Abstract:
A method for adapting a collision avoidance system that avoids a collision of a vehicle with an obstacle, which collision avoidance system is designed to avoid the collision by sensing an actual distance from the obstacle and by outputting a signal on the basis of the falling below of a threshold distance by the actual distance, including: sensing a friction coefficient of an underlying surface on which the vehicle is supported in such a way that the vehicle can be driven, and setting the threshold distance on the basis of the sensed friction coefficient.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2015/072005, filed Sep. 24, 2015, which claims priority to German Patent Application No. 10 2014 219 493.8, filed Sep. 25, 2014, the contents of such applications being incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for adapting a collision warning system, a control device for implementing the method and a vehicle with the control device. 
       BACKGROUND OF THE INVENTION 
       [0003]    A collision avoidance system is known from DE 10 2012 000 949 A1, incorporated by reference herein in the form of a collision warning system, wherein the driver of a vehicle is warned if there is a risk of collision in order to avoid the collision. 
       SUMMARY OF THE INVENTION 
       [0004]    An aspect of the invention is an improved collision avoidance system. 
         [0005]    According to one aspect of the invention, a method for adapting a collision avoidance system that avoids a collision between a vehicle and an obstacle, which is designed to avoid the collision by measuring an actual distance from the obstacle and issuing a signal based on a shortfall of an actual distance in relation to a threshold distance, comprises the following steps:
       Measuring of a friction coefficient of a subsurface on which the vehicle is movably supported, and   setting of the threshold distance based on the measured friction coefficient.       
 
         [0008]    The stated method forms the basis for the deliberation that the threshold distance from which the collision with the obstacle threatens to occur is from a braking distance of the vehicle within which the vehicle can be brought to a standstill without impacting the obstacle. This braking distance is for example dependent on the friction coefficient of the subsurface on which the vehicle is supported. The friction coefficient can change, however, and is not the same everywhere. A fixed value could be used in order to define the threshold distance. The problem here, however, is that it is either no longer possible to avoid all collisions, for example on icy subsurfaces, when the fixed value for the friction coefficient is selected too high, or that the collision avoidance system intervenes too frequently, when for example the subsurface is dry and has a high friction coefficient. 
         [0009]    In this regard, the method described above is applied with the recommendation to measure the friction coefficient of the subsurface and set or adapt the threshold distance depending on the measured friction coefficient. In this manner, the collision avoidance system, adapted to different states, can react differently to potential collisions and avoid them more reliably. 
         [0010]    Here, the friction coefficient can be measured as required. Most practical here is a database which contains the friction coefficient of the subsurface at different positions. Here, the database fulfills the function of a map, on which the friction coefficients of a road as a subsurface at individual road sections are deposited and stored. The database can be deposited at any point to which the vehicle has information access. Thus, it would be possible to deposit the database in the vehicle itself, but also in a network to which the vehicle has access. A combination is also possible, such as a local database in the vehicle which is then updated at regular intervals from the global database. 
         [0011]    In order to measure the friction coefficient, the vehicle can record its position via a global satellite navigation system, for example, and then retrieve the friction coefficient from the database with reference to the recorded position. 
         [0012]    In an additional further development, the method described comprises the following steps:
       Retrieving information which influences the friction coefficient from at least one further database, and   updating the friction value retrieved from the database based on the information retrieved from the further database.       
 
         [0015]    The information in the further database which influences the friction coefficient can be any information which is suitable for specifying the friction coefficient of the subsurface. Thus, this can comprise weather data, for example, from which it can be seen whether the subsurface has been covered with rain or is even icy. 
         [0016]    Alternatively or additionally, the information in the further database which influences the friction coefficient can be information which influences the friction coefficient on the vehicle. For this purpose, vehicle data is deposited in the database such as the material of the wheels, their friction coefficient or chassis properties, on the basis of which the resulting friction coefficient between the subsurface and the vehicle can be estimated as precisely as possible. 
         [0017]    Alternatively or additionally, the method described comprises in a further development the step of updating the friction coefficient retrieved from the database, based on at least one item of sensor information. 
         [0018]    This sensor information can take any form. It is in any case advantageous that both information from the database and local sensor information are evaluated jointly in order to determine the most precise friction value possible. One possibility would be that the sensor information comprises the state of the windscreen wiper, which in turn allows a prediction as to whether or not it will rain. In this manner, a particularly suitable and simple determination of a friction coefficient would be possible from the combination of the information from the database and the sensor information. An additional or alternative possibility would be that the sensor information originates from a humidity sensor and directly describes the degree of humidity on the road. As a further alternative, the sensor information can also arise from a sensor fusion, however, within the scope of which the information from different sensors is merged to form a single item of sensor information, for example for the purpose of specifying information further. 
         [0019]    In general, the sensor information can originate from any sensor within the vehicle. 
         [0020]    Alternatively or additionally, however, it would also be possible to receive the sensor information from a sensor outside the vehicle via the network described above, for example. For this purpose, so-called vehicle ad-hoc networks could be used, for example, which can distribute sensor information in the form of messages between the participants or nodes of the vehicle ad-hoc network. 
         [0021]    In yet another further development, the method described comprises the following step:
       Updating the friction coefficient in the database based on the updated friction coefficient. In this manner, the friction coefficient can be iteratively specified further in the database. In particular in the network described above, this offers the advantage that vehicles which retrieve the updated friction coefficient can achieve precise results with little computing complexity required, wherein the friction coefficient can be maintained at a precise value in the long term through swarm intelligence.       
 
         [0023]    In a particular further development, the collision avoidance system is designed, based on the issued signal, to intervene in the driving dynamics of the vehicle in order to avoid the collision. While the collision avoidance system can react in any way required to the issued signal, and for example warn the driver of the vehicle, so that they initiate the avoidance of the collision by swerving or braking, accidents can also be avoided by active intervention, however, which is elicited for example by insufficient driving skills on the part of the driver. A combination of the previously described reactions to the issued signal would also be possible, whereby the driver is first warned and if they fail to react, an active intervention is made. 
         [0024]    According to a further aspect of the invention, a control device is designed to implement one of the methods described. 
         [0025]    In a further development of the control device described, the device described comprises a memory and a processor. Here, one of the methods described is stored in the memory in the form of a computer program, and the processor is provided to implement the method when the computer program is loaded from the memory into the processor. 
         [0026]    According to a further aspect of the invention, a computer program comprises program code titles in order to implement all steps of the method described when the computer program is implemented on a computer or one of the devices described. 
         [0027]    According to a further aspect of the invention, a computer program product contains a program code which is stored on a data carrier which can be read by a computer, and which, when it is implemented on a data processing facility, implements one of the methods described. 
         [0028]    According to a further aspect of the invention, a vehicle comprises the following:
       A chassis which is movably supported on wheels,   a collision avoidance system which avoids a collision with an obstacle, which is designed to avoid the collision by measuring an actual distance from the obstacle and issuing a signal based on a difference between the actual distance and a set distance, and   one of the described control devices for adapting the collision avoidance system.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The properties, features and advantages of this invention described above, and the manner in which these are achieved, become clearer and easier to understand in conjunction with the following description of the exemplary embodiments, which will be explained in greater detail below with reference to the drawings, wherein: 
           [0033]      FIG. 1  shows a principle representation of a vehicle on a road, and 
           [0034]      FIG. 2  shows a principle representation of a merging sensor in the vehicle shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    In the figures, the same technical elements are assigned the same reference numerals and are described only once. 
         [0036]    Reference is made to  FIG. 1 , which shows a principle representation of the vehicle  2  on a road  4 . 
         [0037]    Within the scope of the present embodiment, the vehicle  2  drives towards a crossroads  6 , on which the traffic is regulated via a signal system with three traffic lights  8 . By way of explaining the present exemplary embodiment, it should here be assumed that the vehicle  2  is moving in a driving direction  10  on the road  4  towards one of the traffic lights  8 , and that another vehicle  12  is waiting in front of this traffic light  8 . 
         [0038]    Within the scope of the present embodiment, the vehicle  2  has a collision avoidance system, yet to be described, in the form of a brake assistant referenced in  FIG. 2 . The brake assistant  14  uses a sensor, such as a radar sensor  16  with radar rays  18 , to measure an actual distance  20  from the other vehicle  12 , and if this actual distance  20  falls below a threshold distance  22  to the other vehicle  12 , the brake assistant  14  automatically brakes the vehicle  2 . 
         [0039]    This will be described in detail further below. First, the vehicle  2  will be described in greater detail below with reference to  FIG. 2 . 
         [0040]    The vehicle  2  comprises a chassis  24  which in the generally known manner is movably supported via wheels  26  on a subsurface such as the road  4 . The wheels  26  can be braked individually for each wheel by a generally known brake control mechanism  28  via brakes  30 , via triggering with brake control signals  32  based on a brake command  34 . This brake command  34  can be generated by a plurality of technical mechanisms in the vehicle  2 , such as a brake pedal controlled by the driver. In the present embodiment, however, the brake command  34  is generated by the brake assistant  14 . 
         [0041]    The brake assistant  14  comprises a trigger mechanism  36 , which essentially generates the brake command  34  based on a comparison of the actual distance  20  and the threshold distance  22 . This is generally known and does not require further explanation. Within the scope of the present invention, the radar sensor  16  is shown as issuing the actual distance  20 . As a rule, the actual distance  20  in the trigger mechanism  36 , taking into account additional sensor information, such as the camera image  38  of an image  40  of a camera  42 , is in the driving direction  10  in front of the vehicle  2 . Details on the subject can be found in the relevant prior art. 
         [0042]    Within the scope of the present invention, the threshold distance  22  depends on a friction coefficient  44 , also known as a friction factor or friction value, which describes a friction between the wheels  26  of the vehicle  2  and the road  4 . The friction coefficient  44  is here advantageously determined as precisely as possible on the route between the vehicle  2  and the other vehicle  12 . For this purpose, a calculation instrument  46  is provided which can determine the braking distance of the vehicle  2  on the road  4  from the friction coefficient  44 , and based on this, the threshold distance  22 , which is necessary in order to bring the vehicle  2  to a standstill via the brakes  30  without colliding with the other vehicle  12 . 
         [0043]    The basis for the friction coefficient  44  is in the present embodiment an initial friction coefficient  48 , which can be stored in a database  50  depending on a position  52  of the vehicle  2  in the form of map data. This database  50  can in general also be arranged outside of the vehicle  2  and be queried, for example, via wireless network communication. 
         [0044]    The position  52  can for example be received from a receiver  54  for a global satellite navigation system, or GNSS, which receives a GNSS signal  58  via an antenna  56  and from this determines the position  52  of the vehicle  2  in the generally known manner. Alternatively, the position can also be determined with other sensors, however, such as a fusion sensor. 
         [0045]    The initial friction coefficient  48  can now be adapted in many different ways to the conditions on the road  4 . For this purpose, for example, sensor information  62  from a sensor  60 , such as a humidity sensor, can be retrieved which describes the state of the road  4  in relation to the actual friction coefficient  44 . If the road  4  is wet, for example, the initial friction coefficient  48  can be reduced accordingly in order to determine the friction coefficient  44 . As additional or alternative sensor information, the status of a windscreen wiper of the vehicle  2 , which is not shown further, could be queried for example. If the windscreen wiper is on, it can be concluded that there is a wet road  10 . 
         [0046]    Further, a vehicle memory  64  can be read, which can contain vehicle-specific data  66  such as material properties of the wheels  26 , chassis data regarding the vehicle  2 , or other data which influences the friction coefficient  44 . Based on this data  66 , the initial friction coefficient  48  can also be adapted. 
         [0047]    Finally, the road state  70  of the road  10  can also be queried from an additional database  68 . This database  68  can for example be a weather map or information database, which provides information about the material from which a road surface of the road  10  is made. Like the database  50 , the additional database  68  can also be arranged internally in the vehicle  2  or externally outside the vehicle  2 . 
         [0048]    Several additional databases  68  can also be present, wherein each additional database is provided by a different service provider. The weather map could be provided by a weather report provider, while the state or local authority could offer data on the road surface. The vehicle-specific data  66  could also be provided as an additional database, which can then be offered by the vehicle manufacturer and their suppliers for use by the local community. 
         [0049]    In order to limit the computing complexity for the friction coefficient  44 ′, a currently determined friction coefficient  44  can be stored as the next initial friction coefficient  48  to a current position  52  in the database  50 .