Crash box

Abstract

A crash box according to one embodiment comprises at least two constituent members each having a U-shaped cross-section that has a bottom part and vertical wall parts. The constituent members are fitted in the same direction, and the vertical wall parts are joined to each other, thereby forming at least one first cylindrical body. The crash box further comprises another identical constituent member. The other constituent member is fitted as a lid body to one of the constituent members constituting the first cylindrical body, and the vertical wall parts are joined to each other, thereby forming a second cylindrical body. The cylindrical bodies receive a collision load input in the axial direction thereof and buckle, thereby absorbing collision energy.

Description

Crash Box

[0001] The present invention relates to a crash box.

[0002] In many cases, crash boxes are provided at the front end of a vehicle frame to deform and absorb collision energy during a vehicle collision. For example, the crash box disclosed in Japanese Patent Laid-Open Publication No. 2011-111036 is a cylindrical body with a closed cross-section structure formed by joining two hat-shaped half bodies face to face. The two half bodies are joined by joining the flanges of each hat-shaped half body.

[0003] The crash box disclosed in JP 2006-123887 A is a cylindrical body with a closed cross section, which is made by joining two components with a U-shaped cross section facing each other. The components are joined by arc welding the open ends of the opposing components.

[0004] In the crash box of JP 2011-111036 A, the flanges of the halves that form the joints protrude on both sides of the outer periphery of the cylindrical body that forms the crash box, so the space required to mount the crash box on the front end of the vehicle frame is increased by the amount of the flanges. Furthermore, the crash box of JP 2006-123887 A does not have a flange that protrudes outward from the cylindrical body, but because it has only one cylindrical body, measures such as increasing the thickness of the cylindrical body are necessary to increase the amount of energy absorbed during a collision. However, doing so increases the mass of the crash box and reduces the energy absorption efficiency, which is the amount of energy absorbed per mass. Therefore, a compact crash box with a structure in which multiple cylindrical bodies are joined together and has good energy absorption efficiency, but with joints that do not protrude outward from the cylindrical body, is desired.

[0005] One aspect of the present technology is a crash box comprising at least two components having a generally U-shaped cross section, the at least two components having a U-shaped bottom and a pair of upright wall portions rising from either side of the bottom, the at least two components being stacked in the same orientation and mating with each other such that the opposing surfaces of the pair of upright wall portions of one component are female and the bottom side of another component is male, and the upright wall portions of the components, which are in surface contact with each other, are joined at a joint to form at least one first cylindrical body, the crash box comprising a further component having a generally U-shaped cross section, the bottom of the other component being fitted between the opposing surfaces of the pair of upright wall portions of one of the at least two components constituting the first cylindrical body, with the other component using its bottom as a lid, and the upright wall portions of both components, which are in surface contact with each other, are joined at a joint to form a second cylindrical body, and each of the cylindrical bodies buckles and deforms when a collision load is input in its axial direction to absorb the collision energy.

[0006] In some embodiments, in order to partially retain the male fitting to the female fitting of the component forming the first cylindrical body, the joint is only a portion of each of the upright wall portions of each of the component members, and the remaining portions of each of the upright wall portions are joined to each other at the joint to form the walls of the first cylindrical body and the second cylindrical body.

[0007] In some embodiments, of the components forming the first cylindrical body, each of the upright wall portions on the side that becomes the male mold when mated has a step portion that restricts the mating depth with the component that becomes the female mold to a predetermined depth, and the step portion is formed by reducing the mating width of each of the upright wall portions at the bottom of the male component and the portion that begins to rise from the bottom over the predetermined depth, and the amount of reduction in the mating width of the step portion is set equal to the plate thickness of the tip portion of each of the upright wall portions of the female component member so that the step portion can receive the tip portion of each of the upright wall portions of the female component member.

[0008] In some embodiments, a fastening portion for joining to at least one of a bumper reinforcement and a side member is integrally provided at an axial end of each of the cylindrical bodies.

[0009] In some embodiments, the bumper reinforcement has a hat cross-sectional member, and the top plate portion of the hat cross-sectional member is arranged facing the crash box side, and the fastening portion fixed to the bumper reinforcement includes a pair of flange portions that sandwich a pair of vertical wall portions of the hat cross-sectional member from above and below, and with the pair of flange portions fastened and fixed to the pair of vertical wall portions of the hat cross-sectional member, the top plate portion faces the axial end portion of each of the cylindrical bodies.

[0010] In some embodiments, the component has a bent portion formed by partially bending the bottom portion, and the bent portion forms a plurality of ridges extending in the axial direction of the cylindrical body.

[0011] In some embodiments, the number of the ridge lines increases as the distance from the collision load input portion of the cylindrical body increases.

[0012] In some embodiments, multiple cylindrical bodies are integrated by fitting one component into another, and the parts that come into contact through the fitting are joined. As a result, the joints do not protrude outward from the cylindrical bodies, as with the flanges of conventional half-split bodies, and the installation space for the crash box can be made compact. Furthermore, it is possible to construct a crash box with a structure in which multiple cylindrical bodies are stacked, which suppresses the increase in mass of the crash box and improves energy absorption efficiency.

[0013] FIG. 1 is a perspective view of a collision energy absorption structure for a vehicle body according to one embodiment; FIG. 2 is a partially exploded perspective view of the collision energy absorption structure of FIG. 1; FIG. 3 is an enlarged perspective view of a crash box constituting the collision energy absorption structure of FIG. 1; FIG. 4 is a cross-sectional view of the crash box of FIG. 3 taken along line IV-IV; FIG. 5 is a cross-sectional view of the crash box of FIG. 3 taken along line V-V; FIG. 6 is an explanatory diagram of an evaluation method for evaluating the collision energy absorption performance of a crash box; FIG. 7 is an FS diagram showing the collision energy absorption performance of the crash box of FIG. 3; FIG. 8 is an explanatory diagram of the deformation state of the crash box after receiving a collision load; FIG. 9 is a cross-sectional view of a crash box according to another embodiment, corresponding to FIG. 5; FIG. 10 is a cross-sectional view of a crash box according to yet another embodiment, corresponding to FIG. 4;

[0014] <Crash Box> Fig. 1 shows a crash box 10 according to one embodiment, which is connected to both left and right ends of a bumper reinforcement 51 at the front of the vehicle. Left and right side members 52 are connected to the rear of the crash box 10, respectively, and a collision load received by the bumper reinforcement 51 is absorbed by the side members 52 via the crash box 10. In Fig. 1, the directions indicated by crossed arrows indicate directions when the forward direction of the vehicle is defined as "forward." The following explanation of directions will be based on these directions. This also applies to figures other than Fig. 1.

[0015] Generally, a total of four crash boxes 10 are provided distributed on the front, rear, left and right sides of the vehicle, and each crash box 10 is sandwiched and joined between a front or rear bumper reinforcement 51 and a front, rear, left and right side member 52 of the vehicle body. Each crash box 10 is made entirely of steel plate, and has the function of buckling and deforming when a collision load is applied from the front or rear of the vehicle via the bumper reinforcement 51, thereby absorbing the collision energy.

[0016] The structure of a single crash box 10 will be described below with reference to Figures 1 to 5. Here, the crash box 10 located on the front left in Figure 1 will be described as a representative example. The crash box 10 located on the front right in Figure 1 can be configured as a mirror image of the crash box 10 located on the front left. Furthermore, a crash box located at the rear of the vehicle (not shown) can be configured similarly to the crash box located at the front.

[0017] As shown in Figures 2 to 5, the crash box 10 is composed of three components 11, 12, and 13. Each component 11, 12, and 13 has a generally U-shaped cross section, including a bottom 11A, 12A, and 13A, and a pair of upright walls 11B, 12B, and 13B rising at approximately right angles from both sides of the bottom 11A, 12B, and 13A. Specifically, two cylindrical bodies 14 and 15 are formed by stacking the three components 11, 12, and 13 in the same orientation. The first cylindrical body 14, which is the lower of the two cylindrical bodies 14 and 15, is configured by fitting vertically between the opposing surfaces of the pair of upright walls 11B of the first component 11, which is the lowest, as a female mold and the bottom 12A of the second component 12, which is the second lowest, as a male mold. In other words, the tip end of the standing wall portion 11B of the first component member 11 overlaps the outer surface of the base end of the standing wall portion 12B of the second component member 12. As a result, the standing wall portions 11B, 12B of the components 11, 12, which are in surface contact with each other, are joined together at joints 14A. The joints 14A are joined by spot welding at the locations indicated by x marks in Figures 3 to 5.

[0018] The second cylindrical body 15, which is the uppermost of the two cylindrical bodies, is configured by fitting the bottom portion 13A of the third component member 13, which is located at the top, between the opposing surfaces of a pair of vertical wall portions 12B of the second component member 12 constituting the first cylindrical body 14, in a male-female manner similar to the relationship between the first and second component members 11 and 12 when constructing the first cylindrical body 14. In other words, the tip end of the vertical wall portion 12B of the second component member 12 overlaps the outer surface of the base end of the vertical wall portion 13B of the third component member 13. As a result, the vertical wall portions 12B, 13B of the second and third component members 12, 13, which are in surface contact with each other, are joined together at a joint 15A. The joint 15A is joined by spot welding at the locations indicated by x's in Figures 3 to 5. In this case, the bottom portion 13A of the third component member 13 serves as a lid for constructing the second cylindrical body 15. Because the third component 13 functions as a lid, the height of the standing wall portion 13B of the third component 13 is made lower than the heights of the standing wall portions 11B, 12B of the first and second component members 11, 12. Specifically, the tip of the standing wall portion 13B of the third component member 13 is aligned with the tip of the standing wall portions 11B, 12B of the second component member 12.

[0019] 4 and 5, the rising angle (the angle formed with a plane extending to both sides of the bottom portion 11A, 12B, 13A) of the pair of upright wall portions 11B, 12B, 13B of the components 11, 12, 13 is smaller than a right angle. That is, the pair of upright wall portions 11B, 12B, 13B of the components 11, 12, 13 are formed so as to widen slightly as they move away from the bottom portion 11A, 12B, 13A. This provides a draft angle, making it possible to press-form the components 11, 12, 13.

[0020] 3 to 5 , each of the upright wall portions 12B of the second component member 12, which serves as a male mold when mated to form the first cylindrical body 14, includes a step portion 12C on each of the left and right sides that limits the mating depth with the first component member 11, which serves as a female mold, to a predetermined depth. The step portion 12C is formed by reducing the mating width of the bottom portion 12A of the second component member 12 and the upright wall portion 12B at the beginning of rising from the bottom portion 12A over a predetermined depth (vertical height in FIGS. 4 and 5 ). The amount of reduction in the mating width of the step portion 12C is set equal to the plate thickness of the tip portion 11C of the upright wall portion 11B of the first component member 11 so that the step portion 12C can receive the tip portion 11C of the upright wall portion 11B of the first component member 11. In this way, in order to partially retain the fit of the second component 12 to the first component 11 in the first cylindrical body 14, the joint 14A of the first and second component members 11, 12 is only a part of each vertical wall portion 11B, 12B of each component member 11, 12, and the remaining portions of each vertical wall portion 11B, 12B are connected to each other at the joint 14A to form the wall portions of the first cylindrical body 14 and the second cylindrical body 15.

[0021] By providing the stepped portion 12C as described above, when the first and second components 11 and 12 are mated, the tip end 11C of the vertical wall portion 11B of the first component 11 fits into the stepped portion 12C, automatically determining the mating depth between the first and second components 11 and 12. This improves the mating workability during manufacturing compared to when the stepped portion 12C is not provided. Furthermore, the stepped portion 12C is formed on the second component 12, which serves as the male mold, and the amount of reduction in the mating width of the vertical wall portion 12B when forming the stepped portion 12C is set to be equal to the thickness of the tip end 11C of the vertical wall portion 11B of the first component 11, which serves as the female mold. Therefore, the stepped portion 12C does not appear on the outer peripheral surface of the first cylindrical body 14 when it is formed, thereby enabling the installation space of the crash box 10 to be made more compact. Furthermore, the step portion 12C is equivalent to providing a bead in the axial direction of the second cylindrical body 15, and can increase the amount of collision energy absorbed by the second cylindrical body 15 without increasing the mass.

[0022] Furthermore, the joint 14A between the first and second components 11, 12 is formed over only a portion of the vertical wall 11B, 12B of each component 11, 12 (i.e., the tip of the vertical wall 11B of the first component 11 and the base of the vertical wall 12B of the second component 12). Therefore, the rising height of the vertical wall 11B, 12B from the bottom 11A, 12A of both components 11, 12 can be reduced compared to when the joint 14A does not extend over only a portion of the vertical wall 11B, 12B of each component 11, 12 (e.g., when the joint extends over the entire vertical wall of the second component as in the embodiment of FIG. 11 ). As a result, manufacturing variations in the width (left-right) position of the vertical wall 11B, 12B of each component 11, 12 to be joined together can be reduced, which in turn reduces welding defects and delayed fracture due to residual stress remaining in the joint 14A after welding.

[0023] <Crash Box Ridgelines> As shown in Figures 2 to 5, the first to third components 11, 12, and 13 have their bottoms 11A, 12A, and 13A partially bent to form bent portions 11D, 12D, and 13D, respectively. These bent portions 11D, 12D, and 13D form multiple ridgelines 11E, 12E, and 13E extending in the axial direction of the first and second cylindrical bodies 14 and 15. Specifically, the bottom 11A of the first component 11 has one bent portion 11D bent upward. This bent portion 11D is not formed at the front end of the first component 11, but extends from slightly rearward of the front end to the rear end. Furthermore, the bent portion 11D is gradually deepened from the front to the rear. As a result, the first component 11 has six ridges 11E, including the bent portions of the upright wall portion 11B rising from the bottom portion 11A.

[0024] Furthermore, two downwardly bent portions 12D are formed side by side in the left-right direction on the bottom 12A of the second component 12. These bent portions 12D are formed in the same bent shape continuously from the front end to the rear end of the second component 12. As a result, the second component 12 has ten ridges 12E formed, including the bent portions of the upright wall portions 12B rising from the bottom 12A.

[0025] Furthermore, the bottom 13A of the third component 13 has one bent portion 13D bent downward. This bent portion 13D is not formed at the front end of the third component 13, but is formed from a position slightly rearward of the front end to the rear end. Moreover, the bent portion 13D is gradually deepened from the front to the rear. As a result, the third component 13 has six ridges 13E, including the bent portion of the upright wall portion 13B rising from the bottom 13A.

[0026] In this way, multiple ridges 11E, 12E, 13E are formed on the bottoms 11A, 12A, 13A of the first to third components 11, 12, 13, respectively, so that the amount of collision energy absorption can be increased without increasing the mass of the crash box 10.

[0027] 1 to 3 , both axial (front-rear) ends of the first and second cylindrical bodies 14, 15 are integrally provided with fastening portions 14B, 14C, 15B, 15C for fixing the crash box 10 to the bumper reinforcement 51 and the side member 52. The fastening portions 14B, 15B for attaching the crash box 10 to the bumper reinforcement 51 are flange portions formed by partially extending forward from the front ends of the first and third component members 11, 13, and each flange portion has two through holes 14D, 15D formed side by side in the width direction (left-right direction) for fastening a bolt 16. Each flange portion (fastening portion 14B, 15B) is formed by extending a flat surface that is not bent by the bottom portions 11A, 13A of the first and third component members 11, 13. The nuts that are screwed onto the threads of the bolts 16 are weld nuts (not shown) that correspond to the through holes 51D of the bumper reinforcement 51 (only a portion of which is shown in FIG. 2).

[0028] The bumper reinforcement 51 has a hat cross-sectional member 51A, and is disposed with a top plate portion 51B of the hat cross-sectional member 51A facing the crash box 10. The fastening portions 14B, 15B of the crash box 10 fixed to the bumper reinforcement 51 are a pair of flange portions that sandwich a pair of vertical wall portions 51C of the hat cross-sectional member 51A from above and below. With the fastening portions 14B, 15B, which are a pair of flange portions, fastened and fixed to the pair of vertical wall portions 51C of the hat cross-sectional member 51A with bolts 16, the top plate portion 51B abuts against and faces the axial front end portions of the cylindrical bodies 14, 15.

[0029] The fastening portions 14C, 15C for attaching to the side member 52 are configured by drilling through holes 14E, 15E for fastening bolts 17 at four locations, one in each of the upright wall portions 11B, 12B of the first and second component members 11, 12. The through hole 14E drilled in the first component member 11 is positioned forward relative to the through hole 15E drilled in the second component member 12. Nuts that thread onto the threads of the bolts 17 are provided as weld nuts 14F, 15F corresponding to the through holes 14E, 15E (only part of which is shown in FIGS. 2 and 3 ). Through holes 52A (only part of which is shown in FIG. 2 ) are also drilled in the side member 52 corresponding to the through holes 14E, 15E, and the bolts 17 pass through the through holes 52A when fastened to the weld nuts 14F, 15F.

[0030] As described above, since the first and second cylindrical bodies 14, 15 are provided with the fastening portions 14B, 14C, 15B, 15C, it is possible to omit the mounting plates that were conventionally required to mount the crash box 10 to the bumper reinforcement 51 and the side member 52. Moreover, the axial front end portions of each cylindrical body 14, 15 of the crash box 10 face and abut against the top plate portion 51B of the bumper reinforcement 51, so that the collision load can be borne by the surface of the top plate portion 51B. Therefore, even if the conventional mounting plates are omitted, the crash box 10 can absorb the collision load with the entire cylindrical bodies 14, 15, just as in the case where mounting plates are provided.

[0031] <Collision Energy Absorption Performance> In general, the collision energy absorption performance of a crash box is required to be evaluated not only against a frontal collision load along the axial direction, but also against a load applied obliquely to the axial direction (for example, a direction forming an angle of about 10 degrees). Therefore, as shown in Figure 6, an experiment was conducted in which collision loads were applied to the crash box 10 shown in Figures 3 to 5 from the front in the axial direction (0 degrees) and from a direction at an angle of 10 degrees (10 degrees, the angle is exaggerated in the figure), and the collision energy absorption performance of the crash box 10 was evaluated. In Figure 6, "J" is a support jig that generates a reaction force on the crash box 10 in response to the collision load.

[0032] Figure 7 shows the results of the above experiment as a load-stroke (FS) diagram. In the FS diagram, the horizontal axis represents the axial stroke of the impacting body due to the buckling deformation of the crash box 10, and the vertical axis represents the load received by the support fixture J. The solid line represents the results when the impact load was applied from the front (0°) in the axial direction, while the dashed line represents the results when the impact load was applied from a direction at an angle of 10 degrees (10°) relative to the axial direction. As can be seen from this FS diagram, the crash box 10 shown in Figures 3 to 5 can stably support a load of approximately 150 kN over the entire deformation stroke for impact loads from both directions. Therefore, the crash box 10 can buckle and deform, collapsing completely as shown in Figure 8, thereby absorbing the impact energy.

[0033] <Advantageous Effects> According to the embodiment described above, two cylindrical bodies 14, 15 are formed by fitting one component 11 or 12 into another component 12 or 13, and joints 14A, 15A are provided at the locations where the two components come into contact through the fitting. Therefore, unlike the flanges of conventional half-split bodies, the joints do not protrude toward the outer periphery of the cylindrical body, making it possible to compact the installation space for the crash box 10. Furthermore, because the crash box 10 has a structure in which two cylindrical bodies 14, 15 are stacked on top of each other, the increase in mass of the crash box 10 can be suppressed, and energy absorption efficiency can be improved.

[0034] <Modification of Ridge Lines> As shown in FIG. 9, in another embodiment, it is also possible to modify the shape of some of the ridge lines of the first component member 11.

[0035] FIG. 9 is a cross-sectional view of the crash box 20 taken at the same position as in FIG. 5 (corresponding to line V-V in FIG. 3). The cross-sectional shape of the crash box 20 taken at the same position as in FIG. 4 (corresponding to line IV-IV in FIG. 3) is the same as that shown in FIG. 4. The first component 21 has inclined surfaces 21F that form the rising portions of each upright wall portion 21B relative to the bottom portion 21A at the axial rear end of the first cylindrical body 24. Furthermore, the inclined surfaces 21F gradually become smaller toward the axial front side of the first cylindrical body 24 and disappear midway. Therefore, the number of ridges 21E formed by the bottom portion 21A of the first component 21 is six in the front portion of the first component 21, the same as in the first component 11 of the embodiment shown in FIGS. 3 to 5, but is increased by two to eight in the rear portion of the first component 21. The second and third components 22 and 23 may have the same configuration as the second and third components 12 and 13 in the embodiment shown in FIGS.

[0036] In this way, the number of ridges 21E on the bottom 21A of the first component member 21 increases as the distance from the collision load input portions (front ends) of the first and second cylindrical bodies 24, 25 increases, thereby enabling the collision energy absorption characteristics of the crash box 20 to be appropriately controlled.

[0037] <Modification of the Third Component> As shown in FIG. 10, in another embodiment, the fitting direction of the third component 13 relative to the second component 12 can be reversed upside down.

[0038] FIG. 10 shows a cross-section of the crash box 30 taken at the same position as in FIG. 4 . The third component 33 is fitted between the tip ends of the upright wall portions 32B of the second component 32, facing the second component 32. The upright wall portions 32B of the second component 32 and the upright wall portion 33B of the third component 33 are joined at their abutting portions. In this case, the joining is performed by, for example, laser welding, because the abutting portions of the upright wall portions of the second component and the third component cannot be sandwiched with spot welding electrodes as in the embodiment shown in FIGS. 3 to 5 . The joining of the first component 31 and the second component 32 can be performed by spot welding, but laser welding is also acceptable. The bent portion 33D of the bottom portion 33A of the third component 33 is bent so as to protrude downward toward the second component 32. Although not shown, a cross-section of this crash box 30 taken at the same position as in FIG. 5 can have the same features as those shown in FIG. 5 .

[0039] According to the crash box 30 of this embodiment, the joint between the upright wall portion 32B of the second component member 32 and the upright wall portion 33B of the third component member 33 does not protrude outside the crash box 30. Therefore, the installation space for the crash box 30 can be made compact.

[0040] <Changing the Overlap of the Standing Wall Portions> As shown in FIG. 11 , instead of partially fitting the second component 12 into the first component 11, as another embodiment, it is also possible to completely fit the second component 42 into the first component 41 and partially fit the third component 43 therein.

[0041] 11 shows a cross section of the crash box 40 taken at the same position as in FIG. 4. The second and third components 42, 43 are fitted at different heights between the vertical wall portions 41B of the first component 41. As a result, the first component 41 and the second component 42 form a first cylindrical body 44, and the vertical wall portions 41B of the first component 41, the bottom portion 42A of the second component 42, and the bottom portion 43A of the third component 43 form a second cylindrical body 45. Although not shown, a cross section of the crash box 40 taken at the same position as in FIG. 5 can have the same features as those shown in FIG. 5.

[0042] The contact portions between the vertical wall portions 41B of the first component member 41 and the vertical wall portions 42B of the second component member 42 can be joined by laser welding. Also, the contact portions between the vertical wall portions 41B of the first component member 41 and the vertical wall portions 43B of the third component member 43 can be joined by spot welding or laser welding.

[0043] <Other embodiments> In the above embodiment, two components are joined together to form one cylindrical body as the first cylindrical body, but in another embodiment, further components may be added to form multiple cylindrical bodies as the first cylindrical body.

[0044] In the above embodiment, fastening portions are provided at both axial ends of the cylindrical body forming the crash box, and the bumper reinforcement is connected to the front of the crash box and the side member is connected to the rear of the crash box. However, in another embodiment, a fastening portion may be provided at only one axial end of the cylindrical body, and the fastening portion may be used to connect to either the bumper reinforcement or the side member. In this case, the other of the bumper reinforcement and the side member can be connected by a mounting plate, as in the prior art.

[0045] <Advantageous Effects of the Above-described Embodiment> Finally, further advantageous effects of the above-described embodiment will be noted.

[0046] In some embodiments, the joining portion is only a portion of each vertical wall portion of each component member to partially retain the male mold of the first cylindrical member fitting to the female mold of the component member. This allows the rising height of the vertical wall portion of each component member from the bottom to be reduced. This reduces manufacturing variation in the position of each vertical wall portion of each component member to be joined together, thereby reducing welding defects and delayed fracture due to residual stress remaining in the joint.

[0047] In some embodiments, each vertical wall portion of the male component includes a step portion that regulates the mating depth with the female component. Therefore, when multiple components are mated, the mating depth is automatically determined, improving workability during manufacturing. Furthermore, the step portion is formed on the male component, and the amount of reduction in the mating width of the vertical wall portion when forming the step portion is set to be equal to the plate thickness of the tip of the vertical wall portion of the female component. Therefore, no step portion appears on the outer peripheral surface when the first cylindrical body is formed, thereby enabling the installation space of the crash box to be compact. Furthermore, the step portion is equivalent to a bead processing in the axial direction of the cylindrical body, allowing for increased collision energy absorption without increasing mass.

[0048] In some embodiments, the axial end of each cylindrical body is integrally provided with a fastening portion for fastening to at least one of a bumper reinforcement and a side member, thereby eliminating the need for a mounting plate for attaching the crash box to at least one of the bumper reinforcement and the side member.

[0049] In some embodiments, the axial ends of the cylinders of the crash boxes face the top plate of the bumper reinforcement, allowing the crash load to be received by the surface of the top plate. Therefore, even if the conventional mounting plates are omitted, the crash boxes can receive the collision load with the entire cylinder, just as if they were equipped with mounting plates.

[0050] In some embodiments, the bottom of the U-shaped component has multiple ridges, which allows for increased crash energy absorption without increasing the mass of the crash box.

[0051] In some embodiments, the number of ridges is increased depending on the distance from the collision load input portion of the cylindrical body, so that the collision energy absorption characteristics of the crash box can be appropriately controlled.

[0052] <Other Embodiments> Although specific embodiments have been described above, the present invention is not limited to these embodiments, and those skilled in the art can make various changes, substitutions, and improvements.

Claims

1. A crash box comprising at least two components having a generally U-shaped cross section, the components having a U-shaped bottom and a pair of upright walls rising from either side of the bottom, the at least two components being stacked in the same orientation and mating with each other, with the opposing surfaces of the pair of upright walls of one component acting as a female mold and the bottom of another component acting as a male mold, and the upright walls of the components, which are in surface contact, being joined at joints to form at least one first cylindrical body; and a further component having a generally U-shaped cross section, the bottom of which serves as a lid and which is fitted between the opposing surfaces of the pair of upright walls of one of the at least two components constituting the first cylindrical body, with the upright walls of both components, which are in surface contact, being joined at joints to form a second cylindrical body; and each of the cylindrical bodies buckles and deforms when a collision load is input in its axial direction, thereby absorbing the collision energy.

2. A crash box according to claim 1, wherein the joints are formed only on a portion of each of the upright wall sections of each of the component members, in order to partially retain the male fitting of the female fitting of the component members forming the first cylindrical body, and the remaining portions of each of the upright wall sections are joined to each other at the joints to form the walls of the first cylindrical body and the second cylindrical body.

3. A crash box according to claim 2, wherein the upright wall portions of the component members forming the first cylindrical body that become male when fitted have step portions that restrict the fitting depth with the component member that becomes female to a predetermined depth, and the step portions are formed by reducing the fitting width of the upright wall portions at the bottom and the portion that begins to rise from the bottom of the male component member over the predetermined depth, and the amount of reduction in the fitting width of the step portions is set equal to the plate thickness of the tip ends of the upright wall portions of the female component member so that the tip ends of the upright wall portions of the female component member can be received in the step portions.

4. A crash box according to any one of claims 1 to 3, wherein the axial end of each of the cylindrical bodies is integrally provided with a fastening part for joining to at least one of a bumper reinforcement and a side member.

5. A crash box according to claim 4, wherein the bumper reinforcement has a hat cross-sectional member with the top plate portion of the hat cross-sectional member facing the crash box, and the fastening portion fixed to the bumper reinforcement comprises a pair of flange portions that sandwich a pair of vertical wall portions of the hat cross-sectional member from above and below, and with the pair of flange portions fastened and fixed to the pair of vertical wall portions of the hat cross-sectional member, the top plate portion faces the axial end portions of each of the cylindrical bodies.

6. A crash box according to any one of claims 1 to 3, wherein the bottom of the component is partially bent to form a bent portion, and the bent portion forms a plurality of ridges extending in the axial direction of the cylindrical body.

7. A crash box according to claim 6, wherein the number of said ridge lines increases as the distance from the collision load input portion of said cylindrical body increases.

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