SE539924C2 - Expansion tank and cooling system comprising such an expansion tank - Google Patents

Abstract

An expansion tank for a cooling system of a motor vehicle comprising:- first and second expansion chambers (10, 20);- a float chamber (30) with a coolant refill opening (31) at an upper end and a bottom wall (32) at a lower end; and- a float (36) arranged in the float chamber.Flow ports (34a, 34b) are arranged in said bottom wall and connected to the expansion chambers. The float is moveable between a closing position, in which the float is in contact with the bottom wall and keeps the flow ports closed to thereby prevent coolant flow between the float chamber and the expansion chambers, and a floating position, in which the float is floating at the surface of the coolant in the float chamber and leaves the flow ports open. A lid (5) is configured to act on the float in order to keep the float in the closing position when the lid is fitted over the refill opening.

Description

AND PRIOR ART The present invention relates to an expansion tank according tothe preamble of claim 1 which is intended to be included in acooling system of a motor vehicle. The invention also relates to acooling system for a motor vehicle provided with such an expansion tank.

A motor vehicle normally has vehicle components with mutuallydifferent cooling requirements, and it is often necessary to useseparate cooling circuits for cooling these vehicle components.As an example, a hybrid vehicle may comprise an electric energystoring device in the form of an electric battery or a set of electricbatteries for supplying electric energy to an electric tractionmotor of the vehicle and one or more power electronic devices,such as for instance an inverter and a DC/DC converter, forcontrolling the flow of electric power between the electric energystoring device and the electric traction motor. These types ofvehicle components of a hybrid vehicle are heated when in use and have to be cooled in order to operate satisfactory. The temperature of the electric batteries of a hybrid vehicle should bekept rather low, normally below approximately 40°C, in order toprevent a too rapid aging thereof, whereas an inverter and a DCconverter may stand higher temperatures, normally up toapproximately 60-100°C. Therefore, two separate cooling circuitsare often used for cooling such vehicle components of a hybridvehicle, wherein a cooling circuit with circulating coolant of lowertemperature is used for cooling the electric batteries and anothercooling circuit with circulating coolant of higher temperature isused for cooling the inverter and DC converter and other possible power electronic devices which require cooling.

When a vehicle component is cooled by coolant circulating in acooling circuit, the vehicle component will give off heat to thecoolant, which is thereby heated and expanded. The resultingtotal volume increase of the coolant in the cooling circuitdepends on the original coolant volume and the temperatureincrease. ln order to prevent the pressure from increasing toomuch in the cooling circuit, the cooling circuit is provided with anexpansion tank which can accommodate the surplus coolant generated in connection with the expansion of the coolant.

A low pressure of the coolant in a cooling circuit implies a risk ofcavitation at the pump inlet of the coolant pump in the coolingcircuit, which may cause damages to the coolant pump. lt istherefore desirable to maintain a certain positive pressure in thecooling circuit. When the coolant expands as a consequence ofheating, the air in the expansion tank is compressed and the pressure in the expansion tank and in the rest of the cooling circuit is thereby increased, which will reduce the risk of cavitation at the pump inlet of the coolant pump.

Another important function of an expansion tank of the above-mentioned type is that it should be possible for the coolantreceived in the expansion tank to be deaerated in the expansiontank before leaving the expansion tank. The air which has beenabsorbed by the coolant when circulating through the coolingcircuit and which therefore accompanies the coolant to theexpansion tank is intended to rise to the surface of the coolantvolume received in the expansion tank in order to accumulate inan air-filled space at an upper part of the expansion tank.

Hereby, the coolant in the expansion tank is deaerated. ln a cooling system of a vehicle with two different coolingcircuits, it is previously known to use a dual chamber expansiontank with a first expansion chamber for accumulating coolantwhich circulates in a first cooling circuit of the cooling systemand an adjacent second expansion chamber for accumulatingcoolant which circulates in a second cooling circuit of the coolingsystem, to thereby save space in the vehicle and reduce theinstallation costs. A dual chamber expansion tank of this type isfor instance previously known from US 2011/0284107 A1.

OBJECT OF THE INVENTIONThe object of the present invention is to achieve a furtherdevelopment of a dual chamber expansion tank of the above- mentioned type so as to provide an expansion tank that is improved in at least some aspect.

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned objectis achieved by an expansion tank having the features defined in claim 1.

The expansion tank of the present invention comprises: - a first expansion chamber configured to receive coolant whichcirculates in a first cooling circuit of a cooling system, the firstexpansion chamber comprising a lower part, in which coolant isto be accumulated, and an upper part, in which air is to beaccumulated; - a second expansion chamber configured to receive coolantwhich circulates in a second cooling circuit of the cooling system,the second expansion chamber comprising a lower part, in whichcoolant is to be accumulated, and an upper part, in which air is tobe accumulated, wherein the lower part of the first expansionchamber is separated from the lower part of the secondexpansion chamber in order to prevent coolant flow between thefirst and second expansion chambers, and wherein the upperpart of the first expansion chamber is connected to the upperpart of the second expansion chamber in order to allow pressureequalization between the first and second expansion chambers; - a float chamber, which has a coolant refill opening at an upperend and a bottom wall at an opposite lower end; - a float arranged in the float chamber; and - a lid which is removably fittable over the refill opening for closing of the refill opening.

One or more first flow ports are arranged in the bottom wall ofthe float Chamber, wherein each first flow port is connected tothe lower part of the first expansion chamber to allow coolant toflow between the float chamber and the lower part of the firstexpansion chamber via this flow port when it is open.Furthermore, one or more second flow ports are arranged in thebottom wall of the float chamber, wherein each second flow portis connected to the lower part of the second expansion chamberto allow coolant to flow between the float chamber and the lowerpart of the second expansion chamber via this flow port when itis open. The float is vertically moveable in the float chamberbetween a lower closing position, in which the float is in contactwith the bottom wall and keeps the first and second flow portsclosed to thereby prevent coolant flow between the float chamberand the first and second expansion chambers, and an upperfloating position, in which the float is floating at the surface of thecoolant in the float chamber and leaves the first and second flowports open. The lid is configured to act on the float in order tokeep the float depressed in the closing position when the lid isfitted over the refill opening, wherein the float is free to rise fromthe closing position to the floating position when the lid is removed from the refill opening.

The first and second expansion chambers are to be connected totwo different cooling circuits where the coolant circulating in oneof the cooling circuits has a higher operating temperature thanthe coolant circulating in the other cooling circuit. The separationof the coolant accumulating lower part of the first expansionchamber from the coolant accumulating lower part of the second expansion chamber makes it possible to prevent the coolant in the two cooling circuits from mixing and it is thereby easy tomaintain two mutually different temperature levels in the coolingcircuits connected to the expansion tank. The pressureequalization between the first and second expansion chambersimplies that the expansion of the coolant of higher temperaturewill cause an increased pressure in both cooling circuits, whichwill reduce the risk of cavitation at the pump in|et of the coolantpump in the cooling circuit where the coolant of lowertemperature is circulating. Furthermore, the arrangement of thefloat chamber and the associated float will make it possible touse one and the same refill opening for both cooling circuits.When the refill opening is open and the float has been allowed toassume its floating position, the lower parts of the float chamberand the first and second expansion chambers will be in fluidcommunication with each other via the first and second flow portsand the level of the coolant in the first and second expansionchambers and the float chamber may thereby be equalized.When the refill opening is closed and the float has been forcedby the lid to assume its closing position, the lower parts of thefloat chamber and the first and second expansion chambers are separated from each other.

According to an embodiment of the invention, the float comprisesa float body and a liquid level indicator which is fixed to the floatbody and extends vertically upwards from the float body. Hereby,an indication of the coolant level in the first and secondexpansion chambers will be given by the liquid level indicator of the float when the refill opening is open.

Further advantageous features of the expansion tank of thepresent invention will appear from the following description and the dependent claims.

The features defined in claim 12. invention also relates to a cooling system having the Further advantageous features of the cooling system of thepresent invention will appear from the following description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, a specific descriptionof embodiments of the invention cited as examples follows below.ln the drawings: Fig 1 is a schematic vertical section through an expansiontank according to an embodiment of the presentinvention, as seen with the float of the expansion tankin a closing position, Fig 2 is a schematic vertical section through the expansiontank of Fig 1, as seen with the float in a floatingposition, Fig 3 is a schematic horizontal section through theexpansion tank of Figs 1 and 2, according to the line III-III in Fig 2, and Fig 4 is an outline diagram of a cooling system comprising an expansion tank according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION An expansion tank 1 according to an embodiment of the presentinvention is illustrated in Figs 1-3. This expansion tank 1 isintended to be included in a cooling system of a motor vehicle,for instance a cooling system 3 of the type illustrated in Fig 4.The expansion tank 1 comprises an outer casing 2 of rigidmaterial, for instance plastic. A first expansion chamber 10 and asecond expansion chamber 20 are provided inside the casing 2.The expansion chambers 10, 20 are separated from the surroundings by the casing 2.

The first expansion chamber 10 is configured to receive coolantwhich circulates in a first cooling circuit 50 (see Fig 4) of thecooling system 3 and the second expansion chamber 20 isconfigured to receive coolant which circulates in a secondcooling circuit 60 of the cooling system 3. Each expansionchamber 10, 20 comprises a lower part 11, 21, in which coolantis to be accumulated, and an upper part 12, 22, in which air is tobe accumulated. The lower part 11 of the first expansionchamber 10 is separated from the lower part 21 of the secondexpansion chamber 20 in order to prevent coolant flow betweenthe first and second expansion chambers 10, 20. Furthermore,the upper part 12 of the first expansion chamber 10 is connectedto the upper part 22 of the second expansion chamber 20 in order to allow pressure equalization between the first and second expansion Chambers 10, 20. ln the illustrated embodiment, thefirst and second expansion chambers 10, 20 are separated from each other by a partition wall 4 arranged inside the casing 2.

A first in|et opening 13 and a second in|et opening 23 areprovided in the casing 2. The first in|et opening 13 is intended tobe connected to a vent conduit 51 (see Fig 4) of the first coo|ingcircuit 50 in order to allow coo|ant and air to flow into the firstexpansion chamber 10 via this first in|et opening 13, whereas thesecond in|et opening 23 is intended to be connected to a ventconduit 61 of the second coo|ing circuit 60 in order to allowcoo|ant and air to flow into the second expansion chamber 20 viathis second in|et opening 23. There could also be two or morein|et openings to the first expansion chamber 10 and/or to the second expansion chamber 20. ln the illustrated embodiment, a pipe socket 15 connected to thefirst in|et opening 13 and another pipe socket 25 connected tothe second in|et opening 23 protrude from a respective side wallof the casing 2. The above-mentioned vent conduits 51, 61 are intended to be connected to these pipe sockets 15, 25.

A first outlet opening 14 and a second outlet opening 24 areprovided in the casing 2. The first outlet opening 14 is located atthe bottom of the first expansion chamber 10 and is intended tobe connected to a coo|ant conduit 52 (see Fig 4) of the firstcoo|ing circuit 50 in order to allow coo|ant to flow out of the firstexpansion chamber 10 via this first outlet opening 14. Thesecond outlet opening 24 is located at the bottom of the second expansion chamber 20 and is intended to be connected to a coolant conduit 62 of the second cooling circuit 60 in order toallow coolant to flow out of the second expansion chamber 20 via this second outlet opening 24. ln the illustrated embodiment, a pipe socket 18 connected to thefirst outlet opening 14 and another pipe socket 28 connected tothe second outlet opening 24 protrude from the underside of thecasing 2. The above-mentioned coolant conduits 52, 62 are intended to be connected to these pipe sockets 18, 28.

The expansion tank 1 further comprises a float chamber 30,which is located inside the casing 2 adjacent to the first andsecond expansion chambers 10, 20. The float chamber 30 has aclosable coolant refill opening 31 (see Fig 2) at an upper end anda bottom wall 32 at an opposite lower end. Coolant may beintroduced into the expansion tank 1 via the refill opening 31 inorder to provide for replenishment of the cooling system 3. A lid5 is removably fittable over the refill opening 31 for closing of therefill opening. ln the illustrated embodiment, the float chamber 30has a sleeve-shaped part 33 at its upper end which protrudesfrom an upper wall 6 of the casing 2, wherein the lid 5 isconfigured for releasable engagement with this sleeve-shapedpart 33. The lid 5 may for instance be provided with an internalthread configured for engagement with a corresponding externalthread on said sleeve-shaped part 33. However, the lid 5 couldalso be configured to be removably fittable over the refill opening31 in any other suitable manner, such as for instance by means of a bayonet joint. 11 At least one closable first flow port 34a and at least one closablesecond flow port 34b are arranged in the bottom wall 32 of thefloat chamber 30. The first flow port 34a is connected to thelower part 11 of the first expansion chamber 10 in order to allowcoolant to flow between the float chamber 30 and the lower part11 of the first expansion chamber 10 via this flow port 34a whenthe flow port is open. The second flow port 34b is connected tothe lower part 21 of the second expansion chamber 20 in order toallow coolant to flow between the float chamber 30 and the lowerpart 21 of the second expansion chamber 20 via this flow port34b when the flow port is open. There could also be two or moresuch first flow ports 34a and/or two or more such second flowports 34b in the bottom wall 32 of the float chamber 30.

The float chamber 30 is with advantage located in the centre ofthe expansion tank 1 between the first and second expansion10, 20. ln the the float chamber 30 is cylindrical and separated from the first and second chambers illustrated embodiment, expansion chambers 10,20 by a cylindrical wall 35.

A float 36 is arranged in the float chamber 30. As illustrated inFigs 1 and 2, the float 36 may comprise a float body 37 and aliquid level indicator 38 which is fixed to the float body 37 andextends vertically upwards from the float body. ln the illustratedembodiment, the liquid level indicator 38 has the form of a pinand is provided with a first marking 39a, which indicates amaximum allowed coolant level in the expansion tank 1, and asecond marking 39b, which indicates a minimum allowed coolant level in the expansion tank 1. 12 The float 36 is vertically moveable in the float chamber 30between a lower closing position (see Fig 1), in which the float36 is in contact with the bottom wall 32 of the float chamber andkeeps the first and second flow ports 34a, 34b closed to therebyprevent coolant flow between the float chamber 30 and the firstand second expansion chambers 10, 20, and an upper floatingposition (see Fig 2), in which the float 36 is floating at thesurface of the coolant in the float chamber 30 and leaves the firstand second flow ports 34a, 34b open. Thus, coolant is preventedfrom flowing between the float chamber 30 and the first andsecond expansion chambers 10, 20 when the float 36 is in theclosing position and allowed to flow between the float chamber30 and the first and second expansion chambers 10, 20 via thefirst and second flow ports 34a, 34b when the float 36 is in the floating position.

The lid 5 is configured to act on the float 36 in order to keep thefloat depressed in the closing position when the lid 5 is fittedover the refill opening 31, as illustrated in Fig 1, wherein the float36 is free to rise from the closing position to the floating positionlid 5illustrated in Fig 2. Hereby, coolant introduced into the expansion when the is removed from the refill opening 31, astank 1 via the refill opening 31 may be distributed to the first andsecond expansion chambers 10, 20 via the float chamber 30 andthe first and second flow ports 34a, 34b as long as no lid 5 isfitted over the refill opening 31, wherein the possibility forcoolant to flow between the different chambers 10, 20, 30 of theexpansion tank 1 is automatically stopped when the lid 5 is fitted over the refill opening 31. 13 ln the illustrated embodiment, an upper end 40 of the liquid levelindicator 38 is configured to be in contact with the lid 5 when thelid is fitted over the refill opening 31, wherein the liquid levelindicator 38 has such a length that a bottom surface 42 of thefloat body 37 is pressed down under the effect of the lid 5 andthe liquid level indicator 38 into fluid-tight contact with the bottomwall 32 of the float chamber 30 when the lid 5 is properly fittedover the refill opening 31. The first and second flow ports 34a,34b have such a position on the bottom wall 32 that they arecovered by the float body 37 when the float 36 assumes the closing position in contact with the bottom wall 32.

An upper part 41 of the float chamber 30 is connected to theupper parts 12, 22 of the first and second expansion chambers20, 30 in order to allow pressure equalization between the floatchamber 30 and the first and second expansion chambers 10, 20.ln the illustrated embodiment, the upper part 41 of the floatchamber 30 is connected to the upper part 12 of the firstexpansion chamber 10 via one or more first pressureequalization channels 43a arranged in the cylindrical wall 35 andto the upper part 22 of the second expansion chamber 20 via oneor more second pressure equalization channels 43b arranged in the cylindrical wall 35.

Fig 1 illustrates a situation where the coolant in the first coolingcircuit 50 has been subjected to a rather low temperatureincrease and where the coolant in the second cooling circuit 60has been subjected to a higher temperature increase, whichimplies that the coolant in the second cooling circuit 60 has been expanded more that the coolant in the first cooling circuit 50. 14 Thus, level 26 expansion Chamber 20 is higher than the coolant level 16 in the in this situation the coolant in the secondfirst expansion chamber 10. The pressure in the first and secondexpansion chambers 10, 20, and thereby the pressure in the firstand second cooling circuits 50, 60, is increased due to theexpansion of the coolant in the first and second cooling circuits.the first expansion chambers 10, 20 implies that the pressure increase in The pressure equalization between and secondthe second expansion chamber 20 also will cause a pressure increase in the first expansion chamber10.

The expansion tank 1 is provided with a pressure relief valve 7for limiting the pressure in the first and second expansionchambers 10, 20 and a return valve 8. The pressure relief valve 7allows air and coolant to flow out from the expansion tank 1 whenthe pressure in the first and second expansion chambers 10, 20,due to an increase of the coolant volume, exceeds a pressurelevel given by the pressure relief valve. Thus, the pressure reliefvalve 7 ensures that the pressure in the first and secondexpansion chambers 10, 20 cannot exceed a predeterminedpressure level. The return valve 8 allows air to flow into theexpansion tank 1 from the surroundings when the pressure in thefirst and second expansion chambers 10, 20, due to a reductionof the coolant volume, becomes lower than a pressure levelgiven by the return valve. ln the illustrated embodiment, thepressure relief valve 7 and the return valve 8 are mounted to thelid 5, but they could as an alternative be mounted to an upper part of the casing 2. ln the illustrated embodiment, the expansion tank 1 is alsoprovided with a first liquid level sensor 17 for detecting when thelevel of the coolant in the first expansion chamber 10 hasdropped to a given lower level and a second liquid level sensor27 for detecting when the level of the coolant in the secondexpansion chamber 20 has dropped to a given lower level. Eachliquid level sensor 17, 27 is mounted to the casing 2 andconfigured to give off a signal when the coolant level in theassociated expansion chamber 10, 20 has reached a given lower level.

A cooling system 3 intended for a motor vehicle is schematicallyillustrated in Fig 4. This cooling system 3 comprises a firstcooling circuit 50 for cooling at least one first vehicle component53 of the motor vehicle by means of coolant circulating in the firstcooling circuit 50 and a second cooling circuit 60 for cooling atleast one second vehicle component 63a, 63b of the motorvehicle by means of coolant circulating in the second coolingcircuit 60. The coolant flowing through the first and secondcooling circuits 50, 60 is preferably water, possibly with anti-freezing additives such as for instance glycol. A coolant pump54, 64 is provided in each cooling circuit 50, 60 in order tocirculate the coolant in the cooling circuit. Furthermore, a coolingdevice 55, 65, for instance in the form of a heat exchanger, isprovided in each cooling circuit 50, 60 in order to remove heat from the coolant circulating therein.

The cooling system 3 is provided with an expansion tank 1 of the14 of the expansion tank 1 is connected to a conduit 52 of the first cooling type described above. The first outlet opening 16 circuit 50 and the second outlet opening 24 of the expansion tank1 is connected to a conduit 62 of the second cooling circuit 60.The first in|et opening 13 of the expansion tank 1 is connected toa vent conduit 51 of the first cooling circuit 50 in order to allowcoo|ant and air to flow from the first cooling circuit 50 and intothe first expansion chamber 10 via this vent conduit 51 and thefirst in|et opening 13 of the expansion tank 1. The second in|etopening 23 of the expansion tank 1 is connected to a ventconduit 61 of the second cooling circuit 60 in order to allowcoo|ant and air to flow from the second cooling circuit 60 and intothe second expansion chamber 20 via this vent conduit 61 andthe second in|et opening 23 of the expansion tank 1. ln theillustrated example, the first cooling circuit 50 is used for coolinga vehicle component in the form of an electric energy storingdevice 53, such as for instance an electric battery or a set ofelectric batteries, for supplying electric energy to an electrictraction motor of a hybrid vehicle, whereas the second coolingcircuit 60 is used for cooling vehicle components in the form ofpower electronic devices, such as for instance an inverter 63aand a DC/DC converter 63b, for controlling the flow of electricpower between the electric energy storing device 53 and the electric traction motor. ln the embodiment illustrated in Fig 4, the cooling system 3 alsocomprises a heating device 56, for instance in the form of a heatexchanger, which is provided in the first cooling circuit 50 inorder to supply heat to the coo|ant circulating therein in asituation when there is a need to increase the temperature of theelectric energy storing device 53 to a suitable operating temperature, such as for instance when the motor vehicle is 17 started in a cold environment with an ambient temperature belowO°C. A control valve 57 provided in the first cooling circuit 50 isconfigured to lead the coolant circulating in the first coolingcircuit 50 either through the cooling device 55 or through theheating device 56 in dependence on the prevailing temperature of the electric energy storing device 53.

The expansion tank according to the invention is particularlyintended for use in a heavy motor vehicle, such as for instance a bus or a truck.

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 personwith ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims (1)

1. _ An expansion tank intended to be included in a cooling system of a motor vehicle, the expansion tank (1) comprising: - a first expansion chamber (10) configured to receive coolantwhich circulates in a first cooling circuit of the cooling system,the first expansion chamber comprising a lower part (11), inwhich coolant is to be accumulated, and an upper part (12), inwhich air is to be accumulated; and - a second expansion chamber (20) configured to receivecoolant which circulates in a second cooling circuit of thecooling system, the second expansion chamber comprising alower part (21), in which coolant is to be accumulated, and anupper part (22), in which air is to be accumulated, wherein the lower part (11) of the first expansion chamber isseparated from the lower part (21) of the second expansionchamber in order to prevent coolant flow between the first andsecond expansion chambers (10, 20), and wherein the upperpart (12) of the first expansion chamber is connected to theupper part (22) of the second expansion chamber in order toallow pressure equalization between the first and secondexpansion chambers (10, 20), characterized in: - that the expansion tank (1) comprises a float chamber (30),which has a coolant refill opening (31) at an upper end and abottom wall (32) at an opposite lower end; - that the expansion tank (1) comprises a lid (5) which isremovably fittable over the refill opening (31) for closing of the refill opening; 19 - that one or more first flow ports (34a) are arranged in thebottom wall (32) of the float Chamber, wherein each first flowport (34a) is connected to the lower part (11) of the firstexpansion chamber (10) to allow coolant to flow between thefloat chamber (30) and the lower part of the first expansionchamber via this flow port when it is open; - that one or more second flow ports (34b) are arranged in thebottom wall (32) of the float chamber, wherein each secondflow port (34b) is connected to the lower part (22) of thesecond expansion chamber (20) to allow coolant to flowbetween the float chamber (30) and the lower part of thesecond expansion chamber via this flow port when it is open; - that a float (36) is arranged in the float chamber (30),wherein the float is vertically moveable in the float chamberbetween a lower closing position, in which the float is incontact with the bottom wall (32) and keeps the first andsecond flow ports (34a, 34b) closed to thereby preventcoolant flow between the float chamber (30) and the first andsecond expansion chambers (10, 20), and an upper floatingposition, in which the float is floating at the surface of thecoolant in the float chamber and leaves the first and secondflow ports (34a, 34b) open; and - that the lid (5) is configured to act on the float (36) in orderto keep the float depressed in the closing position when thelid (5) is fitted over the refill opening (31), wherein the float isfree to rise from the closing position to the floating position when the lid is removed from the refill opening. _ An expansion tank according to claim 1, characterized in that the float (36) comprises a float body (37) and a liquid level indicator (38) which is fixed to the float body and extends vertically upwards from the float body. _ An expansion tank according to claim 2, characterized in that an upper end (40) of the liquid level indicator (38) isconfigured to be in contact with the lid (5) when the lid is fitted over the refill opening (31). _ An expansion tank according to claim 2 or 3, characterized in that the liquid level indicator (38) is provided with a firstmarking (39a), which indicates a maximum allowed coolantlevel in the expansion tank (1), and a second marking (39b),which indicates a minimum allowed coolant level in the expansion tank (1). .An expansion tank according to any of claims 2-4, characterized in that the liquid level indicator (38) has the form of a pin. .An expansion tank according to any of claims 1-5, characterized in that the float chamber (30) is cylindrical. .An expansion tank according to any of claims 1-6, characterized in that an upper part (41) of the float chamber(30) is connected to the upper parts (12, 22) of the first andsecond expansion chambers (10, 20) in order to allowpressure equalization between the float chamber and the first and second expansion chambers. 8. 9. 10.An 11.An 21 1-7, characterized in that the expansion tank (1) comprises a An expansion tank according to any of claimspressure relief valve (7) for limiting the pressure in the first and second expansion chambers (10, 20). An expansion tank according to claim 8, characterized in thatthe pressure relief valve (7) is mounted to the |id (5).expansion tank according to any of claims 1-9,characterized in that the expansion tank (1) comprises:- a first liquid level sensor (17) for detecting when the level ofthe coolant in the first expansion chamber (10) has droppedto a given lower level; and - a second liquid level sensor (27) for detecting when thelevel of the coolant in the second expansion chamber (20) hasdropped to a given lower level. expansion tank according to any of claims 1-10,characterized in that the expansion tank (1) comprises:- a first inlet opening (13), which is intended to be connectedto a vent conduit (51) of said first cooling circuit in order toallow coolant and air to flow into the first expansion chamber(10) via this first inlet opening (13); - a first outlet opening (14), which is intended to be connectedto a coolant conduit (52) of said first cooling circuit in order toallow coolant to flow out of the first expansion chamber (10)via this first outlet opening (14); - a second inlet opening (23), which is intended to beconnected to a vent conduit (61) of said second cooling circuit in order to allow coolant and air to flow into the second 12. 13. 22 expansion chamber (20) via this second inlet opening (23);and - a second outlet opening (24), which is intended to beconnected to a coo|ant conduit (62) of said second coolingcircuit in order to allow coo|ant to flow out of the second expansion chamber (20) via this second outlet opening (24). A cooling system for a motor vehicle comprising:- a first cooling circuit (50) for cooling a first vehiclecomponent (53) of the motor vehicle by means of coo|antcirculating in the first cooling circuit; and - a second cooling circuit (60) for cooling a second vehiclecomponent (63a, 63b) of the motor vehicle by means ofcoo|ant circulating in the second cooling circuit,characterized in that the cooling system (3) comprises anexpansion tank (1) according to claim 11, wherein: - the first inlet opening (13) of the expansion tank (1) isconnected to a vent conduit (51) included in the first coolingcircuit (50) and the first outlet opening (14) of the expansiontank (1) is connected to a coo|ant conduit (52) included in thefirst cooling circuit (50); and - the second inlet opening (23) of the expansion tank (1) isconnected to a vent conduit (61) included in the secondcooling circuit (60) and the second outlet opening (24) of theexpansion tank (1) is connected to a coo|ant conduit (62) included in the second cooling circuit (60). A cooling system according to claim 12, characterized in: 23 - that said first vehicle component (53) is an electric energystoring device for supplying electric energy to an electrictraction motor of the motor vehicle; and - that said second vehicle component (63a, 63b) is a power electronic device.