Abstract:
A universal joint assembly includes a hollow upper shaft, a lower shaft extending at least partially within the upper shaft, and a cage having a plurality of bearing apertures. Each bearing aperture includes a pair of opposed loading pads having a distinct inner wall surface sector extending radially inward into the at least one bearing aperture. The cage receives at least a portion of the lower shaft and is positioned within the hollow upper shaft. The assembly further includes at least one upper tilt pin extending through the upper shaft and a bearing aperture of the plurality of bearing apertures, and a lower tilt pin extending through the lower shaft and a bearing aperture of the plurality of bearing apertures.

Description:
FIELD OF THE INVENTION 
     The subject invention relates to universal joints, and more particularly to a steering column universal joint having sector loading pads. 
     BACKGROUND OF THE INVENTION 
     Universal joints are typically used to transfer torque between two shafts. Some universal joints include a trunion that rotates between input and output yokes. Steering column universal joints may use a molded plastic cage as the trunion while the yokes have pins affixed to them. The pins may be press-fit into apertures in the cage but still allow the cage to spin. The press-fit may be required to eliminate lash. However, it may also add friction when the joint is rocked. Accordingly, it is desirable to provide a universal joint with reduced friction between the cage and the pins. 
     SUMMARY OF THE INVENTION 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     In one aspect of the invention, a cardan joint cage is provided. The Cardan joint cage includes at least one bearing aperture having an inner wall surface and a pair of opposed loading pads extending radially inward into the at least one bearing aperture. 
     In another aspect of the invention, a universal joint assembly is provided. The assembly includes a hollow upper shaft, a lower shaft extending at least partially within the upper shaft, and a cage having a plurality of bearing apertures. Each bearing aperture includes a pair of opposed loading pads having a distinct inner wall surface sector extending radially inward into the at least one bearing aperture. The cage receives at least a portion of the lower shaft and is positioned within the hollow upper shaft. The assembly further includes at least one upper tilt pin extending through the upper shaft and a bearing aperture of the plurality of bearing apertures, and a lower tilt pin extending through the lower shaft and a bearing aperture of the plurality of bearing apertures. 
     In yet another aspect of the invention, a method of fabricating a cardan joint cage is provided. The method includes forming the cardan joint cage with at least one bearing aperture and removing material form a portion of the circumference of the bearing aperture to define a pair of opposed loading pads extending radially inward into the at least one bearing aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of an exemplary embodiment of a universal joint assembly according to the disclosure; 
         FIG. 2  is a perspective view of another exemplary embodiment of a universal joint assembly according to the disclosure; 
         FIG. 3A  is a cross-sectional view of a prior art cage; and 
         FIG. 3B  is a cross-sectional view of an exemplary embodiment of a cardan joint cage according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,  FIG. 1  illustrates a side cross-section of an exemplary cardan joint or universal joint assembly  10 , and  FIG. 2  illustrates a perspective view of universal joint assembly  10  before assembly. 
     Universal joint (U joint) assembly  10  and specifically cardan joint assembly  10  includes an upper shaft  12 , a lower shaft  14 , a cardan joint cage  16 , a lower tilt pin  18 , and upper tilt pins  20  extending through apertures  22  formed in upper shaft  12 . Assembly  10  includes a first axis  24  that allows lower shaft  14  to pivot inside cage  16  and a second axis  26  that allows cage  16  to pivot inside upper shaft  12 . Axes  24  and  26  are in one plane perpendicular to both each other and to a spin axis  28  of U-joint assembly  10 . U-joint assembly  10  is pivotable to transmit torque from upper shaft  12  through cage  16  to lower shaft  14 . 
     As shown in  FIG. 2 , cage  16  includes journal bearing apertures  30  to receive lower tilt pin  18  and journal bearing apertures  32  to receive upper tilt pins  20 . Bearing apertures  30  include an inner wall surface  34  and bearing apertures  32  include an inner wall surface  36 . Typically, inner wall surfaces  34 ,  36  contact respective pins  18 ,  20  over the entire 360° surface of inner wall surfaces  34 ,  36 , which contributes 360° of frictional contact between inner walls  34 ,  36  and pins  18 ,  20  when rocking joint assembly  10 . However, because a load path  40  in cage  16  is generally bi-directional in a transverse plane  42  ( FIG. 3B ) of cage  16 , friction between cage  16  and pins  18 ,  20  is reduced by removing material in unloaded portions  44  of bearings apertures  30 ,  32 , forming inner wall surfaces  50  that are discontiguous with inner wall surfaces  34 ,  36 . Specifically, the inner wall surfaces  34 ,  36  form a first concentric cylinder  52  having sectors that are not contiguous with the adjoining or adjacent sectors of a second concentric cylinder  54  formed by inner wall surfaces  50 . 
       FIG. 3A  illustrates a prior art cage  116  having a bearing aperture  130 , and  FIG. 3B  illustrates cage  16  compared to prior art cage  116 . As shown in  FIG. 3B , material is removed from unloaded portions  44  of bearing aperture  30 . Although not shown, bearing apertures  32  may be modified in the same way as bearing apertures  30 . After removal of material from unloaded portions  44 , material remains in bearing portions  46  about a portion of the circumference of bearing aperture  30 . As such, opposed bearing or loading pads  48  are defined in a sector of the circumference of bearing aperture  30 . 
     In the exemplary embodiment, stiffness of the connection between cage  16  and pins  18 ,  20  is not reduced because the material of the original bearing area  46  remains. However, friction between cage  16  and pins  18 ,  20  is reduced due to removal of material in unloaded portions  44 ; material that caused unnecessary interference with pins  18 ,  20  and contributed to friction when the joint assembly was rocked. With the modification of cage  16  occurring only with the geometry of bearings apertures  30 ,  32 , there is no cost increase to cage  16 . Further, this design allows an increase in aperture tolerances for a given material without creating lash while maintaining current frictional tolerances. 
     With material removed from unloaded portions  44 , each loading pad  48  extends radially inward into bearing aperture  30 ,  32  and defines a sector of concentric cylinder  52  having a radial angle ‘α’ ( FIG. 3B ). In the exemplary embodiment, radial angle ‘α’ of each sector loading pad  48  may be varied based on the magnitude of load  40  and the magnitude of the pivot angle (i.e., how far cage  16  oscillates around pin  18 ,  20 ). For example, radial angle ‘α’ may be between 15° and 120° or between approximately 15° and approximately 120°. In another example, radial angle ‘α’ may be between 75° and 105° or between approximately 75° and approximately 105°. In yet another example, radial angle ‘α’ is 90° or approximately 90°. However, radial angle ‘α’ may be any suitable angle that enables cage  16  to function as described herein. Additionally, radial angle ‘α’ may be varied depending on the stiffness of the material used to fabricate cage  16 . For example, the radial angle ‘α’ of loading pad  48  (corresponding to the size of loading pad  48 ) may be reduced when cage  16  is fabricated from a relatively stiffer material. In a similar manner, the size of leading pad  48  may be increased when cage  16  is fabricated from a relatively compliant material. 
     Inner wall surfaces  50  define sectors of concentric cylinder  54  having a radial angle ‘β’ ( FIG. 3B ). In the exemplary embodiment, radial angle ‘β’ of each sector unloaded portion  44  may be varied based on the magnitude of load  40  and the magnitude of the pivot angle (i.e., how far cage  16  oscillates around pin  18 ,  20 ). For example, radial angle ‘β’ may be between 60° and 165° or between approximately 60° and approximately 165°. In another example, radial angle ‘β’ may be between 75° and 105° or between approximately 75° and approximately 105°. In yet another example, radial angle ‘β’ is 90° or approximately 90°. However, radial angle ‘β’ may be any suitable angle that enables cage  16  to function as described herein. 
     Alternative to the removal of material from unloaded area  44 , cage  16  may be formed with bearing apertures  30 ,  32  having a larger diameter than pins  18 ,  20 , and loading pads  48  may be subsequently coupled to bearing aperture inner walls  34 ,  36  in bearing area  46 . In yet other alternatives, a slot may be molded with a long axis greater than pin diameter and then recesses are machined to create the load pads, a slot may be machined in the recess, or cage  16  may be formed from powder metallurgy or cast (e.g., die cast, investment cast, or metal injection molding). 
     A method of fabricating cardan joint cage  16  includes forming cage  16  with bearing apertures  30 ,  32  to receive lower and upper tilt pins  18 ,  20 . Material from unloaded portions  44  of bearing aperture inner walls  34 ,  36  is removed to define concentric cylinders  52 ,  54  having discontiguous adjoining walls  50  and  34 ,  36 . As such, loading pads  48  are defined in bearing portions  46  of the material of the circumference of bearings apertures  30 ,  32 . 
     Described herein are systems and methods for reducing frictional contact in a universal joint assembly. The system includes a cardan joint cage having bearing apertures to receive tilt pins of the U-joint assembly. Material is removed from unloaded portions of the bearing apertures, which creates a clearance in the areas outside the tilt pin load path and reduces the friction area between the tilt pins and the cage. As such, rotating friction of the system is reduced while high torsional stiffness of the cage is maintained. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.