REAR DRIVE MODULE WHEEL DISCONNECT
TECHNICAL FIELD
The present invention relates to a wheel disconnect system, including a rear
drive module wheel disconnect system including an integrated constant velocity (CV) joint.
BACKGROUND
A conventional AWD driveline for a motor vehicle may include a primary front
drive axle coupled to a secondary or auxiliary rear drive axle. When the driveline is
operating in a 4X2 mode of operation (i.e., four wheels, with two of them operating as
driving wheels), the primary front drive axle must provide tractive forces not only to keep the
motor vehicle moving, but also to overcome the frictional losses of the secondary or auxiliary
rear drive axle that is being driven through the tire/road surface interface. Driveline losses
may be due to oil churning losses, viscous drag, inertia, as well as friction.
In an effort to minimize loss and provide a more fuel efficient driveline when in
a 4X2 mode of operation to improve overall fuel economy, it may be desirable to disconnect
the secondary or auxiliary drive system, including the secondary or auxiliary rear drive axle
and the rear wheels. Wheel hub disconnects generally may be separate from the rear
differential housing and positioned close to each wheel, may be integrated into the rear
differential housing, or may be somewhere in between the wheel and the rear differential
housing. Accordingly, disconnecting the rear wheels may be accomplished at the ends of the
wheels or at the output of a rear drive module (RDM).
A system that disconnects the rear wheels at the ends of the wheels may be
more conventional and/or typical in motor vehicles, but may also be more complicated than a
system that disconnects the wheels at the RDM. While a system that disconnects the wheels
at the RDM may be acceptable since most of the system losses are internal to the RDM, such
a system may undesirably increase the package size and component count of the wheel
disconnect system. It may be desirable to provide a wheel disconnect system that disconnects
the wheels at the output of the rear drive module, while managing to avoid an increased
package size and component count.
SUMMARY
A wheel disconnect system may include a rear drive module and a constant
velocity joint housing. The rear drive module may include a housing, at least one actuator at
least partly disposed within the housing, and at least one dog clutch configured to be
activated by the actuator. The dog clutch may include a first portion configured to move
when the actuator is moved and a second portion configured for engagement with the first
portion. The constant velocity joint housing may be formed integrally with the second
portion of the dog clutch. A wheel may be disconnected from the rear drive module unless
engagement of the first portion and the second portion of the dog clutch allows torque to be
transferred to the wheel.
In an embodiment, a wheel disconnect system may include a rear drive module
and a constant velocity joint housing. The rear drive module may include a housing defining
a cavity configured to be in communication with a source of hydraulic fluid pressure, at least
one piston disposed in the cavity, and at least one dog clutch configured to be activated by the
piston. The piston may be configured to move when the hydraulic fluid pressure is increased.
The dog clutch may include a first portion configured to move when the piston is moved and
a second portion configured for engagement with the first portion. The constant velocity
joint housing may be formed integrally with the second portion of the dog clutch. A wheel
may be disconnected from the rear drive module unless engagement of the first portion and
the second portion of the dog clutch allows torque to be transferred to the wheel.
In another embodiment, a wheel disconnect system may include a rear drive
module and a constant velocity joint housing. The rear drive module may include a housing,
at least one electromagnetic actuator at least partly disposed within the housing, and at least
one dog clutch configured to be activated by the electromagnetic actuator. The
electromagnetic actuator may include at least one ball, an armature plate proximate at least
one ball, and a coil configured to move the armature plate and at least one ball when

activated. The dog clutch may include a first portion configured to move when the balls and
armature plate are moved and a second portion configured for engagement with the first
portion. The constant velocity joint housing may be formed integrally with the second
portion of the dog clutch. A wheel may be disconnected from the rear drive module unless
engagement of the first portion and the second portion of the dog clutch allows torque to be
transferred to the wheel.
A vehicle driveline including a wheel disconnect system is also provided. The
vehicle driveline may include a rear drive axle; at least one wheel; at least one rear half shaft
for distributing torque to the at least one wheel; and a wheel disconnect system. The wheel
disconnect system may include a rear drive module and a constant velocity joint housing.
The rear drive module may include a housing, at least one actuator at least partly disposed
within the housing, and at least one dog clutch configured to be activated by the actuator.
The dog clutch may include a first portion configured to move when the actuator is moved
and a second portion configured for engagement with the first portion. The constant velocity
joint housing may be formed integrally with the second portion of the dog clutch. A wheel
may be disconnected from the rear drive module unless engagement of the first portion and
the second portion of the dog clutch allows torque to be transferred to the wheel.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
FIG. 1 illustrates an AWD vehicle driveline including a wheel disconnect
system according to an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a wheel disconnect system according to an
embodiment of the present invention;
FIG. 3 is a cross-sectional view of a wheel disconnect system according to an
embodiment of the present invention.
DETAILED DESCRIPTION
Reference will now be made in detail to embodiments of the present invention,
examples of which are described herein and illustrated in the accompanying drawings. While
the invention will be described in conjunction with embodiments, it will be understood that
they are not intended to limit the invention to these embodiments. On the contrary, the
invention is intended to cover alternatives, modifications and equivalents, which may be
included within the spirit and scope of the invention as embodied by the appended claims.
Referring to FIG. 1, an AWD vehicle driveline is generally shown. The A WD
vehicle driveline may comprise a primary drive system and a secondary or auxiliary drive
system. The primary drive system may comprise a primary front drive axle 10 and one or
more primary drive wheels 12, 14. The secondary or auxiliary drive system may comprise a
secondary or auxiliary rear drive axle 16 and one or more secondary or auxiliary drive wheels
18, 20. In an embodiment as illustrated, the primary drive system may include two primary
drive wheels, and the secondary or auxiliary drive system may include two auxiliary drive
wheels.
When the AWD vehicle driveline is operating in a 4X4 mode of operation (i.e.,
all four wheels transmit power to the road), torque may be transferred from an engine 22,
through a transmission 24, and into a front driving differential case 26. The torque may be
further split to a front driving differential 28 and a power transfer unit 30. The torque that is
split through the front driving differential 28 (e.g., through the front driving differential gear
set) may then be further distributed via front half shafts 32, 34 to a pair of primary (e.g.,
front) drive wheels 12, 14 of a motor vehicle. The torque distributed to power transfer unit
30 may be provided via a hollow shaft 36 that may directly connect the front driving
differential case 26 to power transfer unit 30. The torque transferred through the power
transfer unit 30 may drive a drive shaft 38 that in turn drives the rear drive axle 16.
Rear drive axle 16 may distribute torque via rear half shafts 40, 42 to a pair of
auxiliary (e.g., rear) drive wheels 18, 20 of the motor vehicle. A wheel disconnect system 44
may be provided to selectively interrupt torque flow to the auxiliary drive wheels 18, 20. In
accordance with an embodiment of the invention, wheel disconnect system 44 may include a
rear drive module 46 and a constant velocity (CV) joint housing 48.
Referring now to FIG. 2, rear drive module 46 may include a housing 50.
Housing 50 may be provided to at least partially house an actuator 52 disposed within
housing 50. In a first embodiment of the invention, actuator 52 may comprise at least one
hydraulic actuation piston 54. In accordance with the first embodiment of the invention,
housing 50 may define at least one cavity 56 configured to be in communication with a
source of hydraulic fluid pressure (not shown). The source of hydraulic fluid pressure may
variably provide fluid pressure to the cavity 56. A hydraulic input and/or line connection 58
may allow hydraulic fluid from a source of hydraulic fluid to enter cavity 56 of the rear drive
module 46. The rear drive module 46 may include at least two cavities 56 in an exemplary
embodiment. A separate hydraulic input and/or line connection 58 may be utilized for each
of the two cavities 56 in an exemplary embodiment. In another exemplary embodiment, a
single hydraulic input and/or line connection 58 may be used to input hydraulic fluid into
both cavities for both wheels. It will be appreciated that the source of hydraulic pressure is
not limited to any particular hydraulic fluid pressure generating device, and may include
without limitation, a pump, valves, accumulator, and electronic control unit (ECU), or any
combination thereof. For example, a pump (not shown) may generate hydraulic pressure. A
switch or signal from the ECU (not shown) may energize and/or control the pump. For
example, the ECU may keep an accumulator (e.g., part of the hydraulic system of a motor
vehicle which absorbs fluctuating fluid delivery, stores fluid at pressure, and can provide a
rapid flow of fluid under pressure) charged to a select or predetermined pressure range as
monitored by a pressure switch. For another example, the ECU may directly pressurize the
rear drive module 46. In another example, the source of hydraulic pressure may be the
pressurized fluid from an automatic transmission.
In accordance with the first embodiment of the invention, at least one piston 54
may be disposed in cavity 56. Piston 54 may be configured to move when the hydraulic fluid
pressure is increased. Piston 54 may be configured to move axially within cavity 56. The
rear drive module 46 may include at least two pistons 54 in an exemplary embodiment (e.g.,
one piston for each rear wheel). Piston 54 may also define at least one pocket 57. Each
pocket 57 may be configured to receive an o-ring seal 59. In an embodiment, there may be
an o-ring seal 59 on the inner diameter and outer diameter of the piston 54.
Referring now to FIG. 3, in a second embodiment of the invention, actuator 52
may comprise at least one electromagnetic ball ramp actuator. The electromagnetic ball ramp
actuator may comprise at least one ball 60, an armature plate 62, a coil 64, and a spring 65.
The electromagnetic ball ramp actuator may function in a conventional manner, such as
known in the art. The electromagnetic ball ramp actuator may be at least partly disposed
within the housing 50. Coil 64 may be configured to generate an electromagnetic field that
may affect a position of the armature plate 62. In particular, the coil 64 may restrain the
armature plate 62 from moving at the same speed as plate portion 68. Plate portion 68 may
comprise a first portion of a dog clutch 66 as described in additional detail below. Both
armature plate 62 and plate portion 68 of dog clutch 66 may each include a ramp in which
balls 60 may be configured to travel. Because coil 64 may restrain the armature plate 62
from moving at the same speed as plate 68, balls 60 may be allowed to move up the ramps in
armature plate 62 and plate portion 68 of the dog clutch 66. The movement of the balls 60
may move the plate portion 68 of the dog clutch 66 away from armature plate 62, thereby
allowing the dog clutch 66 (e.g., first plate portion 68 and second portion 70 as described in
more detail below) to engage. When the balls 60 are at the end of its travel, the armature
plate 62 may be spinning and/or rotating at the same speed as plate portion 68. Upon
deenergization of the coil 64, a spring 65 may be configured to act on the armature plate 62.
The action of the spring 65 may result in a decrease in the total thickness of the
electromagnetic ball ramp actuator as compared to when the coil 64 is energized. The rear
drive module 46 may include at least two electromagnetic ball ramp actuators in an
exemplary embodiment (e.g., one electromagnetic ball ramp actuator for each rear wheel).
Actuator 52 may be configured to activate a dog clutch 66. The rear drive
module 46 may include at least two dog clutches 66 in an exemplary embodiment (e.g., one
dog clutch for each rear wheel). Referring now to both FIGS. 2 and 3, dog clutch 66 may
comprise a first portion 68 and a second portion 70. The first portion 68 of the dog clutch 66
may comprise an axially moveable collar. The axially moveable collar may include dog
clutch features on its radially inner face. The shape and function of dog clutch features may

be as are known in the art. For example, the axially moveable collar may include projections
that are configured to engage corresponding slots (e.g., slots, grooves, recesses, receiving
portions) in the second portion 70 of the dog clutch 66.
The position of the first portion 68 may be configured to be affected by actuator
52. In accordance with a first embodiment of the invention, the first portion 68 of the dog
clutch 66 may be configured to be activated and/or move when piston 54 is moved. In this
first embodiment, a bearing 72 may be disposed between the piston 54 and the first portion
68 of the dog clutch 66 to allow for rotation of the first portion of the dog clutch 68 relative to
the piston 54. In accordance with a second embodiment of the invention, the position of the
first portion 68 of the dog clutch 66 may be configured to depend on whether the coil 64 of
the electromagnetic ball ramp actuator is energized and/or deenergized, thereby allowing
and/or preventing movement of the balls 60. Movement of balls 60 may then activate and/or
move the first portion 68 of the dog clutch 66.
The second portion 70 of the dog clutch may be configured for engagement
with the first portion 68. In at least the first embodiment, a biasing member (e.g., a resilient
biasing member) 74, such as a compression spring, may apply a force against the first portion
68 of the dog clutch 66 in a direction away from engagement of the first portion of the dog
clutch 66 with the second portion 70 of the dog clutch 66. Although a compression spring is
mentioned in detail, other biasing members may be utilized in other embodiments. The
wheel disconnect system 44 may provide for left and right rear wheels 18, 20 and left and
right half shafts 40, 42 to be disconnected from the rear drive module 46 in a default and/or
normal position. To connect rear wheels 18, 20 and/or rear half shafts 40, 42 to the rear drive
module 46 for the AWD feature of the motor vehicle, engagement of the first and second
portions 68, 70 of the dog clutch 66 may allow torque to be transferred to each wheel. To
connect rear wheels 18, 20 to the rear drive module 46, the actuator 52 may be used to affect
movement of the dog clutch 66 such that first and second portions 68, 70 of the dog clutch
are engaged. Accordingly, the wheel disconnect system 44 may be configured for selectively
connecting and disconnecting the rear half shafts 40, 42 and rear wheels 18, 20 from the rear
drive module 46 using the actuator 52 and dog clutch 66.
The torque distributed to the rear drive module 46 may be provided via a
differential that facilitates differential rotation between a pair of output shafts (e.g., a half
shaft 78), for example, as is known in the art. The half shaft 78 may include splines and may
be in splined engagement with the first portion 68 of the dog clutch 66.
Wheel disconnect system 44 may include a constant velocity (CV) joint housing
48 for a CV joint 80. CV joints are provided generally to connect shafts to drive units and are
common in motor vehicles. CV joints may be located at both ends of the rear half shafts 40,
42 that connect to the wheels 18, 20 and the rear drive module 46, as generally shown in FIG.
1. The CV joints 80 may be any of the standard types known in the art, including but not
limited to a ball joint, such as a six ball joint, an eight ball joint, or a ten ball joint, a plunging
tripod joint, a cross groove joint, a fixed ball joint, a fixed tripod joint, or a double offset
joint. The CV joint 80 may include any number of various components, such as a joint boot
(not shown), that are conventional in the art. The CV joint housing 48 may be substantially
similar to a conventional CV joint housing known in the art, but the CV joint housing may be
formed integrally with the second portion 70 of the dog clutch 66. The CV joint housing and
second portion 70 of the dog clutch 66 may, for example, be a one-piece and/or monolithic
structure.
The wheel disconnect system 44 may further include a bearing 82 disposed
between the housing 50 of the rear drive module 46 and the CV joint housing 48. The
bearing 82 may be configured to rotatably support the CV joint housing 48. The rear drive
module 46 may further comprise a retaining clip 76 in order to retain the bearing 82. The
retaining clip 76 may be at least partially disposed within the housing 50 of the rear drive
module 46 or may be integral with the housing 50 of the rear drive module 46. A seal 84
may also be disposed between the housing 50 of the rear drive module 46 and the CV joint
housing 48. The seal 84 may be configured to avoid leakage of lubricating oil from the rear
drive module 46. The wheel disconnect system 44 may also include a bushing disposed
between the half shaft 78 and the CV joint housing 48. The bushing 86 may be configured
for dampening noise or friction.
A wheel disconnect system in accordance with the present invention may allow
for selective disconnection and connection of the rear half shafts and wheels from a rear drive
module. Accordingly, the inventive wheel disconnect system may be configured to
disconnect the rear half shaft from the rear drive module, rather than at the wheel ends. By
integrating the CV joint as part of the dog clutch of the rear drive module, the wheel
disconnect system may be further simplified while reducing package size and component
count of the wheel disconnect system. For example, a wheel disconnect system in
accordance with the present invention may not require a viscous coupling which may result
weight savings. A wheel disconnect system in accordance with the present invention may
also improve fuel economy by eliminating ring gears and differential viscous spin losses and
mechanical rotational losses. A wheel disconnect system in accordance with the present
invention may also be configured for use with existing vehicle mounts with no required
modification to existing rear half shafts.
The foregoing descriptions of specific embodiments of the present invention
have been presented for purposes of illustration and description. They are not intended to be
exhaustive or to limit the invention to the precise forms disclosed, and various modifications
and variations are possible in light of the above teaching. The embodiments were chosen and
described in order to explain the principles of the invention and its practical application, to
thereby enable others skilled in the art to utilize the invention and various embodiments with
various modifications as are suited to the particular use contemplated. The invention has
been described in great detail in the foregoing specification, and it is believed that various
alterations and modifications of the invention will become apparent to those skilled in the art
from a reading and understanding of the specification. It is intended that all such alterations
and modifications are included in the invention, insofar as they come within the scope of the
appended claims. It is intended that the scope of the invention be defined by the claims
appended hereto and their equivalents.
We claim:
1. A wheel disconnect system, comprising:
a rear drive module comprising:
a housing;
at least one actuator at least partly disposed within the housing; and
at least one dog clutch configured to be activated by the actuator, the dog
clutch including:
a first portion configured to move when at least a portion of the
actuator is moved; and
a second portion configured for engagement with the first portion; and
a constant velocity joint housing, wherein the constant velocity joint housing is
formed integrally with the second portion of the dog clutch,
wherein a wheel is disconnected from the rear drive module unless the dog clutch is activated
and permits torque to be transferred to the wheel.
2. The wheel disconnect system in accordance with claim 1, wherein the first portion of
the dog clutch comprises an axially moveable collar.
3. The wheel disconnect system in accordance with claim 2, wherein the axially
moveable collar includes projections that are configured to engage corresponding slots in the
second portion of the dog clutch.
4. The wheel disconnect system in accordance with claim 1, further comprising a biasing
member for applying a force against the first portion of the dog clutch in a direction away
from engagement of the first portion of the dog clutch with the second portion of the dog
clutch.
5. The wheel disconnect system in accordance with claim 4, wherein the biasing
member comprises a spring.
6. The wheel disconnect system in accordance with claim 1, further comprising a
bearing disposed between the housing of the rear drive module and the constant velocity joint
housing configured to rotatably support the constant velocity joint housing.
7. The wheel disconnect system in accordance with claim 1, further comprising a seal
disposed between the housing of the rear drive module and the constant velocity joint housing
to avoid leakage of lubricating oil.
8. The wheel disconnect system in accordance with claim 1, further comprising a
retaining clip disposed within the housing for the rear drive module to retain a bearing.
9. The wheel disconnect system in accordance with claim 1, wherein the rear drive
module further comprises a half shaft engaged with the first portion of the dog clutch.
10. The wheel disconnect system in accordance with claim 9, further comprising a
bushing disposed between the half shaft and the constant velocity joint housing.
11. The wheel disconnect system in accordance with claim 1, wherein the actuator
comprises an electromagnetic actuator comprising:
at least one ball;
an armature plate proximate at least one ball;
a coil configured to generate an electromagnetic field to affect a position of
the armature plate; and
a spring configured to act on the armature plate when the coil is deenergized,
wherein the dog clutch is configured to be activated by movement of at least one ball when
the position of the armature plate is affected by the electromagnetic field.
12. The wheel disconnect system in accordance with claim 1, wherein the housing defines
a cavity configured to be in communication with a source of hydraulic fluid pressure and the
actuator comprises at least one piston disposed in the cavity; the piston configured to move
when the hydraulic fluid pressure is increased; and the dog clutch configured to be activated
by the movement of the piston.
13. The wheel disconnect system in accordance with claim 12, further comprising a pump
for generating hydraulic fluid pressure.
14. The wheel disconnect system in accordance with claim 13, further comprising an
electronic control unit for controlling the pump.
15. The wheel disconnect system in accordance with claim 12, wherein the rear drive
module further comprises an accumulator for storing hydraulic fluid pressure.
16. The wheel disconnect system in accordance with claim 12, further comprising a
bearing disposed between the piston and the first portion of the dog clutch to allow for
rotation of the first portion of the dog clutch relative to the piston.
17. A wheel disconnect system, comprising:
a rear drive module comprising:
a housing including a cavity configured for communication with a source of
hydraulic fluid pressure;
at least one piston disposed in the cavity, the piston configured to move with
respect to a change in hydraulic fluid pressure; and
at least one dog clutch configured to be activated by the piston, the dog clutch
including:
a first portion configured to move when the piston is moved; and
a second portion configured for engagement with the first portion; and
a constant velocity joint housing, wherein the constant velocity joint housing is
formed integrally with the second portion of the dog clutch,
wherein a wheel is disconnected from the rear drive module unless engagement of the first
portion and the second portion of the dog clutch allows torque to be transferred to the wheel.
18. A wheel disconnect system, comprising:
a rear drive module comprising:
a housing;
at least one electromagnetic actuator at least partly disposed within the
housing, the electromagnetic actuator comprising:
at least one ball;
an armature plate proximate at least one ball;
a coil configured to generate an electromagnetic field to affect a
position of the armature plate; and
a spring configured to act on the armature plate when the coil is
deenergized;
at least one dog clutch configured to be activated by the movement of at least
one ball when the position of the armature plate is affected by the
electromagnetic field, the dog clutch comprising:
a first portion configured to move when at least one ball and armature
plate are moved;
a second portion configured for engagement with the first portion; and
a constant velocity joint housing, wherein the constant velocity joint housing is
formed integrally with the second portion of the dog clutch,
wherein a wheel is disconnected from the rear drive module unless engagement of the first
portion and the second portion of the dog clutch allows torque to be transferred to the wheel.
19. A vehicle driveline, comprising:
a rear drive axle;
at least one wheel;
at least one rear half shaft for distributing torque to the at least one wheel; and
a wheel disconnect system, comprising:
a rear drive module comprising:
a housing;
at least one actuator at least partly disposed within the housing;
at least one dog clutch configured to be activated by the
actuator, the dog clutch including:
a first portion configured to move when at least a
portion of the actuator is moved;
a second portion configured for engagement with the
first portion; and
a constant velocity joint housing, wherein the constant velocity joint housing
is formed integrally with the second portion of the dog clutch,
wherein the wheel is disconnected from the rear drive module unless the dog clutch is
activated and permits torque to be transferred to the wheel.

A wheel disconnect system is provided including a rear
drive module (46) and a constant velocity joint housing
(48). The rear drive module includes a housing (50), at
least one actuator (52), and at least one dog clutch
(66). The dog clutch includes a first portion (68)
configured to move when the actuator is moved and a
second portion (70) configured for engagement with the
first portion. The constant velocity joint housing is
formed integrally with the second portion of the dog
clutch. A wheel (18,20) may be disconnected from the
rear drive module unless engagement of the first and
second portions of the dog clutch allows torque to be
transferred to the wheel. In one embodiment, a
hydraulically activated piston (54) may be used to
activate the first portion of the dog clutch. In
another embodiment, a ball ramp may be used to activate
the first portion of the dog clutch. A vehicle
driveline including a wheel disconnect system is also
provided.