EP3133573B1

EP3133573B1 - System and method for collision warning

Info

Publication number: EP3133573B1
Application number: EP15182052.9A
Authority: EP
Inventors: Adam ROHRBACHER
Original assignee: Harman Becker Automotive Systems GmbH
Current assignee: Harman Becker Automotive Systems GmbH
Priority date: 2015-08-21
Filing date: 2015-08-21
Publication date: 2020-01-08
Anticipated expiration: 2035-08-21
Also published as: EP3133573A1

Description

TECHNICAL FIELD

The disclosure relates to a system and a method for collision warning, in particular for a rear-end collision warning system in vehicles.

BACKGROUND

All vehicles today are equipped with brake lights, which provide a very simple collision warning system. The brake lights light up when the brake is applied. The driver of a successive car is thereby informed that the vehicle travelling in front is reducing its speed. The driver of the successive car then needs to estimate the speed and deceleration of the vehicle travelling in front, the remaining distance between the vehicles and the risk of a collision, for example, in order to avoid a collision.
Document DE 199 33 782 A1 discloses a method for avoiding rear-end collisions. A first vehicle monitors its rearward area and determines its own speed, the speed of a successive vehicle and a distance between the two vehicles. If a hazardous situation is detected, an optical or acoustical signal is generated to warn the driver of the successive vehicle. A hazardous situation is detected, for example, when the time interval until a presumable collision might happen falls below a threshold value.
Document US 2014/0049384 A1 discloses a method for warning a following motor vehicle through a motor vehicle travelling ahead, in which a distance between the motor vehicle travelling ahead and the motor vehicle following is measured and compared with a safety distance, which is dependent on a travelled speed of the motor vehicle travelling ahead and when the measured distance undershoots this safety distance, a warning signal is emitted by the motor vehicle travelling ahead to the following motor vehicle.
Document US 2006/0164221 A1 discloses a method for reducing the occurrence and severity of rear-end vehicle collisions. Two or more sensors are located on the front of or forward facing of the lead vehicle and on the rear of or rearward facing of the lead vehicle so as to provide data and information to a controller that processes the sensor information and generates signals to one or more light-emitting mechanisms mounted on or facing rearward of the lead vehicle that emit caution light to warn the driver of the following vehicle about the speed, distance, presence, approach, or other characteristics of nearby vehicles located behind, in front of, and including the lead vehicle.
Document DE 10 2012 219 572 A1 discloses an apparatus for a vehicle for presenting information to a following vehicle. The apparatus may be mounted at the rear or the side of the vehicle and is configured to present simple warning signs or even complex messages. The messages appear to be closer to the following vehicle than the vehicle driving in front. The distance from the vehicle driving in front from which the message is presented to the driver of the following vehicle may be dependent on the distance between the vehicles or on a deceleration of the vehicle driving in front. Sensor monitor the surrounding traffic and determine what might happen in the near future.

SUMMARY

The method described herein includes the following procedures: determining a danger value which is indicative of a potential collision of a first vehicle and a second vehicle; and generating a warning signal, if the danger value crosses a predefined threshold, wherein the danger value is determined by the first vehicle and the warning signal is perceivable to a driver of the second vehicle. The warning signal includes a visual warning signal that is projected onto the driving surface between the first vehicle and the second vehicle at a display distance behind the first vehicle, wherein the display distance is variable depending on the velocity of the first vehicle, the velocity of the second vehicle and the acceleration of the second vehicle, and corresponds to a distance between the first vehicle and the second vehicle at which a collision may still be prevented by the driver of the second vehicle by performing a braking maneuver.
A collision warning system comprises: a determination unit in a first vehicle, the determination unit being configured to determine a danger value which is indicative of a potential collision of the first vehicle and a second vehicle; and a signal unit in the first vehicle, the signal unit being configured to generate a warning signal, if the danger value crosses a predefined threshold, wherein the warning signal is perceivable to a driver of the second vehicle. The warning signal includes a visual warning signal that is projected onto the driving surface between the first vehicle and the second vehicle at a display distance behind the first vehicle, and the display distance is variable depending on the velocity of the first vehicle, the velocity of the second vehicle, and the acceleration of the second vehicle and corresponds to a distance between the first vehicle and the second vehicle at which a collision may still be prevented by the driver of the second vehicle by performing a braking maneuver.

BRIEF DESCRIPTION OF THE DRAWINGS

The method may be better understood with reference to the following description and drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.

Figure 1 is a schematic diagram illustrating an exemplary collision warning system.
Figure 2, including Figures 2A - 2D, illustrates in schematic diagrams an exemplary collision warning system in several situations of varying risk.
Figure 3, including Figures 3A - 3C, illustrates in schematic diagrams exemplary collision warning signals.
Figure 4 is a flowchart of an exemplary method for collision warning.
Figure 5 is a block diagram of an exemplary collision warning system.

DETAILED DESCRIPTION

Referring to Figure 1, the basic principle of an exemplary collision warning system is illustrated. A first vehicle 100 is driving on a road in a first direction. A second vehicle 110 is driving on the same road behind the first vehicle 100 in the same direction. The second vehicle 110 may have the same velocity as the first vehicle 100 or may be slower or faster than the first vehicle 100. If the second vehicle 110 is at a certain distance from the first vehicle 100 and has the same velocity or is slower than the first vehicle 100, there is generally no risk for a collision of the two vehicles 100, 110. If the second vehicle 110 is faster than the first vehicle 100 and the distance between the two vehicles 100, 110 falls below a certain value, there is an increased risk for a collision. The first vehicle 100 may determine the risk for a collision and, if there is an increased risk for a collision, the first vehicle 100 may generate a warning signal which is perceivable to the driver of the second vehicle 110.
To determine the risk of collision, a danger value may be determined which is indicative of a potential collision of the first vehicle 100 and the second vehicle 110. In the simplest case, the danger value may be proportional to the distance between the first vehicle 100 and the second vehicle 110, for example. A warning signal may then be generated if the distance, and therefore the danger value, falls below a certain threshold. The threshold may be dependent on a velocity of the first vehicle 100 and/or the second vehicle 110, as the braking distance generally depends on the velocity of a vehicle. For example, the threshold may have a higher value, if the velocity of the vehicles 100, 110 is high, meaning that a warning signal will be generated earlier when the distance between the vehicles 100, 110 is still rather long. The threshold may have a lower value, if the velocity of the vehicles 100, 110 is low, meaning that a warning signal will be generated later when the distance between the vehicles 100, 110 is shorter. The danger value, however, may not only depend on the distance between the vehicles, but also on the velocity and/or an acceleration of one or both of the vehicles.
The danger value may be determined for a present point of time t0 or may be predicted for a future point of time t0 + Δt, based on current parameters. For example, the danger value may be determined as a ratio of an estimated square of the velocity difference of the vehicles 100, 110 to a doubled pre-estimated remaining distance between the vehicles 100, 110 after a certain time period Δt. Doubling the weight of the pre-estimated remaining distance results in a physically correct function, which allows to determine a necessary pre-estimated deceleration (negative acceleration), that the second vehicle 110 needs to perform in order to avoid a collision with the first vehicle 100. The danger value x(Δt) in this example may then be determined according to the following equation: $x (Δt) = \frac{{[(v_{B (t 0)} + a_{B (t 0)} \times Δt) - v_{A (t 0)}]}^{2}}{2 \times [d_{AB (t 0)} - (v_{B (t 0)} - v_{A (t 0)} + 0,5 \times a_{B (t 0)} \times Δt) \times Δt]}$
Values that are sampled or determined at a particular moment t0 are identified with a corresponding subscript (t0) in equation (1) as well as in the following description. With v_B(t0) being the velocity of the second vehicle 110 at a first time instant t0, v_A(t0) being the velocity of the first vehicle 100 at the first time instant t0, a_B(t0) being the acceleration of the second vehicle 110 at the first time instant t0 and d_AB(t0) being the distance between the first vehicle 100 and the second vehicle 110 at the first time instant t0. The acceleration a_B(t0) of the second vehicle 110 may be positive (second vehicle is gaining speed) or negative (second vehicle is reducing speed/breaking). Equation (1) may be altered by further taking into consideration the acceleration (or deceleration) a_A(t0) of the first vehicle 100. This results in a higher sensitivity of the calculation, which may result in an earlier (or later) generation of the warning signal. The acceleration a_A(t0) of the first vehicle 100, however, is not considered in equation (1) above.
The danger value x(Δt) may be continuously predicted for one or more time instances (different values for Δt are applied). For example, the danger value x(Δt) may be determined with an update rate of 100 milliseconds. This, however, is only an example. The danger value x(Δt) may be determined more or less often. Each time the danger value x(Δt) is determined, three different estimated danger values x(Δt) may be determined, e.g. for Δt1 = 1s, Δt2 = 2s and Δt3 = 3s. The resulting danger value x(Δt) is then indicative of a potential collision of the vehicles 100, 110 in 1s, 2s or 3s. This is, however, only an example. Any other values may be selected for the time period Δt. In another example the danger value x(Δt) may be determined for Δt1 = 2s, Δt2 = 3.5s and Δt3 = 5s, for example. Assuming that at least one of the determined danger values x(Δt1), x(Δt2), x(Δt3) exceeds the threshold, a warning signal is generated earlier, if the values for Δt are chosen higher, which gives the driver of the second vehicle 110 more time to react.
If (v _B(t0) + a _B(t0) × Δt) - v _A(t0) > 0, the second vehicle 110 is closing in on the first vehicle 100.
If d _AB(t0) - (v _B(t0) - v _A(t0) + 0,5 × a _B(t0) × Δt) × Δt > 0, the remaining estimated distance between the first vehicle 100 and the second vehicle 110 after time Δt is greater than 0.
If the danger value x(Δt) is determined using equation (1), then a collision of the two vehicles 100, 110 is more likely, the higher the danger value x(Δt). For example, if the danger value x(Δt) is high at a time instant t0 + Δt, the velocity of the second vehicle 110 needs to be reduced more severely. If, on the other hand, the danger value x(Δt) at time instant t0 + Δt is low, a relatively slow reduction of the velocity of the second vehicle 110 might be sufficient to prevent a collision.
The warning signal may be a warning signal which is audible to the driver of the second vehicle 110. For example, the horn of the first vehicle 100 may be activated. This is, however, only an example. Any other audible warning signal may be generated, such as a siren, buzzer, beeper, chime or chirp, for example, which can be heard by the driver of the second vehicle 110. These are, however, only non-limiting examples.
The warning signal may be a visual warning signal 120 visible for the driver of the second vehicle 110, for example. A visual warning signal may be activated instead or additionally to an audible warning signal. The visual warning signal 120 may be a visible line that is projected onto the driving surface. This visible line may be red, for example, as red is the traditional color of warning and danger. This is, however, only an example. A line projected onto the driving surface may have any color or may change its color depending on the criticality of the situation. For example, the color may change from yellow to red, as the distance between the vehicles 100, 110 decreases and a collision of the vehicles 100, 110 becomes more likely. Such a visible line may be projected onto the driving surface using a laser or any other suitable projection device.
Referring to Figure 2, different conditions of an exemplary collision warning system are illustrated. In a first condition, illustrated in Figure 2A, no warning signal is generated. This is, for example, if the situation is classified as noncritical. The situation may be classified as noncritical, if the distance d_AB between the vehicles 200, 210 exceeds a certain value and/or the second vehicle 210 is driving at a slower or at the same velocity as the first vehicle 200. In such a case the second vehicle 210 does not draw nearer to the first vehicle 200 and there is no potential risk of a collision. If the danger value x(Δt) is determined according to equation (1) for three different time instances t0 + Δt1, t0 + Δt2, t0 + Δt3, it may be below a certain threshold x_ref for all predicted time instances t0 + Δt1, t0 + Δt2, t0 + Δt3, such that x(Δt1) - x_ref < 0, x(Δt2) - x_ref < 0 and x(Δt3) - x_ref < 0. In a second condition, illustrated in Figure 2B, the danger value x(Δt) may fall below the threshold for one of the predicted time instances, such that x(Δt1) - x_ref < 0, x(Δt2) - x_ref < 0 and x(Δt3) - x_ref > 0. This may be because the second vehicle 210 is moving faster than the first vehicle 200 and the distance d_AB between the second vehicle 210 and the first vehicle 200 falls below a predetermined value. The situation may be classified as dangerous and a warning signal 220 may be generated.
If the second vehicle 210 moves even faster than the first vehicle 200 and the distance d_AB reduces (rapidly), the danger value x(Δt) in a third condition may fall below the threshold for even more of the predicted time instances, such that x(Δt1) - x_ref < 0, x(Δt2) - x_ref > 0 and x(Δt3) - x_ref > 0. This is illustrated in Figure 2C. The warning signal 220 that is generated in the third condition may be different from the warning signal 220 that is generated in the second condition. This may be to increase the warning effect of the warning signal. For example, the warning signal 220 may change its color or may begin to flash. The third condition may be classified as a very dangerous traffic situation, for example.
In Figure 2D, a fourth condition is illustrated. The second vehicle 210 may still be moving faster than the first vehicle 200 and the remaining distance d_AB between the vehicles 200, 210 may be dangerously short, such that x(Δt1) - x_ref > 0, x(Δt2) - x_ref > 0 and x(Δt3) - x_ref > 0. The warning signal 220 that is generated in the fourth condition may again be different from the warning signal 220 that is generated in the second or third condition to further increase the warning effect of the warning signal 220. For example, the warning signal 220 may again change its color or may flash faster. Additionally, the brake lights 230 of the first vehicle 200 may begin to flash simultaneously and the cars horn may be activated. The fourth condition may be classified as a highly dangerous traffic situation, for example.
The threshold x_ref may be determined depending on the expected braking performance of an average car. Assuming that the braking distance of an average car driving at 100km/h is 40m, the threshold may be chosen to be x_ref = 9.64 m/s². The driver of the second vehicle 200 would then be warned early enough, so that a braking maneuver to avoid a collision would still be possible. This is, however, only an example. The threshold x_ref may be chosen to be any other lower or higher value. The braking distance of a motor truck at the same velocity is significantly longer. A collision warning system, therefore, may include a detection system, which is configured to detect whether a motor vehicle or a motor truck is driving behind the first vehicle 200. The threshold x_ref may then be adapted accordingly, depending on whether a motor truck or a motor vehicle is detected. For example, the front surface size of the second vehicle 210 may be measured, using a radar or any other suitable detection system. The front size of a motor truck is generally larger than the front size of a motor vehicle.
A visual warning signal may be implemented in different ways. As has already been explained by means of Figures 1 and 2, the warning signal may be a single collision warning line that is projected onto the driving surface between the first vehicle and the second vehicle. The collision warning line may be projected at a display distance d_CW(Δt) behind the first vehicle, as is illustrated in Figure 2. The display distance d_CW(Δt) may be determined in any suitable way. For example, the display distance d_CW(Δt) may be determined according to the following equation: $d_{CW} (Δt) = d_{AB (t 0)} - (v_{B (t 0)} - v_{A (t 0)}) \times (t_{SOS} - Δt) - 0,5 \times a_{B (t 0)} \times {(t_{SOS} - Δt)}^{2}$
With Δt_SOS being a pre-estimated remaining period starting at t0, which indicates a predicted time span after which the danger value x(Δt) will reach the threshold x_ref, if the conditions do not change. The remaining period t_SOS may be constantly calculated, considering the respective parameters, sampled at each sampling instant. To calculate the remaining period t_SOS, equation (1) may be used, replacing x(Δt) by x_ref and forming it to a quadratic equation (basic form: a×t_SOS ² + b×t_SOS + c = 0). Since quadratic equations generally have two solutions, the logically correct solution may be determined (e.g. t_SOS may not take on a negative value), by using an appropriate algorithm.. The display distance d_CW(Δt) according to equation (2) corresponds to the distance at which the driver of the second vehicle 210 still has time Δt left until a hard braking maneuver is necessary to prevent a collision with the first vehicle 200. The display distance d_CW(Δt) may be determined continuously. For example, the display distance d_CW(Δt) may be continuously determined for time instant t0 + Δt1 (e.g. Δt1 = 1s), meaning that the second vehicle 210 will touch the collision warning line in t_SOS - Δt1 and from that time instant has Δt1 left to react, e.g. by performing a hard braking maneuver. In the given example a first warning level (e.g. generating a single collision warning line) is activated if x(Δt3) - x_ref > 0. It follows that t_SOS is less than Δt3 from that time instance t0. The driver of the second vehicle 210, therefore, has a reaction time of almost Δt3 - Δt1 (in the given example Δt3 - Δt1 = 2s) from the time instance the collision warning line is first generated to actually touching the collision warning line (as illustrated in Figure 2D). The display distance d_CW(Δt) of the collision warning line 220 is variable depending on the velocity of the vehicles 200, 210 and the acceleration of the second vehicle 210. The collision warning line 220 provides an intuitive feedback for the driver of the second vehicle 210. If the driver of the second vehicle 210 does not decelerate sufficiently, the second vehicle 210 will get closer and closer to the collision warning line 220. If the second vehicle 210 decelerates sufficiently, the second vehicle 210 will recede from the collision warning line 220 until, finally, a safe distance is reached at which no warning signal is generated (as is illustrated in Figure 1).
Referring to Figure 2D, the collision warning line 220 may be projected directly in front of the second vehicle 210 in the fourth condition, irrespective of the determined display distance d_CW(Δt). The position of the collision warning line 220 may then only be dependent on the position of the second vehicle 210.
The warning signal 220 may be a single collision warning line as is illustrated by means of Figures 1 and 2 as well as Figure 3A. This, however, is only an example. The warning signal may also include more than one line. This is illustrated by means of Figure 3B. Still referring to Figure 3B, the warning signal may additionally include writing as well as signs, icons or illustrations. It is also possible that the warning signal includes only writing, only icons or only signs, for example. Additionally or alternatively, the brake lights of the first vehicle 200 may begin to flash, if the danger value x(Δt) crosses the predefined threshold x_ref, as has already been explained by means of Figure 2D. The brake lights of the first vehicle 200 may flash irrespective of whether the brake is pressed or not.
Referring to Figure 3C, a collision warning line 320a may be visible at a display distance d_CW(Δt1) from the first vehicle 300. An additional second line 320b may be displayed directly in front of the second vehicle 310. The second line 320b may, for example, be displayed during a highly dangerous traffic situation. Projecting two different lines 320a, 320b may illustrate more clearly that the second vehicle 310 is closing in on the first vehicle 300, as the driver of the second vehicle 310 can see the two lines 320a, 320b closing in on each other.
Referring to Figure 4, a method for collision warning includes determining a danger value, which is indicative of a potential collision of a first vehicle and a second vehicle (step 401). The danger value may be determined constantly by the first vehicle. If the danger value crosses a predefined threshold (step 402), a warning signal is generated (step 403). The warning signal may be perceivable to a driver of the second vehicle, as has already been described above.
Referring to Figure 5, a collision warning system includes a calculating unit 510. The calculating unit 510 is configured to determine a danger value, which is indicative of a potential collision of a first vehicle and a second vehicle. The collision warning system further includes a signal unit 520, which is configured to receive the danger value and to generate a warning signal, if the danger value crosses a predefined threshold. The danger value may be dependent on a distance between the first vehicle and the second vehicle, a velocity of the first vehicle, a velocity of the second vehicle and/or an acceleration of the second vehicle, for example. The collision warning system, therefore, may further include a detection unit 530, which is configured to detect parameters of the first and/or the second vehicle. For determining the distance d_AB between the first vehicle and the second vehicle, any suitable proximity sensor may be used. For example, a Doppler effect (e.g. radar), laser, photoelectric (e.g. infrared) or ultrasound sensor may be used. It is also possible to determine the distance between the vehicles by means of sensors including photographic or video cameras. The given examples, however, are only non-limiting examples.
The signal unit 520 does not need to be permanently active. Rather, a warning signal may be displayed only when a situation is classified as dangerous. In this way, traffic participants do not easily grow accustomed to the system. Drivers might more easily get used to a pure distance warning system which constantly displays information concerning a distance between successive vehicles. Drivers might be more likely to ignore displays that are constantly presented. As the collision warning system is intended to become active selectively, it is noticed as an unusual event by traffic participants and stimulates the traffic participants to evaluate a current situation. The collision warning line as has been explained above provides a temporal preview of what might happen if the distance between the vehicles is not increased.
The equations presented above are only examples. Any other algorithm may be used to evaluate the situation and predict a potential collision. The system may be implemented in motor vehicles, as well as motor trucks or motorcycles.
While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims their equivalents.

Claims

A method for collision warning, the method comprising:
determining a danger value (x(Δt)) which is indicative of a potential collision of a first vehicle (10) and a second vehicle (11); and

generating by the first vehicle a warning signal, if the danger value (x(Δt)) crosses a predefined threshold (xref), wherein

the danger value (x(Δt)) is determined by the first vehicle (10),

the warning signal is perceivable to a driver of the second vehicle (11),

the warning signal includes a visual warning signal that is projected onto the driving surface between the first vehicle (10) and the second vehicle (11) at a display distance (d_CW(Δt)) behind the first vehicle (10), and

the display distance (d_CW(Δt)) is variable depending on the velocity of the first vehicle (10), the velocity of the second vehicle (11) and the acceleration of the second vehicle (11) and corresponds to a distance between the first vehicle (10) and the second vehicle (11) at which a collision may still be prevented by the driver of the second vehicle (11) by performing a braking maneuver.
The method of claim 1, wherein the second vehicle (11) is driving behind the first vehicle (10) in the same direction.
The method of claim 1 or 2, wherein the danger value (x(Δt)) is dependent on at least one of
a distance between the first vehicle (10) and the second vehicle (11),
a velocity of the first vehicle (10),
a velocity of the second vehicle (11), and
an acceleration of the second vehicle (11).
The method of any of claims 1 to 3, wherein the danger value (x(Δt)) is constantly predicted for at least one future point of time (t0+Δt1, t0+Δt2, t0+Δtn).
The method of any of the preceding claims, further comprising determining the danger value (x(Δt)) as a ratio of an estimated square of the velocity difference of the first vehicle (10) and the second vehicle (11) to a pre-estimated remaining distance between the first vehicle (10) and the second vehicle (11).
The method of any of the preceding claims, wherein the warning signal further includes
an audible warning signal.
The method of any of claims 1 to 6, wherein the display distance is further dependent on
a distance between the first vehicle (10) and the second vehicle (11).
The method of any of claims 1 to 7, wherein the warning signal is projected in a first color, the color depending on the danger value (x(Δt)).
The method of any of claims 1 to 8, wherein the warning signal includes at least one of
a collision warning line,
an icon,
writing, and
an illustration.
The method of any of the preceding claims, further comprising setting the threshold dependent on at least one of
a distance between the first vehicle (10) and the second vehicle (11),
a velocity of the first vehicle (10),
a velocity of the second vehicle (11),
an acceleration of the second vehicle (11),
an expected braking performance of the second vehicle (11), and
an estimated braking distance of the second vehicle (11).
A computer program product that when executed in a computer causes the computer to perform the method of any of claims 1 to 10.
A collision warning system comprising
a determination unit (51) in a first vehicle (10), the determination unit (51) being configured to determine a danger value (x(Δt)) which is indicative of a potential collision of the first vehicle (10) and a second vehicle (11); and
a signal unit (52) in the first vehicle (10), the signal unit (52) being configured to generate a warning signal, if the danger value (x(Δt)) crosses a predefined threshold (xref), wherein
the warning signal is perceivable to a driver of the second vehicle (11),
the warning signal includes a visual warning signal that is projected onto the driving surface between the first vehicle (10) and the second vehicle (11) at a display distance (d_CW(Δt)) behind the first vehicle (10), and
the display distance (d_CW(Δt)) is variable depending on the velocity of the first vehicle (10), the velocity of the second vehicle (11) and the acceleration of the second vehicle (11) and corresponds to a distance between the first vehicle (10) and the second vehicle (11) at which a collision may still be prevented by the driver of the second vehicle (11) by performing a braking maneuver.
The collision warning system of claim 12, further comprising a detection unit (53), which is configured to detect at least one of
a distance between the first vehicle (10) and the second vehicle (11),
a velocity of the first vehicle (10),
a velocity of the second vehicle (11), and
an acceleration of the second vehicle (11).
The collision warning system of claim 13, wherein the detection unit (53) comprises a sensor including a photographic or video camera, a radar, a laser, an infrared or an ultrasound sensor.