METHOD FOR OPERATING AN ULTRASONIC SENSOR, WHICH IS INSTALLED IN A CONCEALED MANNER, OF A VEHICLE

Abstract

A method is provided for operating an ultrasonic sensor installed in a concealed manner such that a diaphragm of the sensor is connected to a vehicle part whose instantaneous properties influence a directional characteristic of the sensor, where a threshold value is used to suppress interference signals in the case of pulse-echo measurements using the ultrasonic sensor. The method adapts the threshold value to the directional characteristic of the ultrasonic sensor predetermined according to the instantaneous properties of the vehicle part. Further aspects of the invention relate to a driver assistance system including at least one ultrasonic sensor installed in a concealed manner and a computer program product which is designed to execute the method.

Claims

1-10. (canceled)

11. A method for adapting a threshold value, which is used to suppress interference signals in pulse-echo measurements by an ultrasonic sensor that is installed in a concealed manner in a vehicle with a diaphragm of the ultrasonic sensor being connected to a vehicle part, to a directional characteristic of the ultrasonic sensor that is influenced by instantaneous properties of the vehicle part, the method comprising: ascertaining a temperature and determining the threshold value based on the ascertained temperature and a previously determined temperature to directional characteristic relationship; or determining a resonant frequency of an oscillating system formed by the diaphragm and the vehicle part and determining the threshold value based on the determined resonant frequency and a previously determined resonant frequency to directional characteristic relationship.

12. The method of claim 1, wherein the threshold value is determined based on the ascertained temperature, and the temperature is: an external temperature ascertained via a thermometer of the vehicle; or a temperature of the vehicle part ascertained via a temperature sensor situated on the vehicle part or on the ultrasonic sensor.

13. The method of claim 1, wherein the relationship on the basis of which the threshold value is determined is ascertained by prior measurements.

14. The method of claim 1, wherein the threshold value is determined based on determined resonant frequency, and the resonant frequency of the oscillating system is determined via a measurement of an impedance of the ultrasonic sensor.

15. The method of claim 1, wherein the threshold value is determined based on the ascertained temperature, and the determination of the threshold value is based on a value table that associates a plurality of temperature values with respective values for the threshold value.

16. The method of claim 1, wherein the threshold value is determined based on the determined resonant frequency, and the determination of the threshold value is based on a value table that associates a plurality of resonant frequency values with respective values for the threshold value.

17. The method of claim 1, wherein the interference signals include signals of ground reflections, a number of which increases by a widening of the directional characteristic and decreases by a narrowing of the directional characteristic.

18. A method comprising: based on interference signals in pulse-echo measurements, which are performed by an ultrasonic sensor that is installed in a concealed manner in a vehicle with a diaphragm of the ultrasonic sensor being connected to a vehicle part whose instantaneous properties influence a directional characteristic of the ultrasonic sensor, regulating a threshold value used for suppressing the interference signals.

19. The method of claim 7, wherein the threshold value is regulated such that a constant predetermined false alarm rate is maintained.

20. A non-transitory computer-readable medium on which are stored instructions that executable by a processor and that, when executed by the processor, cause the processor to perform a method for regulating a threshold value, which is used to suppress interference signals in pulse-echo measurements by an ultrasonic sensor that is installed in a concealed manner in a vehicle with a diaphragm of the ultrasonic sensor being connected to a vehicle part, the method comprising: adapting the threshold value to a directional characteristic of the ultrasonic sensor that is influenced by instantaneous properties of the vehicle part, the adapting being performed by: ascertaining a temperature and determining the threshold value based on the ascertained temperature and a previously determined temperature to directional characteristic relationship; or determining a resonant frequency of an oscillating system formed by the diaphragm and the vehicle part and determining the threshold value based on the determined resonant frequency and a previously determined resonant frequency to directional characteristic relationship; or regulating the threshold value based on a measurement of the interference signals.

21. A driver assistance system for assisting a driver of a vehicle, the driver assistance system comprising: an ultrasonic sensor installed in a concealed manner in a vehicle part of the vehicle and including a diaphragm that, together with the vehicle part, forms an oscillating system; a control unit, wherein the control unit is configured to perform a method for regulating a threshold value, which is used to suppress interference signals in pulse-echo measurements by the ultrasonic sensor, the method comprising: adapting the threshold value to a directional characteristic of the ultrasonic sensor that is influenced by instantaneous properties of the vehicle part, the adapting being performed by: ascertaining a temperature and determining the threshold value based on the ascertained temperature and a previously determined temperature to directional characteristic relationship; or determining a resonant frequency of an oscillating system formed by the diaphragm and the vehicle part and determining the threshold value based on the determined resonant frequency and a previously determined resonant frequency to directional characteristic relationship; or regulating the threshold value based on a measurement of the interference signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows a vehicle including an ultrasonic sensor installed in a concealed manner, according to an example embodiment of the present invention.

[0031] FIG. 2a shows a simulation of the horizontal aperture angle according to an example embodiment of the sensor of the present invention.

[0032] FIG. 2b shows a simulation of the vertical aperture angle, according to an example embodiment of the sensor of the present invention.

[0033] FIG. 3 shows a diagram of the amplitude of a ground echo signal in relation to the distance from the ultrasonic sensor, according to an example embodiment of the sensor of the present invention.

DETAILED DESCRIPTION

[0034] FIG. 1 schematically shows a vehicle 10 including a driver assistance system 60 according to an example embodiment of the present invention. Driver assistance system 60 includes an ultrasonic sensor 14, a temperature sensor 24, and a control unit 20.

[0035] Vehicle 10 includes a vehicle part 12, which is illustrated as being designed as a bumper 13. Bumper 13 includes an area 11 having reduced wall thickness. Ultrasonic sensor 14 is situated on the inner side of the outer wall of bumper 13 in area 11 having reduced wall thickness. Due to the arrangement on the inner side of the outer wall of bumper 13, ultrasonic sensor 14 is not visible from the outside, ultrasonic sensor 14 is thus installed on vehicle 10 in a concealed manner.

[0036] Ultrasonic sensor 14 is connected to the outer wall of bumper 13 using its diaphragm 16 via an adhesive bond 18 in area 11 having reduced wall thickness. Diaphragm 16 and bumper 13 thus jointly form an oscillating system. The resonant frequency of this oscillating system, which influences an aperture angle 70, 71, is dependent in particular on the material properties of vehicle part 12 and/or bumper 13. Upon increase of the temperature, the resonant frequency decreases, which results in an increase of the aperture angle and, conversely, a reduction of the temperature results in an increase of the resonant frequency, which results in a decrease of the aperture angle.

[0037] Two different horizontal aperture angles 70, 71 are outlined in FIG. 1. Larger aperture angle 70 is reached at high temperatures and smaller aperture angle 71 is reached at low temperatures.

[0038] To recognize objects 30, 31 in the surroundings of vehicle 10, emitted signals 32 are emitted by driver assistance system 60 using ultrasonic sensor 14 and echoes 34 reflected from objects 30, 31 are in turn received. To suppress interference signals, which occur due to reflections of emitted signal 32 by the ground, a threshold value is provided. Only signals whose amplitudes are greater than the threshold value are interpreted as echo 34 of an object 30, 31.

[0039] If the ambient temperature is high, ultrasonic sensor 14 thus has larger opening angle 70, in such a way that emitted signal 32 having a high amplitude is incident not only on centrally located object 30, but rather also on peripherally located further object 31. Accordingly, echoes 34 reflected from objects 30 and 31 also have a high amplitude, in such a way that they are greater than the predetermined threshold value.

[0040] At low ambient temperatures, the directional characteristic of ultrasonic sensor 14 changes, in such a way that it now includes small aperture angle 71. Only centrally located object 30 is still located inside small aperture angle 71 defined by the drop of the signal amplitude. Peripherally located further object 31 is located outside small aperture angle 71 and emitted signal 32 is only incident thereon at greatly reduced amplitude, in such a way that an echo 34 of further object 31 is also greatly reduced in its amplitude. Without an adaptation of the threshold value, the amplitude of echo 34 of further object 31 is now less than the threshold value, so that it is no longer recognized. Further object 31 would thus be outside the field of view of ultrasonic sensor 14 without an adaptation of the threshold value.

[0041] Because of the reduction of aperture angle 70, 71, however, the amplitude of the ground echoes received as interference signals is also reduced, since a vertical aperture angle (not shown in FIG. 1) is accordingly also decreased and emitted signal 32 is only incident on the ground at a greater distance from vehicle 10 and at a reduced amplitude. It is therefore provided according to the present invention that the threshold value be adapted as a function of the instantaneous directional characteristic of the sensor and be lowered in accordance with the situation described with reference to FIG. 1. By lowering the threshold value, echoes 34 of further object 31 can also still be detected in spite of their reduced amplitude, in such a way that the field of view of ultrasonic sensor 14 at reduced temperatures is enlarged in relation to operation without adaptation of the threshold value.

[0042] For the adaptation of the threshold value, it is provided in the example embodiment shown in FIG. 1 that a temperature sensor 24 is situated on bumper 13. In this way, control unit 20 is capable of determining the accurate temperature of vehicle part 12. After the determination of the temperature, for example, a threshold value adapted to the measured temperature can be retrieved from a memory of control unit 20. In alternative example embodiments, temperature sensor 24 can be omitted and a thermometer 22 of vehicle 10 can be used. In this way, the external temperature can be measured and used for an estimation of the temperature of vehicle part 12.

[0043] In another example embodiment of the method, instead of measuring a temperature, the resonant frequency of the sound transducer of ultrasonic sensor 14, which is changed because of a change of the material properties of bumper 13, is measured. This can be carried out, for example, via an impedance measurement.

[0044] In another alternative example embodiment, signals received by ultrasonic sensor 14 are evaluated for a regulation of the threshold value. The threshold value is increased if a false alarm rate is less than a predetermined value and the threshold value is decreased if the false alarm rate is greater than the predetermined value.

[0045] In FIG. 2a, a simulation of the amplitude of an echo signal is plotted as a function of horizontal angle for three different resonant frequencies. The plotted echo signal is scaled and can originate, for example, from an obstacle or from the ground. First curve 40 shows the curve of the echo amplitude for a resonant frequency of 40 kHz, second curve 42 shows the echo amplitude for a resonant frequency of 48 kHz, and third curve 44 shows the echo amplitude for a resonant frequency of 60 kHz.

[0046] In FIG. 2b, vertical aperture angle is plotted accordingly for the three different resonant frequencies 40 kHz, 48 kHz, and 60 kHz.

[0047] As can be inferred from FIGS. 2a and 2b, horizontal aperture angle or vertical aperture angle , respectively, decreases upon increase of the resonant frequency. In this way, the emitted signal is only incident on the ground at a greater distance from the ultrasonic sensor, in such a way that the amplitude of the corresponding echo signal also decreases.

[0048] In FIG. 3, the received signal of pulse-echo measurements is plotted for three different resonant frequencies, the ascertained echo amplitude being indicated on the Y axis and the distance computed from the runtime of the signal being indicated in millimeters on the X axis.

[0049] In the pulse-echo measurement, a time-limited emitted signal is emitted via ultrasonic sensor 14 and subsequently echoes are received. The more time that has passed since the emission, the greater the distance is of the reflecting object. FIG. 3 shows the received signal for resonant frequency of 42 kHz in a first curve 46, a second measurement curve 48 shows the received signal for a resonant frequency of 48 kHz, and a third measurement curve 50 shows the received signal for a resonant frequency of 57 kHz.

[0050] It can be inferred from the illustration of FIG. 3 that, as expected for third measurement curve 50, which corresponds to the highest frequency used, the aperture angle is smallest and thus supplies the smallest echo amplitudes for the ground echoes at short distances. At longer distances from approximately 175 cm, third measurement curve 50 has an increased amplitude compared to second measurement curve 48 and from approximately 225 cm, third measurement curve 50 has the greatest echo amplitude. This can be explained via the improved directional effect due to the smallest aperture angle.

[0051] It is apparent from FIG. 3 that, utilizing the knowledge of the resonant frequency dependent on the environmental conditions and thus utilizing the directional characteristic dependent on the environmental conditions, a threshold value for suppressing ground echoes can be greatly reduced. It is advantageous in particular in this case to combine the threshold value dependent on the directional characteristic with a dependence on the distance, to always be able to specify an optimum threshold value for any distance and for any directional characteristic.

[0052] The present invention is not restricted to the example embodiments described here and the aspects highlighted therein. Rather, a variety of modifications are possible within the scope specified by the claims, which are routine measures for those skilled in the art.