Abstract:
A method of manufacturing an improved doorbeam having increased impact strength and reduced weight. The doorbeam is formed from a continuous metal web having opposing lateral edges and a varying thickness therebetween. The stock is rolled into a tubular configuration, and the lateral edges are welded together. The resultant beam provides extra reinforcing material where needed to provide a balance between weight and strength.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to vehicle doorbeams. 
     II. Description of the Art 
     Vehicle doorbeams are widely used in the automotive industry to enhance the impact strength of vehicle doors and thereby enhance safety. Vehicle manufacturers desire to make vehicles safer for passengers and to improve fuel efficiency. Therefore, doorbeams must strike a balance between strength to resist impacts and reduced weight to increase fuel efficiency. 
     One method to increase the strength of the beam is to increase the thickness of the material from which the beam is fabricated. This improves passenger safety but also increases the weight of the beam, thereby decreasing fuel efficiency. 
     Another technique for increasing beam strength is to add extra reinforcing pieces of metal to the doorbeam as illustrated in U.S. Pat. No. 5,277,469 issued Jan. 11, 1994 to Klippel. These reinforcements add weight to the beam. The reinforcements also increase the complexity, cost, and required labor to fabricate the beam. 
     Another technique for increasing beam strength is to make the doorbeam out of lightweight, high-strength alloys. While the alloys are relatively lightweight, they are expensive to manufacture. Another technique for increasing beam strength is to fabricate the entire beam of a lightweight material, such as aluminum, with a relatively thick cross section and wall thickness. This approach eliminates most of the weight savings. These beams are also difficult and expensive to manufacture, difficult to adapt between different doors, and hard to fit within narrow profile doors. 
     Other methods include fabricating the doorbeam with special geometric cross sections such as trapezoids and ellipses as seen in U.S. Pat. No. 6,020,039 issued Feb. 1, 2000, to Cline et al. Other beams are filled with a composite material in an attempt to improve impact strength. All these beams are difficult, expensive and time consuming to manufacture. They are also difficult to adapt among various doors on different makes and models of vehicles. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome in the present application wherein a one-piece doorbeam is rollformed from a continuous web of stock having a varying thickness profile across its lateral extent. More specifically, a web has stock at least two different thicknesses across its width; and the web is rolled into a tubular shape and welded along the resulting seam. 
     The present invention has a variety of advantages over prior techniques. First, the beam provides thicker walls where needed to increase passenger safety and thinner walls elsewhere to save weight. Second, the complete beam may be fabricated as a single piece without additional pieces, expensive alloys, composite fillers or unusual cross sections. Consequently, the beam is relatively labor-efficient and inexpensive, while providing the necessary strength and desired weight. The beam is also easily adaptable between vehicles by changing the overall length of the resultant rollformed segments. 
     These and other objects, advantages and features of the invention will be more fully understood and appreciated by reference to the detailed description of the preferred embodiments and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view, partially broken away, of the doorbeam mounted within a door; 
     FIG. 2 is a perspective view of the web stock used in fabricating the doorbeam; 
     FIG. 3 is a sectional view of a doorbeam formed from the web stock in FIG. 2; 
     FIG. 4 is a perspective view of an alternative web stock used in fabricating an alternative doorbeam; 
     FIG. 5 is a sectional view of the alternative doorbeam formed from the web stock in FIG. 4; 
     FIG. 6 is a perspective view of a second alternative web stock used in fabricating a second alternative doorbeam; 
     FIG. 7 is a sectional view of the second alternative doorbeam formed from the metal stock in FIG. 6; 
     FIG. 8 is a perspective view of a third alternative web stock used in fabricating a third alternative doorbeam; 
     FIG. 9 is an end view of the third alternative doorbeam formed from the metal stock in FIG. 8; 
     FIG. 10 is a perspective view of a fourth alternative web stock used in fabricating a fourth alternative doorbeam; and 
     FIG. 11 is a longitudinal sectional view of a tubular beam formed from the web stock in FIG.  10 . 
    
    
     DETAILED DESCRIPTION 
     By way of disclosure, and not by way of limitation, a tubular doorbeam constructed in accordance with a preferred embodiment of this invention is illustrated in FIGS. 1-3 and generally designated  10 . 
     I. Construction of Doorbeam 
     The doorbeam  10  is formed from a web stock  40  and generally includes a center section  20  and end portions  30 . The center section  20  interconnects the end portions  30 , which secure the doorbeam  10  in a door  100 , as shown in FIG.  1 . 
     The web stock  40  includes opposing lateral edges  50 , as illustrated in FIGS. 2 and 4. In the preferred embodiment, the web stock  40  is formed from a martinsitic steel (i.e. Martinsite) such as Inland M220 ultra high strength low alloy steel. Of course, other materials that have the suitable properties for the performance requirements of a doorbeam may be used. The edges  50  are generally linear and uniformly spaced from one another, allowing the web stock  40  to have a uniform width. The web stock  40  may include a varying thickness profile, but will be described in relation to the preferred embodiment with the web stock  40  having a first and second thicknesses  42  and  44 , although in some embodiments, more than two thicknesses may be used (not illustrated). The location of the first and second thicknesses  42  and  44  may vary, but in the preferred embodiment, the second thickness  44  is approximately centered between the edges  50  as illustrated in FIG.  2 . The thickness profile between the first and second thickness  42  and  44  may change abruptly or gradually. The type of change may depend on the location of the first and second thickness  42  and  44 . The type of change also may be chosen to ensure that the beam is no thicker at any given point than required, thereby allowing for the optimal balance of weight and impact strength. 
     The web stock  40  is rolled into a tubular shape, and formed into a doorbeam  10 . A cross section of the tubular shape generally includes a varying thickness circumferential profile, relatively proportional to the varying thickness profile of the web stock  40 , rolled into the tubular shape. 
     The web stock  40  is generally rolled into a continuous tubular shape that is then formed into the doorbeam  10 . The beam  10  generally includes a center section  20  and end portions  30 . In some embodiments, the beam  10  may be formed without the end portions. 
     The formed center section  20  includes a first thickness  22 , the second thickness  24 , and a seam  26 . The first thickness  22  and second thickness  24  are the first thickness  42  and second thickness  44  of the web stock  40  rolled into the tubular shape. The first thickness  22  and second thickness  24  are illustrated in FIGS. 3 and 5 as being located approximately opposite on the doorbeam  10 , but may be located almost anywhere on the beam, with varying thickness. The location of the thicknesses depends on the location of the thicknesses on the web stock  40 . Of course any third thickness and/or an additional second thickness on the web stock will show up proportionately on the beam  10 . 
     The seam  26  may be located anywhere on the beam  10  but for ease of manufacture is preferably located as shown in FIGS. 3 and 5, approximately in the middle of the first or second thickness  22  and  24 . In the preferred embodiment, the seam  26  is a weld sean. 
     The end portions  30  are usually brackets formed from the ends of the center section  20 . The end portions  30  are generally well known in the art and may be formed to any shape or size to attach to a variety of doors  100 . The beam  100  may also be formed without end brackets (not illustrated), for example, as an elongate center section  20  that is attached to a door by clamp, fastener, weld, or other means. For ease of manufacture, the end portions  30  may also include the varying thickness. The thickness variations may also increase the strength of the end brackets  30  while saving weight. 
     II. Method of Manufacture 
     The doorbeam  10  starts out as a web stock  40  that includes a first and second thickness  42  and  44  as may be seen in FIGS. 2 and 4. In the preferred embodiment, the first and second thicknesses  42  and  44  are formed while the web stock  40  is formed. Of course, the first and second thickness  42  and  44  may be formed at any other time before the web stock  40  is enclosed upon itself into the tubular shape. The first and second thickness  42  and  44  may be formed by rolling, stamping, or any other process. In the preferred embodiment, the web stock  40  is formed from continuous web stock  40  into a continuous beam, cut to length, and formed into individual doorbeams  10 . A continuous web stock  40  may also be formed into individual metal blanks (not shown) and then formed into the doorbeam  10  or the web stock may be made as individual metal blanks that are formed into the doorbeam  10 . 
     The beam  10  is then welded along the seam  26 . The preferred welder is a laser welder to obtain high weld quality, but any other suitable welding technique may be used. Either before or after the beam is welded, the end brackets  30  are formed. The method of forming end brackets is well known in the art. The end brackets  30  may also be attached by welding, fasteners, or any other means. 
     III. Alternative Embodiments 
     FIGS. 4 and 5 show a first alternative embodiment of the web stock  40 , and a sectional view of the doorbeam  10 . In this alternative embodiment, the web stock  40  is formed having a greater thickness near the lateral edges  50 , than the center. Therefore, the seam  26  is along the area of greater thickness. 
     FIGS. 6 and 7 show a second alternative embodiment of the doorbeam  10 . In this alternative embodiment, the web stock  40  includes a base stock  48  with at least one metal strip  46  attached approximately in the center of the base stock  48 . The base stock  48  forms the first thickness  42 . The combination of the metal strip  46  and the base stock  48  form the second thickness  44 . In the preferred embodiment, the metal strip  46  is attached to the base stock  48  by welding. The methods of welding may include, laser, resistance, electron beam, or any other suitable welding means to attach the metal strip or strips  46  to the base stock  48 . Additional spot welds  54  may be added to further secure the metal strips  46 , as may be seen in FIGS. 6 and 8. 
     FIGS. 8 and 9 show a third alternative embodiment of the doorbeam  10 . The third alternative embodiment is similar to the second alternative embodiment, except that the metal strips  46  are located near each of the lateral edges  50 . Of course, it should be apparent that the metal strips  46  may be located anywhere on the base stock  48 . The actual placement of the metal strips  46  is not critical, so long as when the beam  10  is added to the door  100 , the areas needing extra thickness are somewhat positioned to provide maximum strength against impacts. This positioning may also be set when the end brackets  30  are formed, or when the beam is installed into the door  100 . 
     FIGS. 10 and 11 show a fourth alternative embodiment of the doorbeam  10 . In the fourth alternative embodiment a doorbeam  10  is formed with a high strength center portion  20  and lightweight end portions  30 , as seen in FIG.  11 . The web stock  40  is formed as discussed above with the preferred embodiment. One difference is that the web stock  40  in the fourth alternative embodiment has a much greater distance between the opposing lateral edges than in the preferred embodiment. The web stock  40  is cut into metal blanks  52 , approximately perpendicular to the opposing lateral edges  50 . The width of a metal blank  52  is approximately the circumference of the center section  20  of the doorbeam  10 . The length of the doorbeam  10  is approximately the width between the lateral edges  50  of the web stock  40 . The web stock  40  is rolled into a doorbeam as shown in FIG.  11 . 
     Variations of the fourth alternative embodiment should be readily apparent. For example, varying the proportions of the first and second thicknesses  42  and  44  on the web stock  40  may easily change the proportions of the center section  20  and end brackets  30 . Also, if the web stock  40  is formed as in the second alternative embodiment, with the second thickness  44  located near the edges  50  and the first thickness  42  located near the center, the beam  10  may be formed with a lightweight center portion  30  and high strength end portions  30 . 
     The present invention can be used to create a wide and indeed limitless variety of light-weight, yet high-strength tubular doorbeams  10 , reinforced only as needed for a balance of strength and weight. The present invention results in an improved doorbeam  10  that is manufactured at a lower cost with increased impact strength and decreased weight. 
     The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents.