Abstract:
A trailer suspension system has an axle, a pair of frame hanger brackets, dual trailing arm beams, and a spring. The pair of frame hanger brackets are mounted spaced apart underneath the trailer. The dual trailing arm beams are connected rigidly to the axle at one end and resiliently connected to a respective one of the frame hanger brackets with a pivot means bushing at the other end. The spring intermediate the trailing arm beam and the trailer to support the trailer load. Wherein, the axle connection center is the center of the patch that connects the axle to the longitudinal trailing arm beam, thereby reducing the stress on the axle as well as increasing the stability of the suspension system.

Description:
CROSS-REFERENCE TO PROVISIONAL APPLICATION(S) 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/068,417, filed May 10, 2011 now abandoned; which claims the benefit of U.S. Provisional Application No. 61/395,665, filed May 17, 2010. All the foregoing patent disclosures are incorporated herein by this reference thereto. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to semi-trailer suspensions and, more particularly, to a semi-trailer suspension that has multiple provisions for promoting lateral stability. 
     It is an object of the invention to reduce the vehicle track “offsets” of a semi trailer&#39;s axle beam. 
     It is another object of the invention to increase the lateral stability of a semi-trailer&#39;s suspension in part by the reduction in the vehicle track ‘offsets.’ 
     It is a further object of the invention to reduce the stress in the suspension and in particular reduce the stress on the welds directly on the axle tube, which in part is enabled by other benefits afforded by the reduction in the vehicle track ‘offsets’ 
     A number of additional features and objects will be apparent in connection with the following discussion of the preferred embodiments and examples with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There are shown in the drawings certain exemplary embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the embodiments disclosed as examples, and is capable of variation within the scope of the skills of a person having ordinary skill in the art to which the invention pertains. In the drawings, 
         FIG. 1  is a perspective view a fuel tanker semi-trailer that is provided with an axle suspension in accordance with the invention; 
         FIG. 2  is a perspective view of the suspension in accordance with the invention, including its multiple provisions for promoting lateral stability, and with other matters shown in phantom lines, wherein this suspension is configured for a top-mount style of trailer mount, in contrast to a low-mount style shown by  FIGS. 10-18 ; 
         FIG. 3  is a perspective view comparable to what is shown in solid line in  FIG. 2 , except exploded for the most part; 
         FIG. 4  is an enlarged scale perspective view of an axle sleeve mounted on an axle tube and as encircled in detail IV-IV in  FIG. 3 ; 
         FIG. 5  is an enlarged scale perspective view of the axle sleeve shown in  FIG. 4 , with portions of the axle tube shown in phantom lines; 
         FIG. 6  is a perspective view comparable to  FIG. 5  except showing the axle sleeve exploded; 
         FIG. 7   a  is a rear elevational view of  FIG. 5 , showing the weld pattern of the rear weld slots (eg., the half moons) and the rear mating seam; 
         FIG. 7   b  is a front elevational view of  FIG. 7   a , showing the weld pattern of the front weld slot (eg., the oval) and front mating seams; 
         FIG. 8  is a top plan view of  FIG. 2 , with some matters removed; 
         FIG. 9  is an enlarged scale elevational view taken in the direction of arrows IX-IX in  FIG. 8 , and partly in section; 
         FIG. 10  is perspective view of an alternate embodiment of the suspension in accordance with the invention, which is comparable to the  FIG. 2  embodiment except configured for a low-mount style (ie.,  FIGS. 10-18 ) and not the top-mount style (ie.,  FIGS. 2-9 ); 
         FIG. 11  is a top plan view thereof, and with some matters removed; 
         FIG. 12  is enlarged scale elevational view comparable to  FIG. 9 , except of the low-mount style (ie.,  FIGS. 10-18 ) of the suspension and not the top-mount-style (ie.,  FIGS. 2-9 ); 
         FIG. 13  is an enlarged scale sectional view of the axle beam and axle sleeve taken through the weld slot centerlines in  FIG. 11 , with surrounding sections of the trailing beam; 
         FIG. 14  is an elevation view, partly in section and comparable to  FIG. 13 , except showing the inboard side-edges of the axle sleeve; 
         FIG. 15  is an enlarged scale detail view of detail XV-XV in  FIG. 13 ; 
         FIG. 16  is a flat pattern view obtained by unwrapping until flat the view taken by looking radially inward all along circle XVI-XVI in  FIG. 14 ; 
         FIG. 17  is a reduced scale rear elevational view of the axle beam when the semi-trailer&#39;s right side dual tires have driven up over a curb; 
         FIG. 18  is a perspective view thereof showing the twist induced in the axle tube; and 
         FIG. 19  shows a series of curves on a graph, graphing axle beam rating against offset, wherein each curve represents a different axle wall thickness as indicated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a fuel tanker semi-trailer  29  that is provided with a suspension  30  in accordance with the invention. As shown better by  FIGS. 2-18 , the inventive suspension  30  has multiple provisions for promoting the lateral stability of the semi-trailer. The fuel tanker semi-trailer  29  shown by  FIG. 1  has tandem axles. However, for fuel tankers, triple axle trailers are quite common as well. 
     With general to  FIGS. 2-4  and  8 - 9 , the suspension  30  is disposed between an axle beam  32  and a semi-trailer&#39;s frame  34 . The style of axle beam  32  shown here has a central tube  36  portion flanked by spindle ends  38 . There are two popular ways to manufacture axle beams that have a central tube  36  portion flanked by spindle ends  38 . One way is to construct the axle beam  32  from three separate pieces, namely, a steel tube disposed between flanking, solid axle spindles. The axle spindles are typically friction welded to the ends of the axle tube. The other popular way is to form the axle beam  32  from a single piece of steel tube. The spindle profiles are formed by swaging in the ends of the tube stock. Regardless how the axle beam  32  is given the profiles for its spindle ends  38 , it is the size of the axle tube  36  portion which factors prominently in the “axle beam rating.” 
     Whereas needless to say the ‘axle beam rating’ corresponds to the rated load-carrying capacity of the axle beam  32 , ‘axle beam rating’ corresponds to the load-carrying capacity of the axle beam  32  only. However, the concept of “load-carrying capacity” is a broader concept than ‘axle beam rating’ only, and can refer to any of three (3) ratings or, in the alternative, capacities:—
         one, there is the upper limit, for highway capacity, informally known as the Bridge Law, which states (among other things) that the maximum trailer weight per axle is to be no more than 20,000 lbs ( − 9,000 kg) for tandem axle trailers with a ten foot ( − 3 m) spread between axles, but then only 17,000 lbs ( − 7,700 kg) if closer;   two, there is the axle beam capacity; and   three, there is the suspension capacity.
 
For the suspension  30  and axle beam  32 , capacity in excess of the upper limit for highway capacity is desirable. Sometimes on private property (eg., in industrial complexes) such as where it is lawful to do so, the trailers will be loaded heavier than allowed under the Bridge Law. In consequence, the Bridge Law does not necessarily dictate the capacity that customers want in their suspensions  30  and axle beams  32 . Indeed, some amount of overcapacity is desirable.
       

     The ‘axle beam rating’ of an axle beam  32  with a central axle tube  36  flanked by spindle ends  38  is based on at least the following factors:— 
     (a) wheel configuration (ie., single or dual); 
     (b) suspension type (ie., mechanical spring or air ride); 
     (c) vehicle track; 
     (d) axle tube  36  size (ie., outside diameter and wall thickness); 
     (e) suspension mounting centers; and 
     (f) offset (wherein ‘offset’ is interchangeably referred to as ‘overhang’). 
     Where and how to measure ‘vehicle track’ is shown by  FIG. 11 . For most suspensions, factors (a) through (f) can be readily measured and/or apprised in most contexts. However, for the suspension  30  in accordance with the invention, the factor (e) of ‘suspension mounting centers’  40 - 44  and then also the factor (f) of ‘offset’ are notionally reckoned in ways which are distinctive over the prior art. Where and how to notionally reckon the ‘mounting centers’  40 - 44  for the suspension  30  in accordance with the invention, and the consequent value for the ‘offset’ left by the suspension  30 &#39;s mounting centers  40  on the axle beam  32 , are also shown by  FIG. 11 . But these matters will be more particularly described below following a description of the structure from which the values in  FIG. 11  are reckoned. 
     For the suspension  30  in accordance with the invention, 
     (a) the preferred wheel configuration is dual; 
     (b) the preferred suspension type is air ride; and 
     (c) the nominal vehicle track is 71.5 inches ( − 1.8 m). 
     With reference to  FIG. 8 , dual wheel configurations have an interface between the two wheels  46  on each side of the axle beam  32 . Returning again to  FIG. 11 , the vehicle track is the distance between (1) the interfaces of the left two tires  62  and (2) the interfaces of the right two tires  62 . The measurement of 71.5 inches is pretty standard for the industry as a whole. Vehicle track is nearly always the maximum the law will allow. 
     Given the foregoing, factors (a)-(c) are more or less starting points that are somewhat handed down to a designer by market forces, and are not really customizable design factors. In contrast, factors (d)-(f) are indeed highly-customizable design factors inasmuch as the designer has a menu of options and/or can vary the outcomes in an indefinite number of ways. 
     For the designer, he or she is offered a menu of options for factor (d), concerning axle tube  36  outside diameter and wall thickness. For axle tube  36  diameter, there are generally two options in the industry:—
         5 inch (12.7 cm) diameter, or   5¾ inch ( − 14.6 cm) diameter.
 
Likewise with axle tube  36  thickness, there are options, but in this case there are more than just two generally-accepted options. Industry has standardized the options for wall thickness by giving the options various designations of alphabetic letters. The five most common wall thicknesses for 5 inch (12.7 cm) diameter steel tube (and their respective letter designations) include the following:—
   0.437 inch L-Wall ( − 11.10 mm),   0.460 inch S-Wall ( − 11.68 mm),   0.580 inch H-Wall ( − 14.73 mm),   0.625 inch E-Wall ( − 15.88 mm), and   0.750 inch T-Wall (19.05 mm).
 
Hence the designer has at least ten choices for axle tube  36  size. The designer would likely want to select an appropriate size which gives the designer the axle beam rating (ie., load-carrying capacity) that the designer is striving for. The designer may not want to grossly over-design the suspension  30  its axle beam  32 , nor certainly not under-design either.
       

     It is an aspect of the invention that factors (e) ‘suspension mounting centers’  40 - 44  and (f) ‘offset’ are notionally reckoned in ways which are distinguished from the prior art, and obtaining advantages only obtained by the suspension  30  in accordance with the invention. However, that discussion will be paused until further below and after a more particular description of the construction of the suspension  30 , as follows. 
       FIGS. 2-9  shown one version of the suspension  30 T while  FIGS. 10-18  show an alternate version  30 L of the invention. The  FIGS. 2-9  version of the suspension  30 T comprises a top-mount style of trailer mount. In contrast, the  FIGS. 10-18  version of the suspension  30 L comprises a low-mount style of trailer mount. The contrast between the two styles of trailer mount are perhaps better shown by contrasting  FIG. 9  (top-mount) with  FIG. 12  (low-mount). In  FIG. 9 , the vertical distance between the axle beam  32 &#39;s center and vehicle frame  34  is much greater than the corresponding measurement in  FIG. 12 , and hence why this style is referred to as a low-mount. 
     In spite of differences between the  FIG. 2  version of the suspension  30 T and  FIG. 10  version  30 L, both versions pretty much share all the same aspects which are the basis of the inventively distinct aspects of the suspension  30  overall. 
     With general reference to  FIGS. 2 and 3  as well as  FIGS. 8 and 9 , the suspension  30  comprises left and right trailing beams  50  suspended and pivoted from the vehicle frame  34  by hangers  51 . The trailing beams  50  and hangers  51  are, like so many of the other parts to be described herein, preferably fabricated from steel. That is, preferably plate steel is formed by brake presses to fold at fold lines and thereby produce flanges and/or channels. Connections are formed either by fasteners or by welding as more particularly described in any particular instance. 
     Each trailing beam  50  comprises a head section  52  transforming into a tail section  54 . The head section  52  extends from a crown end holding a ring  55  and then from there, rearwardly to the tail section  54 , which terminates in a seat  56  for an air spring  57 . The ring  55  of the crown end has a resilient bushing is force fitted into it. The bushings of the left and right trailing beams  50  are pivoted to the hangers  51  on the trailer frame  34  by pivot bolts. 
     Preferably trailing beams  50  are formed into a rectangular tubular construction of the plate steel. The ring  55  of each crown end is welded to the crown end, and each ring  55  is correspondingly (and preferably) formed cylindrically from plate steel. 
     The head section  52  of each trailing beam  50  trails rearwardly to a welded connection to its axle sleeve  58 , and then continuing as the tail section  54  trails rearwardly to a seat  56  for the air spring  57 . The air spring  57  is compressed between the vehicle frame  34  above it and the seat  56  underneath it which is on the tail section  54  of the trailing beam  50 . 
       FIG. 3  or  9  show better that, for the top-mount version of suspension  30 T, each trailing beam  50  has a side panel  90  and top panel  91  of plate steel, which top panel  91  is continuous and uninterrupted from the crown end&#39;s ring  55  on through to the seat  56  for the air spring  57 . That is in contrast for a bottom panel  93  for the trailing beam  50  because the bottom panel  93  is partitioned by an opening therethrough due to a throat  80  formed in the side panel  90 . Alternatively,  FIG. 12  shows better that this circumstance is flipped for the low-mount version of the suspension  30 L, wherein each arm has a bottom panel  94  of plate steel that is continuous and uninterrupted from the crown end&#39;s ring  55  to the seat  56  for the air spring  57 . It is the top panel  95  in  FIG. 12  that is partitioned by an opening therethrough from the throat  80  formed in the side panel  90 . 
     Other matters which are illustrated in the drawings include a drum  59  for a brake system (drum  59  shown in  FIG. 2 , brake shoes  61  shown in  FIG. 8 ) forming a hub for mounting wheel rims  46  (see also, eg.,  FIG. 8 ) of dual tires  62  on each side of the axle beam  32 . And then also, there is preferably a shock absorber  63  for each trailing beam  50 , extending between a connection with the hanger  51  and the trailing beam  50  proximate the axle sleeve  58 . As  FIGS. 9 and 12  show better, preferably the trailing beams  50  and shock absorbers  63  are not pivoted from coaxial pivot axes. Additionally, the brake system comprises a pneumatic actuator (eg., as for driving a pivot-link/slack-adjuster, which rotates a shaft terminating in an S-cam that spreads the brake shoes  61 ). 
       FIG. 4  is a rear perspective view of the axle sleeve  58  as it is disposed on the axle beam  32 . The axle sleeve  58  forms a full wrap around the entire circumference of the axle beam  32 . As  FIGS. 5 and 6  show better, the axle sleeve  58  is formed from bisections  64  comprising upper and lower cuff sections  64  (or ‘cuffs’  64  for short:—wherein, the term ‘cuff’ is not a term of art). The cuffs  64  have front and rear meeting edges  68  that meet up when assembled together to form the completed axle sleeve  58 , as shown in  FIG. 4 . 
       FIGS. 5 and 6  show that the upper and lower cuffs  64  are formed with opposite cut-outs through their respective front meeting edges  66 , and opposite half-moons proximate their respective rear meeting edges  68 . These cut-outs function as weld slots  70  and  72 . The front weld slot  70  is preferably an oval or circle (ie., a circle is a special instance of an oval) that is cooperatively formed by both the upper and lower cuff  64 . The rear weld slots  72  comprise a pair of crescent-shaped cut-outs (or half-moons), one in each of the upper and lower cuff  64 . Each rear weld slot  72  has a major diameter that is slightly gapped away from the respective rear meeting edge  68  of the respective cuff  64  by a thin band of solid material. 
       FIG. 7   a  comprises a rear elevation view of the axle beam  32  better showing the weld seams  74  of the axle sleeve  58  to the axle tube  36 . In this  FIG. 7   a , the cuffs  64  are welded to the axle tube  36  by the weld slots  70  and  72  only. 
     In contrast, the upper and lower cuffs  64  are welded together along a weld seam  76  along the rear meeting edges  68 . However, the weld of this weld seam  76  does not penetrate through to and weld into the axle tube  36 . 
     So again, the only places in  FIG. 7   a  where the cuffs  64  are welded to the axle tube  36  is in each of the rear weld slots  72 :—and not along the weld seam  76  of the welded rear meeting edges  68 . 
       FIG. 7   a  also shows better that the upper and lower cuffs  64  are cooperatively formed with shoulder flares  78  which flare inwardly on the axle tube  36 . The shoulder flares  78  cooperatively form an inward spike for the axle sleeve  58  as a whole. FIG.  7   b  comprises a front elevation view of the axle beam  32  better showing the weld seams  74  of the axle sleeve  58  to the axle tube  36  on the front half of the axle tube  36 . To compare  FIG. 7   a  (rear view) with  FIG. 7   b  (front view), the front view of  FIG. 7   b  shows no such shoulder flare in the cuffs  64 . Hence the shoulder flares  78  serve the purpose to extend the length of the rear meeting edges  68  of the cuffs  64 . This affords some of the following advantages. The welded seam  76  formed by the rear meeting edges  68  has a longer length than for the welded seam between the front meeting edges  66 . Moreover, the rear meeting edges  68  and the weld seam  76  for them are continuous from the outboard terminus, and on through the shoulder flares  78  until ultimately reaching the inboard terminus. In contrast, the front meeting edges  66  are opened in large part by the front weld slot  70 , are really very minimized. 
     In  FIG. 7   b  (ie., the front view), the only place where the cuffs  64  are welded to the axle tube  36  is in the front weld slot  70 :—and not along the welded front meeting edges  66 . 
     More significantly, the welded seam  76  formed by the rear meeting edges  68  floats off of the axle tube  36 . The axle sleeve  58  is only fixed to the axle tube  36  at the rear and front weld slots  70 . So, during twisting events, the weld slots  70  and  72  fix the axle sleeve  58  tight to the axle tube  36 , the axle tube  36  can torsionally distort and displace itself inside and under the shoulder flares  78 . 
       FIGS. 8 and 11  are both top plan views.  FIG. 8  shows the top-mount style of the suspension  30 T and  FIG. 11  the low-mount style  30 L. However,  FIGS. 8 and 11  show that both styles of the suspension  30 T and  30 L are arranged very similar to each other from these top plan vantage points. 
     Looking ahead to  FIG. 19 , it comprises a graph. In that graph, the axle beam rating of five specified sizes of axle tube  36  are graphed against offset. The source for  FIG. 19  comes from a Canadian corporation, IMT Corp. of Ingersoll, Ontario, with a division known as Ingersoll Axles. As mentioned before, the terms ‘offset’ and ‘overhang’ are used interchangeably in the industry, and it is believed that the IMT Corp. favors the term “overhang.” Regardless,  FIG. 19  shows a series of curves for the axle beam rating according to offset for the following sizes of axle tubes:—
         0.437 inch L-Wall ( − 11.10 mm) and 5 inch (12.7 cm) diameter,   0.460 inch S-Wall ( − 11.68 mm) and 5 inch (12.7 cm) diameter,   0.580 inch H-Wall ( − 14.73 mm) and 5 inch (12.7 cm) diameter,   0.625 inch E-Wall ( − 15.88 mm) and 5 inch (12.7 cm) diameter, and   0.750 inch T-Wall (19.05 mm) and 5 inch (12.7 cm) diameter.
 
Unsurprisingly, the shorter the offset, the higher the axle beam rating for any given wall thickness of 5 inch tube.
       

     Returning to  FIGS. 8 and 11 , it is an object of the invention to shorten the offset for the suspension  30  in accordance with the invention to what is practicable. A first consideration includes the following:—that is, that it is a preference in accordance with the invention to design the suspension  30  such that the relevant mounting centers  40 - 44  are as wide as possible. However, a countervailing consideration includes the following two factors. That (1) the inboard edges of the inner rubber tires  62  and (2) the inboard edges of the brake shoes  61  both represent outer limits on the width of the various mounting centers  40 - 44  of the suspension  30 , and hence constrain the width of the various mounting centers  40 - 44  of the suspension  30  to definite limits:—but not all the same amount of constraint. 
     Nevertheless, it is an aspect of the invention to widen the relevant mounting centers  40 - 44  as wide as practicable. 
     When an axle beam  32  is under load, it flexes into a shallow U-shape. To skip ahead to  FIG. 17 , it shows a load situation for the axle beam  32  when the semi-trailer  29 &#39;s right side dual tires  62  have driven up over a curb. Again, the axle beam  32  has flexed into a shallow U-shape. In the industry, this U-shaped flexion is referred to as camber. 
     Dual tire arrangements can be contrasted to single tire arrangements as follows. Whereas dual tire arrangements distribute the load on an axle beam  32  among four tires  62  instead of two, dual tire arrangements also force the offset to be twice as great (again, for offset, see  FIGS. 8 and 11 ). In other words, the suspension  30  has to be narrower. Hence dual tire arrangements present design challenges. In the industry, the standard offset is 18.75 inches, and it is no coincidence that the value 18.75 inches is in the center value in the chart of  FIG. 19 . 
     Pause can be taken before  FIG. 11  is more particularly described for what else it shows. This pause is preferably taken to more particularly review  FIGS. 9 and 12 . 
       FIGS. 9 and 12  are comparable elevational views of the suspension  30  in accordance with the invention, with  FIG. 9  showing the top-mount style  30 T and  FIG. 12  the low-mount style  30 L. 
     The head section  52  of the trailing beam  50  transforms into the tail section  54  at a throat  80 . In  FIG. 9 , the throat  80  wraps on top of the axle sleeve  58  from about the 6 o&#39;clock position clockwise to about the 3 o&#39;clock position. In  FIG. 12 , this circumstance is flipped. The throat  80  wraps underneath the axle sleeve  58  from about the 12 o&#39;clock position counter-clockwise to about the 4 o&#39;clock position. 
     In  FIG. 9 , the head section  52  has a bottom panel forming a meeting edge with the axle sleeve  58  at about the 6 o&#39;clock position. This is the ‘chin’ meeting edge. The tail section  54  has a corresponding bottom panel forming a meeting edge with the axle sleeve  58  at about the 3 o&#39;clock position. This is the ‘chest’ meeting edge. The terms ‘chin’ and ‘chest’ are not terms of art. Nevertheless, the axle sleeve  58  is pinched in the throat  80  of the trailing beam  50  and gripped by welded seams  86  and  88  along the chin and chest meeting edges  82  and  84 . 
       FIG. 12  has basically the same arrangement except perhaps inverted. The head section  52  has a top panel forming a meeting edge with the axle sleeve  58  at about the 12 o&#39;clock position. This is the ‘chin’ meeting edge  82 . The tail section  54  has a corresponding top panel forming a meeting edge with the axle sleeve  58  at about the 4 o&#39;clock position. This is the ‘chest’ meeting edge  84 . The axle sleeve  58  in  FIG. 12  (as it was in  FIG. 9 ) is pinched in the throat  80  of the trailing beam  50  and gripped by welded seems along the chin and chest meeting edges  82  and  84 . 
       FIG. 13  is a sectional view of the axle beam  32  and axle sleeve  58  taken through the weld slot centerlines  40  in  FIG. 11 .  FIG. 13  furthermore shows the throat  80  of the trailing beam  50 , as well as the chin meeting edges  82  and the chest meeting edges  84 . The axle sleeve  58  is welded to the axle tube  36  at welds in the weld slots  70  and  72  only. The chin meeting edge  82  is welded to the top of the axle sleeve  58 :—which weld seam  86  does not penetrate through to the axle tube  36 . How the chest meeting edge  84  is welded as better shown by  FIG. 15 . The chest meeting edge  84  is welded by a weld seam  88  laid on top of the weld seam  76  of the rear meeting edges  68  of the cuffs  64  of the axle sleeve  58 . Again, the chest meeting edge  84  is welded by a technique referred to as welding on top of a weld, or double-pass welding. However, like the situation with the chin weld, the welded seam  88  of the chest meeting edges  84  does not penetrate to the axle tube  36 . 
     Hence the weld seams  86  and  88  of both the chin and the chest meeting edges  82  and  84  float on the outside of the axle tube  36 . That way, during twisting events, the weld slots  70  and  72  fix the axle sleeve  58  tight to the axle tube  36 , the axle tube  36  can torsionally distort and displace itself inside and under the chin and particularly the chest meeting edges  84 , and more particularly underneath the shoulder flares  78  of the axle sleeve  58 . 
       FIG. 14  shows that the throat  80  of the trailing beam  50  is welded circumferentially to the outside of the axle sleeve  58 . The welded seam  89  of the throat  80  of the trailing beam  50  does not penetrate to the axle tube  36 . 
     Given the foregoing, the multi-variable concept of ‘mounting centers’  40 - 44  can be more particularly described in connection with  FIGS. 11 and 16 . To begin with,  FIG. 16  is a flat pattern view obtained by unwrapping until flat the view taken by looking radially inward all along circle XVI-XVI in  FIG. 14 . 
       FIG. 11  shows at least 5 mounting centers  40 - 44 . From narrowest to widest,  FIG. 11  shows the following:—
         1—the mounting centers  44  of the air springs  57  to the semi-trailer frame  34 ;   2—the mounting centers  43  of the bushings to the semi-trailer frame  34 ;   3—the mounting centers  42  of chest meeting edge  84  to the shoulder flares  78  of the axle sleeve  58  along the cuffs  64 &#39;s rear meeting edges  68 ;   4—the mounting centers  41  of the chin meeting edge  82  to the axle sleeve  58  along a line where the axle sleeve  58  is not flared out; and   5—the mounting centers  40  of the weld slot centers by which the axle sleeve  58  is welded to the axle tube  36 ;
 
Although shown in  FIG. 11 ,  FIG. 16  shows better that the chest meeting edge  84  is nominally as wide the as rear meeting edges  68  of the shoulder flares  78  of cuffs  64  of the axle sleeve  58 . Returning to  FIG. 11 , it is an aspect of the invention that the chest meeting edge  84  is wider than the chin meeting edge  82  because the chest meeting edge  84  vis-a-vis the air spring  57  supports about four times as much weight as the chin meeting edge  82 . That is, for 100% of the weight of the semi-trailer  29  supported by any trailing beam  50 , the air spring  57  supports about 80% of that weight, and the bushing about 20%. Hence the air spring  57  applies about four times as much of a load to the chest meeting edge  84  as what the bushing applies to the chin meeting edge  82 .
       

     In consequence, it is an aspect of the invention to widen the chest meeting edge  84  in excess of the chin meeting edge  82 . The axle sleeve  58 &#39;s outboard edge is disposed on the axle tube  36  about as far outboard as possible without interfering with other matters like the brake shoes  61  and their mountings. The chest meeting edge  84  is expanded outboard as wide as the axle sleeve  58  will allow. But in order to get the desired width for the chest meeting edge  84 , it has to be expanded inboard, and hence the justification for the shoulder flares  78  of the axle sleeve  58 . 
     Nevertheless, this extra inboard expansion of the chest meeting edge  84  relative to the chin meeting edge  82  means that the mounting centers  42  of the chest meeting edge  84  to the axle sleeve  58  is going to be narrower than the mounting centers  41  for the chin meeting edges  82 . 
     However, the widest mounting centers  40  of all are the weld slot mounting centers  40  on the axle tube  36 . The weld slot mounting centers  40  are the measurement which determines the ‘offset’ value for  FIG. 19 . 
     Reviewing  FIG. 11  once again, the value of ‘vehicle track’ for dual wheel  46  axle beam  32  setups is pretty standard across the industry, and the standard measurement is about 71.5 inches ( − 1.8 m). In other words, the standard ‘vehicle track’ is the limit the law will allow for over-the-road transport.  FIG. 19  shows that for a given wall thickness of axle tube  36 , a designer can obtain a higher capacity if the ‘offset’ is minimized. 
     It is an object of the invention to minimize the ‘offset’ of the axle tube  36  by widening the weld slot mounting centers  40  to the extent practicable. As  FIG. 16  shows, the weld slots  70  and  72  are not laterally centered on the axle sleeve  58 , but instead shifted outboard about as far as possible on the axle sleeve  58  without opening into the outboard edge. 
       FIG. 11  shows that all five mounting centers  40 - 44  characteristic to the invention are widened to the extent that geometry will practically allow. But what has happened in consequence is that, each of the five mounting centers  40 - 44  are different from each other. For example, the inner tires  62  crowd the air springs  57  inward to a greater degree than the bushings, hence the mounter centers  44  for the air springs  57  are narrower than the mounting centers  43  for the bushings. 
     To turn to the chest and chin mounting centers  42  and  41 , once again the chest meeting edge  84  is wider than the chin meeting edge  82 . Since the outboard terminus for each is in about the same longitudinal (fore to aft, vertical) plane, therefore the inboard terminus of the chest meeting edge  84  is indeed inboard of the inboard terminus of the chin meeting edge  82 . Accordingly, the mounting centers  42  for the chest meeting edges  84  are narrower than the mounting centers  41  for the chin meeting edges  82 . 
     But the mounting centers which determine ‘offset’ as used in  FIG. 19  is the weld slot mounting centers  40  as shown in  FIG. 11 . And these mounting centers  40  are the widest of the characteristic mounting centers  40 - 44 . The relatively wide weld slot mounting centers  40  advantageously allow a designer to select a relatively thin walled axle tube  36  to get the desired load carrying capacity. As more particularly described below, the selection of a thinner wall axle tube over a thicker walled one affords multiple advantages. 
       FIGS. 17 and 18  show various forms of distortion of the axle beam  32  when it is under load.  FIG. 17  shows the matter of flexion, which is also referred to as camber. As shown by  FIG. 17 , the axle beam  32  is flexed in flexion across the whole width of the vehicle track, which includes not only the width between the weld slot mounting centers  40  but also across both flanking offsets. 
     In contrast,  FIG. 18  shows that a different circumstance happens with torsion. The axle beam  32  is not distorted in torsion across the whole width of the vehicle track but, instead, only just across the more narrow width of the weld slot mounting centers  40 . 
     The most significant aspects of the invention are achieved by widening the weld slot mounting centers  40  as wide as possible. To begin with, one direct result is that the offset is reduced by a half inch for every one inch of widening of the weld slot mounting centers  40 . Presumptively the designer intends to design the axle beam  32  for an axle beam rating in some excess of the Bridge Law capacity (eg.,  − 20,000 lbs per trailer axle).  FIG. 19  shows that, if the designer can reduce the offset from the industry average of 18.75 inches to 15.75 inches, the designer can not only get by with a slender axle tube (eg., 5 inch O.D. versus 5¾ inch O.D.) and a thinner wall thickness (like perhaps a 0.437 inch L-wall versus a 0.580 H-wall). 
     One of the more significant values behind the twin benefits of a slenderer axle tube  36  and thinner wall thickness includes the following. The resultant slenderer, thinner-wall axle tube  36  distorts easier in flexion (camber) and twisting (torsion). This more supple axle tube  36  thereby takes a lot of pressure off the welds in the weld slots  70  and  72 . 
     Some final remarks about the suspension  30  in accordance with the invention include the following. 
     It is an aspect of the invention that the relatively wide apart trailing beams  50  allows the shock absorbers  63  to be placed further outboard on the suspension  30  also thus improves stability. 
     It is an alternative aspect of the invention that a trailing beam  50  has an axle connection that is greater than the pivot connection (hanger  51 ) center, and thus reduce the vehicle track “offset”. 
     It is another aspect that the trailing beam  50  has an axle connection that is an inch outboard or more of the pivot connection (hanger  51 ) center, and so also reduces the axle track “offset”. 
     It is an additional aspect that trailing arm beam has an axle connection that is outboard of the pivot connection (hanger  51 ) center by an amount of equal to or greater than ¼-th (one-quarter) of the bushing width, and thus additionally reduce the axle track “offset”. 
     It is a further aspect that the trailing beam construction tapers outboard from the pivot connection means (hanger  51 ) to the axle connection center and then tapers back inboard for the air spring seat  56 . 
     It is an alternative aspect of the invention to provide a trailing beam construction that extends from the pivot means (hanger  51 ) and has a throat  80  for the axle sleeve  58  connection that is less than axle sleeve  58  diameter and surrounds the axle sleeve  58  joining to a full axle wrap for structural support, thus allowing the axle beam  32  to be integrated with the brake spiders in place on the axle tube  36 . 
     The invention having been disclosed in connection with the foregoing variations and examples, additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations specifically mentioned, and accordingly reference should be made to the appended claims rather than the foregoing discussion of preferred examples, to assess the scope of the invention in which exclusive rights are claimed. 
     
       
         
               
               
             
           
               
                   
               
               
                 REFERENCE LIST  
                 REFERENCE LIST  
               
               
                 (NUMERICAL) 
                 (ALPHABETICAL) 
               
               
                   
               
             
             
               
                 29, semi-trailer 
                 air spring, 57 
               
               
                 30, 30T, 30L, suspension 
                 axle beam, 32 
               
               
                 32, axle beam 
                 axle tube, 36 
               
               
                 34, frame (trailer) 
                 axle sleeve, 58 
               
               
                 36, axle tube 
                 brake shoes (FIG. 8), 61 
               
               
                 38, spindle ends 
                 chest meeting edge, 84 
               
               
                 40, mounting centers, weld slots 
                 chin meeting edge, 82 
               
               
                 41, mounting centers, chin 
                 cuffs, 64 
               
               
                 42, mounting centers, chest 
                 drum (FIG. 2), 59 
               
               
                 43, mounting centers, bushing 
                 frame (trailer), 34 
               
               
                 44, mounting centers, air spring 
                 front weld slot, 70 
               
               
                 46, wheel/rim (FIG. 8) 
                 front meeting edges, 66 
               
               
                 50, trailing beam 
                 hanger, 51  
               
               
                 51, hanger 
                 head section, 52 
               
               
                 52, head section 
                 mounting centers, bushing, 43 
               
               
                 54, tail section 
                 mounting centers, chest, 42 
               
               
                 55, ring 
                 mounting centers, air spring, 44 
               
               
                 56, seat (for air spring) 
                 mounting centers, chin, 41 
               
               
                 57, air spring 
                 mounting centers, weld slots, 40 
               
               
                 58, axle sleeve 
                 rear weld slots, 72 
               
               
                 59, drum (FIG. 2) 
                 rear meeting edges, 68 
               
               
                 61, brake shoes (FIG. 8) 
                 ring, 55 
               
               
                 62, tires, dual (FIG. 8) 
                 seat (for air spring), 56 
               
               
                 63, shock absorber 
                 semi-trailer, 29 
               
               
                 64, cuffs 
                 shock absorber, 63 
               
               
                 66, front meeting edges 
                 shoulder flares, 78 
               
               
                 68, rear meeting edges 
                 spindle ends, 38 
               
               
                 70, front weld slot 
                 suspension, 30, 30T, 30L 
               
               
                 72, rear weld slots 
                 tail section, 54 
               
               
                 74, weld seams, weld slots 
                 throat (throat section), 80 
               
               
                 76, weld seams, rear meeting edge 
                 tires, dual (FIG. 8), 62 
               
               
                 78, shoulder flares 
                 trailing beam, 50 
               
               
                 80, throat (throat section) 
                 weld seams, weld slots, 74 
               
               
                 82, chin meeting edge 
                 weld seams, rear meeting edge, 76 
               
               
                 84, chest meeting edge 
                 welded seam, chin, 86 
               
               
                 86, welded seam, chin 
                 welded seam, chest, 88 
               
               
                 88, welded seam, chest 
                 welded seam, throat, 89 
               
               
                 89, welded seam, throat 
                 wheel/rim (FIG. 8), 46