Abstract:
The invention relates to a method for the assistance of a driver of a vehicle during a journey along a road, in which bend data indicating the course of a bend in the road extending in front of the vehicle seen in the direction of travel and road condition data indicating the condition of the road surface disposed in front of the vehicle seen in the direction of travel are determined and a recommended maximum speed allowing a safe driving through the bend is determined with reference to the bend data and to the road condition data.

Description:
TECHNICAL FIELD 
     The invention relates to a method for the assistance of a driver of a vehicle during a journey along a road in which bend data setting forth the course of a bend in the road extending in front of the vehicle seen in the direction of travel in which a maximum speed allowing a safe travel through the bend is determined with reference to the bend data. 
     BACKGROUND OF THE INVENTION 
     Such a method is generally known and is used, for example in a driver assistance system to display a maximum speed resulting from the course of the bend to the driver of the vehicle at which the vehicle can drive through the bend safely and/or to warn the driver when the vehicle is approaching the bend at a speed or is driving into the bend at a speed at which a safe driving through of the bend is no longer ensured. 
     It is the underlying object of the invention to provide a driver assistance method by which the driving safety is increased even further. 
     SUMMARY OF THE INVENTION 
     In the method in accordance with the invention for the assistance of a driver of a vehicle during a journey along a road, not only bend data indicating the course of a bend in the road extending in front of the vehicle seen in the direction of travel is determined, but also road condition data are determined which indicate the condition of the road surface disposed in front of the vehicle seen in the direction of travel. A recommended maximum speed allowing a safe driving through the bend is determined by a fusion of the bend data and the road condition data. 
     In other words, it is the underlying general idea of the invention to determine the maximum speed recommended for a safe driving through of a bend not only with reference to the course of the bend, but, additionally to take account of the condition of the road surface extending in front of the vehicle seen in the direction of travel. It is hereby possible to downwardly adapt the maximum speed resulting purely from the course of the bend on the detection of a suboptimal road surface condition which can result in a lesser adhesion of the vehicle wheels to the road surface in order to display a recommended maximum speed to the driver of the vehicle which also still allows a safe driving through of the bend under adverse road conditions. 
     As a result, the invention therefore provides for the determination of a recommended maximum speed for a cornering which takes account of at least one additional relevant environmental parameter, namely the condition of the road surface, and is thus better adapted to the actual circumstances influencing the cornering. The determination of the maximum speed recommended for the cornering in accordance with the invention therefore contributes to being able to drive through the bend with a lower risk of an accident and thus provides higher driving safety overall. 
     In accordance with a preferred embodiment, the road condition data include information on the presence of wetness on the road. The adhesion of a vehicle on a wet road is typically much reduced with respect to the adhesion on a dry road. Since the degree of dryness or of moisture of the road surface is included in the determination of the recommended maximum speed, the determined recommended maximum speed will typically be lower for a wet road than for a dry road. In this way, the method does not only contribute to safer cornering on a dry road, but also on a wet road. 
     Alternatively or additionally, the road condition data can also include information on the quality of the road surface, for example information on the roughness and/or the type of the road surface or information on the presence of ice, snow, sand or oil on the road. 
     The road condition data are advantageously determined by the evaluation of at least one image taken with the help of a camera which detects an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel. 
     The camera can be a component of a rain sensor provided for the control of a windshield wiper and/or it can be a camera of a driver assistance system used for lane recognition, for road sign recognition and/or for the determination of visibility conditions. A multifunctional use of the camera, i.e. that is a use of the camera not only for the determination of the road condition, but also for the control of a windshield wiper, for lane recognition, for road sign recognition and/or for the determination of visibility conditions provides a substantial cost advantage. 
     Not only the presence of wetness can be determined by a suitable evaluation of the image taken with the help of the camera, but the texture of the road surface can, for example, also be analyzed and a conclusion be drawn on the basis thereof on the presence of sand on the road or on a dust road or gravel road and this can be taken into account in the determination of the recommended maximum speed. 
     Alternatively or additionally, at least the presence of wetness on the road can also be determined by a different kind of rain sensor. A rain sensor can preferably also be considered for this purpose which is anyway present in the vehicle, such as a rain sensor which controls the actuation of a windshield wiper. The rain sensor is used in a multifunctional manner in this way, namely for the control of the windshield wiper, on the one hand, and for the determination of the maximum speed recommended for the cornering, on the other hand, whereby a specific cost advantage is also achieved here in addition to the increase in driving safety. 
     Furthermore, the road condition data can alternatively or additionally be received by an internet based service, a radio service such as TMC (for “traffic message channel”), a communications service between the vehicle and another vehicle and/or a communications service between the vehicle and an infrastructure which includes, for example, transmission devices installed along the road. 
     The road condition data received by the aforesaid services can be taken into account in the determination of the recommended maximum speed instead of or supplementary to the road condition data determined by the vehicle&#39;s own camera. A fusion of the road condition data determined by the vehicle&#39;s own camera and the road condition data received from external enables a determination of the actual road condition with increased reliability. 
     In accordance with a further embodiment, the bend data are determined from a digital map made available to the vehicle. Such a digital map is preferably the map of a navigation system installed in the vehicle. Deepening on the quality and in particular on the resolution of the map, it can be sufficient on the determination of the recommended maximum speed to determine the course of the bend to be driven through only with reference to the map. 
     Alternatively or additionally, the bend data can be determined by the evaluation of at least one image taken with the help of a camera which detects an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel. 
     The camera can be the camera of a lane recognition module of a driver assistance system which can be used not only for the detection of the course of a vehicle lane, but rather multifunctionally, i.e. also additionally for the control of a windshield wiper, for the determination of road condition data, for the detection of road signs and/or for the determination of visibility conditions. 
     By a fusion of bend data determined from a digital map and of bend data gained from the camera images, the course of the bend to be driven through can be determined with increased precision, which ultimately contributes to even higher driving safety. 
     In accordance with a further embodiment, a road sign is detected by the evaluation of at least one image taken with the help of a camera which detects an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel and the detected road sign is taken into account in the determination of the recommended maximum speed. 
     The camera used for the road sign recognition can also be a multifunctionally used camera, i.e. a camera which is used in addition to road sign recognition for the control of a windshield wiper, for lane recognition, for the determination of the road condition and/or for the determination of the visibility conditions, whereby the already mentioned cost advantage is achieved. 
     Applicable speed limits can be detected and taken into account in the determination of the recommended maximum speed by a corresponding evaluation of detected road signs for a section of the road and in particular for the bend to be driven through. If, for example, a speed limit of “80 kph” or of “80 kph when wet” applies to a road section with bends, the recommended maximum speed can accordingly be set to 80 kph even if the course of the road or bend and the road condition would theoretically allow a higher maximum speed. 
     In accordance with a further embodiment, the visibility conditions prevailing in an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel are estimated by the evaluation of at least one image taken with the help of a camera which detects the environmental zone and the estimated visibility conditions are taken into account in the determination of the recommended maximum speed. 
     In this manner, for example, the recommended maximum speed can be reduced accordingly under particularly adverse visibility conditions, whereby ultimately even higher driving safety is achieved. The camera can also be a multifunctionally utilized camera here which is used, in addition to the determination of the visibility conditions, for example for the control of a windshield wiper, for lane recognition, for road sign detection and/or for the determination of the road condition, whereby the already mentioned cost advantage is achieved. 
     If the actual speed of the vehicle when approaching or driving into the bend is above the recommended maximum speed, a visual and/or acoustic warning signal can be output to the driver for example. Alternatively or additionally, the vehicle can be slowed down automatically if the actual speed of the vehicle when approaching or driving into the bend is above the recommended maximum speed. 
     A further subject of the invention is furthermore a driver assistance system for the assistance of a driver of a vehicle during a journey along a road comprising a first module for the determination of bend data indicating the course of a road bend extending in front of the vehicle seen in the direction of travel, a second module for the determination of road condition data indicating the condition of the road surface disposed in front of the vehicle seen in the direction of travel, and a processor module, connected to the first and second modules, for the determination of a recommended maximum speed allowing a safe driving through the bend with reference to the bend data and road condition data determined by the first and second modules. 
     The driver assistance system in accordance with the invention enables the carrying out of the method in accordance with the invention with all its advantages described above. The driver assistance system can include, additionally to the modules for the determination of bend data and road condition data, a rain sensor module, a lane recognition module, a road sign detection module, a visibility condition determination module and/or a module for the automatic actuation of a vehicle headlamp or it can be coupled to a navigation system of the vehicle. 
     The preceding modules preferably use a common camera, where present, which detects an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel, whereby a particularly space saving and cost effective construction of the modules is achieved. It is, however, generally also possible to design at least one of the modules or all of these modules autonomously, i.e. that is to equip them with their own respective camera or another suitable detection means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in the following purely by way of example with reference to an advantageous embodiment and to the enclosed drawing. 
         FIG. 1  shows a schematic representation of a driver assistance system of a vehicle in accordance with the invention; and 
         FIG. 2  shows a schematic representation of a driver assistance system of a vehicle in accordance with an alternate embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The core of the driver assistance system  9  shown in  FIG. 1  is a processor module  10 . The processor module  10  is connected to a determination module  20  which includes a camera  30 , for example a digital video camera, and an evaluation unit  40 , connected to the camera  30 , for the evaluation of the images taken by the camera  30 . 
     The camera  30  is configured and is attached to the vehicle such that it detects an environmental zone of the vehicle disposed in front of the vehicle seen in the direction of travel and including a road extending in front of the vehicle. The camera  30  can, for example, be installed in the region of a rear view mirror provided in the region of the vehicle windshield. 
     An image evaluation algorithm implemented in the evaluation unit  40  is configured such that, by the evaluation of the images taken by the camera  30 , wetness deposited on the windshield e.g. in the form of fog, rain or snow can be detected, on the one hand, and the course of the road extending in front of the vehicle seen in the direction of travel can be detected, on the other hand. Whereas the first operation is also called a rain sensor function, the latter operation is known as road lane recognition. 
     In addition, the evaluation unit  40  has the operation of road sign recognition, i.e. the evaluation unit  40  can detect road signs in the camera images and can detect their purpose or content. 
     The evaluation unit  40  additionally includes an image evaluation algorithm which allows information to be derived from the taken camera images on the visibility conditions prevailing in the environmental zone detected by the camera  30  and to determine, for example, whether it is day or night or whether it is foggy. 
     The evaluation unit  40  furthermore provides an image evaluation algorithm which analyzes the texture of the surface of the road disposed in front of the vehicle to detect whether the road is, for example, an asphalted road or a dust road or a gravel road or whether e.g. an asphalted road is regionally covered by a layer of sand, snow or ice. 
     The processor module  10  is further coupled with a vehicle navigation system  50  in which a digital map is stored. The navigation system can determine the then current position of the vehicle on the digital map with the aid of the global positioning system GPS at any time. 
     During the journey, the navigation system  50  delivers information to the processor module  10  on the course of the road on which the vehicle is moving and in particular information on the course of a bend extending in front of the vehicle seen in the direction of travel and to be driven through. 
     At the same time, the processor module  10  receives the data determined with the aid of the lane recognition algorithm from the images of the camera  30  on the course of the road extending in front of the vehicle seen in the direction of travel from the evaluation unit  40  of the determination module  20 . 
     The road course data delivered from the navigation system  50  and from the determination module  20  are fused with one another in the processor module  10 , which results in an improved estimation of a course of a bend and of the distance of the vehicle from the bend. 
     The processor module  10  calculates a maximum speed for the course of the bend estimated in this manner, in particular for the radius of the bend underlying this course of the bend, at which the vehicle can drive through the bend safely under ideal conditions, i.e. that is without being carried out of the bend or starting to slide, while taking account of the vehicle properties such as the mass and friction of the vehicle wheels and while applying the relevant basic physical laws, i.e. that is the vehicle dynamics. 
     A recommended maximum speed is determined in the processor module  10  from the maximum speed calculated for the ideal conditions while taking account of the other data named above, determined by the determination module  20  and delivered to the processor module  10 , said recommended maximum speed not only taking account of the estimated course of the bend, but also of the detected conditions of the road, of the weather and of visibility conditions. 
     For example, the finding that it is night or is foggy or that the road is wet or sandy can thus have the result that the maximum speed calculated for the ideal conditions is corrected downwardly by a specific amount. 
     Furthermore, the recommended maximum speed can be reduced to the preset speed limit value on detection of a speed limit applicable to a bendy road such as can be determined by the road sign recognition algorithm. 
     The recommended maximum speed described in the above manner and determined in the processor module  10  is displayed to the driver of the vehicle by means of a suitable visual and/or acoustic output device  60 . 
     Referring to  FIG. 2 , alternately or additionally to the estimation of the visibility conditions by the evaluation of camera images, the visibility conditions prevailing in front of the vehicle seen in the direction of travel can also be estimated with reference to an automatic actuation of a headlamp  171  of vehicle  107 . An automatic switching on of headlamp  171  can, for example, be evaluated as an indication of adverse visibility conditions, which can have the consequence of a reduction of the recommended maximum speed. Elements in  FIG. 2  that are similar to elements shown in  FIG. 1  have element numbers that differ by 100. Referring to  FIG. 2 , headlamps  171  and driver assistance system  109  are respectively disposed on vehicle  107 . 
     As can be seen from  FIG. 1 , the processor module  10  is furthermore coupled to a vehicle control  70  by which the processor module  10  receives data with respect to the then current yaw rate and vehicle speed which can be determined with the help of sensors known per se. 
     The processor module  10  determines by a comparison of the determined recommended maximum speed with the yaw rate data and vehicle speed data received from the vehicle control  70  whether the vehicle is approaching the bend or is driving into it at a speed which is above the recommended maximum speed. If this is the case, the processor module  10  outputs a corresponding warning signal via the output device  60  to the driver of the vehicle to cause him to reduce the speed of the vehicle for the avoidance of an accident. 
     Alternatively or additionally, it is also conceivable that the processor module  10  intervenes in the vehicle control to avoid an accident and causes an automatic slowing down of the vehicle to the recommended maximum speed. 
     In the present embodiment, the processor module  10 , the evaluation unit  40  of the determination module  20  and the vehicle control  70  are shown as separate units. It is, however, generally also possible to integrate the evaluation unit  40  into the processor module  10  or to integrate the evaluation unit  40  and the processor module  10  into the vehicle control  70 . 
     Furthermore, the processor module  10  can be coupled with a receiver, not shown, which receives signals from outside the vehicle which include information on the conditions of the road, the weather and/or visibility conditions, for example from oncoming vehicles, from an infrastructure installed at the side of the road, via radio or via an internet service in order to use these data in addition to or instead of the data delivered by the determination module  20  for the determination of the recommended maximum speed.