptions, a particular embodiment of the present invention has been described in detail. However, the present invention is not limited to this embodiment, and it will be clear to persons skilled in the art that various other embodiments are possible within the scope of the present invention. For example, in the embodiment described above, the protrusion portions  24  have truncated pyramid shapes, and the holes  26  are formed in the peak portions  24 A of the protrusion portions  24 . However, instead of this, the protrusion portions  24  may be formed as thin columns (polygonal columns, circular columns or the like), as shown in  FIG. 4 . Further, as shown in  FIG. 5 , the protrusion portions  24  may be provided to extend along the vehicle width direction, and the holes  26  may be long holes whose length directions are in the vehicle width direction. 
     Further again, a vehicle bumper structure of the present invention in which, as shown in  FIG. 6 , the bumper reinforcement  14  has a circular arc form which bulges toward the vehicle forward direction can also be applied to a vehicle. In such a case, loads F 10  and F 11  are generated. The loads F 10  and F 11  suppress loads F 8  and F 9 , which act on the front ends  10 A of the left and right front side members  10  at the time of a frontal collision so as to push the front ends  10 A apart to the vehicle width direction outer sides thereof. Consequently, similarly to the embodiment described above, a reduction of the speed dependency of the loads F 1  and F 2  that are generated in the front side members  10  can be avoided. Moreover, costs of repair at times of low-speed collisions can be lowered. 
     Further yet, in the embodiment described earlier, the cross-sectional form of the bumper reinforcement  14  as viewed from the vehicle width direction has a grid or grille form. However, the cross-sectional form of the bumper reinforcement  14  as viewed from the vehicle width direction is not limited to the grid form. 
     Further still, in the embodiments described above, the vehicle bumper structure of the present invention is applied to a front bumper. In addition, the vehicle bumper structure of the present invention is also applicable to a rear bumper.