U.S. patent application number 10/568190 was filed with the patent office on 2007-02-08 for method for triggering a thermostat.
This patent application is currently assigned to DaimlerChrysler AG. Invention is credited to Hans Braun, Ralf Korber, Michael Timmann, Jochen Weeber.
Application Number | 20070029396 10/568190 |
Document ID | / |
Family ID | 34177557 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070029396 |
Kind Code |
A1 |
Braun; Hans ; et
al. |
February 8, 2007 |
Method for triggering a thermostat
Abstract
The invention relates to a cooling system with pulse-width
triggering for the operating elements on the valves of the
thermostat being subjected to closed-loop control in an adaptive
manner. The aim is to reach the required temperature level in the
coolant circuit as quickly as possible initially by predetermined
and stored basic adaptation, taking into account the current
ambient temperature. Depending on the load state and ambient
conditions, three different temperature levels are provided as
desired variables for setting the coolant temperature. Once the
currently required coolant temperature is reached for the first
time after starting, closed-loop control is changed over to fine
adaptation. The coolant temperature which is currently to be set is
kept as constant as possible by fine adaptation as a function of
the desired temperature and the external temperature. If the
desired temperature of the coolant, which temperature is to be
achieved by closed-loop control, changes on account of a change in
the load state of the engine, the newly required temperature level
is set by fine adaptation. This has the advantage that, when the
motor vehicle is started, the coolant temperature which is
currently to be set can be achieved immediately by the basic
adaptation settings.
Inventors: |
Braun; Hans; (Stuttgart,
DE) ; Korber; Ralf; (Stutgart, DE) ; Timmann;
Michael; (Eutingen, DE) ; Weeber; Jochen;
(Filderstadt, DE) |
Correspondence
Address: |
FITCH, EVEN, TABIN & FLANNERY
P. O. BOX 18415
WASHINGTON
DC
20036
US
|
Assignee: |
DaimlerChrysler AG
Stuttgart
DE
|
Family ID: |
34177557 |
Appl. No.: |
10/568190 |
Filed: |
July 31, 2004 |
PCT Filed: |
July 31, 2004 |
PCT NO: |
PCT/EP04/08615 |
371 Date: |
May 17, 2006 |
Current U.S.
Class: |
236/34.5 ;
123/41.02; 123/41.1; 236/34 |
Current CPC
Class: |
F01P 2025/60 20130101;
F01P 7/167 20130101; F01P 2023/08 20130101; G05D 23/19 20130101;
F01P 2031/00 20130101; F01P 2025/13 20130101; F01P 2007/146
20130101; F01P 2023/00 20130101 |
Class at
Publication: |
236/034.5 ;
236/034; 123/041.1; 123/041.02 |
International
Class: |
F01P 7/02 20060101
F01P007/02; F01P 7/00 20060101 F01P007/00; F01P 7/14 20060101
F01P007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2003 |
DE |
103 37 412.4 |
Claims
1. A method for the closed-loop control of a thermostat (11), in
particular in a cooling circuit of an internal combustion engine
(1), wherein, by means of the valves in the thermostat, a small
coolant circuit without a radiator (2) and a large coolant circuit
with a radiator (2) can be separated from one another or connected
to one another in a temperature-controlled manner, or connected to
one another in a mixing mode with a mixing ratio with closed-loop
control of the temperature, and the operating units of the valves
in the thermostat (11) are triggered by a control means (5), and
one of a plurality of possible desired coolant temperatures is set
by opening and closing the valves in the thermostat, characterized
in that closed-loop control to each prespecified desired coolant
temperature involves a first and second closed-loop control phase,
with the first closed-loop control phase in the form of basic
adaptation (40) with stored control parameters setting the
currently prespecified desired coolant temperature as quickly as
possible, and, after the respectively current desired coolant
temperature is reached, the second closed-loop control phase in the
form of fine adaptation (41) with variable control parameters
keeping the currently prespecified desired coolant temperature as
constant as possible.
2. The method as claimed in claim 1, characterized in that, when
the currently prespecified desired coolant temperature is changed,
the new desired coolant temperature is set by fine adaptation.
3. The method as claimed in claim 1, characterized in that the
basic adaptation settings are improved by the corrected fine
adaptation settings.
4. The method as claimed in claim 1, characterized in that, when
the motor vehicle is started, the basic adaptation settings are
matched to the ambient temperature.
5. The method as claimed in claim 4, characterized in that, when
the motor vehicle is started, the basic adaptation settings are
adapted if the ambient temperature has changed at least by a
prespecified temperature interval and the motor vehicle has been
out of operation for a prespecified minimum period.
6. The method as claimed in claim 1, characterized in that the
current desired coolant temperature (TMSoll) is selected from
amongst three different prespecified desired coolant temperatures
as a function of the load.
7. The method as claimed in claim 1, characterized in that the
external air temperature (33) is also entered into the closed-loop
control system in the first and in the second closed-loop control
phase.
8. The method as claimed in claim 1, characterized in that basic
adaptation (40) can be deactivated and, particularly in the event
of a fault, closed-loop control of the coolant is taken over from a
redundant failback level by a proportional controller (43).
Description
[0001] The invention relates to a method for triggering a
thermostat, in particular in a cooling system of a motor
vehicle.
[0002] A cooling arrangement, which forms this generic type, and a
method for operating the cooling arrangement, which forms this
generic type, are known from DE 44 09 547. This cooling arrangement
can be used to set two different coolant temperatures as a function
of specific operating parameters of the vehicle. The influencing
operating parameters in this case are the vehicle speed, the load
state of the internal combustion engine, and the intake air
temperature. As a function of the abovementioned parameters, a
control algorithm is used to decide which temperature level the
coolant should be set to. In this case, the thermostat in the
cooling circuit is triggered by a controller in which the control
algorithm is implemented. The temperature levels provided are
90.degree. Celsius and 110.degree. Celsius.
[0003] The abovementioned two-point closed-loop control systems
tend to oscillate. This problem always occurs when the influencing
variables and their values are in a value range in which the
control algorithm is set to the respectively other temperature
level when there is an extremely small change in the influencing
variables. In addition, methods which are already known do not take
into account the external temperature, that is to say the ambient
temperature, even though the ambient temperatures may fluctuate
greatly and have a great effect on the engine temperature and the
possible cooling power of the cooling system in extreme weather
conditions.
[0004] The problem of oscillation has already been identified in EP
0 744 538 A2. The solution proposed is adaptive closed-loop
control. The proposal made is that of evaluating the system
response to a jump function and using this to adapt the control
parameters in an adaptive fashion.
[0005] The object of the invention is therefore to specify a method
for triggering a thermostat, which method does not tend to
oscillate and also takes into account the ambient temperature.
[0006] The object is achieved by the features of claim 1.
Advantageous embodiments of the invention can be found in the
subclaims and in the description of the exemplary embodiments.
[0007] The solution is achieved mainly by pulse-width triggering
for the operating elements on the valves of the thermostat being
subjected to closed-loop control in an adaptive manner. The aim is
to reach the required temperature level in the coolant circuit as
quickly as possible initially by predetermined and stored basic
adaptation, taking into account the current ambient temperature.
Depending on the load state and ambient conditions, three different
temperature levels are provided as desired variables for setting
the coolant temperature. Once the currently required coolant
temperature is reached for the first time after starting,
closed-loop control is changed over to fine adaptation. The coolant
temperature which is currently to be set is kept as constant as
possible by fine adaptation as a function of the desired
temperature and the external temperature. If the desired
temperature of the coolant, which temperature is to be achieved by
closed-loop control, changes on account of a change in the load
state of the engine, the newly required temperature level is set by
fine adaptation. This has the advantage that, when the motor
vehicle is started, the coolant temperature which is currently to
be set can be achieved immediately by the basic adaptation
settings.
[0008] Fine adaptation is used for adjustment purposes if the
coolant temperature set by basic adaptation deviates from the
desired temperature. The settings obtained by fine adaptation are,
in this case, stored at regular intervals of, for example, 100
seconds, and the basic adaptation settings are overwritten by the
new settings. In this way, basic adaptation is matched to the
currently prevailing ambient conditions and to the driving style of
the driver of the motor vehicle. In this case, the new settings are
determined separately and stored specifically for each of the three
prespecified temperature levels of 80.degree. C., 90.degree. C. and
105.degree. Celsius. Basic adaptation therefore respectively
comprises settings for the temperature level of 80.degree. C., for
the temperature level of 90.degree. C., and for the temperature
level of 105.degree. C.
[0009] In one advantageous embodiment of the invention, the stored
basic adaptation settings are matched to the ambient temperature by
means of a correction function. This correction is made whenever
the ambient temperature has changed by a prespecified temperature
interval of, for example, 8.degree. Celsius and if the motor
vehicle has been out of operation for a prespecified minimum time
period of, for example, 2 hours. In this case, the correction is
made immediately when the vehicle is restarted, even before basic
adaptation begins. Basic adaptation therefore already begins with
corrected settings when the ambient conditions have changed
considerably, for example if the vehicle was turned off overnight,
with the result that it is not necessary to first find new settings
by fine adaptation. This advantage is important when, for example,
the motor vehicle has been switched off on a hot day and is
operated again on a following, cooler day. In this case, contrary
to other adaptive closed-loop control systems, for example in EP 0
744 538 A2 which employs the control parameters used last, in the
method according to the invention, basic adaptation begins with the
adapted control parameters, so that it is not necessary to first
find new control parameters for the new ambient conditions.
[0010] A further advantage of preset basic adaptation is given with
the use of a motor vehicle in different climate zones. In this
case, the cooling arrangement of the vehicle can be matched to the
respective climate zone in an optimum manner by basic adaptation
which is geared toward the respective climate zone. The daily
temperature fluctuations and the variable load conditions of the
engine are compensated for by fine adaptation.
[0011] In one advantageous embodiment, the method according to the
invention has a fallback level such that control of the coolant is
taken over by a proportional controller if the two adaptation
stages fail.
[0012] A further advantage of the method according to the invention
is seen in the ability, in contrast to the prior art, to set three
different temperature levels for the coolant temperature. This has
the advantage that the engine temperature can be matched more
effectively both to the ambient conditions and to the load state of
the engine.
[0013] Exemplary embodiments of the invention are explained below
in greater detail with reference to figures, in which:
[0014] FIG. 1 schematically shows a cooling system with the
influencing variables which are most important for the
invention;
[0015] FIG. 2 shows a simplified Matlab-Simulink representation for
determining the temperature level to be set; and
[0016] FIG. 3 shows a simplified Matlab-Simulink representation of
the adaptive closed-loop control system.
[0017] FIG. 1 schematically shows a typical cooling system for a
six-cylinder internal combustion engine 1. In addition to the
internal combustion engine, a vehicle radiator 2 and a heat
exchanger 3 are integrated in the cooling system. The cooling power
of the vehicle radiator can be influenced by an electrically driven
fan 4. In order to regulate the power of the fan, the electric
motor of the fan is subjected to closed-loop control by a control
device 5. Cooled coolant is taken from the vehicle radiator by
means of the feed line 6 and fed to the cooling lines 8 by the
coolant pump 7 in order to feed the cooling channels (not
illustrated in any detail) for the combustion cylinders 9. The
heated coolant is passed from the combustion cylinders 9 to a
three-way thermostat 11 via return lines 10. Depending on the
position of the valves in the three-way thermostat 11, the coolant
passes out of the internal combustion engine and back again into
the vehicle radiator via the radiator return 12, or back again into
the cooling lines 8 of the internal combustion engine via the
radiator short-circuit 13 and the coolant pump 7.
[0018] Depending on the position of the valves in the three-way
thermostat 11, the cooling system may be operated here, in a manner
known per se, in the short-circuit operating mode, in the mixed
operating mode or in the large cooling circuit. The heat exchanger
3 is connected to the high-temperature branch of the cooling system
in the internal combustion engine via a temperature-controlled
shut-off valve 14. The throughput through the heat exchanger after
the shut-off valve 14 is opened can be regulated with an additional
electric coolant pump 15 and a pulsed shut-off valve 16 in order to
regulate the heating power.
[0019] The operating elements on the valves of the three-way
thermostat 11 are triggered here by the control device 5. The
control device contains a logic component, Logic, in the form of a
microelectronic computer unit. The control device is preferably
formed by the controller of the engine electronics system. The
control algorithms which are outlined in FIGS. 2 and 3 are
implemented in the logic component in the form of software
programs. In this case, the most important operating data for
adaptation of the control parameters are: the actual coolant
temperature, the desired coolant temperature, the external air
temperature, the PWM pulse duty factor for triggering the valves,
and a fault detection means, Failsafe, for activating a fallback
level when the closed-loop control system fails.
[0020] FIG. 2 shows a simplified Matlab-Simulink representation of
the software architecture and the signal flowchart for determining,
according to the invention, the coolant temperature to be set. The
input signals comprising the intake air temperature 21, mass air
flow 22, classification 23 of the driver type, engine speed 24,
fuel injection quantity 25 and external air temperature 26 are
further processed with a five-stage decision cascade, and the
desired coolant temperature 27 which is matched to the current
operating parameters is determined from this. Each stage of the
decision cascade is composed of an EDP program for deciding on and
calculating a desired temperature as a function of the program
input variables. The individual software programs are referred to
below as modules.
[0021] Here, in engines with port injection, the five-stage
decision cascade is composed of the modules KE_ECT (for
KanalEinspritzer [port injector] Engine Cooling Temperature),
ECT_FTK (for Engine Cooling Temperature according to
Fahrertypklassifizierung [classification of driver type]), ECT_AT
(for Engine Cooling Temperature according to Ansauglufttemperatur
[intake air temperature]), ECT_VehSpd (for Engine Cooling
Temperature according to Vehicle Speed) and the module ECT_ExtAir
(for Engine Cooling Temperature according to External Air
Temperature).
[0022] In engines with direct injection, the quantity of fuel is
determined from the injection quantity. In these engines, the
module DE_ECT (for Direkt Einspritzung [direct injection] Engine
Cooling Temperature) is used instead of the module KE_ECT for
calculating a first desired coolant temperature TMSoll1. The
control algorithm contains both modules, for the port injector as
well as for the direct injector, as standard. Which module is used
is set on an engine-specific basis by activating one of the two
modules by means of a program. This choice is represented in the
signal flowchart according to FIG. 2 by the switching element 28.
This procedure has the advantage that only one control algorithm
has to be implemented for the various types of mixture formation,
and said algorithm can then be set to the respective engine
version.
[0023] The first desired coolant temperature TMSoll1 which is
calculated from the fuel input is load dependent, that is to say is
set to 105.degree. Celsius or to 80.degree. Celsius as a function
of the engine speed EngSpd and the quantity of fuel. The first
desired coolant temperature TMSoll1 is weighted using the following
module ECT_FTK as a function of the current classification FTK of
the driver type from the engine controller and either a coolant
temperature of 105.degree. Celsius or of 80.degree. Celsius is
selected in accordance with the classification of the driver type.
The coolant temperature of 80.degree. Celsius is weighted more
heavily, i.e. is selected with preference, for classification of
the driver type as sporty. The result of this weighting is a second
desired coolant temperature TMSoll2.
[0024] After the classification of the driver type, the intake air
temperature is taken into account in the next stage of the decision
cascade. This is done in the module ECT_AT. Detection of the intake
air temperature serves to identify a traffic jam. If the motor
vehicle is stuck in a traffic jam, it is desirable to lower the
desired coolant temperature to 80.degree. Celsius or 90.degree.
Celsius, which is triggered by this traffic jam. This is done by
lowering the coolant temperature to one of the two abovementioned
values if the intake air temperature exceeds a reference value from
the temperature interval 40.degree. Celsius to 50.degree. Celsius.
The result, after taking into account the intake air temperature,
is the desired coolant temperature TMSoll3.
[0025] This desired coolant temperature TMSoll3 which is determined
is evaluated in the decision cascade by means of the next module
ECT_VehSpd using the current vehicle speed. If the vehicle speed
exceeds a first reference value, for example 120 km/h, the coolant
temperature is set to 90.degree. Celsius, and if the vehicle speed
exceeds a second reference value, for example 160 km/h, the desired
coolant temperature is set to 80.degree. Celsius.
[0026] In the last stage of the decision cascade, the desired
coolant temperature TMSoll4 which is evaluated according to the
vehicle speed is evaluated and determined using the external air
temperature. In this way, the previously obtained desired coolant
temperatures can ultimately be overridden in extreme environmental
conditions, for example extreme cold, and a desired coolant
temperature TMSoll5 which is to be ultimately applied can be
determined, said desired coolant temperature TMSoll5 being
predefined as a desired variable for the triggering means of the
fan 4 and the three-way thermostat 11. If the external temperature
exceeds a first reference value of, for example, 12.degree.
Celsius, the temperature is not lowered by the last stage of the
decision cascade. The desired coolant temperature is adapted to the
external temperature when the temperature falls below the first
reference value, of for example 12.degree. Celsius, to a desired
coolant temperature of 90.degree. Celsius. If the external
temperature drops further and if it falls below a second reference
value, of for example minus 15.degree. Celsius, the desired coolant
temperature is set to 105.degree. Celsius independently of the
other influencing variables.
[0027] The desired coolant temperature TMSoll5 which is ultimately
present after the fifth stage is retained as a desired variable for
the adaptive closed-loop control system according to FIG. 3 for a
minimum time period, of for example 100 seconds, independently of
the input signals 21, 22, 23, 24, 25, 26 and of the vehicle speed.
This hold function can be realized, for example, with a holding
element or a program waiting loop. In the signal flowchart in FIG.
2, the hold function of the desired coolant temperature which is
determined is symbolized by a timing holding element 29.
[0028] The desired coolant temperature which is determined by the
decision cascade according to FIG. 2 is finally further processed
by the adaptive open-loop and closed-loop control systems, as
outlined in greater detail in FIG. 3. The input end of the
open-loop control system is provided with signal values for the
desired coolant temperature TMSoll, for the actual coolant
temperature TMIst, for the external air temperature, for the basic
adaptation open-loop and closed-loop control parameters which are
to be read in, GA Parameters, for the activation of basic
adaptation, Activation GA, for the activation of fine adaptation,
Activation FA, and for the activation of the fallback level,
Failsafe, if the open-loop control system operates incorrectly or
fails because, for example, one of the input signals is no longer
available. In FIG. 3, the signal input is symbolically represented
by the connection pins 31, 32, 33, 34, 35, 36 and 37 and denoted
with the corresponding signal value.
[0029] The triggering means for the thermostat 11 comprises the
software module 40 for basic adaptation, the software module 41 for
fine adaptation, the software module 42 for pilot control of the
operating elements on the valves of the three-way thermostat 11,
and a digital proportional controller 43 which may also be in the
form of a software module.
[0030] Basic adaptation is activated when the control device 5 is
connected to the voltage of the vehicle electrical system when the
vehicle is started and the desired coolant temperature is less than
90.degree. Celsius. The desired coolant temperature is used as a
decision criterion for activation of basic adaptation so that a
check by a (German) technical supervisory body of the exhaust gas
limit values is not impeded. To-be precise, engine temperatures of
105.degree. Celsius, which are optimal for exhaust gas levels, are
used for the statutorily prescribed exhaust gas test, so that basic
adaptation cannot be used for setting a desired temperature, which
is determined in accordance with the algorithm from FIG. 2, of
below 105.degree. Celsius. In other words, the three-way thermostat
11 is not triggered by basic adaptation during the exhaust gas
test. In addition, basic adaptation must be active only during
operation of the engine. If basic adaptation were active when the
engine is at a standstill, for example, this would corrupt the
adaptation values in the form of basic adaptation values
GA_Parameters on the terminal 34 in the case of self-adaptation of
basic adaptation at the predominantly prevailing ambient climatic
conditions.
[0031] A self-reset function of the GA_Parameters may be performed,
for example, by the submodule GA_Reset from FIG. 4. This submodule
is integrated in the software module 40 for basic adaptation. The
control deviation between the actual coolant temperature and the
desired coolant temperature is also registered and integrated in
this submodule. If the integral exceeds a specific value, basic
adaptation is reset and the original control parameters are
replaced by new control parameters which, for example, are
calculated from the integrated temperature deviation and the
temperature characteristic diagram of the pilot control means for
triggering the thermostat. At the start of the integral, the actual
temperature has to be within the range of the proportional
controller 43 once. The reset is used to improve the control
parameters of basic adaptation when they are very poor. The reset
also matches basic adaptation to different ambient climatic
conditions.
[0032] The correction factor TMGACorr for varying the controller
parameters of basic adaptation is obtained, for example, from the
mean integrated temperature Tmean of the respective desired
temperature TMSoll of 80.degree. Celsius or 90.degree. Celsius and
the characteristic variable of the pulse-width control TMGAGrad for
the change in the cooling water temperature as a function of the
pulse duty factor of the pulse-width control in accordance with the
following equation: TMGACorr=(Tmean-TMSoll)*TMGAGrad where TMGAGrad
is measured in %/.degree. C. A typical value for a pulse-width
control used was a 3% increase in the pulse duty factor for a
1.degree. temperature decrease in the coolant circuit. The desired
temperature values which are determined in accordance with the
algorithm from FIG. 2 can be used for TMSoll. The correction
determined in this way is still a function of the ambient
temperature.
[0033] The dependence of the settings on the ambient temperature is
taken into account by a further correction function which is
integrated in the software module 40 for basic adaptation. To this
end, the external air temperature is read in at PIN 33 as a digital
value. The effect of the external air temperature on the cooling
power of the cooling system is taken into account by a correction
characteristic diagram and a pulse duty factor of the pulse-width
control is accordingly selected, this pulse duty factor
compensating for the effect of the external temperature. This
compensation may involve, for example, taking into account the
effect of the external temperature as a multiplicative correction
factor for changing the cooling water temperature as a function of
the pulse duty factor TMGAGrad. The correction factor can then
expediently be found in the abovementioned characteristic diagram
as a function of the measured external temperature.
[0034] After the controller has been connected to the voltage of
the vehicle electrical system, basic adaptation is generally active
only once for the following driving cycle. In contrast, fine
adaptation 41 (FIG. 3) runs permanently and begins after the
desired temperature of 80.degree. Celsius or 90.degree. Celsius has
been reached for the first time by basic adaptation and basic
adaptation has ended. By way of example, a threshold value
comparator (not illustrated) can establish when the desired
temperature is reached and then transmit a corresponding start
signal, Activation FA, to the input pin 36 of the fine adaptation
means 41. In contrast to basic adaptation, correction is determined
over time in the case of fine adaptation. The number of time
components of the total operating period of the current fine
adaptation phase in which the actual temperature of the coolant
deviates from the desired temperature is then recorded, for
example. Furthermore, a correction value TMFACorr is calculated in
the fine adaptation means 41, fed back to the basic adaptation
means 40 in a control loop and used to correct triggering of the
pilot control means 42.
[0035] Finally, in the pilot control means 42, the predefined
signal TMGA at the output of the basic adaptation means 40, which
signal contains the correction information, is used to determine
the correction of the pulse-width pulse duty factor in accordance
with the characteristic curves of the operating elements used in
the three-way thermostat, and said correction is additively
superimposed on the controller output of the proportional
controller 43. The superimposition is symbolically represented by
reference numeral 45 in FIG. 3. The process 30 finally outputs a
pulse duty factor of the pulse-width modulation which is used to
operate the operating elements in the three-way thermostat.
[0036] The closed-loop control system according to FIG. 3 has the
advantage, in particular on account of the adaptive superimposition
of basic adaptation and fine adaptation on the output of the
proportional controller 43, that an emergency function can be
provided in a very simple manner. If the basic adaptation means or
the fine adaptation means is not operating correctly, the two
modules can be switched off in a simple manner by a corresponding
signal, Failsafe, which is symbolized at terminal 37. The coolant
temperature is then set solely by the proportional controller
43.
[0037] The ambient conditions are taken into account by detecting
the external air temperature by means of a corresponding
temperature sensor which supplies a temperature signal to the input
of the terminal 33. This measured external air temperature is taken
into account by the software in the proportional controller 43, by
the software in the basic adaptation means 40 and by the software
in the fine adaptation means when determining the controller
settings and adaptation. Said temperature is taken into account
here using a computer by means of temperature characteristic
diagrams which take into account the dependence of the cooling
power on the external temperature. It is thus possible to set
triggering of the three-way thermostat to the current ambient
temperature too. Adaptation can therefore be deactivated
particularly in the case of high external temperatures which may
possibly prevent a desired coolant temperature of 80.degree.
Celsius being reached, since adaptation would be nonsensical in the
case of impossible predefined desired values.
* * * * *