DE102018109786A1 - A method for detecting boiling of a coolant in a cooling system of a motor vehicle, cooling system and internal combustion engine - Google Patents

Abstract

A method is provided for detecting boiling of a coolant in a cooling system of a motor vehicle in which pressure fluctuations of the coolant are determined by means of a pressure sensor and such pressure fluctuations, which have been defined as characteristic of a decay of boiling bubbles, as a beginning or, without countermeasures, in the short term pending boiling of the coolant are evaluated. Such a method may additionally comprise measures for reducing the temperature of the coolant in at least one section of the cooling system, in order to counteract the risk of boiling that has been detected. As a result of the rapid and sufficiently undisturbed spread of pressure fluctuations in the coolant resulting from the decomposition of boiling bubbles, it is possible to ascertain incipient boiling by means of the method also at locations which are located at a relevant distance from the pressure sensor used in the process. Unlike a determination of a risk of boiling based on a temperature sensor, therefore, there is no need to arrange this as close as possible to a particularly endangered for such boiling of the cooling system.

Description

The invention relates to a method for detecting boiling of a coolant in a cooling system of a motor vehicle as well as a cooling system suitable for automated implementation of such a method. The invention also relates to an internal combustion engine with such a cooling system.

Internal combustion engines for motor vehicles generally have a cooling system in which a liquid coolant is pumped by means of one or more coolant pumps in at least one cooling circuit and thereby absorbs heat energy from integrated into the cooling circuit components, in particular an internal combustion engine. This heat energy is then delivered in a coolant radiator and temporarily in a heating heat exchanger to the ambient air, in the case of the heating heat exchanger to the ambient air provided for the air conditioning of the interior of the motor vehicle.

In the operation of such a cooling system, overheating of the coolant must be avoided, since otherwise it could be permanently damaged. By such damage, the functionality of the coolant, for example, in terms of corrosion protection, adversely affected, so that a damaged coolant can lead to premature damage of components of the internal combustion engine, at least in the medium to long term.

To determine the temperature of the coolant and thus the risk of overheating of the coolant temperature sensors are usually used. The problem with this is that the risk of overheating of the coolant at certain points within the cooling system, for example, at a defined point in a cooling passage of an internal combustion engine of the internal combustion engine, is greatest. For the most accurate detection of a risk of overheating, the positioning of a temperature sensor as close as possible to such a location is necessary. However, this is often not possible for structural or fluidic reasons, so that the detection of an overheating hazard based on the measured values of temperature sensors is often inaccurate.

The DE 10 2011 076 098 A1 describes a method by which overheating of coolant in a heat exchanger, which is integrated into an exhaust gas recirculation line of an internal combustion engine, should be avoided. Specifically, the internal combustion engine comprises a high-pressure exhaust gas recirculation line and a low-pressure exhaust gas recirculation line, in each of which a heat exchanger or exhaust gas cooler is integrated. At the risk of coolant overheating, the rate of low-pressure exhaust gas recirculation is increased and that of the high-pressure exhaust gas recirculation lowered to avoid the same. A coolant overheating should be able to be determined by means of a sensor, for example a temperature sensor, a pressure sensor or a dimension sensor, which measures the diameter of a coolant line.

The invention had the object of demonstrating a way to specify as simple as possible the most accurate detection of an overheating hazard for the coolant in a cooling system of an internal combustion engine.

This object is achieved by a method according to claim 1. A suitable for the automated implementation of such a method cooling system is the subject of claim 8 and an internal combustion engine with such a cooling system is the subject of claim 10. Advantageous embodiments of the inventive method and preferred embodiments of the cooling system according to the invention are objects of the other claims and / or emerge from the following description of the invention.

The invention is based on the idea that a boiling of coolant in a cooling system of a motor vehicle announces itself on the basis of gas bubbles, which decay shortly after their formation again. The pressure fluctuations that arise during this decay, which propagate from the location of the disintegration of the gas bubbles, can be detected in an advantageous manner by means of at least one pressure sensor and evaluated with regard to this event. The determined decay of these gas bubbles can then be equated with the imminent risk of boiling of the coolant, which makes it possible to take immediate measures to lower the coolant temperature and thus the risk of boiling, in particular limited to a portion of the cooling system, that of the determination used pressure sensor is assigned.

Accordingly, the invention provides a method for (early) detecting boiling of a (liquid) coolant in a cooling system of a motor vehicle, in particular a cooling system of an internal combustion engine of the motor vehicle, is determined in which by means of a pressure sensor pressure fluctuations of the coolant and those pressure fluctuations that are characteristic were defined for a decay of boiling bubbles (in advance), as an incipient or, without countermeasures, short term boiling of the coolant are considered. Such a method according to the invention can additionally comprise measures for lowering the temperature of the coolant in at least one section of the cooling system, in order to prevent the coolant from flowing counteract recognized boiling risk. Such measures may be, for example, an increase in the flow rate of the coolant in the cooling system as a whole or in a certain portion thereof by increasing the flow rate of a coolant pump or by adjusting a corresponding position of one or more valves for distributing the coolant in different portions of the cooling system. In particular, it may also be intended to guide a larger part and possibly all the coolant over a coolant cooler in order to cool it to an extent which is sufficient for preventing harmful boiling.

As a result of the rapid and sufficiently undisturbed spread of the pressure fluctuations in the coolant resulting from a decomposition of boiling bubbles, it is possible to ascertain incipient boiling by means of a method according to the invention also at locations which are arranged at a relevant distance from the pressure sensor used in the process. Unlike a determination of a risk of boiling based on a temperature sensor, therefore, there is no need to arrange this as close as possible to a particularly endangered for such boiling of the cooling system.

An inventive cooling system for in particular a motor vehicle and in particular an internal combustion engine of such a motor vehicle comprises at least one (first) coolant pump, a (first) coolant radiator and a (first) heat source, which are fluidly connected to each other via coolant lines with a coolant contained therein. Furthermore, a (first) pressure sensor is provided, which is adapted to measure pressure fluctuations of the coolant (directly or indirectly), as well as an evaluation device which is signal-transmitting connected to the (first) pressure sensor and is designed such that it can automatically carry out a method according to the invention ,

According to a preferred embodiment of the method according to the invention, it can be provided that an exceeding of a limit value for the amplitude of the pressure fluctuations is regarded as boiling of the coolant. This limit may be, for example, 50 mbar, wherein the amplitude may have both a positive and a negative sign.

A pressure sensor particularly suitable for use in carrying out a method according to the invention is characterized in that it has a relatively high sampling rate of, in particular, at least 50 Hz or at least 75 Hz or at least 100 Hz. This makes it possible in particular to detect the amplitudes of the typically relatively high-frequency pressure fluctuations or pressure oscillations which result from a disintegration of gas or boiling bubbles in the coolant of a cooling system, in fact isolated. On the other hand, too sluggishly sampled pressure sensors would not allow accurate detection of the individual amplitudes because of variations in pressure around averages, but rather average a number of pressure oscillations, which could adversely affect the detection result.

Preferably, the use of a pressure sensor is provided as part of a method according to the invention, which is acted upon directly by the coolant and thereby can also detect pressure fluctuations of the coolant directly. As a result, a particularly high detection accuracy can be realized. Alternatively, however, it is also possible to detect body or air vibrations, which were directly or indirectly excited by the pressure fluctuations of the coolant, by means of the pressure sensor.

Further preferably, the use of a pressure sensor may be provided which is a cooling channel of an integrated into the cooling system internal combustion engine (eg a diesel engine or a gasoline engine or a combination thereof, ie, for example, a combustion engine with homogeneous compression ignition) or a cooling channel of an integrated in the cooling system exhaust gas turbocharger or a charge air cooler or an EGR cooler of an internal combustion engine according to the invention is assigned, since experience exists in these sections or components of the cooling system according to points with high local boiling risk for the coolant. If, as is also possible, a plurality of pressure sensors are used according to the invention, they may in particular be assigned to several or all of the named sections / components. It can also be provided that a plurality of pressure sensors are associated with components that are parts of different, separate subcooling systems, such as a high-temperature cooling system and a low-temperature cooling system. Accordingly, the aforementioned components may be parts of a first subcooling system separated from a second subcooling system, the second subcooling system having at least a second coolant pump, a second coolant radiator and a second heat source connected via coolant lines to a coolant therein Furthermore, a second pressure sensor comprises, wherein the second pressure sensor with a (other) or the (same) evaluation device is connected signal-transmitting, which is designed such that this (also) automatically run a method according to the invention.

As "allocation" of the or a pressure sensor to a portion or a component of the cooling system is understood that it is arranged in the vicinity of this section or component, that the pressure fluctuations detected by this associated with the coolant contained in this section or in this component can be. In this case, provision may be made in particular for the pressure sensor to be arranged within this section or within this component or directly, ie without any intervening functional component of the cooling system, upstream or downstream thereof (relative to the intended flow direction).

The "functional component" of the cooling system is understood to be components whose function goes beyond the exclusive routing of the coolant (as in a coolant line). In particular, such functional components of the cooling system can be used for conveying, as in the case of a coolant pump, demand-controlled control, for example in the case of a valve or a more complex distribution device, or a functionally desired heat transfer, such as in a cooler or heat exchanger.

As a "separate" or "separate" design of the subcooling systems is meant that this no integral portion, i. no section which is both part of a cooling circuit of the one partial cooling system and part of a cooling circuit of the other partial cooling system include. The separated partial cooling systems can, however, be indirectly connected to a common expansion tank, in particular via at least one compensation pipe and in each case at least one ventilation pipe.

In this case, a "reservoir" for the coolant of the cooling system is understood to be a "reservoir", which serves in particular to compensate for temperature-induced expansions of the coolant by changing the fill level of the coolant in the reservoir. For this purpose, such a surge tank may be partially filled in particular with the coolant and partly with a gas, in particular air. An associated vent line may preferably open into a portion of the surge tank in which the gas is present, while an associated compensation line opens into a coolant receiving portion to an overflow of coolant between the partial cooling systems and the surge tank with the primary aim of compensation of a temperature Allow expansion of the coolant, possibly for a first or during maintenance activities provided filling the cooling systems with the coolant.

If the or a pressure sensor is assigned to a cooling channel of the internal combustion engine, this can be, in particular, a cooling channel of a cylinder housing of the internal combustion engine, since for the operation of a cooling system according to the invention comprising an internal combustion engine it can preferably be provided that at least at times a flow through the cooling channel of the Cylinder housing of the internal combustion engine is prevented, so that then coolant is within the cylinder housing or not or flows only to an extremely small extent. The associated advantage lies in the possibility of advantageous temperature control of the cylinder housing, in particular with the aim of warming up the cylinder housing as quickly as possible after a cold start of the internal combustion engine. An associated problem, however, may be the relatively high local boiling hazard due to the standing coolant. If such a side danger has been recognized based on a method according to the invention, as a countermeasure, for example, an at least slight flow through the cooling channel can be permitted.

The invention also relates to a motor vehicle with a cooling system according to the invention and in particular with an internal combustion engine according to the invention, which is preferably provided for generating a traction drive power for the motor vehicle. The motor vehicle may in particular be a wheel-based and non-rail-bound motor vehicle (preferably a car or a truck).

The indefinite articles ("a", "an", "an" and "an"), in particular in the patent claims and in the description generally describing the claims, are to be understood as such and not as numerical words. Corresponding to this concretized components are thus to be understood that they are present at least once and may be present more than once.

• 1: ein erfindungsgemäßes Kraftfahrzeug;
• 2: eine erste Ausgestaltungsform eines erfindungsgemäßen Kühlsystems;
• 3: eine zweite Ausgestaltungsform eines erfindungsgemäßen Kühlsystems; und
• 4: ein Diagramm zur Verdeutlichung der Veränderung des Druckverlaufs in Kühlmittel bei beginnendem Sieden.

The invention will be explained in more detail with reference to exemplary embodiments illustrated in the drawings. In the drawings shows, in a simplified representation:

• 1 a motor vehicle according to the invention;
• 2 a first embodiment of a cooling system according to the invention;
• 3 a second embodiment of a cooling system according to the invention; and
• 4 : a diagram to illustrate the change in the pressure curve in coolant at the beginning of boiling.

The 1 shows a motor vehicle according to the invention with a cooling system 1 that includes an internal combustion engine.

The internal combustion engine can according to the 2 and 3 an internal combustion engine 2 in the form of a reciprocating engine, in a cylinder housing 3 a plurality of cylinders 4 trains include. The cylinders 4 limit together with it up and down guided piston (not shown) and a cylinder head 5 Combustion chambers in which fresh gas (mainly air) is combusted together with fuel, causing the pistons to be cyclically moved up and down. These movements of the piston are transmitted in a known manner to a crankshaft (not shown) and thereby driven in rotation. About an unillustrated manual or automatic transmission, such a rotating movement of the crankshaft to driven wheels 6 the motor vehicle are transmitted, whereby a traction drive power is provided for the motor vehicle.

The internal combustion engine or components thereof are according to the 2 and 3 in the cooling system 1 integrated, each a first partial cooling system 7 (Main cooling system) and a second partial cooling system 8th (Secondary cooling system).

The main cooling system 7 of the cooling system 1 according to the 3 serves to cool the internal combustion engine 2 , of engine oil for lubrication of the internal combustion engine 2 , from (gearbox) oil of an internal combustion engine 2 associated gearbox (not shown), an exhaust gas turbocharger 9 , in particular a bearing block of the exhaust gas turbocharger 9 , as well as exhaust gas, which is returned via an exhaust gas recirculation line (not shown) from an exhaust line (not shown) to a fresh gas line (not shown) of the internal combustion engine. The main cooling system 7 includes cooling channels 10 . 11 of the cylinder housing 3 and the cylinder head 5 , a motor oil cooler 12 , a transmission oil cooler 13 (with associated thermostatic valve), a cooling channel of the exhaust gas turbocharger 9 , a cooling channel 14 in an EGR valve (not shown) integrated into the exhaust gas recirculation line and also an EGR cooler also integrated in the exhaust gas recirculation line 15 , Furthermore, the main cooling system includes 7 a coolant cooler 16 , two coolant pumps 17 . 18 and a heating heat exchanger 19 , The if necessary by means of an associated radiator bypass 20 bypassable coolant cooler 16 serves to the coolant flowing through this by the transition of heat energy to ambient air, the coolant cooler 16 also flows through, to cool. The heating heat exchanger 19 on the other hand serves, if necessary, ambient air to warm the air provided for the air conditioning of an interior of the motor vehicle comprising the internal combustion engine and thereby to temper. Of the two coolant pumps 17 . 18 of the main cooling system 7 is one as main coolant pump 17 provided, either by electric motor or, preferably, directly or indirectly from an output shaft (in particular the crankshaft) of the internal combustion engine 2 ie mechanically, can be driven. Even with such a mechanical drive of the main coolant pump 17 This can be controlled in terms of the specific (ie in each case based on the drive speed) delivery or controllable and also switched off (ie, then despite rotating drive generating without relevant capacity). It can be provided that in the switched-off state of the main coolant pump 17 whose flow is prevented or made possible. The second (additional) coolant pump 18 of the main cooling system 7 is driven by an electric motor.

A distribution of the from the coolant pumps 17 . 18 of the main cooling system 7 conveyed coolant to different cooling circuits of the main cooling system 7 is required by means of a distributor 21 controlled by a control device 22 the internal combustion engine is controlled.

The concrete functioning of the main cooling system 7 is not central to the understanding of the present invention, so that a more detailed explanation thereof will be omitted.

The secondary cooling system 8th serves to cool the means of a compressor of the exhaust gas turbocharger 9 charged fresh gas (charge air), the internal combustion engine 2 is supplied via the fresh gas train, and a metering device 23 , which is associated with an integrated into the exhaust line SCR catalyst (not shown) and which serves for introducing a reducing agent into the exhaust gas with the aim of a nitrogen oxide reduction. A charge air cooler 24 , which is provided for cooling the charge air to be supplied to the internal combustion engine, ie the fresh gas compressed by means of the compressor of the exhaust gas turbocharger, and a cooling device for the dosing device 23 provided cooling channel are in parallel strands of a cooling circuit of the secondary cooling system 8th integrated. Further, in this cooling circuit (in the portion which is not divided into the two strands) is an electric motor driven coolant pump 25 and a coolant cooler 26 , which is the re-cooling of the cooling circuit of the secondary cooling system 8th flowing coolant through a transition of heat energy to ambient air, the coolant radiator 26 also flows through, serves, integrated. Also the coolant cooler 26 of the secondary cooling system 8th is by means of a radiator bypass 27 bypassable, with a breakdown of Coolant, which is the secondary cooling system 8th flows through, on either the coolant radiator 26 or the associated radiator bypass 27 by means of a control valve 28 , by means of the control device 22 is controllable, is changeable.

The temperature of the coolant may during a regular operation of the internal combustion engine in the main cooling system 7 at least in sections significantly higher than in the secondary cooling system 8th so that the former can also be referred to as a high-temperature cooling system and the latter as a low-temperature cooling system.

Both the coolant cooler 16 of the main cooling system 7 as well as the coolant cooler 26 of the secondary cooling system 8th is a (common) blower 29 assigned, which can be put into operation, if necessary, to the cooling capacity of the coolant radiator 16 . 26 to increase or influence.

The partial cooling systems 7 . 8th further comprise a surge tank 30 partially filled with the coolant and partly with air. Via a connecting line 31 consisting of a coolant receiving (lower) portion of the expansion tank 30 go, is the expansion tank 30 both with the main cooling system 7 as well as with the secondary cooling system 8th fluidly connected. Furthermore connect vent lines 32 with integrated check valves 33 the air intake (upper) section of the expansion tank 30 with different sections of the main cooling system 7 and with the secondary cooling system 8th ,

That in the 3 illustrated cooling system differs from that according to the 2 essentially exclusively in the different embodiment of the distribution device 21 and the adjusting device, by means of a needs-based distribution of the respective auxiliary cooling system 8th flowing coolant on the coolant radiator 26 and the associated radiator bypass 27 is realized. For this purpose, in the cooling system according to the 3 instead of the control valve 28 a self-regulating thermostatic valve 34 intended. In the cooling system according to the 3 is also the exhaust gas turbocharger 9 not integrated into this. For this cooling is not provided by the coolant of the cooling system.

The cooling channel 10 of the cylinder housing 3 , the cooling channel 11 of the cylinder head 5 , the cooling channel of the exhaust gas turbocharger 9 , the EGR cooler 15 and the intercooler 24 is each a pressure sensor 35 assigned, which is in each case arranged such that by means of this high-frequency fluctuations or oscillations of the pressure of the coolant in the range of these components can be determined. The measuring signals of these pressure sensors 35 are sent to the control device 22 transmitted in a function as an evaluation device 22 determined in each case from the measured pressure fluctuations, whether a boiling risk of the coolant contained in these components is given. The evaluation device compares 22 the determined pressure fluctuations with those that are defined as characteristic of a disintegration of boiling bubbles. If a match is found, it is concluded that there is a start of boiling or an impending boiling risk, and by a corresponding activation of at least one of the control device 22 drivable components of the cooling system, the temperature of that coolant lowered, which will then flow through the further operation of the cooling system that component for which a boiling risk has been found.

The 4 clarifies this with reference to an exemplary measurement history for one of the pressure sensors 35 , It can be seen that at an initial boiling fluctuations of the pressure p of the coolant occur whose amplitudes are significantly greater than that by means of high-frequency (100 HZ) sampled pressure sensors 35 is determined for coolant that has no boiling phenomena.

LIST OF REFERENCE NUMBERS

1

cooling system

2

internal combustion engine

3

cylinder housing

4

cylinder

5

cylinder head

6

wheel

7

first partial cooling system / main cooling system

8th

second partial cooling system / secondary cooling system

9

turbocharger

10

Cooling channel of the cylinder housing

11

Cooling channel of the cylinder head

12

Engine oil cooler

13

Transmission oil cooler

14

Cooling channel in the EGR valve

15

EGR cooler

16

Coolant cooler of the main cooling system

17

Main coolant pump of the main cooling system

18

Additional coolant pump of the main cooling system

19

Heater core

20

Radiator bypass of the main cooling system

21

distributor

22

Control and evaluation device

23

metering

24

Intercooler

25

Coolant pump of the secondary cooling system

26

Coolant cooler of the secondary cooling system

27

Radiator bypass of the secondary cooling system

28

control valve

29

fan

30

surge tank

31

connecting line

32

vent line

33

check valve

34

thermostatic valve

35

pressure sensor

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 102011076098 A1 [0005]

Claims (10)

Method for detecting boiling of a coolant in a cooling system (1) of a motor vehicle, characterized in that by means of a pressure sensor (35) determines pressure fluctuations of the coolant and those pressure fluctuations, which are defined as characteristic of a disintegration of boiling bubbles, as a boiling of the coolant get ranked. Method according to Claim 1 , characterized by the application in a cooling system (1) for an internal combustion engine of the motor vehicle. Method according to Claim 1 or 2 , characterized in that exceeding a limit value for the amplitude of the pressure fluctuations as boiling of the coolant is evaluated. Method according to one of the preceding claims, characterized by the use of a pressure sensor (35) which has a sampling rate of at least 50 Hz or at least 75 Hz or at least 100 Hz. Method according to one of the preceding claims, characterized by the use of a pressure sensor (35), which is acted upon directly by the coolant. Method according to one of the preceding claims, characterized by the use of a pressure sensor (35) which comprises a cooling channel (10, 11) of an internal combustion engine (2) integrated into the cooling system (1) or a cooling channel of an exhaust gas turbocharger (9 ) or - an intercooler (24) or - an EGR cooler (15) is assigned. Method according to Claim 6 , characterized in that the cooling passage (10, 11) of the internal combustion engine (2) is a cooling passage (10, 11) of a cylinder housing (3) or a cylinder head (5). Cooling system (1) for a motor vehicle having a (first) coolant pump (17, 18), a (first) coolant cooler (16) and a (first) heat source, which are fluid-conductively connected via coolant lines to a coolant contained therein, characterized by a first) pressure sensor (35) which is adapted to measure pressure fluctuations of the coolant, and an evaluation device (22) signal-transmitting connected to the (first) pressure sensor, which is designed such that it can automatically perform a method according to one of the preceding claims , Cooling system (1) according to Claim 8 comprising a first partial cooling system (7) comprising the said components, characterized by a second partial cooling system (8) separated from the first partial cooling system (7), the at least one second coolant pump (25), a second coolant cooler (26) and a second Heat source, which are connected via coolant lines with a coolant contained therein, and further comprising a second pressure sensor (35), wherein the second pressure sensor (35) with one or the evaluation device (22), which is designed such that this automatically Method according to one of Claims 1 to 7 can perform, signal transmitting connected. Internal combustion engine with an internal combustion engine (2) and a cooling system (1) according to Claim 8 or 9 wherein the cooling system (1) comprises a cooling passage (10, 11) of the internal combustion engine (2) as a heat source.

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