Abstract:
A vehicle suspension assembly includes a control rod pivotally connected between a vehicle frame and an axle. The control rod controls longitudinal and vertical movement of the axle. A spring member is pivotally connected to the frame and fixed to the axle. Air spring assemblies are mounted between the axle and frame. The rigidly mounted spring member exerts torsion forces on the axle to counter roll forces and the air spring assemblies provide favorable ride characteristics adaptable to various trailer load conditions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention generally relates to a tandem axle suspension assembly, and more specifically to a walking beam tandem axle suspension assembly.  
         [0002]     Typically, vehicles such as cargo trailers include a steel leaf spring for suspending an axle from a vehicle frame. The steel leaf spring suspension requires little maintenance and provides favorable loading dock performance. The favorable dock performance results from a relatively small amount of vertical displacement between loaded and unloaded conditions of the leaf spring suspension. However, the leaf spring suspension may provide relatively harsh ride characteristics during unloaded or lightly loaded conditions.  
         [0003]     Another trailer suspension utilizes air springs for each axle. The air springs provide favorable ride characteristics regardless of the load on the trailer. Further, specific ride characteristics can be tailored to a specific load and desired handling characteristics.  
         [0004]     Disadvantageously, an air suspension system may be more expensive than a comparable leaf spring suspension. Air spring suspension systems may also not provide optimal loading dock performance due to height variations between loaded and unloaded conditions. In some instances, conventional air spring suspension systems utilize mechanical add on devices such as an adjustable stop inserted between the trailer frame and the suspension to limit movement relative to a loading dock. Other devices include manually operated jacks that support the trailer at a fixed height. Such devices typically require manual operation before, during and after the loading process. As appreciated, these mechanical add on devices increase weight, expense, and maintenance requirements.  
         [0005]     Accordingly, it is desirable to develop an air spring suspension system with favorable loading dock performance without sacrificing favorable ride characteristics.  
       SUMMARY OF INVENTION  
       [0006]     The suspension assembly of the present invention includes a pivotally attached control rod and a spring member fixed to an axle and pivotally attached to a vehicle frame.  
         [0007]     An air spring assembly is mounted between the axle and the vehicle frame to provide desirable ride characteristics. The control rod includes a first connection to the vehicle frame and a second connection to the axle. The control rod constrains longitudinal and vertical movement of the axle. The spring member is rigidly attached to the axle to counteract forces that can cause roll movements of the vehicle. The rigidly mounted spring member exerts torsion forces on the axle to counter roll forces while the air spring assemblies provide favorable ride characteristics adaptable to various trailer load conditions.  
         [0008]     Accordingly, the suspension assembly of this invention provides favorable loading dock performance and favorable ride characteristics without additional add on devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0010]      FIG. 1  is a perspective view of a tandem axle suspension assembly according to this invention;  
         [0011]      FIG. 2  is a schematic view of the axle assembly shown in  FIG. 1 ;  
         [0012]      FIG. 3  is a schematic view of the suspension assembly with the axles moved away from a neutral position;  
         [0013]      FIG. 4 , is a perspective view of another tandem axle suspension assembly according to this invention;  
         [0014]      FIG. 5  is a schematic view of the axle assembly shown in  FIG. 4 ; and  
         [0015]      FIG. 6  is a schematic view of the axle assembly with the axles moved away from a neutral position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Referring to  FIGS. 1 and 2 , a tandem axle suspension assembly  10  includes a pair of axles  14 , each supported by an air spring assembly  12  relative to a frame  16 . Preferably, the suspension assembly  10  supports axles  14  that are not driven such as are commonly used for cargo trailers, however, a driven axle system may also benefit from the suspension assembly  10  of this invention.  
         [0017]     A control rod  18  includes a pivotal connection  20  to a fixed link plate  30  that is rigidly attached to the frame  16 . The control rod  18  includes a pivotal connection  22  to an axle mount  32  supporting one of the axles  14 . The control rod  18  constrains longitudinal and vertical movement of the axles  14  relative to the frame  16 .  
         [0018]     A spring member  24  includes a pivotal connection  26  to the link plate  30  and fixed connection  28  to the axle mount  32  below the air spring assembly  12 . Preferably, the spring member  24  is a leaf spring having a desired thickness, however, the spring member  24  can also comprise other spring structures, such as rods or plates that exert a biasing force. The axle mount  32  includes a mount plate  36  and an axle plate  34 . The spring member  24  is clamped between the mount plate  36  and the axle plate  34  and secured together by a threaded fastener. The control rod  18  attaches below the axle  14  and the spring member  24  attaches above the axle  14 , however, it is within the contemplation of this invention to reverse the position of the spring member  24  and control rod  18 .  
         [0019]     The spring member  24  and the control rod  18  are connected parallel to each other forming top and bottom movable linkages between the axles  14  and the link plate  30 . Both the pivotal connection  20  for the control rod  18  and the pivotal connection  26  for the spring member  24  are disposed within a common vertical plane  31 . The pivotal connections  20 ,  26  support vertical displacement of the axles  14  to accommodate road inconsistencies.  
         [0020]     A first lateral control arm  38  and a second lateral control arm  44  are attached between the frame  16  and the axle mount  32  to control lateral movement of the axles  14 . The first lateral control arm  38  includes a first segment  40  attached to the frame  16  and a second segment  42  attached to the axle mount  32 . The second control arm  44  includes a first segment  46  attached to the frame  16  and a second segment  48  attached to another axle mount  32 .  
         [0021]     Preferably, the air spring assemblies  12  are of a minimal stroke to limit overall vertical movement of the axles  14  relative to the frame  16  once air is exhausted. The minimal movement between the frame  16  and the axles  14  improves dock performance by minimizing height changes during unloading.  
         [0022]     Referring to  FIG. 3 , the spring member  24  is rigidly attached to the axle mount  32  at the fixed connection  28  to control roll of the axle  14  relative to the frame  16 . The spring member  24  exerts a torsion force on the axle  14  to at least partially counteract forces that cause roll.  
         [0023]     Vertical movement of the axles  14  is resisted by the spring member  24 . The spring members  24  bend in response to vertical movement of the axles  14  from a neutral position (Illustrated by  FIG. 2 ).  FIG. 3  illustrates movement of one axle  14  away from the frame  16  and movement of another axle  14  toward the frame  16  along with the accompanying bend of the spring member  24 . The magnitude of bend on the spring member  24  is greatly exaggerated to illustrate operation.  
         [0024]     The air spring assemblies  12  provide dampening for the suspension assembly  10 . The fixed connection  28  of the spring member  24  resists vertical movement of the axle  14  by exerting a biasing force toward a neutral position ( FIG. 2 ). Resistance to vertical movement by the spring member  24  improves vehicle ride, by resisting lateral roll of the vehicle and improve loading dock performance by limiting vertical displacement of the axles  14  relative to the frame  16 .  
         [0025]     Referring to  FIG. 4 , another tandem axle suspension assembly  70  according to this invention includes a linkage assembly  72  that constrains and controls longitudinal movement of axles  74 . The tandem axle suspension assembly  70  includes the axles  74  supported for movement relative to a frame  76  by air spring assemblies  78 . The air spring assemblies  78  are disposed on each end of the axle  74 , between the axle  74  and the frame  76 .  
         [0026]     A ladder frame  100  is mounted laterally between link plates  86 . The ladder frame  100  includes pivotal connections  102  to a pair of lateral control links  104 . Each of the lateral control links  104  attaches to the ladder frame  100  at one of the pivotal connection  102  and an axle mount  92  by way of a second pivotal connection  106 . The second pivotal connection  106  is disposed laterally opposite the pivotally connection  102 . The lateral control links  104  control and constraint lateral movement of the axles  74 .  
         [0027]     Referring to  FIG. 5 , the linkage assembly  72  includes a control rod  80  with a first pivotal connection  88  to the link plate  86  and a second pivotal connection  90  to the axle mount  92 . A spring member  82  is pivotally attached to the frame  76  at a pivotal connection  96  and rigidly mounted to the axle mount  92  at a fixed connection  98 . Preferably, the second pivotal connection  90  of the control rod  80  and the fixed connection  98  of the spring member  82  to the axle mount  92  are disposed within a common vertical plane  84 . The vertical plane  84  extends transversely to an axis  85 . From the axle mount  92 , the control rod  80  and the spring member  82  extend on opposite sides of the vertical plane  84 . The spring member  82  extends longitudinally to the pivotal connection  96  and the control rod  80  extends longitudinally to the pivotal connection  88  on the link plate  86 .  
         [0028]     Each axle  74  includes one of the air spring assemblies  78  mounted between the axle  74  and frame  76  at segments adjacent each end of the axles  74 . Longitudinal movement of the axles  74  is constrained by the control rod  80  and the spring member  82 . Preferably, the control rod  80  is mounted below the axle  74  and the spring member  82  is mounted above the axle  74 .  
         [0029]     Referring to  FIG. 6 , the linkage assembly  72  is shown with one axle  74  moved away from the frame  76  and the other moved toward the frame  76  to illustrate deformation of the spring member  82 . Displacement of the axles  74  along with deformation of the spring member  82  is greatly exaggerated to illustrate operation of the linkage assembly  72 . The spring member  82  exerts a torsion force on the axles  74  to resist roll movements of the vehicle. Vertical movement of the axle  74  is countered by the torsion force exerted by the spring member  82  in a direction opposite movement of the axle  74  and toward a neutral position ( FIG. 5 ).  
         [0030]     The fixed connection  98  causes the spring member  82  to bend instead of pivot in response to vertical displacement of the axles  74 . The spring member  82  resists this bending, thereby exerting a biasing force opposite displacement of the axle  74 . The biasing force exerted by the spring member  82  on the axle  74  counteracts roll forces on the axle  74 . Resistance by the spring member  82  improves resistance to lateral roll and improves loading dock performance by limiting vertical displacement of the axle  74  relative to the frame  76 .  
         [0031]     The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.