Patent Publication Number: US-6213883-B1

Title: Flexible coupling for steerable drive shaft

Description:
CROSS REFERENCES TO CO-PENDING APPLICATIONS 
     This patent application is a continuation-in-part of Ser. No. 08/746,374 entitled “Constant Velocity Flexible Coupling” filed on Nov. 8, 1996, now U.S. Pat. No. 5,951,400, which is a continuation-in-part of Serial No. 08/415,667 entitled “Constant Velocity Flexible Coupling” filed on Apr. 3, 1995, now abandoned, by the same inventor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is for a constant velocity flexible coupling, and more particularly, pertains to a flexible disc coupled mechanism similar in function to a universal drive joint for use in 4-wheel drive steer devices, such as a 4-wheel drive lawn mower or other such vehicles. 
     2. Description of the Prior Art 
     Four-wheel drive and steer mechanisms have been reserved for high end expensive commercial and industrial equipment ranging in the tens of thousands of dollars. The methods used to achieve power delivery through a pivoting steerable mechanism are effective and durable, but not in the same class as the smaller and more inexpensive and smaller lawn tractors intended for general consumer use. The cost is high and many do not even use CV-joints. Four-wheel drive farm tractors and utility tractors use designs far too expensive and are similar in design to units utilized in front wheel drive cars. 
     Another problem with prior art devices is that of offering a low speed flexible coupling that can function effectively up to 50° angles and yet fit in a relatively short (axial) space and require no sliding connections such as splines for absorbing axial reciprocation. The present invention uses no such spline devices and as such can be fabricated for a much more reasonable price. Four-wheel drive/steer mechanisms have been incorporated in some prior art lawn tractors, but steering and drive devices have limited the steering angle to a low range of steering at approximately 20°. 
     Although disc-type flexible joints are not new, the turning radius of single disc-type flexible joints are limited by the geometry of the single flexible disc. The present invention overcomes this problem by utilizing two flexible disc members coupled by an intermediate joint connector about which both discs flex. 
     Clearly, what is needed is an inexpensive, yet effective and durable drive steer coupling providing for an increased turn angle for use in small vehicles, such as provided by the present invention. 
     SUMMARY OF THE INVENTION 
     The general purpose of the present invention is a constant velocity flexible coupling for use in driving the wheels of a small wheeled vehicle that is powered and steered through each of its four wheels. 
     According to one embodiment of the present invention, there is provided a constant velocity flexible coupling. An output shaft of a differential unit couples to a first yoke which is connected to an inner flexible disc with optional reinforced metal inserts at the securation points. At 90° to the first yoke, an intermediate joint connector is fastened to the first disc. A second disc also attaches to the common joint connector and is parallel and opposite the first disc. A second yoke attaches to the second disc and is oriented 90° to the common joint connector and is aligned to the first yoke. The second yoke attaches to a shaft and a wheel flange which are secured to a pivotal wheel bearing housing which pivots about a mounting bracket secured to one end of differential housing members. 
     According to one embodiment of the present invention, there is provided a flexible coupling, including flexible discs separated by a geometric space. 
     One significant aspect and feature of the present invention is a constant velocity flexible coupling which is simple in design and which is inexpensive. 
     Another significant aspect and feature of the present invention is the utilization of parallel flexible disc members coupled centrally by a joint connector in conjunction with yoke members oriented at 90° to the centrally located joint connector. 
     Yet another significant aspect and feature of the present invention is the flexing of discs about a central common joint connector. 
     Still additional significant aspect and feature of the present invention is the flexing of discs about the ends of yoke members. 
     An additional significant aspect and feature of the present invention is a constant velocity flexible coupling which turns and provides drive force at very severe angles such as up to 50°. 
     A further significant aspect and feature of the present invention is a constant velocity flexible coupling used in conjunction with a 4-wheel drive, 4-wheel steer lawn tractor or other such vehicles. 
     A still further significant aspect and feature of the present invention is the utilization of flexibly aligned discs to absorb axial reciprocation. The self-aligning tendencies of the discs which assist in returning a wheel to the straight ahead position when steering inputs are reduced or neutralized. 
     Having thus described embodiments of the present invention, it is the principal object of the present invention to provide a constant velocity flexible coupling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant 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, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
     FIG. 1 illustrates a perspective view of a constant velocity flexible coupling, the present invention; 
     FIG. 2 illustrates an exploded view of the inner drive components which align between the mounting bracket and the wheel bearing housing; 
     FIG. 3 illustrates the alignment of FIGS. 4A-4B and of FIGS. 5A-5B; 
     FIGS. 4A-4B illustrate a side view of constant velocity flexible couplings utilized at opposing ends of a differential drive assembly; 
     FIGS. 5A-5B illustrate a top view of a differential assembly and opposing flexible couplings of FIGS. 4A-4B. 
     FIG. 6 illustrates a cutaway view of the constant velocity flexible coupling  10  in a turn to the left; 
     FIG. 7 illustrates the members of FIG. 6 where discs  36  and  38  have advanced 90° in rotation; 
     FIG. 8 illustrates the utilization of a plurality of constant velocity flexible couplings with a 4-wheel drive/steer tractor; 
     FIG. 9 illustrates a perspective view of the first alternative embodiment; 
     FIG. 10 illustrates a cross sectional view of the first alternative embodiment; 
     FIG. 11 illustrates a cutaway view of the constant velocity flexible coupling  10  in a turn to the left incorporating flexible coupling discs  160  and  161 ; 
     FIG. 12 illustrates a perspective view of the second alternative embodiment; 
     FIG. 13 illustrates a front view of a constant velocity flexible interface, the third alternative embodiment; 
     FIG. 14 illustrates an end view of the constant velocity flexible interface; 
     PIG.  15  illustrates a cross-sectional view of the constant velocity flexible interface; 
     FIG. 16 illustrates a cutaway view of the constant velocity flexible coupling in a turn to the left incorporating the constant velocity flexible interface; 
     FIG. 17 illustrates an exploded view of the fourth alternative embodiment; and, 
     FIG. 18 illustrates a side view of the fourth alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a perspective view of a constant velocity flexible coupling  10  secured to a housing member  12  and a shaft member  14  of a differential drive later illustrated in the following figures. Visible in FIG. 1 is a mounting bracket  16  having a planar vertical member  18 , a horizontally aligned planar top member  20  generally in the shape of a triangle, and a similarly shaped horizontally aligned planar bottom member  22 . A wheel bearing housing  24 , which functions also as a pivot bracket, pivotally aligns and secures over and about the outer ends of the mounting bracket top member  20  and bottom member  22 , respectively. The one piece wheel bearing housing  24  includes a plurality of planar members including a vertically aligned planar member  26 , an angled planar member  28  extending upwardly and inwardly from the vertically aligned planar member  26 , an L-shaped planar bell crank member  30  being pivotally secured to the top member  20  of the mounting bracket  16 , an angled planar member  32  extending downwardly and inwardly from the vertically aligned planar member  26  and a planar member  34  being pivotally secured to the bottom member  22  of the mounting bracket  16 . The differential drive housing member  12  secures through the vertical planar member  18  of the mounting bracket  16 . Shaft  14  rotates members located between the mounting bracket  16  and the wheel bearing housing  24  including an inner flexible disc  36  and an outer flexible disc  38  of rubber, polyurethane, urethane elastomers, polymers or other suitable materials. A wheel flange  35  having a plurality of studs  37   a - 37   n  aligns in a bearing  39  secured to the wheel bearing housing  24 . An exploded view of these component members is illustrated in FIG.  2  and an assembled view is illustrated in FIG.  4 B. 
     FIG. 2 illustrates an exploded view of the inner drive components which align between the mounting bracket  16  and the wheel bearing housing  24  of FIG. 1, where all numerals correspond to those elements previously and otherwise described. A joint connector  40  secures between the flexible inner and outer discs  36  and  38 . Opposing cylindrical members  42  and  44 , including central bores  42   a  and  44   a,  respectively, are mutually secured by a central connecting rod member  46  to form the joint connector  40 . The inner and outer flexible discs  36  and  38  secure to the joint connector  40  by a plurality of fasteners. Fasteners  48  and  50  extend through opposing holes  52  and  54  in the outer flexible disc  38  to frictionally engage one end of bores  42   a  and  44   a  of the joint connector  40 . In a like and similar fashion, fasteners  56  and  58  extend through holes  60  and  62  in the inner flexible disc  36  to frictionally engage the unoccupied end of bores  42   a  and  44   a  of the joint connector  40 . Inner and outer yokes  64  and  66  align and secure to the inner and outer flexible discs  36  and  38  at points 90° from the attachment of the cylindrical members  42  and  44 . Yoke  64  includes a central bore  68  and opposing outer bores  72  and  74 . A yoke bushing  76  having a fastener bore  78  and a central bore  80  aligns and secures, such as by a weldment, to the bore  68  of the yoke  64 . Yoke bushing  76  accommodates the end of the shaft member  14  illustrated in FIG.  1 . Spacers  82  and  84  having central bores  86  and  88  align and secure, such as by weldment, to outer bores  72  and  74 , respectively, on the inner yoke  64 . Fasteners  90  and  92  extend through holes  94  and  96  of the inner flexible disc  36  to frictionally engage holes  86  and  88  of the yoke spacers  82  and  84 , thus securing the yoke  64  to the inner flexible disc  36 . A hole  98  is centrally located in the inner flexible disc  36  to accommodate the yoke bushing  76  and the end of shaft  14 , if required. The outer flexible disc  38  secures to the outer yoke  66  in much the same manner and fashion. Yoke  66  includes a central bore  100  and opposing outer bores  102  and  104 . A shaft  106  aligns and secures, such as by a weldment, to the central bore  100 . Shaft  106  aligns in a bearing  39  on the wheel bearing housing  24  illustrated in FIGS. 4A-4B. Spacers  108  and  110  having central bores  112  and  114  align and secure, such as by a weldment, to the outer bores  102  and  104 , respectively, of the outer yoke  66 . Fasteners  116  and  118  extend through holes  120  and  122  in the outer flexible disc  38  to frictionally engage holes  112  and  114  of the yoke spacers  108  and  110 , thus securing the yoke  66  to the outer flexible disc  38 . 
     FIG. 3 illustrates the alignment of FIGS. 4A-4B and FIGS. 5A-5B. FIGS. 4A-4B illustrate a side view of a constant velocity flexible coupling  10  incorporated into use with a differential drive assembly  124 . Another constant velocity drive assembly  126  constructed in a fashion similar to the constant velocity flexible coupling  10  is located opposing the constant velocity flexible coupling  10  on the opposing end of the differential drive assembly  124 , where all numerals correspond to those elements previously and otherwise described. Constant velocity drive assembly  126 , being similar in construction to constant velocity drive assembly, is not described for purposes of brevity. 
     Shaft  14  extends from the end of the housing member  12  into the central bore  80  of the yoke busing  76  and is secured therein by a nut and bolt assembly  130  extending through the fastener bore  78  and a corresponding bore  132  in the end of the shaft member  14 , thus coupling the differential drive assembly  126  to the inner components of the constant velocity flexible coupling  10 . Shaft  106  extends from the outer yoke  66  through and is supported by the wheel bearing housing mounted bearing  39  and further extends through and secures to the wheel flange  35  to couple the outer components of the constant velocity flexible coupling  10  to the wheel flange  35  and the wheel bearing housing  24 . The upper portion of the wheel bearing housing  24  pivotally secures to the top planar member  20  of the mounting bracket  16  by engagement of an upper pivot bolt and washer assembly  134  with the top planar bell crank member  30  of the wheel bearing housing  24 . In a similar fashion the lower portion of the wheel bearing housing  24  pivotally secures to the bottom planar member  22  of the mounting bracket  16  by engagement of a lower pivot bolt and washer assembly  136  with the lower planar member  34  of the wheel bearing housing  24 . A control link  138  pivotally secures to the bell crank member  30  by a pivot member  140  and extends to connect to the opposing constant velocity flexible coupling  126  to provide for simultaneous steering of constant velocity flexible couplings  10  and  126  when connected to the steering mechanism of a vehicle such as a small rider lawn mower or other vehicle in which the invention is utilized. 
     MODE OF OPERATION 
     FIGS. 5A-5B illustrate a top view of the differential assembly  124  and opposing constant velocity flexible couplings  10  and  126  secured to each end. The static steering mode of operation is illustrated in dashed lines indicating straight ahead steering. Actuation of the control link  138  to the right by a vehicle steering mechanism, as in a turn to the left, causes the bell crank  30  to be positioned, as illustrated in solid lines, thus causing the wheel bearing housing  24  to pivot about the upper and lower pivot bolt and washer assemblies  134  and  136  of FIGS. 4A-4B. Pivoting of the wheel bearing housing  24  causes the inner flexible disc  36 , of FIGS. 4A-4B, and the outer disc  38  to flex. Flexing about various component members occurs as the wheel flange  35  is propelled by the differential drive assembly  124  as illustrated in FIGS. 6 and 7. 
     FIG. 6 illustrates a cutaway view of the constant velocity flexible coupling  10  in a turn to the left illustrating the flexing of the inner and outer flexible discs  36  and  38  where the joint connector  40  is positioned in horizontal alignment at a point in time during rotation. In the straight ahead and in the turn, steering mode power is delivered from the shaft  14 , through the yoke  64  and its respective spacers  82  and  84 , through the inner flexible disc  36 , through the joint connector  40 , through the outer flexible disc  38 , through the yoke  66  and its respective spacers  108  and  110 , and finally through shaft  106  to the wheel flange  35 . As the flexible discs  36  and  38  rotate, and as a turning action is imitated by the control link  138  of FIGS. 5A-5B, the shafts  14  and  106  are removed from concentric alignment to be angularly displaced from each other thereby causing the flexible discs  36  and  38  to flex and distort in a mirror image-like fashion about a vertical axis while the joint connector  40  is horizontal, such as exhibited and seen from a view line  142  where the vertical axis of the outer disc  38  is described as a line extending through the zone from the spacer  108  to the spacer  110  where contact with the flexible disc  38  is made or, in other words, from the 12 o&#39;clock position to the 6 o&#39;clock position on the disc  38 . A similar vertical axis exists between the zone where spacers  82  and  84  align to the flexible disc  36 . As can be seen from the illustration, discs  36  and  38  flex about these vertical axii, thus flexing the flexible discs  36  and  38  between the respective ends of the cylindrical members  42  and  44  of the joint connector  40 . 
     FIG. 7 illustrates the members of FIG. 6 where the flexible discs  36  and  38  have advanced 90° in rotation with respect to FIG. 6, where all numerals correspond to those elements previously and otherwise described. Illustrated in particular is the flexing of the inner and outer flexible discs  36  and  38  about the vertically aligned joint connector  40  with respect to the horizontally aligned yokes  64  and  66  at a point in time where flexible disc rotation is advanced 90° with respect to the flexible disc position illustrated in FIG.  6 . At this point of rotation, where the joint connector  40  is positioned vertically, the flexible discs exhibit mirror-like image flexings where the discs  36  and  38  are flexed about vertical axii defined as a line through the outer ends of the cylindrical members  42  and  44  where the cylindrical members  42  and  44  meet the disc  38 , the 12 o&#39;clock and 6 o&#39;clock position, and a line through the inner ends of the cylindrical members  42  and  44  where the cylindrical members  42  and  44  meet the disc  36 , the 12 o&#39;clock and 6 o&#39;clock positions. Flexing of the flexible discs  36  and  38  exhibit different degrees of flexing between the positions illustrated in FIGS. 6 and 7 as the discs are rotated between the 0° and 90° positions and, of course, are repeated in various degrees of flex throughout the remaining 270° of rotation to provide a constantly flexing flexible coupling and to absorb axial reciprocation of component members. As steering input is relieved or reduced, the discs  36  and  38 , being sprung and flexed, return to the flat disc memory position, thus returning the wheel bearing housing  24  into straight ahead steering alignment as opposed to most other constant velocity joints which do not automatically return to a neutral straight ahead positioning. 
     FIG. 8 illustrates the use of opposing and similar constant velocity flexible couplings  10  and  126  mounted on differential drive assembly  124  with a 4-wheel steer/drive tractor  144  in a left turn, where all numerals correspond to those elements previously and otherwise described. 
     FIG. 9 illustrates a perspective view of the first alternative embodiment, where all numerals correspond to those elements previously and otherwise described. A disk-shaped constant velocity flexible coupling  160  made of a polymer urethane elastomer, such as K-Prene or other suitable polymer, includes a plurality of raised bosses  162   a - 162   n  and a plurality of extended metal inserts  164   a - 164   n.  Flexible coupling disc  160  can be used in place of both the inner flexible disc  36  and the outer flexible disc  38  of the present invention as previously described. The flexible coupling disc  160  has a centrally located hole  166  to accommodate the yolk bushing  76  and the end of the shaft  14 , if required, as shown in FIG.  2 . Also illustrated in this figure are areas  174   a - 174   n  which are located equal distance between raised bosses  162   a - 162   n.    
     FIG. 10 illustrates a cross sectional view of the flexible coupling disc  160 , where all numerals correspond to those elements previously and otherwise described. Illustrated in particular is the assembly of the metal inserts  164   a - 164   n  which extend from the upper portion  168  to the lower portion  170  of the raised bosses  162   a - 162   n.  Metal inserts  164   a - 164   n  are permanently secured to the inner wall  172  of the flexible coupling disc  160 . The taper of the raised bosses  162   a - 162   n  prevents stress on the polymer urethane elastomer when flexed which further prevents the polymer urethane elastomer from pulling away from the metal inserts  164   a - 164   n  by shifting the stress to the areas  174   a - 174   n  shown in FIG.  11 . 
     FIG. 11 illustrates the members of FIG. 6 where the flexible coupling discs  160  and  161  have advanced 90° in rotation with respect to FIG. 6, where all numerals correspond to those elements previously and otherwise described. Illustrated in particular is the flexing of the flexible coupling discs  160  and  161  about the vertically aligned joint connector  40  with respect to the horizontally aligned yokes  64  and  66  at a point in time where flexible disc rotation is advanced 90° with respect to the flexible disc position illustrated in FIG.  6 . At this point of rotation, where the joint connector  40  is positioned vertically, the flexible discs exhibit mirror-like image flexings where the flexible coupling discs  1060  and  161  are flexed about vertical axii defined as a line through the outer ends of the cylindrical members  42  and  44  where the cylindrical members  42  and  44  meet the flexible coupling disc  161 , the 12 o&#39;clock and 6 o&#39;clock position, and a line through the inner ends of the cylindrical members  42  and  44  where the cylindrical members  42  and  44  meet the flexible coupling disc  160 , the 12 o&#39;clock and 6 o&#39;clock positions. Flexing of the flexible coupling discs  160  and  161  exhibit different degrees of flexing between the positions illustrated in FIGS. 6 and 7 as the discs are rotated between the 0° and 90° positions and, of course, are repeated in various degrees of flex throughout the remaining 270° of rotation to provide a constantly flexing flexible coupling and to absorb axial reciprocation of component members. As steering input is relieved or reduced, the flexible coupling discs  160  and  161 , being sprung and flexed, return to the flat disc memory position, thus returning the wheel bearing housing  24  into straight ahead steering alignment as opposed to most other constant velocity joints which do not automatically return to a neutral straight ahead positioning. Also illustrated in FIG. 11 is the transfer of stress from the raised bosses  162   a - 162   n  to the central area  174   a - 174   n  when the flexible coupling discs are flexed. 
     FIG. 12 illustrates a perspective view of the second alternative embodiment, where all numerals correspond to those elements previously and otherwise described. A constant velocity flexible coupling disk  176  which is constructed similar to the first alternative embodiment and additionally includes a plurality of recessed areas  178   a - 178   n  correspondingly aligned to areas  174   a - 174   n.  Recessed areas  178   a - 178   n  lead to a lesser disk thickness than the corresponding adjacent disk thickness, which increases the flexibility of the flexible coupling disk  176  when flexed. The location of recessed areas  178   a - 178   n  also reduces the tendency of the urethane disk to separate from metal inserts  164   a - 164   n  when stressed without compromising the durability of the flexible coupling disk. 
     FIG. 13 illustrates a front view of a constant velocity flexible interface  210 , the third alternative embodiment, which is constructed of urethane or like material and having an inner portion  212  which extends outwardly from the center to two opposing outer portions  214  and  216 . The inner portion  212  has a relatively thick wall  218  and the outer portions  214  and  216  have relatively thin walls  220  and  222 . The relatively thin walls  220  and  222  of outer portions  214  and  216  form opposing annular lips  232  and  234  as shown in FIG.  13 . 
     The constant velocity flexible interface  210  incorporates mounting plates  224  and  226  constructed of steel or like material, which connect a differential axle  228  and a wheel axle  230  to the outer portions  214  and  216  of the constant velocity flexible interface  210 . The method of securation will later be described in detail in conjunction with FIG.  14 . 
     FIG. 14 illustrates an end view of the constant velocity flexible interface  210 , where all numerals correspond to those elements previously and otherwise described. Illustrated in detail is mounting plate  224  having a recessed planar area  236 , a curved area  238  and an angled straight section  240  with respect to planar area  236 . Located in the center of planar area  236  is a cylindrical axle mount sleeve  242  which is welded or otherwise suitably secured to the mounting plate  224 . A plurality of screws  244   a-n  secure mounting plate  224  to the outer portion  214  of the constant velocity flexible interface  210  (not shown). The method of securation will later be described in detail in conjunction with FIG.  15 . 
     FIG. 15 illustrates a cross-sectional view of the constant velocity flexible interface  210 , where all numerals correspond to those elements previously and otherwise described. Shown in detail is the method of securation of mounting plates  224  and  226  to the outer portions  214  and  216 , respectively, of the constant velocity flexible interface  210 . Mounting plate  226  has a recessed planar area  246 , a curved area  248 , an angled straight section  250 , and an axle mount sleeve  252  identical to that of mounting plate  224 . Screws or like fasteners pass through holes  254  and  256  in the axle mount sleeves  242  and  252  and respectively, secure the differential axle  228  and wheel axle  230  thereto. Annular wedge plates  258  and  260  are aligned on the interior of annular lips  232  and  234 , respectively, and mounting plates  224  and  226  are then positioned over the exterior of annular lips  232  and  234  as shown in FIG. 16. A plurality of screws  244   a - 244   n  then pass through annular wedge plates  224  and  226  and annular wedge plates  258  and  260 . When screws  244   a - 244   n  are torqued in the geometry of the annular wedge plates  258  and  260  in conjunction with the geometry of the angled straight portions  240  and  250  of mounting plates  224  and  226  the frictional engagement forces annular capture of opposing annular lips  232  and  234 . 
     FIG. 16 illustrates a cutaway view of the constant velocity flexible coupling  262  in a turn to the left incorporating the constant velocity flexible interface  210 , where all numerals correspond to those elements previously and otherwise described. The constant velocity flexible coupling  262  is constructed using many of the principles taught in the preferred embodiment and includes a housing member  264 , shaft member  266 , mounting bracket  268 , vertical member  270 , bottom member  272 , wheel bearing housing  274 , vertical planar member  276 , angled planar member  278 , wheel flange  280 , studs  282   a - 282   n,  bearing  284  and shaft  286  which operate similarly to the preferred embodiment. 
     FIG. 17 illustrates an exploded view of the fourth alternative embodiment, where all numerals correspond to those elements previously and otherwise described. Illustrated in particular are alternative inner drive components which function similar to the inner drive components described in the previous embodiments. Now described is geometric member  310 , having bores  312  and  314  which extend through the geometric member  310  parallel to ends  316  and  318  as illustrated. Geometric member  310  connects two flexible coupling disks  320  and  322  which is constructed and function similar to flexible coupling disk  176  described in FIG. 12, having centrally located holes  321  and  323 , plurality of recessed areas  324   a - 324   n  and  326   a - 326   n,  a plurality of raised bosses  328   a - 328   n  and  330   a - 330   n,  a plurality of stainless steel inserts  332   a - 332   d  and  334   a - 334   d  which are bonded to the flexible coupling disks  320  and  322  using a high strength adhesive prior to molding. Flexible coupling disks  320  and  322  are secured together by means of fasteners, such as but not limited to bolts  336  and  340  which pass through stainless steel inserts  334   b  and  334   d,  respectively, then continue through bores  312  and  314 , stainless steel inserts  332   b  and  332   d,  respectively, and secure by means of fasteners such as but not limited to nuts  338  and  342 , respectively. Geometric member  310  acts a spacer between flexible coupling disks  320  and  322  providing space for the disks to flex more easily when stressed. Alternatively, ball and socket joints may be molded into the flexible coupling disks rather than the stainless steel inserts. The ball and socket joints also facilitate flexing of the flexible coupling disks. 
     Comparing FIG. 17 to similar FIG. 2, geometric spacer  310  replaces or substitutes for earlier joint connector  40 . As with the first embodiment, geometric spacer  310  does not change in shape during operation of the fourth embodiment. The flexible discs  320  and  322  flex when steering occurs during shaft rotations, similar to that which is shown in FIGS. 6,  7  and  11 . In other words, geometric spacer  310  will be understood to be rigid. Moreover, when assembled, opposed portions, such as inserts  332   b  and  332   d  of the first flexible disc member  320 , are rigidly connected to each other by the geometric spacer  310  and to corresponding opposed portions such as inserts  334   b  and  334   d  on the second flexible disc member  322 . The geometric spacer  310 , therefore, provides a rigid but spaced apart alignment relationship between the opposed portions such as inserts  332   b,    332   d,    334   b  and  334   d  similar to the relationship between opposed bores  50  and  52  of one flexible disc, and opposed bores  60  and  62  of a second flexible disc in the first embodiment. The inserts  332   a - 332   d  of flexible disc  320  are radially distributed about a centrally located hole  321 , The inserts  334   a - 334   d  of flexible disc  322  are radially distributed about a centrally located hole  323 . 
     Also illustrated in FIG. 17 are yokes  344  and  346  are constructed similarly having extruded studs  348 ,  350 ,  352  and  354  which extend perpendicularly from planar members  356  and  358 . Yokes  344  and  346  include centrally located hollow cylindrical extrusions  364  and  366  and centrally located holes  360  and  362  in planar members  356  and  358  as illustrated. Cylindrical extrusion  364  includes bores  368  and  369  wherein a fastener secures yoke  344  over and about shaft member  14  which is described in the preferred embodiment. Similarly, cylindrical extrusion  366  includes bores  370  and  371  wherein a fastener secures yoke  346  over and about shaft  106  which is also described in the preferred embodiment. Extruded studs  348  and  350  frictionally engage stainless steel inserts  332   a  and  332   c,  respectively. Likewise, extruded studs  352  and  354  frictionally engage stainless steel inserts  334   a  and  334   c.  When incorporated into the preferred embodiment, all components remain secure between mounting bracket  16  and wheel bearing housing  24 , shown in FIG.  1 . FIG. 18 illustrates a side view of the fourth alternative embodiment, where all numerals correspond to those elements previously and otherwise described. Illustrated in particular is the perpendicular orientation of yoke  344  to geometric member  310  (shown in ghost). 
     The present invention provides the controlled steering of a four-wheel driven vehicle, such as a lawn mower. In such applications, the flexible coupling disc has a diameter of between about 5 to 7 inches and a thickness of between about ⅝th to ¾th inches. In one embodiment for use with a wheel driven lawn mower, the diameter of each disc member was 6 inches, the thickness of each disc member was about 0.71 inch and the gap distance between adjacent disc members was about 3 inches from the centerline of the discs through the center axis of the discs. It is believed that the ratio between the diameter, the thickness and the gap distance is relatively constant with respect to the type of driven vehicle. That is, as the disc diameter increases, the thickness and gap distance also increases. 
     The Durometer measurement of the material hardness of the flexible disc falls within the range of hardness of between about 80 to 95, with a preferred range of between about 89-92. Also, it is within the scope of the present invention that the flexible disc may be comprised of a one-piece molding or of a laminated structure provided the Durometer measurement range is satisfied. 
     
       
         
           
               
             
               
                   
               
               
                 CONSTANT VELOCITY FLEXIBLE COUPLING 
               
               
                 PARTS LIST 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 10 
                 constant velocity flexible coupling 
               
               
                   
                 12 
                 housing member 
               
               
                   
                 14 
                 shaft member 
               
               
                   
                 16 
                 mounting bracket 
               
               
                   
                 18 
                 vertical member 
               
               
                   
                 20 
                 top member 
               
               
                   
                 22 
                 bottom member 
               
               
                   
                 24 
                 wheel bearing housing 
               
               
                   
                 26 
                 vertical planar member 
               
               
                   
                 28 
                 angled planar member 
               
               
                   
                 30 
                 bell crank member 
               
               
                   
                 32 
                 angled planar member 
               
               
                   
                 34 
                 planar member 
               
               
                   
                 35 
                 wheel flange 
               
               
                   
                 36 
                 inner flexible disc 
               
               
                   
                 37a-n 
                 studs 
               
               
                   
                 38 
                 outer flexible disc 
               
               
                   
                 39 
                 bearing 
               
               
                   
                 40 
                 joint connector 
               
               
                   
                 42 
                 cylindrical member 
               
               
                   
                 42a 
                 bore 
               
               
                   
                 44 
                 cylindrical member 
               
               
                   
                 44a 
                 bore 
               
               
                   
                 46 
                 central connecting member 
               
               
                   
                 48 
                 fastener 
               
               
                   
                 50 
                 fastener 
               
               
                   
                 52 
                 hole 
               
               
                   
                 54 
                 hole 
               
               
                   
                 56 
                 fasteners 
               
               
                   
                 58 
                 fasteners 
               
               
                   
                 60 
                 hole 
               
               
                   
                 62 
                 hole 
               
               
                   
                 64 
                 yoke 
               
               
                   
                 66 
                 yoke 
               
               
                   
                 68 
                 bore 
               
               
                   
                 70 
                 central bore 
               
               
                   
                 72 
                 outer bore 
               
               
                   
                 74 
                 outer bore 
               
               
                   
                 76 
                 yoke bushing 
               
               
                   
                 78 
                 fastener bore 
               
               
                   
                 80 
                 central bore 
               
               
                   
                 82 
                 spacer 
               
               
                   
                 84 
                 spacer 
               
               
                   
                 86 
                 central bore 
               
               
                   
                 88 
                 central bore 
               
               
                   
                 90 
                 fastener 
               
               
                   
                 92 
                 fastener 
               
               
                   
                 94 
                 hole 
               
               
                   
                 96 
                 hole 
               
               
                   
                 98 
                 hole 
               
               
                   
                 100 
                 central bore 
               
               
                   
                 102 
                 outer bore 
               
               
                   
                 104 
                 outer bore 
               
               
                   
                 106 
                 shaft 
               
               
                   
                 108 
                 spacer 
               
               
                   
                 110 
                 spacer 
               
               
                   
                 112 
                 central bore 
               
               
                   
                 114 
                 central bore 
               
               
                   
                 116 
                 fastener 
               
               
                   
                 118 
                 fastener 
               
               
                   
                 120 
                 hole 
               
               
                   
                 122 
                 hole 
               
               
                   
                 124 
                 differential drive assembly 
               
               
                   
                 126 
                 constant velocity flexible coupling 
               
               
                   
                 130 
                 nut and bolt assembly 
               
               
                   
                 132 
                 bore 
               
               
                   
                 134 
                 upper pivot bolt and washer assembly 
               
               
                   
                 136 
                 lower pivot bolt and washer assembly 
               
               
                   
                 138 
                 control link 
               
               
                   
                 140 
                 pivot 
               
               
                   
                 142 
                 view line 
               
               
                   
                 142a 
                 view line 
               
               
                   
                 144 
                 tractor 
               
               
                   
                 160 
                 flexible coupling disc 
               
               
                   
                 161 
                 flexible coupling disc 
               
               
                   
                 162a-n 
                 raised boss 
               
               
                   
                 164a-n 
                 metal insert 
               
               
                   
                 166 
                 hole 
               
               
                   
                 168 
                 upper portion 
               
               
                   
                 170 
                 lower portion 
               
               
                   
                 172 
                 inner wall 
               
               
                   
                 174a-n 
                 area 
               
               
                   
                 176 
                 flexible coupling disk 
               
               
                   
                 178a-n 
                 recessed area 
               
               
                   
                 210 
                 constant velocity flexible interface 
               
               
                   
                 212 
                 inner portion 
               
               
                   
                 214 
                 outer portion 
               
               
                   
                 216 
                 outer portion 
               
               
                   
                 218 
                 relatively thick wall 
               
               
                   
                 220 
                 relatively thin wall 
               
               
                   
                 222 
                 relatively thin wall 
               
               
                   
                 224 
                 mounting plate 
               
               
                   
                 226 
                 mounting plate 
               
               
                   
                 228 
                 differential axle 
               
               
                   
                 230 
                 wheel axle 
               
               
                   
                 232 
                 annular lip 
               
               
                   
                 234 
                 annular lip 
               
               
                   
                 236 
                 recessed planar area 
               
               
                   
                 238 
                 curved area 
               
               
                   
                 240 
                 angled straight section 
               
               
                   
                 242 
                 axle mount sleeve 
               
               
                   
                 244a-n 
                 screws 
               
               
                   
                 246 
                 recessed planar area 
               
               
                   
                 248 
                 curved area 
               
               
                   
                 250 
                 angled straight section 
               
               
                   
                 252 
                 axle mount sleeve 
               
               
                   
                 254 
                 hole 
               
               
                   
                 256 
                 hole 
               
               
                   
                 258 
                 annular wedge plate 
               
               
                   
                 260 
                 annular wedge plate 
               
               
                   
                 262 
                 constant velocity flexible coupling 
               
               
                   
                 264 
                 housing member 
               
               
                   
                 266 
                 shaft member 
               
               
                   
                 268 
                 mounting bracket 
               
               
                   
                 310 
                 geometric member 
               
               
                   
                 312 
                 bore 
               
               
                   
                 314 
                 bore 
               
               
                   
                 316 
                 end 
               
               
                   
                 318 
                 end 
               
               
                   
                 320 
                 flexible coupling disk 
               
               
                   
                 321 
                 hole 
               
               
                   
                 322 
                 flexible coupling disk 
               
               
                   
                 323 
                 hole 
               
               
                   
                 324a-n 
                 recessed areas 
               
               
                   
                 326a-n 
                 recessed areas 
               
               
                   
                 328a-n 
                 raised bosses 
               
               
                   
                 330a-n 
                 raised bosses 
               
               
                   
                 332a-d 
                 stainless steel inserts 
               
               
                   
                 334a-d 
                 stainless steel inserts 
               
               
                   
                 336 
                 bolt 
               
               
                   
                 338 
                 nut 
               
               
                   
                 340 
                 bolt 
               
               
                   
                 342 
                 nut 
               
               
                   
                 344 
                 yoke 
               
               
                   
                 346 
                 yoke 
               
               
                   
                 348 
                 extruded stud 
               
               
                   
                 350 
                 extruded stud 
               
               
                   
                 352 
                 extruded stud 
               
               
                   
                 354 
                 extruded stud 
               
               
                   
                 356 
                 planar member 
               
               
                   
                 358 
                 planar member 
               
               
                   
                 360 
                 bore 
               
               
                   
                 362 
                 bore 
               
               
                   
                 364 
                 cylindrical extrusion 
               
               
                   
                 366 
                 cylindrical extrusion 
               
               
                   
                 368-371 
                 bores 
               
               
                   
                   
               
            
           
         
       
     
     Various modifications can be made to the present invention without departing from the apparent scope hereof.