DE102008002232A1 - Method for measurement of distance or velocity of object relative to vehicle, involves emitting ultrasonic pulse, which is reflected by object - Google Patents

Abstract

The method involves emitting an ultrasonic pulse, which is reflected by an object (H). The ultrasonic pulses are received and echoed back. The transmission of another ultrasonic pulse is triggered by receiving the echoes of a former previously emitted ultrasonic pulse. An independent claim is included for a device for measurement of distance or velocity of an object relative to a vehicle.

Description

The The invention describes a method and a device for determination distance and / or velocity of an object relative to a Vehicle.

State of the art

in the Range driver assistance systems for motor vehicles came In the past, ultrasonic sensors preferred piezoelectric Basis for use, but almost exclusively in different Einpark functions. It is with a pulse-echo method the Duration of ultrasonic pulses measured at obstacles in the Detection area are reflected. The information thus obtained of the four to six sensors installed per bumper become algorithmically according to the triangulation principle in a central Control unit evaluated so that the distance of the vehicle to the nearest obstacle can be determined. This System consisting of up to twelve ultrasonic sensors and one central Control unit is often referred to as ultrasound system.

at conventional ultrasonic systems, especially in conventional Ultrasonic-based parking aids (US-EPH), are the essential system features the same in every present situation, once before commissioning the parameters of the ultrasound system to the specific geometric Characteristics of the vehicle were adjusted. Although it takes place depending on the situation an assignment to specific special cases takes place in the control unit, however, they do not affect the system properties, such as for example, the cycle time between two consecutive Transmit pulses passes, or to the length or the amplitude of the Transmission pulse. Instead, in any present situation - before an imminent accident just as in any static parking situation - always same send-receive operation, which optimizes the function "parking" is.

For the use in dynamic situations, ie in the current traffic, However, such an ultrasound system is not sufficient. Though is also in principle with the help of such a conventional US EPH possible, the relative speed between the vehicle and Obstruction indirectly, by pursuing the Change of several consecutive distance information. Here, however, the problem arises that the speed information too rare for the requirements of dynamic functions to be updated. Reason for this is an average constant time interval (PRI = Pulse Repetition Interval) between two transmit pulses. The PRI usually depends on this from the desired range coverage and from the speed of sound the present temperature. Hereby the on average constant becomes time interval between two transmit pulses therefore chosen to detect obstacles with each pulse to the end of the measuring range to be able to. With a conventional US EPH is no satisfactory assessment of dynamic situations possible.

A certain progress could already be made in this respect in the DE 103 23 144 A1 describe described device for detecting objects in the vicinity of a vehicle. This device is specially optimized for the detection of objects in the blind spot of a vehicle, where the ultrasound system due to the proximity of the object and the dynamic driving situation for warning a driver in case of impending collision with an object in the blind spot only a small reaction time is available. In this device, the frequency with which ultrasound pulses are emitted for scanning the surroundings of the vehicle, ie the sampling rate, is adapted to the distance of the vehicle to an obstacle which has been determined by receiving an already previously emitted ultrasonic pulse. In particular, the smaller the distance between the vehicle and the obstacle, the more ultrasonic pulses are emitted per unit of time. By the device of DE 103 23 144 A1 Thus, the time resolution of the distance measurement can be increased with decreasing distance between the vehicle and the obstacle.

Advantages of the invention

By The present invention will be an adaptive method and a Device for accelerated and reliable determination distance and / or velocity of an object relative to created a vehicle, which is even better for use are suitable in dynamic situations. It is in particular with increasing shortening of the distance between the vehicle and obstacle at small distances (eg below 3 meters) possible, to increase the sampling rate in an optimal way and at the same time with little circuitry and software engineering effort automatically adapt to the obstacle distance.

basic idea The present invention is an event-triggered, ie event-triggered Emission of ultrasound pulses. This differs from the present one Invention of the methods described above, which on a time triggered emission of ultrasound pulses based.

According to a first embodiment of this In accordance with the invention, a method is proposed for determining the distance and / or velocity of an object relative to a vehicle in which ultrasound pulses are emitted, reflected by the object and received again as an echo, wherein the transmission of a second ultrasound pulse by the reception of the echo a previously emitted first ultrasonic pulse is triggered. This method makes it possible to automatically adjust the sampling rate to the obstacle distance, because the sound propagation time between the vehicle and the obstacle (emitted ultrasonic pulse) or obstacle and vehicle (echo) becomes smaller with decreasing distance at a constant speed of sound.

Preferably is the previously transmitted first ultrasonic pulse of the immediate ultrasonic pulse emitted before the second ultrasonic pulse. Thereby In particular, this allows the sampling rate to be automatic to the approach situation of the nearest one Obstacle is adjusted because with decreasing obstacle distance at constant speed of sound the time between sending an ultrasonic pulse and the reception of his reflected from the obstacle Echoes gets smaller.

Preferably the emission of the second ultrasonic pulse takes place directly in time after receiving the echo of the previously transmitted first ultrasonic pulse. This allows the sampling rate to become shorter as the obstacle distance becomes shorter be increased optimally, as there is no delay between the receipt of the echo of the previously transmitted first ultrasonic pulse and the emission of the second ultrasonic pulse comes.

According to one Particularly advantageous embodiment of the invention is characterized by the Emitting an ultrasonic pulse, receiving its echo and the evaluation of this echo by means of an evaluation in one electroacoustic circuit defines a measuring cycle with one cycle time, wherein a currently running measurement cycle upon receipt of a following Echo is interrupted and a new measurement cycle is started. Preferably, when starting the new measurement cycle another Ultrasound pulse emitted. But it is just as possible to wait for several echoes before starting a new measurement cycle. With this type of triggering, the cycle time automatically starts adjusted the distance of the obstacle to the vehicle. This instant Adjusting the cycle time also provides an optimally fast Reaction to the changed circumstances of the dynamic Situation. In comparison, this is done in the conventional time-triggered methods regardless of the term the ultrasonic pulses and their echoes always a complete Passing a measuring cycle. In addition, in these conventional systems always have an indirect adaptation of the system next following measurement cycle based on the results the distance measurement from the previous measurement cycle. Thereby This measuring cycle adjustment always lags by the duration of one cycle time afterwards, resulting in a total sluggish adaptation of the Cycle time leads.

Preferably becomes with expiry of a predetermined maximum allowed cycle time a timed triggered ultrasound pulse, if so far no echo was received. This is used in an advantageous manner Securing the method according to the invention for the case of a signal loss. It will be after expiration of a maximum Cycle time a time triggered signal emitted when until there was no echo event detected. This time interval preferably defines the lower limit frequency of the system that in the following also idle frequency is called. in case of a Signal abort, so the failure or non-detection of a or more ultrasonic echoes, so are ultrasonic pulses with the idling frequency, ie with a minimum frequency or frequency of sending, which is slightly below the orbit frequency the maximum detection distance is around these two cases to distinguish from each other. The system is running then at least in the conventional, time-triggered mode.

Preferably is the frequency of emission of ultrasound pulses per unit of time also limited upwards. This allows a maximum rotation frequency be fixed, reducing the stability of the scheme the cycle time can be guaranteed particularly well. In this way, rocketing avalanches of echoes are avoided and the broadening of the echo at jagged obstacles performs as desired only to a simple release the next ultrasonic pulse.

Furthermore it is advantageous if the signal length and / or the maximum Signal amplitude of each ultrasonic pulse to be transmitted as a function of of properties of the echo of a previously emitted ultrasonic pulse, such as echo time, echo length and / or echo amplitude, is or will be elected. This adaptation of the sent Ultrasonic pulses by adaptation to the reflection properties and / or to the distance to the nearest obstacle the increase in signal reliability in reception the echoes reflected back from the obstacle.

According to a further advantageous embodiment of the present invention, at least one ultrasonic sensor is used, which can be operated both in the transmission mode and in the reception mode, wherein the different of the ul Ultrasound pulses emitted by ultrasound sensors differ in the modulation of their transmission frequency or transmission amplitude. The simultaneous or quasi-simultaneous operation of a single ultrasonic sensor as a transmitter and receiver is possible in implementation of the feedback by software algorithms and represents an advantageous saving of hardware, which makes sense especially due to the cramped installation situation in a vehicle bumper. In addition, the ultrasonic sensors can be operated in parallel, ie simultaneously, due to the distinctness of their emitted ultrasonic pulses, which is effective and time-saving. With sequential operation of the ultrasonic sensors, the time required increases proportionally with the number of sensors. Ie. In a typical system with four sensors, the time required is therefore about four times higher.

corresponding for the embodiment of the invention in the form of a method is a Device for determining distance and / or speed an object relative to a vehicle proposed, comprising Means for emitting ultrasonic pulses and for receiving the echoes reflected by the object, means being provided for control (C) which are set up, the means for sending (S, S + E) of ultrasonic pulses upon receipt of the echo of a previously emitted first ultrasonic pulse for emitting a second ultrasonic pulse to trigger.

Preferably the device according to the invention comprises means to evaluate the received echoes within a measuring cycle with a cycle time, with the means for control being set up, a currently running measurement cycle when receiving the next To interrupt echoes and start a new measurement cycle, in which preferably a further ultrasonic pulse is emitted.

In terms of the technical effects and advantages of the subject matter Features of this device will be explicit on the designs referenced to the method described above, which fully be referred to.

Further Features and advantages of embodiments of the invention will be apparent from the following description with reference to the attached figures.

Brief description of the figures

It demonstrate:

1a and 1b a schematic, exemplary representation of the device according to the invention in a dynamic situation with decreasing distance to an obstacle;

2 a first advantageous embodiment of the device according to the invention;

3 a second advantageous embodiment of the device according to the invention; and

4 a third advantageous embodiment of the device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS invention

A simple and at the same time efficient realization of an event-triggered measurement, as proposed by the present invention, is a so-called electroacoustic circuit with a transmitter S and a receiver E, as described in US Pat 1 is specified.

In the 1a and 1b schematically illustrates the situation for two different obstacle distances d _a and d _b . The evaluation unit A and the control unit C control the ultrasonic transmitter S via an amplifier. As a result of the activation, the transmitter S emits an ultrasonic pulse (burst) which strikes an obstacle H at a distance d _a and is reflected there. The ultrasonic echo hits the receiver E. There, it is then amplified and forwarded to the evaluation unit A, where it is further processed. If the received echo has successfully passed through the plausibility check of the evaluation unit A, a new transmission pulse is triggered and the cycle in the electroacoustic circuit starts again. At the evaluation unit A, it is possible to measure the transit time T _a , which requires a pulse in the electroacoustic circuit. This time T _a is characteristic of the object distance d _a . In the 1b it is shown how the distance d _a to the obstacle H has decreased to the distance d _b . For this object distance, the transit time T _{b is} characteristic.

Optimal adaptation or regulation of the Pulse Repetition Interval (PRI) to the object distance d is achieved by interrupting the current measurement cycle after the arrival of the first echo and starting a new measurement cycle. If the base distance b between transmitter S and receiver E should not be neglected, then it must be taken into account that the base distance b, the distance to the obstacle d and the distance traveled in the medium 2g (dashed line) are given by the equation d ² = g ² - b ^{2/4 is} related.

According to a preferred embodiment of the present invention, based on the 1 is explained, in conjunction with the previously mentioned as well as with the following explained adaptive principles an improved speed measurement in dynamic situations is possible. Here, a variant is chosen in which the Measurement cycle of the ultrasonic sensors is interrupted when an echo is received and immediately after a new transmission pulse is sent out (event-triggered control). With this type of triggering, the cycle time T is automatically adjusted to the distance d of the obstacle.

In the evaluation unit A, on the one hand, the above-mentioned plausibility check takes place, whether the received echo corresponds to a previously transmitted ultrasonic pulse, and if necessary with which ultrasonic pulse the received echo correlates exactly (with several interleaved echoes received). In the course of the plausibility check, it can also be determined whether the measured distance assumes a realistic value, eg. B. by comparing the last measured distance value with a previous history, ie with a development of the distance value over several individual measurements. As a result, disturbed measurements due to external sound sources can be filtered out. On the other hand, the rotational frequency f is limited to a reasonable range. Thus, as with the known sing-around principle in the case of a signal abort - so in the case of over a predetermined period no longer receiving echoes - ultrasound pulses with an idling frequency (minimum frequency or frequency) are emitted, the slightly below the rotational frequency of the maximum detection distance d _max is. In addition, it is advantageous to introduce a maximum frequency as the upper limit, which must not be exceeded. To achieve this, the detected rotational frequency can be reduced by a waiting time in the evaluation unit A. The advantage of setting a maximum rotational frequency is an increased stability of the regulation of the emission of the ultrasonic pulses. In this way, averted avalanches of echoes are avoided, and the broadening of an echo at a fissured obstacle H desirably leads only to a simple triggering of the signal.

additionally In this embodiment, the adaptation of the transmission pulse length to the obstacle distance d in two different steps above and below take place a defined limit distance. Here are longer Transmit pulses for larger distances used to the larger atmospheric Damping at other distances to balance d. The following described embodiment of a similar adaptive principle also serves to increase the signal reliability, and although by adaptation of the transmission properties of reflection properties the received echoes and / or to the distance d of the sensor device for nearest obstacle H. With this information will now the new transmit pulse generated, with a specific Signal length and maximum signal amplitude. The further that Obstacle H is removed (the larger is d), the more signal intensity is used for a qualitative good echo needed. The influence of the reflection properties of obstacle H determines echo length and echo amplitude: The longer and bigger an echo is, the more larger is the reflection cross section of the obstacle H and the less signal intensity is for needed the next transmission pulse. A balanced Weighting of these three parameters (distance d, echo length and Echo amplitude) is thus used advantageously for adjustment the signal intensity of the subsequently emitted ultrasonic pulses. The exact ratio of these three parameters to each other should be optimally determined in individual cases. For this are analytical methods as well as the use of fuzzy logic.

The relative speed of a moving obstacle H is calculated from the detected transit times (and thus distances) of several successive measuring cycles. It results as the slope in the distance-time diagram or as the derivative of the distance d after the time t. The total cycle time T required for one pass in the electroacoustic circuit is composed of the parts T ₁ and T ₂ : T = T ₁ + T ₂ . In this case, T ₁ denotes the finite time required for the feedback, that is, the time that passes between the receiving of the echo signal and the retransmission of the next ultrasonic pulse due to the system. These include the running time of the evaluation algorithm and the time for transmitting the send command for the next ultrasonic pulse. T _{1 is} assumed to be constant over time. T ₂ denotes the transit time of the ultrasonic pulse in the medium (eg air) and is calculated according to T ₂ = 2d / c, assuming that the base distance b between transmitter S and receiver E is negligible. If the base distance b between transmitter S and receiver E should not be neglected, then it must be taken into account that the base distance b, the distance to the obstacle d and the distance traveled in the medium 2g (dashed line) are given by the equation d ² = g ² - b ^2/4 .

This results in a dependence of the obstacle distance d on the cycle time T as follows:

By forming the derivative d (d) / dt, the velocity can be determined (T ₁ assumed to be constant over time):

in this connection v denotes the relative speed between obstacle and sensor device, and c is the speed of sound at a given temperature.

Practically, the evaluation of the differences of several distance information can be realized, which in turn calculate from the sound transit times, ie from the times of sending and receiving an ultrasonic signal. If two distance values are used for calculating the speed, the following simple dependence of the speed results from the times t1 to t4:

t1

den Zeitpunkt des Aussendens des 1. Sendesignals,

t2

den Zeitpunkt des Empfangens des 1. Echos,

t3

den Zeitpunkt des Aussendens des 2. Sendesignals, und

t4

den Zeitpunkt des Empfangens des 2. Echos.

Where:

t1

the time of transmission of the 1st transmission signal,

t2

the time of receiving the 1st echo,

t3

the time of transmission of the 2nd transmission signal, and

t4

the time of receiving the 2nd echo.

It is generally t2 ≠ t3 due to system internal delays.

Become correspondingly more than two distance values are included in the calculation, this will shift the indices of the last-mentioned equation.

In order to obtain as reliable as possible results for the relative distance and the relative speed, it is advisable to smooth the distance values d _i and the speed values v _i , for which, for example, Kalman filters have proved suitable.

Furthermore it is advantageous when focusing on moving obstacles H, fixed targets to suppress. In this approach from the field The radar technique is used as a criterion for to be detected Moving targets for this purpose a change in distance between two consecutive measurement cycles required a critical, distance-dependent limit.

Having described the implementation of the present invention with reference to FIGS 1 Now further geometries are explained how the invention can be integrated into a vehicle. The following features are also on the above in connection with the 1 to apply the explained implementation.

For parking functions, usually four to six sensors per bumper are installed in the vehicle, so in the following example for generalization of four sensors is assumed. As a first alternative, the simultaneous operation of a single ultrasonic sensor S + E is proposed as the transmitter S and receiver E, as in 2 is shown schematically. This operation can be enabled by implementing the feedback using software algorithms. Thus, only so-called direct echoes of the obstacle H at the distance d are evaluated. Although absolutely simultaneous sending and receiving is not possible in principle, this is not necessary with the sing-around method. Rather, a quasi-simultaneous transmission and reception is used, in which the transmission and reception in very short time intervals alternate.

It is advantageous, all four sensors of a bumper in the mode of 2 to operate. The applied parallel operation of the sensors S + E, as in 3 is shown schematically, is effective and time-saving in information retrieval. In the sensor geometry of the 3 It is advantageous if in parallel operation of the sensors S + E, the transmission pulses of the individual sensors are distinguishable from each other. As a criterion of differentiation, modulation methods of the transmission frequency and / or the transmission amplitude as well as coding methods are available. The in 3 shown operating mode is optimal especially for precrash applications because of the greatly accelerated information acquisition while covering the entire vehicle width.

In 4 a further advantageous embodiment is shown, which schematically shows how the event-triggered system according to the invention can be integrated into a vehicle by utilizing, for example, four existing sensors. This event-triggered between the left and right in 4 switched mode shown. In this case, either the upper or the lower middle sensor serves as transmitter S and the two immediately adjacent sensors serve as receiver E. An event or echo event which leads to switching between the two modes can be defined in advance in a suitable manner, for example, by receiving a direct echo and two cross echoes. However, other definitions for such an event are just as well conceivable, which may depend inter alia on the installation position of the respective sensors in the vehicle. If the predefined event does not take place, a time-triggered transmission pulse is transmitted on the other transmitter after a specified time has elapsed. In this context, reference is again made explicitly to the comments above on the idle frequency. The advantage of in 4 shown operating mode lies in particular in the coverage of the entire vehicle width, without the transmission signals of the individual sensors must necessarily be distinguishable from each other. To improve the uniqueness of the echo assignment is of course in the arrangement of 4 - in similar cher way, as related to 3 described - a differentiation of the transmission signals via modulation method of the transmission frequency and / or the transmission amplitude conceivable. Optionally or additionally, coding of the two active transmitters S is possible. Thus, the situation would be excluded that an echo from a "left cycle" in the following "right cycle" generates an echo signal that would be assigned a wrong distance due to the lack of time synchronization.

As described above, within the scope of the present invention, ultrasound-based safety functions in which the determination of distance and / or speed of an object relative to a vehicle plays a role, by canceling the measurement cycle upon detection of the first and thus the next obstacle H valuable time be won. The thus lower reaction time of the ultrasonic system is a significant advantage over the conventional systems and can be usefully used in the field of active and passive safety functions. In the area of passive safety, for example, information about an imminent collision is important for the deployment of the airbag, the seat belt pretensioner and the like. In particular, such an event-triggered system is advantageous for the early detection of a side impact, since laterally with a 1-sensor system as in 2 can be worked.

According to the invention inertia through the proposed adaptive measures and inflexibility of conventional ultrasound systems reduced or eliminated. Depending on the current need, the inventive adaptive ultrasound system as a parking aid or as a precrash warning system can be used by switching between different operating modes. For operation in precrash mode, various adaptive Among other things, the cycle time is combined T by an event triggering directly to the object distance d adjusted. Thus, the determination of the relative velocity between vehicle and obstacle H accelerates and there are possibilities opened, the ultrasound system for dynamic To make optimal use of purposes. Preferably, therefore, the ultrasonic system be switched to different operating modes, z. B. parking, Precrash mode and dead-angle detection. Switching the modes can, for example, taking into account the following criteria be realized: the vehicle's own speed, or exceeding a predetermined critical threshold for the necessary deceleration, which just avoid a collision or an imminent accident would.

In the entire application and thus in particular in the claims are within the scope of the present invention instead of ultrasonic pulses as well Pulses of electromagnetic waves, in particular radar waves, used. The above explanations apply in the same way also for electromagnetic wave pulses.

The Reference signs and references to figures in the following claims are used only for easier orientation in the Application documents and are in no way to be understood in any way which the claim to one shown in the figures or in the description set forth embodiment.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10323144 A1 [0005, 0005]

Claims (14)

Method for determining the distance (d, d _a , d _b ) and / or speed (v) of an object (H) relative to a vehicle in which ultrasound pulses are emitted, are reflected by the object (H) and received as an echo again be characterized in that the emission of a second ultrasonic pulse is triggered by the receipt of the echo of a previously transmitted first ultrasonic pulse. The method of claim 1, wherein the previously emitted first ultrasonic pulse immediately before the second ultrasonic pulse emitted ultrasonic pulse is. The method of claim 1 or 2, wherein the emitting the second ultrasonic pulse in time immediately after the reception the echo of the previously transmitted first ultrasonic pulse takes place. Method according to one of claims 1 to 3, wherein by emitting an ultrasonic pulse, the reception his echo and the evaluation of this echo by means of an evaluation unit (A) in a electro-acoustic circuit, a measuring cycle with a cycle time is defined, with a currently running measurement cycle on receipt a subsequent echo is interrupted and a new measurement cycle is started, preferably a further ultrasonic pulse is sent out. The method of claim 4, wherein a currently running Measuring cycle when receiving the next or the second, third, fourth, fifth, sixth, seventh, eighth, ninth or tenth next Echoes is interrupted. The method of claim 4 or 5, wherein with expiration a predetermined maximum allowed cycle time on time triggered ultrasound pulse is emitted, if so far no Echo was received. Method according to one of the preceding claims, the frequency of emission of ultrasound pulses is limited upwards per unit of time. Method according to one of the preceding claims, where the signal length and / or the maximum signal amplitude each ultrasonic pulse to be transmitted as a function of characteristics of the echo of a previously emitted ultrasonic pulse, such as for example, echo time, echo length and / or echo amplitude, is or will be elected. Method according to one of the preceding claims, wherein at least one ultrasonic sensor (S + E) is used, the be operated both in transmit mode and in receive mode can, wherein the different of the ultrasonic sensors (S. + E) emitted ultrasonic pulses in the modulation of their transmission frequency or transmit amplitude differ from each other. Device for determining the distance (d, d _a , d _b ) and / or velocity (v) of an object (H) relative to a vehicle, comprising means for emitting (S, S + E) ultrasonic pulses and for receiving (E, S + E) of the reflections reflected from the object, characterized by means for control (C), which are arranged, the means for emitting (S, S + E) of ultrasonic pulses upon receipt of the echo of a previously transmitted first ultrasonic pulse for emitting a second To trigger ultrasonic pulses. Apparatus according to claim 10, wherein the previously emitted first ultrasonic pulse immediately before the second ultrasonic pulse emitted ultrasonic pulse is. Apparatus according to claim 10 or 11, wherein the Means for control (C) are set up, sending out the second Ultrasonic pulse immediately after receiving the echo to trigger the previously transmitted first ultrasonic pulse. Device according to one of claims 10 to 12, further comprising means for evaluating (A) the received Echoes within a measuring cycle with a cycle time, the Means for control (C) are set up, a currently running To interrupt the measuring cycle when receiving the next echo and to start a new measurement cycle, in which preferably another Ultrasonic pulse is emitted. Device according to one of claims 10 to 13, comprising at least one ultrasonic sensor (S + E), the is operable in both transmit mode and receive mode, where which can be emitted by the various ultrasonic sensors (S + E) Ultrasonic pulses in the modulation of their transmission frequency or transmission amplitude differ from each other.