Abstract:
A differential assembly including a casing which rotates about a first axis, the casing having an internal cavity; an elongate cylindrical cross pin which rotates with the casing about the first axis, the cross pin extending along a second axis through the cavity, the second axis substantially perpendicular to the first axis; at least one pinion gear disposed within the cavity and about the cross pin, the pinion gear rotatable about the second axis; and a pair of side gears disposed within the cavity and in meshed engagement with the pinion gear, the side gears rotatable about the first axis. A cross pin retention element is disposed about the cross pin. The cross pin and the retention element are fixed against substantial relative movement therebetween along the second axis, and the retention element is disposed adjacent the pinion gear. The movement of the retention element relative to the casing along the second axis is restricted, whereby the cross pin is retained in the casing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to differentials, and more particularly, to the retention of the cross pin, on which pinion gears are rotatably disposed, therein. 
     Differentials are well known in the prior art and allow each of a pair of output shafts or axles operatively coupled to a rotating input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction with the road while the vehicle is turning. Typically, each of the axles is rotatably fixed to one of a pair of side gears, which are both intermeshed with a pair of first pinion gears. These pinion gears are rotatably disposed about opposite ends of a cylindrical cross pin which extends through diametrically opposite, holes in the circumferential wall of the rotating differential casing. The cross pin is fixed to the casing such that the first pinion gears revolve about the axis of rotation of the axles and side gears with the casing. As will be discussed further hereinbelow, typically, one end of the cross pin is provided with a cross bore which is aligned with holes in the casing; a bolt extends through the casing holes and the cross bore to retain the cross pin to the casing. 
     The casing is typically provided with a ring gear attached about its outer periphery, and which is intermeshed with a second pinion gear which is drivingly rotated by an engine. The cross pin, which is caused to rotate with the casing, imparts a driving force on the first pinion gears, the teeth of which impart a driving force on the teeth of the side gears intermeshed therewith. Hence, rotation of the axles, which are coupled to each other through the side gears and first pinion gears, is achieved. During differentiation, there is relative movement between the first pinion gears and the side gears, and the axles rotate at different speeds. Thus, a differential distributes the torque provided by the input shaft between the two axles and their respective driven wheels. 
     The completely open differential, i.e., a differential without clutches or springs which restrict relative rotation between the axles and the rotating differential casing, is not well suited to slippery conditions in which one driven wheel experiences a much lower coefficient of friction than the other driven wheel: for instance, when one wheel of a vehicle is located on a patch of ice and the other wheel is on dry pavement. Under such conditions, the wheel experiencing the lower coefficient of friction loses traction and a small amount of torque to that wheel will cause a “spin out” of that wheel. Since the maximum amount of torque which can be developed on the wheel with traction is equal to torque on the wheel without traction, i.e. the slipping wheel, the engine is unable to develop any torque and the wheel with traction is unable to rotate. A number of methods have been developed to limit wheel slippage under such conditions. 
     Prior means for limiting slippage between the axles and the differential casing use a frictional clutch mechanism, either clutch plates or a frustoconical engagement structure, operatively located between the rotating case and the axles. Certain embodiments of such prior means provide a clutch element attached to each of the side gears, and which frictionally engages a mating clutch element attached to the rotating casing or, if the clutch is of the conical variety, a complementary interior surface of the casing itself. Such embodiments may also include a bias mechanism, usually a spring, to apply an initial preload between the clutch and the differential casing. By using a frictional clutch with an initial preload, a minimum amount of torque can always be applied to a wheel having traction, e.g., a wheel located on dry pavement. The initial torque generates gear separating forces between the first pinion gears and the side gears intermeshed therewith. The gear separating forces urge the two side gears outward, away from each other, causing the clutch to lightly engage and develop additional torque at the driven wheels. Examples of such limited slip differentials which comprise cone clutches are disclosed in U.S. Pat. Nos. 4,612,825 (Engle), 5,226,861 (Engle), 5,556,344 (Fox), and 5,989,147 (Forrest et al.), issued Nov. 23, 1999, all of which are assigned to the assignee of the present invention and expressly incorporated herein by reference. 
     Certain prior art limited slip differentials provide, between the first of the two side gears and its associated clutch element, interacting camming portions having ramp surfaces. In response to an initiating force, this clutch element is moved towards and into contact with the surface against which it frictionally engages, which may be a mating clutch element attached to the casing, or an interior surface of the casing itself, as the case may be, thereby axially separating the clutch element and its adjacent first side gear, the ramp surfaces of their interacting camming portions slidably engaging, the rotational speed of the clutch element beginning to match that of the differential casing due to the frictional engagement. Relative rotational movement between the ramp surfaces induces further axial separation of the clutch element and the first side gear. Because the clutch element is already in abutting contact with the surface against which it frictionally engages, the first side gear is forced axially away from the clutch element by the camming portions. 
     A transfer block element disposed about the cross pin, between the pinion gears disposed thereon, is provided to transfer axial movement from the first side gear to the second side gear, which is disposed on the opposite side of the cross pin. The transfer block element is allowed to move laterally relative to the cross pin, along the axis of the axles. The transfer block element is abutted by the axially moving first side gear and is forced into abutment with the second side gear, to which is rotatably fixed a second clutch element which also operatively engages the rotating casing, thereby providing additional clutched engagement between the clutch elements and the casing. The following example, which describes a previous limited slip differential having first and second cone clutches and an electromagnetic initiating force, is illustrative: 
     FIG. 1 depicts differential  10  which comprises rotatable casing  12  constructed of joined first and second casing parts  12   a  and  12   b , respectively, and providing inner cavity  14 , which is defined by the interior surface of the circumferential wall portion of first casing part  12   a  and end wall portions  16 ,  18  of first and second casing parts  12   a ,  12   b , respectively. Disposed within cavity  14  are side gears  20 ,  22  and pinion gears  24 ,  26 . The teeth of the side gears and pinion gears are intermeshed, as shown. Pinion gears  24 ,  26  are rotatably disposed upon cylindrical cross pin  28 , which extends along axis  30 . Cross pin  28  is made of a suitable material such as, for example, heat treated 8620 steel. The ends of cross pin  28  are received in holes  32 ,  34  diametrically located in the circumferential wall of casing part  12   a . One end of cross pin  28  is provided with cross bore  36 , which is aligned with holes  38 ,  40  in casing part  12   a , as shown. Bolt  42  extends through hole  38 , cross bore  36  and hole  40  to retain the cross pin in its proper position relative to casing  12 . Portion  44  of bolt  42  is provided with threads which are engaged with hole  38 . 
     Axles  46 ,  48  are received through hubs  50 ,  52 , respectively formed in casing end wall portions  16 ,  18 , along common axis of rotation  54 , which intersects and is perpendicular to axis  30 . Axles  46 ,  48  are respectively provided with splined portions  56 ,  58 , which are received in splines  60 ,  62  of side gears  20 ,  22 , thereby rotatably fixing the side gears to the axles. The axles are provided with circumferential grooves  64 ,  66  in which are disposed C-rings  68 ,  70 , which prevent the axles from being removed axially from their associated side gears. Casing part  12   a  is provided with a large aperture (not shown) located in the circumferential wall thereof, between holes  32 ,  34 , for assembly and service access to C-rings  68 ,  70 . Terminal ends  72 ,  74  of the axles may abut against the cylindrical surface of cross pin  28 , thereby restricting the axles&#39; movement toward each other along axis  54 . 
     Clutch element  76  is attached to side gear  20  and rotates therewith. Clutch element  76  is of the cone clutch variety and has frustoconical surface  78  which is adjacent to, and clutchedly interfaces with, complementary surface  80  provided on the interior of casing part  12   a . Clutch element  82  is also of the cone clutch variety and has frustoconical surface  84  which is adjacent to, and clutchedly interfaces with, complementary surface  86  also provided on the interior of casing part  12   a . Clutch element  82  is provided with annular surface  88  which faces annular surface  90  of side gear  22 . Surface  88  is provided with a plurality of circumferentially-aligned arcuate grooves  92 . Grooves  92  are provided with surfaces which ramp “upwards” toward surface  88  one circumferential direction along the groove. Similarly, surface  90  is provided with an equal plurality of circumferentially-aligned arcuate grooves  94  having surfaces which ramp “upwards” toward surface  90 , but in an opposite circumferential direction. Disposed in each opposed pair of grooves  92 ,  94  is ball  96 . Hence, grooves  92 ,  94  and balls  96  comprise a type of interacting camming mechanism well-known in the art as a ball ramp arrangement. Briefly, relative rotation between clutch element  82  and side gear  22  imparts axial separation therebetween as balls  96  ride up on the ramp surfaces of grooves  92  and  94 . Alternatively, a surfaces  88 ,  90  may be provided with interacting cam surfaces (not shown) which project therefrom and have slidably engaging ramp surfaces which axially separate clutch element  82  and side gear  22  as they rotate relative to one another; this type of camming mechanism, too, is well known in the art. Balls  96  are urged into the deepest portions of grooves  92 ,  94 , and surfaces  88 ,  90  brought into their closest proximity to each other, by means of Belleville spring  98 , which is disposed between surface  100  of clutch element  82  and snap ring  102  received in circumferential groove  104  provided in portion  106  of side gear  22 . 
     Provided on the exterior surface of casing part  12   a  is flange  108 , to which a ring gear (not shown) is attached. The teeth of the ring gear are in meshed engagement with the teeth of a pinion gear (not shown) which is rotatably driven by an engine (not shown), thus rotating differential case  12  within an axle housing (not shown) from which axles  46 ,  48  project. As casing  12  rotates, the sides of holes  32 ,  34  bear against the portions of the cylindrical surface of cross pin  28  in the holes. The rotation of cross pin  28  about axis  54  causes pinion gears  24 ,  26  to revolve about axis  54 . The revolution of the pinion gears about axis  54  causes side gears  20 ,  22  to rotate about axis  54 , thus causing at least one of axles  46 ,  48  to rotate about axis  54 . 
     Electromagnet  110  is rotatably fixed relative to the axle housing (not shown) in which differential  10  is disposed, and is supported on casing portion  12   b  by bearing  112 . The voltage applied to electromagnet  110  may be controlled by a control system (not shown) which is in communication with sensors (not shown) which indicate excessive relative rotation between axles  46 ,  48 . Electromagnet  110  is disposed in close proximity to casing  12 , which rotates relative thereto. As the electromagnet is energized, an initiating force is applied to clutch element  82  by a toroidal electromagnetic flux path (not shown) which is established about the annular electromagnet; the flux path flows through ferrous casing portions  12   a  and  12   b  and through clutch element  82 . Clutch element  82  is thus magnetically drawn into engagement with the casing during operation of the electromagnet. 
     As shown in FIG. 1, during normal differential operation, with electromagnet  110  deactivated, surfaces  88  and  90  of clutch element  82  and side gear  22 , respectively, are closely adjacent and slightly separated. Balls  96  are urged into the deepest portions of slots  92 ,  94  by Belleville spring  98  and by gear separation forces between side gear  22  and pinion gears  24 ,  26 . As viewed in FIG. 1, Belleville spring  98  urges cone clutch element  82  rightward, axially away from snap ring  102 , and the gear separation forces urge side gear  22  leftward, toward clutch element  82 . 
     As electromagnet  110  is activated, further axial separation of cone clutch element  82  and side gear  22  is induced as cone clutch element  82  is magnetically pulled to the left, against the force of Belleville spring  98 , into clutched engagement with casing part  12  through mating frustoconical surfaces  84 ,  86 ; side gear  22  temporarily maintains its axial position. As cone clutch element  82  and side gear  22  separate axially, balls  96  are caused to rotate along the ramping paths of slots  92 ,  94  due to the relative rotation between cone clutch element  82 , which is in frictional engagement with the case, and side gear  22 ; the rotation of the balls along the slots induces yet further axial separation of cone clutch element  82  and side gear  22 , the side gear urged rightward as viewed in FIG. 1, its surface  114  abutting adjacent surface  116  of transfer block element  118 . 
     Transfer block element  118  is disposed about cross pin  28 , and held in position along the cross pin by its opposite ends abutting pinion gears  24 ,  26 . Transfer block  118  moves laterally relative to the cross pin, along axis  54 , such that rightward movement of side gear  22 , described above, is transferred to side gear  20 . Surface  120  of transfer block  118  is brought into abutting contact with surface  122  of side gear  20 . Thus, during actuation of electromagnet  110 , side gear  22  is urged rightward, as viewed in FIG. 1, into abutting contact with transfer block element  118 , which may be made of steel. Transfer block element  118  moves rightward, into abutting contact with side gear  20 ; and side gear  20  moves rightward, urging surface  78  of clutch element  76  into frictional engagement with surface  80  of case part  12   a , thereby providing additional torque transfer capacity to the differential than would otherwise be provided with single cone clutch element  82 . 
     In use, the circumferential wall of casing  12  experiences a substantial amount of stress, the entirety of the energy transferred from the engine to the axles being communicated from the rotating casing through its holes  32 ,  34  bearing on the cylindrical surface at opposite ends of the cross pin. In circumstances where an extraordinary amount of stress is exerted on casing  12 , damage thereto may occur. As mentioned above, cross pin  28  is secured to casing part  12   a  by removable, partially threaded bolt  42  which extends into aligned holes  38 ,  40  in casing part  12   a . Holes such as holes  38 ,  40 , placed near the interface of the casing and the cross pin may compromise the strength of the casing. Further, cross bore  36 , which extends through one end of cross pin  28 , may compromise the strength of the cross pin. It is desirable to eliminate holes such as  38 ,  40 , in the casing wall, and cross bores such as  36  in the ends of the cross pin, which are subject to high shear stresses. 
     Further, in particular circumstances, bolt  42  may back out of its threaded engagement in casing hole  38 , and fall out of casing holes  38 ,  40  and cross pin cross bore  36 , causing cross pin  28  to dislodge from its position within aligned bores  32 ,  34  in casing part  12   a , resulting in complete failure of the differential mechanism. Such a failure renders the vehicle in which differential  10  is installed inoperable. Bolt  42  may be caused to back out of its threaded engagement by continuous vibrations or strains placed on the casing forces during normal operation of differential  10 . A more effective means of retaining the cross pin in aligned bores  32 ,  34  is thus desirable. 
     Bolt  42  is also disposed in a somewhat inconvenient location for service purposes which require removal of the cross pin while the differential is installed in the axle housing. Because bolt  42  is rather long and is disposed such that it must be removed along a line parallel with axis  54 , access to and removal of the bolt while the differential is installed in the axle housing may be hindered. A more accessible means of detachably securing the cross pin to the differential is therefore desirable. 
     Thus, what is needed is a means of retaining the cross pin of a limited slip differential which provides greater casing strength and easier accessibility to the fastener which retains the cross pin to the casing. 
     SUMMARY OF THE INVENTION 
     The present invention provides a differential assembly including a casing which rotates about a first axis, the casing having an internal cavity; an elongate cylindrical cross pin which rotates with the casing about the first axis, the cross pin extending along a second axis through the cavity, the second axis substantially perpendicular to the first axis; at least one pinion gear disposed within the cavity and about the cross pin, the pinion gear rotatable about the second axis; and a pair of side gears disposed within the cavity and in meshed engagement with the pinion gear, the side gears rotatable about the first axis. A cross pin retention element is disposed about the cross pin. The cross pin and the retention element are fixed against substantial relative movement therebetween along the second axis, and the retention element is disposed adjacent the pinion gear. The movement of the retention element relative to the casing along the second axis is restricted, whereby the cross pin is retained in the casing. An embodiment of the inventive differential may be of the limited slip variety, in which the cross pin retention element serves as a transfer block which moves laterally relative to the cross pin. 
     The present invention also provides a differential assembly including a casing rotatable about a first axis; an elongate cylindrical cross pin fixed to the casing, the cross pin extending through the casing along a second axis substantially perpendicular to the first axis, the cross pin having a hole extending laterally therethrough; a pinion gear disposed within the casing and rotatably disposed upon the cross pin, the pinion gear revolving about the first axis; a pair of side gears intermeshed with the pinion gear; a cross pin retention element disposed about the cross pin, the retention element provided with a hole aligned with the lateral cross pin hole, the retention element disposed adjacent the pinion gear and between the side gears; and a fastener extending through the aligned retention element and cross pin holes, whereby the retention element and the cross pin are attached to each other. The cross pin is supported along the second axis within the casing by the engagement of the fastener with the retention element and cross pin holes. An embodiment of the inventive differential may be of the limited slip variety, in which the cross pin retention element serves as a transfer block which moves laterally relative to the cross pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a sectional side view of one embodiment of a prior art differential having its cross pin retained by means of a partially threaded bolt disposed through a hole formed through the differential casing and a cross bore formed in one end of the cross pin; 
     FIG. 2 is a sectional side view of a first embodiment of a limited slip differential having its cross pin retained by means of its transfer block element, in accordance with the present invention; 
     FIG. 3 is a partially-sectioned, perspective view of the differential of FIG. 2; 
     FIG. 4 is a partially exploded assembly view of the differential of FIG. 3; 
     FIG. 5 is a more fully exploded assembly view of the differential of FIG. 3; 
     FIG. 6 is a perspective view of the transfer block element and cross pin assembly of the differential of FIG. 2; 
     FIG. 7A is a perspective view of the cross pin of FIG. 6; 
     FIG. 7B is a top view of the cross pin of FIG. 7A; 
     FIG. 7C is a side view of the cross pin of FIG. 7A; 
     FIG. 7D is an end view of the cross pin of FIG. 7A; 
     FIG. 8A is a perspective view of the transfer block element of FIG. 6; 
     FIG. 8B is a top view of the transfer block element of FIG. 8A in the direction of line  8 B— 8 B; 
     FIG. 8C is an end view of the transfer block element of FIG. 8A in the direction of line  8 C— 8 C; 
     FIG. 8D is a side view of the transfer block element of FIG. 8A in the direction of line  8 D— 8 D; 
     FIG. 9A is a perspective view of the spring pin of FIG. 6; 
     FIG. 9B is a side view of the spring pin of FIG. 9A; 
     FIG. 9C is an end view of the spring pin of FIG. 9A; 
     FIG. 10 is a sectional side view of a second embodiment of a limited slip differential having its cross pin retained by means of its transfer block element, in accordance with the present invention; 
     FIG. 11 is a partially-sectioned, perspective view of the differential of FIG. 10; 
     FIG. 12 is a partially exploded assembly view of the differential of FIG. 11; 
     FIG. 13 is a more fully exploded assembly view of the differential of FIG. 11; 
     FIG. 14 is a perspective view of the transfer block element and cross pin assembly of the differential of FIG. 10; 
     FIG. 15A is a perspective view of the cross pin of FIG. 14; 
     FIG. 15B is a top view of the cross pin of FIG. 14; 
     FIG. 15C is a side view of the cross pin of FIG. 14; 
     FIG. 15D is an end view of the cross pin of FIG. 14; 
     FIG. 16A is a perspective view of the transfer block element of FIG. 14; 
     FIG. 16B is a top view of the transfer block element of FIG. 16A in the direction of line  16 B— 16 B; 
     FIG. 16C is an end view of the transfer block element of FIG. 16A in the direction of line  16 C— 16 C; 
     FIG. 16D is a side view of the transfer block element of FIG. 16A in the direction of line  16 D— 16 D; and 
     FIG. 17 is a side view of the bolt of FIG.  14 . 
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated or simplified in order to better illustrate and explain the present invention. The exemplification set out herein illustrates embodiments of the invention in several forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments disclosed below are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. 
     Referring to FIG. 2, limited slip differential assembly  10 ′ comprises differential casing  12 ′ which is constructed of joined casing parts  12   a ′ and  12   b , and further comprises cross pin  28 ′ and transfer block element  118 ′. Differential  10 ′ is substantially identical to differential  10 , described above, except as indicated herein below. 
     Referring now to FIGS. 3-5, transfer block element  118 ′ is disposed about cross pin  28 ′ and adapted to move laterally relative thereto along axis  54  to transfer movement of side gear  22  to side gear  20 , thereby engaging clutch  76  in the same manner as described above. Notably, although cross pin  28 ′ is disposed within aligned holes  32 ,  34  of casing part  12   a ′, casing  12 ′ is not provided with holes  38 ,  40 , and cross pin  28 ′ is not provided with cross bore  36  at one end thereof, and differential  10 ′ does not rely on bolt  42  to retain the cross pin to the casing. As shown in FIG. 6, transfer block element  118 ′ is attached directly to cross pin  28 ′ by means of spring pin or roll pin  123 . Spring pin  123  (FIG.  9 ), which comprises a rolled sheet of spring steel, extends through centrally-located cross bore  124  which extends perpendicularly to axis  30  through cross pin  28 ′. Spring pin  123  is retained in cross bore  124  by means of an interference fit. Cross pin  28 ′ is shown FIGS. 7A-7D. Notably, as with cross pin  28 , the shear loads associated with torque transmission are exerted on cross pin  28 ′ near its opposite ends, particularly between the circumferential wall of casing part  12   a ′ and the adjacent pinion gears  24 ,  26 . At the longitudinal center of cross pin  28 ′, where cross bore  124  is located, there is no substantial shear stress exerted on the cross pin. Further, vis-a-vis casing part  12   a , casing part  12   a ′ is stronger near hole  34 , for there is no discontinuity in the casing caused by the provision of holes  38 ,  40 . 
     As shown in FIGS.  6  and  8 A- 8 D, like transfer block element  118 , transfer block element  118 ′ includes opposite bearing sides  116 ,  120  for transferring movement of side gear  22  to side gear  20 , as described above, and allows terminal ends  72 ,  74  of axles  46 ,  48 , respectively, to abut the cylindrical side surface of the cross pin. Lateral movement of the transfer block element relative to the cross pin is accommodated by aligned first oblong apertures  126 ,  128  through which the cross pin extends, the diameter of the cross pin slightly smaller than the width (i.e., in a direction perpendicular to both axes  30  and  54 ) of apertures  126 ,  128 , as in differential  10 . Length “L” of oblong apertures  126 ,  128  (FIG. 8C) extends in directions along axis  54 . Spring pin  123  extends through aligned second oblong apertures  130 ,  132  which restrict movement of cross pin  28 ′ along axis  30  while permitting movement of the transfer block element along axis  54 , the diameter of cross bore  124 , and thus of pin  123  inserted therein, somewhat smaller than the width (i.e., in a direction parallel to axis  30 ) of apertures  130 ,  132 . Length “l” of apertures  130 ,  132  (FIG. 8B) extends in directions along axis  54 . Surfaces  134 ,  136  of transfer block element  118 ′ abut pinion gears  24 ,  26 , respectively, as in differential  10 , thereby restricting movement of the transfer block element, and thus the cross pin, relative to casing  12 ′ along axis  30 . Thus it will be understood that transfer block  118 ′ serves as a cross pin retention element. 
     Notably, the cross pin&#39;s movement along axis  54  is restricted by the interface between cross pin  28 ′ and the sides of first oblong apertures  126 ,  128 . That is, the length (i.e., in a direction parallel to axis  54 ) of oblong first apertures  126 ,  128  is slightly greater than that of oblong second apertures  130 ,  132 , and roll pin  123  experiences no substantive shear stress along the directions of axis  54 . The only shear stress which pin  123  experiences is that minor amount associated with supporting the weight of cross pin  28 ′ in the directions along axis  30 , which stress will vary as casing  12 ′ rotates from no stress, when cross pin  28 ′ is horizontal, to a maximum stress, when cross pin  28 ′ is vertical. Notably, surface  138  of transfer block  118 ′ is provided with shallow counterbore  140  surrounding oblong second aperture  130 . In differential  10 ′ counterbore  140  faces a large aperture (not shown) located in the circumferential wall of casing part  12   a ′ between holes  32 ,  34 , for assembly and service access to spring pin  123  and C-rings  68 ,  70 . The tip of one terminal end of spring pin  123  projects into and is exposed within counterbore  140  so that the spring pin may be grasped with a tool, such as, for example, a pair of pliers, and squeezed to a smaller diameter for installation into and removal from cross pin counterbore  124 . Alternatively, pin  123  may be driven into place by tapping one end of thereof with a hammer. 
     Transfer block  118 ′ is provided with U-shaped recesses  142 ,  144  which allow C-rings  68 ,  70  to be installed while transfer block  118 ′ remains in place. This is done by removing cross pin  28 ′ and sliding axles  46 ,  48  inward to that their terminal ends  72 ,  74  extend into central aperture  148 , thereby exposing circumferential grooves  64 ,  66  within U-shaped recesses  142 ,  144 . C-rings  68 ,  70  may then be respectively positioned in grooves  64 ,  66 . Once C-rings  68 ,  70  are in place in grooves  64 ,  66 , axles  46 ,  48  are pulled outwardly until the C-rings are respectively seated into counterbores  145 ,  146  provided in side gears  20 ,  22 . Cross pin  28 ′ is then installed, the inward motion of the axles restricted by their terminal ends  72 ,  74  being in abutment with the axially-extending cylindrical surface of the cross pin. Transfer block  118 ′ is also provided with central aperture  148  which allows terminal ends  72 ,  74  of the axles to abut the cylindrical side surfaces of cross pin  28 ′. 
     A second embodiment of the present invention is shown in FIGS. 10-17. Differential  10 ″ also comprises differential casing  12 ′ and is substantially identical to differential  10 ′ except as indicated hereinbelow. Rather than comprising transfer block  118 ′, cross pin  28 ′ and spring pin  123 , differential  10 ″ instead comprises transfer block element  118 ″, cross pin  28 ″ and bolt  150 . 
     Referring now to FIGS. 11-13, transfer block element  118 ″ is disposed about cross pin  28 ″ and adapted to move laterally relative thereto along axis  54  to transfer movement of side gear  22  to side gear  20 , thereby engaging clutch  76  in the same manner as described above. Notably, as in first embodiment differential  10 ′, cross pin  28 ″ is disposed within aligned holes  32 ,  34  of casing part  12   a ′; casing  12 ′ is not provided with holes  38 ,  40 , and cross pin  28 ″ is not provided with cross bore  36  at one end thereof. As shown in FIG. 11, transfer block element  118 ″ is attached directly to cross pin  28 ″ by means of bolt  150 . Bolt  150  (FIG. 17) comprises cylindrical elongate, nonthreaded portion  152  which extends between terminal end  154  and threaded portion  156 . Adjacent threaded portion  156  is flanged head  158 . Portion  152  of bolt  150  extends through centrally-located, oblong cross hole  160  which extends perpendicularly to axis  30  through cross pin  28 ″. Length “l” of oblong aperture  160  (FIG.  15 BB) extends in directions along axis  54 . The diameter of bolt portion  152  is somewhat smaller than the width of cross hole  160 , i.e., in a direction parallel to axis  30 . Cross pin  28 ″ is shown FIGS. 15A-15D. Again, as in cross pin  28 ′, the shear loads associated with torque transmission are exerted on cross pin  28 ″ near its opposite ends, particularly between the circumferential wall of casing part  12   a ′ and the adjacent pinion gears  24 ,  26 , and at the longitudinal center of cross pin  28 ″, where cross hole  160  is located, there is no substantial shear stress exerted on the cross pin. 
     As shown in FIGS.  14  and  16 A- 16 D, like transfer block  118 ′, transfer block element  118 ″ includes opposite bearing sides  116 ,  120  for transferring movement of side gear  22  to side gear  20 , as described above, and allows terminal ends  72 ,  74  of axles  46 ,  48 , respectively, to abut the cylindrical side surface of the cross pin. Transfer block element  118 ″ is provided with aligned holes  162 ,  164 , the former being threaded to received threaded portion  156  portion of bolt  150 , the latter receiving the terminal end of cylindrical nonthreaded portion  152 . As in first embodiment differential  10 ′, lateral movement of the transfer block relative to the cross pin is accommodated by aligned first oblong apertures  126 ,  128  through which the cross pin extends. Length “L” of oblong apertures  126 ,  128  (FIG. 16C) extends in directions along axis  54 . Bolt portion  152  extends through cross hole  160  in cross pin  28 ″, which restrict movement of cross pin  28 ″ along axis  30  while permitting movement of the transfer block along axis  54 . Surfaces  134 ,  136  of transfer block element  118 ″ abut pinion gears  24 ,  26 , respectively, as in differential  10 ′, thereby restricting movement of the transfer block, and thus the cross pin, relative to the casing along axis  30 ; transfer block  118 ″ thus serving as a cross pin retention element. Notably, as described above, the cross pin&#39;s movement along axis  54  is restricted by the interface between cross pin  28 ″ and the sides of first oblong apertures  126 ,  128 ; bolt  150  experiences no substantive shear stress along the directions of axis  54 . The only shear stress bolt  150  experiences is that associated with supporting the weight of cross pin  28 ″ in the directions along axis  30 , which stress will vary as casing  12 ″ rotates from no stress, when cross pin  28 ″ is horizontal, to a maximum stress, when cross pin  28 ″ is vertical. Notably, surface  138  of transfer block  118 ″ is provided with shallow counterbore  140  surrounding hole  162 , the flange of the bolt head received in the counterbore. In similar fashion to differential  10 ′, counterbore  140  faces a large aperture (not shown) located in the circumferential wall of casing part  12   a ′ between holes  32 ,  34 , for assembly and service access to bolt head  158  and C-rings  68 ,  70 . 
     Those skilled in the art will recognize that application of the above-described, inventive cross pin retention means may also be beneficially applied to open differentials. Such embodiments of the present invention (not shown) need not provide the ability to move the block element laterally relative to the cross pin along axis  54 , to provide the above-mentioned advantages regarding durability and service accessibility. Rather, the block element may serve to only retain the cross pin within the casing in the manner disclosed above. 
     While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.