Abstract:
A differential comprises a first side gear and a second side gear facing the first side gear. A pinion gear set can be between the first side gear and the second side gear. A cam plate comprises a ramped side facing a ramped side of the first side gear. A first lock plate comprises a first side abutting a second side of the cam plate. The first lock plate further comprises a toothed side. A second lock plate comprises a toothed side facing the toothed side of the first lock plate.

Description:
This is a continuation of Application No. PCT/US2014/019198, filed Feb. 28, 2014, which claims the benefit of U.S. provisional application Ser. No. 61/891,017, filed Oct. 15, 2013, which are incorporated herein by reference in their entireties. 
    
    
     FIELD 
     This application relates to differentials, and more specifically to mechanical locking differentials designed to sense wheel speed and automatically lock the device from differentiating rotation. 
     BACKGROUND 
     Existing mechanical locking differentials (M-lockers) are designed to automatically lock the differential when a difference in wheel speed is sensed above a predetermined value. However, the existing design uses friction disks in a wet clutch pack, thus requiring fluid lubrication for engagement. The fluid is subject to degradation and its properties can vary with temperature and degradation. 
     SUMMARY 
     The apparatus disclosed herein overcome the above disadvantages and improves the art by way of a differential which can comprise a first side gear and a second side gear facing the first side gear. A pinion gear set can be between the first side gear and the second side gear. A cam plate comprises a ramped side facing a ramped side of the first side gear. A first lock plate comprises a first side abutting a second side of the cam plate. The first lock plate further comprises a toothed side. A second lock plate comprises a toothed side facing the toothed side of the first lock plate. 
     Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The objects and advantages will also be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of the internal components of a differential having the case and ring gear removed. 
         FIG. 2  is an example of an engagement mechanism in relation to a cam plate and side gear. 
         FIG. 3  is an exploded view of the differential of  FIG. 1 . 
         FIG. 4A  is a perspective view of a first side of a cam plate. 
         FIG. 4B  is a view of a second side of the cam plate. 
         FIG. 5  is a view of a partially assembled differential showing a ramped side of a side gear. 
         FIG. 6  is a view of an eared lock plate. 
         FIG. 7  is a view of a splined lock plate. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the examples which are 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. Directional references such as “left,” “right,” “up,” and “down” are for ease of reference to the figures. 
     In an open mode, a differential is configured to allow two wheels on a motor vehicle to operate at different speeds. In a locked mode, the two wheels are locked so that they rotate at the same speed. One torque path, for a front wheel drive (FWD) vehicle, may include torque transfer from an engine to a transmission to a power transfer unit to a drive shaft to a pinion gear to a ring gear around a differential case to a pinion shaft  101  within the differential. As the pinion shaft  101  rotates, affiliated pinion gears  103  and  104  can transfer differentiated or undifferentiated torque to meshing side gears  190  and  110 . The side gears have internal splines  112  and  192  to transfer torque to externally splined drive axles. Torque is then transferred to affiliated wheels. Since this torque path, as well as rear wheel drive (RWD) and all wheel drive (AWD or 4WD) torque paths, are known, the vehicle driveline is not illustrated. The ring gear and differential case are also not illustrated. Despite the specific reference to FWD, RWD, and AWD systems, it is to be understood that the differential may be used in any suitable environment requiring a differential rotation for two shafts. 
     A mechanical locking differential (M-locker) uses a mechanical device, as opposed to a solenoid or hydraulic device, to go between the locked and open modes. The mechanical device can comprise, for example, one of those described in U.S. Pat. Nos. 6,319,166, 7,438,661, and 8,167,763, assigned to Eaton Corporation and incorporated by reference herein in their entireties. 
     In the example shown in  FIGS. 1-3 , the mechanical device comprises an engagement mechanism, which can comprise a shaft having a first end  200  and a second end  203 , both for coupling to the differential case. The shaft may include a shaft gear  201 . End plates  213  and  214  may have flyweights  210  and  211  between them and a flyweight spring  212  may bias the flyweights  210  and  211 . At least end plate  214  engages with a cone clutch  215 . The shaft may rotate with the cam plate  120  via the shaft gear teeth  201  in mesh with rim teeth  408 . When the shaft rotates due to differential action and the rotation speed is above a predetermined value, the flyweights  210  and  211  spin up. The centrifugal force must be enough to overcome the biasing force of the flyweight spring  212 . The rotation must also be sufficient to overcome the grip between the end plate  214  and the cone clutch  215 . 
     In order to lock the differential (exit open mode), at least one of the flyweights  210  or  211  must engage with the pawl  222  on a lockout mechanism on the second shaft. The second shaft has a first end  220  and a second end  221 , both for coupling with the differential case. If the vehicle travels over a predetermined speed, the centrifugal force on the lockout causes a counterweight  223  to pull the pawl  222  out of the available range of the flyweights  210  and  211  and the differential cannot enter the locked mode. It can only operate in the open mode. The described example is not meant to limit the mechanical device for locking or unlocking the differential described herein. Other mechanical devices are used in the alternative with the differential described herein. 
       FIGS. 1 and 3  show the engagement mechanism in an un-activated state, such as when the differential is stationary, or when operating under a predetermined differential speed such as below 100 RPMs. The flyweights  210  and  211  are biased in a closed position. 
     In  FIG. 2 , the end plate  214  is absent for clarity. The flyweights  210  and  211  have spun-up and the pawl  222  has caught against a step in flyweight  211 . This locks the first shaft from rotation. The shaft gears  201  are geared to rim teeth  408  of the cam plate  120 . The locking creates sufficient force to move the cam plate  120 . Further discussion of engagement mechanisms and their operation can be understood from examples such as U.S. Pat. Nos. 6,319,166, 7,438,661, and 8,167,763. 
     As shown in  FIGS. 4A and 4B , the cam plate  120  has ramps  402  and valleys  403 . The ramps  402  comprise upward ramps  405  leading to crests  404 . The valleys  403  comprise downward ramps  406  leading to ravines  407 . The ramps  402  and valleys  403  are shown with stepwise transitions, and the cam plate  120  can comprise more or fewer stepwise transitions, or the cam plate  120  can comprise smooth transitions between crests  404  and ravines  407  such as by having a single slope therebetween or by having curves therebetween. Also, while five crests  404  and five ravines  407  are shown, more or fewer can be used in practice. 
     Also shown in  FIG. 4A  are detents  401 . While three detents  401  are shown, more or fewer can be used in practice. The detents  401  mate with corresponding holes  115  in the left side gear  110 . The detents  401  and holes  115  are sized so that the detents  401  leave the holes  115  when the above locking of the flyweight  210  or  211  against the pawl  222  creates sufficient force to move the cam plate  120 . The ramps  402  then slide against corresponding side gear ramps  116 . That is, in the open mode, crests  404  rest in side gear ravines  118 , and side gear crests  117  rest in ravines  407 . In the locked mode, the crests “ramp-up” and slide out of the ravines and against opposed ramps as the detents  401  leave the holes  115 . When the differential exits locked mode, the crests “ramp-down” and slide back in to corresponding ravines while the detents  401  re-enter the holes  115 . 
     Cam plate action against the side gear, as well as cam plate and side gear configurations, may be further understood from examples such as U.S. Pat. Nos. 3,606,803, 5,484,347, 6,319,166, RE 28,004, and U.S. Pat. No. 3,831,462, incorporated herein by reference in their entirety. 
     The left side gear  110  is braced against the pinion gears  103  and  104  via meshing engagement of side gear teeth  111  with pinion gear teeth. Any motion of the left side gear  110  as the cam plate  120  “ramps-up” can be passed to the spring-loaded lock plates. 
     In the example shown, no reaction block is used to pass force from the left side gear  110  to the right side gear  190 . Therefore, the “ramp-up” of the cam plate does not also cause compression of the clutch pack  180 . The clutch pack  180  can be operated to enable limited slip, or the clutch pack  180  can be eliminated. 
     The forces created as the cam plate  120  moves against the left side gear  110  can be transferred to the first lock plate  140  and then to the second lock plate  150 , with some absorption by wave spring  130 . Such an arrangement enables the elimination of all wet clutch packs and the use of a reaction block, thus simplifying the differential, reducing weight, and enabling reduction of size. The right side gear  190  can abut the differential case similar to the above-incorporated RE 28,0004 and U.S. Pat. No. 3,831,462 or can be used with other designs having no friction discs adjacent the right side gear. 
     As the cam plate  120  “ramps-up,” first lock plate  140  moves axially with its lock plate inner splines  702  along left side gear outer splines  114 . This compresses a wave spring  130  and first lock plate teeth  704  lock against second lock plate teeth  604 . Each first lock plate tooth  704  is separated by a lock plate groove  703 . Each second lock plate tooth  604  is likewise separated by a plate groove  603 . 
     The wave spring  130  seats against wave spring seat  601 . The wave spring  130  biases the first lock plate  140  away from the second lock plate  150 . As the wave spring  130  pushes against first lock plate  140 , first lock plate  140  pushes against cam plate  120 . This biases the detents  401  in the holes  115 . 
     In embodiments where the second lock plate  150  comprises ears  602 , optional ear guards  151  can be included. The ears  602  and optional ear guards  151  engage with corresponding grooves in the differential case so as to lock the second lock plate  150  from rotating with respect to the case. The first lock plate  140  is forced to rotate with the left side gear  110  via the mating of inner splines  702  with side gear outer splines  114 . 
     An optional coupling ring  160  or thrust washer abuts the second lock plate  150 , and an optional coupling ring or thrust washer  170  abuts the side gear  110  and differential case. 
     When the first lock plate teeth  704  lock against second lock plate teeth  604 , the left side gear  110  is locked to rotate with the differential case. The pinion shaft  101 , locked to the differential case via optional lock pin  102 , must also rotate with the housing. Affiliated pinion gears  103  and  104  are locked to rotate with the left side gear  110  via the meshing of side gear teeth  111  with the pinion gear teeth. Thus, the meshed side gear teeth  191  of right side gear  190  must rotate at the same rate as the left side gear  110 . This gear coupling is in addition to the coupling between the right side gear  190  and the differential case, described below. 
     Right side gear  190  further includes inner spline  192  for coupling to an axle shaft and an outer spline  194  for coupling to clutch pack  180 . The clutch pack  180  can comprise plates with ears  184  and friction discs with splines  181 . The disc splines  181  couple to the right side gear outer spline  194 . Optional ear guards  182  surround the ears  184 , which mate with corresponding grooves in the differential case. A coupling ring  183  or thrust washer is between the differential case and the clutch pack  180 . 
     Because the ears  184  are coupled to the differential case, when the affiliated friction discs are frictionally engaged with the eared plates, the right side gear  190  must rotate, via the spline connection, with the differential case. The friction engagement of the clutch pack  180  can be facilitated by the selection of an appropriate viscosity lubricating fluid. The clutch pack  180  can be used to provide limited slip capability to the differential, or as an alternative the clutch pack  180  can be eliminated. 
     The first lock plate  140  comprises radially extending teeth sized and spaced to mate with radially extending teeth of the second lock plate  150 . In an open mode, the space between first lock plate  140  and second lock plate  150  is sized so that the crests  404  of the cam plate  120  rest in ravines  118  of the left side gear. The spacing is selected so that the crests  404  of the camp plate  120  do not pass crests  117  of the left side gear when the cam plate  120  locks. The design enables positive locking such that the differential operates either fully locked or in open mode. 
     Because of the simplified design, the differential can lock in both directions. That is, the differential can lock no matter which direction the side gears are spinning so long as one of the flyweights  210  or  211  can catch the pawl  222 . 
     An advantage of using the two lock plates is the enhanced reliability offered by the tooth-to-tooth contact. That is, the dog-style coupling is more reliable than the wet friction disc contact, resulting in reduced slippage. In addition, the lock plates can be designed to take up less axial space than friction discs, thus further reducing the size of the differential. The lock plate engagement and use generates less heat than the friction discs, leading to less fluid degradation. And, the elimination of the friction discs reduces the machining to the differential case, leading to less costly manufacture. 
     Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.