Abstract:
A suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels includes a wheel-carrying axle comprising a first end a second end, and a pair of frame bracket assemblies each comprising a resiliently-bushed pivotable connection defining a pivot axis, wherein the frame bracket assemblies are operably coupled to opposite sides of the frame bracket, and wherein the resiliently-bushed pivotable connection comprises a substantially cylindrically-shaped bushing. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the bushing of one of the frame bracket assemblies therein, wherein the aperture of the second end of each trailing arm is nonsymmetrical, thereby causing a nonsymmetrical compression of the bushing about the pivot axis. The suspension system also includes embodiments wherein the aperture of the second end of each trailing arm is nonuniform, thereby reducing rotation of the bushing with respect to the trailing arm, wherein a mating surface of each trailing arm operably coupled to the first and second end of the axle comprise a cavity, thereby reducing a localized stress transferred from the trailing arm to the axle, wherein the second end of each trailing arm further comprises a lip extending radially outward from the aperture and at least one engagement surface extending radially outward from the lip and adapted to abut a bushing-removal tool, as well as other improvements.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/455,946, filed Mar. 19, 2003, entitled TRAILING ARM SUSPENSION WITH OPTIMIZED I-BEAM, which is hereby incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to vehicle suspension systems, and in particular to suspensions for semi tractor-trails incorporating single-piece, cast trailing arms.  
           [0004]    2. Description of the Related Art  
           [0005]    Trailing beam suspensions for semi tractor-trailer combinations are well-known in the trucking industry. The typical trailing beam suspension comprises a hanger bracket suspended from a trailer frame rail. A trailing beam or arm is pivotably connected at one end to the hanger bracket to enable the trailing beam to pivot about a horizontal axis. The pivotable connection may comprise a resiliently bushed connection. The free end of the trailing beam is attached to a spring that is, in turn, attached to the trailer frame rail for cushioning the ride. The spring can comprise a mechanical spring, such as a coil spring, or an air spring. An axle is attached transversely to a pair of trailing beams on either side of the trailer through a rigid or resilient axle-to-beam connection.  
           [0006]    Other suspension and braking components can be attached to the trailing beam and/or the axle, such as a brake assembly, track bars, and shock absorbers.  
           [0007]    Trailing beams can take a variety of shapes and cross sections, and are typically fabricated by welding individual components into the final assembly, thereby providing a beam with a hollow cross section. An example of such a beam is disclosed in U.S. Pat. No. 5,366,237 to Dilling et al. Such beams are typically designed for the maximum stress to which the beam will be subjected at any point on the beam. This approach results in sections of the beam having more material than is necessary for the maximum stress imposed on the beam at that section. This excess material adds to the cost and weight of the beam. Moreover, the welds induce stresses into the beam that can contribute to premature failure of the beam. Weld-induced stresses can be minimized by laying down welds that are of a consistent thickness. However, such detailed welding techniques can also increase the cost of fabrication and the weight.  
           [0008]    Attachment of the axle to the beam is typically through some type of welded connection, such as disclosed in U.S. Pat. No. 5,366,237 to Dilling et al. Welded connections can induce in the axle stresses and cracks that can contribute to premature failure of the axle. Weld-induced axle stresses can be minimized by limiting the welded area to the region around the axle&#39;s neutral axis, and by starting and ending the weld at the same point on the axle. Moreover, the extent and location of the weld can preclude separation of the axle from the beam, which would be desirable in order to replace a damaged axle or beam without replacing the entire suspension.  
           [0009]    Heretofore, resilient bushings have been utilized within the pivotable connection between the beam and the associated hanger bracket. It is also known to use bushing that have apertures extending along the length thereof to alter the spring-rate of the bushing along a particular path. Typically, these apertures are provided in pairs juxtaposed across the bushing. The bushing is then placed within the associated beam with the apertures vertically oriented, thereby altering the spring rate of the bushing for lateral shift of the trailer as compared to the spring rate for the bushing for roll of the trailer. In operation, these bushings are fixed with respect to the beams and pivot about pivot pins that are fixed with respect to the associated hanger brackets. However, these bushings can sometimes rotate with respect to the beam rather than the hanger bracket, thereby changing the orientation of the busing, and the orientation of the apertures located therein, and changing the direction in which the bushing affords a reduction in the spring-rate.  
           [0010]    In previously known systems, significant wear of the trailing arms may occur proximate the hanger brackets during operation of the associated suspension system. Specifically, in many systems the roll of the vehicle causes the beams to shift within and contact the respective hanger brackets in a location about the periphery of the aperture of each beam within which the bushing are located. These areas about the aperture are typically constructed as thin as possible in an attempt to reduce the overall weight of each beam. The contact between the beams and hanger bracket causes excessive wear requiring the replacement of the beams to avoid catastrophic failure of the beams and/or bushings.  
           [0011]    As discussed above, it is known to utilize bushings within the pivotable connection between the beams and hanger brackets, wherein the bushings include apertures extending through the bushings and oriented so as to alter the spring rate in a particular direction of compression while not effecting the spring-rate in others. However, the construction of these specialized bushings is more expensive than bushings that do not include such apertures. Moreover, the specialized bushings require proper orientation of the bushings with respect to the beams at all time, as discussed above.  
           [0012]    Heretofore, maintenance of bushings associated with the pivotable connection between the beams and hanger brackets, i.e., the removal of the bushings from within the beams, has required the use of a specialized tool that abuts or engages the area of the beam near the bushing receiving aperture during extraction or installation of the bushing. As discussed above, these areas are typically quite thin in an effort to reduce the overall weight of each beam, thus providing only small areas for abutment of the tool.  
           [0013]    During operation of the associated suspension system, bending stress are exerted on the axles, with localized points of stress being exerted at the locations of the connection between the trailing arms and the axles, thereby contributing to excessive stress on the axles and decreasing the useful life of the axles. Normal operation of the suspension system also leads to wear of the boot of the air spring each time the boot is allowed to contact the associated beam. This wear of the boot is especially prevalent during times of loading/unloading when air is not being supplied to the air springs.  
           [0014]    Another cause of significant stress within previously known beam configurations, is the concentration of the upwardly directed load bear force exerted by the axle on the beam, and the downwardly directed forces exerted on the ends of the beam by the hanger bracket and air spring. This bending of the each beam results in a compressive force being exerted on the axle and the connection between the beams and the axle.  
           [0015]    A configuration for a trailing arm or beam is desired that increases the lifespan of the beam within normal operating conditions, results in a beam having reduced weight while simultaneously providing increased structural integrity and a reduction to production and operating costs.  
         SUMMARY OF THE INVENTION  
         [0016]    One aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, and a pair of frame bracket assemblies each comprising a resilient-bushed pivotable connection defining a pivot axis, wherein the frame bracket assemblies are operably coupled to opposite sides of the vehicle frame, and wherein the resiliently-bushed pivotable connection comprises a substantially cylindrically shaped bushing. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the bushing of one of the frame bracket assemblies therein, wherein the aperture of the second end of each trailing arm is nonsymmetrical, thereby causing a nonsymmetrical compression of the bushing about the pivot axis.  
           [0017]    Another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, and a pair of frame bracket assemblies each comprising a resiliently-bushed pivotable connection, wherein the frame bracket assemblies are operably coupled to opposite ends of the vehicle frame, and wherein the resilient-bushed pivotable connection comprises an elastically-deformable bushing. The suspension system also includes a pair of trailing arms each comprising a first end operable coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the bushing of one of the frame bracket assemblies therein, wherein the aperture defines an inner surface, and wherein the inner surface is nonuniform, thereby reducing a rotation of the bushing with respect to the trailing arm.  
           [0018]    Yet another aspect of the present invention is to provide a suspension system for suspending a vehicle above a plurality of ground-engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, and a pair of frame bracket assemblies each comprising a frame bracket and a resilient-bushed pivotable connection, wherein the frame bracket assemblies are operably coupled to opposite sides of the vehicle frame. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the resilient-bushed pivotable connection of one of the frame bracket assemblies therein, wherein the second end of each trailing arm comprises a first thickness across a width thereof and a second thickness located proximate the frame bracket that is greater than the first thickness.  
           [0019]    Still yet another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, and a pair of frame bracket assemblies each comprising a resilient-bushed pivotable connection, wherein the frame bracket assemblies are operably coupled to opposite sides of the vehicle frame, and wherein the resiliently-bushed pivotable connection comprises an elastically deformable bushing. The suspension system also includes a pair of trailing arms each comprising a first end comprising a mating surface operably coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the resilient-bushed pivotable connection of the frame bracket assemblies therein, wherein the mating surface of the first end of each of the trailing arms comprises a cavity, thereby reducing a localized stress transferred from the trailing arms to the axle.  
           [0020]    Another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle and comprising a first end and a second end, and a pair of frame bracket assemblies each comprising a resiliently-bushed pivotable connection defining a pivot axis, wherein the frame bracket assemblies are operably coupled to opposite sides of the vehicle frame, and wherein the resilient-bushed pivotable connection comprises a substantially cylindrically-shaped bushing. The suspension system also includes a pair of trailing arms each comprising a first end operable coupled to the first end and the second end of the axle, respectively, and a second end comprising an aperture that receives the bushing of one of the frame bracket assemblies, wherein the second end of each trailing arm further comprises a lip extending radially outward from the aperture and at least one engagement surface extending radially outward from the lip and adapted to abut a bushing-removal tool.  
           [0021]    Still yet another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle, comprising a first end and a second end, a pair of frame bracket assemblies operable coupled to opposite sides of the vehicle frame, and a pair of shock absorbers each comprising a first end operably coupled to the vehicle frame and a second end. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, a second end operable coupled to one of the frame bracket assemblies, and an outwardly extending shock support tang operably coupled to one of the shock absorbers, wherein each of the trailing arms comprises a single-cast piece.  
           [0022]    Still yet another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, a pair of frame bracket assemblies operably coupled to opposite sides of the vehicle frame, and a pair of air springs each comprising a flexible boot. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, a second end operably coupled to one of the frame bracket assemblies, and a top surface comprising a first portion and a second portion, wherein the second portion is adapted to support one of the air springs thereon, and wherein the second portion extends above the first portion, thereby substantially reducing an amount of contact between the trailing arm and the boot of the air spring when the air spring is in a deflated condition.  
           [0023]    Still yet another aspect of the present invention is to provide a suspension system for suspending a vehicle frame above a plurality of ground-engaging wheels that includes a wheel-carrying axle comprising a first end and a second end, and a pair of frame bracket assemblies operably coupled to opposites sides of the vehicle frame. The suspension system also includes a pair of trailing arms each comprising a first end operably coupled to the first end and the second end of the axle, respectively, and a second end operably coupled to one of the frame bracket assemblies, wherein the first end of each trailing arm comprises a tube-shaped portion having a slot extending along the length thereof for receiving the axle therein during assembly. The suspension system further includes a pair of spacer assemblies each operably coupled with the trailing arms and spanning the slot of the first end, thereby reducing an amount of flexure of each trailing arm proximate the coupling between the trailing arm and the axle.  
           [0024]    The present inventive trailing arm and associated suspension system results in an increased operational lifespan for the associated system, reduces the overall weight, while simultaneously providing increased structural integrity and reducing production and operation costs. The trailing arm disclosed herein is more durable, more wear resistant, efficient in use, and is particularly well adapted for the proposed use. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is an elevational view from the side of a portion of a trailer having a suspension assembly according to the invention;  
         [0026]    [0026]FIG. 2 is a top perspective view of the suspension assembly;  
         [0027]    [0027]FIG. 3 is a top perspective view of an I-beam trailing arm;  
         [0028]    [0028]FIG. 4 is a second top perspective view of the trailing arm;  
         [0029]    [0029]FIG. 5 is a side elevational view of the trailing arm;  
         [0030]    [0030]FIG. 6 is a top plan view of the trailing arm;  
         [0031]    [0031]FIG. 7 is a cross-sectional view of the trailing arm, taken along line VII-VII, FIG. 5;  
         [0032]    [0032]FIG. 8 is a cross-sectional view of the trailing arm, taken along line VIII-VIII, FIG. 5;  
         [0033]    [0033]FIG. 9 is a cross-sectional view of the trailing arm, taken along the line IX-IX, FIG. 5;  
         [0034]    [0034]FIG. 10A is a cross-sectional view of the trailing arm, taken along the line XA-XA, FIG. 5;  
         [0035]    [0035]FIG. 10B is an enlarged, partial side view of a bearing sleeve of the trailing arm, taken of the area XB, FIG. 5;  
         [0036]    [0036]FIG. 11 is a side view of an assembly of the trailing arm and an air spring;  
         [0037]    [0037]FIG. 12 is an enlarged bottom view of an axle seat of the trailing arm;  
         [0038]    [0038]FIG. 13 is a side view of an assembly of the axle seat and an axle showing a portion of the welds used to connect the axle to the trailing arm;  
         [0039]    [0039]FIG. 14 is an enlarged perspective view of a shock absorber supporting tang of the trailing arm;  
         [0040]    [0040]FIG. 15 is an top perspective view of the shock absorber supporting tang of the trailing arm;  
         [0041]    [0041]FIG. 16 is an enlarged side view of a proximate end of the trailing arm;  
         [0042]    [0042]FIG. 17A is a cross-sectional view of the trailing arm assembled with the hanger bracket, wherein the cross section of the trailing arm is taken along line XIII-XIII, FIG. 5, and wherein the trailing arm is in a non-deflectional position;  
         [0043]    [0043]FIG. 17B is a cross-sectional view of the trailing arm assembly with the hanger bracket, wherein the cross section of the trailing arm is taken along line XIII-XIII, FIG. 5, and wherein the trailing arm is in a deflected position; and  
         [0044]    [0044]FIG. 18 is an enlarged side view of a spacer assembly as connected with the trailing arm. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in FIGS. 1-3. However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.  
         [0046]    Referring now to FIGS. 1 and 2, a trailing arm suspension assembly  10  according to the invention is shown suspended from a trailer frame  11 , including a trailer frame rail  12 , a first crossbeam  13  (shown in outline) and a second crossbeam  19  (shown in outline), and which supports a trailer  14 . Two identical suspension assemblies  10  are mounted in tandem to the trailer frame rail  12  for supporting the trailer  14  on two sets of wheels  16 . The suspension assembly  10  comprises an improved trailing arm or beam  112  suspended at a proximal end  15  from the trailer frame rail  12  through a hanger bracket  18 . A conventional air spring  24  is attached to a distal end  17  of the trailing arm  112  and to the trailer frame rail  12 . The trailing arm  112  is rigidly connected near its second end to a conventional axle  22  to which wheels  16  (shown in outline) are connected at opposite ends of the axle  22 . The axle  22  has an exterior axle surface  23 . In a typical trailer application, the two identical trailing arm assemblies are used on either side of the trailer  14  to mount the axle  22  to the frame rail  12  and support opposing ends of the axle  22 , as best illustrated in FIG. 2.  
         [0047]    The trailing arm assembly  10  comprises a conventional hanger bracket  18  rigidly connected, such as by bolts (not shown), to the trailer frame rail  12  (shown in outline). The trailing arm  112  is resiliently and pivotably connected at the proximal end  15  to the hanger bracket  18  through a resilient bushing  52  that provides for deflection of the trailing arm  112  relative to the hanger bracket  18  that is a different magnitude along the longitudinal axis of the trailing arm  112  than along the axis of the hanger bracket  18 . The air spring  24  is mounted between the distal end  17  of the trailing arm  112  and the trailer frame rail  12  in a conventional manner, such as with bolted connections (not shown). Alternatively, the air spring  24  can be mounted between a central portion of the trailing arm  112  and the trailer frame rail  12  with the axle  22  mounted at the distal end  17  of the trailing arm  112 .  
         [0048]    A shock absorber assembly  28  is preferably mounted between the trailing arm  112  and the second crossbeam  19  of the trailer frame  11 . In the illustrated example, the shock absorber assembly  28  comprises shock absorber  48  mounted at a first end  20  through a shock absorber bracket  44  to the second crossbeam  19  and at a second end  21  through a shock absorber clevis  46  (FIGS. 13 and 14) to the trailing arm  112 . The clevis  46  is fixedly connected to the trailing arm  112  via welding and the like, as described below.  
         [0049]    The trailing arm assembly  10  can also be selectively provided with a conventional drum brake actuator assembly  26  comprising a brake actuator  30  and an S-cam assembly  38 . The brake actuator assembly  26  can be mounted to the axle  22  through appropriate brackets attached thereto, such as by welding. Alternatively, the brake actuator assembly  26  can be mounted to the trailing beam  112 , thereby eliminating the axle welds. The suspension assembly may further be provided with a conventional disc brake assembly and disc brakes, rather than drum brakes.  
         [0050]    The trailing arm  112  is preferably fabricated using generally conventional casting methods. The configuration of the trailing arm  112  is precisely determined, preferably by finite element analysis, accordingly to the design stresses to which the trailing arm  112  will be subjected at every point in the trailing arm  112 . Thus, excess material is eliminated, reducing weight and cost, and optimizing the beam&#39;s strength-to-weight ratio. The use of casting methods enables the trailing arm  112  to be readily fabricated having the precisely-determined dimensions established from the design process. However, other fabrication methods can be utilized that will provide a beam having a variable cross section corresponding closely to the dimensions established during the design process to maintain the optimized strength-to-weight ratio.  
         [0051]    The trailing arm  112  (FIGS. 3-6) is a rigid, generally elongated member having a proximal end  15  and a distal end  17 , and a longitudinal axis  34  (FIG. 4). The proximal end  15  comprises a hollow cylindrical bushing sleeve  60  having a bushing aperture  68  and defining a central axis  36  orthogonal to the longitudinal axis  34 . The distal end  17  comprises an air spring seat  64  and an axle seat  66  adapted for rigid connection of the axle  22 , as described below. Intermediate the proximal end  15  and the distal end  17 , the trailing arm  112  has an I-beam section  62  (FIG. 8) comprising a web  70 , an upper beam flange  72 , and a lower beam flange  74 . The plane of the web  70  is generally orthogonal to the central axis  36  of the bushing aperture  68  and coplanar with the longitudinal axis  34  of the trailing arm  112 .  
         [0052]    In the illustrated example, the upper flange  72  extends laterally an equal distance on either side of the web  70  and orthogonally thereto. However, the flange  72  can extend beyond the web  70  an unequal distance to accommodate the stresses in the flange, or due to other considerations such as providing clearance to accommodate other suspension components or the incorporation of mounting structures. As best illustrated in FIG. 5, the upper flange  72  varies in thickness along the length of the trailing arm  112  generally increasing in thickness from the bushing sleeve  60  to the air spring seat  64 . The width of the upper flange  72  may also vary depending upon the variation in design stresses along the flange and the size of the trailing arm  112 .  
         [0053]    The lower flange  74  of the illustrated example also extends laterally an equal distance on either side of the web  76  and orthogonally thereto, although the flange  74  can extend beyond the web  70  an unequal distance as discussed above. As best illustrated in FIG. 5, the lower flange  84  varies in thickness along the trailing arm  112 , generally increasing in thickness from the bushing sleeve  60  to the axle seat  66 . The flange thickness will be dependent upon the variation in design stresses along the flange and the size of the trailing arm.  
         [0054]    The air spring seat  64  (FIGS. 3-6,  9  and  11 ) is a generally platelike extension of the upper beam flange  72  and extends laterally beyond the upper flange  72  to provide a suitable seat for mounting and support of the air spring  24 . The air spring seat  64  is integrally formed within the upper flange  72  extending above a lower portion  50  thereof and integrally connected via a bride portion  152  extending in a generally upwardly-inclined direction from the rear welding stud  82  and the air spring seat  64  is an air spring seat reinforcing flange  106 , as shown in FIG. 3. As shown in FIGS. 4 and 6, the reinforcing flange  106  is a generally platelike structure with a width approximately equal to that of the flanges  72 ,  74 . The air spring seat reinforcing flange  106  is integrally formed with the beam web  70  and preferably extends an equal distance laterally of the beam longitudinal axis  34 . However, the flange  106  can extend beyond the axis  34  an unequal distance to accommodate the actual stresses to which the flange  106  will be subjected, or due to the other considerations such as providing clearance to accommodate other suspension components or the incorporation of other mounting structures. The air spring seat  64  is provided with a plurality of mounting apertures  154  for mounting the air spring  24  to the trailing arm  112  using conventional fasteners, such as bolted connections (not shown). In the illustrated example, the air spring  24  includes an upper plate  156 , a lower plate  158 , and a flexibly resilient boot  160  extending therebetween as is known in the art. During periods of operation, the supply of air pressure to the air spring  24  may be reduced or eliminated, thereby allowing the boot  160  to roll about the edges of the lower plate  158  and extend below the lower plate  158 . The elevated position of the air spring seat  64  with respect to the rest of the upper beam flange  72  provides a clearance area between the boot  160  and the trailing arm  112 , thereby reducing wear of the boot  160  and increasing the operating life thereof.  
         [0055]    The axle seat  66  is formed in the distal end  17  of the trailing arm  112  and is adapted to conform to the axle surface  23 . The axle seat  66  comprises a front welding stud  80 , a rear welding stud  82 , and an axle saddle  88  (FIG. 7). The front welding stud  80  is an elongated, generally rodlike member preferably extending laterally an equal distance on either side of the beam longitudinal axis  34 . However, the stud  80  can extend beyond the axis  34  an unequal distance to accommodate the actual stresses to which the stud  80  will be subjected. The rear welding stud  82  is an elongated, generally rodlike member preferably extending laterally an equal distance on either side of the trailing arm  112  longitudinal axis  34 . However, the stud  82  can extend beyond the axis  34  an unequal distance to accommodate the actual stresses to which the stud  82  will be subjected. The front welding stud  80  is fabricated as a lateral extension of the lower flange  74  to provide structural, stress-transferring continuity between the stud  80  and the flange  74 .  
         [0056]    The axle saddle  88  is a generally arcuate, saddle-like structure preferably extending laterally an equal distance on either side of the beam longitudinal axis  34 . However, the saddle  88  can extend beyond the axis  34  an unequal distance to accommodate the actual stresses to which the saddle  88  will be subjected. The axle saddle  88  has an axle saddle contact surface  90  with a curvature somewhat greater than the curvature of the axle surface  23 . Preferably, the contact surface  90  is cast, however, certain applications may require machining. The design process preferably utilizes the finite element analysis method in order to configure the length, width, and thickness of the axle saddle  88  to accommodate the stresses to which the axle saddle  88  will be subjected. In the embodiment shown in FIGS. 3-7, the width of the axle saddle  88  is approximately equal to the width of the upper beam flange  72 . The axle saddle  88  preferably includes a cavity  162  recessed into the contact surface  90 . In the illustrated example, the cavity  162  (FIGS. 12 and 13) is provided a substantially circular shape, however, other geometrical configurations may be utilized. In operation, stress is concentrated on the axle  22  at locations proximate the connections between the trailing arms  112  and the axle  22  by preventing the axle  22  from bending as compared to the locations along the length of the axle  22  not connecting with the trailing arms  112 . The cavity  162  reduces the localized stress proximate the connection points between the trailing arms  112  and the axle  22 .  
         [0057]    An axle saddle stiffening rib  96  (FIG. 13) extends between the axle saddle  88  and the upper flange  72 . The stiffening rib  96  extends generally the same distance laterally of the beam longitudinal axis  34  as the upper flange  72  and the axle saddle  88 . A shock support tang  164  (FIGS. 13-15) extends outwardly from and is integrally molded with the saddle stiffening rib  96 . The tang  164  includes a substantially rectangular mounting portion  166  having a mounting surface  168 , and a structural reinforcement flange  170  formed integrally with the mounting portion  166 . In assembly, the shock absorber clevis  46  is attached to the mounting surface  168  via welding, mounting hardware, or other suitable method.  
         [0058]    As best illustrated in FIG. 13, the axle seat  66  engages the axle  22  so that the axle surface  23  is in contact with the axle saddle contact surface  90 . A rear weld  79  extends around the perimeter of the welding stud  82  along the interface of the welding stud  82  and the axle surface  23 . A front weld  78  extends in a similar manner around the perimeter of the welding stud  80  along the interface of the welding stud  80  and the axle surface  23 . The axle  22  is rigidly connected to the beam  20  by the welds  78  and  79  that traverse the perimeter of each welding stud  80  and  82  respectively, along the interface of the welding studs  80  and  82  and the axle surface  23 . With a curvature of the axle saddle  88  somewhat greater than the curvature of the axle  22 , the top of the axle  22  is in contact with the axle saddle  88  at its junction with the axle saddle stiffening rib  96 . This provides for vertical load transfer directly from the axle  22  to the beam  20  without the vertical load being carried by the beam-to-axle welds.  
         [0059]    The trailing arm  112  (FIG. 2) is connected to the hanger bracket  18  by slidably inserting a resilient bushing  52  into the bushing aperture  68  so that the bushing  52  frictionally engages an inner surface  184  of the aperture  68 , and utilizing a conventional connection  54 , such as a bolted fastener, for the pivotal connection between the trailing arm  112  and the hanger bracket  18 . The trailing arm  112  can pivot about the axis  36 , and the resilient bushing  52  enables the generally horizontal translation of the trailing arm  112  along its longitudinal axis  34  to differ in degree from its generally vertical translation orthogonal to the axis  34 . The inner surface  184  (FIGS. 10A and 10B) of the bushing aperture  68  is preferably provided with a plurality of teeth  186 , preferably with a height of within the range of from about 0.005 inches to about 0.010 inches, thereby limiting relative rotation between the bushing  52  and the trailing arm  112 . It should be noted that the inner surface  184  may include out roughed surfaces so as to engage the bushing  52 . The bushing aperture  68  (FIG. 16) is also preferably nonsymmetrical with respect to the pivot axis  36 . In the illustrated example, the lateral distance A is less than the vertical distance B, thereby compressing a symmetrical bushing  52  more in the lateral direction than in the vertical direction. The greater compression in the lateral direction of the bushing  52  increases the spring rate in that direction, thereby altering the amount of lateral movement of the entire suspension system while leaving the amount of roll available relatively unchanged. It should be noted that the bushing aperture  68  may be provided in other geometrical configurations than as shown.  
         [0060]    The proximate end  15  (FIGS. 6, 17A and  17 B) of each trailing arm  112  is provided with abutment portion  170  surrounding each end of the bushing aperture  68 . In operation, the trailing arm  112  is typically substantially parallel with each arm of the hanger bracket  18 , as shown in FIG. 17A, thereby providing adequate clearance between the trailing arm  112  and the hanger bracket  18 . However, turning the associated vehicle about corners and/or road conditions causing the supported trailer to sway may cause the trailing arms  112  to twist relative to the hanger brackets  18 , as shown in FIG. 17B, thereby causing the trailing arm  112  to contact the hanger bracket at contact points  172 . The increased thickness of the bushing sleeve  60  near the ends thereof provide an increased wear surface, thereby increasing the time between required service, while limiting the total weight of the trailing arm  112  that would be associated with increasing the thickness of the bushing sleeve  60  along the entire length thereof.  
         [0061]    The suspension assembly  10  further includes a pair of spacer assemblies  180  (FIG. 18) each operably coupled to an associated trailing arm  112 . Each spacer assembly  180  includes a rearward support member  182 , a forward support member  184 , a structural support member  186 , and a spacer member  188 . In the illustrated example, each of the members  182 ,  184 ,  186  and  188  comprise a plate-like structure. The members  182 ,  184  and  186  are welded to the trailing arm  112  or attached by another acceptable method, or alternatively, may be integrally formed with trailing arm  112 . If constructed as separate pieces, the members  182 ,  184  and  186  may be attached to the trailing arm  112  either prior to or after connecting the axle  22  with the trailing arm  112 . The spacer  188  is fixedly attached to the rearward support member  182  and the forward support member  184  subsequent to the axle  22  being attached to the trailing arm  112 . The spacer member  188  is attached to the members  182  and  184  via welding, or other suitable method. Alternatively, the spacer member  188  may comprise a bolt, or other adjustable mechanism, that engages the support members  182  and  184 . During operation, the trailing arm  112  absorbs an upwardly directed force at the contact point between the axle  22  and trailing arm  112 , a downwardly directed force exerted by the hanger bracket  18  and a downwardly directed force exerted by the air spring  24 . The combination of these forces may cause a slight bending in the trailing arm  112  about the contact point between the axle  22  and the trailing arm  112 , thereby reducing the width of the axle saddle  88  and placing significant stress on the welds  78  and  79 . The spacer assembly  180  bridges the open end of the axle saddle  88 , thereby preventing or limiting bending of the trailing arm  112  and reducing the fatigue associated therewith.  
         [0062]    As best illustrated in FIG. 16, the proximate end  56  of each trailing arm  112  is provided with a plurality of bushing removal/insertion tool engagement surface  190  each extending radially outward from the bushing sleeve  60 . Each engagement surface  190  includes an aperture  192  extending therethrough for receiving a portion of the tool therein. The engagement surfaces  190  cooperate to increase the area available for engagement of the tool, as compared to a trailing arm that provides only an end surface of the bushing sleeve  60 .  
         [0063]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the foregoing disclosure and drawings without departing from the spirit of the invention, and the scope of the appended claims should be construed as broadly as the prior art will permit.