GB2496296A

GB2496296A - Sensing the environment of a vehicle by means of ultrasound

Info

Publication number: GB2496296A
Application number: GB1219374.4A
Authority: GB
Inventors: Thomas Treptow
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-10-27
Filing date: 2012-10-26
Publication date: 2013-05-08
Also published as: GB201219374D0; DE102011085286A1; FR2982034A1

Abstract

A method for sensing the environment of a vehicle 1 by means of ultrasound, ultrasonic pulses 20, 30 being emitted and the ultrasonic echoes 24, 34 reflected on objects 16, 18 being detected, characterised in that the sensing zone 10 is divided into at least two distance zones 12, 14, the ultrasonic pulses used for sensing in the respective distance zone being emitted independently of each other and being coded by different frequencies. Each ultrasonic pulse 20, 30 may be emitted with a different, selectable amplitude, frequency and pulse length. The scanning rate may be selected for each of the distance zones 12, 14. The scanning rate may be higher in the zones located closer to the vehicle than the zones located further from the vehicle.

Description

Description Title

Method for sensing the environment of a vehicle by means of ultrasound

Prior art

The invention relates to a method for sensinq the environment of a vehicle by means of ultrasound, and to a device for executing the method.

Various driving assistance systems are used in vehicles in order to support the driver in executing various driving manoeuvres. These driving assistance systems include, for example, parking aids, which can autonomously identify parking spaces and guide the vehicle into the parking space. A further example is that of reversing aids, which check the travel path for obstacles during reverse.travel.

Common to all of the systems mentioned is the requirement to acquire an image of the environment that is as accurate as possible, by means of various sensors. Usually1 ultrasonic sensors are used for this purpose. In this -case, a signal is emitted by an ultrasonic sensbr, this ultrasonic signal is reflected by an obstacle and is registered again by a receiver on the vehicle. The distance between the vehicle and the reflector can be calculated from the time that has elapsed between the emitting and the receiving of the signal, and from the known sound propagation velocity.

Known from DE 102 25 614 Al is a circuit arrangement for operating a distance sensor, wherein the distance of a measurement object can be determined from the propagation time of an ultrasonic pulse-In order to increase the measurement rate, successive ultrasonic pulses are emitted with differing frequency. In addition, the time interval between the individual transmission pulses is selected such that no "blind zones" occur. For this purpose, the instants of emission of the pulses with differing frequency are selected such that, for each distance, there are at * least two measurements per total period.

Known from DE 199 01 847 Al is a method in which distance sensors are operated with a time-variable identification, in order to prevent influences of other sources upon the measurement accuracy. For the purpose of impressing the different time-variable identification, the electrical signal for operating the ultrasonic sensor is modulated.

The modulation can be realized, for example, as frequency modulation over a plurality of wave trains.

Environment sensing requires a high scanning rate with, at the same time, a long range. In the case of driving past a parking space, for example, the scanning rate determines the accuracy with which the length of the parking space can be measured. For example, in the case of a scanning rate of 50 Hz, there is a resultant time interval of 20 ins between ultrasonic pulses. A vehicle travelling at a speed of 50 kin/h covers a distance of approximately 28 cm in this time period, with the result that the measurement resolution is limited. The length of the parking space cannot be determined with greater precision. The range of the measuring device, in turn, limits the distance in which obstacles and/or objects delimiting a parking space can be detected.

In comparison with methods in which only pulses having one frequency are used, the known methods for distance measurement by means of ultrasound, in which ultrasonic pulses having differing frequencies are emitted, can increase the scanning rate, but the range cannot be increased by means of these methods.

Disclosure of the invention

The invention proposes a method for sensing the environment of a vehicle by means of ultrasound, ultrasonic pulses beinq emitted and the ultrasonic echoes reflected on objects being detected, the sensing zone being divided into at least two distance zones and the ultrasonic pulses used for sensing in the respective distance zone being emitted independently of each other and being coded by differing frequencies, and distance zones located closer to the vehicle being scanned with ultrasonic pulses of lesser energy than distance zones located further from the vehicle.

The sensing zone in this case is the zone in the environment of the vehicle that is covered by a measuring device based on ultrasound. If this sensing zone is divided, for example, into two distance zones, ultrasonic pulses having two differing frequencies are used for scanning the environment of the vehicle.

The two ultrasonic pulses for the respebtive distance zones are emitted independently of each other. In this case, this can be effected by means of the same ultrasonic generator or by means of two differing, separately disposed ultrasonic generators, and can be effected simultaneously or successively. Since the two ultrasonic pulses are each coded with differing frequencies, echoes of the two ultrasonic pulses, which are detected at a receiver, can be assigned unequivocally. In order to increase the range that can be achieved in scanning by means of ultrasonic pulses., the distance zone located further from the vehicle is scanned with ultrasonic pulses of higher energy than the distance zone located closer to the vehicle. As a result, the amplitude of the ultrasonic pulses that decreases as the distance from the ultrasonic generator increases is at least partially compensated, such that even echoes from objects located at a great distance can be detected. The energy of an ultrasonic pulse can be increased by increasing the amplitude and/or by prolonging the pulse duration. An increase 4z the frequency can also increase the energy of an ultrasonic pulse, but, with an increasing frequency, the attenuation of the ultrasonic pulse increases as it is propagated in the air, such that an increase in the frequency of the ultrasonic pulses is not useful in every case. Furthermore, it is also of little use to increase the power of all ultrasonic pulses; by prolonging the pulse duration andlor increasing the pulse amplitude, without consideration of the particular distance zone, since such an increase has associated disadvantages in the scanning rate that can be attained. Thus, an ultrasonic echo cannot be detected in the proximity of the ultrasonic generator in the period of time in which an ultrasonic pulse is emitted, since the amplitude of the directly received ultrasonic pulse is substantially greater than that of an echo. Accordingly, as a pulse duration increases, the time period in which the measuring system cannot receive any echoes also increases. Increasing the amplitude of the ultrasonic pulses also has associated disadvantages. Thus, following the emission of an ultrasonic pulse, the membranes of the ultrasonic generators and receivers continue to oscillate for a certain period of time. In the period of time in which the membranes continue to oscillate, it is possible to receive ultrasonic echoes, but evaluation of the echoes is rendered more difficult, or prevented, *by the natural oscillation of the membrane.

instead of the sensing zone being divided into two distance zones, it can also be divided into any other optional number of distance zones. Use of the method according to the invention enables the energy of the ultrasonic pulses to be set according to the range required. Since this is effected separately for each distance zone, dead time periods, i.e. time periods in which no ultrasonic echoes can be received, are minimized, as a result of which the scanning rate can be increased.

In one embodiment of the method, the scanning rate can be set for each of the at least two distance zones, independently of the other distance zones.

In order that a determination of the distance by means of detection of an ultrasonic echo is unequivocal, it is necessary to wait for a.ceitain length of time, following emission of an ultrasonic pulse, before the next pulse can be emitted. The ultrasonic pulses propagate at sound velocity, which is approximately 343 mIs at 20 °C. If it is to be possible to unequivocally assign an object distance of, for example, 5 m, the time span that elapses between the emission of two pulses must be at least that required by the pulse from the sound source to the object and back to the receiver. In the case of a maximum object distance of 5 rn, the sound must travel 20 m, for which it requires approximately 29 ms1 in the case of a velocity of 343 mIs. In the case of a maximum object distance of 1 m, the ultrasonic pulse must travel 2 m, for which it requires approximately 6 ins. Because of this fact, it is preferred that distance zones located closer to the vehicle be scanned at a higher rate than distance zones located further from the vehicle.

En a further embodiment of the method, the pulse length can be selected for each of the at least two distance zones, independently of the other distance zones.

As already stated above, the power of an ultrasonic pulse can be increased by prolonging the pulse length, as a result of which an ultrasonic echo can still be reliably detected even in the case of an object at a relatively great distance. Since this results in a prolongation of the dead time period, in which no ultrasonic echoes can be received, it is preferred that distance zones located closer to the vehicle be scanned with pulses of a shorter length than distance zones located further from the vehicle.

In a further embodiment of the method, distance zones located closer to the vehicle are scanned with ultrasonic pulses of a lower frequency than zones located further from the vehicle. As a result, distance zones located further from the vehicle are scanned with pulses of a higher frequency, and therefore a higher energy. Since the attenuation of the ultrasonic pulses in the air increases as the frequency increases, -however, it is preferred, in the case of ultrasonic measuring methods, which generally use higher frequencies, to proceed conversely and to scan distance zones located closer to the vehicle with pulses of higher frequency.

In a further embodiment of the method, the pulse amplitudes can be set for each of the at least two distance zones, independently of the other distance zones. As already explained above, owing to the occurrence of dead time periods and the decrease in amplitude as distance is travelled by the ultrasonic pulse, it is preferred that distance zones located closer to the vehicle be scanned with pulses of lesser amplitudes than zones located further from the vehicle.

Also proposed according to the invention is a device for sensing the environment of.a vehicle according to the.

* method that has just been described. The device comprises a control device, at least one ultrasonic generator and at least one ultrasonic receiver, the-at least one ultrasonic generator being set up to emit at least two differing pulses simultaneously and/or successively, each at a * -different frequency, and the at least one receiver being

-B-

set up to simultaneously andlor successively detect ultrasonic echoes having differing frequencies.

Preferably, the at least one ultrasonic generator is set up to emit each ultrasonic pulse with a different selectable amplitude, frequency and pulse length.

Advantages of the invention The invention, by dividing the sensing zone of a device for sensing the environment of a vehicle into at least two distance zones, enables the ultrasonic pulses used for scanning to be optimised such that the maximum distance in which objects can be detected by means of ultrasonic echoes can be increased, without, the necessity of impairing the scanning rate in zones located closer to the vehicle.

For the method according to the invention, there is generally only a requirement for components such as those already being used in the commonly applied methods for sensing the environment of a vehicle by means of ultrasound. The improvement in the range of the measuring method without associated impairment of the scanning in the near zone can therefore be easily integrated into existing systems, for example through a corresponding.update of the software of a control device.

Brief description of the drawings

Exemplary embodiments of the drawing are represented in the drawings and explained more fully in the description that follows.

Figure 1 shows an embodiment of the device according to the invention, in which the environment of a vehicle is scanned by means of ultrasonic pulses, Figure 2. shows a diagram giving outline representations of the ultrasonic pulses for scanning a sensing zone divided into two distance zones.

Embodiments of the invention Figure 1 shows a vehicle that scans its environment by means of a device according to the invention.

On its front, the vehicle 1 has an ultrasonic generator 4 and an ultrasonic receiver 6. The ultrasonic generator 4 and the ultrasonic receiver 6 are connected to a control device 2. A sensing zone 10, which is located in front of the vehicle 1, is scanned by means of the ultrasonic generator 4 and the ultrasonic receiver 6. In the embodiment shown, this sensing zone 10 is divided into two distance zones, being a near zone 14 and a remote zone 12.

By means of the control device 2, ultrasonic pulses 20, 30 are generated and emitted by the ultrasonic generator 4.

If the ultrasonic pulses 20, 30 are incident upon an obstacle 16, 18, an ultrasonic echo 24, 34 is produced, which is picked up by the ultrasonic receiver 6 and processed in the control device 2. The pulses 20 scan the remote zone 12, and are emitted with a higher energy and lower repetition rate than the pulses 30 that scan the near -zone 14. The pulses 20 for the remote zone 12 are emitted at a frequency that differs from that of the pulses 30 for the near zone 14. As a result, the incoming echoes 24 of a remote obstacle 18 that reflects the ultrasonic pulse 20 can be separated from ultrasonic echoes 34 of the ultrasonic pulse 20 that is reflected by a near obstacle 16.

In addition to the embodiment represented in Figure 1, in which the ultrasonic generator 4 and the ultrasonic receiver 6 are realized as separate units, embcdiments are also possible in which the ultrasonic generator and the ultrasonic receiver constitute one unit. In further embodiments of the invention, it is possible for a plurality of ultrasonic generators 4 andultrasonic receivers 6, or conibihed ultrasonic generators and ultrasonic receivers, to be disposed on the vehicle 1, in order to scan the environment behind the vehicle 1 and/or at the sides.

Figure 2 shows a diagram giving outline representations of the ultrasonic pulses for scanning a sensing zone divided into two distance zones.

In the diagram, the pulse amplitude (A) is plotted on the vertical axis, and the time (t) is plotted on the horizontal axis. Represented in the diagram are ultrasonic ulses 20, which are intehded for the remote sensing zone and which are emitted at a frequency fl, and ultrasonic pulses 30, which are intended for the near zone and which are emitted at a frequency f2. In the embodiment represented in Figure 2, the pulses 20 and pulses 30 are ernittedwith the same amplitude, the pulses only being represented with a slight offset on the vertical axis, in order to improve legibility. As can be seen from Figure 2, the ultrasonic pulses 20 have a pulse duration 22 that is greater than the pulse duration 32 of the pulses 30.

Likewise, it can be seen from the representation that the time span 21 between the emission of two pulses 20 is greater than the time span 3]. between the emission of two pulses 30.

since the energy of a pulse increases with the pulse duration, it follows from Figure 2 that the pulses 20, which are intended for the remote zone, are emitted with a higher energy than the pulses 30, which are intended for the near zone. Likewise, it follows from Figure 2 that the repetition rate of the pulses, and therefore the scanning rate, for the pulses 30 is higher than for the pulses 20.

Accordingly, the near zone is scanned at a higher rate than the remote zone.

The invention is not limited to the exemplary embodiments described here and to the aspects emphasized therein.

Rather, a multiplicity of modifications, which come within the scope of activity of persons skilled in the art, are possible within the ambit specified by the appended claims.

Claims

<claim-text>-12 -Claims 1. Method for sensing the environment of a vehicle (1) by means of ultrasound, ultrasonic pulses (20, 30) being emitted and the ultrasonic echoes (24, 34) reflected on objects (16, 18) being detected, characterized in that the sensing zone (10) is divided into at least two distance zones (12, 14), the ultrasonid pulses (20, 30) used for sensing in the respective distance zone being emitted independently of each other and being coded by differing frequencies.</claim-text> <claim-text>
2. Method according to Claim 2, characterized in that distance zones (12, 14) located closer to the vehicle are scanned with ultrasonic pulses (20, 30) of lesser energy than distance zones (12, 14) located further from the vehicle (1).</claim-text> <claim-text>
3. Method according to Claim 1 or 2, characterized in that the scanning rate can be selected for each of the at least two distance zones (12, 14), independently of the other distance zones (12, 14)
4. Method according to claim 3, characterized in that distance zones (22, 14) located closer to *the vehicle (1) are scanned at a higher rate than distance zones (12, 14) located further from the vehicle (1)
5. Method according to any one of Claims 1 to 4, characteried in that the pulse length (22, 32) can be selected for each of the *at least two distance zones -13 - (12, 14) , independently of the other distance zones (12, 14).
6. Method according to Claim 5, characterized in that distance zones (12, 14) located closer to the vehicle (1) are scanned with ultrasonic pulses of a shorter length (22, 32) than distance zones (12, 14) located further from the vehicle (1) -
7. Method according to any one of Claims 1 to 6, characterized in that distance zones (12, 14) located closer to the vehicle (1) are scanned with ultrasonic pulses of a higher/lower frequency than distance zones (12, 14) located further frcm the vehicle (1)
8. Method according to any one of Claims 1 to 7, characterized in that the pulse amplitude (A) *can be set for each of the at least two distance zones (12, 14), independently of the other distance zones (12, 14).
9. Method according to Claim 8, characterized in that distance zones (12, 14) located closer to the vehicle (1) are scanned with ultrasonic pulses of lesser amplitude (A) than distance zones (12, 14) located further from the vehicle (1) .
10. A method for sensing the environment of a vehicle (1) substantially as herein described with reference to the accompanying drawings.-. 14 -
11. Device for sensing the environment of a vehicle (1) according to a method according to any one of Claims 1 -to 10, comprising a control device (2), at least one ultrasonic generator (4) and at lbast one ultrasonic receiver (6) , the at least one ultrasonic generator (4) being set up to emit at least two differing ultrasonic pulses (20, 30) simultaneously and/or successively, each at a different frequency, and the at least one ultrasonic receiver (6) beinq set up to simultaneously and/or successively detect ultrasonic pulses (20, 30) having differing frequencies.
12. Device according to Claim 11, characterized in that the at least one ultrasonic generator (4) is set up to emit each ultrasonic pulse (20, 30) with a different, selectable amplitude, frequency and pulse length.
1-3. A device for sehsing the environment of a vehicle (1) substantially as herein described with reference to the accompanying drawings.</claim-text>