Abstract:
A differential assembly for a vehicle includes a differential casing rotatable about an axis. The differential casing defines a cavity. A pair of side gears is disposed within the differential casing cavity. First and second pairs of pinion gears are rotatably positioned in the cavity in driving engagement with the side gears. A thrust block has circumferentially spaced apart recesses. Rotation of the thrust block is restricted by the first and second pairs of pinion gears being in communication with the recesses. A spring biases the thrust block into engagement with one of the side gears.

Description:
BACKGROUND 
     The present disclosure relates to differentials for use in automotive drivelines and, more particularly, to a helical gear differential having pre-loaded side gears. 
     Differentials of the type used in automotive drivelines generally may include a planetary gearset supported within a differential casing to facilitate relative rotation (i.e., speed differentiation) between a pair of output shafts. The planetary gearset may include helical side gears fixed for rotation with the ends of the output shafts, which are meshed with paired sets of helical pinion gears. This type of machine is known as a parallel axis helical gear differential. 
     In some differentials it may be desirable to pre-load the differential to provide a limited-slip driveline arrangement. Some differentials are equipped with springs to increase the force required to overcome friction between moveable differential components. The springs are engaged with the side gears and may exhibit wear. 
     SUMMARY 
     The present disclosure provides a differential assembly for a vehicle including a differential casing rotatable about an axis. The differential casing defines a cavity. A pair of side gears is disposed within the differential casing cavity. First and second pairs of pinion gears are rotatably positioned in the cavity in driving engagement with the side gears. A thrust block has circumferentially spaced apart recesses. Rotation of the thrust block is restricted by the first and second pairs of pinion gears being in communication with the recesses. A spring biases the thrust block into engagement with one of the side gears. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic view of an exemplary motor vehicle including a differential assembly constructed in accordance with the teachings of the present disclosure; 
         FIG. 2  is an exploded perspective view of the differential assembly of  FIG. 1 ; 
         FIG. 3  is a cross-sectional side view of the differential assembly of  FIG. 2 ; and 
         FIG. 4  is a partial exploded perspective view of the differential assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     With initial reference to  FIG. 1 , a drivetrain  10  for an exemplary motor vehicle may include an engine  12 , a transmission  14  having an output shaft  16 , and a propeller shaft  18  connecting the output shaft  16  to a pinion shaft  20  of a rear axle assembly  22 . The rear axle assembly  22  includes an axle housing  24 , a differential assembly  26  supported in the axle housing  24 , and a pair of axle shafts  28  and  30 , respectively, interconnected to a left and right rear wheel  32  and  34 , respectively. The pinion shaft  20  has a pinion shaft gear  36  fixed thereto which drives a ring gear  38  that may be fixed to a differential casing  40  of the differential assembly  26 . A gearset  42  supported within the differential casing  40  transfers rotary power from the casing  40  to a pair of output shafts  44  and  45  connected to the axle shafts  28  and  30 , respectively, and facilitates relative rotation (i.e., differentiation) therebetween. While the differential assembly  26  is shown in a rear-wheel drive application, the present invention is contemplated for use in differential assemblies installed in transaxles for use in front-wheel drive vehicles, and/or in transfer cases for use in four-wheel drive vehicles. 
     Turning now to  FIGS. 2-4 , the differential assembly  26  will be described in further detail. The differential assembly  26  may be a parallel-axis helical-gear type differential and includes the differential casing  40 . The differential casing  40  includes a main drum or body  46 , which defines an internal cavity or chamber  48 , and an end cap  50 . Body  46  includes a recess  52  having a mounting surface  54  shaped to mate with a radial flange  56  of cap  50 . The body  46  and cap  50  are secured together by a plurality of bolts  58 . As is known, a ring or bevel gear can be fixed to a radial flange  60  on the differential casing  40  to transfer rotary power (i.e., drive torque) thereto. The differential casing  40  defines a pair of axially aligned openings  62  and  64  in communication with the internal chamber  48 . The axially aligned openings  62  and  64  are adapted to receive the end segments of the pair of driving output shafts  44  and  45  ( FIG. 1 ), hereinafter referred to as axle shafts. 
     The differential assembly  26  includes the gearset  42  that is operable for transferring drive torque from the differential casing  40  to the output shafts  44  and  45  ( FIG. 1 ) in a manner that facilitates speed differentiation therebetween. Gearset  42  may be a helical-type and may be disposed within the internal chamber  48 . The gearset  42  includes a pair of side gears  68   a  and  68   b . The side gears have internal splines  70   a  and  70   b  meshed with external splines, not specifically shown, on the corresponding output shafts  44  and  45  ( FIG. 1 ). In addition, the side gears  68   a  and  68   b  include axial hubs  78   a  and  78   b , respectively, which are retained in corresponding annular sockets  82   a  and  82   b , formed in the main body  46  and the end cap  50  of the differential casing  40 . The side gears  68   a  and  68   b  also include annular chambers  84   a  and  84   b.    
     A spacer  86  may be located between the side gears  68   a  and  68   b  for limiting the amount of axial endplay of the side gears  68   a  and  68   b  within the differential case  40 . A cross pin  90  extends through a passage  92  in the spacer  86  and controls endplay of the axle shafts  44  and  45  ( FIG. 1 ). The outer cylindrical surface of cross pin  90  is sized to closely fit passage  92 . As such, the longitudinal location of cross pin  90  is defined by the position of passage  92 . C-shaped retainers, or C-clips  94 , may be retained in the annular chambers  84   a  and  84   b  for preventing the axle shafts  44  and  45 , respectively, from becoming disengaged with the side gears  68   a  and  68   b . Cross pin  90  is radially retained in position by a longitudinally extending threaded fastener  96 . Fastener  96  may extend through an aperture  98  formed in cross pin  90  as shown in  FIG. 2  or may alternatively be located adjacent to an end face  99  of an alternate cross pin  90   a  shown in  FIG. 3 . As a result of the spacer  86  and fastener  96  being operable to locate cross pin  90 , differential casing  40  need not include specially machined areas to locate and retain cross pin  90  and cross pin  90  need not contact casing  40 . 
     The gearset  42  includes four sets of pinion pairs,  100   a  and  100   b ,  102   a  and  102   b ,  104   a  and  104   b  and  106   a  and  106   b , respectively. For clarity, the pinion pairs  100   a  and  100   b ,  102   a  and  102   b ,  104   a  and  104   b  and  106   a  and  106   b  are hereinafter referred to as a first, second, third and fourth pair of pinion gears  100 ,  102 ,  104  and  106 , respectively. Brake shoes  100   a ′- 106   b ′ cooperate with respective pinion gears  100 - 106 . 
     The four sets of pinion gear pairs  100 - 106  are rotatably supported in complementary sets of pinion bores  110   a  and  110   b ,  112   a  and  112   b ,  114   a  and  114   b , and  116   a  and  116   b . The complementary sets of pinion bores  110   a  and  110   b ,  112   a  and  112   b ,  114   a  and  114   b , and  116   a  and  116   b  are hereinafter referred to as a first, second, third and fourth pair of pinion bores  110 ,  112 ,  114 , and  116 , respectively. The pinion bores  110 - 116  are formed in raised hub segments  120  of the main body  46 . The pinion bores  110 - 116  are arranged in paired sets such that they communicate with each other and with the internal chamber  48 . In addition, the pinion bores  110 - 116  are aligned substantially parallel to the rotational axis A of the axle shafts  44  and  45  ( FIG. 1 ). 
     A window opening  124  may be arranged on the differential casing  40  between the first and the fourth pair of pinion gears  100  and  106 . C-clips  94  may be inserted through window opening  124  when drivingly coupling axle shafts  44  and  45  to differential assembly  26 . 
     With reference to  FIGS. 2 ,  3  and  4 , spring washers  126  and thrust blocks  128  are positioned on axial hubs  78   a  and  78   b  of side gears  68   a  and  68   b , respectively. One of the spring washers  126  is positioned within a recess  130  formed in cap  50 . The other spring washer  126  is positioned within a recess  132  formed in body  46  as part of internal chamber  48 . Recesses  130  and  132  maintain axial position of spring washers  126  to assure that clearance exists between axial hubs  78   a ,  78   b  and spring washers  126 . Each thrust block  128  is positioned between one of spring washers  126  and one of side gears  68   a ,  68   b . It should be appreciated that recesses  130 ,  132  may alternatively be formed in thrust blocks  128  rather than in differential casing  40 . 
     Each spring washer  126  includes a substantially planar land  134  defining an opening  136 . A frustro-conical portion  138  radially outwardly extends from planar land  134  and terminates at an outer edge  140 . Each spring washer  126  may be constructed from a resilient material such as spring steel or an elastomeric plastic. 
     Each thrust block  128  is shaped as a ring having a first substantially planar contact surface  150  and an opposite substantially planar contact surface  152 . The contact surfaces extend substantially parallel to one another. An inner cylindrical wall  154  extends between planar surfaces  150 ,  152 . Thrust block  128  also includes an outer cylindrically shaped surface  156  extending from first surface  150  to second surface  152 . Four sets of scallops  160   a  and  160   b ,  162   a  and  162   b ,  164   a  and  164   b  and  166   a  and  166   b  interrupt outer cylindrical surface  156 . The complementary sets of scallops are hereinafter referred to as first, second, third and fourth pairs of scallops  160 ,  162 ,  164  and  166 , respectively. The scallops  160 - 166  are sized and positioned to receive pinion gear pairs  100 ,  102 ,  104  and  106 , respectively. 
     Pairs of troughs  170   a  and  170   b ,  172   a  and  172   b ,  174   a  and  174   b  and  176   a  and  176   b  are formed on contact surface  150  and extend in a radial direction from inner cylindrical wall  154  to a corresponding scallop  160 - 166 . In similar fashion, another four sets of trough pairs  180  through  186  radially extend from inner cylindrical wall  154  to outer cylindrical surface  156  along contact surface  152 . The four sets of troughs are identified as  180   a ,  180   b ,  182   a ,  182   b ,  184   a ,  184   b ,  186   a  and  186   b . The troughs function to allow lubricant to pass therethrough. 
     After assembly of differential assembly  26 , thrust blocks  128  are axially moveable within chamber  48  but restricted from rotating relative to casing  40  by pinion pairs  100 - 106 . Spring washers  126  are in a compressed state loaded against thrust blocks  128  to transfer load through side gears  68   a  and  68   b  to spacer  86 . The friction between side gears  68   a ,  68   b  and spacer  86  restricts relative rotation between the side gears  68   a ,  68   b  and casing  40  to provide limited slip differentiation. Thrust blocks  128  may be constructed from a number of materials, including plastic, having resistance to compression as well as resistance to wear due to direct sliding contact with side gears  68   a  and  68   b.    
     Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.