Method and apparatus for detecting an object in a motor vehicle environment

A method for detecting an object in a motor vehicle environment uses a detection means which scans the environment at predetermined angular increments φi+−φi (i=1,2, . . ., N). When sensing a reflection signal of the object at an angle φi, the angular increments are refined in the angular range between the adjacent angles φi−1 and φi+1 as a function of signal propagation times ti−1, ti and ti+1 of the reflection signals sensed at the angles φi−1, φi and φi+1.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German patent document 103 12 611.2, filed Mar. 21, 2003 (PCT International Application No. PCT/EP2004/000844, filed Jan. 30, 2004), the disclosure of which is expressly incorporated by reference herein.

The invention relates to a method and apparatus for detecting an object in a detection field such as a motor vehicle detection field, by scanning the environment at predetermined angular increments.

German patent document DE 101 16 277 A1 discloses a device for detecting objects during operation of a motor vehicle, using a scanning detection means (in particular, a laser). Objects moving in relation to the vehicle are classified as regards their size, degree of reflection, speed and acceleration. The object is then identified (for example as a passenger vehicle, an HGV, a motorcycle, a bicycle or a pedestrian) using a subcombination of these evaluation variables.

German patent document DE 195 03 960 A1 also describes an object detection device for vehicles having a laser for emitting light and a device for receiving the light reflected by an object (laser scanner). The pulsed laser scans an environment using a predetermined number of increments, (for example 100), and the distance and speed of the object are determined in computing devices.

An obstacle identification device identifies the detected object on the basis of a distribution pattern of the light intensity received.

One disadvantage of the known radar devices is that the resolution of the laser scanners used is in many applications insufficient in the operating mode to be able to determine reliably the extent of an object to be detected.

One object of the present invention is to provide an improved method and apparatus for detecting an object in a motor vehicle environment, using a detection to scan the environment at predetermined angular increments.

This and other objects and advantages are achieved by the method and apparatus according to the invention, in which a reflection signal of an object is sensed at angles φi (i=1, 2, . . . , N). According to the invention, the angular increments are refined in the angular range between adjacent angles φi−1 and φi+1, as a function of the signal propagation times ti−1, ti and ti+1 of the reflection signals sensed at the angles φi−1, φi and φi+1. In order to detect the object in a motor vehicle environment, a detection unit is used which scans the environment at predetermined angular increments φi+1−φi. For many assisting and safety functions in the vehicle, knowledge of the precise dimensions of the objects located in the environment is indispensable. The method according to the invention ensures highly accurate determination of the dimensions of an object, (for example of a road user such as a vehicle), so that it is possible, for example, to assign it reliably to classes such as a pedestrian, bicycle, passenger car and HGV. Each of these classes is characterized by a specific acceleration behavior and movement pattern in the road traffic, so that a targeted and safe response to a current traffic situation is possible.

In one embodiment of the invention, if the absolute propagation time difference between the signal propagation times ti and ti−1 or ti and ti+1 (corresponding to sensing angles φi−1, φi and φi+1 of the reflection signals) exceeds a predetermined threshold value, at least one additional angle φz (z=1, 2, . . . , N) is sensed in the angular range between the angles φi−1 and φi or φi and φi+1. The predetermined threshold value for the absolute propagation time difference, it should be noted, is selected such that distinctive object features (for example lamps or a radiator grille in a vehicle) lead to measurable propagation time differences between adjacent reflection signals which lie below the predetermined threshold value for the absolute propagation time difference. Absolute propagation time differences between the signal propagation times ti and ti−1 or ti and ti+1 of adjacent reflection signals which exceed the predetermined threshold value, on the other hand, are a clear indication of obvious geometrical changes which can be associated, in particular, with object boundaries (for example the front, right-hand corner of the vehicle). The introduction of the additional angle φz to be sensed in the angular range between the angles φi−1 and φi or φi and φi+1 makes it possible for object boundaries to be determined substantially more accurately. The method, namely the introduction of further angles φiz additionally to be sensed, is continued until reliable detection of the size and classification of the object is ensured.

It is advantageous if the scanning takes place substantially horizontally, vertically and/or at a predetermined angle of inclination. With scanning which is carried out vertically or at a predetermined angle of inclination, the presence and the position of a curb can be detected. This prevents the vehicle from driving onto the curb or ensures that it does so in a manner which is not damaging to the tires. The position and alignment of the curb can also be used for the selection of a desired vehicle position in a parking space. In addition, the knowledge of the position of a curb can be used to find vacant parking spaces which are not provided or delimited by two vehicles but lie in front of, behind or next to a single vehicle and are delimited on the other side by a curb.

Another feature of the invention provides a device for detecting an object in a motor vehicle environment. According to the invention, the device can be used to set individually the angles φi to be scanned, so that a cost-effective sensor system is provided for detecting an object in a motor vehicle environment using one or a very limited number of measuring beams. The system is compact and can be positioned in many locations in the vehicle owing to its low installation depth.

DETAILED DESCRIPTION OF THE INVENTION

An object1illustrated in section in the FIGURE is located in the environment of a motor vehicle (not illustrated in any more detail), and has detection means which scan the environment at predetermined angular increments to detect the object1. The number of angular increments depends on the required resolution accuracy. The object1has a corner4and a bulge5in a surface profile2. If the object1is a motor vehicle, the corner4could be, for example, a front, lateral boundary and the bulge5may be a headlamp. The object1may be a moving road user or road traffic devices having a fixed position. Moving road users are, for example, pedestrians, bicycles, passenger cars and HGVs. Devices having a fixed position are, in particular, street signs and road markings, for example curbs.

The scanning detection means comprises a sensor which indicates the distance, and it is possible to set individually the angles φi (i=1, 2, 3 . . . N) that are to be scanned. The spatially delimited measuring direction of the sensor is indicated by an arrow3. Scanning takes place substantially horizontally in this application (i.e., parallel to a road surface). To facilitate an understanding of the exemplary embodiment, the emitted beam from the sensor associated with the reflection signal6to13is illustrated in the FIGURE, and represents also the reflection signal6to13. For further simplification purposes, the reflection signals6to13which are detected at the angles φ6, φ7to φ13by scanning detection means are illustrated as parallel beams.

The reflection signals7,8,9,11are reflected by a planar face14, which faces the vehicle, of the surface profile2of the object1. The planar face14of the object1takes up the majority of the view of the object1which faces the motor vehicle and can be detected by the laser of the motor vehicle.

In a method for detecting the object1in the motor vehicle environment, when sensing reflection signals6to11at the respective angles φ6to φ11, the angular increments are refined in the angular range between adjacent angles φ6to φ11as a function of the signal propagation times t6to t11of the sensed reflection signals6to11. If the absolute propagation time difference between the signal propagation times t6to t11of two adjacent reflection signals6to11exceeds a predetermined threshold value, at least one angle φ12, which is also to be sensed, is introduced in the angular range between these respectively adjacent reflection signals6to11.

The predetermined threshold value for the absolute propagation time difference corresponds to a threshold value of the path difference for the reflection signals6to13, because the reflection signals6to13all propagate at the speed of light. The path difference is shown in the FIGURE as the path difference window15in relation to the reflection signals7,8,9and11. For a simplified illustration, the path difference window15, which is of equal size for all of the reflection signals6to13, has not been shown in the FIGURE for the reflection signals6,10,12and13. The selected threshold value of the absolute propagation time difference and, correspondingly, the path difference window15is sufficiently large that, in the event of a deviation in the path difference between two adjacent reflection signals6to13which is greater than the path difference window15, it can be assumed that the two reflection signals do not belong to the object1.

The method will be described in detail below. In a first scanning run of the object1with the reflection signals6to11, for example with scanning at constant angular increments, the object1is detected with the reflection signals7to11. That is, the reflection signals7to11are reflected by the object1and detected by the scanning detection means of the motor vehicle, while the reflection signal6is not incident on the object1and passes to the side of it. With the first scanning run, the dimensions, in the case of horizontal scanning the width, of the object1are generally not detected accurately enough in order to be able to uniquely classify the object1. A specific driving behavior of the motor vehicle as a response to the presence of the object1generally cannot be estimated or derived from the results of the first scan.

In order to detect the width of the object1more accurately, the signal propagation times t6to t11of the reflection signals6to11are evaluated for a second scanning run of the object1. For each pair of directly adjacent reflection signals6to11, the absolute propagation time difference of their signal propagation times t6to t11is calculated and compared with the predetermined threshold value for the absolute propagation time difference. The absolute propagation time difference of directly adjacent reflection signals6to11may be greater or less than the predetermined threshold value for the absolute propagation time difference. Correspondingly, it is true that the path difference of two directly adjacent reflection signals6to11lies within the corresponding path difference window15for an absolute propagation time difference less than the predetermined threshold value.

The adjacent reflection signals6and7, however, have an absolute propagation time difference which is greater than the predetermined threshold value for the absolute propagation time difference. All other reflection signals8to11have an absolute propagation time difference (in relation to their respectively adjacent reflection signals7to11) which is less than the prescribed threshold value for the absolute propagation time difference. By a suitable selection of the threshold value for the absolute propagation time difference, the bulge5is also recognized as being associated with the object1.

For accurate determination of the lateral boundary of the object1in the region of the corner4during the second scanning run, at least one further reflection signal12(illustrated for distinguishing purposes as a dashed arrow) is generated at an angle φ12in the angular range between the angles φ6and φ7, at which the reflection signals6and7are received. The latter angular range is therefore scanned with a higher resolution during the second scanning run than during the first scanning run, in order to determine more accurately the boundary of the object1. However, it is also possible for two or more such additional angles to be introduced and sensed in the angular range for the second scanning run.

The additional angle φ12that is to be sensed can be determined in an interval nesting method, for example by halving the angular range between the angles φ6and φ7, or in an iteration method with a suitable weighting. The reflection signal12is likewise reflected by the object1and defines the boundary of the object1much better than the reflection signal7.

If the desired resolution for the width of the object1is still insufficient after the second scanning run, the method is continued. For each pair of directly adjacent reflection signals6to12, in turn the absolute propagation time difference of their signal propagation times t6to t12is calculated and compared with the predetermined threshold value for the absolute propagation time difference. The reflection signals6and12have an absolute propagation time difference which is greater than the predetermined threshold value for the absolute propagation time difference. In a further scanning run, a reflection signal13(illustrated for distinguishing purposes as a dotted arrow) is therefore generated at an angle φ13in the angular range between the reflection signals6and12. The reflection signal13is not reflected by the object1. The method for detecting the object1in the motor vehicle environment can be continued until reliable detection of the object1is ensured by sufficiently accurate determination of the dimensions.

While scanning is carried out horizontally in this exemplary embodiment, it may also be carried out vertically or at a predetermined angle of inclination. With vertical scanning, in addition to the height of the object1, the presence and the height of curbs as the road boundary can also be detected. Curbs have two sharp edges (in each case one edge at the level of the road and at the level of the sidewalk) and a curb wall perpendicular to the road surface. As a result, curbs can be detected very effectively using the method according to the invention both in terms of their position and in terms of their height.