A method for controlling the torque of an electric traction motor of an electric powertrain of a vehicle, wherein the electric traction motor can be selectively disconnected 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 is selectively activatable or deactivatable by means of one or more corresponding engagement devices, by controlling the torque thereof in order to reach the rotational speed target which achieves the synchronization of the rotational speed of the electric motor either with a drivetrain downstream thereof (which may comprise a transmission / a differential and one or more drive wheels connected to the transmission / to the differential, or directly with a drive wheel, if the electric motor is directly coupled with the drive wheel, or if the engagement device is arranged between the transmission and the drive wheel (s)), while respecting the limits of the power absorbed and generated by the motor and the torque limits envisaged for the motor. Moreover, the method ensures an accurate control and a consequent limitation of the wear of the engagement devices.

Description

[0001] "A method for controlling the torque of an electric traction motor of an electric powertrain of a vehicle, wherein the electric traction motor can be selectively disconnected from one or more drive wheels operatively connected thereto"

[0002] ★★★★

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention refers to vehicles having an electric powertrain, of the type which includes electric traction motors distributed between a front axle and a rear axle.

[0006] Prior Art

[0007] In a vehicle with an electric powertrain of the type which includes traction motors distributed between a front axle and a rear axle, a disconnection is generally controlled of at least one electric traction motor with or from one or more corresponding drive wheel operatively associated therewith, when the torque request by the driver can be satisfied by the remaining one or more traction motors. The disconnection is operated with the aim of improving the general efficiency, since the rotational drag of an electric traction motor which is not involved in meeting the torque request by the driver only leads to energy dissipation .

[0008] The disconnection, as well as the subsequent reconnection, are operated by means of a mechanical engagement (which is electrically operated and electronically controlled) generally of the dog clutch (front-teeth) type. This is due to the need to guarantee the possibility of transmitting the torque and to limit the wear in time as compared to, for example, a friction clutch.

[0009] The problem consists in the fact that such engagement devices require a synchronization of the rotational speed of the electric motor with the rotational speed of the drivetrain downstream thereof at the moment of restoring the mechanical connection. The synchronization is necessary in order to avoid an early wear of the engagement teeth, noise at the moment of the engagement and jerky movements in the drivetrain. The drivetrain 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 if the motor is directly coupled with the drive wheel, or if the engagement device is arranged between the transmission and the drive wheel(s).

[0010] The operation of synchronization of the rotational speed of the electric traction motor at the moment of reconnection with the drive train downstream thereof must however be performed while respecting the limits of the power absorbed and generated by the motor, and the torque limits envisaged for the motor. With respect to such needs, the known art substantially does not propose feasible solutions.

[0011] Object of the Invention

[0012] The invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the invention is to provide a method for controlling the torque of an electric traction motor of an electric powertrain of a vehicle, wherein the electric traction motor can be selectively disconnected 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 synchronizing the rotational speed of the electric motor with the drivetrain downstream thereof (which, as mentioned in the foregoing, may comprise a transmission / a differential and one or more drive wheels connected to the transmission / to the differential, or directly one drive wheel if the electric motor is directly coupled to the drive wheel or if the engagement device is arranged between the transmission and the drive wheel (s), while respecting the limits of power absorbed and generated by the motor and the torque limits envisaged for the motor.

[0013] Summary of the Invention

[0014] The object of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein with 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 means of non-limiting example only and wherein:

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

[0018] Figures 2 to 9 show diagrams of powertrains wherein the method according to the invention may be implemented,

[0019] - Figure 10 shows time 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,

[0020] Figure 11 shows a functional block diagram representative of the method according to the invention,

[0021] - Figures 12 to 19 show diagrams representative of steps - or parts thereof - performed in the method according to the invention.

[0022] Detailed Description

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

[0024] The method according to the invention may be implemented on vehicles V with an electric powertrain including:

[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) includes 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 or from the corresponding electric traction motor.

[0027] Figures 2 to 9 show exemplary configurations of electric powertrains which comprise the features under consideration, and which have an electric traction motor which may be selectively connected and disconnected to / 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 drivetrain unit 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 drive, rotatably connected to a drive wheel of one of said front axle FA and rear axle RA and connectable to the electric traction motor via the engagement device, e.g. an axle drive shaft (see Figures 2, 3, 6, 7),

[0029] - a differential having an input shaft connectable to the electric traction motor via 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),

[0030] - a transmission having an input shaft connectable to the electric traction motor via 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 (not shown in the Figures for brevity).

[0031] Of course, upstream of the engagement device there may be provided a direct connection 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 only the differential is specifically shown).

[0032] In detail, with reference to Figures 2 to 9:

[0033] Figure 2 shows a vehicle V with an electric 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 via a transmission GBX1, the electric motor M2 is permanently connected to a rear right wheel RR via a transmission GBX2, and the motor M3 is connected in a disengageable manner to both the front left drive wheel FL and the front right drive wheel FR by means of a front differential FD. A first engagement device FCL is arranged between the differential FD and the wheel FL, whereas a second engagement device FCR is arranged between the differential FD and the wheel FR; thus, both engagement devices are located between the transmission (differential FD) and the drive wheels, and not between the electric traction motor (M3) and the transmission (differential FD);

[0034] Figure 3 shows a vehicle V with an electric powertrain comprising a single electric traction motor Ml associated with the rear axle RA and a single electric traction motor M3 associated with the front axle FA. The electric motor Ml is permanently connected to both the rear left wheel RL and the rear right wheel RR via a rear differential RD, whereas the motor M3 is connected in a disengageable manner to both the front left drive wheel and the front right drive wheel FR via a front differential FD and via engagement devices FCL and FCR according to a configuration identical to the configuration described in Figure 2;

[0035] Figure 4 shows a vehicle V with an electric 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 identical to the configuration of Figure 2, i.e. with the electric motor Ml being permanently connected to the rear left drive wheel RL via the transmission GBX1, and the electric motor M2 being permanently connected to the rear right wheel RR via the transmission GBX2, and moreover comprising a single motor M3 associated with the front axle FA. The motor M3 is connected in a disengageable manner to both the front left drive wheel FL and the front right drive wheel FR via a front differential FD, but unlike Figures 2 and 3 the configuration of Figure 4 envisages a single engagement device FC arranged between the motor M3 and the differential FD; therefore, the engagement device FC is located between the electric traction motor (M3) and the transmission (differential FD);

[0036] Figure 5 shows a vehicle V with an electric powertrain comprising a single 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 has the configuration as per Figure 3, thus the motor Ml is permanently connected to both the front left drive wheel FL and the front right drive wheel FR via the rear differential RD, whereas the front axle FA has the configuration as per Figure 4, i.e. the motor M3 is connected in a disengageable manner to both the front left drive wheel FL and the front right drive wheel FR via a front differential FD, with an 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);

[0037] Figure 6 shows an electric powertrain with a mirror-like configuration with respect to the configuration of Figure 2, specifically comprising an electric traction motor M3 and an electric traction motor M4 which are both associated to 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 via a transmission GBX3, the electric motor M4 is permanently connected to a front right drive wheel FR via a transmission GBX4, and the motor Ml is connected in a disengageable manner to both the rear left drive wheel RL and the rear right wheel RR via 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 is arranged between the differential RD and the wheel RR; therefore, both the engagement devices are located between the transmission (differential RD) and the drive wheels, and not between the electric traction motor (Ml) and the transmission (differential RD);

[0038] - Figure 7 shows a configuration of a powertrain which is mirror-like with respect to the configuration of Figure 3, specifically 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, wherein the electric motor M3 is permanently connected to both the front left drive wheel FL and the front right drive wheel FR via a front differential FD, whereas the motor Ml is connected in a disengageable manner to both the rear left drive wheel RL and the rear right drive wheel RR via a rear differential RD and via the engagement devices RCL and RCR, according to a configuration identical to the configuration described in Figure 6;

[0039] - Figure 8 shows a mirror-like configuration with respect to Figure 4, i.e. comprising 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 configuration of Figure 6, i.e. with the electric motor M3 being permanently connected to the front left drive wheel FL via the transmission GBX3, and the electric motor M4 being permanently connected to the front right drive wheel FR via the transmission GBX4, and moreover comprising a single motor Ml associated with the rear axle RA. The motor Ml is connected in a disengageable manner to both the rear left drive wheel RL and the rear right drive wheel RR via a rear differential RD, but unlike Figures 6 and 7 the configuration of Figure 8 envisages a single engagement device RC arranged between the motor Ml and the differential RD; in other words, the engagement device RC is located between the electric traction motor (Ml) and the transmission (differential RD);

[0040] - Figure 9 shows a mirror-like configuration with respect to 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 corresponds to 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 via the front differential FD, whereas the rear axle RA corresponds to the configuration of Figure 8, and therefore the motor M! is connected in a disengageable manner to both the rear left drive wheel RL and the rear right drive wheel RR via the rear differential RD, with the engagement device RC arranged between the motor Ml and the differential RD. In the same way as in Figure 8, the engagement device RD is located between the electric traction motor (Ml) and the transmission (differential RD).

[0041] The following description refers, as regards the synchronization operation and as regards the method according to the invention, to a general "electric traction motor", obviously assuming that it is a traction motor along the powertrain thereof, up to the respective drive wheel(s), there is arranged an engagement device. This concerns, with reference to Figures 2 to 9, either the motor M3 (Figures 2 to 5) or the motor Ml (Figures 6 to 9), and 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).

[0042] This being said, and with reference to the Figures 1 and 11, the method according to the invention includes determining a target torque value TSpdCtrl Tgtfor an electric traction motor currently disconnected from one or more corresponding drive wheels by means of a corresponding engagement device (FC, RC, FCR, FCL, RCR, RCL) of said one of the front axle FA and rear axle RA in response to a request for a transition to a condition of connection to the one or more corresponding drive wheels, wherein determining the target torque value TspdctriTgt includes:

[0043] - determining (block 2) a target torque value by open-loop calculation TSpdCtrl 0L Tgtas a function of a target rotational speed nMot Tgtof the electric traction motor, as a function of a resisting torque TMot Lossinternal to the electric traction motor dependent on said target rotational speed value nMot Tgt, and optionally as a function of a resisting torque TTrnsm Lossinternal to a transmission connecting the electric traction motor to the corresponding one or more drive wheels dependent on said target rotational speed value nMot Tgt,

[0044] - determining (block 4) a target torque value by closed-loop calculation TSpdCtrl CL Tgtas a function of a difference AnMotbetween the target rotational speednMot_Tgt and a current rotational speed nMot Actof the electric traction motor, and as a function of an upper limit TSpdCtrlprpLim of the torque of the electric traction motor and a lower limit TSpdCtrl RegLimof the torque of the electric traction motor,

[0045] - determining (block 6) the target torque value TSpdCtriTgtas afunction of said target torque value determined by open-loop calculation TSpdCtrl 0L Tgtand target torque value determined by closed-loop calculation TSpdCtrl CL Tgt, and as a function of said upper torque limit TSpdCtrl PrpLimand of said lower torque limit TspactrijiegLim of the electric traction motor.

[0046] Figure 10 shows a set of time diagrams which show the evolution of some values or variables which are involved in the method according to the invention during a manoeuvre of transition from a disconnected condition to a connected condition between the electric traction motor and the corresponding drive wheel (s). The references A, B, C denoted three reference time instants for the manoeuvre, specifically:

[0047] A: sending of the request of transition from a disconnected condition to a connected condition between the electric traction motor and the corresponding drivetrain. In this case, the request concerns the front axle, and the related diagram is depicted in Figure 2; thus, the request for connection concerns the motor M3 and the engagement devices FCL, FCR. This practically corresponds to a request to synchronize the rotational speed of the electric motor and of the drivetrain (drive wheel only or drive wheel and transmission / differential) located downstream of the engagement device in a disconnected condition; the request can be satisfied within the limits of electric power absorption / regeneration and of the related maximum (positive, in the case of propulsion) and minimum (negative, in the case of regeneration) torque values which are output and absorbed by the electric traction motor;

[0048] B: completed synchronization of the rotational speeds, and sending of a request for switching the engagement device to an operative condition which brings about the connection of the electric traction motor;

[0049] C: complete switching of the engagement device to an operative condition which provides the connection of the electric traction motor. The control of the rotational speed of the electric traction motor is no longer required.

[0050] The diagram 10A shows the evolution in time of the rotational speed nMotActof the electric traction motor M3 and of the target rotational speed nMot Tgt. The diagram 10B shows an evolution in time of the torques (in the present case, propulsion torques) output by the set of motors Ml, M2 (torque TM1+M2) and by the motor M3 as per the method according to the invention (TSpdCtri M3), also showing an upper (propulsion) torque limit for the motor M3 (TSpdCtrlPrpLimM3). The diagram IOC shows the evolution in time of the operative condition of the engagement device, specifically of the target condition Tgt and of the current condition Act (discrete values "Connected" and "Disconnected"), whereas the diagram 10D shows a logic state of a variable Motor_Speed_Control_Req representative of the need of controlling the rotational speed of the motor M3. The logic state is binary - therefore either TRUE ("1") or FALSE ("0") - and according to the description the value thereof is "1" from A to C and "0" elsewhere.

[0051] The following Figures 12 to 19 show steps and / or determinations operated as per the method according to the invention, and will now be commented individually.

[0052] Referring to Figure 12, diagram 10, determining the target torque value TSpdCtrl Tgtas a function of the target torque value determined by open-loop calculation Tspactri_OL_Tgt and of the target torque value determined by closed-loop calculation TSpdCtrl CL Tgt(the latter corresponding to a correction of the torque value determined by open-loop calculation TSpdCtrl 0L Tgt, therefore being dimensionally a torque value, but as regards the calculation being a correction which is overlaid to the value TSpdCtrl0LTgt) includes:

[0053] - calculating a sum, block 12, of the target values TSpdctn_OLTgt and TSpdCtrl CL Tgt(which expresses the correction operation mentioned in the foregoing),

[0054] - determining a raw target torque value TSpdCtrlRaw Tgtas the lower (block 14) of: a) the upper torque limit TSpdCtrl PrpLimof the electric traction motor, and b) the greater (block 16, MAX) of the lower torque limit TSpdCtrl RegLimof the electric traction motor and the In other words, considering the technical problem which is solved by the present invention, what has just been described corresponds to defining an upper limit (block 14, MIN) of the sum TSpdCtrl 0L Tgt+ TSpdCtrl CL Tgt, which corresponds to the unlimited result of the torque control achieved by the method according to the invention, as the maximum admissible value of the propulsion torque Tspactri_PrpLim which can be output by the electric traction motor, and to defining a lower limit of the sum TSpdctn_OLTgt + TSpdCtrl CL Tgt(block 16 MAX) as the minimum admissible value of the regeneration torque TSpdCtrl RegLimwhich can be absorbed by the electric traction motor. The propulsion torque value TSpdCtrl PrpLimand the regeneration torque value TSpdCtrl RegLimare denoted as "maximum" and "minimum" due to the sign, since the propulsion torques have positive values and the regeneration torques have negative values; therefore, "maximum" and "minimum" do not necessarily refer to the respective absolute values. The torques TSpdCtrl PrpLimand TspdctrijiegLim are determined by calculations external to the scope of the method according to the invention, and i.a. they are determined as a function of the characteristics of the high-voltage battery which supplies the electric traction motor and of the speed of the electric traction motor, since their purpose is to limit the electric power absorption from, and the electric power supply to, the high-voltage battery. In this regard, the Applicant has already proposed various technical solutions, e.g. those described in the Italian Industrial Invention Applications n. 102023000023517, 102024000000369, 102024000001104.

[0055] Always referring to Figure 12, the calculation of the target torque value TSpdCtrl Tgttakes place as described above if there is a request to synchronize the speed of the electric traction motor. This is represented by a switch SW10 and a block 18, which defines the condition of the presence of the request to synchronize the rotational speed of the electric traction motor with the rotational speed of the drivetrain (either drive wheel only or drive wheel and transmission / differential) located downstream of the engagement device in the disconnected condition by means of a variable Motor_Speed_Control_Req which acquires the logic state "1" (True) when there is a request, and the logic state "0" (False) when there is no request. The condition shown in Figure 12 corresponds to the condition Motor_Speed_Control_Req = True ("1"), whereas in the case opposite to the instance shown in Figure 1 True, and therefore _ _ _ alse "0") the target value Tspactri_Tgt corresponds to zero value (block 19). The variable Motor_Speed_Control_Req is the object of the diagram of the previous Figure 10D.

[0056] The following Figure 13, diagram 20, shows the determination of the target torque value by open-loop calculation TSpdCtrl0LTgt. This includes:

[0057] - determining a raw target torque value calculated in open loop TSpdCtrl 0L Raw Tgtas a sum (block 22) of the resisting torque TMotLossinternal to the electric traction motor, and of the resisting torque TTrnsm Lossinternal to the transmission which connects the electric traction motor to the corresponding one or more drive wheels. As regards the latter aspect, the following description will illustrate the meaning of the term "optionally" used in the description of block 2 with respect to the calculation of TSpdCtrl Tgt;

[0058] - determining the target torque value by open-loop calculation TSpdCtrl0LTgtas the lower (block 24) of: a) the upper torque limit TSpdCtrl PrpLimof the electric traction motor, and b) the greater (block 26, MAX) between the lower torque limit TSpdCtrl RegLimof the electric traction motor and the raw target torque value calculated in open loop TspdCtrl_OL_Raw_Tgt•

[0059] As in the previous case, what has just been described corresponds to defining an upper limit (block 24, MAX) for the value TSpdCtrl 0L Tgt, which corresponds to the non-limited result of the open-loop calculation, as the maximum admissible value of the propulsion torque Tspactri_PrpLim which can be output by the electric traction motor, and to defining a lower limit for the value TspdctriOLTgt (block 26, MAX) as the minimum admissible value of the regeneration torque TSpdCtrl RegLimwhich can be absorbed by the electric traction motor.

[0060] As regards the calculation of the resisting torques TMot_Loss and TTrnsm Loss, reference is to be made to Figures 14 and 15. The torques under consideration are summed because they correspond to actions contrasting the attempt to reach the target rotational speed tMot Tgt; therefore, the electric traction motor involved in the synchronization of the rotational speed with respect to the drivetrain is required to contrast the action of such resisting torques. Both resisting torques depend on the target rotational speed and on a temperature. For the torque TMot Loss, such a temperature corresponds to the temperature of the electric traction motor, which determines the air temperature in the gap between the rotor and the stator of the motor. The lower the temperature, the greater the air viscosity in the gap, the greater the resisting torque TMot Loss. For the torque TTrnsm_Losst such a temperature corresponds to the temperature of the lubricant of the transmission of the electric traction motor. The lower the temperature, the higher the lubricant viscosity of the drivetrain of the electric traction motor, the greater the resisting torque T .nsm Ross.

[0061] On an operative level, the calculation of the torques TMotLossand TTrnsm Lossis performed by using maps, which output the respective values as a function ofnMot_Tgt and of the corresponding temperatures involved.

[0062] Referring to Figure 14, diagram 30, the torque TMotLoss is determined by means of a map M30 which outputs the value TMotLossby using, as input data, nMotTgtand a temperature value of the electric traction motor TempMot. The map M30 in Figure 14 shows, by way of example, four torque curves TMotLossas a function of the rotational speednMot_Tgtr parameterized with respect to corresponding temperature values of the electric traction motor TempMotl, TempMot2, TempMot3, TempMot4, wherein TempMotl < TempMot2 < TempMot3< TempMot4. On a qualitative level, the torque TMotLossincreases as the speed nMotTgtincreases, and decreases as the temperature TempMotincreases.

[0063] Referring to Figure 15, diagram 40, the torque TTrnsm Loss is determined by using a map M40 which outputs a raw value TTrnsm Loss Rawof the torque TTrnsmLossby using, as input data, nMotTgtand a temperature value TempTrnsmof the lubricant of the transmission which connects the electric traction motor to the corresponding drivetrain. The map M40 in Figure 15 shows by way of example four torque curves TTrnsm Loss Rawas a function of the rotational speednMot_Tgtr parameterized with respect to corresponding temperature values of the lubricant of the transmission TempTrnsml, TempTrnsm2, TempTrnsm3, TempTrnsm4, wherein TempTrnsml < TempTrnsm2 < TempTrnsm3 < TempTrnsm4. On a qualitative level, the torque TTrnsm Loss Rawincreases as the speed nMotTgtincreases, and decreases as the temperature TempMotincreases.

[0064] Always referring to Figure 15, the torque TTrnsm_Loss_Raw corresponds to the torque TTrnsmLossif the transmission is located between the electric traction motor and the corresponding engagement device (FC, RC, FCR, FCL, RCR, RCL), i.e. if the transmission remains connected to the motor, irrespective of the condition of the engagement device. This is represented by a switch SW40 which is subjected to a control variable Trnsm_between_Mot_Disc. The control variable Trnsm_between_Mot_Disc acquires the logic state "1" (True) when the transmission remains connected to the motor, irrespective of the condition of the engagement device (i.e. when the transmission is located between the electric traction motor and the engagement device), and the logic state "0" (False) when the transmission is disconnected from the electric traction motor, when the engagement device brings about a disconnection of the electric traction motor from the corresponding one or more drive wheels (i.e. when the transmission is located between the electric traction motor and the engagement device). As a consequence, if Trnsm_between_Mot_Disc = True ("1") holds true, which is the condition represented in Figure 15 and corresponding to the block 42, TTrnsm Loss=r^Trnsm_Loss_Raw holds true. If the contrary holds true, i.e. Trnsm_between_Mot_Disc and thus Trnsm_between_Mot_Disc ("0"), then TTrnsmLossis equal to zero value (block 44), since in conditions of disconnection of the electric motor from the drive wheel (s) the transmission remains connected to the drive wheel (s), and does not perform any antagonistic action with respect to the electric traction motor. In this regard, in the calculation of the target value TSpdCtrl 0L Tgt, the value TTrnsm Lossis taken into account only optionally: if the powertrain is configured in such a way that the connection between the electric traction motor and the transmission is never separated, not even with the disconnection of the engagement device, then the value Trrnsm_Loss is taken into consideration, otherwise it is not.

[0065] Wit reference to Figure 16, diagram 50, and to the following Figures 17 to 19, there will now be described the determination of the target torque value - specifically the target torque correction value - by closed-loop calculation TSpdCtrl CL Tgt. The value TSpdCtrLCLTgtis determined by summing (block 52) a proportional torque correction value TSpdCtrl Propand an integral torque correction value TSpdCtrlInt. Both values TSpdCtrlPropand TSpdCtrlIntdepend on the difference &nMot(diagram 60, block 62) between the target rotational speed nMotTgtand the current rotational speed nMotActof the electric traction motor. The difference AnMotis an input data item for the calculations shown in the following Figures 18,19.

[0066] Referring to Figure 18, diagram 70, determining the proportional torque correction value TSpdCtrlPropincludes:

[0067] - defining a raw target value of proportional torque correction TSpdCtrlPropRawas a function of the difference hnMotbetween the target rotational speed nMotTgtand the current rotational speed nMotActof the electric traction motor, calculating the target value of proportional torque correction TSpdCtrl Propas the lower (block 72, MIN) of: a) a difference (block 74) between the upper torque limit TSpdCtrl PrpLimof the electric traction motor and the target torque value determined by open loop calculation TspdCtrl_OLTgtrand b) the greater (block 76, MAX) of the raw target value of proportional torque correction TSpdCtrlPropRawand a difference (block 78) between the lower limit Tspdctri_RegLim of the torque of the electric traction motor and the target torque value determined by open loop calculation TSpdCtrl 0L Tgt. The value TSpdCtri Prop Rawis extracted from a map M70 as a function of the difference &nMot. The map M70 shows a curve - with qualitative evolution - of values Tspdctrij>rop_Rawas afunction of the difference &nMotwith respect to a value of null correction corresponding to the points hnMot= 0 rpm and TSpdCtrl Prop Raw= 0 Nm, thus with respect to the conditions of speed synchronization between the electric traction motor and the corresponding drivetrain. For positive values of &nMot, i.e. in conditions wherein the current speed nMot Actis lower than the target speed nMot Tgt, also the torque correction values TSpdCtrl Prop Raware positive, and therefore correspond to a correction in the direction of accelerating the electric traction motor to reach the target value nMot Tgt. For negative values of hnMot, i.e. in conditions wherein the current speed nMot Actis greater than the target speed nMot Tgt, also the torque correction values TSpdCtrl Prop Raware negative, and therefore they correspond to a correction in the direction of braking the electric traction motor to reach the target valuenMot_Tgt• The blocks 76 and 72 respectively define the lower limitation and the upper limitation of the value Tspdctrij>rop_Raw • The lower limit, difference 78, corresponds to the difference TSpdCtrl RegLim- TSpdCtrl 0L Tgt, i.e. to the limit value of regeneration power (thus, the minimum value) reduced by the margin which has already been used by the open-loop control. The upper limit, difference 74, corresponds to the difference TSpdCtrl PrpLimTspdctriOLTgtt i.e. to the limit value of propulsion power (thus, the maximum value) reduced by the margin which has already been used by the open-loop control. The result of the upper and lower limits is the proportional torque correction value TSpdCtrl Prop.

[0068] Referring to Figure 19, diagram 80, the integral torque correction value TSpdCtrl Intis determined by means of an integral controller 82 as a function of an unlimited integral torque correction value &TIntdependent on the difference AnMotbetween the target rotational speed nMotTgtand the current rotational speednMotAct of the electric traction motor, and having a lower saturation limit 84 and an upper saturation limit 85. The lower saturation limit 84 is equal to a difference (block 86) TSpdCtriRegLim— TSpdCtri 0L Tgt— TSpdCtri Prop. The value TSpdCtriint is reset (block R82) when the need ceases to control the rotational speed of the electric traction motor in order to achieve synchronization, thus when holds true and therefore

[0069] The upper saturation limit 85 is equal to a difference (block 88) TSpdCtriPrpLim— TSpdCtri0LTgt— TSpdCtriPropwherein:

[0070] - TspactrijiegLim il the lower (regeneration) torque limit of the electric traction motor,

[0071] - Tspactri_PrpLim is the upper (propulsion) torque limit of the electric traction motor,

[0072] - Tspdctri_OL_Tgt is the target torque value determined by open-loop calculation,

[0073] - Tspdctri_Prop is the target value of proportional torque correction.

[0074] The integral torque correction value &TIntis extracted from a map M82 as a function of the difference &nMot• The map M82 shows a curve - with a qualitative evolution - of values &TIntas a function of the difference &nMotwith respect to a null correction value corresponding to the points &nMot= 0 rpm and &TInt= 0 Nm, i.e. with respect to the conditions of speed synchronization between the electric traction motor and the corresponding drivetrain. For positive values of &nMotr i.e. in conditions wherein the current speednMot_Act is lower to the target speed nMot_Tgtr also the integral correction values &TIntare positive, and therefore correspond to a correction in the direction of accelerating the electric traction motor to reach the target value nMot Tgt. For negative values of hnMot, i.e. in conditions wherein the current speed nMot Actis greater than the target speed nMot_Tgtr also the integral correction values &TIntare negative, and therefore correspond to a correction in the direction of braking the electric traction motor to reach the target valuenMotTgt• The blocks 76 and 72 define the lower limitation and the upper limitation of the integral correction value ^TInt. The lower saturation limit corresponds to the difference TSpdCtri RegLim— TSpdCtri 0L Tgt— TSpdCtri Prop, i.e. to the limit value of regeneration power (thus the minimum value) reduced by the margin which has already been used by the open-loop control and by the margin which has already been used by the proportional correction. The upper saturation limit corresponds to the difference Tspdctri_PrpLim ~ TSpdCtri 0L Tgt— TSpdCtri Prop, i.e. to the limit value of propulsion power (thus the maximum value) reduced by the margin which has already been used by the open-loop control. As is commonly known, the integral control is a relatively slow control in comparison with the proportional control, and therefore the proportional control outputs a torque correction value to a first approximation and with a faster determination, whereas the integral control substantially performs a finishing improvement of the "coarse" action of the proportional control. In the first iterations of the calculation, which are still far from the target nMot Tgt, the proportional control is predominant, whereas in the last iterations of the calculation, which are closer to the target nMot_Tgtr the contribution of the proportional control decreases noticeably, and the correction has fundamentally an integral nature. Thanks to the method according to the invention it is therefore 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 is selectively activatable or deactivatable by means of one or more corresponding engagement devices, by controlling the torque whereof in order to reach the rotational speed target which achieves the synchronization while respecting the limits of the power absorbed and generated by the motor, and the torque limits envisaged for the motor. Moreover, the method ensures an accurate control and a consequent limitation of the wear of the engagement devices.

[0075] 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 in the annexed claims.

Claims

CLAIMS1. A method for controlling the torque of an traction electric motor of an electric powertrain of a vehicle, the electric powertrain including:- at least one traction electric motor operatively associated with at least one drive wheel of a front axle of the vehicle- at least one traction electric motor operatively associated with at least one drive wheel of a rear axle of the vehicle, wherein 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 drive wheels of the axle (FA, RA) to the corresponding traction electric motor, and disconnect the one or more drive wheels of the axle (FA, RA) from the corresponding traction electric motor, the method including determining a target torque value (TSpdCtrl Tgt} for a traction electric motor currently disconnected 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 the front axle (FA) and rear axle (RA) in response to a request for returning in a condition of connection of the traction electric motor to the one or more corresponding drive wheels, wherein determining said target torque value (TSpdCtrlTgt) includes:- determining (2) a target torque value by openloop calculation (TSpdCtrl 0L Tgt) as a function of a target rotational speed (TLMotTgt) of the electric traction motor, as a function of a resisting torque (TMotLoss) internal to the traction electric motor dependent on said target rotational speed value (TLMotTgt), and optionally as a function of a resisting torque (TTrnsm Loss) internal to a transmission connecting the traction electric motor tothe corresponding one or more dependent drive wheels by this target rotation speed value (nMotTgt') / - determining (4) a target torque value by closed- loop calculation CTSpdCtrl CL Tgt} as a function of a difference (hnMot) between the target rotational speed ^nMot_Tgt') and a current rotational speed (nMot Act} of the electric traction motor, and as a function of an upper limit (TSpdCtrl PrpLim) of the torque of the traction electric motor and a lower limit (TSpdCtrl RegLim) of the torque of the electric traction motor, determining (6) said target torque value (T’spdctrijrgt')onthe basis of said target torque value determined by open-loop calculation (TSpdCtrl 0L Tgt} and target torque value determined by closed-loop calculation (TSpdCtrl CL Tgt), and on the basis of said upper torque limit (TSpdCtrl PrpLim) and lower torque limit (TspdctrijtegLtm') of the traction electric motor.

2. The method of claim 1, wherein determining said target torque value (TSpdCtrl Tgt) as a function of said target torque value determined by open-loop calculation (T’spdctri_OL_Tgt') and said target torque value determined by closed-loop calculation (TSpdCtrl CL Tgt) includes:- calculating a sum (12) of said target torque value determined by open-loop calculation (TSpdCtrl 0L Tgt) and target torque value determined by closed-loop calculation (TSpdCtrl CL Tgt), determining a raw target torque value (TspdctriRawTgt'l as the lower (14) of:(a) the upper torque limit (TSpdCtrl PrpLim) of the traction electric motor, and(b) the greater (16) of the lower torque limit (TspdctrijtegLtm') of the traction electric motor and the sum (12) of said target torque value determined by open-loop calculation (TSpdCtrl 0L Tgt) and target torque value determined by closed-loop calculation (TSpdCtrl CL Tgt)if there is a request to synchronize the speed of the traction electric motor (Motor_Speed_Control_Req = 1).

3. The method of claim 1 or claim 2, wherein determining that target torque value by open-loop calculation (TSpdCtrl 0L Tgt) includes:- determining a raw target torque value calculated in an open loop (TSpdCtrl 0L Raw Tgt) as a sum of said resisting torque (7MOtLoss) internal to the electric traction motor, and said resisting torque (TTrnsm Loss) internal to a transmission that connects the traction electric motor to the corresponding one or more drive wheels,- determining the target torque value by open-loop calculation (TSpdCtrl0LTgt) as the lower (24) of:(a) the upper torque limit (TSpdCtrl PrpLim) of the traction electric motor, and(b) the greater (26) of the lower torque limit (TspdctrijtegLtm') of the traction electric motor and the raw target torque value calculated in an open loop (TspdCtrl_OL_Raw_Tgt)r wherein said resisting torque (TTrnsm Loss) internal to a transmission that connects the traction electric motor to the corresponding one or more drive wheels is equal to zero value if the transmission is not arranged between the traction electric motor and the corresponding engagement device (FC, RC, FCR, FCL, RCR, RCL).

4. The method according to any of the preceding claims, wherein said resisting torque (TMotLoss) internal to the traction electric motor depends on that target rotational speed value (nMotTgt) and a temperature (TempMot) of the traction electric motor, and said resisting torque (TTrnsm Loss) internal to a transmission connecting the traction electric motor to the corresponding one or more driving wheels depends on saidtarget rotational speed value (nMotTgt') and a temperature (TempTrnsrrl) of a lubricant of said transmission.

5. The method of any of the above claims, wherein determining said target torque value by closed-loop calculation (TSpdCtrl CL Tgt) includes summing (52) a proportional target torque correction value (TSpdCtrl Prop) and an integral target torque correction value (TspdCtrlJnt)•6. The method of claim 5, wherein determining said target proportional torque correction value (TSpdCtrl Prop) includes:- defining a raw target value of proportional torque correction (TSpdCtrl Prop Raw) as a function of the difference (hnMot) between the target rotational speed (nMot Tgt') and the current rotational speed (TLMot Act) of the traction electric motor,- calculating said target value of proportional torque correction (TSpdCtrl Prop) as the lower (72) of:(a) a difference (74) between the upper torque limit (Tspactri_PrpLim ) of the traction electric motor and the target torque value determined by open loop calculation(b) the greater (76) of the raw target value of proportional torque correction (TSpdCtrl Prop Raw) and a difference (78) between the lower limit (TSpdCPrl RegLim) of the torque of the traction electric motor and the target torque value determined by open loop calculation (TspdCtrl_OLTgt)•7. The method of claim 6, wherein said integral torque correction value (TSpdCtrl Int) is determined by means of an integral controller (82) as a function of an unlimited integral torque correction value (AT / nt) dependent on that difference (^nMot) between the target rotational speed (nMot_Tgt') and the current rotational speed {nMotAct} of the traction electric motor and havinga lower saturation limit (84) equal to a difference (86)and an upper saturation limit (85) equal to a difference (88)- Tspdctri_RegLtm is said lower torque limit of the traction electric motor- Tspdctri_PrpLim is said upper torque limit of the traction electric motor- Tspdctri_OLTgt is said target torque value determined by open loop calculation- Tspdctri_Prop is said target value of proportional torque correction.

8. The method of any of the preceding claims, wherein said target torque value calculated by closed- loop (TSpdCtrl CL Tgt) is a target torque correction value.

9. The method of any of the preceding claims, wherein said lower torque limit of the traction electric motor (TSpdCtrl RegLim) is a regeneration torque limit, and wherein said upper torque limit (TSpdCtrl RegLim') of the traction electric motor is a propulsion torque limit.

10. The method of any of the preceding claims, wherein said drive feature extends from the engagement device (FCL, FCR, RCL, RCR, FC, RC) to the one or more corresponding drive wheels, and includes one of:- a direct drive connected in rotation to a drive wheel of one of said front axle (FA) and rear axle (RA) and connectable to the traction electric motor via the engagement device, particularly an axle drive shaft,- a differential (FD, RD) having an input shaft connectable to the traction electric motor via the engagement device and first and second output shafts connected in rotation to corresponding drive wheels of the one of said front axle (FA) and rear axle (RA),- a transmission (GBX1, GBX2, GBX3, GBX4) having aninput shaft connectable to the traction electric motor via the engagement device and an output shaft connected in rotation to a corresponding drive wheel of the one of said front axle (FA) and rear axle (RA).

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