Abstract:
A method for operating a cooling system for a vehicle, for example a rail vehicle, may include circulating a coolant in a first cooling circuit and in a second cooling circuit. A first heat source to be cooled may be arranged in the first cooling circuit and a second heat source to be cooled may be arranged in the second cooling circuit. The coolant may be circulated by pumping the coolant in the first cooling circuit via a first pumping device, and pumping the coolant in the second coolant circuit via a second pumping device. The first pumping device and the second pumping device may each be operated in a normal mode. The method may further include cooling the coolant via at least one cooling element arranged in at least one of the first cooling circuit and the second cooling circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. DE 10 2016 203 985.7, filed on Mar. 10, 2016, the contents of which are hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a method for operating a cooling system for a vehicle, in particular for a rail vehicle. The invention further relates to such a cooling system. 
       BACKGROUND 
       [0003]    A coolant which is used for cooling liquids and objects usually circulates in a cooling system. Such a cooling system can be used in particular in a vehicle in order to cool components of the vehicle as heat sources. It is conceivable here to provide the cooling system with a plurality of cooling circuits and arrange such a heat source in the respective circuit for the purpose of cooling. In this case, a corresponding adaptation of the cooling circuit can be made according to the cooling requirement of the heat source. The circulation of the coolant in the respective cooling circuit is accomplished in this case by means of a pumping device which pumps the coolant in the cooling circuit. 
         [0004]    In the case of heat sources which are critical for operation, in particular components of the vehicle, it is necessary to ensure cooling with very high probabilities and to eliminate a reduction of the cooling and/or a failure of the cooling as far as possible. For this purpose cooling circuits in which these heat sources which are critical for operation are arranged are frequently assigned two such pumping devices in order to use, in the event of failure of one of the pumping devices, the other pumping device for pumping the coolant. At least one of the pumping devices is therefore provided as an emergency pumping device of the cooling circuit. 
         [0005]    Such a configuration of the cooling circuit therefore results in an increased assembly expenditure and/or an increased installation space requirement and/or an increased weight and/or a reduced efficiency of the cooling system. 
       SUMMARY 
       [0006]    The present invention is therefore concerned with the problem of providing improved or at least alternative embodiments for a method for operating a cooling system of the aforesaid type and for such a cooling system, which are in particular characterized by an increased efficiency and/or a reduced installation space requirement and/or a reduced weight. 
         [0007]    This problem is solved according to the invention by the subject matter of the independent claim(s). Advantageous embodiments are the subject matter of the dependent claims. 
         [0008]    The present invention is based on the general idea in a cooling system with two cooling circuits in which respectively one pumping device is provided for pumping a coolant circulated through the respective cooling circuit, of using at least one of the pumping devices of one of the cooling circuits as an emergency pumping device of the other cooling circuit. As a result it is in particular possible to dispense with emergency pumping devices provided specifically for the cooling circuit. This results in a reduction of the installation space requirement and/or the weight and/or the assembly expenditure of the cooling system. In addition, an increased efficiency of the cooling system is achieved as a result since the pumping device used as emergency pumping device pumps coolant in its own cooling circuit and accordingly is not merely used just when another pumping device delivers a reduced cooling capacity or fails. The inventive idea accordingly uses a cooling system comprising a first cooling circuit and a second cooling circuit in which the coolant circulates, wherein in the first cooling circuit a first pumping device is provided and in the second cooling circuit a second pumping device is provided for pumping the coolant. It is preferred here if the same coolant circulates in the first cooling circuit and in the second cooling circuit. Furthermore a heat source for cooling is provided in the respective cooling circuit. That is, a first heat source is provided in the first cooling circuit and a second heat source is provided in the second cooling circuit. The heat sources are in this case cooled by heat exchange with the coolant. For this purpose a cooling of the coolant is required which is accomplished with the aid of at least one cooling means of the cooling system. In a normal mode or a regular mode, both pumping devices are operated in order to pump the coolant in the appurtenant cooling circuit. In the normal mode the cooling circuits are preferably fluidically separated. If an emergency mode arises, which is hereinafter designated as first emergency mode in which the second pumping device provides an at least reduced pumping capacity, in particular fails, coolant is branched off from the second cooling circuit downstream of the second heat source, is pumped by the first pumping device and is returned to the second cooling circuit upstream of the second heat source. That is, in the event of a failure of the second pumping device, the coolant for cooling the second heat source is pumped from the first pumping device and in the case of a reduced pumping capacity of the second pumping device, is additionally pumped by the first pumping device. It is preferred here if the coolant is guided through at least one such cooling means before it is supplied to the second heat source so that the coolant is cooled before it is returned to the second heat source for the purpose of cooling the second heat source. 
         [0009]    It is in particular conceivable here to configure the method in such a manner that the second cooling circuit or the second heat source is prioritized in such a manner that only an emergency mode according to the first emergency mode is provided in which exclusively a pumping of the coolant circulating through the second cooling circuit with the aid of the first pumping device is provided when the pumping capacity of the second pumping device is at least reduced, in particular when the second pumping device fails. Consequently those heat sources can be arranged in the second cooling circuit which are more critical in regard to cooling, in particular require continuous cooling during operation of the cooling system. 
         [0010]    The cooling system can in principle be used in any application. The cooling system is used, for example, in a vehicle to cool components of the vehicle. These components of the vehicle are therefore said heat sources. It is in particular conceivable to use the cooling system in a rail vehicle in order to cool components of the rail vehicle. The vehicle, in particular the rail vehicle, can be electrically driven here so that the cooling system can be used in particular for cooling drive components. It is in particular conceivable here to arrange components which are critical for operation, in particular drive components, as second heat sources in the second cooling circuit, which as explained hereinbefore can be prioritized. 
         [0011]    Naturally it is also possible to operate the cooling system in such a manner that in the event of a second emergency mode occurring, in which the first pumping device provides an at least reduced pumping capacity, in particular fails, coolant is branched off from the first cooling circuit downstream of the first heat source, is pumped by the second pumping device and is supplied to the first cooling circuit upstream of the first heat source. In the second emergency mode therefore, similarly to the first emergency mode, the coolant in the first cooling circuit is pumped by the second pumping device in the event of a failure of the first pumping device and in the case of a reduction in the pumping capacity of the first pumping device, is pumped by the second pumping device in addition to the first pumping device. 
         [0012]    It is further preferred that in the event of a support mode occurring in which the temperature of the coolant in one of the cooling circuits upstream of the appurtenant heat source increases above a predefined value, the pumping device of the other cooling circuit is additionally used for pumping the coolant in the cooling circuit with the excessive temperature of the coolant. The support mode can therefore in particular also take place when no reduced capacity of the other pumping device is present. In this case, preferably at least one temperature sensor is used which determine the temperature of the coolant upstream of the appurtenant heat source and preferably downstream of the appurtenant at least one cooling means. In this case, a first support mode and a second support mode can be present wherein in the first support mode the first pumping device is additionally used for pumping the coolant in the second cooling circuit when the temperature of the coolant in the second cooling circuit upstream of the second heat source increases above a predefined value. Similarly to this in the second support mode the second pumping device is additionally used for pumping the coolant in the first cooling circuit when the temperature of the coolant in the first cooling circuit upstream of the first heat source and preferably downstream of the at least one appurtenant cooling means increases above a predefined value. In this case, the predefined values of the temperature in the first support mode and in the second support mode can be different. The additional pumping in the support mode is accomplished here by branching and returning the coolant from or back to the supported cooling circuit. 
         [0013]    The operating method according to the invention is preferably used in such a cooling system which has a branch line for fluidic communication of the first cooling circuit with the second cooling circuit upstream of the first pumping device and upstream of the second pumping device wherein the branch line is arranged further downstream of the second heat source. That is, the branch line preferably runs from a first branch point of the first cooling circuit arranged upstream of the first pumping device as far as a second branch point of the second cooling circuit arranged upstream of the second pumping device and downstream of the second heat source. The branch line here serves the purpose of branching off the coolant from the second cooling circuit to the first cooling circuit. The cooling system furthermore has a first return line for fluidic communication of the first cooling circuit with the second cooling circuit, which branches off from the first cooling circuit downstream of the first pumping device and opens into the second cooling circuit upstream of the second heat source, preferably downstream of the second pumping device. The first return line here in particular serves the purpose of supplying coolant branched off from the second cooling circuit via the branch line to the second cooling circuit, wherein the coolant has previously been pumped by means of the first pumping device. Furthermore, a valve for regulating the flow of coolant is arranged in the first return line, which in particular allows the volume flow and/or the flow direction of the coolant through the first return line to be regulated. The cooling system is here configured in such a manner that it can be operated according to the invention. That is, in particular that the branch line and the first return line are used for the first emergency mode and/or for the support mode, in particular for the first support mode. In such a configuration, the second heat source or the second cooling circuit is prioritized since only the first pumping device can be used for pumping the coolant in the second cooling circuit and a converse mode according to the second emergency mode is not possible. 
         [0014]    In principle, the first return line can also be used for returning coolant which has been branched off previously from the first cooling circuit to the first cooling circuit, in particular therefore in the second emergency mode. 
         [0015]    Naturally it is also possible to provide a second return line for fluidic communication of the second cooling circuit with the first cooling circuit which branches off from the second cooling circuit downstream of the second pumping device and opens into the first cooling circuit upstream of the first heat source, preferably downstream of the first pumping device. The second return line is therefore used in particular for the second emergency mode and/or for the support mode, in particular for the second support mode. In this case, the coolant can be branched off from the first cooling circuit via said branch line or another branch line. It is preferable here if the branch line is additionally arranged downstream of the first heat source. That is that the first branch point is arranged downstream of the first pumping device and upstream of the first heat source. 
         [0016]    In preferred embodiments a valve is arranged in the second cooling circuit downstream of the second pumping device and upstream of the first return line, which is configured in such a manner that it prevents the flow of coolant from the first return line to the second pumping device via the valve. The valve therefore in particular prevents a flow of coolant in the “wrong” direction. Consequently in particular in the first emergency mode it is prevented that coolant returned via the first return line to the second cooling circuit reaches the branch line bypassing the second heat source. 
         [0017]    A corresponding valve can be arranged similarly in the first cooling circuit downstream of the first pumping device and upstream of the second return line in order to prevent a corresponding “wrong” direction of flow of the coolant, in particular in the second emergency mode. 
         [0018]    Preferred are embodiments in which at least one such valve is configured as a non-return valve. The use of such a non-return valve in particular has the advantage that such a configuration of the cooling circuit for executing the method according to the invention can be accomplished at least partially by means of the non-return valves since these allow a flow of the coolant only in one direction. That is that such a first non-return valve arranged in the first return line prevents the coolant from flowing via the first return line from the second cooling circuit to the first cooling circuit. Similarly to this such a non-return valve arranged in the second return line can prevent a flow of coolant from the first cooling circuit to the second cooling circuit. 
         [0019]    Such a non-return valve further has the advantage that it can be operated with a predefined counter-pressure in such a manner that the non-return valve opens when a counter-pressure is exceeded, in particular continuously. The counter-pressure of the non-return valve can in this case be selected in such a manner that the non-return valve opens at a predefined pressure difference between the first cooling circuit and the second cooling circuit in order to ensure a corresponding flow through the appurtenant line. Consequently at least one such emergency mode can be accomplished in a self-regulating manner. If a pressure loss therefore occurs in one of the cooling circuits as a result of such a reduction in the pumping capacity of the appurtenant pumping device, the non-return valve in the branch line and/or the non-return valve in the appurtenant return line opens in a self-regulating manner in order to achieve such an emergency mode. 
         [0020]    In addition, by using such a non-return valve in the branch line for example, it can be prevented that coolant flows via the branch line from the first cooling circuit to the second cooling circuit. As a result, in particular the second emergency mode is therefore prevented and accordingly the second cooling circuit or the second heat source is prioritized. 
         [0021]    According to advantageous embodiments, a valve for regulating the flow of coolant through the branch line is arranged in the branch line. By means of the valve it is therefore in particular possible to prevent a fluidic communication between the cooling circuits during the normal mode and to regular the volume flow of the coolant through the branch line during the respective emergency mode and/or the support mode. 
         [0022]    Such a configuration of the coolant for operating the method according to the invention can alternatively or additionally be implemented by a control device configured in such a manner that it operates the cooling system according to the method. For this purpose, the control device can be connected to the respective valve in a communicating manner in order to actuate the valves accordingly. Preferably the control device is additionally connected to at least one of the pumping devices in a communicating manner in order to monitor the operating state of the pumping device and/or actuate at least one of the pumping devices. As a result, it is in particular possible to identify whether the pumping capacity of the pumping device is reduced in order to implement the corresponding emergency mode. 
         [0023]    In order to operate the cooling system in the support mode, the control device is further connected in a communicating manner with at least one such temperature sensor in order to implement the corresponding support mode when the temperature of the coolant exceeds the appurtenant predefined value. 
         [0024]    Embodiments prove to be advantageous in which the cooling system comprises at least one pressure-equalizing container for equalizing the pressure in the coolant, which can be fluidically connected to the branch line. The pressure-equalizing container therefore serves the purpose of equalizing for a pressure difference which may exist between the first cooling circuit and the second cooling circuit, wherein this compensation is made via the branch line. 
         [0025]    It is advantageous if two such pressure-equalizing containers, namely a first pressure equalizing container which is assigned to the first cooling circuit and a second pressure equalizing container which is assigned to the second cooling circuit are provided. Thus, an appurtenant pressure-equalizing container is used for pressure compensation in the respective cooling circuit in such an emergency mode and/or in support mode. This in particular allows one of the cooling circuits to be operated when a coolant loss occurs in the other circuit. In particular, it is possible by this means to prioritize one of the cooling circuits, in particular the second cooling circuit insofar that the second cooling circuit can then be operated further in a regulated manner when a coolant loss occurs in the first cooling circuit. 
         [0026]    The respective line, that is the branch line and the respective return line can be arranged arbitrarily in relation to the at least one cooling means. Here it is preferred if the branch line and the respective return line are arranged in such a manner that the coolant is guided through at least one such cooling means and cooled before it is supplied to the appurtenant heat source after return. 
         [0027]    In particular it is conceivable to arrange the branch line upstream of the at least one cooling means. In consequence, the coolant is branched off from the respective cooling circuit in the respective emergency mode or in the support mode before it is guided through the cooling means. 
         [0028]    It is additionally feasible to arrange a throttle device for regulating the flow through the line in at least one of the lines alternatively or additionally to the valve. In particular it is conceivable to provide one such throttle device in at least one of the lines additionally to at least one such non-return valve. Consequently the flow can also be regulated, in particular interrupted when the appurtenant non-return valve allows a corresponding flow. It is preferably here if the respective throttle device is connected to the control device in a communicating manner so that the control device can actuate the throttle device. 
         [0029]    The cooling system can in principle have a separate cooling means for the respective cooling circuit. It is also conceivable to assign a common such cooling means to both cooling circuits. By this means in particular the number of components of the cooling circuit can be reduced. In this case, in particular it is conceivable to guide the respective cooling circuit separate through the common cooling means. 
         [0030]    The common cooling means can have a cooling fluid flowing through it for the purpose of cooling the coolant, which cooling fluid flows through the cooling means in a cooling fluid flow direction. The cooling fluid can in particular be air, for example airflow of the appurtenant vehicle. 
         [0000]    Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the appurtenant description of the figures with reference to the drawings. 
         [0031]    It is understood that the features mentioned previously and to be explained further hereinafter can be used not only in the respectively given combination but also in other combinations or alone without departing from the scope of the present invention. 
         [0032]    Preferred exemplary embodiments of the invention are presented in the drawings and are explained in detail in the following description, where the same reference numbers relate to the same or similar or functionally the same components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    In the figures, in each case schematically and shown in a highly simplified and circuit-diagram-like manner, 
           [0034]      FIG. 1  shows a cooling system in a first operating state, 
           [0035]      FIG. 2  shows the cooling system in a second operating state, 
           [0036]      FIG. 3  shows the cooling system in a further operating state, 
           [0037]      FIG. 4  shows the cooling system in the second operating state in another exemplary embodiment of the cooling system, 
           [0038]      FIG. 5  shows the cooling system in the first operating state in another exemplary embodiment of the cooling system, 
           [0039]      FIG. 6  shows the cooling system from  FIG. 5  in a third operating state, 
           [0040]      FIG. 7  shows the cooling system from  FIG. 5  in a third operating state. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]      FIG. 1  shows a cooling system  1  which is part of a vehicle  2 , in particular a rail vehicle  2 ′, for example an electrically driven rail vehicle  2 ′. The cooling system  1  comprises a first cooling circuit  3  and a second cooling circuit  4  in which a coolant is circulating. With the aid of the coolant, a heat source  5 ,  6  is cooled in the respective cooling circuit  3 ,  4 , the heat source being arranged in the appurtenant cooling circuit  3 ,  4  and having coolant flowing through it or around it. In this case, a first such heat source  5  is arranged in the first cooling circuit  3 , which for example can be a drive component  7  of the vehicle  2 . A second such heat source  6  is arranged in the second cooling circuit  4 , which can also be a drive component  7  of the vehicle  2 . The drive component  7  arranged in the second cooling circuit  4  is more critical with regard to cooling than the drive component  7  arranged in the first cooling circuit  3 . That is, the drive component  7  arranged in the second cooling circuit  4  for driving the vehicle  2  requires a permanent cooling and/or is more important for driving the vehicle  2  than the drive component  7  arranged in the first cooling circuit  3 . 
         [0042]    A first pumping device  8 , for example, a pump  9 , in particular a circulating pump  9 ′ is arranged in the first cooling circuit  3  for pumping the coolant. In addition, a second pumping device  10 , which for example is configured as a pump  9 , in particular as circulating pump  9 ′ is arranged in the second cooling circuit  4  for pumping the coolant. The cooling circuits  3 ,  4  have a common cooling means  11  for cooling the coolant which is arranged in the respective cooling circuit  3 ,  4  downstream of the pumping device  8 ,  10  and upstream of the heat source  5 ,  6 . The cooling means  11  has a cooling fluid flowing through it for cooling the coolant, which flows through the cooling means  11  in a cooling fluid flow direction  13 . In this case, the first cooling circuit  3  and the second cooling circuit  4  are guided separately through the cooling means  11 , wherein the first cooling circuit  3  is guided in relation to the cooling fluid flow direction  13  upstream of the second cooling circuit  4  through the cooling means  11 .  FIG. 1  shows a normal mode  12  of the cooling system  1  in which the first cooling circuit  3  and the second cooling circuit  4  are separated fluidically and the first pumping device  8  pumps the coolant in the first cooling circuit  3  whilst the second cooling device  10  pumps the coolant in the second cooling circuit  4 . As a result, a flow of the coolant is obtained in the respective cooling circuit  3 ,  4  wherein the following references refer to the cooling circuits  3 ,  4  in the sense of upstream and downstream of the flow in the respective cooling circuits  3 ,  4  in the normal mode  12 . 
         [0043]    The cooling system  1  has a branch line  14  which fluidically interconnects the first cooling circuit  3  and the second cooling circuit  4 . Here the branch line  14  runs from a first branch point  15  downstream of the first heat source  5  and upstream of the first pumping device  8  in the first cooling circuit  3  as far as a second branch point  16  arranged downstream of the second heat source  6  and upstream of the second pumping device  10  in the second cooling circuit  4 . A valve  17  is arranged in the branch line  14  which in the example shown is configured as a non-return valve  18 . The non-return valve  18  here only allows a flow of coolants from the second cooling circuit  4  to the first cooling circuit  3 . The non-return valve  18  is loaded with a counter-pressure which is symbolized by a spring  19 . That is, the counter-pressure must be overcome to open the valve  17  for the purpose of flow of the coolant from the second cooling circuit  4  to the first cooling circuit  3 . A first return line  20  connects the first cooling circuit  3  fluidically to the second cooling circuit  4  and runs from the first return point  21  of the first return line  20  in the first cooling circuit  3  as far as a second return point  22  of the first return line  20  in the second cooling circuit  4 . Here the first return point  21  of the first return line  20  is arranged downstream of the first pumping device  8  and upstream of the first heat source  5  and downstream of the cooling means  11 . The second return point  22  of the first return line  20  is arranged upstream of the second heat source  6  and downstream of the second pumping device  10  as well as downstream of the cooling means  11 . A valve  17  is arranged in the first return line  20  which like the valve  17  arranged in the branch line  14  is configured as a non-return valve  18  and is exposed to a counter-pressure and merely allows a flow of coolant from the first cooling circuit  3  to the second cooling circuit  4 . A valve  17  is arranged in the second cooling circuit  4  upstream of the second return point  22  of the first return line  20  and downstream of the second pumping device  10  as well as downstream of the cooling means  11 , which valve is also configured as a non-return valve  18 , is exposed to a counter-pressure and merely allows a flow of coolant from the pumping device  10  to the second heat source  6 . 
         [0044]    In the normal mode  12  shown in  FIG. 1 , as mentioned previously, the cooling circuits  3  and  4  are separate from one another. Accordingly no coolant flows through the branch line  14  or through the first return line  20 . In the diagram sections through which coolant does not flow are shown by dashed lines. That is, in the normal mode  12  shown in  FIG. 1 , the branch line  14  and the first return line  20  are shown by dashed lines. 
         [0045]    In the example shown the respective cooling circuit  3 ,  4  is further assigned a pressure-equalizing container  23 . That is, that the first cooling circuit  3  is assigned a first such pressure-equalizing container  23 ′ whilst the second cooling circuit  4  is assigned a second such pressure-equalizing container  23 ″ wherein the respective pressure-equalizing container  23  serves to equalize the pressure of the coolant in the appurtenant cooling circuit  3 ,  4 . 
         [0046]      FIG. 2  shows an emergency mode  24  of the cooling system  1 . In the emergency mode  24  the second pumping device  10  of the second cooling circuit  4  delivers a reduced capacity or fails, wherein  FIG. 2  shows a state in which the second pumping device  10  has failed. In the emergency mode  24  coolant has branched off downstream of the second heat source  6  from the second cooling circuit  4 , is supplied to the first cooling circuit  24  upstream of the pumping device  8 , pumped by means of the first pumping device  8  and supplied to the second cooling circuit  4  again upstream of the second heat source  6 . That is that in the event of failure of the second pumping device  10  or in the case of a reduced capacity of the second pumping device  10 , the first pumping device  8  is used as emergency pumping device of the second cooling circuit  4 . As a result, the second heat source  6  arranged in the second cooling circuit  4  is also cooled when the second pumping device  10  fails or delivers a reduced capacity. In this case, the coolant is supplied from the second cooling circuit  4  via the branch line  14  to the first cooling circuit  3  and returned via the first return line to the second cooling circuit  4 . In the emergency mode  24  in the example shown the cooling of the coolant via the cooling means  11  is therefore accomplished exclusively in the first cooling circuit  3 . The non-return valve  18  in the branch line  14  ensures that the coolant in the branch line  14  flows from the second cooling circuit  4  to the first cooling circuit  3  whilst the non-return valve  18  in the first return line  20  ensures that the coolant flows via the first return line  20  from the first cooling circuit  3  to the second cooling circuit  4 . The non-return valve  18  arranged in the second cooling circuit  4  further ensures that the coolant flowing via the first return line  20  to the second cooling circuit  4  does not pass via the first pumping device  10  to the branch line  14  but exclusively via the second heat source  6  to the branch line  14 . This non-return valve  18  therefore ensures that the coolant in the emergency mode  24  flows in the correct direction or not in the “wrong” direction. 
         [0047]    The non-return valves  18  exposed to counter-pressure in the branch line  14  and in the first return line  20  ensure that the valves open in a self-regulating manner when the pressure relationships between the first cooling circuit  3  and the second cooling circuit  4  changes as a result of the falling pressure in the second cooling circuit  4  due to the at least reduced capacity of the second pumping device  10  in the second cooling circuit  4 . That is in particular that the emergency mode  24  can be adjusted in a self-regulating manner. Alternatively or additionally, it is conceivable to provide the cooling system  1  or the vehicle  2  with a control device  25  which is connected to the corresponding valves  17  in a communicating manner in order to actuate these. The control device  25  is additionally connected in a communicating manner to at least the second pumping device  10 , preferably to both pumping devices  8 ,  10  in order in particular to actuate the respective pumping device  8 ,  10  and/or interrogate the pumping capacity of the respective pumping device  8 ,  10 . In addition, a temperature sensor  30  for determining the temperature of the coolant upstream or downstream of the appurtenant heat source  5 ,  6 , which is also connected to the control device  25  in a communicating manner, can be provided upstream and/or downstream of the respective heat source  5 ,  6 . 
         [0048]    In the cooling system  1  shown in  FIGS. 1 and 2 , the second cooling circuit  4  or the second heat source  6  is prioritized. That is that the emergency mode  24  can only be operated in favour of the second heat source  6  or the second cooling circuit  7 . If therefore according to  FIG. 3  the first pumping device  8  fails or it delivers a reduced capacity, wherein  FIG. 3  shows a state in which the first pumping device  8  has failed, no pumping of the coolant in the first cooling circuit  3  takes place, accordingly the first cooling circuit  3  is shown by a dashed line. The same applies to the branch line  14  and the first return line  20 . 
         [0049]      FIG. 4  shows a further exemplary embodiment of the cooling system  1  in simplified manner, where the emergency mode  24  is shown in  FIG. 4 . This exemplary embodiment differs from the exemplary embodiments shown in  FIGS. 1 to 3  in particular in that only a single such pressure-equalizing container  23  is provided which is fluidically connected to the branch line  14 . This results in a reduced installation space requirement and a reduced number of components of the cooling system  1 . In addition, no such valve  17  is provided in the branch line  14 . The fluidic connection between the first cooling circuit  3  and the second cooling circuit  4  via the branch line  14  can here in particular be accomplished with the aid of the pressure-equalizing container  23  which can be connected to the control device  25  in a communicating manner. This has the result that both cooling circuits  3 ,  4  are at the same pressure level on the suction side, that is upstream of the pumping devices  8 ,  10 . If a prioritization of the second cooling circuit  4  is required, a valve  17  can be provided (not shown) between the pressure-equalizing container  23  and the first branch point  15  in order, in the event of a failure of the first pumping device  8  and/or in the case of a leak in the first cooling circuit  3 , to separate the second cooling circuit  4  and the pressure-equalizing container  23  from the first cooling circuit  3  so that in such cases a regulated operation of the second cooling circuit  4  is further possible. 
         [0050]      FIG. 5  shows a further exemplary embodiment of the cooling system  1  wherein the normal mode of the cooling system  1  is accomplished in  FIG. 5 . This exemplary embodiment differs from the exemplary embodiment shown in  FIG. 4  in particular in that the first return line  20  is arranged upstream of the cooling means  11 . In this case, the first return point  21  of the first return line  20  is arranged downstream of the first pumping device  8  and upstream of the cooling means  11  whereas the second return point  22  of the first return line  20  is arranged downstream of the second pumping device  10  and upstream of the cooling means  11 . In this exemplary embodiment, a second return line  26  is additionally provided which runs from the first return point  27  of the second return line  26  in the first cooling circuit  3  as far as a second return point  28  of the second return line  26  in the second cooling circuit  4 . The first return point  27  of the second return line  26  is arranged upstream of the first heat source  5  whilst the second return point  28  of the second return line  26  is arranged downstream of the second pumping device  10 . In the example shown, the first return point  27  of the second return line  26  is arranged upstream of the first return point  21  of the first return line  20  whilst the second return point  28  of the second return line  26  is arranged upstream of the second return point  22  of the first return line  20 , wherein a reversed sequence is also conceivable. A valve  17  configured as a non-return valve  18  is arranged in the second return line  26 , which valve is exposed to a counter-pressure and only allows a flow of coolant from the second cooling circuit  4  to the first cooling circuit  3 . In the example shown a throttle device  29  is additionally arranged in the respective return line  20 ,  26  which regulates the flow of coolant through the appurtenant line  20 ,  26 . This regulation by means of the throttle device  29  can be accomplished additionally or alternatively to the valve  17 , in particular to the non-return valve  18 . 
         [0051]    In the normal mode  12  shown in  FIG. 5 , the first cooling circuit  3  and the second cooling circuit  4  are fluidically separated. That is, that the fluidic connection between the cooling circuits  3  and  4  is interrupted via the lines  14 ,  20 ,  26 . 
         [0052]      FIG. 6  shows the cooling system  1  in the emergency mode  24  in which the second pumping device  10  delivers a reduced capacity or fails, wherein  FIG. 6  shows a state in which the second pumping device  10  has failed. In this case, similarly to the variants shown in  FIGS. 2 and 4 , the coolant is branched off from the second cooling circuit  4  downstream of the second heat source  6  to the first cooling circuit  3 , the coolant is pumped through the first pumping device  8  and the coolant is returned to the second cooling circuit  4  upstream of the second heat source  6 . The coolant is branched off via the branch line  14  whilst the coolant is returned via the first return line  20 . For the sake of better clarity, the throttle devices  29  are not shown in  FIG. 6  although these can be present instead of the valves  17  show or alternatively to these. Since the first return line  20  opens at the second return point  22  into the second cooling circuit  4 , which is located upstream of the cooling means  11 , after return to the second cooling circuit  4  the coolant is guided through the cooling means  11  before it is supplied to the second heat source  6 . In the emergency mode  24  shown in  FIG. 6 , the second return line  26  is blocked in such a manner that coolant cannot flow between the first cooling circuit  3  and the second cooling circuit  4 . 
         [0053]    By means of the second return line  26  however, in a further emergency mode  31  which is hereinafter designated as second emergency mode  31 , whilst the previously explained emergency modes  24  are designated as first emergency mode  24 , it is possible to use the second pumping device  10  for pumping the coolant in the first cooling circuit  3  when the first pumping device  8  delivers a reduced pumping capacity or fails. 
         [0054]    Such a second emergency mode  31  is shown in  FIG. 7 , wherein  FIG. 7  shows a state in which the first pumping device  8  has failed. In the second emergency mode  31  coolant is branched off from the first cooling circuit  3  downstream of the first heat source  5 , supplied to the second cooling circuit  4  upstream of the second pumping device  10  and returned to the first cooling circuit  3  upstream of the first heat source  5 . In the example shown, the coolant is branched off via the branch line  14  whilst the coolant is returned via the second return line  26 . In this case, the coolant flows in the second cooling circuit  3  as a result of the arrangement of the first return point  27  of the second return line  26  in the first cooling circuit  3  upstream of the cooling means  11  through the cooling means  11  before it is supplied to the first heat source  5 . 
         [0055]    In the cooling system shown in  FIGS. 5 to 7 , there is therefore no prioritization of one of the cooling circuits  3 ,  4  or the appurtenant heat source  5 ,  6 . Naturally however it is possible to make such a prioritization by means of corresponding control of the valves  17  and/or the throttle devices  29 . 
         [0056]    In all the examples shown it is further possible in a support mode to use the pumping device  8 ,  10  of the other cooling circuit  3 ,  4  for pumping the coolant in one cooling circuit  3 ,  4  when a temperature which lies above a predefined value is determined in this cooling circuit upstream of the appurtenant heat source  5 ,  7 . It is for example possible to use the first pumping device  8  in addition to the second pumping device  10  for pumping the coolant in the second cooling circuit  4  when the coolant upstream of the second heat source  6  has a temperature which lies above the predefined value. The temperature is determined in this case by means of the temperature sensor  30  arranged upstream or downstream of the second heat source  6 . 
         [0057]    Similarly to this, in a second support mode the second support mode the second pumping device  10  can be used in addition to the first pumping device  8  for pumping the coolant in the first cooling circuit  3  when a temperature is determined upstream of the first heat source  5 , in particular by means of the corresponding temperature sensor  30 , which lies above a value which can differ from the value in the first support mode. In the support mode therefore, compared to the emergency mode there is no reduction in the capacity of the appurtenant pumping device  8 ,  10  or no failure of the appurtenant pumping device  8 ,  10 . 
         [0058]    In all the exemplary embodiments, the corresponding valves  17  or throttle devices  29  allow a corresponding regulation of the volume flow or the amount of branched-off and returned coolant.