WO2013020796A1

WO2013020796A1 - Method for operating a driver assistance device, and driver assistance device

Info

Publication number: WO2013020796A1
Application number: PCT/EP2012/064303
Authority: WO
Inventors: Esther WENZEL; Roman SCHLEICHER; Manfred Holzmann; Eiko HAENSEL; Marc Arnon; Simon DORNSTETTER; Alexander Breu; Serdar Sen
Original assignee: Robert Bosch Gmbh
Priority date: 2011-08-09
Filing date: 2012-07-20
Publication date: 2013-02-14
Also published as: DE102011109842B4; DE102011109842A1

Abstract

The invention relates to a method for operating a driver assistance device of a motor vehicle, wherein the driver assistance device monitors the surroundings of the motor vehicle and initiates a braking process having a certain initial braking force if there is a risk of collision with an obstacle. According to the invention, after the initial braking force has been reached, a deceleration braking force is determined and the braking process is continued with the deceleration braking force in a deceleration phase, wherein the deceleration braking force is less than the initial braking force. The invention further relates to a driver assistance device of a motor vehicle.

Description

Description title

Method for operating a driver assistance device and

Fahrerassistenzeinnchtung

The invention relates to a method for operating a

Driver assistance device of a motor vehicle, wherein the

Driver assistance device performs an environment monitoring of the motor vehicle and initiates a braking process with a certain initial braking force in case of risk of collision with an obstacle. The invention further relates to a driver assistance device.

State of the art

Methods of the type mentioned are known from the prior art. They serve to operate the driver assistance device, which is designed for the at least partially at least partially automatic, in particular fully automatic, implementation of a driving operation of the motor vehicle.

In particular, the driver assistance device is intended to avoid collisions or at least to reduce a collision severity. For this purpose, the driver assistance device or a system affiliated with it carries out the environmental monitoring of the motor vehicle. For this purpose, at least one sensor arrangement with at least one sensor is provided in particular. The sensor is, for example, a distance sensor, by means of which the presence of an obstacle in the environment of the

Motor vehicle detected and preferably in addition the removal of

Motor vehicle can be determined to the obstacle. The sensor is preferably arranged to detect the obstacle in the direction of travel or main direction of travel of the motor vehicle. Under the Hauptfahrtriclhtung is to be understood a direction which towards a

Vehicle longitudinal axis in front of the vehicle is. Be at the Environment monitoring detected an obstacle or multiple obstacles, the collision risk is determined for the obstacle or each of the obstacles. This is for example a rating

performed in which, in particular, due to the relative speed between the motor vehicle and the respective obstacle and the distance between the motor vehicle and the obstacle, the probability of a collision is determined. If there is a risk of collision with the obstacle, that is to say if the probability lies above a certain limit, then the driver assistance device prevents the collision

Braking initiated with the specific initial braking force. The braking force is proportional to a braking deceleration of the motor vehicle, ie to a negative acceleration. In the following, the terms braking force and braking deceleration are used synonymously. However, the braking force can also describe the set on a brake system of the motor vehicle for deceleration of the motor vehicle force or the brake pressure.

The initial braking force can, for example, a maximum braking force of the

Brake system of the motor vehicle or at least a fraction of this correspond. However, it can also be a substantially arbitrary,

preferably be specific braking force due to an operating size of the motor vehicle. Under the operating size is, for example, the

Speed of the motor vehicle to understand the distance of the motor vehicle to the obstacle or the relative speed of the motor vehicle to the obstacle. From DE 10 2008 056 204 A1, for example, a driver assistance system for avoiding a collision of a vehicle is known, which is designed to autonomously decelerate the speed of the motor vehicle with a first negative in a critical driving situation of the motor vehicle, which can lead to a collision

Acceleration to perform when a first condition is met.

Subsequently, an autonomous deceleration of the speed of the

Motor vehicle with a second, larger negative acceleration

provided when a second condition is met and before the last time to avoid a collision has elapsed. This approach is justified by the fact that the first negative acceleration should initially be limited in order to avoid that a false estimate of the current situation by an environment sensor and electronics of the motor vehicle to a critical hard braking leads. Only if the driver does not respond to the autonomous deceleration with the first acceleration, then the second, larger negative acceleration is used to avert the impending collision.

This means in total that the driver assistance device in critical situations in which a driver of the motor vehicle makes a mistake in the management of the motor vehicle (for example, because he is inattentive or too late or wrongly responds) briefly at least partially takes over the leadership of the motor vehicle and corrective intervention. Usually, the driver assistance device is designed such that it engages very late in the leadership of the motor vehicle to correct the error of the driver. The braking process is so far introduced with a relatively large initial braking force in order to avoid the collision with the obstacle can. Due to the large initial braking force, the duration of the braking process is usually low. At the same time strong inertial forces act on the driver. Likewise, in particular at the time in which the standstill is reached, or subsequently, a nodding of the motor vehicle occur and additionally act on the driver. Immediately after performing the braking operation or after the completion of the braking process, however, the driver must take over the leadership of the motor vehicle as soon as possible again. In particular, if the driver is distracted or inattentive at the time of performing the braking or has a long reaction time, he is due to the braking initially possibly at least for a short time disoriented and therefore can not react properly, so even the leadership of the motor vehicle not yet again high reliability itself.

Disclosure of the invention

In contrast, the method for operating a

Driver assistance device with the features of claim 1 has the advantage that the driver despite the implementation of the braking process with a

comparatively high initial braking force without further guidance of the

Motor vehicle can take over again. For this purpose, the invention provides that after reaching the Initialbremskraft a Deceleration braking force determined and the braking process in one

Delay phase is continued with this, the

Deceleration braking force is less than the initial braking force. It is, as known from the prior art, the braking process with the specific

Initial braking force introduced and performed during an initial braking phase. After lapse of the initial braking phase but not the

Braking be terminated, but continued in a deceleration phase with the lower deceleration braking force. To the

The initial braking phase is followed by the deceleration phase.

In order to minimize the effects of the autonomous braking process on the driver, the deceleration braking force should be less than

Be initial braking force. It is therefore intended to vary the braking force during the implementation of the braking operation over time and preferably to reduce it steadily. In this way, it is possible for the driver of the motor vehicle to orient himself and to adjust to the driving situation changed by the braking process. He can thus better or more reliable take over the further guidance of the motor vehicle after completion of the braking process. With the described procedure, the

Motor vehicle safely delayed or slowed down, but with much less severity than known from the prior art. With the thus achieved "soft stop" effect is a reduction of

Vehicle preload and the braking process is for the driver

or more inmates of the motor vehicle more comfortable. In addition, the pitch of the motor vehicle, which is excited by the braking process, significantly weaker and has a lower amplitude. The driver is so far less affected than known from the prior art method. Preferably, the braking operation is initiated only when the current speed of the motor vehicle - which before the

Braking process is present - less than or equal to a certain

Maximum speed, for example, 20 km / h to 50 km / h, is.

A development of the invention provides that the deceleration phase immediately after reaching the initial braking force or after a

Initial braking phase is initiated with a certain Initialbremszeitdauer, preferably the deceleration phase to a standstill of Motor vehicle is continued. In the initial braking phase, the actually present braking force is usually adjusted over a certain period of time in the direction of the initial braking force. It may, as known from the prior art, be provided initially to use a smaller braking force and set only after failure of a reaction of the driver within a certain reaction period, the braking force to the initial braking force. As soon as the initial braking force is reached in the initial braking phase, the initial braking phase can be ended and the deceleration phase can be initiated. The delay phase follows in this respect directly to the initial braking phase. Alternatively, the deceleration phase can also be initiated only after the initial braking phase has been carried out over the specific initial braking time duration. During the deceleration phase, the braking operation is continued with the deceleration braking force. This is preferably provided to a standstill of the motor vehicle. After carrying out the

Initial braking phase and the deceleration phase, the motor vehicle is therefore at a standstill. Alternatively, however, it may also be provided that the deceleration phase only until reaching a certain

Speed difference to a pre-braking

Speed. For example, during the

Initial braking phase and the deceleration phase, the speed by the specific speed difference, which may be in particular 10 km / h to 40 km / h, reduced and the braking process then be terminated.

A development of the invention provides that the Initialbremszeitdauer, the Initialbremskraft, the delay brake duration and / or the

Deceleration braking force depending on at least one operating variable of the motor vehicle, in particular the speed, the distance to the obstacle and / or the relative speed of the motor vehicle to the obstacle, are determined. The initial braking time and / or the

Initial braking force are preferably determined such that until the initiation of the subsequent to the initial braking phase deceleration phase, the risk of collision is eliminated or at least significantly reduced. Accordingly, within the initial braking time period, the braking operation is performed with the initial braking force such that the motor vehicle is decelerated to a speed at which the risk of collision with the obstacle no longer exists or at least is no longer probable. For this purpose, the Initial brake duration and / or the initial braking force in dependence on the at least one operating variable of the motor vehicle determined. Accordingly, additionally or alternatively, the deceleration braking force and the

Delay brake time as a function of the at least one

Operating size of the motor vehicle are set to give the driver of the motor vehicle opportunity to reorient themselves so that he can perform the driving of the motor vehicle itself after the completion of the braking process. In this way, the comfort for the driver is to be increased even during the autonomous execution of the braking process.

It may be provided that the aforementioned variables are determined once, continuously or at intervals during the braking process. During the initial braking phase, the initial braking time duration and / or the initial braking force or, during the deceleration phase, the deceleration braking time duration and / or the deceleration braking force are thus determined accordingly. The one-time determination means that the respective variable is determined at the beginning of the respective phase. In the continuous determination, a continuous tracking of the respective size is provided. If the determination is provided at intervals, then there is a certain period of time between two points in time in which the respective variable is to be determined, so that no continuous determination takes place.

A development of the invention provides that after reaching the standstill of the motor vehicle, the braking operation is continued in a holding phase with a holding brake force over a holding brake period. The holding phase is preferably immediately after reaching the standstill of

Motor vehicle initiated. The holding phase follows in this respect directly to the delay phase. To end the delay phase

or to initiate the holding phase, has the

Driver assistance device via means to determine the stoppage of the motor vehicle. The holding brake force is constant in particular over time and preferably corresponds to the deceleration braking force at the time of completion of the

Delay phase or when initiating the holding phase. The

Haltebremszeitdauer can be fixed preset, but also, for example, depending on the severity of the braking process, so the Initial braking time, the initial braking force, the delay brake duration and / or the deceleration braking force determined.

A development of the invention provides that after reaching the standstill of the motor vehicle and / or after the holding phase of the braking operation is continued in a roll-up with a Anrollbremskraft over a Anrollbremszeitdauer, the Anrollbremskraft reduced over the Anrollbremszeitdauer to zero and over time as a function of a state variable of the motor vehicle, in particular an inclination of the motor vehicle, a loading state and / or a direction of movement of the motor vehicle, is determined. Accordingly, the start-up phase or the deceleration phase should be followed by the start-up phase. In this the braking process with the

Anrollbremskraft continued over the Anrollbremszeitdauer. The Anrollbremskraft is reduced to zero. During the Anrollbremsphase the driver of the vehicle is thus given the opportunity controls the

To resume driving operation of the motor vehicle. The Anrollbremskraft is preferably determined in dependence on the at least one state variable of the motor vehicle. The state variable is in particular the inclination of the motor vehicle or the background of the motor vehicle, the loading state and / or the direction of movement. In this way, when the motor vehicle is on an incline, the driver is given the opportunity to set a desired torque of a drive system of the motor vehicle to a value which allows the motor vehicle to start on the incline. This is especially true when the direction of movement of

Motor vehicle is directed against the main direction of travel. In this case, the motor vehicle moves - usually due to the influence of gravity and against a driver's request - backwards. Because the movement is due to the influence of gravity and (at least predominantly) is not effected by the drive system of the motor vehicle, the direction of movement can also be referred to as rolling direction. By determining the

Anrollbremskraft over time, the course of Anrollbremskraft over time is determined.

A development of the invention provides that at least during a present at least during the deceleration phase

Torque reduction phase a target torque of a drive system of Motor vehicle smaller than a default torque of a driver of the motor vehicle, in particular equal to a minimum torque of a drive system is selected. The torque reduction phase is thus initiated in particular at the beginning of the deceleration phase or even already at the beginning of the initial braking phase or the braking process. The

Torque reduction phase runs parallel to initial braking phase, deceleration phase, holding phase and / or start-up phase. Preferably, the torque reduction phase is during the entire initial braking phase and the entire deceleration phase, ie in particular to standstill of

Motor vehicle, in front. During the torque reduction phase, filtering of the driver's default torque is performed.

The default torque of the driver is the moment, which he

for example, by means of an accelerator pedal pretends, so the desired by the driver torque. Usually during the driving of the

Motor vehicle, the desired torque of the drive system, that is, the torque which is set on the drive system, substantially equal to

Default torque or this is adjusted with only a small time delay. During the torque reduction phase, however, the

Target torque of the drive system can be selected smaller than the default torque, so that the drive system does not work against the brake of the motor vehicle during the braking process. Because no moment is needed to accelerate the motor vehicle during the initial braking phase or the deceleration phase, it is advantageous if the nominal torque is completely decoupled from the default torque during the torque reduction phase and equal to the minimum torque of the drive system is selected, ie the moment, which is just an operation of the drive system.

If the drive system has an electric machine, this can

Minimum moment equal to zero or one of one

Secondary system required torque. For an internal combustion engine, the minimum torque must be at least equal to a loss torque, which is present for example due to friction losses. After the motor vehicle has come to a standstill, ie usually after the deceleration phase, the desired torque should usually be greater than the minimum torque, if desired by the driver - to facilitate starting of the motor vehicle on a slope. Alternatively, however, the filtering of the

Preset torque during the entire braking process, including the holding phase and the start-up, be performed.

Furthermore, it may be provided to carry out the torque reduction phase over a minimum period of time. This means that, for example, after completion of the deceleration phase, the torque reduction phase continues until the minimum time duration has been reached or exceeded. The

Minimum duration is chosen such that it is the driver of the

Motor vehicle has sufficient opportunity to adapt to the changed

To adjust the driving situation and react accordingly. Accordingly, a (permanent) accelerator operation by the driver is irrelevant during the minimum period of time. Only when carrying out a demolition action described below, the torque reduction phase can be terminated before the minimum period expires.

A development of the invention provides that to the

Momentsreduzierungsphase connects a torque buildup phase during which the target torque is adjusted to the default torque steadily or stepwise, in particular, the torque buildup of the

Torque build-up phase and / or the desired torque over time as a function of the state variable, preferably the inclination of the motor vehicle, the loading state and / or the direction of movement of the motor vehicle can be determined. Like the torque reduction phase, the torque buildup phase can run parallel to the initial brake phase, the deceleration phase, the hold phase and / or the startup phase. The torque buildup phase immediately follows the torque reduction phase. During the

Torque-building phase is to increase the torque kept constant during the torque reduction phase again, in particular to the

Adjustment torque of the driver. This is provided either steadily or stepwise. In the case of the constant alignments are in the

Contrary to the gradual adjustment no jumps in the course of the target torque over time provided. The torque buildup time may depend on the state quantity. This also applies to the desired torque or to the course of the desired torque over time during the torque buildup phase. The matching is achieved by filtering. The matching can be stopped when falling below a minimum difference between the setpoint torque and the setpoint torque so as not to reach the setpoint torque by the setpoint torque

delay. After falling below the minimum difference, therefore, the setpoint torque is set equal to the default torque.

In particular, it is provided to set the torque buildup time period and / or the setpoint torque over time in such a way that starting of the

Motor vehicle is also easily possible on a slope. So there is a direction of movement of the motor vehicle, which against one

Moving direction is on reaching the default torque is directed, it is advantageous that target torque faster to the default torque

adapt to achieve the desired or predetermined by the driver movement direction.

A development of the invention provides that the

Momentsreduzierungsphase and / or the torque buildup phase are aborted when the driver, in particular by means of at least one accelerator pedal, performs a cancellation action and / or a maximum period of time is exceeded. Situations are conceivable in which the driver wants to accelerate the motor vehicle again immediately after the braking process. If, however, the nominal torque is subjected to filtering during the torque reduction phase or the torque build-up phase so that it is smaller than the default torque, then such acceleration is not possible. For this purpose, the driver should be able to signal to the driver assistance device that, despite the braking process, an acceleration is desired which is stronger than that which can be achieved by means of the momentarily present desired torque. For this purpose, the demolition action is provided, which can be carried out for example by means of the at least one accelerator pedal. The abort action is in particular a pedal change, for example, from a brake pedal to an accelerator pedal, an accelerator pedal zero crossing, ie a complete unloading and subsequent re-actuation of the accelerator pedal, and / or a pumping operation of the accelerator pedal. Under the latter is a quick, multiple pressing the Understood accelerator pedal. When performing the cancel action

Momentsreduzierungsphase and / or torque buildup phase preferably also aborted when the minimum period of

Torque reduction phase has not yet been reached.

Alternatively or additionally, it may be provided that the

Torque reduction phase and / or the torque build-up phase are aborted when a maximum time period is reached or exceeded. It is therefore intended to reduce the torque only over a limited period of time, namely the maximum period of time, because it is assumed that the driver, after the maximum period has elapsed, will take over the leadership of the driver

Motor vehicle can take over again. Therefore, when this condition occurs, the torque reduction phase and / or the

Torque build-up phase aborted and then the target torque adjusted to the default torque or set to this.

A development of the invention provides that with the initiation of

At least one reversible belt tensioner for tightening a seat belt is activated. The motor vehicle therefore has the belt tensioner, which is reversible, that allows a multiple activation. Preferably, the belt tensioners of all safety belts are activated, but in particular only the belt tensioners, which seats are assigned, which are actually occupied. By activating the belt tensioner is the

Tightened seat belt and the driver or another occupant of the motor vehicle held in his seat, so that a displacement of the driver or the occupant due to inertial forces is at least partially prevented.

The invention further relates to a driver assistance device of a

Motor vehicle, in particular for carrying out the method described above, wherein the Fahrerassistzeinrichtung for performing an environmental monitoring of the motor vehicle and for initiating a

Braking is provided with a certain initial braking force in case of collision with an obstacle. The driver assistance device should be designed to achieve this after reaching the initial braking force

To determine deceleration braking force and the braking process in one Delay phase continue with this, wherein the deceleration braking force is smaller than the initial braking force. The driver assistance device can also be provided for carrying out further driving support measures. The method which is to be carried out by means of the driver assistance device can be developed as described above.

The invention will be explained in more detail with reference to the embodiments illustrated in the drawings, without any limitation of the invention. The only one shows

Figure is a diagram in which a braking force and a target brake pressure are plotted over time.

The figure shows a diagram in which two curves 1 and 2 each have a braking force or deceleration a and a curve 3 a desired brake pressure p _So ii over the time t are plotted. The course 1 shows the braking deceleration, which is predetermined by a known from the prior art driver assistance device, while the course 2 predetermined by a driver assistance device according to the invention

Braking delay reflects. The target brake pressure of the curve 3 corresponds to the braking delay according to course 2. It should again on it

be pointed out that the terms braking force and braking deceleration are used interchangeably and are interchangeable. Instead of an initial braking force can therefore be talk of the initial brake delay, without resulting in another meaning.

For t <t _! is a motor vehicle, not shown here in a normal driving operation, with no braking operation is performed. The

Motor vehicle has the driver assistance device, which a

Environment monitoring of the motor vehicle performs. Will be at the

Environment monitoring detected an obstacle in the vicinity of the motor vehicle and there is a risk of collision with this, so passes the

Driver assistance device a braking operation with a specific

Initial braking force a, on. The braking process starts at t = It can be seen that for both courses 1 and 2 the braking deceleration a increases between <tst ₂ with a first, smaller gradient (seen in absolute values). Between t ₂ <tt ₃ is a greater slope of

Braking delay before. Between t ₃ <t <t the braking delay for both curves 1 and 2 remains the same and corresponds to aj. The time span between t, <t <t ₄ is used as the initial braking time At | an initial braking phase called. Alternatively, only the time span in which the initial braking force actually exists, ie t ₃ <t <t ₄ , can represent the initial braking time duration.

The course 1 known from the prior art shows that the

Braking delay a is first increased from a = 0 to a = ai and then remains constant until the end of the braking process at t = t ₈ . Only after completion of the braking process, the braking deceleration drops to zero. The initial braking phase thus extends over the duration of the entire braking process.

According to the invention, that is, according to course 2, on the other hand, after reaching the initial braking force, a deceleration phase is initiated, which is carried out in the exemplary embodiment shown here between t ₄ <tst ₆ . In the deceleration phase, the braking process for a

Retarder brake duration At _{v continued} with a retarding brake force, wherein the deceleration braking force is smaller than the initial braking force. The deceleration phase is up to a standstill of the motor vehicle

performed, so the braking process continued until this. In this case, the initial braking time duration, the initial braking force, the delay braking time duration and / or the deceleration braking force can be determined as a function of at least one operating variable of the motor vehicle. The operating variable, for example, the speed of the motor vehicle, the distance of the motor vehicle to the obstacle and / or the relative speed of the motor vehicle to understand the obstacle.

In the exemplary embodiment shown here, the motor vehicle is at standstill at the time t = t ₆ . After reaching the standstill of the motor vehicle at this time, the braking operation in a holding phase with a holding brake force a _H over a holding brake period At _{H should be} continued. The holding brake period here corresponds to the period between t ₆ <t < t ₇ . During the holding phase, the holding brake force remains constant. The

Holding brake duration is for example given a constant.

The holding phase is followed by a start-up phase of the motor vehicle. In this, the braking operation with a Anrollbremskraft over a

Anrollbremszeitdauer Δί _Α continued. The Anrollbremskraft at the beginning of

Start-up phase corresponds to the holding brake force or the holding brake force at the end of the holding phase. The Anrollbremskraft should now on the

Anrollbremszeitdauer At _{A be} reduced to zero. In this case, for example, a linear reduction over time t can be provided. Alternatively, the Anrollbremskraft also depending on a state variable of the

Motor vehicle are set. The state variable is in particular an inclination of the motor vehicle or of a roadway on which the motor vehicle is located and / or a loading state of the motor vehicle. After the start of the braking process is stopped, so that the

Braking delay from the time t = t _{8 is} again equal to zero.

In contrast to the course 1 of the braking force a allows the

Inventive course 2 of the braking force a gentler deceleration of the motor vehicle, so that the driver after reaching standstill has sufficient time to adapt to the changed driving situation and subsequently resume the driving itself.

Claims

claims

1. A method for operating a driver assistance device of a

Motor vehicle, the Fahrerassistzeinrichtung a

Environment monitoring of the motor vehicle performs and collision with an obstacle braking with a specific

Initial braking force initiates, characterized in that after reaching the initial braking force determines a deceleration braking force and the

Braking is continued in a deceleration phase with this, wherein the deceleration braking force is smaller than the initial braking force.

2. The method according to claim 1, characterized in that the

Delay phase is initiated immediately after reaching the Initialbremskraft or after an initial braking phase with a certain Initialbremszeitdauer, wherein preferably the deceleration phase is continued until a standstill of the motor vehicle.

3. The method according to any one of the preceding claims, characterized

in that the initial braking time duration, the initial braking force, the deceleration braking time duration and / or the deceleration braking force are determined as a function of at least one operating variable of the motor vehicle, in particular the speed, the distance to the obstacle and / or the relative speed of the motor vehicle to the obstacle.

4. The method according to any one of the preceding claims, characterized

characterized in that after reaching the stoppage of

Motor vehicle braking in a holding phase with a

Holding brake force is continued over a holding brake period.

5. The method according to any one of the preceding claims, characterized

characterized in that after reaching the stoppage of Motor vehicle and / or continued after the holding phase of the braking operation in a roll-on with a Anrollbremskraft over a Anrollbremszeitdauer, the Anrollbremskraft reduced over the Anrollbremszeitdauer to zero and over time as a function of a

State variable of the motor vehicle, in particular an inclination of the motor vehicle, a loading state and / or a direction of movement of the motor vehicle, is determined.

Method according to one of the preceding claims, characterized

characterized in that at least during a present at least during the deceleration phase torque reduction phase a

Target torque of a drive system of the motor vehicle smaller than a default torque of a driver of the motor vehicle, in particular equal to a minimum torque of the drive system is selected.

Method according to one of the preceding claims, characterized

characterized in that the torque reduction phase is followed by a torque buildup phase, during which the desired torque is adjusted to the default torque steadily or stepwise, wherein in particular the torque buildup period of the torque buildup phase and / or the desired torque over time as a function of

State variable, preferably the inclination of the motor vehicle, the

Loading state and / or the direction of movement of the motor vehicle to be determined.

Method according to one of the preceding claims, characterized

in that the torque reduction phase and / or the torque buildup phase are aborted when the driver,

in particular by means of at least one accelerator pedal, carries out a cancellation action and / or a maximum period of time is exceeded.

Method according to one of the preceding claims, characterized

characterized in that upon initiation of the braking operation, at least one reversible belt tensioner is activated to tighten a safety belt.

10. Driver assistance device of a motor vehicle, in particular for carrying out the method according to one or more of

The preceding claims, wherein the Fahrerassistzeinrichtung is provided for performing an environmental monitoring of the motor vehicle and for initiating a braking operation with a certain initial braking force in case of risk of collision with an obstacle, characterized

in that the driver assistance device is designed to determine a deceleration braking force after the initial braking force has been reached and to continue the braking force in a deceleration phase therewith, the deceleration braking force being smaller than the deceleration braking force

Initial braking force is.