Abstract:
A pinion shaft and bearing assembly is provided having two different surface finish interfaces. A first surface finish functions to locate the bearing to the pinion. A second surface finish functions to improve the cure time of an adhesive used to retain the bearing to the pinion.

Description:
FIELD 
     The present invention relates generally to a pinion shaft and bearing assembly, and more particularly to a pinion shaft and bearing assembly using an adhesive for improved bearing location and retention of an inner race of a rolling element bearing. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical pinion shaft and bearing assembly uses various mechanisms to maintain sufficient friction between the pinion shaft and the bearing to prevent the bearing from spinning free from or walking off the pinion shaft. These mechanisms include various mechanical methods of coupling the bearing to the pinion shaft such as, for example, press-fitting the bearing to the pinion shaft. The effectiveness of these mechanisms may be enhanced by the addition of an anaerobic adhesive between the pinion shaft and the bearing. 
     Typically, the anaerobic adhesive is applied to the pinion shaft or bearing prior to assembly and is cured in situ. The adhesive fits within gaps formed on the surfaces due to surface roughness. In general applications the cure time for the anaerobic adhesive is a function of the gap between the pinion shaft and the bearing. The cure times are shorter when the anaerobic adhesive is applied to a smaller gap. Also, the relationship between retention strength of the adhesive and surface roughness is integral in the robustness of the assembly where the rougher the surface finish the higher the retention strength achieved. 
     However, the location accuracy (i.e., the radial and axial position) of the bearing on the pinion shaft improves when tight dimensional controls are employed. One result of tight dimensional controls is smooth surface finish. In balancing the needs for tight location accuracy and high bearing retention strength, location accuracy is typically favored. Alternative solutions for preventing bearing spin or walk while maintaining location accuracy include integrated bearing sleeves or mechanical retention of the bearing. However, these alternative solutions may increase cost and may not be practical due to packaging restraints. Accordingly, there is a need in the art for a pinion shaft and bearing assembly that increases the effectiveness of anaerobic adhesives without increasing cure time and without decreasing locational accuracy. 
     SUMMARY 
     A pinion shaft and bearing combination is provided including a pinion shaft with at least two outer regions each having a different surface finish and a pinion bearing with at least two inner regions each having a different surface finish. 
     An embodiment of a pinion shaft and bearing combination is provided having a pinion shaft having a first outer region with a first surface treatment and a second outer region with a second surface treatment. A pinion bearing is disposed on the pinion shaft with the pinion bearing having a first inner region with a third surface treatment and a second inner region with a fourth surface treatment. An adhesive is applied to one or both of the second outer region and the second inner region. The first surface treatment and the third surface treatment cooperate to locate the pinion bearing on the pinion shaft and the second surface treatment and the fourth surface treatment cooperate to improve a performance of the adhesive. 
     In another embodiment of the present invention, the pinion shaft defines a longitudinal axis and includes a first pinion end and a second pinion end disposed opposite the first pinion end along the longitudinal axis. 
     In yet another embodiment of the present invention, the first outer region is located on an outer surface of the pinion shaft and extends from the first pinion end a first distance along the longitudinal axis. 
     In yet another embodiment of the present invention, the second outer region is located on the outer surface of the pinion shaft and extends from the first outer region a second distance along the longitudinal axis. 
     In yet another embodiment of the present invention, the pinion shaft includes a third outer region on the outer surface of the pinion shaft, the third outer region having the first surface treatment and extending from the second outer region a third distance along the longitudinal axis to the second pinion end. 
     In yet another embodiment of the present invention, the first distance is approximately equal to the third distance, and the second distance is greater than the first and third distances. 
     In yet another embodiment of the present invention, the pinion bearing is concentric with the pinion shaft and includes a first bearing end and a second bearing end disposed opposite the first bearing end along the longitudinal axis. 
     In yet another embodiment of the present invention, the first inner region is located on an inner surface of the pinion bearing and extends from the first bearing end a fourth distance along the longitudinal axis. 
     In yet another embodiment of the present invention, the second inner region is located on the inner surface of the pinion bearing and extends from the first inner region a fifth distance along the longitudinal axis. 
     In yet another embodiment of the present invention, the pinion bearing includes a third inner region on the inner surface of the pinion bearing, the third inner region having the third surface treatment and extending from the second inner region a sixth distance along the longitudinal axis to the second bearing end. 
     In yet another embodiment of the present invention, the fourth distance is approximately equal to the sixth distance, and the fifth distance is greater than the fourth and sixth distances. 
     In yet another embodiment of the present invention, the first and third surface treatments result in a surface finish from about 0.10 to about 0.35 μm Ra. 
     In yet another embodiment of the present invention, the second and fourth surface treatments result in a surface having a plurality of indentations about 0.025 mm deep and have a surface finish of about 1.0 to about 3.2 μm Ra. 
     In yet another embodiment of the present invention, the first inner region of the pinion bearing is disposed opposing the first outer region of the pinion shaft and the second inner region of the pinion bearing is disposed opposing the second outer region of the pinion shaft. 
     In yet another embodiment of the present invention, the first inner region is press fit to the first outer region. 
     In yet another embodiment of the present invention, the second surface treatment of the second outer region and the second surface treatment of the second inner region cooperate to define a plurality of gaps between the pinion bearing and the pinion shaft. 
     In yet another embodiment of the present invention, the adhesive is disposed within the gaps. 
     In yet another embodiment of the present invention, the gaps are comprised of at least one of continuous elongated divots, round pockets, diamond pockets, and square pockets. 
     In yet another embodiment of the present invention, the gaps are continuous channels. 
     Further objects, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a side view of a gear and shaft assembly including an embodiment of a pinion shaft and bearing assembly according to the principles of the present invention; 
         FIG. 2  is a side view of an embodiment of a pinion according to the principles of the present invention; 
         FIG. 3  is a cross-sectional view of an embodiment of a bearing according to the principles of the present invention; 
         FIG. 4  is a cross-sectional view of an embodiment of a bearing installed on a pinion according to the principles of the present invention; 
         FIG. 5  is an enlarged cross-sectional view of an embodiment of a bearing installed on a pinion detailing the surface finishes; 
         FIG. 6  is a magnified view of an exemplary surface structure showing a continuous feature; 
         FIG. 7  is a magnified view of an exemplary surface structure showing a pocket surface structure; and 
         FIG. 8  is a further magnified view of an exemplary surface structure showing another pocket surface structure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring to  FIG. 1 , a side view of an exemplary gear and shaft assembly is generally indicated by reference number  10 . The gear and shaft assembly  10  is preferably located in a transmission (not shown) and is supported by at least one member  12 . The member  12  may take various forms, such as a non-rotational housing member, a radial rolling element bearing, or a rotating sleeve shaft without departing from the scope of the present invention. The gear and shaft assembly  10  includes a gear  11 , a shaft  13 , and at least one pinion shaft and bearing assembly  14  according to the principles of the present invention. The gear  11  intermeshes with a second gear (not shown) providing torque and rotation to the gear and shaft assembly  10 . The gear  11  is drivingly mounted to the shaft  13  which integrates the pinion shaft and bearing assembly  14 . The pinion shaft and bearing assembly  14  generally includes a pinion shaft  20  integrated with the shaft  13  and a bearing  40  coupled to the pinion shaft  20 , as will be described in greater detail below. The bearing  40  provides a material more suitable for improving the durability and performance of the pinion shaft  20  than the shaft  13  material alone. 
     Referring to  FIG. 2 , a side view of the pinion shaft  20  proximate to the bearing  40  is illustrated and will now be described in detail. The pinion shaft  20  is generally cylindrical with an approximately circular cross-section, although other cross-sectional shapes may be employed without departing from the scope of the present invention. The pinion shaft  20  has a diameter D 1  and includes a base end  22  and a distal end  24  located opposite the base end  22 . The pinion shaft  20  further includes an outer surface  26  that has a first outer region  28 , a second outer region  30 , and a third outer region  32 . Each of the outer regions  28 ,  30 ,  32  are circumferentially continuous on the pinion shaft  20 . The first outer region  28  extends axially from the base end  22  of the pinion shaft  20  a distance of X 1 . The second outer region  30  extends axially from the first outer region  28  a distance of Y 1 . The third outer region  32  extends axially from the second outer region  24  a distance of Z 1  to the distal end  24  of the pinion shaft  20 . In the example provided, the first and third outer regions  28 ,  32  have a surface with a microfinish below about 0.25 μm Ra. The second outer region  30  has a surface that is treated to create a plurality of features or indentations  31  reaching about 0.025 mm in depth where the surface of the indentations  31  have a microfinish of about 1.0 μm to 3.2 μm Ra. However, it should be appreciated that other microfinishes may be used without departing from the scope of the present invention. The surface finish of the second outer region  30  is greater than or equal to the surface finish of the first outer region  28  and less than the surface finish of the indentations  31 . Additionally, the distances X 1 , Y 1 , Z 1  may be adjusted depending upon the application. In the embodiment provided, distances X 1  and Z 1  are approximately equal and the distance Y 1  is greater than the distances X 1  and Z 1 . However, the distance Y 1  is directly related to a retention force of the bearing  40  on the pinion shaft  20  required for a particular application. 
     Turning now to  FIG. 3 , a cross-sectional view of the bearing  40  is illustrated and will now be described. The bearing  40  is generally cylindrical and includes an inner race or surface  42  that defines a central bore  44 . The central bore  44  has a diameter D 2 . The bearing  40  further includes a first end  46  and a second end  48  opposite the first end  46 . The inner surface  42  includes a first inner region  49 , a second inner region  50 , and a third inner region  52 . The first inner region  49  extends axially from the first end  46  of the bearing  40  a distance of X 2 . The second inner region  50  extends axially from the first inner region  49  a distance of Y 2 . The third inner region  52  extends axially from the second inner region  50  a distance of Z 2  to the second end  48  of the bearing  40 . In the example provided, the first and third inner regions  49 ,  52  have a microfinish below about 0.25 μm Ra. The second inner region  50  has a surface that is treated to create a plurality of features or indentations  51  reaching about 0.025 mm in depth where the surface of the indentations  51  have a microfinish of about 1.0 μm to 3.2 μm Ra. However, it should be appreciated that other microfinishes may be used without departing from the scope of the present invention. The surface finish of the second inner region  50  is greater than or equal to the surface finish of the first inner region  49  and less than the surface finish of the indentations  51 . Additionally, the distances X 2 , Y 2 , Z 2  may be adjusted depending upon the application. In the embodiment provided, distances X 2  and Z 2  are approximately equal and the distance Y 2  is greater than the distances X 2  and Z 2 . However, the distance Y 2  is directly related to a retention force of the bearing  40  on the pinion shaft  20  required for a particular application. Furthermore, the distances X 2 , Y 2 , Z 2  are approximately equal to the distances X 1 , Y 1 , Z 1  respectively. 
     Referring now to  FIG. 4 , a cross-sectional view of the pinion and bearing assembly  14  with the bearing  40  installed on the pinion shaft  20  is illustrated and will now be described. The pinion bearing  40  is installed onto the pinion shaft  20  such that the pinion shaft  20  is located within the central bore  44 . As installed, the first inner region  49  opposes the first outer region  28 , the second inner region  50  opposes the second outer region  30 , and the third inner region  52  opposes the third outer region  32 . Where the first inner region  49  and first outer region  28  contact, the diameters D 1  and D 2  create a first press fit region  60 . The contact between the third inner region  52  and third outer region  32  creates a second press fit region  64 . The press fit is accomplished by providing that diameter D 2  is smaller or equal to the diameter D 1 . The overlap in diameters D 1  and D 2  ensures that there is no space between the pinion bearing  40  and the pinion shaft  20  for the pinion bearing  40  to move once installed on the pinion shaft  20 . Thus the press fit regions  60 ,  64  allow the pinion bearing  40  to be accurately located on the pinion shaft  20  by minimizing relative movement between the parts. 
     As the pinion bearing  40  is installed on the pinion shaft  20 , the second inner region  50  opposes second outer region  30  each having a surface pattern of features or indentations  31 ,  51 . The depth of the indentations  82  is around 0.025 mm thus providing a gap  61 , as shown in  FIG. 5 , of at most around 0.05 mm when two indentations  31 ,  51  are stacked on top of one another. The gap  61  provides a volume  81  for depositing an anaerobic adhesive  80  into the adhesive region  62  by applying it to one of or both of the outer surface  26  of the pinion shaft  20  and the inner surface  42  of the bearing  40  prior to installation. A preferred anaerobic adhesive  80 , for example, Loctite® 609 or 680 Retaining Compound or Loctite® Sleeve Retainer 640 manufactured by Henkel Corporation of Warren, Mich., although various other adhesives may be employed without departing from the scope of the present invention. One result of the surface treatment is that the inner surface  83  of the indentations  82  has a surface roughness of about 1.0 μm to about 3.2 μm Ra. As noted above, the press fit region  60  is accomplished by providing that diameter D 2  is smaller or equal to the diameter D 1  and is used to precisely locate the bearing  40  on the pinion shaft  20 . The press fit also provides an initial retention force resulting from stretching the pinion bearing  40  material and compressing the pinion shaft  20  material. 
     Referring now to  FIGS. 6-8 , magnified views of various embodiments of the indentations  82  in the second outer region  30  of the outer surface  26  of the pinion shaft  20  resulting from various stages of processing are shown and will now be described. Initially the outer surface  26  is honed or ground to slightly larger finished size. Next, laser processing creates the indentations  82 , for example, as continuous elongated channels  82 , shown in  FIG. 6 . When the material is removed from the outer surface  26 , displaced material (not shown) is formed near the indentations  82 . Finally, the outer surface is finished honed producing the surface finish. Any displaced material remaining on the outer surface  26  but outside of the specified diameter is removed. The indentations  82  may also have shapes other than a continuous channel without departing from the scope of the present invention. For example,  FIG. 6  shows the embodiment wherein the indentations  82  take the form of a pattern of continuous, elongated pockets  100 .  FIG. 7  shows another embodiment of the finished surface wherein the indentations  82  form a pattern of round pockets  102 .  FIG. 8  shows still another embodiment of the finished surface wherein the indentations  82  form a pattern of pattern of diamond or square pockets  104 . These surface features described in  FIGS. 6-8  cooperate to form the pockets  82 , as described above. It should be appreciated that other surface features may be employed without departing from the scope of the present invention.  FIGS. 6-8  may also represent the second inner surface  50  of the inner surface  42  of the bearing  40  without departing from the scope of this invention. 
     The description of the invention is merely exemplary in nature and 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.