Abstract:
A modular unitized differential for drive axles of motor vehicles includes a barrel-shaped differential case and a bowl-shaped ring gear. The ring gear is adapted to be selectively positioned relative to the differential case for fastening in a specific position in accordance with the needed gear spacing. The arrangement allows to accommodate different gear ratios between the ring gear and input gear.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to differential transmission mechanisms, particularly a differential utilized in an automotive axle drive. 
     2. Description of the Prior Art 
     A differential gear in a final drive axle of a motor vehicle transmits a rotational input from an engine to two axle shafts. A differential case is rotatably supported on an axle housing. Typically, a differential case comprises two halves: a plain differential case half and a flanged differential case half, usually bolted to each other. The flanged differential case half is provided with a flange that receives a ring gear attached to the flange by a number of bolts. In order to provide the adequate stiffness of the differential gear, the flanged differential case half is conventionally provided with a plurality of stiffening ribs. 
     The ring gear is engaged with a pinion gear of a final drive. In such a case, to account for assembly tolerances, shim packs may be disposed between the ring gear and the flange of the differential case to properly align the ring gear with the pinion gear. Such prior art assemblies are costly and cumbersome. 
     Furthermore, presently, each model of automobile (both cars and trucks) may have variants having different final drive gear ratios for various specific applications. The different final drive gear ratios require different gear teeth combinations, thus automobile manufacturers need to provide differentials with different gear spacings (or offsets). For instance, heavy duty truck drive axle differential manufacturers have to use up to four different flanged differential case halves to cover the offsets of all gear ratios employed. 
     SUMMARY OF THE INVENTION 
     The present invention alleviates the drawbacks of the prior art. The present invention provides selective axial positioning of the ring gear relative to the differential case for welding in a specific position to accommodate different gear ratios between the ring gear and an input gear. The present invention also eliminates bolts or other complicated fastening devices to secure the ring gear to the differential case. Manufacture and assembly tolerances may also be accounted for. 
     The modular unitized differential in accordance with the present invention comprises a flanged differential case and a bowl-shaped ring gear having a concave flange portion. The concave flange portion of the ring gear greatly improves the stiffness and impact resistance of the differential, thus eliminating the need for the stiffening ribs. During the manufacturing of the differential, the ring gear is mounted on the differential case, selectively positioned in a specific axial position by sliding the ring gear relative to the differential case, and welded in place. This arrangement enables to accommodate different gear ratios between the ring gear and input gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a cross-sectional view of the differential case and the ring gear assembly in accordance with the present invention; 
     FIG. 2 is a perspective view of the ring gear. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 of the drawings depicts a modular unitized differential in accordance with the present invention. The differential comprises a differential case  1  rotatably supported on an axle housing (not shown) and a ring gear  10  driven by a pinion gear (not shown) attached to a power driven propeller shaft (not shown). The differential case  1  is generally barrel shaped and includes a differential case body  2  and an external annular flange  5  extending radially outwardly from the differential case body  2 . The differential case body  2  is provided with at least one external boss  6  coaxial with an axis of rotation of the differential case  1 . Conventional side gears and differential pinion gears, not shown, are mounted within the differential case body  2 . 
     In the preferred embodiment, the differential case body  2  includes two halves; a plain differential case half  3  and a flanged differential case half  4 , usually bolted together. The flange differential case half  4  is provided with an external annular flange  5  extending radially outwardly from the flanged differential case half  4 , and the external boss  6  coaxial with an axis of rotation of the differential case  1 . 
     The ring gear  10  comprises an annular toothed portion  11  and a concave flange portion  15 . The annular toothed portion  11  has a circular set of gear teeth  12  formed along its outer periphery, and an internal peripheral surface  13 . The internal peripheral surface  13  of the annular toothed portion  11  is adapted to receive and rest upon the external annular flange  5 . For this reason, an internal diameter of the internal peripheral surface  13  of the annular toothed portion  11  is substantially equal to an external diameter of an external peripheral surface  7  of the annular flange  5 . The concave flange portion  15  of the ring gear  10  extends radially inwardly from the annular toothed portion  11 , and is substantially concave or bowl-like in shape. In the preferred embodiment, the concave flange portion  15  is formed integrally with the annular toothed portion  11 . The concave flange portion  15  greatly increases the stiffness of the differential assembly and provides support more effectively than the conventionally employed stiffening ribs, thus eliminating need for the stiffening ribs. The concave flange portion  15  is provided with an inner peripheral surface  16  defining a central aperture  17  therein. The central aperture  17  in the concave flange portion  15  is adapted to receive the external boss  6  formed on the flanged differential case half  4 , and, therefore, the inner peripheral surface  16  rests upon the external boss  6 . Preferably, an internal diameter of the central aperture  17  is substantially equal to an external diameter of the external boss  6 . 
     During the assembling of the differential gear in accordance with the present invention, the ring gear  10  is attached to the differential case  1  as follows. The ring gear  10  is positioned around the body  2  of the differential case  1  with the gear teeth  12  facing the external annular flange  5  of the differential case body  2 , and then advanced toward the flange  5 . As a result, the inner peripheral surface  13  of the toothed portion  11  of the ring gear  10  fits over external peripheral surface  7  of the external annular flange  5 , and the inner peripheral surface  16  of the concave flange portion  15  of the ring gear  10  fits over an external peripheral surface of the boss  6  of the differential case body  2 . As the next step, the ring gear is selectively positioned relative to the differential case body in accordance with the needed offset by axially sliding it over the case body  2 . Once the desired geometry is achieved, the ring gear  10  is welded to the differential case body  2 . 
     While in accordance with the provisions of the Patent Statutes the preferred embodiments of the present invention has been illustrated and described, it will be apparent to those of ordinary skill in the art that various changes, modifications or variations may be easily made without deviating from the scope of the invention.