SE1650881A1

SE1650881A1 - A method and a system for detecting an obstacle in a coolingsystem

Info

Publication number: SE1650881A1
Application number: SE1650881A
Authority: SE
Inventors: Jarelius Sofie
Original assignee: Scania Cv Ab
Priority date: 2016-06-21
Filing date: 2016-06-21
Publication date: 2017-12-22
Also published as: BR102017010655A2; DE102017005430A1; SE541824C2; DE102017005430B4

Abstract

A method for detecting an obstacle preventing an air flow in an air passageway (13) across a radiator (4) configured to cool liquid coolant in a cooling system (1), comprising the steps of:a) determining an actual cooling capacity and an expected cooling capacity of the radiator,b) comparing said actual and expected cooling capacities to determine a deviation in the actual cooling capacity from the expected cooling capacity,c) assessing whether the deviation as determined on a specific occasion differs from a reference value determined based on previously determined values of said deviation,d) based on the assessment carried out in step c, determining whether an obstacle to the air flow has been introduced or removed in the air passageway prior to said specific occasion.

Description

A method and a svstem for detectinq an obstacle in a coolinq system TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for detecting an obstaclepreventing an air flow in an air passageway across a radiator in acooling system according to the preamble of claim 1. lt also relatesa system according to the preamble of the independent systemclaim, a computer program, a computer program product, anelectronic control unit and a motor vehicle. ln particular, but notexclusively, the invention relates to a method and a system fordetecting an obstacle preventing an air flow across a radiator in acooling system of a motor vehicle. An obstacle is in this context toe.g.passageway, a grille shutter, a radiator blind, etc. be understood as contaminations clogging the air BACKGROUND AND PRIOR ART Cooling systems in motor vehicles commonly rely on intake ofambient air for cooling liquid coolant passing through a radiatorplaced in an air passageway. The liquid coolant is in turn used forcooling e.g. an internal combustion engine or other components orsystems that need cooling, such as e.g. auxiliary power units. lnmotor vehicles equipped with turbochargers, a charge air cooler(CAC) is used to cool the air from the turbocharger before it isforced into the cylinders of the engine. The CAC is sensitive tofreezing when the ambient air temperature is low, and it is therefore common to protect the CAC by placing a radiator blind or a shutter upstream of the CAC, i.e. in, or just downstream of,an air inlet of the cooling system. Such a shutter or radiator blindreduces the air flow and thereby protects the CAC from freezing,but it also affects the cooling capacity of the cooling systemnegatively. Therefore, it is only desirable to use radiator blinds orshutters when needed due to the ambient conditions. Radiatorblinds are therefore typically mounted as a cold season begins,and are not removed until the end of that season approaches.However, at the end of the season, it is easy to forget that aradiator blind has been mounted. Failure to remove the radiatorblind leads to increased fuel consumption and it is thereforedesirable to be able to easily see whether there is a radiator blind mounted or not.

US20140150756 discloses a method for identifying malfunction ofa grille shutter mounted upstream of a CAC in a cooling system ofa motor vehicle. The method uses an air temperature differenceacross the CAC to determine whether the actual cooling capacityof the CAC differs from its expected cooling capacity, and basedthereon, it is identified whether e.g. the grille shutter is closedeven though it is expected to be open. However, this methodrequires that the temperature of the air can be accuratelydetermined both upstream and downstream of the CAC. The method is therefore not suitable for all kinds of cooling systems.

SUMMARY OF THE INVENTION lt is a primary objective of the present invention to provide an, in at least some aspect, improved solution for detecting an obstacle preventing an air flow in an air passageway across a radiator in a cooling system. ln particular, it is an objective to provide such asolution which is robust and reliable and which can be applied in a motor vehicle.

At least the primary objective is, according to a first aspect of theinvention, achieved by means of the initially defined method,comprising the steps of: a) repeatedly over time determining an actual cooling capacityof the radiator and an expected cooling capacity of theradiator, b) comparing said actual cooling capacity and said expectedcooling capacity to determine a deviation in the actualcooling capacity from the expected cooling capacity, c) assessing whether a value of said deviation determined on aspecific occasion differs from a reference value, which reference value is determined based on previouslydetermined values of said deviation, d) based on the assessment carried out in step c, determiningwhether an obstacle to the air flow has been introduced orremoved in the air passageway prior to said specific occasion.

By comparing the actual cooling capacity and the expected coolingcapacity of the radiator over time, it is possible to detect whetheran obstacle has been introduced into or removed from the airpassageway. The values of the determined actual cooling capacityand the expected cooling capacity, or a value representing thedifference between those two, are stored in a memory. Thereference value is determined based on previously stored such values. The determination can be performed at a predetermined frequency, such as once a day or once a week, or after travellinga certain mileage, or when the ambient conditions have changedby a significant amount since the last determination, or based onsome other condition. The obstacle can either be one that hasbeen introduced or removed suddenly between said specificoccasion and an occasion of determination directly preceding saidspecific occasion, such as a radiant blind or a grille shutter, or onethat has developed gradually over time, such as contaminationhaving accumulated in the air passageway. The method accordingto the invention allows an obstacle in the air passageway to bedetected without having to measure the air temperature at differentlocations within the cooling system. Thereby, mounting of air temperature sensors within the cooling system can be avoided.

According to one embodiment, in step a, determining the expectedcooling capacity of the radiator comprises determining a mass flowof coolant through the radiator and estimating an expected massflow of air across the radiator, and based thereon estimating theexpected cooling capacity of the radiator. The mass flow of coolantcan e.g. be accurately determined using signals from one or morepumps, valves and/or thermostats in the cooling system. Theexpected mass flow of air can be estimated using knowncharacteristics of a fan or similar used to suck air across theradiator, and external factors such as ambient air temperature and pressure as well as a current headwind.

According to one embodiment, estimating the expected mass flowof air comprises measuring an ambient air temperature, anambient air pressure, and a rotational speed of at least one fan causing air to flow across the radiator, and based thereon estimating the expected mass flow of air. This gives an accurateestimate of the expected mass flow of air, since the ambientconditions are easy to measure with accuracy and the rotationalspeed and other characteristics of the fan, such as the size andshape, are usually well defined. Also the headwind can be taken into account.

According to one embodiment, predefined values and/or curvesare used in the determination of the expected cooling capacity.Tabulated values can be used. Such tabulated or predefinedvalues or curves are preferably used together with a model of thecooling system. For example, it is known that for a certain type ofradiator, a particular mass flow of air across the radiator at certainambient conditions and a certain mass flow of coolant areexpected to bring about a known cooling of the liquid coolant withinthe radiator. Thus, the expected cooling capacity can be derivedusing a known relationship between the mass flow of coolant, themass flow of air and the cooling capacity for that particularradiator. However, if an obstacle is present in the air passageway,the actual cooling capacity is reduced in comparison with the expected cooling capacity.

According to one embodiment, in step a, determining the actualcooling capacity of the radiator comprises measuring a mass flowof coolant through the radiator. The mass flow of coolant can beaccurately measured using e.g. a mass flow meter, or signals fromone or more pumps, valves and/or thermostats regulating the flowof liquid coolant within the cooling system, such as rotationalspeed and displacement of the pump or pumps and a degree of openness of the valve or valves and/or thermostat. The actual cooling capacity is determined based on the measured mass flowof coolant in combination with other parameters, such as a temperature difference within the cooling system.

According to one embodiment, in step a, determining the actualcooling capacity of the radiator further comprises measuring acoolant temperature before and after the radiator and basedthereon determining a coolant temperature difference, and basedon said coolant temperature difference and said mass flow ofcoolant determining the actual cooling capacity of the radiator.This is a robust and easy way to determine the actual coolingcapacity. Temperature sensors can be provided on each side ofthe radiator, or on each side of the engine or heat generating unit.The temperature is thereby measured on one hand after the engineand before the radiator, and on the other hand after the radiator and before the engine in the direction of flow.

According to one embodiment, in step a, determining the actualcooling capacity of the radiator further comprises measuring acoolant temperature at two different points in time and basedthereon determining a coolant temperature difference, and basedon said coolant temperature difference and said mass flow ofcoolant determining the actual cooling capacity of the radiator.This is an alternative way of determining the actual coolingcapacity with only one temperature sensor for measuring thetemperature of the liquid coolant within the cooling system. Theamount of heat provided to the coolant liquid from e.g. the engineis related to the amount of energy converted by the engine, whichcan be estimated based on the type of fuel, the thermal efficiency of the combustion process, the amount of consumed fuel and the layout of the cooling system. The actual cooling capacity is in thiscase determined based on the assumption that the coolingcapacity is constant over the two different points in time, i.e. thatthe engine or heat generating unit as well as the radiator hasreached a steady state and that the mass flow of coolant and themass flow of air are constant. A thermostat regulating the flow ofcoolant to the radiator is set to a predefined degree of opennesssuch that the mass flow of coolant through the radiator is wellknown. Thus, in this embodiment, the method preferablycomprises regulating the mass flow of coolant through the radiatorto a predefined value, and thereafter measuring the coolanttemperature at a first point in time and at a second point in time.Regulating the mass flow can be achieved e.g. by setting athermostat regulating the mass flow through the radiator to a predefined degree of openness.

According to one embodiment, in step d, it is determined that anobstacle has been introduced or removed if the value of saiddeviation differs from the reference value by more than apredetermined threshold amount. This is an efficient way todetermine that an obstacle has been introduced or removed. Thethreshold amount can be expressed e.g. as a percentage of the reference value or as an absolute number.

According to one embodiment, given that it is in step d determinedthat an obstacle has been introduced or removed, the methodfurther comprises the step of classifying said obstacle based onthe value of said deviation. Said obstacle can e.g. be classified asdirt, or as a radiator blind. Different threshold amounts can be used to classify the obstacle. The classification of the obstacle gives useful input to e.g. a driver of a motor vehicle in which the coolingsystem is mounted, or to a service station, as to which measures can be taken to improve the cooling capacity of the cooling system.

According to one embodiment, given that it is in step d determinedthat an obstacle has been introduced or removed, the methodfurther comprises the step of changing a status code reflecting astatus of the air passageway. The status can be used to send amessage to a driver of a motor vehicle comprising the coolingsystem that an obstacle has been introduced or removed into theair passageway. For example, status codes may be setrepresenting the cases “radiator blind mounted", “air passageway free”, and “air passageway contaminated”.

According to another aspect of the present invention, the abovementioned primary objective is achieved by means of a system fordetecting an obstacle preventing an air flow in an air passagewayacross a radiator in a cooling system, comprising: - means configured to repeatedly over time determine anactual cooling capacity of the radiator and an expectedcooling capacity of the radiator, - means configured to compare said actual cooling capacityand said expected cooling capacity to determine a deviationin the actual cooling capacity from the expected coolingcapacüy, - means configured to assess whether a value of saiddeviation determined on a specific occasion differs from areference value, which reference value is determined based on earlier determined values of said deviation, - means configured to, based on said assessment, determinewhether an obstacle to the air flow has been introduced orremoved in the air passageway prior to said specific occasion.

Advantages and advantageous features of such a system appear from the above description of the proposed method.

The invention also relates to a computer program comprisingcomputer program code for causing a computer to implement theproposed method when the computer program is executed in thecomputer, a computer program product comprising a data storagemedium which can be read by a computer and on which theprogram code of the proposed computer program is stored, anelectronic control unit of a motor vehicle comprising an executionmeans, a memory connected to the execution means and a datastorage medium which is connected to the execution means andon which the computer program code of the proposed computerprogram is stored, and a motor vehicle comprising the proposedelectronic control unit.

Further advantages as well as advantageous features of the present invention will appear from the following detailed descnpüon.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will in the following be described with reference to the appended drawings, in which: Fig. 1 schematically shows a cooling system of an engine ina motor vehicle, Fig. 2 is a flow chart schematically showing the steps of amethod according to an embodiment of the invention, Fig. 3 shows the ratio of actual cooling capacity and expectedcooling capacity as a function of time for a radiator, Fig. 4 is a flow chart schematically showing substeps of amethod according to an embodiment of the invention, Fig. 5 is a flow chart schematically showing substeps of amethod according to an embodiment of the invention, Fig. 6 is a flow chart schematically showing substeps of amethod according to an embodiment of the invention, Fig. 7 shows cooling capacity curves of a radiator, and Fig. 8 shows a schematic drawing of a control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION A cooling system 1 of a combustion engine 2 within a motor vehicleis schematically shown in fig. 1. A liquid coolant channel 3 in theform of a closed loop extends from a radiator 4 toward the engine2, through a retarder 5 and back to the radiator 4. A pump 6 forpumping the liquid coolant is provided between the radiator 4 and7 for temperature of the liquid coolant is provided between the engine the engine 2, a temperature sensor measuring the2 and the retarder 5, and a thermostat 8 is mounted upstream ofthe radiator 4, allowing the amount of liquid coolant that iscirculated through the radiator 4 to be regulated. A bypass channel 9 bypassing the radiator extends from the thermostat to the pump 11 6, so that the thermostat 8 divides the flow of coolant between theradiator 4 and the bypass channel 9 depending on its degree of OpenneSS.

An exhaust channel 10 configured to carry exhaust gases extendsfrom a turbocharger 11 via a charge air cooler (CAC) 12 to theengine 2. An air passageway 13 is provided for carrying ambientair across the CAC 12 and the radiator 4 by means of a fan 14,cooling the exhaust gases within the CAC 12 and the liquid coolantwithin the radiator 4. An air conditioner condenser 15 is located upstream of the CAC 12 in the direction of flow of ambient air.

A control unit 80 configured to control the cooling system 1 is alsoprovided. The control unit 80 is connected to the various sensorsand units of the cooling system and can send and receive signalsto/from those sensors and units, either wirelessly or by means ofwires. Data can also be stored in a memory 82 of the control unit 80, as illustrated in fig. 8 and described further ahead. ln operation of the cooling system 1, the temperature sensor 7senses the temperature of the liquid coolant and the temperaturevalue is communicated to the control unit 80, which controls thedegree of openness of the thermostat 8 such that the liquid coolantflow is suitably divided between the radiator 4 and the bypass channel9.

A method for detecting an obstacle preventing the air flow in theair passageway 13 according to the invention is schematicallyillustrated in fig. 2. The method can e.g. be performed in a cooling system 1 of a combustion engine 2 in a motor vehicle such as the 12 one shown in fig. 1. ln a step 100, which is performed repeatedlyover time, an actual cooling capacity Q_rea| of the radiator 4 isdetermined. ln a step 200, which is performed in connection withthe step 100, an expected cooling capacity Q_exp of the radiator4 is determined. The steps of determining the actual coolingcapacity Q_rea| and the expected cooling capacity Q_exp can becarried out in various different ways depending on e.g. the designof the cooling system, and will be explained in greater detail further ahead. ln a step 300, the actual cooling capacity Q_rea| and the expectedcooling capacity Q_exp are compared to determine a deviation öin the actual cooling capacity Q_rea| from the expected coolingcapacity Q_exp. The deviation ö can be expressed e.g. in terms ofa difference between the actual cooling capacity Q_rea| and theexpected cooling capacity Q_exp, as a ratio thereof, or as apercentage. The value of the deviation ö is stored in a memory. lnfig. 3, the deviation ö expressed in terms of a ratio between theactual cooling capacity Q_rea| and the expected cooling capacity Q_exp is shown as a function of time. ln a step 400, it is assessed whether a value of this deviation ö,as determined on a specific occasion, differs from a referencevalue ö_ref. The reference value ö_ref is a value which thedeviation ö is expected to have based on previously determinedvalues of the deviation ö. For example, it the deviation ö has been increasing slowly over time, a slightly increased value is expected. ln a step 500, it is determined whether, based on the assessment carried out in the previous step, an obstacle to the air flow has 13 been introduced or removed in the air passageway 13 prior to thisspecific occasion, or, more specifically, between this specificoccasion of determining the deviation ö and the previous occasion.For example, it can be determined that an obstacle has beenintroduced or removed if the value of the deviation ö differs fromthe reference value ö_ref by more than a predetermined thresholdamount. ln fig. 3, an obstacle in the form of a radiator blind (notshown) is introduced into the air passageway 13 prior to the timet3 and removed from the air passageway prior to the time t4, atwhich an increase in actual cooling capacity Q_rea| occurs. lf thedeviation ö does not differ significantly from the reference valueö_ref, a large value of the deviation ö may still be used as anindicator that the air passageway 13 is contaminated and that aservice is needed. lf, in step 500, it is not determined that anobstacle has been introduced or removed, steps 100-500 arerepeated on a later occasion, such as the following day or the following week. ln an optional step 600, which is only performed if it is in step 500 determined that an obstacle has been either removed orintroduced, the identified obstacle is classified based on the valueof the deviation ö. For example, if the deviation ö differs from thereference value ö_ref by more than the predetermined thresholdamount, the obstacle may be classified as a radiator blind. lf thedeviation ö differs from the reference value ö_ref by less than thepredetermined threshold amount, the obstacle may be classified as dirt or similar. ln an optional step 700, only performed if it is in step 500 determined that an obstacle has been either removed or 14 introduced or that the deviation ö has exceeded a predeterminedthreshold, that contaminated, a status code indicating the air passageway is heavilyreflecting a status of the airpassageway is changed. A message can be sent to a driverincluding e.g. the classification of the obstacle and the currentstatus of the air passageway 13, such as “air passageway open", “air flow limited", or “radiator blind mounted”.

A method of determining the actual cooling capacity Q_real of theof the schematically illustrated in fig. 4. The method according to this radiator according to an embodiment invention isembodiment may constitute the method step 100 discussed inconnection with fig. 2. lt is carried out in a cooling system 1 in amotor vehicle such as the one illustrated in fig. 1, using a singletemperature sensor 7 for sensing the temperature of the liquid coolant.

A first step 101 is initiated as the combustion engine 2 has reacheda steady state, i.e. when the temperature of the engine 2 isln the first step 101, the thermostat 8 is set to a predefined degree of openness, so that the constant or essentially constant. mass flow of coolant mf_coolant through the radiator 4 is therebyknown by taking the rotational speed and the displacement of the pump 6 and the density of the coolant into account. ln a step 102, a temperature T of the liquid coolant within thecooling system 1 is determined at a first point in time t1 and at asecond point in time t2, the mass flow of coolant mf_coolantthrough the radiator 4 being constant or essentially constant during a time period including those two points in time t1, t2. The temperature of the liquid coolant is in this embodiment determinedby means of the temperature sensor 7. The step 102 is performed in connection with the step 101. ln a step 103, the actual cooling capacity Q_rea| of the radiator 4is estimated based on the amount of heat generated by thecombustion engine 2 and transferred to the liquid coolant, on thetotal amount of liquid coolant within the system 1 and/or the massflow of liquid coolant mf_coolant, the specific heat capacity of theliquid coolant, and on the difference in temperature between thefirst point in time t1 and the second point in time t2. Informationrelating to the power converted by the internal combustion engine2, and thereby the amount of heat generated, can be derivedbased on the type of fuel used and the efficiency of the combustionprocess. The actual cooling capacity Q_rea| is determined underthe assumption that, during a time period including the points intime t1 and t2, the mass flow of coolant mf_flow through theradiator and the mass flow of air across the radiator are constant and the engine 2 has reached a steady state.

A method of determining the expected cooling capacity Q_exp ofthe radiator 4 according to an embodiment of the invention isschematically illustrated in fig. 5. The method according to thisembodiment may constitute the method step 200 discussed inconnection with fig. 2. All steps may preferably be carried out inconnection with the steps 101-103 for determining the actual cooling capacity Q_rea| of the radiator. ln a step 201, an ambient air temperature and air pressure are determined. The ambient air temperature and air pressure can e.g. 16 be communicated to the control unit from external sensors (not shown). ln a step 202, an expected mass flow of air, mf_exp, across theradiator 4 through the air passageway 13 is estimated. Theestimation is based on the ambient air temperature and airpressure determined in step 201 as well as headwind and arotationa| speed of the fan 14 at that time. Together with knowncharacteristics of the air passageway 13, such as its cross section,and the fan 14, such as its shape and size, the expected mass flow of air mf_exp across the radiator 4 can be determined. ln a step 203, the mass flow of coolant mf_coolant through theradiator 4 is determined, e.g. from the rotationa| speed of thepump, the density of the liquid coolant and the degree of opennessof the thermostat. The mass flow of coolant mf_coolant can alsobe measured using a mass flow meter. Of course, if the thermostat8 has been set to a predefined degree of openness, the mass flow of coolant mf_coolant is already well known.

The known mass flow of coolant mf_coolant through the radiator 4and the expected mass flow of air mf_exp across the radiator 4 arein a step 204 used to determine an expected cooling capacityQ_exp of the radiator 4. Such a determination is illustrated in fig.7, showing curves relating the mass flow of coolant mf_coolantthrough the radiator and the mass flow of air mf_air across theradiator 4 to a cooling capacity Q of the radiator 4. ln the exampleshown in fig. 7, the expected cooling capacity Q_exp is shown fora determined mass flow of coolant mf_coolant of 3 kg/s and an expected mass flow of air mf_exp. When an actual cooling capacity 17 Q_rea| which is lower than the expected cooling capacity Q_exphas been determined, a lower actual cooling capacity Q_rea|corresponds to a lower actual mass flow of air mf_real across theradiator 4, given that the mass flow of liquid coolant mf_coolant is the same. ln an alternative method of determining the actual cooling capacityQ_rea| of the radiator, schematically illustrated in fig. 6, thecooling system comprises at least two temperature sensors, ofwhich one is positioned upstream of the radiator and the other oneis positioned downstream of the radiator. ln this embodiment, themass flow of coolant mf_coolant through the radiator is determinedin a step 101' from the rotational speed and the displacement ofthe pump, the density of the liquid coolant and the degree of openness of the thermostat. ln a step 102', a momentary temperature difference of the liquidcoolant within the cooling system is determined using the two temperature sensors. ln a step 103', the temperature difference, the mass flow of coolantmf_coolant and the specific heat capacity of the liquid coolant areused to determine the actual cooling capacity Q_rea| of the radiator.

Computer program code for implementing a method according tothe invention is suitably included in a computer program which isreadable into an internal memory of a computer, such as the in-ternal memory of an electronic control unit of a motor vehicle. Such a computer program is suitably provided through a computer 18 program product comprising a data storing medium readable by an electronic control unit, which data storing medium has thecomputer program stored thereon. Said data storing medium is forexample an optical data storing medium in the form of a CD-ROM-disc, a DVD-disc, etc., a magnetic data storing medium in the formof a hard disc, a diskette, a tape etc., or a Flash memory or a memory of the type ROM, PROM, EPROM or EEPROM.

Fig. 8 illustrates very schematically an electronic control unit 40comprising an execution means 81, such as a central processorunit (CPU), for executing a computer program. The executionmeans 81 communicates with a memory 82, for example of thetype RAM, through a data bus 83. The control unit 80 comprisesalso a non-transitory data storing medium 84, for example in theform of a Flash memory or a memory of the type ROM, PROM,EPROM or EEPROM. The execution means 81 communicates withthe data storing medium 84 through the data bus 83. A computerprogram comprising computer program code for implementing amethod according to the invention is stored on the data storing medium 84.

The invention is of course not in any way restricted to theembodiments described above. On the contrary, many possibilitiesto modifications thereof will be apparent to a person with ordinaryskill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims

1 _

1. A method for detecting an obstacle preventing an air flow in an air passageway (13) across a radiator (4) configured to cool liquid coolant in a cooling system (1), characterised in that it comprises the steps of: a) b)

2. repeatedly over time determining an actual cooling capacity(Q_rea|) of the radiator (4) and an expected cooling capacity(Q_exp) of the radiator (4), comparing said actual cooling capacity (Q_rea|) and saidexpected cooling capacity (Q_exp) to determine a deviation(ö) in the actual cooling capacity (Q_rea|) from the expectedcooling capacity (Q_exp), assessing whether a value of said deviation (ö) determinedon a specific occasion differs from a reference value (ö_ref),which reference value (ö_ref) is determined based onpreviously determined values of said deviation (ö), based on the assessment carried out in step c, determiningwhether an obstacle to the air flow has been introduced orremoved in the air passageway (13) prior to said specificoccasion. The method according to claim 1, wherein, in step a, determining the expected cooling capacity of the radiator (4) comprises determining a mass flow of coolant (mf_coolant) through the radiator (4) and estimating an expected mass flow of air (mf_exp) across the radiator (4), and based thereon estimating the expected cooling capacity (Q_exp) of the radiator.

3. The method according to claim 2, wherein estimating theexpected mass flow of air (mf_exp) comprises measuring anambient air temperature, an ambient air pressure, and a rotationalspeed of at least one fan (14) causing air to flow across theradiator (4), and based thereon estimating the expected mass flow of air (mf_exp).

4. The method according to claim 2 or 3, wherein predefinedvalues and/or curves are used in the determination of the expected cooling capacity (Q_exp).

5. The method according to any one of the preceding claims, wherein, in step a, determining the actual cooling capacity(Q_real) of the radiator (4) comprises measuring a mass flow of coolant (mf_coolant) through the radiator.

6. The method according to claim 5, wherein, in step a,determining the actual cooling capacity (Q_real) of the radiator (4)further comprises measuring a coolant temperature before andafter the radiator (4) and based thereon determining a coolanttemperature difference, and based on said coolant temperaturedifference and said mass flow of coolant (mf_coolant) determining the actual cooling capacity (Q_real) of the radiator (4).

7. The method according to claim 5, wherein, in step a,determining the actual cooling capacity (Q_real) of the radiator (4)further comprises measuring a coolant temperature at two differentpoints in time (t1, t2) and based thereon determining a coolanttemperature difference, and based on said coolant temperaturedifference and said mass flow of coolant (mf_coolant) determining the actual cooling capacity (Q_real) of the radiator (4). 21

8. The method according to any one of the preceding claims,wherein, in step d, it is determined that an obstacle has beenintroduced or removed if the value of said deviation (ö) differs fromthe reference value by more than a predetermined threshold amount.

9. The method according to any one of the preceding claims,given that it is in step d determined that an obstacle has beenintroduced or removed, further comprising the step of classifying said obstacle based on the value of said deviation (ö).

10. The method according to any one of the preceding claims,given that it is in step d determined that an obstacle has beenintroduced or removed, further comprising the step of changing a status code reflecting a status of the air passageway (13).

11. A system for detecting an obstacle preventing an air flow inan air passageway (13) across a radiator (4) in a cooling system(1), characterised in that it comprises: - means configured to repeatedly over time determine anactual cooling capacity (Q_real) of the radiator (4) and anexpected cooling capacity (Q_exp) of the radiator (4), - means configured to compare said actual cooling capacity(Q_real) and said expected cooling capacity (Q_exp) todetermine a deviation in the actual cooling capacity (Q_real) from the expected cooling capacity(Q_exp), 22 - means configured to assess whether a value of saiddeviation (ö) determined on a specific occasion differs froma reference value (ö_ref), which reference value (ö_ref) isdetermined based on earlier determined values of saiddeviation (ö), - means configured to, based on said assessment, determinewhether an obstacle to the air flow has been introduced orremoved in the air passageway (13) prior to said specific occasion.

12. A computer program comprising computer program code forcausing a computer to implement a method according to any oneof the claims 1-10 when the computer program is executed in the computer.

13. A computer program product comprising a data storagemedium (84) which can be read by a computer and on which theprogram code of a computer program according to claim 12 is stored.

14. An electronic control unit (80) of a motor vehicle comprisingan execution means (81), a memory (82) connected to theexecution means (81) and a data storage medium (84) which isconnected to the execution means (81) and on which the computerprogram code of a computer program according to claim 12 is stored.

15. A motor vehicle comprising an electronic control unit (80) according to claim 14.