BE1031156B1 - Method and assistance system for assisting the steering of a two-lane motor vehicle by braking interventions - Google Patents

Abstract

The present invention relates to a method for assisting the steering of a two-lane motor vehicle (1) having two front wheels (21, 22) and two rear wheels (33, 34), wherein a specification is provided with regard to a target yaw rate of the motor vehicle (1) to be achieved, taking into account a current actual yaw rate of the motor vehicle (1), a braking specification is determined for at least one of the wheels (21, 22, 33, 34) of the motor vehicle (1) in order to bring the actual yaw rate closer to the target yaw rate, and a braking intervention takes place in accordance with the determined braking specification. The invention further relates to a driver assistance system (5) for assisting the steering of a two-lane motor vehicle (1) with two front wheels (21, 22) and two rear wheels (33, 34), comprising a control unit (51) which is designed to control a brake (61, 62, 63, 64) assigned to a respective wheel (21, 22, 33, 34), wherein the driver assistance system (5) is designed to carry out an above method, and a steer-by-wire steering system (4) with such a driver assistance system.

Description

Procedure and assistance system for assisting steering of a two-lane

Motor vehicle due to braking interventions

The invention relates to a method for assisting steering of a two-lane

Motor vehicle having two front wheels and two rear wheels. Furthermore, the

Invention a steer-by-wire steering system and a driver assistance system to support

Steering of a two-track motor vehicle with two front wheels and two rear wheels, comprising a control unit which is designed to control a respective wheel associated with

to control the brake.

Steer-by-wire steering systems are described many times in the prior art. For example, DE 10 2018 114 988 A1 discloses a steer-by-wire steering system with a steering handle, a feedback actuator and a steering actuator, wherein a steering command can be specified via the steering handle, which can be converted by the steering actuator into a steering movement of steerable wheels of a motor vehicle. A challenge with steer-by-wire

Steering systems is to ensure that a motor vehicle can be controlled even if faults occur in the

To keep the steer-by-wire steering system controllable. DE 10 2020 100 719 A1 proposes that in the event of a fault in the front or rear axle steering of a motor vehicle with front and rear axle steering, the faulty steering should be switched off and a

Steering movement by means of an autonomous driving mode or a derived target movement. It is also known from DE 10 2019 217 588 A1 that after a

Vehicle collision as a result of which one or more wheels of a vehicle axle are no longer fully or even no longer steerable, steering is carried out using the functioning steering axle and a braking signal is transmitted to one of the vehicle wheels connected to this steering axle.

In addition, DE 10 2018 107 612 A1 discloses a motor vehicle with front and

Rear-wheel steering and torque vectoring on the rear axle, whereby an actual

Motor vehicle condition is compared with a target vehicle behavior of a motor vehicle.

Using rear-wheel steering and a rear-wheel drive to control the

The actual vehicle condition is brought closer to the target vehicle behavior. If the front axle steering and the front wheel drive fail, the

Rear-wheel steering and rear-wheel drive take over control of the vehicle.

Furthermore, WO 2017/001045 A1 discloses a motor vehicle with a

front axle steering system and a rear axle steering system. An autonomous

Driving an automatically controlled front axle steering system is provided. A

The failure detection device can detect a failure of the front axle steering system, with the vehicle then being steered by the rear axle steering system. In addition, if the front axle steering system fails, the front wheels are braked in such a way that the front axle steering system is centered.

In addition, EP 1 384 646 A1 discloses a method and a system in which a vehicle can be additionally steered by controlling the brakes assigned to the wheels of the motor vehicle, in particular in the event of a failure of the normal steering system.

Based on this, there is a further need to improve the steering capability of a

motor vehicle and, in particular in the case of a motor vehicle with a steer-by-wire steering system, to keep the motor vehicle controllable in the event of errors in or on the steering system, and thus to further reduce the risk of personal injury.

To solve this problem, a method according to claim 1 and a

Driver assistance system and a steer-by-wire steering system in accordance with the

Claims. Further advantageous embodiments of the invention are described in the dependent claims and the description and shown in the figures.

The proposed solution provides a method for assisted steering of a two-lane

motor vehicle having two front wheels and two rear wheels, wherein a specification is provided regarding a target yaw rate of the motor vehicle to be achieved, under

Taking into account a current actual yaw rate of the motor vehicle, a braking specification for at least one of the wheels of the motor vehicle to approximate the actual yaw rate to the target

The invention is based in particular on the idea of using a one-sided

Introducing a braking torque into a two-lane motor vehicle with two front and two rear wheels to generate a moment around the vertical axis, which is advantageously used to control the steering of the motor vehicle, in particular a functionally impaired steer-by-wire system.

steering system of a motor vehicle when changing direction and/or to control the motor vehicle with it alone. If a braking torque acts mainly on the front axle of a two-lane motor vehicle, this will affect the

Motor vehicle tends to understeer, while a stronger braking torque on the rear axle tends to oversteer. This property is advantageously used to optimize the steering behavior of the vehicle, especially in the event of at least a partial failure of a motor vehicle's steer-by-wire steering system. The actual yaw rate is advantageously measured. This can be done in particular by a measuring device of an existing ESP (ESP: Electronic Stability Program), or by an additional sensor unit. This is advantageously compared with other values, in particular the

steering angles, lateral accelerations and/or wheel speeds to provide a more accurate

Determination of the actual yaw rate.

According to an advantageous embodiment of the method, the specification regarding the target

Yaw rate is provided taking into account a steering command. The steering command can be given in particular by a driver via a steering handle or in an at least partially autonomous driving mode of the motor vehicle by a

Driver assistance system. Advantageously, a braking torque is introduced in such a way that the vehicle follows the steering commands better.

In particular, the target yaw rate is determined based on the target steering angles of the front and rear wheels. The target steering angles are determined in particular based on a recorded steering command, whereby in the case of a steering command using a steering wheel, the

Target steering angle can be calculated from steering wheel angle and steering wheel rotation speed, in particular taking into account the vehicle speed, the fixed

Dimensions related to the wheelbase and/or the self-steering gradient.

In particular, the target yaw rate can be determined according to the functional

Context can be determined:

Öf* U

Read where:

Wa = desired yaw rate;

V = vehicle speed; [ = wheelbase;

EG = self-steering gradient; and

Ô, = atan(tan(ô;) — tan(6,)), with

Ôf = target steering angle of the front wheels; and

Ô, = Target steering angle of the rear wheels.

The invention provides that the braking specification is determined based on a two-track model, wherein the two-track model in particular takes into account the stationary and unsteady lateral dynamics of the

The two-track model is advantageously used for its stationary

States are solved so that a desired yaw rate as input of the two-track model advantageously has a necessary to achieve the desired yaw rate

Braking torque difference as output.

According to the invention, the two-track model is given the specification regarding the target

Yaw rate is fed as an input variable and using the two-track model for an assumed stationary state of the vehicle as an output variable, a resulting braking torque difference between the wheels is determined, whereby the

The braking torque difference is advantageously used to determine the braking requirement. In particular, the braking torque difference between the left and right wheels is calculated.

According to a further advantageous embodiment, a scaling factor is applied to the determined

braking torque difference is applied, with the scaling factor being less than 1. This

The design is particularly intended to assist the steering, i.e. in particular when the steering of the motor vehicle is still at least partially functional.

Tests have shown that this scaling factor is preferably in a range between 0.05 and 0.2, depending on the maneuver, and more preferably in a range between 0.05 and 0.1. A further advantageous embodiment therefore provides that

Driving status information, in particular information that describes the current driving status of the

motor vehicle, in particular a vehicle speed, a current

Depending on the evaluation of the driving maneuver, the

The scaling factor is advantageously set to a value in a range from 0.05 to 0.2, in particular in a range from 0.05 to 0.1. Driving maneuvers in the limit range advantageously lead to a smaller value for the scaling factor, whereas a so-called "limp-aside" driving maneuver advantageously leads to a larger value for the

Scaling factor. Another advantage is that the scaling factor is particularly speed-dependent, whereby a high driving speed advantageously leads to a high scaling factor within the specified range and a low

Driving speed advantageously leads to a low scaling factor within the 5 specified range.

The method is further advantageous when a detected at least partial failure of a

Steering system of the motor vehicle, in particular in the case of a detected at least partial failure of a steer-by-wire steering system of the motor vehicle, wherein the scaling factor is advantageously set at a higher value the lower the

The targeted braking intervention can advantageously ensure that the motor vehicle follows a steering command better than would be the case with the steering effect that can still be provided by the steering system. In this respect, a method for assisted steering of a two-lane road is particularly

Motor vehicle having two front wheels and two rear wheels, wherein an at least partial failure of a steer-by-wire steering system is detected,

Taking into account a recorded steering specification, a specification regarding a target to be achieved

Target yaw rate of the motor vehicle is provided, taking into account a current actual yaw rate of the motor vehicle, a braking specification for at least one of the wheels of the

motor vehicle to approximate the actual yaw rate to the target yaw rate, and a

Braking intervention takes place according to the specific braking specification, whereby the determination of the

Braking is specified in particular based on a two-track model, in particular as described above.

In particular, it is intended that the braking specification is determined based on the

Two-track model a force difference AFx between the front axle and rear axle of the

motor vehicle, whereby, based on the determined force difference, a brake pressure is determined with which the motor vehicle is specifically braked. The

Determination of the brake pressure is advantageously carried out based on the determined

Force difference taking into account the wheel diameter of the vehicle's wheels and the so-called c, value, which describes a relationship between brake pressure and torque. The c, value is determined experimentally for a particular vehicle model by comparing the measured brake pressure and the braking torque that occurs.

According to an advantageous embodiment, the force difference AFx is determined as follows:

AF, = fu el + 4calel, mlv? + 2620 + ml, v* 2v where: 1 : yaw acceleration,

Ca: lateral tire stiffness, lt : distance from the front axle of the vehicle to the center of mass of the vehicle,

L, :distance from the rear axle of the motor vehicle to the centre of mass of the motor vehicle, m : vehicle mass, and v : local speed (vehicle speed).

An advantageous embodiment provides that the braking specification is calculated, wherein a target yaw moment to be achieved is advantageously determined from the target yaw rate, which is proportional to the target yaw rate, and wherein the target yaw moment is advantageously calculated with a

Value for a current driving speed of the motor vehicle. In particular, it is provided that a brake pressure is calculated by multiplying a desired yaw moment, which is proportional to the desired yaw rate, which is advantageously determined from a steering angle of a steering handle of the motor vehicle, by the vehicle speed. In particular, the determination of the brake pressure in this

Design based on the determination of the force difference AFx to

AF, =) xv +*C, where: 1 : yaw acceleration, v : local speed (vehicle speed), and

C : constant, in particular with C = [80 … 100], further in particular with C = 95.

As an advantageous embodiment, it is therefore provided that a brake pressure is determined for at least one specific wheel of the motor vehicle as a brake specification, in particular for the

Wheels of an axle of the motor vehicle. Advantageously, the brakes of the

motor vehicle with the specific brake pressure. Advantageously, the higher the driving speed of the motor vehicle, the higher the brake pressure determined.

According to a further particularly advantageous embodiment, the method is carried out in the event of a detected at least partial failure of a steering system of the motor vehicle, in particular in the event of a detected at least partial failure of a steer-by-wire system.

Such a partial failure of the steering system is, in particular in the case of all-wheel steering, a failure of the steerability of the front axle of the

Motor vehicle by means of the steering system by controlling the corresponding steering actuator.

In the event of such a partial failure of the steering system, assisted steering is advantageously carried out by means of a method designed according to the invention, in particular by providing a specification regarding a target yaw rate of the motor vehicle to be achieved, taking into account a current actual yaw rate of the motor vehicle.

Braking specification for at least one of the wheels of the vehicle to approximate the actual

yaw rate to the target yaw rate is determined, and a braking intervention according to the determined

Braking is given.

The solution proposed to solve the above-mentioned problem is

Driver assistance system for assisting the steering of a two-lane motor vehicle with two front wheels and two rear wheels, comprising a control unit which is designed to control a brake assigned to a respective wheel, and is designed to carry out a method according to the invention. In particular, the

The driver assistance system is assigned a computing unit that is designed to

To determine the braking specification, in particular the brake pressure as braking specification, whereby the necessary fixed values, in particular the distance between the front axle and the

Rear axle to the center of gravity, stored in the computing unit and the variable

Values, in particular the vehicle speed, from sensors of the motor vehicle of the

According to the invention, the driver assistance system is designed to provide a specification regarding a target yaw rate of the

motor vehicle, taking into account a current actual yaw rate of the

motor vehicle a braking specification for at least one of the wheels of the motor vehicle for

To determine the approximation of the actual yaw rate to the target yaw rate and to carry out a braking intervention according to the determined braking specification. Advantageously, the steering system is supported by the driver assistance system in implementing the steering specification.

Advantageously, the steer-by-wire steering system proposed by the invention comprises a driver assistance system designed according to the invention, in particular an assistance system that is designed to carry out a method designed according to the invention, in particular when a functional impairment of the steer-by-wire steering system has been detected.

Further advantageous details, features and design details of the invention are described in

The following is explained in more detail in connection with the embodiments shown in the figures (Fig.: Figure).

Fig.1 shows a schematic representation of an embodiment of a motor vehicle with a steer-by-wire steering system designed according to the invention;

Fig. 2 in connection with an embodiment of a method according to the invention for determining a brake pressure starting from a stationary equilibrium state, diagram representations for a brake pressure, a

Steering angle and a target lateral acceleration; and

Fig. 3 in connection with a further embodiment of a method according to the invention for determining a brake pressure, diagram representations for a brake pressure, a steering angle and a target lateral acceleration.

With reference to Fig. 1, an embodiment of a two-track motor vehicle 1 with a front left wheel 21, a front right wheel 22, a rear left wheel 33, a rear right wheel 34 and a steer-by-wire steering system 4 is explained in more detail, wherein the steer-by-wire steering system 4 comprises a driver assistance system 5 which is used for

Execution of a method for assisting steering of the motor vehicle 1, in particular in the event that the steer-by-wire steering system 4 is faulty, and a

Steering input not or at least not solely by controlling a

Coupling rod acting on the steerable wheels of the motor vehicle 1 can be implemented by the steering actuator of the steer-by-wire steering system 4.

To assist steering using the driver assistance system 5, the

Driver assistance system 5 a control unit 51 which is designed to control a brake 61, 62, 63, 64 assigned to a respective wheel 21, 22, 33, 34 of the motor vehicle in order to cause a desired yaw of the motor vehicle 1 in accordance with a steering command. For this purpose, in this embodiment, a steering command introduced by a driver via a steering handle is detected by means of the steer-by-wire steering system 4 and a target yaw rate is determined by the driver assistance system 5 taking into account the detected

Steering input provided.

Using sensors 7 connected to the driver assistance system 5 and for

Recording various driving status information, a current actual

Yaw rate of the motor vehicle 1 is determined and, taking into account the determined actual yaw rate, a braking specification for the brakes 61, 62, 63, 64 is determined such that by a

Braking intervention, i.e. a targeted actuation of the brakes 61, 62 assigned to the front wheels 21, 22 or the brakes 63, 64 assigned to the rear wheels 33, 34, in particular, according to the specific braking specification, the actual yaw rate is brought closer to the target yaw rate. In this embodiment, the driver assistance system 5 determines

Brake specification one brake pressure each for the wheels 21, 22, 33, 34

Brakes 61, 62, 63, 64. In this embodiment, it is provided that, depending on the situation, either the left brakes 61, 63 are actuated with the specific brake pressure and the right brakes 62, 64 with a brake pressure of zero or the right brakes 62, 64 with the specific brake pressure and the left brakes 61, 63 with a brake pressure of zero. The idea behind this is that a force difference with respect to a longitudinal force F should be generated in order to be able to achieve the desired target yaw rate.

According to a first variant of the embodiment, it is provided that the determination of the braking specification, i.e. in this embodiment the braking pressure of the brakes 61, 62, 63, 64 of the motor vehicle 1, is determined based on a two-track model. In Fig. 2, for example, for three different steering angles SA1, SA2, SAS, which are shown in the diagram Fig. 2 (b) as angles in degrees over the vehicle speed in km/h (km: kilometer, h: hour), corresponding target yaw rates TLA1, TLA2, TLA3, which are shown in Fig. 2 (c) as acceleration in m/s? (m: meter, s: second) over the

Vehicle speed in km/h, and certain brake pressures BP1, BP2, BP3, which are shown in diagram

Fig. 2 (a) as pressure in bar above the vehicle speed in km/h. A steering command corresponding to the steering angle SA1 therefore results in a target

Yaw rate TLA1 and a brake pressure BP1. In this design variant, a lower brake pressure is generated at a lower steering angle. It can also be seen that in this design variant the brake pressure decreases at higher driving speeds.

The braking pressures result from the force difference AFx of the longitudinal forces E, based on the two-track model, where the force difference is determined with , Zal + A4call mlv? + 2041 + ml, v?

ME zij* _——_-- 2v taking into account that

Ôf > 0,

Ör > 0, _ Wij _ af — Öf B D 01.2: l a, = 6, -B + zo,

F, = Ca *@, (y + B)mv — (For + F,2) + (Fy3 + Fy4). db = AF + (Fy, + F2) * lj — (Fy3 + Fya) +, neglecting the lateral load displacement F,, = Fy2 and Fyz = F4, b b

AF, = Fa * + — Fro * + (with F1 or F2 equal to 0), and solved for the stationary states 1 = 0, ß = 0 when combining the

equations,

E,*T =D *Cp

F, = AF, , because the brakes are only applied on one wheel and F, = 0 on the other wheel, depending on whether AF, > 0 or AF, < 0,

Ny = F, * T (as requirement for the braking torque N,), and

Fy *r p= = (to determine the brake pressure).

P

The following terms apply:

FE, : shear force,

E, : longitudinal force,

CoG : center of mass, a : side slip angle of the tire,

Ô : steering angle of the wheel,

V : local speed, ß : slip angle of the chassis,

Ÿ : yaw rate,

Ÿ : yaw acceleration,

M : vehicle mass,

Ca : lateral tire stiffness, b : track width, l : distance to the center of gravity,

N, : braking torque,

T : wheel radius,

P : brake pressure,

Cp : brake pressure to brake torque coefficient (to be determined experimentally),

Index ,f*: front,

Index “r”: rear,

Index “1”: left front,

Index “2”: right front,

Index “3”: left rear,

Index “4”: right rear.

The force difference determined according to the above formula is converted into the brake pressure by the driver assistance system 5, taking into account the wheel diameter of the wheels 21, 22, 33, 34 and the so-called c_p value (brake pressure to torque). This brake pressure is scaled with a scaling factor of less than 1, whereby a scaling factor with a value between 0.05 and 0.1 has proven to be particularly advantageous. The

Driver assistance system 5 is further developed in this design variant, from

Driving condition information, which can be determined in particular by means of the sensors 7, to evaluate a current driving maneuver, wherein the scaling factor is determined depending on the evaluation of the driving maneuver.

In a second embodiment of the embodiment shown, in contrast to the first embodiment, the braking specification is calculated, whereby a target yaw moment to be achieved is determined from the target yaw rate, which is proportional to the target yaw rate, and the target yaw moment is compared with a value for a current driving speed of the

The driver assistance system 5 is in this second

Design variant designed to determine the force difference AFx of the longitudinal forces F according to the following relationship:

AF, = * U * C ‚where C is a constant used as an adjustment factor.

The brake pressure is then again determined as D = 2,

In Fig. 3, according to this second embodiment variant, three different

Steering angles SA1, SA2, SA3, which are shown in the diagram Fig. 3 (b) as angles in degrees above the

Vehicle speed in km/h (km: kilometer, h: hour), corresponding

Target yaw rates TLA1, TLA2, TLA3, which are shown in Fig. 3 (c) as acceleration in m/s? (m: meter, s:

second) over the vehicle speed in km/h, and certain brake pressures BP1, BP2,

BP3, which are shown in diagram Fig. 3 (a) as pressure in bar versus vehicle speed in km/h. The constant C was set to the value 95 in each case.

The required brake pressure increases with speed so that the driver feels that the vehicle is understeering more. This is advantageous when the main steering comes from the rear wheels and not from the front wheels, especially when

All-wheel steering means that the front wheels can no longer be steered due to a fault, for example as a result of an accident.

The elements shown in the figures and explained in connection with them

Embodiments serve to explain the invention and are not limitative of it.

List of reference symbols 1 Motor vehicle 21 Left front wheel 22 Right front wheel

33 left rear wheel 34 right rear wheel 4 Steer-by-wire steering system 5 Driver assistance system

51 Control unit 61 Brake (left front wheel) 62 Brake (right front wheel) 63 Brake (left rear wheel) 64 Brake (right rear wheel)

7 sensors for recording driving status information

Claims (12)

Expectations 1. Method for assisted steering of a two-lane motor vehicle (1) which has two front wheels (21, 22) and two rear wheels (33, 34), wherein a specification is provided with respect to a target yaw rate of the motor vehicle (1) to be achieved, taking into account a current actual yaw rate of the motor vehicle (1), a braking specification is determined for at least one of the wheels (21, 22, 33, 34) of the motor vehicle (1) in order to approximate the actual yaw rate to the target yaw rate, and a braking intervention is carried out in accordance with the determined braking specification, wherein the braking specification is determined based on a two-lane model, the specification with respect to the target yaw rate is fed to the two-lane model as an input variable, and a resulting braking torque difference between the wheels (21, 22; 33, 34) is determined using the two-lane model for an assumed stationary state of the motor vehicle (1) as an output variable, wherein the braking torque difference the braking specification is determined. 2. Method according to claim 1, characterized in that the specification regarding the desired yaw rate is provided taking into account a steering specification. 3. Method according to one of the preceding claims, characterized in that a scaling factor is applied to the determined braking torque difference, wherein the scaling factor is less than 1. 4. Method according to claim 3, characterized in that a current driving maneuver is evaluated from driving state information, wherein, depending on the evaluation of the driving maneuver, the scaling factor is set with a value in a range from 0.05 to 0.2. 5. Method according to claim 3 or claim 4, characterized in that the method is applied when a detected at least partial failure of a steering system (4) of the motor vehicle (1), wherein the scaling factor is set at a higher value the lower the steering effect that can still be provided by the steering system. 6. Method according to one of the preceding claims, characterized in that the braking specification is additionally calculated, whereby a target yaw rate is determined from the target yaw rate. A desired yaw moment is determined which is proportional to the desired yaw rate, and the desired yaw moment is multiplied by a value for a current driving speed of the motor vehicle (1). 7. Method according to one of the preceding claims, characterized in that a brake pressure for at least one specific wheel of the wheels (21, 22, 33, 34) of the motor vehicle (1) is determined as the braking specification. 8. Method according to claim 7, characterized in that the higher the driving speed of the motor vehicle (1), the higher the brake pressure is determined. 9. Method according to one of the preceding claims, characterized in that the method is carried out when an at least partial failure of a steering system (4) of the motor vehicle (1) is detected. 10. Driver assistance system (5) for assisting the steering of a two-lane motor vehicle (1) with two front wheels (21, 22) and two rear wheels (33, 34), comprising a control unit (51) which is designed to control a brake (61, 62, 63, 64) assigned to a respective wheel (21, 22, 33, 34), characterized in that the driver assistance system (5) is designed to carry out a method for assisting the steering of a two-lane motor vehicle (1) which has two front wheels (21, 22) and two rear wheels (33, 34), wherein in the method a specification is provided with regard to a target yaw rate of the motor vehicle (1) to be achieved, taking into account a current actual yaw rate of the motor vehicle (1), a braking specification for at least one of the wheels (21, 22, 33, 34) of the motor vehicle (1) to approximate the actual yaw rate to the target yaw rate, and braking intervention is carried out in accordance with the determined braking specification. 11. Driver assistance system (5) according to claim 10, characterized in that the driver assistance system (5) is designed to carry out a method according to one of claims 1 to 9. 12. Steer-by-wire steering system (4) comprising a driver assistance system (5) according to claim 10 or claim 11.