METHOD AND DEVICE FOR DETERMINING A ROAD CONDITION

Description

[0001] The present invention relates to a method and a device for determining road surface conditions. In particular, the present invention relates to the detection of a road surface with a risk of aquaplaning. Furthermore, the present invention relates to a motor vehicle with a device for determining road surface conditions. State of the art

[0002] Aquaplaning describes the phenomenon of a tire floating on a film of water on a wet road surface. A wedge of water forms beneath the tire's contact patch, leading to a loss of traction. During aquaplaning, no steering or braking forces can be transmitted to the road. Aquaplaning poses a significant hazard to motor vehicle operation. A particular danger arises from the fact that aquaplaning often occurs without any significant warning to the driver, leaving them caught off guard. During aquaplaning, the tire completely loses contact with the road surface, and the vehicle essentially floats on water. In this state, the vehicle is neither steerable nor controllable by braking.Since aquaplaning only occurs above a critical driving speed, depending on the amount of water displaced per unit of time, accidents are often particularly serious due to the high driving speed.

[0003] From WO 2015 / 070861 A1, a method for determining a road surface is known using a vehicle camera system, in which at least one image of a vehicle's surroundings is taken using the vehicle system, at least one image is evaluated to determine indications of the presence of a road surface when a vehicle drives over the road, the determined indications are taken into account when determining a road surface, and the result of the determination of the road surface can be output.

[0004] WO 2017 / 005689 A1 describes a method for determining at least one tire-specific characteristic of a tire of a motor vehicle, in which an area of ​​the tire of the motor vehicle is captured by means of at least one vehicle-side camera, wherein a tire sidewall of the tire with a tire marking is captured as the area by means of the at least one camera, and the tire marking is identified by means of an evaluation device and the at least one tire-specific characteristic is determined on the basis of the tire marking.

[0005] It is therefore desirable to detect the risk of aquaplaning as early as possible so that the driver or a vehicle assistance system can adjust the driving style accordingly. Consequently, there is a need to determine road surface conditions. In particular, there is a need to identify road surface conditions that pose a risk of aquaplaning. Disclosure of the invention

[0006] The present invention discloses a method for determining a road surface condition with the features of claim 1, a device for determining a road surface condition with the features of claim 7, and a motor vehicle with the features of claim 11. Accordingly, the following is planned:

[0007] A method for determining road surface condition. The method includes the step of providing image data. The image acquisition device captures at least a portion of the space around a vehicle wheel. The method further includes the step of detecting spray water in the provided image data. Finally, the method includes a step for classifying road surface condition using the spray water detected in the provided image data. The classification of the road surface condition includes at least a distinction between a dry road surface, a wet road surface, and a road surface with a risk of aquaplaning. Furthermore, it is planned:

[0008] A device for determining road surface conditions. The device comprises an image acquisition unit and an evaluation unit. The image acquisition unit is designed to acquire image data of at least a portion of the space around a wheel and to provide the acquired image data. The evaluation unit is designed to detect spray water in the provided image data and to classify road surface conditions using the spray water detected in the image data. The classification of the road surface conditions by the evaluation unit includes at least a distinction between a dry road surface, a wet road surface, and a road surface with a risk of aquaplaning. Furthermore, the following is planned:

[0009] A motor vehicle with a device according to the invention for determining the condition of the road surface. Advantages of the invention

[0010] The present invention is based on the understanding that aquaplaning typically occurs unexpectedly for the driver of a vehicle, as well as for the assistance systems of a fully or partially automated vehicle. When aquaplaning occurs, a wedge of water is forced under the tire's contact patch, leading to a loss of traction. As long as aquaplaning has not yet occurred, on a wet road surface with shallow water, the tire can absorb the water via channels in the tread. Due to its surface tension, the water adheres to the tire and is then flung into the wheel well by centrifugal forces. As aquaplaning develops and occurs, the tire must displace increasingly larger amounts of water. This initially increases the amount of water flung from the tire into the wheel well. Furthermore, the increased dynamic pressure also forces more water to the sides and forwards.

[0011] The present invention is therefore based on the idea of ​​taking this knowledge into account and detecting impending aquaplaning by evaluating the spray from at least one wheel of the vehicle and the surrounding area. At least three different conditions can be distinguished. On a dry road surface, there is usually no spray, so the absence of spray indicates a dry road surface. If, on the other hand, spray is present, this is an indication that the road surface is at least wet, i.e., a road surface on which water is present. As long as the vehicle's tire is still in direct contact with the road surface, the spray will consist at least largely of water that is thrown into the wheel well due to the radial movement of the wheel.Furthermore, as the probability of aquaplaning increases, more water will spray to the side or even forward. Therefore, analyzing the spray from a vehicle's wheel can indicate the risk of aquaplaning or confirm the presence of aquaplaning.

[0012] Since a direct correlation exists between the appearance of spray and the risk of aquaplaning, the detected spray can directly indicate a potential aquaplaning hazard. No special, potentially complex or error-prone sensor calibration is required. Therefore, highly reliable detection of potential aquaplaning hazards can be achieved by detecting spray, particularly through optical measurement of the spray at at least one wheel and the surrounding area. Furthermore, it is unnecessary to adjust the aquaplaning detection system after a tire change or a modification of one or more vehicle tire parameters.

[0013] Such reliable aquaplaning detection allows drivers to be warned of potential hazards at an early stage. Furthermore, this information can be integrated into driver assistance systems and systems for fully or partially automated driving, enabling the vehicle's driving style to be adapted to the prevailing weather conditions. This can significantly improve safety.

[0014] According to one embodiment, classifying the road surface condition further includes detecting the risk of micro-aquaplaning. Micro-aquaplaning is defined as a condition in which the vehicle, and in particular at least one wheel of the vehicle, is on the verge of aquaplaning. In this micro-aquaplaning condition, the contact zone between the vehicle's tire and the road surface is virtually nonexistent or at least reduced to a minimum. While the vehicle's braking and / or maneuverability in this condition is still limited, aquaplaning is imminent. This is noticeable, for example, when braking from higher speeds, as the braking distance is significantly increased. This condition is therefore of particular importance because it still allows for controlled intervention in the vehicle's handling.According to the invention, detecting spray water includes determining the direction of its throw. Further parameters for evaluating the spray water in the image data are also possible. Spray water detection can additionally include determining the spray water's exit point in the image data, determining the amount of water in the image data, determining the number of drops in the image data, and / or determining the spray water's throw distance. By determining and evaluating such characteristic properties of the spray water, the probability of aquaplaning occurring, and thus the criticality of the driving situation, can be accurately determined.

[0015] According to one embodiment, detecting splashing water includes determining the proportion of image data containing splashing water. For example, this can be achieved by determining the number of pixels in the image data that represent splashing water. Similarly, it is possible, for example, to determine an area ratio, a pixel ratio, or another ratio between image data containing splashing water and image data without splashing water.

[0016] According to one embodiment, the detection of splashing water includes detecting a change in the proportion of splashing water in the image data. For example, a temporal increase or decrease in pixels associated with splashing water or water droplets in the image data can be determined.

[0017] According to one embodiment, the method includes a step for transmitting the classified road condition to a display device and / or a control unit of the vehicle. In this way, the classified road condition can be displayed to the driver of the vehicle, enabling them to adjust their driving behavior accordingly. It is also possible for a control unit to receive and evaluate the road condition classification, and for a driver assistance system or a fully or partially automated driving system to adjust its control operations accordingly. Furthermore, the road condition classification can also be transmitted to other vehicles or a central data processing unit via a transmission device.

[0018] According to one embodiment of the device for determining road surface conditions, the device includes a lighting unit. The lighting unit is designed to illuminate at least part of the area detected by the image acquisition unit. This illumination can be achieved using visible or invisible light. In particular, illumination with infrared light or light of a predetermined wavelength or wavelength spectrum is also possible. This makes it possible to reliably detect splash water on the vehicle's wheel even in darkness or unfavorable lighting conditions.

[0019] According to one embodiment, the device for determining the road surface condition includes a signaling device. The signaling device is designed to issue a signal when a predetermined road surface condition has been classified. This signal can be, for example, a visual, acoustic, or haptic signal issued to the vehicle's driver. Furthermore, the signal can also include an electronic signal, which is transmitted, for example, to another unit of the vehicle. In this way, the vehicle's control system can be automatically adapted to the classified road surface condition. The signal can also include transmitting the classified road surface condition to an external device, such as another vehicle or a central data processing unit.

[0020] According to one embodiment of a motor vehicle with a device for determining road conditions, the motor vehicle includes a control device designed to adapt at least one function of the motor vehicle using the classified road conditions. In this way, the vehicle's driving behavior can be adapted depending on the classified road conditions. This can increase driving safety.

[0021] The above embodiments and further developments can be combined with one another as appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention. Short description of the drawings

[0022] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. These show: Figure 1: a schematic representation of a motor vehicle with a device for determining a road surface condition according to an embodiment; Figure 2: a schematic representation of a three-zone model for a vehicle tire in wet conditions; Figure 3: a schematic representation of the spray pattern as it forms the basis for determining a road surface condition according to an embodiment; and Figure 4: a schematic representation of a flowchart as it forms the basis of a method for determining a road surface condition according to an embodiment.

[0023] Figure 1Figure 1 shows a schematic representation of a vehicle 1 with a device for determining road surface conditions. The device for determining road surface conditions comprises at least one image acquisition device 11 and an evaluation device 12. The image acquisition device 11 can be, for example, a camera or a camera system with multiple cameras. The cameras of the image acquisition device 11 can, in principle, be any suitable camera, such as a camera for recording monochromatic image data or a camera for capturing color image data. In particular, the image acquisition device 11 can also be a camera already present in the vehicle 1, belonging to a driver assistance system or any other system of the vehicle 1.The image acquisition device 1 is directed at a wheel 21 of a vehicle 1, a side of the vehicle 1, or at least an area surrounding the wheel 21. In other words, at least one wheel 21, or the wheel housing surrounding this one wheel 21, or a side of the vehicle 1 is within the field of view (FOV) of the image acquisition device 11.

[0024] To determine the road surface condition, it is generally sufficient to detect at least one wheel 21 of the vehicle 1 using an image capture device. However, it is also possible to optically detect several wheels 21 of the vehicle 1 using one or more image capture devices 11. For example, one or both rear wheels 21 of a vehicle 1 can be detected using image capture devices 11. Furthermore, it is also possible to additionally or alternatively optically detect one or both front wheels 22 of the vehicle 1 using one or more image capture devices 11. Preferably, however, one or both front wheels are used, as the effect of splash water is greater at the front wheels than at the rear wheels.

[0025] The image acquisition device 11 can acquire image data of a wheel 21 of the vehicle 1 in the visible light spectrum. Colored or monochromatic image data can be acquired. Additionally or alternatively, it is also possible to acquire image data in the non-visible infrared and / or ultraviolet wavelength range.

[0026] The image acquisition device 11 can optically capture at least one wheel 21 of the vehicle 1 in its entirety. Furthermore, it can also optically capture an additional area in the vicinity of the wheel 21 of the vehicle 1. However, it is also possible to optically capture only a portion of the wheel 21 and a suitable surrounding area using the image acquisition device 11. The image area to be captured by the image acquisition device 11 should include not only at least a portion of the wheel 21 or a portion of the wheel housing of the vehicle 1, but also a surrounding area where, in wet road conditions, spray water is to be expected, which is displaced by the wheel 21 when the vehicle 1 moves.

[0027] The image acquisition device 11 can, for example, periodically capture the field of view (FOV) at a predefined frame rate and provide corresponding image data. However, it is also possible to adjust the frame rate for image data acquisition depending on other parameters, such as vehicle speed or similar factors.

[0028] To enable optical detection by the image acquisition device 11 even under unfavorable lighting conditions and in darkness, the field of view of the image acquisition device 11, or if necessary only a portion thereof, can be illuminated by a suitable lighting device 13. The light emitted by the lighting device 13 can be specifically adapted to the wavelength range detected by the image acquisition device 11. For example, if infrared light is detected by the image acquisition device 11, the lighting device 13 can also emit infrared light in the corresponding wavelength range. By using non-visible light, such as infrared light, impairment of other persons, especially drivers of other vehicles or other persons in the vicinity of the vehicle 1, can be avoided.

[0029] The image data acquired by the image acquisition device 11 is then provided to the evaluation device 12. The evaluation device 12 processes the image data provided by the image acquisition device 11 and, in particular, detects elements in the provided image data that can be attributed to splash water. The splash water to be detected in the image data is water that is displaced by the wheel 21, which is monitored by the image acquisition device 11, and / or water that initially adheres to the respective wheel 21 and is flung away from the wheel 21 due to the radial movement of the wheel 21. The evaluation device 12 can determine one or more characteristic properties of the detected splash water in the image data.Based on characteristic properties of the spray water in the image data, the evaluation unit 12 then classifies the road surface condition. This classification of the road surface condition includes at least three classes of road surface conditions: a dry road surface, a wet road surface, and a road surface with a risk of aquaplaning.

[0030] If no or virtually no splash water is detected in the image data acquired by the image acquisition device 11, the road surface is classified as dry. However, if splash water is detected in the image data acquired by the image acquisition device 11, the road surface is at least wet – and there may also be a risk of aquaplaning. Therefore, when splash water is present, an additional analysis is performed to detect a potential aquaplaning hazard based on one or more characteristic properties of the splash water, or, if necessary, to estimate the probability of an aquaplaning hazard.

[0031] On a wet road surface, some of the water will initially adhere to wheel 21. Due to radial motion, some of this water will subsequently be flung away. This spray, which occurs even on a wet road surface without a risk of aquaplaning, is spray that is thrown from wheel 21 into the wheel well of vehicle 1. Therefore, the presence of such spray indicates that the road surface can at least be classified as wet.

[0032] On a wet road surface, water initially flows away through the grooves in the tread of the tire on wheel 21. As long as sufficient water can still flow away, the protruding parts of the tread in such a tire can still maintain contact with the road surface, thus ensuring continued traction and braking performance. With an increasing amount of water and / or increasing speed of the vehicle 1, more water is displaced to the sides and potentially forwards. This also increases the risk of aquaplaning. Therefore, an increase in spray, especially the detection of spray directed laterally and / or forwards, can be interpreted as an indication of an increasing risk of aquaplaning. If the detected spray exceeds a predefined threshold, the road surface condition is classified as "aquaplaning hazard."The total amount of spray water, the amount of spray water detaching from the wheel and being thrown into the wheel well, and / or the spray water directed laterally or forwards can all be evaluated as criteria for detecting a risk of aquaplaning.

[0033] Several different parameters can be used to assess the amount of spray. For example, all pixels in an image (frame) of the image data provided by the image acquisition device 11 can be evaluated, distinguishing between pixels that correspond to spray and those that do not. Accordingly, if a certain number of pixels corresponding to spray are exceeded, a roadway can be classified as at least wet, and if a further threshold is exceeded, the roadway can be classified as having a risk of aquaplaning. Furthermore, it is also possible to sum all surface areas in an image that correspond to spray.In this case, too, the road surface can be classified as wet upon exceeding a first threshold and as having a high risk of aquaplaning upon exceeding a second threshold. Furthermore, it is also possible to analyze changes in the proportion of spray water in the captured image data and, in the case of a rapid increase in the spray water proportion, to conclude that the road surface is wet or has a high risk of aquaplaning. The thresholds for distinguishing between dry, wet, and aquaplaning surfaces can also be adjusted based on other parameters, such as vehicle speed, windshield wiper activity, or ambient temperature.

[0034] Furthermore, it is also possible to determine the angle of the spray in the image data detected by the image acquisition device 11 and to classify the road surface condition based on one or, if applicable, several angles of the spray in the image data. According to the invention, a classification of the road surface condition based on the direction of spray is provided. Furthermore, a classification of the road surface condition based on the spray distance is also possible. Additional parameters, such as the droplet or jet shape of the emerging water, for differentiating the road surface conditions are also possible.

[0035] The classification of road surface conditions may, in addition to the three previously described conditions, also distinguish one or more further road surface conditions. For example, a further road surface condition known as "micro-aquaplaning" is possible. This road surface condition, known as micro-aquaplaning, is one in which there is still some – possibly only slight – adhesion between the wheel 21 and the road surface, but complete aquaplaning is imminent.

[0036] Figure 2Figure 1 shows a schematic representation of a three-zone model for describing the contact between a tire 30 and a road surface 35. The water 37 on the road surface 35 is shown hatched. The contact area of ​​the tire 30 with the road surface 35 can be divided into three zones 31-33. If the vehicle, and thus also the tire 30, moves in the direction of travel indicated by the arrow, an approach zone 31 initially forms on the tire, in which water is located approximately wedge-shaped between the tire 30 and the road surface 35. This approach zone 31 is followed by a transition zone 32. In the area of ​​the contact zone 33, which adjoins the transition zone 32, the tire 30 is in direct contact with the road surface 35, thereby achieving the corresponding adhesion effect.As the water level and / or driving speed increases, the contact zone 33 decreases, and thus the contact area between the tire 30 and the road surface 35 decreases. If this extent of the contact zone 33 approaches zero, the risk of aquaplaning is imminent. This condition is therefore referred to as micro-aquaplaning. If the contact zone 33 no longer exists, meaning that there is water across the entire area between the tire 30 and the road surface 35, aquaplaning occurs, and a vehicle can no longer be controlled or braked during this condition.

[0037] Figure 3Figure 3 shows a schematic representation of the individual spray directions of a tire 30 with direction of travel F. While spray water obviously does not occur on a dry road surface, on a wet road surface, as previously described, spray water initially forms due to the adhesion of water to the surface of the tire 30. This spray water is thrown away from the tire 30 due to its radial movement. This spray water is primarily thrown upwards and rearwards into the wheel well of the vehicle and exits laterally at the rear of the wheel well in the form of drops or jets. This portion of the spray water is in Figure 3Designated with reference number 43. As the water level and / or driving speed increases, more spray is displaced laterally in directions 42. Furthermore, a bow wave can form in the direction of travel F in front of tire 30, which may also cause spray forward in directions 41. In both cases, this spray is caused by increased water pressure due to a risk of aquaplaning. The main point of water exit is always at the bottom, in the area of ​​contact between the tire and the road surface, i.e., at the so-called contact patch of the tire. This is accompanied by water being flung into the wheel wells by centrifugal force, which then exits laterally from the wheel wells, and a significant spray formation in the entire area near the wheels.

[0038] Accordingly, if spray is only present in direction 43, it can be concluded that the road surface is merely wet, whereas with increasing spray in directions 42 and 41, the probability of micro-aquaplaning or aquaplaning also increases. Therefore, the amount and / or direction of spray can be used to infer the road surface condition and, in particular, the probability of impending aquaplaning.

[0039] The classification of the road surface condition, in particular an indication of a wet road surface and the detection of aquaplaning hazards, can then be communicated to the vehicle driver. For example, as the risk of aquaplaning increases, the driver can receive a visual, audible, and / or haptic signal. The driver can then adjust their driving accordingly, for example, by reducing speed, and thus prevent uncontrolled driving due to aquaplaning.

[0040] Furthermore, it is also possible to provide the road surface condition classification, in particular the detection of a wet road surface, as well as the detection of aquaplaning hazards or, where applicable, micro-aquaplaning, or the probability of aquaplaning, to another control system of the vehicle. For example, a driver assistance system can automatically intervene in the vehicle's driving behavior based on the road surface condition classification to prevent uncontrolled driving behavior due to aquaplaning or, if necessary, intervene in the vehicle's control system as soon as aquaplaning occurs in order to avoid dangerous steering and / or braking maneuvers during aquaplaning. Furthermore, a fully or partially automated driving system can also adapt the driving behavior according to the road surface condition classification.

[0041] Furthermore, it is also possible to transmit a detected road condition, in particular the detection of an aquaplaning hazard or the probability of aquaplaning, to other vehicles or a central computer system via a communication device, such as a radio interface or similar. In this way, other road users can also benefit from the road condition classification.

[0042] Figure 4Figure 1 shows a schematic representation of a method for determining a road surface condition according to one embodiment. In a first step S1, image data is acquired and provided by an image acquisition device 11. As previously described, the image acquisition device 11 is directed at at least one wheel 21 of the vehicle, an area surrounding the wheel 21, and / or at least one side of the vehicle 1. In step S2, spray water is detected in the acquired image data. Using the detected spray water in the provided image data, the road surface condition is classified in step S3. The classification includes at least a distinction between three road surface conditions: dry road surface, wet road surface, and aquaplaning road surface. One or more additional road surface conditions are also possible.In particular, the classification can also include, for example, another road surface condition of an impending aquaplaning, which is referred to here as microaquaplaning.

[0043] In summary, the present invention relates to a classification of road surface conditions based on the spray water occurring at a wheel of the vehicle. For this purpose, the space around a wheel of the vehicle is captured by a camera, and the image captured by the camera is analyzed to detect spray water. Based on the detected spray water, a distinction can be made between a dry road surface, a wet road surface, or a road surface with a risk of aquaplaning.

Claims

1. Method for determining a roadway condition, comprising the following steps: providing (S1) image data by means of an image capturing device (11), wherein the image capturing device (11) captures at least part of a space around a wheel of a vehicle (1); detecting (S2) spray water in the image data provided; and classifying (S3) a roadway condition using the spray water detected in the image data provided; wherein the classifying (S3) of the roadway condition comprises a distinction between a dry roadway and a wet roadway, characterized in that the detecting (S2) of spray water comprises determining a projection direction of the spray water, wherein the classifying (S3) of the roadway condition additionally comprises at least one distinction between a wet roadway without risk of aquaplaning and a wet roadway with risk of aquaplaning, wherein the classifying (S3) is carried out on the basis of the projection direction determined.

2. Method according to Claim 1, wherein the classifying (S3) of the roadway condition furthermore comprises detecting a risk of microaquaplaning, wherein an adhesion effect of the wheel on the roadway is still present, but complete aquaplaning is immediately imminent.

3. Method according to Claim 1 or 2, wherein the detecting (S2) of spray water furthermore comprises determining an emergence position of the spray water in the image data, an emergence angle of the spray water in the image data, a water amount of the spray water in the image data, a number of drops in the image data and / or a distinction of a drop or jet form of the spray water.

4. Method according to any of Claims 1 to 3, wherein the detecting (S2) of spray water furthermore comprises determining a proportion of image data with spray water.

5. Method according to any of Claims 1 to 4, wherein the detecting (S2) of spray water furthermore comprises detecting a change in the proportion of spray water in the image data.

6. Method according to any of Claims 1 to 5, comprising a step for transmitting the classified roadway state to a display device and / or a control device of a vehicle (1).

7. Apparatus for determining a roadway condition, comprising: an image capturing device (11) designed to capture and provide image data of at least part of a space around a wheel (21) of a vehicle (1); and an evaluation device (12) designed to detect spray water in the image data provided and to classify a roadway condition using the spray water detected in the image data, wherein the classifying (S3) of the roadway condition comprises a distinction between a dry roadway and a wet roadway, characterized in that the detecting (S2) of spray water comprises determining a projection direction of the spray water, wherein the classifying (S3) of the roadway condition additionally comprises at least one distinction between a wet roadway without risk of aquaplaning and a wet roadway with risk of aquaplaning, wherein the classifying (S3) is carried out on the basis of the projection direction determined.

8. Apparatus according to Claim 7, comprising an illumination device (13) designed to at least partially illuminate the space captured by the image capturing device.

9. Apparatus according to Claim 7 or 8, comprising a signalling device designed to output a signalling if a predetermined roadway condition has been classified.

10. Apparatus according to any of Claims 7 to 9, comprising a transmission device designed to transmit the classified roadway condition to a further apparatus.

11. Motor vehicle (1) comprising an apparatus for determining a roadway condition according to any of Claims 7 to 10.

12. Motor vehicle (1) according to Claim 11, comprising a control apparatus designed to adapt at least one function of the motor vehicle (1) using the classified roadway condition.