U.S. patent application number 12/577229 was filed with the patent office on 2010-04-15 for powertrain for a motor vehicle.
This patent application is currently assigned to MAGNA POWERTRAIN AG & CO KG. Invention is credited to Simon Kaimer, Martin Parigger, Johannes Quehenberger.
Application Number | 20100094519 12/577229 |
Document ID | / |
Family ID | 41821371 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100094519 |
Kind Code |
A1 |
Quehenberger; Johannes ; et
al. |
April 15, 2010 |
POWERTRAIN FOR A MOTOR VEHICLE
Abstract
The invention relates to a powertrain for a motor vehicle having
a permanently driven primary axle, comprising: a drive unit for the
generation of a drive torque; a first clutch for the transfer of a
variable portion of the drive torque to a secondary axle of the
motor vehicle; a second clutch for the deactuation of a torque
transfer section of the powertrain arranged between the first
clutch and the second clutch when the first clutch is opened; and a
control unit for the automatic control of the first clutch, with
the control unit being connected to at least one sensor for the
detection of a wheel slip at the primary axle; with the control
unit being made, starting from a deactuated state of the torque
transfer section, to close the second clutch in dependence on a
detected wheel slip at the primary axle.
Inventors: |
Quehenberger; Johannes;
(Saalbach, AT) ; Kaimer; Simon; (Fernitz, AT)
; Parigger; Martin; (Eggersdorf, AT) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
MAGNA POWERTRAIN AG & CO
KG
Lannach
AT
|
Family ID: |
41821371 |
Appl. No.: |
12/577229 |
Filed: |
October 12, 2009 |
Current U.S.
Class: |
701/69 ;
192/31 |
Current CPC
Class: |
B60W 10/119 20130101;
F16D 2500/70605 20130101; F16D 48/06 20130101; Y10T 477/613
20150115; B60K 17/3515 20130101; B60K 23/0808 20130101; B60W
2520/26 20130101; F16D 21/02 20130101; B60K 17/35 20130101; B60W
2720/403 20130101; F16D 2500/10431 20130101; B60W 10/02 20130101;
B60K 23/08 20130101; F16D 2500/3118 20130101; F16D 2500/5075
20130101; F16D 2500/30428 20130101; B60W 30/18172 20130101 |
Class at
Publication: |
701/69 ;
192/31 |
International
Class: |
F16D 48/12 20060101
F16D048/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2008 |
DE |
10 2008 051 461.6 |
Jan 21, 2009 |
DE |
10 2009 005 378.6 |
Claims
1. A powertrain for a motor vehicle having a permanently driven
primary axle (20), comprising: a drive unit (12) for the generation
of a drive torque; a first clutch (33; 54) for the transfer of a
variable portion of the drive torque to a secondary axle (30) of
the motor vehicle; a second clutch (46) for the deactuation of a
torque transfer section (36) of the powertrain arranged between the
first clutch (33; 54) and the second clutch (46), when the first
clutch (33; 54) is opened; and a control unit (34) for the
automatic control of the first clutch (33; 54), with the control
unit (34) being connected to at least one sensor for the detection
of a wheel slip at the primary axle (20), characterized in that the
control unit (34) is made, starting from a deactuated state of the
torque transfer section (36), to close the second clutch (46) in
dependence on a detected wheel slip at the primary axle (20).
2. The powertrain in accordance with claim 1, wherein a
synchronization device is provided which is in particular
controlled by the control unit (34) and by which the deactuated
torque transfer section (36) can be accelerated before an
engagement of the second clutch (46), in particular at least
approximately to the speed of the secondary axle (30) or primary
axle (20).
3. The powertrain in accordance with claim 2, wherein the control
unit (34) is made to accelerate the torque transfer section (36)
such that a longitudinal acceleration of the vehicle resulting from
the acceleration of the torque transfer section (36) is at least
hardly noticeable for a vehicle occupant and does not exceed an
acceleration limit value which does not exceed or hardly exceeds
the perception threshold, but is as close as possible thereto.
4. The powertrain in accordance with claim 3, wherein the
acceleration limit value is preset in dependence on environmental
factors such as the vehicle speed, the vehicle acceleration, the
noise in a vehicle speed signal or a vehicle acceleration signal,
the road conditions, a wheel slip detected at the primary axle,
pedal positions, steering wheel positions and/or further
values.
5. The powertrain in accordance with claim 2, wherein the control
unit (34) is made to accelerate the torque transfer section (36) in
accordance with a predetermined, in particular constant, speed
gradient and/or a speed gradient taken from a look-up table.
6. The powertrain in accordance with claim 2, wherein the
synchronization device is formed by the first clutch (33; 54).
7. The powertrain in accordance with claim 2, wherein the
synchronization device includes a synchronization apparatus which
is independent of the first clutch (33; 54) and which is integrated
e.g. into the second clutch (46).
8. The powertrain in accordance with claim 7, wherein the
synchronization apparatus is a synchronization apparatus without a
blocking device and in particular integrated into the second clutch
(46).
9. The powertrain in accordance with claim 7, wherein the control
unit (34) is made, starting from a deactuated state of the torque
transfer section (36), first to close the second clutch (45) in
dependence on a detected wheel slip at the primary axle (20) and
then to close the first clutch (33; 54).
10. The powertrain in accordance with claim 1, wherein a speed of
rotation sensor (58) for the detection of the speed of the torque
transfer section (36) is connected to the control unit (34).
11. The powertrain in accordance with claim 10, wherein the control
unit (34) is made to engage the second clutch (45) in dependence on
the speed of the torque transfer section (36) detected by the speed
of rotation sensor (58).
12. The powertrain in accordance with claim 1, wherein a speed of
rotation sensor (58) for the detection of the speed of the
secondary axle (30) is connected to the control unit (34).
13. The powertrain in accordance with claim 10, wherein a speed of
rotation sensor (58) for the detection of the speed of the
secondary axle (30) is connected to the control unit (34) and in
that the control unit (34) is made to engage the second clutch (46)
in dependence on the difference between the speed of the torque
transfer section (36) and the speed of the secondary axle (30).
14. The powertrain in accordance with claim 1, wherein the control
unit (34) and the second clutch (46) are made such that the second
clutch (46) can be engaged so fast that the speed of the
accelerated torque transfer section (36) does not at least
significantly exceed the speed of the secondary axle (30).
15. The powertrain in accordance with claim 1, wherein a blocking
synchronization is provided which only permits an engagement of the
second clutch (46) when the difference between the speed of the
torque transfer section (36) and the speed of the secondary axle
(30) is in a predetermined range.
16. The powertrain in accordance with claim 1, wherein the control
unit (34) is made to reduce the torque of the drive unit (12)
during the engagement of the second clutch (46).
17. The powertrain in accordance with claim 1, wherein the control
unit (34) is made to increase the torque of the drive unit (12)
during the synchronization of the torque transfer section (36), in
particular by the amount required for the synchronization of the
torque transfer section (36).
18. A method for the control of a powertrain of a motor vehicle
having a permanently driven primary axle (20); a drive unit (12)
for the generation of a drive torque; a first clutch (33; 54) for
the transfer of a variable portion of the drive torque to a
secondary axle (30) of the motor vehicle; a second clutch (46) for
the deactuation of a torque transfer section (36) of the powertrain
arranged between the first clutch (33; 54) and the second clutch
(46), when the first clutch (33; 54) is opened; and a control unit
(34) for the automatic control of the first and second clutches
(33, 54, 46) in which method a determination is made whether a
wheel slip is present at the primary axle (20) and, starting from a
deactuated state of the torque transfer section (36), the second
clutch (46) is closed in dependence on a detected wheel slip at the
primary axle (20).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit and priority of German
Patent Application Nos. 102008051461.6 filed Oct. 13, 2008, and
102009005378.6 filed Jan. 21, 2009. The entire disclosures of each
of the above applications are incorporated herein by reference.
FIELD
[0002] The invention relates to a powertrain for a motor vehicle
having a permanently driven primary axle which includes a drive
unit for the generation of a drive torque, a first clutch for the
transfer of a variable portion of the drive torque to a secondary
axle of the motor vehicle, a second clutch for the deactuation of a
torque transfer section of the powertrain arranged between the
first clutch and the second clutch, when the first clutch is
opened, and a control unit for the automatic control of the first
clutch, with the control unit being connected to at least one
sensor for the detection of a wheel slip at the primary axis.
BACKGROUND
[0003] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0004] A powertrain of this type is known, for example, from U.S.
Pat. No. 5,411,110. It provides the operator of the motor vehicle
with the option of choosing between a permanent two-wheel drive
mode in which the drive of the vehicle takes place only via the
primary axle and an automatic four-wheel drive mode, a so-called
"on-demand drive mode", in which under specific driving conditions,
for example when the wheels which are driven by the primary axle
spin, a specific portion of the drive torque is automatically
transferred to the wheels of the secondary axle to provide an
intermittent four-wheel drive.
[0005] To prevent parts of the powertrain which are not required in
permanent two-wheel drive, in particular unnecessary masses, from
being moved, a deactuation of the torque transfer section leading
to the secondary axle is provided in the powertrain of U.S. Pat.
No. 5,411,110 in that the second clutch is disengaged.
[0006] As soon as the operator of the motor vehicle selects the
automatic four-wheel drive mode, the second clutch is closed. The
torque transfer section is now rotationally fixedly connected to
the secondary axle so that, on demand, drive torque can be
transferred to the secondary axle as fast as possible. In the
automatic four-wheel drive mode, the torque transfer section
therefore constantly turns along during the travel since it is
driven by the drive unit with a closed first clutch and by the
secondary axle with an opened first clutch. This is ultimately at
the cost of fuel economy.
SUMMARY
[0007] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0008] It is the underlying object of the invention to provide a
powertrain which allows a fast demand-dependent transfer of drive
torque to the secondary axle with improved fuel efficiency.
[0009] The object is satisfied by a powertrain having the features
of, in particular, a control unit that is made, starting from a
deactuated state of the torque transfer section, to close the
second clutch in dependence on a detected wheel slip of a primary
axle.
[0010] It is therefore the underlying general idea of the invention
also generally to hold the torque transfer section in a deactuated
state in an automatic four-wheel drive mode and only to couple it
rotationally fixedly with the secondary axle by closing the second
clutch when a wheel slip is detected at the primary axle, i.e. when
the averaged speed of the wheels of the primary axle exceeds the
averaged speed of the wheels of the secondary axle by a
predetermined amount (optionally dependent on the steering
angle).
[0011] Not only the first clutch, but also the second clutch is
thus controlled in dependence on the detection of a wheel slip at
the primary axle in the automatic four-wheel drive mode. It can
hereby be ensured that the torque transfer section is already
rotationally fixedly connected e.g. to the secondary axle when the
first clutch starts to transfer the desired portion of the drive
torque to the secondary axle.
[0012] In accordance with the invention, the torque transfer
section is also mainly deactuated in the automatic four-wheel drive
mode under normal driving conditions, whereby the vehicle travels
in a two-wheel mode (2WD) over a longer time period or over longer
distances than with conventional systems and better fuel economy is
thus achieved. At the same time, it can be ensured by the closing
of the second clutch in dependence on the detection of a wheel slip
at the primary axle that the torque transfer section is
rotationally fixedly connected to the secondary axle within a very
short time, for example within a few 100 milliseconds, e.g. within
200 to 300 milliseconds, so that the first clutch can transfer a
desired portion of drive torque to the secondary axle almost
without delay on a demand determined by the control unit. In this
manner, in accordance with the invention, not only increased fuel
efficiency, but also increased driving safety and improved driving
performance are achieved.
[0013] Advantageous embodiments of the invention can be seen from
the description and from the drawing.
[0014] In accordance with an embodiment, the first clutch is a wet
or a dry multi-disk clutch. In this respect, the first clutch can
be part of a transfer case or of a torque diversion device (power
take-off unit) which is supported behind a variable speed gearbox
of the motor vehicle, for example. The second clutch is preferably
a dog clutch which can be actuable electromechanically or
hydraulically.
[0015] To ensure an engagement of the second clutch which is as
soft as possible, i.e. not noticeable for a vehicle occupant, and
simultaneously easy on material, a synchronization device is
preferably provided which is in particular controlled by the
control unit and by which the deactuated torque transfer unit can
be accelerated before an engagement of the second clutch; for
example, can be accelerated at least approximately to the speed of
the secondary axle.
[0016] In accordance with a particularly advantageous embodiment,
the synchronization device is formed by the first clutch. In this
manner, the first clutch satisfies a dual function in that it not
only serves for the synchronization of the torque transfer section
with the secondary axle, but also for the subsequent transfer of
drive torque from the drive unit to the secondary axle. An
additional synchronization device is thus generally not necessary,
whereby a more compact and lighter construction of the powertrain
is achieved, which ultimately benefits an even better fuel
economy.
[0017] In accordance with a further embodiment, the synchronization
device can, however, also include a synchronization apparatus which
is independent of the first clutch and which is provided, for
example, additionally to the first clutch. Such a synchronization
apparatus can, for example, be integrated into the second clutch,
i.e. into the dog clutch, so that the dog clutch so-to-say itself
acts as the synchronization device. In this case, the first and
second clutches are both controlled so that they contribute to a
synchronization together.
[0018] An embodiment is moreover conceivable in which the
acceleration of the deactuated torque transfer section takes place
at least approximately exclusively by the synchronization apparatus
independent of the first clutch, for example by the second clutch,
i.e. the dog clutch. This variant proves to be particularly
advantageous e.g. in a powertrain in which, for space reasons, the
first clutch is arranged at the secondary axle and the second
clutch is arranged at the primary axle. In this case, the
deactuated torque transfer unit is therefore accelerated by the
synchronization apparatus integrated e.g. into the second dog
clutch approximately to the speed of the primary axle. The second
clutch can for this purpose have a synchronization apparatus
without a blocking device so that it can also be engaged when there
is no speed identity between the clutch parts to be brought into
engagement.
[0019] Correspondingly, the control unit in this variant can be
made, starting from a deactuated state of the torque transfer
section, first to close the second clutch in dependence on a
detected wheel slip of a primary axle and then to close the first
clutch.
[0020] The control unit is generally advantageously made to
accelerate the torque transfer section so that a longitudinal
acceleration of the vehicle resulting from the acceleration of the
torque transfer section is at least hardly noticeable for a vehicle
occupant and does not exceed an acceleration limit value which does
not exceed or hardly exceeds the perception threshold, but is as
close to it as possible.
[0021] The acceleration limit value can be preset in dependence on
environmental factors such as the vehicle speed, the vehicle
acceleration, the noise in a vehicle speed signal and/or in a
vehicle acceleration signal, the road conditions, a wheel slip
detected at the primary axle, pedal positions, steering wheel
position and/or further values. It is possible in this manner to
bring the torque transfer section to the speed of the secondary
axle and to connect it rotationally fixedly thereto while taking
account of external circumstances within a very short time and
essentially not noticeable for a vehicle occupant.
[0022] The control unit can furthermore be made to accelerate the
torque transfer section in accordance with a predetermined speed
gradient, in particular a speed gradient which is constant and/or
is taken from a look-up table.
[0023] To monitor the acceleration of the torque transfer section
from the deactuated state into the state synchronized with the
secondary axle, a speed of rotation sensor is preferably provided
and connected to the control unit for the detection of the speed of
the torque transfer section.
[0024] To be able to determine when the torque transfer section and
the secondary axle are rotating at least approximately the same
speed, a speed of rotation sensor for the detection of the speed of
the secondary axle can additionally be connected to the control
unit for a simple engagement of the second clutch which is easy on
the material. Correspondingly, the control unit is preferably made
to engage the second clutch in dependence on the speed of the
torque transfer section detected by the speed of rotation
sensor.
[0025] The control unit can in particular be made to engage the
second clutch in dependence on the difference between the speed of
the torque transfer section and the speed of the secondary axle.
Ideally, the engagement of the second clutch takes place when the
speed difference is equal to zero. In practice, an engagement of
the second clutch can, however, also be possible at small speed
differences.
[0026] Alternatively to an actuation of the second clutch by the
control unit, a blocking synchronization can be provided which only
permits an engagement of the second clutch when the difference
between the speed of the torque transfer section and the speed of
the secondary axle is in a preset range. In this case, the blocking
synchronization ensures that the second clutch can only engage when
the torque transfer section has at least approximately reached the
speed of the secondary axle.
[0027] To facilitate the engagement of the second clutch, the
control unit can be made to reduce the drive torque of the drive
unit during the engagement of the second clutch. This is preferably
a brief torque reduction not noticeable for a vehicle occupant.
Alternatively or additionally, the torque of the clutch, which acts
as a synchronization unit at the primary axle side of the
deactuated torque transfer section, can be reduced to extend the
time window in which there is speed similarity between the torque
transfer section and the axle which should be connected to the
torque transfer section by the second clutch,
[0028] Furthermore, the control unit can be made to increase the
drive torque of the drive unit during the synchronization of the
torque transfer section, in particular by approximately the amount
which is required for the synchronization of the torque transfer
section. In this manner, a fall in the drive torque at the primary
axle caused by the synchronization is compensated and it is
prevented that the vehicle loses speed due to the synchronization
of the torque transfer section or that a vehicle occupant notices
the synchronization procedure.
[0029] The torque required for the synchronization of the torque
transfer section reduces a wheel slip present at the wheels of the
primary axle. The synchronization of the torque transfer section
can thus contribute to the traction control in that the torque used
for the synchronization is selected so that the wheel slip is kept
at a constant low level.
[0030] A further subject of the invention is moreover a method by
which the aforesaid advantages can be correspondingly achieved.
[0031] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0032] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0033] FIG. 1 is a schematic representation of a powertrain in
accordance with the invention in accordance with a first
embodiment;
[0034] FIG. 2 is a schematic representation of an axial
differential with a secondarily connected dog clutch of a secondary
axle of the powertrain of FIG. 1;
[0035] FIG. 3 is a schematic representation of a second embodiment
of a powertrain in accordance with the invention;
[0036] FIG. 4 is a schematic representation of a third embodiment
of a powertrain in accordance with the invention;
[0037] FIG. 5 is a graphic in which the speeds of a primary axle,
of a secondary axle, of a torque transfer section leading from the
primary axle to the secondary axle and the course of the torque
transferred to the secondary axle during the engagement of the
secondary axle from a deactuated state of the torque transfer
section in one of the powertrains from FIGS. 1, 3, 4 are shown;
[0038] FIG. 6 is a schematic representation of a fourth embodiment
of a powertrain in accordance with the invention;
[0039] FIG. 7 is a schematic representation of a fifth embodiment
of a powertrain in accordance with the invention;
[0040] FIG. 8 is a schematic representation of a sixth embodiment
of a powertrain in accordance with the invention;
[0041] FIG. 9 is a schematic representation of a seventh embodiment
of a powertrain in accordance with the invention;
[0042] FIGS. 10A-10C are cross-sectional views of a dog clutch with
synchronization apparatus used in the powertrain of FIG. 9:
[0043] FIG. 11 is a graphic in which the speeds of a primary axle,
of a secondary axle, of a torque transfer section leading from the
primary axle to the secondary axle and the course of the torque
transferred to the secondary axle during the engagement of the
secondary axle from a deactuated state of the torque transfer
section in the powertrain from FIG. 9 are shown; and
[0044] FIG. 12 is a schematic representation of an eighth
embodiment of a powertrain in accordance with the invention.
[0045] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0046] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0047] In FIG. 1, the powertrain of a motor vehicle is shown in
whose front region a drive unit 12 is arranged, in the present
example a combustion engine disposed transversely to the
longitudinal axis of the motor vehicle. The drive unit 12 is
permanently connected via a variable speed gearbox 14 to a front
axle 16 of the motor vehicle including a front axle differential 22
so that front wheels 18 seated on the front axle 16 are permanently
driven by the drive unit 12 during the drive. The front axle 16 is
therefore also called the primary axle 20.
[0048] In a rear vehicle region, the motor vehicle has a rear axle
24 having a rear axle differential 26 and rear wheels 28. The rear
axle 24 forms a secondary drive axle, also called a secondary axle
30, since it can be driven on demand by the drive unit 12.
[0049] For this purpose, a controllable torque diversion device 32
is arranged at the primary axle 20 and an adjustable portion of the
drive torque provided by the drive unit 12 can be diverted by it to
the secondary axle 30. The torque diversion device 32 includes a
multi-disk clutch 33 which is controlled by a control unit 34.
[0050] The output of the multi-disk clutch 33 is connected to the
one end of a torque transfer section 36, e.g. of a Cardan shaft. At
its other end, the torque transfer section 36 is connected to a
bevel gear 38 which is in engagement with a crown wheel 40 which is
connected to a differential cage 42 of the rear axle differential
26 (FIG. 2).
[0051] To prevent the torque transfer section 36 and the
differential cage 42 of the rear axle differential 26 from turning
unnecessarily and consuming energy during the drive and with an
opened multi-disk clutch 33, i.e. on purely front-wheel drive, a
device is provided to deactuate the torque transfer section 36 and
the differential cage 42.
[0052] In the embodiment shown in FIGS. 1 and 2, the deactuation
device is formed by a dog clutch 46 which is arranged at a split
axle 44 of the rear axle 24 in the proximity of the rear axle
differential 26 and which is likewise controllable by the control
unit 34. Alternatively, the dog clutch 46 can also be controlled by
a separate control unit which is separate from the control unit 34
controlling the multi-disk clutch 33 and which is connected to the
control unit 34 via e.g. a CAN bus.
[0053] In FIG. 3, an alternative embodiment of a deactuation device
is shown which includes two dog clutches 46 which can be controlled
by the control unit 34 and which are arranged in the hubs of the
rear wheels 28.
[0054] In FIG. 4, a third embodiment of a powertrain in accordance
with the invention is shown. The powertrain includes a drive unit
12, e.g. a combustion engine, arranged in a front region of the
motor vehicle. Unlike the embodiments described above, the drive
unit 12 of the third embodiment is, however, not aligned
transversely to the longitudinal axis of the motor vehicle, but
parallel thereto.
[0055] The drive unit 12 is connected via a variable speed gearbox
14 to the input shaft 48 of a transfer case 50. A primary output
shaft 52 of the transfer case 50 rigidly connected to the input
shaft 48 is permanently connected to the rear axle 24 of the motor
vehicle via a rear axle differential. Unlike in the embodiments
described above, in the third embodiment, the rear wheels 28 seated
on the rear axle 24 are therefore permanently driven, so that in
this case the rear axle 24 is called a primary axle 20.
[0056] The transfer case 50 includes in a manner known per se a
multi-disk clutch 54 whose input is rotationally fixedly connected
to the input shaft 48 of the transfer case 50 and whose output is
connected via a chain drive 56 or via gears meshing with one
another to the one end of a torque transfer section 36 leading to
the front axle differential 22 of the front axle 16. At the other
end of the torque transfer section 36--in a similar manner as shown
in FIG. 2--a bevel gear is provided which is in engagement with a
crown wheel which is fixedly connected to the differential cage of
the front axle differential 22.
[0057] The multi-disk clutch 54 of the transfer case 50 is
connected to a control unit 34. On demand, a portion of the drive
torque provided by the drive unit 12 can be transferred by a
corresponding control of the multi-disk clutch 54 via the torque
transfer section 36 and the front axle 16 to the front wheels 18.
In this case, the front axle 16 therefore represents the secondary
axle 30.
[0058] To prevent that the torque transfer section 36 and the chain
drive 56 or the gear drive of the transfer case 50 are driven and
move unnecessarily during the drive by the front wheels 18 with an
opened multi-disk clutch 54, i.e. with a purely rear wheel drive, a
device for the deactuation of the torque transfer section 36 is
also provided in the third embodiment shown in FIG. 4.
[0059] The deactuation device shown in FIG. 4 is made in a similar
manner to the deactuation device shown in FIG. 1 and includes a dog
clutch 46 which is controllable by the control unit 34 or by a
control unit separate from the control unit 34 and connected to it
e.g. via a CAN bus and which is arranged in a split axle 44 of the
front axle 16 in the region of the front axle differential 22.
[0060] An alternative deactuation device can also be conceived in
the third embodiment shown in FIG. 4, said alternative deactuation
device being able to be formed in a similar manner to the
embodiment shown in FIG. 3 by dog clutches accommodated in the hubs
of the front wheels 18 and controllable by the control unit 34 or
by a separate control unit.
[0061] The operation of the three powertrains described above takes
place in a mode in which, in addition to a permanent drive of the
primary axle 20, on demand, i.e. for example under predetermined
driving conditions such as wheel slip at the wheels of the primary
axle 20, drive torque of the drive unit 12 is automatically
conducted to the secondary axle 30 and is transferred to the wheels
of the secondary axle 30 under the control of the control unit 34.
In this respect, the drive torque portion transferred to the
secondary axle 30 can be set variably via a corresponding
engagement of the multi-disk clutch 33 included in the torque
diversion device 32 or of the multi-disk clutch 54 of the transfer
case 50 and can thus be matched to the driving conditions. Due to
the automatic engagement on demand of the secondary axle 30, this
drive mode is here called the automatic four-wheel drive mode.
[0062] In addition to the automatic four-wheel drive mode, the
vehicle can additionally have a permanent two-wheel drive mode in
which only the primary axle 20 is driven and/or a permanent
four-wheel drive mode in which both the primary axle 20 and the
secondary axle 30 are permanently driven, with, in the permanent
four-wheel operating mode, either a fixedly preset transfer of the
drive torque to the primary axle 20 and to the secondary axle 30
being conceivable or a transfer adapted in a variably adjustable
manner to the driving conditions.
[0063] A requirement for drive torque to be able to be transferred
as immediately as possible to the secondary axle 30 on demand in
the automatic four-wheel drive mode is that the or each dog clutch
46 is closed as fast as possible. In particular from the deactuated
state of the torque transfer section 36, this requires a
synchronization of the movement of the torque transfer section 36
with the movement of the secondary axle 30. The duration of the
synchronization in this respect depends on the difference of the
speeds of the secondary axle 30 and of the torque transfer section
36, i.e. ultimately, with a completely deactuated torque transfer
section 36, on the vehicle speed.
[0064] To achieve an engagement of the secondary axle 30 as fast as
possible, in accordance with the invention a monitoring of the
wheels of the primary axle 20 for wheel slip is provided. For this
purpose, the control unit 34 is connected to corresponding wheel
slip detectors. The wheel slip detectors can, for example, be speed
of rotation sensors, not shown, which monitor the speeds of the
wheels of the primary axle 20 and of the secondary axle 30.
[0065] As soon as the averaged speed of the wheels of the primary
axle 20 (line A in FIG. 5) exceeds the averaged speed of the wheels
of the secondary axle 30 (line B in FIG. 5) by a predetermined
amount (optionally dependent on the steering angle), the control
unit 34 assumes that there is wheel slip at the primary axle 20 and
that there is a demand for four-wheel drive.
[0066] The control unit 34 therefore instigates the engagement of
the secondary axle 30 at a time t=0 in that it first commands the
synchronization of the torque transfer section 36 with the
secondary axle 30.
[0067] The synchronization takes place with the help of the
multi-disk clutch 54 of the transfer case 50 or with the help of
the multi-disk clutch 33 of the torque diversion device 32 which is
engaged in a controlled manner for this purpose. The multi-disk
clutch 54 requires approximately 70 milliseconds to 80 milliseconds
to run through the release clearance before it starts actually to
accelerate the torque transfer section 36 (curve C in FIG. 5).
[0068] The acceleration of the torque transfer section 36 can take
place in accordance with a fixedly preset speed gradient or in
accordance with a speed gradient which is matched to the driving
conditions and e.g. can be taken correspondingly from a look-up
table.
[0069] As FIGS. 1, 3 and 4 show, the control unit 34 is connected
to a speed of rotation sensor 58 for the monitoring of the speed of
the torque transfer section 36. The speed of rotation sensor 58
allows the control unit 34 to determine the actual acceleration of
the torque transfer section 36 and to compare it with a desired
acceleration or with a desired speed gradient. Alternatively, the
signal of the speed of rotation sensor 58 can be used as an actual
value for a speed regulation, i.e. the multi-disk clutch 54 is
actuated by means of a speed controller such that the named actual
value of the speed is approximated to a desired value.
[0070] The control unit 54 can have a learning routine which allows
it to adapt an originally preset synchronization torque and thereby
to compensate tolerances and temperature effects as well as changes
over the service life which can impair the accuracy of the
multi-disk clutch.
[0071] Furthermore, the learning routine can be used to calibrate
and/or check the system with a disengaged dog clutch 46. The low
torque range and the accuracy of the multi-disk clutch in the low
torque range can in particular be verified and/or checked and/or
other diagnostics can be carried out. For example, the look-up
table in which the transferred torque over the state of engagement
of the multi-disk clutch is stored can be adapted correspondingly
when the acceleration of the torque transfer section 36 is faster
or slower than expected.
[0072] After approximately 230 milliseconds, the movement of the
torque transfer section 36 is synchronized with the movement of the
secondary axle 30, i.e. the speed of the torque transfer section 36
approximately corresponds to the speed of the secondary axle 30 so
that the or each dog clutch 46 can be engaged. A speed of rotation
sensor (not shown) connected to the control unit 34 is provided to
determine the speed of the secondary axle 30.
[0073] Usually, the closing of the dog clutch(es) 46 does not
require any exact coincidence of the speeds of the torque transfer
section 36 and of the secondary axle 30, but rather the engagement
can take place within a speed difference range which corresponds to
a time period marked by the crosses "X" in FIG. 5.
[0074] While taking account of the fact that the engagement of the
dog clutch 46 takes place with a certain delay, the closing of the
dog clutch 46 can already be commanded at a time which is before
the time at which the speed of the torque transfer section 36
achieves the speed of the secondary axle 30. The exact time for the
activation of the dog clutch 46 can easily be determined from the
acceleration of the torque transfer section 36, i.e. from the
preset desired speed gradient or from the actual speed gradient
such as is determined by the monitoring of the speed of the torque
transfer section 36 with the help of the speed of rotation sensor
58.
[0075] In addition, a blocking synchronization apparatus can be
provided which prevents a closing of the dog clutch 46 as long as
the difference between the speed of the secondary axle 30 and the
speed of the torque transfer section 36 is too high. As soon as the
speed difference reaches a permitted range, the blocking
synchronization apparatus allows an automatic engagement of the dog
clutch 46.
[0076] To facilitate the closing of the dog clutch 46 and in
particular the actuation of a selector sleeve associated with it,
the torque provided by the multi-disk clutch 54 (curve D in FIG. 5)
during the engagement of the dog clutch 45 is briefly reduced and
raised, after the closing of the dog clutch 46, to the value which
should ultimately be transferred to the secondary axle 30.
[0077] It is possible by the use of the multi-disk clutch 54 for
the synchronization of the torque transfer section 36 to
synchronize the torque transfer section 36 with the secondary axle
30 within a very short time.
[0078] As a result, the measures described above allow an
engagement of the secondary axle 30 from a deactuated state of the
torque transfer section 36 within a very short time, for example
within 200 milliseconds up to 300 milliseconds.
[0079] Since the torque for the acceleration of the torque transfer
section 36 is diverted from the drive unit 12 and thus from the
primary axle 20, the synchronization of the torque transfer section
36 moreover, additionally to a traction control, contributes to
reducing the wheel slip at the primary axle 20, whereby the wheel
slip at the primary axle 20 can be kept at a low value.
[0080] After the engagement of the secondary axle 30 has taken
place, the powertrain is operated in four-wheel drive mode by the
control unit 34, with a check being made at regular time intervals
whether the four-wheel drive mode is still necessary. If this is no
longer the case, a switch back to the two-wheel drive is made in
that the dog clutch 46 and the multi-disk clutch 33 or 54
respectively are opened again.
[0081] In FIGS. 6 to 9, further embodiments of a power train in
accordance with the invention are shown in which the torque
transfer section 36 can in each case be deactuated or engaged in
the manner described above.
[0082] FIG. 6 shows a fourth embodiment which differs from the
embodiment shown in FIG. 1 in that the dog clutch 46 is arranged at
the primary axle 20, and indeed between the front axle differential
22 and the torque diversion device 32, whereas the multi-disk
clutch 33 is located at the secondary axle 30, i.e. that is the
rear axle 24. More precisely, the multi-disk clutch is connected
between the crown wheel 40 in engagement with the bevel gear 38 of
the torque transfer section 36 and the differential cage 42 of the
rear axle differential 26. In this embodiment, the engagement of
the dog clutch 46 requires a synchronization of the movement of the
torque transfer section 36 with the movement of the primary axle 20
which can be achieved, for example, by an at least partial closing
of the multi-disk clutch 33 at the secondary axle 30.
[0083] FIG. 7 shows a fifth embodiment which only differs from the
fourth embodiment shown in FIG. 6 in that the multi-disk clutch 33
arranged at the rear axle 24 or secondary axle 30 is connected
between a side gear 60 of the rear axial differential 26 and a
split axle 44 of the rear axle 24.
[0084] FIG. 8 shows a sixth embodiment which differs from the
fourth embodiment shown in FIG. 6 in that no rear axle differential
26 is provided, but rather, in addition to the multi-disk clutch 33
connected between the crown wheel 40 and the one split axle of 44
of the rear axle 24, a further multi-disk clutch 33' is connected
between the crown wheel 40 and the other split axle 44'. The rear
axle differential 26 is therefore replaced in this embodiment by
the combination of the two multi-disk clutches 33, 33', with each
of the multi-disk clutches 33, 33' being separately controllable by
the control unit 34.
[0085] Furthermore, a seventh embodiment is shown in FIG. 9 which
only differs from the fifth embodiment shown in FIG. 7 in that the
dog clutch 46 is provided with an integrated synchronization
device. In this case, the synchronization of the movement of the
torque transfer section 36 with the movement of the primary axle 20
can therefore also take place alternatively or additionally to the
multi-disk clutch 33 by the synchronization device of the dog
clutch 46.
[0086] A detailed view of the dog clutch 46 integrated into the
torque diversion device 32 of the powertrain in accordance with the
seventh embodiment is shown in FIG. 10. The dog clutch 46 includes
a first clutch part 62 which is rotationally fixedly connected to
the differential cage of the front axle differential 22 and is
rotatably journaled with respect to a shown split axle of the front
axle 16. A second clutch part 64 of the dog clutch 46 likewise
rotatably journaled with respect to the shown split axle of the
front axle 16 is rotationally fixedly connected to a crown wheel 66
which is in engagement with a bevel gear 68 of the torque transfer
section 36.
[0087] The engagement of the dog clutch 46 takes place by means of
a clutch ring 70 supported rotationally fixedly and axially
displaceably on the second clutch part 64. The clutch ring 70 is
axially movable between a first position in which the clutch ring
70 is only in engagement with the second clutch part 64 (FIG. 10A)
and a second position in which the clutch ring 70 is in engagement
both with the second clutch part 64 and with the first clutch part
62 (FIG. 10C) to transfer torque from the first clutch part 62 to
the second clutch part 64.
[0088] For the axial displacement of the clutch ring 70, a shift
fork 72 is provided which is movable by a motor which is controlled
by the control unit 34.
[0089] With a deactuated torque transfer section 36, the second
clutch part 64 and thus the clutch ring 70 are also stationary.
[0090] So that the clutch ring 70 can be brought into engagement
with the first clutch part 62, a certain speed similarity is
required between the clutch ring 70 or the second clutch part 64
and the first clutch part 62. A synchronization apparatus which
becomes active as soon as the clutch ring 70 is moved in the
direction of the first clutch part 62 is integrated into the clutch
46 for the synchronization of the speed of the clutch ring 70 with
the speed of the first clutch part 62.
[0091] The synchronization apparatus includes a plurality of
synchronization hoops 74 which are arranged around the axle 16 and
20 respectively and which each project over a section of the first
clutch part 62 and of the clutch ring 70. The synchronization hoops
74 are rotationally fixedly connected to the clutch ring 70 and
consequently rotate at the same speed as the second clutch part
64.
[0092] Each synchronization hoop 74 is provided in the region of
its end facing the first clutch part 62 with a friction surface 76
at its inner side. Correspondingly, a friction surface 78 is formed
at the outside of the section of the first clutch part 62 projected
over by the synchronization hoops 74.
[0093] The clutch ring 70 has at its outside a guide 80 in which a
spring ring 82 is supported and is secured against a displacement
in the axial direction. The spring ring 82 presses from the inside
against the synchronization hoops 74, i.e. it exerts a force
against the synchronization hoops 74 outwardly in the radial
direction.
[0094] The section 84 of each synchronization hoop 74 projecting
over the clutch ring 70 is made in ramp-like manner such that the
spring ring 82 is compressed radially inwardly against its
restoring force when the clutch ring 70 is moved to the first
clutch part 62 to engage the clutch 46.
[0095] The force exerted onto the synchronization hoops 74 by the
spring ring 82 has the effect that the friction surfaces 76 of the
synchronization hoops 74 are pressed toward the friction surfaces
78 of the first clutch part. In this respect, the force with which
the friction surfaces 76, 78 are pressed toward one another is the
greater the further the spring ring 82 is compressed.
[0096] In the disengaged state of the clutch 46 (FIG. 10A), the
force exerted by the spring ring 82 onto the synchronization hoops
74 is so small that the friction surfaces are just not in contact,
whereas the friction surfaces 76, 78 are, shortly before the clutch
ring 70 comes into engagement with the first clutch part 62 (FIG.
10B), compressed toward one another with a force which is
sufficient to accelerate the second clutch part 64 to the speed of
the first clutch part 62 at a desired acceleration.
[0097] As can be seen from FIG. 10, the synchronization apparatus
of the clutch 46 is formed without a blocking element. This allows
the clutch 46 also to be engaged when no speed identity is
established between the first and second clutch parts 62, 64, i.e.
even if there is still a certain speed difference between the
clutch parts 62, 64.
[0098] The engagement of the secondary axle 30 of the powertrain of
FIG. 9 will now be explained with reference to FIG. 11 starting
from a deactuated torque transfer section 36.
[0099] As soon as the averaged speed of the wheels of the primary
axle 20 (line A in FIG. 11) exceeds the averaged speed of the
wheels of the secondary axle 30 (line B in FIG. 11) by a
predetermined amount (optionally dependent on the steering angle),
the control unit 34 assumes that there is wheel slip at the primary
axle 20 and that there is a demand for four-wheel drive.
[0100] The control unit 34 therefore instigates the engagement of
the secondary axle 30 at a time t=0 in that it first commands the
synchronization of the torque transfer section 36 with the
secondary axle 30.
[0101] The synchronization takes place with the help of the dog
clutch 46 of the torque diversion device 32 in that the clutch ring
70 is displaced in the direction of the first clutch part 62 to
press the friction surfaces 76, 78 toward one another in a
controlled manner. After approximately 30 ms, a preset
synchronization torque is transferred from the first clutch part 62
via the synchronization hoops 74 to the second clutch part 64
(curve E in FIG. 11), whereby the speed of the torque transfer
section 36 is increased (curve C in FIG. 11). The preset
synchronization torque amounts in the present embodiment to 100 Nm
and is maintained for so long until the speed of the torque
transfer section 36 has at least approximately reached the speed of
the primary axle 20.
[0102] As soon as the speed difference between the primary axle 20
and the torque transfer section 36 falls below a preset limit which
allows a closing of the dog clutch 46 which is essentially not
noticeable for a vehicle occupant, the second clutch part 64 is
brought into engagement with the first clutch part 62 by a still
further displacement of the clutch ring 70, i.e. the dog clutch 46
is completely engaged. In the present embodiment, this takes place
approximately 210 ms after the detection of the wheel slip.
[0103] Even before the torque transfer section 36 (curve C in FIG.
11) has reached the speed of the primary axle 20 (curve A in FIG.
11), which is the case at approximately 210 ms in accordance with
FIG. 11), it is started to engage the multi-disk clutch 33 (curve D
in FIG. 11), at approximately 190 ms in the present embodiment. As
long as the speed of the secondary axle (curve B in FIG. 11) is
higher than the speed of the torque transfer section 36, the
engagement of the multi-disk clutch 33 does not effect any braking
of the torque transfer section 36. That is, for the preparation of
a fast engagement of the multi-disk clutch 33, the release
clearance can already be overcome so that the disks of the
multi-disk clutch 33 are in minimal contact with one another
(so-called "kiss point").
[0104] If the torque transfer section 36 reaches the speed of the
secondary axle 30, the multi-disk clutch 33 can admittedly counter
the further acceleration or synchronization of the torque transfer
section 36 by the control of the kiss point. This is, however,
accepted in order to achieve a faster engagement of the secondary
axle 30 overall. Since the synchronization apparatus of the dog
clutch 46--as already mentioned--is made without a blocking device,
the dog clutch 46 can namely be connected, i.e. that is closed,
despite the speed dissimilarity.
[0105] As a result, a fast engagement of the secondary axle 30 is
achieved in this manner in approximately 250 ms after the detection
of a wheel slip at the primary axle 20, with the drive torque
transferred to the secondary axle 30 developing in accordance with
the curve F in FIG. 11 during this time.
[0106] In FIG. 12, an eighth embodiment is shown which differs from
the seventh embodiment shown in FIG. 9 in that the multi-disk
clutch 33 arranged at the rear axle 24 or secondary axle 30 is not
connected between a side gear 60 of the rear axial differential 26
and a split axle 44 of the rear axle, but rather between the torque
transfer section 36 and the bevel gear 38 of the rear axle
differential 26.
[0107] In the embodiment shown, the multi-disk clutch 33 is a
motor-actuated clutch which is controlled by the control unit 34.
Alternatively, the multi-disk clutch 33 can, however, also be a
clutch which works in a speed dependent manner and which closes, in
particular automatically, as soon as the difference of the speed at
the clutch input and output exceeds a preset amount or opens as
soon as the speed difference falls below a predetermined
amount.
[0108] In addition, a dog clutch 86 controllable by the control
unit 34 is connected between a side gear 60 of the rear axial
differential 26 and a split axle 44 of the rear axle 24. The dog
clutch 86 can be a simple dog clutch which in particular does not
have any synchronization device.
[0109] If both the dog clutch 46 located in the torque diversion
device 32 and the dog clutch 86 arranged at the rear axle 24 are
opened, not only the torque transfer device 36, but also the
multi-disk clutch 33 and the differential cage 42 of the rear axle
differential 26 are deactuated.
[0110] If, starting from this deactuated state, the secondary axle
30 or rear axle 24 are engaged, the torque transfer device 36 is
accelerated, as described with reference to FIGS. 10 and 11, with
the help of the dog clutch 46 of the torque diversion device 32 so
much until the clutch parts of the dog clutch 46 of the torque
diversion device 32 have a speed similarity such that the dog
clutch 46 of the torque diversion device 32 can be completely
closed.
[0111] The speed at the input of the multi-disk clutch 33 also
increases by the acceleration of the torque transfer device 36. Due
to drag torques in the multi-disk clutch 33 and/or because the
multi-disk clutch 33 closes automatically due to the difference of
the speeds at the clutch input and output or because the multi-disk
clutch 33 is engaged by the control unit 34, the speed at the
output of the multi-disk clutch 33 increases, whereby the
differential cage 42 of the rear axle differential 26 connected to
the multi-disk clutch 33 via the bevel gear 38 and the crown wheel
40 also rotates.
[0112] The rotation of the differential cage 42 has the result that
the clutch part of the dog clutch 86 connected to the side gear 60
of the rear axle differential 26 is brought at least approximately
to the speed of the clutch part connected to the split axle 44 of
the rear axle 24 so that the dog clutch 86--controlled by the
control unit 34--can be closed with an at most minimal jolt.
[0113] To determine a speed similarity sufficient for the
engagement of the dog clutch 46 located at the rear axle 24, the
control unit 34 is connected to a speed of rotation sensor 58 which
monitors the speed of the crown wheel 40 and thus of the
differential cage 42 and to sensors, not shown, for the detection
of the speeds of the rear wheels 28.
REFERENCE NUMERAL LIST
[0114] 12 drive unit [0115] 14 variable speed gearbox [0116] 16
front axle [0117] 18 front wheels [0118] 20 primary axle [0119] 22
front axle differential [0120] 24 rear axle [0121] 26 rear axle
differential [0122] 28 rear wheels [0123] 30 secondary axle [0124]
32 torque diversion device [0125] 33 multi-disk clutch [0126] 34
control unit [0127] 36 torque transfer section [0128] 38 bevel gear
[0129] 40 crown gear [0130] 42 differential cage [0131] 44 split
axle [0132] 46 dog clutch [0133] 48 input shaft [0134] 50 transfer
case [0135] 52 primary output shaft [0136] 54 multi-disk clutch
[0137] 56 chain drive [0138] 58 speed of rotation sensor [0139] 60
side gear [0140] 62 clutch part [0141] 64 clutch part [0142] 66
crown gear [0143] 68 bevel gear [0144] 70 clutch ring [0145] 72
shift fork [0146] 74 synchronization hoop [0147] 76 friction
surface [0148] 78 friction surface [0149] 80 guide [0150] 82 spring
ring [0151] 84 section [0152] 86 dog clutch
[0153] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the invention, and all such modifications are intended to be
included within the scope of the invention.
* * * * *