A method for the derating of performance of an electric traction motor of one or more traction units of an electrical powertrain of a vehicle

Abstract

There is described a method for the derating of performance of one or more electric traction motors of an electrical powertrain of a vehicle in conditions of full use of the thermal cooling power available for the powertrain, which operates as a function of the real mission profile of the vehicle and of the global conditions of the traction units.

Description

[0001] "A method for the derating of performance of an electric traction motor of one or more traction units of an electrical powertrain of a vehicle"

[0002] ★★★★

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention relates to vehicles with an electrical powertrain, specifically to BEVs . The invention was developed with particular reference to the derating of performance of one or more electric traction motors of the electrical powertrain in conditions of full use of the thermal cooling power, in order to avoid damages to the traction components due to the temperature .

[0006] Prior Art

[0007] In vehicles with an electrical powertrain, particularly in BEVs, the thermal management of the powertrain is especially focused on the cooling of the high-voltage battery and of the traction components which compose the single traction units of the powertrain. The need of cooling arises from the natural tendency to a thermal power dissipation of the traction components (and of the battery itself, especially under given conditions). The cooling of the powertrain is so critical for the functional integrity of the powertrain itself that, in the case of full use of the available thermal cooling power, it is necessary to implement actions for controlling and reducing the thermal power rejected by the traction components, so as to protect the latter components against overtemperature events and against the consequent damages, essentially by derating the propulsion and regeneration power of the one or more electric traction motors of the electrical powertrain.

[0008] In the prior art, however, such a need is met only approximately, without taking into account the real mission profile of the vehicle and the global conditions of the traction units.

[0009] Object of the Invention

[0010] The invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the invention consists in providing a method for the derating of performance of one or more electric traction motors of an electrical powertrain of a vehicle in conditions of full use of the thermal cooling power which is available for the powertrain, such a method operating as a function of the real mission profile of the vehicle and of the global conditions of the traction units.

[0011] Summary of the Invention

[0012] The object of the invention is achieved by a method having the features set forth in the annexed claims, which form an integral part of the technical disclosure provided herein in relation to the invention.

[0013] Brief Description of the Figures

[0014] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only, and wherein:

[0015] Figures 1 to 8 schematically show some configurations of an electrical powertrain whereon it is possible to implement the method according to the invention,

[0016] - Figure 9 is a block diagram representative of the method according to the invention,

[0017] - Figure 10 shows an aspect of the method according to the invention,

[0018] Figures 11, 11A, 11B, 11C comprise diagrams illustrating a step of the method according to the invention,

[0019] Figures 12, 12A, 12B, 12C comprise diagrams illustrating a further step of the method according to the invention, Figures 13, 13A, 13B, 13C comprise diagrams illustrating a still further step of the method according to the invention,

[0020] Figures 14, 14A, 14B, 14C comprise diagrams illustrating an even further step of the method according to the invention.

[0021] Detailed Description

[0022] As a preliminary discussion, Figures 1 to 8 schematically show some configurations of an electrical powertrain of a vehicle V, whereon it is possible to implement the method according to the invention. Each configuration of electrical powertrain comprises one or more traction units, each comprising an electric traction motor, an inverter operatively connected to the electric traction motor, and a transmission which connects the electric traction motor to one or more drive wheels, and which comprises a transmission lubricant.

[0023] The detailed description of the method will be set forth with reference to the most general possible configuration shown in Figure 1, and it may be applied to all further configurations by simply adapting the inferences to the number of traction units / electric traction motors on board the vehicle V.

[0024] The one or more electric motors are operatively associated with a front axle and / or a rear axle of the vehicle, or to respective single wheels of one and the same axle, as a function of the number and of the characteristics of the traction motors. In this way, there is a power flow exchanged between each motor and (at least) one axle or (at least) one wheel of the vehicle for the traction of the vehicle itself.

[0025] The phrase "power flow" denotes both a power flow into the electric motor (from a battery BT), i.e. a flow which originates a driving action of the same motor, and a power flow leaving the electric motor (and entering the battery BT), i.e. a flow originated when the electric motor is subjected to a drag load (braking or slowing down due to the inertia of the vehicle) and operates as an electric generator. The reference Pn in the Figures (with n= 1, 2, 3, 4 in the presently considered embodiments) represents the general power flow associated with the n-th motor.

[0026] For simplicity, the vehicle configurations schematically shown in the Figures envisage the presence of a single battery for supplying each electric motor, but the method may be applied irrespective of the number or the configuration of the batteries, and irrespective of the association thereof with the one or more electric motors of the powertrain.

[0027] Figure 1 shows a first configuration of a powertrain with four motors, comprising four traction units. Specifically, the powertrain of Figure 1 comprises a first electric motor Ml operatively associated with a rear left wheel RL of the vehicle, a second electric motor M2 operatively associated with a rear right wheel RR of the vehicle, a third electric motor M3 operatively associated with a front left wheel of the vehicle, and a fourth motor M4 operatively associated with a front right wheel of the vehicle V. This means that each electric motor M1-M4 delivers a torque to the wheel operatively associated therewith. Each motor Ml, M2, M3, M4 is associated with a respective inverter, whereas the transmission which connects each motor Ml, M2, M3, M4 to the corresponding (single) drive wheel generally corresponds to a direct drive transmission or, more preferably, to a transmission comprising a reduction gear. Each of the four traction units thus defined comprises one of the motors Ml, M2, M3, M4, the respective inverter and the respective transmission.

[0028] The electric motors Ml, M2, M3, M4 are supplied by a single battery (or battery pack) BT. In the schematic representation of Figure 1, the arrows in solid lines indicate a power flow into the motors Ml, M2, M3, M4 from the battery BT (power absorbed by the motors), whereas the arrows in dashed lines indicate a power flow leaving the motors Ml, M2, M3, M4 towards the battery BT (power generated by the motors).

[0029] Figure 2 shows a second configuration of a powertrain with three motors, comprising three traction units. The powertrain specifically comprises a first electric motor Ml operatively associated with a rear left wheel RL of the vehicle, a second electric motor M2 operatively associated with a rear right wheel RR of the vehicle, and a third electric motor M3 operatively associated with the front axle FA, thereby meaning a condition wherein the electric motor M3 delivers a torque to both the right and the left wheels FR, FL of the front axle FA. Each motor Ml, M2, M3 is associated with a respective inverter, whereas the transmission which connects each motor Ml, M2, M3 to the corresponding one or more drive wheels corresponds, for the motors Ml, M2, to a direct drive transmission or, more preferably, to a transmission including a reduction gear, and for the motor M3 it corresponds to a differential, by means of which it is connected to two drive wheels (FL and FR). Each of the three traction units thus defined comprises one of the motors Ml, M2, M3, the respective inverter and the respective transmission.

[0030] The electric motors Ml, M2, M3 are supplied by a single battery (or battery pack) BT. In the schematic representation of Figures 1, 2, the arrows in solid lines indicate a power flow into the motors Ml, M2, M3 from the battery BT, whereas the arrows in dashed lines indicate a power flow leaving the motors Ml, M2, M3 towards the battery BT. Figure 3 substantially corresponds to a configuration mirroring the configuration of Figure 2, with a first electric motor Ml operatively associated with a front left wheel FL, a second electric motor M2 operatively associated with a front right wheel FR, and a third electric motor M3 operatively associated with a rear axle RA.

[0031] Figure 4 and Figure 5 show a vehicle V with a powertrain with a single motor, including a single electric motor Ml operatively associated with the rear axle only (Figure 3) or with the front axle only (Figure 5). In both cases, a single traction unit is present which comprises the motor Ml, an inverter associated with the motor Ml, and a transmission which connects the motor Ml to the pair of drive wheels of the axle by means of a differential.

[0032] Referring to the Figures 6, 7, they show a vehicle V with a powertrain with two motors, respectively comprising :

[0033] - a first electric motor Ml operatively associated with a rear left wheel RL of the vehicle, and a second electric motor M2 operatively associated with a rear right wheel RR of the vehicle (Figure 6), or

[0034] - a first electric motor Ml operatively associated with a front left wheel FL of the vehicle, and a second electric motor M2 operatively associated with a front right wheel FR of the vehicle (Figure 7).

[0035] The electric motors Ml, M2 are supplied by a single battery (or battery pack) BT and, as in the schematic representation of the previous Figures, the arrows in solid lines indicate a power flow into the motors Ml, M2 from the battery BT, whereas the arrows in dashed lines indicate a power flow leaving the motors Ml, M2 towards the battery BT.

[0036] Each motor Ml, M2 is associated with a respective inverter, whereas the transmission which connects each motor Ml, M2 to the corresponding (single) drive wheel corresponds to a direct drive transmission or, more preferably, to a transmission comprising a reduction gear. Each of the two traction units thus defined comprises one of the motors Ml, M2, the respective inverter and the respective transmission.

[0037] Figure 8 represents a vehicle V with a powertrain with two motors, comprising a first electric motor Ml operatively associated with the rear axle RA, and a second electric motor M3 associated with the front axle FA. Each motor Ml, M3 is associated with a respective inverter, whereas the transmission which connects each motor Ml, M3 to the corresponding pair of drive wheels of the axle comprises a differential. Each of the two traction units thus defined comprises one of the motors Ml, M3, the respective inverter and the respective transmission .

[0038] As stated in the foregoing, the description which follows is set forth with reference to the powertrain of Figure 1, and therefore the employed references apply to said Figure.

[0039] Referring to Figures 9 and 10, according to the invention there is defined a method for the derating of performance of an electric traction motor of one or more traction units of an electrical powertrain of the vehicle V, wherein each traction unit comprises an electric traction motor Ml, M2, M3, M4, an inverter operatively connected to the traction motor, and a transmission which connects the electric traction motor to one or more drive wheels, and which comprises a transmission lubricant, wherein the method (reference 1, Figure 9) includes:

[0040] - defining (block 2, Figure 9), for each traction unit, a first limit of electrical power PTrc Prp Limi, Plrc_Prp_Lim_2r PTrc_Prp_Lim_3r PTrc_Prp_Lim_4 that Can be absorbed by the electric traction motor Ml, M2, M3, M4 under propulsion conditions as a function of a temperature TMot i, TMot2< TMot3, TMot4 of the electric traction motor Ml, M2, M3, M4, of a temperature TInvi, TInv 2, TInv 3, TInv 4of the inverter, of a temperature Ton GBX I, Ton GBX I, Ton GBX 3, Ton GBX 4 of the transmission lubricant, and of a drive mode DrvMode currently selected for powertrain control,

[0041] - defining, for each traction unit, a second limit of electrical power PTrc_Rgn_Lim_l / PTrc_Rgn_Lim_2 / PTrc_Rgn_Lim_3r Pirc Rgn Lim 4 that can be delivered by the electric traction motor Ml, M2, M3, M4 under regeneration conditions as a function of the temperature TMoti, TMot2, TMot3, TMot4 of the electric traction motor Ml, M2, M3, M4, of the temperature TInv1, TInv 2, TInv 3, TInv4 of the inverter, of the temperature TOII_GBX_I / TOII_GBX_2 / TOII_GBX_3 / TOH_GBX_4 of the transmission lubricant, and of the drive mode DrvMode currently selected for powertrain control,

[0042] - defining, for the set of the traction units, a third limit of electrical power PTrc TotprpLim that can be absorbed by the set of the one or more electric traction motors Ml, M2, M3, M4 under propulsion conditions as a function of the highest of the temperature values TMot1, TMotTMot3, TMot4 of each electric traction motor Ml, M2, M3, M4, of the highest of the temperature values Tinv 1, TInv2, TInv 3, TInv4 of each inverter, of the highest of the temperature values TOH_GBX_I, TOH_GBX_2, TOH_GBX_3, Ton GBX 4 of each transmission lubricant, and of the drive mode DrvMode currently selected for powertrain control,

[0043] - defining, for the set of the traction units, a fourth limit of electrical power PTrc Tot RgnLim that can be delivered by the set of the one or more electric traction motors Ml, M2, M3, M4 under regeneration conditions as a function of the highest of the temperature values of each electric traction motor TMot1, TMot2, TMot3, TMot4, of the highest of the temperature values TInvi, TInv 2, Tinv3, TInv4 of each inverter, of the highest of the temperature values TOii_GBx_i, TOii_GBx_2, TOii_GBx_3, TOii_GBx_4 of each transmission lubricant, and of the driving mode DrvMode currently selected for powertrain control, controlling (Figure 10) the powertrain selectively according to the first limit PTrcprpLim i, PTrc_Prp_Lim_2r PTrc_Prp_Lim_3r PTrc_Prp_Lim_4r Of the SOCOnd limit PTrC—Rgn_Lim_1r PTrc_Rgn_Lim_2r PTrc_Rgn_Lim_3r PTrc_Rgn_Lim_4r Of the third limit PTrcTot PrPLim, and of the fourth limit PirC—Tot_Rgn_Lim•

[0044] Referring to Figure 10, the reference A denotes a reference temperature range, wherein there is an availability of thermal cooling power for the traction units of the powertrain, whereas the references B, C, D, E identify a first, a second, a third and a fourth temperature ranges corresponding to different operating modes for the purposes of the method according to the invention. The temperature range A ends at the lower end of the range B, and such boundary denotes the impossibility of further increasing the thermal cooling power for the powertrain of the vehicle.

[0045] The temperature range B corresponds to conditions wherein the cooling power available for the traction components can no longer be increased, but the temperatures of the traction components are still relatively low. In this temperature range a derating of the performances is operated, by individually limiting the regeneration power output by each motor Ml, M2, M3, M4 to the values PTrc_Rgn_Lim_l, PTrC—Rgn_Lim_2l PTrc_Rgn_Lim_3l ?Trc Rgn Lim 4, thus individually involving one or more motors in the intervention. It is a relatively mild intervention, since the mechanical brakes are anyway available for slowing down the vehicle.

[0046] The temperature range C, which is shown herein as superiorly adjacent to the range B, but which in general comprises at least in part temperature values higher than the temperature values of the range B (therefore, a superposition is possible), corresponds to conditions wherein (even more so) there is no longer a possibility of increasing the cooling power available to the traction components, and the temperatures of the traction components are rising. In this temperature range a further intervention of performance derating is operated, by individually limiting the propulsion power output by each motor Ml, M2, M3, M4 to the values Plrc_Prp_Lim_1r P rc_Prp_Lim_2r PprC—Prp_Lim_3r PprC—Prp_Lim_4r thUS individually involving one or more motors in the intervention. It is a more clearly perceivable intervention, since it affects the propulsion of the vehicle .

[0047] The temperature range D, which herein is shown superiorly adjacent to the range C, but which generally comprises, at least in part, temperature values higher than the temperature values of the range C (thus, a superposition is possible), corresponds to conditions wherein the possibility of increasing the cooling power available to the traction components is no longer possible (as for the range C), and the temperatures of the traction components are rising further. In this temperature range a larger intervention of performance derating is performed, by globally limiting the regeneration power expressed by the set of motors Ml, M2, M3, M4 to the value PTrclotRgnLim, thus involving all the motors in the intervention. It is an intervention which has certainly less impact in comparison with a limitation of propulsion, but it is heavier than the intervention implemented in the range C and it relies more heavily on the performance of the mechanical brakes for slowing down the vehicle. Finally, the temperature range E, which herein is shown as superiorly adjacent to the interval D, but which generally comprises, at least in part, temperature values which are higher than the temperature values of the range D (therefore, a superposition is possible), corresponds to conditions wherein not only the possibility of increasing the cooling power for the traction components no longer exists, but wherein the temperatures of the traction components keep on rising and approach critical values.

[0048] In this temperature range, an even further intervention of performance derating is operated, by globally limiting the propulsion power output by the set of the motors Ml, M2, M3, M4 to the value PTrclotRgnLim, thus involving all the motors in the intervention. It is therefore the most extensive intervention, since it affects the availability of propulsion power globally.

[0049] Still referring to the operational implications of the ranges B, C, D, E, it is possible to observe the following: in the intervals B and C, which involve the performance derating of a single motor under regeneration and propulsion conditions, respectively, there is at least one traction component of at least one traction unit having a temperature requiring an individual derating, since it is no longer possible to increase the cooling power available for the traction components,

[0050] - in the intervals D, E, at least one traction component of at least one traction unit has temperatures equal to or higher than the temperatures of the ranges B, C, thus it has temperatures which lead to interventions of performance derating of individual motors; as a consequence, the derating strategy needs to become collective, i.e. it needs to be extended to all traction units, specifically to all electric traction motors.

[0051] By way of example only, if for an electric traction motor it is possible to identify at 150° the temperature at which overtemperature damages occur, then the following division of the ranges B, C, D, E may apply:

[0052] - if the motor has a temperature between 120°C and 125°C, then the temperature is within range B, and therefore the regeneration power of the individual motor is limited, thus requiring more regeneration power from the other motors of the other traction units;

[0053] - if the motor has a temperature between 125°C and 130°C, then the temperature is within range C, and therefore the propulsion power of the individual motor is limited, thus requiring more propulsion power from the other motors,

[0054] - if the motor has a temperature between 130°C and 135°C, then the temperature is within range D, and therefore the regeneration power output by all the motors is limited collectively. This enables limiting the thermal power globally rejected from the electric traction motor, and therefore enables relieving the radiator dedicated to cooling the traction components themselves, thus enabling sending a lower-temperature coolant to the electric motor in more critical temperature conditions,

[0055] - finally, if the motor has a temperature between 135°C and 140°C, then the temperature is within range E, and therefore the propulsion power output by all the motors is limited collectively. Again, this enables limiting the thermal power globally rejected from the electric traction motors, i.e. it enables relieving the radiator dedicated to cooling the traction components themselves, thereby enabling sending a lower-temperature coolant to the electric motor which is in more critical temperature conditions.

[0056] Therefore, all these actions essentially aim at attempting to reduce the temperature increase of the component (in the example, one of the electric traction motors, but the same is true for an inverter and / or a transmission) in critical temperature conditions.

[0057] This being said, it is possible to observe how controlling the powertrain selectively as a function of the first limit, of the second limit, of the third limit and of the fourth limit comprises: controlling the powertrain according to the SeCOnd limit PTrc_Rgn_Lim_l, Pirc—Rgn_Lim_2l Pzrc Rgn Lim 3, Pirc Rgn Lim 4 in the first temperature range B,

[0058] - controlling the powertrain according to the first limit Prp_Lim_1r PRrc_Prp_Lim_2r PRrc_Prp_Lim_3r PRrc_Prp_Lim_4 1^ the second temperature range C, which includes at least in part temperature values higher than the temperature values of the first temperature range B, controlling the powertrain according to the fourth limit PTrcTot Rgn Lim in the third temperature range D, which includes at least in part temperature values higher than the temperature values of the second temperature range C,

[0059] - controlling the powertrain according to the third limit PprcTot prp Lim in the fourth temperature range E, which includes at least in part temperature values higher than the temperature values of the third temperature range D.

[0060] As it will be evident in the light of the description which follows, thanks to the method according to the invention it is possible to find the best compromise among the described operational modes, by considering the current drive mode DrvMode selected for powertrain control. This enables taking into account the real mission of the vehicle, whereof the drive mode DrvMode is a sufficiently reliable indicator: for example, in aggressive and sport driving modes, it is important not to excessively affect the availability of propulsion power, whereas in drive modes which aim at maximizing the driving range it is important not to excessively affect the power delivery to the high- voltage battery under regeneration conditions.

[0061] With reference to the following Figures, there will now be detailed the fashions for determining the power limits in the preferred embodiment of the method according to the invention.

[0062] Referring to Figure 11, diagram 10, the definition - for each traction unit - of the first limit PTrcprpLim i (the index "i" replaces the index numbers for generalization and for brevity of notation) of the electrical power that can be absorbed by the i-th electric traction motor under propulsion conditions includes determining the lowest (block 12, MIN) of:

[0063] - a limit of electrical power PInv Prp Lim± that can be absorbed by the i-th electric traction motor under propulsion conditions to avoid an overtemperature condition of the inverter,

[0064] - a limit of electrical power PMot PrpLim i that can be absorbed by the i-th electric traction motor under propulsion condition in order to avoid an overtemperature condition of the i-th electric traction motor itself,

[0065] - a limit of electrical power Pon GBX prpLim i that can be absorbed by the i-th electric traction motor under propulsion conditions in order to avoid an overtemperature condition of the transmission, in particular of the transmission lubricant thereof.

[0066] The extraction of the lowest value of the three listed values leads to obtaining a raw limit value of electrical power PTrc Prp LimRawi, which corresponds to the minimum value itself. Preferably, the definition of the first limit of electrical power PTrc Prp Lim± moreover comprises limiting a rate of time variation (block 14) of the value PTrcprpLimRaw i, thus of the lowest value extracted at block 12. This essentially aims at avoiding abrupt variations of power availability, which would be certainly perceived by the driver and by the passengers of the vehicle, and which are generally dangerous for the dynamic balance of the vehicle.

[0067] With reference to Figure 11A, diagram 101, the limit of electrical power PInv Prp Lim± is preferably determined via a map M101 which provides the value PPnv PrpLim i by means of curves as a function of a temperature TInv± of the inverter associated with the i-th electric traction motor, and which are parameterized with respect of the currently selected drive mode DrvMode. By way of example, there are illustrated four curves parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvModeS, DrvMode4, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power PInv Prp Limi increases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is important not to affect the availability of propulsion power, and it decreases as the temperature of the inverter TInv± increases, in order to protect the component against damages due to overtemperature .

[0068] Similarly, referring to Figure 11B, diagram 102, the limit of electrical power PMot PrpLim i is preferably determined via a map M102, which provides the value Pinv prPLim i by means of curves as a function of a temperature TMoti of the i-th electric traction motor, and which are parameterized with respect to the currently selected drive mode DrvMode. Again, there are shown four curves parameterized with respect to the (corresponding) drive modes DrvModel, DrvMode2, DrvModeS, DrvMode4 already listed in the foregoing, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power PMotprpLim i increases as the aggressiveness of the drive mode increases (again, since with performance-oriented drive modes it is important not to affect the availability of propulsion power), and it decreases as the temperature of the i-th motor TMoti increases, in order to protect the i-th electric traction motor against damages due to overtemperature .

[0069] Again in a similar fashion, with reference to Figure 11C, diagram 103, the limit of electrical power Pon GBX prp Lim i is preferably determined via a map M103, which provides the value POiiGBX prpLim i by means of curves as a function of a temperature TOiiGBX i of the transmission associated with the i-th electric traction motor, and which are parameterized with respect to the currently selected drive mode DrvMode. Again, there are shown four curves parameterized with respect to the (corresponding) drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4 already listed in the foregoing, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing driving mode, DrvMode4 is the least aggressive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power Pon GBX prp Lim i increases as the aggressiveness of the drive mode increases (again, since with performance-oriented drive modes it is important not to affect the availability of propulsion power), and it decreases as the temperature of the transmission lubricant Ton GBX i increases, in order to protect the transmission against damages due to overtemperature.

[0070] With reference to Figure 12, diagram 20, the definition - for each traction unit - of the second limit Pirc Rgn Lim i (again, the index "i" replaces the reference numbers for generalization and brevity of notation) of the electrical power that can be absorbed by the i-th electric traction motor under regeneration conditions includes determining the highest (block 22, MAX - therefore the lowest in absolute value terms, since the values are negative due to the regeneration mode) of:

[0071] - a limit of electrical power PInv Rgn Lim± that can be delivered by the i-th electric traction motor under regeneration conditions in order to avoid an overtemperature condition of the inverter,

[0072] - a limit of electrical power PMot RgnLim i that can be delivered by the i-th electric traction motor under regeneration conditions in order to avoid an overtemperature condition of the i-th electric traction motor itself,

[0073] - a limit of electrical power Pon GBX Rgn Lim i that can be delivered by the i-th electric traction motor under regeneration conditions in order to avoid an overtemperature condition of the transmission.

[0074] The extraction of the highest value (again, the lowest in absolute value terms) of the three listed values leads to obtaining a raw limit value PTrcRgn LimRaw i corresponding to the highest value itself. Preferably, the definition of the second limit of electrical power Pirc Rgn Lim i moreover comprises limiting a rate of time variation (block 24) of the value Pirc Rgn LimRaw v i.e. of the highest value extracted at block 22. This has substantially the purpose of avoiding abrupt variations of regeneration power which are potentially perceivable by the driver and by the passengers of the vehicle, and which are generally dangerous for the dynamic balance of the vehicle.

[0075] With reference to Figure 12A, diagram 201, the limit of electrical power PInv Rgn Lim± is preferably determined via a map M201, which provides the value PinvRgnLim i by means of curves as a function of the temperature TInv± of the inverter associated with the i-th electric traction motor, and which are parameterized with respect to the currently selected drive mode DrvMode. By way of example, once again, four curves are shown which are parameterized with respect to the drive modes DrvModel, DrvMode2, DrvModeS, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the absolute value of the limit of power Pinv Rgn Lim i (it should be noted that, since it is regeneration power, it always has negative values) decreases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, whereas with drive modes which aim at maximizing the driving range, on the contrary, it is fundamental not to affect the availability of regeneration power. The absolute value of the power limit PinvRgn Lim i, moreover, decreases as the temperature of the inverter Tinvi increases, in order to protect the latter component against damages due to overtemperature.

[0076] Similarly, with reference to Figure 12B, diagram 202, the limit of electrical power PMotRgnLim i is preferably determined via a map M202 which provides the value PMotRgn Lim i by means of curves as a function of a temperature TMoti of the i-th electric traction motor, and which are parameterized with respect to the currently selected drive mode DrvMode. Again, four curves are shown which are parameterized with respect to the (corresponding) drive modes DrvModel, DrvMode2, DrvModeS, DrvMode4 already listed in the foregoing, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel e is the most aggressive and highest-performing drive mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the absolute value of the power limit PMotRgnLim i decreases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, whereas with drive modes which aim at achieving the maximum driving range, on the contrary, it is fundamental not to affect the availability of regeneration power. The absolute value of the limit of power PMot RgnLim v moreover, decreases as the temperature of the inverter TMoti increases, in order to protect the i-th electric traction motor against damages due to overtemperature.

[0077] Again, similarly, referring to Figure 12C, diagram 203, the limit of electrical power Pon GBX RgnLim i is preferably determined via a map M203 which provides the value PoilGBX RgnLim i by means of curves as a function of the temperature TOiiGBX i of the transmission associated with the i-th electric traction motor, and which are parameterized with respect to the currently selected drive mode DrvMode. Again, four curves are shown which are parameterized with respect to the (corresponding) drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4 already listed in the foregoing, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the absolute value of the limit of power Pon GBX RgnLim i decreases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, whereas with drive modes which aim at maximizing the driving range, on the contrary, it is fundamental not to affect the availability of regeneration power. The absolute value of the limit of power Pon GBX RgnLim i, moreover, decreases as the temperature Ton GBX i of the transmission lubricant increases, in order to protect the transmission against damages due to overtemperature.

[0078] Referring to Figure 13, diagram 30, the definition - for the set of the traction units - of the third limit Pirc Tot prPLim (the index "1" is absent, since the limit generally refers to the whole set of traction units) of electrical power that can be absorbed by the electric traction motors of the set of traction units includes determining the lowest value (block 32, MIN) of:

[0079] - a limit of electrical power PInv Tot PrpLim that can be absorbed by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units under propulsion conditions in order to avoid an overtemperature condition of the respective inverters,

[0080] - a limit of electrical power PMotTot prpLim that can be absorbed by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units under propulsion conditions in order to avoid an overtemperature condition of each of the electric traction motors,

[0081] - a limit of electrical power POiiTot GBX prPLim that can be absorbed by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units under propulsion conditions in order to avoid an overtemperature condition of the respective transmissions.

[0082] The extraction of the lowest value of the three listed values leads to obtaining a global raw limit value Pirc Tot prPLimRaw corresponding the lowest value itself. Preferably, the definition of the third limit of electrical power PTrc TotprpLim moreover comprises limiting a rate of time variation (block 34) of the value Pprc Tot prp LimRaw, i.e. of the lowest value extracted at block 32. The purpose thereof is avoiding abrupt variations of power availability, which would certainly be perceived by the driver and by the passengers of the vehicle, and which are generally dangerous for the dynamic balance of the vehicle.

[0083] Referring to Figure 13A, diagram 301, the limit of electrical power PInv TotprpLim is preferably determined via a map M301, which provides the value Pinvnt prpLim by means of curves as a function of the highest (block 3010, MAX) of the temperature values TInvi, TInv 2, TInv 3, TInv4 of each inverter respectively associated with the electric traction motor Ml, M2, M3, M4, which are parameterized with respect to the currently selected drive DrvMode. In other words, the temperature data item input into the map M301 corresponds to the data item of the inverter in more critical temperatures.

[0084] By way of example, as in the previous diagrams, four curves are shown which are parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, which are mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power PInv Totprp Lim increases as the aggressiveness of the drive mode increases, since with performance- oriented drive modes it is important not to affect the availability of propulsion power, and it decreases as the highest value among the temperatures TInvi, TInv 2, Tinv3, TInv4 increases, thus it decreases as the temperature of the inverter in the most critical conditions increases, in order to protect the component against damages due to overtemperature.

[0085] Referring to Figure 13B, diagram 302, the limit of electrical power PMot Tot prpLim is preferably determined, in a similar fashion, via a map M302 which provides the value PMotTot prPLim by means of curves as a function of the highest (block 3020, MAX) of the temperature values TMoti, TMot2, TMot3, TMot4 of each electric traction motor Ml, M2, M3, M4, which curves are parameterized with respect to the currently selected drive mode DrvMode. In other words, the temperature data item input into the map M302 corresponds to the data item of the electric traction motor Ml, M2, M3, M4 in more critical temperature conditions.

[0086] By way of example, in the same way as in the previous diagrams, four curves are shown which are parametrized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power PMotTot prpLim increases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is important not to affect the availability of propulsion power, and it decreases as the highest value among the temperatures TMoti, TMot2, TMot3, TMot4 increases, thus it decreases as the temperature of the electric traction motor (Ml, M2, M3, M4) in the most critical conditions increases, in order to protect the component against damages due to overtemperature .

[0087] Referring to Figure 13C, diagram 303, the limit of the electrical power Pon GBX Tot prpLim is preferably determined, in a similar fashion, via a map M303 which provides the value POiiGBX Tot prpLim by means of curves as a function of the highest (block 3030, MAX) of the temperature values TOii_GBx_i, Toii_GBx_2, Toii_GBx_3, Toii_GBx_4 of each transmission lubricant of the transmissions which are respectively associated with the electric motors Ml, M2, M3, M4, which curves are parameterized with respect to the currently selected drive mode DrvMode. In other words, the temperature data item input into the map M303 corresponds to the data item of the transmission the transmission lubricant whereof is in more critical temperature conditions.

[0088] By way of example, in the same way as in the previous diagrams, four curves are shown which are parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power Pon GBX Tot prPLim increases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is important not to affect the availability of propulsion power, and it decreases as the highest value among the temperatures Toii-GEX-i, Toii_GBx_2r Toii_GBx_3 / TOII_GBX_4 increases, thus it decreases as the temperature of the transmission lubricant in the most critical conditions increases, in order to protect the transmission against damages due to overtemperature . Referring to Figure 14, diagram 40, the definition - for the set of the traction units - of the fourth limit Pirc ot Rgn Lim (once again, the index "i" is absent, since the limit generally regards the set of traction units) of the electrical power that can be delivered by the electric traction motors of the set of the traction units under regeneration conditions includes determining the highest (block 42, MAX - therefore, the lowest in absolute value terms, the values being negative due to the regeneration mode) of:

[0089] - a limit of electrical power PInv Tot RgnLim that can be delivered by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units in regeneration conditions, in order to avoid an overtemperature condition of the respective inverters,

[0090] - a limit of electrical power PMotTot Rgn Lim that can be delivered by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units in regeneration conditions, in order to avoid an overtemperature condition of each of the electric motors themselves,

[0091] - a limit of electrical power Pon Tot GBX RgnLim that can be delivered by the electric traction motors Ml, M2, M3, M4 (generally, by the one or more electric traction motors) of the set of the traction units in regeneration conditions, in order to avoid an overtemperature condition of the respective transmissions.

[0092] The extraction of the lowest value of the three listed elements leads to obtaining a global raw limit value PTrc Tot Rgn LimRaw corresponding to the lowest value itself. Preferably, the definition of the third limit of electrical power PTrc TotRgnLim moreover comprises limiting a rate of time variation (block 44) of the value Pirc Tot Rgn LimRaw, i.e. of the lowest value extracted at the block 42. This essentially aims at avoiding abrupt variations of availability of power, which would certainly be perceived by the driver and by the passengers of the vehicle, and which are generally dangerous for the dynamic balance of the vehicle.

[0093] Referring to Figure 14A, diagram 401, the limit of electrical power PInv Tot RgnLim is preferably determined via a map M401, which provides the value PinvTot Rgn Lim by means of curves as a function of the highest (block 4010, MAX) of the temperature values TInvi, TInv 2, TInv 3, TInv 4of each inverter associated, respectively, with the electric traction motor Ml, M2, M3, M4, and which curves are parameterized with respect to the currently selected drive mode DrvMode. In other words, as has been observed with respect to Figure 13A, the temperature data item input into map M401 corresponds to the data item of the inverter in more critical temperature conditions.

[0094] By way of example, in the same way as in the previous diagrams, four curves are shown which are parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the absolute value of the limit of power Pinv Tot Rgn Lim (it must be noted that, since it is a regeneration power, it always has negative values) decreases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, whereas with drive modes which aim at maximizing the driving range, on the contrary, it is fundamental not to affect the availability of regeneration power. The absolute value of the limit of power PinvRgnLim v moreover, decreases as the highest temperature value among TInvi, TInv 2, TInv 3, TInv4 increases, in order to protect the component against damages due to overtemperature.

[0095] With reference to Figure 14B, diagram 402, the limit of electrical power PMot TotRgnLim is preferably determined, in a similar fashion, via a map M402 which provides the value PMotTotRgnLim by means of curves as a function of the highest (block 4020, MAX) among the temperature values TMoti, TMot2, TMot3, TMot4 of each electric motor Ml, M2, M3, M4 , which curves are parameterized with respect to the currently selected drive mode DrvMode. In other words, the temperature data item input into the map M402 corresponds to the data item of the electric traction motor Ml, M2, M3, M4 in the most critical temperature conditions.

[0096] By way of example, as in the previous diagrams, four curves are shown which are parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and the highest-performing mode, DrvMode4 is the least aggressive driving mode, which aims at maximizing the driving range).

[0097] Qualitatively, the absolute value of the limit of power PMotTotRgnLim (it should be noted that, since it is a regeneration power, it always has negative values) decreases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, whereas with drive modes which aim at maximizing the driving range, on the contrary, it is fundamental not to affect the availability of regeneration power. The absolute value of the limit of power PMotRgnLim i, moreover, decreases as the maximum temperature value among TMot1, TMot2, TMot3, TMot4 increases, in order to protect the component against damages due to overtemperature .

[0098] Qualitatively, the absolute value of the limit of power PMototRgnLim increases as the aggressiveness of the drive mode increases, since with performance-oriented drive modes it is unimportant to affect the regeneration power, and it decreases as the highest value among the temperatures TMoti, TMot2, TMot3, TMot4 increases, thus it decreases as the temperature of the electric traction motor in the most critical conditions increases, in order to protect the component against damages due to overtemperature .

[0099] With reference to Figure 14C, diagram 403, the limit of electrical power P0ii_GBx_Tot_Rgn_Lim is preferably determined, in a similar fashion, via a map M403 which provides the value PoiiGBX TotRgnLim by means of curves as a function of the highest (block 4030, MAX) among the temperature values TOii_GBx_i, Toii_GBx_2, Toii_GBx_3, Toii_GBx_4 of each transmission lubricant of the transmissions which are respectively associated with the electric motors Ml, M2, M3, M4, which curves are parameterized with respect to the currently selected drive mode DrvMode. In other words, the temperature data item input into map M403 corresponds to the data item of the transmission the transmission lubricant whereof is in the most critical temperature conditions.

[0100] By way of example, as in the previous diagrams, four curves are shown which are parameterized with respect to corresponding drive modes DrvModel, DrvMode2, DrvMode3, DrvMode4, mentioned in a decreasing order of aggressiveness (therefore, DrvModel is the most aggressive and highest-performing mode, DrvMode4 is the least aggressive drive mode, which aims at maximizing the driving range). Qualitatively, the value of the limit of power Pon GBX TotRgnLim increases as the aggressiveness of the drive mode increases, because with performance- oriented drive modes it is unimportant to affect the regeneration power, and it decreases as the highest value among the temperatures TOH_GBX_I, TOH_GBX_2, TOH_GBX_3, Ton GBX 4 increases, thus it decreases as the temperature of the transmission lubricant in the most critical conditions increases, in order to protect the transmission from damages due to overtemperature.

[0101] Thanks to the method according to the invention, it is possible to manage the derating of performance of one or more electric traction motors of each traction unit of the electrical powertrain of a vehicle in conditions of full use of the thermal cooling power available for the powertrain, which operates as a function of the real mission profile of the vehicle (thanks to considering the current drive mode DrvMode) and of the global conditions of the traction units (thanks to taking into consideration the current temperatures of the components of each traction unit: inverter, electric traction motor and transmission). Finally, it should be noted that the method can be applied irrespective of the number and the configuration of the traction units. Also in the case of a powertrain having a single motor it is possible to implement the method according to the invention, by simply applying - in the latter case - a coincidence of the first and third and the second and fourth limit of power.

[0102] Of course, the implementation details and the embodiments may be amply varied with respect to what has been described and illustrated, without departing from the extent of the present invention as defined in the annexed claims.

Claims

CLAIMS1. A method for performance derating of a traction electric motor of one or more traction units of an electric powertrain of a vehicle, wherein each traction unit comprises the traction electric motor (Ml, M2, M3, M4), an inverter operatively connected to the traction electric motor (Ml, M2, M3, M4), and a transmission connecting the traction electric motor (Ml, M2, M3, M4) to one or more drive wheels (RL, RR, FL, FR) and including a transmission lubricant, the method including:- defining (2), for each traction unit, a first limit Of electric power (PTrc_PrP_Lim_l, PTrc_Prp_Lim_2, Pprc—prP_Lim_3 / PTrc_prP_Lim_4) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions as a function of a temperature (TMoti, TMot2, TMot3, TMot4) of the traction electric motor (Ml, M2, M3, M4), a temperature (TInv_!, TInv-2, TInv-3, TInv-4) of the inverter, a temperature (TOH_GBXJL, TOH_GBX_2, TOH_GBX_3, Ton GBX 4) of the transmission lubricant, and a drive mode (DrvMode) currently selected for powertrain control,- defining, for each traction unit, a second limitOf electric power (PTrc_Rgn_Lim_l, PTrc_Rgn_Lim_2r PTrc_Rgn_Lim_3r Pirc Rgn Lim 4) that can be delivered by the traction electric motor (Ml, M2, M3, M4) in conditions of regeneration depending on temperature (TMoti, TMot2, TMot3, TMot4) of the traction electric motor (Ml, M2, M3, M4), the temperature of the inverter (TInv r, TInv 2, TInv 3, Tinv_4), the temperature (TOH_GBX_I, TOH_GBX_2, TOH_GBX_3, Ton GBX 4) of the transmission lubricant, and the drive mode (DrvMode) currently selected for powertrain control,- defining, for the ensemble of the traction units, a third limit of electric power (PTrcTot prPLim) that can be absorbed by the ensemble of the one or more tractionelectric motors (Ml, M2, M3, M4) under propulsion conditions as a function of the highest of the temperature values (TMoti, TMot2, TMot3, TMot4) of each traction electric motor (Ml, M2, M3, M4), the highest of the temperature values (TInv1, TInv 2, TInv 3, TInv4) of each inverter, the highest of the temperature values (Toil_GBX_l1 Toil_GBX_2z Toil_GBX_3 / TOII_GBX_4) Of each transmission lubricant, and of the drive mode (DrvMod) currently selected for powertrain control,- defining, for the ensemble of the traction units, a fourth limit of electric power (PTrcTot Rgn Lim) that can be delivered by the set of one or more traction electric motors (Ml, M2, M3, M4) under regeneration conditions as a function of the highest of the temperature values of each traction electric motor (TMot1, TMot2, TMot3, TMot4), the highest of the temperature values (TInv1, TInv 2, TInv 3, Tinv 4) of each inverter, the highest of the temperature values (TOH_GBX_Ir TOH_GBX_2Z TOII_GBX_3Z TOH_GBX_4) of each transmission lubricant, and of the drive mode (DrvMod) currently selected for powertrain control, controlling (B, C, D, E) the powertrain selectively according to the first limit (Pirc prpLim 1, PTCC_Prp_Lim_2r PTrc_Prp_Lim_3r PTrc_Prp_Lim_4)r the SOCOnd limit (Pprc Rgn Lim 1 / Pirc Rgn Lim 2 / Pirc Rgn Lim 3z Pirc Rgn Lim 4), the third limit (PTrcTot prpLim), and the fourth limit (PirC—Tot_Rgn_Lim)•2. The method of claim 1, wherein said defining (2), for each traction unit, the first limit of electric pOWer (PTCC_Prp_Lim_1r PTCC_Prp_Lim_2r PTCC_Prp_Lim_3r PTCC_Prp_Lim_4) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions includes determining the lowest (12) of:- a limit of electric power (Pinv prpLim i) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions to avoid anovertemperature condition of the corresponding inverter,- a limit of electric power (PMotprpLim i) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions to avoid an overtemperature condition of the traction electric motor (Ml, M2, M3, M4) itself,- a limit of electric power (POiiGBX prpLim i) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions to avoid an overtemperature condition of the corresponding transmission, in particular of the transmission lubricant thereof.

3. The method of claim 1, wherein said defining the second limit of electric power (PTrc_Rgn_Lim_i, PTrc_Rgn_Lim_2, PTrc_Rgn_Lim_3, PTrc_Rgn_Lim_4) that can be delivered by the traction electric motor (Ml, M2, M3, M4 ) under regeneration conditions includes determining the highest (22) of:- a limit of electric power (PInvRgnLim i) that can be delivered by the traction electric motor (Ml, M2, M3, M4) in regeneration conditions to avoid an overtemperature condition of the corresponding inverter,- a limit of electric power (PMotRgnLim i) that can be delivered by the traction electric motor (Ml, M2, M3, M4) in regeneration conditions to avoid an overtemperature condition of the traction electric motor (Ml, M2, M3, M4) itself,- a limit of electric power limit (Pon GBX Rgn Lim i) that can be delivered by the traction electric motor (Ml, M2, M3, M4) in regeneration conditions to avoid an overtemperature condition of the corresponding transmission, in particular of the transmission lubricant thereof.

4. The method of claim 1, wherein said defining the third limit of electric power (PTrcTot prPLim) that can beabsorbed under propulsion conditions for the ensemble of traction units includes determining the lowest value (32) of:- a limit of electric power (PInvTot prpLim) that can be absorbed by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units under propulsion conditions to avoid an overtemperature condition of the respective inverters,- a limit of electric power (PMot Tot prpLim) that can be absorbed by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units under propulsion conditions in order to avoid an overtemperature condition of each of the traction electric motors,- a limit of electric power (P0ii_Tot_GBx_prP_Lim) that can be absorbed by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units under propulsion conditions in order to avoid an overtemperature condition of the respective transmissions, in particular of the transmission lubricants thereof.

5. The method of claim 1, wherein the definition of the fourth limit of electric power (PTrcTotRgnLim) that can be delivered under regeneration conditions for the ensemble of the traction units includes determining the highest (42) of:- a limit of electric power (PInvTot Rgn Lim) that can be delivered by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units in regeneration conditions to avoid an overtemperature condition of the respective inverters,- a limit of electric power (PMot Tot Rgn Lim) that can be delivered by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units under regeneration conditions in order to avoid anovertemperature condition of each of the traction electric motors (Ml, M2, M3, M4) themselves,- a limit of electric power (Poii_iot_GBx_Rgn_Lim) that can be delivered by the one or more traction electric motors (Ml, M2, M3, M4) of the ensemble of the traction units under regeneration conditions to avoid an overtemperature condition of the respective transmissions, in particular of the transmission lubricants thereof.

6. The method of claim 2, wherein said defining the first limit of electric power (PTrc_prP_Lim_i, PTrc_prP_Lim_2, Pprc—prP_Lim_3 / PTrc_prP_Lim_4) that can be absorbed by the traction electric motor (Ml, M2, M3, M4) under propulsion conditions further includes limiting (14) a rate of time variation of said lowest value (12).

7. The method of claim 3, wherein said defining, for each traction unit, the second limit of electric pOWer (PprC—Rgn_Lim_1r PprC—Rgn_Lim_2r PprC—Rgn_Lim_3r PprC—Rgn_Lim_4) that can be delivered by the traction electric motor (Ml, M2, M3, M4) under regeneration conditions further includes limiting (24) a rate of time variation of said lowest value (22).

8. The method of claim 4, wherein said defining, for the ensemble of the traction units, the third limit of electric power (PTrcTot prPLim) that can be absorbed by the one or more traction electric motors (Ml, M2, M3, M4) under propulsion conditions further includes limiting (34) a rate of time variation of said lowest value (32).

9. The method of claim 5, wherein said defining, for the ensemble of the traction units, the fourth limit of electrical power (PTrcTot Rgn Lim) that can be delivered by one or more traction electric motors (Ml, M2, M3, M4) under regeneration conditions further includes limiting (44) a rate of time variation of said highest value (42).

10. The method of claim 1, wherein said controlling the powertrain selectively according to the first limit (Pirc Prp Lim 1 / Pirc Prp Lim 2 / Pirc Prp Lim 3 / Pirc Prp Lim 4), the second limit (PTrc_Rgn_Lim_l, PTrC—Rgn_Lim_2l Pprc Rgn Lim 3i PTrc_Rgn_Lim_4), the third limit (PTrc_Tot_prp_Lim), and the fourth limit (PTrc_Tot_Rgn_Lim) includes: controlling the powertrain according to the SeCOnd limit (PTrc_Rgn_Lim_l, Pirc Rgn Lim 2i Pirc Rgn Lim 3i PprcRgn Lim 4) in a first temperature range (B),- controlling the powertrain according to the first limit (PTrC—Prp_Lim_1r PTrc_Prp_Lim_2r PTrc_Prp_Lim_3r PTrc_Prp_Lim_4) a second temperature range (C), the second temperature range (C) including at least in part temperature values higher than the temperature values of the first temperature range (B), controlling the powertrain according to the fourth limit (PTrcTot Rgn Lim) in a third temperature range (D), the third temperature range (D) including at least in part temperature values higher than the temperature values of the second temperature range (C),- controlling the powertrain according to the third limit (PprcTot prp Lim) in a fourth temperature range (E), the fourth temperature range (E) including at least in part temperature values higher than the temperature values of the third temperature range (D).

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