Abstract:
A suspension arrangement for interconnecting a frame and an axle in a vehicle includes a control arm having a first beam and a second beam in parallel, spaced relation, each beam having a first end with a single arm and a second end with an upper arm and a lower arm to define a Y-shape, the first end being pivotally connectable to a vehicle frame, and the second end being connectable to a vehicle axle disposed between the upper and lower arms, and a bushing arrangement mountable to the vehicle axle, the bushing arrangement having an upper portion connecting between the upper arms of the first beam and second beam and a lower portion connecting between the lower arms of the first beam and second beam.

Description:
FIELD OF THE INVENTION 
     The invention is directed to vehicle suspensions, in particular heavy vehicle suspensions. More particularly, the invention is directed to a rear suspension arrangement for interconnecting a frame and axle in a vehicle. 
     BACKGROUND AND SUMMARY 
     Many rear air suspensions allow twist in the axle during roll events (opposite wheel travel in the vertical direction) to provide roll stiffness. However, because of the manner in which the axle is attached to such suspensions, unwanted forces are transferred to the axle. 
     One approach to a solution is shown in U.S. Pat. No. 4,310,171 to Merkle. Merkle shows a vehicle axle attachment having a control arm having two parallel plates shaped to form horizontally spaced lugs at one to attach to the vehicle hangar bracket and vertically spaced lugs at the opposite end to attach to the axle. The vertically spaced lugs are rigidly connected to the axle by way of a flange. With a rigid connection, the roll rate of this arrangement is fixed. 
     A suspension arrangement in accordance with the invention includes a control arm provided as a beam having a first end with a single arm and a second end with an upper arm and a lower arm diverging to define a Y-shape, the first end being connectable to a vehicle frame, and the second end being connectable to a vehicle axle disposed between the upper and lower arms. A bushing arrangement mounts the arms to the vehicle axle, the bushing arrangement having an upper portion connecting to the upper arm and a lower portion connecting to the lower arm, the bushing having a selected rate. 
     The suspension according to the invention improves the transfer of twisting forces to the axle by constraining the axle between two arms of the control arm. The axle is twisted about the center of torsion, allowing increased twist to the axle without the introduction of an extra bending moment in the axle. The invention advantageously adds adjustment of the response of the suspension by way of the axle bushings. 
     According to another aspect of the invention, the control arm is formed of a first beam and a second beam in parallel, spaced relation, the first beam and second beam being interconnected to the axle by the bushing arrangement. The spacing may be varied, according to the invention, to provide the desired mechanical advantage for twisting the axle. The first beam and second beam are relatively thin plate members that provide a weight advantage in the assembly while providing sufficient strength and stiffness in the vertical direction. In addition, forming the first beam and second beam as thin plates provides some lateral flexibility to the suspension assembly for accommodating lateral suspension events. 
     The invention thus provides an improvement in roll rate by a control arm that is much stiffer in the vertical direction than in the lateral direction. 
     According to the invention, the first beam and second beam are interconnected only by the axle bushing arrangement and a second bushing arrangement mounting the beams to the vehicle frame. 
     According to another aspect of the invention, the first beam and second beam are connected to form the control arm with the axle end bushing arrangement disposed between the respective upper arms and lower arms. 
     Preferably, the bushing arrangement includes two upper bushings and two lower bushings. 
     According to another aspect of the invention, the rate of the bushings that attach the beam to the axle may be varied to influence certain suspension characteristics. For example, making the two top bushings stiffer in the fore/aft direction and relatively softer in the vertical direction and making the bottom bushings softer in the fore aft direction and relatively stiffer in the vertical direction can improve roll steer, lateral stiffness, roll rate, toe stiffness and camber stiffness. 
     According to yet another aspect of the invention, the first beam and second beam each include a plate section and flanges extending perpendicularly from edges of the plate section, wherein the first beam and second beam are mutually disposed with the respective flanges extending in opposite directions. 
     According to another aspect of the invention, the suspension arrangement further includes a hanger mountable to the frame, the first end of the control arm being pivotally mounted to the hanger. 
     According to yet another aspect of the invention, the suspension arrangement further includes a spring mountable between the axle and the frame. The spring may be disposed between a seat on an arm mountable to and extending from the axle and a bracket mountable to the frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood by reference to the following detailed description read in conjunction with the appended drawings, in which: 
         FIG. 1  is a side view of a suspension arrangement in accord with the invention; 
         FIG. 2  is a perspective view of the suspension arrangement of  FIG. 1 ; 
         FIG. 3  is a perspective view of an embodiment of a top bushing device for connecting control arms to an axle; 
         FIG. 4  is a perspective view of one embodiment of a bottom bushing device and spring arm for connecting a control arm to the axle and supporting a spring; 
         FIG. 5  is an example of a tuned bushing which may be used in the suspension arrangement of the invention; and, 
         FIG. 6  is another example of a tuned bushing. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of a suspension arrangement in accordance with the invention.  FIG. 2  shows a perspective view of the suspension arrangement of  FIG. 1 . The suspension arrangement connects a vehicle frame rail  10  and vehicle axle  12 . In  FIG. 2 , a vehicle frame rail  11  of the opposite side of the frame is shown, while the frame rail in the foreground of the drawing has been removed for clarity. An assembly of the suspension arrangement of the invention would be mounted on each end of the axle to connect each end of the axle to the respective frame rail.  FIG. 2  illustrates in detail one such assembly; only parts of the opposite side are shown to avoid over-complicating the figure. 
     The suspension interconnects a vehicle axle  12  to the vehicle frame  10 . The axle  12  in the illustration is a driven axle and includes a gear housing  14  which connects to an output shaft of a transmission (not illustrated). The axle  12  also includes a spindle  16  for mounting a wheel or wheels to the axle. The gear arrangement in the gear housing  14  transmits driving force to the spindle to turn the wheels. 
     The suspension includes a control arm  20  extending between the vehicle frame  10  and the axle  12 . In the figures, the control arm  20  is formed by two, parallel beams  22 ,  24 . The embodiment of two parallel beams  22 ,  24  is preferred because it provides relatively light weight control arm with sufficient strength and vertical stiffness and provides a redundancy in the event one beam is disabled. The invention, however, contemplates a single beam forming the control arm  20 , and the following description should be understood in that context. The beams  22 ,  24 , are each shaped in a Y configuration, having a first end  30  with a single arm and a second end with two diverging arms, an upper arm  32  and a lower arm  34 . The terms “upper” and “lower” are relative to the orientation of the beams  22 ,  24  when mounted on a vehicle frame, as portrayed in the figures. Each beam  22 ,  24  is a substantially planar sheet or plate member and the outer edges  28  are bent or formed perpendicularly to form flanges for stiffening the beam. If weight is not an important consideration, the beam may be formed as a plate member of sufficient thickness to provide needed stiffness. Alternatively, the beam may be formed as a box member, having side walls and a perimeter wall enclosing a space. 
     The spacing between beam  22  and beam  24  forming the control arm  20  may be selected to provide a desired mechanical advantage in transferring force to the axle  12 . In addition, the depth of the outer edges  28  of the beams  22 ,  24  may be selected to provide a desired amount of lateral stiffness in the beams. 
     The first end  30  of the control arm  20  is mounted for vertical pivoting movement to a hanger bracket  40  that is attached to the vehicle frame. A hangar bushing arrangement  42  may be used. 
     According to the invention, the axle  12  is mounted to the control arm  20  between the divergent upper arm  32  and lower arm  34 . An upper bushing assembly  50 , shown in the perspective view in  FIG. 3 , connects the upper arms  32  of the control arm  20  to the axle  12 . 
     A lower bushing assembly  60 , shown in perspective view in  FIG. 4 , connects the lower arms  34  of the control arm  20  to the axle  12 . The upper bushing assembly  50  and lower bushing assembly  60  are connected to the axle and clamp the axle between them by U-bolts  44  (only one is visible in  FIG. 2 ). 
     The upper bushing assembly  50 , referring to  FIG. 3 , includes a plate  52  that engages the axle  12 , and has two shoulder and trough formations  54  formed in the plate to engage the U-bolt  44  for securing the upper bushing to the axle. Two bushing mounts  56  are formed in parallel and upstanding on the plate  52 . The bushing mounts  56  have holes  58  that are substantially parallel to the axle. The bushing mounts  56  carry a selected bushing (not illustrated) in the respective holes  58 . The upper arms  32  of the control arm  20  are mounted to the upper bushing assembly  50  by way of fasteners inserted through the bushings in the bushing mounts  56 . 
     In the illustrated embodiment, the beams  22 ,  24  are interconnected at the first end  30  of the control arm  20  and at the diverging upper arm  32  and lower arm  34 , but not therebetween. This provides a degree of lateral flexibility, as discussed below. 
     Turning to  FIG. 4 , the lower bushing assembly  60  includes a seat  62  to engage the bottom of the axle  12 . The seat  62  is between bars  64  having mounting holes which accept the U-bolt  44  for securing the lower bushing assembly  60  to the axle  12  as described above. The lower bushing assembly  60  also includes two bushing mounts  66  disposed below the seat  62 . The bushing mounts  66  are formed with holes parallel to the axle, as in the upper bushing assembly  50 , and carry a selected bushing (not shown). The lower arms  34  of the control arm  20  are mounted to the lower bushing assembly  60  by way of fasteners inserted through the bushings in the bushing mounts  66 . 
     According to the invention, bushings are preferably formed as cylindrical members of resilient material sized and shaped to fit the bushing mounts  56 ,  66 , and the material may be selected for rate or stiffness. Thus, the control arm  20  is attached to the axle with a selected amount of resilience. According to another aspect of the invention, the bushings in each of the bushing mounts  56 ,  66 , may be individually selected, allowing, for example, the upper bushing assembly  50  to have the same or a different bushing rate than the lower bushing assembly  60 , or allowing the two bushings in the each bushing assembly  50 ,  60  to have the same or different rates. Further, each bushing may have a variable rate to effect changes in the suspension characteristics, that is, a bushing may be made to have a different rate in one direction than in another. As shown in  FIG. 5 , one known variable rate bushing  80  employs voids  82  placed in the bushing in a selected portion or portions to soften that portion relative to the rest of the bushing. The voids  82  result in the bushing  80  being softer in a direction of the voids, in the figure along axis A. Alternatively,  FIG. 6  shows a cross section of a bushing  90  formed of different materials, a relatively stiffer material  92  and a relatively softer material  94 . The bushing  90  is relatively stiffer along the axis marked A than along the axis marked B. By selectively orienting a variable rate bushing  80 ,  90 , in the bushing mount  56 ,  66 , the directional rate of the bushing assembly may be tuned. Other arrangements are possible, for example, a bushing may be made with a stiffer material on one half and a softer material on the other half to provide different rates in opposite directions along the same axis. 
     Tuning the rate of the bushing assembly can affect the suspension characteristics. For example, making the two top bushings relatively stiffer in the fore/aft direction and relatively softer in the vertical direction and the bottom bushings relatively softer only in the fore aft direction and relatively stiffer in the vertical direction, which may be done with the variable bushings  80  or  90 , can improve roll steer, lateral stiffness, roll rate, toe stiffness and camber stiffness. 
     The spacing and location of the upper bushing mounts  56  and lower bushing mounts  66  on the respective bushing assembly may be selected to orient the axle at a particular angle to set the pinion angle. 
     Turning again to  FIG. 4 , the lower bushing assembly  60  includes a beam  70  extending from the seat  62  in a direction that, when mounted, is opposite the control arm  20 . The beam  70  includes mounting flanges  72  for a damper  74  (shown in  FIGS. 1 and 2 ), which connects between the beam and the vehicle frame. At the end of the beam  70  is a spring seat  76  to support a spring member, illustrated in  FIGS. 1 and 2  as an air spring  78 . As may be seen in  FIG. 1 , the air spring  78  is mounted between the beam  70  and the vehicle frame. 
     By constraining the axle between the upper arm  32  and lower arm  34  of the control arm  20 , any twist applied to the axle is applied about its axial center and an extra bending moment is not introduced during a roll event. By contrast, in conventional control arm suspensions, which connect to the axle on one side only (e.g., typically top or bottom), there is a bending introduced when the axle is twisted during a roll event. 
     The profile of the control arm  20  with its relatively deep vertical dimension (perpendicular to the axle axis) and relatively narrow lateral dimension (parallel to the axle axis) make it stiffer in the vertical direction than in the lateral direction. The vertical stiffness makes the control arm  20  effective in transferring load into the frame during a roll event. By being less stiff in the lateral direction, the control arm decreases the amount of preload going into the lateral torque rod. The lateral torque rod  80  may be attached between the torque rod bracket  18  seen in  FIG. 1  and the frame rail  11 . 
     The invention has been described in terms of preferred principles, embodiments, and components, however, those skilled in the art will understand that substitutions of equivalents may be made without departing from the scope of the invention as defined by the appended claims.