DE102011108203A1 - Diagnostic method for switchable water pump of cooling system of combustion engine of motor vehicle for error indication of malfunction of switchable water pump, involves carrying out error indication when certain conditions are satisfied - Google Patents

Abstract

The diagnostic method involves carrying out the error indication when the certain conditions are satisfied, where conditions include a measured or calculated temperature of the cooling system (3) during start of the combustion engine (2), and delay time between the start of the combustion engine and a switch-on of the switchable water pump (5), which is more than a delay time threshold.

Description

The invention relates to a diagnostic method for a switchable water pump of a cooling system of an internal combustion engine of a motor vehicle according to the preamble of claim 1.

Water pumps for cooling systems of internal combustion engines are usually driven by a V-belt from the internal combustion engine and are also constantly in operation during operation of the internal combustion engine.

Recently, switchable water pumps are used in motor vehicles, as this can save on the one hand energy and on the other, especially in a cold start of the engine, a faster heating of the engine can achieve, which in turn leads to reduced cold start emissions. Switchable water pumps are either electrically operated and controllable pumps or mechanically operated by the internal combustion engine pumps, which can be coupled by an electrically controllable coupling with the engine or in which a delivery operation, regardless of a general operation of the pump interrupted by a conveyor interruption mechanism can be.

From the DE 10351148 A1 a cooling system with a switchable water pump is known, in which the water pump is switched on and off, inter alia, in dependence on a temperature of the internal combustion engine, an operating state of a passenger compartment heating, a load state of the internal combustion engine and a fault condition of the cooling system.

From the US 20110048390 A1 is also known a cooling system with a switchable water pump. In this system, the switchable water pump can be turned on by a thermostat diagnostic module for the purpose of diagnosing the thermostat.

With regard to a diagnosis of a switchable water pump is known that electrical components such as an electric water pump or an electrically actuated clutch for engaging a driven by an internal combustion engine water pump can be checked by means of common electrical tests for errors such as open circuit or short circuit.

Object of the present invention is to detect a malfunction of a switchable water pump, be it an electric or mechanically driven switchable water pump, and to bring to the display. In particular, this is a malfunction that is not due to an electrical short circuit or an open electrical line.

The object is achieved by a diagnostic method with the features of claim 1. The diagnostic method is suitable for detecting a malfunction of a switchable water pump, which is part of a cooling system of an internal combustion engine of a motor vehicle. In this case, the cooling system has a cooling circuit which is in communication with the internal combustion engine for the purpose of absorbing heat from the side of the internal combustion engine. Such a connection is designed, for example, so that the cooling circuit has cooling channels, which pass through a housing part of the internal combustion engine and which are flowed through by a cooling liquid of the cooling circuit. In this case, the cooling liquid is circulated by a conveying effect of the switchable water pump in the cooling circuit. In addition, for example, an oil cooler for cooling oil of the internal combustion engine can be flowed through by the cooling liquid of the cooling circuit. The cooling system further typically includes a heat exchange device and a thermostatic valve. The heat exchange device serves to cool the cooling fluid by a wind. With the aid of the thermostatic valve, a volume flow of the cooling liquid, which flows through the heat exchange device, adjusted in dependence on a temperature of the cooling circuit.

With the switchability of the water pump is meant that the conveying effect of the switchable water pump on the cooling liquid depending on parameters can be switched on and off. For this purpose, the switchable water pump either an electric drive, which can be switched on and off by means of an intelligent electrical control. Or the switchable water pump has an electrical coupling, by means of which the switchable water pump can be coupled with a drive shaft, wherein the electric coupling can be switched on and disengaged by means of an intelligent electrical control. Or the switchable water pump has an electrically controllable device, by means of which the conveying effect can be interrupted in spite of further operated pump. The electrical control has in all cases advantageously a control device, for example, an engine control unit, which is connected via control lines to the electric drive, or with the electrical coupling, or with the controllable device.

• – eine gemessene und/oder berechnete Temperatur des Kühlsystems ist zu einem Zeitpunkt eines Starts des Verbrennungsmotors kleiner als ein Temperaturschwellwert,
• – eine Verzögerungszeit zwischen dem Zeitpunkt des Starts des Verbrennungsmotors und einem Zeitpunkt eines Einschaltens der schaltbaren Wasserpumpe ist größer als ein Zeitschwellwert,
• – ein Temperaturanstieg der Temperatur des Kühlkreislaufs innerhalb einer vorbestimmten Zeit nach dem Einschalten der schaltbaren Wasserpumpe ist kleiner als ein Temperaturanstiegsschwellwert des Kühlsystems.

The malfunction of the switchable water pump is then recognized as if, at least the following conditions are met simultaneously:

• A measured and / or calculated temperature of the cooling system is less than a temperature threshold at a time of starting the internal combustion engine,
• A delay time between the time of starting the internal combustion engine and a time of switching on the switchable water pump is greater than a time threshold,
• A temperature rise of the temperature of the cooling circuit within a predetermined time after switching on the switchable water pump is smaller than a temperature rise threshold value of the cooling system.

The temperature of the cooling system can in principle be calculated or measured. A calculation can be made, for example, as a function of an external temperature or of an exhaust gas temperature of an exhaust gas of the internal combustion engine and / or as a function of a shutdown time of the internal combustion engine taking into account the dependencies according to the invention. A measurement of the temperature of the cooling system can be carried out by means of a common temperature sensor, which is attached to a suitable point of the cooling circuit. The time of starting the internal combustion engine is the time at which an injection of an air / fuel mixture in the internal combustion engine, followed by combustion of the air / fuel mixture in the internal combustion engine and accompanied by a cranking of the internal combustion engine starts. The time of switching on the switchable water pump is the time at which the water pump begins with the request of the coolant. That is, the timing of turning on the water pump is the one from which the cooling liquid circulates in the refrigeration cycle.

The diagnostic method according to the invention is advantageously used in conjunction with a control and / or regulation method for the switchable water pump, in which control and / or regulation method, the switchable water pump for the purpose of rapid heating of the engine remains switched off after the start of the engine and only after a certain period of the internal combustion engine, namely, when intensive cooling of the internal combustion engine is required, is turned on.

An observation of a simultaneous fulfillment of the conditions mentioned can take place in a suitable electronic control unit or control unit system in which the required information is available. The observation of the simultaneous fulfillment of said conditions means an indication of a malfunction of the switchable water pump. As a result of this error indication, an error entry in an error memory of the control unit or control unit system is advantageously generated in a customary manner. The defect entry can then be read in a likewise known manner by means of a suitable electronic reader, for example in a repair shop. In addition, the fault entry within the motor vehicle can be further processed in such a way that information is output to a driver of the motor vehicle, for example in the form of an information text on a screen.

By the method according to the invention it is possible to detect malfunctions of the switchable water pump, which lead to a heat transport behavior of the cooling system does not take place in a desired manner. Due to the fact that the heat transport behavior of the cooling system of the internal combustion engine also has an influence on the emissions of the internal combustion engine, it is thus indirectly detectable whether the emissions of the internal combustion engine are in an impermissible range.

A first advantageous development of the method according to the invention provides that the error indication only takes place if, in addition, the following condition is fulfilled simultaneously with the above-mentioned conditions: a temperature rise of a measured or calculated temperature of the internal combustion engine after the start of the internal combustion engine and before switching on switchable water pump is greater than a temperature rise threshold of the internal combustion engine. With the temperature of the internal combustion engine is meant a temperature of a component or a liquid of the internal combustion engine. Advantageously, this temperature is measured at a point or calculated for this point, which point heats up very quickly at a start of the engine. By this development, the reliability of the error indication can be increased.

A further advantageous development of the method provides that the fault indication only takes place if, in addition, an engine shutdown time is greater than a shutdown time threshold value. By the engine shut-down time is meant a period between an end of an operation, in particular, a combustion operation, the engine, and a start of the engine. Through this development, the reliability of the fault indication can be further increased, as can be reliably assumed after a longer combustion engine shutdown that in the entire Cooling circuit and in the internal combustion engine, the same temperature prevails.

A further advantageous development provides that the error indication only takes place if, in addition, the following condition is met simultaneously: a running time of the switchable water pump is greater than a transit time threshold value. Through this development, the reliability of the fault indication can be further increased, since after a longer period of the switchable water pump can be reliably assumed that has adjusted with respect to a temperature distribution within the cooling circuit, a new quasi-stationary state, which is significantly different from the temperature distribution within the Cooling system at a time before switching the switchable water pump is different.

A further advantageous development of the diagnostic method according to the invention provides that the temperature of the cooling circuit is measured by means of a cooling circuit temperature sensor, which is arranged outside the internal combustion engine. The arrangement outside of the internal combustion engine ensures that the temperature of the cooling circuit is not directly but only indirectly influenced by the temperature of the internal combustion engine. Thus, the reliability of the error indication can be further increased. Particularly advantageous is the use of a temperature sensor of a thermostat, since such a temperature sensor can be used for a control of the thermostatic valve and can be inexpensively manufactured in a structural unit together with the thermostatic valve.

A further advantageous development of the diagnostic method provides that the temperature of the internal combustion engine is calculated by means of an internal combustion engine temperature model. In this case, the temperature of the internal combustion engine is calculated as a function of the amount of fuel injected into the internal combustion engine and taking into account empirical values. In this way, a temperature sensor can be saved. Alternatively, the temperature of the internal combustion engine may be determined by means of an additional engine temperature sensor, which means higher system costs, but which means a higher reliability of the temperature determination and thus a higher reliability of the fault indication.

A further advantageous embodiment provides that the cooling system contains the thermostat and a heat exchange device. It is controlled or regulated in a known manner by the thermostat, which share of the cooling circuit of the internal combustion engine flows through the heat exchange device. In a very closed thermostat of the cooling circuit is decoupled from the heat exchange device, d. H. the cooling circuit runs completely past the heat exchanger device. With a completely open thermostat, the cooling circuit runs completely through the heat exchange device. In a partially open thermostat, a partial flow of the cooling circuit passes through the heat exchange device and another partial flow passes the heat exchange device. This development now provides that the fault indication only takes place if, in addition, the condition is met simultaneously that the thermostat is completely closed until the expiry of the predetermined time after switching on the switchable water pump.

Further advantages and features will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which like elements are provided with identical reference numerals.

Show

1 a schematic representation of a motor vehicle, suitable for an embodiment of a diagnostic method according to the invention,

2 a schematic representation of the diagnostic method according to the invention,

3 Schematic diagrams to show a time course of selected process parameters.

1 shows a schematic representation of a motor vehicle 1 , suitable for an embodiment of a diagnostic method according to the invention. The motor vehicle has an internal combustion engine 2 and a cooling system 3 for cooling the internal combustion engine 2 on. The cooling system 3 has a cooling circuit 4 , a switchable water pump 5 , a refrigeration cycle temperature sensor 6 , a thermostatic valve 7 and a heat exchange device 8th on. The cooling circuit 4 has a line and channel system, which is shown schematically by a dotted line. The switchable water pump 5 has an electric drive motor, not shown. By means of the switchable water pump 5 is a cooling liquid within the cooling circuit 4 pumped in a circle. The switchable water pump 5 is through a control unit 10 switched on and off depending on parameters. The control unit 10 is about connections 11 indirectly or directly with electrical sensors and actuators of the motor vehicle 1 connected. The connections 11 In this case, analog connections can mean via connection lines, digital connections via communication lines or wireless communication connections. The control unit 10 In this case, it can also mean a combination of control devices, which control devices are communicatively linked to one another. A group of control units can be called a control unit system. The cooling circuit temperature sensor 6 serves to measure the temperature of the cooling system 3 , The cooling liquid of the cooling circuit 4 takes heat from the internal combustion engine 2 and gives up heat in the heat exchange device 8th to an environment. By means of the thermostatic valve 7 which has one of the connections 11 through the control unit 10 is controllable, a proportion of the cooling liquid can be determined, which is the heat exchange device 8th flows through. The internal combustion engine 2 has an engine temperature sensor 9 on, which is located in a cooling passage of the internal combustion engine 2 located and thus within the internal combustion engine 2 is in contact with the cooling liquid. The engine temperature sensor 9 is about one of the connections 11 with the control unit 10 connected.

2 shows a schematic representation of a diagnostic method according to the invention 100 , It takes place immediately after a start 90 of the internal combustion engine 2 a diagnostic start 200 , On the diagnostic start 200 follows a release check 300 in which it is checked whether operating conditions of the motor vehicle 1 are such that a subsequent to the release exam 300 successful error checking 400 leads to correct results.

• – dass eine mittels des Kühlkreislauftemperatursensor 6 gemessene Temperatur TCOst des Kühlsystems 3 bei dem Start 90 des Verbrennungsmotors 2 kleiner als ein Kühlkreislauftemperaturschwellwert STCOst,
• – dass eine Verzögerungszeit tV1 zwischen dem Start 90 des Verbrennungsmotors 2 und einem Einschalten 91 (siehe auch 3) der schaltbaren Wasserpumpe 5 größer ist als ein Verzögerungszeitschwellwert StV1.

The release test 300 has release conditions 310 and a release fulfillment exam 320 on. The release performance test 320 at least checks for a minimum number of release conditions 310 is fulfilled at the same time. For a positive result of the release performance test 320 ie when fulfilling all release conditions 310 the release test 300 Next, the error check is performed 400 , For a negative result of the release performance test 320 ie if at least one of the release conditions is not fulfilled 310 the release test 300 , an end occurs 500 of the diagnostic procedure 100 in the form of a diagnostic interruption 510 , The minimum number of release conditions consists of the following conditions:

• - That one by means of the cooling circuit temperature sensor 6 measured temperature TCOst of the cooling system 3 at the start 90 of the internal combustion engine 2 smaller than a refrigeration cycle temperature threshold STCOst,
• - that a delay tV1 between the start 90 of the internal combustion engine 2 and a power up 91 (see also 3 ) of the switchable water pump 5 is greater than a delay time threshold StV1.

• – dass ein Temperaturanstieg ΔTVM einer mittels des Verbrennungsmotortemperatursensor 9 gemessenen Temperatur TVM des Verbrennungsmotors 2 nach dem Start 90 des Verbrennungsmotors 2 und vor dem Einschalten 91 der schaltbaren Wasserpumpe 5 größer ist als ein Temperaturanstiegschwellwert SΔTVM des Verbrennungsmotors 2 (siehe auch 3)
• – dass eine Verbrennungsmotorabstellzeit tVMst größer ist als ein Verbrennungsmotorabstellzeitschwellwert StVMst,
• – dass eine Laufzeit tLWP der schaltbaren Wasserpumpe 5 größer als ein Laufzeitschwellwert StLWP ist.

The release test 300 continues to have the following release conditions 310 on:

• - That a temperature increase ΔTVM one by means of the engine temperature sensor 9 measured temperature TVM of the internal combustion engine 2 after the start 90 of the internal combustion engine 2 and before switching on 91 the switchable water pump 5 is greater than a temperature rise threshold SΔTVM of the internal combustion engine 2 (see also 3 )
• An engine shutdown time tVMst is greater than an engine shutdown time threshold StVMst,
• - that a running time tLWP the switchable water pump 5 is greater than a runtime threshold StLWP.

With the engine stop time tVMst is a period of time between stopping the engine 2 and the start 90 of the internal combustion engine 2 meant.

• – dass ein Temperaturanstieg ΔTCO des Kühlkreislaufs 4 zu einem Zeitpunkt StV2 der Zeit tV2 nach dem Einschalten 91 der schaltbaren Wasserpumpe 5 kleiner als ein Temperaturanstiegsschwellwert SΔTCO des Kühlkreislaufs 4 ist.

Are all release conditions 310 fulfilled, then receives the release satisfaction test 320 a positive result and the diagnostic procedure proceeds with error checking 400 continued. The error check 400 has fault setting conditions 410 and an error satisfaction check 420 on. In the error satisfaction test 420 it checks if all fault setting conditions 410 are fulfilled simultaneously. For a positive result of the error satisfaction test 420 ie when all fault setting conditions are met 410 , the end is done 500 of the diagnostic procedure 100 in the form of a fault indication 520 , For a negative result of the error satisfaction test 420 ie if all fault setting conditions are not met 410 , an end occurs 500 of the diagnostic procedure 100 in the form of a Gutprüfung 530 , The fault setting conditions 410 have the following condition:

• - That a temperature increase ΔTCO of the cooling circuit 4 at a time StV2 of time tV2 after switching on 91 the switchable water pump 5 smaller than a temperature rise threshold SΔTCO of the refrigeration cycle 4 is.

3 shows schematic diagrams for illustrating a time course of selected process parameters in the diagnostic process 100 , In 3 three diagrams are shown below each other, which all have the same time axis for the time t.

In a first diagram 600 a temperature T is plotted over the time t. A solid curve describes a course of a by means of the cooling circuit temperature sensor 6 measured cooling system temperature TCO, a dashed curve describes a course of a means of Engine temperature sensor 9 measured engine temperature TVM.

In a second diagram 700 is a switching state SZW of the switchable water pump 5 applied over time t. A value 0 stands for a switched-off state and a value 1 for a switched-on state.

In a third diagram 800 is a switching state SZV of the internal combustion engine 2 over time 5 applied. The value 0 stands for a switched-off state and the value 1 for a switched-on state.

At a time t equal to 0, a start takes place 90 of the internal combustion engine 2 , The switching state SZV thus changes at this time from 0 to 1. As a result of the operation of the internal combustion engine 2 the temperature TVM of the internal combustion engine rises 2 represented by the dashed line in the first diagram 600 , strong, whereas the cooling system temperature TCO increases only very slowly. At a time t1, the power is turned on 91 the switchable water pump 5 , whereupon, after a short delay, the cooling system temperature TCO rises sharply and the temperature TVM of the internal combustion engine decreases due to an incipient cooling effect.

• – die Kühlsystemtemperatur TCOst beim Start 90 des Verbrennungsmotors 2 ist niedriger als der Kühlkreislauftemperaturschwellwert STCOst,
• – die Verzögerungszeit tV1 zwischen dem Start 90 des Verbrennungsmotors 2 und dem Einschalten 91 der schaltbaren Wasserpumpe 5 ist größer als der Verzögerungszeitschwellwert StV1,
• – der Temperaturanstieg ΔTVM der mittels des Verbrennungsmotortemperatursensor 9 gemessenen Temperatur TVM des Verbrennungsmotors 2 nach dem Start 90 des Verbrennungsmotors 2 und vor dem Einschalten 91 der schaltbaren Wasserpumpe 5 ist größer ist als der, in 3 nicht dargestellte, Temperaturanstiegschwellwert SΔTVM des Verbrennungsmotors 2,
• – die Laufzeit tLWP der schaltbaren Wasserpumpe 5 ist größer als der, in 3 nicht dargestellte, Laufzeitschwellwert StLWP.

3 represents a case where the release fulfillment test 320 a positive result has:

• - The cooling system temperature TCOst at startup 90 of the internal combustion engine 2 is lower than the cooling circuit temperature threshold STCOst,
• - the delay time tV1 between the start 90 of the internal combustion engine 2 and turning it on 91 the switchable water pump 5 is greater than the delay time threshold StV1,
• - The temperature increase ΔTVM by means of the engine temperature sensor 9 measured temperature TVM of the internal combustion engine 2 after the start 90 of the internal combustion engine 2 and before switching on 91 the switchable water pump 5 is greater than the, in 3 not shown, Temperaturanstiegschwellwert SΔTVM the internal combustion engine 2 .
• - The running time tLWP of the switchable water pump 5 is bigger than the, in 3 not shown, runtime threshold StLWP.

• – der Temperaturanstieg ΔTCO des Kühlkreislaufs 4 zu dem Zeitpunkt StV2 der Zeit tV2 nach dem Einschalten 91 der schaltbaren Wasserpumpe 5 ist größer als ein Temperaturanstiegsschwellwert SΔTCO des Kühlkreislaufs 4.

The error satisfaction check 420 has in the in 3 case shown a negative result:

• - The temperature increase ΔTCO of the cooling circuit 4 at time StV2 of time tV2 after switching on 91 the switchable water pump 5 is greater than a temperature rise threshold SΔTCO of the refrigeration cycle 4 ,

The in 3 Case shown thus ends with a Gutprüfung 530 ,

LIST OF REFERENCE NUMBERS

1

motor vehicle

2

internal combustion engine

3

cooling system

4

Cooling circuit

5

Switchable water pump

6

Cooling circuit temperature sensor

7

thermostatic valve

8th

Heat exchange device

9

Engine temperature sensor

10

control unit

11

links

90

Start of the internal combustion engine

91

Switch on the water pump

100

diagnostic procedures

170

Verbrennungsmotartemperaturmodell

200

diagnosis start

300

release testing

310

release conditions

320

Enable compliance testing

400

error checking

410

Error level condition

420

Error checking compliance

500

diagnosis end

510

cancellation

520

error indication

530

Gutprüfung

600

First diagram

700

Second diagram

800

Third diagram

ΔTCO

Temperature rise of the cooling system

ΔTVM

Temperature increase of the internal combustion engine

SΔTCO

Temperature rise threshold of the cooling system

SΔTVM

Temperature rise threshold of the internal combustion engine

STCOst

Kühlsystemtemperaturschwellwert

StLWP

Runtime threshold of the switchable water pump

STv1

Verzögerungszeitschwellwert

STv2

Time after switching on the water pump

StVMst

Verbrennungsmotorabstellzeitschwellwert

SZW

Switching state of the switchable water pump

SZV

Switching state of the internal combustion engine

T

temperature

TCO

Cooling system Temperature

TCOst

Cooling system temperature when starting the internal combustion engine

t1

time

TLWP

Running time of the switchable water pump

tV1

Delay time between the start of the internal combustion engine and switching on the switchable water pump

tV2

Time after switching on the switchable water pump

TVM

Temperature of the internal combustion engine

tVMst

Verbrennungsmotorabstellzeit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10351148 A1 [0004]
• US 20110048390 A1 [0005]

Claims (7)

Diagnostic method for a switchable water pump ( 5 ) of a cooling system ( 3 ) of an internal combustion engine ( 2 ) of a motor vehicle ( 1 ) to an error indication ( 520 ) a malfunction of the switchable water pump ( 5 ), characterized in that the error indication ( 520 ) then if conditions ( 310 . 410 ) are met simultaneously, under what conditions ( 310 . 410 ) include: a measured and / or calculated temperature (TCOst) of the cooling system ( 3 ) is at a start ( 90 ) of the internal combustion engine ( 2 ) smaller than a cooling system temperature threshold (STCOst), - a delay time (tV1) between the start ( 90 ) of the internal combustion engine ( 2 ) and a switch-on ( 91 ) of the switchable water pump ( 5 ) is greater than a delay time threshold (StV1), - a temperature increase (ΔTCO) of the cooling system ( 3 ) at a time (StV2) after switching on ( 91 ) of the switchable water pump ( 5 ) is less than a temperature rise threshold (SΔTCO) of the cooling system ( 3 ). Diagnostic method according to claim 1, characterized in that the error indication ( 520 ) takes place only if the condition ( 310 . 410 ), which must be fulfilled at the same time, furthermore counts: a temperature increase (ΔTVM) of a measured or calculated temperature (TVM) of the internal combustion engine ( 2 ) after the start ( 90 ) of the internal combustion engine ( 2 ) and before switching on ( 91 ) of the switchable water pump ( 5 ) is greater than a temperature rise threshold (SΔTVM) of the internal combustion engine ( 2 ). Diagnostic method according to claim 1 or 2, characterized in that the error indication ( 520 ) takes place only if the condition ( 310 . 410 ), which must be met simultaneously, further counts: an engine shutdown time (tVMst) is greater than an engine shutdown time threshold (StVMst). Diagnostic method according to one of claims 1 to 3, characterized in that the error indication ( 520 ) takes place only if the condition ( 310 . 410 ), which must be fulfilled simultaneously, also counts: a running time (tLWP) of the switchable water pump ( 5 ) is greater than a runtime threshold (StLWP). Diagnostic method according to one of claims 1 to 4, characterized in that the temperature (TCO) of the cooling system ( 3 ) by means of a cooling circuit temperature sensor ( 6 ), which outside the internal combustion engine ( 2 ) is measured. Diagnostic method according to one of claims 1 to 5, characterized in that the temperature (TVM) of the internal combustion engine ( 2 ) by means of an engine temperature model ( 170 ) is calculated. Diagnostic method according to one of claims 1 to 6, characterized in that the cooling system ( 3 ) a thermostatic valve ( 7 ) and a heat exchange device ( 8th ), wherein in a closed thermostatic valve ( 7 ) the cooling circuit ( 4 ) of the heat exchange device ( 8th ) is decoupled and the error indication ( 520 ) only succeed if to the condition ( 310 . 410 ), which must be fulfilled at the same time, continues to count: the thermostatic valve ( 7 ) is up to the expiration of the predetermined time (tV2) after switching on ( 91 ) of the switchable water pump ( 5 ) closed.

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