IDLE-ABLE AUXILIARY DRIVE SYSTEM
TECHNICAL FIELD
[001 ] The present disclosure relates generally to automotive vehicle drivelines
that can convert between drive systems using two out of four wheels and all four wheels.
More specifically, the present disclosure relates to a power transfer unit that assists with
this conversion and the design and placement of a piston within the power transfer unit
that enables efficient packaging into a vehicle driveline.
BACKGROUND
[002] Current all wheel drive (AWD) vehicle drivelines may comprise a primary
front drive axle coupled to a secondary auxiliary rear drive system. The secondary
auxiliary rear drive system typically includes a power transfer unit, a drive shaft, an
AWD coupling device, a rear axle, and rear half shaft assemblies. When the vehicle is
operating in a 4 x 2 mode, the front primary axle provides tractive forces to keep the
vehicle moving, and to overcome the driveline efficiency losses of the secondary drive
axle that is being driven through the tire/road surface interface. The driveline efficiency
losses are largely due to oil.churning losses, viscous drag, inertia, and friction.
[003] To provide a more fuel efficient driveline for operating in 4 x 2 mode, it is
desirable to have the ability to completely "idle" the secondary auxiliary drive system by
disconnecting the secondary auxiliary drive system from the primary drive system and
allowing the secondary auxiliary drive system to rotationally coast to a stop. Idling the
secondary auxiliary drive system in this manner would remove virtually all of the

driveline efficiency losses from the secondary auxiliary drive system with the exception
of its non-rotating inertia.
SUMMARY
[004] In one embodiment, a power transfer unit (PTU) for a motive device
includes an outer housing and a torque transferring clutch. The PTU also includes a
piston housing located between the outer housing and the torque transferring clutch, and a
piston in the piston housing. The piston is arranged to provide actuation forces to the
torque transferring clutch, and to restrict reaction forces back to the piston housing.
[005] In another embodiment, a torque transferring system may comprise a
motor for supplying torque, a transmission operatively coupled to the motor, a primary
drive axle operatively coupled to the transmission, and a power transfer unit operatively
coupled to the primary drive axle. The power transfer unit may comprise an outer
housing. The outer housing may surround a piston in a piston housing, first coupling
members selectively operatively coupled to the piston, a torque transferring clutch
selectively operatively coupled to the first coupling members, and second coupling
members selectively operatively coupled to the torque transferring clutch. A pinion gear
may operatively couple to the second coupling members. A drive shaft may operatively
couple to the pinion gear. A secondary drive axle may operatively couple to the drive
shaft.
[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 invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS
[007] The accompanying drawings, which are incorporated in and constitute a
part of this specification, illustrate several embodiments of the invention and together
with the description, serve to explain the principles of the invention.
[008] FIG. 1 is an example of a vehicle driveline having an idle-able PTU.
[009] FIG. 2A is an example of a PTU with a non-rotating piston and
non-rotating piston housing.
[010] FIG. 2B is an enlargement of a section of the PTU of Fig. 2A.
[011] FIG. 3 is an example of an electronic control unit (ECU).
[012] FIG. 4 is an example of a wheel hub disconnect.
[013] FIG. 5 is a schematic of an exemplary hydraulic control unit (HCU).
[014] FIG. 6 is an alternative schematic of an exemplary HCU.
DETAILED DESCRIPTION
[015] Reference will now be made in detail to the present exemplary
embodiments, examples of 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.
[016] FIG. 1 shows one example of a front wheel drive vehicle driveline system
for use in, for example, an automobile. The driveline comprises four wheels: first wheel
108, second wheel 109, third wheel 110, and fourth wheel 111. The front wheels, first
wheel 108 and fourth wheel 111, provide tractive forces for 4 x 2 mode, which is a mode
where rear wheels, second wheel 109 and third wheel 110, do not receive torque from the

engine. In 4 x 4 mode, front and rear wheels receive torque from the engine to provide
tractive forces for the vehicle.
[017] Wheels 111 and 108 are part of a front axle, which comprises first and
second constant velocity joint and output half shaft assemblies 104 and 105, primary
drive front transaxle 102, and idle-able power transfer unit (PTU) 101. Primary drive
front transaxle 102 is in mechanical communication with engine 103 and PTU 101, which
may be bolted to the transaxle 102. PTU 101 is in mechanical communication with
pinion gear 107, which is coupled via companion flange 106 to drive shaft 112. Drive
shaft 112 is further coupled to rear drive axle 113, which is connected to first rear half
shaft 114 and second rear half shaft 115. First rear half shaft 114 is coupled to first wheel
hub disconnect 117, which is connected to second wheel 109. Second rear half shaft 115
is coupled to second wheel hub disconnect 118, which is coupled to third wheel 110.
[018] The primary drive system of the vehicle may comprise engine 103,
primary drive front transaxle 102, first and second constant velocity joint and output half
shaft assemblies 104 and 105 and output half shaft 204. The secondary auxiliary drive
system may comprise PTU 101, pinion gear 107, companion flange 106, drive shaft 112,
rear drive axle 113, first rear half shaft 114, and second rear half shaft 115. The
secondary auxiliary drive system can completely and non-rotationally idle while the
vehicle is operating in a 4 x 2 mode and then re-engage the drive system for operation in
a 4 x 4 mode across all operating speeds, including highway operating speeds.
[019] Torque transfers from the engine to a transmission within the primary
drive front transaxle 102 and then to a front drive differential case. The front drive
differential case can divide torque between a front driving differential gear set and PTU

101. The two front half shafts transfer torque to first wheel 108 and fourth wheel 111.
PTU 101 transfers torque, through features described below, to drive shaft 112 then rear
drive axle 113, where it is divided between first rear half shaft 114 and second rear half
shaft 115. Appropriate amounts of torque are transferred to second wheel 109 and third
wheel 110 through, respectively, first wheel hub disconnect 117 and second wheel hub
disconnect 118.
[020] An electronic control unit ("ECU") 120 processes data from sensors 116,
which are connected to various locations along the driveline to determine the appropriate
distribution of torque to each of the vehicle wheels. The amount of torque may be the
same for each of first wheel 108, second wheel 109, third wheel 110, and fourth wheel
111, or the amount of torque to each wheel may vary in response to traction, stability,
braking, steering angle, driveline speed, acceleration, yaw, throttle position, or other
vehicle conditions.
[021 ] Various sensors and communications 116 provide data for processing
within an electronic control unit 120. ECU 120 can determine appropriate amounts of
torque for transfer to second wheel 109 and third wheel 110. In addition, ECU 120 can
control when first wheel hub disconnect 117 and second wheel hub disconnect 118
should connect or disconnect second wheel 109 and third wheel 110 from respective first
rear half shaft 114 and second rear half shaft 115. The connection and disconnection is
facilitated by actuation from a hydraulic control unit ("HCU") 119, as will be further
discussed below. HCU 119 also assists with actuation of a piston 211, as shown in
Figure 2, within PTU 101. ECU 120 may also determine when HCU 119 should actuate
piston 211. A skilled artisan will recognize the arrangement of sensors and

communications 116, the arrangement and operation of ECU 120, and the connection
means to and from HCU 119.
[022] Figures 2A and 2B show one embodiment of an inventive idle-able PTU.
Figure 2A is an enlargement of PTU 101 of Figure 1, and Figure 2B is an enlargement of
a section of the PTU of Figure 2A.
[023] PTU 101 includes a torque transferring clutch in series with actuation
members. In the embodiment shown, the torque transferring clutch is a wet clutch in
series with a synchronized dog clutch. The torque transferring clutch may comprise a
coupling member 218, inner friction discs 219, and outer friction discs 221. The torque
transferring clutch may comprise a multi-plate wet clutch pack 222. The dog clutch may
comprise a dog collar with wet clutch features. In addition, actuation members may
comprise, for example, slave piston 213, inner pins 214, outer pins 220, second needle
thrust bearing 215, friction disc 217, and dog collar 216.
[024] PTU 101 includes a housing that may comprise PTU outer housing cap
229 and PTU outer housing 230. PTU outer housing cap 229 also houses PTU oil
volume area 208 and interfaces with roller bearing assembly 233. PTU outer housing
230 interfaces with PTU pinion housing 231. PTU pinion housing 231 houses pinion
gear 107 and interfaces with at least one speed sensor 232.
[025] As discussed above, torque is divided between the front driving
differential (not shown) and PTU 101. PTU 101 receives torque via a hollow shaft 201
that is in direct connection between the front driving differential case and the input of a
disconnectable hydraulically actuated multi-plate clutch in clutch pack 222. The clutch
pack 222 is an example of a wet clutch, which is a lubricated clutch that can be

selectively compressed to cause the plates to grip one another. The amount of grip
engagement, or stiffness, of the plates correlates to the amount of torque transferred by
the plates. The stiffness of the multi-plate clutch limits the torque transferred through a
right angle gear set, comprised pinion gear 107 and ring gear 224. The right angle gear
set drives drive shaft 112.
[026] When operating in a 4 x 2 vehicle mode, torque is supplied to hollow shaft
201 directly from the front axle differential case. Hollow shaft 201 is radially supported
via needle roller bearing 202 and also at a journal bearing fit at location 203 on output
half shaft 204. The hollow output half shaft 204 spins freely, not transferring torque to
any other portion of PTU 101. The space between output half shaft 204 and tube feature
205 forms a volume where lubricating oil from the transaxle freely flows. Tube feature
205, roller bearing assembly 233, first lip seal 206, and second lip seal 207, respectively,
to form an oil tight volume which keeps the oil from the transaxle (not shown) from
mixing with the gear oil contained within PTU oil volume area 208. Output half shaft
204 connects, through roller bearing assembly 233, to constant velocity joint assembly
236 and constant velocity joint boot 237, which in turn interfaces with right hand outer
output half shaft 238.
[027] To shift the vehicle from a 4 x 2 mode to a 4 x 4 mode of operation,
hydraulic control unit 119 supplies hydraulic fluid to oil port 209, which is secured to
PTU outer housing cap 229 by sealing nut 241. The hydraulic fluid flows into piston
chamber 210 in piston housing 240, where hydraulic pressure builds. Piston housing 240
pilots on the torque transferring clutch, but does not rotate. The pressure forces piston
211 to move axially, which creates thrust and moves first needle thrust bearing 212 and

slave piston 213. The axial movement in turn forces a plurality of inner pins 214 to
engage second needle thrust bearing, which moves axially to urge dog collar 216 to
contact rotating friction surface disc 217.
[028] Additional pressure supplied by hydraulic control unit 119 into piston
housing 240 causes friction to increase between non-rotating dog collar 216 and rotating
friction disc 217. The increasing pressure causes dog collar 216 to begin rotating.
Coupling member 218 and inner friction discs 219 rotate with dog collar 216 through
rotative spline engagement between dog collar 216 and coupling member 218, and
between coupling member 218 and inner friction discs 219 of clutch pack 222.
[029] As the rotating speed of dog collar 216 and friction disc 217 synchronizes,
so does the rotating speed of dog collar 216 and hollow shaft 201. The synchronization is
facilitated through the rotative engagement of friction disc 217 with hollow shaft 201.
[030] Further increases in hydraulic pressure moves dog collar 216 axially and
into mechanical rotative engagement with hollow shaft 201. Mechanical engagement
occurs by mating dog clutch features on the inner radial face of dog collar 216 with
corresponding dog clutch features on the outer radial face of hollow shaft 201. After the
dog collar 216 and the hollow shaft 201 engage, the hollow shaft 201, dog collar 216,
coupling member 218, and inner clutch discs 219 rotate together and the remainder of
PTU 101 remains in idled condition.
[031 ] Additional fluid pressure into piston housing 240 completes the
conversion from 4 x 2 mode to 4 x 4 mode. This additional fluid pressure in piston
chamber 210 of piston housing 240 causes a plurality of outer pins 220, which are
connected to slave piston 213, to contact the outer friction discs 221 of clutch pack 222.

[032] As the additional fluid pressure increases, so does the axial force exerted
from outer pins 220 on clutch pack 222. As clutch pack is loaded axially, torque is
transferred from coupling member 218 to flange half spool 223. Torque applied to flange
half spool 223 applies torque to ring gear 224, which in turn supplies torque to pinion
gear 107. Pinion gear 107 may be splined to companion flange 106, which is in turn
bolted to the drive shaft 112.
[033] Outer pin 220 is shown in Figure 2A as integral with slave piston 213, but
outer pin 220 can be separate from slave piston 213. Inner pin 214 is shown separate
from outer pin 220/ slave piston 213 combination, but inner pin 214 may be integral with
the combination.
[034] Synchronization across clutch pack 222 occurs progressively to transfer
torque from hollow shaft 201 to drive shaft 112, rear drive axle 113, first rear half shaft
114, and second rear half shaft 115. The rotational speed of outer friction discs 221,
coupling member 218, and flange half spool 223 increases until the rotational speed is
synchronized with inner friction discs 219. Through this synchronization, outer friction
discs 221, coupling member 218, flange half spool 223, and inner friction discs 219 are
also synchronized with hollow shaft 201.
[035] When the synchronization of inner friction discs 219 and outer friction
discs 221 is within predefined limits, the rotational speed difference between the rear
vehicle drive wheels, second wheel 109 and third wheel 110, and first rear half shaft 114
and second rear half shaft 115 also synchronize within predefined limits. Torque then
transfers from the primary drive system to the secondary drive system and is controlled

by the number of and extent of engagement of inner friction discs 219 and outer friction
discs 221.
[036] With the primary drive system substantially rotationally synchronized with
the secondary drive system, the rear wheels are connected to the secondary drive system.
As illustrated in Figure 4, hydraulic control unit 119 supplies hydraulic fluid to a wheel
hub hydraulic fluid input 402 for actuation of a wheel hub piston 403 at second wheel
hub disconnect 118. Wheel hub piston 403 causes a dog clutch arrangement at dog clutch
features 409 to engage. The dog clutch features are present on wheel hub dog collar 405,
output stub shaft 411, and second rear half shaft 115. A similar operation occurs at wheel
first wheel hub disconnect 117 to enable the secondary auxiliary drive system to engage
the rear wheels.
[037] Second wheel 109 and third wheel 110 convert from being driven by tire-
road friction to being driven by the driveline in a 4 x 4 configuration. The magnitude of
drive torque transferred through the secondary auxiliary drive system may be controlled
by the torque transfer at clutch pack 222.
[038] When shifting the vehicle from a 4 x 4 mode to a 4 x 2 mode of operation,
and to completely idle the secondary auxiliary drive system during 4 x 2 mode operation,
hydraulic control unit 119 reduces hydraulic pressure within piston chamber 210 to a
predefined level. This allows the combined axial force of first and second bias springs
227 and 228 and clutch pack (222) compliance to create sufficient thrust to push outer
pins 220 out of contact with the closest outer friction disc 221. The clutch pack
compliance is a spring-like force caused by the tendency of inner friction discs 219 and
outer friction discs 221 to spread apart. Ideally, both bias springs 227 and 228 unload to

transfer thrust and prevent any drag. However, in some embodiments, bias springs 227
and 228 may remain slightly compressed.
[039] The thrust transfer disengages the discs of clutch pack 222, which reduces
the torque transfer through clutch pack 222 to a minimum. First bias spring 227 and
second bias spring 228 axially push on inner pins 214 via dog collar 216. The pushing
moves dog collar 216 out of mechanical rotational engagement with hollow shaft 201.
First bias spring 227 and second bias spring 228 continue to move dog collar 216 axially
until friction disc 217 is also out of contact with dog collar 216. This disconnects a front
portion of the auxiliary drive system from the primary drive system.
[040] The thrust from bias springs 227 and 228, combined with clutch pack 222
compliance, also transfers through piston 211, which pushes axially on piston housing
240. Thrust then transfers to needle roller bearing 242. Needle roller bearing 242 is
comprised of a plurality of rollers which pilot in place between piston housing 240 and
thrust bearing 239. Radial needle bearing 242' also comprises a plurality of rollers,
which receive radial loading and radially support piston housing 240 on thrust bearing
239. Needle roller bearing 242 receives and reacts to thrust loads from piston 211. The
thrust loads are transferred in to thrust bearing collar 239, which is threaded on to cap
half spool 235 which abuts shim 234. Shim 234 braces the motion of hollow shaft 201.
Thrust bearing 239 and cap half spool 235 rotate together. Axial thrust from piston 211,
clutch pack compliance, and bias springs 227 and 228 is contained between cap half
spool 235 and flange half side spool taper roller bearing 244, with the majority of the
axial thrust remaining within the torque transferring clutch. Optimally, no axial thrust is
transferred to flange half side spool taper roller bearing 244. Axial thrust transfer to cap

half side spool taper roller bearing 243 is eliminated. Any thrust forces received at cap
half side spool taper roller bearing 243 are from the gear set at pinion gear 107,
[041] The thrust loading of the needle roller bearing 242 and piston housing 240
can create an axial force, which can react back to the disc case of clutch pack 222. The
reaction force caused by the thrust loading remains in the torque transferring clutch.
[042] This departs from the conventional drive system, which does not include
needle roller bearings or a piston housing. In order to accommodate thrust loads from the
torque transferring clutch, the conventional drive system would require stronger, larger
and more costly taper roller bearings for an output half shaft and a flange half side spool.
This would increase the packaging of the conventional drive system.
[043] The embodiment of Figure 2A and 2B allows for a smaller and less costly
cap half side spool taper roller bearing 243 and flange half side spool taper roller bearing
244. The use of piston housing 240 also improves the packaging of PTU 101 by reducing
a housing size requirement for the accommodation of taper roller bearings. The reduced
housing size requirement allows pinion gear 107 to be mounted closer axially to the
interface between pinion gear 107 and primary drive front transaxle 102. This design
allows for additional improvements to packaging capabilities on vehicle drivelines.
[044] The use of non-rotating piston housing 240 also moves the piston 211
location inboard from cap half side spool taper roller bearing 243, thereby allowing the
use of a larger outer diameter sized cap half side spool taper roller bearing 243. This
arrangement reduces the overall axial package of PTU 101 and improves the packaging
of PTU 101 into vehicle platforms.

[045] Moving the location of non-rotating piston housing 240 inboard from a
cap half side spool taper roller bearing 243 has an additional benefit, because the change
in location may accommodate a larger inner diameter sized cap half side spool taper
roller bearing 243.
[046] The radial design freedom on the inner and outer diameters of the cap half
side spool taper roller bearing 243 benefits both a sealing tube feature 205 and the output
half shaft 204. The sealing tube feature 205 and the output half shaft 204 can have
enhanced sectional modulus to handle additional torque and fatigue, when compared to
the conventional drive system. The enhancements benefit the longevity of both the
idle-able auxiliary drive system and the primary drive system of a vehicle.
[047] Also, when shifting from 4 x 4 mode to 4 x 2 mode, the auxiliary drive
system fully disconnects from both rear drive wheels, second wheel 109 and third wheel
110 when HCU 119 reduces hydraulic pressure to wheel hub piston 403. The rear drive
wheels are disconnected after the multiplate clutch pack 222 is unloaded to reduce torque
going to the secondary auxiliary drive system and the synchronized dog clutch at dog
collar 216 is disengaged. After the rear wheels are disconnected at first and second wheel
hub disconnects 117 and 118, hydraulic pressure in piston housing 240 is reduced to
facilitate the disconnection of the PTU from hollow shaft 201.
[048] Figure 4 shows an embodiment of second wheel hub disconnect 118 for
disconnecting third wheel 110 from the auxiliary drive system. When PTU 101 transfers
a minimum of torque onto the auxiliary driveline, the hydraulic pressure to the first wheel
hub disconnect 117 and the second wheel hub disconnect 118 is reduced to a minimum
level. A hydraulic fluid input 402 in wheel hub disconnect housing 401 is connected to

HCU 119 to achieve the pressure reduction. Bias springs 406 and 406' located between
knuckle 408 and wheel hub dog collar 405 cause dog clutch features 409 on each of an
output stub shaft 411, second rear half shaft 115, and wheel hub dog collar 405 to
disengage. This disconnects the rotational connection between the second rear half-shaft
115 and third wheel 110, which is attached via wheel lugs 412 and 412' to output stub
shaft 411 and needle bearing 410, output stub shaft 411 being surrounded by wheel hub
bearing 413. A similar operation also occurs on first rear half-shaft 114.
[049] With the secondary auxiliary drive system fully disconnected from the
primary drive system of the vehicle, and the rear wheels fully disconnected from the
secondary auxiliary drive system, the secondary auxiliary drive system coasts to a
non-rotational stop. The secondary auxiliary drive system is then in an idled condition,
and the fuel economy of the driveline increases.
[050] Figure 3 shows an exemplary schematic for an electronic control unit
(ECU) system. The ECU system comprises sensors 301, ECU 120, HCU 119, and
vehicle bus 319 with associated controller area network (CAN). Sensors 301 collect data
for use in observers 310 and controller 314 of ECU 120. The sensors may comprise one
or more of a steering angle sensor 302, driveline speed sensor 303, longitudinal
acceleration sensor 304, lateral acceleration sensor 305, yaw rate sensor 306, throttle
position sensor 307, brake pedal sensor 308, and hydraulic control unit sensor 309. The
sensors shown in Figure 3 are exemplary only, and the idle-able auxiliary drive system
can operate with additional sensors in the system and may also operate with fewer
sensors than those shown, as will be understood by one skilled in the art. For example,
additional sensors may be associated with vehicle bus 319 and may be dedicated or

undedicated to sending data to ECU 120. The additional sensor data can be supplied to
traction and yaw stability control algorithm controller 315. In an additional embodiment,
additional sensor data from vehicle bus 319 can be distributed by CAN to vehicle model
and kinematics observer 311 for additional processing.
[051] The sensors 301 forward data to the ECU 120, which may comprise at
least one processor with an associated memory and stored algorithms. The processor
may be part of a computer system or on-board chip system. The processor of the ECU
120 may comprise one or more observers 310, which may comprise a vehicle model and
kinematics observer 311. The vehicle model and kinematics observer 311 processes the
data from sensors 301 according to programmed algorithms and creates data related to a
slip angle 312 and vehicle speed 313. Additional data can also be created by vehicle
model and kinematics observer 311, such as bank angle or roll angle data.
[052] The slip angle 312 and vehicle speed 313 data is shared with controller
314, which also collects data from sensors 301. Controller 314 may be a part of the
processor of the ECU 120 having observers 310, or controller 314 may be an additional
processor with associated memory and stored algorithms which cooperate with the
processor having observers 310. A traction and yaw stability control algorithm controller
315 is used to make determinations based upon at least one of the slip angle 312 data,
vehicle speed 313 data, sensors 301 data, additional sensors, and additional data. Based
on the results of the determinations made by the traction and yaw stability control
algorithm controller 315, commands are sent from the controller via the bidirectional
CAN to a vehicle bus 319 for implementation by various vehicle actuators at various
locations along the vehicle drive train. The location and function of the vehicle actuators

are not shown, but are within the knowledge of one of ordinary skill in the art. The
commands from the controller relate to various electronically controlled stability features
associated with the vehicle, including but not limited to traction control, anti-lock
braking, oversteering control, limited slip differential control, and rollover control.
[053] Results from traction and yaw stability control algorithm controller 315
are also forwarded to torque distribution controller 316 and amplifiers 317. Torque
distribution controller 316 helps determine how much torque to transfer from the primary
drive system to the secondary auxiliary drive system. Commands from torque
distribution controller 316 are forwarded to amplifiers 317 for creation of actuation
currents for transmission to HUC 119. HCU 119 interfaces with the vehicle system to
provide hydraulic fluid pressure control as commanded, as described in more detail
below.
[054] The combination of sensors 301, ECU 120, and HCU 119 allows
synchronization of moving parts along the drive train. When hydraulic pressure is
increased in PTU 101, it urges dog collar 216 to engage between hollow shaft 201 and an
input spline collar on clutch pack 222, causing only a clutch spline collar and inner
friction discs 219 to rotate at the same speed as the front driving differential. The
pressure within PTU 101 can be further increased, causing torque to begin being
transferred through multi-plate wet clutch pack 222 in a controlled manner. This results
in increasing rotational speed of the secondary auxiliary drive system until its speed
matches, or synchronizes, with that of the front drive differential. The ECU system of
Figure 3 assists with the matching or synchronization. The ECU system further assists
with the synchronous operation of the wheel hub disconnects so that torque is transferred

smoothly from the front drive differential, through clutch pack 222, to each rear wheel.
The ECU system can determine the extent and timing of mechanical engagement of the
various disclosed coupling members of the drive train. The ECU system also assists with
the extent and timing of disengagement of the various disclosed coupling members of the
drive train for idling of the secondary auxiliary drive system.
[055] Figure 5 shows an example of a hydraulic control unit architecture that
may be used with the disclosed idle-able auxiliary drive system. The architecture
includes several pressure regulating valves ("PRV"). Hydraulic fluid accumulates in an
accumulator 501 and passes a first pressure sensor 502. Fluid then interfaces with first
normally shut PRV 503. When fluid pressure is desired in piston chamber 210, first
normally shut PRV 503 opens while first normally open PRV 506 shuts to supply fluid at
oil port 209 of PTU 101. Fluid is then supplied to power transfer unit supply line 504,
which interfaces with oil port 209.
[056] When pressure is no longer needed at piston chamber 210, or a desired
amount of pressure has been achieved, first normally shut PRV 503 returns to a shut
position. A second pressure sensor 505 lies between PTU supply line 504 and first
normally open PRV 506 and senses pressure between first normally shut PRV 503 and
first normally open PRV 506. First normally open PRV 506 closes when a pressure
increase is needed to actuate piston 211 and re-opens when hydraulic pressure on piston
211 is no longer needed. First normally shut PRV 503 and first normally open PRV 506
can be selectively opened and closed to obtain a desired pressure in non-rotative piston
housing 210 of PTU 101. The open and shut conditions can be selected by controllers
314 of ECU 120.

[057] Hydraulic fluid from accumulator 501 is also supplied to second normally
shut PRV 511. When increased fluid pressure is desired at first wheel hub disconnect
117 and second wheel hub disconnect 118, second normally shut PRV 511 opens while
second normally open PRV 514 shuts. Fluid then passes through third pressure sensor
512 and is supplied to wheel hub disconnect supply line 513 to further distribute to first
wheel hub disconnect 117 and second wheel hub disconnect 118. Wheel hub disconnect
supply line 513 interfaces with a hydraulic fluid input port 402 of each of the wheel hub
disconnects. Second normally open PRV 514 may shut to build fluid pressure at first
wheel hub disconnect 117 and second wheel hub disconnect 118. The open and shut
conditions of second normally open PRV 514 and second normally shut PRV 511 may be
selected by controllers 314 of ECU 120 to control the actuation of respective wheel hub
piston 403 of first and second wheel hub disconnects 117 and 118. First, second, and
third pressure sensors 502, 505, and 512 may supply data to ECU 120 to assist with
regulation of pressure supplied to piston 211 and wheel hub piston 403.
[058] Once hydraulic fluid is used in PTU 101, first wheel hub disconnect 117,
and second wheel hub disconnect 118, the fluid returns to sump 507 and is redistributed
to the system through pump 508 with associated electric motor 509. Check valve 510
prevents backflow of fluid from accumulator 501 to pump 508.
[059] Figure 6 shows a second example of a hydraulic control unit architecture.
Hydraulic fluid accumulates in accumulator 601 and passes pressure sensor 602 before
reaching normally shut PRV 603, which opens when fluid pressure is needed on supply
line 604 to PTU 101 and supply line 605 to wheel hub disconnects 117 and 118.
Normally open PRV 606 may shut when pressure is needed on supply line 604 to PTU

101 and supply line 605 to wheel hub disconnects 117 and 118. The open and shut
conditions of normally open PRV 606 and normally shut PRV 603 may be selected by
controllers 314 of ECU 120 in order to control the actuation of piston 211 and wheel hub
piston 403 of a wheel hub disconnect. Pressure sensor 602 collects pressure data for
processing by ECU 120 for controlling the pressure of hydraulic fluid to piston 211 and
wheel hub piston 403.
[060] After hydraulic fluid is used in PTU 101, first wheel hub disconnect 117,
and second wheel hub disconnect 118, it returns to sump 607 and is redistributed to the
system through pump 608 with associated electric motor 609. Check valve 610 prevents
backflow of fluid from accumulator 601 to pump 608.
[061 ] In the preceding specification, various preferred embodiments have been
described with reference to the accompanying drawings. It will, however, be evident that
various other modifications and changes may be made thereto, and additional
embodiments may be implemented, without departing from the broader scope of the
invention as set forth in the claims that follow. The specification and drawings are
accordingly to be regarded in an illustrative rather than restrictive sense.
[062] For instance, other motive devices having at least one primary drive axle
coupled to a secondary auxiliary drive system can benefit from the improved packaging
of the disclosed PTU. The other motive devices can have a number of wheels other than
four. As another example, other hydraulic control systems can be used in place of the
hydraulic control units shown in Figures 5 and 6.
[063] Other embodiments of the invention will be apparent to those skilled in the
art from consideration of the specification and practice of the invention disclosed herein.

It is intended that the specification and examples be considered as exemplary only, with
the true scope and spirit of the invention being indicated by the following claims.

WE CLAIM:
1. A power transfer unit (101) for a motive device, comprising:
an outer housing (229, 230);
a torque transferring clutch (216, 217, 218, 222);
a piston housing (240) located between the outer housing (229, 230) and the
torque transferring clutch (216, 217, 218, 222); and
a piston (211) in me piston housing (240),
wherein the piston (211) is arranged to provide actuation forces to the torque
transferring clutch (216, 217, 218, 222) and to restrict reaction forces back to the piston
housing (240).
2. The power transfer unit (101) of claim 1, wherein the outer housing (229, 230)
further comprises a hydraulic fluid input (209) that connects to the piston housing (240).
3. The power transfer unit (101) of claim 1, further comprising actuation members
(213, 214, 215, 217, 220), wherein the actuation members (213, 214, 215, 217, 220) arc
located between the torque transferring clutch (216, 217, 218, 222) and the piston (211).
4. The power transfer unit (101) of claim 1, wherein the torque transferring clutch
(216, 217, 218, 222) comprises a synchronizing wet clutch (222) in series with a dog
clutch (216) and the multi-plate wet clutch (222) is configured to supply a variable
amount of torque based on the number and extent of plates (219, 221) selectively
activated.

5. The power transfer unit (101) of claim 1, further comprising a needle thrust
bearing (212), wherein the needle thrust bearing (212) interposes the piston (211) and the
torque transferring clutch (216, 217, 218, 222).
6. The power transfer unit (101) of claim 1, further comprising:
a needle roller bearing (242);
a thrust bearing (239);
a flange half side spool taper roller bearing (244); and
a cap half side spool taper roller bearing (243),
wherein the torque transferring clutch (216, 217, 218, 222) is configured to
generate thrust, and wherein the needle roller bearing (242) is configured to receive thrust
from the torque transferring clutch (216, 217, 218, 222), and
wherein the piston (211) is configured to receive thrust from the torque
transferring clutch (216, 217, 218, 222), the piston housing (240) is configured to receive
thrust from the piston (211), the needle roller bearing (242) is configured to receive thrust
from the piston housing (240), and the thrust bearing (239) is configured to receive thrust
from the needle roller bearing (242),
wherein the torque transferring clutch (216, 217, 218, 222) is configured to
receive a reaction force back from piston (211) in response to the received thrust, and
wherein the cap half side spool taper roller bearing (243) and the flange half side
spool taper roller bearing (244) are configured to receive no thrust from the torque
transferring clutch (216, 217, 218, 222).

7. The power transfer unit (101) of claim 1, further comprising:
a radial needle bearing (242');
a thrust bearing (239); and
a needle roller bearing (242);
wherein the radial needle bearing (242') is configured to radially support the
piston housing (240) on the thrust bearing (239), and
wherein the needle roller bearing (242) and the radial needle bearing (242')
interpose the piston (211) and the piston housing (240).
8. A torque transferring system comprising:
a motor (103) for supplying torque;
a transmission (102) operatively coupled to the motor (103);
a primary drive axle (104, 105) operatively coupled to the transmission (102);
a power transfer unit (101) operatively coupled to the primary drive axle (104,
105), the power transfer unit (101) comprising:
an outer housing (229, 230),
a torque transferring clutch (216, 217, 218, 222),
a piston housing (240) located between the outer housing (229, 230) and
the torque transferring clutch (216, 217, 218, 222);
a piston (211) in the piston housing (240);
first coupling members (213, 214, 215, 217, 220) selectively operatively
coupled to the piston (211), the torque transferring clutch (216, 217, 218, 222)

selectively operatively coupled to the first coupling members (213,214,215,217,
220); and
second coupling members (223, 224) selectively operatively coupled to
the torque transferring clutch (216, 217, 218, 222);
a pinion gear (107) operatively coupled to the second coupling members (223,
224);
a drive shaft (112) operatively coupled to the pinion gear (107); and
a secondary drive axle (113) operatively coupled to the drive shaft (112),
wherein:
the piston (211) is configured to provide variable actuation forces to the
first coupling members (213, 214, 215, 217, 220) to selectively activate the torque
transferring clutch (216, 217, 218, 222),
the torque transferring clutch (216, 217, 218, 222) is configured to transfer
torque from the primary drive axle (104, 105) to the pinion (107) gear by variably
engaging the second coupling members (223, 224) in response to the variable
actuation forces provided by the piston (211), and
torque is supplied to the secondary drive axle (113, 114, 115) from the
pinion gear (107) through the drive shaft (112).
9. The torque transferring system of claim 8, further comprising bias springs (227,
228), wherein the bias springs (227, 228) are configured to move the piston (211),
thereby variably deactivating the torque transferring clutch (216, 217, 218, 222).

10. The torque transferring system of claim 9, wherein the torque transferring clutch
(216, 217, 218, 222) is configured to completely deactivate, thereby causing the pinion
gear (107), drive shaft (112) and secondary drive axle (113, 114, 115) to completely idle.
11. The torque transferring system of claim 8, wherein the torque transferring clutch
(216, 217, 218, 222) comprises a multi-plate wet clutch (222) in series with a dog clutch
(216), and the multi-plate clutch (222) is configured to supply a variable amount of
torque based on the number of plates (219, 221) selectively activated.
12. The torque transferring system of claim 8, further comprising:
a hydraulic control unit (119) for supplying hydraulic fluid to the piston housing
(240); and
a hydraulic fluid input port (209) in the piston housing (240) for communicating
hydraulic fluid to the piston housing (240),
wherein the hydraulic control unit (119) controls an amount of hydraulic fluid
pressure for actuating the piston (211).
13. The torque transferring system of claim 12, further comprising:
first and second rear wheels (109, 110); and
first and second wheel hub disconnects (117, 118), the first and second wheel hub
disconnects (117, 118) comprising, respectively:
wheel hub pistons (403);
wheel hub coupling members (404, 405, 409); and

wheel hub hydraulic fluid input ports (402) in fluid communication with
the wheel hub pistons (403),
wherein the hydraulic control unit (119) controls an amount of hydraulic fluid
pressure to the wheel hub hydraulic fluid input ports (402) for selectively activating the
wheel hub pistons (403), and
wherein the wheel hub pistons (403) engage the wheel hub coupling members
(404, 405, 409) for coupling each of the first and second rear wheels (109, 110) to the
secondary drive axle (113, 114, 115).
14. The torque transferring system of claim 8, further comprising a needle thrust
bearing (212), wherein the needle thrust bearing (212) interposes the piston (211) and the
torque transferring clutch (216, 217, 218, 222).
15. The torque transferring system of claim 8, further comprising:
a needle roller bearing (242); and
a radial needle bearing (242'),
wherein the needle roller bearing (242) is configured to receive thrust from the
torque transferring clutch(216, 217, 218, 222), and
wherein the needle roller bearing (242) and the radial needle bearing (242')
interpose the piston (211) and the piston housing (240).

A power transfer unit (PTU) (101) for a motive device includes an outer
housing (229, 230) and a torque transferring clutch (216, 217, 218, 222). The
PTU (101) also includes a piston housing (240) located between the outer
housing (229, 230) and the torque transferring clutch (216, 217, 218, 222),
and a piston (211) in the piston housing (240). The piston (211) is arranged
to provide actuation forces to the torque transferring clutch (216, 217, 218,
222), and to restrict reaction forces back to the piston housing (240).