Elongated bumper bar with sections twisted rotationally about the axis of elongation

A bumper system for an automotive vehicle includes a rolled steel tube having a box or C-shaped cross section fixed to the forward ends of the side rails of the vehicle so as to extend transversely to the vehicle's longitudinal axis. The forward surface of the vehicle is formed by a plastic fascia which may have sloped surfaces for styling or aerodynamic reasons. The space between the forward end of the bumper bar and the fascia is filled with foam intended to absorb energy in an impact. To better match the sloped sections of the fascia, certain sections of the bumper bar are twisted about the longitudinal axis of the bar to create surfaces inclined relative to the vertical. The bars are formed by roll forming a steel web into an elongated member having generally vertical opposed faces. A section of the rolled member is heated above a metallurgical transition temperature. Then sections to be inclined are twisted about the longitudinal axis of the bumper bar in a die forming station and are then quenched to form a hardened steel member.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates to bumper systems for vehicles and more particularly to a unique bumper bar and method for making the same for use in a bumper system including an exterior fascia having inclined sections, a bumper bar secured to extending frame sections of the vehicle, and plastic foam between the bumper bar and the fascia.

II. Description of the Prior Art

Modern automotive vehicles typically employ bumper systems which include a bumper bar secured to the frame of the vehicle at either the forward or rear end, so as to extend transversely to the center line of the vehicle. The outer face of the bar is covered with a plastic fascia that is designed based on primarily aesthetic and aerodynamic considerations. The fascia may have surfaces inclined relative to the vertical, typically sloping downward and forward. Some or all of the space between the facing surfaces of the bumper bar and fascia may be filled with material such as a foam that absorbs energy between the two.

The system is intended to absorb as much impact energy as possible in the shortest distance possible for purposes of keeping the package size of the bumper at a minimum. Additionally, the mass of the system should be minimized to minimize the energy required to drive the vehicle and thus the vehicle emissions.

In order to achieve these criteria, the distance between the opposed surfaces of the bumper bar and the fascia should be minimized. However, the goal of employing a bumper bar with a conventional boxlike configuration with opposed vertical sidewalls, one connected to the frame and the other to the fascia, and with fascias employing non-vertical surfaces, is difficult to attain. This compromises the design goal of maintaining the bumper bar edge as close as possible to the vehicle exterior surface in order to meet, distribute and dissipate the energy that is absorbed during the collision.

SUMMARY OF THE PRESENT INVENTION

To improve this situation, the present invention contemplates a box-shaped or C-shaped bumper bar, made by a conventional rolling process, which has certain of its sections twisted about the longitudinal axis of the bar so that the forward faces of the bar at these twisted sections are inclined relative to the vertical to more closely match the mating surfaces of fascias with inclined surfaces. These twists may be made at the center section of the bumper bar, at the ends or other sections. A bumper system employing this novel bumper bar will have a smaller dimension along the longitudinal axis of the vehicle, give improved impact performance, and minimize weight relative to a conventional bumper design.

The bumper bars of the present invention may be manufactured by a variety of processes, but the present invention further relates to an improved method of manufacture of such bars. The method involves roll forming the bar in a conventional manner to achieve a box-shaped or C-shaped frame, welding the longitudinal seam to join the edges in a closed shape, if necessary and desired, heating the bar above the transition temperature, preferably to its austenizing temperature, and placing it in a forming tool which twists the selected sections about the longitudinal axis of the bar and bends the bar about the horizontal axis to provide it with the necessary sweep to accommodate the fascia which often has the rearward sweep away from the center. After the shaping, and preferably while in the same forming tool, the bumper beam is quenched.

The bumper bar of the present invention provides enhanced energy absorption performance because energy of impact is absorbed both in translation and in twisting of the inclined beam surfaces back toward the vertical.

Other objects, advantages and applications of the present invention will be made apparent by the following detailed description of a preferred embodiment of the invention. The description makes reference to the accompanying drawings.

The present invention is directed toward a bumper bar system of the general type commonly used in automobiles and light trucks and illustrated in FIG.1. These systems employ a bumper bar10which is usually produced by rolling sheet steel to form a generally box-like configuration which is elongated in the direction normal to the plane of the drawing. The box may be completely closed, as illustrated inFIG. 1, which is usually achieved by securing the free edges of the box as at12by welding, seaming or a similar process. Alternatively, the edges may be left unsecured, achieving a generally “C” cross section.

The bumper bar10is typically secured to the vehicle by attaching it to a pair of side rails14of the vehicle frame (only one of which is shown inFIG. 1) by bolts16or other attachment means, at a pair of spaced points inwardly from the ends of the bumper bar10. The forward side of the bumper system is covered by a plastic fascia18which forms the outer visible portion of the bumper system. This fascia is typically nonrectangular and its contour is determined by both aesthetic and aerodynamic considerations. The space between the rearward surface of the fascia and the forward surface of the bumper bar10may be filled with plastic foam20. The foam may be formed integrally with the fascia, using a dual durometer system, or they may be separate components.

The fascia has a sweep rearwardly from its center section toward its sides and the bumper bar generally indicated at10, illustrated in perspective inFIG. 2, is similarly swept, either in the rolling process or preferably in a post-rolling pressing operation.

The bumper bars10of the prior art employ a variety of cross sections which may vary along the length of the bar and may include indentations, strengthening ribs and the like. Typical bumper bars for use in bumper systems of the type contemplated by this invention are disclosed, for example, in U.S. Pat. Nos. 5,080,410; 6,325,431; 6,343,820; 6,349,521 and 6,352,257. While each of these bars differs from one another in configuration, all generally employ the rectangular cross section, with a top22, a bottom24, a forward side26, and a rearward side28. The forward and rearward sides are aligned generally vertically, at right angles to the top and bottom. As a result, as illustrated inFIG. 1, the spacing between the fascia18and the forward surface26of the bumper bar will vary along its height and contour resulting in different thicknesses of foam20positioned between the two.

These bumper systems are driven by the need to absorb as much impact energy as possible in the shortest distance for purposes of minimizing bumper system package size and minimizing the mass so as not to adversely affect the vehicle's fuel consumption and emissions. The present invention is directed toward the goal of providing a bumper bar forward edge which closely approximates the contour of the fascia so as to minimize the distance between the two and the need for excessive use of foam or other material to fill the gaps between the bumper beam and the fascia.

The preferred embodiment of the bumper bar of the present invention is based on the bumper bar design disclosed in U.S. Pat. No. 6,352,297 to Sundgren et al. The disclosure of that patent is incorporated herein by reference. That bar is characterized by the fact that toward each end of the bar the rear flange surface, i.e. equivalent to28inFIGS. 1 and 2, is formed with a forward extending center section such that it contacts the forward flange, i.e.26, at its midsection. The bar is formed with an array of grooves along its length and transversely to strengthen the bar and improve its collision properties. While incorporation of the improvements in the present invention with the Sundgren et al. bumper bar provides especially advantageous design, the present invention can be employed with any form of bumper bar system.

A bumper bar formed in accordance with the present invention is illustrated in plan view in FIG.3. The beam, generally indicated at30, is elongated and has a top32, a rear flange34, a forward flange36, and a bottom flange38.

As will be subsequently disclosed, the bumper bar is formed by a process which first involves rolling a sheet of steel into the desired cross-sectional configuration. The original cross sections of the material, before pressing, are illustrated inFIGS. 4 and 5by the dotted lines of element31. In this “untwisted” position it will be noted that the side flanges34and36are oriented generally vertically, normally to the end walls32and38. While these untwisted cross sections include transversely oriented elements, and in particular the indentation40located in the rear flange34of the cross section, adjacent the corners of the vehicle, the untwisted sections,31, resemble the prior art bumper bars.FIGS. 4 and 5include the cross sections of the fascia at the centerline of the vehicle, as illustrated at42in FIG.4and on the corners of the vehicle as illustrated at44inFIG. 5with the conventional foam20between the forward face of the bar and the rear face of the fascia. It is important to note that in its twisted position30the forward flange36of the bumper bar is substantially closer to the interior wall of the fascia42or44than it would be in the untwisted position of31.

It should also be noted that in the preferred embodiment of the invention, the twist has been made about an axis which corresponds with one upper or lower edge of the twisted shape. InFIG. 4the twisted contours and the untwisted contours substantially match at the forward top corner of the section indicated by the numeral48. Similarly, at the corner cross section ofFIG. 5, the twisted section30and the untwisted section38closely match at the numeral50. These relatively untwisted points represent locations at which the cross section is locked during the twisting operation in the press as will be subsequently described.

Referring now toFIG. 6, a schematic illustration is shown of the method of processing the rolled bumper bar and includes a first step52by which the bar is roll formed the bar in a conventional manner, and such as in particular to achieve a box-shaped or C-shaped frame. Succeeding step54illustrates the welding of a longitudinal seam to join the edges in a closed shape, if necessary and desired.

Succeeding step56illustrates heating the bar above the transition temperature, preferably to its austenizing temperature. At step58, the part is placed in a forming tool which twists the selected sections about the longitudinal axis of the bar and, at further step60, bends the bar about the horizontal axis to provide it with the necessary sweep to accommodate the fascia, which often exhibits a rearward sweep away from the center. After the shaping, and preferably while in the same forming tool, the bumper beam is quenched at step62.

Referring finally toFIG. 7, an illustration is generally shown of the manner in which a bar is twisted, such as along a center section thereof. In particular, and as shown, a part64is held between a pair of gripping members66and68, such as compressible die members. A suitable torsional or twisting force may be applied, such as generally referenced at70, and in order to twist such as a center section location of the bar. Reference is also made to the cross-sectional view of FIG.4and which shows the center twisted section position of a bar according to the invention.