Process and arrangement for controlling the temperature of a medium

An arrangement and a process for controlling the temperature of a medium, particularly of the cooling water temperature of a motor vehicle engine. At least two energy-consuming units influence the temperature to be controlled, of which at least one can be controlled with respect to its output. A control unit adjusts the output of these units for causing a required influencing of the temperature. The output of each temperature-influencing unit is adjusted by means of a previously determined, energy-minimal characteristic diagram K.sub.E which indicates for each system condition the operating point of the absolutely minimal energy consumption of the energy-consuming units for controlling the temperature according to a respective desired value.

This application claims the priority of 197 19 792.2, filed May 10, 1997,
 the disclosure of which is expressly incorporated by reference herein.
 BACKGROUND AND SUMMARY OF THE INVENTION
 The invention relates to a process and an arrangement for controlling the
 temperature of any solid, liquid or gaseous medium. In the case of
 processes and arrangements of this type, the temperature to be controlled
 is influenced in an appropriate manner by at least two energy-consuming
 units, such as the cooling fans, the circulation pumps of a cooling or
 heating circulation system, chillers, etc. such that the temperature is
 controlled in the respective desired manner; for example, is adjusted to
 the desired value. The medium whose temperature is to be controlled may,
 in particular, be a liquid/gaseous coolant or refrigerant of a cooling or
 air-conditioning system or a heating fluid of a heating circulation
 system, but also any component whose temperature is to be maintained at a
 certain value or within a certain range. A contemplated field of
 application is the control of the cooling water temperature of a
 water-cooled motor vehicle engine or the control of the temperature of the
 engine itself; that is, of the engine block, or of critical points in the
 engine, for example, the temperature of the valve web.
 A process and an arrangement of this type for controlling the coolant
 temperature of an internal-combustion engine, particularly of an
 internal-combustion of a motor vehicle, are described in German Patent
 Document DE 195 08 102 C1, in the case of which at least one coolant pump
 and a cooling fan are used as energy-absorbing, temperature-influencing
 units. A control unit controls the coolant temperature to a
 predeterminable desired value by a corresponding adjustment of the
 rotational speed of the pump and the fan. In this case, the control unit
 compares the time-related efficiencies caused, on the one hand, by the
 operation of the coolant pump and, on the other hand, by those of the fan,
 for the heat transmission between the fan air flow and the coolant on a
 cooler module. For this purpose, a gradient method is used in that the
 heat transfer coefficient for the cooler module is determined, and the
 partial derivations of the coefficient are, on the one hand, formed
 according to the coolant flow generated by the pump and, on the other
 hand, according to the air flow generated by the fan and are used as a
 measurement for the respective time-related efficiency. These time-related
 efficiencies are analyzed in that, in the respective operating position,
 on the basis of the momentary operation point of the coolant circulation
 system, a step-by-step search takes place for a possibly more favorable
 operating point in that the quotients of the time-related efficiency to
 the power consumption for the fan and the pump are compared and, according
 to which quotient is larger, the air flow or coolant flow is increased. It
 is known that gradient methods of this type do not ensure that the
 absolutely most favorable operating point is reached since also an only
 locally most favorable operating point represents a stable point for this
 method.
 In the case of systems with two power-consuming components by means of
 which a certain physical quantity can be influenced, it is known to
 determine in the pertaining output diagram characteristic curves of a
 respective constant value of the physical quantity and to determine, for
 the respective momentary value of the physical quantity, by a tangent
 formation, the pertaining point of the minimal overall power expenditure
 for the two components. In the conference contribution by P. Ambros and U.
 Essers, "Simulation Program for Design and Optimization of Engine Cooling
 Systems for Motor Car", ISATA Conference, Sep. 13, 1993 to Sep. 17, 1993,
 Aachen, this was described with respect to a coolant circulation system of
 a motor vehicle engine in that, for a given coolant temperature, the
 minimal sum of the power consumption of cooling air fan is found, on the
 one hand, and that of a cooling water pump is found, on the other hand.
 For this purpose, the characteristic curves of the constant coolant
 temperature are determined in the two-dimensional output diagram and then
 the point of the minimal overall output for the given coolant temperature
 is determined by means of the tangent formation with the straight line of
 the constant overall output as the tangent. In this case, each
 characteristic curve of the constant coolant temperature may vary as the
 function of the system condition, that is, of vehicle condition
 parameters, such as the outside temperature, the vehicle speed, the engine
 load, etc.
 An object of the invention is to provide a process and an arrangement of
 the initially mentioned type by means of which and by means of relatively
 low real-time computing expenditures in each operating condition of the
 system the medium temperature can be reliably controlled with the lowest
 possible energy consumption and particularly can be maintained at a
 defined desired value in a controlled or regulated manner.
 This and other objects have been achieved according to the present
 invention by providing a process for controlling the temperature of a
 medium, the temperature of the medium to be controlled being influenceable
 by at least two energy-consuming units, at least one of the
 energy-consuming units having a controllable output, wherein the output of
 each of the energy-consuming units is adjusted according to a previously
 determined energy-minimal characteristic diagram which indicates for each
 system condition the operating point of an absolutely minimal overall
 energy consumption of the units for controlling the temperature according
 to a respective desired temperature value.
 This and other objects have been achieved according to the present
 invention by providing an arrangement for controlling the temperature of a
 medium, comprising: at least two energy-consuming units for influencing
 the temperature of the medium to be controlled, at least one of the
 energy-consuming units having a controllable output, and a control unit
 which adjusts the output of each of the energy-consuming units according
 to a previously determined, energy-minimal characteristic diagram which
 indicates for each system condition the operating point of the absolutely
 minimal overall energy consumption of the units for controlling the
 temperature according to a respective desired temperature value.
 According to the invention, the output of each of the energy-consuming
 units provided for influencing the temperature to be regulated is adjusted
 according to a previously determined, characteristic energy-minimal
 diagram which indicates for each system condition, including a respective
 desired value of the temperature to be regulated, the operating point of
 the absolute minimal overall energy consumption of the energy-consuming
 units. As the result of this predetermined characteristic diagram, the
 control unit which carries out the temperature control, after the
 momentary system condition is sensed, is immediately provided with the
 information concerning the operating point for the energy-consuming units
 which is energy-minimal in this condition, which is always an absolute
 energy minimum. This permits a comparatively fast reaction of the
 temperature control to changes of the system condition. Because of this
 global energy minimizing method, it is ensured that the adjusted operating
 point corresponds not only to a local energy minimum but to the absolute
 energy minimum in the corresponding system condition.
 According to further advantageous developments of the present invention, a
 checking of the previously determined energy-minimal characteristic
 diagram is provided at defined time intervals in that, for at least one
 reference system condition, an energy minimum determination is carried out
 according to the above-mentioned conventional tangent method in the case
 of which, after the detection of the momentary system condition, the
 isothermal line pertaining to the desired value of the temperature to be
 regulated is determined in the power or energy consumption diagram of the
 energy-consuming units and then the pertaining tangent or tangent plane of
 the constant minimal overall energy consumption is determined. This
 determined energy-consumption minimum is compared with the energy
 consumption minimum filed in the characteristic diagram for the
 corresponding reference system condition, whereupon the characteristic
 diagram can be appropriately corrected depending on the result of the
 comparison.
 According to certain preferred embodiments, the present invention is used
 for controlling the coolant temperature of a cooling circulation system,
 for example, for a motor vehicle engine, and contains one or several
 energy-consuming units which influence the coolant temperature and which
 have the form of an output-controllable coolant circulation pump and/or of
 an output-controllable fan whose cooling air flow can act on a cooler of
 the cooling circulation system. By way of the control unit, the pump
 and/or the fan are operated such that, on the one hand, the coolant
 temperature is controlled in the desired manner and, on the other hand,
 the overall energy consumption of the temperature-influencing units is
 minimal.
 According to certain preferred embodiments, the present invention is used
 for controlling the coolant temperature of a cooling circulation system
 provided in a motor vehicle, for example, for cooling an
 internal-combustion engine, and contains, as one of the power-consuming
 units, a shutter by means of which the throughput of a ram pressure
 cooling air flow for a cooler of the cooling circulation system can be
 variably adjusted with a driving-power-influencing effect on the
 aerodynamic drag of the vehicle. In this case, the power consumption
 related to the shutter does not primarily result from the energy
 expenditure operating the latter but from the fact that, depending on how
 much air is withdrawn as a cooling air flow for the cooler from the ram
 pressure range which forms increasingly at a higher vehicle speed, the
 aerodynamic drag and thus the energy expenditure required for the moving
 of the vehicle will fluctuate. The use of the shutter therefore allows a
 controlling of the coolant temperature which is optimized with respect to
 a minimal overall energy consumption also in the range of higher driving
 speeds in which the cooling air flow against the cooler can be caused by
 the ram pressure without the requirement of activating a fan for this
 purpose.
 Other objects, advantages and novel features of the present invention will
 become apparent from the following detailed description of the invention
 when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS
 FIG. 1 illustrates a coolant circulation system for the cooling of a motor
 vehicle internal-combustion engine 1 as well as for secondary cooling
 purposes, such as the charge air cooling. A coolant pump 2, whose output
 can be controlled, is used for the circulation of the coolant. By way of a
 branching line section 3, which contains suitable control valves, the
 coolant emerging from the engine 1 arrives at different cooler units of
 the cooling circulation system. In this case, a portion of the coolant is
 guided through a low-temperature coolant cooler 4. According to the
 position of a pertaining valve 5, another portion of the coolant is guided
 either through a main coolant cooler 6 or via a bypass line 7 past this
 main coolant cooler 6. The coolant which leaves the main coolant cooler 6
 and the coolant guided by way of the bypass line 7 are returned to the
 engine 1 by way of the return line 8 in which the cooling water pump 2 is
 situated.
 The coolant emerging from the low-temperature coolant cooler 4 and another
 portion of the coolant branched off the line section 3 leading away from
 the engine 1 arrive in a valve complex 9 which consists of five valves and
 by means of which one and/or the other of these two coolant portions can
 in a controllable manner be supplied to an oil cooler 10 and/or a charge
 air cooler 11. Downstream of these two coolers 10, 11, the pertaining
 coolant flows are combined again and arrive via a line 12 in the return
 line 8 in front of the coolant pump 2. On the other side, the engine oil
 to be cooled flows through the oil cooler 10, which engine oil circulates
 between it and the engine 1. In the charge air cooler 11, the charge air
 coming from the turbocharger 13 is cooled and is subsequently fed to the
 engine 1. The engine exhaust gases are discharged by way of an exhaust gas
 line 14 which is only shown schematically.
 As also illustrated in FIG. 1, the low-temperature coolant cooler 4 and the
 main coolant cooler 6 are part of a cooler block which can be acted upon
 by a cooling air flow 15 and which comprises as additional components an
 air-throughput-controlling shutter 16, a fan 17, whose output can be
 controlled, and a condenser 18 of an air conditioner which is of no
 further interest here. The condenser 18, together with the low-temperature
 coolant cooler 4 arranged laterally thereof, forms a cooling unit which is
 in the front in the air flow direction and which is serially followed by
 the main coolant cooler 6, the shutter 16 and the output-controllable fan
 17. On the upstream side of the front cooling unit, a metering element
 complex 19 is provided which contains two controllable swivelling flaps
 20, 21 by means of which the inflowing cooling air flow 15 can be
 distributed to the area of the low-temperature coolant cooler 4 and that
 of the condenser 18. In the position of the flaps 20, 21 which is shown in
 FIG. 1, only the low-temperature coolant cooler 4 is acted upon by the
 inflowing air flow 15, while in the flap position indicated by a broken
 line, only the condenser 18 is acted upon by the cooling air flow 15.
 Since the metering element complex 19 is used only for distributing the
 air flow 15 to the low-temperature coolant cooler 4, on the one hand, and
 the condenser 18, on the other hand, the flaps 20, 21 are controlled
 between these two end positions in each case into such intermediate
 positions which leave the overall air throughput unchanged so that the air
 flow throughput at the main coolant cooler 6 remains unaffected by the
 metering element complex 19. On the contrary, when the vehicle is stopped
 or at low driving speeds, this overall air throughput is controlled by way
 of the output-controllable fan 17 and, at higher driving speeds, at which
 a sufficient ram pressure exists in front of the metering element complex
 19, is controlled by way of the adjustable shutter 16.
 For controlling or regulating the coolant circulation system and the
 cooling air, a control unit 22 is used which is simultaneously applied as
 an engine timing unit for the vehicle engine 1. On the input side, the
 required measuring information is fed to the control unit, particularly
 the rotational engine speed n, the fuel injection Ke and diverse
 temperature information, such as the ambient temperature T.sub.a, the
 coolant temperature T.sub.C, the charge air temperature T.sub.CA and the
 engine oil temperature T.sub.O which are sensed by way of respective
 temperature sensors which are positioned at the appropriate point. The
 pertaining measuring signal lines are indicated in FIG. 1 by a broken
 line, as are the control lines which originate on the output side of the
 control unit 22 and by way of which the control unit 22 controls the
 various controllable components of the system in a manner which will be
 explained in detail in the following to the extent that it is of interest
 in this case and which is otherwise known to a person skilled in the art.
 Characteristically, in a normal operating mode, with the exception of brief
 extreme situations, the control of the coolant circulation system takes
 place under energy-consumption-minimizing aspects; that is, the various
 energy-consuming components of the cooling water circulation system are
 controlled by the control-unit 22 such that the coolant temperature
 T.sub.K or, in other words, the temperature gradient TG=T.sub.C -T.sub.a
 between the coolant temperature T.sub.C and the outside temperature
 T.sub.a is controlled by means of the overall energy consumption which is
 minimally possible in the respective vehicle operating situation to a
 predetermined desired value. For finding this operating point which is
 most favorable with respect to the energy, a process takes place which
 will be explained in the following with reference to FIG. 2.
 For this purpose, data is recorded beforehand for the particular vehicle or
 the particular engine cooling system concerning the energy consumption;
 that is the power consumption of all energy-consuming units of the coolant
 circulation system in the various operating positions, concerning the
 resulting coolant temperature gradient TG and concerning the other system
 condition parameters relevant to the coolant temperature, such as the
 vehicle speed, the engine load, etc. In particular, the isothermal lines
 for a respectively predetermined desired value of the coolant temperature
 gradient TG is determined in the output diagram which comprises all
 energy-consuming units influencing the coolant temperature. In the case of
 the arrangement of FIG. 1, these are particularly the output-controllable
 coolant pump 2 as well as, in the low speed range, the output-controllable
 fan 17 and, in the high speed range, the shutter 16. For the present
 consideration, the shutter 16 therefore represents an energy-consuming
 component of the system, because its position determines the throughput of
 the cooling air flow 15 which is branched off the ram pressure which, at
 higher driving speeds, forms in front of the inlet side of the metering
 element complex 19. However, the removal of this cooling air flow from
 this ram air affects the aerodynamic drag of the vehicle in the concerned
 driving situation and thus the driving performance. The more the shutter
 16 is opened, the more the driving performance is reduced which increases
 the overall energy consumption correspondingly.
 FIG. 2 shows the output diagram which takes these energy-consuming units
 into account, in which case the driving output of the cooling pump 2 is
 entered on the abscissa and the driving output of the fan 17 is entered on
 the ordinate on the one hand with positive preceding signs and, on the
 other hand, the driving performance reduction caused by the shutter is
 entered on the ordinate with a negative preceding sign. In the case of the
 output demand of the pump 2 and the fan 17, the efficiency is taken into
 account which is obtained for the power transmission path between the
 engine output shaft and the pumps or the fan wheel. As examples, the
 isothermal lines for the selected desired values of the coolant
 temperature gradient TG in the case of fixed remaining system condition
 parameters are listed in the output diagram. Each isothermal line
 therefore indicates the curve for the outputs of the coolant pump 2 and
 the fan 17 or the shutter 16 to be adjusted which are possible for
 achieving a desired temperature gradient value in the case of the given
 system condition, and varies as a function of additional system condition
 parameters, such as the vehicle speed, the engine load and the position of
 the metering element complex 19. The latter takes place because the
 metering elements, that is, the flaps 20, 21 of this complex 19 determine
 by their position how large the proportion of the inflow air 15 is which
 is fed to the low-temperature coolant cooler 4 and therefore contributes
 to the cooling of the coolant, while the airflow proportion fed to the
 condenser 18 does not influence the engine cooling water temperature and
 therefore generally has a different influence on the whole energy
 consumption in the vehicle. As required, the metering element complex 19
 can be included in the energy consideration as an indirectly
 energy-consuming unit.
 For each of the determined isothermal lines of the coolant temperature
 gradient TG, within the previous initialization of the control unit 22,
 the pertaining operating point of the minimal overall energy consumption
 for the coolant-temperature-influencing units, that is, the coolant pump 2
 and the fan 17 and the shutter 16, is determined according to the
 above-mentioned tangent process, in which case it is utilized that the
 lines of the constant overall energy consumption in the output diagram of
 FIG. 2 are straight lines with a certain slope. As an example, the tangent
 T.sub.1 which occurs for the desired temperature gradient value of
 62.degree. C. is indicated by a broken line in FIG. 2. The pertaining
 tangent point P.sub.1 forms the operating point P.sub.1 which is optimal
 with respect to the energy for the given system condition, in that it
 represents the absolute energy minimum for the sum of the energy
 consumption of all coolant-temperature-influencing units for achieving the
 desired temperature gradient value. After the carrying-out of this
 determination of the respective absolute energy minimum for the various
 temperature gradient isothermal lines of a system condition, the
 energy-minimal characteristic curve K.sub.E is obtained which is drawn by
 a thick line in FIG. 2, in which case it relates in its upper half with
 the positive ordinate values to the operation of the fan 17 and, in its
 lower half, with the negative ordinate values to the operation of the
 shutter 16. In a supplementary manner, FIG. 2 indicates for informational
 purposes the limits at which the temperature difference over the engine
 exceeds the thresholds of 10.degree. C. and 15.degree. C.
 In the described manner, the pertaining energy-minimal characteristic
 output curve K.sub.E for the energy-consuming units is determined
 beforehand for each possible normal system operating condition for
 influencing the coolant temperature and the totality of these
 characteristic curves is then stored in the control unit 22 as a directly
 retrievable characteristic diagram. In the subsequent system operation,
 the control unit 22 will then continuously by means of the measuring
 quantities supplied to it query the respective system condition.
 Subsequently, because of the filed energy-minimal characteristic output
 diagram, it will immediately be capable of controlling the coolant
 temperature T.sub.C or analogously the coolant temperature gradient TG to
 a desired value such that in this case the overall energy consumption for
 the energy-consuming coolant circulation system units, that is,
 particularly the coolant pump 2 and the fan 17 or the shutter 16, remains
 minimal. For this purpose, the control unit 22 must carry out no
 high-expenditure real-time optimization calculations but must only file
 the operating point pertaining to the detected system condition in the
 energy-minimal characteristic diagram. As a result, it can comparatively
 rapidly react to condition changes. Since the energy-minimal
 characteristic diagram was obtained by the described global energy minimum
 determination process, it is ensured that the operating point which is in
 each case selected by the control unit represents not only a local but
 always an absolute minimum for the overall energy consumption of the units
 included in the cooling temperature control. The desired value may be
 defined in a fixed manner but advantageously may be defined in a variable
 manner as a function of the operation; for example, lower at high loads.
 In the latter case, the operation-dependent desired values can be filed as
 a characteristic diagram.
 Expediently, it is also provided that from time to time the control unit 22
 carries out a checking of the filed energy-minimal characteristic diagram.
 This can take place, for example, in that at least one reference system
 condition is indicated at which, during such a checking operation, the
 control unit 22 newly determines the pertaining desired temperature value
 isothermal line in the output diagram of the temperature-influencing unit
 and by a tangent formation the energy-minimal operating point and then
 compares this operating point with the corresponding operating point
 previously filed in the characteristic diagram. If a coincidence is
 determined in this comparison within a defined tolerance, this is
 recognized by the control unit 22 as a continuously correct characteristic
 diagram. In contrast, if the control unit determines larger deviations, it
 carries out a corresponding correction and thus an updating of the filed
 energy-minimal characteristic diagram.
 It is understood that, in certain limit situations, the coolant temperature
 control can be carried out by the control unit 22 in other operating modes
 than the described operating mode which is optimal under energy
 consumption aspects. Such exceptional operating phases will, for example,
 be expedient when otherwise the air throughput for the condenser 18 or the
 charge air cooler 11 is no longer sufficient or critical absolute
 pressures or pressure gradients in the coolant circulation system would be
 exceeded.
 By means of the described approach, it is possible to control the engine
 coolant temperature in almost all system operating conditions in an
 energy-optimized manner without the requirement of dimensioning the
 coolant circulation system excessively large as occurs in the case of
 conventional circulation systems with an uncontrolled coolant pump and/or
 an uncontrolled fan as well as a lacking coordination of the rotational
 pump speed and the rotational fan speed. It is understood that, according
 to the application, modifications of the described embodiment can be
 implemented. Thus, optionally the shutter 16 or the fan 17 or the
 controllability of the pump can be eliminated, or additional
 energy-consuming units can be provided for influencing the cooling water
 temperature T.sub.C which are included in the considerations for achieving
 a minimal overall energy consumption, which results in a correspondingly
 higher-dimensional output diagram and thus also in acorrespondingly
 higher-dimensional energy-minimal characteristic diagram. However, in
 every case, the computing expenditure to be carried out by the control
 unit 22 in the continuous driving operation remains clearly lower than
 when a local gradient method is used for finding the most favorable
 operating point with respect to energy in real time.
 It is also clear that the arrangement according to the invention and the
 process according to the invention are not limited to controlling the
 coolant temperature of a motor vehicle engine but can beneficially be used
 wherever any solid, liquid or gaseous medium is to be regulated or
 controlled by at least two energy-consuming units. A variant of the
 arrangement of FIG. 1 according to the invention can be used, for example,
 for controlling the temperature of the engine block itself instead of that
 of the coolant.
 The foregoing disclosure has been set forth merely to illustrate the
 invention and is not intended to be limiting. Since modifications of the
 disclosed embodiments incorporating the spirit and substance of the
 invention may occur to persons skilled in the art, the invention should be
 construed to include everything within the scope of the appended claims
 and equivalents thereof.