Patent Description:
The invention further relates to a method for manufacturing a bumper according to the invention.

A bumper for a motor vehicle with a cross beam element having at least one hollow chamber with a closed cross section, and with a reinforcing element, which extends over part of the length of the cross beam element and joined with the cross beam element is known from <CIT>. The known bumper is characterized by the fact that the latter exhibits a cross beam element consisting of at least two shaped sheet metal parts, for example which are joined together through welding. Viewed in the longitudinal direction of the cross beam element (wherein the longitudinal direction is understood as the direction in which the cross beam element has its greatest extension, and wherein the longitudinal direction runs transverse to the longitudinal direction of the vehicle in the installed state on the vehicle), the cross section of the cross beam element exhibits a hollow chamber. The height of the cross beam element changes in a longitudinal direction in such a way that the cross beam element exhibits a greatest height in a central section. By way of an intermediate section with a smaller height, the central section transitions on both sides into an outer section, which exhibits the smallest height. Situated one atop the other inside of the cross section of the cross beam element or inside of the hollow chamber are two separate reinforcing elements that each exhibit a hollow space and take the form of tubes having a rectangular cross section, wherein their length differs as viewed in the longitudinal direction of the cross beam element. A bumper with this construction having a reinforcing element can be adjusted to legal requirements or crash tests so as to exhibit an optimized deformation behavior given a relatively low weight. The disadvantage here is that this construction made up of several components results in relatively high manufacturing costs for the known bumper.

Known from <CIT> is another bumper with a cross beam element having at least one hollow chamber with a closed cross section, and with a reinforcing element, which extends over part of the length of the cross beam element and is joined with the cross beam element. This bumper is characterized by the fact that several reinforcing elements are situated on the side of the cross beam element facing away from a vehicle front, and each extend over a partial area of the cross member element in its longitudinal direction. The reinforcing elements are each designed as shaped sheet metal parts, which together with the side of the cross member element facing the reinforcing element form a hollow chamber in the installed state. The reinforcing elements are fastened to the outside of the cross beam element, for example in an overlapping area by means of welding or the like. This type of bumper is also associated with a relatively high production outlay due to the separate reinforcing elements that must be joined with the cross beam element or fastened to the cross beam element.

Further known from <CIT> is to manufacture a cross beam element of a bumper in particular out of a lightweight material such as aluminum in an extrusion process and provide it with a separate reinforcing element situated in the cross section of the hollow profile of the cross beam element. Such a bumper is characterized by the fact that the cross section of the cross beam element is at least essentially constant as viewed in the longitudinal direction as the result of the extrusion process.

Known from <CIT> is a single-piece extruded bumper with reinforcing elements according to the preamble of claim <NUM>.

Proceeding from the described prior art, the object of the invention is to further develop a bumper for a motor vehicle with a cross beam element exhibiting a back side designed to be fastened to the motor vehicle with at least one fastening device, preferably in the form of a crash box, and a front side lying opposite the back side, wherein the cross beam element has at least one hollow chamber with a closed cross section, and with a reinforcing element, which extends over part of the length of the cross beam element and is joined with the cross beam element, in such a way as to make manufacturing the bumper simple and inexpensive given the lowest possible weight and best possible crash behavior.

This object is achieved in a bumper for a motor vehicle having the technical features of claim <NUM>.

The invention is based on the idea of making the cross beam element of the bumper together with the reinforcing element in a single manufacturing step in an extrusion process, and then partially removing the reinforcing element from the cross beam element, so that the reinforcing element is only joined (as a single piece) with the cross beam member in those areas where stricter strength requirements are placed on the bumper, in particular to ensure compliance with crash requirements. Understood by a single-piece configuration of the cross beam element and the reinforcing element is a monolithic configuration in which both elements are simultaneously generated in one manufacturing step.

The advantage to such a bumper in particular is that, as opposed to prior art, the reinforcing element does not have to be fastened to the cross beam element in an additional manufacturing step. Rather, it is sufficient that the reinforcing element running over the entire length of the cross beam element and fabricated together with the cross beam element first be removed from areas of the cross beam element. For example, the material removed in the process can be recycled, and hence returned to the production process. In addition, the advantage to the bumper according to the invention is that the single-piece configuration of the cross beam element together with the reinforcing element makes it possible to optimize the strength of the bumper with a given weight or to reduce the weight with a given resistance, provided that a homogeneous material joint without welded seams or the like is present in the area where the reinforcing element is joined to the cross beam element. Beyond that, the special advantage to the single-piece configuration of the cross beam element together with the reinforcing element is that any geometries can in principle be realized for the reinforcing element, and the reinforcing element can be joined to the cross beam element at locations that are not realizable with conventional methods, e.g., by way of a welded joint. For example, when providing a welded joint, it must be possible to form the welded seam from outside, and an overlapping area must typically be provided between the cross beam element and reinforcing element. This is not necessary in the bumper according to the invention, since the reinforcing element and cross beam element can be joined together at nearly any point of the cross section of the bumper.

Advantageous further developments of the bumper according to the invention for a motor vehicle are enumerated in the subclaims. Any combinations of at least two of the features disclosed in the specification, claims and/or figures fall within the framework of the invention.

According to the invention, the reinforcing element is made of at least one closed cross section. In order to form a closed cross section on the reinforcing element while simultaneously minimizing the material required and weight, it is provided that the reinforcing element together with at least one wall of the cross beam element form at least one additional hollow chamber (apart from the at least one hollow chamber in the cross beam element).

In order to reduce the size of the bumper as viewed in the vehicle direction or in a direction running perpendicular to the longitudinal direction of the cross beam element while maintaining good crash or strength properties, it is provided that the reinforcing element run at least essentially over the entire height of the cross beam element in which the at least one hollow chamber is formed on the cross beam element.

In order to enable an even surface without protrusions with the bumper mounted to the vehicle front, it is provided that the reinforcing element be situated on the back side of the cross beam element.

According to the invention the reinforcing element exhibits an end wall situated parallel to the back side of the cross beam element with two connecting bridges preferably situated parallel to each other and running perpendicular to the back side of the cross beam element. Therefore, the reinforcing element has a U-shaped cross section, and its open side is joined with the back side of the cross beam element.

In order to optimize the strength properties of the bumper or reinforcing element while keeping the material required and thus the weight as low as possible, a further development of the latter structural proposal provides that the end wall and connecting bridges exhibit a differing wall thickness. In particular, it can be provided that the end wall exhibits a larger wall thickness than the two connecting bridges. However, depending on the specific requirements, it is also conceivable that the end wall exhibit a smaller wall thickness than the connecting bridges.

The crash properties of the bumper are further optimized by having the connecting bridges of the reinforcing element be at least roughly aligned with at least one transverse wall, which forms the at least one hollow chamber on the cross beam element.

Another optimization involving the strength properties and weight minimization provides that the end wall of the reinforcing element exhibit sections over its height with differing wall thicknesses.

In order to minimize notch effects and thus optimize the crash properties of the bumper, it is further advantageous for the reinforcing element to be rounded or slanted in design in the transitional area to the cross beam element. This precludes any sharp corners or edges that would diminish the strength.

The bumper described to this point can in particular also be bent along its longitudinal direction for purposes of adjustment to the body shape. In addition, the bent shape also improves the strength properties or crash behavior.

In a construction optimized in terms of the crash behavior of the bumper, in which the latter simultaneously exhibits a relatively shallow depth or requires relatively little installation space as viewed in the longitudinal direction of the vehicle, it is provided that the reinforcing element be situated in a central area of the cross beam element as viewed in the longitudinal direction, and that two crash boxes be provided, situated on each side of the reinforcing element and joined with the cross beam element. In particular in conjunction with an arrangement of the reinforcing element on the back side of the cross beam element, this does not increase the required installation space for the bumper by comparison to a bumper without a reinforcing element. However, the reinforcing element can also be situated in the two outer areas of the cross beam element in relation to the longitudinal extension of the cross beam element. This makes sense in particular when additional installation space is required in the central area, for example a number plate or the like.

For reasons both of weight and easiest possible manufacture, it is further provided in particular that the bumper comprises aluminum alloy, preferably from the 6XXX series alloy. The alloys are designated according to the regulations of The Aluminum Association, known to a person skilled in the art.

The invention also encompasses a method for manufacturing a bumper according to the invention as described thus far. The method is characterized by at least the following production steps: In a first step, an endless, single-piece profile cross section is initially fabricated in an extrusion process, wherein the profile cross section exhibits a cross beam element section with at least one hollow chamber and a reinforcing element section. A section is then separated from the endless profile section, wherein the length of the severed section is adjusted to the length of the bumper. Finally, at least one partial area of the length of the reinforcing element section is removed from the profile cross section. The total length of the removed area of the reinforcing element is preferably between <NUM>% and <NUM>% of the length of the bumper.

There are basically different options available for removing the unrequired partial areas of the reinforcing element section from the profile section. The use of punches is preferred, since this can enable rational production at relatively low costs, in particular given large quantities. However, it is also conceivable, for example, to use a laser beam device or milling or other separating methods, in particular in cases where the partial area of the reinforcing element section is only removed after the molding process given a bent bumper.

In the event that the partial area of the reinforcing element section is removed from the profile section via punching, it makes sense, in particular so as to make removing the reinforcing element section easy to do, that the bumper only be deformed after removing the partial area of the reinforcing element section.

Additional advantages, features and details of the invention may be gleaned from the following description of preferred exemplary embodiments as well as based upon the drawing.

The same elements or elements with the same function are marked with the same reference numbers on the figures.

The bumper <NUM> for a vehicle shown in a top view on <FIG> is situated on the vehicle front of the motor vehicle (not depicted), for example. However, use of the bumper <NUM> is not to be confined to a vehicle front; rather, it should also be the case that the bumper <NUM> can be situated on the rear side of the vehicle or tail end of the vehicle.

As evident from <FIG>, the bumper <NUM> is mirror-inverted relative to a plane <NUM>, for example. An X-axis runs perpendicular to the plane <NUM>, denoting the longitudinal direction of the bumper <NUM>. Proceeding from the plane <NUM>, the bumper <NUM> has a curved design as viewed in both directions of the X-axis, i.e., a distance y formed between a transverse axis <NUM> situated perpendicular to the axis <NUM> and the bumper <NUM> enlarges in the direction of the X-axis, starting from the axis <NUM>. In the exemplary embodiment shown, the curvature of the bumper <NUM> is not uniform in design. Rather, the bumper <NUM> exhibits respective sections <NUM> to <NUM> that are roughly straight or even, and connected with each other by curved sections <NUM> arranged between the sections <NUM> to <NUM>. Of course, bending the bumpers <NUM> uniformly or non-uniformly in the direction of the X-axis also lies within the framework of the invention.

The bumper <NUM> comprises aluminum alloy, preferably from the 6XXX series alloy and designed as an extruded part exhibits a front side <NUM> and a back side <NUM>. The back side <NUM> is designed to be joined with two areas spaced relatively wide apart from the axis <NUM> symmetrically to the longitudinal axis <NUM>, each having a crash box <NUM>. Once again purely as an example, the crash box <NUM> exhibits a respective fastening plate <NUM>, which is joined with a side member of the motor vehicle (not depicted). In order to fasten the crash boxes <NUM> to the bumper <NUM>, the latter exhibits fastening openings <NUM>, for example, by means of which the crash box <NUM> can be screwed to the bumper <NUM>, for example.

In the depiction on <FIG>, the bumper <NUM> exhibits a different width B as viewed in the direction of the X- axis. The width B in the area of section <NUM> is greater than in the area of sections <NUM>.

The bumper <NUM> comprises a cross beam element <NUM>, which exhibits a front end wall <NUM> on its front side <NUM>, as visible in particular from <FIG> and <FIG>. The height H of the front end wall <NUM> can vary in size as viewed in the direction of the X-axis. In particular, it is provided that the height H of the front end wall <NUM> be greatest in the central area of the bumper <NUM>, and least in the direction of the lateral borders of the bumper <NUM>, i.e., in the area of sections <NUM>. The varying heights H of the front end wall <NUM> are realized after extruding the bumper <NUM>, in particular in a machining step. As further especially evident from <FIG>, three parallel transverse walls <NUM> to <NUM> spaced apart from each other proceed from the front end wall <NUM> in the direction of the back side <NUM> of the cross beam element <NUM>, and are once again joined as a single piece with a rear end wall <NUM> situated parallel to the front end wall <NUM>. Preferably, the wall thickness d of the transverse walls <NUM> to <NUM> is thinner than the wall thickness D of the front end wall <NUM> and the rear end wall <NUM>. However, the wall thicknesses d, D can also be equal in size. In addition, the front end wall <NUM> extends beyond the respective upper transverse wall <NUM> or lower transverse wall <NUM>. The two end walls <NUM> and <NUM> and transverse walls <NUM> to <NUM> form two closed hollow chambers <NUM>, <NUM>, e.g., designed with a square cross section.

The rear end wall <NUM> of the cross beam element <NUM> is joined as a single piece with a reinforcing element <NUM>. A reinforcing element <NUM> in the sense of this application is an element which serves to strengthen the cross beam element <NUM> in order to obtain better results for example in crash tests or which enables the cross beam element <NUM> to fulfill legal test crash proceedings in a better manner. Furthermore, the reinforcing element <NUM> is an integrated part of the cross beam element <NUM> in a sense that the reinforcing element <NUM> is produced monolithically with the cross beam element <NUM> during extrusion process. The reinforcing element <NUM> is situated on the back side <NUM> of the bumper <NUM>, and in the exemplary embodiment according to <FIG> runs symmetrically to the longitudinal axis <NUM> in the area of the sections <NUM> and <NUM>. The reinforcing element <NUM> depicted on <FIG> exhibits an upper connecting bridge <NUM> and a lower connecting bridge <NUM>, which are situated parallel to each other and parallel to the transverse walls <NUM> to <NUM>. The two reinforcing bridges <NUM>, <NUM> run roughly aligned with the two transverse walls <NUM> to <NUM>, somewhat offset in the direction of the central transverse wall <NUM> on <FIG>. The two connecting bridges <NUM>, <NUM> are joined as a single piece with an end wall <NUM> on the side facing away from the rear end wall <NUM>, thereby forming an additional hollow chamber <NUM> between the end wall <NUM> and reinforcing element <NUM>. In the exemplary embodiment shown, the wall thickness t of the two connecting bridges <NUM>, <NUM> is thinner than the wall thickness S of the end wall <NUM>. As further evident from <FIG>, the wall thickness S is not uniformly large as viewed over the height of the end wall <NUM>, but rather is larger in the area of the two connecting bridges <NUM> and <NUM> than in a central section of the end wall <NUM>.

The reinforcing element 40a shown on <FIG> exhibits an end wall 44a that is elongated in design beyond the two connecting bridges <NUM>, <NUM>, thereby forming a respective reinforcing edge <NUM>, <NUM> that runs in the direction of the X-axis.

As evident in particular based on <FIG>, the transitional area between the reinforcing element <NUM> and cross beam element <NUM> is designed or provided with a respective rounding <NUM>.

The cross beam element <NUM> is fabricated together with the reinforcing element <NUM>, 40a as a single piece in an extrusion process. Reference will now be made to <FIG> to explain the production method or production steps. As depicted therein, manufacturing the bumper <NUM> encompasses a first step <NUM>, in which an endless profile cross section is fabricated. An endless profile section is here understood as a profile cross section whose length as viewed in the direction of the X-axis is greater than the length of the bumper <NUM>. The profile section fabricated at a (conventional) extrusion plant here exhibits both the cross section of the cross beam element <NUM> in the form of a cross beam element section, as well as that of the reinforcing element <NUM>, 40a in the form of a reinforcing element section. Put another way, this means that the profile cross section fabricated in the first step <NUM> also exhibits the reinforcing section <NUM>, 40a as viewed over its entire length. In a second step <NUM>, a section of length to be used in making an individual bumper <NUM> is then severed from the endless profile section.

In a subsequent third step <NUM>, the part of the reinforcing element <NUM>, 40a present in the partial area where no reinforcing element <NUM>, 40a is provided on the finished bumper <NUM> is removed. While this is preferably accomplished via punching, other separating methods can also be provided, in particular machining methods, such as milling or sawing, or severance by means of a laser beam device.

Finally, the bumper <NUM> is formed into its curved or bent shape as depicted on <FIG> in a fourth step <NUM>, for example. The two crash boxes <NUM> can subsequently be mounted on the bumper <NUM> fabricated in this way.

Claim 1:
A bumper (<NUM>) for a motor vehicle, with a cross beam element (<NUM>) exhibiting a back side (<NUM>) which exhibits fastening openings to fasten the bumper (<NUM>) to the motor vehicle with at least one fastening device (<NUM>), in the form of a crash box, and a front side (<NUM>) lying opposite the back side (<NUM>), wherein the cross beam element (<NUM>) has at least one hollow chamber (<NUM>, <NUM>) with a closed cross section, and with at least one reinforcing element (<NUM>; 40a), which exhibits an end wall (<NUM>; 44a) situated parallel to an end wall (<NUM>) of the cross beam element (<NUM>) and at least two connecting bridges (<NUM>, <NUM>) situated parallel to each other and running perpendicular to the end wall (<NUM>) of the cross beam element (<NUM>) and being at least roughly aligned with at least one transverse wall (<NUM>, <NUM>, <NUM>), which form the at least one hollow chamber (<NUM>, <NUM>) on the cross beam element (<NUM>), and which extends over part of the length of the cross beam element (<NUM>) and is joined with the cross beam element (<NUM>) only in those areas where stricter strength requirement are placed on the bumper,
characterized in that
the cross beam element (<NUM>) is designed together with the reinforcing element (<NUM>; 40a) as a single-piece extruded part and wherein the reinforcing element (<NUM>; 40a) is situated on the back side (<NUM>) of the cross beam element (<NUM>) in a central area of the cross beam element (<NUM>) in relation to the longitudinal extension of the cross beam element (<NUM>), and in that two crash boxes are provided, which are situated on each side of the reinforcing element (<NUM>; 40a) and joined with the cross beam element (<NUM>).