Abstract:
A family of axle assemblies that employ a modular concept to maximize part commonality amongst the several axle assemblies. The axle assemblies have a housing assembly that employs a main housing that is formed from a casting that is common to all of the axle assemblies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/259,679 filed Nov. 25, 2015 and U.S. Provisional Application No. 62/313,212 filed Mar. 25, 2016. The disclosure of each of the above-referenced applications is incorporated by reference as if fully set forth in detail herein. 
     
    
     FIELD 
       [0002]    The present disclosure relates to improvements to an axle assembly of the type having an input pinion and a ring gear that are supported for rotation and axial thrust relative to an axle housing via a single bearing that is configured to handle both rotational and thrust loads. The improvements relate to the securing of the input pinion bearing to the axle housing, the provision of a modular axle assembly family having open differential, limited slip differential, locking differential and torque vectoring configurations, and the configuration of the axle housing and clutch in an axle configuration that has a locking differential. 
       BACKGROUND 
       [0003]    Commonly assigned U.S. Pat. Nos. 9,157,515 and 9,028,358 disclose novel axle assemblies that are an improvement over traditional Salisbury and banjo-style axle assemblies for passenger vehicles. While these configurations are relatively new in the art, they are nevertheless susceptible to improvement. 
       SUMMARY 
       [0004]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0005]    In one form, the present teachings provide an axle assembly that includes a housing, an input pinion, a pinion bearing, a retainer plate, a plurality of threaded fasteners, a differential assembly and a ring gear. The housing defines a pinion bearing bore. The pinion bearing is received in the pinion bearing bore and supports the input pinion relative to the housing for rotation about a first axis and for axial thrust in opposite directions along the first axis. The retainer plate is abutted against the single bearing on an end of the single bearing opposite the housing. The threaded fasteners are disposed about a bolt circle and secure the retainer plate to the housing. The threaded fasteners have a centerline and a major diameter. The differential assembly is mounted in the housing for rotation about a second axis that is not parallel to the first axis. The ring gear is meshingly engaged with the input pinion and is coupled to the differential assembly for rotation therewith about the second axis. The centerlines of a first quantity of the threaded fasteners are clustered into a segment. The segment spans less than 180 degrees of the bolt circle and extends radially outward from the first axis beyond the bolt circle by a distance that is less than or equal to five times the major diameter of the threaded fasteners. A second, smaller quantity of the threaded fasteners are not disposed within the segment. 
         [0006]    In another form, the present teachings provide an axle assembly that includes an axle housing assembly, an input pinion, a pinion bearing, a ring gear, a ring gear bearing, a differential assembly, a first spindle, a second spindle and a clutch. The axle housing assembly has a carrier housing and first and second end caps that are mounted to the carrier housing. The first end cap cooperates with the carrier housing to define a differential cavity, while the second end cap cooperates with the carrier housing to define a clutch cavity. The input pinion extends into the differential cavity. The pinion bearing supports the input pinion relative to the carrier housing for rotation about a first axis and for axial thrust in opposite directions along the first axis. The ring gear is disposed in the differential cavity and is meshingly engaged to the input pinion. The ring gear bearing supports the ring gear relative to the carrier housing for rotation about a second axis and for axial thrust in opposite directions along the second axis. The second axis is not parallel to the first axis. The differential assembly is received in the differential cavity and is configured to receive rotary power from the ring gear. The differential assembly has first and second differential outputs. The first spindle is drivingly coupled to the first differential output. The second spindle is drivingly coupled to the second differential output. The clutch is received in the clutch cavity and has a first clutch member and a second clutch member. The clutch is configured to selectively transmit rotary power between the first and second clutch members. The first clutch member is coupled for rotation with the first differential output, while the second clutch member is coupled for rotation with the second spindle. The clutch is a multi-plate friction clutch having a plurality of first clutch plates. The first clutch member has a first annular mount portion and a second annular mount portion that is disposed radially outwardly of the first annular mount portion. The first clutch plates are non-rotatably but axially slidably mounted on the second annular mount portion. The carrier housing defines an annular projection that extends axially into the first clutch member radially between the first annular mount portion and the second annular mount portion. 
         [0007]    In still another form, the present teachings provide an axle assembly that includes an axle housing assembly, an input pinion, a pinion bearing, a ring gear, a ring gear bearing, a differential assembly, a first spindle, a second spindle and a torque-vectoring mechanism. The axle housing assembly has a carrier housing and first and second end caps that are mounted to the carrier housing. The first end cap cooperates with the carrier housing to define a differential cavity, while the second end cap cooperates with the carrier housing to define a torque-vectoring cavity. The input pinion extends into the differential cavity. The pinion bearing supports the input pinion relative to the carrier housing for rotation about a first axis and for axial thrust in opposite directions along the first axis. The ring gear is disposed in the differential cavity and is meshingly engaged to the input pinion. The ring gear bearing supports the ring gear relative to the carrier housing for rotation about a second axis and for axial thrust in opposite directions along the second axis. The second axis is not parallel to the first axis. The differential assembly is received in the differential cavity and is configured to receive rotary power from the ring gear. The differential assembly has first and second differential outputs. The first spindle is drivingly coupled to the first differential output. The second spindle is drivingly coupled to the second differential output. The torque-vectoring mechanism is received in the torque-vectoring cavity and is configured to operate in a neutral mode, which does not affect the rotary power transmitted to the first and second spindles by the differential assembly, a first torque-vectoring mode, in which rotary power transmitted through the first spindle is reduced relative to the neutral mode, and a second torque-vectoring mode in which rotary power transmitted through second spindle is decreased relative to the neutral mode. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0010]      FIGS. 1 through 4  are section views taken through axle assemblies constructed in accordance with the teachings of the present disclosure; 
           [0011]      FIG. 5  is a perspective view of another exemplary axle assembly constructed in accordance with the teachings of the present disclosure; 
           [0012]      FIG. 6  is a front elevation view of a portion of the axle assembly of  FIG. 5 ; and 
           [0013]      FIG. 7  is a section view of a portion of another exemplary axle assembly constructed in accordance with the teachings of the present disclosure. 
       
    
    
       [0014]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0015]    With reference to  FIG. 1 , a first axle assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . The axle assembly  10  can include a housing assembly  12 , an input pinion  14 , a ring gear  16 , a differential assembly  18 , and first and second axle shafts  20  and  22 , respectively. 
         [0016]    The housing assembly  12  can include a main housing  30  and a first end cover  32 . The main housing  30  can be formed of a suitable material, such as cast iron, steel, aluminum or magnesium. In the example provided, the main housing  30  is formed of aluminum in a die casting process. The main housing  30  can have a wall member  34  that can define a pinion mount  36 , a ring gear mount  38 , a first axle shaft mount  40  and a first cover mount  42 . The pinion mount  36  can define a pinion aperture  46 , which is disposed along a first axis  48 , and one or more bearing mounts for receiving associated bearings that support the input pinion  14  relative to the main housing  30  for rotation about the first axis  48 . The ring gear mount  38  can be constructed as an annular hub  50  that is disposed about a second axis  52  and can define a shoulder  54  that can be disposed on a lateral side of the first axis  48  that is opposite the first axle shaft mount  40 . The first axle shaft mount  40  can comprise a bearing bore  58  that can be concentric with the annular hub  50 . The first cover mount  42  can define a cover bore  60 , which can be formed about the second axis  52  concentric with annular hub  50 , and a first cover flange  62  that can extend about the cover bore  60 . In the example provided, the cover bore  60  is stepped or counterbored so as to define a first bore portion  66 , a second bore portion  68  that can be relatively smaller in diameter than the first bore portion  66 , and a first shoulder  70  that can be disposed between the first and second bore portions  66  and  68 . 
         [0017]    The first end cover  32  can be configured to close the lateral side of the main housing  30  on which the cover bore  60  is disposed and can cooperate with the main housing  30  to form a differential cavity  74 . The first end cover  32  can be formed of any suitable material, such as cast iron, steel, aluminum or magnesium. The axle assembly  10  of the particular example provided is configured so that significant thrust loads are not transmitted to or through the first end cover  32  and as such, the first end cover  32  could be formed from a plastic material that may include a structural filler material, such as glass fibers. The first end cover  32  can comprise a wall member  80  that can define a second axle shaft mount  82  and a main housing mount  84 . The second axle shaft mount  82  can define a bearing bore  88  that can be concentric with the annular hub  50 . The main housing mount  84  can be configured to cooperate with the first cover mount  42  to align the axis of the bearing bore  88  so as to be coincident with the second axis  52  and to facilitate the coupling of the first end cover  32  to the main housing  30 . In the example provided, the main housing mount  84  comprises a mounting projection  90  and a second cover flange  92 . The mounting projection  90  can extend from the second cover flange  92  in an axial direction along the second axis  52  and can include a first portion  94  and a second portion  96  that can cooperate to define a shoulder  98 . The second portion  96  can be larger in diameter than the first portion  94  and can be disposed between the second cover flange  92  and the first portion  94  along the second axis  52 . The mounting projection  90  can be received into the cover bore  60  such that the first portion  94  of the mounting projection  90  is received on (and optionally engages in a slip-fit manner) the inside diametrical surface of the second bore portion  68  of the cover bore  60 , the second portion  96  of the mounting projection  90  is received on (and optionally engages in a slip-fit manner) the inside diametrical surface of the first bore portion  66  of the cover bore  60 , and planar surfaces defined by the first and second cover flanges  62  and  92 , respectively, abut one another. An annular seal member  100 , such as an O-ring, can be received on the first portion  94  of the mounting projection  90  and sealingly engaged to the inside diametrical surface of the first bore portion  66  of the cover bore  60 . Additionally or alternatively, a gasket or sealant material (not shown) can be received between the planar surfaces of the first and second cover flanges  62  and  92  to form a fluid-tight seal between the main housing  30  and the first end cover  32 . The first and second cover flanges  62  and  92  can be coupled to one another in any desired manner and may be permanently affixed to one another or releasably coupled to one another. In the example provided, a plurality of threaded fasteners  104  are received through holes formed in the second cover flange  92  and threadably engaged to threaded holes formed in the first cover flange  62  to thereby fixedly but releasably couple the first end cover  32  to the main housing  30 . 
         [0018]    The input pinion  14  is depicted as a hypoid (spiral bevel) pinion in the example provided such that the first axis is offset from and does not intersect the second axis  52 , but it will be appreciated that the input pinion  14  can be any type of bevel pinion. In the particular example provided, the input pinion  14  is constructed in a manner that is described in commonly assigned U.S. Pat. No. 9,103,427, the disclosure of which is hereby incorporated by reference as if fully set forth in detail herein. Briefly, the input pinion  14  is unitarily formed to include a shaft portion  150  and a pinion portion  152 . The shaft portion  150  defines an integral bearing race  156  and can be generally hollow to receive therein a portion of a pinion flange  158  that facilitates the coupling of the input pinion  14  to a rotatable shaft, such as a propshaft (not shown). In the example provided, the input pinion  14  is supported for rotation relative to the main housing  30  by a four-point angular contact bearing  160 , which is the sole means for transmitting thrust loads between the housing assembly  12  and the input pinion  14 . The four-point angular contact bearing  160  can comprise an outer race  162 , an inner race (i.e., the integral bearing race  156 ) and a plurality of bearing balls  166  that can be received on the outer race  162  and the inner race  156 . The outer race  162  can comprise a first race member  170  and a second race member  172 . The first race member  170  can be received in a first one of the bearing mounts  174  that can be concentric with the pinion bore  46  and abutted against a shoulder formed on the pinion mount  36 . The second race member  172  can be received in the pinion bore  46  and can engage the bearing balls  166  on a side of the bearing balls  166  opposite the first race member  170 . An annular retainer plate  180  can be received about the input pinion  14  and fixedly coupled to the main housing  30  to secure the second race member  172  in the pinion bore  46  and can apply a preload force to the outer race  162 . A second bearing  184 , which can be a ball or roller bearing, can be received in a second bearing mount  186  in the main housing  30  and can engage a shaft member  188  that can extend from the pinion portion  152 . While the input pinion  14  has been illustrated and described as having an integral bearing race and being supported for rotation relative to the main housing  30  via a four-point angular contact bearing, it will be appreciated that other input pinion configurations could be employed in the alternative and as such, the input pinion  14  could in the alternative be supported by a pair of tapered roller bearings (not shown). 
         [0019]    An oil seal  190  can be fixedly mounted to the annular retainer plate  180 . In the particular example provided, the oil seal  190  has a seal lip  192  that is formed of PTFE and engages an oil seal surface  194  formed on the input pinion  14 . To ensure that the seal lip  192  of the oil seal  190  is positioned on the main housing  30  concentric with the oil seal surface  194 , the oil seal  190  can be assembled onto the input pinion  14  and the annular retainer plate  180  can be abutted against the main housing  30  (to permit the oil seal surface  194  to position the oil seal  192  and the annular retainer plate  180  relative to the main housing  30 ) before a plurality of threaded fasteners  196  are employed to secure the annular retainer plate  180  to the main housing  30 . Alternatively, the annular retainer plate  180  could be configured with a locating feature, such as an annular lip  198 , that can pilot on a portion of the main housing  30  to thereby position the seal lip  192  concentric with the oil seal surface  194 . While the oil seal  190  has been described as having a seal lip  192  that is formed of a PTFE material, it will be appreciated that any type of oil seal could be employed. 
         [0020]    While the retainer plate  180  has been illustrated as a relatively thin-walled component, it will be appreciated that the retainer plate  180  could be constructed in a more robust manner as shown in  FIGS. 5 and 6 . Construction in this manner permits the integration of a (front) mount FM with the retainer plate  180 . 
         [0021]    With specific reference to  FIG. 6 , the threaded fasteners  196  can be disposed about the first axis  48  in clustered manner that need not be symmetrical. In the example provided, the threaded fasteners  196  are clustered in an area in which the four-point angular contact bearing  160  is relatively highly loaded. The area is a segment S of the bolt circle BC about which the threaded fasteners  196  are disposed. A threaded fastener  196  is considered to be within the segment S if the centerline of the threaded fastener  196  is disposed within the area bounded by segment S or is radially outwardly therefrom by a distance (from the first axis  48 ) that is less than or equal to five (5) times the major diameter of the threaded fastener  196 . The segment S spans less than 180 degrees and preferably less than 120 degrees. In the example shown, the segment S spans less than 90 degrees. Clustering occurs when the segment S can be oriented about the first axis  48  such that the quantity of the threaded fasteners  196  that are disposed within the segment exceeds the quantity of threaded fasteners  196  that are disposed on the bolt circle BC but whose centerlines do not fall within the segment S. In the example shown, clustering of the threaded fasteners  196  occurs because the segment S spans ninety degrees (which is less than 180 degrees) and the segment S can be oriented into the position shown, which places four of the threaded fasteners  196  within the area of the segment S or radially outwardly therefrom by a distance that is less than or equal to five (5) times the major diameter of the threaded fastener  196 , while only three of the threaded fasteners  196  lie along the bolt circle BC outside of the segment S. Those of skill in the art will appreciate that the bolt circle BC can be larger in diameter than the pinion flange  158  so as to permit the threaded fasteners  196  to be inserted through the retainer plate  180  and tightened to the main housing  30  after the pinion flange  158  has been coupled to the input pinion  14 . Alternatively, the pinion flange  158  could be scalloped to provide clearance for the threaded fasteners  196  and the tooling (e.g., socket wrench) needed to tighten the threaded fasteners  196 . 
         [0022]    The ring gear  16  can be disposed in the differential cavity  74  in the housing assembly  12  for rotation about the second axis  52  and can be meshingly engaged to the pinion portion  152  of the input pinion  14 . In the particular example provided, the ring gear  16  is constructed in a manner that is described in commonly assigned U.S. Pat. No. 9,103,427. Briefly, the ring gear  16  can define an integral bearing race  204  and can be generally hollow to receive therein a portion of the annular hub  50  of the main housing  30 . In the example provided, the ring gear  16  is supported for rotation relative to the main housing  30  by a four-point angular contact bearing  206 , which is the sole means for transmitting thrust loads between the housing assembly  12  and the ring gear  16 . The four-point angular contact bearing  206  can comprise an outer race (i.e., the integral bearing race  204 ), an inner race  208  and a plurality of bearing balls  210  that can be received on the outer race  204  and the inner race  208 . The inner race  208  can comprise a first race member  212  and a second race member  214 . The first race member  212  can be received in a third one of the bearing mounts  220  that can be formed on the annular hub  50 . The third one of the bearing mounts  220  can define a shoulder against which the first race member  212  can be abutted. The second race member  214  can be received on the annular hub  50  and can engage the bearing balls  210  on a side of the bearing balls  210  opposite the first race member  212 . An annular retainer plate  222  can be mounted to an axial end of the annular hub  50  via a plurality of threaded fasteners  224  that extend through holes in the annular retainer plate  222  and are received in threaded holes formed in the main housing  30  to thereby fixedly couple the retainer plate  222  to the main housing  30  and apply a preload force to the inner race  208 . 
         [0023]    The differential assembly  18  can be any type of mechanism that can transmit rotary power between the ring gear  16  and the first and second axle shafts  20  and  22 . In the particular example provided, the differential assembly  18  is an open spur gear differential having an internal gear  300 , a planet carrier  302 , a plurality of planet gears  304  and a sun gear  306 . The internal gear  300  can be sized to overhang the planet gears  304  somewhat on a side opposite the ring gear  16  and can be formed in a process that includes cold-coining the internal teeth of the internal gear  300 . The internal gear  300  can be fixedly coupled (e.g., via threaded fasteners or one or more welds) to the ring gear  16 . The planet carrier  302  can include a first carrier body  310 , a second carrier body  312  and a plurality of carrier pins  314  that extend between the first and second carrier bodies  310  and  312 . The first carrier body  310  can include an annular projection  320  that can be received into the annular hub  50  on the main housing  30 . A bearing, such as a roller bearing  322  can be received between the annular hub  50  and the annular projection  320  to support the first carrier body  310  for rotation relative to the main housing  30 . The second carrier body  312  can have an internally splined or toothed aperture  330 . The carrier pins  314  can extend between the first and second carrier bodies  310  and  312 . Each of the planet gears  304  can be journally supported on a corresponding one of the carrier pins  314 . In the example provided, the planet gears  304  comprise a plurality of planet gear pairs. Each planet gear pair consists of a first planet gear  332 , which is meshingly engaged to the teeth of the internal gear  300 , and a second planet gear (not specifically shown) that is meshed with the first planet gear  332  and the teeth of the sun gear  306 . In the example provided, bearings  334  are disposed between each planet gear  304  and its associated carrier pin  314 . The sun gear  306  can define an internally splined or toothed aperture  340 . 
         [0024]    The first axle shaft  20  can be received through a first axle bore  350  in the main housing  30  that extends concentrically through the annular hub  50 . The first axle shaft  20  can include a male splined or toothed segment  352  that can be engaged to the internally splined aperture  340  in the sun gear  306  such that the first axle shaft  20  is non-rotatably coupled to the sun gear  306 . A first axle shaft bearing  360  can be received in the bearing bore  58  in the first axle shaft mount  40  and can support the first axle shaft  20  for rotation relative to the main housing  30 . In the example provided, the wall member  34  of the main housing  30  defines an annular wall  370  that extends about the second axis  52  concentric with but axially offset from the bearing bore  58 . A first axle seal  372  can be received into the annular wall  370  and can sealingly engage the annular wall  370  and the first axle shaft  20 . 
         [0025]    The second axle shaft  22  can be received in a second axle bore  400  formed in the first end cover  32 . The second axle shaft  22  can include a male splined or toothed segment  402  that can be engaged to the internally splined aperture  330  in the second carrier body  312  such that the second axle shaft  22  is non-rotatably coupled to the planet carrier  302 . A second axle shaft bearing  406  can be received in the bearing bore  88  in the second axle shaft mount  82  and can support the second axle shaft  22  for rotation relative to the first end cover  32 . In the example provided, the wall member  80  of the first end cover  32  defines an annular wall  410  that extends about the second axis  52  concentric with but axially offset from the bearing bore  88 . A second axle seal  412  can be received into the annular wall and can sealingly engage the annular wall  410  and the second axle shaft  22 . 
         [0026]    With reference to  FIG. 2 , a second axle assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   a . The axle assembly  10   a  is generally similar to the axle assembly  10  ( FIG. 1 ), except that the axle assembly  10   a  comprises a mechanical limited slip differential assembly  18   a  having a helical gearset. More specifically, the differential assembly  18   a  is an open helical gear differential having an internal gear  300   a , a planet carrier  302   a , a plurality of planet gears  304   a  and a sun gear  306   a . The internal gear  300   a  can be fixedly coupled (e.g., via threaded fasteners or one or more welds) to the ring gear  16  and comprises internal helical gear teeth. The planet carrier  302   a  can include a first carrier body  310   a  and a second carrier body  312   a  that can be fixedly coupled to the first carrier body  310   a . The planet carrier  302   a  can define a plurality of pinion pockets  500  into which the planet gears  304   a  can be received. The first carrier body  310   a  can include an annular projection  320   a , which can be received into the annular hub  50  on the main housing  30 , an internally splined or toothed aperture  340   a , and a first thrust member  504 . A bearing, such as a roller bearing  322  can be received between the annular hub  50  and the annular projection  320   a  to support the first carrier body  310   a  for rotation relative to the main housing  30 . The male splined segment  352  on the first axle shaft  20  can be engaged to the internally splined aperture  340   a  to thereby non-rotatably couple the first axle shaft  20  to the first carrier body  310   a . The first thrust member  504  can be an annular structure that can be disposed proximate a second thrust member  508  formed on the ring gear  16 . A first annular thrust washer  510  can be received between the first and second thrust members  504  and  508 . The second carrier body  312  can be mounted on an annular projection  510  formed on the internal gear  300   a . A retainer, such as an internal snap ring  512 , can be employed to limit movement of the second carrier body  312  along the second axis  52  in a direction away from the internal gear  300   a.    
         [0027]    In the example provided, the planet gears  304   a  comprise a plurality of planet gear pairs and each of the planet gear pairs is received into a corresponding one of the pinion pockets  500 . Each planet gear pair consists of a first planet gear  332   a , which is meshingly engaged to the helical teeth of the internal gear  300   a , and a second planet gear (not specifically shown) that is meshed with the helical teeth of the first planet gear  332   a  and the helical teeth of the sun gear  306   a . Torque transmission between the first planet gears ( 332   a ) and the second planet gears causes the first and second planet gears of each planet gear pair to slide against the internal surfaces of their associated pinion pocket  500 . The sun gear  306   a  can define an internally splined or toothed aperture  330   a  and an annular projection  520  on which the second carrier body  312   a  is received. The male splined segment  402  on the second axle shaft  22  can be engaged to the internally splined aperture  330   a  in the sun gear  306   a  to thereby non-rotatably couple the sun gear  306   a  and the second axle shaft  22 . A second annular thrust washer  524  can be received between the second carrier body  312   a  and the sun gear  306   a . A third annular thrust washer  526  can be received between the sun gear  306   a  and the first carrier body  310   a.    
         [0028]    It will be appreciated that due to the helical configuration of the gearing that makes up the differential assembly  18   a , thrust forces will be created during operation of the axle assembly  10   a . For example, when rotary power is transmitted from the ring gear  16  to the differential assembly  18   a  to drive the first and second axle shafts  20  and  22  (i.e., a drive condition), meshing engagement between the second planet gears and the sun gear  306   a  can generate a thrust force that can be directed from the sun gear  306   a  toward the first carrier body  310   a . The thrust load in the drive condition can be transmitted from the sun gear  306   a , through the third annular thrust washer  526 , to the first carrier body  310   a , through the first annular thrust washer  510  and into the ring gear  16 . It will be appreciated that the first and third annular thrust rings  510  and  526  can be configured to provide a first bias ratio. As another example, when rotary power is transmitted from the differential assembly  18   a  to the ring gear  16  (i.e., a coast condition), meshing engagement between the second planet gears and the sun gear  306   a  can generate a thrust force that can be directed from the sun gear  306   a , through the second annular thrust ring  524 , into the second carrier body  312   a . It will be appreciated that the second annular thrust ring  524  can be configured to provide a second bias ratio. Various properties of the first and third annular thrust rings  510  and  526 , and/or the second annular thrust ring  524  can be selected to vary the first and second bias ratios in a desired manner. Such properties include: the material from which the thrust ring is formed, the configuration and surface area of the thrust ring, the heat-treatment of the thrust ring, coatings and/or platings applied to the thrust ring, and the use of one or more friction materials on the thrust ring or the component(s) in contact with the thrust ring. 
         [0029]    With reference to  FIG. 3 , a third axle assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   b . The axle assembly  10   b  is generally similar to the axle assembly  10  ( FIG. 1 ), except that the axle assembly  10   b  includes a locking clutch  600  and the housing assembly  12   b  has been modified so as to be capable of housing the locking clutch  600 . 
         [0030]    The housing assembly  12   b  is generally similar to the housing assembly  12  ( FIG. 1 ), except that it includes a second end cover  602  and the main housing  30   b  is modified to receive the second end cover  602 . The wall member  34   b  of the main housing  30   b  defines the annular wall  370   b , a second annular wall  604 , and a second cover mount  608 . The outer diametrical surface of the annular wall  370   b  and the inner diametrical surface of the second annular wall  604  can be machined so that they are concentric and cooperate to define a piston cavity  610 . The second cover mount  608  can define a cover bore  612 , which can be formed about the second axis  52  concentric with annular hub  50 , and a third cover flange  614  that can extend about the cover bore  612 . In the example provided, the cover bore  612  is stepped or counterbored so as to define a first bore portion  620 , a first shoulder  622 , and a second bore portion  624  that can be relatively smaller in diameter than the first bore portion  620 . 
         [0031]    So that the casting that forms the main housing  30   b  can be common to the main housing  30  ( FIG. 1 ), the casting is formed with the structure that can be machined as needed to form the second annular wall  604  and the second cover mount  608 . It will be appreciated that this additional structure need not be machined when the main housing  30  ( FIG. 1 ) is to be formed. Additionally, it will be appreciated that the bearing bore  58  ( FIG. 1 ) in the first axle shaft mount  40  ( FIG. 1 ) and the inside diametrical surface of the annular wall  370   b  need not be machined when the casting is to be employed to form the main housing  30   b.    
         [0032]    The second end cover  602  can be configured to cooperate with the main housing  30   b  to form a clutch cavity  630 . The second end cover  602  can be formed of any suitable material, such as cast iron, steel, aluminum or magnesium. The second end cover  602  can comprise a wall member  632  that can define a third axle shaft mount  634  and a main housing mount  636 . The third axle shaft mount  634  can define a bearing bore  638 , which can be configured to receive the first axle shaft bearing  360  that can support the first axle shaft  20   b  for rotation relative to the housing assembly  12   b , and an annular wall  640  into which the first axle seal  372  can be received. The main housing mount  636  can be configured to cooperate with the cover mount  608  to align the axis of the bearing bore  638  so as to be coincident with the second axis  52  and to facilitate the coupling of the second end cover  602  to the main housing  30   b . In the example provided, the main housing mount  636  comprises a mounting projection  634  and a fourth cover flange  646 . The mounting projection  634  can extend from the fourth cover flange  646  in an axial direction along the second axis  52  and can include a first portion  650 , a shoulder  652  and a second portion  654  that can be separated from the first portion  650  by the shoulder  652 . The second portion  654  can be larger in diameter than the first portion  650  and can be disposed between the fourth cover flange  646  and the first portion  650  along the second axis  52 . The mounting projection  634  can be received into the cover bore  608  such that the first portion  650  of the mounting projection  634  is received on (and optionally engages in a slip-fit manner) the inside diametrical surface of the second bore portion  624  of the cover bore  612 , the second portion  654  of the mounting projection  634  is received on (and optionally engages in a slip-fit manner) the inside diametrical surface of the first bore portion  620  of the cover bore  608 , and planar surfaces defined by the third and fourth cover flanges  614  and  646 , respectively, abut one another. An annular seal member  660 , such as an O-ring, can be received on the first portion  650  of the mounting projection  634  and sealingly engaged to the inside diametrical surface of the second bore portion  620  of the cover bore  608 . Additionally or alternatively, a gasket or sealant material (not shown) can be received between the planar surfaces of the third and fourth cover flanges  614  and  646  to form a fluid-tight seal between the main housing  30   b  and the second end cover  602 . The third and fourth cover flanges  614  and  646  can be coupled to one another in any desired manner and may be permanently affixed to one another or releasably coupled to one another. In the example provided, a plurality of threaded fasteners  664  are received through holes formed in the fourth cover flange  646  and threadably engaged to threaded holes formed in the third cover flange  614  to thereby fixedly but releasably couple the second end cover  602  to the main housing  30   b.    
         [0033]    The locking clutch  600  can be any type of clutch and can be integrated into the axle assembly to selectively inhibit speed differentiation between the first and second axle shafts  20   b  and  22 . In the particular example provided, the locking clutch  600  is a hydraulically-operated multi-plate friction clutch having a first clutch member  650 , a second clutch member  660 , a clutch pack  662 , a clutch spring  664 , and a clutch piston  668 . 
         [0034]    The first clutch member  650  can be coupled to the first carrier body  310   b  for rotation therewith. For example, the annular projection  320   b  on the first carrier body  310   b  can be extended relative to the embodiment of  FIG. 1  and can include a male splined or toothed segment  670  that can be engaged by a first annular mount portion  672  of the first clutch member  650 . It will be appreciated that while the annular projection  320   b  is illustrated as being unitarily and integrally formed with the first carrier body  310   b , the annular projection  320   b  and the first carrier body  310   b  could be formed as discrete components that are fixedly coupled together in a suitable manner, such as by friction welding. The first clutch member  650  can further comprise a second annular mount portion  674 , which can be disposed concentrically about the first annular mount portion  672 , and a first radially extending portion  674  that can couple the first annular mount portion  672  to the second annular mount portion  674 . 
         [0035]    The second clutch member  660  can be coupled for rotation with the first axle shaft  20   b . In the example provided, the first axle shaft  20   b  includes a male splined segment  680  that is engaged to a female splined segment formed by a third annular mount portion  682  of the second clutch member  660 . The third annular mount portion  682  can be received within the first annular mount portion  672 . The second clutch member  660  can further comprise a fourth annular mount portion  684 , which can be disposed concentrically about the second and third annular mount portions  674  and  682 , and a second radially extending portion  684  that can couple the third annular mount portion  682  to the fourth annular mount portion  684 . 
         [0036]    The clutch pack  662  can comprise a pressure plate  690 , a plurality of first friction plates  692  and a plurality of second friction plates  694 . The pressure plate  690  and the second friction plates  694  can be non-rotatably but axially slidably engaged to the second annular mount portion  674 . The first friction plates  692  can be non-rotatably but axially slidably engaged to the fourth annular mount portion  684  and interleaved with the second friction plates  694  and optionally the pressure plate  690 . The pressure plate  690  can be moved along the second axis  52  between a first position, in which the first and second friction plates  692  and  694  are engaged to one another to permit the transmission of a predetermined amount of rotary power (i.e., torque) between the first and second clutch members  650  and  660 , and a second position in which the first and second friction plates  692  and  694  are relatively less engaged to one another. In the second position, the first and second friction plates  692  and  694  could be completely disengaged from one another, or could be merely touching one another, or could be engaged to a lesser degree than the degree to which they are engaged in the first position. 
         [0037]    The clutch spring  664  can be configured to bias the pressure plate  690  toward one of the first and second positions. In the example provided, the clutch spring  664  comprises a plurality of helical compression springs that are disposed between the pressure plate  690  and the first radially extending portion  674  and bias the pressure plate  690  toward the second position. 
         [0038]    The clutch piston  668  can be received in the piston cavity  610  and can be sealingly but slidingly engaged to the outer diametrical surface of the annular wall  370   b  and the inner diametrical surface of the second annular wall  604 . In the example provided, the clutch piston  668  is depicted as having discrete seals, such as O-ring type seals, that are assembled to the remainder of the clutch piston  668 , but it will be appreciated that one or both of the seals could be configured as a lip seal that can be overmolded onto (i.e., cohesively bonded to) the remainder of the clutch piston  668 . The piston cavity  610  can be coupled to a source of hydraulic pressure (not shown) that can be selectively applied to the clutch piston  668  to drive the pressure plate  690  into the first position. Axial thrust bearings  696  can be received between the clutch piston  668  and the pressure plate  690 , and between the second radially extending portion  684  and the wall member  632  of the second end cover  602 . Optionally, an axial thrust bearing  698  can be received between the first and second radially extending portions  674  and  684 . 
         [0039]    When the locking clutch  600  is not operated (i.e., hydraulic pressure is not applied to the clutch piston  668  so that the clutch spring  664  can move the pressure plate  690  into the second position), the differential assembly  18   b  operates in the manner of an open differential. When the locking clutch  600  is operated (i.e., hydraulic pressure is applied to the clutch piston  668  so that the pressure plate  690  is moved into the first position), the locking clutch  600  couples the first axle shaft  20   b  to the first carrier body  310   b  for common rotation. Since the first carrier body  310   b  co-rotates with the first carrier body  310  and the second axle shaft  22 , operation of the locking clutch  600  causes common rotation of the first and second axle shafts  20   b  and  22  so that speed differentiation between the first and second axle shafts  20   b  and  22  is inhibited. 
         [0040]    With reference to  FIG. 7 , a portion of an axle assembly similar to that of  FIG. 3  is shown. In this example, the pressure plate  690  is depicted as including a spring foot SF that abuts the clutch springs  664 . The pressure plate  690  can terminate at its radially inner side axially within the first clutch member  650  and radially between the first and second annular mount portions  672  and  674 . Additionally, the annular wall  370   b  can be somewhat longer than that which was illustrated in the example of  FIG. 3  so as to terminate axially within the first clutch member  650  and radially between the first and second annular mount portions  672  and  674 . Configuration of the annular wall  370   b  in this manner aids in directing lubrication into the first clutch member  650 . 
         [0041]    With reference to  FIG. 4 , a fourth axle assembly constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10   c . The axle assembly  10   c  is generally similar to the axle assembly  10   b  ( FIG. 3 ), except that the axle assembly  10   c  includes a torque vectoring mechanism  700  rather than a locking clutch  600  ( FIG. 3 ) and the housing assembly  12   c  has been modified so as to be capable of housing the torque vectoring mechanism  700 . 
         [0042]    The housing assembly  12   c  is generally similar to the housing assembly  12   b  ( FIG. 3 ), except that it includes a third end cover  602   c  and the main housing  30   c  is modified to include the (machined) bearing bore  58  in the first axle shaft mount  40 . The third end cover  602   c  is generally similar to the second end cover  602  ( FIG. 3 ), except that it includes an internally splined or toothed aperture  702  and a second piston cavity  704 . 
         [0043]    The torque vectoring mechanism  700  can include a first sun gear  710 , a second sun gear  712 , a third sun gear  714 , a plurality of compound planet gears  716 , a planet carrier  718 , a first torque vectoring clutch  720  and a second torque vectoring clutch  722 . 
         [0044]    The first sun gear  710  can be fixedly coupled to the first carrier body  310   b . In the example provided, the first sun gear  710  has an internally splined aperture  726  that is engaged to the male splined segment on the annular projection  320   b  of the first carrier body  310   b . The second sun gear  712  can be fixedly coupled to the first axle shaft  20   b . In the example provided, the second sun gear  712  has an internally splined aperture  728  that is engaged to the male splined segment  730  on the first axle shaft  20   b . The third sun gear  714  can be rotatably mounted on the first axle shaft  20   b . A bearing  734  can be received between the third sun gear  714  and the first axle shaft  20   b.    
         [0045]    Each of the compound planet gears  716  comprises a first planet gear  740 , a second planet gear  742  and a third planet gear  744  that are coupled to one another for common rotation. The first planet gear  740  is meshed with the first sun gear  710 , the second planet gear  742  is meshed with the second sun gear  712 , and the third planet gear  744  is meshed with the third sun gear  714 . 
         [0046]    The planet carrier  718  can include a carrier body  750  and a plurality of carrier pins  752  (only one shown). The carrier body  750  can be supported for rotation relative to the housing assembly  12   c  by a first bearing  756 , which can be received in the bearing bore  58  in the first axle shaft mount  40 , and a second bearing  758  that can be disposed between the carrier body  750  and the third sun gear  714 . Each of the carrier pins  752  can be mounted to the carrier body  750  and can journally support an associated one of the compound planet gears  716 . 
         [0047]    The first torque vectoring clutch  720  can be any type of variable force producing clutch, such as a hydraulically operated multi-plate friction clutch having a first inner clutch hub  760 , a first clutch pack  762  and a first piston cartridge  764 . The first inner clutch hub  760  can be formed on the carrier body  750  and can comprise a toothed or splined hub member. The first clutch pack  762  can comprise a first reaction member  770 , a plurality of first clutch plates  772 , a plurality of second clutch plates  774  and a pressure plate  776 . The first reaction member  770  can be non-rotatably and axially fixed to the splines of the internally splined aperture  702  in the third end cover  602   c . The first clutch plates  772  can be axially slidably but non-rotatably coupled to the first inner clutch hub  760 . The second clutch plates  774  can be interleaved with the first clutch plates  772  and can be axially slidably but non-rotatably coupled to the internal splines of the internally splined aperture  702  in the third end cover  602   c . The pressure plate  776  can be axially slidably but non-rotatably mounted on the internal splines of the internally splined aperture  702 . The first piston cartridge  764  can include a first piston  780  and a return spring cartridge  782 . The first piston  780  can be received into the piston cavity  610  on the main housing  30   c  and can be sealingly but slidingly engaged to the outer diametrical surface of the annular wall  370   b  and the inner diametrical surface of the second annular wall  604 . The piston cavity  610  can be coupled to a source of hydraulic pressure (not shown) that can be selectively applied to the first piston  780  to drive the pressure plate  776  toward the first reaction member  770 . The return spring cartridge  782  can comprise a plurality of helical compression springs that can be mounted about and secured to the annular wall  370   b . The helical compression springs of the return spring cartridge  782  can bias the first piston  780  along the second axis  52  in a direction away from the first reaction member  770 . 
         [0048]    The second torque vectoring clutch  722  can be any type of variable force producing clutch, such as a hydraulically operated multi-plate friction clutch having a second inner clutch hub  860 , a second clutch pack  862  and a second piston cartridge  864 . The second inner clutch hub  860  can be coupled to the third sun gear  714  for common rotation and can comprise a toothed or splined hub member. The second clutch pack  862  can comprise a second reaction member  870 , a plurality of first clutch plates  872 , a plurality of second clutch plates  874  and a second pressure plate  876 . The second reaction member  870  can be non-rotatably and axially fixed to the splines of the internally splined aperture  702  in the third end cover  602   c . The first clutch plates  872  can be axially slidably but non-rotatably coupled to the second inner clutch hub  860 . The second clutch plates  874  can be interleaved with the first clutch plates  872  and can be axially slidably but non-rotatably coupled to the internal splines of the internally splined aperture  702  in the third end cover  602   c . The second pressure plate  876  can be axially slidably but non-rotatably mounted on the internal splines of the internally splined aperture  702 . The second piston cartridge  864  can include a second piston  880  and a second return spring cartridge  882 . The second piston  880  can be received into the second piston cavity  704  in the third end cover  602   c  and can be sealingly but slidingly engaged to the third end cover  602   c . The second piston cavity  704  can be coupled to a source of hydraulic pressure (not shown) that can be selectively applied to the second piston  880  to drive the second pressure plate  876  toward the second reaction member  870 . The second return spring cartridge  882  can comprise a plurality of helical compression springs that can be mounted about and secured to an annular wall  890  on the third end cover  602   c  that defines an inner diametrical surface of the second piston cavity  704 . The helical compression springs of the second return spring cartridge  864  can bias the second piston  880  along the second axis  52  in a direction away from the second reaction member  870 . 
         [0049]    When the torque vectoring mechanism  700  is not operated, hydraulic fluid is not provided to the first piston  780  or to the second piston  880  so that the first and second torque vectoring clutches  720  and  722  do not affect the normal (open) configuration of the differential assembly  18   b . In the event that the first and second axle shafts  20   b  and  22  rotate at different rates, the relative rotation between the first and second sun gears  710  and  712  will cause corresponding rotation of the planet carrier  718  about the second axis  52 . 
         [0050]    The torque vectoring mechanism  700  can be operated in a first and second torque vectoring modes to transmit additional torque to one of the first and second axle shafts  20   b  and  22  and reduce the amount of torque that is transmitted to the other one of the first and second axle shafts  20   b  and  22 . Operation of the first torque vectoring clutch  720  (i.e., application of hydraulic pressure to the first piston  780  to drive the first pressure plate  776  toward the first reaction member  770 ) can slow or halt rotation of the planet carrier  718  about the second axis  52 . Due to differences in the pitch diameter between the first and second sun gears  710  and  712 , the relatively smaller second sun gear  712  will be rotate relatively faster than the relatively larger first sun gear  710 , causing additional torque to be transmitted to the first axle shaft  20   b  and a corresponding reduction in the amount of torque that is transmitted to the second axle shaft  22 . Operation of the second torque vectoring clutch  722  (i.e., application of hydraulic pressure to the second piston  880  to drive the second pressure plate  876  toward the second reaction member  870 ) can speed up the rotation of the compound planet gear  716  and cause the planet carrier  718  to reverse its rotational direction about the second axis  52 . Due to differences in the pitch diameter between the first and second sun gears  710  and  712 , the reverse rotation of the planet carrier  718  will have a relatively larger negative effect on the torque that is transmitted to the second sun gear  712  and consequently additional torque to be transmitted to the second axle shaft  22  (via the first planet carrier  718   b ) and a corresponding reduction in the amount of torque that is transmitted to the first axle shaft  20   b.    
         [0051]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.