Abstract:
A shaft has a seal journal with a plurality of raised spherical bumps. These microscopic spherical bumps provide a smooth, edge-free contact surface for the seal which is positioned around the seal journal of the shaft. The valleys or spaces between these bumps serve to retain lubricant, thereby promoting hydrodynamic lubrication between the seal and seal journal, reducing friction and reducing or eliminating wear on the seal.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to journal texturing, and more specifically, to texturing an oil seal journal to provide a raised contour.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many devices, conventionally, utilize a housing filled with fluid or lubricant and shafts passing through the wall of the housing to drive or be driven by an external component. Internal to the housing is a gear set or other mechanical device that modifies the rotational energy, torque or speed supplied from one shaft to another shaft. Such devices must be fluidly sealed from the external environment to ensure that contaminants do not enter the housing nor does fluid leak from the housing to the external environment. However, with the use of rotating shafts in such an arrangement, it is difficult to seal the housing as the rotation of a shaft with respect to a fixed housing wall requires some space between. To aid in fluidly sealing this space, fluid seals are positioned between the shaft and wall. Typical fluid seals are donut-like with a through bore to press against the seal area of the shaft and have an outer surface that engages with an aperture formed in the housing. As a result, the shaft rotates and slides against the fluid seal and the fluid seal presses against the seal area of the shaft to form a barrier between the inside of the housing and the external environment. However, as rotation of the shaft against the seal is resisted by friction, energy is lost to heat due to this resistance. Moreover, the seal and shaft can be worn and damaged due to this friction. As a result, seals and shafts must be replaced which increases labor and maintenance costs and creates downtime.  
           [0003]    To address this problem, seal areas of shafts are plunge ground to create a relatively smooth surface and reduce the frictional resistance between the seal and the seal area on the shaft. Plunge grinding also removes the “threading” effect of the rough turning operation that preceded. However, plunge grinding creates a surface texture containing a series of microscopic peaks and valleys, the size and depth of which is dependent upon the grit of the grinding wheel employed (See FIG. 13). The sharp edges of these “peaks” have the undesirable effect of gradually wearing away the seal lips.  
           [0004]    Research has been performed in an attempt to find alternate ways of reducing friction and seal wear in lieu of or in addition to plunge grinding. As reported in the SAE Technical Paper Series in an article entitled A Friction-Reducing Shaft Surface for Use With Standard Radial Sharp Lip Oil Seals, one possible method of friction reduction is accomplished by shot peening the seal area on the shaft. According to this publication, shot peening is applied to the surface of the seal area on the shaft at a predefined angle. In addition, a specified diameter of shot is used. As a result, microscopic “pockets” are created on the surface of the shaft which enhance hydrodynamic lubrication, thereby reducing friction between the shaft and seal. While this process does provide these benefits, some drawbacks still exist. Specifically, the surface texture created by this process features randomly located “dimple-like” depressions separated by raised “plateaus” with potentially sharp corners which can accelerate seal wear (See FIG. 14). In addition, as the seal area of the shaft is typically a very narrow band on the shaft, applications of shot peening can extend outward beyond the seal area to other undesirable regions such as bearing and gear surfaces. The present invention is developed in light of these and other drawbacks.  
         SUMMARY OF THE INVENTION  
         [0005]    To overcome these and other drawbacks, a shaft is provided having a seal area with a plurality of spherical bumps positioned thereon. The plurality of spherical bumps present no sharp edges to the seal and the depressions between these bumps serve to retain lubricant, thereby promoting hydrodynamic lubrication, reducing energy losses due to friction and reducing or eliminating wear on the seal and the shaft.  
           [0006]    In another aspect, a speed reducer is provided having a shaft with a seal area that has a plurality of spherical bumps positioned thereon. A seal is positioned between the seal area and an aperture in the housing to seal an internal environment of the housing from an external environment of the housing while allowing the shaft to rotate.  
           [0007]    In another aspect, a method for forming the plurality of spherical bumps on the seal area of the shaft is provided. The method includes the steps of forming a plurality of spherical indentations into a cylindrical die or pair of cylindrical dies, pressing the dies against a seal area of a shaft, while rotating the dies to form the plurality of spherical bumps on the surface of the seal area of the shaft.  
           [0008]    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  
       [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a perspective view of a wall, shaft and shaft seal using a shaft seal area having a raised texture according to the present invention;  
         [0011]    [0011]FIG. 2 is a perspective view of a seal surface of a shaft having a raised texture according to the present invention;  
         [0012]    [0012]FIG. 3A is a schematic view of a process for applying a raised texture to a shaft seal area according to the present invention;  
         [0013]    [0013]FIG. 3B is a schematic view showing a process for applying a raised texture to a shaft seal according to the present invention;  
         [0014]    [0014]FIG. 3C is a schematic view of a process for applying a raised texture to a shaft seal surface according to the present invention;  
         [0015]    [0015]FIG. 4 is a perspective view of a die being peened to create spherical indentations according to the present invention;  
         [0016]    [0016]FIG. 5 is a perspective view of the surface of a shot peened die according to the present invention;  
         [0017]    [0017]FIG. 6 is a side view of a shaft having seal areas with a raised texture according to the present invention;  
         [0018]    [0018]FIG. 7 is a speed reducer having shafts with seal areas with raised textures according to the present invention;  
         [0019]    [0019]FIG. 8 is a cross-sectional view of a shaft and seal according to the present invention;  
         [0020]    [0020]FIG. 9 is a perspective view of the formation of dies for applying a raised texture according to the present invention;  
         [0021]    [0021]FIG. 10 is a cross-sectional view of dies forming a raised texture according to the present invention;  
         [0022]    [0022]FIG. 11 is a cross-sectional view of dies forming a raised texture according to the present invention;  
         [0023]    [0023]FIG. 12 is a cross-sectional view of dies forming a raised texture according to the present invention;  
         [0024]    [0024]FIG. 13 is a diagrammatical view of the surface of a journal area according to the prior art;  
         [0025]    [0025]FIG. 14 is a diagrammatical view of the surface of a journal area according to the prior art;  
         [0026]    [0026]FIG. 15 is a diagrammatical view of the surface of a journal area according to the present invention; and  
         [0027]    [0027]FIG. 16 is a side view of a shaft with the surface of a journal area according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring now to FIG. 1, a shaft  10  is shown passing through an aperture in a wall  12 . Shaft  10  is separated from the internal diameter of the aperture by seal  14 . Wall  12  is a wall of an enclosure or housing (as will be described in greater detail) that separates an internal environment  30  from an external environment  32 . Preferably, the housing supports a gear set or other known mechanical device that changes energy, torque or the rotational speed relationship between shafts entering and exiting the housing such as in a speed reducer. However, it is understood that wall  12  can be any barrier having a shaft passing therethrough that requires the area between the shaft and barrier to be sealed.  
         [0029]    In FIG. 6, shaft  10  is shown in greater detail. Here, shaft  10  is generally cylindrical in shape and has two seal journals  16  and two bearing journals  18 . In addition, shaft  10  has a gear journal  20 . The gear journal  20  acts to press against an internal diameter of a gear bore to support the gear. Likewise, bearing journals  18  act to press against the internal diameter of bearings to support those bearings. As a result, the bearing journals  18  allow shaft  10  to be rotatably mounted within the housing  22  (see FIG. 7). Thus, shaft  10  can be rotated with respect to housing  22  to thereby drive or be driven by a gear mounted on gear journal  20 . As shown in FIG. 7, shafts  26  and  28  (which will be described in greater detail) having the same design as that described for shaft  10 , can be positioned in housing  22 . Bearings positioned around bearing journals  18  rotatably support the shafts, while seals positioned around seal journals  16  seal respective ends of the shaft that pass through walls  12  such that the internal environment of the housing does not communicate with the outside environment of the housing.  
         [0030]    As shown in FIG. 7, wall  12  is one wall of a housing structure preferably for a speed reducer  24 . As shown in FIG. 7, speed reducer  24  includes a housing structure  22  having walls  12 . Input shaft  26  is positioned through opposite walls  12 . The shaft  26  may rotate in the wall  12 . Likewise, output shaft  28  is rotatably mounted by opposite walls  12 . Both input shaft  26  and output shaft  28  are similar in design to described input shaft  10 . Likewise, both input shaft  26  and output shaft  28  pass through walls  12  in a same manner as that described in FIG. 1. Gearing is contained within housing structure  22  and is mounted on input shaft  26  and output shaft  28 . The gearing provides a different rotational relationship between input shaft  26  and output shaft  28 .  
         [0031]    As illustrated in FIG. 1, walls  12  serve to differentiate between the internal environment  30 , inside housing structure  22 , and the external environment  32 . The internal environment, protected by housing structure  22 , houses critical components such as bearings, gears and lubricant. As a result, it is critical that the internal environment  30  be fluidly sealed from the external environment  32 . Accordingly, the seal protects the internal environment  30  from external contamination and prevents lubricant from leaking from the internal environment  30  to the external environment  32 .  
         [0032]    To fluidly seal the internal environment  30  from the external environment  32 , seal  14  is positioned between seal journal  16  and wall  12 . Shaft  10  in wall  12  slides against seal  14  during rotation. Some lubricant from within housing structure  22  passes along the inner face between seal  14  and seal journal  16 . This ensures that the amount of friction is reduced.  
         [0033]    Referring now to FIG. 2, seal area  16  is described in greater detail. Seal area  16  includes a plurality of spherical bumps  34  or raised portions which form a raised texture on seal area  16 . Raised bumps  34  are preferably hemispherical in nature.  
         [0034]    As shown in FIG. 8, spherical bumps  34  provide gaps  60  that collect lubricant from the inside of housing structure  22 . The lubricant is retained in the gaps and supports hydrodynamic lubrication between the shaft  10  and the seal  14 . Moreover, as shown in FIG. 15, the addition of the rounded surfaces eliminates the sharp edges as found in the prior art such as illustrated FIGS. 13 and 14. This reduces or eliminates wear on the seal itself.  
         [0035]    Referring now to FIGS.  3 A- 3 C, and  4 , a method of forming spherical bumps  34  onto the seal journal  16  is shown and described. In FIG. 3A, shaft  10  is positioned on rollers  38  between dies  36 . As illustrated in FIG. 4, dies  36  are formed by shot peening, or other known mechanical means of impaling shot, or other material against a metal blank. As illustrated in FIG. 9, particles  62  impact the surface of dies  36  to form spherical indentations  64 . These indentations act as small molds to form the raised surface on seal journal  16 . Alternatively, the spherical indentations  64  can be formed by an alternate method such as EDM. In such a process, an EDM carbon is manufactured having a plurality of bumps. The EDM carbon is then burned into the die to form the plurality of spherical indentations  64 . Alternatively, other methods of formation can be used that include forging, casting, or machining to form spherical indentations  64 . In addition, the process to form spherical indentations can also include chemical etching, laser cutting or rolling a die having a plurality of bumps against the dies  36 .  
         [0036]    In FIG. 3B, dies  36  are pressed against shaft  10  with sufficient force to cause metal deformation at the seal journal  16  in shaft  10 . As shown in FIG. 10, the surface of the seal journal  10  is plastically deformed into the indentations  64  of dies  36 . As this occurs, the spherical bumps  34  are formed. The spherical bumps  34  have substantially the same convex or external shape as the shot or other material which was used to form the dies  36 . The dies  36  are rotated according to the arrow shown in the figure. During this process, shaft  10  may be supported and located by rollers  38  or by center supports engaging shaft  10  as shown in FIG. 16. In FIG. 3C, dies  36  are retracted from shaft  10 . As a result, the seal journal  16  is deformed to include spherical bumps  34 . In FIG. 5, the inverse impressions in die  36  due to shot peening can generally be seen.  
         [0037]    In FIG. 11, another aspect is shown where one of the dies  36  is replaced by a roller  66 . Here, only die  36  provides a raised texture on the seal area, while roller  66  supports shaft  10  from moving due to the force from die  36 . In FIG. 12, another aspect is shown where die  36  is positioned on top of shaft  10  and the rollers  38  counter the force applied by die  36 .  
         [0038]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.