Method and System for Determining a Usable Distance in Front of a Vehicle

Abstract

A method for determining a usable distance between a host vehicle and a moving object is provided. According to the method, a current obstacle free distance is detected in front of the host vehicle, wherein the current obstacle free distance is limited by a current position of the moving object, and a current velocity of the moving object is determined. An extension distance is estimated based on the current velocity of the moving object, and the usable distance is determined based on the current obstacle free distance and the extension distance.

Claims

1. A computer implemented method comprising: determining a usable distance between a host vehicle and a moving object by at least: detecting, via a detection system of the host vehicle, a current obstacle free distance in front of the host vehicle, wherein the current obstacle free distance is limited by a current position of the moving object; determining, via the detection system, a current velocity of the moving object; estimating via a prediction module of the host vehicle an extension distance based on the current velocity of the moving object; and determining, via the prediction module, the usable distance based on the current obstacle free distance and the extension distance.

2. The method according to claim 1, wherein estimating the extension distance comprises estimating by predicting an emergency braking distance and an emergency steering distance of the moving object.

3. The method according to claim 2, wherein estimating the extension distance comprises determining the extension distance as a minimum of the predicted emergency braking distance and of the predicted emergency steering distance.

4. The method according to claim 2, wherein estimating the emergency braking distance comprises predicting the emergency braking distance based on a predefined constant deceleration being applied to the moving object for a predetermined time period.

5. The method according to claim 4, wherein predicting the emergency braking distance further comprises predicting the emergency braking distance based on a predefined jerk being applied to the moving object before and after the predetermined time period, respectively, the jerk being defined as a rate of change per time period of the deceleration of the moving object.

6. The method according to claim 5, wherein the predefined jerk has a respective constant absolute value before and after the predetermined time period.

7. The method according to claim 6, wherein the respective constant absolute values of the jerk before and after the predetermined time period are equal.

8. The method according to claim 2, wherein estimating the emergency steering distance comprises estimating the emergency steering distance based on a predefined maximum lateral acceleration of the moving object.

9. The method according to claim 8, wherein estimating the emergency steering distance comprises estimating the emergency steering distance based on a predefined shape of a trajectory of the moving object during emergency braking.

10. The method according to claim 9, wherein the trajectory comprises two curves having a predefined radius of curvature being opposite to each other and being smoothly connected such that the trajectory has a unique tangent at a connection point of the two curves.

11. The method according to claim 2, wherein estimating the emergency steering distance comprises estimating the emergency steering distance with respect to a predicted position of the moving object at which the moving object will have moved half its width laterally during emergency steering.

12. A system, the system comprising: at least one processor configured to determine a usable distance between the system and a moving object by at least, the at least one processor configured as: a perception module configured to: detecting a current obstacle free distance in front of the system, wherein the current obstacle free distance is limited by a current position of the moving object; and detecting a current velocity of the moving object; and the at least one processor further configured as a prediction module configured to: predict an extension distance based on the current velocity of the moving object; and determine the usable distance based on the current obstacle free distance and the extension distance.

13. The system according to claim 12, further comprising: a detection system configured to detect the current obstacle free distance, the detection system comprising at least one of: a visual system; a RADAR system that is additionally configured to determine the current velocity of the moving object; and a LIDAR system that is additionally configured to determine the current velocity of the moving object.

14. The system according to claim 13, wherein the perception module is further configured to detect the current obstacle free distance in front of the system via the detection system.

15. The system according to claim 14, wherein the perception module is further configured to detect the current velocity of the moving object via the detection system.

16. A non-transitory computer readable medium comprising instructions that when executed by a processor of a computer system, configure the processor to determine a usable distance between a host vehicle and a moving object by at least: detecting a current obstacle free distance in front of the host vehicle, wherein the current obstacle free distance is limited by a current position of the moving object; and detecting a current velocity of the moving object; predicting an extension distance based on the current velocity of the moving object; and determining the usable distance based on the current obstacle free distance and the extension distance.

17. The non-transitory computer readable medium according to claim 16, wherein the instructions, when executed, configure the processor to estimate the extension distance by predicting an emergency braking distance and an emergency steering distance of the moving object.

18. The non-transitory computer readable medium according to claim 17, wherein the instructions, when executed, configure the processor to estimate the extension distance by determining the extension distance as a minimum of the predicted emergency braking distance and of the predicted emergency steering distance.

19. The non-transitory computer readable medium according to claim 17, wherein the instructions, when executed, configure the processor to estimate the extension distance by predicting the emergency braking distance based on a predefined constant deceleration being applied to the moving object for a predetermined time period.

20. The non-transitory computer readable medium according to claim 17, wherein the instructions, when executed, configure the processor to estimate the extension distance by estimating the emergency steering distance based on a predefined maximum lateral acceleration of the moving object.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Exemplary embodiments and functions of the present disclosure are described herein in conjunction with the following drawings, showing schematically:

[0034] FIG. 1 depicts a host vehicle, a target vehicle being detected as a moving object and the free space there between,

[0035] FIG. 2 depicts a schematic block diagram of a system for determining a usable distance between the host vehicle and the target vehicle,

[0036] FIG. 3 depicts an emergency braking maneuver of the target vehicle,

[0037] FIG. 4 depicts a braking profile for the emergency braking of the target vehicle, and

[0038] FIG. 5 depicts an emergency steering maneuver of the target vehicle.

DETAILED DESCRIPTION

[0039] FIG. 1 depicts a host vehicle 11 driving behind a target vehicle 13 in the same current lane 15 of a road. The host vehicle 11 includes a detection system 17 for monitoring the environment of the host vehicle 11. The detection system 17 may include a visual system and/or a radar system and/or a LIDAR system being implemented in the host vehicle 11.

[0040] Via the detection system 17, the existence and the current velocity of the target vehicle 13 are determined. Therefore, the target vehicle 13 may be regarded as a moving object in front of the host vehicle 11.

[0041] The detection system 17 of the host vehicle 11 is further configured to determine an obstacle free space 18 in front of the host vehicle 11. The obstacle free space 18 includes triangular shaped areas which are defined with respect to the host vehicle 11 and obstacles being detected by the detection system 17 in front of the host vehicle 11. From the obstacle free space 18, a minimum distance d.sub.FS with respect to the next obstacle is derived which may be regarded as current obstacle free distance 24 for the host vehicle 11.

[0042] According to the present disclosure, the host vehicle 11 also includes a system 21 (see FIG. 2) configured to determine a usable distance 28 between the host vehicle 11 and the target vehicle or moving object 13. The system 21 is able to additionally consider the movement of the target vehicle 13 when estimating a safety distance for the host vehicle 11 which corresponds to the usable distance 28. Based on the movement of the target vehicle 13, the system 21 is configured to estimate an extension 19 (see FIG. 1) for the obstacle free space 18 corresponding to an extension distance d.sub.ext, 27 for the obstacle free distance d.sub.FS, 24.

[0043] The usable distance 28 is therefore given as the sum of the current obstacle free distance d.sub.FS, 24 and the extension distance d.sub.ext, 27. The usable distance may be also regarded as an effective safety distance for the host vehicle 11 taking into account the movement of the target vehicle 13. For vehicles including conventional systems, the current obstacle free distance d.sub.FS, 24 is simply used as a safety distance for controlling advanced driver assistance systems (ADAS) including lane keeping assistance (LKA), lane change warning (LCW) and side collision warning (SCW). These systems are usually deactivated if the current obstacle free distance d.sub.FS, 24 falls below a certain predefined limit. In other words, conventional systems do not consider the movement of the target vehicle 13 for the decision whether to deactivate the above-mentioned driver assistance systems.

[0044] Due to the movement of the target vehicle 13, however, the driver assistance systems could still be activated in many situations although the obstacle free distance is already below the predefined value or “static safety distance”. According to the present disclosure, the current obstacle free distance d.sub.FS is therefore extended by taking the movement of the target vehicle 13 into account without sacrificing the safety requirements for the host vehicle 11.

[0045] FIG. 2 depicts a schematic diagram of the system 21 for determining the usable distance 28 between the host vehicle 11 and the target vehicle 13 (see FIG. 1) as a moving object in front of the host vehicle 11. The system 21 includes a perception module 23 and a prediction module 25. The perception module 23 is configured to detect the current obstacle free distance d.sub.FS, 24 in front of the host vehicle 11. The perception module 23 is further configured to determine a current velocity 26 of the moving object or target vehicle 13. The obstacle free distance 24 and the current velocity 26 of the target vehicle 13 are determined based on output data provided by the detection system 17 (see FIG. 1) of the host vehicle 11.

[0046] The prediction module 25 receives the current obstacle free distance 24 and the current velocity of the target vehicle 13 from the perception module 23 and is configured to estimate the extension distance 27 based on the current velocity 26 of the moving object or target vehicle 13. The estimation of the extension distance 27 will be described in context of FIGS. 3, 4 and 5 below. The prediction module 25 is further configured to determine the usable distance 28 based on the current obstacle free distance 24 and the extension distance 27. The usable distance 28 is depicted in FIG. 2 as output of the prediction module 25. The usable distance 28 is determined as the sum of the current obstacle free distance 24 and the extension distance 27. As mentioned above, the host vehicle 11 further includes advanced driver assistance systems (ADAS) which are depicted as 29 in FIG. 2. The usable distance 28 is provided by the prediction module 25 for the advanced driver assistance systems 29 in order to decide based on the usable distance 28 whether certain assistance systems like lane keeping assistance (LKA), lane change warning (LCW) and side collision warning (SCW) are to be activated or deactivated.

[0047] In order to estimate the extension distance 27 (see FIG. 1) two types of changes are taken into account for the state of motion of the target vehicle or moving object 13: i) emergency braking, i.e. a change of the state of motion of the target vehicle 13 in longitudinal direction along the current line 15 up to a velocity of almost zero of the target vehicle 13 (see FIG. 3), and ii) emergency steering, i.e. a change of the state of motion of the target vehicle 13 in lateral direction, e.g. in order to avoid a collision with an obstacle in front of the target vehicle 13 (see FIG. 5). Emergency braking and emergency steering may be regarded as “worst cases” for a change of the state of motion of the target vehicle 13, rendering the longest extension distance which still ensures safety for the host vehicle 11. Therefore, the extension distance is estimated as a minimum of an emergency braking distance 35 (see FIG. 3) and an emergency steering distance 51 (see FIG. 5) of the moving object or target vehicle 13 which are each predicted based on a model for the emergency braking and the emergency steering of the target vehicle 13, as will be described in context of FIG. 3 and FIG. 5, respectively.

[0048] FIG. 3 depicts a situation in which the target vehicle 13 performs emergency braking. At the beginning, the target vehicle 13 is at an observed position 31 which corresponds to the position as shown in FIG. 1 in front of the host vehicle 11. That is, the target vehicle 13 is detected by the host vehicle 11 at the position 31 and has a velocity 26 which is also detected by the host vehicle 11 via the detection system 17. In order to predict the emergency braking distance dEB, 35, it is assumed that the target vehicle 13 is at a position 33 after emergency braking and has a velocity of approximately zero.

[0049] In detail, the emergency braking distance 35 is predicted based on a deceleration profile for the target vehicle 13 as shown in FIG. 4 which describes the course of the acceleration during emergency braking. In FIG. 4, the acceleration in m/s2 is shown on the y-axis over time in s on the x-axis. The acceleration includes zero or negative values only in order to describe the deceleration of the target vehicle 13 during emergency braking.

[0050] At the beginning, e.g. during a reaction time of the driver of the target vehicle 13 of approximately one second, the acceleration is still zero, and thereafter a constant increase 41 of the deceleration (negative acceleration) is assumed up to a value of approximately −10 m/s2. The constant increase 41 of the deceleration corresponds to a constant jerk j start of the target vehicle 13 at the beginning of the emergency braking. After reaching the maximum deceleration of −10 m/s2, a constant maximum deceleration 43 is assumed for a predetermined time period 45. In the example of FIG. 4, the predetermined time period is about 5 seconds, i.e. from the instant of time at 2 seconds up to the instant of time at 7 seconds. Thereafter, i.e. at 7 seconds, a constant decrease 47 of a deceleration from −10 m/s2 to approximately zero is assumed. The constant decrease of deceleration corresponds again to a constant jerk j end of the target vehicle 13 at the end of the emergency braking.

[0051] Based on the deceleration profile as shown in FIG. 4, the emergency braking distance dEB, 35 is calculated as a sum of three partial distances as follows:

dext=dj_start+da_const+dj_end  (1)

[0052] d.sub.j.sub.start is the distance which the target vehicle or moving object 13 travels at the beginning of the emergency braking, i.e. during the reaction time and during the constant increase 41 of the deceleration corresponding to the constant jerk of the target vehicle 13. If an initial velocity yin of the target vehicle 13 is given, i.e. as detected by the detection system 17 of the host vehicle 11, the distance travelled by the host vehicle 13 during the beginning of the emergency braking is calculated as follows:

[00001]$\begin{array}{cc}{d}_{j_{\mathrm{start}}}=v_{in}\left(t_{\mathrm{react}}+t_{j_{start}}\right)+\frac{j_{start}{t}_{j_{start}}^3}{6}& \left(2\right)\end{array}$

[0053] t.sub.react and t.sub.j.sub.start are the reaction time and the elapsed time during the beginning of the emergency braking, respectively, wherein each is e.g. 1 second in the example of FIG. 4, and j.sub.start is the constant jerk corresponding to the constant increase 41 of deceleration as shown in FIG. 4.

[0054] The second distance d.sub.a.sub.const is travelled by the target vehicle 13 during a “constant deceleration phase”, i.e. during the predetermined time period 45 as shown in FIG. 4 in which the deceleration has the constant value 43. The second distance is calculated as follows:

[00002]$\begin{array}{cc}{d}_{a_{\mathrm{const}}}=\left(v_{in}+\frac{j_{start}{t}_{j_{start}}^2}{2}\right)t_{a_{const}}+\frac{a_{avg}{t}_{a_{const}}^2}{2}& \left(3\right)\end{array}$

[0055] t.sub.a.sub.const is the predetermined time period 45 for the constant deceleration phase, and aavg is the constant deceleration 43 during this time period 45 (see FIG. 4).

[0056] The third distance d.sub.j.sub.end is travelled by the target vehicle 13 during the end of emergency braking, wherein a constant jerk j.sub.end is assumed again corresponding to the constant decrease 47 of deceleration as shown in FIG. 4. The third distance is calculated as follows:

[00003]$\begin{array}{cc}{d}_{j_{\mathrm{end}}}=\left(v_{in}+\frac{j_{start}{t}_{j_{start}}^2}{2}+a_{avg}{t}_{a_{const}}\right)t_{j_{end}}+\frac{a_{avg}{t}_{a_{\mathrm{end}}}^2}{2}+\frac{j_{\mathrm{end}}{t}_{j_{\mathrm{end}}}^2}{6}& \left(4\right)\end{array}$

[0057] t.sub.j.sub.end is the elapsed time during the constant decrease 47 of the deceleration and j.sub.end is the constant jerk corresponding to this constant decrease 47 of deceleration.

[0058] FIG. 5 depicts the movement of the target vehicle 13 as assumed during emergency steering in order to predict the emergency steering distance d.sub.ES, 51. At the beginning of the emergency steering, the target vehicle 13 is at the observed position 31 corresponding again to the position of the target vehicle 13 as shown in FIG. 1 and as being detected by the detection system 17 of the host vehicle 11. At the end of the emergency steering, the host vehicle 13 is at a position 53 within an adjacent lane 55, i.e. adjacent to the current lane 15 in which the host vehicle 11 and the target vehicle 13 are currently moving (see FIG. 1).

[0059] In order to describe the emergency steering, a trajectory 57 is assumed for the movement of the target vehicle 13 wherein the trajectory 57 includes two curves having a certain constant absolute value for the radius of curvature R, but being opposite to each other regarding the sign. The two curves are connected smoothly such that the trajectory 57 has a unique tangent at a connection point 59 of the two curves.

[0060] For the movement of the target vehicle 13, a constant longitudinal velocity v.sub.long is assumed which corresponds to the current velocity of the target vehicle 13 as detected by the detection system 17 of the host vehicle 11 and to the initial velocity vin as assumed at the beginning of the emergency braking (see FIG. 3). Furthermore, a predefined maximum lateral acceleration a.sub.lat.sub.max is assumed for the target vehicle 13. That is, for the change of the state of motion of the target vehicle 13 in lateral direction the “worst case” is assumed by taking into account the maximum lateral acceleration the target vehicle 13 can achieve. Under these assumptions, the radius of curvature R for the two curves forming the trajectory 57 (see FIG. 5) is calculated as follows:

R=v.sub.long.sup.2/a.sub.lat.sub.max  (5)

[0061] The emergency steering distance 51 is calculated from the starting position 31 of the target vehicle 13 up to the position 59 at which the target vehicle 13 will have moved half its width laterally when moving to the adjacent lane 55 during emergency steering. The distance 51 up to the position 59 can be considered as free from obstacles for the movement of the host vehicle 11 (see FIG. 1) although the movement of the target vehicle 13 is deteriorated by the emergency steering.

[0062] In summary, by considering the possibility of emergency braking and emergency steering for the movement of the target vehicle 13, a minimum extension distance 27 for the current obstacle free distance is estimated based on the emergency braking distance 35 and the emergency steering distance 51 being predicted as described above. Since emergency braking and emergency steering are “worst cases” for the change of the state of motion of the target vehicle 13, the safety for the host vehicle 11 regarding collision avoidance is ensured in spite of the extension 27 of the current obstacle free distance 24. Due to this extension 27, a higher availability for safety functions is provided for the host vehicle 11, including e.g. lane keeping assistance (LKA), lane change warning (LCW), side collision warning (SCW), and for comfort functions like lane centering (LC).