TORQUE TRANSFER DEVICE AND SYSTEM
BACKGROUND
a. Field of Invention
[001] The invention relates generally to a device for a motor vehicle, including a device for
a motor vehicle for the transfer of full driveline torque by clutching a fraction of driveline torque.
b. Description of Related Art
[002] A motor vehicle may be driven on a number of different road surfaces. Different
road surfaces may have different coefficients of friction. A driver may lose control when
transferring to a different road surface. .For example, a driver may oversteer or overcompensate
on changing road surfaces. A difference in rotation between the front and rear wheels may
indicate a slip condition or a loss of traction. Tire compliance standards provide for absorption
of about a 5% difference in rotation between the front and rear wheels. However, in some
circumstances, the rear wheels maybe rotating up to about 6% faster than the front wheel, which
will not be addressed by tire compliance standards. The amount of torque transferred to the rear
wheel may be varied in order to improve driver control and address a slip condition or loss of
traction. Attempting to control the torque transferred to the rear axle of a motor vehicle by
sensing varying road surfaces is complex.
[003] A device to manage the amount of torque that is transferred to the rear axle of a
motor vehicle may be desirable in order to improve control and drivability of die motor vehicle
and redress a slip condition or loss of traction. The device may include a clutch pack for
reducing or increasing torque to the rear wheels. The clutch pack may be designed to meet
vehicle packaging constraints.
[004] A device that may be controlled by sensing parameters other than changing road
surfaces in order to control and manage the amount of torque that is transferred to the rear axle of
a motor vehicle may also be desirable. For example, a device that may be controlled by sensing
rear wheel speed and/or the difference between rear wheel speed and front wheel speed may be
used to improve the control and drivability of a motor vehicle.
SUMMARY
[005] A device for a motor vehicle is provided. The device may comprise an input shaft
for supplying torque, a clutch configured for selectively transferring the torque, a first gear
configured for connection to the clutch, and a second gear connected to the first gear. The
second gear may be fixed to the device so that the second gear is not free to rotate. The device
may further comprise an output shaft for receiving the torque. The device may be configured to
control the amount of torque transferred to the output shaft.
[006] Various features of this invention will become apparent to those skilled in the art
from the following detailed description, which illustrates embodiments and features of this
invention by way of non-limiting examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[007] Embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[008] Fig. 1 is a cross-sectional view of a device in accordance with an embodiment of the
invention.
[009] Fig. 2 is a schematic of a torque path of a device in accordance with an embodiment
of the invention.
[0010] Fig. 3 is a schematic of the relationship between the torque increase to a rear axle of a
motor vehicle and engagement of the clutch of the device in accordance with an embodiment of
the invention.
[0011] Fig. 4 is a schematic showing the interaction between an anti-lock braking system and
a device in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
[0012] Reference will now be made in detail to embodiments of the present invention,
examples of which are illustrated in the accompanying drawings. While the invention will be
described in conjunction with the 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 in or defined by the appended claims.
[0013] Referring now to Fig. 1, which illustrates a cross-sectional view of a device 10 in
accordance with an embodiment of the invention, device 10 includes input shaft 12, clutch 14,
first gear 16, second gear 18, and output shaft 20. First gear 16 and second gear 18 may
comprise a component of a planetary gear set. In an embodiment, first gear 16 and second gear
18 may comprise ring gears as illustrated in Fig. 1. However, it is understood by those of
ordinary skill in the art that first gear 16 may comprise a ring gear, a sun gear, a planet gear and
carrier and second gear 18 may comprise a ring gear, a sun gear, a planet gear and carrier. At
least a portion of device 10 may, for example, be disposed between a drive shaft and a rear
differential of a motor vehicle in an embodiment. Device 10 may be configured to operate under
various temperature conditions. When a motor vehicle is in front wheel drive mode, device 10
may be open in the driveshaft to the rear axle of the motor vehicle. Torque may be transferred
through device 10 to the rear axle by sending an electrical current to clutch 14. When clutch 14
is fully engaged (e.g., locked up), full driveline torque may be transferred to the rear axle of the
motor vehicle and device 10 may overdrive the rear axle. In an embodiment, device 10 may
overdrive the rear axle by 6% as compared to the-front axle. Clutch 14 may be slipped, thereby
controlling the amount of relative overspeed to the rear axle from 0 to 6% in an embodiment. A
powertrain control module (PCM) of the motor vehicle may control the operation of clutch 14.
The PCM may have many inputs, including speed sensors on four wheels of the motor vehicle.
[0014] Input shaft 12 may be provided for supplying torque. Fig. 1 shows an example of
an input shaft flange that might be connected to an input shaft. In an embodiment, input shaft 12
may be rotated by an electric motor. Input shaft 12 may also be rotated by a step-up gear-driven
motor using a ball ramp. A device in accordance with the present invention may provide several
advantages. The device may, for example, without limitation consume only up to about 3 amps
of controlling current, thereby requiring only a relatively small motor in comparison to the
amount of horsepower that may be delivered. By way of further example, without limitation,
device 10 may provide approximately 104 horsepower or more at approximately 2.5 amps of
controlling current. Device 10 may provide, for example, approximately 300 foot-lb of torque or
more at approximately 24 W of power. Referring now to Fig. 2, the torque supplied by input
shaft 12 may be split between first gear 16 and second gear 18.
[0015] Referring again to Fig. 1, clutch 14 may be provided for selectively transferring
torque. Clutch 14 may be provided so that device 10 may control the amount of torque
transferred to output shaft 20. Clutch 14 may be configured to manage just a fraction of the
available (i.e., driveline) torque, while providing a functional equivalent amount of power as a
clutch that is configured to manage all the available (i.e., driveline) torque. For example, clutch
14 may be configured to manage half of the available torque, while providing a functional
equivalent of power as a clutch that is configured to manage all of the available torque. Clutch
14 may be able to manage a fraction of the available torque, for example, by splitting torque
through (e.g., planetary) gear sets as described in more detail below and generally illustrated in
Fig. 2. Because of its configuration to manage only a fraction of the driveline torque, clutch 14
may be adapted or configured to better address vehicle packaging constraints. That is, a clutch
as disclosed in accordance with teachings of embodiments of the present invention may be
smaller in size than a clutch configured to manage all of the available driveline torque.
[0016] The operation of clutch 14 may be configured to vary the speed of rotation of first
ring gear 16. In particular, the operation of clutch 14 may prevent or hinder movement (i.e.,
rotation) of first gear 16 when clutch 14 is engaged, for example, or allow for or facilitate
movement (i.e., rotation) of first gear 16 when clutch 14 is released, for example. By varying the
speed of gear 16, the ratio of the speed of output shaft 20 to the speed of input shaft 12 may be
varied. Referring now to Fig. 3, when clutch 14 is fully engaged and movement of first gear 16
is prevented, all available torque may be transferred from input shaft 12 to output shaft 20,
resulting in a maximum increase in the difference in speed supplied to the front wheel and the
rear wheel of the motor vehicle utilizing device 10. Still referring to Fig. 3, when clutch 14 is
fully released and movement of first gear 16 is fully permitted, no torque is transferred from
input shaft 12 to output shaft 20, resulting in a substantially identical speed supplied to the front
wheel and the rear wheel of the motor vehicle utilizing device 10.
[0017] Accordingly, by operation of clutch 14, device 10 may transfer no torque, partial
torque, or all available torque from input shaft 12 to output shaft 20. Clutch 14 may be
configured to be released (including, for example, fully released) when the speed of the rear
wheel of the motor vehicle differs from the speed of the front wheel of the motor vehicle, which
may be an indication of a slip condition or loss of traction. In accordance with an embodiment
of the invention, clutch 14 may become fully released or fully engaged within approximately 50
milliseconds.
[0018] In an embodiment, device 10 may include pinion gear 22. Pinion gear 22 may be
connected to clutch 14. Pinion gear 22 may also be configured to engage first gear 16. In
particular, pinion gear 22 may include a set of gear teeth that mesh with an additional set of gear
teeth of first gear 16. Pinion gear 22 may therefore act as a clutch control gear.
[0019] Device 10 may include first gear 16 that is provided for connection to clutch 14.
First gear 16 maybe a component of a first planetary gear set. As illustrated, first gear 16 may
comprise a ring gear. However, it is understood by those of ordinary skill in the art that first gear
16 may comprise any component of a first planetary gear set. The first planetary gear set may
include first ring gear 16, a first sun gear (e.g., integrated with input shaft 12), and a first set 26
of planets and planet carrier. First set 26 of planets may include, for example, four planets. The
first planetary gear set may have a first gear ratio. The first gear ratio may be determined by the
diameter of the first planetary gear set. In an embodiment, first ring gear 16 is not configured to
rotate when clutch 14 is fully engaged. When clutch 14 is fully engaged, movement (i.e.,
rotation) of pinion gear 22 is prevented, which in turn prevents movement of first gear 16. In an
embodiment, first gear 16 is configured to rotate when clutch 14 is fully released. When clutch
14 is fully released, movement (i.e., rotation) of pinion gear 22 is allowed, which in turn allows
movement of first gear 16.
[0020] Device 10 may include second gear 18 that is provided for connection to first gear
16. Second gear. 18 may be fixed to device 10 so that second gear 18 is not free to rotate. •
Second gear 18 may be a component of a second planetary gear set. As illustrated, second gear
18 may comprise a ring gear. However, it is understood by those of ordinary skill in the art that
second gear 18 may comprise any component of a second planetary gear set. In other words,
although second gear 18 may be a ring gear that is not configured to rotate, it should be
understood by those of ordinary skill in the art that other components of the second planetary
gear set may be configured not to rotate. In an embodiment, the first and second planetary gear
sets may be connected in series (i.e., back-to-back) via a common carrier 28.
[0021] The second planetary gear set may include second ring gear 18, a second sun gear
(e.g., integrated with output shaft 20), and a second set 32 of planets and planet carrier. Second
set 32 of planets may include, for example, four planets. The second planetary gear set may have
a second gear ratio. The second gear ratio may be determined by the diameter of the second
planetary gear set. The first and second gear ratios may be functionally equivalent in an
embodiment. The second gear ratio may be greater than the first gear ratio in an embodiment. If
the second gear ratio is greater than the first gear ratio, then output shaft 20 may rotate faster
than input shaft 12. This may be described as "torque vectoring" and may allow for increasing
the speed at which a driver can negotiate a curve without losing control of the motor vehicle. It
is understood by those of ordinary skill in the art that any combination of first and second gear
ratios may be used and remain within the spirit and scope of the invention.
[0022] Output shaft 20 may receive the torque supplied by input shaft 12. Torque that is
transferred to output shaft 20 may be supplied to increase the rotation of a rear axle of the motor
vehicle that utilizes device 10. In an embodiment, the torque transferred to output shaft 20 may
be configured to increase the rotation of a rear axle of the motor vehicle up to about 6%, for
example, as illustrated in Fig. 3. Although 6% is mentioned in detail in accordance with an
embodiment of the invention, it is understood by those of ordinary skill in the art that device 10
may be configured to increase the rotation of a rear axle of a motor vehicle more or less than
about 6% and remain within the spirit and scope of the invention.
[0023] In accordance with an embodiment of the invention, a system including device 10
may further include a wheel speed sensor for detecting the speed of a wheel of a motor vehicle or
other means for providing feedback regarding the speed of the rear wheel. In accordance with an
embodiment of the invention, the wheel speed sensor may comprise a rear wheel speed sensor.
Depending upon the feedback received from the wheel speed sensor, the amount of torque
transferred to output shaft 20 may be increased or decreased by engaging or releasing clutch 14,
respectively. In an embodiment, when feedback-from the wheel speed sensor indicates that the
speed of the rear wheel has increased, clutch 14 may be configured to be fully released in order
to decrease the amount of torque transferred to output shaft 20, and ultimately to the rear axle to
which the rear wheel is connected.
[0024] In an embodiment, a system including device 10 may further include a wheel speed
sensor or other means for providing feedback regarding the speed of the wheel for both a rear
wheel and a front wheel of a motor vehicle. Both wheel speed sensors may be included to
provide feedback regarding the speed of the front wheel and the speed of the rear wheel. In
another embodiment, a system including device 10 may further include a wheel speed sensor or
other means for providing feedback regarding the speed of all four wheels of a motor vehicle.
The motor vehicle's PCM may have as inputs at least one speed sensor for at least one wheel of
the motor vehicle. In an embodiment, the motor vehicle's PCM may have as inputs at least one
speed sensor for four wheels of the motor vehicle. The PCM may control clutch 14 of device 10.
In front wheel drive mode, device 10 may be open in the drive shaft to the rear axle. Torque may
be transferred through device 10 to the rear axle by sending an electrical current to clutch 14 of
device 10. When clutch 14 is fully engaged (i.e., locked up), full driveline torque may be
transferred to the rear axle and device 10 may overdrive the rear axle by approximately 6% as
compared to the front axle, as illustrated in Fig. 3, for example. Clutch 14 may be slipped,
thereby controlling the amount of relative overspeed to the rear axle, from Q to 6% as also
illustrated in Fig. 3, for example.
[0025] Referring now to Fig. 4, a motor vehicle's PCM may detect a condition for
requiring engagement of a rear axle at step 100. A condition that may be detected by the PCM
that may require engagement of a rear axle includes torque vectoring detected by a traction
control system, a front tire slip (i.e., vehicle is stuck), or a road condition. A condition that may
be detected by the PCM that may require engagement of a rear axle may also include feedback
from the wheel speed sensors or other means for providing feedback that indicates that there is a
difference in wheel speed between the front and rear wheels. In an embodiment, any detectable
difference in wheel speed between the front and rear wheels may generate feedback indicating a
difference in wheel speed. In another embodiment, only a difference in wheel speed between the
front and rear wheels that meets a predetermined or pre-selected threshold may generate
feedback indicating a difference in wheel speed. Such feedback may be indicative of a slip
condition or loss of traction. When such a condition is detected, electrical current may be sent to
clutch 14 of device 10 and clutch 14 may be engaged (i.e., locked up), thereby transferring all
available torque and overspeeding the rear axle at step 102.
[0026] A determination is made as to whether both rear wheels maintain proper traction at
step 104. Compliance in the tires can handle a 6% overspeed condition. If both rear wheels
maintain proper traction at step 104, then the vehicle may be in all wheel drive mode, as
illustrated at step 106. After the PCM determines that the condition requiring rear axle drive has
been corrected and that all tires have traction, the PCM releases clutch 14, thereby preventing
any torque from being transferred to the rear axle, at step 108. The vehicle may then return to
front wheel drive mode at step 110.
[0027] If both rear wheels do not maintain proper traction at step 104, and the PCM senses
that one or both rear wheels slip, the PCM allows clutch 14 to slip, thereby decreasing the
amount of rear axle overspeed relative to the front axle and full available torque may be
transferred to the rear axle at step 112. PCM may control the magnitude of the rear axle
overspeed by controlling the amount clutch 14 slips at step 114. A new determination may then
be made as to whether both rear wheels maintain proper traction, as illustrated at step 104. If
both rear wheels maintain proper traction at step 104, then steps 106-110 may be completed. If
both rear wheels do not maintain proper traction at step 104, then steps 112-114 may be
completed.
[0028] In accordance with an embodiment of the invention, device 10 may be configured
to be integrated with or used in connection with an anti-lock braking system. An anti-lock
braking system may, for example, help control the transfer of torque to and from the right and
left sides of a motor vehicle. For example, in some anti-lock braking systems, if one wheel is
locked, more torque is provided to the opposing wheel. In particular, an anti-lock braking
system may include a first device for changing the braking torques applied to a left and right
wheel of the motor vehicle, as well as a controller for controlling the first device to prevent the
left and right wheel from locking during operation of the motor vehicle, including during braking
of the motor vehicle. The controller may determine whether one or more wheels are under anti-
lock control, and may control the first device to adjust the left wheel and/or right wheel braking
torque in order to prevent locking. The anti-lock braking system may be used in connection with
or integrated with device 10. Together, the anti-lock braking system and device 10 may thus
control both the braking torques applied to a left and right wheel of the motor vehicle, as well as
the torque selectively transferred from output shaft 20 to an axle (e.g., rear axle) of the motor
vehicle.
[0029] 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. It is intended that the
scope of the invention be defined by the claims and their equivalents.
WE CLAIM
1. A device for a motor vehicle, comprising:
an input shaft for supplying torque;
a clutch for selectively transferring the torque;
a first gear configured for connection to the clutch;
a second gear connected to the first gear, wherein the second gear is fixed to the
device so that the second gear is not free to rotate; and
an output shaft for receiving the torque;
wherein the device is configured to control the amount of torque transferred to the
output shaft.
2. A device in accordance with claim 1, wherein at least a portion of the device is
disposed between a drive shaft and a rear differential of the motor vehicle.
3. A device in accordance with claim 1, wherein the first gear is a component of a
first planetary gear set, the first planetary gear set comprising a first ring gear, a first sun gear,
and a first set of planets and a first planet carrier.
4. A device in accordance with claim 3, wherein the second gear is a component of a
second planetary gear set, the second planetary gear set comprising a second ring gear, a second
sun gear, and a second set of planets and a second planet carrier.
5. A device in accordance with claim 1, wherein torque is split between the first gear
and the second gear.
6. A device in accordance with claim 1, wherein the transfer of torque to the output
shaft is configured to increase rotation of a rear axle of the motor vehicle up to about 6%.
7. A device in accordance with claim 1, wherein the clutch is configured to manage
only a fraction of the available torque, while providing the functional equivalent amount of
horsepower as a clutch that is configured to manage all the available torque.
8. A device in accordance with claim 1, wherein the device is configured to transfer
all available torque when the clutch is fully engaged.
9. A device in accordance with claim 1, wherein the first gear is not configured to
rotate when the clutch is fully engaged.
10. A device in accordance with claim 1, wherein the device does not transfer torque
when the clutch is fully released.
11. A device in accordance with claim 1, wherein the first gear is configured to rotate
when the clutch is fully released.
12. A device in accordance with claim 1, wherein the operation of the clutch is
configured to vary the speed of the first gear, thereby varying the ratio of the speed of the output
shaft to the speed of the input shaft.
13. A device in accordance with claim 1, wherein the clutch is configured to be
released when the speed of a rear wheel of the motor vehicle differs from the speed of a front
wheel of the motor vehicle.
14. A device in accordance with claim 1, wherein the amount of torque transferred to
the output shaft corresponds to feedback received from a wheel speed sensor.
15. A device in accordance with claim 1, wherein the clutch is configured to be fully
released when a wheel speed sensor feedback indicates that the speed of a rear wheel of the
motor vehicle differs from the speed of a front wheel of the motor vehicle.
16. A device in accordance with claim 1, further comprising an anti-lock braking
system for controlling the transfer of torque to and from the right and left sides of the motor
vehicle.
17. A system for a motor vehicle, comprising:
a first device for changing the braking torques applied to a left and right wheel of
the motor vehicle;
a controller for controlling the first device to prevent the left and right wheel from
locking;
a second device, comprising:
an input shaft for supplying torque;
a clutch for selectively transferring the torque;
a first gear configured for connection to the clutch;
a second gear connected to the first gear, wherein the second gear is fixed
to the second device so that the second gear is not free to rotate; and
an output shaft for receiving the torque;
wherein the second device is configured to control the amount of torque
transferred to the output shaft,
wherein the system controls the braking torques applied to a left and right wheel
of the motor vehicle and the torque transferred from the output shaft to an axle.

A device for a motor vehicle is provided. The device may
comprise an input shaft for supplying torque, a clutch
configured for selectively transferring the torque, a first gear
connected to the first gear. The second gear may be fixed to
the device so that the second gear is not free to rotate. The
device may further comprise an output shaft for receiving the
torque. The device may be configured to control the amount of
torque transferred to the output shaft.