Abstract:
A single component bumper beam and lower frame midrail structure, is formed through a hydroforming process to create a uniform “B-shaped” cross-sectional configuration with internal crash triggers to enhance crash performance. The mounting legs of the integral bumper structure are formed with a reduced cross-section at the terminal ends thereof to facilitate insertion into lower frame midrails formed from a pair of horizontally disposed tubes. The terminal end portions of the mounting legs are formed with a longitudinally extending slot to receive a central co-joined wall member formed through the welding of the two vertically oriented tubular members in the lower frame midrails. The single component bumper and longitudinally extending mounting leg structure can be formed by welding together two vertically oriented tubes.

Description:
FIELD OF THE INVENTION 
     This invention relates to a bumper for an automotive vehicle and, more particularly, to a rear bumper and lower frame rail formed from a single hydroformed component for attachment to the lower frame midrails. 
     BACKGROUND OF THE INVENTION 
     Bumpers are mounted at the forward and rearward extremities of a vehicle to protect the chassis of the vehicle from minor impacts. The bumper is mounted to the lower frame rails of the vehicle chassis for support thereof and functions to withstand minor impacts by collapsing to absorb the energy encountered through the impact. 
     The structure of a bumper can be formed in a “B-shaped” configuration with a front face flange and upper and lower cells. This B-shaped structural configuration can be seen in U.S. Pat. No. 6,510,771, issued to Peter Sturrus, et al on Jan. 28, 2003. The Sturrus patent discloses a bumper having a transversely extending member shaped in the “B” configuration with the bumper having upper and lower tubular portions with an intermediate portion between the two tubular cells. Bumpers can be formed through a number of processes, including roll-forming; stamping, such as is depicted in U.S. Pat. No. 6,193,274, issued to Richard Brown, et al on Feb. 27, 2001, in which the bumper support and front rail portion is formed by a central tubing and side tubular members; and extruding, such as is depicted in U.S. Pat. No. 5,727,826, issued to Simon Frank, et al on Mar. 17, 1998, wherein the bumper is formed by two longitudinally spaced wall sections or by integrally forming longitudinal and vertically spaced struts. 
     The frame apparatus disclosed in U.S. Pat. No. 5,882,039, issued to John Beckman, et al on Mar. 16, 1999, is formed through hydroforming and incorporates a cross member extending across the U-shaped frame member to form an engine cradle. U.S. Pat. No. 6,010,155, issued to Ronald Rinehart on Jan. 4, 2000, discloses the connection of longitudinally spaced tubing members via the insertion of one rounded portion of a member into the slotted and split rounded portion of the other tubing member. U.S. Pat. No. 5,839,776, issued to Edvin Clausen on Nov. 24, 1998, discloses vertically spaced tubes between frame rails and the bumper. 
     U.S. Pat. No. 3,557,894, issued to Donald Hanley on Jan. 26, 1971, and U.S. Pat. No. 3,779,283, issued to Elmer Freber on Mar. 26, 1974, teach the forming a go-cart framing through tubes that form a bumper and a substantial portion of the go-cart&#39;s frame structure. Such bumper and frame structure is not particularly well suited to modem automotive manufacture. 
     It would be desirable to provide a bumper and lower frame rail structure that are particularly adaptable to manufacturing through hydroforming processes and which can be utilized in the manufacture of an automobile while providing adequate crash performance characteristics. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to overcome the aforementioned disadvantages of the known prior art by providing a single component bumper and lower frame rail construction that can be attached to and supported from the lower frame midrails. 
     It is a feature of this invention that the bumper structure can be formed through hydroforming processes to enhance manufacturing efficiencies. 
     It is an advantage of this invention that the cross-sectional configuration of the bumper beam can be uniformly manufactured along the entire length of the bumper beam and extending through the lower frame rails. 
     It is still another advantage of this invention that the bumper and lower frame rails are formed into a single structural component having a generally uniform cross-sectional configuration throughout. 
     It is still another feature of this invention that the bumper beam can be formed with crash triggers to direct the deformation of the bumper and lower frame rail in a manner to enhance crash performance. 
     It is a further advantage of this invention that the manufacturing cost of a bumper and lower frame rail can be lowered without sacrificing crash performance characteristics. 
     It is another object of this invention to provide a single component bumper beam and lower frame rail structure that is durable in construction, inexpensive of manufacture, facile in assemblage, and simple and effective in use. 
     These and other objects, features and advantages are accomplished according to the instant invention by providing a single component bumper beam and lower frame rail structure, which can be formed through a hydroforming process to create a uniform “B-shaped” cross-sectional configuration with internal crash triggers to enhance crash performance. The mounting legs of the integral bumper structure are formed with a reduced cross-section at the terminal ends thereof to facilitate insertion into lower frame rails formed from a pair of horizontally disposed tubes. The terminal end portions of the mounting legs are formed with a longitudinally extending slot to receive a central co-joined wall member formed through the welding of the two vertically oriented tubular members in the lower frame rails. The single component bumper and longitudinally extending mounting leg structure can be formed by welding together two vertically oriented tubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a top plan view of the single component bumper and lower frame rail structure attached to the frame midrails to form the rear frame structure for an automobile incorporating the principles of the instant invention; 
         FIG. 2  is a side elevational view of the bumper and lower frame rail structure depicted in  FIG. 1 ; 
         FIG. 3  is an enlarged partial perspective view of the bumper structure incorporating the principles of the instant invention; 
         FIG. 4  is an enlarged perspective detail view of the reduced terminal end portion of the longitudinally extending mounting legs of the bumper structure to be inserted into the lower frame rails, as is depicted in  FIGS. 1 and 2 ; 
         FIG. 5  is a top plan view of the reduced terminal end portion of the mounting leg structure being inserted into the dual tube lower frame midrails as depicted in  FIGS. 1 and 2 ; 
         FIG. 6  is a bottom perspective view of the bumper and lower frame rail structure shown in  FIG. 1 ; and 
         FIG. 7  is an enlarged bottom perspective view of the divergent zone of the lower frame midrail assembly showing the connection of the cross frame members and the shock tower support member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , a bumper and lower frame rail, including the midrails having a shock tower support mounted thereon, forming the rear end of an automobile frame and incorporating the principles of the instant invention, can best be seen. The frame  10  of the automobile is preferably formed from hydroformed tubular members. Such tubular members can be spot-welded and/or MIG-welded to form an integral frame assembly for the rear end of a vehicle. 
     Hydroforming is a process by which a standard tubular stock member is placed into a form shaped to correspond to the particular member to be formed and to correspond to the particular section required for the frame design. A liquid is then introduced into the interior of the tubular stock and pressurized until the tubular stock expands to assume the shape defined by the configured form The expanded and re-shaped tubular stock now has a substantially different shape. By forming cutouts and other access openings into the re-shaped tubular member, spot-welding electrodes can gain access to opposing adjacent sides to create a weld bond between juxtaposed members. In this manner, a frame, as an example, for an automobile can be created using in large part hydroformed tubular members. One skilled in the art will readily recognize that some MIG-welding will be required in areas where access holes are detrimental to the integrity of the frame structure. Preferably, such MIG-welding processes are performed at a sub-assembly or at a supplier level. 
     In the automotive rear end frame  10  depicted in the drawings, the bumper  15  is formed from welded hydroformed members. Similarly, the lower frame midrails  20 , which connect to the bumper  15  and project forwardly therefrom, are also formed from tubular hydroformed members. The shock tower support member  25  is preferably a stamping that is formed into a specific shape and mounted on the lower frame midrails  20 , as is described in greater detail below. 
     The lower frame midrail  20  is formed from two hydroformed tubular members  21 ,  22  that have corresponding first longitudinally extending portions  23  that are welded together at the rearwardmost end of the members  21 ,  22  preferably by MIG-welding along the generally horizontal seam between the members  21 ,  22 . As is best seen in  FIGS. 1 and 5 , the lower frame midrail structure  20  would then have an internal vertical web  24  formed from the adjacent sidewalls of the two tubular members  21 ,  22 , oriented as an exterior member  21  and an interior member  22 . The internal web  24  substantially increases the strength and stiffness of the lower frame midrail  20 , compared to a conventional tubular member. 
     The longitudinally extending portions  23  are positioned for connection to the bumper  15 , as will be described in greater detail below. Forwardly of the longitudinally extending portions  23 , the two tubular members  21 ,  22  diverge to define a divergent portion  28  to provide a lateral spacing between the two members  21 ,  22 . At this point of divergence, the shock tower support  25  is affixed, preferably by welding, to the top of the two tubular members  21 ,  22 . The tubular members  21 ,  22  converge into a second longitudinally extending portion  29  forward of said divergent portion  28 . 
     Unlike conventional shock tower supports, the shock tower support member  25  is adequately supported both inboard and outboard on the laterally spaced members  21 ,  22  in the divergent zone  28  to provide a stable foundation for the shock tower (not shown). The shock tower support stamping  25  transfers road loads directly to the frame  10  and also provides sectional stability for any rear impact loads that might be encountered. This design results in a stiffer, stronger, yet lighter joint than is known in the prior art. 
     To facilitate the use of spot welding techniques, the tubular members  21 ,  22  can be formed with appropriate access openings (not shown) in the sidewalls for passage of a welding electrode. Similarly, cross frame members  30  can be welded between the opposing sides of the lower frame rails  20  to span the lateral distance across the vehicle frame  10 . The cross frame members  30  can be inserted into appropriate openings  27  in the sidewalls of the tubular members  21 ,  22  to permit the passage of the cross frame members  30  internally into the interior tubular member  22  to enable the cross frame members  30  to be welded directly to the interior tubular member  22 . 
     Preferably, as is best seen in  FIG. 6 , at least one of the cross frame members  30  adjacent the shock tower support  25  will pass through appropriate openings  27  in the interior tubular member  22  to engage the exterior tubular member  21  to permit welding between both members  21 ,  22  and the cross frame member  30 . Such fabrication will add cross-vehicle stiffness to the frame  10 , as well as provide a robust joint at the shock tower support  25 . Preferably, the interior and exterior tubular members  21 ,  22  converge so that the lower frame midrail  20  will extend forwardly with a central vertical web  24 , as is shown with respect to the rearward longitudinally extending portions  23 . 
     The bumper  15  can also be constructed from two hydroformed members  16 ,  17 , with the upper tubular member  16  being located on top of the lower tubular member  17 . Preferably both tubular bumper members  16 ,  17  are shaped substantially identically with a rearwardly positioned transverse portion  18  and opposing mounting legs  19 , which eliminate the need for a separate lower frame rail spanning between a conventional lower frame midrail and the bumper. The two tubular members  16 ,  17  can be MIG-welded along the generally horizontally extending seam therebetween to form a dual-celled bumper  15 . Formation of the tubular members through the hydroforming process permits the introduction of deformation triggers  39 , i.e. fold points to direct the deformation of the bumper in a prescribed manner when encountering an impact load. 
     This bumper  15  not only has the transverse portion  18  forming the laterally extending rear bumper beam  12 , but the integrally formed longitudinally extending mounting legs  19 , or lower frame rails, provide the function of mounting the bumper beam  12  to the lower frame midrails  20 . A curved transition portion  13  preferably separates the transverse portion  18  from the longitudinal mounting legs  19 . In conventional bumper design, the bumper beam, lower frame rails, and attachment brackets are separate parts that are assembled to form the bumper structure. The formation of the bumper  15  according to the principles of the instant invention substantially reduces the number of parts required. With the two tubular members  16 ,  17  being welded together in a vertical orientation, the resultant structure has a horizontally oriented internal web  14  that enhances strength and stiffness for the bumper structure  15 . 
     One of ordinary skill in the art will readily realize that the bumper  15  could also be formed through a roll-forming process in which the upper and lower cells of the bumper beam  15  would be separated by a horizontally oriented internal web  14 . While the formation of the tubular members  16 ,  17  through the hydroforming process enables the tubular members  16 ,  17  to have triggers  39  formed therein during the formation process, the crash triggers  39  would have to be formed in the bumper by a separate processing step if the bumper  15  were manufactured through the roll-forming process. 
     Referring particularly to  FIGS. 3-5 , the forward ends of the mounting legs  19  are formed to mate with the dual tube lower frame midrails  20 . Each tubular member  16 ,  17  is formed with a reduced-sized terminal end  35  that can fit between the interior and exterior sidewalls of the lower frame midrails  20 , whereas the remainder of the mounting legs  19  are formed to correspond geometrically with the longitudinally extending portions  23  of the lower frame rails  20 . As a result, the insertion of the reduced-sized terminal end  35  into the rearward ends of the lower frame midrails  20  results in a generally uniformly shaped frame  10  with the overall width and depth of the bumper structure  15  being substantially equal to the overall width and depth of the lower frame midrails  20 . 
     To accommodate the interference between the horizontal internal web  14  of the mounting legs  19  and the vertical internal web  24  of the longitudinally extending portions  23  of the lower frame midrails  20 , the reduced-size terminal end  35  is formed with a slot  37  into the top and bottom walls of both of the upper and lower tubular members  16 ,  17 . When the reduced-size ends  35  of the mounting legs  19  are inserted into the lower frame midrails  20 , the vertical internal web  24  slides into the aligned slots  37 . 
     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.