Abstract:
A shaft assembly having a first shaft and a second shaft interconnected by a bipot joint is disclosed. The first shaft and the second shaft are disposed in overlapping spaced relationship. The bipot joint includes a pivot block sandwiched between the first shaft and the second shaft. The pivot defines a mounting surface abutting one of the first and second shafts, and a semi-annular surface opposing the mounting surface and abutting the other of the first shaft and the second shaft. A fastener extends through a bore defined by the first shaft, the pivot block and the second shaft to interconnect the first shaft, the pivot block and the second shaft. The fastener includes a spring to bias the first shaft, the pivot block and the second shaft together, thereby de-lashing the bipot joint.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The subject invention relates to a shaft assembly, and more specifically to a bipot joint interconnecting a first shaft and a second shaft. 
         [0003]    2. Description of the Prior Art 
         [0004]    Steering shaft assemblies transmit the movement of a steering wheel through an indirect path to a steering gear. The shaft assemblies typically include at least a first shaft and a second shaft, connected by cardan joint, i.e., a universal joint. Cardan joints permit pivoting movement around a single point in space about two mutually perpendicular axis&#39; that are also mutually perpendicular to a spin axis of the shaft at a 0° joint angle. It is desirable for the shaft assembly to maintain a high torsional stiffness, while keeping frictional loss to a minimum. In order to maintain the high torsional stiffness, the cardan joint must be de-lashed, i.e., remove the slack from the joint. Because most cardan joints utilized in the steering shaft assemblies are constructed using multiple pivot pins, the common solution has been to increase the precision of the parts, which drives up the cost to manufacture the shaft assembly. 
         [0005]    A bipot joint utilizes a single pin to achieve the same relative movement between the first shaft and the second shaft as that of the Cardan joints. Typically, the bipot joint includes forming a cross-cut slot into the first shaft, and coupling a T-pin to the second shaft, with the transversely extending leg of the T-pin extending through the cross-cut slot to connect the first shaft and the second shaft. Accordingly, the second shaft is free to rotate about the T-pin axis and the first shaft is free to rotate around the perpendicular axis defined by the transversely extending leg of the T-pin, via the T-pin&#39;s freedom to slide on a surface of the first shaft. Like the cardan style joint, the bipot joint must also be de-lashed, which increases the friction present within the bi-pot joint. Additionally, the bipot joint as described above are prone to wear. 
       SUMMARY OF THE INVENTION AND ADVANTAGES 
       [0006]    The subject invention provides a shaft assembly. The shaft assembly comprises a first shaft having an output end. A second shaft having an input end partially overlaps the output end of the first shaft. A pivot block is disposed between the output end of the first shaft and the input end of the second shaft. The pivot block defines a pivot axis about which the first shaft and the second shaft pivot relative to each other. A fastener interconnects the output end, the pivot block and the input end. The fastener defines a rotational axis, which is transverse to the pivot axis. The first shaft and the second shaft rotate relative to each other about the rotational axis. 
         [0007]    The pivot block includes a mounting surface disposed against one of the output end and the input end, and further includes a semi-annular surface. The semi-annular surface opposes the mounting surface, and is disposed against the other of the input end and the output end. The semi-annular surface facilitates the pivotal movement of the first shaft relative to the second shaft. 
         [0008]    Accordingly, the subject invention provides a shaft assembly having a bipot joint interconnecting the first shaft and the second shaft, which eliminates the lash in the bipot joint by assembling the bi-pot joint sandwich style. This simplified form of assembly does not require the high precision previously required in other types of universal joints utilized in steering shaft assemblies, thereby reducing the manufacturing costs of the steering shaft assemblies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0010]      FIG. 1  is a perspective view of a first embodiment of a shaft assembly; 
           [0011]      FIG. 2  is a side view of the first embodiment of the shaft assembly; 
           [0012]      FIG. 3  is an enlarged fragmentary side view of the first embodiment of the shaft assembly; 
           [0013]      FIG. 4  is a cross sectional view of the first embodiment of the shaft assembly along cut line  4 - 4  shown in  FIG. 3 ; 
           [0014]      FIG. 5  is an enlarged fragmentary side view of a second embodiment of the shaft assembly; and 
           [0015]      FIG. 6  is a cross sectional view of the second embodiment of the shaft assembly along cut line  6 - 6  shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a shaft assembly is generally shown at  20 . The shaft assembly  20  shown in the Figures is embodied as a steering shaft system for a vehicle. The steering shaft system is for transmitting rotational inputs form a steering wheel to a steering gear through an indirect path. It should be appreciated, however, that the subject invention may be configured for any number of uses, and is not limited to the steering shaft shown in the Figures. 
         [0017]    Referring to  FIGS. 1 through 4 , the shaft assembly  20  includes a first shaft  22  having an output end  24 . The output end  24  includes a rectangular cross section, as best seen in  FIGS. 1 ,  4  and  6 . The size of the output end  24  may vary depending on the type of use anticipated for the shaft assembly  20  and the torque transmitted by the shaft assembly  20 . It should be appreciated that while the output end  24  of the first shaft  22  includes the rectangular cross section, the rest of the first shaft  22  may include some other cross sectional shape suitable for the intended use of the shaft assembly  20 . For example, the first shaft  22  may include the output end  24  having the rectangular cross section, while the rest of the first shaft  22  includes a circular cross section suitable for being rotationally supported by a bracket. 
         [0018]    The shaft assembly  20  further includes a second shaft  26  having an input end  28 . The input end  28  partially overlaps the output end  24  of the first shaft  22 . The output end  24  and the input end  28  each include opposing planar surfaces. As shown, the input end  28  includes a rectangular cross section opposing the rectangular cross section of the output end  24 , as best shown in  FIGS. 1 ,  4  and  6 . The size of the input end  28  may vary depending on the type of use anticipated for the shaft assembly  20  and the torque transmitted by the shaft assembly  20 . It should be appreciated that while the input end  28  of the second shaft  26  includes the rectangular cross section, the rest of the second shaft  26  may include some other cross sectional shape suitable for the intended use of the shaft assembly  20 . For example, the second shaft  26  may include the input end  28  having the rectangular cross section, while the rest of the second shaft  26  includes a circular cross section suitable for being rotationally supported by a bracket. 
         [0019]    As best shown in  FIG. 3 , a pivot block  30  is disposed between, i.e., is sandwiched between the output end  24  of the first shaft  22  and the input end  28  of the second shaft  26 . The pivot block  30  defines a pivot axis P about which the first shaft  22  and the second shaft  26  pivot relative to each other. 
         [0020]    The pivot block  30  includes a mounting surface  32 , which is disposed against one of the output end  24  and the input end  28 . The pivot block  30  further includes a semi-annular surface  34 , opposing the mounting surface  32 , and disposed against the other of the input end  28  and the output end  24 . The semi-annular surface  34  facilitates the pivotal movement of the first shaft  22  relative to the second shaft  26 . In other words, the pivot block  30  includes the mounting surface  32  disposed against one of the input end  28  and the output end  24 , and further includes the semi-annular surface  34  disposed against the other of the input end  28  and the output end  24 . It should therefore be appreciated that the pivot block  30  defines the mounting surface  32  on one side and the semi-annular surface  34  on another side opposing the mounting surface  32 , disposed 180° about the pivot axis P relative to the mounting surface  32 . It should also be appreciated that the mounting surface  32  and the semi-annular surface  34  may be disposed against either the input end  28  or the output end  24 . 
         [0021]    Preferably, the mounting surface  32  includes a smooth or flat planar surface to facilitate the rotational movement between the pivot block  30  and the one of the input end  28  and the output end  24  disposed against the mounting surface  32  as will be described below. However, the mounting surface  32  may also include a roughened surface to increase the resistance to rotation between the mounting surface  32  and the one of the input end  28  and the output end  24 . 
         [0022]    Preferably, the other of the output end  24  and the input end  28  disposed against the semi-annular surface  34  of the pivot block  30  defines a concave recess  36 . The concave recess  36  is complimentary in shape to the semi-annular surface  34  of the pivot block  30  for engaging the semi-annular surface  34 . The concave recess  36  supports the semi-annular surface  34  of the pivot block  30  to guide the pivotal movement between the first shaft  22  and the second shaft  26 . 
         [0023]    In the embodiment shown in  FIGS. 1 through 4 , the pivot block  30  includes a shoe  38 . The shoe  38  defines the mounting surface  32 , and further defines a semi-circular groove  40 . A pivot pin  42 , having a circular cross section defining the semi-annular surface  34 , is disposed between the semi-circular groove  40  defined by the shoe  38  and the concave recess  36  defined by the one of the input end  28  and the output end  24 . It should be appreciated that the pivot pin  42  may include a solid rod, a cylindrical tube, or may be formed from flat stock rolled to have a circular cross section. Alternatively, referring to the embodiment shown in  FIGS. 5 and 6 , the pivot block  30  may include a single uniform block defining the mounting surface  32  and the semi-annular surface  34 . 
         [0024]    As best shown in  FIG. 4 , a fastener  44  interconnects the output end  24 , the pivot block  30  and the input end  28 . The fastener  44  defines a rotational axis R, which is transverse to and intersects the pivot axis P. The first shaft  22  and the second shaft  26  rotate relative to each other about the rotational axis R. Accordingly, the first shaft  22  and the second shaft  26  move relative to each other about a point defined by the intersection of the pivot axis P and the rotational axis R. 
         [0025]    The output end  24 , the pivot block  30  and the input end  28  cooperate to define a concentric bore  46 , which extends through the output end  24 , the pivot block  30  and the input end  28 . The fastener  44  extends through the bore  46 . The fastener  44  includes a width W, and the bore  46  defines a diameter D greater than the width W of the fastener  44  to permit the pivotal movement between the first shaft  22  and the second shaft  26 . The diameter D of the bore  46  must be sufficiently large relative to the width W of the fastener  44  to accommodate the pivotal movement between the first shaft  22  and the second shaft  26 . In other words, a larger difference between the diameter D of the bore  46  and the width W of the fastener  44  permits a larger range of pivotal movement between the first shaft  22  and the second shaft  26 . It should be appreciated, that the diameter D of the bore  46  may vary, so that the difference between the diameter D of the bore  46  and the width W of the fastener  44  in the first shaft  22  is different than the difference between the diameter D of the bore  46  and the width W of the fattener in the pivot block  30  or the second shaft  26 . It should also be appreciated that the bore  46  may define an elongated slot, permitting a range of motion in substantially only one direction. 
         [0026]    The fastener  44  includes a first end having a head  50  attached to the first end, and further includes a second end  52  having a spring  54  attached to the second end  52 . The spring  54  biases the output end  24 , the pivot block  30  and the input end  28  together against the head  50 , thereby sandwiching the shaft assembly  20  together to de-lash the shaft assembly  20 . 
         [0027]    Referring to  FIG. 4 , the spring  54  includes at least one spring arm  56  extending from the fastener  44  transverse to the bore  46 . Preferably, the spring  54  includes a pair of spring arms  56  extending across the bore  46  opposite each other. Alternatively, as shown in  FIG. 6 , the spring  54  may include a bowed e-clip  58  coupled to the fastener  44 . The torsional stiffness of the bipot joint created by the interaction of the input end  28 , the pivot block  30 , the output end  24  and the fastener  44  is dependent upon the biasing force supplied by the spring  54 . The higher the biasing force supplied by the spring  54 , the higher the torsional stiffness is. It should be appreciated that the spring  54  may include some other configuration or type of spring  54  not specifically described or shown herein, so long as the spring  54  biases the input end  28 , the pivot block  30  and the output end  24  together to de-lash the shaft assembly  20 . 
         [0028]    Referring to  FIG. 4 , the head  50  defines an aperture  60  and further includes a retaining pin  62  extending through the aperture  60 . The retaining pin  62  includes a length greater than the diameter D of the bore  46 . Accordingly, the retaining pin  62  spans across the bore  46 , and supplies the resistance to which the spring  54  acts to bias the shaft assembly  20  together. Alternatively, as shown in  FIG. 6 , the head  50  may include a cap  64  defining a contact surface greater than the diameter D of the bore  46 , i.e., the fastener  44  may include a cap  64  formed or fixedly attached thereto and having an area larger than the diameter D of the bore  46  to cover the bore  46 . It should be appreciated that the head  50  of the fastener  44  may include other configurations preventing axial movement of the fastener  44  within the bore  46  along the rotational axis R. 
         [0029]    The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. As is now apparent to those skilled in the art, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.