DE102011115878B4 - Method and device for collision warning in motor vehicles - Google Patents

Abstract

Method for warning the driver of a motor vehicle of an imminent collision, a warning being issued to the driver and the time of the warning of the impending collision being a function of a driver reaction time, with a minimum and a maximum driver reaction time (t_rkt_min, t_rkt_max) being specified, driver alertness is determined by monitoring driver activity, a current driver reaction time (t_rkt_akt) is determined as a function of driver alertness, at time (t1) when driver activity is detected, the driver reaction time used to generate the warning is switched to the current driver reaction time (t_rkt_akt) if the current driver reaction time (t_rkt_akt) is less than the maximum driver reaction time (t_rkt_max), with the current driver reaction time (t_rkt_akt) being limited below by the minimum driver reaction time (t_rkt_min), a switchover to the current driver reaction time (t_rkt_akt) only takes place if the current Driver reaction time (t_rkt_akt) is less than half the sum of the maximum and minimum driver reaction time (t_rkt_max + t_rkt_min)/2, and after the driver reaction time has switched to the current driver reaction time (t_rkt_akt), the driver reaction time is returned to the maximum driver reaction time (t_rkt_max) via a predetermined return time (t_rf) is done.

Description

The invention relates to a method for warning a driver of a motor vehicle of an impending collision and a corresponding device.

The driver assistance systems that are becoming increasingly widespread in today's motor vehicles and contribute to increasing road safety and comfort include the collision warning system, in which vehicles driving ahead or other obstacles in front of the vehicle are detected using a sensor system, for example using a radar sensor and/or a monocular or binocular video system, are located. By evaluating corresponding measured data and variables derived therefrom, such as the measured distances and the relative speeds between the vehicle driving ahead and the driver's own vehicle, etc., situations are identified in which a collision would occur without the driver's intervention. The output of a suitable warning signal, which can be an acoustic, haptic and/or visual signal, then draws the driver's attention to the dangerous situation.

Such warning systems can make a significant contribution to traffic safety, but their acceptance has so far suffered from the fact that incorrect warnings occur relatively frequently, which the driver finds annoying. This can result in the driver no longer heeding the warnings or deactivating the system altogether.

In order to reduce such false alarms, disclosed DE 10 2006 043 676 A1 a driver assistance system with a warning function, which has an evaluation device, by means of which the driver's attention is evaluated on the basis of the driving dynamics of the vehicle and the warning function is suppressed if the driver's attention is detected.

Likewise revealed EP 1 750 236 B1 a method for controlling a driver assistance system, which can identify a dangerous situation based on a comparison of measurement data with predetermined limit values and, if it has identified such a dangerous situation, can output a warning signal. An additional control module is provided, which, depending on an input value that allows conclusions to be drawn about actions carried out by a driver, determines a characteristic value for an activity of the driver, determines a time mean value of this characteristic value (A) and, depending on this mean value, threshold calculated. The warning signal is suppressed if the indicator for the driver's activity exceeds this threshold value.

The pamphlet EP 0 605 902 A1 describes a device for determining the state of alertness of a driver of a vehicle by providing means for comparing this state with a reference value. If the driver's attention is low, a warning is generated to increase the driver's attention. The driver should respond to the warning by ending the warning. The reference value of the device for determining driver alertness is corrected as a function of the driver's response time to the warning.

• - einer Fahrweise eines Fahrzeugführers des nachfahrenden Fahrzeugs;
• - einer Fahrzeugkonfiguration des nachfahrenden Fahrzeugs;
• - einer Eigenschaft der befahrenen Fahrbahn; und
• - einer Fahreigenschaft des nachfahrenden Fahrzeugs.

The pamphlet DE 10 2008 019 519 A1 relates to a method for determining the safety distance and/or controlling the longitudinal vehicle speed of a vehicle following a vehicle in front. The safety distance of the following vehicle is determined as a function of at least two of the following parameters and/or the longitudinal vehicle speed of the following vehicle is regulated as a function of at least two of the following parameters:

• - A driving manner of a vehicle driver of the following vehicle;
• - a vehicle configuration of the following vehicle;
• - a characteristic of the driven lane; and
• - a driving characteristic of the following vehicle.

The pamphlet DE 102 38 324 A1 describes a method for monitoring a driver of a motor vehicle, in which, in particular, his state of alertness is differentiated between an active state of the driver and a resting state of the driver. The active state is ascertained as a function of the driver's interventions to drive the motor vehicle, the active state remaining ascertained only temporarily for a certain time after the driver has carried out the intervention. If there is no active state, the rest state of the driver is assumed. The occurrence of driver sleep is evaluated in terms of frequency and duration to provide a measure of driver alertness. In particular, at the beginning of a journey, initial values are determined for the duration or frequency of occurrence of the idle state, and limit values are calculated as a function of this. If at least one limit value for the frequency or the duration of the occurrence of the idle state is exceeded, warnings can be issued to the driver or entries can be made, for example, in a tachograph or a memory can be registered.

The pamphlet DE 10 2005 014 803 A1 relates to a method and a device for controlling a collision avoidance system for a motor vehicle. An obstacle distance between the motor vehicle and an obstacle in front of the motor vehicle is detected by an environment sensor, a minimum collision avoidance time is determined from the obstacle distance and a relative speed of the motor vehicle in relation to the obstacle by a computing unit, and the collision avoidance system outputs at least one first warning signal if the minimum collision avoidance time falls below a first threshold value which was pre-stored in a threshold memory. In order to take into account the driving behavior of each individual driver, a driver's reaction is detected by a reaction detection device, and the first threshold value in the threshold value memory is adjusted by an evaluation and adaptation device depending on the time between the warning signal and the driver's reaction.

As discussed above, collision avoidance systems are designed to warn the driver of impending rear-end collisions, and these systems have their greatest potential in situations where the driver is inattentive at the crucial moment and does not recognize the danger of the rear-end collision himself.

• - einerseits sollen unaufmerksame Fahrer sehr früh gewarnt werden, um eine Maximierung des Nutzens des Kollisionswarnsystems zu erzielen, und
• - andererseits sollen aufmerksame Fahrer sehr spät gewarnt werden, um keine unerwünschten, vom Fahrer als lästig empfundene Warnungen zu erhalten.

A well known dilemma of current collision avoidance systems is the following:

• - on the one hand, inattentive drivers should be warned very early in order to maximize the benefit of the collision warning system, and
• - On the other hand, attentive drivers should be warned very late in order not to receive any unwanted warnings that the driver finds annoying.

Therefore, today's collision warning systems use two fixed assumptions regarding the driver reaction times, with the help of which the warning time can be shifted from "early" to "late", which are referred to hereinafter simply as driver reaction times. A longer reaction time is assumed for inattentive drivers, for example t_Reakt_unaufm=1,200 ms, and a shorter reaction time for attentive drivers, for example t_Reakt_aufm=200 ms. Since the driver's attention cannot be determined directly, it is estimated with the help of the driver's activity, for example with the help of various influencing variables such as longitudinal acceleration, lateral acceleration, steering wheel angular velocity, steering wheel angular velocity gradient, accelerator pedal gradient, turn signal activation, etc.

• - für den Status „Fahrer aktiv“ wird die kürzere Fahrerreaktionszeit t_Reakt_aufm verwendet, und
• - für den Status „Fahrer nicht aktiv“ wird die größere Fahrerreaktionszeit t_Reakt_unaufm eingesetzt.

In the collision warning systems known today, there is therefore a binary switchover between the two values of the driver reaction times in the following manner:

• - the shorter driver reaction time t_Reakt_aufm is used for the "driver active" status, and
• - the larger driver reaction time t_Reakt_unaufm is used for the status "driver not active".

In order to avoid oscillation between the two states, the recognized status “driver active” is usually retained for a fixed period, for example t_Duration_aufm=5 seconds.

With this strategy, today's collision warning systems are on the "safe side", so to speak, in other words the system prefers to warn one time too late than one time too early, which means that if the warning is too late for the inattentive driver, automatic braking may occur.

The invention is therefore based on the object of optimizing the compromise between avoiding unwanted warnings and carrying out desired warnings in good time.

This object is achieved by the method for warning a driver of a motor vehicle of a collision with the features of claim 1 and a corresponding collision warning system with the features of claim 6. Preferred embodiments of the invention are the subject matter of the dependent claims.

• - sind eine minimale und eine maximale Fahrerreaktionszeit vorgegeben,
• - erfolgt eine Bestimmung einer Fahreraufmerksamkeit durch eine Überwachung der Fahreraktivität,
• - wird eine aktuelle Fahrerreaktionszeit als Funktion der Fahreraufmerksamkeit bestimmt, und
• - wird zum Zeitpunkt einer erkannten Fahreraktivität die zur Erzeugung der Warnung verwendete Fahrerreaktionszeit auf die aktuelle Fahrerreaktionszeit umgeschaltet, wenn die aktuelle Fahrerreaktionszeit kleiner als die maximale Fahrerreaktionszeit ist, wobei die aktuelle Fahrerreaktionszeit nach unten durch die minimale Fahrerreaktionszeit begrenzt ist, erfolgt eine Umschaltung auf die aktuelle Fahrerreaktionszeit nur, wenn die aktuelle Fahrerreaktionszeit kleiner als die halbe Summe aus maximaler und minimaler Fahrerreaktionszeit ist, und erfolgt nach erfolgter Umschaltung der Fahrerreaktionszeit auf die aktuelle Fahrerreaktionszeit eine Rückführung der Fahrerreaktionszeit auf die maximale Fahrerreaktionszeit über eine vorgegebene Rückführzeit.

In the method according to the invention for warning the driver of a motor vehicle of an imminent collision, a warning being issued to the driver and the time of the warning of the impending collision being a function of a driver's reaction time,

• - a minimum and a maximum driver reaction time are specified,
• - driver alertness is determined by monitoring driver activity,
• - a current driver reaction time is determined as a function of the driver's attention, and
• - the driver reaction time used to generate the warning is switched to the current driver reaction time at the time when driver activity is detected, if the current driver reaction time is less than the maximum driver reaction time, with the current driver reaction time being limited by the minimum driver reaction time, there is a switchover to the current one Driver reaction time only if the current driver reaction time is less than half the sum of the maximum and minimum driver reaction time, and after the driver reaction time has switched to the current driver reaction time, the driver reaction time is returned to the maximum driver reaction time via a specified return time.

In this way, the driver's reaction time used in the collision warning system can also assume intermediate values, so that a situationally adapted warning time can be implemented that optimizes the compromise between "avoiding unwanted warnings" and "timely implementation of desired warnings". Consequently, the current driver reaction time can assume all values between the specified minimum and the specified maximum driver reaction time.

Since the switchover to the current driver reaction time only takes place if the current driver reaction time is less than half the sum of the minimum and maximum driver reaction time, it is determined in this way that the current driver reaction time determined from the driver activities is at least in the lower half of the the interval formed by the minimum and the maximum driver reaction time.

Furthermore, after the driver's reaction time has been switched over to the current driver's reaction time, the driver's reaction time is returned to the maximum driver's reaction time via a predefined return time. It is expedient here for the time-based feedback to the maximum driver reaction time to take place along a linear function or along a non-linear function, since driver activity observed at a point in time does not necessarily mean that the driver is attentive for a fixed period of time. Therefore, the reduced response time is preferably returned to the maximum value continuously over time. The time profile can be in the form of a ramp with a fixed gradient or along a time-continuous filter, i.e. non-linear.

Preferably, after switching the driver's reaction time to the current driver's reaction time, this is retained for a specified holding time or returned to an intermediate value for the specified holding time along a ramp with a slight incline. After the holding time has expired, the driver's reaction time is returned to the maximum driver's reaction time over the remaining time of the return time. The hold time is shorter than the return time, the remaining time is formed by the difference between the specified return time and hold time, and the intermediate value is the sum of the current driver reaction time and a specified increase variable. The increase variable can be a predefined absolute value or a predefined relative value, for example a percentage of the current driver reaction time.

The driver reaction time is preferably maintained for a predefined holding time or returned to an intermediate value for the holding time only if the determination of the driver activity is based on driver actions with a temporal forecast. In this case, driver actions with a time perspective are preferably implemented by changing the gas pedal and activating the turn signal.

This preferred embodiment is based on the finding that there are differences between the various influencing variables for estimating the reaction time. The driver actions "accelerator pedal change" and "turn signal actuation" are activities that are associated with a time perspective, since the driver activates the turn signal because he is planning a lane change, while the actions "lateral acceleration" and "steering wheel angle speed" are activities of the moment. As an example, the driver steers to now change direction.

Therefore, the current driver reaction time for the two driver actions “accelerator pedal change” and “turn signal actuation” is preferably maintained over a certain period of time, or returned with a very flat ramp, before a complete return to the maximum value takes place.

• - eine Einrichtung zur Bestimmung einer Kollisionsgefährdung,
• - eine Warneinrichtung zur Erzeugung und Ausgabe einer Warnung als Funktion der Kollisionsgefährdung,
• - eine Einrichtung zur Bestimmung einer aktuellen Fahrerreaktionszeit als Funktion der Fahreraufmerksamkeit, und
• - einen Vergleicher zum Vergleichen der aktuellen Fahrerreaktionszeit mit einer vorgegebenen minimalen und maximalen Fahrerreaktionszeit, wobei
• - die Warneinrichtung die Warnung als Funktion der aktuellen Fahrerreaktionszeit erzeugt, wenn die aktuelle Fahrerreaktionszeit kleiner als die maximale Fahrerreaktionszeit ist, wobei die aktuelle Fahrerreaktionszeit nach unten durch die minimale Fahrerreaktionszeit begrenzt ist, wobei die Warneinrichtung nach erfolgter Umschaltung der Fahrerreaktionszeit auf die aktuelle Fahrerreaktionszeit eine Rückführung der Fahrerreaktionszeit auf die maximale Fahrerreaktionszeit über eine vorgegebene Rückführzeit durchführt.

The collision warning system according to the invention, which is set up and designed to carry out the method for warning the driver of a motor vehicle of an imminent collision, comprises:

• - a device for determining a risk of collision,
• - a warning device for generating and issuing a warning as a function of the risk of collision,
• - a device for determining a current driver reaction time as a function of the driver's attention, and
• - A comparator for comparing the current driver reaction time with a predetermined minimum and maximum driver reaction time, where
• - the warning device generates the warning as a function of the current driver reaction time if the current driver reaction time is less than the maximum driver reaction time, the current driver reaction time being limited downwards by the minimum driver reaction time, the warning device providing feedback after the driver reaction time has switched to the current driver reaction time the driver's reaction time to the maximum driver's reaction time over a predetermined return time.

In this case, warnings can be implemented by warning signals, such as acoustic, haptic and/or visual signals to the driver.

Driver alertness can preferably be determined from driver activities.

• 1 Beispiele von Fahrsituationen mit unerwünschten Warnungen bei bekannten Kollisionswarnsystemen,
• 2 den zeitlichen Verlauf der binären Umschaltung der Fahrerreaktionszeit gemäß dem Stand der Technik,
• 3 den zeitlichen Verlauf der Fahrerreaktionszeit gemäß einer ersten Strategie, und
• 4 den zeitlichen Verlauf der Fahrerreaktionszeit gemäß einer zweiten Strategie.

A preferred embodiment of the invention is explained below with reference to the drawings. while showing

• 1 Examples of driving situations with unwanted warnings in known collision warning systems,
• 2 the time course of the binary switching of the driver reaction time according to the prior art,
• 3 the driver reaction time over time according to a first strategy, and
• 4 the driver reaction time over time according to a second strategy.

1 shows a schematic representation of several driving situations in which conventional collision warning systems can result in unwanted collision warnings, although the driver is in control of what is happening. So in the left part of the 1 the situation of a narrow swerving of an own vehicle 1 is shown, which swerves behind a preceding vehicle 2 and changes lanes, with the arrows 3 representing the driving maneuver of the own vehicle. Since a collision warning system arranged in one's own vehicle 1 only detects the approach at a relatively high relative speed, the collision warning system interprets the driving situation as a risk of collision and triggers an unnecessary alarm. If the collision warning system is also equipped with automatic partial braking, automatic braking can occur in extreme cases, which could endanger the driver's own vehicle 1 .

In the middle part of 1 the case is shown in which the preceding vehicle 2 turns along the arrow 4 into a side street and slows down its speed. This can lead to the driver's own vehicle 1 driving into the vehicle 2 driving in front, as a result of which an unnecessary warning signal can be triggered due to the relative speed and the decreasing distance between the vehicles.

In the right part of 1 the situation is shown when vehicle 2 traveling ahead in the direction of arrow 4 brakes and vehicle 1 following in the same direction 3 drives up. Due to the short-term increase in the relative speed between the two vehicles 1 and 2 and the decreasing distance between the vehicles, a warning signal can be triggered even though the driver of the vehicle's own vehicle 1 has the situation under control.

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2 shows the warning behavior of a collision warning system according to the prior art, showing the time course of the driver's reaction time used to trigger the warning. Two driver reaction times are used in the algorithms used, namely a longer driver reaction time t_rkt_max for the inattentive driver and a shorter driver reaction time t_rkt_min for the attentive driver. For safety reasons, the collision warning system is normally operated with the longer driver reaction time t_rkt_max, in other words, an inattentive driver is assumed and the warning signal is triggered as a function of the longer driver reaction time. Because driver alertness cannot be directly determined, various driver activities are monitored and evaluated to arrive at an assessment of driver alertness. Such driver activities are, for example, the longitudinal acceleration of the vehicle, the lateral acceleration of the vehicle, the steering wheel speed or the steering wheel gradient, the accelerator pedal gradient and the turn signal activation. If the assessment of the driving activities reveals an active driver, the collision warning system switches to the short driver reaction time t_rkt_min in binary form and the driver is therefore warned later. The recognized driver status “driver active” is usually maintained for a fixed period t_d. After the holding period has elapsed, the system switches again to the longer driver reaction time t_rkt_max. There is therefore a binary switching between the two fixed driver reaction times. Orders of magnitude for the times are: $$\begin{array}{lll}\text{large driver reaction time t}\_\text{rkt}\_\text{Max}\hfill & =\hfill & 1200\text{ms}\hfill \\ \text{short driver reaction time t}\_\text{rkt}\_\text{at least}\hfill & =\hfill & 200\text{ms}\hfill \\ \text{holding period t}\_\text{i.e}\hfill & =\hfill & 5000\text{ms}\hfill \end{array}$$

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3 shows the first embodiment of the invention as a time profile of the driving reaction time t_rkt. Here, too, the initial state of the system is the greater driver reaction time t_rkt_max. In other words, an inattentive driver is assumed in the initial state and warnings are given to the driver in the collision warning system at an early point in time using the large driver reaction time t_rkt_max.

If the system now detects a corresponding driver activity at a point in time t1, from which it can be concluded that the driver is attentive, a current driver reaction time t_rkt_akt is determined as a function of the driver activity and the system is switched to the current driver reaction time. The boundary conditions apply that the current driver reaction time must be less than the maximum driver reaction time t_rkt_max and that the current driver reaction time t_rkt_akt is limited downwards by the minimum driver reaction time t_rkt_min. As a result of this measure, a shorter driver reaction time adapted to the current driver activity is used for the collision warning, ie the driver is warned of an imminent collision at a later point in time. Since a driver activity observed at a point in time t1 does not necessarily mean that the driver is attentive for a fixed period of time, the reduced current driver reaction time is continuously returned to the maximum value t_rkt_max over time. A linear ramp A or a filter B can be used for this. At time T2, the maximum driver reaction time t_rkt_max is used again. The return time t_rf required to return the driver reaction time from the current driver reaction time t_rkt_akt to the maximum reaction time t_rkt_max can either be preset so that the slope of ramp A or filter B is a function of the return time t_rf. However, the slope of the ramp A or of the filter B can also be specified, as a result of which the return time t_rf is a function of the current driver reaction time t_rkt_akt and the slope. The orders of magnitude of the driver reaction times and the return time are within the in 2 explained areas.

4 shows a further embodiment of the method according to the invention, which is based on differences in the various influencing variables that are used to estimate the driver's reaction time t_rkt. The driver's actions "accelerator pedal change" and "turn signal actuation" are activities of the driver with a time perspective. The driver activates the turn signal because he is planning to change direction and he changes the accelerator pedal position because he wants to accelerate or decelerate. It can therefore be assumed with these activities that the driver will still be active for a certain period of time. In contrast, driver actions such as "lateral acceleration" or "steering wheel angle speed" are driver activities of the moment. The driver steers to change direction now.

Therefore, as in 4 is shown, the reduction in the driver reaction time made at time t1 to the current driver reaction time t_rkt_akt is maintained for a certain holding period t_hlt or returned to an intermediate value t_rkt_zw via a flat ramp C if the determination of driver attention is based on driver activities with a time perspective, such as the " Accelerator pedal change” or the “turn signal actuation”.

The intermediate value t_rkt_zw is calculated from the current driver reaction time t_rkt_akt using an increase variable delta as follows: $$\text{t}\_\text{rkt}\_\text{between}=\text{t}\_\text{rkt}\_\text{act}+\text{delta}.$$

The increase delta can be a fixed value or a percentage of the current driver reaction time, for example 5 percent of the current driver reaction time.

After the holding period t_hlt has elapsed, the driver reaction time t_rkt is returned to the maximum value t_rkt_max along a ramp A or a non-linear function such as a filter B, so that the system again issues early warnings from time t2. The driver reaction time t_rkt is returned to the maximum value t_rkt_max along the ramp A or the filter B in comparison to the situation in FIG 3 with a greater gradient in order to keep the duration of the feedback t_rf approximately constant. For the duration of the return t_rf otherwise apply with regard to 3 made comments.

Reference List

1

own vehicle

2

vehicle ahead

3

Directional arrow own vehicle

4

Directional arrow for the vehicle ahead

t

Time

t1

first time

t2

second point in time

t_rkt_min

minimum driver reaction time

t_rkt_max

maximum driver reaction time

t_rkt

driver reaction time

t_rkt_akt

current driver reaction time

t_react_zw

intermediate value

t_d

fixed holding time

t_rf

return time

t_hlt

holding period

delta

growth

A

linear feedback

B

nonlinear feedback

C

Hold

Claims (7)

A method for warning the driver of a motor vehicle of an impending collision, with a warning being issued to the driver and the time of the warning of the impending collision being a function of a driver reaction time, with a minimum and a maximum driver reaction time (t_rkt_min, t_rkt_max) being specified, driver alertness is determined by monitoring driver activity, a current driver reaction time (t_rkt_akt) is determined as a function of the driver's attention, at the time (t1) of a recognized driver activity, the driver reaction time used to generate the warning is switched to the current driver reaction time (t_rkt_akt) if the current driver reaction time (t_rkt_akt) is less than the maximum driver reaction time (t_rkt_max), the current driver reaction time (t_rkt_akt) after is limited below by the minimum driver reaction time (t_rkt_min), a switchover to the current driver reaction time (t_rkt_akt) only takes place if the current driver reaction time (t_rkt_akt) is less than half the sum of the maximum and minimum driver reaction time (t_rkt_max + t_rkt_min)/2, and after the driver reaction time has switched to the current driver reaction time (t_rkt_akt), the driver reaction time is returned to the maximum driver reaction time (t_rkt_max) via a predetermined return time (t_rf). procedure after claim 1 , characterized in that the temporal feedback to the maximum driver reaction time (t_rkt_max) takes place along a linear function (A) or along a non-linear function (B). procedure after claim 1 , characterized in that after switching the driver's reaction time to the current driver's reaction time (t_rkt_akt), this is retained for a specified holding time (t_hlt) or returned along a ramp with a slight incline to an intermediate value (t_rkt zw) for the specified holding time (t_hlt), before a return to the maximum driver reaction time (t_rkt_max) takes place via the remaining time. procedure after claim 3 , characterized in that the retention of the current driver reaction time (t_rkt_akt) for the holding time (t_hlt) or its return to an intermediate value (t_rkt zw) for the holding time (t_hlt) is only carried out if the determination of the driver's activity on driver actions with a time perspective based. procedure after claim 4 , characterized in that the driver's actions are implemented with a time perspective by changing the gas pedal and turning the turn signal. Collision warning system for warning the driver of a motor vehicle of an impending collision, the collision warning system being set up and designed to carry out the method according to one of the preceding claims, having a device for determining a collision risk, a warning device for generating and issuing a warning as a function of the risk of collision, a device for determining a current driver reaction time (t_rkt_akt) as a function of the driver's attention, and a comparator device for comparing the current driver reaction time (t_rkt_akt) with a predetermined minimum and maximum driver reaction time (t_rkt_min, t_rkt_max), wherein the warning device outputs the warning as a function of the current driver reaction time if the current driver reaction time (t_rkt_akt) is less than the maximum driver reaction time (t_rkt_max), the current driver reaction time (t_rkt_akt) being limited downwards by the minimum driver reaction time (t_rkt_min), the warning device after switching the driver's reaction time to the current driver's reaction time (t_rkt_akt), the driver's reaction time is fed back to the maximum driver's reaction time (t_rkt_max) via a predetermined feedback time (t_rf). collision warning system claim 6 , characterized in that the driver's attention is determined from the driver's activities.

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