Abstract:
A guide cap axially aligns a yoke to an input shaft of a steering system. A cap body has an opening receiving an end of the input shaft. A cap fin guides seating of the yoke to the input shaft by mating to a yoke slit. A finger projection engages a radial recess in the input shaft with a retention force opposing axial removal of the guide cap once installed. A fin notch provides limits to relative axial displacement between the guide cap and yoke and guides axial positioning of the yoke as the yoke bolt is installed, deterring inadvertent threading into the input shaft. The fin anchor mates to a notch of the input shaft providing stability to the fin relative to the input shaft, and fixing rotational position of the guide cap on the input shaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention generally relates to an input shaft cap for a steering system, and more particularly to a guide cap for aligning an intermediate shaft&#39;s connector to an input shaft in a steering system. 
         [0002]    Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear of a pinion, and the pinion in turns moves the rack. The rack is a linear gear that meshes with the pinion, converting circular motion into linear motion along the transverse axis of the car (side to side motion). This motion applies steering torque to the swivel-pin ball joints of the stub axle of the steered wheels via tie rods and a short lever arm called the steering arm. In such rack and pinion steering systems, the steering wheel and steering column are linked to the pinion gear via an intermediate shaft and an input shaft. The intermediate shaft is connected to the input shaft with a yoke. A proper connection between the yoke and input shaft is needed to maintain steering control of the vehicle. The guide cap of the present invention serves to assure a proper connection between the yoke and the input shaft by serving as a guide during installation and by exerting a high retention force to resist axial separation after installation. These and other needs are addressed by various embodiments of the present invention. 
       SUMMARY OF THE INVENTION 
       [0003]    A guide cap of the present invention is part of a steering system having a yoke seated at an end of an input shaft. The guide cap also is seated at the end of the input shaft and serves to align the yoke to the input shaft, while also contributing to the anchoring of the yoke to the input shaft. The guide cap includes a cap body and a fin. The cap body is anchored to the input shaft by a plurality of input shaft engaging members and a fin anchor. Each input shaft engaging member includes a protrusion extending radially inward to sit in a radial recess, such as a circumferential groove, of the input shaft. The fin anchor extends from a portion of the fin into a longitudinal groove of the input shaft, and provides stability to the fin. The projections provide a desired retention force for resisting axial separation of the yoke and guide cap, once installed. 
         [0004]    The guide cap, and in particular the fin, serves as an alignment guide for the yoke during installation. The guide cap is installed first. The axial position of the guide cap is fixed relative to the input shaft within a prescribed tolerance by the input shaft engaging members and the fin anchor. The rotational position of the guide cap is fixed relative to the input shaft by a flat portion of the cap body inner surface, which correlates to a flat portion of the input shaft surface. The inner surface of the cap body and the outer surface of the input shaft are asymmetrical so that when the specific, correlated flats align the cap is installed properly (as opposed to being 180 degrees, or some other arc distance, out of alignment). Secondarily, the rotational position of the cap is fixed relative to the input shaft by the fin anchor mated into the longitudinal groove of the input shaft. The yoke then is installed onto the input shaft and guide cap using the guide cap as a guide for properly aligning the yoke. The yoke includes a slit extending radially and longitudinally. As the yoke is being installed at the end of the input shaft, the slit is aligned with the fin, so that the fin enters the slit as the yoke is moved axially. 
         [0005]    The yoke is secured relative to the guide cap and input shaft by a yoke bolt. The yoke includes a bolt channel extending transversely to each side of the slit. The input shaft includes a whistle notch. The yoke bolt channel is rotationally aligned to the whistle notch when the fin is aligned with the slit. The yoke bolt is threaded through at least part of the yoke bolt channel adjacent to and aligned with the whistle notch. The fin includes a fin notch so that the fin does not interfere with the yoke bolt channel when proper alignment occurs. When the fin sits within the slit, the fin notch accommodates the yoke bolt. The fin notch provides axial limits for aligning the yoke bolt and aids in assuring that the yoke bolt is aligned to the axial position of the whistle notch. The yoke bolt is secured in the bolt channel, and thus the axial position of the yoke bolt may determine the fine axial positioning of the yoke. The fin notch limits the range of such fin axial positioning of the yoke. The bolt secures the yoke to the input shaft when properly aligned within the whistle notch. 
         [0006]    The guide cap provides alignment for setting limits to the axial, radial and rotational position of the yoke relative to the input shaft so that a proper connection between the yoke and input shaft can be established and maintained. In particular, the cap fin serves as a rotational alignment guide during installation of the yoke. The fin assures that the yoke is not installed backwards (i.e. 180 degrees out of alignment), and provides alignment to tolerance when installed correctly. 
         [0007]    As the yoke is moved axially onto the input shaft during installation, the yoke is blocked from further proximal advancement by a seat at the input shaft. Such seat is formed by a transition region where input shaft diameter changes from a narrow diameter (to which the yoke conforms) to a larger diameter. The yoke may be axially displaced slightly during installation to allow the yoke bolt channel to be in axial alignment with the whistle notch. The fin notch serves as a guide for preferred limits of axial displacement of the yoke relative to the cap while the yoke bolt is being installed as it transversely passes through the fin notch. 
         [0008]    The inventions will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is further described in the detailed description that follows, by reference to the noted drawings by way of non-limiting illustrative embodiments of the invention, in which like reference numerals represent similar parts throughout the drawings. As should be understood, however, the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0010]      FIG. 1  is a perspective view of an exemplary rack and pinion steering system for which the guide cap of the present invention may be used; 
           [0011]      FIG. 2  is a perspective view of a portion of a steering system according to an embodiment of the present invention; 
           [0012]      FIG. 3  is a diagram of a yoke bolt properly seated relative an input shaft; 
           [0013]      FIG. 4  is a diagram of a yoke bolt improperly positioned relative to the input shaft; 
           [0014]      FIG. 5  is a planar view of a bolt guide cap according to an embodiment of the present invention; 
           [0015]      FIG. 6  is a cutaway view of the bolt guide cap of  FIG. 5  showing the cap body and skirt; 
           [0016]      FIG. 7  is a perspective view of the bolt guide cap according to another embodiment of the present invention; 
           [0017]      FIG. 8  is a first planar view of the bolt guide cap of  FIG. 7 ; 
           [0018]      FIG. 9  is a second planar view of the bolt guide cap of  FIG. 7 ; 
           [0019]      FIG. 10  is a third planar view of the bolt guide cap of  FIG. 7 ; 
           [0020]      FIG. 11  is a cutaway view of the bolt guide cap of  FIG. 7  seated to an end of the input shaft; 
           [0021]      FIG. 12  is a diagram of a yoke; 
           [0022]      FIG. 13  is another diagram of the yoke; 
           [0023]      FIG. 14  is a top view of a yoke; 
           [0024]      FIG. 15  is a perspective view of a bolt guide cap having a fin being fitted to the notch of the input shaft; and 
           [0025]      FIG. 16  is a diagram of a seating relationship between an input shaft, guide cap and yoke, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In the following description, for purposes of explanation and not limitation, specific details may be set forth to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. Detailed descriptions of well-known components are omitted so as not to obscure the description of the present invention. 
         [0027]      FIG. 1  shows a portion of an exemplary steering system  10  with which the bolt guide cap may be used. Although suitable for use with various steering systems, an exemplary rack and pinion steering system  10  includes an input shaft  12  that couples to a pinion gear. A driver controls vehicle steering by turning a steering wheel. The steering wheel is coupled to a steering column, which in turn is coupled to an intermediate shaft  18 . A yoke  14  connects the intermediate shaft to the input shaft  12 . When a driver turns the steering wheel, the yoke  14  rotates relative to the axis of the input shaft  12  based on linkages through the steering column and intermediate shaft  18 . The yoke  14  is substantially fixed relative to the input shaft  12  and intermediate shaft  18 . Accordingly, rotation of the yoke  14  causes the input shaft  12  to rotate. The pinion gear in turn translates the rotation into lateral movement for adjusting the position of the wheels. For example, in a front wheel drive system, the front wheels are moved.  FIG. 2  shows a portion of the steering system  10 , including the input shaft  12 , yoke  14 , and a guide cap  16 , according to an embodiment of the present invention. Also shown is an umbrella cap  17  that is stretched over a groove of the input shaft  12 . 
       The Problem Identified 
       [0028]    For a driver to maintain steering control of a vehicle, the steering column needs to remain coupled to the input shaft  12  and the rest of the steering system  10 . A yoke  14  is seated at the end portion of the input shaft  12 . If the yoke is not properly seated and secured, vehicle steering control may be lost. The yoke  14  is secured to the input shaft  12  by a yoke bolt  20 .  FIG. 3  shows a relative position of the input shaft  12  and yoke bolt  20 . The input shaft  12  has a crescent shaped cut out, referred to as a whistle notch  22 . The whistle notch  22  has generally the same contour or a more open contour as a portion of the yoke bolt  20  (not accounting for bolt threads). Upon proper installation, the yoke bolt  20  sits in the whistle notch  22 . In particular, a longitudinal direction  24  (depicted as a target into the paper) of the yoke bolt  20  will be substantially parallel to a tangent  26  (depicted as a target into the paper) of the whistle notch surface in a transverse direction (generally perpendicular to the input shaft axis). Because the contours of the yoke bolt  20  and whistle notch  22  generally conform to each other, upon proper installation, axial displacement of the bolt  20  relative to the input axis  12  can be prevented. 
         [0029]    A problem arises however, in a case where the yoke  14  does not have the proper axial or rotational alignment with the input shaft  12  during installation. In a case where there is a rotational offset, the longitudinal direction  24  (shown as a target and arrow offset from the plane of the paper) of the yoke bolt  20  is not substantially parallel to the tangent  26  (shown as a target into the paper) of the whistle notch  22 , as shown in  FIG. 4 . As a result, the yoke bolt  20  is rotationally offset relative to the whistle notch  22  and can dig into the input shaft during installation. In particular when the yoke bolt  20  is secured it will thread into the input shaft  12 . Similarly, the bolt  20  can thread into the input shaft  12  when the yoke  14  and yoke bolt  20  are axially displaced. Such threading disguises as a proper securing of the yoke  14  to the input shaft  12 . For example, the torque created by threading the yoke bolt  20  into the input shaft  12  may fool the plant operator into thinking that the bolt  20  has been properly torqued down. However, when misaligned the yoke bolt  20  is not fit to the whistle notch  22 , and therefore the yoke  14  may not be adequately secured to the input shaft  12 . As a result, the yoke  14  may be displaced either rotationally and/or axially relative to the input shaft  12  upon installation and allow for changes in such displacement during the life of the vehicle. Even if the yoke moves rotationally after installation so that the yoke bolt  20  moves into the whistle notch  22 , the deformed input shaft  12  (resulting from threading the bolt into the shaft) may allow positional an undesirable amount of play between the yoke  14  and input shaft  12  diminishing steering control by the driver. Further, it is possible that steering control may be lost due to a failed alignment. For example axial separation between the yoke  14  and input shaft  12  potentially may occur resulting in complete loss of steering control. Applicants guide cap  16  serves to assure that the yoke  14  is properly seated on the input shaft with the yoke bolt  20  properly aligned within the whistle notch  22  upon installation and over the continued operation of the vehicle. 
         [0030]    The guide cap  16  addresses the problem of axial displacement of the guide cap  16  and yoke  14  relative to the input shaft  12  with input shaft engaging members. Rather than relying upon a tight fitting cap as a means for keeping the cap from sliding axially off the input shaft, the engaging members  28  provide a strong retention capability preventing axial displacement. As a result tolerances for the snugness of the fit of the cap may be relaxed. 
       Guide Cap  16   
       [0031]    The guide cap  16  serves to assure proper installation and alignment of the yoke  14  to the input shaft  12 .  FIGS. 5-6  (and  15 - 16 ) show a guide cap  16  according to an embodiment of the present invention.  FIGS. 7-11  show a guide cap according to another embodiment of the present invention. Like parts are given like numbers. Further, the first embodiment is substantially the same as the second embodiment, while also including a skirt portion  29 . 
         [0032]    The guide cap  16  includes a cap body  24  and a fin  26 , and in some embodiments also includes a skirt  29  (e.g., see  FIGS. 1 ,  5  and  6 ). The cap body  24  is generally ring shaped having a through opening  25  bordered by an inner circumferential wall surface  30  (see  FIG. 9 ). Although a generally smooth, generally cylindrical outer surface is depicted of the cap body, other outer surface shapes may be implemented. Of significance is that the inner wall surface  30  generally conforms to a corresponding circumferential surface portion of the input shaft  12 . For example, the circumferential wall  30  has generally a circular arc shape conforming to a circular arc shape of the input shaft  12 . In a preferred embodiment, the input shaft end portion receiving the guide cap  16  may also have a circumferentially flat portion  33  (as distinguished from the arc shape of another portion(s) or a remaining portion  35  of the circumference). See  FIG. 9 . Most preferably, the cap body inner wall  30  has an asymmetrical contour corresponding to an asymmetrical contour of the input shaft, so as to assure that the cap is installed correctly (e.g., as opposed to being installed backwards or by some other offset arc distance). The corresponding surfaces allow for a coarse rotational alignment between the cap body  24  and the input shaft  12 . 
         [0033]    As part of the cap body  24 , or extending from the cap body  24 , are one or more input shaft engaging members  28 . In one embodiment the members  28  are deflectable fingerlike projections, although other shapes and structures also are contemplated. Of significance is that each member  28  includes a protrusion  31  that extends radially inward to a point more inward than the cap body&#39;s  24  inner circumferential wall surface  30 . Such protrusion  31  aligns to a circumferential groove  32  in the input shaft  12 . See  FIGS. 3 ,  4  and  11 . In a sample embodiment each member  28  provides an estimated 780 N retention force. 
         [0034]    The fin  26  extends radially outward from the cap body  24  and extends longitudinally to a distance exceeding the length of the cap body  24 . The fin  26  has a generally planar first surface  34  at one side and another generally planar surface  36  at an opposite side. Such planar surfaces  34 ,  36  may be parallel, or in other embodiments may have different normal vectors. Along a radially inward edge  39  is formed a notch  38  having an arc contour, (e.g., for accommodating in cross section the yoke bolt fin). Distally beyond the fin notch  38 , a portion of the radially inward edge  39  is generally straight and extends in the axial direction  41 . At a distal portion  40  beyond the cap body  24  in a longitudinal direction, the fin  26  includes an anchor member  42 , referred to herein as a fin anchor. The fin anchor  42  extends radially inward of the longitudinally extending portion of the edge  39 . Such fin anchor  42  also extends radially inward in a manner making it radially inward of the ring member&#39;s inner surface  30 . See  FIG. 6 . The fin  26  also may include a spine  46  wider than a main portion  48  of the fin  26 . The spline  46  adds stiffness to the fin  26  so as to minimize or avoid deflection of the fin before or during installation of the guide cap. The spine  46  also serves as a shield for blocking debris from the area of the yoke slit. In a sample embodiment the spine to yoke clearance upon installation is 2.0-4.0 mm, although other clearances and tolerances may be implemented. 
       Input Shaft  12  and Yoke  14   
       [0035]    Referring to  FIGS. 3-4 , the input shaft  12  includes an end portion  50 , which receives the guide cap  16  and yoke  14 . A longitudinal groove  52  is formed at a distal end of the end portion  50  extending radially inward along an arc portion of the distal end circumference. See  FIGS. 3 ,  4 ,  11  and  15 . Although the longitudinal groove is longer longitudinally than circumferentially in the illustrated embodiment, in other embodiments the groove may be the same or longer in the circumferential direction. The axial length of the longitudinal groove  52  is sufficient to allow the fin anchor  42  to seat into the longitudinal groove  52 . The circumferential length of the groove  52  preferably is a close fit to the corresponding width of the fin anchor  42 . In the sample embodiment the groove  52  width is 2.2 mm and the fin width is 1.9 mm so that the clearance between the fin anchor  42  and the circumferential walls of the groove  52  are 0.15 mm. The fin anchor  42  extends into the groove  52 . In the sample embodiment the fin anchor  42  abut the radially inner surface of the groove  52 . The groove depth for such sample embodiment is 1.65 mm, although the specific depth may differ being lesser or greater in other embodiments. The fin anchor  42  situated in the groove  52  prevents fin wobble and provides a secondary prevention of cap rotation. 
         [0036]    In some embodiments the end portion  50  includes a generally smooth circumferential surface  54 . Over a portion of the axial length of the end portion  50 , the circumferential surface  54  includes one or more flat portions  56 . In addition, the whistle notch  22  is formed in the end portion  50 . In some embodiments the end portion  50  includes a distal portion  58  of a first radius (measured relative to an arc shaped portion of the circumferential surface  54 ) and a proximal portion  60  having a larger radius (as similarly measured relative to an arc shaped portion of the circumferential surface  54 ). The groove  32  is formed in the proximal portion  60 . In a sample embodiment the circumferential groove  32  has a depth of 0.75 mm and the projection  31  of the input shaft engaging member  28  has a corresponding radial length of 0.75 mm for occupying the entire depth of the groove  32 , so as to maximize retention capability. The axial span of each projection  31  is shorter than the axial length of the circumferential groove  32 , to allow a minimal prescribed axial play between the cap  16  and input shaft  12 . In the sample embodiment the amount of play is approximately 0.35 mm, but the specific amount of play may vary in other embodiments. In some embodiments the groove  32  spans an entire circumference of the end portion  50 . In other embodiments the groove  32  spans less than the entire circumference of the end portion  50 . In such other embodiments there may be one or more grooves  32  along the circumference. Although the groove  32  is depicted on the proximal portion  60 , the groove(s)  32  may be formed instead in the distal portion  58 , and may be located on either or both of the surfaces  54 ,  56 . 
         [0037]    Referring to FIGS.  2  and  12 - 14 , the yoke  14  includes a distal portion  82  to which the intermediate shaft  18  connects, and a proximal body  84  for receiving the end portion  50  of the input shaft  12 . The proximal body  84  includes an axial channel  29 , a yoke bolt channel  86  and a slit  88 . The axial channel  29  extends in an axial direction  41 , as defined by the axial length of the input shaft  12 , and receives the end portion  50  of the input shaft  12 . The yoke bolt channel  86  extends in a transverse direction  92  generally perpendicular to an axial direction  41 , and receives the yoke bolt  20 . The slit  88  extends from an outer surface of the yoke  14  radially inward to the axial channel  29 . When the yoke  14  is properly aligned, the slit  88  opens to the axial channel  29  meeting an area where the whistle notch  22  of the input shaft  12  is located. 
         [0038]    The slit  88  intersects the yoke bolt channel  86 , and spans an axial length that in some embodiments is longer than a diameter of the yoke bolt channel  86 . The slit  88  divides the yoke bolt channel  22  into two lengths. In an example embodiment, the yoke bolt  20  enters the yoke bolt channel  86  at an opening, traverses a first length  91  of the channel  86 , traverses the intersecting portion of the slit  88 , then traverses a second length  93  of the channel  86 . In a preferred embodiment the first length  91  is not threaded and the second length  93  is threaded. Such second length includes threads  95 , which correspond to threads on the yoke bolt  20 . As the yoke bolt  20  is tightened to a desired torque by threading to the threads  95  of the yoke bolt channel  86 , the diameter of the axial channel  25  is slightly decreased tightening the yoke  14  to the input shaft  12 . 
         [0039]    The yoke  14  may have a symmetrical inner surface along the axial channel  29 , such as including two symmetrically opposed flats  101 ,  103 , as shown in  FIG. 14 . The end portion  50  also may have two symmetrically opposed flats along its outer circumference. As a result it is possible to install the yoke backwards. The fin  26  serves as a guide during installation preventing such backwards installation. 
         [0040]    As the yoke  14  is installed onto the input shaft  12 , the yoke  14  is blocked from further advancement by a seat  109  on the input shaft (See  FIG. 16 ). Such seat is formed by a transition region where input shaft diameter changes from a narrow diameter (to which the yoke conforms) to a larger diameter. In an example embodiment the seat is formed by as a 0.6 mm bore. The yoke  14  may be axially displaced slightly during installation to allow the yoke bolt channel  86  to be in axial alignment with the whistle notch  22 . The fin notch  38  serves as a guide for preferred limits of axial displacement of the yoke  14  relative to the cap  16  while the yoke bolt  20  is being installed as it transversely passes through the fin notch  38 . At its most proximal positioning along the input shaft  12 , the yoke  14  sits on the seat  109 . The yoke  14  may be displaced relative to the seat  109  during installation as needed for the yoke bolt  20  to align with the whistle notch  22 . 
       The Guide Cap Aids in Alignment and Provides a High Retention Capability 
       [0041]    The guide cap  16  first is installed to the input shaft  12  in a manner which limits axial, rotational and radial play between the guide cap  16  and input shaft  12  to within prescribed tolerances.  FIG. 15  shows the guide cap  16  in the process of being installed. For the guide cap  16  to fit to the input shaft  12 , the flat surface  33  of the cap body inner wall is aligned with a flat surface  56  of the input shaft&#39;s  12  peripheral wall. To avoid installing the cap backwards, the cap  16  is positioned so that the fin anchor  42  is to the same side as the input shaft&#39;s longitudinal groove  52 . The corresponding flat surfaces  33 ,  56  provide a coarse radial and rotational alignment, allowing a prescribed amount of radial play and rotational play between the guide cap  16  and the input shaft  12 . The cap body  24  also may include rigid or deformable ribs  94 ,  96  extending axially and protruding radially, see  FIG. 4 , which minimize radial play. The deformable ribs  94 ,  96  allow for a looser fit between the circumferential wall  30  and the input shaft surface, while filling in a radial separation to achieve contact with the input shaft  12 . 
         [0042]    Referring to  FIGS. 11 and 15 , as the guide cap  16  is moved along the input shaft  12  toward its final seated position, the fin anchor  42  mates to the input shaft longitudinal groove  52  providing fine rotational alignment between the guide cap  16  and input shaft  12  within any transverse plane. The lateral walls of the longitudinal groove  52  and fin anchor  42  are machined to tight tolerances to assure such fine rotational alignment. Further, the radially inward face of the fin anchor  42  may be chamfered to ease the mating of the fin anchor  42  into the input shaft longitudinal groove  52  during installation. Also, the depth of the input shaft longitudinal groove  52  limits the radial depth to which the fin anchor  42  may extend, thereby setting the radial position of the fin anchor  42 . Thus, fine radial alignment is achieved at the distal end of the fin  26 . 
         [0043]    The axial distance along the guide cap  16  between the protrusion(s)  31  of input shaft engaging member(s)  28  and the fin anchor  42  is substantially equal to the axial distance between the input shaft groove  32  and the input shaft longitudinal groove  52  within prescribed tolerances (such as for allowing only a minimal amount of play). As the fin anchor  42  is seating to the input shaft longitudinal groove  52 , the input shaft engaging member(s)  28  snap into engagement with the input shaft groove  32 . For example, as the guide cap  16  slides along the input shaft  12 , the input shaft engaging member(s)  28  are deflected, and thereby biased away from their normal relaxed position, by the surface of the input shaft  12 . Once the guide cap  16  moves sufficiently far along the input shaft  12 , the protrusion(s)  31  encounter the input shaft groove  32  removing all or a portion of the bias. Thus, the input shaft engaging member(s)  28  return toward their normal position with the protrusion(s)  31  resting in the input shaft groove  32 . With the input shaft engaging member(s)  28  engaging the input shaft groove  32  and the fin anchor  42  seated in the input shaft longitudinal groove  52 , the guide cap  16  is fixed relative to the input shaft. Axial play between the guide cap  16  and input shaft  12  is limited by the fit of the input shaft engaging member(s)  28  in the input shaft groove  32  and the fin anchor in the input shaft longitudinal groove  52 . The input shaft engaging members  28  provide a retention force resisting axial separation. 
         [0044]    To prevent overshooting the circumferential groove  32  during installation and to set the axial position of the guide cap  16  relative to the input shaft, the guide cap  16  also includes a seating wedge  99 , (see  FIGS. 7 ,  9  and  16 ). While the projections  31  seated in the circumferential groove  32  provide one means of locating the guide cap axially, the seating wedge  99  provides another means. In particular the projections  31  seat into the groove  32  with a prescribed minimal amount of axial play. The seating wedge  99  seats to a corresponding surface  77  on the input shaft  12  (See  FIG. 16 ). The surface  77  blocks further axial movement of the cap body  24  in the installation direction. Installing the guide cap so that the wedge  99  seats to the corresponding surface  77  assures that the guide cap&#39;s input shaft engaging members  28  do not overshoot the input shaft&#39;s groove  32 . 
         [0045]    The seating wedge  99  is formed on the cap body  24  extending radially inward beyond the majority portion of the cap body inner wall surface  30 . In a sample embodiment the seating wedge  99  is adjacent to the flat surface  33  of the cap body  24 . As shown in  FIG. 16  the outer surface of the input shaft is asymmetrical. Note that the corresponding surface  77  is more proximal than the transition region discussed above where the yoke seat  109  is located. The axial distance between the yoke seat  109  and the corresponding surface  77  preferably exceeds the longitudinal length of the wedge  99  so that the yoke is axially spaced from a distal surface of the seating wedge  99 . In the sample embodiment a 1.84 mm clearance occurs between a distal edge of the wedge  99  and an axially adjacent, corresponding surface of the yoke  14 . Accordingly, the yoke  14 , if axially seated, seats to the yoke seat  109  not to the wedge  99  or another part of the guide cap  16 . 
         [0046]    Rotational play between the cap  16  and input shaft  12  is limited by the corresponding flat surfaces  33 ,  56  and by the fin anchor  42  seated in the input shaft longitudinal groove  52 . The protrusions  31  are seated to a prescribed depth in the input shaft&#39;s groove  32 . Accordingly, the proximal end of the guide cap  16  also achieves fine radial alignment with the input shaft  12 . Thus, radial play of the guide cap  16  is limited by the fin anchor  42  seated to a prescribed depth in the input shaft longitudinal groove  52 , and by the protrusion(s)  31  seated to a prescribed depth of the input shaft groove  32 . Accordingly, the axial, radial, and rotational position of the fin  26  and the fin notch  38  are precisely set relative to the input shaft with minimal prescribed play. 
         [0047]    Next, the yoke  14  is installed. Given the minimal play between the guide cap  16  and input shaft  12 , the yoke  14  may be precisely positioned relative to the input shaft  12  by aligning the yoke  14  precisely with the guide cap  16 . With the guide cap  16  in place, the yoke  14  is slid onto the end portion  50  of the input shaft  12 . The input shaft  12  mates to the axial channel  29  of the yoke  14 . In an example embodiment, the axial channel  29  also may have flat portions and intermediary arc portions defining its surrounding wall. For the yoke  14  to fit to the input shaft  12 , the flat surfaces of the yoke&#39;s axial channel wall are aligned with the flat surfaces  56  of the input shaft  12  peripheral wall. The guide cap&#39;s fin  26  limits the yoke position to one of the two positions where the yoke  14  could slide onto the input shaft  14 . The corresponding flat surfaces of the yoke and input shaft provide a coarse alignment during installation. The guide cap fin  26  may extend approximately to the distal tip of the input shaft  12 . Accordingly, for the yoke  14  to fit to the input shaft, the yoke slit  88  must be aligned with the fin  26 . The distal edges of the fin  26  first encountered by the yoke  14  during installation may be chamfered to ease the mating of the fin  26  into the slit  88  as the yoke  14  is positioned and moved along the input shaft  12 . 
         [0048]    As noted above, the end portion  50  of input shaft  12  has a distal portion  58  with a smaller diameter than that of a proximal portion  60 . The diameter and shape of the yoke&#39;s axial channel generally conforms to that of the distal portion  58 . Thus, eventually as the yoke  14  is moved axially along the input shaft  12 , the yoke will encounter either the cap body  24  or the wider diameter proximal portion  60 . In a preferred embodiment, the yoke  14  first encounters the input shaft  12 , rather than the guide cap  16 . In such embodiment the yoke  14  encounters a transition region between the narrow diameter distal portion  58  and the wider diameter proximal portion  60  of the input shaft  12 . Note, however, that when the yoke bolt  20  is installed the yoke  14  may be displaced axially as needed away from such encountered transition region. Also note that this transition region differs from that where the cap  16  is seated. Thus, the inputs shaft  12  may have at least axial length portion of differing diameter. For example, the end portion  50  may encompass two of such length portion with the border between the end portion  50  and the remainder of the input shaft being the transition region where the cap body  24  seats. 
         [0049]    With the yoke  14  situated on the input shaft  12  in a rotational alignment coarsely determined by corresponding flat surfaces and finely determined by the fin  26 , the yoke bolt  20  may be installed next. The yoke bolt  20  is inserted into the yoke bolt channel  86  and slid through a first length  91  of the channel  86  into the area of the intersecting slit  88 . Also in such area the yoke bolt  20  encounters the whistle notch  22  of the input shaft. If the yoke  14  is precisely aligned, the whistle notch tangential surface is substantially parallel to the transverse direction of the yoke bolt channel  86 . The yoke bolt channel  26  is radially offset from the center of the yoke&#39;s axial channel  25  so that when properly aligned the yoke bolt  20  slides along or offset from the whistle notch  22  for the entire length of the encounter with the whistle notch exposed area without digging into the whistle notch  22 . The yoke bolt  20  slides through such slit area and into the second length  93  of the yoke bolt channel  86 , where it encounters threads  95 . The yoke bolt  20  then continues the rest of the way into the yoke bolt channel  86  with the yoke bolt threads screwing onto the yoke bolt channel threads  95 . The yoke bolt  20  may be screwed inward to a desired torque force to tighten the yoke bolt  20  and thereby tighten the yoke  14  relative to the input shaft  12 . For example, as the yoke bolt  20  is tightened the lengths  91  and  93  are moved together narrowing the slit  88  and slightly reducing the yoke axial channel  29  cross sectional area (e.g., diameter) so as to fit tighter to the input shaft surfaces. 
         [0050]    If precise rotational alignment is not provided for the yoke  14 , then the whistle notch tangential surface and the transverse direction of the yoke bolt channel  86  will not be parallel and the yoke bolt  20  may thread into the input shaft  12 . For example, if not in rotational alignment the yoke bolt  20  may thread into the input shaft at either a first encountered exposed area of the whistle notch  22 , or at a portion encountered thereafter. Such problem has been described above more fully in a separate section. 
         [0051]    With the yoke bolt  20  tightened the yoke  14  is secured to the input shaft  12 . The guide cap  16  assures that the yoke bolt has been positioned in proper rotational relationship with the whistle notch  22 . The guide cap&#39;s fin notch  38  provides limits to axial and radial displacement of the yoke bolt  20  relative to the axial position of the whistle notch  22 . The yoke is machined so that the yoke bolt channel  86  is at a sufficient radial distance relative to the whistle notch  22  so as to avoid threading into the whistle notch  22  when rotationally positioned to a given tolerance. Such fine rotational positioning is achieved by the relationship between the fin anchor  42  and the longitudinal groove  52  of the input shaft  12 . The fin anchor  42  in turn aligns the fin  26 . The fin  26  fits snugly in the slit  88  so that such fine rotational tolerances are achieved. As a result a fine, precise rotational position of the yoke bolt channel  86  is achieved so that the yoke bolt  20  is both radially and rotationally positioned relative to the whistle notch  22  to assure an aligned installation. 
         [0052]    Once the yoke  14  and guide cap  16  are installed on the end of the input shaft  12 , the input shaft engaging members  28  grip the input shaft  12 . The members&#39; projections  31  rest in the circumferential groove  32  and in the sample embodiment resist axial separation forces up to 780 N. 
         [0000]    It is to be understood that the foregoing illustrative embodiments have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the invention. Words used herein are words of description and illustration, rather than words of limitation. In addition, the advantages and objectives described herein may not be realized by each and every embodiment practicing the present invention. Further, although the invention has been described herein with reference to particular structure, materials and/or embodiments, the invention is not intended to be limited to the particulars disclosed herein. The invention is intended to extend to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made in form and details without departing from the scope and spirit of the invention.