Abstract:
A pivot has a low friction rotational property by allowing the elastomeric bushing to rotate with respect to the inner metal. A low friction material can be incorporated between these two components to facilitate the rotation, if desired. The elastomeric bushing helps to isolate the pivot joint and prevent the transmission of vibrations. In one embodiment, the elastomeric bushing is also allowed to pivot about an axis generally perpendicular to its axis of rotation.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional application 60/268,336 filed Feb. 12, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to suspension pivot joints. More particularly, the present invention relates to an elastomeric bushing which allows articulation through flexing of the elastomeric material but also allows pivoting or rotation through sliding of the elastomeric material. 
     BACKGROUND OF THE INVENTION 
     Automobiles and other vehicles normally incorporate suspension systems designed to absorb road shock and other vibrations. Many vehicles are provided with independent suspensions located at each wheel. These suspensions are designed to independently minimize the effect of shock loading on each of the wheels. 
     Suspension systems commonly employ stabilizer bars which interconnect independent suspensions on opposite wheels, lower control arms, upper control arms or strut assemblies, steering linkage and steering knuckles which are typically interconnected to each other through pivot joints such as ball joint assemblies. 
     Conventional ball joint assemblies comprise a ball stud seated in a socket. In a suspension link, each end of the link incorporates a socket, and a ball is seated in each socket. The stud, which extends from the ball of the ball joint assembly, is connected to one of the wheel assembly components. Ball joint assemblies allow articulation of the joined suspension components in both an angular and rotational direction through sliding of the joint components. The articulation due to sliding of the joint components offers low-torque rotation, but these designs do not offer shock isolation, since all of the components are typically made from rigid materials such as metal and/or hard plastic. 
     Another design for the pivot joints is an elastomeric bushing. The elastomeric bushing can be mechanically bonded, it can be chemically bonded during molding or it can be chemically bonded after molding. The elastomeric bushing allows articulation of the suspension components in both an angular and rotational direction through flexing of the elastomeric material. Elastomeric bushings offer excellent shock isolation but they have limited rotational capability because they rely on the flexing of the elastomeric material during rotation. The flexing of the elastomeric material adds a considerate amount of parasitic torque to the pivoting of the suspension and thus leads to a degraded ride performance. In addition, the parasitic torque can complicate the initial assembly of the suspension system. 
     The continued design for pivot joints includes the development of joint assemblies that offer the advantage of shock isolation but also provide the advantage of low-torque rotation. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a pivot joint which offers the isolation characteristics of an elastomeric bushing as well as the free rotation (low-torque) properties of a ball joint assembly. The pivot joint of the present invention provides for high articulation for improved ride and when used as a suspension pivot it provides for free rotation which enables convenient vehicle assembly. The present invention provides these advantages in an efficient package that can also include captivation, sealing and compression rate tunability. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limited the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a side view of a typical MacPherson strut suspension system incorporating the unique pivot joint in accordance with the present invention; 
         FIG. 2  is a side view of a typical wishbone suspension system incorporating the unique pivot joint in accordance with the present invention; 
         FIG. 3  is a vertical cross-sectional view of the pivot joint shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a vertical cross-sectional view of a pivot joint incorporated into a sway bar link in accordance with another embodiment of the present invention; and 
         FIG. 5  is an enlarged view of the pivot joint illustrated in FIG.  4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     There is shown in  FIG. 1  a MacPherson strut suspension system which incorporates the unique pivot joint in accordance with the present invention and which is designated generally by the reference numeral  10 . MacPherson strut suspension system  10  comprises a steering knuckle  12 , a strut  14  having a shock absorber  16 , a lower control arm  18  and a pivot joint  20 . During suspension movements of suspension system  10 , lower control arm  18  pivots about an axis  22  and strut  14  pivots about a point  24  located along the axis of shock absorber  16 . The pivoting movement of lower control arm  18  causes pivot joint  20  to angulate or pivot with respect to a generally vertical axis to compensate for the angular differences between lower control arm  18  and steering knuckle  12 . During a steering maneuver of suspension system  10 , steering knuckle  12  rotates or pivots with respect to lower control arm  18 . The rotating or pivoting movement of steering knuckle  12  with respect to lower control arm  18  causes rotation of pivot joint  20  around the generally vertical axis to compensate for the rotating or pivoting of steering knuckle  12 . Thus, pivot joint  20  must accommodate both the angular movement with respect to the vertical axis as well as the rotational movement of steering knuckle  12  with respect to lower control arm  1 B.  FIG. 1  also illustrates a steering linkage  26  which incorporates a second pivot joint  20 . 
       FIG. 1  also illustrates pivot joint  20  being located at the two pivot points along axis  22  of lower control arm  18 . In this position, suspension movement of suspension system  10  causes rotation of lower control arm  18  and thus the rotation of pivot joints  20 . Any fore and aft impact loading, brake wading or the like to lower control arm  18  are resisted by the pivoting of pivot joints  20 . In the preferred embodiment, outer housing  54  is attached to lower control arm  18  and bolt  70  or its equivalent is secured to or is a part of a lower control rod (not shown) which extends along axis  22  between the two pivot joints  20 . Also, each pivot joint  20  can be secured to a separate portion of the vehicle by bolt  70 . 
     Referring now to  FIG. 2 , a wishbone suspension system  30  is illustrated. Wishbone suspension system  30  comprises a lower control arm  32 , an upper control arm  34 , a steering knuckle  36 , a spring assembly  38 , a shock absorber  40 , a lower pivot joint  20  and an upper pivot joint  20 . During suspension movements of suspension system  30 , lower control arm  32  pivots about an axis  42  and upper control arm  34  pivots about an axis  44 . The pivoting movement of lower control arm  32  causes lower pivot joint  20  to angulate or pivot with respect to a generally vertical axis to compensate for the angular differences between lower control arm  32  and steering knuckle  36 . In a similar manner, the pivoting movement of upper control arm  34  causes upper pivot joint  20  to angulate or pivot with respect to the generally vertical axis to compensate for the angular differences between upper control arm  34  and steering knuckle  36 . During a steering maneuver of suspension system  30 , steering knuckle  12  rotates or pivots with respect to lower control arm  32  and also rotates or pivots with respect to upper control arm  34 . The rotating or pivoting movement of steering knuckle  36  with respect to lower control arm  32  causes rotation of lower pivot joint  20  around the generally vertical axis to compensate for the rotating or pivoting of steering knuckle  36 . In a similar manner, the rotating or pivoting movement of steering knuckle  36  with respect to upper control arm  34  causes rotation of upper pivot joint  20  around the generally vertical axis to compensate for the rotating or pivoting of steering knuckle  36 . Thus, both lower pivot joint  20  and upper pivot joint  20  must accommodate both the angular movement with respect to the vehicle axis as well as the rotational movement around the vertical axis of steering knuckle  36  with respect to lower control arm  32  and upper control arm  34 , respectively.  FIG. 2  also illustrates steering linkage  26  which incorporates another pivot joint  20 . 
       FIG. 2  also illustrates pivot joint  20  being located at the two pivot points along axis  42  of lower control arm  32  and being located at the two pivot points along axis  44  of upper control arm  34 . In these positions, suspension movement of suspension  30  causes rotation of both lower control arm  32  and upper control arm  34  and thus the rotation of pivot joints  20 . Any fore and aft impact loading, brake loading or the like to lower control arm  32  and/or upper control arm  34  are resisted by the pivoting of pivot joints  20 . In the preferred embodiment, outer housing  54  is attached to lower control arm  32  or upper control arm  34  and bolt  70  or its equivalent is secured to or is a part of a lower or upper control rod (not shown) which extends along axis  42  or  44 , respectively, between the two pivot joints  20 . Also, each pivot joint  20  can be secured to a separate portion of the vehicle by bolt  70 . 
     Referring now to  FIG. 3 , pivot joint  20  is illustrated in greater detail. Pivot joint  20  is shown in  FIG. 1  as a lower pivot joint, as a steering pivot joint and as a control arm pivot joint; and in  FIG. 2  as a lower and an upper pivot joint, as a steering pivot joint and as a control arm pivot joint. It is within the scope of the present invention to utilize pivot joint  20  in these applications or in other applications requiring the angulation and/or rotation of pivot joint  20 . 
     Referring now to  FIG. 3 , pivot joint  20  comprises an inner rigid housing  50 , a Self-Lubricating Elastomer (SLE™) sleeve  52  and an outer rigid cup-shaped housing  54 . Inner housing  50  is a generally cylindrical housing defining an annular groove  56 . Sleeve  52  is an annular sleeve disposed around inner housing  50  and it defines an annular rib  58  disposed within groove  56 . Outer housing  54  is generally cup-shaped cylindrical housing disposed around sleeve  52  and inner housing  50 . 
     Sleeve  52  extends below a lower surface  60  of inner housing  50  and below a fully open end of outer housing  54  defined by an outward radial flange  62  of outer housing  54 . Inner housing  50  defines a central bore  64 , sleeve  52  defines a central aperture  66  and outer housing  54  defines an aperture  68  at a closed end of outer housing  54 . Bore  64  and apertures  66  and  68  accommodate a bolt  70  which secures pivot joint  20  to the appropriate suspension component. The portion of sleeve  52  which extends beyond lower surface  60  will be compressed to provide a seal for pivot joint  20 . After bolt  70  is tightened, a plastic cap  72  is fit within aperture  68  to also provide a seal for pivot joint  20 . Outer housing  54  is secured to the appropriate suspension component by being press fit within an aperture or by other means known in the art. In the preferred embodiment, bolt  70  is secured to knuckle  12  or  36  or to the appropriate control rod and outer housing  54  is secured to control arm  18 ,  32  or  34 . 
     Inner member  50  is coated with a low friction material  80  such as, but not limited to, PTFE. Sleeve  52  is bonded, by means known in the art, to outer housing  54 . The components can be designed to be self-captivating through mechanical interlock, if desired. In addition, the components, as is shown in  FIG. 3 , can be designed to be self-sealing against outside contaminants. The spring rate in both the radial and the axial direction can be controlled by the design for sleeve  52 . Pivot joint  20 , shown in  FIG. 3 , provides captivation, sealing and radial/axial tuning. 
     During operation, pivot joint  20  offers shock isolation due to the elastomeric properties of sleeve  52 . Sleeve  52  is also free to rotate about inner housing  50  with minimal windup and therefore low torque. The low-torque rotation is accomplished through the sliding of sleeve  52  on low friction material  80  located on inner member  50  while the outer surface of sleeve  52  is bonded to outer housing  54 . 
     While  FIG. 3  illustrates one design for pivot  20 , pivot  20  could utilize different shapes of inner housing  50 , sleeve  52  and outer housing  54  to adjust package size, load capacity, captivation, spring rates and sealing properties based on application requirements. In addition, coatings or greases different than coating  80  could be used to reduce friction. Finally, other materials for sleeve  52  can be used as long as proper sliding can be achieved between sleeve  52  and inner housing  50 . 
     Referring now to  FIG. 4 , a sway bar link  110  is illustrated having a pivot joint  120  in accordance with another embodiment of the present invention. Sway bar link  110  comprises a longitudinally extending link  112 , an elastomeric joint  114  and pivot joint  120 . Link  112  is a formed metal or composite member which defines a first bushing bore  116  and a second bushing bore  118 . 
     Elastomeric joint  114  comprises an inner tubular member  112 , an annular elastomeric member  124  and a cylindrical outer member  126 . Inner tubular member  122  extends through cylindrical outer member  126  with annular elastomeric member  14  being disposed between them. Typically, annular elastomeric member  124  is bonded to both inner tubular member  122  and cylindrical outer member  126 . Cylindrical outer member  126  is press fit or otherwise secure within first bushing bore  116 . A bolt (not shown) similar to bolt  70  described above, extend through inner tubular member  122  to secure sway bar link  110  to the vehicle and/or the vehicle&#39;s suspension system. 
     Referring now to  FIGS. 4 and 5 , pivot joint  120  comprises an inner tubular member  132 , an annular elastomeric member  134  and an outer generally cylindrical member  136 . Inner tubular member  132  defines a through bore  138  and a generally spherical or contoured outer surface  140 . Through bore  138  accommodates a bolt (not shown) similar to bolt  70  described above, to attach say bar link  110  to the vehicle and/or the vehicle&#39;s suspension system. The outer surface of inner tubular member  132  can be coated with a low friction material  80  as detailed above for inner member  50 , if desired. Annular elastomeric member  134  defines a generally spherical or contoured inner surface  142  which mates with spherical or contoured outer surface  140  of inner tubular member  132 . A generally cylindrical extension  144  extends from each end of elastomeric member  134  as shown in  FIGS. 5 and 6 . Inner tubular member  132  is designed to rotate and pivot within annular elastomeric member  134 . This movement is facilitated by the materials used to manufacture these components or by the addition of a lubricant such as, but not limited to, low friction material  80 . Annular elastomeric member  134  is disposed within and bonded to outer generally cylindrical member  136 . While being described as being bonded to outer member  136 , it is within the scope of the present invention to utilize the compression of annular elastomeric member  134  to create the necessary retention of annular elastomeric member  134  by outer generally cylindrical member  136 . Outer generally cylindrical member  136  is press fit or otherwise secured within second bushing bore  118 . 
     During operation, pivot joint  120  offers shock isolation due to the elastomeric properties of annular elastomeric member  134 . Inner tubular member is free to rotate about annular elastomeric member  134  and outer generally cylindrical member  136  about a first axis  150  with minimal wind-up and therefore low torque. The low torque rotation is accomplished through the sliding of outer surface  140  on inner surface  142  with or without lubrication and/or low friction material  80  while the outer surface of annular member  134  is secured to outer member  136 . In a similar manner, low torque pivoting is accomplished through the sliding of outer surface  140  on inner surface  142  with or without lubrication and/or low friction material  80  around a second axis  152  generally perpendicular to first axis  150 . Circular extensions  144  of annular elastomeric member  134  cushion the interface between inner tubular member  132  and outer generally cylindrical member  136 . 
     Pivot joint  120  can be a direct replacement for pivot joint  20  illustrated at various positions in  FIGS. 1 and 2 . 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.