A method for allocating thermal cooling power in a vehicle with an electric powertrain

Abstract

Method for allocating thermal cooling power in a vehicle with an electric powertrain comprising a refrigeration cycle cooling circuit (CC) through which a refrigerant fluid flows, and including a cabin evaporator (EVAP), for cooling a passenger compartment of the vehicle, and a plurality of cooling devices (CHL1, CHL2), so-called chillers, for cooling one or more batteries of the powertrain, each cooling device (CHL1, CHL2) comprises a battery evaporator (EV_B1, EV_B2) in a heat exchange relationship with a cooling liquid flowing through a battery cooling circuit of the powertrain, wherein it is possible to increase the cooling performances and the comfort in the passenger compartment during the simultaneous activation of the cabin evaporator (EVAP) and of the cooling devices (CHL1, CHL2), thanks to the possibility of dynamically adjusting the number of cooling devices (CHL1, CHL2) which are simultaneously active.

Description

[0001] "A method for allocating thermal cooling power in 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, particularly to BEV (Battery Electric Vehicles). In more detail, the invention has beendeveloped with reference to vehicles with an electric powertrain supplied by a battery (or by batteries) and comprising a refrigeration cycle cooling circuit with a cabin evaporator for the passenger compartment of the vehicle and one or more cooling devices (so-called "chillers") for the thermal conditioning of the battery (or the batteries).

[0006] Known Art

[0007] In the vehicles with an electric powertrain (so- called "BEV") provided with a refrigeration cycle cooling circuit with a cabin evaporator for the passenger compartment of the vehicle and one or more chillers for the thermal conditioning of the battery (or of the batteries), a major technical problem relates to the characteristics of the components being used. Specifically, a cabin evaporator iiss inherently less effective in extracting thermal power from the air, compared to a chiller extracting thermal power from the water of the forced convection cooling circuit of the battery (or the batteries) with which it is in a heat exchange relationship.

[0008] In the known solutions, the cabin evaporator and the one or more chillers are controlled in such a way as to operate with maximum allocated refrigerant fluid flow rates. However, in conditions of maximum workload, the chillers may saturate the global cooling capacity of the refrigeration cycle circuit, thereby preventing the cabin evaporator from meeting the driver's requests. Such a situation is shown in Figure 1, which schematically represents the evolution in time of the cooling thermal power particularly with reference to the values (cooling thermal power of the cabin evaporator) and (cooling thermal power of the one or more chillers) and to a maximum available cooling thermal power threshold Reference A denotes a starting instant of the increment of the cooling load on the refrigeration cycle circuit, while reference B denotes an instant of reaching the maximum available cooling power threshold amounting to the sum of the powers

[0009] The diagram in Figure 1 clearly shows that at instant B the cooling capacity of the refrigeration cycle circuit has been saturated (by reaching the maximum cooling thermal power by the one or more chillers, before the cabin evaporator has reached the respective maximum value of the cooling thermal power In other words, reference C denotes a cooling power domain which is no longer available to the system at the instant B, but which indeed should be available to the cabin evaporator in order to achieve the cooling target for the cabin.

[0010] Object of the Invention

[0011] The present invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the present invention consists in preventing the excessive absorption of the cooling thermal power by one or more chillers of a refrigeration cycle cooling circuit, to the detriment of the cabin evaporator.

[0012] Summary of the Invention

[0013] The object of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention.

[0014] Brief Description of the Figures

[0015] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only and wherein:

[0016] - Figure 1 corresponds to a condition of use of the cooling thermal power according to the known art in a refrigeration cycle cooling circuit for a vehicle with an electric powertrain comprising a cabin evaporator and at least one chiller for the thermal conditioning of the battery of the powertrain,

[0017] - Figure 2 is similar to Figure 1, but it shows a condition of use of the cooling thermal power according to the method of the invention,

[0018] - Figure 3 shows a cooling circuit to which the method according to the invention is applied,

[0019] - Figure 4 iiss a flow chart representative of a method according to the invention,

[0020] - Figure 5 shows the circuit of Figure 4 in a pressure vs. enthalpy diagram,

[0021] - Figure 6 is a diagram of the thermal resistance of one or more chillers as a function of the cooling liquid mass flow rate through a battery cooling circuit thereof, and

[0022] - Figure 7 is a bllock diiagram showing further aspects of the method according to the invention.

[0023] Detailed Description

[0024] As a general premise Figure 2 shows, from a qualitative point of view, the action performed by the method according to the invention. Specifically, and merely from a qualitative point of view, the cooling power domain C is reserved to the cabin evaporator, and it is not drawn by the chillers associated with the one or more batteries of the vehicle. In this fashion, the band of thermal power available to the cabin evaporator is supplemented by a domain C' which substantially corresponds to a dedicated exclusive domain C, which therefore is not available to the chillers.

[0025] Figure 3 schematically shows the general structure of a cooling circuit CC in which the method according to the invention may be implemented. The circuit CC comprises an electrically powered compressor EAC, the delivery port whereof is in fluid communication with the inlet of a condenser CNDS. The outlet of the condenser CNDS is in fluid communication with a first circuit node Nl, from which two circuit branches depart, the former being directed towards the inlet of a cabin evaporator EVAP and the latter towards a second circuit node N2, downstream whereof the second circuit branch divides into a third and a fourth circuit branch, which respectively lead to the inlets of a first cooling device (specifically, a first chiller) CHL1 and of a second cooling device (specifically, a second chiller) CHL2. Each chiller CHL1 and CHL2 comprises a respective battery evaporator EV_B1, EV_B2 (which receives the refrigerant fluid flowing in the circuit CC) in a heat exchange relationship with a cooling liquid which flows through a battery cooling circuit (not shown, but known per se) of the one or more batteries of the electric powertrain.

[0026] Upstream of the evaporator EVAP there is arranged an expansion / lamination valve TXV_EVAP; in the same way, upstream of the battery evaporators of the chillers CHL1 and CHL2 there are arranged respective expansion valves TXV_CHL1 and TXV_CHL2. The expansion / evaporation valves enable - by varying the respective hydraulic resistance as a function of the refrigerant fluid flow rate (in the liquid phase, when they are passed through - in figure 3 the valves are shown as variable hydraulic resistors) - adjusting the pressure of the refrigerant fluid entering the evaporator EVAP and the battery evaporators EV_B1, EV_B2 of the chillers CHL1 and CHL2, i:n such a way as to permit a ccoommpplleettee eevvaappoorraattiioonn of the refrigerant fluid inside them, so as to avoid the inlet into the compressor EAC of a biphasic flow (liquid + vapour). Upstream of each ooff the valves TXV_EVAP,

[0027] TXV_CHL1, TXV_CHL2 there aarree respectively arranged shutoff valves SV_EVAP, SSVV_CCHHLL11,, SV_CHL2. The shutoff valves SV_EVAP, SV_CHL1, SV_CHL2 may alternatively be arranged between tthhee corresponding valve TXV_EVAP, TXV_CHL1, TXV_CHL2 and - respectively - the cabin evaporator EVAP, the battery evaporator of the chiller CHL1 and the battery evaporator of the chiller CHL2 (in other words, the relevant feature is only the positioning thereof upstream of, respectively, the evaporator EVAP and the battery evaporators of the chillers CHL1 and CHL2). The function of the shutoff valves SV_EVAP, SV_CHL1, SV_CHL2, which are normally open valves, is to exclude from the circuit CC the circuit branch downstream thereof, and therefore to exclude the evaporator EVAP or either or both battery evaporators of the chillers CHL1 and CHL2 according to need.

[0028] The outlets of the chillers CHL1 and CHL2 (and therefore of the battery evaporators EV_B1, EV_B2 of the chillers CHL1 and CHL2) converge into a third circuit node N3 and into a single fifth circuit branch which converges, together with the section of the first circuit branch departing from the outlet of the cabin evaporator

[0029] EVAP, into a fourth circuit node N4 downstream whereof the cooling circuit CC is closed at the intake port of the compressor EAC.

[0030] The compressor EAC sends into the circuit CC a total refrigerant fluid flow rate in the vapour phase. The flow rate flows through the condenser turning into the liquid phase an reaches the node Nl, from which it is distributed between the cabin evaporator EVAP (flow rate and the battery evaporators EV_B1, EV_B2 of the chillers CHL1 and CHL2 globally entering the node N2). The flow rates undergo evaporation (at a substantially constant pressure) within the battery evaporators EV_B1, EV_B2 of the chillers CHL1 and CHL2 and the cabin evaporator EVAP, thereby cooling the cooling liquid of the one or more batteries and the cabin air, respectively. The flow rates in the vapour phase are mixed, at node N4, into the flow rate which is drawn back into the condenser EAC in order to be introduced again into the circuit CC. Figure 5 shows the same circuit as Figure 3 (with the exception of a more compact representation of the battery evaporators EV_B1, EV_B2, since they have overlapping coordinates on the p-h, pressure-enthalpy, plane) so as to represent the physical coordinates of the refrigerant fluid during the circulation thereof in the circuit CC. It should be noted, moreover, that the circuit CCCC has a merely exemplary structure. The description in the following also applies to configurations having more than two chillers.

[0031] With combined reference to Figure 3 and to Figures

[0032] 3, 5, according to the invention there is defined a method 1 for allocating thermal cooling power in a vehicle with an electric powertrain, comprising:

[0033] - determining (block 2) a first refrigerant fluid flow rate, corrresponding to a refrigerant fluid flow rate to be delivered to the cabin evaporator EVAP in order to output a target thermal cooling power

[0034] CAB_EVAP,

[0035] - determining (block 4) a second refrigerant fluid flow rate, corresponding to a maximum refrigerant fluid flow rate m.RFR_cHL,LiM to be delivered to the battery evaporators EV_B1, EV_B2 of the plurality of cooling devices CHLl, CHL2 as a function of the refrigerant fluid flow rate to be delivered to the cabin evaporator EVAP. Preferably, this comprises operating a difference between a maximum available flow rate of refrigerant fluid in the refrigeration cycle cooling circuit CC and the first refrigerant fluid flow rate

[0036] - determining (block 6) a target total thermal resistance value of the plurality of cooling devices CHL1, CHL2 such that the refrigerant fluid flow rate passing through the battery evaporators EV_B1, EV_B2 of the plurality of cooling devices CHL1, CHL2 is limited to the second refrigerant fluid flow rate

[0037] - determining (block 8) a number of cooling devices to be kept active at the same time in order to output the target total thermal resistance value specifically, this involves determining a number of cooling devices to the battery evaporators whereof the second refrigerant fflluuiidd flow rate is to be delivered.

[0038] As it is generally known, the thermal cooling powers which may be delivered by the battery evaporator EVAP and by the set of battery evaporators of the chillers CHL1, CHL2 depend on the refrigerant fluid flow rate which passes through them and as well as on the enthalpy variation between the inlet and the outlet, as expressed by the formulae:

[0039] Moreover, the diagram in Figure 3 clearly shows that the cabin evaporator EVAP and the set of chillers CHL1, CHL2 are hydraulically arranged in parallel with each other, and therefore the increment in the hydraulic resistance upstream of the evaporator EVAP increases the refrigerant fluid flow rate which is delivered to the chillers, and vice versa. This means that the control of the flow rates may be implemented by means of the expansion / lamination valves TXV_EVAP, TXV_CHL1, TXV_CHL2. By varying the passagei section through said valves it is possible to vary the hydraulic resistance thereof, and therefore to vary the hydraulic resistance upstream of the evaporators (EVAP and the evaporators within CHL1, CHL2) and the refrigerant fluid flow rates. Due to what has been described in the foregoing, on the other hand, by means of the shutoff valves SV_CHL1 and SV_CHL2 it is possible to decide about the number of chillers which are simultaneously active by simply excluding one oorr mmoorree chillers (the latter option in the case of aa circuit having more than two chillers), speccifiically by excluding the respective battery evaporators by completely closing the corresponding shutoff valve.

[0040] The thermal power exchanged within the chillers CHL1 and CHL2 between the refrigerant fluid ooff the circuit CC and the cooling liquid of the battery cooling circuit may be expressed as the ratio of a difference between the temperature of the cooling liquid entering the chiller and the temperature of the refrigerant fluid in the chiller evaporator (which is assumed to be constant during the evaporation process) to a total thermal resistance of the chillers

[0041] Expressed as formulae: wherefrom, by replacing with the maximum flow rate value of refrigerant fluid deliverable to the plurality of cooling devices (i.e. the chillers), it is possible to compute the target (limit) value of the total thermal resistance wherein: is a temperature of the cooling liquid at the inlet of the one or more cooling devices is a temperature of the refrigerant fluid flowing inside the one or more battery evaporators, is said refrigerant fluid flow rate to be delivered to said cabin evaporator is an enthalpy of the refrigerant fluid delivered to the battery evaporators, is an enthalpy of the refrigerant fluid at the outlet of the battery evaporators.

[0042] The thermall resistance depends on the cooling lliiqquuiidd flow rate aanndd on the number of simultaneously active chillers. Based on the value it is thus possible to determine the number of simultaneously active chillers (and the relating cooling liquid flow rate) which enable providing the thermal resistance and therefore outputting a limited cooling thermal power, adapted to guarantee the availability of the power domain C' in favour of the cabin evaporator EVAP.

[0043] If the value of the target (limit) total thermal resistance is greater than or equal to a threshold value (Figure 7), then only one chiller is kept active, since this corresponds to a more resistive configuration from the thermal point of view. On the contrary, if the value of the target (limit) total thermal resistance is less than said threshold value then both chillers CHL1, CHL2 are activated, since this corresponds to a less resistive configuration from a thermal point of view. In the presence or more than two chillers, it is possible to envisage progressive thresholds for the activation of progressively bigger numbers of chillers.

[0044] Figure 6 shows a diagram M_CHL of the thermal resistance RTH_CHL_TOT as a function of the cooling liquid mass flow rate parametrized with respect to the number of the chillers. The diagram M_CHL is representative of a map which may be used in the method according to the invention by employing, as an input item of data, the resistance The map enables determining the maximum cooling liquid flow rate through each chiller CHL1 and / or CHL2 in order to provide the resistance value

[0045] Referring to Figure 7, reference 100 identifies a block diagram representative of further operations in the method according to the invention. In detail, the diagram 100 shows operations of closed-loop corrections of the value which otherwise may derive from an open-loop calculation,, based on physical considerations translated into a computational model. Specifically, the corrrectionn of the resistance is necessary when the value of the cabin air temperature at the outlet of the cabin evaporator EVAP and / or the temperature of the one or more batteries of the electric powertrain show non-negligible deviations with respect to target values. The feedback branch is represented by a corresponding block 102, which preferably corresponds to a proportional and integral control. The calculation of the resistance in an open loop and the correction in a closed loop represented by the block 102 converge into an adder 104 which outputs a corrected value It should be noted that the feedback takes place upstream of the determination of the number of chillers to be kept simultaneously active: the corrected value once it has been computed, is compared (block 106) with the threshold value in the fashion described for the rated value Specifically, the diagram 100 shows the condition wherein RTH_CHL_TOT,CORR the consequence whereof is the activation of one single chiller (switch 108) and the determination of a maximum cooling liquid flow rate (with reference to the single chiller CHL1 and / or CHL2 which is being kept active) on the basis of a map M_CHL_S equivalent to the map M_CHL of Figure 6, but specific for the single chiller. If the condition is not met, as previously described, a map M_CHL_D is employed which corresponds to the map M_CHL of Figure 6, but which is specific for a double chiller, with the relating determination of the maximum cooling liquid flow rate through the chillers CHL1, CHL2 which are simultaneously active.

[0046] As regards the correction carried out in block 102, the method according to the invention moreover comprises correcting the target total thermal resistance value as a function of an air temperature at the outlet of said cabin evaporator; specifically, it comprises increasing the target total thermal resistance if the air temperature at the outlet of the cabin evaporator EVAP is higher than a target temperature set for the passenger compartment (the action increases the refrigerant fluid flow rate which is delivered to the cabin evaporator EVAP), and decreasing the target total thermal resistance RTH_CHL_TOT,LIM if the air temperature at the outlet of the cabin evaporator is lower than a target temperature set for the passenger compartment ((ssuucchh an intervention reduces the refrigerant fluid flow rate which is delivered to the cabin evaporator EVAP), in such a way as to avoid conditions of insufficient delivery of refrigerant fluid flow rate to the battery evaporator(s) of the chillers CHL1, CHL2 which are currently active for cooling the batteries, thus in such a way as to avoid situations of excessively absorbing cooling thermal power by the cabin evaporator when the cooling target of tthhee passenger compartment has already been achieved.

[0047] As already anticipated in the foregoing, the method moreover comprises correcting the target total thermal resistance value as a function of a temperature of the one or more batteries of the powertrain; specifically, it includes decreasing the target total thermal resistance value upon exceeding a temperature threshold of said one or more batteries. In given conditions, e.g. in case of a great thermal drift of the battery, the correction may prevail over the thermal conditioning needs of the passenger compartment, by using a part of the cooling thermal power portion reserved to the cabin evaporator EVAP.

[0048] Thanks to the method according to the invention, it is possible to increase the cooling performances (and the comfort) in the passenger compartment, during the simultaneous activation of the cabin evaporator and of the chillers CHL1 and / or CHL2, thanks to the possibility of dynamically adjusting the number of the chillers which are active simultaneously. Thanks to the method according to the invention, moreover, it is possible to use thermally controlled expansion / lamination valves, which are far less costly than the electronically controlled expansion valves (the use whereof, however, is not excluded).

[0049] 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 present invention, as defined by the annexed claims.

Claims

CLAIMS1. A method for allocating thermal cooling power in a vehicle with an electric powertrain comprising a refrigeration cycle cooling circuit (CC) through which a refrigerant fluid flows and including a cabin evaporator (EVAP) for cooling a passenger compartment of the vehicle and a plurality of cooling devices (CHL1,CHL2) for cooling one or more batteries of the powertrain, each cooling device comprising a battery evaporator (EV_B1, EV_B2) in a heat exchange relationship with a cooling liquid flowing through a battery cooling circuit of the powertrain, the method comprising:- determining a first refrigerant fluid flow rate corresponding to a coolant flow rate to bedelivered to said cabin evaporator (EVAP) in order to output a target cooling power output- determining a second refrigerant fluid flow rate (mRFR_cHL) corresponding to a maximum flow rate of refrigerant fluid that can be delivered to the battery evaporators (EV_B1, EV_B2) of the plurality of cooling devices (CHL1, CHL2) as a function of said refrigerant fluid flow rate (iiiRFR_ CAB EVAP) to be delivered to said cabin evaporator (EVAP),- determining a target total thermal resistance value of said plurality of cooling devices(CHL1, CHL2) such that the flow rate of refrigerant fluid passing through the battery evaporators (EV_B1, EV_B2) of said plurality of cooling devices (CHL1, CHL2) is limited to said second refrigerant fluid flow rate- determining a number of refrigeration devices (CHL1, CHL2) to be kept active at the same time to output the target total thermal resistance value2. The method according to claim 1, wherein saiddetermining a number of cooling devices to be kept active simultaneously (CHL1, CHL2) comprises determining a number of cooling devices the battery evaporators (EV_B1, EV_B2) of which said second refrigerant flow rate (mRFR_CHL) is to be delivered to.

3. The method according to claim 1 or claim 2, wherein said determining said second refrigerant fluid flow ratecomprises operating a difference between a maximum available flow rate ofrefrigerant fluid in the refrigeration cycle cooling circuit (CC) and said second refrigerant fluid flow rate4. The method according to any one of the previous claims, wherein said target total thermal resistance valueis calculated as:where:is said target total thermal resistance value, is a temperature of the cooling liquid atthe inlet of the one or more cooling devices, is aa temperature of the cooling liquidflowing inside tthhee oonnee oorr mmoorree battery evaporators (EV_B1, EV_B2) is said refrigerant fluid flow rate to bedelivered to said cabin evaporator, is an enthalpy of the refrigerant fluid tobe delivered to ssaaiidd oonnee or more battery evaporators (EV_B1, EV_B2), is an enthalpy of the refrigerant fluidat the outlet of the oonnee or more battery evaporators (EV_B1, EV_B2).

5. The method according to claim 1 or claim 4, wherein if said target total thermal resistance valueis greater than or equal to a threshold valuesaid determining a number of cooling devices to be kept active at the same time (CHL1, CHL2) to output the target overall thermal resistance valuecomprises keeping only one cooling device active.

6. The method according to claim 5, wherein the refrigeration cycle cooling circuit (CC) comprises two cooling devices (CHL1, CHL2), and wherein if said target total thermal resistance valueis less than said threshold value said determining anumber of cooling devices to be kept active simultaneously to output the target total thermal resistance value comprises activating bothcooling devices.

7. The method according to any one of the preceding claims, further comprising correcting the value of said target total thermal resistance value as afunction of an air temperature at the outlet of said cabin evaporator (EVAP).

8. The method according to claim 7, wherein said correcting the value of said target total thermal resistance value comprises increasing thetarget total thermal resistance value ifthe air temperature at the outlet of the cabin evaporator is higher than a target temperature set for the cabin, and reducing the target total thermal resistance valueif the air temperature at the outlet of the cabin evaporator is lower than a target temperature set for the cabin.

9. The method according to claim 7 or claim 8, further comprising correcting (RTH_CHL_TOT,CORR) the value of said target total thermal resistance valueas a function of a temperature of the one or more batteries of the powertrain.

10. The method of claim 9, wherein said correctingthe value of said target total thermal resistance value aass aa function of atemperature of said one or more batteries of the powertrain comprises reducing the value of said target total thermal resistance valueupon exceeding a temperature threshold of said one or more batteries of the powertrain.

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