Abstract:
A differential for a wheel set provided with three modes of operation. A stub axle and wheel axle in combination provide drive torque to one wheel of the wheel set. A single wheel axle provides torque to the other wheel of the wheel set. The stub axle and wheel axle are releasably interconnected by a clutch ring and when connected provide conventional differential operation including equalized torque applied from a propeller shaft to the wheels of the wheel set. Alternatively the clutch ring can also provide connection to the differential casing to insure common rotation of the two wheels. In the third mode, the clutch ring does not connect any of the components and the non-resisted rotation of the stub axle effectively disconnects the wheel axles from the propeller shaft. An actuator provides actuation from a position at the exterior of the differential into and through the case to the clutch ring. The actuator includes bearing type interconnections to achieve axial movement even though the components have different rates of rotation.

Description:
FIELD OF THE INVENTION 
     This invention relates to a vehicle differential having multiple modes of operation and more particularly to a shift mechanism for shifting the differential between the different modes. 
     BACKGROUND OF THE INVENTION 
     A substantial number of vehicles are designed to have the versatility of two-wheel drive and four-wheel drive. In two-wheel drive, either the front pair of wheels or the rear pair of wheels are connected to the vehicle&#39;s power source. In four-wheel drive, both the front and rear pair of wheels are connected to the power source. 
     Each pair of wheels have a pair of axles connected to a differential which in turn is connected to a propeller shaft driven by the vehicle&#39;s power source. A front propeller shaft is connected to the front differential and a rear propeller shaft is connected to the rear differential. One of the propeller shafts is disconnected from the vehicle&#39;s power source for two-wheel drive. 
     Referring to the differential for the wheel set that can be connected and disconnected from the power source (commonly the front wheel set or front pair of wheels), the primary function of the differential is to permit the left and right wheels to rotate at different speeds. This is accomplished by a gear assembly that includes a differential case that is rotatably driven by the propeller shaft. Opposing side gears in the differential case are coupled to the axles and the opposing side gears are coupled together by pinion or spider gears commonly referred to as differential gears which are rotatably mounted to the case of the differential. 
     The arrangement of gears in the differential transmits torque from the propeller shaft to the axles which in turn transmits the torque to a pair of front end or rear end wheels. The torque of the axles is always equal regardless of the speed of the axles relative to each other. When the axles are connected to wheels having similar tractive capacity, the axles rotate equally or, if the vehicle is in a turn, they rotate differently according to the turning radius of each wheel. Differential axle rotation in this case is desirable for normal vehicle operation. When the axles are connected to wheels having substantially different tractive capacity, the wheel having lesser tractive capacity may slip, thus causing the axle connected to it to turn faster than the axle connected to the wheel having greater tractive capacity. Differential axle rotation in this case is undesirable for normal vehicle operation. 
     The above explanation explains two circumstances or modes for a differential, i.e., allowing the differential to provide differential axle rotation and preventing differential axle rotation. A third desired mode occurs when the propeller shaft for that set of wheels is disconnected from the vehicle&#39;s power source, i.e., the vehicle is placed in two-wheel drive. Once the propeller shaft is disconnected from the power source, the propeller shaft is passive (it does not convey a driving torque). However, it is still driven in that the wheels of that wheel set are forced to turn as the vehicle is driven in two-wheel drive and they drive the axles which drive the differential gears which drive the propeller shaft. In this event, it is desirable to separate or disconnect the propeller shaft from the driven axles (the third mode) to avoid unnecessary rotation of the propeller shaft and thereby save energy and wearing. 
     Accordingly, it is an object of the present invention to provide a shift mechanism for the differential for shifting the differential between the above-explained three modes. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In a preferred embodiment of the present invention, the propeller shaft is connected to a pinion gear that drives a ring gear that is connected to a differential case. The differential case (through a cross pin and spider gears) rotates opposing side gears, one of which rotates a first wheel axle and the other a stub axle. The stub axle is adjacent a second wheel axle and a clutch ring is movable between a position of engagement with only the stub axle or a position of engagement with both the stub axle and second wheel axle. 
     If the stub axle is locked to the second wheel axle, the wheels are driven as is typical for a differential as explained above. If the stub axle is unlocked from the second wheel axle, the stub axle rotates freely, i.e., with very little resistance in either direction of rotation. In such case, the propeller shaft is effectively uncoupled from the wheel axles. The first wheel axle, which is connected to the differential assembly will simply drive the differential gears and stub axle (and not the differential case) and thereby allow the propeller shaft and the ring gear and pinion gears to remain idle, assuming that the propeller shaft is also disconnected from the power source. 
     The clutch ring has a third position of engagement whereby it not only locks the stub axle to the second wheel axle but it locks both to the differential case. If either one of the wheel axles are locked to the case, the gears of the case are locked together and prevent relative rotation. Thus, both wheel axles are locked to the differential case and differential rotation of the wheels is prevented. 
     The structure for achieving this three mode positioning includes a clutch ring with inner and outer teeth. The stub axle and second wheel axle are in close adjacency and have matching outer splines. The inner teeth of the clutch ring produce engagement as between the stub axle and the second wheel axle. The differential case is configured to have a ring-shaped or flange portion with inner splines in close proximity to the juncture of the stub axle and second wheel axle. These inner splines of the case are matched to the outer splines of the clutch ring for engagement therebetween. In the desired arrangement, the clutch ring can be moved first into engagement with both axle portions and then, as desired, into engagement also with the inner splines of the differential case. 
     An actuator for actuating movement of the clutch ring includes an inner shift spring assembly connected to posts that extend axially through the differential case to position outside the case and connect to an outer shift ring. The shift ring, shift ring assembly and shift posts rotate with the case but have limited axial movement relative to the case. A shift shaft is coupled to the outer shift ring outside the differential case. The clutch ring is coupled to the inner shift spring assembly and posts at a position inside the differential case. 
     The shift shaft protrudes through the differential carrier where a power source produces the desired linear shifting movement of the shift shaft. The shift shaft does not rotate with the shift ring and thus the coupling to the outer shift ring includes a shift fork including bearing members that allow relative rotation as between the outer shift ring and shift fork but not axial/linear movement. This linear movement of the shift shaft produces linear movement of the shift fork and thus linear movement of the outer shift ring and posts. The clutch ring is rotatably fixed to the stub axle and in two of the three modes has to be capable of rotative motion relative to the differential case and thus the outer shift ring and posts. Thus, the coupling as between the posts and clutch ring includes bearing members (provided by the shift spring assembly) that allows relative rotation as between the posts/shift ring. Thus, linear movement of the shift rings (induced by the shift shaft) induces similar linear movement of the clutch ring. 
     The clutch ring movement is not always subject to instant selective movement and thus the coupling between the posts/shift ring and clutch ring is accomplished by compliant members of the spring assembly which urge the clutch ring into engagement. In the event the splines of the components to be engaged are not in alignment, the clutch ring is thus spring loaded toward engagement and achieves engagement when the splines become aligned. It can also happen that the splines become torque locked when disengagement is attempted and the compliant springs will similarly become spring locked until torque lock up is released. 
     The features as described above will be more fully understood and appreciated upon reference to the following detailed description and the accompanying drawings referred to therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a vehicle chassis illustrating an arrangement of a drive train including a differential as may incorporate the present invention; 
     FIG. 2 is a cross sectional view of a differential incorporating the present invention; 
     FIG. 3 is a perspective view of the differential of FIG. 2 excluding the carrier portion; 
     FIG. 4 is a perspective view of a shifting mechanism provided for the differential of FIGS. 2 and 3; and 
     FIG. 5 is a frontal view of certain of the components of the shifting mechanism of FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is made to FIG. 1 which substantially illustrates a drive train of a vehicle. Illustrated are front wheels  10  and rear wheels  12 . An engine  14  drives a drive shaft  16  connected to a transmission  18 . The transmission drives a rear wheel propeller shaft  20  connected to a rear wheel differential  22  that drives rear wheel axle  24  which in turn drives the rear wheels  12 . A drive connection from the transmission to a transfer case  28  drives a front wheel propeller shaft  30  connected to a front wheel differential  32 . The front wheel differential is connected to front axles  34  which drive the front wheels  10 . 
     As illustrated, the shift mechanism for shifting into and out of four-wheel drive occurs at the transfer case  28  and places front wheel propeller shaft  30  into and out of engagement with the transmission  18  and thus the drive shaft  16  of the engine  14 . The invention is accordingly incorporated into the front differential  32  although it will be understood that the drive train can be arranged to provide the shift mechanism to engage and disengage rear wheel propeller shaft  20  in which case the invention would be incorporated into rear differential  22 . Hereafter whereas the differential may be described as the front differential, it will be understood that such is for descriptive convenience and the invention just as readily can and does apply to the rear wheel differential. 
     Reference is now made to FIG. 2 which illustrates front differential  32  including an outer fixed housing referred to as a carrier  50 . Connected into the left side of the differential carrier (as illustrated) is left axle  34 L and connected into the right side of the differential is right axle  34 R. Axle  34 L terminates at end  40  which is spline fit to a side gear  42 . Axle  34 R terminates at end  44  which is interfit with stub axle  46 . End  44  is rotatable relative to stub axle  46 . Stub axle  46  is spline fit to a second side gear  48  which opposes side gear  42 . 
     Rotatably mounted in the carrier  50  and surrounding the axle ends  40 ,  44 ,  46  and side gears  42 ,  48  is a differential case  52  that rotates relative to the carrier on bearings  54 . Mounted to the case are opposed spider or differential gears  56 , only one of which is shown in FIG.  2 . Spider gears  56  are rotatable relative to case  52  on pivot shaft  58  and they are in splined engagement with opposed side gears  42 ,  48  connected to axle end  40  and stub axle  46 , respectively. 
     Connected to the differential case  52  is propeller shaft  30  which rotatably drives pinion gear  60  (rotatably mounted in differential carrier  50  by bearing  62 ). Gear  60  has gear teeth interfit with gear teeth of ring gear  64  which is bolted to differential case  52  by bolts  66 . Thus, as propeller shaft  30  is rotatably driven by the engine  14 , transmission  18  and transfer case  28 , that rotation is transferred to the differential case  52  which rotates about axis  68  (which also the axis of axles  34 ). As the case  52  is rotated about axis  68 , so too is the pivot shaft  58  of gears  56 . 
     In a conventional differential arrangement, the separate stub axle  46  and axle  34 R are provided as a single axle that is interfit to gear  48  in a manner similar to axle  34 L and gear  42 . As the case  52  and the shaft  58  with gears  56  are rotated about axis  68  (by propeller shaft  30 ), the interfit between gears  56  and gears  42 ,  48  provides for common rotation of axles  34 L and  34 R. This assumes that the resistance to the turning of axles  34 R and  34 L is similar in which case the gears  56  do not rotate around the axis of pivot shaft  58 . Should one of the axles  34 L,  34 R generate a greater resistance to turning than the other, gears  56  rotate about pivot shafts  58  to equalize the torque applied to the two axles and thereby permit differential rotation of the axles. 
     The above operation of the differential is well known to those skilled in the art and further explanation is not necessary. As explained in the introductory portion, the accommodation of differential turning of axles  34 L and  34 R is desirable at times, e.g., when turning the vehicle (which requires the outside wheels to turn faster than the inside wheels) and undesirable at other times (when one wheel of the vehicle loses traction due to engagement with ice or mud on the roadway). As also discussed in the introductory portion, with the propeller shaft  30  disconnected from the engine, it is desirable to disconnect the propeller shaft also from the rotating wheels  10  so that the propeller shaft  30  is permitted to not rotate. The multiple modes for the differential including disconnect as between the wheels and propeller shaft; fixed common rotation of the wheels; and permitted differential rotation of the wheels; is provided by the invention as will now be explained. 
     As explained, axle  34 R is rotatable relative to stub axle  46 . A coupler  70  is provided on the end  44  of axle  34 R. A splined clutch ring  76  engages splines  74  of stub axle  46  and is slidable into an engagement also with splines  72  of coupler  70 . With the clutch ring  76  engaging both the stub axle  46  and axle  34 R, the stub axle  46  and axle  34 R are interlocked. With the clutch ring slid out of engagement with axle  34 R, the axle  34 R and stub axle  46  are free to rotate independently. 
     As can be seen from FIG. 2, the juncture of the axle  34 R and stub axle  46  is contained within case  52 . A flange  78 ,of the case defines a peripheral wall surrounding coupler  70 . The flange  78  is provided with inwardly directed splines  80  that project into the path of the slidable clutch ring  76 . Outwardly directed splines  82  on the clutch ring  76  engage spline  80  on flange  78 . In a first position, the clutch ring can be slid (to the left in FIG. 2) into engagement with stub axle  46  only. In a second position, it can be slid to the right into engagement also with the splines of the axle  34 R. In a third position, it can be slid further to the right into engagement with the splines  80  of case  52  while maintaining engagement with both the stub axle  46  and axle  34 R. 
     The effect of placing the clutch ring in the three positions will be described. With the clutch ring in the center position (engaging both stub axle  46  and axle  34 R and not case  52 ), the differential functions in the conventional manner. If the traction on the two wheels is equal, the propeller shaft drives case  52  which rotates gears  56  about axis  68 , and gears  56  through engagement with gears  42 ,  48  commonly rotate both axles  34 L and  34 R. When turning the vehicle, because the inside wheel travels slower than the outside wheel, the rotational speed of the axles is unequal and the gears  56  will rotate about the pivot shafts  58  to accommodate the travel difference. Should one of the wheels lose traction (e.g., due to ice on the road), that wheel will spin freely and torque will be greatly reduced to both wheels. 
     By shifting the clutch ring to the far right position, the splines  82  of the clutch ring  76  engages splines  80  of the case  52 . The case  52  and axle  34 R (and stub axle  46 ) all rotate together. Shaft  58  rotates around axis  68  at the same rate as axle  34 R and thus the same as gear  48 . This prevents turning of gear  56  about its pivot shaft  58  and because gear  42  is engaged with gear  56 , axle  34 L similarly rotates with case  52  and axle  34 R. There can be no relative turning as between the wheels  10  in this mode. 
     By shifting the clutch ring to the far left, the clutch ring is out of engagement with both axle  34 R and case  52  and stub axle  46  rotates freely relative to both axle  34 R and case  52 . This mode is intended when the propeller shaft  30  is disconnected from the engine at the transfer case and it is desirable to allow the propeller shaft  30  to be passive. However, the wheels will rotate when driven which rotates axles  34 L and  34 R and if the axles are connected to the propeller shaft  30 , the propeller shaft will be driven by the wheels rather than the engine. By disconnecting the axle  34 R from the stub axle  46 , there is virtually no resistance to turning of gear  48  in either direction of rotation. Now axle  34 L (via gear  42 ) urges rotation of gear  56  about pivot shaft  58  and thus urges reverse rotation of gear  48 . Because stub shaft  46  offers no resistance to turning, it freely rotates which avoids forcing the case  52  to turn and allows propeller shaft  30  to thereby remain idle. 
     Actuation of Clutch Ring 
     Referring to FIGS. 2-6, it will be appreciated that clutch ring  76  is surrounded by the case  52 . Case  52  rotates at a different rate (at least some of the time) than clutch ring  76  and whatever actuation is provided for shifting the clutch ring, it has to accommodate this different rate of rotation. In this preferred embodiment, a plurality of shift posts  84  are protruded through openings in the case  52  and they are secured to a shift ring  86 . Shift ring  86  and shift posts  84  rotate with the case  52  but are axially slidable relative to the case  52 . Opposite the shift ring at the inner end of the posts  84  are shift springs  88  located on opposed sides of flange  90  of clutch ring  76  (see also FIGS.  4  and  5 ). Thus, axial movement of shift posts  84  urges axial movement of the clutch ring  76 . The springs  88  provide a bearing (similar to a shift fork) that accommodates relative rotation as between the clutch ring and shift posts. The springs  88  also accommodate engagement delay, i.e., should the splines of the clutch ring be misaligned with the splines  72  of the coupler  70  or the splines  80  of the case  52 , the springs  88  will flex and provide urging engagement and eventually engagement when the respective splines become aligned. Similarly when disengagement is attempted, the splines may be torque locked and disengagement prevented until release of the lock up. The springs will become loaded and provide disengagement upon release of the lock up. 
     Movement of the shift ring  86  is provided by shift shaft  92  which protrudes through carrier  50 . Carrier  50  doesn&#39;t rotate and thus the shift shaft  92  carries shift fork  94  which rides in a groove  96  provided in the periphery of the shift ring  86 . The shift fork provides a bearing for accommodating relative rotation of the shift ring  86 , i.e., the shift fork slides within the groove  96 . 
     The shift shaft  92  is provided with three positioning grooves  98 , one for each of the three positions of the clutch ring and a positioning ball  100  is urged into the respective grooves  98  to resistively permit movement out of the respective positions. In operation, the shift shaft may be moved between the positions (grooves  98 ), e.g., by a motor to shift the clutch ring. As explained, shifting of the clutch ring via the shift shaft is accomplished by accommodating the rotation of the shift ring via the shift fork  94  and then the relative rotation of the clutch ring via the springs  88 . 
     Those skilled in the art will likely conceive of various modifications and changes to the above preferred embodiment whole still incorporating the invention as determined from the claims appended hereto.