Abstract:
A method for determining an object in a surroundings of a motor vehicle includes: scanning a far range, which extends as of a predetermined minimum distance from the radar sensor, using a radar sensor for scanning the far range; detecting objects in the far range based on reflections of a radar signal emitted by the radar sensor; and determining a crossing object in a close range, which lies between the radar sensor and the far range, if a previously detected object is no longer able to be detected in the far range using the radar sensor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a technique for determining an object using a radar sensor, and particularly relates to determining an object crossing in the close range ahead of a vehicle. 
         [0003]    2. Description of the Related Art 
         [0004]    A motor vehicle has a radar sensor for detecting one or more objects. For this detection, the radar sensor emits a radar signal which is able to be reflected at an object and returned to the radar sensor. The reflected signal arriving at the radar sensor is correlated with the emitted signal, and the object is able to be detected. In this context, a distance and/or a speed of the object with respect to the radar sensor may preferably be determined. Such a system may be used particularly within the scope of a driver assistance system which, for example, is supposed to maintain a predetermined distance of the motor vehicle from a preceding motor vehicle. In another example, the system is able to be included in an assistance system for the autonomous or partially autonomous guidance of the motor vehicle. 
         [0005]    The radar sensors used are usually not suitable for determining an object in a close range which extends a few meters from the radar sensor. To detect an object in the close range, a different sensor is normally used, for example, an ultrasonic sensor or a video camera. In spite of that, monitoring the close range, especially with respect to a movable object, which crosses the direction of motion of the motor vehicle may be desirable. For instance, a railroad engine driver on a locomotive is frequently not able to have a look at a region lying directly in front of the locomotive. The starting of the locomotive, while a person is crossing the track, cannot be prevented using a usual radar sensor. An assistant for starting travel of a motor vehicle, for instance, in stop-and-go traffic, also has to scan a close range in order to determine whether, for example, a preceding motor vehicle has left the route or not. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    It is therefore the object of the present invention to provide a method, a computer program product and a device for determining an object in a close range in front of a motor vehicle, which function on the basis of a usual radar sensor. 
         [0007]    A motor vehicle includes a radar sensor. The surroundings of the motor vehicle are subdivided into a far range, which extends as of a predetermined minimum distance from the radar sensor, and a close range which lies between the radar sensor and the far range. A method for determining an object crossing in the close range includes the steps of scanning the far range using the radar sensor, the detecting of objects in the far range, based on reflections of a radar signal emitted by the radar sensor, and determining the crossing object in the close range when a previously detected object in the far range is no longer able to be detected using the radar sensor. 
         [0008]    The object is thus determined on the basis of its shadowing of other objects, even when the object itself is not able to be detected at all, such as with respect to its extension, its speed or the direction of its motion. By concluding that there is an object in the close range with the aid of the determinability of objects in the far range, it is possible to use a usual radar sensor below its physical or product-specific minimum range. A region of the surroundings of the motor vehicle in which an object is able to be determined, may thus also be enlarged without the aid of other sensors. The object is especially able to be determined if it is moving transversely or slantwise to an output direction of the radar signal. The output direction may coincide with a direction of motion of the motor vehicle. Thus, the object may be detected alternatively at the moving or the stationary motor vehicle. 
         [0009]    The object may advantageously be detected in the close range already based on one single measurement. A plausibility check with the aid of several measurements one after another, as is usually required for detecting distant objects, may be omitted. Thus, the region near the motor vehicle that is particularly in danger of an accident may very quickly be investigated for crossing objects. 
         [0010]    In one preferred specific embodiment, only objects in the far range are detected which are evaluated as being relevant for the motor vehicle. The relevance of each object in the far range may be yielded particularly by a measurement quality, a state of motion of the object or its position with respect to the motor vehicle. By rejecting certain objects as irrelevant, an improved determination may take place as to whether an object is able to be detected using the radar sensor. The spatial resolution of the method may thus be increased. 
         [0011]    In one specific embodiment, the object is determined in the close range if the number of objects, that are no longer detectable in the far range having a predetermined speed, changes. This corresponds to looking at a differential proportion of the curve of the number of objects in the far range. A slow change in this number, as may take place during cornering, for example, is thus not able to lead to an erroneous determination of the object in the close range. The quality of the determination may thus be increased. 
         [0012]    The object in the close range may also be determined if a predetermined proportion of the previously detected objects is no longer able to be detected. Thus a statistical evaluation of the objects in the far range may take place, from which one may draw conclusions on the object in the close range. A spatial distribution of the objects in the far range may remain without consideration, in this case. So, the determination of the object in the close range may thus be further improved. 
         [0013]    The object in the close range may also be determined if the sum of the numbers of objects that are no longer detectable exceeds a predetermined threshold value over a predetermined number of past scans. This corresponds to looking at an integral proportion of the number of detectable objects. The object in the close range may thus be determined particularly early. 
         [0014]    One may also look at a combination of the differential proportion, the integral proportion and the relative number of detectable objects, in order to determine the object in the close range as quickly and as selectively as possible. 
         [0015]    Furthermore, a travel situation of the motor vehicle may be determined and the object in the close range may be determined with the aid of the travel situation. This corresponds to a situational evaluation, which may be carried out for scanning the surroundings of the motor vehicle, already for other reasons. In this context, particularly heuristic and experiential values may enter into the determination of the object, which may be derived from the travel situation. 
         [0016]    A computer program product, according to the present invention includes program code means for carrying out the described method when the computer program product is run on a processing device or stored on a computer-readable data carrier. 
         [0017]    A device, according to the present invention, for determining an object in the surroundings of a motor vehicle, includes a radar sensor for scanning a far range, which extends as of a predetermined minimum distance from the radar sensor, and a processing device for detecting objects in the far range, based on reflections of a radar signal output by the radar sensor. In this context, the processing device is prepared for determining a crossing object in a close range, which lies between the radar sensor and the far range, when a previously detected object in the far range is no longer able to be detected using the radar sensor. 
         [0018]    In this context, the radar sensor preferably includes a frequency modulated continuous wave radar. Thereby, distances and relative speeds of distant objects are able to be determined quickly with high resolution. 
         [0019]    The radar sensor is preferably prepared to scan objects in the far range, the far range beginning at a minimum distance of ca. 4 m from the radar sensor. Reflections of objects which are closer than the far range, are usually separated out already during the signal processing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a motor vehicle having a radar sensor. 
           [0021]      FIG. 2  shows a flow chart of a method for object determination at the motor vehicle of  FIG. 1 . 
           [0022]      FIG. 3  shows curves of detectablities of objects in the far range at the motor vehicle of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  shows a system  100  of a motor vehicle  105  having a device  110  installed on board. Device  110  includes a radar sensor  115 , a processing device  120  and optionally, a memory  125 . The motor vehicle may particularly be a passenger car or a truck or even a rail vehicle. 
         [0024]    Radar sensor  115  is prepared to scan surroundings  130  of the motor vehicle. For this purpose, radar sensor  115  is prepared to output a radar signal along a longitudinal axis  135 , which preferably coincides with a direction of motion of motor vehicle  105 . In surroundings  130  of motor vehicle  105  there may be objects which reflect the radar signal back to radar sensor  115 . In a far range  170 , which extends from a predetermined minimum distance of ca. 4 m, for instance, from radar sensor  115 , there are six exemplary objects  140  to  165 . In a close range  175 , which is between far range  170  and radar sensor  115 , there is an additional object  180 , which is represented as a person in exemplary fashion. 
         [0025]    A distinction is generally made between a measurable object  180  and an object that may be followed. First of all, a reflected signal of object  180  has to be recorded in order to measure object  180 . By evaluation a plurality of measurements that took place at different times, object  180  may then also be followed. The usual systems work only with objects  180  that are able to be followed. If an object  180  is located in the close range, measuring it may be possible, but following it is not possible. For example, an available measuring period may be too short to carry out a sufficient number of measurements of object  180 . The measuring period is determined by a speed at which object  180  is moving with respect to radar sensor  115 , and the speed of radar sensor  115  in the direction of the path of motion of object  180 . One has to make certain that object  180  is detected in time, in order still to be able to carry out a measure for avoiding a collision successfully. In the surroundings of a motor vehicle  105 , whose collision with a crossing pedestrian, for example, is to be prevented, the far range, which makes following possible, usually begins at a distance of ca. 4 m from radar sensor  115 . 
         [0026]    The detection range of radar sensor  115  may be restricted to objects which lie within a predetermined circular segment that includes longitudinal axis  135 . Sixth object  165  lies outside the detection range, and may remain undetected by radar sensor  115 . A further restriction for the detectability of objects may originate with their distance from radar sensor  115 . A reflected radar signal of object  180  in close range  175  may not be able to be evaluated with measuring techniques or may be rejected for other reasons during processing, so that object  180  itself is not able to be detected using radar sensor  115 , such as for determining its position or speed. 
         [0027]    In order to determine that object  180  is crossing in close range  175 , that is, that it is moving transversely or at an acute angle to longitudinal axis  135 , the determination of objects  145  to  160  may take place cyclically and detected objects  145  to  160  may be followed up by filing specific data on these objects  145  to  160  in memory  125 , for example. If object  180  moves laterally into close range  175 , objects  140  to  150  which, as seen by radar sensor  115 , lie behind object  180 , are not able to be detected, although they are in far range  170 . Based on the shadowing of objects  140  to  150 , processing device  120  is able to conclude that object  180  is there. That is why a detection, based on measuring technology, of object  180  by radar sensor  115  is not required. 
         [0028]      FIG. 2  shows a flow chart of a method  200  for determining crossing object  180  in close range  175  of radar sensor  115  on board motor vehicle  105  of  FIG. 1 . Method  200  is particularly prepared to be carried out on processing device  120 . In a first step  205 , a radar signal is output by radar sensor  115 . In a subsequent step  210 , reflections of the output radar signal are received. The reflections are returned by objects  140  to  160  in far range  170  of radar sensor  115 . In one preferred specific embodiment, radar sensor  115  works as a frequency modulated continuous wave radar, steps  205  and  210  being carried out permanently. In other specific embodiments, these steps may also be carried out one after the other. 
         [0029]    Preferably at regular intervals, in step  215 , objects  140  to  160  in far range  170  are detected based on a correlation of the output radar signals with the reflected radar signals. The detection is able to include the providing of a plurality of data on respective object  140  to  160 . For example, a measuring time, the amplitude of the reflected signal, a removal, an expansion, a speed, a position of the respective object with respect to radar sensor  115  or additional data may be determined. A representation of the respective object  140  to  160  may be stored in memory  125 . This process may take place for each of objects  140  to  160 . A corresponding representation of each object  140  to  160  may be stored in memory  125 . 
         [0030]    In an optional step  215 , which may be integrated with step  210 , it is checked whether one of objects  140  to  160  is irrelevant. The irrelevance of an object  140  to  160  may come about, for instance, from its direction of motion and speed of motion, its position with respect to motor vehicle  105  or a measuring quality which is able to be derived from the signal strength of the reflected signal. For objects  140  to  160 , that are determined to be irrelevant, step  225  is carried out in which these objects  140  to  160  are rejected. All other objects  140  to  160  are not affected by this. 
         [0031]    In a step  230  it is checked whether all objects  140  to  160 , which were detected at a preceding run-through of method  200 , especially of step  215 , have again been detected in the current run-through. If this is the case, method  200  may branch back to step  205 , and run through again. Otherwise it may be determined, optionally in a step  235 , whether the shadowing of one of the objects  140  to  160  has taken place based on another object  140  to  160  in the far range. In the illustration of  FIG. 1 , for example, object  150  may be shadowed by object  145 , even if object  180  is not staying in close range  175 . If there is a shadowing by an object  140  to  160  in far range  170 , method  200  is able to return to step  205  and run through again. 
         [0032]    Otherwise a travel situation of motor vehicle  105  may be determined in an optional step  240 . A determination of object  180  in close range  175 , carried out in a subsequent step  245 , is then able to take place based on the travel situation. For this purpose, the covering of objects  140  to  160  in individual segments of the detection range of radar sensor  115 , especially a directional angle with respect to longitudinal axis  135  and the distance from radar sensor  115 , may be taken into account. In addition, situational characteristic variables, such as the number and spatial distribution of objects  140  to  160 , an average distance or a measuring quality of these objects  140  to  160  may be observed. Parameters of motion of motor vehicle  105 , particularly a direction of motion, a speed of motion and an acceleration may be taken into account. One or more of these indicators may be weighted as a function of the travel situation and compared to one another. The position of object  180  in close range  175  may thereby be determined more accurately. 
         [0033]    In step  245 , object  180  may also be determined, additionally or alternatively, based on a statistical evaluation.  FIG. 3  shows a plot  300  of detection abilities of objects  140  to  160  in far range  170  of radar sensor  115  on motor vehicle  105  of  FIG. 1 . In the horizontal direction time is plotted, subdivided into equidistant measuring periods T0 to T9. A number is plotted in the vertical direction. 
         [0034]    A first curve  305  relates to a number of objects  140  to  160 , which are detectable by radar sensor  115  in far range  170 . At the beginning this number is 5, and then it goes down to 2, in the range of measuring periods T4 and T5, and subsequently rises again to 5. A second curve  310  relates to an integral proportion of first curve  305 . Each deviation of curve  305  from the number of objects  140  to  160  in measuring period T0 is summed up. The integration time, that is, the number of previous measuring periods T0 to T9, which are taken into account for the integration, is at least 8 in the present illustration, so that a drop in curve  310  is not able to be observed, if the number of objects  140  to  160  in first curve  305  does not change. 
         [0035]    A third curve  315  relates to a differential proportion of first curve  305 . Third curve  315  has a value in each measuring period T0 to T9, which expresses by how much the value of first curve  305  differs in the same measuring period from its value in the preceding measuring period. A high value of third curve  315  indicates a rapid change in the number of detectable objects  140  to  160 . A fourth curve  320  is reproduced numerically and indicates a relative proportion of detectable objects  140  to  160 . For each measuring period T0 to T9, it is indicated how many of objects  140  to  160  are shadowed and how many are detectable without shadowing. The two values are in each case separated from each other by a slash. 
         [0036]    Within the scope of a statistical evaluation, which in particular is able to be carried out in step  245  of method  200  of  FIG. 2 , each of curves  305  to  320  may be investigated and may especially be compared to a threshold value. If one or more of curves  305  to  320  exceed their associated threshold value, a conclusion may be drawn on object  180  being in close range  175  of radar sensor  115  on board of motor vehicle  105  of  FIG. 1 . The statistical observation described may be carried out, in addition or alternatively to the situational evaluation described above with respect to steps  240  and  245 .