Abstract:
A differential assembly includes a housing defining a space containing a volume of hydraulic fluid, the housing including interior surfaces. A gear that rotates in the housing includes surfaces that pass through the fluid as the gear rotates and on which the fluid is carried to the interior surfaces of the housing. A bearing located in the housing is supplied with fluid from a fluid path that hydraulically connects the interior surfaces and the bearing.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to lubrication in a differential mechanism for a motor vehicle. More particularly, the present invention relates generally to a system for directing lubricant from the interior wall of a cover for an axle differential to bearings and a seal located either adjacent to the bearing or at the wheel end. 
     Providing reliable flow of lubrication to the bearings of a differential mechanism, wheel bearings and seals has many challenges. Vehicle incline, cover and carrier geometry and variable speeds are parameters that must be taken into account. In general, lubricating the position behind the ring gear mounting face is a matter of fluid flow management. Differential case ribs, ring gear bolts and the proximity of the carrier wall move a significant amount of lubricant along the side and toward the pinion bearings and this differential position. In most cases, adjusting the entry and exit ports to capture and maintain adequate lubricant is all that is required. 
     It is more difficult, however, to provide lubrication to the bearing located on the carrier farthest away from the ring gear. Cover geometry, differential case openings and the distance of that bearing from the gear teeth all impede lubricant flow from reaching that bearing. This condition is further aggravated at low speed, when the flow rate of lubricant being directed to the vicinity of the bearing is reduced. 
     SUMMARY OF THE INVENTION 
     The invention compensates for these difficulties by defining a specific, lubricant path to the bearing farthest from the ring gear. The differential housing or cover includes a channel with an opening adjacent the ring gear teeth. Lubricant pulled from a sump to the interior surface of the housing wall by the pumping action of the ring gear migrates into this channel, which has a negative angle with respect to a horizontal plane both from ring gear to the cover edge and from the outside wall of the channel toward the inside wall. Gravity delivers the lubricant along the channel to a pickup point on the carrier mating face. The carrier has a passage connecting the cover face to the bearing bore. Lubricant delivered through the channel flows into the bearing bore, from which it flows to the bearings and seals. 
     A differential assembly, according to this invention, includes a housing defining a space containing a volume of hydraulic fluid such as lubricant, the housing including interior surfaces. A gear that rotates in the housing includes surfaces that pass through the fluid as the gear rotates and on which the fluid is carried to the interior surfaces of the housing. A bearing located in the housing is supplied with fluid from a fluid path that hydraulically connects the interior surfaces and the bearing. 
     The bearing is continually supplied with lubricant while the ring gear is rotating. The fluid flow path provides a reliable supply of lubricant to the bearing without the need for a pump or an external power source, and without adding complexity to the cast cover. A minimum number of simple fabrication operations are required to form the radial passage and to install a shield plate. The ribs and channel can be cast integrally with the cover. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       These and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a perspective view of a differential assembly with its components shown mutually spaced in their approximate relative positions; 
         FIG. 2  is an internal view of a cover for the differential assembly of  FIG. 1  to which the lubrication system of this invention can be applied; 
         FIG. 3  is a an internal view of the cover of  FIG. 2  with a rib connected to the cover by attachments; 
         FIG. 4  is a an internal view of the cover of  FIG. 2  with an optional deflector plate installed; 
         FIG. 5  is a perspective view of a vent shield; 
         FIG. 6  is a partial cross sectional perspective view through a quadrant of the housing looking downward toward the right-side bearing showing the rib and shelf of the shield plate; and 
         FIG. 7  is a partial cross section at a lateral side of the housing looking toward the right-side bearing and showing a lubricant passage directed from the channel toward the bearing. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1 , a differential mechanism  10  for transmitting power differentially to left-side and right-side axle shafts includes a housing  12  and cover  14 , preferably of cast aluminum or iron; a ring gear  16  formed with beveled gear teeth  18 ; a carrier  20  secured to the ring gear; bevel pinions  22 ,  24  driveably connected to the carrier by pin  26 ; a right-side bevel gear  28 ; and a left-side bevel gear  28  (hidden from view by the ring gear) in continuous meshing engagement with the bevel pinions. The teeth  18  of ring gear  16  are in mesh with a bevel pinion  30 , which extends through an opening  32  to the differential assembly  10 . Bevel pinion  30  is connected to a companion flange (not shown), which in turn is connected to a driveshaft (not shown), which transfers output torque from a transfer case or a transmission to the differential assembly  10 . 
     The side bevel gears  28  are driveably connected, respectively, to a right-side shaft and left-side shaft (not shown), each shaft being drivable connected to a wheel of the vehicle. The right-side shaft is supported by carrier  20  and an additional bearing (not shown) which may be located in housing  12  or in a remote location at the opposite end of axle tube  36  that extends rightward from the differential housing  12  to the right-side wheel. The carrier  20  is supported in housing  12  at a bearing  34  located in a bore on a local boss  35 . Bearing  34  is secured to the housing  12  by a bracket  38  and bolts  39 ,  40 . Similarly, the left-side shaft is supported by carrier  20  and an additional bearing (not shown) which may be located in housing  12  or at the opposite end of axle tube  48  that extends leftward from the differential housing  12  to the left-side wheel. The carrier  20  is supported on the housing  12  by bearing  42  located in a bore  44  formed in a local boss  46 . Bearing  42  is secured to the housing  12  by a bracket  50  and bolts  52 ,  53 . 
     The cover  14  is secured to the housing  12  by bolts  54 , which extend through a mounting flange  56  and engage tapped holes formed in the housing. A hollow vent tube  58  passes through the wall of the cover. 
     The inner surface of the cover  14  is formed with a depression  60 , which is set back from the adjacent interior surface  62  and sized to accommodate the ring gear. The inner surfaces of the housing  12  and cover  14  together define a fluid sump containing a volume of lubricant located at the bottom of the interior space bounded by the housing and cover. The ring gear  16  rotates through the hydraulic lubricant in the sump wetting the surfaces of the gear teeth formed on the ring gear. 
     Referring now to  FIG. 2 , the inner surface of the cover  14  is preferably formed with two lateral ribs  64 ,  66  and a vertical rib  68  extending from the upper lateral rib, each rib extending inward from the interior surface of the cover. The ribs are preferably cast with the cover  14 . Any of the ribs may be secured to the cover using attachments, as described with reference to  FIG. 3 . The upper lateral rib  64  and lower rib  66  each conform to the inner contour of the cover and intersect side wall  70  of the ring gear depression  60 . The lower rib  66  is inclined from its inner end  72  downward toward a channel  74  located at its opposite end, and it is inclined downward from the inner surface of the cover toward the inner free edge  76 . Preferably these inclinations or slopes of the upper surface of rib  66  are with reference to a horizontal plane. As the ring gear  16  rotates in the differential housing, lubricant carried on the surface of the gear is thrown radially outward from the gear against the inner surface of the cover into the space between the ribs  64 ,  66 . The pitch of the lower rib  66  directs lubricant toward channel  74 , which is cast into the cover  14 . 
       FIG. 3  illustrates an alternative lower rib  77  that is secured to the housing  14  by a series of attachment screws, bolts, or rivets  78 . The lower rib  77  maybe bonded chemically to the interior surface of the cover  14 . The upper surface  80  is inclined as described with reference to  FIG. 2 . 
       FIGS. 4 and 5  illustrate a vent shield  82 , which is supported on the lateral ribs  64 ,  66  and secured to the cover  14  by a fastener  84  that engages a local boss at the upper rib  64 . The shield  82  includes a projection  86 , which covers the space bounded by rib  64 , vertical rib  68  and the wall of the cover, thereby covering the inner end of vent tube  58  against entry of lubricant from without this space. The shield  82  includes a panel  88  that contacts the ribs  64 ,  66  and extends laterally along the ribs toward channel  74 . The lower edge of the shield  82  is formed with a flange  90 , which lies under the inner free edge  76  of rib  66  and extends outward from the free edge, thereby providing a shelf  92 , which carries lubricant from rib  66  to channel  74 . 
     Flange  90  is inclined laterally toward the channel  74  and downward toward bearing  34 . Flange  90  is also inclined downward and away from the free edge  76 . Preferably these inclinations or slopes of flange  90  are with reference to a horizontal plane. 
     The shelf  92 , which is seen best in  FIGS. 6 and 7 , carries lubricant flowing from rib  66  laterally to channel  74 , which is directed downward to the bore  37  formed in the right-side wall of housing  12 . A seal  100 , fitted in an opening  102  formed in boss  35 , seals the right-side bore  35  against entry of containments and passage of fluid from the housing. Alternately, seal  100  may be located at the end of axle tube  36  that extends rightward from the differential housing  12  to the right-side wheel. A similar seal, fitted in an opening formed in boss  44 , seals the left-side bore at the laterally opposite housing wall. Alternately, a similar seal may be fit at the end of axle tube  48  that extends leftward from the differential housing  12  to the left-side wheel. The lower end of channel  74  communicated with a radial passage  104  formed in the wall of housing  12 . Lubricant exiting the inner radial end of passage  104  flows axially inward along bore  37  toward bearing  34  and axially outward along bore  37  toward seal  100 , which prevents flow from the housing. Ultimately, lubricant flows through bearing  34  and returns to the sump at the base of the housing where it is carried upward on the surfaces of the ring gear as it rotates through the sump, thereby continuing the flow cycle through the differential. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.