Abstract:
A novel arrangement of a pinion shaft for a differential assembly having a substantially H-shaped cross-section with added oiling radii. The H-shaped pinion shaft provides substantially reduced weight of the differential pinion shaft, increases a strength-to-weight ratio, and improves lubrication.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a differential assembly, and more particularly to a pinion shaft for the differential assembly for motor vehicles, having an H-shaped cross-section.  
           [0003]    2. Description of the Prior Art  
           [0004]    Conventionally, differential assemblies well known in the prior art, are arranged in a power transmission system of a motor vehicle to allow a pair of output shafts operatively coupled to an input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction with the road while the vehicle is turning. Such a device essentially distributes the torque provided by the input shaft between the output shafts.  
           [0005]    Essential part of the differential assembly is a pinion shaft rotatably supporting differential pinion mate gears in mesh with side gears that are, in turn, drivingly coupled to the output shafts of the motor vehicle. Usually, the pinion shafts of the differential assemblies are cylindrically shaped and have a circular cross-section. Some pinion shafts, known in the prior art, have flattened portions for improving lubrication.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a novel arrangement of a pinion shaft of a differential assembly for motor vehicles.  
           [0007]    In accordance with the present invention, at least a section of the differential pinion shaft that supports a pinion mate gear member, has a substantially H-shaped cross-section with added oiling radii.  
           [0008]    In accordance with the first embodiment of the present invention, an entire length of the pinion shaft has a substantially H-shaped (or I-shaped) cross-section having a substantially uniform size in a lengthwise direction thereof.  
           [0009]    In accordance with the second embodiment of the present invention, the pinion shaft has opposite end sections and a central section. The entire length of the pinion shaft has a substantially H-shaped cross-section, wherein said H-shaped cross-section of said end sections has substantially uniform size across an entire length thereof and said H-shaped cross-section of said central section has a substantially varied size across an entire length thereof.  
           [0010]    In accordance with the third embodiment of the present invention, the pinion shaft has opposite end sections adapted to engage a differential case and a central section rotatably supporting the pinion mate gears, wherein the end sections are substantially cylindrical, while the central section has essentially H-shaped cross-section having a substantially uniform size across an entire length thereof.  
           [0011]    In accordance with the third embodiment of the present invention, the pinion shaft has opposite end sections adapted to engage the differential case and the central section rotatably supporting the pinion mate gears, wherein the end sections are substantially cylindrical, while the central section has essentially H-shaped cross-section having a substantially constant area in a lengthwise direction thereof.  
           [0012]    In accordance with the forth embodiment of the present invention, the pinion shaft has opposite end sections adapted to engage the differential case and the central section rotatably supporting the pinion mate gears, wherein the end sections are substantially cylindrical, while the central section has essentially H-shaped cross-section. The central section, in turn, has a pair of opposite gear bearing segments interconnected by a link segment. The H-shaped cross-section of the gear bearing segments has a substantially uniform size across an entire length thereof and the H-shaped cross-section of the link segment has a substantially varied size across an entire length thereof.  
           [0013]    The differential pinion shaft in accordance with the present invention represents an improvement over the prior art that substantially reduces weight of the differential pinion shaft, increases a strength-to-weight ratio, and improves lubrication. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1 is a partial cross-sectional view of a differential assembly;  
         [0016]    [0016]FIG. 2 is a cross-sectional view of a pinion shaft in accordance with the present invention disposed in a bore of a pinion mate gear member of the differential assembly;  
         [0017]    [0017]FIG. 3 is a perspective view of the pinion shaft in accordance with the first embodiment of the present invention;  
         [0018]    [0018]FIG. 4 is a perspective view of the pinion shaft in accordance with the second embodiment of the present invention;  
         [0019]    [0019]FIG. 5 is a perspective view of the pinion shaft in accordance with the third embodiment of the present invention;  
         [0020]    [0020]FIG. 6 is a perspective view of the pinion shaft in accordance with the forth embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    The preferred embodiment of the present invention will now be described with the reference to accompanying drawings.  
         [0022]    Referring now to FIG. 1 of the drawings, a typical differential assembly for a motor vehicle, generally designated by the reference numeral  10 , is illustrated. The differential assembly  10  is incased in an axle housing  12 , and is adapted to differentially drive a pair of aligned axle shafts  14   a  and  14   b  projecting inwardly of the differential assembly  10  from the opposite directions and, in turn is driven by a drive pinion shaft  16  provided with a drive gear  18  at one end thereof. The drive pinion shaft  16  is mounted for rotation adjacent to the differential assembly  10  as by means of a bearing  20  in the axle housing  12 .  
         [0023]    The differential assembly  10  comprises a differential case  22  rotatably supported at opposite ends thereof by means of a pair of opposite tapered roller side bearings  24  in the axle housing  12 . The differential case  22  has an annular flange  26  to which a ring gear  28  is fastened by any appropriate means, such as by bolts  30 . The ring gear  28  meshes with the drive gear  18 .  
         [0024]    The differential case  22  houses a pair of opposite side gears  32   a  and  32   b  commonly splined to the axle shafts  14   a  and  14   b  for rotation therewith, and a set of pinion mate gear members  34  rotatably supported on a transverse pinion shaft  36 . The side gears  32   a  and  32   b  are in mesh with the pinion mate gear members  34 . The pinion shaft  36  is conventionally retained within the differential case  22  by a locking pin  38  extending through an opening in the pinion shaft  36 .  
         [0025]    Typically, the pinion shaft  36  of the prior art has substantially cylindrical outer peripheral surface, i.e. the pinion shaft has a substantially circular cross-section.  
         [0026]    By contrast, in accordance with the present invention, at least a portion of the pinion shaft  36  supporting the pinion mate gear members  34 , has substantially H-shaped (or I-shaped) cross-section. The H-shaped portion of the pinion shaft  36  includes a web element  38  interconnecting opposite flange members  40   a  and  40   b , as illustrated in FIG. 2, thus defining opposite channels  39  separated by the web element  38 . The flange members  40   a  and  40   b  have curved outer peripheral surfaces  42   a  and  42   b , respectively, complementary to an inner peripheral surface of a bore  44  in the pinion mate gear member  34 . In order to improve lubrication of bearing surfaces of the pinion shaft  36 , distal ends  43   a  and  43   b  of the flange members  40   a  and  40   b , respectively, are rounded off with oiling radii R L . Arrows L in FIG. 2 illustrate a flow of lubricant oil when the pinion mate gear member  34  rotates in the direction of an arrow A relative to the pinion shaft  36 .  
         [0027]    In accordance with the first embodiment of the present invention, illustrated in FIG. 3, a pinion shaft  36   1  has a substantially H-shaped cross-section having a substantially uniform size across an entire length D thereof. Preferably, the pinion shaft  36   1  is made by a metal extrusion process. However, any other appropriate method for making the pinion shaft  36   1 , such as machining, forging or casting, is within the scope of the present invention.  
         [0028]    The pinion shaft  36   1  has opposite end sections  36   a  and  36   b  adapted to engage the differential case  22 , and a central section  36   c  adapted to rotatably support the pinion mate gear members  34 . The pinion shaft  36  further includes an opening  37  at one end section thereof (e.g. the end section  36   b , as shown in FIG. 3) receiving the locking pin  38  for securing the pinion shaft  36   1  to the differential case  22 .  
         [0029]    The second embodiment shown in FIG. 4 comprises a number of parts corresponding to those used in the first embodiment, and they will be referenced by the same reference numerals used in the first embodiment, sometimes without describing in details since similarities between the corresponding parts in those embodiments will be readily perceived by the reader.  
         [0030]    In accordance with the second embodiment of the present invention, a pinion shaft  36   2  has essentially H-shaped cross-section across the entire length thereof. The end sections  36   a  and  36   b  have a substantially uniform size across the entire length thereof. The central section  36   c  includes a pair of opposite gear bearing segments  36   c ′ of a substantially uniform size interconnected by substantially tapered segments  36   c ″ having a varied size. Preferably, the pinion shaft  36   2  is made by a metal forging. However, any other appropriate method for making the pinion shaft  36   2 , such as casting or machining, is within the scope of the present invention.  
         [0031]    The third embodiment of the present invention shown in FIG. 5 comprises a number of parts corresponding to those used in the first and second embodiments, and they will be referenced by the same reference numerals, sometimes without describing in details since similarities between the corresponding parts in those embodiments will be readily perceived by the reader.  
         [0032]    In accordance with the third embodiment of the present invention, a pinion shaft  36   3  has opposite end sections  36   a  and  36   b  adapted to engage the differential case  22 , and a central section  36   c  rotatably supporting the pinion mate gear members  34 , wherein the end sections  36   a  and  36   b  are substantially cylindrical, while the central section  36   c  has substantially H-shaped cross-section having a substantially uniform size across an entire length thereof.  
         [0033]    The forth embodiment of the present invention shown in FIG. 6 comprises a number of parts corresponding to those used in the previous embodiments, and they will be referenced by the same reference numerals, sometimes without describing in details since similarities between the corresponding parts in those embodiments will be readily perceived by the reader.  
         [0034]    In accordance with the forth embodiment of the present invention, a pinion shaft  36   4  has opposite end sections  36   a  and  36   b  adapted to engage the differential case  22 , and a central section  36   c  rotatably supporting the pinion mate gear members  34 , wherein the end sections  36   a  and  36   b  are substantially cylindrical, while the central section  36   c  has a substantially H-shaped cross-section having a substantially varied size in a lengthwise direction thereof. Moreover, the central section  36   c  includes a pair of opposite gear bearing segments  36   c ′ of a substantially uniform size across an entire length thereof, interconnected by a link segment including substantially tapered segments  36   c″.    
         [0035]    Therefore, the differential pinion shaft in accordance with the present invention represents an improvement over the prior art that substantially reduces weight of the differential pinion shaft (by as much as 35-40%), increases a strength-to-weight ratio by about 33%, and improves lubrication.  
         [0036]    The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.