Abstract:
A differential cover for a differential unit of a vehicle includes a central area, a flange area having a lower surface facing a mating direction for mating with a surface of a differential housing. The flange area has a plurality of apertures distributed along the flange area. The flange between centerlines of adjacent apertures defines a plurality of segments, each of which extending further in the mating direction than the lower surfaces of the segment at respective centerlines.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a cover for a differential unit of a vehicle, and more particularly, the present invention relates to a cover for a differential unit that is shaped to optimize sealing between the differential cover and the differential housing.  
         BACKGROUND OF THE INVENTION  
         [0002]    Presently, vehicles are equipped with a differential gearing unit positioned between the vehicle transmission and output axles to supply a driving force to the vehicle wheels. The differential unit, itself, contains gearing to adjust the torque and velocity relationship from that supplied from the transmission output shaft (and into the differential) and the resultant torque and rotational velocity supplied to the output axles. The differential further includes a differential housing and differential cover which assemble to protect the gearing from the external environment and to maintain lubricants within the housing. Accordingly, the sealing relationship between the differential cover and the housing is of critical importance to ensure that lubricants do not leak out and external contaminants, such as dirt, do not enter the working environment of the differential gearing. To effectuate this assembly, a plurality of bolts provide a clamping force to clamp a gasket between the cover and the housing. The bolts connect the cover and the housing and apply a pressing force on the gasket to maximize sealing. While this arrangement does provide sealing capabilities, some drawbacks exist. Specifically, the clamping force applied to the gasket in the immediate proximity of the bolts is greater than the clamping force provided along the cover at positions between the bolts. As such, these areas have a lower clamping force and lower contact sealing stress/pressure distribution, and are therefore more susceptible to leakage than that of areas proximate the bolts. The present invention was developed in light of these and other drawbacks.  
         SUMMARY OF THE INVENTION  
         [0003]    To address these and other drawbacks, a differential cover for a differential unit of a vehicle includes a central area, a flange area having a lower surface facing a mating direction for mating with a surface of a differential housing. The flange area has a plurality of apertures distributed along the flange area. The flange between centerlines of adjacent apertures defines a plurality of segments, each of which extends further in the mating direction than the lower surfaces of the segment at respective centerlines.  
           [0004]    In another aspect, a differential unit for a vehicle includes a housing, a differential cover having a flange, and a gasket positioned between the flange and the housing to seal an interior of the housing from an external environment. The differential cover is attached to the housing by a plurality of bolts which pass through the flange and clamp the differential cover to the gasket to apply a clamping force to the gasket. The flange is elastically deformed at areas between the bolts to provide a clamping force to the gasket. As a result, a combined force on the gasket caused by the elastically deformed areas and the bolts provide a substantially equal clamping force which translates to substantially equal contact sealing pressure distribution on the gasket.  
           [0005]    Further areas of applicability of the present invention will become apparent from the entailed 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  
       [0006]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0007]    [0007]FIG. 1 is a perspective view of a differential unit including a differential housing and cover according to the present invention;  
         [0008]    [0008]FIG. 2 is a schematic view of the bolt layout of a differential cover according to the present invention;  
         [0009]    [0009]FIG. 3 is an exploded perspective view of a differential cover and housing assembly according to the present invention;  
         [0010]    [0010]FIG. 4 is a graphical view of a profile of a segment of a differential cover according to a preferred embodiment of the present invention;  
         [0011]    [0011]FIG. 5 is a chart showing the dimensions of the segment of the differential cover for the graph provided in FIG. 4;  
         [0012]    [0012]FIG. 6 is a cross sectional view along VI-VI of FIG. 2; and  
         [0013]    [0013]FIG. 7 is a graphical view showing and assembly and force/contact sealing pressure distribution on a differential cover according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    Referring now to FIG. 1, differential unit  10  is shown having output axles  12  extending laterally outward therefrom and input shaft  14  that supplies rotational energy from a vehicle transmission (not shown) into differential unit  10 . Differential unit  10 , itself, has a housing  16 , differential cover  18 , and a gasket  20  positioned there between. Cover  18  has a central area  32  and a flange area  24  at an outer periphery of central area  32  that provides a sealing surface to support gasket  20  against housing  16 . Flange area  24  has bolt holes or apertures  34  (see FIG. 3) to allow bolts  22  to pass therethrough to attach to housing  16  and press gasket  20  there between to seal the interior of differential unit  10  from the external environment. Flange  24  also has a lower surface  24 B and an upper surface  24 A.  
         [0015]    Referring to FIG. 3, the assembly of differential cover  18  to housing  16  is shown in greater detail. Here, bolts  22  pass through flange  24  to thread to housing  16  and press gasket  20  between housing  16  and flange  24 . As the abutment of the head of bolts  22  against flange  24  is what provides the clamping force, the maximum amount of clamping force supplied by the bolts  22  is in proximity to the location of bolts  22  along flange  24 . Therefore, it can be seen that the area along flange  24  between bolts  22  exerts a lower clamping force on gasket  20  than does the area immediately proximate the location of bolts  22 . Accordingly, as shown in FIG. 3, the present invention provides a continuous arc between bolts  22  to increase the clamping force at locations distal from bolts  22 .  
         [0016]    Referring to FIGS. 2, 4,  5  and  6 , a preferred embodiment of the present invention is shown and described. In FIG. 2, the dimensions of an example differential cover  18  are shown. These dimensions are described by the following:  
         [0017]    M=223.52 in  
         [0018]    N=209.30  
         [0019]    O=148.59  
         [0020]    P=74.93  
         [0021]    Q=14.22  
         [0022]    R=116.33  
         [0023]    S=116.33  
         [0024]    T=73.02  
         [0025]    U=73.02  
         [0026]    However, the present invention may also be used on other differential cover designs having different dimensions than that shown in FIG. 2, and the present invention is not limited to the specific arrangement shown and described herein. FIG. 6 shows a coordinate system applied to the unfastened flange  24 . Specifically, FIG. 6 describes an X dimension starting from a lower surface  24 A at the center line of an aperture  34  for each bolt  22  and extending along flange  24  until reaching a centerline of an adjacent aperture. This dimension from centerlines along the X axis is hereinafter defined as a segment, such as segment  30 . Likewise, Y defines an axis perpendicular to the X axis that passes through the centerline of each aperture  34 . Accordingly, FIG. 4 and FIG. 5 show the X and Y dimensions of the bottom surface of the flange according to the example of the preferred embodiment. Here, as seen in FIG. 5, the Y dimension of flange  24  remains zero until the edge of the bolt  22  is reached (about 0.55 mm). Thereafter, flange  24  begins to extend along a continuous curve, as described in FIGS. 4 and 5, until reaching a maximum at the midpoint between the centerlines of bolts  22 . Thereafter, the continuous curve extends back toward the X axis until reaching the outer periphery of the adjacent bolt. This continuous curve forms an inverse arc that provides extra clamping force at positions between the bolts  22  (as will be further described herein).  
         [0027]    The operation and assembly of the present invention is now described with reference to FIG. 7. σ B  and F B  is the contact sealing stress and the clamping force provided by the bolts  22  acting to clamp gasket between flange  24  and housing respectively. σ E  and F E  is the contact sealing stress and the spring force against the gasket  20  and housing  16  exerted from the cover between bolts  22 . And, σ E+B  and F E+B  is the combination of those two respectively.  
         [0028]    At the top of FIG. 7, the flange, gasket, and housing  16  are shown in a clamped and fastened relationship with bolts  22 . In this condition, two different forces act to clamp gasket  20  between flange  24  and housing  16 . Specifically, F b  is the clamping force provided by the bolts  22 . As shown, F b  remains constant until the edge of bolt  22  is reached. Thereafter, F b  drops in a curved relationship until reaching a midpoint between the bolts  22 , and then begins to curvingly increase until reaching the edge of the adjacent bolt  22 . However, when assembled, the previously described bowed area, bowed in a direction toward mating with the housing  16 , is now flat. Due to the elastic properties of the metal from which the flange and cover are constructed, the now flat flange area  24  exerts a spring force against the gasket  20  and housing  16 . This force is shown as F e  in FIG. 7. As such, the elastic force due this curved geometry of the flange  24  begins at a minimum force under bolt  22 . Thereafter, the elastic force curvingly increases until reaching the midpoint between the bolts, since the maximum curvature of flange  24  exists at this midpoint. As this force changes in an opposite fashion with respect to that exerted by F b , the combined force F b  and F e  add together to result in an equivalent and even force between bolts  22  as shown in FIG. 7.  
         [0029]    When reviewing FIG. 7, it can be generally understood that to achieve the best combined force F e  plus F b , a flange surface having a curved arc shape is most suitable. However, it is noted that any shape in which flange  24  is shaped more toward a direction of mating between bolts helps equalize the resulting force F e  plus F b , and provides uniform contact sealing stress distribution.  
         [0030]    The assembly of the differential cover  18  to the housing  16  can generally be understood from reviewing FIGS. 3 and 7 (top). First, the cover  18 , gasket  20  and housing  16  is arranged as shown in FIG. 3. Then, bolts  22  are positioned through apertures  34 , through gasket  20  and threaded into cover  16  to thereby clamp the arrangement and flatten flange  24  as shown in FIG. 7.  
         [0031]    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.