EP3146360A1

EP3146360A1 - Method for operating an ultrasonic sensor of a motor vehicle, ultrasonic sensor device, driver assistance system and motor vehicle

Info

Publication number: EP3146360A1
Application number: EP15716814.7A
Authority: EP
Inventors: Michael Hallek; Michael Ludwig
Original assignee: Valeo Schalter und Sensoren GmbH
Current assignee: Valeo Schalter und Sensoren GmbH
Priority date: 2014-05-23
Filing date: 2015-04-17
Publication date: 2017-03-29
Also published as: WO2015176885A1; DE102014107311A1

Abstract

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

Description

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

The present invention relates to a method for operating an ultrasonic sensor of a motor vehicle, wherein during a transmission phase, a transmission signal by exciting a membrane of the ultrasonic sensor with an excitation frequency

is emitted, then during a damping phase, the membrane is excited with an opposite in phase to the excitation frequency damping frequency and then during a receiving phase, a mechanical oscillation of the

Membrane is detected, during the damping phase, an amplitude of the mechanical vibration of the membrane is detected. 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 in

Driver assistance systems, for example, in a so-called parking assistance system used. Today's parking aid systems work according to the echosounding 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 are determined to the object. However, such are

Distance measurement limited in terms of 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 little

Fading time is reached, 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, DE 101 36 628 B4 describes 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. To dampen the membrane vibrations are detected and the membrane in the correct phase

energized opposite to the detected vibrations. In addition, in the context of the damping process, the value of the amplitude and / or the duration of the excitation of the membrane are tracked to the amplitude of the detected membrane oscillation in order to control the

Damping the strength of the remaining membrane vibrations adapt.

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, such as a

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 a

Ultrasonic sensor device, by a driver assistance system and by a

Motor vehicle with the features according to the respective independent

Claims solved. 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. In this case, a transmission signal is emitted by exciting a membrane of the ultrasonic sensor with an excitation frequency during a transmission phase, then during a damping phase, the membrane with a to the Excited frequency excitation frequency opposite phase and then a mechanical oscillation of the membrane is detected during a receiving phase, wherein an amplitude of the mechanical vibration of the membrane is detected during the damping phase. In addition, it is provided that it is determined during the damping phase whether the amplitude falls below a vibration threshold value 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 particular measurement cycles, in which the distance to the object is to be determined, the ultrasonic sensor is in time

operated consecutive phases. In the transmission phase, the membrane of the sensor is excited at a predetermined excitation frequency. For this purpose, the membrane with a corresponding adjusting device, for example a

piezoelectric actuator, are set in mechanical vibrations, so that the membrane 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 one on the

Damping phase Following reception 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 is also an amplitude of the mechanical

Detected vibration of the ultrasonic membrane. For this purpose, again the

Actuating device or the piezoelectric actuator can be used. It is checked for what duration of the detected mechanical vibration a

Vibration threshold exceeds. In addition, it is checked whether the time duration, while the amplitude is exceeded, within a predetermined

Damping time interval is. 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 advantageous if during the receiving phase the

Amplitude of the mechanical vibration of the membrane is detected and a

Receiving interval is determined during which the amplitude of the

Vibration threshold exceeds. 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 one embodiment, a difference duration between an end of a predetermined damping time during which the ultrasonic sensor in the

Damping phase is operated, and determines the reception time interval. 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 may

assume that no echo is received in the present case.

Preferably, the mechanical vibration of the diaphragm detected during the reception phase is used as the reception signal if the time duration of the

Receiving time interval falls below a reference value and / or the difference duration falls below a limit. If the mechanical vibration of the diaphragm detected during the receiving phase is shorter than the predetermined one

Receiving time interval is usually a sham echo and this mechanical oscillation is not detected as a received signal. Even if the time duration between the swinging out and receiving the supposed echo is smaller than the predetermined difference duration, the detected mechanical vibration is not used as a reception 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, initially a predetermined value can be preset. 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

Reception phase begins to be moved backwards. Thus, echoes from the sensor signal can be virtually filtered out.

In particular, the damping time can be adjusted so that the adjusted damping time is equal to a sum of the predetermined damping time, the

Receive time interval and difference duration corresponds. To the original

set damping time so the time duration of the reception 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 are 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, can

For example, a mechanical wear, which usually sets in the course of time, are taken into account.

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

perform inventive method. An inventive driver assistance system comprises at least one

Ultrasonic sensor device. The ultrasonic sensors of the ultrasonic sensor device, for example, in a front bumper and / or in a rear

Be arranged bumper of the motor vehicle. The driver assistance system can be designed, for example, as a so-called parking aid system.

An inventive motor vehicle comprises the inventive

Driver assistance system. The motor vehicle is designed in particular as a passenger car.

The preferred embodiments presented with reference to the process according to the invention

Embodiments 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 are not only in the respectively indicated combination but also in others

Combinations or used alone.

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

Show

1 is 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 shows a digital sensor signal in a further embodiment; and 5 is a flowchart of a method according to an embodiment of the

Invention.

Fig. 1 shows an ultrasonic sensor device 1 in a sectional side view. The ultrasonic sensor device 1 can be part of a driver assistance system of a motor vehicle, for example. This driver assistance system can be used in particular as

Park assist system be formed, in which one or more

Ultrasonic sensor devices 1 at a front and / or at a rear

Be arranged bumper of the motor vehicle. With the help of

Ultrasonic sensor device 1, a distance from the motor vehicle to an object can be determined.

The ultrasonic sensor device 1 comprises an ultrasonic sensor 2

Ultrasonic sensor 2 in turn comprises a housing 3, which may be made of metal or plastic, for example. Furthermore, the ultrasonic sensor 2 comprises a membrane 4, which is made in particular of aluminum. Finally, the ultrasonic sensor 2 comprises an actuating unit 5, which in particular comprises a piezoelectric element. By means of the adjusting unit 5, the membrane 4 can be set in mechanical vibrations. For this purpose, a time-varying electrical voltage is applied to the control unit 5. The membrane 4 of the ultrasonic sensor 2 is excited with a predetermined excitation frequency by means of the setting unit 5, which may in particular be in a range between 40 and 60 kHz, for example at 52 kHz. As a transmission signal ultrasonic waves are thus generated by the membrane 4, which propagate to an object. At the object, the ultrasonic waves are reflected again and get back to the membrane 4.

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 with the actuator 5 and 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 vibration of the membrane 4 should be damped as quickly as possible, otherwise the minimum distances that are detected with the ultrasonic sensor 2 can be reduced. For this purpose, the ultrasonic sensor 2 is operated in an attenuation phase 10 between a transmission phase in which the transmission signal with the diaphragm 4 is emitted and the reception phase 11 in which the reflected signal of the diaphragm 4 is detected, during which the diaphragm 4 is operated with the actuator from one to the excitation frequency in phase opposition damping frequency.

Furthermore, the ultrasound sensor device 1 comprises a control device 6, with which the activation of the ultrasound sensor 2 or the setting unit 5 takes place. The

Control device 6 is also designed to evaluate the mechanical vibration of the diaphragm 4, which is detected with the control unit 5 during the damping phase 10, in the form of sensor signals.

The sensor signals which are evaluated by the control device 6 are shown in FIG. In this case, a first diagram 7 shows an analog sensor signal 9 and the diagram 8 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, the amplitude A1 of the analog sensor signal 9 is plotted. In the diagram 8 on the abscissa also the time t and on the ordinate the amplitude A2 of the digital

Sensor signal 13 applied. The analog sensor signal 9 describes the mechanical oscillation of the membrane 4 during the damping phase 10 and the subsequent receiving phase 11. It can be seen that the amplitude of the oscillation during the damping phase 10 decreases continuously until it falls below a predetermined oscillation threshold value 12. After falling below the

Vibration threshold 12, the ultrasonic sensor 2 in the receiving phase 1 1 are operated. The digital sensor signal 13, which is shown in the graph 8, has, for example, the value 1 when the curve 9 exceeds the oscillation threshold value 12. If the curve 9 falls below the oscillation threshold value 12, the digital sensor signal 13 assumes the value 0.

Fig. 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 shows the case in which the activation of the membrane 4 for damping the mechanical oscillation does not take place in an ideal manner in antiphase to the actual mechanical oscillation of the membrane 4. Here, the mechanical vibration is first damped. After a predetermined time duration, in turn, an increase in the amplitude of the analog sensor signal 9 follows. The amplitude of the analog sensor signal 9 increases in this case such that the oscillation threshold value 12 is exceeded. This is reflected in the digital signal 13 as a signal pulse 14 down. This signal pulse 14 is interpreted by the control device 6 of the ultrasonic sensor device as an echo signal. This supposed echo can also be referred to as a sham echo or as a ghost echo.

In order to avoid the detection of a glimpse, different time intervals and threshold values for the digital sensor signal 13 are predefined within the control device 6. This is illustrated in FIG. 4. For the damping time td, after which the damping phase 10 has ended, a minimum decay time t1 and a maximum decay time t2 are specified. The minimum settling time t1 and the maximum settling time t2 thus limit a predetermined damping time interval 15. In addition, a reference value for a reception time interval 16 is specified. The reception time interval 16 corresponds to the time duration during the mechanical oscillation of the diaphragm 4 during the reception phase 1 1

Vibration 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 flow chart of a method according to the invention for operating an ultrasound sensor 2. The method is started in a step S1 for each measurement cycle of the ultrasound sensor 2. In a step S2, an amplitude of the mechanical vibration of the membrane 4 is detected via the damping phase 10. 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. In this case, it is checked whether the time 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 of the Sum of the previous settling time td, the difference duration tu and the

Receive time interval 16 corresponds. In addition, the detected ticket echo is deleted in the control device 6.

In this way, an echo detected by the control device 6 is only considered 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, during which the membrane 4 is driven and the resonance frequency of the membrane 4 is determined, becomes characterized

for example, not affected. In this way, a cost-effective solution can be provided, with which it can be avoided that bogus echoes are detected.

Claims

claims

1 . Method for operating an ultrasonic sensor (2) of a motor vehicle, in which during a transmission phase a transmission signal is emitted by exciting a membrane (4) of the ultrasonic sensor (2) with an excitation frequency, then during a damping phase (10) the membrane (4) with a is excited to the excitation frequency antiphase damping frequency and then a mechanical oscillation of the membrane (4) is detected during a receiving phase (1 1), wherein during the damping phase (10) an amplitude of the mechanical vibration of the membrane (4) is detected, characterized that

is determined during the damping phase (10), whether the amplitude of a

Oscillation threshold value (12) for a time duration of a predetermined damping time interval (15) falls below (S2).

2. The method according to claim 1,

characterized in that

the mechanical vibration of the diaphragm (4) detected during the reception phase (1 1) is used as a reception signal if the amplitude detected during the damping phase (10) falls below the oscillation threshold value (12) for the duration of the predetermined damping time interval (15).

3. The method according to claim 1 or 2,

characterized in that

during the reception phase (1 1), the amplitude of the mechanical vibration of the diaphragm (4) is detected and a reception time interval (16) is determined during which the amplitude exceeds the oscillation threshold value (12).

4. The method according to claim 3,

characterized in that

a difference duration (tu) between an end of a predetermined one

Damping time (td), during which the ultrasonic sensor (2) is operated in the damping phase (10), and the receiving time interval (16) is determined.

5. The method according to claim 4,

characterized in that

the mechanical vibration of the membrane (4) detected during the reception phase (1 1) is used as the reception signal if the time duration of the reception time interval (16) falls below a reference value and / or the difference duration (tu) falls below a threshold value (S4).

6. The method according to claim 5,

characterized in that

the predetermined damping time (td) is adjusted if the time duration of the reception time interval (16) falls below the reference value and / or the

Difference duration (tu) falls below the limit.

7. The method according to claim 6,

characterized in that

the predetermined damping time (td) is adjusted so that the adjusted damping time is a sum of the predetermined damping time (td),

Receive time interval (16) and the difference duration (tu) corresponds to (S5).

8. The method according to any one of the preceding claims,

characterized in that

a current temperature of the ultrasonic sensor (2) is detected and the

Damping time interval (15) is adjusted as a function of the detected temperature.

9. The method according to any one of the preceding claims,

characterized in that

the damping time interval (15) is adjusted in dependence on an operating state of the ultrasonic sensor (2).

10. An ultrasonic sensor device (1) for a motor vehicle, comprising an ultrasonic sensor (2) and a control device (6), which is designed to carry out a method according to one of the preceding claims.

1 1. Driver assistance system with at least one ultrasonic sensor device (1) according to claim 10.

12. Motor vehicle with a driver assistance system according to claim 1 1.