DE102011109842B4 - Method for operating a driver assistance device and driver assistance device - Google Patents

Abstract

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, if there is a risk of collision with an obstacle, initiates a braking process with a specific initial braking force corresponding to a maximum braking force of a braking system of the motor vehicle, characterized in that after the initial braking force has been reached, a deceleration braking force which is smaller than the initial braking force, determined and the braking process is continued in a deceleration phase with this, the deceleration phase being initiated immediately after an initial braking phase with a certain initial braking time and continued until the motor vehicle comes to a standstill.

Description

The invention relates to a method for operating a driver assistance device of a motor vehicle, the driver assistance device monitoring the surroundings of the motor vehicle and, if there is a risk of collision with an obstacle, initiating a braking process with a specific initial braking force corresponding to a maximum braking force of a braking system of the motor vehicle. The invention also relates to a driver assistance device.

State of the art

Methods of the type mentioned at the beginning are known from the prior art. They are used to operate the driver assistance device, which is designed for at least temporarily, at least partially automatic, in particular fully automatic, driving operation of the motor vehicle. In particular, the driver assistance device is provided to avoid collisions or at least to reduce the severity of a collision. For this purpose, the driver assistance device or a system attached to it monitors the surroundings of the motor vehicle. For this purpose, in particular at least one sensor arrangement with at least one sensor is provided. The sensor is, for example, a distance sensor by means of which the presence of an obstacle in the vicinity of the motor vehicle can be recognized and, preferably, the distance between the motor vehicle and the obstacle can also be determined. The sensor is preferably arranged to detect the obstacle in the direction of travel or the main direction of travel of the motor vehicle. The main direction of travel is to be understood as a direction which lies in the direction of a vehicle longitudinal axis in front of the motor vehicle. If an obstacle or several obstacles are detected during the monitoring of the surroundings, the risk of collision is determined for the obstacle or each of the obstacles. For this purpose, an evaluation is carried out, for example, in which the probability of a collision is determined in particular on the basis of the relative speed between the motor vehicle and the respective obstacle and the distance between the motor vehicle and the obstacle. If there is a risk of collision with the obstacle, that is to say, in particular, if the probability is above a certain limit value, the driver assistance device initiates the braking process with the determined initial braking force in order to avoid the collision. The braking force is proportional to a braking deceleration of the motor vehicle, that is to say 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 force or the braking pressure set on a braking system of the motor vehicle for decelerating the motor vehicle.

The initial braking force can, for example, correspond to a maximum braking force of the braking system of the motor vehicle or at least a fraction thereof. However, it can also be essentially any desired braking force, preferably determined on the basis of an operating variable of the motor vehicle. The operating variable is to be understood as meaning, for example, the speed of the motor vehicle, the distance of the motor vehicle from the obstacle or the relative speed of the motor vehicle from the obstacle.

From the prior art, for example, is the document DE 199 24 255 A1 known. This describes an apparatus and a method for controlling a vehicle speed of an automobile, so that the vehicle speed is kept equal to a target vehicle speed in order to follow a preceding vehicle which is traveling in front of the vehicle at a suitable inter-vehicle distance.

The publications also disclose DE 10 2006 056 627 A1 and DE 10 2005 036 217 A1 in each case a device for ensuring the standstill of a motor vehicle, whereas from the publication DE 102 31 557 A1 a method and a device for triggering and carrying out a deceleration of a vehicle are known.

Finally it is from the pamphlet DE 10 2008 056 204 A1 a driver assistance system for avoiding a collision of a vehicle is known, which is designed to carry out an autonomous deceleration of the speed of the motor vehicle with a first negative acceleration in a critical driving situation of the motor vehicle, which can lead to a collision, if a first condition is met. An autonomous deceleration of the speed of the motor vehicle with a second, larger negative acceleration is then provided if a second condition is met and before the last point in time for avoiding a collision has passed. This procedure is justified by the fact that the first negative acceleration should initially be limited in order to avoid that an incorrect assessment of the current situation by environmental sensors and electronics of the motor vehicle leads to critical emergency braking. Only if the driver does not react to the autonomous deceleration with the first acceleration is the second, larger negative acceleration used to avert the impending collision.

Overall, this means that in critical situations in which a driver of the motor vehicle makes a mistake in driving the motor vehicle (for example because he is inattentive or reacting too late or incorrectly), the driver assistance device briefly takes over the control of the motor vehicle at least partially and takes corrective action. The driver assistance device is usually designed in such a way that it intervenes very late in the guidance of the motor vehicle in order to correct the driver's error. The braking process is initiated with a relatively large initial braking force in order to be able to avoid the collision with the obstacle. Due to the large initial braking force, the duration of the braking process is usually short. At the same time, strong inertial forces act on the driver. Likewise, in particular at or after the point in time at which standstill is reached, the motor vehicle may nod and additionally act on the driver. Immediately after the braking process has been carried out or after the braking process has ended, however, the driver must take control of the motor vehicle again as quickly as possible. In particular, if the driver is distracted or inattentive or has a long reaction time at the time the braking process is carried out, he may initially be disoriented at least for a short time due to the braking process and therefore cannot yet react correctly, i.e. not yet able to drive the motor vehicle again take on high reliability yourself.

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 can easily take control of the motor vehicle again despite performing the braking process with a comparatively high initial braking force. For this purpose, it is provided according to the invention that after the initial braking force has been reached, a deceleration braking force that is smaller than the initial braking force is determined and the braking process is continued with this in a deceleration phase, the deceleration phase being initiated immediately after an initial braking phase with a certain initial braking time and until the Motor vehicle is continued. As is known from the prior art, the braking process is initiated with the specific initial braking force and carried out during an initial braking phase. After the initial braking phase has elapsed, however, the braking process should not be ended, but rather be continued in a deceleration phase with the lower deceleration braking force. The deceleration phase follows the initial braking phase.

In order to minimize the effects of the autonomously performed braking process on the driver, the deceleration braking force should be less than the initial braking force. Provision is therefore made for the braking force to be varied over time while the braking process is being carried out and, preferably, to be reduced continuously. In this way it is possible for the driver of the motor vehicle to orientate himself and to adjust to the driving situation changed by the braking process. He can thus take over the further guidance of the motor vehicle himself better or more reliably after the end of the braking process. With the procedure described, the motor vehicle can be safely decelerated or braked, but with significantly less force than is known from the prior art. With the "soft stop" effect achieved in this way, the vehicle preload is reduced and the braking process becomes more comfortable for the driver or other occupants of the motor vehicle. In addition, the pitching of the motor vehicle, which is excited by the braking process, is significantly weaker and has a lower amplitude. The driver is influenced to a lesser extent than in the case of methods known from the prior art. The braking process is preferably only initiated when the current speed of the motor vehicle - which is present before the braking process - is less than or equal to a certain maximum speed, for example 20 km / h to 50 km / h.

According to the invention, it is provided that the delay phase is initiated immediately after the initial braking phase with the specific initial braking period and continued until the motor vehicle comes to a standstill. In the initial braking phase, the braking force actually present is usually adapted over a certain period of time in the direction of the initial braking force. As is known from the prior art, provision can be made here to first use a smaller braking force and to set the braking force to the initial braking force only after the driver has not responded within a certain reaction period. 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 initiated. In this respect, the deceleration phase immediately follows the initial braking phase. According to the invention, however, the delay phase is only initiated after the initial braking phase has been carried out over the specific initial braking period. During the deceleration phase, the braking process is continued with the deceleration braking force. This is provided until the motor vehicle comes to a standstill. After the initial braking phase and the deceleration phase have been carried out, the motor vehicle is accordingly at a standstill. However, not according to the invention, it can alternatively also be provided to carry out the deceleration phase only until a certain speed difference is reached compared to a speed that was present before the braking process. For example, during the initial braking phase and the deceleration phase, the speed should be reduced by the specific speed difference, which can in particular be 10 km / h to 40 km / h, and the braking process should then be ended.

A further development of the invention provides that the initial braking period, the initial braking force, the decelerating braking period and / or the decelerating braking force 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, to be determined. The initial braking duration and / or the initial braking force are preferably determined in such a way that the risk of collision is eliminated or at least significantly reduced until the delay phase following the initial braking phase is initiated. Accordingly, within the initial braking period, the braking process is carried out with the initial braking force in such a way 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 braking duration and / or the initial braking force are determined as a function of the at least one operating variable of the motor vehicle. Correspondingly, the deceleration braking force and the deceleration braking time duration can additionally or alternatively be determined as a function of the at least one operating variable of the motor vehicle in order to give the driver of the motor vehicle the opportunity to reorient himself so that he can drive the motor vehicle himself after the braking process has ended. In this way, the comfort for the driver should also be increased during the autonomous implementation of the braking process.

It can 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 period and / or the initial braking force or, during the deceleration phase, the decelerating braking period and / or the decelerating braking force are determined accordingly. The one-time determination is to be understood as meaning that the respective variable is determined at the beginning of the respective phase. In the case of continuous determination, constant 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 at which the respective variable is to be determined, so that there is currently no continuous determination.

A further development of the invention provides that after the motor vehicle has come to a standstill, the braking process is continued in a holding phase with a holding brake force over a holding brake period. The holding phase is preferably initiated immediately after the motor vehicle has come to a standstill. In this respect, the hold phase immediately follows the delay phase. In order to end the deceleration phase or to initiate the holding phase, the driver assistance device has means to determine the standstill of the motor vehicle. The holding braking force is constant in particular over time and preferably corresponds to the deceleration braking force at the end of the deceleration phase or when the holding phase is initiated. The holding brake period can be permanently preset, but can also be determined, for example, as a function of the severity of the braking process, that is to say the initial braking period, the initial braking force, the decelerating braking period and / or the decelerating braking force.

A further development of the invention provides that after the motor vehicle has come to a standstill and / or after the stopping phase, the braking process is continued in a rolling-on phase with a rolling-on braking force over a rolling-on braking time, the rolling-on braking force being reduced to zero over the rolling-on braking time and over time as a function of a state variable of the motor vehicle, in particular an inclination of the motor vehicle, a load condition and / or a direction of movement of the motor vehicle is determined. The roll-on phase should therefore follow the holding phase or the deceleration phase. In this, the braking process is continued with the rolling braking force over the rolling braking period. The roll-on braking force is reduced to zero. During the roll-on braking phase, the driver of the motor vehicle is thus given the opportunity to restart the driving operation of the motor vehicle in a controlled manner. The rolling braking force is preferably determined as a function of the at least one state variable of the motor vehicle. The state variable is in particular the inclination of the motor vehicle or the ground of the motor vehicle, the load 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 setpoint torque of a drive system of the motor vehicle to a value which enables the motor vehicle to start on the incline. This applies in particular when the direction of movement of the motor vehicle is directed against the main direction of travel. In this case, that moves Motor vehicle - 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 is (at least predominantly) not caused by the drive system of the motor vehicle, the direction of movement can also be referred to as the rolling direction. By determining the roll-on braking force over time, the course of the roll-on braking force over time is determined.

A further development of the invention provides that at least during a torque reduction phase present at least during the deceleration phase, a setpoint torque of a drive system of the motor vehicle is selected to be less than a specified torque of a driver of the motor vehicle, in particular equal to a minimum torque of a drive system. The torque reduction phase is therefore initiated in particular at the start of the deceleration phase or even at the start of the initial braking phase or the braking process. The torque reduction phase runs parallel to the initial braking phase, deceleration phase, holding phase and / or roll-on phase. The torque reduction phase is preferably present during the entire initial braking phase and the entire deceleration phase, that is to say in particular until the motor vehicle comes to a standstill. During the torque reduction phase, the driver's default torque is filtered.

The driver's default torque is the torque that he specifies, for example by means of an accelerator pedal, that is, the torque desired by the driver. During the driving operation of the motor vehicle, the setpoint torque of the drive system, that is to say the torque that is set on the drive system, is usually essentially the same as the specified torque or is adjusted to this with only a slight time delay. During the torque reduction phase, however, the setpoint torque of the drive system should be selected to be smaller than the specified torque so that the drive system does not work against the brakes of the motor vehicle during the braking process. Because no torque is required to accelerate the motor vehicle during the initial braking phase or the deceleration phase, it is advantageous if the target torque is completely decoupled from the specified torque during the torque reduction phase and is selected to be the same as the minimum torque of the drive system, i.e. the torque that is currently still in operation of the drive system.

If the drive system has an electrical machine, the minimum torque can be zero or correspond to a torque required by a secondary system. For an internal combustion engine, the minimum torque must be at least equal to a loss torque, which is due, for example, to friction losses. After the motor vehicle has come to a standstill, that is usually after the deceleration phase, the setpoint torque should usually be able to be greater than the minimum torque - if desired by the driver - in order to simplify starting the motor vehicle on an incline. Alternatively, however, the specified torque can also be filtered during the entire braking process, that is to say including the holding phase and the rolling phase.

Provision can also be made for the torque reduction phase to be carried out over a minimum period of time. This means that even after the end of the deceleration phase, for example, the torque reduction phase continues until the minimum period is reached or exceeded. The minimum period is selected in such a way that it gives the driver of the motor vehicle sufficient opportunity to adjust to the changed driving situation and to react accordingly. During the minimum period of time, a (permanent) accelerator pedal actuation by the driver is accordingly irrelevant. The torque reduction phase can only be ended before the minimum period has expired if an abort action described below is carried out.

A further development of the invention provides that the torque reduction phase is followed by a torque build-up phase, during which the target torque is continuously or step-wise adjusted to the specified torque, in particular the torque build-up duration of the torque build-up phase and / or the target torque over time as a function of the state variable, preferably the inclination of the motor vehicle, the load condition and / or the direction of movement of the motor vehicle. Just like the torque reduction phase, the torque build-up phase can run parallel to the initial braking phase, deceleration phase, holding phase and / or rolling phase. The torque build-up phase immediately follows the torque reduction phase. During the torque build-up phase, the setpoint torque, which is kept constant during the torque reduction phase, should be increased again, in particular adjusted to the driver's default torque. This is provided either continuously or gradually. In contrast to the step-by-step adaptation, continuous adaptation does not involve any jumps in the course of the setpoint torque over time.

The torque build-up time can depend on the state variable. This also applies to the setpoint torque or the course of the setpoint torque over time during the Moment building phase. Matching is achieved by filtering. The matching can be terminated if the difference between the specified torque and the setpoint torque falls below a minimum, so as not to delay the setpoint torque from reaching the setpoint torque. After falling below the minimum difference, the setpoint torque is set equal to the specified torque.

In particular, it is provided that the torque build-up time period and / or the setpoint torque is defined over time in such a way that the motor vehicle can easily be started even on an incline. If there is a direction of movement of the motor vehicle that is opposite to a direction of movement that the specified torque is aimed at, it is advantageous to adapt the setpoint torque more quickly to the specified torque in order to achieve the direction of motion desired or specified by the driver.

A further development of the invention provides that the torque reduction phase and / or the torque build-up phase are aborted if the driver, in particular by means of at least one accelerator pedal, carries out an abort action and / or a maximum duration is exceeded. Situations are conceivable in which the driver would like to accelerate the motor vehicle strongly again immediately after the braking process. However, if the setpoint torque is subjected to filtering during the torque reduction phase or the torque build-up phase, so that it is smaller than the specified torque, such an 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 currently present setpoint torque. For this purpose, the abort 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 passage, that is, a complete release and subsequent renewed actuation of the accelerator pedal, and / or a pumping process of the accelerator pedal. The latter is understood to mean a rapid, multiple actuation of the accelerator pedal. When the abort action is carried out, the torque reduction phase and / or the torque build-up phase are preferably also aborted if the minimum duration of the torque reduction phase has not yet been reached.

As an alternative or in addition, it can be provided that the torque reduction phase and / or the torque build-up phase are terminated when a maximum duration is reached or exceeded. Provision is therefore made for the torque reduction to be carried out only over a limited period of time, namely the maximum duration, because it is assumed that the driver can take over the control of the motor vehicle again after the maximum duration has elapsed. Therefore, when this condition occurs, the torque reduction phase and / or the torque build-up phase should be terminated and the setpoint torque should then be adjusted to or adjusted to the specified torque.

A further development of the invention provides that when the braking process is initiated, at least one reversible belt tensioner is activated for tightening a seat belt. The motor vehicle accordingly has the belt tensioner, which is designed to be reversible, that is to say allows multiple activation. The belt tensioners of all seat belts are preferably activated, but in particular only the belt tensioners that are assigned to seats that are actually occupied. By activating the belt tensioner, the seat belt is tightened and the driver or another occupant of the motor vehicle is held in his seat, so that displacement of the driver or 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 performing the method described above, the driver assistance device being provided for monitoring the surroundings of the motor vehicle and for initiating a braking process with a specific initial braking force corresponding to a maximum braking force of a braking system of the motor vehicle when there is a risk of collision with an obstacle . In this case, the driver assistance device should be designed to determine a deceleration braking force that is smaller than the initial braking force after the initial braking force has been reached and to continue the braking process with this in a deceleration phase, the deceleration phase being initiated immediately after an initial braking phase with a certain initial braking time and up to a Standstill of the motor vehicle is continued. The driver assistance device can also be provided to carry out further driving support measures. The method that is to be carried out by means of the driver assistance device can be developed in accordance with the above explanations.

• Figur ein Diagramm, in welchem eine Bremskraft und ein Sollbremsdruck über der Zeit aufgetragen sind.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without restricting the invention. It shows the only one

• FIG. 1 shows a diagram in which a braking force and a target braking pressure are plotted over time.

The figure shows a diagram in which two courses 1 and 2 in each case a braking force or braking deceleration a and a curve 3 a target brake pressure p _target are plotted over time t. The history 1 shows the braking deceleration, which is predetermined by a driver assistance device known from the prior art, during the course 2 reproduces the braking deceleration predetermined by a driver assistance device according to the invention. The target braking pressure of the course 3 corresponds to the braking deceleration according to the curve 2 . It should be pointed out again that the terms braking force and braking deceleration are used synonymously and are interchangeable. Instead of an initial braking force, one can therefore speak of the initial braking deceleration, without any other meaningful content arising.

For t t ₁ , a motor vehicle (not shown here) is in normal driving mode, with no braking process being carried out. The motor vehicle has the driver assistance device, which monitors the surroundings of the motor vehicle. If the environment monitoring detects an obstacle in the vicinity of the motor vehicle and there is a risk of collision with it, the driver assistance device initiates a braking process with a specific initial braking force a ₁ . The braking process begins at t = ti.

It can be seen that for both courses 1 and 2 the braking deceleration a increases with a first, smaller slope (seen in absolute values) _{between t 1} <t ≤ t _2. Between t ₂ <t t _{3 there} is a greater gradient in the braking deceleration. The braking deceleration remains for both courses between t ₃ <t ≤ t ₄ 1 and 2 equal and corresponds to a _I. The time span between t ₁ <t t ₄ is referred to as the initial braking _{duration Δt I of} an initial braking phase. Alternatively, only the time span in which the initial braking force is actually present, that is to say t ₃ <t t ₄ , can also represent the initial braking period.

The course known from the prior art 1 shows that the braking deceleration a is initially increased starting from a = 0 to a = a _I and then remains constant until the end of the braking process at t = t _8. Only after the braking process has ended does the braking deceleration drop to zero. The initial braking phase accordingly extends over the duration of the entire braking process.

According to the invention, that is, according to the course 2 , on the other hand, after the initial braking force has been reached, a deceleration phase is initiated which, in the exemplary embodiment shown here, is carried out between t ₄ <t t ₆ . In the deceleration phase, the braking process is continued for a deceleration braking time period Δt _v with a deceleration braking force, the deceleration braking force being smaller than the initial braking force. The deceleration phase is carried out until the motor vehicle comes to a standstill, so the braking process is continued until this point. The initial braking period, the initial braking force, the decelerating braking period and / or the decelerating braking force can be determined as a function of at least one operating variable of the motor vehicle. The operating variable is to be understood as meaning, for example, the speed of the motor vehicle, the distance between the motor vehicle and the obstacle and / or the relative speed of the motor vehicle with respect to the obstacle.

In the exemplary embodiment shown here, the motor vehicle is at a standstill _{at time t = t 6.} After the motor vehicle has come to a standstill at this point in time, the braking process should be continued in a holding phase with a holding brake force a _H over a holding brake time period Δt _H. The holding brake duration here corresponds to the period between t ₆ <t ≤ t ₇ . The holding braking force remains constant during the holding phase. The holding brake time is, for example, given constant.

The stopping phase is followed by a rolling phase of the motor vehicle. In this, the braking process is continued with a roll-on braking force over a roll-on braking time period Δt _A. The rolling braking force at the beginning of the rolling phase corresponds to the holding braking force or the holding braking force at the end of the holding phase. The roll-on braking force should now be reduced to zero _{over the roll-on braking time period Δt A.} For example, a linear reduction over time t can be provided. Alternatively, the roll-on braking force can also be determined as a function of a state variable of the motor vehicle. The state variable is in particular an inclination of the motor vehicle or a roadway on which the motor vehicle is located and / or a load state of the motor vehicle. After the roll-on phase, the braking process is ended, so that the braking deceleration from time t = ts is again equal to zero.

In contrast to the course 1 the braking force a enables the course according to the invention 2 the braking force a smoother deceleration of the motor vehicle, so that the driver has sufficient time after reaching a standstill to adapt to the changed driving situation and then to resume driving himself.

Claims (9)

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, if there is a risk of collision with an obstacle, initiates a braking process with a specific initial braking force corresponding to a maximum braking force of a braking system of the motor vehicle, characterized in that after the initial braking force has been reached, a deceleration braking force which is smaller than the initial braking force, determined and the braking process is continued in a deceleration phase with this, the deceleration phase being initiated immediately after an initial braking phase with a certain initial braking time and continued until the motor vehicle comes to a standstill. Procedure according to Claim 1 , characterized in that the initial braking period, the initial braking force, the decelerating braking period and / or the decelerating 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. Method according to one of the preceding claims, characterized in that after the motor vehicle has come to a standstill, the braking process is continued in a holding phase with a holding brake force over a holding brake period. Method according to one of the preceding claims, characterized in that after the motor vehicle has come to a standstill and / or after the stopping phase, the braking process is continued in a rolling phase with a rolling braking force over a rolling braking time, the rolling braking force being reduced to zero over the rolling braking time and over the Time is determined as a function of a state variable of the motor vehicle, in particular an inclination of the motor vehicle, a load condition and / or a direction of movement of the motor vehicle. Method according to one of the preceding claims, characterized in that at least during a torque reduction phase present at least during the deceleration phase, a target torque of a drive system of the motor vehicle is selected to be less than a specified torque of a driver of the motor vehicle, in particular equal to a minimum torque of the drive system. Method according to one of the preceding claims, characterized in that the torque reduction phase is followed by a torque build-up phase, during which the setpoint torque is steadily or gradually adjusted to the specified torque, with in particular the torque build-up duration of the torque build-up phase and / or the setpoint torque over time as a function of the State variable, preferably the inclination of the motor vehicle, the load condition and / or the direction of movement of the motor vehicle can be determined. Method according to one of the preceding claims, characterized in that the torque reduction phase and / or the torque build-up phase are terminated when the driver, in particular by means of at least one accelerator pedal, carries out an abort action and / or a maximum duration is exceeded. Method according to one of the preceding claims, characterized in that when the braking process is initiated, at least one reversible belt tensioner is activated for tightening a seat belt. Driver assistance device of a motor vehicle, in particular for performing the method according to one or more of the preceding claims, the driver assistance device being provided for monitoring the surroundings of the motor vehicle and for initiating a braking process with a specific initial braking force corresponding to a maximum braking force of a braking system of the motor vehicle when there is a risk of collision with an obstacle , characterized in that the driver assistance device is designed to determine a deceleration braking force that is smaller than the initial braking force after reaching the initial braking force and to continue the braking force in a deceleration phase with the latter, the deceleration phase being initiated immediately after an initial braking phase with a specific initial braking time period is continued until the motor vehicle comes to a standstill.

Images