Abstract:
A drive axle housing system may minimize churning of splash and spray oil within a drive axle housing. The drive axle housing system includes apparatus for incorporation into the axle, the apparatus including an oil churning reduction member that may be affixed to the interior walls of the axle housing. The oil churning reduction member includes interior surfaces adapted to closely align with interior moving gear components of the axle to minimize efficiency losses due to oil movement. The system may also incorporate an annular element, affixed to the axle housing and closely aligned with the backside of a ring gear component of the differential axle. The combined use of the member and the element may substantially reduce torque losses attributable to excessive churning of oil.

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to lubrication of geared final drive axles and, more particularly, to apparatus for reducing efficiency losses associated with gear-induced churning of splash and spray oil. 
     BACKGROUND 
     Drive axles are commonly used in motorized platforms of all types, including trucks, buses, and automobiles, as well as off-road machines utilized in construction, mining, and agricultural fields. Typically, drive axles employ beveled differential gear structures for splitting driveline torque between dual opposed final drive half shafts. Such splitting avoids undue stresses on drivetrain components, and avoids excessive skidding and wear of powered driving tires as a vehicle turns about a radius. 
     Drive axle systems are traditionally lubricated by so-called “splash and spray” oil; that is, oil contained within a nonrotating reservoir is picked up and sprayed about the interior of the housing by at least one rotating gear structure that interfaces with the reservoir. Of course, the lubrication is required to achieve satisfactory operation of the drive axles and to avoid premature failures of associated operating components due to oil starvation, as will be appreciated by those skilled in the art. 
     Although beneficial to meet requisite lubrication demands, one deleterious side effect of splash and spray oil is a loss of torque resulting from efficiency losses created by churning of the oil. Various structures and methods have been utilized to reduce the churning beyond amounts determined necessary to assure effective lubrication. Typical apparatus and techniques have involved uses of interior ducting, shrouds, and baffles to channel and/or redirect the oil to specific regions within the housing to reduce efficiency losses. Others have involved use of inserts strategically positioned to physically displace excess oil within the lubricant reservoir. Although some of these approaches have had modest successes, none have substantially reduced churning losses. To the extent that such losses translate directly into operational expense, i.e. fuel costs, significant motivation remains to further reduce churning losses. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with a first aspect of the disclosure, an oil churning reduction member may be employed to geometrically reshape the interior of a typical axle housing into one that optimally reduces oil churning. The interior configuration of the member may be shaped and sized to closely control spacing between interior surfaces of the member and various gear components rotating inside the housing. The member, circumferentially fixed in place about the interior wall of the housing, can thereby be designed to minimize churning losses within the differential housing environment. 
     In accordance with a second aspect of the disclosure, a separate non-rotatable annular element may be positioned in close proximity to the non-meshing or backside of the ring gear. The element may be effective to further reduce churning losses in and about the immediate vicinity of the rotating ring gear. 
     A third aspect of the disclosure may be the combined effectiveness of the oil churning reduction member and the annular ring element to reduce typical churning losses by up to 50%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top cross-sectional view of a drive axle housing system incorporating features constructed in accordance with the teachings of this disclosure; 
         FIG. 2  is a cross-sectional rear elevation view of the drive axle housing system of  FIG. 1 , as viewed along lines  2 - 2  thereof; 
         FIG. 3  is a perspective view of a first embodiment of an oil churning reduction member incorporating features constructed in accordance with the teachings of this disclosure; 
         FIG. 4  is a perspective view of the embodiment of  FIG. 3 , albeit with reversed orientation to depict opposite sides thereof; 
         FIG. 5  is a front cross-sectional view of the drive axle housing system, taken along lines  5 - 5  of  FIG. 1 ; 
         FIG. 6  is a perspective view of an embodiment of an annular element incorporating features constructed in accordance with the teaching of this disclosure; and 
         FIG. 7  is a view of an alternative embodiment of the disclosed drive axle housing system, shown in a cross-sectional view analogous to that of  FIG. 2 , incorporating features constructed in accordance with the teachings of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of the disclosure is depicted in  FIGS. 1 through 6 . Referring initially to  FIGS. 1 and 2 , a final drive axle  10 , also variously referred to as a differential axle system, is shown in top and rear cross-sectional cutaway views, respectively. The drive axle  10  includes a housing  12  containing a beveled drive pinion gear  14  that rotates a differential carrier  16  via a pinion-driven beveled ring gear  20  affixed to the carrier  16 . The carrier  16  incorporates a differential gear set  18  that includes a pair of left and right side gears  24  and  26 , respectively, which engage a pair of spider gears  28  and  30  splined to a spider shaft  32 , as shown. 
     Those skilled in the art will appreciate that the pinion gear  14  extends from a pinion gear shaft  34 , and effectively engages the differential carrier  16  via the ring gear  20  to split torque between side gears  24  and  26 . Since the side gears, which extend along axis a 1 -a 2  as shown, are respectively splined to left and right half shafts  36  and  38  to which powered vehicular driving wheels (not shown) may be affixed, it will be appreciated that the described structure assures that torque from an engine or prime mover (neither shown) is split between at least a pair of driving wheels, in a typical differentially geared manner. 
     Also incorporated within the axle drive  10  is a wet disc brake assembly  40 , defined by a set of interleaved discs  42  and  44 . The brake assembly  40  circumferentially surrounds the right half axle  38 . Discs  42  are axially splined to a fixed outer brake sleeve  44 . Discs  48  are rotatable relative to discs  42 , as the latter are splined to an inner brake hub  46  adapted to rotate within the sleeve  44 . 
     The foregoing structure details the environment in which disclosed drive axle housing system  49  may be designed and adapted to operate. For example, such a drive axle housing system may be advantageously utilized as part of a transmission or differential axle forming part of a work machine, including but not limited to a truck, track-type tractor, road grader, pipe layer, roller, forestry machine, or other industrial vehicle used in construction, mining, or agriculture. 
     As earlier noted,  FIGS. 3 and 4  display a first embodiment of an oil churning reduction member  50  in reversely oriented views. Thus, it will be noted that the orientations of axis a 1 -a 2 , along which extend side gears  24 ,  26  and half shafts  36 ,  38 , are physically reversed in the respective views to reveal two distinct perspectives of the member  50 . Having a box-shaped exterior that may be readily fixed to and encased within a correspondingly sized and shaped interior of the differential housing  12 , the member  50  includes interior arcuate surfaces that may be proportioned and adapted to closely surround various differential gear components at specific spacial dimensions. The arcuate surfaces within the reduction member  50  may work together to effectively reduce churning of oil produced by rotation of the ring gear  20  through the volume of splash and spray lubricating oil  54  contained within one of two oil reservoirs  52  and  53  of the member  50 . 
     Referring momentarily back to  FIG. 2 , the bottom of the member  50  contains a pair of oil reservoirs, a catch basin reservoir  52  and a so-called “dynamically optimized” reservoir  53 , the latter adapted to contain a relatively limited oil volume in comparison to a typical ring gear-side reservoir. The limited or reduced oil volume acts to reduce the amount of churning that would otherwise be created by the ring gear  20 . 
     The catch basin reservoir  52  collects splash and spray oil upon its gravity-fed return to the reservoir  52 , after the oil has been distributed to the various moving internal components contained within the housing  12 . A medially positioned reservoir separator  51  may protrude upwardly from respective floors of the two reservoirs  52  and  53 , and may act as a dam between the two reservoirs. The level of oil in the catch basin reservoir  52  will generally be higher than the desirably lower level of oil contained in the dynamically optimized reservoir  53 . 
     Within the described environment, the separator  51  may be effective to assure that the amount of splash and spray oil being picked up by the ring gear  20  from the reservoir  53  can be “optimized” to be sufficient but not excessive. The member  50  may also be designed to closely surround the differential carrier  16 , as best shown in  FIG. 2 , where gap D is displayed as the radial distance between the medial portion  51  and the differential carrier  16 . 
     Referring now to  FIG. 5 , a pinion ramp  60  may be proximally positioned, by a distance specifically displayed as gap C, with respect to the beveled pinion gear  14 . The ramp  60  may be angled or sloped downwardly as shown to facilitate the return of splash and spray drive axle housing oil to the catch basin reservoir  52 . The element  50  may also incorporate a pinion gear access opening  62 , as well as access openings  64  and  66 , through which may extend right and left half shafts  38  and  36 , respectively.  FIGS. 2 and 5  reveal a left side disposed radially inner top wall portion  68  of element  50  which may be spaced relatively close to the ring gear  20  as compared to the right side disposed radially outer top wall portion  70  of element  50 . The portion  70  is spaced a relatively much greater distance from the differential carrier  16 . 
     Referring now to  FIG. 6 , an annular element  56  having a flanged portion  58  may be secured as by bolts  72  to the non-rotatable outer bearing cage  74  of the ring gear bearing  78 . The ring gear  20  is supported on, and rotates with, the inner rotatable bearing cage  76  of the ring gear bearing  78 . The annular element  56  may be non-rotatably fixed with respect to, and positioned in close proximity to, the backside  22  ( FIG. 2 ) of the rotatable ring gear  20 . The annular element  56  may be spaced from the backside  22  by a gap or distance A. The distance A ( FIG. 2 ) of approximately 5.0 to 7.0 millimeters (mm), a variable distance as measured between flanged and unflanged portions, may be advantageous for reducing oil churning losses. Moreover, a distance B between the ring gear  20  and the radially outer top wall portion  70  ranges from 53 to 57 mm, a distance C between the pinion ramp  60  and the pinion gear  14  of about 2.5 mm, a distance D between the medial portion  51  of the member  50  and the differential carrier  16  ranging between 3 to 12 mm, a distance E between the floor of the dynamically optimized reservoir  53  and the ring gear  20  of approximately 5 to 12 mm, and an axial distance F between the ring gear  20  and an adjacent vertical wall  55  of the medial portion  51 , ranging between 3 and 9 mm, all contribute to the reduction of churning losses. 
     With respect to a frame of reference for the foregoing listed dimensions between the variously described components, the dimensions may be primarily a function of the oil viscosity and the ring gear rotating speeds, as opposed to the relative component sizes or dimensions of the axle housing per se. Thus, the stated dimensions may, in the described embodiment, be generally associated with transmission and gearbox oil viscosity grades ranging between 20 and 50 SAE, and for ring gear speeds ranging up to 4000 RPM. 
     Those skilled in the art will appreciate that the structure of the described drive axle housing system  49  may be comprised primarily of the member  50  and the element  56 . In combination, the member  50  and element  56  may be effective to reduce axle churning losses by 30 to 50%, thus providing significant potential improvement over existing channeling, shrouding, and baffles designed to redirect splash and spray oil flows within existing drive axle systems. 
     More specifically, the element  50  and its spacing relationships with respect to the internal components of the differential gear axle may be effective to achieve 70% of the overall reduction in friction losses associated with churning. On the other hand, the annular element  56 , nonrotatably fixed to the housing, and situated a relatively small spatial distance of distance A from the backside  22  of the ring gear  20 , maybe effective to achieve the remaining approximately 30% of the total 30 to 50% churning loss reduction. 
     In creating the drive axle housing system  49 , a summation parametric, herein referred to as a Weber summation, Σ W , may be employed to achieve the noted churning reduction levels described herein and heretofore unknown. More specifically, the Weber summation may hereby be defined as:
 
Σ w   A+B+C+D+E+F,  where:
         A is the described spacing or distance between the above identified backside  22  of the ring gear  20  and the annular element  56 ;   B is the described distance between the ring gear  20  and the radially outer top wall portion  70 ;   C is the described distance between the pinion ramp  60  and the pinion gear  14 ;   D is the described distance between the medial portion  51  of the member  50  and the differential carrier  16 ;   E is the described distance between the floor  53  of the reservoir  52  and the ring gear  20 ; and   F is the described axial distance between the ring gear  20  and the medial reservoir separator portion  51 ,  51 ′.       

     In accordance with the above-described calculation, if a drive axle housing system  49  is manufactured having a described Weber summation value of between 71 and 100 millimeters, a reduction of up to 50% in churning losses may be achieved. 
     This first described embodiment defines the member  50  as being formed separately of an axle housing  12 , and installed as a separate component about the interior thereof. By way of example only, the member  50  may be formed as a stamped metallic insert, or of an injection molded plastic such as a polymer plastic adapted for accommodating thermal cycling and adequate to survive the corrosive effects of lubricating oil. Alternatively, the member  50  may be integrally formed with, i.e. die cast as part of, the housing  12 , so as to incorporate the desired internal configurations of the disclosed separate member  50 . In case of the latter, the exterior of the housing could be substantially of the same shape as the interior so as to avoid any unnecessary weight. 
     Those skilled in the art will appreciate that splash and spray oil generated within the member  50  is also designed to lubricate right and left half shafts  64  and  66 , as well as the pinion gear  14  and its associated shaft  34 . 
     A second embodiment of an oil churning reduction member  50 ′ is shown in  FIG. 7 . A difference between the second embodiment  50 ′ and the first embodiment  50 , as best shown in  FIG. 2 , is the use of a thin walled baffle  51 ′ instead of the wider dam-style medial reservoir separator  51 . All other aspects of the two embodiments remain unchanged. The second embodiment  51 ′ displays a gap D′ in  FIG. 7  that is analogous to gap D as shown in  FIG. 2 . Moreover, the gap F′ of  FIG. 7  is analogous to the gap F of  FIG. 2 . The performance parameters of the respective medial reservoir separator members  51  and  51 ′ have been determined to be equivalent. The use of one over the other may be determined from criteria relating to ease of manufacturing; thus by way of example, a cast structure may lend itself more readily to use of a dam-style separator member over the baffles-style separator member for reasons of structural rigidity, among others. 
     INDUSTRIAL APPLICABILITY 
     In general, technology disclosed herein has industrial applicability in a variety of settings such as, but not limited to, improving operating efficiencies of differential axles by minimizing torque losses associated with churning of splash and spray oil. Its industrial applicability extends to virtually all motorized transport platforms, including automobiles, buses, trucks, tractors, industrial work machines and most off-road machines utilized in agriculture, mining, and construction. 
     The disclosed drive axle housing system may offer improved control of the splash and spray oil necessary for lubrication of various moving parts within the axle housing, including the ring and pinion gears. Among other attributes, the system of the present disclosure may find applicability in reducing unnecessary amounts of oil in the proximity of the rotating ring and pinion gears, resulting in reduction in churning loss, and thus promoting enhanced operational efficiency including lower fuel requirements. 
     The features disclosed herein may be particularly beneficial to wheel loaders and other earth moving, construction, mining or material handling vehicles that utilize gear sets adapted for splash and spray oil lubrication within axle housings.