A method for controlling a compressor of an air-conditioning and / or cooling system of a vehicle with an electric powertrain

Abstract

There is described a method (10) for controlling a compressor of an air-conditioning and cooling system comprising an evaporator and a chiller. The method comprises determining (101) a first cooling power requested by the evaporator, and determining (102) a corresponding first target temperature of the refrigerant fluid; determining (102) a minimum temperature of the refrigerant fluid to avoid icing of the evaporator; determining (103) a second cooling power requested by the chiller, and determining (104) a third actual cooling power of the chiller, which is equal to zero if the chiller is not active, is equal to the second cooling power if the chiller is active and the evaporator is inactive, and taking into account the need of avoiding icing on the evaporator if the chiller and the evaporator are both active; determining (105) a second target temperature of the refrigerant fluid at which the chiller provides the third cooling power; determining (106) a third target temperature of the refrigerant fluid, which is equal to the minimum amongst the first and the second target temperatures, if a overheating condition is detected of at least one vehicle component which is cooled by the chiller, otherwise also taking into account a minimum temperature of the refrigerant fluid; estimating (107) the enthalpy values upstream and downstream of the evaporator and the chiller as a function of the measured temperature and pressure, and as a function of the third target temperature of the refrigerant fluid; determining (108) a target flow value of the refrigerant fluid as a function of the sum of the first and of the third cooling power and as a function of the difference between the second and the first enthalpy value; determining (109) a target speed value of the compressor as a function of the target mass flow value of the refrigerant fluid.

Description

[0001] “A method for controlling a compressor of an air-conditioning and / or cooling system of a vehicle with an electric powertrain”

[0002] ****

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention relates to vehicles with an electric powertrain, specifically to BEVs (Battery Electric Vehicles).

[0006] The invention was developed with reference to the management of the compressor of the (cabin) air-conditioning and (battery pack) cooling system of the vehicle. Specifically, the invention concerns a method for determining the speed of the compressor, in order for the latter to meet the cooling power demands of the cabin and of other components of the vehicle, such as the batteries.

[0007] Prior Art

[0008] The vehicles having an electric powertrain generally comprise a pair of radiant elements, arranged in such a position as to intercept a flow of cooling air as the vehicle is travelling. Such radiant elements comprise a condenser and a radiator, the former being arranged in front of the latter in the vehicle travelling direction, so that the air flow intercepted while travelling impinges upon the condenser first, and then on the radiator (after the passage through the condenser). Within the condenser a refrigerant fluid flows, the phase change (gas to liquid) whereof is promoted. The refrigerant fluid circulates in a refrigerant circuit system comprising at least one evaporation element for the fluid, which promotes a phase change reversed with respect to the previous one (liquid to gas). The at least one evaporation element comprises an evaporator of an air-conditioning system for the vehicle cabin, and preferably at least one chiller for cooling a corresponding battery pack of the vehicle. Between the outlet of the condenser and the inlet of each evaporation element (evaporator or chiller) there is interposed a respective thermal expansion lamination valve (TXV). The refrigerant circuit system moreover comprises a compressor, which is interposed between the outlet of the at least one evaporation element and the inlet of the condenser. The compressor increases the pressure of the refrigerant fluid (in the gaseous phase), and it is actuated by a (dedicated) electric motor, which is supplied by the same batteries which provide energy to the vehicle powertrain.

[0009] The documents US 2017 / 0087957 A1 , WO 2022 / 009713 A1 and WO 2021 / 100409 A1 exemplify known solutions in the field of the air- conditioning and / or cooling systems.

[0010] In the known solutions, the target rotational speed of the compressor is determined as a function of the overall cooling demands of the air- conditioning and / or cooling system of the vehicle. Specifically, the control of the compressor is carried out through feedback (in a closed loop) as a function of the difference between the target temperature and the detected temperature, both for the evaporator (which provides for the cabin air- conditioning) and for the chiller (which provides for the battery cooling). Since the compressor is feedback-controlled as a function of a detected temperature, the control is very slow in adapting to a change of the operating conditions. For example, if the system switches from combined operation of both evaporator and chiller to operation of the evaporator only, the speed of the compressor remains higher than necessary for a long time interval, and this may lead to an overcooling problem of the cabin air and, in the worst of cases, to the buildup of ice on the evaporator, with a consequent degradation of the system efficiency (since the presence of ice decreases the ability of the evaporator to exchange heat with the cabin air).

[0011] Object of the Invention

[0012] The invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the invention is (directly) computing a target rotational speed value of the compressor in an open loop, without feedback, in order to meet the overall cooling demands of the air- conditioning and / or cooling system of the vehicle and to rapidly adapt to the variation of the operating conditions, thereby avoiding the problem of overcooling and icing of the evaporator.

[0013] Summary of the Invention

[0014] The object of the invention is achieved by a method having the features set forth in the claims that follow, which are an integral part of the technical teaching provided herein in relation to the invention.

[0015] The method may be implemented by one or more electronic control units of a vehicle.

[0016] Brief description of the Figures

[0017] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only and wherein:

[0018] - Figure 1 shows a diagram of an air-conditioning and cooling system of an electric vehicle;

[0019] - Figure 2 shows various details of an evaporation element of the system of Figure 1 , which provides for cooling one or more components of the electric vehicle (i.e. , a chiller);

[0020] - Figure 3 shows various details of an evaporation element of the system of Figure 1 , which provides for the air conditioning of the cabin of the electric vehicle (i.e., a cabin evaporator);

[0021] - Figure 4 shows a model diagram for determining the mass flow of the cabin air as a function of the speed of the fan which supplies air to the cabin;

[0022] - Figure 5 shows a model diagram for determining the thermal resistance of the cabin evaporator as a function of the mass flow of the cabin air;

[0023] - Figure 6 shows a diagram of the cooling system into which the coolant of the components of the electric vehicle flows;

[0024] - Figure 7 shows operational logics for determining the target cooling power of the chillers of the electric vehicle;

[0025] - Figure 8 shows a model diagram for determining the thermal resistance of the chillers as a function of the mass flow of the coolant;

[0026] - Figure 9 shows operational logics for determining the target evaporation temperature of the refrigerant fluid;

[0027] - Figure 10A is a diagram showing the pressure of the refrigerant fluid as a function of the specific enthalpy thereof;

[0028] - Figure 10B shows a model diagram for determining the pressure of the refrigerant fluid (in the vapour phase) as a function of the temperature thereof; - Figure 11 is a diagram showing the pressure of the refrigerant fluid as a function of the specific enthalpy thereof, in relation to the phase changes taking place in the system of Figure 1 ;

[0029] - Figure 12 shows a model diagram for determining the volumetric efficiency of the compressor of the system of Figure 1 , as a function of the compressor speed and of the compression ratio; and

[0030] - Figure 13 is a block diagram showing the steps of a method for controlling the compressor of the system of Figure 1 , according to one or more embodiments of the invention.

[0031] Detailed description

[0032] As mentioned in the foregoing, the invention is applicable to air- conditioning and / or cooling systems comprising at least one electric compressor actuated by a dedicated electric motor, wherein the actuating electric motor is driven in order to achieve a given target rotational speed of the compressor as a function of the cooling demands.

[0033] In this regard, Figure 1 shows a diagram of an air-conditioning and cooling system 1 of an electric vehicle, through which a refrigerant fluid, e.g. R1234YF, flows. In the diagram of Figure 1 , the dotted lines represent the portions of the system wherein the refrigerant fluid is at high pressure, whereas the thick solid lines represent the low-pressure portions of the system. The system 1 comprises an electric compressor C, which is actuated by a dedicated electric motor, which compresses the refrigerant fluid thus increasing the pressure thereof. The thus compressed refrigerant fluid flows through a condenser CNDS which, as the vehicle travels, is impinged upon by a flow of ambient air with which it exchanges heat, thus promoting a phase change (gas to liquid) of the refrigerant fluid. At the outlet of the condenser CNDS there are arranged a temperature sensor TS1 and a pressure sensor PS1 , which measure the temperature and the pressure of the refrigerant fluid, respectively. The high-pressure refrigerant fluid may be directed through an evaporator EVAP which, when activated, is impinged upon by an air flow from the cabin, with which it exchanges heat, thus promoting a phase change (liquid to gas) of the refrigerant fluid in order to cool the cabin air, and / or through at least one chiller CHL which, when activated, is impinged upon by a flow of coolant with which it exchanges heat, thus promoting a phase change (liquid to gas) of the refrigerant fluid, for cooling a corresponding battery pack of the vehicle (and / or other components of the vehicle). In the presently described example, two chillers CHL1 and CHL2 are arranged in parallel, and they may be activated independently. Generally speaking, the invention is applicable to systems having only one chiller or more than two chillers. At the inlet of each evaporation element (whether it is the cabin evaporator EVAP or any of the chillers CHL1 and CHL2), the refrigerant fluid flows through respective shutoff valves and thermal expansion lamination valves TXV: see the shut-off valve SOV1 and the lamination valve TXV1 at the inlet of the evaporator EVAP, and the valves V1 and V2 at the inlet of the respective chillers CHL1 and CHL2 (such valves acting both as shut-off valves and as lamination valves). The system 1 moreover comprises a temperature sensor TS2 that measures the temperature of the cabin air which impinges on the evaporator EVAP. The refrigerant fluid flowing out of the evaporation elements EVAP, CHL1 and CHL2 flows towards the compressor C, in order to close the circuit of the system 1 .

[0034] Figure 2 shows in detail one of the chillers CHL of the system 1 , and the relating values of interest. The chiller CHL is traversed by the refrigerant fluid which flows in (RFin) and out (RFout), thereby exchanging heat with the coolant, which also flows in (CLin) and out (CLout). The mass flow of the coolant is denoted as mcinchm. Temperature sensors TS_CLjne TS_CLout sense the temperature of the coolant respectively at the inlet and at the outlet.

[0035] Figure 3 shows in detail the evaporator EVAP of the system 1 , and the relating values of interest. The evaporator EVAP is traversed by the refrigerant fluid which flows in (RFin) and out (RFout), thereby exchanging heat with the cabin air, which also flows in (An) and out (Aout). The mass flow of the cabin air is denoted as mAircabEvap. Temperature sensors TS_Anand TS_AOut sense the temperature of the cabin air respectively at the inlet and at the outlet.

[0036] As mentioned in the foregoing, the object of the method according to the invention is to (directly) compute a target rotational speed value of the compressor C in an open loop, without feedback, in order to meet the overall cooling demands of the air-conditioning and / or cooling system 1 of the vehicle and to rapidly adapt to the variations of the operating conditions, thereby avoiding the problems of overcooling and icing on the evaporator.

[0037] In this regard, it should be noted that during operation of the air- conditioning system of the cabin, the control unit of the air-conditioning system sets a target temperature value T AircabEvapoutrgt of the cabin air Aout flowing out of the evaporator EVAP. Such target value represents an input parameter for the method according to the present invention. Moreover, again during operation of the air-conditioning system of the cabin, it is possible to compute the mass flow of the cabin air mAircabEvap as a function of the speed vsiower of the fan that supplies the cabin air An at the inlet of the evaporator EVAP. Specifically, as exemplified in Figure 4, the flow mAircabEvap increases as the speed vsiower increases: for example, the flow mAircabEvap is directly proportional to the speed VBiower. The speed vsiower is therefore a further input parameter of the method according to the invention.

[0038] The cooling power QcabEvap of the evaporator EVAP for the air conditioning of the cabin may be computed via the following equation (1 ), wherein CP_Air is the specific heat of air and TAircabEvapin is the temperature of the cabin air An at the inlet of the evaporator EVAP, as measured by the sensor

[0039] QcabE

[0040] The temperature of the refrigerant fluid remains constant during the evaporation process in the evaporator EVAP. Via the following equation (2), where RrhcabEvap is the thermal resistance of the evaporator EVAP, it is possible to determine a target temperature TRfr@cabEvaPthat the refrigerant fluid shall have in the evaporator EVAP in order to enable developing the demanded cooling power QcabEvap -

[0041] The thermal resistance RrhcabEvap may be determined as a function of the mass flow of the cabin air mAircabEvap. Speciffically, as exemplified in Figure 5, the thermal resistance RrhcabEvap decreases as the flow mAircabEvap increases; for example, the thermal resistance RrhcabEvap is inversely proportional to the flow mAircabEvap.

[0042] Moreover, also during operation of the cabin air-conditioning system, the control unit of the air-conditioning system sets a minimum temperature value TAircabEvapoutMin of the cabin air Aout flowing out of the evaporator EVAP, below which the temperature must not fall in order to avoid icing on the evaporator (due to the low temperature and to the air moisture). Therefore, such a minimum value represents an input parameter for the method according to the present invention. Once the minimum value of the air temperature TAircabEvapOutwn has been defined, it is possible to define a corresponding minimum value TRfr@Min of the temperature of the refrigerant fluid in the evaporator EVAP via the following equation (3):

[0043] It should be noted that the target temperature TAircabEvapOutTgt of the cabin air flowing out of the evaporator EVAP is always set to a value greater than the minimum value TAircabEvapOutwn, and as a consequence also the target temperature TRfr@cabEvaPof the refrigerant fluid in the evaporator EVAP is always higher than the minimum value TRfr@Min.

[0044] If in the system 1 only the cabin air conditioning is in operation (and not, in addition, the cooling of other components), i.e., if only the evaporator EVAP is in operation and the chillers CHL1 and CHL2 are not, then the target temperature TRfr@EvaPof the refrigerant fluid in the evaporation process equals the value TRfr@cabEvaPcomputed via the equation (2) for developing the cooling power requested by the user.

[0045] Turning to the operation of the cooling components of the system 1 , i.e. the chillers CHL1 and CHL2, it is possible to refer to Figure 6, which is a diagram of the cooling system wherein the coolant flows. Specifically, the coolant is pumped by a pump P towards either chiller or both chillers CHL1 and CHL2 arranged in parallel (which may be activated independently). The coolant is cooled by the chillers, and subsequently impinges upon one or more vehicle components in order to cool them. For example, the coolant cools two components COMP1 and COMP2 by flowing through them serially. At the end of the cooling operation, the coolant (which now has a temperature higher than the temperature at the outlet of the chillers) returns to the pump P in order to close the fluidic circuit.

[0046] During the vehicle operation a control unit determines, as a function of the state of the components COMP1 and COMP2, the temperature and the flow of the coolant needed to cool the components COMP1 and COMP2. Such a target temperature is considered as the target temperature Tcinchiioutrgt of the coolant flowing out of the chillers, and the target flow is considered as the target flow rhcinchingt of the coolant at the inlet into the chillers. The values Tcinchiioutrgt and rhcinchingt are therefore further input parameters for the method according to the invention.

[0047] The raw cooling power QchiiRaw of the chillers CHL1 , CHL2 for cooling only the vehicle components may be computed via the following equation (4), where CP_cin is the specific heat of the coolant and Tcinchiiin is the temperature of the coolant CLin at the inlet into the chillers, as measured by the sensor TS_

[0048] QchiiRaw=mc

[0049] On the other hand, in the case of simultaneous operation of the cabin evaporator EVAP and of the chillers CHL1 , CHL2, it is necessary to also take into account the minimum cooling power QcMiMinForcabEvap exchanged between the coolant CLin at the inlet of the chiller at the temperature Tcinchiiin and the refrigerant fluid at the inlet of the chillers at the temperature TRfr@cabEvaP, as well as the limitation of the cooling power QchiiMaxFor Anti-icing 'norder to avoid icing on the evaporator. Such values may be computed via the following equations (5) and (6), where Rrhchii is the thermal resistance of the chiller:

[0050] Therefore, generally, the target cooling power of the chillers Qchiier may be determined according to the method shown in Figure 7, i.e.:

[0051] - in block 71 , if the chillers are not active (condition C1 is false), then Qchiier is settozero, whereas if the chillers are active (condition C1 is true), then Qchiier is set to the value Q72determined in block 72;

[0052] - in block 72, if only the chillers are active (i.e., if the evaporator EVAP is inactive and the condition C2 is true), then Q72is set to the raw value QchiiRaw , whereas if not only the chillers are active (i.e. , if also the evaporator EVAP is active and the condition C2 is false), then Q72is set to the value determined by first selecting the maximum value amongst QchiiRaw and QcMiMinForcabEvap , and then selecting the minimum value amongst the just selected maximum and QchiiMaxForAnti -icing ■ The temperature of the refrigerant fluid remains constant during the evaporation process in the chillers CHL1 , CHL2. Via the following equation (7) it is possible to determine a target temperature TRfr@chii that the refrigerant fluid shall have in the chillers CHL1 , CHL2 for enabling developing the requested cooling power Qcmier-

[0053] TRfr@Chll=T'cinChllln ~ Qchller ’ ^ThChll (7)

[0054] The thermal resistance Rrhchii may be determined as a function of the mass flow of the coolant mcinchii and of the number of active chillers. Specifically, as exemplified in Figure 8, the thermal resistance Rrhchii decreases as the flow mcinchii increases, and as the number of active chillers increases (specifically, the solid line indicates the case of only one active chiller, whereas the dotted line indicates the case of two active chillers); for example, the thermal resistance Rrhchii is inversely proportional to the flow mcinChll.

[0055] If in the system 1 only the cooling of the components COMP1 , COMP2, such as the batteries, is operating (and the cabin air conditioning is not active), i.e. if at least one of the chillers CHL1 , CHL2 is active but the evaporator EVAP is not, then the target temperature TRfr@EvaPof the refrigerant fluid in the evaporation process is equal to the value TRfr@chii computed via the equation (7) for developing the cooling power requested by the cooling of the components only.

[0056] If the cabin evaporator EVAP and the chillers CHL1 , CHL2 are active at the same time, during the evaporation process in the evaporator EVAP and in the chillers CHL1 , CHL2 the pressure of the refrigerant fluid remains constant, and so does the temperature of the refrigerant fluid. The outlet of the evaporator EVAP and of the chillers CHL1 , CHL2 is common (as shown in Figure 1 ), and this implies that the pressure and the temperature of the refrigerant fluid during the evaporation process are the same both for the evaporator EVAP and for the chillers CHL1 and CHL2. Moreover, should critical thermal conditions develop in the components COMP1 , COMP2 (for example a remarkable overheating, which requires a high cooling power), the logic that avoids icing on the evaporator EVAP may be deactivated, in order to take maximum advantage of the cooling power of the system 1 to rapidly cool the components COMP1 , COMP2. Therefore, if both the cabin evaporator EVAP and the chillers CHL1 , CHL2 are active at the same time, the target evaporation temperature TRfr@EvaPof the refrigerant fluid that meets both cooling requirements (i.e., the cabin and the components of the vehicle) and at the same time avoids icing on the evaporator (in a deactivatable way) may be determined according to the method shown in Figure 9, i.e.: in the presence of critical thermal conditions in the components COMP1 , COMP2, and therefore when the anti-icing logic of the evaporator is disabled (condition C3 is true), then the target temperature Tpfr@Evap is set to the minimum value amongst TRfr@chii and TRfr@cabEvap, whereas in the absence of critical thermal conditions of the components COMP1 , COMP2 (condition C3 is true), then the target temperature TRfr@EvaPis set to the value determined by first selecting the minimum value amongst TRfr@chii and TRfr@cabEvap, and then the maximum value amongst the just selected minimum and TRfr@Min.

[0057] Figure 10A is a diagram showing the pressure PRfr of the refrigerant fluid as a function of the specific enthalpy hRfr thereof. In the vapour phase of the refrigerant fluid, i.e. in the surface below the dotted line in the graph of Figure 10A, during the evaporation process there is a direct correlation amongst the temperature TRfr@EvaPand the pressure PRfr@EvaPof the refrigerant fluid. By making use of the curve of Figure 10B, which shows the pressure PRK of the refrigerant fluid (in the vapour phase) as a function of the temperature TR / T thereof, it is possible to determine the pressure of the refrigerant fluid in the evaporation process.

[0058] Reference is now being made to Figure 11 , which is a diagram showing again the plane of pressure PRK (expressed in Mpa) vs. specific enthalpy hRfr (expressed in kJ / kg) of the refrigerant fluid, which is overlaid by a diagram of the system 1 similar to the diagram in Figure 1 , in such a way as to show, in the plane PRfr-hRfr, the phase changes of the refrigerant fluid as a function of the progression thereof in the circuit of the system 1 (in an anti-clockwise direction). At the end of the evaporation process (state S1 in Figure 1 ), the refrigerant fluid is an overheated vapour, so that there is no part of the refrigerant fluid in the liquid phase at the inlet of the compressor C (insofar as this could damage the compressor itself). The lamination valves TXV1 , V1 , V2 determine a fixed increase of the temperature A TsuperHeat of the refrigerant fluid, and the temperature variation A TsuperHeat is determined by the mechanical characteristics of the lamination valves. Therefore, the temperature TRfr@EvaPout of the refrigerant fluid at the end of the evaporation process (state S1 ) is given by the following equation (8):

[0059] The enthalpy value hRfr@EvaPout of the state S1 at the outlet of the evaporation elements EVAP, CHL1 , CHL2 may be obtained by using the enthalpy diagram of the refrigerant fluid, as a function of the pressure PRfr@EvaP(which is determined as a function of the temperature TRfr@EvaPby using the diagram of Figure 10B) and of the temperature TRfr@EvaPout. Also, the enthalpy value hRfr@condout of the state S3 at the outlet of the condenser CNDS may be obtained by using the enthalpy diagram of the refrigerant fluid, as a function of the pressure PRfr@condout and of the temperature TRfr@condout, measured by the sensors PS1 and TS1 , respectively. The pressure PRfr@condout may be considered equal to the pressure PRfr@comPin at the inlet of the condenser CNDS, in the state S2, since the condensation process of the refrigerant fluid may be approximated as a transformation at constant pressure. The lamination process (i.e. , the transformation from state S3 to state S4) may be approximated as an isenthalpic transformation, so that the enthalpy value hRfr@condout at the outlet of the condenser CNDS (in the state S3) is equal to the enthalpy value hRfr@EvaPin at the inlet of the cabin evaporator EVAP and of the chillers CHL1 , CHL2 (in the state S4). Therefore, by using the following equation (9), it is possible to compute a target mass flow value of the refrigerant fluid mRfrTgt as a function of the overall requested cooling power, which amounts to the sum Qcmier + QcabEvap ■

[0060] The density pRfr@EvaPof the refrigerant fluid at the inlet of compressor C (in the state S1 ) may be computed via the following equation (10), where MRfr is the molar mass of the refrigerant fluid and RRtr is a constant characteristic of the refrigerant fluid:

[0061] Once the density pRfr@EvaPhas been determined, it is possible to compute, in an open loop (without feedback), the target speed ncomPTgt of the compressor C (which is expressed in rpm) via the following equation (11 ), where Vcompis the displacement of the compressor and r / voi is the volumetric efficiency of the compressor:

[0062] Specifically, the volumetric efficiency r / voi of the compressor may be determined via one or more maps as a function of the compression ratio ficomp=PRfr@compinl PRfr@Evap and of the speed ncomp of the compressor C. Specifically, the dependence of the efficiency r / voi on the compression ratio ficomp and on the compressor speed ncomp is qualitatively represented by the graph of Figure 12, which shows the evolution of r / voi as a function of ncomp for different values of ficomp, in the present case for four different values ficompi, (3comp2, @comp3, @comp4, so listed in decreasing order (i.e., / 3comPi> / 3comp2> / 3comp3> / 3comP4) ■ Generally speaking, therefore, the efficiency r / voi decreases as the compression ratio ficomp increases.

[0063] Based on what has been set forth in the foregoing, according to the present invention a method 10 for controlling a compressor of an air- conditioning and / or cooling system of an electric vehicle may be schematically shown by the block diagram of Figure 13, which comprises the following steps. At step 101 , determining the cooling power QcabEvap demanded by the cabin evaporator EVAP for the air conditioning of the cabin, via equation (1). At step 102, determining the target temperature of the refrigerant fluid TRfr@cabEvaPfor the cabin evaporator via equation (2), and determining the minimum temperature of the refrigerant fluid TRfr@Min that avoids icing on the evaporator EVAP, via equation (3). At step 103, determining the raw cooling power QcmiRaw demanded by the chillers CHL1 , CHL2 for cooling the vehicle components (e.g., the batteries) via equation (4). At step 104, determining the actual cooling power Qcmier demanded by the chillers CHL1 , CHL2, while also considering the limitations set in order to avoid icing and the power demands of the evaporator EVAP, in the case of combined operation of the evaporator EVAP and of the chillers CHL1 , CHL2, via equations (5) and (6) and via the logic described in Figure 7. At step 105, determining the target temperature of the refrigerant fluid TRfr@chii for the chillers, via equation (7). At step 106, determining a common target temperature of the refrigerant fluid TRfr@EvaPin the evaporation process, via the logic described in Figure 9. At step 107, obtaining the enthalpy values hRfr@Evapin and hRfr@EvaPout at the inlet and at the outlet of the evaporation process (states S2 and S1 of Figure 11 , respectively) as a function of the measured values of temperature and pressure of the refrigerant fluid (for the enthalpy hRfr@EvaPin) and of the estimated values of temperature and pressure of the refrigerant fluid (for the enthalpy hRfr@EvaPout). At step 108, determining a target mass flow value of the refrigerant fluid mRfrTgt as a function of the overall cooling power demanded by the evaporator EVAP and by the chillers CHL1 , CHL2 via equation (9). At step 109, determining (in an open loop, without feedback) a target speed ncomPTgt of the compressor C via equations (10) and (11 ).

[0064] By doing so, it is possible to increase the responsiveness of the air- conditioning and / or cooling system as the vehicle conditions vary, since the target speed of the compressor is computed in an open loop, without any temperature feedback (which would be intrinsically slow). Moreover, when the system switches from combined operation (both cabin evaporator and chillers) to operation where only the cabin evaporator is active, the speed of the compressor may be immediately reduced, in order to meet the cooling power demands of the cabin evaporator only, thereby avoiding the risk of overcooling. In this case, the high responsiveness of the system 1 to the mutated conditions enables avoiding icing on the cabin evaporator.

[0065] Of course, the implementation details and the embodiments may amply vary with respect to what has been described and illustrated herein, without departing from the extent of the invention as defined by the annexed claims.

Claims

CLAIMS1. A method (10) for controlling a compressor (C) of an air- conditioning and / or cooling system (1 ) of a vehicle with an electric powertrain, wherein the air-conditioning and / or cooling system (1 ) comprises a cabin evaporator (EVAP) where a refrigerant fluid exchanges heat with cabin air and at least one chiller (CHL1 , CHL2) where the refrigerant fluid exchanges heat with a coolant, the method comprising:- determining (101 ) a first cooling power (QcabEvap ) requested by said cabin evaporator (EVAP);- determining (102) a first target temperature ( TRfr@cabEvaP) of said refrigerant fluid, so that said cabin evaporator (EVAP) would provide said first cooling power (QcabEvap ), and determining (102) a minimum temperature ( TRfr@Min) of said refrigerant fluid to avoid icing of said cabin evaporator (EVAP);- determining (103) a second cooling power (QcmiRaw) requested by said at least one chiller (CHL1 , CHL2) for cooling one or more components of the vehicle;- determining (104) a third actual cooling power (Qcmier) of saidatleast one chiller (CHL1 , CHL2) by carrying out the following steps: i) if said at least one chiller (CHL1 , CHL2) is not active, setting said third cooling power (Qcmier ) equal to zero; ii) if said at least one chiller (CHL1 , CHL2) is active and said cabin evaporator (EVAP) is inactive, setting said third cooling power (Qcmier) equal to said second cooling power (QcmiRaw)', and iii) if said at least one chiller (CHL1 , CHL2) is active and said cabin evaporator (EVAP) is active, selecting the maximum value amongst said second cooling power (QcmiRaw) andafourth cooling power (QcmiMinForcabEvap) that the at least one chiller (CHL1 , CHL2) would provide if the refrigerant fluid had said first target temperature ( TRfr@cabEvaP), then selecting the minimum value amongst said maximum value just selected and a fifth cooling power (QcmiMaxFor Anti-icing ) that the at least one chiller (CHL1 , CHL2) would provide if the refrigerant fluid had said minimum temperature ( TRfr@Min), and setting said third cooling power (Qcmier) equal to saidselected minimum value;- determining (105) a second target temperature ( TRfr@chii) of said refrigerant fluid, so that said at least one chiller (CHL1 , CHL2) would provide said third cooling power (Qcmier )',- determining (106) a third target temperature ( TRfr@EvaP) of said refrigerant fluid by carrying out the following steps: i) if an overheating condition of at least one component of the vehicle that is cooled by said coolant is detected, setting said third target temperature ( TRfr@EvaP) equal to the minimum value amongst said first target temperature ( TRfr@cabEvaP) and said second target temperature ( 7R / T@C / I / / ); and ii) if said overheating condition does not exist, selecting the minimum value amongst said first target temperature ( TRfr@cabEvaP) and said second target temperature ( TRfr@chii), then selecting the maximum value amongst said minimum value just selected and said minimum temperature ( TRfr@Min) of said refrigerant fluid, and setting said third target temperature ( TRfr@EvaP) equal to said selected maximum value;- estimating (107) a first enthalpy value (hRfr@EvaPin) of said refrigerant fluid upstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2) as a function of the temperature and pressure measured by respective sensors (TS1 , PS1 ) arranged at the outlet of a condenser device (CNDS) of said system (1 );- estimating (107) a second enthalpy value (hRfr@EvaPout) of said refrigerant fluid downstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2) as a function of said third target temperature ( TRfr@EvaP) and as a function of a fixed temperature drop (A TsuPerHeat) produced by respective lamination valves (TXV1 , V1 , V2) arranged at the inlet of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2);- determining (108) a target mass flow value (mRfrTgt) of the refrigerant fluid as a function of the sum of said first cooling power (QcabEvap ) and said third cooling power (Qcmier) andas afunction of the difference between said second enthalpy value (hRfr@EvaPout) and said first enthalpy value (JlRfr@EvaPln)',- determining (109) a target speed value (ncompTgt) of said compressor (C) as a function of said target mass flow value of the refrigerant fluid (itlRfrTgt).

2. The method of claim 1 , wherein the step of determining (101 ) said first cooling power (QcabEvap ) comprises:- receiving from a vehicle control unit a target temperature value ( TAircabEvapoutTgt) of the cabin air set by a user;- measuring (TS_Ajn) the temperature ( TAircabEvapin) of the cabin air entering said cabin evaporator (EVAP);- determining a mass flow (mAircabEvap) of said cabin air that flows through said cabin evaporator (EVAP) as a function of the speed ( vBiower) of a fan of the air-conditioning system; and- computing said first cooling power (QcabEvap ) according to the following equationwhere CP_Air is the specific heat of air.

3. The method of claim 1 or claim 2, wherein the step of determining (102) said first target temperature ( TRfr@cabEvaP) of said refrigerant fluid comprises:- determining a thermal resistance (RrhcabEvap) of said cabin evaporator (EVAP);- measuring (TS_Ajn) the temperature ( TAircabEvapin) of the cabin air entering said cabin evaporator (EVAP); and- computing said first target temperature ( TRfr@cabEvaP) of said refrigerant fluid according to the following equation4. The method of any of the previous claims, wherein the step of determining (102) said minimum temperature ( TRfr@Min) of said refrigerant fluid comprises:- determining a thermal resistance (RrhcabEvap) of said cabin evaporator (EVAP);- measuring (TS_Ajn) the temperature ( TAircabEvapin) of the cabin air entering said cabin evaporator (EVAP);- receiving from a vehicle control unit a minimum temperature value ( TAircabEvapoutMin) of the cabin air;- determining a mass flow (jfiAircabEvap) of said cabin air that flows through said cabin evaporator (EVAP) as a function of the speed ( VBiower) of a fan of the air-conditioning system; and- computing said minimum temperature ( TRfr@Min) of said refrigerant fluid according to the following equationwhere CP_Air is the specific heat of air.

5. The method of claim 3 or claim 4, wherein said thermal resistance (RrhcabEvap) of said cabin evaporator (EVAP) is determined as a function of a mass flow (mAircabEvap) of said cabin air that flows through said cabin evaporator (EVAP), which in turn is determined as a function of the speed (VBiower) of a fan of the air-conditioning system.

6. The method of any of the previous claims, wherein the step of determining (103) said second cooling power (QcmiRaw) comprises:- receiving from a vehicle control unit a target temperature value ( TcinchiioutTgt) and a target mass flow value (mcinchiirgt) of said coolant that flows through said at least one chiller (CHL1 , CHL2);- measuring (TS_CLjn) the temperature ( Tcinchiiin) of the coolant entering said at least one chiller (CHL1 , CHL2);- computing said second cooling power (QcmiRaw) according to the following equationQcmiRaw=mcinChllTgt ’ Cp_Cln ■ (Tcincmiln ~ T ClnChllOutT gt) where CP_cin is the specific heat of the coolant.

7. The method of any of the previous claims, wherein the step of determining (105) said second target temperature ( 7R / T@C / I / / ) of said refrigerant fluid comprises:- determining a thermal resistance (Rrhchii) of said at least one chiller (CHL1 , CHL2);- measuring (TS_CLjn) the temperature ( Tcinchiiin) of the coolant entering said at least one chiller (CHL1 , CHL2); and- computing said second target temperature ( TRfr@chii) of said refrigerant fluid according to the following equation8. The method of claim 7, wherein said thermal resistance (Rrhchii) of said at least one chiller (CHL1 , CHL2) is determined as a function of a mass flow (mcinchii) of said coolant that flows through said at least one chiller (CHL1 , CHL2) and as a function of a number of active chillers.

9. The method of any of the previous claims, wherein the step of estimating (107) said second enthalpy value (hRfr@EvaPout) of said refrigerant fluid downstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2) comprises:- estimating a temperature ( TRfr@EvaPout) of the refrigerant fluid downstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2) by adding up said fixed temperature drop (ATsuPerHeat) and said third target temperature ( TRfr@EvaPy- estimating a pressure (PRfr@EvaP) of the refrigerant fluid downstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2) as a function of said third target temperature ( TRfr@EvaPy and- estimating said second enthalpy value (hRfr@EvaPout) as a function of said temperature ( TRfr@EvaPout) and pressure (PRfr@EvaP) of the refrigerant fluid downstream of said cabin evaporator (EVAP) and said at least one chiller (CHL1 , CHL2).

10. The method of any of the previous claims, wherein said target speed value (ncomPTgt) of the compressor (C) is determined as well as a function of the density (pRfr@EvaP) of the refrigerant fluid, of the displacement ( VcomP) of the compressor (C) and of the volumetric efficiency (r / voi) of the compressor (C).

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