SE540376C2

SE540376C2 - A cooling system comprising two cooling circuits and a common expansion tank

Info

Publication number: SE540376C2
Application number: SE1651710A
Authority: SE
Inventors: Kardos Zoltan; Hall Ola
Original assignee: Scania Cv Ab
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2018-08-28
Also published as: SE1651710A1; DE102017011428A1; DE102017011428B4

Abstract

The present invention relates to a cooling system comprising two cooling circuits (1, 2) and a common expansion tank (4). The cooling system comprises a wall element (5) dividing an inner space of the expansion tank (4) in first chamber (4a) and a second chamber (4b). A static line (1d) of the first cooling circuit (1) is connected to the first chamber (4a) and a deaeration line (1e) of the first cooling circuit (1) is connected to the second chamber (4b) of the expansion tank (4). A static line (2d) of the second cooling circuit (2) is connected to the second chamber (4b) and a deaeration line (2e) of the second cooling circuit (2) is connected to the first chamber (4a) of the expansion tank (4).

Description

A cooling system comprising two cooling circuits and a common expansion tank BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a cooling system comprising two cooling circuits and a common expansion tank according to the preamble of claim 1. The present invention relates further to a vehicle comprising such a cooling system.

Hybrid vehicles may be powered by an electric power unit in combination with some other form of power unit such as a combustion engine. The electric power unit may comprise an electric machine which alternately works as motor and generator, an electric energy storage for storing of electrical energy and power electronics for controlling the flow of electrical energy between the electrical energy storage and the electric machine. The electrical machine, the electrical energy storage and the power electronics are heated during operation and they need to be cooled.

The electrical energy storage may have an optimal efficient operating temperature within the temperature range of 20-25°C. Thus, the electrical energy storage has to be cooled by coolant of a relatively low temperature. The electric energy storage has a high thermal mass. Thus, the temperature of the electric energy storage is changed relatively slowly even during operating conditions when the load on the electrical energy storage is varied rapidly. The power electronics and the electrical machine can usually withstand a higher temperature which may be up to about 60-70°C. Thus, it is suitable to cool the power electronics and the electrical machine by coolant of a higher temperature and in a separate cooling circuit. The electrical machine has a low thermal mass and it can be highly loaded during certain operating conditions. In order to prevent overheating of a component having these properties, the cooling circuit has to have a high cooling capacity.

However, vehicles may comprise other components and mediums to be cooled by coolant of different temperatures. Such components and mediums may be a combustion engine, a hydraulic retarder, charge air, recirculating exhaust gases, engine oil, gearbox oil etc.

WO 2011/050892 shows a hybrid vehicle provided with a first cooling circuit for cooling of an electric drive unit and a second cooling circuit for cooling of an intercooler. The cooling system comprises a common expansion tank receiving coolants from the two cooling circuits.

SUMMARY OF THE INVENTION The object of the present invention is to provide a cooling system comprising two cooling circuits which together have a smaller size than two separate cooling systems of the same cooling capacity and a vehicle comprising such a cooling system.

The above mentioned object is achieved by the cooling system according to claim 1. According to the invention, the cooling system comprises a first cooling circuit and a second cooling circuit provided with a common expansion tank. The common expansion tank comprises a wall element dividing the inner space of the expansion tank in a first chamber and a second chamber. The first cooling circuit comprises a static line connected to the first chamber and a deaeration line connected to the second chamber. The second cooling circuit comprises a static line connected to the second chamber and a deaeration line connected to the first chamber.

After a period of continuous operation of the cooling system, the deaeration lines direct coolant without air to the expansion tank. The coolant leaves the expansion tank via the static lines. Thus, the cooling circuits receive coolant from one of the chambers and direct coolant back to the other chamber. In case the deaeration lines direct coolant at different temperatures to the expansion tank, heat is transferred between the cooling systems in the expansion tank. Consequently, the cooling circuit directing coolant of the higher temperature to the expansion tank obtains an additional cooling in the expansion tank. Due to this fact, the cooling circuit with the higher coolant temperature cools the component in the circuit by means of coolant of a lower temperature. Thus, the heat transfer in the expansion tank result in an increased cooling capacity of the cooling circuit with the higher coolant temperature. In view of this fact, it is possible to design the cooling circuit with the higher coolant temperature with a lower maximum capacity. As a consequence, the cooling system according to the invention can be made smaller than a conventional cooling system including two completely separated cooling circuits. Furthermore, the use of a common expansion tank results in fewer components.

According to an embodiment of the invention, the first cooling circuit is configured to direct coolant to the expansion tank of a lower temperature than the second cooling circuit and that the first cooling circuit is configured to cool a component having a higher thermal mass the component to be cooled by the second cooling circuit. The heat transfer between the cooling circuits in the expansion tank increases the cooling capacity of the cooling circuit having the higher coolant temperature at the same time it decreases the cooling capacity of the cooling circuit having the lower coolant temperature. In case the second cooling circuit has a high load, the temperature of the coolant directed to the expansion tank from the second circuit increases and the heat transfer in the expander tank. The increased heat transfer decreases the cooling capacity of the first cooling circuit. In case the first component has a high thermal mass a temporarily reduced cooling capacity of the first cooling circuit will not significantly influence on the temperature of the first component.

According to a further embodiment of the invention, the expansion tank comprises a coolant passage between the chambers configured to eliminate coolant level differences between said chambers. Such a coolant passage may have a sufficiently large flow area for a providing a coolant between the chambers that evens out coolant level differences in the chambers. The coolant passage should not allow an excessive flow between the chambers that evens out the temperature difference between the chambers. The flow passage may be an orifice arranged in the wall element at a lower level than a minimum coolant level in the expansion tank.

According to a further embodiment of the invention, the expansion tank may comprises an air passage between the chambers configured to eliminate pressure differences between said chambers. Such an air passage can be arranged above the wall element. It has at least to be arranged at a higher level than a maximum coolant level in the expansion tank.

According to a further embodiment of the invention, the second deaeration line is configured to provide an ordinary coolant flow to the expansion tank during operating condition when the second cooling circuit has a low load and to provide an additional coolant flow to the expansion tank during operating condition when the second cooling circuit has a high load. The additional coolant flow in the second deaeration line increases the total coolant flow in the second cooling circuit. Furthermore, it increases the coolant flow rate from the expansion tank to the component to be cooled.

Consequently, this measure increases the cooling capacity of the second cooling circuit further.

According to a further embodiment of the invention, the second deaeration line comprises an ordinary flow passage providing an ordinary flow area through the deaeration line and an additional flow passage providing an additional flow area through the deaeration line and a valve member configured to allow a coolant flow through additional flow passage during operation condition when the second cooling circuit has a high load. The ordinary flow are dimension such that the second deaeration line obtains a suitable coolant flow rate during low load on the second cooling circuit. The additional flow passage is dimensioned such that the second deaeration line obtains a suitably higher coolant flow rate during high load on the second cooling circuit.

According to a further embodiment of the invention, the cooling system comprises a control unit configured to receive information about a parameter related to the load of the second cooling circuit and to initiate a movement of the valve member such that it allows a coolant flow through the additional flow passage when the parameter indicates a high load of the second cooling circuit. In such a case, it is possible to automatically control the coolant flow through the second deaeration line in a simple manner.

According to a further embodiment of the invention, said valve member is configured to allow a coolant flow through the additional flow passage when the pressure of the coolant in the second deaeration line exceeds a predetermined pressure. The pressure of the coolant in the second deaeration line is related to the load on the second cooling circuit. Said valve member may be a check valve. The check valve may be dimensioned to open at pressure defining a boundary between a low load and a high load of the second cooling circuit.

According to a further embodiment of the invention, said valve member is configured to be set in an open position when the temperature of the coolant in the second deaeration line exceeds a predetermined temperature. The temperature of the coolant in the second deaeration line is also related to the load on the second cooling circuit. Said valve member may comprise a valve body arranged in the additional flow passage and a thermostat configured to move the valve body to an open position when the temperature of the coolant in the second deaeration line exceeds the predetermined temperature. Such a thermostat may have a regulating temperature defining a boundary between a low load and a high load of the second cooling circuit.

According to a further embodiment of the invention, the cooling system comprises a valve device configured to be set in a low load position in which it directs the coolant flow in the first deaeration line to the first chamber and the coolant flow in the second deaeration line to the second chamber and in a high load position and in which it directs the coolant flow in the first deaeration line to the second chamber and the coolant flow in the second deaeration line to the first chamber. In case the second circuit has a low load, there is no need to favor the heat transfer in the expansion tank. In this case, cooling circuits works as two separate cooling circuits. In case the second circuit has a high load, it is suitable to favor the heat transfer in the expansion tank in order to increase the cooling capacity of the second cooling circuit.

According to a further embodiment of the invention, the valve device comprises a thermostat configured to sense the temperature of the coolant in the second deaeration line and to set the valve device in the low load position or the high load position in view of this temperature. The thermostat may be dimensioned to have a regulating temperature defining a boundary between low load and high load. The thermostat may be configured to provide to movement of a rod provided with a number of valve bodies to the low load position and the high load position in view of the temperature of the coolant in the second deaeration line.

BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention are described, as examples, and with reference to the attached drawings, in which: Fig. 1 shows a cooling system according to a first embodiment of the invention, Fig. 2 shows a cooling system according to a second embodiment of the invention, Fig. 3a-3c show alternative designs of the valve member in Fig. 2 and Fig. 4a-4b show a cooling system according to a third embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a cooling system comprising a first cooling circuit 1 and a second cooling circuit 2 which are arranged in a schematically indicated vehicle 3. The first cooling circuit 1 comprises a first pump 1a circulating a coolant in the first cooling circuit 1, at least a first component 1b to be cooled by the circulating coolant and a first radiator 1c in which the coolant is cooled by a cooling air flow. The first component 1b has a high thermal mass. Thus, the temperature of the first component lb varies relatively slowly. The first component 1b has a relatively low operating temperature. Thus, the first cooling circuit 1 has to be cooled by coolant of a relatively low temperature. The first component 1b may be an electrical energy storage in a hybrid vehicle or in a pure electrically driven vehicle. The first cooling circuit 1 comprises further a static line 1d having an extension between the first cooling circuit 1 and an expansion tank 4 and a deaeration line 1e having an extension between the first component 1b and an expansion tank 4.

The second cooling circuit 2 comprises a second pump 2a circulating a coolant in the second cooling circuit 2, at least a second component 2b to be cooled by the circulating coolant and a second radiator 2c in which the coolant is cooled by a cooling air flow. The second component 2b has a low thermal mass. Thus, the temperature of the first component 1b may vary rapidly. The second component 2b has a higher operating temperature than the first component 1b. Thus, the second component 2b can be cooled by coolant of a higher temperature than the temperature of the coolant cooling the first component 1b. The second component 2b may be an electric machine which alternately works as motor and generator in a hybrid vehicle or in a pure electrically driven vehicle. The second cooling circuit 2 comprises further a static line 2d having an extension between the second cooling circuit 2 and the expansion tank 4 and a second deaeration line 2e having an extension between the second component 2b and the expansion tank 4.

The expansion tank 4 comprises a wall element 5 dividing an inner space of the expansion tank 4 in a first chamber 4a and a second chamber 4b. The wall element 5 comprises an orifice defining a coolant passage 6a between the chambers 4a, 4b. The coolant passage 6a is located at a lower level than a minimum coolant level in the expansion tank 4. The coolant passage 6a allowing a coolant flow through the wall element 5 evens out coolant level differences between the first chamber 4a and the second chamber 4b. An air passage 6b is arranged in a position above an upper edge 5 a of the wall element 5. The air passage 6b is located at a higher level than a maximum coolant level in the expansion tank 4. The air passage 6b allowing an air flow between the first chamber 4a and the second chamber 4b which evens out pressure differences between the chambers 4a, 4b.

The first static line 1d has an extension between a position immediately upstream of the first pump 1a in the first cooling circuit 1 and the first chamber 4a of the expansion tank 4. The first deaeration line le has an extension between the first component and the second chamber 4b of the expansion tank 4. The second static line 2d has an extension between a position immediately upstream of the second pump 2a in the second cooling circuit 2 and the second chamber 4b of the expansion tank 4. The second deaeration line 2e has an extension between the second component 2b in the second cooling circuit 2 and the first chamber 4a of the expansion tank 4.

At start of the pumps 1a, 2a in the cooling circuits 1, 2, air bubbles may be present in the coolant flow directed, via the deaeration lines 1e, 2e, to the expansion tank 4. After a period of continued operation, substantially only coolant is directed via the deaeration lines 1e, 2e to the expansion tank 4. The first cooling circuit 1 receives coolant, via the first static line 1d, from the first chamber 4a of the expansion tank 4 and the second cooling circuit 2 receives a coolant, via the second static line 1d, from the second chamber 4a of the expansion tank 4. The first cooling circuit 1 direct a part of the coolant flow from the first component 1b, via the first deaeration line 1e, to the second chamber 4b of the expansion tank 4 and the second cooling circuit 2 directs a part of the coolant flow from the second component 2b, via the second deaeration line 2e, to the first chamber 4a of the expansion tank 4. The first cooling circuit 1 and the second cooling circuit 2 direct coolants of different temperatures to the chambers 4a, 4b of the expansion tank 4. Thus, the chambers 4a, 4b receives coolant of different temperatures. The first cooling circuit 1 directs coolant of the lower temperature to the second chamber 4b of the expansion tank and it receives coolant of the higher temperature from the first chamber 4a of the expansion tank 4. The second cooling circuit 2 directs coolant of the higher temperature to the first chamber 4a of the expansion tank and it receives coolant of the lower temperature from the second chamber 4b of the expansion tank 4.

Consequently, heat energy is transferred between the cooling circuits 1, 2 in the expansion tank 4. In case the second cooling circuit 2 has a high load, the temperature of the coolant directed to the expansion tank 4 from the second circuit 2 increases and the heat transfer in the expander tank 4. The increased heat transfer decreases the cooling capacity of the first cooling circuit and it increases the cooling capacity of the second cooling circuit. Since the first component 1b has a high thermal mass a temporarily reduced cooling capacity of the first cooling circuit 1 will not significantly influence on the temperature of the first component 1b. The increased cooling capacity of the second cooling circuit 2 prevent heating of the second component 2b to a too high temperature. In view of this fact, it is possible to design the second cooling circuit 2 with a lower maximum capacity. As a consequence, the cooling system according to the invention can be made smaller than a conventional cooling system including two completely separated cooling circuits.

Fig. 2 shows an alternative embodiment of the cooling system. In this case, the second deaeration line 2e comprises an ordinary flow passage 7 having a flow area defining an ordinary flow rate through the deaeration line 2e and an additional flow passage 8 able to provide an additional flow area through the deaeration line 2e. The additional flow passage 8 is arranged in parallel with the ordinary flow passage 7. The additional flow passage 8 comprises a valve member 9 controlling the flow through the additional flow passage 8.

During operating condition when the second circuit 2 has a low load, the valve member 8 is set in a closed position. The additional flow passage 8 is closed and the coolant flow in the second deaeration line 2e is defined by the ordinary flow passage 7. During operating condition when the second circuit 2 has a high load, the valve member 8 is set in an open position. The increased flow area in the second aeration line 2 e increases the coolant flow rate from the second component 2b, via the second aeration line 2e, to the expansion tank 4. The increased coolant flow rate to the first chamber of the expansion tank 4 results in a corresponding increased coolant flow rate from the second chamber 4b of the expansion tank 4 to the second cooling circuit 2. The increased coolant flow rate increases the heat transfer between the cooling circuits 1, 2 in the expansion tank 4 and the cooling capacity of the second cooling circuit 2.

Fig, 3a shows a first embodiment of the valve member 9 in Fig. 2. In this case, the valve member is designed as a rotatable valve body 9a comprising a circular flow path 7a defining the ordinary flow passage and a straight flow path 8a defining the additional flow passage. A control unit 10 is configured to receive information from a sensor 11 about the temperature or the pressure of the coolant in the second deaeration line 2e. The pressure and/or the temperature of the coolant is related to the load on the second cooling circuit 2. In case the control unit 10 receives information from the sensor indicating that the load on the second cooling circuit 2 is low, it turns the valve member to a turning position in which the straight flow path 8a is disconnected from the coolant flow path in the second deaeration line 2e. In this case, the coolant in the deaeration line 2e flows, via the circular flow path 7a, through valve member 9a. In case the control unit 10 receives information from the sensor indicating that the load on the second cooling circuit 2 is high, it turns the valve member 9a to a turning position in which the straight flow path 8 is connected to coolant flow path in the second deaeration line 2e. In this case, the coolant in the second deaeration line 2e flows through valve member 9a, via the circular flow path 7 as well as via the straight line path 8a.

Fig, 3b shows a second embodiment of the valve member 9 in Fig. 2. In this case, the valve member is designed as a check valve 9b. The check valve 9b is configured to open when the coolant pressure in the deaeration line 2e exceeds a predetermined pressure defining a boundary between a low load and a high load of the second cooling circuit 2. In case the coolant pressure is lower than said predetermined pressure, the check valve 9 is closed and the coolant flow in the second deaeration line 2e is directed via an ordinary flow passage 7b towards the expansion tank 4. In case the coolant pressure is higher than said predetermined pressure, the check valve 9b is opened and the coolant flow is directed via the ordinary flow passage 7b as well as via an additional flow passage 8b towards the expansion tank 4.

Fig. 3c shows a further third embodiment of the valve member 9 in Fig. 2. In this case, the valve member 9c comprises a movably arranged valve body 9ci and a thermostat 9C2. The movable valve body 9c1is movable arranged between a closed position in which it covers an additional flow passage 8c and an open position in which it exposes the additional flow passage 8c. The thermostat 9c2is expanded at a predetermined temperature at which it moves the movable valve body from the closed position to the open position. A coolant temperature above the predetermined temperature defines a high load of the second cooling circuit 2. An ordinary flow passage 7c is arranged at the side of the valve member 9c. In case the coolant temperature is below said predetermined temperature, the coolant flow in the second deaeration line 2e is directed via the ordinary flow passage 7c towards the expansion tank 4. In case the coolant temperature is above said predetermined temperature, the coolant flow is directed, via the ordinary flow passage 7c as well as via an additional flow passage 8c, towards the expansion tank 4.

Fig. 4a and 4b shows a further embodiment of the cooling system. In this case, the cooling system comprises a valve device 12 comprising a valve housing 13. A thermostat 14 is arranged at an end of the valve housing 13 in thermal contact with the coolant flow in the second deaeration line 2e. The thermostat 14 is connected, via a rod 15 to a first pair of valve bodies 16 and a second pair of valve bodies 17. The first pair of valve bodies 16 is movably arranged in relation to a first pair of stationary arranged valve seats 16a. The second pair of valve bodies 17 is movably arranged in relation to a second pair of stationary arranged valve seats 17a. The valve housing 13 comprises a first inlet 18 receiving coolant from the first deaeration line le and a second inlet 19 receiving coolant from the second deaeration line 2e. The valve housing 13 comprises a first outlet 20 directing coolant from the valve housing 13 to the first chamber 4a of the expansion tank 4. The valve housing 13 comprises a second outlet 21 directing coolant from the valve housing 13 to the second chamber 4b of the expansion tank 4. The valve housing 13 comprises a third outlet 22 directing coolant from the valve housing 13 to the second chamber 4b of the expansion tank 4. The valve housing 13 comprises a fourth outlet 23 directing coolant from the valve housing 13 to the first chamber 4a of the expansion tank 4.

During operation of the cooling system, the thermostat 14 senses the temperature of the coolant in the second deaeration line 2e. In case the temperature of the coolant is lower than the regulating temperature of the thermostat 14, the rod 15 and the valve pairs 16, 17 are set in a low load position which is shown in Fig. 4a. The coolant flow in the first deaeration line le enters the valve housing 13 via the first inlet 18. The first pair of valve bodies 16 and the first pair of valve seats 16a are positioned in relation to each other such that the coolant flow from the first deaeration line 1e is directed out from the valve housing 13 via the first outlet 20 and to the first chamber 4a of the expansion tank 4. The coolant flow in the second deaeration line 2e enters the valve housing 13 via the second inlet 19. The second pair of valve bodies 17 and the second pair of valve seats 17a are positioned in relation to each other such that the coolant flow from the second deaeration line 2e is directed out from the valve housing 13 via the third outlet 22 and to the second chamber 4b of the expansion tank 4.

In case the temperature of the coolant in the second deaeration line 2e is higher than the regulating temperature of the thermostat 14, the thermostat 14 provides a movement of the rod 15 and the valve pairs 16, 17 to a high load position which is shown in Fig. 4b. In the high load position, the first pair of valve bodies 16 and the first pair of valve seats 16a are positioned in relation to each other such that the coolant flow from the first deaeration line 1e is directed out from the valve housing 13 via the second outlet 21 and to the second chamber 4b of the expansion tank 4. The second pair of valve bodies 17 and the second pair of valve seats 17a are positioned in relation to each other such that the coolant flow from the second deaeration line 2e is directed out from the valve housing 13 via the fourth outlet 23 and to the first chamber 4a of the expansion tank 4.

Consequently, in the low load position, the coolant flow in the first deaeration line 1e is directed to the first chamber 4a in the expansion tank 4 and the coolant flow in the second deaeration line 2e is directed to the second chamber 4b in the expansion tank 4. In this case, the first cooling circuit 1 receives and directs coolant to the first chamber 4a of the expansion tank 4. The second cooling circuit receives and directs coolant to the second chamber 4b of the expansion tank 4. In this case, the second cooling circuit 2 has a low load and the second cooling circuit has no problem to provide a desired cooling of the second component. In this case, there is substantially no heat transfer between the cooling circuits 1, 2.

In the high load position, the coolant flow in the first deaeration line 1e is directed to the second chamber 4b in the expansion tank 4 and the coolant flow in the second deaeration line 2e is directed to the first chamber 4a in the expansion tank 4. In this case, the first cooling circuit receives coolant from the second cooling circuit 2 in the expansion tank 4 and the second cooling circuit receives coolant from the first cooling circuit 1 in the expansion tank 4. Due to these facts, there is an effective heat transfer between the cooling circuits 1, 2 in the expansion tank. The second cooling circuit 2 obtains an increased the cooling capacity and its ability to perform a desired cooling of the second component 2b. At the same time, the first cooling circuit obtains a decreased cooling capacity. Since the first component 1b has a high thermal mass, a temporarily decreased cooling of the first component 1b will not increase its temperature significantly.

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 comprising two cooling circuits (1, 2) and a common expansion tank (4), wherein the cooling system comprises a first static line (1d) extending between the first cooling circuit (1) and the expansion tank (4), a second static line (2d) extending between the second cooling circuit (2) and the expansion tank (4), a first deaeration line (1e) extending between the first cooling circuit (1) and the expansion tank (4) and a second deaeration line (2e) extending between the second cooling circuit (2) and the expansion tank (4), characterized in that the cooling system comprises a wall element (5) dividing an inner space of the expansion tank (4) in first chamber (4a) and a second chamber (4b), wherein the first static line (1d) is connected to the first chamber (4a), the second static line (2d) is connected to the second chamber (4b), the first deaeration line (1e) is at least during certain operating conditions connected to the second chamber (4b) and the second deaeration line (2e) is at least during certain operating conditions connected to the first chamber (4a).

2. A cooling system according to claim 1, characterized in that the first cooling circuit (1) is configured to direct coolant to the expansion tank (4) of a lower temperature than the second cooling circuit (2) and that the first cooling circuit (1) is configured to cool a component (1b) having a higher thermal mass than a component (2b) to be cooled by the second cooling circuit (2).

3. A cooling system according to claim 1 or 2, characterized in that the expansion tank (4) comprises a coolant passage (6a) between the chambers (4a, 4b) configured to eliminate coolant level differences between said chambers (4a, 4b).

4. A cooling system according to any one of the preceding claims, characterized in that the expansion tank (4) comprises an air passage (6b) between the chambers (4a, 4b) configured to eliminate pressure differences between said chambers (4a, 4b).

5. A cooling system according to any one of the preceding claims, characterized in that the second deaeration line (2e) is configured to provide an ordinary coolant flow to the expansion tank (4) during operating condition when the second cooling circuit has a low load and to provide an additional coolant flow to the expansion tank (4) during operating condition when the second cooling circuit has a high load.

6. A cooling system according to claim 5, characterized in that the second deaeration line ( 2 e) comprises an ordinary flow passage (7, 7a-c) providing an ordinary flow area through the deaeration line ( 2e) and an additional flow passage (8, 8a-c) providing an additional flow area through the deaeration line ( 2e) and a valve member (9, 9a-c) configured to allow a coolant flow through the additional flow passage (8, 8a-c) during operation condition when the second cooling circuit ( 2) has a high load.

7. A cooling system according to claim 6, characterized in that the cooling system comprises a control unit (10) configured to receive information about a parameter related to the load of the second cooling circuit (2) and to initiate a movement of the valve member (9a) to the open position when the parameter indicates that the second cooling circuit (2) has a high load.

8. A cooling system according to claim 6, characterized in that said valve member (9b) is configured to be set in an open position when the pressure of the coolant in the second deaeration line (2e) exceeds a predetermined pressure.

9. A cooling system according to claim 8, characterized in that said valve member is a check valve (9b).

10. A cooling system according to claim 6, characterized in that said valve member (9c) is configured to be set in an open position when the temperature of the coolant in the second deaeration line (2e) exceeds a predetermined temperature.

11. A cooling system according to claim 10, characterized in that said valve member (9c) comprises a valve body (9c1) arranged in the additional flow passage (8b) and a thermostat (9c2) configured to move the valve body (9c1) to an open position when the temperature of the coolant in the second deaeration line ( 2e) exceeds a predetermined temperature.

12. A cooling system according to any one of the preceding claims, characterized in that the cooling system comprises a valve device (12) configured to be set in a low load position in which it directs the coolant flow in the first deaeration line (1e) to the first chamber (4a) and the coolant flow in the second deaeration line (2e) to the second chamber (4b) and in a high load position and in which it directs the coolant flow in the first deaeration line (1e) to the second chamber (4b) and the coolant flow in the second deaeration line (2e) to the first chamber (4a).

13. A cooling system according to claim 12, characterized in that the valve device (12) comprises a thermostat (14) configured to sense the temperature of the coolant in the second deaeration line (2e) and to set the valve device in the low load position or the high load position in view of this temperature.

14. A cooling system according to claim 13, characterized in that the thermostat (14) is configured to provide to movement of a rod (15) provided with a number of valve bodies (16, 17) to the low load position and the high load position in view of the temperature of the coolant in the second deaeration line (2e) .

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