Detection device for fog detection for a motor vehicle

Abstract

Detection device for fog detection (1) for a motor vehicle (5) comprising: an optoelectronic fog sensor device (3) arranged in the front area of ​​the motor vehicle (5), which has a transmitter (11) and a receiver (12) and is designed to apply at least one first optical transmission signal (6) to a spatial area (4) and to detect a reflected reception signal (7) from this spatial area (4), and to generate an electrical signal depending on the strength of the reception signal (7), wherein the detected reception signals correlate with light intensities; at least one further sensor (2) which is provided for detecting data about a vehicle speed and / or for detecting brightness values ​​of the immediate surroundings of the motor vehicle; characterized in that an evaluation unit determines, taking into account the determined data on the vehicle speed and / or the brightness values ​​of the immediate motor vehicle surroundings, whether the received signal (7) is an interference signal or a useful signal; and that a received signal (7) is defined as a useful signal if the received signal (7) exceeds a threshold for fog detection, wherein the threshold for fog detection is adapted according to the determined data on the vehicle speed and / or the brightness values ​​of the immediate motor vehicle surroundings.

Description

[0001] The invention relates to a detection device for fog detection according to the preamble of claim 1.

[0002] Optoelectronic sensor systems (Lidar, "Light Detecting and Ranging"), especially laser-based systems, enable the detection of objects at a distance of more than 100 meters from the vehicle with relatively high measurement accuracy and are already state of the art. Such sensor systems are used to improve driving comfort and increase safety, for example, in lane change assistants, traffic jam assistants, blind spot monitoring, intersection assistants, and pre-crash sensors. Depending on the specific application, the sensor system is installed in the vehicle.

[0003] US Pat. No. 5,118,180 A discloses a method and device for determining a driver's visibility in fog or other interference conditions. A transmitter / receiver device is arranged in the front of a vehicle and functions as a rangefinder. A series of measuring beams is directed by the rangefinder at different measurement areas of the road surface. The radiation backscattered by the road surface is measured. If weather conditions change, for example, due to fog or other interference, the characteristics of the backscattered signal change, or no scattered signal is received at all. The driver is alerted to a dangerous situation by an acoustic or visual warning signal.

[0004] A sensor device for detecting atmospheric disturbances is known from US Pat. No. 5,206,698 A. The sensor device has a transmitter for linearly polarized radiation, a receiver with a first receiving device that measures the intensity of the backscattered radiation from the transmitted beam cone in its polarization plane and perpendicular to it, and with a second receiving device that measures the intensity of the backscattered radiation from an annular spatial region outside the transmitted beam cone. An evaluation device evaluates the measured signals to determine whether a wall of fog, snow, or rain, or a solid obstruction to visibility, is present at a distance to be determined. The type of obstruction and its distance from the lidar device are shown on a display.The lidar device can be used as a distance warning device in a motor vehicle and, in conjunction with a data processing device and a speedometer that measures the speed of the motor vehicle, can be used to achieve an optimal speed of the motor vehicle by influencing the drive and / or braking system, depending on the ambient conditions determined from the measured data.

[0005] US Pat. No. 5,987,152 A discloses a method for determining visibility, particularly for the movement of a motor vehicle. In this method, the original images recorded by an optoelectronic recording device are transformed into image features that identify locations of defined brightness changes in the original images. The current visibility of a driver or an image-processing-based sensor system is determined by determining the distance of the image features relative to the optoelectronic recording device and subsequently filtering the distance values. The advantage over conventional active methods is that, without an active transmitter, the actual contrast of the visual object is incorporated into the determination of visibility, in addition to atmospheric transmissions.

[0006] DE 43 24 308 C1 and DE 39 30 272 A1 each disclose a method for determining visibility in dense fog using a lidar. DE 197 17 399 A1 discloses a device for determining the distance and type of objects as well as the visibility using the pulse-time-of-flight method, with signal processing that compares typical signal shapes, whose rules are stored in a memory, with the acquired signals using fuzzy logic and uses this to determine the distance, assignment of objects, and the type and degree of visibility restriction. WO 2014 / 168851 A1 discloses example methods and systems for detecting weather conditions using on-board vehicle sensors. One example method includes receiving laser data acquired for a vehicle's surroundings, wherein the laser data comprises a plurality of laser data points.The method further comprises associating, by a computing device, the plurality of laser data points with one or more objects in the environment, and determining certain laser data points from the plurality of laser data points not associated with one or more objects in the environment as representative of an untracked object. The method further comprises, based on the one or more untracked objects determined, identifying, by the computing device, an indication of a weather condition of the environment. US 5 349 267 A discloses a device for lighting and / or signaling used in fog. It finds application in the field of lighting and signaling for road vehicles. The device comprises a moisture detection circuit and an optical visibility detection system combined by a combination circuit to activate a fog light.

[0007] However, the systems described above are susceptible to detecting interference signals that are mistakenly identified as fog, which could lead to an unjustified warning message being triggered. This problem arises particularly when the spatial area to be monitored and thus affected by the detection device is comparatively large or not enclosed. For example, received signals can be triggered by reflections from vehicles driving ahead, from bridges, in tunnels, from signs above the roadway, or from branches above the roadway and cannot be reliably distinguished from a signal triggered by fog. Furthermore, the systems described above do not reliably distinguish between restricted visibility caused by rain and restricted visibility caused by fog.However, this reliable distinction is necessary, for example, for automatic control of the rear fog light, since an incorrectly switched on rear fog light can dazzle the following vehicle and thus potentially increase the risk of an accident.

[0008] Discovering these disadvantages, it is the object of the present invention to provide a detection device for fog detection which can more reliably distinguish a fog state from a non-fog state.

[0009] This object is achieved by a detection device for fog detection with the features of claim 1, as well as by a method according to the subordinate method. Advantageous embodiments of the detection device for fog detection are the subject of the dependent claims. It should be noted that the features listed individually in the claims can be combined with one another in any technologically expedient manner and demonstrate further embodiments of the invention. The description, particularly in conjunction with the figures, further characterizes and specifies the invention.

[0010] The invention relates to a detection device for fog detection. According to the invention, the detection device comprises an optoelectronic fog sensor device configured to apply at least one first optical transmission signal to a spatial region and to detect a reflected reception signal from this spatial region. Thus, the fog sensor device is configured as a reflection light barrier, also called an open light barrier. The detection device for fog detection is preferably arranged in the front region of the motor vehicle, and more preferably, the detection device for fog detection is arranged behind the windshield in the vehicle interior.

[0011] An optical transmission signal within the meaning of the invention is, for example, a pulsed or continuous laser beam; preferably, the optical transmission signal is also a pulsed or continuous light generated by a light-emitting diode (LED). The optical transmission signal is preferably in the infrared spectral range, even more preferably in the near-infrared spectral range.

[0012] The spatial area covered is determined by the arrangement of the transmitter and receiver, or by the arrangement of their transmission and reception characteristics. The transmitter and receiver are arranged such that at least a partial overlap exists. Preferably, the transmission and reception characteristics are aligned such that the spatial area covered extends to infinity with increasing distance, for example, because the main transmission direction of the transmitter and the main reception direction of the transmitter, also referred to as their optical axes, run parallel to each other or intersect at an acute angle of less than 10°.

[0013] The exposed spatial area is therefore determined by the conjunction of the optical reception profile of the receiver and the optical beam profile of the transmitter. The connecting line between the geometric center of the exposed spatial area and the geometric center between the transmitter and receiver determines the resulting detection direction.

[0014] Preferably, the transmitter and the receiver are aligned such that their optical axes run parallel or intersect at an acute angle with an angular value of less than 10°, preferably less than 5°, more preferably less than 3°.

[0015] According to a preferred embodiment, the transmitter and receiver are aligned such that their optical axes in the area immediately adjacent to the transmitter and receiver are separated by a distance of less than 20 cm, preferably less than 15 cm, and even more preferably less than 10 cm. For example, the transmitter and receiver are arranged on a common circuit board. For example, the transmitter and receiver are arranged at a distance from each other, with an air vent or rearview mirror base in between.

[0016] The detection device for fog detection is preferably arranged such that its detection direction is perpendicular to a tangential plane of the windscreen in order to reduce unwanted reflections of the optical transmission signal when passing through the windscreen, which would otherwise lead to an additional reduction of the reception signal.

[0017] If there is material in the affected area of ​​space such as fog or very small water droplets, particles, signs, tunnel walls, branches or similar objects, the transmission signal radiated by the transmitter is reflected. The optical transmission signal is reflected depending on the reflective properties of the material in the affected area of ​​space. In the detection of fog according to the invention, the transmission signal radiated by the optical transmitter is reflected more strongly the denser the fog is, i.e. the light intensities detected by the receiver as a received signal consequently become greater the denser the fog is. According to the invention, depending on the strength of the received signal, an electrical signal is output to the evaluation unit for further analysis.

[0018] The spatial area exposed to the invention is preferably located in front of the motor vehicle. In the exposed spatial area, for example, signs, tunnels, bridges or branches above the roadway can trigger an interference signal. An interference signal within the meaning of the invention is therefore a received signal that lies above the background noise (baseline) and is not due to fog. A useful signal within the meaning of the invention, on the other hand, is a received signal that is due to fog. To determine whether the received signal is a useful signal or an interference signal, the detected received signals are analyzed and evaluated in an evaluation unit, taking into account the data on the vehicle operating state and / or the vehicle environment data of the immediate vehicle surroundings, as quickly as possible, i.e. in real time, for example in less than a few decades of milliseconds.

[0019] According to the invention, the received signal is defined as a useful signal based on a threshold value: If the received signal is above a predetermined threshold for fog detection, a fog condition is detected and, for example, a warning signal is issued to the driver and / or the vehicle electronics uses the detection result to control the vehicle's exterior lighting based on it.

[0020] According to the invention, the fog detection threshold is adjusted according to the respective data on the vehicle's operating state and / or the respective vehicle environment data of the immediate vehicle surroundings. The fog detection threshold is preferably determined dynamically, i.e., the fog detection threshold is constantly updated and adjusted, for example, according to the constantly acquired data.

[0021] According to the invention, the data on the vehicle operating state is the vehicle speed.

[0022] According to the invention, the vehicle environment data are data relating to the brightness in the vehicle environment. Preferably, the vehicle environment data in the immediate vicinity of the vehicle are set in relation to the time of day, the season, and the geographical coordinates.

[0023] During heavy rain, for example, the water on the road is stirred up as spray by vehicles driving ahead. This spray consists of very small water droplets and produces a received signal which could correspond to the received signal from fog. Preferably, the amount of rain is continuously determined using an additional sensor, e.g. a rain sensor, and the threshold for fog detection is adjusted accordingly. This means that for a very large amount of rain, the threshold is set high, and for a low amount of rain, the threshold is lowered. By adjusting the threshold in this way, the sensitivity of the optoelectronic fog sensor device is adjusted according to the detected amount of rain, thus avoiding false detection of spray.

[0024] The exposed spatial area is preferably located above the clearance profile specified for roads, so that any motor vehicles traveling ahead are located below the exposed spatial area. In addition, the resulting detection direction intersects the roadway plane, preferably in an angular range of 30°-90°, even more preferably in an angular range of 30°-80°, and most preferably in an angular range of 30°-60°. The angular range is preferably selected such that the exposed spatial area is as far in front of the motor vehicle as possible, while the resulting detection direction, if possible, does not intersect with a motor vehicle traveling ahead. Fog detection in such a specified spatial area makes it possible to detect fog in front of the vehicle without receiving an interference signal from motor vehicles traveling ahead.The driver can therefore be warned early and adjust his driving behavior accordingly, for example by reducing his speed.

[0025] Preferably, the evaluation unit is integrated into the optoelectronic fog sensor device.

[0026] The fog detection device according to the invention further comprises a means of storing the detected received signals as well as the measured data on the vehicle operating state and / or the vehicle environment data of the immediate surroundings of the vehicle. The data is stored, for example, with the corresponding geographical coordinates and time, so that both the temporal progression and the progression of the data along the route can be retrieved. The stored data can, for example, be stored in such a way that the data is available again when the same route is traveled again.

[0027] Preferably, the temporal and / or spatial profile of the received signal is used to additionally differentiate between a foggy state and a non-foggy state. For this purpose, the temporal and / or spatial profile is characterized in the evaluation unit. For example, a slowly increasing temporal and / or spatial profile of the received signal is characteristic of a foggy state, and a stepped increase is characteristic of a tunnel. A stepped temporal and / or spatial profile is a profile in which the detected signal jumps from a lower level to a higher level or from a higher level to a lower level within a predetermined distance or time period. The signal represents the received signal or corresponding data about the vehicle operating state or corresponding vehicle environment data of the immediate vehicle surroundings.Preferably, the specified distance is less than 10 m, more preferably less than 8 m, and the preferred time corresponds to the time in which the preferred distance is covered at the current speed. For example, at a speed of 72 km / h, the specified time period would preferably be 500 ms and more preferably 400 ms.

[0028] For example, the temporal and / or spatial progression of the received signal reflected from a tunnel is stepped. However, in the case of tunnel detection, the detected received signal is most likely above the threshold for fog detection. Considering only the strength of the received signal would therefore incorrectly detect fog. However, a stepped progression of the received signal is not characteristic of fog; thus, a fog condition is excluded by the evaluation unit in the case of a stepped increase in the received signal.

[0029] Preferably, a tunnel is detected via a change in the brightness value, thus avoiding false detection of fog. If the brightness value falls below a threshold of preferably 20%, more preferably 15%, and most preferably 10% of the previously measured brightness value over a specified period of time or over a specified distance, a tunnel is detected. The evaluation unit then switches to tunnel mode "car is currently driving through a tunnel" and the fog measurement is paused. Tunnel detection using a brightness sensor is particularly useful during the day.

[0030] Tunnel mode is exited when it suddenly becomes bright again, i.e., gradually, meaning the brightness value exceeds a predetermined threshold for a specified period of time or over a specified distance. The threshold is preferably between 40% and 60%, more preferably between 45% and 55%, and most preferably 50% of the brightness value detected before tunnel detection.

[0031] Preferably, the distance traveled in tunnel mode is determined, for example, by a counter, preferably via the data bus already available in the vehicle. If a predetermined distance is exceeded, tunnel mode is deactivated again, thus preventing the fog sensor device from being falsely paused.

[0032] Preferably, a detected tunnel, for example, is stored in a database on the vehicle and / or online, along with its geographical coordinates and distance. This data can be used when repeatedly driving the route. This means that the current data is compared with the previously stored data, thus further reducing the likelihood of incorrect tunnel detection due to repeated driving of the route.

[0033] In addition, additional data can be used for plausibility analysis. For example, online data about the region, such as the temperature trend over the past few days, can be compared with the current and / or forecast temperature. For example, in the case of strong temperature fluctuations, the probability of fog can be predicted even before fog is detected.

[0034] For example, the temporal temperature profile for the locations to be passed can be downloaded according to the input in the navigation system at the start of the journey. This can be done, for example, via an additional device automatically connected to the evaluation unit, such as a smartphone or smartwatch, or via an internet connection provided in the vehicle. In addition, routes particularly prone to fog can be stored in the evaluation unit, which are compared with the route suggested by the navigation system or with the current geographical coordinates. If an increased probability of fog is detected for the route specified by the navigation system, a warning message is issued even before fog is detected. The warning message can be visual and / or acoustic and / or haptic.In addition, data available online can be downloaded while driving and / or data from fog warning systems installed along the route can be used. The vehicle surroundings data recorded by the vehicle during the journey can, for example, be collected together with the geographical coordinates in a database stored in the vehicle and thus lead to an improved forecast of the likelihood of fog forming along the route. In addition, the coordinates at which fog was actually detected and the associated data such as temperature, humidity, brightness, etc. can be saved and stored in a database in the vehicle. This database can also be made available online with the driver's consent and, if necessary, also be used by other road users.The data stored in the vehicle and / or online are compared with the vehicle's coordinates and can be used to detect fog or to warn of an increased probability of fog.

[0035] Preferably, the temporal and / or spatial profile of the received signal is analyzed, and the fog detection threshold is adjusted based on the vehicle operating state data and / or the vehicle environment data of the immediate surroundings of the vehicle. Additionally, a database stored in the vehicle and / or an online database can be used during the analysis to predict the probability of fog or to compare it with the current measurement data.

[0036] According to the invention, the method for fog detection in a motor vehicle comprises applying at least one first optical transmission signal to a spatial area and detecting a reflected reception signal from the applied spatial area by an optoelectronic fog sensor device arranged in the front area of ​​the motor vehicle. In a parallel method step, data about the vehicle operating state and / or vehicle environment data from the immediate surroundings of the vehicle are detected via at least one additional sensor. Based on the strength of the reception signal, an electrical signal is generated and transmitted to the evaluation unit.

[0037] Preferably, the received signal and / or the data on the vehicle operating state, namely the vehicle speed, and / or the vehicle environment data, namely the brightness values ​​in the immediate vehicle environment, are evaluated in the evaluation unit.

[0038] Based on the evaluation, taking into account the data determined on the vehicle operating state and / or the vehicle environment data of the immediate vehicle environment, a determination is made as to whether the received signal is an interference signal or a useful signal.

[0039] According to the invention, the determination as to whether the received signal is an interference signal or a useful signal is made on the basis of a threshold for fog detection, wherein the threshold for fog detection is adapted, preferably continuously, on the basis of the determined data on the vehicle operating state and / or the vehicle environment data of the immediate motor vehicle environment.

[0040] Preferably, the detected received signals and / or the determined data on the vehicle operating state and / or the vehicle environment data of the immediate motor vehicle surroundings are stored in the provided evaluation unit. The temporal and / or spatial profile of the received signal and / or the temporal and / or spatial profile of the determined data on the vehicle operating state and / or the vehicle environment data of the immediate motor vehicle surroundings are then preferably evaluated in the evaluation unit. The temporal and / or spatial profile of the received signal and / or the spatial profile of the determined data on the vehicle operating state and / or the vehicle environment data of the immediate motor vehicle surroundings is then used in the further method to determine whether the received signal is a useful signal or an interference signal.

[0041] In the method for fog detection, a visibility range is preferably determined from a useful signal.

[0042] Further features and advantages of the invention will become apparent from the following description of a non-limiting embodiment of the invention, which is explained in more detail below with reference to the figures. These drawings schematically show: Fig. 1: a detection device for fog detection arranged in the front area of ​​a motor vehicle; Fig. 2: a 2D representation of the optical beam profile of an optoelectronic fog sensor device; Fig. 3: a characteristic time course of a received signal and a brightness signal in case of tunnel detection in a non-fog condition; Fig. 4: a characteristic temporal course of a received signal and a brightness signal in case of a fog condition.

[0043] In the different figures, parts that are equivalent in terms of their function are always provided with the same reference symbols, so that they are usually only described once.

[0044] Fig. 1 schematically shows an inventive arrangement of a detection device for fog detection 1 in the front area of ​​a motor vehicle 5, wherein the optoelectronic fog sensor device 3 is arranged behind the windshield in the motor vehicle interior. The optical axis 8 of the optoelectronic fog sensor device 3 intersects the roadway 9 at an angle 10 of approximately 45°. Due to this angular adjustment, the optical axis 8 of the optoelectronic fog sensor device 3, which is mounted at a height of 1 m, is already located at the front bumper at a height of approximately 2.5 m for a hood length of 1.5 m. This ensures that the optical axis 8 of the optoelectronic fog sensor device 3 does not intersect with a motor vehicle 14 traveling ahead.At the same time, the spatial area 4 of the optoelectronic fog sensor device 3 is still located relatively far in front of the motor vehicle 5 at a relatively low height relative to the roadway 9. Schematically, a further sensor 2 is arranged on the roof of the motor vehicle 5, whereby the further sensor 2 can be attached to any location on the motor vehicle 5 that is appropriate for recording the respective data. The data from the further sensor 2 adjusts the fog detection threshold accordingly. If fog is detected, depending on the visibility, both a warning message to the driver and automatic control of the fog light 15 can occur.

[0045] Fig. 2a and Fig. 2b shows a top view of the optical beam profiles 6, 7 of the transmitter 11 and the receiver 12. The transmitter 11 and the receiver 12 are each arranged such that their optical axes intersect. The angle of intersection of the two optical axes, assuming the same optical beam profile, specifies the size of the spatial area 4 exposed to the optoelectronic fog sensor device 3. The exposed spatial area 4 results from the conjunction of the optical beam profile of the transmitter 6 with the optical beam profile of the receiver 7. The connecting line between the geometric center of the exposed spatial area 4 and the geometric center between the transmitter 11 and the receiver 12 specifies the resulting detection direction 8 of the optoelectronic fog sensor device 3.

[0046] The method and device according to the invention are in principle suitable for both the Fig. 2a as well as for the alignment of the optical axes shown in Fig. 2b, since in both cases a plausibility check of the fog detection is carried out despite the extended spatial area being exposed. However, since the risk of false detection increases with increasing spatial area, advantages according to the invention arise particularly in such alignments of the optical axes in which the exposed spatial area is large, for example, ends at a distance from the fog sensor device of more than 2.5 m, preferably more than 3 m, even more preferably more than 5 m. In particular, the advantage according to the invention is achieved when the optical axes intersect at infinity or approximately at infinity, as in Fig. 2b. Such a fog sensor device according to the Fig. The design shown in Figure 2b can be realized comparatively cost-effectively.

[0047] In Fig. Figure 3 shows a motor vehicle 5 equipped with a detection device 1 according to the invention for fog detection in the front area of ​​the motor vehicle 5. A motor vehicle 14 traveling ahead is located below the exposed space 4 and is therefore not detected as an interference signal. However, the exposed space 4 lies above the clearance profile specified for roads, thus the tunnel 13 located in front of the motor vehicle 5 is detected as an interference signal. Fig. Figure 3a shows a characteristic step-like temporal progression of a received signal 7, which was detected by an optoelectronic fog sensor device 3 of a motor vehicle 5 traveling at a constant speed toward a tunnel 13. This characteristic step-like signal already allows a fog condition to be ruled out. The result of the analysis of the temporal progression of a received signal 7 can be verified using the brightness values ​​of the immediate vehicle surroundings, independently obtained by the optoelectronic fog sensor device and detected by a brightness sensor. The temporal progression of the brightness value shows a temporally offset inverse progression of the temporal progression of the received signal 7. Thus, the result based on the detected received signal can be confirmed by an independent measurement method.Especially during the day, tunnels 13 are detected by analyzing the brightness values, and vehicle 5 is switched to tunnel mode. In tunnel mode, the measurement is paused for fog detection.

[0048] In Fig. 4 shows a motor vehicle 5 equipped with a detection device according to the invention for fog detection 1 in the front area of ​​the motor vehicle 5. A motor vehicle 4 traveling ahead is located below the exposed spatial area 4 and is therefore not detected as an interference signal. The fog 16 is represented here by three upward-pointing arrows, with the height of the arrow representing the density of the fog 16. Fig. Figure 4a shows a characteristic monotonically increasing temporal progression of a received signal 7, detected by an optoelectronic fog sensor device 3, of a motor vehicle 5 traveling at a constant speed toward the fog 16. If the received signal 7 is above the threshold adjusted according to the data of the additional sensor 2, a fog condition is detected. In addition, the Fig. The characteristic temporal course of the brightness values ​​shown in Figure 4b can be used to distinguish between a fog state and a non-fog state.

Claims

[1] Detection device for fog detection (1) for a motor vehicle (5) comprising: an optoelectronic fog sensor device (3) arranged in the front area of ​​the motor vehicle (5), which has a transmitter (11) and a receiver (12) and is designed to apply at least one first optical transmission signal (6) to a spatial area (4) and to detect a reflected reception signal (7) from this spatial area (4), and to generate an electrical signal depending on the strength of the reception signal (7), wherein the detected reception signals correlate with light intensities; at least one further sensor (2) which is provided for detecting data about a vehicle speed and / or for detecting brightness values ​​of the immediate surroundings of the motor vehicle; characterized by , that an evaluation unit determines, taking into account the determined data on the vehicle speed and / or the brightness values ​​of the immediate motor vehicle surroundings, whether the received signal (7) is an interference signal or a useful signal; and that a received signal (7) is defined as a useful signal if the received signal (7) exceeds a threshold for fog detection, wherein the threshold for fog detection is adapted according to the determined data on the vehicle speed and / or the brightness values ​​of the immediate motor vehicle surroundings. [2] Detection device for fog detection (1) according to the preceding claim, wherein the temporal and / or spatial course of the received signal (7) is used to determine whether the received signal is a useful signal or an interference signal. [3] Detection device for fog detection (1) according to one of the preceding claims, in which the acted upon spatial area (4) is located above the airspace profile specified for roads and the resulting detection direction (8) of the optoelectronic fog sensor device (3) the roadway plane (9) is in an angular range (10) of preferably 30°-90°, more preferably in an angular range of 30°-80° and most preferably in an angular range of 30°-60°. [4] Detection device for fog detection (1) according to one of the preceding claims, in which the evaluation unit is integrated into the optoelectronic fog sensor device (3). [5] Detection device for fog detection (1) according to one of the preceding claims, wherein the transmitter (11) and the receiver (12) are aligned such that their optical axes run parallel or intersect at an acute angle with an angular amount of less than 10°, preferably less than 5°, more preferably less than 3°. [6] Detection device for fog detection (1) according to one of the preceding claims, wherein the transmitter (11) and the receiver (12) are aligned such that their optical axes in the area directly at the transmitter (11) and receiver (12) have a distance of less than 10 cm, preferably less than 5 cm, more preferably less than 3 cm. [7] Detection device for fog detection (1) according to one of the preceding claims, in which the transmitter (11) emits a transmission signal within the integration time of the receiver (12) and the integration time of the receiver (12) is dependent on the speed. [8] Method for fog detection for a motor vehicle (5), which comprises the following method steps: • Applying at least one first optical transmission signal (6) to a spatial area (4) by means of an optoelectronic fog sensor device (3) arranged in the front area of ​​the motor vehicle (5), comprising a transmitter (11) and a receiver (12); • Detection of a reflected reception signal (7) from the affected spatial area (4) by the optoelectronic fog sensor device (3) arranged in the front area of ​​the motor vehicle (5); • generating an electrical signal based on the strength of the received signal (7); • Measuring data on a vehicle speed and / or measuring brightness values ​​of the immediate surroundings of the motor vehicle with at least one further sensor (2); • a subsequent evaluation of the received signals taking into account the data on the vehicle speed and / or the brightness values ​​of the immediate vehicle surroundings in an evaluation unit; • subsequent determination by the evaluation unit as to whether the received signal (7) is either an interference signal or a useful signal; wherein the determination as to whether the received signal (7) is either an interference signal or a useful signal is made on the basis of a threshold for fog detection, wherein the threshold for fog detection is adapted on the basis of the determined data on the vehicle speed and / or the brightness values ​​of the immediate vehicle surroundings; • Optionally, a warning signal is issued in the event of a useful signal. [9] Method for fog detection for a motor vehicle (5) according to claim 8, wherein the received signals are stored and the temporal and / or spatial course of the received signal (7) is evaluated and the temporal and / or spatial course of the received signal (7) is used to determine between a useful signal and an interference signal. [10] Method for fog detection for a motor vehicle (5) according to one of the preceding claims 8 or 9, wherein the transmitter (11) and the receiver (12) of the fog sensor device (3) are aligned such that their optical axes run parallel or intersect at an acute angle with an angular amount of less than 10°, preferably less than 5°, more preferably less than 3°.

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