GB2489519A

GB2489519A - Method for determining a coolant level in an engine coolant circuit

Info

Publication number: GB2489519A
Application number: GB1105541.5A
Authority: GB
Inventors: Roberto Argolini; Paolo Pasero; Luca Borgia
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2011-03-31
Filing date: 2011-03-31
Publication date: 2012-10-03
Also published as: GB201105541D0

Abstract

An automotive system (100, fig.1) comprises an internal combustion engine 110 provided with an engine coolant circuit 460, a coolant level sensor 464 and temperature sensors 465, 467. The automotive system also comprises an electronic control unit 450 in communication with the coolant level sensor and the temperature sensors, where the electronic control unit (ECU) is configured to generate a first signal when a coolant level in the engine coolant circuit is above or equal a predetermined coolant level threshold and to generate a second signal when the coolant level in the engine coolant circuit is below the predetermined coolant level threshold (see figure 4b). The ECU monitors a number of changes between the first and the second signal over a time interval and can thereby establish that the coolant level in the engine coolant circuit is close to the predetermined coolant level threshold on the basis of the monitored number of changes.

Description

5}IETHCO FOR DET NINDG A COOLANT LEVEL IN AN INTERNAL CC*IBUSTIC*T EN-

GINE COOLANT CIRCUIT

TEQUIQL flflD The present invention relates to an internal combustion engine, espe-cially an internal combustion engine of a motor vehicle, equipped with an engine coolant circuit and to a method for determining a coo-lant level in the engine coolant circuit.

BAVLD

It is known that internal combustion engines are conventionally equipped with an engine coolant circuit, in which a suitable engine coolant, typically a mixture of water and antifreeze, circulates in order to cool the engine block and thus prevent overheating that could lead to engine malfunctioning.

The engine coolant circuit generally comprises a tank for the coo-lant, a switchable pump for circulating the coolant, and a radiator for cooling the coolant once it has passed through the engine block and an engine control unit (ECU) for managing the engine coolant cir-cuit. The engine coolant circuit is normally provided with a coolant level sensor which generates a signal indicative of the quantity of coolant in the engine coolant circuit. Typically the signal generated by the coolant level sensor is used only to establish if the coolant tank is empty or not. However no indication is given that would con-sent to identify the situation when the coolant level in the coolant tank is close to a predetermined value, i.e. for instance the minimum value of coolant in the engine coolant circuit that guarantees the correct operation of the engine. Such an information could be valua-bly used for example to prevent additional overheating or component damaging due to the lack (or loss) of coolant. Furthermore currently it is not possible to recognize any coolant leakage during the normal running of the engine.

In view of the above, it is an object of an embodiment of the present invention to provide for a method to establish when the coolant in the engine coolant circuit is close or equal to a predetermined val-ue, for instance the minimum value.

Another object of an embodiment of the present invention is to use the determined coolant level to selectively provide for an overheat-ing engine protection strategy.

Another object of an embodiment of the present invention is to recog- nize any coolant leakage in the engine coolant circuit so as to fur- ther reduce the risk of component damaging by flagging a faulty func-tioning in the engine coolant circuit.

Still another object is to achieve the above mentioned objects with a simple, rational and rather inexpensive solution.

DIScLOSURE

These and/or other objects are achieved by the features of the embo- diments of the invention as reported in independent claims. The de- pendent claims recite preferred and/or particularly advantageous fea-tures of the embodiments of the invention.

In greater detail, an embodiment of the invention provides for a me-thod for determining a coolant level in an internal combustion engine comprising the steps of generating a first signal when a coolant 1ev-el in an engine coolant circuit is above or equal a predetermined coolant level threshold L,, generating a second signal when the coo-lant level in the engine coolant circuit is below the predetermined coolant level threshold L, monitoring a number of changes between the first and the second signal over a time interval, and establish-ing that the coolant level in the engine coolant circuit is close to the predetermined coolant level threshold on the basis of the moni-tored number of changes.

In this way, by analyzing the signal generated by the coolant level sensor it is possible to obtain additional information on the coolant level in the engine coolant circuit and in particular to identify the situation when the coolant level is close to the above named coolant level threshold which can be chosen for example as a minimum val-ue.

According to an aspect of the invention the method comprises the step of determining, in the establishing phase, that the coolant level is close to the predetermined coolant level threshold Lri if the moni- tored number of changes is above or equal a first predetermined thre-shold of number of changes 3n* In this way it is possible to establish that the coolant level is close to the minimum value by simply monitoring the number of changes between first and second signal and comparing it to a first predeter-mined threshold S. According to an aspect of the invention the method comprises the ad-ditional step of recording a fault of the engine coolant circuit if the monitored number of changes is below a second predetermined thre-shold of number of changesS.

Indeed if the number of changesis very small, for example only one, it means that the coolant level has abruptly decreased.

In this way, it is therefore possible to identify leakage in the en-gine coolant circuit and prevent any damage of the engine by flagging the malfunctioning of the engine coolant circuit.

According to another aspect of the invention a method for operating an internal combustion engine is provided which comprises the steps of determining a coolant level by applying the method for determining a coolant level defined above and applying a first engine overheating protection strategy if the determined coolant level is above or equal the predetermined coolant level threshold L, and applying a second engine overheating protection strategy if the determined coolant 1ev-el is below the predetermined coolant level threshold L11.

Advantageously the determined coolant level in the engine coolant circuit can be used to decide if a second overheating engine protec-tion strategy should be applied.

According to another aspect of the invention the second engine over-heating protection strategy comprises the step of reducing the engine performance.

In this way a predetermined reduction of the engine performance can be applied depending on the level of coolant in the circuit.

According to another aspect of the present invention the method for operating an internal combustion engine canprises the step of moni-taring a parameter indicative of a temperature of the engine and the first overheating protection strategy comprises the step of reducing the engine performance if the monitored parameter indicative of the temperature of the engine is above a predetermined temperature thre-shold; and the second overheating protection strategy comprises the step of cutting off the engine power if the monitored parameter in-dicative of the temperature of the engine is above the predetermined temperature threshold value.

Advantageously it is possible to prevent damaging of the components of the engine by monitoring a parameter indicative of the temperature of the engine and provide for reduction of the engine performance or a cut off of the engine power in case the temperature has reached values above a predetermined temperature threshold depending on pres-ence of coolant in the circuit.

According to another aspect of the present invention a coolant tem-perature is chosen as parameter indicative of the temperature of the engine.

By choosing a coolant temperature as a parameter indicative of the temperature of the engine it is advantageously possible to monitor the temperature of the engine without the need of additional compo- nents, in fact the coolant temperature is measured by a coolant tern-perature sensor which is a component typically already provided for in an internal combustion engine.

According to another aspect of the present invention a temperature of a metallic component of the engine is chosen as a parameter indica-tive of the temperature of the engine.

By choosing a temperature of a metallic component of the engine as parameter indicative of the temperature of the engine it is advanta- geously possible to use a more accurate indicator of the actual tern- perature of the components of the engine, the temperature of the en-gine block.

According to another aspect of the present the reduction of the en-gine performance in the first or in the second engine overheating protection strategy provides for an action chosen between one of the following: reducing the engine speed, reducing the engine load.

In this way, a predetermined reduction of the maximum number of rpm of the engine and/or reduction of the maximum load supplied by the engine can advantageously be applied in order to protect the engine components in case of overheating.

The methods according to an embodiment of the invention can be car- ried out with the help of a computer program comprising a program-code for carrying out the methods described above, and in the form of a computer program product comprising the computer program.

By way of example, the computer program product can be errdDodied an automotive system comprising an internal coritustion engine (ICE), an electronic control unit (ECU) coupled to a sensor and configured to receive a signal and send an output signal to control the ICE.

The ECU comprises a microprocessor and, a data carrier and an engine block and cylinder head having a coolant circuit, at least one sensor associated with the ICE and configured to generate a signal in pro-portion to an engine operating parameter (which may include a coolant level, a coolant temperature, and a block temperature). The computer program (OBD software) is stored in the data carrier which is in com- munication with the microprocessor such that the microprocessor ex-ecutes the computer program and the method described above is carried out.

The method could be also errbodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out the method.

BRIEF DEScRIPTIcfl OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 and 2 are a schematic representation of an automotive system comprising an internal combustion engine.

Figure 3 is a scheme of an internal combustion engine of a motor ye-hide of figure 1.

Figures 4a, 4b and 4c represent the variation of a coolant level sen-sor signal over the time in different circumstances.

Figure 5 is a flowchart representing the steps of the method accord-ing to an embodiment of the invention.

DETAILED DESCRIPTICN

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion cham- ber 150. A fuel and air mixture (not shown) is disposed in the com-bustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid conrnunication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may re-duce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to ex-pansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This exarrple shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust after-treatment devices 280. The after-treatment devic- S es may be any device configured to change the composition cf the ex-haust gases. Some examples of after-treatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems, and a diesel particulate filters.

Other embodiments may include an exhaust gas recirculation (EGR) sys- tem 300 coupled between the exhaust manifold 225 and the intake mani-fold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or de- vices associated with the ICE 110. The ECU 450 may receive input sig- nals from various sensors configured to generate the signals in pro-portion to various physical parameters associated with the ICE 110.

The sensors include, but are not limited to, a mass airflow and tem-perature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temper-ature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate qut-put signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT ac-tuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital cen'-tral processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive sig-nals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Figure 3 is a schematic representation of the internal combustion en-gine 110 of figure 1 and 2.

Figure 3 shows a schematic representation of an internal combustion engine 110 comprising an engine coolant circuit 112, in which a coo- lant, typically a fluid for example a mixture of water and anti-freeze, circulates so as to cool the engine block 120. The engine 110 is equipped with an electronic control unit 450 (ECU) which controls the operation of the engine 110 and regulates the engine coolant cir-cuit 460 through an on board diagnostic (OBD) software.

The engine coolant circuit 460 comprises a coolant tank 461 used as a container for the coolant, a switchable pump 462 for circulating the coolant in the engine coolant circuit 460, and an engine coolant ra- diator 463 for cooling the coolant once it has passed through the en-gine block 120.

The engine coolant radiator 463 is a liquid-air heat exchanger, which is often located in the rear part of the motor vehicle, and which is generally associated with a fan (not shown) that blows air through it in order to improve the efficiency of the heat exchange between coo-lant and air.

The engine coolant circuit 460 is equipped with a coolant level sen-sor 464, located in the coolant tank 461. The coolant level sensor 464 generates a signal which depends on the coolant level in the coo-lant tank 461. The coolant level could be expressed by using other parameters, and relative sensors, such as for example the quantity of coolant which, due to the geometry of the engine coolant circuit 460, is obviously proportional to the coolant level.

The coolant level sensor 464 is connected to the electronic control unit 450 wherein the OBD software provides for the analysis of the signal generated by the coolant level sensor 464.

The engine coolant circuit 460 is equipped with a coolant temperature sensor 465, for example a thermostat, for measuring a parameter in- dicative of the temperature of the coolant in the engine coolant cir-cuit 460, for example the value of the temperature of the coolant.

The coolant temperature sensor 465 is connected via a connecting line 466 to the electronic control unit 450 which monitors the variation of the temperature of the coolant over time.

The engine coolant circuit 460 is also equipped with a metallic com- ponent temperature sensor 467, for example a thermometer or a thermo-couple, placed in contact with a metallic component of the engine block 120 so as to measure a value indicative of the temperature of the engine block 3, for example the value of the temperature of the metallic component of the engine block 3.

The metallic component temperature sensor 467 is connected via a con-necting line 468 to the electronic control unit 450 which monitors the variation of the temperature of the metallic component of the en-gine 110 over time.

In the normal functioning of the engine 110 the coolant level sensor 464 generates a first signal if the coolant level is above or equal a predetermined coolant level threshold L11. The predetermined coolant level threshold L11 represents the minimum coolant level in the engine coolant circuit 460 guaranteeing a correct functioning of the engine 110, i.e. the level that guarantees an appropriate cooling of the en- gine block 120 even in case of overheating. The coolant level thre- shold ki can be determined in an empirical calibration phase and de- pends on various factors comprising for example the type and dimen-sion of the coolant tank 461 and the type of coolant.

If the coolant level is below the predetermined coolant level thre-shold L the coolant level sensor 464 generates a second signal. When the coolant level in the coolant tank 461 changes, for example when the coolant tank 461 is emptied or when the coolant tank 461 is re-filled, the signal generated changes between first and second signal, or vice-versa.

First and second signal could be represented by the same signal with a different value of a characterizing parameter, i.e. frequency or amplitude.

The method for determining a coolant level in the internal combustion engine will now be described together with the relative method for operating an internal combustion engine 110 which is schematically shown in figure 5.

During normal operation of the engine 110 the coolant level sensor 464 generates a first or second signal depending on the coolant level vis-à-vis of the predetermined coolant level threshold Lj..

If the coolant level is above or equal the predetermined coolant 1ev-el threshold L, i.e. the coolant tank 461 is full or in any case above the minimum coolant level, the first signal is generated, Fig-ure 4a.

If the level of coolant is below the predetermined coolant level threshold L, i.e. the coolant tank 461 is empty or almost empty, the second signal is generated.

The method comprises the step of monitoring the variation of the sig-nal generated by the coolant level sensor 464 in a predetermined time interval, for example a time interval in the order of 50 seconds.

If the coolant level is stable, the same signal (first or second) is generated over the time interval and no changes occur. In case of variation of coolant level a switch between the first and the second signal might occur. This normally happens when the variation of coo-lant is such as to move the coolant level above or below the coolant level threshold L, i.e. for exariple enough coolant has left the coo-lant tank 461 to reduce the level of coolant below the minimum value.

Furthermore if the coolant level is close to the coolant level thre-shold L, i.e. the coolant tank 461 has a quantity of coolant very close to the minimum value, a multiple number of changes are expected to be detected in the same time interval. Those changes are in fact caused by oscillations of the coolant level around the coolant level threshold L caused by the normal movements of the engine 110 in oper-ation. Therefore if, in a time interval, a number of changes greater than a predetermined threshold number of changes S is observed (Fig-ure 4b) it can be established that the coolant level in the engine coolant circuit 460 is close to the coolant level threshold L, i.e. the coolant in the coolant tank 461 is equal to, slightly greater or slightly smaller than the minimum value. For example if in a time in-terval of 50 seconds more than 5 changes occur it can be assumed that the coolant level is close to the coolant level threshold L,. The predetermined threshold number of changes ST1 can be determined in a calibration phase and it can vary depending on the engine working condition on which the method is applied.

Mother situation can be identified by analyzing the variation of the signal in a time interval as indicated in Figure 4c. In a predeter-mined time interval, the first signal is generated and then abruptly the second signal is generated instead of the first signal. The ab-rupt change could normally be explained by a damage in the engine coolant circuit 460 causing leakage of the coolant out of the engine coolant circuit 460. A similar situation could occur if the number of changes between first and second signal is below a predetermined threshold of number of changes S, typically a small number of changes for example 3. The reason for the leakage could be for example a dis-connection of a tube. A record of this event is memorized in the electronic control unit 450 and it can be used as a flag for a ser-vice request of the engine coolant circuit 460.

In a normal functioning of the engine 110 the 0DB software is confi-gured to apply an overheating engine protection strategy to protect the engine in case of overheating. Normally this strategy envisages monitoring a parameter indicative of the temperature of the engine and reducing the maximum engine speed and or the maximum engine load if the monitored parameter is above a predetermined temperature thre- shold. The predetermined temperature threshold is set in a calibra- tion phase and depends on many factors comprising the type of parame- ter used as indicative of the temperature of the engine and corres-ponds to the temperature above which the engine components could be damaged if still in operation.

The overheating engine protection strategy is typically applied inde- pendently on the coolant level. To improve the protection of the en-gine in case of overheating while guaranteeing at the same time the best possible engine performance, the coolant level can be used as basis for choosing if to apply the current overheating engine protec-tion strategy or a new overheating engine protection strategy adapted for the diminished amount of coolant in the engine coolant circuit 460. According to an erthodiment of the invention the method comprises the step of applying a second overheating engine protection strategy when the coolant level is below the minimum.

The 0DB software can be configured to selectively apply the first or the second overheating engine protection strategy depending on the coolant level determined by the analysis of the signal generated by the coolant level sensor 464 as described above.

The second overheating engine protection strategy comprises one or more of the following actions: a reduction of the engine speed and a reduction of the engine load. By reducing the maximum torque and the number of rpm, the engine performance is restricted in such a way to avoid any damaging due to overheating, damage that would be exacer-bated by the lack of coolant in the engine coolant circuit 460. The amount of reduction of maximum speed or load can be of the same mag-nitude as per the first overheating engine protection strategy or can assume different values. Maximum values can be empirically determined during a calibration activity.

According to both first and second engine overheating protection strategies a parameter indicative of the temperature of the engine is monitored. When the monitored parameter is above predetermined thre- sholds the first cverheating protection strategy provides for a re-duction of the engine performance and the second engine protection strategy provides for the cut off of the engine power.

According to the first engine overheating protection strategy the maximum temperature threshold T is set to a threshold value Ti if the coolant temperature is used as parameter indicative of the tern-perature of the engine and is set to a threshold value T usually different from threshold value Tie, if the temperature of a metallic component of the engine is used as parameter indicative of the tern-perature of the engine 1.

According to the first engine overheating protection strategy the OBD software provides for a reduction of the engine speed and of the load if the measured temperature of the coolant exceeds the corresponding predetermined threshold value Ti or if the measured temperature of the metallic component of the engine exceeds the corresponding prede-termined threshold value T11. If the engine coolant circuit 460 is equipped with both coolant temperature sensor 465 and metallic compo- nent temperature sensor 467, as soon as one of the two threshold val-ues T1 or is exceeded by its respective measured temperature, the engine performance is reduced by reducing engine load and speed. De-pending on the positions of the sensors 465,467, the calibration of the relative threshold values the type of sensors 465,467 and their relative response time, threshold values Ti or T can be ex- ceeded first. The threshold values Ti and T can be empirically de-termined during a calibration activity.

In the second engine overheating protection strategy the maximum tem- perature threshold is set to threshold value T2 if the coolant tem-perature is used as parameter indicative of the temperature of the engine and is set to threshold value T, usually different from thre- shold value T2, if the temperature of a metallic component of the en-gine is used as parameter indicative of the temperature of the engine 110.

According to the second engine overheating protection strategy the OBD software provides for a cut off of the engine power if the meas- ured temperature of the coolant exceeds the corresponding predeter- mined threshold value T20 or if the measured temperature of the metal-lic component of the engine exceeds the corresponding predetermined threshold value T. If both sensors are present as soon as one of the two threshold values Ta or T is exceeded by its respective measured temperature the 0DB software provides for the cut off of the engine power. As for the first engine overheating protection strategy, de-pending on the positions of the sensors 465,467, the calibration of the relative thresholds, the type of sensors 465,467 and their rela-tive response time, T2 or T»= threshold values can be exceeded first.

The threshold values T2 and can be empirically determined during a calibration activity.

Normally threshold value T is lower than threshold value T, i.e. the maximum allowable temperature of the metallic component is lower in the case of low coolant level compared to the case of coolant above the minimum threshold. In the same way also threshold value T2 is normally lower than threshold value Tie, i.e. the maximum allowable temperature of coolant is lower in the case of low coolant level or lack of coolant compared to the case of coolant above the minimum threshold.

In this way, for low coolant level the maximum temperatures allowed are lowered, both for the metallic component of the engine and for the coolant; consequently the engine is protected more efficiently by allowing a greater increase in temperature of the engine if there is enough coolant in the engine coolant circuit 460 and by cutting off the engine power earlier if the coolant in the coolant tank 461 is not enough. In fact due to decreased amount of coolant, an increased temperature would be more damaging to the engine 1; by setting lower temperature threshold values the 008 software anticipates problematic overheating situations by anticipating the power cut off of the en-gine 110 compared to a situation with enough coolant.

Figure 5 represents a schematic overview of an enbodiment of the present invention. During the normal function of the engine 110 ECU 450 monitors the engine temperature and the coolant level, block 11, where the coolant level is determined according to the method de-scribed above. Depending on the coolant level the ECU 450 decides what protection strategy to errploy. In particular if the coolant lev- el is equal or above the coolant level threshold L the first over-heating engine protection strategy, block 510, is applied otherwise the second overheating engine protection strategy, block 520, is ap- plied. According to a first embodiment of the invention, if the coo- lant level is equal to the coolant level threshold L,, an engine ser-vice is need, and a flag for service is automatically recorded, block 13. Then the presence of a metallic temperature sensor 467 is checked, block 14. If the engine coolant circuit 460 comprises a me- tallic temperature sensor 467 then a parameter indicative of the tem-perature of the metallic component of the engine block 120 is used as reference temperature and then the maximum temperature allowable is set equal to T, block 15. If the engine coolant circuit 460 does not comprise a metallic temperature sensor 467 then a parameter indica-tive of the temperature of coolant in the engine coolant circuit 460 is used as reference temperature and then the maximum temperature al- lowable is set equal to Tie, block 16. At this point the actual tem-perature as measured by the sensor selected according to block 15 and 16 is compared to the maximum temperature, if the temperature meas-ured is above the maximum temperature then the ECU 450 provides for an engine performance reduction otherwise the process starts again from block 11. According to a second ertodiment of the invention, if the coolant level is below the coolant level threshold 1-rn, an engine service is need, and a flag for service is automatically recorded, block 19. Successively the presence of a metallic temperature sensor 467 is checked, block 20. If the engine coolant circuit 460 comprises a metallic temperature sensor 467 then a parameter indicative of the temperature of the metallic component of the engine block 120 is used as reference temperature and then the maximum temperature allowable is set equal to T, block 21. If the engine coolant circuit 460 does not comprise a metallic temperature sensor 467 then a parameter in-dicative of the temperature of coolant in the engine coolant circuit 460 is used as reference temperature and then the maximum temperature allowable is set equal to T2, block 22. In this case, independently on the temperature an engine performance reduction is applied, block 23.

Only at this point, block 24, the actual temperature, as measured by the sensor selected according to block 21 and 22, is compared to the maximum temperature. If the measured temperature is above the maximum temperature then the ECU 450 provides for a power cut off of the en-gine, block 25, otherwise the process starts again from block 11.

While at least one exemplary embodiment has been presented in the foregoing sumary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing surrutiary and detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERflEES 100. Automotive System 110. Internal Combustion Engine 112. Engine coolant circuit 120. Engine Block 125. Cylinder 130. Cylinder head 135. Camshaft 140. Piston 145. Crankshaft 150. Combustion chamber 155. Cam phaser 160. Fuel injector 170. Fuel Rail 180. Fuel Puir 190. Fuel source 200. Intake Manifold 205. Intake duct 210. Intake port 215. Valve 220. Exhaust Port 225. Exhaust manifold 230. Turbocharger 240. Compressor 250. Turbine 260. Intercooler 270. Exhaust system 275. Exhaust pipe 280. Exhaust after-treatment device 290. VGT actuator 300. EGR system 310. EGR cooler 320. EGR valve 330. Throttle Body 340. Mass airflow and temperature sensor 350. Manifold pressure and temperature sensor 360. Combustion pressure sensor 380. Coolant and oil temperature and level sensors 400. Fuel rail pressure sensor 410. Cam position sensor 420. Crank position sensor 430. Exhaust pressure and temperature sensors 440. EGR temperature sensor 445. Accelerator pedal position sensor 450. Electronic Control Unit 460. Engine coolant circuit46l. Coolant tank 462. Coolant pump 463. Radiator 464. Coolant level sensor 465. Coolant temperature sensor 466. Coolant temperature sensor connecting line 467. Metallic component temperature sensor 468. Metallic component temperature sensor connecting line

Claims

1. A method for determining a coolant level in an engine coolant circuit (110) comprising the steps of: (a)generating a first signal when a coolant level in an engine coolant circuit (460) is above or equal a predetermined coolant level threshold (Lu); (b)generating a second signal when the coolant level in the en-gine coolant circuit (460) is below the predetermined coolant level threshold (L,i); (c)monitoring a number of changes between the first and the second signal over a time interval; and (d)establishing that the coolant level in the engine coolant cir-cuit (460) is close to the predetermined coolant level threshold (I) on the basis of the monitored number of changes.

2. A method according to claim 1 wherein the establishing phase (d) comprises the step of determining that the coolant level is close to the predetermined coolant level threshold (L) if the moni-tored number of changes is above or equal a first predetermined threshold (ST1) of number of changes.

3. A method according to claim 1 or 2 domprising the additional step of recording a fault of the engine coolant circuit if the moni-tored number of changes is below a second predetermined threshold (S)of number of changes.

4. A method for operating an internal combustion engine (110) com-prising the steps of: determining a coolant level according to claim 1, 2 or 3 applying a first engine overheating protection strategy if the determined coolant level is above or equal the predetermined coo-lant level threshold (L,ri); and applying a second engine overheating protection strategy if the determined coolant level is below the predetermined coolant level threshold (Lu).

5. A method according to claim 4, wherein the second engine over- heating protection strategy comprises a step of reducing the en-gine performance.

6. A method according to claim 4 or 5 comprising the step of: monitoring a parameter indicative of a temperature of the engine (1); and wherein the first overheating protection strategy comprises the step of reducing the engine performance if the monitored pa-rameter indicative of the temperature of the engine (110) is above a predetermined temperature threshold; and the second overheating protection strategy comprises the step of cutting off the engine power if the monitored parameter indic- ative of the temperature of the engine (110) is above the prede-termined temperature threshold.

7. A method according to claim 6 wherein a coolant temperature is chosen as a parameter indicative of the temperature of the engine (110).

8. A method according to claim 6 wherein a temperature of a metallic component of the engine (110) is chosen as a parameter indicative of the temperature of the engine (110).

9. A method according to any claim from 4 to 8 wherein the reduction of the engine performance provides for an action chosen between one of the following: reducing the engine speed, reducing the en-gine load.

10. A computer program comprising a computer-code for performing the methods according to any claim from 1 to 9.

11. Computer program product on which the computer program according to claim 10 is stored.

12. Internal combustion engine (110) comprising an engine coolant circuit (460) a coolant level sensor (464), an engine control unit (450), a temperature sensor (467, 465) a data carrier asso-ciated with the engine control unit (460) and a computer program according to claim 9 stored in the data carrier.

13. An automotive system (100) comprising an internal combustion en- gine (110) provided with an engine coolant circuit (460) a coo-lant level sensor (464)and a temperature sensor (467, 465), the automotive system (100) also comprising an electronic control unit (450) in communication with the coolant level sensor (464) and the temperature sensor (467, 465) and configured to: generate a first signal when a coolant level in an engine coolant circuit (460) is above or equal a predetermined coolant level threshold a) generate a second signal when the coolant level in the en- gine coolant circuit (460) is below the predetermined coo-lant level threshold (La); b) monitor a nuither of changes between the first and the second signal over a time interval; and c) establish that the coolant level in the engine coolant cir- cuit (460) is close to the predetermined coolant level thre-shold (L1) on the basis of the monitored number of changes