Abstract:
A bumper beam includes a first portion of a first material and a second portion of a second material. The first material has different material properties than the second material. For example, the first material may have a generally higher tensile or yield strength than the second material. In one embodiment, the first material comprises martensitic steel, while the second material comprises a dual-phase, multiphase, complex-phase or TRIP steel. In addition, the first material may have a different thickness than the second material. The bumper beam provides an improved strength to weight ratio than conventional bumper beams. This abstract is provided to comply with the rules requiring an abstract that allows a searcher or other reader to quickly ascertain the subject matter of the disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope of the claims.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a bumper assembly for a motor vehicle, and more particularly to a bumper beam having multiple material properties.  
           [0003]    2. Description of the Related Art  
           [0004]    Automotive designers are continually trying to balance the need for lightweight, fuel efficient automobiles with safety standards and regulations imposed by the government and insurance companies. One such automotive component subject to heavy regulation is bumper assemblies with regard to crash safety standards. The bumper assembly is traditionally comprised of a bumper beam made of a metallic material with the requisite strength to conform to governmental standards for low and high speed crashes. Often, the strong metallic beam is heavy and adds significant weight to the vehicle thereby reducing fuel efficiency. There is a need in the automotive industry to develop a bumper assembly having a bumper beam with an increased strength to weight ratio by lowering the overall weight of the bumper assembly. The improved bumper assembly must still be strong enough to provide excellent performance in high speed and low speed crashes.  
           [0005]    Furthermore, automotive manufacturers desire components that are affordable and easy to produce in a mass production operation. Traditional bumper assemblies are roll-formed whereby a flat steel strip extends through a series of rollers to shape the steel into a desired form. Complex bumper beam designs, while providing the necessary strength to conform to safety standards, add to the time and cost of the manufacturing process. There is a need in the automotive industry to produce a bumper beam that provides strength adequate to conform to safety standards, lightweight to improve fuel efficiency and simple to manufacture.  
         SUMMARY OF THE INVENTION  
         [0006]    The inventors of the present invention have recognized these and other problems associated with the traditional bumper beams described above. To this end, the inventors have developed a bumper beam that weighs less while maintaining high quality standards related to impact or crash testing.  
           [0007]    Specifically, the invention comprises a bumper beam having a first portion comprising a first material, and a second portion comprising a second material. The first material has different material properties than the second material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    In the drawings:  
         [0009]    [0009]FIG. 1 is a perspective view of a bumper beam of the present invention;  
         [0010]    [0010]FIG. 2 is a cross-sectional view of a first embodiment of the bumper beam of the present invention taken along the line  2 - 2  of FIG. 1;  
         [0011]    [0011]FIG. 3 is a perspective view of a second embodiment of a bumper beam of the present invention; and  
         [0012]    [0012]FIG. 4 is a cross-sectional view of the second embodiment of the bumper beam of the present invention taken along the line  4 - 4  of FIG. 3. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring to FIGS. 1 and 3, a bumper beam, generally referred at  10 , is shown according to an embodiment of the invention. The bumper beam  10  is an elongated beam having a first portion  12  and a second portion  14 . In one embodiment, the second portion  14  is fixedly attached to a vehicle (not shown) by traditional techniques, such as fasteners, bracket assemblies, or the like. The first portion  12  extends outwardly from the vehicle and is usually first to contact an external object (not shown) during a crash. The positions of the first portion  12  and second portion  14  are merely illustrative. Alternatively, the second portion  14  may be attached to the vehicle while the first portion  12  extends outwardly from the vehicle.  
         [0014]    One aspect of the invention is that the first portion  12  and the second portion  14  are made from different materials, such as a first material and a second material, respectively. By way of example, the first portion  12  is made from the first material that is generally higher strength (tensile strength or yield strength) than the second material of the second portion  14 . It has been found that forming the first portion  12  with the first material having a greater strength enables the bumper beam  10  to greater withstand the forces generated on the bumper beam  10  during a crash, as compared to a bumper beam made of a single material having a lesser strength than the first material. The second portion  14  is made from the second material having a lesser strength (tensile strength or yield strength) than the first material, but weighing less or the same as the first material. It has been found that the combination of the higher strength first material and the lighter or equal weight second material provides a bumper beam  10  with an increased or higher strength to weight ratio, as compared with traditional bumper assemblies made of a single material. The increased strength to weight ratio provides a bumper beam that conforms to governmental standards regarding high and low speed crashes, while also improving fuel efficiency of the vehicle. As a further example, the second material of the second portion  14  may be of generally higher strength (tensile strength or yield strength) than the first material of the first portion  12  while the first material weighs less than or equal to the second material. Any combination of materials having different material properties that results in an increased or higher strength to weight ratio of the bumper beam is contemplated by the present invention.  
         [0015]    In addition, the first material can be of a different gauge than the second material. For example, the first material of the first portion  12  can have a lesser thickness than the second material of the second portion  14  because the first material comprises a higher strength material than the second material. In contrast, if the second material has a higher strength than the first material, then the second material may have a lesser thickness than the first material.  
         [0016]    In an illustrated embodiment of the invention, the first portion  12  comprises martensitic steel. It has been found that martensitic steel provides very high structural strengths, for example, up to 1500 MPa ultimate tensile strengths, while still having remarkable formability. However, it will be appreciated that the invention is not limited by the specific material for the first material of the first portion  12 , and that the invention can be practiced with other suitable materials that provide the strength needed for bumper assemblies.  
         [0017]    Referring to FIG. 2, a cross-sectional view of a first embodiment of the bumper beam  10  is shown. As seen in FIG. 2, the first portion  12  is generally C-shaped in cross-section and includes a back  16  and two legs  18 . The legs  18  extend generally orthogonally from the back  16  at one or more bending portions  20 .  
         [0018]    Referring to FIG. 4, a cross-sectional view of a second embodiment of the bumper beam  10  is shown. As seen in FIG. 4, the first portion  12  is generally C-shaped in cross-section and includes a back  32  and two legs  34 . The legs  34  extend generally orthongonally from the back  32  at one or more of the bending portions  20 .  
         [0019]    In the illustrated embodiments of the invention, the second portion  14  comprises a dual-phase, multiphase, complex-phase or transformation induced plastic (TRIP) steel. One such material determined suitable for the second portion  14  of the bumper beam  10  is currently marketed under the trade name DI-Form 140T. DI-Form 140T is commercially available from Ispat Inland Inc. of East Chicago, Ind. (www.ispat.com). DI-Form 140T has an ultimate tensile strength of approximately 965 MPa. Although the second material of the second portion  14  is generally of a lower strength than the first material of the first portion  12 , the second material of the second portion  14  weighs less than or equal to the first material of the first portion  12 . It will be appreciated that the invention is not limited by the specific material used for the second portion  14 , and that any material suitable for providing the necessary strength of the bumper assembly, while reducing the weight of the assembly, is acceptable for the second material of the second portion  14 .  
         [0020]    Referring to the first embodiment in FIG. 2, the second portion  14  includes two generally C-shaped sections  21 ,  23  integrally joined together by a connecting segment  22 . Similar to the C-shaped first portion  12 , each C-shaped section  21 ,  23  of the second portion  14  includes a back  26  and two legs  24 ,  28 . One of the legs  24  is generally orthogonal to the back  26 , while the second leg  28  extends angularly from the back  26 . In the illustrated embodiment, the second leg  28  extends at an acute angle with respect to the back  26 . Each C-shaped section  21 ,  23  includes one or more bending portions  20 .  
         [0021]    Referring to the second embodiment in FIG. 4, the second portion  14  includes two generally C-shaped sections  21 ,  23  integrally joined to each other. Each C-shaped section of the second embodiment includes a back  38  and two legs  36 ,  40 . Both legs  36 ,  40  extend generally orthogonally from the back  38  at one or more of the bending portions  20 . The legs  40  of each C-shaped section are integral to form one extended segment between the backs  38  of each C-shaped section. The C-shaped sections are symmetrical about a longitudinal axis, A, whereby the axis A, is midway between the backs  38 .  
         [0022]    The first portion  12  and the second portion  14  of both embodiments are fixedly attached to each other at one or more locations, indicated at  30 , such as by welding, or the like. In the first illustrated embodiment, the first portion  12  and the second portion  14  are welded to each other at each of the legs  18  of the first portion  12  and each of the legs  24  of the second portion  14 . Further, the connecting segment  22  is welded to the back  16  of the first portion  12  at a location  30  along the longitudinal axis, A, of the bumper beam  10 . Finally, the bending portions  20  formed between the back  26  and the legs  28  are welded to each other along the longitudinal axis, A, of the bumper beam  10 . As can be seen in FIG. 2, the bumper beam  10  is generally mirror symmetric with respect to the longitudinal axis, A. As a result, the location  30  at which the back  16  is welded to the connecting section  22  and the location  30  at which the bending portions  20  formed between the back  26  and the legs  28  are welded lie along a midpoint between the legs  18  of the first portion  12 .  
         [0023]    In the second embodiment the first portion  12  and second portion  14  are welded to each other at each of the legs  34  of the first portion  12  and the bending portions at each of the legs  36  of the second portion. Further, the back  32  of the first portion  12  is welded to the legs  40  of the second portion  14  along the axis, A, of the bumper beam  10 .  
         [0024]    It will be appreciated that the locations  30  of the welds to join the first portion  12  and the second portion  14  are only illustrative, and the weld locations  30  may be positioned anywhere suitable for fixedly attaching the first portion  12  and the second portion  14 . Furthermore, other techniques known in the art for attaching the second portion  14  and the first portion  12  are also within the scope of the invention.  
         [0025]    The cross-sectional configurations of the bumper beam  10  shown in the accompanying figures are only two examples of a bumper assembly that provides an increased strength to weight ratio as compared to conventional bumper assembly designs. Any cross-sectional configuration that incorporates two different materials is also contemplated by this invention. The configuration of the bumper beam  10 , as shown, positions the higher strength material only where necessary to absorb forces during a crash. Utilizing the higher strength first material only where necessary allows the remainder of the bumper beam  10  to be manufactured of a lower strength, lighter second material.  
         [0026]    Furthermore, the overall shape of the bumper beam  10 , as shown in the figures, helps to provide additional stiffness to the beam. For example, the cross-sectional configuration of the first portion  12  being generally C-shaped along with the cross-sectional configuration of the second portion  14  with two C-shaped sections provides additional stiffness and helps the bumper beam  10  withstand forces during a crash. One benefit of the cross-sectional configuration of the invention is that the invention may eliminate the need for an energy absorber commonly found in traditional bumper assemblies.  
         [0027]    Finally, the bumper beam  10  of the present invention is also simple to manufacture. As with traditional bumper assemblies, the bumper beam  10  is roll-formed. The first portion  12  and the second portion  14  are welded together and then roll-formed. Once formed, the first portion  12  and second portion  14  are then welded together within the assembly line at additional locations. The two-material design of the bumper assembly  10  of the invention provides the opportunity for in-line welding of the first portion  12  and the second portion  14  to form the bumper beam  10  and reduces extra material handling that may result from using two different materials.  
         [0028]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.