U.S. patent application number 10/399301 was filed with the patent office on 2004-01-22 for method for the temperature regulation of an engine.
Invention is credited to Herynek, Roland, Vollmer, Martin.
Application Number | 20040011304 10/399301 |
Document ID | / |
Family ID | 7698319 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040011304 |
Kind Code |
A1 |
Herynek, Roland ; et
al. |
January 22, 2004 |
Method for the temperature regulation of an engine
Abstract
The invention concerns a method for regulating the temperature
of an engine, in particular an internal combustion engine 12, in
the case of which the engine is interconnected with a radiator 16
via at least one forward-delivery line 35 and at least one
return-delivery line 44 within a cooling circuit 14, which said
radiator can be bypassed via a valve-controlled bypass line 48
between the at least one forward-delivery line 35 and the at least
one return-delivery line 44. Additionally, the cooling circuit 14
comprises at least one pump capable of being controlled via
open-loop and/or closed-loop control, in particular an electric
pump 34 for pumping a coolant through the connecting lines 32 of
the cooling circuit 14, as well as an electronic control unit 52
that controls the cooling capacity of the cooling circuit 14 via
open-loop and/or closed-loop control. It is proposed, according to
the invention, that at least one component temperature of the
engine 12 be determined based on the coolant temperature and the
volumetric flow of the coolant through the engine 12.
Inventors: |
Herynek, Roland; (Oetisheim,
DE) ; Vollmer, Martin; (Stuttgart-Weilimdorf,
DE) |
Correspondence
Address: |
Striker Striker & Stenby
103 East Neck Road
Huntington
NY
11743
US
|
Family ID: |
7698319 |
Appl. No.: |
10/399301 |
Filed: |
April 15, 2003 |
PCT Filed: |
June 20, 2002 |
PCT NO: |
PCT/DE02/02254 |
Current U.S.
Class: |
123/41.1 |
Current CPC
Class: |
F01P 7/164 20130101;
F01P 2025/30 20130101; F01P 2025/32 20130101; F01P 2023/00
20130101; F01P 2025/06 20130101; F01P 11/16 20130101; F01P 2025/46
20130101 |
Class at
Publication: |
123/41.1 |
International
Class: |
F01P 007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2001 |
DE |
10144275.0 |
Claims
What is claimed is:
1. A method for regulating the temperature of an engine, in
particular an internal combustion engine (12), in the case of which
the engine is interconnected with a radiator (16) via at least one
forward-delivery line (35) and at least one return-delivery line
(44) within a cooling circuit (14), which said radiator can be
bypassed via a valve-controlled bypass line (48) between the at
least one forward-delivery line (35) and the at least one
return-delivery line (44), and comprising at least one pump capable
of being controlled via open-loop and/or closed-loop control, in
particular an electric pump (34) for pumping a coolant through the
cooling circuit (14), whereby an electronic control unit (52)
controls the cooling capacity of the cooling circuit (14) via
open-loop and/or closed-loop control, wherein at least one
component temperature of the engine (12) is determined based on a
coolant temperature and a volumetric flow of the coolant through
the engine (12).
2. The method according to claim 1, wherein the volumetric flow of
the coolant pumped through the engine (12) is determined based on
the electrical current (I) required by the pump (34).
3. The method according to claim 1, wherein the volumetric flow of
coolant pumped through the engine (12) is determined based on the
electrical voltage (U) applied to the pump (34).
4. The method according to one of the preceding claims, wherein a
numeric model of the cooling circuit (14) with its components--in
particular the engine (12), the pump (34), and its load curve and
the connecting lines (32)--is stored in data form in the electronic
control unit (52), which said model describes the dependence of at
least one component temperature of the engine (12) on the
volumetric flow of coolant.
5. The method according to claim 4, wherein, to change the
volumetric flow of coolant, at least one correction signal (55) is
generated by comparing at least one determined actual component
temperature with the data on the associated setpoint component
temperature stored in the electronic control unit (52).
6. The method according to one of the preceding claims, wherein the
coolant temperature is detected via at least one temperature sensor
(72).
7. The method according to claim 6, wherein the change in
temperature of the coolant over time is compared with a
time-dependent model for the coolant temperature stored in the
electronic control unit (52), and at least one second correction
signal (56) is generated in accordance with a present deviation of
the actual coolant temperature from the setpoint coolant
temperature.
8. The method according to claim 1, wherein the delivery quantity
of the pump (34) is controlled via open-loop and/or closed-loop
control in accordance with the at least one first (55) and/or the
at least one second (56) correction signal in order to change the
volumetric flow of coolant.
9. The method according to one of the preceding claims, wherein at
least one valve located in the cooling circuit (14), in particular
an electrically controllable valve (46) and/or a radiator blower
(24) associated with the radiator (16), and/or air flaps (20), are
controlled via open-loop and/or closed-loop control in accordance
with at least a first (55) and/or the at least one second (56)
correction signal to obtain a specifiable volumetric flow of
coolant and/or a specifiable coolant temperature.
10. The method according to one of the preceding claims, wherein
the electronic control unit (52) controls--via open-loop and/or
closed-loop control--the cooling capacity of the cooling circuit
(14) and, in particular, the volumetric flow of coolant with
consideration for at least one further parameter, in particular the
pollutant emission of the engine (12)
Description
BACKGROUND OF THE INVENTION
[0001] The invention is based on a method for regulating the
temperature of an engine, in particular an internal combustion
engine of a motor vehicle, according to the general class of the
main claims.
[0002] The need to cool engines, in particular internal combustion
engines, arises from the fact that excessive thermal stress on the
engine can result in an impairment of its operation or even
irreversible engine damage. For example, the surfaces that are in
contact with hot gasses and the lubrication of said surfaces inside
the cylinders of an internal combustion engine can only withstand
the temperatures produced up to a certain extent without damage.
Individual parts, such as spark plugs, nozzles, exhaust valves,
prechambers, etc., or even piston heads must withstand particularly
high mean temperatures. Such parts are therefore produced out of
materials that have particularly high heat resistance and/or that
dissipate heat well.
[0003] To dissipate heat, cooling systems are used, among other
things, in the case of which a coolant flows through coolant
passages that surround the cylinder head and engine block of the
internal combustion engine, for example. At least a portion of the
heat absorbed by the coolant is then released to the surroundings
via a radiator, or it is used to heat the passenger compartment,
for example, by means of an additional heat exchanger provided in
the cooling system.
[0004] The coolant temperature can be measured by a temperature
sensor that is located in the cooling circuit and that detects the
actual temperature of the cooling water at that point in time and
forwards it to an electronic control unit, for example. This
open-loop control monitors the temperature of the coolant and
compares it with a permissible maximum temperature for the coolant
and/or for the engine through which coolant flows that must not be
exceeded during operation.
[0005] A device and a method for cooling an internal combustion
engine is made known in EP 0 442 489 A1, in the case of which a
first temperature sensor detects the temperature of the coolant at
the outlet of the cylinder head. Furthermore, the method described
in EP 0 442 489 A1 comprises a further temperature sensor that is
installed directly on the engine block and serves to determine the
engine oil temperature. If the engine oil temperature rises above a
specified value, the coolant flow that flows through the internal
combustion engine is divided into two different branches. The first
branch of the coolant flow continues to flow through the cylinder
head, while the second, remaining part of the coolant flow flows
through the cylinder block. The volumetric flow of coolant through
the cylinder head can be controlled via closed-loop control in
accordance with the engine oil temperature in the cylinder
head.
[0006] Publication EP 0 894 953 A1 discloses a cooling system for
the internal combustion engine of a motor vehicle having a
plurality of sensors that measures a corresponding number of
parameters of the engine during operation. For example, the cooling
system described in EP 0 894 953 A1 comprises three temperature
sensors, in particular, that are installed in the cylinder head
cooling circuit, the engine block cooling circuit, and at the
outlet of the cylinder head cooling circuit. Each of these sensors
detects a temperature of the engine case and forwards the
corresponding signals to a central electronic control unit of the
cooling circuit.
[0007] Based on the different sensor signals, the central control
unit of the cooling system controls various components of the
cooling system located in the cooling circuit, such as a
cooling-air fan, a coolant pump, or a throttle and/or bypass
valve.
[0008] A disadvantage of the cooling system for the internal
combustion engine of a motor vehicle disclosed in EP 0 894 953 A1
is the fact that a plurality of sensors, in particular temperature
sensors, must be used to determine the engine temperature. Due to
the high mechanical and thermal stresses in the engine compartment
of an internal combustion engine, these sensors are highly
susceptible to malfunction or total functional failure. Moreover,
the use of a plurality of sensors represents a not-inconsequential
cost factor as well as a marked increase in the complexity of the
cooling system and/or its closed-loop control.
[0009] Advantages of the Invention
[0010] In contrast, the method according to the invention for
regulating the temperature of an engine having the characterizing
features of the main claim has the advantage that the number of
sensors used in the cooling system can be reduced to a minimum. The
engine temperature and/or the temperature of individual components
of the engine can be determined in simple fashion by means of the
coolant temperature and the volumetric flow of the coolant that is
directed through the engine and/or individual components of the
engine. In this manner, a plurality of detectors can be eliminated.
On the other hand, however, due to the continuous diagnosis of the
engine temperature, it is ensured that the heat-sensitive parts of
the engine are not damaged.
[0011] Advantageous further developments and improvements of the
method described in the main claim are possible due to the measures
listed in the dependent claims.
[0012] It is particularly advantageous to determine the value for
the volumetric flow of coolant that is required to determine the
component temperature of the engine based on the electrical current
required to operate the coolant circulation pump. During
steady-state operation, an electrical pump for circulating coolant
in the cooling circuit will deliver a constant volumetric flow
given a constant electrical voltage U, a constant electrical
current I, and a rotational speed N of the pump. The operating
point of the pump, i.e., the pressure rise .DELTA.p, as well as the
volumetric flow .DELTA.V/.DELTA.t, can be determined with reference
to the known pump characteristics and the known resistance to flow
of the cooling circuit when the values (U, I, N) mentioned
hereinabove are known.
[0013] For example, the load on the pump and, therefore, the
volumetric flow delivered by the pump, can be deduced from the
rotational speed N of the pump when the state is known (i.e.,
constant electrical voltage U applied to the pump), if said pump
always draws a constant electrical current I. In analogous fashion,
if the pump maintains a constant rotational speed N, the load on
the pump and, therefore, the volumetric flow of the coolant, can be
deduced from the measurement of the electrical current I required
by the pump.
[0014] In this manner, when data that are available anyway, e.g.,
the pump characteristics and the current required by the pump, are
known, the volumetric flow that is delivered can be deduced and,
therefore, when the coolant temperature is known, the sought-after
engine temperature can be deduced as well. Existing operating
parameters of the cooling system are therefore used in very
advantageous fashion to obtain additional information about
critical locations in the cooling circuit. When the method
according to the invention is used, increased expenditure resulting
from additional sensors used to detect the required data is not
necessary, or is necessary only to a limited extent.
[0015] In advantageous fashion, a numeric model of the cooling
circuit with its individual components, in particular the engine
and/or a thermal model of the engine, the tube routing with the
associated resistances to flow, the placement of the valves, and
further parameters that describe the cooling circuit are stored in
an electronic control unit belonging to the cooling circuit. A
model and/or a data set is therefore stored in the electronic
control unit that models the influence or the maximum permissible
deviations of the volumetric flow of coolant on the component
temperature. By comparing the actual component temperature at that
point in time with the data on the associated setpoint component
temperature stored in the electronic control unit, a correction
signal and/or a manipulated variable can therefore be generated
that changes the volumetric flow of coolant through the engine in a
desired fashion in order to adjust the actual coolant temperature
to the setpoint coolant temperature.
[0016] In advantageous fashion, the method according to the
invention uses a second manipulated variable and/or a second
correction signal to ensure that the cooling capacity of the
cooling circuit works in an optional range for the engine. This
second correction signal can be generated directly from the coolant
temperature. To do this, the coolant temperature is detected, e.g,
via a temperature sensor, and the change in coolant temperature
over time is compared with a time-dependent model of the coolant
temperature curve stored in the electronic control unit. For
example, this time-dependent model of the coolant temperature
stored in the electronic control unit can be a computer model of
the coolant temperature curve during a cold start of the motor
vehicle, or it can simulate another typical driving situation. The
theoretical model makes it possible to detect whether the coolant
temperature of the cooling circuit increases to the "correct
extent". To accomplish this, an optimum temperature band width for
the engine--depending on the particular driving situation--can be
stored in the electronic control unit, for example. If the actual
coolant temperature deviates from the setpoint coolant temperature
stored in the electronic control unit for the particular situation,
or if the actual coolant temperature deviates from the specified
temperature band width, a second correction signal is generated.
The open-loop and/or closed-loop control of the cooling circuit by
means of this second manipulated variable can supersede the
corresponding closed-loop control of the volumetric flow, so that
this second closed-loop control can be used as an additional safety
control for the cooling circuit.
[0017] In advantageous fashion, the delivery amount of the
circulation pump, i.e., its rotational speed, in particular, can be
varied in accordance with the correction signals generated. It is
possible, for example, to vary the volumetric flow of coolant and,
therefore, the engine temperature, as needed.
[0018] In addition to the open-loop and/or closed-loop control of
the coolant pump, the valves located in the cooling circuit and
further components associated with the cooling circuit, e.g., a
cooling fan for the radiator of the cooling circuit, can be
controlled via closed-loop control by the electronic control unit
as needed in accordance with the generated correction signals, so
that a volumetric flow of coolant adjusted in optimum fashion for
the particular driving situation and/or an optimized coolant
temperature prevails in the cooling circuit at all times.
[0019] Advantageously, the method according to the invention also
makes it possible for the electronic control unit to control--via
closed-loop control--the cooling capacity of the cooling circuit
and, in particular, the volumetric flow of coolant through the
engine with consideration for further operating parameters of the
vehicle. One example of this is the optimized pollutant emission of
the engine as a function of the cooling capacity delivered to the
engine. A pollutant sensor can forward an appropriate signal to the
electronic control unit of the cooling circuit, so that the
electronic control unit implements an optimized configuration of
the active setting elements of the cooling circuit to obtain
minimal pollutant emissions based on an optimized engine
temperature. For this purpose, a model and/or a data set in the
form of a program map or a data base is contained in the electronic
control unit--in an analogous fashion to the temperature behavior
described hereinabove--that describes the influence of the
volumetric flow of coolant on the pollutant emission of the
vehicle.
[0020] Deviations from the engine parameters that are calculated or
that were stored previously in the electronic control unit can be
not only diagnosed but actively corrected as well by the electronic
control unit. In addition to adjusting the adjustable cooling
circuit components, the electronic control unit can also inform the
vehicle driver about deviations in the cooling system using
appropriate warning signals. The "on-board diagnosis" also makes it
possible to detect errors or defects in the cooling system, such as
blocked valves, pinched connecting lines, or defective pumps.
[0021] In advantageous fashion, the electronic control unit that
controls--via closed-loop control--the active components can be an
engine control unit.
SUMMARY OF THE DRAWINGS
[0022] An exemplary embodiment of the invention is shown
schematically in the drawings and it is described in greater detail
in the subsequent description.
[0023] FIG. 1 is a simplified view of an engine compartment of a
vehicle, in which a vehicle motor with a cooling circuit for this
engine is located.
[0024] FIG. 2 is a block diagram for the temperature regulation of
a vehicle engine according to an exemplary embodiment of the method
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The description, the figures, and the claims contain
numerous features in combination. One skilled in the art will
advantageously consider them individually as well and combine them
into reasonable further combinations.
[0026] FIG. 1 is a simplified, schematic illustration of an engine
compartment 10 of a vehicle, in which an internal combustion engine
12 and a cooling circuit 14 for this internal combustion engine 12
are located. The heat given off by the internal combustion engine
12 is dissipated--preferably outwardly--via the cooling circuit 14,
which forms a cooling system. For this purpose, the cooling circuit
comprises a radiator 16 that is located in the cooling air stream
18 of the moving vehicle. The cooling air stream 18 and,
indirectly, therefore, the cooling capacity of the cooling system,
can be controlled via air flaps 20 that are installed in the body
22 of the vehicle. The cooling capacity of the cooling circuit is a
function of the temperature of the coolant at that point in time
and the volumetric flow of coolant pumped through the cooling
system.
[0027] Additionally, to improve the cooling capacity of the cooling
system, at least one fan is located in the region of the radiator
16 that is composed of a fan wheel 26 and an electric motor 28
driving this fan wheel 26. As an alternative, the air flaps 20 or
additional, further air flaps can also be located between the
radiator 16 and the fan 24.
[0028] The cooling system has an electric coolant pump 34 to pump a
coolant 30 through the connecting lines 32 of the cooling system.
Water is used preferably as coolant, and an appropriate cold
protective can be added to said water for low temperatures.
[0029] The coolant 30, coming from the radiator 16, is directed by
the coolant pump 34 through a forward-delivery line 35 to the
engine 12. To determine the coolant temperature, a temperature
sensor 38 is located in the cooling circuit in the region of a
coolant inlet 36 of the engine 12. The coolant 30 flows through the
engine 12 along paths not shown further in FIG. 1, and it absorbs a
certain amount of heat from the engine 12, then it exits said
engine through a coolant outlet 40. Moreover, in the exemplary
embodiment according to FIG. 1, the internal combustion engine 12
comprises a second coolant inlet 50, via which a portion of the
heated coolant can be directed to a heat exchanger, e.g., for the
passenger compartment of the motor vehicle.
[0030] In further exemplary embodiments of the invention, the use
of a plurality of coolant inlets and coolant outlets is possible.
Cooling circuit architectures that are more complex than the
cooling system shown in the exemplary embodiment in FIG. 1 can also
be combined with the method according to the invention. Only one
highly simplified, schematic cooling circuit is shown in FIG. 1 to
describe the method. It is not intended to represent a limitation
of the possible cooling circuit architecture.
[0031] A further, second temperature sensor 42 that detects the
temperature of the coolant 30 after it leaves the engine 12 is
located in the region of the coolant outlet 40 of the engine 12.
The coolant 30 travels through a return-delivery line 44 back to
the radiator 16 of the cooling circuit. A valve 46 is provided in
the return-delivery line 44 that allows the coolant to bypass the
radiator 16 via a bypass line 48. During a cold start of the
vehicle, for example, it is possible to direct the heated coolant
30 back to the engine 12 immediately after it leaves said engine,
without the temperature of the coolant dropping substantially. This
allows the engine to warm up faster. This results in a marked
reduction in pollutant levels during the starting phase of the
motor vehicle.
[0032] The active components of the cooling system, e.g., the air
flaps 20, the fan 24, the coolant pump 34, the bypass valve 46, and
further components of the cooling circuit not shown explicitly in
the exemplary embodiment, are adjusted and/or controlled via
closed-loop control--with the aid of an electronic control unit 52
that comprises a memory 54, a processing block 66, and a comparing
element 68--over data lines 56 in such a fashion that the engine 12
of the vehicle has a optimum temperature and/or temperature
distribution at any point in time during a driving schedule. This
optimum temperature can be characterized, for example, by the
lowest possible fuel consumption or the lowest possible pollutant
emission of the engine. A pollutant sensor 72 that is also
interconnected with the electronic control unit 52 via a data line
74 is provided to detect the current pollutant emission.
[0033] The method according to the invention for regulating the
temperature of an engine will be explained further hereinbelow with
reference to a block diagram shown in FIG. 2. The active,
adjustable components of the cooling system, such as the air flaps
20, the fan 23, the coolant pump 34, the bypass valve 46, and
further components of the cooling circuit not defined explicitly in
the exemplary embodiment are interconnected with the electronic
control unit 52 via signal lines 56 that also supply the electrical
current to these adjustable components. The further components 60
of the cooling circuit can be additional, adjustable valves or an
additional coolant pump, for example. The temperature sensors 38
and/or 42 for determining the coolant temperature are also
interconnected with the electronic control unit 52 via appropriate
data lines 58.
[0034] The electric coolant pump 34 has an energy supply 62 that
can be coupled to the vehicle's electrical supply system via the
electronic control unit 52, for example. The electronic control
unit 52 detects the working point of the coolant pump 34, i.e., the
volumetric flow delivered by the pump--in the exemplary embodiment
shown in FIG. 22--based on the electrical current I that the
electric pump requires from the energy supply. This signal is also
forwarded to the electronic control unit 52 via a data line 64.
[0035] Based on the actual parameters of the cooling circuit
existing at that point in time, e.g., the actual, detected coolant
temperature and/or the electrical current I required by the coolant
pump 34, the electronic control unit 52 calculates the volumetric
flow of coolant pumped through the cooling circuit, and, based on
this, the engine temperature and/or the temperatures of various
engine components.
[0036] A thermal model of the cooling circuit with its components,
e.g, the line routing, the viscosity change of the coolant, the
position of the valves, the cooling capacity of the radiator 16 and
the fan 24, and further parameters that describe the cooling
system, is stored in the memory 54 of the electronic control unit
52. A data set is therefore contained in the electronic control
unit 52 that models the influence of a certain volumetric flow of
coolant on the engine temperature and/or on the temperature of
various engine components.
[0037] The characteristics of the coolant pump 34 are also stored
in the memory 54 of the electronic control unit 52. The electric
pump 34--during steady-state operation--will deliver a constant
volumetric flow. This takes place with a constant electrical
voltage U, a constant electrical current I, and a specifiable
rotational speed N of the pump. The particular operating point of
the pump, i.e., the pressure rise .DELTA.P and the volumetric flow
.DELTA.V/.DELTA.t, can therefore be determined by the electronic
control unit with reference to the pump characteristics and the
stored resistances to flow of the cooling circuit when the values
for electrical voltage U, electrical current I and rotational speed
N of the pump are known. For example, based on the measurement of
the electrical current I that the pump draws during steady-state
operation given a constant electrical voltage U and a constant
rotational speed N, the electronic control unit can deduce the
volumetric flow delivered by the pump. The electrical current I
required by the coolant pump can therefore be used to evaluate and
diagnose the volumetric flow of coolant delivered by the pump 34.
The volumetric flow of coolant diagnosed in this fashion via the
electrical current of the pump 34 is used together with the coolant
temperature determined, e.g., by the temperature sensor 42, by the
electronic control unit to calculate the actual engine
temperature.
[0038] The data--from the processing block 66--on the determined,
actual engine temperature at that point in time and/or the
volumetric flow of coolant representing this engine temperature is
compared with the model for the optimum coolant temperature and the
optimum volumetric flow of coolant stored in the memory 54 of the
electronic control unit 52 in a comparing element 68 of the
electronic control unit 52. By way of the comparing element 68, the
electronic control unit 52 generates one or more correction signals
56. The correction signal is used to control and/or adjust the
active elements of the cooling circuit, such as the coolant pump
34, the cooling air fan 24, the bypass valve 46 or the air flaps
20. For example, controlling the coolant pump 34 via closed-loop
control makes it possible to adjust the volumetric flow of coolant
through the engine 12 and optimize the temperature of the engine
and/or the temperatures of diverse engine components with regard
for fuel consumption and/or pollutant emission.
[0039] In analogous fashion, the electronic control unit 52 also
delivers a command and control signal to the bypass valve 46 that
can adjust the temperature of the coolant at the coolant inlet 36
to the desired value by opening and/or closing the bypass line 48.
To check the operational capability of this control mechanism, the
temperature sensor 38 can determine the coolant temperature in
front of the coolant inlet 36 of the engine 12 and forward this
signal to the electronic control unit 52. In this fashion, it is
possible to detect a defective component in the cooling circuit if
it does not meet the thermal specifications of the electronic
control unit 52 and the thermal model stored in the electronic
control unit.
[0040] Specifically, in this fashion, the change in temperature of
the coolant over time during the starting phase of the internal
combustion engine can be compared with a time-dependent model of
the coolant temperature for this phase stored in the electronic
control unit. If the actual temperature values deviate from the
specified setpoint temperature values--which can be stored in the
memory 54 of the electronic control unit 52 in the form of a
temperature range--the electronic control unit 52 also issues an
appropriate warning signal that indicates the presence of a
malfunction in the cooling circuit and, therefore, a possible
defective component.
[0041] Moreover, the electronic control unit also has appropriate
pollutant sensors 72, for example, that detect the actual pollutant
emission of the internal combustion engine and report the result to
the processing block 66 of the electronic control unit 52 via a
line 74. The pollutant sensors 72 therefore make it possible to
also adjust the engine temperature to its particular optimum value
by running a comparison 68 with corresponding data stored in the
memory 54 of the electronic control unit.
[0042] The method according to the invention is not limited to the
exemplary embodiment described.
[0043] For example, the actual engine temperature and/or component
temperature of the engine can be diagnosed indirectly via other
characteristic values of the coolant pump. If the pump always draws
a constant electrical current I during steady-state operation,
i.e., when electrical voltage U is constant, then the load on the
pump and, therefore, the volumetric flow that is delivered can be
deduced from the rotational speed N of the pump. By using the
volumetric flow detected in this fashion and the measured coolant
temperature, then, in turn, a component temperature of the engine
can be deduced.
[0044] If another physical variable is used to control the coolant
pump, e.g., electrical current I, then the other characteristic
values (U, N) of the coolant pump must be detected and processed by
the electronic control unit 52. The measurement variables (U, I, N)
are evaluated currently by the electronic control unit 52, where
they are then compared with the computer model and the stored pump
characteristics. Deviations from the data that were calculated or
stored previously in the electronic control unit make it possible,
therefore, to detect faults in the cooling system, e.g., caused by
blocked valves, defective lines, or an inoperative coolant
pump.
[0045] With the method according to the invention, it is possible
to perform an "on-board diagnosis" of the cooling circuit of a
motor vehicle in simple, efficient fashion, which can also ensure,
in particular, that certain pollutant emissions of the internal
combustion engine are adhered to.
* * * * *