Method and control unit for operating an ultrasonic sensor system

Abstract

Method for operating an ultrasonic sensor system (104) of a vehicle (100) with ultrasonic sensors (106) arranged in different orientations on the vehicle (100), wherein the ultrasonic sensors (106) are controlled depending on an orientation of the respective ultrasonic sensor (106), wherein at least two frequency ranges are assigned to an ultrasonic sensor (106) depending on its orientation, and wherein a road condition is determined on the basis of different signal components of a received signal of the ultrasonic sensor (106) depending on its orientation.

Description

Field of invention

[0001] The invention relates to a method and a control unit for operating an ultrasonic sensor system of a vehicle with ultrasonic sensors arranged in different orientations on the vehicle. State of the art

[0002] Ultrasonic sensors in an ultrasonic sensor system emit ultrasonic pulses and receive echoes of these pulses. The distance to a surface that reflected the ultrasonic pulses can be determined from the time of travel between transmission and reception. Since both the ultrasonic pulses and the echoes are sound waves, they propagate spherically from the sound source. Therefore, the sound pressure of the ultrasonic pulses decreases with increasing distance from the ultrasonic sensor. Similarly, the sound pressure of the echo decreases with increasing distance from the surface. Thus, only a fraction of the transmitted sound pressure reaches the ultrasonic sensor as the echo. The echo can be detected in a received signal from the ultrasonic sensor until background noise reaches a sound pressure equal to or higher than the echo.If the background noise is very loud, for example due to a wet road surface, evaluation of the echo may be limited.

[0003] Document DE 10 2011 085 287 A1 discloses a method for determining the road surface condition of a roadway, comprising continuously detecting a road surface using ultrasonic sensors installed in a vehicle; classifying the road surface based on the reflected frequency spectrum; and transmitting data representing the condition of the roadway and the vehicle's position to a Global Positioning System and / or following vehicles or road users.

[0004] German patent application DE 10 2011 118 643 A1 discloses a driver assistance device for a motor vehicle, comprising a first ultrasonic sensor with a membrane for emitting and receiving ultrasonic waves, wherein the first ultrasonic sensor has a first resonant frequency; a second ultrasonic sensor with a membrane for emitting and receiving ultrasonic waves, wherein the second ultrasonic sensor has a second resonant frequency different from the first resonant frequency; and a control device for controlling the ultrasonic sensors, wherein the control device is designed to switch at least the first ultrasonic sensor between a first operating mode in which the first ultrasonic sensor emits the ultrasonic waves with the first resonant frequency and a second operating mode in which the first ultrasonic sensor emits the ultrasonic waves with the second resonant frequency. Disclosure of the invention

[0005] Against this background, the approach presented here comprises a method for operating a vehicle's ultrasonic sensor system with ultrasonic sensors arranged in different orientations on the vehicle, a corresponding control unit, and finally, a corresponding computer program and a machine-readable storage medium according to the independent claims. Advantageous further developments and improvements of the approach presented here are described in the dependent claims. Advantages of the invention

[0006] Embodiments of the present invention can advantageously enable the differently oriented ultrasonic sensors of an ultrasonic sensor system to be operated as separate subsystems. The subsystems can be operated with optimized settings to overcome limitations due to the orientation.

[0007] A method is proposed for operating an ultrasonic sensor system of a vehicle with ultrasonic sensors arranged in different orientations on the vehicle, wherein the ultrasonic sensors are controlled depending on an orientation of the respective ultrasonic sensor, wherein at least two frequency ranges are assigned to an ultrasonic sensor depending on its orientation, and wherein a road condition is determined based on different signal components of a received signal of the ultrasonic sensor depending on its orientation.

[0008] Ideas for embodiments of the present invention can be considered to be based, among other things, on the thoughts and findings described below.

[0009] A vehicle's ultrasonic sensor system can have multiple ultrasonic sensors located at different positions on the vehicle and oriented differently relative to it. The ultrasonic sensors can be arranged in pairs symmetrically to a longitudinal axis of the vehicle and oriented as mirror images of that axis. For example, the ultrasonic sensor system at the front of the vehicle can have ultrasonic sensors oriented forward, obliquely forward, and to the side. At the rear of the vehicle, the ultrasonic sensor system can have ultrasonic sensors oriented backward, obliquely backward, and to the side.

[0010] An ultrasonic sensor is designed to emit sound pulses, referred to as pulses, with frequencies in the ultrasonic range and to receive echoes of these pulses. To do this, the ultrasonic sensor can transmit a pulse or a pulse sequence within a defined frequency range at a specific time. Following the transmission, sounds are received and represented in a received signal for a specific time window. Alternatively, no pulse or pulse sequence can be transmitted at the beginning of the time window. In this case, sounds can also be recorded in the received signal within that time window. The ultrasonic sensor can emit pulses in different frequency ranges.

[0011] The sounds are recorded as a temporal progression of sound intensity at the ultrasonic sensor. The sounds can originate from various sound sources or be echoes of the pulses or pulse sequences. The echoes are represented as part of the sound in the received signal. Background noise and other external noises are also included in the received signal. The received signal is then analyzed to detect echoes.

[0012] Some of the echoes are generated by structures on the road surface in close proximity to the ultrasonic sensor. These echoes are received within a short time after transmission. The initial sound intensity of the echoes from the road surface can be represented by a clutter value, which indicates the size of the structures on the road surface. The coarser the structures, the greater the sound intensity and the higher the clutter value. Conversely, the finer the structures, the lower the sound intensity and the lower the clutter value. With increasing distance from the ultrasonic sensor, the echoes from these structures exhibit progressively lower sound intensities and thus become lost in the background noise.

[0013] Echoes from objects can be detected if the recorded sound intensity of the echo is greater than the instantaneous sound intensity of the background noise recorded before and after the echo. Echoes can be falsely detected if a sound from another source reaches a sufficient sound intensity at the ultrasonic sensor. Cross-echoes can also be recorded. Cross-echoes are echoes from neighboring ultrasonic sensors within the ultrasonic system.

[0014] The sound intensity of background noise can be represented as a noise level. The noise level can be measured at the end of the time window. It can also be measured throughout the entire time window if no pulse has been sent beforehand. The noise level represents the sound intensity of the other sound source.

[0015] The vehicle's wheels generate sound as they roll across the road surface. The sound intensity of this rolling noise is influenced by factors such as the size of the road surface's structure. However, the sound intensity is particularly affected by moisture, mud, and / or wetness on the road surface. On damp or wet roads, a noise known as "wet hissing" occurs, which can largely mask echoes.

[0016] The signal components can be measured simultaneously in at least two frequency ranges. By capturing the signal components in more than one frequency range, the signal components can be measured with high accuracy.

[0017] Two or more signal components from a frequency range can be used to evaluate the noise level of the received signal. The noise level can be evaluated multiple times within a measurement window. A higher repetition rate results in higher accuracy.

[0018] From the received signal of an ultrasonic sensor angled obliquely forward or backward, at least a diffuse ground echo signal can be evaluated. These angled ultrasonic sensors are particularly good at detecting the structure of the road surface in the diffuse ground echo signal because they can be tilted towards the road surface. The diffuse ground echo signal can be represented as a clutter value. Similarly, the noise level of the angled ultrasonic sensor can be evaluated. The noise level can be determined from the clutter value.

[0019] Obliquely rearward-facing ultrasonic sensors can be triggered to transmit pulses in a first frequency range when the noise level exceeds a first noise threshold. This first frequency range can lie between the natural frequency of the ultrasonic sensors and 100 kHz. In a further embodiment, the first frequency range can lie between the natural frequency and 60 kHz. The natural frequency is preferably in a range between 40 kHz and 55 kHz. Alternatively, the obliquely rearward-facing ultrasonic sensors can be triggered to transmit pulses in a first frequency range when the vehicle speed exceeds a first speed threshold. This first frequency range can be higher than the frequency range in which one of the other ultrasonic sensors transmits.Alternatively or additionally, the first frequency range can be higher than a frequency range in which the same ultrasonic sensor transmits when the vehicle speed is below the speed threshold. A first frequency range can encompass high frequencies. The frequencies of the echoes are attenuated by the vehicle speed due to the Doppler effect. By transmitting in the first frequency range, the echoes can be detected in a frequency band where the ultrasonic sensors exhibit high sensitivity. The received signal can specifically reflect the frequency band in which the respective ultrasonic sensor demonstrates high sensitivity.

[0020] Forward-facing ultrasonic sensors can be triggered to transmit pulses in a second frequency range when the noise level exceeds a first noise threshold. This second frequency range has a bandwidth of 30 kHz around the sensors' resonant frequency. In a further embodiment, the second frequency range has a bandwidth of 15 kHz around the resonant frequency. Alternatively, the forward-facing ultrasonic sensors can be triggered to transmit pulses in a second frequency range lower than the first when the vehicle speed exceeds the speed threshold. This second frequency range can include mid-range frequencies. The echo frequencies are boosted by the vehicle speed due to the Doppler effect.By transmitting in the second frequency range, echoes can be detected in the frequency band where the ultrasonic sensors exhibit high sensitivity. The received signal can specifically reflect the frequency band in which the respective ultrasonic sensor has the highest sensitivity.

[0021] Laterally oriented ultrasonic sensors can be activated when the noise level exceeds a first noise threshold to transmit pulses in a third frequency range, where this third frequency range lies between 10 kHz and the sensor's resonant frequency. In a further embodiment, the third frequency range lies between 30 kHz and the resonant frequency. Alternatively, the laterally oriented ultrasonic sensors can be activated when the vehicle speed exceeds the speed threshold to transmit pulses in a third frequency range lower than the first and second frequency ranges. This third frequency range can include low frequencies. Low frequencies are attenuated less than high frequencies. Longer ranges can be achieved with low frequencies.

[0022] At least one noise level can be evaluated from the received signal of a forward- or rear-facing ultrasonic sensor. Forward- or rear-facing ultrasonic sensors can be deactivated to stop transmitting pulses when the noise level exceeds a second noise threshold. Above a certain noise level, echolocation to the rear or front may no longer be effective. The second noise threshold can be higher than the first. Therefore, alternative frequency ranges can be used first, and transmission can be stopped only if the noise level continues to increase. The second noise threshold can be reached at a certain speed. Alternatively, the ultrasonic sensors can be deactivated to stop transmitting pulses when the vehicle speed exceeds a speed threshold. This allows sounds to be recorded and analyzed across the entire time window.The sounds can also include cross-echoes from the other ultrasonic sensors. These cross-echoes can be detected like the echoes and can be evaluated separately.

[0023] The process can be implemented, for example, in software or hardware, or in a hybrid form of software and hardware, for example in a control unit.

[0024] The approach presented here also creates a control unit that is designed to carry out, control or implement the steps of a variant of the procedure presented here in appropriate facilities.

[0025] The control unit can be an electrical device with at least one processing unit for processing signals or data, at least one storage unit for storing signals or data, and at least one interface and / or a communication interface for reading or outputting data embedded in a communication protocol. The processing unit can be, for example, a signal processor, a so-called system ASIC, or a microcontroller for processing sensor signals and outputting data signals depending on the sensor signals. The storage unit can be, for example, flash memory, an EPROM, or a magnetic storage device. The interface can be configured as a sensor interface for reading sensor signals from a sensor and / or as an actuator interface for outputting data signals and / or control signals to an actuator.The communication interface can be configured to read or output data wirelessly and / or via a wired connection. The interfaces can also be software modules, such as those found on a microcontroller alongside other software modules.

[0026] It is also advantageous to have a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, if the program product or program is executed on a computer or device.

[0027] It should be noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments. A person skilled in the art will recognize that the features of the control unit and the method can be suitably combined, adapted, or exchanged to arrive at further embodiments of the invention. Brief description of the drawing

[0028] The following describes embodiments of the invention with reference to the accompanying drawing, whereby neither the drawing nor the description is to be interpreted as limiting the invention. Fig. Figure 1 shows a representation of a vehicle with a control unit according to an exemplary embodiment.

[0029] The figure is merely schematic and not to scale. Identical reference symbols denote identical or equivalent features. Embodiments of the invention

[0030] Fig.Figure 1 shows a representation of a vehicle 100 with a control unit 102 according to an exemplary embodiment. The vehicle 100 has an ultrasonic sensor system 104 with twelve ultrasonic sensors 106. The ultrasonic sensors 106 are numbered from "1" to "6" and from "8" to "13", with the first ultrasonic sensor 106 being located at the front left of the vehicle 100 and oriented laterally to the left, transverse to a longitudinal axis of the vehicle. The second ultrasonic sensor 106 is also located at the front left of the vehicle 100 and is oriented obliquely forward to the left. The third ultrasonic sensor 106 is also located at the front left of the vehicle 100 and is oriented forward in the direction of the longitudinal axis of the vehicle. The fourth ultrasonic sensor 106 is located at the front right of the vehicle 100 and is oriented forward in the direction of the longitudinal axis of the vehicle. The fifth ultrasonic sensor 106 is also located at the front right of the vehicle 100 and is oriented obliquely forward to the right.The sixth ultrasonic sensor 106 is also located at the front right of the vehicle 100 and is oriented laterally to the right, transverse to the vehicle's longitudinal axis. The first and sixth ultrasonic sensors 106 are arranged as mirror images of the vehicle's longitudinal axis. The second and fifth ultrasonic sensors 106 are also arranged as mirror images of the vehicle's longitudinal axis. The third and fourth ultrasonic sensors 106 are likewise arranged as mirror images of the vehicle's longitudinal axis.

[0031] The eighth ultrasonic sensor 106 is located at the rear right of the vehicle 100 and is oriented transversely to the vehicle's longitudinal axis, pointing to the right. The ninth ultrasonic sensor 106 is also located at the rear right of the vehicle 100 and is oriented obliquely to the rear right. The tenth ultrasonic sensor 106 is also located at the rear right of the vehicle 100 and is oriented rearward in the direction of the vehicle's longitudinal axis. The eleventh ultrasonic sensor 106 is located at the rear left of the vehicle 100 and is oriented rearward in the direction of the vehicle's longitudinal axis. The twelfth ultrasonic sensor 106 is also located at the rear left of the vehicle 100 and is oriented obliquely to the rear left. The thirteenth ultrasonic sensor 106 is also located at the rear left of the vehicle 100 and is oriented transversely to the vehicle's longitudinal axis, pointing to the left. The eighth and thirteenth ultrasonic sensors 106 are arranged as mirror images of each other with respect to the vehicle's longitudinal axis.The ninth and twelfth ultrasonic sensors 106 are also arranged in a mirror image with respect to the vehicle's longitudinal axis. The tenth and eleventh ultrasonic sensors 106 are also arranged in a mirror image with respect to the vehicle's longitudinal axis.

[0032] The control unit 102 is connected to the ultrasonic sensor system 104 and is configured to control the ultrasonic sensors 106 depending on their orientation. Frequency ranges for transmitting and / or receiving are assigned to the ultrasonic sensors 106, depending on their orientation. Signal components of received signals from the ultrasonic sensors 106 are also evaluated depending on their orientation.

[0033] In other words, the approach presented here involves a parallel measurement of objects, clutter, and noise in multiple frequency bands to determine the condition of a road.

[0034] Ultrasonic sensors determine the noise level in the last seven milliseconds of a measurement window. By determining the noise level in this range, or by evaluating this signal component, it is ensured that any echoes from distant objects are no longer perceptible and therefore do not play a role in determining the background noise.

[0035] Road conditions can be determined based on the noise levels of the ultrasonic sensors, as tire noise, specifically the so-called "wet whistling" sound, increases the noise level on wet roads. If the noise levels are recorded at the highest possible frequency and quality, even short puddles or damp patches can be reliably detected at high vehicle speeds.

[0036] The noise level can be calculated with improved quality by calculating more than one noise level within the measurement window. Alternatively or additionally, the time required to calculate the noise level within the measurement window can be increased.

[0037] A clutter value can be evaluated as an additional signal component. The clutter value can be determined after the sensor's excitation from sending signals or pulses has subsided. The clutter value measurement can be stopped when no further significant influence on the received signal from the ground echo is expected.

[0038] The clutter value of the ultrasonic sensors can also be used to determine road conditions, since water and ice close the pores of the road surface, resulting in less ground echo and therefore a lower clutter value.

[0039] If no ground echo is expected because the sensor itself and no neighboring sensor have emitted a signal, or because the expected ground echo lies outside the measured frequency range, then the signal component normally used to determine the clutter value can be used to determine a noise level. This improves the quality of the measured wet hiss, as the noise levels can be determined at shorter intervals or over a longer period overall.

[0040] In the approach presented here, all or several sensors are operated in parallel individually with the best possible settings in order to improve road condition detection and object detection.

[0041] The outer sensors (1, 6, 8, 13), positioned perpendicular to the direction of travel, transmit ultrasonic signals at low frequencies (e.g., < 48 kHz). Their echoes are used to detect vehicles in other lanes. Low frequencies are particularly well-suited for echolocation of vehicles in other lanes because, unlike medium and high frequencies, they are less attenuated, thus enabling a greater echolocation range. Some of the echoes are also relayed to the adjacent, innermost sensors (2, 5, 9, 12). These sensors also analyze the so-called cross-echoes, allowing for faster and more reliable object detection. In particularly wet conditions and at very high speeds, ambient noise can become so high that echolocation of objects is no longer possible. In this case, signal transmission is suspended.

[0042] The ground echo is determined using a clutter value by the sensors (2, 5, 9, 12) located further inwards and directed towards the lanes. For this purpose, ultrasonic signals with medium and high frequencies are emitted. Since the frequencies are shifted upwards by the Doppler effect for the sensors facing obliquely forwards and downwards for those facing obliquely backwards, it is advantageous for the sensors facing obliquely forwards (2, 5) to emit ultrasound at medium frequencies (e.g., between 45 kHz and 54 kHz) and the sensors facing obliquely backwards (9, 12) to emit ultrasound at high frequencies (e.g., > 52 kHz). This selection of transmission frequencies ensures that, at least for vehicle speeds at which a ground echo can be determined, the received signals remain within the medium and high frequencies despite the Doppler shift.Some of the ground echoes also reach the adjacent outer sensors (1, 6, 8, 13) and the innermost sensors (3, 4, 9, 10). By evaluating the so-called cross-clutter values, changing ground conditions can be detected more quickly and reliably. At high speeds, the influence of noise is so great that the clutter and cross-clutter values ​​can no longer be reliably determined. A wet environment also increases noise, making it impossible to reliably separate the clutter values ​​from the noise even at lower speeds. In these cases, the transmission of ultrasonic signals is omitted.

[0043] The innermost sensors (3, 4, 9, 10), facing forward and backward, do not emit their own ultrasound. Instead, these sensors analyze the noise. The noise level from the front sensors (3, 4) provides particularly good indications of wind speed and rain intensity. The noise level from the rear sensors (9, 10) provides particularly good indications of the amount of water between the tires and the road surface.

[0044] The front outer sensors (1, 6), positioned transversely to the direction of travel, transmit in a low frequency range depending on the vehicle speed. The clutter measurement window is used for low frequencies to detect ground echoes and measure the distance to objects, but only when sensors (1, 6) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a noise level for low frequencies.

[0045] For medium frequencies, a ground echo is also determined and the distance to objects is measured, but only if the neighboring sensors (2, 5) are transmitting ultrasonic signals. Otherwise, the measurement window in this range is also used to determine a noise level.

[0046] For high frequencies, a noise level can be determined in all measurement windows.

[0047] The rear outer sensors (8, 13), positioned transversely to the direction of travel, transmit in a low frequency range depending on the vehicle speed. The clutter measurement window is used for low frequencies to detect ground echoes and measure the distance to objects, but only when sensors (8, 13) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a noise level for low frequencies.

[0048] For high frequencies, a ground echo is also determined and the distance to objects is measured, but only if the neighboring sensors (9, 12) are transmitting ultrasonic signals. Otherwise, the measurement window in this range is also used to determine a noise level.

[0049] For medium frequencies, a noise level can be determined in all measurement windows.

[0050] The front inner sensors (2, 5), which are oriented towards the driving lane, transmit in a mid-frequency range depending on the vehicle speed. The measurement windows for clutter measurement and object detection are used at low frequencies to detect ground echoes and measure the distance to objects, but only when the adjacent sensors (1, 6) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a noise level at low frequencies.

[0051] For medium and high frequencies, a ground echo is also determined and the distance to objects is measured, but only if the sensors (2, 5) are transmitting ultrasonic signals. Otherwise, the measurement windows in these ranges are also used to determine a noise level.

[0052] The rear inner sensors (9, 12), facing the lane, transmit in a high-frequency range depending on the vehicle speed. The clutter measurement and object detection windows are used for low frequencies to detect ground echoes and measure the distance to objects, but only when the adjacent sensors (8, 13) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a low-frequency noise level.

[0053] For high and medium frequencies, a ground echo is also determined and the distance to objects is measured, but only if the sensors (9, 12) are transmitting ultrasonic signals. Otherwise, the measurement windows in these frequency ranges are also used to determine a noise level.

[0054] The innermost, forward-facing sensors (3, 4) do not emit ultrasonic signals. The clutter measurement and object detection windows are used for mid and high frequencies to detect ground echoes and measure the distance to objects, but only when the adjacent sensors (2, 5) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a noise level for mid and high frequencies.

[0055] For low frequencies, the measurement windows for clutter and objects are used to determine a noise level.

[0056] The rearmost innermost rear-facing sensors (10, 11) do not emit ultrasonic signals. The clutter measurement and object detection windows are used for mid and high frequencies to detect ground echoes and measure the distance to objects, but only when the adjacent sensors (9, 12) are transmitting. Otherwise, the clutter and object measurement windows are used to determine a noise level for mid and high frequencies.

[0057] For low frequencies, the measurement windows for clutter and objects are used to determine a noise level.

[0058] All sensors can always determine a noise level for all frequencies in the last measurement window, "Noise". Similarly, noise levels can always be calculated in all measurement windows for extremely high (>60 kHz) and extremely low frequencies (<43 kHz) where transmission is not possible.

[0059] If the distance to objects or the ground echo does not need to be determined so frequently, then the quality of the noise level measurement can be improved by inserting passive measurements between two active measurements where transmission occurs, and by using the measurement windows of all frequencies for clutter and objects to determine noise levels.

[0060] Measurements of distances to objects, ground echoes, and noise levels can be determined at a higher frequency. This allows for better object detection and a more accurate assessment of road conditions based on noise levels and ground echoes.

[0061] Finally, it should be noted that terms such as "comprising," "encompassing," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Reference numerals in the claims are not to be considered as limitations.

Claims

[1] Method for operating an ultrasonic sensor system (104) of a vehicle (100) with ultrasonic sensors (106) arranged in different orientations on the vehicle (100), wherein the ultrasonic sensors (106) are controlled depending on an orientation of the respective ultrasonic sensor (106), wherein at least two frequency ranges are assigned to an ultrasonic sensor (106) depending on its orientation, and wherein a road condition is determined on the basis of different signal components of a received signal of the ultrasonic sensor (106) depending on its orientation. [2] Method according to claim 1, wherein the signal components are measured simultaneously with at least two frequency ranges. [3] Method according to one of the preceding claims, wherein two or more signal components of a frequency range are used from the received signal to evaluate a noise level. [4] Method according to one of the preceding claims, wherein at least one diffuse ground echo signal is evaluated from the received signal of an ultrasonic sensor (106) directed obliquely forward or obliquely backward. [5] Method according to one of the preceding claims, wherein obliquely rearward-oriented ultrasonic sensors (106) are driven to send pulses in a first frequency range when a noise value is greater than a first noise threshold, wherein the first frequency range lies between a natural frequency of the ultrasonic sensors (106) and 100 kHz, wherein the first frequency range lies in particular between the natural frequency and 60 kHz. [6] Method according to one of the preceding claims, wherein obliquely forward-oriented ultrasonic sensors (106) are driven to send pulses in a second frequency range when the noise level is greater than a first noise threshold, wherein the second frequency range has a bandwidth of 30 kHz around a natural frequency of the ultrasonic sensors, wherein the second frequency range in particular has a bandwidth of 15 kHz around the natural frequency. [7] Method according to one of the preceding claims, wherein laterally oriented ultrasonic sensors (106) are driven to send pulses in a third frequency range when the noise level is greater than a first noise threshold, wherein the third frequency range is between 10 kHz and a natural frequency of the ultrasonic sensors (106), wherein the third frequency range is in particular between 30 kHz and the natural frequency. [8] Method according to one of the preceding claims, wherein at least one noise level is evaluated from the received signal of a rearward or forward-facing ultrasonic sensor (106). [9] Method according to one of the preceding claims, wherein forward- or rearward-facing ultrasonic sensors (106) are driven to not send pulses when the noise level is greater than a second noise threshold. [10] Control unit (102) designed to execute, implement and / or control the method according to one of the preceding claims in appropriate facilities. [11] Computer program product configured to execute, implement and / or control the method according to any one of claims 1 to 9 when the computer program is executed on a computer or device. [12] Machine-readable storage medium on which the computer program product according to claim 11 is stored.

Images