U.S. patent application number 11/663407 was filed with the patent office on 2008-03-13 for method for broadening the function of a transmission brake.
This patent application is currently assigned to ZF Friedrichshafen AG. Invention is credited to Wolfgang Groner, Rupert Kramer, Rainer Petzold, Ulrich Reith, Mario Steinborn.
Application Number | 20080065300 11/663407 |
Document ID | / |
Family ID | 35219388 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080065300 |
Kind Code |
A1 |
Petzold; Rainer ; et
al. |
March 13, 2008 |
Method For Broadening The Function Of A Transmission Brake
Abstract
A method for controlling and regulating a transmission brake
which, for the purpose of synchronization, determines a target
rotational speed of a shaft that is to be synchronized on the basis
of an actual rotational speed of a transmission shaft, and controls
a transmission brake such that the determined target rotational
speed is set for the shaft that is supposed to be synchronized. The
transmission brake also carries out additional functions. These
functions require no, or only minimal, additional hardware
complexity in a cost-neutral way, but considerably increase the
functional and practical value of the transmission brake. The
comfort and speed of shifting operations, the protection, or as the
case may be the detection of error states in sensors, clutch, main
clutch, and motor control are improved, and undesirable
transmission states avoided. It is also possible to account for and
influence other conditions, such as the operation of ancillary
devices.
Inventors: |
Petzold; Rainer;
(Friedrichshafen, DE) ; Steinborn; Mario;
(Friedrichshafen, DE) ; Reith; Ulrich; (Schlier,
DE) ; Groner; Wolfgang; (Friedrichshafen, DE)
; Kramer; Rupert; (Friedrichshafen, DE) |
Correspondence
Address: |
DAVIS BUJOLD & Daniels, P.L.L.C.
112 PLEASANT STREET
CONCORD
NH
03301
US
|
Assignee: |
ZF Friedrichshafen AG
Postfach 2520
Friedrichshafen
DE
D-88038
|
Family ID: |
35219388 |
Appl. No.: |
11/663407 |
Filed: |
July 15, 2005 |
PCT Filed: |
July 15, 2005 |
PCT NO: |
PCT/EP05/07696 |
371 Date: |
September 17, 2007 |
Current U.S.
Class: |
701/54 |
Current CPC
Class: |
B60W 10/10 20130101;
F16H 61/12 20130101; B60W 10/02 20130101; F16D 2500/5018 20130101;
Y10T 477/647 20150115; F16D 2500/50293 20130101; B60W 10/196
20130101; F16D 2500/5108 20130101; F16H 2061/205 20130101; F16H
2302/04 20130101; F16H 2061/047 20130101; F16H 2342/04 20130101;
F16H 2061/1212 20130101; F16H 2312/08 20130101; F16H 2061/0411
20130101; B60W 10/18 20130101; F16H 61/0403 20130101 |
Class at
Publication: |
701/054 |
International
Class: |
F16H 61/04 20060101
F16H061/04; G06F 7/00 20060101 G06F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2004 |
DE |
10 2004 045 828.6 |
Claims
1-16. (canceled)
17. A method for controlling and regulating a transmission brake in
a transmission of a vehicle to carry out synchronization, a target
rotational speed of a shaft, to be synchronized, is determined on a
basis of an actual speed of a transmission shaft, and the
transmission brake is controlled and regulated such that the
determined target rotational speed is set for the shaft to be
synchronized, and the transmission brake is further controlled and
regulated to implement additional drive-train relevant functions,
the method comprising the steps of: taking into account a torque,
dependent on inertial masses of ancillary devices connected to the
transmission when controlling and regulating a braking torque; and
decelerating the ancillary devices, via the transmission brake,
with an engaged clutch between a transmission idler gear and a
transmission shaft.
18. The method according to claim 17, further comprising the step
of operating the transmission brake in a special mode to prevent
unintentional coasting of the vehicle.
19. The method according to claim 18, further comprising the step
of employing the special mode to implement a function for rocking
the vehicle out of ruts.
20. The method according to claim 17, further comprising the step
of at least partially compensating for a torque introduced into the
transmission, through a main clutch located between the
transmission and a vehicle drive motor, by controlling and
regulating the transmission brake.
21. The method according to claim 20, further comprising the step
of at least partially compensating for a torque introduced in the
transmission as a result of overshooting, during a rapid closure of
the main clutch, torque being undesirably high and introduced via
the main clutch, by a set braking torque of the transmission
brake.
22. The method according to claim 17, further comprising the step
of eliminating tooth-on-tooth positions of the transmission by
application of one of a constant torque and a pulsing braking
torque from the transmission brake on a transmission shaft.
23. The method according to claim 17, further comprising the step
of at least one of checking a clutch path signal of the main clutch
for plausibility and calibrating the clutch path signal of the main
clutch by selective control and regulation of the transmission
brake.
24. The method according to claim 23, further comprising the step
of at least one of calibrating the transmission brake by selective
control of the torque transferred to the transmission input shaft,
by the main clutch, and checking for plausibility a connection
between an actuation signal of the transmission brake and the
braking torque being set.
25. The method according to claim 17, further comprising the step
of at least one of checking the plausibility of a motor torque
signal emitted by a motor control and calibrating the motor torque
signal emitted by a motor control with the aid of a defined braking
torque produced by the transmission brake.
26. The method according claim 17, further comprising the step of
determining if the transmission is in a neutral position by
checking the targeted control of the transmission brake.
27. The method according to claim 17, further comprising the step
of taking into account a rotational speed difference, between the
target rotational speed and an actual rotational speed of a braked
transmission shaft, and at least one of a limiting value dependent
on construction and operating conditions of the transmission brake,
when setting at least one of a maximum allowable rotational speed
gradient and a temperature limit value.
28. The method according to claim 17, further comprising the step
of controlling and regulating the braking torque depending on at
least one of an inertial mass to be decelerated and a rotational
energy to be reduced.
29. The method according to claim 17, further comprising the step
of controlling and regulating the braking torque depending on at
least one parameter interpreted as a standard value for at least
one of a desired shift speed and a certain shifting comfort.
30. The method according to claim 17, further comprising the step
of taking into account at least one of the known torque inertia of
masses to be braked, the existing rotational speed gradients on the
transmission brake, a natural rotational speed gradient of the
masses to be braked, and a temperature of the transmission when
setting the transmission torque.
31. The method according to claim 17, further comprising the step
of at least one of engaging or maintaining engagement of a main
clutch with slippage, under motor operating conditions in which,
the motor provides a braking torque and with disengagement of the
main clutch, the transmission brake would be activated, taking into
account the motor braking torque introduced into the transmission
via the main clutch when determining the transmission braking
torque.
32. A method for synchronizing a transmission and implementing
additional drive-train relevant functions by controlling and
regulating a transmission brake, the method comprising the steps
of: detecting an actual speed of a transmission shaft; determining
a target rotational speed of a transmission shaft to be
synchronized based on the actual speed of the transmission shaft;
determining a torque, which is dependent on inertial masses of one
or more ancillary devices connected to the transmission; at least
partially engaging and disengaging the transmission brake to adjust
the transmission shaft to the determined target rotational speed
depending the actual speed of the transmission shaft, with the
target rotational speed of the transmission shaft to be
synchronized and the torque, which is dependent on the inertial
masses of the one or more ancillary devices connected to the
transmission; and controlling the one or more ancillary devices,
connected to the transmission, by at least partially engaging and
disengaging the transmission brake.
Description
[0001] This application is a national stage completion of
PCT/EP2005/007696 filed Jul. 15, 2005 which claims priority from
German Application Serial No. 10 2004 045 828.6 filed Sep. 22,
2004.
FIELD OF THE INVENTION
[0002] The invention relates to a method for broadening the
function of a transmission brake in a conventional
transmission.
BACKGROUND OF THE INVENTION
[0003] Conventional transmissions have been used for some time in
different types of motor vehicles. The predominant construction
method is the so-called countershaft construction method, in which
the torque of an input shaft of the gearbox is transmitted to a
countershaft and from there to an output shaft. Located on the
shafts is a plurality of gearwheel trains corresponding to the
number of gears. Each gearwheel train has at least one idler gear,
which is mounted in a rotatable manner on a shaft, thereby enabling
the simultaneous meshing of the gearwheel trains with different
transmission ratios. When a gear is engaged, the idler gear of the
corresponding gearwheel train is fixed in a torque-proof manner to
the corresponding shaft by means of a coupling element, thereby
enabling torque flow from the input shaft via the countershaft to
the output shaft.
[0004] In order to enable the transmission of high torque with a
small construction volume and low component costs, positive locking
coupling devices, or as the case may be, clutches, are used almost
exclusively. In order to change gears quickly, without shock, and
with low noise and wear, it must be assured, when engaging a gear,
that the parts to be connected in a torque-proof manner by means of
the positive coupling device rotate at approximately the same
rotational speeds. For this synchronization, small-dimension
friction clutches can be used inside the transmission, whereby at
least one separate clutch for synchronization is provided for each
gear train.
[0005] The complexity and number of transmission components can,
however, be reduced in that the synchronization is achieved by
means of a corresponding adjustment of the ratio of the input speed
to the output speed of the transmission. As the output shaft of the
transmission is, as a rule, constantly connected in a
drive-effective manner with the driven wheels of the motor vehicle,
its rotational speed is determined by the driving speed of the
motor vehicle. For that reason, the synchronization is usually done
through the corresponding adaptation of the rotational speed of the
input side of the transmission. If it is necessary to increase the
speed of one shaft, as in the case of down-shifting, for example,
this is implemented by means of the driving motor and the main
clutch of the motor vehicle. For necessary deceleration of a shaft,
a transmission brake is provided at least on the drive side of the
drive train, within the transmission housing or immediately
adjacent to the gearbox, which acts, for example, on the
countershaft. When up-shifting, the transmission brake has the task
of slowing the input side of the transmission to approximately the
rotational speed of synchronization.
[0006] Unless expressly stated otherwise, the word clutch will be
used below to designate a clutch that is located inside the
gearbox, enables torque transfer between a shaft and an idler gear,
and which usually, but not necessarily, is a positive clutch. In
contrast, the clutch that implements torque transfer between the
drive motor and the transmission, and which is usually shifted by
means of a clutch pedal in motor vehicles with a manual
transmission, is designated a main clutch.
[0007] The transmission brake can be actuated hydraulically,
pneumatically, or electromagnetically. Even though an unregulated
transmission brake might be sufficient in some cases, a
transmission brake with adjustable braking force has considerable
advantages in practice. This kind of transmission brake, for
example, can be constructed as a brake that is actuated by two
two-way valves, which are connected to the countershaft via a fixed
transmission ratio.
[0008] While synchronization by means of a transmission brake can
be easily implemented for automatic transmissions for motor
vehicles, the functional principle of synchronizing transmission
brakes can also be used for manual transmissions as well as for
transmissions not used in motor vehicles.
[0009] A transmission brake is known from DE 196 52 916 A1. Here, a
determined output rotational speed of the transmission and
knowledge of the preselected transmission ratio are used to
determine a target coupling rotational speed, and in cases where
the target coupling rotational speed is lower than the determined
actual rotational speed, a target braking gradient is determined
and adjusted by means of valves. After the countershaft has reached
the target coupling rotational speed via the braking action of the
transmission brake, the gear is engaged and the brake disengaged.
This solution is suitable for regulating the synchronization of
normal shifting operations, however, with respect to regulation, is
restricted to the minimum required basic function and by no means
exhausts the technical possibilities of this kind of brake.
[0010] Against this background, the inventive task is to present a
control method, or as the case may be, a regulating method, for a
transmission brake, by means of which, without significant
additional hardware expenses, the function of this brake can be
significantly broadened. For purposes of linguistic simplicity, the
term "control" will henceforth also encompass the term
"regulation." It will be obvious from the context whether control
or regulation is meant, or it will be specified in the concrete
configuration of this type of control.
[0011] The solution of this task is seen in the characteristics of
the main claim, while advantageous embodiments and further
developments of the invention will be apparent from the dependent
claims.
SUMMARY OF THE INVENTION
[0012] The invention is based on the insight that broadening the
functional range of a transmission brake can, without appreciable
increase in hardware complexity, result in considerable improvement
of the comfort and speed of shifting operations; protection from,
or as the case may be, the identification of error statuses in the
sensors, clutch, main clutch and engine management system, and the
avoidance of unwanted states of the transmission. In addition, it
is also possible to take into account and to beneficially influence
additional conditions that were not previously taken into account,
such as the operation of ancillary devices.
[0013] The invention is thus based on a method for controlling and
regulating a transmission brake in a conventional transmission,
which, for the purpose of synchronization, and based on a actual
rotational speed of a gearshaft, determines a target rotational
speed of a shaft that is to be synchronized and controls and/or
regulates a transmission brake in such a way that the gearshaft
that is to be synchronized reaches the determined target rotational
speed. In order to solve the set task, the invention also provides
for control of the transmission brake to be used for carrying out
drive-train relevant functions in addition to that of simply
synchronizing the transmission.
[0014] These drive-train relevant additional functions are
described individually in the dependent claims. Their common
characteristic is that they can be implemented without, or with
only minimal additional hardware requirements, and can therefore be
implemented virtually without additional cost, at the same time as
they considerably improve the functional range and therefore the
practical value of the transmission brake.
[0015] In a first embodiment, the invention provides for the
torque, which is conditional on the inertial masses of the
ancillary drive systems connected to the gearbox, to be taken into
account for the control and/or regulation of the braking torque,
and that ancillary drive systems are decelerated by the
transmission brake with an engaged clutch. Ancillary drive systems
shall be understood here as transmission output shafts which enable
the operation of units or devices by the drive motor of the motor
vehicle in addition to the usual gears that act on the driving
wheels of the motor vehicle. These units or devices can be intended
for operation when the vehicle is at a standstill or during drive
operation.
[0016] Ancillary outputs coupled to the transmission, or as the
case may be, the units or devices connected to the ancillary
drives, may, depending on their type and operating conditions, have
considerable rotational masses, which only diminish slowly when
coupled with an open main clutch to the output side of the
transmission, thus keeping the rotational speed on the output side
of the transmission at a relatively high level for an extended
period of time.
[0017] For safety reasons, it desirable to create the possibility,
through control processes, of decelerating these ancillary drives
and thus considerably reducing the follow-up time. However, it is
very complicated and expensive to install a separate brake in each
ancillary drive, or in each unit or device that is supposed to be
driven, for this purpose alone. In terms of the invention, the
transmission brake that is present in any case can assume this
function without additional component costs by initially opening
only the main clutch, thereby cutting the connection to the drive
motor, when the ancillary drive is shut down. The ancillary drive
that is running down now rotates the gearbox parts involved and can
be decelerated via the transmission brake. There is, of course,
still the option of opening the clutch and coupling the ancillary
drive into the torque flow and letting the ancillary drive run down
without braking.
[0018] A further application of this method for decelerating
ancillary drives results from the fact that ancillary drives with a
low rotational speed, or which are stationary, can only be coupled
into the torque flow of the transmission without having complicated
friction clutches of their own if the shaft that is to be
synchronized has at least approximately the same synchronous
rotational speed, which in this case means almost standing still.
If an ancillary output is driven by the transmission, and is
supposed to continue being driven, one would have to wait after
opening the main clutch and therefore uncoupling the motor vehicle
drive train to engage the second ancillary output until the first
ancillary drive has at least almost run down, meaning that the
shaft that is supposed to be synchronized is almost at a
standstill. This can take some time, depending on the rotational
speed and the rotational mass of the ancillary drive. This time can
be considerably shortened with the method according to the
invention, if the transmission brake, with a closed clutch between
the transmission and the already engaged ancillary drive, and with
an open main clutch, is used to decelerate the ancillary shaft as
well as the shaft that is supposed to be synchronized.
[0019] It is also possible that the motor vehicle is supposed to be
drivable with an engaged ancillary drive. If a common countershaft
is provided in the transmission, upon which the idler gears are
disposed comprising parts of the gearwheel trains of the gear-speed
settings, and if in addition, there are one or more idler gears,
which mesh with the gears on separate output shafts of the
ancillary drives, the countershaft must be reduced to approximately
the synchronous rotational speed, in order to shift into a higher
drive gear. However, because in this case the rotational speed of
the countershaft is kept temporarily at approximately the same
previous level due to the ongoing rotation of the ancillary drive,
which results from its inertial rotational mass, the
synchronization can take a long time without special consideration
of the ancillary drive.
[0020] Therefore, with an engaged ancillary output, the invention
provides for the braking torque from the transmission brake to be
increased relative to the braking torque in simple drive operation
without an engaged ancillary output, in order to decelerate the
ancillary output within a short time in such a way that the
countershaft achieves the new synchronous rotational speed. This
can involve the use of fixed braking torque increases for certain
ancillary outputs; the added braking torque can be read out from a
table, depending on the type of ancillary output and its rotational
speed or depending on the reaction of the rotational speed of the
countershaft; or any other control and regulation method can be
used that produces a controlled increase in the braking torque of
the transmission brake with an engaged ancillary output.
[0021] In a second embodiment of the method according to the
invention, a transmission brake used to synchronize the
transmission is utilized in a special mode to secure the motor
vehicle against unintentional coasting.
[0022] There are many known processes and devices to prevent
unintentional coasting of a stationary motor vehicle without action
being taken by the driver. They usually operate with automatic
control of the main brake or the emergency brake. While systems
that act on the emergency brake usually require actuators that are
used exclusively for this purpose, which makes the vehicle more
expensive and increases the weight of the vehicle, the required
actuators for systems that act on the main brake are already
present in modern vehicles.
[0023] In principle, however, it is not desirable to increase the
complexity of a highly safety-relevant system, such as the brake
control, through additional functions. This disadvantage is avoided
by using the transmission brake to secure the vehicle against
coasting. As the transmission brake is intended only to prevent the
coasting of a stationary vehicle, a relatively small brake can be
used, so that the transmission brake can also take on this
function, in many cases, without being made larger, and in
particular, without requiring additional brake piston sections or
special devices intended exclusively for this purpose. This is even
more applicable, because due to the gear transmission ratio and
also to upstream ratios, for example of an axle gear or a power
divider, the torque necessary to hold the vehicle can be greatly
reduced.
[0024] Even when the braking torque produced by the transmission
brake, or a larger version of the same, is not sufficient to keep
the vehicle stationary on a steep uphill grade, the inventive
coasting stop can nevertheless be advantageously employed in a
majority of cases of use in a motor vehicle. While it is highly
unlikely that a driver will stop on a steep upward grade without
anticipating that the vehicle will roll backward and counteract
this by manually engaging a brake, hardly perceptible downhill
grades, or even only uneven areas of the road surface, for example,
at a traffic light, can often lead to unintentional coasting of the
motor vehicle. The necessary securing of a bus at a bus stop also
requires no major braking force, so that the transmission brake can
easily assume this function.
[0025] If needed, the transmission brake can be given a more robust
form in order to better perform the anti-coasting function. This
more robust form can also benefit the other functions described
here.
[0026] In a special further development of this function of
securing a motor vehicle against unintentional coasting, a rocking
function to get out of ruts can be realized. If a vehicle becomes
stuck in a rut, it can often get out on its own power, if it is
systematically and alternately driven a short distance forward and
backward, if the vehicle also exploits the potential energy gained
each time, along with the drive energy transferred to the wheels,
in order to come to a stop a little higher up on the other side of
the rut, until the wheel finally rolls over the side of the rut. In
doing this, it is important to lose as little as possible of the
achieved height when the wheel of the vehicle rolls back down into
the rut while the driver switches between forward and reverse
gears. Having said that, the brake should be completely disengaged
when the driver starts the next rocking movement with an engaged
forward or reverse gear. An anti-coasting mechanism that interacts
with the emergency brake or the main brake can perform this
function in a satisfactory manner only with considerable regulating
effort, whereas a transmission brake can be controlled with minimal
effort so as to prevent rolling back at precisely the point when
the gear that is supposed to be shifted next is not yet engaged,
while the brake is immediately released when the gear is
engaged.
[0027] A third embodiment of the inventive method provides for a
torque that is applied to the transmission via the main clutch to
be compensated for, wholly or in part, through control of the
transmission brake. It can be particularly useful, for example,
when starting up, to initially intensify the torque present in the
transmission, so that the vehicle is prevented from coasting
backward when starting on an incline. Even when the actual torque
set by the main clutch exceeds the target torque, it can be
compensated for by a corresponding braking torque of the
transmission brake. In the event that the torque transmitted by the
main clutch is also supposed to be reduced, the transmission brake
can reduce the torque applied to the output shaft of the gearbox
until the main clutch is correspondingly positioned. This enables
slower and thus more precise positioning of the clutch, while
quickly achieving the desired torque on the output side of the
transmission at the same time. An additional useful application of
this kind of method will be explained below.
[0028] When engaging a clutch, particularly when there is an
attempt at rapid positioning of the main clutch, overshooting may
occur. This can, for example, be due to a slight continuation of
the movement of clutch components after the target position has
been reached. The greater the actuation speed of the main clutch,
the more it tends toward overshooting. In addition, undesirable
torque peaks can also be produced on the transmission input shaft,
for example, by rapid alteration of load and elastic deformation of
parts of the drive train caused by this, which here too can be
subsumed under the term overshooting. As this is a matter of
processes of very short duration, regulation by means of control of
the motor rotation speed is too slow and therefore not useful.
[0029] By means of a fourth embodiment of the invention, full or
partial compensation for overshooting and the accompanying brief
rise in one of the torques present on the transmission input shaft
is achieved by means of corresponding control of the transmission
brake. The overshooting can be registered by sensors. However, it
will often be possible to at least largely reduce the perceptible
consequences of overshooting for the vehicle occupants by means of
simple control input for the transmission clutch. It can be
provided, for example, that a brief braking pulse is produced via
the transmission brake, starting at a specified positioning speed
of the drive clutch at a specified point in time after beginning or
complete power transmission by the drive clutch. Of course,
extensive control and regulating methods are conceivable, which,
for example, differentiate between different engagement
circumstances and potentially determine the point in time,
duration, and strength of the braking pulse of the transmission
brake by the use of additional parameters. This can be done by
reading the values stored in tables or by means of calculations
made in a relevant control computer.
[0030] In the case of dog-type constant-mesh countershaft
transmissions in particular, but also with other kinds of
transmission, situations may arise in which two claws or in
general, two transmission components are positioned in such
relation to each other that engagement is impossible with the
normal torque transfer capacity, as raised components face each
other, and positive engagement is prevented. Then the transmission
cannot be shifted.
[0031] These kinds of tooth-on-tooth positions in the transmission
can be resolved in a fifth embodiment of the inventive method by
applying constant or pulsing braking torque by means of the
transmission brake. Unlike the method for dissolving such
positions, which is dependent on initial separation of the adjacent
clutch components and an engagement process putting the clutch
elements into an arbitrary, more favorable relative position, the
tooth-on-tooth position can be eliminated quickly and reliably by
this method, without first having to separate the clutch elements.
The dissolution of these tooth-on-tooth positions can therefore be
implemented particularly quickly and reliably, as well as hardly
perceptibly for the occupants of the vehicle. Of course, it is also
possible to first reduce the pressure of the adjacent clutch
elements or to separate the clutch first, in order to minimize wear
on the clutch components, for example. In this case as well, a
smaller rotational speed difference can be reliably achieved
through the production of a braking torque by the transmission
brake, so that during re-engagement a repeat of the tooth-on-tooth
position is virtually impossible.
[0032] A sixth embodiment of the inventive method provides for the
clutch path signal of the main clutch to be checked for
plausibility and/or calibrated through targeted control of the
transmission brake. This can be important, for example, in order to
check or calibrate the sensor values in the case of sensors that
can be influenced by changing magnetic fields, when the sensor
values are erroneous, but which nevertheless deliver values that
are within allowable limits.
[0033] In order to do this, the transmission is placed in a neutral
position and a defined torque is introduced by means of the
transmission brake. When the main clutch is then positioned so that
the torque applied to the transmission by the drive motor via the
clutch is not sufficient to raise the transmission input rotational
speed against the transmission brake, and the main clutch is then
adjusted so that the torque transmitted by the clutch is just
barely sufficient to raise the transmission input rotational speed,
a defined engagement path is then set or, as the case may be, can
be ascertained, which can be used independently, for example of
construction-dependent deviations or clutch wear for the
calibration of the clutch path signal, or as the case may be to
check it.
[0034] If the braking torque of the transmission brake is known,
the torque transmitted by the clutch corresponds, in the clutch
position in which the transmission input shaft is currently turned
against the braking effect of the clutch, to the braking torque of
the transmission brake.
[0035] In order to determine the clutch path in which the torque
conducted by the main clutch exactly corresponds to the braking
torque, the clutch can, in a modification of the method that is
also based on a transmission in a neutral position, a specific
defined braking torque of the transmission brake and a closed main
clutch, be disengaged such that the torque transferred from the
drive motor via the clutch to the transmission is no longer
sufficient to turn the transmission input shaft against the braking
torque of the transmission brake. If both described methods are
implemented, the hysteresis of the clutch can be deduced from the
difference between the derived values, or as the case may be, the
clutch paths.
[0036] If special demands are made for the accuracy of the
calibration, the torque losses that occur inside the transmission
can also be taken into account during the evaluation.
[0037] In a seventh embodiment of the inventive method, the
transmission brake can be calibrated by means of a simple
permutation of an independent input parameter and a parameter that
is supposed to be calibrated or monitored for plausibility through
targeted control of the torque that is to be transferred by the
main clutch to the transmission input shaft, and/or the connection
between an actuation signal of the transmission brake and the
developing braking torque can be checked for plausibility, or as
the case may be, calibrated.
[0038] Thereby, in modification of the method described above, in a
neutral position of the transmission, defined torque will be
applied to the input shaft of the transmission by means of a main
clutch and a drive motor, thereby deriving the signal value, or as
the case may be, the appropriate braking position at which the
braking torque produced on the transmission brake is just as large
as the torque directed into the transmission input shaft. Here too,
analogous to the method described above, the transmission brake can
be gradually released until rotary motion of the transmission
begins, or the transmission brake is increasingly actuated, until
the braking torque is just sufficient to prevent rotary motion of
the input shaft of the transmission. By using both methods,
hysteresis behavior can be determined, and, by taking into account
internal torque losses in the transmission, the accuracy of the
method can be increased.
[0039] Of course, instead of reducing or increasing the braking
torque of the transmission brake, the braking torque of the
transmission brake can alternatively be kept constant, and the main
clutch can be gradually engaged or disengaged, until incipient
slipping of the main clutch is just perceived, or as the case may
be, an end to the slipping of the main clutch, if these clutch
positions, with the aid of known clutch characteristics, can be
associated with a certain torque that is transferred to the
transmission.
[0040] An eighth embodiment of the inventive method provides for
the possibility of checking for plausibility and/or calibrating a
motor torque signal emitted by a motor control with the aid of a
defined braking torque produced by the transmission brake. When the
transmission is in a neutral position and the main clutch is
engaged, the motor torque signal must correspond to the braking
torque produced by the transmission brake. If these values do not
coincide, an error must be assumed. If necessary, additional torque
can be taken into account that might originate from friction in the
transmission, for example.
[0041] A similar approach can be used in a ninth embodiment in
order to check, by means of systematic control of the transmission
brake, whether the transmission is in neutral position. When a
braking torque is applied using the transmission brake with a
disengaged main clutch, the rotational speed of the braked shaft,
with an engaged gear, changes comparatively slowly and
proportionally to the change in vehicle speed, while the change in
rotational speed in the neutral position of the transmission takes
place much faster, as only a few transmission components, and not
the entire vehicle are braked, and in addition the change in speed
of the braked transmission shaft does not take place proportionally
to the change in the driving speed of the vehicle. Both criteria
can be evaluated individually or in combination to establish
whether a gear is engaged or not.
[0042] It is already known that in order to control a transmission
brake, the target speed of a shaft and its actual speed must be
determined and the braking gradient must be controlled on the basis
of the difference between the two speeds. A tenth embodiment of the
inventive method provides for an improvement, in that when
adjusting a speed gradient, in addition to the rotational speed
difference between the target and the actual speed of a braked
shaft, at least one limit value is taken into account, which is
dependent on the construction or the operating conditions of the
transmission gear, in particular a maximum allowable speed gradient
and/or a temperature limit value. In this way, components can be
protected against overload, and, for example, the braking torque
can be limited depending on the state of wear of the transmission
brake or the determined or estimated temperature of the brake
lining.
[0043] In addition, the inertial mass to be braked, or the energy
of rotation to be reduced, can be determined or estimated, and the
braking torque, depending on the inertial mass to be braked and/or
the energy of rotation to be reduced, can be controlled or
regulated. This eleventh embodiment of the invention is
particularly advantageous when the inertial masses of the rotating
components to be braked are very different due to different masses
and diameters of the engaged gears, or due to coupled additional
drives, because in such cases a defined speed progression can only
be set by taking these different masses into account, or as the
case may be, in connection with the speed of the varying energy of
rotation to be reduced. It is particularly advisable, in the case
of larger rotating masses, or as the case may be the larger amounts
of energy that have to be reduced for this reason, to reinforce the
braking force, in order to make the shift times largely independent
of the cited parameters.
[0044] It is also useful to control or regulate the transmission
brake depending on at least one parameter that is interpreted as a
standard value for a desired shifting speed or a certain shifting
comfort. While it is common in the case of automatic transmissions
to provide a choice of two or more different shift-pattern maps,
which, for example, are optimized for racing operation with optimum
acceleration values, or for economical operation with minimum fuel
consumption, the actual gear-shifting process has not previously
been optimized for the needs or requirements of different driving
modes or driving conditions.
[0045] With the inventive method, it is possible, according to a
twelfth embodiment, to selectively influence the speed and comfort
of gear-shifting by varying the deceleration values realized by
means of the brake. In this way, in a racing mode, the braking
torque can be increased compared to normal operation, thereby
achieving shorter shift times. Inversely, in order to achieve
particularly comfortable shifting characteristics with little
jerking and wear, the braking torque realized by the transmission
brake can be reduced compared to normal operation.
[0046] In this connection, it is irrelevant how the parameter is
determined that serves as the standard value for a certain shift
comfort or a desired shift speed. The parameter can, for example,
be explicitly specified by the driver, or it can be automatically
changed after conventional manual changeover of the shifting
characteristics; it can be obtained on the basis of drive
parameters; or it can be read out after personalization of a memory
that is, for example, located in a motor vehicle key. In the
simplest case, it is a matter of switching between two discrete
values. However, a larger number of discrete values is conceivable,
or a continuum as well, for example in the form of a throttle. The
scope of the invention also takes into account a plurality of
parameters, such as shifting frequency, acceleration values, or
motor values, as long as these values can be seen as an
intermediate step in determining a parameter, or in any case,
culminate in an influencing variable affecting the strength of the
transmission brake's effectiveness in achieving different shifting
characteristics.
[0047] In a thirteenth embodiment of the invention, the braking
torque to be set is determined by taking into account the known
torque of inertia of the masses be braked and/or the existing
rotation gradients on the transmission brake as well as optionally
the natural rotation gradients of the masses to be braked and/or
the temperature of the transmission. In this way, it is possible to
set a considerably more exact braking torque, with respect to
comfort, shift speed, wear, and noise development, as well as
achieve the at least approximately equal or selectively different
shifting characteristics for shifting between different gears. If
required, the shifting operation can also be made particularly
wear-resistant.
[0048] Unless, as described above, the main clutch is disengaged
when actuating a transmission brake, it is also always possible,
according to a fourteenth embodiment of the invention, to engaged
the main clutch, or for it to remain engaged, at least under
motor-operation conditions, or as the case may be, to engage it, or
as the case may be to keep it engaged by means of slippage, under
motor operation conditions in which the motor itself provides a
braking torque and in which the transmission brake, with a
disengaged clutch, would be activated.
[0049] In this way, strain on the transmission brake can be
relieved, and in addition, the drive motor can be driven in
so-called trailing mode after shutting off the fuel supply. In such
cases, for the control of the transmission braking torque, there is
a useful determination of and a corresponding allowance for the
motor braking torque that is applied via the main clutch to the
transmission.
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