Method for generating a threshold curve, method for evaluating signals from an ultrasonic sensor, and device for environmental detection

Abstract

Method for generating a threshold curve for evaluating signals from an ultrasonic sensor, wherein the threshold curve (SK) D ) from stored support points (S START , S1 to S7, S ENDE ) is generated, each of which is generated by a corresponding amplitude value (A) START , A1 to A7, A ENDE , A max ) and a temporal position (T START , t1 to t7, t ENDE ) are defined, where a starting support point (S START ) and a terminal support point (S ENDE ) the threshold curve (SK D ) a measurement time window (T Mess ) define, where between the starting support point (S START ) and the final support point (S ENDE ) a first support point (S1) is arranged, whose temporal position (t1) is set to a transmission start time (t S_Start ) of a measurement signal (24) is determined, wherein after the first support point (S1) and before the final support point (S ENDE) at least one further support point (S2 to S7) is arranged, which follows the course of the threshold curve (SK) D ) adapts to a noise signal pattern, characterized in that the amplitude values ​​(A START , A1 to A7, A ENDE , A max ) the support points (S START , S1 to S7, S ENDE ) the threshold curve (SK D ) are digitally generated, with the starting point (S START ) an amplitude value (A3, A ENDE ) is specified, which is smaller than an amplitude value (A1) of the first support point (S1), where a first section (T MStör ) the threshold curve (SK D ) starting from the amplitude value (A3, A ENDE ) the launch base (S START ) increases to the amplitude value (A1) of the first support point (S1).

Description

[0001] The invention relates to a method for generating a threshold curve of the type mentioned in the preamble of claim 1, as well as a method for evaluating signals from an ultrasonic sensor of the type mentioned in the preamble of claim 11 and an associated device for environmental detection in a vehicle for carrying out the methods.

[0002] Known driver assistance systems, such as parking assistance systems, lane departure warning systems, and distance warning systems, are often based on ultrasound technology and use echo sounding for distance measurement. In this process, a diaphragm of at least one ultrasonic sensor is excited at its resonant frequency. In response to this excitation, the sensor emits ultrasonic waves as a measurement signal at a predetermined start time. These emitted ultrasonic waves are reflected by a target object and, in turn, excite the diaphragm of the at least one ultrasonic sensor as a reflected echo signal. This excitation is transferred to a piezoelectric element, which converts this mechanical vibration into an electrical signal and outputs it to an evaluation and control unit for analysis.The electrical signal, in conjunction with the transmission start time, represents the sound propagation time and thus the object distance. Since not only detectable obstacles or objects reflect the ultrasonic waves, but also unwanted structural features or the road surface, measures are taken to suppress unwanted interference signals, such as ground reflections. Typically, the interference signals are suppressed using threshold values ​​or a threshold curve. The threshold curve is generated from reference points, each defined by a temporal position and an amplitude value. These reference points, with a predetermined fixed time interval from the transmission start time and an amplitude value determined based on a corresponding amplitude value of an interference signal pattern to be suppressed at the specified temporal position, are stored in a memory within the ultrasonic sensor.To detect an object, the amplitude (intensity) of the received corresponding echo signal must exceed the previously defined threshold curve for the echo signal or echo information to be recognized as valid. The threshold curve itself is individually determined and set for each ultrasonic sensor on each vehicle. An attempt is made to find a compromise between the system's sensitivity (low threshold curve) and robustness against interference. However, stronger interference usually still exceeds the threshold curve and therefore requires additional filtering in subsequent software processing. This subsequent filtering is usually very computationally intensive and always requires multiple measurements to determine the level of interference and obtain a reliable result. Information that could detect interference even before the actual transmission would be helpful.

[0003] Furthermore, prior art reveals driver assistance systems in which the ultrasonic sensor first "listens" for background noise before generating a transmission signal. The level of the background noise is then compared to a threshold value. This threshold value is defined by a threshold curve, which is later used for comparison with the echo signal. That is, the first time segment of the threshold curve is for detecting background noise, and the second, later time segment is for detecting objects. The threshold values ​​are generated using analogous methods with a capacitor that is charged according to the desired amplitude value. As a result, the connections between two adjacent points correspond to the shape of a charging curve (ascending exponential function) or a discharging curve (decreasing exponential function) of the capacitor.Since the threshold curve has a maximum amplitude value during transmission in order to suppress the measurement signal, the capacitor is charged to its maximum value at the end of the measurement. Therefore, the capacitor is fully charged at the beginning of each measurement, so that only very strong interference can be detected before transmission.

[0004] Document US 2005 / 0041528 A1 (D1) discloses an adaptive comparator circuit for reducing the near-field blind spot in distance sensors. For this purpose, a variable threshold voltage is generated, which is passively coupled to the envelope of the echo signal by means of a capacitor and a diode. After an initial charging of the capacitor to a high value, its voltage, when discharged through the diode, follows the falling signal envelope with a constant voltage offset defined by the diode. When the echo signal is rising, the diode blocks, maintaining the threshold voltage at its current level and thus enabling detection by the signal exceeding the threshold.

[0005] From DE 10 2010 034 263 A1 a method for generating a threshold curve for the evaluation of signals from an ultrasonic sensor is known, in which the threshold curve is generated from support points which are variable both in their amplitude and in their temporal position.

[0006] EP 1 562 050 B1, for example, describes a method and a device for adjusting the threshold of a detection device. The described method provides adaptive threshold control, which varies the detection threshold depending on external conditions. This involves performing a noise level measurement during a time interval in which no reflected measurement signal is expected. Thus, adaptive threshold control is enabled, whose detection threshold or manipulated variable is determined within a time range, preferably at the end of a measurement cycle, in which no reflected signal with a correspondingly high signal level is present.

[0007] The object of the invention is to further develop a method for generating a threshold curve of the type mentioned in the preamble of claim 1, a method for evaluating signals from an ultrasonic sensor of the type mentioned in the preamble of claim 11, and a corresponding device for environmental detection of the type mentioned in the preamble of claim 17, in such a way that a reliable statement about the validity of detected echo signals is made possible.

[0008] This problem is solved according to the invention by a method for generating a threshold curve with the features of claim 1, by a method for evaluating signals from an ultrasonic sensor with the features of claim 11, and by a device for environmental sensing with the features of claim 17. Further features that advantageously define the embodiments of the invention are contained in the dependent claims.

[0009] The advantage achieved with the invention is that background noise can be detected during a measurement without additional time loss and used to assess the validity of the recorded echo signals. Furthermore, the sensitivity of the background noise detection can be adjusted by parameterizing the amplitude value of the starting point of the threshold curve, depending on the installation location and the application.

[0010] The basic idea of ​​the invention is based on the use of a first section of the threshold curve, which is positioned before the start time of the transmission window of the measurement signal, to detect interference signals or noise. The amplitude value of the starting point of the threshold curve is selected to be smaller than the amplitude value of the first point, which marks the beginning of the transmission window. This advantageously allows the sensitivity of the noise detection to be predefined, enabling even weaker interference signals to be detected.

[0011] The inventive method for generating a threshold curve for evaluating signals from an ultrasonic sensor generates the threshold curve from stored reference points, each defined by a corresponding amplitude value and a temporal position. Furthermore, a start reference point and an end reference point of the threshold curve define a measurement time window. A first reference point is arranged between the start reference point and the end reference point, the temporal position of which is set to the transmission start time of a measurement signal. At least one further reference point is arranged after the first reference point and before the end reference point, which adapts the shape of the threshold curve to an interference signal pattern. According to the invention, the amplitude values ​​of the reference points of the threshold curve are generated digitally.In this process, an amplitude value is specified for the starting support point, which is smaller than an amplitude value of the first support point, whereby a first section of the threshold curve rises from the amplitude value of the starting support point to the amplitude value of the first support point.

[0012] In an advantageous embodiment of the method according to the invention, an amplitude value of the end point of the threshold curve at the end of the measurement time window, or an amplitude value of a point located after a transmission time window limited by the temporal position of the first point and a temporal position of a second point, is selected as the amplitude value for the starting point. This allows previously stored amplitude values ​​to be advantageously used to adjust the sensitivity of the noise detection, thus eliminating the need for additional effort to generate different amplitude values ​​for the starting point.

[0013] In a further advantageous embodiment of the method according to the invention, the interference signal pattern can be generated based on detected interference signals, wherein the amplitude values ​​of the support points in a second section of the threshold curve, beginning with the first support point, are defined and stored by analyzing the interference signal pattern. The interference signals can be caused, for example, by reflections from the road surface or reflections from vehicle attachments. Furthermore, the amplitude values ​​of the support points that limit the transmission time window can, for example, be set to a maximum amplitude value of the threshold curve, since no interference noise detection or echo detection is possible during the transmission time window.

[0014] In a further advantageous embodiment of the method according to the invention, the threshold curve in the first section can rise continuously from the amplitude value of the starting support point until the amplitude value of the first support point is reached. The starting support point can, for example, be connected to the first support point by a straight segment.

[0015] In a further advantageous embodiment of the method according to the invention, at least the temporal positions of the start support point, the end support point, and the first and second support points that define the transmission time window can be fixed. The temporal positions of the support points arranged after the transmission time window and before the end support point can be implemented variably. The temporal positions of the time-variable support points can be defined and stored, for example, by analyzing the interference signal pattern. By specifying variable support points, the number of support points required to generate a threshold curve can be reduced, and thus a smaller storage unit can be used in the ultrasonic sensor.Furthermore, the timing of each support point can be advantageously selected individually, so that the threshold curve can be better adapted to an existing interference signal pattern and unwanted interference signals or ground reflections can be more accurately suppressed.

[0016] In a further advantageous embodiment of the method according to the invention, the second section of the threshold curve can be generated from straight line segments, each connecting two temporally successive support points. The use of straight line segments enables a quick and easy reconstruction of the threshold curve.

[0017] The threshold curve generated by the method according to the invention is preferably used in a method for evaluating signals from an ultrasonic sensor, which activates the ultrasonic sensor at a predetermined start time and transmits a measurement signal for a predetermined time period at a predetermined transmission start time. Here, the start time and an end time define a measurement time window within which background noise and, in response to the measurement signal, at least one echo signal are received and evaluated.A first section of the measurement time window, limited by the start time and the transmission start time, is used for the detection of background noise, and a second section of the measurement time window, limited by the transmission start time and the end time, is used for the detection of echo information and for suppressing background noise, wherein during the evaluation received background noise and / or received echo information are compared with the threshold curve according to the invention, which is generated from stored reference points, wherein received echo information and background noise whose amplitudes lie below the threshold curve are suppressed, and received echo signals whose amplitude lies above the threshold curve are evaluated to determine distances to detected objects.

[0018] In an advantageous embodiment of the inventive method for evaluating signals from an ultrasonic sensor, background noise detected within the first section of the threshold curve, defined as the noise measurement time window, can be analyzed and evaluated to assess echo information subsequently detected during the second section of the threshold curve. For example, a weighting factor can be assigned to the echo information detected during the second section of the threshold curve, whereby the weighting factor can be predetermined depending on the background noise detected within the first section of the threshold curve. The echo information detected during the second section of the threshold curve can be further processed or assigned a high weighting factor if no background noise is detected within the first section of the threshold curve.This means that the captured echo information is valid and can be used for object detection. Echo information detected during the second part of the threshold curve can be discarded or assigned a low weighting factor if background noise is detected within the first part of the threshold curve whose amplitude values ​​exceed the threshold. This means that the captured echo signals are invalid due to the detected background noise and cannot be used for object detection.

[0019] In a further advantageous embodiment of the method according to the invention, the interference noise detected within the first section of the threshold curve, which is bounded by the starting support point and the first support point, can be analyzed and evaluated to generate the interference signal pattern. This can be used in particular to generate variable support points if the interference signal measurement window arranged before the transmission time window is sufficiently long.

[0020] The device according to the invention for environmental sensing in a vehicle for carrying out the above-mentioned methods comprises at least one ultrasonic sensor and an evaluation and control unit. The evaluation and control unit activates the at least one ultrasonic sensor at a predetermined start time, which then transmits a measurement signal over a transmission time window beginning at a specified start time. The evaluation and control unit defines a measurement time window limited by the start time and an end time, within which ambient noise and, in response to the measurement signal, at least one echo signal can be received, which the evaluation and control unit then processes.Furthermore, the evaluation and control unit uses a first section of the measurement time window, limited by the start time and the transmission start time, for the detection of background noise, and a second section of the measurement time window, limited by the transmission start time and the end time, for the detection of echo information and for suppressing background noise. During evaluation, the evaluation and control unit compares received background noise and / or received echo information with a threshold curve, which the evaluation and control unit generates from stored reference points using the method described above according to the invention. The evaluation and control unit suppresses received echo information whose amplitudes are below the threshold curve and evaluates received echo signals whose amplitudes are above the threshold curve to determine distances to detected objects.The evaluation and control unit stores the digitally generated threshold curve in a storage unit.

[0021] In an advantageous embodiment of the device according to the invention, the evaluation and control unit can analyze and evaluate the interference noise detected within the first section of the threshold curve, bounded by the starting support point and the first support point, for the purpose of evaluating echo information subsequently detected during the second section of the threshold curve. Furthermore, the evaluation and control unit can analyze and evaluate the interference noise detected within the first section of the threshold curve, bounded by the starting support point and the first support point, for the purpose of generating the interference signal pattern.

[0022] Exemplary embodiments of the invention are explained in more detail below with reference to a graphic representation.

[0023] The illustration shows: Fig. 1 a block diagram of an embodiment of a device according to the invention for environmental detection in a vehicle. Fig. 2 a flowchart of an embodiment of a method according to the invention for generating a threshold curve for evaluating signals from an ultrasonic sensor. Fig. 3. A characteristic curve diagram to represent a signal profile on a digital signal line of an ultrasonic sensor. Fig. 4 a characteristic curve diagram to represent a threshold curve generated with the inventive method for evaluating signals from an ultrasonic sensor.

[0024] As from Fig. As can be seen in Figure 1, an embodiment of a device for environmental sensing in a vehicle comprises several ultrasonic sensors, each of which is connected to a control unit 40 via a digital signal line or a vehicle bus, and of which one ultrasonic sensor 10 is shown as a representative example. In the illustrated embodiment, the ultrasonic sensor 10 comprises a transmitter / receiver unit 20, a signal generator 22 for generating a measurement signal 24, which is transmitted via the transmitter / receiver unit 20, an evaluation and control unit 30, and a storage unit 32.

[0025] As from Fig. 3 and Fig. As can be seen further in Figure 4, the control unit 40 transmits a transmission request signal to the ultrasonic sensor 10 at a time t0, which is active for the duration of a transmission request time window T. AFThe evaluation and control unit 30 activates the ultrasonic sensor 10 shown at a predetermined start time T in response to a rising edge of the transmit request signal. START The ultrasonic sensor 10 transmits via the transmit / receive unit 20 over a transmission time window T. Se-nde starting at a transmission start time t S_Start a measurement signal 24 is output, whereby the evaluation and control unit 30 is set by the start time t START and an end time t ENDE limited measurement time window T Mess The system defines within which background noise 28 and, in response to the measurement signal 24, at least one echo information 26 can be received, which the evaluation and control unit 30 evaluates. The evaluation and control unit 30 uses a signal that is set from the start time T. START and the start time of transmission t S_Start limited first section T MStör of the measurement time window T Messfor the detection of background noise 28, and one from the transmission start time t S_Start and from the end time t EN- DE limited second section T MEcho of the measurement time window T Mess for the detection of echo information 26 and the suppression of background noise 28. The evaluation and control unit 30 compares received background noise 28 and / or received echo information 26 during the evaluation with a Fig. 4 shown threshold curve SK D , which the evaluation and control unit 30 uses from stored support points S START , S1 to S7, S ENDE The evaluation and control unit 30 filters out received echo information 26 and interference signals whose amplitudes are below the threshold curve SK. D lie, and evaluates received echo information 26 to determine distances to detected objects whose amplitude is above the threshold curve SK DThe echo information 26 represents a useful signal component and a noise signal component of the received echo signals. The evaluation and control unit 30 generates the threshold curve SK. D digitally by executing a subsequent action with reference to Fig. 2 described in the invention method for generating a threshold curve and stores the generated threshold curve in the storage unit 32.

[0026] The section within the first part T MStör the threshold curve SK D , which is from the starting point S START and limited to the first support point S1, detected interference noise 28 is used by the evaluation and control unit 30 for the subsequent evaluation during the second section T MEcho the threshold curve SK D The detected echo information 26 is analyzed and evaluated. Furthermore, the evaluation and control unit 30 can analyze the data within the first section T. MStörthe threshold curve SK D Analyze and evaluate the detected interference noise 28 to create the interference signal pattern.

[0027] In the illustrated embodiment, the evaluation and control unit 30 of the ultrasonic sensor 10 transmits the useful signal components 26, for example via a bus system or a digital signal line, to the control unit 40, which evaluates the useful signal components 26 to determine distances to detected objects. This distance information can then be used in driver assistance systems 50, such as a parking assistance system 53 and / or a distance warning system 54 and / or a lane change assistance system 56.

[0028] The following refers to Fig. 2, Fig. 3 to Fig. 4 an embodiment of the inventive method for generating a threshold curve SK Dand an embodiment of the inventive method for evaluating signals 26, 28 of an ultrasonic sensor 10 is described.

[0029] As from Fig. 2 shows a flowchart of an embodiment of the inventive method for generating a threshold curve SK D shows that in step S10 the measurement time window T is defined Mess via the starting point S START and the final support point S ENDE the threshold curve SK D defined. In step S20, the temporal position t1 of a between the starting support point S is defined. START and the final support point S ENDE first support point S1 ordered to the transmission start time t S_Start of the measurement signal 24 is determined. In step S30, after the first support point S1 and before the final support point S ENDE at least one further support point S2 to S7 is arranged, which follows the course of the threshold curve SK. Dadapt to a noise signal pattern. According to the invention, for the starting support point S START an amplitude value A3, A ENDE A value smaller than an amplitude value A1 of the first support point S1 is specified. In step S50, the stored support points S START , S1 to S7, S ENDE the threshold curve SK D , each of which is defined by a corresponding amplitude value A START , A1 to A7, A ENDE , A max and a temporal position t START , t1 to t7, t ENDE be defined, activated and generated using a digital method, wherein a first section T MStör the threshold curve SK D starting from the amplitude value A3, A ENDE the starting base S START increases to the amplitude value A1 of the first support point S1.

[0030] As from Fig. As can be seen further in section 4, the amplitude value A1 of the first support point S1 in the illustrated embodiment corresponds to the threshold curve SK. D a maximum amplitude value A max the threshold curve SK D . As amplitude value A START for the starting point S START Can an amplitude value A ENDE the final support point S ENDE the threshold curve SK D at the end of the measurement time window T Mess or an amplitude value A3 to A7 of a support station S3 to S7 is selected, which is limited by a transmission time window T defined by the time position t1 of the first support station S1 and a time position t2 of a second support station S2 Sende is arranged. In Fig. 4 is representative of the amplitude value A3 of the third support point S3 as a selectable amplitude value A START for the starting point S START depicted.

[0031] The interference signal pattern, which corresponds to the depicted threshold curve SK D The signal to be hidden is created based on detected interference signals 28, where the amplitude values ​​A1 to A7, A ENDE the support points S1 to S ENDE in the second section T, beginning with the first support station S1 MEcho the threshold curve SK D defined and stored by analyzing the interference signal pattern. How from Fig. As can be seen further in section 4, the amplitude values ​​A1 and A2 correspond to the transmission time window T. Sende limiting support points S1, S2 a maximum amplitude value A max the threshold curve SK D The temporal position t2 of the second support point of the threshold curve SK D corresponds to the end-of-transmission time t S_Ende of the broadcast time window T Sende The threshold curve SK D rises in the first section T MStör starting from the amplitude value A STARTthe starting base S START The amplitude increases continuously until the amplitude value A1 of the first support point S1 is reached. In the illustrated embodiment, the starting support point S START connected to the first support point S1 by a straight line segment, where the straight line segment is between a point with an amplitude value A. ENDE the final support point S ENDE specified amplitude value A START the starting base S START is represented by a dash, and where the straight line segment between an amplitude value A3 specified as the amplitude value of the third support point S3 START the starting base S START is shown with a dashed line. Furthermore, in the illustrated embodiment of the threshold curve SK, D at least the temporal positions t START, t ENDE, t 1, t2 of the starting point S START , the final support point S ENDE and the broadcast time window T SendeThe first and second support points S1 and S2, which limit the signal, are fixed. The time positions t3 to t7 after the transmission time window T Sende and before the final support point S ENDE The positions of the support points S3 to S7 can be fixed or variable, depending on the ultrasonic sensor 10 used. The temporal positions t3 to t7 of the time-variable support points S3 to S7 can be defined and stored, for example, by analyzing the interference signal pattern.

[0032] Analogous to the first section T MStör the threshold curve SK D The second section T will also be MEcho the threshold curve SK D generated from straight line segments, each of which has two consecutive support points S1 to S1 ENDE connect them. In a dotted threshold curve SK generated by analogous methods. A The curves correspond to the analogous threshold curve SK. Abetween two temporally adjacent support points S2 / S3, S4 / S 5, S6 / S7, S7 / S8 with different amplitude values ​​A2 / A3, A4 / A5, A6 / A7, A7 / A8 each correspond to the course of a charging curve (ascending exponential function) or a discharging curve (decreasing exponential function) of a capacitor, which is used for the analog methods for generating the analog threshold curve SK A is used. In the analogous threshold curve SK shown. A , which was generated by analog methods known from the prior art, the capacitor is checked after the measurement time window T Mess to the maximum amplitude value A max charged so that the amplitude value A START for the starting point S START also the maximum amplitude value A max is specified.

[0033] The digital threshold curve SK generated by the inventive method Dis preferably used in a method for evaluating signals 26, 28 from an ultrasonic sensor 10. As shown from Fig. As can be seen further in section 3, the ultrasonic sensor 10 will be activated at a predetermined start time T. START Activation occurs, for example, through a rising edge of a trigger pulse as a transmission request on the digital signal line, which is generated by the control unit 40 and transmitted to the ultrasonic sensor 10. The ultrasonic sensor 10 receives this pulse or transmission request and begins after a short delay T. D (Delay) to the start of transmission time t S_Start The device emits ultrasonic waves as a measurement signal 24 and, in response to the transmitted measurement signal 24, returns received echo information as time-of-flight information to the control unit 40. In the illustrated embodiment, during an echo time window T Echothat through an echo start time T E_Start and an echo end time T E_Ende The range is limited, and echo information is detected. In this case, the echo information exceeds the threshold at the echo start time T. E_Start the threshold curve SK D and at the echo end time T E_Ende The echo information falls below the SK threshold curve. D The evaluation and control unit 30 or the control device 40 calculates the object distance based on the elapsed time between a rising edge of the transmission request at time T. START and a falling edge of the echo information at the echo end time T E_Ende The start time of transmission also depends on the transmission time. S_Start and the transmission end time t s_Ende of the transmission process and thus the transmission time window T Sende The transmission process is known. The delay T DThe delay between the transmission request and the transmission process is constant under normal conditions. The measurement signal 24 is transmitted for a predetermined time interval T. Sende sent out, with the start time S START and the end time S ENDE the threshold curve SK D a measurement time window T Mess Define within which background noise 28 and, in response to the measurement signal 24, at least one echo information 26 is received and evaluated. The starting time t START and the start time of transmission t S_Start limited first section T MStör of the measurement time window T Mess is used for the detection of interference noise 28, and a value from the transmission start time t S_Start and from the end time t ENDE limited second section T MEcho of the measurement time window T Messis used for the detection of echo information 26 and for suppressing background noise 28. During the evaluation, received background noise 28 and / or received echo information 26 are compared with the threshold curve SK according to the invention. D compared which from stored support points S START , S1 to S7, S ENDE is generated. In this process, received echo information 26 and background noise 28 are filtered out, the amplitudes of which are below the threshold curve SK. D lie, and received echo signals 26, whose amplitude is above the threshold curve SK D The positions are evaluated to determine distances to detected objects.

[0034] According to the invention, the delay time period T D (Delay) is used for interference noise detection. From the time of the transmission request T STARTThe ultrasonic sensor 10 delivers interference noise 28 and / or echo information 26, whereby the emitted ultrasonic waves are also considered echo information, to the control unit 40. The delay time T shown D (Delay) is not a delay on the signal line, but an internal delay in the ultrasonic sensor 10. Should the delay time T now occur within the delay period T D When an echo signal reaches the ultrasonic sensor 10, the ultrasonic sensor 10 will report this echo signal to the control unit 40. Thus, the ultrasonic sensor 10 detects an echo signal even before an ultrasonic signal is emitted as a measurement signal 24. This echo signal can be interpreted as background noise 28. Since the echo duration is usually significantly longer than the delay time T D (Delay) extends this echo information the transmission time window T Sendeforwards, since the interfering sound 28 also excites the ultrasonic sensor 10 to transmit, so that the dashed downward slope of the transmission time window T Sende earlier than expected, before the actual start time T S_Start at a time t s occurs at which the amplitude of the noise or the noise echo information 28 the threshold curve SK D exceeds. Here, both the interference echo information 28 and a real echo information 26 must exceed the threshold curve SK. D exceed in order to be transmitted to control unit 40.

[0035] The evaluation and control unit 30 or the control unit 40 analyze the interference noise 28, which is present within the interference signal measurement time window T. MStör defined first section of the threshold curve SK D is detected, for the evaluation of subsequently during the second section T MEcho the threshold curve SK Ddetected echo information 26. In the illustrated embodiment, during the second section T MEcho the threshold curve SK D detected echo information 26 is further processed if within the first section T MStör the threshold curve SK D No background noise 28 is detected. This means that the detected echo information 26 is valid and can be used for object recognition. During the second section T MEcho the threshold curve SK D Detected echo information 26 is discarded if within the first section T MStör the threshold curve SK D Interference noise 28 is detected, whose amplitude values ​​define the threshold curve SK. D exceed.

[0036] In an alternative procedure, the data collected during the second section T MEcho the threshold curve SK DThe detected echo information 26 is assigned a weighting factor which is specified depending on the background noise 28 which is present within the first section T MStör the threshold curve SK D is detected. This allows the second section T to be detected. MEcho the threshold curve SK D A high weighting factor is assigned to the detected echo information 26 if within the first section T MStör the threshold curve SK D No background noise 28 is detected. Furthermore, during the second section T MEcho the threshold curve SK D A low weighting factor is assigned to the detected echo information 26 if within the first section T MStör the threshold curve SK D Interference noise 28 is detected, whose amplitude values ​​define the threshold curve SK. D exceed.

[0037] Fig.Figure 4 shows a typical threshold curve SK D with an elevation to suppress ground reflections. Also visible are the time t1 and the amplitude value A1 of the first support point S1, with which the transmission process T Sende begins. The starting point S START Before the first support point, different amplitude values ​​A can be used. ENDE , A3 as starting amplitude value A START can be configured. Two possible starting values ​​for the threshold curve SK are shown. D For noise detection, this means that the amplitude value A3 of the third support point S3 can be selected as an amplitude value A. START for the starting point S START It represents a less sensitive threshold, so that only moderate to very strong disturbances can be detected. The amplitude value A ENDE the final support point S ENDE the threshold curve SK Drepresents a more sensitive threshold, so that even weaker disturbances can be detected.

[0038] Embodiments of the present invention advantageously enable the detection of background noise during a measurement without additional time loss, allowing it to be used to assess the validity of the detected echo signals. Furthermore, the sensitivity of the background noise detection can be adjusted by parameterizing the amplitude value of the starting point of the threshold curve, depending on the installation location and the application.

Claims

[1] Method for generating a threshold curve for evaluating signals from an ultrasonic sensor, wherein the threshold curve (SK) D ) from stored support points (S START , S1 to S7, S ENDE ) is generated, each of which is generated by a corresponding amplitude value (A) START , A1 to A7, A ENDE , A max ) and a temporal position (T START , t1 to t7, t ENDE ) are defined, where a starting support point (S START ) and a terminal support point (S ENDE ) the threshold curve (SK D ) a measurement time window (T Mess ) define, where between the starting support point (S START ) and the final support point (S ENDE ) a first support point (S1) is arranged, whose temporal position (t1) is set to a transmission start time (t S_Start ) of a measurement signal (24) is determined, wherein after the first support point (S1) and before the final support point (S ENDE) at least one further support point (S2 to S7) is arranged, which follows the course of the threshold curve (SK) D ) adapts to a noise signal pattern, characterized by , that the amplitude values ​​(A START , A1 to A7, A ENDE , A max ) the support points (S START , S1 to S7, S ENDE ) the threshold curve (SK D ) are digitally generated, with the starting point (S START ) an amplitude value (A3, A ENDE ) is specified, which is smaller than an amplitude value (A1) of the first support point (S1), where a first section (T MStör ) the threshold curve (SK D ) starting from the amplitude value (A3, A ENDE ) the launch base (S START ) increases to the amplitude value (A1) of the first support point (S1). [2] Method according to claim 1, characterized by , that an amplitude value (A ENDE ) the final support point (S ENDE ) the threshold curve (SK D) at the end of the measurement time window (T Mess ) or an amplitude value (A3 to A7) of a support point (S3 to S7), which is limited by a transmission time window (T) defined by the temporal position (t1) of the first support point (S1) and a temporal position (t2) of a second support point (S2). Sende ) is arranged as an amplitude value (A START ) for the launch base (S START ) is selected. [3] Method according to claim 1 or 2, characterized by , that the interference pattern is created based on detected interference signals (28), where the amplitude values ​​(A1 to A7, A ENDE ) the support points (S1 to S ENDE ) in a second section beginning with the first support point (S1) (T MEcho ) the threshold curve (SK D ) are defined and stored by analyzing the interference signal pattern. [4] Method according to claim 2 or 3, characterized by , that the amplitude values ​​(A1, A2) of the transmission time window (T Sende) limiting support points (S1, S2) a maximum amplitude value (A max ) the threshold curve (SK D ) are equivalent to. [5] Method according to any one of the preceding claims 1 to 4, characterized by , that the threshold curve (SK D ) in the first section (T MStör ) starting from the amplitude value (A START ) the launch base (S START ) increases steadily until the amplitude value (A1) of the first support point (S1) is reached. [6] Method according to claim 5, characterized by , that the starting base (S START ) is connected to the first support point (S1) by a straight section. [7] Method according to any one of the preceding claims 1 to 6, characterized by , that at least the temporal positions (T START , t ENDE, t 1, t2) of the starting support point (S START ) , the final support point (S ENDE ) and the broadcast time window (T SendeThe first and second support points (S1, S2) that limit the boundaries are fixed. [8] Method according to any one of the preceding claims 1 to 7, characterized by , that the temporal positions (t3 to t7) of the after the broadcast time window (T Sende ) and before the final support point (S ENDE The support points (S3 to S7) are arranged in a variable manner. [9] Method according to claim 8, characterized by , that the temporal positions (t3 to t7) of the time-variable support points (S3 to S7) are defined and stored by analyzing the interference signal pattern. [10] Method according to any one of the preceding claims 1 to 9, characterized by , that the second section (T MEcho ) the threshold curve (SK D ) is generated from straight line segments, each of which has two consecutive support points (S1 to S1). ENDE ) connect them. [11] Method for evaluating signals from an ultrasonic sensor, wherein at a predetermined start time (t START ) the ultrasonic sensor (10) is activated and at a transmission start time (t S_Start ) a measurement signal (24) for a specified time interval (T Sende ) is sent out, with the start time (S START ) and an end time (S ENDE ) a measurement time window (T Mess ) define within which background noise (28) and in response to the measurement signal (24) at least one echo information (26) is received and evaluated, wherein a starting time (t START ) and the transmission start time (t S_Start ) limited first section (T MStör ) of the measurement time window (T Mess ) is used for the detection of background noise (28), and a transmission start time (t S_Start ) and from the end time (T ENDE ) limited second section (T MEcho ) of the measurement time window (T Mess) is used to detect echo information (26) and to suppress background noise (28), wherein received background noise (28) and / or received echo information (26) during the evaluation are compared with a threshold curve (SK) D ) are compared, which are from stored support points (S START , S1 to S7, S ENDE ) is generated, whereby received echo information (26) and background noise (28) are suppressed, the amplitudes of which are below the threshold curve (SK). D ) lie, and received echo signals (26) whose amplitude is above the threshold curve (SK) D ) are used to determine distances to detected objects, characterized by , that the threshold curve (SK D ) is produced using a method according to any one of claims 1 to 10. [12] Method according to claim 11, characterized by , that interference noise (28), which is within the interference signal measurement time window (T MStör ) defined first section (TMStör ) the threshold curve (SK D ) is detected, for the evaluation of subsequent events during the second section (T MEcho ) the threshold curve (SK D ) detected echo information (26) is analyzed and evaluated. [13] Method according to claim 12, characterized by , that during the second section (T MEcho ) the threshold curve (SK D ) detected echo information (26) is assigned a weighting factor, the weighting factor being specified depending on the background noise (28) which is present within the first section (T MStör ) the threshold curve (SK D ) is detected. [14] Method according to claim 12 or 13, characterized by , that during the second section (T MEcho ) the threshold curve (SK D ) detected echo information (26) is further processed or assigned a high weighting factor if within the first section (T MStör) the threshold curve (SK D ) no background noise (28) is detected. [15] Method according to any one of claims 12 to 14, characterized by , that during the second section (T MEcho ) the threshold curve (SK D ) detected echo information (26) is discarded or assigned a low weighting factor if within the first section (T MStör ) the threshold curve (SK D ) Interference noise (28) is detected, whose amplitude values ​​define the threshold curve (SK D exceed. [16] Method according to any one of claims 11 to 15, characterized by , that within the area from the starting point (S START ) and the first support point (S1) limited first section (T MStör ) the threshold curve (SK D ) detected noise (28) is analyzed and evaluated to create the noise signal pattern. [17] Device for environmental sensing in a vehicle (1) comprising at least one ultrasonic sensor (10) and an evaluation and control unit (30) for carrying out the method according to one of the preceding claims 11 to 16, wherein the evaluation and control unit (30) detects the at least one ultrasonic sensor (10) at a predetermined start time (t START ) activated, which has a transmission time window (T Sende ) starting at a transmission start time (t S_Start ) emits a measurement signal (24), wherein the evaluation and control unit (30) receives a signal determined by the start time (t START ) and an end time (t ENDE ) limited measurement time window (T Mess ) defines within which background noise (28) and in response to the measurement signal (24) at least one echo information (26) is receivable, which the evaluation and control unit (30) evaluates, wherein the evaluation and control unit (30) has a starting time (t START ) and the transmission start time (tS­_Start ) limited first section (T MStör ) of the measurement time window (T Mess ) used to detect background noise (28), and one from the transmission start time (t S_Start ) and from the end time (t ENDE ) limited second section (T MEcho ) of the measurement time window (T Mess ) for the detection of echo information (26) and for the suppression of background noise (28), wherein the evaluation and control unit (30) during the evaluation compares the background noise (28) and / or the echo information (26) received with a threshold curve (SK) D ) compares which the evaluation and control unit (30) uses from stored support points (S START , S1 to S7, S ENDE ) generated, whereby the evaluation and control unit (30) filters out received echo information (28) whose amplitudes are below the threshold curve (SK). D ) lie, and received echo signals (26) whose amplitude is above the threshold curve (SK) D) lie, evaluates to determine distances to detected objects, characterized by , that the evaluation and control unit (30) the threshold curve (SK D ) digitally generated using the method according to one of claims 1 to 10 and stored in a storage unit (32). [18] Device according to claim 17, characterized by , that the evaluation and control unit (30) within the area from the starting support point (S START ) and the first support point (S1) limited first section (T MStör ) the threshold curve (SK D ) detected background noise (28) for the evaluation of subsequent during the second section (T MEcho ) the threshold curve (SK D ) detected echo information (26) is analyzed and evaluated. [19] Device according to claim 17 or 18, characterized by , that the evaluation and control unit (30) within the area from the starting support point (S START) and the first support point (S1) limited first section (T MStör ) the threshold curve (SK D ) detected interference noise (28) is analyzed and evaluated to create the interference signal pattern.

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