FR2945262A3 - Trajectory correction method for motor vehicle, involves authorizing large sliding of front wheel of vehicle in turning situation with respect to another situation in which vehicle is not over-steered by anti-lock braking system module - Google Patents

Abstract

The method involves implementing a braking process to detect and prevent locking and sliding of a wheel by an anti-lock braking system (ABS) module (2). Difference of thresholds is calculated in the event of over steering of a motor vehicle. Large sliding of a front wheel of the motor vehicle is authorized in a turning situation with respect to another situation in which the vehicle is not over-steered by the ABS module, where the motor vehicle over steers when the motor vehicle is in the turning situation. Independent claims are also included for the following: (1) a data storage medium having a set of instructions for executing a method for correcting a trajectory of a motor vehicle (2) a system for correcting a trajectory of a motor vehicle.

Description

The present invention relates to the control of the dynamic behavior of a motor vehicle, and in particular the control and the automatic correction of the oversteer of a motor vehicle relative to the desired trajectory by the driver when turning. Thus, the invention relates to a method for correcting the trajectory of a motor vehicle. It also relates to a motor vehicle as such implementing such a method.

When a vehicle turns into a bend at a longitudinal speed that is too high given the physical limits imposed by the adhesion between the tires and the ground in the turn, it may become impossible to respect the curvature of the road and the motor vehicle can survive, that is to say that the rear train of the vehicle begins to slide and that the driver loses control of his vehicle. This type of vehicle instability is more commonly called head-to-tail. The vehicle thus deviates from the path desired by the driver, the rear axle deporting outwardly of the turn.

This behavior can also occur with a vehicle with the rear axle driving, if the driver accelerates in a turn.

It is then necessary to detect such a situation of oversteer and act automatically on the motor vehicle so that it returns to the path desired by the driver. The object of the invention is to provide a method for operating a trajectory correction system that makes it possible to remedy the problems mentioned above and to improve the trajectory correction systems known from the prior art. In particular, the invention provides a method of operating a path correction system using simple correction means, improving the stability of the vehicle and being applicable to both motor vehicles using a hydraulically controlled braking system and the like. 'to vehicles using an electrically controlled braking system.

More specifically, the invention proposes a method of correcting the trajectory of a motor vehicle comprising a front axle and a rear axle, and an ABS anti-lock braking system module implementing a braking method for detecting and preventing the locking and sliding of a wheel, characterized in that the ABS module allows a greater slippage of at least one front wheel of the motor vehicle in a turning situation in which the motor vehicle survives in relation to another situation in which the vehicle does not survive.

The ABS module can determine the slip of a wheel when the difference between its speed (Omega) and the vehicle speed (V VH x _Est) exceeds a certain threshold (Threshold Detection Slip 1) and can include a step of calculating a different threshold in case of oversteer of the vehicle to allow greater slippage of at least one front wheel in case of oversteer.

The ABS module can also implement a braking method according to a first threshold (Threshold Detection Slip 1) which corresponds to a start phase of blocking a wheel and a second threshold (Threshold Detection Slip 2 ) which corresponds to a locking phase of a wheel and may comprise a step of modifying these two thresholds in case of oversteer, the two thresholds being thus defined according to the following equations: -In case of non-oversteer, Threshold Detection Slip 1 V VH x East / radius AND Threshold Detection Slip 2 V_VH_x_Est / radius

And in case of oversteer, Threshold Detection Slip 1 = CoeffSx abs threshold1 V VH_x_Est / radius * Gain_Seuill_ESP with Gain_Seuill_ESP <1 AND Threshold Detection Slip 2 = CoeffSx abs threshold2 V VH_x_Est / radius * Gain_Step2_ESP with Gain_Seuil2_ESP <1

where Coeff_Sx_abs_seuill and CoeffSx_abs_seuiI2 represent two slip rates between 0 and 1, V_VH_x_Est represents the longitudinal speed of the motor vehicle, radius represents the radius of the wheel, and Gain_Seuill_ESP and Gain_Seuil2_ESP represent two parameters. The braking process can be implemented by the ABS module comprising the implementation of a greater braking intensity during a recovery of adhesion of a front wheel after a phase of locking / unlocking the front wheel in a situation of oversteer than in another situation.

The braking process of a motor vehicle may comprise a braking mode in which a braking action intensity reference value in the adhesion recovery phase changes at least substantially CoeffSx abs threshold 1 CoeffSx abs threshold 2 * * * linearly with time, firstly according to a first slope (steep open-loop slope) whose value is at least substantially constant, then according to a second slope (low slope retained) whose value is at least substantially constant, the value of the first slope being greater than the value of the second slope, and in a situation of oversteer of the motor vehicle, this instruction of intensity of the braking action can always evolve according to the higher slope in phase of recovery of adhesion of a wheel before.

In a turning situation in which the motor vehicle survives, the method may include a braking control step of the vehicle wheels in which a greater braking torque is commanded on the front axle wheel which is external to the turn of the vehicle. so as to create a moment of yaw on the motor vehicle.

The braking control step of the vehicle wheels may include controlling a braking torque on the front axle wheel that is outside the turn only.

The value of the braking torque on the front axle wheel that is outside the bend can be calculated using a proportional corrector. The method of correcting the trajectory of a motor vehicle may allow the sliding of the front outer wheel at the turn, which causes a slip of the front wheel inside the turn when the motor vehicle survives.

The invention also relates to a data storage medium readable by a computer on which is recorded a computer program comprising software means for implementing the steps of the method of correcting the trajectory of a motor vehicle such as previously described. The invention also relates to a system for correcting the trajectory of a motor vehicle, characterized in that it comprises hardware and / or software means for implementing the method of correcting the trajectory of a motor vehicle such as as previously described.

The invention also relates to a motor vehicle comprising a system 10 for correcting the trajectory as described above.

The accompanying drawings represent, by way of example, an embodiment of a trajectory correction system according to the invention.

Figure 1 is a schematic representation of the trajectory control system according to one embodiment of the invention.

Figure 2 is a diagram of the first module of the trajectory control system according to the embodiment of the invention. Figure 3 is a detailed diagram of an embodiment of a control block of the application of a moment of yaw on the motor vehicle.

Fig. 4 is a diagram of an embodiment of a first block of the control block for applying a yaw moment to the motor vehicle.

Fig. 5 is a diagram of an embodiment of a second block of the control block for applying a yaw moment to the motor vehicle. Figure 6 is a diagram of an embodiment of a first sub-block of the second block.

Fig. 7 is a diagram of an embodiment of a second sub-block of the second block.

Fig. 8 is a diagram of an embodiment of a third sub-block of the second block.

Fig. 9 is a diagram of an embodiment of a fourth sub-block of the second block.

Fig. 10 is a diagram of an embodiment of a third block of the control block for applying a yaw moment to the motor vehicle.

Figure 11 is a diagram of an embodiment of a first block of the ABS module according to the embodiment of the invention.

Fig. 12 is a diagram of an embodiment of a first block of the ABS module according to the embodiment of the invention.

Figure 13 shows schematically the operating principle of the ABS module. Fig. 14 is a graph showing the effects of the invention in an oversteer situation of a motor vehicle.

In the following, for the signal names, the suffix: 30 - 11 designates the left front wheel, 12 designates the right front wheel, 25 21 designates the left rear wheel, 22 designates the right rear wheel, ij thus designates one four wheels of the vehicle.

Similarly, the following abbreviations are used: ESP: Electronic Stability Program control or correction system, ABS: Antilock Braking System (Anti-Blocking System), CML: Yaw control system.

An ESP system aims to keep the vehicle on the path desired by the driver. If the vehicle deviates from this trajectory during a turn (situation of understeer or oversteer), the ESP system will send engine torque and / or braking torque setpoint signals to correct the trajectory of the vehicle. vehicle.

A motor vehicle according to the invention comprises an ESP type trajectory correction system acting on a braking system and / or on a control system of the vehicle engine in order to correct the trajectory in oversteer situation. The trajectory correction system comprises various modules, shown schematically in FIG. 1, interacting and making it possible to develop setpoint signals intended for braking and / or braking control systems. The trajectory correction system comprises hardware and software means for implementing the trajectory correction method according to the invention. In particular, it comprises means governing its operation according to the method of the invention. The software means may comprise computer programs.

During an oversteer, the vehicle deviates from the path desired by the driver: the vehicle turns more than it should. The ESP system has

8 then function to allow the vehicle to turn correcting its trajectory.

The trajectory correction system comprises a first module 1 said oversteer control and a second module 2 consisting of ABS comprising three main submodules 100, 101, 102 which will be detailed later.

The first module 1 says oversteer control works with the inputs and outputs defined in the table below. Inputs Outputs Signal psip ref: Yaw rate Signal T BRK ESP CML ij Req: vehicle reference in rad / s braking torque request from (d (Y_ref) / dt). The yaw rate CML regulation of the ESP to the reference wheel ij translates the trajectory in Nm. Desired by the driver. Signal YawRate Sens: Speed of Signal Flag on Turn: Flag which measured yaw of the vehicle detects an oversteer situation. radish. Signal coming from a sensor, If flag on turn = 1 then the vehicle translates the trajectory realized by the survire, vehicle. If flag on turn = 0 then the vehicle does not survive This first module implements a simplified model of the motor vehicle that allows from the steering angle applied by the driver and the longitudinal speed of the vehicle to calculate a yaw rate reference d (4) _ref) / dt, i.e. the yaw rate that the vehicle should have for the measured steering angle and longitudinal velocity.

For this, the system includes several estimators for determining reference longitudinal velocity information, actual moment applied and load on the wheels. Measurement signals are provided by a set of sensors. These sensors provide, for example, vehicle wheel speed measurement signals, a vehicle yaw rate measurement signal, a vehicle transverse acceleration signal and a longitudinal acceleration signal of the vehicle.

Then, the first module receives the reference yaw rate and the measured yaw rate and allows the use of these data to detect an oversteer situation.

It further includes a CML brake control block which defines a yaw moment to be applied to the vehicle by application of braking forces. The CML block generates braking torque setpoint signals to be applied to each of the wheels to achieve this yaw moment, in particular by means of a distribution block.

The previously mentioned CML brake control module is described below with reference to FIG. 2. It has three inputs and one output detailed in the table below. It allows the development of the output signal from the input signals. The input signals come from other modules. Inputs Outputs psip signal ref: yaw rate signal signal T BRK CML ~ Req: reference of the vehicle. Expressed by four component signal example in rad / s (d (4i_ref) / dt). The speed, each representing a reference yaw, represents the trajectory of the braking torque desired by the driver. of a wheel of the motor vehicle. These setpoint pairs are for example expressed in Nm. YawRate signal Meaning: measured yaw rate signal of the vehicle. Expressed for example in rad / s. This signal is provided by a sensor. signal V VH X East: longitudinal vehicle speed signal (or reference speed). Expressed for example in mis. This signal is developed by estimating the reference speed. In an embodiment shown in FIG. 3, the brake control module CML comprises different blocks.

A first block 22 says Calculate_Error Speed_Lacet makes it possible to calculate an error in yaw rate which reflects the difference between the trajectory desired by the driver and the real trajectory of the vehicle. It includes the entries and exits detailed in the table below. It allows the development of the output signal from the input signals.

Inputs Outputs psip signal ref: error signal yaw rate signal: vehicle reference signal. Expressed for example in rad / s speed error (d (4 -'_ ref) / dt). The yaw rate of yaw. Expressed by reference translates the path desired by the example in rad / s. driver. YawRate Sens signal: The measured yaw rate signal of the vehicle. Expressed for example in rad / s. This signal is provided by a sensor. To calculate the output signal, it is sufficient to differentiate between the reference yaw rate (calculated by a reference generator) and the yaw rate measured according to the formula: error (t) = psip _ ref (t) - YawRate _ Sens (t) This logic is implemented thanks to a subtraction operator described in particular in figure 4.

It should be noted that the psip signal used to calculate the error signal is from the bicycle model which is only valid for speeds above a Threshold Minimum Speed threshold.

A second block 21 said Detect Situation_instable can detect a difference between the path desired by the driver and the real trajectory 15 of the vehicle. It also determines if this difference of trajectory corresponds to a situation of understeer or an oversteer situation. It includes the inputs and outputs detailed in the table below. It allows the elaboration of the output signals from the input signals. Inputs Outputs signal error: signal of signal signal flag under corner: logical signal of speed of yaw. detection of a situation of understeer. Expressed for example in If flag under corner = 1 then the vehicle radish. understeer. If flag under corner = 0 then the vehicle does not understeer. signal YawRate Direction: signal flag on turn: signal logic signal yaw rate detection of an oversteer situation. measured vehicle. If flag on turn = 1 then the Expressed vehicle for example survives. radish. This signal is provided If flag on turn = 0 then the vehicle does not go through a sensor. do not survive. signal V VH X East: Signal signal Flag under activation CML turn: longitudinal speed of the detection signal of a vehicle situation (or understeer speed requiring a reference correction). Expressed by trajectory by applying an example moment in m / s. This yaw signal. is developed by estimating the reference speed. One possible embodiment of this block 21 is described below with reference to FIG.

It comprises for example different sub-blocks 31 to 34 described hereinafter with reference to FIGS. 6 to 9.

A first sub-block 31 known as Determination_signe_psip is described below with reference to FIG. 6. It makes it possible to precisely determine the situation in which the vehicle is located by knowing the sign of the measured yaw rate. It includes the inputs and outputs detailed in the table below. It allows the development of the output signal from the input signal. Inputs Signal outputs YawRate Direction: Positive psip signal signal: Logic signal The measured yaw rate of the vehicle. defining the sign of the speed of Expressed for example in radish. This lace, that is to say if the vehicle turns signal is provided by a sensor. To the right or to the left. If psip_position = 1 then the yaw rate is positive, the vehicle turns to the left. If psip_positif = 0 then the yaw rate is negative, the vehicle turns right. Parameters Threshold hysteresis_positif Positive constant close to zero Threshold hysteresis negative Negative constant close to zero Preferably, the measurement signal of the yaw rate is not filtered. Thus, to avoid detecting changes in the situation due to a sign change caused by noise on the measurement signal, hysteresis is set up by the means shown in FIG. 6: If the YawRate Direction signal becomes greater than one first positive threshold (Threshold hysteresis positive), the positive psip signal goes high. If the YawRate Direction signal falls below a certain negative threshold (Negative_hysteresis_hreshold), the positive psip signal goes low.

For this purpose, two comparators 35 and 36 and a flip-flop 37, for example of the RS type, are used for example.

A second sub-block 33 called Determination_Flag_Sur_Virage is described below with reference to FIG. 7. It makes it possible to determine a situation of oversteer of the vehicle. It includes the entries and exits detailed in the table below. It allows the elaboration of the output signals from the input signals.

Inputs Signal error outputs: signal error signal Flag on turn: logic signal yaw rate. Expressed by detecting an example situation in radish. oversteer. If Flag on Turn = 1 then the vehicle survives. If Flag on turn = 0 then the vehicle does not survive. positive psip signal: logical signal signal detection on turn _G: signal defining the sign of the detection speed of a yaw situation, that is to say if the vehicle oversteer in a left turn. turn right or left. If cornering detection _G = 1 then the Si psip positive = 1 then the vehicle speed turns to the left and the yaw vehicle is positive, the vehicle survives. turn left. If detection on turn G = 0 otherwise. If psip_positif = 0 then the yaw rate is negative, the vehicle turns right. signal V VH X East: signal signal detection on turn D: signal longitudinal speed of the logical vehicle detection of a situation (or reference speed). oversteer in right turn. Expressed for example in m / s. This Si detection on turn D = 1 then the signal is developed by a vehicle turning right and the vehicle estimating the speed to oversteer. reference. If detection on turn D = 0 otherwise. Parameters Threshold Minimum speed Speed threshold (for example, expressed in m / s) above which the calculation of the error signal is valid. C ESP CML threshold ON oversteer The threshold for detecting a gap in yaw rate that determines the beginning of an oversteer situation. C ESP CML threshold OFF oversteer The threshold for detecting a gap in yaw rate that determines the end of an oversteer situation. The second sub-block 33 implements the following logic: In the case of a left turn (positive psip = 1): If error <= - C ESP threshold CML ON oversteer and V VH X East> = 5 Threshold Speed Minimum Then Flag on turn = 1 If error> = - C ESP Threshold CML OFF oversteer and V VH X East> = Threshold Minimum Speed Then Flag on turn = 0 10 Else Flag on turn (t) = Flag on turn (t-1 )

In the case of a right turn (positive psip = 0): If error> = C ESP Threshold CML ON oversteer and V VH X East> = Threshold Minimum Speed 15 Then Flag on turn = 1 If error <= C ESP Threshold CML_OFF Oversteer and V VH X East> _ Minimum Speed Threshold Then Flag on Turn = 0 Otherwise Flag on Turn (t) = Turn Flag (t-1) 20 Logic Signals on G-Turn and Turn-Off Detection are also defined as following: If error <_ - C ESP Threshold CML ON oversteer then detection on turn _G = 1 25 If error> C ESP Threshold CML ON oversteer then detection on turn _D = 1 These logic signals allow to give priority to corrective actions of oversteer rather than understeer correction actions, oversteer being a much more critical situation for the driver.

To implement this logic, for example, comparators 41, 42, 43, 44 and 48 are used, latches 45, 46, for example of the RS type, an AND logic gate 49 and a logic gate 47 controlled by the logic signal. positive psip.

A third sub-block 32 called Determination_Flag_Sous_Virage is described below with reference to FIG. 8. It makes it possible to determine a situation of understeer of the vehicle. To implement this logic, for example, comparators 51, 52, 53, 54 and 60, flip-flops 56, 58, for example of the RS type, an AND logic gate 61, OR logic gates 55, 57 and a gate are used. logic gate 59 controlled by the positive psip logic signal.

A fourth sub-block 34 called Determination_Flag_Sous_Virage_for_Action_CML is described below with reference to FIG. 9. It makes it possible to develop a logic signal for activating a regulation action of the moment of yaw applied to the vehicle in a situation of under -turning of the vehicle. It includes the inputs and outputs detailed in the table below. It allows the development of the output signal from the input signals.

Inputs Signal error outputs: Yaw rate signal error signal. Expressed by Flag under viral activation CML example in radish. logic signal for activating a understeer correction. If signal V VH X East: longitudinal vehicle speed signal (or reference speed). Expressed for example in m / s. This signal is developed by estimating the reference speed. signal detection on turn _G: logical signal for the detection of an oversteer situation in Flag under activation turn CML = 1, then it is necessary to activate means for correcting understeer of the vehicle. If Flag under activation CML turn = 0 then it is not necessary to activate means of correction of understeer of the vehicle. Positive psip signal: A logical signal defining the sign of the yaw rate, that is, whether the vehicle is turning right or left. If psip_position = 1 then the yaw rate is positive, the vehicle turns to the left. If psip_positif = 0 then the yaw rate is negative, the vehicle turns right. left turn. If cornering detection _G = 1 then the vehicle turns to the left and the vehicle survives. If detection on turn G = 0 otherwise. signal detection on turn D: logical signal for detecting a situation of oversteer in a right turn. If cornering detection _D = 1 then the vehicle turns to the right and the vehicle survives. If detection on turn D = 0 otherwise. Parameters Threshold Minimum speed Speed threshold (for example expressed in m / s) above which the calculation of the error signal is valid. C ESP CML_ON threshold under turn Sensing threshold for a yaw rate deviation that determines the start of a understeer correction action. C ESP CML threshold OFF underspeed Detection threshold for a yaw rate deviation that determines the end of a understeer correction action. The fourth sub-block 34 implements the following logic: In the case of a left turn (positive psip = 1): if error> = C ESP threshold CML ON understeer and V VH X East> = Threshold Minimum speed then Flag understeer activation CML = 1 if error <= C ESP Threshold CML OFF understeer or detection on turn_G = 1 then Flag under turn activation CML = 0 else Flag under turn activation CML (t) = Flag under turn activation CML 10 (t- 1)

In the case of a right turn (positive psip = 0): if error <= - C ESP Threshold CML ON understeer and V VH X East> = Threshold Minimum Speed 15 then Flag understeer activation CML = 1 if error> _ - C ESP threshold CML OFF understeer or detection on turn D = 1 then flag under turn = 0 otherwise flag under turn (t) = flag under turn (t-1) 20 To implement this logic, we use for example comparators 71, 72, 73, 74 and 60, flip-flops 77, 78, for example of the RS type, an AND logic gate 81, OR logic gates 75, 76 and a logic gate 79 controlled by the psip_positif logic signal. A third block 24 says Calculate Command_Mfx and shown in FIG. 10 makes it possible to calculate a value of moment of yaw to be applied to the vehicle to release it from an unstable situation, in particular an oversteer situation. 25 30 5 This includes the inputs and outputs detailed in the table below. It allows the elaboration of the output signals from the input signals. Inputs Outputs error signal: signal of error of speed of signal Command Mfx shoelace. Expressed for example in radish. setpoint signal giving the instantaneous value of the yaw moment to be applied to the vehicle. Expressed, for example, in Nm. Flag signal on turn: logical signal for detecting an oversteer situation. If Flag on Turn = 1 then the vehicle survives. If Flag on turn = 0 then the vehicle does not survive. Flag signal under CML activation: logic signal to activate a understeer correction. If Flag under activation CML turn = 1 then it is necessary to activate means of correction of the understeer of the vehicle. If Flag under activation CML turn = 0 then it is not necessary to activate means of correction of understeer of the vehicle. Parameters C ESP Gain Corrector CML_survirage Gain of the corrector correcting an oversteer situation. C ESP Gain Corrector CML understeer Gain corrector corrects a situation of understeer. C ESP CML threshold ON underspeed Detection threshold for a yaw rate deviation that determines the beginning of an understeer correction action. C ESP Threshold CML_ON oversteer A threshold for detecting a yaw rate deviation that determines the beginning of an oversteer correction action. The third block 24 preferably uses a proportional type corrector. It can be modeled thanks to the following equation in the Laplace domain: C (p) = Kp with Kp = C ESP CML_survirage Corrective Gain.

The goal is to correct an error in yaw rate that reflects the difference between the trajectory desired by the driver and the actual trajectory of the vehicle. This results in the following formula: E (t) = psip_ref (t) û YawRate_Sens (t) with: swc-): the error in yaw rate, psip ref (t): the reference yaw rate , 15 YawRate sense (t): the measured yaw rate.

To ensure the continuity of the yaw moment setpoint signal, it is necessary to subtract, from the current value of the error error (t), calculated using the subtractor 22, the value of the detection threshold of a speed difference. of yaw determining the start of an oversteer correction action C ESP CML threshold ON oversteer. This is ensured by a subtractor 91. Thus, when the flag signal Turn turns to 1 (that is to say when the error becomes greater than the threshold C ESP Seuil threshold CML ON oversteer), the ESP system decides to apply to the vehicle a yaw moment, the yaw moment having an initial value of zero. When the flag signal on a turn is in the high state, an output Regulator output obtained by the product of the signals driving a multiplier 92 is output from the logic gate 95.

Thus, the value of the yaw moment necessary to correct an oversteer situation is calculated as follows:

Command Mfx (t) = Kp x (error (r) - error (t ,,)) with: error (tl): the value of the error at the instant when the logic signal 20 Flag on activation turn CML goes to 1.

A fourth block 25 Calculation_Effort_de_Freinage_Total makes it possible to calculate a total braking force reference from the reference of moment of yaw mentioned above. It includes for this purpose the 25 entries and exits detailed in the table below. It allows the development of the output signal from the input signal. Input Signal output Mfx command: signal FxT signal: yaw setpoint signal at total brake force moment set point to apply applied to the motor vehicle. Expressed for example in Nm. To the vehicle. Expressed for example in N.

Adjustment parameter Channel E Route of the vehicle An embodiment of the fourth block 25 has multiplication operators making it possible to develop the output signal according to the relationship: FxT = Command Mfx x 2 Channel _E A sixth block 23 says Choose Wheel allows select the wheel or brakes to obtain a corrective lace moment. It includes the entries and exits detailed in the table below. It allows the elaboration of the output signals from the input signals. Inputs Signal outputs Brake wheel 11: logical signal determining whether the wheel should be braked. If braking wheel 11 = 1 then the ESP system brakes the wheel 11. If braking wheel 11 = 0 then the ESP system does not brake the wheel 11. signal flag on turn: signal logic signal Brake wheel 12: signal detection of a oversteer situation. logic determining if the wheel If flag on turn = 1 then the vehicle must be braked. If braking wheel 12 = 1 then the signal YawRate Sens: measured yaw rate signal of the vehicle. Expressed for example in rad / s.

If flag on turn = 0 then the vehicle does ESP system brakes the wheel 12. does not survive. If braking wheel 12 = 0 then the ESP system does not brake the wheel 12. signal Flag under activation CML turn: signal Brake wheel 21: logical signal signal for detection of a logical situation determining whether the understeer wheel requiring correction must be curbed. trajectory by applying a moment If braking wheel 21 = 1 then the yaw. ESP system brakes the wheel 21. If braking wheel 21 = 0 then the ESP system does not brake the wheel 21. signal Brake wheel 22: logic signal determining whether the wheel should be braked. If braking wheel 22 = 1 then the ESP system brakes the wheel 22. If braking wheel 22 = 0 then the ESP system does not brake the wheel 22. To create the yaw moment evoked previously to correct the trajectory of the vehicle, the mode d embodiment of the invention comprises a braking method for braking the wheels outside the turn.

However, saturation of the rear axle is the cause of the oversteer: it is therefore not recommended to brake the rear wheel. It is therefore held to brake the front wheel outside the turn. To know which of the two front wheels must be braked, it is possible to use the sign of the yaw rate.

A seventh block 26 called Compute_Effort_de_Rreinage_à_la_Roue allows to calculate the set of braking torque to be applied to each wheel of the vehicle. It includes the entries and exits detailed in the table below. It allows the elaboration of the output signals from the input signals. Inputs FxT signal outputs: signal reference signal T BRK CML ij Req: signal to total braking force to apply four components representing the vehicle. For example, each expresses a torque set point N. braking a wheel of the motor vehicle. These setpoint pairs are, for example, expressed in Nm. Brake wheel 11 signal: logical signal determining whether the wheel must be braked. If braking wheel 11 = 1 then the ESP system brakes the wheel 11. Î If braking wheel 11 = 0 then the ESP system does not brake the wheel 11. signal Brake wheel 12: logical signal determining whether the wheel should be braked. If braking wheel 12 = 1 then the ESP system brakes the wheel 12. If braking wheel 12 = 0 then the ESP system does not brake the wheel 12. signal Brake wheel 21: logical signal determining whether the wheel should be braked. then the Si braking wheel 21 = 1 ESP system brakes the wheel 21. If braking wheel 21 = 0 then the ESP system does not brake the wheel 21. signal Brake wheel 22: logic signal determining whether the wheel should be braked. 1 then the Si Brake wheel 22 = ESP system brakes the wheel 22. the If braking wheel 22 = 0 then ESP system does not brake the wheel 22.- Parameters Wheel Radius Wheel Radius For each wheel ij, simply multiply l total braking force to be applied to the vehicle by the signal value Brake wheel ij. A vector is thus obtained comprising the forces to be applied to each of the wheels of the vehicle. It is then sufficient to multiply this vector by the radius of the wheel (wheel radius parameter) in order to obtain the signal T BRK CML_ij Req comprising the braking torque setpoint signals of each of the wheels. Finally, the first oversteer control module 1 thus makes it possible to detect an oversteer situation and according to the proposed embodiment, it comprises a CML block which implements the calculation of braking torques T BRK ESP CML ij Req with the value is that of the signal T BRK CML ij Req explained above.

In addition, the ESP system can advantageously also implement a path correction method in the case of a situation of understeer, which has been mentioned above.

The system of the invention further comprises a second ABS module 2, whose main function is to detect a wheel lock situation and calculate for each wheel a braking torque setpoint (less than or equal to the torque setpoint). entry) which allows to unlock the wheel.

Figure 13 illustrates the behavior of the ABS 2 according to the preferred embodiment of the invention. The curve 110 represents the speed of a wheel, the curve 111 the reference speed, that is to say that of the motor vehicle, the curves 112 and 113 respectively two sliding thresholds defined in more detail later.

In a first zone, the speed of rotation of the wheel drops below the value of the first threshold and the anti-lock function becomes active. This state is named debut_lock. The braking regulation is in closed loop. The braking torque begins to be reduced to limit the slippage of the wheel.

In a second zone, despite the action of closed-loop control, the speed of rotation of the wheel continues to decrease and becomes lower than the second threshold. The braking torque therefore logically continues to be decreased. The regulation remains closed loop. This state is called blocking. After a certain time (depending on the level of adherence and the vehicle speed), the wheel is again driven in rotation and the speed of rotation of the wheel increases.

In a third zone, when the speed of rotation of the wheel becomes greater than the value of the second threshold, the wheel is in the resumption of adhesion phase, and thus the braking torque can, again, be increased. The braking system switches to open loop mode. Thus, the braking torque is re-increased, according to a ramp. This state is named recovery_adherence.

Finally, in a last zone, the speed of rotation of the wheel becomes greater than the first threshold and the wheel is no longer considered to be blocked; the braking torque continues to be increased (always with a ramp) to reach the braking torque desired by the driver or to reduce the sliding of the wheel around the value that maximizes the braking force.

The main block 100 of this module works with in particular the inputs and outputs defined in the following table (this list is not exhaustive). Inputs Outputs Signal W WH 11_Sens: Signal Speed T BRK ABS 11_Sp the wheel 11 in radish. Final signal torque request from a sensor. braking from ABS to wheel 11 in Nm. Signal W WH 12 Direction: Signal Speed T BRK ABS 12 Sp Wheel 12 in rad / s. Final signal torque request from a sensor. braking from the ABS to the wheel 12 in Nm. Signal W WH 21_Sens: Speed of the wheel 21 in radish.

Signal from a sensor. Signal W WH 22 Direction: Speed of the wheel 22 in radish. Signal from a sensor. Signal V VH X East: Longitudinal vehicle speed in m / s (reference speed). Signal Flag on Turn: Flag that detects an oversteer situation. If flag on turn = 1 then the vehicle survives 0 then If flag on turn = vehicle does not survive T signal BRK ESP CML ij Req Brake torque request from the CML regulation of the ESP to the wheel ij in Nm. The basic principle of operation of the ABS module is: to compare the Omega speed of each wheel, for example measured by a sensor placed on the wheel, expressed in radish, at the vehicle speed V VH x East, if a wheel locks, to decrease the braking torque applied on this wheel, - if the wheel is no longer locked, to increase the braking torque, without exceeding the torque requested by the driver. According to this preferred embodiment of the invention, the ABS braking system determines an intensity of the braking action applied to the wheels which is driven according to two different modes, in the most appropriate manner: in a first mode closed loop, the braking torque is reduced by using a regulation with a feedback loop acting on the setpoint value, using a PI (Proportional Integral) type corrector; in a second mode of open loop, that is to say without feedback loop correcting the setpoint, the braking torque is re-increased after unlocking the wheel, in a ramping pace.

The ABS 2 comprises a block 101 which in particular elaborates sliding detection thresholds, and uses the following inputs and outputs: The ABS generates the two threshold signals Threshold Detection Slip 1 and Threshold Detection Slip 2. The first signal of threshold corresponds to the trigger threshold (activation) of the anti-blocking function, for which the system detects a beginning of blocking. In such a case, the system enters the closed loop mode. The second threshold signal corresponds to the threshold from which the locked wheel is considered. From this threshold, the Inputs Outputs Threshold Detection Slip 1: Speed difference between the wheel and the vehicle in rad / s for which we consider that the wheel starts to hang Flag on turn: Flag which Threshold Detection Slip 2: Gap detects a situation of speed between the wheel and the vehicle in oversteer. rad / s for which we consider (threshold 1> If flag oversteer = 1 then threshold 2) that the wheel is blocked. vehicle survives If flag on turn = 0 then the vehicle does not survive V VH X East: Longitudinal vehicle speed in m / s (reference speed).

The system switches to open loop mode in a resumption of adhesion phase, as explained above.

According to the concept of the invention, in a state of oversteer of a motor vehicle, the ABS exhibits a different behavior than in another situation. Indeed, it is important to note that the locking of the wheels of the front axle reduces the oversteer of the motor vehicle. Thus, the management method of the motor vehicle in a state of oversteer exploits this effect to reduce oversteer, accepting up to a certain threshold the sliding of the front wheels of the motor vehicle in oversteer situation.

The embodiment of the invention implements the previous concept thanks to the ABS allowing greater slippage of the front wheels in oversteer situation. ABS, however, remains active to regulate the slippage of the front wheel or wheels, in order to maintain control of the front axle, which is the only one under control in oversteer conditions. This is implemented by modifying the two sliding threshold thresholds Seuil Detection Slip 1 and Threshold Detection Slip 2 mentioned above under oversteer.

Thus, the block 101 of the ABS 2 implements the method of calculating the following thresholds: If flag on turn = 1, the vehicle survives and: Threshold Detection Slip 1 = Coeff Sx abs threshold * V VH x East / radius * Gain_Seuill_ESP with Gain_Seuill_ESP <1 ET Threshold Detection Slip 2 = CoeffSx abs threshold2 * V VH x East / 30 .rayon * Gain_Shoot2_ESP with Gain_Shoot2_ESP <1 10 If flag on turn = 0, the vehicle does not survive and: Threshold Detection Slip 1 radius AND Detection threshold Glide 2 radius

The preceding equations are based on the parameters defined in the following table: Parameters Radius of the wheel Coeff_Sx_abs_seuill Rate 1 of slip to the wheel between 0 and 1, these are adjustment parameters of the strategy of the ABS. Coeff Sx_abs_seuil2 Wheel slip rate 2 between 0 and 1, these are the setting parameters of the ABS strategy. Gain Threshold1 ESP Gain allowing to modify the value of the threshold 1 in the case of an oversteer. Gain Threshold2 ESP Gain allowing to modify the value of the threshold 2 in the case of an oversteer. FIG. 11 represents an embodiment of this block 101.

The ABS 2 further comprises another block 102 which calculates the slope with which the wheel speed is re-increased in open-loop mode, upon resumption of adhesion. According to the embodiment of the invention, the CoeffSx abs threshold * V VH x East / CoeffSx abs threshold2 * V VH x East / dynamic recovery of the wheel is different in a state of oversteer of the motor vehicle.

The evolution of the intensity of the braking action is particular in the open loop mode. Preferably, it evolves temporally substantially increasing in two segments, a first segment having a steep slope and a second segment having a low slope. However, in the case of a vehicle in an oversteer state, it is advantageous to favor a stronger sliding dynamics of the front wheels, and in such a state, the ABS will always choose a ramp with a steep slope. Block 102 uses the following inputs and outputs: Flag on Turn: Flag that detects an oversteer situation. If flag on turn = 1 then the vehicle survives If flag on turn = 0 then the Inputs Outputs ABS Slope Open Loop: Slope that will follow the increase of the braking torque during the open loop mode. Chg Slope: If Chg_Pente = 1, the increase in the braking torque follows a steep slope. If Chg Slope = 0, the increase of the braking torque is done following a slight slope. low slope retained: low vehicle value slope does not survive Thus, this block 102 implements the method including the following step: If Chg_pente = 1 and flag oversteer = 0 Then ABS slope Open Loop = Slope Low restraint, Otherwise Slope ABS Open Loop = strong open loop slope

Where the signal Chg slope changes from value 1 to value 0 at the precise moment when the integrator output reaches the value of the threshold of change of slope Threshold t Chgt slope, from which the system normally passes from the steep slope to the weak slope.

FIG. 12 represents an embodiment of this block 102.

The concept of the invention has been implemented in the particular case of an ABS system operating with certain characteristics. However, this ABS system could be of another nature, however allowing greater slippage of at least one front wheel in case of oversteer, compared to another situation such as a turn with a normal trajectory or a straight line. In addition, this concept of permitting the sliding of one or two wheel (s) before by the ABS has been implemented in a manner combined with the principle of braking the wheel outside the bend, in order to improve the catching up oversteer. However, this concept could be considered separately.

The results of a test carried out with a vehicle equipped with a combined ESP-ABS system according to the embodiment of the invention are described below with reference to FIG. 14. FIG. 14 shows the detection of a oversteer situation 114, during which the signal flag_sur_virage goes from 0 to 1. During the period of

35 oversteer, the front outer wheel at the turn is braked by the first module, as shown by the evolution of the signal T BRK ESP CML ij Req. The ABS slips the outer front wheel and then regains its control, as shown by the evolution of the signal W WH 12 Sens. These landslides cause a small decrease in the longitudinal force (thus a little less yaw moment) but a large decrease in the lateral force undergone by the wheel, which will create an additional moment of yaw which makes it possible to correct the oversteer. . At the same time, the slip of the inner front wheel is noted, observing the signal W WH 11_Sens. Thus, the fact of sliding the wheel 12 causes the slippage of the other driving wheel 11. This behavior makes it possible to slide the front axle and thus to reduce the oversteer.

Finally, the invention has the following advantages: • do not solicit the rear axle which is saturated, • slide the nose gear (which marks the vehicle in the bend), • do not have to calculate a distribution of the yaw moment between the front axle and the rear axle, • check the slippage of the front wheel (s) so as not to saturate the only front axle that is stable, • allow greater slippage so that creating a moment of yaw sufficient to correct an oversteer situation, this yaw moment being finally created according to the embodiment chosen by the combination of the following three effects: o the increase of the longitudinal force, o the degradation of the Lateral effort, o The spinning of the front wheel inside the turn.

The invention also has the following advantages: - A closed-loop control structure that is simple and robust to the uncertainties of the system. The use of proportional-type correctors that use little computing resources and are well controlled. It also applies to electrical technology (electric braking, electric vehicle) than the current hydraulic technology of braking systems.

Claims (12)

1. A method for correcting the trajectory of a motor vehicle comprising a front axle and a rear axle, and an ABS anti-lock braking system module (2) implementing a braking method for detecting and preventing the blockage. and sliding of a wheel, characterized in that the ABS module (2) allows a greater slippage of at least one front wheel of the motor vehicle in a turning situation in which the motor vehicle survives compared to another situation in which the vehicle does not survive. 2. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that the ABS module (2) determines the sliding of a wheel when the difference between its speed (Omega) and the speed of the vehicle ( V VH x East) exceeds a certain threshold (Threshold Detection Slip 1) and in that it comprises a step of calculating a different threshold in case of oversteering of the vehicle to allow a greater slip of at least one front wheel in case of oversteer. 3. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that the ABS module (2) implements a braking method according to a first threshold (Threshold Detection Slip 1) which corresponds at a start phase of blocking of a wheel and a second threshold (Threshold Detection Slip 2) which corresponds to a blocking phase of a wheel and in that it comprises a step of modifying these two thresholds by oversteer case, the two thresholds being thus defined according to the following equations: -In case of no oversteer, 37 38 Threshold Detection Slip 1 Coeff_Sx_abs_seuill * V VH x East / radius AND Threshold Detection Slip 2 Coeff Sx abs threshold2 * V VH x East / radius And in case of oversteer, Threshold Detection Slip _l = Coeff_Sx_abs_slevel V VH_x_Est / radius * Gain_Seuill_ESP with Gain_Seuill_ESP <1 AND Threshold Detection Slip 2 = Coeff Sx abs threshold2 * V VH_x_Est l radius * Gain_Seuil2_ESP with Gain_Seuil2_ESP <1 where Coeff_Sx_abs_seuill and Coeff Sx_abs_seuil2 represent two slip rates between 0 and 1, V VH_x_Est represents the longitudinal speed of the motor vehicle, radius represents the radius of the wheel, and Gain_Seuill_ESP and Gain_Seuil2_ESP represent two parameters. 4. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that the braking process implemented by the ABS module (2) comprises the implementation of a greater braking intensity when a recovery of adhesion of a front wheel after a locking / unlocking phase of the front wheel in a situation of oversteer than in another situation. 5. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that the braking process of a motor vehicle comprises a braking mode in which a set value of intensity of the braking action. in the adhesion recovery phase evolves at least substantially linearly with time, firstly according to a first slope (steep open-loop slope) whose value is at least substantially constant, then according to a second slope (low slope retained) whose value is at least substantially constant, the value of the first slope being greater than the value of the second slope, and in that in a situation of oversteer of the motor vehicle, this instruction of intensity of the braking action always changes according to the upper slope in the adhesion recovery phase of a front wheel. 6. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that in a turning situation in which the motor vehicle survives, it comprises a brake control step of the wheels of the vehicle in which one controls a greater braking torque on the wheel of the front axle which is external to the turn so as to create a moment of yaw on the motor vehicle. 7. A method for correcting the trajectory of a motor vehicle according to the preceding claim, characterized in that the step of controlling the braking of the wheels of the vehicle comprises controlling a braking torque on the wheel of the front axle. which is outside the turn only. 8. A method for correcting the trajectory of a motor vehicle according to claim 6 or 7, characterized in that the value of the braking torque on the wheel of the front axle which is outside the bend is developed through a proportional corrector (91, 92). 9. A method for correcting the trajectory of a motor vehicle according to one of claims 6 to 8, characterized in that it allows the sliding of the front outer wheel at the turn which induces a slip of the inner front wheel to turn when the motor vehicle survives. 10. Data storage medium readable by a computer on which is recorded a computer program comprising software means for implementing the steps of the method for correcting the trajectory of a motor vehicle according to one of the claims. preceding. 11. System for correcting the trajectory of a motor vehicle, characterized in that it comprises hardware and / or software means for implementing the method of correcting the trajectory of a motor vehicle according to one of the claims. 1 to 9. Motor vehicle comprising a system for correcting the trajectory according to the preceding claim.