Abstract:
A vehicle structure includes a combination of hydro-formed, generally tubular shaped rails joined by an overlapping joint to a two-piece cross member. The overlapping joint is formed between a rail aperture and the cross member. To retain the structural strength lost by removing material from the rails, a weld joint is formed about the total perimeter of contact between the rail aperture and the cross member. The cross member includes a shoulder area formed to nest within the rail aperture. The two-piece cross member assembly reduces total parts while providing a plurality of cross member geometries and the necessary tolerance flexibility at the rail connections. The cross member is formed of two generally C-shaped members having butted or overlapping mating surfaces joined by a perimeter weld joint.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates in general to vehicle frames and more specifically to a joint for and method of joining vehicle structural frames.  
         BACKGROUND OF THE INVENTION  
         [0002]    A structural frame for vehicles typically includes beams as well as tubular members. Where sections of the structure connect and/or cross, space requirements often require that portions of one or both of the members be removed. To replace the structural strength lost by material removal, additional structure including mechanical fasteners, weld joints, and braces or brackets are often added. By increasing the number of component parts of a vehicle frame, the cost, time of construction, and complexity of the frame increase.  
           [0003]    Many common vehicle frames include a combination of tubular-shaped members. These tubular-shaped members are commonly manufactured using a hydro-forming process and are often used as longitudinal rails. This permits frame sections to be manufactured from single rail parts. The tubular shape increases the mechanical strength of the member. Where complex geometries are required, including cross member sections, multiple part assemblies are commonly used. These multiple part assemblies commonly use C-shaped members which are joined and reinforced by additional structural members. Disadvantages of this cross member design include the cost and complexity of manufacturing multi-part items and additional structure often required to join these multi-part cross member assemblies to the tubular rails.  
           [0004]    It is therefore desirable to provide a vehicle frame assembly which reduces the amount of component parts, retains the full structural strength of the hydro-formed tubular members at cross member intersections, and reduces the complexity of joining the cross members to the front to back running tubular rails.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the present invention, a vehicle structure includes at least one cross-member having at least one mating shoulder formed thereon. At least one rail having at least one receiving aperture is sized to slidably mate with the mating shoulder. An overlapping joint is formed when the receiving aperture is slidably mated to the mating shoulder. A weld joint is then formed at the overlapping joint to join the rail to the cross-member.  
           [0006]    To retain the structural strength lost by removing the aperture from the rails, the weld joint is formed about the total perimeter at the contact point between the rail aperture and the cross member. A two-piece cross member assembly is used to reduce the total number of parts required for the cross member while retaining the capability of forming the cross member in a plurality of shapes and having the necessary dimensional flexibility for mounting the various vehicle components on the cross members. The two piece cross member is formed of two generally C-shaped members having butted or overlapped mating surfaces. A perimeter weld joint is formed at the mating surfaces to join the two piece assembly into a cross member.  
           [0007]    In one example of the invention, the cross member includes a shoulder area formed adjacent to the attachment point with the aperture in the rail. The shoulder is preferably rounded to provide a seating surface for the rail aperture. The rounded shoulder also provides flexibility in locating the cross member-to-rail joint to permit the vehicle frame to meet vehicle frame construction tolerances. The aperture in the rail is similarly dimensioned to permit flexible construction tolerances during vehicle frame assembly. The rail having the aperture is slidably disposed over the cross member and the weld joint is made to join the two members. In an alternate embodiment, the cross member is positioned above the rail and a similar perimeter weld joint is formed.  
           [0008]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a perspective view of a vehicle frame incorporating the overlapping joints of the present invention;  
         [0011]    [0011]FIG. 2 is a perspective view of a partial assembly having a first rail adjacent to a cross member showing the receiving aperture and shoulder of the present invention prior to joining the first rail to the cross member;  
         [0012]    [0012]FIG. 3 is the partial assembly drawing of FIG. 2 showing the first rail in its mated position with the cross member and a welded overlapping joint of the present invention;  
         [0013]    [0013]FIG. 4 is a perspective view showing an installed first rail and a second rail prior to assembly onto the cross member;  
         [0014]    [0014]FIG. 5 is an elevation view of a two-piece cross member assembly of the present invention following assembly of the two pieces;  
         [0015]    [0015]FIG. 6 is an exploded assembly drawing of the two piece cross member of the present invention prior to assembly; and  
         [0016]    [0016]FIG. 7 is a flow diagram for the steps to form and join the component parts of a vehicle structure of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    The following description is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0018]    Referring to FIG. 1, a preferred embodiment of the present invention is shown. A portion of a vehicle frame  10  includes a first rail  12  overlapped and joined to a cross member  14  at a first overlapping joint  16 . A second rail  18  is similarly overlapped and joined to the cross member  14  at a second overlapping joint  20 . Both the first rail  12  and the second rail  18  are shown as generally tubular-shaped, hydro-formed members. As commonly configured, the first rail  12  and the second rail  18  include one or more bends identified by arrows A and B, respectively. Also as commonly known, each of the first rail  12  and the second rail  18  have open ends C required for the hydro-forming process.  
         [0019]    Referring to FIG. 2, two components of the vehicle frame  10  are shown. The first rail  12  is shown prior to engagement with the cross member  14 . The first rail  12  is preferably a hydroformed single piece tube having integral side rails  22 , a pair of end plates  24 , and eased corners  26 . Each of the side rails  22 , the end plates  24  and the eased corners  26  form a contiguous perimeter for the first rail  12 . The eased corners  26  are generally formed as radii to reduce corner stresses in the rails. The first rail  12  can also be formed of two or more parts wherein any two or more of the integral side rails  22 , the end plates  24  or the eased corners  26  are individual parts requiring assembly/joining to form the first rail  12 . A first rail aperture  28  is formed in the first rail  12  by one of a plurality of known processes. These processes can include cutting, burning, stamping, etc. The first rail aperture  28  includes an outer C-shaped curve  30  and an inner C-shaped curve  32 , respectively. In the embodiment shown, the outer C-shaped curve  30  has a height D and the inner C-shaped curve  32  has a height E.  
         [0020]    The cross member  14  includes a first shoulder  34  having an upper land  36  and a lower land  38 . A second shoulder  40  is also disposed on an opposite end of the cross member  14 . The purpose of the first shoulder  34  and the second shoulder  40  are to receive each of the first rail  12  and the second rail  18 , respectively. In the embodiment shown, the upper land  36  and the lower land  38  are displaced vertically from each other. One skilled in the art will recognize that the present invention is not limited to the configuration shown for the first shoulder  34  and the second shoulder  40 . Multiple variations of the shoulders are possible to suit the required geometry of the vehicle frame  10 .  
         [0021]    In the embodiment shown, the height D of the outer C-shaped curve  30  and the height E of the inner C-shaped curve  32  are adjusted to suit the elevation of the upper land  36  and the lower land  38  respectively. An aperture width F is also shown. The aperture width F is similarly adjustable to suit a cross member width G. Both the height D and the height E for the first rail aperture  28  are also adjustable depending upon the required total standoff when the first rail  12  is connected to the cross member  14 . The first rail  12  is joined to the cross member  14  by overlapping the first rail aperture  28  over the first shoulder  34 . The first rail  12  is joined to the cross member  14  in an assembly direction H. Dimensional tolerances are allowed by the aperture width F, the height D and the height E such that the rails when joined to the cross member  14  are provided with an adjustment direction J permitting the vehicle frame  10  to meet construction tolerances.  
         [0022]    Referring to FIG. 3, the first rail  12  is shown overlapped with the cross member  14  forming the first overlapping joint  16 . A weld joint  42  is formed about a complete perimeter of the first rail aperture  28 . The weld joint  42  (only partially shown in FIG. 3) can be made using a variety of welding processes, including metal inert gas (MIG), tungsten inert gas (TIG), laser welding, stick welding, etc. The weld joint  42  permits the cross member  14  to structurally reinforce the first rail  12  for the material removed in the first rail aperture  28  (shown in FIG. 2).  
         [0023]    Referring now to FIG. 4, the second rail  18  is shown prior to assembly with the cross member  14 . The second rail  18  is formed similar to the first rail  12  and includes a second rail aperture  44 . The second rail aperture  44  includes an outer C-shaped curve  46  and an inner C-shaped curve  48  similar to curves provided for the first rail aperture  28 . The cross member  14  includes the second shoulder  40  having an upper land  50  and a lower land  52 . As previously discussed, the second rail  18  is joined to the cross member  14  in an assembly direction K. Following assembly, the second overlapping joint  20  (shown in FIG. 1) is connected by a weld joint (not shown) similar to the weld joint  42 .  
         [0024]    Referring to FIG. 5, the cross member  14  includes a cross member upper section  54  and a cross member lower section  56  connectably joined at a mating joint  58 . A weld joint  60  (shown in partial length only for clarity) connectably joins the cross member upper section  54  to the cross member lower section  56  along the mating joint  58 . Weld joint  60  can be either a continuous or a non-continuous weld joint for the full perimeter of mating joint  58 , based on the structural requirements of the final assembly.  
         [0025]    Referring to FIG. 6, the cross member  14  is shown prior to assembly of its two component parts. The cross member upper section  54  includes a perimeter wall  62  and a first mating edge  64 . The cross member lower section  56  includes a perimeter wall  66  and a second mating edge  68 . The first mating edge  64  and the second mating edge  68  are joined to form the mating joint  58  (shown in FIG. 5). The mating joint  58  can be formed by overlapping the first mating edge  64  with the second mating edge  68  or by butting these two mating edges.  
         [0026]    Both the cross member upper section  54  and the cross member lower section  56  of the cross member  14  are generally formed by drawing or stamping a metal plate. The advantage of using a single plate to form each of the cross member upper section  54  and the cross member lower section  56  is the overall reduction in parts requiring assembly to form the cross member  14 . Only a single weld joint, i.e., the weld joint  60  shown in FIG. 5, is required to form the cross member  14 .  
         [0027]    Referring to FIG. 7, the method to form an overlapping joint according to the present invention is detailed. In a step  70 , a shoulder ( 34 ,  40 ) is formed onto a cross member  14 . The shoulder ( 34 ,  40 ) can have one or more lands ( 36 ,  38 ,  50 ,  52 ). In a forming step  72 , an aperture ( 28 ,  44 ) is formed in a rail ( 12 ,  18 ). The aperture ( 28 ,  44 ) is formed based on the geometry of the shoulder ( 34 ,  40 ) such that a dimensional adjustment between the rail ( 12 ,  18 ) and the cross member  14  is possible. In a mating step  74 , the aperture ( 28 ,  44 ) of the rail ( 12 ,  18 ) is mated (e.g., overlapped) with the shoulder ( 34 ,  40 ) of the cross member  14 . In a welding step  76 , a weld joint  42  is formed about the perimeter of the aperture ( 28 ,  44 ) where the aperture ( 28 ,  44 ) mates with the shoulder ( 34 ,  40 ) of the cross member  14 , thereby joining the rail ( 12 ,  18 ) to the cross member  14 . In a parallel construction step  78 , the cross member  14  is formed by joining two pieces ( 54 ,  56 ) with a perimeter weld joint  60 . In a parallel adjustment step  80 , the rail ( 12 ,  18 ) is dimensionally-adjusted as necessary, relative to the cross member  14 , to meet a vehicle frame  10  construction tolerance.  
         [0028]    A vehicle frame  10  of the present invention offers several advantages. By forming an aperture in longitudinal rails of a vehicle frame, and overlapping the rails at the aperture to cross members of the vehicle frame, structural rigidity and strength are retained in an assembly which requires a limited number of component parts. Hydro-formed rails can be used as known in the art without the requirement for additional bracing or flanges following assembly of the rails to a cross member. By using a two-piece cross member assembly, multiple component parts previously known for cross member assemblies are reduced and the overall assembly provides structural rigidity and strength at a lower cost and with simpler assembly. The capability of adjusting the aperture size provided in the longitudinal rails provides assembly latitude such that construction tolerances for the overall vehicle frame can be met. A vehicle frame according to principles of the present invention also provides a totally welded vehicle frame assembly thereby reducing the number of component parts and eliminating the need for mechanical fasteners or additional brackets to form the frame assembly.  
         [0029]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.