Pollution detection device for detecting a pollution layer, driver assistance system, motor vehicle and method for detecting a pollution layer

Abstract

A contamination detection device (2) for detecting a contamination layer (3) on an outer part (4) of a device, in particular a motor vehicle (1), with the outer part (4), wherein the contamination detection device (2) has a detection device (11) which is designed to detect vibrations of the outer part (4) and to detect the contamination layer (3) based on the vibration behavior of the outer part (4), characterized in that the contamination detection device (2) has a detection device (12) for characterizing the contamination layer (3) on the outer part (4) and that the detection device (12) has a temperature sensor for measuring a temperature of an ambient area (8) adjacent to the outer part (4), wherein the detection device (11) is designed to detect a layer of dirt as the contamination layer (3),if the temperature detected by the temperature sensor is above a predetermined threshold, and to detect a layer of snow and / or ice as the soiling (3) if the temperature detected by the temperature sensor is below the threshold.

Description

[0001] The invention relates to a soiling detection device for detecting a soiling layer on an external part of a device, in particular a motor vehicle, with an external part. The invention further relates to a driver assistance system with a soiling detection device, a motor vehicle, and a method for detecting a soiling layer.

[0002] The focus here is on the detection of a layer of dirt or grime on the exterior of a device, particularly a motor vehicle. Such a layer of dirt or grime could be, for example, a layer of ice, snow, or grime covering the exterior of the vehicle. Ice layers on the roofs of motor vehicles, especially trucks, pose a significant hazard in road traffic, as they are difficult for the driver to see and can break off while the vehicle is in motion. This can endanger other road users, such as drivers of other vehicles or motorcyclists.

[0003] It may also be desirable to be able to detect layers of dirt or grime on motor vehicles. This is particularly advantageous when the vehicle owner is not a direct user and therefore cannot see the dirt on the vehicle. This is the case, for example, with carsharing vehicles. In this case, the carsharing operator typically does not have the opportunity to constantly monitor the vehicles in their fleet and thus detect any soiling.

[0004] From DE 697 03 637 T2, an ultrasonic detection device for detecting moist foreign bodies on a glass surface is known. This device comprises at least one glass plate of a specific thickness and a piezoelectric transducer connected to the surface of the glass plate. The transducer emits ultrasonic waves into the glass plate and receives signals reflected from the other surface of the glass. By analyzing the changes in these signals, the presence of foreign bodies, such as water droplets, is detected. A specific relationship exists between the operating frequency of the transducer and the resonant frequency of the glass plate, such that these frequencies are neither completely identical nor too dissimilar. In particular, the transducer frequency is slightly higher than the glass resonant frequency, with the difference being maintained within a specific range.This increases the sensitivity in detecting water droplets and other foreign matter on the glass surface.

[0005] German patent application DE 694 05 799 T2 discloses an ultrasonic method for detecting contaminants on the surface of a structure. The method is based on the principle of acoustic impedance differences and uses a probe with a delay block whose acoustic impedance lies between that of de-icing and anti-icing fluids and that of ice. An ultrasonic pulse is sent through the delay block to the interface, and the amplitude of the interface echo is compared, at an oblique incidence, with that of the incident pulse or a reference echo from a clean surface to determine whether a phase inversion has occurred, thereby identifying the type of contaminant.

[0006] A method and system for detecting the probability of ice formation is known from US patent 4,570,881 A. The system comprises a vibrating membrane connected to a metal plate, which is excited to vibrate at its resonant frequency by a piezoelectric element. The system's operating principle is that the membrane is alternately cooled and heated by Peltier elements controlled by a DC generator, while simultaneously measuring changes in the resonant frequency caused by ice deposits. When an ice layer forms on the membrane, its mass increases and its stiffness changes, leading to a change in the resonant frequency. The system uses a microprocessor to measure these frequency changes and trigger an alarm signal when the change exceeds a predetermined threshold.

[0007] US Patent 2008 / 0054762A1 discloses a vibration device for removing deposits, suitable for use on material surfaces such as vehicle windshields or aircraft wings. The device consists of a transducer subunit that converts external energy into mechanical vibration and an amplifying coupling subunit that transmits these vibrations into the material. The generated vibrations break the bond between the deposits and the surface, thus removing unwanted substances such as ice or water. The device can operate at the material's resonant frequency and can also function as a deposit detector when connected to appropriate analytical instruments.

[0008] The object of the present invention is to be able to reliably and easily detect a layer of dirt on a device.

[0009] This problem is solved according to the invention by a contamination detection device, a driver assistance system, a motor vehicle and a method with the features according to the independent claims.

[0010] A contamination detection device according to the invention serves to detect a contamination layer on an external part of a device, in particular a motor vehicle. The contamination detection device comprises the external part. Furthermore, the contamination detection device has a detection element which is designed to detect vibrations of the external part and to detect the contamination layer based on the vibration behavior of the external part.

[0011] The contamination detection device is specifically designed to detect the contamination layer, such as ice, snow, or dirt, on the outer part. The outer part has a front side facing the surrounding area of ​​the device, particularly the area around the vehicle, and a back side opposite the front side. The contamination layer covers at least part of the front of the outer part and can adhere to it.

[0012] The detection device can now record and analyze vibrations of the external part, such as those caused by the operation of the vehicle. These vibrations could include, for example, the vibrations of a hood when the engine is running or the roof of a vehicle while driving. Based on the vibration pattern of the external part, the detection device recognizes the presence of a dirt layer.

[0013] The invention is based on the understanding that the soiling layer adds additional mass to the outer part, thereby altering, and in particular increasing, the vibrating mass. This increased vibrating mass changes the vibration behavior of the outer part compared to an uncoated outer part without the soiling layer. In other words, this means that a deviation of the vibration behavior of the soiled outer part from a reference vibration behavior, particularly the vibration behavior of the uncoated outer part, is detected.

[0014] Based on this deviation, i.e., a change in the vibration behavior, the soiling layer can be easily and reliably detected.

[0015] Particularly preferably, the contamination detection device comprises at least one vibration-generating element separate from the outer part, which is vibrationally coupled to the outer part. The detection device is designed to activate the at least one vibration-generating element for a predetermined period of time to generate vibrations and to detect the contamination level based on the vibration behavior of the outer part.

[0016] To ensure the detection of soiling at all times, a separate vibration-generating element is provided. This element is vibrationally coupled to the outer part and can be controlled by the detection device to generate vibrations. The separate vibration-generating element can, for example, be a magnet, which is controlled by the detection device and thus causes the vibration-coupled outer part to vibrate. Alternatively, the vibration-generating element can be a piezoelectric element or piezoelectric actuator, which is, for example, located on and connected to the back of the outer part, thereby vibrationally coupled to it. Vibration coupling in this context means that a vibration provided by the vibration-generating element is transmitted to the outer part, causing it to vibrate as well.

[0017] The detection device defines and activates at least one vibration-generating element for a predetermined duration. For this purpose, the detection device can, for example, provide a test signal that excites the vibration-generating element for the predetermined duration, transmitting the vibration to the external component. The vibration behavior of the external component is then recorded. Specifically, the vibration behavior after the predetermined duration, i.e., after the vibration excitation of the at least one vibration-generating element has ceased, is recorded. The presence of the contamination layer is detected based on this vibration behavior.Providing the vibration-generating element offers the advantage that contamination detection can be carried out at any time, for example even when the engine is not running or the vehicle is stationary, and on any external parts that typically do not vibrate themselves.

[0018] Preferably, the detection device is designed to determine the vibration behavior, specifically the oscillation period and / or frequency of the outer part. As previously explained, the oscillating mass changes due to the soiling layer on the outer part, since, in addition to the mass of the outer part itself, the mass of the soiling layer is also excited to vibrate, for example, by the vibration-generating element. The resulting change in vibration behavior is then detected, particularly after a predetermined time period, in the form of the oscillation period and / or frequency of the outer part. After the predetermined time period, i.e., after the excitation of the vibration-generating element, the outer part oscillates, and the oscillation period and / or frequency changes due to the additional mass added by the soiling layer compared to a reference oscillation period and / or frequency.The reference oscillation period or frequency is the oscillation period or frequency that the external part exhibits without the dirt layer. These reference values ​​can, for example, be stored for the detection device. The detection device is designed to compare the detected oscillation period and / or frequency with the corresponding reference value after each vibration excitation of the vibration-generating element and, in the event of a deviation, to detect the presence of the dirt layer.

[0019] According to the invention, the contamination detection device includes a detection device for characterizing, in particular for material characterization, the contamination layer on the outer part. In other words, the contamination detection device is designed to recognize what type of contamination layer is present, for example, whether the contamination layer is a layer of snow, a layer of ice, or a layer of dirt.

[0020] According to the invention, the detection device comprises a temperature sensor for measuring the temperature of an ambient area adjacent to the outdoor part. The detection device is designed to recognize a layer of dirt as a contamination layer when the temperature detected by the temperature sensor is above a predetermined threshold, and to recognize a layer of snow and / or ice as a contamination layer when the temperature detected by the temperature sensor is below the threshold.

[0021] Based on the ambient temperature, it can be determined whether the soiling is a layer of snow and / or ice or a layer of dirt. It is considered an ice layer and / or a layer of snow, in particular, if the ambient temperature measured by the temperature sensor is below the freezing point of water, i.e., approximately below 0 degrees Celsius. This value can be defined as a threshold. If the ambient temperature is above 0 degrees Celsius, it can be assumed that the soiling is a layer of dirt. Thus, the soiling can be materially characterized in a particularly simple way based on the measured temperature.

[0022] One embodiment of the invention provides that the contamination detection device is designed to determine the degree of contamination of the outer part based on the magnitude of any deviation of its vibration behavior from a reference vibration behavior of the outer part. The reference vibration behavior is the vibration behavior exhibited by the outer part in an uncontaminated state, i.e., without the contamination layer. The reference vibration behavior is thus the standard behavior of a "clean" outer part. The invention is based on the understanding that the more heavily contaminated the outer part is, i.e., the more snow, ice, and / or dirt is present on the outer part, the more its vibration behavior deviates from the reference vibration behavior. Therefore, the greater the additional mass applied to the outer part by the contamination layer, the more the vibration behavior of the outer part deviates from the standard behavior.The degree of soiling therefore indicates the severity of soiling on the outer part.

[0023] It is particularly advantageous if the vibration-generating element itself has the lowest possible mass and / or stiffness and / or material thickness, so that even with a low degree of contamination, i.e., with a small additional mass applied by the contamination layer, the vibration behavior of the vibration-generating element is influenced and thus the presence of the contamination layer can be reliably detected.

[0024] In a further development of the invention, the contamination detection device includes a communication device designed to transmit the presence of contamination and / or the degree of contamination of the external part to an external receiving device. The contamination detection device can communicate with the external receiving device, particularly wirelessly, via this communication device. The presence of contamination and / or the degree of contamination of the external part is then transmitted to this receiving device via this wireless connection.

[0025] This embodiment is particularly advantageous when a person responsible for the device needs to know the level and / or degree of soiling, but cannot directly see the device, for example, due to spatial distance. In this case, the person can be informed via the communication device that the device, especially the vehicle, is dirty. Such a person could, for example, be the operator of a car-sharing fleet who is supposed to offer clean vehicles to their customers but generally has no way of personally monitoring all the vehicles in their fleet.This car sharing operator can be notified, even over a long distance, via the communication device of the pollution detection system, that a motor vehicle is dirty, whereupon the operator can clean the vehicle in question.

[0026] It may also be provided that the communication device communicates with a mobile phone and / or a car key of the driver of the motor vehicle, so that a driver or owner of the motor vehicle, for example, receives a corresponding message about the presence of the dirt layer and / or the degree of dirt on a screen of his mobile phone and / or his car key.

[0027] Preferably, the contamination detection device comprises an ultrasonic transducer or an ultrasonic sensor, which includes the vibration-generating element. This offers the advantage that conventionally known, easy-to-manufacture ultrasonic transducers can be used for detecting the contamination layer, and in particular, can be used exclusively for contamination detection.

[0028] Preferably, the at least one vibration-generating element is concealed and attached to the rear side of the outer part, facing away from its surroundings. In other words, the at least one vibration-generating element is installed behind the outer part and thus away from its surroundings. In the case of an ultrasonic transducer containing the vibration-generating element, for example, a vibration-generating diaphragm of the ultrasonic transducer, to which a piezoelectric element is attached as the vibration-generating element, can be attached to the rear side, for example, by being glued to the rear. This advantageously prevents the vibration-generating element from being directly exposed to soiling.For example, the ultrasonic transducer can be advantageously protected from the soiling, thus ensuring the ultrasonic transducer's detection capability for recognizing the soiling on the outer part over a long period of time.

[0029] In one embodiment of the invention, the outer part is designed as the roof of a motor vehicle, particularly a commercial vehicle. Thus, especially with the aid of the contamination detection device, a layer of ice on the roof of the commercial vehicle, for example a truck, can be detected. This layer of ice is not normally perceived by the driver of the vehicle due to the height of the truck and therefore cannot be removed. This also prevents, for example, this layer or sheet of ice from sliding off the roof during cornering and endangering other road users.

[0030] The outer part can also be designed as an exterior panel of a motor vehicle. Such an outer part could be, for example, a hood, a bumper, or a fender. In this case, at least one vibration-generating element is located, in particular, concealed behind the outer part and can thus detect, in particular, soiling of the exterior panel of the motor vehicle.

[0031] Particularly preferably, the contamination detection device includes an output device for issuing a warning signal to a person responsible for operating the device. Such a person could, for example, be the driver of the vehicle. This allows the driver to be informed about the presence and / or degree of contamination and, if necessary, to take action. The output device could, for example, be designed to provide a visual warning, an audible signal, or a message to the person, and could be, for example, a screen or a loudspeaker in the vehicle.

[0032] Additionally, depending on the characterization, particularly the material characteristics, of the soiling layer and at least one further value of an environmental parameter and / or a vehicle parameter, the adhesion strength of the soiling layer to the exterior part can also be estimated. Thus, the responsible person can be provided with information on the probability that the soiling layer will detach, for example, when the vehicle is cornering (vehicle parameter) or during dew-off temperatures (environmental parameter). Specific warning signals can then be issued to the driver. The driver can thus be shown, for example, whether there is a risk that a layer of ice on the roof will slide off, for instance, during cornering or during a thaw.

[0033] The invention also relates to a driver assistance system for a motor vehicle with a contamination detection device according to the invention. The driver assistance system is designed, in particular, to inform the driver of the motor vehicle about the presence of a contamination layer on an exterior part of the motor vehicle.

[0034] A motor vehicle according to the invention comprises a driver assistance system according to the invention. The motor vehicle is in particular designed as a passenger car.

[0035] The invention also relates to a method for detecting a soiling layer on an external part of a device, in particular a motor vehicle. For this purpose, vibrations of the external part are detected and the soiling layer is detected based on the vibration behavior of the external part.

[0036] The preferred embodiments and their advantages presented with reference to the contamination detection device according to the invention apply accordingly to the driver assistance system according to the invention, the motor vehicle according to the invention and to the method according to the invention.

[0037] The soiling detection device is not limited to use on motor vehicles. For example, it can also be used to detect soiling on solar panels of a photovoltaic system and / or a solar thermal system. The efficiency of solar systems drops significantly when the solar panels are dirty. With this soiling device, a reference plate could be attached to the solar panels as the external component, allowing the soiling, such as leaves or dirt from the surrounding area, to be detected and reported.

[0038] It may also be intended that the contamination detection device is used to detect contamination of traffic signs and / or information boards, which are covered with dirt, for example, due to dusty roads or in winter, and / or advertising boards.

[0039] The terms "top", "bottom", "front", "back", "horizontal", "vertical", "outside", "inside", "back", "front", etc. indicate the positions and orientations of the contamination detection device when used and arranged as intended on the motor vehicle and when the vehicle occupant is in the vehicle facing forward.

[0040] Further features of the invention are evident from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments of the invention are also to be considered as encompassed and disclosed that are not explicitly shown and explained in the figures, but which can be derived and generated from the explained embodiments by separate combinations of features. Embodiments and combinations of features are also to be considered disclosed that do not exhibit all the features of an originally formulated independent claim.

[0041] This shows: Fig. 1 a schematic representation of an embodiment of a motor vehicle according to the invention with a pollution detection device; Fig. 2 a schematic representation of an embodiment of a commercial vehicle with a contamination detection device; and Fig. 3 A schematic representation of an embodiment of a contamination detection device according to the invention in a cutaway side view.

[0042] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0043] Fig. Figure 1 shows a motor vehicle 1 with a contamination detection device 2. The contamination detection device 2 serves to detect a contamination layer 3 on an exterior part 4 of the motor vehicle 1, for example, a layer of dirt or grime on the exterior part 4 of the motor vehicle 1. The contamination detection device 2 includes the exterior part 4, which in this case is designed as an exterior trim part of the motor vehicle 1, in particular a hood of the motor vehicle 1. However, the exterior part 4 can also be a fender and / or a bumper and / or another exterior trim part of the motor vehicle 1. The contamination layer 3 rests on a front surface 7 of the exterior part 4 facing an area 8 of the surroundings of the motor vehicle 1.The contamination detection device 2 has a detection unit 11, which is designed to detect vibrations of the outer part 4 and, based on the vibration behavior of the outer part 4, to detect the presence of the contamination layer 3. The detection unit 11 can, for example, detect vibrations of the outer part 4 of the motor vehicle 1, which is designed as a hood, when the motor vehicle 1's engine is running. Alternatively, the contamination detection device 2 may have a vibration-generating element 6, which is vibrationally coupled to the outer part 4 and can be controlled by the detection unit 11 to generate vibrations.

[0044] One such embodiment of the contamination detection device 2 with the vibration-generating element 6 is shown in a sectional side view in Fig. Figure 3 shows the following. The vibration-generating element 6 is arranged on the rear side 5 of the outer part 4, opposite the front side 7 of the outer part 4, and is vibrationally coupled to the outer part 4. The front side 7 faces the surrounding area 8 of the vehicle 1 and has the soiling layer 3. The vibration-generating element 6 is a piezoelectric actuator, which is vibrationally coupled to a vibration-generating membrane 10 of an ultrasonic transducer 9. The ultrasonic transducer 9, and thus the vibration-generating element 6, is concealed on the rear side 5 of the outer part 4 and is therefore not visible from the surrounding area 8 of the vehicle 1. The vibration-generating element 6 could also be a magnet.

[0045] The detection unit 11 of the contamination detection device 2 is designed to activate the vibration-generating element 6 for a predetermined period of time. Because the vibration-generating element 6 is vibrationally coupled to the outer part 4, the vibration is also transmitted to the outer part 4. The contamination layer 3 can be detected based on the vibration behavior of the outer part 4, particularly after the predetermined period. For this purpose, the detection unit 11 of the contamination detection device 2 specifically detects the decay time and / or decay frequency of the outer part 4 and compares it with a reference decay time and / or a reference decay frequency.The reference oscillation period or reference oscillation frequency is the oscillation period or frequency that the outer part 4 exhibits after the predetermined time period without the presence of the soiling layer 3. A deviation of the measured value from the reference value indicates the presence of the soiling layer 3.

[0046] In order to also materially characterize the soiling layer 3, the soiling detection device 2 can be equipped with a detection device 12 (see Fig. 1) exhibit. The detection device 12 has a temperature sensor which detects a temperature in the ambient area 8 of the motor vehicle 1 and transmits it to the detection device 11. If the temperature detected by the detection device 12 in the ambient area 8 of the motor vehicle 1 is greater than a predetermined threshold, in particular greater than 0 degrees Celsius, the soiling layer 3 is assumed to be a layer of dirt or grime. However, if the temperature detected by the detection device 12 in the ambient area 8 of the motor vehicle 1 is less than the threshold, in particular less than 0 degrees Celsius, the soiling layer 3 is assumed to be a layer of ice or snow.

[0047] Additionally, the degree of soiling on the outer part 4 can also be detected. For this purpose, the detection device 11 determines the magnitude of the deviation of the vibration behavior of the outer part 4, for example, after the vibration excitation of the vibration-generating element 6 by the detection device 11, from a reference vibration behavior. The outer part 4 exhibits the reference vibration behavior after vibration excitation by the detection device 11 when the outer part 4 is not covered with the soiling layer 3.

[0048] If the level of contamination 3 is present, this or the degree of contamination can be communicated to, for example, a driver of the vehicle 1 via an output device 13 of the contamination detection device 2. The output device 13 can, for example, be designed as a screen in the vehicle 1 or as a loudspeaker in the vehicle 1 and inform the driver of the vehicle 1 of the level of contamination 3 and / or a degree of contamination, for example by means of a warning signal.

[0049] Furthermore, the detection device 11 can also transmit the presence of the soiling layer 3 and / or the degree of soiling to an external receiving device 14. For this purpose, the soiling detection device 2 can have a communication device 20 which transmits the presence of the soiling layer 3 and / or the degree of soiling to the external receiving device 14, in particular by means of a wireless communication link 15. This is particularly advantageous if the motor vehicle 1 is, for example, a vehicle in a carsharing fleet. In carsharing, the vehicles are generally not returned to or picked up from a carsharing operator or a rental car company. A user of the motor vehicle 1 is usually only provided with an electronic access key and the location of the motor vehicle 1.The vehicle 1 is then picked up independently by the user. After use, the vehicle 1 is parked either at a defined point or at any location. Rental companies, in particular, wish to offer their customers maximum convenience and provide them with clean, dirt-free vehicles. However, since rental companies are generally unable to inspect the vehicles themselves and therefore cannot detect the dirt layer 3, it is particularly advantageous if the detection device 11 transmits the presence of the dirt layer 3 via the communication device 20 over the wireless communication link 15 to the receiving device 14, for example, a customer service department of the rental car company.

[0050] Fig.Figure 2 shows another possible application of the contamination detection device 2. In this figure, the contamination detection device 2 is configured to detect an ice layer as the contamination layer 3 on the roof 16 of a commercial vehicle 17, for example, a truck. For this purpose, the detection device 11 can, for example, detect the vibration behavior of the roof 16 while the commercial vehicle 17 is in motion and identify the contamination layer 3 based on this vibration behavior. Furthermore, the vibration-generating element 6, which in turn can be part of an ultrasonic transducer 9, is arranged on the roof 16 of the truck 17 as the outer part 4. Specifically, the vibration-generating element 6 is located below the roof 16 on an inner surface 18 of the roof 16, which is associated with an interior area of ​​the truck 17, and is thus vibrationally coupled to the roof 16.On the outer surface 19, the front 7 of the outer part 4, which faces the surrounding area 8 of the truck 17, the layer of dirt 3, in the form of an ice layer, is present. Such an ice layer can be particularly dangerous because it can break off and fall, for example, when the truck 17 is cornering. The ice layer can then endanger other road users, such as other motor vehicles or motorcyclists. To prevent this, the vibration-generating element 6 is excited to vibrate by means of the detection device 11, the vibration behavior of the roof 16 is determined, and the presence of the dirt layer 3, i.e., the ice layer, is detected if it deviates from the reference vibration behavior.If the ice layer is present, this can be transmitted as a warning signal to output device 13, thus informing the truck driver of the imminent danger of the ice sheet falling.

Claims

[1] Dirt detection device (2) for detecting a dirt layer (3) on an outer part (4) of a device, in particular a motor vehicle (1), with the outer part (4), wherein the dirt detection device (2) has a detection device (11) which is designed to detect vibrations of the outer part (4) and to detect the dirt layer (3) based on a vibration behavior of the outer part (4), characterized by, that the contamination detection device (2) has a detection device (12) for characterizing the contamination layer (3) on the outdoor part (4) and that the detection device (12) has a temperature sensor for measuring a temperature of an ambient area (8) adjacent to the outdoor part (4), wherein the detection device (11) is designed to detect a layer of dirt as the contamination layer (3) when the temperature detected by the temperature sensor is above a predetermined threshold, and to detect a layer of snow and / or ice as the contamination layer (3) when the temperature detected by the temperature sensor is below the threshold. [2] Pollution detection device (2) according to claim 1, characterized by, that the contamination detection device (2) has at least one vibration-generating element (6) separate from the outer part (4), which is vibrationally coupled to the outer part (4), and the detection device (11) is designed to control the at least one vibration-generating element (6) for a predetermined period of time to generate vibrations and to detect the contamination layer (3) based on the vibration behavior of the outer part (4). [3] Pollution detection device (2) according to claim 1 or 2, characterized by , that the detection device (11) is designed to determine the oscillation behavior, namely the oscillation period and / or the oscillation frequency of the external part (4). [4] Pollution detection device (2) according to one of the preceding claims, characterized by, that the contamination detection device (2) is designed to determine a degree of contamination of the external part (4) based on the magnitude of a deviation of the vibration behavior from a reference vibration behavior of the external part (4). [5] Pollution detection device (2) according to any one of the preceding claims, characterized by , that the contamination detection device (2) has a communication device (20) which is designed to transmit the presence of the contamination layer (3) and / or a degree of contamination of the external part (4) to a receiving device (14) external to the device. [6] Pollution detection device (2) according to any one of claims 2 to 5, characterized by , that the contamination detection device (2) comprises an ultrasonic transducer (9) which has at least one vibration-generating element (6). [7] Pollution detection device (2) according to any one of claims 2 to 6, characterized by , that at least one vibration-generating element (6) is arranged concealed against a rear side (5) of the outer part (4) facing away from an environment area (8) of the outer part (4). [8] Pollution detection device (2) according to any one of the preceding claims, characterized by , that the outer part (4) is designed as a roof (16) of a motor vehicle (1), in particular a commercial vehicle (17). [9] Pollution detection device (2) according to any one of the preceding claims, characterized by , that the outer part (4) is designed as an outer cladding part of a motor vehicle (1). [10] Pollution detection device (2) according to any one of the preceding claims, characterized by, that the contamination detection device (2) has an output device (13) for issuing a warning signal to a person responsible for the operation of the device. [11] Driver assistance system for a motor vehicle (1) comprising a pollution detection device (2) according to one of the preceding claims. [12] Motor vehicle (1) with a driver assistance system according to claim 11. [13] Method for detecting a soiling layer (3) on an external part (4) of a device, in particular a motor vehicle (1), characterized by , that vibrations of the outer part (4) are detected with the aid of a contamination detection device (2) according to one of claims 1 to 10 and the contamination layer (3) is detected on the basis of a vibration behavior of the outer part (4).

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