Abstract:
A differential system provides an axle disconnect function, a synchronizer function, and it has the ability to transmit large amounts of torque and has a limited slip differential function in a compact and cost effective module.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 62/022,712 filed Jul. 10, 2014 which is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Currently, 4×4 and 6×4 drivelines, which are commonly used with semi-trailer trucks, incorporate a disconnect feature. The disconnect feature may also be useful in drivelines used with light motor vehicles such as pickup trucks or sport utility vehicles. The disconnect feature allows one drive axle to be disengaged from the driveline (and thus idled) to reduce friction losses and improve fuel economy during cruise conditions. When it is desired for the disconnected drive axle to be re-engaged with the driveline, a multi-plate wet friction clutch or a transmission type synchronizer is typically used to synchronize the idling auxiliary drive axle parts with the vehicle road speed. This wet clutch or synchronizer needs to be of a large enough capacity to transmit a drive torque to the auxiliary drive axle. Accordingly, such systems require a large capacity wet clutch or, alternately, a separate dog clutch due to the high torque level at the axle shaft in the drive torque mode. Further, the auxiliary drive axle typically utilizes an open wheel differential to avoid an added cost of a limited slip differential assembly. 
         [0003]    It would be advantageous to develop a more cost effective system that can provide an axle shaft disconnect function, synchronizer function, a limited slip differential function, and an ability to transmit large amounts of torque in a compact and cost effective unit. 
       SUMMARY 
       [0004]    In one embodiment, a limited slip differential has a first side gear and a second side gear. The second side gear has a first set of axially extending teeth. The embodiment includes an axle engagement assembly comprises a housing, a clutch pack, an engagement sleeve, a thrust plate and an actuating mechanism. The clutch pack has a first set of plates connected for axial and rotational movement with the differential case housing, and a second set of plates connected for axial and rotational movement with the engagement sleeve. The engagement sleeve has a second set of axially extending teeth axially aligned with the first set of axially extending teeth. The engagement sleeve is in continuous engagement with at least one axle shaft. 
         [0005]    In a second embodiment, a limited slip differential has a moveable side gear having a shaft portion and a flange portion. The shaft portion has a gear portion mounted thereon. The flange portion supports a first set of plates of a clutch pack for axial and rotational movement thereon. A differential case extension has a second set of plates of the clutch for axial and rotational movement thereon. An actuator selectively engages the clutch pack and moves the differential side gear into engagement with the differential side pinion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a sectional view of one embodiment of a limited slip differential according to the invention; 
           [0007]      FIG. 1A  is a view of one component of the differential from  FIG. 1 ; and 
           [0008]      FIG. 2  is a sectional view of another embodiment of a limited slip differential according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0009]    It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts of the present invention. Hence, specific dimensions, directions, orientations or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
         [0010]      FIG. 1  illustrates a limited slip differential  100  according to a first embodiment of the invention. The limited slip differential  100  is in driving engagement with a drive pinion  102 , a first output axle half shaft  155 A, and a second output axle half shaft  155 B. The limited slip differential  100  includes a differential assembly  104  and an axle engagement assembly  106 . The drive pinion  102  and the limited slip differential  100  are rotatably disposed in an axle housing  108 . The limited slip differential  100  facilitates at least variable driving engagement between the second output axle and a differential housing  110  of the differential assembly  104 . Further, the limited slip differential  100  has a disconnect function. 
         [0011]    The limited slip differential  100  includes a differential assembly  104  and an axle engagement assembly  106 . A portion of the axle engagement assembly  106  is fixed to the differential assembly  104  for rotation therewith. The differential assembly  104  includes the differential housing  110  (which comprises a ring gear portion  112 , a central portion  114 , and the portion of the axle engagement assembly  106 ), at least one cross shaft  116 , at least one spider pinion gear  118 , a conventional side gear  120 , and an engageable side gear  122 . Side gear  120  and side gear  122  have inward facing teeth  121 A,  121 B that mesh with at least one of the spider pinion gears  118 . 
         [0012]    The central portion  114  is fixed to the ring gear portion  112  and the portion of the axle engagement assembly  106  to define a differential cavity  124 . The at least one cross shaft  116 , the at least a pair of spider pinion gears  118 , the conventional side gear  120 , and the engageable side gear  122  are disposed within the differential cavity  124  and engaged with one another in a conventional manner, which is known in the art. 
         [0013]    The engageable side gear  122  has an inward facing surface  122 A and an outward facing surface  122 B axially opposite the inward facing surface  122 A. The outward facing surface  122 B has a first set of axially extending teeth  123 . 
         [0014]    The axle engagement assembly  106  includes a differential case housing portion  126 , a clutch pack  128 , an engagement sleeve  130 , a thrust plate  132 , a bearing  134 , and an actuating mechanism  136 . The differential case housing portion  126  is fixed to the central portion  114  of the differential housing  110  and is rotatably supported within the axle housing  108 . The clutch pack  128  is disposed within the differential case housing portion  126  and is in driving engagement with the differential case housing portion  126  and the engagement sleeve  130 . The actuating mechanism  136  is sealingly disposed within an annular recess formed in the axle housing  108 . When placed in at least a partially engaged position, the axle engagement assembly  106  facilitates at least variable driving engagement between the housing portion  126  and the engagement sleeve  130  and the axle shaft  155 B. 
         [0015]    The differential case housing portion  126  is a substantially annular shaped member fixed to the central portion  114  of the differential housing  110 . The differential case housing portion  126  is rotatably supported within the axle housing  108 . A plurality of apertures  138  formed through the housing portion  126  allow a portion of the thrust plate  132  to extend therefrom in a radial manner. The apertures  138  facilitate an axial displacement of the thrust plate  132  in response to a force applied thereto by the actuating mechanism  136  through the bearing  134 . 
         [0016]    The differential case housing portion  126  has a differential case clutch pack portion  126 A and a reduced diameter portion  126 B. The reduced diameter portion  126 B is axially adjacent the differential case clutch pack portion  126 A. The actuating mechanism  136  is located radially outward from the reduced diameter portion  126 B. 
         [0017]    A seat portion  140  of the differential case housing portion  126  has a reduced diameter, onto which an inner race of a bearing  142  is disposed. The outer race of the bearing  142  is disposed in a mounting recess  144  formed in the axle housing  108 . 
         [0018]    The clutch pack  128  comprises a first plurality of plates  146  and a second plurality of plates  148 . The first plurality of plates  146  is drivingly engaged with the differential case housing portion  126  through a plurality of slots  147  formed on an inner surface of the differential case housing portion  126 . The slots  147  facilitate axial and rotational movement of the plates  146  on the differential case housing portion  126 . Each of the plates  146  is a clutch plate as is known in the art. As shown, the first plurality of plates  146  includes three plates, however, it is understood that any number of plates may form the first plurality of plates  146 . 
         [0019]    The second plurality of plates  148  is drivingly engaged with the engagement sleeve  130  through a plurality of splines  149  formed on an outer surface of the engagement sleeve  130 . The splines  149  facilitate axial and rotational movement of the plates  148  on the housing portion  126 . Each of the plates  148  is a clutch plate as is known in the art. As shown, the second plurality of plates  148  includes three plates, however, it is understood that any number of plates may form the second plurality of plates  148 . The first plurality of plates  146  interleaved with the second plurality of plates  148  forms the clutch pack  128 . It is understood that a plurality of biasing members (not shown) may also be interleaved between the first plurality of plates  146  and the second plurality of plates  148  to ensure the plates  146 ,  148  are spaced apart in a substantially equidistant manner and to militate against losses caused by unnecessary contact between the plates  146 ,  148  when the clutch pack  128  is uncompressed. 
         [0020]    The engagement sleeve  130  is a hollow, annular flanged member disposed in the differential case housing portion  126 . The engagement sleeve  130  includes a flanged portion  150 , an engagement portion  152 , a splined inner surface  154 , and a splined outer surface  156 . The flanged portion  150  extends in a radial manner from an end of the outer surface  156  and abuts the clutch pack  128  on a first side and a conical spring washer  158 . The conical spring washer  158  is a biasing member disposed between a radially inward extending wall  114  of the central portion  114  and the flanged portion  150  to urge the engagement sleeve  130  away from the differential assembly  104 , causing the engagement sleeve  130  to be drivingly disengaged from the engageable side gear  122 . The radially extending wall  114 A is located between the biasing member  158  and the side gear  122 . The teeth  123  of the side gear  122  are located radially inward from the radially extending wall  114 A. 
         [0021]    The engagement portion  152  comprises a second set of axially extending teeth  153  aligned with the first set of axially extending teeth, also known as the engagement portion  152 . When the axle engagement assembly  106  is in a fully engaged position, the engagement portion  152  is drivingly engaged with the engageable side gear  122 . The splined inner surface  154  is an inner surface of the engagement sleeve  130  which comprises a plurality of splines corresponding to a plurality of splines formed on the second output axle half shaft  155 B. The plurality of splines of the second output axle half shaft is drivingly engaged with the splined inner surface  154  of the engagement sleeve  130  to afford driving engagement therebetween. The engagement sleeve  130  is therefore in continuous engagement with the second output axle half shaft  155 B. 
         [0022]    The splined outer surface  156  is an outer surface of the engagement sleeve  130  which comprises a plurality of splines corresponding to a portion of the second plurality of plates  148  of the clutch pack  128 . The second plurality of plates  148  is drivingly engaged with the splined outer surface  156  of the engagement sleeve  130  to afford driving engagement therebetween. 
         [0023]    The thrust plate  132  is a substantially ring shaped member disposed about the engagement sleeve  130  and disposed against the clutch pack  128 . The thrust plate  132  includes a plurality of tabs  160  radially extending from a remaining portion. When the axle engagement assembly  106  is assembled, the thrust plate  132  is disposed therein and the tabs  160  extend through the apertures  138  formed through the differential case housing portion  126  and contact a portion of the bearing  134 . In response to a force applied thereto by the actuating mechanism  136  through the thrust bearing  134  to the thrust plate  132 , a force is applied to the clutch pack  128 . 
         [0024]    More particularly, the thrust plate  132  has a radially inward portion  161 A in contact with the clutch pack  128 . The thrust plate  132  also has a radially outward portion  161 B in contact with the actuating mechanism  136  and the differential case  126  slots  147 . The thrust plate  132  has a plurality of tabs  160  to facilitate axial and rotational movement of the thrust plate  132  with the differential case  126 . 
         [0025]    The thrust bearing  134  as shown is a ball thrust bearing; however, it is understood that other types of bearings may be used with the axle engagement assembly  106 . A first portion of the thrust bearing  134  is disposed against the plurality of tabs  160  of the thrust plate  132  and a second portion of the bearings is disposed against the actuating piston  136 . 
         [0026]    The actuating mechanism  136  may be a piston, such as a fluid operated piston. The actuating mechanism may be  136 , an electromagnetic solenoid, or a ball ramp and thrust plate. 
         [0027]    The piston  136  is a substantially ring shaped member sealingly disposed in an annular recess  162  in the axle housing  108 . The actuating piston  136  is mounted radially outside the axle housing  108 . The actuating piston  136  includes a pair of annular recesses into which a pair of O-rings  164  is disposed. The O-rings  164  facilitate sealing engagement between the actuating piston  136  and the annular recess  162 . The actuating piston  136  may be axially displaced, towards the differential assembly  104 , in response to application of a pressurized fluid to the annular recess  162  of the axle housing  108 . In response to axial displacement of the actuating piston  136 , a force is applied to the clutch pack  128  and to the engagement sleeve  130 , through the thrust bearing  134  and the thrust plate  132 . Further, it is understood that the axle engagement assembly  106  could incorporate a ball and ramp style actuator, an electromagnetic actuator, or any combination of actuators. 
         [0028]      FIG. 2  illustrates a limited slip differential  200  according to a second embodiment of the invention. The limited slip differential  200  is in driving engagement with a drive pinion  202  and ring gear  212 , a first output axle half shaft (not shown), and a second output axle half shaft  213 . The limited slip differential  200  includes a differential assembly  204  and an axle engagement assembly  206 . The drive pinion  202  and the limited slip differential  200  are rotatably disposed in an axle housing  208 . The limited slip differential  200  facilitates at least variable driving engagement between the second output axle half shaft  213  and a differential housing  210  of the differential assembly  204 . Further, the limited slip differential  200  has a disconnect function. 
         [0029]    A portion of the axle engagement assembly  206  is fixed to the differential assembly  204  for rotation therewith. The differential assembly  204  includes the differential case  210 , a ring gear portion  212  (partially shown), the portion of the axle engagement assembly  206 , at least one cross shaft  216 , at least one spider pinion gear  218 , a conventional side gear (not shown), a side gear biasing member  220 , a moveable side gear shaft  222 , a moveable side gear  256 , and a differential case extension  224 . 
         [0030]    The differential case  210  is fixed to the ring gear portion  212  to define a differential cavity  226 . The side gear  256  is located within the differential case  210 . The portion of the axle engagement assembly  106  is drivingly engaged with the differential case  210 . The at least one cross shaft  216 , the at least one spider gear  218 , and the conventional side gear are disposed within the differential cavity  226  and engaged with one another in a conventional manner, which is known in the art. The moveable side gear  256  is disposed within the differential cavity  226  and may be selectively drivingly engaged with the spider gear  218 . 
         [0031]    The differential case extension  224  is disposed adjacent the differential case  210  and is drivingly engaged therewith. The differential case extension  224  is a hollow annular member which partially encloses at least a portion of the axle engagement assembly  206 . 
         [0032]    The differential case extension  224  has a first axial portion  224 A. A first radial portion  224 B is connected to the first axial portion  224 A. The first radial portion  224 B is radially parallel a flange portion  260 . A second axial portion  224 C is connected to the first radial portion  224 B. The second axial portion radially encloses the flange portion  260  and at least a portion of a thrust plate  238 . 
         [0033]    The axle engagement assembly  206  includes a cover portion  228 , a clutch pack  230 , a ball and ramp actuator  232 , a ball bearing  234 , a needle thrust bearing  236 , and the thrust plate  238 . The cover portion  228  is fixed to the axle housing  208  and supports the ball and ramp actuator  232  and the ball bearing  234 . The clutch pack  230  is disposed within the differential case extension  224  and is in driving engagement with the differential case extension  224  and the moveable side gear  256 . The ball and ramp actuator  232  is disposed against the needle thrust bearing  236  and is in driving engagement with a ball and ramp actuator (not shown). The ball bearing  234  is disposed within the cover portion  228  and rotatably and slidably supports the moveable side gear shaft  222 . The needle thrust bearing  236  is disposed between and in rolling contact with a portion of the ball and ramp actuator  232  and the thrust plate  238 . The thrust plate  238  is in driving engagement with the differential case extension  224 ; however, the thrust plate  238  is axially slidable within the differential case extension  224 . When placed in at least a partially engaged position, the axle engagement assembly  206  facilitates at least variable driving engagement between the differential case extension  224  of the differential case  210  and the moveable side gear shaft  222 . 
         [0034]    While a ball and ramp actuator is disclosed, a fluid piston or an electromagnetic solenoid may also be used. 
         [0035]    The cover portion  228  is a substantially annular shaped member fixed to and sealingly engaged with a distal end of the axle housing  208 . The cover portion  228  may be fixed to the axle housing  208  with a plurality of threaded fasteners; however, it is understood that the cover portion  228  may be fixed thereto in any conventional manner. An annular protuberance  240  extends from the cover portion  228  into the differential cavity  226  and defines a perforation  242  through the cover portion  228 . A second output axle seal  244  is disposed in the perforation for sealingly engaging the second output axle half shaft  213 . A portion of the ball and ramp actuator  232  is non-rotatably disposed on an outer surface of the annular protuberance  240 . A portion of the ball bearing  234  is non-rotatably disposed on an inner surface of the annular protuberance  240 . The cover portion  228  may be configured to receive the ball and ramp actuator (not shown) or may be configured to allow the ball and ramp actuator to be mounted to an outer surface thereof. 
         [0036]    The clutch pack  230  comprises a first plurality of plates  246  and a second plurality of plates  248 . The first plurality of plates  246  is drivingly engaged with the differential case extension  224  through a plurality of splines  245  formed on an inner surface of the differential case extension  224 . The splines  245  permit axial movement of the plates  246 . Each of the plates  246  is a clutch plate as is known in the art. As shown, the first plurality of plates  246  includes three plates, however, it is understood that any number of plates may form the first plurality of plates  246 . The second plurality of plates  248  is drivingly engaged with the moveable side gear shaft  222  through a plurality of splines  247  formed on an outer surface of the moveable side gear shaft  222 . Each of the plates  248  is a clutch plate as is known in the art. As shown, the second plurality of plates  248  includes three plates, however, it is understood that any number of plates may form the second plurality of plates  248 . The first plurality of plates  246  interleaved with the second plurality of plates  248  forms the clutch pack  230 . It is understood that a plurality of biasing members (not shown) may also be interleaved between the first plurality of plates  246  and the second plurality of plates  248  to ensure the plates  246 ,  248  are spaced apart in a substantially equidistant manner and to militate against losses caused by unnecessary contact between the plates  246 ,  248  when the clutch pack  230  is uncompressed. 
         [0037]    The ball and ramp actuator  232  comprises a first plate  250 , a second plate  252 , and a plurality of actuation elements (not shown). The ball and ramp actuator  232  is known in the art; however, it is understood that other types of actuators may be used. When the first plate  250  and the second plate  252  are rotated with respect to one another, the first plate  250  and the second plate  252  become spaced apart and are used to apply a linear force to the clutch pack  230  through the needle thrust bearing  236  and the thrust plate  238 . The ball ramp actuator  232  is located axially adjacent the clutch pack  230 . The actuator  232  is mounted on the annular protuberance  240 , which as an axially extending portion  240 A. The actuator  232  is also located axially between the cover  206  and the thrust plate  238 . It is understood that the axle engagement assembly  206  could incorporate a fluid piston style actuator, an electromagnetic actuator, or any combination of actuators. 
         [0038]    The first plate  250  is a disk shaped member having a plurality of arc-shaped ramps formed therein and oriented to face the second plate  252 . A depth of each of the arc-shaped ramps varies along a length of each of the arc-shaped ramps. A quantity of the ramps corresponds to a number of actuation elements (not shown). The first plate  250  is coupled to the annular protuberance  240  of the cover portion  228 . 
         [0039]    The second plate  252  is a disk shaped member having a plurality of arc-shaped ramps formed therein and oriented to face the first plate  250 . A depth of each of the arc-shaped ramps varies along a length of each of the arc-shaped ramps. A quantity of the ramps corresponds to a number of actuation elements (not shown). The second plate  252  is in driving engagement with the ball and ramp actuator (not shown) to rotate the second plate  252  about the annular protuberance  240  of the cover portion  228 . The second plate  252  is disposed against the needle thrust bearing  236 . 
         [0040]    The actuation elements (not shown) are ball bearings rotatably disposed in the arc-shaped ramps formed in the first plate  250  and the second plate  252 . Alternately, it is understood that the actuation elements may have other shapes. When the first plate  250  and the second plate  252  are rotated with respect to one another, the actuation elements roll within the arc-shaped ramps formed in the first plate  250  and the second plate  252 , which cause the first plate  250  and the second plate  252  to become spaced apart based on a depth of the arc-shaped ramps. 
         [0041]    The needle thrust bearing  236  is disposed between and in rolling contact with the second plate  252  of the ball and ramp actuator  232  and the thrust plate  238 . The needle thrust bearing  236  comprises a plurality of rollers radially arranged in a cage and is well known in the art. A force generated by the ball and ramp actuator  232  is applied to the clutch pack  230  through the needle thrust bearing  236  and the thrust plate  238 . The needle thrust bearing  236  facilitates relative rotation between the second plate  252  of the ball and ramp actuator  232  and the thrust plate  238  while linear force is applied therebetween. 
         [0042]    The thrust plate  238  is a substantially ring shaped member disposed between the needle thrust bearing  236  and the clutch  230 . The thrust plate  238  is in driving engagement with the differential case extension  224  through a plurality of splines (not shown) formed on an inner surface of the differential case extension  224 . The thrust plate  238  is axially slidable along the plurality of splines within the differential case extension  224 . In response to a force applied thereto by the ball and ramp actuator  232  through the bearing needle thrust bearing  236  to the thrust plate  238 , a force is applied to the clutch pack  230 . Thus, the thrust plate  238  is located between the clutch pack  230  and the ball ramp actuator  232 . The thrust plate  238  is also located radially outboard from the protuberance  240  and the output axle engagement portion  222 . 
         [0043]    The ball bearing  234  radially supports the moveable side gear shaft  222  within the annular protuberance  240  while permitting the moveable side gear shaft  222  to move axially, allowing the moveable side gear shaft  222  to drivingly engage and disengage the spider pinion gears  218  and side gear  256  through the side gear  256 . A first portion of the ball bearing  234  is fixed within the annular protuberance and a second portion of the ball bearing  234  is disposed on an outer surface of the moveable side gear shaft  222 . A plurality of spherical elements may be disposed therebetween to facilitate axial movement between the moveable side gear shaft  222  and the cover portion  228 . 
         [0044]    The moveable side gear shaft  222  is an elongate, annular flanged member disposed in the differential cavity  226 . The moveable side gear shaft  222  may be drivingly engaged with the spider gears  218  and may be at least variably drivingly engaged with the differential case extension  224  through the clutch pack  230 . The moveable side gear shaft  222  includes a splined portion  257 , a shaft portion  258 , the flanged portion  260  extending radially from the shaft portion  258 , and an output axle engagement portion  262 . The splined portion  257  comprises axially extending splines located circumferentially about the shaft  222 . 
         [0045]    The shaft portion  258  is substantially cylindrical in shape and connects the splined portion  257  with the flanged portion  260  and the output axle engagement portion  262 . As shown, the shaft portion  258  is partially hollow, but it is understood that the central portion  258  may have another type of construction. 
         [0046]    The flanged portion  260  is a stepped portion of the moveable side gear shaft  222  that extends in a radial manner from the shaft portion  258 . The second plurality of plates  248  is drivingly engaged with the flanged portion  260  through a plurality of splines  261  formed on an outer surface of the flanged portion  260 . The splines  261  permit axial movement of the plates  248 . A portion of the flanged portion  260  extends further radially than a remaining portion to support the clutch pack  230  when the axle engagement assembly  206  is at least variably engaged. Preferably, the portion  260 A of the flanged portion  260  is an axial stop for the plates  248 . At least a portion of the shaft portion  258  is housed within the differential case  210 . 
         [0047]    The output axle engagement portion  262  is a substantially hollow and cylindrical in shape and facilitates driving engagement between the moveable side gear shaft  222  and the second output axle half shaft  213 . At least a portion of the output engagement portion is located radially inward from the clutch pack  230 . The output axle engagement portion is therefore in continuous engagement with the second output axle half shaft  213 . 
         [0048]    The moveable side gear shaft  222  is drivingly and slidably engaged with the second output axle haft shaft  213  through a plurality of splines  264  formed on an inner surface of the output axle engagement portion  262 . The moveable side gear shaft  222  is biased into a position disengaged from the spider gears  218  by the side gear biasing member  220 , which is a conical spring washer. The side gear biasing member  220  is disposed between the spider gears  218  and the shaft portion  258 . In response to a degree of actuation of the ball and ramp actuator  232 , a force applied by the side gear biasing member  220  may be overcome, compressing the side gear biasing member  220  and engaging the geared portion  256  of the moveable side gear shaft  222  with the spider gears. 
         [0049]    In use, the limited slip differential  100 ,  200  facilitates at least variable driving engagement between the second output axle half shaft  213  and one of the housing portion  126  and the differential case extension  224 . Further, the limited slip differential  100 ,  200  has a disconnect function, which drivingly disengages the second output axle  213 ,  155 B from the differential assembly  104 ,  204 . 
         [0050]    The axle engagement assembly  106 ,  206  of the limited slip differential  100 ,  200  utilizes a single shift mechanism to control a degree of engagement of the clutch pack  128 ,  230  and an engagement of the engagement sleeve  130  with the engageable side gear  122  or an engagement of the moveable side gear  256  with the spider gears  218 . Such control allows the axle engagement assembly  106 ,  206  to be used for both a synchronizer function and a limited slip differential function, which engagement of the engagement sleeve  130  with the engageable side gear  122  or an engagement of the moveable side gear  256  with the spider gears  218  (the dog clutch function) acts to transmit torque from the differential assembly  104 ,  204  to the second output axle half shaft  213 . 
         [0051]    Accordingly, the axle engagement assembly  106 ,  206  provides three modes of operation: disconnection of the first and second output axle half shafts for use during a cruising mode of the vehicle, a synchronizer function to accelerate the disengage differential and/or the components of the first and second output axle half shafts to a speed of the vehicle, and a traction mode to engage the first and second output axle half shafts to transmit wheel slip torques while at the same time applying a bias torque via the clutch pack to the differential assembly  104 ,  204  to enhance a tractive effort for all road conditions. Since the limited slip differential function is coupled to the dog clutch function, the limited slip differential function is always engaged when the first and second output axles are engaged, thus providing added tractive effort in the 4×4 or 6×4 mode of operation. The limited slip differential function therefore is aligned with a desire to provide the most available tractive effort regardless of the side to side wheel traction conditions. Consequently, the limited slip differential  100 ,  200  is provided for improved fuel efficiency during cruise conditions when the axle is disconnected from the driveline and added traction during vehicle launching and acceleration when the axle is connected to the driveline and the limited slip differential function is available. 
         [0052]    The axle engagement assembly  106 ,  206  may be placed in three positions: a retracted position, a partially advanced position, and a fully advanced position. When placed in the retracted position, the axle engagement assembly  106 ,  206  provides an open engaged mode of operation. The open engaged mode of operation disengages the second output axle from the differential assembly  104 ,  204 . The dog clutch does not transmit torque in the retracted position but it does transmit torque in the fully advanced position. 
         [0053]    When placed in the partially advanced position, the axle engagement assembly  106 ,  206  provides an energized clutch pack mode of operation. The partially advanced position engages the clutch pack  128 ,  230  to synchronize any idling parts to a road speed but not to engage the engagement sleeve  130  with the engageable side gear  122  or an engagement of the moveable side gear  256  with the spider gears  218 . 
         [0054]    When placed in the fully advanced position, the axle engagement assembly  106 ,  206  provides engagement of the second axle output shaft to the differential assembly  104 ,  204  while maintaining an engagement of the clutch pack  128 ,  230  between the second axle output shaft and the differential housing  110 ,  210 . The fully advanced position engages both the clutch pack  128 ,  230  and the engagement sleeve  130  with the engageable side gear  122  or an engagement of the moveable side gear  256  with the spider gears  218 . The axle engagement assembly  106  can be modulated by controlling a piston fluid pressure. 
         [0055]    In  FIG. 1 , a return spring  162  is provided to retract the actuating piston  136  to the open position when the fluid pressure is reduced to zero. The conical spring washer  158  may be used to release the clutch  128  and the return spring  162  retracts the clutch  128  the rest of the way. The piston low pressure condition is sufficient to compress the return spring  162  but not the spring washer  158 . The piston high pressure condition compresses the spring washer  158  to a flat condition that corresponds to full clutch engagement. 
         [0056]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments, however, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its scope or spirit.