Abstract:
An endplay adjustment mechanism for a co-linear shaft assembly. More specifically, the co-linear shaft assembly includes an input shaft and a mainshaft aligned along a common longitudinal axis. A threaded adjuster plug and a thrust bearing are interdisposed between the input shaft and the mainshaft to permit relative longitudinal positioning therebetween. Accordingly, after the shaft assembly has been assembled into a power transmission device, the threaded adjuster plug is tightened to effectively increase the length of the co-linear shaft assembly, thereby eliminating any excess endplay of the shafts relative to the housing of the power transmission apparatus.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an arrangement for adjusting the axial positioning of a pair of colinear shafts in a power transmission apparatus and, more specifically, to an endplay adjuster assembly disposed between the colinear input shaft and mainshaft of a four-wheel drive transfer case. 
     Many power transmission apparatuses (i.e., transfer cases, transmissions, transaxles, etc.) of the type used in the driveline of motor vehicles are equipped with a pair of colinear and relatively rotatable shafts and a clutch mechanism for transferring drive torque therebetween. For example, a conventional transfer case  10  is shown in FIG. 1 to include a housing assembly  12 , an input shaft  14 , a planetary gearset  16  driven by input shaft  14 , a mainshaft or rear output shaft  18 , and a range clutch  20  operable for selectively coupling rear output shaft  18  for rotation with one of input shaft  14  and an output  22  of planetary gearset  16 . Transfer case  10  also includes a front output shaft  24 , a drive sprocket  26  fixed to front output shaft  24 , a drive sprocket  28  rotatably mounted on rear output shaft  18 , a chain assembly  30  interconnecting driven sprocket  26  to drive sprocket  28 , and a mode clutch  32  operable for selectively coupling drive sprocket  28  to rear output shaft  18 . A shift mechanism  34 , under the control of the vehicle operator, is connected to range clutch  20  and mode clutch  32  to facilitate coordinated actuation thereof for establishing various drive modes. 
     Input shaft  14  is shown to be rotatably supported in a front housing section  12   a  by a front bearing assembly  36 . Likewise, rear output shaft  18  has a pilot hub  38  formed on its forward end which is rotatably supported by a needle bearing assembly  40  that is retained in a pilot bore  42  formed in input shaft  14 . The rearward end of rear output shaft  18  is rotatably supported from rear housing section  12   b  by a rear bearing assembly  44 . Thus, input shaft  14  and rear output shaft  18  are colinear and supported for rotation about a common rotary axis “A”. In addition, a cup plug  46  seals pilot hub  38  of rear output shaft  18  relative to input shaft  14 . 
     During assembly of transfer case  10 , an inner race  36   a  of front bearing assembly  36  is slid onto input shaft  14  until it abuts a radial shoulder surface  48  formed thereon and a snap ring  50  is then mounted in a circumferential groove  51  formed in input shaft  14 , thereby retaining front bearing assembly  36  on input shaft  14 . Input shaft  14  is then installed into housing section  12   a  such that an outer race  36   b  of front bearing assembly  36  engages a radial shoulder surface  52  of housing section  12   a  and then a snap ring  54  is mounted in a circumferential groove  55  formed in housing section  12   a , thereby axially positioning and restraining input shaft  14  relative thereto. Alternatively, front bearing assembly  36  could be initially mounted to housing section  12   a  with input shaft  14  thereafter installed in front bearing assembly  36  and snap ring  50  mounted in the groove  51  formed in input shaft  14 . 
     During continuation of the assembly of transfer case  10 , an inner race  44   a  of rear bearing assembly  44  is slid onto rear output shaft  18  and is axially restrained between a pair of snap rings  56   a  and  56   b  mounted in circumferential grooves  57   a  and  57   b  formed in rear output shaft  18  respectively. Thereafter, rear output shaft  18  is installed in housing section  12   b  such that outer race  44   b  of rear bearing assembly  44  abuts a radial shoulder surface  58  of housing section  12   b  and then a snap ring  60  is mounted in a corresponding groove  61  formed in housing section  12   b . Alternatively, rear bearing assembly  44  could initially be installed in housing section  12   b  with rear output shaft  18  slid into its inner race  44   a  followed by installation of snap ring  56   b . As seen, a hole  62  in housing section  12   b  provides the requisite access to install snap ring  60  and is then sealed by a rubber housing plug  64 . Once pilot hub  38  of rear output shaft  18  is mounted in pilot bore  42 , housing sections  12   a  and  12   b  are then interconnected in a manner well known in the art. 
     In such colinear shaft layouts, the machining tolerances for the groove location, groove width, shoulder locations, and the snap ring width, in conjunction with the necessary design assembly clearances, may stack up to permit an excessive amount of axial movement (i.e., “endplay”) between input shaft  14  and rear output shaft  18  Such endplay has been recognized as contributing to driveline noise or clunk and may also cause increased wear of the driveline components. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to overcome the disadvantages associated with prior art colinear shaft assemblies by providing an endplay adjustment assembly which facilitates axial adjustment of the colinear shafts in a power transmission apparatus to accommodate tolerance variations between the various driveline components. 
     In accordance with the present invention, a preferred embodiment of the endplay adjustment assembly includes an endplay adjuster plug and a thrust bearing operably disposed between a first shaft and a second shaft rotatably supported from a housing. More specifically, the first shaft has a pilot bore for receiving and rotatably supporting one end of the second shaft. The endplay adjustment assembly is operably disposed in the pilot bore between the first shaft and the second shaft. The adjuster plug has external threads which engage internal threads formed in the pilot bore. The thrust bearing is disposed between the adjuster plug and the end of the second shaft. First and second bearing assemblies rotatably support the first shaft and second shaft within the housing. More specifically, bearing seats formed on the shafts and in the housing receive the bearing assemblies. Thereafter, the threaded adjuster plug is tightened to axially displace the first shaft relative to the second shaft, thereby forcing the first bearing assembly against its bearing seats while also forcing the second bearing assembly against its bearing seats. After appropriate tightening of the adjuster plug, the axial positioning of the shafts is optimized in a manner which is independent of machining tolerances, thereby eliminating endplay of the shaft assembly. 
     The present invention is particularly applicable to eliminate endplay in the shaft assembly of a four-wheel drive transfer case, thereby eliminating driveline clunk caused by such endplay. Furthermore, the present invention eliminates the conventional use of snap rings and the need to machine snap ring grooves in the housing and on the shafts. As such, the present invention greatly reduces the axial tolerance stack ups for allowing more precise positioning of critical components and less misalignment therein. As a further advantage, the present invention allows a press fit rather than a slip fit with the first and second bearing assemblies, thus improving bearing durability and overall alignment. As yet an additional advantage, the present invention provides faster and easier assembly and disassembly of the transfer case by eliminating the snap rings and rubber plugs. 
     Additional advantages and features of the present invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects, features and advantages of the present invention will be readily apparent from the following detailed specification and the appended claims which, when taken in conjunction with the accompanying drawings, set forth the best mode currently contemplated for carrying out the invention. Referring to the drawings: 
     FIG. 1 is a sectional view of a conventional transfer case; 
     FIG. 2 is a sectional view of a portion of the transfer case shown in FIG. 1 now equipped with an endplay adjustment assembly according to the present invention; 
     FIG. 3 is an enlarged partial view taken from FIG. 2 showing the endplay adjustment assembly in greater detail; 
     FIG. 4 is an exploded perspective view showing the colinear shaft layout and the components of the endplay adjustment assembly in association therewith; 
     FIG. 5 is an end view of the adjuster plug associated with the endplay adjustment assembly; 
     FIG. 6 is a sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a sectional view showing the endplay adjustment assembly according to an alternative embodiment of the present invention; and 
     FIG. 8 is a sectional view of another alternative embodiment of the endplay adjustment assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the present invention is directed to an arrangement for adjusting the axial positioning between a pair of colinear shafts rotatably supported from a housing in a manner to eliminate relative axial movement (i.e., “endplay”) therebetween. In this regard, the present invention is particularly applicable for use in a motor vehicle power transmission apparatus such as, for example and without limitation, transfer cases, transmissions and transaxles. As discussed in further detail hereafter, the present invention provides means for eliminating the axial endplay by axially positioning a first shaft with respect to a second shaft. 
     Referring now to FIGS. 2 through 6, an apparatus, hereinafter referred to as endplay adjustment assembly  70 , is shown installed in transfer case  10 ′ and which is operable for permitting adjustment of the endplay between input shaft  14  and rear output shaft  18 . To this end, endplay adjustment assembly  70  is incorporated into transfer case  10 ′ in a manner permitting elimination of cup plug  46 , housing plug  64 , snap rings  50 ,  54 ,  56   b  and  60  in addition to the machining of hole  62  and the numerous snap ring grooves  51 ,  55 ,  57   b  and b 1  associated with transfer case  10  of FIG.  1 . 
     In general, endplay adjustment assembly  70  is operably disposed between input shaft  14  and rear output shaft  18  and includes an adjuster plug  72  and a thrust bearing assembly  74 . Adjuster plug  72  includes external threads  76  that are adapted to be threaded onto internal threads  78  formed on an intermediate segment of pilot bore  42  in input shaft  14  which is located between an internally-splined segment  80  and a bearing surface segment  82 . Adjuster plug  72  further includes a front face surface  84 , a rear face surface  86 , and a cylindrical pilot rim  88  which extends axially from rear face surface  86 . Adjuster plug  72  also includes a drive socket  90  formed in front face surface  84  to enable threaded adjustment of the axial position of adjuster plug  72  relative to input shaft  14 . As presently preferred, adjuster plug  72  is made from steel heat-treated to a hardness of approximate fifty-eight to sixty Rockwell C (RC 58-60). Furthermore, a layer of a locking thread sealer or equivalent compound is applied to threads  76  and/or  78  to secure and seal threaded adjuster plug  72  within input shaft  14 , thereby eliminating the need for use of cup plug between input shaft  14  and rear output shaft  18 . 
     Thrust bearing assembly  74  has an inner race  92  defining an aperture  93  adapted to be concentrically mounted on pilot rim  88  of adjuster plug  72 , an outer race  94 , and needle bearings  96  retained between inner race  92  and outer race  94 . Needle bearing  96  are adapted to contact rear face surface  86  of adjuster plug  72  and an end face  98  of pilot hub  38  on rear output shaft  18 . While thrust bearing assembly  74  is disclosed as being of the needle bearing type, those skilled in the art will appreciate that any equivalent thrust-type bearing assembly or thrust plate can be used in substitution therefor. 
     During assembly of transfer case  10 ′, outer race  36   b  of front bearing assembly  36  is press-fit into an annular boss  100  formed in housing section  12   a  into abutting engagement with radial shoulder surface  52 . Thereafter, input shaft  14  is slid through the central aperture in inner race  36   a  of front bearing assembly  36  until inner race  36   a  rests on outer bearing surface  102  of input shaft  14  and abuts radial shoulder  48  of input shaft  14 . Thus, front bearing assembly  36  is seated between shoulder surfaces  48  and  52  when input shaft  14  is rotatably installed in housing section  12   a . Either before or after installation of input shaft  14  into housing section  12   a , adjuster plug  72  is threaded into the intermediate segment of pilot bore  42  to a predefined axial position relative thereto. 
     Outer race  44   b  of rear bearing assembly  44  is press-fit into an annular boss  104  formed in housing section  12   b  into abutting engagement with radial shoulder  58 . Thereafter, rear output shaft  18  is slid through the central aperture in inner race  44   a  of rear bearing assembly  44  until inner race  44   a  rests on outer bearing surface  106  of rear output shaft  18  and abuts snap ring  56   a . Thus, rear bearing assembly  44  is seated between shoulder surface  58  and snap ring  56   a  when rear output shaft is rotatably installed in housing section  12   b . With thrust bearing assembly  74  journally mounted on pilot rim  88  of adjuster plug  72 , pilot hub  38  of rear output shaft  18  is positioned within pilot bore  42 . Once the components are properly aligned, housing sections  12   a  and  12   b  are interconnected to define housing assembly  12 . The sequence of operations disclosed for assembly of transfer case  10  is exemplary and is not intended to limit the present invention. 
     Once transfer case  10 ′ is assembled, a drive tool is inserted into pilot bore  42  of input shaft  14  and its square drive lug is inserted into drive socket  90  in adjuster plug  72 . Rotation of the drive lug causes rotation of adjuster plug  72  for moving adjuster plug  72  in pilot bore  42  from its predefined position toward end face surface  98  of rear output shaft  18 . As a result, thrust bearing assembly  74  is tightened against end face surface  98  of rear output shaft  18 . The reaction forces that result from this tightening process cause forward axial movement of input shaft  14  relative to housing section  12   a  for seating and loading front bearing assembly  36  against shaft shoulder  48  and housing shoulder  52 . The tightening of adjuster plug  72  also causes rearward axial movement of rear output shaft  18  relative to input shaft  14  and housing section  12   b  for seating and loading rear bearing assembly  44  against snap ring  56   a  and housing shoulder  58 . In this manner, input shaft  14  is tightly seated against housing section  12   a  and rear output shaft  18  is tightly seated against housing section  12   b  independent of machining tolerances or stack-ups associated with the components. Adjuster plug  72  can be variably tightened to minimize or completely eliminate endplay between colinear shafts  14  and  18 . Preferably, the drive tool is a power-operated drive wrench capable of quickly tightening adjuster plug  72  in a high volume production environment. 
     Referring now to FIG. 7, transfer case  10 ′ is now shown equipped with an endplay adjustment assembly  170  which is substantially similar to endplay adjustment assembly  70  except that thrust bearing assembly  74  is now replaced with a thrust plate  174 . Thrust plate  174  has a front face surface  176  adapted to engage rear face surface  86  of adjuster plug  72  and a rear face surface  178  adapted to engage end face surface  98  of pilot hub  38  on rear output shaft  18 . Thrust plate  174  further includes an aperture  193  extending between face surfaces  176  and  178  for journally mounting thrust plate  174  on pilot rim  88  of adjuster plug  72 . As before, tightening of adjuster plug  72  relative to input shaft  14  causes thrust plate  174  to engage end surface  98  of pilot hub  38  on rear output shaft  18  for taking up axial clearances between input shaft  14  and housing section  12   a  and between rear output shaft  18  and housing section  12   b.    
     In FIG. 8, adjuster plug  72  is shown with thrust bearing assembly  74  and thrust plate  174  removed such that its rear face surface  86  is in sliding contact or close proximity to end face  98  of pilot hub  38 . In this arrangement, adjuster plug  72  is initially tightened relative to input shaft  14  to take up the axial clearance in the manner previously described. Thereafter, adjuster plug  72  is rotated a small amount in the opposite direction to release any clamping loads between adjuster plug  72  and pilot hub  38  and accommodate relative rotation therebetween. 
     It will be appreciated that a colinear shaft assembly equipped with one of the endplay adjustment assemblies of the present invention represents a significant improvement over the art. While preferred embodiments of this invention have been disclosed herein, it should be further appreciated that modifications may be made without departing from the scope of the present invention. In addition, while various components have been disclosed in an exemplary fashion, various other components may, of course, be employed. It is intended by the following claims to cover these and other departures from the disclosed embodiments which fall within the true spirit of this invention. While shown utilized in a transfer case, one skilled in the art would readily recognize that the present invention is not limited to this application. More specifically, the present application has utility in numerous driveline components which utilize colinear shaft assemblies such as transmissions, differential, and other power transmission apparatuses. Thus, one skilled in the art would recognize the utility of the present invention over and above its use in the transfer case disclosed and illustrated herein.