Patent Publication Number: US-2010124455-A1

Title: Revolute joint with integrated radial compliance

Description:
TECHNICAL FIELD 
     This disclosure relates to pivot joints for connecting linkages. 
     BACKGROUND OF THE INVENTION 
     Steering systems utilize revolute joints to convert the rotational motion of the steering wheel (directly or indirectly communicated to the revolute joint) into the linear motion needed to turn the wheels. In the case of recirculating ball steering systems, rotation of a pitman arm is converted into generally linear movement of a track rod or relay bar, which is coupled to the wheels to turn the vehicle. 
     Revolute joints transfer loads from one relatively rigid component to another relatively rigid component while allowing relative rotation or revolution between the two components. Relative to the central axis of the revolute joint, there are four possible types of movement: revolution, radial displacement, axial displacement, and angulation. 
     SUMMARY 
     A pivot joint assembly is provided, including a housing having a bore therethrough and a central axis coaxial with the bore. A stud is disposed coaxially with the central axis of the bore, and has a bearing surface. A resilient member is disposed between the housing and the stud, and is biased against the housing to accommodate radial loads transferred between the stud and the housing. An inner metal ring is disposed between the resilient member and the bearing surface. The inner metal ring substantially surrounds the bearing surface and is sized for a sliding fit between the bearing surface and an interface surface of the inner metal ring. The stud is configured to pivot about the central axis by a range of at least 40 degrees relative to the housing. 
     One embodiment of the pivot joint assembly further includes one or more sealing elements configured to seal the bearing surface and the interface surface against the passage of foreign material or lubricant. Another embodiment of the pivot joint assembly further includes an axial restraint element configured to prevent axial separation of the stud from the housing. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes and other embodiments for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, isometric view of a recirculating ball steering mechanism having a pivot joint assembly; 
         FIG. 2  is a schematic, partial cross-sectional view of the pivot joint assembly shown in  FIG. 1 ; 
         FIG. 3  is a schematic, cross-sectional view of a second embodiment of a pivot joint assembly having an angled, two-piece resilient member; 
         FIG. 4  is a schematic, cross-sectional view of a third embodiment of a pivot joint assembly having an annular ridge axial restraint and an axial cap; 
         FIG. 5  is a schematic, partial cross-sectional view of a fourth embodiment of a pivot joint assembly having a two-piece inner metal ring and a lubricant nozzle; and 
         FIG. 6  is a schematic, partial cross-sectional view of a fifth embodiment of a pivot joint assembly having a sealing element formed as an integral part of the resilient member. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, there is shown in  FIG. 1  steering mechanism  10 , which may be included in a recirculating ball steering system. The steering mechanism  10  includes a pitman arm  12  and a relay rod  14 . As pitman arm  12  is rotated by a sector gear (not shown) mated to a splined portion  16 , rotation of the pitman arm  12  is transferred as lateral motion to the relay rod  14 . 
     While the present invention is described in detail with respect to automotive applications, those skilled in the art will recognize the broader applicability of the invention. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims. 
     Motion is transferred between the pitman arm  12  and relay rod  14  through a pivot joint assembly  20 . A pin or stud  22  extends between the relay rod  14  and the pitman arm  12 . In the embodiment shown, upper and lower nuts  18  hold the components together. Opposite the splined portion  16  of the pitman arm  12  is a housing  24  which surrounds or substantially surrounds a portion of the stud  22  (the upper portion, as viewed in the figures). 
     As described herein, the pivot joint assembly  20 —and other embodiments of pivot joint assemblies described below—is capable of translating the rotation of the pitman arm  12  into substantially lateral motion of the relay rod  14 . The pivot joint assembly  20  allows rotation of the stud  22  relative to the pitman arm  12  and the housing  24 . Vibrations and road excitations may be transferred from the vehicle&#39;s wheels into the relay rod  14 , causing relay rod  14  to twist or push against the pivot joint assembly  20 . The pivot joint assembly  20  is configured to accommodate some or all of the torque and force created by such relative movement between the relay bar  14  and the pitman arm  12 . 
     Referring now to FIG.  2 —and with continued reference to FIG.  1 —there is shown in  FIG. 2  a close up view of the steering mechanism  10  shown in  FIG. 1 , showing a partial cross section of the pivot joint assembly  20 . The housing  24  has a generally cylindrical bore  26  running therethrough and a central axis  27  coaxial with the bore  26 . As shown and described below in relation to  FIG. 3  (and also in relation to the other embodiments), the bore  26  need not be continuous and may have multiple, offset, or angled portions. 
     Stud  22  has a bearing surface  28  disposed substantially within bore  26  and oriented to be substantially coaxial with the central axis  27 . In the embodiment shown in  FIG. 2 , the bearing surface  28  is substantially cylindrical. The pivot joint assembly  20  further includes a resilient member or bushing  30  disposed between the bore  26  and the bearing surface  28 . Bushing  30  may be a rubber bushing or formed of other material known to those having ordinary skill in the art as being compatible with greases which may be used in the pivot joint assembly  20 . 
     In operation of steering system  10 , the bushing  30  is biased against the housing  24  to accommodate radial loads between the stud  22  and the housing  24 . As used herein, radial refers to displacement or loads generally perpendicular to the central axis  27 . Radial displacement or loads may also be referred to as lateral movement or loads. 
     Additional degrees of freedom of relative movement between the stud  22  and the housing  24  are: axial, which occurs along the central axis  27  (up and down, as viewed in  FIG. 2 ); rotation, revolution or pivoting about the central axis  27 ; and angulation, which occurs as the stud  22  and central axis  27  rock or wobble. Angulation is demonstrated by, for example, the top of stud  22  moving to the right (as shown in  FIG. 2 ) while the bottom of stud  22  stays fixed or moves to the left. 
     An inner metal ring  32  may be disposed between the bushing  30  and bearing surface  28 . The inner metal ring  32  substantially surrounds the bearing surface  28 , and is sized for a sliding fit between an interface surface  34  of the inner metal ring  32  and the bearing surface  28 . The interface surface  34  and bearing surface  28  act similar to a journal bearing to allow rotation of the stud  22  about the central axis  27  relative to the housing  24 . 
     To limit the intrusion of dust, dirt, water, or other foreign material into the gap between the interface surface  34  and the bearing surface  28 , the pivot joint assembly  20  may be equipped with a sealing structure. The pivot joint assembly  20  shown in  FIGS. 1 and 2  includes a thrust bearing  38 , which may also be configured to prevent the ingress of foreign material into, and the egress of lubricant from, the interface surface  34  and bearing surface  28 . 
     As shown in  FIG. 2 , the pivot joint assembly  20  includes an outer can  36  disposed substantially between the bushing  30  and the bore  26 . The outer can  36  may compress the bushing  30  against the inner metal ring  32 , and may assist in assembly of the pivot joint assembly  20 . 
     The stud  22  is configured to pivot about the central axis  27  by a range of at least 40 degrees relative to the housing  24 . For example, without limitation, if the pitman arm  12  has a zero or starting location in the steering mechanism  10 —such as the position corresponding to the non-turning center location of the steering wheel—the pitman arm  12  may rotate away from that center position through a range of at least 20 degrees in either direction of rotation (a total range of 40 degrees) about the central axis  27 . 
     Some embodiments of the pivot joint assembly  20  may be further configured for rotation through a broader range of at least 80 degrees. Although unlikely to occur in embodiments of the pivot joint assembly  20  used within steering systems, the pivot joint assembly  20  may be configured to allow for complete rotation through a range of 360 degrees. 
     In addition to the rotational compliance provided by the interface surface  34  and the bearing surface  28 , the pivot joint assembly  20  is further configured to provide radial compliance between the stud  22  and housing  24 . Radial compliance is the ability of the pivot joint assembly  20  to accommodate relative radial displacement between the stud  22  (which is transferred from the relay rod  14 ) and the housing  34 . This may occur when the relay rod  14  moves quickly in the direction opposite the turning motion of the pitman arm  12 . 
     Bushing  30  is configured to provide radial compliance in a range of approximately 750-2500 newtons per millimeter (N/mm) of radial displacement between the stud  22  and the housing  24 . Some embodiments of the pivot joint assembly  20  may be configured to provide radial compliance in a range of approximately 1200-2000 (N/mm). Additionally, the bushing  30  is configured to provide angulate compliance between the stud  22  and housing  24 . 
     Radial (lateral) compliance may be beneficial for tuning the feel, handling, and response characteristics of the steering mechanism  10 . Changes in radial compliance alter the way the steering mechanism  10  (and associated elements of the vehicle&#39;s steering system) responds to lateral loads. Handling characteristics are affected by radial compliance as a result of increases or decreases in the amount of lateral loading transferred through relay rod  14  to the pitman arm  12 , and compliance therefore also alters the amount of steering response transferred from steerable wheels to the driver (usually felt at the steering wheel). 
     Referring now to  FIG. 3 , there is shown a cross-sectional view of another embodiment of a steering mechanism  110 . A pitman arm  112  translates motion to the relay bar  14  through a pivot joint assembly  120 . The pitman arm  112  and a stud  122  are generally similar to those shown in  FIG. 2 . However, a housing  124  which substantially surrounds the stud  122  has a differently-shaped bore  126  running therethrough. Unlike the bore  26  shown in  FIG. 2 , the bore  126  is not generally cylindrical, but has angled portions. 
     A substantially-cylindrical bearing surface  128  rotates within an interface surface  134  of an inner metal ring  132 , such that the stud  122  may rotate about a central axis (not shown) relative to the housing  124 . Inner metal ring  132  includes radial tab portions  133  which are generally perpendicular to the interface surface  134  (and central axis of stud  122 ). Radial tab portions  133  may be continuous rings, or may have multiple, individual tabs or stakes. Pivot joint assembly  20  does not include an outer metal can (such as outer metal can  36  shown in  FIG. 2 ). 
     The radial tab portions  133  restrict axial movement of the stud  122  relative to the housing  124 . The pivot joint assembly  120  includes a two-piece resilient member formed from a first bushing  130  and a second bushing  131 . The first and second bushings  130  and  131  shown in  FIG. 3  are disposed between the angular portions of the bore  126  and the inner metal ring  132  (including radial tab portions  133 ). 
     First and second bushings  130  and  131  are further configured to provide radial compliance between the stud  122  and housing  124 . Additionally, the first and second bushings  130  and  131  may be configured with differing compliance levels, which allows tuning of both the radial and angulate reactions of the pivot joint assembly  120 . 
     The radial tab portions  133  act as axial restraint elements configured to prevent axial separation of the stud  122  from the housing  124 . In the unlikely event of a loss of the either the first bushing  130  or second bushing  131 , the radial tab portions  133  would not allow the inner metal ring  132 , and therefore the stud  122 , to be completely detached or separated from the housing  124 . 
     To limit the intrusion of dust, dirt, water, or other foreign material into the gap between the interface surface  134  and the bearing surface  128 , the pivot joint assembly  120  may also be equipped with sealing structures. The pivot joint assembly  120  includes two such structures, a first thrust bearing  138  and a second thrust bearing  140 , which, in addition to carrying axial loads, may be configured to prevent the ingress of foreign material into, and the egress of lubricant from, the interface surface  134  and bearing surface  128 . The thrust bearings  138  and  140  may be formed from, or have a coating made from (without limitation): microcellular polyurethane (MCU), polyurethane foam, or rubber. 
     Referring now to  FIG. 4 , there is shown a cross-sectional view of another embodiment of a steering mechanism  210 . A pitman arm  212  translates motion to the relay bar  14  through a pivot joint assembly  220 . The pitman arm  212  is generally similar to those shown in  FIGS. 2 and 3 . However, a housing  224  which substantially surrounds the stud  222  again has a differently-shaped bore  226  running therethrough. Unlike the bore  26  shown in  FIG. 2 , the bore  226  is not generally cylindrical, but includes both offset and angled portions. 
     A substantially-cylindrical bearing surface  228  rotates within an interface surface  234  of an inner metal ring  232 , such that the stud  222  may rotate about a central axis (not shown) relative to the housing  224 . The pivot joint assembly  220  includes a single-piece resilient member, a bushing  230 . The bushing  230  is disposed between the inner metal ring  232  and an outer metal can  236 , and configured to provide radial compliance between the stud  222  and housing  224 . 
     An annular ridge  242  on the outer metal can  236  acts as an axial restraint element configured to prevent axial separation of the stud  222  from the housing  224 . The stud  222  includes a radial ridge  244  on an upper portion thereof. In the unlikely event of a loss of the bushing  230 , the annular ridge  242  would not allow the radial ridge  244  of the stud  222 , and therefore the stud  222 , to be completely detached from the housing  224 . 
     In another embodiment (not shown) of the pivot joint assembly  220 , the annular ridge  242  may be formed directly into the housing  224 . In such an embodiment, the pivot joint assembly  220  may not include the outer metal can  236  and the bushing  230  would be displaced between the housing  224  and inner metal ring  232 . 
     Pivot joint assembly  220  shown in  FIG. 4  does not include separate sealing structures like the first and second thrust bearings  138  and  140 . However an axial cap  246  is configured to prevent the ingress of foreign material into, and the egress of lubricant from, the interface surface  234  and bearing surface  228 . Axial cap  246  is attached to the outer metal can  236 , and therefore also restricts axial movement of the stud  222  relative to the housing  224 . Axial cap  246  may also allow the steering mechanism  210  to be assembled without one of the nuts  18  (shown in  FIGS. 1-3 ). 
     Referring now to  FIG. 5 , there is shown a cross-sectional view of another embodiment of a steering mechanism  310 . A pitman arm  312  translates motion to the relay bar  14  through a pivot joint assembly  320 . 
     The pivot joint assembly  320  includes a two-piece inner metal ring member, such that a substantially-cylindrical bearing surface  328  on a stud  322  rotates within an interface surface  334 , which is formed on a first inner metal ring  332  and a second inner metal ring  333 . Note that the stud  322  is shown as a partial cross section. 
     The pivot joint assembly  320  includes a single-piece resilient member, a bushing  330 . The bushing  330  is disposed between the first and second inner metal rings  332  and  333 , and an outer metal can  336 , and configured to provide radial compliance between the stud  322  and housing  324 . 
     Like the pivot joint assembly  220  shown in  FIG. 3 , the interior of pivot joint assembly  320  is completely sealed. A first sealing element  338  and an axial cap  346  are configured to prevent the ingress of foreign material into, and the egress of lubricant from, the interface surface  334  and bearing surface  328 . First sealing element  338  may be formed from, or have a coating made from, without limitation: microcellular polyurethane (MCU), polyurethane foam, or rubber. 
     In the pivot joint assembly  320 , the axial cap  346  is attached to the second inner metal ring  333 , as opposed to the outer metal can  336 . Axial cap  346  may be attached to the second inner metal ring  333  by rolling or otherwise deforming a lip on the second inner metal ring  333  over the edge of axial cap  346 . An internal nut  352  locks the stud  322  against the second inner metal ring  333  and carries axial loads. 
     A nozzle or zerk fitting  350  is disposed in axial cap  346 . Zerk fitting  350  is a nipple-like lubrication fitting through which grease is applied to the interior of pivot joint assembly  220 , and may be made of zirconium alloy (which may be referred to as a zirc fitting). 
     Referring now to  FIG. 6 , there is shown a cross-sectional view of another embodiment of a steering mechanism  410 . A pitman arm  412  translates motion to the relay bar  14  through a pivot joint assembly  420 . 
     A substantially-cylindrical bearing surface  428  on a stud  422  rotates within an interface surface  434  of an inner metal ring  432 , such that the stud  422  may rotate about a central axis (not shown) relative to the housing  424 . Note that the stud  422  is shown as a partial cross section. The pivot joint assembly  420  includes a single-piece resilient member, a bushing  430 . The bushing  430  is disposed between the inner metal ring  432  and an outer metal can  436 , and configured to provide radial compliance between the stud  422  and housing  424 . 
     An annular ridge  442  on the outer metal can  436  acts as an axial restraint element configured to prevent axial separation of the stud  422  from the housing  424 . The stud  422  includes a radial ridge  444  on an upper portion thereof. In the unlikely event of a loss of the bushing  430 , the annular ridge  442  would not allow the radial ridge  444  of the stud  422 , and therefore the stud  422 , to be completely detached or separated from the housing  424 . 
     The interior of pivot joint assembly  420  is also sealed. An axial cap  446  is configured to prevent the ingress of foreign material into, and the egress of lubricant from, the interface surface  434  and bearing surface  428 . Furthermore, a sealing portion  438  is formed as a continuous, integral portion of the bushing  430 , thereby eliminating the need for an additional sealing element on the lower portion of the pivot joint assembly  420 . 
     Axial cap  446  is attached to the outer metal can  436 , and therefore restricts axial movement of the stud  422  relative to the housing  424 . A thrust bearing  454  carries axial loads to the axial cap  446 , and a pin  456  carries loads from a spring or another elastic member to the thrust bearing  454 . A zerk fitting  450  is disposed in axial cap  446 , allowing grease to be applied into the interior of pivot joint assembly  420 . 
     While the best modes and other embodiments for carrying out the claimed invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.