Bumper crossmember for a motor vehicle

Abstract

Bumper crossmember for a motor vehicle with a crossmember (2) extending transversely to the longitudinal axis of the vehicle and with two crash boxes (3, 3.1) connected thereto, designed as hollow chamber profiles, one of which is connected in each end section with its end pointing away from the vehicle to the crossmember (2) and can be connected with its end pointing towards the vehicle to a structural component belonging to the vehicle, wherein the crash boxes (3, 3.1) are supported with their end faces only partially on the rear of the crossbeam (2), characterized in that the crossbeam (2) has a hat-shaped cross-sectional profile or a wave structure oriented in the vertical direction (z-direction) and that the support in the upper and lower end face regions (10, 12) pointing in the z-direction is continuous, while support in the two lateral end face regions pointing in the y-direction is only partially provided or is not present, wherein the distance of the end face regions of the crash boxes (3, 3.1) not supported on the rear of the crossbeam (2) from the rear of the crossbeam (2) is arranged such that only after a first phase of energy absorption with deformation of the crash box (3, 3.1) is the end face pointing towards the crossbeam (2) fully supported on its rear.

Description

[0001] The invention relates to a bumper crossmember for a motor vehicle with a crossmember extending transversely to the longitudinal axis of the vehicle and with two crash boxes connected thereto, designed as hollow chamber profiles, one of which is connected to the crossmember in each end section with its end pointing away from the vehicle and can be connected with its end pointing towards the vehicle to a structural component belonging to the vehicle, wherein the crash boxes are only partially supported on the rear of the crossmember with their end faces.

[0002] A bumper crossmember serves to protect vehicle components located behind it, as well as the passenger compartment, in the event of a collision, particularly a frontal one. The bumper crossmember has a crossbeam whose longitudinal extension runs perpendicular to the vehicle's direction of travel (x-direction), thus extending in the y-direction. Energy-absorbing components, known as crash boxes, are attached to the crossmember at both ends. These are supported at the rear of the crossmember with their end facing away from the vehicle. The other end of the crash box faces the vehicle and can be connected to, or is connected to, a structural component of the vehicle, typically a longitudinal member. In many cases, such a crash box includes a baseplate at its end facing the vehicle.Such a baseplate protrudes beyond the outer surface of the crash box, similar to a flange. Mounting openings are incorporated into this baseplate to connect the bumper crossmember to the vehicle's structural component.

[0003] Crash boxes serve to absorb impact energy by deforming it in a controlled manner. The energy to be absorbed is thus converted into deformation energy. Crash boxes can be made from a suitable aluminum alloy, typically as hollow chamber profiles. Alternatively, they can be made from steel components, typically consisting of two half-shells abutting each other at their longitudinal edges, usually U-shaped in cross-section. Steel crash boxes typically feature structures that influence wrinkling, such as beads or similar features.

[0004] Regardless of the material and design of a crash box, the applied force must exceed a certain initial threshold for the desired deformation to occur along the length of the crash box under sustained force. This is evident in a force-displacement diagram depicting the deformation behavior of such a crash box during energy absorption, where it manifests as a clearly recognizable initial peak. Sometimes, this initial peak is only reached with a force greater than the permissible force for the specific application. Therefore, attempts have been made to reduce the magnitude of this initial peak, and thus the required initial force, by incorporating longitudinal sections of the crash box that require different energy for deformation.For example, such a crash box can have a thinner wall thickness at its initial section adjacent to the crossmember of a bumper crossmember than in the areas further towards the vehicle. Due to the reduced wall thickness, the height of such an initial peak is naturally reduced. It is also possible to selectively heat areas of such a crash box with lower strength, so that deformation begins in these areas and, due to the lower strength in these sections, only a smaller force is required to overcome the initial peak.

[0005] However, these previously known measures require either a complex design of the crash boxes or additional process steps.

[0006] The generic patent DE 10 2004 008 741 A1 discloses a bumper system in which the crash box is supported on the rear of the cross member only by its side wall facing the center of the cross member. This results in a reduction of the initial force required for wrinkling in the event of a collision.

[0007] DE 196 35 285 A1 describes a side frame structure for vehicles which is similar in principle to the one previously known from DE 10 2004 008 741 A1.

[0008] From DE 195 17 922 A1, a vehicle frame with a longitudinal member and a transverse member is known. In this vehicle frame, the longitudinal member only abuts the rear of the transverse member with the end faces of its side walls pointing in the y-direction. This design also serves to reduce a peak force occurring in the deformation work in the event of a crash.

[0009] Based on this discussed state of the art, the invention therefore aims to further develop a bumper crossmember of the aforementioned type in such a way that not only does the bumper crossmember have a reduced initial peak height during energy absorption without any special measures influencing the strength properties of such a crash box, but also more design freedom is possible in the conception of the crossmember.

[0010] This problem is solved according to the invention by a generic bumper crossmember as mentioned above, in which the crossmember has a hat-shaped cross-sectional profile or a wave structure oriented in the vertical direction (z-direction) and the support in the upper and lower end face regions pointing in the z-direction is continuous, while support in the two lateral end face regions pointing in the y-direction is only partially provided or is not present, wherein the distance of the end face regions of the crash boxes not supported on the rear of the crossmember from the rear of the crossmember is arranged such that only after a first phase of energy absorption with deformation of the crash box is the end face pointing towards the crossmember fully supported on its rear.

[0011] In this bumper crossmember, the crash boxes are only partially supported on the rear side of the crossmember by their end faces facing the crossmember. This partial support means that, initially, the force is only transferred from the crossmember to the end face of each crash box in those sections of the end face that are supported on the rear side. This partial transfer of energy to be absorbed, relative to the circumference of the end face of the crash box, leads to a concentration of force on the supported end face areas. Therefore, in the first phase of deformation, only the sections of the crash box bordering the supported end face areas are deformed. Consequently, in this initial phase of energy absorption, the energy is not transferred circumferentially to the entire end face of the crash box facing the crossmember.Once deformation has begun in the supported end face areas, the initially unsupported end faces also come into contact with the rear of the crossbeam, resulting in the force being transmitted fully into the crash box. Due to this specific interaction, the initial peak in a force-displacement diagram can be significantly reduced. Such a support arrangement can be achieved by appropriately contouring the end face of the crash box facing the crossbeam.

[0012] The end face of such a crash box, facing the crossmember, is supported in the same way in the end face areas opposite each other in the z and y directions. The upper and lower end face areas are continuously, or at least almost completely, supported on the rear side of the crossmember. The other pair of surfaces, or end faces, namely the two lateral end face areas, are supported only partially on the rear side of the crossmember, or not at all, depending on the design of the bumper crossmember. A special feature of this bumper crossmember design is that the degree of support in the end face areas that are not continuously, or at least not almost completely, supported can influence the deformation initialization force that defines the initial peak.Thus, the desired effect can be achieved simply by appropriately contouring the end face of such a crash box facing the crossbeam, by providing a longer or shorter support length.

[0013] With this type of bumper crossmember, since no additional manufacturing steps are required and no special crash boxes are needed, the production costs are not increased compared to conventional connections of a crash box to the crossmember of a bumper crossmember, or at least not significantly higher. The contouring of the end face of such a crash box facing the crossmember can be carried out during the stamping or cutting of the blanks from a sheet of metal, provided it is composed of two press-formed half-shells.

[0014] The aforementioned support of the crash boxes on the crossbeam can also be implemented with crossbeams that have a wave structure oriented in the vertical (z-direction). Such crossbeams are sometimes used because their wave structure provides greater stiffness. The vertical orientation of the wave structure means that the wave structure along the longitudinal extent of the crossbeam comprises the following crest structures, specifically at least three crest structures oriented in the same direction. Two adjacent crest structures are each connected by a flank inclined relative to the horizontal. According to one embodiment of the invention, in such a crossbeam, the upper and lower end face regions of each crash box are supported on such a flank, preferably on a flank oriented in the vertical direction.In this design, the upper flank, on which the upper end face is supported, points upwards. The lower flank, on which the lower end face is supported, points downwards in the upward direction. With this design, the upper and lower end face areas supported by the upwardly pointing flanks are easily accessible to allow for a material-bonded connection of the crash box to the rear of the crossbeam along these supported end face areas, typically by welding the two parts together. Preferably, the lateral end face areas of the crash boxes have a support tab projecting towards the rear of the crossbeam. This tab engages with a crown structure located between the two outer crown structures.In this design, however, the support tab is only supported on the two opposing flanks that connect this central vertex structure to the two outer vertex structures. Depending on the length of the contact area of ​​such a support tab with such a flank of the crossmember, the deformation behavior in the first phase of a deformation process can be influenced. Thus, with this design of the bumper crossmember, at least the vertex structures facing the crash box are not supported at the front face of the crash box. Support in the unsupported front face areas of the crash box occurs after an initial deformation phase, once deformation in the crash box has already been initiated via the supported front face areas.

[0015] The directional terms used in this explanation – x-direction, y-direction, and z-direction – are those commonly used for a vehicle. The x-direction corresponds to the vehicle's longitudinal extent. The y-direction is the vehicle's lateral extent in the direction of its width. The z-direction is the vertical direction.

[0016] The invention is described below with reference to an exemplary embodiment and the accompanying figures. These show: Fig. 1: A perspective view of a bumper crossmember, Fig. 2: a cross-section through the bumper crossmember of the Fig. 1 with a section line in the middle of its longitudinal extent with a view towards the in Fig. 1 shown left end and Fig. 3: a force-displacement diagram illustrating the initial deformation behavior of the bumper crossmember.

[0017] A bumper crossmember 1 comprises a crossmember 2, to which a crash box 3, 3.1 is connected at each of its ends. The crossmember 2 of the bumper crossmember 1 has a wave structure oriented in the z-direction. The profile of the wave structure extends with its apex structures along the longitudinal extent of the crossmember 2. The crossmember 2 is a press-formed steel component.

[0018] Crashbox 3 – which has an identical construction to crashbox 3.1 – is composed of two U-shaped half-shells 4 and 4.1, each press-formed from a single sheet of steel. The two half-shells 4 and 4.1 abut each other at their longitudinal joints and are welded together at this point. At the end facing a vehicle (not shown in the figures), crashbox 3 carries a baseplate 5, which, in the illustrated embodiment, connects the bumper crossmember 1 to a longitudinal member on the vehicle.

[0019] Due to the Fig. 1. The recognizable profiling of the crossbeam 2 in the vertical direction is, as can be seen from Fig. 2 recognizable, also the front face of the crash box 3 facing the rear of the crossbeam 2 is correspondingly profiled.

[0020] As also from Fig. 2 more clearly than in Fig. As can be seen in Figure 1, the wave structure of the cross member 3 has three positive vertex structures 6, 6.1, 6.2 pointing away from the vehicle, and two negative vertex structures 7, 7.1 located between them as recesses opposite the positive vertex structures 6, 6.1, 6.2. Towards the crash box 3, the negative vertex structures 7, 7.1 represent the positive vertex structures, and the vertex structures 6, 6.1, 6.2 represent the negative vertex structures, as they are recessed relative to the vertex structures 7, 7.1. Adjacent vertex structures are connected to each other by a flank 8, 8.1, 8.2, 8.3. These flanks 8, 8.1, 8.2, 8.3 are inclined to the horizontal, at approximately 30 degrees in the illustrated embodiment.

[0021] The contour of the end face of the crash box 3 facing the crossbeam 2 is designed such that the upper end face area 10, provided by the upper wall 9, and the lower end face area 12, provided by the lower wall 11, are supported along their y-direction by a vertically extending flank 8, 8.3, respectively, and joined to this flank by a welded connection. The area of ​​support of the upper and lower end face areas 10, 12 on the flank 8 and 8.3, respectively, is in Fig. 2 are indicated by a block arrow. The vertex structure 7, 7.1 pointing towards the crashbox 3, however, is not supported on the complementary contour 13, 13.1 in the frontal design of the crashbox 3.

[0022] The two side walls 14 of the crash box 3, of which in Fig. 1 where only the side wall 14 is visible, a support tab 15 projects in the direction of the longitudinal extent of the crash box 3 towards the cross member 2. This engages in the negative vertex structure 6.1 located between the vertex structures 7, 7.1 from the perspective of the crash box 3. The support tab 15 is, with respect to its Fig. The recognizable outline geometry of the support bracket 15 is designed so that it is only supported on the mutually inclined flanks 8.1 and 8.2. These support areas are also indicated by a block arrow. The apex of the support bracket 15, which points towards the crossbeam 2, is in turn spaced apart from the apex structure 6.1.

[0023] In the case of absorption of impact energy, as in Fig. As indicated by the block arrow, the impact energy is initially transferred only to the end face areas located on the flanks 8, 8.1, 8.2, 8.3 of the crash box 3. Only when the end face areas directly supported on the rear side of the crossbeam 2 have begun to deform, i.e., have deformed towards the baseplate 5, do the apex structures 6, 7, 7.1, with their sides facing the crash box 3, come into contact with the complementary geometries 13, 13.1 and the apex of the support flange 15. Only then is the crash box 3 deformed across its entire cross-sectional area facing the crossbeam 2 for further energy absorption.

[0024] The in Fig. The design of the support for the crashbox 3 shown in Figure 2, with its end face pointing away from the vehicle at the rear of the crossbeam 2, reveals that the distance between the apex structures 7, 7.1 and the complementary geometries 13, 13.1 of the crashbox 3 is less than the distance between the apex of the support flange 15 and the apex structure 6.1. Thus, the initial force application from the crossbeam 2 to the crashbox 3 is designed in three stages until the force is applied across the entire cross-sectional area of ​​the crashbox. While at the beginning of a deformation phase energy is introduced into the crashbox 3 only via the upper and lower end face regions 10, 12, after the first deformation phase of the crashbox 3, the apex structures 7, 7.1 come into contact with the complementary geometries 13, 13.1 of the crashbox 3, so that these support areas are then also included in the further deformation.Only after further deformation does the side of the apex structure 6.1 facing the crashbox 3 come into contact with the apex of the support flange 15. Subsequently, a force is introduced into the crashbox 3 across its entire cross-sectional geometry.

[0025] The previously described design of the bumper crossmember 1 results in a significantly reduced initial peak when the deformation behavior described above is plotted in a force-displacement diagram. Such a diagram exists for the bumper crossmember 1 in Fig. Figure 3 shows the deformation behavior in the area of ​​the crash box 4. In the embodiment shown in the figures, the aim was to ensure that a maximum force of 140 kN was not exceeded. This aim was achieved due to the special design of the support for the crash boxes 3, 3.1 on the rear side of the crossbeam 2.

[0026] The curve (solid line) showing the deformation behavior of the crash box 3, connected to the rear of the crossmember 2, is contrasted with a curve (dashed line) showing the deformation of a crash box when it is supported on the same crossmember across its entire frontal area facing the rear. The force required for the initial deformation in such a bumper crossmember is significantly higher than the permissible force of 140 kN for the described case. The initial peak is pronounced in this configuration.

[0027] The invention has been described with reference to exemplary embodiments. The described support arrangement of the crash boxes on the crossbeam can also be implemented, for example, if the crossbeam has a hat-shaped cross-sectional profile, especially if the legs are inclined relative to each other and thus the hollow chamber opens further away from the crash box. The upper and lower end face regions of the crash box are then connected to these flanks. The web of the crossbeam connecting the flanks is at least partially spaced away from the end face of the crash box in the area of ​​its side walls.

[0028] For a person skilled in the art, numerous other possibilities arise for implementing the invention, without this needing to be explained in detail within the scope of these explanations. Reference symbol list 1 bumper crossmember 2 crossbeams 3, 3.1 Crashbox 4, 4.1 Half-shell 5 Baseplate 6, 6.1, 6.2 Vertex structure 7, 7.1 Vertex structure 8, 8.1 - 8.3 Flank 9 Wall 10 upper frontal area 11 Wall 12 lower forehead area 13, 13.1 Complementary contour 14 Side wall 15 Support bracket

Claims

[1] Bumper crossmember for a motor vehicle with a crossmember (2) extending transversely to the longitudinal axis of the vehicle and with two crash boxes (3, 3.1) connected thereto, designed as hollow chamber profiles, one of which is connected to the crossmember (2) at each end section with its end pointing away from the vehicle and can be connected to a structural component belonging to the vehicle with its end pointing towards the vehicle, wherein the crash boxes (3, 3.1) are supported with their end faces only partially on the rear of the crossmember (2), characterized by, that the crossbeam (2) has a hat-shaped cross-sectional profile or a wave structure oriented in the vertical direction (z-direction) and that the support in the upper and lower end face regions (10, 12) pointing in the z-direction is continuous, while support in the two lateral end face regions pointing in the y-direction is only provided in sections or is not present, wherein the distance of the end face regions of the crash boxes (3, 3.1) not supported on the rear of the crossbeam (2) from the rear of the crossbeam (2) is arranged such that only after a first phase of energy absorption with deformation of the crash box (3, 3.1) is the end face pointing towards the crossbeam (2) fully supported on its rear. [2] Bumper crossmember according to claim 1, characterized by , that the crash boxes (3, 3.1) are composed of two U-shaped half-shells (4, 4.1) whose longitudinal sides meet at their joints. [3] Bumper crossmember according to claim 1 or 2, characterized by , that the crash boxes (3, 3.1) have a rectangular, in particular square, cross-sectional geometry with rounded edges. [4] Bumper crossmember according to any one of claims 1 to 3, characterized by , that the crossbeam (2) has a wave structure oriented in the vertical direction (z-direction), which wave structure comprises at least three vertex structures (6, 6.1, 6.2) following the longitudinal extent of the crossbeam (2) in the same direction, wherein two vertex structures adjacent in the vertical direction are connected to each other by a flank (8, 8.1 - 8.3) inclined to a horizontal, and that the upper and lower end face region (10, 12) of each crash box (3, 3.1) is continuously or at least largely continuously supported on a flank (8, 8.3). [5] Bumper crossmember according to claim 4, characterized by, that the flanks (8, 8.3) of the crossbeam (2), to which the upper and lower end face regions (10, 12) of a crash box (3, 3.1) are connected, are flanks in which the upper flank (8), on which the upper end face region (10) is supported, points upwards in the vertical direction and the lower flank (8.3), on which the lower end face region (12) is supported, points downwards in the vertical direction. [6] Bumper crossmember according to claim 5, characterized by , that the lateral end face areas of the crash boxes (3, 3.1) carry a support tab (15) projecting towards the rear of the cross member (2), which is supported only on the mutually facing flanks (8.1, 8.2), through which an outer vertex structure (7, 7.1) is connected to the vertex structure (6.1) located between the two outer vertex structures (7, 7.1). [7] Bumper crossmember according to claim 2, characterized by, that the half-shells (4, 4.1) are press-formed parts made from steel sheets. [8] Bumper crossmember according to any one of claims 1 to 7, characterized by , that the crash boxes (3, 3.1) are only connected to the cross member (2) by joining along their continuous support.

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