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Crash box and bumper for a motor vehicle

This application claims the priority of German Patent Application, Serial No. 10 2007 012 137.9, filed Mar. 12, 2007, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

The present invention relates to a crash box for placement between a bumper beam and a side rail of a motor vehicle, and to a bumper provided with such a crash box.

Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.

A standard bumper is typically mounted on the front or rear of a motor vehicle to absorb impact energy and thereby prevent damage to the vehicle structure in the event of a frontal or rear impact. The bumper typically includes a bumper beam which is mounted to the side rails of the vehicle frame through intervention of crash boxes. The bumper beam is provided to introduce energy, generated in the event of a collision, into the crash boxes which convert the impact energy into deformation work. The bumper structure is typically constructed in such a manner that the crash boxes are typically situated in midsection on the side rails and the impact energy is transferred via the bumper beam with smallest possible flexing into the crash boxes and ultimately into the side rails.

German Offenlegungsschrift DE 43 16 164 A1 describes a bumper which includes a slide-in tube made of two longitudinal sections of different cross sections. The longitudinal section with the smaller cross-section is fixedly connected to the bumper beam, whereas the longitudinal section with the greater cross section is mounted on the chassis of the motor vehicle. In the event of an impact, the smaller longitudinal section deforms into the greater longitudinal section, causing the wall of the longer section to fold back and to roll off the greater longitudinal section. Slide-in tubes of this type afford only little lateral stiffness.

A problem common to conventional bumpers is the fact that the available space for energy absorption is not utilized effectively in the event of an impact because the crash boxes form a block when deformed, thereby reducing the deformation path.

It would therefore be desirable and advantageous to address this problem and to obviate other prior art shortcomings.

According to one aspect of the present invention, a crash box for installation between a bumper beam and a side rail of a motor vehicle includes a longitudinal profile made of two U-shaped shells having overlapping ends sized to realize a material doubling for increasing a side stiffness and to suit the side stiffness to a load level, and a flange plate provided on a side-rail-proximal end of the longitudinal profile and having an opening for passage of the longitudinal profile, wherein the side-rail-proximal end of the longitudinal profile is configured with a collar which is turned outwards, with the collar resting against and joined with the flange plate.

The overlapping ends of the shells may be joined together, e.g. by a rolling welding seam. Likewise the collar may be joined to the flange plate through a welding operation.

By doubling the material in the area of the overlapping legs of the shells, the crash box receives a high side stiffness which can be suited to various loads, depending on the vehicle type, by adjusting the area of overlap. The high side stiffness also provides benefits in the event the vehicle is towed.

Energy absorption capability of the crash box is optimized because the longitudinal profile shifts in the event of a collision in length direction and is folded into the interior of the side rail. The longitudinal profile is pushed through the opening in the flange plate into the side rail of the vehicle frame. In this way, the available space can be used in its entirety as deformation path. The even deformation causes a substantially constant force level. Overall, the energy absorption capability is significantly increased.

According to another feature of the present invention, the collar may be turned inwards in a direction of the longitudinal profile. The collar may hereby be configured to wrap around a circumference of the longitudinal profile in the form of a ring. Suitably, the collar is formed of collar portions, with one of the collar portions formed in one piece with one of the shells, and with the other one of the collar portions formed in one piece with the other one of the shells.

The longitudinal profile rests with the collar upon the side-rail-distal side of the flange plate, i.e. on the flange plate side which is adjacent to the side rail, and is welded to the flange plate in this area. This may be realized by a continuous, circumferential welding seam, or intermittent welding seam, or spot welding seam. The stiffness of the collar may be adjusted by varying the geometric configuration of the collar, such as length of its marginal legs, radius of deformation and angle of the margin legs of the collar in relation to the body of the longitudinal profile. In this way, the functionally desired folding operation and its initialization can be controlled and triggered in the event of impact.

According to another feature of the present invention, the longitudinal profile may have rounded corners. The longitudinal profile is thus substantially rectangular with rounded length edges, as viewed in vertical cross section. As a result, side stiffness is further improved and positively affects the deformation and folding process.

According to another feature of the present invention, the longitudinal profile may have a bumper-beam-proximal end in the form of a slanted end surface. In this way, the leading end surface can thus be best suited to various geometries of the bumper beam to simplify assembly.

To adjust transverse stiffness and side stiffness as well as the section modulus, the shells may be made of different material, e.g. a combination of steels of different strength. Also, the material for the shells and the flange plate may differ. Moreover, the longitudinal profile may have varying wall thickness. It is further conceivable to provide the shells and/or the flange plate of different wall thickness. All these measures allow adjustment of the stiffness behavior and adjustment of a targeted deformation behavior of the crash box.

The longitudinal profile may also be manufactured with zones of different material strength through proper heat treatment. In this way, the folding process can be adjusted in dependence on the strength pattern.

According to another aspect of the present invention, a bumper for a motor vehicle includes a bumper beam extending transversely to side rails of a motor vehicle, and a crash box arranged between the bumper beam and one of the side rails, with the crash box including a longitudinal profile made of two U-shaped shells having overlapping ends sized to realize a material doubling for increasing a side stiffness and to suit the side stiffness to a load level, and a flange plate provided on a side-rail-proximal end of the longitudinal profile and having an opening for passage of the longitudinal profile, wherein the side-rail-proximal end of the longitudinal profile is configured with a collar which is turned outwards, with the collar resting against and joined with the flange plate, wherein the longitudinal profile of the crash box is constructed for movement into the side rail in the event of an impact.

The crash box is constructed such as to be able to completely fold into the side rail. As a result, more energy can be absorbed as no remaining block length exists and the available deformation path is fully utilized.

In the event of an impact, the longitudinal profile is pushed into the open end of the side rail, while the side-rail-proximal end of the longitudinal profile remains secured to the flange plate. The longitudinal profile thus everts in the attachment zone with the flange plate and rolls into the side rail. The collar is hereby configured to act as initiator for the folding process.