A method for determining propulsion and regeneration torque limits of an electric traction motor of an electrical powertrain of a vehicle, wherein the electric traction motor can be selectively disengaged from one or more drive wheels operatively connected thereto

Abstract

There is described a method which makes it possible to operate a synchronization of the rotational speed of an electric traction motor, the connection whereof to one or more corresponding drive wheels of an axle can be selectively activated or deactivated by means of one or more corresponding engagement devices, by controlling, and specifically by limiting, the torque thereof in order to reach the target of rotational speed which achieves synchronization, so as to comply with the limits of the power absorbed and generated by the motor and with the torque limits envisaged by the same motor. Moreover, the method ensures a complete safeguard of the high-voltage battery supplying each electric traction motor, together with an optimal use of the torque and the electrical power available for the synchronization, thus reaching said synchronization as rapidly as possible, so as to have the traction assembly available for the torque delivery.

Description

[0001] "A method for determining propulsion and regeneration torque limits of an electric traction motor of an electrical powertrain of a vehicle , wherein the electric traction motor can be selectively disengaged from one or more drive wheels operatively connected thereto"

[0002] ★ ★ ★ ★

[0003] TEXT OF THE DESCIPTION

[0004] Field of the Invention

[0005] The present invention refers to vehicles with an electrical powertrain of the type including electric traction motors distributed between a front axle and a rear axle .

[0006] Prior art

[0007] In a vehicle with an electrical powertrain of the type including traction motors distributed between a front axle and a rear axle , a disconnection is generally controlled of at least one traction motor with respect to one or more corresponding drive wheels operatively connected thereto when the torque request by the driver can be met by the remaining one or more electric traction motors . The disconnection is operated for improving the general ef ficiency, since the rotational dragging of an electric traction motor which is not involved in meeting the torque request by the driver only represents an energy dissipation .

[0008] The disconnection, as well as the following reconnection, are operated by means of a mechanical engagement device (which is operated electrically and controlled electronically) which is generally of the front-teeth type . The purpose thereof is to guarantee the torque transmissibility and to limit the wear in time in comparison with, for example , a friction clutch .

[0009] The problem is that this kind of engagement devices requires synchroni zing the rotational speed of the electric motor with the rotational speed of the traction assembly downstream thereof when re-establishing the mechanical connection . The synchroni zation is necessary to avoid an early wear of the engagement teeth, noise at the moment of the connection and j umps in the kinematic chain . The traction assembly downstream of the electric traction motor may comprise a transmission and one or more drive wheels connected to the transmission, or directly one drive wheel i f the electric motor is directly coupled with the drive wheel , or i f the engagement device is arranged between the transmission and the drive wheel ( s ) .

[0010] The operation of synchroni zing the rotational speed of the electric traction motor when reconnecting the latter with the traction assembly downstream thereof , however, must be operated while respecting the limits of the power absorbed and generated by the motor, and the torque limits envisaged for the motor itsel f . As regards said needs the Applicant has proposed, in the Italian Industrial Invention Patent Application n . 102024000017092 , a method for calculating a target torque value for each electric traction motor involved in a synchroni zation manoeuvre , whereas , generally speaking, the prior art does not provide any solution .

[0011] Obj ect of the Invention

[0012] The invention aims at solving the technical problem described in the foregoing . In particular, the obj ect of the invention is that of providing a method for determining propulsion and regeneration torque limits of an electric traction motor of an electrical powertrain of a vehicle , wherein the electric traction motor can be selectively disengaged from one or more drive wheels operatively connected thereto , which enables managing a phase of restoring the mechanical connection between the electric motor and the corresponding one or more drive wheels while synchroni zing the rotational speeds of the electric motor and of the traction assembly downstream thereof (which, as observed in the foregoing, may comprise a transmission / a di f ferential and one or more drive wheels connected to the transmission / to the di f ferential , or else directly one drive wheel , i f the electric motor is directly coupled with the drive wheel or i f the engagement device is arranged between the transmission and the drive wheel ( s ) , or - in the same fashion - to manage a phase of disconnection by managing the decrease of the rotational speed of the electric traction motor ( down to speed zero ) , while respecting, i . a . , the limits of the power absorbed and generated by the motor . In both instances - reconnection and disconnection - energy is respectively absorbed or recovered, and therefore both the propulsive phase and the regenerative phase are managed .

[0013] Summary of the Invention

[0014] The obj ect of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention .

[0015] Brief Description of the Figures

[0016] The invention will now be described with reference to the annexed Figures , which are provided by way o f non-limiting example only, and wherein :

[0017] - Figure 1 shows a flow chart representative of the method according to the invention,

[0018] Figures 2 to 9 show diagrams of powertrains wherein it is possible to implement the method according to the invention,

[0019] Figure 10 shows a functional block diagram representative of the method according to the invention,

[0020] - Figure 11 shows timing diagrams associated with a manoeuvre of restoring the mechanical connection between an electric traction motor and one or more corresponding drive wheels of the vehicle ,

[0021] - Figures 12 to 25 show diagrams representative of steps - or parts thereof - developed in the method according to the invention .

[0022] Detailed Description

[0023] Referring to Figure 1 , reference number 1 generally denotes a flow chart representative of a method for controlling the torque of an electric traction motor o f an electrical powertrain of a vehicle according to the invention .

[0024] The method according to the invention can be implemented on vehicles V with an electrical powertrain which comprises :

[0025] - at least one electric traction motor operatively associated with at least one drive wheel of a front axle FA of the vehicle ,

[0026] - at least one electric traction motor operatively associated with at least one drive wheel of a rear axle RA of the vehicle , wherein one of said front axle ( FA) and rear axle (RA) comprises at least one engagement device configured to selectively connect and disconnect one or more drive wheels of the one of said front axle ( FA) and rear axle (RA) to / from the corresponding electric traction motor .

[0027] Figures 2 to 9 show exemplary configurations of electrical powertrains which comprise such features , and which include an electric traction motor which can be selectively connected to and disconnected from one or more drive wheels of the axle FA or RA by means of an engagement device , and wherein between the engagement device and the corresponding one or more drive wheels there is arranged a traction assembly which extends from the engagement device to the one or more corresponding drive wheels of the axle FA or RA, and which includes one of:

[0028] - a direct coupling, rotatably connected to a drive wheel of one of said front axle FA and rear axle RA, and connectable to the electric traction motor by means of the engagement device, e.g. a half-shaft (see Figures 2, 3, 6, 7) , a differential, having an input shaft, connectable to the electric traction motor by means of the engagement device, and a first and a second output shafts rotatably connected to corresponding drive wheels of the one of said front axle FA and rear axle RA (see Figures 4, 5, 8, 9) ,

[0029] - a transmission, having an input shaft connectable to the electric traction motor by means of the engagement device, and an output shaft rotatably connected to a corresponding drive wheel of the one of said front axle FA and rear axle RA (which is not shown in the Figures for brevity) .

[0030] Of course, upstream of the engagement device there may be provided a direct coupling to the electric traction motor (see Figures 4, 5, 8, 9) , or else the connection may be mediated by a transmission or a differential (see Figures 2, 3, 6, 7, wherein in particular only the differential is shown) .

[0031] In detail, referring to Figures 2 to 9:

[0032] - Figure 2 shows a vehicle V with an electrical powertrain comprising an electric traction motor Ml and an electric traction motor M2, both being associated with the rear axle RA, and a single electric motor M3 associated with the front axle FA. The electric motor Ml is permanently connected to a rear left drive wheel RL by means of a transmission GBX1, the electric motor M2 is permanently connected to a rear right drive wheel RR by means of a transmission GBX2, and the motor M3 is connected in a disengageable fashion with both the front left drive wheel FL and the front right drive wheel FR by means of a front di f ferential FD . A first engagement device FCL is arranged between the di f ferential FD and the wheel FL, whereas a second engagement device FCR i s arranged between the di f ferential FD and the wheel FR; therefore , both engagement devices are located between the transmission ( di f ferential FD) and the drive wheels , and not between the electric traction motor (M3 ) and the transmission ( di f ferential FD) ;

[0033] - Figure 3 shows a vehicle V with an electrical powertrain comprising a single electric traction motor Ml associated with the rear axle RA and a single electric motor M3 associated with the front axle FA. The electric motor Ml is permanently connected to both the rear left drive wheel RL and the rear right drive wheel RR by means of a rear di f ferential RD, whereas the motor M3 is connected in a disengageable fashion to both the front left drive wheel FL and the front right drive wheel RF by means of a front di f ferential FD and by means of engagement devices FCL and FCR, in a configuration as shown in Figure 2 ;

[0034] - Figure 4 shows a vehicle V with an electrical powertrain comprising a first electric traction motor Ml and a second electric traction motor, both being associated with the rear axle RA according to a configuration as per Figure 2 , i . e . with the electric motor Ml permanently connected to the rear left drive wheel RL by means of the transmission GBX1 , and the electric motor M2 permanently connected to the rear right drive wheel RR by means of the transmission GBX2 , and moreover comprising a single motor M3 associated with the front axle FA. The motor M3 is connected in a disengageable fashion to both the front left drive wheel FL and the front right drive wheel FR by means of a front di f ferential FD, but unlike Figures 2 and 3 the configuration of Figure 4 envisages a single engagement device FD arranged between the motor M3 and the differential FD, i.e. the engagement device FC is located between the electric traction motor (M3) and the transmission (differential FD) :

[0035] - Figure 5 shows a vehicle V with an electrical powertrain comprising a single electric traction motor Ml associated with the rear axle RA and a single electric motor M3 associated with the front axle FA. The rear axle RA follows the configuration as per Figure 3, i.e. the motor Ml is permanently connected to both the front left drive wheel FL and the front right drive wheel FR by means of the rear differential RD, whereas the front axle FA follows the configuration of Figure 4, i.e. the motor M3 is connected in a disengageable fashion to both the front left drive wheel FL and the front right drive wheel FR by means of a front differential FD, with the engagement device FC arranged between the motor M3 and the differential FD. As in Figure 4, the engagement device FC is located between the electric traction motor (M3) and the transmission (differential FD) ;

[0036] - Figure 6 shows an electrical powertrain with a configuration which mirrors the configuration of Figure 2, specifically comprising an electric traction motor M3 and an electric traction motor M4, both being associated with the front axle FA, and a single electric motor Ml associated with the rear axle FA. The electric motor M3 is permanently connected to a front left drive wheel FL by means of a transmission GBX3, the electric motor M4 is permanently connected to a front right drive wheel FR by means of a transmission GBX4, and the motor Ml is connected in a disengageable fashion to both the rear left drive wheel RL and the front left drive wheel FR by means of a rear differential RD. A first engagement device RCL is arranged between the differential RD and the wheel RL, whereas a second engagement device RCR i s arranged between the di f ferential RD and the wheel RR; therefore , both engagement devices are located between the transmission ( di f ferential RD) and the drive wheels , and not between the electric traction motor (M ! ) and the transmission ( di f ferential RD) ;

[0037] - Figure 7 shows a configuration of a powertrain which mirrors the configuration of Figure 3 , which speci fically comprises a single electric traction motor Ml associated to the rear axle RA and a single electric motor M3 associated with the front axle FA, wherein the electric motor M3 is permanently connected to both the front left drive wheel FL and the front right drive wheel FR by means of a front di f ferential FD, whereas the motor Ml is connected in a disengageable fashion to both the left rear drive wheel RL and the left right drive wheel RR by means of a rear di f ferential RD and by means of the engagement devices RCL and RCR, according to a configuration identical to the one described in Figure 6 ;

[0038] - Figure 8 shows a configuration which mirrors the configuration of Figure 4 , and thus comprises an electric traction motor M3 and an electric traction motor M4 , both being associated with the front axle FA according to a configuration identical to the one of Figure 6 , i . e . with the electric motor M3 which is permanently connected to the front left drive wheel FL by means of the transmission GBX3 , and the electric motor M4 which is permanently connected to the front right drive wheel FR by means of the transmission GBX4 , and moreover comprises a single motor Ml associated with the rear axle RA. The motor Ml is connected in a disengageable fashion to both the rear left drive wheel RL and the rear right drive wheel RR by means of a rear di f ferential RD, but unlike the Figures 6 and 7 the configuration o f Figure 8 envisages a single engagement device RC arranged between the motor Ml and the differential RD, i.e. the engagement device RC is located between the electric traction motor (Ml) and the transmission (differential RD) ;

[0039] - Figure 9 shows a configuration which mirrors the one of Figure 5, thus comprising a single electric traction motor M3 associated with the front axle FA and a single electric motor Ml associated with the rear axle RA. The front axle FA follows the configuration of Figure 7, and therefore the motor M3 is permanently connected to both the front left drive wheel FL and the front right drive wheel FR by means of the front differential FD, whereas the rear axle RA follows the configuration of Figure 8, i.e. the motor Ml is connected in a disengageable fashion to both the rear left drive wheel RL and the rear right drive wheel RR by means of the rear differential RD, with the engagement device RC arranged between the motor Ml and the differential RD. As in Figure 8, the engagement device RD is located between the electric traction motor (Ml) and the transmission (differential RD) .

[0040] The description provided in the following refers, as regards the synchronizing operation and as per the method according to the invention, to a general "electric traction motor", it being understood that it is a traction motor along the drivetrain thereof down to the respective drive wheel (s) there is arranged an engagement device. This corresponds, with reference to Figures 2 to 9, to the motor M3 (Figures 2 to 5) or the motor Ml (Figures 6 to 9) , and to the engagement devices FCR, FCL (Figures 2, 3 in combination with the motor M3) , FC (Figures 4, 5 in combination with the motor M3) , RCR, RCL (Figures 6, 7 in combination with the motor Ml) , RC (Figures 8, 9 in combination with the motor Ml) . This being said, and with reference to Figures 1 and 10 , the method according to the invention includes determining a limit value of propulsion torque Tspactri_PrpLim foranelectric traction motor currently being in a disconnection condition from the one or more corresponding drive wheels by means of a corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle ( FA) and rear axle (RA) in response to a request for connection of the electric traction motor to the one or more corresponding drive wheels ( therefore , the limit torque value TSpdCtrl PrpLimrefers to the manoeuvre of transition to the connection condition of the electric traction motor to the one or more corresponding drive wheels ) , and a limit value o f regeneration torque TSpdCtrl RegLimfor an electric traction motor currently being in a connection condition to the one or more corresponding drive wheels by means of a corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle ( FA) and rear axle (RA) in response to a request for disconnection of the electric traction motor from the one or more corresponding drive wheels ( thus , the limit torque value TspactrijiegLim refers to the manoeuvre of transition to the disconnection condition of the electric traction motor from the one or more corresponding drive wheels ) , wherein determining the limit value of propulsion torque Tspdctri_PrpLim and the limit value of regeneration torque spdctri_RegLim includes :

[0041] - determining (block 2 ) a limit value of propulsion torque by means of an open-loop calculation TSpdCtri 0L PrpLimas a function of a reference limit value of propulsion torque TMot PrpLimof the electric traction motor and of a limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions PspdCtrl Prp Li.m r determining (block 2 ) a limit value of regeneration torque by means of an open-loop calculation Tspactri_OL_RegLima s afunction of a reference limit value of regeneration torque TMot RegLimof the electric traction motor and of a limit value of electrical power that can be delivered by the electric traction motor under regeneration conditions PSpdctri_Reg_Lim >

[0042] - determining (block 4 ) a limit value of propulsion torque by means of a closed-loop calculation Tspdctri_CL_PrpLima s afunction of a di fference between the limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions Pspdctri_Prp_Ltm and an electrical power PActabsorbed by the electric traction motor under propulsion conditions , determining (block 4 ) a limit value of regeneration torque by means of a closed-loop calculation TSpdCtrl CL RegLimas a function of a di f ference between a limit value of electrical power that can be delivered by the electric traction motor under regeneration conditions Pspdctri_Reg_Ltm and an electrical power PActdelivered by the electric traction motor under regeneration conditions , determining (block 6 ) the limit value of propulsion torque TSpdCtrl PrpLimas a function o f said limit value of propulsion torque determined by means of an open-loop calculation TSpdCM 0L PrpLimand the limit value of propulsion torque determined by means of a closed- loop calculation TSpdCtri CL PrpLim, determining (block 6 ) the limit value of regeneration torque TSpdCtrl RegLimas a function of said limit value of regeneration torque determined by means of an open-loop calculation TSpdCtrl 0L RegLimand the limit value of propulsion torque determined by means of a closed-loop calculation TSpdCtrl CL RegLim.

[0043] In the following, the values Pspdctri_Prp_Ltm and Pspdctri_Reg_LtmmaY be indicated either by the phrases used in the foregoing (" limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions" and " limit value of electrical power that can be delivered by the electric traction motor under regeneration conditions" ) or, for brevity, by the phrases " limit value of propulsion electrical power" and " limit value of regeneration electrical power" .

[0044] Due to what has been observed in the foregoing, in the present description the reference to propulsion conditions ( including the terminology of the variables , such as e . g . "propulsion torque" ) corresponds to a transition to a connection condition of the electric traction motor, which is currently in a disconnection condition, from the one or more corresponding drive wheels , by means of the corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle FA and rear axle RA, in response to a request for connection of the electric traction motor to the one or more corresponding drive wheels . Similarly, in the present description the reference to regeneration conditions ( including the terminology of the variables , such as e . g . "regeneration torque" ) corresponds to a transition to a disconnection condition of the electric traction motor, which is currently in a connection condition, to the one or more corresponding drive wheels by means of the corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle FA and rear axle RA, in response to the request for disconnection of the electric traction motor from the one or more corresponding drive wheels .

[0045] Figure 11 shows a set of timing diagram showing the evolution of some values or variables involved in the manoeuvre of transition from a disconnection condition to a connection condition between the electric traction motor and the corresponding drive wheel ( s ) ( therefore , said diagrams apply to a manoeuvre wherein the control of the electric traction motor regards the propulsion mode ) . The references A, B, C denote three reference time instants for the maneouvre , speci fically :

[0046] A: sending a request for transition from a disconnection condition to a connection condition between the electric traction motor and the corresponding traction assembly . In this case , the request applies to the front axle , and the relevant diagram is shown in Figure 2 ; therefore , the request for connection regards the motor M3 and the engagement devices FCL, FCR . This practically corresponds to a request for synchroni zing the rotational speeds of the electric motor and of the traction assembly ( drive wheel only or drive wheel and transmission / di f f erential ) located downstream of the engagement device in a disconnection condition; the request may be satis fied within the absorption / regeneration limits of electrical power and the related maximum torque values (positive values , propulsion) and minimum torque values (negative values , regeneration) delivered and absorbed by the electric traction motor ;

[0047] B : completion of the synchroni zation of the rotational speeds ; sending a request for switching the engagement device to an operating condition which achieves the connection of the electric traction motor ;

[0048] C : completion of the switching o f the engagement device to an operating condition which achieves the connection of the electric traction motor . Controlling the rotational speed of the electric traction motor is no longer required .

[0049] The diagram 11A shows the evolution in time of a current rotational speed nMot Actof the electric traction motor M3 and of a target rotational speed nMot Tgt. The diagram 11B shows an evolution in time of the torques ( in the present case , propulsion torques ) delivered by the set of the motors Ml , M2 ( torque TM1+M2) and by the motor M3 ( TSpdCtri M3) according to the teachings of the Italian Industrial Invention Patent Application n . 102024000017092 in the name of the same Applicant , already mentioned in the foregoing, showing an upper (propulsion) torque limit for the motor M3 ( Tspactrij>rpLim_M3 • The diagram 11C shows the evolution in time of the operating condition of the engagement device , speci fically of the target condition T gt and of the current condition Act ( discrete values "Connected" and "Disconnected" ) , whereas the diagram 11D shows a logic state of a variable Motor_Speed_Control_Req representative of the need to control the rotational speed of the motor M3 . The logic state is binary - therefore TRUE (" 1" ) or FALSE (" 0" ) - and, according to what has been described, its value is comprised between " 1" from A to C and " 0" elsewhere .

[0050] The following Figures 12 to 25 show steps and / or determinations operated in the method according to the invention, and will now be commented individually .

[0051] Referring to Figure 12 , diagram 10 , determining the target value of propulsion torque TSpdCtrl PrpLimas a function of the limit value o f propulsion torque determined by means of an open-loop calculation Tspdctri_OL_PrpLim and the target value of the propulsion torque determined by means of a closed-loop calculation Tspdctri_CL_PrpLim ( the latter corresponding to a correction of the torque value determined by means of open-loop calculation TSpdCtrl 0L PrpLim, thus being a torque value from the dimensional point of view, whereas at the level of calculation it is a correction which is superimposed to the value TSpdCtrl 0L PrpLim) includes : - calculating a sum (block 12 ) of the limit value of propulsion torque determined by means of an open-loop calculation TSpdCM 0L PrpLimand of the limit value of propulsion torque determined by means of a closed-loop calculation TSpdCtri CL PrpLim,

[0052] - determining the limit value of propulsion torque Tspactri_PrpLima sthe lower (block 14 , MIN) of : a ) the reference limit value TMot PrpLimof the torque that can be delivered by the electric traction motor under propulsion conditions , b ) the sum 12 of the values TSpdCtri 0L PrpLimand spdCtrl CL PrpLim ) •

[0053] Operatively, what is shown in the diagram 10 corresponds to an upper limitation of the target value Tspdctri_PrpLim to the reference limit value of the torque that can be delivered by the electric traction motor under propulsion conditions TMot PrpLim, in such a way as not to exceed said limit .

[0054] Similarly, referring to Figure 13 , diagram 20 , determining the limit value of regeneration torque TspdctrijiegLima s afunction of the limit value of regeneration torque determined by means of an open-loop calculation TSpdCtrl 0L RegLimand of the limit value of regeneration torque determined by means of a closed-loop calculation TSpdCtrl CL RegLim( the latter corresponding to a correction of the torque value determined by means of an open-loop calculation TSpdCtrl 0L RegLim, thus being a torque value from the dimensional point of view, whereas at the level of calculation it is a correction which is superimposed to the value TSpdCtrl 0L RegLim') includes :

[0055] - calculating a sum (block 22 ) of the limit value of regeneration torque determined by means of an openloop calculation TSpdCtrl 0L RegLimand of the limit value of regeneration torque determined by means of a closed-loop calculation TSpdCtrl CL Pegilm, determining the limit value of regeneration torque TSpdCtrl RegLimas the greater (block 24 , MAX ) of : a ) the reference limit value TMot RegLimof the torque that can be absorbed by the electric traction motor under regeneration conditions , b ) the sum 22 of the values TSpdCtrl 0L RegLimand TspdCtrl_CL_RegLlm •

[0056] Operatively, what is shown in the diagram 20 corresponds to a lower limitation ( considering the values with the respective sign, which is negative because they are regeneration torques ) of the value TspactrijiegLim to the reference limit value of the torque that can be absorbed by the electric traction motor under regeneration conditions TMot RegLim, in such a way as not to exceed said limit .

[0057] The following Figures 14 and 15 show the determination of the values in open loop TSpdCtri 0L PrpLimand TSpdCtrl 0L RegLim, and speci fically the limitation of said values due to the limits of propulsion and regeneration electrical power, which are defined - again, in open loop - according to the teachings of the Italian Industrial Invention Patent Application n . 102023000023517 in the name of the same Applicant .

[0058] Referring to Figure 14 , diagram 30 , the limit value of propulsion torque determined by means of an open-loop calculation TSpdCtri 0L PrpLimis defined as the lower (block 32 , MIN) of the limit value TMot PrpLimof the torque that can be delivered by the electric traction motor under propulsion conditions and a torque value TSpdCtrl 0L PrpPwrLimthat can be delivered by the electric traction motor upon a (maximum admissible ) absorption of electrical power by the electric traction motor under propulsion conditions , which is equal to the limit value of electric propulsion power PSpdctn_PrpLim •

[0059] The reference limit value TMot PrpLimof the torque that can be delivered by the electric traction motor under propulsion conditions is a data item coming from a control unit of the vehicle domain (VCDM) , which receives it from an inverter operatively connected to the electric traction motor ; it may be subj ected to degrading by the inverter itsel f in the presence of high temperatures . Alternatively, it is a data item which i s mapped directly in the control unit VDCM .

[0060] In nominal conditions , the l imit torque is a function of the rotational speed of the motor (number of revolutions ) , and each curve of limit torque - number of revolutions is parameteri zed with respect to the supply voltage of the electric traction motor, i . e . there is the physical presence of a dimensional plan comprising a set of curves of limit torque - number of revolutions for each supply voltage .

[0061] Similarly, with reference to Figure 15 , diagram 40 , the limit value of regeneration torque determined by means of an open-loop calculation TSpdCtrl 0L RegLimis defined as the greater (block 42 , MAX ) between the reference limit value TMot RegLimof the torque that can be absorbed by the electric traction motor under regeneration conditions and a torque value Tspdctri_OL_RegPwrLim that can be absorbed by the electric traction motor upon an electrical power delivery ( the minimum admissible with sign, the maximum admissible as an absolute value ) of electrical power by the electric traction motor under regeneration conditions , equal to the limit value of propulsion electrical power PspdCtrl_RegLlm •

[0062] As stated in the foregoing, the reference limit value TMot RegLimof the torque that can be delivered by the electric traction motor under propulsion conditions is a data item coming from a control unit of the vehicle domain (VDCM) , which receives it from an inverter which is operatively connected to the electric traction motor ; it may be subj ected to degrading by the inverter itsel f in the presence of high temperatures . As an alternative , it is a data item which is mapped directly in the control unit VDCM .

[0063] In nominal conditions , the limit torque is a function of the rotational speed of the motor (number of revolutions ) , and each curve of limit torque - number of revolutions is parameteri zed with respect to the supply voltage of the electric traction motor, and therefore there is the physical presence of a dimensional plan comprising a set of curves of limit torque - number o f turns for each supply voltage .

[0064] The limit values PSpdctri_PrpLim and PSpdctn_RegLim derive from a method for controlling the electrical power which is external to the extent of the invention, and are preferably determined according to the teachings of the Italian Industrial Invention Patent Application n . 102023000023517 . In more detail , and referring to the description of said Patent Application, the limit values Pspdctri_PrpLim and PSpdctn_RegLim are expressed in a fashion corresponding to a quadratic polynomial with respect to the torque of the electric traction motor, and with coef ficients a , b , c depending on the ( current ) rotational speed of the electric traction motor .

[0065] In detail , it is possible to write , for the value Pspdctri_PrpLtm > the following (polynomial ) expression, and therefore the value TSpdCtrl 0LprpPwrLimis determined as the solution of the corresponding equation :

[0066] Similarly, it is possible to write , for the value Pspdctri_RegLtm r the following (polynomial ) expression, and thus the value TSpdCtrl 0L RegPwrLimis determined as a solution of the corresponding equation wherein a , b , c are the coef ficients dependent on the rotational speed of the electric traction motor .

[0067] Substantially, the method according to the invention envisages limiting ( superiorly for propulsion, inferiorly - considering the sign - for regeneration) the values determined in open loop TSpdCM 0L PrpLimandTspactri_OL_RegLim to the torque values belonging to corresponding iso-power geometric loci associated with the limit values PSpdctri_PrpLim and PSpdctn_RegLim • Figure 16 exempli fies some polynomials (parabolas ) representative of the limit value Pspdctri_PrpLtm > whereas Figure 17 graphically shows the meaning of the values Tspdctri_OL_PrpPwrLim and T^pd(:f:riQijiegpwriim, to be understood as solutions of the corresponding quadratic equations .

[0068] The following Figures 18 and 19 show a calculation which does not strictly pertain to the method according to the invention, since it is performed according to the control method described in the Italian Industrial Invention Patent Application n . 102024000017092 , but the result whereof , speci fically a raw target torque valuerspdctri_Raw_Tgt ( either propulsion or regeneration torque , as a function of the condition under which the motor i s operating) for the electric traction motor currently in a disconnection condition from the one or more corresponding drive wheels in response to the request for returning to a connection condition of the electric traction motor to the one or more drive wheels , is involved in the operations of determining the values Tspdctri_CL_PrpLimand TSpdCtri CL RegLimin the preferred embodiments of the method according to the invention . Obviously, as has been suggested, the calculation of the value TSpdCtri Raw Tgtmay be performed also according to other procedures ( for example by means of a calculation model based on maps ) , but what is taught in the Italian Industrial Invention Patent Application n . 102024000017092 constitutes anyway a preferential choice .

[0069] Referring to Figure 18 , diagram 70 , summing up the teachings of the Application 102024000017092 , it is possible to observe that the raw target torque value Tspactri_Raw_Tgt is generally determined as a sum (block 72 ) of :

[0070] - a target value determined in open loop TSpdCtrl 0L Tgt,

[0071] - a torque correction value determined in closed loop TSpdCtrl CL Tgt, which in turn comprises the sum of a proportional correction TSpdCtrl Propand of an integral correction TSpdCtrl Int( therefore implying that said contributions are determined by means of a proportionalintegral control ) , and an integral torque correction value &TIntsubstantially corresponding to a torque variation resulting from the integral control in the interval of calculation update .

[0072] The integral torque correction value &TIntis extracted from a map M70 ( Figure 19 ) as a function of a di f ference AnMot(block D70 ) between the current rotational speed nMot Actof the electric traction motor and the target rotational speed nMot Tgtof the electric traction motor .

[0073] The map M70 shows a curve - with qualitative evolution - of values &TIntas a function of the di f ference AnMotwith respect to a value of zero correction corresponding to the points AnMot= 0 rpm and ^TInt= 0 Nm, i . e . with respect to the conditions of speed synchroni zation between the electric traction motor and the corresponding traction assembly . For positive values of &nMot, i . e . under conditions wherein the current speednMot_Act is lower than the target speed nMot Tgt, the integral correction values &TIntare positive as well , and therefore they correspond to a correction in the direction of the acceleration of the electric traction motor, to pursue the target value nMot Tgt. For negative values of &nMot, i . e . under conditions wherein the current speed nMot Actis higher than the target speednMot Tgt / the integral correction values &TIntare negative as well , and therefore they correspond to a correction in the direction of braking the electric traction motor, to pursue the target value nMot Tgt.

[0074] This being said, and with reference to Figure 20 , diagram 80 , the limit value o f propulsion torque determined by means of a closed-loop calculation Tspactri_CL_PrpLim is determined by means of a first proportional-integral control 82 , which acts as a function of a di f ference (block 84 ) PspdCtri_PrpLim ~ ?Act between the limit value of propulsion electrical power Pspdctri PrpLim t as a function whereof the limit value in open loop TSpdCtrl 0LprppwrLimis determined, as observed with reference to Figures 16 , 17 , and an electrical power PActbeing currently absorbed by the electric traction motor . The first proportional-integral control 82 has a lower saturation limit 85 equal to the opposite —TSpdCtri 0LprpLimof the limit torque value determined in open loop Tspdctri_OL_PrpLim for the electric traction motor currently being in a disconnection condition from the one or more corresponding drive wheels , in response to the request for returning to the connection condition of the electric traction motor to the one or more corresponding drive wheels . This means that the torque correction in closed loop is at the ( lower ) limit , such as to annul what has been determined by means of an open-loop calculation, without ever changing the sign of the torque determined by the external logic.

[0075] The control 82, moreover, has an upper saturation limit (86) equal to the lesser (block 87) of a value of a difference (block 88) and a value of a difference (block 89) TMot Prp Lim-TSpdCtrl OL PrpLim, wherein

[0076] Tspdctri_OL_PrpLim is the limit value of propulsion torque determined by means of an open-loop calculation,

[0077] TMot_prp_Lim is the limit value of propulsion torque, Tspdctri_Raw Tgt is the target torque value (specifically under propulsion conditions) determined by an external logic, preferably as taught in the Application 102024000017092.

[0078] This means that the torque correction in closed loop Tspdctri_CL_PrpLim has a maximum amount equal to the lesser of the margins available for the correction in closed loop of the value TSpdCtrl 0L PrpLim, wherein the first margin is defined with respect to the target value TSpdCtrl Raw Tgt, and the second margin is defined with respect to the limit value TMot Prp Lim. In other words, the margin available for the correction in closed loop is in any case limited by the limit torque that can be delivered by the electric motor under propulsion conditions TMot_Prp_Lim-ifthe torque target TSpdCtrl Raw Tgtcalculated by an external logic, preferably as taught in the Application 102024000017092, is lower than the limit value of the torque that can be delivered by the electric traction motor under propulsion conditions, then the available margin is limited by the torque TSpdCtrl Raw Tgt, which is lower than the torque TMot Prp Lim, because there is no need to exceed the value TSpdCtrl Raw Tgt; on the other hand, if the torque target TSpdCtrl Raw Tgtcalculated by means of an external logic, preferably as taught in the Application 102024000017092, is greater than the limit value of the torque that can be delivered by the electric traction motor under propulsion conditions , then the available margin is limited by the torque TMot Prp Lim, in order not to exceed the value thereof , thus in order to avoid exceeding the torque limits envisaged for the motor .

[0079] Figures 21 and 22 exempli fy the action of the method according to the invention when the electric traction motor operates under propulsion conditions , i . e . during a transition manoeuvre to a connection condition ( transition to a connection condition from a disconnection condition) of the electric traction motor to the corresponding one or more drive wheels .

[0080] With reference to Figure 21 , which shows , at the top, a timing diagram of the electrical power absorbed by the electric traction motor and, at the bottom, a timing diagram of the torque correction in closed loop Tspctctri CL PrpLtm t it is possible to observe what takes place at the time instants A and B (which do not necessarily correspond to the instants dealt with referring to the diagrams of Figure 11 ) : at the time instant A, the electrical power currently being absorbed by the electric traction motor PActexceeds the limit value PspdCtri_PrpLim • The control 82 thus determines a torque correction value TSpdCtrl CL PrpLimwhich progressively decreases ( although it increases by absolute value ) in order to reverse the increasing trend of the power PAct;

[0081] - at the time instant B, the electrical power PActis reduced to the limit value PsPactri_PrpLim • The control 82 no longer commands any variation of the correction Tspdctri cL PrpLim t which is kept at the value reached at instant B .

[0082] With reference to Figure 22 , it shows four timing diagrams including, from top to bottom, a diagram of evolution in time of the electrical power absorbed by the electric traction motor, a diagram of evolution in time of the rotational speed of the electric traction motor, a diagram of evolution in time of a ( synchroni zation) torque delivered by the electric traction motor, and a diagram of evolution in time of a torque correction in closed loop under propulsion conditions . Similarly to the case of Figure 21 , it is possible to observe what takes place at the time instants A, B, C (which do not necessarily correspond to the instants commented for the diagrams of the Figure 11 , 21 ) : at the time instant A, the torque target Tspactri_Raw_Tgt calculated by means of an external logic, preferably as taught in the Application 102024000017092 , becomes greater than the limit value of propulsion torque determined by means of an open-loop calculation Tspdctri_OL_PrpLim t but the electric power currently being absorbed PActhas not yet reached the limit value Pspdctri Prp Lim • The control operated in the method according to the invention commands a correction in closed loop Tspdctri_CL_PrpLim which increases the torque ^ Pspdctri_OL_PrpLim~^'Pspdctri_CL_PrpLim has an increasing trend) in such a way as to satis fy the target TSpdCtrl Raw Tgt;

[0083] - at the time instant B, the correction in open loop TSpdCtrl CLprpLimstops being increased, because it is limited by the limit value of the torque that can be delivered by the electric traction motor under propulsion conditions TMot Prp Lim. In other words , there has been reached the upper saturation limit 86 of the control 82 , which here corresponds to the di f ference 88 ( indeed, it should be noted that at the instant A TSpdctri_Raw TSt is already greater than TMot Prp Lim, thus the upper saturation limit cannot but be determined by TMot_prp_Lim i by means of the minimum operator as per block 87 ) ; - at the time instant C, also the electric power currently being absorbed by the electric traction motor PActreaches the limit value PspdCtri_Prp_Lim • The control 82 decreases the value of the correction in closed loop TSpdctn_CL_PrpLim so as to prevent the torque TspdCtrl_OL_PrpLim~^TspdCtrl_CL_PrpLim to result in values of absorbed electrical power exceeding the limit value Pspdctri_Prp_Lim > since the speed nMot Actis still rising towards nMot Tgt.

[0084] Referring to Figure 23 , diagram 90 , the limit value of regeneration torque determined by means of a closed- loop calculation TSpdCtrl CL RegLimis determined by a second proportional-integral control 92 , which operates as a function of a di f ference (block 94 ) PSpdctri_RegLim ~PAct between the limit value of regeneration electrical power Pspdctri_RegLtm as a function whereof the limit value Tspdctri_OL_RegPwrLim is determined in open loop, as observed with reference to Figures 16 , 17 , as well as an electrical power PActcurrently being delivered by the electric traction motor .

[0085] The second proportional-integral control 92 has a lower saturation limit 95 and an upper saturation limit 96 , the lower saturation limit being equal to the greater (block 97 ) of a value of a di f ference (block 98 ) Pspdctri_Raw_Tgt ~ Pspdctri_OL_RegLtm and a value of a di f ference (block 99 ) wherein

[0086] Tspdctri_OL_RegLtm is the limit value of regeneration torque determined by means of an open-loop calculation,

[0087] TMot_Reg_Lim is the limit value of the regeneration torque that can be absorbed by the electric traction motor,

[0088] Tspdctri_Raw_Tgt is the target torque value determined by an external logic ( speci fically under regeneration conditions ) , preferably as taught in the Application

[0089] 102024000017092 . This means that the torque correction in closed loop Tspactri_CL_PrpLim has a minimum value ( considering the sign, as they are regeneration torques ) equal to the greater ( always considering the sign) of the margins available for the correction in closed loop of the value Tspactri_OL_RegLim t wherein the first margin is defined with respect to the target value TSpdCtrl Raw Tgt, and the second margin is defined with respect to the limit value TMot_Reg_Lim • In other words , the margin available for the correction in closed loop is in any case limited by the limit torque that can be absorbed by the electric motor under regeneration conditions TMot Reg Limi f the target torque TSpdCtrl Raw Tgtcalculated by an external logic, preferably as taught in the Application 102024000017092 , has a higher value (with sign) than the limit torque value (with sign) that can be absorbed by the electric traction motor under regeneration conditions , then the available margin is limited by the torque TSpdCtrl Raw Tgt, which is higher ( considering the sign) than the torque TMot_Reg_Lim t since there is no need to exceed ( in absolute value ) the value TSpdCtrl Raw Tgt; i f , on the contrary, the target torque TSpdCtrl Raw Tgtcalculated by an external logic, preferably as taught in the Application 102024000017092 , has a value (with sign) lower than the limit torque value that can be absorbed by the electric traction motor under regeneration conditions , then the available margin is limited by the torque TMot Reg Lim, in order not to exceed the latter in the absolute value , thus in order to avoid exceeding the torque limits envisaged for the motor .

[0090] Figures 24 and 25 exempli fy the action of the method according to the invention when the electric traction motor is operating under regeneration conditions , i . e . in a transition manoeuvre to a disconnection condition ( transition to a disconnection condition from a connection condition) of the electric traction motor to the corresponding one or more drive wheels .

[0091] Referring to Figure 24 , which at the top shows a timing diagram of electrical power delivered by the electric traction motor and at the bottom shows a timing diagram of the torque correction in closed loop Tspactri_CL_RegLim r it is important to observe what takes place at the time instants A and B (which do not necessarily correspond to the instants commented with reference to the diagrams of Figure 11 : at the time instant A, the electrical power which is currently being absorbed by the electric traction motor PActexceeds , in the absolute value , the limit value Pspactri_RegLim • The control 82 therefore determines a torque correction value TSpdCtrl CL RegLimwhich increases progressively, in order to reverse the decreasing trend of the power PAct( thus , the trend of increasing the absolute value , since it is a power with a negative sign) ;

[0092] - at the time instant B, the electrical power PActis brought to the limit value Pspdctri_RegLim • The control 82 no longer commands any variation of the correction Tspdctri_CL_RegLtm r which is kept at the value reached at the time instant B .

[0093] Referring to Figure 24 , it shows four timing diagrams including, from top to bottom, a diagram of the evolution in time of the electrical power delivered by the electric traction motor, a diagram of the evolution in time of the rotational speed of the electric traction motor, a diagram of the evolution in time of a ( synchroni zation) torque absorbed by the electric traction motor, and a diagram of the evolution in time of a torque correction in closed loop under propulsion conditions . Similarly to the case of Figure 24 , it is important to observe what takes place at the time instants A, B, C (which do not necessarily correspond to the instants commented with reference to the diagrams of Figures 11 , 24 ) : at the time instant A, the target torque Tspactri_Raw_Tgt calculated by an external logic, preferably as taught in the Application 102024000017092 , becomes lower (with sign, but greater in absolute value ) to the limit value of regeneration torque determined by means of an open-loop calculation TSpdCtrl 0L PrpLim, but the currently delivered electrical power PActhas not reached yet the limit value Pspdctri_Reg_Ltm (maximum in absolute value ) . The control operated as per the method according to the invention commands a correction in closed loop TSpdctn_CL_RegLim which decreases the torque Tspdctri_OL_RegLim+Tspdctri_CL_RegLim ( thus increasing the absolute value thereof ) in such a way as to satis fy the target spdCtrl Raw Tgt '

[0094] - at the time instant B, the correction in closed loop TSpdCtrl CL RegLimstops being increased ( in absolute value ) since it is limited by the limit torque value that can be absorbed by the electric traction motor under regeneration conditions TMot Reg Lim. In other words , the upper lower saturation limit of the control 92 has been reached, which in this case corresponds to the di f ference 89 ( indeed, it should be noted that at the instant A Tspdctri_Raw_Tgt is already lower ( greater in absolute value ) than TMot Reg Lim, and therefore the lower saturation limit cannot but be determined by ( and actually it i s determined by) TMot Reg Limby means of the maximum operator as per block 97 ) ;

[0095] - at the time instant C, also the electrical power currently being delivered by the electric traction motor PActreaches the limit value (maximum absolute value ) Pspdctri_Reg_Ltm • The control 92 increases the value of the correction in closed loop TSpdCtrl CL PrpLim( decreasing the absolute value thereof ) in order to prevent the torque Tspdctri OL PrpLim+Tspdctri CL PrpLim from resulting in values of delivered electrical power which exceed the minimum admissible value Pspactri_Prp_Lim > since the speed nMot Actis still increasing towards nMot Tgt.

[0096] Therefore , thanks to the method according to the invention it is possible to operate a synchroni zation of the rotational speed of an electric traction motor the connection whereof to one or more corresponding drive wheels of an axle can be selectively activated and deactivated by means of one or more corresponding engagement devices , by controlling, and speci fically by limiting, the torque thereof in order to reach the target of rotational speed which achieves synchroni zation, so as to comply with the limits of the power absorbed and generated by the motor and with the torque limits envisaged by said motor . Moreover, this ensures a complete safeguard of the high-voltage battery supplying each electric traction motor, together with an optimal use of the torque and the electrical power available for the synchroni zation, while reaching said synchroni zation as rapidly as possible , so as to have the traction assembly available for the torque delivery .

[0097] Of course , the implementation details and the embodiments may amply vary with respect to what has been described and illustrated herein without departing from the extent of the present invention, as defined by the annexed claims .

Claims

CLAIMS1 . A method for controlling the torque of an electric traction motor of an electric powertrain of a vehicle , the electric powertrain including :- at least one electric traction motor operatively associated with at least one driving wheel of a front axle of the vehicle- at least one electric traction motor operatively associated with at least one driving wheel of a rear axle of the vehicle , where one of said front axle ( FA) and rear axle (RA) includes at least one engagement device ( FC, RC, FCR, FCL, RCR, RCL ) configured to selectively connect one or more wheel drive axles ( FA, RA) to the corresponding electric traction motor and disconnect one or more wheel drive axles ( FA, RA) from the corresponding electric traction motor, the method including determining a propulsion torque limit value ( TSpdCtrl PrpLim) for an electric traction motor currently in disconnection condition from the one or more corresponding drive wheels by means of a corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle ( FA) and rear axle (RA) in response to a request for connection of the electric traction motor to the one or more corresponding drive wheels , and a regeneration torque limit value TspdctrijtegLtm ') foranelectric traction motor currently in a connection condition to the one or more corresponding drive wheels by means of a corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL) of said one of those front axles ( FA) and rear axles (RA) in response to a request for disconnection of the electric traction motor from the one or more corresponding drive wheels , wherein said determining the propulsion torque limit value ( Tspactri_PrpLim and the regeneration torque limit value(Tspdctri_RegLim') includes:- determining (2) a limit value of propulsion torque by means of an open-loop calculation (TSpdCtrl 0L PrpLtm} as a function of a reference limit value of propulsion torque (TMot PrpLim) and a limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions ( PSpdctri_Prp_Lim ) >- determining (2) a regeneration torque limit value by means of an open-loop calculation (TSpdCtri 0L RegLim) as a function of a reference limit value of regeneration torque (TMot RegLim) and a limit value of electrical power that can be delivered by the electric traction motor under regeneration conditions ( Pspdctri_Reg_Ltm } t- determining (4) a limit value of propulsion torque by means of a closed-loop calculation (TSpdCtri CL PrpLim) as a function of a difference between the limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions ( Pspdctri_Prp_Lim } and an electrical power (P^ct') absorbed by the electric traction motor under propulsion conditions,- determining (4) a limit value of regeneration torque by means of a closed-loop calculation (rPspdctri_CL_RegLtm')as afunction of a difference between a limit value of electrical power that can be delivered by the electric traction motor in regeneration conditions (Pspdctri_Reg_Lim) and an electrical power (PAct) delivered by the electric traction motor in regeneration conditions,- determining (6) the propulsion torque limit value ( Tspdctri_PrpLim )as afunction of said propulsion torque limit value determined by open-loop calculation ^Tspdctri_OL_PrpLtm') and the propulsion torque limit value determined by closed-loop calculation (TSpdCtrl CLprpLim') ,- determining (6) the regeneration torque limit value (TSpdCtrl RegLim) as a function of said regeneration torque limit value determined by open-loop calculation^Tspdctri_OL_RegLim') and regeneration torque limit value determined by closed-loop calculation (TSpdCtrl CL RegLim) .

2. The method of claim 1, wherein determining (6) the propulsion torque limit value ( TSpdCtrl PrpLim) as a function of said propulsion torque limit value determined by open-loop calculation (TSpdCtrl 0L PrpLtm} and propulsion torque limit value determined by closed-loop calculation (TSpdCtrl CL PrpLim) includes:- calculating a sum (12) of said propulsion torque limit values determined by open-loop calculation ^Tspdctri_OL_PrpLtm') and propulsion torque limit value determined by closed-loop calculation (TSpdCtrl CL PrpLtm} ,- determining the propulsion torque limit valuethe lower (14) of:(a) the reference limit value (TMot PrpLim) of propulsion torque that can be delivered by the electric traction motor under propulsion conditions,(b) said sum (12) of said propulsion torque limit value determined by open loop calculation (TSpdCtrl 0L PrpLim') and propulsion torque limit value determined by closed loop calculation (TSpdCtrl CL PrpLim) .

3. The method of claim 1, wherein the regeneration torque limit value (TSpdCtrl RegLim) is determined as a function of the regeneration torque limit value determined by open-loop calculation (TSpdCtri 0L RegLim) and the regeneration torque limit value determined by closed-loop calculation (TSpdCtrl CL RegLim') includes:- calculating a sum (22) of said regeneration torque limit values determined by open-loop calculation (Tspdctri_OL_RegLim} and regeneration torque limit value determined by closed-loop calculation (TSpdCtrl CL RegLim} ,- determining the regeneration torque limit value (TSpdctri_RegLim} as the greater (24) of:(a) the reference limit value (TMot RegLim) of the torque that can be absorbed by the electric tractionmotor under regeneration conditions , b ) said sum ( 22 ) of said regeneration torque limit value determined by open-loop calculation (TSpdCtri 0L RegLim) and regeneration torque limit value determined by closed-loop calculation ( TSpdCtrl CL RegLim) .4 . The method of claim 2 or claim 3 , wherein said propulsion torque limit value determined by an open-loop calculation ( TSpdCtrl 0L PrpLim') is defined as the lower ( 32 ) of said reference torque limit value ( TMot PrpLim) that can be delivered by the electric traction motor under propulsion conditions and a torque value ( TspdctrijJLj’rpPwrLtm ') that can be delivered by the electric traction motor upon an absorption of electrical power by the electric traction motor in propulsion conditions equal to said limit value of electrical power that can be absorbed by the electric traction motor in propulsion conditions ( PSpdCtrl_Prp_Lim ) •5 . The method of any of claims 2 to 4 , wherein said that regenerative torque limit value determined by openloop calculation ( TSpdCtri 0L RegLim) is defined as the lower ( 42 ) of said reference limit value ( TMot RegLim) o f torque that can be absorbed by the electric traction motor under regenerative conditions and a torque value ^ Tspdctri_OL_RegPwrLim ^ that can be absorbed by the electric traction motor upon an electric power delivery by the electric traction motor in regeneration conditions equal to said limit value of electrical power that can be delivered by the electric traction motor under regeneration conditions ( PSpdctri_Reg_Ltm ) •6. The method of claim 5 , wherein :- named Pspdctri_PrpLtm the limit value of the electrical power that can be absorbed by the electric traction motor under propulsion conditions , and named TSpdCtrl 0L PrpPwrLimthe value of the torque that can be absorbed by the electric traction motor upon an absorption of electricalpower by the electric traction motor under propulsion conditions equal to said limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions Pspactri_Prp_Lim > the valueTspdctri_OL_PrpPwrLtm is determined as the solution of the equation- named PspdctrijiegLim the limit value of the electric power that can be delivered by the electric traction motor in regeneration conditions , and named Tspdctri_OL_RegPwrLim the value of the torque that can be absorbed by the electric traction motor upon a delivery of electrical power by the electric traction motor in regeneration conditions equal to said limit value of the electric power that can be delivered by the electric traction motor in regeneration condi t ionsPSpdCtri Reg Lim, the value TSpdCtrl 0L RegPwrLimis determined as the solutionwherein a , b , c are coef ficients dependent on a rotational speed of the electric traction motor .7 . The method of any of the foregoing claims , wherein each of said propulsion torque limit values determined by closed-loop calculation ( TSpdCtri CL PrpLim) and regeneration torque limit value determined by closed- loop calculation ( TSpdCtrl CL RegLim) is a torque correction value .8 . The method of claim 7 , wherein the propulsion torque limit value determined by closed-loop calculation CPspdctrijJLj’rpLim ') is determined by means of a first proportional-integral control ( 82 ) operating as afunction of a difference PspdctriPrpLim~ ?Act between the limit value of electrical power that can be absorbed by the electric traction motor under propulsion conditions Pspactri_Prp_Lim and the electrical power PActabsorbed by the electric traction motor under propulsion conditions, the first proportional-integral control (82) having a lower saturation limit (85) equal to the opposite (—TspdctrijJLj’rpLtm') of the propulsion torque limit value determined by open loop calculation (TSpdCtrl 0L PrpLtm} for the electric traction motor currently in a condition of disconnection from one or more corresponding drive wheels in response to the request for return in connection condition of the electric traction motor to the one or more corresponding drive wheels, and an upper saturation limit (86) equal to the lesser (87) of a value of a difference TSpdCtrl Raw Tgt— TSpdCtrl 0L PrpLim(88) and a value of a difference (89) TMot_Prp_Ltm Tspdctri OL PrpLtm r whereinTspdctri_OL_PrpLim is said the propulsion torque limit value determined by open loop calculation,TMot_prp_Lim is said reference limit value of propulsion torque.

9. The method of claim 7 or claim 8, where the regeneration torque limit value determined by closed- loop calculation (TSpdCtrl CL RegLim) is determined by means of a second proportional-integral control (92) operating on the basis of a difference (94) PspdctrijiegLim ~ ^Act between the limit value PspdctrijiegLim of electrical power that can be delivered by the electric traction motor in regeneration conditions and the electrical power PActdelivered by the electric traction motor under conditions of regeneration, the second proportional-integral control (92) having a lower saturation limit (95) and an upper saturation limit (96) , the lower saturation limit beingequal to the lower ( 97 ) of a value of a di f ference ( 98 ) Tspdctri_Raw_Tgt ~ TSpdCtrl 0L RegLimand a value of a di f ference ( 89 )r whereinTspactri_OL_RegLim is called the regeneration torque limit value determined by open-loop calculation,Tspdctri_Raw_Tgt isatarget torque value for the electric traction motor,TMot_Reg_Lim is called the regeneration torque limit value , wherein the upper saturation limit ( 96 ) is equal to the opposite ( —TSpdCtri 0L RegLim') °f the regeneration torque limit value ( TSpdCtrl 0L RegLim) determined by open-loop calculation10 . The method of any of the preceding claims , wherein said propulsion conditions correspond to a transition in connection condition of the electric traction motor currently in disconnection condition from the one or more corresponding drive wheels via the corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle ( FA) and rear axle (RA) in response to a request for connection of the electric traction motor to the one or more corresponding drive wheels , and said regeneration conditions correspond to a transition in disconnection condition of the electric traction motor currently in connection condition to the one or more corresponding drive wheels via the corresponding engagement device ( FC, RC, FCR, FCL, RCR, RCL ) of said one of said front axle ( FA) and rear axle (RA) in response to the request for disconnection of the electric traction motor from the one or more corresponding drive wheels .

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