[001] This application relates to torque limiting devices, and more
specifically to locking differentials comprising a torque limiting device.
Background
[002] Vehicle drivelines may include differential devices to split torque to
wheels to adjust the traction of each wheel during vehicle operation. At times it is
advantageous to fully lock the driveline to transmit undifferentiated torque. In this
fully locked condition, it is possible to transmit 100% of the torque available on a
ring gear. If an axle shaft isn't designed to withstand this high torque, it will fail. This
can damage additional axle components and the differential itself.
SUMMARY
[003] The methods and devices disclosed herein overcome the above
disadvantages and improves the art by way of a selectively lockable differential,
which may comprise a plurality of torque sensitive pins; an outer housing; a first side
gear comprising first gear teeth and gear lugs; a second side gear comprising
second gear teeth; a pinion shaft; two pinion gears rotationally coupled to the pinion
shaft, each pinion gear comprising pinion gear teeth coupled to the first gear teeth
and the second gear teeth; and a collar comprising collar teeth for selectively
engaging the gear lugs of the first side gear, the collar being operatively coupled to
the outer housing by the torque sensitive pins.
[004] In addition, a vehicle driveline may comprise a torque transmission
system operatively coupled to transmit torque from an engine to a selectively
lockable differential. The selectively lockable differential may comprise a plurality of
torque sensitive pins, an outer housing, a first side gear comprising first gear teeth
and gear lugs, a second side gear comprising second gear teeth, and a pinion shaft
two pinion gears may be rotationally coupled to the pinion shaft. Each pinion gear
may comprise pinion gear teeth coupled to the first gear teeth and the second gear
teeth. A collar may comprise collar teeth for selectively engaging the gear lugs of
the first side gear. The collar may be operatively coupled to the outer housing by the
torque sensitive pins. A first axle may be operatively coupled to the first side gear,
and a second axle may be operatively coupled to the second side gear.
[005] 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.
[006] 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
[007] Figure 1 is a schematic example of a simplified vehicle driveline.
[008] Figure 2 is an exploded view of a first embodiment of a torque limiting
differential.
[009] Figure 3 is a cross-section of the first embodiment along a first plane.
[01 0] Figure 4 is a second cross-section of the first embodiment along a
second plane.
[01 1] Figure 5 is a view of a locking collar of the first embodiment.
[01 2] Figure 6 is a view of a torque sensitive pin of the first embodiment.
[01 3] Figure 7 is an inner-side view of the left-hand case of the first
embodiment.
[01 4] Figure 8 is an outer-side view of the left-hand case of the first
embodiment.
[01 5] Figure 9 is a cross-section of the left-hand case of the first
embodiment.
[01 6] Figure 10 is an exploded view of a second embodiment of a torque
limiting differential.
[01 7] Figure 11 is a cross-section of the second embodiment along a first
plane.
[01 8] Figure 12 is a cross-section of the second embodiment along a
second plane.
[01 9] Figure 13A is a first view of a collar and collar housing of the second
embodiment.
[020] Figure 13B is a second view of the collar housing.
[021] Figure 14 is a view of a torque sensitive pin of the second
embodiment.
[022] Figure 15 is a cross-section of the left-hand case of the second
embodiment.
[023] Figure 16 is an inner-side view of the left-hand case of the second
embodiment.
[024] Figure 17 is an outer-side view of the left-hand case of the second
embodiment.
[025] Figure 18 is a cross-section of a right-hand case.
[026] Figure 19 is a view into the inner side of the right-hand case.
[027] Figure 20 is a detailed view of the torque sensitive pin interface with
the lock collar.
DETAILED DESCRIPTION
[028] 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" and "right" and "front" and "back" are for ease of
reference to the figures and are not meant to be limiting.
[029] Figure 1 illustrates one example of a vehicle driveline. In this example,
the vehicle is front wheel drive, meaning the primary motive power is connected to
the front drive axle. The engine 106, transmission 107, and power transfer unit 108
are operatively connected at the front of the vehicle to transmit torque directly to a
front left axle 100, and front right axle 10 1. Via wheel hubs 115 and 116, wheels 102
and 103 receive torque to provide traction to the vehicle. Via mechanisms in the
power transfer unit 108, such as a hypoid gear and pinion, the drive shaft 109
receives torque and transmits it to the rear of the vehicle. An optional all-wheel drive
coupling 120 connects to the drive shaft 109, and a rear drive unit 110 may house
an electronic coupling component and rear differential.
[030] The rear differential may be operated in either an open or locked
mode. In the open mode, the left rear wheel 113, via wheel hub 117 and left rear
axle 111, can spin at a speed that is different from the right wheel 114. Likewise, the
right rear wheel 114, via wheel hub 118 and right rear axle 112, can spin at a
different speed than left rear wheel 113. In the locked mode, both left and right rear
wheels 113 and 114 receive the same torque because the left and right rear axle
111 and 112 are locked via internal components in the rear differential.
[031] It should be noted that the driveline of Figure 1 is an example, only,
and the principles claimed herein may be used in a rear wheel drive vehicle, or in a
vehicle having more than one differential device.
[032] The engine 106 can supply a range of rotative power that can be
reduced or enhanced via gear reductions or additions. The engine power is received
as torque in the axles of the vehicle, and, as axles are typically hollow, the axles can
only receive torque up to a limit, and then the axle is subject to failure such as
shearing or torsion. Therefore, axles are typically designed with an Axle Torque
Capacity ("ATC"), which is the maximum engine torque multiplied by the highest
gear ratio which is the highest numerical value of either first or reverse gear
multiplied by the final drive ratio between the hypoid/drive pinion and ring gear. In
the open differential mode, the ATC is split 50:50 to each axle. So, each axle
receives 0.5 x ATC.
[033] However, if the differential is locked, it can be possible to transmit
100% of the available torque to a single axle such that the axle receives 1.0 x ATC.
Because of unpredictable use events or end-user abuse, upgrading the axle may
not be enough to prevent failure. And, end-users may choose a lower capacity axle
in view of competing considerations such as CAFE requirements, added weight,
additional footprint for associated components, and overall operational costs.
Because of the trade-offs, expense, and complications associated with upgrading
axle shafts to a higher strength than is needed for typical operational ranges, it is
difficult to completely prevent the axle from failing in the locked differential mode.
Even when the axle is at 100% of ATC, it is possible to overload the axle shaft
thereby leading to failure.
[034] A torque limiting device as disclosed herein can preserve the integrity
of the axle during high torque conditions. That is, the torque limiting device is
designed to sacrifice itself before the axle shaft failure occurs. Such a limiting device
can shear and return the differential to open mode, thus relieving the axle of excess
torque before the axle shears or suffers torsion. The shearing of the torque limiting
device can also prevent corollary damage to the axle components and to the
differential itself. For example, in semi float type axles, the axle should stay within
the housing even if the differential fails. If the torque limiting device shears, the
vehicle returns to open mode and the vehicle is still operational despite an inability
to return the differential to locked mode.
[035] Within the gear chamber 2 13 is a differential gear set including a pair
of input pinion gears 2 17 . The pinion gears 217 comprise the input gears of the
differential gear set, and are in meshing engagement with a pair of side gears 2 19
and 221 . When the ring gear, fixed to the right hand case 2 11, spins, the pinion
shaft 2 18 spins with it. This in turn spins the side gears 2 19 and 221 . The side gears
2 19 and 221 include sets of internal, straight splines 223 and 225, respectively,
which are in splined engagement with mating external splines on respective left and
right rear axle shafts 111 and 112 . Thus, as the ring gear rotates, the rear axles
rotate.
[036] When the differential operates in an open mode, during normal,
straight ahead operation of the vehicle, no differentiation occurs between the left
and right axles 111 and 112, or between the left and right side gears 2 19 and 221 ,
and therefore, the pinion gears 2 17 do not rotate relative to the pinion shaft 2 18 . As
a result, the left and right hand gear case 212 and 2 11, the pinion gears 2 17, and
the side gears 2 19 and 221 all rotate about an axis of rotation A, as if comprising a
solid unit. However, if the vehicle turns or experiences turbulence that causes the
rear wheels 113 and 114 to spin at different rates, the pinion gears 2 17 rotate
around the pinion shaft 2 18 and 2 16 to enable different side gear speeds with
respect to the pinion shaft rotation.
[037] However, it is sometimes advantageous to lock the left and right rear
axles 111 and 112 so that they must spin at the same rate. Thus, during the locked
mode, a side gear is locked to the housing so that it must rotate with the pinion shaft
2 18 . In the example of Figure 2, the left side gear 2 19 is locked. Via the meshing
engagement, this locks the pinion gears 2 17 with respect to side gear 2 19, which
also locks the side gear 221 .
[038] As above, the locked mode can generate a lot of strain on the various
parts, including the axles, gears, wheel hubs and locking mechanisms. The strain
can lead to damage to the vehicle parts, loss of vehicle control, or loss of
operability. Thus, the locking mechanism (collar) of Figure 2 is operatively provided
with at least one, preferably six to eight, torque limiting devices designed to fail in
lieu of other driveline parts. And, the collar (lock plate) of Figure 10 is operatively
provided with at least one, preferably six to eight, torque limiting devices via a
surrounding collar housing.
[039] The torque limiting devices shear before a rear axle 111 or 112 fails
and before the locking mechanisms themselves fail. That is, the torque limiting
devices will fail when the design limits are reached. The torque limiting devices are
used under a pure shear condition when the differential is locked. That is, the torque
load acts directly on the torque limiting devices, causing a clean shearing of the
devices instead of a gradual or shattering break of the devices.
[040] There are several classes of differentials, one of which is an E-locker,
or electronic locking differential. In one prior design, such as US 7,264,569, the
collar has ears that mate with recesses in the right hand case. The prior art collar
rotates with the case and slides against the case to move between locked and
unlocked mode. The collar may be pressed by push rods to lock against a left hand
side gear. The collar then rotates with the left hand case, right hand case, left and
right locker gears, and pinion gears in a locked mode. In open mode, the collar
rotates with case but does not lock the side gears to the pinion gears, and the axles
are able to rotate at different speeds.
[041] In the example shown in the first embodiment of Figure 2, the lock
collar (lock plate) 2 10 does not have ears to couple to the right or left hand case 2 11
or 212. Instead, lock collar receives torque limiter pins (torque sensitive pins) 200 to
operatively couple to the left hand case 2 12 . Lock collar rotates with the left hand
case 2 12 so long as the torque sensitive pins 200 are intact. If the lock collar 2 12
experiences torque above a predetermined value, the lock collar 2 12 may rotate
and shear the torque sensitive pins 200. Once the torque sensitive pins 200 shear,
the lock collar 2 10 is free to rotate in right hand case 2 11 and the lock collar 2 10
cannot maintain the locked differential mode. That is, the differential can only
operate in the open mode once the torque sensitive pins 200 shear.
[042] The torque flow path from the drive shaft through to the right and left
rear axles is as follows. The drive shaft 109 typically terminates with an input pinion
that couples to a ring gear. The ring gear is usually around the exterior of the
differential case. In the example of Figure 2, the ring gear is around right hand case
2 11 and couples to a flange 2 15 via openings 7 15 and 181 5 . When the input pinion
rotates the ring gear, the whole differential of Figure 2 rotates. Because central
pinion shaft 2 18 passes through the right hand case 2 11, it rotates as the ring gear
rotates. The ring gear connection to the input pinion of the drive shaft is not shown
for clarity, nor is the ring gear shown. An additional housing may surround the ring
gear and its coupling to the input pinion.
[043] The left hand case 212 is coupled to the left rear axle 111 and the
right hand case is coupled to the right rear axle 112 . Through mountings not shown,
the left rear axle 111 can rotate with respect to the left hand case 2 12, and the right
rear axle 112 can rotate with respect to the right hand case 2 11. The torque from
the ring gear is applied to the central pinion shaft 218 to spin it. Central pinion shaft
2 18 passes through two pinions 2 17 . In open mode, the pinions 217 are able to
rotate around the central pinion shaft 218. Additional short cross shafts 2 16 may
couple to the pinion shaft (long cross shaft) 2 18 . The short cross shafts 2 16 may
enable additional pinions 2 17 to rotate within the differential. The short cross shafts
2 16 may couple to the left hand case 2 12 via slotted spring pins 220. The central
pinions 2 17 of the differential may additionally interface with spherical washers 222.
[044] The pinions 2 17 meshingly engage with side gears. The right hand
side gear 221 has internal splines 223 to couple to right hand rear axle1 12, and the
left hand side gear (locker gear) 2 19 has internal splines to couple to left hand rear
axle 111.
[045] So when the pinion shaft 2 18 rotates, the side gears 219 and 221
rotate and thus the rear axles 111 and 112 rotate. In an unlocked, or open, mode,
each side gear can rotate at a different speed than the other side gear because the
side gears can turn with respect to the pinions 2 17 at different rates of speed. In the
locked mode, the locker gear (left hand side gear) 219 is coupled to the lock collar
(lock plate) 2 10, which is coupled via torque sensitive pins 200 to the left hand case
2 12 . The left hand case 212 is coupled to the right hand case 2 11 by lock screws
214 through openings 7 14 and 1814. The right hand case 2 11, as above, is coupled
to the ring gear to turn as the drive shaft pinion applies rotational force. Because the
locker gear 2 19 is locked via lock collar 2 10 to rotate with the case at the same rate
as the pinion shaft 218, the right hand side gear 221 is also locked from differential
rotation and must likewise rotate at the same rate as the locker gear 2 19 . Thus each
rear axle 111 and 112 rotates at the same rate via the locked differential.
[046] Because the locked mode depends on the lock collar 2 10 to achieve
the locked state, its uncoupling from the left hand case 2 12 via shearing of the
torque sensitive pins 200 forces the differential to operate in an open mode only.
The wave spring 261 ensures the lock collar 2 10 disengages from the locker gear
2 19 when either open mode is selected, or when torque sensitive pins 200 shear.
The wave spring may seat in a wave spring recess 708 in the left hand case 2 12.
The wave spring recess 708 may be sized to damp or prevent wave spring vibration
during differential use.
[047] Turning to Figures 7, 8, and 9, Figure 7 illustrates an inner face of the
left hand case 2 12, Figure 8 illustrates an outer side of the left hand case 2 12, and
Figure 9 illustrates a cross section of the left hand case 2 12 . The recess 708 has a
wave spring stop 7 11 for seating the wave spring 261 . Other openings in the left
hand case 212 are discussed elsewhere in the specification.
[048] The right hand case is illustrated in more detail in Figures 18 and 19 .
In the cross-section of Figure 18, the opening 1814 for securing the right hand case
to the left hand case is visible. Also, slots 1816 are available for the slotted spring
pins. Other openings in the right hand case are for various purposes not related to
the torque limiting devices.
[049] A user or an automated electronic control system can select when the
differential moves between open and locked mode. An abridged actuation
mechanism 233 is shown in Figure 2 . Electrical leads 259 couple to an activation
switch or other control means to power stator 257. The powered or unpowered state
of the stator 257 determines whether the ramp plate 253 is "ramped-up" or "ramped
down." When "ramped up", the ramp plate is turned to push peak areas on the ramp
plate 253 against second ends 251 of push rods 247, which urges the push rods
247 towards the lock plate 2 10. First ends 248 push against the lock plate 2 10, and
the lock plate 2 10 slides axially in a recess 250 in the right hand case. The push
rods 247 push the lock plate 2 10 towards the left hand case 2 12 and the lock plate
2 10 slides on the torque sensitive pins 200 that pass through holes 501 in the lock
plate 2 10 . The lock plate has collar teeth 504, each tooth having a wide end 502
and a narrow end 503. These collar teeth 504 mesh with lugs 224 to lock the lock
plate 2 10 with respect to the locker gear 219.
[050] In the "ramped down" position, ramp plate 253 is turned so that the
push rods can rest in valleys of the ramp plate 253. Wave spring 261 can push the
lock plate 2 10, which can in turn push the push rods 247 in to the valleys. The collar
teeth 504 do not engage with lugs 224.
[051] The lock collar 2 10 may have a clearance surrounding the torque
sensitive pins 2 10 to allow the lock collar 2 10 to slide along the pin body 202.
Lubricating fluid within the differential housing may assist with lubricating the
motion. In addition, while the holes 501 in the lock collar 210 are shown in Figure 5
near an outer boundary of the lock collar, the holes 501 may be centered in the
thickest face of the lock collar, or the holes may be otherwise placed radially inward
from the locations illustrated.
[052] The actuation mechanism 233 may further comprise a retaining ring
258, a bearing 254, and a bearing race 255.
[053] The differential may also comprise shim 227 between right hand side
gear 221 and right hand case 2 11. A like shim may be used with left hand side gear
2 19 and left hand case 2 12.
[054] The example of Figure 2 shows the use of 6 torque limiter pins (torque
sensitive pins) 200. However, modifications can be made for fewer or additional
torque limiter pins 200.
[055] As shown in Figure 5, the lock plate 2 10 has holes 501 for receiving
the torque sensitive pins 200. While not shown, the holes 501 may pass deeper in
to the lock plate 2 10 and may pass all the way through the lock plate 210. The collar
teeth 504 have a draft on them. That is, the teeth have a wide end 502 and a narrow
end 503. The draft helps ensure collar tooth 504 engagement with the lugs 224. The
side gear lugs 224 may have a draft angle on them because of their formation
method. To avoid a contact inconsistency, the lock collar 2 10 is also formed with a
draft angle. The angles on the collar teeth and the side gear lugs may be
complementary to ensure smooth meshing engagement.
[056] Since prior lock collars are formed via impact extrusion using a die to
transfer a pattern on to sheets, the collar teeth of prior designs do not have a draft.
The draft on the collar teeth 504 may be formed by machining the pattern impact
extruded on the lock collars, which is very expensive. Or, because the design is
simplified by the removal of the collar ears, the draft may be provided by way of
closed die hot forging. Providing the draft on the lock collar teeth 504 at the same
value as the draft on the lugs 224 enhances smooth and full engagement of the
collar teeth 504 with the lugs 224. The draft angle on the collar teeth 504 may assist
with preventing lock collar failure due to rounding of tooth corners and improper load
sharing, or may prevent failure due to frictional resistance offered by the gear lugs
to the movement of the collar teeth.
[057] Turning for Figure 6, the torque sensitive pins 200 have an end face
204 that may have a notch or groove pattern (Phillips, "straight-head", or other) for
screwing or unscrewing the torque sensitive pin head 201 in to the left hand case
2 12 . While not shown, the pin head 201 is threaded and the openings 7 10 in the left
hand case are threaded so as to fixedly couple the pin head 201 in place. The body
202 of the torque sensitive pin 200 may terminate with a beveled end 205. A
shearing zone, or neck, 203 may be between the pin head 201 and the pin body
202. The shearing zone 203 may include a groove, which may be circumferential,
for ensuring the location of pin shear. The neck may also have the same diameter
as the pin body.
[058] The number and size of torque sensitive pins 200 can vary. For
example, the figures show embodiments having 6 or 8 torque sensitive pins, but
other numbers of pins may be used, such as 4 to 10 . In addition, the ratio of the
diameter of the pin body to the diameter of the pin head can vary, and the ultimate
diameters of the pin heads and pin bodies can vary. The pin should shear at or near
the interface of the pin head with the pin body, and the area of the shear location
203 may be less than the area of the pin body if a groove is placed in the body, thus
reducing the diameter at that location.
[059] Additional considerations arise because the lock collar 2 10 can
receive torque load before the lock collar 2 10 has fully engaged the locker gear.
This can create a bending stress that can differ from an ideal uniformly distributed
load (UDL). So, for Figure 20, the differential is shown in the open mode. The collar
teeth 504 have not yet engaged the lugs 224 of the locker gear (side gear 2 19). The
lock plate 2 10 has a thickness T L that translates along the torque sensitive pin 200.
The torque sensitive pin 200 has a beam thickness T B, which is the length of the pin
that is exposed during the open mode.
[060] The exposed length can experience bending stress that varies based
on the percent of engagennent of the collar teeth 504 with the lugs 224. As the
engagennent percent varies from 5% to 100%, the bending stress varies, and, as the
torque sensitive pin count varies from 4 to 10 pins in the differential, the bending
stress varies with the percentage of tooth 504 to lug 224 engagement.
[061] A further modified scenario may occur if the torque pin is deflected
during usage. This can occur if the load is not uniformly distributed. In such a
scenario, the point load acts at on the pin at the beginning of the lock collar surface
and the torque load distributions and bending stress adjust accordingly. To ensure
that the load breaks the torque sensitive pin at a desired location, such as at the
interface of the pin head with the pin body, a groove maybe included at the shear
location 203. The groove diameter should be slightly less than body diameter.
[062] Since the lock collar 2 10 and torque sensitive pins 200 are placed in
the torque flow path, it is important that when the device fails, the debris should be
contained in a location outside the flow path and such that the debris does not
contaminate other internal components. Thus, the clearance between the left hand
case 2 12 and the lock plate 2 10, the clearance between the lock plate and the right
hand case 2 11, and the length of the pin body 202 may be selected to avoid travel
of torque sensitive pin debris. The torque sensitive pin is also dimensioned and
formed of a material that has a minimal chance of exploding or shattering into many
small pieces. This assists with serviceability of the design. That is, the differential
may be taken apart and the torque sensitive pins 200 may be replaced. The design
is serviceable and the whole part does not always have to be scrapped upon
shearing of the torque sensitive pins. However, it may be necessary to disassemble
portions of the differential and the driveline to effectuate the servicing.
[063] In a second embodiment, shown in Figure 10, rather than dismantling
the axle shafts, bearing caps, bearings, etc of the rear drive axle, the differential
may be serviced to remove the torque pin head and torque pin body after removing
only a housing around the pinion gear and ring gear. In this design, the torque
sensitive pins couple the left hand case to a collar housing (lock plate housing)
thereby operatively coupling to an eared collar within the collar housing. The torque
sensitive pins abut springs in the collar housing to enable the sheared pin body to
be ejected during servicing. The torque sensitive pins can be replaced without
scrapping the whole differential and without dismantling the drive axle and
differential.
[064] Several elements of the first embodiment appear in the second
embodiment and will not be re-discussed.
[065] Turning to Figures 17-1 9, the left hand case 273 couples to the right
hand case 2 11 via lock screws 214 through openings 1614 and 1814. As above, the
coupling may use threading. Openings 16 10 receive, respectively, 8 torque limiter
pins (torque sensitive pins) 274. The torque limiter pins 274 are threaded to the left
hand case 273. The torque limiter pins 274 pass in to lock plate housing 271 where
they abut pin springs 272. The pin springs 272 may have an outer diameter equal to
or less than the outer diameter of the torque limiter pins 274 to avoid having the
spring wrap around the torque limiter pins 274.
[066] A lock plate 270 may reciprocate in the lock plate housing 271 to lock
and unlock the differential. That is, the lock plate 270 may slide from a first position,
where the differential operates in an open mode, to a second position, where the
differential operates in a locked mode. As above, the ramp plate 253, push rods
247, and wave spring 261 may operate to move the lock plate 270. The first end
249 of the push rod abuts the lock plate 270.
[067] Figure 11 shows the differential of the second embodiment along a
plane to illustrate the push rod 247 abutting the lock plate 270. It also illustrates that
the lock plate can slide a distance D in the lock plate housing 271 . Figure 12 shows
the same differential along another plane that shows the torque limiter pins 274
passing through openings 161 0 in the left hand case 273. The torque limiter pins
274 pass into the lock plate housing 271 with the pin springs 272 in abutment. Since
the example of Figure 12 is not to scale, the pin springs 272 may have other
dimensions, such as longer or shorter with respect to the lock plate housing 272,
and the torque limiter pins 274 may have other dimensions, including a longer or
shorter body length. Both figures show the lock plate 270 disengaged from the lugs
224 of the left hand side locker gear 2 19 .
[068] The length of the torque limiter pins, the clearance between the left
hand case 273 and the lock plate housing 271 , and the clearance between the lock
plate housing 271 and the right hand housing 2 11 are selected to contain the
sheared torque limiter pins 274 within an area that does not contaminate other
moving parts of the differential. And, the torque limiter pins 274 are preferably
designed not to explode or create excessive debris upon shearing.
[069] Figures 13A and 13B show the lock plate 270 and lock plate housing
271 in more detail. The lock plate 270 has ears 1301 for sliding in recesses 1302 of
the lock plate housing 271 . The recesses 1302 do not have to span the whole
length of the lock plate housing 271 , and a stop 1303 may be provided. The wave
spring 261 may abut the circumferential rim 1304 provided on the interior of the lock
plate housing so as to be inward of the stop 1303. Abutting the wave spring in this
manner may alleviate the need for an amount of damping depth in the left hand
case, thereby enabling the wave spring recess 1608 to be shallower. A wave spring
stop 16 11 forms a bottom of the wave spring recess 1608 for the wave spring 261 to
seat against.
[070] In addition to abutting the rim 1304, the wave spring 261 biases the
lock plate 270 away from stop 1303, away from the left hand case 273, and towards
the ramp plate 253. With this biasing, when the differential is in an open mode, the
lock plate teeth 1305 do not engage side gear lugs 224 and the lock plate 270
pushes the push rods 247 towards valleys of the ramp plate 253. In a locked mode,
the wave spring 261 is compressed, and peaks of the ramp plate 253 push the push
rods 247, and the push rods 247 push the lock plate 270 towards the left hand case
273 so that the lock plate teeth 1305 engage the side gear lugs 224.
[071] The lock plate 270 of Figure 13 does not show a draft on the lock plate
teeth 1305, though such a draft may be provided, as above.
[072] The lock plate housing 271 additionally has pin holes 1306. The pin
holes 1306 may pass through the lock plate housing 271 , since the pin springs 272
may abut the right hand case 2 11. However, to avoid friction caused when the lock
plate housing 271 is free to rotate, the pin holes 1306 may partially extend into the
lock plate housing 271 , so that the pin springs 272 span between a bottom of the
pin holes 1306 and an end of a torque limiter pin 274. The pin holes 1306 enable a
slide-fitting with the torque limiter pins 274 and the clearance between the pin holes
1306 and the torque limiter pins 274 is designed to account for a bending stress. As
above, the lubricating fluid in the differential may assist with smooth sliding between
parts.
[073] Figure 13B shows an opposite side of the lock plate housing 271 . The
view includes pin holes 1306 and a plurality of recesses 13 10 spaced between each
of the pin holes. The recesses 13 10 align with indexing slots 16 16 in the left hand
case 2 12 . Should the torque limiter pins 274 shear, the lock plate housing 271
becomes free to rotate in the right hand case 2 11. This rotation is possible even if
the wave spring 261 is able to disengage the lock plate 270 from the side gear lugs
224. Because of this ability to rotate, the pin holes 1306 of the lock plate housing
271 may no longer align with the torque pin holes 161 0 of the left hand case. Thus,
when the torque limiter pin heads 141 are unscrewed from the left hand case 2 12,
the pin springs 272 may not eject out the debris. Therefore, a user may manually
turn the lock plate housing 271 by putting a rod, screwdriver, or other prodding
device into an available recess 1310 and by using the prodding device to turn the
lock plate housing in to alignment for proper debris ejection. This design enables the
differential to be serviced without disassembling the differential. It is possible to
replace the torque limiter pins after draining the lubricating fluid from the housing
surrounding the pinion and ring gear and removing only an access panel of that
housing.
[074] The lock plate 270 is in the torque path of the differential and is critical
for locking the locker gear 219 for rotation with the left hand case 2 12, and thus
locking the right rear axle 112 rotation with the left rear axle 111 rotation. Hence, the
differential can only operate in a locked mode if the lock plate housing 271 is braced
by the torque limiter pins 274 and the lock plate 270 is engaged with the locker gear
2 19 . If an amount of torque above a predetermined value pushes on the lock plate
270, the lock plate housing 271 can rotate and shear the torque limiter pins 274.
The lock plate housing 271 , and thereby the lock plate 270, is free to rotate in the
right hand case 2 11. The wave spring can push the lock plate 270 away from an
engaged position with the lugs 224 of the locker gear 2 19 and the differential
operates in the open mode.
[075] The torque limiter pins 274 are designed in size and number according
to the torque capacity of the system and the torque limiter pins are designed to
shear before other components within the drive axle and differential fail via torsion
or shearing. For example, the torque limiter pins 274 may shear under a pure shear
condition. That is, the torque limiter pins may fail due to shear loads or shear
stresses only. Ideally, the applied loads due to torque on the pins are perpendicular
to axis of the pins so that no other loads like bending, torsion, impact etc. act on the
pins. The ultimate strength of the torque limiting system may match the yield
strength of the axle shaft material or the yield strength of the lock collar material. In
other words, when the axle shaft or lock collar should yield, the torque limiting pins
274 instead shear.
[076] The torque limiter pins 274 have an end face, which may have a
groove or other recess to enable screw-in coupling with the left hand case 273. The
pin head 14 1 may be partially or fully threaded for fixedly coupling to the left hand
case 273. The pin body 142 may be shorter than the pin body 202, but in any case,
may terminate with a beveled end 145. A shear location, or neck, 143 may be
provided between the pin head 141 and the pin body 142. The shear location 143
may comprise a groove, which may be circumferential, to facilitate shearing along a
particular plane of the torque limiter pin 274. The neck may also have the same
diameter as the pin body.
[077] Similar to the above examples, it is possible to describe the shear
stresses on the torque limiter pins by contrasting the diameter of the pin body, the
number of pins, and the shear stress. That is, torque loads may be accommodated
by varying the number of pins used, the relative diameters of the pin head, pin body
and or pin neck, and by the use or non-use of a groove at the interface of the pin
head and pin body. In addition, varying the distance of the pins from the central axis
(A or B) can also impact the torque load accommodated before shearing.
[078] Because the lock plate housing 271 should be stationary with respect
to unsheared torque limiter pins, and the lock plate housing should not move along
the length of the torque limiter pins, pin bending stress and pin deflection
considerations are reduced from the first embodiment.
[079] Once the torque limiter pins 274 shear, in order to eject the bodies 142
out of the lock plate housing 271 , the pin heads 141 are unscrewed from the left
hand case 273. To facilitate alignment of the sheared debris with the openings
1610, the lock plate housing 271 is indexed, as above, with respect to the left hand
case 273 so that the pin holes 1306 align with the torque pin holes 161 0 . Once
alignment is achieved, the compressed pin springs 272 eject the pin bodies 142.
New torque limiter pins may then be installed without disassembling the differential
from the pinion and ring gear housing, without further adjustment to the left and right
hand cases 273 and 2 11, and without uninstalling the axles, bearings, etc.
[080] Additionally, the sheared torque limiter pins may be removed by
unthreading the pin heads 141 . Then, constrain the differential rotation manually
and constrain the right hand axle shaft from rotation. Next, turn the ramp plate 253
in either direction, first by activating the stator coil which constrains the ramp plate
rotation and then rotate the ring gear which can be done manually, to overcome
wave spring 261 force. This can be done with or without rotation of the left hand
axle shaft. As the ramp plate pushes against push rods 274, the lock plate 270 can
engage the lugs 224. Rotating the left hand axle will then rotate the locker gear,
which will rotate the lock plate 270 and the lock plate housing 271 . The pin holes
1306 may then be aligned with the empty torque pin holes 16 10, and the tensed pin
springs 272 may eject the slide-fitted sheared pin bodies 142.
[081] 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 being indicated by the following claims.

WE CLAIMS:-
1. A selectively lockable differential, comprising:
an outer housing;
a first side gear comprising first gear teeth and gear lugs;
a second side gear comprising second gear teeth;
a pinion shaft;
two pinion gears rotationally coupled to the pinion shaft, each pinion gear
comprising pinion gear teeth coupled to the first gear teeth and the second gear
teeth;
a collar comprising collar teeth for selectively engaging the gear lugs of the
first side gear; and
a plurality of torque sensitive pins operatively coupled through the outer
housing and configured to shear when torque to the first side gear exceeds a
predetermined value.
2 . The differential of claim 1, wherein the collar further comprises coupling
ears and the differential further comprises a collar housing coupled to the torque
sensitive pins, the collar housing comprising coupling recesses for receiving the
coupling ears, the collar housing at least partially surrounding the collar.
3 . The differential of claim 2, further comprising an actuator and push rods,
wherein the actuator is configured to selectively push the push rods towards the
collar, and when the push rods push the collar, the coupling ears slide in the
coupling recesses and the collar teeth engage with the gear lugs.
4 . The differential of claim 1, further comprising at least one spring between
the outer housing and the collar, the at least one spring biased to push the collar
teeth away from the gear lugs.
5 . The differential of claim 1, further comprising an actuator and push rods,
wherein the actuator selectively pushes the push rods towards the collar, and when
the actuator pushes the push rods towards the collar, the collar slides in the outer
housing and the collar teeth engage with the gear lugs.
6 . The differential of claim 1, wherein each torque sensitive pin comprises a
head with a threaded portion and a body with a smooth portion, wherein the outer
housing comprises a plurality of threaded openings, wherein each of the plurality of
threaded openings receives a corresponding threaded portion of one of the plurality
of torque sensitive pins, wherein the collar further comprises a plurality of collar
holes, wherein each of the plurality of collar holes receives a corresponding smooth
portion of one of the plurality of torque sensitive pins, and wherein the collar is
slidable on the smooth portions to selectively engage and disengage the gear lugs
and the collar teeth.
7 . The differential of claim 2, wherein the collar housing further comprises a
plurality of holes, wherein each hole receives a corresponding one of the plurality of
torque sensitive pins, wherein the differential further comprises a plurality of pin
springs, and wherein each hole houses a corresponding one of the plurality of pin
springs in abutment with the corresponding torque sensitive pin.
8 . The differential of claim 7, wherein each torque sensitive pin comprises a
head with a threaded portion and a body with a smooth portion, wherein the outer
housing comprises a plurality of threaded openings, wherein each of the plurality of
threaded openings receives a corresponding threaded portion of one of the plurality
of torque sensitive pins, wherein each collar housing hole receives a corresponding
smooth portion of one of the plurality of torque sensitive pins, and wherein the pin
springs are biased to push the smooth portions out of the holes.
9 . The differential of claim 7, wherein:
the outer housing comprises at least one slot,
the collar housing further comprises a plurality of recesses distributed
between each of the plurality of holes,
the collar housing is seated in the outer housing such that the recesses are
accessible through the at least one slot, and
the collar is seated in the collar housing.
10 . The differential of claim 1, wherein each torque sensitive pin comprises a
head, a neck, and a body, and the neck has a diameter that enables the pin to
shear at the neck before any other location on the torque sensitive pin.
11. The differential of claim 1, wherein each torque sensitive pin comprises at
least a head interfaced with a body, wherein the distance between the outer housing
and the collar is selected to ensure that each torque sensitive pin shears in an area
at or near the interface of the head and the body, and wherein, when the torque
sensitive pins shear, the collar is rotatable in the outer housing.
12 . The differential of claim 2, wherein each torque sensitive pin comprises
at least a head interfaced with a body, wherein the distance between the outer
housing and the collar housing is selected to ensure that each torque sensitive pin
shears in an area at or near the interface of the head and the body, and wherein,
when the torque sensitive pins shear, the collar housing is rotatable in the outer
housing.
13 . The differential of claim 1, wherein, when the differential receives torque,
each torque sensitive pin is configured to shear before the collar teeth or first gear
teeth yield.
14. The differential of claim 1, wherein the collar teeth have a draft angle and
the gear lugs have a draft angle, and the collar teeth draft angle is complementary
to the gear lug draft angle.
15 . A vehicle driveline comprising the selectively lockable differential of claim
1, the driveline further comprising:
a torque transmission system operatively coupled to transmit torque from an
engine to the selectively lockable differential;
a first axle operatively coupled to the first side gear; and
a second axle operatively coupled to the second side gear,
wherein, when the differential receives torque above a predetermined value,
each torque sensitive pin shears before the first axle or the second axle shears or
before the first axle or the second axle yields to torsion.