ULTRASOUND SENSOR SYSTEM FOR A MOTOR VEHICLE AND METHOD FOR OPERATING THE ULTRASOUND SENSOR SYSTEM

Description

[0001] The present invention relates to the field of ultrasonic sensor technology for motor vehicles and more specifically to an ultrasonic sensor system for a motor vehicle and a method for operating the ultrasonic sensor system.

[0002] Ultrasonic sensors with an electroacoustic transducer arrangement for generating and detecting ultrasonic waves are known for measuring the distance to an object in the vehicle's environment. An ultrasonic wave is emitted, and an echo signal returning from the vehicle's surroundings is detected. The distance to the object is determined based on the signal's travel time. Such measurements are used, for example, by a vehicle's driving or parking assistance system.

[0003] Due to internally or externally induced changes in the electroacoustic transducer arrangement, such as an aging-dependent domain effect of a piezoelectric element, the measurement result can become distorted or the ultrasonic sensor can fail over time. Therefore, multiple ultrasonic sensors can be installed on a vehicle, and the measured values ​​provided by each sensor can be subjected to a plausibility check before evaluation. However, such a plausibility check can also erroneously discard otherwise usable measurement results if the electrical characteristics of the ultrasonic sensor gradually change.

[0004] EP 2 347 231 B1 discloses a functional monitoring device that determines the impedance characteristic of an ultrasonic sensor as a function of an excitation frequency. During the determination of the impedance characteristic, the ultrasonic sensor is excited with a smaller and constant amplitude compared to normal measurement operation.

[0005] German patent DE 10 2012 216 968 A1 teaches that the electrical impedance of an ultrasonic transducer is measured using a test signal, and changes in impedance across the frequency of the test signal are compared with a reference to identify extreme points in the impedance curve. The test signal has an amplitude that differs from the amplitude used for distance measurement.

[0006] DE 10 2014 201 482 A1 teaches that an impedance curve of an ultrasonic transducer is determined by sweeping an excitation signal over a given frequency range with constant voltage amplitude.

[0007] DE 10 2017 203 136 A1 discloses a monitoring unit for a sound sensor that measures the impedance of a sound transducer for different excitation frequencies. The sound transducer is excited with amplitudes that are preferably one or more orders of magnitude smaller than the amplitudes used for distance measurement.

[0008] DE 10 2018 124 024 A1 describes an ultrasonic sensor with test control device.

[0009] Against this background, the present invention aims to improve the condition determination of an ultrasonic sensor.

[0010] Accordingly, an ultrasonic sensor system for a motor vehicle is proposed. The proposed ultrasonic sensor system comprises an ultrasonic sensor with an electroacoustic transducer arrangement for generating and detecting ultrasonic waves and an electrical test device configured to output an electrical test signal to the electroacoustic transducer arrangement and to detect an electrical response signal from the electroacoustic transducer arrangement to the electrical test signal. The proposed ultrasonic sensor system further comprises a test control device configured to detect a characteristic parameter of the electrical response signal at several measuring points by means of the electrical test device while varying the frequency and amplitude of the electrical test signal.

[0011] The electroacoustic transducer arrangement can in particular include an ultrasonic membrane, a sound transducer device attached to the ultrasonic membrane with a mechanical-capacitive, mechanical-resistive, magnetostrictive or electrostrictive operating principle, such as a piezoelectric element, and a coupling circuit for impedance matching of the sound transducer device.

[0012] In particular, such an electroacoustic transducer arrangement can be understood as a nonlinear electrical arrangement with a resistive, an inductive and a capacitive component.

[0013] By proposing to measure an electrical parameter at multiple measuring points while varying not only the frequency but also the amplitude of the test signal, a multidimensional characteristic field of the electroacoustic transducer arrangement can advantageously be measured at least section by section, thus taking into account, in particular, a non-linear amplitude dependence of the parameter.

[0014] By taking such consideration of the amplitude dependence of the electrical parameters of the electroacoustic transducer arrangement, a significantly improved characterization of the state of the ultrasonic sensor can be achieved, and accordingly, a higher-level control device of the motor vehicle can react much better to changes in the state of the ultrasonic sensor.

[0015] The term "measuring point" can, in particular, refer to a specific combination of exactly one frequency and exactly one amplitude of the test signal.

[0016] The test control unit can therefore, in particular, record several parameters, one for each measuring point. The parameters recorded at the multiple measuring points can, in particular, form a characteristic curve or a two- or multi-dimensional characteristic map of the electroacoustic transducer arrangement of the ultrasonic sensor.

[0017] The electrical test signal can, in particular, be an oscillation of an electrical parameter, such as current or voltage, applied to the electroacoustic transducer arrangement, with a defined amplitude and a defined frequency. At each of the measuring points, the amplitude and frequency of the test signal can be constant, especially for the duration of the acquisition of the parameter of the response signal at that measuring point.

[0018] The electrical response signal can in particular be an oscillation of one of the characteristic parameters, such as voltage or current, which is detected at the electroacoustic transducer arrangement while the electrical test signal is applied to the electroacoustic transducer arrangement.

[0019] The electrical test device can be designed by an electrical circuit provided in the ultrasonic sensor, which can be controlled by the test control device to generate the electrical test signal with a frequency and amplitude specified by the test control device and can be used by the test control device to detect the electrical response signal.

[0020] The test control unit can be integrated into the ultrasonic sensor or provided externally to the ultrasonic sensor.

[0021] The test control device can be designed in particular by an application-specific integrated circuit (ASIC), a microprocessor, an electronic control unit (ECU) or the like.

[0022] The acquisition of the characteristic value at the multiple measuring points by varying the frequency and amplitude of the test signal using the test control unit can also be referred to as the "test operation" of the ultrasonic sensor. Activating the electroacoustic transducer arrangement to generate ultrasonic waves and subsequently acquiring reflected ultrasonic waves for distance measurement can also be referred to as the "measurement operation" of the ultrasonic sensor.

[0023] According to one embodiment, the electrical test signal is a constant current signal and the respective characteristic parameter includes an amplitude and / or a phase angle of the voltage of the response signal at the frequency and amplitude of the electrical test signal at the respective measuring point.

[0024] Thus, one or more parameters can be recorded at each measuring point. Preferably, at least the amplitude of the response signal voltage is recorded. Particularly preferably, the phase of the response signal voltage is also recorded. This advantageously allows both the real and complex components of the response from the electroacoustic transducer arrangement to be fully recorded.

[0025] By selecting a constant current signal (signal with constant current amplitude), the testing operation of the ultrasonic sensor can advantageously be carried out under the same conditions as a current-controlled measurement operation of the ultrasonic sensor.

[0026] However, it is also considered as an alternative that the electrical test signal can be a voltage-constant signal and that the respective characteristic value can accordingly be an amplitude and / or a phase of the current strength of the response signal at the frequency and amplitude of the electrical test signal at the respective measuring point.

[0027] According to another embodiment, the multiple measuring points of the test signal are selected according to operating points of a control signal for the ultrasonic sensor during the performance of a distance measurement.

[0028] This means that the testing operation of the ultrasonic sensor can be carried out with the same frequencies and amplitudes of the test signal that are also used for the control signal during the measurement operation of the ultrasonic sensor.

[0029] In this way, the characteristic map acquired during testing (the parameters recorded at the multiple measurement points) can advantageously characterize the resistive, inductive, and capacitive properties of the electroacoustic transducer arrangement at the amplitudes and frequencies relevant to the measurement operation. The characterization thus obtained can be advantageously used to adjust measurement parameters and thereby enable the continued use of an ultrasonic sensor with operating behavior that changes over time.

[0030] According to the invention, the multiple measurement points for a number of different frequencies within a frequency range each comprise exactly one measurement point. The amplitude of each measurement point is selected as a function of the frequency of the measurement point.

[0031] In particular, the multiple measuring points can therefore not cover the entire characteristic field, but can advantageously be selected along a one-dimensional path through the characteristic field of the ultrasonic sensor, in particular a non-linear, non-straight path.

[0032] While it would theoretically be possible to completely test a predefined frequency and amplitude range during testing and thus determine a complete characteristic curve of the ultrasonic sensor, the test can be completed more quickly if only one measurement point is recorded for each of the number of different frequencies. In particular, the test can then be performed during a pause between two measurement cycles of the ultrasonic sensor without interrupting the sensor's operation. This enables "online testing."

[0033] The amplitude of each measurement point can preferably be selected to match the amplitude applied to the electroacoustic transducer arrangement during measurement operation at the same frequency. This advantageously allows only the parameters relevant to the measurement operation to be recorded.

[0034] The frequency range can be selected according to the requirements of the measurement operation. In particular, the frequency range can encompass a frequency of 50 kHz. Most preferably, the frequency range can encompass a range from 40 kHz to 60 kHz, and most preferably from 30 to 70 kHz.

[0035] According to a further embodiment, the multiple measuring points within the frequency range are chosen to be closer together in a first frequency section, in which a high gradient of the parameter to be measured was determined during a previous test of the electroacoustic transducer arrangement, than in a frequency section in which a lower gradient was determined compared to the high gradient.

[0036] The "previous test" can refer, in particular, to an actual execution of the test operation. Specifically, the "previous test" can refer to the most recent execution of the test operation. Thus, the frequency range in which the measurement points are closer together can be adaptively adjusted over the lifetime of the ultrasonic sensor to the areas of the characteristic curve where nonlinearities have been detected. Alternatively, the "previous test" can refer to a test operation performed during the manufacturing of the ultrasonic sensor. However, the "previous test" can also refer, in particular, to a theoretical determination of the characteristic curve and thus to a target characteristic curve; that is, the measurement points could be chosen to be close together where nonlinearities in the response of the electroacoustic transducer arrangement are expected.

[0037] Accordingly, the number of measurements to be carried out and thus the time interval required for the test operation can advantageously be further reduced and / or the accuracy of the determination of the characteristic map in an area of ​​interest can be increased.

[0038] According to the invention, of the amplitudes of any two measuring points at adjacent frequencies within the frequency range, one amplitude is selected at a lower limit and the other amplitude at an upper limit of an amplitude range chosen depending on the adjacent frequencies.

[0039] The amplitude range for the respective frequency can, in particular, be selected such that it covers a predetermined tolerance range around the amplitude with which a control signal is applied to the electroacoustic transducer arrangement during measurement operation at the same frequency.

[0040] In particular, the multiple measuring points can advantageously be chosen along two one-dimensional paths through the characteristic field of the ultrasonic sensor, describing the boundaries of a two-dimensional band within the characteristic field, whereby only one measurement needs to be carried out (only one characteristic value needs to be recorded) for each frequency of the number of frequencies.

[0041] According to a further embodiment, the test control device is configured to report a state of the electroacoustic transducer arrangement to a control device of the motor vehicle, depending on the several parameters detected by the test control device.

[0042] In particular, the test control unit can evaluate the multiple recorded parameters and, depending on the result of this evaluation, report either a fault condition or, for example, an "operational" state to the vehicle's control unit. The report to the control unit can also be made only if a fault condition has been detected.

[0043] For example, the test control unit can compare the recorded parameters, which describe a characteristic curve or a multidimensional characteristic map, with a target characteristic curve or a target characteristic map and determine the fault state or the "ready for operation" state based on the comparison result.

[0044] Accordingly, the vehicle's control device can exclude a faulty ultrasonic sensor from the environmental measurement and / or issue an error message to an operator or maintenance person of the vehicle.

[0045] According to a further embodiment, the ultrasonic sensor system also includes a measurement control unit configured to excite the electroacoustic transducer arrangement to emit an ultrasonic wave by applying an electrical control signal and to perform a distance measurement by subsequently acquiring and evaluating an electrical detection signal from the electroacoustic transducer arrangement. The measurement control unit is configured to perform the distance measurement depending on the several parameters acquired by the test control unit.

[0046] The measurement control unit can be integrated into the ultrasonic sensor or provided externally to the ultrasonic sensor.

[0047] The measurement control device can be designed in particular by an application-specific integrated circuit (ASIC), a microprocessor, an electronic control unit (ECU) or the like.

[0048] The electrical control signal can, in particular, be a constant current signal with a constant frequency. However, it is also conceivable and preferred that a sweep is performed over a predefined frequency range.

[0049] An "electrical detection signal" is understood to be, in particular, the signal that the electroacoustic transducer arrangement returns to the measuring control unit. The electrical detection signal can include echo signals (echo signal pulses) if an ultrasonic wave strikes the electroacoustic transducer arrangement (or one of its ultrasonic membranes) and is converted into such echo signal pulses by the electroacoustic transducer arrangement (or a piezoelectric element or the like thereof).

[0050] During measurement operation, the echo signals can be determined within the detection signal. Based on time-of-flight differences between the application of the electrical control signal and the appearance of the echo signal in the detection signal, the distance to an obstacle in the vehicle's vicinity can be inferred.

[0051] In particular, depending on the parameters detected by the test control unit, the following can be adjusted: the control signal (a frequency, a frequency range and / or an amplitude thereof) and / or a threshold for determining the echo signal in the detection signal and / or a gain factor by which the detection signal is amplified before the echo signal in it is detected.

[0052] If, as proposed, the electrical parameters (the electrical characteristic field of the electroacoustic transducer arrangement) are known and taken into account when performing the distance measurements, the reliability and accuracy of the distance measurement can be advantageously improved.

[0053] According to another embodiment, the ultrasonic sensor includes the test control unit.

[0054] Preferably, the ultrasonic sensor also includes the measurement control unit. Particularly preferably, the test control unit, and optionally also the measurement control unit, can be designed as sections of an application-specific integrated circuit (ASIC) arranged on a printed circuit board in a housing of the ultrasonic sensor.

[0055] Accordingly, it is advantageous to provide an ultrasonic sensor with an extended service life and / or improved consistency of measurement quality over its service life.

[0056] According to a second aspect, a motor vehicle with at least one ultrasonic sensor system as described above is proposed.

[0057] The features, advantages and embodiments described for the ultrasonic sensor system of the first aspect also apply accordingly to the motor vehicle of the second aspect.

[0058] The motor vehicle can be, in particular, a passenger car or a truck. The motor vehicle can be equipped with an assistance system, such as a driver assistance system or a parking assistance system, which may be designed for semi-autonomous or fully autonomous driving. Semi-autonomous driving means, for example, that the assistance system controls the steering and / or the automatic transmission. Fully autonomous driving means, for example, that the assistance system also controls the drive system and the braking system. The assistance system can be implemented in hardware and / or software. In the case of a hardware implementation, the assistance system can, for example, be a computer or a microprocessor.In a software implementation, the assistance system can be designed as a computer program, a function, a routine, part of program code, or an executable object. In particular, the assistance system can be implemented as part of a higher-level vehicle control system, such as an ECU (Engine Control Unit). The assistance system can use the proposed ultrasonic sensor system to monitor and measure the vehicle's surroundings using pulse-echo ultrasonic measurements.

[0059] According to one embodiment of this aspect, each ultrasonic sensor comprises a test control unit and a measurement control unit. According to another embodiment of this aspect, the proposed test control unit can be provided only once centrally in a control device of the motor vehicle and control the test operation of each of several ultrasonic sensors.

[0060] According to a second aspect, a method for operating an ultrasonic sensor system for a motor vehicle is proposed, comprising an ultrasonic sensor with an electroacoustic transducer arrangement for generating and detecting ultrasonic waves, an electrical test device, and a test control device. The method comprises the following steps: outputting an electrical test signal to the electroacoustic transducer arrangement by means of the test device; acquiring an electrical response signal from the electroacoustic transducer arrangement by means of the test device; and acquiring, by varying the frequency and amplitude of the electrical test signal, a characteristic parameter of the electrical response signal at several measuring points by means of the test control device.

[0061] The features, advantages and embodiments described for the ultrasonic sensor system of the first aspect also apply accordingly to the method of the third aspect.

[0062] 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 with reference to preferred embodiments and the accompanying figures. Fig. 1 shows a schematic diagram of an ultrasonic sensor system according to a first embodiment; Fig. 2 shows a schematic diagram of an ultrasonic sensor system according to a second embodiment; Fig. 3 shows a schematic diagram of a vehicle with a number of ultrasonic sensor systems according to a third embodiment; Fig. 4 shows steps of a method for carrying out a test operation according to embodiments; Fig. 5 shows a three-dimensional plot of an exemplary characteristic map of an ultrasonic sensor; and Fig. 6 shows a two-dimensional plot of another exemplary characteristic map of an ultrasonic sensor with measurement points plotted therein.

[0063] In the figures, identical or functionally equivalent elements have been given the same reference symbols, unless otherwise indicated.

[0064] Fig. 1 Figure 1 shows a schematic diagram of an ultrasonic sensor system 1 according to a first embodiment. The ultrasonic sensor system 1 is formed from an ultrasonic sensor 2 and at least one section of a control unit 3. The control unit 3 can, for example, be an electronic control unit (ECU) of a motor vehicle (11 in Fig. 3 ; in Fig. 1 (not shown).

[0065] In the diagram, which is to be understood as purely functional, from Fig. 1 The diagram schematically indicates the outer shape of the housing for the ultrasonic sensor 2. (At a point in the) Fig. 1 On the lower side of the housing of the ultrasonic sensor 2 is an ultrasonic membrane 4, in Fig. 1 The ultrasonic membrane 4 is represented by a membrane pot. A piezoelectric element 5 (an example of a transducer element) is attached to the inner side of the ultrasonic membrane 4, for example, by gluing. The piezoelectric element 5 is electrically connected to a coupling circuit 6. The coupling circuit serves to match the impedance. The arrangement consisting of the ultrasonic membrane 4, the piezoelectric element 5, and the coupling circuit 6 is an example of an electroacoustic transducer arrangement 7.

[0066] A control unit 8 arranged in the housing of the ultrasonic sensor 2 is configured to apply analog electrical oscillating signals to the electroacoustic transducer arrangement 7 and to detect analog electrical oscillating signals applied by the electroacoustic transducer arrangement to the control unit 8.

[0067] The control unit 3, arranged externally to the ultrasonic sensor 2, comprises a measuring control unit 9 and a test control unit 10.

[0068] In the measurement mode of the ultrasonic sensor 2, the measurement control unit 9 exchanges control signals, preferably digital signals, with the sensor's internal control unit 8. In particular, the measurement control unit 9 can thus cause the control unit 8 to apply an electrical control signal, preferably analog and especially oscillating, to the electroacoustic transducer arrangement 7. The control signal excites the ultrasonic membrane 4 to vibrate via the piezoelectric element 5, so that an ultrasonic wave is emitted. Subsequently, the measurement control unit 9 causes the control unit 8 to detect an electrical detection signal supplied by the electroacoustic transducer arrangement 7 for a predetermined period.When an ultrasound wave reflected from the surroundings strikes the ultrasound membrane 4 and causes it to vibrate, the piezoelectric element 5 generates an echo signal (an echo signal pulse) in the electrical detection signal. The detection signal is acquired by the sensor's internal control unit 8 and transmitted, preferably digitally, to the measuring control unit 9. The measuring control unit 9 evaluates the acquired detection signal, identifies the echo signal, and, based on the time difference between the emission of the ultrasound signal and the occurrence of the echo signal, as well as the known speed of sound, determines the distance to an obstacle in the vicinity of the ultrasound sensor 2.

[0069] The electroacoustic transducer arrangement 7 can be understood as an electrical arrangement with resistive, capacitive, and inductive properties. If these properties change, particularly due to aging effects of the piezoelectric element 5 or due to contamination and the like, a mismatch can occur in the control of the electroacoustic transducer arrangement 7 and / or in the acquisition of the detection signals from the electroacoustic transducer arrangement 7, which can impair the quality of the measurement.

[0070] Therefore, in a test operation of the ultrasonic sensor 2, the test control unit 10 of the control unit 3 performs the following: Fig. 4 The steps are illustrated schematically. It will be shown on Fig. 1 in conjunction with Fig. 4 Reference made to.

[0071] In step S1, the measuring control unit 10 exchanges control signals, preferably digital signals, with the sensor-internal control unit 8. In particular, the test control unit 10 can thus cause the sensor-internal control unit 8 (in this case an example of a "test device") to apply an electrical test signal, in particular an analog, in particular an oscillating, electrical test signal to the electroacoustic transducer arrangement 7.

[0072] While the test signal is applied to the electroacoustic transducer arrangement 7 in this manner, the test control device 9 in step S2 detects a preferably digital signal transmitted by the sensor-internal control circuit 8 ("test device"), which is indicative of a preferably analog, preferably oscillating, electrical response signal of the electroacoustic transducer arrangement 7 to the application of the test signal.

[0073] In step S3, the test control unit 10 records a characteristic value of the electrical response signal.

[0074] The test signal can be a constant current signal (an alternating current signal with constant current amplitude), and the electrical response signal can accordingly be a voltage signal that develops when the test signal is applied to the electroacoustic transducer arrangement 7. The measured parameter in this case is a voltage amplitude and, optionally, a phase angle of the electrical response signal.

[0075] The test signal can also be a constant voltage signal, and the electrical response signal can accordingly be a current signal. In this case, the measured parameter can include a current amplitude and, optionally, a phase angle of the electrical response signal.

[0076] As proposed, the frequency and amplitude of the test signal are varied. This means that several measurement points are traversed at different frequencies and amplitudes, and a corresponding parameter is recorded at each measurement point.

[0077] The advantages and details of varying frequency and amplitude are explained below using the following examples: Fig. 5 and 6 will be explained in more detail; first, structural alternatives to the arrangement will be discussed. Fig. 1 described.

[0078] Fig. 2 Figure 1 shows a schematic diagram of an ultrasonic sensor system 1 according to a second embodiment. In the second embodiment, the functionality of the measuring control unit 9 and the functionality of the test control unit 10, as well as the functionality of the electroacoustic transducer arrangement 7 (coupling circuit 6, ultrasonic membrane 4 and piezoelectric element 5), is the same as in the first embodiment; however, the measuring control unit 9 and the test control unit 10 are designed as sections of the sensor's internal control unit 8, and not as sections of the external control unit 3.

[0079] Accordingly, in the second embodiment, the external control unit 3 does not form part of the proposed ultrasound system 1; rather, in the second embodiment, the ultrasound system 1 is completely realized by the ultrasound sensor 2.

[0080] Accordingly, the need to exchange digital control signals with the control unit 3 for performing measurement and testing operations is eliminated. Only measurement results from the distance measurement and / or status information derived from the acquired parameters can be transmitted to the control unit 3 via the ultrasonic sensor 2; otherwise, the acquired parameters can be used internally within the sensor to improve the control of the electroacoustic transducer arrangement 7 during measurement operation.

[0081] The sensor-internal control unit 8 can in particular be an application-specific integrated circuit (ASIC) arranged in the housing of the ultrasonic sensor 2 on a printed circuit board not shown.

[0082] Fig. 3 Figure 1 shows a schematic diagram of a vehicle 11 with a number of ultrasonic sensors 2 and a control unit 3 according to a third embodiment. The ultrasonic sensors 2 are arranged along a left side, a right side, and further along a front bumper and along a rear bumper of the vehicle 11.

[0083] The third embodiment can be combined with both the first and the second embodiment. That is, according to one variant, each of the embodiments described in Fig. 3 shown ultrasonic sensors 2 an integrated test control unit 10 ( Fig. 2 ) exhibit and thus an ultrasonic sensor system 1 ( Fig. 2 ). The vehicle 11 shown can therefore, for example, represent twelve independent ultrasonic sensor systems 1 ( Fig. 2 ). The control unit 3 can operate the ultrasonic sensor systems 1 ( Fig. 2 ) to measure a vehicle's surroundings and use the information obtained to provide a driving or parking assistance function.

[0084] According to another variant, a proposed test control device 10 ( Fig. 1 ) and optionally also a measuring control unit 9 ( Fig. 1 ) in the control unit 3 of the vehicle 11. Thus, the multiple ultrasonic sensors 2 and the control unit 3 can together form an ultrasonic sensor system 1 ( Fig. 1 ) with multiple ultrasonic sensors 2. In this case, the functionality of the test control unit 10 is required ( Fig. 1 ) of the control unit 3 to be trained only once and the test control device 10 ( Fig. 1 ) can centrally view all recorded parameters of the electroacoustic transducer arrangements 7 ( Fig. 1 ) evaluate the ultrasonic sensors 2 and take them into account when controlling the measurement operation.

[0085] Fig. 5 This shows a three-dimensional plot of an example characteristic curve of an ultrasonic sensor. It is displayed on Fig. 5 and, where necessary, also on Fig. 1 und 2 Reference made to.

[0086] The map 13 in Fig. 5 The graph is composed of (not individually labeled due to their large number) measurement points acquired using an ultrasonic sensor system 1 in a very comprehensive test operation. Along an axis labeled "x" is the frequency of a constant-current test signal, along an axis labeled "y" is the amplitude of the current of the constant-current test signal, and along an axis labeled "z" is the amplitude of the voltage of the acquired response signal.

[0087] In map 13 in Fig. 5 Two peaks 12 of the characteristic map 13 are visible, where the amplitude of the characteristic map increases sharply. Furthermore, it can be seen that the peaks 12 exhibit a pronounced amplitude dependence – their frequency shifts towards lower frequencies with increasing amplitude. These nonlinearities arise due to a domain effect inherent in the piezoelectric element 5.

[0088] A central idea of ​​the proposed solution is that better recording of the electrical characteristics of an ultrasonic sensor 2 can be achieved if this is done not only at different frequencies, but also at different amplitudes, and especially at those amplitudes that are actually relevant for the measurement operation of the ultrasonic sensor.

[0089] However, capturing the entire in Fig. 5 The characteristic curve 13 shown involves varying both the frequencies and the amplitudes of the test signal across their entire value range in all possible combinations, resulting in a large number of measurements and consequently a significant amount of time and energy. Ideally, however, the test operation should be performed "online," that is, without or without any significant interruption of the measurement process.

[0090] Based on Fig. 6 - furthermore, also referring to the Fig. 1 und 2 - therefore, a preferred mode for acquiring the electrical characteristics of the electroacoustic transducer arrangement 7 is explained, which in exemplary embodiments is carried out by the test control device 10 ( Fig. 1, 2 ) can be implemented.

[0091] Fig. 6 shows a two-dimensional plot of another exemplary characteristic map 13 of an ultrasonic sensor 2. In Fig. 6 The frequency of the test signal is plotted along the "x" axis and the amplitude of the test signal along the "y" axis, as shown in Fig. 5 The amplitude of the response signal is in Fig. 6 represented by a shading, where the amplitude of the response signal is higher the darker the shading. In particular, in Fig. 6 through shading a theoretical and / or in extensive experiments similar to in Fig. 5 The determined complete characteristic map 13 of the electroacoustic transducer arrangement is shown.

[0092] It should be noted that in measurement mode a sweep can be performed over a defined frequency range, meaning that the measurement operation does not necessarily take place at exactly one frequency and exactly one amplitude, but advantageously along a (not shown) operating curve in the characteristic map 13. Fig. 6 can be done.

[0093] In Fig. 6 Furthermore, measuring points 14, 15 of the characteristic map are shown, which are actually recorded by the test control device 10 according to the exemplary embodiment during the test operation.

[0094] This means that during the test operation, the test control unit 10 varies the frequency of the test signal in such a way that a number of individual frequency points are successively set at the frequencies of the Fig. 6 The measurement points 14 and 15 shown are traversed. According to the invention, exactly one measurement point is acquired for each frequency, and for each such measurement point, a frequency-dependent amplitude is selected. The amplitude is selected (varied) such that the respective amplitude is related to an amplitude of the control signal at the respective frequency during the frequency sweep of the measurement operation. According to one embodiment, only the measurement points designated 14 or only those designated 15 are acquired and essentially correspond to points on a duty cycle of the control signal during the measurement operation.

[0095] According to a particularly preferred embodiment, however, both the measuring points designated 14 and 15 are recorded, and a working curve of the amplitudes of the control signal can run through the characteristic map between the paths defined by the measuring points 14 and 15. That is, the measuring points 14, 15 are selected according to the invention such that, for every two adjacent measuring points 14, 15, one measuring point 15 is selected at a lower limit of an amplitude range and a second measuring point 16 is selected at an upper limit of an amplitude range, wherein the amplitude range is centered around an amplitude of the control signal during measurement operation, for example, at one of the frequencies or at a midpoint between the two frequencies. In this way, with only one frequency sweep of the test signal, the following results: Fig. 6 A first path 14 and a second path 15 through the characteristic map, together defining a two-dimensional band through the characteristic map. This allows for a particularly realistic assessment of the upper and lower limits of the electrical parameters relevant for measurement operation.

[0096] Furthermore, in Fig. 6 A particularly preferred embodiment is illustrated in which the measuring points in a first frequency range 16, where the gradient of the response signal amplitude is low, are selected to be further apart than the measuring points 14, 15 in a second frequency range 17 near the peak 12, where the gradient of the response signal amplitude is high. Accordingly, the number of points to be recorded during testing can be further reduced, particularly in range 16.

[0097] According to the measures described above, it can thus be advantageously possible to obtain a realistic assessment of the properties of the two-dimensional characteristic map of the response signal amplitudes in a range relevant to the measurement process with only a few individual measurements at the specifically frequency-dependent measurement points 14 and 15. This allows for a rapid acquisition of the characteristic map or the parameters at measurement points 14 and 15, which can be carried out, for example, between two measurement cycles of the measurement operation without having to interrupt the measurement operation.

[0098] Several ways are being considered for how the parameters thus recorded (amplitude and, if applicable, phase positions of the electrical response signal, which are set when the electrical test signal is applied to measuring points 14, 15) can be evaluated by the test control unit 10.

[0099] For example, during the operating time of the ultrasonic sensor 12, the height of the peaks 12 ( Fig. 5 , Fig. 6 ), a frequency position of the peaks 12 ( Fig. 5 , Fig. 6 ) or change the ratio of the peak heights to each other. The aforementioned parameters of the peaks 12 can also be changed with a simple test control device 10, such as an application-specific circuit (ASIC) 8 ( Fig. 2 ) or a motor vehicle control unit (ECU) 3 ( Fig. 1 ) can be implemented, easy to determine. The test control unit 10 can determine the degree of change in the peak heights or positions compared to a reference state and use this to assess the condition of the ultrasonic sensor 10. If the condition of the ultrasonic sensor 2 is assessed as faulty, the ultrasonic sensor 2 can, for example, in the Fig. 3In the illustrated embodiment, the surroundings are excluded from the environmental measurement by the control unit 3 (no longer taken into account). The control unit 3 can issue a corresponding warning message to a driver or maintenance person.

[0100] However, it is also conceivable that the determined changes in peak positions do not indicate a faulty condition, but rather that the measurement operation (the distance measurement) is adjusted.

[0101] It is conceivable that the test control unit 10 provides the measurement control unit 9 with an evaluation of the acquired parameters (for example, information about shifted positions and / or heights of the peaks 12) and, depending on this, the measurement control unit 9, for example, causes the control unit 8 of the ultrasonic sensor 2 to increase the amplitude of the drive signal during measurement operation, to adjust a frequency position or frequency range of a sweep of the drive signal during measurement operation, to amplify the detection signal during measurement operation, or to adjust a threshold parameter for the detection of echo signals in the detection signal. Accordingly, the measurement control unit 9 can perform the distance measurement depending on the several parameters acquired by the test control unit 10.This advantageously allows a high measurement quality to be maintained over longer operating periods, even if electrical properties such as resistive, inductive and / or capacitive properties of the electroacoustic transducer arrangement 7 change over time.

[0102] It is also conceivable that the test control unit 10, in addition to the amplitude of the response signal, also records the phase of the response signal relative to the phase of the test signal as a further characteristic parameter and incorporates this into the assessment of the condition of the ultrasonic sensor 2 and / or into the adjustment of the measurement operation of the measurement control unit 9. In particular, the phase can be used to determine and evaluate the inductive and capacitive properties of the electrical transducer arrangement 7. The information obtained in this way can, for example, also be used to adjust parameters of a resonant circuit encompassed by the coupling circuit 6 and thus improve impedance matching to the impedance of the electrical transducer arrangement 7 at the relevant frequencies and amplitudes of the drive signal.

[0103] The measures described above for reporting a fault condition of ultrasonic sensor 2 and / or for adjusting the measuring drive are advantageously carried out on the basis of characteristic values ​​that were recorded at amplitudes of the test signal that correspond to or are related to the amplitudes of the control signal at the respective relevant frequencies in the measuring operation and can therefore have a higher relevance or quality than characteristic values ​​that are recorded at low or other or constant amplitudes of the test signal.

[0104] Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

[0105] In the exemplary embodiments, a piezoelectric element 5 was described; however, the electroacoustic transducer arrangement 7 can also include a different sound transducer based on a mechanical-capacitive, mechanical-resistive, magnetostrictive or electrostrictive operating principle. REFERENCE MARK LIST

[0106] 1 Ultrasonic sensor system 2 Ultrasonic sensor 3 Control unit 4 Ultrasonic membrane 5 Piezoelectric element (sound transducer element) 6 Coupling circuit 7 Electroacoustic transducer arrangement 8 Sensor-internal control unit (test device) 9 Measurement control device 10 Test control device 11 Motor vehicle 12 Peak 13 Characteristic map 14 Measurement points, first path 15 Measurement points, second path 16 Low gradient frequency range 17 High gradient frequency range x, y, z Axes of a plot S1-S3 Process steps

Claims

1. Ultrasonic sensor system (1) for a vehicle (11), comprising: an ultrasonic sensor (2) with an electro-acoustic transducer arrangement (7) for generating and detecting ultrasonic waves and an electrical testing device (8) configured to output an electrical test signal to the electro-acoustic transducer arrangement (7) and to detect an electrical response signal from the electro-acoustic transducer arrangement (7) to the electrical test signal, and a test control device (10) configured to detect a characteristic parameter of the electrical response signal by means of the electrical testing device (8) at multiple measurement points (14, 15) by varying a frequency and an amplitude of the electrical test signal, wherein the multiple measurement points (14, 15) each comprise exactly one measurement point (14, 15) for a number of different frequencies within a frequency range, wherein the amplitude of the respective measurement point (14, 15) is selected as a function of the frequency of the measurement point (14, 15), characterized in that, of the amplitudes of any two measurement points (14, 15) at adjacent frequencies within the frequency range, one amplitude is selected at a lower limit and the other amplitude is selected at an upper limit of an amplitude range chosen as a function of the adjacent frequencies.

2. The ultrasonic sensor system according to claim 1, wherein the electrical test signal is a constant-current signal, and the respective characteristic parameter comprises an amplitude and / or a phase position of the voltage of the response signal at the frequency and amplitude of the electrical test signal at the respective measurement point (14, 15).

3. The ultrasonic sensor system according to any one of the preceding claims, wherein the multiple measurement points (14, 15) of the test signal are selected to correspond to operating points of a drive signal for the ultrasonic sensor (2) during the performance of a distance measurement.

4. The ultrasonic sensor system according to claim 1, wherein the multiple measurement points (14, 15) within the frequency range are selected to be closer together in a first frequency section (17), in which a high gradient of the characteristic parameter to be detected was determined during a previous test of the electro-acoustic transducer arrangement, than in a frequency section (16), in which a gradient lower than the high gradient was determined.

5. The ultrasonic sensor system according to any one of claims 1 to 4, wherein the test control device (10) is configured to report a state of the electro-acoustic transducer arrangement (7) to a control device (3) of the motor vehicle (11) as a function of the multiple characteristic parameters detected by the test control device (10).

6. The ultrasonic sensor system according to any one of claims 1 to 5, further comprising a measurement control device (9) configured to excite the electro-acoustic transducer arrangement (7) to emit an ultrasonic wave by applying an electrical drive signal and to perform a distance measurement by subsequently detecting and evaluating an electrical detection signal from the electro-acoustic transducer arrangement (7), wherein the measurement control device (9) is configured to perform the distance measurement as a function of the multiple characteristic parameters detected by the test control device (10).

7. The ultrasonic sensor system according to any one of claims 1 to 6, wherein the ultrasonic sensor (2) comprises the test control device (10).

8. A vehicle (11) with at least one ultrasonic sensor system (1) according to any one of claims 1 to 7.

9. A method for operating an ultrasonic sensor system (1) for a vehicle (11), which comprises an ultrasonic sensor (2) with an electro-acoustic transducer arrangement (7) for generating and detecting ultrasonic waves and an electrical testing device (8), and further comprises a test control device (10), the method comprising the steps of: Outputting (S1) an electrical test signal to the electro-acoustic transducer arrangement (7) by means of the testing device (8); Detecting (S2) an electrical response signal from the electro-acoustic transducer arrangement (7) by means of the testing device (8); and Detecting (S3), by varying a frequency and an amplitude of the electrical test signal, a characteristic parameter of the electrical response signal at multiple measurement points (14, 15) by the test control device (10), wherein the multiple measurement points each comprise exactly one measurement point for a number of different frequencies within a frequency range, wherein the amplitude of the respective measurement point is selected as a function of the frequency of the measurement point, characterized in that, of the amplitudes of any two measurement points at adjacent frequencies within the frequency range, one amplitude is selected at a lower limit and the other amplitude is selected at an upper limit of an amplitude range chosen as a function of the adjacent frequencies.