DE19754220B4 - Method and device for detecting an impending or potential collision - Google Patents

Abstract

Method for detecting an imminent or possible collision of a motor vehicle with an object,
Wherein a frequency-modulated wave is radiated by means of a device (400) located in or on the motor vehicle,
Whereby a wave reflected by the object is received,
- Wherein the received reflected wave is mixed with a portion of the currently radiated wave, whereby at least one mixing signal is produced, the frequency of which is a measure at least for the distance of the object from the motor vehicle,
- Wherein said mixing signal for further processing via at least one filter (405, 406) is filtered out and
- said filter (405, 406) having a frequency response (10, 11) such that the amplitude of the filtered composite signal (131-136) evaluably takes on different values as the distance between the motor vehicle and the object changes;
characterized in that a current time course of amplitude values of the filtered mixed signal (81, 82), the ...

Description

The The present application relates to a method and a device to detect a possible or imminent collision of a motor vehicle with an object according to the generic term of the main claim.

State of the art

Out a publication of the Fraunhofer Institute for Chemical technology, published under the title "Airbag 2000 "on the occasion of 3rd International Symposium on sophisticated vehicle occupants safety systems from 26. to 27. November 1996 in Karlsruhe, Germany, is a procedure for one Precrash sensor known. An FMCW radar is used. The System compares the amplitude of two harmonics, through bandpass filters selected become. Upcoming collisions may occur at a distance of 1.5 m in advance to be discovered. After a measurement of relative Impact velocity using multiple Doppler cycles the time to impact is calculated at a distance of 0.5 m. The Object size can be associated with the difference in amplitudes the harmonic and the distribution of relative velocities. With the help of this procedure, it is possible an imminent collision of a motor vehicle with an object to recognize early. In connection with a smarter trigger Of security systems, however, it is often desirable to have additional Information, especially about one so-called offset, that is a lateral offset between the motor vehicle and the object to receive. The importance of this information is reflected in it, that in the automotive industry increasingly more the crash behavior of motor vehicles is taken as a benchmark in so-called offset crashes.

In the US 3,893,114 For example, a method and a device for detecting a collision are described. In this case, a continuous wave radar method with a frequency-modulated wave is used. To evaluate a reflected and received back radar signal this is first mixed with the respective current transmission signal and in a second step with the modulation signal. This results in several different mixed products, which include, among other things, Doppler signal components due to the Doppler effect. Based on a comparison of instantaneous values of two selected mixed products, a time is determined which is a measure of the distance and the relative speed of the vehicle to an obstacle. Depending on this time and other conditions, a signal is generated which indicates an imminent collision.

Both Devices according to the above The cited prior art are suitable for making a decision meet if a collision of a vehicle with an obstacle is imminent. However, neither device is capable of lateral movement Offset between the motor vehicle and the object to determine.

The EP 0 024 430 B1 describes a device for avoiding an imminent collision of a motor vehicle with an object that determines a relative speed between the object and the motor vehicle and compares a time profile of this relative speed with stored time profiles of relative speed values.

Task, solution and advantages of the invention

aim It is the object of the present invention to provide a method and a method therefor specify based device, with its or their help more detailed information about a imminent collision of a motor vehicle with an object won can be. This object is achieved by a method having the features of the claim 1 and solved by a device having the features of claim 6. preferred Trainings are in the dependent claims specified.

According to the invention is a current time profile of amplitude values of a filtered mixed signal, due to a change in the Distance between the motor vehicle and the object results, with stored temporal courses of amplitude values of filtered mixed signals compared and Based on this comparison, a lateral offset between the motor vehicle and the object.

A inventive device is characterized in that first Means are available with which temporal courses of amplitude values of filtered mixed signals are storable and that second Means are present with which the stored courses and at least one course based on a current mixed signal of amplitude values are comparable with each other. Preferred embodiments The invention results from the subordinate claims.

Advantage of the invention is that more detailed information about an imminent collision can be obtained according to the tasks. In this case, due to the method according to the invention, the required computing time or the required computational effort is very small, in particular in comparison to an evaluation of radar signals by means of a fast Fourier transformation. This allows for signal evaluation, the advantageous Ver Use of a comparatively simple microcontroller instead of a much more complex and therefore expensive digital signal processor. In addition, the method is particularly suitable for the targeted triggering of a side airbag due to its short computation time.

The Invention is not related solely to a precrash detection with a trip limited by security systems. It can also be used, for example, as part of a parking aid application which focuses on an imminent collision to avoid with an object. Depending on the distance to be monitored and the required Meßauflösung are the measuring frequencies used and filter and Modulation bandwidths then suitable to choose. Optionally, a inventive device also combined for both uses are used.

Out a closer look at the amplitude curve, individual amplitude values or the standard deviation of the obtained amplitude values about that an estimate the size, the Structure and / or the material of the object with which a collision imminent, done. Advantageously, the device according to the invention or the inventive method not isolated, but in combination with known methods for Detection of a collision, for example in combination with known Acceleration sensors, used.

Description of exemplary embodiments

following Be exemplary embodiments of Invention explained with reference to a drawing. Show it

1a to 1d Spectral diagrams for explaining the method underlying the invention,

2 schematic frequency responses of two filters as a function of the radial distance r,

3 two temporal courses of amplitude values which result when carrying out the method according to the invention,

4 a schematic diagram of a device according to the invention,

5 a sketch for the definition of the offset,

6 the relationship between the radial and vertical distance between two vehicles at different offsets,

7 two effectively effective frequency responses as a function of the vertical distance x,

8th exemplary amplitude curves according to the invention and

9 a flow chart for illustrating the method according to the invention.

For the following description of exemplary embodiments, the basic principle of an FMCW radar system is assumed to be known. This is for example in the DE 42 42 700 A1 , the the US 5,483,242 A largely corresponds to described. Accordingly, in such a radar system, a preferably linearly frequency-modulated wave is emitted. Received reflections from an object are mixed with the respective current transmit signal, whereby at least one composite signal is produced whose frequency is a measure at least for the distance of the object from the radar system. In known radar systems, the frequencies of one or more mixed signals are often evaluated by means of a fast Fourier transformation.

1a to 1d shows four spectral diagrams for explaining the method according to the invention. In each case one can see a coordinate system whose abscissa indicates a frequency f and whose ordinate indicates an amplitude or level value P. According to the basic principle of an FMCW radar, the frequency f is proportional to the distance r between a detected object and the radar system. A detected object appears in the form of a spectral line 131 whose frequency is a measure of the distance of the object. Furthermore, in the 1a to 1d frequency responses 10 and 11 two filters drawn. The filters are preferably dimensioned so that their frequency responses have a largely identical course, but have a different center frequency and thus different passbands. Preferably, the passband of each of the two filters is narrower than the frequency range within which realistic mixed signals can occur. Depending on the specific filter circuit used, for example as a Cauer filter, ripples in the frequency responses can occur both in the transmission and in the blocking regions. This is in 1a to 1d symbolized by a training of the frequency responses in the form of a | (sinx) / x | function. However, this course of the frequency responses is only to be understood as an example. For a concrete realization, basically all filter structures with frequency responses can be considered, in which the amplitude values at different frequencies can be evaluated to different values. The passbands of the two frequency responses 10 and 11 partially overlap here. A line 12 indicates the frequency at which the pass bands of the Frequency Domain ge 10 and 11 to cut. The distance r corresponding to this frequency is hereinafter referred to as virtual barrier B _v .

In 1a shows a spectral line 131 , to the right of the frequency responses 10 and 11 is that a radar target has been detected at a distance r ₁ . The height of the spectral line 131 is assumed by way of example and shows a maximum possible amplitude value for this target at this distance. 1b shows a situation in which the radar target is at a distance r ₂ which is smaller than the distance r ₁ . Accordingly, a spectral line occurs at a lower frequency. The spectral lines outlined here 132 and 133 Now occur at the output of each filter when the mixed signal by means of two filters connected in parallel with the frequency responses 10 and 11 is filtered out. The spectral line 132 appears at the output of the filter with the frequency response 11 , the spectral line 133 appears at the output of the filter with the frequency response 10 , The frequencies of the two spectral lines 132 and 133 are identical because they belong to a single radar target at r ₂ . Their amplitude values, however, are different according to the frequency responses 10 and 11 , 1c shows the situation in which the radar target is at a distance r ₃ equal to the virtual barrier B _v . In this case, the filters with the frequency responses appear at the outputs 10 and 11 one spectral line each 134 and 135 which have both the same frequency and the same amplitude. 1d shows the situation in which the radar target is at a distance r ₄ which is smaller than the virtual barrier B _v . In this case, the filters with the frequency responses appear at the outputs 10 and 11 the spectral lines 136 and 137 , which in turn differ according to their amplitude values.

The inventive method according to a first embodiment is based on the principle that for the evaluation of reflected radar signals at least one, preferably even two mutually parallel filters with frequency responses 10 respectively. 11 are provided and that the amplitude values and in particular temporal profiles of amplitude values of the mixed signals filtered by means of this filter are evaluated.

2 shows frequency responses of two filters accordingly 1 on an enlarged scale. Along the abscissa, a distance r is plotted, which is proportional to the frequency of the mixed signals. Along the ordinate, in turn, an amplitude or level value P is plotted. You can see two frequency responses 21 and 22 that the frequency responses 10 and 11 of the 1 correspond. The frequency responses 21 and 22 are shown here again with an idealized, exemplary assumed course. For example, these may be Cauer, Bessel or Butterworth filters. As is known, such filters have a passband 210 which merges into a restricted area in a fluid transition. Within the stopband and also the passband ripples may be present in the frequency response caused by the sidelobes 211 respectively. 221 are indicated. The intersection of passages 210 and 220 As already mentioned, marks the virtual barrier B _v .

3 shows two temporal amplitude curves, which are at the output of the two filters with the frequency responses 21 and 22 result when the distance between a vehicle with a device according to the invention and an object increasingly decreases. For better understanding, it is assumed in this case that the vehicle is approaching an object at a constant speed, so that the distance r decreases linearly. This assumption is usually correct in view of the small distances (0 m to 1.5 m) that are involved in precracking. 3 shows for this case, the amplitude curves that result at the output of the two filters with increasing time t. The beginning of the representation is a time t ₀ at which the distance r between the vehicle and the object first assumes a value that is less than or equal to the virtual barrier B _v . This corresponds to the situation according to 1c in which the amplitude values at the output of the two filters are identical. According to the curve 31 the amplitude values at the output of the filter with the frequency response become 21 now with increasing time t and accordingly with decreasing distance r greater. In contrast, the amplitude values at the output of the filter with the frequency response 22 a course 32 on, which initially becomes smaller with increasing time and consequently decreasing distance r, and then rises again from a point of inflection t ₁ and thus a certain distance r. The actual course of the amplitude values plays no role in the basic understanding of the invention and depends in detail on the concrete realization of the filters and thus on the concrete appearance of the frequency responses 21 and 22 from.

4 shows a schematic representation of a device according to the invention 400 , There is a control and evaluation unit 408 , For example, a microcontroller or a digital signal processor, with an oscillator 401 connected. The frequency of the oscillator is determined by the evaluation and control unit 408 certainly. The output signal of the oscillator is via a send / receive switch 403 a transmitting / receiving antenna 402 fed. Furthermore, a mixer 404 present, which also with the send / receive switch 403 and additionally with the oscillator 401 connected is. This structure corresponds to the known, basic structure of an FMCW radar system.

The output signal of the mixer 404 is according to a preferred embodiment of the invention with two filters arranged parallel to each other 405 and 406 connected. These filters preferably have the in 2 shown frequency responses. The output signals of these filters are the evaluation and control unit 408 fed. The evaluation and control unit 408 includes, inter alia, a memory 409 and a comparator 410 , with which individual amplitude values and temporal courses of amplitude values can be stored and compared. Alternatively or in addition to one of the two filters 405 . 406 can be the output signal of the mixer 404 also directly to the evaluation and control unit 408 be fed. This is through the dashed line 407 indicated. Furthermore, receives the evaluation and control unit 408 a signal 411 that represents the vehicle's own speed. In addition, the evaluation and control unit 408 according to a preferred embodiment of the invention, signals 412 fed to one or more conventional acceleration sensors. Depending on all the signals supplied to it and in accordance with the method explained in more detail below takes place in the evaluation and control unit 408 a decision is made as to whether a collision of the vehicle is imminent and, if necessary, which safety systems have to be activated in which way. The evaluation and control unit 408 then controls actuators 413 and 414 which activate, for example, belt tensioners or airbag systems.

5 shows a schematic representation of a lateral offset, that is, an offset of two vehicles 51 and 52 for the definition of subsequently required quantities. Thus, the radial distance r measured by a radar sensor is split into a vertical distance x and an offset y. Here are the three sizes in the known context:

6 shows this functional relationship between the vertical distance x between a vehicle and an object and the distance r determined by the radar sensor based on several curves. Straight 61 , which indicates a linear relationship between the vertical distance x and the sensor distance r, results at an offset y of zero. The curve 62 results at an offset y of 25 cm, curve 63 at an offset y of 50 cm, curve 64 at an offset y of 75 cm and curve 65 at an offset y of 1 m. As can easily be seen, the sensor distance r deviates progressively from the vertical distance x when the offset y between the two vehicles 51 and 52 gets bigger.

7 shows the effectively effective frequency responses of the two filters 405 and 406 for example, assuming an offset y of 50 cm, if along the abscissa no longer the radial distance r, but now the vertical distance x is plotted. Here, the concrete processes are again to be understood as an example. It is essential that in this consideration, other effectively effective frequency responses arise as in 2 , The concrete appearance of such effectively effective frequency response depends on the respective offset y. This is done according to the contexts according to 6 especially at distances below the virtual barrier B _v clearly. This circumstance can be used to determine the offset y as shown below.

8th shows two temporal courses 81 and 82 of amplitude values at the output of the two filters 405 and 406 if there is an offset of 50 cm between the vehicle and the object. In comparison, the courses in 3 at an offset of 0 cm. The reason for these different characteristics of the courses lies in the different, effectively effective frequency responses according to the 2 and 7 , Again, as already explained, these are a result of the nonlinear relationship between the perpendicular distance x and the radial distance r. Prerequisite for the described relationships is that the reflection of the radar waves accordingly 5 as possible at a central point of the object. Of course, this is only true in a model assumption. However, a "central, central reflection point" can be calculated by a prior statistical evaluation of the distribution of reflected received signals.

9 shows a flowchart of a possible implementation of the method according to the invention. At the beginning of the procedure will be in the steps 90 and 91 the output signals of the filters 405 and 406 in the form of amplitude or level values P1 and P2. In step 93 and in reference to 1c Then in each case a query is made whether P _{1 is} equal to P ₂ . These steps are repeated until the query 93 is satisfied, that is until P _{1 is} actually equal to P ₂ . If this is the case, that is to say that an obstacle violates the virtual barrier B _v , this event is recognized and preferably already regarded as an indication of an imminent or possible collision. For the further process steps, this event now serves as a trigger signal. In step 94 Current time profiles of the amplitude or level values P ₁ (t) and P ₂ (t) corresponding to 2 and 8th taken and in the store 409 saved. With 95 It is indicated that the time duration, how long the time courses P ₁ (t) and P ₂ (t) are recorded, preferably of other sizes, in particular the current distance and the Relativge speed between the vehicle and the object is made dependent. In step 96 At least one of the currently recorded temporal courses of amplitude values is compared with previously stored courses P _S (n, t) of amplitude values. The variable n designates a counter variable that corresponds to it 6 individual amplitude curves P _S (t) to different offsets y. The amplitude curves P _s (n, t) are characteristic amplitude curves which result at different offsets y between the vehicle and a possible obstacle, and which are once used as reference in the memory 409 are stored. According to step 97 is determined on the basis of a comparison of at least one of the amplitude profiles P ₁ (t) or P ₂ (t) with the stored amplitude curves P _S (n, t) of the offset y, assuming that offset y at which the greatest match between P ₁ (t), P ₂ (t) and the stored amplitude curves P _S (n, t).

In principle, a comparison of one of the current amplitude profiles P ₁ (t) or P ₂ (t) with the stored amplitude profiles would suffice for the evaluation. However, due to the redundancy and the required high reliability of the recognition, it is advantageous to use both curves for the determination of the offset y.

According to a preferred embodiment of the method is in step 98 an object classification performed. This is a rough estimate of the size, structure and / or material of the obstacle based on, for example, the absolute size of the obtained amplitude values P at a certain distance r and / or the scattering σ of the received reflection signals. For example, it may be assumed that at the same distance r, the amplitude value of a reflection signal from a large obstacle is greater than the amplitude value from a small obstacle. Likewise, metallic surfaces are known to reflect more strongly than, for example, wood or plastic. On the basis of such a rough object classification can be concluded on the severity and the associated risk of an imminent collision. In step 99 the previously obtained findings are used to activate existing safety systems in the motor vehicle. This can be done according to 4 For example, be airbags or belt tensioners. Preferably, in the decision as to which security systems are activated, a further 100 pieces of information flow into the decision. This can be, for example, signals from acceleration sensors 412 or the vehicle's own speed 411 be.

Claims (9)

Method for detecting an imminent or possible collision of a motor vehicle with an object, - wherein by means of a device ( 400 ), which is in or on the motor vehicle, a frequency-modulated wave is radiated, - wherein a reflected wave from the object is received, - wherein the received reflected wave is mixed with a portion of the currently radiated wave, wherein at least one mixing signal is formed whose frequency is a measure at least for the distance of the object from the motor vehicle, - said mixing signal for further processing via at least one filter ( 405 . 406 ) is filtered out and - said filter ( 405 . 406 ) have such a frequency response ( 10 . 11 ), that the amplitude of the filtered mixed signal ( 131 - 136 ) evaluably takes on different values when the distance between the motor vehicle and the object changes, characterized in that a current time profile of amplitude values of the filtered mixed signal ( 81 . 82 ), which results from a change in the distance between the motor vehicle and the object, with stored time profiles of amplitude values of filtered mixed signals ( 81 . 82 ) is compared ( 96 ) and that a lateral offset (y) between the motor vehicle and the object is determined on the basis of this comparison ( 97 ). Method according to Claim 1, characterized in that the profile of the amplitude values of the filtered mixed signal ( 81 . 82 ) is recorded for a period of time ( 94 ), which depend on ( 95 ) at least one of the relative speed between the vehicle and the object or distance between the vehicle and the object is determined. Method according to claim 1, characterized in that the filter ( 405 . 406 ) has a frequency response whose passband ( 210 . 220 ) is narrower than the frequency range ( 10 . 11 ), within which realistic mixed signals can occur. Method according to Claim 1, characterized in that the mixed signal is produced by means of two filters (parallel to each other) ( 405 . 406 ) is filtered, each filter ( 405 . 406 ) a passband ( 210 . 220 ), which is only partially connected to the passband ( 210 . 220 ) of the other filter overlaps ( 10 . 11 ) and that a state in which the amplitude values of the filtered mixed signal ( 81 . 82 ) from the two filters approximately equal are recognized. Method according to claim 1, characterized in that the size, structure and / or material of the object is estimated on the basis of at least one amplitude value of the mixed signal or on the basis of a scattering of amplitude values of the mixed signal ( 98 ). Device for detecting an imminent or possible collision of a motor vehicle with an object, - with a transmitting device ( 401 . 402 ) for transmitting a frequency-modulated wave, - with a receiving device ( 402 ) for receiving a wave reflected from an object, - with a mixing device ( 404 ) for mixing the received wave with the currently transmitted wave, - with at least one filter ( 405 . 406 ) for filtering out a mixed signal between the transmitted and the received wave, characterized in that - first means ( 409 ) are available with which gradients of amplitude values of filtered mixed signals can be stored and - that second means ( 410 ) are present, with which the stored profiles and at least one based on a current mixing signal waveform of amplitude values are comparable. Apparatus according to claim 6, characterized in that the at least one filter ( 405 . 406 ) have such a frequency response ( 10 . 11 ) that the amplitude of the filtered composite signal evaluably assumes different values when the distance between the motor vehicle and the object changes. Apparatus according to claim 6, characterized in that the at least one filter ( 405 . 406 ) a frequency response ( 10 . 11 ) whose passband ( 210 . 220 ) is narrower than the frequency range within which realistic mixed signals can occur. Apparatus according to claim 6, characterized in that at least two filters ( 405 . 406 ) are connected in parallel with each other, each filter ( 405 . 406 ) a passband ( 210 . 220 ), which is only partially connected to the passband ( 210 . 220 ) of the other filter ( 405 . 406 ) overlaps.