Patent Publication Number: US-2023145211-A1

Title: Cooling system and vehicle comprising such a cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage Patent Application (filed under 35 § U.S.C. 371) of PCT/SE2021/050421, filed May 6, 2021, of the same title, which, in turn claims priority to Swedish Patent Application No. 2050584-8 filed May 19, 2020, of the same title; the contents of each of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a cooling system with capability to facilitate migration of air bubbles in the coolant of the cooling system towards a coolant outlet. 
     BACKGROUND OF THE INVENTION 
     Some of the vehicle components included in a motor vehicle may be cooled by means of coolant circulating in cooling circuit of a cooling system. Absorbed heat may be emitted from the circulating coolant to the surroundings via a radiator which is provided in the cooling circuit and arranged at the front end of the vehicle, wherein coolant flowing through the radiator is cooled by means of ambient air which is blown towards the radiator when the vehicle is in motion. 
     When a vehicle component is cooled by coolant circulating in a cooling circuit, the vehicle component will give off heat to the coolant, which is thereby heated and expanded. The resulting total volume increase of the coolant in the cooling circuit depends on the original coolant volume and the temperature increase. In order to prevent the pressure from increasing too much in the cooling circuit, the cooling circuit is provided with an expansion tank which can accommodate the surplus coolant volume generated in connection with the expansion of the coolant. Another important function of a conventional expansion tank in a cooling system of the above-mentioned type is that it should be possible for the coolant received in the expansion tank to be deaerated in the expansion tank before leaving the expansion tank. In a conventional cooling system of the type where a cooling circuit is connected to an expansion tank in a motor vehicle, there is a small continuous flow of coolant from the cooling circuit to the expansion tank via one or more deaeration lines and from the expansion tank back to the cooling circuit via a so-called static line. The air which accompanies the coolant to the expansion tank is intended to rise to the surface of the coolant volume received in the expansion tank in order to accumulate in an air-filled space at an upper part of the expansion tank. Hereby, the coolant in the expansion tank is deaerated. As an alternative, the cooling system may comprise a separate deaeration device which is arranged in the cooling circuit for separation of air bubbles from the coolant circulating in the cooling circuit, wherein the deaeration device is connected to the expansion tank via a static line in order to allow air bubbles separated from the coolant in the deaeration device to migrate upwards in the static line to the expansion tank. A cooling system of the latter type is for instance previously known from U.S. Pat. No. 7,395,787 B1. 
     By using a deaeration device of the type disclosed in U.S. Pat. No. 7,395,787 B1, it will be possible to achieve deaeration of the coolant in a cooling circuit without requiring any flow of coolant from the cooling circuit to the expansion tank connected to the cooling circuit, which in its turn implies that it will be possible to dispense with conventional deaeration lines for feeding of coolant from the cooling circuit to the expansion tank. Such deaeration lines may be rather costly and may also take up a lot of space, and it is consequently of advantage to be able to dispense with the deaeration lines. 
     The deaeration device included in the cooling system disclosed in U.S. Pat. No. 7,395,787 B1 comprises a deaeration chamber which at its top is provided with an outlet connected to an expansion tank via a static line. The deaeration chamber has a cross-sectional dimension that is substantially larger than the cross-sectional dimension of the coolant feed pipes leading to the deaeration chamber so that the coolant flow is slowed down and given an increased dwell time in the deaeration chamber, which in its turn will give air bubbles in the coolant a chance to migrate in the deaeration chamber to the outlet at the top of the deaeration chamber and then further on to the expansion tank via the static line. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to achieve a further development of a cooling system of the above-mentioned type so as to provide a cooling system that is improved in at least some aspect. 
     According to the present invention, the above-mentioned object is achieved by means of a cooling system having the features defined in the claims. 
     The cooling system of the present invention comprises: 
     a cooling circuit; 
     a coolant pump for circulating coolant in the cooling circuit; 
     an expansion tank for accumulation of coolant; and 
     a deaeration device arranged in the cooling circuit for separation of air bubbles from the coolant circulating in the cooling circuit, wherein the deaeration device is connected to the expansion tank via a static line and comprises a deaeration chamber having: 
     a coolant inlet connected to a feed pipe of the cooling circuit in order to allow coolant circulating in the cooling circuit to flow from the feed pipe into the deaeration chamber via this coolant inlet, 
     a first coolant outlet connected to the coolant pump in order to allow coolant to flow from the deaeration chamber to the coolant pump via this first coolant outlet, wherein the coolant inlet and the first coolant outlet are spaced apart from each other in a longitudinal direction of the deaeration chamber, and 
     a second coolant outlet connected to the expansion tank via the static line and located at a higher position than the first coolant outlet relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. 
     The cross-sectional dimension of the deaeration chamber is larger than the cross-sectional dimension of the feed pipe to thereby allow air bubbles carried along with coolant flowing through the feed pipe to enter the deaeration chamber via the coolant inlet and thereafter migrate in the deaeration chamber to the second coolant outlet. 
     According to the invention, the above-mentioned second coolant outlet, i.e. the coolant outlet connected to the expansion tank via the static line, is located in such a position in relation to the coolant inlet and the first coolant outlet that the coolant flow in the deaeration chamber between the coolant inlet and the first coolant outlet will move said migrating air bubbles in the longitudinal direction of the deaeration chamber towards the second coolant outlet. Furthermore, the first coolant outlet is arranged at a higher position than the coolant inlet relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. 
     Hereby, the air bubbles migrating in the deaeration chamber towards the second coolant outlet do not have to move against the flow direction of the coolant in the deaeration chamber and the coolant flow in the deaeration chamber will consequently not counteract the migration of the air bubbles towards the second coolant outlet. On the contrary, the coolant flow in the deaeration chamber will promote the migration of air bubbles in the deaeration chamber towards the second coolant outlet and an efficient separation of air bubbles from the circulating coolant may thereby be achieved in the deaeration chamber. It has turned out that an efficient separation of air bubbles can be achieved with a higher flow velocity for the coolant in the deaeration chamber when the coolant flow in the deaeration chamber is directed in the intended migration direction for the air bubbles as compared to the case when the coolant flow in the deaeration chamber is directed opposite to the intended migration direction for the air bubbles. It has also turned out that a smaller difference in the cross-sectional dimension between the deaeration chamber and the coolant feed pipe leading to the deaeration chamber is required when the coolant flow in the deaeration chamber is directed in the intended migration direction for the air bubbles as compared to the case when the coolant flow in the deaeration chamber is directed opposite to the intended migration direction for the air bubbles, which in its turn implies that it will be possible to reduce the cross-sectional dimension of the deaeration chamber. A reduction of the difference in the cross-sectional dimension between the deaeration chamber and the coolant feed pipe leading to the deaeration chamber will also result in a favorable reduction of the pressure drop across the deaeration chamber. The deaeration device is to be located at a lower position than the expansion tank in order to allow air bubbles separated from the coolant in the deaeration device to migrate upwards in the static line towards the expansion tank. 
     In addition, by arranging the first coolant outlet at a higher position than the coolant inlet relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface, the coolant flow will have a flow component directed upwards, i.e. a flow component which is parallel and oppositely directed to the local gravity vector gv. Thus, the coolant flow in the deaeration chamber will act on the air bubbles with a force which has a vector component which is parallel and oppositely directed to the local gravity vector gv. The air bubbles will therefore be pushed upwards, towards the second outlet and the static line. This will improve the separation of the air bubbles from the coolant and the evacuation of the air bubbles to the expansion chamber. The effect is especially pronounced for small air bubbles, having low terminal velocity. Thereby an efficient deaeration can be performed. 
     With the above-mentioned deaeration device, the coolant in the cooling circuit may be deaerated in a simple and efficient manner with the use of a component of simple construction which can be produced at low cost. 
     The cross-sectional dimension of the deaeration chamber is preferably so much larger than the cross-sectional dimension of the feed pipe that the relationship between the flow velocity of the coolant flowing through the deaeration chamber between the coolant inlet and the first coolant outlet and the flow velocity of the coolant flowing through the feed pipe is 1:2 or lower, preferably 1:3 or lower. Hereby, it will be possible, by a suitable control of the coolant pump, to adapt the coolant flow through the cooling circuit in such a manner that the flow velocity of the coolant in the feed pipe is sufficiently high to allow this coolant to move air bubbles forward along the feed pipe and into the deaeration chamber at the same time as the flow velocity of the coolant in the deaeration chamber is sufficiently low to allow said air bubbles to migrate in the deaeration chamber to the second coolant outlet of the deaeration chamber. If the flow velocity of the coolant is too low in the feed pipe, air bubbles may get stuck in the feed pipe. If the flow velocity of the coolant is too high in the deaeration chamber, the coolant may carry along air bubbles out of the deaeration chamber via the first coolant outlet. The coolant pump may be controlled in such a manner that the coolant circulating in the cooling circuit is continuously deaerated. However, the coolant pump may as an alternative be configured to adapt the coolant flow in the cooling circuit in such a manner that deaeration is effected intermittently or only at specific occasions. 
     According to an embodiment of the invention, the deaeration chamber has an elongated shape and is arranged with its longitudinal axis vertical, wherein the coolant inlet is located at a lower position than the first and second coolant outlets. A deaeration device with such a deaeration chamber has a rather simple construction and can be produced in a simple and cost-efficient manner. 
     According to another embodiment of the invention, the deaeration chamber has an elongated shape and is arranged with its longitudinal axis inclined in relation to a horizontal plane by an angle of 0-90, preferably by an angle which is &gt;0° and &lt;=90°, more preferably by an angle of 10-90°, most preferably 15-90°. By horizontal plane is herein meant the plane whose normal is parallel to the prevailing gravitational vector. When the deaeration chamber is arranged with its longitudinal axis inclined at an angle greater than 0° in relation to the horizontal plane, air bubbles may rise in the deaeration chamber and hit an inclined upper wall surface in the deaeration chamber, whereupon the air bubbles are conveyed along this wall surface towards the second coolant outlet under the effect of the coolant flow in the deaeration chamber between the coolant inlet and the first coolant outlet Additionally, even at very low flow, air bubbles which have separated from the coolant will rise towards the static line due to the buoyancy of the air bubbles. Thus, an improved deaeration will be achieved. By having the inclination between 10-90° the chamber will, in most cases, be inclined towards the horizontal plane even if the vehicle is travelling on a downwards slope. Thereby the above described effect is still maintained even if the vehicle is moving in hilly terrain. By having the inclination between 15-90° it is ensured that the chamber will be inclined in relation to the horizontal plane for a great majority of a standard trip. This ensures that the deaeration of the cooling system is functioning optimally at practically all times, thereby minimizing the risk of detrimental effects due to air bubbles in the system. The inclination may also be 10-80° or 15-75° so as to take both upwards and downwards slope into consideration. 
     According to another embodiment of the invention, one or more flow guiding members are arranged in the deaeration chamber downstream of the coolant inlet and configured to direct the coolant entering the deaeration chamber via the coolant inlet essentially in parallel with the longitudinal axis of the deaeration chamber. The flow guiding members will direct the coolant flow in the intended migration direction for the air bubbles in the deaeration chamber, which promotes an efficient separation of air bubbles in the deaeration chamber. 
     According to another embodiment of the invention, the deaeration chamber comprises at least one further coolant inlet connected to an associated further feed pipe of the cooling circuit in order to allow coolant circulating in the cooling circuit to flow from this further feed pipe into the deaeration chamber via the associated further coolant inlet. The cross-sectional dimension of the deaeration chamber is preferably larger than the cross-sectional dimension of said further feed pipe to thereby allow air bubbles carried along with coolant flowing through this further feed pipe to enter the deaeration chamber via the associated further coolant inlet and thereafter migrate in the deaeration chamber to the second coolant outlet, wherein this further coolant inlet is located in such a position in relation to the first and second coolant outlets that the coolant flow in the deaeration chamber between this further coolant inlet and the first coolant outlet will move these migrating air bubbles in the longitudinal direction of the deaeration chamber towards the second coolant outlet. Hereby, also air bubbles conveyed into the deaeration chamber together with coolant from the further feed pipe may be efficiently separated from the coolant in the deaeration chamber. 
     The first coolant outlet may be arranged at a higher position than the further coolant inlet relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. The advantages associated with such a configuration has already been discussed above with regards to the coolant inlet and the first coolant outlet and will therefore for the sake of brevity not be reproduced here. 
     Another embodiment of the invention is characterized in: 
     that said cooling circuit and coolant pump constitute a first cooling circuit and a first coolant pump of the cooling system, wherein the cooling system comprises a second cooling circuit and a second coolant pump for circulating coolant in the second cooling circuit; and 
     that the deaeration chamber is provided with: 
     a further coolant inlet connected to a feed pipe of the second cooling circuit in order to allow coolant circulating in the second cooling circuit to flow from this feed pipe into the deaeration chamber via this further coolant inlet, and 
     a further coolant outlet connected to the second coolant pump in order to allow coolant to flow from the deaeration chamber to the second coolant pump via this further coolant outlet. 
     In this case, the deaeration chamber may be used for separating air bubbles from coolant circulating in two different cooling circuits. 
     According to another embodiment of the invention, the cross-sectional dimension of the deaeration chamber is larger than the cross-sectional dimension of said feed pipe of the second cooling circuit to thereby allow air bubbles carried along with coolant flowing through this feed pipe to enter the deaeration chamber via the associated further coolant inlet and thereafter migrate in the deaeration chamber to the second coolant outlet, wherein this further coolant inlet is located in such a position in relation to the second coolant outlet and said further coolant outlet that the coolant flow in the deaeration chamber between this further coolant inlet and this further coolant outlet will move these migrating air bubbles in the longitudinal direction of the deaeration chamber towards the second coolant outlet. Hereby, also air bubbles conveyed into the deaeration chamber together with coolant from the feed pipe of the second cooling circuit may be efficiently separated from the coolant in the deaeration chamber. The number of cooling circuits connected to the deaeration chamber of the deaeration device may also be three or more. 
     The second coolant outlet may be arranged at a higher position than the further coolant inlet relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. The advantages associated with such a configuration has already been discussed above with regards to the coolant inlet and the first coolant outlet and will therefore for the sake of brevity not be reproduced here. 
     According to another embodiment of the invention, the static line has a lower end and an upper end, wherein the static line is connected to the deaeration device at its lower end and wherein: 
     the static line slopes upwards along its entire length from its lower end to its upper end, or 
     the static line is formed by several interconnected length sections which are arranged in series with each other and which consist of one or more first length sections, each of which sloping upwards as seen in a direction along the static line from its lower end towards its upper end, and one or more horizontal second length sections. 
     Hereby, the static line lacks downwardly sloping sections that could prevent air bubbles from migrating from the deaeration device towards the expansion tank. 
     Further advantageous features of the cooling system according to the present invention will appear from the description following below. 
     The invention also relates to a vehicle having the features defined in claim  12 . 
     Further advantageous features of the vehicle according to the present invention will appear from the description following below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, a specific description of embodiments of the invention cited as examples follows below. In the drawings: 
         FIG.  1    is an outline diagram of a cooling system according to a first embodiment of the present invention, 
         FIG.  2    is an outline diagram of a cooling system according to a second embodiment of the invention, 
         FIG.  3    is an outline diagram of a cooling system according to a third embodiment of the invention, 
         FIG.  4    is an outline diagram of a cooling system according to a fourth embodiment of the invention, 
         FIG.  5    is a schematic vertical section through a deaeration device included in the cooling system of  FIG.  1   , 
         FIG.  6    is a schematic vertical section through a deaeration device according to an alternative variant, and 
         FIG.  7    is a schematic vertical section through a deaeration device according to another variant. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     A cooling system  1  according to an embodiment of the present invention is very schematically illustrated in  FIG.  1   . The cooling system  1  comprises a cooling circuit  10  for cooling at least one component  11  by means of coolant circulating in the cooling circuit. The coolant flowing through the cooling circuit  10  is preferably water, possibly with anti-freezing additives such as for instance glycol. A coolant pump  12 , preferably in the form of an electrically driven pump, is provided in the cooling circuit  10  in order to circulate the coolant in the cooling circuit. The cooling system  1  may further comprise an electronic control unit  2  which is connected to the coolant pump  12  and configured to control the operation thereof so as to thereby control the flow velocity of the coolant circulating in the cooling circuit  10 . 
     Furthermore, a cooling device  13 , for instance in the form of a heat exchanger, is provided in the cooling circuit  10  in order to remove heat from the coolant circulating therein. The cooling system  1  may for instance be used in a motor vehicle  3 , for instance in the form of a hybrid or fully electric vehicle, wherein the cooling device  13  may have the form of a radiator, for instance a conventional coolant radiator. In this case, the cooling circuit  10  may be a cooling circuit for cooling a vehicle component  11  in the form of an electric energy storing device, such as for instance an electric battery or a set of electric batteries, for supplying electric energy to an electric traction motor of the vehicle, or a cooling circuit for cooling vehicle components in the form of power electronic devices, such as for instance an inverter and a DC converter, for controlling the flow of electric power between an electric energy storing device of the above-mentioned type and the electric traction motor. The coolant flowing through the radiator  13  is cooled by means of ambient air which is blown towards the radiator when the vehicle  3  is in motion. The vehicle  3  may also be provided with a fan (not shown), which, when so needed, may be operated in order to generate an air flow through the radiator  13 . 
     The cooling system  1  comprises an expansion tank  30  provided with an expansion chamber  31  for accumulation of coolant, wherein this expansion chamber  31  is surrounded by an external casing  32  of the expansion tank. The expansion tank  30  is provided with a closable refill opening  33  which is arranged in the casing  32  at an upper part thereof. Coolant may be introduced into the expansion chamber  31  via this refill opening  33  in order to provide for replenishment of the cooling system. The refill opening  33  is closed by means of a removable lid  34 . Furthermore, the expansion tank  31  is provided with a valve device (not shown) which comprises a pressure relief valve for limiting the pressure in the expansion chamber  31  and a return valve. This valve device may be arranged in the lid  34  or in the casing  32 . The pressure relief valve allows air and coolant to flow out from the upper part of the expansion chamber  31  when the pressure in the expansion chamber, due to an increase of the coolant volume, exceeds a pressure level given by the pressure relief valve. Thus, the pressure relief valve ensures that the pressure in the expansion chamber  31  cannot exceed a predetermined pressure level. The return valve allows air to flow into the upper part of the expansion chamber  31  from the surroundings when the pressure in the expansion chamber, due to a reduction of the coolant volume, becomes lower than a pressure level given by the return valve. 
     The expansion chamber  31  is connected to the cooling circuit  10  via a static line  5  in order to allow the expansion chamber  31  to receive coolant from the cooling circuit  10 . 
     The cooling system  1  comprises a deaeration device  40  arranged in the cooling circuit  10  for separation of air bubbles from the coolant circulating in the cooling circuit, wherein this deaeration device  40  is located at a lower position than the expansion tank  30  and connected to the expansion chamber  31  of the expansion tank  30  via the static line  5  in order to allow air bubbles separated from the coolant in the deaeration device  40  to migrate upwards in the static line  5  towards the expansion chamber  31 . In the embodiment illustrated in  FIG.  1   , the static line  5  is connected directly to the expansion chamber  31  via an opening  35  provided in the casing  32  of the expansion tank. 
     The static line  5  has a lower end  5   a  and an upper end  5   b , wherein the static line  5  is connected to the deaeration device  40  at its lower end  5   a . In the embodiment illustrated in  FIG.  1   , the static line  5  slopes upwards along its entire length from its lower end  5   a  to its upper end  5   b . However, as illustrated in  FIG.  2   , the static line  5  may as an alternative consist of a combination of one or more first length sections  6   a , each of which sloping upwards as seen in a direction along the static line from its lower end towards its upper end, and one or more horizontal second length sections  6   b , wherein these first and second length sections  6   a ,  6   b  are interconnected and arranged in series with each other. 
     The deaeration device  40  comprises a deaeration chamber  41  (see  FIG.  5   ), which is enclosed by a casing  42  and which has: 
     a coolant inlet  43  connected to a feed pipe  15  of the cooling circuit  10  in order to allow coolant circulating in the cooling circuit to flow from the feed pipe  15  into the deaeration chamber  41  via this coolant inlet  43 ; 
     a first coolant outlet  44  connected to the coolant pump  12  in order to allow coolant to flow from the deaeration chamber  41  to the coolant pump  12  via this first coolant outlet  44 , wherein the coolant inlet  43  and the first coolant outlet  44  are spaced apart from each other in a longitudinal direction of the deaeration chamber  41 ; and 
     a second coolant outlet  45  connected to the expansion chamber  31  via the static line  5  and located at a higher position than the first coolant outlet  44  relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. 
     The second coolant outlet  45  is located in an upper part of the deaeration chamber  41  in order to allow air bubbles that have migrated to the upper part of the deaeration chamber to leave the deaeration chamber and enter the static line  5  via the second coolant outlet  45 . Air bubbles may hereby be separated from the coolant in the cooling circuit  10 . The second coolant outlet  45  is preferably located at the highest point in the deaeration chamber  41 , but it may as an alternative be located slightly below the highest point in the deaeration chamber  41 . 
     The cross-sectional dimension of the deaeration chamber  41  is larger than the cross-sectional dimension of the feed pipe  15  such that the flow velocity of the coolant in the deaeration chamber  41  is lower than the flow velocity of the coolant in the feed pipe  15  leading to the deaeration chamber, to thereby allow air bubbles to be carried along with the rather rapid coolant flow in the feed pipe  15  and enter the deaeration chamber  41  via the coolant inlet  43  and thereafter migrate in the deaeration chamber  41  to the second coolant outlet  45 . The slower coolant flow in the deaeration chamber  41  will give the coolant an increased dwell time in the deaeration chamber, which in its turn will give air bubbles in the coolant a chance to migrate in the deaeration chamber  41  to the second coolant outlet  45 . 
     The cross-sectional dimension of the deaeration chamber  41  is preferably so much larger than the cross-sectional dimension of the feed pipe  15  that the relationship between the flow velocity v 1  of the coolant flowing through the deaeration chamber  41  between the coolant inlet  43  and the first coolant outlet  44  and the flow velocity v 2  of the coolant flowing through the feed pipe  15  is 1:2 or lower, preferably 1:3 or lower. 
     The deaeration chamber  41  may have a cylindrical shape, for instance a circular cylindrical shape, but it may as an alternative have any other suitable shape. 
     The electronic control unit  2  may be configured to control the coolant pump  12  in such a manner that the flow velocity of the coolant circulating through the cooling circuit  10  is maintained at such a value during normal operating conditions that the coolant in the cooling circuit is continuously deaerated during the normal operating conditions. However, the electronic control unit  2  may as an alternative be configured to control the coolant pump  12  in such a manner that the flow velocity intermittently or only at specific occasions is set to a value adapted for an efficient deaeration of the coolant in the cooling circuit  10 . 
     The second coolant outlet  45  is located in such a position in relation to the coolant inlet  43  and the first coolant outlet  44  that the coolant flow in the deaeration chamber  41  between the coolant inlet  43  and the first coolant outlet  44  will move migrating air bubbles in the deaeration chamber  41  in the longitudinal direction of the deaeration chamber  41  towards the second coolant outlet  45 . Thus, the migration direction of the air bubbles in the deaeration chamber  41  corresponds to the flow direction of the coolant in the deaeration chamber and the coolant flow in the deaeration chamber  41  will thereby promote the movement of the air bubbles towards the second coolant outlet  45 . 
     The first coolant outlet  44  is arranged at a higher position than the coolant inlet  43  relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. Thereby the coolant flow from the coolant inlet  43  will have a vector component which is opposite the local gravity vector gv and will thereby provide the air bubbles with a flow vector component in an upwards direction which will promote the movement of the air bubbles towards the second coolant outlet  45  even further. 
     In the embodiment illustrated in  FIG.  1   , the deaeration chamber  41  has an elongated shape and is arranged with its longitudinal axis  46  extending in vertical direction. In this case, the above-mentioned flow direction of the coolant in the deaeration chamber  41  is achieved by having the coolant inlet  43  located at a lower position than the first coolant outlet  44 , which gives an upwardly directed coolant flow in the deaeration chamber  41 . However, the deaeration chamber  41  may as an alternative be arranged with its longitudinal axis  46  inclined in relation to a horizontal plane by an angle α of 0-90°, e.g. by an angle α&gt;0° and ⇐90°, or between 10-90°, or 15-90°. When the deaeration chamber  41  is arranged with its longitudinal axis  46  inclined, for instance in the manner illustrated in  FIG.  2   , air bubbles may rise in the deaeration chamber  41  and hit an inclined upper wall surface  47  in the deaeration chamber, whereupon the air bubbles are conveyed along this wall surface  47  towards the second coolant outlet  45  under the effect of the coolant flow in the deaeration chamber  41  between the coolant inlet  43  and the first coolant outlet  44 . 
     One or more flow guiding members  48 ,  49  (see  FIGS.  6  and  7   ) may be arranged in the deaeration chamber  41  downstream of the coolant inlet  43  and configured to direct the coolant entering the deaeration chamber  41  via the coolant inlet  43  essentially in parallel with the longitudinal axis  46  of the deaeration chamber. Such a flow guiding member may for instance have the form of a guide plate  46  or the similar arranged in front of the coolant inlet  43  in order to deflect the incoming coolant flow into a direction essentially in parallel with the longitudinal axis  46  of the deaeration chamber  41 , as illustrated in  FIG.  6   . The flow guiding member may as an alternative have the form of a perforated plate  49  or the similar arranged across the deaeration chamber  41 , as illustrated in  FIG.  7   . 
     In the embodiment illustrated in  FIG.  3   , the cooling system  1  comprises a deaeration device  40  with a deaeration chamber  41  having a coolant inlet  43  and first and second coolant outlets  44 ,  45  arranged in the manner described above with reference to  FIG.  1   , wherein said coolant inlet  43  is connected to a first feed pipe  15  of the cooling circuit  10 . In this case, the deaeration chamber  41  also comprises a further coolant inlet  43   a  connected to an associated second feed pipe  15   a  of the cooling circuit  10  in order to allow coolant circulating in the cooling circuit to flow from this second feed pipe  15   a  into the deaeration chamber  41  via the associated further coolant inlet  43   a . In the illustrated example, the cooling circuit  10  comprises a valve device  16  for controlling the coolant flow towards the first and second feed pipes  15 ,  15   a.    
     The cross-sectional dimension of the deaeration chamber  41  is larger than the cross-sectional dimension of the first feed pipe  15  to thereby allow air bubbles carried along with coolant flowing through the first feed pipe  15  to enter the deaeration chamber  41  via the associated coolant inlet  43  and thereafter migrate in the deaeration chamber  41  to the second coolant outlet  45 . The cross-sectional dimension of the deaeration chamber  41  is preferably so much larger than the cross-sectional dimension of the first feed pipe  15  that the relationship between the flow velocity v 1  of the coolant flowing through the deaeration chamber  41  between the coolant inlet  43  and the first coolant outlet  44  and the flow velocity v 2  of the coolant flowing through the first feed pipe  15  is 1:2 or lower, preferably 1:3 or lower, when the valve device  16  directs the entire coolant flow in the cooling circuit  10  to the first fee pipe  15 . In this case, the electronic control unit  2  may be configured to control the valve device  16  to direct the entire coolant flow in the cooling circuit  10  to the first fee pipe  15  when the coolant in the cooling circuit  10  is to be subjected to an efficient deaeration in the deaeration chamber  41 . 
     In the embodiment illustrated in  FIG.  3   , the cross-sectional dimension of the deaeration chamber  41  is also larger than the cross-sectional dimension of the second feed pipe  15   a  to thereby allow air bubbles carried along with coolant flowing through the second feed pipe  15   a  to enter the deaeration chamber  41  via the associated coolant inlet  43   a  and thereafter migrate in the deaeration chamber  41  to the second coolant outlet  45 , wherein this coolant inlet  43   a  is located in such a position in relation to the first and second coolant outlets  44 ,  45  that the coolant flow in the deaeration chamber  41  between this coolant inlet  43   a  and the first coolant outlet  44  will move these migrating air bubbles in the longitudinal direction of the deaeration chamber  41  towards the second coolant outlet  45 . 
     The first coolant outlet  44  is arranged at a higher position than the coolant inlet  43   a  relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. Thereby the coolant flow from the coolant inlet  43   a  will have a vector component which is opposite the local gravity vector gv and will thereby provide the air bubbles with a flow vector component in an upwards direction which will promote the movement of the air bubbles towards the second coolant outlet  45  even further. 
     In the embodiment illustrated in  FIG.  4   , the cooling system  1  comprises a first cooling circuit  10  for cooling at least one first component  11  by means of coolant circulating in the first cooling circuit and a second cooling circuit  20  for cooling at least one second component  21  by means of coolant circulating in the second cooling circuit. A first coolant pump  12  is provided in the first cooling circuit  10  in order to circulate the coolant in the first cooling circuit  10  and a second coolant pump  22  is provided in the second cooling circuit  20  in order to circulate the coolant in the second cooling circuit  20 . The first and second coolant pumps  12 ,  22  are preferably electrically driven pumps. An electronic control unit  2  is connected to the coolant pumps  12 ,  22  and configured to control the operation thereof so as to thereby control the flow velocities of the coolant circulating in the first and second cooling circuits  10 ,  20 . A cooling device  13 ,  23 , for instance in the form of a radiator or any other suitable type of heat exchanger, may be provided in each cooling circuit  10 ,  20  in order to remove heat from the coolant circulating therein. 
     In the embodiment illustrated in  FIG.  4   , the cooling system  1  comprises a deaeration device  40  with a deaeration chamber  41  having a coolant inlet  43  and first and second coolant outlets  44 ,  45  arranged in the manner described above with reference to  FIG.  1   , wherein the coolant inlet  43  is connected to a feed pipe  15  of the first cooling circuit  10  and the coolant outlet  44  is connected to the first coolant pump  12  in order to allow coolant circulating in the first cooling circuit  10  to flow from the feed pipe  15  into the deaeration chamber  41  via the coolant inlet  43  and allow coolant to flow from the deaeration chamber  41  to the first coolant pump  12  via the coolant outlet  44 . In this case, the deaeration chamber  41  also comprises a further coolant inlet  43   b  connected to a feed pipe  25  of the second cooling circuit  20  and a further coolant outlet  44   b  connected to the second coolant pump  22  in order to allow coolant circulating in the second cooling circuit  20  to flow from the feed pipe  25  into the deaeration chamber  41  via said further coolant inlet  43   b  and allow coolant to flow from the deaeration chamber  41  to the second coolant pump  22  via said further coolant outlet  44   b.    
     The cross-sectional dimension of the deaeration chamber  41  is larger than the cross-sectional dimension of the feed pipe  15  of the first cooling circuit  10  to thereby allow air bubbles carried along with coolant flowing through this feed pipe  15  to enter the deaeration chamber  41  via the associated coolant inlet  43  and thereafter migrate in the deaeration chamber  41  to the second coolant outlet  45 . The cross-sectional dimension of the deaeration chamber  41  is preferably so much larger than the cross-sectional dimension of the feed pipe  15  of the first cooling circuit  10  that the relationship between the flow velocity v 1  of the coolant flowing through the deaeration chamber  41  between the coolant inlet  43  and the first coolant outlet  44  and the flow velocity v 2  of the coolant flowing through this feed pipe  15  is 1:2 or lower, preferably 1:3 or lower, in a situation when the first coolant pump  12  is in operation and the second coolant pump  22  is turned off. 
     In the embodiment illustrated in  FIG.  4   , the cross-sectional dimension of the deaeration chamber  41  is also larger than the cross-sectional dimension of the feed pipe  25  of the second cooling circuit  20  to thereby allow air bubbles carried along with coolant flowing through this feed pipe  25  to enter the deaeration chamber  41  via the associated further coolant inlet  43   b  and thereafter migrate in the deaeration chamber  41  to the second coolant outlet  45 , wherein this further coolant inlet  43   b  is located in such a position in relation to the second coolant outlet  45  and said further coolant outlet  44   b  that the coolant flow in the deaeration chamber between this further coolant inlet  43   b  and said further coolant outlet  44   b  will move these migrating air bubbles in the longitudinal direction of the deaeration chamber  41  towards the second coolant outlet  45 . 
     The further coolant outlet  44   b  is arranged at a higher position than the further coolant inlet  43   b  relative to a local gravity vector gv when the cooling system is mounted to a vehicle and the vehicle is positioned in an upright use position on a horizontal surface. Thereby the coolant flow from the coolant inlet  43   b  towards the coolant outlet  44   b  will have a vector component which is opposite the local gravity vector gv and will thereby provide the air bubbles with a flow vector component in an upwards direction which will promote the movement of the air bubbles towards the second coolant outlet  45  even further. 
     It is of course also possible to connect more than two cooling circuits to one and the same deaeration device  40  of the type described above. 
     The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.