METHOD FOR REDUCING THE TORQUE OF AN ELECTRIC MACHINE IN CASE OF LACK OF VEHICLE TRACTION ON THE GROUND

Abstract

Method for reducing the torque of an electric machine in case of loss of traction in an electric or hybrid motor vehicle, the vehicle comprising an ESP system including a traction control function, an electric machine (ME2) and a control unit (UCE2), the method comprising an early limiting loop and a main control loop: the early limiting loop comprising: - acquisition of the rotational speed (ω2) of a machine shaft, - provision of a maximum acceleration threshold parameter and a maximum deceleration threshold parameter for the rotational speed, - reduction of motor torque if the rotational speed of the machine shaft has a time gradient of acceleration or deceleration greater than the threshold; the main control loop comprising acquisition of the instantaneous rotational speed of each wheel, and a reduction of torque if a wheel slips. Figure 2

Description

Title of the invention: METHOD FOR REDUCING THE TORQUE OF AN ELECTRIC MACHINE IN CASE OF LACK OF TRACTION OF A VEHICLE ON THE GROUND

[0001] The present invention relates generally to the field of traction control systems in motor vehicles, particularly in electric or hybrid vehicles. Particular interest here is a vehicle with at least one axle, front or rear, equipped with an electric drivetrain, namely with an electric motor and a differential transmission driving the two wheels of the axle in question.

[0002] In a motor vehicle, the drive wheels are capable of transmitting torque to the ground, this torque being defined with respect to the axis of the wheel in question.

[0003] The transmission of torque to the ground depends on the coefficient of friction between the tire and the ground at the point of contact between the tire and the ground, which can also generally be called 'adhesion'.

[0004] It may happen that the coefficient of friction does not allow the applied torque to be transmitted between the tire and the ground, in which case wheel slippage occurs.

[0005] Such slippage occurs, for example, in the case of significant braking force. Such slippage can also occur in the case of a drive torque to be transmitted to the ground.

[0006] The driving torque can be positive, meaning that the torque tends to increase the speed of the vehicle, or the torque can be negative, which corresponds to the case where the torque tends to decrease the speed of the vehicle (braking, engine braking including via a resistive electric machine torque with the electric machine in generator mode).

[0007] In this document, we are particularly interested in the anti-slip function, this function consisting of reducing the torque applied to the wheels by a powertrain or electric motor in the event that the adhesion between the tire and the ground proves insufficient to pass the torque applied between the tire and the ground.

[0008] More generally, the present invention relates to traction control (called in the trade ASR) and engine braking control (called in the trade MSR).

[0009] In an electric traction system, in zero-emission mode, the moment of inertia of the rotating parts (machine rotor and transmission element including differential and, where applicable, reduction gear) is smaller than the equivalent moment of inertia in an internal combustion engine, which involves a moving assembly including crankshaft, flywheel, connecting rods, and pistons. It should also be noted that the torque The availability of an electric motor is very significant at a low or zero rotation speed.

[0010] Therefore, during a strong acceleration from zero velocity, a slipping situation may occur.

[0011] Similarly, during the advance of the vehicle, a sudden change in grip of the contact area between the tire and the ground can lead to a slip, whether the torque is positive, i.e. in traction, or negative, i.e. in engine braking.

[0012] It is noted that this is valid not only for the usual case of forward movement (longitudinal movement towards the front of the vehicle), but also for the occasional case of reversing maneuver.

[0013] In the known art, the traction control system identifies the slippage problem and then generates a torque command to be requested from the engine control unit and transmits this torque command to the engine control unit. It should be noted that the engine control unit executes the lower of the two torque commands: the one resulting from the driver's intent and the one requested by the traction control system (generally lower in the case of traction slippage and higher in the case of slippage during engine braking / regenerative braking).

[0014] This correction process takes some time, in practice a few tens of milliseconds for example a time between 60 milliseconds and 100 milliseconds.

[0015] Meanwhile, and in view of the low moment of inertia in electric mode, as mentioned above, a significant wheel slippage could occur, i.e. a surge in wheel rotation speed in the case of traction for example or, conversely, a drastic decrease in the case of engine braking.

[0016] In this context, the inventors sought to propose a solution to reduce the reaction time of the anti-slip function and thus decrease the amplitude of wheel slippage, in order to improve vehicle stability.

[0017] To achieve this objective, the invention proposes a method for reducing the torque of an electric machine in the event of a loss of wheel traction in an electric or hybrid motor vehicle with at least one electrically driven axle, thanks to an electric motor unit. The vehicle includes a dynamic stability control system comprising at least one traction control function acting on the electric motor unit. The electric motor unit comprises at least one electric machine and at least one drive control unit responsible for controlling the torque generated by the electric machine in real time, based on at least one setpoint representing the driver's intent. The method comprises, on the one hand, an early limiting loop and, on the other hand, a main control loop. The early limiting loop comprises: - Acquisition of the rotational speed of a machine shaft, - provision of a maximum acceleration threshold parameter and a maximum deceleration threshold parameter for the rotational speed of the machine shaft, said threshold parameters being representative of maximum vehicle dynamics without wheel slippage, - reduction of motor torque if the rotational speed of the machine shaft has a time gradient of acceleration greater than the maximum acceleration threshold or if the rotational speed of the wheel has a time gradient of deceleration greater than the maximum deceleration threshold, the main control loop comprising: - Acquisition of the rotational speed of each wheel by the dynamic stability control system, - if at least one of the wheel rotation speeds is outside an interval defined by lower and upper wheel rotation limits relative to a reference speed, then the dynamic stability control system calculates an anti-slip torque setpoint and requests the drive control unit to apply said anti-slip torque setpoint.

[0018] Thanks to these provisions, the early limiting loop makes it possible to reduce the reaction time which is typically reduced to a value between 15 ms and 30 ms, compared to 60 ms to 100 ms for the main regulation loop forming the classic anti-slip function.

[0019] This prevents a transient runaway of the slipping wheel or wheels. The proposed method functions as a preventive regulation that intervenes earlier than the so-called curative regulation provided by the conventional traction control system.

[0020] In practice, after the intervention of the early limitation loop, the main regulation loop takes over and manages the traction control function with regard to the instantaneous individual speeds of each wheel.

[0021] Moreover, as will be seen later, what is called 'a command representing the will of the vehicle driver' can come directly from the accelerator pedal or can come from a driving assistance system such as, for example, a speed regulator, a speed limiter, or an adaptive distance following speed regulator.

[0022] Moreover, as will be seen later, the proposed invention can be applied to a single axle (front axle or rear axle of the vehicle) but can be applied equally to a two-axle configuration of the same vehicle.

[0023] In the remainder of this document, the vehicle's dynamic stability control system control unit performing the anti-rollover function will be referred to as the "ASR control unit". slippage, the term "ASR computer" does not imply any functional limitation of this computer, the ABS, MSR and ESP functions can be performed by this computer.

[0024] In the phrase "if the wheel rotation speed has a time gradient of deceleration greater than the maximum deceleration threshold", it must be understood that the time gradient is more pronounced than that which corresponds to the maximum deceleration.

[0025] According to an advantageous option, the early limiting loop is executed iteratively with a recurrence frequency of at least 100 Hz, preferably at least 200 Hz. This provides excellent responsiveness which prevents wheel spin that is detrimental to vehicle stability and tire life.

[0026] According to a particular example, the basic loop is executed iteratively with a frequency of 250 Hz, namely a loop period of 4 ms.

[0027] According to one embodiment, the dynamic stability control system calculates the reference speed, namely an instantaneous longitudinal displacement speed of the vehicle, in order to generate the lower and upper limits of wheel rotation speed, the reference speed being developed from the rotation speeds of each of the vehicle's wheels, and optionally also from information delivered by at least one longitudinal acceleration sensor.

[0028] It is from the reference speed that the ASR computer, with regard to a generally tolerated slip, calculates the lower limit of wheel rotation speed and the upper limit of wheel rotation speed.

[0029] It is noted that the reference speed generally corresponds to the speed of the vehicle body.

[0030] According to one embodiment, the maximum acceleration threshold parameter and the maximum deceleration threshold parameter are determined according to the intrinsic characteristics of the vehicle including among others: its mass, the available drive power on each axle, the tire fitting.

[0031] The maximum acceleration threshold parameters and the maximum deceleration threshold parameters can be obtained from one or more calibration tables. The calibration tables can be the result of test campaigns conducted with different types of vehicles on a surface with very good grip.

[0032] According to one embodiment, in circumstances where the torque generated by the electric machine is tractor, namely tending to increase the kinetic energy of the vehicle, it is the maximum acceleration threshold which caps the torque delivered to the axle.

[0033] This scenario corresponds to wheel slippage during acceleration. It can occur in forward motion but also in reverse.

[0034] According to one embodiment, in circumstances where the torque generated by the electric machine is resistive, namely tending to decrease the kinetic energy of the vehicle, it is the maximum deceleration threshold which limits the torque delivered to the axle.

[0035] This scenario corresponds to wheel slippage during engine braking deceleration. Here too, this can occur in forward motion as well as in reverse.

[0036] According to one embodiment, if an anti-slip torque command is issued by the dynamic stability control system to the drive control unit, said anti-slip torque command prevails over the early limiting loop based on the maximum acceleration threshold or and the maximum deceleration threshold.

[0037] The present invention also relates to an electric or hybrid motor vehicle, comprising at least one electrically powered axle by means of an electromotor unit, a dynamic stability control system including at least one traction control function acting on the electromotor unit, the electromotor unit comprising at least one electric machine and at least one motor control unit responsible for controlling the torque generated by the electric machine in real time, the motor control unit being configured to implement the method as defined above.

[0038] According to one embodiment, the electrically powered axle is the rear axle and the front axle is powered by a hybrid powertrain (including an internal combustion engine).

[0039] The present invention also relates to an electric or hybrid motor vehicle, comprising a first axle electrically powered by a first electromotor group and a second axle electrically powered by a second electromotor group, a dynamic stability control system including at least one traction control function acting on the first and second electromotor groups, the first electromotor group comprising at least one first electric machine and at least one first drive control unit responsible for controlling the torque generated by the first electric machine in real time, the second electromotor group comprising at least one second electric machine and at least one second drive control unit responsible for controlling the torque generated by the second electric machine in real time,The first control unit and the second drive control unit are configured to implement the process as defined previously.

[0040] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates in top view a synoptic diagram of the vehicle equipped with the traction control function; - [Fig.2] shows a block diagram illustrating the operation of the process according to the present invention; - [Fig.3] represents a first example of a chronogram of a situation with increasing speed - [Fig.4] schematically illustrates in top view a synoptic diagram of the vehicle equipped with the traction control function; - [Fig.5] represents a top view of a second example of a synoptic diagram of a vehicle with two electrically powered axles.

[0041] In the different figures, the same references designate identical or similar elements.

[0042] In [Fig.1], a VHL vehicle is schematically represented, with a front axle AV with steering and driving wheels and a rear axle ARR with selectively driven wheels (in so-called '4x4' mode).

[0043] In the configuration shown in [Fig.1], the front axle is powered by a hybrid powertrain.

[0044] In an alternative configuration shown in [Fig.5], the front axle is driven by a purely electric electromotor unit.

[0045] The vehicle in question may be a passenger vehicle, a utility vehicle, a van, a recreational vehicle, a minibus, a coach, a truck, etc.

[0046] As in the example of [Fig.1], the front axle is powered by means of a hybrid powertrain which includes an internal combustion engine ICE and a first electric machine denoted ME1.

[0047] The hybrid powertrain is engaged with the front axle shafts 21G,21D via the first TRI transmission.

[0048] As known in itself and not described in detail, the first TRI transmission includes a differential and a reduction gear which allows the rotational speed to be lowered from the rotational speed of the hybrid machine noted col to the rotational speed of the front wheel shafts 21G,21D.

[0049] A first transmission ratio RI is thus determined between col and the rotation speed of the front wheel shafts 21G,21D, so that the rotation speed of the differential ring is equal to RI x col, also noted in compact form Rlcol.

[0050] The rear axle is powered by an electromotor unit, referred to herein as the second electromotor unit. The second unit The electric motor is equipped with a second electric machine, designated ME2, and includes a second transmission, TR2.

[0051] The second electric machine ME2 is in selective engagement with the wheel shafts 22G,22D of the front axle via the second transmission TR2.

[0052] As known in itself and not described in detail, the second transmission TR2 includes a differential and a reducer which allows the rotational speed to be lowered from the rotational speed of the electric machine denoted co2 down to the rotational speed of the rear wheel shafts 22G,22D.

[0053] A second transmission ratio R2 is thus determined between co2 and the rotational speed of the rear wheel shafts 22G,22D, so that the rotational speed of the differential ring is equal to R2 x co2, also noted in compact form R2co2.

[0054] In the normal case, the front axle rotates at the same speed as the rear axle, so we have substantially Rlcol= R2co2.

[0055] This is also true in curves where the differential is used, even if the outside wheels turn faster than the inside wheels, the above equality remains true at the level of the differential rings.

[0056] A computer, designated CMM, is planned to control the operation of the internal combustion engine ICE and the electric machine ME1 associated with the internal combustion engine in this hybrid powertrain.

[0057] The second electric machine ME2 is controlled by a second control unit UCE2 via a power device called inverter INV2. The second control unit UCE2 is referred to herein as the second motor control unit.

[0058] In addition, a supervisory unit, also called a SUP supervisor, is planned, configured to coordinate the needs for positive motor control and regenerative braking.

[0059] To communicate with each other, it is planned that the first control unit CMM, the second control unit UCE2, the supervisor computer SUP and the battery management computer 13 will communicate via a multiplexed network 15, for example a CAN type network, as known per se.

[0060] The CAN network data rate is at least 500 kilobits / s. In practice, a CAN network with a data rate of 1 megabit / s can be used. If necessary, a private multiplexed network can be used to avoid any latency in the transmission of messages from the ASR computer to the engine control unit.

[0061] The vehicle is equipped with a B ATT battery, also known as a traction battery. The electrochemical technology of the battery can be any within the meaning of the present invention. It can, for example, be lithium-ion technology.

[0062] As known in itself, a battery management computer 13 is provided, otherwise known in the trade as BMS from the English 'Battery Management System', the functions of which are not detailed here.

[0063] Although [Fig.1] illustrates a configuration with a single electrically powered axle, the present invention also applies to a configuration with two electrically powered axles, without an internal combustion engine, as seen in [Fig.5].

[0064] The vehicle is equipped with a dynamic stability control system noted ESP including at least one traction control function.

[0065] Moreover, generally, the dynamic stability control system includes, as is known in itself, an anti-lock braking system (ABS) function.

[0066] For the traction control function, the ESP dynamic stability control system acts on the electric motor groups if there are two or on the electric motor group if there is only one.

[0067] We are particularly interested here in the anti-slip function, this function consisting of reducing the torque (tractor or resistor, i.e. positive or negative) applied to the wheels by the electro-motor unit in the event that the adhesion between the tire and the ground proves insufficient.

[0068] As a reminder, the present invention relates to traction control (called in the trade ASR) and engine braking traction control (called in the trade MSR), and the computer in charge of these functions is called 'ASR computer' for the sake of brevity.

[0069] In variant [Fig. 5], there are two electrically driven axles. The front axle is driven by an electric motor unit called the first electric motor unit. The first electric motor unit is equipped with a first electric machine, designated ME1, and includes a first three-phase transmission. There is no internal combustion engine in this configuration.

[0070] The first electric machine ME1 is controlled by a first control unit UCE1 via a power device called inverter INV1 (or 'inverter' in industry jargon) which includes power switches connected to the phases of the stator.

[0071] The first control unit UCE1 replaces the CMM computer of [Fig.1],

[0072] The other elements of the configuration of [Fig.5] are identical or similar to those of [Fig.1] and therefore not described again here.

[0073] As illustrated in [Fig.2], the ESP dynamic stability control system acquires signals from the four wheel speed sensors, one on each wheel.

[0074] This information is noted as VRARG, VRARD, for the left and right rear wheel signals respectively, and VRAVG, VRAVD for the left and right front wheel signals respectively.

[0075] As illustrated in [Fig.2], the ASR computer also acquires information from a 3-axis acceleration sensor denoted 31 and a steering wheel angle sensor denoted 32.

[0076] Furthermore, block 30 represents the driver's intent, which may, depending on the circumstances, originate directly from the accelerator pedal. In other driving situations, a command issued by a driver assistance system such as cruise control is also considered equivalent to the driver's intent; in this case, the command is no longer directly linked to the position of the accelerator pedal.

[0077] The engine torque command resulting from the driver's intention is noted TTL.

[0078] Advantageously according to the present invention, the ASR computer continuously calculates a reference speed and iteratively generates, as a function of this reference speed, on the one hand a lower limit of wheel rotation speed and on the other hand an upper limit of wheel rotation speed.

[0079] The method proposed by the present invention comprises, for an electrically driven axle considered, a two-level logic, namely a logic with two loops, each loop having its own logic and a distinct reaction time.

[0080] More specifically, the process uses on the one hand an early limitation loop and on the other hand a main regulation loop.

[0081] The early limiting loop is managed locally at the level of the electric machine and the electric machine's motor control unit. The electric machine includes an output shaft with a speed sensor for the rotation of this output shaft.

[0082] The logic involved uses a maximum acceleration threshold parameter and a maximum deceleration threshold parameter for the rotational speed of the machine shaft. These threshold parameters can be expressed in rad / s² or as an equivalent in m / s² if one considers the linear speed of the vehicle, taking into account the average wheel radius and a gear ratio.

[0083] These threshold parameters represent maximum vehicle dynamics without wheel slippage. These maximum acceleration and maximum deceleration threshold parameters can be obtained from one or more calibration tables. The calibration tables may be the result of test campaigns conducted with different types of vehicles on a surface with very good grip.

[0084] The early limitation loop includes the following actions: - acquisition of the rotational speed (œ2 or respectively col) of a machine shaft, - provision of maximum acceleration threshold parameters and maximum deceleration threshold parameters for the machine shaft rotation speed, - reduction of motor torque if the rotational speed of the machine shaft has a time gradient of acceleration greater than the maximum acceleration threshold or if the rotational speed of the wheel has a time gradient of deceleration greater than the maximum deceleration threshold.

[0085] The early limiting loop is executed iteratively with a recurrence frequency of at least 100 Hz, preferably at least 200 Hz. This provides excellent responsiveness, preventing wheel spin that could compromise vehicle stability and damage the tire. The comfort and safety of the driver and vehicle occupants are improved.

[0086] It should be noted that the maximum acceleration and maximum deceleration threshold parameters are determined based on the intrinsic dynamic characteristics of the vehicle, including, among other things: its mass, the available drive power on each axle, and the tire size. The use of other characteristics as well is possible. Optionally, the vehicle's load can be entered to adjust the maximum acceleration and deceleration thresholds.

[0087] The main control loop comprises: - Acquisition of the rotational speed of each wheel by the dynamic stability control system, - if at least one of the wheel rotation speeds is outside an interval defined by lower and upper wheel rotation limits relative to a reference speed, then the dynamic stability control system calculates an anti-slip torque setpoint and requests the drive control unit to apply said anti-slip torque setpoint.

[0088] The dynamic stability control system calculates the reference speed, namely an instantaneous longitudinal displacement speed of the vehicle, in order to generate the lower and upper limits of wheel rotation speed, the reference speed being developed from the rotation speeds of each of the vehicle's wheels in particular the last sampled values, i.e. the most recent.

[0089] The calculation of the reference speed may optionally also use longitudinal acceleration information provided by the 3-axis sensor 31.

[0090] The lower and upper limits of wheel rotation speed represent a certain amount of slippage tolerated before acting.

[0091] In [Fig. 2], TQS1 designates the torque setpoint calculated by the SUP supervisory computer for the powertrain (or respectively the first electric motor unit) and resulting from the driver's input. TQS2 designates the torque setpoint calculated by the SUP supervisory computer for the second electric motor unit and resulting from the driver's input.

[0092] TQC1 designates the torque command requested by the ASR computer to the first control unit CMM or UCE1. TQC2 designates the torque command requested by the ASR computer to the second drive control unit UCE2.

[0093] In [Fig.2], reference 62 designates a set of software functions responsible for implementing torque limitation in the second motor control unit UCE2.

[0094] col denotes the rotational speed of the shaft of the first electric machine ME1. co2 denotes the rotational speed of the rotor shaft of the second electric machine ME2.

[0095] Figure 3 illustrates circumstances where the torque generated by the electric machine is pulling, namely, the generated torque tends to increase the kinetic energy of the vehicle. Figure 3 illustrates a case of starting from a standstill, i.e., the speed is zero at the beginning of the sequence and concerns the first driven axle.

[0096] The line referenced 61 illustrates a maximum possible acceleration under conditions of very good adhesion; this is the time evolution or derivative of the velocity. It is possible to express this acceleration or evolution of the velocity either as the linear speed of the vehicle or as the rotational speed of the output shaft of the electric machine (case shown in [Fig. 3], at a given instant).

[0097] Curves 63 and 64 represent over time the rotational speed of the machine output shaft in the motorized axle considered.

[0098] Curve 63 illustrates the behavior resulting from wheel speed loss without implementation of the present invention, while curve 64 represents the behavior resulting from wheel speed loss with implementation of the present invention. It can be seen that the surge in output shaft speed between times t1 and t2 has been completely eliminated.

[0099] The reduction of engine torque occurs locally at the level of the engine control unit if the rotational speed of the output shaft has a time gradient of acceleration greater than the maximum acceleration threshold 61, and this without intervention of the ASR computer or more generally of the ESP dynamic stability control system.

[0100] The regulation provided by the main regulation loop and the torque setpoints TQC1, TQC2 delivered by the ASR computer takes place between times t2 and t3.

[0101] Figure 4 illustrates circumstances where the torque generated by the electric machine is resistive, namely the generated torque tends to decrease the kinetic energy of the vehicle.

[0102] The line referenced 71 illustrates a maximum possible deceleration under conditions of very good adhesion, expressed as indicated above as a speed linear of the vehicle or as in rotational speed of the output shaft of the electric machine (case represented in [Fig.4]).

[0103] Curves 73 and 74 represent over time the rotational speed of the output shaft in the motorized axle considered.

[0104] Curve 53 illustrates the behavior resulting from wheel speed loss without implementation of the present invention, while curve 54 represents the behavior resulting from wheel speed loss with implementation of the present invention. It can be seen that the dip in output shaft speed between times t1 and t2 has been completely eliminated.

[0105] The reduction of motor torque occurs locally at the level of the motor control unit if the rotational speed of the output shaft has a time gradient of deceleration greater than the maximum deceleration threshold 71.

[0106] With reference to Figures 3 and 4, the time interval between times t1 and t2 is, in one example, on the order of 10 ms to 30 ms. This is therefore an early intervention that can be described as 'preventive' when compared to the conventional intervention of the traction control function, which has a slightly longer response time.

[0107] In the main loop, the method provides for the transmission of an anti-slip torque command issued by the dynamic stability control system to the drive control unit, and the execution of said anti-slip torque command by the drive control unit.

[0108] As soon as the anti-slip torque command is issued by the dynamic stability control system's computer and received by the engine control unit, this torque command replaces the torque command initiated by the driver. This results in a reduction of torque (tractor or load). In other words, the anti-slip torque command from the dynamic stability control system temporarily overrides the driver's torque command, providing a very responsive reduction in torque value.

[0109] The rest of the time, under normal conditions, the anti-slip torque setting is neutral and the torque setting resulting from the driver's will prevails.

Claims

1. Demands A method for reducing the torque of an electric machine in the event of a loss of wheel traction in an electric or hybrid motor vehicle with at least one electrically driven axle via an electric motor unit, the vehicle including a dynamic stability control (ESP) system including at least one traction control function acting on the electric motor unit, the electric motor unit comprising at least one electric machine (ME1) and at least one drive control unit (UCE2) responsible for controlling the torque generated by the electric machine in real time, based on at least one setpoint representing the driver's intent, the method comprising, on the one hand, an early limiting loop and, on the other hand, a main control loop: the early limiting loop comprising: - Acquisition of the rotational speed (CO2) of a machine shaft, - Provision of a maximum acceleration threshold parameter and a maximum deceleration threshold parameter for the rotational speed of the machine shaft, said threshold parameters being representative of maximum vehicle dynamics without wheel slippage, - reduction of motor torque if the rotational speed of the machine shaft has a time gradient of acceleration greater than the maximum acceleration threshold or if the rotational speed of the wheel has a time gradient of deceleration greater than the maximum deceleration threshold, the main control loop comprising: - Acquisition of the rotational speed of each wheel by the dynamic stability control system, - if at least one of the wheel rotation speeds (VRARG, VRARD, VRAVG, VRAVD) is outside an interval defined by lower and upper wheel rotation limits relative to a reference speed, then the dynamic stability control system calculates an anti-slip torque setpoint and requests the drive control unit to apply said anti-slip torque setpoint.

2. A method according to claim 1, characterized in that the early limiting loop is executed iteratively with a recurrence frequency of at least 100 Hz, preferably at least 200 Hz.

3. A method according to any one of claims 1 to 2, characterized in that the dynamic stability control system calculates the reference speed, namely an instantaneous longitudinal displacement speed of the vehicle, in order to generate the lower and upper limits of wheel rotation speed, the reference speed being developed from the rotation speeds of each of the wheels of the vehicle, and optionally in addition from information delivered by at least one longitudinal acceleration sensor.

4. A method according to any one of claims 1 to 3, characterized in that the maximum acceleration threshold parameter and the maximum deceleration threshold parameter are determined as a function of the intrinsic characteristics of the vehicle including among other things: its mass, the available drive power on each axle, the tire fitting.

5. A method according to any one of claims 1 to 4, characterized in that in circumstances where the torque generated by the electric machine is pulling, namely tending to increase the kinetic energy of the vehicle, it is the maximum acceleration threshold which caps the torque delivered to the axle.

6. A method according to any one of claims 1 to 4, characterized in that in circumstances where the torque generated by the electric machine is resistive, namely tending to decrease the kinetic energy of the vehicle, it is the maximum deceleration threshold that limits the torque delivered to the axle.

7. A method according to any one of claims 1 to 6, characterized in that if an anti-slip torque command (TQC2) is issued by the dynamic stability control system to the drive control unit, said anti-slip torque command prevails over the early limiting loop based on the maximum acceleration threshold or and the maximum deceleration threshold.

8. Electric or hybrid motor vehicle, comprising at least one electrically powered axle by means of an electric motor unit, a dynamic stability control (ESP) system including at least one traction control function acting on the electric motor unit, the electromotor group comprising at least one electric machine (ME2) and at least one motor control unit (UCE2) responsible for controlling the torque generated by the electric machine in real time, the motor control unit being configured to implement the method according to any one of claims 1 to 7.

9. Motor vehicle according to claim 8, characterized in that the electrically powered axle is the rear axle and the front axle is powered by a hybrid powertrain.

10. Electric or hybrid motor vehicle, comprising a first axle electrically powered by a first electric motor unit and a second axle electrically powered by a second electric motor unit, a dynamic stability control (ESP) system including at least one traction control function acting on the first and second electric motor units, the first electric motor unit comprising at least one first electric machine (EM1) and at least one first drive control unit (DCU1) responsible for controlling the torque generated by the first electric machine in real time, the second electric motor unit comprising at least one second electric machine (EM2) and at least one second drive control unit (DCU2) responsible for controlling the torque generated by the second electric machine in real time,the first control unit and the second motor control unit being configured to implement the method according to any one of claims 1 to 7.

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