Abstract:
A cross-member for a trailer frame and a frame incorporating the same. The cross-member extends between longitudinally aligned rails designed to pivotally support a dumping body thereon. The cross-member includes a cylindrical tube having a wall defining a bore therethrough. A planar member is received within the bore and is axially aligned therewith. The tube includes one or more axially aligned openings proximate a central region thereof. The planar member is disposed intermediate the openings and is aligned axially with the openings. The cross-member is substantially rigid under tension and at least a portion thereof is flexible under torsion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a standard utility application claiming priority from U.S. Provisional Application Ser. No. 60/933,455, filed Jun. 6, 2007, the entire specification of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This invention generally relates to trailers. More particularly the invention relates to cross-members of semi-trailers. Specifically, the invention relates to a cross-member for a trailer that comprises an elongate tube with a planar member extending through the bore thereof and being connected to an interior surface thereof, and where the cross-member is relatively inflexible in bending and tension, while remaining relatively flexible overall in torsion. 
   2. Background Information 
   Trailer frames usually consist of two longitudinal frame rails that are joined together by cross-members at intervals along their length. The cross-members are essential not only to hold the longitudinal rails together, but are also used at points where concentrated loads are put into the longitudinal rails, such as the regions on the frame where the kingpin, suspension and body are mounted. Trailers, particularly trailers designed to carry construction materials such as gravel, asphalt, boulders, debris, etc., may be taken over terrain that is not very smooth. When the tires on one side of the trailer are raised or lowered with respect to the other side of the trailer and to the kingpin, such as during diagonal axle-walk, a relative twist is put into the longitudinal rails. This twisting motion, or torsion, can lead to failure of the rails and/or members of the frame. 
   Generally, there are two approaches to handling twisting between the longitudinal rails. The first approach is that the frame cross-members can be made torsionally strong and rigid in order to resist sizeable twisting loads. Torsionally rigid cross-members will tend to have a solid or tubular cross-sectional shape that is generally of a circular or square configuration. One problem experienced with torsionally rigid cross-members is that the torque, carried from one side of the trailer to the other by the cross-members, also induces a stress into the rails. This stress is frequently at the same position as the maximum, or nearly maximum, bending stress. Making trailer frame cross-members strong enough and rigid enough to resist these substantial twisting loads usually requires that additional material or a different material be used to construct the cross-members. These cross-members are often manufactured to be heavier and/or stronger. Using additional or costlier materials tends to raise the overall price of the trailer, thus reducing the profit margin for the manufacturer. Also, using additional materials has the side-effect of reducing the possible legal payload that the trailer can ultimately carry because of weight restrictions. This tends to cut into the operator profits. 
   The second approach taken to handling twisting is to make the frame cross-members torsionally flexible so that they tend to flex and bend under sizeable twisting loads. Flexible cross-members typically have an open-type of cross-sectional shape, such as that of an I-beam or a member with a channel along its length. However, utilizing flexible cross-members to resist the twisting loads also has shortcomings. This is particularly true when the cross-members are used for supporting primarily vertical loads such as attaching the body to the frame. If the vertical load is supported at a lateral position, i.e., at a position other than directly over the longitudinal frame rails, then a bending moment and its consequent bending stress are induced in the cross-member at its connection zone with the longitudinal frame. In these instances, the maximum torsional stress induced by the twist between the two longitudinal frame rails will also tend to coincide with the maximum bending stress as is the case with torsionally rigid cross-members. This combination of stresses can lead to failure of the rails and cross-members of the trailer. 
   There is therefore a need in the art for an improved cross-member for use in the manufacture of trailer frames. 
   SUMMARY OF THE INVENTION 
   The device of the present invention is an improved cross-member for use in the manufacture of trailer frames, and a trailer frame incorporating the same. The cross-member extends between longitudinally aligned rails designed to pivotally support a dumping body thereon. The cross-member includes a cylindrical tube having a wall defining a bore therethrough. A planar member is received within the bore and is axially aligned therewith. The tube includes one or more axially aligned openings proximate a central region thereof. The planar member is disposed intermediate the openings and is axially aligned with the openings. The cross-member is substantially rigid under tension with a portion thereof generally flexible and a portion generally rigid under torsion. 
   Consistent with the foregoing and in accordance with the invention as embodied and broadly described herein, the device of the present invention is described with reference to longitudinal, lateral and transverse directions as indicated in the figures attached hereto. Most trailer frames consist of two main frame rails that extend substantially parallel to each other along the majority of the trailer length in a longitudinal direction. Cross-members run laterally and generally orthogonal to the frame rails. The present invention is a cross-member that at least spans the distance between two longitudinally aligned frame rails. The cross-member of the present invention may extend laterally beyond the frame rails. 
   In the present invention the planar member is similar to the web of an I-beam. The tube has portions removed to form one or more openings or windows that face substantially in the longitudinal direction and are generally parallel to the planar member within the bore of the tube. The planar member provides strength and rigidity to the cross-member and the openings in the tube wall provide torsional flexibility to the cross-member. When a trailer is loaded under different conditions, it is sometimes necessary for the cross-members to be stiff in some deflection modes and flexible in other deflection modes. The cross-member in accordance with the present invention is relatively stiff or rigid in tension in the lateral direction and in bending about a longitudinal axis. The cross-member of the present invention is torsionally rigid about an axis extending from the longitudinal frame rail partially toward the center between the longitudinal members and relatively torsionally flexible in a substantially central portion between the two longitudinal frame rails, i.e., the cross-member is torsionally rigid proximately its outer ends and torsionally flexibly proximate its middle region. Portions of the cross-members which extend laterally outwardly beyond the frame rails may be torsionally rigid or torsionally flexible. One advantage of this type of construction is that the maximum torsional stresses and maximum bending stresses occur in different areas of the cross-member. This results in a cross-member that can be lighter in weight without increasing the maximum combined stress in the cross-member. None of the prior art has this combination of flexibility and stiffness in the aforementioned deflection modes. 
   In one embodiment of the present invention, the cross-members extend through apertures in the trailer&#39;s frame rails, and the protruding ends of the cross-members may be coupled with the dumping body. Thus larger bending and torsional loads may be applied to the cross-member of the present invention with the same resulting combined stress than was possible in cross-members of the prior art. Applying these loads to a cross-member in accordance with the present invention, will cause the distribution of the load and reduce the stresses in the frame rails and in the cross-members. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which: 
       FIG. 1  is an isometric view a trailer having a side dumping body where the trailer incorporates a flexible cross-member in accordance with the present invention; 
       FIG. 2  is an isometric view of the trailer cross-member in accordance with the present invention; 
       FIG. 3  is an isometric view of a portion of a trailer frame comprising a pair of frame rails and a cross-member extending therebetween; 
       FIG. 4A  is a perspective view of a portion of a prior art cross-member and frame rail, wherein the cross-member is a thin-walled cylindrical tube, and illustrating the degree to which this type of cross-member is stressed when the trailer frame is subjected to a twisting load, such as having the wheels on one side of the trailer being lifted; 
       FIG. 4B  is a perspective view of a portion of the cross-member and frame rail of  FIG. 4A  illustrating the degree of stress in the cross-member and frame rail when a load is dumped from a load body supported by the trailer frame; 
       FIG. 5A  is a perspective view of a portion of another prior art cross-member and frame rail, wherein the cross-member is a thick-walled cylindrical tube, and illustrating the degree to which this type of cross-member is stressed when the trailer frame is subjected to a twisting load; 
       FIG. 5B  is a perspective view of the prior art cross-member and frame rail of  FIG. 5A  illustrating the degree of stress in the cross-member and frame rail when a load is dumped from a load body supported by the trailer frame; 
       FIG. 6A  is a perspective view of a portion of yet another prior art cross-member and frame rail, where the cross-member is an I-beam, and illustrating the degree to which this type of cross-member is stressed when the trailer frame is subjected to a twisting load; 
       FIG. 6B  is a perspective view of the prior art cross-member and frame rail of  FIG. 6A  illustrating the degree of stress in the cross-member and frame rail when a load is dumped from a load body supported by the trailer frame; 
       FIG. 7A  is a perspective view of a portion of the cross-member and frame rail in accordance with the present invention and illustrating the degree to which this type of cross-member is stressed when the trailer frame is subjected to a twisting load; and 
       FIG. 7B  is a perspective view of the cross-member and frame rail of  FIG. 7A  illustrating the degree of stress in the cross-member and frame rail when a load is dumped from a load body supported by the trailer frame. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   It will be readily understood that the components of the instant invention, as generally described and illustrated in  FIGS. 1 ,  2 ,  3 ,  7 A and  7 B herein, could be arranged and designed in a wide variety of different configurations. But, the following more detailed description of the invention, as represented in these aforementioned figures is not intended to limit the scope of the invention as claimed, but is merely representative of possible embodiments of the invention. The prior art is shown in  FIGS. 4A-6B . 
   Referring to  FIG. 1 , there is shown a trailer  8  that includes a dumping body  10  pivotally mounted on a trailer frame  12 . Trailer frame  12  comprises a pair of spaced apart frame rails  14 ,  16 . Frame rails  14 ,  16  are connected to each other by way of one or more cross-members  18  in accordance with the present invention. 
   A reference axis is shown in  FIGS. 1 and 2  and is herein defined in order to aid in describing the present invention. A lateral direction is indicated by arrow  11   a , a longitudinal direction is indicated by arrow  11   b  and a transverse direction is indicated by arrow  11   c . A lateral axis of cross-member  18  is aligned along lateral direction  11   a . A longitudinal axis of trailer  8  and frame rails  14 ,  16  is aligned along longitudinal direction  11   b , and a transverse axis, which is mutually orthogonal with the longitudinal and lateral axes  11   b ,  11   a , is aligned along transverse direction  11   c . The lateral, longitudinal, and transverse axes and directions will be represented hereinafter in this description as  11   a ,  11   b , and  11   c  respectively. 
     FIGS. 2 and 3  show a cross-member  18  in accordance with the present invention. Cross-member  18  comprises a generally cylindrical tube  20  and a planar member  22 . Tube  20  has a peripheral wall  24  that is of a circular cross-sectional shape. Wall  24  has a first end  24   a  and a second end  24   b  and is of a length “L”. Wall  24  defines a bore  26  therethrough that is of a diameter “D”. Bore  26  extends from first end  24   a  through to second end  24   b . Tube  20  extends laterally between frame rails  14  and  16  and has a lateral axis  11   a  that extends between first and second ends  24   a ,  24   b.    
   In accordance with a specific feature of the present invention, at least one, and preferably two windows or openings  28  are defined in wall  24 . Windows  28  extend laterally along wall  24  and have an origin region at  28   a  and a termination region at  28   b . Windows  28  are generally parallel to lateral axis  11   a  of tube  20 . Origin and termination regions  28   a ,  28   b  are spaced a distance inwardly from first and second ends  24   a ,  24   b  respectively. As shown in  FIG. 3 , when cross-member  18  is secured to rails  14 ,  16 , the two windows  28  are situated intermediate rails  14 ,  16  with the origin and termination regions  28   a ,  28   b  thereof being spaced a distance inwardly of rails  14 ,  16 .  FIG. 2  shows wall  24  defining two windows  28  therein that are spaced circumferentially equidistant from each other in wall  24 . The origin regions  28   a  of the two windows  28  and the termination regions  28   b  thereof are substantially aligned with each other in the longitudinal direction  11   b . Each window  28  opens toward one of the front end  10   a  and back end  10   b  of trailer  10  as shown in  FIG. 1 . Windows  28  are provided to reduce the overall weight of cross-member  18  and give cross-member  18  a greater torsional flexibility than would be the case if peripheral wall  24  was substantially solid. Windows  28  significantly reduce the torsional stiffness about lateral axis  11   a  in a middle portion A ( FIG. 3 ) of tube  20 . Windows  28  do not reduce the torsional stiffness at the ends  24   a ,  24   b  of tube  20 . Windows  28  also allow access for planar member  22  to be welded to tube  20 . 
   In accordance with yet another specific feature of the present invention, planar member  22  is received within bore  26  of cross-member  18 . Planar member  22  has a first end  22   a , a second end  22   b  and lateral edges  22   c ,  22   d . A web  30  extends between lateral edges  22   c ,  22   d . Web  30  has a length that preferably is substantially equal to length “L” of tube  20 . Web  30  further has a height extending between lateral edges  22   c  and  22   d  that is substantially equivalent to diameter D of tube  20 . Web  30  is thus tightly received within bore  26 . Web  30  effectively divides tube  20  into two substantially semicircular chambers  32 ,  34  ( FIG. 2 ). Preferably, first end  22   a  of planar member  22  is substantially coplanar with first end  24   a  of tube  20  and second end  22   b  of planar member  22  is substantially coplanar with second end  24   b  of tube  20 . Web  30  of planar member  22  preferably extends in a transverse direction  11   c . Furthermore, web  30  and windows  28  are generally parallel to each other and to lateral axis  11   a . Windows  28  allow access for planar member  22  to be welded to the inner surface of tube  20 . Planar member  22  adds significant stiffness in the lateral direction  11   a  and significant bending stiffness about longitudinal axis  11   b . However, planar member  22  adds relatively little torsional stiffness about lateral axis  11   a  and relatively little bending stiffness about transverse axis  11   c.    
   Cross-member  18  spans the distance “W” between frame rails  14 ,  16 . Frame rails  14 ,  16  preferably each include a web  38  ( FIG. 3 ) that defines an aperture  40  therein. Apertures  40  are laterally aligned with each other. Apertures  40  are complementary sized and shaped to receive an end  24   a ,  24   b  of cross-member  18  therein. A portion of tube  20  may extend laterally outwardly beyond web  38  of rails  14 ,  16 . This portion is indicated at  44  ( FIG. 1 ). A mounting apparatus  46  for dumping body  10  attaches to portion  44  of cross-member  18 . Because windows  28  are intermediate frame rails  14 ,  16 , portions  44  of cross-members  18  are relatively strong and stiff on the outside of frame rails  14 ,  16 . This strength is necessary to handle the loads on the mounting apparatus  46  due to the mass of dumping body  10  and the mass of the cargo (not shown) to be carried therein. 
   The advantages of the present invention are readily apparent when the stresses in the prior art are compared to the stresses in the present invention.  FIGS. 4A-6B  illustrate the possible stresses in the cross-members  80  and frame rails  82  disclosed in the prior art while  FIGS. 7A-7B  illustrate the possible stresses in cross-members  18  and frame rails  14 ,  16  of the present invention. The stresses experienced in any of these systems may be calculated using Finite Element Analysis or FEA. For the purposes of illustration only, three prior art cross-members are shown, namely, a thin-walled tube  80  having a circular cross-sectional shape extending from a frame rail  82  ( FIGS. 4A ,  4 B), a thick-walled tube  180  having a circular cross-sectional shape in a frame rail  182  ( FIGS. 5B ,  5 B), and an I-beam  280  in a frame rail  282  ( FIG. 6A ,  6 B). An example of the possible stresses experienced in these systems is shown by the degree of hatching surrounding the connection zones between the end of the cross-member  80 ,  180  and  280  and frame rails  82 ,  182  and  282 . The greater the illustrated stress level, the closer the hatching on the illustration.  FIGS. 4A ,  5 B,  6 A show the stresses in the prior art cross-members  80 ,  180  and  280  when a twisting load is applied to the frame  82 ,  182 ,  282  by having the wheels on one side of the trailer lifted off the ground.  FIGS. 4B ,  5 B and  6 B show the stresses in the prior art cross-members  80 ,  180 ,  280  and frame rails  82 ,  182 ,  282  when the load carried in the dumping body on the trailer is being dumped. These possible illustrated stresses in prior art devices can be compared with the illustration of possible stresses that may be experienced in the cross-member  18  and frame rail  14  of the present invention.  FIG. 7A  shows the possible stresses in cross-member  18  of the present invention when a twisting load is applied to the trailer frame by having the wheels on one side of the trailer lifted off the ground.  FIG. 7B  shows the possible stresses in the region of the weld, or connection zone  60 , of cross-member  18  and rail  14  when the load (not shown) carried in the dumping body is being dumped. 
   The stresses illustrated in all of these figures show a critical level indicated by the closest hatching in the figure. In  FIG. 4A , for example, based on the illustrated stress levels, the structure is most likely to fail at the welds  84 . The stresses near the weld  84  in the thin round cross-member  80  are used as a baseline for this comparison. 
   As shown in  FIG. 5B , using the thick-walled tube  180  tends to lower the stresses near the weld  184  under dumping loads, but has very little effect on the maximum stress near the weld  184  under twisting loads shown in  FIG. 5A . 
   As shown in  FIGS. 6A ,  6 B, using an I-beam for the cross-member  280  tends to lower the stresses under dumping loads ( FIG. 6B ), but increases the stresses under twisting loads ( FIG. 6A ). 
   As shown in  FIGS. 7A ,  7 B, using the cross-member  18  of the present invention tends to lower the stresses near the weld  60  to beneath the reference level for both loading conditions as selected previously in reference to  FIG. 4A . 
   The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respect only as illustrative and not restrictive. The scope of the invention, therefore, is indicated by the appended claims. All changes within the meaning and range of equivalency of the claims are to be embraced within their scope. 
   In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. 
   Moreover, the description and illustration of the invention are an example and the invention is not limited to the exact details shown or described.