Abstract:
A bumper assembly ( 10 ) for an automotive vehicle is described. In an example embodiment, the assembly comprises a beam and a fascia at least partially covering the beam. The beam comprises at least one crush can ( 12 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of International Application No. PCT/US01/28583 filed Sep. 12, 2001. 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to bumpers and, more particularly, to bumper beams. 
     Bumpers typically extend widthwise across the front and rear of a vehicle and are mounted to rails that extend in a lengthwise direction. A typical bumper includes a steel beam or reinforcing member attached to vehicle rails and covered by a fascia. Such steel beams are heavy and typically deform, or buckle, on impact. Energy from an impact therefore may be transferred to the vehicle rails and result in additional damage to the vehicle. 
     Energy absorbing bumper systems attempt to reduce vehicle damage as a result of a collision by managing impact energy and intrusion while not exceeding a rail load limit of the vehicle. The efficiency of a bumper system is defined as the amount of energy absorbed over distance. A high efficiency bumper system absorbs more energy over a shorter distance than a low efficiency bumper system. High efficiency is achieved by building load quickly to just under the rail load limit and maintaining that load constant until the impact energy has been dissipated. 
     Some known energy absorbing bumper systems include a beam and an energy absorber coupled to the beam. The energy absorber is effective in absorbing energy from an impact. Separately fabricating an energy absorber and assembling the energy absorber to the beam increases both the fabrication and assembly costs of a bumper assembly as compared to a simple steel beam bumper. 
     Other known energy absorbing bumper systems utilize a foam resin, such as described in U.S. Pat. No. 4,762,352 and U.S. Pat. No. 4,941,701. Foam based systems typically have slow loading upon impact, which results in a high displacement. Further, foams are effective to a sixty or seventy percent compression, and beyond that point, foams become incompressible so that the impact energy is not fully absorbed. The remaining impact energy is absorbed through deformation of a backup beam and/or vehicle structure. Foams are also temperature sensitive so that displacement and impact absorption behavior can change substantially with temperature. Typically, as temperature is lowered, foam becomes more rigid, resulting in higher loads. Conversely, as temperature rises, foams become more compliant resulting in higher displacements and possible vehicle damage. 
     Still other known bumper systems include crash cans. The crash cans are separately fabricated and attached directly to a beam in alignment with the vehicle rails. The crash cans absorb energy during impact, e.g., an offset impact, and facilitate preventing damage to the beam. Separately fabricating and attaching the crash cans to the beam, however, increases bumper assembly costs and complexity. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, a bumper assembly for an automotive vehicle is provided. The bumper assembly comprises a beam and a fascia at least partially covering the beam. The beam comprises at least one crush can. 
     In another aspect, an energy absorbing beam for a bumper assembly is provided. The beam comprises a frame and a body extending from the frame. The body comprises a first transverse wall, a second transverse wall spaced from the first wall, and at least one crush can between the first and second walls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective front view of a bumper beam; 
         FIG. 2  is a perspective rear view of a portion of the bumper beam shown in  FIG. 1 ; 
         FIG. 3  is a perspective front view of a portion of the bumper beam shown in  FIG. 1 ; and 
         FIGS. 4 ,  5 , and  6  are cross-sectional views through line  4 — 4  in  FIG. 3  and showing different crush can wall configurations. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A thermoplastic bumper beam that includes tunable crush cans is described below in detail. The term tunable, as used herein, means that characteristics, e.g., wall angles, of the crush cans can be selected to provide a desired operating result, as described below in more detail. The crush cans are sometimes described herein as being integral with the beam, which means that the crush cans are formed as a component of, and not separately from, the beam, which results in a one-piece unitary structure for the beam. The term integral also includes constructions in which the beam is molded in segments, and then the segments are secured together, e.g., welded. 
     Combining the crush cans with the beam results in a bumper system that absorbs energy without necessitating a separate energy absorber attached to the beam. For example, impact forces during low speed impacts are maintained just below a predetermined level by deforming the beam until the kinetic energy of the impact event has been absorbed. When the low speed impact is over, the beam returns substantially to its original shape and retains sufficient integrity to withstand subsequent impacts. 
     Further, combining the efficient energy absorbing properties of a thermoplastic beam with the integrated crush cans is believed to provide improved impact absorbing performance over traditional metal beams. In addition, the thermoplastic beam with integrated crush cans is believed to provide more efficient impact absorption than thermoplastic beams that do not include crush cans. 
     The bumper beam can be fabricated from one of many plastic materials including, for example, Xenoy® material which is commercially available from General Electric Company, Pittsfield, Mass. The beam is not limited to practice with such material and other materials can be used. 
     More specifically, the characteristics of the material utilized to form the beam include high toughness/ductility, thermally stable, high energy absorption capacity, a good modulus-to-elongation ratio and recyclability. While the beam may be molded in segments, the beam also can be of unitary construction made from a tough plastic material. An example material for the beam is Xenoy material, as referenced above. Of course, other engineered thermoplastic resins can be used. Typical engineering thermoplastic resins include, but are not limited to, acrylonitrile-butadiene-styrene (ABS), polycarbonate, polycarbonate/ABS blend, a copolycarbonate-polyester, acrylic-styrene-acrylonitrile (ASA), acrylonitrile-(ethylene-polypropylene diamine modified)-styrene (AES), phenylene ether resins, blends of polyphenylene ether/polyamide (NORYL GTX® from General Electric Company), blends of polycarbonate/PET/PBT, polybutylene terephthalate and impact modifier (XENOY® resin from General Electric Company), polyamides, phenylene sulfide resins, polyvinyl chloride PVC, high impact polystyrene (HIPS), low/high density polyethylene (l/hdpe), polypropylene (pp) and thermoplastic olefins (tpo). The beam also could, for example be fabricated (e.g., compression molded) from a glass mat thermoplastic (GMT), such as Azdel® material (commercially available from Azdel, Inc., Shelby, N.C. and described in U.S. Pat. No. 5,643,989). 
     Referring now specifically to the drawings,  FIGS. 1 and 2  are a front perspective view of a bumper  10  including integral tunable crush cans  12  and a rear view of a portion of bumper  10 , respectively. A fascia (not shown) ordinarily would be secured to beam  10  and typically is formed from a thermoplastic material which is amenable to finishing utilizing conventional vehicle painting and/or coating techniques. The fascia envelopes beam  10  such that beam  10  is not visible once attached to the vehicle. 
     Beam  10  has a generally rectangular cross sectional shape and includes a frame  14 . A body  16  that extends from frame  14  includes first and second longitudinally extending flanges  18  and  20 . Flanges  18  and  20  define a channel  22  that also extends longitudinally. A plurality of reinforcing and stiffening ribs  24  are positioned between flanges  18  and  20  in channel  22 , and also on exterior surfaces  26  and  28  of flanges  18  and  20 . 
     Beam  10  also includes vehicle attachment portions  30 ,  32 , and includes openings  34  for securing beam  10  to the frame rails of the vehicle. Reinforcing members  36  extend from body  16  to attachment portion  32 . Crush cans  12  generally are located in alignment with the vehicle rails when bumper  10  is secured to a vehicle. By positioning crush cans  12  in alignment with the vehicle rails, such crush cans operate to facilitate reducing damage to the vehicle during an impact. 
     Referring to  FIG. 3 , which is a perspective front view of a portion of bumper  10 , crush can  12  includes a plurality of walls  50 ,  52 ,  54 . Also, and referring to  FIGS. 4 ,  5  and  6 , which are cross sectional views through line  4 — 4  in  FIG. 3  and illustrate alternative crush angles A, B, C, varying crush angles A, B, C results in different stiffness and impact characteristics. For example, by changing walls  50 ,  52 ,  54  to be more upright, crush can  12  is more stiff. Also, positioning walls  50 ,  52 ,  54  closer together results in increasing the stiffness of crush can  12 . In addition, spacing of ribs  24  can be altered, i.e., beam  10  becomes more stiff as ribs  24  are spaced closer together. 
     By varying at least the wall angles A, B, C, the spacing of walls  50 ,  52 ,  54 , and the spacing of ribs  24 , crush can  12  is tunable to provide a desired stiffness. Since vehicles have different weights and operating applications (e.g., non-commercial passenger vehicle, commercial passenger vehicle, light truck), bumper  10  can be tuned for a particular vehicle weight and application. 
     Of course, other variables can be used to for tuning crush cans  12 . For example, crush can  12  can also be tailored for specific applications by varying the wall thickness of walls  50 ,  52 ,  54 . For example, the nominal thickness of the walls may broadly range from about 1.75 mm to about 3.0 mm. More specifically, for certain low impact applications the nominal wall thickness may generally range from about 1.75 mm to about 2.0 mm and for other applications the walls would more likely be in the range of about 2.5 mm to 3.0 mm. 
     Another aspect in appropriately tuning crush cans  12  is the selection of the thermoplastic resin to be employed. The resin employed may be a low modulus, medium modulus or high modulus material as needed. By carefully considering each of these variables, crush cans  12  can meet the desired energy impact objectives. 
     As explained above, integrating crush cans with an injection molded thermoplastic beam is believed to provide enhanced energy absorption efficiency over steel beams and simple thermoplastic beams. Enhanced impact performance translates to reduced costs of repair for low speed “fender benders” and reduced vehicle damage during higher speed collisions. Further, since a separate energy absorber is not utilized, cost savings also are believed to be achieved with such a bumper beam configuration. The combination of the thermoplastic beam and the tunable crush cans provides an efficient, fast loading and controlled impact event. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.