Patent Abstract:
A self-steering axle suspension system utilizing a rotary damper coaxially aligned with and acting directly about the king pin centerline on one side of the vehicle is disclosed. When used as such, the rotary damper constitutes a rotary stabilizer. The rotary stabilizer is used to control the steerability of the self-steering axle suspension system and has a self-centering axle mechanism incorporated therein.

Full Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to stabilizers used in self-steering axle suspension systems for wheeled vehicles. More particularly, the present invention relates to a rotary damper used as a stabilizer in self-steering axle suspension systems for wheeled vehicles to suppress oscillations during travel of the vehicle and to control the steerability of the self-steering axle suspension system. 
   Self-steering axle suspension systems in the medium and heavy duty truck and semi-trailer industry are known. Typically, such suspensions are made self-steering by adjusting the pitch or caster angle of the wheels so that the drag of the wheels as the vehicle proceeds in the forward direction causes the suspension (including the wheels of the system) to steer automatically in response to steering of the (typically front) steering axle of the vehicle and in response to steering created by other vehicle motion such as vehicle cornering (i.e., as the vehicle goes into a turn). Typical of self-steering axle suspension systems are those referred to as pusher, tag or trailing axles found on trucks and semi-trailers. They may be of the liftable or non-liftable type. 
   In most self-steering axle suspensions in common use, a pair of dampers is used to suppress (dampen) oscillations during automatic steering at the self-steering axle resulting from travel of the vehicle. Typically, such dampers are in the form of conventional shock absorbers either with, or without, an external auxiliary coil spring. Such devices are often referred to as stabilizers for the self-steering axle suspension systems and they control the steerability of the suspension. In such a damper, a cylinder is provided which houses a fluid reservoir that is almost completely filled with an incompressible hydraulic fluid. This cylinder is separated into two chambers by a piston having an orifice, or orifices, in its head, thus to form a flow path between the two chambers, but which otherwise seals the two chambers against fluid flow therebetween. Dampening is accomplished by attaching one end of the stabilizer (usually by a piston rod connected to the piston head) to one of the components of the steering assembly of the suspension and the other end of the stabilizer to the axle beam structure of the suspension or vehicle. Since the orifice(s) in the piston head restricts flow between the two chambers as the piston slides in the cylinder due to oscillations experienced during vehicle operation (e.g. road shocks and wheel shimmy), such oscillations are appropriately dampened and tracking is stabilized. 
     FIG. 1  illustrates a conventional self-steering axle suspension system generally designated by reference numeral  10 . Conventional self-steering axle suspension system  10  includes linear stabilizers generally designated  12 ,  14 . Stabilizers  12 ,  14  are in the form of a pair of laterally extending shock absorbers  16 ,  18  having auxiliary coil springs  20 ,  22 . Stabilizers  12 ,  14  are each mounted, at one end, to a bracket, which in turn, is mounted to a laterally extending axle beam and, at another end, to a steering assembly component such as the steering arm of the steering knuckle (as shown). Stabilizers  12 ,  14  supress steering oscillations during road travel of the vehicle and control the steerability of the self-steering axle suspension system  10 . The coil springs  20 ,  22  provide a self-centering feature in known manner. Stabilizers  12 ,  14  are positioned in opposite orientations such that they are mirrored about the vehicle centerline in order to control the steering action and self-centering in both directions for the vehicle. 
   Linear stabilizers, such as those illustrated in  FIG. 1  as reference numerals  12 ,  14  are relatively heavy, expensive, bulky and require high maintenance. With regard to the latter drawback, linear stabilizers are subject to damage due to road debris and the like. For this reason, enclosed housing designs have been implemented; however, such designs have only reduced but have not eliminated the maintenance required for linear stabilizers. In addition, maintenance operations, especially out in the field, are cumbersome and correspondingly difficult and time consuming. 
   In view of the foregoing, there is a need for a relatively lightweight self-steering axle suspension system stabilizer. There is also a need for a relatively inexpensive self-steering axle suspension system stabilizer. Further, there is a need for a relatively compact self-steering axle suspension system stabilizer. Moreover, there is a need for a self-steering axle suspension system stabilizer that requires little maintenance and is relatively easy to maintain. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to a self-steering axle suspension system utilizing a rotary damper acting directly about the king pin centerline on one side of the vehicle in a manner such that the rotary damper constitutes a rotary stabilizer. The rotary stabilizer is coaxially aligned with the king pin centerline. The rotary stabilizer is used to control the steerability of the self-steering axle suspension system. The rotary stabilizer may also have a self-centering axle mechanism incorporated therein. The present invention is also directed to a rotary stabilizer component used in a self-steering axle suspension system. 
   A rotary stabilizer designed in accordance with the principles of the present invention and used in a self-steering axle suspension system is preferably relatively lightweight, translating into increased payload capacity and more readily permitting compliance with relevant bridge weight and stress laws and regulations. The stabilizer is preferably relatively inexpensive, having fewer components than conventional stabilizers used in self-steering axle suspension systems. In addition, only a single stabilizer is required for control of the steerability of the suspension system in both steering directions. The stabilizer is preferably compact, fitting tight in relation to the axle or axle beam and acting directly about the king pin centerline. The stabilizer is preferably relatively low maintenance insofar as it includes a fully-enclosed housing and it is mounted above the axle in a position where it is less likely to be subjected to road debris and the like. Maintenance of the stabilizer is also relatively easy, as it is positioned above the king pin centerline in coaxial relationship therewith and is positioned above the axle or axle beam, permitting its relatively simple installation, removal and replacement. The stabilizer preferably includes material that resists velocity motion and the accompanying oscillations that would otherwise occur during road travel of the vehicle. The stabilizer also preferably includes material that provides for self-centering of the self-steering axle suspension system. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     Reference has been and will frequently be made to the following figures, in which like reference numerals refer to like components, and in which: 
       FIG. 1  is a perspective view of a self-steering axle suspension system using conventional linear stabilizers; 
       FIG. 2A  is an elevational view of a self-steering liftable axle suspension system shown in its ground engaging position; 
       FIG. 2B  is an elevational view of the same self-steering liftable axle suspension system shown in its lifted position; 
       FIG. 3  is a perspective view of the self-steering liftable axle suspension system shown in  FIGS. 2A and 2B  and shown as being designed in accordance with the principles of the present invention; 
       FIG. 4  is a perspective view of a rotary stabilizer designed in accordance with the principles of the present invention and being designed for use in a self-steering axle suspension system; 
       FIG. 5  is another perspective view of the rotary stabilizer shown in  FIG. 4  being partially cut away to illustrate internal features thereof; 
       FIG. 6  is a perspective view of a portion of the self-steering axle suspension system shown in  FIG. 2 ; 
       FIG. 7  is another perspective view of the portion of self-steering axle suspension system shown in  FIG. 6 ; 
       FIG. 8  is a perspective view of a portion of a self-steering axle suspension system having another embodiment of a rotary stabilizer designed in accordance with the principles of the present invention; 
       FIG. 9  is sectional view of the portion of the self-steering axle suspension system shown in  FIG. 8  taken along line  9 - 9  thereof; 
       FIG. 10  is perspective view of the rotary stabilizer shown in  FIG. 8 ; 
       FIG. 11  is a top plan view of the rotary stabilizer shown in  FIG. 8 ; 
       FIG. 12  is an elevational view of the rotary stabilizer shown in  FIG. 8 ; and 
       FIG. 13  is a horizontal sectional view of the rotary stabilizer shown in  FIG. 8  showing the interior of the housing thereof. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 2A ,  2 B and  3  illustrate a self-steering axle suspension system generally indicated by reference numeral  30 . The illustrated self-steering axle suspension system  30  is a self-steering auxiliary lift-axle type of suspension system having a parallelogram, trailing arm geometry. The axle suspension system  30  is preferably a relatively lightweight suspension designed to permit compliance with any applicable bridge weight and stress regulations, such as the Federal Bridge Formula associated with relevant laws and regulations applicable within the United States of America. 
   While suspension system  30  is described as having these additional features, it will be appreciated that the present invention applies to all self-steering axle suspension systems for wheeled vehicles. 
   The suspension  30  illustrated in the figures is representative of an embodiment of the steerable, wheel-bearing lift axle suspension systems disclosed in U.S. Pat. No. 5,403,031 and U.S. Pat. No. 5,620,194. The entire disclosure of U.S. Pat. No. 5,403,031 and the entire disclosure of U.S. Pat. No. 5,620,194 are hereby incorporated herein by reference. 
   With respect to suspension system  30 , the majority of the components positioned on one side of the vehicle will have correspondingly similar components positioned on the other side. Accordingly, in this description, when reference is made to a particular suspension component, it will be understood that a similar component is present on the opposite side of the vehicle, unless otherwise apparent. It will be appreciated that like elements are duplicated on opposite sides of the vehicle centerline. 
   As shown, suspension system  30  includes a pair of longitudinally extending parallel beams  34 ,  36  on each side of the vehicle, preferably constructed as cast aluminum beams. Beams  34 ,  36  are pivotally connected at their forward ends in known manner by pivots  38 ,  40  to a side rail frame hanger bracket  42  which, in turn, is fastened to a longitudinal frame member  44  for the vehicle. Frame member  44  extends longitudinally and preferably has a C-shaped cross-section in conventional manner. 
   Parallel beams  34 ,  36  are also pivotally connected at their rearward ends to an axle seat  46  by pivots  48 ,  50 . Pivot  48  preferably includes an eccentric cam  52  designed to permit adjustment of the caster angle, permitting self-steering operation of the suspension system. Adjustment of the caster angle is made by turning eccentric cam  52  the requisite amount. The adjustable caster angle is typically oriented within the range of about positive three degrees to positive six degrees from the king pin centerline. 
   Axle seat  46  is mounted onto a laterally extending fabricated axle  54  having a hollow axle body  56  and gooseneck portions  58  on each end of the axle body (see  FIG. 3 ). An inline lift air spring  60  is mounted to beams  34 ,  36  through brackets  62 ,  64 , which in turn are fastened to beams  34 ,  36 . A vertical ride air spring  66  is mounted on axle seat  46  and connected to frame member  44  through upper air spring bracket  68 . 
   Steering knuckles  70  are rotatably mounted on opposite ends of the axle  54  by king pin assemblies (not shown) in known manner. King pins are used to mount the steering knuckles to the axle at  71 , as shown in  FIG. 3 . Each steering knuckle  70  includes a steering arm  72 , and a laterally extending tie rod  74  links the steering arms  72  of the steering knuckles  70  mounted on opposite sides of the vehicle. 
   Referring to  FIGS. 3 and 6 , at least one of the steering knuckles  70  includes an upper plate  76  for mounting a rotary stabilizer  78  used to control the steerability of the suspension system. The rotary stabilizer  78  is preferably mounted on the upper plate  76  of the steering knuckle  70  by bolts or similar fasteners. The stabilizer  78  includes a central shaft  80  that preferably is coaxially aligned with the king pin used for mounting its adjacent steering knuckle  70  to that end of the axle  54 . The shaft  80  is fixedly connected to the axle  54 , preferably by a bracket  82  secured thereto and preferably secured to the gooseneck portion  58  of the axle  54 . 
   When one rotary stabilizer  78  is used (as shown), total weight and cost are minimized. When a rotary stabilizer is mounted on each side of the axle beam, size per stabilizer is minimized, translating into better packaging. 
     FIG. 2A  illustrates suspension  30  in its lowered or ground-engaging position, as opposed to its lifted or raised position, which is illustrated in  FIG. 2B . Raising and lowering of suspension  30  is accomplished by the expansion and contraction of the inline lift air springs  60  and the vertical ride air spring  66 . By expanding the vertical air spring  66  and exhausting the inline air springs  60 , the wheels are lowered into engagement with the ground surface, which is shown in  FIG. 2A . By expanding inline air springs  60  and exhausting vertical air spring  66 , the wheels are lifted from engagement with the road surface, which is shown in  FIG. 2B . The control of fluid in the air springs  60 ,  66  for accomplishing the lifting and lowering of the wheels is conventional and well known in the art. 
   Referring to  FIG. 4 , rotary stabilizer  78  includes a mounting base  84  having a generally planar construction. Mounting base  84  preferably has a generally round shape with the addition of ear-like protrusions  86  spaced approximately ninety degrees from adjacent protrusions  86 . A mounting bore  88  is preferably machined within each protrusion  86  to permit the rotary stabilizer  78  to be mounted to the upper plate  76  of the steering knuckle  70  by appropriate fasteners (see  FIG. 3 ). 
   The rotary stabilizer  78  includes a housing  90 . Shaft  80  is positioned within housing  90  and extends axially in relation thereto. A portion of shaft  80  extends axially out of housing  90  and is exposed from the housing, as shown. The housing is generally cylindrical and preferably forms a unitary construction with mounting base  84  of stabilizer  78 . The mounting base  84  and the housing  90  are together rotatably maneuverable about the shaft  80 , as further described. 
   Referring to  FIG. 5 , as shown, the housing  90  of the rotary stabilizer  78  is partitioned into two or more fixed volume chambers  92 A,  92 B sized to accommodate the wheel cut specifications for the self-steering axle suspension system  30  in both directions. The wheel cut specification for the self-steering axle suspension system  30  illustrated in  FIG. 3  is twenty-eight degrees. Under such circumstances, the chambers  92 A,  92 B illustrated in  FIG. 5  preferably are sized to include an arc angle of about sixty degrees. Chamber  92 A serves as a fluid reservoir for viscous material such as an incompressible hydraulic fluid, and its boundaries are defined by radially extending walls within housing  90  and the top and bottom walls of the housing. It will be appreciated that the top surface of the mounting base  84  for the stabilizer  78  may serve as the bottom wall of the housing  90  for this purpose. 
   As further shown, panes  96 A,  96 B are preferably associated with chambers  92 A,  92 B, respectively, and partition each such chamber into two variable volume sub-chambers. The sum of the variable volume sub-chambers for a particular chamber  92 A,  92 B is equal to the total volume of the chamber. 
   Each pane  96 A,  96 B preferably projects radially from the shaft  80  and preferably bisects the arc angle for its associated chamber  92 A,  92 B when the suspension system is in its resting (centered) position. The panes  96 A,  96 B may be formed with the shaft  80  as a unitary component, or alternatively may be secured to the shaft  80  by appropriate means. Pane  96 A includes orifices  100  to provide for a fluid flow path during steering of the suspension system  30 , which controls the steerability of the suspension system. Pane  96 B may or may not include orifices, as desired. 
   As further shown, rotary stabilizer  78  also preferably includes resilient members  102  used for self-centering. Resilient members  102  may be formed with an elastomer-type material. For illustrative purposes, resilient members  102  are shown as being rubber cushion inserts having orifices or holes to permit their expansion and compression. However, it will be appreciated that the resilient members may take a variety of forms, such as, for example, air bladders, coil springs, etc. In the illustrative embodiment, the rubber cushion inserts  102  are positioned under compression within chamber  92 B on opposite sides of pane  96 B. 
   Referring now to  FIGS. 6 and 7 , as shown, the mounting base  84  and housing  90  of the rotary stabilizer  78  are fixedly mounted to the steering knuckle  70 , specifically to the upper plate  76  thereof. In addition, the shaft  80  of the rotary stabilizer  78  is fixedly mounted to the axle  54  through its bracket  82  (shown as being fastened to the gooseneck portion  58  of the axle  54 ) and is aligned with the king pin along its centerline. 
   In operation, when the vehicle corners, a force is imparted upon the self-steering axle suspension system  30 , causing the suspension system to steer in the appropriate direction. At this time, the steering knuckles  70  rotate about their respective king pins. At least one of the linked steering knuckles  70  carries the mounting base  84  and the housing  90  of the rotary stabilizer  78 . As the housing  90  of the stabilizer  78  rotates about its shaft  80 , the volumes of the variable volume sub-chambers within fluid reservoir chamber  96 A vary in accordance with the steering direction and cause the viscous fluid to flow through the orifices  100  of the radially extending pane  96 A, which, with shaft  80  and pane  96 B, remains stationary relative to the axle. In addition, during such steering action, one of the rubber cushion inserts  102  is also further compressed when its associated radially extending wall defining one of the boundaries of chamber  92 B rotates with the housing towards the pane such that the wall presses against the insert. When this happens, the insert  102  is further compressed between that wall and pane  96 B and its resilient nature tends to prevent further compression. As a result, there is additional control of the steerability of the system  30  by limiting free movement of the steering knuckles. 
   Upon straightening of the vehicle, however, the steering force imparted on the self-steering axle suspension system  30  is reduced to such an extent that the spring back force imparted on pane  96 B by the force differential between the overly compressed rubber cushion insert  102  and the expanded (less compressed) rubber cushion insert  102  on the opposite side of pane  96 B will overcome such steering force and cause the rotary stabilizer  78  to return to its resting (centered) position in a controlled manner due to the viscous fluid return flow through the orifices  100  of pane  96 A. 
   It will be appreciated by those skilled in the art that the self-steering and self-centering of the rotary stabilizer used in the above illustrated embodiment of the present invention may be tuned by varying, for example, the size of the stabilizer, the size of the chambers, the number of pane orifices, the size of the pane orifices, the material and configuration of the resilient members, and the composition of the viscous material. 
     FIGS. 8-13  illustrate an alternative embodiment of a rotary stabilizer identified generally by reference numeral  110  shown mounted on the upper plate of a steering knuckle used in association with a self-steering axle suspension system. Rotary stabilizer  110  includes an outer housing element  112 , an inner housing element  114  and a central shaft  116 . The central shaft  116  is preferably keyed to the inner housing element  114 . Central shaft  116  may be used as a king pin, as shown. The outer housing element  112  may include protrusions  118  (one of which is shown in  FIG. 8 ). Each protrusion  118  may have a mounting bore  120  machined through it to permit mounting of rotary stabilizer  110  to an upper plate member of a steering knuckle, as shown. Viscous material  115  is contained in the space within outers housing element  112  and inner housing element  114 . In preferred embodiments, the viscous material surrounds a rotor element extending radially from inner housing element. 
   In operation, when the vehicle corners, a force is imparted upon the self-steering axle suspension system, causing the suspension system to steer in the appropriate direction. At this time, the steering knuckles mounted on opposite ends of the axle rotate about their respective king pins, which in this preferred illustrated case at least one of which may be the central shaft  116 , as shown. At least one of the linked steering knuckles carries the outer housing element  112  of the rotary stabilizer  110 . As the outer housing element  112  rotates in relation to the inner housing element  114  and the keyed shaft  114 , the viscous material  115  acts in shear to provide resistance to the rotary motion of the steering knuckle resulting in smooth motion and controlled steering of the self-steering axle suspension system. 
   Alternatively, any of several self-steering mechanisms may be used to cause the rotary stabilizer  110  to return to its resting (centered) position in a controlled manner, as desired. As one example, when the steering knuckle rotates about the king pin/central shaft, it may bear against a leaf spring having sufficient force to cause the steering knuckle to return to the resting position upon straightening of the vehicle. 
   It will be appreciated by those skilled in the art that while this invention has been described with reference to certain illustrative embodiments, it will be understood that this description shall not be construed in a limiting sense. Rather, various changes and modifications can be made to the described embodiments without departing from the true spirit and scope of the invention, as defined by the following claims. Furthermore, it will be appreciated that any such changes and modifications will be recognized by those skilled in the art as an equivalent to one or more elements of the following claims, and shall be covered by such claims to the fullest extent permitted by law.

Technology Classification (CPC): 1