Patent Publication Number: US-2006016149-A1

Title: Frame structure for motor vehicle superstructures

Description:
This application claims the priority of German application 10 2004 036 071.5, filed Jul. 24, 2004, the disclosure of which is expressly incorporated by reference herein.  
     BACKGROUND AND SUMMARY OF THE INVENTION  
      The present invention relates to a frame structure for a motor vehicle superstructure including first and second beams which are conjoined to form a “T” and a joint present between the beams, and in which the first beam and the second beam are made of tubes with elliptical cross sections having secondary axes which run parallel to one another,  
      A frame structure of the type mentioned above, known from European document EP 0631 924 A1, includes two extruded beams which are conjoined to form a “T.” The beams are realized as hollow tubes. A type of joint is crafted on one of the two beams, and a free end of the joint exhibits retainers for the other beam. The latter beam receives the free end of the joint.  
      German document DE 195 19 779 A1 relates to a side portion of the frame of a passenger car chassis, which comprises two openings for doors bordered by a vertical beam. Running between the upper side rail and the lower side rail is a median column, which is connected to the side rail through a joint of the type described above.  
      One object of this invention is to develop a frame structure for a motor vehicle superstructure in which the beams conjoined to form a “T” and a connecting joint are designed to give the frame structure optimal weight and stiffness.  
      According to the invention, this object can be achieved by having the joint realized as a cross section expansion emanating from the first beam, while the joint, when viewed lengthwise along the second beam, has a defined length from an outermost edge of the first beam spanning toward the second beam. Further features and embodiments are defined by the claims.  
      Advantages obtained primarily through the invention include optimal weight and stiffness resulting from elliptical cross sections of the first and second beams as well as superior placement of the joint in relation to those of similarly designed frame structures. The joint length is a critical characteristic, and is based on the claimed equation: 
 
 L =(1.50 to 1.70)× {overscore (AC)} 
 
 Correspondingly, the same is true for AC, which is defined by the following equation:  
         AC   _     =       B   ⁢           ⁢   %     2         
 
      The lateral edge of the joint is a concave continuous line, which contributes to tension reduction. The general shape of the joint can be observed in the way it opens tangentially into the second beam and forms a sharp angle where it intersects the first beam at its section of maximum diameter. Finally, it is advantageous if the cross section expansion is shaped through internal high pressure forming and if the cross section expansion and the joint are bulged from the same piece as the second beam.  
      An embodiment of the invention is shown in the drawings and is described in further detail below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an oblique schematic view of a frame structure according to the invention, and  
       FIG. 2  shows various frame structures so as to provide a weight comparison.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A frame structure  1  is designed for the superstructure of a motor vehicle (both of which are not illustrated), namely the base, side wall, etc., of the superstructure. The frame structure  1  includes two beams, namely a first beam  2  and a second beam  3 , which conjoin to form a “T.” The beams  2  and  3  are attached to one another through the interposition of a joint  4  and are constructed of tubes made from extruded steel, light metal, etc. The tubes also exhibit an elliptical cross section with main axes HaI and HaII and secondary axes NaI and NaII, maximum diameters DmgI and DmgII, and minimum diameters DmkI and DmkII. The secondary axes NaI and NaII—as well as the main axes HaI and Hall—of the first and second beams  2  and  3  run parallel to one another.  
      The joint  4  is shown as an internal high pressure formed cross section expansion of the second beam  3  and is bulged from the same piece as the second beam  3 . The joint  4  is symmetrically bisected by a median plane MII running through the second beam  3 , which runs vertically to a median plane MI of the first beam  2 . The median planes MII and MI can also intersect one another at angles between 45° and 90°. A length L of the joint  4 , which begins at an edge Bae of the first beam  2  and runs parallel to the median plane MII of the second beam  3 , is defined by the following equation: 
 
 L =(1.50 to 1.70)× {overscore (AC)} 
 
      The optimal value for this equation is used below. 
 
 L =(1.61)× {overscore (AC)} 
 
 In this equation, AC is the length running from the outer origin A of the joint  4  to the location C where the joint meets the maximum diameter DMgII of the second beam  3 . 
 
      The length of AC is defined by the following equation:  
         AC   _     =         B   ⁢           ⁢   %     -   B     2         
 
 In this equation, B % is equal to the maximum expansion, and B is equal to the maximum diameter DmgII, of the second beam  3 . 
 
      A lateral edge Bs of the joint is realized as a concave continuous line  6 , which opens tangentially into the second beam  3  and forms a sharp angle α with an edge BDmgI of the first beam  2 . This angle a is preferably between 30° and 42°. Furthermore, the joint  4  of the second beam  3  has a connecting curve  7  turned toward the first beam  2 , which overlaps certain portions of the first beam  2 . A joint  4  is connected to the first beam  2  along the connecting curve  7  through welding, adhesives, etc.  
      In addition to the frame structure having the first beam  2  and the second beam  3  conjoined at a joint  4 , different frame structures  8  and  9  are shown in  FIG. 2 . The frame structure  8  consists of a first beam  10  and a second beam  11 . The frame structure  9  consists of a first beam  12  and a second beam  13  as well. The second beams  11  and  13  found in frame structures  7  and  8  are joined, without the interposition of a joint, to respective first beams  10  and  12 . The beams found in frame structure  1  are approximately the same dimensions of those in frame structures  8  and  9 . With square tubing, the frame structure  9  is approximately 36% heavier than frame structure  8 , which is made of elliptical tubing. Frame structure  8  in turn is 13% heavier than frame structure  1 . Owing to the specifics of its design, the stiffness of frame structure  1  is higher than those of frame structures  7  and  8 .  
      The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.