Method and system for controlling the trajectory of a vehicle

Abstract

Method and system for vehicle trajectory control. 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) for measuring the slip difference (ΔSmes) between the front axle and the rear axle. The method is characterized in that it further comprises a step (300) for determining a setpoint for the slip difference between the front axle and the rear axle, and a step (400) for determining torque setpoints to be applied to the front axle and the rear axle, as a function of the difference between the setpoint for the slip difference and the measured slip difference (ΔSmes). (Figure 1)

Description

Title of the invention: Method and system for controlling the trajectory of a vehicle

[0001] 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.

[0002] Modern vehicles are currently equipped with vehicle stability control systems that correct oversteer or understeer relative to the driver's intent. These systems measure the vehicle's yaw angle and attempt to correct it by adjusting the torque settings on the front and rear axles.

[0003] However, none of these existing trajectory control systems manages to satisfactorily correct the vehicle's behavior so that it closely matches the driver's demands. Furthermore, these existing trajectory control systems are often complex, computationally intensive, and a source of inter-system conflicts, since other types of vehicle regulation act on the vehicle's torque commands, notably controlling the available power of the vehicle's engines.

[0004] 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 situations of oversteer or understeer.

[0005] 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 setpoint for the slip difference between the front axle and the rear axle, and a step of determining torque setpoints to be applied to the front axle and the rear axle, as a function of the difference between the measured slip difference and the setpoint for the slip difference.

[0006] Thanks to the invention, the torque commands applied to the front and rear axles no longer only take into account driver inputs such as steering wheel angle and accelerator pedal position, but also take into account the actual situation as close as possible to the vehicle's wheels, reported by measuring the inter-axle slip difference.

[0007] According to an advantageous feature of the trajectory control method according to the invention, the step of determining the slip deviation setpoint uses a The corrective yaw moment is determined based on the difference between a desired yaw rate and a measured yaw rate. Thus, the slip deviation setting takes into account oversteer or understeer situations in the vehicle, in order to better correct them.

[0008] 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 vehicle's behavior.

[0009] 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.

[0010] In one embodiment of the trajectory control method according to the invention, the torque commands to be applied to each axle are obtained by adding or subtracting a corrective torque to a torque command weighted by dynamic weighting coefficients that depend on the measured slip deviation and the dynamic load distribution between the front and rear axles. This takes into account the torque command pre-calculated by the vehicle's other control systems, adapting it in a non-conflicting manner to provide appropriate torque commands on each axle of the vehicle.

[0011] In one embodiment of the trajectory control method according to the invention, the vehicle has four drive wheels, and the torque command to be applied to one of the front or rear axles is distributed to each wheel as a torque command on the wheel in question 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 in question, is precisely adapted to the torque requirement on each wheel.

[0012] Advantageously, the trajectory control method according to the invention includes a control loop that measures the difference between the torque produced on each wheel and the setpoint torque on the wheel, said control loop taking into account the Ackermann slip effect. Thus, the correction made by the control loop is more precise.

[0013] According to an advantageous feature of the trajectory control method according to the invention, the application of said torque commands on the front axle and on the rear axle is conditional upon a step of comparing the slip difference measured between the front and rear axles and an estimated slip difference, the application is not carried out if the estimated slip difference is less than the measured slip difference. Thus, if no deviation from the trajectory or no oversteer or understeer behavior of the vehicle is detected, the torque control, derived from driver inputs and constraints from 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 avoids intersystem conflicts. Optionally, when the estimated slip difference is less than the measured slip difference, the steps for determining the trajectory control method according to the invention are not implemented, thereby saving computational resources.

[0014] Advantageously, the application of torque commands to the front and rear axles is only carried out below a certain vehicle speed threshold. This is because other control systems may come into play if the vehicle travels above this speed threshold.

[0015] Advantageously, the distribution of said torque commands on each wheel is only carried out below a vehicle speed threshold, and above a vehicle steering wheel angle threshold.

[0016] The trajectory control method according to the invention is advantageously implemented, at least in part, in a computer program comprising program code instructions for the execution of the steps of the method according to the invention, when said program is executed on one or more computing units, these computing units being able to be computers of the vehicle or remote computers of the vehicle.

[0017] The invention also relates to a vehicle trajectory control system 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 the rear axle, as a function of the difference between the slip difference setpoint and the measured slip difference.

[0018] The trajectory control system according to the invention has advantages similar to those of the trajectory control method according to the invention.

[0019] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0020] [Fig. 1] represents steps in a method for controlling the trajectory of a vehicle, according to the invention, in one embodiment of the invention,

[0021] [Fig.2] schematically represents parameters of the control process of the [Fig. 1], in this embodiment of the invention,

[0022] [Fig.3] represents a vehicle trajectory control system, according to the invention, in this embodiment of the invention,

[0023] [Fig.4] represents a step in determining torque setpoints at the wheel in function of torque setpoints on a front axle and on a rear axle of the vehicle, this step being part of the control procedure of the [Fig. 1], and

[0024] [Fig.5] represents means for correcting torque setpoints at the wheel of the vehicle, implemented in the control process of the [Fig.l].

[0025] According to one embodiment of the invention, a vehicle trajectory control method 1, shown in [Fig. 1], is implemented in a trajectory control system 2, shown in [Fig. 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 located remotely from the vehicle, for example, computing means receiving data from the vehicle and sending computing results back to the vehicle. In this embodiment of the invention, the vehicle is assumed to be a four-wheel-drive electric or hybrid electric vehicle.

[0026] A first step 100 of the trajectory control method 1 is the measurement of a slip difference between the front and rear axles of the vehicle, this measurement step 100 providing as output a measured slip difference ASmes. In this application, "slip" refers to a ratio between a speed difference and a speed.

[0027] For example, a slip S of a wheel of radius r and rotational speed co is calculated as $ _ where Vx is the speed of the vehicle including the wheel.

[0028] In this step 100, the difference between the average slip of the front axle wheels and the average slip of the rear axle wheels is measured more precisely (which amounts to calculating the difference between the average speeds of the two axles and dividing it by the vehicle's speed Vx). For this purpose, the speed of each wheel of the vehicle is measured by wheel speed sensors integrated into the vehicle's wheels, providing:

[0029] - the rotational speed of the left front wheel,

[0030] - the rotational speed of the right front wheel,

[0031] - the rotational speed corl of the left rear wheel,

[0032] - the correct rotation speed of the right rear wheel.

[0033] Wheel speed sensors are measurement means for the trajectory control system 2 according to the invention. Alternatively, these sensors are replaced by wheel speed estimation algorithms.

[0034] As seen in [Fig.2], we refer to:

[0035] - Vx the speed of the vehicle,

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044] -Rgf the radius of the vehicle's front left wheel, -Rdf the radius of the vehicle's front right wheel, -Rgr the radius of the left rear wheel of the vehicle, -Rdr the radius of the right rear wheel of the vehicle. Therefore, in this measurement step 100, we have as shown [Fig.3]: ASmes = 100* (Rgf*aifl+Rdf*<.afr ^-(Rgr^wrl+Rdr^uyrr) Vx In this embodiment of the invention, the slip is expressed as a percentage, but alternatively it could be calculated as a raw ratio or using a different reference speed than the vehicle speed. A second step 200 of the method 1 according to the invention is the comparison between the slip deviation ASmes measured previously between the front axle and the rear axle of the vehicle, and a corresponding estimated slip deviation ASest. The estimated slip deviation ASest is calculated using driver inputs, which are the steering wheel angle ô and the vehicle speed Vx, which depends on the accelerator pedal position, and is independent of the real-time wheel rotation speeds used in measurement step 100. More specifically: Kjdy / With :

[0045]

[0046]

[0047]

[0048]

[0049] And:

[0050]

[0051]

[0052]

[0053]

[0054] Or: - R / dy and Rrdy represent respectively the average dynamic radius of the front axle wheels and the average dynamic radius of the rear axle wheels. - wf is the vehicle's track width, that is, the distance between the left rear wheel and the right rear wheel of the vehicle. - ôs2 is a constant parameter representing the specific drift of the rear axle responsible for the steering performance of said vehicle -1 is the wheelbase of the vehicle, that is, the distance between the front axle (tire-ground contact point of the front axle wheels) and the rear axle (tire-ground contact point of the rear axle wheels), i.e., ai+a2 on [Fig.2].

[0055] It should be noted that for visibility reasons some parameter letters are indexed in the equations but not necessarily in the figures and text.

[0056] In this step 200, the difference between the estimated slip deviation ASest and the measured slip deviation ASmes is calculated.

[0057] If this difference is negative:

[0058] If ASest - ASmes < 0, then the following steps 300 to 800 of the trajectory control method 1 are inhibited, which notably saves computing resources. The trajectory control method 1 therefore loops back to measurement step 100. Furthermore, if the calculated deviation is negative, it means that the driver's request is contrary to the need to stabilize the vehicle; the vehicle's computer therefore activates a safety function to stabilize the vehicle.

[0059] On the contrary, if this difference is positive:

[0060] ASest - ASmes > 0, for example ASest = 10% and ASmes = 6%, then wheel control can be improved to meet the driver's demand, and we proceed to the next step 300 of the control method 1 according to the invention. This condition is optionally associated with a positive deviation threshold, for example, we proceed to the next step 300 of the control method 1 according to the invention only if ASest - ASmes > 2%.

[0061] The next step 300 is the determination of a slip difference setpoint ASreq between the front axle and the rear axle. For this, a desired yaw rate V7d is used, calculated by calculation means 302 from the steering wheel angle ô and the vehicle speed Vx. The calculation means 302 notably use the wheel model expressed above in relation to the estimated slip difference ASest.

[0062] As a reminder, as shown in Figure 2, the vehicle is fixed in a relative orthonormal frame {Ot, Xt, Yt] which follows the vehicle's trajectory, with the Xt axis being tangent to this trajectory. With respect to an absolute orthonormal frame {O, X, Y] , the Xt axis forms an angle with the X axis of this frame, called the yaw angle V'. The desired yaw rate V' therefore corresponds to an estimate of the derivative of this yaw angle V with respect to time, as desired by the driver.

[0063] A measured yaw rate V'mcs, corresponding to the real derivative of this yaw angle V7 with respect to time, is further measured, in this determination step 300, by an inertial measurement unit measuring this value at the center of gravity of the vehicle.

[0064] Calculation means 304 then calculate, in this determination step 300, a corrective yaw moment Mrec as a function of the difference A between the desired yaw rate V' and the measured yaw rate V'mes:

[0065] M rec = IzWmes - (2 VxbQ 2b} - 2b2*5 + wrtH, with: (a^caf+ci2^cai} A = / 77(7,¾ WHERE: * is the multiplication operator

[0066] m is the mass of the vehicle,

[0067] ■ is the yaw acceleration measured by the inertial measurement unit

[0068] "ai is the distance between the center of mass of the vehicle and the front axle of the vehicle

[0069] ' is the distance between the center of mass of the vehicle and the rear axle of the vehicle

[0070] "caf is a front wheel drift stiffness coefficient, specific to the properties tires in particular

[0071] ' because is a coefficient of rear wheel drift rigidity, specific to the properties tires in particular

[0072] - / 5 is the vehicle's drift angle (different from the tire drift angle) (matics)

[0073] and: 2 days. ustw = "d[2s^Sn- k^signk,> k7 >0 “o

[0074] where: a = A yy

[0076] sign(O) G [-1, 1]

[0077] kx and k2 being predetermined constants (gains).

[0078] Since Mrec is a function of A ip, this corrective moment adjusts itself to counter this pursuit error by making ustw, which is a sliding variable, converge towards zero in a finite time.

[0079] It should be noted that the calculation of the integral in the sliding variable ustw is performed in the Laplace domain. Furthermore, as soon as 17 approaches zero or becomes zero, the driver's intention is realized at 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 step 200, which compares the control method according to the invention.

[0080] Furthermore, depending on the drift stiffness of the front and rear wheels and the vehicle speed, the corrective moment Mrec is adaptive in that it is calibrated according to road conditions, and more specifically, thanks to the sliding variable, it adapts to an observed difference in slip between the left and right wheels of the front and rear axles. The expression for the corrective moment Mrec allows the target corrective moment value to be modulated according to the vehicle dynamics: if slippage is observed, the corrective moment Mrec is intentionally reduced to stabilize the vehicle.

[0081] In this step 300 of determining a slip deviation setpoint ASreq Between the front and rear axles, calculation means 306 of the trajectory control system 2 according to the invention are then used, providing the slip deviation setpoint ASreq as a function of the previously calculated correction moment Mrec. For this purpose, the calculation means 306 use the inverse transfer function of the transfer function G, giving the correction moment Mrec as a function of the corresponding slip deviation, which is by construction the slip deviation setpoint ASreq:

[0082] Mrec / Rdyit \2 j wf} with ) TT~

[0083] Where s is the Laplace variable, Rdyn the average dynamic radius of the vehicle's wheels and Csf is the dynamic radius of a wheel of the vehicle (the wheels being considered identical in this calculation).

[0084] Calculation means 302 to 306 are therefore also means of determining the slip deviation setpoint ASreq.

[0085] In a step 400, torque setpoints Cl and C2 are then determined to be applied respectively to the front axle and the rear axle of the vehicle, depending on the difference AScib between the slip deviation measured ASmes in the measurement step 100 and the previously calculated slip deviation setpoint ASreq.

[0086] For this purpose, calculation means 408 of the trajectory control system 2 according to the invention are used, which take as input the difference AScib between the measured slip deviation ASmes obtained in the previous measurement step 100 and the slip deviation setpoint ASreq 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 AScib as a function of a corrective torque Leur such that:

[0087] H = ^Jal+J„,k2 )i'

[0088] where

[0089] - k is the transmission ratio between the engine torque and the vehicle wheels,

[0090] -Jm is the inertia of the motor, and

[0091] -Jeq is the equivalent inertia of the front traction system.

[0092] The corrective torque rcur is therefore a torque allowing to correct a set engine torque, in an adaptive manner to the road conditions of the vehicle, thanks to the calculation of the corrective moment, this correction of the set engine torque allowing to stick as closely as possible to the driver's will according to the vehicle's capabilities.

[0093] Correlating the slip deviation setpoint ASreq with the measured slip deviation ASmes in this step 400 of determining the torque setpoints Cl and C2 allows us to get as close as possible to the required torque setpoint correction engine, given that the slip difference measured at the center of gravity of the vehicle is not a reflection of a slip difference measured at the front and rear axles of the vehicle, and vice versa.

[0094] In this step 400 of determining torque setpoints Cl and C2, the corrective torque Ecur determined by inversion of the transfer function Ecur is then subtracted or added to a torque command Tess on each axle, derived from the driver's torque demand (or taken equal to this driver's torque demand) and weighted by dynamic weighting coefficients respectively Ksi, Ks2, to obtain respectively the torque setpoint Cl to be applied on the front axle, and the torque setpoint C2 to be applied on the rear axle:

[0095] C^^ress-F™

[0096] C2 = Kx2 *Fess + Fc„

[0097] With:

[0098]

[0099] and

[0100] where:

[0101] - a is the mass distribution between the front axle and the rear axle, therefore a parameter intrinsic to the vehicle model,

[0102] - “ is a coefficient of friction, ax the lateral acceleration and g the gravity,

[0103] - h is the distance between the center of gravity (center of mass) of the vehicle and the point ground contact

[0104] - Ssat is a maximum slip value that we do not wish to exceed.

[0105] Alternatively, the curative couple Fc„r is subtracted from to obtain the instruction of torque C2 to be applied to the rear axle, and the corrective torque F(?Mr is added to *Fess to obtain the torque setting Cl to be applied to the front axle.

[0106] Ksi and Ks2 are therefore dynamic weighting coefficients based on acceleration, speed and load distribution on the vehicle, allowing the torque to be distributed between the front and rear axles of the vehicle without overriding the driver's will.

[0107] It should be noted that, for the sake of simplicity in this request, the Tess torque command is assumed to be equal on each axle, but this torque demand can of course differ from one axle to another, the vehicle's computer deriving this torque command from the driver's intent, taking into account the power available at each front or rear axle of the vehicle. In particular, if the vehicle has an electric motor on each front or rear axle, the Tess torque command is a function of the electrical power available at the motor driving the axle, and of the electrical power available in the vehicle's traction / propulsion battery.

[0108] The step 400 of determining the torque setpoints Cl 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 Cl and C2 on each axle.

[0109] The next step 500 of the control method 1 according to the invention is to verify that the vehicle speed Vx is below a vehicle speed threshold Vseuil, set for example at 70 km / h (kilometers per hour). If this is not the case (branch N in [Fig. 1]), the control method 1 does not apply the torque commands Cl and C2 determined in the preceding step 400 to the vehicle axles, as the driving conditions do not allow for dynamic modification of the torque commands without compromising vehicle stability. In this case, the control method 1 loops back to the measurement step 100.

[0110] If on the contrary the speed Vx of the vehicle is less than or equal to this speed threshold Vthreshold (branch Y on the [Fig.1]), in a subsequent step the steering angle ô is compared with a steering angle threshold ôthreshold, equal for example to 50 degrees.

[0111] If in this step 600, it is determined that the steering angle ô is less than the steering angle threshold ôseuil (branch Y on the [Fig.1]), then the next step 700 of the control method 1 according to the invention is the application of the torque commands Cl and C2 determined in the previous step 400 to the front axle and rear axle of the vehicle respectively.

[0112] If, on the contrary, in this step 600, it is determined that the steering angle ô is greater than or equal to the steering angle threshold ôseuil (branch N on the [Fig.1]), then the next step 800 of the control method 1 according to the invention is the distribution of the torque setpoints Cl and C2 determined in the previous step 400 on each wheel of the vehicle.

[0113] As shown [Fig.4], in step 800 of the distribution of torque setpoints Cl and C2, the torque setpoint Cl on the front axle is weighted by a dynamic weighting coefficient based on the slip difference between the left and right wheels of the front axle, similarly to step 400, to obtain a torque setpoint Cgf of the left front wheel and a torque setpoint Cdf of the right front wheel:

[0114] Cgf = (1 / 2 - Kf / 2) * Cl

[0115] Cdf = (1 / 2 + Kf / 2) * Cl

[0116] with

[0117] where A Sf is a slip difference measured between the left wheel and the right wheel of

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128] 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 based on the slip difference between the left and right wheels 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 A Sr is a slip difference measured between the left wheel and the right wheel of the vehicle's rear axle. The dynamic coefficients Kf and Kr allow for precise adjustment of the torque requirement on each wheel. Finally, in this step 800, the torque commands 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 command applied to it to be reduced. Figure 5 shows this control loop on the front axle wheels, a loop that can easily be transposed to the rear axle wheels. The control loop uses the difference e between the measured slip difference ASf between the right and left wheels of the front axle, and a theoretical slip difference ASfth between the right and left wheels of the front axle. This difference e is received as input to a controller 802, which calculates the torque setpoints Cgf and Cdf on the left and right front wheels using the equations mentioned previously: The theoretical slip deviation ASfth is determined by means 804 for modeling this theoretical deviation, using other vehicle data, notably 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 whereby, when cornering, the inside wheels of the vehicle tend to lose traction and accelerate because the support 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 ASfth modeled by the Modeling methods 804, from the angle to the steering wheel.

[0129] The modeling means 804 and the regulator 802 are means for determining wheel torques of the trajectory control system 2 according to the invention.

[0130] Of course, other types of control loops can be used in this step 800. For example, the input to the controller 802 takes, as an alternative, 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 alternative, the Ackerman effect is not taken into account. In yet another alternative, the control operates by measuring the difference between the torque produced on each wheel and the torque setpoint on the wheel in question.

[0131] Of course, the invention is not limited to the examples just described, and many modifications 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 commands Cl and C2 on the front axle and the rear axle being directly applied to the axles as soon as the speed condition below the threshold speed Vthreshold is met.

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 (ASmes) between the front axle and the rear axle, a step of determining (300) a slip difference setpoint (ASreq) between the front axle and the rear axle, and a step of determining (400) torque setpoints (Cl, C2) to be applied to the front axle and to the rear axle, as a function of the difference between the slip difference setpoint (ASreq) and the measured slip difference (ASmes), the method being characterized in that the step of determining (300) the slip difference setpoint (ASreq) uses a corrective yaw moment (Mrec) determined as a function of a difference between a desired yaw rate L.. ) and a measured yaw rate (m ). V des '' mes

2. A trajectory control method according to claim 1, in which a calculation of the corrective yaw moment (Mrec) comprises at least one term (caf, car) whose parameters depend on the level of adhesion of the vehicle wheels to the ground.

3. A trajectory control method according to claim 1 or 2, wherein a calculation of the corrective yaw moment (Mrec) comprises sliding mode control terms.

4. A trajectory control method according to any one of the preceding claims, in which the torque setpoints (Cl, C2) to be applied to each axle are obtained by adding or subtracting a curative torque (Peur) from a torque command (Fess) weighted by dynamic weighting coefficients (Ksi, Ks2) which depend on the measured slip difference (ASmes) and the distribution of dynamic loads between the front axle and the rear axle.

5. A trajectory control method according to the preceding claim, in which the vehicle has four drive wheels, and in which the torque setpoint (Cl, 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 (ASf, ASr) between the wheels of said axle.

6. A trajectory control method according to the preceding claim, comprising a regulation 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 regulation loop takes into account the Ackermann sliding effect.

7. A trajectory control method according to any one of the preceding claims, in which an application of the torque setpoints (Cl, C2) on the front axle and on the rear axle is conditioned by a comparison step (200) between the measured slip difference (ASmes) between the front axle and the rear axle and an estimated slip difference (ASest), said application not being carried out if the estimated slip difference (ASest) is less than the measured slip difference (ASmes).

8. A trajectory control method according to the preceding claim, in which the application of the torque instructions (Cl, C2) to the front axle and to the rear axle is only carried out below a vehicle rolling speed threshold (Vseuil).

9. A trajectory control method according to claims 5 and 7, in which the distribution of one of the torque instructions (Cl, C2) on each wheel is only carried out below a vehicle rolling speed threshold (Vseuil), and above a vehicle steering wheel angle threshold (ôseuil).

10. 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 (ASmes) between the front axle and the rear axle, means for determining (302, 304, 306) a slip difference setpoint (ASreq) between the front axle and the rear axle, and means for determining (408) torque setpoints (Cl and C2) to be applied to the front axle and to the rear axle, as a function of the difference (AScib) between the measured slip difference (ASmes) and the slip difference setpoint (ASreq), the system being characterized in that the means for determining (302, 304, 306) a slip difference setpoint (ASreq) use a corrective yaw moment (Mrec) determined as a function of a difference between a desired yaw rate Lj, ) and a measured yaw rate (w ). V of

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