The invention relates to a method for operating a battery cooler system, and to a battery cooler system.

In electrically operated vehicles or in hybrid vehicles, the battery modules generate heat during operation, which heat is often dissipated by way of a cooling circuit. Here, for the cooling of the battery modules, it is expedient to use a sub-circuit of a vehicle air-conditioning system that is already provided in the vehicle. Since most battery cells are combined to form separate battery modules which are thermally decoupled from one another, such that no heat is exchanged between the individual battery modules, the battery cooling circuit is often split into multiple cooling branches which are assigned to in each case one or more of the battery modules. In this case, it is the intention for the cooling branches to be flowed through in parallel by the refrigerant. It is known for the battery cooling circuit to be assigned a dedicated expansion device which is provided between an outlet of the gas cooler and an inlet into a branching means which splits the refrigerant into the individual cooling branches. Here, as an expansion device, use is made of a known thermostatic expansion valve (TXV) which controls the refrigerant throughflow in accordance with the conditions in the battery cooling circuit, or use is made of a fixed throttle in the case of a refrigerant circuit operated with R744. In this case, the pressure drop in the thermostatic expansion valve accounts for approximately 60 to 95% of the total pressure difference, whereas the pressure drop in the branching means amounts to merely 3 to 10%. A reason for this is that the pressure difference between the high-pressure branch and the low-pressure branch of the vehicle air conditioning system is considerably greater in the presence of high ambient temperatures than in the presence of low temperatures. The thermostatic expansion valve or the fixed throttle must however supply an adequate amount of refrigerant, that is to say an adequate refrigerant flow, to the evaporator even in the presence of the minimum operating temperature and thus a minimal pressure difference; this is possible only if the pressure drop in the branching means is small. Therefore, known branching means are configured for a small pressure drop . To ensure the longest possible service life of the individual battery cells, it must be ensured that only a very small temperature difference of no more than 5 K prevails between the individual battery cells. The small pressure drop across the branching means however makes it difficult to realize a homogeneous distribution of the refrigerant, which in the presence of relatively high temperatures is always present in a liquid-gaseous mixture upstream of the branching point, to the various cooling branches.

Owing to the phase mixture in the branching means, it is also necessary for the known branching means to be installed in an exactly vertical orientation in order, even in the presence of a small throughflow, to realize as homogeneous as possible a distribution of the two- phase mixture to the various outlet lines.

Furthermore, in the case of the cooling of battery modules, a cooling arrangement must function even in the presence of low ambient temperatures of, for example, down to -10°C or below, by contrast to a passenger compartment cooling arrangement, which is normally deactivated in the presence of such temperatures .

In the presence of such low temperatures, however, the fraction of liquid refrigerant upstream of the branching means is substantially 100%, for which the known branching means are not configured.

It is an object of the invention to ensure homogeneous cooling performance in a battery cooler circuit over the entire range of ambient temperatures of both summer and winter.

Said object is achieved by means of a method for operating a battery cooler system, wherein the battery cooler system has a refrigerant circuit with a compressor, with a gas cooler, with a pressure reducer and with a battery cooling circuit with at least one cooling branch. The pressure reducer has a shut-off valve, which is connected to a controller, and has at least one throttle stage with a throttle point with a fixedly predefined flow cross section. The pressure drop across the pressure reducer is configured for a minimum operating temperature, and the shut-off valve is operated in pulsed fashion in a manner dependent on the ambient temperature.

In the presence of low ambient temperatures, for example under winter weather conditions, the pressure difference between the high-pressure side and the low- pressure side of the refrigerant circuit is considerably lower than that in the presence of high ambient temperatures, for example on a hot summer day. According to the invention, the pressure reducer is configured such that the battery cooling circuit is operated optimally in the presence of low ambient temperatures. Higher ambient temperatures would, in the case of this operating mode, lead to an excessively large flow of refrigerant through the pressure reducer, such that the refrigerant would no longer be able to be fully evaporated in the battery cooler, and said refrigerant would for the most part exit the battery cooler again still in the liquid state, which could have an adverse effect on the cooling function.

To prevent this, in the presence of relatively high ambient temperatures, the shut-off valve is intermittently switched into its closed state, with a throughflow through the battery cooler circuit, in particular through a battery evaporator, being stopped, in pulsed fashion. By means of pulse-width-modulated operation of the shut-off valve, it is thus possible with simple means, and over the entire temperature range in which the vehicle or the battery system is intended to operate, to achieve an optimum supply of liquid refrigerant, which firstly ensures adequately homogeneous impingement of liquid refrigerant on, for example, the internal evaporator surface of the battery evaporator, and secondly prevents overdosing of liquid refrigerant. Since the flow cross section of the throttle point is configured for low operating temperatures, it is the case even in the presence of low ambient temperatures that there is always a refrigerant flow through the pressure reducer large enough to realize adequate cooling performance for the battery, and the battery cells of all of the battery modules can be kept very homogeneously at the same operating temperature. The pulsed operation serves to prevent an excessive amount of liquid refrigerant passing into the one or more cooling branches, which would not be fully evaporated and would thus reduce the cooling performance.

The minimum operating temperature corresponds, for example, to an ambient temperature of approximately -10-0°C. In the presence of the minimum operating temperature, the shut-off valve may be operated so as to be continuously open, in order to realize the maximum throughflow of refrigerant.

The geometry of the cooling branch which serves as an evaporator in the region of a battery module may be configured as a standard U-shape rather than an expensive meandering shape, such as is otherwise used.

By contrast, in the presence of relatively high ambient temperatures, for example of approximately 30-40°C, the shut-off valve is preferably operated so as to be closed for approximately 40-90% of the time. Comparisons of the operating parameters of the battery cooler system and of the refrigerant cooling circuit in the presence of low operating temperatures of approximately -10 °C and high operating temperatures of approximately +40°C show that the cooling performance is reduced by approximately 40% in the presence of low ambient temperatures. The higher performance in the presence of high ambient temperatures is compensated by way of the closing times of the shut-off valve. The shut-off valve is preferably operated such that the shut-off valve is opened or closed for approximately 10-60 seconds, in particular approximately 25-40 seconds, at a time, in order to prevent overly frequent switching of the valve. It has been found that, owing to the high thermally active mass of the battery modules, uniform and adequate cooling performance is attained even with such long switching times.

The throttle point may be configured, and the shut-off valve operated, such that, downstream of the throttle point, the refrigerant is present substantially in the liquid state. In the presence of high ambient temperatures, it is also possible for the refrigerant to be present entirely in the supercritical state downstream of the throttle stage. In both cases, the refrigerant is preferably only in a single phase, such that it can be easily split to different cooling branches.

The flow diameter of the throttle point is, for optimization for winter conditions in the presence of low ambient temperatures, configured for example for a pressure difference of 10 bar (1 MPa) and an enthalpy difference in the cooling branches of 240 kJoule/kg.

The object of the invention is also achieved by way of a battery cooling system by means of which, in particular, a method as described above can be implemented, the battery cooler system having a refrigerant circuit with a compressor, with a gas cooler, with a pressure reducer and with a battery cooling circuit with at least one cooling branch. The pressure reducer has a shut-off valve, which is connected to a controller, and has at least one throttle stage with a throttle point with a fixedly predefined flow cross section, which throttle point is configured for a minimum operating temperature. The controller and the shut-off valve are configured for pulse-width-modulated operation. As described above, such a battery cooling system provides optimum cooling performance of the entire range of ambient temperatures from winter conditions to high ambient temperatures in summer, of approximately -10 to +40°C.

The shut-off valve is preferably switched by way of an electromagnet which is controlled and activated by the controller .

The pressure reducer preferably has a branching means for splitting the coolant flow to at least two cooling branches, such that multiple battery modules, which may be arranged spatially and thermally separately from one another, can be cooled uniformly under the same conditions at the same time. The throttle point is preferably integrated into the shut-off valves in order to reduce the number of separate components.

Rather than being arranged in the shut-off valve, it would also be possible for the throttle point to be arranged in the branching means, for example in the region of an inlet or of a main line of the branching means upstream of the branching point to the individual cooling branches.

In the pressure reducer there is preferably provided a second throttle stage, which may be arranged in particular in the branching means, for example downstream of a branching point in the outlet lines which lead to the two cooling branches.

It is also possible for the throttle stage to be arranged directly upstream of the branching point. In that case, too, homogeneous distribution to the individual cooling branches is realized even if the refrigerant is in the form of a gas-liquid mixture downstream of the throttle point, because, owing to the short distance, the gas phase and the liquid phase remain well enough mixed that a homogeneous distribution in particular of the liquid fractions of the refrigerant to the individual cooling branches is realized.

The mixing of gas phase and liquid phase can be assisted by way of a filter directly downstream of the throttle point. Each of the throttle points may for example be realized by way of a calibrated bore in the body of the shut-off valve, or else by way of a prefabricated pipe which has a calibrated internal diameter and which is inserted into the flow path of the refrigerant in the shut-off valve .

In the refrigerant circuit there is preferably provided an evaporator of a vehicle air-conditioning system, upstream of which there is connected a shut-off valve which is bridged by way of a bypass with a safety valve. The safety valve ensures that, in the presence of a positive pressure in the high-pressure branch of the refrigerant circuit (approximately 12 to 15 MPa) , pressure equalization with respect to the low-pressure side can take place. In this case, there is no need for a dedicated safety valve in the battery cooling circuit, such that the shut-off valve can be simplified .

The invention will be described in more detail below on the basis of an exemplary embodiment and with reference to the appended figures. In the drawings: figure 1 is a schematic illustration of a vehicle air-conditioning system having a battery cooler system according to the invention for carrying out a method according to the invention; figure 2 shows a schematic sectional view of a branching means of a battery cooler system according to the invention in a first embodiment; figure 3 shows a schematic sectional view of a branching means of a battery cooler system according to the invention in a second embodiment; figure 4 shows a schematic sectional view of a pressure reducer of a battery cooler system according to the invention in a third embodiment; - figure 5 is a schematic illustration of a switching cycle of a shut-off valve of a battery cooler system according to the invention; figure 6 is a diagrammatic illustration of the maximum pressure difference at the pressure reducer of the battery cooler system according to the invention as a function of the ambient temperature ; - figure 7 is a diagrammatic illustration of the enthalpy difference for the evaporation of R744 as a function of the ambient temperature; and figure 8 shows a Mollier diagram of the refrigerant R744, showing the working range of the battery cooler system in the presence of low and high ambient temperatures.

Figure 1 shows a refrigerant circuit 10 of a vehicle air-conditioning system (not illustrated in any more detail) . A refrigerant, in this case R744, flows through multiple cooling sub-circuits. Said refrigerant is compressed in a compressor 12 before being cooled in a gas cooler 14, for example by cooling by means of ambient air. The gaseous, highly pressurized refrigerant subsequently passes through an inner heat exchanger 16, in which it releases some of its heat energy to expanded refrigerant on a return flow path. In a first cooling sub-circuit 18, the refrigerant flow is through an evaporator 20 of the vehicle air conditioning system, by means of which a vehicle interior compartment is cooled, for example. Upstream of the evaporator 20 there is arranged a shut- off valve 22 by means of which the cooling sub-circuit 18 can be shut off when cooling is not required. In this example, the shut-off valve 22 comprises a pressure reduction stage in the form of an opening of reduced cross section, which acts as a throttle point and which, by way of the pressure reduction, effects a partial expansion of the refrigerant.

The pressure reduction from the high-pressure side to the low-pressure side is realized here by way of a fixedly predefined cross-sectional constriction, such as is known for R744 refrigerant circuits. The diameter of said throttle point is selected inter alia in a manner dependent on the required performance of the evaporator .

The shut-off valve 22 is bridged by way of a bypass line 24 with a safety valve 26. The safety valve 26 is configured so as to permit a refrigerant flow through the cooling sub-circuit 18 when a critical pressure threshold is reached at the safety valve 26, which critical pressure threshold may for example be approximately 120-150 bar (12 - 15 MPa) .

In general, when using R744 as refrigerant, the refrigerant circuit must be protected against overpressure. This is realized in this case by way of the safety valve 26, which in the event of a sudden increase in pressure opens a flow connection from the high-pressure side to the low-pressure side of the refrigerant circuit. Said bypass function is in this case available under all operating conditions. Such a pressure rise may occur for example in the event of intense vehicle acceleration, in the case of which the compressor throughput cannot be regulated downward rapidly enough, such that a large amount of gas is conducted into the gas cooler 14.

The refrigerant flowing back from the evaporator 20 passes through the inner heat exchanger 16 again and through an accumulator 28, in which any liquid refrigerant that is present is separated off, before the refrigerant flows back to the compressor 12. In parallel with respect to the first cooling sub- circuit 18, the refrigerant flows through a battery cooling circuit 30, which is part of a battery cooler system 32. The battery cooler circuit may have a cooling power of approximately 0.5 to 2 kW. Battery cells of a hybrid or electric vehicle (not illustrated in any more detail here) are in this case arranged in multiple modules, which are cooled by two cooling branches 34, 36 connected in parallel. Thus, in this case, the battery cooler circuit 30 is divided into two cooling branches 34, 36 which, after passing through the battery modules, open into a common return suction line 38. The cooling branches 34, 36 serve as evaporators, in which the liquid refrigerant situated therein absorbs the heat from the battery cells and thus changes into the gaseous state.

Downstream of the outlet of the evaporator 20, the first cooling sub-circuit 18 opens into the return suction line 38.

A pressure reducer 40 is arranged upstream of the two cooling branches 34, 36. In the variant illustrated here, the pressure reducer 40 has a shut-off valve 42 which is arranged upstream of a branching means 44.

In a possible embodiment which will be described further below (see figure 4), the shut-off valve 42 and the branching means 44 are combined in a single component. They may however also be formed as separate components. It would also be possible to dispense with the shut-off valve 42 and to realize the pressure reduction entirely by way of the branching means 44.

The shut-off valve 42 is connected to a controller 46 which can define the opening state of the shut-off valve 42. In this example, the shut-off valve 42 can assume only the two control states "open" and "closed".

In this example, directly downstream of the shut-off valve 42, there is arranged a temperature sensor Ti which is likewise connected to the controller 46. Here, a second temperature sensor T ₂ , which is likewise connected to the controller 46, is provided directly at the connecting point 48 of the two cooling branches 34, 36.

Figures 2 to 4 show various embodiments of the branching means 44. For clarity, the reference sign 44 has been used for all three embodiments.

The branching means 44 illustrated in figure 2 has a body 50 into which there is recessed an inlet 52 which transitions into a main line 54. At the end of the main line 54 there is situated a branching point 56, proceeding from which the main line 54 splits into two outlet lines 58, which in these examples are in each case of identical form. Each of the outlet lines 58 transitions into an outlet 60, by means of which the respective outlet line 58 is connected to one of the two cooling branches 34, 36 of the battery cooler circuit 30. A throttle stage is integrated into the branching means 44, which throttle stage has a constriction which acts as a throttle point and which thus effects a pressure reduction downstream of the throttle point. In the example shown in figure 2, the throttle stage is realized, by way of in each case one calibrated bore 62 of fixedly predefined diameter and length, in each of the outlet lines 58. In this case, the calibrated bore 62 directly adjoins the branching point 56, and is thus situated directly downstream of the main line 54 as before . Instead of a branch into two outlet lines 58, it would also be possible to provide a branch into more than two outlet lines 58. Equally, it would be possible for multiple distributors 44 to be provided in further battery cooler circuits (not shown) connected in parallel with respect to the battery cooler circuit 30.

In this example, the throttle stage is provided downstream of the branching point 56. This has the effect that the refrigerant, which in the main line 54 is present entirely or substantially entirely in a single phase (supercritical or liquid depending on the ambient temperature, as will be described in more detail below) , is split uniformly into the two outlet lines 58. Owing to the uniform state of aggregation, a non-vertical installation position of the branching means 44 also does not pose any problems.

Here, there is provided within the inlet 52 a filter 64 which prevents contamination of the branching means 44.

In these examples, the inlet 52 is formed in a connector piece 66 by way of which the branching means 44 can be connected to the pipelines of the battery cooler circuit 30 or to the shut-off valve 42 (see figure 4 ) .

The calibrated bore 62 has for example a diameter of 0.2-1.0 mm and a length of 10-40 mm, wherein, with increasing length of the throttle point, the flow becomes more stable, and the tendency for vibrations to be generated in the flow is also reduced. Figure 3 shows an embodiment of a branching means 44 in which the throttle stage is provided in the region of the main line 54. In this case, the pressure reduction takes place already upstream of the branching point 56. Downstream of the throttle point there is arranged a filter 68 which homogenizes the refrigerant downstream of the throttle point by virtue of the liquid and gaseous fractions being thoroughly mixed, such that a homogeneous distribution to the two outlet lines 58 is realized.

In the example of figure 3, the throttle point is formed by a separate, inserted pipe 70 with a calibrated internal diameter. Internal diameters and lengths may be selected in the same way as in the case of the calibrated bore 62 of the preceding exemplary embodiment .

To fasten the pipe 70 in the body 50 of the branching means 44, there is provided a threaded sleeve 72 which is screwed into the connector piece 66 of the inlet 52. Instead of the threaded sleeve 72, it would also be possible for use to be made of a plug-in sleeve which is plugged into the connector piece 66.

The threaded sleeve 72 has an end stop 74 which serves for precise positioning of the pipe 70 in the main line 54. At the inlet side, the pipe 70 is covered by a filter 64 which prevents contamination of the branching means 44. The calibrated internal diameter of the inserted type 70 can be produced with high precision as a bore.

Instead of the inserted pipe 70, it would also be possible in the main line for a bore to be formed in the body 50, as has been described for example with regard to figure 2 for the outlet lines 58. Analogously, in the embodiment illustrated in figure 2, it would also be possible, instead of the calibrated bores 62, for in each case one pipe 70 with calibrated internal diameter to be inserted into the outlet lines 58.

Furthermore, it is possible to provide in the branching means 44 not only one throttle point but two throttle points which are in series in terms of flow, wherein the first throttle point is arranged in the main line 54 and the second throttle point is formed by in each case one constriction in each of the outlet lines 58.

Figure 4 shows a pressure reducer 40 which has two throttle stages in series in terms of flow.

The pressure reducer 40 is in this case composed of a branching means 44 and of a shut-off valve 42, these being screwed together by way of the connector piece 66 of the branching means 44. In this example, the branching means 44 corresponds to the branching means 44 illustrated in figure 2. It would however also be possible for use to be made of a branching means as per the embodiment illustrated in figure 3, or some other suitable branching means 44.

In this example, the shut-off valve 42 is switched by way of an electromagnet 76 which is connected to the controller 46 of the battery cooler system 32. By means of the electromagnet 76, the shut-off valve 42 is switched between its two switching states "open" and "closed", wherein the refrigerant flow through the inlet 78 of the shut-off valve 42 is either permitted in full or is completely stopped. Directly downstream of a valve seat 80 of the shut-off valve 42, a first throttle stage is realized, in this case by way of a calibrated bore 82, which constitutes a narrowing of the throughflow cross section for the refrigerant. The cross section of the calibrated bore 82 is narrowed in relation to the cross section of the inlet 78 and also in relation to the cross section of the adjoining inlet 52 of the branching means 44. In this way, a first expansion of the refrigerant, and a first pressure reduction, is effected in the calibrated bore 82.

In the branching means 44, a second throttle stage is formed, in this case by way of the narrowings formed by the calibrated bores 62 in the outlet lines 58, which effect a second pressure reduction and a further expansion of the refrigerant.

Instead of the calibrated bore 82 in the body of the shut-off valve 42, it would also be possible for a calibrated bore or a pipe 70 with calibrated internal diameter to be provided in the inlet 52 of the branching means 44. In this way, the construction of the shut-off valve 42 can be further simplified. From the outlet lines 58, the refrigerant flows into the two cooling branches 34, 36 of the battery cooler circuit 30.

In the embodiment illustrated in figure 1, the battery cooler system 32 is configured such that, in the presence of low ambient temperatures under "winter conditions", that is to say in the presence of temperatures between approximately -10 and 0°C, a pressure difference of approximately 10 bar and an enthalpy difference of approximately 240 kJ/kg are attained across the pressure reducer. The pressure difference may also be configured with regard to a pressure difference between the high-pressure side and the low-pressure side of the overall refrigerant circuit 10. These parameters are attained through the specific design of the throttle stages of the pressure reducer 40.

It is important that the refrigerant flow realized through the cross-sectional narrowings in the throttle stages is great enough to provide adequate cooling performance for the battery modules in the battery cooler circuit 30 even in the presence of low ambient temperatures. Under these ambient conditions, the phase boundary to the supercritical state is overshot by only approximately 1 to 5 Kelvin (see also figure 8) . In the presence of the ambient temperatures that prevail in summer, that is to say temperatures up to approximately +40°C, a considerably greater pressure difference prevails between the high-pressure side and the low-pressure side of the refrigerant circuit 10 and of the battery cooler circuit 30. To prevent an excessively large flow rate of liquid coolant through the branching means 44 under such conditions, which would not be able to be fully evaporated in the cooling branches 34, 36 and would thus reduce the cooling performance of the evaporator 20 for the air conditioning of the passenger compartment, the shut-off valve 42 is operated in pulsed fashion.

This is illustrated schematically in figure 5. The solid curve indicates that, in the presence of high ambient temperatures, the shut-off valve 42 is, by way of the controller 46, operated with pulse width modulation in such a way that the cooling performance is optimized. The opening duration of the shut-off valve 42 is calculated by the controller 46 from the values signaled by the temperature sensors ΤΊ and T ₂ , that is to say from the refrigerant temperature at the inlet 52 of the branching means 44 and the refrigerant temperature after said refrigerant has passed through the cooling branches 34, 36 of the battery cooler circuit 30. The time period for which the shut-off valve 42 remains closed between two opening states may amount to 30 seconds or more; this also applies to the time period for which the shut-off valve 42 is open between the closed phases. This is possible because the battery cooler circuit 30 with the battery modules has a higher thermally active mass than, for example, the evaporator 20 of the vehicle air-conditioning system.

In winter, that is to say in the presence of low ambient temperatures and a small pressure difference, it is by contrast the case that the shut-off valve 42 is continuously open (see dashed line in figure 5) .

Figures 6 and 7 show the pressures prevailing on the high-pressure side of the refrigerant circuit 10 and on the low-pressure side thereof as a function of the ambient temperature. The pressure profile of the high- pressure side is denoted by rhombuses, whereas the pressure profile on the low-pressure side is denoted by squares. It can be read from figure 6 that, in the presence of winter conditions between -10 and 0°C, a pressure difference of between 7 and 9 bar (0.7 to 0.9 MPa) is to be expected, whereas, in the presence of summer conditions between 25 and 40 °C ambient temperature, considerably higher pressure differences prevail, for example 35 to 65 bar (3.5 to 6.5 MPa), wherein a pressure difference of even 90 bar may prevail . From such a measurement, it is possible, for an existing battery cooler system 32 in a refrigerant circuit 10, to calculate the optimum configuration of the pressure reducer 40. For this purpose, it is also necessary to take into consideration the enthalpy difference during the evaporation of the refrigerant, in this case R744, which is plotted as a function of the ambient temperature in figure 7.

The pressure difference between the high-pressure side and low-pressure side greatly increases with rising ambient temperature. Since the mass flow that is generated changes approximately with the square root of the pressure difference, it is the case for example that, for an ambient temperature of -10°C, the possible cooling performance of the battery cooler circuit 30 is reduced by approximately 40% in relation to an ambient temperature of +40°C. If the battery cooler system 32 and in particular the pressure reducer 40 are optimized for operation in the presence of low ambient temperatures, this has the effect that, during operation in the presence of high ambient temperatures, the shut-off valve 42 should be closed for approximately 30-90% of the time.

The configuration of the rest of the refrigerant circuit 10, in particular of the cooling sub-circuit 18, which serves for the vehicle air-conditioning system evaporator 20, is not affected by these considerations, as only the pressure reducer 40 in the battery cooler circuit 30 has to be configured correspondingly . Figure 8 shows, on the basis of a Mollier diagram, the cycles that are passed through for operation of the refrigerant circuit 10 under summer conditions (high ambient temperatures) and winter conditions (low ambient temperatures) .

The upper cycle in the graph, with the points A to G, describes the operation in the presence of high ambient temperatures .

The high-pressure side, which in this case is preferably at between 80 and 120 bar, is operated in the supercritical range. From point A to point B, the compression of the refrigerant in the compressor 12 takes place. From point B to point C, the supercritical refrigerant is cooled in the gas cooler 14. From point C to point D, further cooling on the high-pressure side of the refrigerant circuit 10 is realized by way of the inner heat exchanger 16. From point D to point E, a pressure reduction takes place in the first throttle stage of the pressure reducer 40, wherein the pressure reduction takes place at most as far as the liquid boundary, such that the refrigerant remains in only single-phase form, or is in the supercritical state, when it enters the branching means 44. From point E to point F, the further pressure reduction in the second throttle stage of the pressure reducer 40 takes place, in this case in the outlet lines 58 of the branching means 44. From point F to point G, the cooling of the battery modules in the cooling branches 34, 36 of the battery cooler circuit 30 takes place, wherein the refrigerant is evaporated and absorbs the heat from the battery modules. Finally, from point G to point A, the refrigerant flows via the return suction line 38, passing through the inner heat exchanger 16, back to the compressor 12, wherein said refrigerant absorbs heat from the high-pressure branch.

In winter operation (lower cycle in figure 8, with points a-f) , the same cycle is performed below the critical point. From point a to point b, the refrigerant is compressed, and from point b to point d, said refrigerant is cooled. After the expansion of the refrigerant in the first throttle stage of the pressure reducer 40 (point d to point e) , the refrigerant is entirely in the liquid phase. Only when it passes through the second throttle stage (point e to point f) can the refrigerant have gaseous fractions.

In the example described here, the refrigerant is, however, still in only single-phase form when it reaches the branching means 44. In this way, a homogeneous distribution to the two cooling branches 34, 36 is possible more easily than in the presence of a phase mixture.