Cooling system using a two-phase refrigerant for cooling a plurality of components, comprising a vapor-phase refrigerant recirculation flow for stabilizing a centrifugal compressor

Abstract

A cooling system, using a two-phase refrigerant, for cooling a plurality of components, said system including at least one cooling circuit comprising: - a compressor (3), - a condenser (6) for the refrigerant coming from the compressor, - an electronically controlled forced ventilation device (7) configured to provide a determined air flow rate capable of impinging on said condenser, - an expansion valve (9), for expanding the refrigerant coming from the condenser (6), - a plurality of heat exchangers (2, 2A, 2B, 2C) coupled to different components to be cooled, and - at least one separator tank (10), for separating the liquid phase from the vapor phase of the refrigerant contained therein, said at least one separator tank having: - a calm tube (T), - a first inlet (11), for receiving expanded refrigerant from the expansion valve, - a first outlet (12), via which the gaseous phase refrigerant is supplied to said compressor (3), - a second outlet (13), for supplying the liquid phase refrigerant from said separator tank to at least one of said plurality of heat exchangers, and - a second inlet (20), for returning to the separator tank the refrigerant that has passed through said at least one of said plurality of heat exchangers, wherein said system further includes an electronic control unit (E), configured to control the rotational speed of said forced ventilation device in order to maintain the total mass of refrigerant in the separator tank between a predetermined minimum threshold and a predetermined maximum threshold.

Description

[0001] Cooling system using a two-phase refrigerant for cooling a plurality of components, comprising a vapor-phase refrigerant recirculation flow for stabilizing a centrifugal compressor

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the invention

[0004] The present invention relates to cooling systems for cooling a plurality of components, in particular for cooling a plurality of on-board systems of a vehicle, such as for example the electric battery, the traction electric motor and the passenger compartment of an electric vehicle.

[0005] Background of the invention

[0006] The Applicant has already proposed solutions in the field of integrated cooling systems for various on-board components of a vehicle. See for example the Italian patent application 102024000019057.

[0007] In recent times, there is a need to integrate the cooling systems of the various un-buciiu components of a vehicle with each other. Studies and experiences conducted by the Applicant have, however, led to the identification of a series of problems that can compromise the efficiency and reliability of a cooling system, used to perform a temperature regulation function for multiple vehicle components simultaneously. The main problem is related to the fact that each cooling circuit associated with a given component requires a different cooling power and consequently a different refrigerant flow rate. This imposes the need to control the flow rate of the refrigerant in the different circuits of the system, always guaranteeing efficient and reliable operation.

[0008] A further problem in integrated cooling systems of the different components of a vehicle lies in the fact that, should the maximum required powers be very high, a mechanical compressor would not be able to handle the required refrigerant flow rates and a turbomachine would be necessary to supply the refrigeration circuit of the system, such as for example a centrifugal compressor. In particular, a centrifugal compressor is characterized by the ability to handle high fluid flow rates but unstable operating conditions, commonly known as surging, could occur when theflow rates involved are low.

[0009] Indeed, cooling systems designed to operate on a multiplicity of different components may find themselves operating under very variable operating conditions, requiring equally diversified powers and refrigerant flow rates. In particular, during conditions of low energy demand, such as driving at reduced and constant speeds, the powers that need to be managed and the related required flow rates are relatively low. Conversely, in high-intensity scenarios, such as fast charging or operation at high speeds, the energy to be dissipated increases significantly and with it the refrigerant flow rates. However, turbomachines, and in particular centrifugal compressors, have a limited capacity to handle extreme flow rate variations, thus risking falling into operating conditions having very low efficiencies or, in extreme cases, conditions of operational instability, as already highlighted previously.

[0010] A cooling system of the type identified in the field of the invention is known from document US 2022 / 169903 A1.

[0011] Object of the invention

[0012] It is therefore an object of the present invention to provide a cooling system capable of cooling a plurality of different components simultaneously, in particular a plurality of on-board systems of a vehicle, which guarantees efficient and reliable operation of the system, despite the different cooling powers required by the different components.

[0013] A further object of the invention is to achieve the aforementioned objective with a constructively simple and low-cost system.

[0014] Summary of the invention

[0015] In view of achieving the aforementioned objects, the invention has for its object a cooling system using a two-phase refrigerant, for cooling a plurality of components, in particular a plurality of on-board systems of a vehicle, such as for example the electric battery, the traction electric motor and the passenger compartment of an electric vehicle,

[0016] wherein said system includes at least one cooling circuit comprising: - a compressor, in particular a centrifugal compressor,

[0017] - a condenser for the refrigerant coming from the compressor,- an electronically controlled forced ventilation device configured to provide a determined air flow rate capable of impinging on said condenser, - an expansion valve, for expanding the refrigerant coming from the condenser,

[0018] - a plurality of heat exchangers coupled to different components to be cooled, and

[0019] - at least one separator tank, for separating the liquid phase from the vapor phase of the refrigerant contained therein, said at least one separator tank having:

[0020] - a calm tube,

[0021] - a first inlet, for receiving expanded refrigerant from the expansion valve,

[0022] - a first outlet, via which the gaseous phase refrigerant is supplied to said compressor,

[0023] - a second outlet, for supplying, by means of at least one pump (15, 15A, 15B, 15C), the liquid phase refrigerant from said separator tank to at least one of said plurality of heat exchangers, and,

[0024] - a second inlet, for returning to the separator tank the refrigerant that has passed through said at least one of said plurality of heat exchanger, wherein said system further includes an electronic control unit, configured for controlling the rotational speed of said forced ventilation device in order to maintain the total mass of refrigerant in the separator tank between a predetermined minimum threshold and a predetermined maximum threshold,

[0025] wherein the separator tank has a main chamber communicating with said calm tube that is arranged and configured such that the level of the refrigerant in the calm tube is substantially a direct function of the total mass of refrigerant in the separator tank, and

[0026] wherein the electronic control unit is configured to control the rotational speed of said forced ventilation device as a function of the output signal from a level measuring device associated with said calm tube, in such a way as to maintain the liquid level within the calm tube, and consequently the total mass of refrigerant in the separator tank, between said predetermined minimum threshold and said predetermined maximum threshold.The electronic control unit can be configured to detect the liquid level in the calm tube with a determined periodicity and to consequently control the forced ventilation device with said periodicity.

[0027] The electronic control unit can also be configured to control the forced ventilation device with reference to multiple threshold values of the liquid level in the calm tube, both upwards and downwards. For example, the forced ventilation device can be controlled to generate different discrete variations in the fluid flow rate, as different threshold values are exceeded, upwards or downwards. Or the forced ventilation device can be adjusted continuously.

[0028] Thanks to the aforementioned characteristics, the electronic control unit of the system according to the invention is capable of monitoring the total mass of fluid present in the separator tank and of regulating the condensation process of the refrigerant vapor. This occurs by modulating the amount of heat extracted from the condenser via the regulation of the forced ventilation device. This control allows condensing only the amount of refrigerant useful for maintaining the total mass of refrigerant in the separator tank within the predetermined maximum and minimum limits, even as the flow rates of two-phase fluid entering from the multiple heat exchangers vary.

[0029] It should be considered that the thermal power absorbed by each heat exchanger associated with the cooling system described above is variable over time. The refrigerant that exits a heat exchanger and returns to the separator tank via said second inlet is partly vapor and partly liquid. The percentage of vapor depends on the thermal power absorbed in the heat exchanger and on further control choices and is therefore variable. Consequently, the vapor flow rate that from the separator tank goes to the compressor is also variable instant by instant. If the balance of masses entering and exiting the separator tank is not controlled, there is a risk that the separator tank will empty or fill completely. If the separator tank empties completely, the liquid pump draws vapor and cannot supply the heat exchanger which no longer receives refrigerant and can therefore no longer perform its function of cooling the component associated with it. Conversely, if the separator tank fills totally with liquid, there is a risk that the compressor receives liquid fluid and becomes damaged.Inside the tank the two-phase fluid can be in continuous boiling and in a turbulent state due to the system hydraulics and therefore it is not possible to establish a stationary and quiescent liquid level. Consequently, it is necessary to recreate in the calm tube an environment equivalent to that of the tank under its average conditions, in order to be able to measure the liquid level precisely. This allows effectively addressing the problem of controlling the total mass of two-phase fluid contained in the separator tank.

[0030] In other words, the aforementioned problems have been solved in the system described above thanks to the provision of a level measuring device, associated with the mentioned calm tube, designed and configured such that the level of the refrigerant in the calm tube is substantially a direct function of the total mass of refrigerant present in the separator tank, without being influenced by the disturbing phenomena described above.

[0031] In a preferred embodiment, the level measuring device comprises a float disposed within the calm tube and configured to occupy substantially the entire cross-section of the calm tube, and a sensor of any type, suitable for detecting the position of the float within the calm tube.

[0032] In a different embodiment, the sensor can be of the type including a guide and measurement rod, on which the float is guided and which allows detecting the position of the float relative to said rod.

[0033] In a further embodiment, the separator tank can be equipped with any type of level measuring sensor known in the state of the art, capable of guaranteeing the same purpose

[0034] In a preferred embodiment, the separator tank has a housing defining said main chamber and the calm tube is disposed outside or inside the housing and has a lower end, communicating with the main chamber adjacent to a lower end of the main chamber, and an upper end, communicating with the main chamber adjacent to the upper end of the main chamber. In particular, the upper end of the calm tube communicates with the main chamber of the separator tank via a restricted passage of determined width. This restricted passage allows equalizing the vapor phase pressure between the calm tube and the main chamber of the separator tank when pressure variations are slow and / or moderate, while allowing maintaining a minimal overpressure in the calm tube when fast pressure drops occur in the main chamber of the separator tank. This servesto prevent the refrigerant in the calm tube from evaporating quickly, causing the float to bounce and thus giving rise to inaccurate level measurements.

[0035] In place of said restricted passage it is also possible to provide an automatic valve (check valve) that enables bidirectional flow when the pressure delta between the tank and the calm tube is below a predetermined value and that does not allow flow from the calm tube towards the main chamber of the separator tank when the pressure delta exceeds the predetermined value. In this second case the pressure between the tank and the calm tube is equalized via the opening from the liquid side but rapid boiling under the float is avoided.

[0036] The cooling system according to the invention can be implemented according to different configurations. In a first example, said second inlet and said second outlet of the separator tank are configured for the circulation of refrigerant through a plurality of heat exchangers associated with different components to be cooled.

[0037] In a further embodiment, multiple separator tanks can be provided, each having its second outlet and its second inlet configured for the circulation of the refrigerant through a respective heat exchanger of a plurality of heat exchangers associated with different components to be cooled.

[0038] Thanks to the aforementioned characteristics, it is possible to obtain an efficient and reliable cooling system, capable of cooling a plurality of components even in the presence of different cooling power demands. In particular, the system management logic provides that the electronic control unit, based on the signal detected by the level sensor associated with the calm tube, actuates and regulates the forced ventilation device. This allows supplying the condenser with a precise quantity of air, necessary to condense a fraction of refrigerant vapor equal to that generated in the heat exchangers. This configuration ensures the stability and efficiency of the system as it maintains the level of the refrigerant liquid in the separator tank within the predefined operating range.

[0039] Brief description of the figures

[0040] Further characteristics and advantages of the invention will become apparent from the following description with reference to the attacheddrawings, provided by way of non-limiting example only, in which:

[0041] - figure 1 is a schematic of a cooling system according to the invention, according to a first simplified configuration,

[0042] - figure 2 is a schematic of a cooling system according to the invention in a second configuration.

[0043] Detailed description of the invention

[0044] In figure 1, reference numeral 1 indicates as a whole a cooling system using a two-phase refrigerant. Figure 1 refers to a simplified example, in which the refrigerant of the system 1 is circulated through a single heat exchanger 2, associated with a specific component to be cooled, for example the electric battery of an electric vehicle. The coolant circulating in system 1 is used to cool in the heat exchanger 2 a further coolant (for example air or a dielectric oil, or water, or a lubricating oil, or other temperature regulation fluid) which is used to cool the electric battery of the electric vehicle. Naturally, the case described above is given here solely as an example, it being evident that the system according to the invention is of general application.

[0045] Still with reference to figure 1, number 3 indicates a compressor, particularly of the centrifugal type, which receives refrigerant from a line 4 and supplies compressed refrigerant at its outlet, via a line 5, to a condenser 6.

[0046] The structure and operation of the condenser 6 is not described or illustrated here, as such construction details can be implemented in any known manner. In the example, associated with the condenser 6 is a forced ventilation device 7, electronically controlled, which supplies a flow of air through the condenser 6 in order to cause condensation of the refrigerant. However, this is not a limitation as it is possible to use any other known system capable of guaranteeing condensation of the refrigerant inside the condenser 6. The refrigerant exiting the condenser 6 reaches via a line 8 an expansion valve 9 of any known type.

[0047] Reference numeral 10 indicates a separator tank, for separating the liquid phase from the vapor phase of the refrigerant contained therein. The construction structure of the separator tank 10 can be implemented in any known manner.The separator tank 10 has a first inlet 11, for receiving expanded refrigerant from the expansion valve 9, a first outlet 12 (with which a pressure regulator 18 of any known type is associated), via which the refrigerant is supplied to said compressor 3, a second outlet 13, for supplying the liquid phase refrigerant from the separator tank 10 to the heat exchanger 2, via a line 14 in which a pump 15 is interposed, for example electrically driven. The refrigerant exiting the heat exchanger 2 returns to the separator tank 10, via a line 16 and a second inlet 20.

[0048] In the heat exchanger 2, the refrigerant coming from the separator tank 10 absorbs a variable thermal power Q, depending on the needs of the component to whose cooling the heat exchanger 2 is dedicated.

[0049] The separator tank 10 comprises a housing H of any known type, defining internally a main chamber 17 for the refrigerant. The refrigerant contained in the main chamber 17 is in a two-phase state, i.e., partly in the liquid state and partly in the vapor state. As has already been previously illustrated, for the correct operation of the system, it is necessary to constantly and continuously monitor the flows entering and exiting the main chamber 17 of the separator tank 10, in order to prevent the tank 10 from emptying completely or filling completely.

[0050] For this purpose, in the system according to the invention, the electrically driven forced ventilation device 7 is controlled, with a determined periodicity, by at least one electronic control unit E, based on a signal S indicative of the total mass of refrigerant contained in the separator tank 10.

[0051] The signal S is sent by a level sensor device associated with a calm tube T, having a lower end communicating with the main chamber 17 of the separator tank 10, adjacent to the lower end of the main chamber 17, and an upper end communicating with the main chamber 17 of the separator tank 10, adjacent to the upper end of the main chamber 17.

[0052] Thanks to said arrangement, the liquid level in the calm tube T is not affected by the turbulence to which the refrigerant is subjected inside the main chamber 17 of the separator tank 10. This turbulence derives both from the fluid flows entering the main chamber 17, from the boiling vapor state of part of the fluid in the chamber 17, and from any vibrations and movements to which the separator tank 10 is subjected in case it is installed on board a vehicle.The cooling system management logic provides that, based on the signal S detected by the level sensor device associated with the calm tube T, the electronic control unit E actuates and regulates the forced ventilation device 7. This allows sending to the condenser 6 a precise quantity of air, necessary to condense a fraction of refrigerant vapor equal to the amount of vapor developed in the heat exchanger 2. This configuration guarantees stability and efficiency to the system, since the separator tank 10 maintains the liquid level within the predefined operating range.

[0053] Specifically, thanks to the sensor S present in the calm tube T, the electronic control unit E regulates the rotational speed of the forced ventilation device 7, determining the amount of fluid that needs to be condensed to maintain the correct level of refrigerant liquid inside the separator tank 10.

[0054] Furthermore, it is possible to identify a fraction of non-condensed refrigerant vapor that, under conditions of low energy demand, i.e. , in the case where, for example, the battery packs and electric motors are under low stress, remains within the cycle and ensures the correct operation of the centrifugal compressor 3 without compromising its performance. This fraction, in addition to the one coming from the heat exchanger 2, allows the centrifugal compressor 3 to operate with a refrigerant flow rate adequate to fall within the optimal operating range, thus guaranteeing high efficiency and stability, even under conditions where the heat exchanger 2 generates a small amount of vapor. Moreover, with the present system for controlling the amount of fluid to be condensed, the refrigerant exiting the condenser has low enthalpy. Furthermore, the excess vapor flowing back to the centrifugal compressor is colder compared to other types of control, known as “hot gas cycle”, which take the hot vapor from the compressor outlet, at high enthalpy, and send it back to its inlet, increasing the flow rate in the compressor but raising the suction temperature and worsening its efficiency. Specifically, the present invention exploits a low-enthalpy vapor phase cycle to avoid reducing compression efficiency and to avoid increasing the end-of-com pression temperatures to the detriment of the amount of heat required for the desired condensation. The use of a low-enthalpy cycle according to the invention therefore reduces the required compression work.Figure 2 illustrates a solution almost identical to the solution illustrated in figure 1 but more complete. Indeed, a plurality of heat exchangers 2A, 2B and 2C are illustrated which interface with different onboard components of a vehicle, such as for example the electric battery, the traction electric motor and the passenger compartment of an electric vehicle.

[0055] Naturally, while the principle of the invention remains, the construction details and embodiments may vary widely from what has been described and illustrated by way of example only, without thereby departing from the scope of the present invention, as defined in the attached claims.

Claims

CLAIMS1. A cooling system, using a two-phase refrigerant, for cooling a plurality of components, in particular on-board systems of a vehicle, such as for example the electric battery, the traction electric motor and the passenger compartment of an electric vehicle,said system including at least one cooling circuit comprising:- a compressor (3),- a condenser (6) for the refrigerant coming from the compressor (3), - an electronically controlled forced ventilation device (7) configured to provide a determined airflow rate capable of impinging on said condenser (6),- an expansion valve (9), for expanding the refrigerant coming from the condenser (6),- a plurality of heat exchangers (2, 2A, 2B, 2C) coupled to different components to be cooled, and- at least one separator tank (10), for separating the liquid phase from the vapor phase of the refrigerant contained therein, said at least one separator tank having:- a calm tube (T),- a first inlet (11), for receiving expanded refrigerant from the expansion valve (9),- a first outlet (12), via which the gaseous phase refrigerant is supplied to said compressor (3),- a second outlet (13), for supplying, by means of at least one pump (15, 15A, 15B, 15C), the liquid phase refrigerant from said separator tank (10) to at least one of said plurality of heat exchangers (2; 2A, 2B, 2C), and - a second inlet (20), for returning to the separator tank (10) the refrigerant that has passed through said at least one of said plurality of heat exchangers (2; 2A, 2B, 2C),wherein said system further includes an electronic control unit (E), configured for controlling the rotational speed of said forced ventilation device (7) in order to maintain the total mass of refrigerant in the separator tank between a predetermined minimum threshold and a predetermined maximum threshold,wherein the separator tank (10) has a main chamber (17) communicating with said calm tube (T) that is arranged and configured such that the level of the refrigerant in the calm tube (T) is substantially a direct function of the total mass of refrigerant of the separator tank (10), and wherein the electronic control unit (E) is configured to control the rotational speed of said forced ventilation device (7) as a function of the output signal from a level measuring device (F, L) associated with said calm tube (T), in such a way as to maintain the liquid level within the calm tube, and consequently the total mass of refrigerant in the separator tank, between said predetermined minimum threshold and said predetermined maximum threshold.

2. The system according to claim 1 , characterized in that said level measuring device (L, F) comprises a float (F), disposed within the calm tube (T) and configured to occupy substantially the entire cross-section of the calm tube, and a sensor (L) for detecting the position of the float.

3. The system according to claim 1, characterized in that the separator tank (10) has a housing (H) defining said main chamber (17) and that the calm tube (T) is disposed outside or inside the housing (H) and has:a lower end (22), communicating with the main chamber (17) adjacent to a lower end of the main chamber (17), andan upper end (23), communicating with the main chamber (17) adjacent to the upper end of the main chamber (17).

4. The system according to claim 1 , characterized in that the second inlet (20) and the second outlet (13) of the separator tank (10) are configured for the circulation of the refrigerant through a plurality of heat exchangers (2A, 2B, 10A) associated with different components to be cooled.

5. The system according to claim 1, characterized in that said compressor (3) is a centrifugal compressor.

6. An electric or hybrid vehicle, comprising:- a passenger compartment,- at least one electric battery pack,- at least one traction electric motor, and- at least one cooling system (1) according to any one of the preceding claims.

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