DE102014107311A1 - Method for operating an ultrasonic sensor of a motor vehicle, ultrasonic sensor device, driver assistance system and motor vehicle - Google Patents

Abstract

The invention relates to a method for operating an ultrasonic sensor (2) of a motor vehicle, in which a transmission signal is emitted by exciting a membrane (4) of the ultrasonic sensor (2) with an excitation frequency during a transmission phase, then during a damping phase (10) the membrane (10) 4) is excited with an anti-phase to the excitation frequency attenuation frequency and then a mechanical oscillation of the membrane (4) is detected during a receiving phase (11), wherein during the damping phase (10) an amplitude of the mechanical vibration of the membrane (4) is detected, wherein it is determined during the damping phase (10) whether the amplitude falls below a vibration threshold value (12) for a time duration of a predetermined damping time interval (15) (S2).

Description

The present invention relates to a method for operating an ultrasonic sensor of a motor vehicle, wherein during a transmission phase, a transmission signal is emitted by exciting a membrane of the ultrasonic sensor with an excitation frequency, then during a damping phase, the membrane is excited with an inverse phase to the excitation frequency attenuation frequency and then during a mechanical vibration of the membrane is detected during a reception phase, wherein an amplitude of the mechanical oscillation of the membrane is detected during the damping phase. Moreover, the present invention relates to an ultrasonic sensor device. Furthermore, the present invention relates to a driver assistance system and a motor vehicle with such a driver assistance system.

The interest is directed in the present case in particular to a method for operating an ultrasonic sensor for a motor vehicle. Such ultrasonic sensors can be used in driver assistance systems, for example in a so-called parking aid system. Today's parking aid systems work according to the echosounder method. In this case, an ultrasound signal or an ultrasound wave is emitted by the ultrasound sensor, reflected by an object and in turn received by the ultrasound sensor. Due to the duration of the ultrasonic wave, the distance from the ultrasonic sensor to the object can be determined. However, such distance measuring methods are limited in their range. This applies to both the maximum range and the minimum distance.

The minimum distance is given by the transmission duration, in which the ultrasonic waves are emitted, and the so-called decay time. The settling time itself represents the time at which the excited membrane can decay again to receive ultrasonic waves reflected from the object. If a low fade time is achieved, this means that smaller distances to an object can be detected. Such a reduction of the decay time can be achieved by a material damping of the membrane of the ultrasonic sensor itself. Alternatively or additionally, an active damping can be provided. Here, the membrane is stimulated for the duration of the decay process with an antiphase oscillation.

In this context, the describes DE 101 36 628 B4 a method for operating an ultrasonic transducer for emitting and receiving ultrasonic waves by means of a membrane. To emit ultrasonic waves, the membrane is energized for a predetermined period of time, then the membrane vibrations are damped and recorded to receive ultrasonic waves, the membrane vibration. For damping, the membrane vibrations are detected and the membrane excited in the opposite phase to the detected vibrations. In addition, as part of the damping process, the value of the amplitude and / or the duration of the excitation of the membrane of the amplitude of the detected membrane vibration tracked to adjust the attenuation of the strength of the remaining membrane vibrations.

A disadvantage of the active damping of the membrane of the ultrasonic sensor is that the phase of the vibration of the membrane must be measured correctly during the decay process and the antiphase damping oscillation must be output correctly. If this antiphase excitation is not optimally determined, it may happen that the decaying oscillates and instead of a constant reduction of the amplitude of the membrane oscillation even partially higher amplitudes can be achieved. This non-synchronicity is reflected, for example, in the form of a brief dip in the amplitude of the oscillation during the decay time. This in turn means that a later increase in the amplitude of the membrane oscillation due to the non-ideal excitation is detected by a control device of the ultrasonic sensor as an echo signal.

It is an object of the present invention to provide a solution as an ultrasonic sensor of the type mentioned, which is actively attenuated during the swinging, can be operated reliably more easily.

This object is achieved by a method by an ultrasonic sensor device, by a driver assistance system and by a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description and the figures.

An inventive method is used to operate an ultrasonic sensor of a motor vehicle. During a transmission phase, a transmission signal is emitted by exciting a membrane of the ultrasonic sensor with an excitation frequency, then during an attenuation phase the membrane is excited with an inverse phase frequency to the excitation frequency and then a mechanical oscillation of the membrane is detected during a reception phase, wherein during the damping phase an amplitude of the mechanical vibration of the membrane is detected. It is also provided that it is determined during the damping phase, whether the amplitude falls below a vibration threshold for a time duration of a predetermined damping time interval.

The ultrasonic sensor is for determining a distance between the ultrasonic sensor and an object. In respective measuring cycles in which the distance to the object is to be determined, the ultrasonic sensor is operated in temporally successive phases. In the transmission phase, the membrane of the sensor is excited at a predetermined excitation frequency. For this purpose, the diaphragm can be set into mechanical oscillations with a corresponding adjusting device, for example a piezoelectric actuator, so that the diaphragm emits ultrasonic waves as the transmission signal. In the subsequent damping phase, the membrane is driven by means of the adjusting device with an anti-phase to the excitation frequency damping frequency. In a subsequent to the damping phase receiving phase, a mechanical vibration of the membrane is detected. For this purpose, usually the actuating element or the piezoelectric actuator is used. This detected mechanical vibration can then be used as a received signal or as an echo signal.

During the damping phase, an amplitude of the mechanical vibration of the ultrasound membrane is also detected. For this purpose, again the adjusting device or the piezoelectric actuator can be used. It is checked for what duration of time the detected mechanical vibration exceeds a vibration threshold. In addition, it is checked whether the time duration, while the amplitude is exceeded, is within a predetermined damping time interval. The damping time interval may be limited by a predetermined minimum settling time and a predetermined maximum settling time. In this way it can be determined whether the decay behavior of the membrane of the ultrasonic sensor takes place as intended or whether the excitation of the membrane with the damping frequency possibly leads to an excitation of the oscillation of the membrane. In this way, the functionality of the ultrasonic sensor can be easily checked.

Preferably, the mechanical vibration of the membrane detected during the reception phase is used as a reception signal if the amplitude detected during the damping phase falls below the threshold value during the time duration of the predetermined damping interval. If the duration of the mechanical vibration of the membrane during the damping phase in the damping time interval, it can be assumed that the active damping of the membrane has led to a damping of the vibration of the membrane. In this case, it can furthermore be assumed that a mechanical oscillation subsequently detected in the reception phase can be used as the reception signal.

Furthermore, it has been shown to be advantageous if, during the reception phase, the amplitude of the mechanical oscillation of the diaphragm is detected and a reception interval is determined during which the amplitude exceeds the oscillation threshold value. In this way it can be checked in the reception phase based on the duration of the mechanical vibration of the membrane, whether a received signal or an echo is present. If the reception time interval differs from conventionally known values, then it can be assumed that the mechanical oscillation of the diaphragm does not originate from the echo of the ultrasonic signal. In this case, a so-called apparent echo may be present.

In an embodiment, a difference duration between an end of a predetermined damping time during which the ultrasonic sensor is operated in the damping phase and the reception time interval is determined. In other words, it is checked after which time, after the attenuation of the membrane has occurred, a supposed echo of the ultrasonic signal arrives at the membrane. If this difference in duration differs from conventionally known values, then it can be assumed that no echo is received in the present case.

Preferably, the mechanical vibration of the membrane detected during the reception phase is used as the reception signal, if the time duration of the reception time interval falls below a reference value and / or the difference duration falls below a limit value. If the mechanical vibration of the diaphragm detected during the reception phase is shorter than the predetermined reception time interval, it is usually a fake echo, and this mechanical vibration is not detected as a reception signal. Even if the time duration between the decay and the reception of the supposed echo is smaller than the predetermined difference duration, the detected mechanical oscillation is not used as a received signal.

Preferably, the predetermined damping time is adjusted if the time duration of the reception time interval falls below the reference value and / or the difference duration falls below the limit value. For the damping time during which the ultrasonic sensor is operated in the damping phase, first a predetermined value be specified. In particular, if the reception time interval is less than the reference value and / or the difference duration is less than the limit value, the damping time can be increased. In this way, the time from which the receiving phase begins can be moved backwards. Thus, echoes from the sensor signal can be virtually filtered out.

In particular, the attenuation time may be adjusted so that the adjusted attenuation time corresponds to a sum of the predetermined attenuation time, the receive time interval, and the difference duration. To the originally set damping time so the time duration of the receiving time interval and the time duration of the difference duration can be added. Only after this time duration, the receiving phase of the ultrasonic sensor can begin. Thus, ultrasonic signals reflected from an object can be more reliably detected.

In one embodiment, a current temperature of the ultrasonic sensor is detected and the damping time interval is adjusted as a function of the detected temperature. Hereby, the influence of the temperature on the mechanical vibration behavior of the membrane of the ultrasonic sensor can be taken into account. Thus, different values for the damping time interval for different temperatures can be stored in a memory unit of a control device.

Furthermore, it is advantageous if the damping time interval is adjusted as a function of an operating state of the ultrasonic sensor. Here too, for example, an operating period of the ultrasonic sensor can be taken into account. Thus, for example, a mechanical wear, which usually sets in the course of time, be considered.

An ultrasonic sensor device according to the invention for a motor vehicle comprises an ultrasonic sensor and a control device which is designed to carry out the method according to the invention.

A driver assistance system according to the invention comprises at least one ultrasound sensor device. The ultrasonic sensors of the ultrasonic sensor device can be arranged, for example, in a front bumper and / or in a rear bumper of the motor vehicle. The driver assistance system can be designed, for example, as a so-called parking aid system.

A motor vehicle according to the invention comprises the driver assistance system according to the invention. The motor vehicle is designed in particular as a passenger car.

The preferred embodiments presented with reference to the method according to the invention and their advantages apply correspondingly to the ultrasonic sensor device according to the invention, the driver assistance system according to the invention and the motor vehicle according to the invention.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. All the features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively indicated combination but also in other combinations or alone.

The invention will now be described with reference to a preferred embodiment and with reference to the accompanying drawings.

Show

1 a schematic representation of an ultrasonic sensor device for a motor vehicle;

2 . 3 analog and digital sensor signals received during a damping phase and a receiving phase of the ultrasonic sensor with a control device of the ultrasonic sensor device;

4 a digital sensor signal in another embodiment; and

5 a flowchart of a method according to an embodiment of the invention.

1 shows an ultrasonic sensor device 1 in a sectioned side view. The ultrasonic sensor device 1 For example, it may be part of a driver assistance system of a motor vehicle. This driver assistance system can be designed, in particular, as a parking aid system in which one or more ultrasound sensor devices 1 be arranged on a front and / or on a rear bumper of the motor vehicle. With the help of the ultrasonic sensor device 1 a distance from the motor vehicle to an object can be determined.

The ultrasonic sensor device 1 includes an ultrasonic sensor 2 , The ultrasonic sensor 2 again comprises a housing 3 , which may be made of metal or plastic, for example. Furthermore, the ultrasonic sensor comprises 2 a membrane 4 , which is made in particular of aluminum. Finally, the ultrasonic sensor includes 2 an actuator 5 in particular comprising a piezoelectric element. By means of the actuator 5 can the membrane 4 be placed in mechanical vibrations. For this purpose, at the actuator 5 applied a time-varying electrical voltage. The membrane 4 of the ultrasonic sensor 2 is at a predetermined excitation frequency by means of the actuator 5 stimulated, which may be in particular in a range between 40 and 60 kHz, for example at 52 kHz. As a transmission signal from the membrane 4 thus generating ultrasonic waves that propagate down to an object. At the object, the ultrasonic waves are reflected again and get back to the membrane 4 back.

The ultrasonic sensor 2 in this case also serves to receive the reflected ultrasonic waves. The membrane 4 is set in mechanical vibration by the reflected ultrasonic waves. This can be done with the actuator 5 or the piezoelectric element are detected, which outputs a time-varying electrical voltage as a result of the mechanical excitation.

Between the transmission of the signal and the reception of the reflected signal, the mechanical oscillation of the membrane should 4 attenuated as quickly as possible, otherwise the minimum distances with the ultrasonic sensor 2 can be reduced. For this purpose, the ultrasonic sensor 2 between a transmission phase in which the transmission signal with the membrane 4 is sent out, and the receiving phase 11 in which the reflected signal of the membrane 4 is detected, in an attenuation phase 10 operated while the the membrane 4 is operated with the actuator from one to the excitation frequency in phase opposition damping frequency.

Furthermore, the ultrasonic sensor device comprises 1 a control device 6 , with which the control of the ultrasonic sensor 2 or the actuator 5 he follows. The control device 6 is also adapted to the mechanical vibration of the membrane 4 that with the actuator 5 during the damping phase 10 is detected to evaluate in the form of sensor signals.

The sensor signals associated with the controller 6 are evaluated in 2 shown. This shows a first diagram 7 an analog sensor signal 9 and the diagram 8th the associated digital sensor signal 13 , On the abscissa in the diagram 7 the time t is plotted and on the ordinate of the diagram 7 is the amplitude A1 of the analog sensor signal 9 applied. In the diagram 8th is also the time t on the abscissa and the amplitude A2 of the digital sensor signal on the ordinate 13 applied. The analog sensor signal 9 describes the mechanical vibration of the membrane 4 during the damping phase 10 and the subsequent reception phase 11 , It can be seen here that the amplitude of the oscillation during the damping phase 10 decreases continuously until it reaches a predetermined oscillation threshold 12 below. After falling below the oscillation threshold value 12 can the ultrasonic sensor 2 in the reception phase 11 operate. The digital sensor signal 13 that in the graph 8th is shown, for example, has the value 1 on when the curve 9 the oscillation threshold 12 exceeds. If the curve 9 the oscillation threshold 12 falls below, takes the digital sensor signal 13 the value 0.

2 illustrates the case by the vibration of the membrane is attenuated by the anti-phase attenuation signal. In comparison, the embodiment according to FIG 3 the case in which the control of the membrane 4 to dampen the mechanical vibration is not ideal antiphase to the current mechanical vibration of the membrane 4 he follows. Here, the mechanical vibration is first damped. After a predetermined time duration in turn follows an increase in the amplitude of the analog sensor signal 9 , The amplitude of the analog sensor signal 9 in this case increases in such a way that the oscillation threshold value 12 is exceeded. This is reflected in the digital signal 13 as a signal pulse 14 low. This signal pulse 14 is from the controller 6 the ultrasonic sensor device interpreted as an echo signal. This supposed echo can also be referred to as a sham echo or as a ghost echo.

To avoid detecting a glimpse, are within the control device 6 different time intervals and thresholds for the digital sensor signal 13 specified. This is in 4 clarified. For the damping time td, after which the damping phase 10 is completed, a minimum settling time t1 and a maximum settling time t2 is specified. The minimum settling time t1 and the maximum settling time t2 thus limit a predetermined damping time interval 15 , It also becomes a reference value for a reception time interval 16 specified. The reception time interval 16 corresponds to the time duration during the mechanical oscillation of the membrane 4 during the reception phase 11 the oscillation threshold 12 exceeds. In addition, a limit value for a difference duration tu is specified. The difference duration tu corresponds to the time interval between an end of the damping phase or the end of the damping time td and the reception time interval 16 ,

5 shows a flowchart of a method according to the invention for operating an ultrasonic sensor 2 , The method is performed in a step S1 for each measurement cycle of the ultrasonic sensor 2 started. In a step S2, above the damping phase 10 an amplitude of the mechanical vibration of the membrane 4 detected. In addition, it is checked whether the amplitude of the mechanical vibration of the vibration threshold 12 during the predetermined damping time interval 15 exceeds. If this is the case, it can be assumed that the decay process is OK. Alternatively, the ultrasonic sensor could be defective. If the query is satisfied in step S2, the method is ended in step S3.

If the query in step S2 is not fulfilled, the method is continued in a step S4. This checks whether the duration of the reception time interval 16 falls below the reference value and / or whether the difference duration tu is smaller than the limit value. If this is not fulfilled, there is either no echo or the echo is not a false echo. Then, the process is ended in step S3.

However, if one of the conditions according to step S4 is fulfilled, the method is continued in step S5. In this case the decay time td is adjusted. In particular, the settling time td is adjusted so that the adjusted settling time is the sum of the previous settling time td, the difference time tu and the receiving time interval 16 equivalent. In addition, the detected ticket echo in the control device 6 deleted.

In this way, one with the control device 6 captured echo is not taken into account or filtered out under certain circumstances and not generally. This can be used to prevent real echoes from being filtered out of the signal. In addition, the duration of the settling time td is reconstructed when the apparent echo is present. The filtering of the signal is based on this time duration. A blindness detection of the ultrasonic sensor 2 while the membrane 4 is driven and the resonance frequency of the membrane 4 is determined, for example, is not affected. In this way, a cost-effective solution can be provided, with which it can be avoided that bogus echoes are detected.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10136628 B4 [0004]

Claims (12)

Method for operating an ultrasonic sensor ( 2 ) of a motor vehicle in which during a transmission phase, a transmission signal by exciting a membrane ( 4 ) of the ultrasonic sensor ( 2 ) is emitted at an excitation frequency, then during an attenuation phase ( 10 ) the membrane ( 4 ) is excited with an anti-phase to the excitation frequency attenuation frequency and then during a receiving phase ( 11 ) a mechanical vibration of the membrane ( 4 ), wherein during the damping phase ( 10 ) an amplitude of the mechanical vibration of the membrane ( 4 ), characterized in that during the damping phase ( 10 ) determines whether the amplitude has a vibration threshold ( 12 ) for a time duration of a predetermined damping time interval ( 15 ) falls below (S2). Method according to claim 1, characterized in that during the receiving phase ( 11 ) detected mechanical vibration of the membrane ( 4 ) is used as a receive signal, if during the attenuation phase ( 10 ) detected amplitude the oscillation threshold ( 12 ) for the duration of the predetermined damping time interval ( 15 ) falls below. Method according to claim 1 or 2, characterized in that during the receiving phase ( 11 ) the amplitude of the mechanical vibration of the membrane ( 4 ) and a reception time interval ( 16 ), during which the amplitude determines the oscillation threshold ( 12 ) exceeds. Method according to claim 3, characterized in that a difference duration (tu) between an end is a predetermined damping time (td) during which the ultrasonic sensor ( 2 ) in the damping phase ( 10 ) and the reception time interval ( 16 ) is determined. Method according to claim 4, characterized in that during the receiving phase ( 11 ) detected mechanical vibration of the membrane ( 4 ) is used as the receive signal if the time duration of the receive time interval ( 16 ) falls below a reference value and / or the difference duration (tu) falls below a limit value (S4). Method according to Claim 5, characterized in that the predetermined attenuation time (td) is adapted if the duration of the reception time interval ( 16 ) falls below the reference value and / or the difference duration (tu) falls below the limit value. A method according to claim 6, characterized in that the predetermined damping time (td) is adjusted so that the adjusted damping time of a sum of the predetermined damping time (td), the reception time interval ( 16 ) and the difference duration (tu) corresponds to (S5). Method according to one of the preceding claims, characterized in that a current temperature of the ultrasonic sensor ( 2 ) and the damping time interval ( 15 ) is adjusted depending on the detected temperature. Method according to one of the preceding claims, characterized in that the damping time interval ( 15 ) in dependence on an operating state of the ultrasonic sensor ( 2 ) is adjusted. Ultrasonic sensor device ( 1 ) for a motor vehicle, with an ultrasonic sensor ( 2 ) and with a control device ( 6 ) which is adapted to perform a method according to any one of the preceding claims. Driver assistance system with at least one ultrasonic sensor device ( 1 ) according to claim 10.  Motor vehicle with a driver assistance system according to claim 11.

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