Abstract:
A rack and pinion steering gear ( 10 ) comprises a housing ( 12 ). A pinion gear ( 22 ) rotatably mounted in the housing ( 12 ). Teeth ( 28 ) of the pinion gear ( 22 ) engage teeth of a rack bar ( 30 ) that extends through the housing ( 12 ) and that is movable relative to the housing ( 12 ). A yoke assembly ( 38 ) is located in the housing ( 12 ) for at least partially supporting and guiding movement of the rack bar ( 30 ) relative to the pinion gear ( 22 ). The yoke assembly ( 38 ) comprises a first member ( 46 ) for contacting the rack bar ( 30 ) and a second member ( 48 ) for pivotally supporting the first member ( 46 ). Structure ( 70 ) of the second member ( 48 ) engages structure ( 58 ) of the first member ( 46 ) to enable the first member ( 46 ) to pivot in all directions about a point of rotation (P). The point of rotation (P) is spaced from a location of engagement of the first and second members ( 46  and  48 ).

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a rack and pinion steering gear and, more particularly, to a rack and pinion steering gear having a yoke assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    A known rack and pinion steering gear includes a pinion gear that is rotatably mounted in a housing and is connectable with a steering wheel of a vehicle. A rack bar extends through the housing and has opposite end portions that are connectable with steerable vehicle wheels. Gear teeth formed on the rack bar are disposed in meshing engagement with gear teeth on the pinion gear. A yoke assembly is disposed in the housing to support and guide movement of the rack bar relative to the housing. The yoke assembly includes a yoke bearing having an arcuate surface across which the rack bar moves. The support provided by the yoke assembly helps to ensure proper lash between the gear teeth of the rack bar and the gear teeth of the pinion gear.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is a rack and pinion steering gear. The rack and pinion steering gear comprises a housing. A pinion gear is rotatably mounted in the housing. A rack bar extends through the housing and is movable relative to the housing. The rack bar has teeth in meshing engagement with teeth of the pinion gear. A yoke assembly is located in the housing for at least partially supporting and guiding movement of the rack bar relative to the pinion gear. The yoke assembly comprises a first member for contacting the rack bar and a second member for pivotally supporting the first member. Structure of the second member engages structure of the first member to enable the first member to pivot relative to the second member in all directions about a point of rotation. The point of rotation is spaced from a location of engagement of the first and second members.  
           [0004]    According to another aspect, the rack and pinion steering gear comprises a housing. A pinion gear is rotatably mounted in the housing. A rack bar extends through the housing and is movable relative to the pinion gear. The rack bar has teeth in meshing engagement with teeth of the pinion gear. A yoke assembly is located in the housing for at least partially supporting and guiding movement of the rack bar relative to the pinion gear. The yoke assembly comprises a first member for contacting the rack bar and a second member for rotatably supporting the first member. A first one of the first and second members includes a pocket and a second one of the first and second members includes a protrusion that is receivable in the pocket. The pocket and the protrusion are partially spherical and allow pivoting of the first member relative to the second member in all directions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:  
         [0006]    [0006]FIG. 1 is a sectional view of a rack and pinion steering gear constructed in accordance with the present invention;  
         [0007]    [0007]FIG. 2 is an enlarged view of a yoke bearing of the rack and pinion steering gear of FIG. 1;  
         [0008]    [0008]FIG. 3 is a view taken along line  3 - 3  in FIG. 2;  
         [0009]    [0009]FIG. 4 is a view similar to FIG. 2 and illustrating a second embodiment of the yoke bearing;  
         [0010]    [0010]FIG. 5 is a view similar to FIG. 2 and illustrating a third embodiment of the yoke bearing; and  
         [0011]    [0011]FIG. 6 is a view similar to FIG. 2 and illustrating a fourth embodiment of the yoke bearing. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    A sectional view of a rack and pinion steering gear  10  constructed in accordance with the present invention is illustrated in FIG. 1. The rack and pinion steering gear  10  includes a housing  12 . Preferably, the housing  12  is made of cast metal. The housing  12  includes an axially extending passage  14 , extending perpendicular to the plane of FIG. 1. A pinion passage  16  extends into the housing  12  and tangentially intersects the axially extending passage  14 . A yoke bore  18  also extends into the housing  12  and connects with the axially extending passage  14 . The yoke bore  18  extends in a direction perpendicular to the axially extending passage  14 . In FIG. 1, axis A represents a central axis of the yoke bore  18 . Axis A extends in a direction perpendicular to the axially extending passage  14 . As shown in FIG. 1, the yoke bore  18  is located on a side of the axially extending passage  14  opposite the pinion passage  16 . The yoke bore  18  terminates at a threaded opening  20 .  
         [0013]    A pinion gear  22  is located in the pinion passage  16  of the housing  12 . Two bearing assemblies  24  and  26  rotatably support the pinion gear  22  in the housing  12 . A first bearing assembly  24  is located at one end of the pinion gear  22 . A second bearing assembly  26  is located at an opposite end of the pinion gear  22 . A plurality of teeth  28  extends around the outer circumference of the pinion gear  22 . The pinion gear  22  is connected with the vehicle steering wheel (not shown) in a known manner.  
         [0014]    A portion of an axially extending rack bar  30  extends through the axially extending passage  14  of the housing  12 . The rack bar  30  has opposite end portions (not shown) that are connected to the steerable wheels (not shown) of a vehicle through tie rods (not shown). The rack bar  30  has a generally cylindrical main body  32  having a generally circular outer surface  34 . An upper surface  36  of the rack bar has a plurality of teeth (not shown). The plurality of teeth of the rack bar  30  is disposed in meshing engagement with the plurality of teeth  28  of the pinion gear  22 .  
         [0015]    A yoke assembly  38  is located within the yoke bore  18  of the housing  12 . The yoke assembly  38  at least partially supports and guides movement of the rack bar  30  relative to the housing  12 . The yoke assembly  38  comprises a yoke bearing  40 , a spring  42 , and a yoke plug  44 .  
         [0016]    [0016]FIGS. 2 and 3 show enlarged views of the yoke bearing  40  of the yoke assembly  38 . For clarity, the yoke bearing  40  in FIGS. 2 and 3 will be referred to with reference to axis A. The yoke bearing  38  includes first and second members  46  and  48 , respectively. In one embodiment, the first and second members  46  and  48  are formed from zinc. Alternatively, the first and second members  46  and  48  may be formed from a polymer or thermoplastic material.  
         [0017]    The first member  46  has a cylindrical main body portion  50  that includes a cylindrical side wall  52  and first and second surfaces  54  and  56 , respectively. The cylindrical main body portion  50  has a diameter that is less than a diameter of the yoke bore  18 . The first surface  54  of the main body portion  50  of the first member  46  is arcuate for contacting the outer surface  34  of the rack bar  30 . In one embodiment, the arc of the first surface  54  is a dual radius arc so that line contact is established in the locations where the first surface contacts the outer surface  34  of the rack bar  30 .  
         [0018]    The second surface  56  of the main body portion  50  of the first member  46  is opposite the first surface  54  along axis A. The second surface  56  is generally flat and extends in a plane that is perpendicular to axis A. A partially spherical protrusion  58  is centered on the second surface  56  and extends outwardly of the second surface in a direction opposite the first surface  54 . The protrusion  58  has a partially spherical outer surface  60 . A circle is formed where the outer surface  60  of the protrusion  58  mates with the second surface  56  of the first member  46 . The circle is centered on axis A. The second surface  56  extends radially, relative to axis A, outwardly of the protrusion  58 .  
         [0019]    The second member  48  also includes a cylindrical main body portion  62  that includes a cylindrical side wall  64  and opposite first and second surfaces  66  and  68 , respectively. The diameter of the second member  48  is larger than the diameter of the first member  46  and is approximately equal to the diameter of the yoke bore  18 . A seal (not shown) may extend around the side wall  64  of the second member  48  for creating a fluid-tight seal between the second member and a surface defining the yoke bore  18 .  
         [0020]    The first surface  66  of the second member  48  is generally flat and extends in a plane that is perpendicular to axis A. A partially spherical pocket  70  or recess extends from the first surface  66  into the main body portion  62  of the second member  48 . The pocket  70  is defined by an inner surface  72 . In the embodiment illustrated in FIG. 2, the inner surface  72  of the pocket  70  is a dual radius surface so that the inner surface forms an annular peak  86  within the pocket. An opening to the pocket  70  is circular and is located in the plane of on the first surface  66  of the second member  48 . The opening is centered on axis A. The opening has a diameter that is less than the diameter of the circle that is formed where the protrusion  58  of the first member  46  meets the second surface  56  of the first member  46 .  
         [0021]    The second surface  68  of the second member  48  is generally flat and extends in a plane that is parallel to the plane of the first surface  66 . A recess  74  extends from the second surface  68  into the main body portion  62  of the second member  48 . An opening to the recess  74  is circular and is located in the plane of the second surface  68  of the second member  48 . The circular opening is centered on axis A. A side wall  76  and an end wall  78  define the recess  74 . The side wall  76  extends perpendicular to the second surface  68  and the end wall  78  extends parallel to the second surface  68 . A cylindrical spring guide  80  extends outward of the end wall  78  of the recess  74 . The spring guide  80  is centered on axis A and terminates at an end wall  82  that is located within the recess  74 .  
         [0022]    When the yoke bearing  40  is assembled, the protrusion  58  of the first member  46  is inserted into the pocket  70  of the second member  48 . When the outer surface  60  of the protrusion  58  engages inner surface  72  of the pocket  70 , a gap  84  (FIGS. 2 and 3) separates the second surface  56  of the first member  46  from the first surface  66  of the second member  48 . Since the inner surface  72  of the pocket  70  is a dual radius surface, the outer surface  60  of the protrusion  58  engages the annular peak  86  of the inner surface  72  of the pocket  70 . As a result, the area of contact between the first and second members  46  and  48  is annular or ring-shaped. Preferably, the diameter of the annular area of contact between the first and second members  46  and  48  is greater than one-half the diameter of the opening on the first surface  66  of the second member  48 . The larger the diameter of the annular area of contact, the more stable the first member  46  is relative to the second member  48 .  
         [0023]    When supported by the second member  48  of the yoke bearing  40 , the first member  46  of the yoke bearing may be pivoted in any direction. The first member  46  pivots about a point P that would form the center of the protrusion  58 . The pivot point P in FIG. 2 is located on axis A, above the second surface  56  of the first member  46 . A width of the gap  84  between the second surface  56  of the first member  46  and the first surface  66  of the second member  48  determines an amount of pivotal movement of the first member relative to the second member. When the second surface  56  of the first member  46  contacts the first surface  66  of the second member  48 , further pivotal movement of the first member in that particular direction is prevented. Preferably, the first member  46  may pivot by about ten degrees, relative the second member  48 , in every direction. During the pivotal movement of the first member  46  relative to the second member  48 , the area of contact between the first and second members remains annular and remains located at the peak  86  of the inner surface  72  of the pocket  70  of the second member  48 .  
         [0024]    The yoke plug  44  is shown in FIG. 1. The yoke plug  44  is cylindrical and includes a threaded outer surface  88  and a generally flat end surface  90 . Although not shown in FIG. 1, a cylindrical spring guide may extend outwardly, along axis A, of the end surface  90  of the yoke plug  44 . The spring  42  of the yoke assembly  38  illustrated in FIG. 1 is a helical compression spring. The spring  42  has a first axial end  92  and a second axial end  94 . The spring  42  also has a known spring constant.  
         [0025]    To assemble the yoke assembly  38  into the rack and pinion steering gear  10 , the first member  46  of the yoke bearing  40  is inserted into the yoke bore  18  so that the first surface  54  of the first member contacts the rack bar  30  on a side of the rack bar opposite the pinion gear  22 . The second member  48  of the yoke bearing  40  is then inserted into the yoke bore  18  so that the protrusion  58  from the second surface  56  of the first member  46  is received in the pocket  70  of the first surface  66  of the second member. The first axial end  92  of the helical spring  42  is then inserted into the recess  74  on the second surface  68  of the second member  48 . The first axial end  92  of the spring  42  engages the end wall  82  of the recess  74  and the spring guide  80  is received in the spring. The yoke plug  44  is then screwed into the yoke bore  18 . The end surface  90  of the yoke plug  44  engages the second axial end  94  of the spring  42 . The yoke plug  44  is screwed into the yoke bore  18  a distance sufficient to place a predetermined bias on the yoke bearing  38 .  
         [0026]    During operation of the rack and pinion steering gear  10 , the rack bar  30  moves through the axially extending passage  14  of the housing  12  to turn the steerable wheels of the vehicle. During this movement, the rack bar  30  may also move in a direction perpendicular to the axially extending passage  14 . The yoke assembly  38  supports the rack bar  30  during this movement and helps to maintain engagement of the rack bar with the pinion gear  22 .  
         [0027]    During movement of the rack bar  30 , the first member  46  of the yoke bearing  40  pivots relative to the second member  48  of the yoke bearing. The first member  46  pivots to a position that provides the least resistance or interference to movement of the rack bar  30 . Since the diameter of the main body portion  50  of the first member  46  is smaller than the diameter of the yoke bore  18 , the yoke bore does not interfere with the pivotal movement of the first member. Preferably, the pivot point P of the first member  46  corresponds to the center of the rack bar  30 . Thus, the outer surface  34  of the rack bar  30  will not interfere with or limit the pivotal movement of the first member  46  about point P.  
         [0028]    [0028]FIG. 4 shows a second embodiment of the yoke bearing  40   a  of the yoke assembly  38   a  of the rack and pinion steering gear  10   a  constructed in accordance with the present invention. Portions of the yoke bearing  40   a  of FIG. 4 that are the same as, or similar to, portion of the yoke bearing  40  illustrated in FIGS. 2 and 3 have the same reference numerals with the suffix “a” attached.  
         [0029]    The yoke bearing  40   a  of FIG. 4 is identical to the yoke bearing  40  of FIGS. 2 and 3 with the exception that the inner surface  72   a  defining the pocket  70   a  on the first surface  66   a  of the second member  48   a  is not a dual radius surface. The inner surface  72   a  has the same radius as the partially spherical protrusion  58   a  that extends from the second surface  56   a  of the first member  46   a.  Thus, when the second member  48   a  supports the first member  46   a,  the area of contact between the first and second members is also partially spherical and is approximately equal to the area of the inner surface  72   a  of the pocket  70   a.    
         [0030]    The yoke bearing  40   a  of FIG. 4 functions in the same manner as the yoke bearing  40  of FIGS. 2 and 3. However, since the area of contact between the first and second members  46   a  and  48   a  of the yoke bearing  40   a  is greater than the area of contact in the yoke bearing  40 , frictional resistance to the pivotal movement of the first member  46   a  relative to the second member  48   a  is greater in yoke bearing  40   a.  This frictional resistance may be combated by forming the outer surface  60   a  of the protrusion  58   a  and the inner surface  72   a  of the pocket  70   a  from a low friction material, such as Teflon coated Bronze, or by placing a lubricant, such as grease, between the two surfaces.  
         [0031]    [0031]FIG. 5 shows a third embodiment of the yoke bearing  102  of the rack and pinion steering gear  10  constructed in accordance with the present invention. Structure of the rack and pinion steering gear  10  not shown in FIG. 5 will be referred to using the same reference numerals as was used in FIG. 1. The yoke bearing  102  of FIG. 5 includes first and second members  104  and  106 , respectively.  
         [0032]    The first member  104  of the yoke bearing  102  has a cylindrical main body portion  108  that includes a cylindrical side wall  110  and opposite first and second surfaces  112  and  114 , respectively. The cylindrical main body portion  108  has a diameter that is less than a diameter of the yoke bore  18 . The first surface  112  is arcuate for contacting the rack bar  30 . In one embodiment, the arc of the first surface  112  is a dual radius arc so that line contact is established in the locations where the first surface contacts the rack bar  30 . The second surface  114  is generally flat and extends in a plane that is perpendicular to axis A. A partially spherical pocket  116  or recess extends from the second surface  114  and into the main body portion  108  of the first member  104 . The pocket  116  is defined by an inner surface  118 . In the embodiment illustrated in FIG. 5, the inner surface  118  of the pocket  116  is a dual radius surface so that an annular peak  120  is formed on the inner surface within the pocket. An opening to the pocket  116  is circular and is located in the plane of the second surface  114  of the first member  104 . The opening is centered on axis A.  
         [0033]    The second member  106  also includes a cylindrical main body portion  122 . The main body portion  122  of the second member  106  includes a cylindrical side wall  124  and opposite first and second surfaces  126  and  128 , respectively. The diameter of the second member  106  is larger than the diameter of the first member  104  and is approximately equal to the diameter of the yoke bore  18 . The first surface  126  of the second member  106  is generally flat and extends in a plane that is perpendicular to axis A. A partially spherical protrusion  130  is centered on the first surface and extends outwardly of the first surface  126  in a direction opposite the second surface  128 . The protrusion  130  has a partially spherical outer surface  132 . A circle is formed where the outer surface  132  of the protrusion  130  mates with the first surface  126  of the second member  106 . The circle has a diameter that is greater than the diameter of the opening of the pocket  116  in the second surface  114  of the first member  104 . The circle is centered on axis A. The first surface  126  of the second member  106  extends radially, relative to axis A, outwardly of the protrusion  130 .  
         [0034]    The second surface  128  of the second member  106  is generally flat and extends in a plane that is parallel to the plane of the first surface  126 . A recess  134  extends from the second surface  128  into the main body portion  122  of the second member  106 . An opening to the recess  134  is circular and is located in the plane of the second surface  128  of the second member  106 . The opening to the recess  134  is centered on axis A. A side wall  136  and an end wall  138  define the recess  134 . The side wall  136  extends perpendicular to the second surface  128  and the end wall  138  extends parallel to the second surface  128 . A cylindrical spring guide  140  extends outward of the end wall  138  of the recess  134 . The spring guide  140  is centered on axis A and terminates at an end wall  142  that is located within the recess  134 .  
         [0035]    When the yoke bearing  102  is assembled, the protrusion  130  of the second member  106  is inserted into the pocket  116  of the first member  104 . When the outer surface  132  of the protrusion  130  of the second member  106  engages inner surface  118  of the pocket  116  of the first member  104 , a gap  144  separates the second surface  114  of the first member  104  from the first surface  126  of the second member  106 . Since the inner surface  118  of the pocket  116  is a dual radius surface, the outer surface  132  of the protrusion  130  engages the peak  120  of the inner surface  118  of the pocket  116 . As a result, the area of contact between the first and second members  104  and  106  is annular or ring-shaped. Preferably, the diameter of the annular area of contact between the first and second members  104  and  106  is greater than one-half the diameter of the opening on the second surface  114  of the first member  104 . The larger the diameter of the annular area of contact, the more stable the first member  104  is relative to the second member  106 .  
         [0036]    When supported by the second member  106  of the yoke bearing  102 , the first member  104  of the yoke bearing may be pivoted in any direction. The first member  104  pivots about a point P that would form the center of the spherical protrusion  130 . Thus, the pivot point P in FIG. 5 is located on axis A, below the first surface  126  of the second member  106 . The gap  144  between the second surface  114  of the first member  104  and the first surface  126  of the second member  106  determines the amount of pivotal movement of the first member  104  relative to the second member  106 . When the second surface  114  of the first member  104  contacts the first surface  126  of the second member  106 , further pivotal movement of the first member  104  in that particular direction is prevented. Preferably, the first member  104  may pivot by about ten degrees, relative to the second member  106 , in every direction. During the pivotal movement of the first member  104  relative to the second member  106 , the area of contact between the first and second members  104  and  106  remains annular and remains located at the peak  120  of the inner surface  118  of the pocket  116  of the first member  104 .  
         [0037]    [0037]FIG. 6 shows a fourth embodiment of the yoke bearing  102   a  of the rack and pinion steering gear  10   a  constructed in accordance with the present invention. Portions of the yoke bearing  102   a  of FIG. 6 that are the same as, or similar to, portion of the yoke bearing  102  illustrated in FIG. 5 have the same reference numerals with the suffix “a” attached.  
         [0038]    The yoke bearing  102   a  of FIG. 6 is identical to the yoke bearing  102  of FIG. 5 with the exception that the inner surface  118   a  defining the pocket  116   a  on the second surface  114   a  of the first member  104   a  is not a dual radius surface. The inner surface  118   a  also has the same radius as the partially spherical protrusion  130   a  from the first surface  126   a  of the second member  106   a.  Thus, when the second member  106   a  supports the first member  104   a,  the area of contact between the first and second members  104   a  and  106   a  is also partially spherical and is approximately equal to the area of the inner surface  118   a  of the pocket  116   a.    
         [0039]    The yoke bearing  102   a  of FIG. 6 functions in the same manner as the yoke bearing  102  of FIG. 5. However, since the area of contact between the first and second members  104   a  and  106   a  of the yoke bearing  106   a  is greater than the area of contact in the yoke bearing  102 , frictional resistance to the pivotal movement of the first member  104   a  relative to the second member  106   a  is greater in yoke bearing  102   a . This frictional resistance may be combated by forming the outer surface  132   a  of the protrusion  130   a  and the inner surface  118   a  of the pocket  116   a  from low friction material or by placing a lubricant, such as grease, between the two surfaces.  
         [0040]    From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, although a pivotal movement of about ten degrees between the first and second members of the yoke bearing is preferred, it should be realized that the present invention is not limited to pivotal movement of about ten degrees and that other angles of pivotal movement are contemplated by this invention. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.