Abstract:
An axle assembly of this invention includes an axle beam having a top section, a bottom section and two side sections. The top and bottom sections are of a first thickness that is greater than the thickness of material comprising the two side sections. The thicknesses of each of the sections are tailored to carry expected loads. The top and bottom sections are the primary load bearing sections for loads exerted on the axle. Therefore, the top and bottom sections are of increased thickness and the side sections that encounter a reduced load are of a reduced thickness, providing a more efficient use of material.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to a vehicle axle beam, and specifically to a method of fabricating a vehicle axle beam with a varying wall thickness. 
   Conventional solid axle beams have been used for vehicle axles. The solid axle beam provides a rigid, durable structure capable of withstanding the bending and torsional loads typically encountered. The bending and torsional loads on an axle beam are not uniform. Some segments of the axle beam experience less loading then other segments and may not require the same structure. A solid axle beam is relatively heavy and adds considerable weight to a vehicle. 
   Conventional hollow axle beams reduce weight while still providing the structure to bear the bending and torsional loads encountered by a vehicle axle. Typically, a hollow axle beam is formed from a round or square tube section. Round or square tube sections are typically formed from a single sheet of material rolled or folded to abut along longitudinal segments. The seam formed by the abutted longitudinal segments is then welded. A square tubular section provides favorable bending loading performance. Bending loads are primarily carried across two sides of the square beam. The two loaded sides are required to be of a minimum thickness. Disadvantageously, non-loaded sides of the square tube are of the same minimum thickness required of the loaded sides. 
   Accordingly, it is desirable to design an axle and method of fabricating an axle having a wall thickness tailored to the expected load. 
   SUMMARY OF THE INVENTION 
   The present invention is an axle beam and method of fabricating an axle beam that includes a tailored wall thickness in cross-section to accommodate bending loads. 
   The axle beam assembly of this invention includes a square tube having a top section, a bottom section and two side sections. The top and bottom sections are of a first thickness that is greater than the thickness of material of the side sections. The top and bottom sections are the primary load bearing sections for loads exerted on the axle. Therefore, the top and bottom sections are of increased thickness and the side sections that encounter a reduced load are of a reduced thickness. This provides a more efficient use of material. 
   Accordingly, the axle and method of fabricating an axle of this invention provides a wall thickness tailored to expected loads. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
       FIG. 1  is a plan view of an axle according to this invention; 
       FIG. 2  is a tubular section according to this invention; 
       FIG. 3  is a schematic view of a stepped plate prior to fabrication of the tubular section; 
       FIG. 4  is another tubular section according to this invention; 
       FIG. 5  is a stepped plate for fabricating the tubular section shown in  FIG. 4 ; and 
       FIG. 6  is a schematic representation of the method of fabricating a tubular section for an axle beam. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , an axle assembly  10  includes a hollow axle beam  12  and king pin bosses  14  for mounting of a vehicle wheel. The hollow axle beam  12  is formed from a single sheet of material folded to form a closed shape. The axle beam  12  includes a cross-section composed of walls of thicknesses tailored to support differing loads across different sections. The axle assembly  10  illustrated in  FIG. 1  is a drop axle and is only one of many possible configurations that would benefit from this invention. 
   Referring to  FIG. 2 , the variable thickness of the axle beam  12  formed by this method allocates material according to application loading requirements. Square hollow members are preferred for support of bending loads on the axle beam  12 . These bending loads (schematically shown by arrows  13  in  FIG. 1 ) are greater on top and bottom sections  16 ,  18  of the beam  12  than on first and second side sections  22 ,  24 . The top and bottom sections  16 ,  18  include an increased thickness compared to the first and second side sections  22 ,  24  that do not support a significant portion of the bending loads. 
   The axle beam  12  is shown in cross-section with each section having a tailored thickness. Preferably, the cross-section is constant along the entire length of the axle beam  12 . The top and bottom sections  16 , 18  include a first thickness  20 . The first thickness  20  provides sufficient material to support loads applied on the axle beam  12 . The first and second side sections  22 , 24  are of a second thickness  26 , thinner than the first thickness  20 . The thickness of material of the top and bottom sections  16 , 18  relative to the thickness  26  at the first and second side sections  22 , 24  is application dependent. A worker skilled in the art with the benefit of this disclosure would understand the specific dimensions required to support the applicable loads for any specific axle beam  12 . Further, it should be understood that a tubular axle member having differing number of sides will likely benefit from this invention. 
   The axle beam  12  is preferably formed by folding a single sheet of material onto itself to form a closed shape. A seam  28  is welded to secure abutted ends of the sheet of material together. The terms, top, bottom and sides are used for explanation purposes relative to normal vehicle orientation. In practice, the specific position of the thicker and thinner faces of the axle beam  12  would correspond to application specific loading requirements. 
   Referring to  FIG. 3 , the axle beam  12  is formed with a stepped plate  30 . The stepped plate  30  includes five segments  32 , 34 , 36 , 37 , and  38  orientated to form an enclosed shape. The first and fifth segments  32 , 38  are of the first thickness  20  and form the top section  16  of the axle beam  12 . The second and fourth segments  34  and  37  include the thickness  26 , and form the first and second side sections  22 , 24 . The third segment  36  is of the first thickness  20  and forms the bottom section  18 . The first and fifth segments  32 ,  38  are folded to abut longitudinally and form the seam  28  along the top section  16  of the axle beam  12 . A weld  29  along the seam  28  of the first and fourth segments  32 ,  34  forms the closed square shaped axle beam  12 . 
   Preferably, the seam  28  is welded such that the abutted first and fifth segments  32 ,  38  are permanently attached to each other to form the rigid axle beam  12 . A worker skilled in the art with the benefit of this invention would understand that any welding method or location can be used to permanently attach ends of the plate that form the seam  28   
   Referring to  FIG. 4 , another axle beam  12 ′ according to this invention includes the seam  28  disposed on one of the first and second side sections  22 ,  24 . The top and bottom sections  16 , 18  remain composed of the first thickness  20  that is greater than the second thickness  26  of the first and second side sections  22 , 24 . Because the seam  28  is disposed within one of the first and second side sections  22 ,  24  another stepped plate configuration is used. Placing the seam  28  on one of the first and second side sections  22 , 24 , removes the weld  29  from the load bearing top and bottom sections  16 ,  18 . In some axle beam applications, it may be advantageous to eliminate the seam  28  from the load carrying sections. 
   Referring to  FIG. 5 , a stepped plate  40  used to fabricate the axle beam  12 ′ with the seam  28  on one of the first and second side sections  22 ,  24 . The stepped plate includes five segments  42 , 44 , 46 , 48 , and  50 . The second and fourth segments  44 ,  48  include the first thickness  20  to form the top and bottom sections  16 , 18  of the axle beam  12 ′. First, third and fifth segments  42 ,  46 ,  50  are of the thickness  26  that will form the first and second side sections  22 ,  24 . The plate  40  is folded onto itself to abut the first and fifth segments  42 , 50  and form the seam  28 . The seam  28  is subsequently welded to form the closed shape. Preferably, the seam  28  is welded such that the abutted first and fifth segments  42 ,  50  are permanently attached to each other to form the rigid axle beam  12 . 
   Referring to  FIG. 6 , a method for fabricating an axle beam  12  having a tailored thickness about the cross-section is illustrated. The initial step indicated at  60  includes a plate  59  having a thickness  62 . The thickness  62  is uniform throughout the plate  59 . Preferably, the thickness  62  across the entire plate  59  is of the final thickness dimension required for the top and bottom sections  16 , 18  of the completed axle beam  12 . A process indicated at  64  deforms the plate  59  such that stepped segments  65  are formed having tailored thicknesses. The process indicated at  64  can be a stamping or rolling process to shape the cross-section of the plate  60 . Further, the method of this invention may begin with a plate formed as indicated at  64  complete with the desired variations in thickness. 
   The plate  59  with the variable thickness cross-section is then folded longitudinally as indicated at  70 . Segments  66  and  68  are abutted against each other to form the closed structure of the axle beam  12 . The axle beam  12  includes the thicker sections of the first thickness  20  across the top and bottom sections  16 , 18  and the thinner walls of the second thickness  26  across the first and second side sections  22 , 24 . The abutted segments  66 , 68  form the top section  16 . The seam  28  created between the abutted segments  66 , 68  is then welded as indicated at step  72 . Once the tubular member is completed and the seam  28  welded, kingpin bosses  14  or other desired end assemblies are attached as indicated at  74 . 
   The axle beam  12  of this invention includes a cross-section composed of walls of thicknesses tailored to support differing loads across different sections. The load specific allocation of material reduces overall axle assembly weight while supporting expected loads. The tailored wall thickness of this invention may be applied to axle beams of differing geometries according to application specific requirements. 
   The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.