Method and system for controlling the trajectory of a vehicle

Abstract

The present invention relates to a method for controlling the trajectory of a vehicle equipped with a front axle and a rear axle, comprising a step (100) of measuring a slip difference (ΔSmes) between the front axle and the rear axle, the method being characterised in that it further comprises a step (300) of determining a setpoint for the slip difference between the front axle and the rear axle, and a step (400) of determining torque setpoints to be applied to the front axle and to the rear axle, as a function of the difference between the slip difference setpoint and the measured slip difference (ΔSmes).

Description

[0001]DESCRIPTION Title of the invention: Method and system for controlling the trajectory of a vehicle The present invention relates to the field of the automotive industry, and more specifically concerns a method and a system for controlling the trajectory of a vehicle. Currently, recent vehicles are equipped with trajectory control systems for correcting a situation of oversteer or understeer of the vehicle, in relation to the wishes of the driver of the vehicle. These trajectory control systems use the measurement of a yaw angle of the vehicle and attempt to correct it by modifying the torque setpoints on the front and rear axles of the vehicle. However, none of these existing trajectory control systems manages to satisfactorily correct the behavior of the vehicle, so that it corresponds as closely as possible to the driver's request. In addition, these existing trajectory control systems are often complex,consuming computing resources and sources of inter-system conflicts, since other types of vehicle regulation act on the vehicle torque setpoints, in particular controlling the available power of the vehicle's engines. The present invention remedies at least in part the drawbacks of the prior art by providing a method for controlling the trajectory of a vehicle, and a system for controlling the trajectory of a vehicle, which in particular make it possible to stick as closely as possible to the driver's request by correcting oversteer or understeer situations. To this end, the invention proposes a method for controlling the trajectory of a vehicle equipped with a front axle and a rear axle, comprising a step of measuring a slip difference between the front axle and the rear axle, the method being characterized in that it further comprises a step of determining a slip difference setpoint between the front axle and the rear axle,and a step of determining torque setpoints to be applied to the front axle and to the rear axle, as a function of the difference between the measured slip difference and the slip difference setpoint. Thanks to the invention, the torque setpoints applied to the front and rear axles no longer only take into account driver inputs such as the steering wheel angle and the position of the accelerator pedal, but also take into account the actual situation as close as possible to the vehicle wheels, fed back by the measurement of the inter-axle slip difference. According to an advantageous characteristic of the trajectory control method according to the invention, the step of determining the slip difference setpoint uses a corrective yaw moment determined as a function of a difference between a desired yaw rate and a measured yaw rate. Thus, the slip difference setpoint takes into account situations of oversteer or understeer of the vehicle,to better correct them. In one embodiment of the trajectory control method according to the invention, the calculation of the corrective yaw moment advantageously includes at least one term whose parameters depend on the level of adhesion of the vehicle's wheels to the ground. These parameters use, for example, wheel drift stiffness coefficients, which depend on the tire properties, to better model the behavior of the vehicle. In one embodiment of the trajectory control method according to the invention, the calculation of the corrective yaw moment advantageously includes sliding mode control terms. These terms make it possible, for example, to reduce the difference between the yaw rate desired by the driver and the measured yaw rate of the vehicle. In one embodiment of the trajectory control method according to the invention,the torque instructions to be applied to each axle are obtained by adding or subtracting a curative torque to a torque command weighted by dynamic weighting coefficients which depend on the measured slip difference and the dynamic load distribution between the front axle and the rear axle. Thus, the torque command precalculated by the other vehicle control systems is taken into account, adapting it in a non-conflicting manner so as to provide appropriate torque instructions on each axle of the vehicle. In one embodiment of the trajectory control method according to the invention, the vehicle has four drive wheels, and said torque instruction to be applied to one of the front or rear axles,is distributed on each wheel in a torque setpoint on the wheel considered of said axle as a function of a slip difference between the wheels of said axle. This distribution using the slip difference between the wheels of the axle considered, it is precisely adapted to the torque requirement on each wheel. Advantageously, the trajectory control method according to the invention comprises a regulation loop measuring the difference between a torque produced on each wheel and said torque setpoint on the wheel, said regulation loop taking into account the Ackermann slip effect. Thus the correction carried out by the regulation loop is more precise. According to an advantageous characteristic of the trajectory control method according to the invention,an application of said torque setpoints on the front axle and on the rear axle is conditioned on a step of comparison between the slip difference measured between the front axle and the rear axle and an estimated slip difference, said application not being carried out if the estimated slip difference is less than the measured slip difference. Thus, if no trajectory deviation or if no oversteer or understeer behavior of the vehicle is detected, the torque command, derived from the driver inputs and the constraints of other vehicle control systems, is applied to the front and rear axles of the vehicle, without modification by the trajectory control method according to the invention. This makes it possible to avoid inter-system conflicts. Possibly when the estimated slip difference is less than the measured slip difference, the steps of determining the trajectory control method according to the invention are not implemented,which saves computing resources. Advantageously, the application of the torque setpoints to the front axle and to the rear axle is only carried out below a vehicle running speed threshold. Indeed, other regulation systems are likely to come into play if the vehicle is traveling above this speed threshold. Advantageously again, the distribution of one of said torque setpoints to each wheel is only carried out below a vehicle running speed threshold, and above a vehicle steering wheel angle threshold. The trajectory control method according to the invention is advantageously implemented, at least in part, in a computer program comprising program code instructions for executing the steps of the method according to the invention, when said program is executed on one or more computing units,these calculation units may be vehicle computers or remote computers of the vehicle. The invention also relates to a trajectory control system for a vehicle equipped with a front axle and a rear axle, comprising means for measuring a slip difference between the front axle and the rear axle, the system being characterized in that it further comprises means for determining a slip difference setpoint between the front axle and the rear axle, and means for determining torque setpoints to be applied to the front axle and to the rear axle, as a function of the difference between the slip difference setpoint and the measured slip difference. The trajectory control system according to the invention has advantages similar to those of the trajectory control method according to the invention. Other characteristics and advantages of the invention will become apparent from the following description on the one hand,and several exemplary embodiments given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which: [fig 1] represents steps of a method for controlling the trajectory of a vehicle, according to the invention, in one embodiment of the invention, [fig 2] schematically represents parameters of the control method of figure 1, in this embodiment of the invention, [fig 3] represents a system for controlling the trajectory of the vehicle, according to the invention, in this embodiment of the invention, [fig 4] represents a step of determining torque setpoints at the wheel as a function of torque setpoints on a front axle and on a rear axle of the vehicle, this step being part of the control method of figure 1, and [fig 5] represents means for correcting torque setpoints at the wheel of the vehicle,implemented in the control method of Figure 1. According to one embodiment of the invention, a method 1 for controlling the trajectory of a vehicle, shown in Figure 1, is implemented in a trajectory control system 2, shown in Figure 3. The trajectory control system 2 comprises software and hardware means, integrated into the vehicle. Alternatively, certain means of the trajectory control system 2 are remote from the vehicle, for example calculation means receiving data from the vehicle and sending calculation results back to the vehicle. In this embodiment of the invention, it is assumed that the vehicle is a four-wheel drive electric or hybrid electric vehicle. A first step 100 of the trajectory control method 1 is the measurement of a slip difference between the front axle and the rear axle of the vehicle, this measurement step 100 providing as output a measured slip difference ΔSmes. We call "slip",in this application, a relationship between a speed difference and a speed. For example, a slip S of a wheel of radius r and rotation speed ω is calculated ^^^^, comme ^ = ^ where Vx is the speed of the vehicle containing the wheel. In this step 100, the difference between an average slip of the wheels of the front axle of the vehicle and an average slip of the wheels of the rear axle of the vehicle is measured more precisely (which amounts here to calculating the difference between the average speeds of the two axles and dividing it by the speed Vx of the vehicle). For this, the speed of each wheel of the vehicle is measured by wheel speed sensors integrated into the wheels of the vehicle, and providing: - the rotation speed ωfl of the left front wheel, - the rotation speed ωfr of the right front wheel, - the rotation speed ωrl of the left rear wheel, - the rotation speed ωrr of the right rear wheel. The wheel speed sensors are measuring means of the trajectory control system 2 according to the invention. As a variant, these sensors are replaced by wheel speed estimation algorithms.As seen in Figure 2, we refer to: - Vx the speed of the vehicle, -Rgf the radius of the front left wheel of the vehicle, -Rdf the radius of the front right wheel of the vehicle, -Rgr the radius of the rear left wheel of the vehicle, -Rdr the radius of the rear right wheel of the vehicle. We therefore have in this measurement step 100, as shown in Figure 3: ∆^^^^ = 100. In this embodiment of the invention, the slip is expressed in percentages, but alternatively it could be calculated in gross ratio or using a reference speed other than the vehicle speed. A second step 200 of the method 1 according to the invention is the comparison between the slip difference ΔSmes previously measured between the front axle and the rear axle of the vehicle, and a corresponding estimated slip difference ΔSest. The estimated slip difference ΔSest is calculated via the driver inputs which are the steering wheel angle δ and the vehicle speed Vx, which depends on the accelerator pedal pressure position, without any link to the real-time wheel rotation speeds which are used in the measurement step 100. More precisely: With : - ^ ^^^ and ^ ^^^^^^ represent respectively the average dynamic radius of the wheels of the front axle and the average dynamic radius of the wheels of the rear axle. - wf is the track of the vehicle, i.e. the distance between the left rear wheel and the right rear wheel of the vehicle, - δs2 is a constant parameter representing the specific drift of the rear axle responsible for the guidance performance of said vehicle - l is the wheelbase of the vehicle, i.e. the distance between the front axle (tire-ground contact point of the wheels of the front axle) and the rear axle (tire-ground contact point of the wheels of the rear axle), i.e. a1+a2 in Figure 2. It should be noted that for visibility reasons, some parameter letters are subscripted in the equations but are not necessarily so in the figures and the text. In this step 200, the difference between the estimated slip deviation ΔSest and the measured slip deviation ΔSmes is calculated.If this difference is negative: ΔSest – ΔSmes < 0, then the following steps 300 to 800 of the trajectory control method 1 are inhibited, which in particular saves computing resources. The trajectory control method 1 therefore loops back to the measurement step 100. Moreover, in the case where the calculated difference is negative, it is because the driver's request goes in the opposite direction to stabilizing the vehicle, the driver's computer therefore activates a safety function in order to stabilize the vehicle. On the contrary, if this difference is positive: ΔSest – ΔSmes > 0, for example ΔSest = 10% and ΔSmes = 6%, then the wheel control can be improved to satisfy the driver's request, and we move on to the next step 300 of the control method 1 according to the invention. This condition is possibly associated with a positive deviation threshold, for example we move on to the next step 300 of the control method 1 according to the invention only if ΔSest – ΔSmes > 2%.The next step 300 is the determination of a slip deviation setpoint ΔSreq between the front axle and the rear axle. For this, a desired yaw rate ^ is used. ^^ , calculated by calculation means 302 from the steering wheel angle δ and the speed Vx of the vehicle. The calculation means 302 use in particular the wheel model expressed above in relation to the slip difference ΔSest estimated. For the record, as visible in Figure 2, the vehicle is fixed in a relative orthonormal reference frame {Ot, Xt, Yt} which follows the trajectory of the vehicle, the Xt axis being tangent to this trajectory. With respect to an absolute orthonormal reference frame {O, X, Y}, the Xt axis forms an angle with the X axis of this reference frame, called the yaw angle ^. The desired yaw rate ^^^therefore corresponds to an estimate of the derivative of this yaw angle ^ with respect to time, as desired by the driver. A measured yaw rate ^̇mes, corresponding to the real derivative of this yaw angle with respect to time, is further measured, in this determination step 300, by an inertial unit measuring this value at the level of the center of gravity of the vehicle. Calculation means 304 then calculate, in this determination step 300, a corrective yaw moment Mrec as a function of the difference ∆^̇ between the desired yaw rate ^^^ and the measured yaw rate ^̇mes: with : where: − * is the multiplication operator − m is the mass of the vehicle, − is the yaw acceleration measured by the inertial unit − ^ ^ is the distance between the center of mass of the vehicle and the front axle of the vehicle − ^ ^is the distance between the center of mass of the vehicle and the rear axle of the vehicle −^ ^^ is a coefficient of front wheel drift stiffness, specific to the properties of the tires in particular − ^ ^^ is a coefficient of rear wheel drift stiffness, specific to the properties of the tires in particular − ^ is the vehicle drift angle (different from the tire drift angle) ^^^^ ( 0 ) ∈ [ −1, 1 ] ^ ^ and ^ ^ being predetermined constants (gains). Mrec being a function of ∆^̇, this rectifying moment adjusts so as to counter this tracking error ^ by converging ^ ^^^ , which is a sliding variable, towards zero in a finite time. It should be noted that the calculation of the integral in the sliding variable ^ ^^^, is carried out in the Laplace domain. Furthermore, as soon as ^ reaches the vicinity of zero or is zero, it is because the driver's wishes are realized at the level of the vehicle's wheels and the calculation means 302 to 304 of the trajectory control system 2 according to the invention are therefore deactivated due to the comparison step 200 of the control method according to the invention. Furthermore, by depending on the drift rigidities of the front and rear wheels, and the speed of the vehicle, the rectifying moment Mrec is adaptive in the sense that it is calibrated according to the road conditions, and more specifically thanks to the sliding variable it adapts to an observed slip difference of the left and right wheels of the front and rear axles.The expression of the rectifying moment Mrec makes it possible to modulate the rectifying moment value to be achieved according to the dynamics of the vehicle: if slippage is observed, the rectifying moment Mrec is intentionally reduced to stabilize the vehicle. In this step 300 of determining a slippage deviation setpoint ΔSreq between the front axle and the rear axle, calculation means 306 of the trajectory control system 2 according to the invention are then used, providing the slippage deviation setpoint ΔSreq as a function of the previously calculated rectifying moment Mrec. For this, the calculation means 306 use the inverse transfer function of the transfer function G giving the rectifying moment Mrec as a function of the corresponding slippage deviation, which is by construction the slippage deviation setpoint ΔSreq:. Where s is the Laplace variable, Rdyn the average dynamic radius of the vehicle wheels and Csf is the dynamic radius of a wheel of the vehicle (the wheels being considered identical in this calculation). The calculation means 302 to 306 are therefore also means for determining the slip deviation setpoint ΔSreq. Then, in a step 400, torque setpoints C1 and C2 are determined to be applied respectively to the front axle and to the rear axle of the vehicle, as a function of the difference ΔScib between the slip deviation measured ΔSmes in the measurement step 100 and the slip deviation setpoint ΔSreq previously calculated. For this, calculation means 408 of the trajectory control system 2 according to the invention are used, which take as input the difference ΔScib between the measured slip deviation ΔSmes obtained in the previous measurement step 100 and the slip deviation setpoint ΔSreq calculated in the previous step 300 of determining this setpoint.The calculation means 408 use the inverse transfer function of the transfer function H giving this difference ΔScib as a function of a curative couple Γcur such that:. where - k is the transmission ratio between the engine torque and the vehicle wheels, -Jm is the engine inertia, and -Jeq is the equivalent inertia of the front-wheel drive system. The curative torque Γcur is therefore a torque allowing to correct a setpoint engine torque, adaptively to the vehicle's road conditions, thanks to the calculation of the corrective moment, this correction of the setpoint engine torque allowing to stick as closely as possible to the driver's wishes according to the vehicle's capabilities. Correlating the slip deviation setpoint ΔSreq with the measured slip deviation ΔSmes in this step 400 of determining torque setpoints C1 and C2, allows to get as close as possible to the need for correction of the engine torque setpoint, given that the slip deviation recorded at the vehicle's center of gravity is not a reflection of a slip deviation measured at the front and rear axles of the vehicle, and vice versa.In this step 400 of determining torque setpoints C1 and C2, the curative torque Γcur determined by inversion of the transfer function Γcur is then subtracted from or added to a torque command Γess on each axle, derived from the driver's torque request (or taken equal to this driver's torque request) and weighted by dynamic weighting coefficients respectively Ks1, Ks2, to obtain respectively the torque setpoint C1 to be applied to the front axle, and the torque setpoint C2 to be applied to the rear axle: ^. ^ = ^ ^^ ∗ Γess − Γ ^^ ^ ^ = ^ ^^ ∗ Γess + Γ ^^ With : - ^ is the mass distribution between the front and rear axles, therefore an intrinsic parameter of the vehicle model, - is a coefficient of friction, a xlateral acceleration and g gravity, - h is the distance between the center of gravity (center of mass) of the vehicle and the point of contact with the ground, - ^ ^^^ is a maximum slip value that we do not want to exceed. Alternatively, the curative torque Γ ^^^ is subtracted from ^ ^^ ∗ Γess to obtain the torque setpoint C2 to be applied to the rear axle, and the curative torque Γ ^^^ is added to ^ ^^∗ Γess to obtain the torque setpoint C1 to be applied to the front axle. Ks1 and Ks2 are therefore dynamic weighting coefficients depending on the acceleration, speed and load distribution on the vehicle, making it possible to distribute the torque between the front and rear axles of the vehicle without overriding the driver's wishes. It should be noted that to simplify this request, the torque command Γess is taken to be equal on each axle, but this torque request can of course differ from one axle to another, the vehicle's computer deriving this torque command from the driver's wishes, taking into account the power available at each front or rear axle of the vehicle.In particular, if the vehicle has an electric motor per front or rear axle, the torque control Γess is a function of the electrical power available on the motor driving the axle, and of the electrical power available in the traction / propulsion battery of the vehicle. The step 400 of determining the torque setpoints C1 and C2 on each axle is therefore implemented by the calculation means 408 and by multipliers and subtractors, all of which can be considered as means of determining these torque setpoints C1 and C2 on each axle. The following step 500 of the control method 1 according to the invention is the verification of the fact that the speed Vx of the vehicle is below a speed threshold Vseuil of the vehicle, set for example at 70km / h (kilometers per hour).If this is not the case (branch N in Figure 1), the control method 1 does not apply the torque setpoints C1 and C2 determined in the previous step 400, to the axles of the vehicle, the driving conditions not allowing the torque commands to be modified dynamically without harming the stability of the vehicle. In this case, the control method 1 loops back to the measurement step 100. If, on the contrary, the speed Vx of the vehicle is less than or equal to this speed threshold Vseuil (branch Y in Figure 1), in a following step 600, the steering wheel angle δ is compared with a steering wheel angle threshold δseuil, equal for example to 50 degrees.If in this step 600, it is determined that the steering wheel angle δ is less than the steering wheel angle threshold δthreshold (branch Y in FIG. 1), then the next step 700 of the control method 1 according to the invention is the application of the torque setpoints C1 and C2 determined in the previous step 400 to the front axle and the rear axle of the vehicle respectively. If, on the contrary, in this step 600, it is determined that the steering wheel angle δ is greater than or equal to the steering wheel angle threshold δthreshold (branch N in FIG. 1), then the next step 800 of the control method 1 according to the invention is the distribution of the torque setpoints C1 and C2 determined in the previous step 400 to each wheel of the vehicle.As shown in Figure 4, in step 800 of distribution of the torque setpoints C1 and C2, the torque setpoint C1 on the front axle is weighted by a dynamic weighting coefficient depending on the slip difference between the left wheel and the right wheel of the front axle, in a similar manner to step 400, to obtain a torque setpoint Cgf of the left front wheel and a torque setpoint Cdf of the right front wheel: Cgf = (1 / 2 - Kf / 2) * C1 Cdf = (1 / 2 + Kf / 2) * C1 with where ∆^^ is a slip difference measured between the left wheel and the right wheel of the front axle of the vehicle. Similarly in this step 800, the torque setpoint C2 on the rear axle is weighted by a dynamic weighting coefficient depending on the slip difference between the left wheel and the right wheel of the rear axle, to obtain a torque setpoint Cgr for the left rear wheel and a torque setpoint Cdr for the right rear wheel: Cgr = (1 / 2 - Kr / 2) * C2 Cdr = (1 / 2 + Kr / 2) * C2 with.where ∆^^ is a slip difference measured between the left wheel and the right wheel of the rear axle of the vehicle. The dynamic coefficients Kf and Kr allow the torque requirement on each wheel to be precisely adapted. Finally, in this step 800, the torque setpoints Cgf, Cdf, Cgr, Cdr are applied to the corresponding wheels of the vehicle, a control loop allowing the difference between the torque produced on a wheel and the torque setpoint applied to it to be reduced. Figure 5 shows this control loop on the wheels of the front axle, this loop being easily transposable for the wheels of the rear axle. The control loop uses the difference ε between the measurement ΔSf of the slip difference between the right and left wheels of the front axle, and a theoretical slip difference ΔSfth between the right and left wheels of the front axle.This difference ε is received as input to a regulator 802 which calculates the torque setpoints Cgf and Cdf on the front left and front right wheels using the equations mentioned previously:. The theoretical slip deviation ΔSfth is determined by means 804 for modeling this theoretical deviation, using other vehicle data, in particular the torque measured on the right front wheel and the torque measured on the left front wheel. Advantageously, the modeling means 804 take into account the Ackerman slip effect, also known as the Jeantaud slip effect when cornering. This effect is due to the natural phenomenon that when cornering, the inside wheels of the vehicle tend to stall and accelerate because the pressure is lower on these inside wheels than on the outside wheels of the vehicle. The modeling of this phenomenon is known and makes the theoretical slip deviation ΔSfth modeled by the modeling means 804 depend in particular on the steering wheel angle. The modeling means 804 and the regulator 802 are means for determining wheel torques of the trajectory control system 2 according to the invention.Of course, other types of control loops can be used in this step 800. For example, the input of the regulator 802 takes, as a variant, the speed differential between the right and left wheels of the front axle, instead of taking as input the slip difference between these wheels. In another variant, the Ackerman effect is not taken into account. In yet another variant, the control works by measuring the difference between a torque produced on each wheel and the torque setpoint on the wheel in question. Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.In particular, in an embodiment of the invention where the electric or hybrid electric vehicle does not have four-wheel drive but only one electric motor per axle, steps 600 and 800 of the control method according to the invention are not carried out, the torque setpoints C1 and C2 on the front axle and the rear axle being directly applied to the axles as soon as the speed condition below the speed threshold Vseuil is achieved.

Claims

CLAIMS 1- Method for controlling the trajectory of a vehicle equipped with a front axle and a rear axle, comprising a step of measuring (100) a slip difference (ΔSmes) between the front axle and the rear axle, the method being characterized in that it further comprises a step of determining (300) a slip difference setpoint (ΔSreq) between the front axle and the rear axle, and a step of determining (400) torque setpoints (C1, C2) to be applied to the front axle and to the rear axle, as a function of the difference between the slip difference setpoint (ΔSreq) and the measured slip difference (ΔSmes). 2- A trajectory control method according to claim 1, in which the step of determining (300) the slip deviation setpoint (ΔSreq) uses a corrective yaw moment (Mrec) determined as a function of a difference between a desired yaw speed (^̇ ^^^ ) and a measured yaw rate (^̇ ^^^). 3- A trajectory control method according to claim 2, in which a calculation of the corrective yaw moment (Mrec) comprises at least one term ( ^ ^^ , ^ ^^) whose parameters depend on the level of adhesion of the vehicle wheels to the ground. 4- A trajectory control method according to claim 2 or 3, in which a calculation of the corrective yaw moment (Mrec) comprises sliding mode control terms. 5- A trajectory control method according to any one of the preceding claims, in which the torque setpoints (C1, C2) to be applied to each axle are obtained by adding or subtracting a curative torque (Γcur) from a torque command (Γess) weighted by dynamic weighting coefficients (Ks1, Ks2) which depend on the measured slip difference (ΔSmes) and the distribution of dynamic loads between the front axle and the rear axle.6- A trajectory control method according to the preceding claim, in which the vehicle has four drive wheels, and in which the torque setpoint (C1, C2) to be applied to one of the front or rear axles is distributed (800) to each wheel in a torque setpoint on the wheel in question (Cdr, Cdf, Cgr, Cgf) of said axle as a function of a slip difference (ΔSf, ΔSr) between the wheels of said axle. 7- A trajectory control method according to the preceding claim, comprising a control loop measuring the difference between a torque produced on each wheel and the torque setpoint on the wheel (Cdr, Cgr, Cdf, Cgf), and in which said control loop takes into account the Ackermann slip effect. 8- A trajectory control method according to any one of the preceding claims, in which an application of the torque setpoints (C1, C2) on the front axle and on the rear axle is conditioned on a comparison step (200) between the measured slip difference (ΔSmes) between the front axle and the rear axle and an estimated slip difference (ΔSest), said application not being carried out if the estimated slip difference (ΔSest) is less than the measured slip difference (ΔSmes).9- A trajectory control method according to the preceding claim, in which the application of the torque setpoints (C1, C2) to the front axle and to the rear axle is only carried out below a vehicle rolling speed threshold (Vthreshold). 10- A trajectory control method according to claims 6 and 8, in which the distribution of one of the torque setpoints (C1, C2) to each wheel is only carried out below a vehicle rolling speed threshold (Vthreshold), and above a vehicle steering wheel angle threshold (δthreshold).11- System (2) for controlling the trajectory of a vehicle equipped with a front axle and a rear axle, comprising means for measuring a slip difference (ΔSmes) between the front axle and the rear axle, the system being characterized in that it further comprises means for determining (302, 304, 306) a slip difference setpoint (ΔSreq) between the front axle and the rear axle, and means for determining (408) torque setpoints (C1 and C2) to be applied to the front axle and to the rear axle, as a function of the difference (ΔScib) between the measured slip difference (ΔSmes) and the slip difference setpoint (ΔSreq).

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