Predictive routing of a transportation vehicle

A method and a device for predicting the future course of a roadway for a transportation vehicle driving on a road, wherein the road has a first section, a bend and a second section, and the bend is arranged between the first and the second section. The method determines an approximated course of a road derived from a digital map material using an original clothoid segment, wherein the clothoid segment has a starting point on the first section, an end point on the second section, and the clothoid segment sweeps over the angle defined by the bend between the first and the second section, and continuously corrects the original clothoid segment by subsequent corrective clothoid segments, wherein the corrective clothoid segments take into account the curvature of the route actually traveled by the transportation vehicle after the starting point.

PRIORITY CLAIM

This patent application claims priority to German Patent Application No. 10 2017 212 254.4, filed 18 Jul. 2017, the disclosure of which is incorporated herein by reference in its entirety.

SUMMARY

Illustrative embodiments relate to a method for route guidance of a transportation vehicle with the aid of predictive route data, a corresponding device, and a use of the method.

DETAILED DESCRIPTION

Digital maps are currently used in a transportation vehicle in the transportation vehicle's own navigation system mainly for navigation purposes, wherein digital map data are also increasingly being used in transportation vehicle guidance by assistance systems. Thus, for example, an anticipatory ACC system can use such map data to adjust the speed before bends in the road, or to improve a lateral guidance assistance system with the aid of map data. If the digital map data does not match the reality, this can lead to functional restrictions or improper interventions of the assistance systems.

Inside the transportation vehicle, the digital map data of the navigation system is distributed to the various control units of the assistance systems. To reduce the volume of data in the distribution of information, the underlying map material is sampled and approximated by clothoid segments. Because of the limited bandwidth of the transmission a tradeoff must be made between accuracy and look-ahead range, in the sense that a high degree of accuracy allows a short look-ahead distance and a low accuracy allows a broad look-ahead distance. In this situation, it is possible that curvatures in the course of a road are underestimated due to the approximation.

Document WO 2004/0097453 A1 relates to a driver assistance device for transportation vehicles, with a course prediction module and an interface to a navigation system, which supplies information to the course prediction module about the course of the road. In the navigation system, information about the road course is stored on a data medium, such as a CD-ROM or DVD, and the information about the current position of the driver's own transportation vehicle is supplied by a satellite-based positioning system. By using this information, the driving course can be predicted and, in particular, a curved road trajectory can be anticipated before the curve is actually entered. If, however, a driving dynamics parameter such as the yaw rate has an offset, then there will be a constant or gradually drifting difference between the directly measured yaw rate and the yaw rate calculated by the navigation system on the basis of the road curvature. Enduring discrepancies, or those which fluctuate in size, then indicate that information provided by the navigation system about the road course contains errors.

Document DE 10 2009 047 476 A1 relates to a method for determining a cutting trajectory, which enables a transportation vehicle to cut a section of a curve in a road. In this method, information about the curve section is received and the curve section is divided into at least one curve segment with a segment length and a starting curvature, wherein the curve segment is either a straight-line segment or an arc segment or a curve segment, whose curvature is a function of an arc length of the curve segment. A cutting trajectory is then determined from the at least one curve segment, so that the cutting trajectory in a certain point of the curve section has a predetermined offset in relation to a center of the road.

The disclosed embodiments improve and correct the underestimation of the curvature of a road curve based on digital map data.

This is achieved by a method, a device and the use of the method.

The disclosed method for predicting the future course of a road for a transportation vehicle driving on a road, wherein the road has a first section, a bend and a second section, and the bend is arranged between the first and the second section, comprises:determining an approximated road course derived from a digital map material using an original clothoid segment, wherein the original clothoid segment has a starting point on the first section, an end point on the second section, and the original clothoid segment sweeps over the angle defined by the bend between the first and the second section,continuously correcting the original clothoid segment by subsequent corrective clothoid segments, wherein the corrective clothoid segments take into account the curvature of the route actually traveled by the transportation vehicle after the starting point.

The method performs an online correction of the approximated map data under the assumption that the approximation of the exact map material is shape-preserving. The term shape-preserving is understood to mean that the swept angle of a curve is correct and the starting point and the end point of the approximating clothoid segment match those of the map. This allows the possibility of correcting the curvature ahead when traveling along the clothoid segment.

The first section in the present case is defined as a section of road before the bend under examination, and the second section is defined as a section of road after this bend. The two sections can have different shapes. For example, for a simple curve the sections may be straight line sections arranged before or after the curve. Another option, such as in the case of an S-bend, would be a straight-line section as the first section and the beginning of the second curve as the second section, so that the first part of the S-bend is covered by the definition of the two sections with a curve arranged between them. The same then applies to the second part of the S-bend.

Optionally, the corrective clothoid segments have the starting point and the end point of the original clothoid segment and the corrective clothoid segment sweeps over the angle defined by the curve between the first section and the second section. In addition, the current position of the transportation vehicle is also a component of the respective corrective clothoid segment, i.e., the corresponding clothoid segment for the current position of the transportation vehicle contains the current position.

The curvature of the path already traveled from the starting point may be determined and compared with the curvature of the original clothoid segment. If the curvature of the path already traveled is less than the curvature of the original clothoid segment up to the angle defined by the path traveled, then the size of the curvature ahead for the correction by the corrective clothoid segment is increased for the current position. The curvature of the original clothoid segment is therefore compared with the actual curvature. If the curvatures do not match, assumptions can be made about the future course of the road.

Optionally, the curvature which is actually traveled after the starting point of the original clothoid is determined on the basis of driving dynamics parameters, from measurements of an environmental sensor device and/or from position determinations of the transportation vehicle. Possible driving dynamics parameters are the yaw rate, or, for example, an environmental sensor device can perform a driving lane recognition, which is used as a basis for determining the curvature and/or performing a satellite-based position determination. The actual data thus determined can be used to determine the curvature of the path already traveled.

A forward-looking environmental sensor device may determines the curvature of the section of road located in front of the current position of the transportation vehicle, and the curvature ahead and the end position of the road section ahead are taken into account in determining a corrective clothoid segment. In other words, based on an appropriate environmental sensor device, for the road section ahead, for example, the course of the road markings is determined for the visible range of the environment sensor devices. From the course of the road markings it is possible to determine both the curvature of the road section as well as the position on the road section ahead, at which a change in the curvature starts to occur. From the curvature ahead and the position at which the curvature starts to change, a corrective clothoid segment can be predicted.

Optionally, to determine a corrective clothoid segment the curvature of the path previously traveled and the position of a transportation vehicle traveling ahead after the starting point of the original clothoid segment are taken into account. In this way, by tracking a transportation vehicle traveling ahead the original clothoid can be corrected in a predictive manner.

The disclosed device for predicting the future course of a road for a transportation vehicle driving on a road, wherein the road has a first section, a bend and a second section, and the bend is positioned between the first and the second section, and wherein the device is configured and designed to carry out the method described above, comprises:a digital map system,an approximation system, which determines from the map data of the map system an original clothoid segment with starting and endpoints for approximating the course of the road,a system for determining the actual curvature of the path already traveled by the transportation vehicle after the starting point,a system for comparing the actual curvature and the predicted curvature of the original clothoid segment, anda system for correcting the original clothoid segment by corrected clothoid segments on the basis of the comparison.

The device may have a system for determining the actual curvature of the path traveled by a transportation vehicle ahead on the future path of the transportation vehicle, wherein the actual curvature of the path traveled by the transportation vehicle ahead is used for comparison with the predicted curvature of the original clothoid segment.

Optionally, the device has a system for determining the actual curvature of a section of the road ahead of specified length. This actual curvature of the road section ahead can be used for comparison with the predicted curvature of the original clothoid segment. Such a system can be implemented, for example, by a camera system, such as is used for driving lane detection.

A disclosed use of the method described above for predicting the route of a roadway takes place in an ACC system and/or a lateral guidance assistance system of the transportation vehicle.

FIG. 1shows a transportation vehicle1, which is located on a two-lane highway or road2, wherein the road2is divided into two lanes by side markings3and4and a center marking5. The transportation vehicle is located on a first section6, which in the example ofFIG. 1is realized by a straight section, and is moving towards a bend7, wherein the transportation vehicle1is still some distance from the vertex of the bend, i.e., the apex of the bend. After the bend7, the road2transitions into a second section8, which in this example is again formed by a straight section.

FIG. 2shows the situation ofFIG. 1with a transportation vehicle1on the road2before the right-hand bend7. The real course of the road2contained in the digital map material consists of a first section6, a sharp bend7and a second section8directly following the bend7. By the approximation of the road course, a clothoid segment9is formed, which starts as early as point10on the first section6before the bend7and stops on the second section8after the bend7at point11. The clothoid segment9located between the points10and11, which represents the approximation and is hereafter referred to as the original clothoid9, is clearly more weakly curved than the real bend7. Due to the lower curvature of the original clothoid9which functions as a prediction of the course of the road, this can cause a predictive ACC assistance system to fail to adequately reduce the speed of the transportation vehicle1before the bend7. As a consequence, a lateral guidance system may no longer be able to negotiate the bend7independently, due to restricted levels of intervention.

FIG. 3shows the further course of the traffic situation ofFIG. 2. The transportation vehicle1, starting from the starting point10of the original clothoid9, has driven further in the direction of the bend7, but is still on the first section6leading up to the bend7. It is obvious that the transportation vehicle1cannot follow the prediction based on the original clothoid9due to the actual course of the road. As a result, an online correction of the approximated map data, i.e., the original clothoid9, is performed.

In doing so, the assumption is made that the approximation of the exact map material by the original clothoid9is shape-preserving. In other words, the angle swept through by the curve7is correct and the starting and end points10,11of the original clothoid9agree with those of the map. In addition, the path traveled by the clothoid9represents a lower limit, i.e., the actual driven path of the transportation vehicle1through the bend7between the points10and11is greater than or equal to the original clothoid section9.

This allows the possibility of correcting the curvature ahead while the transportation vehicle1is traveling. To this end, the curvature from the original clothoid segment9is compared with the actual curvature of the path traveled, which can be effected on the basis of driving dynamics parameters such as the yaw rate, by a lane detection using a camera or environment sensor device and/or position data via GPS. If the curvatures do not match, assumptions can be made about the future course of the road.

In the scenario ofFIG. 3, the transportation vehicle1is still located on the first section6before the bend7. The original clothoid9, however, already has an increasing curvature for the angle of the current position of the transportation vehicle. Since the actual driven curvature is less than the predicted curvature, it can be assumed that the size of the curvature ahead needs to be corrected upwards, so that a corrective clothoid segment12with starting and end points10,11is obtained, wherein inFIG. 3the part of the corrective clothoid segment12in front of the transportation vehicle1is represented as a solid line, while the part of the corrective clothoid segment12already traveled is represented as a dashed line. Here the curvature at the apex of the bend, which represents the maximum curvature, is important.

InFIG. 4, the transportation vehicle has reached the beginning of the bend7and the actual curvature of the already traveled path between the starting point10of the original clothoid9and the current position of the transportation vehicle1up to this situation was also shorter than the first corrective clothoid segment12shown inFIG. 3. Because the shape preservation of the map material can be assumed and the angle swept through by the curve, in the example here 90°, is correct, the size of the curvature ahead must therefore be corrected further upwards, which leads to the second corrective clothoid13ofFIG. 4with the starting and end points10,11, wherein the upcoming part of the second corrected clothoid13now passes through the bend7.

FIG. 5shows a traffic situation similar to that ofFIG. 2, in which the ego-transportation vehicle1is located at the starting point10of the original clothoid9. In contrast to the original situation ofFIG. 2, a further transportation vehicle14is located on the road2, which is driving in the same direction ahead of the ego-transportation vehicle1and is therefore already on the first section6nearer to the start of the bend7. If the ego-transportation vehicle1is equipped with a suitable environmental sensor device, for example, such as a radar, which is usually a component of an ACC assistant, then the ego-transportation vehicle1can detect that the path already traveled by the transportation vehicle14ahead does not follow the curvature of the approximate original clothoid9. Thus, in the situation ofFIG. 5it is already possible for the ego-transportation vehicle1to perform a correction of the original clothoid9and to determine based on the already traveled path of the transportation vehicle14ahead, the measured position16of the transportation vehicle14traveling ahead and the end position11of the original clothoid9, a corrective clothoid15which better approximates the course of the road. The corrective clothoid15determined based on the position of the transportation vehicle in front14does not yet completely follow the course of the road, a situation which can be further corrected by subsequent measurements of the transportation vehicle in front15. In other words, by tracking a transportation vehicle15traveling in front the clothoid15shown inFIG. 5, which reproduces the course of the road, can be determined earlier.

FIG. 6shows a schematic representation of the device for predicting the future course of the road. In this case the device20comprises a map system21, which allows access to a digital map. Usually this map system21is part of a navigation system and the map is stored on a DVD, for example. It can also take the form of an online access to a digital map on the internet. In an approximation system22, the original clothoid9is determined for the current road section from the digital map.

In a further system23, the curvature of the route previously traveled by the ego-transportation vehicle1is determined. At the same time, the curvature of the route of a transportation vehicle traveling ahead is optionally determined in a system24. In another system25, the curvature of the future driving route ahead of the ego-transportation vehicle1is also optionally determined. The measured curvatures and the curvature of the original clothoid9are then passed to a system26for comparing the original curvature with the measured curvatures, and a system27determines a correction of the original clothoid9along the route of the ego-transportation vehicle1based on the comparison.

LIST OF REFERENCE NUMERALS

1transportation vehicle—ego—transportation vehicle2road3left road boundary4right road boundary5center line6first section7bend8second section9original clothoid—predicted course of road10starting point11end point12first correction of the original clothoid13second correction of the original clothoid14transportation vehicle traveling in front15correction to the original clothoid based on the transportation vehicle traveling in front16point of departure—position of the transportation vehicle ahead20device for predicting the road course21map system22approximation system23system for determining the curvature of the path traveled24system for determining the curvature of the path traveled by a transportation vehicle in front25system for determining the curvature of the future path26system for comparing the original curvature with the measured curvatures27system for correcting the original clothoid