Method for operating a motor vehicle, in which state variables and map data are used to deduce non-slip properties of a surface, driver assistance system, and motor vehicle

Abstract

The invention relates to a method for operating a motor vehicle (10), in which at least one measurement device of a driver assistance system (12) is used to measure at least one state variable which is evaluated by an evaluation device (28) of the driver assistance system (12) with regard to non-slip properties of a surface in the surrounding region of the motor vehicle (10). The evaluation device (28) also uses at least one empirical data parameter for assessing the non-slip properties of the surface. In order to prevent a collision of the motor vehicle (10) with an obstacle, the driver assistance system (12) performs an assistance function which effects autonomous braking of the motor vehicle (10). The evaluation device (28) uses, as the at least one experience variable, map data which indicate at at least one point in the surrounding region of the motor vehicle (10) an increased probability of slippery road conditions arising. The invention also relates to a driver assistance system (12) and to a motor vehicle (10) comprising the driver assistance system (12).

Description

[0001] Method for operating a motor vehicle, in which the slip resistance of a surface is determined based on state variables and map data, driver assistance system and motor vehicle

[0002] The invention relates to a method for operating a motor vehicle, in which at least one state variable is detected by means of at least one detection device of a driver assistance system. The at least one state variable is evaluated by an evaluation device of the driver assistance system with regard to the slip resistance of a surface in the vicinity of the motor vehicle. The evaluation device additionally uses at least one empirical value to assess the slip resistance of the surface. To avoid a collision of the motor vehicle with an obstacle, the driver assistance system executes an assistance function, wherein the assistance function causes autonomous braking of the motor vehicle. Furthermore, the invention relates to a driver assistance system, which is preferably designed to carry out the method, and to a motor vehicle equipped with the driver assistance system.

[0003] An important function of a motor vehicle's driver assistance system is autonomous emergency braking (AEB). If a potential collision with an object or obstacle is detected and the driver fails to react, the system automatically brakes the vehicle. This is intended to ensure that the vehicle comes to a stop in time before the obstacle or does not collide with it.

[0004] US 2020 / 0231145 A1 describes a driver assistance system in which a camera detects a traffic sign indicating a slippery or wet road. Furthermore, weather conditions affecting the road on which a vehicle equipped with the driver assistance system is traveling are checked. For example, a vehicle's navigation system can receive current weather information. If a vehicle's control unit detects that slippery road conditions exist, the start time of an emergency braking system is brought forward, whereby the emergency braking system is designed to decelerate the vehicle.

[0005] The object of the present invention is to provide a method of the type mentioned at the outset which provides a high degree of reliability in assessing the slip resistance of the subsurface, as well as to provide a corresponding driver assistance system and a motor vehicle with the driver assistance system.

[0006] This object is achieved by a method having the features of patent claim 1, a driver assistance system having the features of patent claim 11, and a motor vehicle having the features of patent claim 12. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims and in the following description.

[0007] In the method according to the invention for operating a motor vehicle, at least one state variable is detected by means of at least one detection device of a driver assistance system. The at least one state variable is evaluated by an evaluation device of the driver assistance system with regard to the slip resistance of a surface in the vicinity of the motor vehicle. The evaluation device additionally uses at least one empirical value to assess the slip resistance of the surface. To avoid a collision of the motor vehicle with an obstacle, the driver assistance system executes an assistance function, wherein the assistance function causes the motor vehicle to brake autonomously.The evaluation device uses map data as the at least one empirical value, wherein the map data indicate an increased probability of slippery road conditions occurring at at least one location in the vicinity of the motor vehicle.

[0008] This is based on the realization that map data can be used to accurately and precisely assign a real, frequent occurrence of slippery road conditions in the past to the respective locations in the vicinity of the vehicle. This makes such empirical values ​​in the form of map data particularly reliable. Furthermore, updating the map data offers the opportunity to take into account changing probabilities of slippery road conditions occurring at specific locations. The map data thus provides a highly reliable basis for the evaluation system to assess the slip resistance of the surface in the vicinity of the vehicle.

[0009] Since the evaluation device also considers at least one state variable, which is evaluated with regard to the current condition of the surface in the vicinity of the motor vehicle, the method provides a particularly high level of reliability in assessing the slip resistance of the surface. In particular, knowledge of reduced slip resistance or increased slipperiness of the surface ahead of the motor vehicle is very helpful when executing the assistance function that causes the vehicle to brake autonomously. This is because when the surface has reduced slip resistance, it makes sense to initiate autonomous braking earlier than when the surface is non-slip and dry.

[0010] By evaluating the at least one state variable, the evaluation device can determine in particular whether the increased slipperiness or reduced slip resistance of the ground is possibly due to the fact that there is currently snow and / or ice on the ground and / or because the ground is currently wet. In this case, the map data is also used, which contains the empirical variable or the empirical value that slippery road conditions actually occur with an increased probability at at least one location in the vicinity of the motor vehicle. Accordingly, to assess the slip resistance of the ground, different variables are advantageously combined, namely the at least one state variable and the at least one empirical variable in the form of the map data. This provides a high level of significance for the assessment of slip resistance.

[0011] Preferably, the evaluation device uses map data indicating an increased frequency of accidents at at least one location in the vicinity of the motor vehicle, wherein the accidents are at least partly caused by slippery road conditions. By taking the increased frequency of accidents into account, not only an abstract or theoretically higher risk of slippery road conditions is used when assessing the slip resistance of the surface. Rather, the real conditions in the form of the actually more frequent occurrence of accidents provide an indication that a reduced slip resistance of the surface can be expected at the relevant locations in the vicinity of the motor vehicle. This contributes to the high reliability of the assessment of the slip resistance of the surface.

[0012] The map data preferably indicate the presence of a bridge and / or a depression in the area surrounding the motor vehicle, the presence of the bridge and / or the depression being used by the evaluation device. This is based on the knowledge that, for example, a location in the area surrounding the motor vehicle, in the form of a bridge, towards which the motor vehicle is driving, is comparatively highly exposed. Therefore, temperatures are often cooler in the area of ​​the bridge than before or after the bridge. In wet road conditions and temperatures around freezing point, this can result in reduced skid resistance due to, for example, freezing wetness or snow remaining on the bridge. Such factors can be taken into account by the evaluation device when the driver assistance system executes the assistance function that causes the autonomous braking of the motor vehicle.

[0013] The same applies to depressions in the terrain, where cold air can collect more easily than at other locations on a road used by a vehicle. Therefore, it is useful for the evaluation system to use the presence of the bridge and / or depression contained in the map data as an empirical value to assess the slip resistance of the subsurface.

[0014] The presence of the bridge and / or depression in the vicinity of the motor vehicle can be detected additionally or alternatively by means of a camera or similar sensor device of the driver assistance system. However, this requires that the bridge and / or depression are already within the detection range of the sensor device of the driver assistance system. In contrast, by using the map data indicating the presence of the bridge and / or depression in the vicinity of the motor vehicle, the corresponding condition can already be taken into account before the bridge and / or depression can be detected, for example, by means of the camera. The map data can be made available to the evaluation device from an internal storage device of the driver assistance system. This ensures very rapid and fail-safe access to the map data. This is advantageous.

[0015] Additionally or alternatively, the map data can be provided to the evaluation device by a communication device of the driver assistance system, wherein the communication device is configured for wireless data reception. This is particularly advantageous for providing the evaluation device with particularly up-to-date map data and thus empirical data.

[0016] The map data can be wirelessly transmitted to the communication device by at least one warning device located in the vicinity of the motor vehicle. Such a warning device can be stationary and / or mobile. If the warning device is stationary or fixed, it can be very reliably ensured that the vehicle's communication device receives the map data and thus the empirical values ​​when driving past the warning device.

[0017] The mobile warning device can, in particular, be provided by another motor vehicle configured for vehicle-to-vehicle communication. This is particularly advantageous if the mobile warning device in the form of the other motor vehicle has more up-to-date map data than the motor vehicle that has the evaluation device. This allows the motor vehicle that has the evaluation device to access the current map data provided by the other motor vehicle.

[0018] Additionally and alternatively, the map data can be transmitted wirelessly from a server device to the communication device. This is also advantageous to ensure that the evaluation device has the most up-to-date and comprehensive empirical data available for evaluation in the form of map data.

[0019] Preferably, by means of at least one sensor device of the

[0020] A driver assistance system detects a temperature in the surroundings of the motor vehicle as the at least one state variable. For example, the sensor device can be designed as a temperature sensor. Particularly when ambient temperatures are around freezing, the likelihood of slippery road conditions is increased. This is because any water present on the surface can then freeze and / or, in the event of snowfall, snow can remain on the surface. Therefore, the ambient temperature is a very informative state variable for assessing the slip resistance of the surrounding surface. Furthermore, the state variable can be measured particularly easily in the form of the ambient temperature.

[0021] Additionally or alternatively, the presence of liquid and / or frozen water on the ground surrounding the motor vehicle can be detected as the at least one state variable by means of at least one sensor device of the driver assistance system. The presence of, for example, snow and / or ice and / or liquid water on the ground is regularly associated with reduced slip resistance of the ground. Therefore, it is advantageous to detect such state variables using the sensor device.

[0022] Preferably, the driver assistance system uses a rain sensor as the at least one sensor device. Particularly if the rain sensor is already provided to control the operation of windshield wipers of the motor vehicle, the state variable detected by the rain sensor, in the form of the presence of water, for example, on a windshield of the motor vehicle, can advantageously be used additionally to assess the slip resistance of the surface in the vicinity of the motor vehicle.

[0023] Additionally and alternatively, at least one camera can be used as the at least one sensor device of the driver assistance system. This is based on the realization that, for example, the presence of water and / or ice and / or snow on the ground in the vicinity of the motor vehicle can be very easily determined by evaluating images or image data captured by the camera.

[0024] Preferably, a receiving device of the driver assistance system is used as the at least one detection device, which receives weather data as the state variable. This is also advantageous in order to be able to assess the slip resistance of the surface in the vicinity of the motor vehicle as realistically as possible.

[0025] Additionally or alternatively, the evaluation device can use the meaning of a traffic sign located in the vicinity of the motor vehicle as the at least one empirical value. For example, the traffic sign can indicate an increased risk of slipping or slippery snow or ice. Such traffic signs can be detected, for example, using a camera associated with the driver assistance system. Additionally or alternatively, the traffic sign and its meaning can be included in the map data.

[0026] Preferably, if a reduced slip resistance of the surface in the surroundings of the motor vehicle is detected, a length of a time period remaining until the motor vehicle impacts the obstacle is increased, wherein if the time period is exceeded, the autonomous braking of the motor vehicle is effected by executing the assistance function of the driver assistance system.

[0027] In particular, the driver assistance system can include autonomous emergency braking (AEB) as an assistance function. This is based on the knowledge that a threshold value for the length of time below which autonomous braking of the vehicle is triggered is usually designed for dry or non-skid road conditions. However, if the road surface is less slippery, the vehicle requires a longer distance to achieve a certain reduction in speed.

[0028] By increasing the time period below which autonomous braking is triggered when the reduced slip resistance of the surface in the vehicle's surroundings is detected, more time is available for autonomous braking. This ensures that the vehicle comes to a stop in front of the obstacle or does not collide with it, despite the reduced slip resistance of the surface. This is particularly advantageous.

[0029] The driver assistance system according to the invention for a motor vehicle has at least one detection device for detecting at least one state variable. The at least one state variable can be evaluated by an evaluation device of the driver assistance system with regard to the slip resistance of a surface in the vicinity of the motor vehicle. The evaluation device is designed to additionally use at least one empirical value when assessing the slip resistance of the surface. The driver assistance system is designed to perform an assistance function to avoid a collision of the motor vehicle with an obstacle, by means of which autonomous braking of the motor vehicle can be effected.The evaluation device is designed to use map data as the at least one empirical value, wherein the map data indicates an increased probability of slippery road conditions occurring at at least one location in the vicinity of the motor vehicle. Such a driver assistance system, which is designed in particular to implement the method according to the invention, ensures high reliability in assessing the slip resistance of the surface.

[0030] The motor vehicle according to the invention has the driver assistance system according to the invention. Consequently, the method can be implemented by the motor vehicle during operation, in which the evaluation device uses, on the one hand, the at least one state variable and, on the other hand, the map data as the at least one empirical variable to assess the slip resistance of the surface in the vicinity of the motor vehicle. This is advantageous for the useful and improved operation of the motor vehicle.

[0031] The advantages and preferred embodiments described for the method according to the invention also apply to the driver assistance system according to the invention and to the motor vehicle according to the invention and vice versa.

[0032] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combination specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments are also to be considered encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate feature combinations from the explained embodiments. Embodiments and feature combinations are also to be considered disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0033] Further features of the invention emerge from the claims, the figures, and the description of the figures. These show:

[0034] Fig. 1 schematically shows a situation in which a motor vehicle equipped with a driver assistance system travels along a road with reduced slip resistance, wherein the driver assistance system avoids a collision of the motor vehicle with another motor vehicle traveling ahead despite the reduced slip resistance;

[0035] Fig. 2 shows the motor vehicle according to Fig. 1, wherein in particular components of the driver assistance system of the motor vehicle are shown schematically;

[0036] Fig. 3 is a flow chart illustrating the evaluation of state variables and empirical variables by an evaluation device of the driver assistance system, whereby autonomous braking is triggered earlier when a reduced slip resistance of the surface in the vicinity of the motor vehicle is detected; and

[0037] Fig. 4 schematically shows a temporal sequence of events during the earlier triggering of autonomous braking due to the reduced slip resistance of the surface in the surroundings of the motor vehicle.

[0038] In the figures, identical or functionally identical elements are provided with identical reference symbols.

[0039] Fig. 1 shows a motor vehicle 10 having a driver assistance system 12. The motor vehicle 10 is traveling along a lane 14 of a road 16, with slippery road conditions prevailing at least in this lane 14 of the road 16. For example, this may be due to snow and / or ice on the lane 14, and / or because the lane 14 is wet.

[0040] The driver assistance system 12 of the motor vehicle 10 can execute an assistance function 18 (see Fig. 3) to avoid a collision of the motor vehicle 10 with an obstacle, wherein the assistance function 18 causes an autonomous braking of the motor vehicle 10.

[0041] Autonomous braking 18, in particular autonomous emergency braking (AEB), is an important function of the driver assistance system 12. This assistance function 18 ensures that the motor vehicle 10 is braked in a timely manner if a driver of the motor vehicle 10 fails to react by actuating a braking device of the motor vehicle 10 in time to bring the motor vehicle 10 to a stop before the collision with an obstacle. As an example, Fig. 1 illustrates a situation in which the obstacle located in front of the motor vehicle 10 in the direction of travel is another motor vehicle 20.

[0042] When the driver assistance system 12 executes the assistance function 18, which causes the autonomous braking of the motor vehicle 10, a time period remaining until the impact of the motor vehicle 10 with the obstacle, in this case in the form of the additional motor vehicle 20, can be calculated. The time period or time until the impact can be calculated by taking into account a distance of the motor vehicle 10 from the additional motor vehicle 20 and the relative speed of the motor vehicle 10 with respect to the additional motor vehicle 20 (see Fig. 4).

[0043] If the time remaining until the collision between motor vehicle 10 and another motor vehicle 20, i.e., the time to collision (TTC) at an unchanged driving speed of motor vehicle 10, is exceeded, the assistance function 18 of driver assistance system 12 causes autonomous braking of motor vehicle 10. This ensures, in particular, that motor vehicle 10 comes to a stop before it collides with the other motor vehicle 20. The threshold value for the length of the time period below which the motor vehicle 10 is automatically braked by the driver assistance system 12 is typically designed for dry road conditions. In dry road conditions, the surface has a high level of slip resistance, so that the autonomous braking of motor vehicle 10 results in a strong deceleration.

[0044] In the present case, however, the situation should be considered that slippery road conditions exist at least on lane 14, on which the motor vehicle 10 and the other motor vehicle 20 are traveling (see Fig. 1). Under these slippery road conditions, a reduced deceleration is achieved when braking the motor vehicle 10. Under slippery road conditions, it is therefore expedient to trigger the autonomous braking, which is represented in Fig. 4 by a block 22, earlier. The time remaining until the collision is plotted on an abscissa 24 in Fig. 4, and the deceleration of the motor vehicle 10 is plotted on an ordinate 26. Accordingly, in Fig. 4, a height of the block 22 indicates a strength of the deceleration during the autonomous braking.

[0045] To assess the slip resistance of the surface in the vicinity of the motor vehicle 10, in this case, to assess the slip resistance of, for example, lane 14 (see Fig. 1), an evaluation device 28 of the driver assistance system 12 takes into account, on the one hand, state variables 30 and, on the other hand, empirical variables 32 (see Fig. 3). The state variables 30 are currently present variables describing the state in the vicinity of the motor vehicle 10, which are detected by at least one detection device of the driver assistance system 12.

[0046] As examples of detection devices of the driver assistance system 12 that can be used in this context, a camera 34 and a rain sensor 36 are shown in Fig. 2 in a highly schematic manner. The camera 34, like the rain sensor 36, can be arranged behind a windshield 38 of the motor vehicle 10. Accordingly, the camera 34 can be a front camera designed to detect the surroundings to the front of the motor vehicle 10.

[0047] For reasons of clarity, only the camera 34 is shown in Fig. 1 of the detection devices of the driver assistance system 12 shown as examples in Fig. 2, which are designed to detect state variables 30. As an additional or alternative sensor device, the driver assistance system 12 can have a temperature sensor 40, shown schematically in Fig. 2, which is designed to detect a temperature in the environment of the motor vehicle 10. Also shown schematically in Fig. 2 as an example of a further detection device for detecting state variables 30 is a receiving device 42, which can receive, in particular, weather data.

[0048] In order to be able to assess the skid resistance in the surroundings of the motor vehicle 10, in this case, for example, lane 14, with particularly high reliability, the evaluation device 28 not only considers or evaluates the state variables detected by the at least one detection device. Rather, the evaluation device 28 uses at least one empirical variable 32 to assess the skid resistance of the subsurface (see Fig. 3), wherein the empirical variables 32 in this case include map data.

[0049] The empirical variables 32 in the form of the map data indicate that at least one location in the vicinity of the motor vehicle 10 has an increased probability of slippery road conditions occurring. For example, the map data may include the empirical variable 32 that there is an increased risk of slipping at least on the roadway or lane 14 because the road 16 leads over a bridge (not shown) or through a depression in the terrain (also not shown). Furthermore, the empirical variables 32 in the form of the map data may indicate that at least one location in the vicinity of the motor vehicle 10 has an increased frequency of accidents, wherein these accidents are at least partly caused by slippery road conditions.

[0050] The map data can be made available to the evaluation device 28 from an in-vehicle storage device 44 of the driver assistance system 12 (see Fig. 2). The storage device 44 can, for example, be part of a navigation system of the motor vehicle 10. The navigation system can, in particular, comprise a device for determining the position of the motor vehicle 10. In particular, taking into account the position of the motor vehicle 10, it is very easy to determine whether there are locations in the vicinity of the motor vehicle 10 ahead at which the empirical variables 32 in the form of the map data indicate an increased probability of slippery road conditions occurring. According to Fig. 2, the driver assistance system 12 can have a communication device 46 designed to wirelessly receive data. Current map data, in particular, can be received via this communication device 46.Additionally or alternatively, the map data stored in the storage device 44 can be updated via the communication device 46. When using the communication device 46, the map data can be obtained, in particular, via vehicle-to-X communication and made available to the evaluation device 28.

[0051] For example, the communication device 46 can be configured for vehicle-to-vehicle communication and receive the preferably current map data from a mobile device such as the additional motor vehicle 20 (see Fig. 2). Another possibility for receiving the map data via the communication device 46 is schematically illustrated in Fig. 2. Accordingly, a stationary warning device 48 can be arranged in the vicinity of the motor vehicle 10, which is configured for wireless transmission of the map data.

[0052] Additionally or alternatively, the device illustrated in Fig. 2 as the stationary warning device 48 may be a server device on which current map data is preferably available. Accordingly, the server device can provide the map data and thus the empirical variables 32 (see Fig. 3) to the driver assistance system 12.

[0053] In the following, some situations will be considered in which the state variables 30 and the empirical variables 32 according to Fig. 3 are used to assess the slip resistance of the ground in the environment of the motor vehicle 10.

[0054] For example, the current temperature in the surroundings of the motor vehicle 10 can be detected by means of the temperature sensor 40, wherein it can be determined that the temperature in the surroundings of the motor vehicle 10 is close to 0° Celsius and thus close to the freezing point. This state variable 30 is taken into account by the evaluation device 28 (see Fig. 3). In addition, map data indicating that the road 16 will lead over a bridge can be used as the empirical variable 32. This is based on the knowledge that bridges are often somewhat colder than other parts of the road 16. Therefore, when the road 16 is wet, there may be an increased risk of slippery road conditions on the bridge (not shown) due to a frozen road surface.The information about the presence of the bridge in the surroundings ahead of the motor vehicle 10 can be stored in the storage device 44 of the driver assistance system 12 and / or obtained via a cloud-based service, as explained in Fig. 2 with reference to the server device.

[0055] Furthermore, it is possible for the presence of the bridge in the surroundings ahead of the motor vehicle 10 to be detected by means of the camera 34 and / or by means of a further sensor device, for example by means of a lidar device (not shown) of the driver assistance system 12.

[0056] Fig. 1 shows that a traffic sign 50 may be installed on road 16, which may indicate, for example, the presence of a bridge in the vicinity of motor vehicle 10 ahead and / or slippery conditions and / or a risk of skidding. If such an empirical value 32 is captured by camera 34, this can also be taken into account for the early initiation of autonomous braking.

[0057] In addition, the traffic sign 50 and its meaning can be included in the map data, which are evaluated as the at least one empirical value 32 (see Fig. 3).

[0058] As a further example, consider the case where the current local temperature in the surroundings of the motor vehicle 10 is detected by means of the temperature sensor 40, and it is determined that this temperature is in the range of 0° Celsius. Furthermore, the camera 34 can detect that the road 16 ahead of the motor vehicle 10 is wet. This can be additionally or alternatively detected by the rain sensor 36. Furthermore, the presence of wet road conditions can be detected via the receiving device 42, which receives weather data or a weather report.

[0059] Furthermore, the evaluation device 28 can determine, based on the empirical variables 32 in the form of the map data, that an upcoming section of the road 16 has, based on experience, a reduced skid resistance or an increased probability of slippery road conditions. In this context, the map data can, in particular, contain the empirical variable 32 that accidents occur frequently on this road section that are caused or at least partly caused by slippery road conditions.

[0060] The evaluation device 28 of the driver assistance system 12 thus takes into account, on the one hand, the at least one state variable 30 and, on the other hand, the at least one empirical variable 32 in order to determine that the autonomous braking should be triggered earlier because the road 16 ahead is more slippery than in dry road conditions, at least in the area of ​​the lane 14 traveled by the motor vehicle 10.

[0061] Fig. 4 shows, by way of example, that certain steps can precede the autonomous braking initiated earlier in the present case, which is illustrated in Fig. 4 by block 22. For example, at a first time 52, the driver of motor vehicle 10 can be informed of the distance between motor vehicle 10 and the preceding motor vehicle 20. In the present case, consider the case where the driver of motor vehicle 10 does not reduce the driving speed of motor vehicle 10 and thus approaches the other motor vehicle 20.

[0062] At a later time 54, a warning can be issued to the driver of the motor vehicle 10 that a frontal impact with the obstacle, in this case in the form of the further motor vehicle 20, is imminent if the driver continues not to slow down the driving speed of the motor vehicle 10.

[0063] According to Fig. 4, the case shall be considered in which the driver of the motor vehicle 10 does not initially react to this warning, but then brakes at least a little.

[0064] Further bars 56 indicate in Fig. 4 that corresponding actuations of the braking device of the motor vehicle 10 carried out by the driver of the motor vehicle 10 are amplified by the driver assistance system 12.

[0065] It should be assumed in Fig. 4 that even this increase in the braking effect is not sufficient to come to a stop in time before reaching the other motor vehicle 20 or at least to avoid colliding with the other motor vehicle 20. Subsequently, at a further time 58, the braking system of the motor vehicle 10 is prefilled with brake fluid or the pressure of the brake fluid is increased, so that the maximum braking effect of the braking system is then available very quickly when autonomous braking is carried out.

[0066] A left boundary line 60 of block 22 in Fig. 4 indicates the time at which the autonomous emergency braking of the motor vehicle 10 is initiated by the assistance function 18 (see Fig. 3) of the driver assistance system 12. This time is shifted further to the left according to the situation explained with reference to Fig. 1. The autonomous braking is therefore carried out earlier because the evaluation device 28, taking into account the state variables 30 and the empirical variables 32 in the form of the map data, concludes that slippery road conditions exist on the road 16. Thus, despite the slippery road conditions on the section of the road 16 ahead of the motor vehicle 10, a collision between the motor vehicle 10 and the other motor vehicle 20 can be prevented.

[0067] Overall, the examples show how improved autonomous braking, in particular in the form of autonomous emergency braking, can be carried out because both the at least one state variable 30 and the at least one empirical variable 32 in the form of map data are taken into account by the evaluation device 28 in order to assess the slip resistance of the ground in the surroundings ahead of the motor vehicle 10.

Claims

Patent claims 1. A method for operating a motor vehicle (10), in which at least one state variable (30) is detected by means of at least one detection device of a driver assistance system (12), which state variable is evaluated by an evaluation device (28) of the driver assistance system (12) with regard to a slip resistance of a surface in the surroundings of the motor vehicle (10), wherein the evaluation device (28) additionally uses at least one empirical variable (32) to assess the slip resistance of the surface, and in which, in order to avoid a collision of the motor vehicle (10) with an obstacle, the driver assistance system (12) executes an assistance function (18) which causes autonomous braking of the motor vehicle (10), characterized in that the evaluation device (28) uses map data as the at least one empirical variable (32).which indicate an increased probability of slippery road conditions occurring at at least one location in the vicinity of the motor vehicle (10).

2. Method according to claim 1, characterized in that the evaluation device (28) uses map data which indicate an increased frequency of accidents at the at least one location in the surroundings of the motor vehicle (10), the accidents being at least partly caused by slippery road conditions.

3. Method according to one of the preceding claims, characterized in that the map data indicate the presence of a bridge and / or a depression in the surroundings of the motor vehicle (10), the presence of the bridge and / or the depression being used by the evaluation device (28).

4. Method according to one of the preceding claims, characterized in that the map data are made available to the evaluation device (28) by an internal vehicle storage device (44) of the driver assistance system (12).

5. Method according to one of the preceding claims, characterized in that the map data are made available to the evaluation device (28) by a communication device (46) of the driver assistance system (12) which is designed to receive data wirelessly.

6. The method according to claim 5, characterized in that the map data of the communication device (46) are transmitted wirelessly by at least one stationary and / or mobile warning device (48) arranged in the surroundings of the motor vehicle (10) and / or by a server device.

7. Method according to one of the preceding claims, characterized in that by means of at least one sensor device (40) of the driver assistance system (12) a temperature in the surroundings of the motor vehicle (10) and / or a presence of liquid and / or frozen water on the ground in the surroundings of the motor vehicle (10) is detected as the at least one state variable.

8. The method according to claim 7, characterized in that a rain sensor (36) and / or a camera (34) are used as the at least one sensor device of the driver assistance system (12).

9. Method according to one of the preceding claims, characterized in that a receiving device (42) of the driver assistance system (12) is used as the at least one detection device, which receives weather data as the state variable, and / or a meaning of a traffic sign (50) located in the surroundings of the motor vehicle (10) is used by the evaluation device (28) as the at least one empirical variable (32).

10. Method according to one of the preceding claims, characterized in that when a reduced slip resistance of the ground in the surroundings of the motor vehicle (10) is detected, a length of a time period remaining until an impact of the motor vehicle (10) on the obstacle is increased, below which time period the assistance function (18) causes the autonomous braking of the motor vehicle (10).

11. A driver assistance system (12) for a motor vehicle (10), comprising at least one detection device for detecting at least one state variable (30) which can be evaluated by an evaluation device (28) of the driver assistance system (12) with regard to the slip resistance of a surface in the surroundings of the motor vehicle (10), wherein the evaluation device (28) is designed to additionally use at least one empirical variable (32) to assess the slip resistance of the surface, and in which the driver assistance system (12) is designed to carry out an assistance function (18) to avoid a collision of the motor vehicle (10) with an obstacle, by means of which autonomous braking of the motor vehicle (10) can be effected, characterized in that the evaluation device (28) is designed to use map data as the at least one empirical variable (32).which indicate an increased probability of slippery road conditions occurring at at least one location in the vicinity of the motor vehicle (10).

12. Motor vehicle (10) with a driver assistance system (12) according to claim 11.

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