FR2940218A3 - Trajectory correction system operating method for motor vehicle, involves controlling high braking torque on wheels of front and rear axles of motor vehicle so as to create yawing moment on motor vehicle to permit braking control of wheels - Google Patents

Abstract

The method involves controlling high braking torque on wheels of front and rear axles of a motor vehicle (1) so as to create a yawing moment on the motor vehicle to permit braking control of the wheels in a steering situation in which the motor vehicle is under-steered, where the braking torque is developed by utilizing a proportional corrector. The yawing moment is created proportional to a difference between a differential amount of theoretical yawing speed and measured yawing speed of the vehicle, and a yawing speed error threshold beyond which the brake control is implemented. Independent claims are also included for the following: (1) a data recording medium having a set of instructions for executing a process of operating a trajectory correction system of a motor vehicle (2) a trajectory correction system 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 automatic correction of the understeer of a motor vehicle relative to the desired path of the driver in a turn.

Indeed, when a motor vehicle enters a bend at a longitudinal speed too high given the physical limits imposed by the adhesion between the tires and the ground in the bend, it becomes impossible to respect the curvature of the road and the motor vehicle begins to understeer.

This behavior can also occur if the driver accelerates in a turn.

In the understeer phenomenon, the vehicle deviates from the trajectory desired by the driver, the nose gear being deported outward of the turn.

It is then necessary to detect such a situation of understeer and to act automatically on the motor vehicle so that it returns to the path desired by the driver.

Application FR 2 776 786 discloses a method of detecting a situation of understeer in which a difference in behavior of a motor vehicle is calculated from the angle applied by the driver to the steering wheel, from the longitudinal velocity of the vehicle and the transverse acceleration of the vehicle.

The aim of the invention is to provide a method for operating a trajectory correction system making it possible to remedy the problems mentioned above and to improve the MS \ REN123FR.dpt correction systems known from the prior art. In particular, the invention provides a method of operating a course 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 to vehicles using an electrically controlled braking system.

According to the invention, the method governs the operation of a system for correcting the trajectory of a motor vehicle comprising a front axle and a rear axle. It is characterized in that, in a cornering situation in which the motor vehicle understeers, it comprises a step of braking control of the wheels of the vehicle in which a greater braking torque is controlled on the wheel of the axle. rear which is inside the turn 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 rear axle wheel that is inside the turn only. The value of the braking torque on the rear axle wheel that is inside the bend can be calculated using a proportional corrector. The braking control step may be designed to cause a yaw moment proportional to the difference between: the difference between a theoretical yaw rate of the vehicle determined by a steering wheel steering angle and a measured yaw rate of the vehicle and a yaw rate error threshold beyond which the vehicle wheel braking control step is performed. MSIREN123EN.dpt20 The step of controlling the braking of the wheels of the motor vehicle can be implemented only if the difference between a theoretical yaw rate of the vehicle determined by a steering angle of the steering wheels and a yaw rate of the measured vehicle exceeds a threshold.

According to the invention, the data recording medium is readable by a computer on which is recorded a computer program comprising software means for implementing the steps of the operating method defined above. According to the invention, the system for correcting the trajectory of a motor vehicle is characterized in that it comprises hardware and / or software means for implementing the operating method defined above. The system may comprise a proportional type corrector determining a braking torque setpoint to be provided by a braking system of the motor vehicle.

According to the invention, the motor vehicle comprises a correction system defined above.

The accompanying drawings represent, by way of example, an embodiment of a trajectory correction system according to the invention. Figure 1 is a diagram of an embodiment of a motor vehicle equipped with a trajectory correction system according to the invention.

Fig. 2 is a diagram of a control module for applying a yaw moment to the motor vehicle. Figure 3 is a detailed diagram of an embodiment of the control module for applying a yaw moment to the motor vehicle.

Figure 4 is a diagram of a yaw moment setpoint generating means to be applied.

FIG. 5 is a diagram of a means of calculating a total braking force to be applied to the motor vehicle.

Figure 6 is a diagram of a means for selecting a wheel of the motor vehicle.

Figure 7 is a diagram of a means for calculating the braking forces to be applied to each of the wheels of the motor vehicle.

Figure 8 is a graph showing the effects of the invention in a situation of understeer of a motor vehicle.

In the following, for the signal names, the suffix: 11 designates the left front wheel, 12 designates the right front wheel, 21 designates the left rear wheel, 22 designates the right rear wheel, ij thus designates one of the four wheels of the vehicle. 25 The following abbreviations are also used: ESP: Electronic Stability Program control or correction system, ABS: Anti-Blocking System (ABS), 30 ASR: Anti-skid system (for Anti Skid) Regulation), BFD: brake distribution system (for Brake Force Distribution), MS \ REN 123 EN.dpt 15 20 PI corrector: integral proportional corrector, CML: yaw moment control system, CSV: subtrack control system -turn.

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

The motor vehicle 1 represented in FIG. 1 comprises a system 5 for correction of trajectory acting on a braking system 2 and / or on a system 3 for controlling the engine of the vehicle. The trajectory correction system comprises different interacting modules and makes it possible to develop setpoint signals intended for braking and / or brake control systems. The trajectory correction system comprises hardware and software means for implementing the operating 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.

A first module 7, referred to as a Reference Model, comprises a simplified model of the motor vehicle which makes it possible, starting from the steering angle applied by the driver and the longitudinal speed of the vehicle, to calculate a reference yaw rate d (P_ref) / dt, that is, the yaw rate that the vehicle should have for the measured steering angle and longitudinal velocity.

A second estimator module 8 includes several estimators for determining reference longitudinal velocity, actual moment, and load information on the wheels. Measurement signals are supplied by a set of sensors 4. These sensors provide, for example, signals for measuring the vehicle wheel speeds, a signal for measuring the yaw rate of the vehicle, a signal transverse acceleration of the vehicle and a longitudinal acceleration signal of the vehicle.

A third module 14 called Detectors receives the reference yaw rate and the yaw rate measured and allows the use of these data to detect a situation of understeer or oversteer.

A fourth module 9 called CML brake control defines a moment of lace to be applied to the vehicle by application of braking forces. It develops 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 10. These setpoint signals are transmitted to a sixth module 11 said arbitration.

A fifth module 13 called Motor Control and Brake CSV elaborates deceleration instructions signals of the vehicle. These signals comprise a motor torque setpoint signal and a braking setpoint signal enabling a deceleration which alone or in combination can decelerate the motor vehicle. These signals are transmitted to a sixth module 11 called arbitration.

The sixth module 11 performs the arbitration between the motor torque and braking torque setpoint signals from the different modules and the conductor 6. Finally, a single motor torque setpoint signal is transmitted to the engine control system 3. and braking torque setpoint signals are transmitted to the braking system 2.

MSIREN 123GB.dpt In an understeer, the vehicle deviates from the driver's intended course of travel: the vehicle is turning less than it should. The driver can not register in the turn even by significantly increasing the steering angle of the steering wheels via the steering.

The purpose of the ESP system is to allow the vehicle to turn while correcting the vehicle's trajectory. Since the main cause of understeer is excessive longitudinal speed, the ESP system can act on means to decelerate the vehicle. In particular, the system can reduce the engine torque delivered by the engine and / or activate the braking system.

However, depending on the driving situation (especially in case of poor grip ...), these actions may prove insufficient. This is why the method according to the invention proposes to complete these actions with a strategy of controlling the application of a yaw moment on the motor vehicle obtained by braking a judiciously chosen wheel of the vehicle. This action allows you to enter the vehicle again in the turn.

As we will see later, a Flag signal under CML activation turns to choose when the understeer adjustment must be applied to this correction in yaw moment.

The fourth module previously mentioned is described below with reference to FIG. 2. It presents four inputs and one output detailed in the table below. It allows the development of the output signal from the input signals. Inputs Outputs psip signal ref: yaw rate signal signal T BRK CML Req MS \ REN123EN.dpt of vehicle reference. Expressed by four component signal example in rad / s (d (4) _ref) / dt). The speed, each representing a reference yaw, represents the trajectory of the braking torque desired by the driver. This signal is from a vehicle wheel provided by the first module. automobile. 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 signal flag signal on turn: logic 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. This signal is provided by the third module. Flag signal under CML activation: logical signal for detecting a situation of understeer requiring correction of trajectory by application of a yaw moment. This signal is provided by the third module. In an embodiment shown in Figure 3, the fourth module comprises different blocks.

A first block 21 called Elaboration_du_Signal_de_Command allows to develop a yaw moment control signal to be applied to the MS \ REN123FR.dpt 5 motor vehicle to correct a situation of understeer. It includes the inputs and outputs detailed in the table below. It allows the development of the output signal from the input signals. Inputs Outputs psip signal ref: signal signal signal Mfx command: reference signal of the vehicle. set of yaw moment to Expressed for example in rad / s (apply to the motor vehicle (4'_ref) ldt). The yaw rate of Expressed for example in Nm. Reference reflects the trajectory desired by the driver. This signal is provided by the first module. YawRate Sens signal: The measured yaw rate signal of the vehicle. Expressed for example in radish. This signal is provided by a sensor. Adjustment parameters C ESP Gain Corrector CMLsubtrike Gain a proportional corrector of the module 9 C ESP CML threshold Understeer Threshold for detecting a situation of understeer requiring regulation by applying a yaw moment on the vehicle. One possible embodiment of this block 21 is described hereinafter with reference to FIG. 4. MS \ REN 123 FR. The first block 21 preferably uses a proportional type corrector 214. It can be modeled by the following equation in the Laplace domain: C (p) = Kp The goal is to correct an error in yaw rate that translates the difference between the trajectory desired by the driver and the actual trajectory of the vehicle. This results in the following formula: &, ct) = psip_ref (t) where YawRate_Sens (t) with: Eo): the error in yaw rate, psip ref (t): the reference yaw rate, YawRate sense (t): the measured yaw rate.

To ensure the continuity of the yaw moment setpoint signal, it is necessary to subtract, at the current value of the error E, i, (t), calculated using a subtractor 211, the value of the detection threshold of a situation of understeer requiring the application of a yaw moment C ESP Seuil CML ON understeer. This is ensured by a subtractor 213. Thus, when the logic signal Flag under activation turn CML goes to 1 (that is to say when the error becomes greater than the threshold C_ESP_Seuil_CML ON_sub-turn), the ESP system decides to apply to the vehicle a yaw moment, the yaw moment having an initial value of zero.

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

Command Mfx (t) = Kp x (Ewct) - Eq, (t,)) with:

MS \ REN 123FR.dpt Ew (ä>: the value of the error at the moment when the Fiag logic signal under CML activation turns to 1.

In the embodiment shown in FIG. 3, the fourth module 5 comprises a second block 22.

The second block 22 Calculation_Effort_de_Freinage_Total makes it possible to calculate a total braking effort setpoint from the yaw moment setpoint mentioned previously. It includes for this purpose the 10 inputs and outputs detailed in the table below. It allows the development of the output signal from the input signal. Input Signal output Command_Mfx: Signal signal FxT: Total brake effort setpoint signal to be applied to the vehicle. Expressed for example in N. yaw moment set apply to the Expressed by motor vehicle. Example Nm. This signal is provided by the first block 21. Adjustment parameter Channel_E Route of the vehicle 15 An embodiment of the second block 22 is shown in FIG. 5. It presents two multiplication operators 221 and 222 making it possible to elaborate the output signal according to the relation: FxT = Command Mfx x 2 Channel_E In the embodiment represented in FIG. 3, the fourth module comprises a third block 23. MS \ REN 123 EN.dpt The third block 23 called Choice_roue allows to select the wheel or brakes to obtain a corrective lace moment. 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 YawRate Direction: signal signal signal Brake wheel 11: measured yaw rate of the vehicle. Expressed logic determining if the wheel for example in radish. This signal is provided must be braked. by a sensor. 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 flag on turn = 0 then the vehicle does ESP system brakes wheel 12. does not survive. If braking wheel 12 = 0 then this signal is provided by the third ESP system does not brake the module. 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 braked. trajectory by applying a moment If braking wheel 21 = 1 then the yaw. This signal is provided by the ESP system brakes the wheel 21. third module. If braking wheel 21 = 0 then the MS \ REN 123 FR.dpt system ESP does not brake the wheel 21. signal Brake wheel 22: logic signal determining whether the wheel should be braked. If brake wheel 22 = 1 then ESP system brakes wheel 22. If brake wheel 22 = 0 then ESP system does not brake wheel 22. Parameters Positive hysteresis threshold Positive constant close to zero Threshold negative hysteresis Negative constant close to zero For create the yaw moment mentioned above to correct the trajectory of the vehicle, it is necessary to brake the wheels inside the turn. However, saturation of the front axle is the cause of understeer: it is therefore not recommended to brake the front wheel. It is therefore held to brake the rear wheel inside the turn. To know which of the two rear wheels must be braked, it is possible to use the sign of the yaw rate.

A possible embodiment of this block 23 is described below with reference to FIG.

A psip positive logic signal is defined by a hysteresis operator 231. This hysteresis makes it possible to take into account the errors that can be had on the YawRate_Sens signal. If the YawRate Sens signal exceeds the positive hysteresis Threshold threshold, the yaw rate is positive and the positive psip logic signal goes to 1. If the YawRate Direction signal crosses the MSIREN 123 FR.dth threshold Threshold negative hysteresis down , the yaw rate is negative and the psip_positif logical signal goes to O.

Thus, if positive psip = 1 and flag under activation CML turn = 1 then braking the wheel 21 and the logic signal braking wheel 21 is at 1.

If psip_positif = 0 and flag under turn activation CML = 1 then one brakes the wheel 22 and the flag braking wheel 22 passes to 1.

This logic is implemented thanks to the means shown in Figure 6 where the door 235 is a door and NOT and the doors 236 and 237 are AND gates.

In the embodiment shown in FIG. 3, the fourth module 15 comprises a fourth block 24.

The fourth block 24 Calculation_Effort__Freinage_à_la_Roue allows to calculate the set of braking torque to be applied to each wheel of the vehicle. It includes for this purpose the inputs and outputs detailed in the table below. It allows the elaboration of the output signals from the input signals. Inputs Outputs signal FxT: signal reference signal T BRK CML j 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. MS \ REN 123 EN.dpt signal Brake wheel 11: logic signal determining whether the wheel must be braked. then the If Brake wheel 11 = 1 ESP system brakes the wheel 11. If Brake 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. 1 then the Si Brake wheel 12 = ESP system brakes the wheel 12. the If braking wheel 12 = 0 then ESP system does not brake the wheel 12. signal Brake wheel 21: logical signal determining if the wheel needs to be braked. 1 then the Si Braking wheel 21 = ESP system brakes the wheel 21. the If braking wheel 21 = 0 then ESP system does not brake the wheel 21. signal Brake wheel 22: logical signal determining whether the wheel should be braked. 1 then the Si Brake wheel 22 = ESP system brakes the wheel 22. If brake wheel 22 = 0 then the MS \ REN 123 EN.dpt ESP system does not brake the wheel 22. Parameters Wheel Radius Wheel Radius For each wheel ij it is sufficient to multiply the total braking force to be applied to the vehicle by the value of the signal 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 (/ Req including the braking torque setpoint signals of each of the wheels.

One possible embodiment of this fourth block 24 is shown in FIG. 7 where the means 241, 242, 243, 244 and 246 are multiplication operators and the means 245 is a concatenation means.

In an alternative embodiment, not shown, in a situation of understeer of the vehicle, it is possible to combine a slowing action of the vehicle and an action of applying a moment of yaw. In the case where the slowing action of the vehicle is obtained by braking the wheels, the rear inner wheel cornering is more braked than the other wheels of the vehicle so as to create on it a moment of yaw.

The results of a test carried out with a vehicle equipped with an ESP system according to the invention are described below with reference to FIG. 8. The vehicle included an electric braking system. The top graph is about understeer and its detection. Note that from the moment t = 2.2s and t = 3.8s, there is a gap MSIREN 123 FR. significant dpt25 between Psip ref and YawRate Sens signals. This is due to a situation of understeer which is detected from the instant t = 2.25s (and up to t = 3.7s). Detection is done on the yaw rate error.

The lower graph refers to the action of applying a yaw moment. From a moment t = 2.4s, an application activation signal of a yaw moment is implemented. The ESP system thus brakes progressively the wheel 21 by sending a reference signal T BRK CML 21_Req. This braking is maintained until time t = 3.6s. When the understeer situation ends, braking is progressively withdrawn (thanks to the proportional corrector). Preferably, the application of the braking torque is done continuously (even if the braking torque setpoint occurs while the vehicle is under-steering).

The invention has the following advantages: The corrector used is simple: It is a proportional. Preferably, to apply the calculated yaw moment, only the inner rear wheel is braked. This strategy has the advantage of: • not loading the front axle which is saturated, • sliding the rear axle (which marks the vehicle in the bend), • not having to calculate a distribution of the yaw moment between the lane. front axle and rear axle.

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 resource and are well controlled. MS \ REN 123 EN.dpt 5 It applies equally to electric technology (electric braking, electric vehicles) as well as to the current hydraulic technology of braking systems. MSIREN123FR.dpt

Claims (9)

Claims: 1 Operating method of a system (5) for correcting the trajectory of a motor vehicle (1) comprising a front axle and a rear axle, characterized in that, in a cornering situation in which the motor vehicle it includes a braking control step of the vehicle wheels in which a greater braking torque is controlled on the rear axle wheel which is inside the turn so as to create a yaw moment on the vehicle. automobile. Operating method according to claim 1, characterized in that the braking control step of the vehicle wheels comprises controlling a braking torque on the rear axle wheel which is internal to the turn only. 3. Operating method according to claim 1 or 2, characterized in that the value of the braking torque on the wheel of the rear axle which is inside the turn is produced by means of a proportional corrector (214). 4. Operating method according to one of the preceding claims, characterized in that the braking control step is intended to cause a yaw moment proportional to the difference between: the difference between a theoretical yaw rate of the vehicle determined by a steering angle of the steering wheels and a measured yaw rate of the vehicle, and a yaw rate error threshold (C ESP CML threshold ON understeer) beyond which the control step of braking of the vehicle wheels. MS \ REN 123 EN.dpt 19 5. Operating method according to one of the preceding claims, characterized in that it implements the brake control step of the motor vehicle wheels only if the difference between a theoretical yaw rate of the vehicle determined by an angle steering wheel speed and measured vehicle yaw rate exceeds a threshold (C ESPS CML threshold ON understeer). 6. Data storage medium readable by a computer on which is recorded a computer program comprising software means for implementing the steps of the operating method according to one of the preceding claims. 7. System (5) for correcting the trajectory of a motor vehicle (1), characterized in that it comprises material means (7, 8, 9, 10, 11, 12, 13, 14) and / or software for implementing the operating method according to one of claims 1 to 6: 8. Correction system (5) according to claim 7, characterized in that it comprises a corrector (214) of the proportional type determining a braking torque setpoint to be provided by a braking system (2) of the motor vehicle. 9. Motor vehicle comprising a correction system according to claim 7 or 8. MS \ REN 123 FR. filing