KR20070090025A - Motor vehicle rear wheel braking control in breaking situation with asymmetric grip - Google Patents

Abstract

The invention concerns a method for controlling braking of the rear wheels of a motor vehicle having at least four steering wheels (103 to 106) which consists in detecting the presence of a braking situation with asymmetric grip, determining a braking pressure setpoint in the form of a maximal braking pressure difference between the right and left rear wheel based on the value of the vehicle instantaneous longitudinal speed and the turn angle of the front wheels, transmitting, in case of braking situation with asymmetric grip, said braking setpoint value to the braking actuators of said rear wheels so as to correct the vehicle instability.

Description

MOTOR VEHICLE REAR WHEEL BRAKING CONTROL IN BREAKING SITUATION WITH ASYMMETRIC GRIP}

The present invention relates to controlling braking of a rear wheel of a vehicle having four or more steerable wheels in the event of an asymmetrical grip braking situation.

An asymmetric grip braking situation is a situation where a difference in coefficient of friction occurs between a right tire and a left tire of a vehicle, which causes the vehicle to deviate from its path and / or to pivot about a vertical axis.

US Patent Application No. 2002/0198646 describes a method for compensating for disturbance by applying control in the form of a steering angle setting value for a vehicle, the steering angle setting value being determined according to the grip coefficient and constant for a predetermined coefficient. Do. However, these settings do not adapt well to the various situations that may occur.

French patent application 03/14931 describes a steering control method and apparatus, which method depends on the state model of the vehicle formed during modeling the disturbance of the yaw rate of the vehicle. In this method, with the aid of a state observer based on the state model, it is possible to determine the value of the disturbance and then to determine the set value of the rear wheel steering angle to allow asymptotic removal of this disturbance. Therefore, a setting value depending on the longitudinal instantaneous speed of the vehicle and the disturbance is obtained, and as a result, the disturbance cannot be detected and the path of the vehicle can be stabilized. This method is operated by closed loop control to determine the new setpoint as a function of the previous setpoint that is introduced back to the state observer. This closed loop operation causes a slight delay in the response of the control system, which responds only relatively slowly to sudden changes in the situation, such as a rapid change in speed or a fast change in front steering angle.

Therefore, according to the prior art described in the above two patent documents, only the rear wheel steering angle can be controlled intensively to correct the instability of the vehicle, whereby the stability of the vehicle having four steerable wheels can be improved.

However, the Applicant found that during the study, in the event of asymmetrical grip braking of the wheels, the instability of the vehicle can be compensated for by treating the braking parameters governing the operation of the steerable rear wheel brake actuators in a special manner. .

Accordingly, the present invention is a braking control method and a braking control device for a rear wheel of a vehicle having four or more steerable wheels, which are intended to be used in an asymmetrical grip braking situation, in particular a braking which enables to increase the path stability of the vehicle. It is an object to provide a control method and a braking control device.

According to the present invention, the above-mentioned problem is solved by a braking control method for the rear wheel of a vehicle having four or more steerable wheels.

Detecting the presence of an asymmetrical grip braking situation,

A setpoint of the braking pressure which makes it possible to correct the instability of the vehicle in the form of a maximum difference in braking pressure between the right rear wheel and the left rear wheel as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle. To determine, and

-In the event of an asymmetrical grip braking situation, transmitting the setpoint of the braking pressure to the braking actuator of the rear wheel.

Furthermore, according to the invention, the above-mentioned problem is solved by a braking control device for the rear wheel of a vehicle having four or more steerable wheels, which device is suitable for implementing the method according to the invention,

Means for detecting the presence of an asymmetrical grip braking situation,

A setpoint of the braking pressure which makes it possible to correct the instability of the vehicle in the form of a maximum difference in braking pressure between the right rear wheel and the left rear wheel as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle. Means for determining,

Means for transmitting the setpoint of the braking pressure to the braking actuator of the rear wheel in the event of an asymmetrical grip braking situation.

Thus, the method and apparatus according to the invention allow braking control to be adapted for driving situations characterized by the front wheel steering angle, the longitudinal instantaneous speed of the vehicle and the presence of an asymmetrical grip situation.

According to an advantageous feature of the method according to the invention, the setpoint of the braking pressure remains constant for the duration of the asymmetric grip braking situation and corresponds to the setpoint determined when such a braking situation occurs.

According to another advantageous feature of the method according to the invention, the method further comprises limiting the set value of the braking pressure between a minimum and a maximum allowable value for the braking pressure differential of the vehicle.

The previously defined method may be advantageous in parallel with the step aimed at steering control of the steerable wheels of the vehicle, resulting in a more effective correction of vehicle instability in the event of asymmetric grip braking. This parallelism may be advantageously performed in accordance with one of three variants described below.

According to a first variant embodiment, the method according to the invention,

Determining a setting value of the rear wheel steering angle as a function of the setting value of the braking pressure, based on the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle,

In the event of an asymmetric grip braking situation, transmitting the set value of the rear wheel steering angle to the steering actuator of the rear wheel.

According to a second variant embodiment, the method according to the invention,

Determining, based on the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle, a first intermediate setpoint of the rear wheel steering angle as a function of the setpoint of the braking pressure,

Estimating the disturbance of the yaw rate of the vehicle as a function of the previous setpoint of the rear wheel steering angle,

Determining a second intermediate setpoint of rear wheel steering angle as a function of said disturbance;

Determining the current set point of the rear wheel steering angle by correcting the first intermediate set point of the rear wheel steering angle to the second intermediate set point of the rear wheel steering angle;

In the event of an asymmetric grip braking situation, transmitting said current set value of rear wheel steering angle to said steering wheel steering actuator, and

In the absence of an asymmetrical grip braking situation, transmitting the first intermediate setpoint of the rear wheel steering angle to the steering actuator of the rear wheel.

According to a third variant embodiment, the method according to the invention,

Estimating the disturbance of the yaw rate of the vehicle as a function of the previous setpoint of the rear wheel steering angle,

Determining a current setpoint of rear wheel steering angle as a function of said disturbance,

In the event of an asymmetrical grip braking situation, transmitting the current set value of the rear wheel steering angle to the steering actuator of the rear wheel.

According to a feature of the method according to the first and second embodiments, the disturbance of the yaw rate of the vehicle includes a state of the vehicle including the longitudinal instantaneous speed of the vehicle, the yaw rate of the vehicle, the front wheel steering angle and the rear wheel steering angle. Determined by the model, in this state model, the disturbance of the step change type acts on the yaw rate of the vehicle.

Preferably, the set value of the rear wheel steering angle determined based on the disturbance is determined to asymptotically remove the disturbance at the yaw rate.

According to another feature of the method according to the first and second embodiments, the set value of the rear wheel steering angle determined on the basis of the disturbance is proportional to the disturbance of the yaw rate and is the second intermediate of the rear wheel steering angle. The proportional coefficient between the set value and the disturbance is as follows.

Where M is the total mass of the vehicle,

L ₁ is the distance from the center of gravity to the front axle,

L ₂ is the distance from the center of gravity to the rear axle,

D ₁ is the stiffness of the forward drift,

D ₂ is the stiffness of the rear drift, and

V is the longitudinal instantaneous speed of the vehicle.

According to a feature of an apparatus for implementing the method according to the first embodiment, the apparatus comprises:

Means for determining, based on the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle, a set value of the rear wheel steering angle as a function of the set value of the braking pressure,

Means for transmitting the set value of the rear wheel steering angle to the steering actuator of the rear wheel in the event of an asymmetrical grip braking situation.

Preferably, the device is

A first two-dimensional table for determining a set value of the braking pressure as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle;

A second two-dimensional table for determining a set value of the rear wheel steering angle as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle;

The first two-dimensional table and the second two-dimensional table, wherein the pair consisting of the value of the instantaneous instantaneous speed of the vehicle and the value of the front wheel steering angle, the greater the set value of the braking pressure rear wheel steering The set value of the angle is determined to be large.

According to another feature, the apparatus further comprises means for maintaining the setpoint of the braking pressure constant for the duration of the asymmetrical grip braking situation.

According to another feature, the apparatus further comprises means for limiting the set value of the braking pressure between a minimum and a maximum allowable value for the braking pressure differential of the vehicle.

According to another feature of the device, the means for transmitting the set value of the braking pressure to the braking actuator of the rear wheel comprises an antilock braking module.

Finally, the object of the present invention is a vehicle comprising a braking control device in which the control method as described above is performed.

The invention is now described in more detail with reference to the embodiments taken by way of non-limiting example and illustrated in the accompanying drawings.

1 is a schematic diagram of a vehicle equipped with a control system according to an aspect of the present invention.

2 is a functional diagram of a system in accordance with aspects of the present invention.

3A, 3B, 3C and 3D are functional diagrams of a first portion of the system of FIG.

4 is a functional diagram of a second portion of the system of FIG.

1 is a schematic diagram of a vehicle equipped with a control system according to an aspect of the present invention. The vehicle comprises a chassis 100, two steerable front wheels 103 and 104 and two steerable rear wheels 105 and 106, which are connected to the chassis 100 by a suspension mechanism not shown. have. In addition, the vehicle uses the rack 108 disposed between the front wheels 103 and 104 and the front wheel 103 using the rack 108 at the will of the vehicle driver in accordance with a mechanical or electric command from a steering wheel (not shown). And a rack actuator 109 capable of setting the direction of 104.

The steering assistance control system is embodied in the form of a control unit 101, for example a sensor 113 of the steering angle of the front wheels 103 and 104 arranged on the rack actuator 109, and a rotation sensor for one of the front wheels, for example. Sensor 115 of the instantaneous speed of the vehicle, and sensor 114 of the rotational speed of the vehicle about a vertical axis passing through the yaw rate of the vehicle, ie the center of gravity of the vehicle.

According to a variant embodiment of the invention, the invention also comprises means for determining the braking pressure of the rear wheels 105 and 106, for example in the form of sensors 116 and 117. In addition, the braking pressure of the front wheel can be estimated based on other measured physical quantities, for example by a model of the vehicle.

The control system also provides sensors 118 and 119 for steering angles (angle of the wheel with respect to the longitudinal axis of the vehicle) of the rear wheels 105 and 106, and steering actuators for enabling the direction of the rear wheels 105 and 106 to be set. And 120 and 121. However, a single sensor 118 and a single actuator 120 may be sufficient to detect the steering angle and orient the rear wheels 105 and 106. The position and speed sensors may be of the optical or magnetic type, for example of the hall-effect type, and cooperate with a coder fixed to the moving part but the sensor does not rotate. By averaging the instantaneous speeds determined on the basis of sensors installed near the front wheels or the rear wheels, the longitudinal instantaneous speed V of the vehicle can be obtained. In this case, it is contemplated to provide one sensor 115 per front wheel or rear wheel. Alternatively, the control unit 101 receives a value of the vehicle's longitudinal instantaneous speed V coming from another control module, such as a wheel lock prevention module ABS, which other control module uses its own speed value. You need to decide for that.

The control unit 101 receives measurements from the random access memory, read only memory, the central processing unit, and the sensors 113 to 119 and sends commands to the actuators 120 and 121 in particular ( May be implemented in the form of a microprocessor with an input / output interface that allows for;

As shown in FIG. 2, the control unit 101 includes an input module 202, a state observer 203, a disturbance removal module 204, and a direct determination module (also known as a " feedforward " module). 205, adder 208, time delay module 225, antilock braking module 207 (better known as ABS, abbreviation for "antilock system"), and ABS module 207 To a control module 206. The various modules may be implemented in one and the same control unit or may be implemented as control units which are separate but in communication with each other.

The input module 202 delivers to these modules the values of the physical quantities required by the modules 203, 204, 205 and 206, respectively. The manner and dependencies of the modules 203, 204, 205 and 206 are described in more detail below. The direct determination module 205 determines the first setpoint 218 of the rear wheel steering angle, and the disturbance removal module 204 determines the second setpoint 219 of the rear wheel steering angle. These two setpoints 218 and 219 are summed by an adder 208. The output 220 of the adder 208 is introduced back to the input module 202 through the time delay module 225. The output 220 corresponds to a set value of the rear wheel steering angle transmitted in the form of a control amount for the steering actuators 120, 121 of the rear wheels.

The input module 202 receives from the sensors 113 to 119 various measurements, ie the longitudinal instantaneous speed 212 of the vehicle, the yaw rate 213 and the front wheel steering angle 214. The input module 202 also receives an output 215 from the time delay module 225, which corresponds to the previous setting of the rear wheel steering angle. In addition, the input module 202 receives the detection flag FL 216 of the asymmetric grip braking situation from the ABS module 207. This flag can usually take three values, 0, +1, -1, respectively, meaning asymmetric grip braking, no asymmetric grip braking to the right, or asymmetric grip braking to the left. The antilock braking module, ie the ABS module 207, is provided with means for generating information on the presence of an asymmetric grip braking situation based on various measured quantities (yaw rate, wheel steering angle, etc.) in a known manner. These means are not described in detail herein. According to a particular embodiment, the control unit 101 also receives the measured values 210, 211 of the braking pressure of the right front wheel and the left front wheel via the input module 202.

The direct determination module 205 uses the first setpoint 218 of the rear wheel steering angle based on the longitudinal instantaneous speed 212, the yaw rate 213 and the value of the front wheel steering angle 214, or in a variant embodiment. According to this, it is determined based on the braking pressure 210 of the right front wheel and the braking pressure 211 of the left front wheel. This first setpoint is determined based on simulations performed on the vehicle in an asymmetrical grip braking situation and corresponds to a first approximation of the ideal setpoint. Various exemplary embodiments of the direct determination module 205 are provided herein and are shown in FIGS. 3A-3D.

According to the first exemplary embodiment of the direct decision module 205 shown in FIG. 3A, the direct decision module 205 may,

A reference value generating element 310 for generating a reference value (eg 3.5 rad / s) of the steering angle,

Three weighting elements 302, 303, 304 which are connected to the output of the reference value generating element 310 and respectively apply a gain of 0, +1 or -1 to the output of the reference value generating element 310. Wow,

A selection switch 305 having three inputs for receiving the outputs of the three gains 302, 303, 304 as inputs and whose output is controlled by the value of the flag FL 216,

A two-dimensional table 301 having as input the value of the longitudinal instantaneous velocity 212 and the value of the front wheel steering angle 214, and

A multiplier 306 which multiplies the signals 311 and 312 generated from the selector switch 305 and the table 301 respectively and outputs a first setpoint 218 of the rear wheel steering angle.

The direct determination module 205 enables the generation of a first setpoint 218 proportional to the steering angle reference value generated at the reference value generation element 310, wherein the proportional coefficient of the first setpoint is the longitudinal instantaneous velocity. And the value of the front wheel steering angle. The two-dimensional table is the result of a simulation aimed at providing, for example, a proportional coefficient in consideration of the maximum possible value of the steering angle to each pair of longitudinal instantaneous speeds and values of front wheel steering angles in an empirical and experimental manner. The selector switch 305 makes it possible to generate a zero reference value in the absence of asymmetrical grip braking, and in the case of asymmetrical grip braking, depending on whether the asymmetry in the grip is on the right or left side, i.e. the flag FL 216 According to the value of), it is possible to assign an appropriate symbol to the reference value obtained in the two-dimensional table 301. In this exemplary embodiment, the reference value is constant and preferably corresponds to the maximum value that can be tolerated by the set value of the rear wheel steering angle. In the first embodiment of the direct determination module 205 a constant setpoint is produced, which constant is determined according to the longitudinal instantaneous speed and the front wheel steering angle.

The second exemplary embodiment of the direct determination module 205 shown in FIG. 3B determines the reference value as a function of the braking pressure values P _D 210 and P _G 211 for the right front wheel and the left front wheel according to the following relationship. It differs from that shown in FIG. 3A in that the reference value generating element 310 is replaced with the module 410.

Where P _D and P _G are the braking pressures of the right front wheel and the left front wheel,

μ is the coefficient of friction of the brake pads,

φ is the surface of the brake piston,

R _e is the effective radius, ie the average distance from the center to the area where the brake pads come into contact with the disc, and

e is the gauge of the vehicle, that is, the distance between the right wheel and the left wheel.

Specifically, in the case of a disc brake, the braking torque C _brake is given by the following relationship.

Therefore, yaw torque caused by right / left asymmetric grip braking is estimated by the following equation.

If the braking pressure is expressed in bar, it is approximately as follows.

Further, the rear wheel steering angle applied to correct _yaw torque C _yaw is as follows.

Thus, ultimately, the relationship 1 between the rear wheel steering angle and the braking pressure is obtained. Thus, in the second embodiment of the direct determination module 205, a set value determined according to the difference between the braking pressures applied to the front wheels is generated.

A third exemplary embodiment of the direct determination module 205 shown in FIG. 3C is a module 510 for determining a reference value by performing temporal filtering between two constant values generated by elements 511 and 512, respectively. Is different from that shown in FIG. 3A in that it replaces the reference value generating element 310. The two constant values are preferably the minimum initial value (usually 0 rad / s) and the final maximum value (eg 3.5 rad / s) of the set value of the rear wheel steering angle. Thus, in the third embodiment of this direct decision module 205, a setpoint value is derived between the two constant values, and the derivation speed can be adjusted by the temporal filter 510.

A fourth exemplary embodiment of the direct determination module 205 shown in FIG. 3D is to determine a reference value or a maximum set value as a function of the braking pressure values P _D 210 and P _G 211 for the right front wheel and the left front wheel. It differs from that shown in FIG. 3C in that the element 512 is replaced by the same module 612 as the module 410 previously described in FIG. 3B. Therefore, in the fourth embodiment of this direct determination module 205, the set value is derived between a constant initial value and a final maximum value, and the final maximum value is determined according to the braking pressure difference between the front wheels, and likewise converges to the final value. The speed can be adjusted by the temporal filter 510.

The state observer 203 shown in FIG. 2 makes it possible to estimate the information that is not measured and necessary for control, specifically disturbance acting on the vehicle. The state observer 203 is based on a state model of a vehicle with two steerable wheels, for example by assuming that a temporal disturbance d of step change type can act directly on the yaw rate of the vehicle over a defined time interval. Can be configured. Variables modeling the behavior of the steering actuator 120 may be added to the model. The state equation associated with the state model, including disturbance of the yaw rate, is, for example:

The formula uses the following symbols,

X: state vector in (n, 1) dimension

: (n, 1) 차원의 상태 벡터의 시간 도함수

: Temporal derivative of state vector of dimension (n, 1)

X ₁ : First input vector in (m, 1) dimension

X ₂ : Second input vector in (m, 1) dimension

Y: output vector in (p, 1) dimension

A: state matrix of dimensions (n, n)

B: first input matrix of dimension (n, m)

C: second input matrix of dimension (n, m)

D: output matrix with dimensions (p, n)

Here, p, n and m are integers of 1 or more.

In the exemplary embodiment given herein, n = 4, p = m = 1 and the vectors and matrices are defined accordingly.

Several constants used in the model are each represented as

M (kg): the total mass of the vehicle,

I _z (Nm): moment of inertia of the vehicle with respect to the vertical axis through the center of gravity of the vehicle,

L ₁ (m): distance from the center of gravity to the front axle,

L ₂ (m): distance from the center of gravity to the rear axle,

D ₁ (N / rad): stiffness of the front drift,

D ₂ (N / rad): rigidity of the rear drift,

τ: response time of the actuator 120,

The various variables used in the model are each represented as follows.

V (m / s): longitudinal instantaneous velocity of the vehicle (212),

(rad/s) : 요 레이트(213),

(rad / s): yaw rate (213),

d (rad / s): disturbance of yaw rate (217),

α _c1 (rad): measured value, the value of the current front wheel steering angle (214),

α _c2 (rad): the value 220 of the current rear wheel steering angle, i.e., the set value applied as the output 220 to the actuator 120 of the control unit 101,

α _p2 (rad): value 215 of the previous rear wheel steering angle output by the time delay module 225,

β (rad): The angle of drift, that is, the angle between the vehicle's instantaneous velocity vector and the vehicle's longitudinal axis.

Based on this state model, we apply the typical theory of linear observers. The state observer 203 based on the state model may be configured in the following manner.

ego,

Where K (V) is a matrix of dimensions (4, 1) and constitutes an adjustment parameter of the state observer that depends on the longitudinal instantaneous velocity (V) of the vehicle, where the symbol "^" It is an estimated value. The parameter K (V) represents the confidence in the state model. For example, when K (V) = 0, the confidence is maximum and the state model is secured as a state observer.

The coefficients of this matrix K (V) are calculated by numerical approximation procedures known in the field of automatic control, for example by applying a solution of the so-called Ricatti differential equation.

In addition, the differential equation for the state observer 203 can be recorded as follows.

의 함수로서 외란

를 결정할 수 있게 한다. 이에 따라

에 대하여 다음과 같은 식이 얻어진다.This state observer makes it possible to determine the relationship between the state of the vehicle determined on the basis of the measured or estimated value and the entire set of disturbances acting on the vehicle. More specifically, the state observer applies the Laplace transform to equation (2), where X, X ₁ = α _c2 , X ₂ = α _c1 and

Disturbance as a function of

To determine. Accordingly

The following equation is obtained.

Where s is a Laplace variable, where H ₁ , H ₂ and H ₃ are transformation functions defined as follows.

And here

.

.

Indeed, the differential equation (2) or (3) is discretized and the solution given by the relationship (4) is approximated by well-known numerical solutions, such as the Euler method.

The disturbance removal module 204 determines a set value of the rear wheel steering angle to allow asymptotic removal of the disturbance. By applying this setting, disturbances regarding the physical quantity under consideration, in this case disturbances about yaw rate, cannot be observed, which is also evident through the stabilization of the vehicle's path and the improved road grounding of the vehicle.

에 대한

의 편도함수를 제로로 하여

가 요 레이트

에 미치는 영향 을 제거하는 조건을 전술한 행렬 방정식에 부가하면, 상기 설정값은

의 함수로서 표현된다. 결국, 안정화된 상태에서는 외란의 값이 어떠하더라도, 구체적으로는 외란의 값이 제로이거나 제로가 아니더라도, 요 레이트는 동일한 것으로 판단된다. 제2 후륜 조향 각도의 설정값에 대해, 외란

에 대한 비례성의 관계를 다음과 같은 형태로 부가하면,

For

With the partial derivative of zero

Flexible rate

Adding a condition to remove the effect on the matrix equation described above,

Is expressed as a function of As a result, even in the stabilized state, even if the disturbance value is specifically, even if the disturbance value is zero or non-zero, the yaw rate is determined to be the same. Disturbance with respect to setting value of the second rear wheel steering angle

If we add the relation of proportional to, in the form

The following equation is obtained.

에 비례하고, 비례 계수(G)는 차량의 종방향 순간 속도(V)에 좌우된다.Accordingly, the set value of the second rear wheel steering angle is disturbed estimated by the state observer 203.

In proportion to, the proportional factor G depends on the longitudinal instantaneous velocity V of the vehicle.

의 결정에 사용된 이전 설정값(α_p2)(215)을 입력으로서 갖는다.The adder 208 sums the set values ((α _{c2 _ ff} ) 218 and (α _{c2 _ rp} ) 219) generated by the direct determination module 205 and the disturbance removal module 204, respectively. The adder 208 generates as output 220 a value α _c2 220 representing the set value of the steering angle, which value will be transmitted to the steering actuator 120 and added to the rear wheel of the vehicle. The value α _c2 is also introduced via the time delay module 225 to the input module 202 which provides an input value to the state observer 203. Thus, the state observer 203 is disturbed

It has as input the previous set value α _p2 215 used for the determination of.

Only when the value of flag FL 216 indicates that the asymmetric grip braking situation is not present, adder 208 considers the output value of disturbance removal module 204. Or, in other words, the state observer 203 and / or the incremental disturbance removal module 204 generate a zero output in the absence of an asymmetrical grip braking situation, in which case it is generated directly by the determination module 205. Only the set value 219 is transmitted to the steering actuator 120.

Thus, the control unit 101 comprises on the one hand an open loop component (modules 202, 205) which makes it possible to determine the set value of the first rear wheel steering angle, together with the set value of the second rear wheel steering angle. And a closed loop component (modules 202, 203, 204, 205) that allows estimation. The first setpoint is the result of the simulation and represents the first approximate setpoint, while the second setpoint represents the correction applied to the first setpoint, which correction is based on the exact state model of the vehicle and previously determined It is determined by considering the corrected set point. Thus, the system remains very accurate due to the corrections applied by the state observer and disturbance rejection module, and also changes in the situation due to the presence of an open loop component that determines the first setpoint that is approximate but immediately applied without a response delay. Very quickly to changes in longitudinal instantaneous speed or front wheel steering angle).

According to an essential feature of the invention, the control module 206 generates a setpoint 230 corresponding to the maximum allowable difference in braking pressure between the right rear wheel and the left rear wheel in the event of an asymmetrical grip braking situation. This setpoint 230 depends on the longitudinal instantaneous speed 212 of the vehicle and the value 214 of the front wheel steering angle of the vehicle. In this example (FIG. 4), the control module 206 includes a two-dimensional table 701 that receives values 212 and 214 as inputs and a first selection switch 703 having two inputs, wherein 2 The first of the three inputs is the output of the two-dimensional table 701, and the remaining inputs are the outputs of the constant generating element 702, in which the constant takes a zero value. The selection switch 703 is controlled by the value of the flag FL 216, and if the flag is not zero, the output of the two-dimensional table 701 is selected, and if the flag is zero the output of the constant generating element 702 is Is selected.

The control module 206 also includes a second select switch 705 having two inputs, the output of the second select switch being looped back to the first input via the time delay module 704. The second input of the second selection switch is the output of the first selection switch 703. The second selection switch 705 is also controlled by the flag FL 216, and when the flag FL 216 takes a value indicating that an asymmetrical grip braking condition exists, the function of the second selection switch is to determine the output value. To fix it. Therefore, the output value of the second selection switch is fixed to the value determined by the two-dimensional table 701 at the moment of the asymmetrical grip braking situation, and remains fixed even if the vehicle speed or front wheel steering angle changes during the braking step. . In the opposite situation, the output of the first selection switch 703 is selected.

The control module 206 preferably includes a limiter element 706 at the output of the second selector switch 705 which indicates that the output value of the control module 206 lies between the minimum and maximum allowable values. Function to ensure. The output value of the control module may be a value given according to a relative scale (for example, a percentage between 0 and 100%) when the setpoint 230 is used as a proportional factor with respect to the maximum value of the pressure difference setpoint, or the absolute pressure It may be a value given depending on the scale. In addition, the control module 206 is activated only when the value of the flag FL 216 indicates that the asymmetric grip braking situation is output, and outputs a zero value when there is no asymmetric grip braking situation.

In the exemplary embodiment described above, the vehicle is equipped with an anti-lock braking (ABS) module 207, and the pressure difference setting value is transmitted to the ABS module, thereby organizing the braking control command of the actuator. Thus, in this case the ABS module 207 acts on the braking actuator to ensure that the set value of the braking pressure is applied to the rear wheel of the vehicle.

The module 206 for determining the setpoint of the braking pressure can be used equally well with the direct determination module 205, which produces only the uncorrected steering setpoint, or is obtained from modeling and does not need to be calibrated. In a loop system that generates a combination of the two components, a combination of modules 203 and 204, or a combination of modules 203, 204 and 205 may be used, in which case the modules 203 and 204 are delivered by the module 205. It serves to correct the value. Depending on which combination is selected, the steering setpoint transmitted to the steering actuator may be the first intermediate setpoint 218 (module 205 alone), the second intermediate setpoint 219 (module 203 and 204 combination). Or a corrected setpoint 220 (combination of modules 203, 204 and 205).

In the case of an asymmetric grip braking situation, the larger the allowable braking pressure difference may be, the larger the setting value 220 of the steering angle is. Therefore, the two-dimensional table 701 of the control module 206 and the two-dimensional table 301 of the direct determination module 205. ), And when the two modules 205 and 206 are used simultaneously, one table must consider the other. Thus, the value 230 of the braking pressure differential is determined as a function of the first braking pressure setpoint 218 determined by the direct determination module 205. Thus, the simulation of determining the two-dimensional table described above should take into account the combination chosen between the embodiment of module 205 and the embodiment of module 206. This feature makes it possible to ensure better vehicle stability through the integrated control and simultaneous control of the two parameters described above, namely the braking pressure and the steering angle.

The present invention greatly improves the road foldability of the vehicle when used in conjunction with the rear wheel steering angle setting value and thus improves the riding comfort felt by the driver, and in driving situations (yaw rate, longitudinal speed, presence of asymmetrical grip braking conditions, etc.). Benefit from a well-adapted braking pressure setpoint.

Claims (17)

A braking control method for a rear wheel of a vehicle having four or more steerable wheels, Detecting the presence of an asymmetrical grip braking situation, A set value of the braking pressure 230 which makes it possible to correct the instability of the vehicle in the form of a maximum difference in braking pressure between the right rear wheel and the left rear wheel, the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle. Determining as a function of, and In the event of an asymmetrical grip braking situation, transmitting the setpoint of the braking pressure to the braking actuator of the rear wheel. Braking control method of the rear wheel comprising a. 2. The method of claim 1, wherein the set value of the braking pressure remains constant for the duration of the asymmetric grip braking situation and corresponds to a set value determined when such a braking condition occurs. 3. The method of claim 1 or 2, further comprising limiting the set value of the braking pressure to between a minimum and a maximum allowable value for the braking pressure differential of the vehicle. The method according to any one of claims 1 to 3, Determining a setpoint value 218 of the rear wheel steering angle as a function of the setpoint value of the braking pressure, based on the value 212 of the longitudinal instantaneous speed of the vehicle and the value 214 of the front wheel steering angle, In the event of an asymmetrical grip braking situation, transmitting the setpoint 218 of the rear wheel steering angle to the steering actuator 120 of the rear wheel. Braking control method of the rear wheel further comprising. The method according to any one of claims 1 to 3, Determining a first intermediate setpoint 218 of rear wheel steering angle as a function of the setpoint value of the braking pressure, based on the value 212 of the longitudinal instantaneous speed of the vehicle and the value 214 of the front wheel steering angle. Wow, Estimating the disturbance 217 of the vehicle's yaw rate 213 as a function of the previous setpoint 215 of the rear wheel steering angle, Determining a second intermediate setpoint 219 of rear wheel steering angle as a function of said disturbance, Determining the current setpoint 220 of the rear wheel steering angle by correcting the first intermediate setpoint 218 of the rear wheel steering angle to the second intermediate setpoint 219 of the rear wheel steering angle; In the event of an asymmetrical grip braking situation, transmitting the current setting value 220 of the rear wheel steering angle to the steering actuator 120 of the rear wheel, and In case no asymmetric grip braking situation exists, transmitting the first intermediate setpoint 218 of the rear wheel steering angle to the steering actuator 120 of the rear wheel. Braking control method of the rear wheel further comprising. The method according to any one of claims 1 to 3, Estimating the disturbance 217 of the yaw rate 213 of the vehicle as a function of the previous setpoint 215 of the rear wheel steering angle, Determining a current setpoint 219 of rear wheel steering angle as a function of said disturbance, and In the event of an asymmetrical grip braking situation, transmitting the current set point 219 of the rear wheel steering angle to the steering actuator 120 of the rear wheel. Braking control method of the rear wheel further comprising. The vehicle yaw rate disturbance 217 is determined by a state model of the vehicle including the longitudinal instantaneous speed of the vehicle, the yaw rate of the vehicle, the front wheel steering angle and the rear wheel steering angle. In this state model, the step change type disturbance acts on the yaw rate of the vehicle. 8. The method of claim 7, wherein said set value (219) of rear wheel steering angle determined on the basis of disturbance is determined to asymptotically remove disturbance at yaw rate. 9. The second intermediate setting of the rear wheel steering angle according to claim 5, wherein the set value 219 of the rear wheel steering angle determined on the basis of the disturbance is proportional to the disturbance of the yaw rate. The proportional coefficient between the value and the disturbance

(Where M is the total mass of the vehicle, L ₁ is the distance from the center of gravity to the front axle, L ₂ is the distance from the center of gravity to the rear axle, D ₁ is the stiffness of the front drift, D ₂ is the stiffness of the rear drift, And V is the longitudinal instantaneous velocity of the vehicle) Braking control method of the rear wheel, characterized in that. The braking control method for a rear wheel according to any one of claims 1 to 9, wherein the set value of the braking pressure is determined in consideration of a yaw rate of the vehicle. A braking control device for a rear wheel of a vehicle having four or more steerable wheels, the device being suitable for carrying out the method as claimed in any one of claims 1 to 10, Means for detecting the presence of an asymmetrical grip braking situation, A set value of the braking pressure 230 which makes it possible to correct the instability of the vehicle in the form of a maximum differential of the braking pressure between the right rear wheel and the left rear wheel; Means 206 for determining as a function of Means (207) for transmitting the setpoint of the braking pressure to the braking actuator of the rear wheel in the event of an asymmetrical grip braking situation Braking control device of the rear wheel comprising a. The method of claim 11, wherein the method of claim 4 is Means 205 for determining, based on the value 212 of the longitudinal instantaneous velocity of the vehicle and the value 214 of the front wheel steering angle, a set value 218 of the rear wheel steering angle as a function of the set value of the braking pressure. and, Means for transmitting the setpoint 218 of the rear wheel steering angle to the steering actuator 120 of the rear wheel in the event of an asymmetrical grip braking situation. Braking control device of the rear wheel further comprises. The method of claim 12, A first two-dimensional table 701 for determining the setpoint 230 of braking pressure as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle, A second two-dimensional table 301 for determining the setpoint 218 of the rear wheel steering angle as a function of the value of the longitudinal instantaneous speed of the vehicle and the value of the front wheel steering angle. Wherein the first two-dimensional table and the second two-dimensional table, the pair of values of the instantaneous instantaneous speed of the vehicle and the value of the front wheel steering angle, wherein the set value 230 of the braking pressure is And the larger the set value (218) of the rear wheel steering angle is, the larger the rear wheel braking control device is. 14. A method according to any one of claims 11 to 13, further comprising means (704, 705) for maintaining the setpoint of braking pressure (230) constant for the duration of an asymmetrical grip braking situation. Braking control device of rear wheel. 15. The apparatus according to any one of claims 11 to 14, further comprising means (706) for limiting the set value of the braking pressure between a minimum and a maximum allowable value for the braking pressure differential of the vehicle. Rear wheel brake control device. The rear wheel braking control device according to any one of claims 11 to 15, wherein the means for transmitting the set value of the braking pressure to the braking actuator of the rear wheel includes an antilock braking module. A vehicle comprising the rear wheel brake control device according to any one of claims 11 to 16.

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