[001] 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
[002] 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
[003] 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.
[004] 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.
[005] 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
[006] Figure 1 is a view of the internal components of a differential having
the case and ring gear removed.
[007] Figure 2 is an example of an engagement mechanism in relation to a
cam plate and side gear.
[008] Figure 3 is an exploded view of the differential of Figure 1.
[009] Figure 4A is a perspective view of a first side of a cam plate.
[01 0] Figure 4B is a view of a second side of the cam plate.
[01 1] Figure 5 is a view of a partially assembled differential showing a
ramped side of a side gear.
[01 2] Figure 6 is a view of an eared lock plate.
[01 3] Figure 7 is a view of a splined lock plate.
DETAILED DESCRIPTION
[014] 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.
[01 5] 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 10 1 within the differential. As the pinion shaft 10 1
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.
[01 6] 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 US Patent 6,31 9,1 66, US Patent 7,438,661 , and US Patent 8,1 67,763, assigned
to Eaton Corporation and incorporated by reference herein in their entireties.
[01 7] In the example shown in Figures 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 2 13 and 214 may have flyweights 2 10 and
2 11 between them and a flyweight spring 2 12 may bias the flyweights 2 10 and 2 11.
At least end plate 214 engages with a cone clutch 2 15 . 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 2 10 and 2 11 spin up. The centrifugal force must
be enough to overcome the biasing force of the flyweight spring 2 12 . The rotation
must also be sufficient to overcome the grip between the end plate 214 and the
cone clutch 2 15.
[01 8] In order to lock the differential (exit open mode), at least one of the
flyweights 2 10 or 2 11 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 2 10 and 2 11 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.
[01 9] Figures 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 2 10 and
2 11 are biased in a closed position.
[020] In Figure 2, the end plate 2 14 is absent for clarity. The flyweights 2 10
and 2 11 have spun-up and the pawl 222 has caught against a step in flyweight 2 11.
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 US Patent 6,31 9,1 66, US Patent 7,438,661 , and
US Patent 8,167,763.
[021] As shown in Figures 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.
[022] Also shown in Figure 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 2 10 or 2 11 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 .
[023] Cam plate action against the side gear, as well as cam plate and side
gear configurations, may be further understood from examples such as US Patents
3,606,803, 5,484,347, 6,31 9,166, RE 28,004, and 3,831 ,462, incorporated herein by
reference in their entirety.
[024] 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.
[025] 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.
[026] 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 3,831 ,462 or can be used with other designs having no friction discs
adjacent the right side gear.
[027] 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.
[028] 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.
[029] In embodiments where the second lock plate 150 comprises ears 602,
optional ear guards 15 1 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.
[030] 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.
[031] 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 10 1, 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 19 1 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.
[032] 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 18 1. 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.
[033] 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 canbe 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.
[034] 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.
[035] 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 2 10 or 2 11 can catch the pawl 222.
[036] 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.
[037] 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.

WE CLAIMS:-
1. A differential comprising:
a first side gear comprising a gear side and a ramped side;
a second side gear comprising a gear side facing the first side gear;
a pinion gear set between the first side gear and the second side gear;
a cam plate comprising a ramped side facing the ramped side of the first
side gear, the cam plate further comprising a second side;
a first lock plate comprising a first side abutting the second side of the
cam plate, the first lock plate further comprising a toothed side; and
a second lock plate comprising a toothed side facing the toothed side of
the first lock plate.
2 . The differential of claim 1, wherein the toothed side of the first lock plate
comprises radially extending teeth, and wherein the toothed side of the
second lock plate comprises radially extending teeth.
3 . The differential of claim 1, further comprising a wave spring between the first
lock plate and the second lock plate to bias the first lock plate away from the
second lock plate.
4 . The differential of claim of claim 3, wherein the second lock plate further
comprises a wave spring seating surface to abut the wave spring.
5 . The differential of claim 1, wherein the first side gear comprises an external
spline, and wherein the first lock plate comprises an internal spline in
engagement with the external spline of the first side gear.
6 . The differential of claim 5, wherein:
the second lock plate further comprises radially extending ears,
the differential further comprises a case comprising ear grooves,
the lock plate ears are seated in the ear grooves,
the cam plate comprises external gear teeth,
the differential further comprises a mechanical device for selectively
locking against the cam plate, and, when the mechanical device locks
against the cam plate, the cam plate rotates with respect to the first side gear
and the cam plate presses the first lock plate against the second lock plate
thus rotationally locking the first side gear to the case.
7 . The differential of claim 1, wherein the second lock plate further comprises
radially extending ears, wherein the differential further comprises a case
comprising ear grooves, and wherein the lock plate ears are seated in the ear
grooves.
8 . The differential of claim 1, wherein the cam plate comprises external gear
teeth, wherein the differential further comprises a mechanical device for
selectively locking against the cam plate, and, when the mechanical device
locks against the cam plate, the cam plate rotates with respect to the first
side gear and the cam plate presses the first lock plate against the second
lock plate.
9 . The differential of claim 1, further comprising:
a wet clutch pack ;and
a case surrounding the wet clutch pack, the first side gear, the second
side gear, the first lock plate, the second lock plate, the cam plate, and the
pinion set,
wherein the wet clutch pack is between the second side gear and the
case.
10 . The differential of claim 1, further comprising a case surrounding the first side
gear, the second side gear, the first lock plate, the second lock plate, the cam
plate, and the pinion set, wherein the second side gear abuts the case.
11. The differential of any one of claims 1- 10, wherein the first side gear further
comprises:
a neck extending away from the ramped side;
a plurality of side gear crests and a plurality of side gear ravines; and
a set of splines between the neck and the plurality of side gear crests and
the plurality of side gear ravines, and
wherein the first lock plate comprises a set of internal splines and the first
lock plate is splined to the set of splines on the first side gear, and
wherein the neck of the first side gear rotates within the second lock plate.
12 . The differential of any one of claims 1- 10, wherein the cam plate further
comprises a plurality of crests and a plurality of ravines, wherein the side
gear further comprises a plurality of side gear crests and a plurality of side
gear ravines, and wherein the cam plate is movable between an open mode,
where the crests align in the side gear ravines and the side gear crests align
in the ravines, and a locked mode, where the crests slide towards the side
gear crests and away from the side gear ravines.
13 . The differential of any one of claims 1- 12, wherein the side gear further
comprises holes, wherein the cam plate further comprises detents, and
wherein the cam plate is movable between an open mode, where respective
holes align with respective detents, and a locked mode, where the respective
detents move out of the respective holes.
14. The differential of claim 12 or 13, wherein, when the cam plate is moved into
the locked mode, the toothed side of the first lock plate engages the toothed
side of the second lock plate.