Method for detecting the boiling of a coolant in a cooling system of a motor vehicle, cooling system and internal combustion engine

Abstract

Method for detecting boiling of a coolant in a cooling system (1) of a motor vehicle, wherein pressure fluctuations of the coolant are determined by means of a pressure sensor (35) and such pressure fluctuations, which are defined as characteristic of a breakup of boiling bubbles, are evaluated as boiling of the coolant, characterized by the use of a pressure sensor (35) which is assigned to a cooling channel (10) of a cylinder housing (3) of an internal combustion engine (2) integrated into the cooling system (1), wherein at least temporarily a flow through the cooling channel (10) is prevented, wherein when a boiling hazard has been detected, a flow through the cooling channel (10) is permitted.

Description

[0001] The invention relates to a method for detecting the boiling of a coolant in a motor vehicle cooling system and to a cooling system suitable for the automated execution of such a method. The invention also relates to an internal combustion engine with such a cooling system.

[0002] Internal combustion engines in motor vehicles typically have a cooling system in which a liquid coolant is pumped by one or more coolant pumps in at least one cooling circuit, absorbing heat energy from components integrated into the cooling circuit, particularly the internal combustion engine. This heat energy is then released to the ambient air in a coolant radiator and, at times, to a heater core. In the case of the heater core, this heat energy is released to the ambient air intended for climate control of the vehicle's interior.

[0003] In the operation of such a cooling system, overheating of the coolant must be avoided, as this could otherwise cause permanent damage. Such damage negatively affects the coolant's functionality, for example, with regard to corrosion protection, so that a damaged coolant can lead to premature damage to internal combustion engine components, at least in the medium to long term.

[0004] Temperature sensors are typically used to determine the coolant temperature and thus the risk of overheating. The problem is that the risk of overheating is greatest at specific points within the cooling system, for example, at a defined location in a cooling channel of an internal combustion engine. For the most accurate detection of overheating, a temperature sensor needs to be positioned as close as possible to such a point. However, this is often not possible due to structural or fluid dynamic constraints, meaning that overheating detection based on temperature sensor readings is frequently inaccurate.

[0005] German patent DE 10 2011 076 098 A1 describes a method for preventing coolant overheating in a heat exchanger integrated into the exhaust gas recirculation (EGR) line of an internal combustion engine. Specifically, the engine comprises a high-pressure EGR line and a low-pressure EGR line, each with an integrated heat exchanger or exhaust gas cooler. To prevent coolant overheating, the low-pressure EGR rate is increased and the high-pressure EGR rate is decreased. Coolant overheating is detected by a sensor, such as a temperature sensor, a pressure sensor, or a dimensional sensor that measures the diameter of the coolant line.

[0006] DE 11 2009 001 675 T5 discloses a method for diagnosing the cooling system of an internal combustion engine for a motor vehicle, in which dynamic hydraulic pressure values ​​in the cooling system are recorded using pressure sensors and the condition of the cooling system is inferred from this. In this way, local boiling of coolant in the cooling system can be detected.

[0007] The invention was based on the objective of demonstrating a way to detect and react to a risk of overheating of the coolant in a cooling system of an internal combustion engine in the simplest possible manner.

[0008] This problem is solved by a method according to claim 1. A cooling system suitable for the automated execution of such a method is the subject of claim 5, and an internal combustion engine with such a cooling system is the subject of claim 7. Advantageous embodiments of the method according to the invention and preferred configurations of the cooling system according to the invention are the subject of further claims and / or will become apparent from the following description of the invention.

[0009] The invention is based on the idea that the boiling of coolant in a motor vehicle's cooling system is heralded by gas bubbles that disintegrate shortly after their formation. The pressure fluctuations resulting from this disintegration, which propagate from the point of the gas bubbles' disintegration, can advantageously be detected by means of at least one pressure sensor and evaluated with regard to this event. The detected disintegration of these gas bubbles can then be equated with the imminent risk of the coolant boiling, which makes it possible to take immediate measures to reduce the coolant temperature and thus the risk of boiling, particularly also limited to a section of the cooling system to which the pressure sensor used for detection is located.

[0010] Accordingly, the invention provides a method for the (early) detection of 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, in which pressure fluctuations of the coolant are determined by means of a pressure sensor and such pressure fluctuations, which have been defined (in advance) as characteristic of the disintegration of boiling bubbles, are interpreted as the onset of boiling of the coolant or, without countermeasures, as imminent boiling of the coolant. The method according to the invention additionally includes measures for lowering the temperature of the coolant in at least one section of the cooling system in order to counteract the detected risk of boiling.Such measures may include, for example, increasing the flow rate of the coolant in the cooling system as a whole or in a specific section thereof by increasing the delivery capacity of a coolant pump or by adjusting the position of one or more valves to distribute the coolant to different sections of the cooling system. In particular, it may also be necessary to route a larger portion, or possibly all, of the coolant through a coolant radiator to cool it sufficiently to prevent harmful boiling.

[0011] Due to the rapid and sufficiently undisturbed propagation of pressure fluctuations in the coolant resulting from the disintegration of boiling bubbles, it is possible to detect the onset of boiling using this method even at locations a significant distance from the pressure sensor. Unlike when detecting boiling risk based on a temperature sensor, there is therefore no need to position the sensor as close as possible to a point in the cooling system particularly susceptible to boiling.

[0012] According to the invention, a pressure sensor is used which is assigned to a cooling channel of an internal combustion engine (e.g., a diesel engine or a gasoline engine or a combination thereof, i.e., an internal combustion engine with homogeneous compression ignition) integrated into the cooling system, since this section or component of the cooling system contains areas with a particularly high local risk of the coolant boiling over. The cooling channel of the internal combustion engine is a cooling channel of the cylinder housing of the internal combustion engine. For the operation of a cooling system according to the invention, comprising an internal combustion engine, it is provided that the flow through the cooling channel of the cylinder housing of the internal combustion engine is prevented at least temporarily, so that coolant is then either stagnant within the cylinder housing or does not flow at all or only to an extremely small extent.The associated advantage lies in the possibility of advantageous temperature control of the cylinder housing, particularly with the aim of warming the cylinder housing as quickly as possible after a cold start of the internal combustion engine. However, a related problem can be the relatively high risk of local boiling due to the stagnant coolant. If such a risk of boiling is detected according to the inventive method, at least a slight flow through the cooling channel is permitted as a countermeasure.

[0013] A cooling system according to the invention, particularly for a motor vehicle and especially for an internal combustion engine of such a motor vehicle, comprises at least a (first) coolant pump, a (first) coolant radiator, and a cooling channel of a cylinder housing of an internal combustion engine as a (first) heat source, which are fluidly connected to one another via coolant lines containing a coolant. Furthermore, a (first) pressure sensor is provided, which is configured to measure pressure fluctuations of the coolant in the cooling channel of the cylinder housing (directly or indirectly), as well as an evaluation device connected to the (first) pressure sensor for signal transmission, which is designed such that it can automatically carry out a method according to the invention.

[0014] According to a preferred embodiment of the method according to the invention, exceeding a limit value for the amplitude of the pressure fluctuations can be interpreted as the boiling of the coolant. This limit value can be, for example, 50 mbar, where the amplitude can have either a positive or a negative sign.

[0015] 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, in particular at least 50 Hz, at least 75 Hz, or at least 100 Hz. This makes it possible, in particular, to accurately and precisely detect the amplitudes of the typically high-frequency pressure fluctuations or oscillations resulting from the disintegration of gas or boiling bubbles in the coolant of a cooling system. Pressure sensors with excessively slow sampling rates, on the other hand, would not allow for precise detection of individual amplitudes due to pressure fluctuations around mean values, but would instead average several pressure oscillations, which could negatively affect the measurement result.

[0016] Preferably, in a method according to the invention, a pressure sensor is used which is directly exposed to the coolant and can therefore directly detect pressure fluctuations of the coolant. This allows for particularly high measurement accuracy. Alternatively, however, it is also possible to detect body or air vibrations that were directly or indirectly excited by the pressure fluctuations of the coolant using the pressure sensor.

[0017] If, as is also possible, several pressure sensors are used, at least one additional pressure sensor can be assigned to one, several, or all of the following sections / components: a cooling channel of an exhaust gas turbocharger integrated into the cooling system, or an intercooler, or an EGR cooler of an internal combustion engine according to the invention, since experience has shown that these sections or components of the cooling system also contain areas with a particularly high local risk of the coolant boiling over. It is also possible for several pressure sensors to be assigned to components that are parts of different, separate partial cooling systems, for example, a high-temperature cooling system and a low-temperature cooling system.Accordingly, the aforementioned components can be parts of a first partial cooling system, which is separated from a second partial cooling system, wherein the second partial cooling system comprises at least a second coolant pump, a second coolant cooler and a second heat source, which are connected to a coolant contained therein via coolant lines, and which further comprises a second pressure sensor, wherein the second pressure sensor is connected by signal transmission to a (different) or the (same) evaluation device, which is designed in such a way that it (also) can automatically execute a method in which pressure fluctuations of the coolant are detected by means of the second pressure sensor and such pressure fluctuations, which are defined as characteristic of a breakup of boiling bubbles, are evaluated as a boiling of the coolant.

[0018] The "assignment" of a pressure sensor to a section or component of the cooling system means that it is positioned in such a proximity to that section or component that the pressure fluctuations it detects can be attributed to the coolant contained in that section or component. In particular, the pressure sensor may be located within that section or component, or directly upstream or downstream of it (with respect to the intended flow direction), i.e., without any intervening functional component of the cooling system.

[0019] Components whose function extends beyond simply conveying the coolant (as in a coolant line) are considered "functional components" of a cooling system. In particular, such functional components can serve for conveyance, as in a coolant pump; for demand-based control, as in a valve or a more complex distribution device; or for a functionally intended heat transfer, as in a radiator or heat exchanger.

[0020] The term "separate" or "separate" design of the partial cooling systems means that they do not include an integral section, i.e., a section that is part of both a cooling circuit of one partial cooling system and a cooling circuit of another. However, the separate partial cooling systems may be indirectly connected to a common expansion tank, in particular via at least one expansion line and at least one vent line each.

[0021] An "expansion tank" is understood to be a reservoir for the coolant of the cooling system, designed to compensate for temperature-related expansion of the coolant by changing the coolant level within the expansion tank. Such an expansion tank can be partially filled with coolant and partially with a gas, particularly air. An associated vent line preferably leads into a section of the expansion tank containing the gas, while another equalization line leads into a section containing the coolant. This allows coolant to flow between the individual cooling systems and the expansion tank, primarily to compensate for temperature-related expansion of the coolant, and optionally also for initial filling of the cooling systems with coolant during maintenance.

[0022] 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 intended for generating propulsion power for the motor vehicle. The motor vehicle can, in particular, be a wheeled and not rail-bound vehicle (preferably a passenger car or a truck).

[0023] The indefinite articles (“a”, “an”, “one”, and “ones”), particularly in the patent claims and in the description generally explaining the patent claims, are to be understood as such and not as numerals. Accordingly, components specified by these articles are to be understood as existing at least once and potentially existing multiple times.

[0024] The invention is explained in more detail below with reference to embodiments illustrated in the drawings. The drawings show, in simplified form: Fig. 1: a motor vehicle according to the invention; Fig. 2: a first embodiment of a cooling system according to the invention; Fig. 3: a second embodiment of a cooling system according to the invention; and Fig. 4: A diagram illustrating the change in pressure profile in coolant at the onset of boiling.

[0025] The Fig. Figure 1 shows a motor vehicle according to the invention with a cooling system 1 comprising an internal combustion engine.

[0026] The internal combustion engine can be used according to the Fig. 2 and Fig. 3 comprises an internal combustion engine 2 in the form of a reciprocating piston engine, which forms a plurality of cylinders 4 in a cylinder housing 3. The cylinders 4, together with pistons (not shown) moving up and down within them and a cylinder head 5, define combustion chambers in which fresh gas (mainly air) is combusted together with fuel, causing the pistons to move cyclically up and down. These piston movements are transmitted in a known manner to a crankshaft (not shown), thereby causing it to rotate. This rotating motion of the crankshaft can be transmitted to driven wheels 6 of the motor vehicle via a manual or automatic transmission (not shown), thus providing propulsion power for the motor vehicle.

[0027] The internal combustion engine or its components are, according to the Fig. 2 and Fig. 3 integrated into the cooling system 1, which comprises a first partial cooling system 7 (main cooling system) and a second partial cooling system 8 (secondary cooling system).

[0028] The main cooling system 7 of cooling system 1 according to the Fig. 3 serves to cool the internal combustion engine 2, the engine oil for lubricating the internal combustion engine 2, the (transmission) oil of a manual transmission (not shown) associated with the internal combustion engine 2, an exhaust gas turbocharger 9, in particular a bearing support of the exhaust gas turbocharger 9, and exhaust gas, which is returned via an exhaust gas recirculation line (not shown) from an exhaust stream (not shown) to a fresh gas stream (not shown) of the internal combustion engine. The main cooling system 7 comprises cooling channels 10, 11 of the cylinder housing 3 and the cylinder head 5, an engine 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 an EGR cooler 15, also integrated into the exhaust gas recirculation line.The main cooling system 7 further comprises a coolant radiator 16, two coolant pumps 17, 18, and a heater core 19. The coolant radiator 16, which can be bypassed as needed by means of an associated radiator bypass 20, serves to cool the coolant flowing through it by transferring heat energy to the ambient air, which also flows through the coolant radiator 16. The heater core 19, on the other hand, serves to warm and thus temper ambient air, which is intended for air conditioning the interior of the motor vehicle containing the internal combustion engine, as needed. Of the two coolant pumps 17, 18 of the main cooling system 7, one is designated as the main coolant pump 17, which can be driven either electrically or, preferably, directly or indirectly by an output shaft (in particular the crankshaft) of the internal combustion engine 2, i.e., mechanically.Even with such a mechanical drive for the main coolant pump 17, its specific delivery rate (i.e., related to the drive speed) can be controlled or regulated, and it can also be switched off (i.e., generating no relevant delivery rate despite the rotary drive). It can be provided that, in the switched-off state of the main coolant pump 17, the flow through it is either prevented or enabled. The second (auxiliary) coolant pump 18 of the main cooling system 7, on the other hand, is driven by an electric motor.

[0029] The distribution of the coolant supplied by the coolant pumps 17, 18 of the main cooling system 7 to different cooling circuits of the main cooling system 7 is controlled as required by means of a distribution device 21, which can be controlled by a control device 22 of the internal combustion engine.

[0030] The specific functioning of the main cooling system 7 is not of central importance for understanding the present invention, so a more detailed explanation is omitted in this regard.

[0031] The auxiliary cooling system 8 serves to cool the fresh gas (charge air) charged by a compressor of the exhaust gas turbocharger 9, which is supplied to the combustion engine 2 via the fresh gas stream, as well as a metering device 23, which is associated with an SCR catalyst (not shown) integrated into the exhaust stream and serves to introduce a reducing agent into the exhaust gas with the aim of reducing nitrogen oxides. A charge air cooler 24, which is provided for cooling the charge air supplied to the combustion engine, i.e., the fresh gas compressed by the compressor of the exhaust gas turbocharger, and a cooling channel provided for cooling the metering device 23 are integrated into parallel sections of a cooling circuit of the auxiliary cooling system 8.Furthermore, an electrically driven coolant pump 25 and a coolant radiator 26 are integrated into this cooling circuit (in the section not divided into the two lines). The coolant radiator 26 serves to recool the coolant flowing through the cooling circuit of the auxiliary cooling system 8 by transferring heat energy to the ambient air, which also flows through the coolant radiator 26. The coolant radiator 26 of the auxiliary cooling system 8 can also be bypassed by means of a radiator bypass 27. The distribution of coolant flowing through the auxiliary cooling system 8 to either the coolant radiator 26 or the associated radiator bypass 27 can be changed by means of a control valve 28, which can be controlled by the control device 22.

[0032] The temperature of the coolant during regular operation of the internal combustion engine can be significantly higher in the main cooling system 7 than in the secondary cooling system 8, at least in certain sections, so that the former can also be referred to as a high-temperature cooling system and the latter as a low-temperature cooling system.

[0033] Both the coolant cooler 16 of the main cooling system 7 and the coolant cooler 26 of the auxiliary cooling system 8 are assigned a (common) fan 29, which can be put into operation as required to increase or influence the cooling capacity of the coolant coolers 16, 26.

[0034] The partial cooling systems 7, 8 further comprise an expansion tank 30, which is partially filled with coolant and partially with air. The expansion tank 30 is fluidly connected to both the main cooling system 7 and the secondary cooling system 8 via a connecting line 31, which extends from the coolant-receiving (lower) section of the expansion tank 30. Furthermore, vent lines 32 with integrated check valves 33 connect the air-receiving (upper) section of the expansion tank 30 to various sections of the main cooling system 7 and to the secondary cooling system 8.

[0035] The one in Fig. The cooling system shown in Figure 3 differs from the one shown in Figure 3. Fig. 2 essentially only in the different design of the distribution device 21 and the actuating device, by means of which a demand-based distribution of the coolant flowing through the respective auxiliary cooling system 8 to the coolant radiator 26 and the associated radiator bypass 27 is realized. For this purpose, the cooling system according to the Fig. 3. Instead of the control valve 28, a self-regulating thermostatic valve 34 is provided. In the cooling system according to the Fig. Furthermore, the exhaust gas turbocharger 9 is not integrated into this. It is not cooled by the coolant of the cooling system.

[0036] Each of the cooling channels 10 of the cylinder housing 3, 11 of the cylinder head 5, 9 of the exhaust gas turbocharger, 15 of the EGR cooler, and 24 of the charge air cooler is assigned a pressure sensor 35, which is configured to detect high-frequency fluctuations or oscillations in the coolant pressure within these components. The measurement signals from these pressure sensors 35 are transmitted to the control device 22, which, acting as an evaluation device 22, determines from the measured pressure fluctuations whether there is a risk of boiling of the coolant contained in these components. The evaluation device 22 compares the detected pressure fluctuations with those defined as characteristic of the rupture of boiling bubbles.If a match is detected, a conclusion is drawn that boiling has begun or that there is an imminent risk of boiling, and by appropriately controlling at least one of the components of the cooling system that can be controlled by the control device 22, the temperature of the coolant that will subsequently flow through the component for which a risk of boiling has been detected is lowered.

[0037] The Fig. Figure 4 illustrates this using an example measurement profile for one of the pressure sensors 35. It can be seen that during initial boiling, fluctuations in the pressure p of the coolant occur, the amplitudes of which are significantly larger than those determined by the high-frequency (100 Hz) sampled pressure sensors 35 for coolant that does not exhibit boiling phenomena. REFERENCE MARK LIST 1 Cooling system 2 Internal combustion engine 3 cylinder housings 4 cylinders 5 cylinder head 6 wheels 7 first partial cooling system / main cooling system 8 Second partial cooling system / secondary cooling system 9 exhaust gas turbochargers 10 Cooling channel of the cylinder housing 11. Cylinder head cooling channel 12 Engine oil coolers 13 Gearbox oil coolers 14 Cooling channel in the EGR valve 15 EGR coolers 16 Coolant radiators of the main cooling system 17 Main coolant pump of the main cooling system 18 Auxiliary coolant pump of the main cooling system 19 heating heat exchangers 20 Main cooling system cooler bypass 21 Distribution device 22 Control and evaluation device 23 Dosing device 24 Intercoolers 25 Coolant pump of the auxiliary cooling system 26 Coolant cooler of the auxiliary cooling system 27. Cooler bypass of the auxiliary cooling system 28 Control valve 29 blowers 30 expansion tanks 31 Connecting line 32 Vent line 33 Check valve 34 Thermostatic valve 35 Pressure sensor

Claims

[1] Method for detecting boiling of a coolant in a cooling system (1) of a motor vehicle, wherein pressure fluctuations of the coolant are determined by means of a pressure sensor (35) and such pressure fluctuations which are defined as characteristic of a breakup of boiling bubbles are considered as a boiling of the coolant, characterized by the use of a pressure sensor (35) which is assigned to a cooling channel (10) of a cylinder housing (3) of an internal combustion engine (2) integrated into the cooling system (1), wherein at least temporarily a flow through the cooling channel (10) is prevented, wherein when a risk of boiling has been detected a flow through the cooling channel (10) is allowed. [2] Method according to claim 1, characterized by , that exceeding a limit value for the amplitude of pressure fluctuations is interpreted as the coolant boiling. [3] Method according to any one of the preceding claims, characterized bythe use of a pressure sensor (35) having a sampling rate of at least 50 Hz or at least 75 Hz or at least 100 Hz. [4] Method according to any one of the preceding claims, characterized by the use of a pressure sensor (35) that is directly exposed to the coolant. [5] Cooling system (1) for a motor vehicle comprising a (first) coolant pump (17, 18), a (first) coolant radiator (16) and a cooling channel (10) of a cylinder housing (3) of an internal combustion engine (2) as a (first) heat source, which are fluidly connected via coolant lines to a coolant contained therein, characterized bya (first) pressure sensor (35) configured to measure pressure fluctuations of the coolant in the cooling channel (10), and an evaluation device (22) connected to the (first) pressure sensor (35) via signal transmission, which is designed to automatically execute a method according to one of the preceding claims. [6] Cooling system (1) according to claim 5 comprising a first partial cooling system (7) comprising the components mentioned therein, characterized bya second partial cooling system (8) separated from the first partial cooling system (7), comprising at least a second coolant pump (25), a second coolant cooler (26) and a second heat source, which are connected to a coolant contained therein via coolant lines and which further comprises a second pressure sensor (35), wherein the second pressure sensor (35) is connected to an evaluation device (22) via signal transmission, which is designed in such a way that it can automatically execute a procedure in which pressure fluctuations of the coolant are detected by means of the second pressure sensor (35) and such pressure fluctuations, which are defined as characteristic of a breakup of boiling bubbles, are evaluated as a boiling of the coolant. [7] Internal combustion engine comprising an internal combustion engine (2) and a cooling system (1) according to claim 5 or 6.

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