Patent Description:
Advanced driver assistance systems (ADAS) have been developed to support drivers in order to drive a host vehicle more safely and comfortably. These systems comprise, for example, active control of Electronic Power Assistance Steering (EPAS) like Lane Keeping Assistance (LKA), Lane Change Warning (LCW) and Side Collision Warning (SCW).

Due to safety reasons, an obstacle free distance or space in a lane in front of the host vehicle needs to be above a certain predetermined limit. The free distance or space in front of the host vehicle is usually determined by visual and/or radar systems which are installed on the host vehicle.

When determining the free distance or space, the shortest distance to an obstacle is usually detected without considering whether the obstacle or object in front of the vehicle is moving or stationary. For example, if the detected obstacle is a further vehicle moving in the same lane in front of the host vehicle with at least the same velocity, the actual safety distance required for the assistance systems to perform properly is longer than the predetermined safety distance considering stationary objects only. This is due to the fact that the further vehicle will not be at the detected position when the host vehicle will arrive there.

As a consequence, the assistance systems will not be enabled (or will be deactivated if they were enabled before) if the detected obstacle free distance or space is smaller than the predetermined limit, although it is actually not required to set the assistance systems aside for safety reasons. Instead, the safety of the host vehicle could be improved in such a situation with respect to an environment comprising moving objects if the assistance systems mentioned above were activated. This holds true although the actual detected obstacle free distance might be somewhat below the predetermined safety distance taking into account stationary objects only. In other words, it may be more dangerous to leave these assistance systems in a deactivated state than having such systems activated in a surrounding in which moving objects slightly undershoot the predetermined safety distance.

<CIT> discloses a method and a system comprising the features according to the respective preamble of claims <NUM> and <NUM>.

<CIT> discloses a method for monitoring an environment of a vehicle. A target object located in the environment of the vehicle is assessed regarding endangerment by observing how another vehicle passes the target object.

<CIT> discloses a method for determining a situation requiring emergency braking of a vehicle.

Accordingly, there is a need to provide a method and a system for determining an actually usable free distance with respect to a moving object in front of a host vehicle.

The present invention provides a computer implemented method, a computer system and a non-transitory computer readable medium according to the independent claims. Embodiments are given in the subclaims, the description and the drawings.

In one aspect, the present invention is directed at a computer implemented method for determining a usable distance between a host vehicle and a moving object. According to the method, a current obstacle free distance is detected in front of the host vehicle via a detection system 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 via the detection system. An extension distance is estimated based on the current velocity of the moving object via a prediction module of the host vehicle, and the usable distance is determined based on the current obstacle free distance and the extension distance via the prediction module.

The usable distance may be regarded as an effective safety distance in order to decide whether assistance systems like lane keeping assistance (LKA), lane change warning (LCW) and side collision warning (SCW) are to be activated (or should remain activated). The current obstacle free distance which takes into account the "static situation" only at the current instant of time is prolonged by the extension distance which is based on the movement of the vehicle, i.e. based on its current velocity. For example, the usable distance may be the sum of the current obstacle free distance and the extension distance.

Due to the prolongation of the current obstacle free distance by the extension distance, the assistance systems mentioned above will be available for supporting a driver of the host vehicle in situations in which these systems would not be available if the extension distance were not taken into account. Conversely, unnecessary cycles of deactivation and activation can be avoided for the assistance systems.

Therefore, the safety of a driver and further occupants in the host vehicle is improved by increasing the availability of assistance systems in an environment comprising moving objects. However, the dependence of the extension distance on the current velocity of the moving object may be defined in such a manner that a certain safety margin is not exceeded which takes into account sudden changes of the movement (e.g. due to braking and/or steering) of the object under consideration.

The extension distance is estimated by predicting an emergency braking distance and an emergency steering distance of the moving object, wherein the extension distance may be determined as a minimum of the predicted emergency braking distance and the predicted emergency steering distance. Therefore, emergency braking and emergency steering are taken into account when estimating the extension distance in order to consider the "worst case" for changing the movement of the object. In other words, the current obstacle free distance is prolonged by the extension distance in order to yield the usable distance without sacrificing the safety for the host vehicle since emergency braking and emergency steering of the object (e.g. a preceding vehicle) are taken into account for estimating and therefore restrict the extension distance. The extension distance may be determined as a minimum of the two predicted distances since emergency braking and emergency steering need to be considered independently and it is not known in advance which of these will have the stronger effect.

The emergency braking distance may be predicted based on a predefined constant deceleration which is applied to the moving object for a predetermined time period. Therefore, the emergency braking distance is predicted based on a straightforward model assuming a constant deceleration of the moving object.

Hence, the prediction or estimation of the safety distances to ensure a proper performance of the assistance systems is facilitated. The predefined constant deceleration may be based on empirical values, e.g. being determined for the emergency braking behavior of known vehicles. In addition, the value for the constant deceleration may depend on the type and/or size of the moving object which is detected in front of the host vehicle. In this case, the constant deceleration may be selected from a group of predefined values including a respective value for each type and/or range for the size of the moving object.

The emergency braking distance may further be predicted based on a predefined jerk being applied to the moving object before and after the predetermined time period, respectively, wherein the jerk is defined as a rate of change per time period of the deceleration of the moving object. The predefined jerk may be a respective constant absolute value before and after the predetermined time period, and these respective constant absolute values for the jerk may be equal.

The predefined jerk may be adapted to the constant deceleration during the predetermined time period such that the jerks describe an increase of the deceleration before the predetermined time period and a decrease of deceleration after the predetermined time period. By using the predefined jerks the straightforward model for describing the emergency braking is refined, wherein predefining the jerk before and after the predetermined time period may also be based on empirical values. Hence, the execution of the method may again be facilitated by using a straightforward model for emergency braking including predefined values.

The emergency steering distance of the moving object may be predicted based on a predefined maximum lateral acceleration of the moving object. That is, due to the emergency steering distance a sudden movement of the object in lateral direction is taken into account, i.e. in a direction perpendicular to the current moving direction of the host vehicle within a lane. The predefined maximum lateral acceleration may describe the "worst case" for the sudden movement of the object in the lateral direction. Therefore, the emergency steering distance may correspond to a safety margin for the extension distance when considering the lateral movement of the object.

The emergency steering distance may further be predicted based on a predefined shape of a trajectory of the moving object during emergency braking. In detail, the trajectory may include 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. Such a predefined shape for the trajectory of the moving object may be regarded as a straightforward model for the movement of the object which may facilitate the prediction and the estimation of the safety distances required for the assistance systems.

The emergency steering distance may be determined 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. The predicted position of the laterally moving object during emergency steering may therefore define a safety margin again for estimating the extension distance, in this case regarding the lateral movement. It is assumed that the moving object will not be a risky obstacle after the host vehicle will have covered the current obstacle free distance plus the emergency steering distance determined based on the "half width" of the moving object performing emergency steering. Hence, the safety of the host vehicle will not be sacrificed in favor of extending the current obstacle free distance.

In another aspect, the present invention is directed at a system for determining a usable distance between a host vehicle and a moving object, said system comprising a perception module and a prediction module. The perception module is configured to detect a current obstacle free distance in front of the host vehicle via a detection system of the host vehicle, wherein the current obstacle free distance is limited by a current position of the moving object, and to determine a current velocity of the moving object via the detection system. The prediction module is configured to predict an extension distance based on the current velocity of the moving object, and to determine the usable distance based on the current obstacle free distance and the extension distance.

As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a combinational logic circuit, a field programmable gate array (FPGA), a processor (shared, dedicated, or group) that executes code, other suitable components that provide the described functionality, or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor.

In summary, the system according to the invention comprises two modules for performing the steps as described above for the corresponding method. Therefore, the benefits and advantages as described above for the method are also valid for the system according to the disclosure.

The detection system of the host vehicle may comprise a visual system and/or a RADAR system and/or a LIDAR system being configured to detect the current obstacle free distance, wherein the RADAR system and/or the LIDAR system may additionally be configured to determine the current velocity of the moving object.

The visual system, the RADAR system and/or the LIDAR system may already be implemented in the host vehicle. Therefore, the current obstacle free distance and the current velocity of the moving object may already be available for other assistance systems. Hence, the system may be implemented at low cost, e.g. by generating suitable software for the perception module and for the prediction module.

In another aspect, the present invention is directed at a computer system, said computer system being configured to carry out several or all steps of the computer implemented method described herein.

The computer system may comprise a processing unit, at least one memory unit and at least one non-transitory data storage. The non-transitory data storage and/or the memory unit may comprise a computer program for instructing the computer to perform several or all steps or aspects of the computer implemented method described herein.

In another aspect, the present invention is directed at a non-transitory computer readable medium comprising instructions for carrying out several or all steps or aspects of the computer implemented method described herein.

Exemplary embodiments and functions of the present invention are described herein in conjunction with the following drawings, showing schematically:.

<FIG> depicts a host vehicle <NUM> driving behind a target vehicle <NUM> in the same current lane <NUM> of a road. The host vehicle <NUM> includes a detection system <NUM> for monitoring the environment of the host vehicle <NUM>. The detection system <NUM> may include a visual system and/or a radar system and/or a LIDAR system being implemented in the host vehicle <NUM>.

Via the detection system <NUM>, the existence and the current velocity of the target vehicle <NUM> are determined. Therefore, the target vehicle <NUM> may be regarded as a moving object in front of the host vehicle <NUM>.

The detection system <NUM> of the host vehicle <NUM> is further configured to determine an obstacle free space <NUM> in front of the host vehicle <NUM>. The obstacle free space <NUM> includes triangular shaped areas which are defined with respect to the host vehicle <NUM> and obstacles being detected by the detection system <NUM> in front of the host vehicle <NUM>. From the obstacle free space <NUM>, a minimum distance dFS with respect to the next obstacle is derived which may be regarded as current obstacle free distance <NUM> for the host vehicle <NUM>.

According to the present invention the host vehicle <NUM> also includes a system <NUM> (see <FIG>) configured to determine a usable distance <NUM> between the host vehicle <NUM> and the target vehicle or moving object <NUM>. The system <NUM> is able to additionally consider the movement of the target vehicle <NUM> when estimating a safety distance for the host vehicle <NUM> which corresponds to the usable distance <NUM>. Based on the movement of the target vehicle <NUM>, the system <NUM> is configured to estimate an extension <NUM> (see <FIG>) for the obstacle free space <NUM> corresponding to an extension distance dext, <NUM> for the obstacle free distance dFS, <NUM>.

The usable distance <NUM> is therefore given as the sum of the current obstacle free distance dFS, <NUM> and the extension distance dext, <NUM>. The usable distance may be also regarded as an effective safety distance for the host vehicle <NUM> taking into account the movement of the target vehicle <NUM>. For vehicles including conventional systems, the current obstacle free distance dFS, <NUM> 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 dFS, <NUM> falls below a certain predefined limit. In other words, conventional systems do not consider the movement of the target vehicle <NUM> for the decision whether to deactivate the above-mentioned driver assistance systems.

Due to the movement of the target vehicle <NUM>, 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 invention the current obstacle free distance dFS is therefore extended by taking the movement of the target vehicle <NUM> into account without sacrificing the safety requirements for the host vehicle <NUM>.

<FIG> depicts a schematic diagram of the system <NUM> for determining the usable distance <NUM> between the host vehicle <NUM> and the target vehicle <NUM> (see <FIG>) as a moving object in front of the host vehicle <NUM>. The system <NUM> includes a perception module <NUM> and a prediction module <NUM>. The perception module <NUM> is configured to detect the current obstacle free distance dFS, <NUM> in front of the host vehicle <NUM>. The perception module <NUM> is further configured to determine a current velocity <NUM> of the moving object or target vehicle <NUM>. The obstacle free distance <NUM> and the current velocity <NUM> of the target vehicle <NUM> are determined based on output data provided by the detection system <NUM> (see <FIG>) of the host vehicle <NUM>.

The prediction module <NUM> receives the current obstacle free distance <NUM> and the current velocity of the target vehicle <NUM> from the perception module <NUM> and is configured to estimate the extension distance <NUM> based on the current velocity <NUM> of the moving object or target vehicle <NUM>. The estimation of the extension distance <NUM> will be described in context of <FIG>, <FIG> and <FIG> below. The prediction module <NUM> is further configured to determine the usable distance <NUM> based on the current obstacle free distance <NUM> and the extension distance <NUM>. The usable distance <NUM> is depicted in <FIG> as output of the prediction module <NUM>. The usable distance <NUM> is determined as the sum of the current obstacle free distance <NUM> and the extension distance <NUM>. As mentioned above, the host vehicle <NUM> further includes advanced driver assistance systems (ADAS) which are depicted as <NUM> in <FIG>. The usable distance <NUM> is provided by the prediction module <NUM> for the advanced driver assistance systems <NUM> in order to decide based on the usable distance <NUM> whether certain assistance systems like lane keeping assistance (LKA), lane change warning (LCW) and side collision warning (SCW) are to be activated or deactivated.

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

<FIG> depicts a situation in which the target vehicle <NUM> performs emergency braking. At the beginning, the target vehicle <NUM> is at an observed position <NUM> which corresponds to the position as shown in <FIG> in front of the host vehicle <NUM>. That is, the target vehicle <NUM> is detected by the host vehicle <NUM> at the position <NUM> and has a velocity <NUM> which is also detected by the host vehicle <NUM> via the detection system <NUM>. In order to predict the emergency braking distance dEB, <NUM>, it is assumed that the target vehicle <NUM> is at a position <NUM> after emergency braking and has a velocity of approximately zero.

In detail, the emergency braking distance <NUM> is predicted based on a deceleration profile for the target vehicle <NUM> as shown in <FIG> which describes the course of the acceleration during emergency braking. In <FIG>, the acceleration in m/s<NUM> 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 <NUM> during emergency braking.

At the beginning, e.g. during a reaction time of the driver of the target vehicle <NUM> of approximately one second, the acceleration is still zero, and thereafter a constant increase <NUM> of the deceleration (negative acceleration) is assumed up to a value of approximately -<NUM>/s<NUM>. The constant increase <NUM> of the deceleration corresponds to a constant jerk jstart of the target vehicle <NUM> at the beginning of the emergency braking. After reaching the maximum deceleration of -<NUM>/s<NUM>, a constant maximum deceleration <NUM> is assumed for a predetermined time period <NUM>. In the example of <FIG>, the predetermined time period is about <NUM> seconds, i.e. from the instant of time at <NUM> seconds up to the instant of time at <NUM> seconds. Thereafter, i.e. at <NUM> seconds, a constant decrease <NUM> of a deceleration from -<NUM>/s<NUM> to approximately zero is assumed. The constant decrease of deceleration corresponds again to a constant jerk jend of the target vehicle <NUM> at the end of the emergency braking.

Based on the deceleration profile as shown in <FIG>, the emergency braking distance dEB, <NUM> is calculated as a sum of three partial distances as follows: <MAT> djstart is the distance which the target vehicle or moving object <NUM> travels at the beginning of the emergency braking, i.e. during the reaction time and during the constant increase <NUM> of the deceleration corresponding to the constant jerk of the target vehicle <NUM>. If an initial velocity vin of the target vehicle <NUM> is given, i.e. as detected by the detection system <NUM> of the host vehicle <NUM>, the distance travelled by the host vehicle <NUM> during the beginning of the emergency braking is calculated as follows: <MAT> treact and tjstart are the reaction time and the elapsed time during the beginning of the emergency braking, respectively, wherein each is e.g. <NUM> second in the example of <FIG>, and jstart is the constant jerk corresponding to the constant increase <NUM> of deceleration as shown in <FIG>.

The second distance daconst is travelled by the target vehicle <NUM> during a "constant deceleration phase", i.e. during the predetermined time period <NUM> as shown in <FIG> in which the deceleration has the constant value <NUM>. The second distance is calculated as follows: <MAT> taconst is the predetermined time period <NUM> for the constant deceleration phase, and aavg is the constant deceleration <NUM> during this time period <NUM> (see <FIG>).

The third distance djend is travelled by the target vehicle <NUM> during the end of emergency braking, wherein a constant jerk jend is assumed again corresponding to the constant decrease <NUM> of deceleration as shown in <FIG>. The third distance is calculated as follows: <MAT> tjend is the elapsed time during the constant decrease <NUM> of the deceleration and jend is the constant jerk corresponding to this constant decrease <NUM> of deceleration.

<FIG> depicts the movement of the target vehicle <NUM> as assumed during emergency steering in order to predict the emergency steering distance dES, <NUM>. At the beginning of the emergency steering, the target vehicle <NUM> is at the observed position <NUM> corresponding again to the position of the target vehicle <NUM> as shown in <FIG> and as being detected by the detection system <NUM> of the host vehicle <NUM>. At the end of the emergency steering, the host vehicle <NUM> is at a position <NUM> within an adjacent lane <NUM>, i.e. adjacent to the current lane <NUM> in which the host vehicle <NUM> and the target vehicle <NUM> are currently moving (see <FIG>).

In order to describe the emergency steering, a trajectory <NUM> is assumed for the movement of the target vehicle <NUM> wherein the trajectory <NUM> 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 <NUM> has a unique tangent at a connection point <NUM> of the two curves.

For the movement of the target vehicle <NUM>, a constant longitudinal velocity vlong is assumed which corresponds to the current velocity of the target vehicle <NUM> as detected by the detection system <NUM> of the host vehicle <NUM> and to the initial velocity vin as assumed at the beginning of the emergency braking (see <FIG>). Furthermore, a predefined maximum lateral acceleration alatmax is assumed for the target vehicle <NUM>. That is, for the change of the state of motion of the target vehicle <NUM> in lateral direction the "worst case" is assumed by taking into account the maximum lateral acceleration the target vehicle <NUM> can achieve. Under these assumptions, the radius of curvature R for the two curves forming the trajectory <NUM> (see <FIG>) is calculated as follows: <MAT>.

The emergency steering distance <NUM> is calculated from the starting position <NUM> of the target vehicle <NUM> up to the position <NUM> at which the target vehicle <NUM> will have moved half its width laterally when moving to the adjacent lane <NUM> during emergency steering. The distance <NUM> up to the position <NUM> can be considered as free from obstacles for the movement of the host vehicle <NUM> (see <FIG>) although the movement of the target vehicle <NUM> is deteriorated by the emergency steering.

Claim 1:
Computer implemented method for determining a usable distance (<NUM>) between a host vehicle (<NUM>) and a moving object (<NUM>),
the method comprising:
- detecting a current obstacle free distance (<NUM>) in front of the host vehicle (<NUM>) via a detection system (<NUM>) of the host vehicle (<NUM>), wherein the current obstacle free distance (<NUM>) is limited by a current position (<NUM>) of the moving object (<NUM>),
- determining a current velocity (<NUM>) of the moving object (<NUM>) via the detection system (<NUM>),
- estimating an extension distance (<NUM>) based on the current velocity (<NUM>) of the moving object (<NUM>) via a prediction module (<NUM>) of the host vehicle (<NUM>), and
- determining, via the prediction module (<NUM>), the usable distance (<NUM>) based on the current obstacle free distance (<NUM>) and the extension distance (<NUM>),
wherein the extension distance (<NUM>) is estimated by predicting an emergency braking distance (<NUM>) of the moving object (<NUM>) and characterized in that the extension distance (<NUM>) is also estimated by predicting an emergency steering distance (<NUM>) of the moving object.