Abstract:
An energy absorbing device, for use in a vehicle to absorb impact energy, includes an attachment bracket for fastening a bumper member to a vehicle frame. The bracket includes at least two energy absorbing walls that have apertures to accommodate bolts. Upon a collision, the bolts shear the bracket walls along cutting lines.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an energy absorbing device, and more particularly to an energy absorbing device in a (motor) vehicle bumper system to absorb impact energy originating from a car accident. 
     Customarily, there are several different requirements for optimally-functioning bumper systems in vehicles. Presently the car manufactures operate with three levels of impact—low up to 4-8 km/h, intermediate from 4-8 to 16 km/h and finally impacts at a speed exceeding 16 km/h. 
     Normally, the impact at the low and the intermediate speeds is taken care of by the bumper member itself and a reversible or non-reversible energy absorbing element, usually located between the bumper member and extending to or into the longitudinal members of the vehicle. The impact energy of a collision at a speed over 16 km/h will finally mostly be absorbed by deformation of one or more front/rear side members of the vehicle frame. 
     The energy absorbing elements may be a thin-walled folding member which can be filled with foam or other resilient material. The drawback of filling the member is that it is then not totally compressible due to the solid block being made. Furthermore, it also has the drawback of having a varying force over the displacement due to the varying resistance when making folds. 
     Other design principles commonly used are: absorbing energy by inverting a tube wall; absorbing energy by means of pressing a tube through a restriction, thus reducing the tube diameter; pressing a fluid or a wax through apertures in a cylinder or a piston, typical in a reversible system; and expanding the diameter of a tube by forcing a substantially solid member through the tube. These solutions often have the drawback of having to provide a flange for attachment to the side member. 
     It is known that these folding members—customarily based on relatively small diameter tubes—may be unstable and tend to bend out when subjected to an impact load that is not co-axial with the member or arising at an angle to the member. This is important since it is well known that a large portion of front and rear vehicle impacts arise at an angle to the vehicle&#39;s longitudinal axis and thus result in non-axial loads. It is also known that many of these members lock solid when subjected to a non-axial load or a load arising at an angle to the member. 
     Furthermore, from JP 60121147 it is known to absorb impact energy by a special design of a bumper-attaching member comprising several elongated holes having a width smaller than the diameter of fastening members (bolts) extending through the holes. Upon a moderate speed crash of the vehicle, the received impact force will be transferred via the fastening bolts into the edges of the holes. The impact energy will then be absorbed by widening of the holes due to successive movement of the bolts along the holes. The shortcomings of this solution are apparently the limited amount of energy that can be absorbed by a simple deformation/enlarging of the holes. A possible compensation for this drawback requires a substantial increase of the wall thickness of the attaching member and, thus, increase in weight and costs of the device, effecting negatively both performance and price for the vehicle. 
     SUMMARY OF THE INVENTION 
     Consequently, it is an object of the present invention to provide a novel low weight energy absorbing device that exhibits substantially improved absorption of impact energy. Another object of the invention is to provide a low cost and easily assembled energy absorbing device. Still another object of the invention is to provide an energy absorbing device with no limits regarding the applied material improving the total strength of the bumper beam (system). 
     These and other objects of the present invention are achieved by the energy absorbing device as described and defined below, including the preferred embodiments of the device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail by way of examples of preferred embodiments of the energy absorbing device with reference to the attached drawings, wherein: 
     FIG. 1 shows schematically in a perspective partial view the assembled energy absorbing device; 
     FIG. 2 is a perspective schematic view of the fastening energy absorbing device prior to assembling; 
     FIG. 3 shows the fastening energy absorbing means from FIG. 2 after absorption of a moderate amount of impact energy; and 
     FIG. 4 is a schematic perspective illustration of a preferred embodiment/design of the energy absorbing device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates in a perspective fragmentary view a preferred embodiment of the energy absorbing device usable according to the present invention. An attachment bracket  1  shown as a close (chamber) shape of substantially rectangular cross-section comprises two substantially parallel and flat energy absorbing walls  11  connected by a pair of side walls  13  extending between the energy absorbing walls  11  so as to define a closed chamber of a bracket shape, preferably extruded in a suitable Al-alloy. The attachment bracket is partly accommodated inside a typical side member  4  of a car frame. 
     The front part or the rear part, depending on the orientation/localization of the bracket  1 , is further re-shaped into a suitable functional configuration ensuring a simplified sturdy attachment bracket  1  that can be fastened to the cross-wise extending bumper beam  2 . The side member  4  itself is integrated by any conventionally applied means into the frame/car body structure  5 . 
     FIG. 2 shows schematically a detailed embodiment of the attachment bracket  1  comprising the energy absorbing walls  11  and the pair of perpendicularly extending side walls  13  which define the closed chamber of the bracket  1 . 
     Each of the energy absorbing walls  11  are provided with apertures  12  to accommodate a pair of bolts  3  extending vertically through the apertures located in the respective parallel walls  11 . Still another pair of apertures  14 ′ are located at the front end of the bracket body which includes another special/possible configuration shaped as a fork to simplify connection/attachment to the bumper beam  2  (not shown in the Figure) by partially removing/cutting a portion of each of the connection side walls  13 . 
     FIG. 3 illustrates changes in the energy absorbing walls  11  in the attachment bracket  1  from FIG. 2 due to impact. As apparent from the Figure, the originally circular apertures  12 , after being affected by the impact load transferred from the bumper beam (not shown in the Figure) into the bracket  1  by the fastening/shearing bolts  3 , are transformed into elongated apertures  14  by shearing of the wall material. This shearing results in stripes  17  being carved from wall material and successively nested/disposed longitudinally along the connecting (vertical) side walls  13 . A corresponding transfer of load with similar change in the shape/configuration of the aperture(s) could occur with the front aperture  14 ′—depending on the dimensions and the total design of the attachment front part of the bracket. 
     A preferred/optimal configuration of the attachment bracket  1  according to the present invention is illustrated in FIG.  4 . Several design/constructional adaptions are provided in one of the vertical/connecting walls  13 , and particularly the wall adjacent to the apertures  14  which accommodate the combined fastening/shearing bolts (not shown in the Figure). As seen from the Figure, three kinds of indentations  18 ,  19  and  20  are stamped into at least one extruded wall  13  of the bracket, and these indentations have different and beneficiary effects on the controlled energy absorption. 
     First of all, reshaping the wall  13  in the vicinity of the apertures  14  into a wavelike configuration (rills)  19  ensures that a larger portion of the wall  13  is encompassing/supporting the not shown fastening bolts  3 , thus releasing the axial load of the bolts. 
     The second indentation shown as a substantially rectangular recession  18  in the side wall  13  serves primarily as a guiding means for the wall material against the nearest bolt during the shearing action. 
     The third indentations  20  are channel-like, and define the path to be sheared by the bolts. These indentations act as guiding means for the bolts during the shearing action, and also guide the sheared material stripes to the inside of the bracket wall. 
     The present invention is not limited to the above examples described by way of practical embodiments of the energy absorbing device. The actual bolts can, apart from the shown circular cross-section, also have, for example, an oval or rectangular shape (configuration) without departing from the spirit of the present invention. However, it is important that the bolt has a configuration (geometry) that ensures shearing of material and not just a simple cutting that results in substantially less energy absorption. 
     Furthermore, the above described use of Al-alloy extruded hollow shapes providing a base member for manufacturing of the fastening brackets is just a weight/cost optimal solution. Other material, e.g. steel, and manufacturing/shaping techniques can be used within the scope of the present invention. 
     The mutual orientation of the energy absorbing and (vertical) connecting walls of the fastening bracket, respectively, can be adapted to the actual needs/space demands so that the energy absorbing walls can extend vertically or in any other angle.