Abstract:
A disconnect shaft arrangement interposes a biasing element between a shoulder formed on the disconnect shaft and a cup-shaped washer, in which the cup-shaped washer is sized and configured to be axially displaceable with respect to the disconnect shaft. The cup-shaped washer selectively engages an axially fixed adjacent structure, such as a thrust washer, during disengagement of the disconnect shaft and attendant spring compression. The present disconnect shaft arrangement obviates the need for a retaining ring against which the spring compresses, such that the relatively deep retaining ring groove needed for such a retaining ring need not be cut into the outer surface of the disconnect shaft. Removal of material in the outer surface of the shaft is therefore minimized, such that the torque transmission capability of the shaft is maximized.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/708,401, filed Oct. 1, 2012 and entitled SPRING LOADED SHAFT ASSEMBLY, the entire disclosure of which is hereby expressly incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Disclosure 
         [0003]    The present disclosure relates to a spring biased shaft arrangement, and in particular, to a spring biased shaft used to selectively engage internal gearing of a transmission. 
         [0004]    2. Description of the Related Art 
         [0005]    Large industrial machinery, such as earth moving equipment and other construction vehicles, may use individual power transmission units mounted at the hub of each driven wheel. These individual power transmission units are sometimes referred to as “wheel drives” and may house a transmission device which provides large gear reduction for the heavy loads, large wheels and low speeds frequently employed by such vehicles. Wheel drives may receive power from a drive shaft drivingly connected to the vehicle power source and output a lower-speed, higher-torque rotation. 
         [0006]    In some configurations, gearing mechanisms of wheel drives are selectively engageable with the driven input shaft, such that the wheel drive is configurable into driving and free-wheeling configurations. In the driving configuration, the input shaft is operably coupled to the output hub via the gearing mechanism, while the free-wheeling configuration renders the input shaft operably decoupled from the output hub such that the wheel is free to spin independent of influence by the vehicle power source. To achieve this selective engagement, some wheel drive units include a coupling shaft or sleeve which is axially displaceable to selectively engage the powered input to the gearing mechanism, and ultimately to the output hub. Generally speaking, such axially displaceable coupling shafts or sleeves are manipulated by the drive unit operator, either manually or automatically, to toggle the drive unit between engaged and disengaged configurations. 
         [0007]    One known wheel drive unit with an axially translatable shaft which operates as a disconnect mechanism is disclosed in U.S. Pat. No. 6,607,049 to Cigal. A portion of this known mechanism is illustrated as disconnect mechanism  112  in  FIGS. 1A and 1B . Mechanism  112  includes disconnect shaft  114 , which is axially displaceable between engaged and disengaged positions. More particularly, shaft  114  is shown in the engaged position in  FIG. 1A , in that shaft  114  is rotatably fixed to both input coupler  118  and output gear  122 , thereby transferring motive force and torque therebetween. Spring  168  is compressed by application of force F ( FIG. 1B ) when disconnect shaft  114  is moved from the engaged position to the disengaged position, and operates to bias shaft  114  back toward the engaged position. Spring  168  is interposed between thrust washers  178  positioned at respective axial terminal ends of spring  168 . At the input-side axial end of spring  168 , thrust washer  178  abuts a shoulder formed in the spindle of the wheel drive, while the output-side axial end of spring  168  utilizes retaining ring  124 . Retaining ring  124  is connected to a corresponding groove formed in disconnect shaft  114 . The retaining ring groove formed in shaft  114  reduces the overall diameter of shaft  114  in the vicinity of retaining ring  124 , by a sufficient amount that the minor diameter of shaft  114  (i.e., the smallest diameter) is the diameter of the retaining ring groove. 
         [0008]    In the context of wheel drive mechanisms, substantial force and torque may be transmitted via the above described axially translatable disconnect shafts. Accordingly, it is desirable to produce disconnect shaft arrangements and assemblies which maximize power transmission capability while avoiding unnecessary cost, weight and/or size. Therefore, what is needed is a disconnect shaft arrangement that is robust, cost effective and capable of handling a large amount of torque and force for a given shaft size. 
       SUMMARY 
       [0009]    The present disclosure provides a disconnect shaft arrangement which interposes a biasing element between a shoulder formed on the disconnect shaft and a cup-shaped washer, in which the cup-shaped washer is sized and configured to be axially displaceable with respect to the disconnect shaft. The cup-shaped washer selectively engages an axially fixed adjacent structure, such as a thrust washer, during disengagement of the disconnect shaft and attendant spring compression. The present disconnect shaft arrangement obviates the need for a retaining ring against which the spring compresses, such that the relatively deep retaining ring groove needed for such a retaining ring need not be cut into the outer surface of the disconnect shaft. Removal of material in the outer surface of the shaft is therefore minimized, such that the torque transmission capability of the shaft is maximized. 
         [0010]    In one form thereof, the present disclosure provides a transmission disconnect system including: a disconnect shaft axially moveable between an engaged position and a disengaged position along a longitudinal shaft axis, the disconnect shaft having a first end defining a first minor diameter and a second end opposite the first end; a first torque transmitter rotatably fixed to the first end of the disconnect shaft such that a torque is transmissible between the first torque transmitter and the disconnect shaft; a second torque transmitter rotatably fixed to the second end of the disconnect shaft when the disconnect shaft is in the engaged position and rotatably decoupled from the second end of the disconnect shaft when the disconnect shaft is in the disengaged position, such that the torque is transmissible from the first torque transmitter to the second torque transmitter via the disconnect shaft when the disconnect shaft is in the engaged position; a cup-shaped washer having a longitudinal washer axis, the cup-shaped washer including: a sidewall having an length measured along the longitudinal washer axis; and a mounting flange extending radially inwardly from a first terminal axial end of the sidewall to define a mounting bore having a diameter larger than the first minor diameter of the disconnect shaft, the first end of the disconnect shaft axially translatable within the mounting bore; a second axial end of the sidewall opposite the first axial end and defining a seating surface transverse to the longitudinal washer axis, the second axial end disposed nearer to the first end of the disconnect shaft than the first axial end when the cup-shaped washer is mounted to the disconnect shaft; and a biasing element constrained against axial displacement by the mounting flange of the cup-shaped washer and biasing the disconnect shaft into the engaged position. 
         [0011]    In another form thereof, the present disclosure provides a transmission including a disconnect shaft axially moveable between an engaged position and a disengaged position along a longitudinal shaft axis, the disconnect shaft including a first end defining a first minor diameter; a second end opposite the first end; and a central portion disposed between the first end and the second end, the central portion defining a shoulder extending radially outward; an input coupler rotatably fixed to the first end of the disconnect shaft such that a torque is transmissible between the input coupler and the disconnect shaft; an output gear rotatably fixed to the second end of the disconnect shaft when the disconnect shaft is in the engaged position and rotatably decoupled from the second end of the disconnect shaft when the disconnect shaft is in the disengaged position, such that the torque is transmissible from the input coupler to the output gear via the disconnect shaft when the disconnect shaft is in the engaged position; a cup-shaped washer having a longitudinal washer axis, the cup-shaped washer including: a sidewall having an length measured along the longitudinal washer axis; and a mounting flange extending radially inwardly from a first terminal axial end of the sidewall to define a mounting bore having a diameter larger than the first minor diameter of the disconnect shaft, the first end of the disconnect shaft axially translatable within the bore; a second axial end of the sidewall opposite the first axial end and defining a seating surface transverse to the longitudinal washer axis; a seating structure interposed between the input coupler and the output gear, the seating structure axially fixed and having a bore large enough to allow passage of the disconnect shaft therethrough, the bore small enough to prevent passage of the second axial end of the cup-shaped washer therethrough; and a biasing element captured between the cup-shaped structure and shoulder of the disconnect shaft, such that the biasing element urges the seating surface of the cup-shaped washer toward the seating structure, and urges the disconnect shaft into the engaged position. 
         [0012]    In yet another form thereof, the present disclosure provides a cup-shaped washer including: an annular sidewall having an length measured along a longitudinal washer axis; and a mounting flange extending radially inwardly from a first terminal axial end of the sidewall to define a mounting bore having a splined inner periphery adapted to be rotatably fixe to a splined outer surface of a shaft; and a seating flange extending radially outwardly from a second terminal axial end of the sidewall opposite the first terminal axial end, the seating flange defining a seating surface substantially perpendicular to the longitudinal washer axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above-mentioned and other features and advantages of the present disclosure, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0014]      FIG. 1A  is a an elevation, cross-sectional view of a portion of a wheel drive utilizing a known spring loaded shaft assembly arrangement, with the disconnect shaft shown in an engaged position; 
           [0015]      FIG. 1B  is an elevation, cross-sectional view of the portion of the wheel drive of  FIG. 1A , with the disconnect shaft shown in a disengaged position; 
           [0016]      FIG. 2A  is an elevation, cross-sectional view of a wheel drive transmission assembly utilizing a disconnect shaft arrangement made in accordance with the present disclosure, in which the disconnect shaft shown in an engaged position; 
           [0017]      FIG. 2B  is an elevation, cross-sectional view of a portion of the transmission assembly shown in  FIG. 2A , illustrating the disconnect shaft in a disengaged position; 
           [0018]      FIG. 3A  is an elevation, cross-sectional partial view of the transmission disconnect system shown in  FIG. 2A , illustrating only the disconnect shaft and adjacent components in their respective engaged configurations; 
           [0019]      FIG. 3B  is an elevation, cross-sectional view of the transmission disconnect system shown in  FIG. 3A , with the components shown in their respective disengaged configurations; 
           [0020]      FIG. 4  is a perspective view of a cup-shaped washer made in accordance with the present disclosure; 
           [0021]      FIG. 5  is an elevation, cross-sectional view of the cup-shaped washer shown in  FIG. 4 ; 
           [0022]      FIG. 6A  is an elevation, sectional view of a disconnect shaft made in accordance with the present disclosure; and 
           [0023]      FIG. 6B  is an enlarged elevation view of a portion of the shaft shown in  FIG. 6A , illustrating a snap ring groove formed therein. 
       
    
    
       [0024]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates an exemplary embodiment of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0025]      FIGS. 2A and 2B  illustrate wheel drive transmission unit  10  including transmission disconnect system  12  in engaged and disengaged configurations, respectively. As described in detail below, transmission disconnect system  12  is engaged when disconnect shaft  14  has first end  16  rotatably affixed to input coupler  18 , and has a second end  20  rotatably affixed to output gear  22 . Thus, in the engaged position shown in  FIG. 2A , disconnect shaft  14  rotatably fixes input coupler  18  to output gear  22 . By contrast,  FIG. 2B  illustrates a disengaged configuration of transmission disconnect system  12  in which force F has been applied to disconnect shaft  14  to axially displace shaft  14  toward input coupler  18 . When so displaced, second end  20  becomes rotatably decoupled from output gear  22 . Although coupler  18  (having internal splines) and gear  22  (having external splines) are used for input and output torque transmitters in the exemplary embodiment illustrated in the figure, it is of course contemplated that any combination of gears and couplers may be used. For purposes of the present disclosure, “gearing component” refers to couplers or other gearing components with internal splines, gears or other gearing components with external splines, and/or components with both internal and external splines. 
         [0026]    As described in detail below, transmission disconnect system  12  includes cup-shaped washer  24  to facilitate toggling of disconnect shaft  14  between the engaged and disengaged positions, while maximizing the capacity of disconnect shaft  14  to transfer torque between input coupler  18  and output gear  22 . 
         [0027]    1. Wheel Drive Unit 
         [0028]    In the exemplary embodiment illustrated in  FIGS. 2A and 2B , transmission disconnect system  12  is used to selectively engage or disengage planetary gear system  26  housed within wheel drive transmission unit  10 . Planetary gear system  26  is engaged when disconnect shaft  14  is rotatably fixed to output gear  22  ( FIG. 2A ), which in turn drives wheel hub  28  with a substantial gear reduction relative to input coupler  18  as described in further detail below. 
         [0029]    Wheel drive transmission unit  10  may be mounted to a vehicle frame via mounting holes  30 , establishing spindle  32  as the component of transmission unit  10  that is rotationally and axially fixed with respect to the other components thereof. A powered shaft (not shown) is rotatably fixed to input coupler  18  and operably connected to a vehicle power source, such as an engine, battery bank, or the like. Inner, female splines formed along the bore of input coupler  18  engage male outer splines  34  formed along a portion of the outer surface of first end  16  of disconnect shaft  14 , thereby rotatably fixing disconnect shaft  14  to input coupler  18 . When disconnect shaft  14  is in the disengaged position shown in  FIG. 2B , motive force provided to input coupler  18  serves only to rotate disconnect shaft  14 . On the other hand, when disconnect shaft  14  is in the engaged position as shown in  FIG. 2A , motive force provided to input coupler  18  is transmitted to output gear  22  via disconnect shaft  14 , thereby providing driving torque to wheel hub  28  via planetary gear system  26  (as further described below). 
         [0030]    Second end  20  of disconnect shaft  14  includes male outer splines  36 , which are sized and configured to intermesh with correspondingly formed female inner splines within the bore of output gear  22  ( FIG. 2A ). When so engaged, disconnect shaft  14  and output gear  22  are rotatably affixed to one another such that torque is transmissible to output gear  22  from input coupler  18 . Output gear  22 , in turn, acts as a sun gear in planetary gear system  26 , with outer splines of sun gear  22  engaging correspondingly formed outer splines on a plurality of planet gears  38 . As sun gear  22  rotates, planet gears  38  orbit sun gear  22  around longitudinal axis A 1  of disconnect shaft  14  (which is coaxial with input coupler  18  and output gear  22 ), such that planet gears  38  circumnavigate disconnect shaft  14 . Planet gears  38 , in turn, are rotatably coupled to gear carrier  40  via planet shafts  42 , so that the circumnavigation of planet gears  38  about sun gear  22  rotates gear carrier  40  about axis A 1 . 
         [0031]    The outer splines of planet gears  38  also engage correspondingly formed inner splines of ring gear  44 , thereby causing ring gear  44  to rotate when sun gear  22  is rotating (although at a much slower speed). Ring gear  44 , in turn, is affixed to wheel hub  28  (as well as to transmission cover  46 ) via bolt  48 . Thus, wheel hub  28  rotates at the same rotational speed as ring gear  44 , thereby rotating a wheel connected to wheel hub  28  (i.e., by wheel connector bolts  50 ). 
         [0032]    Gear carrier  40  is also in splined engagement with outer splines formed on idler gear  52 , such that rotation of gear carrier also rotates idler gear  52  as planet gears  38  circumnavigate disconnect shaft  14 . Idler gear  52 , in turn, meshingly engages outer splines of secondary planet gears  54 , which are rotatably coupled to secondary gear carrier  56  via secondary planet shafts  58 . Secondary gear carrier  56  is rotatably coupled to spindle  32 , thereby facilitating circumnavigation of secondary planet gears  54  about idler gear  52 . Planet gears  38 ,  54  cooperate with idler gear  52  and ring gear  44  to provide substantial reduction in the rotational speed of ring gear  44 , and therefore also wheel hub  28 , as compared with the rotational speed of input coupler  18 . 
         [0033]    To reconfigure disconnect shaft  14  from the engaged to the disengaged position, force F ( FIGS. 2B and 3B ) is applied along axis A 1  to axially displace disconnect shaft  14  out of splined engagement with output gear  22  (and therefore also further into splined engagement with input coupler  18 ). In the illustrated embodiment, such application of force may be provided manually by the user of wheel drive transmission unit  10 , i.e., by pushing on the terminal end of second end  20  of disconnect shaft  14 . As used herein, “terminal end” refers to the axial terminus of a structure, (e.g., shaft  14 , cup-shaped washer  24  or spring  68 ) beyond which no material of the structure extends. Exemplary embodiments of mechanisms which may be used to facilitate reconfiguration of disconnect shaft  14  between the engaged and disengaged positions may be found in U.S. Pat. No. 6,607,049 to Cigal filed Mar. 6, 2001 and entitled “Quick Disconnect for an Integrated Drive Unit” and U.S. Patent Application Publication No. 2012/0031212, filed May 9, 2011 and entitled “Quick Disconnect for a Drive Unit,” the entire disclosures of which are hereby expressly incorporated by reference herein. 
         [0034]    Although transmission disconnect system  12  is illustrated in the context of wheel drive transmission unit  10  shown in  FIGS. 2A and 2B  and described in detail above, it is contemplated that transmission disconnect system  12  may also be used in other systems in which first and second torque transmitters axially spaced from one another are to be selectively coupled and decoupled from one another by disconnect shaft  14 . Moreover, transmission disconnect system  12  may be used for any transmission application, where “transmission” refers to any mechanism for transferring motive force from an input to an output. Changes in torque and speed between the input and output, such as those changes accomplished by use of planetary gear system  26  described above, need not be performed by a transmission made in accordance with the present disclosure. 
         [0035]    2. Transmission Disconnect System 
         [0036]    For example, turning to  FIGS. 3A and 3B , disconnect shaft  14  is shown independently of most components within wheel drive transmission unit  10 , illustrating only the components which interact directly with disconnect shaft  14 . Broadly speaking, disconnect shaft  14  is rotatably fixed to input coupler  18  (i.e., a torque transmitter) and is selectively rotatably fixed to output gear  22  (i.e., a second torque transmitter). In the illustrated exemplary embodiment, disconnect shaft  14  includes central portion  60  having diameter D CS  ( FIG. 6A ) larger than diameters D FS  D SS  ( FIG. 6A ) of first and second ends  16 ,  20  respectively, thereby creating first shoulder  62  and second shoulder  64  at the axial ends of central portion  60 . As illustrated, second shoulder  64  bears against washer  66  in the engaged position. Washer  66 , in turn, is axially fixed within transmission unit  10 , so that such abutment defines the end of axial travel of disconnect shaft  14  toward output gear  22 . First shoulder  62  provides a bearing surface for the output-side axial end of biasing element  68 , while the opposing input-side axial end of biasing element  68  abuts cup-shaped washer (as described in greater detail below). 
         [0037]    In the illustrated embodiment, biasing element  68  is a compression spring which is slightly compressed in the engaged position of  FIG. 3A  and more fully compressed in the disengaged position of disconnect shaft shown in  FIG. 3B . Thus, spring  68  urges disconnect shaft  14  toward its engaged position, and reconfiguration of disconnect shaft  14  into the disengaged position requires that force F ( FIG. 3B ) overcomes such biasing force (as well as any frictional forces which may be present on disconnect shaft  14 ). 
         [0038]    Cup-shaped washer  24  is illustrated in  FIGS. 4 and 5 . Washer  24  includes sidewall  70  having a generally arcuate configuration, such as a cylindrical or a slightly conical shape, such that sidewall  70  defines longitudinal axis A 2  of washer  24 . However, it is appreciated that sidewall could take any cross-sectional profile while still defining a generally longitudinal structure having axis A 2 . At one axial terminal end of sidewall  70  (i.e., the output-side axial end), mounting flange  72  extends radially inward toward axis A 2  and defines washer bore  74 . Bore  74  includes a plurality of gear splines formed around the periphery thereof, which are sized and configured to engage outer splines  34  at first end  16  of disconnect shaft  14  as described in further detail below. 
         [0039]    At the opposing (i.e., input-side) axial terminal end of sidewall  70 , seating flange  76  extends radially outwardly away from axis A 2 . This outward extension of seating flange  76  provides a generally planar seating surface  84  ( FIG. 5 ) which bears against thrust washer  78  ( FIG. 3B ) and thereby maintains proper alignment and coaxiality of longitudinal axis A 1  of disconnect shaft  14  and longitudinal axis A 2  of cup-shaped washer  24  as shaft  14  moves axially through bore  74 . More particularly, when seating surface  84  of seating flange  76  bears against the adjacent surface of thrust washer  78 , the planar configuration of seating surface  84  and the perpendicularity of such plane with respect to longitudinal axes A 1 , A 2  ensures that axes A 1 , A 2  remain parallel and coincident, and thereby ensures that first end  16  of transmission shaft  14  remains able to smoothly slide within bore  74  of washer  24  without binding or creating undue friction. 
         [0040]    Mounting  86  ( FIG. 5 ) of mounting flange  72  provides the bearing surface for the input-side axial terminal end of spring  68 . As best seen in  FIG. 5 , sidewall  70  of washer  24  defines cavity  80  extending axially from inner surface  82  of mounting flange  72  and seating surface  84  of seating flange  76 , which provides a space for axial travel of lock ring  90  (as shown in  FIGS. 3A and 3B , and described in detail below). 
         [0041]    In the exemplary embodiment illustrated in  FIG. 5 , cup-shaped washer  24  defines overall axial extent E of 0.65 inches between opposing axial terminal ends thereof. Major diameter D MW , defined by the radial extent of seating flange  76 , is 1.72 inches. Diameter D SW . defined by sidewall  70 , is 1.50 inches. In this exemplary embodiment, thickness T is 0.0897 inches throughout the material of cup-shaped washer  24 . Accordingly, this exemplary embodiment of washer  24  is sized and configured for use in a standard commercial wheel drive, such as transmission unit  10  shown in  FIG. 2A . One such exemplary transmission unit is the Model 8 Power Wheel® Planetary Gear Drive available from Auburn Gear, Inc. of Auburn, Ind. Power Wheel® is a registered trademark of Auburn Gear, Inc. of Auburn, Ind. 
         [0042]    Moreover, the exemplary thickness T specified above facilitates production of cup-shaped washer  24  by a stamping process, thereby facilitating production of washer  24  in large volumes at low cost, while also imparting sufficient strength and rigidity to washer  24  to ensure minimal material deformation and long service life in use. When produced by stamping, sidewall  70  includes a slight amount of draft, such that sidewall  70  is slightly conical (with diameter D SW  decreasing slightly toward mounting flange  72 ). In this exemplary stamped embodiment, washer  24  is made from steel, such as 1010 carbon steel. 
         [0043]    Bore  74  of washer  24  is sized to allow first end  16  of disconnect shaft  14  (and outer splines  34 ) to be received therein upon assembly and use of transmission disconnect system  12 . In the exemplary embodiment illustrated in  FIGS. 3A and 4 , bore  74  includes inner splines  88  formed around the periphery thereof which matingly engage outer splines  34  to rotatably fix washer  24  to disconnect shaft  14 , while also having a clearance fit that allows free axial travel of washer  24  with respect to disconnect shaft  14 . This rotatably fixed arrangement prevents any relative rotation of washer  24  with respect to spring  68  during operation of transmission unit  10 , thereby protecting spring  68  from friction and/or torsional movement at its area of contact with mounting flange  72 . However, it is contemplated that bore  74  may exclude splines  88 . 
         [0044]    Whether including or excluding splines  88 , the smallest diameter defined by bore  74 , i.e., minor diameter D BW ′ ( FIG. 5 ), is larger than the minor diameter D FS ′ of first end  16  of disconnect shaft  14  ( FIG. 6A ), while the largest diameter defined by bore  74 , i.e., major diameter D BW , is also larger than major diameter D FS  of first end  16 . This allows cup-shaped washer  24  to axially slide over the outer surface of first end  16  freely. In an exemplary embodiment, major diameter D FS  of first end  16  of shaft  14  (i.e., at the lands of outer splines  34 ) is between 0.994 inches and 0.998 inches, and the corresponding major diameter of bore  74  is equal to 1.0 inches or greater. The clearance between the respective minor diameters D FS ′, D BW ′ of first end  16  and bore  74  may be the same or similar. 
         [0045]    In an exemplary embodiment, second end  20  of disconnect shaft  14  defines major diameter D SS  with a corresponding minor diameter D SS ′ defined by the depth of outer splines  36 . Diameters D SS , D SS ′ may be any diameters as appropriate to allow outer splines  36  to mate with the corresponding inner splines of output gear  22 , and may be the same or different from diameter D FS  of first end  16 . In one exemplary embodiment diameter D SS  is between 0.854 and 0.859 inches. 
         [0046]    Diameter D CS  ( FIG. 6A ) of central portion  60  may be any diameter larger than diameters D FS  and D SS , such as 1.30 inches in the above-described exemplary embodiment. The overall axial length L of disconnect shaft  14  may be about 9 inches in this exemplary embodiment, with first and second ends  16 ,  20  and central portion  60  occupying whatever portion of overall length L is needed as required or desired for a particular application. Of course, it is contemplated that disconnect shaft  14  may take on other sizes and configurations for larger or smaller applications or other alternative designs. 
         [0047]    Lock ring  90  is provided to constrain the axial travel of cup-shaped washer  24  toward input coupler  18 , as illustrated in  FIG. 3A . With disconnect shaft  14  in the engaged position as shown in  FIG. 3A , spring  68  is extended and cup-shaped washer  24  is biased into abutting engagement with lock ring  90  as illustrated. The axial position of lock ring  90  is designed to ensure that gap  92  is maintained between seating surface  84  of seating flange  76  and the adjacent surface of thrust washer  78  as illustrated in  FIG. 3A . In an exemplary embodiment, extent E G  of gap  92  is between 0.010 inches and 0.016 inches. Gap  92  allows washer  24  to rotate together with disconnect shaft  14  without frictional interference from thrust washer  78 , which is axially and rotationally fixed to the adjacent structures of transmission unit  10 . 
         [0048]    To retain lock ring  90  in the desired axial position upon first end  16 , notch  94  may be provided along the outer surfaces or lands of outer splines  34  as shown in  FIG. 6B . In an exemplary embodiment, notch  94  is 1.4 inches from the axial terminal end of first end  16 , which provides proper axial spacing to create gap  92  in the engaged position of shaft  145  as described above. Notch  94  may be small, as it accommodate a relatively small lock ring  90  (e.g., a lock ring having a nominal inside diameter of 0.925 inches with a nominal thickness of 0.042 inches). Moreover, lock ring  90  may be a relatively small, thin component because lock ring  90  needs only to restrain the minimal biasing force placed upon lock ring  90  by spring  68  in its nearly fully extended configuration. 
         [0049]    In an exemplary embodiment, notch  94  is between 0.046 and 0.052 inches wide and reduces the major diameter of splines  34  by between 0.035 and 0.045 inches. This minimal reduction in diameter and minimal overall size of notch  94  minimizes any stress riser effect which may result from the addition of notch  94 , and ensures that the overall minor diameter of first end  16  of disconnect shaft  14  is the minor diameter of splines  34  rather than the minor diameter created by notch  94 . Stated another way, notch  94  extends into the material of shaft  14  less than splines  34 . Accordingly, the maximum torsional strength of first end  16  is the same or nearly the same both before and after notch  94  is formed in shaft  14 . 
         [0050]    When force F is applied to disconnect shaft  14  as shown in  FIG. 3B , shaft  14  is reconfigured into the disengaged position. As the reconfiguration begins, axial displacement of first end  16  of shaft  14  (and therefore, also of lock ring  90 ) toward input coupler  18  allows seating flange  76  to come into contact with the adjacent surface of thrust washer  78 . Thereafter, further axial movement of disconnect shaft  14  toward the fully disengaged position of  FIG. 3B  compresses spring  68 , which is captured between mounting flange  72  of washer  24  and shoulder  62  of shaft  14  and constrained against axial displacement toward input coupler  18  by washer  24 . As this compression occurs, lock ring  90  axially traverses the annular space  96  formed between an inner surface of sidewall  70  of washer  24  and the adjacent outer surface defined by the lands of splines  34  on first end  16  of shaft  14 . Overall axial extent E ( FIG. 5 ) of washer  24 , and more particularly the axial extent of cavity  80 , are sufficient to allow sufficient axial travel of lock ring  90  to fully disengage outer splines  36  of second end  20  of shaft  14  from the corresponding inner splines of output gear  22 . More particularly, the axial extent of cavity  80  allows lock ring to remain within annular space  96  as disconnect shaft is reconfigured from the engaged position of  FIG. 3A  to the disengaged position of  FIG. 3B . Meanwhile, washer  24  axially travels up outer splines  34 , thereby allowing first end  16  to protrude more deeply into the bore formed within input coupler  18  while seating flange  76  remains seated upon thrust washer  78 . 
         [0051]    When force F is removed from disconnect shaft  14 , spring  68  is allowed to bias outer splines  36  of second end  20  back into engagement with output gear  22 . Provided such splines are properly aligned, the biasing force of spring  68  will return disconnect shaft  14  to the engaged position. As this return to the engaged position completes, lock ring  90  comes into contact with inner surface  82  of mounting flange  72 , and lock ring  90  draws cup-shaped washer  24  out of engagement with thrust washer  78 . This frees washer  24  to rotate without frictional interaction with thrust washer  78 . 
         [0052]    Moreover, rotation of cup-shaped washer  24  with respect to thrust washer  78  while disconnect shaft  14  is in the disengaged configuration of  FIG. 3B  will not occur in normal operation, as there is no normal need or benefit to apply motive force to input coupler  18  when such motive force cannot be transmitted to output gear  22 . Although some such rotation may occur during maintenance or diagnostic procedures, no significant wear of cup-shaped washer  24  or thrust washer  78  will occur during operation of transmission unit  10  because no contact therebetween occurs when disconnect shaft  14  is positioned to transmit torque between input coupler  18  and output gear  22 . 
         [0053]    While this disclosure has been described as having exemplary designs, the present disclosure can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.