Abstract:
A differential, comprising a gear case, a side gear, an actuator, and a collar. The gear case comprising a central axis and recesses. The side gear configured to rotate around the central axis. The side gear comprising radially outward-extending locking members comprising side gear segments separated by plural grooves. The actuator surrounding the central axis. The collar configured to translate bi-directionally along the central axis. The collar comprising ears and radially inward-extending locking members comprising collar segments separated by plural grooves. The actuator is configured to move the collar relative to the side gear to move the ears axially in the recesses. When the actuator moves the collar to a locked position, the collar segments are configured to engage the side gear segments. When the actuator moves the collar to an unlocked position, the side gear segments are configured to pass through the grooves of the radially inward-extending locking members.

Description:
PRIORITY 
     This application claims the benefit of priority of U.S. provisional patent application 61/683,298, filed Aug. 15, 2012, incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to locking differentials. More specifically, the disclosure relates to locking differentials of the collar style having a low stroke length yet high engagement length. 
     BACKGROUND 
     Traction modifying locking differentials typically include a gear case defining a gear chamber, and disposed therein, a differential gear set including at least one input pinion gear and a pair of output side gears. Typically, such a “locking differential” includes a locking mechanism to selectively prevent rotation of one of the side gears relative to the gear case, the engagement of the locking mechanism being initiated by an actuator. 
     The torque capacity of the locking mechanism in a locking differential is a function of the axial travel of the locking mechanism, as it moves between the locked and unlocked conditions. The travel of the locking mechanism is limited by the axial travel of an “inner ramp plate” disposed adjacent the differential case. By way of example only, in a commercial embodiment of a locking differential made in accordance with the teachings of U.S. Pat. No. 6,551,209, the locking members have an axial travel of about 4 mm and an effective “locking engagement” of about 3 mm. In another example within the teachings of U.S. Pat. No. 7,264,569, the differential has a locking member with a travel of about 8 mm to 12 mm and an engagement length of about 8 mm. 
     SUMMARY 
     The present disclosure proposes a locking differential with a low stroke length, low travel, and a high locking engagement length. 
     A differential comprises a gear case comprising a central axis and recesses. A side gear is configured to rotate around the central axis. The side gear comprises radially outward-extending locking members. The radially outward-extending locking members further comprise side gear segments separated by plural grooves. An actuator surrounds the central axis. A collar is configured to translate bi-directionally along the central axis. The collar comprises ears and radially inward-extending locking members. The radially inward-extending locking members further comprise collar segments separated by plural grooves. The actuator is configured to move the collar relative to the side gear such that the ears move axially in the recesses. When the actuator moves the collar to a locked position, the collar segments are configured to engage the side gear segments. When the actuator moves the collar to an unlocked position, the side gear segments are configured to pass through the grooves of the radially inward-extending locking members. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an axial cross-section of a locking differential in its un-actuated, unlocked condition. 
         FIG. 2  is a view taken from the left in  FIG. 1  with the end cap removed. 
         FIG. 3  is an alternative view of a locking differential in an un-actuated, unlocked condition. 
         FIG. 4  is a view of a biasing spring arrangement with the collar in a locked condition. 
         FIG. 5  is an axial cross-section showing the locking differential in its un-actuated, unlocked condition, and illustrating the “travel” of the locking mechanism. 
         FIG. 6A  is a view of the locked condition illustrating the alignment and face-to-face engagement of the segments. 
         FIG. 6B  is another view of the locked condition. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the examples illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  is an axial cross-section of a locking differential. The locking differential shown in  FIG. 1  includes a gear case  11  and an end cap  12 , which may be attached to the gear case  11  by any suitable means, such as a plurality of bolts (not shown). The gear case  11  and the end cap  12  cooperate to define a gear chamber, generally designated  13 . The gear case  11  defines annular hub portions  27  and  29 , on which may be mounted bearing sets for providing rotational support for the rotating differential device relative to an outer differential housing or “carrier” (not shown). 
     Torque input to the locking differential is typically by means of an input ring gear which may be attached to a flange  15 . Disposed within the gear chamber  13  is a differential gear set including a pair of input pinion gears  17 . As is typical, the input pinion gears  17  are mounted rotatably about a pinion shaft  18 , the pinion shaft  18  being secured relative to the gear case  11  by any suitable means. The pinion gears  17  comprise the input gears of the differential gear set, and are in meshing engagement with a pair of side gears  19  and  21 . The side gears  19  and  21  define sets of internal, straight splines  23  and  25 , which are configured to be in splined engagement with mating external splines on a pair of axle shafts (not shown). 
     During normal, straight ahead operation of the vehicle, no differentiation occurs between the left and right axle shafts, or between the left and right side gears  19  and  21 . Therefore, the pinion gears  17  do not rotate relative to the pinion shaft  18 . The pinion shaft  18  rotates as an outer ring gear, surrounding the case, is rotated. As a result, the gear case  11 , the pinion gears  17 , and the side gears  19  and  21  all rotate about an axis of rotation A, as if comprising a solid unit. When the vehicle turns, the side gears  19  and  21  can rotate at different rates because they can rotate against the pinion gears  17 . If a locked condition is desired, the side gears  19  and  21  can be locked from differential rotation by preventing at least one of the side gears  19  and  21  from rotating at a rate different from the case rotation rate. In the illustrated example, the locked mode entails locking one side gear  19  to rotate with the case. Because this in effect prevents the pinion gears  17  from rotating about the pinion shaft  18 , the other side gear  21  cannot rotate at a rate that is different from the first side gear, and the other side gear  21  rotates at the same rate as the case. 
     Referring now primarily to  FIG. 1 , the locking differential includes a rotation prevention mechanism, generally designated  31 , which is disposed entirely within the gear case  11  and is operably associated with the side gear  19 . The locking differential also includes an actuation mechanism, generally designated  33 , which is external to the gear case  11  in this example. 
     The rotation prevention mechanism  31  comprises a generally annular collar  35  which includes, about its outer periphery, a plurality of ears  37 , shown in  FIGS. 2 and 4 . By way of example only, there are provided six ears  37 . Each of the ears  37  is received within a mating, axially-extending recess  39  defined by the gear case  11 , such that the collar  35  is prevented from rotating relative to the gear case  11 , but is permitted to move axially between the locked position shown in  FIGS. 6A and 6B  and an unlocked position shown in  FIGS. 3 ,  4  and  5 . 
     Disposed about an inner periphery of the collar  35  are a plurality of collar lock members  41 . Interdigitated therewith is a plurality of side gear lock members  43  disposed about an outer periphery of the side gear  19 . By way of example only, there are nine of the collar lock members  41  and nine of the side gear lock members  43 . Each collar lock member  41  has a circumferential gap between the next, and each side gear lock member  43  has a circumferential gap between the next. The gaps are sufficient to enable the collar lock members  41  to slide between the side gear lock members  43  in the direction out of the page in  FIG. 2 . That is, the collar  35  can slide along an axis in the direction out of the page of  FIG. 2  so that the collar lock members  41  pass between the side gear lock members  43 . The gaps can be adjusted to offer minimal clearance between lock members. Or, the gaps and number of lock members can be adjusted to have much greater clearances between lock members so as to have a minimum number of lock members, sufficient only to provide adequate force to engage the collar  35  with the side gear  19 . However, the lock members must have enough clearance to facilitate movement of the collar member  35  from its unlocked position (shown in  FIGS. 3 ,  4  and  5 ) to its locked position (as shown in  FIGS. 6A and 6B ). 
     Additionally, each lock member is segmented by having grooves therein. That is, collar lock member  41  comprises six segments  72  and side gear  19  comprises six segments  71 . The segments and grooves allow the side gear  19  to rotate relative to the collar  35  even while the collar lock members  41  remain in proximity to the side gear lock members  43 . The side gear segments  71  pass between the collar segments  72  when the differential is unlocked, yet the side gear segments  71  are in face-to-face engagement with the collar segments  72  when the differential is locked. 
     While the segments and grooves are illustrated as having squared edges, the segments and grooves may have rounded or beveled edges, or the segments may taper along their length or width with or without rounded or beveled edges. In addition, each collar segment  72  may be parallel to each other collar segment  72 . The collar segments  72  may be polyhedrons, each with a central axis along its longest length, and the longest central axis of each collar segment  72  may be parallel to each other collar segment. This is likewise for the side gear segments  71 , so that each side gear segment  71  may be parallel to each other side gear segment. Each side gear segment may be a polyhedron having a longest central axis, the longest central axis may be parallel to each other longest central axis of the other side gear segments. To enable the smooth rotation of the collar with respect to the side gear, each longest central axis of each side gear segment may be parallel to each longest central axis of each collar segment. 
       FIG. 1  represents the “unlocked” condition of the rotation prevention mechanism  31 .  FIGS. 6A and 6B  represent the “locked” condition. In  FIG. 2 , the lock members  41  and  43  are centered relative to each other to show a position where the collar  35  can slide relative to the side gear  19 .  FIGS. 6A and 6B  show that each collar lock member  41  can be in face-to-face engagement with an adjacent side gear lock member  43  to lock the differential. Each side gear segment  71  abuts a collar segment  72  in a manner that does not allow the rotation of the side gear  19  relative to the collar  35 . That is, the collar  35  slides so that the grooves in the collar  35  no longer align with the side gear segments  71  and the grooves in the side gear  19  no longer align with the collar segments  72 . A narrow face on the side gear segment  71  abuts a narrow face on a collar segment  72 . While the rotation direction of the side gear  19  has been shown in  FIGS. 6A and 6B  to be clockwise with respect to  FIG. 2 , rotation in the opposite direction is also possible. 
     The combination of lock members and segments, as disclosed, greatly reduces the travel necessary to lock and unlock the differential. The collar must axially move only the width of a segment to engage or disengage the lock members. A clearance distance can be included to accommodate a clearance length between collar segments  72  and side gear segments  71 . 
     As seen in  FIG. 5 , the side gear  19  may also comprise a lip  62 . The lip  62  may be sized to prevent the collar from moving past the side gear segments  71  toward the end cap  12 . A clearance gap may be present between the lip  62  and the side gear segments  71  to allow collar segments  72  to freely rotate in the clearance gap. 
     Compared to prior direct acting coils, the disclosed locking differential has a low stroke length and a high locking engagement length. That is, prior differentials with direct acting coils have a low force and low travel length, which limits the total engagement length. The prior engagement length was equal to the coil travel minus the clearance.
 
Prior Engagement Length=(coil travel−clearance)  Eq. 1.
 
     By creating multiple engagement overlaps via the segments, the new locking mechanism total engagement length is not limited to the length of travel of the coil travel. Instead, the engagement length can be determined as the coil travel minus the clearance times the number of overlaps.
 
New Engagement Length=(coil travel−clearance)×(number of overlaps)  Eq. 2.
 
     Referring again to  FIG. 1 , and in conjunction with  FIG. 3 , the gear case  11  defines a plurality of cylindrical openings  45 . Slidably disposed within each opening  45  is an elongated, generally cylindrical actuation member  47 . By way of example only, there are three of the actuation members  47 . Each actuation member  47  has a first end  49  in engagement with the collar member  35 , and a second end  51  extending somewhat out of the gear case  11 . Each of the ends  51  may be configured to be somewhat hemi-spherical so that ends  51  may slide on ramp surfaces  55 . The three actuation members  47  may engage at the ears  37  which are at the 2 o&#39;clock, 6 o&#39;clock, and 10 o&#39;clock positions in  FIG. 2 . 
     Disposed about the gear case  11  at the end adjacent the side gear  21  is the actuator  33  which includes a single ramp plate  53  which defines a plurality of ramp surfaces  55  and intervening valleys. There is one ramp surface  55  with an apex and one valley for each actuation member  47 . This is a “pin-and-ramp” style device, having one ramp plate and one set of “pins” (i.e., the actuation members  47 ) provided for an axial travel of the actuation members  47 . The “inner” ramp plate is the member which has “travel.” 
     Because of the spacing between segments, the “travel” is significantly decreased over the prior art. For example, the segments may be sized for a 1.5 mm stroke length. However, the engagement length is 6 mm. This is in contrast to the prior art where the stroke length was roughly equal to the engagement length. 
     The actuator  33  further includes an electromagnetic coil, generally designated  57 . The function of the electromagnetic coil is to exert the required retarding torque on the ramp plate  53 , thus initiating ramp-up of the actuation members  47 . As used herein, the term “ramp-up” in regard to the actuation members  47  includes moving the members  47  from the fully retracted position shown in  FIGS. 3 and 4 , wherein the coil  57  is not energized (corresponding to the un-actuated, unlocked condition), to a fully extended position, wherein the coil  57  is energized (corresponding to the actuated, locked condition). The electromagnetic coil  57  may cause the ramp plate  53  to rotate so that the peaks of ramps push the actuation members (pins) towards the collar  35 . The ears  37  of the collar slide in the corresponding recesses  39  of the gear case  11  so that the collar  35  moves towards the end cap  12  and away from the ramp plate  53  to the locked condition. 
     The collar member  35  is biased toward the un-actuated, unlocked condition by means of a wave spring  61 , shown in  FIGS. 3 and 4 . A number of different biasing arrangements could be utilized, though the wave spring  61  facilitates a compact packaging of the rotation prevention mechanism  31 . When the electromagnetic coil  57  is de-energized, the ramp plate  53  may rotate so that valleys of the ramp plate  53  align with the actuation members  47 . The wave spring  61  then pushes the collar  35  away from the end cap  12  and towards the ramp plate  53  to unlock the differential. Thus, the collar  35  is able to move bi-directionally along an axis A-A in  FIG. 1  based on whether the actuator  33  is ramped-up or not. 
     As shown somewhat schematically in  FIG. 1 , the electromagnetic coil  57  is energized by means of a pair of electrical leads  59 , the reference numeral “ 59 ” also being used hereinafter to identify an electrical input signal to the actuator  33 . 
     While the ramp and coil actuation has been illustrated, other actuation means, such as ball and ramp may be used. The actuation means used must be capable of moving the collar with respect to the side gear. 
     The locking differential may be controlled in either of a pair of modes. The differential may be controlled manually, i.e., wherein the driver manually selects the locked mode (rather than the unlocked mode). The differential may operate in the locked mode after the mode is manually selected. Alternately, the locking differential may be allowed to operate in an automatic mode wherein, by way of example only, the vehicle microprocessor senses an operational condition, such as an incipient wheel slip, and transmits an appropriate electrical signal to the locking differential, thereby locking the side gear  19  relative to the gear case  11 , to prevent any further differentiation there between. 
     In the case of automatic actuation of the locking differential, under certain operation conditions, such as when the vehicle is turning, or a slight difference in tire size exists, it is permissible for a certain amount of differentiating action to occur between the side gears  19  and  21 . However, the example of  FIG. 1  does not include illustrations for a clutch pack or other mechanism which retards or limits differentiating action. The example instead operates like an “open differential” in either an un-actuated, unlocked mode or in an actuated, locked mode. 
     The differential may comprise sufficient inputs, such as the electrical leads  59 , to enable manual or automatic operation. If necessary, the differential may comprise affiliations such as CAN, bus, computing (storage, processing, and programming), etc to effectuate the manual or automatic operation and may further comprise outputs and other hardware and software to send signals indicating locked or unlocked conditions. 
       FIG. 5  illustrates the travel “T” of the collar member  35 , in moving between locked ( FIGS. 6A and 6B ) and unlocked ( FIGS. 3 ,  4  and  5 ) conditions. The travel T is equal to the width of a segment plus a clearance. In this example, the travel is equal to about 1.5 mm. The stroke length, or distance an actuation member must move to engage the collar  35  with the side gear, is also about 1.5 mm in this example. Thus, instead of traveling the entirety of the engagement length to unlock or lock the differential, the travel is reduced significantly to a fraction of the engagement length. 
     The engagement length (i.e., the axial length of the engagement) between the lock members  41  and  43  is about 6 mm in this example. This is because 1 segment on a collar lock member  41  provides approximately 1 mm of width to engage with approximately 1 mm of width on a segment of a side gear lock member  43 . Since there are 6 segments on each lock member, a lock member additively has approximately 6 mm of engagement length. 
       FIG. 6A  illustrates one example of a locked condition. The collar  35  is aligned with the side gear  19  so that collar segments  72  no longer align with grooves in the side gear locking members  43 . The side gear locking members  43  are in face-to-face engagement with the collar locking members  41 , and segments  71  of the side gear locking members  43  are no longer in alignment with grooves in the collar locking members  41 . As shown in  FIG. 6B , the grooves in the side gear locking members  43  are aligned with the grooves in the collar locking members  41 . 
     The number, width, length, and spacing of segments and locking members may vary from that illustrated, and the rotation direction of the side gear  19  may be clockwise (as illustrated) or counterclockwise. In addition, since the drawings are not to exact scale, the width of the collar and the expanse of the segments on the side gear  19  may vary. The placement of the segments on the side gear  19  may be leftward, as in  FIG. 1 , rightward, as in  FIG. 3 , or the segments may span from left to right or some intermediate length to that shown in  FIGS. 1 and 3 . 
     In the preceding specification, various descriptions have been made with reference to the accompanying drawings. It will, however, be evident that various other modifications and changes may be made thereto, and additional aspects may be implemented, without departing from the broader scope of the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.