WO2015057128A1

WO2015057128A1 - Arrangement and method to diagnose a cooling system in a vehicle

Info

Publication number: WO2015057128A1
Application number: PCT/SE2014/051101
Authority: WO
Inventors: Ola Hall; Hans WIKSTRÖM
Original assignee: Scania Cv Ab
Priority date: 2013-10-18
Filing date: 2014-09-25
Publication date: 2015-04-23
Also published as: SE1351238A1; SE539360C2

Abstract

The present invention concerns an arrangement and a method to diagnose a cooling system in a vehicle. The arrangement comprises a control unit (13) that comprises or has access to a model (M) that simulates operation of the cooling system with the aid of several parameters (p, q_n), with which model (M) it is possible to determine an ideal value (p_i) of at least a first parameter (p) that is related to the performance of the cooling system. The control unit (13) is adapted to estimate an ideal value (p_i) of the first parameter (p) with the aid of the model (M), to receive information concerning a present value (p_är) of the first parameter (p), and to determine a deviation (A) between the ideal value (p_i) and the present value (p_är) of the first parameter (p). The control unit (13) has access to information concerning a maximum acceptable deviation (A_max) of the first parameter (p) at which service of the cooling system should be carried out. The arrangement comprises an indicator arrangement (17) that is adapted to indicate that service of the cooling system should be carried out if the deviation (A) is larger than the maximum acceptable deviation (A_max).

Description

Arrangement and method to diagnose a cooling system in a vehicle

BACKGROUND AND PRIOR ART

The present invention concerns an arrangement and a method to diagnose a cooling system in a vehicle according to the preambles to claims 1 and 11.

Cooling systems in vehicles perform more poorly with time due to contamination, wear, corrosion, etc. If, for example, the size or capacity of the heat transfer surface in a cooler becomes reduced as a consequence of, for example, contamination, the cooling fluid pump must provide an increased flow of cooling fluid through the cooler and the cooling fan must provide an increased flow of air through the cooler in order to compensate for the loss of the heat transfer surface. The cooling fan and the cooling fluid pump are driven directly or indirectly by the combustion engine, which results in the fuel consumption of the combustion engine increasing as the performance of the cooling system is impaired. An impaired performance of the cooling system results also in it having an insufficient capacity to cool the combustion engine when it is placed under a heavy load. It may be the task of the cooling system to cool also other components and media, such as charge air, recirculating exhaust gases and oil in a hydrodynamic retarder. Insufficient cooling in these cases may result in the combustion engine attaining reduced power, increased emission of nitrogen oxides in the exhaust gases, and a reduced braking capacity of the retarder.

The performance of a cooling system is rapidly reduced if the vehicle is used in dirty surroundings. In such cases the cooler, which is generally located at the front of the vehicle, can become more or less clogged by contaminants that are carried by the cooling flow of air that is drawn through the cooler. The coolers of certain types of vehicle that are frequently driven in more or less heavily contaminated surroundings are cleaned at short intervals. The rate at which a cooler becomes dirty can differ remarkably between different vehicles. It can be concluded that the cooler of certain vehicles is cleaned far too rarely, while other coolers are cleaned unnecessarily. SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an arrangement that makes it possible to provide service for a cooling system in a vehicle before it has acquired a performance that is too strongly reduced, and at the same time to avoid unnecessary service of cooling systems.

Thus, the arrangement comprises a control unit that has access to a model that comprises a first parameter and at least one operating parameter. The first parameter has a value that is related to the performance of the cooling system. One or several operating parameters define the operating condition at which the first parameter is determined in the model. The model may comprise also parameters that are related to the specific vehicle and its components. According to the invention, the control unit estimates an ideal value of the first parameter with the aid of the model. The ideal value concerns the value of the parameter when the cooling system is in pristine condition, and has at this time its optimal performance. The control unit receives information about the true present value of the said first parameter during operation of the cooling system. The control unit determines the deviation that exists between the ideal value and the true value of the first parameter. The deviation may be the difference, the ratio or another correlation between these values that can be defined as a deviation. The magnitude of the deviation is related to the magnitude of the reduction in the performance of the cooling system, relative to the performance when it was new. The control unit has access to information concerning a maximum acceptable deviation for the first parameter, at which deviation service of the cooling system should be carried out. The arrangement comprises an indicator arrangement that is adapted to demonstrate when service of the cooling system should be carried out. The control unit activates the indicator arrangement such that it demonstrates that service should be carried out on occasions at which the above-mentioned deviation is larger than the maximum acceptable deviation. In this case, an indication is always received concerning when it is time to carry out service of the cooling system. It is in this way possible to carry out service of the cooling system before its performance is reduced to a level that is unacceptably low. As long as the indicator arrangement does not demonstrate that service should be carried out, it can be assumed that the system has a good performance. Unnecessary service of the cooling system can in this way be avoided. According to one embodiment of the present invention, the control unit is adapted to calculate the ideal value of the first parameter with the aid of the said model. The model in this case is a mathematical model. The model comprises at least one mathematical correlation between the parameters that are included. The mathematical correlation is designed such that it is possible to calculate an ideal value of the said first parameter with the aid of information concerning the values of other parameters. These may be operating parameters that define the operating condition at which the ideal parameter is calculated or vehicle-specific parameters that are specific for the vehicle.

According to one embodiment of the present invention, the control unit is adapted to calculate the ideal value of the first parameter with the aid of a model that simulates operation of the cooling system when it is in a steady-state condition. More or less steady-state operating conditions arise temporarily during operation of a vehicle. The term "steady-state operating condition" is used to denote a condition in which one or several operating parameters that are included in the model has or have essentially constant value or values. The control unit can calculate derivatives of the relevant operating parameters in order to estimate whether a steady-state operating condition has arisen. When the derivatives of the relevant operating parameters do not exceed a certain value, the control unit makes the assessment that a steady-state operating condition has arisen and it thus calculates an ideal value of the first parameter for this operating condition. The control unit receives at the same time information concerning the true value of the said first parameter at this operating condition, on which the control unit determines the possible deviation, if any, between the said values.

According to another embodiment of the present invention, the control unit is adapted to calculate the ideal value of the first parameter with the aid of a model that simulates operation of the cooling system in real time. This model may contain, in addition to a first parameter, operating parameters and vehicle-specific parameters, also simulation of the function of the thermostat. The first parameter can in this case be calculated in pre-determined dynamic conditions. The first parameter in this case may be constituted by the derivative of, for example, a temperature or other variable that changes during the dynamic condition. Alternatively, the first parameter may be a maximum value or a minimum value of, for example, a temperature or other variable that changes during the dynamic condition. According to a further embodiment of the present invention, the control unit is adapted to calculate the ideal value of the first parameter with the aid of the said model essentially continuously during operation of the cooling system. The first parameter is in this case calculated essentially continuously from the time at which the circulation of the cooling fluid in the cooling system starts until it stops. This model contains, in addition to a first parameter, operating parameters and vehicle-specific parameters, also logic circuits to control the cooling fan, cooling fluid pump and thermostat, in cases in which this is under active control. The calculated ideal value of the first parameter is continuously compared with the true present value of the first parameter that is received.

According to a further embodiment of the present invention, the said model comprises a database with stored information concerning at least one ideal value of the first parameter and at least one operating parameter, which values were defined when the cooling system was in pristine condition. The model in this case is a statistical model. It records the value of said first parameter during a period in which the vehicle is in its pristine condition. Since the vehicle is in pristine condition, it is assumed that the cooling system has its optimal performance and that the recorded value can therefore be regarded as an ideal value. The value of the ideal first parameter and the said operating parameter can be stored in a first database in the model. It is not in this case required that the model comprise any vehicle-specific parameters. This model, therefore, can be introduced into all types of vehicle without adaptation. The control unit in this case can be adapted to receive information concerning the present value of the first parameter and the said operating parameter, and to estimate a deviation between the present value and the stored ideal value of said first parameter when the control unit receives a value of the said operating parameter that corresponds to the stored value of the operating parameter. More than one operating parameter is generally required to define an operating condition. According to a further embodiment of the present invention, the first parameter is constituted by the temperature or the derivative of the temperature of a cooling fluid that circulates in the cooling system. The cooling fluid that circulates in the cooling system absorbs heat energy when it cools the combustion engine and, where relevant, other components or media in the cooling system. The cooling fluid emits the absorbed heat energy in a cooler that may be cooled by air, located at a front part of the vehicle. If the ability of a cooling system to emit heat energy or to absorb heat energy falls, the system achieves an impaired performance. The temperature of the cooling fluid in an appropriate position in the cooling system may constitute a first parameter that indicates whether the ability of the cooling system to transfer heat has fallen in any part of the cooling system. The derivative of the temperature of the cooling fluid defines the speed with which the temperature of the cooling fluid changes, which also may be an appropriate first parameter. Also the maximum temperature or the minimum temperature of the cooling fluid may constitute an appropriate first parameter, in order to determine under certain operating conditions whether the performance of the cooling system is impaired. Other alternative first parameters are the temperature and the derivative of the temperature of components and media that are cooled by the cooling fluid. If, for example, the cooling system cools charge air in an intercooler, the temperature or the derivative of the temperature of the charge air may constitute a first parameter that can be used to assess the performance of the cooling system.

According to one embodiment of the present invention, the control unit is adapted to collect information from a sensor that determines a value that is related to the said first parameter. It is an advantage if such a sensor is a temperature sensor that determines the temperature of the cooling fluid at appropriate positions in the cooling system. Alternatively, a temperature sensor may determine the temperature of a component or a medium that is cooled by the cooling system. A control unit that receives information essentially continuously from a temperature sensor can estimate with the aid of this information the derivative of the temperature and a maximum or minimum temperature in certain operating conditions.

According to one embodiment of the present invention, the said indicator arrangement is adapted to indicate that the cooling system needs to undergo service by displaying this information on a display in a driver's compartment in the vehicle, by transmitting the information to a workshop, or by storing the information in the vehicle. Thus, several ways to indicate that a cooling system needs to undergo service are available.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention will be described as examples below with reference to attached drawings, of which: Figure 1 shows a cooling system with an arrangement according to present invention and

Figure 2 shows a flow diagram that describes a method according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 shows a cooling system to cool a combustion engine 1 in a vehicle 2, shown schematically. The cooling fluid is circulated in the cooling system with the aid of a cooling fluid pump 3 that is arranged in an inlet line 4 to the combustion engine 1.

After the cooling fluid has passed through the combustion engine 1 it is led to an outlet line 5. The outlet line 5 in this case comprises an oil cooler 6 for the cooling of oil in a hydrodynamic retarder and an intercooler 7 for the cooling of charge air. Thus, the cooling system in this case does not cool solely the combustion engine 1. The cooling system can be exploited for the cooling of further components and media such as, for example, recirculating exhaust gases in an EGR cooler.

The cooling system comprises a thermostat 8 that determines the temperature of the cooling fluid in the outlet line 5 at a position downstream of the oil cooler 6 and intercooler 7. In operating conditions in which the thermostat 8 determines that the cooling fluid has a temperature that is lower than the regulation temperature, it leads the cooling fluid to a bypass line 9. The bypass line 9 leads cooling fluid back to the inlet line 4 and to the cooling fluid pump 3 for repeated circulation in the cooling system without the cooling fluid being cooled. In operating conditions in which the thermostat 8 determines that the cooling fluid has temperature that is higher than the regulation temperature, it leads the cooling fluid to a cooler 10 that is arranged at a front part of the vehicle 2. The cooling fluid is cooled in the cooler 10 by air that flows through the cooler 10 with the aid of a cooling fan 12 and the vehicle headwind. After the cooling fluid has been cooled in the cooler 10, it is led through a return line 11 back to the inlet line 4 and the cooling fluid pump 3 for repeated circulation in the cooling system.

The cooling system is equipped with an arrangement that diagnoses the performance of the cooling system. The arrangement comprises a control unit 13 that may be a computer or similar component that is provided with software to control the diagnosis of the cooling system. The software defines a model M that simulates operation of the cooling system with the aid of several parameters p, q_n. At least one of the said parameters constitutes a first parameter p that is related to the performance of the cooling system. Other parameters q_n constitute operating parameters that define an operating condition of the vehicle, and vehicle- specific parameters. The control unit 13 receives information during operation from a sensor 14a that determines the temperature of the cooling fluid after it has cooled the combustion engine 1, and from a sensor 14b that determines the temperature of the cooling fluid after it has passed through the cooler 10. The temperature of the cooling fluid can constitute such a first parameter p. The control unit 13 in this case receives information also from a sensor 15 that determines the temperature of the charge air in association with the intercooler 7. Also this parameter is related to the performance of the cooling system and can constitute such a first parameter p either as an alternative or in addition to the aforementioned parameter. The model M may comprise relationships between the parameters p, q_n that define the heat exchange in the cooling system.

The cooling fluid in the cooling system receives, in this case, a supply of heat energy and heating when it is led through the combustion engine 1 and the intercooler 7. It receives a supply of heat energy also in the retarder 6 on occasions when the retarder is activated. The cooling fluid is cooled in the cooler 10 where it emits heat energy to the air that flows through the cooler. The parameters q_n of the model that are related to operation may be related to the heat transfer that the circulating cooling fluid in the cooling system receives in the combustion engine 1, the oil cooler 6, the intercooler and the cooler 10. The parameters q_n that are related to operation may be related also to the operation of the combustion engine 1, the cooling fluid pump 3 and the cooler 12.

The control unit 13 receives information during operation concerning the operating- related parameters q_n from unit 16, shown schematically. The control unit 13 can estimate with the aid of the model a value of the first parameter p and can in this way determine when the performance of the cooling system has fallen to a level at which it is time to obtain service of the cooling system. When this is the case, it is demonstrated through an indicator arrangement 17. The indicator arrangement 17 can indicate that the cooling system needs to undergo service in several different ways. It may take place through the information being displayed on a display in a driver's cabin in the vehicle 2. Alternatively, the indicator arrangement 17 may transmit a signal to a workshop when service of the cooler needs to be carried out. The workshop in this way is made aware that this service is to be carried out as soon as the vehicle arrives at the workshop. According to a further alternative, the information about the need for service of the cooler may be stored in the vehicle in an appropriate manner. This need for service can in this way be noticed and the necessary measures taken on the next occasion that the vehicle is at workshop for some other type of service, repair or similar.

Figure 2 shows a flow diagram that describes the function of the arrangement and the basic steps of a method to diagnose the performance of a cooling system in a vehicle. The control unit 13 has, at Step a, been provided with a model M that simulates the operation of the cooling system. The operation is simulated with the aid of several parameters p, q_n that are included in the model, where at least a first parameter p of the said parameters is related to the performance of the cooling system during operation, and where parameters constitute operating parameters q_n that define the operating condition at which a value of the first parameter p is determined. The model may comprise also parameters that define the properties of the specific vehicle. The control unit 13 has, at Step b, access to information that defines a maximum acceptable deviation A_max for the said first parameter p at which the performance of the cooling system has fallen to a level at which service of the cooling system should be carried out. The control unit 13 estimates, at Step c, an ideal value p; of the said first parameter p with the aid of the model M. The ideal value p_; of the said first parameter p is the value that the parameter p has when the cooling system is functioning in an optimal manner. A cooling system functions in an optimal manner in its pristine condition. The components of the cooling system are subject to wear and contamination during operation, which leads to the performance of the cooling system gradually becoming impaired. It is possible that the cooling system again recover essentially its optimal performance through service of the cooling system, which may involve at least one of cleaning of the cooler 10 and exchange of components that are functioning poorly. When the vehicle is no longer in its pristine condition, the control unit 13 receives during operation, at Step d, information about the present value ρ_&· of the said first parameter p. The control unit 13 receives in this case information from the sensors 14a, 14b, 15 concerning at least one of the temperature of the cooling fluid and the temperature of the charge air. The present value p_¾- of the first parameter p is the true value of the first parameter p in the cooling system. Since the present value p is related to the performance of the cooling system, it will gradually deviate more and more from the ideal value p;of the first parameter, as the cooling system is worn and becomes dirty, corroded, worn, etc. The control unit 13 estimates, at Step e, a deviation A between the present value of the said first parameter p and the ideal value p;. The deviation A may constitute a difference between the present value ρ^ and the ideal value p_; of the first parameter, the ratio between the present value par and the ideal value pi, or it may be defined in some other suitable manner.

The control unit 13 assesses, at Step f, whether the deviation A is larger than the maximum acceptable deviation A_max. If the control unit 13 determines that the deviation is smaller than the maximum acceptable deviation A_max , the control unit 13 concludes that the cooling system has a sufficiently good performance and that service of the cooling system is not justified. The process thus is repeated from Step c, where the control unit 13 receives again a present value p^ of the said first parameter p. If the control unit 13 determines that the deviation is larger than the maximum acceptable deviation A_max , the control unit 13 concludes that the performance of the cooling system has fallen to a level at which it needs to undergo service. The control unit 13 activates, at Step g, the indicator arrangement 17, which demonstrates in an appropriate manner that service of the cooling system should be carried out. A first embodiment described in more detail

The model M may be designed in various manners. According to a first embodiment, the control unit 13 is equipped, at Step a, with a calculation model M that simulates the cooling system in a steady-state operating condition with the aid of at least a first parameter p and a number of operating parameters q_n. The term "steady-state operating condition" is here used to denote that at least one of the temperature of the cooling fluid in the cooling system and the temperature of the charge air, which can be defined as the first parameter p, has a value that has been stabilised at an essentially constant level, as have also the operating parameters q_n that are included in the model and that may concern the engine power supplied, the rate of revolution of the engine, the fan speed, the power developed by the retarder, or the speed of the vehicle. The model M contains also vehicle-specific parameters that are related to the components of the vehicle, such as type of combustion engine 1, cooler 10, cooling fan 12, cooling fluid pump 3, oil cooler 6, etc. The control unit 13 receives information essentially continuously from the sensors 14a, 14b, 15 concerning the temperature of the cooling fluid and the temperature of the charge air that can relate to the value of the first parameter p, and information from the unit 16 concerning other operating parameters q_n that are included in the model. The control unit 13 calculates the derivative of at least several of the said parameters p, q_n essentially continuously. When the derivative of the said parameters p, q_n does not exceed a pre-determined value, it is concluded that they have an essentially constant value and that a steady-state operating condition has been reached. When this occurs, the control unit 13 calculates, at Step c, an ideal value p; of the said first parameter p, with the aid of the model M, and the present values of the operating parameters that have been received. Thus it calculates the temperature that at least one of the cooling fluid and the charge air would have in the currently prevalent operating conditions if the cooling system were in pristine condition. A further condition for the control unit 13 to carry out this calculation is that the temperature of the cooling fluid is higher than the regulation temperature, i.e. that the thermostat is open such that cooler fluid circulates through the cooler 10.

The control unit 13 receives, at Step d, information from the sensors 14a, 14b, 15 concerning the true temperature of at least one of the cooling fluid and the charge air, i.e. p^ of the said first parameter p. The control unit 13 estimates, at Step e, the deviation A between the calculated value p_; of the said first parameter p and the measured present value par of the said first parameter p. If the deviation exceeds the pre-determined maximum deviation A_max , the control unit 13b activates the indicator arrangement 17, which, at Step g, indicates that the cooling system needs to undergo service. Otherwise, the process continues, at Step c, and calculation of a new ideal value pi of the said first parameter p as soon as a new steady-state operating condition according to the description given above arises.

A second embodiment

According to a second embodiment, the control unit 13 is equipped, at Step a, with a calculation model M that simulates the cooling system in real time with the aid of at least a first parameter p and at least one operating parameter q_n. The model M contains also information about the performance and operating properties of vehicle-specific components. The model comprises also simulation of the temperature regulation function of the thermostat 8. The thermostat 8 may be a passive component that opens and leads cooling fluid to the cooler 10 at a constant regulation temperature.

Alternatively, the thermostat 8 may be actively controlled such that it leads cooling fluid to the cooler 10 at different regulation temperatures under different operating conditions. The calculation model in this case is adapted to calculate ideal values of the first parameter under suitable dynamic operating conditions. It is an advantage in this case that the control unit 13 calculate the value of a first parameter p in the form of the derivative of the temperature of the cooling fluid or the derivative of the temperature of the charge air. The first parameter p in this case concerns the speed at which the temperature of the cooling fluid or the temperature of the charge air temperature changes.

The control unit 13 receives essentially continuously information from the sensors 14a, 14b, 15 concerning at least one of the temperature of the cooling fluid and the temperature of the charge air. In operating conditions in which a retarder is activated or when the combustion engine is placed suddenly under an increased load, the temperature of the cooling fluid in the cooling system rises. In operating conditions in which a driver releases the accelerator pedal without braking, following a period of high load on the combustion engine, the temperature of the cooling fluid in the cooling system falls. In the case in which the cooling system is functioning well, the temperature of the cooling fluid falls more rapidly than it does in a cooling system that is functioning less well. When an operating condition arises in which the cooling fluid or the charge air experiences a rapid change in temperature, the control unit 13 calculates, at Step c, an ideal value p_; of the first parameter, which in this case is the temperature of the cooling fluid. The control unit 13 receives at essentially the same time information from the said sensors 14a, 14b, 15 concerning the temperature of the cooling fluid and the temperature of the charge air, and calculates the corresponding present values ρ^ of the first parameter p. The control unit 13 estimates, at Step e, the deviation A between the calculated ideal value pi of the said first parameter p and the measured present value ar of the said first parameter p. If the deviation exceeds the pre-determined maximum acceptable deviation Amax , the control unit 13 activates the indicator arrangement 17, which, at Step g, indicates that the cooling system needs to undergo service. Otherwise, the process starts, at Step c, with calculation of a new ideal value pi of the said first parameter p as soon as a new operating condition as described above arises. A third embodiment

According to a third embodiment, the control unit 13 is equipped, at Step a, with a calculation model M that comprises a first parameter p and at least one operating parameter q_n, although it is an advantage if it is equipped with several operating parameters qn. The model is provided also in this case with information concerning the performance and operating properties of the components that are included in the specific vehicle 2. The control unit is provided, at Step b, with information concerning a maximum acceptable deviation A_max of the first parameter p from an ideal first parameter value p; that is attained when the cooling system is new and demonstrates its optimal performance. The control unit 13 receives also in this case information from the unit 16 concerning the operating parameters q_n that are included in the model M. The model comprises also information about the logic that is responsible for the control of the cooling fan 12, cooling fluid pump 3, and, where relevant, the thermostat 8. The control unit 13 in this case calculates continuously during operation, with the aid of the model M, an ideal value pi of the first parameter p after the start of the cooling system, which takes place at Step c. The calculated ideal value p; of the first parameter value p, which may be the temperature of at least one of the cooling fluid and the charge air, is compared essentially continuously with temperature values received from the sensors 14a, 14b, 15. The control unit 13 determines the deviation A between the ideal value p; and the present value ρ_¾· of the first parameter p, which takes place at Step e. The magnitude of the deviation A indicates the degree to which the performance of the cooling system has become impaired relative to its optimal performance. If the deviation exceeds the pre-determined maximum acceptable deviation

, the control unit 13 activates the indicator arrangement 17, which, at Step g, indicates that the cooling system needs to undergo service. Otherwise, the process continues at Step c. When the performance of a cooling system has been impaired, the cooling fan 12 and the cooling fluid pump must 3 work harder in order for the cooling system to be able to maintain the required cooling effect. When the performance of the cooling system falls, this results in an increased fuel consumption of the combustion engine 1 that drives the cooling fan 12 and the cooling fluid pump 3. As a supplement to solely indicating when it is time to carry out service of the cooling system, the control unit can indicate the increase in fuel consumption that is experienced due to the impairment in performance that the cooling system has undergone. The method M can be modified further such that it receives information from a GPS unit that provides information about the route forward. With the aid of this information and information concerning the properties of the specific vehicle, it is possible to estimate the degree of engagement of the cooling fan 12 and the cooling fluid pump 3, and to estimate future actual values ρ^ and ideal values pi of the first parameter p.

A fourth embodiment According to a fourth embodiment, the control unit 13 is equipped, at Step a, with a model M of a statistical nature. The control unit 13 is provided, at Step b, with information concerning a maximum acceptable deviation of a first parameter p from an ideal parameter value pi. When the cooling system is in its pristine condition, the control unit 13 creates, at Step c, a first ideal database in the statistical model M. The ideal database comprises stored information concerning ideal p; first parameter values p and operating parameters q_n that are received from the unit 16 during appropriate operating conditions. It is preferable that an ideal database be created with information about ideal first parameter values p; and operating parameter values q_n during several appropriate operating conditions. This database with ideal parameter values p_; is created during a relatively short period when the vehicle is in its pristine condition, and during which it can be guaranteed that the cooling system has an optimal performance.

The derivative of the temperature of the cooling fluid in the cooling system can, for example, define the first parameter p. The derivative of the temperature of the cooling fluid when the thermostat is fully open can be defined as a function of the supply of heating power and the removal of heating power in the cooling system. The heating power is supplied to the cooling system through the combustion engine 1, the intercooler 7 and the oil cooler 6 when it is activated. The heating power is withdrawn from the cooling system in the cooler 10. The magnitude of the heating power that is withdrawn depends primarily on the temperature of the surrounding air and the flow of air through the cooler 10. The flow of air through the cooler 10 depends, in turn, on factors such as the speed of the vehicle 2, the rate of revolution of the cooling fan 12, and vehicle- specific properties such as type of driver's cabin. The thermal inertia has also a certain significance. Appropriate operating conditions are in this case conditions in which the derivative of the temperature has a large positive or large negative value. In addition to the derivative of the temperature, also the maximum of the derivative of the temperature can be defined as an ideal first parameter value. A large positive value of the derivative of the temperature is obtained in an operating condition in which the vehicle is braked with the aid of the retarder. A large amount of heating power is in this case supplied to the cooling fluid, which leads to the temperature of the cooling fluid increasing. A more effective cooling effect is obtained in a new cooling system with an optimal performance than is obtained in a cooling system that has a poorer performance. The derivative of the temperature and a maximum value of the derivative of the temperature will thus be larger in the cooling system with the poorer performance than they are in the cooling system with the higher performance. The derivative of the temperature and the maximum derivative of the temperature of the cooling fluid temperature are therefore good indications of the performance of the cooling system.

The value of the derivative of the temperature or the maximum of the derivative of the temperature can be stored in the first database as a function of operating parameters q_n, which may be constituted by, for example, the cooling power in the cooler 10 or the rate of revolution of the combustion engine 1. Appropriate operating conditions are obtained also when the derivative of the temperature has a large negative value. A large negative value of the derivative of the temperature is obtained when the vehicle is rolling forwards with a relatively high speed without the accelerator pedal or the retarder being activated. The cooling fluid in the cooling system is in this case supplied with a significantly greater cooling in the cooler 10 than the heating that it receives in the combustion engine 1 and the intercooler 7. In a cooling system with an optimal performance, a more rapid cooling of the cooling fluid is in this case obtained, and thus a derivative of the temperature is obtained that has a larger negative value than it has in a cooling system with a poorer performance. A maximum negative derivative of the temperature or a minimum temperature of the cooling fluid can be recorded, as an alternative, in this operating condition as first parameter p. During the continued operation of the vehicle, the control unit 13 collects, when the operating condition specified above arises, values concerning the first parameter p and related operating parameters q from the unit 16. During such a period, the control unit 13 creates a second database in the statistical model M with actual values of the first parameter p and related operating parameter values q_n. At Step e, the control unit 13 compares the present values of the first parameter p in the second database with ideal parameter values in the first database at corresponding operating parameters q_n. The control unit 13 determines a deviation A between the actual value of the first parameter and the ideal value pi of the first parameter p. If the deviation exceeds the predetermined maximum acceptable deviation A_max , the control unit 13 activates the indicator arrangement 17, which, at Step g, indicates that the cooling system needs to undergo service. Otherwise, the process continues at Step d. Step c can in this case be omitted, since the ideal value pi of the first parameter p has already been stored in the model M.

No special calculations that take the specific vehicle and its components into consideration need to be carried out in this case, since the ideal values p; of the value of parameter p and the related operating parameters q_n are received and stored in a first database when the vehicle is in its pristine condition. Such an arrangement to diagnose a cooling system in a vehicle can be installed at all types of vehicle without it needing to be adapted to the specific type of vehicle and its components.

The invention is not in any way limited to the embodiment that has been described in the drawings: it can be freely varied within the scope of the patent claims. The cooling system can have an essentially freely chosen design and it can cool a freely chosen number of components or media. The various models can also be combined with each other in an appropriate manner.

Claims

1. An arrangement to diagnose a cooling system in a vehicle, whereby the arrangement comprises a control unit (13) that comprises or has access to a

model (M) that simulates operation of the cooling system with the aid of several parameters (p, q_n) that are included in the model, with which model (M) it is possible to determine an ideal value (pi) of at least a first parameter (p) that is related to the performance of the cooling system, whereby the control unit (13) is adapted to estimate an ideal value (p;) of the first parameter (p) with the aid of the model (M), to receive information concerning a present value (par) of the first parameter (p) and to determine a deviation (A) between the ideal value (p and the present value (p^) of the first parameter (p), characterised in that the control unit (13) has access to information concerning a maximum acceptable deviation (A_max) of the first parameter (p) at which service of the cooling system should be carried out, and that the arrangement comprises an indicator arrangement (17) that is adapted to indicate that service of the cooling system should be carried out if the deviation (A) is larger than the maximum acceptable deviation (A_max).

2. The arrangement according to claim 1, characterised in that the control unit (13) is adapted to calculate the ideal value (p of the first parameter (p) with the aid of the said model (M).

3. The arrangement according to claim 2, characterised in that the control unit is adapted to calculate the ideal value (p of the first parameter (p) with the aid of the said model (M) that simulates operation of the cooling system when it is in a steady- state operating condition.

4. The arrangement according to claim 2, characterised in that the control unit is adapted to calculate the ideal value (pO of the first parameter (p) with the aid of the said model (M) that simulates operation of the cooling system in real time.

5. The arrangement according to claim 2, characterised in that the control unit is adapted to calculate the ideal value (pO of the first parameter (p) with the aid of the said model (M) essentially continuously during operation of the cooling system.

6. The arrangement according to claim 1, characterised by the steps of obtaining an ideal value (p of the said first parameter (p) and a value of at least one operating parameter (q_n) when the cooling system is in its pristine condition, and storing this information in a database that is comprised within the said model.

7. The arrangement according to claim 6, characterised in that the control unit (13) is adapted to receive information concerning the present values of the first parameter and the said operating parameters (q_n) that are components of the model (M), and to estimate a deviation (A) between a present value (par) and the stored ideal value (ρ;) of said first parameter (p) when the control unit (13) receives a value of the said operating parameter (q_n) that corresponds to the stored value of the operating parameter (q_n).

8. The arrangement according to any one of the preceding claims, characterised in that the first parameter (p) is constituted by the temperature or the derivative of the temperature of a cooling fluid that circulates in the cooling system.

9. The arrangement according to any one of the preceding claims, characterised in that the control unit (13) is adapted to collect information from a sensor (14a, 14b, 15) that determines a value that is related to the said first parameter (p_ar).

10. The arrangement according to any one of the preceding claims, characterised in that the said indicator arrangement (17) is adapted to indicate that the cooling system needs to undergo service by displaying this information on a display in a driver's compartment in the vehicle, by transmitting the information to a workshop, or by storing the information in the vehicle.

11. A method to diagnose a cooling system in a vehicle, whereby the method comprises the steps:

a) to use a model (M) that simulates operation of the cooling system with the aid of several parameters (p, q_n) that are included in the model, where at least a first parameter of the said parameters (p) is related to the performance of the cooling system during operation,

b) to obtain information concerning a maximum acceptable deviation (A_max) of the said first parameter (p) at which the performance of the cooling system has fallen to a level that requires service of the cooling system, c) to estimate an ideal value (ρ;) of the said first parameter (p) with the aid of present values of other parameters (q_n) that are included in the model (M),

d) to receive information concerning a present value (ρ_¾.) of the said first parameter

(p), e) to determine a deviation (A) between the present value (ρ_&) and the ideal value (pi) of the said first parameter (p),

f) to assess whether the deviation (A) is larger than the maximum acceptable deviation (Amax). ^and

g) to indicate that service of the cooling system should be carried out if the deviation (A) is larger than the maximum acceptable deviation (A_max).

12. The method according to claim 11, characterised by the step of estimating the ideal value (pi) of the first parameter (p) through calculating it with the aid of the said model (M).

13. The method according to claim 12, characterised by the step of calculating the ideal value (p of the first parameter (p) with the aid of the said model (M) that simulates operation of the cooling system when it is in a steady-state operating condition.

14. The method according to claim 12, characterised by the step of calculating the ideal value (p of the first parameter (p) with the aid of the said model (M) that simulates operation of the cooling system in real time.

15. The method according to claim 12, characterised by the step of calculating the ideal value (ρ;) of the first parameter (p) with the aid of the said model (M) essentially continuously during operation of the cooling system.

16. The method according to claim 11, characterised by the steps of obtaining an ideal value (pi) of the said first parameter (p) and a value of at least one operating parameter (q_n) when the cooling system is in its pristine condition, and storing this information in a database.

17. The method according to claim 16, characterised by the step of receiving information concerning the present value of the first parameter and the operating parameter (q_n) during subsequent operation of the cooling system, and estimating a deviation (A) between a present value (ρ_&·) and the stored ideal value (p of the first parameter (p) when the operating parameter (q_n) has the corresponding value.

18. The method according to any one of the preceding claims 11-17, characterised by the step of using a first parameter (p) that is constituted by the temperature or the derivative of the temperature of a cooling fluid that circulates in the cooling system.

19. The method according to one any one of the preceding claims 11-18, characterised by the step of collecting information from a sensor (14a, 14b, 15) that determines the present value of the first parameter (ρ^).

20. The method according to any one of the preceding claims 11-19, characterised by the step of indicating that the cooling system needs to undergo service by displaying this information on a display in a driver's compartment in the vehicle, by transmitting the information to a workshop, or by storing the information in the vehicle.