Method and device for measuring an external surround of a vehicle by means of ultrasound

Abstract

The invention relates to a method for measuring an external surround (40) of a vehicle (10), comprising the following steps: determining (S1) an ambient temperature of an ultrasonic transceiver (20, 21) of the vehicle (10), selecting (S2) a carrier frequency for an ultrasonic transmission signal of the ultrasonic transceiver (20, 21) on the basis of the determined ambient temperature of the ultrasonic transceiver (20, 21), transmitting (S3) the ultrasonic transmission signal at the selected carrier frequency into the external surround (40) of the vehicle (10) by means of the ultrasonic transceiver (20, 21), and receiving (S4) an ultrasonic reception signal by means of the ultrasonic transceiver (20, 21).

Description

[0001] METHOD AND DEVICE FOR MEASURING AN EXTERNAL ENVIRONMENT

[0002] OF A VEHICLE USING ULTRASOUND

[0003] The present invention relates to a method and a device for measuring the external environment of a vehicle using ultrasound. The present invention further relates to a computer program product.

[0004] Vehicles, particularly motor vehicles, are equipped with ultrasonic transceivers that transmit ultrasonic signals into the vehicle's surroundings and receive ultrasonic signals from the vehicle's surroundings. Based on the signal propagation time between the transmission of an ultrasonic signal and the occurrence of an ultrasonic echo in the ultrasonic signal, which echo is due to a reflection of the ultrasonic signal from an object in the vehicle's surroundings, a distance to the object in the vehicle's surroundings is determined. The actual position of the reflection point can be determined by trilateration or the like. With trilateration, an object such as a pole appears essentially point-like when viewed two-dimensionally.

[0005] Especially in automated driving, e.g., automated parking or automated starting, even small or narrow obstacles such as posts or horizontal poles must be reliably detected. The temperature-dependent directional characteristics of ultrasonic transceivers can make such detection difficult at different temperatures.

[0006] US Pat. No. 8,054,20213 B2 discloses a method for determining whether an object is located in the interior of a vehicle. In this method, the frequency of an ultrasonic horn is varied depending on the temperature in order to keep the wavelength constant. Against this background, one object of the present invention is to further improve the measurement of the external environment of a motor vehicle using ultrasound.

[0007] Accordingly, a method for measuring the external environment of a vehicle is proposed, the method comprising the following steps: determining an ambient temperature of an ultrasonic transceiver of the vehicle; selecting a carrier frequency of an ultrasonic transmission signal of the ultrasonic transceiver as a function of the determined ambient temperature of the ultrasonic transceiver; transmitting the ultrasonic transmission signal at the selected carrier frequency by means of the ultrasonic transceiver into the external environment of the vehicle; and receiving an ultrasonic reception signal by means of the ultrasonic transceiver.

[0008] With a temperature-constant carrier frequency, a change in the ambient temperature changes the wavelength of the ultrasonic transmission signal. The change in wavelength results in a change in the directivity of the ultrasonic transmission signal. By selecting the carrier frequency of the ultrasonic transmission signal depending on the ambient temperature, the wavelength of the ultrasonic transmission signal can be kept constant at different ambient temperatures or at least the change in wavelength depending on the ambient temperature can be reduced. By keeping the wavelength constant at different ambient temperatures or at least reducing the change in the wavelength, the directivity of the ultrasonic transceiver can be kept constant or at least the change in the directivity due to the ambient temperature can be reduced.

[0009] A temperature that is crucial for the propagation of the ultrasonic transmission signal is the temperature of a medium in which the ultrasonic transmission signal propagates, usually the surrounding air in which the ultrasonic transmission signal propagates. In embodiments, the temperature of the air in which the ultrasonic transmission signal propagates is therefore measured and used as the ambient temperature. However, it is also possible, for example, to measure the temperature of a sensor, the temperature of a bumper, or a temperature at another location, e.g., a temperature in the rear of the vehicle when ultrasonic transmission signals are transmitted in the front area of ​​the vehicle, and use this as the ambient temperature.

[0010] The distance of an object from the ultrasonic transceiver can be calculated from ultrasonic echoes in the received ultrasonic signal, which are the result of a reflection of the transmitted ultrasonic signal from an object in the vehicle's external environment. If multiple ultrasonic transceivers are used, the object's position can be determined using trilateration.

[0011] The carrier frequency can be selected depending on the ambient temperature using a look-up table containing carrier frequency values ​​for ambient temperatures and / or ranges of ambient temperatures. Alternatively, or in combination, the carrier frequency can be calculated using a formula stored in a processor with memory. The carrier frequencies of the look-up table or formula can be determined mathematically, through simulations, or through measurements.

[0012] An ultrasonic transceiver is often optimized for a specific optimal transmission carrier frequency or a narrow frequency band around this optimal transmission carrier frequency. In ultrasonic transceivers commonly used in vehicles, a membrane, particularly one made of metal, is excited by a piezoelectric element. The piezoelectric element is electrically excited. This type of electroacoustic transducer represents a resonant system. If a carrier frequency different from the optimal transmission carrier frequency is selected to excite the piezoelectric element, the output power of the ultrasonic transmission signal is reduced.

[0013] In the receive path, the ultrasonic transceiver is often also optimized for a specific optimal receive carrier frequency or a narrow frequency band around this optimal receive carrier frequency. If the ultrasonic transceiver receives an ultrasonic received signal with a carrier frequency different from the optimal receive carrier frequency, the electrical power required to convert the ultrasonic received signal into an electrical signal is reduced.

[0014] In embodiments, an ultrasonic transceiver is desired with a transfer function in which an attenuation of the ultrasonic transmission signal, in particular the sound pressure, by 3 dB compared to the maximum of the ultrasonic transmission signal at the optimal carrier frequency only occurs at a deviation of 3 kHz, preferably 5 kHz. For example, if the optimal carrier frequency is 52 kHz, an attenuation of the ultrasonic transmission signal by 3 dB should preferably only occur at carrier frequencies greater than 57 kHz or less than 47 kHz.

[0015] In embodiments, the carrier frequency for the ultrasonic transceiver is between 42 and 62 kHz, preferably between 45 and 59 kHz, more preferably between 48 and 56 kHz.

[0016] According to embodiments, a supplied electrical power for generating the ultrasonic transmission signal and / or an amplification of an electrical signal into which the ultrasonic reception signal is converted by the ultrasonic transceiver is selected depending on the selected carrier frequency of the ultrasonic transmission signal.

[0017] If the selected carrier frequency deviates from the optimal carrier frequency, less electrical power is converted into mechanical power in different types of ultrasonic transceivers. This can be compensated for by increasing the supplied electrical power to generate the ultrasonic transmission signal. To compensate for the temperature-dependent speed of sound, different carrier frequencies are used, thus achieving a constant wavelength. If the same electrical power is used with a transfer function from electrical to mechanical power that is not constant, one obtains directional characteristics for the different carrier frequencies at which the angular dependence of the ultrasonic transmission signal is the same, since they have the same wavelength. However, the directional characteristics have different absolute values.This would mean that a reflection by an object at the same position in the ultrasonic received signal would be stronger or weaker depending on the ambient temperature. To compensate for this, the electrical power used to generate the ultrasonic transmitted signal can be adjusted. For this purpose, values ​​for both the carrier frequency and the power can be stored in a lookup table, for example, depending on the ambient temperature, or formulas for calculating the carrier frequency and power as a function of temperature can be stored in a processor with memory.

[0018] When receiving ultrasonic signals, they essentially have the carrier frequency of the ultrasonic transmitted signals. Since ultrasonic received signals with different carrier frequencies can be converted into electrical signals in different ways, ultrasonic received signals of equal strength could be converted into electrical signals of different strengths depending on their carrier frequency, which was selected based on the ambient temperature. To compensate for this, the amplification of the electrical signal can be adjusted. For this purpose, values ​​depending on the ambient temperature and / or the carrier frequency can be stored in a look-up table, for example, or formulas for calculating the amplification depending on the ambient temperature and / or the carrier frequency can be stored in a processor with memory.

[0019] According to one embodiment, a directional characteristic of the ultrasonic transceiver at a first ambient temperature and a correspondingly selected carrier frequency differs from the directional characteristic of the ultrasonic transceiver at a different second ambient temperature and a correspondingly selected carrier frequency in terms of propagation angle and / or signal strength less than the directional characteristic of the ultrasonic transceiver at the first ambient temperature differs from the directional characteristic of the ultrasonic transceiver at the second ambient temperature, each time using the same carrier frequency. Changes in the carrier frequency as a function of temperature should result in a directional characteristic of the ultrasonic transceiver that is as temperature-independent as possible. For this purpose, the electrical power for the ultrasonic transmission signal can also be adjusted.A temperature-constant directivity is sometimes not possible over the entire desirable temperature range of -40 °C to 60 °C or up to 80 °C due to the properties of the ultrasonic transceiver, but even a directivity that changes less with temperature can improve the method for measuring the external environment of a vehicle.

[0020] According to one embodiment, the carrier frequency is selected depending on humidity, air pressure, or air composition. The ambient temperature is usually the most important parameter for the wavelength assigned to a carrier frequency; other factors such as humidity, air pressure, or air composition can also influence the wavelength at a carrier frequency. If data is available, e.g., from a corresponding sensor, these influences can also be taken into account when selecting the carrier frequency.

[0021] According to one embodiment, the electrical power supplied to generate the ultrasonic transmission signal is selected depending on the air humidity, air pressure, or air composition. Other influences such as air humidity, air pressure, or air composition can also be taken into account when determining the power used to generate the ultrasonic transmission signal in order to compensate for influences on the conversion of electrical power into mechanical power of the ultrasonic transmission signal.

[0022] According to one embodiment, the ambient temperature of the ultrasonic transceiver is determined using a temperature sensor of the vehicle and / or from external data, e.g., from the Internet, and / or using a temperature sensor of the ultrasonic transceiver, in particular a temperature sensor of an ASIC of the ultrasonic transceiver. Vehicles often have temperature sensors that measure the vehicle's exterior temperature, e.g., for warnings about ice formation. The data from such a temperature sensor can be used to determine the ambient temperature. ASICs, such as those often found in the module that includes the ultrasonic transceiver, can also contain temperature sensors; this data can also be used to determine the ambient temperature.Vehicles are often equipped with internet access, which retrieves information about the local temperature and uses it to determine the ambient temperature. A suitable ambient temperature for performing this method is the air temperature immediately adjacent to the ultrasonic transceiver.

[0023] According to one embodiment, the ambient temperature is determined from measurements of the ultrasonic transceiver, in particular from measuring temperature-dependent changes in the piezoelectric effect of the ultrasonic transceiver's membrane or from time-of-flight measurements, in particular between two adjacent ultrasonic transceivers with a known distance. In such a measurement between two adjacent ultrasonic transceivers, the received signal strength at the ultrasonic transceiver is often very low, but can still be sufficient for the specific task of time-of-flight measurement. Such measurements can provide direct access to the ambient temperature of the air or the ultrasonic transceiver.

[0024] Different temperature measurement methods as well as data and information about temperatures can also be combined to determine the ambient temperature.

[0025] According to one embodiment, the ultrasonic transceiver is arranged on a front apron, a rear apron, or a bumper. For vehicle applications such as parking aids or automated parking or reversing, ultrasonic transceivers are mounted at such suitable locations on the vehicle. This results in technical requirements, e.g., regarding the robustness of the ultrasonic transceiver, and aesthetic requirements for the ultrasonic transceivers.

[0026] The ultrasonic transceivers used should, for example, be suitable for being mounted on the front of the vehicle at speeds over 100 km / h and / or up to 250 km / h and be able to withstand impact from raindrops; the ultrasonic transceivers should, for example, be able to dry off as quickly as possible after the vehicle has been driven through rain or snow and remain functional; the ultrasonic transceivers should, for example, have as little impact as possible on the vehicle's aerodynamics. Such requirements are poorly met, for example, by an ultrasonic horn whose opening and shape lead to turbulence and are associated with a deterioration in aerodynamics and would direct snowflakes, rain, or spray into the horn.

[0027] According to one embodiment, the ultrasonic transceiver is designed with a flat membrane facing the vehicle's exterior environment. For example, a flat membrane is designed without attachments or superstructures such as horns, adaptation layers, e.g., A / 4 layers, and / or is arranged flatly in the surface of a front apron, a rear apron, or a bumper. A flat membrane blends in well with the appearance of a vehicle. Water droplets or melting snow can easily drip off a flat membrane, especially one mounted perpendicular to the vehicle's horizontal plane. A flat membrane only minimally disrupts the vehicle's aerodynamics and offers little surface area for wind forces to act on.

[0028] According to one embodiment, the flat membrane of the ultrasonic transceiver is in direct contact with the air of the vehicle's external environment and / or is painted. A membrane, e.g., a metal membrane, especially a painted membrane, is resistant to impacting raindrops and / or wind. Omitting adaptation layers, e.g., A / 4 layers, can reduce efficiency when converting electrical power into mechanical power, but can increase the robustness of the ultrasonic transceiver against environmental influences.

[0029] Furthermore, a device for measuring the external environment of a vehicle is proposed, comprising: an ultrasonic transceiver configured to transmit ultrasonic transmission signals into the external environment of the vehicle and to receive ultrasonic reception signals from the external environment of the vehicle; a temperature determination unit for determining the ambient temperature of the ultrasonic transceiver; a selection unit for selecting a carrier frequency of the ultrasonic transmission signals of the ultrasonic transceiver depending on the ambient temperature of the ultrasonic transceiver.

[0030] The units described here, for example, the temperature detection unit or selection unit, can be implemented in hardware and / or software. For example, the units can be implemented on a microprocessor with associated memory. The microprocessor, including memory, can be implemented, for example, on a central control unit of the motor vehicle or as an ASIC near the ultrasonic transceiver. The microprocessor can receive external data, e.g., from the Internet, on the ambient temperature, e.g., via a data bus.

[0031] According to one embodiment, the ultrasonic transceiver is designed with a membrane that is flat toward the vehicle's exterior environment. In particular, the flat membrane of the ultrasonic transceiver is in direct contact with the air in the vehicle's exterior environment or is painted. A painted, flat membrane that is flush with a vehicle component can blend in well with the vehicle's appearance, a deterioration in the vehicle's aerodynamics can be avoided, and / or rain and snow can be blown away from the ultrasonic transceiver by the wind.

[0032] According to one embodiment, a bumper, a front apron, a rear apron, a sill, a door, a tailgate, a roof, or a motor vehicle comprise the device for measuring an external environment of a vehicle or it is attached to the underbody. The device for measuring an external environment of a vehicle can, for example, be integrated into a component that is then mounted in the bumper, in the front apron, or in the rear apron. The device can also be distributed across multiple components of the motor vehicle, e.g., a control unit located in the engine compartment, and an ultrasonic transceiver arranged on the bumper, on the front apron, or on the rear apron.

[0033] Furthermore, a computer program product is proposed which comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method described above.

[0034] A computer program product, such as a computer program means, can be provided or delivered, for example, as a storage medium, such as a memory card, USB stick, CD-ROM, DVD, or in the form of a downloadable file from a server in a network. This can be done, for example, in a wireless communications network by transmitting a corresponding file with the computer program product or the computer program means.

[0035] The embodiments and features described for the proposed device apply accordingly to the proposed method and, conversely, the embodiments and features described for the proposed method also apply to the proposed device.

[0036] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0037] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic plan view of a motor vehicle with ultrasonic transceivers and an obstacle;

[0038] Fig. 2 shows a diagram illustrating the dependence of a sound speed c of an ultrasonic transmission signal in air on a temperature T;

[0039] Fig. 3 shows a diagram illustrating the dependence of a wavelength A of the ultrasonic transmission signal on the temperature T ;

[0040] Fig. 4 shows a polar diagram illustrating the influence of temperature T on a directional characteristic of an ultrasonic transceiver;

[0041] Fig. 5 shows a diagram illustrating a reflection of the ultrasonic transmission signal of the ultrasonic transceiver by an obstacle outside the sensor axis at different temperatures;

[0042] Fig. 6 shows a diagram illustrating an adjustment of a carrier frequency of the ultrasonic transmission signal as a function of temperature T in order to compensate for the effect of temperature on the wavelength A;

[0043] Fig. 7 is a diagram illustrating the compensation of the effect of temperature T on the wavelength A in air by adjusting the carrier frequency of the ultrasonic transmission signal;

[0044] Fig. 8 shows a polar diagram illustrating a compensated influence of temperature T on the directional characteristic of an ultrasonic transceiver;

[0045] Fig. 9 shows a flowchart for a method for measuring an external environment of a vehicle using an ambient temperature-dependent carrier frequency of an ultrasonic transceiver; and Fig. 10 schematically shows an apparatus for measuring an external environment of a vehicle.

[0046] In the figures, identical or functionally equivalent elements have been given the same reference numerals unless otherwise stated.

[0047] Fig. 1 shows an exemplary vehicle, a motor vehicle 10, with multiple ultrasonic transceivers 20, 21. The multiple ultrasonic transceivers 20, 21 are arranged in a front apron and a rear apron, both of which are not visible in the top view, of the motor vehicle 10. In the schematic illustration, the ultrasonic transceivers 20, 21 are shown mounted for better visibility. In most motor vehicles 10, the ultrasonic transceivers 20, 21 are flush-mounted, so that they do not protrude, or only protrude minimally, from the front apron or rear apron.

[0048] The ultrasonic transceivers 20, 21 are often designed with a cup-shaped membrane, the flat side of which is painted in the color of the motor vehicle 10. The flat area of ​​the membrane is fitted into the plane of the front apron or rear apron. A cylindrical area adjoins the flat area of ​​the membrane. The cylindrical area can have a greater wall thickness than the flat area. The membrane can be connected to the cylindrical area with a housing of the ultrasonic transceiver 20, 21. The ultrasonic transceivers 20, 21 are often only recognizable by a silicone decoupling between the front apron or rear apron and the ultrasonic transceiver 20, 21, which is indicated by a circle. The membrane of the ultrasonic transceivers 20, 21 is excited by a piezo element. The ultrasonic transceiver 20, 21 is an electroacoustic transducer that converts electrical signals into sound and vice versa.

[0049] For the ultrasonic transceiver 21, a main radiation direction 30 for an ultrasonic

[0050] The transmitted signal is shown. The ultrasonic transceiver 21 radiates the ultrasonic transmitted signal into an external environment 40 of the motor vehicle 10. The ultrasonic transceiver 21 is an anisotropic radiator. The ultrasonic transceiver 21 radiates its maximum power perpendicular to the flat side of the membrane. In the horizontal plane through the main beam direction 30, the ultrasonic transmitted signal has an aperture angle of approximately 150°. In the vertical plane through the main beam direction 30, the aperture angle is approximately 90°.

[0051] An obstacle 50 is shown in the periphery of the ultrasonic transmission signal propagation. If the aperture angle of the ultrasonic transmission signal decreases in the horizontal plane, the obstacle 50 may no longer be hit by the ultrasonic transmission signal of the ultrasonic transceiver 21, or the signal strength may no longer be sufficient. If the obstacle 50 is also not hit by ultrasonic transmission signals from another ultrasonic transceiver 20, it can no longer be detected by the ultrasonic transceivers 20, 21. Such a change in the aperture angle can be caused by a change in the ambient temperature of the ultrasonic transceivers 20, 21.

[0052] The directional characteristic of the ultrasonic transceiver 21 for transmitting ultrasonic signals is significantly influenced by the ratio of the wavelength in the propagation medium (air) and the geometric dimensions of the membrane, particularly the flat side of the membrane, and / or the flexural vibration. This applies similarly to the directional characteristic when receiving ultrasonic signals, i.e., the angle-dependent sensitivity of the ultrasonic transceiver 21.

[0053] Fig. 2 shows a diagram illustrating the dependence of the speed of sound c in m / s of an ultrasonic transmission signal in air on the temperature T of the air. In the ambient temperature range relevant for vehicles between approximately -40°C and 80°C, the speed of sound varies between approximately 305 m / s and approximately 375 m / s, with temperatures up to approximately 60°C being more relevant. With a constant carrier frequency of the ultrasonic transmission signal, the wavelength therefore increases. Fig. 3 shows a diagram illustrating the dependence of a wavelength A of the ultrasonic transmission signal in arbitrary units, arb. units, on the temperature T of the air. If a fixed carrier frequency is set for an ultrasonic transmission signal of the ultrasonic transceiver 21, the wavelength decreases by more than 10% when the air in the environment 40 of the ultrasonic transceiver 21 cools from 20°C to -40°C and increases by more than 5% when the temperature increases from 20°C to 60°C.

[0054] The relationships between the speed of sound c and various air conditions such as temperature, pressure, humidity, and CO2 concentration are well known, see for example Bohn, Dennis A. “Environmental Effects on the Speed ​​of Sound.” Journal of The Audio Engineering Society 36 (1988): 223-231 or Cramer, Owen P. “The variation of the specific heat ratio and the speed of sound in air with temperature, pressure, humidity, and CO2 concentration.” Journal of the Acoustical Society of America 93 (1993): 2510-2516. In addition to the air temperature, other factors and parameters can also be taken into account which influence the wavelength of the ultrasonic transmitted signal.

[0055] Fig. 4 shows a polar diagram illustrating the influence of temperature T on the field of view or the directional characteristic 61, 62, 63 of an ultrasonic transceiver 21. The polar diagram shows a vertical section through the angle-dependent distribution of the radiation intensity of the ultrasonic transceiver 21. The ultrasonic transceiver 21 is aligned with its main beam direction towards 0° in the plane of representation. If one now moves in the vertical plane on a circle around the ultrasonic transceiver 21, the radiation power received at a detector decreases with increasing angle until, after the maximum aperture angle is reached, there is no, or only a very low, sound pressure to one side. The aperture angle can be defined as the angular range in which the sound pressure or level of the ultrasonic transmission signals drops by 3 dB in both directions relative to the main beam direction, in Fig.4, this is the case at approximately 80° to 100°. A horizontal section through the angle-dependent distribution of the intensity of the radiation of the ultrasonic transceiver 21 would result in an aperture angle of approximately 140° to 160° for the directional characteristic 61, 62, 63 of the ultrasonic transceiver 21.

[0056] The polar diagram now shows the directional characteristic 61 for 60 °C, the directional characteristic 62 for 20 °C, and the directional characteristic 63 for -40 °C. The opening angle of the directional characteristics 61, 62, 63 increases with increasing temperature. The flat side of the membrane of the ultrasonic transceiver 21 is a membrane area with a diameter of approximately 15 mm, which radiates ultrasonic transmission signals directly into the environment 40 of the motor vehicle 10. The directional characteristics 61, 62, 63 now change, with a constant excitation frequency, with the change in wavelength A due to the temperature-dependent speed of sound c.

[0057] Fig. 5 shows a diagram illustrating a reflection 71, 72 of the ultrasonic transmission signal of the ultrasonic transceiver 21 by an obstacle 50 at different temperatures. The diagram shows the curve of the ultrasonic reception signal, as amplitude A in arbitrary units, arb. units, versus the time after the transmission of the ultrasonic transmission signal, the Time of Flight (ToF). If an obstacle 50 is not located in the main beam direction of the ultrasonic transceiver 21, but rather at the edge of the aperture angle, it can happen that the obstacle 50 is still hit by the ultrasonic transmission signal at a temperature of 60 °C with such a signal strength that the reflection 71 of the ultrasonic transmission signal in the ultrasonic reception signal exceeds a threshold value 80 for detecting obstacles.At a temperature of -40 °C, however, the obstacle 50 lies outside the opening angle or in the outer range of the opening angle, so that the reflection 72 of the ultrasonic transmitted signal in the ultrasonic received signal remains below the threshold value 80 for detecting obstacles. The obstacle 50 would then be detected at 60 °C, but at -40 °C the obstacle would no longer be detected. The threshold value 80 can be varied within a time interval after the ultrasonic transmitted signal has been transmitted; in the diagram in Fig. 5 this can be seen as a reduction. Even if, for the sake of simplicity, the example is based on simple peak detection - determining whether a reflection in the ultrasonic received signal can be recognized as an echo - peak heights are also relevant for classifying objects such as the obstacle 50, e.g. distinguishing whether it is a low or a tall object.

[0058] Fig. 6 shows a diagram illustrating an adjustment of the carrier frequency of the ultrasonic transmission signal as a function of the temperature T in order to compensate for the effect of the temperature on the wavelength A. The carrier frequency f of the ultrasonic transmission signal is shown in arbitrary units, arb. units, as a function of the temperature T in °C. In order to avoid the effect of the change in the directional characteristic and the consequences for the detection of obstacles shown in Fig. 4 and Fig. 5, a temperature-dependent carrier frequency f 92 can be selected instead of a fixed, non-temperature-dependent, uncorrected carrier frequency f 91 , so that the wavelength A remains constant, or at least changes less than with a fixed carrier frequency f 91 .

[0059] Fig. 7 shows a diagram illustrating the compensation of the effect of temperature T on wavelength A in air by adjusting the temperature-dependent carrier frequency f 92 of the ultrasonic transmission signal. The wavelength A in air is plotted in arbitrary units, arb. units, as a function of temperature T in °C. The diagram shows the uncorrected curve of wavelength A as a function of temperature 101, known from Fig. 3, at the fixed, non-temperature-dependent, uncorrected carrier frequency f 91 . However, if the temperature-dependent carrier frequency f 92 is used, the corrected curve of wavelength A as a function of temperature 102 results. By changing the carrier frequency f 92 as a function of temperature, a constant wavelength A can be achieved.

[0060] Fig. 8 shows a polar diagram with a representation of the compensated influence of the temperature T on the directional characteristic of the ultrasonic transceiver 21. The polar diagram of Fig. 8 corresponds to the polar diagram of Fig. 4, whereby instead of the constant carrier frequency in Fig. 4 with the resulting change in the wavelength A due to the temperature-dependent speed of sound c, the temperature-dependent carrier frequency f 92 from Fig. 6 was used. The temperature-dependent carrier frequency f 92 keeps the wavelength A constant, as shown in the corrected curve of the wavelength A as a function of the temperature in Fig. 7. As a result, the curves for the directional characteristic 11 1 for 60 ° C, the directional characteristic 112 for 20 ° C and the directional characteristic 113 for -40 ° C lie one above the other. The opening angles of the directional characteristics 111, 112, and 113 are the same and an effect as shown in Fig. 5 can be avoided.

[0061] In order to ensure that the directional characteristics 1 11 , 1 12 , and 113 are the same for the different ambient temperatures, in addition to the carrier frequency, the power for the ultrasonic transmission signals can also be adjusted if a transfer function for the conversion of electrical to mechanical power is not constant in the range of the carrier frequencies used.

[0062] The necessary values ​​for the electrical power to generate the ultrasonic transmission signal can, for example, come from a stored sensor model; be measured and stored individually for each sensor on the production line; or be determined on the vehicle by determining the transfer function from electrical to acoustic power, e.g. from electrical or acoustic data.

[0063] Values ​​for the temperature-dependent carrier frequency f 92 and, if applicable, also for the power of the ultrasonic transmission signal at the respective selected carrier frequency f 92 can be stored in a look-up table, so that temperatures or temperature ranges are assigned carrier frequencies as well as signal strengths, powers or powers of the ultrasonic transmission signal, so that a directional characteristic that does not change with temperature is achieved through the selection. Alternatively, or in combination, formulas for the calculation can be stored in a microprocessor with a memory. Both a look-up table and a calculation can also be implemented in hardware, e.g., ASICs. A completely temperature-independent directional characteristic over the desired temperature range cannot always be achieved. For example,the transfer function of electrical power into sound power of the ultrasonic transceiver 21 can result in the carrier frequency not being able to be changed to such an extent that the wavelength A remains constant at different temperatures without the sound power being reduced. However, even partial compensation for temperature effects represents an improvement. Fig. 7 shows how the constant wavelength A 102 is achieved using a temperature-dependent carrier frequency f 92. A wavelength A that lies between the constant wavelength A 102 and the uncorrected curve of the wavelength A also brings an improvement. When the temperature-dependent carrier frequency f 92 is selected, the directional characteristics of the ultrasonic transceiver 21 at two different temperatures differ less in terms of propagation angle and / or signal strength than the directional characteristics when using the same carrier frequency at the two (different) temperatures.

[0064] Alternatively or in addition to adjusting the electrical power to generate the ultrasonic transmission signals, the amplification of an electrical signal in the reception path, which is created by converting the ultrasonic reception signal into the electrical signal, can also be adjusted depending on the ambient temperature or the carrier frequency used. For this purpose, too, calculation formulas can be stored in a microprocessor with a memory, either alternatively or in combination. Both a look-up table and a calculation can also be implemented in hardware, e.g. ASICs. The necessary values ​​for the amplification can, for example, come from a stored sensor model; be measured and stored for each individual sensor on the production line; or be determined on the vehicle by determining the transfer function from electrical to acoustic power, e.g. from electrical or acoustic data.

[0065] Fig. 9 shows a flowchart for a method for measuring the external environment of a vehicle using an ambient temperature-dependent carrier frequency of an ultrasonic transceiver. In a step S1, the ambient temperature of the ultrasonic transceiver 21 is determined. The determination can be made using an outside temperature sensor present in the motor vehicle 10. However, these sensors or their evaluation are often slow. An ASIC arranged on the ultrasonic transceiver 21 and having its own temperature sensor can also be used to determine the temperature. Temperature data obtained from the Internet and combinations of different methods for determining the ambient temperature can also be used. For the best possible implementation of the method, an air temperature directly at the membrane, in particular the flat side of the membrane, of the ultrasonic transceiver 21 is desirable.

[0066] Temperature can also be determined from measurements on and with the ultrasonic transceiver 21. The piezoelectric effect of the piezoelectric element used to excite the membrane is temperature-dependent. This temperature dependence changes the electrical characteristics of the electroacoustic transducer. Using control electronics, the electrical characteristics can be measured, thus determining the temperature.

[0067] In a step S2, the carrier frequency of the ultrasonic transmission signal of the ultrasonic transceiver 21 is selected depending on the ambient temperature of the ultrasonic transceiver 21. The selection can be made using a look-up table. Alternatively, formulas or algorithms can be stored in a processor with a memory, which calculate the carrier frequency from the ambient temperature.

[0068] In a step S3, the ultrasonic transmission signal is transmitted into the vehicle's external environment by the ultrasonic transceiver 21. The ultrasonic transmission signal is transmitted at the selected carrier frequency and can be encoded in a variety of ways, e.g., amplitude or frequency modulation, frequency or phase shift keying, or a multiplexing method such as time-division multiplexing. Typically, a large number of ultrasonic pulses are transmitted consecutively, with pauses between them. The ultrasonic transceiver is sensitive to the ultrasonic reception signal for a short time after the transmission of an ultrasonic pulse, during the pause between the pulses.

[0069] In a step S4, the ultrasonic reception signal is received by the ultrasonic transceiver 21. The received ultrasonic reception signal can be used to search for reflections of the ultrasonic transmission signal from objects, e.g., obstacle 50, and the distance from the objects to the ultrasonic transceiver 21 can be determined from travel time calculations.

[0070] Fig. 10 schematically shows a device 120 for measuring an external environment of a vehicle.

[0071] The ultrasonic transceiver 21 is configured to transmit ultrasonic transmission signals into the external environment 40 of the vehicle 10. The ultrasonic transceiver 21 is an electroacoustic transducer. A piezoelectric element is excited by an electrical signal with a carrier frequency. The piezoelectric element excites a membrane to vibrate, which is transmitted to the air as ultrasound. The membrane can be pot-shaped, with a cylindrical region adjoined by a flat, round region with a diameter of approximately 15 mm. In particular, the flat region generates ultrasonic transmission signals in the air as ultrasonic waves. Ultrasonic waves impinging on the membrane can excite the piezoelectric element as ultrasonic reception signals and generate a piezoelectric voltage that can be measured.

[0072] A temperature determination unit 130 is configured to determine the ambient temperature of the ultrasonic transceiver 21. The temperature determination unit 130 may, for example, comprise a thermocouple and its evaluation electronics. The temperature determination unit may also comprise a data input and evaluation electronics. Vehicle-external data, e.g., temperature data from the Internet, or vehicle-internal data, e.g., from a temperature sensor of the motor vehicle 10, can be received via the data input and evaluated in the temperature determination unit 130. The temperature determination unit 130 may, for example, be implemented with a microprocessor with a memory, e.g., an ASIC.

[0073] A selection unit 140 is used to select the carrier frequency of the ultrasonic transmission signals of the ultrasonic transceiver 21 depending on the ambient temperature of the ultrasonic transceiver 21. The selection unit 140 can be implemented, for example, with a microprocessor with a memory, e.g., an ASIC. In particular, the selection unit 140 can also be implemented using the same microprocessor as the temperature determination unit 130.

[0074] The ultrasonic transceiver 21, the temperature detecting unit 130 and the selecting unit 140 may be arranged in or on a housing.

[0075] Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

[0076] LIST OF REFERENCE SYMBOLS

[0077] 10 motor vehicle

[0078] 20, 21 Ultrasonic transceiver

[0079] 30 Main beam direction

[0080] 40 external environment

[0081] 50 obstacles

[0082] 61 Directional characteristic at 60 °C

[0083] 62 Directional characteristic at 20 °C

[0084] 63 Directional characteristic at -40 °C

[0085] 71 Reflection in the ultrasonic received signal at 60 °C

[0086] 72 Reflection in the ultrasonic received signal at -40 °C

[0087] 80 threshold

[0088] 91 uncorrected carrier frequency f

[0089] 92 temperature-dependent carrier frequency f

[0090] 101 uncorrected curve of wavelength A as a function of temperature

[0091] 102 corrected curve of wavelength A as a function of temperature

[0092] 111 corrected directivity at 60 °C

[0093] 112 corrected polar pattern at 20 °C

[0094] 113 corrected polar pattern at -40 °C

[0095] 120 Device for measuring the external environment of a vehicle

[0096] 130 Temperature detection unit

[0097] 140 Selection unit for selecting a carrier frequency

[0098] 51 Determination of an ambient temperature of the ultrasonic transceiver

[0099] 52 Selection of the carrier frequency of the ultrasonic transmission signal of the ultrasonic transceiver

[0100] 53 Sending the ultrasonic transmission signal with the ultrasonic transceiver 21 into the external environment of the vehicle

[0101] 54 Receiving the ultrasonic reception signal with the ultrasonic transceiver 21

Claims

PATENT CLAIMS 1. A method for measuring an external environment (40) of a vehicle (10), comprising the following steps: Determining (S1) an ambient temperature of an ultrasonic transceiver (20, 21) of the vehicle (10), Selecting (S2) a carrier frequency of an ultrasonic transmission signal of the ultrasonic transceiver (20, 21) depending on the determined ambient temperature of the ultrasonic transceiver (20, 21), Transmitting (S3) the ultrasonic transmission signal with the selected carrier frequency by means of the ultrasonic transceiver (20, 21) into the external environment (40) of the vehicle (10), and Receiving (S4) an ultrasonic reception signal by means of the ultrasonic transceiver (20, 21).

2. The method according to claim 1, wherein a supplied electrical power for generating the ultrasonic transmission signal and / or an amplification of an electrical signal into which the ultrasonic reception signal is converted is selected as a function of the selected carrier frequency of the ultrasonic transmission signal.

3. Method according to claim 1 or 2, wherein a directional characteristic of the ultrasonic transceiver (20, 21) at a first ambient temperature and the correspondingly selected carrier frequency differs from the directional characteristic of the ultrasonic transceiver (20, 21) at a different second ambient temperature and the correspondingly selected carrier frequency in terms of propagation angle and / or signal strength less than the directional characteristic of the ultrasonic transceiver (20, 21) at the first ambient temperature differs from the directional characteristic of the ultrasonic transceiver (20, 21) at the second ambient temperature, in each case when using the same carrier frequency.

4. Method according to one of the preceding claims, wherein the carrier frequency is selected as a function of air humidity, air pressure or composition of the air.

5. Method according to one of claims 2 to 4, wherein the electrical power supplied for generating the ultrasonic transmission signal is selected as a function of air humidity, air pressure or composition of the air.

6. Method according to one of the preceding claims, wherein the ambient temperature of the ultrasonic transceiver (20, 21) is determined with a temperature sensor of the vehicle (10) and / or from data provided externally to the vehicle, e.g. from the Internet, and / or with a temperature sensor of the ultrasonic transceiver, in particular a temperature sensor of an ASIC of the ultrasonic transceiver.

7. Method according to one of the preceding claims, wherein the ambient temperature is determined from measurements of the ultrasonic transceiver (20, 21), in particular from measurement of temperature-dependent changes in the piezoelectric effect of the membrane of the ultrasonic transceiver (20, 21) or from transit time measurements.

8. Method according to one of the preceding claims, wherein the ultrasonic transceiver (20, 21) is arranged on a front apron, a rear apron, a sill, a door, a tailgate, a roof, on the underbody or a bumper.

9. Method according to one of the preceding claims, wherein the ultrasonic transceiver (20, 21) is designed with a membrane that is flat towards the external environment (40) of the vehicle (10).

10. The method according to claim 9, wherein a flat region of the membrane of the ultrasonic transceiver (20, 21) is in direct contact with the air of the external environment (40) of the vehicle (10) and / or is painted.

11. Device (120) for measuring an external environment (40) of a vehicle (10), in particular for carrying out the method according to one of claims 1 to 10, comprising: an ultrasonic transceiver (20, 21) which is designed to transmit ultrasonic transmission signals into the external environment (40) of the vehicle (10) and to receive ultrasonic transmission signals from the external environment Environment of the vehicle to receive ultrasonic reception signals, a temperature determination unit for determining the ambient temperature of the ultrasonic transceiver (20, 21), a selection unit for selecting a carrier frequency of the ultrasonic transmission signals of the ultrasonic transceiver (20, 21) depending on the ambient temperature of the ultrasonic transceiver (20, 21).

12. Bumper, front apron, rear apron, sill, door, tailgate, roof, underbody or motor vehicle (10) with a device (120) according to claim 11.

13. A computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 10.

Images