A method of determining the minimum allowable temperature of the traction battery of a vehicle with electric powertrain during use of the vehicle

Abstract

A method (10) of determining the minimum allowable temperature of the cells of a traction battery of a vehicle with electric powertrain during use of the vehicle is described. A first value of minimum allowable temperature (TBatt_Cell_Min_Drv_Tgt) associated to a currently-selected drive mode is determined (102), as a function of a first input parameter (DriveMod) that indicates the currently-selected drive mode, a second input parameter (SOC) that indicates the state of charge of the traction battery, a third input parameter (PDrvTgtRaw) that indicates the power requested by the driver of the vehicle to the powertrain, and a fourth input parameter (PCons) that indicates the power absorbed by the auxiliary electric loads of the vehicle. An actual value of minimum allowable temperature (TBatt_Cell_Min_Tgt) is determined (104) as a function of the first value of minimum allowable temperature (TBatt_Cell_Min_Drv_Tgt), the value of the first input parameter (DriveMod), and the values of one or more further input parameters. The additional input parameters are selected from: a fifth input parameter (Q̇Heat_Batt_Max) that indicates the maximum heating power deliverable for heating the traction battery; a sixth input parameter (TBatt_Cell) that indicates the current temperature of said traction battery; and a seventh input parameter (ΔtEnd_Mission) that indicates the remaining duration of the current driving mission.

Description

[0001] “A method of determining the minimum allowable temperature of the traction battery of a vehicle with electric powertrain during use of the vehicle”

[0002] ****

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the invention

[0005] The present invention relates to vehicles with electric powertrain, particularly BEV-type (Battery Electric Vehicle) or HEV-type (Hybrid Electric Vehicle) vehicles, equipped with a traction battery that stores the chemical energy required for the movement of the vehicle.

[0006] The invention has been developed with reference to the management of the temperature of the cells of the traction battery of the vehicle during use of the vehicle (i.e. , in driving conditions). In particular, the invention relates to a method of determining a value of the minimum allowable temperature of the cells of the traction battery in driving conditions.

[0007] Prior art

[0008] In an electric- or hybrid-traction vehicle, the temperature of the cells of the traction battery influences the maximum electrical power that can be absorbed by the battery during charging or delivered by the battery during discharging. Furthermore, the temperature of the battery cells also determines the amount of thermal energy stored in the battery. It will be noted that in the present description reference is made to the chemical energy stored by the battery and the thermal energy stored by the battery. Chemical energy is the useful energy stored through a reversible charging process by the battery cells, which can be supplied by the battery in the form of electric current to power the loads of the vehicle (both propulsive and non-propulsive). Thermal energy is instead energy stored following an increase in the temperature of the battery pack, which cannot be usefully transformed into electric current, and which is essentially destined to be dissipated as heat.

[0009] Heating of the battery (implemented by one or more heating devices provided in the vehicle) involves significant energy consumption. In known electric or hybrid vehicles, during use (i.e., in driving conditions) an algorithm defines a single value of the minimum allowable temperature of the traction battery cells. The definition of a single value of the minimum allowable temperature, valid in all driving conditions, does not allow to best manage the balance between obtaining a minimum level of power performance from the battery, and minimizing the energy spent by the battery heating system for heating the battery, depending on the current driving mission.

[0010] Therefore, the need is felt in the art to develop an algorithm to determine the minimum allowable temperature of the cells of the traction battery of the vehicle also as a function of different driving conditions.

[0011] Object of the invention

[0012] The object of the invention is to solve the above-mentioned technical problem. In particular, the object of the invention is to provide a method of determining a value of the minimum allowable temperature of the cells of the traction battery that, also as a function of the driving “mission” requested by the driver, allows to obtain a correct balance between the level of power performance obtainable from the battery and the energy spent for heating the battery.

[0013] Summary of the invention

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

[0015] The method can be implemented by one or more electronic control units of a vehicle (e.g., by a control unit of the Battery Management System (BMS), and / or by a control unit of the powertrain of the vehicle).

[0016] Brief description of the figures

[0017] The invention will now be described with reference to the attached figures provided purely by way of non-limiting example, in which:

[0018] Figure 1 is a block diagram illustrating the phases of a method of determining a value of the minimum allowable temperature of the cells of the traction battery in driving conditions, according to one or more embodiments of the present disclosure;

[0019] Figures 2 to 4 are block diagrams illustrating some steps of a phase of the method of determining the value of the minimum allowable temperature of the cells of the traction battery in driving conditions, in particular a phase that allows to determine a value of minimum allowable temperature associated to the driving mode currently used;

[0020] Figures 5 and 6 are two diagrams that exemplify the time course of some signals and physical quantities used in the steps of the method illustrated in Figures 3 and 4;

[0021] Figures 7 and 8 are block diagrams illustrating some steps of another phase of the method of determining the value of the minimum allowable temperature of the cells of the traction battery in driving conditions, in particular a phase that allows to apply corrective factors to the value associated to the driving mode to determine the actual value of the minimum allowable temperature of the cells of the battery; and

[0022] Figure 9 is a block diagram summarizing the phases of a method of determining the value of the minimum allowable temperature of the cells of the traction battery in driving conditions, according to one or more embodiments of the present disclosure.

[0023] Detailed description

[0024] As mentioned, the invention relates to a method that has the object of determining the value of the minimum allowable temperature of the cells of the traction battery of a vehicle in different driving conditions and as a function of the driving mission requested by the driver. The method therefore implements a control algorithm of the battery management system during the use phase of the vehicle, and can be implemented by a control unit of the battery management system (or BMS) and / or by a control unit of the powertrain of the vehicle.

[0025] The different driving missions that can be requested (selected) by the driver are characterized by respective values of nominal propulsive power of the vehicle, which can be reduced within acceptable limits as the state of charge (SOC) of the traction battery decreases. For example, a “racing” driving mission will have a higher nominal propulsive power than the nominal propulsive power of a touring driving mission. Therefore, during the discharging phase, the traction battery must be able to deliver a certain minimum guaranteed electric power for the propulsion of the vehicle and the possible powering of additional auxiliary electric loads (i.e. , non-propulsive electric loads such as the cabin conditioning system, the battery conditioning system, the on-board electronic systems, and the like), and the value of such minimum guaranteed power may depend on the selected drive mode. Furthermore, the limit (maximum) values of the current that can be delivered by the battery during the discharging phase or absorbed by the battery during the charging phase are usually defined by the supplier of the battery cells, as a function of the temperature of the battery cells and the state of charge of the battery. Qualitatively, the maximum power that can be delivered by the battery during the discharging phase increases as the temperature of the battery cells and the state of charge increase.

[0026] As illustrated in the block diagram of Figure 1 , the method 10 can substantially comprise two phases indicated by the references 102 and 104. In the phase 102, further described below, a value of minimum allowable temperature for the cells of the traction battery TBatt_ceii_Min_Drv_Tgt associated to the drive mode currently used is determined instant by instant (e.g., at each computation iteration of the method, which can have an iteration or refresh time in the range between 10 and 100 milliseconds), based on the values of a first input parameter Drive Mod which indicates the current drive mode selected by the driver of the vehicle, a second input parameter SOC which corresponds to the state of charge of the traction battery, and further input parameters PDrvTgtRaw and Peons which will be further described below. In step 104, further described below, an actual value of the minimum allowable temperature TBatt_ceii_Min_Tgt is determined instant by instant (e.g., at each computation iteration of the method) as a function of the temperature value associated to the drive mode TBatt_ceii_Min_Drv_ rgt computed in step 102, the value of the input parameter DriveMod, and the values of further (corrective) input parameters QHeat_Batt_Max, TBatt_ceii and AtEndjviission which will be further described below. Substantially, therefore, the operation block 104 carries out a correction or adjustment of the value associated to the drive mode TBatt_ceii_Min_Drv_ rgt computed in step 102.

[0027] The functioning of the operation block 102 for determining the value of minimum allowable temperature TBatt_ceii_Min_Drv_Tgt associated to the drive mode will now be described with reference to Figures 2 to 6.

[0028] In particular, as illustrated in Figure 2, the value of minimum allowable temperature TBatt_ceii_Min_Drv_Tgt associated to the drive mode can be determined by selecting, as a function of the parameter DriveMod, one of a plurality of temperature values associated to the different drive modes. For example, in Figure 2, six different values are indicated TBatt_Cell_Min_Drv_1_Tgt, TBatt_Cell_Min_Drv_2_Tgt, TBatt_Cell_Min_Drv_3_Tgt,

[0029] TBatt_Cell_Min_Drv_4_Tgt, TBatt_Cell_Min_Drv_5_Tgt, TBatt_Cell_Min_Drv_6_Tgt, assuming that the vehicle is equipped with six different drive modes that the driver can select from. Of course, in other embodiments the vehicle may provide more or less than six drive modes, and therefore more or less than six temperature values may be present, which will be generically indicated by TBatt_ceii_Min_Drv_i_ Tgt with i = 1 , N (N = 6 in the example considered here). The parameter DriveMod can be received from a vehicle control unit.

[0030] As exemplified in the block diagram of Figure 3, the ithminimum temperature value TBatt_ceii_Min_Drvj_Tgt associated to the ithdrive mode can in turn be determined as a function of the state of charge SOC using one or more respective characteristic maps (e.g., implemented by analytical, piecewise or look-up table functions) and a gain factor Gain. The state of charge SOC can be computed by and received from a vehicle control unit (e.g., a battery control unit). In particular, in a step 302, a temperature value TBatt_umMin_Hi that represents the minimum nominal temperature of the battery that guarantees the nominal performance of the vehicle defined by the ithdrive mode is determined via a first characteristic map, as a function of the parameter SOC. In a step 304, a second characteristic map is used to determine, as a function of the parameter SOC, a temperature value TBatt_umMin_Lo that represents the minimum temperature of the battery which, while not guaranteeing the nominal performance of the vehicle corresponding to the selected drive mode, allows for a reduction in the energy required by the battery conditioning (i.e. , heating) system to heat the battery. It will be understood that each of the N drive modes of the vehicle is associated to at least one pair of respective characteristic maps 302, 304. As exemplified in Figure 3, the characteristic maps 302, 304 are structured in such a way that from a qualitative point of view both the value TBattjjmMin a and the value TBatt_umMin_Lo increase as the state of charge SOC increases, since, for low levels of the state of charge, it is acceptable for the vehicle performance to be reduced, and it is also acceptable for the energy used to heat the battery to be reduced. Once the upper and lower limits TBattjjmMin_Hi and TBatt_umMin_Lo have been determined, in step 306 the difference between them is computed to determine the amplitude of the allowed range ATBattjjmMin. The ithminimum temperature value TBatt_ceii_Min_Drvj_Tgt associated to the ithdrive mode can finally be computed, in a step 308, by adding with sign - at each computation iteration of the procedure - a quantity equal to the product between the amplitude of the allowed range ATBattjjmMin and the gain factor Gain (i.e. , a quantity ATBattj mMin- Gain) to the temperature value TBatt_cett_Min_Drvj_Tgt computed at the previous iteration, and limiting the output value TBatt_cett_Min_Drvj_Tgt to the value TBattjjmMinju at the high end and to the value TBattjjmMinj.o at the low end. In other words, at the first iteration of the procedure the output value TBatt_ceii_Min_Drvj rgt is initialized to a certain starting value between TBattjjmMinju and TBatt_umMin_Lo (for example, equal to TBattjjmMinju, or equal to TBattjjmMinj.o, or equal to the arithmetic mean of these two values). At each subsequent iteration (e.g., every 100 milliseconds), a certain variation factor equal to ATBattjjmMin- Gain (which can be positive or negative) is computed and this variation factor is added (with sign) to the previous value of the temperature TBatt_ceii_Min_Drvj_Tgt to determine the new current value of the temperature TBatt_ceii_Min_Drvj_Tgt (which will still be limited between TBatt_LimMin_Hi and T BattJJmMinJ-o) ■

[0031] The gain factor Gain physically represents the part of the temperature range ATBattjjmMin that is increased or decreased (depending on the sign of the gain factor) at each computation iteration of the summation 308 (considering that, by implementing the algorithm in a vehicle control unit, the summation is computed step-by-step in successive time steps and not as an analytical function). Figure 4 is a block diagram that exemplifies one way of computing the gain factor Gain. In a step 402, the total (instantaneous) power required from the battery PReq rot is determined as the sum of a first contribution PDrvTgtRaw that is equal to the (instantaneous) power required by the driver of the vehicle (regardless of any limitations imposed by the vehicle control logic) and a second contribution Peons that is equal to the (instantaneous) power required by the auxiliary electrical loads of the vehicle (e.g., the compressor of the conditioning system, the electric heater of the conditioning fluid, the DC / DC converter). The values of the contributions PDrvTgtRaw and Peons can be sensed by means of appropriate sensors of the vehicle, and received from a vehicle control unit. In a step 404, a power value PBattum_Lo that represents the limit power deliverable by the battery when the battery is at the lowest temperature TBatt_umMin_Lo is determined by means of a characteristic map, as a function of the parameter SOC. In a step 406, the requested power PReq_Tot is compared with the deliverable power PBattum_Lo and a binary signal Need_More_Pwr is consequently produced, which is asserted (true) when the total power requested from the battery PReq_Tot is higher than the power deliverable by the battery PBattum_Lo when the battery is at the temperature TBatt_umMin_Lo, and is de-asserted (false) otherwise. So, if the signal Need_More_Pwr is asserted, it indicates that the battery temperature TBatt_LimMin_Lo is too low to guarantee the overall power request, and it is necessary to warm up the battery to pass to the value TBattjjmMin u.

[0032] Still referring to Figure 4, the signal Need_More_Pwr is processed in a delay block DL1 . The delay block DL1 works as exemplified in the diagram of Figure 5, which illustrates the time courses of a generic input signal IDDL and a generic output signal OutDL of a generic delay block DL, and a generic delay having duration AtDeiay. Substantially, the delay block DL delays the propagation of only the rising edges of the respective input signal IIIDL by an amount equal to the time interval AtDeiay, while the falling edges of the input signal IIIDL are propagated substantially without delay. As a consequence, any assertions of the input signal IIIDL whose overall duration is shorter than the duration of the interval AtDeiay are completely filtered out by the delay block DL (see for example times to, ti and t2 in Figure 5), while assertions of the input signal IDDL whose overall duration is longer than the duration of the interval AtDeiay are initially filtered out (i.e., the output signal OutDL remains low for a period equal to AtDeiay) and then propagated (see for example times ts, t4 and ts in Figure 5). In other words, the delay block DL performs a sort of “debouncing” of the input signal IDDL with a filter time equal to AtDeiay. So, returning to Figure 4, the signal Need_More_Pwr is processed in a first delay block DL1 which acts as discussed in relation to Figure 5 using a filter time equal to AtDeiay_i to produce a respective output signal. Furthermore, the signal Need_More_Pwr is logically complemented in a block 408 to produce its logically complementary signal, and that complementary signal is processed in a second delay block DL2 which acts as discussed in relation to Figure 5 using a filter time equal to AtDeiay_2 to produce a respective output signal. The filter times AtDeiay_2 and AtDeiay_i may be the same or different. A first selector S1 receives a positive value Gain_lnc at a first input and a null (zero) value at a second input, as well as the output signal from block DL1 as a selection signal. Therefore, when the output signal from block DL1 is asserted, selector S1 produces as output a signal with a (positive) value equal to Gain_lnc, while when the output signal from block DL1 is de-asserted, selector S1 produces as output a signal with a null value. A second selector S2 receives a negative value Gain_Dec at a first input and the output signal of the first selector S1 at a second input, as well as the output signal from block DL2 as a selection signal. Therefore, when the output signal from block DL2 is asserted, selector S2 produces as output the parameter Gain with a (negative) value equal to Gain_Dec, while when the output signal from block DL2 is de-asserted, selector S2 produces as output the parameter Gain with a (positive) value equal to Gain_lnc or zero.

[0033] Overall, the set of steps and operations described by referring to Figures 3, 4 and 5 can be further understood by referring to Figure 6, which exemplifies a possible time behavior of the signals Need_More_Pwr, Gain and TBatt_ceii_Min_Drv_i_Tgt. At time to the signal Need_More_Pwr is asserted (changes from zero to one), the gain factor Gain changes from the negative value Gain_Dec to zero and the minimum temperature value TBatt_ceii_Min_Drv_i_Tgt remains equal to the lower limit value TBatt_LimMin_Lo. At time ti, while the signal Need_More_Pwr remains asserted (equal to one), the time interval of duration AtDeiay_i expires, therefore the selector S1 produces as output the value Gain_lnc and the gain factor Gain changes from zero to the positive value Gain_lnc. As a result, the minimum temperature TBatt_ceii_Min_Drvj_Tgt starts to rise from the lower limit value TBatt_umMin_Lo to the upper limit value TBatt_LimMin_Hi. At time t2, when the minimum temperature TBatt_ceii_Min_Drvj_Tgt reaches the upper limit value TBatt_umMin_Hi, it stabilizes (i.e. , it stops rising) while the other signals maintain their previous values (the signal Need_More_Pwr remains asserted and the gain factor Gain remains equal to Gain nc). At time ts, the signal Need_More_Pwr is de-asserted (changes from one to zero), the gain factor Gain changes from the positive value Gainjnc to zero, and the value of the minimum temperature TBatt_ceii_Min_Drvj_Tgt remains equal to the upper limit value TBatt_umMin_Hi. At time t4, while the signal Need_More_Pwr remains deasserted (equal to zero), the time interval of duration AtDeiay_2 expires, so the selector S2 produces as output the value Gain_Dec and the gain factor Gain changes from zero to the negative value Gain_Dec. As a result, the minimum temperature TBatt_ceii_Min_Drvj_ Tgt starts to decrease from the upper limit value TBatt_umMin_Hi to the lower limit value TBatt_umMin_Lo. At time ts, when the minimum temperature TBatt_ceii_Min_Drvj_Tgt reaches the lower limit value TBatt_umMin_Lo, it stabilizes (i.e., it stops decreasing) while the other signals maintain their previous values (the signal Need_More_Pwr remains deasserted and the gain factor Gain remains equal to Gain_Dec).

[0034] The functioning of the operation block 104 for determining the actual value of the minimum allowable temperature TBatt_ceii_Min_Tgt will now be described with reference to Figures 7 and 8.

[0035] As illustrated in Figure 7, in a first phase of the operation block 104 a numerical value Ratt_Batt_wu is determined which indicates the (estimated) ratio between the (expected) time in which the battery heating is inactive and the total (expected) time of the driving mission. In particular, with operations 702 and 704 the time interval AtBatt_wu necessary for the battery heating is computed. With operation 702, the difference between the minimum temperature TBatt_ceii_Min_Drv_ Tgt computed with the operation block 102 and the actual battery temperature TBatt_ceii (which can be detected by means of appropriate sensors of the vehicle, and received from a vehicle control unit) is computed. Operation 704 multiplies the difference just computed in step 702 by the battery thermal capacity CThrm_Batt divided by the maximum heating thermal power QHeat_Batt_Max available to heat the battery, thus obtaining the time interval AtBatt_wu. Next, operation 706 computes the difference between the remaining duration of the driving mission AtEndjviission (i.e., the time that is estimated to elapse between the current instant and the end of the current driving mission) and the time AtBatt_wu needed to heat the battery, thus obtaining the value of the time interval AtRem_Atter_Batt_wu which represents the time of the driving mission during which the battery heating will be inactive. With operations 708 and 710, the numeric value Ratt_Batt_wu that indicates the ratio between the time in which the battery heater is inactive and the total time of the driving mission is computed by dividing the maximum value chosen between AtRem_After_Batt_wu and zero by the value of the remaining duration of the driving mission AtEnd_ Mission.

[0036] As illustrated in Figure 8, in a second phase of the operation block 104 the actual value of the minimum allowable temperature TBatt_ceii_Min_Tgt is determined. Substantially, a selector S3 receives at a first input the minimum temperature TBatt_ceii_Min_Drv_ rgt computed with the operation block 102, at a second input a temperature TBatt_LimMin_saf, and a control signal Ctr, so that if the control signal Ctr is asserted (equal to one) the temperature TBatt_ceii_Min_Tgt is equal to the temperature TBatt_ceii_Min_Drv_Tgt, while if the control signal Ctr is de-asserted (equal to zero) the temperature TBatt_ceii_Min_Tgt is equal to the temperature TBatt_LimMin_saf. In particular, the temperature TBatt_LimMin_saf is the minimum constant battery temperature value that ensures that the battery can deliver a minimum power sufficient to drive the vehicle in safety mode, and can therefore be a constant value stored in a vehicle control unit. Qualitatively, the temperature value TBatt_LimMin_saf is always lower than or equal to the temperature TBatt_ceii_Min_Drv_Tgt this means that, in safety mode, a smaller amount of electrical energy is spent to heat the battery than would be spent in any other of the drive modes of the vehicle. The control signal Ctr of selector S3 is produced at the output of a logic gate OR 801 .

[0037] The first input of the logic gate OR 801 receives a binary drive mode bypass signal (or flag) ByPassDrvMod, which is asserted (equal to one) or deasserted (equal to zero) as a function of a characteristic map 804 (e.g., implemented by an analytic, piecewise or look-up table function) as a function of the value of the parameter DriveMod that indicates the current drive mode selected by the driver of the vehicle. Indicatively, the binary signal (or flag) ByPassDrvMod is asserted if a performance-oriented (aggressive) drive mode is currently selected, in which it is appropriate to bring the battery to a higher temperature that allows for high performance (e.g., in the “sport”, “race max boost”, “race fast lap” and “race endurance” modes), while it is de-asserted if a more relaxed drive mode is currently selected, in which it is appropriate to reduce energy consumption to increase the vehicle autonomy (e.g., in the “GT” and “max range” modes). Substantially, therefore, if a more performance-oriented drive mode is selected, the signal ByPassDrvMod forces, via the logic gate OR 802, the assertion of the signal Ctr, and consequently the temperature TBatt_ceii_Min_Tgt is set equal to the temperature TBatt_ceii_Min_Drv_ Tgt which is determined as a function of the drive mode.

[0038] The second input of the logic gate OR 802 receives a binary signal (or flag) from the output of a set-reset (SR) flip-flop 806. Substantially, the flip-flop 806 is set (by asserting the signal at the set input S of the flip-flop, produced by a comparator 808) when the numeric value Ratt_Batt_wu (which indicates the ratio of the time in which the battery heater is inactive to the total time of the driving mission) is higher than or equal to a certain higher threshold Ratt_Ht, and is reset (by asserting the signal at the reset input R of the flip-flop, produced by a comparator 810) when the numeric value Ratt_Batt_wu is lower than or equal to a certain lower threshold Ratt_Lo. So, substantially, comparators 808 and 810 together with the set-reset flip-flop 806 behave overall as a hysteretic comparator, which asserts the second input signal of the logic gate OR 802 when the value Ratt_Batt_wu rises above the higher threshold Rattj-a and de-asserts the second input signal of the logic gate OR 802 when the value Ratt_Batt_wu falls below the lower threshold Ratt_Lo.

[0039] Therefore, the set of operations illustrated in Figure 8 substantially has the effect of setting the temperature TBatt_ceii_Min_Tgt to the value of the temperature TBatt_ceii_Min_Drv_Tgt if a performance-oriented drive mode is selected (first input of the logic gate OR 802) or if the time during which the battery heater is inactive is long (second input of the logic gate OR 802), or setting the temperature TBatt_ceii_Min_Tgt to the value of the temperature TBatt_LimMin_saf if the time during which the battery heater is inactive is short, which may happen for example if the trip is short compared to the time needed for the vehicle “warm-up”.

[0040] Therefore, as can be seen from the preceding description, the method 10 of determining the value of the minimum allowable temperature of the battery cells TBatt_ceii_Min_ Tgt described here is substantially divided into two phases, as also exemplified in the block diagram of Figure 9: in phase 102, a value of the minimum allowable temperature TBatt_ceii_Min_Drv_Tgt associated to the drive mode currently used is defined instant by instant, taking into account the current drive mode, the state of charge of the battery and the instantaneous overall power demand; and in phase 104, an actual value of the minimum allowable temperature TBatt_ceii_Min_Tgt is defined instant by instant, taking into account the value of minimum allowable temperature associated to the current drive mode and other corrective parameters that take into account the estimated residual duration of the driving mission and the ratio between the time in which the battery heating system is inactive and the total time of the driving mission.

[0041] Thanks to the instant invention, it is possible to improve the temperature management of the cells of the traction battery also as a function of the drive mode selected by the driver, which allows: obtaining good vehicle performance by increasing the minimum allowable temperature of the battery as a function of the driving mission, and increasing the range of the vehicle by reducing the use of the battery heating system as a function of the driving mission.

[0042] Of course, the details of construction and the embodiments may be widely varied with respect to what is described and illustrated without departing from the scope of the invention as defined by the attached claims.

Claims

CLAIMS1. A method (10) of determining the minimum allowable temperature of the cells of a traction battery of a vehicle with electric propulsion unit during use of the vehicle, the method comprising: determining (102) a first value of minimum allowable temperature (TBatt_ceii_Min_Drv_Tgt) associated to a currently selected drive mode, as a function of the value of a first input parameter (DriveMod) that indicates the currently selected drive mode, the value of a second input parameter (SOC) that indicates the state of charge of said traction battery, the value of a third input parameter (PDrvTgtRaw) that indicates the power requested by the driver of the vehicle to the propulsion unit, and the value of a fourth input parameter (Peons) that indicates the power absorbed by the auxiliary electrical loads of the vehicle; and determining (104) an actual value of minimum allowable temperature (TBatt_ceii_Min_Tgt) as a function of said first value of minimum allowable temperature (TBatt_ceii_Min_Drv_Tgt), the value of said first input parameter (DriveMod), and the values of one or more further input parameters selected amongst:- a fifth input parameter (QHeat_Batt_Max) that indicates the maximum heating power deliverable for heating said traction battery;- a sixth input parameter (TBatt_ceii) that indicates the current temperature of said traction battery; and- a seventh input parameter (AtEndjviission) that indicates the remaining duration of the current driving mission.

2. A method (10) according to claim 1 , wherein the step of determining (102) said first value of minimum allowable temperature ( TBatt_Cell_Min_Drv_Tgt) COfTI prises: selecting, as a function of the value of said first input parameter (DriveMod), a respective first correlation map (302) between the state of charge (SOC) of the traction battery and a higher threshold temperature ( Batt_LimMin_Hi), wherein said higher threshold temperature (TBatt_umMin_Hi) increases as the state of charge (SOC) increases; selecting, as a function of the value of said first input parameter (DriveMod), a respective second correlation map (304) betweenthe state of charge (SOC) of the traction battery and a lower threshold temperature (TBatt_umMin_Lo), wherein said lower threshold temperature ( TBatt_umMin_Lo) increases as the state of charge (SOC) increases and, for the same state of charge (SOC), is lower than said higher threshold temperature ( TBatt_umMin_Hi)', applying said selected first correlation map (302) to the value of said second input parameter (SOC) to determine (102) said higher threshold temperature ( TBatt_umMin_Hi) and applying said selected second correlation map (304) to the value of said second input parameter (SOC) to determine (102) said lower threshold temperature ( TBatt_umMin_Lo) determining (306) a first difference (ATBattj mwn) between said higher threshold temperature ( TBatt_umMin_Hi) and said lower threshold temperature ( TBatt_umMin_Lo)', computing (308) the product between said first difference (ATBatt_umMin) and a gain factor ( Gain) to determine a corrective temperature factor, and summing (308) said corrective temperature factor to a previous value of said first value of minimum allowable temperature ( TBatt_ceii_Min_Drv_Tgt) to determine a current value of said first value of minimum allowable temperature (TBatt_ceii_Min_Drv_Tgt), wherein said first value of minimum allowable temperature (TBatt_ceii_Min_Drv_Tgt) is limited at the high end by said higher threshold temperature (TBatt_umMin_Hi) and at the low end by said lower threshold temperature ( TBatt_LimMin_Lo).

3. A method (10) according to claim 2, wherein said higher threshold temperature (TBatt_umMin_Hi) guarantees that the electric powertrain of the vehicle can provide a nominal power equal to a nominal propulsive power associated to the currently selected drive mode (DriveMod), and said lower threshold temperature (TBatt_LimMin_Lo) does not guarantee that the electric powertrain of the vehicle can provide said nominal power equal to the nominal propulsive power associated to the currently selected drive mode (DriveMod).

4. A method (10) according to claim 2 or claim 3, comprising determining said gain factor ( Gain) by applying the following steps: adding up (402) said third input parameter (PorvTgtRaw) and said fourth input parameter (Peons) to determine an instantaneous total power (PReq_Tot) requested to said traction battery;selecting a further correlation map (404) between the state of charge (SOC) of the traction battery and the limit power (PBattum_Lo) deliverable by the traction battery when the traction battery is at said lower threshold temperature (TBatt_umMin_Lo), wherein said deliverable limit power (PBattum_Lo) increases as the state of charge (SOC) increases; applying said selected further correlation map (404) to the value of said second input parameter (SOC) to determine said deliverable limit power (PBattLim_Lo) asserting (406) a first control variable (Need_More_Pwr) if said instantaneous total power (PReq_Tot) is higher than said deliverable limit power (PBattum_Lo) and de-asserting (406) said first control variable (Need_More_Pwr) otherwise; in response to assertion (DL1 , S1 ) of said first control variable (Need_More_Pwr), setting said gain factor (Gain) to a positive gain value (Gain_lnc)', and in response to de-assertion (DL2, S2) of said first control variable (Need_More_Pwr), setting said gain factor (Gain) to a negative gain value (Gain_Dec).

5. A method (10) according to claim 4, wherein said gain factor (Gain) is set to said positive gain value (Gain_lnc) with a certain first delay (AtDeiay_i) with respect to assertion (DL1 , S1 ) of said first control variable (Need_More_Pwr), and said gain factor (Gain) is set to said negative gain value (Gain_Dec) with a certain second delay (AtDeiay_2) with respect to deassertion (DL2, S2) of said first control variable (Need_More_Pwr).

6. A method (10) according to any of the previous claim , wherein the step of determining (104) said actual value of minimum allowable temperature (TBatt_ceii_Min_Tgt) comprises: computing (702, 704, 706, 708, 710) a first numerical parameter (Ratt_Batt_wu) indicative of the ratio between an estimated time during which the battery heating is inactive and the estimated total time of the driving mission (AtEnd_Mission),' asserting (802) a second control variable (Ctr) in response to said first input parameter (DriveMod) indicating (804) that the currently selected drive mode is a performance-oriented one, and / or in response to said first numerical parameter (Ratt_Batt_wu) being higher than or equal to(806, 808) a certain upper threshold value (Ratt_Hi)’, de-asserting (802) said second control variable ( Ctr) in response to said first input parameter (DriveMod) indicating (804) that the currently selected drive mode is a range-oriented one and said first numeric parameter (Ratt_Batt_wu) being lower than or equal to (806, 810) a certain lower threshold value (Rattj.o) in response to said second control variable ( Ctr) being asserted, setting (S3) said actual value of minimum allowable temperature ( TBatt_ceii_Min_Tgt) equal to said first value of minimum allowable temperature ( TBatt_Cell_Min_Drv_Tgt)', and in response to said second control variable ( Ctr) being deasserted, setting (S3) said actual value of minimum allowable temperature ( TBatt_ceii_Min_Tgt) equal to a predetermined temperature value ( TBatt_LimMin_saf) lower than or equal to said first value of minimum allowable temperature ( TBatt_ceii_Min_Drv_Tgt), said predetermined temperature value ( TBatt_umMin_saf) being so as to guarantee that said traction battery can deliver a minimum power sufficient to drive the vehicle in a safety drive mode.

7. A method (10) according to claim 6, wherein the step of computing (702, 704, 706, 708, 710) said first numerical parameter (Ratt_Batt_wu) comprises: computing (702) a first difference between said first value of minimum allowable temperature (TBatt_ceii_Min_Drv_Tgt) and said sixth input parameter (TBatt_ceii) multiplying (704) said first difference by a stored value of the thermal capacity (Crhrm_Batt) of said traction battery, and dividing (704) said product by said fifth input parameter ( QHeat_Batt_Max) to estimate a first time interval (AtBatt_wu) necessary for heating said traction battery; computing (706) a second difference between said seventh input parameter (AtEndjviission) and said first time interval (AtBatt / vu) to estimate a second time interval (AtRem_After_Batt_wu) indicative of an estimated time during which heating of the traction battery will be inactive; and dividing (710) said second time interval (AtRem_After_Batt_wu) by said seventh input parameter (AtEndjviission) to determine said first numerical parameter (Ratt_Batt_wu), said first numerical parameter (Ratt_Batt_wu) being limited (708) to zero at the low end.

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