Abstract:
A universal joint hub comprising a generally spherical body having two flat areas on opposing exterior sides and at least one opening into an open body interior. The hub has two flat areas on opposing interior surfaces of the body orthogonal to the exterior flat areas and an exterior circumferential groove extending between the exterior flat areas on a given plane. Four apertures extend into the body and are positioned orthogonal to each other on the given plane with each aperture disposed in one of the flat areas. A bushing is disposed in each aperture having a face exposed to the exterior surface. A circumferential band is disposed in the circumferential groove coupling each of the bushings.

Description:
BACKGROUND 
     The invention relates generally to universal joints. More specifically, embodiments of the invention relate to ball hubs for use in universal joints and methods of manufacture. 
     In today&#39;s vehicles, the steering system generally includes a common shaft, supported by a steering column, coupling a steering wheel to a steering gear assembly for transmitting directional rotation from a user to a steering geometry to provide directional control. The shaft typically passes through a vehicle firewall that separates passenger and engine compartments. To provide for various vehicle steering column designs, safety considerations and user comforts, the shaft has to navigate a complicated route necessitating two or more joints that connect the rotating shafts allowing for freedom of rotation regardless of the different angles the steering shaft experiences. 
     A Cardan, or yoke type universal joint, is frequently used to accomplish the transitions between steering shaft angles. This type of universal joint is common in the industry and includes two yokes and a cross shaft. Bearing surfaces couple the cross shaft to the yokes, allowing for a predetermined freedom of movement in two planes. 
     Gaining in popularity is the ball hub universal joint, shown in FIGS. 1 and 2, that provides for a reduction in weight, size, and NVH (Noise, Vibration and Harshness). This type of universal joint includes a first shaft  17  having at one end a ball hub  19 , that is usually attached with a long pin  21  allowing for a first axis of pivotal motion. The long pin  21  passes through one side of the ball hub  19  along an equator, through the first shaft  17 , and back into the ball  19 . The ball  19  is received in a cup  23  that is rigidly attached to a second shaft  25 . The ball hub  19  is retained in the cup  23  using two short pins  27 ,  27 ′ that allow for a second axis of pivotal motion orthogonal to the first axis. Each short pin  27 ,  27 ′ passes through the outside of the cup  23  and into the ball  19  along the equator. 
     For most passenger car and light truck applications, the ball hub and cup can be made from self-lubricating plastics such as Teflon®, Delrin®, or others, thereby obviating the need for low friction bearing surfaces between the moving parts (pins, ball and cup). However, for applications that are subjected to severe driving conditions which result in high dynamic torque loads, metal offers greater robustness and durability than most self-lubricating plastics. The metal parts need low friction load bearing surfaces. 
     To minimize friction and NVH in both axis of rotation, bushings are placed into the ball hub  19  pin holes where the long pin  21  and short pins  27 ,  27 ′ couple the first shaft  17  to the ball hub  19  and to the cup  23  as shown in FIG.  3 . The bushings are typically made of a self-lubricating material. Each bushing has an associated flange surface to minimize friction between surfaces of the first shaft  17  and ball hub  19 , and the ball hub  19  and cup  23 . The long pin  21  bushings  29 ,  29 ′ locate their flange surfaces  33 ,  33 ′ on the interior of the ball hub  19 , the short pin  27 ,  27 ′ bushings  31 ,  31 ′ locate their flange surfaces  35 ,  35 ′ on the exterior of the ball hub  19 . 
     While bushing inserts solve one problem, they create a problem of their own. Depending on the design specification, the allowable rotational lash or play between the first and second shafts may be specified at a minimum. Precise, low clearance fits would therefore be required between the long  21  and short  27 ,  27 ′ pins and ball hub  19  to meet the lash specification of the steering shaft. Since a bushing is a removable cylindrical guide, where one low clearance fit existed between the pin and mating surface, another low clearance fit between the bushing and mating surface is created. The clearance between the three components increases rotational lash above design specifications. Further, the bushings can rotate when the joint is being exercised causing binding of the joint. This in turn increases the torque necessary to rotate the shaft while concomitantly decreasing the joint articulation. 
     The prior art has addressed this shortcoming by decreasing the internal diameter of the bushings such that the insertion of the pins causes the bushings to expand, reducing the clearance fit between the long  21  and short  27 ,  27 ′ pins, bushings  29 ,  29 ′,  31 ,  31 ′ and ball hub  19 . However, during assembly, insertion of the pins can shave the inner diameter of the bushings resulting in unacceptable lash. Additionally, the bushings would not expand sufficiently to reduce clearance between the bushing and ball hub to achieve an acceptable lash. 
     SUMMARY 
     The inventors have discovered that it would be desirable to have a low lash ball hub for use in a universal joint and methods for manufacturing, for applications such as steering column shafts that experience a high torque load. One aspect of the invention provides a universal joint hub comprising a generally spherical body having two flat areas on opposing exterior sides and at least one opening into an open body interior. The hub has two flat areas on opposing interior surfaces of the body orthogonal to the exterior flat areas and an exterior circumferential groove extending between the exterior flat areas on a given plane. Four apertures extend into the body and are positioned orthogonal to each other on the given plane with each aperture disposed in one of the flat areas. A bushing is disposed in each aperture having a face exposed to the exterior surface. A circumferential band is disposed in the circumferential groove coupling each of the bushings. 
     The method begins with forming a generally spherical body having two flat areas on opposing exterior sides and at least one opening into an open body interior. Forming two flat areas on opposing interior surfaces of the body, the interior flat areas orthogonal to the exterior flat areas. Forming an exterior circumferential groove extending between the exterior flat areas on a given plane and creating four apertures extending into the body and positioned orthogonal to each other on the given plane with each aperture disposed in one of the flat areas. Disposing a bushing in each of the apertures, each bushing having a face exposed to the exterior surface and disposing a circumferential band in the circumferential groove thereby coupling each of the bushings. 
     Other objects and advantages of the method will become apparent to those skilled in the art after reading the detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a prior art ball hub universal joint. 
     FIG. 2 is an opposing view of the prior art ball hub shown in FIG.  1 . 
     FIG. 3 is an isometric projection of the prior art ball hub shown in FIG.  1 . 
     FIG. 4 is an isometric projection of an exemplary ball hub with groove in accordance with one embodiment of the invention. 
     FIGS. 5 a  and  5   b  are exemplary views of a long pin bushing. 
     FIGS. 6 a  and  6   b  are exemplary views of a short pin bushing. 
     FIGS. 7 a  and  7   b  are exemplary views of an alternative long pin bushing. 
     FIGS. 8 a  and  8   b  are exemplary views of an alternative short pin bushing. 
     FIG. 9 is a view along line  9 — 9  in FIG. 4 with bushings and circumferential band. 
     FIG. 10 is a view along line  10 — 10  in FIG.  9 . 
     FIG. 11 is an isometric projection of an exemplary ball hub in accordance with another embodiment of the invention. 
     FIG. 12 is a view along line  12 — 12  in FIG. 11 with bushings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. The invention is taught for use in articulating a steering column shaft as an application. However, the invention is not limited by this example and can be applied to other applications requiring a hub for a universal joint. While the description refers to a “ball” hub, the term should not be regarded as limiting. Further, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected,” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting, and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     In a first embodiment of the invention a hollow, spherical hub  41  is provided. A groove  37  having a predetermined depth and width is positioned on the outer surface along an equatorial plane  47  of the hub as shown in FIG. 4. A cup (not shown) of matching correspondence receives the hub  41 . The invention can replace a preexisting, prior art ball hub design. The hub  41  and cup are not limited by size. 
     The hub  41  is a hollow, generally spherical section that can be metal, an alloy, ceramic or other material composition. The hub  41  has one or more openings  44  to the interior  46 . The opening  44  and interior  46  are configured to receive the shaft  17 . Four holes are provided through the hub  41  into the interior  46  for receiving the long  21  and short  27 ,  27 ′ pins. Two short pin holes  43 ,  43 ′ and two long pin holes  45 ,  45 ′ are positioned orthogonal to each other along an equatorial plane  47 , with associated pin holes sharing the same axis of rotation 180° apart. The short pin holes  43 ,  43 ′ are located on exterior flats  49 ,  49 ′, and the long pin holes  45 ,  45 ′ are positioned in the groove  37 . 
     Each hole  43 ,  43 ′,  45 ,  45 ′ receives a self-lubricating bushing  51 ,  53 , as shown in FIGS. 5-8, that extends from the ball hub  41  exterior surface to the interior surface. To minimize clearance between the ball hub  41  pin hole  43 ,  43 ′,  45 ,  45 ′ diameters and the outer diameter of the: bushings  51 ,  53 , the inner diameter for all bushings  51 ,  53  are molded smaller than the long  21  and short pin  27 ,  27 ′ outer diameters to create an interference fit between the outer diameter of the pins  21 ,  27 ,  27 ′ and the inner diameter of the bushings  51 ,  53 . Stress-relieving slots  55  are molded into the bushings along the axial length of the bushing  51 ,  53  and radially, on an associated flange surface  33 ,  33 ′,  35 ,  35 ′ having a predetermined surface area and configuration, in a substantially vertical axis alignment, thereby providing a slot running the length of the bushing to the edge of the flange surface. The flange surfaces can be of any configuration and thickness. The slots  55  have a predetermined depth and width depending upon the long  21  and short  27 ,  27 ′ pin dimensions (O.D. and length) and the desired thickness of the bushing          (       O   .   D   .     -     I   .   D   .         2     )     .                          
     The rotational load placed on the long  21  and short pins  27 , 27 ′, and bushings  51 ,  53  is confined to the equatorial plane  47 . Positioning the stress relieving slots  55  in the vertical axis effectively removes the slot  55  from any load. The stress relieving slot  55  can be located on the inner diameter of a bushing  55  and outer surface of the associated flange surface  33 ,  35  as shown in FIGS. 5 and 6, or, on the outer diameter and inner surface of the flange  33 ,  35  as shown in FIGS. 7 and 8. The stress relieving slots  55  allow each bushing  51 ,  53  to expand, filling the clearance between the bushings and ball hub  41  as described below. 
     Referring to FIG. 9, a circumferential band  57  of a compatible material or the same material comprising the bushings  51 ,  53  is applied in the groove  37 , by molding or other means, coupling together the four bushings  51 ,  53  as one assembly and forming a continuous ring around the circumference, or equatorial plane  47  of the ball hub  41 . Since the circumferential area of the band  57  is greater than that of the exposed, exterior bushing  51 ,  53  areas, contraction or shrinkage of the band  57  after application exceeds the strength of the stress relieving slots  55  causing them to either partially or completely fracture, and thereby open as shown in FIGS. 9 and 10 with the bushing  51 ,  53  embodiments shown in FIGS. 5 and 6. Once the slots  55  fracture by the circumferential band  57  contraction, the inner diameter of each bushing  51 ,  53  is increased thereby allowing the pins  21 ,  27 ,  27 ′ to be inserted without shaving the bushing  51 ,  53 . If a portion of a bushing  51 ,  53  stress-relieving slot  55  did not fracture during circumferential band  57  contraction, pin insertion competes fracturing, reducing clearance between the ball hub, bushing and pin resulting in reduced lash. 
     The circumferential band  57  additionally prohibits each bushing  51 ,  53  from rotating eliminating torque to rotate and articulation issues. Additionally, the machining of the circumferential groove  37  around the ball hub  41  reduces the wall thickness in the areas where the long pin  21  holes are located, allowing the holes  45 ,  45 ′ to be punched rather than drilled. 
     Another embodiment of the invention is shown in FIGS. 11 and 12. In this embodiment, a groove  65  having a predetermined depth, length and cross-section is broached along the interior flats of the ball hub  61  radial to the long pin  21  holes on the long pin axis. On the exterior flats of the ball hub  61 , a groove  63  having a predetermined depth, length and cross-section is broached radial to the short pin  27 ,  27 ′ holes on the short pin axis. The groove  63 ,  65  cross-section can be rectangular, dovetail or others. The groove  63 ,  65  can be at any angle with respect to the axis of rotation and length. Bushings  67 ,  69 , similar to those shown in FIGS. 5 through 8 but having keys  71 ,  73  in matching correspondence with the broached grooves  63 ,  65  are inserted in the long  45 ,  45 ′ and short  43 ,  43 ′ pin holes. The grooves and mating key on the flange areas of the bushings provide a bushing anti-rotation feature. A radius on the insertion end of the long  21  and short  27 ,  27 ′ pins minimize bush shaving during pin insertion. 
     While the various embodiments of the hub discuss the application of bushings, bushings having associated flange surfaces, and a circumferential band, these appliances can be assembled as separate pieces constituting one assembly, or as one homogeneous molding. Various molding and assembly techniques can be employed to achieve the same result. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.