U.S. patent application number 09/752932 was filed with the patent office on 2001-09-06 for method and system for controlling a drive train of a motor vehicle.
Invention is credited to Lohrenz, Frank.
Application Number | 20010020207 09/752932 |
Document ID | / |
Family ID | 6918662 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010020207 |
Kind Code |
A1 |
Lohrenz, Frank |
September 6, 2001 |
Method and system for controlling a drive train of a motor
vehicle
Abstract
A gear ratio of an automatic transmission is set by a fuzzy
logic circuit which evaluates a braking torque desired by a motor
vehicle driver and which carries out a change in the transmission
gear ratio in order to support the braking torque of a brake
system. After changing the transmission gear ratio, the braking
torque desired by the driver is again evaluated and, in accordance
with the evaluation result, the transmission gear ratio is, if
appropriate, again adjusted in view of the desired braking torque.
A drive train control system is also provided.
Inventors: |
Lohrenz, Frank; (Regensburg,
DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
6918662 |
Appl. No.: |
09/752932 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09752932 |
Jan 2, 2001 |
|
|
|
PCT/DE98/01832 |
Jul 2, 1998 |
|
|
|
Current U.S.
Class: |
701/57 ;
701/51 |
Current CPC
Class: |
B60W 2050/0057 20130101;
F16H 59/48 20130101; F16H 61/0213 20130101; F16H 61/21 20130101;
F16H 2061/0096 20130101; F16H 59/24 20130101; F16H 2061/0081
20130101; F16H 59/54 20130101 |
Class at
Publication: |
701/57 ;
701/51 |
International
Class: |
G06F 019/00 |
Claims
I claim:
1. A method for controlling a drive train of a motor vehicle,
comprising: automatically setting, by using stored maps, a
transmission ratio of an automatic transmission at least as a
function of a speed of a motor vehicle and as a function of one of
a position of an accelerator pedal and a substitute variable for
the position of the accelerator pedal; evaluating, with a fuzzy
logic circuit, signals characterizing a driving state of the motor
vehicle and subsequently producing, with the fuzzy logic circuit,
control signals for setting the transmission ratio; assessing, with
the fuzzy logic circuit, a braking torque desire of a driver of the
motor vehicle only after a brake pedal has been actuated for a
given period of time and changing the transmission ratio for
assisting a braking torque of a brake system; and assessing, with
the fuzzy logic circuit, the braking torque desire of the driver
again after changing the transmission ratio, and, if appropriate,
adapting the transmission ratio again to the braking torque desire
in accordance with an assessment result.
2. The method according to claim 1, which comprises, after adapting
the transmission ratio again, assessing, with the fuzzy logic
circuit, the braking torque desire of the driver again and changing
the transmission ratio in steps until a demanded braking torque is
achieved.
3. The method according to claim 1, which comprises: determining
the transmission ratio for assisting the braking torque with the
fuzzy logic circuit in parallel with a map-based calculation of the
transmission ratio; and calculating, with the fuzzy logic circuit,
a change in the transmission ratio by using an actual transmission
ratio present in the automatic transmission.
4. The method according to claim 1, which comprises: determining
the transmission ratio for assisting the braking torque with the
fuzzy logic circuit in parallel with a map-based calculation of the
transmission ratio; and setting, with the fuzzy logic circuit, the
transmission ratio to a statically determined transmission ratio if
the statically determined transmission ratio results in an increase
of the transmission ratio.
5. The method according to claim 1, which comprises: deriving
driving state variables of the motor vehicle; and calculating, with
the fuzzy logic circuit, the braking torque desire of the driver
from the driving state variables.
6. The method according to claim 1, which comprises: generating a
control signal with the fuzzy logic circuit; using the control
signal as a rotational speed threshold for a comparison with a
rotational speed of a turbine of the automatic transmission; and
inducing a change in the transmission ratio for assisting the brake
torque, if the rotational speed of the turbine falls below the
rotational speed threshold.
7. The method according to claim 1, which comprises: generating a
control signal with the fuzzy logic circuit; using the control
signal as a rotational speed threshold for a comparison with an
output rotational speed of the automatic transmission; and inducing
a change in the transmission ratio for assisting the brake torque,
if the output rotational speed of the automatic transmission falls
below the rotational speed threshold.
8. The method according to claim 1, which comprises maintaining the
transmission ratio for assisting the braking torque until given
exit conditions are met.
9. In combination with a brake system having a break pedal, a drive
train control system for a motor vehicle, comprising: a drive train
controller for setting, based on stored map data, a transmission
ratio as a function of at least a motor vehicle speed and as a
function of one of an accelerator pedal position and a substitute
variable for the accelerator pedal position; said drive train
controller including a fuzzy logic circuit, a signal line
connecting said fuzzy logic circuit to the brake system; said fuzzy
logic circuit evaluating vehicle driving state signals and vehicle
load signals for generating control signals for setting the
transmission ratio; and said fuzzy logic circuit evaluating a
braking torque desire of a driver, the braking torque desire being
communicated by the brake system, and said fuzzy logic circuit
performing a change in the transmission ratio for assisting a
braking action of the brake system once the brake pedal has been
actuated for a given period of time.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application No. PCT/DE98/01832, filed Jul. 2, 1998,
which designated the United States.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for controlling a drive
train of a motor vehicle and to a drive train control system.
[0004] In conventional transmission control systems for motor
vehicles, the transmission ratio of the transmission is set
automatically as a function of the position of the accelerator
pedal and of the speed of travel by using stored maps. Instead of
using the position of the accelerator pedal as such, it is also
possible to use a signal of a so-called electronic accelerator
pedal (E-Gas for short) or some other variable derived from the
engine torque demanded by the driver. In this case, various driving
parameters and operating states of the motor vehicle are taken into
account as is described in International Publication WO 97/01051.
The respective gear to be selected or--in the case of continuously
variable transmissions--the transmission ratio to be set is
selected by control circuits operating by fuzzy logic methods. This
logic describes expert knowledge gained from experience in the form
of what is referred to as a basic set of rules. These rules are
then used for regulating operations or control operations of the
motor-vehicle transmission. The fuzzy logic circuit produces
control signals, which, among other things, define the transmission
ratio of the transmission and, in the case of automatic step-change
transmissions, the gear to be selected.
[0005] Published, Non-Prosecuted German Patent Application DE 196
37 210 A1 discloses a conventional integrated drive train control
system for a motor vehicle. The drive train control system
interprets the position of the accelerator pedal and of the brake
pedal as a wheel torque desired by the driver. It has a calculating
device which receives the positions of the accelerator pedal and
the brake pedal and which produces central control parameters for
the drive unit and for those units of the drive train that exert a
decelerating effect.
[0006] There are driving situations in which it would be expedient
if actuation of the brakes by the driver were assisted by the drive
train of the motor vehicle, when traveling downhill for example.
This can, for example, be accomplished by the suppression of
upshifts specified by a map, i.e. by retaining the existing
transmission ratio.
[0007] European Patent Application EP 0 531 154 A2 discloses a
transmission control system, with which the transmission ratio,
which is determined as a function of the position of the
accelerator pedal and of the speed of travel by using stored maps,
can be corrected. For this purpose, a correction factor is
determined by a fuzzy unit as a function of the driver's desire for
braking, of the tractive resistance and of the current transmission
ratio, and is added to the corresponding map value.
SUMMARY OF THE INVENTION
[0008] It is accordingly an object of the invention to provide a
method for controlling a drive train of a motor vehicle and a drive
train control system which overcome the above-mentioned
disadvantages of the heretofore-known methods and systems of this
general type and which detect a driver's desire or intention for
braking and which assist the desired braking action sensitively and
in an effective manner by controlling the transmission ratio of the
automatic transmission.
[0009] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method for
controlling a drive train of a motor vehicle, the method including
the steps of:
[0010] automatically setting, by using stored maps, a transmission
ratio of an automatic transmission at least as a function of a
speed of a motor vehicle and as a function of one of a position of
an accelerator pedal and a substitute variable for the position of
the accelerator pedal;
[0011] evaluating, with a fuzzy logic circuit, signals
characterizing a driving state of the motor vehicle and
subsequently producing, with the fuzzy logic circuit, control
signals for setting the transmission ratio;
[0012] assessing, with the fuzzy logic circuit, a braking torque
desire of a driver of the motor vehicle only after a brake pedal
has been actuated for a given period of time and controlling the
transmission ratio for assisting a braking torque of a brake
system, for example by changing or maintaining a transmission
ratio; and
[0013] assessing, with the fuzzy logic circuit, the braking torque
desire of the driver again after changing the transmission ratio,
and, if appropriate, adapting the transmission ratio again to the
braking torque desire in accordance with an assessment result.
[0014] The invention has in particular the advantage that it
requires only little additional expenditure or outlay. The basic
circuit components and sensor signals required are already
available in the control system known for example from the
above-mentioned patent applications.
[0015] Moreover, no additional sensors are required. Essentially
only a few different or additional fuzzy algorithms are required.
Adaptation to the driver's desire or intention for braking can be
carried out very sensitively since it takes place in several stages
if required. Once the driver's desire for braking has been
evaluated and the transmission ratio has been changed accordingly,
the driver's desire for braking is in each case reassessed if the
brake is still being activated, and the transmission ratio is
adapted if necessary, and so forth.
[0016] According to another mode of the invention, after adapting
the transmission ratio, the braking torque desire of the driver
again is assessed again and the transmission ratio is changed in
steps until a demanded braking torque is achieved.
[0017] According to yet another mode of the invention, the
transmission ratio for assisting the braking torque is determined
with the fuzzy logic circuit in parallel with a map-based
calculation of the transmission ratio, and a change in the
transmission ratio is calculated, with the fuzzy logic circuit, by
using an actual transmission ratio present in the automatic
transmission.
[0018] According to a further mode of the invention, the
transmission ratio for assisting the braking torque is determined
with the fuzzy logic circuit in parallel with a map-based
calculation of the transmission ratio, and the transmission ratio
is set to a statically determined transmission ratio if the
statically determined transmission ratio results in an increase of
the transmission ratio.
[0019] According to yet a further mode of the invention, driving
state variables of the motor vehicle are derived, and the fuzzy
logic circuit calculates the braking torque desire of the driver
from the driving state variables.
[0020] According to another mode of the invention, a control signal
is generated with the fuzzy logic circuit, the control signal is
used as a rotational speed threshold for a comparison with a
rotational speed of a turbine of the automatic transmission, and a
change in the transmission ratio for assisting the brake torque is
induced, if the rotational speed of the turbine falls below the
rotational speed threshold.
[0021] According to yet another mode of the invention, a control
signal is generated with the fuzzy logic circuit, the control
signal is used as a rotational speed threshold for a comparison
with an output rotational speed of the automatic transmission, and
a change in the transmission ratio is induced for assisting the
brake torque, if the output rotational speed of the automatic
transmission falls below the rotational speed threshold.
[0022] According to a further mode of the invention, the
transmission ratio for assisting the braking torque is maintained
until given exit conditions are met.
[0023] With the objects of the invention in view there is also
provided, a drive train control system, including:
[0024] a drive train controller for setting, based on stored map
data, a transmission ratio as a function of at least a motor
vehicle speed and as a function of one of an accelerator pedal
position and a substitute variable for the accelerator pedal
position;
[0025] the drive train controller including a fuzzy logic
circuit,
[0026] a signal line connecting the fuzzy logic circuit to a brake
system;
[0027] the fuzzy logic circuit evaluating vehicle driving state
signals and vehicle load signals for generating control signals for
setting the transmission ratio; and
[0028] the fuzzy logic circuit evaluating a braking torque desire
of a driver, the braking torque desire being communicated by the
brake system, and the fuzzy logic circuit controlling the
transmission ratio, for example by changing or maintaining the
transmission ratio, in order to assist a braking action of the
brake system once a brake pedal has been actuated for a given
period of time.
[0029] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0030] Although the invention is illustrated and described herein
as embodied in a method and system for controlling the drive train
of a motor vehicle, it is nevertheless not intended to be limited
to the details shown, since various modifications and structural
changes may be made therein without departing from the spirit of
the invention and within the scope and range of equivalents of the
claims.
[0031] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a block diagram of a motor vehicle controlled in
accordance with the method according to the invention and provided
with a drive train control system according to the invention;
[0033] FIG. 2 is a structogram illustrating the method according to
the invention;
[0034] FIG. 3 is a graph illustrating a temporal course of measured
braking times;
[0035] FIG. 4 is a graph illustrating a temporal course of braking
decelerations of the motor vehicle; and
[0036] FIGS. 5a and 5b are a flow diagram of the program executed
in the case of the method according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 1 thereof, there is shown a
schematically illustrated motor vehicle 1 which has an engine 2,
which is controlled by an engine control system 3. An engine output
shaft 4 is connected through the use of a torque converter or
hydrodynamic coupling to an automatic transmission 5, which is
controlled by an electronic drive train or transmission control
system 6 according to the invention--also referred to below simply
as a control system. In the exemplary embodiment, the transmission
5 is embodied as a step-change transmission or multi-step
transmission, but a control system 6 according to the invention
could equally well be used for a continuously variable transmission
or to control the other devices in a motor vehicle. A control
system of this kind may for example be used in a motor vehicle to
control not only an automatic transmission but also a rear-wheel
steering system, a traction control system or a cruise control
system. The crucial component of the control system 6 is a fuzzy
logic circuit 7. A transmission output shaft 8 is connected to the
driven wheels of the motor vehicle, here symbolized by a driven
wheel 9.
[0038] The driver of the motor vehicle communicates his or her
commands or, more precisely, his or her intentions to the engine
control system 3 through the use of an accelerator pedal 10.
[0039] When a brake pedal 11 is actuated, the brakes of the motor
vehicle, which are here indicated schematically by a brake system
22, are actuated. The motor vehicle is furthermore provided with a
wheel-slip or traction control system (ASR) 12 and an anti-lock
brake system (ABS) 13, which are connected by signal lines or a bus
15 to one another and to the engine control system 3 and
transmission control system 6 for the purpose of exchanging
signals. Via a signal line 16, the engine control system 3 sends
the engine 2 signals that control the ignition, the injection and
the throttle valve (the latter only if there is a corresponding
control device).
[0040] The driver determines the drive range of the automatic
transmission 5 in the customary manner through the use of a
selector lever 17. The selector-lever signals are transmitted via a
mechanical connection 18a to the transmission 5 and via an electric
signal line 18b to the control system 6. Via a signal line 19, the
control system 6 sends control signals to the transmission 5,
defining the respective transmission gear and controlling the
required shift operations or--in the case of a continuously
variable transmission--the respective transmission ratio.
[0041] The speed nab of the transmission output shaft 8 is
transmitted to the control system 6 by a speed sensor 20 via a
signal line 21. At least the signal lines 15 that connect the
control units 3, 6, 12 and 13 to one another can include individual
signal lines or a bidirectional bus, e.g. a known CAN (Control Area
Network) or LAN (Local Area Network) bus. The control units and
systems 3, 12 and 13 need not be present. If they are, however, it
is advantageous if the transmission control system 6 has access to
the sensor signals (e.g. for the wheel speeds) supplied by them and
to variables derived therefrom.
[0042] The brakes 22 are also controlled by the ABS system 13 when
the latter is active. They are connected to it by a bidirectional
signal line 24, via which control and state signals are
transmitted. The operating state of the brakes 22 and hence also
the desire or the intention for braking on the part of the driver,
as expressed by actuation of the brake pedal 11, are communicated
via another signal line 25 to the control system 6 and the fuzzy
logic circuit 7. As already described, for example in International
Publication WO 97/01051, membership functions are processed in the
fuzzy logic circuit.
[0043] As is known, the drive train of the motor vehicle including
the engine 2, the automatic transmission 5 and a number of other
components, which are not explicitly shown here since they are
known per se and are not essential to the invention, such as the
hydrodynamic coupling and one or more differentials, is controlled
in such a way that the transmission ratio of the automatic
transmission is defined automatically as a function at least of the
position of the accelerator pedal 10 and the speed of the motor
vehicle using maps stored in the transmission control system 6. The
fuzzy logic circuit 7 evaluates various signals characterizing
driving states and the load state of the motor vehicle and then
produces control signals that define the transmission ratio.
[0044] According to the invention, the fuzzy logic circuit 7
assesses or analyzes a desire for braking torque or vehicle
deceleration on the part of the driver of the motor
vehicle--expressed through actuation of the brake pedal 11--and
implements a change in the transmission ratio that assists the
braking action of the brake system 22. After changing the
transmission ratio, the fuzzy logic circuit 7 reassesses the
driver's desired braking torque and, if appropriate, adapts the
transmission ratio to the desire for braking torque on the part of
the driver again in accordance with the result of the assessment by
once again changing the transmission ratio. This is repeated until
the desired braking effect has been achieved.
[0045] The above-mentioned method for controlling the drive train
of a motor vehicle and the mode of operation of the associated
control system will now be explained in detail with reference to
FIGS. 2 to 5. A block or stage 30 (FIG. 2) represents the "static
transmission ratio input", i.e. the customary setting or definition
of the transmission ratio of the transmission 5 by shift
characteristics stored in one or more shift maps or map memories of
the control system 6.
[0046] A block or stage 31 represents the "decision function for a
possible downshift", which forms the heart of the invention. This
block receives the brake signal representing the desire for braking
torque via a (signal) line 25, the signals from the selector lever
17 via a line 32, and, via a line 34, the signals from a .+-.
switch, through the use of which the driver can increase or reduce
the transmission ratio by one step in each case. Via a line 35, the
block 31 receives sensor signals representing the turbine speed or
output speed of the transmission 5. Via a line 36, it receives
signals through the use of which the driver can manually select
special shift maps, e.g. a power-oriented map in a "power" mode,
and a map provided for the purpose of careful driving in wintry
road conditions in a "snow" mode.
[0047] Via a line 38, the block 31 receives signals that
characterize special driving states, indicating for example that
the motor vehicle is traveling around a bend or that brake slip is
occurring, this being signaled by the ABS system 13. Via a signal
line 39, it receives from the automatic transmission 5 the actual
transmission ratio of the latter.
[0048] Block 30 is connected by a line 40 and block 31 by a line 41
to a block or prioritization stage 42, in which prioritization or a
selection function is performed. The static transmission ratio
input, i.e. the definition of the transmission ratio through the
use of maps and the "dynamic" decision function according to the
invention, through the use of which the transmission ratio is
defined to match the desire for braking torque on the part of the
driver, take place in parallel. In the case of the decision
function, the statically specified gear (or transmission ratio) is
not used as the output variable or reference; instead, each new
gear stage is determined on the basis of the actual transmission
ratio physically present (selected) in the automatic transmission
5. If the static gear input by block 30 and the transmission ratio
selection proposed in block 31 for the purpose of increasing the
braking power give different values for the transmission ratio,
prioritization or selection is performed in block 42 to select a
resultant transmission ratio as a function of predetermined
conditions and transmit it via a line 44 to the automatic
transmission 5, in particular to a shift sequence control system
contained in the latter.
[0049] If the map-based or static gear calculation results in a
larger transmission ratio--corresponding to a lower gear--, this
larger transmission ratio is set in the transmission 5. This means
that, in this case, the statically calculated transmission ratio is
prioritized. To activate a change in the transmission ratio that is
not map-based, predetermined input conditions must be met.
Predetermined conditions or requirements must likewise be met for
deactivation of such a change in the transmission ratio.
[0050] The driver's desire for a given braking torque is determined
either from directly measured variables of the brake system 22 or
from derived system variables. One example of a directly measured
system variable is the brake pressure produced by the driver. If
there are suitable sensors at the brake pedal, it is also possible
to use the rate of displacement and the position of the brake pedal
11 as measured variables for detecting or calculating the intensity
of braking.
[0051] Assessment and calculation of a desire for braking torque on
the part of the driver takes place only once a predetermined period
of time has elapsed since the beginning of the braking operation.
If the braking operation begins at time t0 (FIG. 3 and FIG. 4),
assessment of an initial braking deceleration begins at a time t1.
At a time t2, the first change in the transmission ratio is
complete. If the brake continues to be actuated, measurement of a
second braking time begins at this time. Here too, the
corresponding second assessment of the braking deceleration begins
only after a predetermined period of time t3-t2 and ends at a time
t4. If the brake continues to be actuated after time t4, an
additional third assessment of the braking deceleration takes place
after the expiry of a predetermined time period. As already
mentioned, this process continues until the required braking
assistance has been achieved with the automatic transmission 5.
[0052] Braking activity is only assessed, that is to say the
braking time and intensity of braking are determined only at times
when the driver is actuating the brake system 22, i.e. the
assessment variables (e.g. the braking time) are reset to zero or
to their initial value. Also, when the brake is released, a time
period may be provided before the braking operation is regarded as
complete.
[0053] A number of decision blocks or stages are shown in the flow
diagram in FIGS. 5a, 5b, namely a first decision stage 31, a second
decision stage 45 and an N.sup.th decision stage 46. The assessment
and calculation algorithms performed by the fuzzy logic circuit 7
in these decision stages are the same.
[0054] However, the variables processed for the purpose of
determining the desired intensity of braking in each individual
decision stage in which a decision is in each case taken on a
subsequent change in the transmission ratio to assist braking are
independent. That is to say, each change in the transmission ratio
to assist braking is followed by reassessment of the braking
activity with independent values for the braking intensity. These
reassessments are represented by respective arrows 43, 48 and 49
indicating a data transfer. If it is found in the decision block 45
for the second change in the transmission ratio that the entry
conditions for a (further) change in the transmission ratio to
assist braking have not been met, the exit conditions are checked
in a block 50. If they are present, the program returns to block 30
and thus to a definition or setting of the transmission ratio on
the basis of maps.
[0055] In the case of the flow diagram in FIGS. 5a, 5b, the
prioritization block 42 is not shown to avoid cluttering the
drawing. The static transmission ratio input (static transmission
ratio setting) 30 and the blocks or stages 47 for a change in the
transmission ratio, which carry out the respectively decided change
in the transmission ratio, are connected directly to the automatic
transmission 5 by the lines 44.
[0056] The decision on a possible change in the transmission ratio
additionally takes account of a driver classification and the load
state of the motor vehicle, which have been determined by the fuzzy
logic circuit 7 in a known manner. The driver classification can be
performed indirectly through the use of a selected driver program
or directly through the use of a characteristic quantity that
characterizes the driver ("driver value"). The load state can be
determined through the use of a calculated and derived load value
or through the use of a variable (e.g. a differential torque) that
characterizes the load state.
[0057] The state variables are all processed in the fuzzy logic
circuit 7, which, for its part, produces a control signal that
brings about the change in the transmission ratio. To produce this
control signal, it is also possible to use a number of fuzzy
systems of different configuration. The relevant system is then
selected as a function of the respectively selected adapted driving
program. It is also possible to use fuzzy systems selected as a
function of the manually specified driving program (for sporty or
winter driving).
[0058] The control signal produced by the fuzzy logic circuit 7 is
used as a speed threshold for the turbine speed of the automatic
transmission 5 and is compared to it. If the turbine speed is below
the value of the control signal, a proposal to change the
transmission ratio is transmitted from block 31 to the
prioritization stage 42. Instead of the turbine speed, it is also
possible to use the transmission output speed for this
comparison.
[0059] If the transmission control system 6 detects system faults
that are critical in terms of safety, e.g. the failure of a speed
sensor signal, which do not allow a clear decision on a change in
the transmission ratio, the change in the transmission ratio is not
carried out. The static transmission ratio input according to a map
is prioritized.
[0060] In certain driving states that are critical in terms of
safety, e.g. cornering, occurrence of brake slip, slippery road
surface etc., changes in the transmission ratio that are demanded
for the purpose of assisting braking are suppressed. Manual
intervention by the driver via the selector lever 17 or a manual
gear input through the use of a button 34 ("Tiptronik" function)
are interpreted as directly intended by the driver and are
therefore given higher priority. It is thereby possible to suppress
a change demanded in the transmission ratio or to reverse a change
in the transmission ratio that has already been carried out.
[0061] If a change in the transmission ratio to assist braking has
been carried out, the following alternatives are possible:
[0062] Holding the active transmission ratio,
[0063] Changing the transmission ratio to the static value
specified by the map,
[0064] Changing the transmission ratio to continue brake
assistance.
[0065] A further change in the transmission ratio in the direction
of a higher ratio (corresponds to another downshift) takes place if
the entry conditions are met once again upon reassessment of the
braking deceleration.
[0066] The active transmission ratio is maintained until the exit
conditions are met. Before the exit conditions can be checked, the
entry conditions must no longer be met. This can be accomplished,
for example, by the control signal produced by the fuzzy logic
circuit 7 being exceeded by the turbine speed or when the braking
operation is ended.
[0067] If the entry conditions are no longer met, checking of the
exit conditions thus takes place. For this purpose, the
acceleration state of the motor vehicle is used as an input
variable. Depending on the respective acceleration level (in the
case of positive acceleration), the following alternatives are
available:
[0068] Small positive or negative acceleration level.fwdarw.the
transmission ratio is maintained.
[0069] Medium positive acceleration level.fwdarw.the vehicle must
maintain this acceleration level for a predetermined distance or
for a defined period of time, after which the transmission ratio is
released, i.e. a statically determined transmission ratio or one
determined on the basis of a map is adopted.
[0070] Large positive acceleration level.fwdarw.the transmission
ratio is released, i.e. the static transmission ratio is
adopted.
[0071] When the set transmission ratio is departed from, additional
operating states are taken into account, e.g. a "fast-off" state,
in which the accelerator pedal is suddenly released. This means
that a smaller transmission ratio is not set in the case of an
"unstable" accelerator pedal. An unstable accelerator pedal of this
kind is present, for example, when the driver is playing with the
accelerator pedal.
* * * * *