DE102005045499B4 - Coolant circuit for an internal combustion engine and method for controlling a coolant flow through a coolant circuit - Google Patents

Abstract

A coolant circuit for an internal combustion engine, comprising a controllable thermostatic valve controlling the flow of the coolant through a radiator, a temperature measuring device for measuring a radiator outlet temperature or engine outlet temperature of the coolant, and a control device for opening or closing the thermostatic valve in dependence on the temperature measured by the temperature measuring device in that the temperature measuring device measures the ambient temperature and the engine outlet temperature (MAT) and the radiator outlet temperature (KAT) of the coolant, and in that the control device (8) measures the measured engine outlet temperature (MAT) with a lower and / or upper limit defined as a function of the measured ambient temperature the engine outlet temperature (MAT) and the measured radiator outlet temperature (KAT) with a lower limit of radiator outlet temperature defined as a function of the ambient temperature measured r (KAT) compares and the thermostatic valve (7) opens or closes when at least one of these limits is exceeded or fallen short of.

Description

The invention relates to a coolant circuit according to the preamble of claims 1 or 2 and a method for controlling a coolant flow through a coolant circuit of an internal combustion engine according to the preamble of claims 10 or 11.

Automotive internal combustion engine coolant circuits are typically designed to include, in addition to a radiator leg with a radiator streamed by the airflow, a bypass branch through which the coolant can be passed after engine start bypassing the radiator, for faster heating the internal combustion engine and thus during cold start or warm-up for lower pollutant emissions and lower fuel consumption. In order to control the coolant flow through the cooler branch or the bypass branch, a thermostatic valve is usually provided in the cooler branch, which is closed at low coolant temperatures and is opened when the coolant temperature exceeds a predetermined value. When the thermostatic valve is opened, the hot cooling water flowing from the internal combustion engine into the radiator hits the cold radiator tubes which have an ambient temperature. As a result, high local temperature differences are caused there especially at low ambient temperatures, which in turn lead to thermal stresses in the radiator tubes. A resulting different length expansion of individual radiator tubes may in the worst case have cracks in the radiator result. The same problems can be observed in particular with coolant circuits with a controllable thermostatic valve, where the internal combustion engine is operated with higher cooling water temperatures, which promote the occurrence of thermal stresses, in order to avoid heat losses and to increase the efficiency at partial load.

From the DE 196 21 674 C2 a coolant circuit for an internal combustion engine of the aforementioned type with a controllable thermostatic valve is already known, with which the amount of coolant flowing through the radiator is controlled. The coolant circuit there still contains an additional heat storage branch, which is opened or closed by a control unit in dependence on the coolant temperature.

The coolant temperature can be determined there when entering the internal combustion engine or when exiting from it.

Next discloses the DE 103 16 017 A1 a method for controlling and / or regulating a cooling system of an internal combustion engine, wherein the mixing ratio between a radiator branch and a bypass branch of the cooling system is adjusted by a wax-operated thermostatic valve in dependence on the coolant temperature. The coolant temperature is measured there both at the entrance to the engine and at the exit from the same.

From the DE 103 11 188 A1 Furthermore, a method and a device for demand-driven cooling of internal combustion engines is known in which a thermostat between a bypass branch and a cooler branch of a coolant circuit opens the cooler branch more and more from a certain operating temperature and thereby keeps the coolant inlet temperature to the engine approximately constant.

From the DE 101 63 943 A1 is a method for controlling electrically actuated components, such as an electrically actuated thermostatic valve, a cooling system, the components are controlled by a control unit in dependence on the current operating point of the motor vehicle such that there is an optimal overall efficiency of the motor vehicle and / or the cooling system , Among other things, influencing factors such as vehicle speed, ambient temperature, coolant temperature at various points in the cooling circuit, engine temperature and engine load are taken into account. The disadvantage is that only a one-sided optimization of the coolant temperatures is pursued for the purpose of optimum efficiency, without being able to control the wear of the components by this operation.

The DE 43 24 178 A1 discloses a cooling system for an internal combustion engine of a motor vehicle with a thermostatic valve having an electrically heatable expansion element. The expansion element is heated in dependence on operating and / or environmental variables of the internal combustion engine, in order to bring about a cooling of the coolant in the cooling system. A disadvantage is that the proposed expansion element is not suitable for accurate control. Thus, only the opening of the thermostatic valve can be made by heating the expansion material, while the closing of the thermostatic valve by the possibly cooling expansion material takes place. As a result, the described cooling system is only limitedly suitable for dynamic control strategies.

Proceeding from this, the present invention seeks to provide an optimized control strategy for a map cooling with a coolant circuit of the type mentioned, with the without affecting the thermodynamic Advantages Thermal stresses in the radiator and in the combustion engine and thus in particular minimize the load on the radiator.

This object is achieved according to a first variant of the invention in that the ambient temperature and the engine outlet temperature and the Kühleraustrittstemperatur of the coolant are measured that the measured engine outlet temperature with a determined as a function of the measured ambient temperature lower and / or upper limit of the engine outlet temperature and the measured radiator outlet temperature with a lower limit of the radiator outlet temperature set as a function of the measured ambient temperature, and that the thermostatic valve is opened or closed when at least one of these limits is exceeded or fallen below.

A second variant of the invention, on the other hand, provides that only the ambient temperature is measured, while the engine exhaust temperature (MAT) and coolant exit temperature (KAT) are calculated or predicted from temperature models, for example, by calculating or predicting the calculated or predicted engine exit temperature (MAT) The measured ambient temperature upper and / or lower limits of the engine outlet temperature (MAT) and the calculated or predicted radiator outlet temperature (KAT) are compared with a lower limit of radiator outlet temperature (KAT) determined as a function of the measured ambient temperature, and the thermostatic valve is opened or closed if at least one of these limits is exceeded or fallen short of.

In order to allow stable control and to prevent the thermostatic valve from fluttering when the measured or calculated engine inlet or engine outlet temperature alternately passes the respective upper or lower limit in short intervals from above and below, hysteresis belts also become available for the specified upper and lower limits provided, that is different switching points at an approach from above or below to the respective limit.

A preferred embodiment of the invention provides that the closed at the start of the engine thermostatic valve is opened by the control device when the lower limit of the engine outlet temperature is exceeded by a predetermined temperature.

In the subsequent warm-up phase of the internal combustion engine, the thermostatic valve is closed according to another preferred embodiment of the invention, when the lower limit of the engine outlet temperature is exceeded, and will be opened again when the upper limit of the engine outlet temperature is exceeded.

A still further preferred embodiment of the invention provides that the thermostatic valve is opened when either the lower limit of the radiator outlet temperature falls below or the upper limit of the engine outlet temperature is exceeded.

If, due to a driving style, an extreme ambient temperature or the like, the lower limits of the radiator outlet temperature and the motor outlet temperature are simultaneously undershot over a predetermined period of time, the thermostatic valve is suitably closed and only reopened when the lower limit of the engine outlet temperature is exceeded by a predetermined temperature.

As with known map controls, the thermostatic valve is also controlled in dependence on the speed and the load of the internal combustion engine according to maps, in which the dependence of the engine outlet temperature of the engine speed and the engine load is taken into account.

In the following the invention will be explained in more detail with reference to an embodiment shown in the drawing. Show it:

1 a schematic representation of a coolant circuit of an internal combustion engine;

2 a representation of coolant temperature limits as a function of the ambient temperature at an engine load of less than, for example, 60% of full load;

3 a representation of coolant temperature limits as a function of the ambient temperature at an engine load of more than, for example, 60% of full load.

The In 1 illustrated coolant circuit 1 an internal combustion engine 2 of a motor vehicle is flowed through in a known manner by a coolant, usually cooling water. The at 3 from the internal combustion engine 2 Exiting heated coolant flows through a pipe 4 in a cooler branch 5 or a bypass branch 6 , wherein the amount of the through the cooler branch 5 or the bypass branch 6 directed coolant by means of a controllable thermostatic valve 7 is changed as needed. The thermostatic valve 7 is from a control unit 8th controlled, for example, an engine control unit of the motor vehicle. The radiator branch 5 includes one with a blower 9 provided by ambient air flowed cooler 10 from which the cooled coolant through a pipe 11 to the internal combustion engine 2 flows back into it at 12 re-enters. The bypass branch 6 flows, bypassing the radiator 10 also in the line 11 , The coolant circuit 1 further includes a heating branch 13 with a heating valve 14 and one with a fan 15 provided heating heat exchanger 16 for heating a passenger compartment of the vehicle by opening the heating valve 14 with hot, at 23 out of the engine 2 exiting coolant can be applied. After passing through the heating branch 13 The coolant is also at 12 in the internal combustion engine 2 returned. Before entering the internal combustion engine 2 the coolant flows through a coolant pump 17 , which is used to circulate the coolant through the coolant circuit 1 serves. The coolant circuit 1 also contains two temperature sensors 18 and 19 of which one 18 between the internal combustion engine 2 and the thermostatic valve 7 is arranged and at 3 the engine outlet temperature MAT measures, that is the temperature of the engine 2 escaping hot coolant while the other 19 behind the radiator 10 is arranged and at 24 the radiator outlet temperature KAT measures, that is the temperature of the radiator 10 exiting cooled coolant. The two temperature sensors 18 and 19 , another, anywhere, for example, near the radiator 10 , vehicle mounted temperature sensor 20 for measuring the ambient temperature and the adjustable thermostatic valve 7 are via signal lines 21 with the control unit 8th connected.

The thermostatic valve 7 is at the start of the internal combustion engine 2 closed for faster heating of the cold engine 2 to ensure lower pollutant emissions and lower fuel consumption. If at the end of the starting phase of the engine 2 the thermostatic valve 7 is opened, this flows out of the engine 2 escaping coolant into the radiator 10 what at a high engine outlet temperature MAT when the coolant hits the ambient temperature having individual radiator tubes 22 the radiator 10 due to the large temperature difference to significant local thermal stresses and a different linear expansion of individual radiator tubes 22 in the cooler 10 lead and in the worst case cracks in the radiator 10 can result. The same applies if the thermostatic valve 7 is opened after the internal combustion engine 2 previously by closing the thermostatic valve 7 operated at partial load with higher coolant temperatures to avoid heat loss and increase its efficiency.

As a remedy, an optimized control strategy is now described, with the thermal stresses in the radiator 10 and thus the burden of the radiator 10 without compromising on the thermodynamic benefits of the system. To carry out this optimized control strategy, the engine outlet temperature MAT of the engine 2 Upper limits and lower limits and for the radiator outlet temperature KAT lower limits depending on the respective ambient temperature set and these limits in the control unit 8th stored in the form of maps, of which in 2 and 3 two are shown by way of example. The maps are in later operation of the internal combustion engine 2 together with those from the temperature sensors 18 . 19 and 20 measured actual temperatures of the engine outlet temperature MAT, the radiator outlet temperature KAT and the ambient temperature for controlling the thermostatic valve 7 used. In this case, the dependence of the engine outlet temperature MAT of the engine load and the engine speed is taken into account by different maps, as in 2 and 3 for an engine load of less than 60% of full load or more than 60% of full load exemplified.

As can be seen from the exemplary illustration in 2 It can be seen, increase at an engine load of less than 60% of full load both the upper limit and the lower limit of the engine outlet temperature MAT and the lower limit of the radiator outlet temperature with increasing ambient temperature, but they have a slightly different course over the ambient temperature. As a result, the differences between the upper limit of the engine exit temperature MAT, the lower limit of the engine exit temperature MAT, and the lower limit of the radiator exit temperature KAT also vary with the ambient temperature.

As from the also exemplary representation in 3 can be seen, however, have at an engine load of more than 60% of the full load, the upper limit of the engine outlet temperature MAT and the lower limit of the radiator outlet temperature KAT a substantially independent of the ambient temperature constant course, while the lower limit of the engine outlet temperature MAT between -25 ° C and + 20 ° C recorded a slight increase, but smaller than the corresponding increase in 2 is. Next are in 3 the absolute values of the upper limit of the engine outlet temperature MAT, the lower limit of the engine outlet temperature MAT and the lower limit of the radiator outlet temperature KAT are slightly lower than in 2 and the difference between the upper and lower limits of the engine outlet temperature MAT on the one hand and the lower limit of the radiator outlet temperature KAT on the other hand, slightly lower.

Depending on the requirements, the upper and lower limits of the engine outlet temperature MAT and the lower limit of the radiator outlet temperature KAT may also have a different profile than the ambient temperature.

During operation of the motor vehicle, the control unit compares 8th that of the temperature sensor 18 measured respective actual engine outlet temperature MAT or that of the temperature sensor 19 measured respective actual radiator outlet temperature KAT with the upper and / or lower limit of the engine outlet temperature MAT or with the lower limit of the radiator outlet temperature KAT, in the associated map of the instantaneous engine load and engine speed for that of the temperature sensor 20 measured actual ambient temperature are stored and changes the setting of the thermostatic valve 7 if any of the following conditions are met:
If, for example, in a starting phase of the internal combustion engine 2 the lower limit of the engine outlet temperature MAT is exceeded by a predetermined temperature value, the thermostatic valve 7 opened, since this means the end of the start phase.

When in a warm-up phase of the internal combustion engine 2 the lower limit of the engine outlet temperature MAT is undershot, the thermostatic valve 7 closed and the coolant through the bypass branch 6 to increase the engine temperature faster. If, at the end of the warm-up phase, the upper limit of the engine outlet temperature MAT is exceeded, the thermostatic valve will be activated 7 re-opened to a portion of the coolant through the radiator branch 5 to lead.

When driving the motor vehicle, ie in normal operation of the internal combustion engine 2 , is the thermostatic valve 7 only open if either the lower limit of the radiator outlet temperature KAT is exceeded or the upper limit of the engine outlet temperature MAT is exceeded.

If, due to the driving mode or an extreme ambient temperature, the lower limit of the engine outlet temperature MAT and the lower limit of the radiator outlet temperature KAT are simultaneously undershot for a predetermined period of time, for example a few seconds, the thermostatic valve becomes 7 closed until the lower limit of the engine outlet temperature MAT is exceeded by a predetermined temperature value.

To enable a stable control, hysteresis belts are also provided for the upper and lower limits of the engine outlet temperature MAT and for the lower limits of the radiator outlet temperature KAT. H. slightly different switching points when approaching these limits from above or from below.

LIST OF REFERENCE NUMBERS

1

Coolant circuit

2

internal combustion engine

3

Coolant outlet

4

Coolant line

5

cooler branch

6

bypass branch

7

thermostatic valve

8th

control unit

9

fan

10

cooler

11

Coolant line

12

Coolant inlet

13

Heating branch

14

Heating valve

15

fan

16

Heater core

17

Coolant pump

18

temperature sensor

19

temperature sensor

20

temperature sensor

21

signal lines

22

cooler tubes

23

Coolant outlet heating branch

MAT

Motor outlet temperature

KAT

Cooler outlet temperature

Claims (18)

Coolant circuit for an internal combustion engine, with a flow of the coolant through a radiator controlling controllable thermostatic valve, a temperature measuring device for measuring a radiator outlet temperature or engine outlet temperature of the coolant, and a control device for opening and closing of the thermostatic valve in dependence on the temperature measured by the temperature measuring device temperature, characterized characterized in that the temperature measuring device measures the ambient temperature and the engine outlet temperature (MAT) and the radiator outlet temperature (KAT) of the coolant, and that the control device ( 8th ) the measured Engine outlet temperature (MAT) at a lower and / or upper limit of engine outlet temperature (MAT) determined as a function of the ambient temperature measured and the measured radiator outlet temperature (KAT) at a lower radiator outlet temperature (KAT) lower limit determined as a function of the ambient temperature measured and the thermostatic valve ( 7 ) opens or closes if at least one of these limits is exceeded or fallen short of. Coolant circuit for an internal combustion engine, comprising a controllable thermostatic valve controlling the flow of coolant through a radiator and a control device for opening or closing the thermostatic valve, characterized in that the control device ( 8th ) compares a calculated engine exit temperature (MAT) with a lower and / or upper engine exhaust temperature limit (MAT) and a calculated radiator outlet temperature (KAT) with a lower radiator outlet temperature (KAT) lower limit set as a function of the measured ambient temperature; Thermostatic valve ( 7 ) opens or closes if at least one of these limits is exceeded or fallen short of. Coolant circuit according to claim 1 or 2, characterized in that the control device ( 8th ) at the start of the internal combustion engine ( 2 ) closed thermostatic valve ( 7 ) opens when the lower limit of the engine outlet temperature (MAT) is exceeded by a predetermined temperature. Coolant circuit according to one of claims 1 to 3, characterized in that the control device ( 8th ) the thermostatic valve ( 7 ) in a warm-up phase of the internal combustion engine ( 2 ) closes when the lower limit of the engine outlet temperature (MAT) is exceeded. Coolant circuit according to claim 4, characterized in that the control device ( 8th ) the thermostatic valve ( 7 ) reopens in the warm-up phase when the upper limit of the engine outlet temperature (MAT) is exceeded. Coolant circuit according to one of the preceding claims, characterized in that the control device ( 8th ) the thermostatic valve ( 7 ) when driving, when either the lower limit of the radiator outlet temperature (CAT) is exceeded or the upper limit of the engine outlet temperature (MAT) is exceeded. Coolant circuit according to one of the preceding claims, characterized in that the control device ( 8th ) the thermostatic valve ( 7 ) closes when at the same time the lower limits of the radiator outlet temperature (KAT) and the engine outlet temperature (MAT) are exceeded for a predetermined period of time. Coolant circuit according to claim 7, characterized in that the control device ( 8th ) the thermostatic valve ( 7 ) closes until the lower limit of the engine outlet temperature (MAT) is exceeded by a predetermined temperature. Coolant circuit according to one of the preceding claims, characterized in that the control device ( 8th ) when opening and closing the thermostatic valve ( 7 ) the dependence of the engine outlet temperature (MAT) on the speed and the load of the internal combustion engine ( 2 ) taken into account by a map control. A method for controlling a coolant flow through a coolant circuit of an internal combustion engine with a radiator and a controllable thermostatic valve, characterized in that the ambient temperature and the engine outlet temperature (MAT) and the radiator outlet temperature (KAT) of the coolant are measured that the measured engine outlet temperature (MAT) with a lower and / or upper limits of the engine outlet temperature (MAT) and the measured radiator outlet temperature (KAT) are compared with a lower limit of the radiator outlet temperature (KAT) determined as a function of the ambient temperature measured, and that the thermostatic valve ( 7 ) is opened or closed if at least one of these limits is exceeded or fallen short of. Method for controlling a coolant flow through a coolant circuit of an internal combustion engine with a radiator and a controllable thermostatic valve, characterized in that the ambient temperature is measured, that the engine outlet temperature (MAT) and the radiator outlet temperature (KAT) of the coolant are calculated or predicted that the calculated or predicted engine exit temperature (MAT) with a lower and / or upper engine exhaust temperature limit (MAT) determined as a function of ambient temperature and the calculated or predicted radiator exit temperature (KAT) compared to a lower radiator exit temperature (KAT) limit determined as a function of ambient temperature measured , and that the thermostatic valve ( 7 ) is opened or closed if at least one of these limits is exceeded or fallen short of. A method according to claim 10 or 11, characterized in that the thermostatic valve ( 7 ) at the start of the internal combustion engine ( 2 ) is closed and is opened when the lower limit of the engine outlet temperature (MAT) is exceeded by a predetermined value. Method according to one of claims 10 to 12, characterized in that the thermostatic valve ( 7 ) in a warm-up phase of the internal combustion engine ( 2 ) is closed when the lower limit of the motor outlet temperature (MAT) is exceeded. A method according to claim 13, characterized in that the thermostatic valve ( 7 ) in the warm-up phase of the internal combustion engine ( 2 ) is reopened when the upper limit of the engine outlet temperature (MAT) is exceeded. Method according to one of claims 10 to 14, characterized in that the thermostatic valve ( 7 ) is opened while driving when either the Lower limit of the radiator outlet temperature (CAT) or the upper limit of the engine outlet temperature (MAT) is exceeded. Method according to one of claims 10 to 15, characterized in that the thermostatic valve ( 7 ) is closed, if at the same time the lower limits of the radiator outlet temperature (KAT) and the engine outlet temperature (MAT) are exceeded for a predetermined period of time. A method according to claim 16, characterized in that the thermostatic valve is kept closed until the lower limit of the engine outlet temperature (MAT) is exceeded by a predetermined temperature. Method according to one of claims 10 to 17, characterized in that when opening and closing the thermostatic valve ( 7 ) the dependence of the engine outlet temperature (MAT) on the speed and the load of the internal combustion engine ( 2 ) is taken into account by a map control.

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