GB2539798A

GB2539798A - Method and device for the detection of objects in the environment of a vehicle

Info

Publication number: GB2539798A
Application number: GB1609309.8A
Authority: GB
Inventors: Klotz Albrecht; Pampus Christian; Schumann Michael
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2015-05-29
Filing date: 2016-05-26
Publication date: 2016-12-28
Anticipated expiration: 2036-05-26
Also published as: GB201609309D0; FR3036809B1; GB2539798B; CN106199614A; FR3036809A1; DE102015209878B3; CN106199614B

Abstract

A method for the detection of objects (fig.2, 26) in the environment of a vehicle (1). An ultrasonic sensor (16, 18) emits ultrasonic pulses (52) and receives echoes back has a range (20), in which it can recognise objects (26) via the reflected echoes (56); ultrasonic echoes with an amplitude above an adaptive threshold value are classed as an echo of an object. The threshold value (fig.5, 42, 44) is dynamically selected so that a predetermined rate of ground echoes (54) or constant false alarm rate (CFAR) is erroneously classed as an echo of an object and a tracking filter is used to filter out stochastically occurring ground echoes. An optimal filter may be used to filter out Doppler-shifted ground echoes and CHIRP modulation may be applied to the transmitted signal. Trilateration may also be used to determine the position of objects where sensor beams overlap. The method and device may be used in a driver assistance system.

Description

Description Title

Method and device for the detection of objects in the 5 environment of a vehicle The invention relates to a method for the detection of objects in the environment of a vehicle with at least one ultrasonic sensor, wherein the at least one ultrasonic sensor emits ultrasonic pulses and receives back reflected ultrasonic echoes. Other aspects of the invention relate to a device for execution of the method, a driver assistance system comprising such a device and a vehicle comprising such as driver assistance system.

Prior art

In the automotive field, various driver assistance systems are used that are intended to support the driver when executing various driving manoeuvres. These include parking assistance systems, for example, which detect the environment by means of sensors assigned to the vehicle, determine possible parking spaces in the environment and support the driver in parking. Another driver assistance system warns the driver of objects that are located in the blind spot, for example.

For their function the driver assistance systems require data about the surroundings of the vehicle, wherein a plurality of sensors, in particular ultrasound-based sensors, are used for this. The ultrasound-based sensors emit ultrasonic signals and receive echoes reflected by objects in the environment. The distance between the sensor and the reflecting object is calculated from the runtime of the ultrasonic signal as well as the known velocity of sound in air. A sensor of this kind has a visual range within which it can recognise objects. The visual range is given on the one hand by the radiation characteristics of the ultrasonic transducer. The sound is emitted in the form of a sonic beam, which has a certain beam angle. The beam angle of the sensors defines a range here in which the sound pressure has fallen to -3 dB with reference to the sound pressure measured on the main axis of the sensor. The beam angle of the sonic beam is dependent here on physical factors such as the size of the membrane and the configuration of the acoustic horn as well as on the ultrasonic frequency used, wherein larger beam angles are achieved for lower ultrasonic frequencies.

In addition to the beam angle of the sonic beam, the characteristic curve used, which represents a time-dependent threshold value, is decisive for the visual range of the ultrasonic sensor. Only ultrasonic echoes with an amplitude lying above this threshold value are recognised by the sensor as an echo. This threshold value and the characteristic curve are selected as a function of time in order to mask out frequently occurring reflections of the ultrasound from the road or ground, called ground echoes below, in a certain time window or distance range. The provision of such a time-dependent threshold value is known from DE 196 45 339, for example.

If the threshold value selected is too low, too many ground echoes are erroneously recognised as an object. If the threshold value selected is too high, on the other hand, the visual range of the sensor is severely restricted, as weaker ultrasonic echoes from objects located at the edge of the sonic beam are no longer registered.

A method is known from DE 103 23 639 Al for the detection of an object with adaptive adjustment of detection properties of a detection device. The detection device is first operated at maximum range and sensitivity. If it is established that disturbance data, for example sporadic reflections from loose chippings, is detected with the set detection parameters, the characteristic curve parameters of the detection device are changed, wherein the detection range is reduced spatially in size until no stochastic disturbance data is detected any longer.

A driver assistance system is known from DE 10 2004 047 485 Al with sensors for measuring a parking space. It is provided here not only to evaluate a single echo detected by the sensors. Instead several echo signals are identified in the received signal of a sensor and are used for an evaluation. The echo signals are evaluated by means of a tracking filter, wherein echo signals that are attributable to ground reflections are filtered out.

DE 10 2011 075 484 Al describes a method for improving the range of an ultrasonic measuring system. Emitting modulated signals and detecting them again is described here. It is proposed in this case to use an optimal filter, wherein optimal filters adapted for various velocities are used in each case.

A method and a device for determining the distance of objects are known from DE 102 59 902 Al. It is provided in this case to subtract an empty signal when evaluating received signals. The empty signal contains disturbance components such as clutter and noise. Furthermore, an adaptive adjustment of the threshold value is undertaken for detection. In the adjustment, a predetermined false alarm rate is permitted.

The optimal choice of the threshold value dictates the visual range of an ultrasonic sensor. A disadvantage of the known prior art is that no optimisation of the threshold value takes place with respect to a large visual range of the ultrasonic sensor.

Disclosure of the invention

A method for the detection of objects in the environment of a vehicle with at least one ultrasonic sensor is proposed, wherein the at least one ultrasonic sensor emits ultrasonic pulses and receives back reflected ultrasonic echoes. The at least one ultrasonic sensor has a visual range in which it can recognise objects via reflected echoes, wherein a threshold value is provided for masking out ground echoes, wherein ultrasonic echoes with an amplitude above the threshold value are classed as an echo of an object. It is also provided that an adaptive adjustment of the threshold value is undertaken, wherein the threshold value is selected so that a predetermined rate of ground echoes is permitted, which are erroneously classed as an echo of an object and ground echoes are filtered out from the ultrasonic echoes classed as echoes of an object, wherein a) a tracking filter is used to filter out stochastically occurring ground echoes and/or b) an optimal filter is used to filter out Doppler-shifted ground echoes.

In the method it is provided to specify the threshold value in such a way that the visual range of the at least one ultrasonic sensor is as large as possible. To do this, the threshold value selected must be as small as possible. The threshold value is normally selected so that no ground echoes are erroneously classed as an echo of an object. The threshold value is time-dependent, wherein this assumes its maximum in a time range in which the probability of ground echoes is at its highest.

For the detection of objects the time-dependent echo signal of an ultrasonic echo is compared with the likewise time-dependent threshold value. If the amplitude of the echo signal exceeds the amplitude of the threshold value, the received ultrasonic signal is classed as an echo of an object.

In the proposed method it is provided to reduce the threshold value targetedly so far that a predetermined rate of ground echoes has an amplitude above the threshold value and are thus initially classed as an echo of an object. In this case the threshold value is not set fixedly, but is adjusted in ongoing operation. This means, for example, that the threshold value is reduced from a predetermined starting value until the predetermined rate of ground echoes classes as an echo of an object is reached. The term rate is understood in this case as the number of ground echoes that for each ultrasonic pulse emitted by the ultrasonic sensor has an amplitude greater than the threshold value and is thus erroneously classed as an echo of an object. If on every tenth ultrasonic pulse emitted a ground echo is registered as an echo of an object, for example, the rate is 0.1 or 10%. If from a statistical viewpoint a ground echo is registered as an echo of an object for every ultrasonic pulse emitted, the rate is 1 or 100-. The rate can also be greater than 1 or 100. In this case the amplitude of the echo signal exceeds the threshold value more than once, wherein a distance from the ultrasonic sensor can be assigned via the runtime of each instance of the threshold value being exceeded. If the rate of ground echoes is greater than the preset value, the threshold value is accordingly increased again. To adjust the threshold value, any adjustment method known to the person skilled in the art can be used. For example, known methods from radar technology such as CFAR (constant false alarm rate) and CA-CFAR (cell-averaging constant false alarm rate) can be used. For the operation of a typical driver assistance system such as a blind spot assistant or a parking assistant, for example, it is necessary, however, that ground echoes are reliably masked out, since classing of a ground echo as an object during a parking process, for example, could trigger a braking intervention and in the case of a blind spot assistant it could result in an unjustified warning. It is therefore provided to carry out filtering linked to the detection of the echoes.

In the filtering, according to variant a) a tracking filter is used to filter out stochastically occurring ground echoes. It is checked by the tracking filter how the echo behaves over a greater timespan. For example, if an echo only occurs sporadically, meaning that it is recognised only once and does not occur again in following ultrasonic pulses, then it is highly probable that it is a disturbance that must be filtered out. Furthermore, it is preferably checked by the tracking filter how the distance calculated from the runtime of the ultrasonic signal behaves. If the calculated distance remains constant, although a vehicle to which the ultrasonic sensor is assigned has moved in the meantime, it is highly probable that it is a ground echo. If several ultrasonic sensors are arranged distributed on the vehicle and if their visual ranges overlap at least partially, then the plausibility of measuring results of one ultrasonic sensor can be checked by way of measuring results of other ultrasonic sensors. For example, if adjacent ultrasonic sensors also detect echoes, the calculated distance of which likewise does not change on movement of the vehicle, the probability of the presence of a ground echo increases sharply. If the visual ranges of at least two ultrasonic sensors overlap at least partially, trilateration can be carried out for objects recognised, wherein during the filtering of objects with the tracking filter not only the relative distance from the vehicle but also the direction is used. If the distance and direction of an object in front of or behind the vehicle do not change in spite of the vehicle's own movement, this is a ground echo, which has to be masked out, and is therefore filtered out.

The emitted ultrasonic signals are preferably modulated.

To do this, chirp signals are used, for example, meaning signals of a certain duration within which the frequency is varied. In a chirp-up signal, for example, the ultrasonic frequency is raised continuously, while in a chirp-down signal the frequency is continuously lowered.

To mask out disturbances, it is preferably provided to use an optimal filter (matched filter), which is set to the modulated signal. It is easily possible to filter out signals with a shape or modulation that does not correspond to the modulated signal emitted by means of the optimal filter. Ground echoes that represent reflections of the ultrapulses emitted cannot be filtered out initially using this, as these likewise have the modulation. However, if the vehicle moves, the so-called Doppler effect occurs, which leads to a frequency shift of the ultrasonic signals. The Doppler effect acts in a direction-dependent manner in this case, wherein ultrasonic echoes that are received parallel to the driving direction are maximally subject to the Doppler shift, while for ultrasonic echoes that are received perpendicular to the driving direction, the Doppler effect does not occur. The Doppler shift can be utilised to filter out ground echoes targetedly via a suitably adjusted optimal filter. Use is made in this case of the fact that ground echoes normally occur directly ahead of the front of the vehicle or directly behind the rear of the vehicle, meaning that the ground echoes occur parallel to the driving direction and are thus entirely subject to the Doppler effect.

It is therefore preferred to modulate the emitted ultrasonic pulses and to set up an optimal filter to let through the modulated signals without a Doppler shift. As the vehicle speed increases and thus the Doppler effect increases, the visual range of the ultrasonic sensors is divided increasingly into a range that lies substantially perpendicular to the driving direction and a range that lies substantially parallel to the driving direction. As the vehicle speed increases, more and more echoes that occur from the range parallel to the driving direction are masked out. Echoes from the range perpendicular to the driving direction, on the other hand, can pass the filter.

The bandwidth of the modulated ultrasonic pulses is preferably increased as the vehicle speed increases. In the case of a chirp signal, the bandwidth describes the frequency interval within which the frequency of the ultrasonic pulse is varied. Enlarging the bandwidth reduces the selectivity of the optimal filter, so that the attenuation of echoes that occur parallel to the driving direction is not too great and echoes from objects that lie directly in the driving direction can still be detected.

The visual range of the ultrasonic sensor can be controlled by selection of the bandwidth of the modulated ultrasonic pulses as well as adjustment of the corresponding optimal filter. If a visual range that is limited to an area perpendicular to the driving direction is desired, the bandwidth of the modulated ultrasonic pulses is reduced. If on the other hand it is desired that the visual range of the ultrasonic sensor also extends to an area in the driving direction, the visual range can be expanded in that the bandwidth of the modulated ultrasonic pulses is increased. For example, the bandwidth is varied by 1 kHz to 10 kHz, wherein the carrier frequency of the ultrasound emitted typically lies in the range from 40 kHz to 60 kHz.

In particular, the filtering by tracking filter with trilateration and an adjustment of the bandwidth of modulated ultrasonic pulses can also be combined. If an echo is registered by an ultrasonic sensor oriented in the driving direction, for example, but trilateration fails due to the fact that the echo is not detected by the adjacent ultrasonic sensors, then it must be either a ground echo or an object that lies in the centre of the visual range of the ultrasonic sensor, thus an object that is located directly in front of or behind the vehicle. The ground echoes affected by the Doppler effect are suppressed increasingly by the optimal filter by a sequence of modulated ultrasonic pulses in which the bandwidth is reduced from ultrasonic pulse to ultrasonic pulse. A combination of tracking filter with trilateration and an adaptation of the bandwidth of modulated ultrasonic pulses can thus be carried out in that in a first filter step, a trilateration of an echo is carried out by means of adjacent ultrasonic sensors and, if the trilateration is not possible, in a second filter step modulated ultrasonic pulses are emitted with a bandwidth reduced from pulse to pulse, wherein ultrasonic echoes that are no longer recognised in the case of ultrasonic pulses with a reduced bandwidth are classed as ground echoes and filtered out.

The adaptation of the threshold value is preferably carried out as a function of the speed of the vehicle.

The adaptation of the threshold value is preferably carried out in such a way that when the vehicle is stationary, a rate of 0.1 ground echoes per ultrasonic pulse emitted is attained and this rate even rises to up to 5 ground echoes per ultrasonic pulse emitted as the speed of the vehicle increases. The rate preferably lies at a maximum of 2 ground echoes per ultrasonic pulse emitted and in particular preferably at a maximum of 1 ground echo per ultrasonic pulse emitted. The maximum value is preferably reached at a vehicle speed of 50 km/h.

The visual range of the ultrasonic sensor is determined not only by the threshold value but also by the sound pressure, which declines towards the edges of the sonic beam. In this case a larger beam angle of the sonic beam is attained for lower ultrasonic frequencies, so that a larger visual range of the ultrasonic sensor is set as a consequence. It is therefore preferably provided to set the visual range of the ultrasonic sensor by adjusting the ultrasonic frequency. The ultrasonic frequency is varied preferably within a range of 20 to 80 kHz, preferably from 40 to 60 kHz, especially preferably from 45 kHz to 55 kHz, wherein for lower ultrasonic frequencies larger visual ranges and for higher ultrasonic frequencies smaller visual ranges are achieved accordingly.

Furthermore, the visual range of the ultrasonic sensor is preferably influenced by intervention in the adaptive setting of the threshold value. In this case the visual range is increased by reducing the threshold value and conversely the visual range is reduced by increasing the threshold value.

A beam angle can also be defined for the visual range, wherein this beam angle defines a beam within which an object can be recognised by the sensor. The beam angle of this visual range is accordingly enlarged by the use of low sound frequencies and low threshold values. Within this visual range a further subdivision can also be achieved as described on account of the Doppler effect for a moving car, wherein ultrasonic echoes from an area parallel to the driving direction are strongly attenuated by using a small bandwidth of the modulated ultrasonic pulses in the visual range of the ultrasonic sensor.

Another aspect of the invention is to provide a device for the detection of objects in the environment of a vehicle, which device comprises a control apparatus and at least one ultrasonic sensor. The device is preferably formed and/or configured to execute the method described here. The features described as part of the method apply correspondingly to the device and conversely the features described as part of the device apply correspondingly to the method. In particular, the control apparatus is configured to execute one of the methods described herein.

Furthermore, an aspect of the invention is to provide a driver assistance system, which comprises one of the devices described here for the detection of objects in the environment of the vehicle.

The driver assistance system or the device contained therein for the detection of objects in the environment of the vehicle preferably comprises several ultrasonic sensors, which are each oriented parallel to the driving direction of the vehicle, thus either in or opposite to the driving direction. The driver assistance system is also preferably configured to warn of objects in the blind spot of the vehicle and/or to recognise free parking spaces when driving past.

In a particularly preferred configuration of the driver assistance system, the device has eight ultrasonic sensors, wherein four ultrasonic sensors are oriented in the driving direction and four ultrasonic sensors are oriented opposite to the driving direction.

The invention further relates to a vehicle, which comprises one of the driver assistance systems described here.

Advantages of the invention The visual range of an ultrasonic sensor can be maximised by the proposed method. The visual range of an ultrasonic sensor is determined by its sonic beam as well as the receiving characteristic curve and the threshold value. It is advantageously proposed to adjust the threshold value adaptively. The threshold value is reduced here so sharply that disturbance signals, in particular ground echoes, are permitted at a certain rate. Objects in the environment of a vehicle are nevertheless reliably detected, as filtering is advantageously used that filters out ground echoes erroneously recognised as an echo of an object.

In the proposed method, larger visual ranges with a larger beam angle are thus achieved without modifications to the 10 ultrasonic sensors.

Due to the larger visual range or the larger beam angle, the number of sensors that are required for all-round monitoring of the environment can advantageously be reduced. For example, a sensor arranged on the front of the vehicle can not only detect a distance from an obstruction ahead of the vehicle, but at the same time also measure parking spaces while the vehicle is driving past.

With the aid of the larger visual range of an ultrasonic sensor mounted on the front or on the rear of the vehicle, for example, monitoring of the blind spot can also take place, for example. In particular, a blind spot assistant (SVA, side view assist) can be implemented as a result without additional sensors oriented laterally.

Alternatively or in addition, improved functionality can be achieved with the same number of sensors due to the enlarged visual range. Due to the enlarged visual range of the individual ultrasonic sensors, the visual ranges of adjacent ultrasonic sensors can overlap at least partially. In the overlap area, not only distances but also directions of objects can be determined by trilateration. The quality of the data made available by the environment sensors is significantly enhanced by this.

For example, the accuracy of measurement of a parking space can be significantly increased by this.

Brief description of figures

Figure 1 shows the visual range of ultrasonic sensors of a device from the prior art, Figure 2 shows the visual range of a device according to the invention for the detection of objects in the environment of a vehicle, Figure 3 shows the masking out of ground echoes when the vehicle is travelling, Figure 4a shows a vehicle with 12 ultrasonic sensors, Figure 4b shows a vehicle with 8 ultrasonic sensors and Figure 5 shows the time curve of an adaptively adjusted threshold value.

A device 12' for the detection of objects 26 in the environment of a vehicle 1 according to the prior art is shown in figure 1. The device 12' comprises several ultrasonic sensors 16', 18', wherein in the representation according to figure 1 an ultrasonic sensor 16' is shown by way of example on the vehicle front, which is oriented forwards, and an ultrasonic sensor 18' is shown that is oriented towards the right side. The ultrasonic sensors 16' and 18' are connected to a control apparatus 14'.

In figure 1 it is shown how the vehicle 1 drives past a parking space 24, wherein the dimensions of the parking space 24 are measured by the ultrasonic sensor 18' oriented to the side. The kerb 28, which delimits the parking space 24 to the side, and two objects 26, here parked vehicles, which delimit the parking space 24 to the front and rear, are recognised by the ultrasonic sensor 18'. As is evident from figure 1, the ultrasonic sensor 18' has a visual range 22', which is suitable for measuring the parking space 24. A corresponding visual range 20' of the ultrasonic sensor 16' oriented forwards can recognise the objects 26 that delimit the parking space 24 to the front and rear if applicable, measurement of the depth of the parking space 24 with the ultrasonic sensor 16' is not possible due to the restricted visual range 20'.

In the following description of embodiments of the invention, identical or similar components or elements are designated by identical or similar reference signs, wherein a repeated description of these components or elements is dispensed with in individual cases. The figures represent the object of the invention only schematically.

In figure 2, a vehicle 1 with a device 12 according to the invention for the detection of objects 26 in the environment of the vehicle 1 is shown. The device 12 comprises by way of example two ultrasonic sensors 16, 18, which are arranged in the area of the vehicle front. One ultrasonic sensor 16 is oriented forwards, another ultrasonic sensor 18 is oriented to the side. The ultrasonic sensors 16, 18 are connected to a control apparatus 14.

It can be gathered from the illustration in figure 2 that the ultrasonic sensor 16 oriented forwards has a visual range 20 and the ultrasonic sensor 18 oriented to the right side has a visual range 22. The visual ranges 20, 22 represent the area within which the ultrasonic sensors 16, 18 can recognise objects 26 in the environment of the vehicle 1 by reflected ultrasonic echoes. The visual ranges 20, 22 are markedly enlarged here by reduction of the threshold value that the amplitude of an ultrasonic echo must exceed to be recognised as an echo of an object 26. Due to the enlargement of the visual ranges 20, 22, the ultrasonic sensor 16 oriented forwards is now also able to measure the parking space 24, as this can recognise the two objects 26 delimiting the parking space 24 as well as the kerb 28, which marks the depth of the parking space 24.

It can further be gathered from the illustration in figure 2 that the visual ranges 20, 22 of the two ultrasonic sensors 16, 18 partially overlap in an overlap area 29. In this overlap area 29, trilateration can be carried out, meaning that in the situation represented in figure 2 not only can the distance of the object 26 be determined, but the direction of the object 26 relative to the vehicle 1 can also be determined.

Figure 3 shows the vehicle 1 with the device 12 according to the invention, which comprises two ultrasonic sensors 16, 18 as well as the control apparatus 14. The vehicle 1 continues to move along in a driving direction 50. Ultrasonic pulses 52 are emitted by the ultrasonic sensor 16, which pulses are reflected by objects 26. Echoes 56 reflected by the objects 26 are recognised again by the ultrasonic sensor 16, so that the control apparatus 14 can determine the distance to the object 26 from the signal runtime.

As well as echoes 56 from objects 26 in the environment of the vehicle 1, reflections from the roadway itself can be produced, such as a ground echo 54, for example. If the amplitude of the ground echo 54 is above the threshold value, this is treated initially by the control apparatus 14 as an echo 56 of an object 26. However, for the functioning of driver assistance systems of the vehicle 1 it is necessary to mask out ground echoes 54 reliably.

If the vehicle 1 moves along in the driving direction 50, the ultrasound is subject to the Doppler effect. Ultrasonic pulses or echoes that are parallel to the driving direction SO are displaced in frequency due to the Doppler effect.

It is preferably provided to modulate the ultrasonic pulse 52 emitted, for example in the form of a chirp signal, in which the ultrasonic frequency rises with the time in the case of a chirp-up signal, for example. Filtering is then carried out, wherein an optimal filter is used, which is configured to the modulated chirp signal of the ultrasonic pulse 52. Due to this, separation of the echo 56 of the object 26 from the ground echo 54 is possible, because the object 26 lies in a direction relative to the vehicle 1 that is perpendicular to the driving direction 50. The echo 56 is thus not subject to the Doppler shift. The ground echo 54 in turn is incident on the ultrasonic sensor 16 from a direction that lies parallel to the driving direction 50. The ground echo 54 is thus Doppler-shifted. The filtering used, in particular by means of the optimal filter, can filter out the Doppler-shifted ground echo 54. A tracking filter is then preferably used to filter out other ground echoes 54 on account of the distance and/or position relative to the movement of the vehicle 1.

The filtering can be implemented wholly or partially in the control apparatus 14. The filtering by optimal filter is preferably already carried out by corresponding means in the ultrasonic sensors 16, 18 and the filtering by tracking filter by the control apparatus 14.

Due to the filtering carried out, the visual range 20 of the ultrasonic sensor 16 is substantially divided into two areas 58, 60, wherein a first area 58 lies substantially parallel to the driving direction SO and a second area 60 lies substantially perpendicular to the driving direction 50. Due to the filtering carried out, especially by means of an optimal filter, Doppler-shifted echoes, in particular Doppler-shifted ground echoes 54, are strongly attenuated, so that the visual range 20 of the ultrasonic sensor 16 can be limited substantially to the second area 60 perpendicular to the driving direction 50.

In figures 4a and 4b a vehicle 1 is shown in each case with a driver assistance system 10, which comprises a device 12 according to the invention for the detection of objects 26 in the environment of the vehicle 1. The two execution variants shown of the device 12 differ due to the number of ultrasonic sensors 16-19 in each case.

In the execution variant in figure 4a, the device 12 comprises twelve ultrasonic sensors 16 -19 in all, wherein four ultrasonic sensors 16 are arranged at the front of the vehicle 1 and four ultrasonic sensors 17 are arranged at the rear of the vehicle 1. The ultrasonic sensors 16 and 17 are each oriented parallel to the driving direction, meaning that the ultrasonic sensors 16 point in the driving direction and the ultrasonic sensors 17 point opposite to the driving direction. In addition, two ultrasonic sensors 18 on the front of the vehicle are oriented to the side of the vehicle 1 and two ultrasonic sensors 19 are also provided on the rear of the vehicle 1, which are oriented partially laterally.

In figure 4a, a visual range 20 of an ultrasonic sensor 16 oriented in the driving direction, a visual range 21 of an ultrasonic sensor 17 oriented opposite to the driving direction, a visual range 22 of an ultrasonic sensor 18 oriented to the side and a visual range 23 of an ultrasonic sensor 19 oriented partially laterally are shown by way of example.

The ultrasonic sensors 18 pointing to the side as well as the ultrasonic sensors 19 partially oriented to the side are normally used for monitoring the blind spot and for recognising parking spaces. The ultrasonic sensors 16 and 17 pointing in or opposite to the driving direction are normally used for measuring the distance of the vehicle 1 from obstructions, in particular in connection with parking of the vehicle 1. As can be gathered from the illustration in figure 4a, the visual ranges of the ultrasonic sensors 16 -19 are so large that overlap areas 29 are created.

In the execution variant in figure 4a, the overlap areas 29 are used to improve the quality of the sensor data. 15 Thus the position of an object can be determined by trilateration in the overlap areas 29, for example.

The execution variant Illustrated in figure 4b corresponds to that in figure 4a, wherein the ultrasonic sensors 18 pointing to the side and the partially laterally oriented ultrasonic sensors 19 have been dispensed with, so that the device 12 in figure 4b only comprises eight ultrasonic sensors 16, 17 in all. The respective visual ranges 20, 21 of the ultrasonic sensors extend at least partially to the side, without additional ultrasonic sensors 18, 19 oriented to the side being required, cf. figure 4a. This information can be used in the context of measuring parking spaces or to warn of objects in the blind spot. The vehicle 1 shown in figure 4b, which comprises a driver assistance system 10 with a device 12, can thus warn a driver about objects in the blind spot or recognise free parking spaces when driving along without other ultrasonic sensors having to be arranged.

Figure 5 shows a diagram that represents the time curve of the adaptive threshold value. A time t is entered on the X-axis and an amplitude A on the Y-axis. To be recognised as an echo of an object 26, the amplitude A of an echo signal must be greater than the amplitude of the threshold value.

A typical ground echo signal 30 is entered in figure 5. The ground echo signal 30 has its amplitude maximum here in an area 32. The area 32 corresponds to a time interval or a distance interval relative to an ultrasonic sensor 16, 18.

According to the prior art, a threshold value 40 is normally specified such that the ground echo signal 30, or its amplitude, by no means exceeds the threshold value 40.

As can be gathered from the illustration in figure 4, the threshold value 40 selected in this case is very large, as even in poor road conditions, such as loose chip-Pings, for example, all ground echoes occurring should be reliably masked out.

In addition, an adapted threshold value 42 for a stationary vehicle, meaning a speed of zero, is entered in figure 5. The adapted threshold value 42 lies clearly below the threshold value 40, due to which the sensitivity of the corresponding ultrasonic sensor is significantly increased. This can thus register even ultrasonic echoes that are reflected by objects located at the edge of the sonic beam, at which the sound pressure has already declined markedly. The reduction in the threshold value by the adapted threshold value 42 means that even in isolated instances the amplitude of the ground echo signal 30 can lie briefly above the adapted threshold value 42. The ground echoes that are erroneously classed in this case as an echo of an object are suppressed by subsequent filtering.

In addition, an adapted threshold value 44 is entered in figure 5 for vehicle speeds > 0. This adapted threshold value 44 is again significantly reduced, wherein it is accepted that from a statistical viewpoint, for every ultrasonic pulse emitted the amplitude of the ground echo signal exceeds the threshold value once, and thus one ground echo per ultrasonic pulse emitted is classed as an echo of an object. This high rate of misdetections can be accepted, as at higher driving speeds the ground echoes can occur due to a tracking filter.

As can likewise be gathered from figure 5, all threshold values or curves are time-dependent, wherein their amplitude maximum occurs respectively in the area 32, in which the amplitude of the ground echo signal 30 is greatest. The threshold values or curves fall away both in direction t = 0 and for t to -.

The invention is not restricted to the embodiments described here and the aspects highlighted therein. On the contrary, a plurality of modifications that lie in the scope of expert action is possible in the area indicated by the claims.

Claims

Claims 1. Method for the detection of objects (26) in the environment of a vehicle (1) with at least one ultrasonic sensor (16 -19), wherein the at least one ultrasonic sensor (16 -19) emits ultrasonic pulses (52) and receives ultrasonic echoes back, and the at least one ultrasonic sensor (16 -19) has a visual range (20 -23), in which it can recognise objects (26) via reflected echoes (56), wherein a threshold value (42, 44) for masking out ground echoes (54) is provided, wherein ultrasonic echoes with an amplitude above the threshold value (42, 44) are classed as an echo (56) of an object (26), characterised in that an adaptive adjustment of the threshold value (42, 44) is made, wherein the threshold value (42, 44) is selected so that a predetermined rate of ground echoes (54) is erroneously classed as an echo (56) of an object (26), and ground echoes (54) are filtered out of the ultrasonic echoes classed as echoes (56) of an object (26), wherein a) a tracking filter is used to filter out stochastically occurring ground echoes (54) and/or b) an optimal filter is used to filter out Doppler-shifted ground echoes (54).
2. Method according to claim 1, characterised in that the threshold value (42, 44) is adjusted as a function of the speed of the vehicle (1).
3. Method according to claim 2, characterised in that the adjustment of the threshold value (42, 44) is made in such a way that when the vehicle (1) is stationary, a rate of 0.1 ground echoes (54) per ultrasonic pulse (52) emitted is attained, and this rate rises to up to 5 ground echoes (54) per ultrasonic pulse (52) emitted as the speed of the vehicle (1) increases.
4. Method according to one of claims 1 to 3, characterised in that at least two ultrasonic sensors (16 -19) with at least partially overlapping visual ranges (20 -23) are used, wherein trilateration is carried out for recognised objects (26), and in the filtering objects (26) ahead of and behind the vehicle (1) are discarded if their relative position to the vehicle (1) remains unchanged in spite of a movement of the vehicle (1).
5. Method according to one of claims 1 to 4, characterised in that the ultrasonic pulses (52) emitted by at least one ultrasonic sensor (16 -19) are modulated, wherein the optimal filter is configured to allow the passage of the modulated signals without Doppler shifting.
6. Method according to claim 5, characterised in that the bandwidth of the modulated ultrasonic pulses (52) is enlarged as the speed of the vehicle (1) increases.
7. Method according to claim 5 or 6, characterised in that the visual range (20) of the at least one ultrasonic sensor (16 -19) is set by the selection of the bandwidth of the modulated ultrasonic pulses (52), wherein the visual range (20) is restricted to a second area (60) perpendicular to a driving direction (50) when the bandwidth is reduced and is expanded by a first area (58) in the driving direction (50) when the bandwidth is enlarged.
8. Method according to one of claims 1 to 7, characterised in that the visual range (20 -23) of the at least one ultrasonic sensor (16 -19) is set by the selection of the threshold value (42, 44), wherein the visual range (20 -23) is enlarged by a reduction in the threshold value (42, 44) and conversely the visual range (20 -23) is made smaller by an increase in the threshold value (42, 44).
9. Device (12) for the detection of objects (26) in the environment of a vehicle (1) comprising a control apparatus (14) and at least one ultrasonic sensor (16 -19), characterised in that the device (12) is configured to execute the method according to one of claims 1 to 8.
10. Driver assistance system (10) with a device (12) for the detection of objects (26) in the environment of a vehicle (1) according to claim 9.
11. Driver assistance system (10) according to claim 10, characterised in that the device comprises several ultrasonic sensors (16, 17), wherein the ultrasonic sensors (16, 17) are oriented parallel to the driving direction of the vehicle (1), and that the driver assistance system (10) is configured to warn of objects (26) in the blind spot and/or recognise free parking spaces when driving past.
12. Vehicle (1), characterised in that the vehicle (1) comprises a driver assistance system according to claim 10 or 11.