A method for controlling the torque output of one or more electric traction motors of an electric powertrain of a vehicle as a function of speed limits of components of the powertrain

Abstract

There is described a method which enables controlling, in propulsion conditions, an electric powertrain of a vehicle (V), wherein each electric motor is operatively connected to one or more corresponding drive wheels (RL, RR, FL, FR) of the vehicle (V) by means of one or more propulsion components. The control acts according to a value of total limit torque (or barycentric torque ) which operates both in order to prevent overspeed in the electric traction motors, and in order to respect those limits of the system which are not necessarily connected to overspeed (by means of the total limit torque TLimPrp), moreover maximising performances by maximizing the torque delivery in the proximity of the limit of overspeed in the one or more electric traction motors of the electric powertrain.

Description

[0001] "A method for controlling the torque output of one or more electric traction motors of an electric powertrain of a vehicle as a function of speed limits of components of the powertrain"

[0002] ★★★★

[0003] TEXT OF THE DESCRIPTION

[0004] Field of the Invention

[0005] The present invention refers to vehicles with an electric powertrain, in particular BEVs. The invention was developed with particular reference to the vehicles having an electric powertrain including at least one electric traction motor operatively connected to at least one wheel of the vehicle itself.

[0006] Known Art

[0007] In the vehicles with an electric powertrain, in particular BEVs, the electric power available for the electric traction motors and the torque which can be developed by the same motors are generally more than sufficient to cause problems of (rotational) speed drift of the propulsion components, such as the motors, the transmission, the tyres. Referring to Figure 1, which shows a diagram of resisting force F as a function of a rotational speed w of a traction motor or of a set of traction motors), the problem derives from the fact that the maximum propulsion force FP- both in a first horizontal section at constant values and in a second hyperbolic section at constant maximum power - is systematically greater than a resistance to advancement FR(so-called coast down drag). This means that this condition occurs both below a limit speed wLIMof the propulsion component being considered, and when the limit speed is reached. This implies that the propulsion components are never intrinsically limited in the respective rotational speed, and that therefore they are subject to problems of speed drift (so-called overspeed - this term will be used in the following description for the sake of brevity, without necessarily abandoning the phrase "speed drift").

[0008] Object of the Invention

[0009] The invention aims at solving the technical problem outlined in the foregoing. Specifically, the object of the invention consists in providing a method for controlling the torque delivered by one or more electric traction motors of an electric powertrain of a vehicle as a function of speed limits of components of the powertrain, so as to ultimately avoid overspeed problems of the propulsion components.

[0010] Summary of the Invention

[0011] The object of the invention is achieved by means of a method having the features set forth in the claims that follow, which form an integral part of the technical disclosure provided herein in relation to the invention.

[0012] Brief Description of the Figures

[0013] The invention will now be described with reference to the annexed Figures, which are provided by way of non-limiting example only, and wherein:

[0014] - Figure 1, already described in the foregoing, shows the evolution of a propulsion force of an electric traction motor and of a resisting force as a function of the rotational speed of the electric motor,

[0015] - Figures 2 to 9 exemplify functional diagrams of a powertrain of a vehicle in which it is possible to implement the method according to the invention,

[0016] - Figure 10 is a flow diagram exemplifying a method according to the invention,

[0017] Figure 11 is a functional block diagram exemplifying the method according to the invention,

[0018] Figures 12 to 20 show aspects of the method according to the invention.

[0019] Detailed Description As a general premise, and referring to the Figures 2 to 9, the method according to the invention may be applied to vehicles V with an electric powertrain, comprising a front axle and a rear axle, and wherein at least either the front or the rear axle comprises at least a traction unit including an electric motor and an operative connection of the electric motor to the respective axle or to a respective axle wheel. For this reason, said operative connection comprises one or more propulsion components, which phrase will be used in the following description.

[0020] Figures 2 to 9 exemplify embodiments of the vehicle V in which it is possible to implement the method according to the invention, and which differ in the configuration of the powertrain. In all the Figures, reference BT generally denotes a battery of the vehicle V, which may be a single battery or a battery pack with distributed arrangement and architecture. The reference P followed by a subscript denotes a power flow which is either delivered (solid-line arrow) or absorbed (dotted- line arrow) by the electric motors of the traction units, the index corresponding to the denomination of the corresponding motor.

[0021] Figure 2 shows a vehicle V with an electric powertrain including a first and a second traction unit, which are associated with the rear axle RA, and a third and a fourth traction unit associated with the front axle FA. This Figure represents the most general configuration of a powertrain to which the method according to the invention is applicable, and it will be taken as a reference in the following description.

[0022] The first traction unit comprises a first electric traction motor Ml, associated (in the same way as the first traction unit as a whole) with a rear left wheel RL of the rear axle, the second traction unit comprises a second electric traction motor M2, associated (in the same way as the second traction unit as a whole) with a rear right wheel RR of the rear axle. The third traction unit comprises a third electric traction motor M3, associated (in the same way as the third traction unit as a whole) with a front left wheel FL of the front axle, the fourth traction unit comprises a fourth electric traction motor M4, associated (in the same way as the fourth traction unit as a whole) with a front right wheel FR of the front axle.

[0023] The mechanical connection between the motors Ml, M2, M3, M4 of the respective traction units and the wheels RL, RR, FL, FR is achieved by means of a direct coupling or by means of a reduction gear. Thus, what defines the set of the propulsion components varies as a function of the features of the mechanical connection.

[0024] Figure 3 shows a vehicle V with an electric powertrain including a first and a second traction unit associated with the rear axle RA, and a third traction unit associated with the front axle FA.

[0025] The first traction unit comprises a first electric traction motor Ml, associated (in the same way as the first traction unit as a whole) with a rear left wheel RL of the rear axle, the second traction unit comprises a second electric traction motor M2 associated (in the same way as the second traction unit as a whole) with a rear right wheel RR of the rear axle, and the third traction unit comprises a third electric motor M3 associated (in the same way as the third traction unit as a whole) with the front axle. The mechanical connection between the motors Ml, M2 of the respective traction units and the wheels RL, RR is achieved by means of a direct coupling or by means of a reduction gear, while the mechanical connection between the motor M3 of the third traction unit and the front axle is achieved by means of a differential gear.

[0026] Figure 4 shows a vehicle V with an electric powertrain which has a substantially reversed configuration in comparison with the vehicle of Figure 3. The powertrain of the vehicle V of Figure 4 includes a first and a second traction unit associated with the front axle FA, and a third traction unit associated with the rear axle RA.

[0027] The first traction unit comprises a first electric traction motor Ml associated (in the same way as the first traction unit as a whole) with a front left wheel FL of the front axle, the second traction unit comprises a second electric traction motor M2 associated (in the same way as the second traction unit as a whole) with a front right wheel FR of the front axle, and the third traction unit comprises a third electric traction motor M3 associated (in the same way as the third traction unit as a whole) with the rear axle. The mechanical connection between the motors Ml, M2 of the respective traction units and the wheels FL, FR is achieved by means of a direct coupling or by means of a reduction gear, while the mechanical connection between the motor M3 of the third traction unit and the front axle is achieved by means of a differential gear.

[0028] Figure 5 shows a vehicle V with an electric powertrain with a single traction unit, operatively associated with the rear axle RA. The front axle FA does not include any drive wheels. The powertrain of the vehicle V in Figure 5 includes a first traction unit associated with the rear axle RA. The first traction unit comprises a first electric motor Ml associated (in the same way as the first traction unit as a whole) with the rear axle RA. The mechanical connection between the motor Ml and the axle RA is achieved by means of a differential gear. Figure 6 shows a vehicle V with an electric powertrain with a single traction unit operatively associated with the front axle. The rear axle RA does not include any drive wheels. The powertrain of the vehicle V in Figure 6 includes a first traction unit associated with the front axle FA. The first traction unit comprises a first electric motor Ml associated (in the same way as the first traction unit as a whole) with the front axle FA. The mechanical connection between the motor Ml and the axle FA is achieved by means of a differential gear.

[0029] Figure 7 shows a vehicle V with an electric powertrain including a first and a second traction unit associated with the rear axle RA.

[0030] The first traction unit comprises a first electric traction motor Ml associated (in the same way as the first traction unit as a whole) with a rear left wheel RL of the rear axle, and the second traction unit comprises a second electric traction motor M2 associated (in the same way as the second traction unit as a whole) with a rear right wheel RR of the rear axle. The mechanical connection between the motors Ml, M2 of the respective traction units and the wheels RL, RR is achieved by means of a direct coupling or by means of a reduction gear.

[0031] Figure 8 shows a vehicle V with an electric powertrain having a substantially reversed configuration with respect to the vehicle of Figure 7. The powertrain of the vehicle V of Figure 8 includes a first and a second traction unit associated with the front axle FA. The first traction unit comprises a first electric traction motor Ml associated (in the same way as the first traction unit as a whole) with a front left wheel FL of the front axle, and the second traction unit comprises a second electric traction motor M2 associated (in the same way as the second traction unit as a whole) with a front right wheel FR of the front axle. The mechanical connection between the motors Ml, M2 of the respective traction units and the wheels FL, FR is achieved by means of a direct coupling or by means of a reduction gear.

[0032] Figure 9 shows a vehicle V having an electric powertrain with a single traction unit on each axle. The powertrain of the vehicle V in Figure 9 includes a first traction unit associated with the rear axle RA and a second traction unit associated with the front axle FA.

[0033] The first traction unit comprises a first electric traction motor Ml associated (in the same way as the first traction unit as a whole) with the rear axle RA, whereas the second traction unit comprises a second electric traction motor M3 associated (in the same way as the second traction unit as a whole) with the front axle FA. The mechanical connection between the motors Ml, M3 of the respective traction units and the axles RA, FA is achieved by means of respective differential gears.

[0034] Referring to the Figures 10, 11 (and to the most general case of a powertrain shown in Figure 2), the method according to the invention for controlling the torque output by one or more electric traction motors Ml, M2, M3, M4 of an electric powertrain of a vehicle V, wherein each electric motor is operatively connected to one or more corresponding drive wheels RL, RR, FL, FR of the vehicle V by means of one or more propulsion components, comprises:

[0035] - determining (block 2) a limit rotational speed value Mot_Lim_lr W Mot_Lim_2r W Mot_Lim_3r W Mot_Lim_4 for each electric traction motor Ml, M2, M3, M4 (the subscript number 1, 2, 3, 4 denotes the association with the motors Ml, M2, M3, M4) as a function of one or more limit rotational speed values of the corresponding one or more propulsion components, determining a limit value VLimof a vehicle advancement speed (block 4) as a function of one or more limit advancement speed values, each determined on the basis of the limit rotational speed value wMotLim i, w Mot_Lim_2, W Mot_Lim_3, wMot_Lim_4 of a corresponding electric traction motor Ml, M2, M3, M4,

[0036] - determining (block 6) a first value of total limit torque TLimprpthat can be output by the one or more electric traction motors Ml, M2, M3, M4 of the powertrain as a function of one or more of a maximum torque value TMaxdetermined on the basis of a limit of electrical power that can be absorbed by the electric powertrain, a value of maximum total torque TTCSMax determined on the basis of a vehicle grip limit, and a value of maximum total torque TTgtrequested to the electric powertrain by a driver of the vehicle (so-called barycentric torque),

[0037] - determining (block 8) a second value of total limit torque TMaxSpdLim that can be output by one or more electric traction motors of the powertrain in order to prevent exceeding the limit rotational speed value WMot_Lim_lr W Mot_Lim_2r W Mot_Lim_3r W Mot_Lim_4 Of each electric traction motor Ml, M2, M3, M4 as a function of the first value of total limit torque TLimprpand a difference between the limit rotational speed wMotLim i, w Mot Lim2, w Mot Lim 3, w Mot Lim 4 of each electric traction motor Ml, M2, M3, M4 and a current rotational speed wMot i, w Mot2, w Mot3, w Mot 4 of the same electric traction motor,

[0038] - controlling the one or more electric traction motors Ml, M2, M3, M4 of the electric powertrain as a function of the second value of total limit torque TMaxSpdLim•

[0039] Each step of the method according to the invention will now be detailed with reference to Figures 12 to 20, and on the general basis of the functional block diagram of Figure 11. Each of said Figures schematically shows a determination operated in the development of the method according to the invention, and indicates one or more input values and one or more output values of each determination .

[0040] Referring to Figure 12, reference number 10 denotes a block diagram representative of the determination operated at block 2 of the Figures 10 and 11. In more detail, determining a limit rotational speed value ^MotLim i (with i = 1, 2, 3, 4 in the general case presently being considered), thus wMot_Lim_2, wMot_Lim_3, w MotLim 4) for each electric traction motor Ml, M2, M3, M4 as a function of one or more limit rotational speed values of the corresponding one or more propulsion components comprises selecting the lesser (block 12, MIN) of the one or more values of limit rotational speed of the corresponding one or more propulsion components. Depending on the type of mechanical connection between the electric traction motor and the corresponding one or more drive wheels, the one or more propulsion components comprise, for each electric traction motor Ml, M2, M3 at least one, preferably all, of:

[0041] - a lubricant of a transmission that connects the electric traction motor to the one or more corresponding drive wheels of the vehicle, an inverter operatively associated with the electric traction motor,

[0042] - a driveline extending from the electric traction motor to the one or more drive wheels operatively connected thereto.

[0043] Always referring to Figure 12, the limit rotational speed determined with respect to the lubricant of a transmission connecting the electric traction motor Mi (with i = 1, 2, 3, 4 in the general case presently being considered) to the one or more corresponding drive wheels of the vehicle includes a limit rotational speed wGbx max i defined as a function of a maximum admissible temperature for the lubricant Ton GBX i- The temperature Ton GBX i is used as an input item of data to a map 14 which yields the value wGbx max i as a function of the value of admissible temperature for the lubricant Ton GBX i•

[0044] The limit rotational speed determined with respect to an inverter operatively associated with the electric traction motor Mi (with i = 1, 2, 3, 4 in the general case presently being considered) includes a limit rotational speed Winvmax i imposed (and tolerated) by the inverter. In this case, it is generally a fixed item of data, which does not require mapping.

[0045] The limit rotational speed determined with respect to the driveline extending from the electric traction motor Mi (with i = 1, 2, 3, 4 in the general case presently being considered) to the one or more drive wheels operatively connected thereto includes a limit rotational speed wNom Lim i in the absence of faults. Also in this case, it is generally a fixed item of data, which does not require mapping. The item of data may be specific for each traction unit - and thus for each driveline (and therefore the notation wNom Lim± - with index i - as stated in the foregoing applies) or it may be a single value for the whole powertrain, irrespective of the configuration and calibrated as a function of the most critical propulsion component (and therefore a simplified notation wNomLim, without the index I, would apply). An example of single value wNom Lim may comprise a value calibrated as a function of a rotational speed limit of the tyre of the vehicle. It may be a limit calibrated indifferently on any of the tyres, if the frame configuration of the vehicle allows for it - for example tyres having the same size and / or a symmetrical load distribution on the axles and / or a symmetrical or slightly asymmetrical torque distribution between the axles FA and RA - or it may be a value calibrated on the tyre(s) in more critical situations, e.g. in the case of a vehicle with tyres having different sizes between the axle FA and the axle RA and / or with a very asymmetrical load distribution between the axles and / or with a very asymmetrical torque distribution between the axles.

[0046] If the configuration of the powertrain, and particularly the nature of the connection between the motor and the corresponding drive wheel(s) requires the combined use of all of the three values aGbx max i, Winv max i, ^Nom Lim i, such values are sent to block 12 for extracting the lesser value among them, which value is assumed as the value of limit rotational speed aMotLim i (output of block 12).

[0047] Referring to Figure 13, it shows a determination, operated at block 4, of the diagrams of the Figures 10 and 11, regarding a limit value VLimof the vehicle advancement speed. The latter is determined as a function of the limit advancement speed values VMotLim i (with i = 1, 2, 3, 4 in the general case presently being Considered, thus Vi4ot_Lim_lz HMot—Lim_2, A c. Lim 3 IlMot—Lim_4)r each being determined on the basis of the limit rotational speed value aMotLim i (with i = 1, 2, 3, 4 in the general case presently being considered, thus WMot_Lim_iz w Mot_Lim_21 w Mot_Lim_31 w Mot_Lim_4) of a corresponding electric traction motor Mi, wherein the correspondence is given by the index i. Each value VMotLim i is further determined as a function of a rolling radius RwheeiMoti - which is a dynamic rolling radius - of one or more drive wheels operatively connected with the electric traction motor Mi.

[0048] By way of example, if the limit rotational speed <Afct Lim i is expressed in [rpm] and the radius Rwheei Mot i is expressed in [m], the speed VMotLim i expressed in [km / h] may be obtained by means of the following relationship

[0049] 2?T■60■ Lim i'^WheelMoti

[0050] I'Mot-Lim 1000■RatioGbxiwherein RatioGBx i represents a transmission ration between the drive wheel(s) and the corresponding electric motor Mi.

[0051] Always referring to Figure 13, reference 20 generally denotes a block diagram showing the determination of the speed VLim, which corresponds to the selection of the lesser (block 22, "MIN") of the values VMotLim i, with 1 = 1, 2, 3, 4 in the general case presently being described. The meaning is clear: VLimis determined by using, as the most stringent condition, the maximum speed which is attained first, thus the lesser of the speeds VMot-Lim_i.

[0052] Referring to Figure 14, it shows a block diagram of the determination operated at block 6, and reference 30 generally denotes the diagram of the same determination. The first value of total limit torque TLimprpis a limit torque value which is not connected to the risk of overspeed of the electric traction motors, nor is it a value specific for each electric motor; rather, it corresponds to an overall value for the whole powertrain (so-called barycentric value), which takes into account the limits of torque delivery of the powertrain which are due to reasons other than overspeed.

[0053] As can be seen in the diagram of Figure 14, the maximum torque TMaxwhich appears among the input values for the determination as per block 6 is determined based on a limit of electric power that can be absorbed by the electric powertrain, and it is defined as the sum of single maximum torques TMax ±(thus TMax= TMaxi + TMax 2+ TMax3 + TMax4). The value of the maximum torque TMaxmay be determined for example according to the teachings of the patent applications n. 102023000023517, 102024000000369 and 102024000001104, and moreover generally depends on the conditions of torque distribution between the axle FA and the axle RA, and on the conditions of torque distribution between the right and the left wheel of the same axle.

[0054] Similarly, the value of maximum total torque TTCSMax determined on the basis of a vehicle grip limit is obtained, in the general case presently being considered, as a sum of maximum torques TTCSMax i (i.e. as a "barycentric" torque value) which are determined for each single drive wheel by a traction control algorithm implemented on board the vehicle (thus, TTCSMax = TTCSMax 1 + TTcS_Max_2 + TpcS_Max_3 + TpcS_Max_4)•

[0055] The target total torque TTgtrequested to the powertrain by a driver of the vehicle is by definition a barycentric torque, because it is defined as the sum of the torques T± delivered by each motor Mi, thus TTgt= Ti + T2+ T3+ T4.

[0056] As can be seen in Figure 14, the determination operated at block 6 selects the lesser value (block 32, "MIN") among the torques TMax, TTCS Max, TTgt, which value is assumed as the first value of total limit torque TLimPrp, which - as stated in the foregoing - corresponds to a limit of barycentric nature due to factors which are not directly dependent on overspeed.

[0057] Figures 15 to 20 show block diagrams representative of the determinations operated within block 8. As can be seen in Figure 11, the block 8 receives as input what for the blocks 2, 4, 6 represents output data, i.e. the values Mot_Lim_lr WMot_Lim_2r WMot_Lim_3 / WMot_Lim_4 (generally, the values wMotLim i), the value VLimand the value TLimprp, and yields as output the second value of total limit torque TMaxspdLim- Determining the value TMaxspdLim comprises determining a value of total limit torque which is defined by means of an open-loop control TMaxSpdLim on and a value of total limit torque which is defined by means of a closed-loop control (TMaxSpdLim CL), wherein referring to Figure 15, general reference 40, the value TMaxSpdLim comprises a sum (block 42) of the values TMaxSpdLim_OL and TMaxSpdLim_CL•

[0058] In Figure 16, reference 50 generally denotes a block diagram representative of the determination of the value of total limit torque defined by means of an open-loop control TMaxsPdLim OL• This is determined as the lesser value (block 51, "MIN") between the first value of total limit torque TLimPrp, and a product (block 52) of a resisting force (or coast down drag) FCD, acting on the vehicle, by a reference value RwheeiRef of the wheel radius of the vehicle. Therefore, the value TLimPrpis an upper limit value for the torque TMaxspdLim_oL•

[0059] As regards RwheeiRef, it is chosen differently as a function of the configuration of the powertrain, also taking into account that it may not be the same for the wheels of the axle FA and for the wheels of the axle RA. By way of example, the radius Rwheei Ref is chosen equal to the radius of the rear wheels in the case of a powertrain with rear-wheel or four-wheel drive (or in the condition of rear-wheel or four-wheel drive, in the case that the front axle may temporarily be made non-propulsive), and equal to the radius of the front wheels in the case of front-wheel drive (or in the condition of front-wheel drive if the axle may temporarily be non-propulsive).

[0060] As regards the force FCD (which is a resisting force), it is calculated with reference to the speed VLim, i.e. with reference to a condition of dynamic equilibrium of the vehicle at the speed VLimand by means of the following expression (which is known per se): PcD ~ 1’VLim + f2‘VLim + / s

[0061] Wherein fi, f2, fs are the coast down coefficients characteristic for the vehicle V.

[0062] In the calculation of the force FCD, strictly speaking, it should be necessary to involve other factors, such as the action of the wind or the slope of the road surface. However, by operating a hybrid control which comprises a portion in a closed loop and a portion in an open loop, it is simpler to assign to the closed- loop correction the compensation of the effects which are not directly contemplated in the open-loop calculation .

[0063] This being said, in Figure 16 it may be observed that the calculation of the force FCD is operated by means of an adder 54 which considers the coefficient fa, the double product of the coefficient fi by the value VLim (block 56 - in this fashion, VLimis considered in its squared value), and a product of the coefficient f2 by the value VLim(block 58).

[0064] As regards the portion of closed-loop control, the reference Figures are Figures 17 to 20. Figure 17 shows (diagram 60) the determination of a difference of the reference rotational speeds Aw on which the closed-loop control is based. In more detail, the value of total limit torque defined by a closed-loop control TMaxSpdLim CL depends on the difference of the reference rotational speeds Aw, wherein the difference Aw is determined as the lesser (block 61) of the differences (wMotLim i - wMoti) between the value of limit rotational speed wMotLim i for each i-th motor Mi and a value of current rotational speed wMoti for the same i-th motor Mi, in conditions of absence of spin of the at least one drive wheel operatively connected to the same motor. In detail, the diagram 60 of Figure 17 shows four switches 62, 63, 64, 65 the output whereof becomes input data for the block 61, i.e. for extracting the lesser value which then becomes the item of data Aw.

[0065] The switches 62, 63, 64, 65 are associated with the calculation operated on the motors Ml, M2, M3, M4, respectively, and are each governed by a variable Spinnig_OvrSpdMoti (with i = 1, 2, 3, 4 in the general case presently being considered) associated with each of the motors Ml, M2, M3, M4 and representative of a condition of overspeed due to a spin of the drive wheel operatively connected to the electric motor Ml, M2, M3, M4, respectively.

[0066] Upstream of each switch 62, 63, 64, 65 there is a block, respectively 66, 67, 68, 69, which operates the difference wMotLim i - wMoti for the corresponding electric motor. As can be seen in the diagram, the output of each switch 62, 63, 64, 65 corresponds to the difference wMotLim i - wMoti only if the logic state of the variable Spinnig_OvrSpdMoti is "0" (FALSE), i.e. if a spin of the corresponding drive wheel is not taking place. This means that, if a drive wheel is spinning, it no longer has any defined kinematic relationship with the remaining motors of the powertrain (or, generally, with the torque control operated in the powertrain) , and therefore it is purposeless to apply a barycentric torque limitation - i.e. the value TMaxSpdLim - to an electric traction motor connected to a spinning wheel.

[0067] If the logic state of the variable Spinnig_OvrSpdMoti is "1" (TRUE), then the output of the corresponding switch is a fixed value High_Value, which is calibrated in such a way as to exceed any difference wMotLim i - wMoti which the powertrain of the vehicle V may encounter, thereby excluding the possibility of determining the difference Aw on the basis of the value High_Value, since it derives from the application of a minimum operator (between the differences wMotLim i wMoti) at block 61. This is simply a possibility of implementation (as regards the control) for subtracting an item of data by the method according to the invention, and for assigning the processing of the same item of data to another method or algorithm involved in the management of such data, e.g. the traction control algorithm mentioned in the foregoing, which may e.g. update the corresponding value TTCS Maxi as a function of the detected spin condition.

[0068] With reference to Figure 18 (diagram 70), the value of total limit torque defined by means of a closed-loop control TMaxSpdLim CL comprises in turn a fraction defined by means of proportional control TMaxSpdLim CL Prop and a fraction defined by means of an integral control TMaxSpdLim CL int, both depending on the difference of reference rotational speed Aw. In more detail, the value TMaxspdiLim CL is defined by selecting the lesser value (block 72, "MIN") between:

[0069] - a difference (block 74) between the first value of total limit torque TLimprpand the value of total limit torque defined by means of an open-loop control TMaxSpdLim_OL!

[0070] - the greater value (block 76, "MAX") between a sum (block 78) of the fraction TMaxSpdLim CLprop, defined by means of a proportional control, and of the fraction TMaxSpdLim CL int, defined by means of an integral control, and the opposite of the value of total limit torque defined by means of an open-loop control -TMaxSpdLim OL•

[0071] This means that: the value TMaxSpdLim CL has a lower limit corresponding to the value -TMaxSpdLim OL, i.e. the closed- loop correction TMaxSpdLim CL may at most result in a zeroing of the torque TMaxSpdLim OL determined in an open loop, but not in a sign inversion of the same torque, the value TMaxSpdLim CL has an upper limit corresponding to the value of the difference TLimPrp- TMaxSpdLim OL, which represents a part of torque which is still available for the closed-loop correction, since it is anyway impossible to control the powertrain to deliver a barycentric torque TMaxspdLim exceeding the torque TLimPrPfas this would lead to infringing the system limits as regards the maximum available power for supplying the electric traction motors and / or the conditions of torque distribution between the axle FA and the axle RA and / or the conditions of torque distribution between the right and the left wheel of the same axle and / or the grip limits of the vehicle and / or the torque request by the driver. Therefore, the maximum closed-loop correction TMaxspdLim CL must be equal to the value of the difference TLimPrp—TMaxSpdLim_OL.

[0072] As regards the definition of the proportional fraction TMaxspdLim CL Prop and of the integral fraction TMaxspdLim CL int, reference is made to the Figures 19 (proportional, diagram 80) and 20 (integral, diagram 90). As is generally known in the field of automatic control, the proportional fraction TMaxspdLim CL Prop of the correction TMaxspdLim CL operates a first correction which is less accurate, whereas the integral fraction TMaxspdLim_cL_int of the correction TMaxsPdLim_cL operates a second accurate correction, and therefore closes the gap between the proportional correction TMaxsPdLim CL Prop and the target value of the overall closed-loop correction TMaxSpdLim_CL•

[0073] As regards the proportional fraction TMaxsPdLim CL Prop, it is defined as the lesser value (block 82) between the difference (block 84) TLimPrp- TMaxsPdLim OL and the greater value (block 85) between the opposite of the value of total limit torque, defined by means of an open-loop control, -TMaxSpdLim OL and a raw value of proportional correction TMaxSpdLim_cL_Prop_Raw which is read from a map 88, which provides a value of torque correction AT as a function of the difference AwMot. The map 88 defines the correction AT as a torque increase or decrease starting from a neutral (or zero) value C88 having the coordinates AwMot = 0 rpm and AT = 0 Nm. If the difference AwMothas a value greater than the coordinate AwMotof the point C88, this means that the electric traction motor for which the difference AwMotis determined (and which, due to the observations referred to Figure 17, is already the motor in the most critical conditions in the powertrain, as regards overspeed) has a current rotational speed wMoti which is lesser than the limit speed wMotLim i,and therefore an acceleration (AT > 0) is required in order to reach the limit wMotLim i (the method operates focusing on the performance, and therefore it generally aims at taking advantage of all the margin available), whereas if the difference AwMothas a value lesser than the coordinate AwMotof the point C88, this means that the electric traction motor for which the difference AwMothas been determined has a current rotational speed wMoti greater than the limit speed ^Mot Lim i,and therefore a deceleration (AT < 0) is needed in order to reach the limit wMotLim i•

[0074] As regards the integral fraction TMaxSpdLim CL int, it is defined by an integral controller 92 as a function of the difference AwMotand within a correction range defined by a lower saturation limit 94 and an upper saturation limit 96. The lower saturation limit 94 is defined as the sum (block 98) of the reciprocals of the values TMaxSpdLim OL and T^axspdLim CL Prop (thUS,—T^axspdLim OL—TMaxSpdLim CL Prop), whereas the lower saturation limit 96 is defined as the difference between the value TLimprpand the values TMaxSpdLim_oL and TMaxSpdLim_cL_Prop• The meaning is as follows: as regards the upper saturation limit, it represents the correction margin of the barycentric torque which is still available for the integral correction, starting from the first value of total limit torque TLimprp, by subtracting the value of the second total limit torque, which is determined in an open loop, TMaxspdLim OL, and by further subtracting the part of the closed-loop correction which is processed by the proportional control, TMaxsPdLim CL Prop• The extent of the integral correction thus depends i.a. on the proportional correction: if the target value of AwMotis remote (point C88), the majority of the closed-loop correction is proportional and the integral correction is involved by a lesser degree, while if the target value of AwMotis near (point C88), the proportional correction is nearly zero (see also the evolution of the torque correction AT in the map 88) and the majority of the closed-loop correction shifts towards the integral correction;

[0075] - as regards the lower saturation limit, it is defined in such a way that the integral correction may not exceed the values of the total limit torque determined in a closed loop, TMaxSpdLim OL, and of the proportional fraction of the closed-loop correction TMaxspdLim CL prop• In other words, applying an integral correction may result at most in a zeroing of the total limit torque, TMaxspdLim, but not in a sign reversal thereof.

[0076] Thanks to the method according to the invention, it is possible to control the powertrain of the vehicle V (in propulsion conditions, i.e. in conditions of electric power absorption by the one or more electric traction motors) as a function of a value of total limit torque (or barycentric torque) which operates both in order to prevent overspeeds of the electric traction motors and in order to meet the system limits which are not necessarily connected to overspeed (by means of the total limit torque TLimPrp), moreover maximizing the performance by maximizing the torque delivery in the proximity of the limit of the overspeed of the one or more electric traction motors of the electric powertrain. Substantially, the first value of total limit torque (or barycentric torque) TLimPrprepresents the maximum barycentric torque deliverable as a function of the limits of the powertrain which are not directly connected to overspeed, whereas the second value of total limit torque (or barycentric torque) TMaxSpdLim represents the maximum barycentric torque which can be delivered as a function of the limits of the powertrain in order to prevent overspeed. Controlling the electric motor as a function of the value TMaxSpdLim involves, according to what has been described in the foregoing, applying the maximum value TMaxSpdLim to the total (barycentric) torque globally delivered by the electric traction motors (or by the electric traction motor, if only one is present), which may correspond to the second value TMaxSpdLim which is the sum of the contributions TMaxSpdLim_oL and TMaxSpdLim_cL (each being other than zero), or to the value TLimPrp(see the upper limits of the Figures 18 and 19) if the system limits have been reached which are not connected to overspeed.

[0077] Of course, the implementation details and the embodiments may amply vary with respect to what has been described and illustrated, without departing from the extent of the present invention, as set forth in the annexed claims.

Claims

CLAIMS1. A method for controlling the torque output of one or more traction electric motors (Ml, M2, M3, M4) of an electric powertrain of a vehicle (V), wherein each electric motor is operatively connected to one or more corresponding drive wheels (RL, RR, FL, FR) of the vehicle (V) by means of one or more propulsion components, the method comprising:- determining (2) a limit rotational speed value (C>Mot—Lim_1, A-Co-Lim 2r WMot_Lim_3l ^Mot_Lim_4r A-Co-Lim i) for each traction electric motor (Ml, M2, M3, M4) as a function of one or more limit rotational speed values of the corresponding one or more propulsion components,- determining (4) a limit value (VLim) of a vehicle advancement speed as a function of one or more limit Speed Values (Vnot-Lim-l, VMot_Lim_2 / VMot_Lim_4rVMotLim i), each determined on the basis of the limit rotational speed value (wMot_Lim_i, WMot_Lim_2, WMot_Lim_3, <Afct Lim 4; <AfctLim i) of a corresponding traction electric motor of the powertrain,- determining (6) a first value of total limit torque (TLimprp) that can be output by the one or more traction electric motors (Ml, M2, M3, M4) of the powertrain as a function of one or more of a maximum torque value (TMax) determined on the basis of a limit of electrical power that can be absorbed by the electric powertrain, a value of maximum total torque (TTCSMax) determined on the basis of a vehicle grip limit, and a value of total maximum torque (TTgt) requested to the electric powertrain by a driver of the vehicle,- determining (8) a second value of total limit torque (TMaxSpdLim) that can be output by one or more traction electric motors (Ml, M2, M3, M4) of the powertrain to prevent exceeding the limit rotational speed value (<a)Mot_Lim_l / WMot_Lim_2 / WMot_Lim_3r WMot_Lim_4r^MotLim i) of each electric traction motor (Ml, M2, M3, M4) as a function of said first value of total limit torque (TLimprp) and a difference between the limit rotational speed (<a)Mot_Lim_l / WMot_Lim_2 / WMot_Lim_3 / <j)Mot_Lim_4r ^Mot Lim i) of each traction electric motor (Ml, M2, M3, M4) and a current rotational speed (wMot i, o Mot2, o Mot 3, WMot 4; ^Mot i) of the traction electric motor itself,- controlling one or more traction electric motors (Ml, M2, M3, M4) of said electric powertrain according to the said second value of total limit torque (TMaxSpdLim)•2. The method of claim 1, wherein determining a limit rotational speed value (wMot_Lim_i, WMot_Lim_2, WMot_Lim_3, ^Mot Lim 4; ^Mot Lim i) for each electric traction motor (Ml, M2, M3, M4) as a function of one or more limit rotational speed values of the corresponding one or more propulsion components further includes selecting the lesser of one or more values of limit rotational speed (wMotLim 1, ^Mot_Lim_21 ^Mot_Lim_3, ^Mot_Lim_4! ^Mot_Lim_i) of the corresponding one or more propulsion components.

3. The method of claim 2, wherein said one or more propulsion components comprise, for each electric traction motor, at least one, preferably all, of: a transmission lubricant that connects the traction electric motor to one or more corresponding drive wheels (RL, RR, FL, FR) of the vehicle (V), an inverter operatively associated with the traction electric motor (Ml, M2, M3, M4),- a driveline extending from the traction electric motor (Ml, M2, M3, M4) to one or more drive wheels (RL, RR, FL, FR) operatively connected thereto.

4. The method of claim 3, wherein:- the limit rotational speed (wGbx max i, wGbXmax2,^Gbx max 3, ^Gbx max 4; ^Gbx max i;) determined with respect to a lubricant of a transmission connecting the traction electric motor (Ml, M2, M3, M4) to one or morecorresponding drive wheels of the vehicle includes a limit rotational speed defined as a function of a maximum admissibile temperature for the lubricant (Ton GBX I, Toil_GBX_2 / Toil_GBX_3 / Toil_GBX_4z Toil_GBX_i / )r the limit rotational speed determined with respect to an inverter (MInv_max_i, wInv-max-2, wInv-max-3, Winvmax4; MinvmaXi;) operatively associated with the traction electric motor includes a limit rotational speed imposed by the inverter,- the limit rotational speed (wNom Lim i) determined with respect to the driveline extending from the traction electric motor to one or more drive wheels operatively connected thereto includes a limit rotational speed in the absence of faults.

5. The method of any of the preceding claims, wherein each of said one or more limit values of speed Of advancement (VMot_Lim_lz lie. Lim2 / Iti.Lim :■ / lie. Lim 4,' VMotLim i) determined on the basis of the limit rotational speed value (WMot_Lim_l / WMot_Lim_2 / <j)Mot_Lim_3r WMot_Lim_4r ^Mot Lim i) of a corresponding traction electric motor is further determined as a function of a rolling radius (Rwheei Mot i) of one or more drive wheels operatively connected to the electric traction motor.

6. The method of any of the preceding claims, wherein said determining a second value of total limit torque (TMaxSpdLim) includes determining (50, 70) a value defined by an open-loop control (TMaxSpdLim OL) and a value defined by a closed-loop control (TMaxSpdLim CL), the second value of total limit torque (TMaxSpdLim) including a sum of said value defined by an open-loop control (TMaxSpdLim OL) and value defined by a closed-loop control (TMaxSpdLim CL)•7. The method of claim 6, wherein said value defined by an open-loop control (TMaxSpdLim OL) includes the lesser (51) of:- the first value of total limit torque (TLimPrp),and- a product of a resisting force (FCD) acting on the vehicle at a speed of advancement equal to the vehicle limit value of speed of advancement (VLim) and a reference value (RwheeiRef) of a wheel radius of the vehicle.

8. The method of claim 6 or claim 7, wherein said value defined by a closed-loop control (TMaxSpdLim CL) depends on a reference difference of rotational speed (AwMot), said reference difference of rotational speed being determined as the lesser of the differences between the limit rotational speed value (wMot Lim i, wMot Lim i, WMot_Lim_3, WMot_Lim_4; WMot_Lim_i) and a current rotational speed value (wMot I, wMotI, wMot 3, wMot 4; wMot i) for each electric motor in conditions of absence of slip of the at least one drive wheel.

9. The method of claim 8, wherein said value defined by a closed-loop control (TMaxSpdLim CL) comprises a fraction defined by a proportional control (TMaxSpdLim CL prop) and a fraction defined by an integral control (TMaxSpdLim CL int)1 said fraction defined by proportional control (TMaxSpdLim CL Prop) and fraction defined by integral control (TMaxSpdLim CL int) depending on said reference difference of rotational speed (AwMot)•10. The method of claim 9, wherein said determining a value defined by a closed-loop control (TMaxSpdLim CL) includes selecting the lower value (72) of:- a difference (74) between said first value of total limit torque (TLimprp) and said value defined by an open-loop control (TMaxSpdLim_oL),- the greater (76) of the sum of said fraction defined by proportional control (TMaxSpdLim CL Prop) and said fraction defined by integral control (TMaxSpdLim CL int), and the opposite of said value defined by an open-loop control (TMaxSpdLim_oL)•

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