Abstract:
A power transfer unit that includes a structure, a tube and a seal. The structure defines a boss that projects along an axis. The boss has a first portion, which defines a gripping surface, and a second portion that defines a sealing surface. The tube has an end that is disposed concentrically about at least a portion of the boss. The seal is received between and sealingly engaged against the structure and the tube. The seal includes a seal body with a seal member and a coupling portion. The seal member sealingly engages the sealing surface and the coupling portion frictionally engages the gripping surface.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a power transmission device with a torque-resistant seal. 
     With reference to  FIG. 1 , a portion of a power transfer unit  200  is illustrated to include a housing  202 , a cover  204 , a static shaft  206 , an input gear  208 , a pair of bearings  210 , an intermediate gear  212  and an output pinion  214 . The housing  202  can include a wall member  220  that can define a cavity  222  in which the static shaft  206 , the input gear  208 , the intermediate gear  212 , the output pinion  214  and a lubricant  224  can be received. The wall member  220  can further define a boss  226  having a generally cylindrical outer surface  228  that can extend into the cavity  222 . The cover  204  can be coupled to an end of the housing  202  and can close an end of the cavity  222  opposite the boss  226 . The static shaft  206  can be a hollow, tubular structure that can extend between the boss  226  and the cover  204 . The bearings  210  can be coupled to the housing  202  and the cover  204  and can support the input gear  208  for rotation in the housing  202 . The intermediate gear  212  can be rotatably coupled to the input gear  208  and meshingly engaged with the output pinion  214 . An annular space  230  can be disposed between the static shaft  206  and the input gear  208  to accommodate the lubricant  224 . Seals  232  and  234  of various types are employed to prevent the lubricant  224  from entering a hollow interior  238  of the static shaft  206 . For example, a first one of the seals  232  can comprise an O-ring that is disposed in an annular groove  240  formed about the boss  226 , while the other one of the seals  234  can comprise an O-ring that is disposed between the inner diameter of an aperture  246  in the cover  204  and the inner cylindrical surface  248  of the static shaft  206 . 
     During operation of the power transfer unit  200 , rotary power is transmitted from the input gear  208 , through the intermediate gear  212  and into the output pinion  214 . A shear force generated in the lubricant  224  during rotation of the input gear  208  can be transmitted to the static shaft  206 . In some situations, the shear force transmitted through the lubricant  224  can cause the application of a sufficient amount of torque to the static shaft  206  to cause the static shaft  206  to rotate and possibly leak. 
     SUMMARY OF THE INVENTION 
     This section provides a general summary of some aspects of the present disclosure and is not a comprehensive listing or detailing of either the full scope of the disclosure or all of the features described therein. 
     In one form, the present disclosure provides a power transfer unit that includes a structure, a tube and a seal. The structure defines a boss that projects along an axis. The boss has a first portion, which defines a gripping surface, and a second portion that defines a sealing surface. The tube has an end that is disposed concentrically about at least a portion of the boss. The seal is received between and sealingly engaged against the structure and the tube. The seal includes a seal body with a seal member and a coupling portion. The seal member sealingly engages the sealing surface and the coupling portion frictionally engages the gripping surface. 
     In another form, the present disclosure provides a method for forming a power transfer unit. The method includes: providing a tube; installing a seal to the tube, the seal including a seal lip and a coupling portion; installing the tube over a boss on a structure, the seal lip being sealingly engaged to a sealing surface formed on the boss and the coupling portion being sealingly engaged to a gripping surface formed on the boss; and mounting a gear to the structure such that the gear is concentrically disposed about the boss. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. The drawings are illustrative of selected teachings of the present disclosure and do not illustrate all possible implementations. Similar or identical elements are given consistent identifying numerals throughout the various figures. 
         FIG. 1  is a sectional view of a portion of a prior art power transfer unit; 
         FIG. 2  is a schematic illustration of a vehicle having a power transfer unit constructed in accordance with the teachings of the present disclosure; 
         FIG. 3  is a sectional view of a portion of the power transfer unit of  FIG. 2 ; 
         FIG. 4  is an enlarged portion of  FIG. 3 ; 
         FIG. 5  is a perspective view of a portion of another power transfer unit constructed in accordance with the teachings of the present disclosure; and 
         FIG. 6  is a view similar to that of  FIG. 4  but illustrating a portion of yet another power transfer unit constructed in accordance with the teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 2 , a vehicle  8  having a power transfer unit  10  constructed in accordance with the teachings of the present disclosure is schematically illustrated. The vehicle  8  can include a source of rotary power, such as an engine  16 , a transmission  18  and the power transfer unit  10 . Rotary power output from the engine  16  is received by the transmission  18  and transmitted to a front differential  22  and the power transfer unit  10 . The rotary power transmitted to the front differential  22  is transmitted to a pair of front vehicle wheels  24 , while the rotary power transmitted to the power transfer unit  10  is transmitted (via a propshaft  26 ) to a rear differential  28  where the rotary power is transmitted to a pair of rear vehicle wheels  30 . 
     With reference to  FIGS. 3 and 4 , the power transfer unit  10  is partially illustrated as including a housing  34 , a cover  36 , a static tube  38 , an input gear  40 , a pair of bearings  42 , an intermediate gear  44 , an output pinion  46  and first and second seals  48  and  50 , respectively. 
     The housing  34  can include a wall member  54  that can define a cavity  56  in which the static tube  38 , the input gear  40 , the intermediate gear  44 , the output pinion  46  and a lubricant  58  can be received. The wall member  54  can further define a hollow boss  60 , which can extend into the cavity  56 , and a first bearing seat  62  that can be disposed concentrically about the boss  60 . The boss  60  can include a gripping surface or first surface  64  and a sealing surface or second surface  66 . The first and second surfaces  64  and  66  can be generally cylindrically shaped and the second surface  66  can be smaller in diameter than the first surface  64 . The inside corner between the wall member  54  and the first surface  64  and inside corner between the first and second cylindrical surfaces  64  and  66  can be broken by a fillet radius  68  (as shown) or an undercut (not shown). The outside corner between the first and second cylindrical surfaces  64  and  66  and the outside corner between the second surface  66  and an axial end face  70  of the boss  60  can be broken by a radius (not shown) or a chamfer  72 . 
     The cover  36 , which can be conventional in its construction, can be coupled to an end of the housing  34  and can close an end of the cavity  56  opposite the boss  60 . The cover  36  can include an aperture  74  and a second bearing seat  76  that can be disposed concentrically about the aperture  74 . 
     The static tube  38  can be a hollow, tubular structure that can extend between the boss  60  and the cover  36 . The length of the static tube  38  can be selected to axially overlap the first surface  64  of the boss  60 . A chamfer  78  can be formed on the inside diameter of an end  80  of the static tube  38  proximate the wall member  54 . 
     The bearings  42  can be coupled to the housing  34  and the cover  36  and can support the input gear  40  for rotation in the housing  34 . The bearings  42  can include an inner race  82 , which can be press-fit to the input gear  40 , an outer race  84  and a plurality of bearing elements (e.g., rollers  86 ) that are disposed between the inner and outer races  82  and  84 . The outer races  84  can be received in the first and second bearing seats  62  and  76  and press-fit to the housing  34  and the cover  36 , respectively. 
     The intermediate gear  44  can include a gear portion  90 , a gear mount  92  and a hollow shaft portion  94 . The gear portion  90  can be adapted to meshingly engage another gear (not shown) in the power transfer unit  10  to receive rotary power therefrom. The hollow shaft portion  94  can be press-fit to the inner races  82  of the bearings  42  and can extend coaxially about the boss  60 . The intermediate gear  44 , which is illustrated to be a bevel ring gear, can be fixedly coupled to the gear mount  92  and meshingly engaged with the output pinion  46 , which can be rotatably mounted on bearings (not shown) that are mounted to the housing  34 . In the particular example provided, the output pinion  46  is a bevel pinion. An annular space  96  can be disposed between the static tube  38  and the input gear  40  to accommodate the lubricant  58 . 
     With specific reference to  FIG. 4 , the first seal  48  can include a case  100  and a seal body  102 . The case  100  can be formed of a sheet metal material and can be generally Z or S shaped so as to include an annular body  106 , a first flange  108  and a second flange  110 . The annular body  106  is sized to be fixedly coupled to the inside surface  112  of the static tube  38 . In the particular example provided, the annular body  106  is sized to be press-fit to the inside surface  112  of the static tube  38 , but it will be appreciated that other coupling means, including adhesives, can be employed to fixedly couple the case  100  to the static tube  38 . The first flange  108  can be coupled to a first end of the annular body  106  and can extend radially outwardly therefrom. The second flange  110  can be coupled to a second, opposite end of the annular body  106  and can extend radially inwardly therefrom. The seal body  102  can be formed of a suitable material, such as an elastomer, and can be fixedly coupled (e.g., bonded) to the case  100 . The seal body  102  can include a body portion  120 , a seal member  122  and a coupling portion  124 . In the particular example provided, the body portion  120  extends over a majority of the annular body  106  and abuts the second flange  110 . The seal member  122  can be coupled to or integrally formed with the body portion  120  and can sealingly engage the second surface  66  of the boss  60 . In the particular example provided, the seal member  122  is an annular lip. The coupling portion  124  can extend from the body portion  120  on a side opposite the second flange  110 . The coupling portion  124  can define an annular gripping surface  130  that can frictionally engage the first surface  64  of the boss  60 . The coupling portion  124  can extend from the body portion  120  in a direction generally parallel to a longitudinal axis of the boss  60 . The coupling portion  124  can extend coaxially with the annular body  106  and can be disposed onto or over the first flange  108 . It will be appreciated that the chamfer  72  on the corner between the first and second surfaces  64  and  66  can aid installation of the coupling portion  124  onto the first surface  64  when the static tube  38  is installed to the housing  34 . It will also be appreciated that the chamfer  72  on the corner between the second surface  66  and the axial end face  70  of the boss  60  can aid installation of the seal member  122  onto the second surface  66 . It will be further appreciated that the first flange  108  can be employed as a “stop,” which can be employed to position the seal member  122  relative to the static tube  38  in a desired location, and/or as a flange against which tooling can be abutted when the first seal  48  is installed to the static tube  38 . 
     Returning to  FIGS. 3 and 4 , the second seal  50  can be disposed in the aperture  74  and can sealingly engage the cover  36  and the static tube  38  in a conventional manner. Accordingly, the second seal  50  will not be discussed in detail herein. 
     During operation of the power transfer unit  10 , rotary power is transmitted from the input gear  40 , through the intermediate gear  44  and into the output pinion  46 . A shear force generated in the lubricant  58  during rotation of the input gear  40  can be transmitted to the static tube  38 . The shear force transmitted through the lubricant  58  can apply a torque to the static tube  38  which can be resisted by the friction that is generated through contact between the seal member  122  and the second surface  66 , as well as between the annular gripping surface  130  and the first surface  64 . 
     It will be appreciated that the coupling portion  124  of the seal body  102  may, but need not, sealingly engage the first surface  64  of the boss  60 . To further increase the friction between the annular gripping surface  130  and the first surface  64 , it will be appreciated that one or both of the annular gripping surface  130  and the first surface  64  can be modified. For example, knurls  150  could be formed onto the first surface  64  or the first cylindrical surface could be formed in a non-cylindrical manner (e.g., with teeth or splines, or with a square or hexogonal shape). 
     A portion of another power transfer unit  10   a  constructed in accordance with the teachings of the present disclosure is illustrated in  FIG. 6 . The power transfer unit  10   a  can be generally similar to the power transfer unit  10  ( FIG. 2 ) described in detail above, except that the first surface  64   a  on the boss  60   a  can be equal in diameter to the diameter of the second surface  66   a  to thereby simplify the geometry of the housing  34   a . In this example, the case  100   a  can be formed of a sheet metal material and can be generally Z or S shaped so as to include an annular body  106 , a first flange  108   a  and a second flange  110 . The annular body  106  can be sized to be fixedly coupled to the inside surface  112  of the static tube  38 . In the particular example provided, the annular body  106  is sized to be press-fit to the inside surface  112  of the static tube  38 , but it will be appreciated that other coupling means, including adhesives, can be employed to fixedly couple the case  100   a  to the static tube  38 . The first flange  108   a  can be coupled to a first end of the annular body  106  and can include a radially inwardly extending portion  1000  and an axially extending portion  1002 . The second flange  110  can be coupled to a second, opposite end of the annular body  106  and can extend radially inwardly therefrom. The seal body  102 a can be formed of a suitable material, such as an elastomer, and can be fixedly coupled (e.g., bonded) to the case  100   a . The seal body  102 a can include a body portion  120 , a seal member  122  and a coupling portion  124   a . In the particular example provided, the body portion  120  extends over a majority of the annular body  106  and abuts the second flange  110 . The seal member  122  can be coupled to or integrally formed with the body portion  120  and can sealingly engage the second surface  66   a  of the boss  60   a . In the particular example provided, the seal member  122  is an annular lip. The coupling portion  124 a can extend from the body portion  120  on a side opposite the second flange  110  and can be coupled to the axially extending portion  1002 . The coupling portion  124   a  can define an annular gripping surface  130   a  that can frictionally engage the first surface  64   a  of the boss  60 . The coupling portion  124   a  can extend from the body portion  120  in a direction generally parallel to a longitudinal axis of the boss  60   a . The coupling portion  124   a  can extend coaxially with the annular body  106  and can be disposed onto or over the first flange  108   a . It will be appreciated that the chamfer  72  on the corner between the second surface  66   a  and the axial end face  70  of the boss  60   a  can aid installation of the coupling portion  124   a  onto the first surface  64   a  and the seal member  122  onto the second surface  66   a . 
     It will be appreciated that the above description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples is expressly contemplated herein, even if not specifically shown or described, so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the teachings of the present disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims.