Abstract:
A fabricated drop axle is described. A pair of axle stub ends is oppositely retained within a saddle having a recess through which accessories can pass.

Description:
TECHNICAL FIELD 
     The following relates generally to a drop axle for a vehicle and more specifically to a fabricated drop axle for a commercial vehicle and a method of manufacturing a fabricated drop axle for a commercial vehicle. 
     BACKGROUND 
     There exist several drop axles in the commercial vehicle freight industry. Drop axles support wheels at either end and provide clearance between the wheels for various components, such as drive shafts and discharge tubes on commercial vehicles. 
     Previous drop axle assemblies typically comprised formed tubes and a pair of spindles for holding wheels. The spindles were mounted to opposite ends of the tube, and the tube had formed therebetween a generally U-shaped indent to provide clearance for various components. It is desired that the spindles are coaxially aligned with each other; however, such formed-tube drop axles frequently result in misalignment between the spindles. Spindle misalignment causes accelerated tire wear and increased stresses at the intersections between axles and vehicle suspensions. One solution is to correct any misalignment by straightening the ends of the tubes after initial forming. This increases the cost to manufacture the tubes. 
     In an attempt to mitigate some of the disadvantages of formed-tube drop axles, manufacturers hot-form the tubes. Hot-formed tubes, however, require post-forming quenching and tempering to restore mechanical properties lost during hot-forming. The post-forming heat treatment further requires shot-blasting to remove scale, a by-product of heat treatment. 
     A further disadvantage to formed tubes is that forming the tubes necessarily results in thinning of the walls of the tube in high-stress regions, resulting in stress risers. Manufactures attempt to mitigate these stress risers by using thicker, heavier tubes, thereby increasing the weight and cost of their drop axles. In the commercial freight industry, increasing the weight of truck components adversely impacts fuel economy and profits. 
     Before forming, tubes have generally circular cross-sections. During forming, the circular cross-section is forced into an oval shape. This is often unavoidable as the material needs to stretch on the outside radii, and compress on the inside radii in order to form to the U-shaped indent. The tension on the outer radius of the tube and compression on the inner radius cause the top and bottom to be pulled together, distorting the circular cross section into an oval shape. In typical applications it is required that brackets be welded to the axle in various locations. When a bracket needs to be welded near a distorted area of the tube, custom fitting is often required to fit a bracket to a non-uniform region, adding cost to assembly. 
     SUMMARY 
     In one aspect, a saddle for a fabricated drop axle is provided. The saddle is arcuately formed about an axis to coaxially retain therein a pair of spaced apart and opposed axle stub ends, and defining a recess that substantially bisects the axis. 
     In another aspect, a fabricated drop axle is provided. The fabricated drop axle comprises: (a) a pair of opposed and spaced apart axle stub ends, each having a saddle end and a spindle end; and (b) a saddle arcuately formed about an axis to coaxially retain therein the saddle ends of the respective axle stub ends, and defining a recess that substantially bisects the axis. 
     In a further aspect, a method of manufacturing a saddle plate for a fabricated drop axle is provided. The method comprises: (a) forming a saddle plate by removing a substantially central portion of a blank to define an aperture; and (b) pressing the saddle plate substantially across the aperture about an axis over an arcuate die having a radius corresponding to a radius of an axle to be received in the saddle to transform the saddle plate into a saddle and the aperture into a recess bisecting the axis. 
     In a still further aspect, a method of manufacturing a fabricated drop axle is provided. The method comprises: (a) forming a saddle plate by removing a substantially central portion of a blank to define an aperture; (b) pressing the saddle plate substantially across the aperture about an axis over an arcuate die having a radius corresponding to a radius of an axle to be received in the saddle to transform the saddle plate into a saddle and the aperture into a recess bisecting the axis; (c) wherein pressing the saddle plate transforms the saddle plate into a saddle and the aperture into a recess bisecting the axis; (d) placing coaxially, opposed and spaced apart in a jig a pair of axle stub ends, each having a saddle end and a spindle end, the saddle ends each facing each other; (e) coaxially aligning the saddle with the saddle ends, the recess substantially overlapping the space between the saddle ends; and (f) mating the saddle to the axle stub ends. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: 
         FIG. 1  is a front left perspective view of an embodiment of a fabricated drop axle; 
         FIG. 2A  is a top view of a first embodiment of a saddle plate used in a saddle of the fabricated drop axle; 
         FIG. 2B  is a top view of a second embodiment of a saddle plate used in the saddle of the fabricated drop axle; 
         FIG. 3A  is a top view of the saddle used in the fabricated drop axle; 
         FIG. 3B  is a top right perspective view of the saddle used in the fabricated drop axle; 
         FIG. 3C  is a front view of the saddle used in the fabricated drop axle; 
         FIG. 3D  is a side view of the saddle used in the fabricated drop axle; 
         FIG. 4A  is a front view of an embodiment of an axle stub end used in the fabricated drop axle; 
         FIG. 4B  is a side view of an embodiment of the spindle used in the fabricated drop axle; 
         FIG. 5A  is a front view of the fabricated drop axle; 
         FIG. 5B  is a side view of the fabricated drop axle; 
         FIG. 5C  is a top view of the fabricated drop axle; 
         FIG. 6A  is a top view of a bottom plate used in the fabricated drop axle; 
         FIG. 6B  is a top left perspective view of the bottom plate used in the fabricated drop axle; 
         FIG. 6C  is a front view of the bottom plate used in the fabricated drop axle; 
         FIG. 6D  is a side view of the bottom plate used in the fabricated drop axle; 
         FIG. 7A  is a top view of a top plate used in the fabricated drop axle; 
         FIG. 7B  is a top left perspective view of the top plate used in the fabricated drop axle; 
         FIG. 7C  is a front view of the top plate used in the fabricated drop axle; 
         FIG. 7D  is a side view of the top plate used in the fabricated drop axle; 
         FIG. 8A  is a top view of a support brace used in the fabricated drop axle; 
         FIG. 8B  is a top left perspective view of the support brace used in the fabricated drop axle; 
         FIG. 8C  is a front view of the support brace used in the fabricated drop axle; 
         FIG. 8D  is a side view of the support brace used in the fabricated drop axle; 
         FIG. 9  is a cross sectional view of the fabricated drop axle taken along line A-A in  FIG. 5A ; and 
         FIG. 10  is a flow chart illustrating a method of manufacturing an embodiment of the drop axle. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be described with reference to the figures. It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practised without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Also, the description is not to be considered as limiting the scope of the embodiments described herein. 
     A fabricated axle assembly comprises two symmetrical straight cylindrical tubes each having a spindle on an end. The two cylindrical tubes are joined in the centre by a fabricated “drop” section, or saddle. The saddle is provided with a recess to allow for the passage of ancillary vehicle equipment such as a drive shaft on a tractor trailer or straight truck or a centre discharge tube on a semi-trailer or tanker. The fabricated axle assembly further comprises a pair of support braces to strengthen joints between the saddle and the cylindrical tubes. The support braces serve to increase the surface area for welding the saddle to the cylindrical tube, thereby providing stronger joints. A bottom plate spans the distance between the axle stub ends along the saddle. A top plate is disposed between the axle stub ends and substantially corresponds to the aperture. The bottom and top plates are provided to strengthen the saddle and to provide for longer weld joints. 
     Referring now to  FIG. 1 , an embodiment of the fabricated drop axle  101  is shown. The fabricated drop axle  101  comprises a pair of opposed axle stub ends  121 , a saddle  111 , and a top plate  151 . The fabricated drop axle further comprises a pair of support braces  131  shown in  FIGS. 8A to 8D , and a bottom plate  141  shown in  FIGS. 6A to 6D . 
     As best shown in  FIGS. 4A to 4B , each axle stub end  121  comprises a rigid, cylindrical tube  125  having a radius R axle  and an axial length L axle . The axle stub end  121  has a spindle end having a spindle  123  for rotatably mounting thereto a wheel. The axle stub end  121  further has a saddle end for attaching to the saddle as described herein. It will be appreciated that the dimensions of the spindle  123  may vary depending on the application, but these are typically determined by the type and size of a hub of the wheel to be mounted thereto. The length L axle  of the axle stub end  121  is dictated by the desired track-length between wheels, and can vary from one application to another. The radius R axle  is dependent on the desired load rating for the fabricated drop axle  101 , and the design of a suspension axle seat. Similarly, the thickness of the cylindrical tube  125  typically ranges from 0.500″ to 0.750″, depending upon the desired gross axle weight rating of the fabricated drop axle  101 ; however, the present specification is not to be limited in this regard. 
     As can be best seen in  FIGS. 3A to 3D , the saddle  111  will be described in greater detail. In embodiments, the saddle  111  has a pair of flat, substantially parallel flanges  119 . Each flange  119  has an inner surface and an outer surface and is generally U-shaped, defining a central recess  115  having a radius R recess . The inner surface of the first flange is substantially parallel and spaced apart from the inner surface of the second flange by a distance substantially equal to the diameter of each axle stub end  121 . The first and second flanges are joined at either side of their respective recesses  115  (at the tops of their respective U-branches) by two saddle segments  117 . Saddle segments  117  are arcuately formed about an axis parallel to, and equidistant from, the flanges  119 . Saddle segments  117  have a radius R saddle  substantially equal to the radius of each axle stub end  121 . Each saddle segment  117  is thereby configured to receive and partially encircle an axle stub end  121 . The recess  115  substantially bisects the axis about which saddle segments  117  are arcuately formed. It will be appreciated that the saddle may be monolithically formed as hereinafter described in greater detail, or fabricated by suitably mating the saddle segments  117  to the flanges  119 . 
     In typical applications, the inner saddle radius R saddle  is approximately 2.5″ to accommodate an axle stub end  121 , which typically has an outer radius R axle  of approximately 2.5″. In embodiments, saddle  111  is mated to each of the axle stub ends  121  by welding the adjacent portion of the saddle segment  117  with each of the axle stub ends  121 . 
     Support braces  131  enhance the strength of the assembly, as hereinafter described in greater detail. It will be appreciated, however, that the axle stub ends  121  can be mated to the saddle  111  using any suitable method, including fasteners, clamps and adhesives. 
     In preferred embodiments, the fabricated drop axle assembly  101  further comprises at least one of a top plate  151 , a bottom plate  141  and support braces  131 . It will be appreciated that the top plate  151 , bottom plate  141  and support braces  131  strengthen the fabricated drop axle assembly in embodiments where the axle stub ends  121  are welded to the saddle  111 . Welded joints commonly fail towards their starts or ends. With the support braces in place, a continuous weld circumscribes the axle stub end  121  along the portion between the axle stub end  121  and the support brace  131  that continues from the intersection between the axle stub end  121  and the saddle segment  117 . It will be appreciated that the continuous weld thereby eliminates weld starts and ends. In embodiments, the top plate  151 , bottom plate  141  and support braces  131  may not be required, provided that other suitable techniques to join the saddle  111  to the axle stub ends  121  are provided. For instance, fasteners may be used to join the saddle  111  to the axle stub ends. 
     A more detailed description of the top plate  151  will now be provided with reference to  FIGS. 1 and 7A to 7D . In embodiments, the fabricated drop axle comprises a top plate  151 . Top plate  151  comprises a pair of opposed and parallel tab plates  155  each respectively extending from either edge of an axially extending arcuate plate  153 . The distance between the inner surfaces of the tab plates  155  is defined by the inner chord length of the arcuate plate  153 . Arcuate plate  153  has an outer radius R top  substantially identical to the radius R recess  of the recesss  115  and an axial dimension substantially identical to the diameter of the axle stub end  121  and the distance between the inner surfaces of the opposed flanges  119 . The respective outer surfaces of the tab plates  153  are parallel and spaced apart a distance substantially equal to the distance between the respective saddle ends of each of the axle stub ends  121 . The top plate  151  is mated to the saddle  111  by welds along the intersection between the saddle  111  and the top plate  151 . The entire fabricated drop axle assembly  101  may be further strengthened by welding the tab segments  155  to the saddle ends of the axle stub ends  121 . It will be appreciated that the shape and dimensions of the top plate  151  may be correspondingly adjusted with respect to deviations in the design of the saddle  111 . 
     In embodiments, the fabricated drop axle preferably comprises a pair of support braces  131 , as best viewed in  FIGS. 8A to 8D , and  FIG. 9 . Each support brace  131  is an arcuate, axially extending plate. The inner radius R support  of the support brace  131  is substantially identical to the radius R axle  of the axle stub end  121 . The support brace  131  has an outer chord distance substantially equal to the diameter of the axle stub end  121 . It will be appreciated that this chord is further substantially identical to the distance between the inner surfaces of the respective parallel flanges  119 . The axial length of the support brace  131  is preferably less than the distance between the edge of the flange  119  and the recess  115  such that the axial edges of support brace  131  are entirely in contact with the flanges  119 . In embodiments, each support brace is welded along its edges adjacent to the axle stub ends  121  and flanges  119 . 
     In preferred embodiments, the fabricated drop axle further comprises a bottom plate  141  as shown in  FIGS. 6A to 6D . The bottom plate  141  is arcuate and has an outer radius R bottom  approximately equal to the outer radius R flange  of the flange  119 . The bottom plate  141  axially extends a distance substantially equal to the distance between the inner surfaces of the flanges  119 . Each end of the bottom plate  141  is notched to partially abut one of the axle stub ends  121 . Bottom plate  141  further strengthens the fabricated drop axle assembly in the same manner as described with reference to top plate  151 . The bottom plate  141 , being disposed between the flanges  119 , has edges abutting the flanges  119 . This defines an adjacent portion along which the bottom plate  141  may be welded to the saddle  111 . Each of the ends of bottom plate  141 , being notched to partially abut one of the axle stub ends  121 , forms an adjacent edge with the axle stub end  121  along which a weld is applied. 
     In embodiments, a method is provided for manufacturing the fabricated drop axle  101 . 
     Referring now to  FIG. 4 , an axle stub end  121  as heretofore described has a substantially straight length of cylindrical tube  125  having a spindle end and a saddle end. Spindle  123  can be attached to the spindle end of the cylindrical tube  125  using any suitable means. In embodiments, the spindle  123  may be welded to the spindle end of the cylindrical tube  125 . In further embodiments, cylindrical tube  125  is formed to have a “near net” spindle end (i.e., the cylindrical tube  125  is initially produced to have a spindle end substantially similar to the finished spindle shape); pre-formed cylindrical tube  125  is then machined to a final shape and size substantially identical to the spindle  123 . Preferably, the regions of the spindle  123  which mate to bearings of a wheel are heat treated to improve wear resistance. 
     The saddle end of the cylindrical tube  125  is machined “on centre” with respect to the spindle, so that the cylindrical tube  125  can be accurately located for mating with the saddle  111 , as hereinafter described in greater detail. 
     Having reference to  FIGS. 2A, 2B, 3A to 3D, and 10 , a method of manufacturing the saddle  111  is described. At block  1  in  FIG. 10 , a pre-form blank  211  (or  211 ′)as shown in  FIGS. 2A and 2B  is created from one of various methods. In embodiments, the pre-form blank  211  has a pre-form aperture  215  cut at its centre. Cutting may be achieved by blanking or plasma cutting. At block  2  in  FIG. 10 , pre-form blank is formed into the saddle  111  by a suitable mechanical or hydraulic press over a die having a radius substantially similar to the desired radius R saddle  of the finished saddle  111 . After formation, the saddle plate  211  acquires the shape of saddle  111  and the aperture is bent upon itself to form the recess. In embodiments, the saddle plate  211  is fabricated from a circular plate  213  having at its centre a circular aperture  215 . 
     As will be appreciated, the saddle plate  211  is preferably fabricated of high strength structural steel having physical and chemical properties suited to the application. The selected material is preferably suited to welding. In typical embodiments, the saddle plate  211  has a thickness in the range of ⅜″ to ¾″; however, the thickness is dictated by the desired GAWR (Gross Axle Weight Rating) of the axle. It will be appreciated, however, that other axle dimensions may be accommodated by increasing or decreasing the inner saddle radius R saddle  so that it is substantially the same as the outer radius R axle  of the axle stub ends  121 . The amount of drop required in the axle will dictate the dimensions of the saddle plate  211  and dimensions of the press dies. 
     In preferred embodiments, the plate  211  is substantially circular or oval, as shown in  FIGS. 2A and 2B , respectively. In preferred embodiments, the aperture  215  is similarly circular or oval. It will be appreciated that rounded edges and corners are less prone to failures resulting from stress concentrations. It will be further appreciated, however, that the plate  211  and the aperture  215  may take other forms, such as squares or rectangles. In embodiments, for example, the plate is square and the aperture is circular. In other embodiments, however, the plate is square and the aperture is oval. It will be appreciated that other shape combinations may be achieved, provided that the recess formed by the recess in saddle  111  resulting from formation of the saddle plate  211  provides clearance for various commercial vehicle components. 
     Support braces  131 , top plate  151  and bottom plate  141  are manufactured in a similar manner, with appropriate modification, as the saddle  111 , as heretofore described. Each begins as a pre-form blank having a suitable shape obtained by blanking or cutting, including by plasma, laser or water jet. Each is then formed, as respectively shown in blocks  6 ,  9 , and  12  of  FIG. 10 , by any suitable mechanical or hydraulic press over a die having a radius substantially identical to the inner radius of the finished piece. In embodiments for example, support braces  131  are arcuately formed over a die having a radius substantially equal to the radius of the axle stub end  121 . 
     The manufacture of the constituent components of the fabricated drop axle  101  having been described, reference will now be made to  FIGS. 1 and 5  for an understanding of a method of assembling the fabricated drop axle  101 . 
     In a welding jig (not shown), the axle stub ends  121  are coaxially aligned opposite each other, as shown at block  3  of  FIG. 10 . The saddle end of each cylindrical tube  125  having been “on centre” machined with respect to the spindle  123 , the axle stub ends  121  are accurately and coaxially aligned by locating features that register on each spindle  123  and on the area of each cylindrical tube that was “on centre” machined. 
     Once both axle stub ends  121  have been located in the welding jig, the saddle  111  is placed over the saddle ends of the axle stub ends  121 , as shown at block  4  of  FIG. 10 , and welded along the adjacent portion, as shown at block  5  of  FIG. 10 . 
     The axle stub ends  121  and saddle  111  having been mated, the resulting assembly is pivoted in the welding jig 180 degrees about the axis of rotation of the axle stub ends  121 , so that the flanges  119  project away from the base of the welding jig. Each support brace  131  is then located between the flanges  119  so that the inner arcuate surface of the support brace  131  interfaces with a portion of the saddle end of the axle stub end  121 , as shown at block  7  of FIG.  10 . Each support brace  131  is then welded to each respective axle stub end  121  and the saddle  111  along the edges of the support brace  131  respectively adjacent to each axle stub end  121  and the saddle  111 , as shown at block  8  of  FIG. 10 . 
     In embodiments, the bottom plate  141  is aligned between the inner surfaces of the flanges  119  so that the outer radius of the bottom plate  141  is substantially aligned with the radius R saddle  of the saddle  111 . The bottom plate  141  is then welded to the saddle  111 , preferably along the full length of the intersection of the bottom plate  141  and the saddle  111 , as shown at block  13  of  FIG. 10 . 
     The resulting assembly is again rotated in the welding jig by 180 degrees about the axis of rotation of the axle stub ends  121  so that the flanges  119  project toward the welding jig and the saddle sections  117  projects away from the welding jig. The top plate  151  is then introduced between the axle stub ends  121  so that the arcuate plate  153  is substantially coaxial with the aperture  115  of the saddle  111 , and so that the substantially semi-circular tab ends are substantially coaxial with the axle stub ends  121 , as shown at block  10  of  FIG. 10 . The top plate  151  is then welded to the assembly along the portions adjacent therewith, as shown at block  11  of  FIG. 10 . 
     Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. The entire disclosures of all references recited above are incorporated herein by reference.