ENERGY ABSORBING DEVICE

Abstract: Energy absorbing device attached to a bumper in a vehicle comprising fastening/shearing fastening device (bolts) adapted to absorb impact energy by shearing the walls of the attachment means.

Description: "Energy absorbing device" The present invention relates to an energy absorbing device, and more particularly to the energy absorbing device applied in a (motor) vehicle bumper system to absorb impact energy originating from a car accident. Customarily there are several different requirements and requests to optimally functioning bumper systems for 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 are taken care of by the bumper member itself and a reversible or non-reversible absorber, 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 being not total compressibility due to the solid block being made when compressed. Furthermore, it also has the drawback of 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. 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 members - customarily based on relatively small diameter tubes - may be unstable and tend to bend out when subjected to an impact load being 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 are arising at an angle to the vehicle's longitudinal axis and thus resulting 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 provided by several elongated holes having a width being 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 and the impact energy is absorbed by widening of the holes due to successive move of the bolts along the holes. The shortcomings of this solution are apparently the limited amount of energy which could 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. Consequently, it is an object of the present invention to provide a novel low weight energy absorbing device exhibiting 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 limitation with regard to the applied material improving the total strength of the bumper beam (system). These and other objects of the present invention are met by provision of a novel energy absorbing device as described and defined in the attached patent claim 1 and the preferred embodiments of the device as disclosed in the dependent claims 2- 6. The invention will now be described in details by way of examples of preferred embodiments of the energy absorbing device in the following referring to the attached drawings, Figs. 1 -4, where 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. Figure 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 11 comprises two substantially parallelly extending energy absorbing walls 11 connected by (a pair of) side walls 13 extending to the energy absorbing walls 11 and thus defining a closed chamber of the 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 1 fastening to the cross-wise extending bumper beam 2. The side member 4 itself is integrated by any conventionally applied means in frame/car body structure 5. Figure 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 defining the closed chamber of the bracket 1. The energy absorbing walls 11 are provided with apertures 12 to accommodate a pair of bolts 3 extending vertically through the apertures being located in the respective parallel walls 11. Still another pair of apertures 14' is located at the front end of the bracket body showing 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 the connection side walls 13. Figure 3 illustrates changes in the energy absorbing walls 11 in the attachment bracket 1 from Figure 2. As apparent from the Figure, the originally circular apertures 14, after being imposed to the impact load transferred from the bumper beam (not shown in the Figure) into the bracket 1 by means of the fastening/shearing bolts 3, are transferred into elongated apertures 14 by shearing of the walls material, something resulting in stripes 17 being carved of wall material and successively nested/disposed longitudinally along the connecting (vertical) side walls 13. A corresponding transfer of load with similar change of the aperture(s) shape/configuration could occur with the front aperture 14' - dependent 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 Figure 4. Several design/constructional adaptions are provided in one of the vertical/connecting walls 13 - the one adjacent to the apertures 14 for accommodation of 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 the (extruded) wall 13 of the bracket having different and beneficiary effect on the controlled energy absorption. First of all, reshaping of the wall 13 in the vicinity of apertures 14 into the 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 substantially rectangular recession 18 in the side wall 13 serves primarily as guiding means for the wall material against the nearest bolt during the shearing action. The third indentations 20 are channel-like, defining the path to be sheared by the bolts, acting as guiding means for the bolts during the shearing action, also guiding 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 be of e.g. oval or rectangular shape (configuration) without departing from the spirit of the present invention. However, it is important that the actually applied bolt has a configuration (geometry) ensuring shearing of material and not a simple cutting resulting 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 could 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, could be adapted to the actual needs/space demands so that the energy absorbing walls can extend vertically or in any other angle.

Claims: Claims 1. Energy absorbing device, particularly in a vehicle for absorbing impact energy comprising an attachment bracket (1) for (fastening) a bumper member (2) to the vehicle frame (side member), said bracket (1) having (at least) two longitudinally extending energy absorbing walls (11) provided with one or more apertures (12) to accommodate one or more extending bolts (3), wherein the bolts (3) upon a collision impact/vehicle crash are shearing the respective bracket walls (11) and/or other walls of the vehicle (frame) structural members along predetermined cutting lines. 2. Device according to claim 1 , where the bracket (1) has a close chamber configuration defined by (a pair of) side walls (13) connecting the energy absorbing walls (11), and where the connecting bracket walls (13) are preferentially further provided with indentations (18) acting as guiding means for the bolts, ensuring controlled shearing deformation of the bracket energy absorbing walls (11) by steering of the shearing path of the bolts (3). 3. Device according to claim 1 or 2, where the apertures (12) in the bracket walls (11) are situated at (close to) the side connecting walls (13) of the attachment bracket, thus utilizing the wall as a dolly. 4. Device according to claim 1 , 2 or 3, where the side wall (13) of the bracket (1) is substantially indented (19) parallelly to the bolt extension, thus bringing a larger portion of said side wall (13) into the vicinity of the bolt, ensuring more efficient support for the bolt's axial load. 5. Device according to claim 2, 3 or 4, where the guiding indentations (20) in the bracket walls (11) acting as guiding means for the bolts (3) during the shearing action also ensure that the sheared material is conveyed inside along the bracket wall (13). 6. Device according to one or more preceding claims, where the attachment bracket (1 ) has a close chamber configuration wherein its end part attached to the bumper member (2) exhibits a shaped/adapted cross-sectional configuration.

Inventors: PEDERSEN ROALD HELLAND, PEDERSEN, ROALD, HELLAND
Applicants: NORSK HYDRO AS, PEDERSEN ROALD HELLAND, NORSK HYDRO ASA, PEDERSEN, ROALD, HELLAND
Application year: 1999
Main classification: B60R19
IPC codes: B60R19, F16F7