SE541554C2

SE541554C2 - A cooling system for cooling of objects with coolant at three different temperatures and a vehicle comprising such a system

Info

Publication number: SE541554C2
Application number: SE1750060A
Authority: SE
Inventors: Henrik Höglund; Johan Linderyd; Jonas Aspfors; Zoltan Kardos
Original assignee: Scania Cv Ab
Priority date: 2017-01-26
Filing date: 2017-01-26
Publication date: 2019-10-29
Also published as: DE102018000132B4; DE102018000132A1; SE1750060A1

Abstract

The present invention relates to a cooling system for cooling objects (3, 4, 15, 35) with coolant of three different temperatures (T, T, T). The cooling system comprises a first valve device (6) configured to direct coolant to a radiator (8) and/or a radiator bypass line (9). A second valve device (12) configured to receive coolant from the radiator line (7) and /or the radiator bypass line (9) and distribute it to a first object inlet line (3a), a second object inlet line (15a) and a third object inlet line (4a, 35a). An initial coolant flow in the first object inlet line (3a) is mixed with two warmer coolant flows such that a mixed coolant flow at a first temperature (T) cools the first object (3). An initial coolant flow in the second object inlet line (15a) is mixed with one warmer coolant flow in a mixing line (16) by means of a third valve device (17) such that a mixed coolant flow at a second temperature (T) cools the second object (15). An unmixed coolant flow at the third temperature (T) is directed, via the third object inlet line (4a, 35a), to the third object (4, 35).

Description

A cooling system for cooling of objects with coolant at three different temperatures and a vehicle comprising such a system BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a cooling system for cooling of objects with coolant at different temperatures according to the preamble of claim 1 and a vehicle comprising such a cooling system.

During normal operation of a conventional cooling system for a combustion engine, coolant at a temperature within the range of 80-90°C is directed to the combustion engine. Thus, all parts of the combustion engine will be cooled by coolant of the same temperature. However, the cylinder head in an internal combustion engine receive more heat energy from the combustion processes than the cylinder block. In operating conditions in which the internal combustion engine is placed under a heavy load for a long period, the cylinder head can achieve a very high temperature. It is known to cool the cylinder head by coolant in a low temperature cooling circuit and the cylinder block by coolant in a high temperature cooling circuit.

Cooling systems can also be used for cooling other objects such as the working medium in a condenser of a WHR system (Waste Heat Recovery System). In order to achieve a high thermal efficiency in a WHR-system, the working medium in the condenser is to be cooled to a condensation temperature as low as possible and substantially without subcooling. Consequently, in order to achieve a high thermal efficiency in a WHR-system, the working medium is to be cooled by coolant at a specific temperature and flow. In case the WHR system receives heat energy from the exhaust gases of the combustion engine, the required cooling of the working medium in the condenser may vary rapidly. In such cases, it is difficult to provide a continuously cooling of the working medium in the condenser resulting in a high thermal efficiency of a WHR-system.

The cooling system can also be used for cooling of charge air in a charge air cooler. Twin turbo installations can be used to increase the power of a combustion engine by supplying charge air of a high pressure to the combustion engine. In a twin turbo installation, the charge air is compressed in a first stage by a low pressure compressor and in a second stage by a high pressure compressor. The amount of charge air which can be received and compressed in the compressors depends on the specific volume of the charge air. The charge air leaving the low pressure compressor has a raised pressure and a raised temperature. In order to reduce the specific volume of the charge air and increase the amount of charge air which can be received and compressed in the high pressure compressor, the charge air can be cooled in a charge air cooler arranged in a position between the compressors. It is desired to use coolant of a low temperature to cool the charge air. The charge air leaving the high pressure compressor can be cooled in a further charge air cooler, for example, by air of ambient temperature in order to decrease the specific volume of the charge air and increase the amount of charge air which can be delivered to the combustion engine.

SUMMARY OF THE INVENTION The purpose of the present invention is to provide a relatively simple cooling system comprising one radiator which is able to cool objects with coolant at at least three different temperatures.

The above mentioned purpose is achieved by the cooling system according to claim 1. The first valve device makes it possible to direct the coolant flow to the radiator or a radiator bypass line in order to cool the coolant to a suitable operating temperature. The second valve device makes it possible to direct coolant from the radiator and/or the radiator bypass line to all three objects to be cooled. The second valve device directs a coolant flow to the first object via the first object inlet line. However, the first inlet line also receives coolant flows from the second object outlet line and the third object outlet line. Since these coolant flows have ben heated by the second object and the third object, the mixed coolant flow entering the first object has a first temperature which is higher than the coolant temperature at the second valve device. The second valve device provides a coolant flow to the second object via the second object inlet line. However, the second inlet line also receives a coolant flow from the mixing line which has been heated by the first object. The mixing line comprises a third valve making it possible to supply a desired amount of warm coolant to the second object inlet line. Thus, it is possible to give the coolant flow entering the second object a variable second temperature with a high accuracy. The coolant flow entering the second object has a second temperature which is higher than the coolant temperature at the second valve device. Finally, the second valve device provides a coolant flow to the third object via the third object inlet line. This coolant flow is not mixed with any other coolant flows. Thus, the coolant flow entering the third object has a third temperature which corresponds to the coolant temperature at the second valve device. The third coolant temperature is lower than the first coolant temperature and the second coolant temperature. Thus, the cooling system is able to deliver coolant at three different temperatures to objects to be cooled.

According to an embodiment of the invention, the cooling system comprises a control unit configured to control the first valve device, the second valve device and the third valve device. The control unit may control the valve devices such that coolant at suitable temperatures are delivered to the respective objects. In this case, it is possible to provide an individual cooling of each object.

According to an embodiment of the invention, the control unit is configured to estimate a suitable third coolant temperature and to control the first valve device such that it directs a coolant flow to the radiator such that the coolant leaving the radiator has a temperature which is lower or equal to the third temperature. The coolant leaving the radiator is directed, via the third object inlet line, to the third object. Thus, the coolant leaving the radiator has to have a temperature which is lower or equal to the third coolant temperature. The third object may be the cylinder head of a combustion engine. It is known that different temperatures in different parts of a combustion engine can improve the fuel economy. A lower temperature in the cylinder head than in the cylinder block can improve the fuel economy of the combustion engine. The third coolant temperature may be relatively close to ambient temperature. The third coolant temperature may be around 30°. Alternatively or in combination the third object is a charge air cooler arranged in a position between a low pressure compressor and a high pressure compressor. It is useful to cool the charge air in a position between the compressors to a temperature as low as possible in order to increase the efficiency of the compressors.

According to an embodiment of the invention, the control unit is configured to estimate a suitable second temperature of the coolant to be directed to the second object and to control the second valve device and the third valve device such that they directs a mixed coolant flow at the estimated second temperature to the second object. The control unit controls the second valve member such that it directs a coolant flow of a relatively low temperature to the second object inlet line and the third valve device such that a coolant flow of a higher temperature is directed via the mixing line to the second object inlet line. The third valve device is controlled such that a mixed coolant flow at the estimated second temperature is directed to the second object. The second object may be the working medium in a condenser of a WHR system. In such a case, the control unit may be configured to determine a suitable condensation temperature of the working medium in the condenser and to estimate a coolant flow and a second coolant temperature at which the working medium obtains the determined condensation temperature and to control the second valve device and the third valve device such that they directs the estimated coolant flow at the second coolant temperature to the second object. In case ethanol is the working medium, the second coolant temperature may be around 70°C.

According to an embodiment of the invention, the control unit is configured to estimate a suitable first temperature of the coolant to be directed to the first object and to control the second valve device such that it directs a coolant flow to the first object inlet line which in a mixed state with the coolant flows from the second object outlet line and the third object outlet line creates a coolant flow at the first temperature to the first object. The first object may be cylinder block of a combustion engine. The cylinder block are heated during the combustion processes in the cylinders and need to be cooled. A suitable first coolant temperature may be in the range of 80-90°C.

According to an embodiment of the invention, the first valve device is a three way valve. The three way valve may comprises one inlet opening and two outlet openings. The three way valve may receive a coolant flow from the first object outlet line and direct a first part of it to the radiator and a remaining part of it to the radiator bypass line. In this case, the first valve device is designed as a single valve. Preferably, the first valve device is adjustable in a stepless manner. In this case, it is possible to vary the coolant flow to the radiator and the radiator bypass line with a high accuracy. Alternatively, the first valve device is designed as two two way valves wherein a first two way valve is arranged in a radiator inlet line and a second two way valve is arranged in the radiator bypass line.

According to an embodiment of the invention, the second valve device is a three way valve. The three way valve may receive a coolant flow from the radiator bypass line and directs a part of it to the first object inlet line and a remaining part of it to the second object inlet line and the third object inlet line. Alternatively, the three way valve directs the entire coolant flow from the radiator bypass line and a part of the coolant flow from the radiator to the first object inlet line. In this case, a remaining part of the coolant flow from the radiator is directed to the second object inlet line and the third object inlet line. In this case, the second valve device is designed as a single valve. Preferably, the second valve device is adjustable in a stepless manner. In such a case, it is possible to adjust the coolant flow to the inlet lines to the respective objects with a high accuracy. Alternatively, the second valve device is designed as two two way valves wherein a first two way valve is arranged in the first object inlet line and a second two way valve is arranged in a radiator outlet line.

According to an embodiment of the invention, the third valve device is a two way valve. Preferably, the second valve device is adjustable in a stepless manner. In such a case, it is possible to adjust the coolant flow from the mixing line to the second object inlet line with a high accuracy.

According to an embodiment of the invention, the control unit is configured to receive information from a number of temperature sensors arranged in different positions of the cooling system and to control the valve devices by means of this information. The control unit may receive information about the coolant temperature in the first object inlet line, in the second object inlet line, in the third object inlet line, in the first object outlet line and in a position downstream of the radiator. In view of such temperature information, it is possible for the control unit to control the valve devices such possible differences between the actual coolant temperatures and the estimate coolant temperatures can be eliminated. However, the control unit may receive information about other operating parameters than the actual coolant temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention are described, as examples, with reference to the attached drawings, in which: Fig. 1 shows a cooling system according to a first embodiment of the invention and Fig. 2 shows a cooling system according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a schematically disclosed vehicle 1 powered by a combustion engine 2. The combustion engine 2 comprises cylinder block 3 and cylinder head 4. The vehicle 1 may be a heavy vehicle and the combustion engine 2 may be a diesel engine. The vehicle 1 comprises a cooling system configured to cool the cylinder block 3 and the cylinder head 4. A pump 5 circulates coolant in the cooling system. The cooling system comprises a cylinder block inlet line 3 a directing coolant to the cylinder block 3. When the coolant has circulated through the cylinder block 3, it is received in a cylinder block outlet line 3b. A first valve device in the form of a first three way valve 6 is arranged at an end of the cylinder block outlet line 3b. The first three way valve 6 has one inlet opening and two outlet openings. The cooling system comprises a radiator inlet line 8a directing coolant to a radiator 8 and a radiator outlet line 8b receiving coolant from the radiator 8. The cooling system comprises a radiator bypass line 9 directing coolant past the radiator 8. The first three way valve 6 is controlled by a control unit 10. The first three way valve 6 is adjustable in a stepless manner. Thus, it is possible for the first three way valve 6 to receive coolant from the cylinder block outlet line 3b and distribute it in a stepless manner to the radiator inlet line 8a and the radiator bypass line 9. A radiator fan 11 and ram air provides a cooling air flow through the radiator 8. Other coolers such as, for example, a charge air cooler may be mounted in a position upstream of the radiator 8.

The coolant leaving the radiator 8 is distributed, to a cylinder head inlet line 4a and a condenser inlet line 15 a. The cooling system comprises a second valve device in the form of a second three way valve 12. The second valve device 12 may direct a part of the coolant leaving the radiator 8 to the cylinder block inlet line 3 a. Alternatively or in combination, the second three way valve 12 receives coolant from the bypass line 9. The second three way valve may distribute the coolant from the bypass line 9 to the cylinder block inlet line 3, the cylinder head inlet line 4a and the condenser inlet line 15a. The second three way valve 12 is controlled by the control unit 10. The second three way valve 12 is adjustable in a stepless manner.

A mixing line 16 receives coolant from the cylinder block outlet line 3b and directs it to the condenser inlet line 15 a. A third valve device in the form of a two way valve 17 controls the coolant flow through the mixing line 16 the two way valve 17 is adjustable in a stepless manner and it is controlled by the control unit 10. A cylinder head outlet line 4b receives coolant from the cylinder head 4 and directs it, via a condenser outlet line 15b, to the cylinder block inlet line 3a. Thus, the entire coolant flow is led to the cylinder block 3. The cooling system comprises a plurality of sensors sensing the temperature of the coolant in different positions of the cooling system. In this case, a first sensor Si senses a first coolant temperature T1in the cylinder block inlet line 3a, a second sensor S2senses a second coolant temperature T2in the condenser inlet line 15a, a third sensor S3senses a third coolant temperature T3in the cylinder head inlet line 4a, fourth sensor S4senses an initial coolant temperature To in the cylinder block out line 3b and a fifth temperature sensor S5senses the radiator coolant temperature TKin the radiator outlet line 8b.

The vehicle is provided with a WHR-system (Waste Heat Recovery system) comprising a closed circuit 21 with a circulating working medium. A pump 22 which pressurizes and circulates a working medium in a closed a circuit 21. In this case, the working medium is ethanol. However, it is possible to use other kinds of working mediums such as for example R245fa. The pump 22 directs the working medium to an evaporator 23. The working medium is heated in the evaporator 23, for example, by exhaust gases from the combustion engine. The working medium is heated in the evaporator 23 to a temperature at which it evaporates. The working medium is circulated from the evaporator 23 to an expander 24. The pressurised and heated working medium expands in the expander 24. The expander 24 generates a rotary motion which may be transmitted, via a suitable mechanical transmission 25, to a shaft 26 of the power train of the vehicle 1. Alternatively, the expander 24 may be connected to a generator transforming mechanical energy into electrical energy. The electrical energy may be stored in a battery. The stored electrical energy can be supplied to an electrical engine for driving of the vehicle 1 or a component on the vehicle in a later state.

When the working medium has passed through the expander 24, it is directed to the condenser 15. The working medium is cooled in the condenser 15 by coolant from the condenser inlet line 15a to a temperature at which it condenses. The working medium is directed from the condenser 15 to a receiver 28. The pressure in the receiver 28 can be varied by means of a pressure regulator 28a. The pump 22 sucks working medium from the receiver 28. A second control unit 29 controls the operation of the WHR-system. The second control unit 29 controls the operation of the pump 22 and the expander 24. The WHR-system makes it possible to transform thermal energy from the exhaust gases to mechanical energy or electrical energy. A pressure sensor 30 or a temperature sensor senses the condensation pressure or the condensation temperature of the working medium in the condenser 15.

The temperature of exhaust gases and thus the heating effect of the working medium in the evaporator 23 varies during different operating conditions. In order to maintain a substantially continuously high thermal efficiency in the WHR-system, the working medium is to be cooled with an adjustable cooling effect in the condenser 15. It is favourable to establish a condensation pressure as low as possible at the different operating conditions. However, it is suitable to avoid negative pressure in the WHR-system by practical reasons. In view of these facts, it is suitable to provide a cooling of the working medium in the condenser 15 to a condensation pressure just above lbar. Consequently, in order to maintain a high thermal efficiency it is necessary to adjust the cooling effect of the working medium in the condenser 15 in view of the supplied heat energy from the exhaust gases such that the condensation pressure will be just above 1 bar. The working medium ethanol has a condensation temperature of 78°C at 1 bar. In this case, it is suitable to accomplish a condensation temperature of just above 78°C in the condenser 15.

During operation, the control unit 10 receives information from the fourth sensors S4about the initial coolant temperature T0in the cooling system. During operating conditions when the initial coolant temperature T0is too low, the first three way valve 6 distributes the entire coolant flow to the bypass line 9. The second three way valve 12 receives the coolant flow from the radiator bypass line 9 and directs a part of it to the cylinder block inlet line 3 a and a remaining part of it to the cylinder head inlet line 4a and the condenser inlet line 15 a. Thus, the second way valve 12 directs coolant at the initial temperature To to the cylinder block inlet line 3a, the cylinder head inlet line 4a and the condenser inlet line 15 a. However, the cylinder block inlet line 3 a are mixed with coolant flows from the cylinder head outlet line 3b and from the condenser outlet line 15b. Since these coolant flows have been heated in the cylinder head 3 and in the condenser 15, the coolant flow entering the cylinder block 3 has a first temperature Ti which is higher temperature than the initial coolant temperature T0.

The control unit 10 receives information from the second control unit 28 about the operating condition of the WHR system. The control unit 10 may, for example, receive information from the sensor 30 about the actual condensation temperature in the condenser 15. The control unit 10 determines a desired condensation temperature of the working medium in the condenser 15. When ethanol is used as working medium, a condensation temperature of about 80°C is desirable during most operating conditions. The control unit 10 estimates a required flow and second temperature T2of the coolant to be directed to the condenser 15 in order to provide the determined condensation temperature in the condenser 15. The mixing line 16 receives a coolant flow from the cylinder block outlet line 3b. Since the coolant in the mixing line 16 has been heated in the cylinder block 3, the temperature of the coolant in the mixing line 16 is higher than the initial coolant temperature To. The control unit 10 controls the two way valve 17 such that it distribute an estimated coolant flow to the condenser inlet line 15a such that the mixture of the coolant flow from the mixing line 16 and the initial part of the condenser inlet line 15a obtains the estimated second coolant temperature T2for cooling the working medium to the determined condensation temperature. The cylinder head inlet line 4a directs coolant to the cylinder head 3 in an unmixed state. Thus, the coolant flow entering the cylinder head 3 has a third coolant temperature T3corresponding to the initial temperature T0.

During operating conditions when the initial coolant temperatures To is too high, the control unit 10 controls the first three way valve 6 such that it distributes the entire coolant flow to the radiator 8. In this case, the coolant has a radiator temperature TRwhen it leaves the radiator 8 which is clearly lower than the initial temperature To. The second way valve 12 is controlled such that a part of the coolant flow in the radiator outlet line 8b is directed to the cylinder block inlet line 3a. A remaining part of the coolant flow in the radiator outlet line 8b is directed to the cylinder head inlet line 4a and the condenser inlet line 15 a. In this case, coolant at the radiator temperature TRis directed to the cylinder block inlet line 3 a, the cylinder head inlet line 4a and the condenser inlet line 15a. However, the cylinder block inlet line 3a are mixed with coolant flows from the cylinder head outlet line 3b and from the condenser outlet line 15b. Since these coolant flows have been heated in the cylinder head 3 and in the condenser 15, the coolant flow entering the cylinder block 3 has a first temperature Ti which is higher than the radiator temperature TR. The control unit 10 controls the two way valve 17 such that the initial coolant flow in the condenser inlet line 15a is mixed with a warmer coolant flow from the mixing line 16 such that a coolant flow of a second temperature T2is directed to the condenser 15. Thus, the second temperature T2is higher than the radiator temperature TR. Finally, a coolant flow at a third temperature T3,which corresponds to the radiator temperature TR, is directed to the cylinder head 4.

According to a third alternative, the initial coolant temperatures To in the cylinder block outlet line 3b is within an acceptable temperature range. In this case, the control unit 10 controls the first three way valve 6 such that it directs a part of the coolant flow to the radiator 8 and a remaining part of the coolant flow to the radiator bypass line 9. In this case, the second way valve 12 can be controlled in two different manners. In one manner, the second valve device 12 directs the entire coolant flow from the bypass line 9 and a part of the coolant flow from the radiator outlet line 8b to the cylinder block inlet line 3a. The remaining part of the coolant flow from the radiator outlet line 8b is directed to the cylinder head inlet line 4a and the condenser inlet line 15a. In this case, the coolant flow entering the cylinder block 3 has a first coolant temperature T1which is related to the flows and the temperatures the coolants in the radiator outlet line 8b, the bypass line 9, the cylinder head outlet line 4b and the condenser outlet line 15b. The coolant flow entering the condenser 15 has a second coolant temperature T2which related to the flows and the temperatures of the coolants in the radiator outlet line 8b and the mixing line 16. The coolant entering the cylinder head 4 has a third temperature T3corresponding to the radiator temperature TR.

In the other manner, the second three way valve 12 is controlled such that it directs a part of the coolant flow from the bypass line 9 to the cylinder block inlet line 3 a and a remaining part of the coolant flow from the bypass line 9 to the cylinder head inlet line 4a and the condenser inlet line 15 a. The entire coolant flow from the radiator 8 is directed to the cylinder head inlet line 4a and the condenser inlet line 15a. In this case, the coolant entering the cylinder block 3 has a first coolant temperature T1which is related to the flows and the temperatures of the coolants from the bypass line 9, the cylinder head outlet line 4b and the condenser outlet line 15b. The coolant entering the condenser 15 has a second temperature T2which is related to the flows and the temperatures of the coolants from the radiator 8, the bypass line 9 and the mixing line 16. The coolant entering the cylinder head 4 has a third coolant temperature T3which is related to the flows and the temperatures the coolants from the radiator 8 and the bypass line 9. Consequently, it is possible to create coolant flows at three different and suitable temperatures T1, T2, T3for cooling of the cylinder block 3, the cylinder head 4 and the working medium in the condenser 15 at the most operating conditions.

Fig 2 shows an alternative embodiment of the cooling system. An exhaust line 31 of the combustion engine is indicated in Fig. 2. The combustion engine 2 is provided with a high pressure turbo unit 32 comprising a turbine 32a and a compressor 32b, and a low pressure turbo unit 33 comprising a turbine 33a and a compressor 33b. The exhaust gases are initially led through the turbine 32a of the high pressure turbo unit 32. The high pressure turbine 32a is thus provided with driving power which is transmitted, via a connection, to the compressor 32b of the high pressure turbo unit 32. The exhaust gases are thereafter led through the turbine 33a of the low pressure turbo unit 33. The low pressure turbine 33a is provided with driving power which is transmitted, via a connection, to the compressor 33b of the low pressure turbo unit 33. The low pressure compressor 33b drawn air into an air inlet line 34. The air in the inlet line 34 is compressed in a first stage by the low pressure compressor 33b to a first pressure. The compressed air is cooled in a first charge air cooler 35. The cooled compressed air is compressed in a second stage in the high pressure compressor 32b. The air in the air inlet line 34 is cooled in a second stage in a second charge air cooler 36 arranged at a front portion of the vehicle in a position upstream of the radiator 6b before it is directed to the combustion engine 2.

In this case, the cooling system also is configured to cool the above mentioned objects 3, 4, 15 and the charge air in the first charge air cooler 35. The cooling system comprises a charge air cooler inlet line 35a directing coolant from the radiator outlet line 8b to the first charge air cooler 35. A charge air cooler outlet line 35b directs coolant from the charge air cooler 35 to the cylinder block inlet line 3a. The charge air cooler inlet line 35a and the cylinder head inlet line 4a are arranged in parallel. Thus, the charge air is cooled in the first charge air cooler 35 by coolant of the same third temperature T3which cools the cylinder head 4. In addition to this difference, the cooling system in Fig. 2 has a corresponding function as the cooling system in Fig. 1.

The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims

1. A cooling system for cooling of objects (3, 4, 15, 35) with coolant at three different temperatures (T1, T2, T3), wherein the cooling system comprises - a radiator inlet line (8a) configured to direct coolant to a radiator (8) and a radiator outlet line (8b) configured to receive coolant from the radiator (8), - a radiator bypass line (9) configured to direct coolant past the radiator (8), - a first object inlet line (3a) configured to direct coolant at a first temperature (T1) to a first object (3) to be cooled and a first object outlet line (3b) configured to receive coolant from the first object (3), - a second object inlet line (15a) configured to direct coolant at a second temperature (T2) to a second object (15) to be cooled and a second object outlet line (15b) configured to receive coolant from the second object (15), - a third object inlet line (4a, 35a) configured to direct coolant at a third temperature (T3) to a third object (4, 35) to be cooled and a third object outlet line (4b, 35b) configured to receive coolant from the third object (4, 35), - a first valve device (6) configured to receive coolant from the first object outlet line (3b) and direct it to the radiator inlet line (8a) and/or the radiator bypass line (9), - a second valve device (12) configured to receive coolant from the radiator outlet line (8b) and /or the radiator bypass line (9) and distribute it to the first object inlet line (3a), the second object inlet line (15a) and the third object inlet line (4a, 35a), characterized in that second object outlet line (15b) and the third object outlet line (4b, 35b) directs coolant to the first object inlet line (3a) and that the cooling system comprises a mixing line (16) directing coolant from the first object outlet line (3b) to the second object inlet line (15a) and a third valve device (17) configured to control the coolant flow through the mixing line (16) to the second object inlet line (15a).

2. A cooling system according to claim 1, characterized in that the cooling system comprises a control unit (10) configured to control the first valve device (6), the second valve device (12) and the third valve device (17).

3. A cooling system according to claim 2, characterized in that the control unit (10) is configured to estimate a suitable third coolant temperature (T3) and to control the first valve device (6) such that it directs a coolant flow to the radiator (8) such that the coolant leaving the radiator (8) has a temperature which is lower or equal to the third coolant temperature (T3).

4. A cooling system according to claim 2 or 3, characterized in that the control unit (10) is configured to estimate a suitable second temperature (T2) of the coolant flow to be directed to the second object (15) and to control the second valve device (12) and the third valve device (17) such that they together directs a coolant flow at the estimated second temperature (T2) to the second object (15).

5. A cooling system according to any one of the claims 2 to 4, characterized in that the control unit (10) is configured to estimate a suitable first temperature (Ti) of the coolant to be directed to the first object (3) and to control the second valve device (12) such that it delivers a coolant flow to the first object inlet line (3a) which in a mixed state with the coolant flows from the second object outlet line (15b) and the third object outlet line (4b, 35b) creates a coolant flow at the first temperature (T1) to the first object (3).

6. A cooling system according to any one of the preceding claims, characterized in that the first object is the cylinder block (3) of a combustion engine (2).

7. A cooling system according to any one of the preceding claims, characterized in that the second object is the working medium in a condenser (15) of a WHR system.

8. A cooling system according to claim 4 and 7, characterized in that the control unit (10) is configured to determine a suitable condensation temperature of the working medium in the condenser (15) and estimate a second temperature (T2) and the coolant flow to be directed to the second object (15) at which the working medium obtains the determined condensation temperature and to control the second valve device (12) and the third valve device (17) such that the estimated coolant flow at the second temperature (T2) is directed to the second object (15).

9. A cooling system according to any one of the preceding claims, characterized in that the third object is the cylinder head (4) of a combustion engine (2).

10. A cooling system according to any one of the preceding claims, characterized in that the third object is a charge air cooler (35) arranged in a position between a low pressure compressor (33b) and a high pressure compressor (32b).

11. 1 1. A cooling system according to any one of the preceding claims, characterized in that the first valve device is a three way valve (6).

12. A cooling system according to any one of the preceding claims, characterized in that the second valve device is a three way valve (12).

13. A cooling system according to any one of the preceding claims, characterized in that the third valve device is a two way valve (17).

14. A cooling system according to claim 2 or any one of the preceding claims 3-13 in combination with claim 2, characterized in that the control unit (10) is configured to receive information from a number of temperature sensors (S1, S2, S3, S4, S5) arranged in different positions of the cooling system and to control the valve devices (6, 12, 17) by means of this information.

15. A vehicle comprising a cooling system according to any one of the preceding claims 1-14.